Note: Descriptions are shown in the official language in which they were submitted.
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Method and Wireless Communication Hub for Data Communications
[001) Field of the Invention
[002] The present invention relates to broadband communication networks and
more
particularly to wireless broadband communications.
[003] Background of the Invention
[004] In the past, broadband communication was achieved by providing high
bandwidth cable connections between a provider and a client. The cables are
commonly in
the form of coaxial cables, twisted pair copper telephone lines, or fibre
optic cables. A
broadband signal is transmitted down the cable toward the client end. For
example, cable
television involves a same signal transmitted to each client within a group of
clients. The
signals are sent in one direction only thus providing a one directional data
link. Each client
then decodes portions of the signal as desired.
[005] Information being sent to the clients, commonly called the down link or
forward link, is usually transmitted at a much higher capacity than the up
link or return
link. Such asymmetry in communications prevents clients from both generating
and
distributing substantial amounts of information into the network. As a
consequence, the
distribution of high content information by the network is exceedingly
hierarchical,
requiring the producers of information to access the hub nodes wherefrom the
information
is transmitted to the clients. Generally, subscribers desire a high bandwidth
feed from a
service provider and lower bandwidth feed to the service provider. An
arrangement is
similar for television on demand where television programs are provided to a
client from
the service provider and clients only send small data packets including
ordering
information etc. to the service provider.
(006] It is well known that one of the most expensive aspects of any broadband
communication network is the cost of running cable from a service provider to
each client.
For example, fibre optic cables are estimated to cost tens of thousands of
dollars per mile
of installed cable. This results from labour costs, costs of routing the
cables and obtaining
rights to bury the cables, costs of repairing damaged cables and so forth. It
would be highly
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advantageous to obviate any need to lay new cable in order to support
broadband
communication over a wide area and more particularly bi-directional
communication
between a service provider and a client subscriber or between client
subscribers, especially
in view of the growing need by clients to be able to access and use ever
increasing amounts
of return link capacity. Additionally, adding the capability to existing
wireline
infrastructure is expensive and problematic, often requiring the special
conditioning of old
lines or the addition of new infrastructure. In many areas, infrastructure is
simply not in
place, forcing those desiring broadband communications to face the daunting
task of not
only installing links to clients, but also installing totally new switching
systems.
[007] The convergence of the Internet and television services has given rise
to a need
to provide high bandwidth bi-directional communication. Other applications
such as video
conferencing, require high bandwidth in both transmit and receive directions.
Conventional
broadband data distribution services are not capable of supporting such
requirements.
(008] In an attempt to overcome this problem, cable service providers have
released a
cable modem for use in providing Internet services over a standard cable
connection. Such
a connection has many known problems. The bandwidth is limited by the cable
itself and
division of subscribers into groups requires the addition of new hardware. The
bandwidth
to any given client is limited by the number of active subscribers in their
group and by the
physical limitations on the information carrying capacity of the coaxial
cable. Further, such
a system is highly asymmetric and incapable of, for example, supporting
extensive video
interactivity between client subscribers.
[009] Telephone system operators have also tried to overcome the above noted
problems with broadband data distribution by developing high speed modems that
condition signals for distribution over twisted pair telephone lines. These
modems, called
Digital Subscriber Line (DSL) modems, are most commonly represented by a class
of
modems called Asymmetric DSL (ADSL). Some of the drawbacks of these systems
are
that they require the twisted pair telephone lines to be in good condition in
order that the
modems can be effectively used.
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[0010] Also, networks employing ADSL are highly asymmetrical, having forward
link
capacity significantly larger than return link capacity. In addition, unless
the ADSL links
are in good condition and relatively short, supporting high quality video
services becomes
problematic. Another significant problem faced with ADSL is the requirement
for a public
telephone subscriber line network to be in place in order to facilitate
deployment. Such a
requirement for an in-place infrastructure is simply impossible in many
regions of the
world, hence deployment of ADSL is limited to those regions that are well
developed
economically and have a solid technological base.
[0011] Another attempt to overcome the above known problems is known Local
Multipoint Distribution Service (LMDS) or Local Multipoint Communication
Systems
(LMCS). LMDS (LMCS) is a wireless, two-way broadband technology designed to
allow
network integrators and communication service providers to bring a wide range
of high-
value, quality services to homes and businesses. Services using LMDS
technology include
high-speed Internet access, real-time multimedia file transfer, remote access
to corporate
local area networks, interactive video, video-on-demand, video conferencing,
and
telephony among other potential applications.
(0012] In the United States, the FCC became interested in the possibility of
LMDS
bringing long needed competition to the telecommunication marketplace, where
it has the
use of 1.3 GHz of RF spectrum to transmit voice, video and fast data to and
from homes
and businesses. With current LMDS technology, this roughly translates to a 1
Gbps digital
data pipeline. Canada already has 3 GHz of spectrum set aside for LMCS. Many
other
developing countries see this technology as a way to bypass the expensive
implementation
of cable or fiber optic networks.
[0013] LMDS uses low powered, high frequency (25 -31 GHz) signals transmitted
over a distance of 3-5 kilometers. These zones of coverage, or cells, are
created by
sectorial antennas and switching systems mounted on rooftops of urban
buildings and
towers. These cells are typically spaced 4-5 kilometers (2.5 - 3.1 miles)
apart. LMDS cell
layout determines the cost of building transmitters and the number of
households covered.
With circular cells of 4 kilometers in radius, about 50 square kilometers
falls within a
single cell. In urban areas, this translates to about 80,000 homes within a
single cell.
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(0014] Despite the promise of LMDS there are a number of issues that
compromise its
acceptance as a widely deployed and ubiquitous wireless multimedia
distribution system.
One significant drawback to the deployment of LMDS systems is the large signal
attenuation that is faced by the frequencies used in transporting the data
between the hub
and subscriber terminals. This signal attenuation is exacerbated by rain,
foliage, building
blockage, and other factors related to the absorption, refraction, or
reflection of the signal
by obstacles in the propagation path. The underlying phenomena are well
understood but
are of such severity that current deployments of LMDS are limited to
situations where the
links are free from obstructions and where attenuation by rain or snow is
sufficiently
countered.
[0015] Another issue, also related to propagation characteristics, is that the
intended
polarization reuse schemes for increasing the capacity of LMDS systems are
also prone to
degradation by the same phenomena that attenuate the signal. As a consequence
there are
issues of deployment and capacity, which bring into question the economic
viability of
LMDS systems.
[0016] Though there is much promise in LMDS systems operating at 28 GHz, the
effect of the propagation environment makes wide scale deployment problematic.
Though
initial expectations assumed this technology could provide services to
everybody within a
coverage area, most current plans are for providing service only to those
locations where a
signal is received without even nominal propagation impairments. Also, current
trends in
LMDS are mainly for providing commercial access to broadband communication.
[0017] In view of the problems faced by LMDS due to its use of frequencies
around a
28GHz band, the most obvious solution to the above noted problems is to
develop a system
using frequencies more robust to propagation degradation. Typically these
frequencies are
in bands substantially lower than 28GHz. The difficulty with using bands at
lower
frequencies is that there is insufficient bandwidth to support the density of
communications
demanded by broadband digital services and what bandwidth is available is
often shared
with other users such as satellite systems or dedicated point to point
communications links.
In order to effectively use other frequency bands for broadband wireless
communications it
is therefore necessary to devise a system which can co-exist with primary
users and in
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addition, use limited bandwidth in such a manner that effective broadband
communications
can be established. At present, such a solution is unavailable for use with
the types of data
throughput anticipated and currently required.
[0018] A great deal of the early discussion of LMDS applications centered on
the
transmission of video. With the recent surge of interest in the Internet and
the
accompanying demand for bandwidth, fast data appears to be the greatest
application for
this technology. With 1.3 GHz of spectrum, LMDS can provide a pipeline for a
great deal
of data. Homeowners pay about $30 per month for video, but businesses
regularly pay over
$1000/month for a high speed T1 (1.544 Mbps) line from phone companies.
[0019] Using only the 850 MHz unrestricted bandwidth, along with a modulation
scheme such as quadrature phased shift keying (QPSK), well over 100 T1
equivalent lines
can be provided in a cell formed by an omnidirectional LMDS transceiver even
without
splitting cells into separate sectors. Though it has been proposed that by
using horizontal
and vertical polarized sectors within a cell, LMDS providers can re-use
bandwidth and
multiply the number of T1 equivalents available, insufficient polarisation
isolation makes
such claims dubious especially in applications wherein subscribers are
individuals and not
businesses. A typical commercial LMDS application is believed to be able to
provide a
downlink throughput of 51.84 - 155.52 Mbp/s and a return link of 1.544 Mbp/s
(T1). This
capacity translates into potential to provide "full service network" packages
of integrated
voice, video and high-speed data services. Actual service carrying capacity
depends on
how much of the spectrum is allocated to video versus voice and data
applications.
Assuming that 1 GHz of spectrum is available, an all-video system could
provide in the
order of 275 channels of digital broadcast quality television plus on-demand
video
services. Unfortunately, LMDS has many known drawbacks and even though an LMDS
television system was installed in Brooklyn in the early 1990's, it has failed
to find wider
acceptance.
[0020] It is an object of the present invention to provide a robust broadband
wireless
communication system for use in delivering data from a service provider to a
plurality of
clients. It is another object of the present invention to provide a system for
operation at
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lower frequencies than LMDS, which provides many of the benefits of LMDS
without
many of the drawbacks.
[0021] Summary of the Invention
[0022] In accordance with an aspect of the invention, there is provided a
wireless
communication hub comprising:
a plurality of radiators each associated with an oblong microcell and for
radiating a narrow beam outward from the hub within the oblong microcell,
different
radiators for radiating within different oblong microcells, radiators
associated with
adjacent oblong microcells for radiating within different frequency ranges
such that
adjacent oblong microcells are frequency isolated and at least two spatially
isolated oblong
microcells within a same half of a rosette are associated with radiators for
radiating within
a same frequency range and are for radiating beams having sufficiently low
side lobe levels
for providing the spatial isolation;
a plurality of modulators each for modulating a signal based on data received
and
for providing the modulated signal to a radiator from the plurality of
radiators;
a receiver for receiving a signal relating to other wireless communication
hubs, the
information for use in determining configuration information of the wireless
communication hub and transmitted by other than the wireless communication
hub;
a processor for determining a hub configuration based on at least a received
signal
and for providing a feedback signal relating to the determined hub
configuration; and,
a control circuit for controlling the wireless communication hub in response
to the
feedback signal.
[0023] In accordance with another aspect of the invention, there is provided a
wireless
communication hub comprising:
a plurality of radiators each associated with an oblong microcell and for
radiating a narrow beam outward from the hub within the oblong microcell,
different
radiators for radiating within different oblong microcells, radiators
associated with
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adjacent oblong microcells for radiating within different frequency ranges
such that
adjacent oblong microcells are frequency isolated and at least two spatially
isolated oblong
microcells within a same half of a rosette are associated with radiators for
radiating within
a same frequency range and are for radiating beams having sufficiently low
side lobe levels
for providing the spatial isolation;
a plurality of modulators each for modulating a signal based on data received
and
for providing the modulated signal to a radiator from the plurality of
radiators;
a processor for providing the data to the modulator;
a feedback port for receiving a feedback signal relating to interference
caused by
other than the wireless communication hub; and,
a control circuit for controlling the wireless communication hub in response
to a
feedback signal received at the feedback port to alter an aspect of the hub in
response
thereto.
[0024] In accordance with yet another aspect of the invention, there is
provided a
communication architecture comprising:
a plurality of similar overlapping rosettes each rosette defined by radiation
from an
antenna hub comprising at least 4 directional radiators for radiating power at
frequencies
associated with a microcell forming a portion less than the whole of the
rosette, the rosette
comprising:
a number of microcells greater than 3, adjacent microcells within a same
rosette
associated with different radiated frequencies;
the hub comprising:
a messaging circuit for generating a radio frequency management message
indicating data relating to a hub in which the messaging circuit is disposed;
a receiver for receiving radio frequency management messages during use;
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a processor for processing the radio frequency management messages to
determine a
configuration for the rosette that is unlikely to interfere with existing
rosettes already in
operation; and
a control circuit for changing characteristics of the microcells within the
rosette for limiting inter-rosette interference.
[0025] In accordance with yet another aspect of the invention, there is
provided a
method of arranging a plurality of overlapping rosettes, each rosette defined
by radiation
from an antenna hub comprising a plurality of directional radiators for
radiating power at
frequencies associated with a microcell forming a portion of the rosette less
than the
whole, the rosette comprising:
a number of microcells, adjacent microcells within a same rosette associated
with
different radiated frequencies;
the method comprising the steps of:
receiving a radio frequency management signal from at least another hub,
the radio frequency management signal including information on the location
and
transmission characteristics of the at least another hub;
processing the received radio frequency management signal to determine
characteristics of the hub that are unlikely to substantially interfere with
the at least another
hub; and
tuning the hub to reduce a potential of interference.
[0026] In accordance with yet another aspect of the invention, there is
provided a
method of supporting hierarchical wireless communications within a same
wireless
communication environment comprising the steps of:
providing a plurality of overlapping rosettes, each rosette defined by
radiation from
an antenna hub comprising a plurality of directional radiators for radiating
power at
frequencies associated with a microcell forming a portion of the rosette less
than the
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whole, the rosette comprising a number of microcells, adjacent microcells
within a same
rosette associated with different radiated frequencies;
the method comprising the steps of:
detecting a radio frequency signal that other than originates from the hub;
classifying the received radio frequency signal to identify a source thereof;
determining a hierarchy of the received radio frequency signal relative to
the rosette; and,
when the determined hierarchy is higher than that of the hub, preventing
hub transmissions from interfering with the received radio frequency signal.
[0027] In accordance with yet another aspect of the invention, there is
provided a
communication architecture comprising:
a plurality of similar overlapping rosettes each rosette defined by radiation
from an
antenna hub comprising at least 8 directional radiators for radiating power at
frequencies
associated with a microcell forming a portion less than the whole of the
rosette, the rosette
comprising:
a number of microcells greater than 7, adjacent microcells within a same
rosette associated with different radiated frequencies, some microcells within
the rosette
associated with same frequencies and spatially isolated from microcells
associated with a
same frequency, wherein the at least 8 radiators are for radiating signals
having sufficiently
low sidelobes to provide said spatial isolation, radiators associated with
adjacent
microcells for radiating at different frequencies such that the adjacent
microcells are
frequency isolated;
a detector within each rosette for detecting interference with signals other
than those transmitted by a hub of the architecture;
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a processor for classifying the interference to determine a source thereof
and, when the source has a higher priority than the hub, for providing a
feedback signal
relating to the detected interference; and,
a control circuit for changing a characteristic of the rosette for limiting
the
detected interference.
[0028] In accordance with yet another aspect of the invention, there is
provided a
method of supporting wireless communications within a same wireless
communication
environment comprising the steps of:
providing a plurality of overlapping rosettes, each rosette defined by
radiation from
an antenna hub comprising a plurality of directional radiators for radiating
power at
frequencies associated with a microcell forming a portion of the rosette less
than the
whole, the rosette comprising a number of microcells, adjacent microcells
within a same
rosette associated with different radiated frequencies;
the method comprising the steps of:
detecting a radio frequency management signal originating from a similar
hub and containing data relating to the similar hub encoded therein;
determining a set of hub characteristics for reducing inter hub interference
based on the detected radio frequency management signal;
providing the determined characteristics to a control circuit; and,
setting hub characteristics in accordance with the determined
characteristics.
[0029] There are significant advantages to wireless systems operating at lower
than 28
GHz frequencies and preferably in the range of 2-7 GHz. First, the electronics
for driving
the system is less costly since semiconductor devices operating at lower
frequencies are
currently cheaper and plentiful. Second, the attenuation due to rain and other
obstacles is
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reduced. Third, the antennas are physically smaller and are easily designed
having high
directivity and low sidelobe levels.
[0030] Brief Description of the Drawings
[0031] The invention will now be described with reference to the attached
drawings in
which:
[0032] Fig. la is a simplified diagram of a plurality of sectorised
overlapping LMDS
cells, sectorisation supported by frequency allocation within each sector
using different
frequencies in each sector according to prior art proposals;
(0033] Fig. lb is a simplified diagram of a plurality of sectorised
overlapping LMDS
cells, sectorisation supported by polarisation allocation within each sector
according to
other prior art proposals;
[0034] Fig. 2a is a simplified diagram of limited frequency reuse within a
known
cellular system according to the prior art and showing frequency reuse of a
single
frequency every eighth cell;
[0035] Fig. 2b is a simplified diagram of limited frequency reuse within known
cellular
systems wherein frequency reuse occurs by using two frequency ranges within a
single cell
and arranging cells according to Fig. 2a;
[0036] Fig. 3 is a simplified diagram of a plurality of cells each comprising
16 oblong
microcells according to the invention and showing frequency channel reuse;
[0037] Fig. 4 is a transmitter according to the invention;
[0038] Fig. Sa is a simplified diagram of a single cell design used in
simulating results
of the application of the invention to a multicell configuration broadband
communication
network;
[0039] Fig. Sb is a graph of the PDF for co-channel interference within a
rosette as
shown in Fig. Sa;
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[0040] Fig. Sc is a graph showing how C/I within a rosette according to Fig.
Sa is
invariant with distance away from the hub;
[0041] Fig. Sd is a graph showing measurements that were taken in a highly
foliated
urban environment where the of is about 3 dB; and
[0042] Fig. 6a is a simplified diagram of a constellation of rosettes wherein
microcells
of like frequency ranges within different rosettes are oriented 180 degrees
relative one to
another;
[0043] Fig. 6b is a graph of an estimated Probability Distribution Function
(PDF)
based on C/I calculations showing the probability of achieving a stated C/I in
the
configuration of Fig. 6a wherein approximately 33% of terminals receive a C/I
of 14 dB or
better;
[0044] Fig. 6c is a graph of C/I for a typical receiver situated along the
boresight axis
of the main lobe defining a microcell as a function of radial distance from
the rosette
centre;
[0045] Fig. 7a is a simplified diagram of a constellation of rosettes having
irregular
offset alignments between microcells within adjacent rosettes and associated
with a same
channel frequency range;
[0046] Fig. 7b is a graph of an estimated Probability Distribution Function
(PDF)
based on C/I calculations showing the probability of achieving a stated C/I in
the
configuration of Fig. 7a wherein approximately 97% of terminals receive a C/I
of 14 dB or
better;
[0047] Fig. 7c is a graph of C/I for a typical receiver situated along the
boresight axis
of the main lobe defining a microcell as a function of radial distance from
the rosette.
[0048] Fig. 8 shows two rosette hubs spaced in relation to each other;
(0049] Fig. 9 illustrates a C/ (No+Io) distribution plot for a single rosette;
[0050] Fig. 10 shows six possible channel sequences for each rosette;
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[0051] Fig 11 shows the orientation for each of the four channels within a
single
rosette in relation to magnetic north, in a clockwise direction;
[0052] Fig. 12a illustrates co channel interference for a first hub when a
best
configuration second hub is placed in relation to the first;
[0053] Fig. 12b illustrates co channel interference for a first hub when a
worst
configuration second hub is placed in relation to the first hub;
[0054] Fig. 13 shows how the installation of a second rosette causes a drop in
C/
(Io+No) for subscribers using the first hub;
[0055] Fig.l4 shows a graph of simulation results comparing interference
probability
for 24 and 48 petal rosettes;
[0056] Fig. 15 shows simulation results for when EIRP of a second hub is
varied;
[0057] Fig. 16a shows a distribution for the first hub when the second hub has
a
moderated EIRP.
(0058] Fig. 16b shows a graph of the interference probability with respect to
C/ (Io+No)
for the first hub when the second hub has moderated EIRP;
(0059] Fig. 17 shows the interference probability vs C/ (Io+No) when the
spacing
between hubs is varied;
[0060] Fig. 18 shows a graph illustrating the relationship between aggregate
bit rate
and. capacity efficiency in terms of data capacity;
[0061] Fig. 19a shows the effect of co channel interference probability for
subscribers
having different antenna beamwidths;
[0062] Fig. 19b shows a C/ (Io+No) interference probability curve as a
function of
different antenna beamwidths;
[0063] Fig. 20 shows a C/ (Io+No) plot for a system comprising 7 rosettes
placed in
spaced relation to one another;
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[0064] Figure 21 a illustrates a C/ (Io+No) distribution plot for an increase
in EIRP
without the expense of decreasing the already existing C/ (Io+No);
[0065] Figure 21b illustrates a C/ (Io+No) distribution plot for a 7 rosette
system
according to a third solution; and
[0066] Fig. 22 illustrates capacity efficiency for different modulation
techniques;
[0067] Fig. 23 illustrates a simplified flow diagram of a method of
effectively filling
unused bandwidth without affecting bandwidth allocation;
[0068] Fig. 24 is a simplified block diagram of a full duplex petal
configuration for a
system according to the invention; and,
[0069] Fig. 25 is a simplified block diagram of a system according to the
invention.
[0070] Detailed Description of the Invention
[0071] The present invention presents a wireless communication architecture
allowing
significant frequency reuse while mitigating the deleterious effects of radio
propagation
and systemic self interference. Further, the carrier to interference levels
(C/I) are limited to
improve system performance. This is achieved by dynamic monitoring of the
propagation
environment, by dynamically assigning frequency bands, and by controlling the
radiated
power of all terminals.
[0072] In most wireless systems using fixed beam antennas, an effort is made
to
mitigate co-channel interference. The degree to which such interference is
reduced
determines the information carrying capacity of the contiguous wireless
network deployed
over a service area.
[0073] Frequency re-use and co-channel interference reduction is undertaken
with
LMDS systems. Referring to Figs. la and lb, two proposed LMDS systems are
shown
applying sectorisation. In Fig. 1 a, a central antenna 1 is disposed within a
circular
transmission area. The antenna comprises four sectorial transmitters operating
at different
frequencies with each sector operating with a different frequency. Directional
receivers are
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installed at client sites to receive the signal from an associated
transmitter. The receivers
are positioned to receive a signal from a particular transmitter having a
clear signal at the
receiver location. Because there is no frequency reuse, the total bandwidth of
such a
system is no better than a same frequency use in all four sectors. With a same
frequency
used in each cell.
[0074] In Fig. lb, the antenna comprises four sectorial transmitters operating
at a same
frequency with adjacent sectors operating with different polarisations.
Directional receivers
are installed at client sites to receive the signal from an associated
transmitter. The
receivers are positioned to receive a signal from a particular transmitter
having a clear
signal at the receiver location. Because of polarisation usage, each cell has
twice the
bandwidth of other LMCS cells
[0075] Frequency re-use and co-channel interference mitigation is also carried
out in
cellular and PCS telephony systems. Modeling the coverage areas of a cellular
system as
hexagons, as shown in Fig. 2a, like frequency hexagonal cells are separated by
a distance
D that is substantially greater than the nominal radius (R) of the hexagonal
cell. Frequency
re-use is thus achieved over the contiguous coverage area and co-channel
interference is
mitigated by counting on the propagation path loss between cells of like
frequency to be
sufficiently high as to result in significant attenuation of co-channel
signals and isolation of
cells.
[0076] In other embodiments of the cellular and PCS telephony systems, the
same
frequencies are used in a single hexagonal cell, as shown in Fig. 2b. In this
embodiment
the like frequencies are re-used 3 times per hexagonal cell as shown, for
instance, by the
re-use of (f'a) in cell number 2. Co-channel interference is mitigated by two
process here;
firstly by the sectoral isolation achieved by using sectorizing antennas and
secondly, by
spacing cells containing like-frequencies by the cell spacing D described
above.
[0077] In each instance shown in Figs. 2a and 2b, each hexagonal cell has 1
/7th the
bandwidth of the entire frequency range.
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[0078] Information carrying capacity as a function of cell radius and coverage
area is
an issue with LMDS systems. This also relates to the frequency re-use
considerations.
First, the size of the area serviced by a single frequency range in an LMDS
system is large
and therefore bandwidth to each individual client is limited. Further, when
two channels
are used in accordance with standard LMDS frequency re-use practices (as shown
for
instance in Fig. 2b), the LMDS bandwidth of approximately 1 GHz results in
each sector
having approximately SOOMHz of bandwidth. With four quadrants, a total of 2
GHz of
bandwidth is supported in a single circular area. In essence, over 1000 T1
line equivalents
can be supported within each cell, assuming 1 Bit/S/Hz efficiencies in the
modem
technology.
[0079] In practical terms this means that with 80,000 homes in the coverage
area of a
4 Km radius LMDS cell, an overall bandwidth of 2GHz results in an average
available
bandwidth of 25,000 bits/sec per home. There are some draw backs to this
scenario. It is
impossible, for instance, to dynamically allocate bandwidth when a quadrant
has more
usage than a neighbouring quadrant, even when a client is able to receive
signals from the
transmitters associated with each quadrant, because in order to do this, the
receiver needs
to be physically moved and/or the antenna polarization must be changed. As a
consequence
there is the possibility, because of the broad sectorization, of not being
able to dynamically
assign information carrying capacity as needed. To do so would involve
installation of a
more complex and dynamic interference monitoring system to oversee the
operation of the
contiguous network, and would require dynamic reporting of interference by the
client
terminals.
[0080] The issue of terminal complexity is already exacerbated by the high
cost of the
28 GHz component technology present in LMDS terminals. Large radii LMDS
systems
furthermore, require higher dynamic range and higher power amplifiers further
increasing
cost. Lowering the power amplifier output has the commensurate effect of
lowering the
information rate of the link. This becomes an issue, especially in the return
link from the
client when it is desirable to have high return link capacity, as would be the
case for a
client have a transmitting video server or providing Internet service
connectivity to other
clients.
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CA 02360282 2001-10-30
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[0081] It has now been found that a plurality of low cost hubs each for
communicating
with a substantially smaller area and each supporting frequency reuse provides
a more
effective broadband communication network. Use of radio frequency technology
operating
in the 3-7 GHz range and preferably in the 5.2/5.8 GHz range is low cost, and
will most
likely remain so in comparison to 28 GHz technologies simply because of the
issues of
ease of volume manufacturing and availability of more diverse semiconductor
technologies. Smaller service areas entail shorter path distances thereby
allowing the use of
lower power RF amplifiers. For those desiring high capacity return links,
increasing return
link amplifier output power and dynamic range is easily achievable with this
invention.
[0082] It is evident to those of skill in the art that increasing frequency
reuse results in
increased overall bandwidth and the attendant problems of co-channel
interference.
However, it has been found that the co-channel interference can be controlled
by the
physical orientation of an antenna and a rosette according to the invention,
and
furthermore, by applying technology capable of universal addressing and
control of both
client and hub terminals by TCP/IP and other standard IP protocols, a wide
ranging and
dynamically effective modicum of system control are exercisable limiting co-
channel
interference. Furthermore, because of the non-reliance on polarization
discrimination as
with LMDS, and because of the overlap of non-alike oblong microcells of this
invention, it
is possible to dynamically assign and re-assign capacity. This latter facility
also is very
useful in contending with strong, singular multipath interferes that arise in
wireless
systems; ie a modicum of frequency and angulax diversity becomes available to
the client
terminals with this invention.
[0083] Referring to Fig. 3, two circular transmission areas in the form of
cells
according to the invention are shown. A single cell 9 is broken into a number
of oblong
microcells 8. The microcells 8 are also referred to as picocells and petals.
Preferably, each
oblong microcell 8 overlaps its neighbouring microcells. Microcells are
assigned different
frequencies with possible reuse of frequencies within a single cell. Because
of the
appearance of the microcells, petals, within a cell, the architecture of a
cell is referred to,
herein, as a rosette. Preferably, overlap of microcells is substantial such
that a majority of
subscribers receive signals from two or more microcell transmitters.
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[0084] The centre of the rosette 9 contains a hub system 10 comprising a
transceiver
shown in more detail in Fig. 4. In the hub system 10, RF wireless signals are
converted to
digital data and routed by a Carrier Sense Multiple Access System (CSMA) to
and from
individual microcells 8. Data is sent from one rosette 9 to another rosette 9
via dedicated
interconnecting links based on any of fibre optic communication, dedicated
microwave
wireless communication, point-to-point atmospheric laser communication, and
wireline
communication techniques. One of skill in the art will know criteria for
selecting a point to
point communication method for use between cell hubs. As a result, it is
possible to route
data generated by a subscriber in one microcell 8 within a cell 9 to another
subscriber in a
microcell 8 of another cell 9. This is particularly useful for supporting
communication
media such as telephones, video conferencing, and Internet communications. The
system
accommodates non-wireless subscribers that are connected to the network via
the CSMA
system either at the hub or along the inter-rosette link. Optionally, non-
wireless subscribers
gain access to the system using Ethernet, TCP/IP, a modem or another
communication
system.
[0085] Typically, the physical configuration of each rosette 9 is a same
configuration,
as is the electronic system that defines the hub 10 and its antenna. Of
course, using a same
physical configuration and Hub allows employment of economies of scale in hub
production and facilitates maintenance, upgrading, use, installation, and
technical support
of the system. In practice, rosettes are placed over a coverage area in such a
manner that
microcells containing like-frequencies do not align with each other or
illuminate a same
coverage area. The microcells 8 in Fig. 3 are assigned a channel - frequency
range - from 4
available frequency ranges A, B, C, and D. When the radiators have
sufficiently small
sidelobe levels by spacing the microcells that are within channel A by at
least three other
microcells, overlap between radiated signals is substantially eliminated.
Consequently, it is
possible to electromagnetically isolate signals of like frequency microcells.
Isolation is
further enhanced by having subscribers to the system use highly directional
antennas
having narrow beam widths. Preferably, antennas having a beamwidth of 7.5-15
degrees at
-3dB power contour are used. Preferably side lobe levels are less than -35dB
at more than
45 degrees azimuth with respect to a peak for a rosette having 32 microcells
with 4
frequency bands each reused 8 times.
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[0086] It is, therefore, possible to reuse frequency ranges within a single
cell and to
reuse a same frequency pattern in adjacent cells. Frequency reuse is shown in
Fig. 3 with
frequencies repeating within each quadrant of the cell 9. Thus, each frequency
is reused
four times. This provides sufficient isolation between cells of a same
frequency range
while supporting substantial overlap between adjacent microcells. Each
microcell operates
independently of all other microcells so that clients within a microcell axe
provided two
way communication with the antenna in the hub 10. Of course, because of
microcell
overlap, a single client often has a choice between two or even three
different microcells.
This is more significant at distances further from the Hub where signal
attenuation is a
greater concern.
[0087] Though the diagram of Fig. 3 shows 16 petals in each rosette, it is
preferred that
a single rosette 9 comprise 32 or 48 petals. Four frequency channels are still
generally
sufficient. This allows for substantial frequency reuse and considerable
flexibility. It
allows sufficient flexibility in orienting adjacent cells to minimize
interference. It also
results in an amount of microcell overlap that is advantageous as set out
hereinbelow.
[0088] Rosettes do not have to have a same transmission range; alternatively
stated,
cells can vary in size. Typically, large rosettes are used in areas where
subscriber density is
low whilst rosettes having smaller radii are disposed in areas where
subscriber density is
high. Isolation between microcells is predicated on the propagation
environment. Because
of the high degree of frequency reuse within the system according to the
invention, it is
important to ensure that the co-channel interference experienced by a
subscriber is kept at
or below such a level that a useable Signal to Noise plus Interference ratio
is maintained at
both the subscriber and hub ends of the communication link. In order to do
this a number
of system level design considerations are followed, which are listed below.
[0089] A lower power frequency band is used for communication with users close
to
the rosette hub or not substantially affected by propagation losses. The lower
power band
allows the use of lower power amplifiers for equivalent radius cells. The
lower frequency
allows the use of lower power amplifiers for equivalent radii of cells. Higher
power bands
are provided for users more distant from the hub or those who are
substantially affected by
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propagation losses. Thus each microcell is effectively divided into a near-in
microcell and
a far-away microcell.
[0090] Effective isotropic radiated power (EIRP) Quantification: Subscribers
within a
rosette are assigned frequencies having specific EIRPs. Like frequencies in
microcells of a
same rosette are assigned the same EIRPs. For every rosette and its
microcells, the EIRP
assignments span the difference in EIRP between low and high power bands
typically span
the difference in EIRP between near-in and far-away subscribers, which are
respectively
close to the hub or on the periphery of the cell's coverage area. The far-away
EIRP is
typically the highest EIRP allowed by licensing regulations and in essence,
defines the
extent of the rosette.
[0091] Dynamic Propagation and Interference Environment Monitoring: Every
subscriber terminal has the facility to monitor the signal environment and
report back to a
system controller the level and source of detected interference. Every
microcell of a rosette
contains a unique identifier in its downlink data stream. Every subscriber
also has a unique
identifier that is detected and decoded by the hub. As part of this monitoring
system, the
subscriber terminal reports to the system controller the EIRP Quantification
requirement
data so that it is assigned an appropriate downlink data channel. Further,
such a monitoring
and feedback system allows for dynamic assignment of a receiver of a
particular subscriber
to one of the antennas within the hub that transmits to the area where the
receiver is
located. Thus, because of overlapping adjacent microcells, selection of a
microcell from a
plurality of available microcells is possible. This allows for system
redundancy in case of
failure, environmental changes and so forth. It also supports load balancing
between
adjacent microcells because subscribers at an edge of a microcell, or more
accurately stated
an area within two adjacent microcells, are optionally served by the channels
within that
microcell or within an adjacent microcell.
[0092] Each microcell contains a number of high capacity, wideband RF data
channels.
These channels use a modulation technique that is robust in face of multipath
and co-
channel interference. Typically QPSK is employed. Each channel has a
connection to the
CSMA data hub, typically built to the IEEE 802.3 standard and called
"Ethernet."
CA 02360282 2001-10-30
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[0093] Data Processing and Delivery
[0094] Referring to Fig. 4, a simplified block diagram of a transmit antenna
and a
receive antenna for use in the hub 10 is shown. A wide area network in the
form of an
Ethernet network is in communication with an antenna driving circuit. Frames
are received
and buffered in volatile memory. Once complete, the frames are provided as
superframes
to a scrambling encoding processor for encoding. From the scrambling encoding
processor,
the data is provided to an RF modulator for modulating the data within the
frequency range
of the microcell. The RF modulator modulates the data and provides a modulated
signal to
the antenna,. The antenna is for radiating a signal that is highly directional
and has low
sidelobes. From the antenna is radiated a signal forming the microcell
transmission signal.
[0095] Since the system supports bi-directional communication, the receiver
block
diagram is also shown. A receive antenna receives an RF signal from a client.
The signal is
demodulated to extract the signal data and the data is decoded by a
descrambling decoding
processor. The data is then arranged in frames and provided to an Ethernet
encoder for
transmission via the Ethernet. This same block diagram applies to individual
subscriber
antennas as well. In this fashion, the subscriber appears to be connected via
a LAN to the
hub and the hub appears connected via the LAN to other hubs. The resulting
network acts
as if locally installed even though it may span many kilometers.
[0096] In use, Ethernet data frames identified as being for a remote wireless
subscriber
are identified, accepted by an Ethernet interface, and organised into
microcells based on
the subscriber location. Frames of data are labeled and stored in a temporary
volatile
memory. At instances these frames are retrieved en masse and assembled into
large
superframes, which typically not only contain the Ethernet information frames
but also
frames of data identifying the microcell and giving other system level
information.
[0097] Super frames of data are then scrambled, encoded, and encoded with
synchronization bytes. The data is then modulated and sent out on the RF
channel. At the
subscriber terminal, all data transmitted is demodulated and decoded. Data
identified for
the subscriber is retrieved, segmented as the original Ethernet frames and
provided to the
subscriber Ethernet interface as such. From the interface, the data is
provided to the
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subscriber CPU. System level information is also decoded and provided to the
CPU and
specifically, to that application program running on the CPU that controls the
subscriber
terminal.
[0098] On the return link to the hub there are a number of techniques that
mediate the
flow of data from all of the subscribers registered on a channel. Receiving
lower
bandwidth data from subscribers at the hub, identifying the data and
performing actions
accordingly is well known in the art of communications and is not detailed
herein. For the
purpose of the present description, it is assumed that the subscriber data is
packaged as
Ethernet frames, and encoded, synchronized, and modulated in much the same
manner as
the down link data. Of course, it is evident that this need not be so.
[0099] Hub and Subscriber Antenna Characteristics
[00100) An important design issue to the system is the antenna used at both
the
subscriber and hub end. According to the present embodiment and because of the
significant frequency reuse in the system it is important that antennas used
in the system
reject interference. It has been found that a level of co-channel interference
experienced
overall is directly related to the side lobe levels of antennas used in the
system.
[00101] The antennas, other than having low side lobe levels are designed with
narrow,
highly collimated beams. Multipath delay spread is a problem in high-speed
wireless
delivery systems and one way to mitigate this problem is to only accept
signals having a
delay spread no greater than 10% of the bit duration. For rosettes operating
over 2 km
ranges with 5 Megabit per second data rates, this translates to a beam width
of about 8
degrees, after which a steep attenuation in the main lobe is desirable in
order to reject
multipath.
[00102] In accordance with a further embodiment polarised antennas are used
and
signals having different polarisations are transmitted to, in effect, double
the bandwidth of
the system. For example, if a rosette comprises 2 frequency ranges and two
polarisation
states - vertical and horizontal, the result is four frequency ranges each
having twice the
bandwidth of four separate frequency ranges each having like polarisation
covering a same
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CA 02360282 2001-10-30
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overall frequency range. Therefore, polarisation and other techniques may be
employed
within a rosette in order to increase bandwidth.
[00103] It is preferred that sidelobes from all antennas are limited according
to the
equation below:
C =hOlog(N-1)+SL +af
Io
wherein C/Io is a carrier to interference ratio and is a threshold in dB for
operation of a
demodulator of the modulated signal at a known performance level with Io, the
interference
noise, substantially greater than thermal noise No, N is equal to a number of
like frequency
petals within a rosette, SL is mean sidelobe level of the radiators at angles
greater (M-
O.5)X(BW,,) away from the free space main lobe of the beam where BWh is the
width of
the individual microcell, and of is dependent upon the environmental factors
associated
with scattering of signals as expressed in dB.
[00104] When radiators meeting this requirement are used, the receive antennas
act to
filter out noise and the transmit antennas act to reduce transmitted inter-
microcell
interference. Therefore, the entire system acts to provide isolation between
microcells of
same carrier frequencies.
[00105] Examples
[00106] The Unlicensed National Information Infrastructure Frequency
Allocations
from S.lSGHz to 5.825GHz were used in a series of experiments conducted in an
urban
residential and commercial environment characterized by high foliage and roof
top/building presence in the signal path. Tests were conducted with rosette
petals having
11.25 degrees beamwidths in azimuth and elevation. Furthermore, simulation
studies were
conducted to examine the behaviour of constellations of rosettes over a
contiguous
coverage area. The simulations, where possible, used data taken from the
experiments.
[00107] In both the experiments and simulation studies, frequencies were
reused every
45 degrees thus requiring four different frequency ranges each reused 8 times.
A parabolic
Tx/Rx low sidelobe antenna having -30dB sidelobes and a gain of 25 dBiC was
used at the
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CA 02360282 2001-10-30
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hub with subscriber antennas having similar characteristics. 200 MHz of
spectrum was
assigned to the system for the transmit (forward link) direction and 100 MHz
was assigned
to the return link. Therefore, each petal is assigned SOMHz of bandwidth in
the forward
link and 25 MHz in the return link.
[00108] Simulations where conducted on the carrying capacity of a 5.2/5.8 GHz
rosette
system as described and compared to a typical 28 GHz LMDS system. .Assuming a
cell
size of one kilometer in radius, there are approximately 5000 homes within a
cell and
approximately 160 homes within a petal. Thus the bandwidth to each home during
maximum usage (all homes demanding as much bandwidth as possible) is 50/160
MHz or
approximately 1 /3 megabits/second per home in the forward direction when
using a robust
modulation scheme for DVBS/ QPSK (ETSI 300 421) generating an information
density
of 1 bit/sec/Hz. This is substantially more than the 16,000 bits/second for
the prior art
LMDS system. Since, at any time it is unlikely everyone within a same area is
using the
communication medium to its fullest, most subscribers will always see a
substantially
greater amount of bandwidth.
[00109] Next, an analysis is presented below for demonstrating the behavior of
systemic
C/I in a broadband network according to the invention. The analysis considers
singular
rosettes and constellations of rosettes operating over a large contiguous
area.
[00110] The primary constraint on spectrum reuse in wireless systems is co-
channel
interference. Most of the literature studying the channel assignment problem
has been
aimed at cellular phone systems where the antennas used are either
omnidirectional or have
provide for sectors within a cell having very wide sectorial beam widths. When
a sector is
assigned a frequency range or channel, the term frequency sector is used. A
reused
frequency sector is a repeated frequency assignment or channel within two
different
sectors. Reused frequency sectors are typically spaced by a number of cell
radii apart as is
the case with, for example, 800 and 1900 MHz wireless (cellular and PCS)
telephony, and
can be reused within a cell as shown in Figs. 2a and 2b. With LMDS, it is
proposed to
reuse frequencies in different sectors within a same cell by employing
polarization
isolation. Otherwise, LMDS makes use of a same frequency sector only once in
the cell.
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Whatever the case, in LMDS the frequency is reused in the next cell as shown
in Figs. 1 a
and 1 b.
[00111] The channel assignment problem in rosette systems that utilise highly
directive
antennas is quite different. The same frequency sectors are used a
multiplicity of times in a
same cell. Adjacent cells also have exactly the same configuration of
directive antennas,
microcells, and frequencies, and spacing between adjacent rosettes is often
smaller than the
rosette radii. In fact, like frequency microcells commonly overlap. Further,
the position and
the configuration of interlacing of the cells is changed by rotating the
microcells with
respect to each other, and in so doing, the co-channel interference seen by
the subscriber
terminals within the cells is also changed.
[00112] The high directionality of the microcell and subscriber antennas
significantly
attenuates the co-channel interference originating from other like-frequency
microcells.
The degree to which co-channel interference is attenuated is dependent on a
number of
factors, such as antenna height, average beamwidth and sidelobe level of both
the
transmitting and receiving antennas, and the propagation environment. This
last factor is
spatially variable, has a pronounced effect on the C/I that is at the
receiving terminal, and
ultimately places limits and constraints on narrowness and spatial separation
of like
frequency microcells in a rosette. Narrowing the beamwidth of a microcell and
reducing
the angular spacing between like frequency microcells beyond a certain point,
for instance,
results in no commensurate increase in the frequency reuse factor of a
rosette, regardless of
the sidelobe level, simply because multipath scattering rises to significantly
deleterious
levels under such conditions.
[00113) Experimentally, it has been found that in 5.2 GHz rosettes operating
with a 45
degree spacing between like-frequency 11.25 degree width microcells,
scattering degrades
the isolation between like-frequency microcells by a nominal, af, of 8 dB
above what is
predicted with free-space side-lobe level measurements of the microcell
antenna patterns.
This factor, af, is believed to be the aggregate of many multiple reflections
and has not
been separately identified. They are generated by radiation emanating from the
sidelobes
as well as the principle lobe of the microcell antenna. It is believed that
this factor is
CA 02360282 2001-10-30
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strongly dependent on wavelength and polarisation of the frequency and
dimensions of the
objects situated within the propagation environment.
[00114] Additionally, it has been found that the propagation path loss
exponent for the
environment described above is typically between -2.4 and -3.4; and that it
varies both as
a function of antenna height and distance separating transmitting and
receiving antennas.
These findings are based on over 400 detailed measurements taken in highly
foliated urban
residential environments typical of proposed service areas for the present
invention, and
are consistent with other findings in current literature on urban 5.2 GHz
propagation and
such fields as C and Ku Band satellite communications where antenna side-lobe
degradation by multipath scatter is noted.
[00115] While it is impossible to quantify the individual sources of the
multipath which
contributes to as, it is possible to contend with strong singular reflections
that are often
present and significantly deleterious because they are at levels within the
same order of
magnitude as direct and desired microcell signals
[00116] According to an embodiment, such strong direct scattered signals are
monitored
by the receiving terminal. Analysis of the signals results in identification
of an originating
microcell. This function is undertaken by the Systemic Co-Channel Interference
Controller
(SCIC), which oversees the operation of the rosettes forming a contiguous
network. The
SCIC is provided with an ability to switch radiation emanating from any
microcell on and
off, thereby facilitating the sampling and registration of strong interferers
by receivers.
Problematic radiators that generate strong multipath interference are turned
off. Because of
substantial overlap between adjacent microcells, the resulting rosette likely
maintains
coverage of most of the same area. Of course, when two radiators are used for
a single
microcell, one near-in and one far-away, only the radiator that results in the
interference is
affected. Alternatively, the terminals being interfered with are assigned
interference free
channels. For example, addition of a fifth channel for use when substantial
interference
exists is a possible solution.
(00117] Simulation results set out below are based on a rosette configuration
with 8
petals per frequency group as shown in Fig. 7. Each beam is 11.25 degrees in
azimuth with
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CA 02360282 2001-10-30
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each subsequent beam offset by 45 degrees. There are in total 4 groups of
petals with each
group offset from the next. Only one group is shown in Fig. 7.
[00118] Both intracellular and intercellular interference are analysed. Only
interference
from beams using a same frequency is considered. Adjacent channel interference
is
ignored. Experiments and simulations described below were conducted with the
following
parameters:
Parameter Default value
Frequency 5.2 GHz
Maximum Cell Radius 2000m
Subscriber Height l lm
Tower Height 25m
Subscriber Up tilt Angle 0 degrees
Tower Antenna Down Tilt Angle 0 degrees
Subscriber Antenna Beamwidth 11.25 degrees @ -3dB Contour
Hub Antenna Beamwidth 11.25 degrees@, -3dB Contour
Sidelobe Levels (all antennas)-30 dB
Rosette Packing Architecture Hexagonal
EIRP Constant for all hubs
Environment: Propagation Path loss 2.9+/-0.5
[00119] The antenna pattern used in simulation, was
P(B.~) - (sin"' 8 sin" ~)
where P defines the equal gain contours of the antenna pattern, and the values
of m and n
are simulation factors adjusted to generate simulated main lobes, resulting in
patterns with
a3dB beam width of 11.25 degrees in azimuth (0) and in elevation (~). This
closely follows
that used in experimental and prototype systems. Such a pattern gives a
nominal directive
gain of 25 dBi. A sidelobe level of-30 dB was used for all angles greater that
30 degrees
away from the main lobe. Both subscriber and hub antennas were alike in the
simulations
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and the experimental trials
[00120] A path loss exponent of 2.5 was used in the simulations. This is in
line with
experimental results where the path loss for the average terminal has a mean
of about 2.9
with a variance of 0.5 for the urban environment
[00121] A power control strategy was utilised to minimize intracellular
interference.
The dynamic range of power produces circumferential zones of coverage around
the hub.
A user in a given zone is provided a transmit tower antenna transmitting
enough power to
reach the outermost subscriber in the zone. Users of a same channel in a
different
microcells are then constrained to being in a same zone, and thus at a same,
constant EIRP.
This power control strategy was used throughout the simulations. It is assumed
that each
cell is identical in how its dynamic range is divided into power zones and
attributed
channels to the respective zones. In the 5.15-5.35 GHz frequency plan embodied
within the
experimental system, typically two zones would arise; a low power zone, near-
in, for
communications within the immediate area of the hub typically to a radius of
700 meters,
given a 25 dBm/MHz EIRP limit, and a high power zone, far-away, for
communications to
the periphery typically 1500-2000 meters for a 34 dBm/MHz EIRP limit.
[00122] Intracellular Interference
[00123] Intracellular Interference is the co-channel interference that a
receiver within a
designated microcell in a single rosette experiences due to the other like-
frequency
microcells within a same rosette. A single rosette used in the measurement and
simulation
is shown in Fig. Sa. The PDF for such interference is shown in Fig. Sb.
[00124] The co-channel interference experienced is due solely to the azimuth
position of
the receiver within the microcell and the sidelobe level. In a case where
there is no
multipath scattering then:
C =hOlog(N-1)+SL+afI
to
where SL is the ratio between the received power in the desired microcell and
the mean
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CA 02360282 2001-10-30
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sidelobe level; note that SL depends on the azimuth position of the receiver
with respect to
the main lobe; N is the number of like frequency microcells in the rosette;
and of is the
multipath scatter factor, which in ideal circumstances is equal to 0.
[00125] Fig. Sc shows how the C/I under such circumstances is invariant with
distance
away from the hub. Fig. Sd shows measurements that were taken in a highly
foliated urban
environment where the of is about 3 dB. The measurements also demonstrate the
invariance with distance of C/I.
[00126] Intercellular Interference
[00127] Intercellular interference is the co-channel interference that a
receiver within a
designated microcell in a single rosette experiences due to the other like-
frequency
microcells in adjacent rosettes.
[00128] In the simulation study, a constellation of 19 rosettes packed into a
hexagonal
architecture was assumed as shown in Fig. 6a. Interference as seen by a
subscriber in a
randomly chosen target microcell was calculated; this interference is based on
radiated
signals simulated based on all other like-frequency microcells in the
constellation.
[00129] In the first case, microcells were aligned as shown in Fig. 6a.
Typically 4000
random placements of a subscriber were undertaken and the resultant C/I was
calculated
based on the criteria given above. The resulting data was used to generate a
Probability
Distribution Function (PDF), which shows the probability of achieving a stated
C/I in the
given scenario shown in Fig. 6a. The resulting PDF is shown in Fig. 6b.
Accordingly,
approximately 33% of the terminals in this situation receive a C/I of 14 dB or
better; which
is close to the threshold of QPSK modem operation.
[00130] Fig. 6c shows the C/I that a typical receiver situated along the
boresight axis of
the main lobe defining a microcell would experience as a function of radial
distance from
the rosette centre. Accordingly, at distances greater than 1200 meters from
the hub the C/I
of the average user along the centre of the microcell is below 14 dB.
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[00131] The effect of rosette rotation is demonstrated in Fig. 7a, where the
rosettes in
the 19 element hexagonal constellation are changed in alignment with respect
to each
other, thereby no longer having regular alignment shown in Fig. 6a.
(00132] The resulting PDF of C/I is shown in Fig. 7b. Accordingly, in this
situation with
rosette rotation, about 97% of the users experience a C/I of 14 dB and
greater.
[00133] Fig. 7c shows the C/I that a typical receiver situated along the
central axis of a
microcell would experience as a function of radial distance from the rosette
centre under
circumstances of rosette rotation. Accordingly, even at 2000 meters from the
hub the C/I of
the average user is approximately 15 dB and greater.
[00134] These results demonstrate the beneficent effects that rosette rotation
and
microcell interlacing has on C/I performance, and ultimately, the information
carrying
capacity of such a highly organized wireless architecture.
[00135] Systemic Co-Channel Interference Control
[00136] A brief description of the SCIC was given above. The algorithm
operates in
controlling the overall co-channel interference generated by the microcells
and their client
subscriber terminals. This control is possible because every microcell radio
terminal, be it
hub or subscriber, has an address in the form of an Internet Protocol (IP)
address.
Similarly, the means of communicating between the SCIC computer and the
rosette
network is, for example, via TCP/IP (Transport Control Protocol/Internet
Protocol).
[00137] The SCIC attempts to maintain a figure of merit for the constellation
of rosettes
forming a contiguous network. The Mean Systemic Co-channel Interference Ratio
(MSCIR) is preferably maintained, and it is the ratio of desired carrier power
radiated by a
hub of a rosette to a subscriber to the interferening co-channel carrier power
generated by
emissions from all other like frequency microcells within the rosette and
other adjacent
rosettes.
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[00138] The MSCIR is affected by the following functions:
(a) maintaining a specific side lobe suppression level for microcell and
subscriber antenna beams;
(b) positioning microcells of adjacent rosettes in such manner that like-
frequency zones of illumination are geographically isolated from each other
and do not
geometrically align;
(c) creating isolation between subscribers and interfering zones of
illumination
by mechanically or electrically steering subscriber antenna beams away from
such zones;
(d) having the subscriber terminal actively monitor the propagation
environment and report co-channel interference levels due to interfering
signals from other
microcells;
(e) adjusting the EIRP's of hub and subscriber terminals.
[00139] Rosette Frequency Grouping to effect the establishment of a MSCIR
[00140] Preferably, a compliment of frequencies divided into N distinct
groupings of
channels is assigned; each grouping is assigned to a specific microcell and
repeatedly
assigned to the adjacent N+l; 2N+-1; 3N+1;... microcells of the rosette. In
this manner the
azimuth spacing of like-frequency oblong microcells in a rosette has a maximum
possible
spacing for a selected frequency reuse ratio. Preferably when the number {M}
of oblong
microcells per full rosette is a multiple of the number {N}, the number of
microcells
having exactly the same channel band is equal to (M/N}.
(00141] The individual channels of a distinct grouping are blocked into sub-
groups of
fixed EIRP, each sub-group stepped in EIRP with respect to the other.
Subscribers are
assigned channels only from a sub-group where the E1RP is sufficient to meet
the MSCIR
requirement. The stepping is of a dynamic range for meeting MSCIR requirements
of near-
in and far-away subscribers within the microcell.
[00142] Data Routing within the Rosette System
[00143] In encoding and modulating data within the directional forward link RF
signal
transmitted from each radiator, any of a number of transmission schemes is
useful
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CA 02360282 2001-10-30
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provided they are robust enough to contend with the vagaries of the
propagation
environment and the co-channel interference Typically, a TDM divided stream in
which
concatenated blocks of data in the stream are identified for specific
subscribers resident
within a microcell is used. Each frequency range, channel, interfaces with a
local area
network (LAN) resident within the hub. For example, the LAN is a Carrier
Sensed
Multiple Access System using Collision Detection typically known as the
Ethernet or
IEEE802.3 Standard. Data on the Ethernet is received by an electronic
subsystem that
interfaces with an individual channel of a microcell. The data is received as
a standard
Ethernet Frame. This frame of data is buffered in a volatile memory, and then
buffered
frames are retrieved, concatenated with spacing between frames filled with
either dummy
bits or system specific bits to form super frames. The super frames are then
scrambled,
Viterbi encoded, Reed-Solomon encoded, and modulated for transmission. Super
frames
thus created are then TDM slotted and radiated into the microcell on a signal
at the channel
frequency. One standard that is suitable for this type of forward link data
distribution is
based on the ETSI (European Technical Standards Institute) 300-421.
[00144] This standard also specifies the use of QPSK modulation, which is
robust in
face of co-channel interference.
[00145] A subscriber receives data super frames modulated within an RF
frequency
within a microcell. The subscriber system demodulates all data contained in
the super
frames and detects Ethernet frames directed specifically to the subscriber's
computer and
communication system. Ethernet data frames identified for the subscriber are
presented to
the subscriber computer as Ethernet Frames on the subscriber LAN. Therefore,
each
subscriber appears connected to a LAN. Lost or corrupted frames are ignored,
leaving it to
the higher levels of the serving protocol to either retransmit the lost data
in the case of, for
example, TCP/IP sessions between the subscriber and network or simply continue
the
streaming of data in the case, for example, of UDP packet streaming for video
services.
Each microcell channel is given a unique identifier imbedded in the
concatenated forward
link bit stream of super frames. Each subscriber transmission is given a
unique identifier,
which is imbedded in the return link data to the hub. There is a return link
channel
accessible by all subscribers within a microcell. Access to the channel is in
a TDM slotted
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CA 02360282 2001-10-30
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format, which is pre-arranged by the hub controller. Requests for access or
transmission of
short data messages are done on a random access, contention basis within
available TDM
return link slots
[00146] Using Ethernet as a wireline access protocol and TDM with reservation
and
contention slots, it is possible to devise a system that supports efficient bi-
directional data
transmission over the wireless communication medium within a cell. The
resulting
communication is applicable to many fields including voice, video and data
communication.
[00147] A system according to the present invention is suitable for many
communication applications. These include Internet service provision, video on
demand,
interactive television, voice networks, and so forth. Because of the wireless
technology
employed, there is little installation cost, no cables to run, and very
simple, unintrusive
user setup procedures. Also, the chances that a communications link will be
lost due to
digging and so forth are non existent since the system is not based on a
physical
connection to the subscriber's location. The architecture provides a system
that is modular,
scalable, and transparent to data or protocols communicated through the
architecture.
Because of the high bandwidth that is supported, there are many commercial,
medical, and
educational applications for the technology.
[00148] The system envisaged operates in the 5150-5350 MHz bands on the
forward
link and 5725-5825 MHz bands on the return link, however it can be scaled to
any
frequency. Operating in these stated bands requires sharing on a co-channel
basis of
frequencies common to a number of Low Earth Orbiting (LEO) satellite systems,
which
axe primary users of these bands. In these bands, the lower bands are used to
transmit
signals from a hub while the higher bands are used to transmit signals from
subscribers to
the hub. This limits interference with satellite bands to those signals
emanating from the
hubs. To further mitigate interference to the satellites it is necessary to
use highly directive
antennas, having the characteristics stated above, and orient these antennas
below the
horizon by 3 degrees so that the -30 dB sidelobes are maintained at elevation
angles of 22
degrees above the horizon. Further, the maximum EIRP's in the band 5150-5250
MHz
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CA 02360282 2001-10-30
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must not exceed 25 dBm/MHz and in the band 5250-5250 it must not exceed 34
dBm/Mhz.
[00149] Designing a system using rosettes for wireless transmission of data is
dependent
upon, power received at an antenna, a path loss exponent, co channel
interference, different
modulation techniques and capacity efficiency.
[00150] In Figure 8, an example is shown of two rosette hubs spaced in
relation to each
other. The first rosette 80 is set up in a location, providing data access to
a number of
users. Once more demands are placed on the available bandwidth provided by the
first
rosette 80, a second rosette is provided to handle the increased data traffic.
The second
rosette 81, should be oriented in relation to the first rosette such that
there is a minimal
amount of single frequency channel interference between the two rosettes 80
and 81, and
that the system capacity is preferably maximized. The sequence of the second
rosette EIRP
is determined in order to minimize co-channel interference.
[00151] Co-channel interference is calculated as a ratio is calculated as
ratio of desired
signal over the aggregate total of undesired signals, including noise, which
occupy the
same channel.
~~~'~ ~ I ~+ ~ ~)
[00152] Where the desired carrier signal C = PR, the aggregate total of
undesired signals
occupying the same channel is interference Io = h + I., and noise = No. PR is
the total power
received by a receiving antenna with an effective area AR.
[00153] There are three types of interference, Io, for a single channel: intra-
cell
interference, or inter-cell interference.
[00154] Intra-cell Interference is caused by same channels of a same rosette
interfering
with one another. The intra cell interference is dependent on the angle of the
single
frequency channel itself within the rosette 82. Where in this case, I. is the
sum of the five
other interfering frequency-like micro-cells, 83 84 85 86 87, from the same
rosette.
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CA 02360282 2001-10-30
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[00155] Inter-cell Interference is caused by same channels of different
rosettes
interfering with each other. Inter cell interference is dependent upon a
distance D from the
other interfering rosette hubs, as well as on an angle of the single frequency
channel within
the interfering rosette.
[00156] Power received at an antenna is dependent upon the area of the
antenna, gain of
the antenna, the angular orientation of the antenna to a transmitter, and the
transmitter
power EIRP. The path loss exponent is experimentally measured from an outdoor,
roof
mounted system, where the surrounding environment has moderate foliage
providing
attenuation to the received signal. Different modulation techniques affect the
capacity
efficiency of the system. Higher bit rate modulation techniques are more
efficient but are
also more susceptible to noise. Different modulation techniques are used for
different
users,
[00157] depending on the available C/ (Io+No). Users having higher C/ (Io+No)
will
therefore obtain higher data transfer rates. The following table outlines the
modulation
technique which is useable for a given C/ (Io+No).
~.:' I l~~t~.-ac~~~l~~t~orc Tc~t~iqr~~. ~'L~I~~c~t~r
ldl~) ~.~~~~ci (E~it' Hz)
~:1~9 Ni~~je (1
ltl BE~'~K ~-~~~~htaac ~~~tf~ l~~y~r~~:)1
l i.~1 ~,~ 1~'."~~ ( ~tlildrtf'~tE~l.
~~~1'c1.1~: 4~1i~ ~i;~~llt1~~;!~
2(~. 1~1 ~,~~t~~ ~ lf1-~tiit~.' C"~lJctH1"iT~(I!"4
~l'13~~tllt:~G'
110 (~ El leitl~tl,)
2t~ ~'i~ ~.~~Ifl fif~.~-state q~~it<~tt~rc
~~~~l~lit~~dc
r~~c~i~h~tic~rv)
[00158] Figure 9, shows simulation data for a single rosette 80, where in this
case the
rosette coverage area is 4000m x 4000m with an EIRP = 34dBm/Mhz., 24 petals
are shown
in the simulated rosette pattern, visually representing C / (No+Io) for the 24
microcells of
the rosette. Intra-cell interference, I., is approximated as a function of the
angle. As
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the angle decreases the transmitting gain of the antenna is reduced with no
change in
propagation path loss. As a result, the co channel interference drops.
[00159] Co-channel interference deteriorates with distance from the rosette
hub center
due to the inclusion of noise. As distance from the hub center increases,
intra-cell
interference becomes less dominant since the intra-cell interference is
approximately equal
to C/ No after 1 OOOm from the rosette center. In this case h = 0 as there are
no other rosette
used in the simulation.
[00160] Each rosette comprises 24 micro-cells, divided into 4 groups of like-
frequency
channels, each of which is reused in 6 equiangular spaced intra-cells. Figure
10 shows the
six possible different channel sequences for each rosette. The six possible
channel
sequences are: ABCD, ABDC, ACBD, ACDB, ADBC, ADCB. Furthermore, each of the
four channels within a single rosette are oriented at an angle a, for instance
in relation to
magnetic north, in a clockwise direction, as is shown in Figure 11.
[00161] All angle measurements are chosen with respect to magnetic north in a
clockwise direction. The possible values for the angle, a, are: a = 0°,
a = 15°, a = 30°,
a = 45°. Once the four frequencies within a rosette are orientated at
60°, with respect to
magnetic north and in a clockwise direction, the exact same configuration is
observed as in
orientation at 0°. There are 4 unique angular orientations. Therefore
each rosette supports
up to a total of 24 different configurations, 4 angular and 6 different
channel sequences.
[00162] In placing the second rosette 81 in relation to the first rosette 80,
care must be
taken to minimize the Intra-cell and inter-cell Interferences. The simulation
parameters for
each of the rosette hubs, 80 and 81 are: EIRP = 34 dBm/MHz, Path loss exponent
=
0.0002D + 2.5589. The first hub 80, has a coverage area of 2000m x 2000m, at
an
orientation a = 0°, with a frequency sequence ABCD, serving 3000 users.
[00163] Figure 12a shows the co channel interference for the first hub when a
best
configuration second rosette 81 is placed in relation to the first 80. The
second hub 81 is
oriented SOOm away from the first and at a = 60° in relation to the
first 80, using the same
frequency sequence as the first, ABCD. A worst case configuration for the
first rosette 80,
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is shown in Figure l2b,when a second rosette 81, in a worst case
configuration, is oriented
SOOm away, at an angle a = 30°, using the same ABCD sequence. The mean
co channel
interference available to existing subscribers is used as a gauge for
obtaining the optimum
configuration. Clearly the area of minimal co channel interference for the
best case
configuration is greater than the area of coverage for the worst case
configuration. The best
case configuration allows a greater rosette coverage area having minimal co
channel
interference.
[00164] Figure 12a represents the C/(Io+No) of subscribers of the first
rosette 80. Users
oriented in an opposite region of interfering hub receive more interference.
This
interference is explained by receiver gain, since in this region subscribers'
receiver
antennas are pointing towards the second hub 81. As a result the receiver gain
will be set to
near peak gain causing a higher inter-cell interference.
[00165] The installation of the second rosette 81 causes a drop in C/ (Io+No)
for
subscribers using the first hub. As is shown in Figure 13, the co channel
interference drops
from 29.736 dB to 26.037 dB. Re orienting and re sequencing the second hub 81
causes
improvement to C/ (Io+No) for the first hub, up to 26.514 dB. However, this
improvement
is mostly insignificant. The C/ (Io+No) distribution of users varies with
different
configurations, with little deviation in mean C/ (Io+No).
[00166] Reducing C/ (Io+No) for either of the two hubs is desirable. However
in order to
offer an increased reduction in co channel interference, more variability in
rosette
parameters must be examined. A rosette comprising 48 micro-cells, divided into
8 groups
of like-frequency channels each, with each of which is reused in 6 equiangular
spaced
intra-cells, yields a rosette with 8 possible angular rosette orientations
with 5,040 different
channel sequences. Therefore with 48 micro cells each rosette supports up to a
total of
40,320 different configurations. Since the number of configurations is greatly
increased,
there is a higher chance of significantly reducing co channel interferences.
[00167] Figure 14 shows a graph of simulation results where 24 and 48 petal
rosettes
are compared. Simulation parameters used for both rosettes are: EIRP = 23
dBm/MHz,
Path loss exponent = 0.0002D + 2.7589, Number of users = 3000, Range of users
=
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CA 02360282 2001-10-30
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1000m. The first 48 petal rosette has a coverage area of 1000m x 1000m,
oriented at a =
0°, with the frequency sequence ABCDEFGH. The second hub is located at
a distance of
300m form the first, with a= 60°.
[00168] From simulations it was found that optimum configuration for the first
hub's
users, based on the mean C/ (Io+No) for users of the first rosette, is at an
orientation 0° with
a sequence of ABCDEFGH. The worst configuration is for the second hub at a =
37.5°,
with a sequence of ACBDEFGH. For the simulated 24 petal rosette, the optimum
configuration yields an angle orientation a=0°, and sequence ABCD,
while the worst
configuration yields an angle a=30°, and sequence ABCD. Therefore with
more variable
parameters for each rosette, the co channel interference is reduced.
[00169] Doubling the number of channels as in the 48-petals rosette, improves
the mean
[00170] C/ (Io+No), regardless of the orientation and sequence of the second
rosette.
This is due to the narrower beamwidth of each petal within the rosette. The
transmitter gain
does not decrease with angle for a 48 petal rosette as much as it does for a
24-petal rosette,
and therefore C/ (Io+No) improves. However, even with an optimum configuration
for the
second rosette, existing subscribers to the first rosette obtain a decreased
C/ (Io+No).
Considering that twice the amount of equipment is needed for 48-petals
rosettes, the
additional cost incurred is often not worthwhile for such little performance
improvement.
[00171] Controlling of the EIRP also allows for improvement in the system co
channel
interference. By reducing the EIRP of a most 'interfering' micro-cell from the
second hub,
the mean C/ (Io+No) of the first hub's subscribers will improve. It is desired
that any new
inclusion of a rosette does not affect the C/ (Io+No) of existing hub's
subscribers. Therefore
modification of EIRP for each petal from within the rosette is performed
accordingly.
[00172] For simulation purposes after including the second rosette, 81, the
following
parameters are utilized. At least 80% users falling within the first hub have
a C/ (Io+No) of
> lSdB, and all users of the first hub have a C/ (Io+No) of > OdB.
[00173] The EIRP for the first hub is 23 dBm/MHz, the path loss exponent =
0.0002D +
2.7589. The first hub has a coverage area of 1000x1000m, with a = 0°
and with a ABCD
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CA 02360282 2001-10-30
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sequence. The second hub is located 300m away, at an angular orientation of
60° to the
first, with a= 0° and an ABCD sequence. The number of users is 3000.
[00174] Figure 15 shows simulation results for the second hub when the EIRP is
varied,
or moderated, for each of the petals 1 to 6, in order of angular deviation
clockwise from
magnetic north. Figure 16 illustrates the C/ (Io+No) distribution plot of the
first hub when
the EIRP of the second hub is moderated. In Figure 16a, a distribution plot is
shown for the
first hub when the second hub has a moderated EIRP.
[00175] Figure 16b shows a graph where of the interference probability with
respect to
C/ (Io+No) for the first hub when the second hub has moderated EIRP. For each
micro-cell
within the second rosette, the first rosette's micro-cell that provides
subscribers with the
most interference is determined. Then the EIRP of the second rosette's micro-
cell is
reduced until subscribers provided by that first rosette micro-cell fulfill
the two criteria
assumptions: at least 80% users falling within the first hub have a C/ (Io+No)
of > lSdB,
and all users of the first hub have a C/ (Io+No) of > OdB.
[00176] Varying the EIRP within the hub is one way to increase the co channel
interference, however determining optimum hub separation is also a possibility
for
reducing C/ (Io+No). Figure 17 shows a graph of interference probability vs.
C/ (Io+No). For
simulation purposes a fixed EIRP of 23 dBm/MHz is used for both hubs, the path
loss
exponent = 0.0002D + 2.7589, the second hub is located 200 to 1000m away from
the first,
at an angular orientation of 60° to the first, with 3000 users. In
Figure 17, the C/(Io+No) is
determined for subscribers to the first hub as the separation of the second
hub is varied
from 200m to 1000m. For distances less than 800m the C/ (Io+No) distribution
approaches
C/ (h+No) as inter-cell interference ceases to be significant and thus
moderation the second
hubs EIRP is unnecessary.
[00177] EIRP Moderation is also a critical parameter for capacity performance.
Having
a homogenous distribution of users over a fixed area of a region, capacity
efficiency is
investigated by placing 2 hubs in the region with varying hub separation
therebetween. In
this simulation the area of a region was 3000m x 3000m, with both hubs having
an EIRP
of 23 dBm/MHz., the path loss exponent is 0.0002D + 2.7589 and the number of
users =
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CA 02360282 2001-10-30
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1500 per square kilometer of coverage. The first has coverage of 1000m x 1500m
and the
second hub coverage varies from 1000m to 3000m x 1500m.
[00178] Figure 18 shows a graph illustrating the Aggregate Bit Rate vs.
Capacity
Efficiency plot for capacity performance. Capacity efficiency initially
exhibits an almost
linear relationship with hub separation and remains constant after a certain
distance as
inter-cell interference becomes negligible. Different modulation techniques
exhibit merits
over other modulation techniques for various hub separations. In tests, a
mixed modulation
technique yielded the best performance. Advantageously when EIRP moderation is
used,
capacity efficiency receives a 50% - 400% increase for small hub separations.
[00179] Receiver acceptance beamwidth is also critical to system performance.
Antennas having a wider beamwidth have lower manufacturing cost. However using
these
wider beamwidth antennas is desirable as long as C/ (Io+No) performance is not
compromised. Figure 18 shows simulation results for four different antenna
gain patterns
for various beamwidths.
[00180] Figure 19 shows the effect of co channel interference probability for
subscribers
having different antenna beamwidth. In the simulation a coverage area of 3000m
x 3000m,
with a path loss exponent = 0.0002D + 2.7589 and 1500 users per square
kilometer is
assumed. Increasing the beamwidths of the subscribers' antennas results in
more
susceptibility to interference. Unfortunately, increasing the system co
channel interference
leads to deterioration of system capacity.
[00181] Figure 20 shows a C/ (Io+No) plot for a system comprising of 7
rosettes placed
in spaced relation to one another. A first rosette, 200, is initially disposed
at a first location.
From the resulting co channel interference from this rosette it is evident
that this rosette is
placed first into the system since it's distribution is fairly symmetric about
the hub center.
Additional rosettes were added in order from left to right and from bottom to
top, in
sequence, up to rosette 206. For this simulation the coverage area is 3000m x
3000m, with
a user density of 1500 per square kilometer, wherein users are distributed
homogeneously.
The path loss exponent = 0.00002D+2.27589 and the default EIRP = 23dBm/MHz.
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[00182] From the co channel interference distribution shown in Figure 20 it is
evident
that there are gaps between the rosettes where the C/ (Io+No) is low. These
are primarily
due to two factors: EIRP moderation and inter-cell interference. EIRP
moderation results
from regions which are supported by low EIRP micro-cells. It is desirable to
increase the
C/ (Io+No) of these gaps so as to maximize system data capacity.
[00183] A first solution for increasing the co-channel interference of the
system is to re-
orient and re-sequence channels of the new rosettes. The new added rosette is
re-orientated
and re-sequenced an optimum configuration is determined, such that number of
users
receiving a co channel interference of > lSdB is maximized.
[00184] A second solution is to directly increase the EIRP of the micro-cells,
however,
this needs to be done without the expense of decreasing the already existing
C/ (Io+No)
available to the users. EIRP moderation is performed for non-interfering
petals for the new
rosette which are interfered by existing rosettes. The EIRP is increased until
C/ (Io+No) of
all its users > lSdB, thereby offering an improvement in system data capacity.
[00185] A third solution is to combine the first and second solutions. Figure
21 a
illustrates a C/ (Io+No) distribution plot for a 7 rosette system according to
the second
solution; and Figure 21b illustrates a C/ (Io+No) distribution plot for a 7
rosette system
according to the third solution. The capacity efficiency for different
modulation techniques
is shown in Figure 22.
[00186] Rosette systems have been described in detail in US Patent Application
09/305/672. These high speed wireless systems are designed for license-exempt
application where there may be a plurality of hub stations run by independent
service
providers or in licensed frequency applications where the a service provider
has a high
density of terminals. In either case a high level of co-channel interference
sometimes arises
which is due to inter-cell emissions of signals between rosette cells.
Furthermore, in a
license-exempt environment, there may be other users of frequencies within the
channels,
not associated with the rosette system who also produce co-channel
interference. Detecting
this co-channel interference is important to the preservation of a meaningful
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CA 02360282 2001-10-30
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communication links, and as well, to protecting against interference with the
sources) of
the interference, which can be one or more co-channel users.
[00187] In both the licensed and unlicensed applications there may also be the
problem
of sharing the channel on a non-interference basis with users which are not
communication
links. Such users may be radiolocation systems and Earth Exploration Satellite
Systems
(Active). These co-channel users may have regulatory rights to share channel
with the
rosette, or may even hold primary rights, requiring the rosette to move off
the channel or
cease transmission for some duration until the primary user has terminated its
transmissions. To do this there is a requirement of the rosette system
technology to be
capable of detecting the presence of primary users' signals or signals of the
users which
share the channel on an equal basis, and to limit the transmissions from the
rosette in such
manner that co-channel interference is not problematic. This undertaking
commonly is
called Dynamic Frequency Selection (DFS) and implies that a radio
communications
device is capable of dynamically selecting a useable channel only after non-
interference
has been established. If the channel is shared on a secondary basis with a
primary user, the
radio communications device must be ready to detect the presence of the
primary user and
within a specified time, move to another channel or terminate its
communications. In a
shared channel situation, the terminal ensures that signals do not interfere
with the shared
user. This may entail reducing the power on the communications link to lower
limit or
moving to another channel, or simply ceasing communications until the shared
channel
user no longer was detected. There is usually a regulatory etiquette or
channel occupancy
requirement as to how a shared channel users operate on a co-channel basis. In
a
primary/secondary allocation it is incumbent for the secondary user to
mitigate its
transmissions when a primary user is operating.
[00188] Many types of co-channel interference are experienced by the rosette
system
and need to be mitigated thereby. The rosette with its high directivity
antennas and low
side lobe levels significantly mitigates intra-cell co-channel interference as
described
above. These qualities in electromagnetic performance also give the rosette a
significant
degree of robustness in face of interference and furthermore, are beneficial
to maintaining
an overall low level of co-channel interference to other users, which is a
positive feature.
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[00189] In the event that co-channel interference is detected on a specific
petal, or it is
determined that a petal is causing co-channel interference, that petal and its
associated
channel can be removed from operation, thereby mitigating the co-channel
interference
effects. The act of removing a single or few petals due to co-channel
interference, results
in the preservation of the remainder of the rosette's capability to maintain
communications
link; a feature that is lost with omni-directional or large sector cellular
systems. This ability
to localize and isolate sectors having co-channel problems in a dynamic manner
is
exploited within the rosette, but requires the incorporation of a number of
technical
features.
[00190] Total removal of a petal or petals would be detrimental to the
subscriber
terminals within the affected petal unless they can be offloaded to adjacent
petals.
However, to do this requires that the control system of the rosette have a
record of each
terminal's signal quality and reception characteristics of other adjacent
petals' channels,
which is information that can only derived by the subscriber terminal with
subsequent
transfer to the control system physically resident at the hub of the rosette.
[00191] Total removal of sectors from the rosette need not always be exercised
as a
means of interference control. The concentric assemblage of petals around the
rosette with
its periodic distribution of channel frequencies lends itself to another
important attribute of
the rosette: the ability to alter its EIRP contour as a function of its
azimuth angle
perimeter position - and to effectively rotate the constellation of its
channel frequencies
distributed in the azimuth angle (perimeter position). These attributes are
especially useful
when rosettes become located close to each other. Given that it is expected
that rosettes
will be installed on an ad-hoc basis by service providers that may or may not
know of the
presence of each other, it is then incumbent of the rosettes to be able to
adapt their EIRP
contours and channel frequency distributions automatically and in such a
manner that co-
channel interference is limited. Methods and processes have been developed
which allow
such contours to be produced in such a manner that the mean co-channel
interference
(MCCI) level of the assemblage of rosettes is both established and preserved
as rosettes
are added on an ad-hoc basis. Such operation requires several characteristics.
First of all,
there must be an etiquette that is respected by all the rosettes of this
proposed system. This
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is the etiquette of First Come/First Claim. By that it is meant that the first
rosette installed
in service area establishes an EIRP contour that is non-interfering of other
non-rosette
users of the commonly claimed channels, accordingly, be it on a primary,
secondary, or
any other basis as deigned by the regulations. Once this contour is
established it will be
maintained and de facto claimed. Subscriber terminals will become associated
with the
rosette only after the contour is established. If primary users occupy the
channel frequency
after the de facto claim, then the rosette will offload subscriber terminals
or in the worst
case, abandon them. If secondary users, not associated with the rosette occupy
the channel
frequency, then offloading of subscriber terminals will be exercised and in
worst cases
abandoned.
[00192] If secondary rosettes, come to the service area after the first
rosette, the
secondary rosette will adjust its EIRP contour and channel frequency plan in
such a
manner that the subscriber terminals registered on the first rosette are
minimally affected.
[00193] Abandonment of subscriber terminals as mentioned may on occasion
occur.
This is a risk that is inherent with the license-exempt operational scenario
where other
primary users may be present, or when shared channel users are present. In the
shared
channel case, it is likely that the other users will be operating at same
frequencies. The first
rosette will of course have particular radiation pattern. There will be a
sequence of
frequencies distributed in a repeating pattern around the rosette, there may
or may not be
missing sectors due to the identification of co-channel radiation sources that
were
established prior to the first rosette; these may for instance be radar
systems which, for
example in the 5-6 GHz band, of have primary allocations of channels.
[00194] For the case where the adjacent interferer is another rosette, the
deformation of
the radiation EIRP pattern and the sequence of frequency (Frequency Sequence
Code:
FSC) bands around the perimeter is based on the distance separating the
rosettes, the FSC
of the interfering rosette, the EIRP of the interfering rosette's cells, and
the long term
estimate on the propagation path loss exponent for the link path between the
rosettes.
Some of these parameters are embodied in a special Medium Access Control (MAC)
layer
word that is broadcast on occasion by every rosette. The control word is
called the Radio
Frequency Management Message (RFMM), and it will be detailed below.
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[00195] Every rosette broadcasts an RFMM. Consider the first rosette that is
installed in
a service area. We assume that the rosette uses a complement of license-exempt
frequencies and that interferers, some of which may be rosettes and others
which may be
none-rosette Wireless Access Stations ( point to point) , RLANs (ad hoc,
mobile, or
nomadic), or Metropolitan Area Network (MAN) wireless nodes - hub stations or
subscriber terminals operating at a distance from the MAN hub in a point to
multipoint
configuration, are yet to be in place. This first rosette, which is also the
first occupier of
the service area, monitors the environment by tuning to every transmit channel
that can be
assigned to each petal, and for a period of time, monitors for co-channel
interference. This
interference manifests itself in several ways. If the interference is due to a
non-rosette
device, the signal will appear as a interference power at some level above the
thermal noise
floor of the receiver. This level of interference is estimated and classified
by an
Interference Signal Processor (ISP) and passed to the Mean Co-Channel Signal
Level
Processor (MCCSLP). Within the ISP the interference is classified by its
characteristics: if
it is continuous or bursty in an aperiodic manner, it can be generally
construed as being
due to a communications link signal. If it is pulsed with long term
periodicity it can be
construed as a radar signal and conceivably further identified by radar signal
characteristics
such as scan interval, pulse duration, pulse repetition rate, rise time, fall
time, and nature of
modulation ( such as continuous CW, FM, or FM chirp).
[00196] For example, in an urban environment, given the low Effective
Isotropic
Radiated powers that are allowed by regulatory authorities for license-exempt
applications
(such as the 5 GHz UNII band), cell hubs can be separated by distances of only
500
meters. Since the rosette is a high frequency reuse hub station, a
multiplicity of such hub
stations can be subject to significant co-channel interference.
[00197] In order to implement the system of the present invention, it is
highly beneficial
to make use of all unallocated bandwidth. Unfortunately, bandwidth is in high
demand and
is allocated to many different functions. Some of these functions such as
earth exploration
satellite systems (active) (EESS) and radar make use of the bandwidth in
highly inefficient
manners. For example , a (EESS) uses a frequency band reserved for earth
exploration
and imagery on an occasional basis, usually once every 5-20 days over the same
region of
CA 02360282 2001-10-30
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earth. Typically, such a satellite only transmits Synthetic Aperture Radar
signals to the
earth at substantial intervals and for very short durations. As such, much of
the time the
bandwidth remains unused. For RADAR systems, the issues are different. Here
the
bandwidth is used most of the time, but only in very isolated locations. Thus
in most places
the bandwidth remains unused. Fig. 23 is a simplified flow diagram of a method
of
improving bandwidth utilization by supporting different priority levels for
different signals
wherein signaling systems having lower priorities cede in the presence of
signals having
higher priorities.
[00198] As is evident to those of skill in the art, either system uses its
bandwidth in a far
less than efficient fashion. That said, it is important to maintain the
bandwidth allocation
for each of these important and expensive systems. Referring to Fig. 23, a
simplified flow
diagram of a method of effectively filling unused bandwidth without affecting
bandwidth
allocation is shown. Here, a plurality of known signal sources are identified
and prioritized
in a hierarchical fashion. The list of known signal sources is stored along
with signature
data indicative of a method of identifying signals from each of the sources.
[00199] Each system is now provided with a receiver for receiving radio
frequency
signals and a processor for processing thereof to determine a source for or a
signature of
the received signal. When the determined source or signature is indicative of
a source
having a higher priority than the system in which the processor is located,
the processor
provides a feedback signal to a control circuit. The control circuit acts to
control the system
to prevent interference with the higher priority signal. Typically, this is
achieved by
turning off any transmitter that potentially interferes with the higher
priority signal.
[00200] For example, when the higher priority signal originates from a
satellite, the
transmitter or transmitters are turned off for a short period of time until
the signal of higher
priority ceases to be received. When the higher priority signal originates
from a RADAR
system, then the hub is reconfigured to other than interfere with the RADAR
signal. This
may require repositioning of the hub, replacing one or more transmitters
within the hub,
changing frequency allocation of the hub, ceasing transmission in certain
petals of the
rosette produced by the hub and so forth. Of course, the action taken is more
of a
permanent correction than was necessary when the satellite signal was
detected.
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[00201] Though the potential corrective actions seem onerous in some cases,
the
resulting additional available bandwidth makes onerous changes in the presence
of higher
priority signaling worthwhile in most cases.
[00202] Of course, when the detected signal is of a lower priority than the
signals with
which it interferes, the hub takes no corrective action. Alternatively, the
hub takes
corrective action in accordance with predetermined preferences set by the hub
operator.
(00203] Preferably, the processor is provided with an updated list of priority
signals and
signatures whenever the list is changed.
[00204] There are numerous possible corrective actions for ensuring that
interference
does not occur. For example, a frequency within the interfering area may be
changed,
transmission may be interrupted, signal strength may be modified, signal angle
may be
corrected, EIRP of signals may be adjusted to ensure better range for
preventing
interference and so forth.
[00205] Referring to Fig. 24, a block diagram of a system according to the
invention is
shown. Here a first petal 241 and a Nth petal 244 are shown. Each petal
includes an
antenna 2401 for receiving RF signals and an antenna 2402 for transmitting RF
signals.
The transmit antenna 2402 is coupled to transmit hardware 2403. The receive
antenna 2401
is coupled to receive hardware 2406. The transmit circuitry includes a
modulator 2404 for
modulating data within the signal and the receive circuitry includes a
demodulator 2407 for
extracting data from a received RF signal. An interface circuit 2405
interfaces with wired
communication systems.
[00206] A petal configuration controller 2408 is coupled to each petal for
providing for
petal related information gathering and for petal related control. The petal
configuration
controller 2408 is coupled to a microcontroller 2409 for determining control
data based on
data and feedback received at the antennas as sampled at RF sampler 2410 and
processed
at interference signal processor 2411. The microcontroller 2409 is for
providing the control
data to the petal configuration controller 2408 for modifying configuration of
a petal. Of
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course, since each petal is similar, control of individual petals or of all
petals is possible
independently or in conjunction one with another.
[00207] Referring to Fig. 25, a block diagram of a system according to the
invention is
shown. Here a first petal 251 and a Nth petal 254 are shown. Each petal
includes an
antenna 2501 for receiving RF signals. The antenna is coupled to transmit
hardware 2503
through a switch 2502. The switch allows signals to be switchably received by
antenna
2501 and provided to the RF signal receive hardware 2506 or transmitted from
the transmit
hardware 2503 to the antenna 2501. The transmit circuitry includes a modulator
2504 for
modulating data within the signal and the receive circuitry includes a
demodulator 2507 for
extracting data from a received RF signal. An interface circuit 2505
interfaces with wired
communication systems.
[00208] A petal configuration controller 2508 is coupled to each petal for
providing for
petal related information gathering and for petal related control. The petal
configuration
controller 2508 is coupled to a control circuit in the form of microcontroller
2509 for
determining control data based on data and feedback received via the petal
configuration
controller and for providing the control data to the petal configuration
controller 2508 for
modifying configuration of a petal. Of course, since each petal is similar,
control of
individual petals or of all petals is possible independently or in conjunction
one with
another.
[00209] Numerous other embodiments may be envisaged without departing from the
spirit or scope of the invention.
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