Note: Descriptions are shown in the official language in which they were submitted.
CA 02294452 1999-12-20
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yIETROPOLITAi'1 WIDE AREA i~'ET~VORh
BACKGROUND
1. Technical Field '
:.
The present disclosure relates to a metropolitari wide area net<vork for
telecomrnunicatior. systems. In particular, this invention relates to the
integration of a wireless
point to mufti point system operating in the millimeter microwave radio range
with an intelligent
rnetropolitan area broadband backbone nenvork to enable a variety of enhanced
voice,
broadband data and multimedia telecommunication services.
Description of Related Art
In the art, point-to-point narrow band, point to mufti point narrow band and
point to point
broadband fxed wireless systems are generally known. Point to mufti point
radio technology is
also a known technology which has been generally used for narrowband
communications, such
as voice. Narrow band systems are typically systems that are capable of
generating at or below
2 5 1.544 megabits pe: second of data in a single circuit or channel, whereas
broadband systems are
capable of generating data rates above 1.544 megabits per seconds per circuit
or channel. While
narrowband "point to mufti point" systems have been used for voice
communications, point to
mufti point systems have rot been generally applied to broadband
telecommunications
networks.
AMEPIQE~ SNcFI'
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Today's narrowband point to mufti point systems can aggregate a group of up to
twenty
four 64 kilobits per second channels together in what is called a "T1 line."
However, this T1 line
is still considered a narrowband facility when it is used to support multiple
voice channels.
Narrowband point to mufti point systems have also been in use in Europe for
voice telephone
networks for several years.
Point-to-point broadband technology is also well known. In the 37 Gigahertz or
"GHz"
to 40 GHz range (typically referred to as "38 GHz"), point-to-point broadband
wireless systems
are in use. When a 38 GHz broadband wireless links is engineered properly, its
performance is
functionally cquivalcnt to that of fiber optic tclccommunications.
Fixed wireless technology is gaining popularity as means for transmission of
telecommunication services because of its low cost, rapid installation and
ease of operation.
Connecting two sites with point-to-point wireless service largely consists of
installing roof top
antennas on the top of two buildings, with the accompanying indoor equipment.
Physical wires
do not have to be connected between the buildings, representing a significant
advantage over
copper or fiber technology. Bringing fiber or copper to buildings entails
tremendous labor and
other costs associated with digging up streets, obtaining permits, etc.
Because the deployment of
broadband fixed wireless systems does not require civil construction in most
instances, it is thus
2 o faster and more economical to install than traditional methods of "last
mile" interconnection in
metropolitan area telecommunications networks.
Current 38 GHz fixed wireless technology has a number of characteristics that
make it an
attractive commercial telecommunications transport medium. The 38 GHz wireless
technology
2 5 provides a high bandwidth path for voice, data, multimedia and video.
Current technology
permits link distances of up to five miles. Since all millimeter microwave
propagation is subject
to rainfall degradation, actual distance is a function of geographical
location or "rain region." In
climates where heavy rainfall is common, shorter link distances may be
required to achieve
performance and availability equivalent to that of fiber.
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Millimeter wave radio propagation at 38GHz generally requires unobstructed
line-of
sight transmission. In practice, small diameter antennas are mounted on office
building
rooftops, and in some cases in office building windows. These antennas
typically range from 12
to 24 inches in diameter, although smaller antennas are also in use.
Manufacturers indicate
mean time bctwccn failure (MTBF) statistics in excess of 10 years for the
radio and modem
components, indicating that the hardware is highly reliable. Current 38 GHz
fixed wireless
technology is therefore ideally suited for high availability broadband point-
to-point commercial
voice and data applications ranging from 1.544 Megabits per second (T1) to 45
Megabits per
second (DS3) capacities.
One example of a typical wireless point-to-point broadband commercial
application is
the interconnection of multiple servers in a campus local area network (LAN).
Another such
application is metropolitan wide area networking. Here multiple campus LANs
within the same
city are interconnected via wireless facilities at 38 GHz. Dedicated access to
inter-exchange
carriers (IXCs), Internet Service Providers (ISPs) and other alternate access
arrangements are
common point-to-point business applications for 38 GHz wireless links. In the
38 GHz range,
cellular and personal communication services (PCS) operators may deploy high
availability
wireless facilities in their backbone networks to support back haul between
antenna sites, base
stations and mobile telephone switching offices (MTSO's). Wireless point-to-
point technology
2 0 at 38 GHz is also being used to provide mission critical protection
channels and other point-to-
point alternate routing where extension is required from a fiber network to a
location that is not
served by fiber. Finally, interconnection with the public switched telephone
network (PSTN) for
the provision of local dial tone by competitive local exchange carriers
{CLECs) utilizing point-
to-point wireless technology at 38 GHZ is becoming increasingly popular.
Figure 2 illustrates a basic point-to-point wireless facility providing
customer
interconnection to services. This connection will support broadband (data,
video ete.) and
narrowband (voice) applications. A customer building is shown as 200 and may
contain multiple
tenants. It is connected to another building 202 that houses a
telecommunications network
3 o switch 203. These buildings are connected by a wireless link between two
roof top antennas:
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one antenna 204 at the customer building, the other antenna 205 at the
building housing the
switch 203. The bandwidth of this connection could be up to 28 T1 circuits, or
DS3 (45
Megabits per second). The switch 203 connects to the PSTN 206, or public
switched telephone
network for local service, and to long distance networks 207 for long distance
service. The
switch 203 is also able to provide dial up access to the Internet 208.
Figure 3 is a representation of the FCC spectrum allocation plan for 38. GHz,
consisting
of 14 total channels. Each channel is 100 MegaHertz (MHZ) in bandwidth. Each
100 MHZ
channel consist of two 50 MHZ sub channels, one sub channel to transmit and
the other sub
channel to receive. These two 50 MHZ sub channels are separated by 700 MHZ of
spectrum. As
shown in Figure 3, sub channel lA is 50 MHZ wide and it is a transmitting
channel, whereas sub
channel 1B is 50 MHZ wide and it is a receiving channel. Sub channel lA is
separated from sub
channel 1B by 700MHz. This band plan yields 14 channels (1400 MHZ or 1.4 GHz)
of
spectrum in the FCC allocated 38 to 40 GHz range.
Referring to Figure 4, a basic spectrum management problem associated with the
use of
point-to-point wireless systems in a metropolitan area is shown. Because
buildings are close to
each other in a metropolitan area, the broadcast of information over wireless
links may overlap,
making the use of the same channel (lA/1B) in contiguous systems impossible.
In this figure,
2 0 one antenna from one building is transmitting its signal to the antenna of
the intended receiver,
but a portion of the signal is also being received by the antenna on the
adjacent building. Such
signal corruption is termed "co-channel interference."
In Figure 4, a host building 401 containing a switch 402 is connected via four
rooftop
antennas 403A, 403B, 403C and 403D respectively to remote buildings 404A,
404B, 404C and
404D, each with its own corresponding rooftop antenna. Shown between these
buildings is a
conceptual representation of the spectrum being utilized by each of these
point-to-point wireless
systems. As buildings get close together, transmission signals between
buildings begin to
overlap. To prevent the co-channel interference described in the preceding
paragraph, different
3 o channels must be used to connect buildings that are in close proximity.
For instance, channel
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1 A/1B is used for building 404D and channel 2A/2B is used for building 404C.
Even though
channel lA/1B partially overlaps the transmission of 2A/2B, the use of
different frequencies
(channels) by the two systems provides protection from co-channel
interference. Thus the
antenna of one building may be transmitting a portion of its signal to the
wrong receiving
antenna, but each system is "tuned" to a different frequency and transmission
from neighboring
systems using other frequencies is ignored.
The frequency management technique shown in Figure 4 avoids co-channel
interference
in wireless networks deployed in dense urban areas, however the use of FCC
channels to avoid
l0 co-channel interference does not maximize the information transport
capacity of the licensed
spectrum and is therefore inefficient. A solution to this problem is needed.
Figure ~ illustrates an additional spectrum management problem associated with
point-
to-point systems. Building 501 connects to Building 502 through channel 1.
Building 503
connects to building 504 through channel 2. The solid connection lines 505,506
represent the
wireless transmission that is intended. However, because the "transmit beam"
is about 2 degrees
at the source, signals can be received by other systems that are not planned
but happen to be in
the range of the transmit beam of the originating system. The dotted line 507
represents such a
case, where the system in building 4 incorrectly receives the transmission of
the system in
2 0 building 1. If t<vo distinct frequencies were used, there would be no co-
channel interference.
Once again, frequency management in point-to-point wireless networks requires
the use of
multiple channels to avoid interference rather than allowing the spectrum to
be used to drive
incremental bandwidth.
2 5 Rooftop space is expensive and in many cases there are restrictions on the
number, size
and position of antennas deployed on a roof. Because point-to-point systems
use separate
antennas for each wireless connection, space becomes a limiting factor on
building rooftops. As
the number of point-to-point systems located on a building increases, not only
do spectrum
manabement considerations limit the number of systems which can be deployed,
but the physical
3 0 space available for each antenna on the roof also constrains the number of
systems. Thus, a
CA 02294452 2003-03-21
solution is required which permits the expansion of wireless network capacity,
and thus the
number of users, without a corresponding increase in the number of antennas on
rooftops.
Point-to-point systems provide users with what is called a full period
connection.
Full period connections are "always on" (connected and active), awaiting the
transport of
information. Full period wireless connections utilize dedicated spectrum
which, once
assigned, is unavailable to other users. Point-to-point wireless systems are
therefore
appropriate for applications involving continuous or lengthy transmissions.
Point-to-point
systems do not e~ciently support variable bit rate or "bursty" data services
where the
requirement for bandwidth is not constant but rather variable. Bandwidth
utilized by point-
to-point systems for variable bit rate applications is wasted, as each system
utilizes the
allocated channel on a full time "always on" basis regardless of the amount of
information
or the duration of transmissions on the link. A solution is required to more
e~ciently
utilize spectrum for "bursty" data services like LAN to LAN data transmission.
It is a feature of one embodiment of the present invention to create a "full
featured"
local metropolitan area broadband telecommunications network infrastructure
capble of
supporting advanced voice and data services.
It is another feature of an embodiment of the present invention to use the
wireless
sperm as a key enabler of access to a local metropolitan area broadband
telecommunications network offering advanced voice and data services.
It is a feature of one embodiment of the present invention to maximize the
utilization of allocated spectrum available in local metropolitan area
broadband
telecommunications networks.
It is a feature of certain embodiments of the present invention, to overcome
the
spectrum management limitations associated with the use of point-to-point
fixed wireless
telecommunications systems.
6
CA 02294452 2003-12-17
It is another feature of one embodiment of the present invention to allow the
utilization of multiple channels to drive additional network capacity in local
metropolitan
area broadband telecommunications networks.
It is yet another feature of one embodiment of the present invention to
minimize the
number of wireless telecommunications systems required on rooftops to provide
access to
local metropolitan area broadband telecommunications networks.
SUMMARY
In accordance with one farm of the present network, a wide area communication
network includes at least two hub sites which are interconnected by a
communication
backbone. Each hub site provides wireless coverage in at least one sector. At
last two
remote sites reside in each sectors and are coupled to a corresponding hub
site via a point
to mufti point broadband wireless system. The network preferably includes at
least one
service node which is accessible to the remote sites via the hub sites and
backbone.
In accordance with another form of the present network, a broadband local
metropolitan area telecommunication network provides fixed broadband wireless
local loop
access to a plurality of subscribers. The subscribers including a subscriber
radio unit
operating on a frequency corresponding to a cell sector in which said
subscriber resides. At
least one of the subscribers has a plurality of associated customer premise
equipment and
includes means for performing statistical multiplexing among the plurality of
customer
premise equipment the subscriber radio unit. The network includes a plurality
of hub sites
which are interconnected by a Sonet based backbone. The hub sites each include
a plurality
of hub site radio units which operate on a selectable frequency with at least
one subscriber
radio unit corresponding to a cell sector. The hub sites further include means
for
dynamically allocating communication bandwidth among a plurality of
subscribers within
each said cell sector. The network preferably includes a plurality of value
added service
nodes which are coupled to the backbone and are accessible to subscribers
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through the hub sites and backbone. The network further includes a central
operations node
which is connected to each of said hub sites by a control network and provides
remote access
and control of the hub sites as well as remote control subscriber access to
the value added
service nodes.
These and other features, objects and advantages of the present network
embodiments
will become apparent from the following detailed description of illustrative
embodiments
thereof, which is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a pictorial diagram illustrating a local metropolitan area broadband
telecommunications network utilizing fixed wireless point-to-point systems
operating at 38 GHz
to provide customer access to a local metropolitan area broadband
telecommunications network.
Fig. 2 is a pictorial diagram illustrating a typical point-to-point system
configuration
known in the art for providing customer access to telecommunications services
via a switch.
2 0 Fig. 3 is a pictorial diagram illustrating a spectrum allocation plan for
38 GHz, with 100
MHZ channels divided into 50 MHZ subchannels for the transmission and
reception of signals,
wherein each transmit and receive subchannel is separated by 700 MHZ of
spectrum.
Fig. 4 is a pictorial diagram illustrating a point-to-point fixed wireless
systems deployed
2 5 in a hubbed network configuration in accordance with the prior art in
which there is a one to one
relationship between hub and customer building wireless systems. Areas of
overlap illustrate a
co-channel interference phenomenon encountered in point-to-point fixed
wireless networks.
Fig. 5 is a diagram which illustrates another co-channel interference
phenomenon
3 0 encountered in point-to-point fixed wireless systems of the prior art.
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Fig. GA is a diagram illustrating a fixed wireless point to mufti point
implementation in
which there exists a one to many relationship between hub and customer systems
within a sector
employed in the present system.
Fig. GB is a block diagram further illustrating the hub of Figure GA as used
in the present
network.
Fig. 7 is a diagram illustrating the present local metropolitan area broadband
telecommunications network utilizing point to mufti point fixed wireless
technology operating at
38 GHZ to provide customer access to a backbone network and various
telecommunications
seances.
Fig. 8 is a block diagram of an embodiment subscriber system used in the
present
system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
2 0 1. Network Topolo~.~,y
The present network utilizes a fixed wireless microwave scheme which allows a
many to one
relationship between hub systems and remote systems located in customer
buildings. This
technology, termed "multiple access" or "point to mufti point," can support
traditional voice and
2 5 data telephony services as well as commercial and residential broadband
multimedia services by
combining improvements in spectrum efficiency (and thus available bandwidth)
with enhanced
intelligence in the metropolitan wide area network.
Figure 6A illustrates a point to mufti point system, characterized by a "one
to many"
3 0 relationship between hub and customer building radio systems. In Figure
6A, a hub site 601 is
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equipped with antennas 602, 603 and 604. Antenna 602 transmits to a "sector"
GOS, which
covers the physical space occupied by multiple subscriber buildings 606, 607,
608 and 609.
Antennas on buildings 606, 607, 608 and 609 in sector 605 all communicate with
the single hub
antenna 602 of sector 605. Sectors can be from 15 to 90 dcgrccs wide. All of
the buildings in a
sector generally utilize a single channel, so co-channel interference is no
longer an issue for
buildings within the same sector.
To prevent co-channel interference at the edges of sectors, the hub site 601
assigns
frequencies to adjacent sectors which are substantially separated from each
other. For example,
sector 602 may be assigned channel lA/1B and sector 604 then assigned channel
2A/2B. Thus
point to mufti point systems permit full utilization of each channel assigned
within a sector to
transport information, in contrast to the spectrum management requirements of
point-to-point
systems which require the utilization of multiple channels in the same
geographical area merely
to avoid co-channel interference.
Figure 6B illustrates an exemplary embodiment of a hub site 601 for use in the
present
network. Antennas 602, 603...60n, correspond to frequency channels. Generally,
one
frequency channel is assigned to a corresponding cell sector 605. However, in
cases where
additional bandwidth is required, the present network provides for the
assignment of multiple
2 o channels to one or more cell sectors. Each antenna preferably includes a
corresponding hub
radio unit 620. To avoid signal losses associated with coaxial lines and
waveguides at 38 GHZ,
the hub radio units are preferably coupled to a corresponding antenna as an
integral unit which is
mounted on a roof top or tower.
2 5 The hub site also includes hub indoor units 622 which are coupled to the
hub radio units
620 via an interfacility link G24. The interfaciiity link G24 is a wide band
connection, preferably
taking the form of a fiber connection. The Hub IDU's are connected to one or
more hub
controllers 626 which manage the operation and data transfer within the hub
site 601. A
backbone interface 628 is included to enable connection and data transfer with
a network
3 0 backbone.
to
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Figure 7 illustrates an embodiment of the present network in a commercial
metropolitan
area network utilizing 38 GHz multiple access wireless technology. The network
includes a
broadband backbone 702, which can be implemented using fiber, copper or
wireless technology.
The large squares located on the ring represent point to mufti point hubs 704,
each covering at
least one cell sector 706. In a commercial urban environment, cell sectors 706
are deployed such
that bandwidth is directed toward geographic locations with appropriate
building (customer)
density. Once on the backbone 702, customer traffic is routed to any number of
network nodes
providing value added services. Examples of such service nodes are local
exchange carrier
switches 706, inter-exchange earner switches 708 and Internet access points
710 and video
1 o service points 712. The present network also includes at least one central
operations node 713
which is connected to each of the hubs 704 through a control network 715, such
as a frame relay
network.
The architecture of the 38 GHz point to mufti point wireless network generally
consists
of cells 714 with a 3-5 mile diameter (1.5 - 3 mile link distances). Each cell
714 consists of a
number of sectors 706-1, 706-2,..., 706-n, ranging in sector width from 15 to
90 degrees. A hub
704 is located in the center of each cell, and multiple remote subscriber
systems (subscribers)
716 located in customer buildings within a sector communicate with hub radio
equipment to
establish wireless links. Bandwidth within a given sector is allocated among
the remote
2 0 subscriber systems provisioned in that sector by the corresponding hub
704. A sector may
utilize the full bandwidth of a single licensed channel, or multiple channels
can be "stacked" in a
sector to meet overall customer demand for bandwidth. When multiple channels
are employed
an additional hub radio unit 620 and antenna for that sector are added to the
hub 704.
2 5 The assignment of the optimum sector width is a nontrivial problem. One
design
objective is to minimize the cost of the required Effective Radiated Power
(ERP). Narrow
sectors yield higher antenna gain, so less power is needed to achieve a given
ERP. However
each sector requires it's own radio system, so narrow sectors increase the
equipment cost
required to cover a given geographical area. In the final analysis, hub design
is a function of
3 0 overall customer demand for capacity and the geographical distribution of
customer locations.
1t
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Preferably, in the present point to mufti point metropolitan area network,
hubs 704 are
interconnected on the backbone 702 by fiber or high capacity microwave radio
facilities in a
SONET ring configuration. Service nodes such as Inter exchange Carriers 708,
Internet Service
Providers 710, Local PSTN switches 706 and video sources 712 are
interconnected to the fiber
ring, in some cases via co-location with the hubs. Thus, once customers are
connected via
wireless access links to the network, any and all services supported by the
various service nodes
will be accessible.
This network approach requires a transport and routing capability on the
backbone to
facilitate connections between multiple customer locations and between
customer locations and
network service nodes. Asynchronous Transfer Mode (ATM) is the preferred
transport layer
protocol for the present metropolitan area network architecture. It is also
envisioned that more
traditional connection-oriented or synchronous telephony transport protocols
will be utilized as
operators transition to full ATM networks over time. For this reason, both ATM
(OC-3c) and
STM (DS-3) interfaces are preferably included between hubs 704 and the
backbone 702.
2. Wireless ATM
This network architecture utilizes Asynchronous Transfer Mode (ATM) as primary
means of
2 0 transport in the network. ATM is a packetized transmission technology
which organizes information
into cells. The cells have a "header" and a "payload". The header describes
what kind of data is in
the payload and where the data is to terminate. The cells propagate through
the network via diverse
paths and can arrive out of sequence at the point of termination. Header
information contained in
the cells permits reconstruction of the correct cell sequence prior to
delivery to the customer premise
equipment. ATM cells can transport many standard telecommunications voice,
data and video
services by encapsulating the data in the payload. Thus, ATM is capable of
integrating voice, data
and video in a single telecommunications transport network.
A key architectural element of the present network is the use of ATM in the
point to mufti point
3 0 system wireless transport (air interface): Customer specific services
(Ethernet, Frame Relay, DS-1,
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DS-3, ISDN, Voice) are encapsulated in the ATM payload between subscribers 716
and hub 704.
Thus services which are most efficiently handled by a cell-based protocol
benefit from end-to end
ATM transport in the network, while services which for the time being must be
channelized on the
backbone are time division multiplexed at the hub 704. In either case, the
transport of all services
via ATM over the air enables important bandwidth on demand functionality in
the network.
3 Modulation and System CaDacity
Wireless equipment utilizing modulation techniques such as QPSK and 4FSK,
yield an
effective data rate of one bit per Hertz per second. As 38 GHZ spectrum is
allocated in SO MHZ
full duplex channels (that is, SO MHZ of spectrum in each direction for a
total of 100 MHZ per
licensed channel), the maximum point-to-point data rate of today's fixed
wireless technology is
45 Mb/s, or DS-3. Higher order modulation techniques such as 1 G QAM and 64
QAM, along
with improvements in overall system gain will yield data rates of 4-5 bits per
Hz per second or
more. This translates to a significant increase in available bandwidth per
channel. Thus data
rates of OC-3 (155 Mb/s) per channel per sector and higher are attainable at
38 GHZ. Spectrum
efficiencies in the range of 6-8 bits per Hz per second are expected. Multi
sector, multi channel
cells supporting overall data rates of several gigabits per second of
available bandwidth are
readily achievable based on relatively conservative engineering. Less
conservative designs will
2 0 yield higher cell capacities.
4. Bandwidth on Demand
Because data is encapsulated into cells for transport by the wireless network,
it is
possible to utilize radio spectrum more efficiently than would otherwise be
possible in non-
ATM wireless implementations. This is the result of a technique called
"statistical
multiplexing." Statistical multiplexing takes advantage of the random
origination of data
transmission in a system and the fact that all users do not require bandwidth
at all times.
Statistical multiplexing allows cells containing data originated by different
users to be
3 0 transported by the minimum required spectrum. In this sense, users share
the allocated spectrum
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in a wireless ATM network, and the aggregate bandwidth requirement of all
users in the system
is served by the spectrum that is available within the system at any given
moment in time.
This results in "statistical gain" in data capacity which allows
telecommunications
network operators to "oversubscribe" wireless Links based on the assumption
that all users in a
given subscriber location (e.g. mufti-tenant office building) will not require
all capacity allocated
to that location at all times. Over subscription rates (statistical gain) as
high as 10 to one (10:1)
are possible for links on which the majority of the information is transported
in short bursts
("bursty data") as in the case of LAN-LAN communications. Statistical gains of
2:1 or 3:1 are
l0 more typical of networks in which the mixture of traffic is more heavily
skewed toward voice or
other services requiring point-to-point connections through the network
(circuit) for the duration
of the communication session.
ATM cell headers also contain parameters which allow individual cells to be
prioritized.
Thus cells with the highest priority are transported across the network
instantly, while cells with
lower priorities may be delayed until the higher priority cells have been
switched. This attribute
of ATM permits the support of services with varying "Quality of Service", or
QOS. When this
priority system is used in conjunction with statistical multiplexing, it
allows information to be
transported over wireless networks very efficiently. For instance a large file
can be broken into
2 0 cells and transmitted over the network with other cells of smaller files
interspersed in the packet
stream. Thus, the small files do not have to wait for the large file
transmission to be completed,
and the network operates more efficiently overall.
Dynamic bandwidth allocation between subscribers 716 within a given sector
706. Thus,
2 5 momentary requirements for high bit rate bursts to a given subscribers 716
are met by utilizing
bandwidth within the sector 706 not in use by other subscribers at the time.
This is
accomplished via variable on-demand assignment of time slots (Time Division
Multiple Access
or TDMA) or frequencies (Frequency Division Multiple Access or FDMA) to
subscribers, or
through a combination of both multiplexing techniques (Demand Assigned
Multiple Access or
3 0 DAMA).
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When these techniques fo dynamically allocate bandwidth between buildings in a
sector
are combined with ATM statistical multiplexing (over subscription) of
bandwidth allocated to
customers within individual buildings, the result is a tremendous increase in
the information
transport capacity of wireless spectrum utilized in networks of the present
invention. Capacity is
further increased with the use of highly efficient modulation schemes such as
16 QAM and 64
QAM.
5 Rubbing Architecture
The present system utilizes a deployment strategy known as "hubbing", which
conccntratcs one end of many wireless links on a single building rooftop or
"hub". Each hub 704
can connect to many remote radio systems 71 G using wireless links. Hubs 704
in a metropolitan
area may be interconnected in a ring, mesh or other backbone network topology
via wireless,
fiber, or other high capacity telecommunication facilities. Hubs 704 are
equipped with ATM
switching or TDM multiplex equipment to bridge wireless links across the
backbone 702 to
establish connections between subscribers or to connect subscribers to other
locations on the
network to access services. Via hubbing, networking is employed to
significantly increase the
effective range of wireless access links as well as to provide access to a
variety of voice, data
2 o and multimedia services.
The present hubbing architecture is applicable to both point-to-point and
point to
multipoint fixed wireless systems. In a point-to-point wireless system, each
hub supports one
antenna for each link it connects to the backbone network. Therefore, rooftop
space imposes a
2 5 limitation on the number of antennas (and thus links to the network) that
can be supported by a
single hub using point-to-point fixed wireless systems. Figure 1 illustrates
an embodiment of
the network architecture employing 38 GHz point-to-point wireless
telecommunications systems
in which the wireless facilities connect customer locations to a metropolitan
area backbone
network. This system employs a point-to-point system, in which communication
occurs
3 o between a hub 100 and specific buildings 102 or campuses 104. The backbone
network consists
CA 02294452 1999-12-20
WO 98/58477 PCT/US98/12888
of high capacity telecommunications transport facilities 106 connecting the
hubs in a ring
configuration, with each hub connecting to individual buildings or campus
locations over a "last
mile" wireless connection.
In point to multipoint fixed wireless systems, a smaller number of hub
antennas provides
connections to customer buildings in a sector varying between 15 and 90
degrees and containing
many customer buildings. In either cast, the hubbing architecture provides
efficient access to a
network backbone thereby enabling communication between subscribers and
allowing
subscriber access to value added services attached to the network.
to
6. Remote Subscriber Systems Equipment and Services Sunnort
In the present system, a subscribers 716 can take the form of a single
customer, a muiti-
user system in a building or even a campus of customers. Figure 8 illustrates
an embodiment of a
subscriber system for use with a mufti-user system in a building.
Referring to Figure 8, antennas 802 are integrated with radio transceivers in
compact
sealed outdoor units (ODU) 804 for installation on building rooftops. The
ODU's are preferably
secured by standard 4 inch pole mounts for rapid, low cost installation and
non-obtrusiveness.
2 o Outdoor units 804 are connected to indoor units (IDU) 806 typically
located in common space
within a building via an inter-facility link (IFL) 808 consisting of either
coaxial cable or fiber.
Utilizing fiber in the IFL 808 provides significant benefit in installations
where in-
building conduit is already tightly packed with telecommunications facilities
and little room
2 5 exists to pull new cable. This is a commonly encountered installation
problem. Because fiber is
much thinner than coaxial cable, it is much more readily pulled through
existing building
conduit than coaxial cable, making the job of installation much faster and
less costly than would
otherwise be the case.
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Another advantage of using fiber in the IFL 808 has to do with signal loss
between the
IDU 80G and the ODU 804. Physical properties of coaxial cable limit signal
propagation to less
than 1000 feet in most cases. This places a limitation on the separation
between the ODU 804
and the IDU 806 in a building. Since the common space provided for
telecommunications
equipment (including the IDU) in most commercial office buildings is located
in the basement
and the ODU 804 is roof mounted, this poses a problem for installations in
larger buildings of
floors or more. Fiber optic cable poses no such distance limitation, between
the IDU 806 and
the ODU 804. Thus installations are not hampered by the location of common
space for
telecommunications equipment in buildings.
Indoor units 806 are used to interface with customer premises equipment (CPE)
810. A
preferred embodiment of the indoor unit includes a chassis with slots for
receiving service
specific line cards 812. Line cards 8I2 are physically inserted in the chassis
when customers are
installed, and are activated via software commands from a centralized network
operations center.
Line cards 812 are provisioned to support specific telecommunications services
(DS-1, DS-3,
ISDN, Frame Relay, Ethernet, Token Ring, ATM, etc.) The line cards 812 in turn
connect to a
backplane for protocol conversion to ATM for transmissions to the hub, and
from ATM to
service specific protocols for transmissions from the hub. A chassis can
preferably support 10 -
line cards 812, each of which may provide multiple ports for interconnection
with CPE. For
20 example, a typical DS-1 line card permits the connection of 4 DS-1 lines (4
x DS-1) per card.
Line cards are inexpensive, thus the incremental cost to add customers to the
network once the
basic remote system equipment is in place in a building is quite low. Once
installed, services
provided by the line card 812 can be locally enabled, or preferably, remotely
enabled by
commands generated by the central operations node 713 (Figure 7) which are
transported over
2 5 the network.
In this way, indoor units scale to cost effectively meet the demand for
telecommunications services. Most small to mid-sized commercial office
buildings can be
supported by the 10-20 card chassis described above. In very large buildings,
two or more IDUs
3 0 can be interconnected in "daisy chain" fashion to expand the number of
service interfaces
t7
1
CA 02294452 1999-12-20
WO 98/58477 PCT/US98/12888
available; and installed on different floors where common space and main
distribution frames
may be located to serve customers. The present invention also provides for
very small, low cost
indoor units with fixed service interfaces to serve Small Office/Home Office
(SOHO) and
residential customers. Rather than employing a chassis and backplane
architecture, these small
IDU's are fully integrated sealed units manufactured at low cost to support a
predefined set of
services. An example of a low-end IDU of this sort would provide interfaces
for multiple 64
KB/s voice lines and an ISDN or Ethernet port for connection to a remote
office LAN.
7. Operational Considerations
In addition to improved spectrum efficiencies and resulting bandwidth
increases, significant
operational and equipment costs savings are achievable with point to mufti
point radio technology
at 38 GHz. Operational complexities are eliminated by rcpiacing multiple
antennas on a hub roof
top with one or more point to mufti point hub antennas, and installation costs
are likewise reduced.
Once a hub 704 is installed, adding customers to the network becomes a matter
of installing
subscriber systems 7I6 in customer buildings within a covered section 70G.
This is in contrast to
the requirement to engineer and install equipment supporting two ends of every
link as in the case
of today's point-to-point 38 GHz wireless technology.
2 0 Also, service provisioning and configuration changes are manageable
remotely via software
definable service attributes downloaded through the network to subscriber
systems located in
customer buildings. Services are provisioned, monitored, modified and
controlled from a central
Network Operations Center by technicians with appropriate authorization.
System software enables
"see through" provisioning of services from the hub to the end-user service
interface card in the
remote subscriber system.
8. Services
The present network can support any and all services supportable by wire line
3 0 telecommunications technologies. These services include two broadly
defined categories: traditional
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CA 02294452 1999-12-20
WO 98/58477 PCT/US98/12888
telecommunications services and emerging broadband multimedia services.
Traditional telecommunications services for the commercial market include; (1)
voice
grade local and long distance services, (2) point-to-point dedicated
facilities at DS-1, n x DS-I
and DS-3 speeds for voice and data, (3) switched data services such as
switched 56 Kb/s and
Frame Relay, and (4) high capacity point-to-point data facilities, operating
at OC-3 speeds and
above.
Emerging broadband multimedia services supported by the present network
include high
1 o speed Internet access, web hosting and information services, native LAN-
LAN services such as
Ethernet and Token Ring, and video services such as desktop video
conferencing, business
related commercial video programming, and on-demand video training (distance
learning).
Wireless customer access links to the network are provisioned at virtually any
data rate to meet
the bandwidth requirements of such services.
Residential customers are provided services which include a subset of the
above for
telecommuting and Small Office/Home Office (SOHO) applications. A package of
services for
these customers may include local and long distance telephone service, high
speed Internet access
for information services and e-mail, and selectable video programming. Access
to the network can
2 o be provisioned at any speed for residential customers as well.
ATM Quality of Service (QOS) parameters can be used to support usage based
broadband
multimedia data services. For example, a customer can subscribe to a 2 megabit
Committed
Information Rate (CIR) connection to the network. The overhead in this
customer's ATM cells
2 5 would guarantee 2 megabits of actual throughput each and every time the
customer required this
amount of bandwidth on the network. When the 2 megabits of network capacity
(spectrum in a
point to multipoint fixed wireless access network) is not in use by the
customer, it is available for
other transmissions on the network.
3 0 ATM QOS parameters can be used to provide varying levels of throughput on
the network
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WO 98/58477 PCT/US98/12888
allowing network operators to establish pricing to coincide with these levels
of throughput. For
voice services which are particularly intolerant to the delays inherent in non-
sequential cell
transport. Permanent Virtual Circuits (PVC's) guarantee immediate throughput
at predefined data
rates. PVC's utilize constant fixed bandwidth in the network each time there
is a request for service.
Even though the delays associated with the re-sequencing of cells are measured
in milliseconds,
the accumulated effect of such delays can be detected by the human ear. PVC's
overcome this
problem in ATM networks by effectively establishing an end-lo-end path through
the network over
which cells are sent sequentially. In essence, a PVC is a circuit switched
connection through an
ATM network. In fixed wireless point to multipoint networks, bandwidth is
allocated on a full time
1 o basis between the subscriber system and the hub for the duration of the
voice call.
Other ATM-based services are provisioned using Switched Virtual Circuits
(SVC's) which
allocate bandwidth to user transmissions according to a hierarchical priority
scheme ranging from
guaranteed data throughput rates to transport of data on a "capacity
available" basis. SVC's most
effectively support variable bit rate (bursty) data services such as LAN
communications, with QOS
parameters employed to manage throughput in relation to the criticality of the
data and the cost of
the service to the customer.
In the present network, event data is collected and stored on the system for
billing based on
2 0 the type of service provided to the customer. Billing for data services
can take into account the time
of day the service was provided, the network resources utilized by the
customer (e.g., peak data
rates, sustained data rates, number of packets/bytcs transferred), Quality of
Service provided,
number of packets dropped due to congestion or other network transmission
errors, and other factors
not typically considered in billing algorithms for traditional
telecommunications services. For voice
2 5 services, billing data is collected from in traditional CaII Detail Record
(CDR) format by the switch
equipment deployed in the network.
The point-to-multipoint broadband metropolitan area network of the present
invention will
support a broad range of future business and personal telecommunications
services such as vehicular
3 0 data applications using on-board computer systems that inlcgrale city and
hibhway road maps with
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global positioning data and local traffic eformation ~Co~l~sion
avoidailce;radar is anothcar.suitable
,vehicular application. Additionally point-to-multipoint networks can support
a host of personal
computing applications with wireless broadband connectivity, including
personal digital assistants,
hand-held ~Veb terminals and campus-wide mobile LANs.
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