Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
TECHNIQUES FOR GENERATING AND USING A RESERVATION MAP
Cross Reference to Related Anulications
[001] The present application claims priority to U.S. Patent Provisional
Application
Serial No. 60/784,105, filed March 20, 2006, by E. Gerhardt et al, entitled:
"Link
Utilization Mechanism For Aggregation Of Disjoint Radio Bandwidth," the
contents of
which are incorporated herein in their entirety by reference.
[002] The present application is a continuation-in-part of and claims the
benefit of
previously filed, co-pending US Patent Application, Serial No. 10/730,753,
filed
December 8, 2003, by Brent Saunders et al, entitled: "Radio Communication
System
Employing Spectral Reuse Transceivers", which claims priority to US
Provisional
Application Serial No. 60/432,223, filed December 10, 2002, by Edward Gerardt
et al,
entitled: "Link Utilization Mechanism for Aggregation of Disjoint Radio
Bandwidth," the
contents of both of which are incorporated herein in their entirety by
reference.
Background of the Invention
Field of the Invention
[003] The invention is directed to communication systems and, more
particularly to a
reservation map for frequency allocation in communication systems with
transceivers
operating as secondary users in a primary user frequency band.
Description of the Prior Art
[004] Some radio spectrum licensees have a plurality of adjacent or disjoint
radio
channels or combinations thereof to support communication services such as,
for
example, analog voice services. Typically, user channel allocations will have
standard
bandwidths of 6.25, 12.5-, 25- or 50-kHz or multiples thereof. One concem of
licensees
is the efficient utilization of their aggregate bandwidth. In the example of
analog push-
to-talk voice services, some have chosen to use fixed-frequency or manual
channelized
radios. While these radios are inexpensive, they may offer poor utilization of
the radio
channels if they have a dedicated frequency or frequency pair; if the user
only uses the
radio ten-percent of the time, then ninety-percent of the user channels'
bandwidth is
wasted.
[005] In another example, frequencies from different primary users are
utilized
harvested for use on a secondary use basis
1
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
[006] In the above examples, additional radios could share the frequencies by
using a
"listen-before-talk" user discipline. This will improve the spectral
efficiency btit some
users may have to wait until the frequency becomes clear or manually adjust
the
frequency if the radio has that capability and try again. Trunked radios offer
an
improvement over the mechanisms described above. Trunked radios signal a
repeater
station and the repeater will select' a clear channel for the' caller. There
are several
trunking protocols that can be selected, all of which share a disadvantage
also shared by
other push-to-talk mechanisms: the channelization of the radios is inflexible
and
efficiency of band usage may be low.
[007] The radios described above and similar radios are inflexible in that
they must be
used only on a channel of fixed bandwidth (such as 12.5- or 25-kHz) and must
remain on
the same frequency throughout the duration of the session, making higher
utilization of
the bandwidth difficult. In addition, these radios do not easily allow
additional services
such as Ethernet and IP (Internet Protocol) digital services to co-exist and
use the
bandwidth when not used by the radios.
Problems of the Prior Art
[008] A class of radios can receive multiple carriers simultaneously. In one
example, a
point-to-multipoint multicarrier master station radio can receive a data
stream spread over
the multiple carriers. A common problem in point-to-multipoint networks is how
to share
the band in the remote-to-master station direction (upstream). Various
solutions for
sharing the upstream bandwidth ("access method") have been implemented, such
as
TDMA, Aloha, slotted Aloha, and many others.
[009] All these access methods have some sort of implicit or explicit
signaling. TDMA
has implicit signaling in the fixed TDMA frame structure. The remote stations
use the
TDIVSA. clock to identify which slots in the frame are available for each
site, based on a
slot-numbering scheme and a site-numbering scheme. In one form of slotted
Aloha, the
master station signals that a message was lost by sending ACK and NAK signals
based
on message sequence numbers. All such signaling schemes exact a cost on
network
throughput due to the signaling overhead and the effectiveness of the
bandwidth-sharing
scheme. The efficiency of the signaling scheme can be affected by many
factors,
including transit delay (especially satellite or low-speed networks), round-
trip signaling
2
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
delay, raw bandwidth overhead, interaction with higher-layer protocol timers
and others.
The cost of the sharing scheme comes in the form of some combination of
throughput,
jitter, delay and other factors.
Brief Summary of the Invention
[010] The present invention is directed to improvements in cognitive radios of
the type
described in published US Patent Publication No. 2004/0142696 Al, which is the
parent
of this application and more particularly to techniques for using a
reservation map.
[011] In accordance with the present invention, there are a plurality of
transceivers
operating as a part of a network. One transceiver is designated as the master
or the
master station transceiver and controls communications with the other
transceivers. The
stations of the network are designed to operate as secondary users in a
frequency band in
which primary users have been allocated priority access to the frequency
spectrum:
Disjoint bandwidth assigned to a primary user can be aggregated or bandwidth
assigned
to multiple primary users can be harvested for secondary use. The frequency
spectrum in
use is divided into a plurality of transmission channels which can be utilized
in a
frequency hopping manner based on interference measurements. Individual remote
stations monitor each of the frequency hopping channels for the presence of
interfering
transmissions from stations not participating in the network. Each remote
station
identifies transmission frequencies of the bandwidth that are free from
interference and
can be utilized as perceived from the viewpoint of that remote station. The
remote station
creates a clear channel assessment map for its surroundings and transmits that
to the
central or master station. The central or master station is sometimes called a
master
station. The master station then gathers the clear channel assessment maps
from each of
the individual remote terminals and creates a master clear channel assessment
map which
identifies all frequencies that are free for transmission by the transceivers
of the network.
It then transmits a reservation map identifying those frequencies to all of
the stations
participating in the network.
[012] In the present invention the network uses a dynamic frequency hopping
sequence
based on frequencies identified as available in the reservation map. A pseudo-
random
sequence is used to select clear channels identified in the reservation map.
If, for
example, the network is using 20 hopping channels simultaneously to achieve
the desired
3
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
bandwidth, it will select twenty of the available hopping channels out of the
available
(non-busy) hopping channels and transmit in those hopping channels for a dwell
period.
It will then select another set of twenty available hopping channels out of
the available
hopping channels and use those during the next dwell period. This process
continues
until ongoing spectral analysis detects a change to the list of available
hopping channels
(new iirnterference or formerly biusy or blocked hopping channels become
available). A
new reservation map is sent to reflect the change of circumstances in the
spectrum being
used. Based on that information new hopping sequences are used in the network,
to take
into account the changes in interference caused by stations, not within the
network,
becoming active or inactive. '
Brief Description of the Drawings
[013] A preferred embodiment of the invention will now be described with
reference to
the following figures.
[014] Figure 1 illustrates a network architecture in accordance with one
aspect of the
invention.
[015] Figure 2 illustrates mapping of bandwidth associated with a plurality of
user
channels into a plurality of frequency hopping channels.
[016] Figure 3A shows a first band plan in which user channels are overlaid
with a
plurality of hopping channels in one arrangement.
[017] Figure 3B shows a second band plan in which user channels are overlaid
with a
plurality of hopping channels in a different arrangement.
[018] Figure 4 is a timing diagram showing how a clear channel list is
generated.
[019] Figure 5 shows how a beacon preamble message is organized.
[020] Figure 6 shows how an initialization burst is organized.
[021] Figure 7 shows how a data message burst is organized.
[022] Figure 8 shows generation of multicarrier ticklers.
[023] Figure 9 shows'a channel access mechanism utilized in US Patent
Application
Publication No. 2004/0142696 Al.
[024] Figure 10 illustrates a high-level transmission protocol for use in
carrying out
communications between a master and remote units in accordance with one aspect
of the
invention.
4
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
[025] Figure 11 illustrates the components of the master station transmit
portion of the
Figure 10 protocol.
[026] Figure 12 illustrates the remote transmit portion of the Figure 10
protocol.
[027] Figure 13 illustrates how chime-in requests for channel access are
generated and
how chime-in frequencies are assigned to remote stations in accordance with
one aspect
of the invention.
Detailed Description of the Invention
[028] Before describing in detail the particular improved band utilization and
improved
interference avoidance mechanisms in accordance with the present invention, it
should be
observed that the present invention resides primarily in a novel operational
situation,
namely, aggregation of user channels or harvesting of unused bandwidth in one
or more
bands and not in the particular detailed configurations thereof. Accordingly,
the
structure, control and arrangement of these conventional improvements have
been
illustrated in the drawings by readily understandable diagrams which show only
those
specific details that are pertinent to the present invention, so as not to
obscure the
disclosure with structural details which will be readily apparent to those
skilled in the art
having the benefit of the description herein. Thus, the illustrations of the
figures do not
necessarily represent the mechanical structural arrangement of the exemplary
system, but
are primarily intended to illustrate the major structural and functional
components of the
system in a convenient functional grouping, whereby the present invention may
be more
readily understood.
[029] Figure 1 illustrates a network architecture in accordance with one
aspect of the
invention. As shown in Figure 1, there is a master site transceiver 10 (also
called a
master or a master station) and a plurality of remote site transceivers 12
(also called
remotes). In the embodiment shown, each remote site transceiver communicates
only
with the master site transceiver although other network arrangements are
reflected in the
invention in which remote sites may communicate with the master site through
other site
transceivers. Additionally, remote sites may communicate among themselves in
other
non-preferred embodiments of the invention.
[030] Each of the transceivers 10 and 12 illustrated in Figure 1 use multiple
frequencies
of a random access discrete address set for signalling sets of supervisory
conditions. The
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
particular frequencies utilized for communication using frequency hopping
among the
multiple frequencies of the random access discrete address set are described
more
hereinafter.
[031] Referring now to Figure 2, a diagram, generally indicated by 10,
illustrates an
exemplary overlaying of an aggregation of user channels with 6.25 kHz hopping
channels. A radio band, generally indicated by 11, has a plurality of
allooated user
channels 14 to one or more licensees. (This differentiates herein allocated
"user
channels" from "hopping channels"; "hopping channels" are the overlay
frequency
hopping channels that a frequency hopping radio uses.) User channels 14 may
include a
mixture of bandwidths; in the non-limiting example of Figure 2, the allocation
of user
channels includes 6.25, 12.5-, 25- and 50-kHz channels 14.
[032] User channels 14 may be viewed as a channel space or aggregation,
generally
indicated by 15, comprising user channels 14 allocated to the licensee.
Aggregation 15
may be viewed as a 6.25 kHz overlay, generally indicated by 16, wherein each
6.25 kHz
user channel 25 is comprised of one 6.25 kHz frequency-hopping channel
("hopping
channel") 24 and each 12.5 kHz user channel 20 is comprised of two 6.25 kHz
hopping
channels 17. Similarly, each 25 kHz user channe121 in aggregation 15 is
comprised of
two outer 6.25 hopping channels 18 and two inner 6.25 kHz hopping channels 19.
Similarly, each 50 kHz user channe122 in aggregation 15 is comprised of four
outer 6.25
hopping channels 23 and four inner 6.25 kHz hopping channels 22.
[033] The 6.25 kHz overlay 16 represents the set of 6.25 kHz hopping channels
over
which a radio comprising the present invention will frequency hop. However,
the order
of channel hopping can be modified from the order shown in the figure to
lessen
interference to silent receivers.
[034] Aggregating a set of user channel allocations 14 or harvesting unused
bandwidth
form primary users provides many advantages if a selective frequency hopping
radio,
such as the present invention, is used rather than conventional fixed-
frequency or
manually agile radios. A frequency hopping radio can selectively hop over the
entire
allocation, gaining throughput efficiency due to the advantage of packet
multiplexing, as
will be understood by one skilled in the radio art. In the non-limiting
example of voice
applications, conventional analog push-to-talk radios can be blocked from
completing a
6
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
call if the correct type of allocation is not available. For example, if no 25-
kHz user
channel is available for a 25-kHz radio, the call will be blocked, even if
there are two or
more 12.5-kHz user channels available. By using a selective frequency-hopping
digital
radio, the entire pool of user channel allocations in the form of an
aggregation 15 will be
available to all radios. As will be known to one skilled in the radio art,
digital radios can
often provide voice, video and data services at adjustable or selectable
quality of service
and voice or image quality. In addition, spare capacity in the aggregated
network may be
used for a variety of data services, including Ethernet bridging and IP; this
would not be
readily available in conventional or trunked analog voice services.
[035] A further advantage of the present invention is the optional application
of
interference detection to enable sharing of aggregation 15 by a mixture of
conventional
and digital radios, said digital radios comprising the present invention.
While the
interference-detection features of the present invention typically are used to
avoid
interfering with primary licensees or other secondary licensees, in an
aggregation 15, the
interference-detection features may be used to detect the activity of
conventional radios
that use user channels within aggregation 15 on an equal basis with other
radios in the
aggregation. Licensees may be motivated to allow a mixture of analog and
digital radios
due to the cost of complete equipment replacement; thus, some analog radios
can
continue to operate without change while the network enjoys the advantages 'of
the
present invention, improving spectral efficiency for new installations or
replacement
radios in a phased replacement program.
[036] It should be noted that a single band is used in the example. However,
the present
invention anticipates that an aggregation 15 could be comprised of a plurality
of bands.
In such a case, aggregation 15 would operate in the same manner as a single
band. As
one skilled in the radio art will understand, a radio must be able to hop in
(operate in) all
the bands in the aggregation in order to enjoy the advantages of a multi-band
aggregation.
The present invention also contemplates harvesting unused bandwidth from a
plurality of
primary users.
[037] It should be noted also that the term band has a wide range of meanings
in the
radio art. It can refer broadly, for example, to the entire range of UHF
frequencies (the
UHF band). It can also refer to administrative or regulatory subdivisions of
larger bands,
7
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
such as the 420-450 MHz UHF band or the yet smaller police band within the 420-
450
MHz band. The present invention anticipates all these and similar meanings.
The
aggregations can comprise user channels from the same band; similarly, the
aggregations
can comprise user channels from a plurality of bands.
[038] Referring now to Figure 3A, a diagram illustrates a band plan, generally
indicated
by 20, in which 6.25,' 12.5, 25 and 50-kHz user channels are overlaid, as
might be
prescribed by a radio spectrum regulatory agency such as the FCC (Federal
Communications Commission). In the diagram, band 20 is comprised of a series
of 6.25
kHz user channels 21. Overlaying band 20 is a series of 12.5 kHz user channels
23 in
overlay 22. Note that in this example, the edges of 12.5 kHz user channels 23
align with
an edge of two 6.25 kHz user channels 21 and the center of 12.5 kHz user
channel 23
aligns with an edge of a 6.25 kHz user channel 21. Similarly, 25 kHz user
channels 25 of
overlay 24 align with an edge of two 12.5 kHz user channels 23. The center of
25 kHz
user channel 25 is on an edge of a 12.5 kHz user channel 23. Similarly, 50 kHz
user
channels 27 of overlay 26 align with an edge of two 25 kHz user channels 25.
The center
of 50 kHz user channe127 is on an edge of a 25 kHz user channe125. Note that
overlay
20 has a one-half user channel (3.125 kHz) guard band 29. Overlay 22 similarly
has a
guard band comprised of one-half of a 12.5 kHz user channel plus guard band 29
(6.25 +
3.125 kHz). Overlay 23 similarly has a guard band comprised of one-half of a
12.5 kHz
user channel plus guard band 29 (6.25 + 3.125 kHz). Overlay 25 similarly has a
guard
band comprised of one-half of a 25 kHz user channel plus guard band 29 (12.5 +
3.125
kHz). Overlay 27 similarly has a guard band comprised of one-half of a 50 kHz
user
channel plus guard band 29 (25 + 3.125 kHz).
[039] Referring now to Figure 3B, which is similar to Figure 3A, except that
overlay
user channels 63, 65 and 67 of Figure 3B are shifted left 3.125 kHz compared
to Figure
3A. This shift to the left (lower frequency) has the effect, for example, that
the left edge
of 12.5 kHz user channel 63 is on the center of 6.25 kHz user channel 61,
rather than on
an edge of 6.25 kHz user channe161 compared to Figure 3A.
[040] These band plans are representative of band plans that a radio spectrum
regulatory
agency such as the FCC might construct for VHF, UHF and other radio bands.
8
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
[041] Note that one practical difference between the representative band plans
of Figure
3A and Figure 3B is that, for example, in Figure 3A, 25 kHz user channel 25
has two
center overlay 6.25 kHz user channels 29 and two outer overlay 6.25 kHz user
channels
29; whereas in Figure 3B, 25 kHz user channel 65 has one center 6.25 kHz user
channel
29, two interior 6.25 kHz user channels 29 and two half-6.25 kHz (3.125 kHz)
outer user
channels.
[042] It will be shown below that this has some impact on selecting a hopping
sequence
to minimize interference to conventional or trunked radios in an aggregation
or
bandwidth used for harvesting since use of 6.25 kHz overlay user channels 21
and 61 in
the center of a 25 kHz user channel 25 or 65, for example, has a greater
interference
effect than an outer overlay user channel 21 or 61, as will be understood by
one skilled in
the radio art.
[043] Figure 4 is a timing diagram showing how a clear channel list is
generated.
[044] Clear channel assessment is performed at both the master site and at
each of the
remote sites. Each remote site transmits information about clear channels that
it senses in
its area and transmits that information to the master site. The master site
aggregates the
information from each of the remote sites into a master clear channel list
which identifies
clear channels available at all sites throughout the network. The master list
of clear
channels is maintained at the master site and is transmitted to all remote
sites in the
network using a reservation map. By transmitting only on a clear channel, a
respective
site is insured that it will not interfere with any primary user of the
spectrum of interest.
[045] Figure 4 is a sequence diagram of one methodology through which the
master site
maintains and distributes this aggregate list of clear channels to all the
remote sites in the
network. When not transmitting a message to the master, each remote user is
sequentially
stepping through and monitoring its current list of clear channels (that it
has previously
obtained from the master unit), in accordance with a pseudo random hopping
sequence
known a priori by all the users of the network from a message that may be
transmitted to
it by the master site transceiver.
[046] During the preamble period of any message being transmitted by the
master at
step 331, each remote transceiver scans all 480-6.25 KHz frequency bins within
the 217-
220 MHz spectrum for the presence of energy at step 332. Any bin containing
energy
9
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
above a prescribed threshold is masked as a non-clear channel, while the
remaining ones
of the 480 possible channels are marked as clear channels. Similarly, the
master checks
for clear channels when a remote station is transmitting a preamble.
[047] In one embodiment, with each remote site transceiver having generated a
clear
channel list as a result of preamble scanning step 332, the master transceiver
then
sequentially interrogates each remote in the'network for its clear chainnel
list via a clear
channel request message in step 333. In response to receiving a clear channel
request
message, a respective remote site transceiver transmits back to the master
channel at step
334 the clear channel list it obtained during the preamble portion of the
master's message.
The master site transceiver continues to sequentially interrogate each of the
remote site
transceivers, via subsequent clear channel list requests, until it has
completed
interrogation of the last remote site.
[048] In another embodiment, a remote station reports new interference any
time the
remote is given a chance to transmit. Preferably this will occur when the
remote has a
chance to transmit using a single carrier transmission (which occurs from time
to time)
since the hopping sequence is suspect.
[049] In step 335, the master site transceiver logically combines all of the
clear channel
lists from all the interrogated remote transceivers to produce an 'aggregate'
clear channel
list. This aggregate clear channel list is stored in the master transceiver
and broadcast in
step 336 to all of the remote transceivers. The aggregate clear channel list
is broadcast to
the remotes using a single carrier transmission since the hopping sequence is
suspect. An
initialization (beacon) message is transmitted on a single carrier. As the
aggregate clear
channel list is received at a respective remote site transceiver it is stored
in memory.
[050] Any type of message may be sent using a single carrier transmission.
[051] Figure 5 shows how beacon preamble messages are organized.
[052] As noted above, in accordance with the present invention, all actions,
including
the assembly of the communication network itself, are initiated by the master
site
transceiver. When the master site transceiver first comes up, it is the only
member of the
network. An initial task of the master is to determine whether there are any
remote sites
who wish to join the network, and then grant permission and enable such remote
sites to
become active network participants, thereby assembling the network for its
intended use
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
(e.g., telemetry from a plurality of transducer sites). Once one or more
remote site
transceivers have joined the network, the master may transmit messages to
those remote
sites, and may grant permission to the remote sites to transmit messages back
to the
master site. To this end, the master site employs the four message formats
shown in
Figures 5-8.
[053] More particularly, Figure 5 shows the contents of a'beacori preamble'
burst, that
is periodically transmitted by the master for the purpose of stimulating a
response from
any remote site who wishes to join the network. To this end, the beacon
preamble
comprises a single carrier burst, a first portion 281 of which is pure carrier
on a
frequency, which the master has determined after a scan of the spectrum of
interest to be
a clear channel. This clear channel carrier portion 281 is followed by a field
282
containing an alternating series of 1's and 0's, and terminated by a field
283, that contains
a unique word specifically associated with a search for joining the network
action. As
will be described, in the course of scanning the (480) channels in (3 MHz)
band of
interest for the presence of activity, and detecting a beacon preamble, a
remote site will
proceed to transmit back to the master site a response burst containing only
the carrier it
has detected in the beacon preamble. The use of the carrier (which the master
has
previously determined to be a clear channel) in the beacon preamble ensures
that the
response by the remote site will not interfere with another user of the
network.
[054] Figure 6 shows the contents of an initialization burst, which is
transmitted by the
master site to a remote site who is desirous of joining the network and has
successfully
responded to the master 'beacon preamble' shown in Figure 5, described above.
Because
the remote site has no knowledge of any clear channel other than the channel
on which
the master's beacon preamble was transmitted, it continues to listen on that
channel for a
follow-up initialization message from the master site. The follow-up or
initialization
message of Figure 6 is a single carrier message (the same clear channel which
was
detected by the remote site as the beacon of Figure 5) containing a preamble
291 of pure
carrier, which is followed by a field 292 of alternating l's and 0's, and a
unique word field
293, which is different from the unique word field 283. This is followed by a
message
field 294, which contains prescribed information that enables the remote site
to join the
network, including the clear channel reservation map, the PN sequence used to
hop
11
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
through the reservation map, the seed for the PN sequence and the preamble
channel
number. As the remote transceiver is not locked to the master site
transceiver, this last
item ensures that the remote will properly identify the number of the channel
on which it
has responded to the master, and thereby enable the remote site to properly
use the
reservation map for messaging.
[055] Figure' 7 shows the configuration of a standard data message burst used
for the
transmission of information between a master site and a remote site (other
than
initialization of the remote site, as described above with reference to
Figures 5 and 6). In
particular, a data message burst contains a single channel preamble, an
initial portion 301
of which is pure carrier, followed by an alternating series of l's and 0's
(302), and being
terminated by a unique word field 303, that is different from the unique word
fields of the
message formats of Figures 5 and 6. The preamble, which may typically be on
the order
of several tens (e.g., 48) of symbols, is followed by a multicarrier data
field 304 of N
symbols in length.
1056] Figure 8 shows at a high level how multi carrier ticklers are formed.
Respectively
different sets of clear channels are used as tickler tones sets by the master
site transceiver
to initiate a prescribed response in a remote site transceiver, and by the
remote site
transceiver to initiate a response in the master site transceiver. In
particular, as will be
described, -the master site transceiver may transmit a 'media open' tickler
tone set to
indicate that the network is available for the transmission of messages from a
remote site
transceiver to the master site; an 'access grant' tickler tone set granting
access to the
network to the first in time, access-requesting remote site transceiver; and a
'master
access' tickler tone set to indicated to the network that the master site
transceiver is about
to broadcast a message. In a less preferred embodiment, a remote site
transceiver may
transmit an 'access request' tone set. This tone set is transmitted by a
remote site having
data to transmit to the master site transceiver, after the expiration of a
random delay
period following detection of the media open tickler tone set from the master
site
transceiver. Tickler tones may be comprised of sets of multiple frequencies
(e.g., from
three to five frequencies) extracted from the clear channel list and are
transmitted
simultaneously over a prescribed symbol span, e.g., on the order of four to
five symbols.
12
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
[057] Figure 9 shows an exemplary implementation from the parent application
of one
form of how channel access is generated.
[058] The communication routine for the case in which the remote site has data
to
transmit and is awaiting permission from the master site to transmit that data
(to the
master site transceiver), is now described. In order to indicate that the
network media is
'open' for niessage requests, the master site transceiver transmits a 'media
open' tickler
371.
[059] As shown in the contention and backoff diagram of Figure 9, each remote
site
transceiver with a pending message awaiting transmission will respond through
a random
slotted back off, before transmitting an access request. Thereafter, the
requesting remote
transceiver waits for the master site to transmit an 'access grant' tickler.
Once a remote
node has been granted access to the channel, the master node listens for a
transmission
from the remote node for a period of time known as an acquisition of signal
(AOS)
timeout period.
[060] In the contention and backoff diagram of Figure 9, it can be seen that
remote
transceiver RTU2 will not attempt to send a data message, since it will not
detect an
access grant, as the access grant 373 from the master is transmitted at the
same time that
remote transceiver RTU2 is transmitting an access request. Remote transceiver
RTU3
never attempts to send an access -request, because it sees an access grant
being
transmitted by the master prior to RTU 3 initiating an access request, so that
RTU3
knows that the access grant from the master site is intended for another
remote
transceiver.
[061] Where the master site transceiver transmits a data message to a remote
site, it
transmits a prescribed master access tickler. In response to this tickler, the
remote site
transceiver transitions to a receive state and receives the message. This is
followed by the
master site transceiver transmitting a message.
[062] Figure 10 illustrates a high level transmission protocol preferred for
use in
carrying out communications between a master and remote units in accordance
with one
aspect of the invention. At a high level, the protocol for communications
includes three
components. There is a first portion of a frame in which the master
transceiver transmit;
13
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
that section is designated 1000 in Figure 10. It is followed by a section of
time during
which one or more remote stations will transmit (1010) to the master. In
between the
intervals 1000 and 1010, there is a period 1020 during which chime-in requests
for access
from the remote terminals can be sent to the master.
[063] Figure 11 illustrates the components of the master station transmit
portion of the
Figure 10 protocol. The master transmit interval 1000 is comprised of a start
of fraine
component 1100, a reservation map 1110, and a master transmit component 1120.
The
start of frame component comprises a carrier portion 1101 and a symbol timing
recovery
portion 1102.
[064] The master station transmit portion 1110 is comprised of one or more
addressed
messages 1111 and optionally 1112. A master station that may need to transmit
to more
than one station has the capability to expand the master station transmit
interval to
accommodate the number of addressed messages that are scheduled for
transmission.
[065] The reservation map 1120 contains the clear channel access map that is
generated
from the individual clear channel access maps transmitted by each remote to
the central
master station.
[066] Figure 12 illustrates the remote station transmit portion of the Figure
10 protocol.
The period 1010 shown in Figure 10 during which remote stations transmit can
contain,
in the preferred embodiment, messages transmitted by the first remote to be
granted
access followed by, in an optional embodiment, transmissions from other nodes
which
have been granted access 1220.
[067] Figure 13 illustrates how chime-in requests for channel access
are..generated and
how chime-in frequencies are assigned to remote stations in accordance with
one aspect
of the invention. The reservation map 1120, described in conjunction with
Figure 11
either explicitly or implicitly defines the end of frame constituting the
period of time
during which the master station transmits. Following the end of frame, the
chime-in
period 1020 begins.
[068] The present invention has very low overhead. Its efficiency comes
because it
enables all remote stations to signal their need for upstream bandwidth
simultaneously
during a chime-in period. After a fixed frame period and any time that the
master station
completes transmitting all remote sites may signal for a brief period
simultaneously, each
14
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
in a designated frequency. The transmission need not contain any information.
It can be a
simple unmodulated carrier, indicating that the site needs make a
transmission. Sites that
need not transmit at the moment do not signal. During this brief period, the
master station
scans all of the carriers simultaneously, noting which sites transmitted. The
carriers are
the same frequencies used for frequency-hopping data transmissions. The chime-
in
period 'can be initiated implici'tly by the expiration of time from a master
station
transmission or explicitly by receipt of a command signal from the master
station.
[069] The efficiency of this scheme can be attributed to three factors: the
chime-in
signaling period can be quite short, on the order of a few milliseconds, for
all remote
radios in the network to signal; all remote radios signal simultaneously over
that short
period; and the master station can initiate a signaling period as frequently
or infrequently
as needed.
[070] In the preferred embodiment, the remote stations use the following
mechanism to
select their designated signaling carrier frequency: a site's assigned Site ID
(assigned by
the Network Management System) is used as an index into the current hopping
sequence
being used. For example, the remote site with Site ID '3' would signal in the
third carrier
in the present hopping sequence. To further amplify the example, if the
hopping
sequence happened to be hopping channels 7, 8, 11, 15, 22, 28, ... and so on,
then remote
site 3 would use hopping channel 11 (assuming the site IDs started with ' 1'
rather than
'0').
[071] As described earlier, in the present invention, the network uses a
dynamic
hopping sequence based on interference measurements. A pseudo-random sequence
is
used to select hopping channels in the band that are not busy. If, for
example, the
network is using 20 hopping channels simultaneously to achieve the desired
bandwidth, it
will select twenty of the available hopping channels out of the available (non-
busy)
hopping channels and transmit in those hopping channels for a dwell period. It
will then
select another set of twenty available hopping channels out of the available
hopping
channels and use those during the next dwell period. This process continues
until the
continuing spectral analysis, described earlier, detects a change to the list
of available
hopping channels (new interference or formerly busy or blocked hopping channel
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
becomes available). After that time, new hopping sequences are used in the
network, to
take into account the change in interference analysis.
[072] The selection of a signaling channel for a particular site, described
earlier is based
on the current hopping sequence. If there are more sites than hopping channels
in the
present sequence (due to the number of simultaneous hopping channels needed or
restrictions due to interference), the signaling will, in the preferred
embodiment, occur in
cycles. For example, if 20 hopping channels are used in the hopping sequence
and there
are 32 remote sites, sites 1-20 will signal in the first signaling period; in
the second
signaling period, sites 21-32 will signal. In the preferred embodiment, the
master station
will signal for cycle 1 of the signaling period, and after that period has
ended will signal
immediately for cycle 2. By this method, large numbers of sites can signal,
adding only a
few milliseconds to the signaling period per twenty sites (in the present
example).
[073] In the preferred embodiment, the master station uses the following basic
process
for managing the multiple access method:
[074] a"frame" is dynamic in size (asynchronous); a new frame begins any time
that
the master station designates one through a signal.
[075] Typically, the master or master station:
[076] --transmits one or more messages downstream
[077] --sends a start-of-frame signal
[078] --the first cycle of remote stations signal for upstream access
[079] --as needed, the master station signals for additional cycles of
upstream access
signaling
[080] --the master or master station then selects the next station to transmit
from those
stations that signaled for upstream access, using a round-robin algorithm for
fair access.
[081] --in the first transmission from a thus-selected remote site, that site
includes a
metric of its dynamic need along with the data transmission (which could be
user data or
management data). In the present embodiment, the master station may, after the
first
transmission of the presently transmitting site, enable further transmissions
according to
the metric received or signal for the next site in it list of sites needing
upstream
bandwidth. The decision to enable another site to transmit before a previous
site has
exhausted its backlog of data can be based on a variety of network performance
criteria
16
CA 02646736 2008-09-19
WO 2007/109170 PCT/US2007/006698
well known to one skilled in the art, such as meeting a maximum jitter or
delay criteria or
meeting an application-determined priority. If a site will have no more data
to send after
its current transmission, its metric of need will indicate this condition so
that the master
station may select a new site to transmit.
[082] In the present embodiment, the master station may end the downstream
transmission at any time for iupdates to the reservation*map or hopping
sequence and/or to
transmit downstream data. Afterwards, the master station may begin a new frame
(additional signaling) or continue enabling remote stations to transmit based
on the
previously collected signaling information. This choice will be based on the
network
performance criteria described above (jitter, delay, priority, etc.). As
noted, many criteria
will be apparent to one skilled in the art for determining the order in which
upstream
access is enabled and these are anticipated by the present invention,
including simple
round-robin schemes and application bandwidth requirements such as packet
voice or
video.
[083] Thus, use of the reservation map provides substantial flexibility in
using channels
of a frequency band on a secondary basis while reducing the likelihood of
substantial
interference to priority users.
[084] While we have shown and described an embodiment in accordance with the
present -invention, it is to be understood that the same is not limited
thereto but is
susceptible to numerous changes and modifications as known to a person skilled
in the
art. We therefore do not wish to be limited to the details shown and described
herein, but
intend to cover all such changes and modifications as are obvious to one of
ordinary skill
in the art.
17
