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Claims  |
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We claim:
1. A communication system for communicating in a communication region
comprising,
interrogator including,
interrogator memory for storing interrogator code including a broadcast
command and a directed command and including bandwidth code for
controlling the bandwidth of said collection periods,
interrogator processor means connected for accessing said interrogator
memory and for processing said interrogator code to sequence said
broadcast command and said directed command,
interrogator transceiver means connected to said interrogator processor
means for sending said commands and receiving said responses in said
communication region over said common communication channel including
sending said broadcast command and said directed command a plurality of
times,
each of said tags having a unique tag ID and each including,
a tag transceiver for sending said responses to and receiving said commands
from said interrogator transceiver means over said common communication
channel,
a tag memory for storing information including tag code, a tag processor,
connected to said tag transceiver to receive said broadcast command and
said directed command said plurality of times, for processing said tag
code to send one of said responses to said interrogator through said tag
transceiver for one or more of said plurality of times, said processor
including selection means for selecting one of said tag communication
periods when one of said responses is to be sent.
2. The communication system of claim 1 wherein, said broadcast command
requests tag ID'S from all tags,
for each tag, said tag processor sends a tag ID with said response upon
receipt of said broadcast command,
for each tag for which said interrogator receives a tag ID, said
interrogator processor sends said directed command to acknowledge that
said tag ID has been received.
3. The communication system of claim 1 wherein each of said tags includes a
controllable power means for providing power to said tag transceiver in a
low-power state for a sleep mode and in a normal-power state for an awake
mode where said tag processor controls said power means to select said
lower power state or said normal-power state.
4. The communication system of claim 3 wherein,
said broadcast command requests all tags but one specific tag to go to said
sleep mode,
for each tag except said one specific tag, said tag processor upon receipt
of said broadcast command causes said tag to go to said sleep mode,
for said specific tag, said interrogator processor sends said directed
command to command an action by said specific tag,
said tag processor for said specific tag upon receipt of said directed
command sends said response including the tag ID to said interrogator.
5. The communication system of claim 3 wherein said interrogator includes
wake-up means for sending a wake-up signal to said tags and wherein each
of said tags includes wake-up detection means connected to said tag
transceiver and responsive to said wake-up signal from said interrogator
for providing a signal to said tag processor to cause switching to said
normal-power state.
6. The communication system of claim 3 wherein said tag transceiver in each
of said tags includes,
a radio frequency transmitter,
a radio frequency receiver,
an antenna connected to said transmitter and receiver.
7. The communication system of claim 2 wherein said interrogator collects
the tag ID's from tags in the communication region using communications
between said interrogators and said tags during said plurality of
collection periods, said interrogator having in said interrogator code,
synchronizing code for sending synchronizing signals to said tags to
initiate each of said collection periods,
each said tag having means for inhibiting sending a tag ID after receipt of
said directed command.
8. The communication system of claim 7 wherein said interrogator
establishes said collection periods as collection periods CP(1), CP(2), .
. . , CP(p), . . . , CP(P) having respectively listen periods LP(1),
LP(2), . . . , LP(p), . . . , LP(P) and having respectively acknowledge
periods AP(1), AP(2), . . . , AP(p), . . . , AP(P).
9. The communication system of claim 8 wherein said bandwidth code sets the
bandwidth of each collection period by setting the duration of the
respective listen period.
10. The communication system of claim 9 wherein for one or more subsequent
listen periods after the first listen period LP(1), the listen periods are
shorter in duration than the listen period LP(1).
11. The communication system of claim 10 wherein said first listen period
LP(1) and said one or more subsequent listen periods each have durations
that permit receipt of separate transmissions of tag IDs from a plurality
of tags.
12. The communication system of claims 11 wherein for a plurality of said
one or more listen periods, each successive listen period is approximately
one-half the duration of the preceding listen period.
13. The communication system of claim 9 wherein for said listen periods,
each of said tags has response means for distributing the tag ID to a
particular response time during the respective listen period.
14. The communication system of claim 13 wherein said particular response
time is determined for each said tag by a hash table algorithm using the
tag ID for said tag.
15. The communication system of claim 13 wherein said response means
includes means to randomly determine said particular response time for
each said tag.
16. The communication system of claim 2 wherein said interrogator collects
the tag ID's from tags in the communication region using communications
between said interrogators and said tags during said plurality of
collection periods, said interrogator having in said interrogator code,
synchronizing code for sending synchronizing signals to said tags to
initiate each of said collection periods,
each said tag having means for inhibiting sending a tag ID after receipt of
said directed command and for sending a tag ID only once for each
collection period.
17. The communication system of claim 1 wherein said interrogator
transceiver includes,
a radio frequency transmitter,
a radio frequency receiver,
an antenna connected to said transmitter and receiver.
18. The communication system of claim 1 wherein said interrogator
transceiver means includes a plurality of transceivers each including,
an antenna,
a radio frequency transmitter connected to said interrogator processor to
provide output signals to said antenna for transmission to said tags,
a radio frequency receiver connected to said antenna to receive signals
from said tags to provide input signals to said interrogator processor.
19. The communication system of claim 1 wherein said interrogator
transceiver means includes a plurality of spatially diverse transceivers
each including,
an antenna having a polarization,
a radio frequency transmitter connected to said interrogator processor to
provide output signals to said antenna for transmission to said tags,
a radio frequency receiver connected to said antenna to receive signals
from said tags to provide input signals to said interrogator processor,
wherein the polarization for an antenna of one of said transceivers is
different from the polarization of an antenna of another one of said
transceivers.
20. The communication system of claim 1 wherein said interrogator
transceiver means includes,
a plurality of transceivers where a particular one of said transceivers is
selectable to be active for said transceiver means, each transceiver
including,
an antenna,
a radio frequency transmitter connected to said interrogator processor to
provide output signals to said antenna for transmission to said tags,
a radio frequency receiver connected to said antenna to receive signals
from said tags to provide input signals to said interrogator processor,
wherein the antenna from one or more of said transceivers is polarization
diverse and spatially diverse from the antenna of another one of said
transceivers,
signal strength detection means for detecting the signal strength of the
signals received from said tags and for providing a signal strength
indication to said interrogator processor from each of said receivers,
a switch under control of said interrogator processor for selecting, for
each of said tags, a transceiver having the highest signal strength as
said particular one of said transceivers.
21. The communication system of claim 1 wherein each of said tags includes
a battery power unit.
22. The communication system of claim 1 wherein said interrogator includes
an interface unit for providing communications relating to tags from and
to a computer.
23. The communication system of claim 1 wherein one or more of said tags is
connected to a unit for communicating information between said
interrogator and said unit.
24. The communication system of claim 1 wherein said tags have sleep and
awake modes and said interrogator collects messages from said tags in the
communication region using communications between said interrogators and
said tags during a collection period,
said interrogator having in said interrogator code,
synchronizing code for sending a synchronizing signal to said tags to
initiate said collection period,
each said tag having in said tag code,
mode code for controlling the sleep mode and awake mode of the tag
processor,
sensing code for sensing said synchronizing signal if said tag is in said
awake mode,
send code for sending said response including a tag message to said
interrogator in response to said synchronizing signal from said
interrogator if said tag is in the awake mode.
25. The communication system of claim 24 wherein said tag processor is
interruptible in response to an interrupt signal and wherein said system
includes a unit connected to said tag for providing said interrupt signal
for signaling the presence of said tag message and wherein said mode code
is responsive to said interrupt signal to cause said tag to be in the
awake mode.
26. The communication system of claim 25 wherein said interrogator
processor after receipt of said tag message sends an acknowledge signal as
a directed command to said tag.
27. The communication system of claim 26 wherein said acknowledge signal
causes said tag to be in the sleep mode.
28. The communication system of claim 24 wherein said tag is connected to a
unit providing said tag message and said interrogator processor receives
said tag message from said unit when said tag is in the awake mode.
29. The communication system of claim 28 wherein said interrogator
transceiver means includes,
a plurality of transceivers where a particular one of said transceivers is
selectable to be active for said transceiver means, each transceiver
including,
an antenna,
a radio frequency transmitter connected to said interrogator processor to
provide output signals to said antenna for transmission to said tags,
a radio frequency receiver connected to said antenna to receive signals
from said tags to provide input signals to said interrogator processor,
wherein the antenna from one or more of said transceivers is polarization
diverse and spatially diverse from the antenna of another one of said
transceivers,
signal strength detection means for detecting the signal strength of the
signals received from said tags and for providing a signal strength
indication to said interrogator processor from each of said receivers,
a switch under control of said interrogator processor for selecting for
each of said tags a transceiver having the highest signal strength as said
particular one of said transceivers.
30. The communication system of claim 24 wherein said tag processor is
operable in a low-power state during said sleep mode and is operable in a
normal-power state during said awake mode and is operable to be set in
said normal-power state in response to a reset signal and wherein said tag
processor includes a reset input for resetting tag processor operation and
includes a unit connected to said reset input for providing said reset
signal.
31. The communication system of claim 1 wherein said tags have sleep and
awake modes and said interrogator collects messages from said tags in the
communication region using communications between said interrogators and
said tags during a collection period,
said interrogator having in said interrogator code,
wake-up code for sending a wake-up signal to said tags,
synchronizing code for sending a synchronizing signal to said tags to
initiate a collection period,
each said tag having a controllable power gate for providing power to said
tag transceiver in a low-power state and in a normal-power state where
said tag processor controls said power gate to select said normal-power
state in response to said wake-up signal, and each said tag having in said
tag code,
code for controlling the sleep mode in the low-power state,
code for sensing said synchronizing signal if said tag is in said awake
mode,
code for sending a message as part of a response to said interrogator in
response to a synchronizing signal from said interrogator if said tag is
in the awake mode.
32. A communication system for efficiently communicating with a large
number of tags in a communication region formed by a plurality of cells
where the location of the tags in the region may not be known and where
tags may be removed from or introduced into the region comprising,
a plurality of interrogators, one for each cell, for communicating with
said tags in said plurality of cells, each cell having a corresponding
interrogator, said tags and said corresponding interrogator communicating
over a common communication channel with a sequence including a plurality
of collection periods, said collection periods including interrogator
communication periods for said interrogator to send commands over said
communication channel to said tags and including tag communication periods
for said tags to send responses over said communication channel to said
corresponding interrogator, where said responses from different tags
collide if tag communication periods for said different tags coincide and
where said responses from said different tags do not collide if the tag
communication periods for said different tags do not coincide, each of
said interrogators including,
interrogator memory for storing interrogator code including a broadcast
command and a directed command and including bandwidth code for
controlling the bandwidth of said collection periods,
interrogator processor means connected for accessing said interrogator
memory and for processing said interrogator code to send said broadcast
command and to send said directed command,
interrogator transceiver means connected to said interrogator processor
means for sending said commands and receiving said responses tags within
the interrogator cell over said common communication channel, said
communications including sending said broadcast command and said directed
command a plurality of times,
each of said tags located in one or more of said cells within said
communication region, each of said plurality of tags including,
a tag transceiver for sending and receiving communications to and from said
interrogator transceiver means over said common communication channel,
a tag memory for storing information including tag code,
a tag processor, connected to said tag transceiver, for processing said tag
code to receive said broadcast command and said directed command said
plurality of times, and to send a response to said interrogator for one or
more of said plurality of times,
a computer connecting to each of said interrogators for controlling the
operation of said interrogators.
33. The communication system of claim 32 wherein said cells are not
contiguous.
34. The communication system of claim 32 wherein said cells are
overlapping.
35. The communication system of claim 32 wherein each tag has a unique tag
ID.
36. The communication system of claim 32 includes controllable power means
for providing power to said tag transceiver in a low-power state and in a
normal-power state where said tag processor controls said power means to
select said normal-power state or said low-power state.
37. The communication system of claim 36 wherein said interrogator includes
wake-up means for sending a wake-up signal to said tags and wherein each
of said tags includes wake-up detection means connected to said tag
transceiver and responsive to said wake-up signal from said interrogator
for providing a signal to said tag processor to cause switching to said
normal-power state.
38. The communication system of claim 32 wherein said tag transceiver in
each of said tags includes,
a radio frequency transmitter,
a radio frequency receiver,
an antenna connected to said transmitter and receiver.
39. The communication system of claim 32 wherein each of said tags has a
unique tag ID and said interrogator collects the tag ID's from tags in the
communication region using communications between said interrogators and
said tags during a plurality of collection periods, said broadcast command
requests tag ID's from all tags,
for each tag, said tag processor sends a tag ID with said response upon
receipt of said broadcast command,
for each tag for which said interrogator receives a tag ID, said
interrogator processor sends said directed command to acknowledge that
said tag ID has been received, said interrogator having in said
interrogator code,
synchronizing code for sending synchronizing signals to said tags to
initiate each of said collection periods,
each said tag having means for inhibiting sending a tag ID after receipt of
said directed command.
40. The communication system of claim 32 wherein said interrogator
transceiver means includes a plurality of transceivers each including,
an antenna,
a radio frequency transmitter connected to said interrogator processor to
provide output signals to said antenna for transmission to said tags,
a radio frequency receiver connected to said antenna to receive signals
from said tags to provide input signals to said interrogator processor.
41. The communication system of claim 32 wherein said interrogator
transceiver means includes a plurality of spatially diverse transceivers
each including,
an antenna having a polarization,
a radio frequency transmitter connected to said interrogator processor to
provide output signals to said antenna for transmission to said tags,
a radio frequency receiver connected to said antenna to receive signals
from said tags to provide input signals to said interrogator processor,
wherein the polarization for an antenna of one of said transceivers is
different from the polarization of an antenna of another one of said
transceivers.
42. The communication system of claim 32 wherein each of said tags includes
a battery power unit.
43. The communication system of claim 32 wherein said interrogator includes
an interface unit for providing communications relating to tags from and
to a computer.
44. The communication system of claim 32 wherein one or more of said tags
is connected to one or more units for communicating for each tag
information between said interrogator and said one or more units through
said tag.
45. The communication system of claim 32 wherein said tags have sleep and
awake modes and said interrogator collects messages from said tags in the
communication region using communications between said interrogators and
said tags during a collection period,
said interrogator having in said interrogator code,
synchronizing code for sending a synchronizing signal to said tags to
initiate a collection period,
each said tag having in said tag code,
mode code for controlling the sleep mode and awake mode of the tag
processor,
sensing code for sensing said synchronizing signal if said tag is in said
awake mode,
send code for sending to said interrogator a response including a tag
message in response to a synchronizing signal from said interrogator if
said tag is in the awake mode.
46. The communication system of claim 32 wherein said tags have sleep and
awake modes and said interrogator collects messages from said tags in the
communication region using communications between said interrogators and
said tags during a collection period,
said interrogator having in said interrogator code,
wake-up code for sending a wake-up signal to said tags,
synchronizing code for sending a synchronizing signal to said tags to
initiate a collection period,
each said tag having a controllable power gate for providing power to said
tag transceiver in a low-power state and in a normal-power state where
said tag processor controls said power gate to select said normal-power
state in response to said wake-up signal, and each said tag having in said
tag code,
code for controlling the sleep mode in the low-power state,
code for sensing said synchronizing signal if said tag is in said awake
mode,
code for sending a response including a tag message to said interrogator in
response to a synchronizing signal from said interrogator if said tag is in
the awake mode.
47. Apparatus for identifying items through transmission and reception of
signals comprising:
a plurality of tags, one for each of said items;
an interrogator for communicating with said tags,
said tags and said interrogator communicating over a common communication
channel with a communication protocol including a sequence, common to all
tags, said sequence including a plurality of collection periods, each
collection period having,
interrogator communication periods for said interrogator to send commands
over said communication channel to said tags,
a listen period having time slots during which one or more of said
plurality of tags can communicate a tag identifying signal to said
interrogator, where tag identifying signals from different tags collide if
the time slots for said tag identifying signals for said different tags
coincide and where tag identifying signals from different tags do not
collide if the time slots for said tag identifying signals for said
different tags do not coincide,
an acknowledge period during which said interrogator can communicate
acknowledge signals to said tags,
said interrogator including,
bandwidth control means for controlling the bandwidth of the collection
periods by controlling the duration of the listen periods,
signal sending means, operable for each of said collection periods, for
sending a signal to the tags to signal the commencement of the listen
period,
receiver means, operable for each of said collection periods, for receiving
tag identifying signals during said listen period from a subset of said
tags,
acknowledge sending means, operable for each of said collection periods,
for sending acknowledge signals during said acknowledge period to said
subset of said tags,
each of said tags including,
signal receiving means, operable for one or more of said collection
periods, for receiving the signal from the signal sending means so as to
identify the start of the listen period,
identification sending means, operable for one or more of said collection
periods, for sending a tag identifying signal during the listen period,
acknowledge receiving means, operable for one or more of said collection
periods, for receiving an acknowledge signal from said interrogator during
the acknowledge period.
48. In a communication system for communicating in a communication region
over a common communication channel between an interrogator and a
plurality of tags, where the interrogator includes,
interrogator memory for storing interrogator code including a broadcast
command and a directed command, interrogator processor means connected for
accessing said interrogator memory, interrogator transceiver means
connected to said interrogator processor means,
and where each of said tags includes,
a tag transceiver for sending and receiving communications to and from said
interrogator transceiver means over said common communication channel, a
tag memory for storing information including tag code, a tag processor,
connected to said tag transceiver,
the method comprising,
processing, in said interrogator processor, said interrogator code to
sequence said broadcast command and said directed command a plurality of
times,
sending and receiving communications in said communication region over said
common communication channel by said interrogator transceiver, including
sending said broadcast command and said directed command said plurality of
times, said communications having a sequence including a plurality of
collection periods, said collection periods including interrogator
communication periods for said interrogator to send commands over said
communication channel to said tags and including tag communication periods
for said tags to send responses over said communication channel to said
interrogator, where said responses from different tags collide if tag
communication periods for said different tags coincide and where said
responses from said different tags do not collide if the tag communication
periods for said different tags do not coincide,
in each of said tags,
receiving said broadcast command and said directed command said plurality
of times by said tag transceiver,
processing said tag code to send a response to said interrogator through
said tag transceiver for one or more of said plurality of times,
for each of two or more of said plurality of tags, sending a response over
said common communication channel such that at some times, a collision of
responses occurs during one of said plurality of times and such that at
another one of said plurality of times, no collision of responses occurs.
49. The communication method of claim 48 wherein,
said broadcast command requests tag ID's from all tags,
for each tag, said tag processor sends a tag ID with said response upon
receipt of said broadcast command,
for each tag for which said interrogator receives a tag ID, said
interrogator processor sends said directed command to acknowledge that
said tag ID has been received.
50. The communication method of claim 49 has a unique tag ID and said
interrogator collects the tag ID's from tags in the communication region
using communications between said interrogators and said tags during a
plurality of collection periods, said interrogator,
executing synchronizing code in said interrogator code for sending
synchronizing signals to said tags to initiate each of said collection
periods,
executing bandwidth code in said interrogator code for controlling the
bandwidth of said collection periods,
each said tag having means for inhibiting sending a tag ID after receipt of
a command.
51. The communication method of claim 50 wherein said interrogator
establishes said collection periods as collection periods CP(1), CP(2), .
. . , CP(p), . . . , CP(P) having respectively listen periods LP(1),
LP(2), . . . , LP(p), . . . , LP(P) and having respectively acknowledge
periods AP(1), AP(2), . . . , AP(p), . . . , AP(P).
52. The communication method of claim 51 wherein said bandwidth code sets
the bandwidth of each collection period by setting the duration of the
respective listen period.
53. The communication method of claim 52 wherein for one or more subsequent
listen periods after the first listen period LP(1), the listen periods are
shorter in duration than the listen period LP(1).
54. The communication method of claim 53 wherein said first listen period
LP(1) and said one or more subsequent listen periods each have durations
that permit receipt of separate transmissions of tag IDs from a plurality
of tags.
55. The communication system of claim 54 wherein for a plurality of said
one or more listen periods, each successive listen period is approximately
one-half the duration of the preceding listen period.
56. The communication method of claim 52 wherein for said listen periods,
each of said tags has response means for distributing the tag ID to a
particular response time during the respective listen period.
57. The communication method of claim 56 wherein said particular response
time is determined for each said tag by a hash table algorithm using the
tag ID for said tag.
58. The communication method of claim 56 wherein said response means
includes means to randomly determine said particular response time for
each said tag.
59. The communication method of claim 49 wherein each of said tags has a
unique tag ID and said interrogator collects the tag ID's from tags in the
communication region using communications between said interrogators and
said tags during a plurality of collection periods, said interrogator
executing said interrogator code including,
executing synchronizing code for sending synchronizing signals to said tags
to initiate each of said collection periods,
executing bandwidth code for controlling the bandwidth of said collection
periods,
each said tag inhibiting sending a tag ID after receipt of said directed
command and for sending a tag ID only once for each collection period.
60. The communication method of claim 48 includes a controllable power
means for providing power to said tag transceiver in a low-power state for
a sleep mode and in a normal-power state for an awake mode where said tag
processor controls said power means to select said low-power state or said
normal-power state.
61. The communication method of claim 60 wherein,
said broadcast command requests all tags but one specific tag to go to said
sleep mode,
for each tag except said one specific tag, said tag processor upon receipt
of said broadcast command causes said tag to go to said sleep mode,
for said specific tag, said interrogator processor sends said directed
command to command an action by said specific tag,
said tag processor for said specific tag upon receipt of said directed
command sends said response including the tag ID to said interrogator.
62. The communication method of claim 60 wherein said interrogator includes
wake-up means for sending a wake-up signal to said tags and wherein each
of said tags includes wake-up detection means connected to said tag
transceiver and responsive to said wake-up signal from said interrogator
for providing a signal to said tag processor to cause switching to said
normal-power state.
63. Apparatus for identifying items through transmission and reception of
signals comprising:
a plurality of tags, one for each of said items;
an interrogator for communicating with said tags,
said tags and said interrogator communicating over a common communication
channel with a communication protocol, said communication protocol
including a sequence common to all tags, said sequence including a
plurality of collection periods, each collection period having,
a synchronization period during which said interrogator can communicate
with said plurality of tags,
a listen period having time slots during which one or more of said
plurality of tags can communicate a tag identifying signal to said
interrogator over said communication channel, where tag identifying
signals from different tags collide if the time slots for said tag
identifying signals for said different tags coincide and where tag
identifying signals from different tags do not collide if the time slots
for said tag identifying signals for said different tags do not coincide,
and
an acknowledge period during which said interrogator can communicate
acknowledge signals to said tags over said communication channel,
said interrogator including,
interrogator memory for storing interrogator code including one or more
broadcast commands and one or more directed commands and including
bandwidth code for controlling the bandwidth of said tag communication
periods,
interrogator processor means connected for accessing said interrogator
memory and for processing said interrogator code to sequence said
broadcast commands and said directed commands,
signal sending means, operable for each of said collection periods, for
sending during said synchronization period one of said broadcast commands
over the common communication channel to the tags to signal the
commencement of the listen period,
receiver means, operable for each of said collection periods, for receiving
tag identifying signals over the common communication channel from said
tags during said listen period,
acknowledge sending means, operable for each of said collection periods,
for sending acknowledge signals as directed commands over the common
communication channel to said tags during said acknowledge period,
each of said tags including,
signal receiving means, operable for one or more of said collection
periods, for receiving said one of said broadcast commands from said
signal sending means during said synchronization period so as to identify
the start of the listen period,
identification sending means, operable for one or more of said collection
periods, for sending a tag identifying signal during one of a plurality of
time slots during the listen period,
acknowledge receiving means, operable for one of said collection periods,
for receiving an acknowledge signal from said interrogator during the
acknowledge period,
control means, operable for said one or more of said collection periods,
for controlling said identification sending means,
said control means operative, before said acknowledge receiving means
receives said acknowledge signal and during each of said one or more of
said collection periods, for selecting one of said time slots for sending
a tag identifying signal whereby two or more of said plurality of tags may
each send a respective tag identifying signal over said common
communication channel such that during one time slot of a listen period a
collision of tag identifying signals may occur and such that during
another time slot of a listen period no collision of tag identifying
signals occurs,
said control means operative, after said acknowledge receiving means
receives said acknowledge signal, for inhibiting said identification
sending means from sending said tag identifying signal.
64. The communication system of claim 63 wherein said interrogator code
includes code for controlling the duration of said collection periods.
65. The communication system of claim 64 wherein said interrogator code
establishes said collection periods as the P collection periods CP(1),
CP(2), . . . , CP(p), . . . , CP(P) having respectively P synchronization
periods SP(1), SP(2), . . . , SP(p), . . . , SP(P), having respectively
the P listen periods LP(1), LP(2), . . . , LP(p), . . . , LP(P) and having
respectively the P acknowledge periods AP(1), AP(2), . . . , AP(p), . . .
, AP(P) and wherein each of said listen periods has a plurality of time
slots.
66. The communication system of claim 65 period LP(1) is followed by one or
more subsequent listen periods LP(2), . . . , LP(p), . . . , LP(P) and
where one or more of the subsequent listen periods LP(2), . . . , LP(p), .
. . , LP(P) are shorter in duration than the first listen period LP(1)
whereby one or more of said subsequent listen periods have fewer time
slots than said first listen period. |
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