U.S. patent application number 12/772920 was filed with the patent office on 2011-02-24 for power control for point-to-multipoint services provided in communication systems.
This patent application is currently assigned to Qualcomm Incorporated. Invention is credited to Tao Chen, Edward G. Tiedemann, JR., Jun Wang.
Application Number | 20110045864 12/772920 |
Document ID | / |
Family ID | 23071111 |
Filed Date | 2011-02-24 |
United States Patent
Application |
20110045864 |
Kind Code |
A1 |
Chen; Tao ; et al. |
February 24, 2011 |
POWER CONTROL FOR POINT-TO-MULTIPOINT SERVICES PROVIDED IN
COMMUNICATION SYSTEMS
Abstract
To enable point-to-multipoint communication services in an
existing cellular communication system infrastructure, each member
subscriber station, i.e., a subscriber station participating in
such a service, is receiving a forward link shared channel, and in
certain embodiments additionally a forward link dedicated channel.
Because transmission on the forward link channels from neighboring
sectors presents interference to the transmission from the sector
serving the subscriber station, it is desirable to control the
forward link channel transmission power to the minimum acceptable
power. Additionally, a transmission form each member subscriber
station on a reverse link channel presents interference to other
subscriber stations. Therefore, it is desirable to control the
reverse link channel transmission to the minimum signal level.
Consequently, a method and apparatus for a power control that
enables point-to-multipoint services in an existing infrastructure
of a wireless cellular telephone system is disclosed.
Inventors: |
Chen; Tao; (San Diego,
CA) ; Wang; Jun; (La Jolla, CA) ; Tiedemann,
JR.; Edward G.; (Concord, MA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
Qualcomm Incorporated
San Diego
CA
|
Family ID: |
23071111 |
Appl. No.: |
12/772920 |
Filed: |
May 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10113257 |
Mar 28, 2002 |
7742781 |
|
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12772920 |
|
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60279970 |
Mar 28, 2001 |
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Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04L 29/06027 20130101;
H04L 69/04 20130101; H04L 69/16 20130101; H04L 12/189 20130101;
H04L 69/32 20130101; H04W 52/0219 20130101; H04L 12/1877 20130101;
H04W 52/14 20130101; H04L 29/06 20130101; Y02D 30/70 20200801; H04W
80/00 20130101; Y02D 70/1222 20180101; H04L 65/608 20130101; H04L
65/4076 20130101; H04L 69/22 20130101; H04W 52/0216 20130101; H04L
67/22 20130101; H04L 69/161 20130101; H04W 52/54 20130101; H04W
84/042 20130101; H04L 63/0442 20130101; H04W 52/12 20130101; H04L
9/30 20130101; H04L 65/607 20130101; H04W 52/327 20130101; H04L
12/185 20130101; H04L 67/14 20130101; H04L 2463/101 20130101; H04W
4/06 20130101; H04W 52/08 20130101; Y02D 30/00 20180101; H04L
63/061 20130101; H04L 69/164 20130101; H04W 52/322 20130101; Y02D
30/30 20180101; H04W 72/04 20130101; Y02D 70/124 20180101; H04L
63/068 20130101; H04L 67/04 20130101; H04W 52/16 20130101; H04L
63/164 20130101 |
Class at
Publication: |
455/522 |
International
Class: |
H04W 52/04 20090101
H04W052/04 |
Claims
1. A method for power control for point-to-multipoint services in a
communication system, comprising: determining at each subscriber
station belonging to a group a quality metric of a forward link
shared channel while a subscriber station remains an active
subscriber station and forgoing determining when the active
subscriber station becomes passive: and transmitting the determined
quality metric on a reverse link common channel.
2. The method as claimed in claim 1, wherein said transmitting the
determined quality metric comprises: transmitting the determined
quality metric on a reverse link common channel if the determined
quality metric is less than a threshold.
3. The method as claimed in claim 2, wherein said transmitting the
determined quality metric if the determined quality metric is less
than a threshold comprises: transmitting the determined quality
metric if the determined quality metric is less than a
pre-determined threshold.
4. The method as claimed in claim 2, further comprising: increasing
the threshold by a first amount if an information sent on the
forward link shared channel is received with sufficient decoder
metric.
5. The method as claimed in claim 2, further comprising: decreasing
the threshold by a second amount if an information sent on the
forward link shared channel is received with insufficient decoder
metric.
6. A method for power control for point-to-multipoint services in a
communication system, comprising: determining at each subscriber
station belonging to a group a quality metric of a forward link
shared channel; and transmitting the determined quality metric,
wherein said transmitting the determined quality metric comprises
transmitting the determined quality metric on a reverse link common
channel monitored by the subscriber station.
7. The method as claimed in claim 6, wherein said transmitting the
determined quality metric comprises: requesting by a subscriber
station an assignment of a reverse link dedicated channel over the
reverse link common channel monitored by the subscriber station;
and transmitting the determined quality metric on the reverse link
dedicated channel.
8. The method as claimed in claim 7, wherein said requesting by a
subscriber station an assignment of a reverse link dedicated
channel comprises: requesting by a subscriber station an assignment
of a reverse link dedicated channel over an access channel.
9. An apparatus for power control for point-to-multipoint services
in a communication system, comprising: means for determining at
each subscriber station belonging to a group a quality metric of a
forward link shared channel while a subscriber station remains an
active subscriber station and forgoing determining when the active
subscriber station becomes passive; and means for transmitting the
determined quality metric on a reverse link common channel.
10. The apparatus as claimed in claim 9, wherein said means for
transmitting the determined quality metric comprises: means for
transmitting the determined quality metric on a reverse link common
channel if the determined quality metric is less than a
threshold.
11. The apparatus as claimed in claim 10, wherein said means for
transmitting the determined quality metric if the determined
quality metric is less than a threshold comprises: means for
transmitting the determined quality metric if the determined
quality metric is less than a pre-determined threshold.
12. The apparatus as claimed in claim 10, further comprising: means
for increasing the threshold by a first amount if an information
sent on the forward link shared channel is received with sufficient
decoder matrix.
13. The apparatus as claimed in claim 10, further comprising: means
for decreasing the threshold by a second amount if an information
sent on the forward link shared channel is received with
insufficient decoder matrix.
14. An apparatus for power control for point-to-multipoint services
in a communication system, comprising: means for determining at
each subscriber station belonging to a group a quality metric of a
forward link shared channel; and means for transmitting the
determined quality metric, wherein said means for transmitting the
determined quality metric comprises means for transmitting the
determined quality metric on a reverse link common channel
monitored by the subscribed station.
15. The apparatus as claimed in claim 14, wherein said means for
transmitting the determined quality metric comprises: means for
requesting by a subscriber station an assignment of a reverse link
dedicated channel over the reverse link common channel monitored by
the subscriber station: and means for transmitting the determined
quality metric on the reverse link dedicated channel.
16. The apparatus as claimed in claim 15, wherein said means for
requesting by a subscriber station an assignment of a reverse link
dedicated channel comprises: means for requesting by a subscriber
station an assignment of a reverse link dedicated channel over an
access channel.
17. An apparatus for power control for point-to-multipoint services
in a communication system, comprising: a subscriber station
configured to: determine a quality metric of a forward link shared
channel while the subscriber station remains an active subscriber
station and forgoing determining when the active subscriber station
becomes passive; and transmit the determined quality metric on a
reverse link common channel.
18. The apparatus as claimed in claim 17, wherein said subscriber
station . transmits the determined quality metric by being
configured to transmit the determined quality metric on a reverse
link common channel if the determined quality metric is less than a
threshold.
19. The apparatus as claimed in claim 17, wherein said subscriber
station transmits the determined quality metric by being configured
to transmit the determined quality metric if the determined quality
metric is less than a pre-determined threshold.
20. The apparatus as claimed in claim 18, wherein said subscriber
station is further configured to increase the threshold by a first
amount if an information sent on the forward link shared channel is
received with sufficient decoder metric.
21. The apparatus as claimed in claim 18, wherein said subscriber
station is further configured to decrease the threshold by a second
amount if an information sent on the forward link shared channel is
received with insufficient decoder metric.
22. An apparatus for power control for point-to-multipoint services
in a communication system, comprising: a subscriber station
configured to determine a quality metric of a forward link shared
channel; and transmit the determined quality metric, wherein said
subscriber station is further configured to transmit the determined
quality metric on a reverse link common channel monitored by the
subscriber station.
23. An apparatus for power control for point-to-multipoint services
in a communication system, comprising: a subscriber station
configured to determine a quality metric of a forward link shared
channel; and transmit the determined quality metric, wherein said
subscriber station is further configured to: request an assignment
of a reverse link dedicated channel over the reverse link common
channel monitored by the subscriber station; and transmit the
determined quality metric on the reverse link dedicated
channel.
24. The apparatus as claimed in claim 23, wherein said subscriber
station is further configured to request an assignment of a reverse
link dedicated channel over an access channel.
25. A computer-readable storage medium including
computer-executable instructions encoded thereon for: determining
at each subscriber station belonging to a group a quality metric of
a forward link shared channel while a subscriber station remains an
active subscriber station and forgoing determining when the active
subscriber station becomes passive; and transmitting the determined
quality metric on a reverse link common channel.
26. A computer-readable storage medium including
computer-executable instructions encoded thereon for: determining
at each subscriber station belonging to a group a quality metric of
a forward link shared channel; and transmitting the determined
quality metric, wherein said transmitting the determined quality
metric comprises transmitting the determined quality metric on a
reverse link common channel monitored by the subscriber station.
Description
[0001] claim of priority UNDER 35 U.S.C. .sctn.120
[0002] The present Application for Patent is a Divisional of patent
application Ser. No. 10/113,257 entitled "Power Control For
Point-To-Multipoint Services Provided In Communication Systems"
filed Mar. 28, 2002, now allowed, which claims priority to U.S.
Provisional application 60/279,970 filed Mar. 28, 2001, and
assigned to the assignee hereof and hereby expressly incorporated
by reference herein.
BACKGROUND
[0003] 1. Field
[0004] The present invention relates to point-to-multipoint
services, in a wireline or a wireless communication system. More
specifically, the present invention relates to a method and an
apparatus for a power control in such a point-to-multipoint
services communications system.
[0005] 2. Background
[0006] Communication systems have been developed to allow
transmission of information signals from an origination station to
a physically distinct destination station. In transmitting
information signal from the origination station over a
communication channel, the information signal is first converted
into a form suitable for efficient transmission over the
communication channel. Conversion, or modulation, of the
information signal involves varying a parameter of a carrier wave
in accordance with the information signal in such a way that the
spectrum of the resulting modulated carrier is confined within the
communication channel bandwidth. At the destination station the
original information signal is replicated from the modulated
carrier wave received over the communication channel. Such a
replication is generally achieved by using an inverse of the
modulation process employed by the origination station.
[0007] Modulation also facilitates multiple-access, i.e.,
simultaneous transmission and/or reception, of several signals over
a common communication channel. Multiple-access communication
systems often include a plurality of remote subscriber terminals
requiring intermittent service of relatively short duration rather
than continuous access to the common communication channel. Several
multiple-access techniques are known in the art, such as time
division multiple-access (TDMA), Frequency division multiple-access
(FDMA), and amplitude modulation multiple-access (AM). Another type
of a multiple-access technique is a code division multiple-access
(CDMA) spread spectrum system that conforms to the "TIA/EIA/IS-95
Mobile Station-Base Station Compatibility Standard for Dual-Mode
Wide-:Band Spread Spectrum Cellular System," hereinafter referred
to as the IS-95 standard. The use of CDMA techniques in a
multiple-access communication system is disclosed in U.S. Pat. No.
4,901,307, entitled "SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION
SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS," and U.S. Pat. No.
5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN
A CDMA CELLULAR TELEPHONE SYSTEM," both assigned to the assignee of
the present invention.
[0008] A multiple-access communication system may be a wireless or
wire-line and may carry voice and/or data. An example of a
communication system carrying both voice and data is a system in
accordance with the IS-95 standard, which specifies transmitting
voice and data over the communication channel. A method for
transmitting data in code channel frames of fixed size is described
in detail in U.S. Pat. No. 5,504,773, entitled "METHOD AND
APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION", assigned to
the assignee of the present invention. In accordance with the IS-95
standard, the data or voice is partitioned into code channel frames
that are 20 milliseconds wide with data rates as high as 14.4 Kbps.
Additional examples of a communication systems carrying both voice
and data comprise communication systems conforming to the "3rd
Generation Partnership Project" (3GPP), embodied in a set of
documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS
25.213, and 3G TS 25.214 (the W-CDMA standard), or "TR-45.5
Physical Layer Standard for cdma2000 Spread Spectrum Systems" (the
IS-2000 standard).
[0009] In a multiple-access communication system, communications
between users are conducted through one or more base stations. A
first user on one subscriber station communicates to a second user
on a second subscriber station by transmitting data on a reverse
link to a base station. The base station receives the data and can
route the data to another base station. The data is transmitted on
a forward link of the same base station, or the other base station,
to the second subscriber station. Likewise, the communication can
be conducted between a first user on a mobile subscriber station
and a second user on a landline station. A base station receives
the data from the user on a reverse link, and routes the data
through a public switched telephone network (PSTN) to the second
user.
[0010] In a wireless communication system, maximizing a capacity of
the communication system in terms of the number of simultaneous
telephone calls that can be handled is extremely important. The
capacity in a spread spectrum communication system can be maximized
if the transmission power of each subscriber station is controlled
such that each transmitted signal arrives at a base station
receiver at the same signal level. However, if a signal transmitted
by a subscriber station arrives at the base station receiver at a
power level that is too low, quality communications cannot be
achieved due to interference from the other subscriber stations. On
the other hand, if the subscriber station transmitted signal is at
a power level that is too high when received at the base station,
communication with this particular subscriber station is acceptable
but this high power signal acts as interference to other subscriber
stations. This interference may adversely affect communications
with other subscriber stations. Therefore, each subscriber station
needs to transmit the minimum signal level expressed as e.g., a
signal-to-noise ratio, that allows transmitted data recovery.
[0011] Consequently, the transmission power of each subscriber
station within the coverage area of a base station is controlled by
the base station to produce the same nominal received signal power
at the base station. In an ideal case, the total signal power
received at the base station is equal to the nominal power received
from each subscriber station multiplied by the number of subscriber
stations transmitting within the coverage area of the base station
plus the power received at the base station from subscriber
stations in the coverage area of neighboring base stations.
[0012] The received power is determined by an attenuation of the
transmitted power by a path loss of the link. The path loss can be
characterized by two separate phenomena: average path loss and
fading. In many communication systems, e.g., IS-95, W-CDMA,
IS-2000, the forward link and the reverse link are allocated
separate frequencies, i.e., the forward link operates on a
different frequency than the reverse link. However, because the
forward link and reverse link frequencies are within the same
general frequency band, a significant correlation between the
average path losses of the two links exists. On the other hand,
fading is an independent phenomenon for the forward link and
reverse link and varies as a function of time.
[0013] In an exemplary CDMA system, each subscriber station
estimates the path loss of the forward link based on the total
power at the input to the subscriber station. The total power is
the sum of the power from all base stations operating on the same
frequency assignment as perceived by the subscriber station. From
the estimate of the average forward link path loss, the subscriber
station sets the transmit level of the reverse link signal. Should
the reverse link channel for one subscriber station suddenly
improve compared to the forward link channel for the same
subscriber station due to independent fading of the two channels,
the signal as received at the base station from this subscriber
station would increase in power. This increase in power causes
additional interference to all signals sharing the same frequency
assignment. Thus a rapid response of the subscriber station
transmit power to the sudden improvement in the channel would
improve system performance. Therefore, it is necessary to have the
base station continually contribute to the power control mechanism
of the subscriber station.
[0014] Thus, the subscriber station's transmit power is controlled
by one or more base stations. Each base station, with which the
subscriber station is in communication, measures the received
signal strength from the subscriber station. The measured signal
strength is compared to a desired signal strength level for that
particular subscriber station. A power adjustment command is
generated by each base station and sent to the subscriber station
on the forward link. In response to the base station power
adjustment command, the subscriber station increases or decreases
the subscriber station transmit power by a predetermined amount. By
this method, a rapid response to a change in the channel is
effected and the average system performance is improved. Note that
in a typical cellular system, the base stations are not intimately
connected .and each base station in the system is unaware of the
power level at which the other base stations receive the subscriber
station's signal.
[0015] When a subscriber station is in communication with more than
one base station, power adjustment commands are provided from each
base station. The subscriber station acts upon these multiple base
station power adjustment commands to avoid transmit power levels
that may adversely interfere with other subscriber station
communications, and yet provide sufficient power to support
communication from the subscriber station to at least one of the
base stations. This power control mechanism is accomplished by
having the subscriber station increase its transmit signal level
only if every base station, with which the subscriber station is in
communication, requests an increase in power level. The subscriber
station decreases the subscriber station's transmit signal level if
any base station, with which the subscriber station is in
communication, requests that the power be decreased. A system for
base station and subscriber station power control is disclosed in
U.S. Pat. No. 5,056,109 entitled "METHOD AND APPARATUS FOR
CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE
SYSTEM," issued Oct. 8, 1991, assigned to the assignee of the
present invention.
[0016] In addition to the above-described reverse link power
control, it is also desirable to control the relative power used in
each traffic channel transmitted on a forward link by the base
station. To enable such a control, each remote station measures the
power of traffic channels received form a base station, generates
control information in response, and transmits the control
information back to the base station. The primary reason for
providing such control is to accommodate the fact that in certain
locations the forward link may be unusually disadvantaged. Unless
the power being transmitted to the disadvantaged subscriber station
is increased, the signal quality may become unacceptable. An
example of such a location is a point where the path loss to one or
two neighboring base stations is nearly the same as the path loss
to the active base station, i.e., a base station communicating with
the subscriber station. In such a location, the total interference
would be increased three times over the interference seen by a
subscriber station at a point relatively close to the active base
station. In addition, the interference coming from the neighboring
base stations does not fade in unison with the signal from the
active base station as would be the case for interference coming
from the active base station. A subscriber station in such a
situation may require 3 to 4 dB additional signal power from the
active base station to achieve adequate performance. At other
times, the subscriber station may be located where the
signal-to-interference ratio is unusually good. In such a case, the
base station could transmit the desired signal using a lower than
normal transmitter power, reducing interference to other signals
being transmitted by the system.
[0017] The above described wireless communication service is an
example of a point-to-point communication service. In contrast, a
point-to-multipoint service is a service where the information
transmitted by a source of the information is intended for a
plurality of mobile stations. The basic model of a
point-to-multipoint system comprises a set of users, a group of
which is served by one or more sources of information, which
provide information with a certain contents, e.g., news, movies,
sports events and the like, to be transmitted to the users. Each
user's subscriber station participation in the point-to-multipoint
service (a member subscriber station) monitors a forward link
shared channel. Because the source of information fixedly
determines the content, the users are generally not communicating
back. Examples of common usage of such a point-to-multipoint
services communication systems are TV broadcast, radio broadcast,
and the like. Alternatively, the source of information is a user--a
member of the group, which transmits information intended for the
remaining members of the selected group. If the user wishes to
talk, he presses a push to talk (PTT) button. Typically, the
talking user's voice is routed from the subscriber station to a
transceiver station on a dedicated reverse link. The transceiver
station then transmits the talking user's voice over the forward
link shared channel. As in case of the point-to-point communication
system, such a communication system allows both landline and
wireless subscriber station to access the system. Such a
point-to-multipoint service is also referred to as a group service.
Examples of the group service communication system use is in
dispatch services, such as local police radio systems, taxicab
dispatch systems, Federal Bureau of Intelligence and secret service
operations, and general military communication systems.
[0018] The above-mentioned point-to-multipoint service
communication systems are generally highly specialized
purpose-build communication systems. With the recent, advancements
in wireless cellular telephone systems there has been an interest
of utilizing the existing infrastructure of the--mainly
point-to-point cellular telephone systems--for point-to-multipoint
services. As used herein, the term "cellular" system encompasses
system operating on both cellular and personal communication system
(PCS) frequencies.
[0019] The power control mechanism for subscriber stations acting
as point-to-point units described above is not directly applicable
to point-to-multipoint services. As discussed, the wireless
cellular telephone systems assign a dedicated forward and reverse
link between two or more communicating users. In contrast, the
point-to-multipoint services typically rely on assigning a shared
forward link to be monitored by all the users in the group.
Furthermore, in a point-to-multipoint services, in general,
majority of the subscriber stations are passive (i.e. just
listening) at any one time. When a subscriber station is passive,
it does not necessarily have an established reverse link on which
to transmit information to the base station. Because the power
control method in the existing infrastructure is based on a
point-to-point communications model, there is a need in the art for
a method and apparatus for a power control that enables group
services in an existing infrastructure of a wireless cellular
telephone system.
SUMMARY
[0020] In one aspect of the invention, the above stated needs are
addressed by controlling a reverse link channel power by
determining sectors whose coverage area contain active subscriber
stations belonging to a group; and transmitting reverse link power
control commands on a forward link common channel from the
determined sectors. The forward link common channel is received at
each subscriber station belonging to a group; and the reverse link
transmission power is adjusted at the active subscriber stations
belonging to a group in accordance with the reverse link power
control commands contained in the forward link common channel.
[0021] In another aspect of the invention, the above stated needs
are addressed by controlling a reverse link channel power in a
point-to-multipoint communication system by transmitting user data
on a forward link common channel; and transmitting reverse link
power control commands on a forward link dedicated channel. The
above stated needs are further addressed by receiving at each
subscriber station belonging to a group a forward link common
channel; receiving at each subscriber station belonging to a group
a forward link dedicated channel; and adjusting at the active
subscriber stations belonging to a group reverse link transmission
power in accordance with reverse link power control commands
contained in the forward link dedicated channel.
[0022] In yet another aspect of the invention, the above stated
needs are addressed by controlling a reverse link channel power in
a point-to-multipoint communication system by determining at the
access network sectors whose coverage area contain active
subscriber stations belonging to a group; and transmitting reverse
link power control commands on a forward link dedicated channel
from the determined sectors. The above stated needs are further
addressed by receiving at each subscriber station belonging to a
group a forward link common channel; receiving at each active
subscriber station belonging to a group a forward link dedicated
channel; and adjusting at the active subscriber stations belonging
to a group reverse link transmission power in accordance with
reverse link power control commands contained in the forward link
dedicated channel.
[0023] In one aspect of the invention, the above stated needs are
addressed by controlling a forward link channel power in a
point-to-multipoint communication system by monitoring at a sector
at least one reverse link channel to detect a quality metric of a
forward link shared channel; and adjusting the forward link shared
channel power in accordance with the worst quality metric.
[0024] In another aspect of the invention, the above stated needs
are addressed by controlling a forward link channel power in a
point-to-multipoint communication system by determining at each
subscriber station belonging to a group a quality metric of a
forward link shared channel; and transmitting the determined
quality metric.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 illustrates a conceptual diagram of a group services
communication system;
[0026] FIG. 2 illustrates a conceptual diagram of a forward link
channel with fixed rate of data; and
[0027] FIG. 3 illustrates a conceptual diagram of a forward link
channel with variable rate of data.
DETAILED DESCRIPTION
Definitions
[0028] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment described
herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other embodiments.
[0029] The terms point-to-point communication is used herein to
mean a communication between two subscriber stations over a
dedicated forward communication channel and dedicated reverse
communication channel.
[0030] The term point-to-multipoint communication service is used
herein to mean a communication wherein a plurality of subscriber
stations are receiving communication from--typically--one source.
Such services may comprise, e.g., group service, in which the
source is a subscriber station; a broadcast service, in which the
source is a central station; or a multicast service, in which the
recipients comprise a sub-set of the plurality of subscriber
stations.
[0031] The term access network is used herein to mean a collection
of base stations (BS) and one or more base stations' controllers.
The access network transports data packets between multiple
subscriber stations. The access network may be further connected to
additional networks outside the access network, such as a corporate
intranet or the Internet, and may transport data packets between
each access terminal and such outside networks.
[0032] The term base station is used herein to mean the hardware
with which subscriber stations communicate. Cell refers to the
hardware or a geographic coverage area, depending on the context in
which the term is used. A sector is a partition of a cell. Because
a sector has the attributes of a cell, the teachings described in
terms of cells are readily extended to sectors.
[0033] The term subscriber station is used herein to mean the
hardware with which an access network communicates. A subscriber
station may be mobile or stationary. A subscriber station may be
any data device that communicates through a wireless channel or
through a wired channel, for example using fiber optic or coaxial
cables. A subscriber station may further be any of a number of
types of devices including but not limited to PC card, compact
flash, external or internal modem, or wireless or wireline phone. A
subscriber station that is in the process of establishing an active
traffic channel connection with a BS is said to be in a connection
setup state. A subscriber station that has established an active
traffic channel connection with a BS is called an active subscriber
station, and is said to be in a traffic state.
[0034] The term forward channel/link is used herein to mean a
communication channel/link through which a base station sends
signals to an subscriber station.
[0035] The term reverse channel/link is used herein to mean a
communication channel/link through which the subscriber station
sends signals to the base station.
[0036] The term physical channel is used herein to mean a
communication route over which a signal propagates described in
terms of modulation characteristics and coding.
[0037] The term logical channel is used herein to mean a
communication route within the protocol layers of either the base
station or the subscriber station.
[0038] The term communication channel is used herein to mean a
physical channel or a logical channel in accordance with the
context.
[0039] The term soft hand-off is used herein to mean a
communication between a subscriber station and two or more sectors,
wherein each sector belongs to a different cell. The reverse link
communication is received by both sectors, and the forward link
communication is simultaneously carried on the two or more sectors'
forward links.
[0040] The term softer hand-off is used herein to mean a
communication between a subscriber station and two or more sectors,
wherein each sector belongs to the same cell. The reverse link
communication is received by both sectors, and the forward link
communication is simultaneously carried on one of the two or more
sectors' forward links.
[0041] The term puncture is used herein to mean replacing a first
information content of a first size with a second information
content of a first size.
[0042] The term dedicated channel is used herein to mean a channel
modulated by information specific to an individual subscriber
station.
[0043] The term common channel is used herein to mean a channel
modulated by information shared among all subscriber stations.
[0044] The term user data or payload is used herein to mean data
other than control data.
[0045] The term control data is used herein to mean data enabling
operation of entities in a communication system.
DESCRIPTION
[0046] FIG. 1 illustrates a conceptual diagram of a communication
system 100 capable of providing point-to-multipoint services in
accordance with embodiments of the present invention. For tutorial
purposes, the following description illustrates a group call:
however, one of ordinary skills in the art understands how to apply
the disclosed concepts to other point-to-multipoint services. A
(calling) group is defined by the group's membership, comprising
users of subscriber stations talking to one another frequently
enough to establish the calling group. The calling group is said to
be in a sleep state when no member is either idle or active, e.g.,
all members are either powered off or do not participate in the
calling group. The calling group is in the idle state when at least
one member participates in the group. The calling group is in the
active state when one of at least two members initiates a group
call. A group call is divided into active and silent periods. The
group call is in the active period when there are transmissions
between the members without long idle periods. The group call is in
a silent period when there is no member transmitting any traffic
for a period extending the long idle period.
[0047] In an active period, a group user on a member subscriber
station, e.g., member subscriber station 102(1) communicates user
information (voice or data) to other group users on member
subscriber stations 102(2) through 102(5) via an access network
comprising base stations 104 and a controller 110. For brevity, the
term "member subscriber station" is used hereinafter to mean "user
on a subscriber station" unless stated otherwise. Although the term
base station is used, one of ordinary skills in the art recognizes
that the embodiments are equally applicable to sectors. The base
stations 104 are connected to the controller 110 by backhauls 112.
The term backhaul is used to mean a communication link between a
controller and a base station. The backhaul 112 can be implemented
in a number of connection types including, e.g., a microwave or
wire-line E1 or T1, optical fiber, and other connection types known
to one of ordinary skills in the art. The controller 110 is
connected to an interface unit 114, interfacing the communication
system 100 with other services (not shown), e.g., a public switched
telephone network (PSTN), packed data serving node (PDSN), and
other services known to one of ordinary skills in the art.
[0048] When a member subscriber station, e.g., the subscriber
station 102(1), desires to transmit user data to the group aver the
reverse link, the member subscriber station needs to request a
reverse link assignment and request to transmit. In one embodiment,
the subscriber station 102(1), sends an access channel message
requesting a reverse link to base station, e.g., base station
104(1). The access message is sent on an access channel. The access
channel is a reverse link channel used by subscriber stations for
communicating to the base station. The access channel is used for
short signaling message exchanges such as call originations,
responses to pages, and registration. An access attempt is sent by
the subscriber station in a series of access probes. Each access
probe carries the same information but is transmitted at a higher
power level than the previous one. The access probes continue until
a base station acknowledgment is received at the subscriber
station. However, one skilled in the art recognizes that other
access arrangements as described in a provisional application Ser.
No. 60/279,970, entitled "METHOD AND APPARATUS FOR GROUP CALLS
USING DEDICATED AND COMMON CHANNELS IN WIRELESS NETWORKS," filed
Mar. 28, 2001, assigned to the assignee of the present invention
are equally applicable.
[0049] Once the communicating (active) member subscriber station
102(1) is assigned a reverse link channel 108(1), the subscriber
station 102(1) may transmit information to a base station 104(1).
The reverse link assignment are detailed in the above-mentioned a
provisional application Ser. No. 60/279,970, entitled "METHOD AND
APPARATUS FOR GROUP CALLS USING DEDICATED AND COMMON CHANNELS IN
WIRELESS NETWORKS," filed Mar. 28, 2001, assigned to the assignee
of the present invention are equally applicable. The base station
104(1) routes the received information to base stations 104(2) and
104(3), and transmits the received information on a forward link
shared channel 106(1) to the user 102(2). The base stations 104(2)
and, 104(3) transmit the routed information on the forward link
shared channels 106(2) and 106(3). To receive the information from
the active member subscriber station 102(1), all the member
subscriber stations of an active group, i.e., the subscriber
stations 102(1) through 102(5) are assigned to monitor the forward
link shared channel(s) 106 of their individual base stations 104
during active group calls. In general, the forward link shared
channels 106(1), 106(2), and 106(3) assigned by the respective base
stations or 104(1), 104(2), and 104(3) are different from one
another. However, to allow improved reception of member subscriber
stations 102 located in overlapping coverage areas, the forward
link shared channel 106 may be transmitted synchronously by more
than one sector or base station 104. The method for improved
reception of the forward link common shared channel in overlapping
coverage areas is disclosed in U.S. Pat. No. 6,731,936, entitled
"METHOD AND SYSTEM FOR A HANDOFF IN A BROADCAST COMMUNICATION
SYSTEM," issued on May 4, 2004, assigned to the assignee of the
present invention.
[0050] In one embodiment, the forward link shared channel 106 is
modulated by the user information intended to the group member
subscriber stations, and control data, necessary for the call
maintenance, e.g., signaling information, power control
information, and other types of information known to one skilled in
the art. However, the limited capacity of the forward link shared
channel may prevent modulation by both the call information and the
call maintenance information. Consequently, in another embodiment,
only the user information is transmitted on the forward link shared
channel 106, and the call maintenance information may be modulated
on an additional forward link channel. In that case, each
subscriber station 102 must monitor, in addition to the forward
link shared channel, the additional forward link channels,
comprising the call maintenance information. Such an additional
channel may be a dedicated channel or a common channel, as
described in the above-mentioned provisional application Ser. No.
60/279,970, entitled "METHOD AND APPARATUS FOR GROUP CALLS USING
DEDICATED AND COMMON CHANNELS IN WIRELESS NETWORKS," filed Mar. 28,
2001, assigned to the assignee of the present invention are equally
applicable.
[0051] In one embodiment, passive subscriber stations 102(2),
102(3), and 102(4) do not establish reverse links to any of the
base stations 104. Note that if subscriber stations 102(2), 102(3),
and 102(4) are completely passive, the individual base stations may
be unaware of whether the subscriber stations are in their
corresponding coverage areas. Even if a subscriber station
registers with the base station when it enters the coverage area of
a base station, the base station has no way of knowing when the
subscriber station has left the base station coverage area.
[0052] Even if subscriber stations 102(2), 102(3), and 102(4) are
passive, they still may use reverse link channel to communicate
with the base stations. In the preferred embodiment, passive
subscriber stations 102(2), 102(3), and 102(4) use the access
channel to signal the base station if they are in need of more
power from the forward link broadcast channel. Such a use of a
reverse link channel is described in the above-mentioned
provisional application Ser. No. 60/279,970, entitled "METHOD AND
APPARATUS FOR GROUP CALLS USING DEDICATED AND COMMON CHANNELS IN
WIRELESS NETWORK," filed Mar. 28, 2001, assigned to the assignee of
the present invention are equally applicable.
[0053] It is well known in the art that base stations may be
sectorized into two or more sectors. Consequently, where the term
base station is used herein, it is implied that the term may refer
to an entire base station or to a single sector of a multisectored
base station. Furthermore, although in the description above, the
common information was provided by the subscriber station 102(1),
one of ordinary skills in the art understands that the concepts
disclosed are equally applicable for the common information being
provided by a source connected to the communication system 100 via
the interface unit 110.
[0054] A standard cellular system is comprised of a plurality of
base stations each of which provides communication for subscriber
stations located within a limited coverage area. Together the
plurality of base stations provides coverage to an entire service
area. However, if the forward link shared channel is transmitted
from every base station in the system at all times, the cost of the
system can be quite high. A more efficient and economical manner
which provides higher overall capacity for the system is to
transmit the forward link shared channel only from those base
stations in whose coverage areas is a subscriber station
participating in a point-to-multipoint service located.
Consequently, the corresponding resources are available for other
point-to-point or point-to-multipoint services. In addition, the
other users in the coverage area of the base stations which are not
transmitting the forward link shared channel are not subject to
interference therefrom.
[0055] As the description of the point-to-multipoint communication
system indicates, to maximize capacity, the power control of the
forward link broadcast channel is required. Furthermore, a power
control of any dedicated forward link or reverse link channels is
required.
Reverse Link Power Control
[0056] Reverse link power control is the method of controlling
power of channels comprising the reverse link. In reverse link
power control, the base station measures the quality metric of the
signal received from the subscriber station transmitting on a
reverse link channel, compares the measured quality metric against
a threshold (a set point) and requests that the active subscriber
station increases or decreases transmitted power level in
accordance with a result of the comparison. The term active
subscriber station (talker) is used herein to mean a subscriber
station transmitting user data on a reverse traffic channel. As
discussed above, in a group call, only one or few subscriber
stations belonging to a group transmit user data on a reverse link
at one time. Consequently, no member passive subscriber station
(listener) has an established reverse link traffic channel to any
of the base stations. The term passive is used herein to mean a
subscriber station monitoring a forward link shared channel and any
additional forward link channel if the additional forward link
channel is transmitted, and not transmitting any user data on the
reverse link. Of course, the passive subscriber stations may
transmit non-user data, i.e., control and feedback data on an
appropriate channel of the reverse link. The additional forward
link channel may comprise a dedicated channel over which the
subscriber station receives e.g., signaling information, power
control information, overhead information and other types of
information known to one skilled in the art. The assignment of
channels for the forward link shared channel and the optional
additional forward link channel(s) is communication system
dependent. Thus, for example, in a communication system in
accordance with the IS-2000 standard, examples of forward channel
assignments are listed in Table 1.
TABLE-US-00001 TABLE 1 Forward Link Group Common Dedicated Reverse
link I F-SCH F-DCCH or F- R-DCCH or FCH R-FCH F-BCCH F-DCCH or F-
R-DCCH or FCH R-FCH F-CCCH F-DCCH or F- R-DCCH or FCH R-FCH II
F-SCH None No reverse link transmission by listeners.sup.1 F-BCCH
None No reverse link transmission by listeners.sup.1 F-CCCH None No
reverse link transmission by listeners.sup.1 III F-SCH F-CPCCH for
No reverse talker link transmission by listeners.sup.1 F-CPCCH for
R-DCCH or all R-FCH or combination.sup.2 F-BCCH F-CPCCH for No
reverse talker link transmission by listeners.sup.1 F-CPCCH for
R-DCCH or all R-FCH or combination.sup.2 F-CCCH F-CPCCH for No
reverse talker link transmission by listeners.sup.1 F-CPCCH for
R-DCCH or all R-FCH or combination.sup.2 Notes: .sup.1Necessary
system data are transmitted by the listeners using the reverse
access channel (R-ACH), reverse enhanced access channel (R-EACH),
or reverse common control channel (R-CCCH). .sup.2For example
talker utilizes the R-FCH, the listeners utilize R-DCCH.
Abbreviations: F-SCH Forward Supplemental Channel F-BCCH Forward
Broadcast Channel F-CCCH Forward Common Control Channel F-DCCH
Forward Dedicated Control Channel F-FCH Forward Fundamental Channel
F-CPCCH Forward Common Power Control Channel R-DCCH Reverse
Dedicated Control Channel R-FCH Reverse Fundamental Channel
[0057] One skilled in the art recognizes, that channel assignment
given in Table 1 both for the forward channels and the reverse
channels is for tutorial purpose only. Consequently, additional
combinations of the forward link shared channel and the optional
additional forward link channel exist as disclosed in a co-pending
application Ser. No. 10/113,098, entitled "METHOD AND APPARATUS FOR
CHANNEL MANAGEMENT FOR POINT-TO-MULTIPOINT SERVICES IN A
COMMUNICATION SYSTEM," filed Mar. 28, 2002, assigned to the
assignee of the present invention. Furthermore, one of ordinary
skills in the art killed in the art will be able to adapt the ideas
of the invention disclosed in the presented embodiments to
communication systems in accordance with other standards.
[0058] In a channel assignment method utilizing both forward link
shared channel and the individually assigned dedicated forward link
channels i.e., Group 1 of Table 1, all the sectors whose coverage
area contain subscriber stations participating in the group call
utilize a power control sub-channel, e.g., an F-PCSCH, which is
punctured at a pre-determined rate, e.g., 800 bits-per second (bps)
onto each of the individually assigned dedicated forward link
channel, e.g., F-DCCH or F-FCH for the subscriber stations that
transmit on a reverse link.
[0059] In a channel assignment method utilizing only the common
forward link traffic channel, i.e., Group II of Table 1, in one
embodiment, the sectors whose coverage area contains only listeners
participating in the call do not transmit any reverse power control
signals. The sector(s) whose coverage area contain(s) the active
subscriber station(s) utilizes a sub-channel, e.g., a forward power
control sub-channel (F-PCSCH), which is punctured at a
pre-determined rate, e.g., 800 bits-per second (bps) onto the
common forward link traffic channel, for reverse link power
control. In an alternative embodiment, the power control
information is not punctured into the common forward link traffic
channel as a F-PCSCH, but the power control information is
transmitted as a sub-stream of a Common Power Control Channel
(F-CPCCH), i.e., the power control information is inserted into a
pre-defined position into the common forward link power control
channel. The active subscriber station(s) process the received
F-PCSCH or the sub-stream of the F-CPCCH and adjust the
transmission power accordingly. The passive subscriber stations in
the sectors transmitting the sub-channel ignore the F-PCSCH or the
F-CPCCH information. A control unit located at the individual
sector, at a base station comprising the sector, at the controller,
or any other element comprising the access network, determines
whether a coverage area of a sector contains active subscriber
station.
[0060] In a channel assignment method utilizing a forward link
shared channel and the subscriber stations transmitting on a
reverse link, e.g., Group III of Table 1, in one embodiment, the
sectors whose coverage area contains only listeners participating
in the call do not transmit any reverse power control signals. The
sector(s) whose coverage area contain(s) the active subscriber
station(s) utilizes a dedicated power control sub-channel, e.g.,
the F-PcSCH, to each of the subscriber stations transmitting on a
reverse link.
Forward Link Power Control
[0061] Forward link power control is the method of controlling
power of the channels comprising the forward link. In a forward
link shared channel, each group call member subscriber station
measures a quality metric of the received common forward link
traffic channel, and transmits a feedback information to the
sector(s) transmitting the common forward link traffic channel for
the member subscriber station. In one embodiment, the quality
metric comprises a signal-to-noise ratio expressed in terms of
energy per bit over interference (E.sub.b/N.sub.t). However, one of
ordinary skills in the art understands that other quality metrics,
e.g., bit-error-rate, frame-error-rate, and other quality metrics
known in the art may be used. The feedback is transmitted on a
reverse link established . between the member subscriber station
and the sector. Each sector receives the feedback from those member
subscriber stations in the sector's coverage area that transmit on
reverse link and adjusts the transmit level to ensure that the
desired quality of service (QoS) is delivered to all the member
subscriber stations. A control unit located at the individual
sector, at a base station comprising the sector, at the controller,
or any other element comprising the access network, determines the
transmit level.
[0062] As discussed above, the forward link condition for each
subscriber station is different. Therefore, the sector is likely to
receive conflicting forward link quality measurements form each
subscriber station. The sector must then process the conflicting
forward link quality measurements and make a power adjustment of
the forward link shared channel. The sector adjusts the forward
link shared channel to satisfy the power requirement of the
subscriber station, which reports .the worst forward link quality
metric.
[0063] In the above-described embodiment, all member subscriber
stations report the quality metric upon updating the quality metric
measurement. To decrease the reverse link signaling load and
increase battery life of a subscriber station, in another
embodiment, the subscriber stations report the measured quality
metric back to the base station only if the measured quality metric
is not satisfactory. Thus, each member subscriber station measures
the quality metric and compares the measured quality metric to a
threshold. If the quality metric is better than the threshold, the
subscriber station abstains from reporting the quality metric.
Consequently, only the subscriber stations with a measured quality
metric below the threshold report the quality metric. The base
station then adjusts the common forward link traffic channel power
to satisfy the power requirement of the subscriber station, which
reports the worst forward link quality metric.
[0064] When the subscriber station determines the forward link
channel quality metric, the subscriber station needs to feed back
the forward link channel quality metric to the base station on a
reverse link. As discussed above, only active subscriber station(s)
transmit a reverse link traffic channel, which may be used for the
feedback. Consequently, passive subscriber stations do not have an
established reverse link traffic channel to any of the base
stations. However, the passive remote stations may need to use a
reverse link to communicate with base stations information
necessary for call maintenance, e.g., handoff messages, power
control, and other information known to one of ordinary skills in
the art. Furthermore, passive subscriber stations may desire to
communicate; therefore, the passive subscriber stations need to use
a reverse link for requesting a reverse traffic channel
assignment.
[0065] The different exemplary embodiments of reverse link channel
assignment in a communication system in accordance with the IS-2000
standard are listed in Table 1, and will be discussed in that
context. Furthermore, one of ordinary skills in the art will be
able to adapt the ideas of the invention disclosed in the presented
embodiments to communication systems in accordance with other
standards.
[0066] In accordance with one embodiment, each passive subscriber
station is assigned a reverse link dedicated channel, e.g..
Dedicated Control Channel (R-DCCH), upon joining an active group.
(E.g., Group I, Group III of Table 1). The subscriber station uses
the R-DCCH for signaling both for regular calls, (e.g., reporting
of forward link pilots) and signaling related to the group call
(e.g., quality metric reporting of forward link broadcast channel,
request for a reverse link traffic channel assignment.) When
transmitting the R-DCCH, the member subscriber station also
transmits a Reverse Pilot Channel (R-PCH) and a Reverse Power
Control Sub-channel (R-PCSCH). The R-PCSCH carries feedback on a
quality metric of the common broadcast forward link channel.
[0067] In one embodiment, the data rate on the forward link shared
channel is fixed; the sector uses full rate (800 bps in accordance
with the IS-2000 standard and 1600 bps in accordance with W_COMA
standard) forward power control. The forward link 200 for a fixed
rate as illustrated in FIG. 2 is defined in terms of frames 202. A
frame is a structure comprising a determined time span. Because the
data rate is fixed, each frame 202 is transmitted with the same
power P.sub.f. Therefore, the current power control method is able
to measure the quality metric of the Forward Link Shared Channel. A
Forward Link Shared Channel quality metric may comprise, e.g., a
signal to interference and noise ratio (SINR) expressed, for
example, as energy per bit over noise (Eb/Nt). A required target
decoder metric performance of the member subscriber station
determines a Forward Link Shared Channel quality metric required
for that subscriber station. Such a decoder metric may be e.g., a
decoded frame error rate (FER), bit error rate (BER), and/or other
decoder metric known to one skilled in the art. The member
subscriber station measures the Forward Link Shared Channel quality
metric, compares the quality metric against a fixed or adaptive
threshold, and sends power control commands in accordance with the
comparison results. In one embodiment, the power control commands
204 comprise a stream of up or down commands (similar to
FPC.sub.--MODE=`000` in accordance with IS-2000 standard). The
quality metric measurement and comparison can be carried out
reliably by the subscriber station because, as discussed, the data
rates on the Forward Link Shared Channel are fixed, therefore, do
not change without notice to the member subscriber station. In an
exemplary embodiment of an adaptive threshold adjustment, the
threshold is increased by a first step, e.g., 0.5 dB, when a data
frame of the Forward Link Shared Channel is received correctly.
This threshold is decreased by a smaller step, e.g., 0.5
dB/(I/FER.sub.desired-1), when data frame on the Forward Link
Shared Channel is received incorrectly. The FER.sub.desired
represents the desired frame erasure rate for the Forward Link
Shared Channel.
[0068] In another embodiment, utilizing the Forward Link Shared
Channel and the individually assigned dedicated forward traffic
channels, the quality metric of the Forward Link Shared Channel can
be determined form the highest quality metric of the individually
assigned dedicated forward traffic channel used by the member
subscriber station. Because the rates transmitted on the Forward
Link Shared Channel and the individually assigned dedicated forward
traffic channels are different, a proper rate translation between
the Forward Link Shared Channel and the individually assigned
dedicated forward traffic channels must be made. The Forward Link
Shared Channel quality metric is determined by scaling the quality
metric of the individually assigned dedicated forward traffic
channel in accordance with the rate translation.
[0069] The sector receives the power control commands transmitted
on the reverse link dedicated channel and, in accordance with one
embodiment, decreases a power transmit level of the Forward Link
Shared Channel by an amount, e.g., 0.5 dB, when the feedback from
all member subscriber station requests decrease of power. The
sector increases the power transmit level by the same amount when
at least one member subscriber station requests increase of
power.
[0070] In another embodiment, the feedback is in a form of messages
on R-DCCH.
[0071] In another embodiment, the sectors use a split feedback on
the Forward Link
[0072] Shared Channel and the individually assigned dedicated
forward traffic channels if the dedicated forward traffic channels
are assigned. The split feedback divides the reverse link stream
power control commands into two sub-streams. As discussed, the
power control stream in accordance with the IS-2000 comprises a
stream of 800 bps. Thus, the first sub-stream can comprise, e.g.,
power control commands send at 400 bps, the second sub-stream then
comprises, power control commands send at 400 bps The sub-streams
may be formed, e.g., by assigning the odd-numbered feedback bits to
the first sub-stream and the even-numbered feedback bits to the
second sub-stream. The first sub-stream carries the power control
commands for the Forward Link Shared Channel, the second sub-stream
carries the power control commands for the dedicated forward
traffic channels. In accordance with this method, the feedback
stream power control commands for the Forward Link Shared Channel
from each member subscriber station in the same sector can be in
the form of a sequence of up and down commands (similar to
FPC_MODE=`001` or `010` in accordance to IS-2000 standard) or a
stream of Erasure Indicator Bits (EIB) (similar to
FPC.sub.--MODE=`110` in accordance to IS-2000 standard). From this
set of feedback for the Forward Link Shared Channel, the sector can
set the transmit level for that Forward Link Shared Channel to meet
the quality requirement and conserve power consumption. The EIB
feedback also gives the base station a fast feedback on the member
subscriber station reception of the Forward Link Shared Channel.
This specific feedback facilitates the physical layer to start the
re-transmission earlier than the NAK (negative acknowledge) from
higher layers, if such re-transmission is desired and feasible. The
feedback on the dedicated channels is processed in accordance with
any method applicable to point-to-point power control method.
[0073] The sector receives the power control bits and, in
accordance with one embodiment, increases a power transmit level of
the broadcast forward traffic channel by a first amount, e.g., 0.5
dB, when the feedback from at least one member subscriber station
requests increase of power or indicates an erasure. The sector
decreases the power transmit level by a second amount when each
member subscriber station requests decrease of power or indicates
no erasure.
[0074] In another embodiment, the data rate on the forward link
shared channel is transmitted with a variable data rate, as
illustrated in FIG. 3. Because the data rate is variable, each
frame 300 is transmitted with a power P corresponding to the data
rate transmitted in that frame. Thus, e.g., frame 300(n) a
full-rate frame, is transmitted with a power P.sub.f3, a half-rate
frame 300(1) is transmitted with a power P.sub.f2, and an
eighth-rate frame 300(2) is transmitted with a power P.sub.f1. To
enable the subscriber station power control to correctly estimate
the forward link shared channel quality metric, the feedback power
control commands for reverse link power control utilize a
sub-channel, e.g., a forward power control sub-channel (F-PCSCH),
which is punctured at a pre-determined rate, e.g., 800 (bps) onto
the common forward link traffic channel with a constant power. In
an alternative embodiment, the power control information is not
punctured into the common forward link traffic channel as a
F-PCSCH, but the power control information is transmitted as a
sub-stream of a Forward Common Power Control Channel (F-CPCCH),
i.e., the power control information is inserted into a pre-defined
position into the common forward link common power control channel.
The power control bits for reverse link power control can be used
to measure the Forward Link Shard Channel quality metric.
[0075] In one embodiment, the feedback power control commands for
forward link power control may be sent as messages on the
individually assigned R-DCCH.
[0076] In one embodiment, the feedback power control commands for
forward link power control may be sent as an EIB on a R-PCSCH. In
one embodiment, the power control bits corresponding to a frame are
grouped to form a single EIB. In another embodiment, some bits in a
frame are grouped to form an EIB while the remaining bits convey
detailed amount of SINR deficit or surplus detected by the member
MS. In one embodiment, if no dedicated channels are assigned
individually, all the power control commands sent on the R-PCSCH
are utilized to control the Forward Link Shared Channel.
[0077] Alternatively, the passive member subscriber station are not
assigned R-DCCH. (E.g., Group 11, Group III of Table 1.) The
passive member subscriber, stations use access channels, e.g.,
R-ACH, R-EACH, or control channels, e.g., R-CCCH, or to send any
information to the base station.
[0078] Consequently, in accordance to one embodiment, instead of
providing a power control feedback in a form of continuous stream
of power commands, the power control feedback is provided in a form
of messages modulated on the R-ACH, R-EACH, or the R-CCCH. This
alternative is attractive in that the member subscriber stations
does not continually update the quality metrics of a forward link
shared channel, but send a feedback message only when the updated
quality metrics falls below a certain threshold. In one embodiment,
the message is sent when a frame error rate (FER) averaged over the
most recent 50 frames is 4% or higher. However, one of ordinary
skills in the art recognizes that, in an alternative embodiment,
the message may be generated every time the quality metrics is
updated. Within the message, several fields or quality indications
may be included. For example, there may be a field indicating the
strength at which the subscriber station perceives the pilot signal
from the base station. Alternatively, there may be a field
indicating the strength or quality at which the subscriber station
perceives the forward link broadcast channel. There may be a field
indicating the signal strength or quality of both the pilot channel
and the forward link broadcast channel. There may be a field which
indicates the difference between or the ratio of the pilot signal
strength to the forward link broadcast channel strength; the
quality of the group call channels, the desired increase in
received signal to noise and interference ratio, and other related
information known to one skilled in the art.
[0079] The base station periodically decreases the forward link
shared channel transmit power level by a first amount if the sector
does not receive a feedback message from a member subscriber
station requesting power increase. The base station increases the
forward link shared channel transmit power level by a second amount
when messages requesting power increase are received from one or
more member subscriber station.
[0080] The message based power control is slower than the bit
stream power control. Consequently, should a member subscriber
station require faster power control, e.g., due to worsening of
condition of the link, and, consequently, of the received signal,
the member subscriber station can use a message conveyed on the
R-ACH, R-EACH, or control channels, e.g., R-CCCH, to request
assignment of a reverse pilot channel R-PCH and R-PCSCH.
Alternatively, the base station may determine that a particular
member subscriber station consistently requires transmit power
level adjustment. The base station then assigns the particular
member subscriber station the R-PCH and R-PCSCH. Furthermore, the
R-PCH/R-PCSCH can be gated. The term gating as used herein means
activating transmission of the R-PCH/R-PCSCH only in pre-determined
power control groups (PCG). If the condition of the link further
worsen, the subscriber station may request, or be assigned, an
R-DCCH, a R-FCH or combination.
[0081] If there are no individually assigned F-DCCHs, (e.g., Group
II or Group III of Table 1) all bits carried on the R-PCSCH are
used for the power control of the forward link shared channel. In
one embodiment, the PC bits corresponding to a frame are grouped to
send a single EIB. In another embodiment, some bits in a frame's
time are grouped to send an EIB while the others convey detailed
amount of S/(N+1) deficit or surplus detected by the member MS.
Dedicated Forward Link Channel
[0082] As discussed in the co-pending application Ser. No.
10/113,098, entitled "METHOD AND APPARATUS FOR MANAGEMENT FOR
POINT-TO-MULTIPOINT SERVICES IN A COMMUNICATION SYSTEM," filed Mar.
28, 2002, the forward link shared channel is modulated by traffic
information, signaling messages necessary to maintain the call,
(e.g., a pilot strength measurement message, handoff direction
message, handoff completion message, and other messages known to
one of ordinary skills in the art), and messages related to the
group-call, (e.g., a start and an end of a call, request and grant
of a right to transmit, and other messages known to one of ordinary
skills in the art.) Because the F-SCH(s) is a common channel,
proper subscriber station addressing information must be employed,
so that the subscriber station can discern common information from
information directed to the subscriber station. Because the
signaling messages and the overhead of subscriber station
addressing negatively affects the traffic capacity, alternatively,
the forward link shared channel is modulated only by the traffic
information and the signaling messages are carried on an additional
forward link channel. The additional forward link channel is a
dedicated channel assigns to each individual member subscriber
station.
[0083] Because the dedicated forward link channels are assigned
individually to each member subscriber station, the transmit power
level of the dedicated channels can be controlled by methods
applicable to point-to-point communication. Thus, the subscriber
station determines quality metric of the dedicated forward link
channel, reports it back to a base station and the base station
adjusts the power level of the dedicated forward link channel.
[0084] The base station may utilize the determined transmit power
level of the dedicated forward link channel to determine a transmit
power level of the forward link shared channel by proper rate
translation of information transmitted on the forward link shared
channel and the dedicated forward link channel for each member
subscriber station. The base station then adjusts the a transmit
power level of the forward link shared channel to satisfy the
subscriber station with the highest power requirement.
[0085] Because the dedicated forward link channel is modulated by
signaling and overhead information, there may be insufficient
activity on the forward link channel to assure sufficient accuracy
of determination of transmit power level of the dedicated forward
link channel via the rate translation. Consequently, the base
station monitors the activity on both the forward link shared
channel and the dedicated forward link channel, and sends
`keep-alive` frames on the dedicated forward link channel to ensure
sufficient activity for accuracy of the rate translation.
[0086] Those of ordinary skill in the art will recognize that
although the various embodiments were described in terms of
flowcharts and methods, such was done for pedagogical purposes
only. The methods can be performed by an apparatus, which in one
embodiment comprises a processor interfaced with a transmitter, a
receiver and any other appropriate blocks of the AT and/or AP.
[0087] Those of ordinary skill in the art would understand that
information and signals may be represented using any of a variety
of different technologies and techniques. For example, data,
instructions, commands, information, signals, bits, symbols, and
chips that may be referenced throughout the above description may
be represented by voltages, currents, electromagnetic waves,
magnetic fields or particles, optical fields or particles, or any
combination thereof.
[0088] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein may
be implemented as electronic hardware, computer software, or
combinations of both. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled artisans may implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present invention.
[0089] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0090] The steps of a method or algorithm described in connection
with the embodiments disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module may reside in RAM memory,
flash memory, ROM memory, EPROM memory, EEPROM memory, registers,
hard disk, a removable disk, a CD-ROM, or any other form of storage
medium known in the art. An exemplary storage medium is coupled to
the processor such the processor can read information from, and
write information to, the storage medium. In the alternative, the
storage medium may be integral to the processor. The processor and
the storage medium may reside in an ASIC. The ASIC may reside in a
user terminal. In the alternative, the processor and the storage
medium may reside as discrete components in a user terminal.
[0091] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
[0092] A portion of the disclosure of this patent document contains
material, which is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure, as it appears in the
Patent and Trademark Office patent file or records, but otherwise
reserves all copyright rights whatsoever.
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