U.S. patent application number 11/280460 was filed with the patent office on 2006-04-13 for congestion control in a wireless communication system using the battery level.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Catherine Livet, Guang Lu, Shamim Akbar Rahman, Maged Zaki.
Application Number | 20060079268 11/280460 |
Document ID | / |
Family ID | 32965688 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060079268 |
Kind Code |
A1 |
Livet; Catherine ; et
al. |
April 13, 2006 |
Congestion control in a wireless communication system using the
battery level
Abstract
A method for congestion control in the uplink of a wireless
communication system having a wireless transmit/receive unit (WTRU)
and a radio network controller (RNC) begins by receiving an
interference report for each user. The average noise rise for each
user calculated and congestion relieving measures are implemented
based upon the average noise rise and the WTRU battery level. A
method for congestion control in the downlink of a wireless
communication system having a WTRU and a RNC begins by receiving a
transmission power report for each user. The transmission power for
each user is calculated, and congestion relieving measures are
implemented based upon the average transmission power and the WTRU
battery level.
Inventors: |
Livet; Catherine; (Montreal,
CA) ; Lu; Guang; (Montreal, CA) ; Rahman;
Shamim Akbar; (Montreal, CA) ; Zaki; Maged;
(Pierrefonds, CA) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600
30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
|
Family ID: |
32965688 |
Appl. No.: |
11/280460 |
Filed: |
November 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10726426 |
Dec 3, 2003 |
|
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|
11280460 |
Nov 16, 2005 |
|
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60454081 |
Mar 11, 2003 |
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Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04W 24/10 20130101;
Y02D 30/70 20200801; H04M 1/724 20210101; H04W 52/0261
20130101 |
Class at
Publication: |
455/522 |
International
Class: |
H04B 7/00 20060101
H04B007/00 |
Claims
1. A method for congestion control in the uplink of a wireless
communication system having a wireless transmit/receive unit (WTRU)
and a radio network controller (RNC), comprising the steps of:
receiving an interference report for each user; calculating the
average noise rise for each user; and implementing congestion
relieving measures based upon the average noise rise and the WTRU
battery level.
2. The method according to claim 1, wherein said implementing step
includes the steps of: comparing the average noise rise to a rate
reduction threshold; and if the average noise rise is greater than
the rate reduction threshold, then performing rate reduction for
the user having the highest interference level and terminating the
method; if the average noise rise is less than the rate reduction
threshold, then comparing the average noise rise to a rate recovery
threshold; and if the average noise rise is less than the rate
recovery threshold, then performing rate recovery based upon the
interference level and the WTRU battery level.
3. The method according to claim 2, wherein said performing rate
recovery step includes the steps of: ranking the users based on
interference level from lowest to highest into a candidate list;
selecting the user with the lowest interference level from the
candidate list; checking the selected user's WTRU battery level;
and if the battery level is below the low level, then performing
rate recovery for the selected user and terminating the method; if
the battery level is above the low level, then selecting the next
user from the candidate list and repeating said checking step.
4. A method for congestion control in the uplink of a wireless
communication system having a wireless transmit/receive unit
(VVTRU) and a radio network controller (RNC), comprising the steps
of: (a) receiving an interference report for each user; (b)
calculating the average noise rise for each user; (c) comparing the
average noise rise to a rate reduction threshold; (d) if the
average noise rise is greater than the rate reduction threshold,
then performing rate reduction for the user having the highest
interference level and terminating the method; (e) if the average
noise rise is less than the rate reduction threshold, then (i)
comparing the average noise rise to a rate recovery threshold; and
(ii) if the average noise rise is less than the rate recovery
threshold, then (A) ranking the users based on interference level
from lowest to highest into a candidate list; (B) selecting the
user with the lowest interference level from the candidate list;
(C) checking the selected user's WTRU battery level; and (D) if the
battery level is below the low level, then performing rate recovery
for the selected user and terminating the method; (E) if the
battery level is above the low level, then selecting the next user
from the candidate list and repeating step (e)(ii)(C).
5. A method for congestion control in the downlink of a wireless
communication system having a wireless transmit/receive unit (WTRU)
and a radio network controller (RNC), comprising the steps of:
receiving a transmission power report for each user; calculating
the transmission power for each user; implementing congestion
relieving measures based upon the average transmission power and
the WTRU battery level.
6. The method according to claim 5, wherein said implementing step
includes the steps of: comparing the average transmission power to
a rate reduction threshold; if the average transmission power is
greater than the rate reduction threshold, then comparing the
average transmission power to a rate recovery threshold; if the
average transmission power is greater than the rate recovery
threshold, then performing rate recovery for the user with the
lowest transmission power and terminating the method; if the
average transmission power is less then the rate reduction
threshold, then performing rate reduction based upon the average
transmission power and the WTRU battery level.
7. The method according to claim 6, wherein said performing rate
reduction step includes the steps of: ranking the users based on
transmission power from highest to lowest into a candidate list;
selecting the user with the highest transmission power from the
candidate list; checking the selected user's WTRU battery level; if
the battery level is below the low level, then performing rate
reduction and terminating the method; if the battery level is above
the low level, then selecting the next user from the candidate list
and repeating said checking step.
8. A method for congestion control in the downlink of a wireless
communication system having a wireless transmit/receive unit (WTRU)
and a radio network controller (RNC), comprising the steps of: (a)
receiving a transmission power report for each user; (b)
calculating the transmission power for each user; (c) comparing the
average transmission power to a rate reduction threshold; (d) if
the average transmission power is greater than the rate reduction
threshold, then comparing the average transmission power to a rate
recovery threshold; (i) if the average transmission power is
greater than the rate recovery threshold, then performing rate
recovery for the user with the lowest transmission power and
terminating the method; (e) if the average transmission power is
less than the rate reduction threshold, then ranking the users
based on transmission power from highest to lowest into a candidate
list; (i) selecting the user with the highest transmission power
from the candidate list; (ii) checking the selected user's WTRU
battery level; (iii) if the battery level is below the low level,
then performing rate reduction and terminating the method; (iv) if
the battery level is above the low level, then selecting the next
user from the candidate list and repeating step (e)(ii).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. patent application
Ser. No. 10/726,426 filed Dec. 3, 2003 which in turn claims benefit
of U.S. Provisional Application No. 60/454,081, filed Mar. 11,
2003, which are incorporated by reference as if fully set forth
herein.
FIELD OF INVENTION
[0002] The present invention relates generally to wireless
transmit/receive unit (WTRU) battery conservation in wireless
communications systems, and more particularly, to a method of
achieving WTRU battery conservation with assistance from the
network and from radio resource management (RRM).
BACKGROUND
[0003] It is known that battery life for a WTRU is an important
aspect of the quality of service that an end user perceives, and
any measure that could achieve battery savings is a desirable
accomplishment in wireless communication system design. Some of the
existing systems and methods for conserving battery power relate to
reducing the power of at least part of the WTRU to conserve battery
life. For example, in U.S. Pat. No. 5,539,925, a base station sends
a signal to a mobile station to turn off the mobile station for a
length of time communicated in the message. At the end of the "off"
period, the mobile station will automatically restart itself to
determine whether it needs to remain active or whether it can be
turned off for an additional period.
[0004] U.S. Pat. No. 6,463,042 relates to a method in which a
wireless terminal receives a header packet and estimates the power
level of the header packet. The wireless terminal then receives a
portion of a following data packet, and estimates the power level
of the data packet. A comparison is made between the power level of
the header packet and the power level of the data packet. If the
power levels are approximately equal, then the wireless terminal
will receive and process the remainder of the data packet. If the
power level of the header packet is greater than the power level of
the data packet, then this is an indication that the base station
is operating in quasi-discontinuous transmission (Q-DTX) mode and
that the wireless terminal can ignore the remainder of the data
packet and put some of the components into a low power mode.
[0005] In U.S. Pat. No. 6,463,307, a hibernation request is made by
either the base station or the mobile terminal. Parameters relating
to the hibernation period, including when to wake the mobile
terminal to check for paging messages or whether the mobile
terminal has a data packet to send, are then set by the base
station and transmitted to the mobile terminal. Once the
hibernating period has ended, if there are any waiting paging
messages, the mobile terminal is awakened and the paging messages
are checked. If there are no paging messages, then a determination
is made whether the mobile terminal has any pending data packets to
send. If there are pending data packets, then the mobile terminal
is awakened and the packets are sent. If there are no pending
packets, then the mobile terminal returns to the hibernation
mode.
[0006] The systems and methods described above relate only to the
powering-down of components to conserve battery power, and not to
methods for conserving battery power while the WTRU is actively
transmitting. It would, therefore, be desirable to achieve battery
savings when the WTRU is active.
SUMMARY
[0007] The present invention enables the radio resource management
(RRM) in the radio network side to reduce wireless transmit/receive
unit (WTRU) battery consumption. The WTRU reports its battery level
information to the network. The RRM in the network can then make
informed decisions to maximize the battery life of the WTRU while
still maintaining the required quality of service (QoS) and system
capacity. Based on reported battery levels, different RRM actions
can be taken relating to call admission control, congestion
control, user link maintenance, handover, power control, block
error rate (BLER) target, and application configuration. The
invention is described making reference to a universal mobile
telecommunication system (UMTS) frequency-division duplex
(FDD)/time-division duplex (TDD) system, but is applicable to any
wireless system, including IEEE 802.11 and global system for mobile
communications (GSM).
[0008] A method for congestion control in the uplink of a wireless
communication system having a WTRU and a RNC begins by receiving an
interference report for each user. The average noise rise for each
user calculated and congestion relieving measures are implemented
based upon the average noise rise and the WTRU battery level.
[0009] A method for congestion control in the uplink of a wireless
communication system having a WTRU and a RNC begins by receiving an
interference report for each user. The average noise rise for each
user is calculated, and the average noise rise is compared to a
rate reduction threshold. If the average noise rise is greater than
the rate reduction threshold, then rate reduction is performed for
the user having the highest interference level, and the method
terminates. If the average noise rise is less than the rate
reduction threshold, then the average noise rise is compared to a
rate recovery threshold. If the average noise rise is less than the
rate recovery threshold, then the users are ranked based on
interference level from lowest to highest into a candidate list.
The user with the lowest interference level is selected from the
candidate list and the selected user's WTRU battery level is
checked. If the battery level is below the low level, then rate
recovery is performed for the selected user and the method
terminates. If the battery level is above the low level, then
selecting the next user from the candidate list is selected and
that user's battery level is checked.
[0010] A method for congestion control in the downlink of a
wireless communication system having a WTRU and a RNC begins by
receiving a transmission power report for each user. The
transmission power for each user is calculated, and congestion
relieving measures are implemented based upon the average
transmission power and the WTRU battery level.
[0011] A method for congestion control in the downlink of a
wireless communication system having a WTRU and a RNC begins by
receiving a transmission power report for each user. The
transmission power for each user is calculated and the average
transmission power is compared to a rate reduction threshold. If
the average transmission power is greater than the rate reduction
threshold, then the average transmission power is compared to a
rate recovery threshold. If the average transmission power is
greater than the rate recovery threshold, then rate recovery is
performed for the user with the lowest transmission power and the
method terminates. If the average transmission power is less than
the rate reduction threshold, then the users are ranked based on
transmission power from highest to lowest into a candidate list.
The user with the highest transmission power is selected from the
candidate list and the selected user's WTRU battery level is
checked. If the battery level is below the low level, then rate
reduction is performed and the method terminates. If the battery
level is above the low level, then the next user is selected from
the candidate list and that user's battery level is checked.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A more detailed understanding of the invention may be had
from the following description of a preferred embodiment, given by
way of example and to be understood in conjunction with the
accompanying drawings wherein:
[0013] FIG. 1 illustrates radio network controller (RNC) RRM
actions according to WTRU battery level;
[0014] FIG. 2 is a flow chart of the RNC RRM behavior upon
receiving the WTRU battery level;
[0015] FIG. 3 is a flowchart of a call admission control procedure
incorporating checking the WTRU battery level;
[0016] FIG. 4 is a flowchart of a congestion control procedure
incorporating checking the WTRU battery level;
[0017] FIGS. 5a-5c are flowcharts of user link maintenance
procedures incorporating checking the WTRU battery level; and
[0018] FIG. 6 is a flowchart of a handover procedure incorporating
checking the WTRU battery level.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0019] An implementation of the invention is described in the
following preferred embodiment, which is applicable to a UMTS
(FDD/TDD) system. The invention is, however, applicable to any
wireless system including, e.g., IEEE 802.11 and GSM. Hereafter a
WTRU includes, but is not limited to, a user equipment, a mobile
station, a fixed or mobile subscriber unit, a pager, or any other
type of device capable of operating in a wireless environment. When
referred to hereafter, a base station includes, but is not limited
to, a base station, a Node-B, a site controller, an access point,
or other interfacing device in a wireless environment.
[0020] FIG. 1 shows the exchange of information in a UMTS system
100, including a WTRU 102 and an RNC 104. The WTRU 102 reports its
battery level to the network as follows. The RNC 104 requests the
WTRU 102 to report the battery level measurement by sending a
Measurement Control Message 110 in the downlink. In the message
110, the RNC 104 configures the WTRU 102 with the measurement
reporting criteria, such as the frequency of reporting for
periodic-based reporting or the threshold for threshold-based
reporting. The WTRU 102 reports its battery level by sending a
Measurement Report Message 112 according to the reporting criteria
dictated by the RNC 104. In order to conserve battery power, the
report message 112 can be transmitted along with other
measurements. For example, in UMTS networks, the battery level can
be reported in a manner similar to any other measurement (i.e., via
radio resource control (RRC) signaling).
[0021] The information contained in the report message 112 can
include the number of remaining minutes of talk time and the number
of remaining minutes of idle time. This number can be either an
instantaneous value based on the current transmission environment
and current type of service (e.g., voice or data), or an average
value based on the conditions for the last X minutes.
Alternatively, the reported battery level can be the percentage of
available battery power remaining. The WTRU 102 can be set to send
the report message 112 periodically, or to send the report message
112 when a threshold is reached. The periodic reporting can range
from one second to ten minutes, with a preferred default value of
one minute. For the threshold based reporting, the WTRU may take
frequent measurements, but will only send a measurement report to
the RNC when a certain threshold is crossed. The types of evaluated
thresholds include low, medium, and high thresholds, and will be
explained in detail below.
[0022] The RRM in the RNC 104 makes informed decisions based on the
reported battery level of the WTRU 102. In general, the
measurements used by the RRM to make a decision are those typically
used in the art in connection with each type of decision, with the
battery level of the WTRU 102 being used as an additional
criterion. Some of the other measurements used by the RRM include
downlink interference signal code power (ISCP), received signal
code power (RSCP), and pathloss.
[0023] The procedures affected by the battery level measurement
will be discussed in greater detail below. Viewed as a signal
exchange between the WTRU 102 and the RNC 104, the admission
control procedure 120 is triggered by an admission request 122 sent
by the WTRU 102. The admission control 120 indicates whether a call
has been admitted by sending an admission response 124. A
congestion control procedure 130 will configure the WTRU 102 for a
new transmission rate by sending a signal 132. A link maintenance
procedure 140 will configure the WTRU 102 for a new transmission
rate by sending a signal 142. A handover procedure 150 will
configure the WTRU 102 for handover by sending a signal 152. A
power control procedure 160 will change the BLER target of the WTRU
102 by sending a signal 162.
[0024] FIG. 2 describes the RRM behavior 200 in the RNC 104 upon
receiving the battery level report message 112 from the WTRU 102.
The RRM in the RNC 104 first receives the WTRU battery measurement
report message 112 (step 202). The RNC RRM then updates the WTRU
battery level parameter and stores it in a database (step 204). All
other procedures have access to this parameter, since the procedure
behavior changes according to the WTRU battery level as explained
in connection with each procedure below. Three battery level
thresholds are used as triggers: low, medium, and high. These
thresholds are the same as those mentioned above in connection with
the threshold-based battery level reporting. It should be
understood by those of skill in the art that the specific battery
levels and thresholds are design parameters that will vary with
each implementation. Accordingly, these specific levels and
thresholds will not be described hereinafter.
[0025] The WTRU battery level is checked to determine if it is
below the low threshold (step 206). If the battery level above the
low threshold, then the WTRU battery level is checked (step 210) to
determine if it is above the medium threshold. The higher the BLER
target is, the higher the transmission power that is needed and the
battery will be drained faster. Therefore, it is desirable to
adjust the BLER target based on the current battery level. If the
battery level is below the medium threshold, the current BLER
target is maintained (step 212), and the procedure is terminated
(step 214).
[0026] If the battery level is above the medium threshold (step
210), the BLER target is set to the "high quality BLER" target
(step 220). Next, the current level of compression is evaluated
(step 222). If the current level of compression is the highest
level of compression, then switch to the lower level of compression
(step 224) and terminate the procedure (step 214). Otherwise,
maintain the current compression level and terminate the procedure
(step 214).
[0027] If the WTRU battery level is below the low threshold (step
206), then the BLER target is set to the "low quality BLER" target
(step 230) to extend the battery life. Next, link maintenance is
triggered (step 232) to reduce the battery consumption rate, as
explained below. The application configuration and the compression
level are adjusted (step 234) to conserve battery power, as
explained below. The procedure then terminates (step 214).
[0028] Call Admission Control
[0029] Referring now to FIG. 3, the Call Admission Control (CAC)
procedure 300 begins by triggering CAC (step 302), which is done
when the WTRU 102 requests call admission from the RNC 104 (signal
122 in FIG. 1). Then the WTRU's battery level is checked (step
304). The next step taken by the CAC procedure 300 depends directly
upon the battery level and whether the current call is real time
(shown as "RT" in FIG. 3) or non-real time (shown as "NRT" in FIG.
3).
[0030] If the battery level is low, CAC will only allow handover
into a cell at the guaranteed bit rate for real time calls, and
will only allow handover into the cell at the lowest bit rate
(TFC1) for non-real time calls (step 306). If the battery level is
medium, CAC will only admit calls at the guaranteed bit rate for
real time calls, and will admit at TFC2 (the second lowest bit
rate) or a lower bit rate for non-real time calls(step 308). If the
battery level is high, for both real time and non-real time calls,
CAC will admit the call at the maximum bit rate or lower (step
310). The CAC behavior according to the battery level is summarized
in the following table. TABLE-US-00001 TABLE 1 CAC behavior
according to battery level. Battery CAC behavior CAC behavior level
(real time services) (non-real time services) 1. Low Only allow
handover into Only allow handover into the cell and consider the
the cell and consider TFC1 guaranteed bit rate for (lowest rate)
for admission the admission decision decision for handover. and
physical resource Assign physical resources assignment. No other
types based on the accepted bit of accesses are admitted. rate. No
other types of accesses are admitted. 2. Medium Consider the
guaranteed Consider TFC2 (second bit rate only for the lowest rate)
or lower for admission decision and admission decisions. Assign
assign physical physical resources based on resources based on the
the accepted bit rate. guaranteed bit rate. (Where TFC4 bit rate
> TFC3 bit rate > TFC2 bit rate > TFC1 bit rate > 0.)
3. High Consider the maximum Consider the maximum bit bit rate and
below for rate and below for the the admission decision admission
decision and and assign physical assign physical resources
resources based on the based on the accepted bit accepted bit rate.
rate.
[0031] After the bit rate determination has been made according to
the current WTRU battery level (steps 306, 308, or 310), the CAC
procedure 300 proceeds to step 312, where the cell load is checked
to determine the allowable call admission bit rate. The accepted
bit rate for the call is chosen by selecting the lower admission
rate as determined by the battery level and the cell load (step
314). Lastly, the physical resources required for the call are
allocated (step 316) and the procedure terminates (step 318).
[0032] Besides the traditional criteria used to decide whether or
not to admit the user and the bit rate for admission (e.g.,
interference, carrier power, cell load), the RNC 104 also adjusts
the assigned bit rate depending on the WTRU battery level. The
criteria that are evaluated for CAC depend on the procedure design
and can vary, per known CAC procedures.
[0033] Also, code fragmentation in TDD is minimized for WTRUs with
a low battery level. There are usually multiple solutions to assign
the Orthogonal Variable Spreading Factor (OVSF) codes required by a
call, in terms of the number of timeslots used and which codes to
use in the tree. The fewer timeslots that are used, the lower the
code fragmentation is. To minimize code fragmentation, the RNC RRM
should allocate the codes in as few timeslots as possible. This
reduces the possibility that the WTRU 102 raises its power level
when it is far from the base station. Once the call has been
admitted, the RNC 104 sends a response message to the WTRU (signal
124 in FIG. 1).
[0034] Congestion Control
[0035] Congestion control performs rate reduction and rate recovery
in both the uplink and the downlink. For the present invention, the
WTRU's battery level is considered when performing rate recovery in
the uplink and rate reduction in the downlink. FIG. 4 shows a flow
chart of a congestion control procedure 400 in accordance with the
present invention. It is noted that the criteria used in the
congestion control procedure 400 depend upon the design of the
procedure. FIG. 4 shows a slow congestion control procedure, which
uses the average noise rise in the uplink and the average transmit
power in the downlink as criteria to decide whether or not to
trigger rate control. It is to be understood that the slow
congestion control procedure is only an example, and that the
present invention is equally applicable to any congestion control
procedure.
[0036] Referring now to FIG. 4, the congestion control procedure
400 begins by receiving measurement reports for interference and
transmission power for each user (step 402). Next, the average
noise rise in the uplink and the transmit power in the downlink are
calculated for all users (step 404). These measurements are stored
at the RNC, and are used several times during this procedure. When
evaluating the uplink, a determination is made whether the average
noise rise exceeds the threshold for rate reduction (step 406). If
the average noise rise is above the rate reduction threshold, then
rate reduction is performed for the user with the highest
interference level (step 408) and the procedure terminates (step
409).
[0037] If the average noise rise is below the rate reduction
threshold (step 406), a separate determination is made comparing
the average noise rise to the threshold for rate recovery (step
410). If the average noise rise is above the rate recovery
threshold, then there is no need to invoke rate recovery (step 412)
and the procedure terminates (step 409). If the average noise rise
is below the rate recovery threshold, then the user with the lowest
measured interference is selected (step 414). As noted above, the
interference is measured for all users in step 402, and can be
sorted either in step 402 or step 414. Next, the selected user's
WTRU battery level is checked to determine whether it is below the
low battery level (step 416). If the battery level is above the low
level, then rate recovery is performed for the selected user (step
418) and the procedure terminates (step 409). If the battery level
is below the low level, then the next user in the candidate list
for rate recovery is selected (step 420) and step 416 is
repeated.
[0038] On the downlink, the average transmit power is compared to
the threshold for rate reduction (step 430). If the average
transmit power is below the rate reduction threshold, a separate
determination is made comparing the average transmit power to the
threshold for rate recovery (step 432). If the average transmit
power is above the rate recovery threshold, then there is no need
to invoke rate control (step 434) and the procedure terminates
(step 409). If the average transmit power is below the rate
recovery threshold, then rate recovery is performed for the user
with the lowest transmit power (step 436) and the procedure
terminates (step 409). As noted above, the transmission power for
each user is stored in step 402, and can be sorted either in step
402 or step 436.
[0039] If the average transmit power is above the rate reduction
threshold (step 430), then the user with the highest transmit power
is selected (step 438). Next, the selected user's WTRU battery
level is checked to determine whether it is below the low battery
level (step 440). If the battery level is above the low level, then
rate reduction is performed for the selected user (step 442) and
the procedure terminates (step 409). If the battery level is below
the low level, then the next user in the candidate list for rate
reduction is selected (step 444) and step 440 is repeated.
[0040] In the procedure 400 on the uplink, if the RNC 104 has
detected that the congestion situation has been relieved (the
average noise rise is lower than the threshold for rate recovery),
the RNC 104 uses the battery level of the WTRU 102 as an additional
criterion. Increasing the uplink transmission rate drains the
battery faster, because a higher transmission rate uses more power
than a lower transmission rate. The congestion control ranks the
WTRUs 102 according to their interference level from low
interference to high interference. The congestion control then
selects the WTRU 102 with the lowest interference level. If the
selected WTRU's battery level is below the low threshold, the
congestion control should pick the next WTRU 102 in the candidate
list. If the battery level of the WTRU 102 is greater than the low
level, then rate recovery can be performed.
[0041] In the procedure 400 on the downlink, the RNC 104 detects
congestion based on the average value of recently received
measurements. Once congestion is detected (the average transmit
power is greater than the threshold for rate reduction), the RNC
104 chooses the user with highest transmit power for rate
reduction. Decreasing the downlink receiving bit rate drains the
battery faster because the WTRU 102 requires additional time to
receive the same amount of data. Therefore, the RNC 104 uses the
battery level of the WTRU 102 as an additional criterion for
deciding whether to implement rate reduction. If the selected
WTRU's battery level is below the low threshold, the congestion
control should pick the next WTRU 102 in the candidate list.
Otherwise, rate reduction can be performed for the selected WTRU.
If the average transmit power is lower than the threshold for rate
recovery, rate recovery should be conducted. Increasing the
downlink receiving bit rate reduces the time for WTRU 102 to
receive the same amount of data, thus extending battery life.
Therefore, WTRU 102 battery level is not a criterion for rate
recovery in the downlink.
[0042] Once the rate reduction or rate recovery is performed at the
RNC 104, the RNC 104 reconfigures the WTRU 102 for the new rate
(signal 132 in FIG. 1).
[0043] User Link Maintenance
[0044] Referring now to FIGS. 5a-5c, the user link maintenance
procedure can be triggered by three different events: (1) upon
receipt of a battery level measurement report at the RNC, (2) upon
receipt of the VVTRU transmit power measurement on the uplink, and
(3) upon receipt of the code transmit power measurement on the
downlink.
[0045] FIG. 5a shows a user link maintenance procedure 500 that is
performed upon receipt of a battery level measurement report (step
502). A determination is made whether the WTRU battery level is
below the low level (step 504). If the battery level is below the
low level, then the user's bit rate is decreased if operating in
the uplink and the bit rate is increased if operating in the
downlink (step 506) and the procedure terminates (step 507).
[0046] If the battery level is above the low level (step 504), then
a separate determination is made whether the battery level is above
the high level (step 508). If the battery level is below the high
level, then there is no need to invoke link rate control (step 510)
and the procedure terminates (step 507). If the battery level is
above the high level, then a separate determination is made whether
the user link rate was reduced by another rate reduction procedure
due to the triggering of a battery level measurement report (step
512). If the link rate was not previously reduced, then there is no
need to invoke link rate control (step 510) and the procedure
terminates (step 507). If the link rate was previously reduced,
then a determination is made whether the transmission power and the
measured interference are low (step 514). If both the transmission
power and the measured interference are not low, then there is no
need to invoke link rate control (step 510) and the procedure
terminates (step 507). If both the transmission power and the
measured interference are low, then rate recovery is performed, in
which the uplink and downlink rates for the user are restored to
the last rates used before the rate reduction (step 516) and the
procedure terminates (step 507).
[0047] FIG. 5b shows a user link maintenance procedure 520 that is
performed upon receipt of the WTRU transmit power in the uplink
(step 522). The WTRU transmit power is checked to determine if it
is above the threshold for rate reduction (step 524). If the
transmit power is above the rate reduction threshold, then rate
reduction is performed (step 526) and the procedure terminates
(step 527). If the transmit power is below the rate reduction
threshold (step 524), then a separate determination is made whether
the WTRU transmit power is below the threshold for rate recovery
(step 528). If the transmit power is below the rate recovery
threshold, then another determination is made whether the WTRU
battery level is below the low level (step 530). If the battery
level is above the low level, then rate recovery is performed (step
532) and the procedure terminates (step 527). If the battery level
is below the low level, then rate recovery is not performed (step
534) and the procedure terminates (step 527). If the transmission
power is above the threshold for rate recovery (step 528), then
rate recovery is not performed (step 534) and the procedure
terminates (step 527).
[0048] FIG. 5c shows a user link maintenance procedure 540 that is
performed upon receipt of the code transmit power measurement in
the downlink (step 542). The code transmit power is checked to
determine if it is above the threshold for rate reduction (step
544). If the code transmit power is below the rate reduction
threshold, a determination is made whether the code transmit power
is below the threshold for rate recovery (step 546). If the code
transmit power is above the rate recovery threshold, then there is
no need to invoke link rate control (step 548) and the procedure
terminates (step 549). If the code transmit power is above the rate
recovery threshold, then rate recovery is performed (step 550) and
the procedure terminates (step 549).
[0049] If the code transmit power is above the rate reduction
threshold (step 544), then the WTRU battery level is checked to
determine if it is below the low level (step 552). If the battery
level is above the low level, then rate reduction is performed
(step 554) and the procedure terminates (step 549). If the battery
level is below the low level, then rate reduction is not performed
(step 556) and the procedure terminates (step 549).
[0050] The WTRU battery measurement report can be a trigger of the
user link maintenance procedure. If the RNC 104 receives a battery
report message 112 indicating a low battery level, the WTRU bit
rate in the uplink is decreased to reduce the battery consumption
rate, which is especially useful for long calls. The RNC 104
configures the WTRU 102 for a lower bit rate (signal 142 in FIG.
1). In the downlink, the RNC 104 increases the bit rate
transmitting to the WTRU 102, thus shortening the power-on time of
the WTRU 102. If the RNC 104 receives a battery report message 112
indicating a battery level above the low level, and if the bit rate
was reduced before due to low battery, the link rate in uplink and
downlink will be restored to the previous rate before the last rate
reduction.
[0051] In the downlink, if user link maintenance is triggered by
another measurement, for example, by code transmit power, the RNC
104 uses the battery level of the WTRU 102 as an additional
criterion for rate reduction. The criteria used depends on the
design of the link maintenance control procedure 500, 520, 540.
Different approaches in performing link maintenance control may use
different criteria. For example, the link maintenance control
procedures described above use uplink WTRU transmit power and
downlink code transmit power. If the WTRU's battery level is below
the low threshold, decreasing the downlink receiving bit rate
increases the time for the WTRU 102 to receive the same amount of
data, thus draining the WTRU 102 battery faster. Therefore, the
link maintenance should not decrease the receiving bit rate for the
WTRU 102.
[0052] In the uplink, if the user link maintenance is triggered by
another measurement, for example, by the WTRU transmit power, the
RNC 104 uses the battery level of the WTRU 102 as an additional
criterion for rate recovery. If the WTRU's battery level is below
the low threshold, increasing the uplink transmission bit rate
drains the battery faster. Thus, the link maintenance should not
increase the transmission bit rate for the WTRU 102.
[0053] Handover
[0054] FIG. 6 shows a handover procedure 600 in accordance with the
present invention. The RNC first receives a handover request (step
602) and then checks if there are additional handover requests
waiting to be processed (step 604). If there are additional
handover requests, the WTRU with the lowest battery level is
selected (step 606). Next, the number of soft handover legs are
determined, and the number is kept as low as possible when
operating in FDD (step 608). If, at step 604, there are no
additional requests, step 606 is skipped, and the procedure
continues with step 608. Lastly, the handover is performed (step
610) and the procedure terminates (step 612).
[0055] A higher priority for handover is given to a WTRU 102 with a
low battery level (signal 152 in FIG. 1). The battery level can be
used to decide the number of soft handover legs for FDD, where the
lower the battery level, the fewer the number of handover legs that
should be assigned. In FDD, the WTRU 102 can have simultaneous
radio link connections (soft handover legs) in different cells. The
more handover legs that are established, the faster the WTRU's
battery will be consumed due to the extra processing needed for the
extra handover legs.
[0056] Power Control
[0057] The BLER target is changed according to the WTRU battery
level. At call admission, the RNC RRM checks the service and
determines the BLER target based upon the service type. The service
type is the quality of service class, for example, conversational,
streaming, interactive/background, signaling AM/UM, or other
service type. For each service type, there are two possible BLER
targets for the RNC RRM when considering WTRU battery level.
[0058] The first possible BLER target is the "low quality BLER,"
which is the minimum BLER acceptable by the network and can be used
by the WTRU 102 when its battery level is below the low threshold.
The second possible BLER target is the "high quality BLER," which
is better than the low quality BLER and can be used by the WTRU 102
when its battery level is above the medium threshold. A WTRU needs
to transmit with higher power in order to meet a high quality BLER
target, so the battery needs to have sufficient power to prevent a
rapid depletion.
[0059] During a call, the power control is triggered based on the
WTRU battery level (signal 162 in FIG. 1). An example of the
numerical values both of the BLER target for several different
service types is shown in Table 2. These values should be
operations, administration, and maintenance (OA&M)
configurable. The power control procedure can be triggered by the
battery level measurement report, as shown in steps 220 and 230 of
FIG. 2. TABLE-US-00002 TABLE 2 BLER target for different battery
levels. Uplink BLER Downlink BLER Low High Low High Traffic Class
Quality Quality Quality Quality Conversational 10.sup.-2 5 .times.
10.sup.-2 10.sup.-2 5 .times. 10.sup.-2 Streaming 10.sup.-2 5
.times. 10.sup.-2 10.sup.-2 5 .times. 10.sup.-2
Interactive/Background 10.sup.-3 5 .times. 10.sup.-3 10.sup.-3 5
.times. 10.sup.-3 Signaling AM/UM 10.sup.-3 5 .times. 10.sup.-3
10.sup.-3 5 .times. 10.sup.-3
[0060] Application Configuration
[0061] For non-real time (NRT) calls, compression layers can be
configured to provide multiple levels of coding compression.
Application configuration uses the battery level of the WTRU 102 as
the only criterion to determine the compression level. The lower
the battery level, the higher the level of compression that will be
configured. At the application level, i.e., outside the UMTS
terrestrial radio access network (UTRAN), the application can be
optimized to provide different levels of information. For example,
in the case of a low battery level during Web browsing, the
application can be configured to only allow the download of text
and not pictures. The battery level measurement report can trigger
the application configuration procedure as described above in
connection with steps 224 and 234 of FIG. 2.
[0062] While this invention has been particularly shown and
described with reference to preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and details may be made without departing from the scope of the
invention as described hereinabove.
* * * * *