U.S. patent application number 11/083868 was filed with the patent office on 2005-07-28 for method and apparatus for power control a communication.
Invention is credited to Chaponniere, Etienne F., Chen, Tao.
Application Number | 20050164730 11/083868 |
Document ID | / |
Family ID | 25237564 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050164730 |
Kind Code |
A1 |
Chen, Tao ; et al. |
July 28, 2005 |
Method and apparatus for power control a communication
Abstract
In a communication system (100), a method and apparatus provide
for efficient power control between base station (101) and mobile
stations (102-104). A controller is configured for determining duty
cycle of a communication channel, and for controlling power level
of the communication channel based on the determined duty cycle.
The controller may compare the determined duty cycle against a duty
cycle threshold. An adjustment for controlling power level may be
based on the comparison.
Inventors: |
Chen, Tao; (San Diego,
CA) ; Chaponniere, Etienne F.; (San Diego,
CA) |
Correspondence
Address: |
Qualcomm Incorporated
Patents Department
5775 Morehouse Drive
San Diego
CA
92121-1714
US
|
Family ID: |
25237564 |
Appl. No.: |
11/083868 |
Filed: |
March 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11083868 |
Mar 17, 2005 |
|
|
|
09823011 |
Mar 30, 2001 |
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Current U.S.
Class: |
455/522 ;
455/67.11; 455/69 |
Current CPC
Class: |
H04W 52/26 20130101;
H04W 52/241 20130101; H04W 52/12 20130101; H04W 52/16 20130101 |
Class at
Publication: |
455/522 ;
455/067.11; 455/069 |
International
Class: |
H04B 007/00 |
Claims
What is claimed is:
1. In a communication system, a method comprising: determining
traffic to pilot channel power ratio of a traffic channel for
communication between a mobile station and a base station in said
communication system, wherein said traffic to pilot channel power
ratio is determined based on communications of said traffic
channel; determining duty cycle of data frame transmissions of a
dedicated control channel associated with said traffic channel,
wherein said dedicated control channel is for maintaining
communications of said traffic channel, wherein said duty cycle of
data frame transmissions is based on the possible number of frame
transmissions over a period of time; adjusting said traffic to
pilot channel power ratio based on said determined duty cycle;
communicating said traffic channel in accordance with said
determined traffic to pilot channel power ratio, and said dedicated
control channel in accordance with said adjusted traffic to pilot
channel power ratio.
2. In a communication system, an apparatus comprising: means for
determining traffic to pilot channel power ratio of a traffic
channel for communication between a mobile station and a base
station in said communication system, wherein said traffic to pilot
channel power ratio is determined based on communications of said
traffic channel; means for determining duty cycle of data frame
transmissions of a dedicated control channel associated with said
traffic channel, wherein said dedicated control channel is for
maintaining communications of said traffic channel, wherein said
duty cycle of data frame transmissions is based on the possible
number of frame transmissions over a period of time; means for
adjusting said traffic to pilot channel power ratio based on said
determined duty cycle; means for communicating said traffic channel
in accordance with said determined traffic to pilot channel power
ratio, and said dedicated control channel in accordance with said
adjusted traffic to pilot channel power ratio.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.120
[0001] The present Application for Patent is a Continuation and
claims priority to patent application Ser. No. 09/823,011 entitled
"Method and Apparatus for Power Control in a Communication System"
filed Mar. 30, 2001, now allowed, and assigned to the assignee
hereof and hereby expressly incorporated by reference herein.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates generally to the field of
communications, and more specifically, to communications in the
code division multiple access communication system.
[0004] 2. Background
[0005] Code division multiple access (CDMA) communication systems
have been in commercial operations for a number of years. In CDMA
communication systems, a number of users in the same geographical
area may choose to operate on a common carrier frequency. The
signal from each user is encoded according to a unique assigned
code. A receiver decodes each signal according to the assigned
code. A receiver may receive signals from different users with
common carrier frequency. While a signal for one user is being
decoded, the signals transmitted from all other users may be
treated as interference. Excessive transmission level may cause
interference on other signals. In a CDMA system, the power level of
signals transmitted by different users of the system is controlled
to control the interference level. Moreover, for effective
utilization of the channel resources in the CDMA communication
system, the power level of each transmitted signal is controlled.
The power level of each signal is controlled at the transmitter to
maintain an adequate quality of reception at a receiving end. Other
reasons, such as conserving battery power, for controlling power
level of signals in a CDMA system are well known by one of ordinary
skill in the relevant art. To this end as well as others, there is
a need for an effective signal power control in a CDMA
communication system.
SUMMARY
[0006] In a communication system, a method and apparatus provide
for efficient power control between a base station and mobile
stations. A controller is configured for determining duty cycle of
a communication channel, and for controlling power level of the
communication channel based on the determined duty cycle. The
controller may compare the determined duty cycle against a duty
cycle threshold. An adjustment for controlling power level may be
based on the comparison.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The features, objects, and advantages of the present
invention will become more apparent from the detailed description
set forth below when taken in conjunction with the drawings in
which like reference characters identify correspondingly throughout
and wherein:
[0008] FIG. 1 illustrates a communication system capable of
operating in accordance with various embodiments of the
invention;
[0009] FIG. 2 illustrates a communication system receiver, for
operation in a mobile station and a base station, capable of
operating in accordance with various embodiments of the
invention;
[0010] FIG. 3 illustrates a flow chart for controlling power level
of a communication channel between a mobile station and a base
station, capable of having adjusted operating parameters in
accordance with various embodiments of the invention; and
[0011] FIG. 4 illustrates a flow chart used for controlling power
level of a communication channel between a base station and a
mobile station in accordance with various embodiments of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0012] system for wireless communications in accordance with the a
code division multiple access (CDMA) technique has been disclosed
and described in various standards published by the
Telecommunication Industry Association (TIA). Such standards
include the TIA/EIA-95 standard, TIA/EIA-IS-2000 standard, IMT-2000
standard, and WCDMA standard, all incorporated by reference herein.
A copy of the standards may be obtained by writing to TIA,
Standards and Technology Department, 2500 Wilson Boulevard,
Arlington, Va. 22201, United States of America. The "3rd Generation
Partnership Project" (3GPP) is embodied in a set of documents
includes Document No. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and
3G TS 25.214, and known as the WCDMA standard; the "TIA/EIA/IS-95
Remote Station-Base Station Compatibility Standard for Dual-Mode
Wideband Spread Spectrum Cellular System" is known as the IS-95
standard; the "TR-45.5 Physical Layer Standard for cdma2000 Spread
Spectrum Systems" is known as the CDMA-2000 standard; each
incorporated by reference herein. The specification generally
identified as WCDMA specification, incorporated by reference
herein, may be obtained by contacting 3GPP Support Office, 650
Route des Lucioles-Sophia Antipolis, Valbonne-France.
[0013] Generally stated, a novel and improved method and an
accompanying apparatus provide for efficient control of signal
power level in a CDMA communication system. One or more exemplary
embodiments described herein are set forth in the context of a
digital wireless data communication system. While use within this
context is advantageous, different embodiments of the invention may
be incorporated in different environments or configurations. In
general, the various systems described herein may be formed using
software-controlled processors, integrated circuits, or discrete
logic. The data, instructions, commands, information, signals,
symbols, and chips that may be referenced throughout the
application are advantageously represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or a combination thereof. In addition, the blocks
shown in each block diagram may represent hardware or method steps.
The exemplary embodiment described herein is set forth in the
context of a digital communication system. While use within this
context is advantageous, different embodiments of the invention may
be incorporated in different environments or configurations. In
general, the various systems described herein may be formed using
software-controlled processors, integrated circuits, or discrete
logic. The data, instructions, commands, information, signals,
symbols, and chips that may be referenced throughout the
application may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or a combination thereof. In addition, the blocks
shown in each block diagram may represent hardware or method
steps.
[0014] FIG. 1 illustrates a general block diagram of a
communication system 100 capable of operating in accordance with
any of the code division multiple access (CDMA) communication
system standards. Generally, communication system 100 includes a
base station (BS) 101 that provides communication links between a
number of mobile stations, such as mobile stations 102-104, and
between the mobile stations 102-104 and a wireline network 105. BS
101 may include a number of components, such as a mobile station
controller, a base station controller, and a radio frequency
transceiver. For simplicity, such components are not shown. BS 101
may also be in communication with other base stations (not shown.)
BS 101 communicates with each mobile station 102-104 via a forward
link. The forward link may be maintained by a forward link signal
transmitted from BS 101. The forward link signals targeted for
several mobile stations 102-104 may be summed to form a forward
link signal 106. Each of the mobile stations 102-104 receiving
forward link signal 106 decodes the forward link signal 106 to
extract the information that is targeted for its user. At the
receiving end, the receiver may treat as interference the portion
of the received forward link signal 106 targeted for others.
[0015] Mobile stations 102-104 communicate with BS 101 via a
corresponding reverse link. Each reverse link is maintained by a
reverse link signal, such as reverse link signals 107-109 for
respectively mobile stations 102-104. BS 101 may also transmit a
predefined series of data bits on a pilot channel via the forward
link to all mobile stations to assist each mobile station in
decoding the forward link signal 106. Each of the mobile stations
102-104 may transmit a pilot channel to BS 101. The pilot channel
transmitted from a mobile station may be used for decoding the
information carried by the reverse link signal transmitted from the
same mobile station. The use and operation of a pilot channel are
well known. A transmitter and a receiver for communicating via the
forward and reverse links are included in each mobile stations
102-104, and BS 101.
[0016] FIG. 2 illustrates a block diagram of a receiver 200 used
for processing CDMA signals. Receiver 200 demodulates the received
signal to extract the information carried by the received signal.
Receive (Rx) samples are stored in RAM 204. Receive samples are
generated by a radio frequency/intermediate frequency (RF/IF)
system 290 and an antenna system 292. Antenna system 292 receives
an RF signal, and passes the RF signal to RF/IF system 290. RF/IF
system 290 may be any conventional RF/IF receiver. The received RF
signals are filtered, down-converted, and digitized to form RX
samples at baseband frequencies. The samples are supplied to a
demultiplexer (demux) 202. The output of demux 202 is supplied to a
searcher unit 206, and finger elements 208. A control system unit
210 is coupled thereto. A combiner 212 couples a decoder 214 to
finger elements 208. Control system unit 210 may be a
microprocessor controlled by software, and may be located on the
same integrated circuit or on a separate integrated circuit.
[0017] During operation, receive samples are supplied to demux 202.
Demux 202 supplies the samples to searcher unit 206, and finger
elements 208. Control unit 210 configures finger elements 208 to
perform demodulation of the received signal at different time
offsets based on search results from searcher unit 206. The results
of the demodulation are combined and passed to decoder 214. Decoder
214 decodes the data, and outputs the decoded data.
[0018] In general for searching, searcher 206 may use non-coherent
demodulation of a pilot channel to test timing hypotheses and phase
offsets corresponding to various transmitting sources and
multi-paths. The demodulation performed by finger elements 208 may
be performed via coherent demodulation of other channels such as
control and traffic channels. The information extracted by searcher
206 by demodulating a pilot channel may be used in finger elements
208 for demodulation of other channels. The searcher 206 and finger
elements 208 may provide both pilot channel searching, and
demodulation of control and traffic channels. The demodulation and
searching can be performed at various time offsets. The results of
the demodulation may be combined in combiner 212 before decoding
the data transmitted on each channel. Despreading of the channels
is performed by multiplying the received samples with the complex
conjugate of the PN sequence and assigned Walsh function at a
single timing hypothesis, and digitally filtering the resulting
samples, often with an integrate and dump accumulator circuit (not
shown). Such a technique is commonly known in the art. Receiver 200
may be used in BS 101 and mobile stations 102-104 for decoding the
information on respectively reverse and forward links signals. BS
101 may employ several of receiver 200 to decode the information
transmitted from several mobile stations at the same time.
[0019] Receiver 200 may also perform interference cancellation
through a correlation process. The received samples, after being
read from RAM 204, are passed through a correlation process for
each received signal. The correlation process may collectively be
described as the operations of searcher 206, finger element 208,
and combiner 212. Since the received samples contain samples from
the signals transmitted from more than one transmitting source, the
correlation process may be repeated for each received signal. The
correlation process for each received signal may be unique because
each signal may require a different correlation parameters as of
those found in operations of searcher 206, finger element 208, and
combiner 212. Each signal may include a traffic channel and a pilot
channel. The PN sequence assigned to the traffic channel and pilot
channel carried by each signal may be different. The correlation
process may include channel estimation, which includes estimating
the channel fading characteristics based on the result of
correlating with the pilot channel. The channel estimation
information is used for correlating with the traffic channel. Each
traffic channel is then decoded.
[0020] The result from each correlation process may pass through a
decoding process in decoder 214. If the transmitted channel is
encoded via a convolutional encoding process, decoding step 214 is
performed according to the utilized convolutional code. If the
transmitted channel is encoded via a turbo encoding process,
decoding step 214 is performed according to the utilized turbo
code.
[0021] Each signal may be decoded to provide enough information
about whether a pass indicator is produced for each cyclic
redundancy check (CRC) associated with each transmitted frame of
data. Operation and use of CRC in a communication system are well
known. If the CRC is passed, the decoded result of the channel
associated with the passed CRC may be passed on for further
receiving operation.
[0022] The signals received by BS 101 may be input to receiver 200.
Antenna system 292 and RF/IF system 290 receive the signals from
the mobile stations to produce the samples of the received signals.
The received samples may be stored in RAM 204. Receiver 200 may
incorporate a number of searchers 206, a number of finger elements
208, a number of combiners 212, and a number of decoders 214 for
simultaneously performing the correlation process and the decoding
process for all the signals received from different mobile
stations. However, only one antenna system 292 and RF/IF system 290
may be necessary.
[0023] Each time a correlation process is started, searcher 206 and
finger element 208 may start anew for determining non-coherent
demodulation of a pilot channel to test timing hypotheses and phase
offsets. Searcher 206, or finger element 208, or searcher 206 and
finger element 208 in combination, may determine the signal to
interference ratio (S/I) for each received signal. The ratio Eb/I
may be synonymous with the ratio S/I. The ratio Eb/I is a measure
of signal energy over interference per unit of a data symbol or
data bit. Therefore, S/I and Eb/I may be interchangeable in some
respects. The interference (I) may typically be defined as the
power spectral density of interference and the thermal noise.
[0024] To control interference, the system controls the signal
level transmitted from each transmitting source, or the data rate
of the communication link, or both. Generally, each MS determines
the needed reverse link power level to support both the traffic
channel and the pilot channel. Various power control schemes for
controlling power levels of signals transmitted from an MS in a
communication system are known. One or more examples are described
in the Mobile Station-Base Station Compatibility Standard for
Wideband Spread Spectrum Cellular Systems, otherwise known as
TIA/EIA-95 and TIA/EIA-2000 standards, incorporated by reference
herein. The output power level of each MS is controlled by two
independent control loops, open loop and closed loop. The open loop
power control is based on the need of each MS to maintain an
adequate communication link with the BS. Therefore, the MS closer
to the BS needs less power than the MS further away. A strong
receive signal at the MS indicates less propagation loss between
the MS and the BS, and, thus, requires a weaker reverse link
transmit power level. In the open loop power control, the MS sets
the transmit power level of the reverse link based on independent
measurements of S/I of at least one received channel, such as
pilot, paging, sync, and traffic channels. The MS may make the
independent measurement prior to power level setting on the reverse
link.
[0025] FIG. 3 illustrates a flow diagram 300 of an exemplary closed
loop power control method. Operation of closed loop power control
method 300 begins once an MS in communication system 100 seizes a
forward link traffic channel. After the initial access attempt by
the MS, the MS sets an initial reverse channel power level. The
initial power level setting on the reverse link is then adjusted
during the communication link via the closed loop power level
control 300. The closed loop power control 300 operates with a
faster response time than the open loop control. The closed loop
power control 300 provides correction to the open loop power
control. The closed loop power control 300 operates in conjunction
with the open loop control during a traffic channel communication
link to provide the reverse link power control with a large dynamic
range.
[0026] To control the power level of the reverse link signal of a
mobile station via the closed loop 300, BS 101 at step 301 measures
the signal to interference ratio (S/I) of the reverse link signal
transmitted from the mobile station. The measured S/I is compared
with a set point S/I at step 302. The measured S/I may be in the
form of Eb/I which is a ratio of bit energy over interference, and
consequently, the set point may be in the same form. The set point
is selected for the mobile station. The set point may be initially
based on open loop power setting by the mobile station.
[0027] If the measured S/I is higher than the set point, at step
303, BS 101 orders the mobile station to power down the power level
of its reverse link signal by an amount, for example 1 dB. When the
measured S/I is higher than the set point, it indicates that the
mobile station is transmitting on the reverse link at a signal
power level higher than is needed to maintain an adequate reverse
link communication. As a result, the mobile station is ordered to
lower the signal power level of its reverse link to reduce the
overall system interference. If the measured S/I is lower than the
set point, at step 304, BS 101 orders the mobile station to power
up the power level of its reverse link signal by an amount, for
example 1 dB. When the measured S/I is lower than the set point, it
indicates that the mobile station is transmitting on the reverse
link at a signal power level lower than is needed to maintain an
adequate reverse link communication. As a result of increasing the
power level, the mobile station may be able to overcome the
interference level and provide an adequate reverse link
communication.
[0028] The operations performed at steps 302-304 may be referred to
as the inner loop power control. The inner-loop power control keeps
the reverse link (S/I) at the BS 101 as close as possible to its
target threshold as provided by the set point. The target S/I is
based on the set point selected for the mobile station. The power
up or power down may be performed several times during a time
frame. One time frame may be divided into 16 power control groups.
Each power control group consists of several data symbols. The
power up or power down command may be transmitted 16 times per
frame. If one frame of data has not been received at step 305, the
power control loop 300 continues to measure S/I of the reverse link
signal during the next power control group at step 301. The process
is repeated at steps 302-304 until at least one frame of data is
received from the mobile station.
[0029] A single set point or target may not be satisfactory for all
conditions. Therefore, the set point used at step 302 may also
change depending on a desired reverse link frame error rate. If one
frame of data has been received at step 305, a new S/I set point
may be calculated at step 306. The new set point becomes the new
S/I target for the mobile station. The new set point may be based
on a number of factors including the frame error rate. For example,
if the frame error rate is above a predetermined level, indicating
unacceptable frame error rate, the set point may be raised to a
higher level. By raising the set point to a higher level, the
mobile station consequently increases its reverse link transmit
power level via the comparison at step 302 and power up command at
step 304. If the frame error rate is below a predetermined level
indicating above an acceptable frame error rate, the set point may
be lowered to a lower level. By lowering the set point to a lower
level, the mobile station consequently decreases the reverse link
transmit power level via the comparison at step 302 and power down
command at step 303. The operations performed at steps 305-306,
looping back from step 306 to step 302 to indicate a new set point,
and looping back to step 301 for measuring the S/I of the new
frames, may be viewed as the outer loop operation. The outer-loop
power control may command once every frame, and the closed loop
power control may command once every power control group. One frame
and one power control group may be, respectively, 20 and 1.25 mSec
long.
[0030] The system may also employ a forward link power control
scheme to reduce interference. The MS communicates to the BS
periodically about the voice and data quality. The frame error rate
and quality measurements are reported to the BS via a power
measurement report message. The message contains the number of
frames received in error on the forward link during an interval.
The power level of the forward link signal is adjusted based on the
number of frame errors. Since such a quality measurement feedback
is based on the frame error rate, such a mode of the forward link
power control is much slower than reverse link power control. For
fast response, a reverse link erasure bit may be used to inform the
BS whether the previous frame was received with or without error.
The channel power gain may be continuously adjusted while
monitoring the message or the erasure bit as a way of controlling
forward link power level.
[0031] For communication of data, the forward link may be
transmitted to the MS at a fixed power level while adjusting the
effective forward link data rate targeted for the MS. The data rate
adjustment on the forward link when viewed for the overall system
is a form of interference control. Note that the forward link power
control is generally for controlling interference in a coverage
area, and/or for sharing a limited communication resources. When
the feedback quality measurement is indicating poor reception, the
data rate may be lowered while keeping the power level constant to
overcome the effect of the interference. The data rate may also be
lowered to allow other mobile stations to receive forward link
communication at a higher data rate.
[0032] According to at least one of the CDMA Spread Spectrum System
standards, incorporated by reference herein, in addition to the
open loop and closed loop power control schemes, the MS adjusts the
output power level by attributes of a code channel as specified by
the standard. In CDMA-2000, the MS sets the output power of the
enhanced access channel header, the enhanced access channel data,
and the reverse common control channel data relative to the output
power level of the reverse pilot channel. The output power level of
the reverse pilot channel is set by the open and closed loop power
controls. The MS maintains a power level ratio between the code
channel power level and the reverse pilot channel power level. The
ratio may be defined by the data rate used in the code channel.
Generally, a table provides the values for the ratio at different
data rates. The ratio generally increases for higher data rates. A
ratio equal to one or less than one may also be possible. At a
ratio equal to one, the power level of the pilot channel as set by
the power control loop 300 is equal to the power level of the code
channel. During transmission of data on a traffic channel, the data
rate and the traffic channel power level may be adjusted. The power
level may be selected based on a relative power of the reverse link
pilot. Once an allowable data rate is selected, a corresponding
channel gain with respect to the reverse link pilot power level is
used to set the traffic channel power level.
[0033] In data mode, a BS may be providing communication links to a
large number of MSs at different data rates. For example, one MS in
a forward link connected state may be receiving data at a low data
rate, and another MS receiving at a high data rate. On the reverse
link, the BS may be receiving a number of reverse link signals from
different MSs. An MS based on an independent measurement may decide
and request a desired data rate from the BS. The desired forward
link data rate may be communicated to the BS via a data rate
control (DRC) channel. The data rate may also be selected by the
base station based on certain metrics. The metrics may include the
transmit power level of the power control sub-channel and/or power
level of one or more forward traffic channels. The BS attempts to
provide a forward link data transfer at the requested data
rate.
[0034] On the reverse link, the MS may autonomously select a
reverse link data rate from a number of possible reverse link data
rates. The selected data rate may be communicated to the BS via a
reverse rate indicator channel. The MS may request a desired data
rate or request a non-specified data rate. The BS in response may
determine a data rate that the MS may use. The BS communicates to
the MS at the determined data rate. The determined data rate may be
used for a limited duration. The duration may be determined by the
BS. Each MS may also be limited to a predetermined grade of
service. A grade of service may limit the maximum available data
rate on the forward and/or reverse links. Moreover, the
communication of data may not be continuous in a way that, perhaps,
voice data are communicated. A receiver may be receiving packets of
data at different intervals. The interval for different receiver
may be different. For example, a receiver may be receiving data
sporadically while another receiver may be receiving data packets
within short time intervals.
[0035] Communication of data at high data rates takes a greater
transmit/receive signal power level than at low data rates. The
forward and reverse links may have similar data rate activities in
the case of voice communications. The forward and reverse links
data rates may be limited to low data rates since the voice
information frequency spectrum is limited. Possible voice data
rates are commonly known and described in a code division multiple
access (CDMA) communication system standard such as IS-95 and
IS-2000, incorporated by reference herein. For data communications,
however, the forward and reverse links may not have similar data
rates. For example, an MS may be retrieving a large data file from
a database. In such a case, the communication on the forward link
is predominantly occupied for transmission of data packets. The
data rate on the forward link may reach 2.5 Mbps in a data mode.
The data rate on the forward link may be based on a data rate
request made by the MS. On the reverse link, the data rate may be
lower, and may range from 4.8 to 153.6 Kbps.
[0036] Generally, in communication system 100, in accordance with
various embodiments, duty cycle of a communication channel is
determined, and power level of the communication channel is
controlled based on the determined duty cycle. Each transmission of
the communication channel may be in a time frame, For example, each
time frame may be for duration of 20 mSec. The data rate of each
time frame may range from 1250 to 14400 bits per seconds. As such,
the number of bits in each frame may be different depending on the
data rate. The channel may be used for communication of user and
signaling information during a call between the user and a
destination. The user may be using a mobile station, such as mobile
stations, 102-104 for the call. Any of the mobile stations 102-104
may be a cellular phone. The destination may be base station
101.
[0037] In accordance with an embodiment, the communication channel
may a dedicated control channel (DCCH). A DCCH channel may be used
for communication of user and signaling information for maintaining
a traffic data call between a user and a destination, such as,
respectively, mobile stations 102-104 and base station 101. The
number of DCCH frames transmitted over a period of time may be
different depending on the usage. As such, the time between
transmission of DCCH time frames during the traffic data call may
be different. For example, even though traffic data may be
communicated, a transmission of a frame of the communication
channel, such as DCCH, may not necessarily take place. In another
situation, several time frames of the communication channel, such
as DCCH, may be transmitted in a short period of time. Therefore,
the duty cycle of the transmission of the frames of the
communication channel, such as DCCH, may be different at different
times. To effectively control transmission power level of the
communication, in accordance with various embodiments, the power
level of the communication channel, such as DCCH, is based on the
duty cycle of the frame transmission of the communication
channel.
[0038] In accordance with various embodiments, the determined duty
cycle may be compared against a duty cycle threshold. The duty
cycle threshold may be predetermined. The duty cycle may be
determined by a control system in communication system 100. The
duty cycle may be based on a communication history of received or
transmitted frames. One such a control system may reside in mobile
stations 102-104, such as control unit system 210, or in base
station 101. In case when a controller in base station 101
determines the duty cycle, the determined duty cycle may be
communicated to the mobile station 102-104 in communication with
base station 101. The control system may perform a process for
comparing the determined duty cycle to a duty cycle threshold. The
duty cycle threshold may be adjusted from time to time.
[0039] Depending on the difference between the determined duty
cycle and the duty cycle threshold, an adjustment may be made for
controlling power level of the communication channel. Such an
adjustment may be made in different ways to effect the power level
of the communication channel. For example, when the duty cycle
reaches a level close to a continuous transmission, the adjustment
may be minimal, or no adjustment at all. When the duty cycle is
low, the channel condition may change drastically between the
transmissions. In case of low duty cycle, the adjustment may be
more than minimal.
[0040] In accordance with an embodiment, the adjustment for
controlling power level of the DCCH may be in a form of modifying a
code channel to pilot channel power ratio associated with a traffic
channel between the user and the destination. The user may be a
mobile station 102-104, and the destination may be base station
101. The modified code channel to pilot channel power ratio may be
used to control power level of the DCCH. Such a modification may be
in a form of providing a correction factor. The correction factor
may be applied to the code channel to pilot channel power ratio to
arrive at the modified ratio. In another example, a table with
predetermined entries may be used for selecting the modified ratio.
The entries in the table may be derived from the ratios used for
the traffic channel. The entries may also, or alternatively, depend
on factors such as the speed of the channel fading, the number of
multi-paths at the receiver, and transmit and receive signal and
antenna diversity.
[0041] The difference between the traffic channel power ratio and
the modified ratio for the DCCH channel may depend on the
difference between the determined duty cycle and the duty cycle
threshold. For example, when the duty cycle is high, the difference
between the determined duty cycle and the threshold may be minimal.
In case of high duty cycle, the difference between the traffic
channel power ratio and the modified power ratio used for the DCCH
may be minimal. In case of low duty cycle, the difference between
the determined duty cycle and the duty cycle threshold may be high.
In case of low duty cycle, the channel characteristic may have
changed drastically between the transmissions. In case of low duty
cycle, the difference between the traffic channel power ratio and
the modified power ratio used for DCCH may be more than minimal.
Depending on the determined duty cycle, a code channel to pilot
channel power ratio may be selected and used for controlling the
DCCH power level. In case the ratio for controlling the power level
of the DCCH is determined by base station 101, the selected or
modified ratio may be communicated to the mobile station 102-104 in
communication with base station 101.
[0042] In accordance with various embodiments, the communication
channel may be between mobile station 102-104 and base station 101.
Normally, for controlling signal power level between the mobile
stations 102-104 and base station 101, each mobile station 102-104
may have a power control loop in base station 101. Each power
control loop, such as power control loop 300, is operating to
control the signal power level between a mobile station 102-104 and
base station 101. A power control loop may include one or more
parameters for its operation. For example, power control loop 300
includes S/I set point. The set point parameter is calculated at
step 306. To calculate the set point, the frame error rate is
compared to a threshold. The frame error rate threshold is another
parameter used in operation of power control loop 300. The set
point parameter is used at step 302 to decide whether to step up or
down the power level of the signal transmitted from the mobile
station 102-104. In accordance with various embodiments, the set
point parameter may be adjusted, based on the duty cycle, at the
power control outer loop at base station 101. In alternative or in
combination, the frame error rate threshold may be adjusted, based
on the duty cycle, to effect an increase or decrease in transmit
power level of signals from the mobile station 102-104.
[0043] In accordance with various embodiments, the code channel to
pilot channel power ratio may be indirectly adjusted by adjusting a
target power level of the pilot channel for controlling power level
of the communication channel. The adjustment may be based on the
duty cycle. By keeping the power ratio the same and adjusting the
pilot channel target power level, the amount of power allocated to
the communication channel may be controlled. Such a control is
based on the determined duty cycle. When the communication channel
is between a mobile station 102-104 and a base station 101, the
adjusted target power level of the pilot channel may be
communicated to the mobile station in communication with base
station 101. The communication channel, in this case, and the pilot
channel originate from the mobile station.
[0044] In accordance with various embodiments, controlling the
power level of the communication channel based on the determined
duty cycle may be by adjusting a power level of a power control
sub-channel. A power control sub-channel may be used by base
station 101 for controlling reverse link channels. In this case,
the power control sub-channel originates from the base station 101.
Base station 101 transmits power control sun-channel at a power
level with respect to the forward link traffic channel. The power
level may be adjustable and fixed in relative to the forward link
traffic channel. The mobile stations 102-104 measure the difference
between the power levels of the power control sub-channel and the
forward link traffic channel. The mobile stations 102-104 use the
measured difference in calculation of determining a frame error
rate set point. The frame error rate set point is communicated to
the base station 101. Base station 101 takes into effect the
received frame error rate set point in the power control loop 300
for adjusting the power level of the communication channel.
[0045] Referring to FIG. 4, a flow chart 400 for controlling power
level of a communication channel is shown in accordance with
various embodiments. At step 401, the duty cycle of the
communication channel, such as DCCH, is determined. At step 402, a
controller in base station 101, or controller 210 in mobile
stations 102-104 may decide whether to control power level of the
communication channel based on the determined duty cycle. At step
403, the determined duty cycle is compared to a duty cycle
threshold. Based on the comparison which determines the difference
between the threshold and the determined duty cycle, an adjustment
may be made for controlling power level of the communication
channel. The adjustment may be made by several ways. At step 405,
modifying a code channel to pilot channel power ratio may be
incorporated for making the adjustment for controlling the power
level of the communication channel. At step 406, a code channel to
pilot channel ratio may be selected, for example from a table, to
control the power level. At step 407, a parameter associated with a
power control loop, such as power control loop 300, may be adjusted
to control the power level. At step 408, the target level for the
pilot channel may be changed to effect the power level of the
communication channel. At step 409, the power level of the power
control sub-channel may be adjusted to control the power level of
the communication channel. The adjustments shown in flow chart 400
may be made in any combinations or individually.
[0046] Those of skill in the art 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.
[0047] 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.
[0048] 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. 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 that 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.
[0049] The previous description of the preferred embodiments is
provided to enable any person skilled in the art to make or use the
present invention. The 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 the use of the inventive faculty. 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.
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