Title of Invention

METHOD AND DEVICE FOR POWER CONTROL IN A WIRELESS COMMUNICATION SYSTEM

Abstract A method for generating a power control command in a transceiver in a wireless communication system, where method comprises the steps of calculating, at the beginning of a predefined time period, a quality measure reference value (306), generating, repeatedly during the predefined time period, an estimated quality measure value (307) of a signal received at the transceiver, genarting a power control command (313) in dependence of the estimated quality measure value (307) and the quality measure reference value (306), and generating, a number of times during the predefined time penod, a modified quality measure reference value (309) from the quality measure reference value (306) The step of generating the power control command comprises comparing the estimated quality measure value (307) with the modified quality measure reference value (309) A power control unit (300), comprising a quality measure estimator (308), a calculator (310), a first controller (303), a second controller (302) and an inner loop element (312), is configured to implement the method.
Full Text Technical Field
The present invention relates to a method for generating a power control command n
a transceiver in a wireless communication system. The invention also relates to a
power control unit and a computer readable medium configured to implement the
method and a wireless communication transceiver comprising the power control unit
The present invention further relates to a method for controlling a power level of
signals trensmitted in a wireless communication system to a first transceiver from a
second transceiver.
Description of Related Art
In wireless communications systems the transmission channel between a transmitter
in a transceiver and a receiver in another transceiver is formed by a radio link As an
example, the transmitter could be included in a base station, and the receiver could
be included in a user equipment, such as a mobile station (for the downlink
transmission direction), or vice versa (for the uplink transmission direction)
Power control in wireless communications systems is employed to compensate for
variations in the channel (such as propagation delays and fading effects) and to
ensure that an acceptable transmission quality for all users in the system is
maintained
Multipath fading is due to reflections of a propagating radio signal sent from a
transmitter to a receiver It could cause a power level of a received signal to vary
very rapidly with deep fading dips now and then To compensate for this effect, a
closed power control loop is typically used
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In many wireless communication systems, such as WCDMA (Wideband Code
Division Multiple Access), power is the most important resource since different users
on different channels are transmittin simultaneously on the same radio frequency It
is therefore important to keep the transmitted power level on each channel as low as
possible, while maintaining an acceptable performance quality at the receiver Also,
in WCDMA, the "near-far" problem needs to be minimized Near-far refers to the
ratio of signal strength from a mobile station close to a base station to a mobile
station far away from the base station, which needs to be as close to unity as possible
(1 e the base station needs to receive signal power of the same order from all mobile
stations irrespective of their distance from the base station, to avoid one user
blocking the others)
The solution is typically a closed power control loop which adjusts the transmitted
power m order to maintain a received and estimated Signal-to-Interference Ratio
(SIR) value at a given target value (a SIR reference value) In the 3GPP (Third
Generation Partnership Project) solution for a WCDMA system specification number
25 214, "Physical layer procedures (FDD)", power control for a WCDMA system is
described. The closed power control loop for WCDMA, uplink or downlink,
typically comprises elements to form an inner power control loop and an outer power
control loop in a receiver of a device in the wireless communication system
The outer power control loop typically sets the SIR reference value based on a
deviation of an estimated block error rate (BLER) value from a BLER reference
value. The inner power control loop compares the estimated SIR value to the SIR
reference value Based on this comparison, the inner loop sets a power request, a
Transmit Power Control (TPC) command, to be sent to a transmitter of another
device in the wireless communication system The TPC command indicates if a
requested change is to increase or to decrease the transmitted power. The outer loop
typically operates at a rate much lower than that of the inner loop For a 3 GPP
WCDMA system the outer loop operation performs at a rate of 10-100 Hz, whereas
the inner loop operation may perform at a rate of 1500 Hz
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In a WCDMA system a number of data bits are typically collected in a transport
block and several transport blocks are contained in a Transmission Time Interval
(TFI) A transport block comprises a number (1-8) of frames (each 10 ms)
transmitted during a TTI A receiver, in order to decode the data in the transport
block, typically needs to receive the complete TTI, and the outer power control loop
updates the SIR reference value once every TTI, which is 10-80 ms for the 3GPP
WCDMA system
The actual SIR value will however vary within the TTI, even if the SIR reference
value is kept constant within this time. Thus the TPC commands that are produced on
a slot-by-slot basis during a TTI may be optimal for the first slot, but non-optimal for
the rest of the slots in the same TTI
The published patent applications WO 03/055098, WO 01/20808 and US
2002/0187802 are examples of prior art documents in the same technical area
WO 03/055098 describes a power control method, which is complemented with soft
information (such as an uncoded bite error rate) estimation and extra regulation for
producing a SIR reference based a comparison between the uncoded bit error rate
estimate and an uncoded bit error rate reference
It is a pu/pose of one or more embodiments of the present invention to provide a
method of generating and updating or modifying the SIR reference value several
times during a TTI in such a way that the effect of varying SIR values during the TTI
is minimized
Summary
According to one or more embodiments of the invention the above and other
problems are solved by a method for generating a power control command in a
transceiver (such as a mobile station or a base station) in a wireless communication
system The method comprises the steps of calculating, at the beginning of a

predefined time period, a quality measure reference value, generating, repeatedly
during the predefined time period, an estimated quality measure value of a signal
received at the transceiver, generating a power control command in dependence of
the estimated quality measure value and the quality measure reference value, and
generating, a number of times during the predefined time period, a modified quality
measure reference value from the quality measure reference value The step of
generating the power control command comprises comparing the estimated quality
measure value with the modified quality measure reference value
The step of generating the modified quality measure reference value comprises
calculating, at a given point in time during he predefined time penod, an effective
quality measure value from estimated quality measure values previously generated
and generating the modified quality measure reference value in dependence of a
difference between the effective quality measure value and said quality measure
reference value. The method is thus adjusting the reference value for the quality
measure taking the variations in estimated quality measure values into account by
generating this effective quality measure value, which corresponds to the duality
measure at a certain constant value
The step of calculating the effective quality measure value may comprise calculating
at one or more of a linear average, an exponential average or a logarithmic average
from the estimated quality measure values previously generated
The step of generating the modified quality measure reference value may also
comprise setting the modified quality measure reference value to a predetermined
threshold value for a remaining time of the predefined time penod, where the
predefined time penod may be divided into a number of sub penods, if the value of
the modified quality measure reference value for a next sub penod becomes zero or
negative. The predetermined threshold value may for example be set to zero
According to one or more embodiments of the invention a computer readable
medium are configured to implement the method for generating a power control
command
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According to an alternative embodiment of the invention, there is provided a method
for controlling a power level of signals transmitted in a wireless communication
system to a first transceiver from a second transceiver. The method comprises the
steps of calculating, at the beginning of a predefined time period, a quality measure
reference value, generating, repeatedly during the predefined time period, an
estimated quality measure value of a signal received at the first transceiver,
generating a power control command in dependence of the estimated quality measure
value and the quality measure reference value; transmitting the power control
command to the second transceiver, adjusting in the second transceiver, in
dependence of the power control command, the power levels of signals transmitted to
the first transceiver, and generating, a number of times during the predefined time
period, a modified quality measure reference value from the quality measure
reference value The step of generating the power control command comprises
comparing the estimated quality measure value with the modified quality measure
reference value
The first transceiver may be a mobile station and the second transceiver may be a
base station in the wireless communication system, or the first transceiver may be a
base station and the second transceiver may be a mobile station
The step of generating the modified quality measure reference value may comprise
calculating, at a given point in time during the predefined time period, an effective
quality measure value from estimated quality measure values previously generated
and generating the modified quality measure reference value in dependence of a
difference between the effective quality measure value and said quality measure
reference value
The method is thus adjusting the reference value for the quality measure taking the
variations in estimated quality measure value into account by generating this
effective quality measure value, which corresponds to the quality measure at a
certain constant value
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Further, the step of calculating the effective quality measure value may comprise
calculating one or more of a linear average, an exponential average or a logarithmic
average from the estimated quality measure values previously generated
The step of generating the modified quality measure reference value may also
comprise setting the modified quality measure reference value to a predetermined
threshold value for a remaining time of the predefined time period, where the
predefined t»me period may be divided into a number of sub periods, if the value of
the modified quality measure reference value for a next sub penod becomes zero or
negative. The predetermined threshold value may for example be set to zero.
In yet an alternative embodiment, there is provided a power control unit in a
transceiver (such as a mobile station or a base station) in a wireless communications
system The power control unit comprises a first controller configured to calculate,
at the beginning of a predefined time penod, a quahty measure reference value and a
quality measure estimator configured to generate, repeatedly during the predefined
time penod, an estimated quality measure value of a signal received at the
transceiver. The power control unit may also compnse an inner loop element
configured to generate a power control command in dependence of the estimated
quality measure value and the quality measure reference value The power control
unit may further compnse a second controller configured to generate, a number of
times dunng the predefined time penod, a modified quality measure reference value
from the quality measure reference value The inner loop element, which may be a
third controller, may be configured to generate the power control command by
comparing the estimated quality measure value with the modified quality measure
reference value.
The power control unit may further compnse a calculator configured to calculate, at
a given point in time dunng the predefined time penod, an effective quality measure
value from estimated quality measure values previously generated The second
controller is configured to generate the modified quality measure reference value in
dependence of a difference between the effective quality measure value and the said
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quality measure reference value
In particular, the calculator may be configured to generate the effective quality
measure value by calculating one or more of a linear average, an exponential average
or a logarithmic average of the estimated quality measure values previously
generated
Further, the second controller may further be configured to generate the modified
quality measure reference value as a predetermined threshold value for a remaming
time of the predefined time period, where the predefined time period may be divided
into a nurober of sub periods, if the value of tne modified quality measure reference
value for a next sub period becomes zero or negative. The predetermined threshold
value may for example be set to zero
The power control unit may further be included in a wireless communication
transceiver, which may be a mobile station or a base station
For the various embodiments, the estimated quality measure value may be an
estimated signal-to-interference ratio (SIR) value and the quality measure reference
value may be a SIR reference value The estimated SIR value may be estimated
based on received pilot symbols Similarly, the effective quality measure value may
be an effective SIR value and the modified quality measure reference value may be a
modified SIR reference value
Further, for the various embodiments, the predefined time period may be divided into
a number of sub periods. Generating the modified quality measure reference value
may be done each sub period More particularly, the predefined time period may be
one or more transmission time intervals in a wideband code division multiple access
(WCDMA) system and the sub period may be a slot or a fraction of a slot in a
WCDMA system
According to the various embodiments of the invention, the quality measure
reference value, such as an SIR reference value, will be adjusted and updated more
8

often than in the prior art solutions, allowing power control commands to be
generated more accurately Hereby a power control system implementing these
methods will operate more efficiently and the overall wireless communication
system capacity will be increased. In addition, unnecessary power requests from the
various users of the wireless communication system may be avoided
The above features and advantages do not limit the present invention, and those
skilled in the art will recognize additional features and advantages upon reading the
following detailed description, and upon viewing the accompanying drawings.
Brief Description of the Drawings
The embodiments of the invention will now be described more fully below with
reference to the drawings, in which
Fig 1 is an illustration of a power control system employed in a wireless
communication system
Fig 2 illustrates a block diagram of a prior art power control unit in a 3GPP
WCDMA wireless communication system,
Fig. 3 illustrates a timing structure in a 3GPP WCDMA wireless communication
system,
Fig 4 illustrates a block diagram of a power control unit according to an embodiment
of the present invention
Fig. 5a shows a graphic illustration of SIR values, SIR reference values and effective
SIR reference value versus time, obtained by embodiments of the invention
Fig. 5b shows an alternative graphic illustration of SIR values; SIR reference values
and effective SIR reference value versus time, obtained by embodiments of the
invention
9

Fig 6 is an example of a flow diagram of the SIR reference regulation performed by
an outer control loop according to an embodiment of the present invention
Detailed Description
Fig 1 illustrates a power control system 600 operating as a closed power control loop
in one direction in a wireless communication system The power control system 600
comprises at least a first transceiver 601 and a second transceiver 602 They
communicate with each other over a wireless transmission channel 603 with radio
signals carrying different kinds of information The first transceiver 601 comprises at
least a first receiver 604, at least a first transmitter 605 and at least one power control
unit 606, which for example may be the power control unit 100 or 300 to be
described below in relation to Fig 2 and Fig 4 The second transceiver 602
comprises at least a second receiver 607 and at least a second transmitter 608. If the
first transceiver 601 is a base station and/or a radio network controller in the wireless
communication system, the power control system 600 is employed for the uplink
transmission direction; and vice versa, if the first transceiver 601 is a mobile unit in
the mobile communication system, the power control system 600 is employed for the
downlink tiansmission direction However, the power control system may usefully
be employed in both the uplink and the downlink If so, the uplink scenario the
second transceiver would also comprise a second power control unit. However, for
the purpose of simplifying the description of the power control system 600, the
power control unit 606 is in Fig 1 only shown in the first transceiver 601 An
information signal 609 is transmitted from the second transmitter 608 over the
wireless transmission channel 603, which affects the signal in a random and
unknown manner before it is received by the first receiver 604 The first receiver 604
processes the signal, by for example amplifiying, filtering, frequency
downconverting, sampling, despreading, decoding and demterleaving, and forms a
processed received signal 610, which is input to the power control unit 606, which
10

produces the transmit power control (TPC) command 611. The TPC command 611 is
processed by the first transmitter 605 to form a radio signal 612 carrying the TPC
command for transmission over the wireless transmission channel 603 The TPC
radio signal 612 is received and processed by the second receiver 607 to form a
control signal 613, vhich is input to control the power level of the second transmitter
608 The transmitted data signal 609 is then controlled in its transmitted power
Fig. 2 shows a schematic block diagram of a prior art power control unit 100 used in
a transceiver of a device in a WCDMA wireless communication system based on the
3GPP specification, where power control typically is supported in both uplink and
downlink propagation directions The power control unit 100 will be associated with
a receiver of the base station for the uplink power control and with a receiver of the
mobile station for the downlink power control
The purpose of the outer power control loop in a device in the wireless
communicationsystem is to set ana continuously adjust a reference value for a signal
quality measure for the inner power control loop to aim at Typically, the quality
measure value is a signal-to-interference ratio (SIR) value, and the quality measure
reference- value is a SIR reference value 102 A SIR estimator 106 generates a SIR
estimate value 103 from received pilot symbols 107 and provides the SIR estimate
value 103 to an inner loop element 104 Since the pilot symbols 107 are known at the
receiver and have experienced the same propagation conditions on the wireless
transmission channel as the information signal, the SIR value for the information
signal may be estimated
The inner power control loop element 104 affects a new SIR value by producing
Transmit Power Control (TPC) commands 105 to be sent to another device (not
shown) in the wireless communication system informing how that device should
adjust its transmitted power The transmitted power is typically adjusted in a
predetermined manner. If the SIR estimate value 103 is below the SIR reference
value 102, a TPC command 105 is sent to the transceiver of the other device to
11

increase its power, and if the SIR estimate value 103 is above the SIR reference
value 102, a TPC command 105 is sent to the transceiver of the other device to
decrease its power The transmitted power is typically adjusted in discrete steps in
decibels (dB) The step size is network parameter configured by the wireless
communication system and it is for WCDMA ± 0 5,1; 1 5 or 2 dB A new TPC
command 105 is sent every slot, which is every 10/15= 0 667 ms, or equivalent: the
inner loop 104 is working at a frequency of 1500 Hz to compensate for fast fading
The SIR reference value 102 is generated and controlled by an outer control loop
element 101 based on a Block Error Rate (BLER) reference value 108, which is a
network parameter set by the wireless communication system, and an estimated
BLER value 109, an additional quality measure for the received blocks of data A
BLER estimator 110 bases its estimation for the estimated BLER value for a
transport channel on Cyclic Redundancy Check (CRC) error oits on each block of
data. These bits have special coding properties, such that if they are found to be in
error, the bits in the transport block are considered decoded in er-or by the receiver.
The receiver processes the CRC error bits and forms a CRC error flag 111 If this
flag is in a state of "not set", it is assumed that it will be possible to correctly recover
the block of data in the receiver Otherwise, if the flag is "set" the whole block of
data is considered to be erroneous The estimated BLER value for a transport channel
is found by processing the CRC error flags 111 in the BLER estimator 110
The outer control loop element 101 updates the SIR reference value 102 once every
Transmission Time Interval (TTI), which is 10-80 ms for the 3GPP WCDMA
system. A transport or code block comprises a number (1-8) of frames (each of 10
ms duration) transmitted during a TTI The outer loop operates thus much slower
than the inner loop, which instead updates the TPC command 105 every slot (0 667
ms).
In Fig 3, a typical timing structure in a WCDMA system is illustrated A TTI 201
consists of 1 up to 8 radio frames 202 Each frame 202 of 10 ms is split into 15 slots
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203, each of length 2560 chips (0 26 ms per chip) or 10/15= 0 667 ms in time Each
slot 203 corresponds to one power control period for the inner loop For example, on
the dedicated downlink physical WCDMA channel (DPCH) each slot 203 carries the
data bits, the TPC command, the pilot bits and a Transport Channel Indicator (TPCI).
The data and the pilot bits are encodec as symbols (not shown), each representing a
number of bits. The total number of bits in a slot is determined by the WCDMA
spreading factor (SF). The value of the SF is, for WCDMA, in the range of 2 to 512
The main purpose of power control in a wireless communication system is typically
to control the sent power from the transmitters, in such a way that a quality measure
at a receiver is maintained at and follows a given reference value. Different systems
may use different quality measures and combinations of different quality measures.
In a WCDMA solution, the BLER reference value 108 may for example be updated
every TTI, but in reality updating the BLER reference value 108 is done even less
often. The SIR reference value 102 is in the prior art solutions typically kept constant
for each TTI, which may be as long as 80 ms, depending on the number of frames
per TTI In reality the actual SIR value, and thus the SIR estimate value 103, varies
during this time. This is due to the effects of fading, noise and other disturbances,
which m turn depend on the relative movement of the receiver of one device and the
transmitter of another device, which are usually difficult to fully compensate for by
power control
For this reason the TPC command 105 may be updated based on a SIR reference
value 102 that is no longer the ideal reference value for the remaining time of the
TTI The BLER value is a measured or estimated quality measure and it depends, for
a received transport block, on the SIR variations during a corresponding TTI This
means that the BLER value will vary between TTIs with the same SIR reference
value, which may result in either too high BLER or unnecessarily high power
requests from the transmitter, which in turn results in reduced system capacity, e g. a
reduced number of simultaneous users in the communication system
13

One purpose of embodiments of the present invention is therefore to adjust the
reference value for the quality measure taking these variations into account. This is
achieved by computing an effective new quality measure value, which corresponds
to a constant quality measure value resulting in the same BLER value. A quality
measure reference value is further generated by a first controller in the outer loop
element and input to a new second controller or regulator included in, or associated
with, the outer loop element or the inner loop element The quality measure reference
value may for example be generated once every predefined time period, and is
generated based on a regulation of the estimated BLER value towards the BLER
reference value. The predefined time period may be a TTI or a certain number of
TTIs The second controller in turn generates a modified quality measure reference
value a number of times during the predefined time period, such as once every sub
period, e g once per slot, based on a difference between a calculated effective quality
measure value and the original quality measure reference value (that was generated
by the first controller) An effective quality measure value calculator, which may be
included in, or associated with, the outer loop element or the inner loop element,
derives the effective quality measure value, as will be described in detail below,
based on the estimated quality measure value The modified quality measure
reference value and the estimated quality measure value are further input to a third
controller, the inner loop element, which compares the modified quality measure
reference value with the estimated quality measure value and generates a power
control command once every sub period, in dependence of the comparison The
power control command indicates a required power adjustment for the signals of
another transmitting wireless communication device
For the sake of illustration we now refer to SIR as the quality measure for the inner
loop element and BLER as an additional quality measure for the outer loop element,
but it should be understood that the invention is not limited to this combination of
quality measures Bit error rate (BER) is another possible quality measure choice for
the outer loop element for example
14

The BLER value depends on the SIR values during a corresponding TT1. If the SIR
value were to be constant there would be a relationship between tlie SIR value and
the BLER value such that a higher SIR value would represent a lower BLER value
and vice versa However, the SIR value is in reality varying, but the receiver needs to
maintain a constant (low) BLER For example, when the SIR value is varying during
a TTI it would be beneficial to compute, or predict, a value of a constant SIR that
would correspond to a certain BLER According to an embodiment of the present
invention such a SIR value is computed to form an effective quality measure value,
the effective SIR, denoted SIR in the following Thus, obtaining a certain BLER
value is equivalent to obtaining a certain desired effective SIR value This effective
SIR value is calculated based on a number of estimated SIR values during the current
time period, for example a TTI The value of SIR is updated each sub period, for
example each slot In one or more embodiments of the invention the SIR reference
value is adjusted several times during a time period, 1 e several times during a TTI
A new modified SIR reference value is generated based on the certain effective SIR
several times during the predefined time period, such as once every sub period,
which may be for example a slot, or a fraction of a slot
The SIR value may be an average value of the different SIR values during the
duration of a TTI, which may e g be 1,2,4 or 8 frames By predicting the SIR value
and allowing the SIR reference value to be updated within the predefined time
period, e g. the TTI, the effects of varying SIR estimate values are taken into account
in the power control system
15
The SIR value may be defined and predicted or calculated in various ways.
Examples of definitions are shown in equations 1,2 and 3
A Linear effective SIR, is a linear average and is defined by


where N is the number of SIR values obtained during the predefined time period, for
example during the TTI Nmay thus also be equal to the number of sub periods
comprised in the TTI. If for example a new SIR value is estimated every slot, N will
be equal to the number of slots in the TTI, which for WCDMA is an integer between
1 and 8. It should be noted, however, that the SIR may be calculated for any sub
period and N need thus not be the number of sub periods in the time period

As yet another alternative, an Exponential effective SIR may be used, and it is
defined by
Alternatively, a Logarithmic effective SIR may be used It is defined by

These definitions has empirically been found to map the effective SIR on to a BLER
in slightly different ways, thus different implementations may use different
definitions The Linear effective SIR and the Logarithmic effective SIR have been
found to be most useful, if the SIR variations are small, and in a range of low SIR
values; whereas the Exponential effective SIR provides a low uncertainty mapping
for larger SIR variations as well Alternatively, different combinations of definitions
may be used for calculating the effective SIR, based on the range of the estimated
SIR values.
With reference now to Fig 4, a block diagram of an example of a power control unit
300 according to one or more embodiments of the present invention is illustrated A
power control unit 300 that comprises a first controller 303, a second controller 302
16

and a third controller 312 is shown The controllers may be realized for example as
PI or PID regulators, although other regulators may be used The power control unit
300 comprises a first controller 303, which may be a BLER controller (outer Icop
controller), which compares a BLER estimate value 304 (estimated in a BLER
estimator 316 based on CRC error flags 315) with a BLER reference value 305 and
generates a quality measure reference value, here denoted SIR reference value, 306
once every predefined time period, for example once per TTI Compared to the prior
art in Fig. 2, the power control urrt 300 comprises an additional regulator element,
the second controller 302, which may be a SIR controller. The SIR reference value
306 is input to the second controller, the SIR controller 302 Additionally, a SIR
estimate value 307 is produced by the SIR estimator 308 based on received and
processed pilot symbols 314, repeatedly during the TTI, such as once every sub
period, for example once every slot The SIR estimate value 307 is input to the third
controller, an inner loop element 312 According to one or more embodiments of the
invention, is the SIR estimate value 307 also input to a SIR calculator 310 The
SIR calculator 310 calculates the effective SIR value, SIR 311, by for exarrple any
of the equations 1,2 or 3, based on the SIR estimate value 307 The SIR 311 maybe
generated and updated once per sub period The SIR calculator 310 and the second
controller 302 may be included, oi associated with either of the outer loop controller
303 or the inner loop element H2 The SIR value 311 is input to the SIR controller
302, which compares the SIR value 311 with the SIR reference value 306 and
produces a modified SIR reference value 309 This is performed a number of times
during the TTI, such as once per slot This modified reference value is thus updated
several times within the time period of a TTI The modified SIR reference value 309
may be generated once every sub period and is the reference input to the third
controller 104, the inner loop element The purpose of the controlling performed by
the SIR controller 302 is to minimize the error (effective SIR error) between the
requested effective SIR value, which is the SIR reference value 306, and the actual
17

effective SIR value 311, by updating the modified SIR reference value 309 several
times during the predefined time period
In the following, the terminology for a SIR reference value will be SlRref and for a
modified SIR reference value, SIR ref
The SIR calculator 310 further needs to keep track of the timing, at which instant
within the TTI the present SIR value relates to The power control unit 300 may
therefore be associated with a timer for registering an expiration of the predefined
time period and registration of the sub periods The timer is accordingly updated for
keeping track of which sub period, of the N possible sub periods in the predefined
timee period, is being processed
It should be understood that the illustration of Fig 4 may or may not represent
physical circuit implementations, depending for example on whether the power
control unit 300 is implemented in hardware or software, or in some combination
thereof. For example, in software-based implementation, the illustrated elements may
comprise processing functions implemented by stored computer program
instructions, or microcode, etc
An optimisation with respect to modified SIR reference values at each slot may be
done over many TTIs A weight on the modified SIR reference value may be
included in the optimisation in order to keep the modified SIR reference value as
small as possible.
In an example of an embodiment of the invention, the optimisation works to
18
minimize the effective SIR error, and is performed by minimizing the absolute
effective SIR error over MTTI time periods This error is shown in equation 4.


A new optimal selection, according to the above criteria, of a modified SIR reference
value may be computed every time a new SIR measurement or estimation is made,
that is, each sub period, for example once every slot
In the optimisation several considerations need to be taken into account, such as the
dynamics between the modified SIR reference value and actual SIR value and such
as limitations and constraints on the SIR value and the rate of change of the SIR
values. For example, in a WCDMA system, there are limitations such as allowed
power step sizes and how often to change the SIR value In WCDMA it is only
possible to change a SIR reference value betwsen consecutive slots The power is
decreased or increased in fixed steps of usually 1 dB
In another embodiment of the invention, an optimisation is performed considering
only the current TTI (M=l) and with respect to the remaining modified SIR reference
values of that TTI at a specific sub period in the time period,

for N-n remaining modified SIR reference values, where N is the total number of
SIR values during a time period, for example a TTI At the end of a TTI, when
running out of time to obtain the correct effective SIR, the optimal values of the
modified SIR reference 309 will, typically, deviate more from the original SIR
reference value 306 The final modified SIR reference value, SIRref (N), may be far
from the original SIR reference value, the SIR reference value 306 This may cause
a control problem for the subsequent TTI since instant changes of the SIR value are
prevented by dynamics Therefore, in yet another embodiment of the invention a
suitable weight or constraint is placed on the final modified SIR reference value to
improve the performance of the control loop for subsequent transmission time
intervals
19

The solutions presented above result in time-varying control algorithms, but time-
mvanant control algorithms may also be considered
Now a discussion in greater detail will be given for an example of an embodiment of
a control algorithm for the SIR controller 302 This algorithm may be realized with
low complexity for the solution when considering only a current TTI (M=1) and with
respect to the remaining modified SIR reference values of that "?TI. It we assume that
there is a new SIR reference value estimated every sub period, which may for
example be a slot of a TTI, and that For (at a specific slot number, n) the remaining
slots of the predefined time period, such as the TTI, it is possible to obtain
SIR(n) = SlRref (n), then it will be possible with instantaneous changes of the SIR
value. Then the optimisation may be done for each TTI individually.
Again, the terminology for a SIR reference value 306 will be SlRref and for a S'R
reference value 309, SIRref
20
Fig 5a and Fig 5b shows two examples of graphic illustrations of the criteria behind
how to choose the modified SIR reference value at the slot number n+l, based on
information up to slot number n For illustration purposes the SIR values are drawn
as unrealistic straight lines At n, the modified SIR reference value needs to be
chosen so that a goal for the SIR controller 302 is fulfilled, the goal being to
produce SlRref values to obtain the same area, equal to N SIRref , below a
SIRref curve and a SIR curve during A' sub periods of the time period
To obtain this goal, a value for the remaining modified SIR reference values,
hereafter denoted AS(n+\), needs to be chosen at slot number n+\, where
n+1={1 N), such that


where Sn is the contribution to the area from n SIk values, an accumulated SIR
value, and A5(n+l) is the contribution of the area from the remaining N- n SIR
reference values yet to be obtained Fig 5a and Fig 5b illustrate two sceranos of
SIR contribution to the area at slot number n Sn is for example calculated by one of
equations 1-3 The SlKref value was obtained by the comparison of the estimated
BLER value with the BLER reference value in the BLER controller. Fig 5b shows a
situation when a larger AS(n+1) is required compared with the situation in Fig 5a
If the value of AS (n+1) at slot number n+1 becomes zero or negaive, the modified
signal-to-interference ratio reference value needs to be set at a predetermined
threshold value for the remaining time of the time period The threshold value could
for example be set to zero.
If the Linear effective SIR is used as the SIR definition, the remaining modified SIR
reference values, i.e AS(n+1), should be chosen such that

will be fulfilled.
The first part of the right-hand side of equation 6b is then equal to a definition of Sn
with Linear effective SIR and the second part is equal to the design choice of
AS(n+1).
21
Equation 6b may be rewritten as


Equation 8 may be expressed in terms of the definitions in equation 6a as
If all remaining modified SIR reference values are chosen to be equal, the smallest
variance in the actual SIR is obtained This means that the modified new SIR
reference value at the next instant in time, at slot r,+l, should be chosen such that



Alternatively, using the Exponential effective SIR instead, the smallest SIR variance
is obtained if the modified new SIR reference value is chosen such that


Yet an alternative equation for a modified new SIR reference value to be obtained at
n+1 is shown in Equation 11, when based on the Logarithmic effective SIR
22



Here the corresponding definitions become

The factor K, is a constant that determines the number of slots during which an
incorrect effective SIR may be corrected The correction may be spread out for a
number of slots Correction during one slot corresponds to Kl = 1,1 e all correction
is pe formed once only, and correction during a fixed number of slots corresponds to
a constant Kt estimated SIR and SIRref for the previous slots
A negative modified SIR reference value corresponds to a situation where there is
knowledge of the system that the effective SIR value for the current TTI will be high
enough. Then the transmitter may turn off its power resulting in a zero SIR value
Fig. 6 is a flow diagram that illustrates an example of a method 500 for determining a
modified SIR reference value at a slot n+\ by use of an effective SIR value In the
following the example of the linear effective SIR is used The sub period is within
the predefined time period and method 500 runs once every sub period for all N sub
periods within the predefined time period In the following, the sub period is
assumed to be a slot and the predefined time period is a TTI in a WCDMA wireless
system, however the time periods of the present invention are not limited to these
time periods
23

At step 501, a SIR estimate value is generated based on received pilot symbols and
the estimate is input to the SIR calculator at a slot n Further a SIR reference value,
which has been generated by the BLER controller based on the BLER reference
value and the estimated BLER value, is input to the SIR controller Then the method
proceeds to step 502, in which the SIR calculator updates an accumulated SIR
value, Sn, with the current estimated SIR value Sn is the SIR based on slot number
1 n Sn is input to the SIR controller and then the method proceeds with step 504
At step 504, a check is made if it is the start of a new TTI If n=N the previous TTI
has just finished, thus a new TTI is at hand If this is the case, ihe accumulated SIR
value, Sn and n are set to zero at an initialisation step 503 If in step 504 it was
found that we are not at the beginning of a new TTI, ∆S(N+1) is calculated
according to equation 6a at step 505 It may graphically be viewed as the right-most
area in any of the graphs in Fig 5a or Fig 5b This area illustrates the remaining
modified SIR reference values times the time left of the TTI Then at step 506, the
modified SIR reference value, valid for slot number n+\, is generated by the SIR
controller according to any of equations 8, 9,10 or 11, depending on which
definition of the effective SIR was used
The modified SIR reference value is then output from the SIR controller and input to
the inner loop controller at step 507 Then the time slot number n is updated at step
508. Then the process starts over at step 501 This modified SIR reference value is
now assumed to be valid for all remaining slots up to N, however in the next run the
modified SIR reference value is updated again with a new value The prccess thus
runs though a whole TTI with a new update of the modified SIR reference value
every slot
In reality, instantaneous changes in the modified SIR reference value are, as
discussed previously, not utilized, but instead the modified SIR reference value will
need to be changed by a fixed step, by for example 1 dB When approaching the end
24

of a TTI, with a limited amount of time left to reach the wanted level of the SIR
reference value, there may be problem of unwanted large variations up and down in
the SIR value Thus, there may be a need to fulfil an end condition with a set final
value constraint
So, in yet another embodiment of the invention, a final value constraint for the SIR
value needs to be fulfilled, as will be discussed in greater detail below Here the
Logarithmic effective SIR, as defined by equation 2, is used for illustration.
Keeping the current modified SIR reference value until getting close to the end of the
TTI, and then ramping it (stepwise) to the correct value, i.e the SIR reference value,
provided that the SIR value is equal to the SIR reference value, results in the
following contribution to the effective SIR, A(n)

where SIR dBstep is the SIR step size m decibels (dB) and where the first part of the
right hand side of equation 12 is analogous to the area below a SIR-vs -time curve
without the ramping, and the second part is the area contribution from the ramping
part A(n) is thus measured in decibels (dB)
Either an increase or a decrease in the modified SIR reference value is performed
depending on whether the expected contribution is too small or too large.
This leads to a modified SIR reference value (in decibels) for the next time slot, n+\,
which equals

An end condition, when n is approaching N, needs to be satisfied and is given by the
inequality
25


where nramp are an assumed average or typical number of steps needed by the ramp
at the end of a TTI In this embodiment there will thus be a compromise between the
wanted area and the last modified SIR reference value If the modified SIR reference
value is to be at the level of the SIR reference value at the last slot of a TTI, in order
to have an optimal starting value for the start of the next TTI, then the ramping down
or up at the end may result in the total area slightly different from the intended,
optimal, area
In yet another alternative embodiment, the invention may further increase system
capacity if it is utilized in a way that power is saved Due to coding it may be
possible to predict the success of a current transmission of a block before all the bits
of the coded block have been received The decoder may for example be able to
reconstruct the full block before all the bits have been received Then it is possible to
reduce the power, or equivalently the SIR value, during the remaining part of the
TTI. This is possible due to the fact that the quality of the remaining bits will not
have influence on the success of the current block reception This will decrease the
power needed and thus increase system capacity
In yet another embodiment, an effective SIR value may be used as an additional net
planning parameter utilized by the base stations Then the SIR value associated with
a certain mobile unit may be increased during parts of the TTI and decreased for
other parts of the TTI provided that the effective SIR value, and thus the BLER
26

value, is the same This way of scheduling the transmitted power from each mobile
unit in the system, also improves system capacity.
With reference again to Fig 1, a power con'rol system is schematically shown in
which the power control algorithms according to embodiments of the invention
would operate The at least one power control unit 606, may for example be the
power control unit 300 described above in relation to Fig 4
Although embodiments of the present invention have been described and shown, the
invention is not restricted to them, but may also be embodied in other ways within
the scope of the subject matter defined in the following claims For example, while
the embodiments of the invention have been described with respect to WCDMA, the
invention is not limited thereto but may certainly be applicable to other wireless
communication systems and combinations of different wireless communication
systems. Further, the power control method may be supported in both uplink and
downlink
The term "transceiver" used in this specification includes various kinds of mobile
communication units present in a mobile communication system Also the present
invention is not limited to single-band or single-mode transceivers, but includes
transceivers serving more than one wireless communication system.
The terms "mobile unit" or "mobile station" used in this specification include various
kinds of portable or wireless communication equipment, such as mobile telephones,
pagers, electronic organizers, smart phones, communicators, headsets and other
communication apparatus
27

We Claim
1 A method for generating a power control command in a transceiver (601, 602) in a
wireless communication system,
the method comprising
calculating, at the beginning of a predefined time period, a quality measure
reference value (306),
generating, repeatedly during the predefined time period, an estimated quality
measure value (307) of a signal received at the transceiver,
generating a power control command (313) in dependence of the estimated quality
measure value (307) and the quality measure reference value (306),
characterized in that
the method further comprises,
calculating, at a given point in time during the predefined time period, an effective
quality measure value (311) from estimated quality measure values (307)
previously generated,
generating, a number of times during the predefined time period, a modified
quality measure reference value (309) in dependence of a difference between the
effective quality measure value (311) and said quality measure reference value
(306), and
generating the power control command by comparing the estimated quality
measure value (307) with the modified quality measure reference value (309)
2 The method according to claim 1, wherein the step of calculating the effective
quality measure value (311) comprises calculating at least one of a linear average,
an exponential average and a logarithmic average from the estimated quality
measure values (307) previously generated
3 The method according to any one of claims 1 -2, wherein the estimated quality
measure value (307) is an estimated signal-to-interference ratio value, and
the quality measure reference value (306) is a signal-to-interference ratio reference
value
4 The method according to claim 3, wherein the predefined time period is divided
into a number of sub periods, and wherein the step of generating the modified
28

signal-to-interference ratio reference value (309) for a given sub period, n+1,
comprises calculating



where SlRref is the modified signal-to-interference ratio reference value (309),
SlRref is the signal-to-interference ratio reference value (306), Kx is a constant
and SIR(k) is the estimated signal-to-interference ratio value (307) for the k th sub
penod
The method according to claim 3, wherein the predefined time period is divided
into a number of sub periods, and wherein the step of generating the modified
signal-to-interference ratio reference value (309) for a given sub penod, n+1,
comprises calculating

where SlRref is the modified signal-to-interference ratio reference value (309),
SIRre f is the signal-to-interference ratio reference value (306), Kt is a constant
and SIR(k) is the estimated signal-to-interference ratio value (307) for the k th sub
period
The method according to claim 3, wherein the step of generating the modified
signal-to-interference ratio reference value (309) for a given sub period, n+1,
comprises calculating

where SIRref is the modified signal-to-interference ratio reference value (309),
SIRref is the signal-to-interference ratio reference value (306), K1 is a constant
and SIR(k) is the estimated signal-to-interference ratio value (307) for the k th sub
period
29

7 The method according to any one of claims 4- 6, wherein Kt = 1 /(N - n),
where N is a number of sub periods in the predefined time period and n is a present
sub period number
8 The method according to any one of claims 4-7, wherein the step of generating the
modified signal-to-interference ratio reference value further compnses setting the
modified signal-to-interference ratio reference value to a predetermined threshold
value for a remaining time of the predefined time period, if the value of
SlRref (n+1) becomes zero or negative
9 The method according to claim 8, wherein the predetermined threshold value is set
to zero
10 The method according to claim 1, wherein the step of generating the modified
quality measure reference value (309) comprises setting the modified quality
measure reference value to a maximum value for a first part of the predefined time
period and a minimum value for a second part of the predefined time period
11 The method according to any one of claims 1-10, wherein the wireless
communication system is a wideband code division multiple access system
12 The method according to any one of claims 1-11, wherein the predefined time
period is at least one transmission time interval (201) in a wideband code division
multiple access system
13 The method according to any one of claims 4-9, wherein the sub penod is a slot
(203) in a wideband code division multiple access system
14 The method according to any one of claims 4-9 wherein the sub penod is a fraction
of a slot in a wideband code division multiple access system
15 The method according to any one of claims 1-14, wherein the transceiver is a
mobile station
30

16 The method according to any one of claims 1-14, wherein the transceiver is a base
station
17 A power control unit (300) for use in a wireless communication transceiver, the
power control unit comprising
a first controller (303) configured to calculate, at the beginning of a predefined
time period, a quality measure reference value (306),
a quality measure estimator (308) configured to generate, repeatedly during the
predefined time period, an estimated quality measure value (307) of a signal
received at the transceiver,
an inner loop element (312) configured to generate a power control command
(313) in dependence of the estimated quality measure value (307) and the quality
measure reference value (306),
characterized in that
the power control unit further comprises
a calculator (310) configured to calculate, at a given point in time during the
predefined time period, an effective quality measure value (311) from estimated
quality measure values (307) previously generated,
a second controller (302) configured to generate, a number of times during the
predefined time period, a modified quality measure reference value (309) in
dependence of a difference between the effective quality measure value (311) and
said quality measure reference value (306), and
wherein the inner loop element (312) is configured to generate the power control
command (313) by comparing the estimated quality measure value (307) with the
modified quality measure reference value (309)
18 The power control unit according to claim 17, wherein the calculator (310) is
configured to generate the effective quality measure value (311) by calculating at
least one of a linear average, an exponential average and a logarithmic average of
the estimated quality measure values (307) previously generated
19 The power control unit according to any one of claim 17-18, wherein the estimated
quality measure value (307) is an estimated signal-to-interference ratio value, the
quality measure reference value (306) is a signal-to-interference ratio reference
value
31

20 The power control unit according to claim 19, wherein the predefined time period
is divided into a number of sub periods, and wherein the second controller (302) is
configured to generate the modified signal-to-interference ratio reference value
(309) for a given sub period, n+\, by calculating

where SlRref is the modified signal-to-interference ratio reference value (309)
SIRref is the signal-to-interference ratio reference value (306), K1 is a constan
and SIR(A:) is the estimated signal-to-interference ratio value (307) for the k th sub
period
The power control unit according to claim 19, wherein the predefined time penod
is divided into a number of sub periods, and wherein the second controller is
configured to generate the modified signal-to-interference ratio reference value
(309) for a given sub period, n+l, by calculating

where SIRref is the modified signal-to-interference ratio reference value (309),
SlRref is the signal-to-interference ratio reference value (306), Kt is a constant
and SIR(k) is the estimated signal-to-interference ratio value (307) for the k th sub
period
The power control unit according to claim 19, wherein the predefined time period
is divided into a number of sub periods, and wherein the second controller (302) is
configured to generate the modified signal-to-interference ratio reference value
(309) for a given sub period, n+l, by calculating

where SIRref is the modified signal-to-interference ratio reference value (309),
SlRref is the signal-to-interference ratio reference value (306), Kt is a constant
32

and SIR(A:) is the estimated signal-to-interference ratio value (307) for the k th sub
period
23 The power control unit according to any one of claims 20-22,
wherein Kt = 1 /(TV - n),
where N is a number of sub periods in the predefined time period and n is a present
sub period number
24 The power control unit according to any one of claims 19-23, wherein the second
controller (302) further is configured to generate the modified signal-to-
interference ratio reference value as a predetermined threshold value for the
remaining time of the predefined time period, if the value of SlRref (n+1) becomes
zero or negative
25 The power control unit according to claim 24, wherein the predetermined threshold
value is set to zero
26 The power control unit according to any one of claims 17- 25, wherein the
predefined time period is at least one transmission time interval (201) in a
wideband code division multiple access system
27 The power control unit according to any one of claims 20- 23 wherein the sub
period is a slot (203) in a wideband code division multiple access system
28 The power control unit according to any one of claims 20- 23, wherein the sub
period is a fraction of a slot in a wideband code division multiple access system
29 A wireless communication transceiver comprising a power control unit according
to any one of claims 17 to 28
30 The wireless communication transceiver according to claim 29, wherein the
wireless communication transceiver is a mobile station in a wireless
communication system
33

34
31 The wireless communication transceiver according to claim 29, wherein the
wireless communication transceiver is a base station in a wireless communication
system
32 A computer readable medium having stored thereon program code for performing
the method of any one of claims 1 to 16 when said program code is run on a
computer processor

A method for generating a power control command in a transceiver in a wireless
communication system, where method comprises the steps of calculating, at the beginning
of a predefined time period, a quality measure reference value (306), generating,
repeatedly during the predefined time period, an estimated quality measure value (307) of
a signal received at the transceiver, genarting a power control command (313) in
dependence of the estimated quality measure value (307) and the quality measure
reference value (306), and generating, a number of times during the predefined time
penod, a modified quality measure reference value (309) from the quality measure
reference value (306) The step of generating the power control command comprises
comparing the estimated quality measure value (307) with the modified quality measure
reference value (309) A power control unit (300), comprising a quality measure estimator
(308), a calculator (310), a first controller (303), a second controller (302) and an inner
loop element (312), is configured to implement the method.

Documents:

02588-kolnp-2007-abstract.pdf

02588-kolnp-2007-claims.pdf

02588-kolnp-2007-correspondence others 1.1.pdf

02588-kolnp-2007-correspondence others.pdf

02588-kolnp-2007-description complete.pdf

02588-kolnp-2007-drawings.pdf

02588-kolnp-2007-form 1 1.1.pdf

02588-kolnp-2007-form 1.pdf

02588-kolnp-2007-form 2.pdf

02588-kolnp-2007-form 3.pdf

02588-kolnp-2007-form 5.pdf

02588-kolnp-2007-gpa.pdf

02588-kolnp-2007-international exm report.pdf

02588-kolnp-2007-international publication.pdf

02588-kolnp-2007-international search report.pdf

02588-kolnp-2007-priority document.pdf

2588-KOLNP-2007-(01-02-2012)-CORRESPONDENCE.pdf

2588-KOLNP-2007-(01-02-2012)-FORM-3.pdf

2588-KOLNP-2007-(01-02-2012)-OTHERS.pdf

2588-KOLNP-2007-(06-01-2012)-CORRESPONDENCE.pdf

2588-KOLNP-2007-(06-01-2012)-FORM-3.pdf

2588-KOLNP-2007-(31-07-2012)-CORRESPONDENCE.pdf

2588-KOLNP-2007-ABSTRACT 1.1.pdf

2588-KOLNP-2007-AMANDED CLAIMS.pdf

2588-KOLNP-2007-CANCELLED PAGES.pdf

2588-KOLNP-2007-CORRESPONDENCE 1.1.pdf

2588-KOLNP-2007-CORRESPONDENCE 1.2.pdf

2588-KOLNP-2007-CORRESPONDENCE 1.4.pdf

2588-KOLNP-2007-CORRESPONDENCE-1.3.pdf

2588-KOLNP-2007-CORRESPONDENCE.pdf

2588-KOLNP-2007-DESCRIPTION (COMPLETE) 1.1.pdf

2588-KOLNP-2007-DRAWINGS 1.1.pdf

2588-KOLNP-2007-EXAMINATION REPORT.pdf

2588-KOLNP-2007-FORM 1-1.1.pdf

2588-kolnp-2007-form 18.pdf

2588-KOLNP-2007-FORM 2-1.1.pdf

2588-KOLNP-2007-FORM 3-1.1.pdf

2588-KOLNP-2007-GPA.pdf

2588-KOLNP-2007-GRANTED-ABSTRACT.pdf

2588-KOLNP-2007-GRANTED-CLAIMS.pdf

2588-KOLNP-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

2588-KOLNP-2007-GRANTED-DRAWINGS.pdf

2588-KOLNP-2007-GRANTED-FORM 1.pdf

2588-KOLNP-2007-GRANTED-FORM 2.pdf

2588-KOLNP-2007-GRANTED-FORM 3.pdf

2588-KOLNP-2007-GRANTED-FORM 5.pdf

2588-KOLNP-2007-GRANTED-SPECIFICATION-COMPLETE.pdf

2588-KOLNP-2007-INTERNATIONAL PUBLICATION.pdf

2588-KOLNP-2007-OTHERS 1.1.pdf

2588-KOLNP-2007-OTHERS 1.2.pdf

2588-KOLNP-2007-PA.pdf

2588-KOLNP-2007-REPLY TO EXAMINATION REPORT 1.1.pdf

2588-KOLNP-2007-REPLY TO EXAMINATION REPORT.pdf

2588-KOLNP-2007-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

abstract-02588-kolnp-2007.jpg


Patent Number 255727
Indian Patent Application Number 2588/KOLNP/2007
PG Journal Number 12/2013
Publication Date 22-Mar-2013
Grant Date 19-Mar-2013
Date of Filing 11-Jul-2007
Name of Patentee TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Applicant Address S-164 83 STOCKHOLM
Inventors:
# Inventor's Name Inventor's Address
1 ANDERSSON, LENNART ANNIES VÄG 6, S-266 97 HJÄRNARP
2 BERNHARDSSON, BO SPJUTGRÄNDEN 5, S-224 75 LUND
3 LINDOFF, BENGET MORKULLEVÄGEN 45, S-237 36 BJÄRRED
4 NILSSON, JOHAN TRULSIBRUNNVÄGEN 20 A, S-236 38 HÖLLVIKEN
PCT International Classification Number H04B 7/005
PCT International Application Number PCT/EP2005/013646
PCT International Filing date 2005-12-19
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 040301319 2004-12-20 U.S.A.
2 60/650,634 2005-02-07 U.S.A.