Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02463375 2004-04-30
DESCRIPTION
RADIO COMMUNICATION APPARATUS
AND TRANSMISSION RATE CONTROL METHOD
Technical Field
The present invention relates to a radio
communication apparatus with a variable transmission
rate and a transmission rate control method.
Background Art
A conventional radio communication apparatus is
explained using a document "Performance of SIR-Based
Transmit Power Control using Outer Loop in the forward
Link of DS-CDMA (TECHNICAL REPORT OF IEICE AP96-148,
EMCJ96-83, RCS96-162. MW96-188 (1997-02).'° This
document describes a transmission power control. method
in CDMA. The following is an explanation of this
description.
In transmission power control, measurement of SIR
w indicating the reception quality and
,increment/decrement of transmission power are performed
at every slot cycle (0.625 ms). In this case, if the
measured SIR is greater than the target SIR a command
to reduce transmission power is sent to the base station
( transmission side) and if the measured values is smaller
than the target SIR a command to increase transmission
power is sent to the base station. The base station
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increments or decrements transmission power according
to this command.
Furthermore, the base station controls the outer
loop taking into account the fact that the target SIR
to acquire the required quality ( FER : Frame Error Rate )
varies depending on the environment of a mobile station.
To be more specific, FER is measured from decoded data.
This FER is compared with the target FER in every several
frames and if the measured value is greater, the ~tacrget
SIR is increased and if the measured 'value is smaller,
the target STR is reduced.
The prior art performs transmission power control
not only by sending a transmission power control command
to the transmitting side based on the SIR measured by
I5 the mobile station but also by changing the target SIR
through outer loop control.
However, the prior art has the following problem.
That is, the target SIR increases depending on the
environment and transmission rate of the mobile station
and the receptio~t SIR sometimes decreases due to fading,
etc. In such a case, the mobile station instructs the
base station to increase transmission power to make the
reception SIR come closer to the target SIR, considerably
increasing transmission power of the base station to the
mobile station, which is likely to increase interference
with other mobile stations to an intolerable degree.
Disclosure of Invention
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Tt is an ob~ecti°ve of the present invention to
provide a radio comu~tunication s,pparatus and transmission
rate control method capable of aon~trollirtg transmission
p~ov~er of a base st:ation directed to a rnob~.le stat~,on
S apgropriately without being affected by the environment
o.f the mobile stdt:ion or traasrnission rata.
This ob~sctive is aohieved by a radio communication
apparatus and t:~arvsmission rate control method that
switch the transmission rate of a, transmiss~.on signal
based on reCept:ioi'u quality inforWa:tion from the other
end of cornmun3cat3.on, or according to the environment
o:E the other end of aommunioati.on and transmit tha
signals at the sw~.tahed trari,smission ra~Ce.
~.5 Bxief Descr3.pt~.on of Drawings
FxG . I is a b~.oek diagram showing a configuration
of a base station appara,~CUS according to Embodiment 2
of the pr~asent ~.av~ent3.on;
FIG.2 is a bl.oak diagram showing a oonfiguration
oaf a aominunicatiQn terminal apparatus that oarri~s out
° a radio aommuni.aation yvith the base station apparatus
aac:cording to the e.mbodirnerit above:
FIG. 3 is a block d~.agram to e~cpla3.n a desired signal
reception power memsurement method in the cammunicat~.on
terminal apparatus above;
FIG. i.s a block diagram to explain a method of
measuring signal-tc~-interference plus noise ratio in the
aommurticc'ttion term~.nal a~,~paratus above;
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FIG S is a diagram to explain a method of
signal-to-interference plus noise ratio in the
communication terminal apparatus above;
FIG.6 is a data frame configuration diagram used
in a communication by the base station apparatus of the
present invention;
FIG.7 is another data frame configuration diagram
used in a communication by the base station apparatus
of the present invention;
FIG. 8 is a sequence diagram between the base station
apparatus and'communication terminal apparatus of the
present invention;
FIG.9 is another sequence diagram between the base
station apparatus and communication terminal apparatus
of the present invention;
FIG. 10 is another sequence diagram between the base
station apparatus and communication terminal apparatus
of the present invention;
FIG.11 is another sequence diagram between the base
station apparatus and communication terminal apparatus
of the present invention;
FIG.12 is a flow chart to explain a transmission
rate switching method in the base station apparatus
according to the embodiment above;
FIG.13 is another flow chart to explain a
transmission rate switching method in the base station
apparatus according to the embodiment above;
FIG.14 is another flow chart to explain a
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transmission rate switching method in the base station
apparatus according to the embodiment above;
FIG.15 is another flow chart to explain a
transmission rate switching method in the base station
5 apparatus according to the embodiment above;
FIG.16 is a block diagram showing a configuration
of a base station apparatus according to Embodiment 2
of the present invention;
FIG.17 is a block diagram showing a configuration
of a communication terminal apparatus that carries out
a radio communication with the base station apparatus
according to the embodiment above;
FIG.18 is a block diagram to explain a method of
measuring desired signal reception power in the
communication terminal apparatus above;
FIG.19 is a block diagram to explain a method of
measuring signal-to-interference plus noise ratio in the
communication terminal apparatus above;.
FIG.20 is a flow chart to explain a method of
switching the transmission rate in the base station
apparatus according to the embodiment above;
FIG.21 is another flow chart to explain a method
of switching the transmission rate in the base station
apparatus according to the embodiment above;
FIG.22 is another flow chart to explain a method
of switching the transmission rate in the base station
apparatus according to the embodiment above;
FIG.23 is another flow chart to explain a method
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of switching the transmission rate i.n the base station
apparatus according to the embodiment above;
FIG.24 is another flow chart to explain a method
of switching the transmission rate in the base station
apparatus according to the embodiment above;
FIG.25 is another flow chart to explain a method
of switching the transmission rate an the base station
apparatus according to the embodiment above;
FIG.26 is another flow chart to explain a method
of switching the transmission rate in the base station
apparatus according to the embodiment above;
FIG.27 is another flow chart to explain a method
of switching the transmission rate in the base station
apparatus according to the embodiment above;
FIG.28 is a diagram to explain transmission rate
control between layers in the base station apparatus of
the present invention; and
FIG.29 is a flow chart to explain transmission rate
control between layers in the base station apparatus of
the present inverition .
Best Mode for Carrying out the Invention
With reference now to the attached drawings, the
embodiments of the present invention are explained in
detail below.
(Embodiment 1)
FIG.1 is a block diagram showing a configuration
of a base station apparatus according to Embodiment 1
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of the present invention . In this base station apparatus ,
a signal received from antenna 10I is sent to reception
RF circuit 103 via duplexer 102 to use a same antenna
for both transmission and reception. At reception RF
circuit 103, the reception signal is amplified and
converted to an intermediate frequency or a baseband
frequency.
The frequency-converted signal is demodulated by
demodulator 104. The demodulation result is sent to
separator 105 , where it is separated into reception data
and a signal for transmission rate switching control.
Transmission rate switching controller 106 sends
a transmission rate switching signal to transmission
frame generator 107 based on the received control signal.
The operation of the transmission rate switching control
circuit will be explained later.
Regarding transmission, the transmission data are
modulated by modulator 108 and sent to transmission RF
circuit I09. Transmission RF circhit 109 converts the
frequency of the= transmission data and then amp-lifies
it. This transmission signal is sent from antenna 101
,via duplexer 102.
FIG.2 is a block diagram showing a configuration
of a communication terminal apparatus that carries out
a radio communication with the base station apparatus
according to Embodiment 1 of the present invention.
A signal received from antenna 201 is sent to
reception RF circuit 203 via duplexer 202 to use a same
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antenna for both transmission and reception, where it
is amplified and converted to an intermediate frequency
or a baseband frequency. The frequency-converted
signal is demodulated by demodulator 204. At the same
time, the output signal of the reception RF circuit is
sent to reception quality measurement circuit 205 , where
the reception quality is measured.
This reception quality includes, for example,
receivedsignalstrength,desiredsignalreception power,
signal to interference ratio (SIR), Signal-to-
Interference plus Noise Ratio ( hereinaf ter abbreviated
as "SINR" ) . The received signal strength is obtained by
measuring the power of reception RF. The use of the
received signal strength makes the circuit configuration
simplest and allows the use in an environment free of
interference signals.
The reception power of a desired signal is measured
by multiplying. the reception signal by a known signal.
_ In this case, if an interference signal exists, using
the received signal strength alone would end up reporting
the reception power of the desirecZ signal and the
interference signal, and this would mean that the
reception power of a desired signal required by the
terminal might not always be reported. Therefore, in
order to measure and report the reception power of the
desired signal required by the terminal, it is desirable
to use SINR as the reception quality which is the most
reliable information as an index to determine an error
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rate characteristic.
A measurement circuit for the desired signal
reception power is shown in FIG.3. This circuit extracts
the known pattern component of the reception signal;
complex conjugate circuit 302 carries out a complex
conjugate operation on the known pattern held by the base
station; complex multiplication circuit 301 carries out
a complex multiplication on the known pattern component
of the reception signal and the known pattern subjected
to the complex conjugate operation and calculates the
position of the desired reception signal on the complex
plane ( position of the black circle in FIG . 5 ) ; and power
measurement circuit 303 measures the power from this
calculation result.
I5 On the other hand, an SINR measurement circuit is
shown in FIG.4. This circuit extracts the known pattern
component of the reception signal; complex conjugate
circuit 402 carries out a complex conjugate operation
on the known pattern held by the base station; complex
multiplication c~.rcuit 401 carries out a complex
multiplication on the known pattern component of the
reception signal and the known pattern subjected to the
complex conjugate operation and calculates the position
of the desired reception signal on the complex plane
(position of the black circle in FIG.5); and the power
is measuredfrom this calculation result. Furthermore,
interference signal -r noise power measurement circuit
404 measures interference signal power + noise power from
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a mean value of vector sum of squares between the position
of each reception signal (position of the white circle
in FIG. 5 ) and position of the desired reception signal
(position of the black circle in FIG. S). Furthermore,
5 desired power measurement circuit 403 measures the
desired power from the calculation result above. Then;
ratio calculation circuit 405 calculates the ratio
between the output of interference signal + noise power
measurement circuit 404 and the output of desired power
10 measurement circuit 403. SINR is calculated from this.
The reception quality measurement result
calculated in this way is sent to multiplexing circuit
206. Multiplexing circuit 206 assigns the transmission
data and reception quality measurement result to a
transmission slot. Modulation circuit 207 modulates
such transmission data and transmission RF circuit 208
converts the frequency and amplifies. This
transmission signal is sent from antenna 201 via duplexer
202.
Here, how the transmission rate switching.
information is reported from the communication terminal
apparatus to the base station apparatus is explained.
There are two types of reporting; reporting all the time
and reporting on an as-needed basis. Since the first
method performs reporting all the time, it can switch
the transmission rate with high precision but the amount
of communication increases.
In the case of voice communications, voice
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information (message) is often transmitted multiplexed
with control information in one slot as shown in ~IG.6.
Therefore, reporting all the time is possible in voice
communications or low-speed data communications.
In the latter method, only a small amount of
communication is required because reporting is performed
only when required. It is desirable to use this method
for packet communications to realize high-speed data
communications. In packet communications, ~ .
intermittent information is sent in. a short time. Thus,
as shown in FIG.7(a) and FIG.?(b), control information
is not multiplexed in a slot but a flag indicating whether
it is a message or control information is used. FIG.7(a)
shows a case where a flag is set to indicate a message.
FIG.7(b) shows a case where a flag is set to indicate
control information.
Then, the timing for switching the transmission
rate is explained. There are four methods of timing for
switching the transmission rate as shown below:
The first method is explained using FIG.8. -.While
w the transmission terminal apparatus is measuring the
yreception quality, there are moments the reception
quality deteriorates drastically. In a mobile
communication environment, in the case of non-line-
of-sight (non-LOS) communication called "shadowing",
for example, the received signal strength decreases
drastically by 10 dB or more. While monitoring such a
situation, reporting is made when the reception quality
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deteriorates drastically. Upon reception of this
reception quality report, the base station apparatus
switches the transmission rate. When the reception
quality improves , which is measured on the communication
terminal side periodically or by a demand from the base
station, the base station apparatus switches the
transmission rate to the original transmission rate .
The timing at which the reception quality deteriorates
or improves drastically can be detected by performing
threshold judgment on the reception quality such as
reception field density, for example.
Then, the second method is explained using FIG.9.
The base station apparatus measures the reception
quality. If the reception quality deteriorates
drastically, this can be determined as non-LOS
communication called °'shadowing." Shadowing is
determined by the position of the antenna of the
communication terminal apparatus and the antenna of the
. base station apparatus and not affected by differences
in the carrier fr~:quency. Therefore, in such a case, it
w is possible that the reception quality will also
v.deteriorate drastically in the communication terminal
apparatus. Thus, the base station apparatus sends a
request for reporting the reception quality to the
communication terminal apparatus. The communication
terminal apparatus measures the reception quality and
reports it to the base station apparatus. The base
station apparatus performs transmission rate switching
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control according to the reported reception quality.
When the reception quality improves , which is measured
on the communication terminal side periodically or by
a request from the base, the base station apparatus
switches the transmission rate to the original
transmission rate. The timing at which the reception
quality deteriorates or improves drastically can be
detected by performing threshold judgment on the
reception quality, for example, received signal
1Q strength.
Then, the third method is explained using FIG.10.
If there is an error in the message received, the
communication terminal apparatus issues a
retransmission request. The base station apparatus
sends a request for reporting the reception quality to
the communication terminal apparatus when the
communication terminal apparatus issues a
retransmission request. The communication terminal
apparatus measures the reception quality and reports it
to the base stat~.on apparatus. The base station
w apparatus performs transmission rate switching control
.,according to the reported reception quality. For
example, if the reported reception quality measured by
the communication terminal apparatus is lower than a
predetermined value, the base station apparatusswitches
the transmission rate. When the reception quality
improves, which is measured on the communication
terminal side periodically or by a demand from the base
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station, the base station apparatus switches the
transmission rate to the original transmission rate.
The timing at which the reception quality deteriorates
or improves drastically can be detected by perforfning
threshold judgment on the reception quality, for example.
received signal strength.
Then, the fourth method is explained using FIG.11.
The base station apparatus monitors the transmission
power of itself . The base station apparatus controls the
transmission power based on a transmission power control
signal sent from the communication terminal apparatus,
and if the quality of transmission from the base station
apparatus to the communication terminal apparatus
deteriorates, the communication terminal apparatus
requests an increase of transmission power. If this
request is judged to be excessive transmission power
taking into account tha amount of interference with
others, the base station apparatus performs transmission
rate switching control. Judgment of excessive
transmission powe r can be performed by threshold
judgment, for example. Moreover, if a predetermined
~., allowable amount of transmission power has been secured,
then the base station apparatus switches the
transmission rate to the original transmission rate.
This predetermined allowable amount of transmission
power is. determined appropriately according to the
amount of transmission rate control~_ed. For example, if
the transmission rate is reduced to 1 j2 , tha transmission
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rate is switched when at least an allowable amount of
3 d8 has been secured.
By the way, combining some of the 4 methods above
can eliminate delays in switching the transmission rate
5 and perform delicate control.
Thus, the reception quality measurement result of
the downlink signal transmitted from the base station
apparatus shown in FIG. 1 is measured by the communication
terminal apparatus in FIG.2 and reported to the base
10 station on the uplink. The base station switches the
transmission rate based on the reception quality
measured and received on the uplink by the transmission
terminal apparatus.
Here, the operation of the transmission rate
15 switching control circuit is explained in detail.
FIG.12 is a flow chart of the transmission rate switching
control circuit. In ST11, the base station apparatus
compares the reception quality measurement result
reported from the communication terminal apparatus with
threshold 1. He~e,.a case when SIR is used as the
reception quality is explained, but the same applies when
,the received signal strength, desired signal reception
power or SINR is used. This threshold 1 is 'set according
to the transmission rate, but in a. CDMA communication
system; it is set according to the spreading factor or
the number of multiplexing codes.
If the reception quality measurement result ( SIR)
is greater than threshold 1, the same transmission rate
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is used. If SIR is smaller than threshold 1, the channel
condition is determined to be bad and the transmission
rate is changed to a 1/2 transmissa.on rate (ST12).
Moreover, as shown in FIG.13, the base station
apparatus compares the reception quality measurement
result reported from the communication terminal
apparatus with threshold 1 ( ST21 ) and if SIR is greater
than threshold l, the same transmission rate is used:
If SIR is smaller than threshold 1, the transmission~rate
is switched to such a transmission rate that SIR is
greater than threshold 1 ( ST22 ) . In CDMA, the spreading
factor is switched. Thus, SIR exceeds threshold 1 and
more accurate control can be performed on varying
reception quality. This makes it possible to improve the
reception quality of the other end oicommunication even
if the condition of the communication path with the other
end of communication deteriorates drastically and reduce
the amount of interference with others because the target
reception quality is reduced and transmission power is
reduced. Therefc5re, it is possible to enhance the effect
of switching the transmission rate.
Moreover, as shown in FIG.14, the base station
apparatus compares the reception quality measurement
result reported from the communication terminal
apparatus with threshold 2 ( ST31 ) and if SIR is smaller
than threshold 2 , the same transmission rate is used and
if SIR is greater than threshold 2 , the channel condition
is determined to be good and the transmission rate is
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switched to a double transmission rate (1/2 spreading '
factor)(ST32). Here, threshold 2 corresponds to a
double transmission rate and is seat greater than
threshold Z. Thus, while the channel condition is good,
the transmission rate is increased to transmit as much
data as possible. That is, if the condition of the
communication path with the other end of communication
is good, faster transmission is possible while
maintaining the reception quality of the other end of
communication. However, since the transmission power
does not increase, interference with others does not
increase.
Moreover, as shown in FIG.15, threshold n is set
(ST41) and the base station apparatus compares the
reception quality measurement result reported from the
communicationterminalapparatuswith threshold n(ST42).
If SIR is smaller than threshold r~, threshold n is
switched to threshold n+1 corresponding to the next
fastest transmission rate ( ST43 ) . Tf SIR is greater than
threshold n, the: nth fastest transmission rate.
(spreading factor) is set (ST44). That is, the
transmission rate is switched to such a transmission rate
that SIR is set to a value between threshold n and
threshold n+1 corresponding to the two transmission
rates. Threshold n corresponds to the nth fastest
transmission rate and is greater than threshold n+1. In
this case, the fastest transmission is possible on
condition that the reception quality be satisfied. This
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allows more accurate control over the transmission rate
according to the channel condition.
Using such a method, it is possible ~to switch the
transmission rate of the base station according to .the
reception quality of the communication terminal
apparatus. This not only avoids the reception quality
of the other end of communication from continuing to be
bad but also reduces transmission power because the
target reception quality reduces, which reduces .
interference with others. Therefore, it is possible to
control the transmission power of the base station to
the communication terminal apparatus appropriately
without being affected by the environment of the
communication terminal apparatus and transmission
speed.
(Embodiment 2)
FIG.16 is a block diagram showing a configuration
of a base station apparatus accorduing to Embodiment 2
of the present invention.
In this bass station apparatus , a signal received
from antenna 101.is sent to reception RF circuit 103 via
duplexer 102 to use a same antenna for both transmission
and reception. At reception RF circuit 103, the
reception signal is amplified and converted to an
intermediate frequency or a baseband frequency.
The frequency-converted signal is demodulated by
demodulator 104. The demodulation result is sent to
separation circuit 105, where it is separated into
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reception data and transmission poraer control signal.
Transmission rate switching control circuit 106
sends a transmission rate switching signal to
transmission frame generator 107 based on the
transmission power control signal. The operation of the
transmission rate switching control circuit will be
explained later.
Regarding transmission, the transmission data are
modulated by modulation circuit 108 and sent to
transmission RF circuit 109. Transmission RF circuit
109 converts~fhe frequency of the transmission data.
This transmission signal is sent from antenna 101 via
duplexer 102.
FIG.17 is a block diagram showing a configuration
of a communication terminal apparatus that carries out
a radio communication with the base station apparatus
according to Embodiment 2 of the present invention.
A signal received from antenna 201 is sent to
reception RF circuit 203 via duplexer 202 to use a same
antenna for bothetransmission and reception, where it
is amplified and converted to an intermediate frequency
or a baseband frequency. The frequency-converted
signal is demodulated by demodulator 204. At the same
time, the output signal of the reception RF circuit is
sent to transmission power control value calculation
circuit 205, where the transmission power control signal
is determined.
This transmission power control signal includes,
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for example, received signal strength, desired signal
reception power, signal to interfererrce ratio ( SIR ) , and
signal-to-interference plus noise ratio. Moreover,
concerning the amount of information sent as a
5 transmission power signal, there are cases with 2 pieces
of information on whether to increase/decrease the
transmission power, 3 pieces of information on whether
to increase/maintain/decrease the transmission power or
4 or more pieces of information with more detailed
10 setting of the amount of control than the above cases.
First, fhe case where the control information
consists of 2 pieces of information is explained. If the
received signal strength is based, the power of reception
RF is measured. If the measured power is greater than
15 a threshold, a control signal is generated so that the
transmission power from the base station is reduced and
if the measured power is smaller than the threshold, the
control signal is created so that the transmission power
from the base station is increased. Such a method based
20 on the received signal strength has the simplest circuit
configuration . Furthermore , this method can be used in
,an environment where there is no interference signal.
If the desired signal reception power is based, the
reception signal is measured by multiplying the
reception signal by a known signal. If an interference
signal exists , using the received signal strength alone
would not mean that the reception power of the desired
signal arid that of the interference signal have been
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z1
reported. Therefore, it is necessary to measure and
report the reception power of the desired signal required
by the communication terminal apparatus. Thus, it is
desirable to use SINR as the reception quality, which
is the most reliable information as an index to determine
error rate characteristics.
The desired signal reception power measurement
circuit is shown in FIG.18. This cj.rcuit extracts the
known pattern component of the reception signal; complex
conjugate circuit 302 carries out a complex conjugate
operation on the known pattern held by the base station;
complex multiplication circuit 301 carries out a complex
multiplication and calculates the position of the
desired reception signal on the complex plane (position
of the black circle in FIG.5); and power measurement
circuit 303 measures the power based on this calculation
result . If the power measured by comparison circuit 1801
is greater than threshold 3, a control signal is
generated so that the transmission power from the base
station is reduced and if the measured power is smaller
than threshold 3 , the control signal is generated so that
the transmission power from the base station is
increased.
On the other hand, an SINK measurement circuit is
shown in FIG. 19. This circuit extracts the known pattern
component of the reception signal; complex conjugate
circuit 402 carries out a complex conjugate operation
on the known pattern held by the base station; complex
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multiplication circuit 40I carries out a complex
multiplication and calculates the position of the
desired reception signal on the complex plane (position
of the black circle in FIG.5) ; and the power is measured
based on this calculation result. Furthermore,
interference signal + noise power measurement circuit
404 measures interference signal power + noise power from
a mean value of vector sum o~ squares between the position
of each reception signal (position of the white circle
in FIG. 5 ) and position of the desired .reception signal
(position of 'the black circle in FICi.5) . Furthermore,
desired power measurement circuit 403 measures desired
power. Then, ratio calculation circuit 405 calculates
the ratio between the output of interference signal power
+ noise power measurement circuit 404 and the output of
desired power measurement circuit 403. If the power
ratio measured by comparison circuit 1901 is greater than
threshold 3, a control signal is generated so that the
transmission power from the base station is reduced and
if the measured dower ratio is smaller than threshold
3, a control signal is generated so that the transmission
vpower from the base station is increased.
Then, the case where the control information has
3 pieces of information, is explained. In the case of 3
pieces of information, threshold 3 and threshold 4 which
is greater than threshold 3 , are used as thresholds . If
the power ratio measured is smaller than threshold 3,
a control signal is generated so that the transmission
CA 02463375 2004-04-30
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power from the base station is increased. If the
measured power ratio is greater than threshold 3 and
smaller than threshold 4 , a control signal is generated
so that the transmission power from the base station is
retained. If the measured power ratio is greater than
threshold 4, a control signal is generated so that the
transmission power from the base station is reduced.
Moreover, if' the control information has 4 or more
pieces of information, the number of thresholds 'is set
to (number of control information pieces - 1) to
determine conf rol information divided into smaller
pieces through threshold judgment based on comparison
among a plurality of thresholds.
The transmission power control information
calculated in this way is sent to multiplexing circuit
206. Multiplexing circuit 206 assigns the transmission
data and transmission power control information to a
transmission slot. Modulation circuit 207 modulates
such transmission data and transmission RF circuit 208
converts the frequency and amplifies the transmission
data. This transmission signal is sent from antenna 201
.via duplexer 202.
Thus, the transmission power control signal based
on the reception quality of the downlink signal
transmitted from the base station apparatus shown in
FIG.16 is generated by the communication terminal
apparatus shown in FIG.17 and reported to the base
station apparatus on the uplink. The base station
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apparatus switches the transmission rate based on the
transmission power control signal measured by the
communicationterminalapparatus received onthe uplink.
Here, the operation of the transmission rate
switching control circuit is explained in detail.
FIG.20 is a flow chart showing transmission rate
switching control. The base station apparatus
estimates the reception quality by accumulating the
transmission power control information reported from the
communication terminal apparatus (ST51) and compares it
with threshold 1 (ST52). This threshold 1 is set
according to the transmission rate but in the CDMA
communication system, it is set according to the
spreading factor or the number of multiplexing codes.
If reception quality estimated value (SIR
estimated value ) is greater than threshold 1 , the channel
condition is determined to be good and the same
transmission rate is used. If the SIR estimated value
is smaller than threshold 1, the channel condition is
determined to b ~ bad and the transmission rate as
switched to a 1/2 transmission rate (X2 spreading
factor) (ST53) .
Thus, the transmission rate is switched based on
the channel estimation result, making it possible to
reduce interference with others. Furthermore, the use
of the transmission power control bit for channel
estimation can reduce the amount of information to be
sent from the other end of communication without the need
CA 02463375 2004-04-30
for special control information about transmission rate
control.
Furthermore, as shown in FIG.21, the base station
apparatus estimates the reception quality by
5 accumulating the transmission power control information
reported from the communication terminal apparatus
( ST61 ) and compares it with threshold I ( ST62 ) . . If the
SIR estimated value is greater than threshold I, the
channel condition is determined to be good and the .same
10 transmission rate is used. If the SIR estimated value
is smaller than threshold 1, the channel condition is
determined to be bad and SIR may be changed to such a
transmission rate that SIR is greater than threshold 1
(ST63). This allows more accurate control over varying
15 reception quality. That is , it is possible not only to
improve the reception quality of the other end of
communication even if the channel condition with the
other end of communication deteriorates drastically but
also to reduce the transmission power because the target
20 reception quality reduces, also reducing znterf~rence
with others. Therefore, it is possible to enhance the
effect of transmission rate switching.
As shown in FIG.22, the base station apparatus
estimates the reception quality by accumulating the
25 transmission power control information reported from the
communication terminal apparatus (ST71) and compares it
with threshold 2 ( ST72 ) . If the SIR estimated value is
smaller than threshold 2, the channel condition is
CA 02463375 2004-04-30
~6
determined to be bad and the same transmission rate is
used. If the SIR estimated value is greater than
threshold 2, the channel condition is determined to be
good and the transmission rate may be switched to a double
transmission rate (1/2 spreading factor) (ST73).
Threshold 2 corresponds to a double transmission rate
and is greater than threshold 1.
In this way, while the channel condition is good;
the transmission rate is increased to transmit as .much
IO data as possible. That is, if the channel condition with
the other end=of communication is good, faster
transmission is possiblewhilemaintainingthe reception
quality of the other end of communication. By the way,
since transmission power is not increased, interference
with others does not increase.
As shown in FIG.23, the base station apparatus
estimates (ST82) the reception quality by accumulating
the transmission power control information reported from
the communication terminal apparatus by setting
threshold n (STS.) and compares it with threshold n
'. (ST84). If the SIR estimated value is smaller than
threshold n, threshold n is changed to threshold n+I,
which corresponds to the next fastest transmission rate
(ST83). If the SIR estimated value is greater than
2S threshold n, the nth fastest transmission rate
(spreading factor) is set {ST85). That is, a
transmission rate is selected so that the SIR estimated
value is between threshold n and threshold n+I
CA 02463375 2004-04-30
27
corresponding to two transmission rates. Threshold n
corresponds to the nth fastest transmission rate and is
greater than threshold n+1. In this case, the fastest
transmission is possible on condition that the reception
quality be satisfied. This allows more accurate control
of transmission rate according to the channel condition.
Furthermore, the operation of smother transmission
rate switching control circuit is explained. As shown
in FIG.24, for example, the base station apparatus
determines the required transmission power based on the
transmission power control information reported from the
communication terminal apparatus. This transmission
power is compared with threshold 4 (ST91).
This threshold 4 is determined according to the
amount of interference with others generated by
increasing the limit value or transmission power of the
transmitter. Threshold 4 is also set according to the
transmission rate, but in the CDMA communication system
it is set according to the spreading' factor or the number
of multiplexing.~odes. That is, if transmission is
performed with X 16 spreading or X 256 spreading, there
is a X 16 difference in terms of sp~:eading factor and so
the threshold of transmission power at X 16 spreading is
16 times the threshold of transmission power at X256
spreading. The same applies to the number of
multiplexing codes.
If the transmission power is smaller than threshold
4, the same transmission rate is used. If the
CA 02463375 2004-04-30
28
transmission power is greater than threshold 4,
interference with others is determined to be great and
the transmission rate is switched to a 1/2 transmission
rate ( X 2 spreading factor ) ( ST92 ) . This allows the
optimal or fastest transmission on condition that
interference with others be within the allowable range.
Furthermore, as shown in FIG.2S, the base station
apparatus determines the required transmission power
based on the transmission power control information
reported from the communication terminal apparatus.
This transmission power is compared with threshold 4
(ST101) and if the transmission power is smaller than
- threshold 4 , the same transmission rate is used and if
the transmission power is greater than threshold 4,
interference with others is determined to be great and
a transmission rate (spreading facto=) is selected so
that the transmission power is smaller than threshold
4 (ST102). This can prevent an excessive amount of
interference from generating.
Furthermore, as shown in FIG.26; the base saation
apparatus determines the required transmission power
based on the transmission power control information
reported from the communication terminal apparatus.
This transmission power is compared with threshold 5
(ST111) and if the transmission power is greater than
threshold 5 , the same transmission rate is used and if
the transmission power is smaller than threshold 5,
interference with others is determined to be small and
CA 02463375 2004-04-30
29
the transmission rate may be switched to a double
transmission rate(1/2spreadingfactor)(ST112). Here,
threshold 5 corresponds to a double transmission rate
and is smaller than threshold 4.
Furthermore, as shown in FIG.27, threshold n is set
(ST121) and the base station apparatus compares the
transmission power based on the transmission power
control information reported from the communication
terminal apparatus with threshold n (ST123). If,the
transmission power i.s greater than threshold n,
threshold n is changed to threshold n+1, which
corresponds to the next fastest transmission rate
(ST122). If the transmission power is smaller than
threshold n, the nth fastest transmission rate
(spreading factor) is set (ST124). That is, a
transmission rate is selected so that the transmission
power is a value between threshold n and threshold n+1
corresponding to two transmission rates. Threshold n
corresponds to the nth fastest transmission rate and is
smaller than threshold n+1. In this case, the fastest
transmission is possible on condition that the amount
,of interference with others be controlled within a
ascertain range.
Furthermore, the base station sets transmission
power in various ways; transmitting with the
transmission power prior to switching every time the
transmission rate is switched, transmitting with the
transmission power prior to switching reduced by a
CA 02463375 2004-04-30
certain value and transmitting with the transmission
power prior to switching increased by a certain value.
The first method is valid to reliably improve the
communication quality for the terminal. In the
5 configuration of the present embodiment, a transmission
power control signal input to transmission rate
switching control circuit 106 can be sent to transmission
RF circuit I09. Transmission RF circuit 109 controls
increase/decrease of the transmission power based~on the
10 transmission power control signal.
The second method is a method of setting
transmission power by subtracting a certain value from
the transmission power when switching the transmission
rate. This is because the transmission power possibly
15 reaches a great value when the channel is improved for
the terminal, generating great interference with other
terminals . In this configuration of the embodiment, the
transmission power control signal input to transmission
rate switching control circuit 106 can be changed to such
20 a control signal=that the transmission power is reduced
by a certain value when switching the transmission rate .
Transmission RF circuit 109 controls increase/decrease
of the transmission power based on the transmission power
control signal. In this case, the transmission power
25 control accumulated value also needs to be reduced by
a certain value.
The third method is a method of increasing the
transmission power within the allowable range of
CA 02463375 2004-04-30
31
interference with others and is va7.id to improve the
communication quality. Tn the configuration of this
embodiment, the transmission power control signal input
to transmission rate switching control circuit 106 can
be changed to such a control signal that the transmission
power is increased by a certain value when the
transmission rate is switched. In this case, the
transmission power control accumulated value also needs
to be increased by a certain value.
For a certain value to decrease , in the CDMA system
for example,-transmission with power reduced by 3dB
allows one additional communication terminal apparatus
communicating with a similar spreading factor.
Furthermore, together with the transmission power
control information, the reception quality information
can also be reported from the communication terminal
apparatus using the method explained in Embodiment 1.
The method of reporting from the cornmunication terminal
apparatus to the base station apparatus and its timing
are the same as those in Embodiment 1.
Transmission rate switching control is normally
performed based on the accumulated value of transmission
power control information and if the reception quality
on the communication terminal apparatus side
deteriorates drastically, the reception quality
information is reported from the communication terminal
apparatus to the base station apparatus and the base
station apparatus performs transmission rate switching
CA 02463375 2004-04-30
32
control.
Furthermore, the base station apparatus sends a
request for measurement of the reception quality to the
communication terminal apparatus at the timing at which
thecommunicationterminal apparatusgenerates a request
for resend of ARQ control information, etc., and the
communication terminal apparatus measures the reception
quality and reports it to the base station apparatus.
The base station apparatus performs t=ansmissio~n.rate
switching based on the reception quality reported.
Then, tire control between layers in the
transmission rate control method described in
Embodiments 1 and 2 above is explained. FIG.28 is a
diagram to explain how the transmission rate is
controlled between layers.
In this control, as shown in FIG.28, allowable
transmission power (fallow) set in a radio resource
control ( RRC ) layer of layer 3 is sent to layer 3 ( physical
Iayer). In layer Z, average transmission power is
compared with aL~.owable transmission power (Pal:low).
Then, a message~(MPHY-STATITS) such as "Allowable
transmission power has been reached" or "Allowable
transmission power has been exceeded" or °'Average
transmission power is X dB below allowable transmission
power" is indicated from layer 1 to the medium access
control (MAC) layer of layer 2. The allowable
transmission power is appropriately set by the radio
resource control layer ( layer 3 ) according to the system
CA 02463375 2004-04-30
33
load such as the traffic condition.
Here, the message "Allowable transmission power
has been reached" or "Allowable transmission power has
been exceeded" indicates that the channel condition is
determined to be bad and it is necessary to lower the
transmission rate. On the other hand, the message
"Average transmission power is X dB below allowable
transmission power"indicatesthatthe channelcondition
is recovered and the transmission rate can be increased.
I0 Details of control. are explained using FIG.29.
Here, a case with the downlink is explained. First, the
radio resource control layer monitors the downlink
traffic condition and determines the initial
transmission rate on the downlink through negotiation
between the radio resource control layer (layer 3) and
medium access control layer (layer 2). Then, a
communication is started.
During a communication, in ST131, at least one frame
of average transmission power (Pave) is monitored in
layer 1. The transmission rate is controlled according
to this channel condition.
First, this average transmission power (Pave) is
compared with allowable transmission power (Pallowj and
the di fference between these two ( D = Fallow - Pave } is
obtained. Then, in ST132, it is determined whether
average transcriission power (Pave) exceeds allowable
transmission power (Fallow) or not. If average
transmission power (Pave) exceeds allowable
CA 02463375 2004-04-30
34
transmission power (fallow), a message "Allowable
transmission power has been reached" or "Allowable
transmission power has been exceeded" is indicated in
ST133.
According to this message, the transmission rate
is lowered in medium access control layer ( lays= 2 ) and
total ( average ) transmission power is reduced in Layer
1. This reduces interference with other communication
terminals.
If average transmission power (Pave) does not
exceed allowable transmission power (fallow), it is
determined whether the difference is at least a
predetermined value (Pstep) in ST134. This Pstep is a
power step corresponding to the difference between the
changed transmission rate and orig:inai transmission rate
when the transmission rate is lowered.
If difference (D) between average transmission
power (Pave) and allowable transmission power (fallow)
is smaller than predetermined value (Pstep), the same
transmission rate is used. If difference (D) between
average transmission power (Pave) and allowable
transmission power (fallow) is greater than
predetermined value ( Pstep ) , layer I indicates a message
"Average transmission power is X dB below allowable
transmission power" in STI35. Then, according to this
message , medium access control layer ( layer 2 ) increases
the transmission rate and layer I increases the total
transmission power within the range of XdB. This makes
CA 02463375 2004-04-30
it possible to ,immediately send the transmission signal
that has been buffered due to the lowered transmission
rate.
In FIG.29, it is only determined whether the
5 transmission rate is "increased° or '°maintained'° or
"lowered," but judgment is not limited to this; it is
also possible to freely set a command to make the
transmission rate variable beyond this limitation.
Then, a case where the aforementioned transmission
10 rate control is actually performed is explained.
According to.the existing method of changing the
transmission rate, the downlink is designated for burst
transmission and the uplink is designated for continuous
transmission. Therefore, the transmission rate is
15 changed according to this. That is, transmission power
itself is not changed on the downlink, and, for example,
transmission is performed only in the first half of a
frame, and on the uplink, transmission power is lowered
and transmission is performed through rate matching
20 without perforat~.ng the frame. 'rhe medium access
'. control layer (layer 2) selects the transmission rate
among a rate set specified by the radio resource control
layer ( layer 3 ) . At this time , the physical layer ( layer
1) creates and adds a word indicating the current
25 transmission rate as instructed by the medium access
control layer (layer 2).
Furthermore, when each base station performs the
transmission rate control above separately, negotiation
CA 02463375 2004-04-30
is required when diversity handover takes place. For
example, a method by which all base stations select a
specific transmission rate through negotiation in the
upper layer and another method by which no transmission
rate control is performed during diversity handover are
possible examples of this.
The explanation above describes the case where the
parameter monitored in layer 1 is transmission power:
but FER, SIR or interference power can also be cased as
IO the parameter monitored in layer I.
The explanation above describes the case where the
transmission rate control shown in FIG.29 is performed
on the downlink, but the transmission rate control shown
in FIG.29 can also be applied to the uplink.
Transmission rate control orr the downlink is used
to reduce interference with others but transmission rate
control on the uplink is not only used to reduce
interference with others but also used to achieve power
saving or when there are hardware restrictions.
Embodiments-1 and 2 above describe the apparatus
shown in FIG.I and FIG.I6 as the base station apparatus
.and the apparatus shown in FIG.2 and FIG.17 as the
communication terminal apparatus, but the present
invention is also applicable to the case where the
apparatus shown in FIG.I and FIG. I6 is the communication
terminal apparatus and the apparatus shown in FIG.2 and
FIG.17 is the base station apparatus.
Furthermore, Embodiments 1 and 2 describe the case
CA 02463375 2004-04-30
37
with a transmission.rate sat to X2 or 1/2, but is the
present. invention,, the transmission rate can also be set
to other magnifications according ito various conditions .
As explained above, in the radio commuhication~
apparatus and transmission rate~aontrol method.of the
present invention, the base station caa switch the'
transmission.rate of the base station based ori. a
transmission power control signal of the base statioa
that the terminal has determined by measuring th~'
~ reception quality'. This allows appropriate control :by
the base statv'on over transmission power :to the mobile
station without being affected by the environment of the
mobile station ,or transmission speed.
This application is based on the Japanese Patent
Publication No. 2000-49663.
,, .
Industrial Applicability . ~ '
The present invention is applicable to a base
station apparatus and communication terminal. apparatus
'1a a digital radio communication system.
