1. A wireless communication system comprising: a transmitter and a receiver, 5 wherein the receiver comprises: a signal-to-noise ratio (SNR) calculation unit which calculates a SNR of a baseband signal of a signal received from the transmitter; and an indication information generation unit which generates transmission strength indication information indicating transmit power of the transmitter based on a history of 10 the SNR calculated by the SNR calculation unit, and wherein the transmitter comprises: a transmission unit which controls the transmit power based on the SNR.

2. The wireless communication system according to claim 1, 15 wherein the receiver includes: an antenna which transmits and receives radio waves to and from the transmitter; a reception unit which converts the radio waves received by the antenna into a baseband signal; 20 a storage unit which stores past SNR and past transmission strength indication information; an SNR comparison unit which compares a current SNR and current transmission strength indication information to the past SNR and the past transmission strength indication information; and 25 an indication information generation unit which generates transmission strength 33 indication information indicating the transmit power of the transmitter based on a comparison result of the SNR comparison unit, wherein the transmitter includes: an indication information extraction unit which acquires the transmission 5 strength indication information generated by the receiver, and wherein the transmission unit controls the transmit power based on the transmission strength indication information input from the indication information extraction unit. 10 3. The wireless communication system according to claim 1 or 2, wherein the SNR calculation unit calculates the SNR based on a signal after a Fourier transform on the baseband signal.

4. The wireless communication system according to any one of claims 1 to 3, further 15 comprising: a demodulation unit which demodulates the baseband signal, wherein the SNR calculation unit calculates the SNR. based on a signal point error of a signal demodulated by the demodulation unit. 20 5. The wireless communication system according to any one of claims 1 to 4, further comprising: an output-of-transmitter determination unit which generates the transmission strength indication information based on a transmission output of the transmitter. 25 6. The wireless communication system according to any one of claims 1 to 5, further comprising: a transmission path information comparison unit which generates the transmission strength indication information based on variation in transmission path information. 5

7. A receiver comprising: an SNR calculation unit which calculates an SNR of a baseband signal of a signal received from a transmitter; and an indication information generation unit which generates transmission strength i 0 indication information indicating transmit power of the transmitter based on a history of the SNR calculated by the SNR calculation unit. 15 >tii Dated this 12"' day of December 2013 Of Anand and Anand Advocates Agent for the Applicant

2
DESCRIPTION
WIRELESS COMMUNICATION SYSTEM, RECEIVER
TECHNICAL FIELD
5 [0001]
The present invention relates to a wireless communication system and a receiver.
BACKGROUND ART
[0002]
10 When a transmission path characteristic (transmission path information) has
been degraded in a wireless communication device of the related art, automatic
transmitter power control (ATPC) may be used to further increase an output of a
transmitter than before the degradation. As disclosed in Patent Document 1, a wireless
communication device includes an output level detection timer which controls an output
15 level of a transmission unit in a control value set in a transmission side according to a
reception input level detected by a reception side and sets a first predetermined time in
which the transmission unit is allowed to be in an excessive control state, an output level
control value setting means which outputs a predetermined control value used to control
the output level, and an output level detection means which sets the control value to the
20 predetermined control value after the first predetermined time has elapsed.
Document of the prior art
[Patent Document]
[0003]
25 [Patent Document 1 ]
3
Japanese Unexamined Patent Application, First Publication No. 2004-266552
DISCLOSURE OF INVENTION
[Problems to be solved by the invention]
5 [0004]
Incidentally, because there is a distortion characteristic that distortion increases
when the transmitter increases transmit power, a desired to undesired signal (D/U) ratio
of a transmission signal increases. Here, the distortion characteristic of the transmitter
is also varied due to a plurality of other factors such as the number of transmission
10 frequencies, the temperature of the transmitter, and variation in a transmission circuit.
However, even when these factors overlap in the transmitter of the related art, it
is necessary to limit the output of the transmitter to a low level with a margin so that the
D/U ratio can be secured. That is, there is a problem in that the output of the transmitter
is limited to be low even when the output of the transmitter can be increased without
15 degrading the D/U ratio in the transmitter of the related art.
[0005]
The present invention has been made in view of the above-described points, and
provides a wireless communication system and a receiver capable of increasing a
transmitter's output without degrading the signal-to-noise ratio (SNR).
20 [Means for solving the problem]
[0006]
(1) The present invention has been made to solve the above-described problem.
According to an aspect of the present invention, there is provided a wireless
communication system including a transmitter and a receiver, wherein the receiver
25 includes: an SNR calculation unit which calculates an SNR of a baseband signal of a
4
signal received from the transmitter; and an indication information generation unit which
generates transmission strength indication information indicating transmit power of the
transmitter based on a history of the SNR calculated by the SNR calculation unit, and
wherein the transmitter includes: a transmission unit which controls the transmit power
5 based on the SNR.
[0007]
(2) According to the aspect of the present invention, in the above-described
wireless communication system, the receiver includes: an antenna which transmits and
receives radio waves to and from the transmitter; a reception unit which converts the
10 radio waves received by the antenna into a baseband signal; a storage unit which stores a
past SNR and past transmission strength indication information; an SNR comparison unit
which compares a current SNR and cuiTent transmission strength indication information
to the past SNR and the past transmission strength indication information; and an
indication information generation unit which generates transmission strength indication
15 information indicating the transmit power of the transmitter based on a comparison result
of the SNR comparison unit, the transmitter includes: an indication information
extraction unit which acquires the transmission strength indication information generated
by the receiver, and the transmission unit controls the transmit power based on the
transmission strength indication information input from the indication information
20 extraction unit.
[0008]
(3) According to the aspect of the present invention, in the above-described
wireless communication system, the SNR calculation unit calculates the SNR based on a
signal alter a Fourier transform on the baseband signal.
25 [0009]
5
(4) According to the aspect of the present invention, the above-described
wireless communication system further includes: a demodulation unit which demodulates
the baseband signal, wherein the SNR calculation unit calculates the SNR based on a
signal point error of a signal demodulated by the demodulation unit.
5 [0010]
(5) According to the aspect of the present invention, the above-described
wireless communication system further includes: an output-of-transmitter determination
unit which generates the transmission strength indication information based on a
transmission output of the transmitter.
10 [0011]
(6) According to the aspect of the present invention, the above-described
wireless communication system further includes: a transmission path information
comparison unit which generates the transmission strength indication information based
on variation in transmission path information.
15 [0012]
(7) According to an aspect of the present invention, there is provided a receiver
including: an SNR calculation unit which calculates an SNR of a baseband signal of a
signal received from a transmitter; and an indication information generation unit which
generates transmission strength indication information indicating transmit power of the
20 transmitter based on a history of the SNR calculated by the SNR calculation unit.
[Effect of the Invention]
[0013]
According to the present invention, an output of a transmitter can be increased
without degrading an SNR.
25
6
BRIEF DESCRIPTION OF DRAWINGS
[0014]
FIG. I is a block diagram of a wireless communication system according to a
first embodiment of the present invention.
5 FIG. 2 is a flowchart illustrating an example of an operation according to the
first embodiment of the present invenfion.
FIG. 3 is a flowchart illustrating an example of an operation according to the
first embodiment of the present invention.
FIG. 4 is a flowchart illustrating an example of an operation according to the
10 first embodiment of the present invention.
FIG. 5 is a block diagram of a wireless communication system according to a
second embodiment of the present invention.
FIG. 6 is a flowchart illustrating an example of an operation according to the
second embodiment of the present invention.
15 FIG. 7 is a block diagram of a wireless communicafion system according to a
third embodiment of the present invention.
FIG. 8 is a flowchart illustrating an example of an operation according to the
third embodiment of the present invention.
FIG. 9 is a flowchart illustrafing an example of an operation according to the
20 third embodiment of the present invenfion.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0015]
(First embodiment)
25 Hereinafter, the first embodiment oi' the present invention will be described in
7
detail with reference to the drawings.
FIG. 1 is a block diagram illustrating a wireless communication system la
according to the first embodiment of the present invention.
The wireless communication system la includes a first wireless station 100 and
5 a second wireless station 200.
The first wireless station 100 includes a modulation unit 1, a transmission unit 2,
an antenna 3, a reception unit 12, a demodulation unit 13, and an ATPC indication
information extraction unit 14.
[0016]
10 The modulation unit 1 modulates input transmission information and outputs a
modulated modulation signal to the transmission unit 2.
The transmission unit 2 converts the modulation signal input from the
modulation unit 1 into a radio frequency (RF) signal of strength indicated by ATPC
indication information input from an ATPC indication information extraction unit 14.
15 Here, the ATPC indication information is information indicating the strength of the RF
signal output by the transmission unit 2. The transmission unit 2 outputs the RF signal
obtained by the conversion to the antenna 3.
The antenna 3 transmits the RF signal input from the transmission unit 2 to the
second wireless station 200. The antenna 3 receives the RF signal transmitted from the
20 wireless station 200, and outputs the received RF signal to the reception unit 12.
[0017]
The reception unit 12 converts the RF signal input from the antenna 3 into a
baseband signal, and outputs the baseband signal obtained by the conversion to the
demodulation unit 13.
25 The demodulation unit 13 demodulates the baseband signal input from tlic
8
reception unit 12 into transmission information. The demodulation unit 13 extracts
control information from the transmission information and outputs the extracted control
information to the ATPC indication information extraction unit 14.
The ATPC indication information extraction unit 14 extracts the ATPC
5 indication information from the control information input from the demodulation unit 13,
and outputs the extracted ATPC indication information to the transmission unit 2.
[0018]
The second wireless station 200 includes an antenna 4, a reception unit 5, a
demodulation unit 6, a D/U calculation unit 7, a D/U comparison unit 8, an ATPC
10 indication information creation unit 9, a modulation unit 10, a transmission unit 11, and a
past D/U storage unit 81.
[0019]
The antenna 4 transmits the RF signal input from the transmission unit 11 to the
first wireless station 100. The antenna 4 receives the RF signal transmitted from the
15 second wireless station 200, and outputs the received RF signal to the reception unit 5.
The reception unit 5 converts the RF signal input from the antenna 4 into a
baseband signal, and outputs the baseband signal obtained by the conversion to the
demodulation unit 6 and the D/U calculation unit 7. The reception unit 5 measures the
strength of the RF signal received by the antenna 4, and outputs a received electric field
20 strength signal indicating the measured strength to the ATPC indication information
creation unit 9.
The demodulation unit 6 demodulates the baseband signal input from the
reception unit 5 into transmission information. The demodulation unit 6 outputs the
transmission information obtained by the demodulation.
25 [0020]
9
The D/U calculation unit 7 (SNR calculation unit) performs a fast Fourier
transform (FFT) process on the baseband signal input from the reception unit 5. The
D/U calculation unit 7 calculates each of powers of baseband signals of desired and
undesired bands of a signal, and calculates a D/U ratio (SNR) which is the ratio
5 therebetween. The D/U calculation unit 7 outputs D/U ratio information indicating the
calculated D/U ratio to the D/U comparison unit 8.
[0021]
The D/U comparison unit 8 (SNR comparison unit) receives the D/U ratio
information from the D/U calculation unit 7. The D/U comparison unit 8 receives the
10 ATPC indication information from the ATPC indication information creation unit 9.
The D/U comparison unit 8 reads past D/U ratio information and past
output-of-transmitter information recorded on the past D/U storage unit 81. The D/U
comparison unit 8 generates output-of-transmitter limitation information for limiting the
strength of an RF signal to be transmitted from the transmission unit 2 of the first
15 wireless station 100 by comparing the latest D/U ratio and the latest D/U ratio indicated
by the ATPC indication information to a past D/U ratio indicated by past D/U ratio
information and a past output of the transmitter indicated by past output-of-transmitter
information. That is, the D/U calculation unit 7 generates the output-of-transmitter
limitation information based on a D/U ratio histor)' and an output-of-transmitter history.
20 The D/U comparison unit 8 outputs the D/U ratio information and the generated
output-of-transmitter limitation information to the ATPC indication information creation
unit 9. In addition, the D/U comparison unit 8 causes the latest D/U ratio information
and the latest output-of-transmitter information to be stored in the past D/U storage unit
81.
25 |:0022|
10
The ATPC indication information creation unit (indication information
generation unit) 9 generates ATPC indication information based on the received electric
field strength information input from the reception unit 5 and the output-of-transmitter
limitation information input from the D/U comparison unit 8. The ATPC indication
5 information creation unit 9 outputs the generated ATPC indication information to the
modulation unit 10 and the D/U comparison unit 8.
The modulation unit 10 modulates the input transmission information and the
ATPC indication information input from the ATPC indication information creation unit 9
and outputs a modulated modulation signal to the transmission unit 11.
10 The transmission unit 11 converts the modulation signal input from the
modulation unit 10 into an RF signal, and outputs the RF signal to the antenna 4.
The past D/U storage unit 81 stores a table in which the past D/U ratio
information and the output-of-transmitter information indicating the output of the
transmitter are associated. When the number of records of the stored table has exceeded
15 a predetermined number, the past D/U storage unit 81 deletes old records corresponding
to an excess of records beyond the predetermined number, and holds a predetermined
number of records.
[0023]
FIG. 2 is a flowchart illustrating an example of an operation according to the
20 first embodiment.
(Steps 10)
The antenna 3 transmits an RF signal input from the transmission unit 2 to the
second wireless station 200. Thereafter, the process proceeds to step S11.
(Step SI 1)
25 The antenna 4 receives the RF signal transmitted from the first wireless station
100. The antenna 4 outputs the received RF signal to the reception unit 5. Thereafter,
the process proceeds to step SI2.
(Step SI2)
The reception unit 5 converts the RF signal input from the antenna 4 into a
5 baseband signal. The reception unit 5 measures the strength of the RF signal received
by the antenna 4. Thereafter, the process proceeds to step 813.
[0024]
(Step 813)
The D/U calculation unit 7 generates a baseband signal (referred to as a section
10 baseband signal) of a predetermined fixed time from the baseband signal obtained by the
conversion in step 812. The D/U calculation unit 7 performs an FFT process on the
section baseband signal, and calculates 1(a)) which is a signal amplitude in a frequency
domain of the section baseband signal.
The D/U calculation unit 7 calculates signal strengths of baseband signals of
15 desired and undesired bands from I((JO) indicating the signal amplitude in the frequency
domain obtained from a result of the FFT process. The D/U calculation unit 7
calculates a D/U ratio based on a difference between the calculated signal strengths.
Specifically, assuming that a center frequency of the desired band is (OQ and a
width of the desired band is Aco, the D/U calculation unit 7 calculates signal strength D of
20 a baseband signal of the desired band at co satisfying ©o - 1/2Aco < co < o)o + 1/2A©
according to Equation (1).
[0025]
12
J'fi)0+l/2Ari>. .7
\I{m)\d0 ... (1)
[0026]
Also, Ao3 is a predetermined value. In addition, the D/U calculation unit 7
calculates the signal strength U of the baseband signal of the undesired band according to
5 Equation (2).
[0027]
*fi>Q-i/2Ai&. 2 r*
[0028]
Here, a is a lower frequency when the signal strength of the undesired band is
10 calculated. The D/U calculation unit 7 pre-stores a satisfying 0 < a < coo + l/2Aa), In
addition, b is an upper frequency when the signal strength of the undesired band is
calculated. The D/U calculation unit 7 pre-stores b satisfying ©0 + 1/2A© < p.
The D/U calculation unit 7 outputs D/U ratio information indicating a D/U ratio,
which is a value obtained by dividing D shown in Equation (1) by U shown in Equation
15 (2), to the D/U comparison unit 8. Thereafter, the process proceeds to step S14.
(Step SI4)
The D/U comparison unit 8 generates output-of-transmitter limitation
information based on an output-of-transmitter history, a D/U ratio history, a current
output of the transmitter, and a current D/U ratio. Also, details of step 814 will be
20 described later.
(Step SI5)
Based on output-of-transmilter limitation information transmitted from the
13
second wireless station 200, the ATPC indication information extraction unit 14 controls
the strength of the RF signal output by the transmission unit 2. Also, details of step S15
will be described later.
[0029]
5 FIG. 3 is a flowchart illustrating an example of an operation according to the
first embodiment. This flowchart is a detailed description of the process of step S14 in
FIG. 2.
(StepSHl)
The D/U comparison unit 8 receives ATPC indication information from the
10 ATPC indication information creation unit 9, and extracts a record of an output of the
transmitter higher than a current output of the transmitter indicated by the ATPC
indication information from the table stored by the past D/U storage unit 81. The D/U
comparison unit 8 calculates a value d(D/U) obtained by subtracting a current D/U ratio
indicated by the current D/U ratio information input from the D/U calculation unit 7 from
15 the highest ratio of past D/U ratios included in respective extracted records. The D/U
comparison unit 8 writes the current output of the transmitter and the current D/U ratio to
the past D/U storage unit 81. Thereafter, the process proceeds to step S142.
[0030]
(Step SI42)
20 The D/U comparison unit 8 determines whether d(D/U) calculated in step S14 is
less than 0. When it is determined that d(D/U) is less than 0 (Yes), the process proceeds
to step SI44. When it is determined that d(D/u) is greater than or equal to 0 (No), the
process proceeds to step SI43.
(Step SI43)
25 The D/U comparison unit 8 generates output-of-transmitler limitation
14
information which does not limit an increase in power of the transmitter of the
transmission unit 2. Thereafter, the process proceeds to a start process of FIG. 4.
(Step SI44)
The D/IJ comparison unit 8 generates output-of-transmitter limitation
5 information to decrease the power of the transmitter of the transmission unit 2.
Thereafter, the process proceeds to the start process of FIG. 4.
[0031]
FIG. 4 is a flowchart illustrating an example of an operation according to the
first embodiment. This flowchart is a detailed description of the process of step S15 in
10 FIG. 2.
(StepSISl)
The ATPC indication information creation unit 9 outputs ATPC indication
information to the modulation unit 10 based on the output-of-transmitter limitation
information generated in step SI43 and the strength (received electric field strength) of
15 the RF signal measured in step S12.
Specifically, when the received electric field strength is less than a
predetermined lower limit threshold value of reception strength, the ATPC indication
information creation unit 9 generates ATPC indication information indicating a value, for
example, which is 1% higher than the cuiTcnt power of the transmitter of the
20 transmission unit 2. When the received electric field strength is greater than a
predetermined upper limit threshold value of the reception strength, the ATPC indication
information creation unit 9 generates ATPC indication information indicating a value, for
example, which is 1% lower than the current power of the transmitter of the transmission
unit 2.
25 The A'l'PC indication information creation unit 9 generates Al'PC indication
15
information based on the output-of-transmitter limitation information generated in step
SI 44 and the strength (received electric field strength) of the RF signal measured in step
SI 2.
Specifically, when the received electric field strength is greater than the
5 predetermined upper limit threshold value of the reception strength, the ATPC indication
informafion creation unit 9 generates ATPC indication information indicafing a value, for
example, which is 1% lower than the current power of the transmitter of the transmission
unit 2. When the received electric field strength is less than the predetermined upper
limit threshold value of the reception strength, the ATPC indication information to
10 maintain the current power of the transmission unit 2 is generated. Thereafter, the
process proceeds to step SI52.
[0032]
(Step SI52)
The modulation unit 10 modulates the input transmission information and the
15 ATPC indication information generated in step S151 after superimposing the
transmission information and the ATPC indication information, and generates a
modulation signal. Thereafter, the process proceeds to step SI53.
(Step SI53)
The transmission unit 11 converts the modulation signal generated in step SI52
20 into an RF signal, and outputs the RF signal to the antenna 4. Thereafter, the process
proceeds to step SI 54.
(Step SI54)
The antemia 4 transmits the RF signal to the second wireless station 200.
Thereafter, tlie process proceeds to step SI 55.
25 [0033]
16
(Step SI55)
The antenna 3 receives the RF signal transmitted from the first wireless station
100, and outputs the received RF signal to the reception unit 12. Thereafter, the process
proceeds to step SI56.
5 (Step 8156)
The reception unit 12 converts the RF signal input in step SI 55 into a baseband
signal. Thereafter, the process proceeds to step S157.
(Step SI57)
The demodulation unit 13 demodulates the baseband signal obtained by the
10 conversion in step SI56 into transmission information. The demodulation unit 13
extracts control information from the transmission information. Thereafter, the process
proceeds to step SI58.
(Step SI58)
The ATPC indication information extraction unit 14 extracts ATPC indication
15 information from the control information extracted in step S157. Thereafter, the process
proceeds to step SI59.
(Step SI59)
The transmission unit 2 converts the modulation signal input from the
modulation unit 1 into an RF signal with strength indicated by the ATPC indication
20 information extracted in step SI58, and outputs the RF signal to the antenna 3.
Thereafter, the process proceeds to an end process.
[0034]
In this manner, according to the first embodiment, in the wireless
communication system including the first wireless station 100 and the second wireless
25 station 200, the second wireless station 200 includes the D/U calculation unit 7 which
17
calculates a D/U ratio of a baseband signal of a signal received from the first wireless
station 100 and the ATPC indication information creation unit 9 which generates
transmission strength indicafion information indicating transmit power of the first
wireless station 100 based on a history of the D/U ratio calculated by the D/U calculation
5 unit 7, and the first wireless stafion 100 includes the transmission unit 2 which controls
the transmit power based on the SNR.
Thereby, in the first embodiment of the present invention, it is possible to vary
an output of the transmitter from the D/U ratio estimated according to a received signal,
and perform communication using a maximum output of the transmitter capable of being
10 implemented without degrading a D/U ratio of a signal according to a state of a wireless
communication path.
In addition, because the D/U ratio is calculated in a receiver side in the first
embodiment, the system can be configured at a lower cost compared to a wireless
communication device of the related art having a circuit which calcvilates the D/U ratio in
15 a transmitter side.
[0035]
(Second embodiment)
Hereinafter, the second embodiment of the present invention will be described in
detail with reference to the drawings.
20 FIG. 5 is a block diagram illustrating a wireless communication system 1 b
according to the second embodiment of the present invention. The wireless
communication system lb (FIG. 5) according to the second embodiment includes the first
wireless station 100 and a second wireless station 200a.
When the wireless communication system lb according to the second
25 embodiment and the wireless communication system la (1*IG. 1) according to the first
18
embodiment are compared, a reception unit 5a, a demodulation unit 6a, and a D/U
calculation unit 7a are different. However, functions provided in the other components
are the same as in the first embodiment. A description of the same functions as in the
first embodiment is omitted here.
5 [0036]
The reception unit 5a converts an RF signal input from the antenna 4 into a
baseband signal, and outputs the baseband signal obtained by the conversion to the
demodulafion unit 6a. The reception unit 5a measures the strength of the RF signal
received by the antenna 4, and outputs a received electric field strength signal indicating
10 the measured strength to the ATPC indication information creation unit 9.
The demodulation unit 6a demodulates the baseband signal input from the
reception unit 5a into transmission information. The demodulation unit 6a outputs
signal point error information indicating an error (signal point error) in a distance
between a signal point actually obtained by demodulafing the baseband signal on a signal
15 space diagram and an original signal point to the D/U calculation unit 7a. The
demodulation unit 6a outputs the demodulated transmission information.
The D/U calculafion unit 7a calculates a D/U ratio based on a magnitude of the
signal point error indicated by the signal point error information input from the
demodulation unit 6a. Specifically, a table indicating a relationship between a signal
20 point error and a D/U ratio actually measured in advance is stored in the D/U calculation
unit 7a, and a D/U ratio corresponding to the signal point error input from the
demodulation unit 6a is extracted.
[0037]
FIG. 6 is a flowchart illustrating an example of an operation according to the
25 second embodiment.
19
In the second embodiment, the process proceeds to step S20 after the same
processes as steps SIO and Sll of the i^irst embodiment illustrated in FIG. 2 are
performed.
(Step S20)
5 The reception unit 5a converts the RF signal input from the antenna 4 into a
baseband signal. The reception unit 5a measures a received electric field strength signal
indicating the strength of the RF signal received by the antenna 4. Thereafter, the
process proceeds to step S21.
(Step S21)
10 The demodulation unit 6a demodulates the baseband signal obtained by the
conversion in step S20 into transmission information. The demodulation unit 6a
generates signal point error information indicating an error (signal point error) in a
distance between a signal point obtained by the demodulation and a logical signal point.
The demodulation unit 6a outputs the transmission information obtained by the
15 demodulation. Thereafter, the process proceeds to step S22.
[0038]
(Step S22)
The D/U calculation unit 7a calculates the D/U ratio based on a magnitude of the
signal point error indicated by the signal point eiTor information generated in step S21.
20 Specifically, a table indicating a relationship between a signal point error and a D/U ratio
actually measured in advance is stored in the D/U calculation unit 7a, and a D/U ratio
corresponding to the signal point error generated in step S21 is read from the table.
Thereafter, the process proceeds to step S23.
The respective processes of steps S23 and S24 arc similar to those of steps S14
25 and S15 in the first embodiment.
20
[0039]
In this manner, according to the second embodiment, a D/U ratio is calculated
from the signal point eiTor calculated by the demodulation unit 6a. Thereby, it is
possible to calculate the D/U ratio in a small calculation amount compared to when the
5 D/U ratio is calculated using frequency conversion such as FFT.
Although the D/U ratio has been calculated using the table indicating the
relationship between a signal point error and a D/U ratio actually measured in advance in
the second embodiment, an equation indicating the relationship between the signal point
error and the D/U ratio may be stored in the D/U calculation unit 7a and the D/U ratio
10 may be calculated by substituting the signal point error input from the demodulation unit
6a into the equation.
[0040]
(Third embodiment)
Hereinafter, the third embodiment of the present invention will be described in
15 detail with reference to the drawings.
The third embodiment is different from the first and second embodiments in that
output-of-transmitter information and transmission path information are used in addition
to the D/U ratio when an output-of-transmitter limitation signal is generated.
Here, the generation of the output-of-transmitter limitation signal using the
20 output-of-transmitter information and the generation of the output-of-transmitter
Hmitation signal using the transmission path information will be described.
[0041]
The generation of the output-of-transmitter Hmitation signal using the
output-oJ-lransmitter information will be described. In the wireless station device,
25 variation occurs in the distortion characteristics due to a temperature, an individual
21
difference of the wireless station device, or the like. Here, a wireless device having a
worst distortion characteristic which is assumed to occur in the wireless station device is
considered. In this wireless device, there is a threshold value a of an output of the
transmitter which is a maximum output of the transmitter at which the distortion
5 characteristic does not deteriorate anymore even when it is supplied. The
output-of-transmitter determination unit 15 to be described later generates an
output-of-transmitter limitation signal which does not limit an increase in power because
the distortion characteristics do not directly deteriorate according to an increase in an
output of the transmitter if the current output of the transmitter is less than a. On the
10 other hand, because the distortion characteristic further deteriorates with an increase in an
output of the transmitter if the current output of the transmitter is greater than a, it is
difficult to directly increase power, hi this case, when the output of the transmitter is
changed, the output-of-transmitter determination unit 15 causes the D/U comparison unit
8b to make a further determination using the D/U ratio.
15 [0042]
The generation of the output-of-transmitter limitation signal using the
transmission path information will be described. The reception unit 5b includes a
function of compensating for variation in the transmission path characteristics
(transmission path information). A maximum value of variation in the transmission
20 path information capable of being compensated for by the reception unit 5b is assumed to
be a threshold value p. If the variation in the transmission path information is less than
p and the variation in the transmission path information is in a range in which
compensation by the reception unit 5b is possible when the D/U ratio has deteriorated, it
is possible to determine that the increase in the output of the transmitter is the cause oJ'
22
deterioration in the transmission path information. In this case, the transmission path
information comparison unit 17 to be described later outputs the output-of-transmitter
limitation signal to decrease an output of the transmitter. On the other hand, in a
situation in which the variation in the transmission path information is greater than p and
5 it is difficult for the reception unit 5b to compensate for the variation in the transmission
path information, it is difficult to determine whether the D/U ratio has deteriorated due to
an increase in the output of the transmitter or the D/U ratio has deteriorated due to
variation in the transmission path information. In this case, the transmission path
information comparison unit 17 generates the output-of-transmitter limitation signal to
10 maintain the current output of the transmitter.
[0043]
FIG. 7 is a block diagram illustrating a wireless communication system Ic
according to a third embodiment of the present invention. The wireless communication
system Ic (FIG. 5) according to the third embodiment includes the first wireless station
15 100 and a second wireless station 200b.
When the wireless communication system I c according to the third embodiment
and the wireless communication system la (FIG. 1) according to the first embodiment are
compared, a reception unit 5b, an output-of-transmitter determination unit 15, a D/U
comparison unit 8b, a transmission path information comparison unit 17, an ATPC
20 indication information creation unit 9b, and a past D/U storage unit 81b are different.
However, functions provided in the other components are the same as in the first
embodiment. Descriptions of the same functions as in the first embodiment are omitted
here.
[0044]
25 The reception unit 5b converts an RF signal input from the antenna 4 inlo a
23
baseband signal, and outputs the baseband signal obtained by the conversion to the
demodulation unit 6 and the D/U calculation unit 7. The reception unit 5b outputs a
received electric field strength signal indicating the strength of the RF signal received by
the antenna 4 to the ATPC indication information creation unit 9b. The reception unit
5 5b generates fading state information which is transmission path information based on a
tap coefficient of a transversal equalizer to be used to compensate for transmission path
loss in a process of converting the RF signal into a baseband signal. The fading state
information is represented by a sum of tap coefficients. In the third embodiment,
transmission path quality is indicated to be good if a value indicated by the transmission
10 path information is large and indicated to be bad if the value indicated by the
transmission path information is small. The reception unit 5b outputs the transmission
path information to the transmission path information comparison unit 17.
[0045]
The output-of-transmitter determination unit 15 receives the ATPC indication
15 information from the ATPC indication information creation unit 9b. The
output-of-transmitter determination unit 15 compares the above-described predetermined
threshold value a to a current output of the transmitter indicated by the ATPC indication
information. When the current output of the transmitter is less than the threshold value
a, output-of-transmitter limitation information which does not limit an increase in power
20 is output to the ATPC indication information creation unit 9b. When the current output
of the transmitter is greater than the threshold value a, D/U ratio-power comparison
signals for comparing current and past D/U ratios and current and past transmit powers
are output to the D/U comparison unit 8b.
[0046]
25 The D/U comparison unit 8b reads the past D/U ratio and the past output of the
24
transmitter from the past D/U storage unit 81b. Upon determining that the current
output of the transmitter input from the ATPC indication information creation unit 9b is
greater than the past output of the transmitter and the current D/U ratio indicated by the
ATPC indication information input from the D/U calculation unit 7 is greater than the
5 past D/U ratio, the D/U comparison unit 8b outputs output-of-transmitter limitation
information, which does not limit an increase in power, to the ATPC indication
information creation unit 9b. Upon determining that the current output of the
transmitter is greater than the past output of the transmitter and the current D/U ratio is
less than the past D/U ratio, the D/U comparison unit 8b outputs a transmission path
10 determination signal for determining variation in transmission path information to the
transmission path information comparison unit 17.
[0047]
When the transmission path determination signal is input from the D/U
comparison unit 8b, the transmission path information comparison unit 17 performs the
15 following operation. The transmission path information comparison unit 17 receives
transmission path information from the reception unit 5b, The transmission path
information comparison unit 17 reads the past transmission path information from the
past D/U storage unit 81b. The transmission path information comparison unit 17
calculates a transmission difference which is the difference between the current
20 transmission path information and the past transmission path information, and outputs the
output-of-transmitter limitation signal to increase the output of the transmitter to the
ATPC indication information creation unit 9b when the transmission difference is less
than the predetermined threshold value p. When the transmission difference is greater
than the predetermined threshold value (1 the output-of-transmitter limitation signal to
25 maintain the current output of the transmitter is output to the AfPC indication
25
information creation unit 9b.
[0048]
The ATPC indication information creation unit 9b receives received electric field
strength information from the reception unit 5b. The ATPC indication information
5 creation unit 9b receives and outputs the output-of-transmitter limitation information
from the output-of-transmitter determination unit 15. The ATPC indication information
creation unit 22 receives and outputs the output-of-transmitter limitation information
from the D/U comparison unit 8b. The ATPC indication information creation unit 9b
receives the output-of-transmitter limitation infoimation from the transmission path
10 information comparison unit 17. Based on the input output-of-transmitter limitation
information and received electric lield strength information, the ATPC indication
information creation unit 9b generates ATPC indication information, and outputs the
generated ATPC indication information to the modulation unit 10, the
output-of-transmitter determination unit 15, and the D/U comparison unit 8b.
15 [0049]
The past D/U storage unit 81b stores a table in which a past D/U ratio, a past
output of the transmitter, and past transmission path information are associated. When
the number of records of the stored table has exceeded a predetermined number, the past
D/U storage unit 81b deletes old records corresponding to an excess of records beyond
20 the predetermined number, and holds a predetermined number of records.
[0050]
FIG. 8 is a flowchart illustrating an example of an operation according to the
third embodiment of the present invention. In the third embodiment, the process
proceeds to step S30 after steps SIO and SI 1 of the first embodiment illustrated in I'lC). 2.
25 (Step S30)
26
The reception unit 5b converts an RF signal input from the antenna 4 into a
baseband signal. The reception unit 5b measures the strength of the RF signal received
by the antenna 4 (received electric field strength). The reception unit 5b generates
fading state information (transmission path information) indicated by a sum of tap
5 coefficients based on tap coefficients of a transversal equalizer to be used to compensate
for transmission path loss in a process of converting the RF signal into a baseband signal.
Thereafter, the process proceeds to step S31.
Because the respective processes of steps S31 and S33 are similar to those of
steps S13 and SI 5 (see FIG. 2) in the first embodiment, description thereof is omitted.
10 The process of step S32 will be described later in detail using FIG. 9.
[0051]
FIG. 9 is a flowchart illustrating an example of an operation according to the
third embodiment of the present invention.
(StepS321)
15 The output-of-transmitter determination unit 15 determines whether a current
output of the transmitter indicated by the ATPC indication information generated in step
S328 or S329 is greater than the predetermined threshold value a. When it is
determined that the current output of the transmitter is greater than the threshold value a
(Yes), D/U ratio-power comparison signals used to compare current and past D/U ratios
20 and current and past powers of the transmitter are output to the D/U comparison unit 8b.
Thereafter, the process proceeds to step S322. When it is determined that the current
output of the transmitter is less than the threshold value a (No), the process proceeds to
step S326.
[0052]
25 (Step S322)
27
The D/U comparison unit 8b receives the D/U ratio-power comparison signals
from the output-of-transmitter determination unit 15 and performs the following
operation. The D/U comparison unit 8b reads the past output-of-transmitter information
from the past D/U storage unit 81 b. The D/U comparison unit 8b calculates a value AP
5 obtained by subtracting the past output of the transmitter indicated by the past
output-of-transmitter information from the current output of the transmitter indicated by
generated ATPC indication information in step S328 or S329.
The D/U comparison unit 8b reads the past D/U ratio information from the past
D/U storage unit 81b. A value A(D/U) obtained by subtracting the past output of the
10 transmitter indicated by the past D/U ratio information from the current output of the
transmitter indicated by the D/U ratio information generated in step S31 is calculated.
Thereafter, the process proceeds to step S323.
[0053]
(Step S323)
15 The D/U comparison unit 8b determines whether AP calculated in step S322 is
positive and A(D/U) is positive. When it is determined that AP is positive and A(D/U) is
positive (Yes), the transmission path determination signal is output to the transmission
path information comparison unit 17. Thereafter, the process proceeds to step S324.
Otherwise (No), the process proceeds to step S327.
20 (Step S324)
The transmission path information comparison unit 17 receives the transmission
path determination signal output in step S323, and performs the following operation.
The transmission path information comparison unit 17 reads the past transmission path
information from the past D/U storage unit 81b. Tiic transmission path information
,28
comparison unit 17 calculates a value AW obtained by subtracting the past transmission
path information from the current transmission path information generated in step S30.
Thereafter, the process proceeds to step S325.
[0054]
5 (Step S325)
The transmission path information comparison unit 17 determines whether the
pre-storcd threshold value P is greater than AW calculated in step S324. When it is
determined that AW is greater than p (Yes), the process proceeds to step S328. When it
is determined that AW is less than P (No), the process proceeds to step S329.
10 (StepS326)
The output-of-transmitter determination unit 15 outputs the output-of-transmitter
limitation information, which does not limit the increase in power, to the ATPC
indication information creation unit 9b. Thereafter, the process proceeds to step S49
(not illustrated). Here, the process of step S49 is similar to the process of step S15 in
15 the first embodiment.
(Step S327)
The D/U comparison unit 8b outputs the output-of-transmitter limitation
information, which does not limit the increase in power, to the ATPC indication
information creation unit 9b. Thereafter, the process proceeds to step 849.
20 [0055]
(Step S328)
The ATPC indication information creation unit 9b receives output-of-transmitter
limitation information to decrease power from the transmission path information
comparison unit 17, and generates A'fPC indication information indicating a decreased
25 value of the output of the transmitter. Thereafter, the process proceeds to step S49.
29
(Step S329)
The ATPC indication information creation unit 9b receives output-of-transmitter
hmitation information to maintain power from the transmission path information
comparison unit 17, and generates ATPC indication information indicating a held value
5 of the output of the transmitter. Thereafter, the process proceeds to step S49.
Here, the process of step S49 is similar to the process of step S15 of the first
embodiment.
[0056]
In this manner, according to the third embodiment of the present Invention, there
10 are provided an output-of-transmitter determination unit which generates transmission
strength indication information based on a transmission output of the transmitter and a
transmission path information comparison unit which generates the transmission strength
indication information based on variation in transmission path information. Thereby, it
is possible to distinguish D/U radio degradation due to an increase in an output of the
15 transmitter and D/U ratio degradation due to transmission path degradation and execute
an ATPC process based on an actual state of distortion characteristics of a wireless
communication device. Therefore, it is possible to further improve communication
quality.
Also, instead of fading state information, received electric field strength may be
20 used in the transmission path informafion.
[0057]
Although the first, second, and third embodiments of the present invention have
been described above in detail with reference to the drawings, specific configurations are
not limited to these embodiments, and various designs can be made without departing
25 from the scope of the present invention.
INDUSTRIAL APPLICABILITY
[0058]
According to a wireless communication system according to the present
invention, an output of a transmitter can be increased without degrading an SNR.
5 [0059]
Priority is claimed on Japanese Patent Application No. 2011-128011, filed June
8, 2011, the content of which is incorporated herein by reference.
[Description of Reference Symbols]
[0060]
10 1 Modulation unit
1 a Wireless communication system
lb Wireless communication system
1 c Wireless communication system
2 Transmission unit
15 3 Antenna
4 Antenna
5 Reception unit
5 a Reception unit
5b Reception unit
20 6 Demodulation unit
6a Demodulation unit
7 D/U calculation unit
7a D/U calculation unit
8 D/U comparison unit
25 8b D/U comparison unit
31
9 ATPC indication information creation unit
9b ATPC indication information creation unit
10 Modulation unit
11 Transmission unit
5 12 Reception unit
13 Demodulation
14 ATPC indication information extraction unit
81 Past D/U storage unit
81 b Past D/U storage unit
10 1 GO First wireless station
200 Second wireless station
200a Second wireless station
200b Second wireless station
32

WE CLAIM:
1. A wireless communication system comprising:
a transmitter and a receiver,
5 wherein the receiver comprises:
a signal-to-noise ratio (SNR) calculation unit which calculates a SNR of a
baseband signal of a signal received from the transmitter; and
an indication information generation unit which generates transmission strength
indication information indicating transmit power of the transmitter based on a history of
10 the SNR calculated by the SNR calculation unit, and
wherein the transmitter comprises:
a transmission unit which controls the transmit power based on the SNR.
2. The wireless communication system according to claim 1,
15 wherein the receiver includes:
an antenna which transmits and receives radio waves to and from the
transmitter;
a reception unit which converts the radio waves received by the antenna into a
baseband signal;
20 a storage unit which stores past SNR and past transmission strength indication
information;
an SNR comparison unit which compares a current SNR and current
transmission strength indication information to the past SNR and the past transmission
strength indication information; and
25 an indication information generation unit which generates transmission strength
33
indication information indicating the transmit power of the transmitter based on a
comparison result of the SNR comparison unit,
wherein the transmitter includes:
an indication information extraction unit which acquires the transmission
5 strength indication information generated by the receiver, and
wherein the transmission unit controls the transmit power based on the
transmission strength indication information input from the indication information
extraction unit.
10 3. The wireless communication system according to claim 1 or 2, wherein the SNR
calculation unit calculates the SNR based on a signal after a Fourier transform on the
baseband signal.
4. The wireless communication system according to any one of claims 1 to 3, further
15 comprising:
a demodulation unit which demodulates the baseband signal,
wherein the SNR calculation unit calculates the SNR. based on a signal point
error of a signal demodulated by the demodulation unit.
20 5. The wireless communication system according to any one of claims 1 to 4, further
comprising:
an output-of-transmitter determination unit which generates the transmission
strength indication information based on a transmission output of the transmitter.
25 6. The wireless communication system according to any one of claims 1 to 5, further
comprising:
a transmission path information comparison unit which generates the
transmission strength indication information based on variation in transmission path
information.
5
7. A receiver comprising:
an SNR calculation unit which calculates an SNR of a baseband signal of a
signal received from a transmitter; and
an indication information generation unit which generates transmission strength
i 0 indication information indicating transmit power of the transmitter based on a history of
the SNR calculated by the SNR calculation unit.
15
>tii Dated this 12"' day of December 2013
Of Anand and Anand Advocates
Agent for the Applicant