JP5324499B2 - Receiver, program and method for controlling transmission power of transmitter based on fluctuation of radio quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver capable of controlling a transmission power for radio quality at a comparatively long time interval without following instant fluctuation of fading in real-time, and alleviating a transmission delay and a processing load based on feedback from the receiver. <P>SOLUTION: The receiver includes an average value calculation means, a standard deviation calculation means, a necessary transmission rate output means, a necessary average value deriving means, and a feedback signal generation means. The average value calculation means calculates an average value in the radio quality of received signals. The standard deviation calculation means calculates a standard deviation in the radio quality. The necessary transmission rate output means outputs a necessary transmission rate. Using the average value and the standard deviation, the necessary average value deriving means calculates a necessary average value of the radio quality needed for actualizing the necessary transmission rate. The feedback signal generation means generates a difference value between the present average value outputted from the average value calculation means and the necessary average value outputted from the necessary average value deriving means, and return it to a transmitter. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a technique for controlling transmission power of a transmitter based on variation in wireless quality in a wireless communication system.

  With respect to a wireless communication system, a transmitter may transmit radio waves with higher power than necessary depending on the distance or interference with the receiver. Such radio waves not only become interference signals to the surroundings, but also cause a problem of increased power consumption in the transmitter. In this case, it is preferable that the transmitter performs transmission power control (TPC) on radio waves to be transmitted to the receiver.

  Conventionally, there is a technique in which a receiver measures radio quality (for example, received signal strength (RSS)) in a received signal and feeds back the value to the transmitter to control the transmission power of the transmitter. . In order to control to the optimum transmission power, there is a technique using a frame error rate (FER) of a received signal (see, for example, Patent Documents 1 and 4). There is also a technique using a bit error rate (BER) (see, for example, Patent Document 3) and a technique using a SIR (Signal to Interference Ratio) (see, for example, Non-Patent Document 1).

  As a wireless communication system in which transmission power control is actively used, for example, there is an uplink using a code division multiple access (CDMA) system. CDMA can separate transmission signals by assigning different spreading patterns to each wireless terminal. The spreading codes are not completely orthogonal, and codes with different spreading patterns cause intersymbol interference.

  When the distance between the wireless terminal and the base station is long, the transmission signal from the wireless terminal is greatly attenuated before reaching the base station. When the wireless terminal does not execute transmission power control, the wireless quality of the transmission signal is greatly degraded due to intersymbol interference based on signals from other wireless terminals. Therefore, it is necessary for all wireless terminals to execute transmission power control so that the reception power reaching the base station is equal. In addition, transmission by the wireless terminal with the minimum necessary transmission power leads to suppression of power consumption of the wireless terminal.

  On the other hand, according to the downlink of CDMA2001x EV-DO, adaptive modulation and hybrid automatic repeat request (HARQ) are adopted using a time division multiple access (TDMA) method. Yes. The transmitter in the base station always transmits a signal with maximum power. On the other hand, the receiver in the terminal determines a transmission rate defined by the modulation scheme, the coding rate of the error correction code, and the maximum number of HARQ retransmissions based on the SIR, and feeds back to the transmitter.

  Adaptive modulation and coding (AMC) is a technique for changing the transmission rate of a wireless communication system such as a cellular communication network or a wireless local area network (LAN) according to wireless quality. For example, for CDMA2001x EV-DO, the transmission rate of adaptive modulation is defined by a combination of a combination of symbol modulation method and error correction code coding rate (MCS: Modulation and Coding Set) and the upper limit of the number of packet retransmissions by HARQ. (DRC: Data Rate Control). Based on the wireless quality, the MCS that can communicate with a certain level of FER is selected and communicated. HARQ is a method in which when an error is detected from information bits of a received packet, the transmitter retransmits the same packet, and the receiver combines the packets to reduce the number of packet retransmissions.

JP-A-10-51379 JP 2003-348010 A JP 2005-130531 A JP 2007-184864 A

K. Mori, T. Nagaosa, and H. Kobayashi, "Downlinkpower control based on predicted SIR for CDMA cellular packet communications", IEEE54th Vehicular Technology Conference 2001 Fall, vol.3, pp. 1879-1883, October 2001

  According to the above-described prior art, in a communication path environment where fading fluctuation is large, the transmitter requires high-frequency transmission power control in order to follow the fading fluctuation. The receiver must always measure the radio quality and feed back the value to the transmitter. Feedback of measurement values from the receiver to the transmitter not only causes transmission delay but also has a large processing load. For this reason, there is a problem that it is difficult to follow instantaneous fluctuations in fading. When the instantaneous fluctuation of fading cannot be followed, communication cannot be performed based on the optimum transmission rate with respect to the radio quality, and the transmission speed characteristic is also deteriorated.

  Therefore, the present invention controls the transmission power and the processing load based on the feedback from the receiver by controlling the transmission power for the radio quality of a relatively long time interval without following the instantaneous fluctuation of fading in real time. It is an object to provide a receiver, a method, and a program that can be reduced.

According to the present invention, a receiver based on an adaptive modulation scheme in which the transmission rate is variable according to the radio quality of the received signal and a HARQ (Hybrid Automatic Repeat Request) scheme in which the packet error rate is variable according to the number of retransmissions. In
Demodulation means for demodulating the received signal and outputting radio quality;
An average value calculating means for calculating an average value in wireless quality;
A standard deviation calculating means for calculating a standard deviation in wireless quality;
A required transmission rate output means for outputting the required transmission rate;
A required average value deriving means for calculating a required average value of radio quality required to realize the required transmission rate using the average value and the standard deviation;
And a feedback signal generating means for generating a difference value between the current average value output from the average value calculating means and the required average value output from the required average value deriving means and returning the difference value to the transmitter. .

  According to another embodiment of the receiver of the present invention, the radio quality is preferably a desired signal to interference / noise signal power ratio (SINR).

According to another embodiment of the receiver of the present invention, the required average value derivation means is
An estimation function deriving means for deriving an estimation function representing a maximum transmission rate with respect to the average value of the radio quality for each different electric field strength variation (K factor) using the statistical average value and standard deviation of the radio quality;
Calculate the field strength variation using the current average value and the current standard deviation of the current radio quality, select an estimation function corresponding to the field strength variation, and set the estimated maximum transmission rate corresponding to the current average value for the estimation function. An estimated maximum transmission rate deriving means to derive,
It is also preferable to have required average value deriving means for deriving the minimum average value at which the estimated maximum transmission rate is equal to or higher than the required transmission rate as the required average value.

  According to another embodiment of the receiver of the present invention, it is preferable that the estimation function deriving unit has a table in which an estimation function is assigned to a statistical average value and standard deviation of radio quality.

According to another embodiment of the receiver of the present invention, the estimation function deriving means includes:
A probability density function calculating means for calculating a probability density function of radio quality based on a statistical average value and standard deviation of radio quality;
A packet error rate calculating means for calculating a packet error rate based on a probability density function;
A frame error rate calculating means for calculating a frame error rate using the packet error rate;
Maximum transmission rate selection means for selecting a maximum transmission rate at which the frame error rate is equal to or less than a predetermined threshold;
An average packet retransmission count calculating means for calculating an average packet retransmission count at the maximum transmission rate based on the packet error rate;
Maximum transmission rate calculating means for calculating the maximum transmission rate at the maximum transmission rate based on the frame error rate and the average number of packet retransmissions;
It is also preferable to have estimation function calculation means for calculating a plurality of estimation functions representing the maximum transmission rate with respect to the average value of the radio quality for each different electric field strength fluctuation calculated using the average value and the standard deviation of the radio quality.

According to the present invention, for a wireless system using an FDD (Frequency Division Duplex) scheme in which the uplink and downlink are configured with different frequencies, the transmitter for the receiver described above,
Modulation means for modulating data to be transmitted to the receiver into a transmission signal;
Transmission power amplification means for amplifying transmission power for a transmission signal;
Demodulation means for obtaining a difference value from the signal received from the receiver;
Transmission power control means for controlling transmission power for each transmission signal in the transmission power amplifying means using the difference value.

According to the present invention, there is provided a wireless communication system having the above-described receiver and the above-described transmitter,
When the transmitter is a base station and there are a plurality of mobile terminals as receivers for the downlink from the base station, the base station performs slot slotting for the plurality of receivers by round-robin scheduling. It is characterized by assigning.

According to the present invention, for a wireless system using a TDD (Time Division Duplex) system in which the upper and lower links are configured at the same frequency, the transceiver is equipped with the function of the receiver described above,
Modulation means for modulating data to be transmitted to the receiver into a transmission signal;
Transmission power amplification means for amplifying transmission power for a transmission signal;
Demodulation means for obtaining a difference value from the signal received from the receiver;
Transmission power control means for controlling the transmission power for each transmission signal in the transmission power amplification means based on the difference value from the demodulation means or the required average value from the required average value deriving unit.

According to the present invention, there is provided a computer mounted in a receiver based on an adaptive modulation scheme in which a transmission rate is variable according to radio quality of a received signal and a HARQ scheme in which a packet error rate is variable according to the number of retransmissions. In the program to function,
The receiver has a demodulator that demodulates the received signal and outputs radio quality,
An average value calculating means for calculating an average value in wireless quality;
A standard deviation calculating means for calculating a standard deviation in wireless quality;
A required transmission rate output means for outputting the required transmission rate;
A required average value deriving means for calculating a required average value of radio quality required to realize the required transmission rate using the average value and the standard deviation;
Generating a difference value between the current average value output from the average value calculating means and the required average value output from the required average value deriving means, and causing the computer to function as a feedback signal generating means for returning to the transmitter And

According to the present invention, a program for causing a computer mounted on a transmitter to transmit a signal to the above-described receiver functions.
The transmitter is
A modulator that modulates data to be transmitted to the receiver into a transmission signal;
A transmission power amplification unit that amplifies transmission power for a transmission signal;
A demodulator that demodulates the signal received from the receiver and obtains a difference value;
The computer is caused to function as transmission power control means for controlling transmission power for each transmission signal in the transmission power amplification means using the difference value.

According to the present invention, a transmitter adopting a communication scheme based on an adaptive modulation scheme in which the transmission rate is variable according to the radio quality of the received signal and an HARQ scheme in which the packet error rate is variable in accordance with the number of retransmissions. And a transmission power control method in a communication system comprising a receiver,
The receiver has determined the required transmission rate in advance,
A transmitter, wherein the transmitter transmits a signal to the receiver;
A second step in which the receiver demodulates the received signal and outputs the radio quality;
A third step of calculating an average value and standard deviation in radio quality;
A fourth step in which the receiver uses the average value and the standard deviation to calculate a required average value of radio quality required to achieve the required transmission rate;
A fifth step in which the receiver generates a difference value between the current average value and the required average value in the radio quality, and returns the difference value as a feedback signal to the transmitter;
A transmitter in which the transmitter demodulates the feedback signal received from the receiver and obtains a difference value;
The transmitter has a seventh step of controlling the transmission power for each transmission signal in the transmission power amplification unit using the difference value.

  According to the receiver, method and program of the present invention, it is possible to provide feedback from the receiver by controlling the transmission power for the radio quality of a relatively long time interval without following the instantaneous fluctuation of fading in real time. It is possible to reduce transmission delay and processing load.

It is explanatory drawing showing the transmission power control of the base station as a transmitter. It is explanatory drawing showing transmission power control of the portable terminal as a transmitter. It is a functional block diagram of the receiver in this invention. It is a function block diagram of the transmitter which opposes the receiver of this invention. It is a functional block diagram of the required average value derivation | leading-out part of the receiver in this invention. It is a functional block diagram of a required average value deriving unit based on theoretical analysis. It is a graph showing the convolution of a probability density function. It is a functional block diagram of the required average value derivation | leading-out part based on a table. It is a graph showing the maximum transmission rate with respect to average SINR in a stationary environment and a fading environment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram illustrating transmission power control of a base station as a transmitter.

  A base station as a transmitter controls transmission power so that a mobile phone as a receiver can receive with equal power. For each mobile phone, the base station increases the transmission power as the distance between them increases, and decreases the transmission power as the distance between them increases.

  A packet communication system based on time division multiple access (TDMA) is employed in a wireless communication system targeted by the present invention. The transmitter controls the transmission power so that the communication quality with respect to the receiver is always constant at a frequency of several hundred times per second. The transmission power is determined based on an instantaneous value of a desired signal-to-noise signal power ratio (SINR) in a signal received by the receiver. “SINR” is the ratio (dB) between the power of the desired signal and the sum of the power of the interference and noise signals.

  One base station transmits radio waves to a large number of mobile terminals under the area. In this case, the transmitter of the base station executes transmission power control for each mobile terminal. For example, according to TD-CDMA (Time Division-CDMA), a base station alternately transmits a downlink and an uplink by a switch. In the downlink, slots are assigned to each mobile terminal by round robin scheduling. According to the present invention, in order to determine transmission power based on SINR, scheduling can be executed by simple round robin without using the PF (Proportional Fair) algorithm used in CDMA2001x EV-DO. .

  The wireless communication system targeted by the present invention includes an adaptive modulation method in which the transmission rate is variable according to the radio quality of the received signal, and a HARQ (Hybrid Automatic Repeat Request) method in which the packet error rate is variable according to the number of retransmissions. With. According to HARQ, each time a packet is retransmitted, the packet error rate (PER) is improved by combining the reliability of the same packet transmitted in the past. This reduces the average number of packet retransmissions.

Hereinafter, an embodiment when the present invention is applied to two wireless systems will be described.
[1] Application to a radio system using an FDD (Frequency Division Duplex) scheme in which the upper and lower links are configured at different frequencies [2] Using a TDD (Time Division Duplex) scheme in which the upper and lower links are configured at the same frequency Application to wireless system

[1] Application to a radio system using the FDD scheme in which the upper and lower links are configured with different frequencies

  FIG. 2 is an explanatory diagram illustrating transmission power control of a mobile terminal as a transmitter in an FDD wireless system.

  According to FIG. 2, a plurality of portable terminals as transmitters control transmission power so that a base station as a receiver can receive with equal power. Here, the mobile terminal needs to increase the transmission power as the distance from the base station increases. On the other hand, the mobile terminal may have a smaller transmission power as the distance from the base station becomes closer. Therefore, the mobile terminal should be controlled so that the transmission power does not increase unnecessarily.

  FIG. 3 is a functional configuration diagram of a receiver according to the present invention applied to an FDD wireless system.

  The receiver 1 may be a mobile terminal reception unit in the downlink or a base station reception unit in the uplink. Assuming downlink, the radio quality in the mobile terminal is based on the common channel pilot signal received from the base station, and is, for example, SINR. As a wireless communication system, for example, a downlink of a cellular system of CDMA2000 EV-DO standardized by 3GPP2 (3rd Generation Partnership Project 2) is assumed. When the wireless communication system is a cellular system, the mobile terminal is, for example, a mobile phone.

  According to FIG. 3, the receiver 1 includes a data transmission / reception unit 100, a modulation unit 111, an encoding unit 112, a demodulation unit 121, and a decoding unit 122, as in the existing wireless communication apparatus. The demodulator 121 demodulates the received signal and outputs radio quality. The demodulated received signal is decoded by the decoding unit 122 and output to the data transmitting / receiving unit 100. Data to be transmitted output from the data transmitter / receiver 200 is encoded by the encoder 112 and modulated by the modulator 111. The modulated transmission signal is transmitted to the transmitter 2 via the antenna.

  According to the present invention, the receiver 1 includes an average value calculation unit 131, a standard deviation calculation unit 132, a required average value derivation unit 133, a required transmission rate output unit 134, and a feedback signal generation unit 135. These functional components are realized by executing a program that causes a computer mounted on a receiver (for example, a mobile phone or a base station) to function.

The average value calculation unit 131 receives the SINR from the demodulation unit 121 and calculates an average SINRγ ⁻ in a short section (several tens to several hundreds ms). The average SINRγ ⁻ is an average value with respect to fluctuation due to Rayleigh fading. The average value and the mean square value may be calculated using a section average, a simple moving average (SMA), or an exponential smoothing moving average (EMA). The calculated average SINRγ ⁻ is output to the required average value deriving unit 133.

  The standard deviation calculating unit 132 receives the SINR from the demodulating unit 121 and calculates the standard deviation σ of SINR in a short section for obtaining an average value. The calculated standard deviation σ of SINR is output to required average value deriving unit 133.

  The required transmission rate output unit 134 outputs the required transmission rate. The required transmission rate is, for example, the maximum transmission rate in a wireless communication system. The required transmission rate is output to the required average value deriving unit 133.

Required average value derivation unit 133, the average SINRγ from the average value calculator 131 ^- enter the, type the standard deviation σ from the standard deviation calculating section 132, and inputs a required transmission rate from the required transmission rate output unit 134. The required average value derivation unit 133, the average SINRganma ^- calculated using and standard deviation sigma, required average value of radio quality needed to achieve the required transmission rate (required average SINR). The required average SINR is output to feedback signal generation section 135.

  The feedback signal generation unit 135 generates a difference value between the current average SINR output from the average value calculation unit 131 and the required average SINR output from the required average value derivation unit 133. The difference value is included in the data packet, and the data packet is returned to the transmitter (closed loop control).

  FIG. 4 is a functional configuration diagram of a transmitter applied to an FDD wireless system.

  According to FIG. 4, the transmitter 2 is similar to the existing wireless communication device in that the data transmitter / receiver 200, the modulator 211, the encoder 212, the transmission power amplifier 213, the demodulator 221, and the decoding Part 222. The data to be transmitted output from the data transmitting / receiving unit 200 is encoded by the encoding unit 212 and modulated by the modulation unit 211. The modulated transmission signal is amplified by transmission power amplifying section 213 with different transmission power for each receiver and transmitted. Further, the signal received from the receiver 1 is demodulated by the demodulator 221 and decoded by the decoder 222. The decoding unit 222 acquires the average SINR difference value included in the signal received from the receiver 1.

  According to the present invention, the transmitter 2 further includes a transmission power control unit 231. The transmission power control unit 231 receives the difference value (and transmission rate) of the average SINR received from the receiver 1 from the decoding unit 222, and based on the difference value, transmits for each transmission signal in the transmission power amplification unit 213. Control power. Further, the modulation unit 211 may be controlled based on the transmission rate received from the receiver 1. The transmission power control unit 231 holds a transmission power value (and transmission rate) for each receiver. Then, the transmission power control unit 231 controls the transmission power based on the previous transmission power and the difference value of the average SINR in the feedback signal from the receiver. In the initial state, the maximum power in the transmitter is set as the transmission power.

  According to the present invention, the transmission power of the transmitter is controlled so that the PER or FER does not exceed the threshold value by using statistical values such as an average and a standard deviation instead of an instantaneous value of radio quality in a received signal of the receiver. Is done. The transmission power control is executed every time interval such as 0.5 seconds or 1 second in which the radio quality statistics do not change.

[2] Application to a radio system using the TDD scheme in which the upper and lower links are configured with the same frequency

  FIG. 5 is a functional configuration diagram of a transceiver according to the present invention applied to a TDD wireless system.

  As the transceiver 3, a portable terminal is assumed. The radio quality in the portable terminal is based on a common channel pilot signal received from the base station, and is, for example, SINR. When the wireless communication system is a cellular system, the mobile terminal is, for example, a mobile phone. According to FIG. 5, transmission power can be controlled using radio quality of a received signal without using a feedback signal (open loop control). Note that FIG. 5 can also be executed for closed-loop control.

  The transceiver 3 in FIG. 5 further includes a transmission power amplifying unit 213 and a transmission power control unit 231 as compared with the receiver 1 in FIG. The transmission power amplification unit 213 amplifies the transmission signal output from the modulation unit 111 and outputs it to the antenna.

  The transmission power control unit 231 inputs the difference value (and transmission rate) of the average SINR received from the opposing transceiver from the decoding unit 122. The transmission power control unit 213 controls the transmission power for each transmission signal in the transmission power amplification unit 213 based on the difference value. Further, the transmission power control unit 231 can also control transmission power based on the required SINR output from the required average value deriving unit 133.

  The transmission power control unit 231 holds the transmission power value (and transmission rate). Then, the transmission power control unit 231 controls the transmission power based on the previous transmission power and the difference value of the average SINR in the feedback signal from the receiver. In the initial state, the maximum power in the transmitter is set as the transmission power.

  According to the present invention, transmission power is controlled so that PER or FER does not exceed a threshold value using statistical values such as average and standard deviation instead of instantaneous values of radio quality in received signals of a transceiver. The transmission power control is executed every time interval such as 0.5 seconds or 1 second in which the radio quality statistics do not change.

Next, the required average value deriving unit will be described. Below, two embodiment of a required average value derivation part is described.
[1] Derivation of estimation function based on theoretical analysis [2] Derivation of estimation function based on table

[1] Derivation of estimation function based on theoretical analysis

  FIG. 6 is a functional configuration diagram of a required average value deriving unit based on theoretical analysis.

  According to FIG. 6, the required average value deriving unit 133 includes an estimation function deriving unit 1331, an estimated maximum transmission rate deriving unit 1332, and a required average value deriving unit 1333.

Estimating function deriving unit 1331, the average SINRganma ^- and each field strength variation (K factor) based on the standard deviation sigma, average SINRganma ^- deriving a function representing the maximum transmission speed for. Here, the “maximum transmission rate” means a transmission rate when there is no competing traffic. The plurality of estimation functions are referred to by the estimated maximum transmission rate deriving unit 1332.

Estimated maximum transmission rate deriving unit 1332, the current average SINRγ the current radio quality ^- to calculate the K-factor using and the current standard deviation sigma. Then, select the estimation function corresponding to the K-factor, the current average SINRγ for the estimation function ^- deriving an estimated maximum transmission rate corresponding to the. The estimated maximum transmission rate is output to the required average value deriving unit 1333.

The required average value deriving unit 1333 receives the estimated maximum transmission rate and the required transmission rate. Then, the required average value deriving unit 1333 derives the minimum average SINRγ ^{− at} which the estimated maximum transmission rate is equal to or higher than the required transmission rate as the required average SINRγ ⁻ . The required average SINRγ ⁻ is output to the feedback signal generation unit 135. The required average SINR is derived at a time when the average value and the standard deviation as statistics are constant, for example, every 0.5 seconds or every second.

  According to FIG. 5, the estimation function deriving unit 1331 includes a probability density function calculating unit 311, a packet error rate characteristic storage unit 312, a packet error rate calculating unit 313, a frame error rate calculating unit 314, and a maximum transmission rate selection. Unit 315, average packet retransmission count calculation unit 316, maximum transmission rate calculation unit 317, and estimation function calculation unit 318.

γ：ＳＩＮＲ
γ⁻：平均ＳＩＮＲ
Ｋ：ライスフェージングにおけるＫファクタ
ｆ(γ｜γ⁻,Ｋ)：確率密度関数 Probability density function calculation section 311, the average SINRganma ^- and based on the standard deviation sigma, the probability density function of SINR: calculating the (PDF Probability Density Function). For example, it is calculated by the following formula. The calculated probability density function is output to the packet error rate calculation unit 313.

γ: SINR
γ ⁻ : Average SINR
K: K factor in rice fading f (γ | γ ⁻ , K): probability density function

σ：ＳＩＮＲの標準偏差 “Rice fading” refers to fluctuations in electric field strength caused by a direct wave when there is a line of sight and a reflected wave when diffracted by an obstacle. The “K factor” represents the ratio of the electric field intensity of the direct wave to the electric field intensity of the reflected wave (= the electric field intensity of the direct wave / the electric field intensity of the reflected wave). As the K factor number increases, the magnitude of fluctuations in the communication path due to fading decreases, so the chance of packet retransmission by HARQ decreases. K-factor, as follows, the mean SINRganma ^- is calculated by and standard deviation sigma.

σ: Standard deviation of SINR

  The packet error rate characteristic storage unit 312 stores in advance the packet error rate for each MCS (Modulation and Coding Set) for an AWGN (Additive White Gaussian Noise) channel. MCS means a combination of a quadrature modulation scheme of a transmission signal and a coding rate of an error correction code. According to white noise, the power spectrum derived by Fourier transform has the same intensity at all frequencies (light including all frequencies is white).

  The packet error rate calculation unit 313 calculates a probability density function for each transmission rate and for each number of retransmissions (1 to n) as a packet error distribution by convolving the probability density function PDF. Here, the calculation amount of the convolution calculation in the probability density function PDF is on the order of the square of the sample points.

  Then, the packet error rate calculation unit 313 calculates the packet error rate PER for each MCS based on the probability density function PER and the packet error rate PER for each MCS in the packet error rate characteristic storage unit 344. Specifically, the probability density function PDF is multiplied by the packet error rate PER for each MCS in the AWGN communication channel stored in the packet error rate characteristic storage unit 340. The packet error rate PER for each MCS is calculated by integrating the multiplication result.

  FIG. 7 is a graph showing the convolution of the probability density function.

  In FIG. 7A, the horizontal axis represents SINR, and the vertical axis represents probability density. The dotted line represents the probability distribution of the combined SINR for each packet transmission, and the solid line represents the packet error distribution for each packet transmission. FIG. 7B also shows SINR on the horizontal axis and the packet error rate on the vertical axis. The curve represents the packet error rate characteristic when a predetermined MCS is used for the AWGN communication path. The packet error rate in the AWGN communication channel is a value when the soft decision information combining of packets by HARQ is not performed, and is stored in the packet error rate characteristic storage unit 312 in FIG.

ｆ(γ|γ⁻,Ｋ,ｎ)：ｎ回目のパケット送信時の確率密度関数
図７（ａ）の点線で表される軟判定情報合成後のＳＩＮＲの確率分布に、図６（ｂ）の曲線で表されるＡＷＧＮ通信路におけるパケット誤り率特性を乗算したものが、パケット誤り分布と定義される。このパケット誤り分布は、図６（ａ）の実線で表される。 According to FIG. 7A, soft decision at the time of packet retransmission in HARQ is performed by convolving the probability density function of SINR at the time of the first packet reception with the packet error distribution at the time of (n−1) th packet transmission. It represents the probability distribution of SINR after information synthesis. That is, the combined SINR probability distribution in the second transmission is obtained by convolving the combined SINR probability distributions in the first transmission. Further, the probability distribution of the combined SINR in the third transmission can be obtained by convolving the probability distribution of the combined SINR in the second transmission and the first transmission. The convolution is based on the following equation:

f (γ | γ ⁻ , K, n): Probability density function at the time of n-th packet transmission FIG. 6B shows the probability distribution of SINR after the soft decision information synthesis represented by the dotted line in FIG. Multiplying the packet error rate characteristic in the AWGN channel represented by the curve is defined as a packet error distribution. This packet error distribution is represented by a solid line in FIG.

  A probability density function PDF for each number of packet retransmissions at each transmission rate is defined as a packet error distribution.

The frame error rate calculation unit 314 calculates the frame error rate PER when retransmission is performed up to the maximum packet retransmission count N using the packet error rate PER for each transmission rate. Here, without considering the effect of improving the packet error rate in HARQ, it may be assumed that the packet error rate PER at retransmission is the same as the packet error rate PER at the first packet transmission. Further, from the probability density function PDF, based on the packet error rate PER that changes according to the number of retransmissions, the packet error rate PER is treated as an independent event for each number of retransmissions, and the frame error rate FER is calculated. Good. That is, the frame error rate may be unrelated to the number of retransmissions, or may depend on the maximum number of packet retransmissions in each MCS. For the same MCS, every time the number of packet retransmissions increases, the packet error rate PER decreases. For each transmission rate, the frame error rate FER (Frame
Error Rate) is derived.

  The frame error rate calculation unit 314 calculates the packet error rate PER and the frame error rate FER based on the probability density function f (γ). The frame error rate FER is output to the maximum transmission rate selection unit 315 and the maximum transmission rate calculation unit 317. The packet error rate PER is output to the average packet retransmission count calculation unit 316.

Here, the “transmission rate” is a discrete value based on the transmission speed. According to CDMA2000 EV-DO Rev. A, it is defined by 14 types of DRC Index. Table 1 shows the relationship between DRC Index and DRC Rate (transmission rate).

  The maximum transmission rate selection unit 315 selects the maximum transmission rate at which the frame error rate is equal to or less than a predetermined threshold. The selected maximum transmission rate is output to average packet retransmission count calculation section 316 and maximum transmission rate calculation section 317.

フレーム誤り率算出部からは、各Ｐ(n)（n：再送回数、最初はn=1）が出力される。 The average packet retransmission count calculation unit 316 calculates the average packet retransmission count at the maximum transmission rate based on the packet error rate. Mean SINRganma ^- and using a packet error rate PER of the maximum transmission rate derived from the standard deviation sigma, derives the average number of retransmissions. The average number of retransmissions Nave is derived as follows using the upper limit Nmax of the number of packet retransmissions.
Nave: Average number of packet retransmissions Nmax: Maximum number of packet retransmissions by HARQ F: Frame error rate P (n): Packet error rate at the time of n-th packet reception by HARQ
(P (0) = 1)

Each P (n) (n: number of retransmissions, initially n = 1) is output from the frame error rate calculation unit.

Ｒmax：パケット誤りが無いときの最大伝送速度
「パケット誤りがないときの最大伝送速度」とは、競合するトラヒックが無く、且つ、パケット誤りが発生しないときの伝送速度を意味する。 The maximum transmission rate calculation unit 317 calculates the maximum transmission rate R at the maximum transmission rate based on the frame error rate F and the average number of retransmissions Nave at the maximum transmission rate. For example, it is calculated as follows.

Rmax: Maximum transmission rate when there is no packet error The “maximum transmission rate when there is no packet error” means a transmission rate when there is no competing traffic and no packet error occurs.

Estimating function calculating unit 318, average SINRganma ^- and each field strength variation (K factor) based on the standard deviation sigma, average SINRganma ^- deriving a function representing the maximum transmission speed for. The plurality of estimation functions are referred to by the estimated maximum transmission rate deriving unit 1332.

[2] Derivation of estimation function based on table

  FIG. 8 is a functional configuration diagram of the required average value deriving unit based on the table.

  8, the required average value deriving unit 133 includes an estimated function deriving unit 1331, an estimated maximum transmission rate deriving unit 1332, and a required average value deriving unit 1333, as in FIG. Here, the point different from FIG. 6 is that the estimation function deriving unit 1331 includes a table representing the standard deviation with respect to the average value.

Estimating function deriving unit 1331, the average SINRganma ^- and enter a standard deviation sigma, and outputs the estimation function. Estimating function deriving unit 1331, the average SINRganma ^- and the quantization respectively the standard deviation sigma, average SINRganma ^- and holds the estimated function corresponding to the standard deviation sigma as a table. Thereby, the calculation time required for calculating the estimation function can be shortened. According to FIG. 8, the table, the entered average SINRganma ^- and estimation function at a portion standard deviation σ match is selected.

  FIG. 9 is a graph showing the maximum transmission rate with respect to the average SINR in a stationary environment and a fading environment.

According to the graph of FIG. 9, the horizontal axis represents the average SINR of the communication path, and the vertical axis represents the maximum transmission rate. The stationary environment is represented as K factor = 100, and the fading environment is represented as K = 1. A large K-factor number means that the channel fluctuation due to fading is small, and a small K-factor number means that the channel fluctuation due to fading is large. According to FIG. 9, when the K factor is different, the maximum transmission rate with respect to the average SINR is greatly different. According to the present invention, the average SINRganma ^- based on and K-factor, which is estimated from the standard deviation sigma, it is possible to accurately estimate the maximum transmission rate.

  As described above in detail, according to the receiver, method, and program of the present invention, transmission power is controlled with respect to radio quality over a relatively long time interval without following real-time fluctuations in fading. As a result, transmission delay and processing load based on feedback from the receiver can be reduced.

  In addition, for a wireless communication system employing adaptive modulation and HARQ, it is necessary to control the transmission power of the transmitter so that the minimum average SINR that realizes a predetermined PER or FER according to the required transmission rate is obtained. Power consumption can be reduced while maintaining the transmission speed.

  Various changes, modifications, and omissions of the above-described various embodiments of the present invention can be easily made by those skilled in the art. The above description is merely an example, and is not intended to be restrictive. The invention is limited only as defined in the following claims and the equivalents thereto.

DESCRIPTION OF SYMBOLS 1 Receiver 100 Data transmission / reception part 111 Modulation part 112 Coding part 121 Demodulation part 122 Decoding part 131 Average value calculation part 132 Standard deviation calculation part 133 Required average value derivation part 134 Required transmission rate output part 135 Feedback signal generation part 1331 Estimation function Deriving unit 1332 Estimated maximum transmission rate deriving unit 1333 Required average value deriving unit 311 Probability density function calculating unit 312 Packet error rate characteristic storage unit 313 Packet error rate calculating unit 314 Frame error rate calculating unit 315 Maximum transmission rate selecting unit 316 Average packet retransmission Number calculation unit 317 Maximum transmission rate calculation unit 318 Estimation function calculation unit 2 Transmitter 200 Data transmission / reception unit 211 Modulation unit 212 Encoding unit 213 Transmission power amplification unit 221 Demodulation unit 222 Decoding unit 231 Transmission power control unit

Claims (11)

In a receiver based on an adaptive modulation scheme in which a transmission rate is variable according to radio quality of a received signal and a HARQ (Hybrid Automatic Repeat Request) scheme in which a packet error rate is variable according to the number of retransmissions,
Demodulating means for demodulating the received signal and outputting the radio quality;
Average value calculating means for calculating an average value in the wireless quality;
A standard deviation calculating means for calculating a standard deviation in the wireless quality;
A required transmission rate output means for outputting the required transmission rate;
Using the average value and the standard deviation, required average value deriving means for calculating a required average value of the radio quality required to realize the required transmission rate;
Feedback signal generating means for generating a difference value between the current average value output from the average value calculating means and the required average value output from the required average value deriving means and returning the difference value to the transmitter. Features receiver.   The receiver according to claim 1, wherein the radio quality is a signal-to-interference and noise power ratio (SINR). The required average value derivation means includes:
An estimation function deriving means for deriving an estimation function representing a maximum transmission rate with respect to the average value of the radio quality for each different electric field strength variation (K factor) using the statistical average value and standard deviation of the radio quality;
Calculate the electric field strength fluctuation using the current average value and the current standard deviation of the current radio quality, select the estimation function corresponding to the electric field intensity fluctuation, and estimate the maximum transmission rate corresponding to the current average value for the estimation function. An estimated maximum transmission rate deriving means for deriving
The receiver according to claim 1, further comprising required average value deriving means for deriving a minimum average value at which the estimated maximum transmission rate is equal to or higher than the required transmission rate as a required average value. The estimation function deriving means includes:
A probability density function calculating means for calculating a probability density function of radio quality based on a statistical average value and standard deviation of radio quality;
Packet error rate calculating means for calculating a packet error rate based on the probability density function;
Frame error rate calculating means for calculating a frame error rate using the packet error rate;
Maximum transmission rate selection means for selecting a maximum transmission rate at which the frame error rate is a predetermined threshold value or less;
An average packet retransmission count calculating means for calculating an average packet retransmission count at the maximum transmission rate based on the packet error rate;
Maximum transmission rate calculation means for calculating a maximum transmission rate at the maximum transmission rate based on the frame error rate and the average number of packet retransmissions;
An estimation function calculating means for calculating a plurality of estimation functions representing a maximum transmission rate with respect to the average value of the radio quality for each of different electric field strength fluctuations calculated using the average value and the standard deviation of the radio quality, The receiver according to claim 3. The estimation function deriving means includes:
4. The receiver according to claim 3, further comprising a table in which an estimation function is assigned in advance to a statistical wireless quality average value and standard deviation. About the radio | wireless system using the FDD (Frequency Division Duplex) system comprised by the frequency from which an up-and-down link differs, It is a transmitter with respect to the said receiver of any one of Claim 1 to 5,
Modulation means for modulating data to be transmitted to the receiver into a transmission signal;
Transmission power amplification means for amplifying transmission power for the transmission signal;
Demodulation means for obtaining the difference value from the signal received from the receiver;
Transmitter having transmission power control means for controlling transmission power for each transmission signal in the transmission power amplification means using the difference value. A wireless communication system comprising the receiver according to any one of claims 1 to 5 and the transmitter according to claim 6.
When the transmitter is a base station and there are a plurality of portable terminals as receivers for the downlink from the base station, the base station performs round-robin scheduling on the plurality of receivers. A wireless communication system characterized by allocating slots. A wireless system using a TDD (Time Division Duplex) system in which upper and lower links are configured with the same frequency, the transceiver having the function of the receiver according to any one of claims 1 to 5, ,
Modulation means for modulating data to be transmitted to the receiver into a transmission signal;
Transmission power amplification means for amplifying transmission power for the transmission signal;
Demodulation means for obtaining the difference value from the signal received from the receiver;
Transmission power control means for controlling transmission power for each transmission signal in the transmission power amplification means based on a difference value from the demodulation means or a required average value from the required average value deriving unit. A transceiver. In a program for causing a computer mounted on a receiver to function based on an adaptive modulation method in which a transmission rate is variable according to radio quality of a received signal and a HARQ method in which a packet error rate is variable according to the number of retransmissions,
The receiver has a demodulator that demodulates the received signal and outputs the radio quality,
Average value calculating means for calculating an average value in the wireless quality;
A standard deviation calculating means for calculating a standard deviation in the wireless quality;
A required transmission rate output means for outputting the required transmission rate;
Using the average value and the standard deviation, required average value deriving means for calculating a required average value of the radio quality required to realize the required transmission rate;
Generate a difference value between the current average value output from the average value calculation means and the required average value output from the required average value derivation means, and cause the computer to function as a feedback signal generation means that sends the difference value back to the transmitter A program for a receiver characterized by that. A program for causing a computer mounted on a transmitter to transmit a signal to the receiver according to any one of claims 1 to 5,
The transmitter is
A modulation unit that modulates data to be transmitted to the receiver into a transmission signal;
A transmission power amplifier for amplifying transmission power for the transmission signal;
A demodulator that demodulates the signal received from the receiver and obtains the difference value;
A program for a transmitter, which causes a computer to function as transmission power control means for controlling transmission power for each transmission signal in the transmission power amplification means using the difference value. Communication composed of a transmitter and a receiver adopting a communication scheme based on an adaptive modulation scheme in which the transmission rate is variable according to the radio quality of the received signal and a HARQ scheme in which the packet error rate is variable in accordance with the number of retransmissions. A transmission power control method in a system, comprising:
The receiver has determined a required transmission rate in advance,
A first step in which the transmitter transmits a signal to the receiver;
A second step in which the receiver demodulates the received signal and outputs the radio quality;
A third step of calculating an average value and a standard deviation in the radio quality;
A fourth step in which the receiver uses the average value and the standard deviation to calculate a required average value of the radio quality required to realize the required transmission rate;
A fifth step in which the receiver generates a difference value between a current average value in radio quality and the required average value, and returns the difference value to the transmitter as a feedback signal;
A sixth step in which the transmitter demodulates the feedback signal received from the receiver and obtains the difference value;
The transmitter has a seventh step of controlling the transmission power for each transmission signal in the transmission power amplifying unit using the difference value.

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