JP2013106067A - Digital radio communication device and digital radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital radio communication device capable of reducing the deterioration of communication quality and throughput in a multipath fading environment.SOLUTION: A digital radio communication device performs communication by adaptively selecting a desired modulation class from a plurality of modulation classes composed of the set of a modulation scheme and a coding rate. The digital radio communication device includes: a modulation class decision unit 533 for selecting the modulation class of the next transmission data, on the basis of the own quality information related to the own reception quality on a transmission signal from the self-device included in a reception signal from an opposite communication device; based on the reception signal, mating quality information generation units (512, 514, 516, 531, 532) for generating mating quality information related to the mating reception quality on the opposite communication device; and to transmit the mating quality information to the opposite communication device, a modulation processing unit 534 for modulating the mating quality information by the modulation scheme of the modulation class selected by the modulation class decision unit 533.

Description

  The present invention relates to a digital wireless communication apparatus and a digital wireless communication method that employ an adaptive modulation method.

  As an example of a digital wireless communication system, a PHS (Personal Handyphone System), an iBurst system, and the like that comply with the wireless communication standard of the TDMA-TDD communication system are known. In such a wireless communication system, one or both of the communication devices may be movable. In that case, while the user can enjoy the benefits of mobility, if the user moves away from the radio propagation distance, communication is interrupted for that period. Even when there is no movement of the communication device, there may be a period in which communication is interrupted due to a change in the radio wave propagation path. Therefore, in the wireless communication system, it is very difficult to avoid interruption during communication.

  On the other hand, as a wireless communication system, the transmission status by mutual transmission is acquired by feedback from the receiving side, and based on the acquired information, for example, transmission output, modulation scheme to be selected when supporting multiple modulation schemes, etc. An adaptive modulation technique is known that adaptively changes and maintains optimal wireless communication (see Non-Patent Document 1, for example).

  In general, the modulation scheme is higher in required SNR (signal noise ratio) and weaker in noise as the amount of information per symbol is larger. On the other hand, a modulation scheme with a low required SNR tends to reduce the amount of portable information per symbol. That is, throughput and noise resistance are in a trade-off relationship, and it is generally difficult to flexibly cope with environmental changes with the support of only one modulation method.

  Therefore, modulation with a high required SNR instead of a large amount of portable information from a modulation class with a low required SNR but a small amount of portable information by a plurality of combinations of modulation schemes and coding rates (hereinafter referred to as modulation classes) Prepare multiple classes in stages. And if the current SNR is low, instead of sacrificing the throughput, the location ratio is improved by selecting a modulation scheme with a low required SNR. Conversely, if the current SNR is high, the required SNR is high. An adaptive modulation scheme that improves throughput by selecting a modulation scheme becomes effective.

  In adopting the adaptive modulation method, for example, there is a method in which the received SNR is fed back from the opposite communication device. That is, it is generally difficult to directly know how the quality of the radio wave emitted by the own device is evaluated in the opposite communication device. Therefore, it is possible to realize adaptive modulation for determining the next and subsequent modulation classes by placing the transmission signal from the opposite communication device that has received the radio wave and notifying the latest received radio wave quality as feedback information. .

  Here, reception SNR is often used as signal quality for estimating SINR (signal interference noise ratio) in digital communication. SINR is obtained by adding a known training symbol signal sequence s (k) near the beginning of the transmission signal from the transmission / reception side, and transmitting the received signal sequence r (k) and s (k) on the reception side. Can be obtained from Here, k indicates a symbol length.

  Such a training symbol signal sequence is often used also for signal position detection, and in many cases, is arranged at a portion relatively close to the beginning of the entire transmission signal sequence. On the receiving side, the sampling sequence r (t) of the received signal sequence r that maximizes the correlation with the known signal sequence s is obtained, and the received signal position is determined. Here, t indicates an index of a sampling sequence starting from sampling at an arbitrary time.

  Also, in the adaptive modulation system, generally, an identifier that can easily determine which modulation class is a radio wave to be emitted is given. In other words, when the modulation class is adaptively changed on the transmitting side, if the receiving side cannot know which modulation class is selected, it performs demodulation corresponding to all possible modulation classes and performs decoding. I need to try. Such a configuration has a large circuit scale and takes a long processing time, so that it is generally difficult to implement.

  In order to avoid this, there is a method in which a part of the transmission signal is modulated with a fixed modulation scheme and an information symbol with high SNR tolerance with sufficient redundancy is provided. In this method, prior to demodulating the main information symbols of the received signal, the receiving side demodulates and decodes information symbols that are part of the fixed modulation scheme of the received signal, and investigates the carried signal pattern. . The modulation class associated with the signal pattern is assumed to be the modulation class used for the information symbol. According to this method, it is possible to reduce the circuit scale and the processing time.

  In order to notify such a modulation class, an information symbol modulated and given by a fixed modulation method can be reused as a substantially known symbol signal for both transmission and reception after decoding. SINR can be obtained from Such an additional signal sequence does not need to be particularly near the beginning of the transmission signal sequence, and can be arranged near the end of the entire transmission signal sequence.

  In digital wireless communication, generally, a transmission signal is transmitted divided into times. This single transmission signal period is temporarily called a burst. As a burst configuration, for the reasons described above, a training symbol signal sequence known by the receiving side is often arranged at the head portion, the tail portion, or both.

  FIG. 3 is a diagram illustrating an example of a transmission burst in digital wireless communication. In this transmission burst, a preamble time, a front training symbol, an information symbol, a rear training symbol, and a guard time are sequentially arranged from the front to the rear. The preamble time is a time for avoiding interference with a burst transmitted and received before the transmission burst and for ramping up. The front training symbol and the rear training symbol are symbols known to the receiving side. In particular, the rear training symbol may be provided with several types of patterns for carrying very little information.

  An information symbol carries user data and is a symbol signal modulated by an arbitrary modulation method. This information symbol modulation method may be different from the training symbol modulation method, and a modulation method with high transmission efficiency such as the QAM method is generally selected. The backward guard time is a time for avoiding interference with a burst that is ramped down and transmitted / received after the transmission burst.

  In digital wireless communication using a transmission burst having the configuration shown in FIG. 3, in order to detect a burst from a received signal, first, a signal sequence including the received burst is confirmed from the front and correlated with a known training symbol signal sequence. The timing when becomes the maximum is detected. Then, assuming that the detected timing is the head of the training symbol signal, an information symbol signal portion is extracted. Thereafter, the information symbol signal is demodulated according to the modulation scheme applied to the information symbol signal.

  Here, the modulation method used for the transmission signal at time x is derived from the received signal quality that the opposite communication apparatus performs feedback from the past transmission. This is based on the premise that the propagation path status will not change within an extremely short time.

High Capacity-Spatial Division Multiple Access (HC-SDMA) WTSC- 2005-032 (ATIS / ANSI) ”

  However, under a multipath fading environment, when the moving speed of the communication device increases, the amount of fading fluctuation per unit time increases, so that temporal coherence is not maintained, and the above assumption is not necessarily satisfied. For this reason, the probability that the setting of the modulation class based on the feedback of the reception quality from the opposite communication apparatus for the own transmission signal is not necessarily appropriate increases.

  As a result, there is a concern that the BER (bit error rate) is deteriorated and the communication quality and the throughput are lowered although the reception quality feedback from the opposite communication apparatus is good. Further, when the moving speed of the communication apparatus is further increased, when a modulation class with a high coding rate is selected, it is almost impossible to demodulate, resulting in poor throughput.

  Accordingly, an object of the present invention made in view of such a point is to provide a digital wireless communication apparatus and a digital wireless communication method capable of reducing a decrease in communication quality and throughput under a multipath fading environment.

An invention of a digital wireless communication apparatus according to a first aspect of achieving the above object is a digital wireless communication that performs communication by adaptively selecting a required modulation class from a plurality of modulation classes composed of a combination of a modulation scheme and a coding rate. A device,
A modulation class determination unit that selects a modulation class of the next transmission data based on self-quality information related to the self-reception quality for the transmission signal from the own device included in the reception signal from the opposite communication device;
A partner quality information creating unit that creates partner quality information related to the partner reception quality for the opposite communication device based on the received signal;
A modulation processing unit that modulates the partner quality information according to a modulation scheme of a modulation class selected by the modulation class determining unit in order to transmit the partner quality information to the opposite communication device;
With
The partner quality information creation unit creates first partner quality information and second partner quality information based on the discontinuous known first training signal and second training signal included in the received signal, respectively. Create third partner quality information based on the first partner quality information and the second partner quality information,
The modulation processing unit modulates the third partner quality information;
It is characterized by this.

Further, the invention of the digital wireless communication apparatus according to the second aspect to achieve the above object is a digital wireless communication in which a required modulation class is adaptively selected from a plurality of modulation classes consisting of a combination of a modulation scheme and a coding rate. A wireless communication device,
A modulation class determination unit that selects a modulation class of the next transmission data based on self-quality information related to the self-reception quality for the transmission signal from the own device included in the reception signal from the opposite communication device;
A partner quality information creating unit that creates partner quality information related to the partner reception quality for the opposite communication device based on the received signal;
A modulation processing unit that modulates the partner quality information according to a modulation scheme of a modulation class selected by the modulation class determining unit in order to transmit the partner quality information to the opposite communication device;
With
The partner quality information creation unit creates first partner quality information and second partner quality information, respectively, based on the discontinuous known first training signal and second training signal included in the received signal,
The modulation processing unit modulates the first partner quality information and the second partner quality information,
The modulation class determining unit selects the modulation class based on first self-quality information and second self-quality information included in a received signal from the opposite communication device;
It is characterized by this.

The invention according to a third aspect is the digital wireless communication apparatus according to the first aspect,
The counterpart quality information creation unit creates the third counterpart quality information based on a comparison between the first counterpart quality information and the second counterpart quality information.
It is characterized by this.

The invention according to a fourth aspect is the digital wireless communication apparatus according to the second aspect,
The modulation class determining unit selects the modulation class based on a comparison between the first self-quality information and the second self-quality information;
It is characterized by this.

Further, the invention of the digital wireless communication method according to the fifth aspect to achieve the above object is a digital wireless communication in which a required modulation class is adaptively selected from a plurality of modulation classes consisting of a combination of a modulation scheme and a coding rate. A wireless communication method,
A first step of selecting a modulation class of the next transmission data based on self-quality information related to the self-reception quality of the transmission signal from the own device included in the reception signal from the opposite communication device by the modulation class determining unit; ,
A second step of creating partner quality information related to the partner reception quality for the opposite communication device based on the received signal by the partner quality information creating unit;
A third step of modulating the partner quality information by a modulation method of a modulation class selected by the modulation class determining unit in order to transmit the partner quality information to the opposite communication device by a modulation processing unit;
In the second step, first partner quality information and second partner quality information are created based on the discontinuous known first training signal and second training signal included in the received signal, respectively. Create third partner quality information based on the quality information and second partner quality information,
In the third step, the third partner quality information is modulated.
It is characterized by this.

  According to the present invention, it is possible to reduce a decrease in communication quality and throughput in a multipath fading environment.

It is a figure which shows an example of the communication system using the digital radio | wireless communication apparatus concerning one embodiment of this invention. It is a functional block diagram which shows schematic structure of the principal part of the digital radio | wireless communication apparatus shown in FIG. It is a figure which shows an example of the transmission burst in digital radio | wireless communication.

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

  FIG. 1 is a diagram illustrating an example of a communication system using a digital wireless communication apparatus according to an embodiment of the present invention. FIG. 1 shows one base station 10 that is a digital wireless communication device and one wireless terminal 20 that is a digital wireless communication device for the sake of simplicity. The base station 10 and the wireless terminal 20 are connected via a wireless link to perform wireless communication. Here, it is assumed that wireless communication is performed according to the burst format shown in FIG. Therefore, the front training symbol in FIG. 3 corresponds to the first training signal, and the rear training symbol corresponds to the second training signal. For the sake of simplicity, it is assumed that the user data carried by the information symbol is only SINR feedback data (quality information) described later.

  FIG. 2 is a functional block diagram showing a schematic configuration of a main part of the digital wireless communication apparatus shown in FIG. Both the base station 10 and the wireless terminal 20 have the same configuration. The digital wireless communication apparatus shown in FIG. 2 includes an antenna 100, a wireless unit 200, an analog / digital conversion unit (ADC) 300, a memory 400, a symbol processing unit 500, and a digital / analog conversion unit (DAC) 600.

  The symbol processing unit 500 includes a reception symbol processing unit 510, a transmission symbol processing unit 530, a known forward training symbol storage unit 550, and a known backward training symbol storage unit 560. Reception symbol processing section 510 includes maximum correlation timing detection section 511, reception forward training symbol SINR estimation section 512, information symbol demodulation processing section 513, backward training symbol pattern estimation section 514, SINR feedback data decoding section 515, and reception backward training symbols. A SINR estimation unit 516 is provided.

  The transmission symbol processing unit 530 includes a front / rear SINR comparison unit 531, a SINR feedback data creation unit 532, a modulation class determination unit 533, an information symbol modulation processing unit 534, a rear training symbol pattern determination unit 535, a rear training symbol addition unit 536, And the front training symbol provision part 537 is provided. The symbol processing unit 500 is configured as software executed on any suitable processor such as a CPU (Central Processing Unit), or by a dedicated processor specialized for each processing, for example, a DSP (Digital Signal Processor). Can be configured.

  In FIG. 2, the received signal incident from the antenna 100 is processed by the radio unit 200, then timely sampled by the ADC 300, converted into a digital signal, and stored in the memory 400.

  In reception symbol processing section 510, maximum correlation timing detection section 511 compares the correlation between the latest received signal sequence stored in memory 400 and the known forward training symbol stored in known forward training symbol storage section 550. To do. When the correlation value becomes equal to or greater than an arbitrary threshold value, the maximum correlation timing detection unit 511 assumes that the subsequent signal is a received burst, and the received signal sampling sequence from the antenna 100 is a received burst sampling signal sequence. Store in memory 400.

  Further, the maximum correlation timing detection unit 511 detects the maximum correlation timing by comparing the forward training symbol length portion of the received burst sampling signal sequence stored in the memory 400 with the known signal sequence while shifting each timing. In practice, the received burst sampling signal sequence in the same memory is used by shifting the index to the start position of each input signal.

  Each received burst sampling signal sequence is subjected to oversampling processing as necessary, and then divided into three systems of a front training symbol, an information symbol, and a rear training symbol. The forward training symbol is supplied to the reception forward training symbol SINR estimation unit 512. Then, reception forward training symbol SINR estimation section 512 estimates reception forward training symbol SINR based on the known forward training symbol stored in known forward training symbol storage section 550. This reception forward training symbol SINR corresponds to first partner quality information related to the partner reception quality for the opposite communication device.

  The information symbol is demodulated by the information symbol demodulation processing unit 513 with a modulation class corresponding to a known backward training symbol estimated by a backward training symbol pattern estimation unit 514 described later. Thus, when the information symbol is correctly demodulated, the demodulated output is supplied to the SINR feedback data decoding unit 515 to decode the SINR feedback data. The decoded SINR feedback data is positioned as a report (feedback data) of the reception SINR of the previous transmission data from the opposite communication device to the communication device. That is, it corresponds to self-quality information related to self-reception quality.

  The backward training symbol is first supplied to the backward training symbol pattern estimation unit 514, and the correlation with the known backward training symbol for each modulation class stored in the known backward training symbol storage unit 560 is sequentially examined. Then, the known backward training symbol pattern having the maximum correlation is estimated to be the received backward training symbol, and the modulation class is supplied to the information symbol demodulation processing unit 513. It should be noted that a portion for carrying information is provided behind the information symbol, and this portion may function as a modulation class, or may be substituted for a known backward training symbol after demodulation.

  Thereafter, the backward training symbols are supplied to the received backward training symbol SINR estimation unit 516. Then, reception rear training symbol SINR estimation section 516 estimates reception rear training symbol SINR based on the known rear training symbol stored in known rear training symbol storage section 560. This reception backward training symbol SINR corresponds to second partner quality information related to the partner reception quality for the opposite communication device.

  On the other hand, when SINR feedback data is transmitted to the opposite communication apparatus, the transmission symbol processing unit 530 performs the following control. First, in the front and rear SINR comparison unit 531, the reception forward training symbol SINR estimated by the reception forward training symbol SINR estimation unit 512 of the reception symbol processing unit 510 and the reception backward training symbol estimated by the reception rear training symbol SINR estimation unit 516 SINR is compared. The comparison result is supplied to the SINR feedback data creation unit 532.

  SINR feedback data creation section 532 creates a SINR value (corresponding to third partner quality information) to be transmitted as SINR feedback data from the following table based on the comparison result from front and rear SINR comparison section 531. Therefore, the reception forward training symbol SINR estimation unit 512, the backward training symbol pattern estimation unit 514, the reception backward training symbol SINR estimation unit 516, the front and rear SINR comparison unit 531, and the SINR feedback data creation unit 532 include the counterpart quality information creation unit. It is composed.

  As the SINR obtained in the above table, when the difference between the received forward training symbol SINR and the received backward training symbol SINR is small, the smaller SINR is adopted. If the difference between the received forward training symbol SINR and the received backward training symbol SINR is large, the smaller SINR is adopted and the offset is subtracted so that a lower modulation class is selected. Yes.

  Also, SINR feedback data from the opposite communication apparatus decoded by SINR feedback data decoding section 515 is supplied to modulation class determining section 533. Then, modulation class determining section 533 selects a modulation class as an information symbol in the next transmission burst based on SINR feedback data. The following table is an example of modulation classes supported by the digital wireless communication apparatus according to the present embodiment and specifications for each modulation class. In the present embodiment, the lower number modulation classes are arranged such that the desired SINR is smaller and the data rate is smaller.

  The modulation class determination unit 533 stores a pair of the modulation class and the desired SINR in the above table, compares the value of the decoded SINR feedback data with the desired SINR corresponding to the youngest modulation class, and compares the desired SINR with the desired SINR. Select the highest numbered modulation class that satisfies. The selected modulation class is supplied to the information symbol modulation processing unit 534 and the backward training symbol pattern determination unit 535. The rear training symbol pattern determination unit 535 determines a rear training symbol pattern of the corresponding modulation class from the known rear training symbols for each modulation class stored in the known rear training symbol storage unit 560, and the determined rear training symbol The pattern is supplied to the rear training symbol assigning unit 536.

  Then, the transmission information symbol for the opposite communication device created by the SINR feedback data creation unit 532 is modulated by the modulation scheme corresponding to the modulation class determined by the modulation class determination unit 533 by the information symbol modulation processing unit 534. Thereafter, in the rear training symbol giving unit 536, the rear training symbol corresponding to the modulation class determined by the rear training symbol pattern determining unit 535 is given to the transmission information symbol. The front training symbol stored in the training symbol storage unit 550 is given.

  Thereafter, the transmission information symbol to which the front training symbol and the rear training symbol are added is converted into an analog signal by the DAC 600, further converted into a radio signal by the radio unit 200, and radiated from the antenna 100.

  As described above, the digital radio apparatus according to the present embodiment estimates the modulation scheme of the information symbol included in the received signal from the received signal and acquires SINR feedback data decoded into the information symbol. Thereby, the SINR in the opposite communication device of the transmission signal transmitted by the communication device last time can be known.

  Further, when the difference between the SINR estimated from the front training symbol and the SINR estimated from the rear training symbol is large, a modulation class having a lower required SINR is selected. As a result, a decrease in BER due to high-speed mobile communication in a multipath fading environment can be suppressed, and as a result, a decrease in communication quality and throughput can be reduced. Even in a multipath environment, a modulation class with a better data rate is selected in situations where the moving speed is at the stop or walking level and there is little fading fluctuation per hour. It can be improved further.

  In the digital radio communication apparatus according to another embodiment of the present invention, in the digital radio communication apparatus shown in FIG. 2, the reception forward training symbol SINR and the reception backward training symbol SINR estimated by the reception forward training symbol SINR estimation unit 512 are provided. The received backward training symbol SINR estimated by the estimation unit 516 is supplied to the information symbol modulation processing unit 534 without passing through the front and rear SINR comparison unit 531 and the SINR feedback data creation unit 532, and is fed back to the opposite radio apparatus.

  Also, the reception forward training symbol SINR (corresponding to the first self-quality information) and the reception backward training symbol SINR (corresponding to the second self-quality information) transmitted from the opposite communication apparatus and decoded by the SINR feedback data decoding unit 515 And a modulation class determining unit 533 selects a modulation class in transmission based on the comparison result. At that time, as in the case of the above embodiment, an offset is given to the comparison result to select a modulation class. Thereby, the effect similar to the said embodiment can be acquired.

  The present invention is not limited to the above-described embodiment, and various modifications or changes can be made without departing from the spirit of the invention.

10 base station 20 wireless terminal 100 antenna 200 wireless unit 300 analog / digital conversion unit (ADC)
400 memory 500 symbol processing unit 510 received symbol processing unit 511 maximum correlation timing detection unit 512 reception forward training symbol SINR estimation unit 513 information symbol demodulation processing unit 514 backward training symbol pattern estimation unit 515 SINR feedback data decoding unit 516 reception backward training symbol SINR Estimating section 530 Transmission symbol processing section 531 Pre- and post-SINR comparison section 532 SINR feedback data creation section 533 Modulation class determination section 534 Information symbol modulation processing section 535 Back training symbol pattern determination section 536 Back training symbol assignment section 537 Forward training symbol assignment section 550 Known Front training symbol storage unit 560 Known rear training symbol storage unit 600 Digital / analog converter unit (DAC)

Claims (5)

A digital wireless communication apparatus for adaptively selecting a required modulation class from a plurality of modulation classes consisting of a combination of a modulation scheme and a coding rate and communicating.
A modulation class determination unit that selects a modulation class of the next transmission data based on self-quality information related to the self-reception quality for the transmission signal from the own device included in the reception signal from the opposite communication device;
A partner quality information creating unit that creates partner quality information related to the partner reception quality for the opposite communication device based on the received signal;
A modulation processing unit that modulates the partner quality information according to a modulation scheme of a modulation class selected by the modulation class determining unit in order to transmit the partner quality information to the opposite communication device;
With
The partner quality information creation unit creates first partner quality information and second partner quality information based on the discontinuous known first training signal and second training signal included in the received signal, respectively. Create third partner quality information based on the first partner quality information and the second partner quality information,
The modulation processing unit modulates the third partner quality information;
A digital wireless communication device. A digital wireless communication apparatus for adaptively selecting a required modulation class from a plurality of modulation classes consisting of a combination of a modulation scheme and a coding rate and communicating.
A modulation class determination unit that selects a modulation class of the next transmission data based on self-quality information related to the self-reception quality for the transmission signal from the own device included in the reception signal from the opposite communication device;
A partner quality information creating unit that creates partner quality information related to the partner reception quality for the opposite communication device based on the received signal;
A modulation processing unit that modulates the partner quality information according to a modulation scheme of a modulation class selected by the modulation class determining unit in order to transmit the partner quality information to the opposite communication device;
With
The partner quality information creation unit creates first partner quality information and second partner quality information, respectively, based on the discontinuous known first training signal and second training signal included in the received signal,
The modulation processing unit modulates the first partner quality information and the second partner quality information,
The modulation class determining unit selects the modulation class based on first self-quality information and second self-quality information included in a received signal from the opposite communication device;
A digital wireless communication device. The counterpart quality information creation unit creates the third counterpart quality information based on a comparison between the first counterpart quality information and the second counterpart quality information.
The digital wireless communication apparatus according to claim 1. The modulation class determining unit selects the modulation class based on a comparison between the first self-quality information and the second self-quality information;
The digital wireless communication apparatus according to claim 2. A digital wireless communication method for adaptively selecting and communicating a required modulation class from a plurality of modulation classes consisting of a combination of a modulation scheme and a coding rate,
A first step of selecting a modulation class of the next transmission data based on self-quality information related to the self-reception quality of the transmission signal from the own device included in the reception signal from the opposite communication device by the modulation class determining unit; ,
A second step of creating partner quality information related to the partner reception quality for the opposite communication device based on the received signal by the partner quality information creating unit;
A third step of modulating the partner quality information by a modulation method of a modulation class selected by the modulation class determining unit in order to transmit the partner quality information to the opposite communication device by a modulation processing unit;
In the second step, first partner quality information and second partner quality information are created based on the discontinuous known first training signal and second training signal included in the received signal, respectively. Create third partner quality information based on the quality information and second partner quality information,
In the third step, the third partner quality information is modulated.
A digital wireless communication method.

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