JP2019092014A - Frame error rate prediction device, wireless communication device and wireless communication system - Google Patents

Abstract

To provide a technique for accurately predicting a frame error rate even in the presence of a subcarrier in which received power drops significantly in the convolutional coding orthogonal frequency division multiplexing method.SOLUTION: A frame error rate predicting apparatus 1110 of a communication system that communicates by simultaneous transmission in a plurality of frequency bands according to the convolutional coding orthogonal frequency division multiplexing method includes a frame error rate prediction unit 3030 that calculates a pairwise error rate of an error path in decoding processing for convolutional coding and predicts a frame error rate on the basis of propagation path characteristic information representing attenuation of propagation path power and noise power estimated in a communication path in consideration of symbol errors within a predetermined distance occurring between symbols farther than the nearest symbol specified by information of an interleaving scheme and a modulation scheme in an error pattern of the received signal.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a frame error rate prediction apparatus, and a configuration of a wireless communication apparatus and a wireless communication system using the same.

  In recent years, offloading of mobile traffic has progressed in the ISM (industrial, scientific, and medical radio) band, and it is desired to improve the frequency utilization efficiency of a wireless local area network (LAN). In order to realize high frequency utilization efficiency, it is necessary to be able to achieve a frame error rate (FER) sufficiently low for practical use and to use a transmission rate as high as possible. In general, it is conceivable to control MCS (modulation and coding scheme) according to the propagation condition so that FER is about 1% to 10%. Here, MCS refers to a table of predetermined combinations of modulation schemes and channel coding rates (see, for example, Patent Document 1). For example, when the reception condition of the receiver is poor, or when transmission data that requires communication with a low error rate uses MCS with a low transmission rate, conversely, when the reception condition of the receiver is good, a relatively high error Transmission data that allows rates is adaptively controlled using a decision method such as using a high transmission rate MCS.

  As a method of controlling to a suitable MCS in a wireless LAN, there is known a method of adjusting the MCS according to the transmission success rate and the number of retransmissions, and selecting the MCS suitable for the propagation situation (see Non-Patent Document 1) . However, in this method, since frame transmission is performed with MCS that does not match the propagation condition until an optimal MCS is selected, throughput may be reduced due to retransmission and low rate transmission. Therefore, to improve transmission efficiency, it is desirable to predict FER (Frame Error Rate) in advance and to determine MCS based on the result. However, to achieve that, high-accuracy FER prediction is required.

  Since FER can be calculated from the frame size and the bit error rate (BER) after decoding, FER can be predicted by predicting the BER after decoding.

In general, when it is accurately predicted that the FER will be approximately 1% to 10% in a wireless LAN, it is necessary to estimate the BER accurately in a region where the BER is approximately 10 ⁻⁵ . In such a low BER area, it is known that the post-decoding error rate can be accurately determined by pairwise error probability (PEP) (Non-Patent Document 2).

  In the case where the error rate is determined by PEP in the currently popular IEEE 802.11a or later wireless LAN, it is necessary to determine the PEP in convolutional coded OFDM (COFDM: coded orthogonal frequency division multiplexing). The PEP in COFDM has been studied in Non-Patent Document 3 and so on.

  In Non-Patent Document 3, analysis of PEP is performed when bit errors after interleaving can be regarded as random. When it can be regarded as random error, an error path in which the Hamming distance is separated by the minimum free distance becomes dominant, and the frequency response of the propagation path can also be regarded as random. Non-Patent Document 3 uses this property to formulate a BER independent of the power delay profile of the propagation path from the PEP of the error path having the minimum free distance. It can be said that this method can accurately predict BER in a low BER region in an environment that can be regarded as a random error.

  However, assuming a practical wireless LAN operation, the communication path is not necessarily an environment that can be regarded as a random error. In a wireless LAN such as IEEE802.11a, since the bandwidth and interleaving size are not sufficiently wide and only delay dispersion of several hundreds of [ns] is considered, the occurrence of bit errors can be sufficiently dispersed. It may not be possible. Therefore, the frequency response can not be regarded as random equivalently, and the above-mentioned approximate expression of Non-Patent Document 3 does not hold, which does not depend on the frequency response of the propagation path. In addition, the premise that the PEP of the error path of the minimum free distance dominates does not hold, and it is necessary to consider the PEP of the error path having the Hamming distance greater than the minimum free distance. Therefore, in the approximate expression derived in Non-Patent Document 3, BER in a wireless LAN environment can not be accurately approximated.

  In order to solve such a problem, the technique disclosed in Non-Patent Document 4 estimates a bit error rate prediction at a transmitter, a receiver, or both in a communication system that communicates by convolutional coding OFDM. Considering the pairwise error rate (PEP) of the error path farther than the minimum free distance of the convolutional coding for each of the set of MCS based on the information representing the power attenuation by the selected communication path and the noise power , Predict bit error rate after decoding. As frame error rate prediction, a frame error rate is predicted based on a predicted bit error rate.

  FIG. 12 is a diagram for explaining the concept of the process of Non-Patent Document 4 as described above.

  As shown in FIG. 12, according to Non-Patent Document 4, a convolutionally encoded signal is subjected to interleaving processing by an interleaving unit and then mapped to an error bit in an error path as being mapped to a single band. The pairwise error rate (PEP) is calculated from the signal point distance determined by the SNR of the subcarrier to be selected and the modulation scheme.

  On the other hand, Non-Patent Document 5 and Non-Patent Document 6 propose WLAN systems that simultaneously use multiple bands such as 5 GHz, 2.4 GHz and 920 MHz in order to increase spectral efficiency. Here, the proposed multiple frequency band WLAN system searches for available radio resources from multiple frequency bands by carrier sensing. If two or more available bands are found, the encoded payload in the frame is divided into multiple parts, which are mapped onto the available bands, properly modulated, and the modulated symbols simultaneously Will be sent. At the receiver side, the frames divided into multiple bands are integrated and decoded. Since there are different propagation characteristics for each band, the system proposed here can improve spectral efficiency by using idle resources distributed in multiple bands while obtaining frequency diversity. it can.

Unexamined-Japanese-Patent No. 2010-41074 specification

Unexamined-Japanese-Patent No. 2011-211433 specification

Unexamined-Japanese-Patent No. 2013-18756 specification

S. Biaz and S. Wu, “Rate adaptation algorithms for IEEE 802.11 networks: A survey and comparison,” 2008 IEEE Symposium on Computers and Communications, pp. 130-136, July 2008.

A. Martinez, A. Guillen i Fabregas, and G. Caire, “Error probability analysis of bit-interleaved coded modulation,” IEEE Transactions on Information Theory, vol. 52, no. 1, pp. 262-271, Jan. 2006.

Y. Hori and H. Ochiai, “Performance analysis and interleaver structure optimization for short-frame BICM-OFDM systems,” IEEE Transactions on Wireless Communications, vol. 15, no. 1, pp. 651-662, Jan. 2016.

菅 et al., “Bit Error Rate Prediction of Convolutionally Coded OFDM Transmission Suitable for IEEE 802.11 Wireless LAN,” IEICE Technical Report IT 2016-125, Mar. 2017.

N. Egashira, K. Yano, S. Tsukamoto, J. Webber, M. Sutoh, Y. Amezawa, and T. Kumagai, “Integrated synchronization scheme for WLAN systems employing multiband simultaneous transmission,” Proc. 2017 IEEE Wireless Commun. Netw. Conf. (WCNC).

K. Yano, N. Egashira, S. Tsukamoto, J. Webber, and T. Kumagai, “Channel access balancing for multi-band wireless LAN by using alternative primary channel,” Proc. 2017 IEEE Wireless Comman. And Netw. Conf. ).

However, the prior art as disclosed in Non-Patent Document 4 is different from the conventional art as disclosed in Non-Patent Document 5 and Non-Patent Document 6 above in transmission quality for each band, so transmission quality is different. It is considered that the combined modulation scheme is used separately in each band.
Therefore, there is a problem that each bit in the same frame is subjected to different modulation, and PEP can not be calculated with the existing technology framework because it is affected by different propagation paths.
Furthermore, in the OFDM system under a multipath environment, symbol errors between distant symbols occur with a certain probability, because there are subcarriers in which the received power drops significantly. In the PEP calculation process as disclosed in Non-Patent Document 4, there is also a problem that since errors in adjacent symbols are taken into consideration, there is no consideration in the case of errors in symbols farther from the adjacent symbols.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a communication system by convolutional coding orthogonal frequency division multiplexing in the case where there are subcarriers for which received power is greatly reduced. Another object of the present invention is to provide a frame error rate prediction apparatus capable of accurately predicting a frame error rate.
Another object of the present invention is that, in a communication system using simultaneous transmission of a plurality of bands, a frame error can be accurately detected even if there are subcarriers for which the received power drops when the modulation scheme is different for each band and the propagation environment is different. To provide a wireless communication apparatus and a wireless communication system capable of predicting a rate and setting a modulation scheme adaptively for each band.

  According to one aspect of the present invention, there is provided a frame error rate prediction apparatus of a communication system for performing multi-level modulation on convolutionally encoded symbols and performing communication using orthogonal frequency division multiplexing, which is employed in convolutional coding. Storage means for storing information of interleaving scheme of convolutional coding and information of modulation scheme of multilevel modulation, propagation path characteristic information representing attenuation of propagation path power estimated in communication path, and Based on the noise power, symbol errors within a predetermined distance between symbols separated from the nearest symbol, which are specified by the interleaving and modulation scheme information stored in the storage means in the error pattern of the received signal, are considered Then, calculate the pairwise error rate of the error path in the decoding process for convolutional coding, The pairwise error rate is, and a frame error rate estimating means for estimating the frame error rate.

  Preferably, the predetermined distance is a distance at which the squared Euclidean distance between the error symbol and the correct symbol taking into account the power attenuation of the communication path for the error pattern of the symbol error to be considered is smaller than a predetermined value.

  Preferably, for the error pattern that can be generated by the configuration of the encoder for convolutional coding, the predetermined distance signals the squared Euclidean distance between the error symbol and the correct symbol corresponding to the error bit in the error pattern. It is a predetermined upper limit value of the sum of the integer coefficients when the minimum Euclidean distance between points is divided into the square and the integer coefficients.

According to another aspect of the present invention, there is provided a radio communication apparatus for performing simultaneous transmission in a plurality of frequency bands by means of convolutional coding orthogonal frequency division multiplexing, which is a propagation path for each frequency band transmitted from a receiving apparatus. Receiving means for receiving, as feedback information, propagation path characteristic information representing power attenuation and noise power estimation value, and a coding rate of convolutional coding preset as employed in the convolutional coding orthogonal frequency division multiplexing system And storage means for storing information of a set of modulation schemes, convolutional encoding processing means for performing convolutional encoding processing on a transmission data string, interleaving means for interleaving the outputs of the encoding processing means, Parser means for dividing an interleaved signal according to a plurality of frequency bands, and output from the parser means Modulating means for performing multi-level coding and performing orthogonal frequency division multiplexing modulation with a plurality of subcarriers, and based on feedback information, set the throughput to the maximum among the combinations of the coding rate and the modulation scheme stored in the storage means. Selecting means for selecting a pair to be selected, the selecting means storing interleaving scheme information of convolutional encoding and modulation scheme information of multilevel modulation, which are preset as employed in the convolutional encoding scheme. Information of the interleave method and modulation method stored in the storage means in the error pattern of the received signal based on the storage means of the above and the propagation path characteristic information representing attenuation of the power of the propagation path and noise power estimated in the communication path Consider symbol errors within a predetermined distance that occur between symbols farther than the nearest symbol identified by A pairwise error rate calculation means for calculating a pairwise error rate of an error path in decoding processing for convolutional coding; a frame error rate prediction means for predicting a frame error rate based on the calculated pairwise error rate; Modulation scheme selecting means for selecting a set having a maximum throughput within a predetermined frame error rate based on the frame error rate, and for the transmission data according to the set selected by the modulation scheme selection unit , Transmission means for performing and performing convolutional coding and modulation processing.
Preferably, the predetermined distance is a distance at which the squared Euclidean distance between the error symbol and the correct symbol taking into account the power attenuation of the communication path for the error pattern of the symbol error to be considered is smaller than a predetermined value.

Preferably, for the error pattern that can be generated by the configuration of the encoder for convolutional coding, the predetermined distance signals the squared Euclidean distance between the error symbol and the correct symbol corresponding to the error bit in the error pattern. It is a predetermined upper limit value of the sum of the integer coefficients when the minimum Euclidean distance between points is divided into the square and the integer coefficients. According to still another aspect of the present invention, there is provided a wireless communication system for performing simultaneous transmission in a plurality of frequency bands by means of convolutional coding orthogonal frequency division multiplexing, comprising a receiving apparatus, the receiving apparatus comprising: Average received power for each frequency band, channel characteristic information representing attenuation of channel power and communication path state estimation means for estimating noise power, average received power for each estimated frequency band, channel characteristic information and noise And a first transmitting means for transmitting power, and further comprising a transmitting device, wherein the transmitting device is a propagation path representing the attenuation of the average reception power for each frequency band and propagation path power transmitted from the receiving device. A receiver configured to receive characteristic information and an estimated value of noise power as feedback information, and is preset to be employed in convolutional coding orthogonal frequency division multiplexing. Storage means for storing information on the combination of the coding rate of the convolutional encoding and the modulation scheme, convolutional encoding processing means for performing convolutional encoding processing on the transmission data string, and output of the encoding processing means Interleaving means for performing interleaving processing, parser means for dividing the signal after interleaving processing according to a plurality of frequency bands, multi-level coding of the output from the parser means, orthogonal frequency division by a plurality of subcarriers The modulation circuit comprises: modulation means for multiplex modulation; and selection means for selecting a set that maximizes throughput among the combinations of coding rate and modulation scheme stored in the storage means based on feedback information, the selection means comprising: , Information of convolutional encoding interleaving method preset as that adopted in convolutional encoding method and multilevel modulation Based on storage means for storing modulation scheme information, and on the basis of propagation path characteristic information representing the attenuation of the propagation path power and noise power estimated on the communication path, the average reception power for each frequency band, and noise power Decoding processing for convolutional coding in consideration of symbol errors within a predetermined distance occurring between symbols separated from the nearest symbol specified by information of interleaving method and modulation method stored in storage means in error pattern Based on the pairwise error rate calculation means for calculating the pairwise error rate of the error path in the above, the frame error rate prediction means for predicting the frame error rate on the basis of the calculated pairwise error rate, and the predicted frame error rate. Select a modulation scheme that selects the set with the highest throughput within a predetermined frame error rate And transmission means for transmitting a modulation signal for the transmission data train modulated by the modulation means in accordance with the set selected by the modulation scheme selection unit.
(Definition of terms)
In the present specification, the meaning of terms is as follows.

"Pairwise error rate (PEP)" and, when the code word C _L of the length L from the transmitter and is transmitted, the receiver side of this sequence, when decoding contain errors and C _L ', the code word C _L refers to the probability determining mistakenly codeword C _L '.

  The “minimum free distance” means that, in the convolutional code, when the code words for two information sequences u and v are c (u) and c (v), two code sequences of all error paths and true paths are used. The minimum value of the Hamming distance.

  The “power delay profile” indicates how received power is distributed in the delay time domain, assuming that a propagation path is composed of multiple paths with different delay times. That is, in the propagation path of the implementation, the impulse response has a time spread because the path length is different for each path. Therefore, the "power delay profile" is represented by the squared average value of the impulse response.

  The "diversity order" refers to the number of subcarriers for which the frequency response of each subcarrier to which different bits are mapped between the codeword corresponding to a certain error path and the transmission codeword can be regarded as random (uncorrelated). In an environment where channel errors can be regarded as random errors, the diversity order is maximum (the frequency response of the channel through which different bits have passed between the codeword corresponding to the error path and the transmission codeword is uncorrelated). If the diversity order is lower, burst errors are likely to occur and the BER is degraded.

  The "error path" refers to a path in which a bit error occurs when the path is selected by maximum likelihood decoding for a convolutional code.

  The “error pattern” refers to a code word of an error path corresponding to a section different between the true path and the error path. In a predetermined convolutional code, since the number of error patterns that can occur is limited according to the generator polynomial, they are numbered and referred to as, for example, “p th error pattern”.

  The “Hamming distance” refers to the number of different bits in corresponding positions in two bit strings.

According to the present invention, in a communication system based on convolutional coding orthogonal frequency division multiplexing, a frame error rate prediction device capable of accurately predicting a frame error rate even when there is a subcarrier in which received power drops significantly. To provide.
Another object of the present invention is that, in a communication system using simultaneous transmission of a plurality of bands, a frame error can be accurately detected even if there are subcarriers for which the received power drops when the modulation scheme is different for each band and the propagation environment is different. To provide a wireless communication apparatus and a wireless communication system capable of predicting a rate and setting a modulation scheme adaptively for each band.

FIG. 1 is a block diagram for describing a configuration of a wireless communication system according to a first embodiment. It is a conceptual diagram for demonstrating typically transmission and reception processing by an OFDM system. FIG. 10 is a diagram showing an error path at d _H = 5 of a convolutional code having a constraint length of 3 and a generator polynomial (5, 7) ₈ ; It is a conceptual diagram explaining flame | frame error rate prediction of this Embodiment, and is a figure contrasted with FIG. FIG. 16 is a block diagram for describing a configuration of an adaptive rate control unit 1110. 5 is a flowchart for describing adaptive rate control according to the first embodiment. FIG. 5 is a diagram showing constellations of in-phase components of 16 QAM and subsets thereof used in a wireless LAN. It is a figure which shows the example of the pattern of distance (DELTA) (under bar) between symbols of an error symbol. It is a figure which shows the generation | occurrence | production ratio of each symbol error pattern in simulation. It is a figure which shows the parameter of the simulation used in FIG. It is a figure which shows comparison with FER prediction and a simulation result. It is a figure for demonstrating the concept of the process of a nonpatent literature 4. FIG.

Hereinafter, configurations of a wireless communication system and a wireless communication apparatus according to an embodiment of the present invention will be described. In the following embodiments, components and processing steps denoted by the same reference numerals are the same or equivalent, and the description thereof will not be repeated if not required.
(Issues of frame error rate prediction in a communication system for simultaneous transmission of multiple bands)
In the following, as a premise for describing the embodiment of the present invention, the technique disclosed in Non-Patent Document 4 described above is used for simultaneous transmission of multiple bands as disclosed in Non-Patent Document 5 and Non-Patent Document 6. The problems in the case of application to the communication system are briefly summarized.

  In the following description, it is assumed that the wireless communication system uses simultaneous transmission of a plurality of bands and is based on convolutional coding orthogonal frequency division multiplexing. However, the frame error rate prediction apparatus of the present embodiment is not limited to simultaneous transmission of a plurality of bands, and is also applicable to single frequency band transmission.

Consider a trellis path (hereinafter referred to as a true path) that produces a codeword with all 0 configuration bits and a path (hereinafter referred to as an error path) that produces a codeword separated by a Hamming distance d _H (the convolutional code is a linear code. There is no loss of generality even if you set a true path and an error path like
FIG. 3 is a diagram showing an error path at d _H = 5 of a convolutional code having a constraint length of 3 and a generator polynomial (5, 7) ₈ .

  In this case, the true path corresponds to the code word ..., 0, 0, 0, 0, 0, 0, ..., and the error path corresponds to the code word ..., 1, 1, 0, 1, 1, 1, ... Do. Since the error path leaves the true path at a certain position on the trellis (t = 2 in FIG. 3) and then merges, it has a pattern of bits different only in this section.

Furthermore, as described below, a frame error rate is predicted based on such error patterns that may occur for a given convolutional code.
According to Non-Patent Document 4, conditional PEP is expressed by the following equation.

Error path e _{t, p} a (underscore) interleaves, the sub-carrier number w th error bit error pattern is mapped k _w, the intra-symbol bit positions for transmitting in the sub-carrier and i _w. Further, the distance represented by Δ _w (i _w ) is a square Euclidean distance between the signal point when there is no error and the signal point when there is an error bit, for the symbol to which the error bit is assigned. Also, H _k represents the frequency response of the k th subcarrier, and H _kw is the frequency response of the subcarrier to which the w th error bit is mapped. Furthermore, H (under bar) and Δ (under bar) are vectors having H _kw and Δ _w (i _w ) as elements, respectively.

  In this case, PEP finds expected values for H (under bar) and Δ (under bar)

Is given by the following equation.

Here, E {...} _a represents an expected value operation for a. In equation (1), assuming that the propagation path changes for each transmission frame, in order to derive post-decoding FER in the case of transmitting a plurality of frames, an expected value is obtained for the frequency response H _kw of the subcarrier. Also, Δ _w (i _w ) can be determined from the true path and error path, and the interleaver structure, but in practice the true path depends on the input bit of the encoder and Δ _w (i _w ) is a random variable Become. Therefore, in Equation (1), the expected value is also obtained for Δ _w (i _w ). Further, according to Non-Patent Document 4, conditional PEP is given by the following equation.

According to the equation (1), in order to derive the PEP, it is sufficient to obtain an expected value of H _kw and Δ _w (i _w ) for the equation (2).
Here, it is considered to obtain an expected value for Δ _w (i _w ).
Since Δ _w (i _w ) is a finite discrete random variable having a probability density different depending on the bit position i _w in the symbol, it is as follows.

Here, assuming that m _iw possible values of the discrete random variable Δ _w (i _w ), the following relationship is established.

In the region where the error rate is low, it is expected that symbol errors will be dominated by cases where errors occur in adjacent signal points.
If the minimum Euclidean distance between the signal points and _{d min, w = 1, ...} , d H relative to Δ _w (i _w) = a d _min ² become term is dominant in the U sections expectations Be done. In addition, U patterns occur with equal probability P, and are determined from the modulation scheme and the error path (coder configuration), and the configuration of the interleaver and parser.
Thus, the conditional pairwise error rate is expressed as:

In the above equation, d _H is the Hamming distance of the error path, as described above, and is determined from the configuration of the encoder.

H _kw is the frequency response of the propagation path, and can be estimated on the receiver side.

  However, there are the following problems in applying the above equation to a system with simultaneous transmission of multiple bands.

  1) Communication in a single band is assumed, and it is formulated that the average SNR in the band is single. Therefore, it is not possible to calculate the PEP in the case where the SNR is largely different for each band, such as simultaneous transmission in multiple bands.

2) Further, since Δ _w (i _w ) = d _min ² , when the modulation scheme is changed for each band, the fact that the distance between signal points is different is not taken into account.

  3) In the low FER region, assuming that the symbol errors occurring between adjacent symbols are dominant, only the symbol errors occurring between adjacent symbols are considered, and the sum of the symbol error patterns is approximated by one term. However, since there are sub-carriers in which the received power drops significantly in practice, symbol errors between distant symbols occur with a certain probability. Therefore, PEP can not be accurately calculated by the calculation method in which only symbol errors between adjacent symbols are considered.

Therefore, in the following, a configuration for coping with such a problem will be described.
First Embodiment
FIG. 1 is a block diagram for explaining the configuration of the radio communication system according to the first embodiment.

  Referring to FIG. 1, transmitting apparatus 1000 performs error correction coding section 1002 for performing error correction coding processing using convolutional code on data of a transmission sequence, and data for error correction coding. The parallel-to-parallel conversion is performed on the output from the interleaving unit 1004 that performs interleaving processing, the interleaving unit 1004 that performs interleaving processing, the parser 1006 that divides the data stream after interleaving into data streams for each of multiple bands, and the parser 1006 The data stream is divided into the number of subcarriers based on the selected MCS, and modulation units 1010.1 to 1010.3 for performing subcarrier modulation on the divided data are provided.

  Although not particularly limited, in FIG. 1, three bands are used as a plurality of bands, and it is assumed that modulation sections 1010.1 to 1010.3 are provided corresponding to these three bands, respectively. . In the following, as an example, the 5 GHz, 2.4 GHz and 920 MHz bands of the ISM band are used as such three bands.

  Further, transmitting apparatus 1000 performs inverse Fourier transform processing and guard interval addition processing on the digital signals output from modulation sections 1010.1 to 1010.3 to perform orthogonal frequency division multiplexing (OFDM: orthogonal frequency division multiplexing). ) OFDM modulation units 1012.1 to 1012.3 for generating symbols and performing digital-to-analog conversion processing, orthogonal modulation processing, up-conversion processing, power amplification processing, etc. on signals after OFDM modulation It includes high frequency processing units (RF units) 1014.1 to 1014.3 to be executed, and antennas 1020.1 to 1020.3 for transmitting high frequency signals from the RF units 1014.1 to 1014.3.

  Note that the RF units 1014.1 to 1014.3 also execute low noise amplification processing, down conversion processing, quadrature demodulation processing, and the like on the signals received by the antennas 1020.1 to 1020.3.

  Also, the modulation scheme of subcarrier modulation is not particularly limited, and it is assumed that there are, for example, types such as BPSK, QPSK, 16 QAM, 64 QAM, and the like.

  Further, transmitting apparatus 1000 receives the estimated values of average received power, power delay profile and noise power from receiving apparatus 2000 side through RF sections 1014.1 to 1014.3 to execute demodulation and decoding processing. Control processing for adaptively changing the MCS based on the received signal processing unit 1100 and the average received power, the power delay profile, and the noise power estimated value, and the coding rate and modulation unit of the error correction coding unit 1002. And an adaptive rate control unit 1110 for controlling the modulation scheme in 101.about.101.30.3.

  The communication method of the average received power from the receiving apparatus 2000, the power delay profile, and the estimated value of the noise power may be the same communication method as that of data transmission, or may be another communication method.

  The receiving apparatus 2000 executes low noise amplification processing, down conversion processing, quadrature demodulation processing, and the like of the signals of the antennas 2002.1 to 2002.3 and the antennas 2002.1 to 2002.3 respectively corresponding to the three bands described above. Executes OFDM demodulation processing such as analog-to-digital conversion processing, guard interval removal processing, Fourier transform processing, etc. on the signals from the RF units 2010.1 to 2010.3 and RF units 2010.1 to 2010.3, respectively Received data by the inverse processing of the modulation units 1010.1 to 1010.3 with respect to the signals from the OFDM demodulation units 2012. Demodulation units 2014.1 to 2014.3 for generating a row, demodulation units 2014.1 to 2014. On the signal from the despreader, the deinterleaver 2016 for deinterleaving the signal sequence from the deparser 2015, and the error correction process by the convolutional code And an error correction unit 2018 for performing the process.

  Also in the receiving apparatus 2000, the RF units 2010.1 to 2010.3 execute orthogonal modulation processing, up conversion processing, power amplification processing, and the like for transmitting the average received power, the power delay profile, and the estimated value of the noise power. It shall be.

  Receiving apparatus 2000 further calculates the estimated value of the average received power, the estimated value of the power delay profile, and the estimated value of the noise power by, for example, a pilot signal or the like in the signal received via RF units 2010.1 to 2010.3. The estimated values from the average received power / power delay profile / noise power estimation unit 2100 and the average received power / power delay profile / noise power estimation unit 2100 to be performed are converted into transmission signals, and the RF units 201.about.2010 And a transmission processing unit 2110 for transmitting from the antenna 2002 to the transmitting apparatus 1000 via the communication section 3.

  FIG. 2 is a conceptual diagram for schematically explaining transmission and reception processing in the OFDM system shown in FIG.

  As shown in FIG. 2, the convolutionally encoded and interleaved transmission signal is mapped for each subcarrier as a complex signal by a predetermined modulation scheme, and is subjected to digital-to-analog conversion after inverse Fourier transformation to perform quadrature modulation etc. It is subjected to frequency conversion processing including and sent to the transmission line.

  The signal received from the transmission path is subjected to frequency inverse conversion including quadrature detection, analog-to-digital converted, and Fourier-transformed, and the demapped received signal is subjected to de-interleave processing and error correction processing using a convolutional code. Be done.

A convolutional code is a linear code, and consider a trellis path (hereinafter, true path) which produces a code word having all 0 configuration bits and a path (hereinafter, error path) which produces a code word separated by Hamming distance d _H.

  FIG. 4 is a conceptual diagram for explaining frame error rate prediction according to the present embodiment, which is to be compared with FIG.

  As shown in FIG. 4, in this embodiment, since the parser divides the transmission data sequence into bands, the case where error bits in an error path are mapped to different bands is considered.

That is, as will be described later, the bands to be mapped are calculated from the configuration of the interleaver and the parser, a coefficient representing the average power of each band is introduced, and a difference in received power for each band is taken into account. The distance between signal points is calculated from the modulation scheme of the band to which is mapped, the pairwise error rate is calculated, and the frame error rate is predicted. Furthermore, when calculating the PEP, the PEP is calculated in consideration of symbol errors occurring between distant symbols.
[Configuration of prediction processing of FER]
FIG. 5 is a block diagram for explaining the configuration of adaptive rate control section 1110 shown in FIG.

  Referring to FIG. 5, adaptive rate control section 1110 includes MCS storage section 3020 for storing information on a set of MCSs set in advance, and an estimated value of average received power sent from the receiving apparatus 2000 side. The frame error rate (FER) is calculated for each MCS stored in the MCS storage unit 3020 based on the information on the frame size used for communication in response to the estimated value of the power delay profile and the estimated value of the noise power. An MCS selection unit 3040 that selects the MCS that achieves the maximum throughput among the MCSs lower than the FER preset and required in the system based on the FER prediction unit 3030 that predicts MCS and the predicted FER value. And.

  The operation of the FER prediction unit 3030 will be described in more detail later.

  FIG. 6 is a flowchart for explaining adaptive rate control according to the first embodiment.

  Referring to FIG. 6, first, on the receiving apparatus 2000 side, an average received power / power delay profile / noise power estimation unit 2100 executes estimation of average received power, power delay profile, and noise power (S100).

  The estimation of the power delay profile and the estimation of the noise power are not particularly limited, and for example, the methods disclosed in the following documents can be used.

Known Literature 1: T. Cui and C. Tellambura, “Power delay profile and noise variance estimation for OFDM,” IEEE Communications Letters, vol. 10, no. 1, pp. 25-27, Jan 2006
Also, there is no particular limitation on the estimation of the average received power, but, for example, publicly known documents 2: S. Hong, Y. Li, YC He, G. Wang, and M that can use the method disclosed in the following documents: Jin, “A cyclic correlation based blind SINR estimation for OFDM systems,” Communications Letters, IEEE, vol. 16, no. 11, pp. 1832-1835, Nov. 2012.
When the power delay profile is estimated including the received power (ie, as _{b b} P _b ), it is not necessary to separately estimate the average received power, and only the power delay profile is estimated.

  The estimated value is transmitted from the receiver 2000 (S102), received by the transmitter 1000 (S104), and the FER predictor 3030 of the transmitter 1000 transmits a pairwise error rate frame within an error path for each time point in the frame. The predicted value of the frame error rate is calculated for each MCS by calculating the sum at step S108 (S108), and the MCS selection unit 3040 specifies a prescribed one of the predetermined MCSs based on the calculated frame error rate. In the range which achieves FER, MCS which becomes the largest throughput is selected (S110).

  According to the selected MCS, error correction coding section 1002 performs convolutional coding at the selected coding rate, and modulation section 1010 performs subcarrier modulation in the selected multilevel modulation scheme ( S112).

  The modulated data is transmitted from transmitting apparatus 1000 (S114) and received by receiving apparatus 2000 (S116).

With such processing, the receiver can estimate the average received power, the power delay profile, and the noise power, and can adaptively change the coding rate and the modulation scheme at the time of feedback to the transmitter. . Therefore, by accurately predicting the frame error rate (FER), it is possible to reduce the number of frame transmissions in MCS that do not match the propagation situation and to improve the throughput.
[Operation Performed by FER Predictor 3030]
Below, the operation | movement which the FER estimation part 3030 performs is demonstrated according to numerical formula.

1. Characteristics of the Method of the Present Embodiment As will be apparent from the following description, the prediction of FER of the present embodiment has the following characteristics.

  1) Calculate the band to be mapped from the configuration of the interleaver and the parser, introduce a coefficient representing the received power of each band, and consider the difference in received power for each band.

  2) The distance between the signal points is calculated from the modulation scheme of the band to which the error bit is mapped, the pairwise error rate is calculated, and the frame error rate is predicted.

  3) Calculate PEP in consideration of symbol errors that occur between symbols that are farther than the nearest symbol interval.

  A more detailed description will be given below.

2. System Model In the following, let B be the number of available bands as a system for simultaneous communication of multiple frequency bands. In the example of FIG. 1, B = 3.

  Also, although not particularly limited, as an example, information bits are provided to the error correction coding unit 1002 at a coding rate of R = 1/2.

  At this time, the generated codeword is expressed by the following equation.

L _frame is the codeword length, and c _j ∈ {0, 1} is the j-th encoded bit in codeword c (under bar). Note that, in the following, a character x with an underbar is described as “x (underbar)”, and the character x represents a vector.

  The codewords are interleaved and divided into a plurality of available bands by an interleaving unit 1004 and a parser 1006.

  Then, as described above, each of the divided codewords is individually modulated in each band and mapped to corresponding subcarriers.

If the jth coded bit c _j is mapped to the ith bit of the modulated symbol on the kth subcarrier in the bth band, this mapping is expressed as:

The frame to be transmitted is generated by applying OFDM modulation processing to the modulated symbols mapped to the subcarriers.

Now, in the following embodiment, although the propagation path (channel) is static in a frame, it is considered that it varies independently in each frame (block fading).
The channel impulse response h ′ _b (under bar) of the b-th band is expressed as follows.

If h _b (under bar) is any vector according to a compound Gaussian distribution with mean 0 and variance 1, then P _b is an L _b × L _b diagonal matrix with nonnegative real values p _l on the main diagonal components (L _b is the length of the channel impulse response).

The diagonal component p _l is the power delay profile of the L _b taps of the frequency selective channel and satisfies the following equation:

It is assumed that the maximum multipath delay time from the primary arrival path does not exceed the guard interval (GI) length.

  At the receiver side, it is assumed that the reception signal of the kth subcarrier in each band after OFDM demodulation is represented by the following equation (6).

Here, when _{b b} is the received signal power of the b-th band, X _{k, b} is a transmission symbol normalized to an average power of 1, and Z _{k, b} is an average of 0 and variance σ ² It is a frequency domain representation of complex additive white Gaussian noise (AWGN), and H _{k, b} is a channel coefficient of the frequency domain of the k th subcarrier in the b th band.

In this embodiment, it is assumed that the power delay profile P _b , the noise variance σ ² and the received power バ ン ド_{b in} each band are estimated on the receiving side and sent back as feedback information to the transmitting side.

Here, H _{k, b} is given by the following equation (7).

Here, K _{fft, b} is the fast Fourier transform (FFT) size of the b-th band, and g ^H _{Kfft, b} (k) is a vector extracted from the k-th column of the FFT matrix.

  In order to make a maximum likelihood estimation of the transmitted information bits, we calculate the metrics of all the possible paths on the trellis diagram.

  The path metric is given by the sum of branch metrics along the path. The j-th bit metric is given by equation (8) below.

Where ψ ^-1 is the inverse mapping of ψ in equation (4), and f (Y _{k, b} | X, H _{k, b} ) is the conditional probability density function of the received signal in equation (6) And χ ⁱ _q (b) is a set of signal points for which the i-th bit of the modulation scheme of the b-th band is q∈ {0, 1}.

  Therefore, the maximum likelihood estimation of the transmitted information bits is obtained by the following equation (9).

Here, c '(under bar) is a candidate codeword and C is a set of possible codewords.
[Frame error rate (FER) prediction]
The trellis diagram is widely used to analyze convolutional codes, and as also shown in FIG. 3, in the trellis diagram, the codewords correspond to the trellis paths one to one.

  If the metric for any error path is larger than the correct path, an error event will occur after the Viterbi decoding process.

For example, although FIG. 3 shows a trellis diagram with generator polynomials (5, 7) ₈ , since the convolutional code is linear, in the description of this embodiment, the correct path is considered to be all zero paths. Even if you decide, you won't lose generality.

  In FIG. 3, the error path drawn as [0, 0, 1, 1, 0, 1, 1, 1, 0, 0, ...] leaves the correct path at t = 2 and the correct path at t = 4. It joins.

  The error path has a bit pattern different from the correct path during a period apart from the correct path, and in this embodiment, this different bit pattern is called an error pattern. For example, in FIG. 3, the error pattern is [1, 1, 0, 1, 1, 1].

The error pattern is determined by the generator polynomial. Also, each error pattern is numbered p. An error path having the pth error pattern starting at the tth trellis position is represented as et _{, p} (under bar).

Furthermore, the event that the metric related to the error path et _{, p} (under bar) exceeds the metric of the true path is denoted as ε _{t, p} and its probability Pr (ε _{t, p} ) is also , PEP (et _{, p} (under bar)).
(Representation of FER based on union bound in wireless LAN environment)
FER is the probability that at least one error event will occur in a frame.

  And, in the following, taking a wireless LAN as an example, a formula of prediction of FER will be derived.

In the following, it is assumed that interleaving processing is performed for each OFDM symbol in one frame to be transmitted, and L _sym is defined as an interleaver size equal to the number of bits encoded in the OFDM symbol.

  For example, in the wireless LAN system of the IEEE 802.11a / n / ac standard, the interleaving process is repeated for each OFDM symbol.

Thus, c _j and c _{j + Lsym} are mapped on the same subcarrier in the same band, and in a wireless LAN environment, channel variations are considered negligible within one frame, so the effects of the same channel fading are You can consider it as receiving.

Therefore, PEP (et _{, p} (under bar)) is periodic and the following equation holds.

Therefore, in order to obtain FER, error events occurring in one OFDM symbol are considered. The probability that at least one error event occurs in the OFDM symbol can be expressed as equation (10).

Here, t ′ is an index in the range of 1 to RL _sym (R is a coding rate). The union bound of equation (10) is expressed by the following equation (11).

Here, union bound refers to a relationship representing the upper bound of the probability of a sum event as expressed by the following equation. In the following example, although two events are described, the same applies to the sum event of multiple events, and the upper bound of the probability that any error event is generated by Viterbi decoding is the probability that all event errors occur. Represented by the sum of

As a result, FER is expressed as the following equation (12).

In the following description, as described above, interleaving processing is described as the same processing is repeated for each OFDM symbol in a frame.

However, more generally, it is possible that interleaving processing is repeated for each predetermined block in a frame. In this case, the exponent of the right shoulder of Equation (12) is the number of blocks present in one frame, and RLsym can be a period corresponding to one block in the trellis diagram. That is, in the frame, the transmission bit is a trellis diagram corresponding to one block when it is divided for each block length set so that propagation channel fluctuation for the coded sequence after de-interleaving processing can be regarded as periodic. The block error rate is calculated as the sum of the pairwise error rates in the interval of (2), and the frame error rate is predicted from the block error rate and the number of blocks included in the frame, assuming that the block error rates are equal to one another.
(Pairwise error rate for simultaneous communication of multiple frequency bands)
Next, pairwise error rate PEP (et _{, p} (under bar)) is derived in simultaneous communication in a plurality of frequency bands.

Since PEP (et _{, p} (under bar)) is the probability that the metric of the error path exceeds the metric of the correct path, the following equation (13) is obtained.

Here, et _{, p} (j) (under bar) is the j-th element of et _{, p} (under bar), and the distance d _H is the Hamming weight of et _{, p} (under bar) (correct path and error path H _w ) and j _w represents the position of the w th error bit in et _{, p} (j) (under bar). For example, in the example shown in FIG. 3, the error path [0, 0, 1, 1, 0, 1, 1, 1, 0, ...] has five error bits, and the position of each error bit is j _{1 = 3, j 2 = 4} , j 3 = 6, j 4 = 7, and a j ₅ = 8.

Further, referring to the procedure in Non-Patent Document 3, the conditional PEP has the following formula (Eq. 10), because the error path contains d _H miscoded bits different from the correct path. 14) and (15) give.

Here, H below is a channel coefficient vector.

Also, the following is a squared Euclidean distance vector between the correct symbol and an error symbol of size d _H :

Furthermore, for the w th error bit, i _w , k _w and b _w are the bit positions in symbol, subcarrier and band respectively. They are given as follows.

Also, it is defined as follows.

FIG. 7 is a diagram showing a constellation of 16 QAM in-phase signals used in a wireless LAN and a subset thereof.

  For example, in FIG. 7, the transmitted bits are mapped onto bit positions i = 1 and i = 2.

In FIG. 7, the correct symbol and the incorrect symbol are represented by “o” and “x”, respectively. From FIG. 7, in general, Δb _w (i _w ) depends on the bit position and symbol position to which the error bit is mapped.

Then, Δ b _w (i _w ) is expressed as the following equation.

In FIG. 7, γ b _w (i _w ) is 1 or 4 for i = 1.

  Since the information bits are randomly generated, the correct symbol position is also random.

Thus, Δ b _w (i _w ) is a discrete random variable, the distribution of which is determined by the constellation and bit positions.

  Now, let U be the number of all possible Δ (under bar) patterns. Since transmission symbols are generated from random information bits, each pattern can be said to occur with equal probability P in the high SNR area.

  The probability P can be calculated by considering the constellation and bit position to which the error bit is mapped.

  Thus, for equation (14), the expected value for Δ (under bar) is given as equation (16).

Here, in Equation (16), when U has a large value, calculation of all patterns is unrealistic.

  Therefore, assuming that the symbol error corresponding to the nearest signal position is dominant in the high SNR region, equation (16) considers that all symbol errors consider only the term corresponding to the adjacent symbols. , Is approximated. That is, the case where the following relational expression is established is considered.

However, in a multipath environment, some subcarriers may be greatly attenuated.
In such a case, it is not possible to ignore the possibility of errors in symbols farther than the adjacent symbols on the signal space diagram.

Therefore, the above assumption in Non-Patent Document 3 is not compatible with the environment of the multipath transmission line.
(Consideration of symbol error in the present embodiment)
Therefore, in the following, PEP is calculated in consideration of symbol errors that occur between symbols that are farther than the nearest symbol interval.

Since patterns with smaller Δb _w (i _w , u) are more likely to occur, the calculation of FER predictions requires a relatively small Euclidean distance to efficiently improve the prediction accuracy. Consider only patterns.

In order to consider such patterns, calculate m _delta as follows.

FIG. 8 is a diagram showing an example of such a pattern of intersymbol distance Δ (under bar) of error symbols.
Here, it is assumed that d _H = 5, Γ = 13 and the number of available bands is three.
The modulation scheme used in each band shall be QPSK, 16 QAM and 64 QAM for bands 1, 2 and 3, respectively.
In the case of an error pattern as shown in FIG. 3, it is assumed that erroneous bits are mapped to bands 1, 2, 2, 3 and 3 in order by interleaving processing and parser processing, and similarly, the bit position is 1 , 1, 2, 2, and 1.
Considering the division of signal points of each modulation scheme as well as the division of signal points based on gray labeling by bit position as shown in FIG. 7, there is a possibility that a symbol separated from an adjacent symbol may be erroneous Only the 2nd, 4th and 5th bits of the error bit are available.
1) First, according to the selection rule as shown in FIG. 8, all elements are d ² _{b, min} , and those having m _delta = 5 are counted.
This corresponds to the first row of the table of FIG. 8 and to the consideration of only the term corresponding to the distance between symbols which is closest to the symbol error.
2) Furthermore, as possible patterns, any one of the second, fourth, and fifth error bits is a symbol that is adjacent at a second distance (hereinafter referred to as a second proximity symbol). The condition of the intersymbol distance 4d ² _{b, min} of) is satisfied, the intersymbol distance d ² _{b, min} of the other remaining elements, and m _delta = 8 are also listed. As shown, a total of three patterns can be considered 3) Similarly, there are three patterns with m _delta = 11,
4) There is one pattern with m _delta = 13.

As there are no other patterns in which m _delta is 以下 = 13 or less, except in the above case, eight patterns are considered in FIG. 8 as a total.

Even for other error patterns, if the value of Γ is set in the same manner as the processing in the table in FIG. 8, the band to be mapped and the bit position are determined according to interleaving processing and parser processing, so m Under the condition that _delta is less than or equal to Γ, the corresponding pattern is also determined. Here, Γ indicates that “the error pattern that can be generated by the convolutional encoder having a predetermined configuration, the squared Euclidean distance Δb of each correct symbol and each correct symbol to which d _H error bits in the error pattern correspond. _w (i _w, u) value defining an upper limit of the sum of the integer coefficients upon decomposing the square d ² _bw minimum Euclidean distance between signal points, _min and integer coefficient γ _{bw (i w,} u) in " It can be said. For example, the FER prediction unit 3030 calculates a pairwise error rate as described below for a pattern in which the value of m _delta is equal to or less than the value of Γ set in advance in this manner. Includes rate calculator.

  Define the total number of counted patterns as U ′, eg, in FIG. 8 U ′ = 8. Therefore, PEP is approximated by the following equation (17).

By setting it as Formula (17), the subject mentioned above is solved as follows.

1) By setting the average received power of each band as _bw , the SNR is switched according to the band to which an error bit is mapped.

2) The inter-signal point distances d _bw and min are switched according to the modulation scheme used in the band to which the codeword error bit is mapped.

  3) By setting the value of Γ, for example, so that errors other than the closest symbol are also taken into consideration, the PEP takes into consideration the symbol error that occurs between symbols that are farther than the nearest symbol interval. Can be calculated.

(17) is still conditioned by the channel coefficient vector H (under bar). Therefore, by further obtaining an expected value of H, it can be expressed as follows.
(When the channel value can be regarded as a constant (when the channel is static))
This case corresponds to setting H _{kw, bw} as a constant in equation (17).
(Calculation of PEP when propagation path value fluctuates)
In general, the channel coefficient H (under bar) is considered as a random variable.

  Therefore, by taking the expectation value for H (under bar) in the equation (17), the averaged PEP can be obtained, and the FER can be obtained by the equation (12).

  The expected value over H (under bar) is equal to the expected over h (under bar), which is easily calculated because each element h is independent.

  In order to calculate the expected value, the molecule in the root of Equation (17) is transformed as in Equation (18) and Equation (19) below.

Here, the following equation holds.

The eigenvalue decomposition of A can be expressed as A = VΛV ^H.
Here, v (under bar) = V ^H h (under bar) is defined. Also, since V is a unitary matrix, the amplitude of each element follows the Rayleigh distribution of the probability distribution below.

Therefore, the following equation (20) is obtained.

Here, r is determined as follows.

r = min (number of propagation paths in band 1, number of code word error bits mapped to band 1) +
min (number of propagation paths in band 2, number of code word error bits mapped to band 2) +
...
min (number of propagation paths in band B, number of code word error bits mapped to band 2)
= R ₁ + r ₂ + ... + r _B
From equations (17) and (20), PEP can be approximated as equation (21).

Taking the expectation value for | v _l | (ie, h (under bar)), the following equation (22) is obtained.

Here, λ w can be calculated from the average received power _{b b} of each band, the power delay profile, and the configuration of the interleaver and parser.

  By substituting Equation (22) into Equation (12), the FER prediction unit 3030 includes a frame error rate calculation unit that predicts a frame error rate (FER).

In the above description, the value of Γ is set in advance, and FER prediction unit 3030, for example, determines the pattern such that the value of m _delta is less than or equal to the value of Γ set in this way. It has been described that the pairwise error rate is calculated.

  However, the range of symbol errors to be considered is not necessarily limited to the configuration to be limited under such conditions.

  For example, a pairwise error rate may be calculated by selecting a symbol error pattern such that the input value of the Q function in the above equation (17) is equal to or less than a predetermined value.

  That is, in Equation (17), the following equation, which is the value of the numerator in the root code in the Q function, may select a symbol error pattern less than or equal to a predetermined value.

In this case, it is equivalent to selecting a pattern in which the sum of squared Euclidean distances of the error symbol and the correct symbol taking into account the power attenuation of the propagation path is as small as possible.

  FIG. 9 is a diagram showing the occurrence rate of each symbol error pattern in a simulation assuming IEEE 802.11n.

  In FIG. 9, the horizontal axis represents the distance between symbols corresponding to a symbol error, where “1” is the closest, “2” is the second proximity, and “3” is the third proximity. It shows each.

  On the other hand, FIG. 10 is a figure which shows the parameter of the simulation used in FIG.

  Each bar graph indicates that the SNR is 4 to 24 (dB).

  As can be seen from FIG. 9, in the realistic SNR range, even if the SNR is improved, errors between adjacent symbols do not necessarily become dominant, and the rate of occurrence does not approach 100%.

  Therefore, even when the received power of a certain subcarrier falls deeply even in the high SNR region, symbol errors occur between symbols farther from the nearest symbol, so considering only the errors of the adjacent symbols, the PEP is lowered to approximate It will be done.

  For this reason, the approximation accuracy of the pairwise error rate is degraded if the symbol error between the symbols distant from the nearest symbol is not taken into consideration.

  FIG. 11 is a diagram showing comparison of FER prediction and simulation results according to the present embodiment.

  In addition, in FIG. 11, it simulates as communication in three frequency bands, The modulation system of 5 GHz band is 16 QAM, the modulation system of 2.4 GHz band is 64 QAM, The modulation system of 920 MHz band is 64 QAM .

  In each frequency band, the bandwidth is 20 MHz, the frame size is 12000 bits, the FFT size is 63 per band, and the number of data subcarriers is 52 per band.

  The size of the interleaver is (depth) × (width) = 26 × 32. Also, Γ = 16 is set.

  In FIG. 11, “Conventional” is a prediction result in the case where only adjacent symbol errors are considered, “Simulation” is a result of simulation using the parameters shown in FIG. 11, and “Proposed” is As described in the embodiment, this is a result of prediction taking into consideration symbol errors occurring between symbols that are farther than the nearest symbol interval.

As shown in FIG. 11, it can be seen that, by using the frame error rate prediction method of the present embodiment, a predicted value closer to the simulation result can be obtained.
As described above, according to the configuration of the present embodiment, in a communication system based on convolutional coding orthogonal frequency division multiplexing, a frame error rate is accurately predicted even when there is a subcarrier in which received power drops significantly. Is possible.

  Further, according to the configuration of the present embodiment, in a communication system using simultaneous transmission of a plurality of bands, even if there is a subcarrier in which the received power drops when the modulation scheme differs for each band and the propagation environment becomes different, It is possible to predict frame error rates.

  Then, by setting the modulation method or the like based on the predicted frame error rate, it is possible to realize a larger throughput.

  The embodiment disclosed this time is an illustration of a configuration for specifically implementing the present invention, and does not limit the technical scope of the present invention. The technical scope of the present invention is indicated not by the description of the embodiment but by the scope of claims, and includes modifications within the scope of wording and meaning of the scope of claims. Is intended.

  1000 transmitter, 1002 error correction coder, 1004 interleaver, 1006 parser, 1010.1 to 1010.3 modulator, 1012.1 to 1012.3 OFDM modulator, 1014.1 to 1014.3 RF unit, 1020 .1 to 1020.3 antenna, 1100 reception processing unit, 1110 adaptive rate control unit, 2000 reception apparatus, 2002.1 to 2002.3 antenna, 2010.1 to 2010.3 RF unit, 2012.1 to 2012.3 OFDM Demodulation Unit, 2014.1 to 2014.3 Demodulation Unit, 2015 Deparser, 2016 Deinterleave Unit, 2018 Error Correction Unit, 2100 Average Received Power / Power Delay Profile / Noise Power Estimation Unit, 2110 Transmission Processing Unit, 3020 MCS Storage Unit, 3030 FER prediction unit, 040 MCS selection unit.

Claims (7)

A frame error rate prediction apparatus of a communication system in which multi-level modulation is performed on convolutionally encoded symbols and communication is performed by orthogonal frequency division multiplexing,
Storage means for storing information on an interleaving scheme of convolutional encoding preset as one adopted in the convolutional encoding scheme and information on a modulation scheme of the multilevel modulation;
In accordance with the information on the interleaving scheme and the modulation scheme stored in the storage means in the error pattern of the received signal, based on the propagation path characteristic information representing the attenuation of the propagation path power and noise power estimated on the communication path The pairwise error rate of the error path in the decoding process for the convolutional coding is calculated taking into consideration symbol errors within a predetermined distance occurring between symbols separated from the nearest adjacent symbol, and the calculated pairwise error And a frame error rate predicting means for predicting the frame error rate by a rate.   The predetermined distance is a distance by which a square Euclidean distance between an error symbol and a correct symbol taking into account the power attenuation of the communication path into consideration is taken as an error pattern of a symbol error to be considered, smaller than a predetermined value. Frame error rate prediction device.   The predetermined distance is a square Euclidean distance of the inter-symbol distance between an error symbol and a correct symbol in the error pattern, for an error pattern that can be generated by the configuration of the encoder for the convolutional encoding. The frame error rate predicting apparatus according to claim 2, wherein the frame error rate predicting apparatus is a predetermined upper limit value of the sum of the integer coefficients when the minimum Euclidean distance between points is divided into a square and the integer coefficients. A wireless communication apparatus that communicates by simultaneous transmission in a plurality of frequency bands by convolutional coding orthogonal frequency division multiplexing,
Receiving means for receiving, as feedback information, received power for each frequency band, propagation path characteristic information representing attenuation of propagation path power, and noise power estimated value transmitted from a receiving apparatus;
Storage means for storing information of a set of a coding rate of a convolutional coding and a modulation scheme set in advance as employed in the convolutional coding orthogonal frequency division multiplexing system;
Convolutional coding processing means for performing the convolutional coding process on a transmission data string;
Interleaving means for interleaving the output of the encoding means;
Parser means for dividing the signal after the interleaving process according to the plurality of frequency bands;
Modulation means for subjecting the output from the parser means to multi-level encoding and performing orthogonal frequency division multiplex modulation with a plurality of subcarriers;
And selecting means for selecting a set that maximizes throughput among the sets of the coding rate and the modulation scheme stored in the storage means based on the feedback information.
The selection means is
Storage means for storing information on an interleaving scheme of convolutional encoding preset as one adopted in the convolutional encoding scheme and information on a modulation scheme of the multilevel modulation;
In accordance with the information on the interleaving scheme and the modulation scheme stored in the storage means in the error pattern of the received signal, based on the propagation path characteristic information representing the attenuation of the propagation path power and noise power estimated on the communication path Pairwise error rate calculation means for calculating a pairwise error rate of an error path in the decoding process for the convolutional coding, taking into consideration symbol errors within a predetermined distance occurring between symbols separated from the nearest neighbor symbol;
Frame error rate prediction means for predicting a frame error rate based on the calculated pairwise error rate;
And d) modulation scheme selection means for selecting the set that achieves the maximum throughput within a predetermined frame error rate based on the predicted frame error rate.
A wireless communication apparatus, further comprising transmission means for performing convolutional coding and modulation processing on transmission data according to the set selected by the modulation scheme selection unit and transmitting the transmission data.   The predetermined distance is a distance by which the squared Euclidean distance between an error symbol and a correct symbol taking into account the power attenuation of the communication path, the error pattern of the symbol error to be considered is smaller than a predetermined value. Wireless communication device.   The predetermined distance is a square Euclidean distance of the inter-symbol distance between an error symbol and a correct symbol in the error pattern, for an error pattern that can be generated by the configuration of the encoder for the convolutional encoding. The wireless communication apparatus according to claim 5, wherein the predetermined upper limit value is the sum of the integer coefficients when the minimum Euclidean distance between points is divided into a square and the integer coefficients. A wireless communication system for performing communication by simultaneous transmission in a plurality of frequency bands by convolutional coding orthogonal frequency division multiplexing,
Equipped with a receiver,
The receiving device is
Communication path state estimation means for estimating received power for each frequency band, propagation path characteristic information representing attenuation of propagation path power, and noise power;
First transmission means for transmitting the estimated channel characteristic information and noise power;
Further comprising a transmitter;
The transmitting device is
Receiving means for receiving, as feedback information, received power for each frequency band, propagation path characteristic information representing attenuation of propagation path power, and noise power estimated value transmitted from a receiving apparatus;
Storage means for storing information of a set of a coding rate of a convolutional coding and a modulation scheme set in advance as employed in the convolutional coding orthogonal frequency division multiplexing system;
Convolutional coding processing means for performing the convolutional coding process on a transmission data string;
Interleaving means for interleaving the output of the encoding means;
Parser means for dividing the signal after the interleaving process according to the plurality of frequency bands;
Modulation means for subjecting the output from the parser means to multi-level encoding and performing orthogonal frequency division multiplex modulation with a plurality of subcarriers;
And selecting means for selecting a set that maximizes throughput among the sets of the coding rate and the modulation scheme stored in the storage means based on the feedback information.
The selection means is
Storage means for storing information on an interleaving scheme of convolutional encoding preset as one adopted in the convolutional encoding scheme and information on a modulation scheme of the multilevel modulation;
In accordance with the information on the interleaving scheme and the modulation scheme stored in the storage means in the error pattern of the received signal, based on the propagation path characteristic information representing the attenuation of the propagation path power and noise power estimated on the communication path Pairwise error rate calculation means for calculating a pairwise error rate of an error path in the decoding process for the convolutional coding, taking into consideration symbol errors within a predetermined distance occurring between symbols separated from the nearest neighbor symbol;
Frame error rate prediction means for predicting a frame error rate based on the calculated pairwise error rate;
Modulation scheme selecting means for selecting the set that achieves the maximum throughput within a predetermined frame error rate based on the predicted frame error rate;
A wireless communication system, further comprising transmission means for transmitting a modulation signal for the transmission data sequence modulated by the modulation means according to the group selected by the modulation scheme selection portion.