JP2008010987A - Receiver and wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver and a wireless communication system in which good error correction capability can be exhibited even if the likelihood criteria in the same error correction demodulation unit are different because the likelihood is altered depending on its received field strength and iterative decoding is performed using likelihood information effective for an error correction iterative decoder. <P>SOLUTION: The receiver 200 comprises an OFDM demodulator 220 for performing OFDM demodulation of an OFDM signal transmitted from a transmitter 100, a weighting factor calculating section 230 for calculating the strength of the OFDM demodulation signal, a section 240 for generating likelihood information for performing error detection iterative demodulation from the OFDM demodulation signal, a section 250 for altering the likelihood information based on the calculation value at the weighting factor calculating section 230, a buffer 260 for holding the altered likelihood information until it is stored by the error correction demodulation unit, and a section 270 for performing error correction iterative demodulation using the likelihood information held in the buffer 260. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a receiver and a wireless communication system using an OFDM (Orthogonal Frequency Division Multiplexing) transmission system, and in particular, the error detection unit of a signal input to an error detection iterative decoder is large, The present invention relates to a receiving apparatus and a wireless communication system capable of preventing deterioration of decoding characteristics due to fluctuations and maintaining good error correction decoding characteristics.

  In a digital wireless communication system using a conventional OFDM transmission scheme, convolutional coding is performed on a transmission signal by an error detection coding circuit on the transmission device side, and the convolutionally coded signal is transmitted to a subcarrier in the frequency domain by 16QAM. (Quadrature Amplitude Modulation) or the like is mapped, and an IFFT (Inverse Fast Fourier Transform) circuit collectively converts the signal on the frequency axis to the signal on the time axis to generate an OFDM signal. The OFDM signal is wirelessly transmitted in a packet preceded by a reception control preamble. For example, Non-Patent Document 1 discloses the generation of an OFDM modulated signal.

  On the other hand, on the receiving device side, automatic gain control (AGC) is performed by using the reception control preamble at the head of the packet so that the reception level falls within the dynamic range of the A / D converter. The analog signal is converted to a digital signal, the frequency offset is compensated for from the preamble signal, and the signal on the time axis is collectively converted from the signal on the time axis to the signal on the frequency axis by the fast Fourier transform circuit. The likelihood information for mapping and input to the Viterbi decoder was calculated, and Viterbi decoding was performed.

  However, in a wireless communication system, the propagation path between the transmission apparatus and the reception apparatus is not uniquely determined, and the receiver receives a superposition of signals that have passed through several different propagation paths, and thus is affected by multipath fading. Moreover, when each is moving, it receives to the influence of Doppler fading. For this reason, each packet and each subcarrier of the OFDM signal receive different propagation path characteristics, the amplitude and phase fluctuate, and reception performance deteriorates.

Thus, as a method for preventing deterioration of reception performance and maintaining good decoding characteristics, for example, there is an OFDM demodulator described in Patent Document 1. This OFDM demodulator uses the reception control preamble attached to the head of the packet, and the propagation path characteristics received by the preamble part and the data part based on the assumption that the multipath fading characteristic is constant in the packet is Under the assumption that they are equivalent, the received power of each subcarrier is equivalent to the data part by multiplying the amplitude of each corresponding subcarrier using the propagation path characteristics obtained from the preamble for propagation path estimation. Is weighted. Then, the absolute value of the signal obtained by approximating the power average value of the previous subcarrier of the propagation path estimation preamble and weighted by the power becomes equal to the power average value of all subcarriers of the previous subcarrier of the propagation path estimation preamble. In this way, the input of the Viterbi decoder is created.
802.11 high-speed wireless LAN textbook issued by IDC Japan JP 2002-111626 A

  However, such a conventional OFDM demodulator is effective in a digital wireless communication system in which electric field fluctuations and propagation path characteristics in the same packet are considered to be constant, but turbo coding (Turbo coding) ) And LDPC codes (Low Density Parity Check codes), a type that exhibits better error correction capability as the error correction unit (code length) collectively processed by the error correction iterative decoder increases. In a digital wireless communication system that employs the above encoding method, an error correction unit must be increased. As a result, the length of the packet to be transmitted on the transmission device side is increased, or the packet is divided into a plurality of packets and transmitted. Therefore, there is a high probability that the field strength and propagation path characteristics when receiving the beginning of the packet on the receiver side are different from the field strength and propagation path characteristics when receiving the packet end. Alternatively, the field strength and propagation path characteristics at the time of receiving the first packet and the last packet are likely to be different, and the same error correction decoding unit data transmitted in different packets is normalized by the preamble of each packet. Since the error correction iterative decoding is performed using the likelihood information, there is a situation in which the coding gain is reduced.

  The present invention has been made in view of the above, and even if the likelihood criteria of signals within the same error correction decoding unit are different, the likelihood is changed according to the received electric field strength, and error correction repetition is performed. An object of the present invention is to provide a receiving apparatus and a wireless communication system that can exhibit good error correction capability because iterative decoding is performed using likelihood information effective for the decoder.

  The receiving apparatus of the present invention comprises: a receiving means for receiving a transmitted OFDM signal; an OFDM demodulating means for OFDM demodulating the received signal received by the receiving means; and a signal of an OFDM demodulated signal demodulated by the OFDM demodulating means. Weighting factor calculating means for calculating strength, likelihood generating means for generating likelihood information for performing error detection iterative decoding from the OFDM demodulated signal, and the likelihood information based on the calculated value in the weighting factor calculating means A likelihood changing unit that changes the error information, a buffer that holds until the likelihood information changed by the likelihood changing unit is accumulated for the error correction decoding unit, and error correction iteration using the likelihood information held in the buffer An error correction iterative decoding means for performing decoding is employed.

  A radio communication system according to the present invention is a radio communication system using an OFDM transmission system in which an error correction decoding unit of a signal input to an error correction iterative decoder is divided into a plurality of symbols and transmitted, and transmission data is error-corrected. An error correction coding means for coding in a correction coding unit, an OFDM modulation means for dividing the data encoded by the error correction coding means into one symbol unit and converting it into an OFDM signal, and defining the OFDM signal A packet generation unit that sequentially inserts packets into a packet to generate a packet; a transmission device that includes a transmission unit that wirelessly transmits the packet; a reception unit that receives an OFDM signal transmitted from the transmission device; and the reception unit OFDM demodulating means for OFDM demodulating the received signal received by the OFDM demodulator, and the OFDM demodulated signal demodulated by the OFDM demodulating means Weighting factor calculating means for calculating the signal strength of the signal, likelihood generating means for generating likelihood information for performing error detection iterative decoding from the OFDM demodulated signal, and the likelihood based on the value calculated by the weighting factor calculating means. A likelihood changing means for changing the degree information, a buffer for holding the likelihood information changed by the likelihood changing means until the error correction decoding unit is accumulated, and an error using the likelihood information held in the buffer The receiving apparatus includes an error correction iterative decoding unit that performs correction iterative decoding.

  According to the present invention, likelihood information that should be originally low likelihood is prevented from being increased in likelihood by normalization, and error information is propagated to other bits when iterative decoding is performed. Therefore, it is possible to maintain good error correction performance and realize a voice call with less noise. In video communication, it is possible to realize a digital wireless system in which a clear video without block noise can be seen.

  In addition, the error correction decoding performance is improved particularly in a Gaussian noise environment, and error correction iterative decoding is performed using accurate likelihood, so that the error correction capability is improved and the probability that the decoding result is error-free is increased. Get higher. As a result, the probability of retransmission can be reduced, traffic between the transmitting and receiving apparatuses can be suppressed, communication at a higher transmission rate is possible, and a digital wireless communication system with high sound quality and high image quality can be realized. Further, when the retransmission control of the digital wireless communication system is combined with H-ARQ, an error-free operation can be obtained with a smaller number of retransmissions, so that the effect of further improving the transmission efficiency can be obtained.

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

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a radio communication system according to Embodiment 1 of the present invention. The present embodiment is an example applied to a digital radio communication system in which an error correction decoding unit of a signal input to an error correction iterative decoder is divided into a plurality of symbols and transmitted in a communication system using an OFDM transmission scheme. is there.

  1, the wireless communication system includes a transmission apparatus 100 including an error correction coding unit 110, an OFDM modulation unit 120, a packet generation unit 130, and a transmission antenna 140, a reception antenna 210, an OFDM demodulation unit 220, and a weighting factor calculation unit 230. , A likelihood generating unit 240, a likelihood changing unit 250, a buffer 260, and a receiving apparatus 200 including an error correction iterative decoding unit 270.

  The error correction encoding unit 110 encodes the transmission data 101 in units of error correction encoding. The OFDM modulation unit 120 divides the data encoded by the error correction encoding unit 110 for each symbol unit and converts it into an OFDM signal. The packet generator 130 sequentially inserts OFDM signals into a prescribed packet to generate a packet. The transmission antenna 140 radiates the generated packet into space.

  The reception antenna 210 receives the OFDM signal transmitted from the transmission device 100. The OFDM demodulator 220 performs OFDM demodulation on the received signal.

  The weighting factor calculation unit 230 is a signal strength measurement unit that calculates the signal strength of the OFDM demodulated signal. In particular, the weighting factor calculation unit 230 calculates the absolute power value of the received symbol and weights the likelihood information input to the error correction iterative decoding unit 270 using the absolute power as a weighting factor. Also, the weighting factor calculation unit 230 weights the likelihood information input to the error correction iterative decoding unit 270 according to the received electric field level.

  The likelihood generation unit 240 generates likelihood information for performing error detection iterative decoding from the OFDM demodulated signal. The likelihood changing unit 250 changes the likelihood information based on the value calculated by the weight coefficient calculating unit 230. The buffer 260 holds the likelihood information changed by the likelihood changing unit 250 until the error correction decoding unit is accumulated. The error correction iterative decoding unit 270 performs error correction iterative decoding using the likelihood information held in the buffer 260.

The operation of the radio communication system configured as described above will be described below.
[Overall operation of wireless communication system]
First, the overall operation of the wireless communication system will be described.

  Transmission data 101 is subjected to error correction coding for each predetermined error correction unit by error correction coding section 110 of transmission apparatus 100 and output to OFDM modulation section 120.

  In the OFDM modulation unit 120, the data corrected by the error correction coding unit 110 is mapped, a pilot and a guard band are inserted, fast inverse Fourier transformed, a guard interval is added, and a series of OFDM signal generation is performed. Processing is performed to generate an OFDM modulated signal (see Non-Patent Document 1).

  In the packet generation unit 130, OFDM modulation signals are sequentially placed on packets to which a known transmission path estimation preamble pattern is added in advance, and wirelessly transmitted by the antenna 140. The mapping of the OFDM modulation unit 120 uses arbitrary multilevel modulation such as BPSK, QPSK, DQPSK, 8PSK, 16QAM, and 64QAM. In this embodiment, the case of performing 16QAM is taken as an example.

  In reception-side apparatus 200, the received signal received from antenna 210 is subjected to predetermined radio reception processing such as down-conversion and frequency conversion in OFDM demodulator 220, and then a band for each symbol using a propagation path estimation preamble. Internal equalization is performed, guard intervals are deleted, fast Fourier transform is performed, and pilots and guard bands are removed (see Non-Patent Document 1).

  Weighting factor calculation section (signal strength measurement section) 230 calculates the mean square value of subcarriers for each symbol from the output data of OFDM demodulation section 220. The likelihood generation unit 240 demaps the output of the OFDM demodulation unit 220 for each symbol, and calculates likelihood information. The likelihood generation unit 240 is normalized by dividing by the mean square value calculated by the weight coefficient calculation unit 230, and de-maps by the same mapping as that in the OFDM modulation unit 120 of the transmission apparatus 100.

  In likelihood changing section 250, the mean square value calculated by weighting coefficient calculating section 230 is added to the likelihood information to change the likelihood information. The buffer 260 accumulates the likelihood information changed by the likelihood changing unit 250 until it accumulates in error correction units. The error correction iterative decoding unit 270 receives the changed likelihood information from the buffer 260 for each error correction decoding unit, and performs error correction iterative decoding.

Hereinafter, the operation of each unit will be described in more detail.
[Operation of Error Correction Encoding Unit 110]
First, the error correction encoding unit 110 of the transmission device 100 will be described. In the present embodiment, an example in which a turbo encoder is used as an example of the configuration of the error correction encoding unit 110 will be described, but other error correction encoding methods using LDPC encoding and the like can be similarly applied.

  FIG. 2 is a block diagram showing a schematic configuration of the turbo encoder.

  As shown in FIG. 2, the turbo encoder 150 includes an interleaver 151, XOR circuits 152a to 152d, delay units 153a to 153h, a selector 154, and a parallel-serial converter 155. The XOR circuits 152a and 152b and the delay units 153a to 153d constitute a first recursive systematic convolutional encoder 156, and the XOR circuits 152c and 152d and the delay units 153e to 153h include a second recursive systematic convolutional code. The generator 157 is configured. The transmission data 158 is input to the interleaver 151, the XOR circuit 152 a, and the parallel / serial converter 155, and the parallel / serial converter 155 outputs an output 159.

Recursive systematic convolutional encoders 156 and 157 are connected via an interleaver 151. Transmission data 158 (similar to transmission data 101 in FIG. 1) is input to parallel-serial converter 155. On the other hand, the transmission data 158 is input to the first recursive systematic convolutional encoder 156, subjected to systematic encoding, and output to the selector 154. Transmission data 158 is rearranged in bit order by interleaver 151, input to second recursive systematic convolutional encoder 157, systematically encoded, and output to selector 154. The selector 154 regularly selects the data input from each and outputs it to the parallel-serial converter 155. The parallel / serial converter 155 converts the input data to serial data in parallel and outputs it as an output 159.
[Data Flow of Transmitting Device 100]
A data flow from the OFDM modulation unit 120 to the packet generation unit will be described.

  FIG. 3 is a block diagram illustrating a data flow of the transmission device 100.

  The encoded data 161 subjected to error correction coding by the error correction coding unit 110 (FIG. 1) is subjected to OFDM modulation by the OFDM modulation unit 120, and an OFDM symbol 162 is generated. The OFDM symbol 162 generated by the OFDM modulation unit 120 is sequentially inserted into the symbol part of the packet 163 to which the transmission path estimation preamble is added at the head by the packet generation unit 130 to form a packet.

Next, the operation of each unit of the receiving device 200 will be described.
[Operation of Weighting Factor Calculation Unit 230]
The weight coefficient calculation unit 230 is a signal strength measurement unit.

  The IQ component of the de-mapping data of each subcarrier calculated by the OFDM demodulator 220 (FIG. 1) of the receiving apparatus 200 is In, Qn (n is a subcarrier number), and the mean square of the subcarriers for each symbol When the value is M and the number of subcarriers is N, the root mean square value M is obtained by the following equation (1).

〔尤度生成部２４０の動作〕
尤度生成部２４０について説明する。尤度情報の算出手段はいくつか知られており、以下はそのうちの一例である。尤度情報の算出手段は任意の方法で良く以下の例に限定されない。

[Operation of Likelihood Generation Unit 240]
The likelihood generation unit 240 will be described. Several means for calculating likelihood information are known, and the following is an example. The likelihood information calculation means may be any method and is not limited to the following example.

  4 is a diagram illustrating an example of 16QAM mapping, FIG. 5 is a graph illustrating a likelihood generation method for the first and third bits, and FIG. 6 is a likelihood generation method for the second and fourth bits. It is a graph.

  As shown in FIG. 4, in 16QAM mapping, 4 bits are allocated per point, the first and second bits are allocated to the I axis, and the third and fourth bits are allocated to the Q axis. On the transmitting apparatus 100 side, this mapping point is transmitted, but the signal points de-mapped on the receiving apparatus 200 side are scattered from the mapping point at the time of transmission due to the influence of noise or the like. Then, for the first and third bits, the likelihood as shown in FIG. 5 is calculated from the scattered de-mapping points on the I-axis and Q-axis coordinates. Similarly, for the second and fourth bits, The likelihood as shown in FIG. 6 is calculated. 5 and 6, the plus side represents the likelihood of the bit “0” and the minus side represents the likelihood of the bit “1”.

Note that the likelihood information may be converted into a logarithm in order to reduce the calculation amount of the error correction iterative decoder.
[Operation of Likelihood Changer 250]
The likelihood changing unit 250 will be described. The likelihood information calculated by the likelihood generator 240 is a signal accompanied by likelihood information for each bit. If this signal is Sb and the output of the weighting factor calculation unit is H, the likelihood So after the change is calculated by the following equation (2).

So = Sb × H (2)
[Operation of Error Correcting Iterative Decoding Unit 270]
The error correction iterative decoding unit 270 will be described. In the present embodiment, a configuration example in which the error correction iterative decoding unit 270 uses a turbo decoder will be described. The same applies to sum-product decoding for decoding LDPC codes.

  FIG. 7 is a block diagram showing a schematic configuration of the turbo decoder.

  As shown in FIG. 7, the turbo decoder 280 includes a first decoder 281, a second decoder 282, interleavers (interleavers) 283 and 284, and de-interleavers (de-interleavers) 285 and 286. It is prepared for.

  The first decoder 281 and the second decoder 282 are assumed to be a soft decision method that outputs a real-valued likelihood information output signal in response to a real-valued likelihood information input signal. Further, these decoders 281 and 282 can input a priori likelihood that gives the reliability of the signal before decoding, and can generate an external likelihood that gives the reliability of the signal after decoding. .

  The first decoder 281 receives the likelihood information 287 and the prior likelihood value 288 stored in the buffer 260 (FIG. 1), and the first decoder 281 transmits the signal sequence together with the decoded information signal sequence. The external value 291 is output. In addition, the second decoder 282 includes the likelihood information 287 stored in the buffer 260 interleaved by the interleaver 283 and the prior value 289 obtained by interleaving the external value 291 of the first decoder 281 with the interleaver 284. Is input, and the second decoder 282 outputs the decoded information sequence 292 and the external likelihood 290 of the signal sequence.

  The external likelihood 290 output from the second decoder 282 is de-interleaved by the de-interleaver 285 and input to the first decoder 281 as a prior likelihood value 288.

  As described above, the turbo decoder 280 repeats decoding while supplying the external value and the prior likelihood value to each other by the first decoder 281 and the second decoder 282, and ends when a predetermined number of times or an error occurs. When the detection is not performed, the information sequence 292 output from the second decoder 282 is de-interleaved by the de-interleaver 286 and output as a decoding result 293.

  As described above in detail, according to the present embodiment, receiving apparatus 200 has OFDM demodulating section 220 that OFDM demodulates the OFDM signal transmitted from transmitting apparatus 100, and the weight for calculating the signal strength of the OFDM demodulated signal. A coefficient calculation unit 230, a likelihood generation unit 240 that generates likelihood information for performing error detection iterative decoding from the OFDM demodulated signal, and a likelihood that the likelihood information is changed based on the calculated value in the weight coefficient calculation unit 230 A change unit 250, a buffer 260 that holds the changed likelihood information until the error correction decoding unit is accumulated, an error correction iterative decoding unit 270 that performs error correction iterative decoding using the likelihood information held in the buffer 260, If the transmission period for transmitting a signal of one error correction decoding unit is long, or the influence of multipath fading on the propagation path, Even in a situation where the influence of electric field fluctuation and Doppler fading due to movement of the transmission device side becomes large, the likelihood information input to the error correction iterative decoding unit 270 is based on the weighting factor calculated by the weighting factor calculation unit 230. By changing it, it is possible to prevent a decrease in coding gain and maintain good error correction performance.

  Further, in the present embodiment, weight coefficient calculation section 230 calculates the absolute power value of the received symbol and weights the likelihood information input to error correction iterative decoding section 270 using the absolute power as a weight coefficient. Therefore, it is possible to prevent the likelihood information that should originally be a low likelihood from becoming large due to normalization, and to prevent the error information from propagating to other bits during iterative decoding. Can do. As a result, it is possible to maintain good error correction performance, for example, it is possible to realize a voice call with less noise, and in video communication, it is possible to realize a digital wireless system in which a beautiful image without block noise can be seen. .

  In addition, since the likelihood information input to the error correction iterative decoding unit 270 is weighted according to the received electric field level, the error correction decoding performance is improved particularly in a Gaussian noise environment, and an accurate likelihood is used. Since error correction iterative decoding is performed, the error correction capability is improved, and the probability that the decoding result is error-free increases. As a result, the probability of retransmission can be reduced, traffic between the transmitting and receiving apparatuses can be suppressed, communication at a higher transmission rate is possible, and a digital wireless communication system with high sound quality and high image quality can be realized. In addition, when the retransmission control of the digital wireless communication system is combined with H-ARQ, an error-free operation can be obtained with a smaller number of retransmissions, so that the transmission efficiency can be further improved.

(Embodiment 2)
FIG. 8 is a block diagram showing a configuration of a radio communication system according to Embodiment 2 of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.

  In FIG. 8, the wireless communication system includes a transmission apparatus 100 including an error correction coding unit 110, an OFDM modulation unit 120, a packet generation unit 130, and a transmission antenna 140, a reception antenna 210, an OFDM demodulation unit 220, a table reference unit 311, and The receiving apparatus 300 includes a weight coefficient calculation unit 310 including a memory 312, a likelihood generation unit 240, a likelihood change unit 250, a buffer 260, and an error correction iterative decoding unit 270.

  The receiving apparatus 300 includes a weight coefficient calculation unit 310 including a table reference unit 311 and a memory 312 instead of the weight coefficient calculation unit 230 of FIG.

  The memory 312 stores a conversion table of transmission output versus mean square value.

  The weighting factor calculation unit 310 inputs in advance the output of a standard signal generator that can be output at an arbitrary transmission power to the antenna 210 of the receiving apparatus 300, and associates this transmission output with the mean square value for transmission output versus mean square. A value conversion table is created and stored in the memory 312.

  The table reference unit 311 obtains a mean square value of the subcarriers calculated from the output of the OFDM modulation unit 220, converts the mean square value into received signal power with reference to a conversion table stored in the memory 312, The result is output to the likelihood changing unit 250 as a weighting coefficient.

  Thus, according to the present embodiment, receiving apparatus 300 stores, as a conversion table, a calculated value calculated when a signal whose input signal strength is known in advance is input as weighting coefficient calculating section 310. 312 and a table reference unit 311 that outputs the input signal strength by referring to the conversion table from the calculated value of the received signal strength, and inversely converts the mean square value measured in advance with the specified input power by referring to the table. Since the received power is obtained, the nonlinearity in the predetermined radio reception process can be absorbed, and thus the weighting factor can be calculated with more accurate received power. Therefore, it is possible to maintain good error correction performance, and it is possible to obtain an effect that voice communication and video communication with less errors and noise can be performed.

(Embodiment 3)
FIG. 9 is a block diagram showing a configuration of a radio communication system according to Embodiment 3 of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.

  9, the wireless communication system includes a transmission apparatus 100 including an error correction encoding unit 110, an OFDM modulation unit 120, a packet generation unit 130, and a transmission antenna 140, a reception antenna 210, an OFDM demodulation unit 220, and a weighting factor calculation unit 410. , A likelihood generating unit 240, a likelihood changing unit 250, a buffer 260, and a receiving apparatus 400 including an error correction iterative decoding unit 270.

  Weighting factor calculation section 410 calculates the reciprocal of the average value of the Euclidean distance, which is the difference between the demodulated signal of OFDM demodulation section 220 and the ideal transmission signal point, and outputs the calculated value as a weighting coefficient.

  Thus, according to the present embodiment, weighting factor calculation section 410 calculates the reciprocal of the average value of the Euclidean distance, which is the difference between the demodulated signal of OFDM demodulation section 220 and the transmission signal point, and calculates the calculated value as Since it is output as a weighting factor, the weighting factor is calculated from the reciprocal of the average Euclidean distance of the received symbol, and the likelihood information input to the error correction iterative decoding unit 270 is weighted. Therefore, since the likelihood information is corrected not only from the amplitude error but also from the degree of the phase error, it is possible to change the more accurate likelihood information in the likelihood changing means even in a fading environment, Better error correction performance can be maintained, and there is an effect that voice communication and video communication with less errors and noise can be performed.

(Embodiment 4)
FIG. 10 is a block diagram showing a configuration of a radio communication system according to Embodiment 4 of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.

  10, the wireless communication system includes a transmission apparatus 100 including an error correction encoding unit 110, an OFDM modulation unit 120, a packet generation unit 130, and a transmission antenna 140, a reception antenna 210, an OFDM demodulation unit 220, and a weight coefficient calculation unit 510. , A moving average calculation unit 520, a likelihood generation unit 240, a likelihood change unit 250, a buffer 260, and an error correction iterative decoding unit 270.

  The weighting factor calculation unit 510 may be any of the weighting factor calculation unit 230 in FIG. 1, the weighting factor calculation unit 310 in FIG. 8, or the weighting factor calculation unit 410 in FIG.

  Weighting factor calculation unit 510 calculates a weighting factor by the method described in Embodiments 1 to 3, and outputs the calculated weighting factor to moving average calculation unit 520.

  Moving average calculation section 520 obtains a moving average value of weighting coefficients corresponding to a predetermined number of symbols, and outputs it to likelihood changing section 250.

  As described above, according to the present embodiment, moving average calculation section 520 calculates a weighting factor that averages the demodulated signal of OFDM demodulation section 220 in a plurality of symbol sections, so that it is based on the moving average value of received symbols. Since the likelihood information is weighted, the weight coefficient can be prevented from fluctuating suddenly, the deterioration of error correction decoding performance due to the influence of sudden noise can be suppressed, voice communication with less errors and noise, and There is an effect that video communication is possible.

(Embodiment 5)
The buffer 260 in the first to fourth embodiments is configured as buffer means for holding the likelihood information of the likelihood changing unit 250 until it is accumulated up to the error correction decoding unit, and normalizing and outputting the maximum value.

  If the buffer 260 is configured in this way, it is not necessary to increase the dynamic range of the error correction iterative decoding unit 270, the circuit scale can be reduced, and the receiving apparatus can be reduced. Further, since current consumption can be reduced, the portable device can be operated for a long time. In addition, since the battery can be made small, it is light and convenient to carry.

  The above description is an illustration of a preferred embodiment of the present invention, and the scope of the present invention is not limited to this.

  In the present embodiment, the name “wireless communication system” is used. However, this is for convenience of explanation, and of course, a digital wireless communication system, an OFDM demodulator, or the like may be used.

  Further, each circuit unit constituting the wireless communication system, for example, OFDM demodulator and likelihood generator, type of buffer, number and connection method, and any modulation scheme (8PSK, 16QAM, etc.) Good.

  The receiving apparatus and the wireless communication system according to the present invention employs an OFDM transmission method, and the coding gain is reduced due to the influence of flat fading on the propagation path, the fluctuation of the received electric field due to the movement of the receiving terminal, and the influence of Doppler fading. This is particularly useful in an environment where

1 is a block diagram showing a configuration of a wireless communication system according to Embodiment 1 of the present invention. The block diagram which shows schematic structure of the turbo encoder of the radio | wireless communications system which concerns on the said embodiment. A block diagram showing a data flow of a transmitting apparatus of the wireless communication system according to the above embodiment The figure which shows the example of 16QAM mapping of the radio | wireless communications system which concerns on the said embodiment. The figure which shows the likelihood production | generation method of the 1st, 3rd bit of the radio | wireless communications system which concerns on the said embodiment. The figure which shows the likelihood production | generation method of the 2nd, 4th bit of the radio | wireless communications system which concerns on the said embodiment. The block diagram which shows schematic structure of the turbo decoder of the radio | wireless communications system which concerns on the said embodiment. FIG. 2 is a block diagram showing a configuration of a radio communication system according to Embodiment 2 of the present invention. Block diagram showing a configuration of a wireless communication system according to a third embodiment of the present invention Block diagram showing a configuration of a wireless communication system according to a fourth embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Transmission apparatus 110 Error correction encoding part 120 OFDM modulation part 130 Packet generation part 140 Transmission antenna 200,300,400,500 Reception apparatus 210 Reception antenna 220 OFDM demodulation part 230,310,410,510 Weight coefficient calculation part 240 Likelihood Generation unit 250 Likelihood change unit 260 Buffer 270 Error correction iterative decoding unit 311 Table reference unit 312 Memory 520 Moving average calculation unit

Claims (8)

Receiving means for receiving the transmitted OFDM signal;
OFDM demodulating means for OFDM demodulating the received signal received by the receiving means;
Weighting factor calculating means for calculating the signal strength of the OFDM demodulated signal demodulated by the OFDM demodulating means;
Likelihood generating means for generating likelihood information for performing error detection iterative decoding from the OFDM demodulated signal;
Likelihood changing means for changing the likelihood information based on the calculated value in the weight coefficient calculating means;
A buffer for holding the likelihood information changed by the likelihood changing means until the error correction decoding unit is accumulated;
An error correction iterative decoding means for performing error correction iterative decoding using likelihood information held in the buffer.   The receiving apparatus according to claim 1, wherein the weighting factor calculating unit calculates an absolute power value of the received symbol and weights the likelihood information input to the error correction iterative decoding unit using the absolute power as a weighting factor.   The receiving apparatus according to claim 1, wherein the weighting factor calculating unit weights likelihood information input to the error correction iterative decoding unit according to a received electric field level.   The weighting factor calculating means refers to the conversion table based on a memory that stores a calculation value calculated when a signal whose input signal strength is known in advance is input as a conversion table, and the received signal strength calculation value. The receiving apparatus according to claim 1, further comprising table reference means for outputting input signal strength.   The receiving apparatus according to claim 1, wherein the weighting factor calculating means calculates the reciprocal of the average value of the Euclidean distance, which is the difference between the demodulated signal of the OFDM demodulating means and the transmission signal point, and outputs the calculated value as a weighting factor. .   The receiving apparatus according to claim 1, wherein the weighting factor calculating unit calculates a weighting factor obtained by averaging demodulated signals of the OFDM demodulating unit over a plurality of symbol intervals.   The receiving apparatus according to claim 1, wherein the buffer holds an output of the likelihood changing unit as an error correction decoding unit and outputs a calculated value normalized by the maximum value. A wireless communication system using an OFDM transmission scheme in which an error correction decoding unit of a signal input to an error correction iterative decoder is divided into a plurality of symbols and transmitted.
Error correction encoding means for encoding transmission data in error correction encoding units;
OFDM modulation means for dividing the data encoded by the error correction encoding means for each symbol unit and converting the data into OFDM signals;
Packet generating means for sequentially inserting the OFDM signal into a prescribed packet to generate a packet;
A transmission device comprising transmission means for wirelessly transmitting the packet;
Receiving means for receiving an OFDM signal transmitted from the transmitting device;
OFDM demodulating means for OFDM demodulating the received signal received by the receiving means;
Weighting factor calculating means for calculating the signal strength of the OFDM demodulated signal demodulated by the OFDM demodulating means;
Likelihood generating means for generating likelihood information for performing error detection iterative decoding from the OFDM demodulated signal;
Likelihood changing means for changing the likelihood information based on the calculated value in the weight coefficient calculating means;
A buffer for holding the likelihood information changed by the likelihood changing means until the error correction decoding unit is accumulated;
A wireless communication system comprising: a receiving device including: an error correction iterative decoding unit that performs error correction iterative decoding using likelihood information held in the buffer.

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