JP5480589B2 - Communication apparatus, relay method and program thereof - Google Patents

Description

The present invention relates to a communication device , a relay method thereof, and a program.

  In general, a wireless communication system has flexibility that is not constrained by a cable. However, on the other hand, there is a high probability that a data error will occur upon reception, and reliability is low compared to wired communication. For example, when data is received, the signal strength of the radio signal becomes very weak due to attenuation of a received signal (hereinafter also referred to as received data), and the signal-to-noise ratio (SN ratio) becomes small. Therefore, the probability that a demodulation error will occur increases. In addition, since the radio waves reflected on various objects arrive at the receiving node after being delayed from the direct waves, it is necessary for the receiving node to combine these plural radio waves having different delay times and intensities. Therefore, signal distortion may occur in the received data, which also causes data errors. In this way, when the receiving node has a low SN ratio and demodulates a distorted signal, the probability of occurrence of a data error is high. Therefore, for example, data protection may be performed using an error correction code.

  If the distance between the transmitting and receiving nodes is some distance away, a necessary SN ratio cannot be ensured on the receiving node side, and therefore a relay device may be provided between the transmitting node and the receiving node (Patent Document 1). The relay device receives data (radio signal) transmitted from the transmission node, and performs demodulation and decoding using an error correction code on the data. Then, re-encoding and re-modulation are performed, and the re-modulated data is transmitted to the receiving node. Thereby, since the influence of noise and distortion is removed, data having the same quality as the original data transmitted from the transmitting node can be relayed to the receiving node side.

  In addition, redundant transmission by diversity is known as a technique for improving the reliability of wireless communication. Redundant transmission is a technique in which a plurality of communication paths from a transmission node to a reception node are provided, and the same data as the data transmitted from the transmission node is transmitted to the reception node using the plurality of different communication paths.

  When a plurality of communication paths (hereinafter sometimes referred to as transmission paths) are used, even if communication on any of the communication paths is interrupted, data can be sent and received via the remaining communication paths. The communication quality from the node to the receiving node can be maintained. Therefore, if redundant transmission is used, there is no loss of transmission data due to the communication path being cut off, and retransmission control processing for recovering the data loss is unnecessary.

  Therefore, redundant transmission is often used in systems that require extremely high reliability, synchronous data transfer systems that are not allowed to use retransmission processing, and the like. Further, in the case of redundant transmission, the receiving node receives a plurality of data via a plurality of communication paths and combines and decodes them, so that a diversity effect is obtained.

JP 2006-54675 A

A Practical Scheme for Wireless Network Operation, IEEE Trans. On Comm., VOL. 55, NO. 3, MARCH 2007

  Even if data protection using error correction codes is performed to reduce the occurrence of data errors, if the received data contains more errors than the error correction code correction capability, the relay device The error cannot be corrected. In this case, data containing an error is relay-transmitted toward the receiving node.

  Here, the principle of occurrence of data error in wireless communication will be described with reference to FIG. FIG. 10A shows an outline of a modulation signal in a binary phase shift keying (BPSK).

  In the BPSK system, for example, when the data symbol to be modulated is “0”, the phase of the carrier signal is 0 degree (point A), and when the data symbol is “1”, the phase of the carrier signal is 180 degrees (B Phase modulation is performed so that The receiving node maps the modulation point on the received BPSK on the in-phase axis, and acquires the position on the in-phase axis as a metric value. If the metric value is positive, the received data symbol is acquired as “0”, and if the metric value is negative, it is acquired as “1”.

  The BPSK modulated signal immediately after being modulated by the transmitting node contains almost no noise component. Therefore, in the modulation signal, the metric values of the data symbols “0” and “1” are approximately +1.0 and −1.0, respectively. However, noise is superimposed on the radio signal passing through the communication path, or distortion is generated. In this case, the receiving node (or relay device) generates metric values distributed in a Gaussian distribution as shown in FIG. 10A due to the influence of noise. The greater the noise component contained in the received data (received signal), the greater the spread of this distribution. For example, if the spread of the distribution in the region where the sign of the metric value is positive exceeds the metric value 0 and enters the negative region, the receiving node erroneously determines the data symbol “0” as “1”. End up. The opposite event also occurs. Such a malfunction causes a data error in the receiving node.

  Next, an outline of redundant transmission using three communication paths will be described with reference to FIG. In addition, the numerical value attached | subjected in the figure shows the metric value in each point. Since the influence of noise and distortion in the communication path varies with time, the metric value shown in the figure represents an instantaneous value focusing on a certain transmission bit.

  When the transmission data bit is “0”, the transmission node 50 modulates and transmits this bit “0” as the metric value +1.0. The signal transmitted from the transmission node 50 is affected by attenuation and distortion on the communication path, and varies from the metric value +1.0 at the time of transmission when received by each relay device. For example, the relay device 51 receives a metric value + 0.4 signal, the relay device 52 receives a metric value + 0.5, and the relay device 53 receives a metric value−0.1. Here, since the metric value is positive, the relay apparatuses 51 and 52 decode the data normally (bit “0”), modulate it, and relay-transmit it. On the other hand, the relay device 53 receives the metric value −0.1, and relays the data bit with an incorrect metric value −1.0.

  Similarly to the communication path from the transmission node to each relay apparatus, the wireless signal is affected by noise and distortion in the communication path from each relay apparatus to the reception node. The receiving node 54 receives metric values +0.3, +0.4, and −1.1 as received data from each relay device, and synthesizes and decodes them. Here, for example, it is assumed that synthesis decoding by metric value addition is performed in the receiving node 54 (three metric values are summed and used as a synthesized metric value). In this case, the combined metric value is −0.4, that is, a negative number, and the receiving node 54 erroneously determines that the combined received data symbol is “1”.

  In this way, when data including an error is re-encoded in the relay device, the data with the error superimposed is relayed and transmitted. As a result, even if combining decoding is performed at the receiving node, a data error occurs and the diversity effect by combining decoding cannot be sufficiently obtained.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to reduce the probability of occurrence of relay data errors.

In order to solve the above problem, a communication apparatus according to an aspect of the present invention includes a first conversion unit that converts a frequency of a reception signal to obtain a frequency conversion signal, and a waveform storage unit that stores a waveform of the frequency conversion signal. , from the frequency converted signal, and decoding means for obtaining decoded signals, encoding means for encoding said decoded signal is stored in the signal and the waveform storage means obtained by by that encoding the encoding means said second converting means for converting one of the frequency and waveform, depending on the reception state of the received signal, the signal obtained by converting the frequency of the signal obtained by by that encoding the encoding means and characterized in that it has a transmission means for transmitting one of a signal obtained by converting the frequency of the stored waveform in the waveform storing means.

  According to the present invention, the probability of occurrence of relay data errors can be reduced.

The figure which shows an example of a structure of the relay apparatus concerning one embodiment of this invention. The figure which shows an example of a structure of the receiving node 40 concerning this embodiment. The figure which shows an example of the outline | summary of relay transmission. The flowchart which shows an example of operation | movement of the relay apparatus 10 shown in FIG. FIG. 6 is a diagram illustrating an example of a configuration of a relay device according to a second embodiment. 9 is a flowchart illustrating an example of the operation of the relay apparatus 10 according to the second embodiment. FIG. 9 is a diagram illustrating an example of a configuration of a relay device 10 according to a third embodiment. FIG. 10 is a diagram showing an example of a data (packet) format according to the third embodiment. FIG. 9 is a diagram illustrating an example of a configuration of a receiving node 40 according to the third embodiment. The figure which shows an example of a prior art.

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

(Embodiment 1)
FIG. 1 is a diagram illustrating an example of a configuration of a relay apparatus according to an embodiment of the present invention.

  The relay device 10 includes a receiving antenna 11, a radio receiving unit 12, a demodulating unit 13, an analog / digital converter (AD converter) 14, a waveform memory 15, and a sampling unit 16 as a configuration related to reception processing. The decoding unit 17 and the error detection unit 18 are provided. In addition, the relay apparatus 10 includes a re-encoding unit 19, a relay data selection unit 20, a digital / analog converter (DA converter) 21, a modulation unit 22, and a wireless transmission unit 23 as a configuration related to relay transmission. And a transmission antenna 24.

  First, a configuration related to reception processing will be described. The reception antenna 11 receives a radio signal transmitted from the transmission node as reception data. The radio reception unit 12 converts the radio signal received by the reception antenna 11 from a high frequency band signal to an intermediate frequency band signal. In addition, the wireless reception unit 12 is provided with an automatic gain circuit, and the automatic gain circuit adjusts the converted signal to a more appropriate signal level.

  The demodulator 13 demodulates the intermediate frequency signal adjusted to an appropriate level by the radio receiver 12. Specifically, demodulation is performed on analog reception baseband signals of an in-phase channel (I channel) and a quadrature channel (Q channel).

  The AD converter 14 converts the baseband signal into digital data (received digital signal). The received digital data is stored in the waveform memory 15 and sent to the sampling unit 16. The received digital data stored in the waveform memory 15 is a metric value of each data bit on the time axis.

  The sampling unit 16 extracts a data bit string from the received digital data according to the data clock. The extracted data bit string is sent to the decoding unit 17. The decoding unit 17 performs a decoding process using an error correction code on the data bit string to generate decoded data. For error correction, various error correction codes such as convolutional code, (RS) code, and low density parity check code (LDPC) can be employed, and the method is not particularly limited. Here, a checksum for error detection is added to the decoded data in advance at the time of transmission from the transmission node, separately from the error correction code.

  The error detection unit 18 verifies the checksum added to the decoded data and detects whether or not uncorrected error bits are included in the decoded data. As the checksum, a cyclic redundancy check (CRC) code or the like may be used. Note that such a checksum does not have the ability to correct individual error data, but can detect whether or not error data is included in the entire data packet. Therefore, even if the data error is not completely corrected by the processing by the decoding unit 17 and the uncorrected error is included in the decoded data, the error detecting unit 18 can detect the data error.

  Next, a configuration related to relay transmission processing will be described. The re-encoding unit 19 performs error correction encoding processing by the same method as that of the transmission node (transmission device), and encodes the decoded data again.

  Based on the control signal (error detection result) from the error detection unit 18, the relay data selection unit 20 re-encoded data re-encoded by the re-encoding unit 19 or received digital data stored in the waveform memory 15. Select one of the data. Then, the selected data is output to the DA converter 21 as transmission digital data. For example, when it is determined by the error detection unit 18 that uncorrected error bits are not included in the decoded data, the relay data selection unit 20 selects re-encoded data and outputs it to the DA converter 21. To do. On the other hand, when the error detection unit 18 determines that the uncorrected error bit is included in the decoded data, the relay data selection unit 20 receives the reception digital data that is the reception data before the error correction processing. Select it and output it to the DA converter 21. As described above, the received digital data is a metric value when the relay apparatus 10 receives the received digital data.

  The DA converter 21 converts the transmission digital data into an analog transmission baseband signal. The modulation unit 22 modulates the analog transmission baseband signal into an intermediate frequency band signal to generate remodulated data. The wireless transmission unit 23 converts the intermediate frequency band signal into a high frequency band signal. The transmitting antenna 24 transmits a radio signal as relay data to a receiving node (receiving device).

  Next, an example of the configuration of the receiving node 40 according to the present embodiment will be described with reference to FIG.

  The reception node 40 includes a reception antenna 41, a wireless reception unit 42, a demodulation unit 43, an AD converter 44, a sampling unit 45, a plurality of metric storage units 46 (46 a to 46 c), and a metric synthesis unit 47. It is comprised and comprises. Since the configuration other than the metric storage unit 46 and the metric synthesis unit 47 performs the same function as the configuration of the relay apparatus 10 described in FIG. 1, the description may be omitted here. Specifically, the reception antenna 41 corresponds to the reception antenna 11, the wireless reception unit 42 corresponds to the wireless reception unit 12, the demodulation unit 43 corresponds to the demodulation unit 13, and the AD converter 44 corresponds to the AD converter 14. Correspondingly, the sampling unit 45 is a component corresponding to the sampling unit 16.

  The metric storage unit 46 stores the metric value extracted by the sampling unit 45 according to the data clock. Each metric storage unit 46 stores metric values sent via a plurality of communication paths (different relay apparatuses 10). In this case, three metric storage units 46a to 46c are provided, and the received metric values respectively transmitted from the three relay devices 10 are stored in each.

  The metric synthesizer 47 synthesizes and decodes data received via a plurality of communication paths. That is, a metric value for each data bit is synthesized. In the metric synthesis unit 47 according to this embodiment, three metric storage units 46a to 46c are provided in order to exemplify the case of synthesizing and decoding data transmitted from three communication paths.

  In the above, an example of the configuration of the relay device 10 and the reception node 40 has been described with reference to FIGS. 1 and 2. Note that the relay device 10 and the reception node 40 have a built-in computer. The computer includes main control means such as a CPU, and storage means such as ROM (Read Only Memory), RAM (Random Access Memory), and HDD (Hard Disk Drive). In addition, the computer includes input / output means such as a keyboard, a mouse, a display, a button, or a touch panel. These constituent units are connected by a bus or the like, and are controlled by the main control unit executing a program stored in the storage unit.

  Next, an example of relay transmission will be described with reference to FIG. Here, a case where relay transmission is performed by redundant transmission in a communication system in which three relay apparatuses 10 described in FIG. 1 are arranged will be described.

  The data transmitted from the transmission node 30 is relay-transmitted in each relay device (the first relay device 10a, the second relay device 10b, and the third relay device 10c), and finally combined in the reception node 40. Decrypted. FIG. 3 shows the metric value at each point and the magnitude of the influence of noise and distortion generated in each communication path. These values are instantaneous values focusing on a certain transmission bit.

  The first relay device 10a and the second relay device 10b receive the received data (radio signal) sent from the transmission node 30, accurately decodes it, and relays and transmits data that does not contain an error. . On the other hand, the third relay apparatus 10c is assumed to include error bits that could not be corrected in the decoded data. That is, the received data received by the third relay device 10c includes a number of errors exceeding the correction capability of the error correction code.

  In this case, the first and second relay apparatuses 10 relay and transmit the re-encoded data. That is, the relay data selection unit 20 selects the re-encoded data generated by the re-encoding unit 19 and relays the data. On the other hand, in the third relay device 10c, since the error data is included in the decoded data, the received data is relayed and transmitted as it is. That is, the relay data selection unit 20 selects the data stored in the waveform memory 15 and relays the data.

  When receiving node 40 receives the reception data (radio signal) transmitted from first relay device 10a, reception node 40 stores the metric value of each data bit included in the reception data in metric storage unit 46a. Similarly, the metric value of each data bit included in the received data received from the second relay device 10b is stored in the metric storage unit 46b, and each data included in the received data received from the third relay device 10c. The bit metric value is stored in the metric storage unit 46c.

  When the reception node 40 has received all of the data from the three relay devices 10, the metric synthesis unit 47 performs synthesis decoding. Here, the data symbol “0” transmitted as the metric value +1.0 from the transmission node 30 is normally decoded in the first relay device 10a and the second relay device 10b. Therefore, relay transmission is performed from these two relay apparatuses with a metric value +1.0. On the other hand, the third relay device 10c relays and transmits the demodulated data as it is. That is, the third relay device 10 c performs relay transmission with the same metric value −0.1 as the metric value received from the transmission node 30.

  Data relayed from each relay device 10 is affected by noise and distortion on the communication path to the receiving node 40. As a result, the reception node 40 receives the reception data from the first to third relay devices 10 as metric values +0.3, +0.4, and −0.2, respectively.

  Here, the receiving node 40 performs synthesis decoding by adding metric values. That is, the three metric values are summed to calculate the combined metric value +0.5. Thereby, since the calculated metric value is a positive number, the receiving node 40 acquires the combined received data symbol as “0”. That is, the receiving node 40 can normally receive the same value as the data symbol transmitted by the transmitting node 30.

  Next, an example of the operation in the relay apparatus 10 shown in FIG. 1 will be described with reference to FIG. Here, the operation when relay transmission is performed will be described as an example.

  When the relay device 10 receives data (wireless signal) at the receiving antenna 11, this process starts (YES in S101). When this processing starts, the relay device 10 first converts the frequency band of the received data in the radio reception unit 12 and demodulates the converted data into an analog reception baseband signal in the demodulation unit 13. (S102).

  Subsequently, in the AD converter 14, the relay device 10 converts the baseband signal into received digital data, outputs the received digital data to the sampling unit 16, and stores the received digital data in the waveform memory 15 (S103).

  The relay device 10 performs sampling in the sampling unit 16 and performs decoding processing using an error correction code on the sampled data bit string in the decoding unit 17 (S104). As described above, a detection checksum is added to the decoded data.

  Here, the relay device 10 verifies the checksum in the error detection unit 18 and detects whether or not the uncorrected error bit is included in the decoded data, and the re-encoding unit 19 detects the decoded data. Is encoded again to generate re-encoded data (S105). As a result of error detection by the error detection unit 18, if uncorrected error bits are not included in the decoded data (NO in S 106), the relay device 10 selects re-encoded data in the relay data selection unit 20. , It is output to the DA converter 21 (S108). On the other hand, if uncorrected error bits are included in the decoded data (YES in S106), the relay device 10 selects the data stored in the waveform memory 15 in the relay data selection unit 20, and converts it to DA. It outputs to the converter 21 (S107). That is, when uncorrected error bits are included in the decoded data, the data before error correction processing is output to the DA converter 21.

  Thereafter, the relay device 10 performs DA conversion in the DA converter 21 to convert the digital data into an analog transmission baseband signal (S109). Then, the modulation unit 22 modulates the baseband signal into an intermediate frequency band signal, and the wireless transmission unit 23 converts the intermediate frequency band signal into a high frequency band signal (S110). Thereafter, the relay device 10 transmits the converted data (radio signal) to the receiving node 40 through the transmission antenna 24 (S111).

  As described above, according to the first embodiment, when data including a number of errors exceeding the correction capability of the error correction code is relayed, not the decoded data after the error correction process but the data before the error correction process is used as it is. Relay transmission.

  Conventionally, there has been no configuration for detecting whether or not an uncorrected error is included in decoded data after error correction processing, and switching and relaying data based on the result. For this reason, there is a case where a data error occurs on the receiving node side as a result of overlapping the error, but according to the present embodiment, it is possible to reduce the occurrence of the data error due to such a situation.

(Embodiment 2)
Next, Embodiment 2 will be described. In the first embodiment, the relay data is switched based on whether or not an error bit that could not be corrected is included. On the other hand, in the second embodiment, a case will be described in which a signal-to-noise ratio (SN ratio) of received data (received signal) is estimated and relay data is switched using this estimated value as a reference. Note that when the SN ratio of the received signal is reduced, the distribution of the demodulation metric at the receiving node is widened, and the probability that a bit error occurs is increased. Thus, the probability that the received data includes error bits, the number of generated error bits, and the like can be estimated from the SN ratio of the received data.

  FIG. 5 is a diagram illustrating an example of the configuration of the relay apparatus 10 according to the second embodiment. In addition, the same code | symbol is attached | subjected to the structure which performs the function similar to FIG. 1 which demonstrated Embodiment 1, and the description may be abbreviate | omitted.

  In addition to the configuration of the first embodiment, the relay apparatus 10 is newly provided with an SN ratio estimation unit 25. The SN ratio estimation unit 25 estimates the SN ratio of the received signal from the intermediate frequency band signal received from the wireless reception unit 12. Then, the estimated SN ratio is compared with a preset threshold value. Here, this threshold value is used as a criterion for determining whether or not the number of errors exceeding the correction capability of the error correction code is included. Therefore, a suitable value is set based on an empirical rule or the like.

  If the estimated signal-to-noise ratio exceeds the threshold value as a result of the comparison, it is determined that there are few errors in the received data, and a message to that effect is output to the relay data selection unit 20. If the estimated SN ratio does not exceed the threshold value, it is determined that there are many errors included in the received data (exceeds the correction capability by the error correction code), and that fact is output to the relay data selection unit 20 To do.

The relay data selection unit 20 is stored in the waveform memory 15 as re-encoded data re-encoded by the re-encoding unit 19 based on the control signal from the S / N ratio estimation unit 25 (S / N ratio estimation result). One of the received digital data is selected. Then, the selected data is output to the DA converter 21 as transmission digital data. For example, when the SN ratio estimation unit 25 determines that the number of error bits included in the received data (intermediate frequency band signal) is small (the SN ratio exceeds the threshold value), the relay data selection unit 20 Re-encoded data is selected and output to the DA converter 21.
On the other hand, when the SN ratio estimation unit 25 determines that there are many error bits included in the received data (the SN ratio does not exceed the threshold value), the relay data selection unit 20 performs reception before error correction processing. The received digital data stored in the waveform memory 15 as data is selected. Then, it is output to the DA converter 21. As described above, the received digital data is a metric value when the relay apparatus 10 receives the received digital data.

  The above is the description of the configuration of the relay device 10 according to the second embodiment. Note that the configuration of the receiving node 40 is the same as that in FIG. 2 describing the first embodiment, and thus the description thereof is omitted here.

  Next, an example of the operation in the relay apparatus 10 according to the second embodiment will be described with reference to FIG. Here, the operation when relay transmission is performed will be described as an example.

  When the relay device 10 receives data (wireless signal) at the receiving antenna 11, this process starts (YES in S201). When this process starts, the relay device 10 first converts the frequency band of the received data in the wireless reception unit 12 (S202). Then, the SN ratio estimation unit 25 estimates the SN ratio of the received signal from the converted intermediate frequency band signal, and the demodulator 13 demodulates the analog reception baseband signal (S203).

  Subsequently, in the AD converter 14, the relay device 10 converts the baseband signal into digital data, outputs the received digital data after the conversion to the sampling unit 16, and stores it in the waveform memory 15 (S204). .

  The relay apparatus 10 performs sampling in the sampling unit 16 and performs decoding processing using an error correction code on the sampled data bit string in the decoding unit 17 (S205). Thereafter, the relay device 10 re-encodes the decoded data in the re-encoding unit 19 to generate re-encoded data (S206).

  Here, the relay apparatus 10 uses the re-encoded data re-encoded by the re-encoding unit 19 based on the SN ratio estimation result from the S / N ratio estimation unit 25 in the relay data selection unit 20 or the waveform memory. 15 selects one of the received digital data stored in 15. As a result of the S / N ratio estimation, if the estimated S / N ratio exceeds the threshold value (YES in S207), the relay apparatus 10 selects re-encoded data in the relay data selection unit 20, and converts it to the DA converter 21. (S209). On the other hand, if the estimated SN ratio does not exceed the threshold value (NO in S207), the relay device 10 selects the data stored in the waveform memory 15 in the relay data selection unit 20, and sends it to the DA converter 21. Output (S208). That is, the data before error correction processing is output to the DA converter 21.

  Thereafter, the relay device 10 performs DA conversion in the DA converter 21 to convert the digital data into an analog transmission baseband signal (S210). Then, the modulation unit 22 modulates the baseband signal into an intermediate frequency band signal, and the wireless transmission unit 23 converts the intermediate frequency band signal into a high frequency band signal (S211). Thereafter, the relay device 10 transmits the converted data (radio signal) to the receiving node 40 at the transmission antenna 24 (S212).

  As described above, according to the second embodiment, the relay data is switched based on the SN ratio of the received signal. In this case, the same effect as that of the first embodiment can be obtained.

(Embodiment 3)
Next, Embodiment 3 will be described. In the first and second embodiments described above, the communication method using a single carrier using the BPSK modulation method has been described as an example. On the other hand, in the third embodiment, a case will be described in which the communication method involves secondary modulation, such as an orthogonal frequency division multiplexing (OFDM) communication method and a spread spectrum (SS) communication method. Here, a case where an OFDM communication system is employed will be described as an example of a communication system involving secondary modulation.

An example of the configuration of the relay apparatus 10 according to the third embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure which performs the function similar to FIG. 1 which demonstrated Embodiment 1, In addition to the structure of Embodiment 1, the description may be abbreviate | omitted. Thus, an FFT processing unit 26, an equalizer 27, an inverse FFT processing unit 28, and a preamble adding unit 29 are newly provided.

  Here, the AD converter 14 converts the analog reception baseband signal obtained by the processing by the demodulation unit 13 into reception digital data. The converted received digital data is stored in the waveform memory 15 and sent to the sampling unit 16. The received digital data according to the third embodiment is an OFDM signal as a time domain, and holds a metric value of data bits in a subcarrier.

  The sampling unit 16 extracts data samples at sampling points necessary for Fourier transform (FFT) from the received digital data sequence. Note that when each OFDM symbol includes a guard interval as the OFDM signal format, the sampling unit 16 removes the guard interval.

  The FFT processing unit 26 performs a Fourier transform process on the time-domain OFDM signal to convert it to a frequency-domain OFDM signal (frequency-domain signal). The equalizer 27 corrects the variation in the phase and amplitude caused by the channel characteristics for the frequency domain signal output from the FFT processing unit 26. Here, the data (packet) format according to the third embodiment has the configuration shown in FIG. In the OFDM signal according to the format, a preamble part (signal related to communication control) is added before the data payload part in which application data is held. The equalizer 27 estimates the channel characteristics using the preamble part. Then, the data payload portion is corrected based on the estimated channel characteristics.

  The decoding unit 17 performs error correction processing on the signal output from the equalizer 27. However, channel coding in the OFDM communication system often uses scramble or interleave processing together with simple error correction coding. Therefore, the decoding unit 17 performs processes such as descrambler and deinterleaver necessary for these processes as necessary.

  The re-encoding unit 19 performs error correction encoding processing on the decoded data generated by the decoding unit 17 by the same method as that of the transmission node, and encodes the decoded data again. When scramble or interleave processing is performed in addition to the error correction encoding processing, the re-encoding unit 19 performs processing such as scrambler and interleaver as necessary as in the decoding unit 17. The re-encoded data generated by the re-encoding unit 19 is a frequency domain OFDM signal.

  The inverse FFT processing unit 28 performs an inverse Fourier transform process to process a frequency domain OFDM signal into a time domain OFDM signal. The preamble adding unit 29 adds a preamble part to the head part of the OFDM signal. As a result, data having the format shown in FIG. 8 is obtained.

  Based on the control signal (error detection result) from the error detection unit 18, the relay data selection unit 20 re-encoded data re-encoded by the re-encoding unit 19 or received digital data stored in the waveform memory 15. Select one of the data. Note that the SN ratio may be estimated as in the second embodiment, and relay data may be selected based on the estimation result.

  Here, consider the case where the relay data selection unit 20 selects re-encoded data as relay data. In this case, the data (radio signal) relay-transmitted from the relay device 10 toward the reception node 40 has a waveform equivalent to a signal that is not affected by the channel characteristics immediately after being transmitted from the transmission node 30. In other words, the channel characteristics from the transmission node 30 to the relay device 10 are removed from the radio signal relayed from the relay device 10, and the signal received by the reception node 40 is received from the relay device 10. Only the channel characteristics up to the node 40 are included.

  As described above, when the relay apparatus 10 relays re-encoded data, the preamble part of the data to be relayed is generated by the preamble adding part 29. The preamble part is the same as the preamble part included in the OFDM signal immediately after being transmitted from the transmission node 30. Therefore, the communication path characteristics included in the preamble part received by the receiving node 40 include only the characteristics from the relay device 10 to the receiving node 40. Therefore, the receiving node 40 receives the data payload portion and the preamble portion that have received the same channel characteristics. Thereby, in the receiving node 40 (an equalizer 49 described later), the influence of the channel characteristics received by the data payload portion can be accurately corrected based on the received reference to the preamble portion.

  Consider the case where the relay data selection unit 20 selects the received digital data stored in the waveform memory 15 as relay data. In this case, the waveform memory 15 stores not only the data payload portion but also the preamble portion as a time waveform. Here, both the waveform of the preamble part and the data payload part stored in the waveform memory 15 include the communication path characteristics from the transmission node 30 to the relay device 10. Therefore, when the preamble part and the data payload part are relayed and transmitted, the channel characteristics from the relay apparatus 10 to the receiving node 40 are further superimposed on the relay data. Also in this case, the receiving node 40 receives the data payload portion and the preamble portion that have received the same channel characteristics. Thereby, in the receiving node 40 (an equalizer 49 described later), the influence of the channel characteristics received by the data payload portion can be accurately corrected based on the received reference to the preamble portion.

  Next, an example of the configuration of the receiving node 40 according to the third embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure which performs the function similar to FIG. 2 which demonstrated Embodiment 1, and the description may be abbreviate | omitted.

  In addition to the configuration of the first embodiment, the reception node 40 is newly provided with an FFT processing unit 48 and an equalizer 49 as functions necessary for OFDM reception.

  The FFT processing unit 48 performs a Fourier transform process on the time-domain OFDM signal to convert it to a frequency-domain OFDM signal. The equalizer 49 corrects the frequency domain OFDM signal converted by the FFT processing unit 48. Specifically, phase and amplitude fluctuations caused by channel characteristics are corrected. At this time, the equalizer 49 estimates the channel characteristic using the preamble part, and corrects the data payload part based on the estimated channel characteristic.

  As described above, according to the third embodiment, a preamble part added to relay transmission can be appropriately selected. As a result, the same effect as that of the first embodiment can be obtained even in a communication scheme involving secondary modulation such as the OFDM scheme.

  The above is an example of a typical embodiment of the present invention, but the present invention is not limited to the embodiment described above and shown in the drawings, and can be appropriately modified and implemented without departing from the scope of the present invention. . For example, the second embodiment and the third embodiment may be combined. That is, if either an error is detected or the signal-to-noise ratio exceeds a threshold value, the data in the waveform memory 15 is relayed, otherwise the re-encoded data is relayed. You may comprise.

  In the above-described embodiment, the case where there are three communication paths has been described as an example, but the present invention is not limited to this. For example, by increasing or decreasing the number of metric storage units 46 (or storage areas) in the receiving node 40, the number of various communication paths can be accommodated.

  In the above-described embodiment, the relay device, the reception node, and the transmission node are described as separate devices, but the present invention is not limited to this. For example, the relay device and the transmission node may be realized as the same device, and the device may have both a transmission function for transmitting transmission data and a relay function. Further, the relay device and the receiving node may be realized as the same device (communication device).

  In addition, the present invention can take an embodiment as a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of a single device.

(Other embodiments)
The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (11)

First conversion means for converting the frequency of the received signal to obtain a frequency converted signal;
Waveform storage means for storing the waveform of the frequency conversion signal ;
Decoding means for obtaining a decoded signal from the frequency converted signal ;
Encoding means for encoding the decoded signal ;
Second converting means for converting one of the frequency of the stored waveform signal and the waveform storage means obtained by by that encoding the encoding means,
Depending on the reception state of the received signal, either the converted signal the frequency of said encoding means converts the frequency of the signal obtained by by that coded signal and said waveform storage means with the stored waveform and transmitting means for transmitting,
A communication apparatus comprising: When the second conversion means converts the frequency of the signal obtained by the encoding, a communication control signal is newly added to the signal converted from the frequency , and the second conversion means is the waveform storage means. When the frequency of the waveform stored in is converted, the communication control signal included in the waveform is corrected.
The communication apparatus according to claim 1. An error determination means for detecting an error in the decoded signal ;
The second converting means converts the frequency of the waveform stored in the waveform storing means when the amount of error detected from the decoded signal exceeds a predetermined error threshold;
The communication apparatus according to claim 1 or 2, characterized in that An error determination means for detecting an error in the decoded signal ;
The second converting means converts the frequency of the signal obtained by the encoding when the amount of error detected from the decoded signal does not exceed a predetermined error threshold;
The communication apparatus according to claim 1 or 2, wherein The decoding means decodes digital data based on the frequency converted signal using an error correction code,
The second converting means converts the frequency of the waveform stored in the waveform storage means when an error exceeding the correction capability of the error correcting code is included in the received signal, and corrects the error correcting code. When the error exceeding the capability is not included in the received signal, the frequency of the signal obtained by the encoding is converted .
The communication apparatus according to claim 1 or 2, wherein By verifying the added checksum to said decoded signal, further comprising a detection means for detecting errors included in the decoded signal,
The second converting means converts the frequency of the waveform stored in the waveform storage means when the detecting means detects the error, and the encoding means when the detecting means does not detect the error. Convert the frequency of the signal obtained by
The communication apparatus according to claim 1 or 2, wherein Measuring means for measuring a noise ratio with respect to the received signal;
The second conversion means converts the frequency of the waveform stored in the waveform storage means when the noise ratio measured by the measurement means exceeds a predetermined threshold;
The communication apparatus according to claim 1 or 2, wherein The second converting means converts the frequency of the signal obtained by the encoding when the noise ratio detected from the received signal is equal to or less than a predetermined threshold;
The communication device according to claim 7. A threshold used as a criterion for determining whether or not an error exceeding the correction capability of the error correction code is included in the received signal is compared with a result of estimating the signal-to-noise ratio of the received signal. And further has an estimation means for
The second conversion means converts the frequency of the waveform stored in the waveform storage means when the estimated noise ratio exceeds the threshold value, and the estimated noise ratio is less than or equal to the threshold value. In the case of converting the frequency of the signal obtained by the encoding,
The communication apparatus according to claim 1 or 2, wherein A relay method in a communication device,
Converting the frequency of the received signal to obtain a frequency converted signal;
Storing the waveform of the frequency conversion signal ;
Obtaining a decoded signal from the frequency converted signal ;
Encoding the decoded signal ;
Converting any frequency of the signal obtained by the encoding and the stored waveform ;
And transmitting in response to the reception state of the received signal, one of a signal obtained by converting the frequency of the waveform of the stored converted signal with the frequency of the signal obtained by the encoding,
A relay method for a communication apparatus, comprising: Computer
First conversion means for converting the frequency of the received signal to obtain a frequency converted signal;
Waveform storage means for storing the waveform of the frequency conversion signal ;
Decoding means for obtaining a decoded signal from the frequency converted signal ;
Encoding means for encoding the decoded signal ;
Second converting means for converting one of the frequency of the stored waveform signal and the waveform storage means obtained by by that encoding the encoding means,
Depending on the reception state of the received signal, either the converted signal the frequency of said encoding means converts the frequency of the signal obtained by by that coded signal and said waveform storage means with the stored waveform and transmitting means for transmitting,
Program to function as.

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