JP2015154449A - Receiving device, communication apparatus, and receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a receiving device whose receiving performance is improved.SOLUTION: A receiving device in a communication system to which a differential modulation system is applied includes: a differential demodulation unit 3 for demodulating a receiving signal and generating a first demodulation signal; a temporary determination unit 4 for determining the first demodulation signal and generating a first determination value; a differential modulation unit 5 for differentially modulating the first determination value and generating a reference signal; a filter unit 6 for filtering the receiving signal by a filter coefficient based on the reference signal and generating an interference-suppressed signal; a differential demodulation unit 7 for demodulating the interference-suppressed signal and generating a second demodulation signal; a determination unit 8 for determining the second demodulation signal and generating a second determination value; and a selection unit 9 for selecting either one of the first determination value and the second determination value.

Description

  The present invention relates to a receiving device, a communication device, and a receiving method for receiving a signal transmitted by differential space-time coded transmission.

  In wireless signal transmission, a diversity technique for suppressing the influence of fading and the like is used. In recent years, differential space-time coding (STBC), which can obtain a diversity effect by sending a signal according to a specific rule using a plurality of transmitting antennas, makes the processing of the receiving apparatus easy. It is a feature and is used in various systems.

  In STBC, propagation path estimation is required in the receiving apparatus. On the other hand, Non-Patent Document 1 discloses differential space-time coding (DSTBC: Differential Space Time Block Coding) that eliminates the need for channel estimation by performing differential coding in units of STBC blocks. . For example, in DSTBC by two-antenna transmission, two symbols are configured as one block, differential encoding is performed from data of two blocks, and reception data of two blocks is differentially demodulated on the receiving side, Demodulate the data. When this DSTBC is applied, as described in Non-Patent Document 1, it is possible to configure a receiving apparatus that can extract the transmission diversity effect by a simple method. Similarly to DSTBC, signal processing is performed in units of blocks, but transmission bits are mapped to a matrix and transmitted, and a PAPR (Peak to Average Power Ratio) of a signal after differential modulation is provided by giving a characteristic to the mapping rule. An improved DSTM (Differential Space Time Modulation) method is also known, and a transmission diversity effect can be obtained as in the case of DSTBC.

  Non-Patent Document 2 discloses a method for compensating for the influence of propagation path fluctuations in a high-speed moving environment in a communication system using DSTBC. In the method described in Non-Patent Document 2, using the past received signal and the signal determined in the past, the propagation path information of the time corresponding to some past blocks is generated from the determination result, and weighted addition is performed. Compensates for the difference between the two time propagation paths used for differential demodulation, thereby improving the performance. According to this method, in a differential modulation method that does not require a pilot signal, it is possible to improve performance in an environment where propagation path fluctuation is large with a small amount of computation while suppressing a decrease in throughput due to addition of an additional known sequence.

  On the other hand, in wireless communication, it is known that various types of interference can cause performance degradation. For example, in a system to which broadband transmission is applied, it may happen that the signal is distorted due to the frequency selectivity of the propagation path and cannot be demodulated correctly. This phenomenon occurs due to delayed waves in a multipath environment, and the distortion changes variously depending on the characteristics of the propagation path, that is, the number of delay waves, the phase relationship and the magnitude of each delay wave, and therefore narrows equalization processing and signals. This is dealt with by using a multi-carrier transmission scheme such as OFDM (Orthogonal Frequency Division Multiplexing). The former generally estimates the preceding wave and the delayed wave of the received signal, adjusts the phase, etc., and combines them to effectively utilize the delayed wave and improve performance. This method requires a pilot sequence for channel estimation. Further, the latter can easily realize demodulation processing including propagation path estimation processing by superimposing signals on each subcarrier and transmitting them in parallel by a technique such as DFT (Discrete Fourier Transform). In order to eliminate interference between transmission symbols, a redundant sequence called a guard interval or a cyclic prefix having a length longer than an assumed maximum delay amount is often added. As described above, many known methods use a redundant sequence to take measures against multipath.

V. Tarokh, H .; Jafarkhani, “A Differential Detection Scheme for Transmit Diversity,” IEEE Journal on Selected Areas in Communications, Vol. 18, pp 1169-1174, July 2000. Kubo, “Demodulation method based on decision feedback transmission path prediction for differential space-time block coding”, IEICE Technical Report RCS2012-163, Nov. 2012.

  The technique disclosed in Non-Patent Document 2 improves performance without adding redundancy such as pilot signals by decision feedback processing in a system that transmits differential coding, particularly differential space-time coded signals. However, there is a problem that performance improvement cannot be expected for interference such as delayed waves. In addition, for the equalization processing and the OFDM system, it is necessary to add a redundant part to the signal to allow a reduction in throughput. In any system, when the terminal assumed as an application using differential modulation moves at high speed, it is necessary to update the estimated propagation path with high frequency, and it is possible to take a countermeasure against delay waves without adding redundancy. It is necessary to realize a differential signal transmission system. Further, when differential coding is used in combination with transmission diversity as in the differential space-time modulation scheme, interference suppression becomes even more difficult.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a receiving device, a communication device, and a receiving method with improved reception performance.

  In order to solve the above-described problems and achieve the object, the present invention is a receiving apparatus of a communication system to which a differential modulation method is applied, and is a first apparatus for demodulating a received signal to generate a first demodulated signal. 1 differential demodulation unit, a temporary determination unit that determines the first demodulated signal and generates a first determination value, and a differential that differentially modulates the first determination value to generate a reference signal A modulation unit; a filter unit that filters the received signal with a filter coefficient based on the reference signal to generate a signal after interference suppression; and a second demodulator that demodulates the signal after interference suppression and generates a second demodulated signal. A differential demodulator, a determination unit that determines the second demodulated signal and generates a second determination value, a selection unit that selects one of the first determination value and the second determination value; It is characterized by providing.

  According to the present invention, it is possible to suppress an interference signal such as a delayed wave without making it necessary to add a redundant signal such as a pilot signal, and as a result, it is possible to obtain a receiving apparatus with improved reception performance. There is an effect that it is possible. In addition, there is an effect that it is possible to obtain a receiving apparatus that can perform propagation path estimation with improved follow-up performance to propagation path fluctuation.

FIG. 1 is a diagram illustrating a configuration example of a receiving apparatus according to the first embodiment. FIG. 2 is a diagram illustrating a configuration example of a receiving apparatus according to the second embodiment. FIG. 3 is a diagram illustrating a configuration example of a receiving apparatus according to the third embodiment. FIG. 4 is a diagram illustrating a frame configuration example.

  Hereinafter, embodiments of a receiving device, a communication device, and a receiving method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a first embodiment of a receiving device according to the present invention. The receiving apparatus according to the present embodiment includes a plurality of receiving antennas 1, an RF unit 2, a differential demodulation unit 3, a provisional determination unit 4, a differential modulation unit 5, a filter unit 6, a differential demodulation unit 7, a determination unit 8, and A selection unit 9 is provided to configure a wireless communication system.

  A reception operation in the reception apparatus having the configuration shown in FIG. 1 will be described. It is assumed that a differentially encoded signal is received.

  Each of the signals received by the plurality of receiving antennas 1 is subjected to predetermined RF (Radio Frequency) processing such as down-conversion, gain adjustment, band limitation and the like in the RF unit 2, and then is converted into a digital signal value by A / D conversion. Is output after being converted to. The signal output from the RF unit 2 is input to the differential demodulation unit 3 and the filter unit 6. The signal input to the differential demodulator 3 is demodulated and determined by a series of processes of the differential demodulator 3 and the provisional determination unit 4 in the same manner as the existing technology, and a provisional decision bit string is generated. The For example, when differential space-time coding is applied to the received signal, the differential demodulator 3 performs a matrix or vector multiplication operation for each block having a plurality of time symbols as a unit of modulation. Perform dynamic demodulation. The provisional determination unit 4 makes a hard decision on the signal after differential demodulation. The provisional determination unit 4 may generate a soft decision value by performing a soft decision instead of the hard decision. When generating a soft decision value, the determination reliability based on the soft decision value in a determination value selection operation described later. Can be used. The temporary determination bit generated by the temporary determination unit 4 is input to the selection unit 9 and the differential modulation unit 5.

  The differential modulation unit 5 performs differential encoding on the temporary determination value generated by the temporary determination unit 4. The differential encoding performed here is the same differential encoding as that performed by the transmission apparatus that is the transmission source of the signal received by the receiving antenna 1. The signal obtained by performing differential encoding is output to the filter unit 6 as a reference signal corresponding to the transmission waveform (the signal before demodulation output from the RF unit 2).

  The filter unit 6 receives a reception signal (signal output from the RF unit 2) and a reference signal (signal output from the differential modulation unit 5), and adaptively applies a filtering coefficient (hereinafter referred to as a filter coefficient). And filter the received signal using the filter coefficient. As a method for generating the filter coefficient, for example, a minimum mean square error (MMSE) standard is used. As a filter coefficient generation method based on the MMSE standard, for example, a method called SMI (Sample Matrix Inversion) is known. In this method, in a configuration in which a reference signal and a corresponding signal to be filtered (received signal) are input and these least square errors are output, a filter is applied so that the output least square error is minimized. Configure. By re-encoding the differential demodulation result and applying differential modulation again, a reference signal can be generated and a spatial filtering function can be realized. As a result, the signal that has passed through the filter unit 6 is in a state in which interference is suppressed. The differential demodulation unit 7 and the determination unit 8 perform the same processing as the differential demodulation unit 3 and the temporary determination unit 4 on the output signal from the filter unit 6. If the filter coefficients of the filter unit 6 are appropriately configured, the determination result obtained by performing the differential demodulation process and the determination process in the differential demodulation unit 7 and the determination unit 8 is determined by the provisional determination unit 4. It can be expected that the reception quality is improved as compared with the temporary determination result.

  The determination result in the temporary determination unit 4 and the determination result in the determination unit 8 are input to the selection unit 9, and the selection unit 9 selects the higher quality among the input determination results, and the final determination result Output as. As the determination result selection means, when the temporary determination unit 4 and the determination unit 8 output soft decision values, a method of statistically comparing them and switching the selection at a constant time interval can be considered. As a statistic used for selection, a variance value of the absolute value of the soft decision value can be considered. Further, instead of using the soft decision value, the variance of the value obtained by removing the modulation component from the signal immediately after the differential demodulation result (the signal output from the differential demodulation units 3 and 7) may be used (in FIG. A signal line (signal output path) from the dynamic demodulation units 3 and 7 to the selection unit 9 is not shown). For example, if the modulation is QPSK, each signal point is distributed at four points every 90 degrees, so by multiplying the phase by four, ideal received signal points are collected in one place and the phase dispersion value of that value is obtained. Can be used as an index of quality used for selection. In addition to this, assuming that the filter coefficient is not obtained immediately after startup, such as using a received signal that does not pass through the filter until immediately after synchronization in the frame synchronization process, the selection operation is controlled in conjunction with the synchronization process. Also good.

  As described above, the receiving apparatus according to the present embodiment generates a first determination value by differentially demodulating a received signal in a communication system to which differential encoding is applied, and uses the first determination value. A reference signal is generated by differential modulation, a received signal before differential demodulation is filtered based on the generated reference signal, a second determination value is generated by differential demodulation of the received signal after filtering, One of the first determination value and the second determination value is selected as the final determination result.

  According to the receiving apparatus according to the present embodiment, in a system to which differential encoding is applied, instead of using a known sequence with a small amount added to a communication frame as a reference signal, a provisional determination result is used as a reference signal. Therefore, when the quality of the first determination value (provisional determination value) is above a certain level, it is possible to generate a signal in which interference is suppressed using a filter and differentially demodulate the signal to obtain a determination value Therefore, reception performance can be improved. In addition, the filter coefficient generated using only the known signal added for synchronization in the communication frame needs to be updated according to the fluctuation of the propagation path response. The signal can be continuously supplied to the received signal of the unknown data portion to follow the propagation path fluctuation.

  In this embodiment, an example of a receiving apparatus having two receiving antennas 1 has been described. However, the present invention can be implemented as long as the receiving apparatus has two or more receiving antennas. Even when the number of reception antennas is two or more, the RF unit 2 performs frequency conversion corresponding to each reception antenna, filtering for band limitation, etc. for each reception branch, and the differential demodulation unit 3 performs differential demodulation. The results are added and diversity combined to make a provisional decision. The filter unit 6 may constitute a spatial filter whose input is the number of reception branches and whose output is 1. In addition, even if the diversity method by increasing the number of receiving antennas is changed or combined with selection diversity, the present invention can be similarly implemented as long as the number of branches selected by selection diversity is two or more. Further, in FIG. 1, which is the configuration of the present embodiment, the differential demodulation and determination processing constituting the flow of the received signal for generating the provisional determination value exists at a plurality of locations, but the circuit configuration is configured by hardware. However, the same function can be realized by mounting one differential demodulating unit and determining unit by using a common circuit and switching by a switch.

Embodiment 2. FIG.
FIG. 2 is a diagram illustrating a configuration example of a second embodiment of the receiving device according to the present invention. In the present embodiment, the same reference numerals are given to portions common to the receiving apparatus of Embodiment 1 (see FIG. 1), and description thereof is omitted. The present embodiment is a configuration suitable for a case where a transmission diversity system such as a differential space-time coding system is applied, and a receiving apparatus receives signals of both transmission diversity branches.

  As shown in FIG. 2, the receiving apparatus according to the present embodiment adds a filter unit 10, a differential demodulating unit 11, and a combining unit 12 to the receiving apparatus according to the first embodiment. The differential space-time signal generator 13 is replaced. Filter unit 10 and differential demodulator 11 perform the same processing as filter unit 6 and differential demodulator 7 in the receiving apparatus of the first embodiment.

  When the transmission diversity method is applied, a plurality of different signals are generated. Here, as an example, a case will be described in which transmission is two antennas, that is, differential space-time coding in which a block is composed of two symbols. When the number of antennas on the transmission side is 2, two different signals are generated on the transmission side and reach the reception side, so there are two reference signal sequences (corresponding to signals transmitted from the respective transmission antennas). Therefore, the differential space-time signal generation unit 13 performs differential encoding corresponding to each transmission antenna on the temporary determination value generated by the temporary determination unit 4 to generate two reference signals. The filter unit 6 performs filtering by configuring a filter using one reference signal and the filter unit 10 uses the other reference signal, and the differential demodulation unit 7 differentially processes the signal output from the filter unit 6. The differential demodulator 11 differentially demodulates the signal output from the filter unit 10 and outputs the demodulated signal. Thereafter, the reception signals output from the differential demodulation units 7 and 11 are combined by the combining unit 12 and passed to the determination unit 8. As a combining process in the combining unit 12, for example, a method of generating by adding both differential demodulation results at each time can be considered.

  As described above, according to the present embodiment, improvement in reception performance can be expected in a scheme that restores and combines each transmission signal and applies transmission diversity such as differential space-time coding. When differential space-time coding is used, it is not essential to perform filtering, differential demodulation, and synthesis on signals of all branches of transmission diversity as shown in FIG. The filter may be configured to receive only one signal of transmission diversity based on the reference signal. As a result, a system that can be expected to receive only one of the transmission diversity can obtain an effective effect in terms of circuit scale and power consumption. Similarly, in the case of transmission diversity including three or more transmission antennas, a filter / differential demodulator may be similarly arranged in parallel with respect to two or less of the transmission diversity branches. .

Embodiment 3 FIG.
FIG. 3 is a diagram illustrating a configuration example of a third embodiment of the receiving device according to the present invention. In the present embodiment, the same reference numerals are given to portions common to the receiving apparatus of Embodiment 1 (see FIG. 1), and description thereof is omitted. In the receiving apparatus of the present embodiment, a known sequence such as a sync word included in the frame configuration is used in addition to the provisional determination value.

  As shown in FIG. 3, the receiving apparatus according to the present embodiment adds a synchronization control unit 14 to the receiving apparatus according to the first embodiment (see FIG. 1), and the differential modulation unit 5 serves as a reference signal generation unit. The configuration is replaced with 15.

  In a scheme using a differential modulation scheme such as differential space-time coding, a pilot signal is not normally inserted, but for the purpose of bit timing synchronization, frame synchronization, frequency synchronization, etc., the frame configuration example shown in FIG. Thus, a part of the frame is composed of a known sequence called a sync word, a preamble or the like. In the receiving apparatus according to the present invention, if there is an error in the tentative determination of the generation source for the reference signal sequence generated using the tentative determination result, all subsequent reference signals are also erroneous, causing a problem. To solve this problem, if the data string in the long symbol section is a sync word and the preamble part is a fixed signal pattern, error propagation can be prevented by temporarily terminating the differentially encoded sequence. Since the known sequence portion can be predicted at the reception side after synchronization is established, the accuracy of filtering can be further improved by switching the reference signal to the known signal at the reception time of the known sequence. .

  For example, the synchronization control unit 14 performs frame synchronization by detecting a sync word from the bit string of the determination pattern, and obtains time information such as the number of a symbol currently being processed and a known sequence such as a sync word and a preamble as a reference signal generation unit 15. To supply. The reference signal generation unit 15 determines whether the signal being processed is a known sequence based on the time information received from the synchronization control unit 14, and if the signal is a known sequence, supplies the known sequence to the filter unit 6 as a reference signal. If it is a data part that is not a known series, as in the case of the differential modulation part 5 shown in FIG. 1, a filter part using a signal obtained by differentially modulating the provisional determination result again based on the differential modulation rule as a reference signal 6 is supplied.

  Thus, by applying the configuration of the present embodiment, the quality of the reference signal is improved and the filtering accuracy is also improved. As a result, the quality of received data can be improved. Further, since the reference signal of the known sequence part does not depend on the differential encoding method, it is possible to wirelessly transmit the known sequence unit using a sequence other than the differential space-time coding or the differential modulation method. .

  In the present embodiment, an example has been described in which the synchronization control unit 14 is added to the receiving apparatus of the first embodiment illustrated in FIG. 1 and modified, but the second embodiment illustrated in FIG. It is possible to similarly modify the receiving apparatus as a base. Further, the input signal of the synchronization control unit 14 is a bit string signal from the determination unit, but the synchronization control unit 14 detects the output signal of the filter unit 6 before differential demodulation and the output signal of the RF unit 2 by the synchronization control unit 14. May be given as an input signal.

  In each of the embodiments, the differential modulation scheme, particularly the differential spatio-temporal modulation scheme, has been described as an example. However, in addition to the DSTBC known as the differential spatio-temporal modulation scheme, each block is similarly The present invention can also be applied to the case of transmitting DSTM in which differential modulation processing is performed and signals are transmitted in matrix units, and similar effects can be obtained. Also, in an environment where the terminal moves at high speed, the reference signal sequence length for forming the MMSE filter is adjusted, or the time axis direction averaging processing such as IIR (Infinite Impulse Response) is incorporated in the filter coefficient generation processing Thus, it becomes possible to follow the fluctuation of the propagation path. Moreover, although the example which uses a temporary determination result as a reference signal of an adaptive filter was shown about the whole embodiment, you may feed back the output of the selection part 9 as a reference signal.

  According to each embodiment, in a communication system with large propagation path fluctuation due to high-speed movement such as train radio, the transmission band can be widened while using differential modulation, and a high-performance receiver can be realized. It is done.

  As described above, the receiving apparatus according to the present invention is useful for a communication system to which differential coding is applied, and is particularly suitable for a receiving apparatus for signals subjected to differential space-time coding.

  DESCRIPTION OF SYMBOLS 1 Reception antenna, 2 RF part, 3, 7, 11 Differential demodulation part, 4 Temporary determination part, 5 Differential modulation part, 6,10 Filter part, 8 Determination part, 9 Selection part, 12 Synthesis part, 13 Differential A spatio-temporal signal generator, 14 synchronization controller, 15 reference signal generator.

Claims (8)

A receiving device of a communication system to which a differential modulation method is applied,
A first differential demodulator that demodulates a received signal to generate a first demodulated signal;
A temporary determination unit that determines the first demodulated signal and generates a first determination value;
A differential modulation unit that differentially modulates the first determination value to generate a reference signal;
A filter unit that filters the received signal with a filter coefficient based on the reference signal to generate a signal after interference suppression;
A second differential demodulator for demodulating the interference-suppressed signal to generate a second demodulated signal;
A determination unit that determines the second demodulated signal and generates a second determination value;
A selection unit for selecting one of the first determination value and the second determination value;
A receiving apparatus comprising:   The selection unit selects one of the first determination value and the second determination value based on a variance value obtained from the first demodulated signal and a variance value obtained from the second demodulated signal. The receiving apparatus according to claim 1. The first determination unit and the determination unit perform a soft decision,
The selection unit selects one of the first determination value and the second determination value based on a variance value of the first determination value and a variance value of the second determination value. The receiving device according to claim 1. When the received signal is transmitted using a plurality of transmission antennas,
The differential modulation unit generates a plurality of reference signals corresponding to the plurality of transmission antennas,
The filter unit filters the received signal with a plurality of filter coefficients based on the plurality of reference signals to generate a plurality of interference-suppressed signals corresponding to the plurality of reference signals,
The second differential demodulator demodulates each of the plurality of interference-suppressed signals to generate a plurality of second demodulated signals,
The determination unit determines each of the plurality of second demodulated signals to generate a plurality of second determination values,
The selection unit selects the first determination value or a combined second determination value obtained by combining the plurality of second determination values. 4. The receiving device according to 2 or 3.   The filter unit filters the received signal with a filter coefficient based on a known sequence in a time interval in which the known sequence is transmitted, and receives the filter signal based on the reference signal in a time interval other than the time interval in which the known sequence is transmitted. The receiving apparatus according to claim 1, wherein the signal is filtered.   The receiving apparatus according to claim 1, wherein the differential modulation scheme is a differential space-time coding scheme.   A communication apparatus comprising the receiving apparatus according to claim 1. A reception method in a communication system to which a differential modulation method is applied,
A first differential demodulation step of demodulating the received signal to generate a first demodulated signal;
A provisional determination step of determining the first demodulated signal to generate a first determination value;
A differential modulation step of differentially modulating the first determination value to generate a reference signal;
A filter step of generating a signal after interference suppression by filtering the received signal with a filter coefficient based on the reference signal;
A second differential demodulation step of demodulating the interference-suppressed signal to generate a second demodulated signal;
A determination step of determining the second demodulated signal to generate a second determination value;
A selection step of selecting one of the first determination value and the second determination value;
A receiving method comprising:

Images