JP2015041920A - Receiver, transmitter and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a receiver capable of reducing the deterioration of reception performance without using a pilot signal.SOLUTION: A receiver for receiving a signal differentially coded on the basis of a plurality of symbols includes: a differential demodulation unit 16 for differently demodulating the reception signal; a determination processing unit 17 for generating a determination result of a received series using the result of the differential demodulation and a transmission series candidate; a separation unit 15 for separating a preceding wave and a delayed wave using the determination result and a plurality of reception signals having different reception time; a signal correction unit 14 for correcting the reception signal using the result of separation by the separation unit 15 using a reception signal received in the past and the determination result generated by the determination processing unit 17 using the reception signal received in the past. The differential demodulation unit 16 performs differential demodulation of the reception signal after corrected by the signal correction unit 14.

Description

  The present invention relates to a receiving device, a transmitting device, and a communication system.

  In wireless signal transmission, a diversity technique for suppressing the influence of fading and the like is used. In particular, in recent years, STBC (Space Time Block Coding), which can obtain a diversity effect by sending a signal according to a specific rule using a plurality of transmitting antennas, is characterized in that the processing of the receiving apparatus is simple. Is used in various systems.

  However, in STBC, propagation path estimation is necessary in the receiving apparatus. For this reason, Non-Patent Document 1 discloses DSTBC (Differential Space Time Block Coding) that eliminates the need for channel estimation by performing differential encoding 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 decoded on the receiving side, Demodulate the data.

  A spatio-temporal modulation system, which is a more generalized version of the above DSTBC, has been devised. In the method of Non-Patent Document 2, a matrix and transmission information bits are mapped 1: 1, and transmission is performed. On the other hand, the method of Non-Patent Document 1 is different in that a matrix is formed by combining a plurality of symbols (two in the case of two antenna DSTBC) to which transmission information bits are mapped. It is known that the former has an advantage that transmission power can be made constant if an appropriate mapping matrix is selected.

  In the technique of Non-Patent Document 2, mapping from transmission information bits to signals is determined by associating elements and information bits in a set G whose elements are composed of matrices. The set G can be configured as a group, and in particular, by being configured as a cyclic group, it is possible to obtain the property that the multiplication result of the transmission signal candidate (the element of the cyclic group) becomes another transmission signal candidate. .

V. Tarokh, H .; Jafarkhani, “A Differential Detection Scheme for Transmit Diversity,” IEEE Journal on Selected Areas in Communications, Vol. 18, NO. 7, pp 1169-1174, July 2000. B. L. Hughes, “Optical Space-Time Contests From Groups,” IEEE Transactions on Information Theory, Vol. 49, no. 2, pp. 401-410, February 2003.

  However, according to the above-described conventional technique, there is a problem that reception performance is deteriorated with respect to an interference wave such as a delayed wave. As a factor of the reception performance deterioration, for example, there is intersymbol interference generated due to the influence of a delayed wave or the like between symbols in a block.

  In broadband transmission, the above-described conventional technique is used in combination with block transmission using multicarrier such as OFDM (Orthogonal Frequency Division Multiplexing) or single carrier block transmission. However, in these transmissions, there is a problem that high PAPR (Peak to Average Power Ratio) is generated, resulting in high performance of the amplifier. In addition, there is a problem that processing such as DFT (Discrete Fourier Transform) is required in the circuit, and the processing becomes complicated.

  On the other hand, a method of synthesizing delayed waves by equalization processing with a single carrier is also being studied. In the method using equalization processing, the propagation path coefficient is calculated by adding a pilot signal or the like. The differential encoding originally does not require addition of a pilot and is a system that is strong against propagation path fluctuations, but a pilot is inserted for equalization processing. For this reason, it is necessary to design a pilot insertion interval to cope with a decrease in throughput and a propagation path that fluctuates at high speed, and there is a problem that the merit of differential encoding is lost.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a reception device, a transmission device, and a communication system that can reduce deterioration in reception performance without using a pilot signal.

  In order to solve the above-described problems and achieve the object, the present invention is a receiving apparatus that receives a signal differentially encoded in units of a plurality of symbols, and a differential demodulator that differentially demodulates the received signal And a determination processing unit that generates a determination result of a received sequence using the differential demodulation result and the held transmission sequence candidate, and a plurality of received signals having different determination times and reception times. The separation unit that separates the preceding wave and the delayed wave, the result separated by the separation unit using the received signal received in the past, and the determination processing unit generated using the received signal received in the past And a signal correction unit that corrects the reception signal using a determination result, wherein the differential demodulation unit differentially demodulates the reception signal corrected by the signal correction unit. .

  According to the present invention, it is possible to reduce the degradation of reception performance without using a pilot signal.

FIG. 1 is a diagram illustrating a configuration example of a transmission apparatus according to an embodiment. FIG. 2 is a diagram illustrating an example of a signal format after adding redundant symbols. FIG. 3 is a diagram illustrating a configuration example of the receiving device according to the embodiment.

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

Embodiment.
FIG. 1 is a diagram illustrating a configuration example of an embodiment of a transmission apparatus according to the present invention. As illustrated in FIG. 1, the transmission apparatus according to the present embodiment includes a mapping unit 1, a differential modulation unit 2, a redundancy unit 3, and antennas 4-1, 4-2. The transmission apparatus according to the present embodiment performs transmission by differential encoding in units of blocks composed of a plurality of symbols.

The operation of the transmission apparatus according to this embodiment will be described. The mapping unit 1 converts the transmission bit sequence into a bit string by space-time modulation. As a specific conversion process at this time, for example, a process of mapping the elements of the set G made up of all transmission signal candidates before differential encoding and the bits may be considered. As an example, a set G ₁ shown in the following equation (1) is defined as a set of matrices composed of signal candidates before differential encoding.

The converted bit string is input to the differential modulation unit 2 as a signal S (k) before differential encoding. The differential modulation unit 2 performs differential modulation processing (differential encoding processing) on the signal S (k) to generate a differential modulation signal C (k). The differential modulation processing can be expressed by the following equation (2).
C (k) = C (k−1) S (k) (2)

  The redundancy unit 3 adds a redundant symbol using the differential modulation signal. Specifically, the redundancy unit 3 copies, for example, the second half symbol of the block of the differential modulation signal and adds it to the front of the block. FIG. 2 is a diagram illustrating an example of a signal format after adding redundant symbols. In the example of FIG. 2, transmission diversity for performing two-antenna transmission is assumed, and an example in which one block is composed of two symbols is shown. c1 (k) and c2 (k) are elements of the matrix C (k), and are scalar values that mean transmission data for each symbol. In the example of FIG. 2, the symbols in the latter half of the block are copied for each block and added before the block. This redundant symbol can be considered to correspond to a guard interval or CP (Cyclic Prefix) used in a system such as OFDM, but in this embodiment, single carrier transmission is assumed, and an existing system such as OFDM is used. There is no need for post-mapping DFT processing to be used. This operation can prevent interference between blocks even when there is a delayed wave having a delay time of one symbol or less. Specifically, the signal of block k interferes with C (k + 1) redundant symbol c2 (k + 1) even if a delay wave having a delay time of one symbol or less is added, but it interferes with the main body of the block. Does not cause. On the receiving side, by extracting the signal of the block body, the influence of interference between the blocks can be ignored.

  In the above example, the configuration in which the copy of the second half symbol of the block is arranged before the block has been described, but the symbol to be copied is not limited to this. For example, the first half symbol of the block may be copied and placed in front of the block. Alternatively, a component of two or more symbols may be copied and placed before the block. Further, in a system in which two symbols are one block, all symbols may be continuously transmitted twice. Also in this case, the redundant component can be added before the block as described above, and as a result, interference between the blocks can be avoided. Although an example in which space-time modulation is performed has been described here, the operation of the redundancy unit 3 is not limited to the case of performing space-time modulation, and can be applied to any transmission device that performs block transmission.

  The differential modulation signal to which redundant symbols are added by the redundancy unit 3 is transmitted from the antennas 4-1 and 4-2.

  Next, a received signal processing method will be described. FIG. 3 is a diagram illustrating a configuration example of the receiving apparatus according to the present embodiment. As shown in FIG. 3, the receiving apparatus of this embodiment includes an antenna 11, a signal extraction unit 12, a storage unit 13, a signal correction unit 14, a separation unit 15, a differential demodulation unit 16, and a determination processing unit 17.

  As an example, a case will be described in which redundant symbols are added by copying the latter half symbols as shown in FIG. When there is a delayed wave having a delay time of one symbol in the received signal, the received signal received by the antenna 11 is input to the signal extraction unit 12 in the receiving apparatus of the present embodiment. The signal extraction unit 12 extracts the block main body portion in FIG. 2 and inputs it to the storage unit 13 and the signal correction unit 14 as reception signals for each block. The received signal Y (k) of the block k is expressed by the following equation (3).

Y (k) = HC (k) + VC (k) F (3)
However, V is a propagation path coefficient matrix of a delayed wave component, and F is a matrix shown in the following formula (4).

  The matrix F has an effect of reversing the order of elements in the matrix. As described in Equation (3), only the transmission signal of a single block appears as a component in the received signal by processing on the transmission side (addition of redundant symbols), but the components of the preceding wave and the delayed wave are separated, Intersymbol interference cannot be removed. For example, when VC (k) F interferes with HC (k) and lowers the SNR, the reception performance deteriorates.

Here, when the transmission signal S is selected from the set G ₁ as described above, the following equation (5) is established.
SF = −FS (5)

That is, matrix multiplication can be exchanged by adding a sign. By using this property, the preceding wave component and the delayed wave component of the received signal can be separated. Consider multiplying the received signal Y (k−1) past one block by the determination result X (k). If the determination result is correct, that is, if X (k) = S (k), the multiplication result is as shown in the following expression (6) from the expressions (2) and (5).
Y (k-1) S (k) = HC (k) -VC (k) F (6)

From the equations (3) and (6), the preceding wave component HC (k) and the delayed wave component VC (k) F can be separated by addition and subtraction. If these are set as P (k) and Q (k), the following equations (7) and (8) are obtained. That is, the preceding wave and the delayed wave can be separated using a plurality of received signals having different reception times (in this example, Y (k), Y (k-1)) and the determination result.
P (k) = (Y (k) + Y (k−1) S (k)) / 2 (7)
Q (k) = (Y (k) −Y (k−1) S (k)) / 2 (8)

In the configuration example of FIG. 3, the accumulation unit 13 accumulates the reception signal input from the signal extraction unit 12. Thereby, the accumulation | storage part 13 can hold | maintain the past received signal. The separation unit 15 uses the past received signal and the determination result X (k) (determining the determination result X (k) as the transmitted signal S (k)) by the determination processing unit 17, and P (k), Q (k) is generated. The separation results (P (k), Q (k)) are input to the signal correction unit 14 and the differential demodulation unit 16. The signal correcting unit 14 and the differential demodulating unit 16 perform, for example, processing in which a delayed wave is suppressed using the separation result. That is, for example, the signal correction unit 14 obtains Y (k + 1) + Q (k) S for the new reception signal Y (k + 1) using the correct determination result S and Q (k) as described below. Y (k + 1) + Q (k) S can be expanded as shown in the following equation (9). Therefore, it can be expected that the preceding wave component of Y (k + 1) is extracted by obtaining Y (k + 1) + Q (k) S.
Y (k + 1) + Q (k) S = HC (k + 1) + VC (k + 1) F + VC (k) FS
= HC (k + 1) (9)

  The estimated value (Y (k + 1) + Q (k) S) of the preceding wave is input to the differential demodulator 16. The differential demodulator 16 multiplies Y (k + 1) + Q (k) S and P (k). The multiplication result is input to the determination processing unit 17. The determination processing unit 17 obtains a correlation between the signal candidate and the value input from the differential demodulation unit 16 for possible signal candidates held therein, and selects the candidate having the highest correlation value as the determination result X (k). The determination result is obtained. Conventionally (Non-Patent Documents 1 and 2) are performed by the following equation (10) at the time of determination, but in this embodiment, the processing of the differential demodulation unit 16 and the determination processing unit 17 is combined to remove the delayed wave. This is equivalent to performing the process shown in Expression (11) as the process for performing the determination.

  Through the above processing, the determination processing unit 17 can generate a determination result series. In the receiving apparatus according to the present embodiment, the received signal is separated into a plurality of components, the effect of intersymbol interference applied to the received signal is suppressed, or signal quality such as SNR (Signal to Noise Ratio) is improved. By performing the above, it is possible to obtain an effect that the reception performance can be improved. Also, by using the receiving apparatus of this embodiment, when performing differential encoding transmission by single carrier transmission in an environment including a delay wave, the components of the preceding wave and the delay wave are separated without using a pilot signal. Reception performance can be improved.

Hereinafter, a processing method in which the processing shown in the above embodiment is partially changed will be described. In the above description, transmission signal candidates using the set G ₁ shown in Equation (1) are assumed, but the mapping matrix is not limited to this example, and any matrix that satisfies Equation (5) above may be used. In general, if the mapping matrix S configured by a 2 × 2 matrix that configures a block with two symbols using two transmission antennas has the form shown in the following formula (12), the above formula (5 Is satisfied.

When one of the mapping matrix sets in the above formula (12) is selected and data is transmitted, the receiving apparatus performs signal separation and determination processing by the same processing as in the above example using the set G _1. Therefore, the reception performance can be improved.

In addition, transmission candidates other than the set of mapping matrices satisfying Expression (5) may be included. For example, in addition to the set G ₁ , elements (elements) of the set G ₂ represented by the following expression (13) may be transmission candidates. Original and set G ₂ based on the the combined group of set G ₁ and single out the transmission signal candidates S from (a set G _1, the original union of the set G _2). At this time, if the transmission signal candidate is an element of G ₁ , the above expression (5) is satisfied, and if it is an element of the set G ₂ , the following expression (14) is satisfied.

  SF = FS (14)

When the transmission signal candidate S is selected from a group obtained by combining the element of the set G ₁ and the element of the set G ₂ , the demultiplexing unit 15 of the reception apparatus receives the reception signal Y (k−1) past one block and the determination result X when multiplying (k), if X (k) is the set G ₂ original results can not be obtained of the formula (6), to obtain the results of the following formula (15) instead. However, it is assumed that the determination result X (k) = S (k).
Y (k-1) X (k) = HC (k) + VC (k) F (15)

Further, when the above equation (15) is obtained, if X (k−1) is an element of the set G ₁ , the following equation (16) is obtained, and as a result, similarly to the equation (6): Become.
Y (k-2) X (k-1) X (k) = HC (k) -VC (k) F (16)

From the above, even if the determination result belongs to the set G _2, if the determination result of past blocks belong to the set G _1, it is separated of the preceding wave and the delayed wave therefrom. The process of separating the preceding wave and the delayed wave may be performed by going back to the determination result where the element of the set G ₁ appears. Also in the process corresponding to formula (9), candidate the expression for suppressing the delay waves depending sets G ₁ belonging (a former set G ₁₎ belongs to the set G ₂ different. That is, the signal correction unit 14, the original determination candidate when belonging to the set G _2, is corrected as in the following equation (17) instead of equation (9).
Y (k + 1) -Q (k) S = HC (k + 1) + VC (k + 1) F-VC (k) FS
= HC (k + 1) (17)

With the above processing, delay wave suppression and reception performance improvement effects can be obtained in the same manner even when the transmission signal candidates include elements other than the elements of the set G ₁ .

Further, separation performance may be improved by averaging as follows. A case where the transmission signal candidate belongs to the set G ₁ will be described as an example. If the transmitted signal candidates belonging to all the set G _1, when multiplied by the decision value sequence of an odd number of blocks in the received signal, rvalue similar to equation (6) is obtained. That is, when n is an odd number, the following formula (18) is obtained.
Y (k−n) S (k−n + 1)... S (k) = HC (k) −VC (k) (18)

  On the other hand, if n is an even number, the sign on the right side of Equation (18) changes to addition rather than subtraction. Therefore, the delayed wave component and the preceding wave component in block k can be estimated from these results. Actually, Y may be affected by noise depending on the time, so different results are obtained at different n. Therefore, for example, HC (k) can be separated by adding the values of the equation (18) obtained for different n in the range of even even number n. Therefore, when the channel coefficient matrix H does not depend on time, noise can be averaged and the separation performance of the separation unit 15 can be improved.

In the above example, the transmitted signal candidates for the sake of simplicity has been described for the case belonging to the set G _1, it can also be applied to a case where the set G _1, the union of the set G ₂ select the transmission signal candidates. As shown in the equations (15) and (6), the combination of the determination results of the series determines how the preceding wave and the delayed wave overlap (whether the delayed wave is added to or subtracted from the preceding wave). Limited to the street. For this reason, since it is possible to estimate the overlapping method from the determination result, for example, when it is desired to extract the preceding wave component, by adding the same number of combinations that become the sum and the combination that becomes the difference, the delayed wave component is canceled, Averaging can be performed to improve the estimation accuracy of the preceding wave component.

  In the above description, an example of receiving a signal (a signal to which a redundant symbol is added) transmitted from the transmission apparatus of the present embodiment has been described. However, the preceding wave and the delayed wave in the reception apparatus of the present embodiment are described. This separation method can also be applied to the case of receiving a signal to which no redundant symbol is added. When receiving a signal to which no redundant symbol is added, the signal extraction unit 12 may not be provided.

  As described above, in the present embodiment, the method for separating a signal to improve reception performance for a signal including a delayed wave having a short delay time has been described. Is not limited to the above example. For example, as a method other than those described above, the preceding wave component may be suppressed and the determination process may be performed using a delayed wave. Moreover, it is good also as a structure which suppresses both signals, determines separately, and selects either based on received signal power. Further, instead of suppressing the delay wave, the signal correction unit 14 may add the reception signal multiplied by the delay wave component and the coefficient matrix to increase the reception power of the corrected preceding wave. In any of the examples, reception performance can be improved with respect to a signal subjected to delay wave interference. Further, in the present embodiment, the configuration in which the number of reception antennas is one is shown, but the same processing can be performed for the configuration of reception diversity. Although the number of transmitting antennas is two in FIG. 1, the number is not limited to two, and may be one or three or more.

  As described above, in the present embodiment, in the receiving device, the storage unit 13 holds the past received signal, and the separation unit 15 determines the past received signal and the determination result X (k) by the determination processing unit 17. Based on the above, the preceding wave and the delayed wave are separated. The signal correction unit 14 and the differential demodulation unit 16 are configured to perform processing in which the delayed wave is suppressed using the separation result of the separation unit 15. For this reason, it can be expected that a preceding wave component of Y (k + 1) is extracted, intersymbol interference can be suppressed, and reception performance can be improved. In the present embodiment, a part of the symbols of the block to be transmitted is copied and added as a redundant symbol for transmission, and the receiving apparatus extracts only the main part of the block for processing. For this reason, inter-block interference can be removed and reception performance can be improved.

  As described above, the receiving device, the transmitting device, and the communication system according to the present invention are useful for a communication system that performs transmission by differential space-time coding.

  DESCRIPTION OF SYMBOLS 1 Mapping part, 2 Differential modulation part, 3 Redundancy part, 4-1, 4-2, 11 Antenna, 12 Signal extraction part, 13 Storage part, 14 Signal correction part, 15 Separation part, 16 Differential demodulation part, 17 Judgment processing part.

Claims (9)

A receiving device that receives a signal differentially encoded in units of a plurality of symbols,
A differential demodulator that differentially demodulates the received signal;
A determination processing unit that generates a determination result of a sequence received using the differential demodulation result and the transmission sequence candidate held;
A separation unit that separates the preceding wave and the delayed wave using the determination result and a plurality of reception signals having different reception times;
A signal for correcting the received signal using a result separated by the separating unit using a received signal received in the past and a determination result generated by the determination processing unit using a received signal received in the past A correction unit;
With
The differential demodulator differentially demodulates the reception signal corrected by the signal correction unit.   The signal correction unit suppresses a delayed wave component of the reception signal using a result separated by the separation unit, and uses the suppressed result as the corrected reception signal. The receiving device described.   The receiving apparatus according to claim 2, wherein the signal correcting unit obtains an estimated value of a preceding wave of the received signal using the result of separation by the separating unit and uses the estimated value as the corrected received signal.   The signal correction unit uses the result of separation by the separation unit to suppress a delayed wave component of the reception signal and the result of separation by the separation unit, A second suppression result obtained by suppressing a component of the preceding wave is obtained, and either one of the first suppression result and the second suppression result is selected and used as the corrected received signal, The receiving device according to claim 1.   The signal correction unit suppresses a component of a preceding wave of the reception signal using a result separated by the separation unit, and uses the suppressed result as the corrected reception signal. The receiving device described. The received signal is transmitted by replicating a part of the symbols in a block composed of a plurality of symbols after differential encoding in the transmission device, and adding the duplicated symbols before the block. Signal,
A signal extraction unit that extracts the plurality of symbols of the received signal excluding the duplicated symbols and inputs the extracted result to the differential demodulation unit;
The receiving apparatus according to claim 1, further comprising: A transmission device that performs transmission in units of blocks each composed of a plurality of symbols,
A differential modulator for differentially encoding the transmission sequence;
A redundancy unit that duplicates a part of the block composed of a plurality of symbols after the differential encoding and generates a transmission signal in which the duplicated symbol is added before the block;
With
A transmission apparatus that transmits the transmission signal. A transmitting device;
The receiving device according to claim 1, which receives a signal transmitted from the transmitting device;
A communication system comprising: A transmission device according to claim 7;
The receiving device according to claim 6, which receives a signal transmitted from the transmitting device;
A communication system comprising:

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