JP6873340B2 - Transmitters, communication systems, communication methods, control circuits and programs - Google Patents

Description

The present invention relates to a transmitting device, a receiving device, a communication system, and a communication method that perform transmission diversity transmission on a signal that is primarily modulated by a frequency shift keying method.

The FSK (Frequency Shift Keying) method is known as a modulation method in which the fluctuation amount of the envelope of the transmission signal is small and excellent power efficiency can be realized.

On the other hand, as a method for improving transmission quality, a transmission diversity method in a wireless communication system including a plurality of transmission antennas such as a MISO (Multiple-Input Single-Auto) system and a MIMO (Multiple-Input Multi-Auto) system has been used so far. Proposed.

As one of the transmission diversity methods, Non-Patent Document 1 discloses an STBC technique using STBC (Space-Time Block Code), which is a spatiotemporal block code. In the STBC technique described in Non-Patent Document 1, a plurality of orthogonal series are generated by performing complex conjugate and sign inversion on a plurality of symbols that are continuous in time, and the orthogonal series are transmitted differently. Transmit from the antenna. In STBC technology, the transmission sequence is orthogonally coded in two dimensions, time and space. The coding in STBC technology, or STBC coding, is commonly referred to as Alamouti coding. On the other hand, the receiving device that receives the STBC-encoded and transmitted signal can easily estimate the transmission bit sequence by decoding the received two symbols using the transmission line information. As a result, in the STBC technology, the diversity gain corresponding to the number of transmitting antennas, that is, the transmission full diversity gain can be obtained.

S. M. Alamouti, "A Simple Transmit Diversity Technology Technology for Wireless Communications," IEEE Journal on Select Areas in Communications, Vol. 16, No. 8, pp. 1451-1458, October 1998.

However, according to the coding rules in STBC technology, there is a code inversion process between two temporally continuous symbols in a signal transmitted from one transmitting antenna. Therefore, when STBC coding is applied to a signal that is first-order modulated by the FSK modulation method, the amplitude value periodically drops to 0 at the symbol boundary, so that the amount of fluctuation of the envelope increases and the power efficiency is increased. There was a problem that it caused a decrease in the number of people.

The present invention has been made in view of the above, and an object of the present invention is to obtain a transmitter capable of suppressing the fluctuation amount of the envelope even when STBC coding is applied.

In order to solve the above-mentioned problems and achieve the object, the transmission device according to the present invention has two or more transmission antennas, a modulation unit that generates a modulation signal by frequency shift modulation, and a phase rotation of the modulation signal. A coding processing unit that generates a transmission signal transmitted from each of two or more transmission antennas by performing spatiotemporal block coding with the addition of the above, and the coding processing unit is a unit of frequency shift modulation. When is used as a symbol, a phase rotation process is performed on some of the symbols of the coding unit that encodes the modulated signal in a spatiotemporal block and the signal that is spatiotemporally block encoded by the coding unit in units of a plurality of symbols. The spatiotemporal block coding is provided with a phase rotation unit to be applied, and positive and negative codes are used between symbols corresponding to transmission signals transmitted continuously in time from one transmission antenna of two or more transmission antennas. Including the process of inverting, the phase rotation process is performed so as to suppress the decrease in the amplitude value of the transmitted signal caused by the inverting of the positive and negative codes while maintaining the spatiotemporal orthogonality in the spatiotemporal block coding .

The transmitter according to the present invention has an effect that the fluctuation amount of the envelope can be suppressed even when STBC coding is applied.

The figure which shows the configuration example of the communication system which concerns on Embodiment 1. A flowchart showing an example of a processing procedure of the transmitting device according to the first embodiment. The figure which shows the structural example of the coding processing part of Embodiment 1. The figure which showed the transmission signal in the transmitting antenna given by the equation (1) of Embodiment 1 on the IQ plane. The figure which showed the signal transition of Embodiment 1 when the modulation index in FSK modulation was 0.75 on the IQ plane. The figure which showed the signal transition of Embodiment 1 in the case where the FSK modulation unit performs modulation by the 4FSK method on the IQ plane. The figure which shows the signal transition of Embodiment 1 when the FSK modulation part oversampled by phase interpolation on the IQ plane. The figure which shows the structural example of the decoding processing part of Embodiment 1. The figure which shows the structural example of the control circuit which concerns on Embodiment 1. The figure which shows the structural example of the coding processing part which concerns on Embodiment 2. The figure which shows the operation example in the IQ axis exchange part which concerns on Embodiment 2.

Hereinafter, the transmitting device, the receiving device, the communication system, and the communication method according to the embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a diagram showing a configuration example of a communication system according to a first embodiment of the present invention. The communication system 3 of the present embodiment includes a transmitting device 1 and a receiving device 2. FIG. 1 also shows a configuration example of the transmitting device 1 and the receiving device 2.

As shown in FIG. 1, the transmission device 1 in the present embodiment includes FSK modulation units 10a and 10b, a coding processing unit 11, and transmission antennas 12a and 12b. The transmitting antennas 12a and 12b are examples of two or more transmitting antennas. The FSK modulation units 10a and 10b are modulation units that generate a modulation signal by frequency shift keying. Specifically, the FSK modulation units 10a and 10b primary-modulate the transmission bit sequence by the FSK method. That is, the FSK modulation units 10a and 10b map the transmission bit sequence to the FSK modulation symbol sequence. The transmission bit sequence may be a bit sequence that has undergone preprocessing such as interleaving and error correction coding. Hereinafter, the modulated signal primary-modulated by the FSK method is also referred to as an FSK signal. The coding processing unit 11 performs spatio-temporal block coding (STBC coding) in which phase rotation is added to the two signals primary-modulated by the FSK modulation units 10a and 10b, respectively, so that the transmitting antenna 12a , 12b, respectively, to generate a transmission signal to be transmitted. The spatiotemporal block coding with phase rotation is a process of STBC coding the input signal and rotating the phase of a part of the symbols of the signal after STBC coding, as will be described later. The coding processing unit 11 outputs the generated transmission signal to the corresponding transmission antennas 12a and 12b, respectively. The transmitting antennas 12a and 12b radiate the transmission signal output from the coding processing unit 11 as radio waves.

Further, the transmission device 1 may perform post-processing such as addition of CP (Cyclic Prefix) to the STBC coding result. In this case, for example, CP addition units corresponding to the number of transmission antennas are provided between the coding processing unit 11 and the transmitting antennas 12a and 12b, and the coding processing unit 11 adds the corresponding CP to the processed signal. Output to the unit. The CP addition unit adds CP to the signal output from the coding processing unit 11, and outputs the signal after CP addition to the corresponding transmitting antenna.

Here, an example in which the number of transmitting antennas is 2 will be described. The STBC coding to which the phase rotation processing of the present embodiment is added is not limited to the case where the number of transmitting antennas is 2, and can be applied to the case where the number of transmitting antennas is 3 or more. That is, the transmitting device 1 may include two or more transmitting antennas. When there are three or more transmitting antennas, the FSK modulation unit is provided for the number of transmitting antennas, and the coding processing unit 11 generates signals for the number of transmitting antennas by STBC coding to which phase rotation processing is added. Then, output to the corresponding transmitting antennas.

Although FIG. 1 illustrates the components related to baseband signal processing among the components of the transmission device 1, the transmission device 1 may include components (not shown in FIG. 1). For example, the transmission device 1 may include a filter, an analog unit that performs analog signal processing, and the like, in addition to the components shown in FIG. Further, the transmission device 1 shown in FIG. 1 includes the same number of FSK modulation units 10a and 10b as the number of transmission antennas, but one FSK modulation unit generates and generates FSK signals corresponding to the number of transmission antennas. The signal may be output to the coding processing unit 11. For example, one FSK modulator may generate FSK signals for the number of transmitting antennas by time division.

In this embodiment, it is premised that the transmission diversity method, that is, the Aramouti coding disclosed in Non-Patent Document 1 is used as the STBC coding. Further, in the present embodiment, the STBC coding unit is referred to as a “block”, and the frequency shift keying unit, that is, the FSK modulation data unit is referred to as a “symbol”. The FSK-modulated signal is a signal having a frequency corresponding to a bit value, and is a signal sampled at a certain time interval. The FSK-modulated signal "symbol" is a signal having a frequency corresponding to a bit value, and the time signal constituting the "symbol" is called a "sample".

In the present embodiment, an example in which FSK modulation is performed as the primary modulation will be described, but the primary modulation method is not limited to FSK modulation, such as MSK (Minimum Shift Keying) modulation and GMSK (Gaussian MSK) modulation. It may be a modulation method that transmits information based on the phase rotation of the signal.

As shown in FIG. 1, the receiving device 2 of the present embodiment includes a receiving antenna 20, a decoding processing unit 21, and FSK demodulation units 22a and 22b. The receiving antenna 20 receives the signal transmitted from the transmitting device 1 and outputs the received signal to the decoding processing unit 21. The decoding processing unit 21 performs STBC decoding while canceling the phase rotation performed in the transmission device 1. Specifically, the decoding processing unit 21 generates the same number of decoding signals as the transmitting antenna of the transmitting device 1 by performing phase rotation processing and STBC decoding on the received signal output from the receiving antenna 20. The decoded signal is output to the corresponding FSK demodulation units 22a and 22b. The phase rotation processing in the decoding processing unit 21 will be described later. The FSK demodulation units 22a and 22b perform demodulation corresponding to the FSK method, which is the primary modulation, that is, frequency shift demodulation, on the result decoded by the decoding processing unit 21, to estimate the transmission bit series. Find the bit sequence.

When the transmission bit sequence is subjected to preprocessing such as error correction coding in the transmission device 1, the reception device 2 deinterleaves and error correction / decoding with respect to the demodulation result by the FSK demodulation units 22a and 22b. Decryption processing corresponding to preprocessing such as is performed. When the soft determination error correction decoding is performed on the demodulation result by the FSK demodulation units 22a and 22b, the FSK demodulation units 22a and 22b may obtain the soft determination value. Further, when CP is added in the transmitting device 1, the receiving device 2 includes a CP removing unit that removes the CP at the subsequent stage of the receiving antenna 20, and the received signal from which the CP has been removed by the CP removing unit is received. It is output to the decoding processing unit 21.

Further, although FIG. 1 shows an example of one receiving antenna, there may be a plurality of receiving antennas. When there are a plurality of receiving antennas, the decoding processing unit 21 or the receiving diversity decoding unit (not shown) provided in front of the decoding processing unit 21 synthesizes the received signals received by the plurality of receiving antennas, and the decoding processing unit 21 synthesizes them. Phase rotation processing and STBC decoding are performed on the received signal.

Although FIG. 1 illustrates the components of the receiving device 2 related to baseband signal processing, the receiving device 2 may include components (not shown in FIG. 1). For example, the receiving device 2 may include a filter, an analog unit that performs analog signal processing, and the like. In the receiving device 2, time synchronization processing, frequency synchronization processing, transmission line estimation, and the like are also performed, but since general processing can be applied to these processing, the functional unit that performs these processing is illustrated. I will omit the explanation. In the following description of the operation of the receiving device 2, it is assumed that time synchronization processing, frequency synchronization processing, transmission line estimation, and the like are ideally performed. If time synchronization processing, frequency synchronization processing, transmission line estimation, etc. are not ideally performed, an error may occur, but the coping method for dealing with the error is with a receiving device that performs general STBC decoding. Since the same is true, the description thereof will be omitted.

Next, the operation of this embodiment will be described. First, the overall operation of the transmission device 1 will be described. FIG. 2 is a flowchart showing an example of the processing procedure of the transmission device 1 according to the first embodiment.

The FSK modulation units 10a and 10b generate an FSK signal by performing FSK modulation on the transmission bit sequence (step S101). The FSK modulation units 10a and 10b output the generated FSK signal to the coding processing unit 11.

The coding processing unit 11 generates an STBC coded signal by performing STBC coding on the two FSK signals output from the FSK modulation units 10a and 10b, respectively (step S102). The STBC coded signal includes symbols corresponding to the transmitting antennas 12a and 12b, respectively, as will be described later.

The coding processing unit 11 performs phase rotation processing on some symbols in the STBC coded signal (step S103). The coding processing unit 11 divides the signal after the phase rotation processing into transmission signals corresponding to the transmission antennas 12a and 12b, and outputs the transmission signals to the corresponding transmission antennas 12a and 12b. The FSK signal has the advantage that the fluctuation of the envelope is small, but when STBC coding is applied, the amplitude value periodically drops to 0 at the boundary of the symbols due to the code inversion processing performed on the symbols that are continuous in time. .. This causes the envelope of the transmitted signal to fluctuate. In the present embodiment, in order to suppress the fluctuation of the envelope, the STBC coded signal is reduced so as to reduce the influence of the code reversal process of the symbols that are continuous in time while maintaining the spatiotemporal orthogonality in the STBC coded. Phase rotation processing is applied to some of the symbols in the above to rotate the phase of some of the symbols. The details of the phase rotation processing will be described later.

The transmitting antennas 12a and 12b transmit the transmission signal output from the coding processing unit 11 to the receiving device 2 by transmitting it as a radio wave (step S104).

Next, the configuration and operation of the coding processing unit 11 of the transmission device 1 of the present embodiment will be described. FIG. 3 is a diagram showing a configuration example of the coding processing unit 11 of the first embodiment. The coding processing unit 11 phase-rotates the FSK signals output from the FSK modulation units 10a and 10b into a coding unit 110 that STBC-encodes the FSK signals and some symbols of the STBC-encoded signals by the coding unit 110. A phase rotating unit 111 for processing is provided.

Assuming that the FSK signal vector generated by the FSK modulation units 10a and 10b is s (bold), s (bold) is a vertical vector having _{sm, 1} , sm _{, and 2 as elements.} Note that sm _{and n} indicate the nth symbol in the mth block. m and n are natural numbers. The maximum value of n is the number of symbols that are input for the STBC coding process for one block, and is determined according to the number of transmitting antennas. When the number of transmitting antennas is 2, the maximum value of n is 2. Is. At this time, the transmission signal matrix x (bold) output from the coding processing unit 11 can be represented by the following equation (1). x ^(k) _{m and t} are the t-th transmitted signals transmitted from the k-th transmitting antenna, and θ (−π <θ ≦ π) is the phase rotation amount of the phase rotation processing performed in the phase rotating unit 111. Represent each. k and t are natural numbers. The maximum value of t is determined according to the number of transmitting antennas, and when the number of transmitting antennas is 2, the maximum value of t is 2. In the configuration example shown in FIG. 1, the transmitting antenna 12a is the first transmitting antenna, and the transmitting antenna 12b is the second transmitting antenna. j is an imaginary unit. ^{* Indicates} the complex conjugate.

The transmission signal matrix x (bold) represented by the above equation (1) shows the result of performing STBC coding and phase rotation processing on the FSK signal vector. Before the phase rotation processing, that is, the matrix in which "x e ^jθ " is deleted from the lowermost matrix of the above equation (1) is a matrix showing the STBC-encoded signal, and is generated by the coding processing unit 11. It is a matrix showing the signals to be produced. When there is no phase rotation processing, in the mth block, the transmission signal x ^{( 2 )} _{m, 1} = −s ^* _{m, 2} is transmitted from the transmission antenna 12b to the first or first symbol, and the second or second symbol is transmitted. X ^{( 2 )} _{m, 2} = s ^* _{m, 1} is transmitted to the eyes. As described above, the STBC coding includes a process in which the positive and negative codes are inverted between the symbols corresponding to the transmission signals transmitted continuously in time from one of the two or more transmitting antennas. In the example shown by the equation (1), the symbols of the first symbol and the second symbol of the transmission signal transmitted from the transmission antenna 12b are inverted. Therefore, at the boundary between the transmission signal of the first symbol and the transmission signal of the second symbol, the amplitude value of the transmission signal drops to near 0 due to the influence of the inversion of the positive and negative signs.

In the present embodiment, as shown in the equation (1), the phase rotating unit 111 is generated by inverting the positive and negative signs of the symbols of the transmitted signals in each transmitting antenna while maintaining the spatiotemporal orthogonality in the STBC code. Phase rotation processing is performed so as to suppress a decrease in the amplitude value of the transmitted signal.

In equation (1), phase rotation processing is applied _{to sm, 2,} s ^* _{m, and 1} , which are elements of the STBC coding matrix corresponding to the transmission signal of the second symbol in the block. The position of the symbol in the block to which is applied is not limited to this example. For example, as shown on the left side of the following equation (2), the transmission signal at the first symbol may be subjected to phase rotation processing. Further, as shown in the center and the right side of the following equation (2), the two transmission signals on the diagonal line of the matrix may be subjected to phase rotation processing. When the two transmission signals on the diagonal of the matrix are subjected to the phase rotation processing, the positive and negative signs of the phase rotation amount are inverted between the two transmission signals.

Further, in the coding process in the coding processing unit 11 given by the equations (1) and (2), the process is closed in the block which is the STBC coding unit, but it is given by the following equation (3). As described above, the same effect can be obtained even if the phase rotation processing is continuously performed across the blocks.

FIG. 4 is a diagram showing the transmission signal in the transmission antenna 12b given by the equation (1) on the IQ plane. In the example shown in FIG. 4, it is assumed that the FSK modulation units 10a and 10b are FSK-modulated so that the phases are continuous between the symbols, and the phase rotation amount given by the phase rotation unit 111 is θ = π / 2. It is supposed to be. Sample 30 shows the final sample of the symbol immediately before the symbol to be subjected to the phase rotation processing, that is, the symbol −s ^* _{m, 2 of the first symbol in the block.} The sample 31 is a sample at the beginning of ^{the symbol −s *} _{m, 1 in} ^{which the positive and negative codes of the symbols s *} _{m, 1} of the second symbol in the block to be subjected to the phase rotation processing are matched with the positive and negative codes of the first symbol. Shown.

As shown in the equation (1), the sign inversion of the plus-minus sign occurs between the symbol of the first symbol and the symbol of the second symbol. Sample 32 shows the first sample in the symbol in which the positive and negative signs ^{of the symbol −s *} _{m, 1 are inverted.} Sample 33 shows a sample in which the sample 32 is phase-rotated with a phase rotation amount of π / 2. As shown in FIG. 4, when the phase rotation unit 111 does not perform phase rotation, the amplitude value of the transmission signal drops to near 0 due to the influence of sign inversion at the symbol boundary between the first symbol and the second symbol. The amount of fluctuation in the envelope of the transmitted signal increases. However, as shown in FIG. 4, the phase of the first sample of the second symbol is changed from 0 to π / by performing the phase rotation processing of the phase rotation amount π / 2 on the sample 32 which is the first sample of the second symbol. Transition to 2, and the increase in the fluctuation amount of the envelope of the transmitted signal is suppressed.

The phase rotation amount θ given by the phase rotation unit 111 to suppress the fluctuation amount of the envelope of the transmission signal may be any value, but when the modulation index in FSK modulation is 1.0, for example. As shown in FIG. 4, θ = π / 2 is suitable for suppressing an increase in the fluctuation amount of the envelope of the transmitted signal.

The suitable phase rotation amount θ can be obtained from the final sample of the previous symbol and the first sample of the next symbol. The final sample of the previous symbol and the first sample of the next symbol depend on the number of modulation values, the modulation index, and the like. FIG. 5 is a diagram showing the signal transition of the first embodiment on the IQ plane when the modulation index in FSK modulation is 0.75. Sample 34 shows the final sample of the symbol immediately before the symbol to be subjected to the phase rotation processing, that is, the symbol −s ^* _{m, 2 of the first symbol in the block.} The sample 35 is a sample at the beginning of ^{the symbol −s *} _{m, 1 in} ^{which the positive and negative codes of the symbols s *} _{m, 1} of the second symbol in the block to be subjected to the phase rotation processing are matched with the positive and negative codes of the first symbol. Shown. Sample 36 shows the first sample in the symbol in which the positive and negative signs ^{of the symbol −s *} _{m, 1 are inverted.} As shown in FIG. 5, when the modulation index is 0.75, the increase in the fluctuation amount of the envelope of the transmission signal is suppressed by rotating the sample 36 in phase with θ = π / 4. In the example shown in FIG. 5, the same effect can be obtained even when θ = π / 2 or θ = −π / 4. In order to suppress the fluctuation of the envelope, it is desirable that the final sample of the previous symbol and the first sample after the phase rotation processing of the next symbol are close to each other, but considering that the spatiotemporal orthogonality is maintained, one transmission is performed. It is necessary to consider not only the signals transmitted from the antenna but also the signals transmitted from other transmission signals. For example, if the envelope fluctuation amount of one of the two transmitting antennas is reduced, the envelope fluctuation amount of the other transmitting antenna may be increased. Therefore, for example, a method of determining the phase rotation amount so that the phase transition, that is, the envelope fluctuation amount is the same for all the transmitting antennas can be considered.

FIG. 6 shows the signal transition of the first embodiment on the IQ plane when the number of modulation multi-values in the FSK modulation units 10a and 10b is 4, that is, when the FSK modulation units 10a and 10b perform modulation by the 4FSK method. It is a figure shown. The phase transition 37 indicates the phase of transition in one sample in the symbol immediately before the symbol to be subjected to the phase rotation processing. Within the symbol, the phase of transition in one sample is fixed, and # 0, # 1, # 2, and # 3 shown in FIG. 6 indicate four samples of the previous symbol. Sample 38 shows the final sample of the symbol immediately before the symbol to be subjected to the phase rotation processing, that is, the symbol −s ^* _{m, 2 of the first symbol in the block.} Sample 39 shows a sample in which a phase transition amount for transitioning between one sample is added to sample 38. Sample 40 shows a sample in which the positive and negative signs of sample 39 are inverted. ^{That is, the sample 40 corresponds to the symbol s *} _{m, 1} of the second symbol in the block, ^{and the sample 39 corresponds to −s *} _{m, 1} in which the positive and negative signs of the sample 40 are inverted.

As shown in FIG. 6, suitable phase rotation amount θ includes sample 39, which is a sample in which a phase transition amount transitioning between one sample in an FSK signal is added to sample 38, and sample 40, which is a code-inverted sample 39. It is the value obtained by multiplying the angle formed by, by 1/2. In the example shown in FIG. 6, θ = π / 2. In other words, it is as follows. The two symbols whose positive and negative signs are inverted are designated as the first symbol and the second symbol, and the transmission signal corresponding to the first symbol is transmitted from one transmitting antenna before the transmission signal corresponding to the second symbol. And. Further, it is assumed that each of the first symbol and the second symbol is composed of one or more samples. At this time, in the phase rotation process, the phase rotation unit 111 encodes a sample in which a phase transition amount for transitioning between one sample of the FSK signal is added to the sample at the end of the first symbol and a sample at the beginning of the second symbol. The second symbol is subjected to a phase rotation of the amount of phase rotation obtained by multiplying the phase difference from the inverted sample by 1/2.

Further, the FSK modulation units 10a and 10b oversample the FSK signal by phase interpolation, so that the fluctuation amount of the envelope of the transmission signal can be further suppressed. FIG. 7 is a diagram showing the signal transition of the first embodiment on the IQ plane when the FSK modulation units 10a and 10b are oversampled by phase interpolation. FIG. 7 shows the signal transition of the transmission signal of the transmission antenna 12a under the same conditions as in FIG. 4 on the IQ plane. Sample 41 shows the final sample of the previous symbol, which is the symbol immediately before the symbol to be subjected to the phase rotation processing, when oversampling is not performed. Sample 42 shows the final sample of the previous symbol when oversampled. Sample 43 shows the first sample in the next symbol which is the symbol to be subjected to the phase rotation processing before the phase rotation processing is performed. The sample 44 is a sample 43 subjected to a phase rotation process. As shown in FIG. 7, the line connecting the sample 41 and the sample 44 is farther from 0 than the line connecting the sample 41 and the sample 43. As described above, by adding the phase rotation after STBC coding, the drop to the amplitude value 0 is suppressed. Further, the line connecting the sample 42 and the sample 44 is farther from 0 than the line connecting the sample 41 and the sample 44. That is, by oversampling the samples constituting the FSK signal by phase interpolation, the distance between the final sample in the previous symbol and the first sample after the phase rotation is shortened. By oversampling the samples constituting the FSK signal by phase interpolation in this way, it is possible to further suppress an increase in the amount of fluctuation in the envelope of the transmitted signal.

Further, in the present embodiment, the number of transmitting antennas is two, but even when three or more transmitting antennas are provided, each transmitting antenna maintains the spatiotemporal orthogonality in the STBC code as in the above-mentioned example. The same effect can be obtained by performing the phase rotation processing so as to reduce the influence of the sign inversion. As an example, V.I. Tarok, H. et al. Jafarkhani, and A. R. Calderbank, "Space-Time Block Codes from Orthogonal Designs," IEEE Transitions on Information Theory, Vol. 45, No. 5, July 1999. An example of the phase rotation processing in the phase rotation unit 111 with respect to the STBC code when the number of transmission antennas disclosed in the above is three is shown in the following equation (4).

The phase rotation amount θ can be determined in advance when the phase transition amount in one sample is fixed. When the phase transition amount is not fixed, the phase rotation unit 111 determines θ for each symbol.

As described above, even when STBC coding is applied to a signal primaryly modulated by the FSK method by STBC coding and phase rotation processing by the coding processing unit 11, as compared with the conventional STBC coding, It is possible to suppress the drop of the amplitude value to the vicinity of 0 and suppress the increase in the fluctuation amount of the envelope of the transmitted signal. As a result, in the present embodiment, there is no significant deterioration in power efficiency in any of the transmitting antennas as compared with the conventional STBC coding. Further, in the processing in the coding processing unit 11, the spatiotemporal orthogonality between the transmitting antennas is maintained as in the conventional STBC coding, so that the transmission diversity gain does not deteriorate.

Next, the decoding process in the decoding processing unit 21 of the receiving device 2 in the first embodiment will be described. FIG. 8 is a diagram showing a configuration example of the decoding processing unit 21 of the first embodiment. Here, for the sake of simplification of the description, an example in which the number of receiving antennas is 1 will be described as shown in FIG. The decoding processing unit 21 performs phase rotation processing for canceling the phase rotation performed in the transmission device 1 on the received signal input from the reception antenna 20, and phase rotation by the phase reverse rotation unit 210 and the phase reverse rotation unit 210. It includes a decoding unit 211 that STBC decodes the processed signal. It is assumed that the transmission line estimation unit (not shown) performs the transmission line estimation and the transmission line estimation result is input to the decoding processing unit 21.

Here, the transmission path value between the transmitting antenna 12a and the receiving antenna 20 is h _1, and the transmission path value between the transmitting antenna 12b and the receiving antenna 20 is h ₂ . Further, the received signal corresponding to the first symbol of the m-th block received by the receiving antenna 20 is rm _{, 1,} and the received signal corresponding to the second symbol of the m-th block received by the receiving antenna 20 is set to rm, 1. Let it be rm _{, 2} . At this time, the received signal vector r (bold) _{m of the m-th block having rm, 1} , rm _{, and 2} as elements is given by the following equation (5). eta (in bold) and eta _{m, 1} is the thermal noise component contained in the r _{m, 1,} and eta _{m, 2} is the thermal noise component contained in the r _{m, 2,} the thermal noise vector whose elements Represent.

In the following, it is assumed that the transmission device 1 performs the phase rotation processing represented by the equation (1). The phase reverse rotation unit 210 reverses the phase of the received signals rm _{and 2} corresponding to the second symbol by the phase rotation amount θ of the phase rotation process performed by the transmission device 1. That is, the phase reverse rotation unit 210 _{performs phase rotation processing on the received signals rm and 2} with a phase rotation amount −θ. As a result, it becomes the same as the state in which the conventional STBC-encoded signal is received, so that the conventional STBC decoding can be applied.

The decoding unit 211 performs STBC decoding on the signal subjected to the phase reverse rotation processing by the phase reverse rotation unit 210. The decoding result vector s (bold) ′ obtained by STBC decoding can be expressed by the following equation (6). Decoding result vector s (bold) _'is a vector of the decoded result _{s'm, 1} corresponding to _{s m, 1,} and _{s m, 2} corresponding to the decoding result _{s'm, 2} and the element. eta (bold) _{'is, η'm, 1,} a vector having _{η'm, 2 elements, η'm, 1, η'm} , 2 are decoded result _s'm, 1, _s'm It is an equivalent noise component contained in each of _{2 and 2.}

The decoding unit 211 described above based on the received signals rm _{, 1 and the received signals rm, 2} after the phase reverse rotation processing _{, and the transmission line values h 1} , h ₂ input as the transmission line estimation result. The decoding results s'm _{, 2} can be obtained from the equation (6). This is the same as the conventional STBC decoding.

As can be seen from the above equation (6), the output signal s (bold)'in the decoding processing unit 21 is the maximum ratio synthesis of the transmission line gain between the two transmitting antennas 12a and 12b and the receiving antenna 20. Therefore, the transmission diversity gain is obtained. Therefore, in the present embodiment, the spatiotemporal orthogonality between the transmitting antennas is maintained even when the transmitting device 1 performs the phase rotation processing in addition to the STBC coding, and is full as in the conventional STBC coding. Diversity gain is obtained.

In the above description, the decoding process when the phase rotation process represented by the equation (1) is performed is shown. As shown by the matrix on the left side in the equation (2), even when the phase rotation processing is added to the signal of the first symbol in the coding processing unit 11, the phase rotation processing is performed on the second symbol. The phase reverse rotation processing may be applied to _{the received signals rm and 1} of the first symbol in the same manner as in the case of adding. After that, by applying the STBC decoding represented by the equation (6), the estimation results s'1, ₂ , s'm _{, 2} can be obtained in the same manner.

As shown in the matrix on the center and right side in the equation (2), even when the phase rotation process is performed, the phase reverse rotation unit 210 is similarly placed at the position where the phase rotation process is performed in the transmission device 1. The phase may be reversed.

Further, as shown in the equation (3), even when the phase rotation process is continuously applied across the blocks, the phase reverse rotation unit 210 is similarly subjected to the phase rotation process in the transmission device 1. It suffices to apply the reverse rotation of the phase to the point.

Further, as shown in the equation (4), even when the number of transmitting antennas is 3 or more, the phase reverse rotation unit 210 similarly rotates the phase in the reverse rotation at the position where the phase rotation processing is performed in the transmission device 1. Should be applied. After that, the decoding unit 211 performs the STBC decoding process according to the number of antennas, so that the estimation result of each symbol can be obtained.

In the present embodiment, the description has been made on the premise that the Aramouti coding disclosed in Non-Patent Document 1 is applied. However, not limited to this, as the coding in the present invention, other coding can be applied as long as it is an STBC that encodes by complex conjugate and code inversion of the signal.

Next, the hardware configuration of this embodiment will be described. The FSK modulation units 10a and 10b and the coding processing unit 11 of the transmitting device 1 shown in FIG. 1, the decoding processing unit 21 of the receiving device 2, and the FSK demodulation units 22a and 22b are each realized by a processing circuit which is an electronic circuit. To.

The processing circuit may be dedicated hardware or a control circuit including a memory and a CPU (Central Processing Unit, central processing unit) that executes a program stored in the memory. Here, the memory corresponds to, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, a magnetic disk, an optical disk, or the like. FIG. 9 is a diagram showing a configuration example of the control circuit according to the first embodiment. When the processing circuit is a control circuit including a CPU, this control circuit is, for example, the control circuit 300 having the configuration shown in FIG.

As shown in FIG. 9, the control circuit 300 includes a processor 300a, which is a CPU, and a memory 300b. When it is realized by the control circuit 300 shown in FIG. 9, it is realized by the processor 300a reading and executing the program corresponding to each process stored in the memory 300b. The memory 300b is also used as a primary memory in each process performed by the processor 300a.

As described above, in the present embodiment, the transmission device 1 STBC-encodes a plurality of FSK-modulated symbols, and performs phase rotation processing on the STBC-encoded signal. In particular, in the phase rotation processing, some symbols are subjected to the phase rotation processing so as to reduce the influence of the code inversion processing that occurs at the symbol boundary of each transmitting antenna while maintaining the spatiotemporal orthogonality in the STBC code. As a result, it is possible to prevent the amplitude value of the transmission signal from periodically dropping to the vicinity of 0, and it is possible to suppress the fluctuation amount of the envelope of the transmission signal, thereby preventing a decrease in power efficiency.

Embodiment 2.
FIG. 10 is a diagram showing a configuration example of the coding processing unit according to the second embodiment. The coding processing unit 11a of the second embodiment deletes the phase rotation unit 111 and adds the IQ axis exchange unit 112 to the coding processing unit 11 of the first embodiment. The transmission device of the present embodiment is the same as the transmission device 1 of the first embodiment except that the coding processing unit 11a is provided instead of the coding processing unit 11. Hereinafter, in the description of the present embodiment, the parts different from the first embodiment will be described, and the description overlapping with the first embodiment will be omitted.

In the first embodiment, the coding processing unit 11 shown in FIG. 1 performs the phase rotation processing to add the phase rotation amount θ to the signal after STBC coding. In the present embodiment, the phase rotation process is performed with the phase rotation amount θ = π / 2 by exchanging the real number component and the imaginary number component of the signal after STBC coding represented by the complex number, that is, IQ axis exchange. Get the same effect as before. That is, in the present embodiment, the same effect as that of the first embodiment can be obtained without the arithmetic processing of the phase rotation processing.

The operation of the IQ axis exchange unit 112 will be described in detail. The IQ axis exchange unit 112 is an axis exchange unit that exchanges the values of the real number component and the imaginary number component and performs complex conjugate processing on some symbols of the STBC-encoded signal by the coding unit 110. FIG. 11 is a diagram showing an operation example of the IQ axis exchange unit 112 according to the second embodiment. Of the signals after STBC coding, the value of the symbol 45 to be subjected to the phase rotation processing is a + jb. j represents an imaginary unit. The symbol 46 is a symbol 45 in which the real number component and the imaginary number component are exchanged, that is, the IQ axes are exchanged. The value of the symbol 46 is b + ja. Next, the symbol 47 is obtained by taking a complex conjugate with respect to the IQ axis exchanged symbol value. The value of symbol 47 is b-ja. The symbol 47 is obtained by rotating the phase of the symbol 45 by π / 2.

In the second embodiment, the IQ axis exchange unit 112 realizes a process equivalent to the phase rotation process of the phase rotation amount θ = π / 2 by performing the IQ axis exchange and the complex conjugate process. As a result, it is possible to achieve the same effect as that of the first embodiment while reducing the arithmetic processing as compared with the first embodiment. The coding processing unit 11a can be realized by a processing circuit in the same manner as the coding processing unit 11. Since the receiving device of the second embodiment is the same as the receiving device 2 of the first embodiment, the description thereof will be omitted.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 Transmitter, 2 Receiver, 3 Communication system, 10a, 10b FSK modulation unit, 11,11a coding processing unit, 12a, 12b transmission antenna, 20 reception antenna, 21 decoding processing unit, 22a, 22b FSK demodulation unit, 110 Coding unit, 111 phase rotation unit, 112 IQ axis exchange unit, 210 phase reverse rotation unit, 211 decoding unit.

Claims (9)

With two or more transmitting antennas
A modulator that generates a modulated signal by frequency shift keying,
A coding processing unit that generates a transmission signal to be transmitted from each of the two or more transmission antennas by performing spatio-temporal block coding in which a phase rotation is added to the modulation signal.
Equipped with a,
The coding processing unit is
When the unit of frequency shift keying is a symbol, a coding unit that encodes the modulated signal in a spatiotemporal block with a plurality of symbols as a unit, and
A phase rotation unit that performs phase rotation processing on some symbols of the signal coded by the coding unit in a spatiotemporal block,
With
The spatiotemporal block coding includes a process in which positive and negative codes are inverted between symbols corresponding to transmission signals transmitted continuously in time from one of the two or more transmitting antennas.
The transmission is characterized in that the phase rotation processing is performed so as to suppress the decrease in the amplitude value of the transmission signal caused by the inversion of the plus and minus signs while maintaining the spatiotemporal orthogonality in the spatiotemporal block coding. apparatus. The two symbols whose positive and negative signs are inverted are designated as the first symbol and the second symbol, and the transmission signal corresponding to the first symbol from the one transmitting antenna precedes the transmission signal corresponding to the second symbol. Sent, each of the first and second symbols consists of one or more samples.
In the phase rotation process, the phase rotation unit includes a sample obtained by adding a phase transition amount for transitioning between one sample of the modulation signal to the sample at the end of the first symbol and a sample at the beginning of the second symbol. transmitting apparatus according to claim 1, the phase rotation of the phase rotation amount obtained by multiplying 1/2 to the phase difference, characterized in that applied to the second symbol between the sample obtained by sign inversion. With two or more transmitting antennas
A modulator that generates a modulated signal by frequency shift keying,
A coding processing unit that generates a transmission signal to be transmitted from each of the two or more transmission antennas by performing spatio-temporal block coding in which a phase rotation is added to the modulation signal.
With
The coding processing unit is
When the unit of frequency shift keying is a symbol, a coding unit that encodes the modulated signal in a spatiotemporal block with a plurality of symbols as a unit, and
An axis exchange unit that exchanges the values of the real number component and the imaginary number component and performs complex conjugate processing on some symbols of the signal coded by the space-time block by the coding unit.
Send device you comprising: a. The transmitter according to any one of claims 1 to 3,
A receiving device that receives the transmission signal transmitted by the transmitting device as a receiving signal, and
A communication system characterized by comprising. A transmitter equipped with two or more transmitting antennas
A modulation step that generates a modulation signal by frequency shift keying,
A coding processing step of generating a transmission signal to be transmitted from each of the two or more transmission antennas by performing spatio-temporal block coding in which a phase rotation is added to the modulation signal.
Only including,
The coding processing step is
When the unit of frequency shift keying is a symbol, a coding step of coding the modulated signal in a spatiotemporal block with a plurality of symbols as a unit, and
A phase rotation step in which a phase rotation process is performed on some symbols of a signal coded in a spatiotemporal block by the coding step, and a phase rotation step.
Including
The spatiotemporal block coding includes a process in which positive and negative codes are inverted between symbols corresponding to transmission signals transmitted continuously in time from one of the two or more transmitting antennas.
In the phase rotation step,
Communication characterized in that the phase rotation processing is performed so as to suppress a decrease in the amplitude value of the transmission signal caused by the inversion of the plus and minus signs while maintaining the spatiotemporal orthogonality in the spatiotemporal block coding. Method. The two symbols whose positive and negative signs are inverted are designated as the first symbol and the second symbol, and the transmission signal corresponding to the first symbol from the one transmission antenna precedes the transmission signal corresponding to the second symbol. Each of the first and second symbols is composed of one or more samples.
In the phase rotation process, a sample in which a phase transition amount that transitions between one sample of the modulated signal is added to the sample at the end of the first symbol and a sample in which the first sample of the second symbol is code-inverted are used. The communication method according to claim 5 , wherein a phase rotation of a phase rotation amount obtained by multiplying the phase difference between the two by 1/2 is applied to the second symbol. A transmitter equipped with two or more transmitting antennas
A modulation step that generates a modulation signal by frequency shift keying,
A coding processing step of generating a transmission signal to be transmitted from each of the two or more transmission antennas by performing spatio-temporal block coding in which a phase rotation is added to the modulation signal.
Including
The coding processing step is
When the unit of frequency shift keying is a symbol, a coding step of coding the modulated signal in a spatiotemporal block with a plurality of symbols as a unit, and
An axis exchange step in which the values of the real number component and the imaginary number component are exchanged and the complex conjugate processing is performed on some symbols of the signal coded by the spatiotemporal block by the coding step.
Communication how to comprising a. A control circuit for controlling a transmitter equipped with two or more transmitting antennas.
A modulation step that generates a modulation signal by frequency shift keying,
A coding processing step of generating a transmission signal to be transmitted from each of the two or more transmission antennas by performing spatio-temporal block coding in which a phase rotation is added to the modulation signal.
To the transmitter
The coding processing step is
When the unit of frequency shift keying is a symbol, a coding step of coding the modulated signal in a spatiotemporal block with a plurality of symbols as a unit, and
A phase rotation step in which a phase rotation process is performed on some symbols of a signal coded in a spatiotemporal block by the coding step, and a phase rotation step.
Including
The spatiotemporal block coding includes a process in which positive and negative codes are inverted between symbols corresponding to transmission signals transmitted continuously in time from one of the two or more transmitting antennas.
In the phase rotation step,
It is characterized in that the phase rotation processing is performed so as to suppress a decrease in the amplitude value of the transmission signal caused by the inversion of the plus-minus sign while maintaining the spatio-temporal orthogonality in the spatio-temporal block coding. Control circuit to do. A program for controlling a transmitter equipped with two or more transmitting antennas.
A modulation step that generates a modulation signal by frequency shift keying,
A coding processing step of generating a transmission signal to be transmitted from each of the two or more transmission antennas by performing spatio-temporal block coding in which a phase rotation is added to the modulation signal.
To the transmitter
The coding processing step is
When the unit of frequency shift keying is a symbol, a coding step of coding the modulated signal in a spatiotemporal block with a plurality of symbols as a unit, and
A phase rotation step in which a phase rotation process is performed on some symbols of a signal coded in a spatiotemporal block by the coding step, and a phase rotation step.
Including
The spatiotemporal block coding includes a process in which positive and negative codes are inverted between symbols corresponding to transmission signals transmitted continuously in time from one of the two or more transmitting antennas.
In the phase rotation step,
It is characterized in that the phase rotation processing is performed so as to suppress a decrease in the amplitude value of the transmission signal caused by the inversion of the plus-minus sign while maintaining the spatio-temporal orthogonality in the spatio-temporal block coding. Program to do.

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