The present disclosure relates to a transmitting apparatus, a receiving apparatus, a communication apparatus, a wireless communication system, a control circuit, a storage medium, a transmission method, and a reception method for wireless communication.
As a problem in wireless communication, performance degradation due to various types of interference is widely known. For example, a propagation path having frequency selectivity can distort a signal, preventing the signal from being correctly demodulated. This phenomenon is caused by delayed waves in a multipath environment. The way signals are distorted varies depending on the characteristics of a propagation path, that is, the number of delayed waves, the phase relationships between delayed waves, the magnitude of delayed waves, etc. When a plurality of base stations are installed, the plurality of base stations use the same frequency for effective frequency utilization. When the plurality of base stations use the same frequency, the plurality of base stations use the frequency at a distance from each other to prevent mutual interference. However, at a receiving apparatus that receives a transmission signal from a certain base station, a transmission signal from another base station using the same frequency can interfere, that is, what is called co-channel interference can occur, depending on geographical conditions, the position of the receiving apparatus, etc.
As a measure against co-channel interference including delayed waves, Patent Literature 1 discloses a technique to suppress interference signals included in reception signals received by a plurality of antennas by multiplying the reception signals by weights to adjust amplitude, phase, etc. and combining the reception signals. For the calculation of the weights to adjust amplitude, phase, etc., there are a weight calculation algorithm using a known sequence, a blind weight calculation algorithm, etc.
As techniques to reduce or prevent degradation in communication performance due to fading, diversity techniques are applied in wireless communication. For example, as a method of transmit diversity, there is a method in which a plurality of orthogonal sequences are generated by space-time block coding (STBC) and transmitted by different antennas. STBC allows receiving apparatuses to obtain full diversity gain.
STBC treats a plurality of symbols as one block. In general, the number of antennas is associated with the number of symbols treated as one block. For example, in STBC transmission with two antennas, two symbols are used as one block. To demodulate STBC symbols received by a receiving apparatus, it is necessary to estimate transmission path information. As a method that can obtain the effects of diversity by STBC and eliminates the need to estimate transmission path information, there is differential space-time block coding (DSTBC) in which differential coding is performed in units of blocks in STBC. For example, in DSTBC transmission with two antennas, a 2×2 matrix is generated with two symbols as one block, and differential coding is performed between matrices of two consecutive blocks. A receiving apparatus generates a 2×2 matrix using two symbols received, and performs differential decoding between matrices of two blocks for demodulation.
Patent Literature 1: Japanese Patent No. 6526348
When applying a weight calculation algorithm using a known sequence, a receiving apparatus needs to detect and generate an interference signal from reception signals to calculate weights. The technique described in Patent Literature 1 uses channel estimation to generate an interference signal. Channel estimation requires an inverse matrix operation. However, if a known sequence is not orthogonal, a desired signal cannot be completely separated from an interference signal, which results in a problem of reducing weight accuracy. Furthermore, to cope with both a delayed wave from the base station and co-channel interference from another base station, the delayed wave cannot be separated by an inverse matrix operation using a desired signal and an interference signal, and channel estimation considering the delayed wave is required to cope with the delayed wave, which results in a problem of increasing circuit scale.
To solve the above problems and achieve an object, a transmitting apparatus according to the present disclosure includes: a mapping unit to modulate a transmission bit sequence to generate a modulated symbol sequence; a known sequence mapping unit to modulate a known bit sequence to generate a known symbol sequence; a selection unit to select one of the modulated symbol sequence or the known symbol sequence and output the selected one as a transmission symbol sequence; and an encoder to perform differential space-time block coding on the transmission symbol sequence. The known sequence mapping unit generates the known symbol sequence so that a matrix obtained by differential space-time block coding performed by the encoder becomes a matrix with two rows and two columns that includes 0 in the first row and the first column, −1 in the second row and the first column, 1 in the first row and the second column, and 0 in the second row and the second column.
Hereinafter, a transmitting apparatus, a receiving apparatus, a communication apparatus, a wireless communication system, a control circuit, a storage medium, a transmission method, and a reception method according to embodiments of the present disclosure will be described in detail with reference to the drawings. First Embodiment.
Although the single base station 10 and the single mobile station 20 are included in the wireless communication system 1 in
In
In order for the mobile station 20 to perform interference suppression, the base station 10 inserts a known symbol sequence represented by complex numbers into a transmission signal.
First, the configuration and operation of the transmitting apparatus 11 included in the base station 10 will be described.
The operation of the transmitting apparatus 11 will be described.
The known sequence mapping unit 102 modulates the known bit sequence, that is, maps the known bit sequence into a symbol sequence represented by complex numbers (step S102) to generate a known symbol sequence, and outputs the known symbol sequence to the selection unit 103. The known sequence mapping unit 102 performs mapping intended for DSTBC encoding. For example, when DSTBC encoding is performed in units of two symbols, the known sequence mapping unit 102 performs mapping in units of two symbols. In the present embodiment, two known symbol sequences s0[k, 1] and s0[k, 2] output from the known sequence mapping unit 102 select one of two ways expressed by formula (1).
Formula 1:
(s0[k, 1], s0[k, 2])=(1,0), (0,1) (1)
The selection unit 103 selects one of the modulated symbol sequence acquired from the mapping unit 101 or the known symbol sequence acquired from the known sequence mapping unit 102, based on bit selection information included in the control information from the control device 30 (step S103), and outputs the selected one as a transmission symbol sequence.
The DSTBC encoder 104 performs DSTBC encoding on the transmission symbol sequence acquired from the selection unit 103 (step S104), and outputs the DSTBC-encoded symbol sequence as DSTBC symbols to the radio unit 105. In the following description, DSTBC encoding by the DSTBC encoder 104 is sometimes referred to as differential space-time block coding. As DSTBC encoding, the DSTBC encoder 104 generates a modulated symbol matrix S[k] with two modulated symbols of the transmission symbol sequence acquired from the selection unit 103 as one block. As shown in formula (2), the DSTBC encoder 104 multiplies the modulated symbol matrix S[k] by a DSTBC matrix C[k−1] one block before to generate a DSTBC matrix C[k], and outputs the DSTBC matrix C[k] as DSTBC symbols to the radio unit 105. Although several formulas are shown in formula (2) below, the several formulas are collectively referred to as formula (2). The same applies to cases where two or more formulas are shown in the following.
At this time, k represents a block number, and k=1, 2, . . . . In the following description, a block with the block number k is referred to as a block k. s[k, 1] and s[k, 2] are two modulated symbols acquired by the DSTBC encoder 104 from the selection unit 103. s*[k, 1] and s*[k, 2] are the complex conjugates of s[k, 1] and −s[k, 2], respectively. As shown in formula (2), C[k] is required in the processing of the next block, and thus is output and internally held until the next processing. In formula (2), multiplication and addition and subtraction are performed on all elements as matrix operations. However, for example, only the two elements c[k, 1] and c[k, 2] may be calculated by a matrix operation, and c*[k, 1] and −c*[k, 2] may be calculated by exchanging signs, taking complex conjugates, etc. to reduce the amount of operation.
The DSTBC encoder 104 outputs, as the DSTBC symbols, c[k, 1] and −c*[k, 2], or c[k, 2] and c*[k, 1] in this order to the radio unit 105. In the present embodiment, the DSTBC encoder 104 outputs c[k, 1] and −c*[k, 2] in this order to the radio unit 105.
At the time of a first operation or initializing DSTBC encoding, the DSTBC encoder 104 replaces C[k−1] with an initial value C′. The initial value C′ is shown in formula (3).
If DSTBC encoding is initialized when the block number k is k′, C′ is expressed by formula (4).
Formula 4:
C[k′]=S[k′]C′ (4)
When the transmission symbol sequence output from the selection unit 103 is the known symbol sequence s0[k, 1] and s0[k, 2] input from the known sequence mapping unit 102, the DSTBC encoder 104 generates a DSTBC matrix C0[k] expressed by formula (5) by DSTBC encoding.
From formula (1), S0[k] is equal to one of two types, J0 and J1, shown in formula (6).
At this time, when S0[k] is J0, formula (7) holds. When S0[k] is J1, formula (8) holds.
Thus, the known sequence mapping unit 102 generates a known symbol sequence so that a matrix obtained by DSTBC encoding performed by the DSTBC encoder 104 is a specific matrix. As described above, the known sequence mapping unit 102 generates a known symbol sequence so that the specific matrix includes 0 and 1, or includes 0, 1, and −1.
The radio unit 105 performs processing such as waveform shaping, digital/analog (D/A) conversion, upconversion, and amplification processing on the DSTBC symbols acquired from the DSTBC encoder 104 to generate a transmission signal (step S105), and transmits the transmission signal from the antenna 106 to the mobile station 20 (step S106). Processing to generate a transmission signal in the radio unit 105 is general processing and does not limit the present embodiment. In the present embodiment, the base station 10 is configured conforming to one transmitting antenna. However, the base station 10 may be configured conforming to two transmitting antennas since DSTBC is a transmit diversity technique. In this case, the base station 10 requires two radio units 105 and two antennas 106 for two transmitting antennas. In this case, the DSTBC encoder 104 outputs c[k, 1] and −c*[k, 2] in this order to one radio unit 105, and outputs c[k, 2] and c*[k, 1] in this order to the other radio unit 105.
Next, the configuration and operation of the receiving apparatus 21 included in the mobile station 20 will be described.
Each antenna 201 receives transmission signals etc. transmitted from the base station 10. Each radio unit 202 generates a reception symbol sequence from a reception signal. The known symbol sequence determination unit 203 detects the reception timing of each known symbol sequence using the known symbol sequence. Each first delay unit 204 delays the reception symbol sequence by processing delay time of the known symbol sequence determination unit 203. Each second delay unit 205 delays the reception symbol sequence by time required for weight calculation. The control unit 206 performs control based on information on the known symbol sequence inserted into a desired signal. The combining control unit 207 specifies a combining method for the block combining unit 208 based on the reception timings and information for combining symbols. The block combining unit 208 combines the reception symbol sequences in units of DSTBC blocks and extracts interference signals. The weight calculator 209 calculates interference suppression weights from the interference signals. The weight multiplier 210 multiplies the reception symbol sequences by the interference suppression weights and further combines the reception symbol sequences to perform interference suppression on the reception symbol sequences. The demodulator 211 performs demodulation processing on the interference-suppressed reception symbol sequences to obtain a reception bit sequence. In
The operation of the receiving apparatus 21 will be described.
Each radio unit 202 performs processing such as amplification processing, downconversion, analog/digital (A/D) conversion, and waveform shaping on the reception signal acquired from the antenna 201 to generate a reception symbol sequence represented by complex numbers (step S202). Each radio unit 202 outputs the generated reception symbol sequence to the known symbol sequence determination unit 203, the first delay unit 204, and the second delay unit 205. Processing to generate a reception symbol sequence in each radio unit 202 is general processing, and does not limit the present embodiment.
The control unit 206 outputs the known symbol sequence to the known symbol sequence determination unit 203, based on known symbol sequence information indicating the known symbol sequence inserted into a desired signal input from the outside, and outputs the information for combining symbols to the combining control unit 207 (step S203).
The known symbol sequence determination unit 203 calculates the correlation between the reception symbol sequence acquired from each radio unit 202 and the known symbol sequence acquired from the control unit 206, and detects the position of the known symbol sequence inserted into the DSTBC-encoded reception symbol sequence, that is, the reception timing of the known symbol sequence (step S204). For example, the known symbol sequence determination unit 203 outputs, as the reception timing of the known symbol sequence, the timing at which the correlation value becomes maximum to the combining control unit 207.
Each first delay unit 204 delays the reception symbol sequence acquired from the radio unit 202 by a first time, specifically, a delay caused from processing by the known symbol sequence determination unit 203 and the combining control unit 207 (step S205). Thus, each first delay unit 204 ensures that the reception symbol sequence processed by the block combining unit 208 at a processing timing output from the combining control unit 207 is the known symbol sequence.
Each second delay unit 205 delays the reception symbol sequence acquired from the radio unit 202 by a second time, specifically, a processing delay required by the weight calculator 209 to calculate the interference suppression weights (step S206). Thus, the second delay unit 205 ensures that the weight multiplier 210 multiplies by the interference suppression weights from the head of the known symbol sequence inserted into the reception symbol sequence.
The combining control unit 207 generates the processing timing at which the block combining unit 208 combines reception symbols, based on information on the position of the known symbol sequence in each of the reception symbol sequences acquired from the known symbol sequence determination unit 203, that is, the reception timings of the known symbol sequences. The combining control unit 207 also generates combining method specification information for the block combining unit 208, based on the information for combining symbols acquired from the control unit 206 (step S207). The combining control unit 207 outputs the generated processing timing and combining method specification information to the block combining unit 208.
The block combining unit 208 combines the reception symbol sequence acquired from each first delay unit 204 with a reception symbol sequence having a different DSTBC block in units of DSTBC blocks at the processing timing acquired from the combining control unit 207, according to the combining method specification information acquired from the combining control unit 207 (step S208). When the transmission signal in the block k is c0[k, 1] and −c0*[k, 2], formula (9) holds where r0, n[k, 1] and r0, n[k, 2] are the reception symbol sequence in the block k acquired from the first delay unit 204 corresponding to a receiving antenna n. h1, n[k, 1] and h1, n[k, 2] are channel information on the path 10P-1, h2, n[k, 1] and h2, n[k, 2] are channel information on the path 10P-2, A[k, 1] and A[k, 2] are the amounts of variation of the delayed wave with respect to the preceding wave, and wn[k, 1] and wn[k, 2] are noise components.
Formula 9:
r
0,n
[k,1]=h1,n[k,1]c0[k,1]+h2,n[k,1](c0[k,1]+Δ[k,1])+wn[k, 1] (9)
r
0,n
[k,2]=h1,n[k,2](−c0*[k,2])+h2,n[k,2](−c0*[k,2]+Δ[k,2])+wn[k,2]
Here, suppose that variations in the channel information in the block k and a block k−1 can be ignored. When S0[k] based on which c0[k, 1] and c0[k, 2] are generated is J0, formula (10) holds.
On the other hand, when S0[k] based on which c0[k, 1] and c0[k, 2] are generated is J1, formula (11) holds.
In formulas (10) and (11), rin[k, 1] and rin[k, 2] are the interference signals. That is, when S0[k] based on which c0[k, 1] and c0[k, 2] are generated is J0, the block combining unit 208 can extract the interference signal by subtracting r[k−1, 1] from r[k, 1] and subtracting r[k−2, 2] from r[k, 2]. When S0[k] based on which c0[k, 1] and c0[k, 2] are generated is J1, the block combining unit 208 can extract the interference signals by adding r[k, 1] and r[k−1, 2] and subtracting r[k−2, 1] from r[k, 2]. As shown in formula (10) or (11), multiplication processing is not included in the extraction of the interference signal, so that the block combining unit 208 can accurately extract the interference signal without the occurrence of noise enhancement. Thus, the block combining unit 208 can extract the interference signals by combining the reception symbol sequences by adding or subtracting the symbols in units of DSTBC-encoded blocks at the processing timing.
The combining method specification information acquired by the block combining unit 208 from the combining control unit 207 is information indicating whether or not to extract the delayed wave using formula (10) or (11). The block combining unit 208 outputs the extracted delayed wave to the weight calculator 209. In the present embodiment, the block combining unit 208 performs combining processing on the consecutive blocks k and k−1. However, if variations in the transmission path information can be ignored, the combining processing does not necessarily have to be performed on consecutive blocks. For example, if variations in the transmission path information can be ignored between the block k and a block k−2, the block combining unit 208 may perform the combining processing on the block k and the block k−2.
The weight calculator 209 calculates the interference suppression weights for suppressing the interference signal rin[k, 1] and rin[k, 2], using the interference signal rin[k, 1] and rin[k, 2] acquired from the block combining unit 208 (step S209). For example, the weight calculator 209 calculates interference suppression weights w00, w11, w01, and w10 to achieve whitening. The weight calculator 209 outputs the calculated interference suppression weights to the weight multiplier 210.
The weight multiplier 210 performs interference suppression using the interference suppression weights acquired from the weight calculator 209 to obtain interference-suppressed reception symbol sequences. Specifically, the weight multiplier 210 multiplies the reception symbol sequence delayed by each second delay unit 205 by the interference suppression weights acquired from the weight calculator 209 (step S210). For example, when the weight multiplier 210 acquires the interference suppression weights w00, w11, w01, and w10 from the weight calculator 209, the interference-suppressed reception symbol sequence r′n[k,1] and r′n[k, 2] is expressed by formula (12). Formula 12:
r′
1
[k,1]=w00r1[k,1]+w01r2[k,1]
r′
2
[k,1]=w10r1[k,1]+w11r2[k,1]
r′
1
[k,2]=w00r1[k,2]+w01r2[k,2]
r′
2
[k,1]=w10r1[k,2]+w11r2[k,2]
The weight multiplier 210 outputs the interference-suppressed reception symbol sequences r′n[k, 1] and r′n[k, 2] to the demodulator 211.
The demodulator 211 performs demodulation processing on the interference-suppressed reception symbol sequence r′n[k, 1] and r′n[k, 2] acquired from the weight multiplier 210 (step S211) to generate a reception bit sequence.
Next, the hardware configuration of the transmitting apparatus 11 according to the first embodiment will be described. In the transmitting apparatus 11, the radio unit 105 is a communication device. The antenna 106 is an antenna element. The mapping unit 101, the known sequence mapping unit 102, the selection unit 103, and the DSTBC encoder 104 are implemented by processing circuitry. The processing circuitry may be memory storing a program and a processor that executes the program stored in the memory, or may be dedicated hardware. The processing circuitry is also referred to as a control circuit.
The program can be said to be a program that causes the base station 10 to perform a first step in which the mapping unit 101 modulates a transmission bit sequence to generate a modulated symbol sequence, a second step in which the known sequence mapping unit 102 modulates a known bit sequence to generate a known symbol sequence, a third step in which the selection unit 103 selects one of the modulated symbol sequence or the known symbol sequence and outputs the selected one as a transmission symbol sequence, and a fourth step in which the DSTBC encoder 104 performs differential space-time block coding on the transmission symbol sequence. In the second step, the known sequence mapping unit 102 generates the known symbol sequence so that a matrix obtained by differential space-time block coding performed by the DSTBC encoder 104 becomes a specific matrix.
Here, the processor 91 is, for example, a central processing unit (CPU), a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a digital signal processor (DSP), or the like. The memory 92 corresponds, for example, to nonvolatile or volatile semiconductor memory such as random-access memory (RAM), read-only memory (ROM), flash memory, an erasable programmable ROM (EPROM), or an electrically EPROM (EEPROM) (registered trademark), or a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a digital versatile disc (DVD), or the like.
The above has described the hardware configuration of the transmitting apparatus 11. The hardware configuration of the receiving apparatus 21 is the same. In the receiving apparatus 21, the antennas 201 are antenna elements. The radio units 202 are communication devices. The known symbol sequence determination unit 203, the first delay units 204, the second delay units 205, the control unit 206, the combining control unit 207, the block combining unit 208, the weight calculator 209, the weight multiplier 210, and the demodulator 211 are implemented by processing circuitry. The processing circuitry may be memory storing a program and a processor that executes the program stored in the memory, or may be dedicated hardware.
As described above, according to the present embodiment, the base station 10 including the transmitting apparatus 11 ensures that a matrix obtained when the DSTBC encoder 104 performs DSTBC encoding on the known symbol sequence is Jo or Ji. The mobile station 20 including the receiving apparatus 21 combines reception symbol sequences with different DSTBC-encoded block numbers. This allows the receiving apparatus 21 to extract an interference signal with high accuracy. The transmitting apparatus 11 can transmit a signal that allows the receiving apparatus 21 to accurately extract an interference signal.
In the first embodiment, the single base station 10 is included, and a suppression target is a delayed wave. A second embodiment describes a configuration where the number of the base stations 10 is two, and co-channel interference in a wireless communication system is suppressed.
Although the two base stations 10 and the single mobile station 20 are included in the wireless communication system 2 in
In
In order for the mobile station 20 to perform interference suppression, each of the base stations 10-1 and 10-2 inserts a known symbol sequence represented by complex numbers into a transmission signal. Note that the known symbol sequence of the base station 10-1 and the known symbol sequence of the base station 10-2 are made different from each other. The base stations 10-1 and 10-2 transmit transmission signals in synchronization. The lengths of the known symbol sequences and the insertion positions of the known symbol sequences in the base stations 10-1 and 10-2 are the same. Thus, the transmission timings of the known symbol sequences inserted into the transmission signal from the base station 10-1 and the transmission signal from the base station 10-2 coincide with each other.
For example, in
First, the configuration and operation of the base stations 10-1 and 10-2 will be described. As described above, the configuration of the base stations 10-1 and 10-2 is the same as the configuration of the base station 10 of the first embodiment illustrated in
Formula 13:
s
0,1
[k, 1]=−s0,2[k, 1]
s
0,1
[k, 2]=−s0,2[k, 2] (13)
For example, when the output of the known sequence mapping unit 102 of the base station 10-1 satisfies formula (1), the output of the known sequence mapping unit 102 of the base station 10-2 satisfies formula (14).
Formula 14:
(s02[k,1], s0.2[k,2])=(−1,0),(0, −1) (14)
Next, the configuration and operation of the mobile station 20 will be described. The configuration of the mobile station 20 is the same as the configuration of the mobile station 20 of the first embodiment illustrated in
Formula 15:
r
0,n
[k,1]=hn[k, 1]c0,1[k, 1]+gn[k, 1]c0,2[k,1]+wn[k, 1]
r
0,n
[k,2]=hn[k,2](−c0,1*[k, 2])+gn[k, 2](−c0,2*[k, 2])+wn[k, 2]
Here, suppose that variations in the channel information in the block k and the block k-1 can be ignored. When S0[k] based on which c0,1[k, 1] and c0,1[k, 2] are generated is J0, and formula (13) holds, formula (16) holds.
On the other hand, when S0[k] based on which c0,1[k, 1] and c0,1[k, 2] are generated is J1, and formula (13) holds, formula (17) holds.
That is, by the base station 10-1 satisfying formula (1) and the base station 10-2 satisfying formula (13), the interference signals are combined in the same phase when the desired signals are canceled by formula (16) or formula (17). This allows the mobile station 20 to extract the interference signal with higher accuracy. If formula (18) is satisfied, the interference signals can be combined in the same phase when the desired signals are canceled by formula (19) or (20).
Note that in the present embodiment, the interference signals can be combined in the same phase, but the interference signals do not necessarily have to be made in the same phase when the desired signals are canceled. Furthermore, φ in formula (18) may be changed for each block k.
As described above, according to the present embodiment, the wireless communication system 2 includes the plurality of base stations 10, and the base stations and 10-2 each including the transmitting apparatus 11 use different known symbol matrices for the base stations Also in this case, the mobile station 20 including the receiving apparatus 21 can extract an interference signal with high accuracy with respect to a desired signal by combining reception symbol sequences with different DSTBC-encoded block numbers.
The first and second embodiments have described the cases of communication from the base station 10 including the transmitting apparatus 11 to the mobile station 20 including the receiving apparatus 21. A third embodiment describes a communication apparatus including the transmitting apparatus 11 and the receiving apparatus 21.
The transmitting apparatus according to the present disclosure has the effect of being able to transmit a signal that allows a receiving apparatus to accurately extract an interference signal.
The configurations described in the above embodiments illustrate an example and can be combined with another known art. The embodiments can be combined with each other. The configurations can be partly omitted or changed without departing from the gist.
This application is a continuation application of International Application PCT/JP2021/012363, filed on Mar. 24, 2021, and designating the U.S., the entire contents of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | PCT/JP2021/012363 | Mar 2021 | US |
Child | 18234612 | US |