JP2008263631A - Radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system capable of fine control of error immunity of a space-time trellis code. <P>SOLUTION: A transmitter comprises an input means for inputting a frame; a coding means for coding a symbol in the frame according to a first coding scheme among a plurality of different coding schemes for at least either error immunity or transmission efficiency and for coding another symbol in the frame, according to a second coding scheme, different from the first coding scheme, among the plurality of different coding schemes; and a transmitting means for transmitting a frame constituted of the plurality of coded symbols. A receiver comprises a receiving means for receiving a transmitted frame; an estimating means for estimating transmission line characteristics based on the received frame; and a decoding means for decoding the received frame, according to decoding schemes which are switched, in synchronism with switching of the coding schemes for coding in accordance with the coding means, and the transmission line characteristics. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radio communication system, and more particularly to a radio communication system using a plurality of antennas.

Space-Time Trellis Codes (STTC), which is one of space-time codes, is encoded in a radio transmission system that receives signals transmitted from two or more transmitting antennas using one or more receiving antennas. (For example, see Non-Patent Document 1). The major factors that determine the transmission error tolerance of a code are the number of code states and the number of output symbols, and a code corresponding to the number of states and the number of values is designed. Conventionally, in an error correction code, the error resilience capability can be finely controlled by controlling the coding rate such as a puncturing technique for thinning out parity bits.
V. Tarokh, N. Seshadri, and AR Calderbank, `` Space-time codes for high data rate wireless communication: Performance criterion and code construction '', IEEE Trans. Information Theory, vol. 44, No. 2, pp. 744 -765, March 1998.

  In STTC, a control method corresponding to puncturing has not been studied other than control of error resilience determined by the number of modulation levels and the number of trellis states. Therefore, it is difficult to perform fine control of STTC error tolerance.

  Therefore, an object of the present invention is to provide a wireless communication system capable of performing fine control of error tolerance of a space-time trellis code.

According to the radio communication system of the present invention, a radio comprising a transmitter that transmits a frame including a plurality of symbols after space-time coding and a receiver that receives the frame via a transmission path and performs space-time decoding. In a communication system,
The transmitter encodes a symbol of the frame with a first encoding scheme among a plurality of encoding schemes different from at least one of error tolerance and transmission efficiency, and an input means for inputting the frame, Encoding means for encoding other symbols in the frame with a second encoding method different from the first encoding method among the plurality of different encoding methods; and the plurality of encoded Comprising a transmission means for transmitting a frame comprising the symbols of
The receiver is synchronized with switching of a receiving unit that receives the transmitted frame, an estimating unit that estimates a transmission path characteristic based on the received frame, and a coding method encoded by the coding unit. And decoding means for decoding the received frame in accordance with the decoding method to be switched and the transmission path characteristics.

  The wireless communication apparatus according to the present invention includes: an input unit that inputs a frame including a plurality of symbols; and a first code of a plurality of space-time coding methods that are different from each other in error tolerance and transmission efficiency. A symbol in the frame is encoded by the encoding method, and another symbol in the frame is encoded by a second encoding method different from the first encoding method among the plurality of different encoding methods. Encoding means for encoding, and transmission means for transmitting a frame composed of the plurality of encoded symbols.

  The wireless communication device of the present invention encodes a symbol in the frame by a first encoding method among a plurality of space-time encodings that are different from each other in error tolerance and transmission efficiency, The other symbols of the frame are encoded by a second encoding method different from the first encoding method among the plurality of different encoding methods, and consist of the plurality of encoded symbols. In a radio communication apparatus that receives the frame from a transmitter that transmits a frame via a transmission path and performs space-time decoding, a receiving unit that receives the transmitted frame, and a transmission path based on the received frame Estimating means for estimating characteristics, a decoding scheme switched in synchronization with switching of an encoding scheme encoded by the transmitter, and the received frame according to the transmission path characteristics. Characterized by comprising a decoding means for decoding.

  According to the wireless communication system of the present invention, it is possible to perform fine control of error tolerance of a space-time trellis code.

Hereinafter, a wireless communication system according to an embodiment of the present invention will be described in detail with reference to the drawings.
(First embodiment)
As shown in FIG. 1, the wireless communication system according to the present embodiment includes a transmitter 13 and a receiver 23, and the transmitter 13 includes an STTC encoder 131, first and second transmission antennas, and a receiver 23. Includes an STTC decoder 231, a transmission path estimator 232, and a receiving antenna.

  The STTC encoder 131 STTC-encodes transmission data, and two output symbols (referred to as codewords) u1 (n) and u2 (n) are respectively transmitted to the first transmission antenna and the second transmission antenna. To the transmission line 31. Here, n (n = 0, 1,..., N−1) is a symbol number, and one frame is composed of N symbols (N is a natural number of 2 or more). The STTC encoder 131 can realize intermediate error tolerance and transmission efficiency between these two coding schemes by switching transmission symbol sequences by switching coding schemes having different error tolerance and transmission efficiency. The STTC encoder 131 will be described in detail later with reference to FIG.

  In the transmission line 31, the output symbols from the first transmission antenna and the second transmission antenna are multiplied by independent transmission line gains α1 and α2, respectively, and independent white noise η (n) is added for each symbol. Is input to the receiving antenna.

The transmission path estimator 232 receives the reception symbol r (n) input to the reception antenna. When a pilot signal is mixed in the transmission signal, the transmission path estimator 232 performs transmission path estimation from the reception symbol r (n) to obtain a transmission path gain. α1 and α2 can be detected.
The STTC decoder 231 performs a decoding process using the transmission line gains α1 and α2 to obtain received data. When the STTC decoder 231 performs a decoding process, the STTC decoder 231 performs decoding using a corresponding decoding method in synchronization with the encoding method encoded by the STTC encoder 131. For example, the transmitter 13 and the receiver 23 make it known in advance which encoding scheme of which frame of the transmission symbol sequence is to be encoded. The STTC decoder 231 will be described in detail later with reference to FIG.

  In the radio communication system according to the present embodiment, the transmission symbol sequence is transmitted by changing the encoding scheme in the STTC encoder 131, and the STTC decoder 231 decodes the transmission symbol sequence by a decoding scheme corresponding to the encoding scheme. Received data is obtained. Here, as a specific example, the STTC encoder 131 changes the encoding scheme in two types of 8 states (4-PSK) and 8 states (8-PSK), and the STTC decoder 231 performs decoding accordingly. The case where the method is switched will be described below. First, a description will be given corresponding to each encoding method, and then a case where the encoding method corresponding to the wireless communication system of the present embodiment is changed will be described.

First, an 8-state STTC encoder 131_pa1 for 4-PSK will be described with reference to FIGS. 2 (A), 2 (B), and 2 (C).
As shown in FIG. 2A, the STTC encoder 131_pa1 converts a serial transmission bit string having a value of 0 or 1 into 2-bit parallel data by a serial parallel (S / P) converter. This data is input to a circuit composed of a register and an exclusive OR adder. As shown in FIG. 2A, when register contents are represented by R0, R1, and R2, the state of the STTC encoder 131_pa1 is:
4R2 + 2R1 + R0
Since R0, R1, and R2 each have a value of 0 or 1, the state takes 8 types of values from 0 to 7, and the number of states is 8. The STTC encoder 131_pa1 generates two systems of 2-bit parallel data. These four kinds of 2-bit data are converted into four kinds of symbols (symbols) having values from 0 to 3 by binary decimal conversion, and further mapped to 4-PSK signals by corresponding integers to complex numbers. Is done. That is, the bit data is as shown in FIG.
00 (data) → 0 (symbol) → +1 (4-PSK signal),
10 (data) → 1 (symbol) → + j (4-PSK signal),
01 (data) → 2 (symbol) → −1 (4-PSK signal),
11 (data) → 3 (symbol) → −j (4-PSK signal),
Is mapped.
In the 4-PSK, 8-state STTC encoder 131_pa1, as shown in FIG. 2 (C), the state transitions that can be taken by the symbols from the nth to the (n + 3) th are 8 inputs and 8 outputs. It becomes a state transition.

Next, the 8-state STTC encoder 131_pa2 for 8-PSK will be described with reference to FIGS. 3 (A), 3 (B), and 3 (C).
As shown in FIG. 3A, the STTC encoder 131_pa2 converts a serial data bit string having a value of 0 or 1 into 3-bit parallel data by a serial parallel (S / P) converter. This data is input to a circuit composed of a register and an exclusive OR adder. As shown in FIG. 3A, when the register contents are represented by R0, R1, and R2, the state of the STTC encoder 131_pa2 is:
4R2 + 2R1 + R0
Since R0, R1, and R2 are values of 0 or 1, respectively, the state takes 8 types of values from 0 to 7 as in the case of 4-PSK, and the number of states is 8 The STTC encoder 131_pa2 generates two systems of 3-bit parallel data. These 8 types of 3-bit data are converted into 8 types of symbols having values from 0 to 7 by binary decimal conversion, and further mapped to 8-PSK signals by corresponding integers to complex numbers. That is, the bit data is as shown in FIG.
000 (data) → 0 (symbol) → +1 (8-PSK signal),
100 (data) → 1 (symbol) → +1/2 ^1/2 + j / 2 ^1/2 (8-PSK signal),
010 (data) → 2 (symbol) → + j (8-PSK signal),
110 (data) → 3 (symbol) → −1/2 ^1/2 + j / 2 ^1/2 (8-PSK signal),
001 (data) → 4 (symbol) → −1 (8-PSK signal),
101 (Data) → 5 ^{(symbols) → -1/2 1/2 -j / 2 1/2} (8-PSK signal),
011 (data) → 6 (symbol) → −j (8-PSK signal),
111 (data) → 7 (symbol) → +1/2 ^1/2 −j / 2 ^1/2 (8-PSK signal),
Is mapped.
With reference to FIG. 3C, description will be made of state transitions that can be taken by the nth to n + 3 symbols in the 8-PSK, 8-state STTC encoder 131_pa2. In this case, the state transition is 8 inputs and 8 outputs.

  The state transition in the case of 4-PSK and 8-state described above and the state transition in the case of 8-PSK and 8-state are compared with reference to FIG. 2 (C) and FIG. 3 (C). Both are 8-input 8-output state transitions, but in the case of 8-PSK, 8-state compared to 4-PSK, 8-state, the number of states transitioning from a certain state is larger. Many. Specifically, in FIG. 2C (in the case of 4-PSK, 8-state), for example, the transition destination from state 0 is limited to states 0, 1, 2, and 3. Further, the transition destination from the state 1 in FIG. 2C is limited to the states 4, 5, 6, and 7. On the other hand, in FIG. 3C (in the case of 8-PSK, 8-state), for example, the transition destination from state 0 is allowed to transition to all states from state 0 to state 7. Further, in FIG. 3C, the transition destination from the state 1 is allowed to transition to all the states from the state 0 to 7.

In general, when the state transition is limited, the number of state transition candidates that must be considered when searching for the most likely state transition by the decoder is reduced, and the decoding performance is improved. Therefore, from the viewpoint of state transition, the state transition in the case of 4-PSK, 8-state (FIG. 2C) is more than the state transition in the case of 8-PSK, 8-state (FIG. 3C). Strong error tolerance. 2B and 3C, the distance between signal points is smaller in the case of 8-PSK than in the case of 4-PSK. 4-PSK has higher error tolerance.
Further, in terms of the number of bits transmitted per symbol, that is, transmission efficiency, the case of 8-PSK (FIG. 3A) is 3, while the case of 4-PSK (FIG. 2) is 2. Therefore, 8-PSK has higher transmission efficiency than 4-PSK.
In the present embodiment, by providing encoding schemes having different error tolerance and transmission efficiency, an appropriate encoding scheme is selected depending on whether error tolerance or transmission efficiency is prioritized.

Next, the STTC encoder 131 of the wireless communication system according to the present embodiment will be described with reference to FIGS. 4 (A) and 4 (B). FIG. 4A is a combination of the 4-PSK, 8-state case and the 8-PSK, 8-state case.
The STTC encoder 131 includes adders 1311, 1312 and 1313, and switches (SW) 1314, 1315, 1316 and 1317 in addition to the S / P converters and registers shown in FIGS. It has.

As shown in FIG. 4, the STTC encoder 131 corresponds to 4-PSK, 8-state in FIG. 2 when all the switches (SW) are connected to the terminal 1, and all the switches (SW). Is connected to the terminal 2 corresponds to 8-PSK and 8-state in FIG. That is, when all the switches (SW) are connected to the terminal 1, the S / P converter converts the serial data into 2-bit parallel data, and the mapping units 134 and 135 select 4-PSK. On the other hand, when all the switches (SW) are connected to the terminal 2, the S / P converter converts the serial data into 3-bit parallel data, and the mapping units 134 and 135 select 8-PSK.
A control unit (not shown) gives an instruction to switch each switch to switches 1314, 1315, 1316, and 1317, and an instruction to select 4-PSK or 8-PSK to mapping units 134 and 135.

  As shown in FIG. 4B, in the state transition from the nth to the (n + 3) th symbol, the nth symbol is 8-PSK, 8-state, the (n + 1) th symbol and the (n + 2) th symbol are 4-PSK, 8-state. The (n + 3) th symbol is in the 8-PSK, 8-state state. That is, the nth symbol and the (n + 3) th symbol have lower error tolerance than the (n + 1) th symbol and the (n + 2) th symbol, and the nth and (n + 3) th symbols have higher transmission efficiency than the (n + 1) th symbol and the (n + 2) th symbol. Therefore, in the state transition from the nth to the (n + 3) th symbol, an error tolerance and transmission efficiency intermediate between 8-PSK, 8-state and 4-PSK, 8-state are realized as a whole. .

Next, the STTC decoder 231 will be described with reference to FIG. As shown in FIG. 5, the STTC decoder 231 includes a transmission symbol candidate output unit 2311, an adder, a multiplier, a Viterbi calculator 2312, and a switching control unit 2313.
The transmission symbol candidate output unit 2311 outputs a transmission symbol candidate transmitted from each transmission antenna of the transmitter 13 in accordance with an instruction from the switching control unit 2313. For example, as shown in FIG. 5, the nth transmission symbol candidate q1 (n) from the first transmission antenna and the nth transmission symbol candidate q2 (n) from the second transmission antenna are output.
Each n-th transmission symbol candidate is multiplied by a transmission line gain by a multiplier, and the multiplied product is added by an adder. Then, using the multiplier,
-Α1 q1 (n)-α2 q2 (n), where n = 0, 1, ..., N-1
α1: Gain of the transmission path from the first transmitting antenna to the receiving antenna,
α2: gain of the transmission path from the second transmitting antenna to the receiving antenna,
Get. Then, an adder adds the received symbol r (n),
e (n) = r (n) −α1q1 (n) −α2q2 (n)
Get. The transmission path gain is estimated based on the received symbol by the transmission path estimator 232.

The Viterbi computing unit 2312 inputs this e (n), and is an evaluation value | e (n) | ²
And a symbol series that minimizes the evaluation value is searched for.

  The switching control unit 2313 synchronizes with 8-PSK, 8-state encoding, 4-PSK, and 8-state encoding, and performs 8-PSK, 8-state decoding, and 4-PSK, An instruction for switching decoding of 8-state is output to transmission symbol candidate output section 2311 and Viterbi calculator 2312. The switching control unit 2313 receives a control signal indicating this switching from the transmitter 13 for switching between 8-PSK and 8-state encoding and 4-PSK and 8-state encoding, or in advance. It is set by the transmitter 13 and the receiver 23 to realize switching synchronization.

  By the way, in this embodiment, in the example shown in FIG. 4B, the ratio between the case of 8-PSK and 8-state and the case of 4-PSK and 8-state is 1: 1. However, by changing this ratio, it is possible to finely control error resilience and transmission efficiency.

  Further, for example, the transmitter 13 grasps the transmission path characteristics and obtains necessary error resilience, and synchronizes the encoding switching with the receiver 23. In this case, the transmission path characteristics are ascertained when the two-way transmission between the transmitter 13 and the receiver 23 is TDD (Time Division Duplex) performed in the same frequency band in a time division manner, and is received by the transmission antenna. If there is a transmission path estimator that estimates the transmission path characteristics from the received signal, the transmitter 13 can grasp the transmission path characteristics. On the other hand, in the case of FDD (Frequency Division Duplex) in which this bidirectional transmission is performed in different frequency bands, the transmitter 13 is notified of the transmission path characteristics from the receiver 23 which is the communication partner of the transmitter 13. The transmission path characteristics can be grasped. In this case, the transmission path characteristics to be known by the transmitter need not be precise transmission path characteristics, but may be quantized transmission path characteristics or a signal-to-noise ratio value.

  According to the present embodiment described above, by controlling the number of parallel bits and the state structure of the encoder for each symbol, it is possible to realize control with high error tolerance and transmission efficiency.

(Second Embodiment)
Unlike the case where the number of states in the first embodiment is the same (the number of states is 8), the wireless communication system of this embodiment is a combination of 8-PSK, 8-state, and 4- This corresponds to the combination of PSK and 4-state. This embodiment is the same as the first embodiment except that what is 4-PSK and 8 state in the first embodiment changes to 4-PSK and 4-state. A description of the same components as those in the first embodiment will be omitted.
In the radio communication system according to the present embodiment, the transmission symbol sequence is transmitted by changing the encoding scheme in the STTC encoder 131, and the STTC decoder 231 decodes the transmission symbol sequence by a decoding scheme corresponding to the encoding scheme. Received data is obtained. Here, as a specific example, the STTC encoder 131 changes the encoding method in two types of 8 states (8-PSK) and 4 states (4-PSK), and the STTC decoder 231 performs decoding accordingly. The case where the method is switched will be described below. First, a description will be given corresponding to each encoding method, and then a case where the encoding method corresponding to the wireless communication system of the present embodiment is changed will be described.

First, the 4-state STTC encoder 131_pa3 for 4-PSK will be described with reference to FIGS. 6 (A) and 6 (B).
As shown in FIG. 6A, the STTC encoder 131_pa3 converts a serial transmission bit string having a value of 0 or 1 into 2-bit parallel data by an S / P converter. This data is input to a circuit composed of a register and an exclusive OR adder. As shown in FIG. 2A, when the contents of the registers are represented by R0 and R1, the state of the STTC encoder 131_pa3 is
2R1 + R0
Since R0 and R1 are values of 0 or 1, respectively, the state takes four types of values from 0 to 3, and the number of states is 4. The STTC encoder 131_pa3 generates two systems of 2-bit parallel data. These four kinds of 2-bit data are converted into four kinds of symbols (symbols) having values from 0 to 3 by binary decimal conversion, and further mapped to 4-PSK signals by corresponding integers to complex numbers. Is done. That is, the bit data is
00 (data) → 0 (symbol) → +1 (4-PSK signal),
10 (data) → 1 (symbol) → + j (4-PSK signal),
01 (data) → 2 (symbol) → −1 (4-PSK signal),
11 (data) → 3 (symbol) → −j (4-PSK signal),
Is mapped.

In the 4-PSK, 4-state STTC encoder 131_pa3, as shown in FIG. 6B, the state transitions that can be made with the symbols from the nth to the (n + 3) th are four inputs and four outputs. It becomes a state transition.
On the other hand, the STTC encoder in the case of 8-PSK and 8-state is the one described in the first embodiment with reference to FIG. 3 (A), FIG. 3 (B), and FIG. 3 (C). It is the same.

  Comparing the case of 4-PSK and 8-state in the first embodiment with the case of 4-PSK and 4-state in the present embodiment, the number of states is reduced in this embodiment, so that error tolerance is improved. It has deteriorated. However, in the case of this embodiment, the amount of calculation for decoding decreases because the number of states is small. Since both are 4-PSK, the transmission efficiency is the same.

Next, the STTC encoder 131 of the wireless communication system of this embodiment will be described with reference to FIGS. 7A and 7B. FIG. 7A is a combination of the 4-PSK and 4-state cases and the 8-PSK and 8-state cases.
The STTC encoder 131 includes an adder 1318 and switches (SW) 1319, 1320, and 1321, in addition to the S / P converters and registers shown in FIGS. 6A and 3A.

In the STTC encoder 131, as shown in FIG. 7A, the case where all the switches (SW) are connected to the terminal 1 corresponds to 4-PSK and 4-state in FIG. The case where all the switches (SW) are connected to the terminal 2 corresponds to 8-PSK and 8-state in FIG. That is, when all the switches (SW) are connected to the terminal 1, the S / P converter converts the serial data into 2-bit parallel data, and the mapping units 134 and 135 select 4-PSK. On the other hand, when all the switches (SW) are connected to the terminal 2, the S / P converter converts the serial data into 3-bit parallel data, and the mapping units 134 and 135 select 8-PSK.
A control unit (not shown) gives an instruction to switch each switch to switches 1319, 1320, and 1321 and an instruction to select 4-PSK or 8-PSK to the mapping units 134 and 135.

  As shown in FIG. 7B, in the state transition from the nth to the (n + 3) th symbol, the nth symbol is 8-PSK, 8-state, the (n + 1) th symbol and the (n + 2) th symbol are 4-PSK, 4-state. The (n + 3) th symbol is in the 8-PSK, 8-state state. That is, the nth symbol and the (n + 3) th symbol have lower error tolerance than the (n + 1) th symbol and the (n + 2) th symbol, and the nth and (n + 3) th symbols have higher transmission efficiency than the (n + 1) th symbol and the (n + 2) th symbol. Therefore, in the state transition from the nth to the (n + 3) th symbol, an error tolerance and transmission efficiency intermediate between 8-PSK, 8-state, and 4-PSK, 4-state are realized as a whole.

(Third embodiment)
Unlike the combination of 8-PSK and 4-PSK as in the fourth and second embodiments, the wireless communication system of the present embodiment has the same modulation scheme and differs only in the number of states. , And 4-PSK and 4-state. This embodiment is the same as the first embodiment except that the 8-PSK and 8-state in the first embodiment are changed to 4-PSK and 4-state. A description of the same components as those in the first embodiment will be omitted.
In the radio communication system according to the present embodiment, the transmission symbol sequence is transmitted by changing the encoding scheme in the STTC encoder 131, and the STTC decoder 231 decodes the transmission symbol sequence by a decoding scheme corresponding to the encoding scheme. Received data is obtained. Here, as a specific example, the STTC encoder 131 changes the encoding scheme in two types of 8-state of 4-PSK and 4-state of 4-PSK, and the STTC decoder 231 switches the decoding scheme accordingly.

  The STTC encoder in the case of 4-PSK and 8-state is the same as that described with reference to FIGS. 2A, 2B, and 2C in the first embodiment. is there. On the other hand, the STTC encoder in the case of 4-PSK and 4-state is the one described in the second embodiment with reference to FIG. 6 (A), FIG. 6 (B), and FIG. 6 (C). It is the same.

Next, the STTC encoder 131 of the wireless communication system of this embodiment will be described with reference to FIGS. 8A and 8B. FIG. 8A is a combination of the 4-PSK and 4-state cases and the 4-PSK and 8-state cases.
The STTC encoder 131 includes adders 1322 and 1323, and switches (SW) 1324, 1325, and 1326 in addition to the S / P converters and registers shown in FIGS. 6A and 2A. .

In the STTC encoder 131, as shown in FIG. 8A, the case where all the switches (SW) are connected to the terminal 1 corresponds to 4-PSK and 8-state in FIG. The case where all the switches (SW) are connected to the terminal 2 corresponds to 4-PSK and 4-state in FIG. In this case, regardless of whether all switches (SW) are connected to either terminal 1 or terminal 2, the S / P converter converts the serial data into 2-bit parallel data, and the mapping units 134 and 135 are 4-PSK. Mapping with.
A control unit (not shown) gives an instruction to switch each switch to switches 1324, 1325, and 1326.

  As shown in FIG. 8B, in the state transition from the nth to the (n + 3) th symbol, the nth symbol is 4-PSK, 8-state, the (n + 1) th symbol and the (n + 2) th symbol are 4-PSK, 4-state. The (n + 3) th symbol becomes 4-PSK, 8-state. In this case, the nth symbol and the (n + 3) th symbol have higher error resistance than the (n + 1) th symbol and the (n + 2) th symbol. Therefore, in the state transition from the nth symbol to the n + 3th symbol, the error tolerance between 4-PSK, 8-state and 4-PSK, 4-state is realized as a whole. Also, the transmission efficiency is the same as the transmission efficiency of 4-PSK because both are 4-PSK in this embodiment. Also, since 4-state has a smaller amount of computation, when it is desired to reduce the amount of computation, the ratio of 4-PSK and 4-state is increased within an allowable error tolerance range.

Note that the present embodiment is not limited to a combination of 4-PSK, 4-state, and 4-PSK, 8-state. For example, a combination of 64-QAM (Quadrature Amplitude Modulation), 64-state, 4-PSK, 64-state may be used. FIG. 9A shows the state transition when these 64-QAM (Quadrature Amplitude Modulation), 64-state, and 4-PSK, 64-state are combined. In FIG. 9A, since there are 64 transition states, details of the state transition are omitted. According to the state transition shown in FIG. 9A, it is possible to realize error tolerance between 64-QAM and 64-state and 4-PSK and 64-state.
In addition, there are combinations of 64-QAM and 64-state and 4-PSK and 16-state. FIG. 9B shows the state transition when these 64-QAM and 64-state are combined with 4-PSK and 16-state. Also in FIG. 9B, since there are 64 transition states as in FIG. 9A, details of the state transition are omitted. According to the state transition shown in FIG. 9B, it is possible to realize error tolerance between 64-QAM and 64-state and 4-PSK and 16-state.
In general, increasing the number of states increases error resilience, but as the number of states increases, the degree of improvement in error resilience decreases. In the case of 4-PSK and 64-state, the error tolerance does not increase as the calculation amount increases compared to the case of 4-PSK and 16-state. Therefore, when FIG. 9A and FIG. 9B are compared, it can be said that the method shown in FIG. 9B is more appropriate from the viewpoint of the amount of calculation.

(Fourth embodiment)
The wireless communication system of this embodiment is for controlling the error resilience of a specific symbol in a frame, unlike the control of the average error resilience of a symbol in one frame in the previous embodiments. It is.
As shown in FIG. 10A, the wireless communication system of this embodiment includes a transmitter 14 and a receiver 24. The transmitter 14 includes a 16-state STTC encoder 141, S / P converters 142 and 143. 128-point IDFTs 144 and 145, P / S converters 146 and 147, and guard interval adding units 148 and 149, respectively. The receiver 24 includes a guard interval removing unit 241, an S / P converter 242, a 128-point DFT 243, a P / S converter 244, and a 16-state STTC decoder 245. In the present embodiment, a case where one frame is applied to OFDM in which multicarrier transmission is performed with 128 subcarriers will be described as an example.

The 16-state STTC encoder 141 performs 16-QAM, 16-state STTC encoding on a frame made up of 128 symbols to generate two symbol sequences. Also, the 16-state STTC encoder 141 obtains information on transmission path conditions (that is, transmission path characteristics), and sets a modulation scheme for each subcarrier based on this information. For example, as shown in FIG. 10B, a subcarrier having a notch in the transmission path characteristic is modulated by a 4-PSK modulation method having a stronger error tolerance than 16QAM.
Each of the S / P converters 142 and 143 receives a symbol string composed of 128 symbols and performs serial / parallel (S / P) conversion into 128 signals.
The 128-point IDFTs 144 and 145 respectively perform 128 discrete Fourier transforms on 128 signals.
The P / S converters 146 and 147 respectively convert 128 signals subjected to inverse discrete Fourier transform to parallel-serial conversion and combine them into one signal.
The guard interval adding units 148 and 149 each copy 32 points at the rear end of the frame as guard symbols in order to remove inter-frame interference, and transmit them from the first transmission antenna and the second transmission antenna. To do.

  In the transmission path 32, output symbols from the first transmission antenna and the second transmission antenna are multiplied by independent transmission path gains α1 and α2, respectively. In addition, it is assumed that output symbols from the first transmission antenna and the second transmission antenna receive transmission line gains β1 and β2 and there are delayed arrival waves that arrive at delay times T1 and T2. These delay times T1 and T2 are assumed to be shorter than the above-described guard time for 32 points. Symbols output from the first transmitting antenna and the second transmitting antenna are respectively multiplied by transmission line gains α1 and α2, and multiplied by β1 and β2, respectively, and arrived at delay times T1 and T2, respectively. The white noise η (n) independent for each symbol is added and then input to the receiving antenna.

The guard interval removal unit 241 removes the guard interval.
The S / P converter 242 inputs a symbol string composed of 128 symbols from which the guard interval has been removed, and performs serial-parallel (S / P) conversion into 128 signals.
The 128-point DFT 243 performs a discrete Fourier transform on 128 signals.
The P / S converter 244 performs parallel-serial conversion on the 128 signals that have been subjected to inverse discrete Fourier transform, and combines them into one signal.
The 16-state STTC decoder 245 performs STTC decoding to obtain received data.

  Normally, STTC is designed under the condition that the transmission path characteristics are constant within the frame, but as shown by the frequency characteristics of the transmission path in FIG. 10B, the characteristics are not constant because of the frequency selective transmission path. In some cases, the decoding characteristics deteriorate. In the present embodiment, the subcarrier modulation scheme corresponding to the notch frequency of the transmission path characteristic is replaced with 4-PSK, 16-state STTC. That is, as shown in FIG. As described above, the radio communication system according to the present embodiment can adaptively replace a subcarrier that receives a notch with transmission path characteristics in an STTC encoded frame with an STTC having high error tolerance.

  Here, a computer simulation result for verifying the effect of the present embodiment will be described with reference to FIG. In the simulation, in the transmission line 32 shown in FIG. 10 (A), α1, α2, β1, and β2 vary for each IDFT output block, and η varies with a Gaussian distribution for each sample. α1 and α2 are set to be 3 dB larger than β1 and β2. Further, T1 and T2 vary in a uniform distribution within the guard interval, and it is assumed that the transmitter 14 has a known notch position by transmission of a control signal from the receiver 24. Further, the transmitter 14 adopts 16-state STTC, non-notch subcarrier adopts 16-QAM, 16-state STTC, and notch subcarrier adopts 4-PSK, 16-state STTC. To do.

  FIG. 11 shows the result of computer simulation, showing the relationship between the SNR, which is the transmission path characteristic of the transmission path 32, and the throughput, which is the number of bits successfully transmitted per unit subcarrier. 16QAM, 8PSK, and 4PSK shown in FIG. 11 are prior arts that allocate 16-state 16QAM, 8PSK, and 4PSK STTCs to all subcarriers, and 16QAM / 4PSK shown in FIG. This embodiment has been described in the present embodiment in which 16QAM or 4PSK STTC is adaptively assigned to each subcarrier. When there is no frame loss, the throughput of the prior art is 4 for 16QAM, 3 for 8PSK, and 2 for 4PSK. According to the computer simulation result shown in FIG. 11, it can be seen that the wireless communication system of the present embodiment is effective when the SNR is between 17 dB and 24 dB.

(Fifth embodiment)
Unlike the above-described embodiment, the wireless communication system of this embodiment is a case where a plurality of transmission outputs are transmitted from the same antenna. That is, for example, in the diagram showing the encoder of FIG. 4A, the first transmission output and the second transmission output are respectively sent from the first transmission antenna and the second transmission antenna to the transmission path. However, in the present embodiment, for example, in FIG. 4A, the first transmission output and the second transmission output are transmitted from the same single transmission antenna in time division or frequency division. Including cases. Hereinafter, a description will be given with reference to FIG.
In the present embodiment, as shown in FIG. 12, the switches s ₁ , s ₂ , and s ₃ included in the selector 151-1 are controlled according to the transmission path estimator 150. In FIG. 12, black circles indicate switch ON and white circles indicate switch OFF. For example, FIG. 12 shows a case where s ₁ is turned on and s ₂ and s ₃ are turned off. In this case, the first embodiment described with reference to FIG. The STTC encoding / decoding transmission described in the above. This selection is effective, for example, when the correlation between the transmission path from the first transmission antenna 152 to the receiver antenna and the transmission path from the second transmission antenna 153 to the receiver antenna is weak. To be selected. This selection is performed by the transmission path estimator 150 detecting the outline of the transmission path state.

  Next, a transmission path state detection method will be described with reference to FIG.

  For example, in bidirectional communication between a base station and a terminal, if transmission from the base station to the terminal is defined as downlink transmission, and transmission from the terminal to the base station is defined as uplink transmission, the uplink and downlink are time-divisionally divided in the same frequency band. In the case of TDD (Time Division Duplex) in which bidirectional communication is performed by switching, the characteristics of the uplink and downlink transmission paths are the same. Therefore, the base station receives the uplink transmission signal from the terminal, and the received signal From the characteristics, it is possible to detect the downlink transmission path characteristics. Also, the base station can be notified of the downlink transmission path characteristics detected by the terminal receiver, and the base station transmitter can use the transmission path characteristics.

  On the other hand, in the case of FDD (Frequency Division Duplex) in which the upstream and downstream bidirectional communications are performed in different frequency bands, the downstream transmission path characteristic is notified from the receiver of the terminal that is the communication partner of the base station transmitter. By doing so, the transmitter of the base station can detect the transmission path characteristics.

In FIG. 12, for example, when only s ₂ is turned ON, the outputs u ₁ (n) and u ₂ (n) of the first and second 4-PSK mappers 105 and 106 are respectively time-division multiplexers 154. Is input. If u ₁ (n) and u ₂ (n) are in time width T and frequency bandwidth F as shown in FIG. 14A, they are shown in FIG. 14B and FIG. 14C. Thus, u ₁ (n) and u ₂ (n) are time-division multiplexed to the time width T and the frequency bandwidth 2F by the time-division multiplexing operation.

For example, when only s ₃ is turned ON, the outputs u ₁ (n) and u ₂ (n) of the first and second 4-PSK mappers 105 and 106 are respectively input to the frequency division multiplexer 155. Is done. If u ₁ (n) and u ₂ (n) are in time width T and frequency bandwidth F, as shown in FIGS. 14 (B) and 14 (C), by frequency division multiplexing operation, u ₁ (n) and u ₂ (n) are multiplexed by time division into a time width T and a frequency bandwidth 2F.

  Such selection of time division multiplexing and frequency division multiplexing is selected as follows, for example. When the correlation between the transmission path from the first transmission antenna 152 to the receiver antenna and the transmission path from the second transmission antenna 153 to the receiver antenna is strong and STTC is not effective, frequency division is performed. Multiplexing or time division multiplexing is selected. Of these, frequency division multiplexing is completely divided into upper and lower frequency bands, so if the characteristics of one band are always poor, the transfer characteristics of the output of the mapper that uses that band will always be poor. In such a case, time division multiplexing is selected because it causes trouble.

In the case of time division multiplexing or frequency division multiplexing, the receiver receives the first transmission output and the second transmission output as separated reception signals r1 (n) and r2 (n), so that the decoder Then, a Viterbi calculator searches for a symbol series that minimizes the next evaluation value. That is,
| R1 (n) −α1q1 (n) | ² + | r2 (n) −α2q2 (n) | ² , where n = 0, 1,..., N−1
Search for a symbol sequence that minimizes. If there is no transmission path fluctuation for each symbol, α1 = α2. Note that, as described above, in the wireless communication system in which this time division multiplexing or frequency division multiplexing is selected, the required transmission is compared with the wireless communication systems from the first embodiment to the fourth embodiment. Although the bandwidth is doubled, the first transmission output and the second transmission output are transmission modes in which the first transmission antenna and the second transmission antenna are orthogonal to each other in terms of time or frequency. Since the error tolerance is strong, a large number of modulations can be increased.

  Therefore, when a wide transmission bandwidth is given, the first transmission output and the second transmission output are transmitted by time division or frequency division, and when the transmission bandwidth is limited, the fourth embodiment starts from the fourth embodiment. As in the seventh embodiment, a control unit (not shown) sends the first transmission output and the second transmission output from the first transmission antenna and the second transmission antenna to the transmission path, respectively. There is also a selection method of controlling.

Also, for example, with the encoder of FIG. 4A, the 4-PSK first transmission output and the 4-PSK second transmission output are amplitude-multiplexed into 16-QAM from the same single transmission antenna. There is also a transmission form for transmission, and this case will be described with reference to FIG. In FIG. 15, the switches s ₁ and s ₂ are controlled according to the transmission path estimator 150. In FIG. 15, as in FIG. 12, black circles indicate switch ON and white circles indicate switch OFF. For example, FIG. 15 shows a case where s ₁ is turned on and s ₂ is turned off. In this case, the case described in the first embodiment with reference to FIG. STTC encoding / decoding transmission.

As another example, for example, when s ₂ is turned ON and s ₁ is turned OFF, in this case, for example,
A large-amplitude 4-PSK signal is represented by X = ± 2 ± 2j,
A small amplitude 4-PSK signal is represented by Y = ± 1 ± 1j,
Then, the 16-QAM signal is
Z = X + Y = (± 3, ± 1) + (± 3, ± 1) j
It is expressed. As is apparent from this display, one of the 4-PSK first transmission output and the 4-PSK second transmission output is added under the condition that the amplitude is doubled to be synthesized in the form of 16-QAM. Can do. Further, the transmission band in this case is the same as in the first to fourth embodiments. Further, the transmission power in this case is the total power of the first transmission antenna and the second transmission antenna in the first to fourth embodiments, and is transmitted from one transmission antenna.
In addition, since the receiver receives the first transmission output and the second transmission output as separated reception signals r1 (n) and r2 (n), the decoder has a minimum evaluation value for the next evaluation. A simple symbol series is searched with a Viterbi calculator. That is, the decoder
| R (n) −αq (n) | ² , where n = 0, 1,..., N−1,
Search for q (n) that minimizes. If there is no transmission path fluctuation for each symbol, α is a transmission gain between transmission and reception, and q (n) is a transmission 16-QAM candidate when two 4-PSKs are combined.

  When fading of the transmission path is significant, transmission from the first transmission antenna and the second transmission antenna is performed using the wireless communication system from the first embodiment to the fourth embodiment, and the transmission path is When fading is small, it is preferable to transmit by 16-QAM as in the wireless communication system of this embodiment.

  According to the wireless communication system of the embodiment shown in FIG. 12 or FIG. 15, an optimal transmission method can be selected according to the transmission path characteristics and the allowable bandwidth.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, in the embodiment shown in FIG. 15, 16-QAM transmission includes the output of the first 4-PSK mapper 105 that inputs two bits at the same time, and the second 4-bit that inputs two bits at the same time. This is realized by synthesizing the outputs of the PSK mapper 106 and generating a 16-QAM signal. Instead, a 16-QAM mapper that inputs four bits simultaneously is prepared as a new component. In some embodiments, 16-QAM signal transmission is realized.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a block diagram of a wireless communication system according to a first embodiment of the present invention. (A) is a block diagram of an 8-state STTC encoder for 4-PSK, (B) is a diagram showing signal points for 4-PSK mapping, and (C) is a diagram of FIG. 2 (A). The figure which showed the transition of the state which can be taken with the nth to n + 3 symbol by an encoder. (A) is a block diagram of an 8-state STTC encoder for 8-PSK, (B) is a diagram showing signal points for 8-PSK mapping, and (C) is a diagram of FIG. The figure which showed the transition of the state which can be taken with the nth to n + 3 symbol by an encoder. (A) is a block diagram of the STTC encoder according to the first embodiment, and (B) shows state transitions that can be taken by the nth to n + 3 symbols by the encoder of FIG. 4 (A). Figure. The block diagram of the STTC decoder of FIG. 1, and the figure which showed the transmission path estimator. (A) is a block diagram of a 4-state STTC encoder for 4-PSK, and (B) is a state transition that can be taken by the nth to n + 3 symbols by the encoder of FIG. 6 (A). FIG. (A) is a block diagram of the STTC encoder of the second embodiment, and (B) shows state transitions that can be taken by the nth to n + 3 symbols by the encoder of FIG. 7 (A). Figure. (A) is a block diagram of the STTC encoder of the third embodiment, and (B) shows state transitions that can be taken by the nth to n + 3 symbols by the encoder of FIG. 8 (A). Figure. (A) is the figure which showed the state transition of the STTC encoder which combined 64-QAM, 64-state and 4-PSK, 64-state, (B) is 64-QAM, 64-state and 4- The figure which showed the state transition of the STTC encoder which combined PSK and 16-state. (A) is a block diagram of the radio | wireless communications system which concerns on the 4th Embodiment of this invention, (B) is a figure which shows the subcarrier modulation system and state transition which are set corresponding to this characteristic. The figure which shows the computer simulation result for verifying the effect of 4th Embodiment. The block diagram of the transmitter used with the radio | wireless communications system of 5th Embodiment. The figure explaining acquisition of the transmission line characteristic in each case of FDD ((A) of Drawing 13) and TDD ((B) of Drawing 13). (A) is a figure which shows the signal output from the 1st and 2nd 4-PSK mapper, (B) is a figure for demonstrating the example of time division multiplexing, (C) is frequency division. The figure for demonstrating multiplexing. The block diagram of the transmitter used with the radio | wireless communications system of the modification of 5th Embodiment.

Explanation of symbols

13, 14 ... Transmitter, 23, 24 ... Receiver, 31, 32 ... Transmission path, 131, 131_pa1, 131_pa2, 131_pa3 ... STTC encoder, 105 ... First 4 -PSK mapper, 106 ... second 4-PSK mapper, 132, 133, 134, 135 ... mapper, 141 ... 16 state STTC encoder, 142, 143, 242 ... S / P converter, 146, 147, 244... P / S converter, 148, 149... Guard interval adding unit, 231... STTC decoder, 232. ..16 state STTC decoder, 1311, 1312, 1313, 1318, 1322, 1323 ... adder, 1314, 1315, 1316, 1317, 1319, 13 0,1321,1324,1325,1326 ... switch, 2311 ... transmission symbol candidate output unit, 2312 ... Viterbi calculator, 2313 ... switching control unit.

Claims (17)

In a wireless communication system comprising a transmitter that transmits a frame including a plurality of symbols after space-time coding and a receiver that receives the frame via a transmission path and performs space-time decoding.
The transmitter is
Input means for inputting the frame;
A symbol in the frame is encoded by a first encoding scheme among a plurality of encoding schemes different in at least one of error resilience and transmission efficiency, and the other symbols in the frame are encoded in the different plurality of codes. Encoding means for encoding with a second encoding scheme different from the first encoding scheme of encoding schemes;
Transmitting means for transmitting a frame composed of the plurality of encoded symbols,
The receiver
Receiving means for receiving the transmitted frame;
Estimating means for estimating transmission path characteristics based on the received frame;
A wireless communication system, comprising: a decoding unit that decodes the received frame in accordance with a decoding method that is switched in synchronization with switching of the encoding method encoded by the encoding unit and the transmission path characteristic. The encoding means includes
An internal register having a state transition structure for determining a relationship between an input of the encoding means and an output of the encoding means;
The encoding means selects the state transition structure at least every time one symbol or a plurality of symbols is input to the encoding means,
The radio communication system according to claim 1, wherein the decoding unit selects a state transition structure of the decoding unit in synchronization with selection of the state transition structure. The encoding means performs encoding by a space-time trellis,
The radio communication system according to claim 1, wherein the decoding unit performs decoding by a space-time trellis.   4. The wireless communication system according to claim 1, wherein the transmission unit transmits the frame by one of frequency hopping and multi-carrier. 5. The transmitter further comprises acquisition means for acquiring transmission path characteristics of a frame transmitted by the transmission means,
The said encoding means determines the said 1st encoding system and the said 2nd encoding system based on this transmission-line characteristic, The any one of Claims 1-4 characterized by the above-mentioned. Wireless communication system.   The transmission means may divide the frame into any one of spatial multiplexing, amplitude multiplexing, time division multiplexing, and frequency division multiplexing, or a plurality of spatial multiplexing, amplitude multiplexing, time division multiplexing, and frequency division multiplexing. The wireless communication system according to claim 1, wherein transmission is performed by switching between different types of multiplexing systems.   7. The radio according to claim 1, wherein the transmission unit determines a multiplexing method to be used based on at least one of an allowable bandwidth and a transmission path characteristic. Communications system. Input means for inputting a frame including a plurality of symbols;
A symbol in the frame is encoded by a first encoding method among a plurality of space-time encoding methods that are different in at least one of error resilience and transmission efficiency, and the other symbols in the frame Encoding means for encoding a second encoding scheme different from the first encoding scheme among the plurality of different encoding schemes;
A wireless communication apparatus comprising: a transmission unit configured to transmit a frame including a plurality of encoded symbols. The encoding means includes
An internal register having a state transition structure for determining a relationship between an input of the encoding means and an output of the encoding means;
9. The wireless communication according to claim 8, wherein the encoding unit selects the state transition structure every time at least one symbol or a plurality of symbols is input to the encoding unit. apparatus.   The wireless communication apparatus according to claim 8 or 9, wherein the encoding means performs encoding by a space-time trellis.   The radio communication apparatus according to claim 8, wherein the transmission unit transmits the frame by multicarrier. And further comprising acquisition means for acquiring transmission path characteristics of a frame transmitted by the transmission means,
The said encoding means determines the said 1st encoding system and the said 2nd encoding system based on this transmission-line characteristic, The any one of Claims 8-11 characterized by the above-mentioned. Wireless communication device.   The transmission means may divide the frame into any one of spatial multiplexing, amplitude multiplexing, time division multiplexing, and frequency division multiplexing, or a plurality of spatial multiplexing, amplitude multiplexing, time division multiplexing, and frequency division multiplexing. The wireless communication apparatus according to any one of claims 8 to 12, wherein transmission is performed by switching between different types of multiplexing systems.   The radio according to any one of claims 8 to 13, wherein the transmission means determines a multiplexing scheme to be used based on at least one of an allowable bandwidth and a transmission path characteristic. Communication device. A symbol in the frame is encoded by a first encoding method among a plurality of space-time encoding methods that are different in at least one of error resilience and transmission efficiency, and the other symbols in the frame From a transmitter that transmits a frame composed of the plurality of encoded symbols, and a second encoding method different from the first encoding method among the plurality of different encoding methods. In a wireless communication apparatus that receives the frame via a transmission line and performs space-time decoding,
Receiving means for receiving the transmitted frame;
Estimating means for estimating transmission path characteristics based on the received frame;
A wireless communication apparatus comprising: a decoding unit that decodes the received frame in accordance with a decoding method that is switched in synchronization with switching of an encoding method encoded by the transmitter and the transmission path characteristic. The transmitter selects a state transition structure that determines a relationship between an input before encoding and an output after encoding every time at least one symbol or a plurality of symbols is input to the encoding means. And
16. The wireless communication apparatus according to claim 15, wherein the decoding unit selects a state transition structure of the decoding unit in synchronization with selection of the state transition structure. The transmitter performs encoding by a space-time trellis,
The wireless communication apparatus according to claim 15 or 16, wherein the decoding means performs decoding by a space-time trellis.

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