JP2006074564A - Wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the effect of variations in transmission paths in the case of decoding a space-time trellis coded signal. <P>SOLUTION: A transmitter includes: a first rearrangement means 101 that rearranges a plurality of symbols in a frame so that a plurality of the symbols passing through transmission paths with similar characteristics are arranged at positions close to the original positions in the frame; a coding means 102 for coding the frame whose symbols are rearranged; and first inverse rearrangement means 103, 104 for restoring a plurality of the rearranged symbols to the originally arranged symbols, and a receiver includes: an estimate means 204 for estimating the transmission path characteristic on the basis of the received frame; a second rearrangement means 202 for applying rearrangement similar to that by the first rearrangement means to a plurality of the symbols in the received frame; a decoding means 203 for decoding the frame whose symbols are rearranged by referencing the transmission path characteristic; and a second inverse rearrangement means 205 for applying rearrangement similar to that by the first inverse rearrangement means to a plurality of the symbols in the decoded frame. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 wireless 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). STTC is designed based on the assumption that the channel characteristics are constant in the frame from the start to the end of the code state transition, and if the channel characteristics fluctuate in the frame, the design condition of the space-time code There is a problem that the decoding characteristic deteriorates. Therefore, it is important to improve transmission error characteristics. 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.

  STTC is designed on the assumption that the channel characteristics are invariant (slow fading that varies from frame to frame and does not change in the frame) between the start and end of the code state transition (in the frame). There are many. Therefore, when STTC is applied to frequency hopping (FH: Frequency Hopping) transmission, there is a problem including transmission path fluctuation in a frame due to transmission path characteristic fluctuation for each frequency.

  By the way, 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, in view of the problems in the prior art, the present invention provides a wireless communication system capable of reducing the influence of transmission path fluctuations when decoding a signal encoded by a space-time trellis code. Objective.

  It is another object of the present invention to provide a radio communication system capable of performing fine control of error tolerance of a space-time trellis code.

According to the wireless communication system of the present invention, the transmitter includes a transmitter that transmits a frame including a plurality of symbols after space-time encoding, and a receiver that receives the frame via a transmission path and performs space-time decoding. In a wireless communication system,
The transmitter has an input means for inputting the frame, and a plurality of symbols in the frame such that a plurality of symbols passing through transmission lines having similar characteristics are arranged in the vicinity of the frame. A first rearranging unit for rearranging; an encoding unit for encoding the rearranged frames; a first reverse rearranging unit for returning the plurality of symbols before rearrangement; and the rearranged unit. Transmission means for transmitting a frame consisting of a plurality of symbols,
The receiver includes: a receiving unit that receives the transmitted frame; an estimation unit that estimates a transmission path characteristic based on the received frame; and a plurality of symbols in the received frame. A second rearrangement unit that performs rearrangement similar to the rearrangement unit, a decoding unit that decodes the rearranged frame with reference to the transmission path characteristics, A second reverse rearrangement unit that rearranges the plurality of symbols in the same manner as the first reverse rearrangement unit is provided.

Further, according to the wireless communication system of the present invention, 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 the wireless communication system provided,
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 a decoding means for decoding the received frame according to the decoding method to be switched and the transmission path characteristics.

According to the wireless communication system of the present invention, it is possible to reduce the influence of transmission path fluctuations when decoding a signal encoded by a space-time trellis code.
Further, according to the wireless communication system of the present invention, it is possible to perform fine control of error tolerance of the 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)
The wireless communication system of this embodiment includes a transmitter 10 and a receiver 20 as shown in FIG. The transmitter 10 includes a first reordering device 101, an STTC encoder 102, a first reverse reordering device 103, a second reverse reordering device 104, and a first 4-PSK (Phase-Shift Keying) mapping. Device 105, second 4-PSK mapper 106, first FH transmitter 107, and second FH transmitter 108. The receiver 20 includes an FH receiver 201, a second rearranger 202, an STTC decoder 203, a transmission path estimator 204, and a third reverse rearranger 205.

In this embodiment, assuming 4-PSK transmission, baseband transmission symbols defined by four integers of 0, 1, 2, and 3 are defined by binary-decimal conversion for every two transmission bits. To do. In 4-PSK, integer values of 0, 1, 2, and 3 are, for example, as shown in FIG.
0 → + 1,
1 → + j,
2 → -1,
3 → -j,
Corresponds to the complex value of. Here, j ² = −1.

The first rearranger 101 inputs a plurality of transmission symbols as one transmission frame, and transmits in this transmission frame so that the frequencies when transmitting adjacent transmission symbols in one transmission frame are close to each other. Rearrange symbols. The first rearranger 101 is similar in the characteristics of the transmission path through which adjacent symbols pass, based on the assumption that the transmission path characteristics of nearby frequencies are similar and the transmission path characteristics of far frequencies are different. The sort is done.
A specific example will be described with reference to FIG. As shown in FIG. 2A, 8 transmission symbols,
x (0), x (1), x (2), x (3), x (4), x (5), x (6), x (7)
As one transmission frame, and each symbol has four different frequencies,
f0, f1, f2, f3
Next, description will be made based on an example of transmission by frequency hopping (FH). However, it is assumed that f0 <f1 <f2 <f3. In the example shown in FIG. 2 (A), the hopping pattern has a frequency for each symbol,
f0, f3, f1, f2, f0, f3, f1, f2,
An example of hopping pattern is shown below. That is, this pattern is repeated for each frame. Then, when the 4-PSK four-state space-time trellis code is used, the first rearranger 101 converts eight transmission symbol sequences into
x (0), x (4), x (2), x (6), x (3), x (7), x (1), x (5)
Convert to the order of.

  The STTC encoder 102 receives the symbol sequence rearranged by the first rearranger 101, performs STTC encoding, and generates two systems of symbol sequences. As shown in FIG. 3C, the STTC encoder 102 includes a delay unit to which one of the two symbol sequences is input. That is, in the case of FIG. 3C, the STTC output 2 is output with a delay from the STTC output 1.

Specifically, the STTC encoder 102 inputs the symbol sequence rearranged by the first rearranger 101 and takes an STTC output 1 that takes an integer value of 0, 1, 2, or 3,
X (1, 0), X (1, 4), X (1, 2), X (1, 6), X (1, 3), X (1, 7), X (1, 1), X (1, 5),
And STTC output 2 that takes an integer value of 0, 1, 2, or 3,
X (2, 0), X (2, 4), X (2, 2), X (2, 6), X (2, 3), X (2, 7), X (2, 1), X (2, 5),
And two symbol strings are generated. In this example, the STTC encoder 102 performs 4-PSK four-state STTC encoding, and generates an output with the state transition as shown in FIG. Also, the delay output causes the transmission output sequence 2 (STTC output 2 in FIG. 3C) to become an output sequence delayed by one symbol with respect to the transmission output sequence 1 (STTC output 1 in FIG. 3C).

The first reverse sorter 103 and the second reverse sorter 104 receive the STTC output 1 and the STTC output 2 output from the STTC encoder 102, respectively, before the first sorter 101 sorts them. Return a sequence of transmitted symbols. Then, the first reverse rearranger 103 and the second reverse rearranger 104 output the respective output signal sequences to the first 4-PSK mapper 105 and the second 4-PSK mapper 106.
Specifically, the first reverse sorter 103 and the second reverse sorter 104 receive the transmission output sequence 1 and the transmission output sequence 2, respectively.
X (1, 0), X (1, 1), X (1, 2), X (1, 3), X (1, 4), X (1, 5), X (1, 6), X (1, 7),
X (2, 0), X (2, 1), X (2, 2), X (2, 3), X (2, 4), X (2, 5), X (2, 6), X (2, 7),
These transmission output sequences are generated by rearranging (in reverse order) as follows, and output to the first 4-PSK mapper 105 and the second 4-PSK mapper 106, respectively.

  The first 4-PSK mapper 105 and the second 4-PSK mapper 106 receive the output signal sequences from the first reverse sorter 103 and the second reverse sorter 104, respectively, and are complex values. Convert to

The first FH transmitter 107 and the second FH transmitter 108 receive the output signal sequences of the first 4-PSK mapper 105 and the second 4-PSK mapper 106, respectively, and transmit one transmission symbol. Hop each time, and transmit from the first transmission antenna and the second transmission antenna, respectively.
Specifically, the first FH transmitter 107 and the second FH transmitter 108 sequentially hop each symbol at frequencies of f0, f3, f1, f2, f0, f3, f1, and f2, respectively. .

  Signals output from the first transmission antenna and the second transmission antenna reach the receiver 20 via the transmission path 30. In this embodiment, it is assumed that the transmission path characteristics are steady in each signal frame. Here, the term “steady in each signal frame” indicates an environment in which each symbol has no time variation in each signal frame. Further, there may be a frequency variation in each symbol within each signal frame.

  On the other hand, the FH receiver 201 receives a signal that has passed through the transmission path 30 with one receiving antenna and converts it into a baseband symbol.

The second rearranger 202 rearranges the baseband symbols that are the output symbols of the FH receiver 201 in the order in which the first rearranger 101 rearranges the input to the output. In other words, the rearrangement rule needs to be shared in advance by the transmitter 10 and the receiver 20.
Specifically, this rearrangement is based on baseband symbols,
Y (0), Y (1), Y (2), Y (3), Y (4), Y (5), Y (6), Y (7)
Then, according to the example of the first sorter 101 in the above example, the second sorter 202 converts the baseband symbol into
Y (0), Y (4), Y (2), Y (6), Y (3), Y (7), Y (1), Y (5),
Sort by.

The STTC decoder 203 performs decoding on the output signal sequence of the second rearranger 202. The STTC decoder 203 performs decoding by searching for a symbol sequence that minimizes the next evaluation value using the Viterbi algorithm.
| Y (n) −α1 q (1, n) −α2 q (2, n) | ²
However,
n = 1, 2,..., 7,
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,
q (1, n): candidate for the n-th transmission symbol of the first transmission antenna,
q (2, n): candidate for the nth transmission symbol of the second transmission antenna,
It is. The transmission path estimator 204 estimates α1 and α2 based on the signal received by the receiver 20. That is, the transmission signal from the transmitter 10 is multiplexed with a pilot signal separately from the information symbol, the receiver 20 receives the pilot signal, and the transmission path estimator 204 performs transmission path estimation. α1 and α2 are accurately detected.

A third reverse rearranger 205 rearranges the output of the STTC decoder 203 to obtain a reproduced symbol. Specifically, the output symbol of the STTC decoder 203 is
y (0), y (4), y (2), y (6), y (3), y (7), y (1), y (5)
Then, the third reverse sorter 205 is
y (0), y (1), y (2), y (3), y (4), y (5), y (6), y (7)
This is a one-frame playback symbol.

  In general, STTC is designed on the assumption that the transmission path characteristics are constant within a frame. Therefore, when frequency hopping transmission is performed in an environment where the transmission path characteristics have frequency selectivity, each transmission symbol has a variety of transmission symbols. Since the signal passes through a frequency transmission line, transmission is performed in a situation where the transmission line characteristic is not constant within the frame. If the transmission path characteristics have frequency selectivity, it can be assumed that the transmission path characteristics are likely to be relatively similar at nearby frequencies and are likely to be different at distant frequencies.

  Therefore, in the present embodiment, the symbol sequence to be frequency hopped is rearranged in advance in the order in which the frequency change is small in the STTC coding input, so that the change in the transmission path characteristics is small in the frame. After STTC encoding, the symbols are rearranged in the order of the original symbol strings. By this operation, each transmission symbol is transmitted in a state where the transmission path characteristics are almost constant in the frame, so that it is possible to avoid a problem in frequency hopping transmission of a normal STTC encoded symbol.

  The STTC modulation method is not limited to 4-PSK, but can be expanded to 8-PSK, 16-QAM (Quadrature Amplitude Modulation), 64-QAM, etc. The number of states is not limited to 4, and A number of states STTC can be used. Further, the number of transmission antennas is not limited to two, and the number of reception antennas is not limited to one. Of course, the frame length is not limited to 8 symbols, and the FH pattern is arbitrary.

Specifically, an example in which the frame length is 8 symbols and 8 types of frequencies are used will be described with reference to FIG. 8 transmit symbols,
x (0), x (1), x (2), x (3), x (4), x (5), x (6), x (7)
As one transmission frame, and each symbol has eight different frequencies,
f0, f1, f2, f3, f4, f5, f6, f7
Next, a description will be given based on an example of transmission by frequency hopping. However, it is assumed that f0 <f1 <f2 <f3 <f4 <f5 <f6 <f7. In the example shown in FIG. 2 (A), the hopping pattern has a frequency for each symbol,
f0, f5, f2, f4, f7, f1, f3, f6,
An example of hopping pattern is shown below. Then, the first reordering unit 101 divides the eight transmission symbol sequences so that the frequency change of the input to the STTC encoder 102 becomes smooth.
x (0), x (5), x (2), x (4), x (7), x (1), x (3), x (6)
Rearrange so that it is converted in the order of.

Further, FH transmission can be realized using a frequency synthesizer, or can be realized using an inverse discrete Fourier transformer (IDFT).
For example, when x (0), x (1), x (2), and x (3) are hopped to f0, f3, f1, and f2, four IDFT input points are represented by u (0), u (1), u (2), u (3)
In the first IDFT process, u (0) = x (0), the other input points are no input,
In the second IDFT process, u (3) = x (1), other input points are no input,
In the third IDFT process, u (1) = x (2), other input points are no input,
In the fourth IDFT process, u (2) = x (3), the other input points are no input,
In this way, FH transmission can be realized by four IDFT processes. In this case, FH reception can be realized using a discrete Fourier transformer (DFT).

  Here, a computer simulation result for verifying the effect of the present embodiment will be described with reference to FIGS. 4, 5, 6, and 7. In the simulation, hopping transmission using 13 frequencies from f1 to f13 is transmitted for each symbol, a signal is input to one of 16 IDFT inputs, and transmission symbols are sequentially transmitted. Realized by receiving with DFT. A guard section (T) corresponding to 50% of the IDFT / DFT window section is set.

  FIG. 4 shows a symbol structure when transmission symbols are transmitted. One frame is made up of 130 symbols. In one frame, a unit in which 13 symbols are transmitted at any one of 13 frequencies from f1 to f13 is repeated 10 times.

  FIG. 5 shows a symbol structure immediately before the STTC decoder 203 performs STTC decoding on the received symbol sequence. That is, the symbol structure shown in FIG. 5 is such that the second rearranger 202 rearranges the order of the symbols, first 10 symbols that pass through f1, and then 10 symbols that pass through f2. Are arranged in the order of consecutive frequencies, and the influence of frequency changes is reduced.

Next, simulation results are shown in FIGS. This simulation uses 4-TCK, 4-state STTC with a frame length of 130 symbols. Further, the transmission path model is a two-wave Gaussian distribution variation model in which the side wave level is 3 dB smaller than the main wave in Case 1 shown in FIG. 6, and the main wave and the side wave are 2 in Case 2 shown in FIG. It is a wave Gaussian distribution fluctuation model. In addition, the time interval between the main wave and the sub wave varies in a uniform distribution within the range of the guard interval T.
FIGS. 6 and 7 are respectively the case of Case 1 and Case 2, respectively, the proposed method (Proposed) for rearranging the symbol order described in the present embodiment and the conventional method (Conventional) for not rearranging the symbol order. The frame error probability is shown. In the case of Case 1 in FIG. 6, the wireless communication system of the present embodiment has a signal-to-noise ratio (SNR) of the transmission line ranging from 15 dB to 27 dB which is the entire range shown in FIG. 6. Is effective. On the other hand, in the case of Case 2 in FIG. 7, it can be seen that the wireless communication system of the present embodiment is effective when the SNR of the transmission path is in the range from 21 dB to 27 dB. In any case, it can be seen that the wireless communication system of the present embodiment is particularly effective in an environment where the SNR of the transmission path is 24 dB to 27 dB.

(Modification 1) In the above example, the first rearranger 101 rearranges the transmission symbol sequence on the assumption that there is no temporal variation in transmission path characteristics within one transmission frame. When it is assumed that there is a time variation in the transmission path characteristics within the frame, the transmission symbol sequence is rearranged in a range where it is assumed that there is no time fluctuation in the transmission path characteristics. For example, assuming that the transmission path characteristics are different between the first 4 symbols and the latter 4 symbols in one transmission frame, eight transmission symbol sequences of one transmission frame are
x (0), x (1), x (2), x (3), x (4), x (5), x (6), x (7)
The first sorter 101 is, for example,
x (1), x (3), x (2), x (0), x (4), x (6), x (7), x (5)
Or
x (0), x (2), x (3), x (1), x (5), x (7), x (6), x (4)
The transmission symbol sequence is rearranged as follows. The former is a rearrangement that places importance on resistance to frequency fluctuations, and the latter is a rearrangement that places importance on resistance to time fluctuations.

(Modification 2) When the transmitter 10 can know the outline of the transmission path characteristics from the transmitter 10 to the receiver 20, the transmitter 10 and the receiver 20 according to the frequency fluctuation and time fluctuation of the transmission path characteristics. Adaptive control is possible.
Specifically, when there is almost no frequency fluctuation in the transmission line, rearrangement is unnecessary regardless of whether there is time fluctuation, the first rearranger 101 does not process anything, and the STTC encoder 102 x (0), x (1), x (2), x (3), x (4), x (5), x (6), x (7),
In contrast, STTC encoding is performed. When there is a frequency variation in the transmission path, the rearrangement is controlled according to the magnitude of the time variation.
When there is almost no time variation in the transmission path, the first rearranger 101 performs x (0), x (4), x (2), x (6), x ( 3), x (7), x (1), x (5),
The STTC encoder 102 performs STTC encoding after rearranging in this order. When there is a time variation in the transmission path, the first rearranger 101 performs rearrangement as shown in the first modification, and the STTC encoder 102
x (1), x (3), x (2), x (0), x (4), x (6), x (7), x (5)
Or
x (0), x (2), x (3), x (1), x (5), x (7), x (6), x (4)
In contrast, STTC encoding is performed.

In addition, when there is a notch only in a specific frequency part, the first rearranger 101 rearranges the transmission symbols into a frequency part with a notch and a frequency part without a notch, respectively, and then The STTC encoder 102 performs STTC encoding. Specifically, for example, in the case of a characteristic in which there is a notch only in the frequency portion of f2, the symbols x (3) and x (7) that the first rearranger 101 hops at the frequency of f2 Except
x (0), x (1), x (2), x (4), x (5), x (6), x (3), x (7),
As described above, the STTC encoder 102 performs STTC encoding by rearranging the symbols after dividing them into symbols that pass frequencies other than f2 and symbols that pass frequencies of f2.

  In order to perform control according to such transmission path characteristics, the transmitter 10 needs to grasp the transmission path characteristics. In the case of TDD (Time Division Duplex) in which bidirectional transmission between the transmitter 10 and the receiver 20 is performed in a time division manner in the same frequency band, the transmission path characteristic is estimated from the received signal received by the transmitter 10. If a transmission path estimator (not shown) is provided, the transmitter 10 can grasp the transmission path characteristics. Further, the transmitter 10 may be notified of the channel characteristics estimated by the channel estimator 204 from the receiver 20, and the transmitter 10 may use the channel 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 10 is notified of the transmission path characteristics from the receiver 20 which is the communication partner of the transmitter 10. The transmission path characteristics can be grasped. In this case, the receiver 20 obtains transmission path characteristics by the transmission path estimator 204. TDD and FDD will be described with reference to FIG. 24 in a later eighth embodiment.

  According to the radio communication system of the present embodiment as described above, the influence of transmission path fluctuations occurs when a signal encoded by a space-time trellis code is decoded by rearranging a transmission symbol sequence to a transmission symbol having a frequency to be transmitted. Can be reduced.

(Second Embodiment)
The radio communication system according to the present embodiment is applied to multicarrier transmission such as OFDM (Orthogonal Frequency Division Multiplexing) instead of the frequency hopping transmission described in the first embodiment. As shown in FIG. 8, the wireless communication system according to the present embodiment includes a transmitter 11 and a receiver 21, and the transmitter 11 has a first FH transmission as compared with the transmitter 10 according to the first embodiment. The only difference is that a first IDFT (Inverse Discrete Fourier Transformer) (IDFT) 111 and a second IDFT 112 instead of the second FH transmitter 108 are provided in place of the device 107. The receiver 21 includes a Discrete Fourier Transformer (DFT) 211 instead of the FH receiver 201 as compared with the receiver 20 of the first embodiment due to the change of the transmitter 11. Only that is different.
The first IDFT 111 and the second IDFT 112 input the output signal sequences of the first 4-PSK mapper 105 and the second 4-PSK mapper 106, respectively, multiplex the signals on the frequency axis and time Convert to an on-axis signal and send it.
The DFT 211 separates the received signal on the time axis into a signal on the frequency axis, and outputs the signal to the second rearranger 202.
For example, when one frame is composed of eight symbols and eight symbols are processed every four symbols as shown in FIG. 9A, the first IDFT 111 and the second IDFT 112 having four inputs and four outputs. Performs the IDFT operation twice, and the 4-input 4-output DFT 211 performs the DFT operation twice. Further, in this case, for example, in the case of frequency characteristics having a notch only in the frequency portion of f3, the STTC encoder 102
x (0), x (1), x (2), x (4), x (5), x (6), x (3), x (7)
As shown, the symbols passing through frequencies other than f3 (x (0), x (1), x (2), x (4), x (5), x (6))) and the frequency of f3 are passed. The STTC encoding is performed by rearranging the symbols into the symbols (x (3), x (7)) to be performed.

In addition, when one frame is composed of 8 symbols and 8 symbols are collectively processed as shown in FIG. 9B, the 8-input 8-output first IDFT 111 and the second IDFT 112 are IDFT. The calculation is performed once, and the 8-input 8-output DFT 211 performs the DFT calculation once. Also, in this case, for example, in the case where there is a notch in the frequency part of f4 and f5, the STTC encoder 102
x (0), x (1), x (2), x (3), x (6), x (7), x (4), x (5)
As described above, STTC encoding is performed by rearranging symbols that pass through frequencies other than f4 and f5 and symbols that pass through frequencies f4 and f5.

  According to the wireless communication system of the present embodiment described above, even in OFDM transmission, when a signal encoded by a space-time trellis code is decoded by rearranging a transmission symbol sequence to a transmission symbol having a frequency close to that of transmission. The influence of transmission path fluctuations can be reduced.

(Third embodiment)
The radio communication system according to the present embodiment is applied to a system that combines not only the frequency hopping transmission described in the first embodiment but also the OFDM (Orthogonal Frequency Division Multiplexing) transmission. As shown in FIG. 10, the wireless communication system according to the present embodiment includes a transmitter 12 and a receiver 22, and both the transmitter 12 and the receiver 22 are a combination of the first embodiment and the second embodiment. It is. That is, the first IDFT 111 is added between the first 4-PSK mapper 105 and the first FH transmitter 107 of the transmitter 10 of the first embodiment, and the second 4-PSK mapper 106 and the first FPS transmitter 107 are added. The transmitter 12 of this embodiment is obtained by adding the second IDFT 112 between the two FH transmitters 108, and the FH receiver 201 and the second rearranger 202 of the receiver 20 of the first embodiment. The receiver 22 of this embodiment is obtained by adding the DFT 211 between them.

The first IDFT 111 and the second IDFT 112 input the output signal sequences of the first 4-PSK mapper 105 and the second 4-PSK mapper 106, respectively, multiplex the signals on the frequency axis and time Convert to an on-axis signal. Then, the first FH transmitter 107 and the second FH transmitter 108 input the changed transmission symbol sequences, hop each of the transmission symbol sequences, and transmit from the first transmission antenna and the second transmission antenna, respectively. .
Specifically, for example, one frame is composed of 16 symbols of x (0), x (1),..., X (14), x (15), and is transmitted at 16 frequencies from f0 to f15. When four-point IDFT and DFT are used, as shown in FIG. 11, every four symbols are input to the first IDFT 111 and the second IDFT 112, and frequency hopping is performed for each output block of these IDFTs. In the case of performing hopping as shown in FIG. 11, prior to STTC encoding, the first rearranger 101 performs x (0), x (1), x (2), x (3), x (8), x (9), x (10), x (11), x (12), x (13), x (14), x (15), x (4), x (5), x (6), x (7)
Sort as follows. Therefore, the frequency change becomes gradual, and the influence of transmission path fluctuation can be reduced when a signal encoded by a space-time trellis code is decoded. Similarly to the above-described embodiment, when there is a notch at a specific frequency, rearrangement that separates the notch frequency portion from the other portions is performed. Further, in this case, the first FH transmitter 107 and the second FH transmitter 108 set the frequency to be hopped to the center frequency of each 4 symbols and hop every 4 symbols. That is, the first FH transmitter 107 and the second FH transmitter 108 are center values of f0, f1, f2, and f3, center values of f8, f9, f10, and f11, and center values of f12, f13, f14, and f15. , F4, f5, f6, f7.

  According to the wireless communication system of the present embodiment described above, a signal encoded by a space-time trellis code can be obtained by rearranging a transmission symbol sequence to a transmission symbol having a frequency close to that even in transmission using a combination of OFDM and FH. When decoding, it is possible to reduce the influence of transmission path fluctuations.

(Fourth embodiment)
As shown in FIG. 12, the wireless communication system of 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 wireless communication system of the present embodiment, the transmission symbol sequence is transmitted by changing the encoding scheme in the STTC encoder 131, and the STTC decoder 231 converts the transmission symbol sequence in a decoding scheme corresponding to this encoding scheme. Decrypted to obtain received data. 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. 13 (A), 13 (B), and 13 (C).
As shown in FIG. 13A, 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. 13A, when the contents of the registers 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, 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. 13C, 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. 14 (A), 14 (B), and 14 (C).
As shown in FIG. 14A, 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. 14A, 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, 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.
In the 8-PSK, 8-state STTC encoder 131_pa2, state transitions that can be taken by the nth to n + 3 symbols will be described with reference to FIG. 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 will be compared with reference to FIG. 13C and FIG. 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. 13C (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 state 1 in FIG. 13C is limited to states 4, 5, 6, and 7. On the other hand, in FIG. 14C (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. 14C, the transition destination from state 1 is allowed to transition to all states from 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. 13C) is more than the state transition in the case of 8-PSK, 8-state (FIG. 14C). Strong error tolerance. 13B and 14C), the distance between signal points is smaller in the case of 8-PSK than in the case of 4-PSK. -PSK has higher error tolerance.
Further, in terms of the number of bits transmitted per symbol, that is, transmission efficiency, 8-PSK (FIG. 14A) is 3, while 4-PSK (FIG. 13) 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. 15 (A) and 15 (B). FIG. 15A 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 illustrated in FIGS. It has.

As shown in FIG. 15, the STTC encoder 131 corresponds to 4-PSK, 8-state in FIG. 13 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, 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. 15B, in the state transition from the nth to the (n + 3) th symbol, the nth symbol is 8-PSK, 8-state, the n + 1th 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. 16, 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. 16, 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. 15B, 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.

(Fifth embodiment)
Unlike the case where the number of states in the fourth embodiment is the same (the number of states is 8), the wireless communication system of the present 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 fourth embodiment except that what is 4-PSK, 8 state in the fourth embodiment changes to 4-PSK, 4-state. A description of the same components as those in the fourth embodiment will be omitted.
In the wireless communication system of the present embodiment, the transmission symbol sequence is transmitted by changing the encoding scheme in the STTC encoder 131, and the STTC decoder 231 converts the transmission symbol sequence in a decoding scheme corresponding to this encoding scheme. Decrypted to obtain received data. 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, a 4-state STTC encoder 131_pa3 for 4-PSK will be described with reference to FIGS. 17 (A) and 17 (B).
As shown in FIG. 17A, 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. 13A, when the register contents 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. 17B, in this case, the state transitions that can be taken by 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 with reference to FIGS. 14A, 14B, and 14C in the fourth embodiment. It is the same.

  When 4-PSK and 8-state in the fourth embodiment are compared with 4-PSK and 4-state in this 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, with reference to FIG. 18A and FIG. 18B, the STTC encoder 131 of the wireless communication system of the present embodiment will be described. FIG. 18A 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 converter and the register shown in FIGS. 17A and 14A.

In the STTC encoder 131, as shown in FIG. 18A, 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. 18B, 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.

(Sixth embodiment)
Unlike the combination of 8-PSK and 4-PSK as in the fourth and fifth 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 fourth embodiment except that the 8-PSK and 8-state in the fourth embodiment are changed to 4-PSK and 4-state. A description of the same components as those in the fourth embodiment will be omitted.
In the wireless communication system of the present embodiment, the transmission symbol sequence is transmitted by changing the encoding scheme in the STTC encoder 131, and the STTC decoder 231 converts the transmission symbol sequence in a decoding scheme corresponding to this encoding scheme. Decrypted to obtain received data. 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. 13A, 13B, and 13C in the fourth embodiment. is there. On the other hand, the STTC encoder in the case of 4-PSK and 4-state is the same as that described with reference to FIGS. 17A, 17B, and 17C in the fifth embodiment. It is the same.

Next, the STTC encoder 131 of the wireless communication system of this embodiment will be described with reference to FIGS. 19 (A) and 19 (B). FIG. 19A 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. 17A and 13A. .

In the STTC encoder 131, as shown in FIG. 19A, 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. Map with.
A control unit (not shown) gives an instruction to switch each switch to switches 1324, 1325, and 1326.

  As shown in FIG. 19B, 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. 20A shows a state transition when these 64-QAM (Quadrature Amplitude Modulation), 64-state, and 4-PSK, 64-state are combined. In FIG. 20A, since there are 64 transition states, details of the state transition are omitted. According to the state transition shown in FIG. 20A, 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. 20B shows the state transition when these 64-QAM and 64-state are combined with 4-PSK and 16-state. Also in FIG. 20B, since there are 64 transition states as in FIG. 20A, details of the state transition are omitted. According to the state transition shown in FIG. 20B, 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 comparing FIG. 20A and FIG. 20B, it can be said that the method shown in FIG. 20B is more appropriate from the viewpoint of the amount of calculation.

(Seventh 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. 21A, the wireless communication system according to the present embodiment includes a transmitter 14 and a receiver 24. The transmitter 14 includes a 16-state STTC encoder 141 and 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. 21B, 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. However, as shown by the frequency characteristics of the transmission path in FIG. 21B, 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. 21A, α1, α2, β1, and β2 vary with a Gaussian distribution for each IDFT output block, and η varies with 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. 22 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. 22 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. 22, 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.

(Eighth 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. 15A, 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 this embodiment, for example, in FIG. 15A, the first transmission output and the second transmission output are transmitted from the same single transmission antenna by 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. 23, 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. 23, black circles indicate switch ON and white circles indicate switch OFF. For example, FIG. 23 shows a case where s ₁ is turned on and s ₂ and s ₃ are turned off. In this case, the fourth 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 method for detecting a transmission path state 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. 23, 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. 25 (A), they are shown in FIG. 25 (B) and FIG. 25 (C). 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. 25 (B) and 25 (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 fourth embodiment to the seventh 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. 15A, 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. 26, the switches s ₁ and s ₂ are controlled according to the transmission path estimator 150. In FIG. 26, as in FIG. 23, black circles indicate switch ON and white circles indicate switch OFF. For example, FIG. 26 shows a case where s ₁ is turned on and s ₂ is turned off. In this case, as described in the fourth embodiment described 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 expressed as 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 first 4-PSK transmission output and the second 4-PSK transmission output is added to the 16-QAM form by adding the two-amplitude conditions. Can do. Further, the transmission band in this case is the same as that from the fourth embodiment to the seventh embodiment. Furthermore, the transmission power in this case is the total power of the first transmission antenna and the second transmission antenna in the fourth to seventh 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 sequence 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 fourth embodiment to the seventh embodiment, and the transmission path 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. 23 or FIG. 26, 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. 26, the 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 the figure which showed the example which FH transmits to 4 types of different frequencies, and (B) is the figure which transmits 8 transmission symbols by FH to 8 types of different frequencies. The figure which showed the example. (A) is a figure which shows the state transition in 4-state STTC encoding of 4-PSK, (B) is a figure which shows the signal point of the mapping of 4-PSK, (C) is the STTC code of FIG. The block diagram which shows an example of a generator. The figure which shows the symbol structure at the time of transmission of a transmission symbol by computer simulation. The figure which shows the symbol structure just before carrying out STTC decoding of the received symbol row | line | column by computer simulation. The figure which shows the computer simulation result in the Gaussian distribution fluctuation model of 2 waves whose level of a subwave is 3 dB smaller than a main wave. The figure which shows the computer simulation result in the Gaussian distribution fluctuation | variation model of two waves with the same level of a main wave and a subwave. The block diagram of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. (A) is a figure in case IDFT processes 8 symbols every 4 symbols, (B) is a figure in case IDFT processes 8 symbols collectively. The block diagram of the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. The figure in the case of inputting into 1st IDFT and 2nd IDFT for every 4 symbols, and performing frequency hopping for every output block of these IDFT. The block diagram of the radio | wireless communications system which concerns on the 4th Embodiment of this 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. 13 (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 of the fourth embodiment, and (B) shows state transitions that can be taken by the nth to n + 3 symbols by the encoder of FIG. 15 (A). Figure. The block diagram of the STTC decoder of FIG. 12, and the figure which showed the transmission-line 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. 17 (A). FIG. (A) is a block diagram of the STTC encoder of the fifth embodiment, and (B) shows state transitions that can be taken by the nth to n + 3 symbols by the encoder of FIG. 18 (A). Figure. (A) is a block diagram of the STTC encoder of the sixth embodiment, and (B) shows state transitions that can be taken by the nth to n + 3 symbols by the encoder of FIG. 19 (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 7th 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 7th Embodiment. The block diagram of the transmitter used with the radio | wireless communications system of 8th Embodiment. The figure explaining acquisition of the transmission line characteristic in each case of FDD ((A) of Drawing 24) and TDD ((B) of Drawing 24). (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 8th Embodiment.

Explanation of symbols

10, 11, 12, 13, 14 ... transmitter, 20, 21, 22, 23, 24 ... receiver, 30, 31, 32 ... transmission path, 101 ... first reordering , 102, 131, 131_pa1, 131_pa2, 131_pa3, STTC encoder, 103, first reverse rearranger, 104, second reverse rearranger, 105, first. 4-PSK mapper, 106 ... second 4-PSK mapper, 107 ... first FH transmitter, 108 ... second FH transmitter, 134 ... mapper, 141 16-state STTC encoder, 142, 143, 242 ... S / P converter, 146, 147, 244 ... P / S converter, 148, 149 ... guard interval adding unit, 201 ..FH receivers 202 ... 2, 203, 231... STTC decoder, 204, 232... Transmission path estimator, 205, third reverse rearranger, 241, guard interval removal unit, 245. .. 16-state STTC decoder, 1311, 1312, 1313, 1318, 1322, 1323 ... adder, 1314, 1315, 1316, 1317, 1319, 1320, 1321, 1324, 1325, 1326 ... switch, 2311 ... Transmission symbol candidate output unit, 2312 ... Viterbi calculator, 2313 ... Switch control unit

Claims (12)

In a wireless communication system comprising a transmitter for space-time encoding and transmitting a frame including a plurality of symbols, and a receiver for receiving the frame via a transmission path and space-time decoding,
The transmitter is
Input means for inputting the frame;
First rearranging means for rearranging the plurality of symbols in the frame so that the plurality of symbols passing through transmission lines having similar characteristics are arranged at positions in the vicinity of the frame;
Encoding means for encoding the rearranged frames;
First reverse rearranging means for returning the plurality of symbols before being rearranged;
Transmission means for transmitting a frame composed of the rearranged symbols,
The receiver
Receiving means for receiving the transmitted frame;
Estimating means for estimating transmission path characteristics based on the received frame;
A second rearrangement unit that rearranges the plurality of symbols in the received frame in the same manner as the first rearrangement unit;
Decoding means for decoding the rearranged frames with reference to the transmission path characteristics;
A wireless communication system, comprising: a second reverse rearrangement unit that rearranges the plurality of symbols in the decoded frame in the same manner as the first reverse rearrangement unit.   The first rearrangement means is within a time interval in which the fluctuation of the transmission path characteristics depending on time is assumed to be small, or in a frequency section in which the fluctuation of the transmission path characteristics depending on the frequency is assumed to be small. 2. The radio communication system according to claim 1, wherein symbols in the frame are rearranged so that symbols arranged in the vicinity in the frame including the rearranged symbols have similar transmission path characteristics. . The transmitter further comprises acquisition means for acquiring transmission path characteristics of a frame transmitted by the transmission means,
The first rearranging means acquires the time interval in which the fluctuation of the channel characteristic depending on time is assumed to be small and the frequency period in which the fluctuation of the channel characteristic depending on the frequency is assumed to be small. The wireless communication system according to claim 2, wherein the determination is made according to transmission path characteristics.   The first rearrangement means has a transmission frequency in which symbols arranged in the vicinity in the rearranged frames are close to each other within a time interval in which fluctuations in transmission path characteristics depending on time are assumed to be small. The wireless communication system according to claim 1, wherein rearrangement is performed as follows. The transmitter further comprises acquisition means for acquiring transmission path characteristics of a frame transmitted by the transmission means,
5. The radio according to claim 4, wherein the first rearranging unit determines a time interval in which a fluctuation in transmission path characteristics depending on time is assumed to be small according to the acquired transmission path characteristics. Communications system. In a wireless communication system comprising a transmitter for space-time encoding and transmitting a frame including a plurality of symbols, and a receiver for receiving the frame via a transmission path and 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;
Radio communication comprising decoding means for decoding the received frame in accordance with a decoding method switched in synchronization with switching of an encoding method encoded by the encoding means and the transmission path characteristics system. 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 wireless communication system according to claim 6, 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 wireless communication system according to any one of claims 1 to 7, wherein the decoding means performs decoding by a space-time trellis.   9. The radio communication system according to claim 1, wherein the transmission unit transmits the frame by any one of frequency hopping and multicarrier. 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 Claim 6-9 characterized by the above-mentioned. Wireless communication system.   The transmission means divides 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 radio communication system according to any one of claims 6 to 10, wherein transmission is performed by switching between different types of multiplexing systems.   The radio according to any one of claims 6 to 11, wherein the transmission means determines a multiplexing method to be used based on at least one of an allowable bandwidth and a transmission path characteristic. Communications system.

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