JP2006013610A - Wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication system for ensuring excellent transmission characteristics under a state of a broader transmission path. <P>SOLUTION: A wireless transmission apparatus comprises: a division means for dividing a transmission bit sequence into a plurality of bit sequences; a modulation means for modulating some bit sequences by a space division multiplex system, modulating the other bit sequences by a temporal space coding system, and modulating a plurality of the bit sequences by adjusting a distance between signal points modulated by the space division multiplex system and a distance between signal points modulated by the temporal space coding system; and a transmission means for summating the modulated signals by the space division multiplex system and the temporal space coding system and transmitting the summated signals. A wireless receiver comprises: a first demodulation means for demodulating the received signal on the basis of the space division multiplex system and the temporal space coding system; an estimate means for estimating an index for denoting a state of the transmission path on the basis of the received signal; an extract means for modulating the demodulated signal on the basis of the system used by the first demodulation means and extracting the received signal corresponding to the different system from the system on which the demodulated signal is based on the basis of the index; and a second demodulation means for demodulating the extracted received signal by the system different from the system adopted by the first demodulation means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless communication system, and more particularly, to a multiple-input multiple-output (MIMO) wireless communication system.

  In high bit rate wireless transmission, MIMO (Multiple-Input Multiple-Output) using a plurality of transmission / reception antennas is an effective method.

  MIMO transmission methods include space division multiplexing (SDM) (for example, see Non-Patent Document 1), which increases the transmission bit rate by simultaneously transmitting a plurality of information from a plurality of transmitting antennas, and a plurality of information. Space-Time Coding (STC: Space-Time Coding) (for example, see Non-Patent Document 2), which improves error tolerance of transmission bits by simultaneously transmitting information under the constraint conditions from the transmitting antennas of It is a technique.

  SDM is extremely effective for increasing the transmission rate, but the transmission characteristics depend on the transmission conditions. For example, when the correlation of the propagation path between antennas is high, or when the signal-to-noise ratio (SNR) is high. ) Is low, there is a drawback that the transmission performance is extremely lowered.

  On the other hand, the STC transmits transmission information from a plurality of transmission antennas with constraints, that is, transmission with redundancy, so that the transmission rate cannot be increased compared with the SDM. Even when the path correlation is high or the SNR is low, there is an advantage that transmission performance is hardly deteriorated. SDM and STC, which are typical transmission methods in such MIMO, have advantages and disadvantages, respectively, and there is a problem that the application range is limited.

In STC, the one based on the trellis coding method is called space-time trellis coding (STTC) (for example, see Non-Patent Document 3). STTC needs to be set according to a modulation scheme such as 4PSK (Phase-Shift Keying), 8PSK, 16QAM (Quadrature Amplitude Modulation), 64QAM, and 256QAM, and the performance improves as the number of trellis transition states increases. There is a problem that an increase in the number of state transitions to be considered leads to an increase in the amount of computation. For example, in the STPS for 4PSK, the state transitions to be considered are 16 for 4 states, 32 for 8 states, and 64 for 16 states. Further, in 16QAM STTC, it is 256 in 16 states.
A. van Zelst, R. van Nee, and GA Awater, `` Space Division Multiplexing (SDM) for OFDM System '', IEEE Proceeding of VTC-Spring 2000, pp. 6-10, 1998. D. Agrawal, V. Tarokh, A. Naguib, and N. Seshadri, `` Space-Time Coded OFDM for High Data-Rate Wireless Communication over Wideband Channels '', IEEE Proceeding of VTC '98, pp. 2232-2236, 1998. 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.

  SDM transmits multiple pieces of information from multiple transmitting antennas simultaneously without any constraints, so it is extremely effective in increasing the transmission bit rate. However, when the correlation of the propagation path between antennas is high, the signal-to-noise ratio Is low, the separation performance of the spatially multiplexed signal in the receiver deteriorates, so that the transmission rate is extremely lowered.

  On the other hand, since the STC transmits information simultaneously under a constraint condition from a plurality of transmission antennas, an increase in transmission rate error resistance cannot be expected, but there is an advantage that error tolerance of transmission bits can be increased. Thus, SDM and STC, which are typical transmission methods in MIMO, each have advantages and disadvantages, and there is a problem that the application range is limited.

  Furthermore, the conventional transmission method using STTC requires a space-time encoder / decoder according to the modulation scheme and the number of states, and the amount of computation increases as the number of modulation multi-values and the number of states increase. There is a problem.

The present invention provides a wireless communication system that ensures good transmission characteristics in a wide range of transmission path conditions in view of the prior art.
The present invention also provides a wireless communication system that simplifies the circuit in a transmission system that uses various space-time code systems for multilevel modulation in view of the prior art.

According to a radio communication system of the present invention, in a radio communication system including a radio transmitter that transmits signals from a plurality of antennas and a radio receiver that receives the transmitted signals by a plurality of antennas,
The wireless transmitter includes a dividing unit that divides a transmission bit string into a plurality of bit strings, and modulates some of the divided bit strings by a space division multiplexing method, and space-time coding other bit strings. And modulating the distance between the signal points of the modulated signal modulated by the space division multiplexing method and the distance between the signal points of the modulated signal modulated by the space-time coding method. Modulation means; and transmission means for adding and transmitting a modulation signal modulated by the space division multiplexing method and a modulation signal modulated by the space-time coding method,
The radio receiver indicates a first demodulation means for demodulating a received signal based on one of the space division multiplexing method and the space-time coding method, and indicates a transmission path condition from the received signal. An estimation unit that estimates an index, and a method in which the demodulated signal is modulated by a scheme used in the first demodulation unit, and a scheme different from the scheme of the demodulated signal from the received signal based on the index Extracting means for extracting a corresponding received signal, and second demodulating means for demodulating the extracted received signal in a system different from the system employed in the first demodulating means.

Further, according to the wireless communication system of the present invention, in the wireless communication system including a wireless transmitter that transmits signals from a plurality of antennas and a wireless receiver that receives the transmitted signals,
The wireless transmitter includes a dividing unit that divides a transmission bit string into a plurality of bit strings, a signal of a modulated signal that is encoded by the space-time encoding method and the plurality of divided bit strings are encoded by the space-time encoding method. Modulation means for modulating so that the distance between points is different, and transmission means for adding and transmitting a plurality of signals modulated by a space-time coding system,
The radio receiver is configured to demodulate a received signal based on the space-time coding method, an estimation unit that estimates an index indicating a transmission path condition from the received signal, and the demodulated signal. And extracting means for extracting the received signal different from the demodulated signal from the received signal based on the indicator, and modulating the received signal by the method used by the first demodulating means, And a second demodulating means for demodulating in a method corresponding to the above.

According to the wireless communication system of the present invention, good transmission characteristics can be ensured in a wide range of transmission path conditions.
Further, according to the wireless communication system of the present invention, the circuit can be simplified in a transmission system using various space-time code systems for multilevel modulation.

Hereinafter, a wireless communication system according to an embodiment of the present invention will be described in detail with reference to the drawings.
Hereinafter, a QAM (Quadrature Amplitude Modulation) signal transmission by a MIMO (Multiple-Input Multiple-Output) system using two transmitting antennas and two receiving antennas will be described in detail.

First, before describing each embodiment, a QAM signal will be briefly described. There are the following four types of representative QAM signals.
4QAM: 2 bits (a ₀ , a ₁ ) are mapped to signal points on 4 types of complex space 16QAM: 4 bits (a ₀ , a ₁ , b ₀ , b ₁ ) are mapped on 16 types of complex spaces Map to signal point
64QAM: 6 bits (a ₀ , a ₁ , b ₀ , b ₁ , c ₀ , c ₁ ) are mapped to signal points on 64 types of complex space
256QAM: 8 bits (a ₀ , a ₁ , b ₀ , b ₁ , c ₀ , c ₁ , d ₀ , d ₁ ) are mapped to signal points on 256 types of complex space
However, a ₀ , a ₁ , b ₀ , b ₁ , c ₀ , c ₁ , d ₀ , d ₁ are bits having a value of 0 or 1, respectively.

[4QAM] 4QAM is the same as 4PSK (Phase-Shift Keying). That is, 4QAM determines the real and imaginary components of four types of signal points in any of the four quadrants distinguished by the real and imaginary axes in the complex space with 2 bits (a ₀ , a ₁ ). Is equivalent to 4PSK. More specifically, (a ₀ , a ₁ ) is the real component and imaginary component of the signal point,
A _r = ± 8, A _i = ± 8 j (hereinafter, j ² = −1)
These are the real component and imaginary component of the signal point of 4QAM.

[16QAM] 16QAM is a complex plane distinguished by (a ₀ , a ₁ ), and further determines the real component and imaginary component of four types of signal points with 2 bits (b ₀ , b ₁ ). It is. That is, (b ₀ , b ₁ ) represents the real component and imaginary component of the signal point respectively.
B _r = ± 4, B _i = ± 4j,
The real and imaginary components of the 16QAM signal point are
A _r + B _r = ± 12, ± 4,
A _i + B _i = ± 12j, ± 4j,
Can be displayed.

[64QAM] 64QAM is a complex plane distinguished by (a ₀ , a ₁ , b ₀ , b ₁ ), and further has 2 bits (c ₀ , c ₁ ) and real components of four kinds of signal points. The imaginary component is determined. That is, (c ₀ , c ₁ ) represents the real component and imaginary component of the signal point,
C _r = ± 2, C _i = ± 2j,
The real and imaginary components of the 64QAM signal point are
A _r + B _r + C _r = ± 14, ± 10, ± 6, ± 2,
A _i + B _i + C _i = ± 14j, ± 10j, ± 6j, ± 2j,
Can be displayed.

[256QAM] 256QAM is a complex number plane distinguished by (a ₀ , a ₁ , b ₀ , b ₁ , c ₀ , c ₁ ), and (D ₀ , d ₁ ) with 2 bits and 4 types of It determines the real and imaginary components of the signal point. That is, (d ₀ , d ₁ ) represents the real component and imaginary component of the signal point,
D _r = ± 1, D _i = ± 1j,
The real and imaginary components of the 256QAM signal points are
A _r + B _r + C _r + D _r = ± 15, ± 13, ± 11, ± 9, ± 7, ± 5, ± 3, ± 1,
A _i + B _i + C _i + D _i = ± 15j, ± 13j, ± 11j, ± 9j, ± 7j, ± 5j, ± 3j, ± 1j,
Can be displayed.

When the signal points of each QAM are displayed in this way, as shown in FIG. 2, the components of the complex signal are (A _r , A _i ), (B _r , B _i ), (C _r , C _i ), As is clear from the fact that the amplitude is halved in the order of (D _r , D _i ), the bits are (a ₀ , a ₁ ), (b ₀ , b ₁ ), (c ₀ , c ₁ ). , (D ₀ , d ₁ ) in the order of additional noise on the transmission path, it becomes easy for an error to occur in the reproduced bits in the radio receiver. That is, error tolerance is weakened.

(First embodiment)
The wireless communication system of this embodiment is an example in the case of 16QAM. That is, the real component and the imaginary component of the 16QAM signal point can be displayed as a 4PSK signal having a large amplitude A = (A _r , A _i ) and a 4PSK signal having a small amplitude B = (B _r , B _i ).
In this embodiment, (A _r , A _i ) is transmitted by SDM (Space Division Multiplexing) considering that error tolerance is strong, and (B _r , B _i ) is STC considering that error tolerance is weak. (Space-Time Coding) is used for transmission.

As shown in FIG. 1, the wireless communication system according to the present embodiment includes a wireless transmitter 10 and a wireless receiver 20. The wireless transmitter 10 includes a bit divider 101, a first 4PSK modulator 102, a 4PSK-STC modulator 103, a second 4PSK modulator 104, adders 105 and 106, a first transmitting antenna 107, a second A transmission antenna 108 is provided. The radio receiver 20 includes a first reception antenna 201, a second reception antenna 202, a transmission path estimator 203, a 4PSK-MLD demodulator 204, a third 4PSK modulator 205, a fourth 4PSK modulator 206, and an addition. 207, 208, subtracters 209, 210, 4PSK-STC demodulator 211, and bit synthesizer 212.
In this embodiment, the information bit string (transmission bit string) to be transmitted including information in the wireless transmitter 10 is 12 bits (x ₁ , x ₂ ,..., X ₁₂ ). However, x _i (i = 1, 2,..., 12) is 0 or 1.

The bit divider 101 receives a transmission bit string, divides the transmission bit string, and outputs it. In the present embodiment, a 12-bit string is divided into 4-bit strings and output to each modulator. Specifically, the bit divider 101 inputs 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) 2 bits at a time to the first 4PSK modulator 102. Similarly, the bit divider 101 inputs 4 bits (x ₅ , x ₆ , x ₇ , x ₈ ) 2 bits at a time to the second 4PSK modulator 104 and inputs 4 bits (x ₉ , x ₁₀ , x ₁₁ , x ₁₂ ) are input to the STPS modulator for 4PSK and the 4PSK-STC modulator 103 two bits at a time.

The first 4PSK modulator 102 modulates the received bit string and generates a 4PSK signal. Specifically, the first 4PSK modulator 102, from a bit string of 2 bits at each time t and time t + 1,
A ₁ (t) = ± 8 ± 8j, A ₁ (t + 1) = ± 8 ± 8j,
4PSK signals are generated.

Similarly to the first 4PSK modulator 102, the second 4PSK modulator 104 modulates the received bit string to generate a 4PSK signal. Specifically, the second 4PSK modulator 104, from a bit string of 2 bits at each time t and time t + 1,
A ₂ (t) = ± 8 ± 8j, A ₂ (t + 1) = ± 8 ± 8j,
4PSK signals are generated.

The 4PSK-STC modulator 103 modulates the received bit string and generates a 4PSK signal of the digital part 2 series. Specifically, the 4PSK-STC modulator 103 generates a first series of 4PSK signals from a 2-bit bit string at a certain time t and time t + 1,
B ₁ (t) = ± 4 ± 4j, B ₁ (t + 1) = ± 4 ± 4j,
And a second series of 4PSK signals,
B ₂ (t) = ± 4 ± 4j, B ₂ (t + 1) = ± 4 ± 4j,
Is generated. However,
B ₂ (t) = − B ₁ (t + 1) ^* , B ₂ (t + 1) = B ₁ (t) ^* ,
There is a relationship. Here, () ^* represents the complex conjugate of ().

This STC modulation is a method by Alamouti as an example.
SM Alamouti, `` A simple transmitter diversity technique for wireless communications '', IEEE Journal on Selected Areas in Communications, (JSAC), vol. 44, no. 10, pp. 1451-1458, Oct. 1998.
It is described in. In addition, it is not limited to this Alamouti technique, for example,
D. Agrawal, V. Tarokh, A. Naguib, and N. Seshadri, `` Space-Time Coded OFDM for High Data-Rate Wireless Communication over Wideband Channels '', IEEE Proceeding of VTC'98. Pp. 2232-2236, 1998.
May be applied.

The adder 105 adds the output of the first 4PSK modulator 102 and the output of the first series of the 4PSK-STC modulator 103 and outputs the added signal to the first transmission antenna 107. Specifically, the adder 105 outputs the _{A 1 (t) + B 1} (t), A 1 (t + 1) at time _{t + 1 + B 1 (t} + 1) a first transmitting antenna 107 at a certain time t. Then, the first transmitting antenna 107 transmits A ₁ (t) + B ₁ (t) at a certain time t, and A ₁ (t + 1) + B ₁ (t + 1) at a time t + 1.
The adder 106 adds the output of the second series of the 4PSK-STC modulator 103 and the output of the second 4PSK modulator 104 and outputs the added signal to the second transmission antenna 108. Specifically, the adder 106 outputs _A 2 at a certain time _{t (t) + B 2 (} t), with _A 2 time _{t + 1 (t + 1)} + B 2 a (t + 1) to the second transmitting antenna 108. Then, the second transmitting antenna 108 transmits A ₂ (t) + B ₂ (t) at a certain time t, and A ₂ (t + 1) + B ₂ (t + 1) at a time t + 1.
That is, the signals transmitted from the respective antennas at time t and time t + 1 are 16QAM signals in which a large-amplitude 4PSK signal and a small-amplitude 4PSK signal are combined.

The signal transmitted from the antenna is affected by noise, gain, and the like on the transmission path 30. The path gain from the first transmitting antenna 107 to the first receiving antenna 201 is h ₁₁ , the path gain from the first transmitting antenna 107 to the second receiving antenna 202 is h ₁₂ , and the second gain from the second transmitting antenna 108 is The path gain from one receiving antenna 201 to h ₂₁ and the path gain from the second transmitting antenna 108 to the second receiving antenna 202 are set to h ₂₂ , and these path gains are constant between times t and t + 1. Then, the input of the first receiving antenna 201 at time t is
u ₁ (t) = h ₁₁ (A ₁ (t) + B ₁ (t)) + h ₂₁ (A ₂ (t) + B ₂ (t)) + n ₁ (t),
The input of the second receiving antenna 202 at time t is
u ₂ (t) = h ₁₂ (A ₁ (t) + B ₁ (t)) + h ₂₂ (A ₂ (t) + B ₂ (t)) + n ₂ (t),
The input of the first receiving antenna 201 at time t + 1 is
u ₁ (t + 1) = h ₁₁ (A ₁ (t + 1) + B ₁ (t + 1)) + h ₂₁ (A ₂ (t + 1) + B ₂ (t + 1)) + n ₁ (t + 1),
The input of the second receiving antenna 202 at time t + 1 is
u ₂ (t + 1) = h ₁₂ (A ₁ (t + 1) + B ₁ (t + 1)) + h ₂₂ (A ₂ (t + 1) + B ₂ (t + 1)) + n ₂ (t + 1),
It is expressed. Note that n ₁ (t), n ₂ (t), n ₁ (t + 1), and n ₂ (t + 1) are mutually independent white Gaussian noises at times t, t, t + 1, and t + 1, respectively.

In the radio receiver 20, first, the received signals u ₁ (t), u ₂ (t), u ₁ (t + 1), and u ₂ (t + 1) are converted into A ₁ (t), A ₂ (t), A ₁ ( t + 1) and A ₂ (t + 1) are separated and reproduced, and then B ₁ (t) and B ₂ (t + 1) are separated and reproduced. Here, for convenience of the following description, the received signals u ₁ (t), u ₂ (t), u ₁ (t + 1), and u ₂ (t + 1) are expressed as follows.
u ₁ (t) = h ₁₁ A ₁ (t) + h ₂₁ A ₂ (t) + v ₁ (t), where v ₁ (t) = h ₁₁ B ₁ (t) + h ₂₁ B ₂ (t) + n ₁ (T),
u ₂ (t) = h ₁₂ A ₁ (t) + h ₂₂ A ₂ (t) + v ₂ (t), where v ₂ (t) = h ₁₂ B ₁ (t) + h ₂₂ B ₂ (t) + n ₂ (T),
u ₁ (t + 1) = h ₁₁ A ₁ (t + 1) + h ₂₁ A ₂ (t + 1) + v ₁ (t + 1), where v ₁ (t + 1) = h ₁₁ B ₁ (t + 1) + h ₂₁ B ₂ (t + 1) + n ₁ (T + 1),
u ₂ (t + 1) = h ₁₂ A ₁ (t + 1) + h ₂₂ A ₂ (t + 1) + v ₂ (t + 1), where v ₂ (t + 1) = h ₁₂ B ₁ (t + 1) + h ₂₂ B ₂ (t + 1) + n ₂ (T + 1).

The transmission path estimator 203 receives a received signal from each receiving antenna. In addition to the information signal, a pilot signal is multiplexed in the transmission signal from the wireless transmitter 10. The transmission path estimator 203 performs transmission path estimation based on this pilot signal, and estimates h ₁₁ , h ₁₂ , h ₂₁ , and h ₂₂ described above.

The 4PSK-MLD demodulator 204 performs demodulation based on maximum likelihood decoding (MLD) for the 4PSK signal. Details of MLD are described in, for example, the following documents.
A. van Zelst, R. van Nee, and GA Awater, `` Space Division Multiplexing (SDM) for OFDM System '', Proceeding of VTC-Spring 2000, pp. 6-10, 1998.
Since there are 16 possible transmission signals of A ₁ (t) and A ₂ (t), the 4PSK-MLD demodulator 204 sets these candidates as A ₁ (t) ′ and A ₂ (t) ′, respectively. , U ₁ (t) ′, u ₂ (t) ′ and candidates A ₁ (t) ′, A ₂ (t) ′ that minimize the difference between u ₁ (t), u ₂ (t) Estimated. here,
u ₁ (t) ′ = h ₁₁ A ₁ (t) ′ + h ₂₁ A ₂ (t) ′,
u ₂ (t) ′ = h ₁₂ A ₁ (t) ′ + h ₂₂ A ₂ (t) ′,
It is. In this way, the 4PSK-MLD demodulator 204 reproduces A ₁ (t) and A ₂ (t) to obtain bits.

The 4PSK-MLD demodulator 204 demodulates the transmission signals A ₁ (t + 1) and A ₂ (t + 1) in the same manner as in the case of A ₁ (t) and A ₂ (t). That is, since there are 16 possible transmission signals of A ₁ (t + 1) and A ₂ (t + 1), the 4PSK-MLD demodulator 204 designates these candidates as A ₁ (t + 1) ′ and A ₂ (t + 1) ′, respectively. The candidates A ₁ (t + 1) ′ and A ₂ (t + 1) ′ that minimize the difference between u ₁ (t + 1) ′ and u ₂ (t + 1) ′ and u ₁ (t + 1) and u ₂ (t + 1). Estimated as a transmission signal. here,
u ₁ (t + 1) ′ = h ₁₁ A ₁ (t + 1) ′ + h ₂₁ A ₂ (t + 1) ′,
u ₂ (t + 1) ′ = h ₁₂ A ₁ (t + 1) ′ + h ₂₂ A ₂ (t + 1) ′,
It is. In this way, the 4PSK-MLD demodulator 204 reproduces A ₁ (t + 1) and A ₂ (t + 1) to obtain bits.
As described above, the bits modulated by the first 4PSK modulator 102 and the second 4PSK modulator 104 can be obtained by the 4PSK-MLD demodulator 204.

Next, in order to obtain bits modulated by the 4PSK-STC modulator 103, the bits obtained by the 4PSK-MLD demodulator 204 are again modulated, and h ₁₁ , h ₁₂ , The transmission path 30 is reproduced by h ₂₁ and h ₂₂ , and A ₁ (t) and A ₂ (t), A ₁ (t + 1) and A ₂ (t + 1) through the transmission path 30 are calculated, and the first receiving antenna B ₁ (t) and B ₂ (t + 1) are obtained from the received signals received by 201 and the second receiving antenna 202 and demodulated to obtain the bits before being modulated by the 4PSK-STC modulator 103. be able to.

That is, the third 4PSK modulator 205 obtains A ₁ (t) and A ₁ (t + 1) based on the bits obtained by the 4PSK-MLD demodulator 204, and the fourth 4PSK modulator 206 performs 4PSK-MLD demodulation. A ₂ (t) and A ₂ (t + 1) are obtained based on the bits obtained by the unit 204. Using these A ₁ (t), A ₂ (t), A ₁ (t + 1), A ₂ (t + 1), and h ₁₁ , h ₁₂ , h ₂₁ , h ₂₂ obtained by the transmission path estimator 203 Considering the gain assumed to have been received on the transmission path 30, the adder 207, 208 calculates a signal assumed to be received by the wireless receiver 20.

Then, by subtracting the signal calculated by the transmission model from the reception signal from the first reception antenna 201 by the subtracter 209, the above-described v ₁ (t), v ₂ (t), v ₁ (t + 1), v ₂ (t + 1) is obtained. That is,
_{v 1 (t) = u 1} (t) -h 11 A 1 (t) -h 21 A 2 (t)
= H ₁₁ B ₁ (t) + h ₂₁ B ₂ (t) + n ₁ (t)
_{= H 11 B 1 (t)} -h 21 B 1 (t + 1) * + n 1 (t),
_{v 2 (t) = u 2} (t) -h 12 A 1 (t) -h 22 A 2 (t)
= H ₁₂ B ₁ (t) + h ₂₂ B ₂ (t) + n ₂ (t)
_{= H 12 B 1 (t)} -h 22 B 1 (t + 1) * + n 2 (t),
v ₁ (t + 1) = u ₁ (t + 1) −h ₁₁ A ₁ (t + 1) −h ₂₁ A ₂ (t + 1)
= H ₁₁ B ₁ (t + 1) + h ₂₁ B ₂ (t + 1) + n ₁ (t + 1)
= H ₁₁ B ₁ (t + 1) + h ₂₁ B ₁ (t) ^* + n ₁ (t + 1),
_{v 2 (t + 1) =} u 2 (t + 1) -h 12 A 1 (t + 1) -h 22 A 2 (t + 1)
= H ₁₂ B ₁ (t + 1) + h ₂₂ B ₂ (t + 1) + n ₂ (t + 1)
= H ₁₂ B ₁ (t + 1) + h ₂₂ B ₁ (t) ^* + n ₂ (t + 1),
Get.

The 4PSK-STC demodulator 211 reproduces B ₁ (t) and B ₂ (t + 1) based on the obtained v ₁ (t), v ₂ (t), v ₁ (t + 1), and v ₂ (t + 1). Bits modulated by the 4PSK-STC modulator 103 can be obtained.
The 4PSK-STC demodulator 211 performs the following calculation on v ₁ (t), v ₂ (t), v ₁ (t + 1), and v ₂ (t + 1).

w ₁ (t) = h ₁₁ ^* v ₁ (t) + h ₂₁ v ₁ (t + 1) ^{*
_{= H 11 * h 11 B 1}} (t) -h 11 * h 21 B 1 (t + 1) * + h 11 * n 1 (t)
+ H ₂₁ h ₁₁ ^* B ₁ (t + 1) ^* + h ₂₁ h ₂₁ ^* B ₁ (t) + h ₂₁ n ₁ (t + 1) ^{*
_{= H 11 * h 11 B 1}} (t) + h 21 * h 21 B 1 (t) + h 11 * n 1 (t) + h 21 n 1 (t + 1) *,
w ₁ (t + 1) ^* = − h ₂₁ ^* v ₁ (t) + h ₁₁ v ₁ (t + 1) ^{*
_{= -H 21 * h 11 B 1}} (t) + h 21 * h 21 B 1 (t + 1) * -h 21 * n 1 (t) + h 11 h 11 * B 1 (t + 1) * + h 11 h 21 * B 1 (T) + h ₁₁ n ₁ (t + 1) ^{*
_{= H 11 * h 11 B 1}} (t + 1) * + h 21 * h 21 B 1 (t + 1) * -h 21 * n 1 (t) + h 11 n 1 (t + 1) *,
w ₂ (t) = h ₁₂ ^* v ₂ (t) + h ₂₂ v ₂ (t + 1) ^{*
_{= H 12 * h 12 B 1}} (t) -h 12 * h 22 B 1 (t + 1) * + h 12 * n 2 (t) + h 22 h 12 * B 1 (t + 1) * + h 22 h 22 * B 1 ( t) + h ₂₂ n ₂ (t + 1) ^{*
_{= H 12 * h 12 B 1}} (t) + h 22 * h 22 B 1 (t) + h 12 * n 2 (t) + h 22 n 2 (t + 1) *,
w ₂ (t + 1) ^* = − h ₂₂ ^* v ₂ (t) + h ₁₂ v ₂ (t + 1) ^{*
_{= -H 22 * h 12 B 1}} (t) + h 22 * h 22 B 1 (t + 1) * -h 22 * n 2 (t) + h 12 h 12 * B 1 (t + 1) * + h 12 h 22 * B 1 (T) + h ₁₂ n ₂ (t + 1) ^{*
_{= H 12 * h 12 B 1}} (t + 1) * + h 22 * h 22 B 1 (t + 1) * -h 22 * n 2 (t) + h 12 n 2 (t + 1) *.

4 PSK-STC demodulator 211 based on the arithmetic _expression, than _{w 1 (t) + w 2} (t), B 1 (t) is _{reproduced, w 1 (t + 1)} + w 2 from the _{(t + 1), B 1} ( t + 1) is played back. ^{_{Further, B 2 (t) = -}} B 1 (t + 1) *, B 2 (t + 1) = the B 1 ^{(t) *} of the _{equation, B 2 (t), B} 2 (t + 1) can also be reproduced The bits demodulated by the 4PSK-STC modulator 103 can be obtained.

  The bit combiner 212 combines the bit obtained by the 4PSK-MLD demodulator 204 and the bit obtained by the 4PSK-STC demodulator 211 to obtain a received bit string.

  According to the present embodiment described above, in 16QAM transmission in which 4-bit information is mapped to 16 kinds of signal points on a complex number space and transmitted, 2 bits mapped to have strong error resistance out of 4 bits. Each transmission method in which SDM has high transmission efficiency but is likely to cause transmission errors, while STC has low transmission efficiency but is unlikely to cause transmission errors. It is possible to realize transmission utilizing the characteristics of

By the way, this embodiment is not limited to the transmission by 2 transmission 2 receiving antennas, For example, as shown in FIG. 3, it can be easily extended to the transmission by 4 transmission 4 receiving antennas.
Note that the STC by Alamouti is applied to two transmitting antennas, but the STC applied to four transmitting antennas is, for example,
V. Tarokh, H. Jafarkhani, and AR Calderbank, `` Space-Time Block Codes from Orthogonal Designs '', IEEE Trsns. Information Theory, vol. 45, no. 5, pp. 1456-1467, July 1999.
Or
MO Damen, KA Meraim, and JC Belfoire, `` Diagonal Algebraic Space-Time Block Codes '', IEEE Trans. Information Theory, vol.48, n0.3, pp. 628-636, March 2002.
It can be realized by the method described in the above.
Among these, the decoding of STC described in the latter document includes, for example,
MO Damen, A. Chkeif, and JC Belfoire, `` Lattice Code Decoder for Space-Time Codes '', IEEE Communications Letter, vol. 4, no. 5, pp. 161-163, May 2000.
However, the Sphere decoding can be applied in place of the 4PSK-MLD demodulator in the SDM demultiplexing demodulation at the radio receiver.

Further, in this embodiment, 16QAM transmission is realized by mixing and transmitting large amplitude 4PSK SDM and small amplitude 4PSK STC, but the present invention is not limited to this. For example, as shown in FIG. 4, 64QAM transmission is mixed transmission of large amplitude 16QAM SDM and small amplitude 4PSK STC, or large amplitude 4PSK SDM and small amplitude as shown in FIG. It is also possible to realize this by mixed transmission of 16QAM STC.
4 and 5 are compared, in terms of transmission efficiency, the former is better because the number of bits allocated to the SDM is larger, but from the viewpoint of error resilience, the latter is better. Is better because the number of bits allocated to the STC is larger.

In this embodiment,
A large-amplitude 4PSK signal is expressed as A ₁ (t), A ₁ (t + 1) = ± 8 ± 8j,
A 4PSK signal having a small amplitude is represented by B ₁ (t), B ₁ (t + 1) = ± 4 ± 4j.
And set the level
± (12, or, 4) ± (12j, or, 4j),
Although a uniform lattice-like 16QAM signal is set as shown in FIG. 1, the relationship of the levels is not limited to this. For example,
A large amplitude 4PSK signal is represented by A ₁ (t), A ₁ (t + 1) = ± 10 ± 10 j,
A small amplitude 4PSK signal is represented by B ₁ (t), B ₁ (t + 1) = ± 2 ± 2j.
And set the level
± (12, or, 8) ± (12j, or, 8j),
It is also possible to set a non-uniform grid-like 16QAM signal such as In this case, the error resistance of the large amplitude 4PSK signal is increased, but the error resistance of the small amplitude 4PSK is decreased. This setting is effective when the SLD MLD demodulation performance is poor. In this way, by appropriately controlling the level relationship according to the transmission path condition, it is possible to ensure good transmission characteristics in a wide range of transmission path conditions.

(Second Embodiment)
In the present embodiment, a wireless communication system that performs adaptive control according to transmission path conditions will be described with reference to FIG. In the first embodiment, 16QAM transmission is always transmitted by a mixture of SDM and STC. However, in this embodiment, for example, according to a transmission path condition, according to a signal to noise ratio (SNR). All are transmitted by SDM, transmitted by mixing SDM and STC, or all transmitted by STC.

In the wireless communication system of the present embodiment, the wireless transmitter newly includes a third receiving antenna 143, a transmission path estimator 144, and a controller 145, and the wireless receiver newly includes a controller 255 and a first controller. 3 transmission antennas 256 are provided. In addition, the modulator and demodulator used in this embodiment are also different from those in the first embodiment.
That is, in the wireless transmitter 11, instead of the first 4PSK modulator 102, 4PSK-STC modulator 103, and second 4PSK modulator 104 in the first embodiment, the first 16QAM, 4PSK modulator 140 is used. , 16QAM, 4PSK-STC modulator 141, and second 16QAM · 4PSK modulator 142. Along with this change, unlike the wireless transmitter 10 of the first embodiment, the wireless transmitter 11 can employ a 16QAM modulation scheme in each modulator.

  In association with the wireless transmitter 11, the wireless receiver 21 also uses a 16QAM · 4PSK instead of the 4PSK-MLD demodulator 204, the third 4PSK modulator 205, the fourth 4PSK modulator 206, and the 4PSK-STC demodulator 211. An MLD demodulator 250, a third 16QAM / 4PSK modulator 251, a fourth 16QAM / 4PSK modulator 252, and a 16QAM / 4PSK-STC demodulator 253; Due to these changes, unlike the wireless receiver 20 of the first embodiment, the wireless receiver 21 can cope with modulation / demodulation of 16QAM.

  The third receiving antenna 143 is for estimating a transmission path condition, and receives a signal from the wireless receiver 21. The transmission path estimator 144 detects the transmission path status of the frequency of the signal transmitted from the wireless receiver 21 to the wireless transmitter 11 based on the received signal received by the third receiving antenna 143. The transmission path estimator 144 detects the transmission path status by, for example, SNR (signal-to-noise ratio). For example, when the wireless transmitter 11 of the present embodiment is a base station and the wireless receiver 21 is a terminal, the SNR of the transmission path is determined by notifying the transmission path status via an uplink from the terminal to the base station. The transmitter 11 can detect a downlink transmission path condition. Also, for example, when bi-directional communication between a base station and a terminal is performed in a time division manner on the same frequency transmission path, the transmission path status is detected using the transmission path estimator 144 from the quality of the signal received by the base station. Is possible.

The controller 145 instructs each modulator to indicate which modulation method to use in each modulator according to the transmission path condition detected by the transmission path estimator 144. In an example to be described later, the control is changed according to the magnitude of the SNR that is the transmission path condition detected by the transmission path estimator 144. This control is based on the fact that in order to perform accurate transmission even when the SNR changes, low error tolerance is allowed when the SNR is high, and high error tolerance is required when the SNR is low.
Specifically, the controller 145 and the controller 255 perform high-efficiency SDM transmission for all 16-bit information when the SNR is high and low error tolerance is allowed at time t and time t + 1. If the SNR is medium and medium error resilience is required, 12-bit information is executed by mixed transmission of SDM and STC, and the SNR is low and strong error resilience is allowed. In such a case, control is performed so that all STC transmissions are performed on 8-bit information.

  Similar to the control performed by the controller 145 at the wireless transmitter 11, the controller 225 also performs control according to the transmission path condition at the wireless receiver 21. The 16QAM • 4PSK-MLD demodulator 250 and the 16QAM • 4PSK-STC demodulator 253 included in the wireless receiver 21 perform demodulation using a method corresponding to the modulation method selected by the wireless transmitter 11. Further, the third 16QAM · 4PSK modulator 251 and the fourth 16QAM · 4PSK modulator 252 included in the wireless receiver 21 perform modulation using the same modulation method as that selected by the wireless transmitter 11. Information on these modulation schemes is transmitted by being included in a transmission signal transmitted from the wireless transmitter 11 to the wireless receiver 21. Other configurations are the same as those of the first embodiment.

Next, control contents of the wireless transmitter 11 and the wireless receiver 21 according to the transmission path state will be described.
(1) When it is determined that the SNR of the received signal received by the wireless receiver 21 is high, (2) When the SNR of the received signal received by the wireless receiver 21 is determined to be medium, (3) Radio reception When it is determined that the SNR of the received signal received by the device 21 is low, the modulation method and the demodulation method in the wireless transmitter 11 and the wireless receiver 21 are changed. Here, it is determined whether the magnitude of the SNR is any one of the above (1) to (3) by comparison with the first and second threshold values (first threshold value> second threshold value). . That is, the controller 145 determines (1) when the SNR is greater than the first threshold, and determines (2) when the SNR is equal to or less than the first threshold and greater than the second threshold. When the SNR is less than or equal to the second threshold, it is determined as (3). These first and second threshold values need to be set appropriately with reference to the performance of the wireless transmitter 11 and the wireless receiver 21, and are preferably set with reference to experiments or simulations.

(1) When SNR is high: All 16QAM transmissions are executed by SDM transmission. That is, in the wireless transmitter 11, 16 information bits are set to (x ₁ , x ₂ ,..., X ₁₆ ). However, x _i (i = 1, 2,..., 16) is 0 or 1. The bit divider 101 inputs 8 bits (x ₁ , x ₂ ,..., X ₈ ) 4 bits at a time to the first 16QAM · 4PSK modulator 140, and the first 16QAM · 4PSK modulator 140 Is
A ₁ (t) = ± (12, or 4) ± (12, or 4) j,
A ₁ (t + 1) = ± (12, or 4) ± (12, or, 4) j
16QAM signals are generated. Similarly, the bit divider 101 inputs 8 bits (x ₉ , x ₁₀ ,..., X ₁₆ ) 4 bits at a time to the second 16QAM · 4PSK modulator 142, and the second 16QAM · 4PSK. The modulator 142 is
A ₂ (t) = ± (12, or, 4) ± (12, or, 4) j,
A ₂ (t + 1) = ± (12, or 4) ± (12, or, 4) j
16QAM signals are generated. The radio transmitter 11, _A 1 (t) to the time t from the first transmitting antenna 107, and transmits each _A 1 a (t + 1) at time t + 1. The radio transmitter 11, _A 2 (t) to the time t from the second transmit antenna 108, and transmits each _A 2 a (t + 1) at time t + 1.

In the wireless receiver 21, the 16QAM · 4PSK-MLD demodulator 250 reproduces information bits (x ₁ , x ₂ ,..., X ₁₆ ) by MLD demodulation of the 16QAM signal. In this case, it is not necessary to operate the 16QAM · 4PSK-STC modulator 141, the third 16QAM · 4PSK modulator 251, the fourth 16QAM · 4PSK modulator 252, and the 16QAM · 4PSK-STC demodulator 253. 255 controls to turn off these power supplies or to set the battery saving mode.

(2) When the SNR is medium: As in the first embodiment, transmission for ₁₂ information bits (x ₁ , x ₂ ,..., X ₁₂ ) is performed using SDM for a large amplitude 4PSK signal. This is done by mixing transmission and STC transmission for small amplitude 4PSK signals.

(3) When SNR is low: All 16QAM transmissions are performed by STC transmission. That is, in the wireless transmitter 11, 8 information bits are set to (x ₁ , x ₂ ,..., X ₈ ). However, x _i (i = 1, 2,..., 8) is 0 or 1. The bit divider 101 inputs 8 bits (x ₁ , x ₂ ,..., X ₈ ) in units of 4 bits to the 16QAM · 4PSK-STC modulator 141, and the 16QAM · 4PSK-STC modulator 141
B ₁ (t) = ± (12, or 4) ± (12, or 4) j,
B ₁ (t + 1) = ± (12, or 4) ± (12, or, 4) j
The first series of 16QAM signals,
B ₂ (t) = ± (12, or, 4) ± (12, or, 4) j,
B ₂ (t + 1) = ± (12, or 4) ± (12, or, 4) j
The second series of 16QAM signals are generated. However,
B ₂ (t) = − B ₁ (t + 1) ^* ,
B ₂ (t + 1) = B ₁ (t) ^* ,
There is a relationship. This STC is based on the Alamouti method, as in the first embodiment. The radio transmitter 11, _B 1 (t) to the time t from the first transmitting antenna 107, and transmits each _B 1 and (t + 1) at time t + 1. The radio transmitter 11 from the second transmit antenna 108, _B 2 (t) to the time t, and transmits each _B 2 a (t + 1) at time t + 1.

In the wireless receiver 21, the 16QAM · 4PSK-STC demodulator 253 reproduces information bits (x ₁ , x ₂ ,..., X ₈ ) by STC demodulation on the 16QAM signal. In this case, the first 16QAM · 4PSK modulator 140, the second 16QAM · 4PSK modulator 142, the 16QAM · 4PSK-MLD demodulator 250, the third 16QAM · 4PSK modulator 251 and the fourth 16QAM · 4PSK modulation. The controller 252 does not need to be operated, and the controller 255 controls the power supply to be turned off or set to the battery saving mode.

  In the above-described adaptive control, the transmission average power differs depending on the modulation mode, and therefore, gain adjustment of the transmission power is necessary according to the modulation mode.

In summary, at times t and t + 1, when the SNR is high and low error tolerance is allowed, the 16-bit information is all executed by high-efficiency SDM transmission, and the SNR is medium and medium. When error tolerance is required, 12-bit information is executed by mixed transmission of SDM and STC. When SNR is low and strong error tolerance is allowed, all STC is accepted for 8-bit information. Run in transmission.
Therefore, an appropriate tradeoff between transmission efficiency and error resilience is realized according to the SNR.

  In the receiver, it is necessary to know the modulation method of transmission, but in communication, in addition to transmission / reception of information bits, transmission / reception of control signals is performed, and the current transmission is any modulation method for the control signals. If such control information is included, the receiver can identify the modulation method of the received signal.

  The adaptive control based on the above SNR can be replaced with adaptive control based on the magnitude of the correlation between the paths between the transmitting and receiving antennas. That is, when the correlation is low at time t and time t + 1 and the SDM can be separated and demodulated with high accuracy at the receiver, all the 16-bit information is executed by highly efficient SDM transmission, and the correlation is moderate. In this case, it is executed by mixed transmission of SDM and STC for 12-bit information, and when correlation is high and it is difficult to separate and demodulate SDM by a receiver, it is executed by STC transmission for all 8-bit information. .

(Third embodiment)
In the present embodiment, a wireless communication system that ensures minimum 4PSK transmission regardless of transmission path conditions, for example, SNR, and increases transmission efficiency according to the transmission path conditions will be described with reference to FIG.

  In the wireless communication system of the present embodiment, the first 16QAM • 4PSK modulator 140, the 16QAM • 4PSK-STC modulator 141, and the second 16QAM • 4PSK modulator 142 in the wireless transmitter 11 of the second embodiment. Instead, the wireless transmitter 12 includes a first 4PSK / 16QAM / 64QAM modulator 150, a first 4PSK-STC modulator 151, and a second 4PSK / 16QAM / 64QAM modulator 152. With this change, the radio receiver 22 uses the 16QAM • 4PSK-MLD demodulator 250, the third 16QAM • 4PSK modulator 251, and the fourth 16QAM • 4PSK modulator in the radio receiver 21 of the second embodiment. Instead of the 252 and 16QAM · 4PSK-STC demodulator 253, a 4PSK-STC demodulator 260, a second 4PSK-STC modulator 261, and a 4PSK · 16QAM · 64QAM-STC demodulator 262 are provided. Other configurations are the same as those of the second embodiment.

In this embodiment, at time t and time t + 1, 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) are always subjected to 4PSK STC transmission, and strong error tolerance is ensured regardless of the SNR. Thus, since the controller 145 and the controller 255 are controlled, reliable transmission is performed. As the SNR is improved, additional bits are transmitted by the SDM, and the higher the SNR, the more the controller 145 and the controller 255 increase the number of modulation levels for the additional bits, 4, 16, 64. Control and increase transmission efficiency. The present embodiment is applied to a case where it is desired to perform reliable transmission even if the transmission bit is at least regardless of the SNR.

Next, the control contents of the wireless transmitter 12 and the wireless receiver 22 according to the transmission path state will be described.
(1) When it is determined that the SNR of the received signal received by the wireless receiver 21 is low, (2) When the SNR of the received signal received by the wireless receiver 21 is determined to be medium, (3) Radio reception When it is determined that the SNR of the received signal received by the device 21 is high, (4) When the SNR of the received signal received by the wireless receiver 21 is determined to be higher than the case of (3), The modulation method and the demodulation method in the wireless transmitter 11 and the wireless receiver 21 are changed. Here, the magnitude of the SNR is any one of the above (1) to (3) by comparing with the first, second and third thresholds (first threshold> second threshold> third threshold). It is determined whether or not That is, the controller 145 determines (1) when the SNR is equal to or smaller than the third threshold, and determines as (2) when the SNR is larger than the third threshold and equal to or smaller than the second threshold. When the SNR is greater than the second threshold and less than or equal to the first threshold, it is determined as (3), and when the SNR is greater than the first threshold, it is determined as (4). These first, second, and third threshold values need to be appropriately set with reference to the performance of the wireless transmitter 12 and the wireless receiver 22, and can be set with reference to experiments or simulations. desirable.

(1) When SNR is low: 4PSK STC transmission is executed. That is, the wireless transmitter 12 sets 4 information bits to (x ₁ , x ₂ , x ₃ , x ₄ ). However, x _i (i = 1, 2, 3, 4) is 0 or 1. The bit divider 101 inputs the 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) in units of 2 bits to the first 4PSK-STC modulator 151, and the first 4PSK-STC modulator 151 Is
A ₁ (t) = ± 8 ± 8j,
A ₁ (t + 1) = ± 8 ± 8j
The first series of 4PSK signals,
A ₂ (t) = ± 8 ± 8j,
A ₂ (t + 1) = ± 8 ± 8j
The second series of 4PSK signals are generated. However,
A ₂ (t) = − A ₁ (t + 1) ^* ,
A ₂ (t + 1) = A ₁ (t) ^*
There is a relationship. This STC is based on the Alamouti method, as in the first embodiment. The radio transmitter 12, from the first transmitting antenna 107, _A 1 (t) to the time t, and transmits each _A 1 a (t + 1) at time t + 1. The radio transmitter 12 from the second transmit antenna 108, _A 2 (t) to the time t, and transmits each _A 2 a (t + 1) at time t + 1.

In the wireless receiver 22, the 4PSK-STC demodulator 260 reproduces information bits (x ₁ , x ₂ , x ₃ , x ₄ ) by STC demodulation for the 4PSK signal. In this case, the first 4PSK / 16QAM / 64QAM modulator 150, the second 4PSK / 16QAM / 64QAM modulator 152, the second 4PSK / STC modulator 261, the 4PSK / 16QAM / 64QAM-STC demodulator 262 are operated. The controller 255 performs control to turn off these power supplies or set the battery saving mode.

(2) When the SNR is medium: Mixed transmission of 4PSK STC and 4PSK SDM is executed. That is, the wireless transmitter 12 sets 12 information bits to (x ₁ , x ₂ ,..., X ₁₂ ). However, x _i (i = 1, 2,..., 12) is 0 or 1. The bit divider 101 inputs 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) of the 2 bits by 2 bits to the first 4PSK-STC modulator 151 for the first 4PSK-STC modulation. The device 151 is
A ₁ (t) = ± 8 ± 8j,
A ₁ (t + 1) = ± 8 ± 8j
The first series of 4PSK signals,
A ₂ (t) = ± 8 ± 8j,
A ₂ (t + 1) = ± 8 ± 8j
The second series of 4PSK signals are generated. However,
A ₂ (t) = − A ₁ (t + 1) ^* ,
A ₂ (t + 1) = A ₁ (t) ^*
There is a relationship. Next, the bit divider 101 inputs 4 bits (x ₅ , x ₆ , x ₇ , x ₈ ) 2 bits at a time to the first 4PSK · 16QAM · 64QAM modulator 150, and the first 4PSK · The 16QAM and 64QAM modulator 150 is
B ₁ (t) = ± 4 ± 4j,
B ₁ (t + 1) = ± 4 ± 4j
4PSK signals are generated. Similarly, the bit divider 101 inputs 4 bits (x ₉ , x ₁₀ , x ₁₁ , x ₁₂ ) 2 bits at a time to the second 4PSK / 16QAM / 64QAM modulator 152 and inputs the second 4PSK / The 16QAM / 64QAM modulator 152 is
B ₂ (t) = ± 4 ± 4j,
B ₂ (t + 1) = ± 4 ± 4j
4PSK signals are generated. Then, the wireless transmitter 12 transmits A ₁ (t) + B ₁ (t) from the first transmitting antenna 107 at time t, and A ₁ (t + 1) + B ₁ (t + 1) at time t + 1. Further, the wireless transmitter 12 transmits A ₂ (t) + B ₂ (t) from the second transmitting antenna 108 at time t and A ₂ (t + 1) + B ₂ (t + 1) at time t + 1. That is, the signals transmitted from the respective antennas at time t and time t + 1 are 16QAM signals obtained by combining a large amplitude 4PSK signal and a small amplitude 4PSK signal, respectively.

In the wireless receiver 22, the 4PSK-STC demodulator 260 first performs 4PSK STC demodulation on the received signal, reproduces (x ₁ , x ₂ , x ₃ , x ₄ ), and then the second 4PSK-STC. After the modulator 261, the adders 207 and 208, and the subtracters 209 and 210 remove A ₁ (t), A ₁ (t + 1), A ₂ (t), and A ₂ (t + 1) components from the received signal, The 4PSK / 16QAM / 64QAM-STC demodulator 262 performs MLD demodulation on the 4PSK signal to reproduce (x ₅ , x ₆ ,..., X ₁₂ ).

(3) When SNR is high: Mixed transmission of 4PSK STC and 16QAM SDM is executed. That is, in the radio transmitter 12, the information bits of 20 bits _{(x 1, x 2, ···} , x 20). However, x _i (i = 1, 2,..., 20) is 0 or 1. The bit divider 101 inputs 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) of the 2 bits by 2 bits to the first 4PSK-STC modulator 151 for the first 4PSK-STC modulation. The device 151 is
A ₁ (t) = ± 8 ± 8j,
A ₁ (t + 1) = ± 8 ± 8j
The first series of 4PSK signals,
A ₂ (t) = ± 8 ± 8j,
A ₂ (t + 1) = ± 8 ± 8j
The second series of 4PSK signals are generated. However,
A ₂ (t) = − A ₁ (t + 1) ^* ,
A ₂ (t + 1) = A ₁ (t) ^* ,
There is a relationship. Next, the bit divider 101 inputs 8 bits (x ₅ , x ₆ ,..., X ₁₂ ) 4 bits at a time to the first 4PSK / 16QAM / 64QAM modulator 150, and the first 4PSK The 16QAM / 64QAM modulator 150 is
B ₁ (t) = ± (6, or, 2) ± (6, or, 2) j,
B ₁ (t + 1) = ± (6, or 2) ± (6, or 2) j,
16QAM signals are generated. Similarly, the bit divider 101 inputs 8 bits (x ₁₃ , x ₁₄ ,..., X ₂₀ ) 4 bits at a time to the second 4PSK / 16QAM / 64QAM modulator 152 and outputs the second 4PSK. The 16QAM / 64QAM modulator 152 is
B ₂ (t) = ± (6, or, 2) ± (6, or, 2) j,
B ₂ (t + 1) = ± (6, or 2) ± (6, or 2) j,
16QAM signals are generated. Then, the wireless transmitter 12 transmits A ₁ (t) + B ₁ (t) from the first transmitting antenna 107 at time t, and A ₁ (t + 1) + B ₁ (t + 1) at time t + 1. Further, the wireless transmitter 12 transmits A ₂ (t) + B ₂ (t) from the second transmitting antenna 108 at time t and A ₂ (t + 1) + B ₂ (t + 1) at time t + 1. That is, the signals transmitted from the respective antennas at time t and time t + 1 are 64QAM signals obtained by combining a large amplitude 4PSK signal and a small amplitude 16QAM signal, respectively.

In the wireless receiver 22, first, the second 4PSK-STC modulator 261 performs STC demodulation of 4PSK on the received signal to reproduce (x ₁ , x ₂ , x ₃ , x ₄ ), and then the second 4PSK-STC modulator 261, adders 207 and 208, and subtracters 209 and 210 remove A ₁ (t), A ₁ (t + 1), A ₂ (t), and A ₂ (t + 1) components from the received signal. After that, the 4PSK · 16QAM · 64QAM-STC demodulator 262 performs MLD demodulation on the 16QAM signal to reproduce (x ₅ , x ₆ ,..., X ₂₀ ).

(4) When SNR is higher: Mixed transmission of 4PSK STC and 64QAM SDM is executed. That is, in the wireless transmitter 12, the 28 information bits are (x ₁ , x ₂ ,..., X ₂₈ ). However, x _i (i = 1, 2,..., 28) is 0 or 1. Similarly to the case of (3), the bit divider 101 inputs 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) of these 2 bits at a time to the first 4PSK-STC modulator 151. The first 4PSK-STC modulator 151 is similar to the case of (3),
A ₁ (t) = ± 8 ± 8j,
A ₁ (t + 1) = ± 8 ± 8j,
The first series of 4PSK signals,
A ₂ (t) = ± 8 ± 8j,
A ₂ (t + 1) = ± 8 ± 8j,
The second series of 4PSK signals are generated. However,
A ₂ (t) = − A ₁ (t + 1) ^* ,
A ₂ (t + 1) = A ₁ (t) ^* ,
There is a relationship. Next, the bit divider 101 inputs 12 bits (x ₅ , x ₆ ,..., X ₁₆ ) 6 bits at a time to the first 4PSK / 16QAM / 64QAM modulator 150, and the first 4PSK The 16QAM / 64QAM modulator 150 is
B ₁ (t) = ± (7, or 5, or 3, or 1) ± (7, or 5, or 3, 3, or 1) j,
B ₁ (t + 1) = ± (7, or 5, or 3, 3, or 1) ± (7, or 5, or 3, 3, 1)
64QAM signals are generated. Similarly, the bit divider 101 inputs 12 bits (x ₁₇ , x ₁₈ ,..., X ₂₈ ) 6 bits at a time to the second 4PSK / 16QAM / 64QAM modulator 152 and outputs the second 4PSK. The 16QAM / 64QAM modulator 152 is
B ₂ (t) = ± (7, or 5, or 3, 3, or 1) ± (7, or 5, or 3, or 1) j,
B ₂ (t + 1) = ± (7, or 5, or 3, or 1) ± (7, or 5, or 3, or 1) j
64QAM signals are generated. Then, the wireless transmitter 12 transmits A ₁ (t) + B ₁ (t) from the first transmitting antenna 107 at time t, and A ₁ (t + 1) + B ₁ (t + 1) at time t + 1. Further, the wireless transmitter 12 transmits A ₂ (t) + B ₂ (t) from the second transmitting antenna 108 at time t and A ₂ (t + 1) + B ₂ (t + 1) at time t + 1. That is, the signals transmitted from the respective antennas at time t and time t + 1 are 256QAM signals in which a large amplitude 4PSK signal and a small amplitude 64QAM signal are combined.

In the wireless receiver 22, first, the second 4PSK-STC modulator 261 performs 4PSK STC demodulation on the received signal to reproduce (x ₁ , x ₂ , x ₃ , x ₄ ), and then the second 4PSK-STC modulator 261, adders 207 and 208, and subtractors 209 and 210 remove A ₁ (t), A ₁ (t + 1), A ₂ (t), and A ₂ (t + 1) components from the received signal. After that, the 4PSK · 16QAM · 64QAM-STC demodulator 262 performs MLD demodulation on the 64QAM signal to reproduce (x ₅ , x ₆ ,..., X ₂₈ ).

  In the above-described adaptive control, the transmission average power differs depending on the modulation mode, and therefore, gain adjustment of the transmission power is necessary according to the modulation mode.

In summary, at time t and t + 1, 4 bits (x ₁ , x ₂ , x ₃ , x ₄ ) are always subjected to 4PSK STC transmission, and strong error tolerance is ensured regardless of the SNR. And reliable transmission is performed. As the SNR improves, additional bits are transmitted by SDM, and the higher the SNR, the greater the number of modulation levels for the additional bits, 4, 16, 64, and the transmission efficiency increases. Further, the adaptive control based on the above SNR can be replaced with adaptive control based on the magnitude of the correlation between the paths between the transmitting and receiving antennas.

(Fourth embodiment)
In the present embodiment, the circuit can be simplified by realizing equivalent transmission characteristics by 4PSK STTC for a transmission system using various multi-level modulation space-time codes. By dividing the multilevel modulation signal into a plurality of 4PSK signals, the circuit only needs to be an STTC encoder / decoder for 4PSK. In this case, even if the number of states is increased, the STTC for 16, 64QAM is used. Such an advantage that does not become a huge amount of calculation will be described below.

As shown in FIG. 8, the wireless communication system of the present embodiment includes a wireless transmitter 13 and a wireless receiver 23. The wireless transmitter 13 includes a bit divider 155, a first STTC encoder 156, a second STTC encoder 157, adders 105 and 106, and a transmission antenna connected to each adder. The wireless receiver 23 includes one receiving antenna, an adder 265 that inputs a signal from the receiving antenna, a transmission path estimator 266, a first STTC decoder 267, a third STTC encoder 268, and a second STTC decoding. A multiplier 273, multipliers 269 and 270, adders 271 and 272, and a bit combiner 274.
The present embodiment will be described in detail below with reference to FIG. 8 by taking space-time coded transmission as an example for a 16 QAM (Quadrature Amplitude Modulation) signal.

16 kinds of complex signals determined from 16-QAM 4-bit data are (± 1, ± 3) + (± 1, ± 3) j
This complex signal is composed of two 4PSK signals each having a large amplitude and a small amplitude determined by 2-bit data,
± 2 ± 2j (large amplitude),
± 1 ± 1j (small amplitude)
Can be represented by the addition of The 2-bit data that determines a large-amplitude 4PSK signal has a feature that transmission errors are less likely to occur than 2-bit data that determines a small-amplitude 4PSK signal.

  In the wireless transmitter 13, the bit divider 155 divides the transmission bit string every 4 bits, further divides each 4-bit data every 2 bits, and assigns one of the 2 bits to a large-amplitude 4PSK signal, The other 2 bits are used as data to be allocated to a small amplitude 4PSK signal.

  The first STTC encoder 156 receives data to be allocated to the large amplitude 4PSK signal from the bit divider 155, and the second STTC encoder 157 is the data to be allocated to the small amplitude 4PSK signal from the bit divider 155. Enter.

Each 2-bit data is input to a 4PSK space-time trellis code (STTC) encoder instead of a 4PSK modulator as in the above-described embodiment, and a 4PSK encoded signal is input. Here, as an STTC encoder, for example, a document
A. van Zelst, R. van Nee, and GA Awater, `` Space Division Multiplexing (SDM) for OFDM System '', IEEE Proceeding of VTC-Spring 2000, pp. 6-10, 1998.
The number of trellis transition states shown in Fig. 4 is used, and the transmission is performed from two transmission antennas. The state transition of this STTC encoder is shown in FIG.

In the first STTC encoder 156 and the second STTC encoder 157, four types of 4PSK complex signals are represented by four integer signals 0, 1, 2, and 3. When a signal sequence composed of a plurality of signals is called a frame, an output frame of the 4PSK modulator, that is, an input frame of the STTC encoder, for example, is composed of the following six signals as one frame:
0, 2, 3, 1, 2, 0
The first STTC output frame input to the first transmit antenna is
0, 0, 2, 3, 1, 2,
Then, the second STTC output frame input to the second transmission antenna is
0, 2, 3, 1, 2, 0
It becomes. Each integer signal in this frame is converted back to a complex signal and transmitted from each antenna.

Based on this principle, the bit divider 155 inputs one 2-bit data to the first STTC encoder 156, and the first STTC encoder 156 transmits the signal from the first and second transmission antennas. ,
u ₁ (k) = ± 2 ± 2j, u ₂ (k) = ± 2 ± 2j
Are generated respectively. k is a signal number representing time. Similarly, the bit divider 155 inputs the other 2-bit data to the second STTC encoder, and the second STTC encoder 157 sends out signals from the first and second transmission antennas,
v ₁ (k) = ± 1 ± 1j, v ₂ (k) = ± 1 ± 1j
Are generated respectively. Then, the output signals from the first transmission antenna and the second transmission antenna are added by the adders 105 and 106, respectively.
u ₁ (k) + v ₁ (k), u ₂ (k) + v ₂ (k)
become.

Assuming that the transmission path condition is a fading environment that is steady in each signal frame and has no frequency selectivity, the signal transmitted from the transmission antenna is affected by noise, gain, and the like on the transmission path 33. If the path gain from the first transmitting antenna to the receiving antenna is h ₁ , the path gain from the second transmitting antenna to the receiving antenna is h _2, and these path gains are constant between time t and t + 1, the time The input of the receiving antenna of t is
r (k) = h ₁ (u ₁ (k) + v ₁ (k)) + h ₂ (u ₂ (k) + v ₂ (k)) + n (k)
It can be expressed as. Here, h ₁ and h ₂ are complex Gaussian signals that are uncorrelated with each other. n (k) is a complex Gaussian signal with additional noise. In addition to the information signal, a pilot signal is multiplexed in the transmission signal, the wireless receiver 23 receives the pilot signal, and the transmission path estimator 266 performs transmission path estimation, and h ₁ , h ₂ Is accurately detected.

In the wireless receiver 23, the first STTC decoder 267 and the second STTC decoder 273 perform two-stage decoding. First, the first STTC decoder 267 performs decoding on the output signal of the first STTC encoder 156.
The first STTC decoder 267 outputs a signal sent from the first antenna and a signal sent from the second antenna of the STTC signal that would have been generated by the first STTC encoder 156, respectively, to p ₁ (k ), P ₂ (k). There are four candidates for p ₁ (k) and p ₂ (k), ± 2 ± 2j, respectively. The first STTC decoder 267 is
d ₁ = | r (k) −h ₁ p ₁ (k) −h ₂ p ₂ (k) | ²
Is used as an evaluation value, and a signal sequence of p ₁ (k) and p ₂ (k) that minimizes d ₁ is searched by the Viterbi algorithm. This corresponds to searching for the most likely signal (that is, the bit string before being encoded) input to the first STTC encoder 156.

Next, in order to obtain bits modulated by the second STTC encoder 157, the bits obtained by the first STTC decoder 267 are modulated again, and h ₁ obtained by the transmission path estimator 266 is obtained. h ₂ is used to reproduce the transmission path by the transmission path replica, calculate u ₁ (k) and u ₂ (k) through the transmission path 33, and v ₁ (k) from the received signal received by the receiving antenna By obtaining v ₂ (k) and demodulating it, the bits before being modulated by the second STTC encoder 157 can be obtained.

That is, the input signal of the searched first STTC encoder 156 is STTC encoded by the third STTC encoder 268. The third STTC encoder 268 has the same characteristics as the first STTC encoder 156. The signal generated by the third STTC encoder 268 is
u ₁ (k) = ± 2 ± 2j, u ₂ (k) = ± 2 ± 2j
become. The u ₁ (k) and u ₂ (k) components included in the received signal r (k) are converted into transmission replicas including multipliers 269 and 270 and an adder 271 shown in FIG.
s (k) = r (k) −h ₁ u ₁ (k) −h ₂ u ₂ (k)
To remove. Then, second STTC decoder 273 performs decoding on the output signal of second STTC encoder 157. The second STTC decoder 273 receives the transmission signal from the first transmission antenna and the transmission signal from the second transmission antenna of the STTC signal that would be generated by the second STTC encoder 157, respectively. Assume q ₁ (k) and q ₂ (k). Candidates for q ₁ (k) and q ₂ (k) are 0, 1, 2, and 3, respectively, expressed as integers. The second STTC decoder 273 is
d ₂ = | s (k) −h ₁ q ₁ (k) −h ₂ q ₂ (k) | ²
Is used as an evaluation value, and a signal sequence of q ₁ (k) and q ₂ (k) that minimizes d ₂ is searched by the Viterbi algorithm. This corresponds to searching for the most likely signal input to the second STTC encoder 157 (that is, the bit string before being encoded).

  That is, in the radio receiver 23, first, the input of the first STTC encoder 156 is reproduced by the first STTC decoder 267 with respect to the received signal, and the first STTC encoded signal component is obtained from the received signal. After the removal, the input of the second STTC encoder 157 is reproduced by the second STTC decoder 273. As described above, STTC transmission of 16QAM signals can be realized by two 4-STTC transmissions.

  In the present embodiment, the number of STTC states is four, but the number of STTC states is not limited to four, and STTCs having the conventional number of states such as 8, 16 can be used. As described above, the decoding characteristic improves as the number of states increases. For example, the state transition when the number of states is 8 is as shown in FIG.

  Further, the first STTC encoder 156 and the second STTC encoder 157 need not have the same number of states. In this embodiment, the number of transmission antennas is 2 and the number of reception antennas is 1. However, the present invention is not limited to this. In particular, the number of reception antennas can be easily increased without changing the configuration on the transmission side.

(Fifth embodiment)
This embodiment shows an embodiment applied to 64QAM transmission with reference to FIG. That is, this embodiment shows an example that it is not only applicable to 16QAM transmission as in the fourth embodiment.

64 types of complex signals determined from 64QAM 6-bit data (± 1, ± 3, ± 5, ± 7) + (± 1, ± 3, ± 5, ± 7) j
This complex signal is composed of three 4PSK signals ± 4 ± 4j (large amplitude) with large amplitude, medium amplitude, and small amplitude determined by 2-bit data,
± 2 ± 2j (medium amplitude),
± 1 ± 1j (small amplitude)
Can be represented by the addition of The 2-bit data that determines a 4PSK signal with a large amplitude has a feature that transmission errors are less likely to occur than the 2-bit data that determines a 4PSK signal with a small amplitude.

In the wireless transmitter 14, the bit divider 160 divides the transmission bit string into 6 bits, further divides each 6-bit data into 2 bits, and converts each 2-bit data into the first STTC encoder 156. , The second STTC encoder 157 and the third STTC encoder 161, and the encoders respectively output the encoded output signals u ₁ (k) and u ₂ (k), v _1. (K) and v ₂ (k), w ₁ (k) and w ₂ (k) are generated. Then, the output signals from the first transmission antenna and the second transmission antenna are added by the adders 105 and 106, respectively.
u ₁ (k) + v ₁ (k) + w ₁ (k),
u ₂ (k) + v ₂ (k) + w ₂ (k)
become.

A signal transmitted from a transmission antenna that assumes a fading environment that is stationary in each signal frame and has no frequency selectivity, is affected by noise, gain, and the like on the transmission path 33. If the path gain from the first transmitting antenna to the receiving antenna is h ₁ , the path gain from the second transmitting antenna to the receiving antenna is h _2, and these path gains are constant between time t and t + 1, the time The input of the receiving antenna of t is
r (k) = h ₁ (u ₁ (k) + v ₁ (k) + w ₁ (k)) + h ₂ (u ₂ (k) + v ₂ (k) + w ₂ (k)) + n (K)
It can be expressed as. h ₁ and h ₂ are complex Gaussian signals that are uncorrelated with each other. n (k) is a complex Gaussian signal with additional noise. In addition to the information signal, a pilot signal is multiplexed in the transmission signal. The radio receiver 24 receives the pilot signal, and the transmission path estimator 266 estimates the transmission path. H ₁ and h ₂ Is accurately detected.

In the wireless receiver 24, the STPS for 4PSK of the first STTC encoder 156, the second STTC encoder 157, and the third STTC encoder 161 is decoded in three stages by a decoder. First, the first STTC decoder 267 reproduces the input signal of the first STTC encoder 156 for r (k) as shown in the fourth embodiment, and the fourth STTC code With the generator 275,
u ₁ (k) = ± 4 ± 4j, u ₂ (k) = ± 4 ± 4j
Play. The u ₁ (k) and u ₂ (k) components included in the received signal r (k) are
s (k) = r (k) −h ₁ u ₁ (k) −h ₂ u ₂ (k)
To remove. Next, the second STTC decoder 276 reproduces the input signal of the second STTC encoder 157 for s (k), and the fifth STTC encoder 278
v ₁ (k) = ± 2 ± 2j, v ₂ (k) = ± 2 ± 2j
Play. The v ₁ (k) and v ₂ (k) components included in the received signal s (k) are
t (k) = s (k) −h ₁ v ₁ (k) −h ₂ v ₂ (k)
To remove. Next, the third STTC decoder 280 reproduces the input signal of the third STTC encoder 161 for s (k). As described above, according to the present embodiment, even in 64QAM transmission, STTC transmission by a 4PSK STTC encoder and decoder can be realized without using a STTC encoder and decoder for 64QAM.

(Sixth embodiment)
In the fourth embodiment, the 16PSK signal is regarded as a combination of two 4PSK signals, and in the second embodiment, the 64QAM signal is regarded as a combination of three 4PSK signals. Not. In the present embodiment, as an example of this, a radio communication system in which a 64QAM signal is regarded as a combination of a 4PSK signal and a 16QAM signal will be described with reference to FIG.

For example, 64 kinds of complex signals determined from 6-bit data of 64QAM, for example,
(± 1, ± 3, ± 5, ± 7) + (± 1, ± 3, ± 5, ± 7) j
This complex signal is a 4PSK signal determined by 2-bit data ± 4 ± 4j
And 16QAM signal (± 2 ± 1) + (± 2 ± 1) j determined by 4-bit data
Can be represented by the addition of Therefore, in the wireless transmitter 15, the bit divider 155 divides the transmission bit string every 6 bits, further divides the 6 bits into 2 bits and 4 bits, and the former 2 bits are the first STTC codes for 4PSK. Input to the encoder 165, the encoded signal,
u ₁ (k), u ₂ (k) = ± 4 ± 4j
And the latter 2 bits are input to a second STTC encoder 166 for 16QAM to generate an encoded signal,
v ₁ (k), v ₂ (k) = (± 2 ± 1) + (± 2 ± 1) j
Is generated. Then, u ₁ (k) + v ₁ (k) is transmitted from the first transmission antenna, and u ₂ (k) + v ₂ (k) is transmitted from the second transmission antenna.

In the wireless receiver 25, the first STTC code is received by the first STTC decoder 285 for 4PSK with respect to the received signal r (k) as in the operation of the wireless receiver 23 in the fourth embodiment. The s (k) from which the u ₁ (k) and u ₂ (k) components contained in r (k) are removed using the transmission replica is reproduced from The second STTC decoder 287 regenerates the second STTC encoder input.

(Seventh embodiment)
In the fourth, fifth, and sixth embodiments, STTC is used as the space-time coding method, but the present invention is not limited to this. In the present embodiment, an example in which a space-time block code (STBC) is used as a space-time code instead of STTC will be described with reference to FIG. STBC is described in detail, for example, in the following document.
S. Alamouti, `` A simple transmitter diversity technique for wireless communications '', IEEE J. Select Areas. Commun., Vol. 16, pp.1451-1258 ,. Oct. 1998.
In this embodiment, instead of the first STTC encoder 156 and the third STTC encoder 268 in the fourth embodiment, a first STBC encoder 172 and a second STBC encoder 293, respectively. Instead of the first STTC decoder 267, an STBC decoder 290 is used.

  The STBC encoding is a linear transformation for an arbitrary complex signal, and is a modulator (for example, a first STBC encoder 172 and a second STBC encoder 293 in FIG. 12) prior to the modulator ( Bit data needs to be converted into a complex signal by the 4PSK modulators 171 and 292) of FIG. Therefore, a demodulator (4PSK demodulator 291 in FIG. 12) for converting a complex signal into bit data is required after the STBC decoder (STBC decoder 290 in FIG. 12).

In the wireless transmitter 16, the bit divider 170 divides the transmission bit string every 4 bits, further divides each 4-bit data every 2 bits, and inputs one 2 bits to the 4PSK modulator 171. The complex 4PSK signal x (k) = ± 2 ± 2j is generated, and this signal is input to the first STBC encoder 172. The output of the first STBC encoder 172, that is, the signal transmitted from the first and second transmitting antennas,
u ₁ (k) = ± 2 ± 2j, u ₂ (k) = ± 2 ± 2j
It is. By the way, the relationship between these signals and x (k) is
u ₁ (k) = x (k), u ₁ (k + 1) = x (k + 1),
u ₂ (k) = − x (k + 1) ^* , u ₂ (k + 1) = x (k) ^*
It becomes. That is, processing is performed for every two consecutive 4PSK output signals x (k) and x (k + 1).

The other 2-bit data is input to the STTC encoder 173, and the STTC encoder 173 transmits signals from the first and second transmission antennas.
v ₁ (k) = ± 1 ± 1j, v ₂ (k) = ± 1 ± 1j
Are generated respectively. Therefore, from the first and second transmit antennas, respectively
u ₁ (k) + v ₁ (k), u ₂ (k) + v ₂ (k)
Output signal is transmitted.

A signal transmitted from a transmission antenna that assumes a fading environment that is stationary in each signal frame and has no frequency selectivity, is affected by noise, gain, and the like on the transmission path 33. If the path gain from the first transmitting antenna to the receiving antenna is h ₁ , the path gain from the second transmitting antenna to the receiving antenna is h _2, and these path gains are constant between time t and time t + 1, The input of the receiving antenna at time t is
r (k) = h ₁ (u ₁ (k) + v ₁ (k)) + h ₂ (u ₂ (k) + v ₂ (k)) + n (k)
It can be expressed as. h ₁ and h ₂ are fading gains and are uncorrelated complex Gaussian signals. n (k) is an additive noise, which is a complex Gaussian signal. In addition to the information signal, a pilot signal is multiplexed in the transmission signal, the wireless receiver 23 receives the pilot signal, and the transmission path estimator 266 performs transmission path estimation, and h ₁ , h ₂ Is accurately detected.

  In the wireless receiver 26, the STBC decoder 290 and the STTC decoder 294 perform two-stage decoding. First, the STBC decoder 290 performs decoding on the output signal of the first STBC encoder 172. The STBC decoder 290 performs the following calculation on the received signal r (k) to obtain y (k) and y (k + 1).

y (k) = h ₁ ^* r (k) −h ₂ r (k + 1) ^*
y (k + 1) * = − h ₂ ^* r (k) −h ₁ r (k + 1) ^*
By determining these y (k) and y (k + 1) by the 4PSK demodulator 291, the first bit string is reproduced. That is, the output signal of the 4PSK demodulator 291 becomes the first bit string.

Next, STBC encoding of the reproduced first bit string is performed by the second STBC encoder 293 of the wireless receiver 26. The second STBC encoder is set to have the same characteristics as the first STBC encoder. The signal generated by the second STBC encoder 293 is
u ₁ (k) = ± 2 ± 2j, u ₂ (k) = ± 2 ± 2j
become. With these signals, u ₁ (k) and u ₂ (k) components included in the received signal r (k) using the transmission path replica are
s (k) = r (k) −h ₁ u ₁ (k) −h ₂ u ₂ (k)
To remove. Then, the STTC decoder 294 decodes the STTC encoder 173 output signal with respect to s (k), and reproduces the input signal of the STTC encoder 173. That is, the radio receiver 26 first reproduces the first bit string by STBC decoding with respect to the received signal, removes the signal component based on the first STBC encoder 172 from the received signal, The bit string is reproduced by STTC decoding.
As described above, space-time coding of 16QAM signals combining STTC and STBC can be realized.

(Eighth embodiment)
In the present embodiment, a case where adaptive modulation for controlling transmission efficiency and error tolerance is applied according to a transmission path condition will be described with reference to FIG.
The adaptive modulation technique observes the transmission path condition by wireless transmission, and when the transmission path condition is good, for example, the efficiency of 64QAM transmission is reduced, and the transmission efficiency is reduced to 16 QAM and 4PSK as the transmission path condition deteriorates. Instead, it is a technique that increases error resilience.
When adaptive modulation is performed in the conventional STTC, the STTC has different encoder and decoder configurations for each of 64QAM, 16QAM, and 4PSK, and it is necessary to provide a corresponding one for each.
As is clear from the fourth and fifth embodiments, the STTC encoder and decoder for 4PSK can perform STTC encoding / decoding for 16QAM and 64QAM. Apply the form to realize adaptive modulation.

  In the wireless transmitter 17, it is necessary to grasp the state of the transmission path. In the case of TDD (Time Division Duplex) in which bi-directional transmission is performed in the same frequency band in a time division manner, a reception signal received by the transmission antenna is received. If there is a transmission path estimator that estimates the transmission path state from Further, in the case of FDD (Frequency Division Duplex) in which bidirectional transmission is performed in different frequency bands, it is easily performed by having the communication partner notify the transmission path status. FIG. 13 assumes the former case.

  The wireless communication system of this embodiment is different from the above-described embodiment in that the wireless transmitter 17 includes a switch ON / OFF control unit 180 and a bit divider 175 having a switch that can switch the output of the transmission bit string. Accordingly, the wireless receiver 27 has a bit synthesizer 298 that can change the bits to be synthesized. Other configurations are the same as those described in the above embodiment.

The transmission path estimator 144 includes on / off control of the switches SW1-1, SW1-2, and SW1-3 included in the bit divider 175, a second STTC encoder 166, and a third STTC encoder. On / off control of the power source 176 is performed. Note that SW1-1 is always On during operation.
For example, when the transmission path estimator 144 determines that the transmission path state is inferior due to noise or the like, the second STTC is turned off by setting SW1-2 and SW1-3 to Off in order to transmit a 4PSK encoded signal. The power supply of the encoder 166 and the third STTC encoder 176 is turned off. At this time, transmission bits are supplied only to the first STTC encoder 165, and only the outputs u ₁ (k) and u ₂ (k) of the first STTC encoder 165 are output. Transmitted from the second antenna. In this way, the wireless transmitter 17 transmits a 4PSK encoded signal.

Also, when the transmission path estimator 144 determines that the transmission path state is medium, as described in the fourth embodiment, SW1-2 is turned on and SW1- 3 is turned off, the power of the second STTC encoder 166 is turned on, and the power of the third STTC encoder 176 is turned off. At this time, the outputs u ₁ (k) and u ₂ (k) of the first STTC encoder 165 and the outputs v ₁ (k) and v ₂ (k) of the second STTC encoder 166 are Is output and transmitted from the first and second antennas. In this way, the wireless transmitter 17 transmits a 16QAM encoded signal.

Further, when the transmission path estimator 144 determines that the transmission path state is good, as described in the fifth embodiment, in order to transmit a 64QAM encoded signal, SW1-2, SW1-3 Is turned on, and the power sources of the second STTC encoder 166 and the third STTC encoder 176 are turned on. At this time, the outputs u ₁ (k), u ₂ (k) of the first STTC encoder 165, the outputs v ₁ (k), v ₂ (k) of the second STTC encoder 166, and The outputs w ₁ (k) and w ₂ (k) of the third STTC encoder 176 are output and transmitted from the first and second antennas. In this way, the wireless transmitter 17 transmits a 64QAM encoded signal corresponding to the second embodiment.

Next, control by the wireless receiver 27 will be described.
The encoded signal for the transmission bit is stored in the information field of the packet. Usually, a transmission signal often has a packet structure, and therefore, if it has a packet structure, this encoded signal can be included. In addition, the packet has a header for storing various control signals. This header includes control information indicating whether the current transmission signal is 4PSK, 16QAM, or 64QAM. Then, the radio receiver 27 can identify which of the signals received with reference to this header.

  The wireless receiver 27 determines whether the received signal is 4PSK, 16QAM, or 64QAM with reference to the header. Based on this determination, On / Off of the fourth STTC encoder 275 and the second STTC decoder 276, ON / OFF of the fifth STTC encoder 278 and the third STTC decoder 280, bit synthesis ON / OFF of each switch in the device 298 is controlled. This control is performed by a control unit (not shown) in the wireless receiver 27. Note that SW2-1 is always On during operation.

  If the control unit determines 4PSK, the fourth STTC encoder 275, the second STTC decoder 276, the fifth STTC encoder 278, and the third STTC decoder 280 are turned off, and SW2-2 , SW2-3 is set to Off. At this time, the output of the first STTC decoder 267 becomes a reproduction bit, and data reproduction of 4PSK encoded transmission is performed.

  In addition, when the control unit determines that 16PSK, the fourth STTC encoder 275 and the second STTC decoder 276 are turned on, and the fifth STTC encoder 278 and the third STTC decoder 280 are turned off. SW2-2 is set to On and SW2-3 is set to Off. At this time, the outputs of the first STTC decoder 267 and the second STTC decoder 276 become reproduction bits, and data reproduction of 16QAM encoded transmission corresponding to the fourth embodiment is performed.

  Further, if the control unit determines that 64QAM, the fourth STTC encoder 275, the second STTC decoder 276, the fifth STTC encoder 278, and the third STTC decoder 280 are turned on, and SW2 -2, SW2-3 is turned on. At this time, the outputs of the first STTC decoder 267, the second STTC decoder 276, and the third STTC decoder 280 become reproduction bits, and data reproduction of 64QAM encoded transmission corresponding to the fifth embodiment is performed. It becomes.

  As described above, according to the present embodiment, adaptive STTC encoding / decoding for 4PSK, 16QAM, and 64QAM can be realized by a 4PSK STTC encoder and decoder.

  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. 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. The figure explaining the intensity | strength of error tolerance according to the signal score of QAM. The block diagram in the case of transmission by 4 transmission 4 receiving antennas which is a modification of FIG. The block diagram in the case of mixed transmission of 16QAM SDM and 4PSK STC, which is a modification of FIG. The block diagram in the case of the mixed transmission of 4DMK SDM and 16QAM STC which is the modification of FIG. The block diagram of the radio | wireless communications system which concerns on the 2nd Embodiment of this invention. The block diagram of the radio | wireless communications system which concerns on the 3rd Embodiment of this invention. The block diagram of the radio | wireless communications system which concerns on the 4th Embodiment of this invention. (A) is a figure which shows the state transition of the state number 4 in a 4PSK STTC encoder, (b) is a figure which shows the state transition of the state number 8 in a 4PSK STTC encoder. The block diagram of the radio | wireless communications system which concerns on the 5th Embodiment of this invention. The block diagram of the radio | wireless communications system which concerns on the 6th Embodiment of this invention. The block diagram of the radio | wireless communications system which concerns on the 7th Embodiment of this invention. The block diagram of the radio | wireless communications system which concerns on the 8th Embodiment of this invention.

Explanation of symbols

10, 11, 12, 13, 14, 15, 16, 17 ... wireless transmitter, 20, 21, 22, 23, 24, 25, 26, 27 ... wireless receiver, 30, 33 ... Transmission path, 101, 155, 160, 170, 175 ... bit divider, 102 ... first 4PSK modulator, 103 ... 4PSK-STC modulator, 104 ... second 4PSK modulator 105, 106, 207, 208, 265, 271 ... adder, 107, 108 ... transmitting antenna, 140 ... first 16QAM / 4PSK modulator, 141 ... 16QAM / 4PSK-STC modulation 142, second 16QAM / 4PSK modulator, 143, receiving antenna, 144, 203, 266, transmission path estimator, 145, 225, controller, 150, first. 4P K · 16QAM · 64QAM modulator, 151 ... first 4PSK-STC modulator, 152 ... second 4PSK · 16QAM · 64QAM modulator, 156, 165 ... first STTC encoder, 157, 166 ... second STTC encoder, 161, 176, 268 ... third STTC encoder, 171 ... 4PSK modulator, 172 ... first STBC encoder, 173 ... STTC encoder, 180 ... control unit, 201 ... first receiving antenna, 202 ... second receiving antenna, 204 ... 4PSK-MLD demodulator, 205 ... Third 4PSK modulator, 206... Fourth 4PSK modulator, 209, 210... Subtractor, 211, 260... 4PSK-STC demodulator, 212, 274, 298. 250 ... 16QAM / 4PSK-MLD demodulator, 251 ... third 16QAM / 4PSK modulator, 252 ... fourth 16QAM / 4PSK modulator, 253 ... 16QAM / 4PSK-STC demodulator 256 ... 3rd transmit antenna, 261 ... 2nd 4PSK-STC modulation, 262 ... 4PSK, 16QAM, 64QAM-STC demodulator, 267, 285 ... 1st STTC decoder 269 ... multipliers, 273, 276, 287 ... second STTC decoder, 275 ... fourth STTC encoder, 278 ... fifth STTC encoder, 280,. Third STTC decoder, 290 ... STBC decoder, 291 ... 4PSK demodulator, 293 ... second STBC encoder, 294 ... STTC decoder

Claims (12)

In a wireless communication system comprising a wireless transmitter for transmitting signals from a plurality of antennas and a wireless receiver for receiving the transmitted signals by a plurality of antennas,
The wireless transmitter is
A dividing means for dividing the transmission bit string into a plurality of bit strings;
Among the plurality of divided bit strings, some bit strings are modulated by a space division multiplexing method, other bit strings are modulated by a space-time coding method, and between signal points of modulated signals modulated by the space division multiplexing method Modulation means for adjusting and modulating the distance magnitude and the distance between signal points of the modulated signal modulated by the space-time coding method;
A transmission means for adding and transmitting the modulated signal modulated by the space division multiplexing scheme and the modulated signal modulated by the space-time coding scheme;
The wireless receiver
First demodulation means for demodulating a received signal based on any one of the space division multiplexing scheme and the space-time coding scheme;
Estimating means for estimating an index indicating a transmission path condition from the received signal;
Extraction that modulates the demodulated signal by the method used by the first demodulating means and extracts a received signal corresponding to a method different from the demodulated signal method from the received signal based on the index Means,
A wireless communication system, comprising: second demodulation means for demodulating the extracted received signal by a method different from the method adopted by the first demodulation means.   The modulation means modulates such that a distance between signal points of a modulated signal modulated by a space division multiplexing method is larger than a distance between signal points of a modulated signal modulated by a space-time coding method. The wireless communication system according to claim 1.   The modulation means modulates such that a distance between signal points of a modulated signal modulated by a space division multiplexing method is smaller than a distance between signal points of a modulated signal modulated by a space-time coding method. The wireless communication system according to claim 1. The extraction means includes
Reproducing means for reproducing the output of the transmitting means from the output of the first demodulating means;
Reproduction means for reproducing the transmission path condition transmitted by the output of the transmission means from the output of the reproduction means;
The wireless communication system according to any one of claims 1 to 3, further comprising subtracting means for subtracting the output of the reproducing means from the received signal. The wireless transmitter further comprises an acquisition means for acquiring an index indicating a transmission path condition,
The wireless communication system according to any one of claims 1 to 4, wherein the modulation unit changes a modulation scheme based on the index.   6. The wireless communication system according to claim 5, wherein the modulation means further comprises control means for controlling the number of modulation multi-values based on the index.   The radio communication system according to claim 5 or 6, wherein the transmission means multiplexes and transmits a pilot signal. In a wireless communication system including a wireless transmitter that transmits signals from a plurality of antennas and a wireless receiver that receives the transmitted signals,
The wireless transmitter is
A dividing means for dividing the transmission bit string into a plurality of bit strings;
A modulation unit that encodes the plurality of divided bit sequences by space-time coding and modulates the modulation signals so that the distances between the signal points of the modulation signals modulated by these space-time coding methods are different;
Comprising a transmission means for adding and transmitting a plurality of signals modulated by a space-time coding system;
The wireless receiver
First demodulation means for demodulating a received signal based on the space-time coding scheme;
Estimating means for estimating an index indicating a transmission path condition from the received signal;
Extracting means for modulating the demodulated signal in a manner used by the first demodulating means, and extracting a received signal different from the demodulated signal from the received signal based on the index;
2. A radio communication system comprising a second demodulating means for demodulating in a manner corresponding to the extracted received signal. The extraction means includes
Reproducing means for reproducing the output of the transmitting means from the output of the first demodulating means;
Reproduction means for reproducing the transmission path condition transmitted by the output of the transmission means from the output of the reproduction means;
9. The wireless communication system according to claim 8, further comprising subtracting means for subtracting the output of the reproducing means from the received signal. The wireless transmitter further comprises an acquisition means for acquiring an index indicating a transmission path condition,
The wireless communication system according to claim 8 or 9, wherein the modulation means changes a modulation method based on the index.   The wireless communication system according to claim 10, wherein the modulation means further comprises control means for controlling the number of modulation multi-values based on the index.   The radio communication system according to claim 10 or 11, wherein the transmission means multiplexes and transmits a pilot signal.

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