JP5360744B2 - Transmission system combining frequency domain equalization and asynchronous detection method in frequency selective MIMO communication channel for FSK signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission system that allows signal separation between antennas and compensation of a frequency selectivity communication path in transmission of SISO and transmission of multi-input and multi-output by a single transmitter and a single receiver in which both the transmitter and the receiver use a plurality of antennas. <P>SOLUTION: Under an environment of a frequency selectivity communication path in transmission using a frequency-shift keying (FSK) system adopting an asynchronous energy detection system, an analog signal is sampled before input to a detector on the reception side so as to execute frequency domain equalization (FDE) to its discrete time signal. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a data transmission system in a digital wireless communication system. In particular, with respect to FSK signals employing the asynchronous detection system, in multi input to the frequency-selective channel, multiple-output (Multiple-Input Multiple-Output, MIMO, hereinafter referred to as "MIMO".) Simple reception mechanism system The present invention provides a method for realizing excellent bit error rate characteristics.

As a first conventional technique, there is a maximum likelihood sequence estimation (hereinafter referred to as “MLSE”) method using the Viterbi algorithm. The MLSE for the FSK signal compares the received sequence with all sequences that may have been transmitted. As an example, in order to decode a binary sequence of length L bits, the path metric of 2 ^L different code sequences that may have been transmitted (in the received sequence Y, between signal points with the replica signal) The most probable code sequence X that minimizes this path metric is selected.

As a third conventional technique, there is frequency domain equalization (hereinafter referred to as “FDE”). The receiver side converts the received data into the frequency domain by fast Fourier transform (FFT), and simultaneously performs frequency equalization and signal separation using a method called Nulling that multiplies the MMSE criterion weight matrix. After this processing, the data is demodulated by returning to the time domain by inverse fast Fourier transform (IFFT).
As a fourth conventional technique, there is a Reed-Solomon code (hereinafter referred to as “RS code”). RS encoding is applied to binary data, and redundant bits having redundancy are added to the binary data in addition to information bits. On the receiving side, RS decoding is performed on the obtained binary data, and if there is a bit whose determination is wrong, it is corrected.

  Since the asynchronous energy detection method of the FSK signal is a non-linear modulation method, an example using MLSE has been studied for equalization of the frequency selective channel for the detector output. However, the Viterbi algorithm increases the number of states required for equalization as the number of multipath delay waves considered increases, so the number of states necessary for equalization increases exponentially. , Difficult to use.

The first aspect of the present invention is a transmission using a frequency shift modulation (FSK) method employing an asynchronous energy detection method, and in a frequency selective channel environment, before receiving the input to the detector on the receiving side. By sampling an analog signal and performing frequency domain equalization on the discrete time signal , the transmitter and receiver have a single transmitter with multiple antennas, multiple inputs with a single receiver, multiple inputs In the transmission of output (MIMO), the transmission system is capable of signal separation between antennas and compensation of a frequency selective communication path.

The present invention first invention in the, sampling is performed at the rate of c times within one symbol time relative to the received FSK signal T _S, performs FDE for discrete time signal obtained by so Thus, frequency selectivity is equalized in the frequency domain.
According to a second aspect of the present invention, the analog signal is sampled before the energy detector and the FDE is performed on the discrete time signal, thereby achieving both asynchronous detection and linear equalization technology. This is a transmission system that realizes the use of the FSK signal in the MIMO communication path adopting the asynchronous detection system (claim 2).

  The second invention in the present invention realizes the MIMO systemization of the FSK signal with a simple system configuration by performing signal separation between data streams transmitted from each antenna simultaneously with equalization by FDE in the MIMO communication path It is characterized by that.

  According to a third aspect of the present invention, when the Reed-Solomon code (RS code) is applied to the binary data to be transmitted, the number of bits included in one byte of the RS code is one symbol in multi-level modulation. RS code is selected so that it is an integral multiple of the number of bits included in RS, and binary data is RS encoded, then modulated and transmitted to a multi-level modulation signal, and on the receiving side, binary data obtained by symbol determination On the other hand, the transmission system performs RS decoding.

  The third aspect of the present invention is characterized in that it is not necessary to synchronize the phase on the receiving side by installing an energy detector in the subsequent stage of the FDE.

  As described above, the present invention is a transmission method using an FSK signal that employs an energy detection method, obtains a discrete time signal by sampling a received signal, performs FDE on the output, and then detects the signal with an energy detector. This makes it possible to use linear equalization technology for FSK signals that employ an asynchronous detection method that does not require synchronization of the phase of the received signal on the receiving side, and to make the FSK signal a MIMO communication channel with a simple system configuration. It can be realized.

First, the outline of the present invention will be described with reference to FIG. FIG. 1 shows the case of the SISO system. On the transmitter side, the modulated data is divided into blocks of n symbols, and a cyclic prefix (hereinafter referred to as “GI”) is used as a guard interval (hereinafter referred to as “GI”) as shown in FIG. CP ”) is added and transmitted from the transmitting antenna. The receiver side samples the analog reception signal at the sampling frequency f _s = 1 / Δt to obtain a discrete time signal. Here, if c sample values are taken per symbol, T _s = cΔt. The discrete time signal thus obtained is compensated for intersymbol interference (hereinafter referred to as “ISI”) of the frequency selective channel by FDE. Thereafter, detection is performed using the energy detector shown in FIG. The signal input to the energy detector is sampled at the time of equalization by FDE and becomes a discrete time signal. However, since the sampling division number c is sufficiently large, it can be regarded as a continuous signal. This continuous signal is detected by M energy detectors, and symbol determination is performed by a hard decision using the M outputs to obtain received data bits. In the case of a MIMO system, the system is as shown in FIG. 4, and FDE performs signal separation between data streams transmitted from each antenna simultaneously with ISI compensation.
The signal y (k) obtained after GI removal at the receiver side is expressed by the following equation.

In Equation 1, y (k) is the received signal vector of the k-th symbol, x (k) is the transmitted signal vector, w (k) is the noise vector, and the multipath delay wave number is L. The channel matrix H _l is expressed by a matrix of n _R × n _T as shown in Equation 2 when the number of transmitting antennas n _T and the number of receiving antennas n _R , and is a time-invariant complex Gaussian variable for the FFT processing block unit. Take the elements of. Here, the case of n _T = 1 and n _R = 1 is the SISO system.

Next, the received signal y (k) that has passed through the multipath channel is converted into the frequency domain by FFT, and then frequency domain equalization and signal separation are simultaneously performed using the MMSE weight matrix W _MMSE (k) of Equation 3. Do (Nulling in the frequency domain).

In Equation 3, G (j) is a MIMO channel matrix at the j-th point on the frequency axis, σ ² is noise variance, and In is an n _{T- th} unit matrix. Then, return to the time domain by IFFT.

The discrete time signal output from the FDE is input to the energy detector. In the energy detector, the detector 1 detects the energy of the frequency f ₁ and the detector M detects the energy of the frequency f _M. Wherein _{e 1} the output of the energy detector in each _{frequency, ..., e l, ...,} and e _M. However e _l means the energy of the received signal frequency is f _l. The signal input to the energy detector is sampled at the time of equalization by FDE and becomes a discrete time signal. However, since the sampling division number c is sufficiently large, it can be regarded as a continuous signal. These continuous signals are detected by M energy detectors, and symbol determination is performed by hard decision using the output thereof, and received data bits are obtained.

FIG. 5 shows a system when RS code is further applied to the present invention. On the transmission side, RS encoding is performed on the binary data to be transmitted, redundant bits are added to the information bits, and then M-FSK modulation is performed. On the receiving side, RS decoding is performed on the obtained binary data, and if an error has occurred in symbol determination, it is corrected. Not only M-FSK but also multi-level modulation, when an error occurs in symbol determination, a maximum of log ₂ M errors are generated in a binary data sequence. This can be regarded as a burst error. Since the RS code performs error correction in byte units, by selecting the RS code so that the number of bits included in one byte in the RS code is an integer multiple of the number of bits included in one symbol in multilevel modulation, Efficient error correction is possible.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples from the first.

The communication path between the transmitting and receiving antennas is a 2-path frequency selective quasi-static Rayleigh fading channel with 1 dB attenuation that is independent of each other. The delay profile of this channel is shown in FIG.
The M-FSK signal was implemented for M = 2,4,16. The division number c is c = 8 when M = 2, c = 16 when M = 4,
When M = 16, c = 32. The modulation index of the M-FSK signal is 0.7.

  One block of FDE includes 16 symbols (that is, n = 16). Therefore, one block of FDE is c × n = 128 points in M = 2 of M-FSK, 256 points in M = 4, 512 points in M = 16, and Guard Interval length is c × n / 4 points. . It is also assumed that channel estimation of the communication channel is complete on the receiving side.

For an SISO system with 1 × 1 antennas, the error rate (Bit) by computer simulation when M = FSK M = 2 in FIG. 7, M = 4 in FIG. 8, and M = 16 in FIG. (Error Rate, BER) characteristics. In all cases, SISO systems and 2 × 2, 4 × 4 MIMO systems are implemented. As an object to be compared, BER characteristics are shown when the equalizer is not used, when MLSE is used, and when the FDE weight matrix is the ZF weight matrix W _ZF (k) of Equation 4. 7 to 9, MLSE in SISO transmission and FDE MMSE, which is the inventive method, have degradations of 10.0 dB, 11.0 dB, and 10.5 dB at M = 2, 4, and 16, respectively. However, when using MMSE weights and using ZF weights, it can be seen that the FDE equalizer can be applied to the FSK energy detection method and ISI can be removed.

Further, for a SISO system having 1 × 1 antennas and a 2 × 2, 4 × 4 MIMO system, M-FSK M = 2 in FIG. 10, M = 4 in FIG. 11, M in FIG. The BER characteristic by computer simulation when = 16 is shown. As a comparison object, BER characteristics when using ZF weight in FDE are shown. It can be seen that MIMO communication using M-FSK can be realized with the invented transceiver system configuration both when using MMSE weights and when using ZF weights. Furthermore, compared to the SISO channel, the MIMO channel simultaneously transmits multiple streams for each transmission antenna (spatial multiplexing), so the transmission speed is twice as high for the 2x2 antenna and four times as high as the 4x4 antenna. It has gained.

  Subsequently, BER characteristics are shown in FIG. 13 for the system shown in FIG. 5 in which RS encoding is performed. This time, we performed RS (15,11) coding for 16-valued-FSK with M = 16, modulation index h = 0.7, and MIMO 2 × 2 antenna. Comparing the case of RS (15,11) coding and the case of no coding, the coding gain of about 0.7dB is obtained with ZF standard and about 1.8dB with MMSE standard by applying RS coding. I understand that.

  The present invention relates to a data transmission system in a digital wireless communication system. In particular, linear equalization technology can be used for FSK signals, which are nonlinear modulation methods that employ energy detection, and MIMO systemization is possible with a simple configuration, and transmission speed can be reduced. It can be used as a digital wireless communication system that realizes improvement and excellent bit error rate characteristics.

It is a figure which shows the system model of the SISO system of a transmitter / receiver. It is a figure which shows addition of a guard interval. It is a figure which shows the system model of an energy detector. It is a figure which shows the system model of the MIMO system of a transmitter / receiver. In the MIMO system, it is a figure which shows the system model of the transmitter / receiver which performed RS encoding. It is a model figure which shows the outline of a multipath channel model. It is the figure which showed the comparison result of the BER characteristic by computer simulation when 2-FSK is used for the modulation in the SISO system. It is the figure which showed the comparison result of the BER characteristic by the computer simulation when 4-FSK is used for the modulation in the SISO system. It is the figure which showed the comparison result of the BER characteristic by the computer simulation when 16-FSK is used for the modulation in the SISO system. It is the figure which showed the comparison result of the BER characteristic by the computer simulation when 2-FSK is used for the modulation in the 2 × 2, 4 × 4 MIMO system. It is the figure which showed the comparison result of the BER characteristic by computer simulation at the time of using 4-FSK for a modulation | alteration in a 2 * 2 and 4 * 4 MIMO system. It is the figure which showed the comparison result of the BER characteristic by computer simulation at the time of using 16-FSK for a modulation | alteration in a 2 * 2 and 4 * 4 MIMO system. It is the figure which showed the comparison result of the BER characteristic by computer simulation when 16-FSK is used for modulation and RS (15,11) encoding is performed in a 2 × 2 MIMO system.

Claims (3)

Among transmissions using frequency shift keying (hereinafter referred to as “FSK”), which employs an asynchronous energy detection method, input to the detector on the receiving side in a frequency selective channel environment A single transmitter using multiple antennas for both the transmitter and receiver by sampling the analog signal before performing frequency domain equalization (FDE) on the discrete time signal. , A transmission system capable of signal separation between antennas and compensation of frequency selective channels in multi-input, multiple-output (MIMO) transmission by a single receiver .   In claim 1, by sampling the analog signal before the energy detector and performing FDE on the discrete time signal, both the asynchronous detection method and the linear equalization technique are compatible, and the asynchronous detection method is adopted. A transmission method that realizes the use of FSK signals on MIMO channels.   The number of bits included in one byte in the RS code when the Reed-Solomon code (hereinafter referred to as “RS code”) is converted to binary data to be transmitted. The RS code is selected so that it is an integral multiple of the number of bits included in one symbol in the modulation, the binary data is RS-coded, then modulated and transmitted to a multi-level modulation signal, and obtained by symbol determination on the receiving side A transmission method that performs RS decoding on binary data.