JP2008072403A - Eigenmode transmission method in frequency-selective channel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein research for the MIMO (Multiple-Input Multiple-Output) system which uses a plurality of antennas for transmission and a plurality of antennas for receiving has increased recently, in response to an increasing demand for high-speed and large-capacity communication in radio communication, however, since the MIMO system is capable of multiplexed signal transmission at the same frequency, and at the same time, it has become clear that the channel capacity increases the number-of-antennas min (M, N) times than in the SISO (Single-Input Single-Output) system, where M is the number of transmitting antennas and N is the number of receiving antennas, a frequency selective channel, having a delay in channels between antennas suffers from degradation of characteristics due to the influence of delay waves and interference waves. <P>SOLUTION: As a data transmission method in a frequency selective MIMO channel system, eigenmode transmission is realized, by inserting zero zones that are called "guard intervals" into a signal, in advance, on the transmitter side in the MIMO eigenmode system. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a data transmission system in a digital wireless communication system. In particular, the present invention provides a method for realizing an error control method for improving a transmission rate in a multiple-input multiple-output (MIMO) system in a frequency selective channel.

  There is eigenmode transmission as a conventional technique. When both transceivers know channel statement information (CSI), the singular value decomposition of the channel matrix is performed and the processing is performed by the transceiver, so that the communication given as an M × N matrix The path can be treated as a min (M, N) single-input single-output (SISO) system. Since the transmitter can know the channel gain for the decomposed SISO channel, a large transmission power is given to a channel with a large gain in advance, and a small amount of power is allocated to a channel with a small gain, or power. By not allocating, it is possible to expand the communication path capacity.

  In the above-described prior art, the influence of multipath cannot be ignored under an actual wireless communication path environment. However, until now, MIMO eigenmode transmission has been considered only on frequency non-selective channels, and has not been considered much on frequency selective channels.

  An object of the present invention is to provide an application method in a frequency selective channel environment in a MIMO eigenmode transmission system.

  The first invention in the present invention is applied to eigenmode transmission by singular value decomposition of a channel channel matrix by adding a guard interval to a transmission signal in a frequency selective MIMO channel environment. It is characterized by optimal power distribution based on the water injection theorem in eigenmode channels.

The second invention in the present invention is characterized in that the first invention is applied to a SISO multipath communication path.

As described above, the present invention can use transmission power without waste by performing singular value decomposition including not only the direct wave but also the delay wave power when the channel channel matrix in the transceiver is known. , Transmission efficiency can be improved.

  In the invention according to claim 1, by performing eigenmode transmission including delayed wave power by inserting a guard interval section into a transmission signal in a frequency selective MIMO communication path, a system with good transmission efficiency is obtained. Can be realized.

  According to the second aspect of the present invention, transmission without wasting delay wave power can be realized by applying eigenmode transmission to the SISO multipath channel.

  First, the outline of the present invention will be described with reference to FIG. The transmitter first performs QAM or PSK modulation of the information sequence, performs unitary matrix calculation by singular value decomposition (SVD), and then assigns each power to each antenna based on the water injection theorem. Performs optimal power distribution to the mode channel for transmission. On the receiving side, eigenmode channels are separated by unitary matrix operation. When the channel matrix in the frequency selective channel is expanded in the space-time direction, it is given by the following equation.

At this time, assuming that n _R is the number of receiving antennas, n _T is the number of transmitting antennas, and L is the number of multipaths for each channel, the channel matrix size is n _R L × n _T (2L-1), and the size of the transmission matrix Is given by n _T (2L-1) × 1, and the size of the reception matrix is given by n _R L × 1. However, the reception matrix can generally be expressed as an arbitrary n _R N-dimensional column vector. At this time, the size of the channel matrix is n _R N × n _T (N + L-1), and the size of the reception matrix Is given as n _R N × 1. Here, in order to use 100% of the energy of the transmission signal on the receiving side, (L-1) guard interval sections are added in advance before and after the transmission signal vector, and zeros are inserted. The channel matrix size at this time is n _R (N + 2L-2) x n _T (N + 3L-3), the transmission matrix size is n _T (N + 3L-3) x 1, and the reception matrix size Becomes n _R (N + 2L-2) × 1.

The number size of the channel matrix at the 2 _{n R (N + L-1} ) × n T N, the size of the transmission matrix is n _T N × 1, the size of the receive matrix is 1 × n _R (N + L- 1). Therefore, K≡rank (H) ≦ min {n _R (N + L-1), n _T N}, and the maximum number of independent eigenmode channels obtained by singular value decomposition of the channel matrix H is K. It becomes.

  Also, the transmission rate for the symbol time interval of the physical channel is R = N / (N + L-1).

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

  As an example, FIG. 2 shows a process schematic diagram of a 4-path channel model in a 4 × 1 MIMO system. By inserting a guard interval of 3 symbols for each symbol, all the energy of the transmitted signal is utilized.

The application to SISO is when n _T = n _R = 1, and the received signal at this time is given by the following equation.

  Embodiments of the present invention will be described below.

  The communication channel is a 4x1 MIMO system, and each channel is a 0dB, 3dB, or 6dB attenuated quasi-static Rayleigh fading channel, and a tapped delay line multipath model with a delay per symbol is used. Assumes. The transmission capacity was calculated when power was allocated equally to each antenna and when optimal power distribution was performed based on the water injection theorem.

  FIG. 3 shows each transmission capacity. The horizontal axis is the average received SNR per receiving antenna. By optimally allocating power to the transmitting antennas, the transmission capacity was improved compared to the equally distributed power. In addition, in both the equal power distribution and the optimum power distribution, the result of the largest transmission capacity was observed when each multipath had the same power.

  FIG. 4 shows the error rate (Bit Error Rate, BER) characteristics of the 2 × 2 MIMO system and FIG. 5 shows the 4 × 4 MIMO system by computer simulation. An SC / MMSE (Soft Canceller followed by Minimum Mean Square Error) equalizer is used for comparison. However, both perform LDPC coding at a coding rate of 0.5. The gain for the SC / MMSE equalizer is about 2 dB in FIG. 4 and about 1.5 dB in FIG. In addition, when the water injection theorem is used, a gain is obtained, although slightly, compared to the equal power.

Fig. 6 shows the BER characteristics by computer simulation of the SISO system. DFE (Decision Feedback Equalizer) is used as a comparison target. A gain of about 15 dB is obtained around 10 ^-3 .

The present invention relates to a data transmission system in a digital wireless communication system. In particular, it can be used as a method for realizing an error control method for improving the transmission rate in a MIMO system in which frequency selectivity is considered.

It is a figure which shows the system model of MxM MIMO eigenmode transmission with L multipath. It is a model figure which shows the outline of the 4 path | pass channel model in a 4x1 MIMO system. It is a figure which shows the characteristic of the transmission capacity in the 4 path | route channel model in a 4x1 MIMO system. It is the figure which compared the BER characteristic in the 2 path channel model in 2x2 MIMO system with the SC / MMSE equalizer. It is the figure which compared the BER characteristic in the 2 path channel model in the 4x4 MIMO system with the SC / MMSE equalizer. It is the figure which compared the BER characteristic in the 5-path channel model in a SISO system with a DFE equalizer.

Claims (2)

Multi-input multiple-output (MIMO, hereinafter referred to as MIMO) transmission by a single transmitter using multiple antennas for both transmitter and receiver in a frequency-selective channel environment In this transmission method, the channel control on the transmitter side including the delay wave power is performed, and the power control of the transmitter is performed using the eigenmode transmission transmitted as each channel to increase the transmission efficiency. 2. The eigenmode transmission method according to claim 1, wherein the channel is applied to a multipath communication path with a single transmission / reception antenna (single-input single-output, SISO, hereinafter referred to as SISO) for MIMO. A transmission method for canceling interference and inter-symbol interference (ISI).