Arbitrary Multiplexing Rates for Video Broadcasting

Abstract
MIMO-OFDM can not only effectively enhance the transmission rate and capacity of the wireless communication system but also effectively combat multipath fading and intersymbol interference (ISI). MIMO-OFDM technology has become one of the most proming solutions in the high data rate wireless channel transmission. In the OFDM system with transmit diversity, when the receiver knows the channel information better, the space-time codes can be decoded effectively. In order to enhance frequency efficiency, the receiver also needs to know the channel information for coherent demodulation. So channel estimation is directly related to the system performance.
In this paper, we present an improved DFT-based channel estimation method. The conventional discrete Fourier transform (DFT)-based approach will cause energy leakage in multipath channel with non-sample-spaced time delays. The improved method uses symmetric property to extend the LS estimate in frequency domain, and calculates the changing rate of the leakage energy, and selects useful paths by the changing rate. The computer simulation results show the improved method can reduce the leakage energy efficiently, and the performance of the improved channel estimation method is better than the LS and conventional DFT algorithm.
Keywords:MIMO-OFDM, LS, DFT, LMMSE, Wireless communication.
I.Introduction
MIMO-OFDM can not only effectively enhance the transmission rate and capacity of the wireless communication system but also effectively combat multipath fading and intersymbol interference (ISI). MIMO-OFDM technology has become one of the most proming solutions in the high data rate wireless channel transmission. In the OFDM system with transmit diversity, when the receiver knows the channel information better, the space-time codes can be decoded effectively. In order to enhance frequency efficiency, the receiver also needs to know the channel information for coherent demodulation. So channel estimation is directly related to the system performance by now, many channel estimation algorithms have been presented. Least squares (LS) approach is introduced in.
The LS estimation is the simplest channel estimation. This algorithm has lower complexity. However, it has larger mean square error (MSE) and easily influenced by noise and intercarrier interference. Linear minimum mean square error (LMMSE) algorithm is introduced in. LMMSE algorithm is a simplified algorithm of Minimum Mean Square Error (MMSE). Although they can achieve better performance than LS, they have higher computational-complexity and need to know the channel statistics which are usually unknown in real system. In and, the algorithms of reducing the complexity of the LMMSE are proposed. But these two modified methods still require exact channel covariance matrices.
In this paper, we focus on DFT-based channel estimation method. This algorithm can make good compromise between performance and computational complexity. Most of the published work on DFT-based channel estimation assumes each path delay is an integer multiple of the sampling interval in multipath channel. However, it is difficult to ensure this condition in real system because of the complexity and incomprehensibility of the transmission channel. In nonsample- spaced multipath channels, the channel impulse response will leak to all taps in the time domain. Reference propose a method to reduce leakage power by calculating energy increasing rate. Another approach is also proposed by extending the LS estimate with a symmetric signal of its own in. Based on these two methods, we propose a new method to solve the problem of energy leakage.