A Channel Estimation Algorithm For MIMO-OFDM Systems Based On Training Sequence

1. IntroductionSupporting high mobility will be an important character of the future wireless communication systems. It challenges the channel estimation technique a lot and there are two tough problems in front of us, they are multipath fading channel and bandwidth efficiency. Orthogonal Frequency Division Multiplexing (OFDM) technique changed the frequency selective multipath fading channel into flat fading channel in frequency domain which effectively mitigates the effects of multipath propagation and, hence, increase data rate. In additional, Multiple Input Multiple Output (MIMO) technique can generate independently parallel multi-channel data stream in spatial at the same time, which directly and effectively increase the transmission efficiency. Therefore, combining MIMO and OFDM is believed to have the ability to achieve two purposes, the one is high transmission speed, the other is strongly reliability. Accurate channel estimation is crucial for the performance of wireless communication systems.The channel estimation methods can be divided into three categories, they are non-blind channel estimation, blind channel estimation and semi-blind channel estimation. The non-blind channel estimation generally is applicable to the continuous transmission or burst transmission system. The algorithm based on pilot symbols or trained sequence, the receiver achieves the initial estimate. When the system sends the useful information, the algorithm will use the results of the initial decision to update and complete the real-time channel estimation. The biggest different between non-blind and blind channel estimation is that the blind method is based on the limited characters of the transmitted information symbols and their statistical trait. So this kind of algorithm has the most frequency efficiency. Using the information from blind channel estimation algorithm and known sampling symbols to finish channel estimation, semi-blind channel estimation solves the problems of spectrum waste from none-blind channel estimation and high complication of blind channel estimation methods. Hence the semi-blind channel estimation algorithm for MMO-OFDM system is regarded to be a promising way for channel estimation.2. A Channel Estimation Algorithm for MIMO-OFDM Systems based on Training SequenceTo overcome the inadequacies of the original algorithm, this paper proposes a semi-blind channel estimation for MIMO-OFDM systems based on Training Sequence. In this paper, a novel pilot pattern with higher frequency efficiency is proposed, and we use a reasonable manner to insert Pilot so that the system greatly reduced the training cycle, increased data rates. Secondly, through the pilot transmission, we can get the characteristics of the transmission channels and make full preparations of the channel estimation. Finally, we have adopted a revised DDCE formula for tracking the channel changes and further enhanced the accuracy of estimates.3. Simulation and ConclusionIn this paper, a novel pilot pattern with higher frequency efficiency is proposed, and a linear minimum mean squared error LMMSE channel estimator is derived for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. In order to track the time-varying channel, an improved direct decision method is further adopted. Theoretical analysis and numerical results show that the new channel estimation scheme can offer a good performance and a high ability to track the time-varying channel and it requires a low complexity especially for systems with a large number of transmit antennas.