Simulation Research On The Key Technologies Of MIMO-OFDM Transmission System In LTE Downlink

Along with the rapid development of society, the MIMO-OFDM system in LTE downlink has been a hot spot in current research field of communication, meanwhile key technologies for LTE downlink physical layer hold the dominancy in system optimization. And therefore, this paper is aimed to probe in depth into three relevant key technologies, namely OFDM, MIMO and link adaptation.This paper lays its foundation on OFDM, MIMO and link adaptation technologies, and then, in combination of LTE standard, analyzes in detail the modeling process on LTE downlink platform; a MIMO-OFDM communication simulation platform in LTE downlink physical layer is set up, which is based on IT++. Thanks to it that IT++is not only compatible with Matlab and at least neck and neck with C in velocity, but also contains many communication modules that can be called directly. In compare to conventional platforms, the platform used here is more efficient, and consumes much less user time.On the MIMO-OFDM communication simulation platform established in LTE downlink physical layer, this paper conducts research on pre-coding technique based on spatial multiplexing, mainly targeting at the ZF algorithm, MMSE algorithm, SVD algorithm, as well as certain algorithms based on water power, namely SVD algorithm, GMD algorithm, DPC algorithm and THP algorithm. Study discovers that ZF algorithm performs worst, MMSE algorithm is a little better than ZF algorithm, but both of them are of low complexity; SVD algorithm comes between the former two, the performance of SVD algorithm with water power is a little poorer than one without, while of better channel capacity; GMD algorithm is of the best performance but also high complexity; DPC algorithm outperforms THP in performance but its transmission power is high. In order to more effectively use the channel conditions, improve system performance, this article combines SVD pre-coding and adaptive modulation techniques. Since the conventional adaptive modulation Chow and Fischer algorithm cannot be directly applied to the LTE system, in this paper, an improved algorithm for Fischer is proposed, the improved algorithm proposed is also combined with SVD pre-coding algorithm, which is applied in the LTE downlink MIMO-OFDM transmission system successfully. In comparison with the classical algorithm, results show that the improved algorithm of Fischer in this paper reduces the computational complexity. At the same time, the system performance of SVD pre-coding with the adaptive modulation has been greatly improved.