TD-LTE Downlink Precoding Technology Investigation

LTE is the main technology of future mobile telecommunications. In order to increase the transmit rate, MIMO multi-antenna technology was adopted in LTE. MIMO technology can increase the system capacity, improve the transmit performance, and it's convenient to be integrated with other physical layer technologies, so it has been one of the key technology of LTE physical layer. MIMO precoding can eliminate the influence of channel correlation effectivelyand restrain the influence of the. system performance which is brought by the lack of matrix order. In this paper we mainly pay attention to the LTE precoding technologyCurrent research on precoding technology has obtained some achievements. In the first part of this paper, we will introduce three kinds of precoding method, and analyse the basic theory of this three precoding technology. In the limited feedback sector precoding technology, we will introduce the design method of codebook and the select criterion of codeword. In the sector vector precoding design based on GMD method, we will discuss two precoding scheme, ZF and MMSE. We will also discuss the precoding technology based on SVD decompose and the water fill arithmetic.Secondly, this thesis describes the work flow of LTE physical layer. We expatiate the precoding technology background and some technologies which concern precoding. We mainly analyze the technology of layer mapping and precoding in 3GPP protocol.Furthermore, we discuss precoding algorithm, rank select algorithm and precoding matrix (PMI) select algorithm. Moreover, we present the complexity of the precoding algorithm. On the basis of theory analysis, in allusion to different codebook select criteria, small delay CDD precoding, different feedback delay precoding, different frequency domain precoding granularity and big delay CDD, we carry out some link-level simulations. From the simulation result, we can see that in the MIMO spatial multiplexing system in which transmit antennas are larger than layers, precoding can improve the system performance markedly; Small delay CDD system has few improvement to system performance. Along with the feedback delay and precoding granularity become larger, the system performance will reduce; etc.In the end of the paper, we propose an adaptive precoding scheme based on study of simulation result and the former research conclusion. From the simulation result, we can conclude that the adaptive precoding scheme has a better performance than general fixed precoding mode.