The Research And Implementation For MIMO And Resource-mapping Of TD-LTE Small Cell Downlink

On the nowadays, Long Term Evolution (LTE) is one of the most popular mobile communication technologies, and it adopts the Multiple In Multiple Out (MIMO) and Frequency Division Multiplexing (OFDM) technology to meet the requirements of high-speed data transmission and efficient utilization of spectrum. At present, the increasing density of mobile users and exponential growth of data traffic motive the miniaturization of LTE base station, and Large Scale Integration (VLSI) is a feasible solution for implementation of small base station.In this paper, the key baseband modules of MIMO:layer mapping and precoding, and the basic module of OFDM:resource mapping in the downlink of small cell are studied. In addition, the design towards to VLSI and implementation on FPGA are carried out. The main contributions include:(1) Based on analyzing LTE protocols and deeply studying the implementation of physical layer protocol, the paper designed the hardware architecture of layer-mapping, precoding and resource-mapping and also proposed an order for processing downlink physical channels and downlink physical signals.(2) To solve the resource conflict problems in Physical Downlink Shared Channel (PDSCH) resource allocation, a systematic avoidance mechanism is proposed from three aspects:the mapping classification, jump condition and jump processing. In order to support the three types of resource allocation using in PDSCH and all configurations of system bandwidth in LTE, an efficient PDSCH resource mapping framework is also proposed through extracting parameters from bitmap, reusing memory and sharing mapping logic.(3) In the process of expanding Physical Downlink Control Channel (PDCCH), it is found that the mapping logic described in protocol is not suitable for hardware implementation. A more appropriate remapping logic is designed. And it supports three kinds of CFI configurations.(4) A new precoding operation that shifting input data to approach the result of input data multiplying by the precoding matrix is presented. It can help to avoid the use of multipliers on the premise of assuring accuracy of data.(5) The modules are firstly simulated with Modelsim and integrated with FPGA respectively, and then they are applied in the downlink transmitter, simulated and integrated in the system. The independent simulations and integrations verify that modules have the advantages of less delay, low cost and low complexity. And the system result shows that the functions of modules are comprehensive.