Circuit Design Of TD-LTE Baseband Signal Generator

With the commercial prevalence of TD-LTE and the competition intensification of mobile terminal market, terminal manufacturers have turned to the development of the entire network standard equipment. Thus, design and implementation of a baseband signal generator that can satisfy the requirements of TD-LTE and low cost makes great sense.TD-LTE baseband signal generator is designed based on FPGA+DAC platform.The baseband modulation subsystem generate of various standard compatible baseband modulated signals using quadrature modulation.OFDM subsystem complies with the referenced protocol and realizes IFFT and CP under multi-bandwidth. IFFT subsystem that supports OFDM is the key to this thesis, because IFFT under 15MHz adopts 1536-point transformation of radix 3, conventional IFFT algorithm cannot optimize accordingly when used in TD-LTE scenario with high hardware resource usage rate.With the comparison of FFT memory sharing structure and pipeline structure, balance of data through put rate and hardware resource rate, an IFFT structrue of mix radix and pipeline is designed. To save FPGA resouces, Matlab is used to get the optimized wordlength. In RTL design, shift and add algorithm replaced multiplication, number of multiplication is reduced through adding compound items in data multiplication process.Modulation like PSK, QAM and GMSK can be correctly modulated. In the test of OFDM baseband system of TD-LTE,EVM of QPSK,16QAM and 64QAM signal in the physical downslink channel are respectively 1.63%?1.27% and 0.89%, meet the design specification and can be used in practice in wireless communications.