A Design Of Channel Estimation Algorithm For CMMB Baseband Receiver

CMMB protocol is a China mobile multimedia broadcasting protocol, it adapts the orthogonal frequency division multiplexing modulation method (OFDM). OFDM method is commonly used in the fourth generation mobile systems, and enjoys the merits of high transmission speed, high bandwidth efficiency and high reliability. Meanwhile, the receiver need high synchronization and channel estimation performance to avoid the inter-symbol interference and the inter-carrier interference. So, as an important part of the design of CMMB baseband receiver, this paper mainly focused on the simulation and evaluation of channel estimation algorithm, and a adaptive multi-mode channel estimation algorithm for DSP implementation.Firstly, this paper has introduced some basis theory of CMMB baseband channel estimation, such as the current development of mobile multimedia technology, OFDM modulation principle, CMMB physical layer data distribution and the construction of CMMB baseband receiver. Next, we have analyzed the implementation process of channel estimation module and divided it into three sub-modules, respectively:the discrete pilot estimation, the data carrier estimation and the channel equalization, of which the first two sub-modules’algorithm has been evaluated and optimized. This paper has summarized the algorithm and presents a improved DFT algorithm that has improved in two aspects:smooth the varying channel and reduce Gaussian noise in time domain.In order to evaluate the performance of channel estimation algorithm, this paper presents a evaluation platform build on Matlab/Simulink, and according setting different wireless channel parameters on this platform, we can obtain BER/SNR curve. The wireless channels we used in the simulation process include the AWGN channel and three multi-path channels. The simulation result indicates that the improved algorithm we presented has a better performance, especially in the multipath channel.In addition, for ease of DSP hardware, this paper presents an adaptive multi-mode channel estimation algorithm, which use SNR as the switching indicator. Multi-mode algorithm works as follows:choose different channel estimation algorithm for good or bad real-time channel, under a better channel running low complexity algorithm, and under a severe channel running high complexity algorithm to balance the implementation performance and power consumption of CMMB baseband receiver. The final adaptive multi-mode algorithm consist of the following:use LS algorithm as pilot position estimation algorithm, use the two-step Gaussian interpolation algorithm as data carrier estimation algorithm for good channel, use improved DFT algorithm as data carrier estimation algorithm for severe channel, the SNR switching threshold is SNR0.01=10. This set of algorithm can meet the demand of high performance, low power consumption in the mobile multimedia terminal transmission.