The Design Of Channel Estimation Based On CMMB System

Due to its features of multipath immunity and bandwidth efficiency, OFDM (Orthogonal Frequency Division Multiplexing)has been favored for both Europe DAB(Digital Audio Broadcasting) and DVB(Digital Video Broadcasting),and its has been a prime candidate for B3G(Beyond 3rd Generation) communications. The China Mobile Multimedia Broadcast (CMMB) system,its fhysical layer modulation also apply OFDM architecture.The requirements for OFDM system such as high data rate, high quality and high mobility, make channel estimation and signal detection techniques more strict.The present thesis mainly discusses channel estimation technology in design of baseband demodulator chip that is based on Orthogonal Frequency Division Modulat ion(OFDM), represented by China Mobile Multimedia Broadcast (CMMB) The present thesis firstly introduces wireless broadcast channel propagating characteristics, and then analyzes channel model employed by CMMB system stimulation modeling, and influence of the baseband demodulator brought by receiver non-ideal factor. Since channel in OFDM system has frequency selective and time varying characteristic, casusing amplitude and phase distortion of the transmission signal, the channel estimation must be performed dynamically on the channel, so as to obtain channel information at the receiver in time and implement demodulation in realtime and accurately. Therefore, the thesis introduces specifically a common channel estimation interpolation of OFDM system,proposing a wiener interpolation algorithm adapted for CMMB demodulator by means of simulation, in conjunction with characteristics of CMMB physical layer frame protocol and transmission channel. The plan can reduce the system implementation complexity and withstand the multi-path and the Doppler frequency shift effectively,achieve a good performance in the bad environm ent as well. It can achieve 2-5dB system performance gain compared other Interpol ation algorithms.Meanwhile the thesis proposes a dynamic estimate algorithm,through pre-estimate system Doppler frequency shift to choose time-estimate coefficient flexibly, it can improve the system performance under the high Doppler frequency shift and solves the problem in the LMMSE used for the pilot estimate.Last the thesis proposes a threshold channel estimation method for further reducing hardware power of channel estimation module.The simulate resultes indicate that the hardware power of threshold channel estimation is about one sixth of wiener channel estimation when channel is not in a bad environment.