Abstract
Abstract In the design for a 4×4 transmitter according to DVB-T SPEC, we proposed a baseband equivalent channel model and designed a baseband receiver. The baseband equivalent channel model includes multipath fading channel, additive white Gaussian noise(AWGN) and carrier frequency offset. The receiver consist of symbol timing detection, CFO estimation, FFT processor, channel estimation, K-BEST detector, demapper, Viterbi decoder and Reed-Solomon decoder. Besides, we design of adaptive modulation based on LLR under different channel condition. The adaptive modulation use six modulation schemes which are 64QAM, 64HQAM(α = 2,β = 1), 64HQAM(α = 4,β = 1), 64HQAM(α = 2,β = 2), 64HQAM(α = 4,β = 2), 64HQAM(α = 4,β = 4), where and are two parameters in hierarchical modulation. The video data is divided into three parts according to their importance. Therefore, data partition, hierarchical modulation and adaptive modulation improve PSNR significantly under different channel conditions.