Ofdm And Sc-fde, Channel Estimation And Equalization,

IEEE 802.16a standard adopts OFDM and SC-FDE as candidate standards for the next generation broadband wireless access network. Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique. It has many advantages such as high spectral efficiency, robustness to frequency selective fading and easiness of equalization. Its main disadvantages are sensitivity to synchronization errors and high peak-to-average power ratio (PAPR). Single Carrier - Frequency Domain Equalization (SC-FDE) technique is different from conventional single carrier transmission technique. In SC-FDE systems, information is transmitted in blocks, and equalization is performed in frequency domain.Coherent demodulation scheme is often adopted in OFDM system so as to acquire high performance. It needs channel state information, which is obtained through channel estimation. Channel estimation methods can be grouped into non-blind estimation, blind estimation and semi-blind estimation. Considering complexity and performance, OFDM systems usually adopt non-blind estimation.The direct DFT based channel estimation method uses comb-type pilot symbol and discrete Fourier transform (DFT) to estimate the channel. In this paper, we propose an equivalent time domain processing method to the direct DFT based method. In the new method, the operations to obtain channel impulse response are completely performed in time domain. Theoretical study shows that the proposed method has the same performance with the original method, but it has lower complexity and higher real-time characteristic in many cases.The pilot symbols will increase the PAPR of OFDM signal in some cases. PAPR reduction technologies are often used in transmitter. It causes the larger distortion in OFDM signal with comb-type pilots and introduces performance loss. In this article, we apply Newmann phasing scheme to optimize pilot symbols in order to reduce the PAPR deterioration. The optimized comb-type pilots can ease the burden of PAPR reduction in transmitter and effectively decrease the signal distortion caused by PAPR reduction.MMSE equalization is often used in SC-FDE system. This article explores the channel estimation and equalization of SC-FDE systems and acquires MMSE equalization coefficient after some derivations.