A study of joint tracking algorithms of carrier frequency offset and sampling clock offset for OFDM-based WLANs

Abstract

We present three joint tracking algorithms of carrier frequency and sampling clock offsets for OFDMbased WLAN systems, such as IEEE 802.11a standard. In such systems, one symbol usually contains a few pilots so that the estimation accuracy mid robustness of conventional methods do not satisfv the system requirement. In this paper. three joint tracking algorithms for accurate frequency and sampling estimation are presented. The first method is performed by one-dimensional least square estimation and averaging over L symbols. The second algorithm compares the phase difference of the current symbol with the subsequent D-th symbol and gives better performance, especially when SNR or synchronization offset is smaller. And the third method uses twodimensional linear least square estimation within the frequency aid time domains. Siniulations using these algorithms have been performed with 16-QAM modulation schemes. Simulation results show that tlu-ee algorithms can improve the estimation accuracy and robustness.

A Study of Iterative Joint Synchronization for Time Offset and Frequency Offset in IEEE802.16d WirelessMAN OFDM System

“…m TFFT, would give rise to circular shift and still causes phase rotation as shown in the equation below: bi k = ai,k e ej2zAf (t+At) dt m(kT-Tg +At)+iAt TFFT *Hk(i -m) + n' (8) If this integer part of Af is corrected (m=O), the residual time offset At would lead to a progress phase rotation that linearly towards the edges of the bandwidth. At the edge of the 1218 (4) (5) bandwidth, the maximum phase rotation is + wAttT, (TS TFFT/NC).…”

“…A joint algorithm of frequency offset and time offset synchronizations was proposed in [5] for IEEE802.11 a. But, it improves the channel estimation accuracy and synchronization robustness by Least Square (LS) estimation over L successive symbols.…”