CiteULike: dcastros Athaudage

BER sensitivity of OFDM systems to time synchronization error

CRN Athaudage — 2008-06-03T14:47:10-00:00

Communication Systems, 2002. ICCS 2002. The 8th International Conference on, Vol. 1 (2002), pp. 42-46 vol.1.

This paper presents the details of a simulation based study performed to investigate the BER performance degradation (sensitivity) of OFDM systems due to time synchronization error at the demodulator. It is shown that an OFDM system incorporating a cyclic prefix (CP) has an asymmetric effect on the received constellation with synchronization error away from CP introducing intersymbol interference (ISI), while that towards the CP introducing only a phase error. We approximate the time synchronization error by a Gaussian distributed random variable, in order to evaluate the BER sensitivity of OFDM systems to timing error. The BER performance was evaluated for an AWGN channel and a multipath fading channel in terms of the synchronization error variance. The results of this investigation will be useful in developing time synchronization algorithms in OFDM systems to achieve a particular BER performance target for a given channel condition.

Adaptive OFDM synchronization algorithms based on discrete stochastic approximation

V Krishnamurthy — 2008-02-25T19:19:01-00:00

Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on], Vol. 53, No. 4. (2005), pp. 1561-1574.

This paper presents discrete stochastic approximation algorithms (DSA) for time synchronization in orthogonal frequency division multiplexing (OFDM) systems. It is shown that the discrete stochastic approximation algorithms can be effectively used to achieve a significant reduction in computational complexity compared to brute force maximum-likelihood (ML) methods for OFDM synchronization. The most important property of the proposed algorithms is their recursive self-learning capability-most of the computational effort is spent at the global or a local optimizer of the objective function. The convergence of the algorithms is analyzed. An adaptive version of the discrete stochastic approximation algorithm is also presented for tracking time-varying time delays and frequency offsets in time-selective fading channels. Detailed numerical examples illustrate the performance gains of these DSA-based synchronization algorithms.

A low complexity timing and frequency synchronization algorithm for OFDM systems

CRN Athaudage — 2007-11-11T15:35:11-00:00

Global Telecommunications Conference, 2002. GLOBECOM '02. IEEE, Vol. 1 (2002), pp. 244-248 vol.1.

The paper presents a low complexity discrete stochastic approximation algorithm for time and frequency synchronization in OFDM systems. The proposed technique can track the conditions of a slowly time varying channel where synchronization parameters, namely the symbol timing and frequency offset, vary slowly with time. The most important property of the proposed algorithm is its self-learning capability - it spends most of the computational effort at the global minimizer of the objective function. In particular, we show that the algorithm achieves an /spl epsiv/=(1-/spl rho/)/(1+/spl rho/) reduction in computational cost (in terms of complex multiplications to be performed), where /spl rho/=N/sub cp//N is the ratio between cyclic prefix length (N/sub cp/) and number of subcarriers (N) of the OFDM system (e.g. N=512 and N/sub cp/=64 gives /spl epsiv/=78%). Numerical examples illustrate the synchronization accuracy of the proposed technique in terms of symbol timing and frequency offset estimation errors.