We develop synchronization algorithms for both the downlink and the uplink of quasi-synchronous and asynchronous orthogonal frequency division multiple access systems. Unlike existing alternatives, the proposed time-and carrier-offset estimators do not require the transmission of known sequences and exhibit performance independent of the underlying channel zero locations. The only necessary assumption is that there are virtual subcarriers which are not occupied by any user. We derive a closed-form variance expression for the carrier-offset estimator at high signal-to-noise ratio (SNR), as a function of the number of active users and the SNR. We compare our method with alternative ones and validate our theoretical derivations with simulation results.
Bibliographical noteFunding Information:
Manuscript received December 16, 2000; revised May 21, 2001 and October 29, 2001. This work was supported in part by the Italian Ministry for the University and Scientific and Technological Research under the national project “OFDM Systems with Applications to WLAN Networks,” in part by IST-1999-10322 SATURN project funded by the European Community (EC) and in part by the National Science Foundation (NSF) under Wireless Initiative Grant 9979443. Some of the results in this paper have been previously reported in M. Pompili, S. Barbarossa, G. B. Giannakis, “Channel-independent nondata aided synchronization of generalized multiuser OFDM,” in Proc. ICASSP 2001, Salt Lake City, UT, May 2001, pp. 2341–2344, and in S. Barbarossa, M. Pompili, G. B. Giannakis, “Time and frequency synchronization of orthogonal frequency division multiple access system,” in Proc. ICC 2001, Helsinki, June 2001, pp. 1674–1678.
- Multicarrier systems
- Multiple access