EURASIP Journal on Applied Signal Processing
A Novel Frequency Offset Estimation Method for Distributed MIMO Systems with Large Estimation Range
RSKT '09 Proceedings of the 4th International Conference on Rough Sets and Knowledge Technology
IEEE Transactions on Communications
MILCOM'06 Proceedings of the 2006 IEEE conference on Military communications
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It is known that the multiple access interference (MAI) of a quasi-synchronous (QS) multicarrier direct signal code division multiple access (DS-CDMA) system can be substantially reduced by using signature sequences having optimized cross correlation at small shifts around the origin. This paper shows that the time-frequency cross correlation function rather than the usual (time-domain) cross correlation determines the MAI when the system is operated in the presence of carrier frequency offset (CFO), which arises due to the frequency-accuracy limit of the oscillator. Several known sets of sequences having optimized time-domain cross correlation are investigated for their MAI-minimization capabilities in the presence of CFO. It is found that: (i) a system using Walsh codes or Suehiro-Hatori (1985) polyphase sequences can be driven into outage as a result of significant worst-case MAI and (ii) it is possible to minimize the MAI for systems using preferentially phased Gold codes cyclic-shift m-sequences or Lin-Chang 9see ibid., vol.45, p.221-6, 1997) sequences only if the product of chip period and maximum frequency deviation is less than around 0.01. Implications of these findings to practical implementation of systems are discussed