Abstract
In this paper, we consider the frequency offset estimation for Orthogonal Frequency-Division Multiple Access (OF-DMA) uplink (UL) transmissions. We first analyze the negative effect of Multi-Access-Interference (MAI) on OFDMA UL, and then propose two interference reduction/elimination methods, i.e., the Reduced-Rank-Projector (RRP) and Shift-Sampling-Projector (SSP) methods, to eliminate/reduce the heavy MAI due to the frequency offsets. Finally, we propose a new training sequence group named the Round-Robin Training Sequence Group (RRTSG), which has a high interference mitigation capabilities for OFDMA UL transmission. The Cramer-Rao Lower Bound (CRLB) for an unbiased frequency offset estimator in a Multiple Access (MA) system is also derived. Numerical results show that the proposed methods are suitable to eliminate/mitigate the effect of the frequency offset on OFDMA UL transmission.
Highlights
Orthogonal Frequency-Division Multiple Access (OFDMA) is an effective Multiple Access (MA) scheme that divides the total signal bandwidth into multiple orthogonal subcarrier groups, with each group being allocated to one user [1]
Numerical results show that the proposed methods are suitable to eliminate/mitigate the effect of the frequency offset on OFDMA UL transmission
OFDMA UL Signal Model In OFDMA, each user is modulated by complex data symbols from a signal constellation, e.g., phase-shift keying (PSK) or quadrature amplitude modulation (QAM)
Summary
Orthogonal Frequency-Division Multiple Access (OFDMA) is an effective Multiple Access (MA) scheme that divides the total signal bandwidth into multiple orthogonal subcarrier groups, with each group being allocated to one user [1]. In uplink (UL) transmission, different users have different frequency offsets and result an interference-limited system [2]. Multi-Access Interference (MAI) may appear between neighboring users due to the frequency offsets. The effect of the frequency offset on OFDM/OFDMA has been analyzed considerably (see [4,5,6]). Carrier Frequency Offset and I/Q Imbalances compensations in OFDM Systems by considering subcarrier allocation are studied [16]. Synchronization in OFDMA considering the effect of MAI has been studied [17,18,19,20,21,22]. Perfect timing synchronization is considered, and only UL frequency offset estimation is discussed in this paper. E x and Var x denote the mean and the variance of x , respectively
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