Cancellation of Multiuser Interference due to Carrier Frequency Offsets in Uplink OFDMA

Abstract

Abstract-In uplink orthogonal frequency division multiple access (OFDMA) systems, multiuser interference (MUI) occurs due to different carrier frequency offsets (CFO) of different users at the receiver. In this paper, we present a multistage linear parallel interference cancellation (LPIC) approach to mitigate the effect of this MUI in uplink OFDMA. The proposed scheme first performs CFO compensation (in time-domain) followed by K DFT operations (where K is the number of users) and multistage LPIC on these DFT outputs. We scale the MUI estimates by weights before cancellation and optimize these weights by maximizing the average signal-to-interference ratio (SIR) at the output of the different stages of the LPIC. We derive closed-form expressions for these optimum weights. The proposed LPIC scheme is shown to effectively cancel the MUI caused by the other user CFOs in uplink OFDMA. While our proposed approach performs CFO compensation in time-domain, an alternate approach proposed recently by Huang and Letaief performs CFO compensation and interference cancellation in frequency-domain. We show that our approach performs better than the Huang & Letaief's approach when the magnitude of the CFO differences (between desired user CFO and other user CFOs) are small, whereas their approach performs better when the magnitude of the individual CFOs (of other users) are small. Since the CFO values can be arbitrary at the receiver, in order to make the receiver robust under various CFO conditions, we propose simple metrics based on CFO knowledge, which the receiver can compute and use to choose between the time-domain (ours) and the frequency-domain (Huang & Letaief's) cancellers so that better performance among the two approaches is achieved under various CFO conditions. Index Terms-Carrier frequency offset, circular convolution, linear parallel interference cancellation, optimum weights, signalto-interference ratio, uplink OFDMA.

Low Complexity Interference Aware Distributed Resource Allocation for Multi-Cell OFDMA Cooperative Relay Networks

“…However, in case of imperfect synchronization, the multiuser interference (MUI) may occur due to the different carrier frequency offsets between different users. This MUI can be mitigated using some cancellation techniques such as the one proposed in [11].…”

Complexity and Performance Comparison of Filter Bank Multicarrier and OFDM in Uplink of Multicarrier Multiple Access Networks

“…COMPUTATIONAL COMPLEXITY Table I summarizes the computational complexity of OFDMA, as presented in [7] and [9], and also that of SMTMA for different CFO compensation techniques. It is assumed that there are P users and N=P subcarriers are assigned to each user from a total of N. All operations involve complex numbers and the complexity expressions refer to the number of complex multiplications (CMs) for each case.…”

“…Huang and Letaief [8] proposed the addition of a PIC to the CLJL method. Similarly, a PIC may be adopted to reduce MAI after DFT block in SUD [9]. Successive interference cancellation (SIC) and linear multiuser detectors have also been suggested in [10] and [11], respectively.…”

Improving the OFDMA Performance with Common Carrier Frequency Offset Correction

“…Some approaches to dealing with CFOs in an OFDMA system can be found in the literature [5]- [10]. The CFO correction method that is conventionally used in single-user OFDM can be directly applied for different subscribers to cancel the estimated CFOs before the discrete-time Fourier transform (DFT) [5].…”