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.

A Multiuser Detection Algorithm in the Uplink SC-FDMA System for Green Communication Network

“…The serial interference cancellation algorithm is based on subcarrier interference cancellation, which increases the receiver processing delay and reduces the signal real-time processing performance; on the other hand, the PIC algorithm can be applied on all subcarriers at the same time and eliminate interference, but its precision is limited [31]. Therefore, the Optimal Weight Parallel Interference Cancellation (OWPIC) algorithm is proposed in this paper to eliminate multiuser access interference introduced by frequency offsets, in order to improve the accuracy of the parallel interference cancellation algorithm and reduce iterations.…”

Generalised grouped minimum mean‐squared error‐based multi‐stage interference cancellation scheme for orthogonal frequency division multiple access uplink systems with carrier frequency offsets

“…Orthogonal frequency division multiple access (OFDMA) has recently attracted a great deal of research interest because of its potential of high spectral efficiency, inherent immunity to multipath fading and simplified equalisation [1][2][3][4][5][6][7][8][9][10][11][12]. It has been selected as one of the physical-layer multiple-access technologies in the recent wireless metropolitan area network (MAN) standard IEEE 802.16 [13] and 3GPP-LTE [14].…”

“…Firstly, CFO estimation is a difficult job in uplink OFDMA, apparently because of the presence of multiple CFOs [3,8,12,15,16]. Secondly, the detection is also challenging even given perfect CFO estimation, because the compensation of one user's CFO would misalign other users and cause severe MUI [5,9,11,[17][18][19][20]. It is a common practice to employ a particular synchronisation policy where the CFOs are estimated during the downlink phase and compensated at each user before uplink transmission [8,21].…”

“…In [17], the CLJL scheme (named after the four authors' initials) was proposed to compensate the CFOs after the discrete Fourier transform (DFT) using circular convolution rather than before the DFT. Apart from the CLJL scheme, other schemes can be roughly grouped into two categories: one is for interference cancellation (IC) schemes including parallel IC (PIC) using circular convolution, such as Huang-Letaief circular convolution (HLCC) [10] and weighted linear PIC (WLPIC) [11] schemes, and also including selective PIC (SPIC) [9] and successive IC (SIC) schemes [18]; the other is for minimum mean squared error (MMSE)-based schemes [5,19,20]. On one hand, the above IC schemes, namely, CLJL, HLCC, WLPIC, cannot provide satisfactory performance when the normalised CFOs (by subcarrier spacing) are greater than 0.3 (or less than −0.3), whereas the range of the normalised CFOs [-0.5, 0.5) is more reasonable [19].…”

Cancellation for frequency offset in OFDM system based on TF-LMS algorithm

“…However, the training sequence needs lots of symbols. MANOHAR et al [19] proposed a multistage linear parallel interference cancellation (LPIC) to mitigate the effect of this multi-user interference (MUI) on the uplink of OFDM algorithm, which needed a large complex.…”