BER Analysis of SCMA-OFDM Systems in the Presence of Carrier Frequency Offset

Sparse code multiple access (SCMA) building upon orthogonal frequency division multiplexing (OFDM) is a promising wireless technology for supporting massive connectivity in future machine-type communication networks. However, the sensitivity of OFDM to carrier frequency offset (CFO) poses a major challenge because it leads to orthogonality loss and incurs intercarrier interference (ICI). In this paper, we investigate the bit error rate (BER) performance of SCMA-OFDM systems in the presence of CFO over both Gaussian and multipath Rayleigh fading channels. We first model the ICI in SCMA-OFDM as Gaussian variables conditioned on a single channel realization for fading channels. The BER is then evaluated by averaging over all codeword pairs considering the fading statistics. Through simulations, we validate the accuracy of our BER analysis and reveal that there is a significant BER degradation for SCMA-OFDM systems when the normalized CFO exceeds 0.02.

A Message Passing Detection based Affine Frequency Division Multiplexing Communication System

The new generation of wireless communication technology is expected to solve the reliability problem of communication in high-speed mobile communication scenarios. An orthogonal time frequency space (OTFS) system has been proposed and can effectively solve this problem. However, the pilot overhead and multiuser multiplexing overhead of the OTFS are relatively high. Therefore, a new modulation technology based on the discrete affine Fourier transform was proposed recently to address the above issues in OTFS, referred to the affine frequency division multiplexing (AFDM). The AFDM attains full diversity due to parameter adjustment according to the delay-Doppler profile of the channel and can achieve performance similar to the OTFS. Due to the limited research on the detection of AFDM currently, we propose a low-complexity yet efficient message passing (MP) algorithm for joint interference cancellation and detection, which takes advantage of the inherent channel sparsity. According to simulation results, the MP detection performs better than the minimum mean square error and maximal ratio combining detection.