Achievable Sum-rate of variants of QAM over Gaussian Multiple Access Channel with and without security
Shifa Showkat, Zahid Bashir Dar, Shahid Mehraj Shah · Advances in engineering research/Advances in Engineering Research · 2024
The performance of next-generation wireless systems (5G/6G and beyond) at the physical layer is primarily driven by the choice of digital modulation techniques that are bandwidth and power-efficient, while maintaining high data rates.Achievable rates for Gaussian input and some finite constellations (BPSK/QPSK/QAM) are well studied in the literature.However, new variants of Quadrature Amplitude Modulation (QAM) such as Cross-QAM (XQAM), Star-QAM (S-QAM), Amplitude and phase shift keying (APSK), and Hexagonal Quadrature Amplitude Modulation (H-QAM) are not studied in the context of achievable rates for meeting the demand of high data rates.In this paper, we study achievable rate region for different variants of M-QAM like Cross-QAM, H-QAM, Star-QAM and APSK.We also compute mutual information corresponding to the sum rate of Gaussian Multiple Access Channel (G-MAC), for hybrid constellation scheme, e.g., user 1 transmits using Star-QAM and user 2 by H-QAM.From the results, it is observed that S-QAM gives the maximum sum-rate when users transmit same constellations.Also, it has been found that when hybrid constellation is used, the combination of Star-QAM & H-QAM gives the maximum rate.In the next part of the paper, we consider a scenario wherein an adversary is also present at the receiver side and is trying to decode the information.We model this scenario as Gaussian Multiple Access Wiretap Channel (G-MAW-WT).We then compute the achievable secrecy sum rate of two user G-MAC-WT with discrete inputs from different variants of QAM (viz, X-QAM, H-QAM and S-QAM).It has been found that at higher values of SNR, S-QAM gives better values of SSR than the other variants.For hybrid inputs of QAM, at lower values of SNR, combination of APSK and S-QAM gives better results and at higher values of SNR, combination of HQAM and APSK gives greater value of SSR.