Signal design for higher capacity correlated fading signature multiple access

Fading signature multiple access (FSMA) is a promising radio access technology that utilizes the difference in users’ fading channels for joint signal detection. However, channels’ correlation has direct impact to degrade the capacity of wireless communications considerably. In this paper, efficient signal design methods are proposed to mitigate the correlation effects and maintain highest achievable channel capacity of correlated FSMA system. Two methods named as unequal power signal constellation (UPSC) and rotated signal constellation (RSC) are considered and compared with the conventional identical signal constellation (ISC) technique. Based on the principles of maximizing the minimum Euclidean distance of composite received signals, user’s data can be recovered using maximum likelihood detection irrespective of correlation values (ρ). For highly correlated channels, utilizing constellation rearrangement of the transmitted signals enables maximum achievable capacity by resolving the possible ambiguity of signal detection. For example, it is shown for four users employing QPSK modulation and communicating with three antenna receiver that maximum 8 bit/s/Hz can be achieved using UPSC and RSC compared with 4.64 bit/s/Hz for ISC at extreme correlation level of ρ = 1. The superiority of these methods provides a potential step towards efficient utilization of the available spectrum for next generation wireless and mobile communications in different channel environments.