Ergodic Capacity Analysis of MSK-Type Signal-Based Uplink Asynchronous NOMA With Imperfect CSI and SIC Over Generalized Fading Channels

Recently, asynchronous non-orthogonal multiple access (ANOMA), that can further enhance the performance of NOMA, has gained much attention. Considering the demands of resource-constrained wireless communications and green communications, power-efficient minimum shift keying-type (MSK-type) signals have also been introduced into uplink ANOMA, but they are only for a basic flat fading channel and perfect conditions. In this paper, an uplink ANOMA based on MSK-type signals with imperfect channel state information and successive interference cancellation over generalized fading channels is proposed, and its ergodic capacity is investigated. Specifically, the system model is first established. Then, a moment generating function (MGF)-based ergodic capacity expression applicable to general fading channels with known MGF is derived. Based on the expression, the integral expressions for the ergodic capacity over Rayleigh and Rician fading channels are exactly derived, respectively, and their closed-form expressions are also provided by exploiting the Gauss-Laguerre method. Further, their expressions with perfect conditions, asymptotic expressions at high signal-to-noise ratio (SNR), and high SNR slopes are also derived. The accuracy of the expression is verified by numerical and simulation results. It also shows the superiority of the proposed scheme over conventional OMA and ANOMA with linear modulation, and the relationship between system performance and time offsets, imperfect conditions, channel differences, and modulation formats.