Capacity bounds of low-dense NOMA over rayleigh fading channels without CSI

Upper and lower bounds on capacity of low-dense code-domain NOMA were investigated in the context of 5G New Radio (5G-NR), under the worst hypothesis of no channel knowledge at the receiver, i.e. operation without channel state information (CSI). The impact of peculiar features of 5G-NR on capacity bounds of optimum receivers was investigated. The upper bound, defined as the system capacity with perfect CSI, and the lower bound corresponding to a pilot-based communication model, were found. These bounds indicated that the achievable rates of low-dense code-domain NOMA without CSI are lower, as expected, than those with perfect CSI, although the above gap vanishes to negligible values, when some of the system parameters, in particular speed of variation of the channel against symbol duration, number of simultaneous users, and system load, i.e. number of users vs. number of resource elements, favorably combine.