Abstract
The original user relay (UR) selection scheme of non-orthogonal multiple access-based cooperative opportunistic multicast scheme, which realizes inter-group cooperation between two multicast groups, ignores the distribution trend of candidate UR in the cell and adopts fixed efficient relay selection range (ERSR) to select UR. It results in high UR selection ratio. Then the coverage efficiency, defined as the ratio of successfully received users to URs, is low. To tackle this problem, a range-division user relay (RDUR) selection scheme is proposed in this paper. Firstly, it divides the circular coverage range of base station into several continuous annular areas (AAs). Secondly, different ERSRs are assigned to unsuccessfully received users in different AAs. Under different ERSR assignments, the performances of UR selection ratio and coverage ratio are analyzed. Lastly, the radius set of ERSR that optimizes system coverage efficiency is used to perform UR selection. From simulation results, with different radius sets, analytical results of UR selection ratio and coverage ratio match well with their simulated ones. It is proved that ERSR allocation affects UR selection ratio and coverage ratio. With RDUR scheme, coverage efficiency increases by at least 14% and capacity efficiency has also been improved.
Highlights
With the advancement of high-traffic mobile broadband services, the amount of mobile data has increased sharply
Simulation results shows that the coverage efficiency increases by at least 14% in comparision to the original user relay (UR) selection scheme of COM-non-orthogonal multiple access (NOMA) systems
Simulation results and analysis of the proposed range-division user relay (RDUR) scheme are shown
Summary
With the advancement of high-traffic mobile broadband services, the amount of mobile data has increased sharply. RDUR supplies optional radius for USU’s ERSR to reduce the number of unnecessary URs. Simulation results shows that the coverage efficiency increases by at least 14% in comparision to the original UR selection scheme of COM-NOMA systems. The number of UR in the ERSR of USU after the first stage of COM-NOMA follows Poisson distribution. Simulation results show that the analytic result matches well with the simulated one It verifies that UR redundancy exists in COM-NOMA with original UR selection scheme, when the number of MG user is high (more than 100). Under different ERSR radius sets, by utilizing the characteristics of Poisson distribution that its parameter is equal to its mathematical expectation, the expressions of UR selection ratio is derived.
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