A Fair Power Allocation Approach to NOMA in Multiuser SISO Systems

Abstract

Abstract-A non-orthogonal multiple access (NOMA) approach that always outperforms orthogonal multiple access (OMA) called Fair-NOMA is introduced. In Fair-NOMA, each mobile user is allocated its share of the transmit power such that its capacity is always greater than or equal to the capacity that can be achieved using OMA. For any slow-fading channel gains of the two users, the set of possible power allocation coefficients are derived. For the infimum and supremum of this set, the individual capacity gains and the sum-rate capacity gain are derived. It is shown that the ergodic sum-rate capacity gain approaches 1 b/s/Hz when the transmit power increases for the case when pairing two random users with i.i.d. channel gains. The outage probability of this approach is derived and shown to be better than OMA.The Fair-NOMA approach is applied to the case of pairing a near base-station user and a cell-edge user and the ergodic capacity gap is derived as a function of total number of users in the cell at high SNR. This is then compared to the conventional case of fixed-power NOMA with user-pairing. Finally, Fair-NOMA is extended to K users and it is proven that the capacity can always be improved for each user, while using less than the total transmit power required to achieve OMA capacities per user.

Dynamic Fractional Frequency Reuse Diversity Design for Intercell Interference Mitigation in Nonorthogonal Multiple Access Multicellular Networks

“…However, this behavior will change as SNR increases and for considerably larger values, the capacity performance of fixed and fair NOMA approaches will be almost similar as shown in Figure 5. This behavior has also been highlighted in [42] and as the SNR approaches infinity no matter how much power is allocated to the stronger user, the capacity increase will be constant.…”

“…Outage performance of proposed scheme can be analyzed by obtaining probability of edge users being in outage from (12) for the proposed scheme. For conventional NOMA and OMA schemes, outage probabilities were approximated as shown in detail by Oviedo [42]. Final formulas have been included for reference in the Appendix.…”

“…Outage performance analysis has already been performed for NOMA and OMA systems in previous works like Oviedo [42], which has been utilized in this paper for comparison purposes. According to channel gain information (|ℎ 2 | > |ℎ 1 |), 1 and 2 will be present in the edge and center region of the cell, respectively.…”

“…Here, outage probability expressions have been presented from [42] for OMA users that are given with respect to channel gain experienced within a cluster by users in different cell zones. Proof.…”

Fundamentals of Power Allocation Strategies for Downlink Multi-User NOMA With Target Rates

“…One thing that is not addressed in this paper is the fact that the channel SNR gains can be used in the design of the power allocation coefficients. Comparing these results to the multiuser approaches similar to that in [11] can provide a very quick and simple assessment as to whether the channel SNR gains are strong enough to support the target rates. Further studies about how this type of phenomenon is exhibited and described theoretically in more complex cellular deployments is also critical, such as in multi-point and heterogeneous cellular networks.…”