Abstract
The distributed antenna systems (DAS) and non-orthogonal multiple access (NOMA) are the key technologies to boost the data rate of the cellular system in terms of small cell and multiple access, respectively. To meet the high data rate requirements for 5G and beyond, we suggest a framework of using NOMA in DAS. In the proposed scheme, RRUs which are geographically distributed in the cell serve the cell-edge users within their own coverage. Meanwhile, the macro BS, which covers the entire cell region with relatively high transmit power, supports both the cell-center and the cell-edge users with identical resources by using NOMA. Compared to the conventional DAS where the macro BS and the RRU serve the cell-center and the cell-edge users, respectively, the proposed framework also boosts the data rate of the cell-center user by improving the reliability of successive interference cancellation (SIC) at the cell-center user. In the proposed framework, this paper also proposes the optimal power allocation rules maximizing the user fairness in two different cases of instantaneous channel gain information (CGI) and channel distribution information (CDI) known at the transmitter. Also, the power allocation methods maximizing the sum-rate with a minimum rate constraint and the weighted sum-rate are presented in the case of CGI known at the transmitter. Simulation results show that the proposed framework of using NOMA in DAS can boost data rates more in a variety of system environments compared to the conventional NOMA or DAS.
Highlights
Supporting a large number of users with high data rates is one of the most rewarding challenges for generation wireless communications
We propose the optimal power allocation rules for non-orthogonal multiple access (NOMA) in the distributed antenna systems (DAS) in the cases of channel gain information (CGI) and channel distribution information (CDI) known at the transmitter
NUMERICAL RESULTS This section shows the numerical results of the proposed power allocation methods for NOMA in DAS
Summary
Supporting a large number of users with high data rates is one of the most rewarding challenges for generation wireless communications. A. CONTRIBUTIONS This paper proposes the framework of using NOMA in DAS to boost the system throughput for both user fairness and sum-rate problems. The above studies have shown that NOMA can improve fairness and sum-rate performances compared to OMA; they do not apply NOMA signaling to the DAS. The authors of [31] propose a hybrid HetNet framework where small cells employ NOMA and the massive MIMO is deployed at the macro BS This is different from our framework, where the macro BS employs NOMA and distributed RRUs send cooperation signals for supporting weak cell-edge users. The optimal power allocation rules for the max-min fairness and the sum-rate maximization problems are proposed in Section IV and Section V, separately. E[·] denotes the expectation and CN (μ, σ 2) denotes complex Gaussian distribution with mean μ and variance σ 2
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