Max-Min Fairness of K-User Cooperative Rate-Splitting in MISO Broadcast Channel With User Relaying
Max-Min Fairness of K-User Cooperative Rate-Splitting in MISO Broadcast Channel With User Relaying
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DOI：
10.1109/twc.2020.3002891
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发表时间：
2019-10
影响因子：
10.4
通讯作者：
Yijie Mao;B. Clerckx;Jian Zhang;V. Li;M. Arafah
中科院分区：
文献类型：
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作者：
Yijie Mao;B. Clerckx;Jian Zhang;V. Li;M. Arafah
协作速率分割(CRS)策略依赖于发射机处的线性预编码速率分割和中继用户对公共消息的机会性传输，最近被证明在具有用户中继的两用户多输入单输出(MISO)广播信道(BC)中优于典型的非协作速率分割(NRS)、协作非正交多址(C-NOMA)和空分多址(SDMA)。在该工作中，将现有的两用户CRS传输策略推广到$K$用户的情况。研究了联合优化预编码器、消息拆分、时隙分配和中继用户调度的问题，以最大化基站发射功率约束下用户的最小速率为目标。针对用户调度问题的离散性和非凸性，本文提出了一种两阶段低复杂度算法来解决该问题。首先提出了基于选择$K_{1}$($K_{1})个最强用户的集中式和分散式中继协议，然后提出了一种基于逐次凸近似(SCA)的算法来联合优化时隙、预编码器和消息拆分。数值结果表明，在广泛的网络负载(欠载和过载)和用户部署(具有不同的信道强度)条件下，CRS算法的最差可达速率显著高于NRS和SDMA算法。重要的是，与CRS文献中的传统算法相比，所提出的基于SCA的算法在没有任何码率损失的情况下显著降低了计算复杂度。因此，我们得出结论：所提出的与两阶段算法相结合的$K$用户CRS比现有的传输方案更有效。
Cooperative Rate-Splitting (CRS) strategy, relying on linearly precoded rate-splitting at the transmitter and opportunistic transmission of the common message by the relaying user, has recently been shown to outperform typical Non-cooperative Rate-Splitting (NRS), Cooperative Non-Orthogonal Multiple Access (C-NOMA) and Space Division Multiple Access (SDMA) in a two-user Multiple Input Single Output (MISO) Broadcast Channel (BC) with user relaying. In this work, the existing two-user CRS transmission strategy is generalized to the $K$ -user case. We study the problem of jointly optimizing the precoders, message split, time slot allocation, and relaying user scheduling with the objective of maximizing the minimum rate among users subject to a transmit power constraint at the base station. As the user scheduling problem is discrete and the entire problem is non-convex, we propose a two-stage low-complexity algorithm to solve the problem. Both centralized and decentralized relaying protocols based on selecting $K_{1}$ ( $K_{1} ) strongest users are first proposed followed by a Successive Convex Approximation (SCA)-based algorithm to jointly optimize the time slot, precoders and message split. Numerical results show that by applying the proposed two-stage algorithm, the worst-case achievable rate achieved by CRS is significantly increased over that of NRS and SDMA in a wide range of network loads (underloaded and overloaded regimes) and user deployments (with a diversity of channel strengths). Importantly, the proposed SCA-based algorithm dramatically reduces the computational complexity without any rate loss compared with the conventional algorithm in the literature of CRS. Therefore, we conclude that the proposed $K$ -user CRS combined with the two-stage algorithm is more powerful than the existing transmission schemes.