多小区无线系统中基于机会式用户选择的多播协调
Coordinated Multicasting with Opportunistic User Selection in Multicell Wireless Systems
AI总结：
本文研究多小区多天线系统中的机会式用户选择多播，提出两层编码方案及基于SCA的发送协方差矩阵、码率和用户子集联合优化算法，以最大化或均衡组速率并降低反馈开销。
摘要：
本文针对多小区多天线无线系统，研究了采用机会式用户选择（OUS）的物理层多播。通过采用两层编码方案，在每个衰落块中应用速率自适应信道码，使被选定的用户子集（该子集在不同块间变化）能够成功解码；同时跨多个块使用应用层纠删码，确保每个用户在足够数量的块中成功解码后都能恢复消息。每个块中的发送信号和码率机会式地决定了能够成功解码的用户子集，并可被选择以最大化长期多播效率。OUS的使用不仅有助于避免由信道最差用户引起的速率限制，还有助于协调不同小区和多播组之间的干扰。本文提出了高效算法，用于设计每个块中的发送协方差矩阵、物理层码率以及目标用户子集。在单组场景中，系统参数通过最大化组速率来确定，组速率定义为物理层码率乘以每个块中能够成功解码的用户比例。在多组场景中，系统参数通过考虑一个组速率均衡优化问题来确定，该问题通过逐次凸近似（SCA）方法求解。为了进一步降低反馈开销，我们还考虑了每个块中只有部分用户反馈其信道向量的情况，并提出了一种基于期望组速率均衡的设计。除SCA外，还引入了样本平均近似技术来处理该问题中出现的概率项。计算机仿真验证了所提方案的有效性。
英文摘要：
Physical layer multicasting with opportunistic user selection (OUS) is examined for multicell multi-antenna wireless systems. By adopting a two-layer encoding scheme, a rate-adaptive channel code is applied in each fading block to enable successful decoding by a chosen subset of users (which varies over different blocks) and an application layer erasure code is employed across multiple blocks to ensure that every user is able to recover the message after decoding successfully in a sufficient number of blocks. The transmit signal and code-rate in each block determine opportunistically the subset of users that are able to successfully decode and can be chosen to maximize the long-term multicast efficiency. The employment of OUS not only helps avoid rate-limitations caused by the user with the worst channel, but also helps coordinate interference among different cells and multicast groups. In this work, efficient algorithms are proposed for the design of the transmit covariance matrices, the physical layer code-rates, and the target user subsets in each block. In the single group scenario, the system parameters are determined by maximizing the group-rate, defined as the physical layer code-rate times the fraction of users that can successfully decode in each block. In the multi-group scenario, the system parameters are determined by considering a group-rate balancing optimization problem, which is solved by a successive convex approximation (SCA) approach. To further reduce the feedback overhead, we also consider the case where only part of the users feed back their channel vectors in each block and propose a design based on the balancing of the expected group-rates. In addition to SCA, a sample average approximation technique is also introduced to handle the probabilistic terms arising in this problem. The effectiveness of the proposed schemes is demonstrated by computer simulations.
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