Exploiting the degree of freedom in the frequency domain and the near-far effect among different access points (APs), this paper proposes an opportunistic transmission scheme in cell-free massive MIMO-OFDM systems. The key idea is to orthogonally assign subcarriers among different users, so that there is only one user on each subcarrier. Then, a user is only served by its near APs through opportunistic selection, while the far APs are deactivated to avoid wasting power over their channels with severe propagation losses. Moreover, the number of active APs per subcarrier becomes small due to the opportunistic selection, making the use of downlink pilots and coherent detection feasible. As corroborated by numerical results, the proposed scheme can bring a significant performance boost in terms of both power efficiency and spectral efficiency.
翻译:本文探讨频率领域自由的程度和不同接入点的近距离效应,提出了无细胞大型MIMO-OFDM系统的机会性传输计划,关键的想法是在不同用户之间分配子载体,这样每个子载体只有一名用户,然后,用户只能通过机会选择获得其接近的AP服务,而远处的AP则被停止使用,以避免在频道上浪费权力,造成严重传播损失。此外,由于机会性选择,每个子载体的活性AP数量越来越少,因此使用下行连接试点项目和连贯检测是可行的。 数字结果证实,拟议的计划可以在功率和光谱效率两方面带来显著的绩效提升。