On the Performance of Cell-Free Massive MIMO Relying on Adaptive NOMA/OMA Mode-Switching
On the Performance of Cell-Free Massive MIMO Relying on Adaptive NOMA/OMA Mode-Switching
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DOI：
10.1109/tcomm.2019.2952574
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发表时间：
2020-02
影响因子：
8.3
通讯作者：
M. Bashar;K. Cumanan;A. Burr;H. Ngo;L. Hanzo;P. Xiao
中科院分区：
文献类型：
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作者：
M. Bashar;K. Cumanan;A. Burr;H. Ngo;L. Hanzo;P. Xiao
分析了基于非正交多址(NOMA)的无小区大规模多输入多输出(MIMO)系统的下行链路(DL)，其中信道状态信息(CSI)利用导频进行估计。假设用户被分组到多个集群中。相同的导频序列被分配给相同集群内的用户，而分配给所有集群的导频是相互正交的。首先，在没有下行链路训练的情况下，假设在用户端采用连续干扰消除(SIC)，基于他/她的信道统计，推导出用户的带宽效率(BE)。接下来，调用经典的最大-最小优化框架，以在每个接入点(AP)功率限制下最大化用户的最小BE。将基于NOMA的无小区大规模MIMO的最大-最小用户BE与其正交多址(OMA)对手部分的用户BE进行比较，其中所有用户都采用正交导频。最后，给出了数值结果，并提出了一种基于系统平均每个用户BE的工作模式切换方案，其中模式集由模式={OMA，NOMA}给出。我们的数值结果证实了NOMA和OMA模式之间的切换点既取决于信道的相干时间长度，也取决于总用户数。
The downlink (DL) of a non-orthogonal-multiple-access (NOMA)-based cell-free massive multiple-input multiple-output (MIMO) system is analyzed, where the channel state information (CSI) is estimated using pilots. It is assumed that the users are grouped into multiple clusters. The same pilot sequences are assigned to the users within the same clusters whereas the pilots allocated to all clusters are mutually orthogonal. First, a user’s bandwidth efficiency (BE) is derived based on his/her channel statistics under the assumption of employing successive interference cancellation (SIC) at the users’ end with no DL training. Next, the classic max-min optimization framework is invoked for maximizing the minimum BE of a user under per-access point (AP) power constraints. The max-min user BE of NOMA-based cell-free massive MIMO is compared to that of its orthogonal multiple-access (OMA) counter part, where all users employ orthogonal pilots. Finally, our numerical results are presented and an operating mode switching scheme is proposed based on the average per-user BE of the system, where the mode set is given by Mode = { OMA, NOMA }. Our numerical results confirm that the switching point between the NOMA and OMA modes depends both on the length of the channel’s coherence time and on the total number of users.