基于相移导频的联合用户关联与导频分配实现可扩展无蜂窝大规模多输入多输出
Joint User Association and Pilot Assignment via Phase-Shifted Pilots for Scalable Cell-Free mMIMO
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中文总结 AI 辅助
该研究提出基于自适应相移导频的联合用户关联与导频分配框架，突破正交导频序列数量限制，可大幅增加可调度UE数量，同时提升信道估计性能与连通性、公平性指标。
中文摘要 AI 辅助
无蜂窝大规模多输入多输出（CF-mMIMO）可在覆盖区域内提供均匀服务，该服务依赖于对每个用户设备（UE）的精确信道估计。这些估计值由正交导频序列获得，而序列数量受信道相干块限制。因此，随着UE密度增加，序列会被复用，由此产生的导频污染限制了系统的可扩展性。本文提出一种基于自适应相移（APS）导频设计的联合用户关联（UA）与导频分配（PA）框架，其中所有UE共享单个全带导频，且在频域应用的UE专属相移会将其信道冲激响应（CIR）置于接入点（AP）时域的连续非重叠区间内。因此，AP可分离的UE数量由子载波数量而非正交序列数量决定，UA被建模为0/1背包问题，其中物品权重为抽头数，容量为子载波数量。分析与仿真表明，所提设计调度的UE数量是传统交织（CI）基准的两倍以上；在总导频功率相等时，其均方误差（MSE）与CI基准相当，在每个子载波功率相等时，MSE更低；此外，通过在每个候选链路的分配值中惩罚UE现有连接的数量，进一步提升了第5百分位连通性和Jain公平性指数。
英文摘要
Cell-free massive multiple-input multiple-output (CF-mMIMO) promises uniform service across the coverage area, and this service relies on accurate channel estimation for every user equipment (UE). These estimates are obtained from orthogonal pilot sequences, whose number is bounded by the channel coherence block. As a result, the sequences are reused as the UE density increases and the resulting pilot contamination limits the scalability. This paper proposes a joint user association (UA) and pilot assignment (PA) framework built on the adaptive phase-shifted (APS) pilot design, in which all UEs share a single full-band pilot and a per-UE phase shift applied in the frequency domain places their channel impulse responses (CIRs) in contiguous, non-overlapping intervals of the time domain at the access point (AP). The number of UEs that an AP can separate is thus set by the number of subcarriers rather than by the number of orthogonal sequences, and the UA is formulated as a $\mathbf{0/1}$ knapsack problem whose item weights are the numbers of taps and whose capacity is the number of subcarriers. Analysis and simulations show that the proposed design more than doubles the number of UEs scheduled by the conventional interleaved (CI) benchmark. It attains the same mean-squared error (MSE) as the CI benchmark under an equal total pilot power, and a lower MSE under an equal per-subcarrier power. It further improves the 5th-percentile connectivity and Jain's fairness index by penalizing the number of existing connections of a UE in the value assigned to each candidate link.
