Zhang Peng, Willems Frans M J
IMEC the Netherlands, 5656AE Eindhoven, The Netherlands.
Department of Electrical Engineering, Technical University of Eindhoven, 5612AZ Eindhoven, The Netherlands.
Entropy (Basel). 2020 Apr 7;22(4):418. doi: 10.3390/e22040418.
We investigate the downlink of a cell-free massive multiple-in multiple-out system in which all access points (APs) are connected in a linear-topolpgy fronthaul with constrained capacity and send a common message to a single receiver. By modeling the system as an extension of the multiple-access channel with partially cooperating encoders, we derive the channel capacity of the two-AP setting and then extend the results to arbitrary -AP scenarios. By developing a cooperating mode concept, we investigate the optimal cooperation among the encoders (APs) when we limit the total fronthaul capacity, and the total transmit power is constrained as well. It is demonstrated that achieving capacity requires a water-pouring distribution of the total available fronthaul capacity over the fronthaul links. Our study reveals that a linear growth of total fronthaul capacity results in a logarithmic growth of the beamforming capacity. Moreover, even if the number of APs would be unlimited, only a finite number of them need to be activated. We found an expression for this number.
我们研究了一种无蜂窝大规模多输入多输出系统的下行链路，其中所有接入点（AP）通过容量受限的线性拓扑前传链路相连，并向单个接收器发送公共消息。通过将该系统建模为具有部分协作编码器的多址接入信道的扩展，我们推导出了双AP设置的信道容量，然后将结果扩展到任意AP场景。通过提出协作模式概念，我们研究了在限制前传链路总容量且总发射功率也受限的情况下，编码器（AP）之间的最优协作。结果表明，要实现容量，需要在各前传链路上对可用前传链路总容量进行注水分配。我们的研究表明，前传链路总容量的线性增长会导致波束成形容量的对数增长。此外，即使AP的数量不受限制，也只需激活有限数量的AP。我们找到了该数量的表达式。
