Abstract
This paper considers a multi-antenna multicast system with programmable metasurface (PMS) based transmitter. Taking into account of the finite-resolution phase shifts of PMSs, a novel beam training approach is proposed, which achieves comparable performance as the exhaustive beam searching method but with much lower time overhead. Then, a closed-form expression for the achievable multicast rate is presented, which is valid for arbitrary system configurations. In addition, for certain asymptotic scenario, simple approximated expressions for the multicase rate are derived. Closed-form solutions are obtained for the optimal power allocation scheme, and it is shown that equal power allocation is optimal when the pilot power or the number of reflecting elements is sufficiently large. However, it is desirable to allocate more power to weaker users when there are a large number of RF chains. The analytical findings indicate that, with large pilot power, the multicast rate is determined by the weakest user. Also, increasing the number of radio frequency (RF) chains or reflecting elements can significantly improve the multicast rate, and as the phase shift number becomes larger, the multicast rate improves first and gradually converges to a limit. Moreover, increasing the number of users would significantly degrade the multicast rate, but this rate loss can be compensated by implementing a large number of reflecting elements.
Highlights
By the year 2022, there will be 28.5 billion networked devices, and the overall mobile data traffic will reach up to 77 exabytes per month according to Cisco Visual Networking Index forecast [2]
The programmable metasurface (PMS) deployed 1m away from the base station (BS) consists of NRF sub-metasurface, each of which consists of L reflecting elements with the size of 12 × 12 mm2
The multicast rate improves as the reflection coefficient β becomes larger due to a less power loss caused by PMS reflection
Summary
By the year 2022, there will be 28.5 billion networked devices, and the overall mobile data traffic will reach up to 77 exabytes per month according to Cisco Visual Networking Index forecast [2]. Each PMS is connected with a controller which communicates with the transmitter via a separate wireless control link for coordination and exchanging channel state information (CSI) and smartly adjusts the phase shifts of reflecting elements. Such communication mode is especially useful when the direct link between the transmitter and receiver is blocked [11,12,13]. The existing experiments all focus on the scenario with only a single RF chain Motivated by these observations, in this paper, we propose a PMS-based transmitter including multiple RF chains for multicast communication systems, taking into account of finite phase shifts, and present a detailed analysis on the achievable system performance. Z ∼ CN (0, δ2) denotes a circularly symmetric complex Gaussian random variable (RV) z with zero mean and variance δ2, and z ∼ N (0, δ2) denotes a real valued Gaussian RV
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