Cooperative Beamforming With Predictive Relay Selection for Urban mmWave Communications

Abstract

While millimeter wave (mmWave) communications promise high data rates, their sensitivity to blockage and severe signal attenuation presents challenges in their deployment in urban settings. To overcome these effects, we consider a distributed cooperative beamforming system, which relies on static relays deployed in clusters with similar channel characteristics, and where, at every time instance, only one relay from each cluster is selected to participate in beamforming to the destination. To meet the quality-of-service guarantees of the network, a key prerequisite for beamforming is relay selection. However, as the channels change with time, relay selection becomes a resource demanding task. Indeed, estimation of channel state information for all candidate relays, essential for relay selection, is a process that takes up bandwidth, wastes power and introduces latency and interference in the network. We instead propose a unique, predictive scheme for resource efficient relay selection, which exploits the special propagation patterns of the mmWave medium, and can be executed distributively across clusters, and in parallel to optimal beamforming-based communication. The proposed predictive scheme efficiently exploits spatiotemporal channel correlations with current and past networkwide Received Signal Strength (RSS), the latter being invariant to relay cluster size, measured sequentially during the operation of the system. Our numerical results confirm that our proposed relay selection strategy outperforms any randomized selection policy that does not exploit channel correlations, whereas, at the same time, it performs very close to an ideal scheme that uses complete, cluster size dependent RSS, and offers significant savings in terms of channel estimation overhead, providing substantially better network utilization, especially in dense topologies, typical in mmWave networks.Index Terms-mmWave, cooperative relay beamforming, relay selection, 2-hop relaying, mmWave channel modeling, Vehicle-to-Infrastructure.

Programmable Active Mirror: A Scalable Decentralized Router

“…Several possible scalable router use-cases are examples of cooperative diversity, which is used as an umbrella term for multiantenna, relay-reliant, multiuser, or multihop schemes intended to increase channel capacity in communication networks [6]- [9]. A substantial body of theoretical cooperative diversity research exists, often focusing on optimizing the capacity of a hypothetical network consisting of a base station and several cellphone users given power constraints and incomplete channel state information [10]- [14]. While these analytical works have not explored the challenges, potential, and emergent capabilities of large-scale relay array hardware, such as the scalable router, their analysis might be fruitfully adapted for specific scalable router use scenarios.…”

Queue-Aware Beam Scheduling for Half-Duplex mmWave Relay Networks

“…2) The newBP scheduler for the diamond network D For the diamond network D, choose parameters ρ > 0, τ > 0 and β i,j > 0, with i ∈ [N ] and j ∈ [2]. Denoted by U i (t) and V i (t) as the physical and virtual queues (backlog), respectively, with i = 0 indicating the source node and i = N +1 indicating the destination node, otherwise indicating the relay nodes.…”

“…However, mmWave transmissions suffer from high propagation loss and penetration loss, resulting in very limited range/coverage and very high susceptibility to blockage. One effective way to mitigate these effects and to increase the communication range is beamforming in combination with relaying [2], where the former is achieved by utilizing large antenna arrays on the transceivers and pointing their beams towards each other, and the latter refers to using intermediate nodes to relay the source signal to the destination [3].…”

“…The source and destination cannot communicate with each other directly because the distance between them is too large to achieve the required data rate and/or some obstacles are in between preventing direct communication. Given a set of static relays between a source-destination pair, several relay selection schemes for two-hop or multi-hop mmWave settings have been proposed in recent literature [2,3,7,8]. However, these works are limited in the selection of a single relay path with the largest end-to-end signal to noise ratio (SNR), the utilization of multiple relay paths in combination with an efficient beam scheduling scheme to further increase the network throughput is yet unexplored.…”

“…A link is active only if both nodes focus their beams to face each other. We go beyond the limitations in most existing works [2,3,7,8] which have considered only single path selection. Here we take the general optimality of the beam scheduling approach in [9,10] and find actual computational algorithms (both offline and online) to approach the beam scheduling theory in [9,10], which is information theoretically optimal for the 1-2-1 networks within a gap that depends only on the network size but not on the link capacities (i.e., on SNR).…”