Fifth-generation (5G) wireless networks harness the extensive spectrum available in the millimeter-wave (mmWave) frequency bands which set them apart from current wireless systems in terms of directivity, propagation loss, and susceptibility to blockages. Sub-6 GHz systems can attain omni-directional coverage, displaying limited sensitivity to physical obstacles. Still, they are incapable of achieving the same level of service quality as systems outfitted with electronically steerable directional antennas offering reduced propagation loss and higher gains due to the beam directionality. In our framework, we investigate the utilization of directional, steerable mmWave antennas as integral components. The nodes communicate by manipulating the orientation of their antennas, i.e., steering their beams. To minimize dependence on a base station, the nodes are categorized into primary antennas (PAs) and secondary antennas (SAs), and they communicate in three phases: Uplink (SA to PA), Downlink (PA to SA), and PA-PA. We delve into the impact of optimal steering of the main lobe beams transmitted by these antennas as well as optimizing the time sharing among three phases. Within each phase, we assume that the nodes follow a random transmission scheduling scheme and derive the achievable rates accordingly. Through meticulous design of polynomial-time heuristics, we maximize the overall network capacity.

In this paper, we consider a device-to-device (D2D) millimeter Wave (mmWave) network that allocates a spectrum band with bandwidth BcHz exclusively to support communication of N cooperative D2D pairs over Rayleigh fading channels. The available bandwidth is divided into Ncnon-overlapping sub-bands. Each node is equipped with a directional antenna that is capable of steering its beam within its field of view. Also, each transmitter can adjust its transmit power. Aiming at maximizing the network throughput, the cooperative D2D pairs form Ncdisjoint coalitions, where the D2D pairs in a particular coalition share the same sub-band for communication and hence cause co-channel interference. We address this question: What is the best coalition among the D2D pairs, the optimal beams steering angles of directional antennas of the D2D pairs within each coalition, and the optimal transmit powers such that the network throughput is maximized? We formulate the network throughput maximization problem, subject to certain constraints, and we propose an iterative method, based on the block coordinate descent (BCD) algorithm, to solve the constrained optimization problem. Specially, we propose a coalitional game approach for coalition formation among the D2D pairs. We numerically investigate the effects of different system parameters (e.g., N, Nc, the antenna gain, the maximum allowed total transmit power), as well as the impact of optimizing coalition formation only, and optimizing transmit power only, on the network throughput maximization.