Mobile communications have been undergoing a generational change every ten years or so. However, the time difference between the so-called "G's" is also decreasing.While fifth-generation (5G) systems are becoming a commercial reality, there is already significant interest in systems beyond 5G, which we refer to as the sixth generation (6G) of wireless systems. In contrast to the already published papers on the topic, we take a top-down approach to 6G. More precisely, we present a holistic discussion of 6G systems beginning with lifestyle and societal changes driving the need for next-generation networks. This is followed by a discussion into the technical requirements needed to enable 6G applications, based on which we dissect key challenges and possibilities for practically realizable system solutions across all layers of the Open Systems Interconnection stack (i.e., from applications to the physical layer). Since many of the 6G applications

No abstract

We consider an uplink time-division duplex cellfree massive multiple-input multiple-output (MIMO) system in which many user equipments (UEs) are simultaneously served by many access points (APs) via simple matched filtering processing. The propagation channel is modeled via the Ricean distribution, which includes a dominant line-of-sight component on top of diffuse scattering. The Ricean K-factor of each link varies with the UE location (relative to the locations of the APs). The system performance in terms of the spectral efficiency is investigated taking into account imperfect channel knowledge. Power and APweighting control is exploited to maximize the lowest spectral efficiency across all UEs. This optimization problem can be efficiently solved via the bisection method by solving a sequence of linear feasibility problems together with the generalized eigenvalue problem. We show that by optimally selecting the power control and AP-weighting coefficients, the per-UE throughput increases significantly. Furthermore, we propose an AP selection scheme to reduce the backhaul requirements in a cell-free massive MIMO system, with slight compromise in performance.

No abstract