While multi-user (MU) massive MIMO is a critical technology for next generation wireless systems, its complexity poses significant operational challenges as it entails several processes. These include user selection, precoding, power distribution among the users, and Modulation and Coding Scheme (MCS) selection. While many studies have been conducted on MU-MIMO, most have made invalid assumptions (e.g., every non-zero signal received at a user yields a non-zero rate) or excluded some essential steps (e.g., MCS selection). We revisit the problem of operating a single-cell massive MIMO network with zero-forcing precoding, and develop real-time network operation algorithms. First, we relax the real-time constraint and perform an offline study to obtain a target performance for online algorithms. The joint problem can be solved exactly offline for small to medium sized settings using branch-reduce-and-bound. For larger settings, we note that, given a choice of user selection, the problem reduces to a power distribution problem that can be solved exactly. Thus, the joint problem reduces to a search over user-sets where for each considered user-set, a power distribution problem is solved. We propose various search methods and evaluate their performance. For online operation, we leverage the problem structure to propose an algorithm based on three ideas: i) grouping, 2) MCS-aware power distribution, and 3) an iterative process to remove users that see a zero rate. The algorithm achieves 94% of the performance target set by the offline study results.

We investigate the performance of a hybrid non-orthogonal multiple access (NOMA) multi-cell downlink system (called hybrid as different users can have different successive interference cancellation (SIC) capabilities) by first formulating and solving a centralized proportional fair scheduling genie-assisted problem that jointly performs user selection, power allocation, power distribution, and modulation and coding scheme (MCS) selection. While such a genie is practically infeasible, it upper bounds the achievable performance. The results indicate that hybrid NOMA with a maximum of 2 multiplexed users can bring significant gains over a traditional OMA system (as long as enough users have the maximum SIC capability). Additionally, results show that the simple equal power allocation scheme (often used in the literature) yields performance lower than half the upper bound. Thus, we propose a simple static coordinated power allocation scheme across all cells for NOMA using a simple power map that is easily calibrated offline and show that with the calibrated power map, performance improves by 80%. Finally, we focus on the online scenario and propose a family of practical scheduling algorithms, each of them exhibiting a different trade-off between complexity (i.e., run-time) and performance.