# Design of Non-Orthogonal Beamspace Multiple Access for Cellular Internet-of-Things

## TL;DR

This paper introduces a non-orthogonal beamspace multiple access framework for cellular IoT, enabling massive connections with limited spectrum by non-orthogonal beam and time-frequency domain strategies, improving system performance.

## Contribution

It proposes a novel non-orthogonal beamspace multiple access scheme and three beam construction algorithms, addressing CSI acquisition and beam design challenges in massive IoT connectivity.

## Key findings

- Significant performance gains over baseline schemes.
- Derived an upper bound on weighted sum rate.
- Validated effectiveness through extensive simulations.

## Abstract

In this paper, we study the problem of massive connections over limited radio spectrum for the cellular Internet-of-Things (IoT) in the fifth-generation (5G) wireless network. To address the challenging issues associated with channel state information (CSI) acquisition and beam design in the context of massive connections, we propose a new non-orthogonal beamspace multiple access framework. In particular, the user equipments (UEs) are non-orthogonal not only in the temporal-frequency domain, but also in the beam domain. We analyze the performance of the proposed non-orthogonal beamspace multiple access scheme, and derive an upper bound on the weighted sum rate in terms of channel conditions and system parameters. For further improving the performance, we propose three non-orthogonal transmit beam construction algorithms with different beamspace resolutions. Finally, extensive simulation results show that substantial performance gain can be obtained by the proposed non-orthogonal beamspace multiple access scheme over the baseline ones.