Over-the-Air Implementation of Uplink NOMA

TL;DR

This paper demonstrates a practical over-the-air uplink NOMA system implementation, addressing real-world synchronization and channel estimation challenges, and validating the system through experiments and simulations.

Contribution

It presents the first practical over-the-air implementation of uplink NOMA with solutions for synchronization, channel estimation, and multi-user detection.

Findings

Successful over-the-air uplink NOMA transmission

Effective CFO and time synchronization methods

Low-complexity iterative LMMSE detector performance

Abstract

Though the concept of non-orthogonal multiple access (NOMA) was proposed several years ago, the performance of uplink NOMA has only been verified in theory, but not in practice. This paper presents an over-the-air implementation of a uplink NOMA system, while providing solutions to most common practical problems, i.e., carrier frequency offset (CFO) synchronization, time synchronization, and channel estimation. The implemented CFO synchronization method adopts the primary synchronization signal (PSS) of LTE. Also, we design a novel preamble for each uplink user, and it is appended to every frame before it is transmitted through the air. This preamble will be used for time synchronization and channel estimation at the BS. Also, a low-complexity, iterative linear minimum mean squared error (LMMSE) detector has been implemented for multi-user decoding. The paper also validates the proposed architecture numerically, as well as experimentally.