Over-the-Air Implementation of Uplink NOMA

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.Comment: 6 pages, 7 figures, in Proc. IEEE Global Communications Conference (GLOBECOM), 201

On the Performance of QPSK Modulation Over Downlink NOMA: From Error Probability Derivation to SDR-Based Validation

“…In these three articles, the analysis was limited to only two users contrary to our implementation which extended the analysis to a larger number of users. Another experimental demonstration of NOMA with more than two users is described in [13], where the authors study the performance of this multiple access technique for uplink communications which remains different from our testbed derived for downlink NOMA.…”

Improving NOMA Multi-Carrier Systems With Intentional Frequency Offsets

“…where f c is the carrier frequency, f n is the frequency of the nth sub-carrier, p(t) is the pulse shaping function, and a n (b n ) is the data symbol transmitted on the nth sub-carrier for the user 1 (2). P k is the transmit power for the kth user with the total power constraint P at BS, i.e.…”

“…Thus, the received signal at the kth user becomes r k (t) = e −j2πfct x(t)+n k (t) where n k (t) is the white Gaussian noise at User k with variance σ 2 k . Without loss of generality, we assume that User 1 has a better channel, i.e., σ 2 1 < σ 2 2 and this order is known by the transmitter and both users. Thus, the mth sub-carrier correlation demodulator at User k provides the decision variable for transmitted symbols a m and b m…”

“…In FAP-NOMA, the SIC detection is used with some modifications. Based on the assumption of User 1 being the stronger user, it can use the sample set of r 2 1 to decode the intended symbols for User 2 and subtract them from the received signal. Then, it will be able to decode its own symbols with no interference from User 2.…”

“…In most of the work in the literature, perfect synchronization in time and frequency is a common presumption. In fact, the asynchrony is mostly considered as an impairment [1], [2] where different synchronization methods are applied to eliminate it [3]. However, by using appropriate transceiver design, asynchrony can indeed be beneficial.…”