1 research outputs found
Multidimensional Constellations for Uplink SCMA Systems --- A Comparative Study
Sparse code multiple access (SCMA) is a class of non-orthogonal multiple
access (NOMA) that is proposed to support uplink machine-type communication
services. In an SCMA system, designing multidimensional constellation plays an
important role in the performance of the system. Since the behaviour of
multidimensional constellations highly depends on the type of the channel, it
is crucial to employ a constellation that is suitable for a certain
application. In this paper, we first highlight and review the key performance
indicators (KPIs) of multidimensional constellations that should be considered
in their design process for various channel scenarios. We then provide a survey
on the known multidimensional constellations in the context of SCMA systems
with their design criteria. The performance of some of those constellations are
evaluated for uncoded, high-rate, and low-rate LTE turbo-coded SCMA systems
under different channel conditions through extensive simulations. All
turbo-coded comparisons are performed for bit-interleaved coded modulation,
with a concatenated detection and decoding scheme. Simulation results confirm
that multidimensional constellations that satisfy KPIs of a certain channel
scenario outperform others. Moreover, the bit error rate performance of uncoded
systems, and the performance of the coded systems are coupled to their
bit-labeling. The performance of the systems also remarkably depends on the
behavior of the multi-user detector at different signal-to-noise ratio regions.Comment: Under Review in an IEEE journa