2 research outputs found
Beyond Powers of Two: Hexagonal Modulation and Non-Binary Coding for Wireless Communication Systems
Adaptive modulation and coding (AMC) is widely employed in modern wireless
communication systems to improve the transmission efficiency by adjusting the
transmission rate according to the channel conditions. Thus, AMC can provide
very efficient use of channel resources especially over fading channels.
Quadrature Amplitude Modulation (QAM) is an ef- ficient and widely employed
digital modulation technique. It typically employs a rectangular signal
constellation. Therefore the decision regions of the constellation are square
partitions of the two-dimensional signal space. However, it is well known that
hexagons rather than squares provide the most compact regular tiling in two
dimensions. A compact tiling means a dense packing of the constellation points
and thus more energy efficient data transmission. Hexagonal modulation can be
difficult to implement because it does not fit well with the usual power-
of-two symbol sizes employed with binary data. To overcome this problem,
non-binary coding is combined with hexagonal modulation in this paper to
provide a system which is compatible with binary data. The feasibility and
efficiency are evaluated using a software-defined radio (SDR) based prototype.
Extensive simulation results are presented which show that this approach can
provide improved energy efficiency and spectrum utilization in wireless
communication systems.Comment: 9 page
A Survey on Design and Performance of Higher-Order QAM Constellations
As the research on beyond 5G heats up, we survey and explore power and
bandwidth efficient modulation schemes in details. In the existing publications
and in various communication standards, initially square quadrature amplitude
modulation (SQAM) constellations (even power of 2) were considered. However,
only the square constellations are not efficient for varying channel conditions
and rate requirements, and hence, odd power of 2 constellations were
introduced. For odd power of 2 constellations, rectangular QAM (RQAM) is
commonly used. However, RQAM is not a good choice due to its lower power
efficiency, and a modified cross QAM (XQAM) constellation is preferred as it
provides improved power efficiency over RQAM due to its energy efficient two
dimensional (2D) structure. The increasing demand for high data-rates has
further encouraged the research towards more compact 2D constellations which
lead to hexagonal lattice structure based constellations, referred to as
hexagonal QAM (HQAM). In this work, various QAM constellations are discussed
and detailed study of star QAM, XQAM, and HQAM constellations is presented.
Generation, peak and average energies, peak-to-average-power ratio,
symbol-error-rate, decision boundaries, bit mapping, Gray code penalty, and
bit-error-rate of star QAM, XQAM, and HQAM constellations with different
constellation orders are presented. Finally, a comparative study of various QAM
constellations is presented which justifies the supremacy of HQAM over other
QAM constellations. With this, it can be claimed that the use of the HQAM in
various wireless communication systems and standards can further improve the
performance targeted for beyond 5G wireless communication systems