  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.
