3 research outputs found
Diversity of Linear Transceivers in MIMO AF Half-duplex Relaying Channels
Linear transceiving schemes between the relay and the destination have
recently attracted much interest in MIMO amplify-and-forward (AF) relaying
systems due to low implementation complexity. In this paper, we provide
comprehensive analysis on the diversity order of the linear zero-forcing (ZF)
and minimum mean squared error (MMSE) transceivers. Firstly, we obtain a
compact closed-form expression for the diversity-multiplexing tradeoff (DMT)
through tight upper and lower bounds. While our DMT analysis accurately
predicts the performance of the ZF transceivers, it is observed that the MMSE
transceivers exhibit a complicated rate dependent behavior, and thus are very
unpredictable via DMT for finite rate cases. Secondly, we highlight this
interesting behavior of the MMSE transceivers and characterize the diversity
order at all finite rates. This leads to a closed-form expression for the
diversity-rate tradeoff (DRT) which reveals the relationship between the
diversity, the rate, and the number of antennas at each node. Our DRT analysis
compliments our previous work on DMT, thereby providing a complete
understanding on the diversity order of linear transceiving schemes in MIMO AF
relaying channels.Comment: 16 pages, 7 figure
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
A Survey on MIMO Transmission with Discrete Input Signals: Technical Challenges, Advances, and Future Trends
Multiple antennas have been exploited for spatial multiplexing and diversity
transmission in a wide range of communication applications. However, most of
the advances in the design of high speed wireless multiple-input multiple
output (MIMO) systems are based on information-theoretic principles that
demonstrate how to efficiently transmit signals conforming to Gaussian
distribution. Although the Gaussian signal is capacity-achieving, signals
conforming to discrete constellations are transmitted in practical
communication systems. As a result, this paper is motivated to provide a
comprehensive overview on MIMO transmission design with discrete input signals.
We first summarize the existing fundamental results for MIMO systems with
discrete input signals. Then, focusing on the basic point-to-point MIMO
systems, we examine transmission schemes based on three most important criteria
for communication systems: the mutual information driven designs, the mean
square error driven designs, and the diversity driven designs. Particularly, a
unified framework which designs low complexity transmission schemes applicable
to massive MIMO systems in upcoming 5G wireless networks is provided in the
first time. Moreover, adaptive transmission designs which switch among these
criteria based on the channel conditions to formulate the best transmission
strategy are discussed. Then, we provide a survey of the transmission designs
with discrete input signals for multiuser MIMO scenarios, including MIMO uplink
transmission, MIMO downlink transmission, MIMO interference channel, and MIMO
wiretap channel. Additionally, we discuss the transmission designs with
discrete input signals for other systems using MIMO technology. Finally,
technical challenges which remain unresolved at the time of writing are
summarized and the future trends of transmission designs with discrete input
signals are addressed.Comment: 110 pages, 512 references, submit to Proceedings of the IEE