4,371 research outputs found
Multidimensional Index Modulation in Wireless Communications
In index modulation schemes, information bits are conveyed through indexing
of transmission entities such as antennas, subcarriers, times slots, precoders,
subarrays, and radio frequency (RF) mirrors. Index modulation schemes are
attractive for their advantages such as good performance, high rates, and
hardware simplicity. This paper focuses on index modulation schemes in which
multiple transmission entities, namely, {\em antennas}, {\em time slots}, and
{\em RF mirrors}, are indexed {\em simultaneously}. Recognizing that such
multidimensional index modulation schemes encourage sparsity in their transmit
signal vectors, we propose efficient signal detection schemes that use
compressive sensing based reconstruction algorithms. Results show that, for a
given rate, improved performance is achieved when the number of indexed
transmission entities is increased. We also explore indexing opportunities in
{\em load modulation}, which is a modulation scheme that offers power
efficiency and reduced RF hardware complexity advantages in multiantenna
systems. Results show that indexing space and time in load modulated
multiantenna systems can achieve improved performance
Robustness maximization of parallel multichannel systems
Bit error rate (BER) minimization and SNR-gap maximization, two robustness
optimization problems, are solved, under average power and bit-rate
constraints, according to the waterfilling policy. Under peak-power constraint
the solutions differ and this paper gives bit-loading solutions of both
robustness optimization problems over independent parallel channels. The study
is based on analytical approach with generalized Lagrangian relaxation tool and
on greedy-type algorithm approach. Tight BER expressions are used for square
and rectangular quadrature amplitude modulations. Integer bit solution of
analytical continuous bit-rates is performed with a new generalized secant
method. The asymptotic convergence of both robustness optimizations is proved
for both analytical and algorithmic approaches. We also prove that, in
conventional margin maximization problem, the equivalence between SNR-gap
maximization and power minimization does not hold with peak-power limitation.
Based on a defined dissimilarity measure, bit-loading solutions are compared
over power line communication channel for multicarrier systems. Simulation
results confirm the asymptotic convergence of both allocation policies. In non
asymptotic regime the allocation policies can be interchanged depending on the
robustness measure and the operating point of the communication system. The low
computational effort of the suboptimal solution based on analytical approach
leads to a good trade-off between performance and complexity.Comment: 27 pages, 8 figures, submitted to IEEE Trans. Inform. Theor
On the MIMO Channel Capacity of Multi-Dimensional Signal Sets
In this contribution we evaluate the capacity of Multi-Input Multi-Output (MIMO) systems using multi-dimensional PSK/QAM signal sets. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and the AWGN channel. However, since this gap becomes narrower when the receiver diversity order is increased, for higher-order receiver diversity the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher SNR. The tradeoffs between diversity gain, multiplexing gain, complexity and bandwidth are studied
Space-Time Signal Design for Multilevel Polar Coding in Slow Fading Broadcast Channels
Slow fading broadcast channels can model a wide range of applications in
wireless networks. Due to delay requirements and the unavailability of the
channel state information at the transmitter (CSIT), these channels for many
applications are non-ergodic. The appropriate measure for designing signals in
non-ergodic channels is the outage probability. In this paper, we provide a
method to optimize STBCs based on the outage probability at moderate SNRs.
Multilevel polar coded-modulation is a new class of coded-modulation techniques
that benefits from low complexity decoders and simple rate matching. In this
paper, we derive the outage optimality condition for multistage decoding and
propose a rule for determining component code rates. We also derive an upper
bound on the outage probability of STBCs for designing the
set-partitioning-based labelling. Finally, due to the optimality of the
outage-minimized STBCs for long codes, we introduce a novel method for the
joint optimization of short-to-moderate length polar codes and STBCs
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