10,633 research outputs found
Low-Density Parity-Check Codes for Nonergodic Block-Fading Channels
We solve the problem of designing powerful low-density parity-check (LDPC)
codes with iterative decoding for the block-fading channel. We first study the
case of maximum-likelihood decoding, and show that the design criterion is
rather straightforward. Unfortunately, optimal constructions for
maximum-likelihood decoding do not perform well under iterative decoding. To
overcome this limitation, we then introduce a new family of full-diversity LDPC
codes that exhibit near-outage-limit performance under iterative decoding for
all block-lengths. This family competes with multiplexed parallel turbo codes
suitable for nonergodic channels and recently reported in the literature.Comment: Submitted to the IEEE Transactions on Information Theor
Differential Amplify-and-Forward Relaying in Time-Varying Rayleigh Fading Channels
This paper considers the performance of differential amplify-and-forward
(D-AF) relaying over time-varying Rayleigh fading channels. Using the
auto-regressive time-series model to characterize the time-varying nature of
the wireless channels, new weights for the maximum ratio combining (MRC) of the
received signals at the destination are proposed. Expression for the pair-wise
error probability (PEP) is provided and used to obtain an approximation of the
total average bit error probability (BEP). The obtained BEP approximation
clearly shows how the system performance depends on the auto-correlation of the
direct and the cascaded channels and an irreducible error floor exists at high
signal-to-noise ratio (SNR). Simulation results also demonstrate that, for
fast-fading channels, the new MRC weights lead to a better performance when
compared to the classical combining scheme. Our analysis is verified with
simulation results in different fading scenarios
Optimizing Pilot Overhead for Ultra-Reliable Short-Packet Transmission
In this paper we optimize the pilot overhead for ultra-reliable short-packet
transmission and investigate the dependence of this overhead on packet size and
error probability. In particular, we consider a point-to-point communication in
which one sensor sends messages to a central node, or base-station, over AWGN
with Rayleigh fading channel. We formalize the optimization in terms of
approximate achievable rates at a given block length, pilot length, and error
probability. This leads to more accurate pilot overhead optimization.
Simulation results show that it is important to take into account the packet
size and the error probability when optimizing the pilot overhead.Comment: To be published on IEEE ICC 2017 Communication Theory Symposiu
Green Communication via Power-optimized HARQ Protocols
Recently, efficient use of energy has become an essential research topic for
green communication. This paper studies the effect of optimal power controllers
on the performance of delay-sensitive communication setups utilizing hybrid
automatic repeat request (HARQ). The results are obtained for repetition time
diversity (RTD) and incremental redundancy (INR) HARQ protocols. In all cases,
the optimal power allocation, minimizing the outage-limited average
transmission power, is obtained under both continuous and bursting
communication models. Also, we investigate the system throughput in different
conditions. The results indicate that the power efficiency is increased
substantially, if adaptive power allocation is utilized. For instance, assume
Rayleigh-fading channel, a maximum of two (re)transmission rounds with rates
nats-per-channel-use and an outage probability constraint
. Then, compared to uniform power allocation, optimal power
allocation in RTD reduces the average power by 9 and 11 dB in the bursting and
continuous communication models, respectively. In INR, these values are
obtained to be 8 and 9 dB, respectively.Comment: Accepted for publication on IEEE Transactions on Vehicular Technolog
- âŠ