592 research outputs found
Analysis of Outage Probability and Throughput for Half-Duplex Hybrid-ARQ Relay Channels
International audienceWe consider a half-duplex wireless relay network with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the average throughput and outage probability of the multirelay delay-limited (DL) HARQ system with an opportunistic relaying scheme in decode-and-forward (DF) mode, in which the best relay is selected to transmit the source's regenerated signal. A simple and distributed relay selection strategy is considered for multirelay HARQ channels. Then, we utilize the nonorthogonal cooperative transmission between the source and selected relay for retransmission of source data toward the destination, if needed, using space-time codes. We analyze the performance of the system. We first derive the cumulative density function (cdf) and probability density function (pdf) of the selected relay HARQ channels. Then, the cdf and pdf are used to determine the exact outage probability in the lth round of HARQ. The outage probability is required to compute the throughput-delay performance of this half-dublex opportunistic relaying protocol. The packet delay constraint is represented by L, which is maximum number of HARQ rounds. Furthermore, simple closed-form upper bounds on outage probability are derived. Based on the derived upper bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N+1, where N is the number of potential relays. In addition, simulation shows that our proposed scheme can achieve higher average throughput, compared with direct transmission and conventional tho-phase relay networks
A Simple Cooperative Diversity Method Based on Network Path Selection
Cooperative diversity has been recently proposed as a way to form virtual
antenna arrays that provide dramatic gains in slow fading wireless
environments. However most of the proposed solutions require distributed
space-time coding algorithms, the careful design of which is left for future
investigation if there is more than one cooperative relay. We propose a novel
scheme, that alleviates these problems and provides diversity gains on the
order of the number of relays in the network. Our scheme first selects the best
relay from a set of M available relays and then uses this best relay for
cooperation between the source and the destination. We develop and analyze a
distributed method to select the best relay that requires no topology
information and is based on local measurements of the instantaneous channel
conditions. This method also requires no explicit communication among the
relays. The success (or failure) to select the best available path depends on
the statistics of the wireless channel, and a methodology to evaluate
performance for any kind of wireless channel statistics, is provided.
Information theoretic analysis of outage probability shows that our scheme
achieves the same diversity-multiplexing tradeoff as achieved by more complex
protocols, where coordination and distributed space-time coding for M nodes is
required, such as those proposed in [7]. The simplicity of the technique,
allows for immediate implementation in existing radio hardware and its adoption
could provide for improved flexibility, reliability and efficiency in future 4G
wireless systems.Comment: To appear, IEEE JSAC, special issue on 4
DMT Optimality of LR-Aided Linear Decoders for a General Class of Channels, Lattice Designs, and System Models
The work identifies the first general, explicit, and non-random MIMO
encoder-decoder structures that guarantee optimality with respect to the
diversity-multiplexing tradeoff (DMT), without employing a computationally
expensive maximum-likelihood (ML) receiver. Specifically, the work establishes
the DMT optimality of a class of regularized lattice decoders, and more
importantly the DMT optimality of their lattice-reduction (LR)-aided linear
counterparts. The results hold for all channel statistics, for all channel
dimensions, and most interestingly, irrespective of the particular lattice-code
applied. As a special case, it is established that the LLL-based LR-aided
linear implementation of the MMSE-GDFE lattice decoder facilitates DMT optimal
decoding of any lattice code at a worst-case complexity that grows at most
linearly in the data rate. This represents a fundamental reduction in the
decoding complexity when compared to ML decoding whose complexity is generally
exponential in rate.
The results' generality lends them applicable to a plethora of pertinent
communication scenarios such as quasi-static MIMO, MIMO-OFDM, ISI,
cooperative-relaying, and MIMO-ARQ channels, in all of which the DMT optimality
of the LR-aided linear decoder is guaranteed. The adopted approach yields
insight, and motivates further study, into joint transceiver designs with an
improved SNR gap to ML decoding.Comment: 16 pages, 1 figure (3 subfigures), submitted to the IEEE Transactions
on Information Theor
Link Quality Control Mechanism for Selective and Opportunistic AF Relaying in Cooperative ARQs: A MLSD Perspective
Incorporating relaying techniques into Automatic Repeat reQuest (ARQ)
mechanisms gives a general impression of diversity and throughput enhancements.
Allowing overhearing among multiple relays is also a known approach to increase
the number of participating relays in ARQs. However, when opportunistic
amplify-and-forward (AF) relaying is applied to cooperative ARQs, the system
design becomes nontrivial and even involved. Based on outage analysis, the
spatial and temporal diversities are first found sensitive to the received
signal qualities of relays, and a link quality control mechanism is then
developed to prescreen candidate relays in order to explore the diversity of
cooperative ARQs with a selective and opportunistic AF (SOAF) relaying method.
According to the analysis, the temporal and spatial diversities can be fully
exploited if proper thresholds are set for each hop along the relaying routes.
The SOAF relaying method is further examined from a packet delivery viewpoint.
By the principle of the maximum likelihood sequence detection (MLSD),
sufficient conditions on the link quality are established for the proposed
SOAF-relaying-based ARQ scheme to attain its potential diversity order in the
packet error rates (PERs) of MLSD. The conditions depend on the minimum
codeword distance and the average signal-to-noise ratio (SNR). Furthermore,
from a heuristic viewpoint, we also develop a threshold searching algorithm for
the proposed SOAF relaying and link quality method to exploit both the
diversity and the SNR gains in PER. The effectiveness of the proposed
thresholding mechanism is verified via simulations with trellis codes.Comment: This paper has been withdrawn by the authors due to an improper proof
for Theorem 2. To avoid a misleading understanding, we thus decide to
withdraw this pape
- …