1,033 research outputs found
Backlog and Delay Reasoning in HARQ Systems
Recently, hybrid-automatic-repeat-request (HARQ) systems have been favored in
particular state-of-the-art communications systems since they provide the
practicality of error detections and corrections aligned with repeat-requests
when needed at receivers. The queueing characteristics of these systems have
taken considerable focus since the current technology demands data
transmissions with a minimum delay provisioning. In this paper, we investigate
the effects of physical layer characteristics on data link layer performance in
a general class of HARQ systems. Constructing a state transition model that
combines queue activity at a transmitter and decoding efficiency at a receiver,
we identify the probability of clearing the queue at the transmitter and the
packet-loss probability at the receiver. We determine the effective capacity
that yields the maximum feasible data arrival rate at the queue under
quality-of-service constraints. In addition, we put forward non-asymptotic
backlog and delay bounds. Finally, regarding three different HARQ protocols,
namely Type-I HARQ, HARQ-chase combining (HARQ-CC) and HARQ-incremental
redundancy (HARQ-IR), we show the superiority of HARQ-IR in delay robustness
over the others. However, we further observe that the performance gap between
HARQ-CC and HARQ-IR is quite negligible in certain cases. The novelty of our
paper is a general cross-layer analysis of these systems, considering
encoding/decoding in the physical layer and delay aspects in the data-link
layer
Optimal Control of a Single Queue with Retransmissions: Delay-Dropping Tradeoffs
A single queue incorporating a retransmission protocol is investigated,
assuming that the sequence of per effort success probabilities in the Automatic
Retransmission reQuest (ARQ) chain is a priori defined and no channel state
information at the transmitter is available. A Markov Decision Problem with an
average cost criterion is formulated where the possible actions are to either
continue the retransmission process of an erroneous packet at the next time
slot or to drop the packet and move on to the next packet awaiting for
transmission. The cost per slot is a linear combination of the current queue
length and a penalty term in case dropping is chosen as action. The
investigation seeks policies that provide the best possible average packet
delay-dropping trade-off for Quality of Service guarantees. An optimal
deterministic stationary policy is shown to exist, several structural
properties of which are obtained. Based on that, a class of suboptimal
-policies is introduced. These suggest that it is almost optimal to use a
K-truncated ARQ protocol as long as the queue length is lower than L, else send
all packets in one shot. The work concludes with an evaluation of the optimal
delay-dropping tradeoff using dynamic programming and a comparison between the
optimal and suboptimal policies.Comment: 29 pages, 8 figures, submitted to IEEE Transactions on Wireless
Communication
Green communication via Type-I ARQ: Finite block-length analysis
This paper studies the effect of optimal power allocation on the performance
of communication systems utilizing automatic repeat request (ARQ). Considering
Type-I ARQ, the problem is cast as the minimization of the outage probability
subject to an average power constraint. The analysis is based on some recent
results on the achievable rates of finite-length codes and we investigate the
effect of codewords length on the performance of ARQ-based systems. We show
that the performance of ARQ protocols is (almost) insensitive to the length of
the codewords, for codewords of length channel uses. Also, optimal
power allocation improves the power efficiency of the ARQ-based systems
substantially. For instance, consider a Rayleigh fading channel, codewords of
rate 1 nats-per-channel-use and outage probability Then, with a
maximum of 2 and 3 transmissions, the implementation of power-adaptive ARQ
reduces the average power, compared to the open-loop communication setup, by 17
and 23 dB, respectively, a result which is (almost) independent of the
codewords length. Also, optimal power allocation increases the diversity gain
of the ARQ protocols considerably.Comment: Accepted for publication in GLOBECOM 201
Improved Delay Estimates for a Queueing Model for Random Linear Coding for Unicast
Consider a lossy communication channel for unicast with zero-delay feedback.
For this communication scenario, a simple retransmission scheme is optimum with
respect to delay. An alternative approach is to use random linear coding in
automatic repeat-request (ARQ) mode. We extend the work of Shrader and
Ephremides, by deriving an expression for the delay of random linear coding
over field of infinite size. Simulation results for various field sizes are
also provided.Comment: 5 pages, 3 figures, accepted at the 2009 IEEE International Symposium
on Information Theor
Energy efficiency of error correction on wireless systems
Since high error rates are inevitable to the wireless environment, energy-efficient error-control is an important issue for mobile computing systems. We have studied the energy efficiency of two different error correction mechanisms and have measured the efficiency of an implementation in software. We show that it is not sufficient to concentrate on the energy efficiency of error control mechanisms only, but the required extra energy consumed by the wireless interface should be incorporated as well. A model is presented that can be used to determine an energy-efficient error correction scheme of a minimal system consisting of a general purpose processor and a wireless interface. As an example we have determined these error correction parameters on two systems with a WaveLAN interfac
Robust streaming in delay tolerant networks
Delay Tolerant Networks (DTN) do not provide any end to end connectivity guarantee. Thus, transporting data over such networks is a tough challenge as most of Internet applications assume a form of persistent end to end connection. While research in DTN has mainly addressed the problem of routing in various mobility contexts with the aim to improve bundle delay delivery and data delivery ratio, little attention has been paid to applications. This paper investigates the support of streaming-like applications over DTN. We identify how DTN characteristics impact on the overall performances of these applications and present Tetrys, a transport layer mechanism, which enables robust streaming over DTN. Tetrys is based on an
on the fly coding mechanism able to ensure full reliability without retransmission and fast in-order bundle delivery in comparison to classical erasure coding schemes. We evaluate our Tetrys prototype on real DTN connectivity traces captured from the Rollerblading tour in Paris. Simulations show that on average, Tetrys clearly outperforms all other reliability schemes in terms of bundles delivery service
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