23 research outputs found
Online multipath convolutional coding for real-time transmission
Most of multipath multimedia streaming proposals use Forward Error Correction
(FEC) approach to protect from packet losses. However, FEC does not sustain
well burst of losses even when packets from a given FEC block are spread over
multiple paths. In this article, we propose an online multipath convolutional
coding for real-time multipath streaming based on an on-the-fly coding scheme
called Tetrys. We evaluate the benefits brought out by this coding scheme
inside an existing FEC multipath load splitting proposal known as Encoded
Multipath Streaming (EMS). We demonstrate that Tetrys consistently outperforms
FEC in both uniform and burst losses with EMS scheme. We also propose a
modification of the standard EMS algorithm that greatly improves the
performance in terms of packet recovery. Finally, we analyze different
spreading policies of the Tetrys redundancy traffic between available paths and
observe that the longer propagation delay path should be preferably used to
carry repair packets.Comment: Online multipath convolutional coding for real-time transmission
(2012
Erasure Codes with a Banded Structure for Hybrid Iterative-ML Decoding
This paper presents new FEC codes for the erasure channel, LDPC-Band, that
have been designed so as to optimize a hybrid iterative-Maximum Likelihood (ML)
decoding. Indeed, these codes feature simultaneously a sparse parity check
matrix, which allows an efficient use of iterative LDPC decoding, and a
generator matrix with a band structure, which allows fast ML decoding on the
erasure channel. The combination of these two decoding algorithms leads to
erasure codes achieving a very good trade-off between complexity and erasure
correction capability.Comment: 5 page
Enhanced Recursive Reed-Muller Erasure Decoding
Recent work have shown that Reed-Muller (RM) codes achieve the erasure
channel capacity. However, this performance is obtained with maximum-likelihood
decoding which can be costly for practical applications. In this paper, we
propose an encoding/decoding scheme for Reed-Muller codes on the packet erasure
channel based on Plotkin construction. We present several improvements over the
generic decoding. They allow, for a light cost, to compete with
maximum-likelihood decoding performance, especially on high-rate codes, while
significantly outperforming it in terms of speed
Enabling Realistic Cross-Layer Analysis based on Satellite Physical Layer Traces
We present a solution to evaluate the performance of transport protocols as a
function of link layer reliability schemes (i.e. ARQ, FEC and Hybrid ARQ)
applied to satellite physical layer traces. As modelling such traces is complex
and may require approximations, the use of real traces will minimise the
potential for erroneous performance evaluations resulting from imperfect
models. Our Trace Manager Tool (TMT) produces the corresponding link layer
output, which is then used within the ns-2 network simulator via the
additionally developed ns-2 interface module. We first present the analytical
models for the link layer with bursty erasure packets and for the link layer
reliability mechanisms with bursty erasures. Then, we present details of the
TMT tool and our validation methodology, demonstrating that the selected
performance metrics (recovery delay and throughput efficiency) exhibit a good
match between the theoretical results and those obtained with TMT. Finally, we
present results showing the impact of different link layer reliability
mechanisms on the performance of TCP Cubic transport layer protocol.Comment: 6 pages, 5 figures and 1 table. Submitted at PIMRC 201
Physical Channel Access (PCA): Time and Frequency Access Methods Emulation in NS-2
We present an NS-2 module, Physical Channel Access (PCA), to simulate
different access methods on a link shared with Multi-Frequency Time Division
Multiple Access (MF-TDMA). This tech- nique is widely used in various network
technologies, such as satellite communication. In this context, different
access methods at the gateway induce different queuing delays and available
capacities, which strongly impact transport layer performance. Depending on QoS
requirements, design of new congestion and flow control mechanisms and/or
access methods requires evaluation through simulations.
PCA module emulates the delays that packets will experience using the shared
link, based on descriptive parameters of lower layers characteris- tics. Though
PCA has been developed with DVB-RCS2 considerations in mind (for which we
present a use case), other MF-TDMA-based appli- cations can easily be simulated
by adapting input parameters. Moreover, the presented implementation details
highlight the main methods that might need modifications to implement more
specific functionality or emulate other similar access methods (e.g., OFDMA)
On-the-fly erasure coding for real-time video applications
This paper introduces a robust point-to-point transmission scheme: Tetrys,
that relies on a novel on-the-fly erasure coding concept which reduces the
delay for recovering lost data at the receiver side. In current erasure coding
schemes, the packets that are not rebuilt at the receiver side are either lost
or delayed by at least one RTT before transmission to the application. The
present contribution aims at demonstrating that Tetrys coding scheme can fill
the gap between real-time applications requirements and full reliability.
Indeed, we show that in several cases, Tetrys can recover lost packets below
one RTT over lossy and best-effort networks. We also show that Tetrys allows to
enable full reliability without delay compromise and as a result: significantly
improves the performance of time constrained applications. For instance, our
evaluations present that video-conferencing applications obtain a PSNR gain up
to 7dB compared to classic block-based erasure codes