Forward error-correction coding
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06-10-2010, 03:19 PM
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The packet transport service provided by representative packet-switched networks, including IP networks, is not reliable and the quality-of-service cannot be guaranteed. Packets may be lost due to buffer overflow in switching nodes, be discarded due to excessive bit errors and failure to pass the cyclic redundancy check at the link layer, or be discarded by network control mechanisms as a response to congestion somewhere in the network. Forward Error Correction coding has often been proposed for end-to-end recovery from such packet losses. However, the use of FEC in this application provides a double-edged sword. From an end user’s perspective, FEC can help recover the lost packets in a timely fashion through the use of redundant packets, and generally adding more redundancy can be expected to improve performance provided this added redundancy does not adversely affect the network packet loss characteristics. On the other hand, from the network’s perspective, the widespread use of FEC schemes by end nodes will increase the raw packet-loss rate in a network because of the additional loads resulting from transmission of redundant packets. Therefore, in order to optimize the end-to-end performance, the appropriate tradeoff, in terms of the amount of redundancy added, and its effect on network packet-loss processes, needs to be investigated under specific and realistic modeling assumptions.
We provide a study of the overall effectiveness of packet-level FEC coding, employing interlaced Reed-Solomon codes, in combating network packet losses and provide an information- theoretic methodology for determining the optimum compromise between end-to-end performances and the associated increase in raw packet-loss rates using a realistic model-
based analytic approach. Intuitively, for a given choice of block length we expect that there is an optimum choice of redundancy, or channel coding rate, since a rate too high is simply not powerful enough to effectively recover packet losses while a rate too low results in excessive raw packet losses due to the increased overhead which overwhelms the packet recovery capabilities of the FEC code. The optimum channel coding rate results in an optimum compromise between these two effects.
Here we focus on evaluating the capability of FEC in recovering packet losses over IP networks using residual packet-loss rate as the performance measure. In terms of characterizing end-to-end performance, we assume that performance is directly proportional to the source coding rate, or network load, that can be supported for a fixed residual packet-loss rate. The analytic procedure developed is then used to determine the maximum load that can be supported as a function of coding parameters. By modeling the fully interleaved network transport channel as a block interference channel, we provide information theoretic bound on the performance achievable with FEC. This bound provides a useful context for assessing the efficacy of FEC in this application as a function of coding parameters.
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10-01-2011, 01:59 PM
what are the possible mathematical model for FEC
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Joined: Mar 2010
20-01-2011, 11:43 AM
actually the mathematical model in "gilbert loss model"
i am suggest you to read following pages to know well about Forward error-correction coding
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Joined: Apr 2012
25-06-2012, 05:13 PM
Forward Error Correction Coding
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In telecommunication, Information theory and coding theory forward error correction(FEC) or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels.
The central idea is the sender encodes their message in a redundant way using an error correcting code(ECC).
The redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message, and often to correct these errors without retransmission.
In existing system a recursive algorithm to compute the packet-loss statistics (block error density), through which the exact residual packet-loss rate after decoding was computed.
Surprisingly, all numerical results given indicates that the resulting residual packet-loss rates with coding are always greater than without coding, i.e., FEC is ineffective in this application.
The increase in the redundant packets added to the data will increase the performance, but it will also make the data large and it will also lead to increase in data loss.
We propose a model-based analytic approach for evaluating the overall efficacy of FEC coding more accurately than existing system.
We study both single-session and multiple-session scenarios, and we reduce the complexity in multiple-session scenario.
Our model has a great potential in recovering the packet losses caused by congestion at a bottleneck node.
FEC is a system of error control for data transmission, where the sender adds redundant data to its messages. This allows the receiver to detect and correct errors (within some bounds) without the need to ask the sender for additional data. In this module we add redundant data to the given input data, known as FEC Encoding.
Interleaving is a way of arranging data in a non-contiguous way in order to increase performance. It is used in data transmission to protest against burst errors. In this module we arrange the data (shuffling) to avoid burst errors which is useful to increase the performance of FEC Encoding.
Implementation of the Queue:
In this module we receive the data from the sender and voluntarily creating the packet loss in order to evaluate the performance of the FEC. Then we transfer the data to the receiver.
By implementing interleaving we can improve the performance of FEC