An Access Point-Based FEC Mechanism

An Access Point-Based FEC Mechanism

For Video Transmission over Wireless LANs

Abstract

Forward Error Correction (FEC) is one of the mostcommon means of performing packet error recovery in data transmissions.FEC schemes typically tune the FEC rate in accordancewith feedback information provided by the receiver. However, thefeedback and FEC rate calculation processes inevitably have afinite duration, and thus the FEC rate implemented at the sendermay not accurately reflect the current state of the network. Thus,this paper proposes an Enhanced Random Early Detection ForwardError Correction (ERED-FEC) mechanism to improve thequality of video transmissions over Wireless Local Area Networks(WLANs). In contrast to most FEC schemes, the FEC redundancyrate is calculated directly at the Access Point (AP). Moreover, theredundancy rate is tuned in accordance with both the wirelesschannel condition (as indicated by the number of packet retransmissions)and the network traffic load (as indicated by the APqueue length). The experimental results show that the proposedERED-FEC mechanism achieves a significant improvement inthe video quality compared to existing FEC schemes withoutintroducing an excessive number of redundant packets into thenetwork.

Existing System

The lost packets during timeouts, or in response to explicit receiverrequests. By contrast, in FEC schemes, the effects of potentialpacket losses are mitigated in advance by transmittingredundant packets together with the source packets such theta block of packets can be successfully reconstructed at the receiverend even if some of the packets within the block are lostduring transmission. Of the two approaches, FEC schemes resultin a lower retransmission latency, and are therefore widelypreferred for the delivery of video streams over wireless networks Conventional FEC mechanisms are sender-based, i.e., the redundantpackets are generated and encoded at the sender end.Broadly speaking, sender-based FEC schemes can be categorizedas either Static FEC (SFEC) or Dynamic FEC (DFEC). InSFEC schemes, the number of redundant packets added to thesource packets remains constant irrespective of changes in thenetwork condition. The recovery performance of SFEC schemesis therefore somewhat unpredictable because they fail to capturethe real-time network conditions and adjust the FEC redundancyrate accordingly.

Disadvantages

• The FEC rate is tuned dynamically in accordance with changes in the channel condition or network load. In most DFEC schemes, the FEC rate is tuned at the sender based on information provided by the receiver.
• The FEC redundancy rate is traditionally calculated at the application layer based on feedback information such as that provided by acknowledgement messages.

Proposed System

The evaluating the impact of packets losses on the percentage of successfully decoded frames at the receiver end. To calculate theerror propagation due to packet losses, the interdependenciesof the coded frames must be considered. The MPEG-4 standarddefines three frame types for compressed video streaming,namely I frame P frame (Predictive-coded) andB frame. I frames are encoded anddecoded independently of any other frames in the sequence. The number of FEC redundantpackets generated by the four schemes under light and heavytraffic loads, respectively. In the case of a light load, thenumber of FEC redundant packets generated by the SFECand RED-FEC schemes remains approximately constant asthe packet loss rate increases since neither scheme considersthe channel condition when evaluating the FEC redundancyrate. By contrast, the ACFEC and ERED-FECschemes both consider the packet loss rate when determiningthe FEC redundancy rate, and thus for both algorithms, thenumber of redundant packets increases with an increasingpacket loss rate. In the case of a heavy load, the number ofFEC redundant packets generated by the SFEC and ACFECalgorithms is the same as that generated for a light traffic loadsince both algorithms ignore the effects of congestion whendetermining the FEC redundancy rate.

Advantages

• The ACFEC and ERED-FEC schemes, no appreciable degradation in the DFR or PSNR occurs since both schemes take account of the packet loss rate when computing the number of FEC redundant packets per block.

• The video quality without overloading the network with redundant packets. The experimental results have shown that the ERED-FEC scheme yields a higher Decodable Frame Rate (DFR) and Peak Signal-to-Noise.

Module Description

Adaptive Cross-layer FEC mechanism (ACFEC)

The proposed an AdaptiveCross-layer FEC mechanism (ACFEC) in which loss informationwas retrieved from the ARQ function of the MAC layer andthe redundancy rate was controlled adaptively in accordancewith changes in the network condition. However, ACFEC doesnot take the effect of the network traffic load into consideration.As a result, packets may be lost at the wireless AP under heavynetwork loads due to a self-induced congestion problem.

Enhanced Random Early Detection Forward Error Correction (ERED-FEC)

The proposes an Enhanced Random Early Detection Forward Error Correction (ERED-FEC) mechanism for improvingthe quality of video transmissions over wireless LANs(WLANs). In the proposed approach, redundant FEC packetsare generated dynamically at the AP in accordance with boththe condition of the wireless channel and the current networktraffic load. The channel condition is evaluated by monitoringthe number of packet retransmissions. As the number of retransmissionsincreases the condition of the wireless channeldeteriorates), a greater number of redundant FEC packets aregenerated. Conversely, as the channel condition improves, thenumber of FEC packets is reduced.

Forward Error Correction (FEC)

The basic principle of FEC entails injecting redundantpackets into the video stream together with the source Thus, provided that no morethan packets are lost in transmission, the source transmissionpackets can be successfully recovered at the receiver. SinceFEC schemes enable the recovery of source packets whichwould otherwise be lost, the effective loss rate in the transmissionnetwork is lower than the actual loss rate. In FEC codec, redundant packets are derived from the originalpacket using conventional coding theory techniques. Of thevarious traditional error correcting codes available for this purpose,Reed-Solomon (RS) code has attracted particularinterest. RS code provides an ideal error protection capabilityagainst packet losses since it is a maximum distance separablecode, no other coding scheme exists capable of recoveringlost source data symbols from a lesser number of receivedcode symbols.

Sender-Based FEC Mechanisms

The proposed a sender-based Constant Error Rate FEC (CER-FEC) scheme for enabling the dynamic QoS control ofreal-time multimedia streams over heterogeneous environmentscomprising wired and wireless connections. As shown in the proposed scheme, the packet error rate is periodicallyobserved at the receiver side and any change in the error rateis fed back to the sender. Upon receiving this information, thesender calculates the number of redundant packets required torestore the error rate to its original value. In other words, theFEC redundancy rate is dynamically controlled in such a wayas to maintain a constant packet error rate at the receiver end.

Contribution of Present

The major contribution of the present study is to propose anew AP-based FEC mechanism (ERED-FEC) for improving thequality of video transmissions over wireless LANs (WLANs).The literature contains many proposals for sender-based FECschemes which have a finite duration to feedback informationfrom the receiver. Thus, the FEC rate determined atthe sender end may not accurately reflect the current networkcondition.

AP-Based FEC Mechanisms

The number of redundant packets is increased as the queue length shortens, but is reduced as the queue length grows. Importantly, when the queue is near to full, no FEC packets are generated in order to avoid overloading the network. By adopting this approach, the RED-FEC mechanism improves the quality of the delivered video stream without injecting an excessive number of redundant packets into the network.

Flow Diagram

CONCLUSION

This paper has presented an AP-based FEC mechanism (ERED-FEC) for improving the quality of video transmissionsover WLANs. In contrast to many FEC schemes, in which theFEC rate is determined at the sender end on the basis of informationprovided by the receiver, in the FEC mechanism proposedin this study, the FEC redundancy rate is determined at thewireless access point (AP).Moreover, the FEC redundancy rateis calculated in accordance with both the wireless channel conditionand the network traffic load. As a result, the ERED-FECmechanism significantly improves the video quality withoutoverloading the network with redundant packets. The experimentalresults have shown that the ERED-FEC scheme yields ahigher Decodable Frame Rate (DFR) and Peak Signal-to-Noise Ratio (PSNR) than existing AP-based FEC mechanisms underboth light and heavy network traffic loads.In a future study, the recovery performance of the ERED-FECmechanism will be further enhanced by utilizing an FEC interleaving/de-interleaving strategy. In addition, the feasibility ofextending the ERED-FEC scheme and networks will also beaddressed.

Hardware Requirements

Processor:Pentium III / IV

Hard Disk:80 GB

Ram:1 GB

Monitor :15VGA Color

Mouse:Ball / Optical

CD-Drive:LG 52X

Keyboard: 108 Keys

Software Requirements

Operating System :Windows XP professional

.Net FRAMEWORK :.net 4.0

Front End :Microsoft Visual Studio .Net 2010

Language :Visual C#.Net

Back End :SQL Server 2005

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