Video transmission over the wireless network faces many challenges. The most critical challenge is related to packet loss. To overcome the problem of packet loss, Forward Error Correction is used by adding extra packets known as redundant packet or parity packet. Currently, FEC mechanisms have been adopted together with Automatic Repeat request (ARQ) mechanism to overcome packet losses and avoid network congestion in various wireless network conditions. In the current Adaptive FEC mechanism, the FEC packets are decided by the average queue length and average packet retransmission times. The Adaptive FEC mechanisms have been proposed to suit the network condition by generating FEC packets adaptively in the wireless network. However, the current Adaptive FEC mechanism has some major drawbacks such as the reduction of recovery performance which injects too many excessive FEC packets into the network. This is not flexible enough to adapt with varying wireless network condition. Therefore, the enhancement of Adaptive FEC mechanism (AFEC) known as Enhanced Adaptive FEC (Enface) has been proposed. The aim is to improve recovery performance on the current Adaptive FEC mechanism by injecting FEC packets dynamically based on varying wireless network conditions. Based on the findings, the optimal amount of FEC generated by Enface mechanism can recover high packet loss and produce good video quality An Enhanced Random Early Detection Forward Error Correction (ERED-FEC) mechanism is implemented to improve the quality of video transmissions over Wireless Local Area Networks (WLANs).
Keywords |
| Forward error correction, Video transmission, Wireless network, Packet loss, Video quality. |
INTRODUCTION |
| In a wireless network, as the external environment changes, the channel error rate varies. In order to cope with
errors, accurate channel-condition estimation and an effective error control mechanism is needed. Video
communication is fundamentally different from data communication, since interactive video applications are delay and
loss sensitive. Unlike data packets, late arriving video packets are useless to the video decoder. Furthermore, due to
busty and location dependent errors, each user in a multicast system will most likely lose different packets. Therefore, a
simple ARQ (Automatic Repeat request) based scheme is not appropriate for video multicast services over wireless
channels since it can cause a large number of retransmissions. A promising solution for error control in multicasting
over wireless networks is the use of forward error correction (FEC), where redundant information is sent a-priori by the
source station, in order to be used by the receivers to correct errors/losses without contacting the source. The advantage
of using FEC for multicasting is that a single parity packet can be used to correct independent single-packet losses
among different receivers. The efficiency of FEC-based approaches for error correction in wireless multicasting has
been shown via simulations [1]-[4]. Although these simulation results provide some insights on the way FEC should be
applied, they do not consider a wireless network with multi-rate capabilities. Broadly speaking, sender-based FEC
schemes can be categorized as either Static FEC (SFEC) or Dynamic FEC (DFEC). In SFEC schemes, the number of
redundant packets added to the source packets remains constant irrespective of changes in the network condition. The
recovery performance of SFEC schemes is therefore somewhat unpredictable because they fail to capture the real-time
network conditions and adjust the FEC redundancy rate accordingly. Thus, various DFEC schemes have been proposed
in recent years. In most DFEC schemes, the FEC rate is tuned at the sender based on information provided by the
receiver. |
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RELATED WORK |
Forward Error Correction (FEC) |
| The basic principle of FEC entails injecting redundant packets (h) into the video stream together with the source
transmission packets (k) such that packet losses can be recovered at the receiver end without the need for
retransmission. In other words, as shown in Fig. 1, the original block is encoded as (n,k) packets, where n is the
summation of source packets (k) and redundant packets (h) . Thus, provided that no more than packets are lost in
transmission, the source transmission packets can be successfully recovered at the receiver. |
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SENDER-BASED FEC MECHANISMS |
Constant Error Rate FEC (CER-FEC) |
| Proposed a sender-based Constant Error Rate FEC (CER-FEC) scheme for enabling the dynamic QoS control
of real-time multimedia streams over heterogeneous environments comprising wired and wireless connections. As
in the proposed scheme, the packet error rate is periodically observed at the receiver side and any change in the
error rate is fed back to the sender. Upon receiving this information, the sender calculates the number of redundant
packets required to restore the error rate to its original value. In other words, the FEC redundancy rate is
dynamically controlled in such a way as to maintain a constant packet error rate at the receiver end. |
Cross-Layer FEC (CL-FEC) |
| Proposed an efficient Cross-Layer FEC (CL-FEC) scheme for wireless video multicasting designed to
maintain the received video quality for all the users above a certain pre-specified level. In the proposed scheme,
each user periodically reports the number of packets received out of the previously transmitted packets. The sender
then calculates the number of packets which each user has lost and determines the maximum number of packets
which can be decoded by all the users (i.e. the number of decodable packets for the user with the greatest number of
packet losses). |
Adaptive FEC (AFEC) |
| An adaptive FEC (AFEC) protocol for facilitating the end-to-end transport of real-time traffic whose timing
constraints rule out the use of retransmission-based congestion control or QoS provisioning schemes. In the
proposed approach, the degree of FEC redundancy is tuned in accordance with the current network delay.
Specifically, the number of redundant packets is increased as the network delay decreases, but is reduced as the
delay increases. |
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Basic Concept of ERED-FEC Mechanism |
| Enhanced Random Early Detection Forward Error Correction (ERED-FEC) mechanism is implemented for
improving the quality of video transmissions over wireless LANs (WLANs). In the proposed approach, redundant
FEC packets are generated dynamically at the AP in accordance with both the condition of the wireless channel and
the current network traffic load. The channel condition is evaluated by monitoring the number of packet
retransmissions. As the number of retransmissions Increases (i.e., the condition of the wireless channel
deteriorates), a greater number of redundant FEC packets are generated. Conversely, as the channel condition
improves, the number of FEC packets is reduced. The network traffic load is evaluated by monitoring the queue
length at the wireless AP. If the queue is almost empty, i.e., the network is only lightly loaded, the number of
redundant FEC packets is increased. By contrast, if the queue is nearly full, i.e., the network is heavily loaded; the
number of FEC packets is reduced. By adopting this approach, the ERED-FEC algorithm significantly improves the
video quality without overloading the network with an excessive number of redundant packets. An analytical model
is proposed for predicting the quality of MPEG-4 video streams delivered over WLANs with FEC protection in
terms of the effective packet loss rate and the Decodable Frame Rate (DFR) [22], [23]. It is shown that the model
provides the ERED-FEC mechanism with the means to determine the FEC redundancy rate required to guarantee
the QoS requirements of video transmissions over lossy wireless networks. Fig. 5 illustrates the basic architecture of
the AP-based ERED-FEC mechanism proposed in this study. (Note that an assumption is made that the wired segment of the video delivery path is loss free.) As shown, the ERED-FEC mechanism consists of five components,
namely (1) a packet type classifier (2)a packet loss monitor (3) a video quality model (4) a network load monitor
and (5) a FEC packet generator. During video streaming, the streaming server encapsulates the video data in Realtime
Transport Protocol (RTP) packets and delivers them to the receiver through the wireless AP. When packets
arrives at the AP, the ERED-FEC controller retrieves the packet header from the UDP, and identifies the packet
type by checking the RTP header. Once a complete block of video packets has arrived, the packet loss monitor
estimates the packet loss rate by examining the number of packet retransmissions associated with the block. An
appropriate FEC redundancy rate is then determined via the video quality model (i.e., the DFR). Finally, the EREDFEC
mechanism checks the queue length at the AP in order to evaluate the current network traffic load, and then
uses this information to adjust the FEC redundancy rate (if required). |
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PROBLEM DEFINITION & OBJECTIVE |
Problem Definition |
| In this research work different papers were studied to find the problem. The following problems were found that
are given below: |
| • There is no guarantee that the FEC rate implemented at the sender end accurately reflects the current network
condition. |
| • The loss of data packets during the transmission of data from source to destination. |
| • The data redundancy problem is their when same packets are sending again and again on the same network. |
| • Resource allocation problem during the FEC mechanism for video transmission of data. |
Objective |
| The following objectives are performed in this research work : |
| • To implement the Enhanced Random Early Detection Forward Error Correction (ERED-FEC) mechanism for
improving the quality of video transmissions over wireless LANs. |
| • To perform Resource scheduling during the transmission. |
| • To Calculate the Frame rate of the videos over the WLAN. |
| • To Compare the RED-FEC, ERED-FEC and EERED-FEC Algorithm and analyze the result being obtained. |
CONCLUSION AND FUTURE WORK |
| This paper has presented an AP-based FEC mechanism for improving the quality of video transmissions over
WLANs. In contrast to many FEC schemes, in which the FEC rate is determined at the sender end on the basis of
information provided by the receiver, in the FEC mechanism proposed in this study, the FEC redundancy rate is
determined at the wireless access point (AP).Moreover, the FEC redundancy rate is calculated in accordance with both
the wireless channel condition and the network traffic load. As a result, the FEC mechanism significantly improves the
video quality without overloading the network with redundant packets. Our future work will include further evaluation
of the proposed approach. The different reviews are studied from the different papers. |
References |
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