International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
Performance Analysis Of Adaptive Cross
Layer FEC Mechanism For Video
Transmission Over Wireless Networks
K .SreenivasaRao#1 , K.Sri Rama Krishna *2
#1 Dept Of ECE, SSN College Of Engineeering &Technology, Ongole, A.P, India
*2 Dept Of ECE, VR Siddhartha Engineering College , Vijayawada, A.P, India
Abstract - The major challenges of video transmission over
wireless networks is to have less error rate and to improve
the quality of service. Many error control mechanisms are
developed for video transmission on wireless networks. An
Adaptive Cross-Layer FEC mechanism for Wireless
Networks is used for video transmission which uses feedback
to calculate the redundancy rate. The Cross-Layer FEC
mechanism performs better in reducing error rate.
Keywords--Adaptive Forward Error Correction, CrossLayer, Wireless network, Video Transmission
I.Introduction
With the advancements in technology for wireless
networks there is a demand for multimedia data
transmission on the network with high data rates and low
errors with quality of service [5].There is a lot of demand
for video transmission on the wireless networks. To
reduce error rate for video transmission many error
control techniques are developed. Two basic approaches
are F o r w a r d
Error C o r r e c t i o n (FEC) and
Automatic Repeat R e q u e s t
(ARQ) [1-2].ARQ
request the retransmission of the lost/corrupted packets by
using acknowledgment signal., FEC transmits original
data with some redundant data, called parities, to allow
reconstruction of lost/corrupted packets at the receiver. Of
the two mechanisms, FEC has been commonly suggested
for video applications due to the strict delay requirements
and semi-reliable nature of video streams However,
notice that the addition of bit redundancy is opposite to
the idea of video compression/coding which aims to the
reduction of the bit rate. Therefore, generally, FEC must
be carefully designed. Due to the same reason, the
problem of joint video and channel coding is studied by
the scientific community in the last years.
The FEC function is implemented on the application
layer. The redundancy rate is either static or controlled by
application- layer programs, based on feedback
information from the transport layer or the application
layer. The conventional FEC approaches not effective to
ISSN: 2231-5381
recover lost packets, since they fail to capture the realtime network conditions and to adjust the redundancy
rates accordingly. An efficient FEC mechanism to be able
to accurately detect channel fluctuations and to
dynamically manipulate the redundancy rate.
The Adaptive Cross-Layer FEC mechanism (ACFEC)
is implemented at the wireless Access Point (AP) [4],.
The wireless AP is used to monitor traffic flows and to
capture varying channel conditions. By employing a
cross-layer scheme, ACFEC mechanism depends on the
functionalities of different layers. The ARQ function at
the MAC layer is able to effectively detect a packet loss,
the ACFEC mechanism retrieves the information on the
loss from the MAC layer, and adaptively controls the
redundancy rates in accordance with the current network
conditions.
In [4], adaptive FEC mechanism titled “RED-FEC.” is
proposed The RED-FEC is abstractly constructed around
the idea of the random early detection algorithm, which
uses the queue length of an AP as the congestion
indicator. Under this approach, the redundancy rate is
calculated based on the queue length. The RED-FEC
gradually reduces the redundancy rates, as the queue
length increases.
The rest of the paper is organized as follows: Section 2
discusses
cross-layer approaches; Adaptive control
CFEC mechanism is introduced in Section 3; Section 4
presents the simulation results; and, finally, conclusions
are discussed in Section 5.
II. Cross-Layer Approach
Cross- layer approaches have been proposed to
provide various QoS supports and to overcome the
limitations posed by wireless networks [7] for different
applications
which
require
different
QoS
guarantees.Cross-layer approaches achieve significant
gains in performance by leveraging the functionalities of
different network layers.
The authors [9] classify cross-layer architectures into the
following four categories:
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
• Top-down approach: The higher layer protocols order
the parameters and strategies of the next lower layer.
• Bottom-up approach: In this approach, a lower layer
performs optimization without triggering awareness on
the higher layers.
• Application-centric approach: The application layer
optimizes parameters and strategies of each lower layer.
• MAC-centric approach: In this approach, the MAC layer
determines the QoS level of each flow, based on the
requirements of the application layer.
cross layer provide excellent analysis and solutions for
multimedia data transmission over wireless networks
when compared with the existing approaches.
III. Adaptive Cross-Layer FEC Mechanism
Application
UDP lite
IP
MAC
Adaptive
CrossLayer
FEC
controller
Physical
Fig. 1. Adaptive Cross-Layer FEC Architecuture
Fig. 1 shows that the adaptive FEC
which is
implemented at the wireless AP. The adaptive FEC
controller connected with the User Datagram Protocol
(UDP) and the Medium Access Control (MAC) protocol
and adaptive mechanism is achieved between layers[8].
Real-time Transport Protocol (RTP) encapsulates the
video data packets, and delivers them to the receiver
through the wireless AP. When a packet arrives at the AP,
the adaptive FEC controller retrives the packet header
from the UDP, and identifies the packet type by checking
the RTP header. IEEE 802.11 defines MAC-Level
acknowledgments which are a stop-and-wait ARQ
mechanism in nature in the unicast transmission mode to
recover errors.
Once each frame is sent out, the sender does not send any
further frames until it receives an acknowledgement
(ACK) from the receiver. If the AP fails to receive the
ACK prior to timeout, the same frame is remitted again.
The MAC layer will report the failure to the upper layer,
if the retransmission counter reaches the Retry Limit .The
process translates into the fact that the frame is not
successfully delivered to the receiver. The adaptive FEC
controller retrieves the failure information, and uses it to
adaptively control the redundancy rates.
The packet-level FEC encoder generates error correction
packets, based on a certain number of source packets that
constitute a single block. When the source packets are
transmitted to the receiver through the wireless AP, the
adaptive FEC controller classifies the video data packets,
and groups them in blocks.
The adaptive error control mechanism at MAC layer
monitors the transmission results of video data packets by
snatching up the failure information. If the transmission
fails, the failure counter in the adaptive controller
increases by one. After transmitting one block of the
video data packets, the adaptive controller uses the failure
counter to adjust the number of redundant FEC packets to
be generated. By accurately detecting packet losses and
adjusting the redundancy rates accordingly, the number of
FEC packets increases or decreases to meet the need of
the receiver and to overcome the packet losses. No FEC
packets are generated, when the all-video data packets of
one block arrive in the receiver successfully
1. At application layer, when the raw video comes,
appropriate source code is applied
to get encoded video bitstream
2. A modified version of UDP, called UDP Lite, is
introduced in which allows partial checksums on
packet data by enabling application layer to specify
how many bytes of the packet are sensitive and must
be check summed. If bit errors occur in the sensitive
region, the receiver drops the packet; otherwise it is
passed up to the application layer
3. Packets are fragmented to equal length radio units at
MAC layer CRC is added for error detection
4. For (every arriving packet)
If (the packets is the video packet) then Save the
video packet into the buffer.
5. Verify the transmission result
If (the transmission failed) then Increase
failure_counter
6. If (a block is transmitted) then If
(failure_counter > 0) then
Generate _FEC(failure_counter) .
The adaptive controller uses the failure counter to adjust
the number of redundant FEC packets to be generated and
are adjusted to meet the need of the receiver and to
overcome the packet losses.
7. Clear the buffer memory failure_counter = 0
IV. Simulation Results
The ACFEC mechanism is compared with the REDFEC mechanism and the static FEC mechanism.The video
traffic sequence was transmitted consisted of frames, with
each frame encapsulated in the RTP/UDP lite/IP packet.
one FTP flow and two CBR flows were adopted over
User Datagram Protocol lite. The transmission rate of the
CBR flow was 200 kb/s.
Adaptive FEC Mechanism.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 10 - Oct 2013
Packet Loss rate Vs PSNR (dB)
40
35
30
PSNR (dB)
ACFEC
25
REDFEC
20
STATIC FEC
15
10
0.0045 0.0085
0.125
0.165
0.205
Packet Loss rate
The above figure demonstrates that the ACFEC achieves
a higher video quality, in terms of PSNR, when
compared with REDFEC and Static FEC mechanisms.
The resulting video quality of the RED-FEC is similar to
that of the static-FEC, while the REC-FEC adjusts the
redundant rates, based on the volume of a traffic load.
V. Conclusion
An Adaptive Cross-Layer FEC mechanism is used to
enhance the quality of video transmission over Wireless
Networks. The proposed ACFEC mechanism depends on
the functionalities of different layers. The Automatic
Repeat reQuest (ARQ) function is applied on the MAC
layer to detect lost packets. The redundancy rates are
adaptively controlled based on the loss information.
ACFEC mechanism adaptively controls the redundancy
rates to overcome channel fluctuations, under various
network conditions, a higher recovery than other
conventional methods, while generating a much less
volume of redundant traffic.
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About the Authors
K.Srinivasa Rao is graduated in B.Tech
(ECE) from the JNT University, Hyderabad in
2000. He obtained M.Tech in Instrumentation
& control systems during 2006 from J.N.T.U.
College of Engineering, Kakinada. His areas of interest include
Multimedia data transmission on Wireless Networks. Presently
working as an Associate Professor in ECE department of
SSNCET, Ongole
Dr.K.Sri Rama Krishna has more than two decades of
experience in teaching and research. He is graduated in B.Tech
(ECE) from the JNT University, Kakinada in
1986 and obtained MS from Birla Institute
of.Technology and Science., Pilani in 1992
and PhD from
Andhra University,
Visakhapatnam in 2002. His main research
interests areas are, ANN for RF & Microwaves, ANN for
Pattern Recognition tasks in Remote Sensing Currently he has
over 60 publications in national and international journals and
in proceedings of national and international conferences. Now,
he is working as Professor and head of ECE dept VR
Siddhartha Engineering College,Vijayawada .
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