JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
ELECTRONICS AND COMMUNICATION ENGINEERING
PERFOMANCE ANALYSIS OF AMPLIFYING-ANDFORWARD AND DECODE-AND-FORWARD
PROTOCOLS IN COOPERATIVE COMMUNICATION
1
NIRALI MEHTA, 2 PURAN GOUR
1
M.Tech scholar, NIIST, Bhopal
ECE Dept., NIIST, Bhopal
2 Prof.
alayanya@yahoo.com
ABSTRACT : Co-operative communication in which a source and relay cooperate to send a message to
destination, can provide spatial diversity against fading in wireless network. We derive performance for the
error probability of amplify and forward and decode and forward protocols in the communication. we will
analyze that with help of error correcting code decode and forward protocol gives better performance than
amplify and forward protocols.
1 . INTRODUCTION
In the wireless transmission the signal quality suffers
occasionally severely from a bad channel quality due
to effects like fading caused by multi path
propagation. To reduce such effects diversity can be
used to transfer the different samples of the same
signal over essentially independent channels. In this
paper diversity is realized by using third station as
relay. At the relay amplify and forward and decode
and forward protocols will be used. In such system
combinations of several relaying protocols and
different combing methods are examined to see their
effects on the performance. The transmission
protocols used this this paper are two important
protocols in cooperative communication.
Although the noise of the partner is amplified in this
scheme, the destination still receives two
independently-faded versions of the signal and is thus
able to make better decisions for the transmitted
symbols.
A potential challenge in this scheme is that sampling,
amplifying, and retransmitting analog values may be
technologically on-trivial. Nevertheless, amplify-andforward is a simple method that lens itself to analysis,
and therefore has been very useful in furthering the
understating of cooperative communication system.
3. DECODE AND FORWARD PROTOCOL
2. AMPLIFY AND FORWARD PROTOCOL
Fig. 2 – Decode and Forward Method
Fig. 1 – Amplify and Forward Method
Laneman and wornell first proposed amplify-andforward as cooperative signaling scheme. Amplify
and forward is conceptually the most simple of the
cooperative signaling methods. Each user is this
method receives a noisy version of the signal
transmitted by its partner. As the name implies, the
user then amplifies and retransmits this noisy signal
(figure 1)The destination will combine this
information sent byu the user and partner and will
make a final decision on the transmitted symbol.
The first work proposing a decode-and-forward
protocol for user was by Sendonaris, Erkipand and
Aazang. Nowadays wireless transmission is very
seldom analogue and the relay has enough computing
power, so decode-and-forward is most often the
preferred method to process the data in the relay. The
received signal is first decoded and the re-encoded. So
there is no amplified noise in the sent signal, as is the
case using Amplify –and-forward protocol.
[Reference – 5]
There are two main implementations of such a system.
The relay can decode the original message
completely. This requires a lot of computing time, but
ISSN: 0975 – 6779| NOV 11 TO OCT 12 | VOLUME – 02, ISSUE - 01
Page 175
JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
ELECTRONICS AND COMMUNICATION ENGINEERING
has numerous advantages. If the source message
contains an error correcting code, received bits errors
might be corrected at the relay station. Or if there is
no such code implemented a checksum allows the
relay to detect if the received signal contains errors.
Depending on the implementation an erroneous
message might not be sent to the destination.
But it is not always possible to fully decode the source
message. The additional delay caused to fully decode
and process the message could be coded to protect
sensitive data. In such a case, the incoming signal is
just decoded and re-encoded symbol by symbol.
Amplify and Forward versus Decode and Forward
Fig. 3 – Comparison between Amplify-andForward Method and decode-and-forward
method
Normally the performance of the AAF diversity
protocol compared with DAF protocol is better. As
per the figure if we use error correcting code with the
DAF protocol than it will give the better performance
than AAF protocol. The comparison is based on the
bit error rate and signal to noise ratio of the signal.
AAF is often used when the relay has only limited
computing time/power available or the time delay,
caused by the relay to de- and encoded the message,
has to minimized. Of course when an analogue signal
is transmitted a DAF protocol is not used. [Reference
– 2]
The idea behind the AAF protocol is simple. The
signal received by the relay was attenuated and needs
to be amplified before it can be sent again. In doing so
the noise in the signal is amplified as well. which is
the main downfall of this protocol.
Nowadays a wireless transmission is very seldom
analogue and relay has enough computing power, so
DAF is most often the preferred method to process the
data in the relay. The received signal is first decoded
and then re-encoded. So there is no amplified noise in
the sent signal, as is the case using a AAF protocol.
There are two main implementations of such a system.
[Reference – 7]
The relay can decode the original message
completely. This requires a lot of computing time, but
has numerous advantages. If the source message
contains an error correcting code, received bit errors
might be corrected at the relay station. DAF gives
better performance than AAF protocol.
4. REFERENCES
[1] Cao and B. Vojcic, “Cooperative coding using
serial concatenated convolutional codes,” in Proc. of
Wireless Commun. And Networking Conf., New
Orleans, LA, Mar. 2005, pp. 1001–1006.
[2] A. stefanov and E. Erkip, “Cooperative coding for
Wireless networks,” IEEE Trans. Commun., vol. 52,
no. 9, sept. 2004.
[3] M. Janani, A. Hedayat, T.E. Hunter and A.
Nosratinia, “Coded Cooperation in wireless
Communication: spacetime transmission and
Iterative decoding” IEEE Trans. Signal Processing,
vol. 52, no. 2, pp 362–371, Feb. 2004.
[4] A. Sendonaris, E. Erkip, and B. Aazhang, “User
Cooperation diversity- Part II: Implementation
Aspects
and performance analysis,” IEEE Trans.
Commun., vol. 51, no. 11, pp. 19391948, Nov 2003.
[5] A. Sendonaris, E. Erkip and B.Aazhang, “User
Cooperation diversity-Part I: System description,
IEEE
Trans. Commun., vol. 51, no. 11, pp. 19271938, Nov 2003.
[6] T. E. Hunter and A. Nosratinia, “Cooperative
Diversity Through coding,” in Proc. IEEE
International Symposium On Information Theory
(ISIT), Laussane, Switzerland, July 2002, p. 220.
[7] J. N. Laneman, G. W. Wornell, and D. N. C. Tse,
“An Efficient Protocol for Realizing Cooperative
Diversity in Wireless Networks,” Proc. IEEE ISIT,
Washington, DC, June 2001, p. 294.
[8] J G Proakis, “Digital Communication 4ed,” MH
2001.
[9] A. E. G. T Cover,, “Capacity theorems for the
Relay Channel, IEEE Trans. Inf. Theory, vol. IT-25,
No. 5, pp. 572584, Sep 1979.
[10]E. C. van der Meulen “Three terminals
Communication Channels,” Adv.Appl. Prob, vol. 3,
pp. 120154, 1971.
ISSN: 0975 – 6779| NOV 11 TO OCT 12 | VOLUME – 02, ISSUE - 01
Page 176