International Journal of Electrical and Computer Engineering (IJECE) Vol.
No.
February 2017, pp.
ISSN: 2088-8708.
DOI: 10.
11591/ijece.
PC-APC Schemes in Multipath Diversity System to Get Higher Throughput Sanjit Ningthoujam.
Manash Pratim Dutta.
Subhasish Banerjee.
Chandan T.
Bhunia.
Swarnendu K.
Chakraborty Department of Electronics and Computer Engineering.
National Institute of Technology.
Arunachal Pradesh.
India
Article Info
ABSTRACT
Article history:
This paper is studied about a new protocol of Packet combining (PC) and Aggressive Packet Combining Scheme (APC) in multipath diversity system to get higher throughput.
In the proposed protocol of PC and APC schemes, two and three copies of a packet are sent in two and three paths.
If either of the copies is received without any erroneous then select the correct one and discard all other copies.
Again if all copies are found as erroneous then combine the erroneous copies and perform XOR operation in case of PC and bit by bit majority logic in case of APC in order to get the original copy.
The paper is implemented using Mat lab and found that new proposed protocols are getting higher throughput and probability of receiving successful packet at the receiver side.
Thus, performance of error prone wireless network can be improved by applying either PC or APC in multipath diversity system.
Received Aug 8, 2016 Revised Jan 19, 2017 Accepted Jan 31, 2017 Keyword:
APC
ARQ
BEC
ELA post reception selection Combining Selection combining Copyright A 2017 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Sanjit Ningthoujam.
Department of Electronics and Computer Engineering.
National Institute of Technology.
Arunachal Pradesh.
India 791112.
Email: sanjit.
ningthoujam@gmail.
INTRODUCTION
Automatic Repeat Request (ARQ) techniques are mainly implemented for error control by retransmitting duplicate copies in wireless network.
Normally, the receiver discards all erroneous copies and request for retransmission.
However, an erroneous packet may contain both erroneous and correct bits and hence the packet may contain useful information.
Therefore, to get the correct information, it is deployed by combining multiple erroneous copies at the receiver side.
Chakraborty et.
suggested that PC is one of the simplest implementation of space diversity reception for combating fading in wireless communication In PC technique, only one error can be corrected and therefore, if double errors are found at same bit location of two copies then PC technique is not useful.
Therefore, retransmission of duplicate packet has been Moreover.
APC was introduced by Leung .
for error correction and optimizes Backward Error Correction (BEC).
Many researchers .
have been studied and conclusively established that PC techniques provide higher throughput but low error correction capability to that of APC schemes.
The error prone wireless network having bit error rate varies from 10 -4 to 10-2 is neither reason of assuming nor any logic to apply only single path in case of conventional PC and APC techniques.
Therefore, in the paper new protocol of PC and APC are introduced in order to reduce the dependency of a single path/route which gives more stable in wireless netwok.
The remaining of the paper is organized as follows.
Reviews of conventional PC.
APC and ELAPOR-SC are introduced in Section 2.
Section 3 discusses about new protocols of PC and APC and Section 4 describes mathematical analysis of throughput and probability of error.
Section 5 illustrates the simulation result using Mat lab and finally, conclusion is discussed in Section 6.
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PRELIMINARIES
Packet Combining Scheme (PC) PCis proposed to locate erroneous bits received by the receiver.
The technique of PC scheme are given here: let original packet be Au00001111Ay.
Instead of these bits, the copy is received erroneously as Au00001110Ay.
The receiver requests for duplicate copy after storing of received erroneous copy.
Again, it is assumed that receiver received the copy as Au00011111Ay, which is also an erroneous.
By combining erroneous copies at the receiver using XOR operation, it can identify the error location.
The example is given here.
------------------------------------------------XOR 00010001
From the above example, 4th and 8th bit positionsfrom MSB are identified as erroneous bits.
To get original packet by Chakraborty, the erroneous bits are converting receivedAu1Ay to Au0Ay or vice versa.
Again, let original Packet as Au11110000Ay At the receiver 1st erroneous copy: 10110000 .
rroneous occurs at 2nd bit position from MSB) 2nd erroneous copy: 10110000 .
rroneous occurs at 2 nd bit position from MSB) a.
XORed 00000000 The operation cannot be identified erroneous bit position when erroneous occurs at same bit So, it is failed to correct erroneous copy.
Aggressive Packet Combining Scheme (APC) APC is a modified version of Majority Packet Combining.
This technique isused for obtaining high error correction capability in wireless networks.
Examples of APC are given here:
Au00111Ay is assumed as original packet which is sent form sender to receiver.
It is also assumed that the original packet is received as erroneous.
Therefore, the receiver request for duplicate copies from sender.
Let all the copies are received with error as: 1sterroneous copy: 00011, 2nd erroneous copy : 00110 and 3rd erroneous copy:00011.
00011 are generated at the receiver side after performing bit by bit majority logic on three erroneous Error detection scheme is applied at receiver to check the generated copy is original or not.
If it is not actual packet, least reliable bits will be chosen from majority logic.
Therefore, in the example the 3rd and 5th bit from the MSB is chosen.
Brute force correction method is applied as in PC technique to the 3rd and 5th bits, followed by error correction method.
This process may lead to get actual packet.
If actual packet is not generated in the above process then it will discard all erroneous copiesandrequests for duplicate copies.
Error Location Algorithm-POR-SC Liang et.
introduced Error Location Algorithm (ELA) which is an enhanced version of Automatic Repeat Request-POR-SC.
The scheme operates as follow: if any one of the received copies is correct, then it is accepted.
However, if all copies are erroneous then in order to get correct copy, it performed ELA-POR-SC.
In this scheme, three copies are sent from transmitter to receiver.
At least one copy is found as correct then proceed for the next packet otherwise performing ELA-POR-SC.
It is assumed that A.
C are the three received of erroneous copies of the same transmitted packet from transmitter over three diversity channels, then:
AA=(A xored C).
(A xored B) BB=(A xored B).
(B xored C) CC=(A xored C).
(B xored C) In AA.
BB, and CC, every A1A indicates an error in the copy of A.
B and C respectively.
In this case, the original packet can be retrieved by using S=AA xored A (=BB xored B = CC xored C) However, the retrieval process fails when it is found as double, triple error and so on.
In this time, erroneous copies are discarded and request for next duplicate copies by sending NAK.
IJECE Vol.
No.
February 2017 : 337 Ae 343
IJECE
ISSN: 2088-8708
Table 1.
Examples of ELA-POR-SC.
Original Packet at Sender Receiver (Erroneous bits are underline.
A-11110011
AA=00010000,
B-01100011
S=11100011 (Original C-11100010
A-01001111
BB=10000000,
B-10001111
S=00001111(Original C-00001101
A-10101000
CC=00001000,
B-11101010
S=10101010(Original C-10100010
PROPOSED PROTOCOLS
Proposed Protocols of PC Scheme In this new PC scheme, duplicate copies of a same packet are transferredfrom sender to receiver by using two paths .
The step wise procedures are illustrated below:
The first copy is sent original as Au11100011Ay in first path but erroneously received as 10100011.
As in PC scheme, duplicate copy will be sent in second path by shifting three bits from LSB to MSB as It is assumed that the copy has been found error at 2ndbit position from MSB as 01111100.
order to get the original bit sequence, the received copy will be shifted back from MSB to LSB by three bits at the receiver side as 11100011.
The two erroneous copies are stored and performed XOR operation to locate the erroneous bit position and apply brute force method as conventional PC scheme .
rroneous bits are underline.
The example is given below:
Original packet as Au11100011Ay 1st erroneous copy-10100011 2nd erroneous copy-11100011 a.
XORed 01000010 This technique overcomes the limitation of conventional PC as receiver will be detected same bit error location in two erroneous copies.
Proposed protocol of APC In this protocol, triplicate copies of same packet are sent in three paths from sender to receiver.
The stepwise procedures are illustrated below:
The first copy is sent in first path as original packet.
The second copy will be sent after three bits shifting from LSB to MSB in second path.
The receiver will perform three bits shifting from MSB to LSB.
The third copy will be sent in third path after six bits shifting from LSB to MSB and at receiver side the six bits will be shifted back from MSB to LSB in order to get the original sequence of bits position.
The three copies are stored in receiver and perform Aggressive Packet Combining Scheme to get the original packet.
The examples of proposed protocols are illustrated as below:
Table 2.
Erroneous may happen at any two bits position Original Packet Sender 1st copy -11110011 2nd copy -01111110 3rd copy -11001111 1st copy -11110000 2nd copy -00011110 3rd copy -11000011 1st copy -00001111 2nd copy -11100001 3rd copy -00111100 Receiver (Erroneous bits are underline.
1st copy -00110011 2nd copy-11110101 3rd copy -11000011 a 11110011 .
riginal packet after majority packet combinin.
1st copy-01110001 2nd copy-11111100 3rd copy-10010000 a 11110000 .
riginal packet after majority packet combinin.
1st copy -00010111 2nd copy -11001111 3rd copy -00001111 a.
riginal packet after majority packet combinin.
PC-APC Schemes in Multipath Diversity System to Get Higher Throughput (Sanjit Ningthouja.
A ISSN: 2088-8708
ANALYSIS
It is assumed that the sender sends bit 1 to receiver using single path and receiver receives bit 0 instead of 1.
Let a be the probability of receiving bit error .
eceived 0 instead of 1 and vice vers.
and therefore, 1- AA be the probability of correction bit at the receiver side.
For AnA packet size, the probability of error correction is given by Equation 1.
PC= .
- AA)n .
And Probability of error is given by Equation .
PE=.
- AA).
It is assumed that in proposed PC and APC the sender sends two and three copies of n packet size in two and three paths then the probability of receiving at least one correct copy .
is given by Equation 3 X=1-.
- AA).
Y=1-.
- AA).
Throughput .
of proposed PC and Proposed APC will be given by Equations .
THpc= .
-Ap.
Ap.
THapc=.
-Aap.
Aap.
Where Apc=[.
- AA).
- AA).
]/2.
Aapc=[.
- AA).
- AA).
- AA).
]/3 RESULTS Comparisons of proposed APC and PC Schemes in Term of Probability of Successful Packet Received at the Receiver Side Figure 1.
512 Bits Packet Size IJECE Vol.
No.
February 2017 : 337 Ae 343 Figure 2.
1024 Bits Packet Size
IJECE
ISSN: 2088-8708
Comparison of Proposed PC and Conventional PC Schemes in Term of Throughput Figure 3.
512 bits packet size Figure 4.
1024 bits packet size Comparison of Proposed APC and Conventional APC Schemes in Term of Throughput Figure 5.
512 bits packet size Figure 6.
1024 bits packet size
CONCLUSION
In wireless networks, data transmission is high chance to get failured and thus, retransmission of duplicate copies from sender to receiver may drastically reduce the throughput.
In orderto reduce retransmission of duplicate copies, erroneous copies are combinedtoget original copy.
The technique is done by PC and APC but they have low performance.
Therefore,new proposed techniques are introduced to increase the performance of the conventional PC and APC.
In the results, figure 1 and figure 2 clearly showed that comparison of proposed techniques of APC and PC in term of probability of receiving at least one correct packet at the receiver.
In figures 3-6, it is also clearly evident that proposed PC and APC techniques using multipath provide higher throughput in bit error rate varies 10 -4 to 10-2 and packet size from 512 to 1024 bits.
Thus, multipath PC-APC is outperformed in terms of throughput and probability of receiving atleast one correct copy.
REFERENCES