error correction schemes for wireless sensor networks

Error Correction Schemes for Wireless

Sensor Networks

Al-Nharian University/ Info.& Comm.

Eng. Dept. 4/19/2015

Aim of the Project

Proposal of error correction schemes that are

suitable for WSN providing less number of

packet retransmissions and hence low energy

when operating over fading channels.


Eng. Dept. 4/19/2015

Background and Project task One of the main challenges in the deployment of

wireless networked sensing applications is ensuring

reliable sensor data collection and aggregation,

while satisfying low-cost, low-energy operating

constraints of such applications

Since data transmitted over wireless media are vulnerable to corruption by noise, error control

schemes are necessary to keep the Bit Error Rate

(BER) low.

Two basic methods to recover erroneous packets in any network ; Automatic Repeat Request (ARQ), and

Forward Error Correction (FEC).

Al-Nharian University/ Info.& Comm. Eng. Dept.

4/19/2015

Outline of Main Research Steps Literature review for both Error Correction Codes and

Wireless Sensor Networks.

Study of coding methods for Wireless Sensor Networks applications.

Analysis and Simulation of the efficient coding methods with possible modification considering

concatenation, hybrid, and variable code words

length and packet size.

WSN Simulation based Implementation of the most promising coding methods.

Assessments of Results for simulated Schemes

Writing-up the thesis


Eng. Dept. 4/19/2015

System Model Every coding method tested follow the main

communication system model as shown below;


Eng. Dept.

Information

Source

Demodulator Decoder

Encoder Modulator

Comm. Channel

Information Destination

u v

u v

4/19/2015

Assumptions &Parameters

Channels considered are

AWGN It is a basic noise model used

Flat fading Channel here the coherence bandwidth of the channel is larger than the bandwidth of the signal.

Therefore, all frequency components of the signal will

experience the same magnitude of fading.

Frequency-selective fading the coherence bandwidth of the channel is smaller than the bandwidth of the

signal. Different frequency components of the signal

therefore will experience uncorrelated fading.


Eng. Dept. 4/19/2015

Assumptions &Parameters (Cont.2)

Modulation: Binary Phase Shift Keying (BPSK)

(Baseband model is considered).

Coding Methods :

o Binary BCH Code

o Reed Solomon Code

o Convolutional code

o Concatenation of block and convolutional Codes

oHybrid (Code concatenation with ARQ)


Eng. Dept. 4/19/2015


Brief for BCH code

It is defined over binary GF(2^m) or non-binary version over GF(q).

For any positive integer m and t there exist a BCH code with the following parameters:

o Block length: n=2m-1

o Error correction capability: t

o Parity check bits: r=n-k m.t

o Minimum distance: d 2t+1

The codes are able to correct any error pattern of size t or less, in a code vector of length n.

Needs long, iterative and complex decoding algorithms .


Eng. Dept. 4/19/2015

RS code

They are non-binary BCH codes with code symbols from a

GF(q). The most important Feature of Reed - Solomon (RS)

codes that the minimum distance of a RS code is one greater than

its number of parity-check symbols. For given (n,k,t) RS gives

maximum free distance. Thus it is considered as the most

efficient BCH coding scheme.

o Code parameters

For any positive integer t < 2m - 1, there exists a t-symbol

error correcting RS code with symbols from GF(2m) with the

following parameters:


Eng. Dept.


4/19/2015

Convolutional codes

A convolutional code is specified by three parameters (n, k, m)

where k input bit, n output bits and m is the maximum length of

the k shift registers (memory stages)


Eng. Dept.


k

4/19/2015

Concatenation of Codes An error correction coding scheme in which two different error

correction codes are used in cascade is called concatenated code.

Advantage: Relatively simple decoding & achieve high

coding gain.

Usually : Outer Code is Reed-Solomon, while Inner Code is

convolutional code


Eng. Dept.

Outer encoder

Channel

Inner encoder

Inner decoder

Outer decoder

4/19/2015

Hybrid ARQ Code

Hybrid automatic repeat request (hybrid ARQ or HARQ) is a combination of high-rate forward error-correcting

coding and ARQ error-control

The FEC code is chosen to correct an expected subset of all errors that may occur, while the ARQ method is used

as a call-back for the message to be resent again.

In its simplest form, the HARQ decoder performs FEC decoding first. If the channel produce uncorrectable

errors, the FEC decoder fails in decoding and packet

retransmission is requested. 4/19/2015


Eng. Dept.

WSN Simulators Different simulators may be used for WSN;

oOPNET

oOMNET++/CASTALIA

o TOSSIM

oANSOFT

oNS2

It seems that none of the above are suitable for

the project task (where there is a difficulty in

simulating WSN environment that supports

packet content generation and modification

due to coding methods)


Eng. Dept. 4/19/2015

NWSNS NWSNS = Nahrain university Wireless Sensor

Network Simulator

This is a Matlab based simulator package created and developed in the Information Eng. College, Al-Nahrain University, Iraq. NWSNS simulates most important operations, tasks and parameters that are required in real WSN environments. Different packet sizes, coding and modulation methods, network coverage area, clusters, Energy, Throughput, Error rates, Wireless channel models are considered in the simulator.

4/19/2015 Al-Nharian University/ Info.& Comm.

Eng. Dept.

NWSNS Parameters NWSNS is built to provide flexibility in varying the following parameters;

1- The Size (dimension)of the geographical area of WSN

2- The number of sensor nodes

3- Number of Mobile nodes (and their speed)

4- Packet size and number of packets

5- Wireless channel type & parameters (fading, Doppler, Freq.)

6- Transmission parameters (Bit & Packet Rate, Carrier freq.)

7- Coding Scheme (BCH, RS, Conv., Concat., Interleaving, ARQ)

8- Coder/ Decoder/ Interleaver Parameters (k, n, t, Symbol, Depth).

9- Initial and Total Energy

10- Measurements (SNR, BER, PER, Throughput, Energy) Al-Nharian University/ Info.& Comm.

Eng. Dept. 4/19/2015


Eng. Dept. 4/19/2015

Start WSN program

Input network parameters and all initializations

Mobility of SN (% of total number of

nodes)

Assign SNR (Initialize Error

counter)

Start of Packet Based loop(Np)

Chose a node to generate and transmit data

randomly

Outer Encoder (RS Code)

Inner Encoder (Convolutional

Code)

BPSK modulation

Sending data through channel

Last packet

Inner Decoder (Convolutional

Code)

Outer Decoder (RS Code)

Error Counter(Bit and Packet)

Last SNR value

Measurements and Display of

Results

End

NO

YES

YES

NO

Demodulation/Detection

Errors

NO

YESMax.Retransmission

s

YES

NO

Retransmission


Eng. Dept.

Basic GUI of NWSNS

4/19/2015


Eng. Dept. 4/19/2015

Initial Simulation Results

Tests Carried out;

o Error rate and throughput for RS code with 100

nodes

o Error rate and throughput for Concatenated

code with 100 nodes

o Measurements involved ( PER, BER,

Throughput (in terms of Bit & Packet per sec.)


Eng. Dept. 4/19/2015

Test Results


Eng. Dept. 4/19/2015

5 6 7 8 9 10 11 12 13 10

-5

10 -4

10 -3

10 -2

10 -1

10 0

Eb/No

BE

R

BER Performance of different systems over AWGN

Results of Hybrid Concatenated Code

Test Parameters; Area (square); 1x1,10x10,100x100,1000x1000 (Km)

No. of Nodes =50,100, 200, 400 nodes

Percentage of Mobile Nodes (25%, 50%, 75%, 100% )

Codes RS(255,223), Conv.(3,1), ARQ(N=4)

No. of Packets : 10000 packets

Measurements ( PER, BER, Throughput in terms of Bit & Packet per sec)


Eng. Dept. 4/19/2015

Test Results #1


Eng. Dept. 4/19/2015

Error Performance of Different Systems over AWGN channel with Hybrid Code, 10000 Packets.

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

6 7 8 9 10 11 12 13 14 10

-3

10 -2

10 -1

10 0

Eb/No

PE

R

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Test Results #2


Eng. Dept. 4/19/2015

Error Performance of Different Systems over Flat Fading channel with Hybrid Code, 10000 Packets.

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

6 8 10 12 14 16 18 20 10

-4

10 -3

10 -2

10 -1

10 0

Eb/No

PE

R

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Test Results #3


Eng. Dept.

Error Performance of Different Systems over Multipath Selective (SUI-1) Fading channel with Hybrid Code, 10000 Packets.

Sys. #150 SN, 25% mob., 11 Km, D. shift 20 Hz

Sys. #2 50 SN, 25% mob., 11 Km, D. shift 40 Hz






6 8 10 12 14 16 18 20 22 24 26 10

-4

10 -3

10 -2

10 -1

10 0

Eb/No

PE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #4


Eng. Dept.









6 8 10 12 14 16 18 20 22 24 26 10

-4

10 -3

10 -2

10 -1

10 0

Eb/No

PE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #5


Eng. Dept.

Error Performance of Different Systems over Multipath Selective channel (SUI-1) with Hybrid Code, 10000 Packets.

6 8 10 12 14 16 18 20 22 24 26 10

-3

10 -2

10 -1

10 0

Eb/No

PE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1








Test Results #6


Eng. Dept.

Error Performance of Different Systems over Multipath Selective channel (SUI-1) with Hybrid Code, 10000 Packets.

6 8 10 12 14 16 18 20 22 24 26 10

-3

10 -2

10 -1

10 0

10 1

Eb/No

PE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1





Sys. #5 400 SN, 100% mob.,10001000 Km, D. shift 200 Hz



Test Results #7


Eng. Dept. 4/19/2015

Throughput variation with SNR of Different Systems over AWGN channel with Hybrid Code, 10000 Packets

6 8 10 12 14 16 18 20 22 24 26

10 2.3

10 2.4

10 2.5

10 2.6

Eb/No

Th

rou

gh

pu

t(P

acket/se

c)

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

Test Results #8


Eng. Dept.

Throughput variation with SNR of Different Systems over Flat Fading channel with Hybrid Code, 10000 Packets

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

6 8 10 12 14 16 18 20 22 24 26

10 2.2

10 2.3

10 2.4

10 2.5

10 2.6

Eb/No

Th

rou

gh

put(

Pa

cket/

sec)

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Test Results #9


Eng. Dept.

Throughput variation with SNR of Different Systems over Multipath channel (SUI-1) with Hybrid Code, 10000 Packets








0 2 4 6 8 10 12 14 16 18 20 0

50

100

150

200

250

300

350

400

450

500

Eb/No

Th

rou

gh

put(

Pa

cket/

sec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #10


Eng. Dept.









0 2 4 6 8 10 12 14 16 18 20 0

50

100

150

200

250

300

350

400

450

500

Eb/No

Th

rou

gh

put(

Pa

cket/

sec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #11


Eng. Dept.









0 2 4 6 8 10 12 14 16 18 20 -100

0

100

200

300

400

500

Eb/No

Th

rou

gh

put(

Pa

cket/

sec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #12


Eng. Dept.









0 2 4 6 8 10 12 14 16 18 20 -100

0

100

200

300

400

500

Eb/No

Th

rou

gh

put(

Pa

cket/

sec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #13


Eng. Dept.

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

Error Performance of Different Systems over AWGN channel with Hybrid Code, 10000 Packets.

6 7 8 9 10 11 12 13 14 15 10

-4

10 -3

10 -2

10 -1

Eb/No

BE

R

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Test Results #14


Eng. Dept.

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

Error Performance of Different Systems over Flat Fading channel with Hybrid Code, 10000 Packets.

6 8 10 12 14 16 18 20 10

-4

10 -3

10 -2

10 -1

Eb/No

BE

R

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Test Results #15


Eng. Dept.

6 8 10 12 14 16 18 20 22 24 26 10

-4

10 -3

10 -2

10 -1

10 0

Eb/No

BE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1









Test Results #16


Eng. Dept.


6 8 10 12 14 16 18 20 22 24 26 10

-5

10 -4

10 -3

10 -2

10 -1

10 0

Eb/No

BE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1








Test Results #17


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6 8 10 12 14 16 18 20 22 24 26 10

-3

10 -2

10 -1

10 0

Eb/No

BE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #18


Eng. Dept.









6 8 10 12 14 16 18 20 22 24 26 10

-3

10 -2

10 -1

10 0

Eb/No

BE

R

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1

Test Results #19


Eng. Dept.

Throughput variation with SNR of Different Systems over AWGN channel (SUI-1) with Hybrid Code, 10000 Packets

6 8 10 12 14 16 18 20 22 24 26

10 5.8

10 5.9

Eb/No

Th

rou

gh

pu

t(B

it/s

ec)

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

Test Results #20


Eng. Dept.

Throughput variation with SNR of Different Systems over Flat Fading channel (SUI-1) with Hybrid Code, 10000 Packets

Sys. #150 SN, 25% mob., 11 Km

Sys. #2100 SN, 50% mob., 1010 Km

Sys. #3200 SN, 75% mob., 100100 Km

Sys. #4400 SN, 100% mob., 10001000 Km

6 8 10 12 14 16 18 20 22 24 26

105.8

105.9

Eb/No

Thro

ughput(

Bit/s

ec)

Sys. #1

Sys. #2

Sys. #3

Sys. #4

Test Results #21


Eng. Dept.








0 2 4 6 8 10 12 14 16 18 20 3

4

5

6

7

8

9

10 x 10

5

Eb/No

Th

rou

gh

pu

t(B

it/S

ec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1


Test Results #22


Eng. Dept.








0 2 4 6 8 10 12 14 16 18 20 3

4

5

6

7

8

9

10 x 10

5

Eb/No

Th

rou

gh

put(

Bit/S

ec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1


Test Results #23


Eng. Dept.

0 2 4 6 8 10 12 14 16 18 20 3

4

5

6

7

8

9

10 x 10

5

Eb/No

Th

rou

gh

put(

Bit/S

ec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1









Test Results #24


Eng. Dept.

0 2 4 6 8 10 12 14 16 18 20 3

4

5

6

7

8

9

10 x 10

5

Eb/No

Th

rou

gh

put(

Bit/S

ec)

Sys. #7

Sys. #6

Sys. #5

Sys. #4

Sys. #3

Sys. #2

Sys. #1









Conclusions A successful simulator is built to meet the required WSN

simulation tasks and parameters.

The initial results confirm the need for error correction scheme that reduce the errors to some extends so that the consumed

energy will be reduced accordingly.

The increase of Doppler (or the mobile node speed) degrades the performance of the systems and reduce their throughput.

Thus more sophisticated coding scheme is required under such

condition.

The use of HARQ improved the error and throughput performance over fading channels on the expense of (possibly)

more packet retransmissions.

Further conclusions will be drawn when actual energy measurements will be involved after completing the full

investigation regarding consumed energy required based on

packet size and maximum number of retransmission involved in

ARQ scheme. 4/19/2015


Eng. Dept.

Future Work Proposal of a coding schemes that are the most

promising ones to achieve the highest throughput

with least energy consumption.

Further investigation is required on the best coding parameters of the constituent encoders used in

HARQ arrangement.

Modifying the simulator to take into account the routing algorithm so that the network layer protocol

performance will be covered together with the

coding and modulation applied at the physical

layer.


Eng. Dept.

THANK YOU


Eng. Dept. 4/19/2015

error correction schemes for wireless sensor networks

Documents

arq alnharian university

error correction codes

o error correction capability

code symbols

rs code

forward error correction

code vector of length

o block length