Journal of Emerging Technologies in Web Intelligence Contents

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128 JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010The Test case taken up consists of a 60-bit messageencoded into four frames by the encoder. This setup isshown in FigureFigure.8 Channel error simulationIn this case, the number of bit errors introduced is zeroand hence the encoder output and the received channelsymbols are identical. The output of the channel errorsimulator is written to a file, which will then be taken asthe input for the decoder.Decoding received symbolsThe input to the Viterbi decoder is the file containingchannel errors, given as output by the channel errorsimulator. The decoder takes this file as input and thenperforms decoding and tries to recover the originalmessage. The decoding simulation is shown in figure 9Figure 10. An example depictionThe message is encoded into four frames and ispassed to the channel error simulator to introduce variousamounts of bit errors and the decoder performance isanalyzed.Figure.9 Decoding simulation resultWhile encoding messages are encoded in frame, so thatdecoder can start from a known state for each frame.Figure 9 shows decoding of channel symbols containingonly one frame.Performance of Viterbi DecoderThe Viterbi decoder implemented in this project is aHard-decision decoder capable of decoding the channelsymbols encoded by half-rate,(7,5) convolution encoderwith a constraint length of 3. Various amounts of biterrors are simulated and the performance of the decoderis then analyzed.In the first case, three random bit errors areintroduced in each frame. The performance of thedecoder for this test case is shown if following ScreenShot.© 2010 ACADEMY PUBLISHER
JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010 129It is found that the Viterbi decoder is able to recover theoriginal message in most of the cases when 5 random biterrors are introduced in each frame, thus offering almost100% error correction when there is 33% error in thereceived channel symbols.The next test case involves introducing seven bit errorsper frame and the performance of the decoder in this caseis shown in following snap.It is found that the decoder recovers the originalmessage when three random bit errors are produced ineach frame of the received channel symbols, offering100% error correction capability for 3 random bit errors.In the next test case, Five bit errors are introduced in eachframe as shown in screen shot as follows.It is found that the performance of the decoderdeteriorates as the bit error increases to 7 errors perframe. The decoded messages differ from originalmessage and on an average only 32% of the errors arecorrected on a trial run with 10 samples.When the number of bit errors per frame is furtherincreased to 9 bit errors per frame, the performance of thedecoder still goes down and the original message in notrecovered by the decoder as indicated in next screen shot.The performance of the decoder for this test case isshown in the following screen shotIt is found that in case of nine bit errors per frame, theerror recovery rate falls to as low as 8.2% on average runwith 10 samples.© 2010 ACADEMY PUBLISHER
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