Journal of Emerging Technologies in Web Intelligence Contents

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