ICT Projects: CONCLUSION of WCDMA SYSTEM WITH DIFFERENT CHANNEL CONDITIONS

PERFORMANCE ANALYSIS ON MODULATION TECHNIQUES IN

WCDMA SYSTEM WITH DIFFERENT CHANNEL CONDITIONS

CONCLUSION

6.1     Conclusion

In telecommunication field the major challenges is to convey the information as efficiently as possible through limited bandwidth, though the some of information bits are lost in most of the cases and signal which is sent originally will face fading. To reduce the bit error rate the loss of information and signal fading should be minimized.

In our thesis we analyze two modulation techniques, QPSK and 16-QAM to reduce the error performance of the signal and compare which technique is better through Rayleigh Fading Channel in the presence of AWGN.

The performance of W-CDMA system in AWGN channel shows that QPSK modulation technique has a better performance compared to that of 16-QAM. Furthermore, similar trend is found when the channel is subjected to multipath Rayleigh fading with Doppler shift. The performance of QPSK and 16-QAM modulation technique in W-CDMA system degrades as the mobility is increased from 60kmph to 120kmph for both QPSK and 16-QAM. However, QPSK shows better performance compared to that of 16-QAM in LOS channel and multipath Rayleigh fading channel. In other words, 16-QAM suffers signal degradation and error pruned when the simulations are done in these channels. As the number of users is increased, the QPSK modulation technique performs poorly in W-CDMA system. Unfortunately, the simulation for 16-QAM has failed to show the expected results in m files. This is because the 16-QAM modulation scheme experiences adjacent carrier interference when the simulation is carried out. Therefore, it results in inconsistence of data or signal throughput causing abnormal values of BER and eventually affecting the performance of WCDMA system. It is expected that 16-QAM will show performance degradation similar like QPSK as the number of users is increased but with lower performance compared to that of QPSK. In general, the reason that causes poor performance of W-CDMA system when the number of users in increased is because the value of cross correlation between the codes is not 0 and thus it causes interference. Many studies and researches have showed that 16-QAM modulation technique is a primary candidate for high speed data transmission in 3G mobile communication [20][21],[25]. High Speed Downlink Packet Access (HSDPA) is considered as a 3.5G where it has the capability to boost up the data rates of up to 10.7 Mbps using 16-QAM in a static environment. However, higher data rate modulation scheme (e.g.16-QAM) suffers significant degradation in noise and Multipath Rayleigh fading channel compared to lower data rate modulation technique (e.g. QPSK). The errors are resulted from interference between adjacent carriers phase in constellation of M-ary QAM. Larger value of M of M-ary QAM suffers more signal degradation. Thus, it is suggested that high data rate modulation technique such as 16-QAM needs an error correction coding such as convolutional coding or turbo coding so that the interference from the adjacent carrier phase in the constellation of 16-QAM can be eliminated if not minimized.

6.2     Suggestion for Future Work

A more complete WCDMA system can be developed using the suggested method as they are explained as follows.

1.      Generate binary data source for various data rates for various services that can be offered by W-CDMA system in 3G environment. For example 144 Kbps for suburban (indoor/outdoor), urban vehicular and pedestrian, and 2 Mbps for indoor office.

2.      Implement error correction scheme such as convolution coding and turbo coding particularly with M-QAM modulation technique in WCDMA system. Higher order QAM modulation schemes are vulnerable to error. Therefore, error correction coding ensures higher chances of signal survivability in AWGN and multipath Rayleigh channel and thus enhances the performance of the system.



3.      It is proposed that Rician fading is included in the channel in addition of AWGN and multipath Rayleigh fading channel. Then, comparison can be made between these channels.

4.      Also, it is proposed that other sequence generator is employed to generate unique chip code and spread the bandwidth of WCDMA system such as Gold Sequence Generator, and Kasami Sequence Generator beside the PN Sequence Then, comparison can be made to determine which one is having a better performance and good BER characteristics.

5.      A complete uplink and downlink W-CDMA system can be implemented in the WCDMA system for a comprehensive study.

6.      A RAKE receiver or a smart antenna (Multiple Input and Multiple Output) is suggested to be used in this system to exploit the delayed signals arrived at the antenna caused by multipath Rayleigh fading.

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Saturday, April 28, 2012

CONCLUSION of WCDMA SYSTEM WITH DIFFERENT CHANNEL CONDITIONS

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