BIT ERROR RATE REDUCTION IN W- CDMA NETWORK USING ADAPTIVE MODULATION TECHNIQUE
Department: Electronic And Computer Engineering
Onoh, G. N.
Bit error rate (BER) is a performance indicator that specifies the number of bits corrupted or destroyed as they are transmitted from the source to the destination. The transmission from base station to mobile station using Quadrature phase shift keying (QPSK) and Quadrature Amplitude Modulation (QAM) technique were considered in Wide- band Code Division Multiple access (W-CDMA) environment. The environmental characteristics have been modelled by many technical researchers. However, such models, no matter how accurate result in co-channel interference, multiple access interference and wastage of power when they are deployed in the environment for which they were not developed. This work presents an adaptive modulation technique using empirical and statistical path loss models derived from 2116.4MHz and 910MHz. Experimental data collected in Imo state from twelve existing and newly installed base stations with MTN Nigeria. The results of the experimental measurements were used to develop path loss models for Urban (category A) and Sub-urban (category B) when any of the modulation techniques is configured at the base station. The measurement results showed that the path loss increases by 20.15dB per decade for QAM modulation technique, 14.94dB per decade for QPSK modulation technique and 21.104dB per decade for GMSK modulation technique for Urban category A. and 25dB for QAM and 10.8dB for QPSK modulation technique respectively for Sub–urban category B. Variation in path loss between the measured data and predicted values from Okumura-Hata model were calculated by finding the mean square error (MSE) which were found to be 4.16dB for QAM modulation, 2.033dB for QPSK modulation and 10.96dB for GMSK modulation respectively; and the results show that the values of signal to noise ratio (SNR) from 10-12dB, the modulation scheme that yielded the desired BER of 10-3 is QPSK modulation technique while SNR values greater than 18dB, QAM modulation technique can be used doubling the capacity compared with QPSK modulation technique. Comparing the modified Hata model with those developed for the two categories showed that either the developed models using QAM, QPSK, GMSK and modified Hata model can be adaptively used in Urban and Sub-urban areas of Imo State to maintain an acceptable bit error rate constraints of 10-3 for voice and 0.00 for data communication.
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