Comparative Performance Analysis of Modulation Techniques of Wideband Code Division Multiple Access (W-CDMA) System for Maximum Data Throughput

Abstract

The performance of W-CDMA as a platform of the third generation (3G) technology can be greatly improved by the choice of a modulation technique used. With the explosion in the usage of mobile telephone, internet, high speed data and multimedia traffic, active researches into higher order modulation techniques becomes relevant. This paper focused on the comparative performance analysis of two digital modulation techniques - Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying (QPSK) employed in W-CDMA system. Site investigation was conducted and the Received Signal Strength (RSS) measurement taken. From the RSS, the pathloss was evaluated and was used to estimate two Quality of Service (QoS) parameters - the signal-to-Noise ratio (SNR) as well as the Bit Error Rate (BER) of the modulation techniques under study. These parameters were used to characterize the modulation techniques upon which a comparative performance analysis was obtained to achieve maximum data throughput. The result of the analysis revealed that as SNR decreases, errors increase. The average estimated SNR of QPSK was slightly greater than that of QAM, showing 15.89dB (50.4%) against 15.64dB (49.6%) for QAM. Given that errors will increase as SNR does decrease, the BER of QAM technique was observed to be higher than QPSK. This means the signal states of QAM are closer together and so contain more bits per symbol. This makes a lower level of noise enough to move the signal to a different decision point than in QPSK. Therefore modulation scheme implemented in any form of wireless network affects the error performance which in turn affects the data rate as well as the throughput of the communicating devices.