Investigation of the Effectiveness of Modulation Technique for Wireless Communication with QPSK base Encoding

Today 3G system wireless access method used for communication where used GSM and CDMA. but OFDM has the potential to surpass the capability of CDMA structures and provide the wireless access method for 4G systems. In This Paper presents a methods for used maximum spectral efficiency from Orthogonal Frequency Division Multiplexing (OFDM) systems. the application of OFDM in multiuser structures, besides has focused on approaches for improving the system spectral efficiency. This Technique will have to improve the spectral efficiency to achieve the capacities required. Our research will have providing the capacity to facilities and features for necessitate 100 Mbps through a fixed network, and provide on-demand, with adjustable bandwidth provision. It will also combine a range of applications including cellular phones, cordless phones, and mobile data networking for personal, residential and business uses. this paper investee of harmful effects on OFDM, OFDM show the effect of band pass filtering with QPSK encoding technique, for use of a raised cosine guard period, Additive White Gaussian Noise (AWGN) on modulation BER rate, clip ping distortion, frequency offset errors, and time synchronization error. These techniques utilize knowledge of the radio channel response, to enhance the frequency, and subcarrier modulation. modulation autonomously enhances the modulation system, applied to each subcarrier so that the spectral productivity is exploited, while preserving a target Bit Error Rate (BER), and also study OFDM technology with multipath.