International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 2, February 2012) 286 Enhancing quality of service using OFDM technique for next generation network. B.K Mishra 1 , S.K Singh 2 , Mahendra Sharma 3 , Umesh Sharma 4 1 Principal-Thakur College of Engineering & Technology , Thakur Village, Kandivali (East) Mumbai-400101, 2 Research Scholar- Mukesh Patel School of Technology , Management & Engineering, NMIMS University, Santacruz, Mumbai-400056. MobNo. +919892434085. India 3 Assistant Professor-Thakur College of Science and Commerce, Kandivali (East), Mumbai -400101 India 4 PG Student-Thakur College of Science and Commerce, Kandivali (East), Mumbai -400101 India 1 Drbk.mishra@thakureducation.org, 2 sksingh14@gmail.com 3 smahendra@live.com, 4 umeshek777@gmail.com Abstract— The migration to 4G networks will bring a new level of expectation to wireless communications. As after digital wireless revolution made mobile phones available for everyone, the higher speeds and packet delivery of 4G networks will make high quality multimedia available everywhere. The key to achieving this higher level of service delivery is a new air interface. Orthogonal Frequency Division Multiplexing (OFDM) is an alternative wireless modulation technology to CDMA. OFDM has the potential to surpass the capacity of CDMA systems and provide the wireless access method for 4G systems. OFDM is a digital modulation and multiplexing technique. In this paper, various digital modulation techniques has been discussed such as BPSK, QPSK, 8-PSK and 16-PSK. Architecture has been designed and simulated in MATLAB with various configurations of OFDM technique. The main objective of the current research work is to measure Bit Error Rate with different modulation schemes and come to the best configuration to achieve better utilization of bandwidth. The configuration has been tested with analog and digital modulation techniques and results have been compared. Keywords- OFDM; 3G; 4G; BPSK; QPSK; Bit Error Rate. I. INTRODUCTION Orthogonal Frequency Division Multiplexing (OFDM) is an alternative wireless modulation technology to CDMA. OFDM has the potential to surpass the capacity of CDMA systems and provide the wireless access method for 4G systems. OFDM is a modulation scheme that allows digital data to be efficiently and reliably transmitted over a radio channel, even in carriers. These carriers are regularly spaced in frequency, forming a block of spectrum. The frequency spacing and time synchronization of the carriers is chosen in such a way that the carriers are orthogonal, meaning that they do not cause interference to each other. This is despite the carriers overlapping each other in the frequency domain. The name ‗OFDM‘ is derived from the fact that the digital data is sent using many carriers, each of a different frequency (Frequency Division Multiplexing) and these carriers are orthogonal to each other, hence Orthogonal Frequency Division Multiplexing. In OFDM, usable bandwidth is divided into a large number of smaller bandwidths that are mathematically orthogonal using fast Fourier transforms (FFTs). Reconstruction of the band is performed by the inverse fast Fourier transform (IFFT). Some of basic design related issues of OFDM scheme has been discussed in past [1]. II. RELATED WORK Quadrature Phase Shift Keying is also called as 4- PSK where 4 phases are used. In QPSK modulation a cosine carrier is varied in phase while keeping a constant amplitude and frequency. QPSK uses four points on the constellation diagram, equi spaced around a circle. With four phases, QPSK can encode two bits per symbol, with Gray coding to minimize the BER — twice the rate of BPSK. Analysis shows that this may be used either to double the data rate compared to a BPSK system while maintaining the bandwidth of the signal or to maintain the data-rate of BPSK but halve the bandwidth needed. Various scheme has been taken in past to simulate and measure BER in QPSK modulation system. The QPSK signal consists of two parts in phase and quadrature phase. In phase gives the real part of the signal and quadrature gives the imaginary part of the signal. Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal called carrier wave.Any digital modulation scheme uses a finite number of distinct signals to represent digital data.