MIT International Journal of Electrical and Instrumentation Engineering, Vol. 3, No. 2, August 2013, pp. 62–66 62 BER Performance Comparison between QPSK and 4-QA Modulation Schemes Manish Trikha ME Scholar NITTTR Chandigarh, INDIA E-mail: mainsh.trikha@gmail.com Manas Singhal ME Scholar, NITTTR Chandigarh, INDIA E-mail: manas.singhal.ec@gmail.com Neha Sharma Assistant Professor MIT, Moradabad, UP, INDIA E-mail: nehasharmaei@gmail.com Ritu Rajan ME Scholar, NITTTR Chandigarh, INDIA E-mail: riturajan11@gmail.com Pankaj Bhardwaj Assistant Professor, MIT, Moradabad, UP INDIA E-mail: april5pankaj@gmail.com ABSTRACT The performance of QPSK and QAM system that are used to encode the data stream in wireless communications. In order to choose the most suitable modulation, several criteria such as power effciency, bandwidth effciency, and bit error rate are used for evaluation. This paper focuses on error performance of phase modulation and amplitude modulation schemes on the method to reduce bit error rates with the help of convolutional coding which is extensively used in GSM cellular system’s encoder. AWGN channel has been reported here. To fnd out the best BER performance between QPSK and AQM we use SIMULINK software. Keywords: 4-QAM, QPSK,BER, AWGM, SIMULINK. I. INTRODUCTION In a digital transmission, BER is the percentage of bits with errors divided by the total number of bits that have been transmitted, received or processed over a given time period. The rate is typically expressed as 10 to the negative power. For example, four erroneous bits out of 100,000 bits transmitted would be expressed as 4 × 10-5, or the expression 3 × 10-6 would indicate that three bits were in error out of 1,000,000 transmitted. BER is the digital equivalent to signal-to-noise ratio in an analog system. II. QUADRATURE PHASE-SHIFT KEYING (QPSK) Quadrature Phase Shift Keying (QPSK) is a form of Phase Shift Keying in which two bits are modulated at once, selecting one of four possible carrier phase shifts (0, 90, 180, or 270 degrees). QPSK allows the signal to carry twice as much information as ordinary PSK using the same bandwidth. QPSK is used for satellite transmission of MPEG2 video, cable modems, videoconferencing, cellular phone systems, and other forms of digital communication over an RF carrier. Fig. 1: QPSK Symbol Constellation Sometimes this is known as quaternary PSK, quadriphase PSK, 4-PSK, or 4-QAM. QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol, shown in the diagram withgray coding to minimize the bit error rate (BER) — sometimes misperceived as twice the BER of BPSK A. Bit Error Rate Although QPSK can be viewed as a quaternary modulation, it is easier to see it as two independently modulated quadrature ISSN No. 2230-7656 ©MIT Publications