International Journal of Computer Applications (0975 – 8887) Volume 131 – No.18, December 2015 5 Performance Analysis of Digital Communication Systems in Presence of AWGN Implementing Filter Technique Deepak Kumar Chy. Department of Electrical & Electronics Engineering University of Information Technology & Sciences (UITS) Dhaka, Bangladesh. Md. Khaliluzzaman Department of Computer Science & Engineering International Islamic University Chittagong (IIUC) Chittagong, Bangladesh. Md. Faisal Faruque Department of Computer Science & Engineering University of Information Technology & Sciences (UITS) Dhaka, Bangladesh. ABSTRACT In digital communication system, data must encounter in a band limited environment. The fact is that constraining the bandwidth of the transmitted signal necessarily increases the probability of BER at the receiver. The system performance in terms of BER is evaluated with as well as without filter developing digital communication model. The likelihood of BER and SER is compared. The results show that Raised Cosine filter exhibits almost equal performance in comparison with rest of the filters. The worst case scenario is obtained while introducing no filtering technique despite applying the modulation scheme QAM. Roll off factor 0.22 has taken into account as Raised cosine filter act as FIR filter at that factor. In this paper inter symbol interference (ISI) is examined and it is seen that ISI plays an important role in digital communication systems. It is also observed that overall transmission errors are less while increasing the ratio of bit energy per symbol (E b /N 0 ). MATLAB communication environment has been used for simulation. General Terms BER, SER, Raised Cosine filter, Equiripple filter, Hamming Window filter, QAM Keywords ISI, Likelihood, Roll off factor, Band limited 1. INTRODUCTION In modern digital communication system, digital modulation affords more capacity of information, high data security, better quality communications and efficient bandwidth utilization. Although digital communication is much better than the analog communication, still it has certain issues that need to be addressed. Especially when it comes to wireless communication, one of the major research considerations becomes the effect of multipath propagation. A thorough analysis is necessary for strategic planning of any system designed by doing comparative study of different modulation techniques with and without filter via different multipath communication channels. In this paper AWGN channel is considered. To study and draw the graph in terms BER versus Eb/No in presence of AWGN channel for various QAM modulation schemes with and without filter is tested using computer simulation. Therefore, understand the system could go whether for suitable modulation technique with filter or merely suitable modulation technique to suit the channel quality can suggest better performance [1] [2]. In this work, a digital communication model using QAM i.e. M= 16, 32, 64 with digital filtering and without filtering is proposed. The design criteria of filters at transmitter (Tx) and receiver (Rx) is carefully designed using MATLAB environment with the requirements of reducing inter-symbol interference (ISI). Nyquist‟s condition of reducing ISI is considered introducing Raised Cosine filter at transmitter side for band limited transmitting signal. On the other hand same Raised Cosine filter, Equiripple and Hamming window filter are used at the receiver side for detecting noisy signal. The remaining paper is organized as follows. In Section II, Modulation Techniques are described. In Section III, Additive White Gaussian Noise (AWGN) is explained. In Section IV Digital FIR filters i.e. Raised Cosine, Equiripple, Hamming Window filter are described and simulation results are given in Section V. This paper is concluded in Section VI. 2. MODULATION TECHNIQUES One way to communicate a message signal whose frequency spectrum does not fall within that fixed frequency range, or one that is unsuitable for the channel, is to change a transmittable signal according to the information in the message signal. This alteration is called modulation, and it is the modulated signal that is transmitted. The receiver then recovers the original signal through a process called demodulation. 2.1 Digital Modulation Digital modulation schemes transform digital signals into waveform that are compatible with the nature of the communications channel. One category uses a constant amplitude carrier and the other carries the information in phase or frequency variations (FSK, PSK). A major transition is from the simple Amplitude Modulation (AM) and Frequency Modulation (FM) to digital techniques such as Quadrature Phase Shift Keying (QPSK), Frequency Shift Keying (FSK), Minimum Shift Keying (MSK) and Quadrate Amplitude Modulation (QAM) [4]. 2.2 M-Quadrature Amplitude Modulation QAM is used in applications including microwave digital radio, DVB-C (Digital Video Broadcasting Cable), and so on.