IJEEE, Vol. 1, Issue 3 (2014)
e-ISSN: 1694-2310 | p-ISSN: 1694-2426
PERFORMANCE EVALUATION OF BER FOR AWGN, AWGN MULTIPATH AND RAYLEIGH FADING CHANNELS 1
Neena Thakur, 2 Ranjana Thakur
1,2
Department of Electronics and Communication Engineering, S.E.C.G., Mohali, Punjab, India 1
neenu999thakur@gmail.com, 2fb.chhotie92@yahoo.com
Abstract-The objectives of this paper are to study, analyze and evaluate the performance of BER (Bit Error Rate) in mobile multipath fading propagation channel. The parameters which are considered for the performance evaluation are AWGN, AWGN Multipath, Rayleigh fading channel and Hadamard code generator. The results are derived for different types of digital modulation (i.e. BPSK, QPSK) using Matlab Simulation link. Keywords- Spread Spectrum, AWGN, BPSK, QPSK, BER, SNR. I. INTRODUCTION Spread spectrum is a radio communication system in which the baseband signal bandwidth is intentionally spread over a large bandwidth by injection of higher frequency noise-like signal [2]. In this transmission technique the frequency spectrum of a data signal is spread using a code uncorrelated with that signal. As a result the bandwidth occupancy is much higher than required. The codes used for spreading have low cross- correlation values and are unique to every user. This is the reason that a receiver which has knowledge about the code of the intended transmitter is capable of selecting the desired signal.This paper has been proposed a simulink-based model of the performance of BER in AWGN, Rayleigh and AWGN multipath channel using digital modulation techniques.
Fig. 1 Constellation diagram of BPSK.
The combination of two bits in QPSK forms four distinct symbols (i.e. 00, 01, 10, and 11). When the symbol is changed to next symbol than the phase of the carrier is changed by 45o.
II. MODULATION TECHNIQUES A. BPSK (Binary Phase Shift Keying) BPSK is the simplest form of PSK. It uses two phases, one phase represents logic 1 and the other phase represents logic 0 [3]. As the input digital signal changes state (i.e. from 1 to 0 or from 0 to 1) the phase of the output carrier shifts between two angles that are separated by 180o. Hence, other names for BPSK are phase reversal keying (PRK) and 2-PSK. B. QPSK (Quadrature Phase Shift Keying) QPSK is one example of M-ary PSK modulation technique. In QPSK, two successive bits in the data sequence are grouped together. This reduces the bit rate or signalling rate and thus reduces the bandwidth of the channel [4].
Fig. 2 Constellation diagram of QPSK.
III. NOISE AND INTERFERENCE A. SNR (Signal to Noise Ratio) The signal to noise ratio is the ratio between the wanted signal and the unwanted background noise. SNR= P (signal) P (noise) Usually SNR is expressed in a logarithmic basis using decibels as – SNR (dB) = 10log10 P (signal) P (noise)
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B. BER (Bit Error Rate) Bit Error Rate is defined as the rate at which errors occur in a transmission system. BER is the ratio of number of errors to the total number of transmitted bits. BER
=
number of errors total number of transmitted bits
C. AWGN (Additive White Gaussian Noise) AWGN is commonly used to transmit signal while signal travel from the channel [5]. AWGN channel add white Gaussian noise to the signal that passes through it. The mathematical expression of received signal isr (t) = s (t) + n (t) where, s (t) is transmitted signal and n (t) is background noise.
Fig. 3 Block diagram for two users in case of AWGN or Rayleigh channel.
D. Rayleigh Fading Rayleigh fading is primarily caused by multipath reception. When no line of sight path exists in between transmitter and receiver the objects in the environment attenuate, reflect, refract and diffract the signal before it arrives at the receiver. This propagation environment is known as Rayleigh fading. The resultant signal received at the receiver is the sum of all the reflected and scattered waves [6]. IV. HADAMARD CODES Hadamard codes are orthogonal codes used for spreading in communication system in which the receiver is perfectly synchronised with the transmitter [2]. The hadamard codes are the individual row of a hadamard matrix. Hadamard matrices are square matrices whose matrices are +1 or -1 and whose rows and columns are manually orthogonal. Because of this orthogonality property, the cross-correlation between any two hadamard codes of the same matrix is zero, when system is perfectly synchronised. V. SIMULATION MODEL Simulink (simulation and link), developed by the Math works, is an environment for multi-domain simulation and Model-based Design for dynamic and embedded systems [7]. With Simulink, models are built by dragging and dropping blocks from the library browser onto the graphical editor and connecting them with lines that establish mathematical relationships between blocks. It can be set up simulation parameters by double clicking the blocks. The simulation block diagrams used in this paper are shown below-
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Fig. 4 Block diagram for two users in case of AWGN multipath channel.
Table 1: Simulation Parameters
Parameter
Value
Spreading Code
Hadamard Code
No. of users
2
Noise Channel
AWGN, Rayleigh, AWGN multipath
Modulation Technique
BPSK, QPSK
SNR
0, 3, 5, 7, 9
Doppler Shift
10, 20, 30, 40, 50
Code Length
64
VI. SIMULATION RESULTS This section of the paper presents and discusses all the results obtained by the computer simulation program written in matlab 7.12.0 following the analytical approach of a wireless communication system considering AWGN, AWGN multipath, Rayleigh fading channels. The results are represented in terms of SNR vs. BER graph in case of AWGN, AWGN multipath channels and in case of Rayleigh fading channel the results are represented in terms of Doppler shift vs. BER graph [6]. A. BER Performance of AWGN Channel for BPSK and QPSK
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VII. CONCLUSIONS From the simulation results, the BER of a digital communication system is an important figure of merit used to quantify the integrity of the data transmitted through the system [5]. In this paper we analyze two modulation techniques- BPSK and QPSK to reduce the error performance of the signal and compare which technique is better through different fading channels. The results show that BPSK modulation technique has better performance compared to that of QPSK. It is also observed that BER is minimum for AWGN and maximum for Rayleigh fading channel. Fig. 5 SNR vs. BER Graph for AWGN channel
B. BER Performance of AWGN Multipath Channel for BPSK and QPSK
Fig. 6 SNR vs. BER Graph for AWGN multipath channel
C. BER Performance of Rayleigh Fading Channel for BPSK and QPSK
ACKNOWLEDGMENT We would like to convey our sincere thanks to the person involved either directly or indirectly in this project especially for Mrs. Garima Saini, Assistant Professor, ECE, NITTTR, Chandigarh, who has been great person in supervising, guiding and encouraging throughout the whole duration of the project.
REFERENCES [1]. Khalid Hamid Bilal, Ibrahim Khider Eltahir and Amin Babiker, “Performance Evaluation of DS-WCDMA”, 2013 International Conference On Computing, Electrical And Electronic Engineering (ICCEEE). [2]. Ahmed Ziani, Abdellatif Medouri, “Analysis of Different Pseudo-Random and Orthogonal Spreading Sequences in DSCDMA”. [3]. Sakshi Gupta, Himanshu Sharma, “Performance Investigation for Different Modulation Techniques in WCDMA with Multipath Fading Channels”, International Journal of Advanced Research in Computer Science and Software Engineering Volume 2, Issue 7, July 2012. [4]. Sanjay Sharma, “Digital Communication”, 2nd Edition January 2010. [5]. Sudhir Babu, Dr. K.V Sambasiva Rao, “Evaluation of BER for AWGN, Rayleigh and Rician Fading Channels under Various Modulation Schemes”, International Journal of Computer Applications (0975 – 8887) Volume 26– No.9, July 2011. [6]. Nuzhat Tasneem Awon, Md. Mizanur Rahman, Md. Ashraful Islam, A.Z.M. Touhidul Islam, “Effect of AWGN & Fading (Rayleigh & Rician) channels on BER performance of a WiMAX communication System”, (IJCSIS) International Journal of Computer Science and Information Security,Vol. 10, No. 8, August 2012. [7]. Md. Abdul Kader, Farid Ghani and R.Badlishah, “Development and Performance Evaluation of Hierarchical Quadrature Amplitude Modulation (HQAM) for Image Transmission over Wireless Channels”, Third International Conference on Computational Intelligence, Modelling & Simulation,2011.
Fig. 7 Doppler shift vs. BER Graph for Rayleigh channel
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