Performance Evaluation of Pseudo-random Noise and Hadamard-walsh Sequences for Hamming Coded Wcdma System over Awgn and Fading Channels

In this paper, the impact of pseudorandom noise (PN) sequence code and Hadamard–Walsh sequence code on the performance of a Wideband Direct Sequence Code Division Multiple Access (WCDMA) system with Hamming coding or without error correction and detection coding under quadrature phase-shift keying (QPSK) modulation over an Additive White Gaussian Noise (AWGN) channel and fading channel is investigated. The study is made with the development of a computer program written in MATLAB source code and its application on the processing of a simulated digital signal. The simulation results of estimated Bit error rate (BER) show the performance of WCDMA system with Hamming coding is highly effective for AWGN channel but less effective to combat inherent interference in the communication system. It is anticipated that the performance of the communication system degrades with the increasing of noise power. Keyword: Pseudo-random noise (PN) sequence, Hadamard-Walsh sequence, Bit error rate (BER), Hamming coding, Wideband Code Division Multiple Access (WCDMA) Introduction In a multiple access system, a large number of users share a common channel to transmit information to a receiver. The system has to manage resources appropriately in order to cover and support all the users that want to access the system. More than one user is allowed to share a channel by use of direct sequence spread spectrum (DS-SS) signals (Scholtz, 1982, Pickholtz et all. 1982). In a DS-SS system, each user is assigned a unique code sequence (Dinan, et all.1998) that allows the user to spread the information signal across the assigned frequency band. Signals from the various users are separated at the receiver by crosscorrelation of the received signal with each of the possible user code sequences. Possible narrow band interference is also suppressed in this process. By designing these code sequences to have relatively small crosscorrelation, the cross-talk inherent in the demodulation of the signals received from multiple transmitters is minimized. This multiple access method is CDMA, which is a form of a DSSS system (Raitola, 1996, Prasad, et all. 1998). The Wideband Direct-Sequence CDMA (WCDMA) is 3G-system operation in 5MHz *Corresponding Author, Email: [email protected] 1. Lecturer, Dept. of Telecommunication and Electronic Engineering, Hajee Mohammad Danesh Science and Technology University (HSTU), Dinajpur-5200, Bangladesh. 2. Assistant Programmer, Dhaka University of Engineering Technology (DUET), Gazipur, Bangladesh. Performance Evaluation of Pseudo-Random Noise http://www.bdresearchpublications.com/journal/ 1123 bandwidth to support both high-rate packet data and circuit-switched data (Rappaport, 2006, Wang, et all. 2002). This modulation transforms an informationbearing signal into a transmission signal with a much larger bandwidth. This transformation is achieved by encoding the information signal with a code signal that is independent of the data and has much larger spectral width than the data signal. This spreads the original signal power over a much broader bandwidth, resulting in a lower power density. The ratio of transmitted bandwidth to information bandwidth is called the processing gain, Gp of the DS-SS system: Gp = Bt/Bi, where Bt is the transmission bandwidth and Bi is the bandwidth of the information bearing signal. In DS-SS transmitter the data is spreader by multiplying with a pseudorandom noise (PN) sequence. A PN sequence is a binary sequence that exhibits randomness properties but has a finite length and is therefore deterministic. A single pulse or symbol of the PN waveform is called chip. They are used to implement synchronization and uniquely code individual user signals across the transmission interface. The PN sequence is usually generated using sequential logic circuits i.e. feedback shift register (Dixon, 1994). A DS-SS receiver is based on a correlator, which utilizes correlation properties of the PN codes (Dixon, 1994). The correlators attempt to match the incoming received signal with each of the candidate prototype waveforms (PN sequences) known a priori to the receiver. The received DS-SS signal for a single user can be represented as ( ) s s s c s 2 E S ( t) = m (t )p (t )c o s 2 π f t + θ T where m (t) is the data sequence, p (t) is the PN spreading sequence, fc is the carrier frequency and θ is the carrier phase angle at t = 0. However, popular code sequences that can be found in practical DSSSsystems are: Hadamard-Walsh codes, M-sequences, Gold codes and Kasamicodes. In this paper, we used also Hadamard-Walsh code instead of PN sequence code under same condition. Walsh-sequences have the advantage to be orthogonal, in this way we should get rid of any multi-access interference under a perfect synchronization. In particular, the Hadamard-Walsh codes of length N; N = 2n, n = 1,2, ..., can be often generated using Hadamard matrices HN (Harmuth, 1970) with The rows (or columns) of the matrix HN are the Hadamard-Walsh codes. with H0 = [1] HN = H N/2 H N/2