C N Deshmukh et al., International Journal of Wireless Communications and Network Technologies, 4(1), December – January 2015, 9-15 9 ABSTRACT Recent generation communication system has a serious challenge of accommodating more users within limited allocated bandwidth without affecting the system performance. OFDM is used to cater for increased data rate of wireless medium with good performance. Diversity techniques play an important role in achieving higher performance level under imperfect channel condition. In this paper we propose a DWT-OFDM Diversity to achieve better performance in terms of SNR and bit error rate (BER) for SV model based standard UWB channel. The performance of different discrete wavelets are analyzed and compared with FFT based OFDM. The result indicates better BER performance in case of lower order wavelet. Key words: BER, DWT, FFT, ISI, OFDM, SNR, SV Model, UWB 1. INTRODUCTION Orthogonal Frequency Division Multiplexing (OFDM) constitute of combination of modulation and multiplexing wherein independent signal that are subset of main signal are multiplexed. The signal itself is first split into independent channel, modulated by data and further re-multiplexed to create OFDM carrier. As the subcarriers in OFDM are orthogonal, it allows simultaneous transmission of multiple sub carriers in a compact frequency space without interference. OFDM can provide large data rates even under channel impairment. Efficient compact spectral utilization can be achieved in OFDM scheme with help of minimally separated sub-carriers [3, 5]. Similarly OFDM scheme convert a broadband frequency selective channel into parallel flat fading narrow band sub channel. In order to mitigate the problem of ISI (Inter symbol interference) caused by complex multipath wireless channel a cyclic prefix (CP) [4] is added to each symbol in OFDM system. The cyclic prefix causes ripples in the power spectral density of the UWB signal [2]. On the other hand wavelet based modulation satisfies orthogonality criterion. We can derive benefits of OFDM even when traditional sinusoid carriers of FFT based OFDM are replaced with suitable wavelets. Wavelet based system have better to immunity to impulse and narrow band noises as compared to FFT OFDM [2, 4]. In addition to this wavelet based OFDM does not require any CP leading to increase in spectral efficiency, reduce complexity and better symbol rate. Discrete wavelet transform (DWT) are being considered as alternative platforms for replacing IFFT and FFT [6, 14-15]. It utilizes low pass filter and high pass filter, operating as Quadrature Mirror Filters (QMF) satisfying perfect reconstruction and ortho-normal properties. The purpose of this paper is to demonstrate the diversity advantage provided by use of DWT in lieu of FFT in OFDM system. DWT has been introduced as a highly efficient and flexible method for sub-band decomposition of signal. Section 2 presents the traditional FFT OFDM and wavelet OFDM whereas Section 3 describes the system and channel model. In Section 4 simulation environment with result are discussed. Section 5 concludes the paper 2. FFT OFDM AND WAVELET OFDM 2.1 FFT-OFDM OFDM system is used as modulation method that divides a given bandwidth into multiple smaller sub-bands. In time domain, an N-point FFT OFDM system can be represented as: s[n]= ଵ √୒ ∑ S ୩ e ୒ଵ ୩ୀ଴ ୨ଶ஠୬୩/୒ , n=0,1,2,……N-1 (1) Where s[n] is the discrete form of s(t), N is the number of sub-channels, ଵ √ே is a scaling factor with n as the index of the prevalent subcarrier. S k is the BPSK mapped input symbol of k th sub-channel. The number of FFT points used is same as the number of narrowband sub-channels over which the input symbols are multiplexed. Each of the resulting narrowband sub-channels is modulated by the mapped input bits. Cyclic prefix (CP) at least equal to the length of the channel response, L is pre-appended to each OFDM symbol to contest ISI. To account for the CP, Equation 1 can be expressed as [7]: s[n]= ଵ √ே ∑  ௞  ேଵ ௞ୀ଴ ௝ଶగ௡௞/ே , -N g ≤≤− 1 (2) Performance Analysis of DWT-OFDM Diversity for Standard SV-Model Based UWB System C N Deshmukh 1 , V T Ingole 2 1 Dept of Electronics & Telecommunication Engg., PRMIT&R, Badnera, Maharashtra-India,cndesh1968@gmail.com. 2 Director, IBSS College of Engineering, Ghatkheda-Amravati, Maharashtra-India,vtingole@gmailcom ISSN 2319 - 6629 Volume 4, No.1, December – January 2015 International Journal of Wireless Communications and Networking Technologies Available Online at http://warse.org/pdfs/2014/ijwcnt02412015.pdf