Wavelet based OFDM for Power line Communication Sagar Chandra Kar, Sattar Hussain and Xavier Fernando Department of Electrical Engineering, Ryerson University sagarchandra.kar@ryerson.ca,sattar.hussain@ryerson.ca, fernando.ee@ryerson.ca Abstract—Power line Communication (PLC) system offers cheaper mode of signal communication facilities. However, in fast Fourier transform (FFT) based OFDM system, a cyclic prefix (CP) of the same length as the channel impulse response needs to be added after each symbol to avoid inter symbol and inter carrier interference. This paper investigates the benefits of a filter bank based Wavelet Transform OFDM (WTOFDM) approach that doesn’t need the cyclic prefix and hence has higher throughput. Different types of wavelets based OFDM links are compared by simulation and the bi-orthogonal wavelet is found to be the best for PLC applications. Keywords: Wavelets, OFDM, FFT, IFFT Inverse discrete wavelet transform (IDWT), Power line communication (PLC). I. INTRODUCTION Over the last few years, PLC is receiving increasing attention due to various emerging applications such as smart grid communications, smart home applications, utility applications, advance metering and real time energy pricing control. The core competency of PLC systems lies in the fact that it shouldn’t generate additional interference that may impact the power transmission quality while providing reliable communications over frequently varying power line channels. International bodies like IEEE and ITU have been working on various PLC standards such as IEEE P 1901 that promises up to 500 Mb/s. PLC systems may offer broadband or narrowband communications. Broadband PLC works at a frequency range from 150 kHz to 34 MHz and provides faster internet access and supports small LAN networking [1] while narrowband PLC works with frequency range up to 150 kHz and can be used for some specific applications such as central management of power consumption, remote meter reading, commanding. Conventionally PLC uses OFDM which relies on forward in inverse fast Fourier transforms (IFFT and FFT). These algorithms generate number of parallel orthogonal sub carriers and then modulate the digital data for transmission. These orthogonal subcarriers provide frequency domain spreading and enable advanced schemes such as adaptive bit loading and power control. OFDM also helps overcoming attenuation in high frequency bands typical in power line channels. However, OFDM systems require the addition of cyclic prefix to eliminate inter symbol and inter carrier interferences because of the circular convolution property of the FFT. Wavelet transformation is an alternative technique that can be used in PLC systems. Compared to FFT and IFFT transforms, that use exponential sinusoids as the basis function, wavelet transform uses different wavelets as the basis function. The properties of the transform depend on the basis function. Usually, wavelet transform is used to extract information from many different kinds of data, including – but certainly not limited to – audio signals and images. For certain classes of signals, wavelet analysis provides more precise information about signal data than other signal analysis techniques such as FFT. Discrete wavelet transform (DWT) is the sampled version of the continuous wavelet which is based on sub- band coding and is known for its fast computation of wavelet transform. DWT is easy to implement and provides substantial reduction in computation time and resources required for representing digital signals. Common applications of DWT are video compressing, internet communications, object reorganization, numerical analysis. In wavelet-based OFDM, the wavelet transform replaces FFT block. WTOFDM system has better spectrum efficiency than the conventional OFDM since the subcarriers need no guard interval and no pilot tones are required. WTOFDM can be designed in different ways to suit the transmission medium by using an appropriate wavelet basis. Hence, it offers excellent performance in different signal transmission environment and for this reason it is considered as a potential candidate for PLC systems. Due to the fact that delay spreads in the power line are much smaller compared to other environments, the transmission symbols in WTOFDM can be made much shorter and, therefore, WTOFDM offers much better robustness to impulsive noise. Furthermore, WTOFDM provides higher transmission efficiency and handles deeper notches. More importantly, WTOFDM uses linear convolution that does not need cyclic prefix while the FFT transform uses circular convolution that need cyclic prefix to transmit data bits. Note that the extra symbols added in the FFT OFDM represent a loss in the achievable data rate which becomes significant in highly-dispersive channels. When the FFT signal is sampled, the window interval may or may not have integer number of cycles. Spectral leakage occurs in case of not having integer number of cycles. For spectral leakage the side lobe is appeared as a real frequency and it creates distortion. This problem can be solved by wavelet transform. In this work, we have used different kinds of wavelet in the simulated model to compute the least bit error rate. The obtained results indicate that Bi-orthogonal wavelet has a lower bit rate compared to other wavelet schemes. Bi- CCECE 2014 1569892831 1 978-1-4799-3010-9/14/$31.00 ©2014 IEEE CCECE 2014 Toronto, Canada