Broadband access and home networking through powerline networks

by 1979- Amirshahi-Shirazi, Pouyan

iii The increasing interest in modern multimedia applications, such as broadband Internet, HDTV, etc. requires new access techniques for connecting the private premises to a communication backbone. One promising technology, Broadband over Powerlines (BPL), uses electric powerlines as a high speed digital data channel to connect a group of private users to a very high data rate backbone, such as fiber optic. The lines in power delivery network can be categorized based on several criteria. Depending on line voltage, HV (high voltage), MV (medium voltage), and LV (low voltage) grids are typically defined. Most HV/MV transformers locations are equipped with a high-speed fiber connection. Therefore, MV lines can act as the first pipeline of high-speed connection from backbone to the home users. In this dissertation, we explore the potential of this technology and then examine the system performance enhancement for such channel environment using different modulation and coding techniques. Although for nearly a century some elementary transmission models of these lines have been available, no serious attempt has gone into a comprehensive BPL channel modeling for high frequency spectra. In this research we use a new modeling of multiconductor wave propagation in overhead lines, considering transient effects. The model identifies independent wave modes for overhead lines and it is useable over a wide range of frequencies. The proposed model incorporates realistic ground admittance, appropriate for higher frequencies used by broadband over powerline communications. By calculating the lossy ground impedance for multi-conductor lines, we derive a transfer iv function for these networks. By applying water filling in spectral domain, we were able to express the channel capacity of powerline networks, using the developed transfer function. The powerline channel suffers from multipath fading and frequency selectivity. Nevertheless, the calculated channel capacity limit promises very high data rates over this channel. Furthermore, LV powerline channels suffer from impulsive bursty noise. In this dissertation two models for this noise are presented and discussed. One of the major burdens of BPL is the electromagnetic compatibility (EMC) of this technology to other wireless systems. Since electric wires might radiate electromagnetic waves at high frequencies, precautions need to be employed in order to avoid any interference to other wireless devices. This issue is also investigated in this research briefly. The well-known multi-carrier technique, Orthogonal Frequency Division Multiplexing (OFDM), is considered as the modulation scheme for BPL by most researchers. By the application of OFDM, the most distinct property of power-line channel, its frequency selectivity, can be easily coped with. Moreover, OFDM can perform better than single carrier modulation in the presence of impulsive noise. In this dissertation the bit error rate (BER) performance of the OFDM system under impulsive noise and frequency fading is theoretically analyzed and closed form expressions for this performance is derived. In order to make a very efficient use of the allocated bandwidth and energy in OFDM, adaptive allocation algorithms should be employed. These algorithms are studied comprehensively in this thesis. Additionally, an iterative algorithm v is proposed to predict and cancel the impulsive noise in the OFDM system over powerline channels. Enhancement techniques, such as coding can help an OFDM system to achieve the capacity limit as close as possible. A theoretical upper bound on the performance of coded OFDM system is obtained, given perfect interleaving. The effect of the interleaver length on coding performance is also studied. Simulations show that the upper bound is quite tight for the case of employing a longer interleaver. The effect of interleaver size on the system performance is studied, as well. In this dissertation we also employ Digital Fountain codes, which are a new class of erasure detecting codes. These codes are considered the state-of-the-art discovery in coding theory due to their simplicity and performance. Indoor wireless connectivity is always appealing to consumers because of its ease of use. For this reason, indoor optical wireless communications through lighting LEDs has been investigated in this research. A suitable channel model is proposed for this system and the corresponding transmission capacity values are calculated. It is shown that the combination of BPL and white LED technology makes an efficient method for fulfilling the premise of broadband access for home networking, while providing efficient and low-cost lighting.