PERFORMANCE ANALYSIS OF OFDM TECHNIQUES USING TURBO CODES FOR BROADBAND OVER POWER LINES

Abstract

The focus of the project entitled “PERFORMANCE ANALYSIS OF OFDM TECHNIQUES USING TURBO CODES FOR BROADBAND OVER POWER LINES” is to ultimately improves bit error rate in addition to peak to average power. The demand for high data rate services has been increasing very rapidly and there is no slow down in sight. Almost every existing physical medium capable of supporting broadband data transmission to our homes, offices and schools has been or will be used in the future. This includes both wired (Digital Subscriber Lines, Cable Modems, Power Lines) and wireless media. Often these services require very reliable data transmission system experience many degradations, such as large attenuation, noise, multi path, interference, time variation, nonlinearity’s, and must meet many constraints, such as finite transmit power and most importantly finite cost. One physical-layer dealing with these impairments is multi carrier modulation. Orthogonal Frequency Division Multiplexing (OFDM) has become a popular modulation method in high speed wireless communications. By partitioning a wideband fading channel into flat narrowband channels, OFDM is able to mitigate the detrimental effects of multi path fading using a simple one- tap equalizer. However, in the time domain OFDM signals suffers from large envelope variations, which are often characterized by the Peak to Average Ratio(PAR) PAR signals like OFDM, require that transmission amplifiers operate at very low power efficiencies to avoid clipping. As we know that channel suffers with multi path fading and frequency selectivity. Nevertheless, the calculated channel capacity limit promises very high data rates over this channel, subject to simple fixes. Enhancement techniques, such as coding (Turbo Codes) can help an OFDM system to achieve this limit as close as possible. The smart use of coding and power allocation in OFDM will be useful to the desired performance at higher data rates. There is a growing need to quickly transmit information wirelessly and accurately. Engineers have already combine techniques such as orthogonal frequency division multiplexing (OFDM) suitable for high data rate transmission with forward error correction (FEC) methods over wireless channels. In this thesis, we enhance the system throughput of a working OFDM system by adding turbo coding. Simulation is done over a time varying, frequency selective Rayleigh fading channel. The temporal variations in the simulated wireless channel are due to the presence of channel. The temporal variations in the simulated wireless channel are due to the presence of Doppler, a sign of relative motion between transmitter and receiver. The wideband system has 48 data sub-channels, each is individually modulated according to channel tate information acquired during the previous burst. The end goal is to increase the system throughput while maintaining system performance under a bit error rate (BER) of 10-2. The results we obtained are preliminary. The lack of resources prevented us from producing detailed graphs of our findings.