Evaluation of multiuser OFDM schemes over home-plug system

Wahab Ahmed Hasan
Dr. Nasser N. Al-Ani

Abstract: Since high bit rate for data transmission is required for broadband internet, High Definition TVs (HDTV) and other services, Power-Line Communications (PLC) are a technology that provides a very high-speed digital data transmission using the regular Low Voltage (LV) power lines as the transmission media. With multiple outlets in almost every room, power lines are already the most pervasive network in the home and this will reduce the cost for realization of new telecommunications networks. PLC channel constitutes a rather hostile medium for data transmission, it is characterized by frequency-dependent attenuation, multipath, colored noise, narrow band interference and impulsive noise. This requires powerful Forward Error Correction (FEC) coding scheme along with appropriate modulation technique to overcome these impairments. In this thesis, the PLC modem was designed based on efficient modulation technique, Orthogonal Frequency Division Multiplexing (OFDM), due to its resistance to frequency selective fading, tolerance to multipath and abilities in resolving channel impairments to achieve a high transmission capacity, and FEC (Turbo code) is used to correct errors produced during signal transmission at different code rate. This thesis proposes three multiuser OFDM schemes based on spreading the data of each user over all subcarriers at the transmitter. The three schemes considered here are: user multiplexed scheme, coded multiplexing scheme, and mapper multiplexing scheme. Multiuser PLC modem was implemented using Matlab Simulink (R2007a) to investigate their performance under PLC channel,_where the result shows that the using of turbo coding offers performance about (5.1 dB) gain over un-coded systems, and also achieves (3 dB) gain as SNR enhancement between first and sixth iteration. Further the user multiplexed scheme offers performance about (1.2 dB) better than codevcd multiplexed scheme, while in the QAM mapping multiplexer scheme the performance is different from user to user according to number of subchannels and number of bits that each user has, then a video was_transmitted using the proposed design, and the received video is compared for various SNR.