Characterization of μ-Law adaptive companding technique for OFDM-based systems

Abstract

High Peak-to-Average-Power Ratio (PAPR) of transmitted signals is a common problem in broadband telecommunication systems using an orthogonal frequency division multiplexing (OFDM) modulation scheme. Companding techniques have been recently used to alleviate this high PAPR, with adverse effects on the efficiency and linearity of power amplifiers. This thesis presents two contributions to the OFDM field. An adaptive companding scheme with an offset, amidst two nonlinear companding levels, is proposed to achieve better PAPR reduction while maintaining an acceptable bit error rate (BER) level. Study cases have included the effect of companding on the OFDM signal with and without an offset. A novel closed-form approximation for the BER of the proposed companding scheme is presented, and its accuracy is studied by comparisons with simulation results. The performance of the proposed system is evaluated over an extensive set of standard metrics, such as the complementary cumulative distribution function (CCDF) of PAPR, BER, time domain representation, power spectral density (PSD) and probability density function (PDF). Practical emulation of real time OFDM-based system has been implemented and evaluated using Field Programmable Gate Array (FPGA) platform. On the other hand, the effect of companding on OFDM-link performance has been well studied yet limited to Gaussian channels. In this thesis, an improved impulsive noise mitigation technique is proposed for μ-law companded OFDM system in the presence of impulsive and additive white Gaussian noise (AWGN) channels. The proposed system performance is assessed over a wide-range system parameters that involve BER and threshold optimization. Simulation results indicate that while impulsive noise causes degradation in the bit-error performance of companded OFDM, the degradation is moderate under mild impulsive noise densities. Furthermore, the improved uniformity of the companded OFDM envelope makes it easier to identify and remove noise impulses at the receiver via nonlinear pre-processors such as blanking, clipping or their hybrid.

Date of Award	2015
Original language	American English
Supervisor	NAZAR Ali (Supervisor)