Analysis and performance improvement of serial modulation systems with frequency domain equalization including effects of hardware impairments.

摘要

This thesis investigates the performance characteristics of a special type of Generalized Multi-Carrier (GMC) transmission methods known as serial modulation. The well-known form of GMC is Orthogonal Frequency Division Multiplexing (OFDM) which is proved as an efficient transmission scheme in fading channels. Serial modulation with Frequency Domain Equalization (FDE) can be regarded as a Discrete Fourier Transform (DFT) precoded OFDM. In this thesis we show that this method can effectively reduce the undesirable out-of-band radiation generated by nonlinear high power amplifiers. Equivalently it can reduce the required power back-off value of the amplifier to achieve a specific out-of-band radiation. We also propose a modified version of the selected mapping algorithm to reduce the out-of-band radiation of this system.; We introduce Turbo Frequency Domain Equalization (TFDE) as an efficient scheme for serial modulation receivers which benefits from good performance of iterative systems and simplicity of equalization in the frequency domain. To optimize TFDE, we compare the performance and complexity of non-adaptive TFDE and adaptive TFDE. In the former case the equalizer is fixed during iterations while in the latter case it changes with respect to feedback information. Moreover, we compare TFDE with Low Density Parity Check (LDPC) and convolutional codes.; The performance evaluation of TFDE like other turbo systems requires extensive simulations. To reduce the complexity of this process, we propose the Bit Error Rate Transfer (BERT) chart method to analyze the performance of this system. We develop this method for both adaptive and non-adaptive TFDE and different constellations. We will show that this method performs better than the well-known analysis method for turbo systems, Extrinsic Information Transfer (EXIT) chart, when the block length is small. However, for asymptotic analysis the EXIT chart is shown to be more stable.; We consider the effect of deviation in the local oscillators' frequency in the form of frequency offset and phase noise. We propose joint synchronization and turbo equalization methods to compensate for the effect of phase error when the system suffers from frequency offset alone or in combination with phase noise. In the proposed joint synchronization and equalization methods, the phase error is estimated using the soft symbols generated in the feedback loop based on the decoder output a priori information. We show that these methods can almost completely compensate for the effect of phase error.