Boosted PTS Method with Mu-Law Companding Techniques for PAPR Reduction in OFDM Systems

This paper proposes an enhanced PAPR reduction technique which combines an enhanced PTS method with Mu-Law companding. The enhanced PTS method improves performances in both the partitioning and phase rotation steps. Enhancement in partitioning is achieved through a judicious incorporation of AP-PTS scheme into the IP-PTS. As for phase rotation, an optimal set of rotation vectors is derived based on the correlation properties of candidate signals. The PAPR reduction of this enhanced PTS method is further improved by annexing Mu-Law companding at the end of the enhanced PTS. This application of Mu-Law characteristic in the time domain of OFDM signal significantly improves the PAPR reduction capability of the approach. Simulation results show that the PAPR performance of the enhanced PTS method with Mu-Law companding technique on various scenarios with different modulation schemes is better than that of the PRP-PTS. This approach can be considered as a very attractive candidate for achieving a significant reduction of PAPR, while maintaining a low computational complexity

A Novel PTS Scheme for PAPR Reduction of Filtered-OFDM Signals without Side Information

In this paper, a novel partial transmit sequence (PTS) scheme is proposed for reducing the peak-to-average power ratio (PAPR) of filtered orthogonal frequency division multiplexing (f-OFDM) systems. The PTS method is modified such that no side information (SI) transmission is needed. The data and pilot recovery are accomplished by a simple detector, making use of the correlation property of the Hadamard sequence and the transparency property of the pilot signal and an iterative phase detection is further added in a fading channel. Simulation results show that the modified solution provides a higher correct detection probability without increasing the system complexity nor affecting the PAPR suppression performance

FPGA Implementation of Circularly Shifted PTS Technique for PAPR Reduction in OFDM

In today’s world, the ongoing trend in 4G has adopted multi-carrier transmission schemes like OFDM, OFDMA and MIMO-OFDM. OFDM has proven to be one of the most promising schemes used for transmission of signals. It still exists with some of the drawbacks, out of which, the high peak to average power ratio gives rise to non-linear distortion, inter-symbol interference and out-of-band radiation. There has been various ways developed and implemented to reduce peak to average power ratio. Comparing between all the techniques to reduce peak to average power ratio, it has been found that the best method is partial transmit sequence technique. This technique was first proposed by Muller and Huber in the year 1997. Within the years there have been various modifications with this technique which has been proposed and implemented. Today’s world is a digital world where an analog form of communication can be transformed to digital form of communication. Weste and Skellern were the first to propose the OFDM method in VLSI. The partial transmit sequence technique in FPGA has been proposed by Junjun et.al. and Varahram et.al. In this thesis work an efficient FPGA implementation of circularly shifted partial transmit sequence (CS-PTS) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) signals has been carried out. It eliminates the search for optimum phase factors from a given set, which manifests improved PAPR at reduced computational complexity as compared to conventional PTS (C-PTS). The amplitude of the signal is reduced by rotating each of the partially transmitted sequence anti-clockwise by a pre-determined degree and the peak power is reduced by circularly shifting the quadrature component of the partially transmitted sequence after phase rotation

New methods of partial transmit sequence for reducing the high peak-to-average-power ratio with low complexity in the ofdm and f-ofdm systems

The orthogonal frequency division multiplexing system (OFDM) is one of the most important components for the multicarrier waveform design in the wireless communication standards. Consequently, the OFDM system has been adopted by many high-speed wireless standards. However, the high peak-to-average- power ratio (PAPR) is the main obstacle of the OFDM system in the real applications because of the non-linearity nature in the transmitter. Partial transmit sequence (PTS) is one of the effective PAPR reduction techniques that has been employed for reducing the PAPR value 3 dB; however, the high computational complexity is the main drawback of this technique. This thesis proposes novel methods and algorithms for reducing the high PAPR value with low computational complexity depending on the PTS technique. First, three novel subblocks partitioning schemes, Sine Shape partitioning scheme (SS-PTS), Subsets partitioning scheme (Sb-PTS), and Hybrid partitioning scheme (H-PTS) have been introduced for improving the PAPR reduction performance with low computational complexity in the frequency-domain of the PTS structure. Secondly, two novel algorithms, Grouping Complex iterations algorithm (G-C-PTS), and Gray Code Phase Factor algorithm (Gray-PF-PTS) have been developed to reduce the computational complexity for finding the optimum phase rotation factors in the time domain part of the PTS structure. Third, a new hybrid method that combines the Selective mapping and Cyclically Shifts Sequences (SLM-CSS-PTS) techniques in parallel has been proposed for improving the PAPR reduction performance and the computational complexity level. Based on the proposed methods, an improved PTS method that merges the best subblock partitioning scheme in the frequency domain and the best low-complexity algorithm in the time domain has been introduced to enhance the PAPR reduction performance better than the conventional PTS method with extremely low computational complexity level. The efficiency of the proposed methods is verified by comparing the predicted results with the existing modified PTS methods in the literature using Matlab software simulation and numerical calculation. The results that obtained using the proposed methods achieve a superior gain in the PAPR reduction performance compared with the conventional PTS technique. In addition, the number of complex addition and multiplication operations has been reduced compared with the conventional PTS method by about 54%, and 32% for the frequency domain schemes, 51% and 65% for the time domain algorithms, 18% and 42% for the combining method. Moreover, the improved PTS method which combines the best scheme in the frequency domain and the best algorithm in the time domain outperforms the conventional PTS method in terms of the PAPR reduction performance and the computational complexity level, where the number of complex addition and multiplication operation has been reduced by about 51% and 63%, respectively. Finally, the proposed methods and algorithms have been applied to the OFDM and Filtered-OFDM (F-OFDM) systems through Matlab software simulation, where F-OFDM refers to the waveform design candidate in the next generation technology (5G)

Generalized DFT: extensions in communications

Discrete Fourier Transform (DFT) is a restricted version of Generalized DFT (GDFT) which offers a very limited number of sets to be used in a multicarrier communication system. In contrast, as an extension on Discrete Fourier Transform (DFT) from the linear phase to non-linear phase, the proposed GDFT provides many possible carrier sets of various lengths with comparable or better performance than DFT. The availability of the rich library of orthogonal constant amplitude transforms with good performance allows people to design adaptive systems where user code allocations are made dynamically to exploit the current channel conditions in order to deliver better performance. For MIMO Radar systems, the ideal case to detect a moving target is when all waveforms are orthogonal, which can provide an accurate estimation. But this is not practical in distributed MIMO radars, where sensors are at varying distances from a target. Orthogonal waveforms with low auto- and cross-correlations are of great interest for MIMO radar applications with distributed antennas. Finite length orthogonal codes are required in real-world applications where frequency selectivity and signal correlation features of the optimal subspace are compromised. In the first part of the dissertation, a method is addressed to design optimal waveforms which meets above requirements for various radar systems by designing the phase shaping function (PSF) of GDFT framework with non-linear phase. Multicarrier transmission such as orthogonal frequency-division multiplexing (OFDM) has seen a rise in popularity in wireless communication, as it offers a promising choice for high speed data rate transmission. Meanwhile, high peak-to-average power ratio (PAPR) is one of the well-known drawbacks of the OFDM system due to reduced power efficiency in non-linear modules. Such a situation leads to inefficient amplification and increases the cost of the system, or increases in interference and signal distortion. Therefore, PAPR reduction techniques play an essential role to improve power efficiency in the OFDM systems. There has been a variety of PAPR reduction methods emphasizing different aspects proposed in the literature. The trade-off for PAPR reduction in the existing methods is either increased average power and/or added computational complexity. A new PAPR reduction scheme is proposed that implements a pre-designed symbol alphabet modifier matrix (SAM) to jointly modify the amplitude and phase values of the original data symbol alphabets prior to the IFFT operation of an OFDM system at the transmitter. The method formulated with the GDFT offers a low-complexity framework in four proposed cases devised to be independent of original data symbols. Without degrading the bit error rate (BER) performance, it formulates PAPR reduction problem elegantly and outperforms partial transmit sequences (PTS), selected mapping technique (SLM) and Walsh Hadamard transform (WHT-OFDM) significantly for the communication scenarios considered in the dissertation

PAPR and ICI reduction techniques for OFDM based satellite communication systems

Multi-carrier systems such as orthogonal frequency division multiplexing (OFDM) are significantly affected by peak-to-average-power ratio (PAPR). Unfortunately, the high PAPR inherent to OFDM signals envelopes will occasionally drive high power amplifiers (HPAs) to operate in the nonlinear region of their characteristic curve. The nonlinearity of the HPA exhibits amplitude and phase distortions, which cause loss of orthogonality among the subcarriers (SCs), and hence, inter-carrier interference (ICI) is introduced in the transmitted signal. The ICI power is proportional to the amplitude of the signal at the amplifier input and it may cause a considerable bit error rate (BER) degradation. A plethora of research has been devoted to reduce the performance degradation due to the PAPR problem inherent to OFDM systems. Some of the reported techniques such as amplitude clipping have low-complexity; on the other hand, they suffer from various problems such as in-band distortion and out-of-band expansion. Signal companding methods have low-complexity, good distortion and spectral properties; however, they have limited PAPR reduction capabilities. Advanced techniques such as coding, partial transmit sequences (PTS) and selected mapping (SLM) have also been considered for PAPR reduction. Such techniques are efficient and distortionless, nevertheless, their computational complexity is high and requires the transmission of several side information (SI) bits. In this thesis, a new low-complexity scheme is proposed based on the PTS that employs two inverse fast Fourier transforms (IFFTs) and two circulant transform matrices, in order to reduce complexity and improve the system performance. Furthermore, the low-complexity scheme is simplified by omitting one of the circulant transform matrices in order to reduce both the computational complexity and the number of SI bits at the cost of a small reduction in PAPR and BER performance. It is well known that, accurate PAPR estimation requires oversampling of the transmitted signal, which in turn results in increased complexity. More importantly, minimising the PAPR does not necessarily minimise the distortion produced by the nonlinearity of the HPA. Therefore, minimising PAPR does not necessarily imply that the BER will be minimised too. Efficient and less complex schemes for BER reduction of OFDM systems in the presence of nonlinear HPA and/or carrier frequency offset (CFO) are proposed. These proposed techniques are based on predicting the distortion introduced by the nonlinearity of HPA and/or CFO. Subsequently, techniques such as the PTS and SLM are invoked to minimise the distortion and BER. Three distortion metrics are adopted in this thesis: inter-modulation distortion (IMD), peak interference-to-carrier ratio (PICR) and distortion-to-signal power ratio (DSR). Monte Carlo simulations will confirm that the DSR and PICR are more reliable than the PAPR and IMD for selecting the coefficients of the PTS and SLM to minimise the BER. Furthermore, complexity analyses demonstrate that the proposed schemes offer significant complexity reduction when compared to standard PAPR-based methods. A closed form solution for accurate BER for the OFDM signals perturbed by both the HPA nonlinearity and CFO was derived. Good agreement between the simulation results and the theoretical analysis can be obtained for different HPA parameters and CFOs. Finally, efficient approaches to reduce the impact of nonlinear power amplifiers with respect to the BER of OFDM systems are proposed. These are approaches based on: the well-established PAPR schemes, a power amplifier model and a simple single point cross correlator. The optimum phase sequence within the proposed approaches is selected by maximising the correlation between the input and output of the power amplifier model. Simulation results have confirmed that the BER using the proposed approaches is almost identical to the DSR, while the complexity is reduced significantly for particular system configurations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo