A joint OFDM PAPR reduction and data decoding scheme with no SI estimation

The need for side information (SI) estimation poses a major challenge when selected mapping (SLM) is implemented to reduce peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. Recent studies on pilot-assisted SI estimation procedures suggest that it is possible to determine the SI without the need for SI transmission. However, SI estimation adds to computational complexity and implementation challenges of practical SLM-OFDM receivers. To address these technical issues, this paper presents the use of a pilot-assisted cluster-based phase modulation and demodulation procedure called embedded coded modulation (ECM). The ECM technique uses a slightly modified SLM approach to reduce PAPR and to enable data recovery with no SI transmission and no SI estimation. In the presence of some non-linear amplifier distortion, it is shown that the ECM method achieves similar data decoding performance as conventional SLM-OFDM receiver that assumed a perfectly known SI and when the SI is estimated using a frequency-domain correlation approach. However, when the number of OFDM subcarriers is small and due to the clustering in ECM, the modified SLM produces a smaller PAPR reduction gain compared with conventional SLM

PAPR reduction techniques in optical OFDM:A Review

In the past few years, number of users and demand for bandwidth has increased due to increased usage of internet and real time applications like video and audio streaming and Voice over IP (VoIP). OFDM has proved to be a very reliable technique in optical communication to satisfy these needs by providing high data rates along with robustness against fiber impairments like chromatic dispersion and polarization mode dispersion. But it suffers from major problem of high peak to average power ratio. High PAPR induces nonlinearities in fibers due to Kerr effect as well as in ADC/DAC. Several techniques have been developed to combat this problem in OFDM systems. This paper reviews some of most common and recently developed PAPR reduction techniques in optical OFDM systems

Physical-Layer Encryption Using Digital Chaos for Secure OFDM Transmission

Due to the broadcasting nature of passive optical network (PON), data security is challenging. For the transmission of orthogonal frequency division multiplexing (OFDM) signals, the high peak-to-average power ratio (PAPR) is considered as one of the major drawbacks. This chapter reviews the digital chaos-based secure OFDM data encryption schemes, where the transmission performance is improved via PAPR reduction. The digital chaos is incorporated into the signal scrambling approaches: selective mapping (SLM), partial transmit sequence (PTS); and precoding approaches: discrete Fourier transform (DFT) and Walsh-Hadamard transform (WHT) for PAPR reduction. Multi-fold data encryption is achieved with a huge key space provided by digital chaos, to enhance the physical-layer security for OFDM-PON, while the pseudo-random properties of digital chaos are applied for PAPR reduction, which consequently improves the transmission performance. The evidences of these encryption approaches are presented in terms of theories, simulations, as well as experimental demonstrations. The chaotic data encryption schemes could be promising candidates for next-generation OFDM-PON

CO-OFDM Elastic Optical Networks - Issues on Transmission, Routing, and Bandwidth Allocation

The use of orthogonal frequency division multiplexing (OFDM) technology helps an optical transmission system to break the limitation of wavelength grids by wavelength division multiplexing (WDM), in which a flexible and elastic transmission paradigm is created, so as to achieve better energy and spectrum efficiency and flexibility of the fiber resource. By jointly considering the nonlinear effect of Mach-Zehnder modulator (MZM) and amplified spontaneous emission (ASE) noise, we first provide an analytical model on the bit error rate (BER) performance for a single elastic optical transmission line. A novel adaptive transmission strategy in OFDM-based elastic optical transmission systems is proposed. Based on the adaptive transmission strategy, an optimization problem is formulated and solved via mathematical programming. By using proposed adaptive transmission strategy, the routing and bandwidth allocation (RBA) problem is formulated in elastic optical networks and numerically solved to route a set of lightpaths into a network according to the static or dynamic traffic demands with the best energy efficiency, where the laser transmit power, modulation level, number of subcarriers, and routing path of each node pair, are jointly determined. Case studies via extensive numerical experiments are conducted to verify the proposed strategy and gain better understanding on the solutions of formulated optimization problem. By further extending proposed adaptive transmission strategy, we propose a novel adaptive radio-over-fiber (RoF) transmission system for next-generation cloud radio access network (C-RAN). By considering nonlinear distortion from both MZM and high power amplifier (HPA), a 2 x 2 MIMO-OFDM baseband model for simulating the required ESNR of end-to-end RoF transmission system is developed. The RoF system for current C-RAN and proposed RoF system for future C-RAN are presented. We also propose a model to analyze the power consumption for the optical part of RoF transmission system. By performing case studies, proposed RoF system is demonstrated to be more energy efficient than current RoF system.4 month

Computationally Efficient Modified PTS for PAPR Reduction in MIMO-OFDM

Nowadays wireless communication has taken its leap for a high data rate using the multi-carrier transmission technique.Orthogonal frequency division multiplexing(OFDM) is one of such popular method for achieving this high information rate.OFDM has several advantages,but one of the main drawbacks is its high peak-to-average power ratio(PAPR).This is due to a large number of the subcarrier,which leads to distortion problem at receiver. An OFDM signal with the high PAPR requires power amplifier’s(PAs)with large dynamic ranges.Such PAs are less efficient,costly to manufacture and very much difficult to design.There have been a large number of techniques are available in the literature to reduce the PAPR, such as Partial transmit sequence,Selective mapping,Block Coding, Tone rejection,etc.However,the challenging part is that most of the PAPR reduction schemes come with high computational complexity.Recent PAPR reduction techniques such as partial transmit sequence(PTS)has been considered as most popular for PAPR reduction.This research work explores to find a solution for the PAPR reduction by using PTS technique, which has been implemented by using sub-blocks partitioning.In sub-block partition consists of OFDM data frame which is partitioned into several sub-blocks.An adjacent partitioning(AP)method can be perceived as the best of the existing partitioning method when the cost and PAPR reduction performance are considered together.A new technique is based on modified PTS using phase rotation and circular shifting to attain the overall reduction of PAPR in MIMO-OFDM system, but computational complexity does not decrease for the same.A Co-operative PTS technique which is mainly based on alternative PTS technique is applied.In this technique although a slight loss of PAPR reduction performance is there but with much lower computational complexity

Performance evaluation of T-transform based OFDM in underwater acoustic channels

PhD ThesisRecently there has been an increasing trend towards the implementation of orthogonal frequency division multiplexing (OFDM) based multicarrier communication systems in underwater acoustic communications. By dividing the available bandwidth into multiple sub-bands, OFDM systems enable reliable transmission over long range dispersive channels. However OFDM is prone to impairments such as severe frequency selective fading channels, motioned induced Doppler shift and high peak-to-average-power ratio (PAPR). In order to fully exploit the potential of OFDM in UWA channels, those issues have received a great deal of attention in recent research. With the aim of improving OFDM's performance in UWA channels, a T-transformed based OFDM system is introduced using a low computational complexity T-transform that combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthonormal unitary transform. Through real-world experiment, performance comparison between the proposed T-OFDM system and conventional OFDM system revealed that T-OFDM performs better than OFDM with high code rate in frequency selective fading channels. Furthermore, investigation of different equalizer techniques have shown that the limitation of ZF equalizers affect the T-OFDM more (one bad equalizer coefficient affects all symbols) and so developed a modified ZF equalizer with outlier detection which provides major performance gain without excessive computation load. Lastly, investigation of PAPR reduction methods delineated that T-OFDM has inherently lower PAPR and it is also far more tolerant of distortions introduced by the simple clipping method. As a result, lower PAPR can be achieved with minimal overhead and so outperforming OFDM for a given power limit at the transmitter

Hybrid clipping and companding techniques based peak to average power ratio reduction in orthogonal frequency division multiplexing based differential chaos shift keying system

In this paper, a hybrid approach using clipping and companding techniques is introduced to reduce the peak to average power ratio (PAPR) of orthogonal frequency division multiplexing based differential chaos shift keying (OFDM-DCSK), which is the major drawback of the OFDM-DCSK. The hybrid function is processed at the end of the transmitter before transmitting the signal. However, there is no need for an inverse function at the receiver, which decreases the system complexity. Several techniques have been proposed in the literature for decreasing the PAPR value. Clipping and companding are active methods in terms of reducing the PAPR. Finally, the PAPR reduction and bit error rate (BER) performances are evaluated. The simulation results show that this technique gives better performance as compared with the clipping and companding techniques