Crest factor reduction techniques for OFDM telecommunication systems

Two popular Crest Factor Reduction techniques applicable to OFDM signals have been studied and implemented within this project. To provide adequate background, a brief description of OFDM communication systems is included in the first sections, and the problem of high Peak to Average Power Ratio in multi-carrier transmission schemes is presented. An overview of the most relevant Crest Factor Reduction techniques is performed, and the Clipping and Filtering and Peak Windowing algorithms are selected as implementation candidates due to their protocol agnostic nature. Several implementation architectures have been discussed, and the most computationally efficient one has been used to implement both algorithms within srsRAN, an open source, full software radio implementation of an LTE network with all of its components. In order to provide a comprehensive evaluation of the developed algorithms, an extensive measurement campaign has been designed and carried out, comprised of synthetic testing, as well as experimental physical signal measurements in a laboratory setting, and an outdoor measurement campaign. To speed up the measurement process, an automated measurement system has been designed in MATLAB, which remotely operates a signal analyser to perform spectrum and statistical power measurements, as well as IQ sample collection of the generated LTE signals. This measurement system has been used to carry out unwanted emissions tests following the LTE conformance testing procedures, which are also discussed within this document. For the outdoor measurements, an LTE single cell network has been deployed using a software radio transceiver and an LTE phone, with the aim of assessing the end to end quality of service improvements provided by the developed algorithms. The gathered results illustrate that the implemented Crest Factor Reduction techniques can provide significant network performance gains in situations with limited available transmission power. Additional gains provided by these techniques include increased efficiency in the operation of power amplification stages, and reduced network deployment costs.Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructur

A New Scheme For Reduction Of Peak-To-A Verage Power Ratio In Orthogonal Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM) is an attractive modulation method for channels with a non-flat frequency response. as it saves the need for complex equalizers. However. its main disadvantage is the high peak-to-average power ratio (PAPR) of the output signal. which may take values within a range that is proportional to the number of carriers in the system. As a result, a linear behavior of the system over a large dynamic range is needed and therefore the efficiency of the output amplifier is reduced. Many methods have been proposed to reduce the PAPR of the OFDM signal. among them a clipping technique which has been focused and investigated.OFDM signal, among them a clipping technique which has been focused and investigated. This thesis proposes a new scheme to reduce the PAPR. We name it Off technique. Further the effects of clipping scheme as well as the new scheme on the OFDM system performance in terms of Bit Error Rate (BER) and PAPR reduction is investigated. The results obtained indicate that both parameters, i .e. the reduction in PAPR and BER of this scheme were worse than those of the Clipping Scheme. In conclusion, results indicate that Off Technique does not offer a better solution to PAPR reduction in the OFDM system

Digital signal processing techniques for peak-to-average power ratio mitigation in MIMO–OFDM systems

The focus of this thesis is to mitigate the very large peak-to-average transmit power ratios (PAPRs) inherent to conventional orthogonal frequency division multiplexing (OFDM) systems, particularly in the context of transmission over multi-input multi-output (MIMO) wireless broadband channels. This problem is important as a large PAPR generally needs an expensive radio frequency (RF) power amplifier at the transmitter due to the requirement for linear operation over a wide amplitude range and such a cost would be compounded when multiple transmit antennas are used. Advanced signal processing techniques which can reduce PAPR whilst retain the integrity of digital transmission therefore have considerable potential for application in emergent MIMO–OFDM wireless systems and form the technical contributions of this study. [Continues.

Enhanced Multicarrier Techniques for Professional Ad-Hoc and Cell-Based Communications (EMPhAtiC) Document Number D3.3 Reduction of PAPR and non linearities effects

Livrable d'un projet Européen EMPHATICLike other multicarrier modulation techniques, FBMC suffers from high peak-to-average power ratio (PAPR), impacting its performance in the presence of a nonlinear high power amplifier (HPA) in two ways. The first impact is an in-band distortion affecting the error rate performance of the link. The second impact is an out-of-band effect appearing as power spectral density (PSD) regrowth, making the coexistence between FBMC based broad-band Professional Mobile Radio (PMR) systems with existing narrowband systems difficult to achieve. This report addresses first the theoretical analysis of in-band HPA distortions in terms of Bit Error Rate. Also, the out-of band impact of HPA nonlinearities is studied in terms of PSD regrowth prediction. Furthermore, the problem of PAPR reduction is addressed along with some HPA linearization techniques and nonlinearity compensation approaches

An Optical Design Configuration for Wireless Data Transmission

The concept of 2D barcodes is of great relevance for use in wireless data transmission between handheld electronic devices. In a typical setup, any file on a cell phone for example can be transferred to a second cell phone through a series of images on the LCD which are then captured and decoded through the camera of the second cell phone. In this research, a new approach for data modulation in 2D barcodes is introduced, and its performance is evaluated in comparison to other standard methods of barcode modulation. In the proposed method, Orthogonal Frequency Division Multiplexing (OFDM) modulation is used together with Differential Phase Shift Keying (DPSK) over adjacent frequency domain elements to modulate intensity of individual pixels. It is shown that the bit error rate performance of the proposed system is superior to the current state of the art in various scenarios. A specific aim of this study is to establish a system that is proven tolerant to camera motion, picture blur and light leakage within neighboring pixels of an LCD. Furthermore, intensity modulation requires the input signal used to modulate a light source to be positive, which requires the addition of a dc bias. In the meantime, the high crest factor of OFDM requires a lower modulation index to limit clipping distortion. These two factors result in poor power efficiency in radio over fiber applications in which signal bandwidth is generally much less than the carrier frequency. In this study, it is shown that clipping a bipolar radio frequency signal at zero level, when it has a carrier frequency sufficiently higher than its bandwidth, results in negligible distortion in the pass band and most of the distortion power is concentrated in the baseband. Consequently, with less power provided to the optical carrier, higher power efficiencies and better receiver sensitivity will result. Finally, a more efficient optical integrated system is introduced to implement the proposed intensity modulation method which is optimized for radio over fiber applications

Analysis and Implementation of PAPR reduction algorithms for C-OFDM signals

Nowadays multicarrier modulation has become a key technology for communication systems; for example C-OFDM schemes are used in wireless LAN (802.11a/g/n), terrestrial digital television (DVB-T) and audio broadcaster (DAB) in Europe, and discrete multitone (DMT) in x.DSL systems. The principal difficulty with OFDM is the occurrence of the coherent alignment of the time domain parallel signals at the transmitted side which forces system designer to introduce either additional hard computationally device or a suitable power back-off at the high power amplifier in order to cope with the large magnitude signal fluctuation. This leads to a significant increment in computational cost in the former case whereas in a worse allowable power utilization in the latter case with respect to the original system. However since both allowable power and computational cost are subject to a design as well as regulatory limit others solution must be accomplished. Peak reduction techniques reduce maximum-to-mean amplitude fluctuations nominating as a feasible solution. Peak-to-average power ratio is the key metric to measure this amplitude fluctuations at transmitter and to give a clear figure of merit for comparison among different techniques

Digital predistortion of RF amplifiers using baseband injection for mobile broadband communications

Radio frequency (RF) power amplifiers (PAs) represent the most challenging design parts of wireless transmitters. In order to be more energy efficient, PAs should operate in nonlinear region where they produce distortion that significantly degrades the quality of signal at transmitter’s output. With the aim of reducing this distortion and improve signal quality, digital predistortion (DPD) techniques are widely used. This work focuses on improving the performances of DPDs in modern, next-generation wireless transmitters. A new adaptive DPD based on an iterative injection approach is developed and experimentally verified using a 4G signal. The signal performances at transmitter output are notably improved, while the proposed DPD does not require large digital signal processing memory resources and computational complexity. Moreover, the injection-based DPD theory is extended to be applicable in concurrent dual-band wireless transmitters. A cross-modulation problem specific to concurrent dual-band transmitters is investigated in detail and novel DPD based on simultaneous injection of intermodulation and cross-modulation distortion products is proposed. In order to mitigate distortion compensation limit phenomena and memory effects in highly nonlinear RF PAs, this DPD is further extended and complete generalised DPD system for concurrent dual-band transmitters is developed. It is clearly proved in experiments that the proposed predistorter remarkably improves the in-band and out-of-band performances of both signals. Furthermore, it does not depend on frequency separation between frequency bands and has significantly lower complexity in comparison with previously reported concurrent dual-band DPDs