427 research outputs found
Peak to average power ratio (PAPR) reduction technique in orthogonal frequency division multiplexing (OFDM) using block coding
Orthogonal Frequency Division Multiplexing (OFDM) signal is considered a good candidate for wireless systems because it offers diversity gain in frequency selective channels. As in other multicarrier schemes, however, OFDM suffers from high peak to average power ratio (PAPR). This is a major drawback of the scheme and ways of minimizing the PAPR have been researched. Block coding scheme is the technique to reduce the peak-to-average power ratio of OFDM signals and also to detect transmission errors. The reason is that in the time domain, a multicarrier signal is the sum of many narrowband signals. At some time instances, this sum is large and at other times is small, which means that the peak value of the signal is substantially larger than the average value. This high PAR is one of the most important implementation challenges that face OFDM, because it reduces the efficiency. The main purpose in this project, is to make a comparison over the PAPR reduction technique using block coding and without block coding. The capability of Block Coding scheme to reduce the Bit Error Rate (BER) in an OFDM system was also measured. The simulation developed in Matlab simulation environment
On the efficiency of PAPR reduction schemes deployed for DRM systems
Digital Radio Mondiale (DRM) is the universally, openly standardized digital broadcasting system for all frequencies including LW, MW, and SW as well as VHF bands. Alongside providing high audio quality to listeners, DRM satisfies technological requirements posed by broadcasters, manufacturers and regulatory authorities and thus bears a great potential for the future of global radio. One of the key issues here concerns green broadcasting. Facing the need for high-power transmitters to cover wide areas, there is room for improvement concerning the power efficiency of DRM-transmitters. A major drawback of DRM is its high peak-to-average power ratio (PAPR) due to the applied transmission technology based on Orthogonal Frequency Division Multiplexing (OFDM), which results in non-linearities in the emitted signal, low power efficiency, and high costs of transmitters. To overcome this, numerous schemes have been investigated for reducing PAPR in OFDM systems. In this paper, we review and analyze various technologies to reduce PAPR providing that the technical feasibility and DRM-specific system architecture and edge conditions regarding the system performance in terms of modulation error rate, compliance with frequency mask, and synchronization efficiency are ensured. All evaluations are carried out with I/Q signals which are monitored in real operation to present the actual performance of proposed PAPR techniques. Subsequently, the capability of the best approach is evaluated via measurements on a DRM test platform, where achieved transmit power gain of 10 dB is shown. According to our evaluation results, PAPR reduction schemes based on active constellation extension followed by a filter prove to be promising towards practical realization of power-efficient transmitters. © 2016, The Author(s)
An efficient wireless power transmitter based on companded OFDM signals
In this work, a waveform design using a combination of OFDM and companding technique is proposed to improve the wireless power transfer (WPT) efficiency without sacrificing the wireless information transfer performance. Employing a Simultaneous Wireless Information and Power Transfer (SWIPT) scheme called Power Splitting (PS) protocol, the transfer of power and data is achieved simultaneously between a Power Beacon (PB) and a receiver node.Furthermore, in order to capture all important nonlinear behaviors of a real energy harvester rectifier circuit, a curve fitting-based nonlinear rectifier model is used.Results show that the use of this companding technique allows the power amplifier (PA) to generate and transmit signals for WPT in a more efficient way, improving also the conversion efficiency of the energy harvester.Fil: Fernández, Santiago. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de Investigaciones en IngenierĂa ElĂ©ctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras. Instituto de Investigaciones en IngenierĂa ElĂ©ctrica "Alfredo Desages"; Argentina. Universidad Nacional del Sur; Argentina. Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras; ArgentinaFil: Gregorio, Fernando Hugo. Universidad Nacional del Sur; Argentina. Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de Investigaciones en IngenierĂa ElĂ©ctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras. Instituto de Investigaciones en IngenierĂa ElĂ©ctrica "Alfredo Desages"; ArgentinaFil: LĂłpez MartĂnez, Javier. Instituto Universitario de InvestigaciĂłn En Telecomunic; España. Communications And Signal Processing Lab; España. Universidad de Málaga, Cei AndalucĂa Tech, Etsi Telecom; EspañaFil: Cousseau, Juan Edmundo. Universidad Nacional del Sur; Argentina. Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - BahĂa Blanca. Instituto de Investigaciones en IngenierĂa ElĂ©ctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras. Instituto de Investigaciones en IngenierĂa ElĂ©ctrica "Alfredo Desages"; Argentina2021 XIX Workshop on Information Processing and Control (RPIC)San JuanArgentinaResearch to Practice Inclusive Communitie
NOVEL OFDM SYSTEM BASED ON DUAL-TREE COMPLEX WAVELET TRANSFORM
The demand for higher and higher capacity in wireless networks, such as cellular,
mobile and local area network etc, is driving the development of new signaling
techniques with improved spectral and power efficiencies. At all stages of a
transceiver, from the bandwidth efficiency of the modulation schemes through highly
nonlinear power amplifier of the transmitters to the channel sharing between different
users, the problems relating to power usage and spectrum are aplenty. In the coming
future, orthogonal frequency division multiplexing (OFDM) technology promises to
be a ready solution to achieving the high data capacity and better spectral efficiency in
wireless communication systems by virtue of its well-known and desirable
characteristics.
Towards these ends, this dissertation investigates a novel OFDM system based on
dual-tree complex wavelet transform (D
Generalized discrete Fourier transform with non-linear phase : theory and design
Constant modulus transforms like discrete Fourier transform (DFT), Walsh transform, and Gold codes have been successfully used over several decades in various engineering applications, including discrete multi-tone (DMT), orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) communications systems. Among these popular transforms, DFT is a linear phase transform and widely used in multicarrier communications due to its performance and fast algorithms. In this thesis, a theoretical framework for Generalized DFT (GDFT) with nonlinear phase exploiting the phase space is developed. It is shown that GDFT offers sizable correlation improvements over DFT, Walsh, and Gold codes. Brute force search algorithm is employed to obtain orthogonal GDFT code sets with improved correlations. Design examples and simulation results on several channel types presented in the thesis show that the proposed GDFT codes, with better auto and cross-correlation properties than DFT, lead to better bit-error-rate performance in all multi-carrier and multi-user communications scenarios investigated. It is also highlighted how known constant modulus code families such as Walsh, Walsh-like and other codes are special solutions of the GDFT framework. In addition to theoretical framework, practical design methods with computationally efficient implementations of GDFT as enhancements to DFT are presented in the thesis. The main advantage of the proposed method is its ability to design a wide selection of constant modulus orthogonal code sets based on the desired performance metrics mimicking the engineering .specs of interest.
Orthogonal Frequency Division Multiplexing (OFDM) is a leading candidate to be adopted for high speed 4G wireless communications standards due to its high spectral efficiency, strong resistance to multipath fading and ease of implementation with Fast Fourier Transform (FFT) algorithms. However, the main disadvantage of an OFDM based communications technique is of its high PAPR at the RF stage of a transmitter. PAPR dominates the power (battery) efficiency of the radio transceiver. Among the PAPR reduction methods proposed in the literature, Selected Mapping (SLM) method has been successfully used in OFDM communications. In this thesis, an SLM method employing GDFT with closed form phase functions rather than fixed DFT for PAPR reduction is introduced. The performance improvements of GDFT based SLM PAPR reduction for various OFDM communications scenarios including the WiMAX standard based system are evaluated by simulations. Moreover, an efficient implementation of GDFT based SLM method reducing computational cost of multiple transform operations is forwarded. Performance simulation results show that power efficiency of non-linear RF amplifier in an OFDM system employing proposed method significantly improved
Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods
There are a lot of optimization needs in the research and design of wireless communica- tion systems. Many of these optimization problems are Nondeterministic Polynomial (NP) hard problems and could not be solved well. Many of other non-NP-hard optimization problems are combinatorial and do not have satisfying solutions either. This dissertation presents a series of Particle Swarm Optimization (PSO) based search and optimization algorithms that solve open research and design problems in wireless communications. These problems are either avoided or solved approximately before.
PSO is a bottom-up approach for optimization problems. It imposes no conditions on the underlying problem. Its simple formulation makes it easy to implement, apply, extend and hybridize. The algorithm uses simple operators like adders, and multipliers to travel through the search space and the process requires just five simple steps. PSO is also easy to control because it has limited number of parameters and is less sensitive to parameters than other swarm intelligence algorithms. It is not dependent on initial points and converges very fast.
Four types of PSO based approaches are proposed targeting four different kinds of problems in wireless communications. First, we use binary PSO and continuous PSO together to find optimal compositions of Gaussian derivative pulses to form several UWB pulses that not only comply with the FCC spectrum mask, but also best exploit the avail- able spectrum and power. Second, three different PSO based algorithms are developed to solve the NLOS/LOS channel differentiation, NLOS range error mitigation and multilateration problems respectively. Third, a PSO based search method is proposed to find optimal orthogonal code sets to reduce the inter carrier interference effects in an frequency redundant OFDM system. Fourth, a PSO based phase optimization technique is proposed in reducing the PAPR of an frequency redundant OFDM system. The PSO based approaches are compared with other canonical solutions for these communication problems and showed superior performance in many aspects. which are confirmed by analysis and simulation results provided respectively. Open questions and future
Open questions and future works for the dissertation are proposed to serve as a guide for the future research efforts
Practical Guidelines for Approaching the Implementation of Neural Networks on FPGA for PAPR Reduction in Vehicular Networks
Nowadays, the sensor community has become wireless, increasing their potential and applications. In particular, these emerging technologies are promising for vehicles' communications (V2V) to dramatically reduce the number of fatal roadway accidents by providing early warnings.
The ECMA-368 wireless communication standard has been developed and used in wireless sensor
networks and it is also proposed to be used in vehicular networks. It adopts Multiband Orthogonal
Frequency Division Multiplexing (MB-OFDM) technology to transmit data. However, the large
power envelope fluctuation of OFDM signals limits the power efficiency of the High Power Amplifier
(HPA) due to nonlinear distortion. This is especially important for mobile broadband wireless and
sensors in vehicular networks. Many algorithms have been proposed for solving this drawback.
However, complexity and implementations are usually an issue in real developments. In this paper,
the implementation of a novel architecture based on multilayer perceptron artificial neural networks
on a Field Programmable Gate Array (FPGA) chip is evaluated and some guidelines are drawn
suitable for vehicular communications. The proposed implementation improves performance in
terms of Peak to Average Power Ratio (PAPR) reduction, distortion and Bit Error Rate (BER) with
much lower complexity. Two different chips have been used, namely, Xilinx and Altera and a
comparison is also provided. As a conclusion, the proposed implementation allows a minimal
consumption of the resources jointly with a higher maximum frequency, higher performance and
lower complexity.This work has been partly funded by projects TERESA-ADA (TEC2017-90093-C3-2-R)
(MINECO/AEI/FEDER, UE) and ELISA (TEC2014-59255-C3-3-R)
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.
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