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

Predistortion performance considering Peak to Average Power ratio reduction in OFDM context

International audienceSome recent communication systems like DVB-T2 standard set up a PAPR reduction technique followed by a linearization's one. So in such a scenario, the performance of the linearization is influenced undoubtedly by the PAPR reduction method. In this paper, we revisit the EVM metric and evaluate a closed form regarding the performance of both the PAPR reduction technique and the linearization's one. We choose the predistortion as a linearization technique and define a predistortion error. Assuming that the baseband OFDM signal is characterized as a complex Gaussian process, we consider the three top categories of PAPR reduction methods presented in [2] and we first study the distribution of the resulted signal. Then, we derive some theoretical expressions of the first and second order moments of the predistortion error and show that the error depends mainly on the PAPR of the signal after PAPR reduction method and on the predistortion quality. Some simulations compared to our proposed model confirm our results

Novel DWT-DAPSK based transceivers for DVB-T transmission and next generation mobile networks

Digital wireless communication has become one of the most exciting research topics in the electronic engineering field due to the explosive demands for high-speed wireless services, such as cellular video conferencing. The second generation Terrestrial Digital Video Broadcasting (DVB- T2) has been demonstrated to provide digital communication services with very high spectral efficiency and significantly improved performance. Orthogonal Frequency Division Multiplexing (OFDM) systems have been increasingly deployed in mobile networks for their spectral efficiency and optimum bit error rate. An OFDM system is a multi-carrier system which transmits signals from a single source at different frequencies simultaneously as parallel components. A distinguishing feature of the OFDM system is its ability to preserve high bandwidth efficiency in high speed data streams. Among the different types of OFDM systems, wavelet based systems have been demonstrated to have much better bandwidth and channel performance compared to the Discrete Fourier transform (DFT) and Discrete Cosine Transform (DCT) based systems. The DFT and DCT systems suffer from several disadvantages including less bandwidth efficiency due 'to the need for guard interval and highly complex system design. Discrete Wavelet transform (DWT) based OFDM systems naturally overcome these disadvantages by their design methodology and the technique of transmitting concentrated energy over small spectral coefficients. Several types of modulation schemes such as DPSK, QAM are employed in OFDM systems, which introduce certain penalties such as increased bandwidth and complexity of the system design. So a multilevel differential modulation technique namely Differential Amplitude and Phase Shift Keying (64 DAPSK) has been proposed as an alternative solution. DAPSK-OFDM is very suitable for high date-rate digital mobile radio channel with additive white Gaussian noise (A WGN). In this research work it has been f demonstrated that a combination of DWT -OFDM with DAPSK modulation can be employed to achieve very low peak-to-average power ratio (PAPR), improved bit error ratio (BER), and much reduced inter symbol interference (ISI) & inter-carrier interference (IeI) in wireless mobile network applications. A mathematical model has been proposed for the DWT-OFDM system with DAPSK modulation scheme in this work. The system performance has been evaluated via simulation using Matlab Simulink package and also verified using Matlab programming. This proposed DWT-OFDM with 64DAPSK hybrid system is demonstrated to have better BER (by an order of magnitude for an SNR of 25dB) performance and improved P APR (by 7.2dB) and interference values. It is also demonstrated that including companding with this system results in further reduction of PAPR. Finally, the simulation results also demonstrate that DWT-DAPSK scheme can be successfully employed in DVTB-T2 systems due to its very high spectral efficiency, much improved BER and significantly reduced PAPR performance

Constellation design for future communication systems: a comprehensive survey

[EN] The choice of modulation schemes is a fundamental building block of wireless communication systems. As a key component of physical layer design, they critically impact the expected communication capacity and wireless signal robustness. Their design is also critical for the successful roll-out of wireless standards that require a compromise between performance, efficiency, latency, and hardware requirements. This paper presents a survey of constellation design strategies and associated outcomes for wireless communication systems. The survey discusses their performance and complexity to address the need for some desirable properties, including consistency, channel capacity, system performance, required demapping architecture, flexibility, and independence. Existing approaches for constellation designs are investigated using appropriate metrics and categorized based on their theoretical algorithm design. Next, their application to different communication standards is analyzed in context, aiming at distilling general guidelines applicable to the wireless building block design. Finally, the survey provides a discussion on design directions for future communication system standardization processes.This work was supported in part by the Basque Government under Grant IT1234-19, in part by the PREDOC under Program PRE_2020_2_0105, and in part by the Spanish Government through the Project PHANTOM (MCIU/AEI/FEDER, UE) under Gran

Bit Loading and Peak Average Power Reduction Techniques for Adaptive Orthogonal Frequency Division Multiplexing Systems

In a frequency-selective channel a large number of resolvable multipaths are present which lead to the fading of the signal. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Significant improvement in performance is achieved by adaptively loading the bits on the subcarriers based on the channel state information from the receiver. Imperfect channel state information (CSI) arises from noise at the receiver and also due to the time delay in providing the information to the transmitter for the next data transmission. This thesis presents an investigation into the different adaptive techniques for loading the data bits on the subcarriers. The choice of the loading technique is application specific. The spectral efficiency and the bit error rate (BER) performance of adaptive OFDM as well as the implementation complexity of the different loading algorithms is studied by varying any one of the parameters, data rate or BER or total transmit power subject to the constraints on the other two. A novel bit loading algorithm based on comparing the SNR with the threshold in order to minimize the BER is proposed and its performance for different data rates is plotted. Finally, this thesis presents a method for reducing the large peak to average power ratio (PAPR) problem with OFDM which arises when the sinusoidal signals of the subcarriers add constructively. The clipping and the probabilistic approaches were studied. The probabilistic technique shows comparatively better BER performance as well as reduced PAPR ratio but is more complex to implement

Linear amplification with multiple nonlinear devices

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e ComputadoresIn mobile wireless systems, where there are strict power and bandwidth constrains it is desirable to adopt energy efficient constellations combined with powerful equalizer. However, this increased spectral efficiency of multilevel modulations comes at the expense of reduced power efficiency, which is undesirable in systems where power consumption is a constraint. Hence, minimization of the transmitted energy would enable a significant reduction in the total energy consumption of the wireless mobile devices. A simple and practical constellation optimization design would optimize the transmitted energy with a minimum increase in system complexity. The constellation decomposition in terms of a sum of BPSK (Bi-Phase Shift Keying) sub-constellations, relies on an analytical characterization of the mapping rule were the constellation symbols are written as a linear function of the transmitted bits. Moreover, large constellations in general and non-uniform constellations in particular are very sensitive to interference, namely the residual ISI (Inter-Symbol Interference) at the output of a practical equalizer that does not invert completely the channel effects. IB-DFE(Iterative Block DFE) is a promising iterative frequency domain equalization technique for SC-FDE schemes (Single-Carrier with Frequency Domain Equalization) that allows excellent performance. Therefore it is possible to use the decomposition of constellations on BPSK components to define a pragmatic method for designing IB-DFE receivers that can be employed with any constellation. In this thesis we consider SC-DFE schemes based on high orderM-ary energy optimized constellations with IB-DFE receivers. It is proposed a method for designing the receiver that does not require a significant increase in system complexity and can be used for the computation of the receiver parameters for any constellation. This method is then employed to design iterative receivers, implemented in the frequency-domain, which can cope with higher sensitivity to ISI effects of the constellations resulting from the energy optimization process.Fundação para a Ciência e Tecnologia - MPSat (PTDC/EEA-TEL/099074/2008) projec

Doppler compensation algorithms for DSP-based implementation of OFDM underwater acoustic communication systems

In recent years, orthogonal frequency division multiplexing (OFDM) has gained considerable attention in the development of underwater communication (UWC) systems for civilian and military applications. However, the wideband nature of the communication links necessitate robust algorithms to combat the consequences of severe channel conditions such as frequency selectivity, ambient noise, severe multipath and Doppler Effect due to velocity change between the transmitter and receiver. This velocity perturbation comprises two scenarios; the first induces constant time scale expansion/compression or zero acceleration during the transmitted packet time, and the second is time varying Doppler-shift. The latter is an increasingly important area in autonomous underwater vehicle (AUV) applications. The aim of this thesis is to design a low complexity OFDM-based receiver structure for underwater communication that tackles the inherent Doppler effect and is applicable for developing real-time systems on a digital signal processor (DSP). The proposed structure presents a paradigm in modem design from previous generations of single carrier receivers employing computationally expensive equalizers. The thesis demonstrates the issues related to designing a practical OFDM system, such as channel coding and peak-to-average power ratio (PAPR). In channel coding, the proposed algorithms employ convolutional bit-interleaved coded modulation with iterative decoding (BICM-ID) to obtain a higher degree of protection against power fading caused by the channel. A novel receiver structure that combines an adaptive Doppler-shift correction and BICM-ID for multi-carrier systems is presented. In addition, the selective mapping (SLM) technique has been utilized for PAPR. Due to their time varying and frequency selective channel nature, the proposed systems are investigated via both laboratory simulations and experiments conducted in the North Sea off the UK’s North East coast. The results of the study show that the proposed systems outperform block-based Doppler-shift compensation and are capable of tracking the Doppler-shift at acceleration up to 1m /s2.EThOS - Electronic Theses Online ServiceIraqi Government's Ministry of Higher Education and Scientific ResearchGBUnited Kingdo