Coherent Optical DFT-Spread OFDM

We consider application of the discrete Fourier transform-spread orthogonal frequency-division multiplexing (DFT-spread OFDM) technique to high-speed fiber optic communications. The DFT-spread OFDM is a form of single-carrier technique that possesses almost all advantages of the multicarrier OFDM technique (such as high spectral efficiency, flexible bandwidth allocation, low sampling rate and low-complexity equalization). In particular, we consider the optical DFT-spread OFDM system with polarization division multiplexing (PDM) that employs a tone-by-tone linear minimum mean square error (MMSE) equalizer. We show that such a system offers a much lower peak-to-average power ratio (PAPR) performance as well as better bit error rate (BER) performance compared with the optical OFDM system that employs amplitude clipping.Comment: This idea was originally submitted at Nov. 28th, 2009. After many times of rejection and resubmission, it was finally accepted by the journal of Advances in Optical Technologie

Physical waveform research for beyond 52.6 GHz in 5G NR networks

Historically, in order to fulfil all the requirements for the new generations, the frequency bands have been expanded from generation to generation. In particular for the fifth generation new radio (5G NR), where the use of millimetre wave (mmWave) frequencies can offer higher bandwidths, communications in frequencies beyond 52.6 GHz seem really promising and are now under discussion in the 3rd Generation Partnership Project (3GPP) standardisation for the 5G NR future releases. More concretely, both academia and industry are doing research for the frequency range between 52.6 GHz and 114.25 GHz. The reasons why communications beyond 52.6 GHz are interesting is because in those frequencies, high data rate and low latency can be provided due to the large and contiguous channel bandwidth that is available. Also, new use cases can be explored in this frequency range since high accuracy positioning is possible at higher carrier frequencies, such as Orthogonal Frequency Division Multiplexing (OFDM) radar sensing, that allows new kinds of services. New challenges appear at higher frequencies, or other implementation issues that were not critical in lower frequencies start to become dominant and have to be taken into consideration while defining the new modulations and comparing the possible candidates. The main problems that have to be faced at higher frequencies are the poor propagation conditions (propagation losses are higher than in frequencies below 52.6 GHz), and the radio frequency (RF) impairments that electronic components may have, especially the lower power amplifier (PA) efficiency. Therefore, in order to have a good signal quality, if the peak to average power ratio (PAPR) of the original signal is high, the back-off should be high to make the PA work in the linear region. Thus, the waveform design has to be focused on generating signals with “nearly constant” envelope in order to be able to work closer to the saturation zone of the amplifier without distorting the signal. Also, another problem that has to be taken into account is the large phase noise (PN) present at these frequencies. The main goal of this work is the comparison between different modulations for discrete Fourier transform (DFT) Spread OFDM (DFTs-OFDM) in order to find a suitable candidate that can be part of the 5G NR communications for carrier frequencies beyond 52.6 GHz, and targeting specially low spectral efficiency (between 1 and 2 bps/Hz). Therefore, the main modulation references are pulse shaped π/2- binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) supported in 5G NR Release 15 up link (UL). In this Thesis, several modulation candidates have been tested under realistic conditions by using a 3GPP 5G NR compliant radio link simulator in Matlab. In order to find the best candidate, the waveforms should be able to present good characteristics that can overcome the problems present in mmWave communications. The main contribution of this thesis is to propose a new "constrained" phase shift keying (PSK) modulation, called CPSK, which applies a constraint to the symbols that are transmitted in order to reduce the PAPR of the signal. The results have shown that under the mmWave communications conditions (such as low PA efficiency and high PN), the new CPSK modulations can provide significant improvement with the evaluated PA model when compared to QPSK modulation, and together with extensive link level performance evaluations, a clear link budget gain can also be shown for specific CPSK modulation candidates and pulse shaped π/2-BPSK

Equalization of MIMO Channels in LTE-Advanced

LTE-Advanced is one of the most evolving and competing standards that target the high speed 4G wireless communications. In order to meet the target of this new cellular technology developed under auspices of the 3GPP standardization bodies, it is necessary to ensure that this technology is able to provide the headline requirements recommended for the terrestrial components of the IMT-Advanced radio interface for 4G broadband mobile communications. One of the key radio technologies that will enable LTE-Advanced to achieve the high data throughput rates is the use of MIMO antennas that play an important role as the conventional communications like using more bandwidths and higher modulation types are limited. Together with this are the downlink OFDMA and the uplink SC-FDMA techniques that are employed to improve the system architecture burdened with the data rates rising pretty well above what was previously in use. The combination of these technologies will help LTE-Advanced keep pace with other wireless technologies that may be competing to offer very high data rates and high level of mobility. But achieving the high data rate up to 1 Gbits/s in 4G mobile networks over wide frequency bandwidths and recovering the original information without being corrupted and downgraded has been a daunting task for engineers. Thus, this paper will briefly discuss the performances of MIMO equalization techniques such as MMSE, ZF and ZF-SIC equalizers in a Rayleigh multichannel fading.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Numerical study of a hybrid optical DMT/DFT-S QAM modulation

A hybrid modulation offers the peak-to-average power ratio (PAPR) robustness of discrete Fourier transform spread (DFT-S) QAM (quadrature amplitude modulation) with the bit rate optimization of discrete multi-tone (DMT) modulation. We examine via simulation under what circumstances this hybrid can increase achievable bit rate. Hybrid PAPR reduction allows us to increase the peak-to-peak voltage at the modulator electrical input to increase the signal mean power at the modulator output. We propose a methodology to identify the optimal driving strategy. We optimize the bit rate for the available spectrum, i.e., the spectral efficiency, taking into account the bandwidth limited nature of the transmitter. The final optimization we propose is the partition of the available spectrum into a lower frequency band for DFT-S QAM and a higher frequency band for DMT. The modulation level of the DFT-S QAM is also optimized. We compare the optimal hybrid performance versus DMT performance for a range of bit rates for a given modulation bandwidth. Improved performance comes at the cost of greater DSP complexity for the hybrid solution. We compare the number of complex multipliers required to implement hybrid versus DMT for both dispersive and non-dispersive systems

Spectrally and Energy Efficient Wireless Communications: Signal and System Design, Mathematical Modelling and Optimisation

This thesis explores engineering studies and designs aiming to meeting the requirements of enhancing capacity and energy efficiency for next generation communication networks. Challenges of spectrum scarcity and energy constraints are addressed and new technologies are proposed, analytically investigated and examined. The thesis commences by reviewing studies on spectrally and energy-efficient techniques, with a special focus on non-orthogonal multicarrier modulation, particularly spectrally efficient frequency division multiplexing (SEFDM). Rigorous theoretical and mathematical modelling studies of SEFDM are presented. Moreover, to address the potential application of SEFDM under the 5th generation new radio (5G NR) heterogeneous numerologies, simulation-based studies of SEFDM coexisting with orthogonal frequency division multiplexing (OFDM) are conducted. New signal formats and corresponding transceiver structure are designed, using a Hilbert transform filter pair for shaping pulses. Detailed modelling and numerical investigations show that the proposed signal doubles spectral efficiency without performance degradation, with studies of two signal formats; uncoded narrow-band internet of things (NB-IoT) signals and unframed turbo coded multi-carrier signals. The thesis also considers using constellation shaping techniques and SEFDM for capacity enhancement in 5G system. Probabilistic shaping for SEFDM is proposed and modelled to show both transmission energy reduction and bandwidth saving with advantageous flexibility for data rate adaptation. Expanding on constellation shaping to improve performance further, a comparative study of multidimensional modulation techniques is carried out. A four-dimensional signal, with better noise immunity is investigated, for which metaheuristic optimisation algorithms are studied, developed, and conducted to optimise bit-to-symbol mapping. Finally, a specially designed machine learning technique for signal and system design in physical layer communications is proposed, utilising the application of autoencoder-based end-to-end learning. Multidimensional signal modulation with multidimensional constellation shaping is proposed and optimised by using machine learning techniques, demonstrating significant improvement in spectral and energy efficiencies

Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation

A new line of research on communications and signals design for Wireless Power Transfer (WPT) has recently emerged in the communication literature. Promising signal strategies to maximize the power transfer efficiency of WPT rely on (energy) beamforming, waveform, modulation and transmit diversity, and a combination thereof. To a great extent, the study of those strategies has so far been limited to theoretical performance analysis. In this paper, we study the real over-the-air performance of all the aforementioned signal strategies for WPT. To that end, we have designed, prototyped and experimented an innovative radiative WPT architecture based on Software-Defined Radio (SDR) that can operate in open-loop and closed-loop (with channel acquisition at the transmitter) modes. The prototype consists of three important blocks, namely the channel estimator, the signal generator, and the energy harvester. The experiments have been conducted in a variety of deployments, including frequency flat and frequency selective channels, under static and mobility conditions. Experiments highlight that a channeladaptive WPT architecture based on joint beamforming and waveform design offers significant performance improvements in harvested DC power over conventional single-antenna/multiantenna continuous wave systems. The experimental results fully validate the observations predicted from the theoretical signal designs and confirm the crucial and beneficial role played by the energy harvester nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication

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

A comparison between APSK and QAM in wireless tactical scenarios for land mobile systems

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