145 research outputs found

    Nyquist-SEFDM: Pulse shaped multicarrier communication with sub-carrier spacing below the symbol rate

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    A new waveform design which simultaneously compresses bandwidth and suppresses out-of-band power leakage is studied in this work considering future 5th generation (5G) requirements. Thus, doubly created interference, coming from less than symbol rate packed sub-carriers and pulse shaping filters, is introduced. Therefore, this work, through using specially designed detectors, deals with the doubly created interference problem. It paves the way to non-orthogonal signal detection and non-orthogonal carrier aggregation (CA) system designs; both of importance to future wireless and wired communication systems

    Transmission Experiment of Bandwidth Compressed Carrier Aggregation in a Realistic Fading Channel

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    In this paper, an experimental testbed is designed to evaluate the performance of a bandwidth compressed multicarrier technique termed spectrally efficient frequency division multiplexing (SEFDM) in a carrier aggregation (CA) scenario1. Unlike orthogonal frequency division multiplexing (OFDM), SEFDM is a non-orthogonal waveform which, relative to OFDM, packs more sub-carriers in a given bandwidth, thereby improving spectral efficiency. CA is a long term evolution-advanced (LTE-Advanced) featured technique that offers a higher throughput by aggregating multiple legacy radio bands. Considering the scarcity of radio spectrum, SEFDM signals can be utilized to enhance CA performance. The combination of the two techniques results in a larger number of aggregated component carriers (CCs) and therefore increased data rate in a given bandwidth with no additional spectral allocation. It is experimentally shown that CA-SEFDM can aggregate up to 7 CCs in a limited bandwidth while CA-OFDM can only put 5 CCs in the same bandwidth. In this work, LTE-like framed CA-SEFDM signals are generated and delivered through a realistic LTE channel. A complete experimental setup is described together with error performance and effective spectral efficiency comparisons. Experimental results show that the measured BER performance for CA-SEFDM is very close to CA-OFDM and the effective spectral efficiency of CA-SEFDM can be substantially higher than that of CA-OFDM

    Experimental SEFDM Pipelined Iterative Detection Architecture with Improved Throughput

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    In spectrally efficient frequency division multiplexing (SEFDM), the separation between subcarriers is reduced below the Nyquist criteria, enhancing bandwidth utilisation in comparison to orthogonal frequency division multiplexing (OFDM). This leads to self-induced inter-carrier interference (ICI) in the SEFDM signal, which requires more sophisticated detectors to retrieve the transmitted data. In previous work, iterative detectors (IDs) have been used to recover the SEFDM signal after processing a certain number of iterations, however, the sequential iterative process increases the processing time with the number of iterations, leading to throughput reduction. In this work, ID pipelining is designed and implemented in software defined radio (SDR) to reduce the overall system detection latency and improve the throughput. Thus, symbols are allocated into parallel IDs that have no waiting time as they are received. Our experimental findings show that throughput will improve linearly with the number of the paralleled ID elements, however, hardware complexity also increases linearly with the number of ID elements

    Design and Performance of SEFDM Signals with Power Allocation

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    This work presents preliminary investigations into the use of power allocation for the multi-carrier non-orthogonal spectrally efficient frequency division multiplexing (SEFDM) signalling format. SEFDM is utilized to improve the spectral efficiency compared to conventional orthogonal frequency division multiplexing (OFDM), by violating the orthogonality condition and getting the sub-carriers closer to each other. In this paper, subcarriers within the same SEFDM symbol are allocated different power levels. Results show that such power allocation is beneficial to SEFDM from several perspectives: i) Overall system stability enhancement; ii) a drastic complexity reduction in SEFDM detector; iii) peak to average power ratio (PAPR) performance improvement

    Spectrally Efficient FDM System with Probabilistic Shaping

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    This work proposes and explores the use of probabilistic shaping for the non-orthogonal multicarrier spectrally efficient frequency division multiplexing (SEFDM) system. The system design considers the reverse concatenation architecture which cascades the constant composition distribution matching (CCDM) algorithm together with soft-decision forward error correction (SD-FEC)-LDPC code for the probabilistic shaping scheme. The non-orthogonal signalling is implemented by discrete Fourier transform (DFT)-based SEFDM modulation with matched filtering demodulation and advanced interference cancellation detection. The high achievable spectral efficiency, low computation complexity and reliability make SEFDM a good candidate for multicarrier signalling for beyond 5G communications. By adding extra shaping gain and flexibility of rate adaptation, the combination of two capacity-achieving techniques provides significant insight of further performance improvement. In this paper, we investigate the performance of the proposed probabilistically shaped-SEFDM (PS-SEFDM) system with regular QAM constellations. The presented results of the proposed system show less required power and bandwidth saving compared to OFDM when achieving the same error performance and same spectral efficiency

    Bandwidth Compressed Waveform for 60 GHz Millimeter-Wave Radio over Fiber Experiment

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    A bandwidth compressed waveform termed spectrally efficient frequency division multiplexing (SEFDM) is experimentally demonstrated in a 60-GHz millimeter-wave (mm-wave) radio-over-fiber scenario to increase transmission data rates without changing signal bandwidth and modulation format. Experimental results show the advantages of SEFDM and confirm that the bit rate of SEFDM signals can be substantially higher than that of orthogonal frequency-division multiplexing (OFDM) signals. Experimentally, a 2.25 Gbit/s 4QAM OFDM signal is transmitted through 250 m of OM-1 multi-mode fiber and then it is optically up converted to 60 GHz band at the photodiode before delivery to a mm-wave antenna for transmission over a 3 meter wireless link. The work demonstrates that when the OFDM signal is replaced by an SEFDM signal using the same modulation format and occupying the same bandwidth, the bit rate can be increased, by a factor of up to 67%, to 3.75 Gbit/s at the expense of a 3-dB power penalty. Additionally, a bandwidth compressed 4QAM SEFDM is shown to outperform an 8QAM OFDM of the same spectral efficiency, thereby verifying that a lower order modulation format may replace a higher order one and achieve performance gain

    Using zero padding for robust channel Estimation in SEFDM systems

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    The First 15 Years of SEFDM: A Brief Survey

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    Spectrally efficient frequency division multiplexing (SEFDM) is a multi-carrier signal waveform, which achieves higher spectral efficiency, relative to conventional orthogonal frequency division multiplexing (OFDM), by violating the orthogonality of its sub-carriers. This survey provides the history of SEFDM development since its inception in 2003, covering fundamentals and concepts, wireless and optical communications applications, circuit design and experimental testbeds. We focus on work done at UCL and outline work done other universities and research laboratories worldwide. We outline techniques to improve the performance of SEFDM and its practical utility with focus on signal generation, detection and channel estimation

    mm-Wave Data Transmission and Measurement Techniques: A Holistic Approach

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    The ever-increasing demand on data services places unprecedented technical requirements on networks capacity. With wireless systems having significant roles in broadband delivery, innovative approaches to their development are imperative. By leveraging new spectral resources available at millimeter-wave (mm-wave) frequencies, future systems can utilize new signal structures and new system architectures in order to achieve long-term sustainable solutions.This thesis proposes the holistic development of efficient and cost-effective techniques and systems which make high-speed data transmission at mm-wave feasible. In this paradigm, system designs, signal processing, and measurement techniques work toward a single goal; to achieve satisfactory system level key performance indicators (KPIs). Two intimately-related objectives are simultaneously addressed: the realization of efficient mm-wave data transmission and the development of measurement techniques to enable and assist the design and evaluation of mm-wave circuits.The standard approach to increase spectral efficiency is to increase the modulation order at the cost of higher transmission power. To improve upon this, a signal structure called spectrally efficient frequency division multiplexing (SEFDM) is utilized. SEFDM adds an additional dimension of continuously tunable spectral efficiency enhancement. Two new variants of SEFDM are implemented and experimentally demonstrated, where both variants are shown to outperform standard signals.A low-cost low-complexity mm-wave transmitter architecture is proposed and experimentally demonstrated. A simple phase retarder predistorter and a frequency multiplier are utilized to successfully generate spectrally efficient mm-wave signals while simultaneously mitigating various issues found in conventional mm-wave systems.A measurement technique to characterize circuits and components under antenna array mutual coupling effects is proposed and demonstrated. With minimal setup requirement, the technique effectively and conveniently maps prescribed transmission scenarios to the measurement environment and offers evaluations of the components in terms of relevant KPIs in addition to conventional metrics.Finally, a technique to estimate transmission and reflection coefficients is proposed and demonstrated. In one variant, the technique enables the coefficients to be estimated using wideband modulated signals, suitable for implementation in measurements performed under real usage scenarios. In another variant, the technique enhances the precision of noisy S-parameter measurements, suitable for characterizations of wideband mm-wave components

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

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    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
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