48 research outputs found
Timing-Error Tolerance Techniques for Low-Power DSP: Filters and Transforms
Low-power Digital Signal Processing (DSP) circuits are critical to commercial System-on-Chip design for battery powered devices. Dynamic Voltage Scaling (DVS) of digital circuits can reclaim worst-case supply voltage margins for delay variation, reducing power consumption. However, removing static margins without compromising robustness is tremendously challenging, especially in an era of escalating reliability concerns due to continued process scaling. The Razor DVS scheme addresses these concerns, by ensuring robustness using explicit timing-error detection and correction circuits. Nonetheless, the design of low-complexity and low-power error correction is often challenging. In this thesis, the Razor framework is applied to fixed-precision DSP filters and transforms. The inherent error tolerance of many DSP algorithms is exploited to achieve very low-overhead error correction. Novel error correction schemes for DSP datapaths are proposed, with very low-overhead circuit realisations. Two new approximate error correction approaches are proposed. The first is based on an adapted sum-of-products form that prevents errors in intermediate results reaching the output, while the second approach forces errors to occur only in less significant bits of each result by shaping the critical path distribution. A third approach is described that achieves exact error correction using time borrowing techniques on critical paths. Unlike previously published approaches, all three proposed are suitable for high clock frequency implementations, as demonstrated with fully placed and routed FIR, FFT and DCT implementations in 90nm and 32nm CMOS. Design issues and theoretical modelling are presented for each approach, along with SPICE simulation results demonstrating power savings of 21 β 29%. Finally, the design of a baseband transmitter in 32nm CMOS for the Spectrally Efficient FDM (SEFDM) system is presented. SEFDM systems offer bandwidth savings compared to Orthogonal FDM (OFDM), at the cost of increased complexity and power consumption, which is quantified with the first VLSI architecture
Spectrum Optimisation in Wireless Communication Systems: Technology Evaluation, System Design and Practical Implementation
Two key technology enablers for next generation networks are examined in this thesis, namely Cognitive Radio (CR) and Spectrally Efficient Frequency Division Multiplexing (SEFDM). The first part proposes the use of traffic prediction in CR systems to improve the Quality of Service (QoS) for CR users. A framework is presented which allows CR users to capture a frequency slot in an idle licensed channel occupied by primary users. This is achieved by using CR to sense and select target spectrum bands combined with traffic prediction to determine the optimum channel-sensing order. The latter part of this thesis considers the design, practical implementation and performance evaluation of SEFDM. The key challenge that arises in SEFDM is the self-created interference which complicates the design of receiver architectures. Previous work has focused on the development of sophisticated detection algorithms, however, these suffer from an impractical computational complexity. Consequently, the aim of this work is two-fold; first, to reduce the complexity of existing algorithms to make them better-suited for application in the real world; second, to develop hardware prototypes to assess the feasibility of employing SEFDM in practical systems. The impact of oversampling and fixed-point effects on the performance of SEFDM is initially determined, followed by the design and implementation of linear detection techniques using Field Programmable Gate Arrays (FPGAs). The performance of these FPGA based linear receivers is evaluated in terms of throughput, resource utilisation and Bit Error Rate (BER). Finally, variants of the Sphere Decoding (SD) algorithm are investigated to ameliorate the error performance of SEFDM systems with targeted reduction in complexity. The Fixed SD (FSD) algorithm is implemented on a Digital Signal Processor (DSP) to measure its computational complexity. Modified sorting and decomposition strategies are then applied to this FSD algorithm offering trade-offs between execution speed and BER
A practical system for improved efficiency in frequency division multiplexed wireless networks
Spectral efficiency is a key design issue for all wireless communication systems. Orthogonal frequency division multiplexing (OFDM) is a very well-known technique for efficient data transmission over many carriers overlapped in frequency. Recently, several studies have appeared that describe spectrally efficient variations of multi-carrier systems where the condition of orthogonality is dropped. Proposed techniques suffer from two weaknesses: firstly, the complexity of generating the signal is increased. Secondly, the signal detection is computationally demanding. Known methods suffer either unusably high complexity or high error rates because of the inter-carrier interference. This study addresses both problems by proposing new transmitter and receiver architectures whose design is based on using the simplification that a rational spectrally efficient frequency division multiplexing (SEFDM) system can be treated as a set of overlapped and interleaving OFDM systems. The efficacy of the proposed designs is shown through detailed simulation of systems with different signal types and carrier dimensions. The decoder is heuristic but in practice produces very good results that are close to the theoretical best performance in a variety of settings. The system is able to produce efficiency gains of up to 20% with negligible impact on the required signal-to-noise ratio
Wireless multi-carrier communication system design and implementation using a custom hardware and software FPGA platform
Field Programmable Gate Array (FPGA) devices and high-level hardware development languages represent a new and exciting addition to traditional research tools, where simulation models can be evaluated by the direct implementation of complex algorithms and processes. Signal processing functions that are based on well known and standardised mathematical operations, such as Fast Fourier Transforms (FFTs), are well suited for FPGA implementation. At UCL, research is on-going on the design, modelling and simulation of Frequency Division Multiplexing (FDM) techniques such as Spectrally E - cient Frequency Division Multiplexing (SEFDM) which, for a given data rate, require less bandwidth relative to equivalent Orthogonal Frequency Division Multiplexing (OFDM). SEFDM is based around standard mathematical functions and is an ideal candidate for FPGA implementation. The aim of the research and engineering work reported in this thesis is to design and implement a system that generates SEFDM signals for the purposes of testing and veri cation, in real communication environments. The aim is to use FPGA hardware and Digital to Analogue Converters (DACs) to generate such signals and allow recon gurability using standard interfaces and user friendly software. The thesis details the conceptualisation, design and build of an FPGA-based wireless signal generation platform. The characterisation applied to the system, using the FPGA to drive stimulus signals is reported and the thesis will include details of the FPGA encapsulation of the minimum protocol elements required for communication (of control signals) over Ethernet. Detailed testing of the hardware is reported, together with a newly designed in the loop testing methodology. Veri ed test results are also reported with full details of time and frequency results as well as full FPGA design assessment. Altogether, the thesis describes the engineering design, construction and testing of a new FPGA hardware and software system for use in communication test scenarios, controlled over Ethernet
ΠΠΎΠ³Π΅ΡΠ΅Π½ΡΠ½ΡΠΉ ΠΏΡΠΈΠ΅ΠΌ Π½Π΅ΠΎΡΡΠΎΠ³ΠΎΠ½Π°Π»ΡΠ½ΡΡ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎ-ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΡΡ ΠΌΠ½ΠΎΠ³ΠΎΡΠ°ΡΡΠΎΡΠ½ΡΡ ΡΠΈΠ³Π½Π°Π»ΠΎΠ² ΠΏΡΠΈ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠΈ Π°Π»Π³ΠΎΡΠΈΡΠΌΠ° Ρ ΠΎΠ±ΡΠ°ΡΠ½ΠΎΠΉ ΡΠ²ΡΠ·ΡΡ ΠΏΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ
Introduction. Spectrally efficient frequency division multiplexing (SEFDM) is a promising technology for improving spectral efficiency. Since SEFDM signals transmitted on subcarriers are not orthogonal, interchannel interference occurs due to the mutual influence of signals transmitted on adjacent subcarriers. Algorithms for receiving SEFDM signals can be distinguished into element-by-element coherent detection and maximum-likelihood sequence estimation (MLSE). The former method, although being simpler, is characterized by a low bit error rate performance. The latter method, although providing for a higher energy efficiency, is more complicated and does not allow high absolute message rates.Aim. To consider a trade-off solution to the problem of coherent detection of SEFDM signals under the condition of significant interchannel interference, namely, the use of an iterative algorithm of element-by-element processing with decision feedback at each subcarrier frequency.Materials and methods. Analytical expressions for the operation of a demodulator solver were derived. A simulation model for transmission of SEFDM signals was built in the MatLab environment, including element-by-element detection with decision feedback.Results. The simulation results confirmed the efficiency of the proposed algorithm. For error probabilities p =102β¦103, the energy gains reach values from 0.2 to 7.5 dB for different values of the non-orthogonal subcarrier spacing. At the same time, the efficiency of the detection algorithm with decision feedback turns out to be significantly lower than that when using the detection algorithm MLSE.Conclusion. The proposed detection algorithm can be used in future generations of mobile communications, which require high transmission rates. By reducing the computational complexity of the algorithm, it is possible to provide for a lower power consumption of mobile devices.ΠΠ²Π΅Π΄Π΅Π½ΠΈΠ΅. Π Π½Π°ΡΡΠΎΡΡΠ΅Π΅ Π²ΡΠ΅ΠΌΡ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎ-ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΠ΅ ΡΠ°ΡΡΠΎΡΠ½ΠΎΠ΅ ΠΌΡΠ»ΡΡΠΈΠΏΠ»Π΅ΠΊΡΠΈΡΠΎΠ²Π°Π½ΠΈΠ΅ (Spectrally efficient frequency division multiplexing β SEFDM) ΡΠ²Π»ΡΠ΅ΡΡΡ ΠΌΠ½ΠΎΠ³ΠΎΠΎΠ±Π΅ΡΠ°ΡΡΠ΅ΠΉ ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΠ΅ΠΉ, ΠΈΡΠΏΠΎΠ»ΡΠ·ΡΠ΅ΠΌΠΎΠΉ Π΄Π»Ρ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΡ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΠΎΠΉ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΈ ΡΠΊΠΎΡΠΎΡΡΠΈ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΈ ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΈ. ΠΠ»Π³ΠΎΡΠΈΡΠΌΡ ΠΏΡΠΈΠ΅ΠΌΠ° SEFDMΡΠΈΠ³Π½Π°Π»ΠΎΠ² ΠΌΠΎΠΆΠ½ΠΎ ΡΠ°Π·Π΄Π΅Π»ΠΈΡΡ Π½Π° 2 ΠΊΠ»Π°ΡΡΠ°: ΠΏΠΎΡΠ»Π΅ΠΌΠ΅Π½ΡΠ½ΡΠΉ ΠΊΠΎΠ³Π΅ΡΠ΅Π½ΡΠ½ΡΠΉ ΠΏΡΠΈΠ΅ΠΌ ΠΈ ΠΏΡΠΈΠ΅ΠΌ Π²ΡΠ΅ΠΉ ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΡΡΠ»ΠΊΠΈ. ΠΠ΅ΡΠ²ΡΠΉ ΠΌΠ΅ΡΠΎΠ΄ Π±ΠΎΠ»Π΅Π΅ ΠΏΡΠΎΡΡ, Π½ΠΎ ΠΎΠ±Π»Π°Π΄Π°Π΅Ρ Π½ΠΈΠ·ΠΊΠΎΠΉ ΠΏΠΎΠΌΠ΅Ρ
ΠΎΡΡΡΠΎΠΉΡΠΈΠ²ΠΎΡΡΡΡ. ΠΡΠΈ ΠΏΡΠΈΠ΅ΠΌΠ΅ Π²ΡΠ΅ΠΉ ΠΏΠΎΡΡΠ»ΠΊΠΈ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎ ΠΏΠΎΠ»ΡΡΠ΅Π½ΠΈΠ΅ Π²ΡΡΠΎΠΊΠΎΠΉ ΡΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ, Π½ΠΎ ΡΠ΅Π°Π»ΠΈΠ·Π°ΡΠΈΡ ΡΠ°ΠΊΠΎΠ³ΠΎ ΠΏΡΠΈΠ΅ΠΌΠ° ΠΎΡΠ΅Π½Ρ ΡΠ»ΠΎΠΆΠ½Π° ΠΈ Π½Π΅ ΠΏΠΎΠ·Π²ΠΎΠ»ΡΠ΅Ρ ΡΠ΅Π°Π»ΠΈΠ·ΠΎΠ²Π°ΡΡ Π²ΡΡΠΎΠΊΠΈΠ΅ Π°Π±ΡΠΎΠ»ΡΡΠ½ΡΠ΅ ΡΠΊΠΎΡΠΎΡΡΠΈ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΈ ΡΠΎΠΎΠ±ΡΠ΅Π½ΠΈΠΉ.Π¦Π΅Π»Ρ ΡΠ°Π±ΠΎΡΡ. Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½ΠΈΠ΅ ΠΊΠΎΠΌΠΏΡΠΎΠΌΠΈΡΡΠ½ΠΎΠ³ΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ Π·Π°Π΄Π°ΡΠΈ ΠΊΠΎΠ³Π΅ΡΠ΅Π½ΡΠ½ΠΎΠ³ΠΎ ΠΏΡΠΈΠ΅ΠΌΠ° SEFDM-ΡΠΈΠ³Π½Π°Π»ΠΎΠ² Π² ΡΡΠ»ΠΎΠ²ΠΈΡΡ
ΡΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΌΠ΅ΠΆΠΊΠ°Π½Π°Π»ΡΠ½ΠΎΠΉ ΠΈΠ½ΡΠ΅ΡΡΠ΅ΡΠ΅Π½ΡΠΈΠΈ, Π° ΠΈΠΌΠ΅Π½Π½ΠΎ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ Π½Π° ΠΊΠ°ΠΆΠ΄ΠΎΠΉ ΠΏΠΎΠ΄Π½Π΅ΡΡΡΠ΅ΠΉ ΡΠ°ΡΡΠΎΡΠ΅ ΠΈΡΠ΅ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ Π°Π»Π³ΠΎΡΠΈΡΠΌΠ° ΠΏΠΎΡΠ»Π΅ΠΌΠ΅Π½ΡΠ½ΠΎΠΉ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠΈ Ρ ΠΎΠ±ΡΠ°ΡΠ½ΠΎΠΉ ΡΠ²ΡΠ·ΡΡ ΠΏΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ.ΠΠ°ΡΠ΅ΡΠΈΠ°Π»Ρ ΠΈ ΠΌΠ΅ΡΠΎΠ΄Ρ. ΠΠΏΠΈΡΠ°Π½ΠΈΠ΅ ΡΠ°Π±ΠΎΡΡ Π΄Π΅ΠΌΠΎΠ΄ΡΠ»ΡΡΠΎΡΠ° ΡΠ΅ΡΠ°ΡΡΠ΅Π³ΠΎ ΡΡΡΡΠΎΠΉΡΡΠ²Π° Π²ΡΠΏΠΎΠ»Π½Π΅Π½ΠΎ Π°Π½Π°Π»ΠΈΡΠΈΡΠ΅ΡΠΊΠΈΠΌ ΠΌΠ΅ΡΠΎΠ΄ΠΎΠΌ. ΠΠΌΠΈΡΠ°ΡΠΈΠΎΠ½Π½Π°Ρ ΠΌΠΎΠ΄Π΅Π»Ρ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΈ SEFDM-ΡΠΈΠ³Π½Π°Π»ΠΎΠ² Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ Π² ΠΏΡΠΈΠ΅ΠΌΠ½ΠΈΠΊΠ΅ Π°Π»Π³ΠΎΡΠΈΡΠΌΠ° ΠΏΠΎΡΠ»Π΅ΠΌΠ΅Π½ΡΠ½ΠΎΠΉ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠΈ Ρ ΠΎΠ±ΡΠ°ΡΠ½ΠΎΠΉ ΡΠ²ΡΠ·ΡΡ ΠΏΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ ΠΏΠΎΡΡΡΠΎΠ΅Π½Π° Π² ΡΡΠ΅Π΄Π΅ MatLab.Π Π΅Π·ΡΠ»ΡΡΠ°ΡΡ. Π Π΅Π·ΡΠ»ΡΡΠ°ΡΡ ΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ, ΡΡΠΎ ΠΏΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½Π½ΡΠΉ Π°Π»Π³ΠΎΡΠΈΡΠΌ ΡΠ²Π»ΡΠ΅ΡΡΡ Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΡΠΌ. ΠΡΠΈ Π΄ΠΎΠΏΡΡΡΠΈΠΌΠΎΠΉ Π²Π΅ΡΠΎΡΡΠ½ΠΎΡΡΠΈ ΠΎΡΠΈΠ±ΠΎΠΊ p =102β¦103 ΡΠ½Π΅ΡΠ³Π΅ΡΠΈΡΠ΅ΡΠΊΠΈΠΉ Π²ΡΠΈΠ³ΡΡΡ Π΄ΠΎΡΡΠΈΠ³Π°Π΅Ρ Π·Π½Π°ΡΠ΅Π½ΠΈΠΉ 0.2β¦7.5 Π΄Π Π΄Π»Ρ ΡΠ°Π·Π»ΠΈΡΠ½ΠΎΠ³ΠΎ Π½Π΅ΠΎΡΡΠΎΠ³ΠΎΠ½Π°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠ°Π·Π½ΠΎΡΠ° ΠΏΠΎΠ΄Π½Π΅ΡΡΡΠΈΡ
ΡΠ°ΡΡΠΎΡ. Π ΡΠΎ ΠΆΠ΅ Π²ΡΠ΅ΠΌΡ ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΡ Π°Π»Π³ΠΎΡΠΈΡΠΌΠ° ΠΎΠ±Π½Π°ΡΡΠΆΠ΅Π½ΠΈΡ Ρ ΠΎΠ±ΡΠ°ΡΠ½ΠΎΠΉ ΡΠ²ΡΠ·ΡΡ ΠΏΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ ΠΎΠΊΠ°Π·ΡΠ²Π°Π΅ΡΡΡ ΡΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎ Π½ΠΈΠΆΠ΅, ΡΠ΅ΠΌ ΠΏΡΠΈ ΠΏΡΠΈΠ΅ΠΌΠ΅ Π²ΡΠ΅ΠΉ ΠΈΠ½ΡΠΎΡΠΌΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΡΡΠ»ΠΊΠΈ.ΠΠ°ΠΊΠ»ΡΡΠ΅Π½ΠΈΠ΅. ΠΡΠ΅Π΄Π»ΠΎΠΆΠ΅Π½Π½ΡΠΉ Π°Π»Π³ΠΎΡΠΈΡΠΌ ΠΏΡΠΈΠ΅ΠΌΠ° ΠΌΠΎΠΆΠ΅Ρ Π±ΡΡΡ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ Π² Π±ΡΠ΄ΡΡΠΈΡ
ΠΏΠΎΠΊΠΎΠ»Π΅Π½ΠΈΡΡ
ΠΌΠΎΠ±ΠΈΠ»ΡΠ½ΠΎΠΉ ΡΠ²ΡΠ·ΠΈ, Π² ΠΊΠΎΡΠΎΡΡΡ
ΡΡΠ΅Π±ΡΡΡΡΡ Π²ΡΡΠΎΠΊΠΈΠ΅ ΡΠΊΠΎΡΠΎΡΡΠΈ ΠΏΠ΅ΡΠ΅Π΄Π°ΡΠΈ. ΠΠ»Π°Π³ΠΎΠ΄Π°ΡΡ ΡΠ½ΠΈΠΆΠ΅Π½ΠΈΡ Π²ΡΡΠΈΡΠ»ΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ ΡΠ»ΠΎΠΆΠ½ΠΎΡΡΠΈ Π°Π»Π³ΠΎΡΠΈΡΠΌΠ° Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΡΡ ΠΌΠ΅Π½ΡΡΠ΅Π΅ ΡΠ½Π΅ΡΠ³ΠΎΠΏΠΎΡΡΠ΅Π±Π»Π΅Π½ΠΈΠ΅ ΠΌΠΎΠ±ΠΈΠ»ΡΠ½ΡΡ
ΡΡΡΡΠΎΠΉΡΡΠ²
Spectrally efficient FDM communication signals and transceivers: design, mathematical modelling and system optimization
This thesis addresses theoretical, mathematical modelling and design issues of Spectrally Efficient
FDM (SEFDM) systems. SEFDM systems propose bandwidth savings when compared to
Orthogonal FDM (OFDM) systems by multiplexing multiple non-orthogonal overlapping carriers.
Nevertheless, the deliberate collapse of orthogonality poses significant challenges on the
SEFDM system in terms of performance and complexity, both issues are addressed in this work.
This thesis first investigates the mathematical properties of the SEFDM system and reveals the
links between the system conditioning and its main parameters through closed form formulas
derived for the Intercarrier Interference (ICI) and the system generating matrices. A rigorous
and efficient mathematical framework, to represent non-orthogonal signals using Inverse Discrete
Fourier Transform (IDFT) blocks, is proposed. This is subsequently used to design simple
SEFDM transmitters and to realize a new Matched Filter (MF) based demodulator using the
Discrete Fourier Transforms (DFT), thereby substantially simplifying the transmitter and demodulator
design and localizing complexity at detection stage with no premium at performance.
Operation is confirmed through the derivation and numerical verification of optimal detectors
in the form of Maximum Likelihood (ML) and Sphere Decoder (SD). Moreover, two new linear
detectors that address the ill conditioning of the system are proposed: the first based on
the Truncated Singular Value Decomposition (TSVD) and the second accounts for selected ICI
terms and termed Selective Equalization (SelE). Numerical investigations show that both detectors
substantially outperform existing linear detection techniques. Furthermore, the use of the
Fixed Complexity Sphere Decoder (FSD) is proposed to further improve performance and avoid
the variable complexity of the SD. Ultimately, a newly designed combined FSD-TSVD detector
is proposed and shown to provide near optimal error performance for bandwidth savings of 20%
with reduced and fixed complexity.
The thesis also addresses some practical considerations of the SEFDM systems. In particular,
mathematical and numerical investigations have shown that the SEFDM signal is prone to high
Peak to Average Power Ratio (PAPR) that can lead to significant performance degradations.
Investigations of PAPR control lead to the proposal of a new technique, termed SLiding Window
(SLW), utilizing the SEFDM signal structure which shows superior efficacy in PAPR control
over conventional techniques with lower complexity. The thesis also addresses the performance
of the SEFDM system in multipath fading channels confirming favourable performance and
practicability of implementation. In particular, a new Partial Channel Estimator (PCE) that
provides better estimation accuracy is proposed. Furthermore, several low complexity linear
and iterative joint channel equalizers and symbol detectors are investigated in fading channels
conditions with the FSD-TSVD joint equalization and detection with PCE obtained channel
estimate facilitating near optimum error performance, close to that of OFDM for bandwidth
savings of 25%. Finally, investigations of the precoding of the SEFDM signal demonstrate a
potential for complexity reduction and performance improvement.
Overall, this thesis provides the theoretical basis from which practical designs are derived to
pave the way to the first practical realization of SEFDM systems
Non-Orthogonal Signal and System Design for Wireless Communications
The thesis presents research in non-orthogonal multi-carrier signals, in which: (i) a new signal format termed truncated orthogonal frequency division multiplexing (TOFDM) is proposed to improve data rates in wireless communication systems, such as those used in mobile/cellular systems and wireless local area networks (LANs), and (ii) a new design and experimental implementation of a real-time spectrally efficient frequency division multiplexing (SEFDM) system are reported. This research proposes a modified version of the orthogonal frequency division multiplexing (OFDM) format, obtained by truncating OFDM symbols in the time-domain. In TOFDM, subcarriers are no longer orthogonally packed in the frequency-domain as time samples are only partially transmitted, leading to improved spectral efficiency. In this work, (i) analytical expressions are derived for the newly proposed TOFDM signal, followed by (ii) interference analysis, (iii) systems design for uncoded and coded schemes, (iv) experimental implementation and (v) performance evaluation of the new proposed signal and system, with comparisons to conventional OFDM systems. Results indicate that signals can be recovered with truncated symbol transmission. Based on the TOFDM principle, a new receiving technique, termed partial symbol recovery (PSR), is designed and implemented in software de ned radio (SDR), that allows efficient operation of two users for overlapping data, in wireless communication systems operating with collisions. The PSR technique is based on recovery of collision-free partial OFDM symbols, followed by the reconstruction of complete symbols to recover progressively the frames of two users suffering collisions. The system is evaluated in a testbed of 12-nodes using SDR platforms. The thesis also proposes channel estimation and equalization technique for non-orthogonal signals in 5G scenarios, using an orthogonal demodulator and zero padding. Finally, the implementation of complete SEFDM systems in real-time is investigated and described in detail
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
Bandwidth Compressed Waveform and System Design for Wireless and Optical Communications: Theory and Practice
This thesis addresses theoretical and practical challenges of spectrally efficient frequency division multiplexing (SEFDM) systems in both wireless and optical domains. SEFDM improves spectral efficiency relative to the well-known orthogonal frequency division multiplexing (OFDM) by non-orthogonally multiplexing overlapped sub-carriers. However, the deliberate violation of orthogonality results in inter carrier interference (ICI) and associated detection complexity, thus posing many challenges to practical implementations. This thesis will present solutions for these issues. The thesis commences with the fundamentals by presenting the existing challenges of SEFDM, which are subsequently solved by proposed transceivers. An iterative detection (ID) detector iteratively removes self-created ICI. Following that, a hybrid ID together with fixed sphere decoding (FSD) shows an optimised performance/complexity trade-off. A complexity reduced Block-SEFDM can subdivide the signal detection into several blocks. Finally, a coded Turbo-SEFDM is proved to be an efficient technique that is compatible with the existing mobile standards. The thesis also reports the design and development of wireless and optical practical systems. In the optical domain, given the same spectral efficiency, a low-order modulation scheme is proved to have a better bit error rate (BER) performance when replacing a higher order one. In the wireless domain, an experimental testbed utilizing the LTE-Advanced carrier aggregation (CA) with SEFDM is operated in a realistic radio frequency (RF) environment. Experimental results show that 40% higher data rate can be achieved without extra spectrum occupation. Additionally, a new waveform, termed Nyquist-SEFDM, which compresses bandwidth and suppresses out-of-band power leakage is investigated. A 4th generation (4G) and 5th generation (5G) coexistence experiment is followed to verify its feasibility. Furthermore, a 60 GHz SEFDM testbed is designed and built in a point-to-point indoor fiber wireless experiment showing 67% data rate improvement compared to OFDM. Finally, to meet the requirements of future networks, two simplified SEFDM transceivers are designed together with application scenarios and experimental verifications