Optimisation of wireless communication system by exploitation of channel diversity

Communication systems are susceptible to degradation in performance because of interference received through their side lobes. The interference may be deliberate electronic counter measure (ECM), Accidental RF Interference (RFI) or natural noise. The growth of interference communication systems have given rise to different algorithms, Adaptive array techniques offer a possible solution to this problem of interference received through side lobes because of their automatic null steering in both spatial and frequency domains. Key requirement for space-time architecture is to use robust adaptive algorithms to ensure reliable operation of the smart antenna. Space division multiple access (SDMA) involves the use of adaptive nulling to allow two or more users (mobiles) in the same cell to share same frequency and time slot. One beam is formed for each user with nulls in the direction of other users. Different approaches have been used to identify the interferer from desired user. Thus a basic model for determining the angle of arrival of incoming signals, an appropriate antenna beam forming and adaptive algorithms are used for array processing. There is an insatiable demand for capacity in wireless data networks and cellular radio communication systems. However the RF environment that these systems operate in is harsh and severely limits the capacity of traditional digital wireless networks. With normal wireless systems this limits the data rate in cellular radio environments to approximately 200 kbps whereas much higher data rates in excess of 25Mbps are required. A common wireless channel problem is that of frequency selective multi-path fading. To combat this problem, new types of wireless interface are being developed which utilise space, time and frequency diversity to provide increasing resilience to the channel imperfections. At any instant in time, the channel conditions may be such that one or more of these diversity methods may offer a superior performance to the other diversity methods. The overall aim of the research is to develop new systems that use a novel combination of smart antenna MIMO techniques and an advanced communication system based on advanced system configuration that could be exploited by IEEE 802.20 user specification approach for broadband wireless networking. The new system combines the Multi-input Multi-output communication system with frequency diversity in the form of an OFDM modulator. The benefits of each approach are examined under similar channel conditions and results presented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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

Physical Layer Techniques for Indoor Wireless Visible Light Communications

The growing demand for bandwidth-hungry applications and increasing number of smart interconnected devices has increased the data traffic on radio access networks. Subsequently, the saturating spectral efficiencies in crowded radio frequency spectrum has impelled the researchers to exploit the optical spectrum for communications. In particular, many developments in the visible light communication (VLC) as a combined lighting and communications system have taken place. Despite abundant optical bandwidth, the data transmission rates and power efficiencies in VLC are partly limited by the electrical channel bandwidth and the type of signalling sets which can be used in this intensity modulated, direct detected system. In order to improve the power and spectral efficiencies, this thesis focuses on physical layer (PHY) techniques. The state-of-the-art single channel modulations (SCM) based on M-PAM, multi-channel modulations (MCM) based on OFDM, and IEEE standardised multi-colour modulations are investigated comprehensively through simulations and theoretical analysis, over representative VLC channels considering the optical properties of front-end devices. The bit error performances and spectral efficiencies of DC-biased and non DC-biased MCM systems are compared. A new vector coding based MCM is proposed to optimally utilise the channel state information at the transmitter as an alternative to optical OFDM. The throughputs, peak-to-average power ratios and DC-bias requirements of SCM and MCM systems are investigated which show that the lower DC-bias requirements reduce power consumed for the same throughput in SCM systems when compared to MCM systems. A new quad-chromatic colour shift keying (CSK) system is proposed which reduces power requirements and complexity, enhances throughput and realises a four-dimensional signalling to outperform the IEEE standardised tri-chromatic CSK system. For improved power efficiency and throughput of VLC PHY, use of rate-adaptive binary convolutional coding and Viterbi decoding is proposed along with frequency domain channel equalisation to mitigate temporal dispersion over representative VLC channels

Coherent receiver design and analysis for interleaved division multiple access (IDMA)

This thesis discusses a new multiuser detection technique for cellular wireless communications. Multiuser communications is critical in cellular systems as multiple terminals (users) transmit to base stations (or wireless infrastructure). Efficient receiver methods are needed to maximise the performance of these links and maximise overall throughput and coverage while minimising inter-cell interference. Recently a new technique, Interleave-Division Multiple Access (IDMA), was developed as a variant of direct-sequence code division multiple access (DS-CDMA). In this new scheme users are separated by user specific interleavers, and each user is allocated a low rate code. As a result, the bandwidth expansion is devoted to the low rate code and not weaker spreading codes. IDMA has shown to have significant performance gains over traditional DS-CDMA with a modest increase in complexity. The literature on IDMA primarily focuses on the design of low rate forward error correcting (FEC) codes, as well as channel estimation. However, the practical aspects of an IDMA receiver such as timing acquisition, tracking, block asynchronous detection, and cellular analysis are rarely studied. The objective of this thesis is to design and analyse practical synchronisation, detection and power optimisation techniques for IDMA systems. It also, for the first time, provides a novel analysis and design of a multi-cell system employing a general multiuser receiver. These tools can be used to optimise and evaluate the performance of an IDMA communication system. The techniques presented in this work can be easily employed for DS-CDMA or other multiuser receiver designs with slight modification. Acquisition and synchronisation are essential processes that a base-station is required to perform before user's data can be detected and decoded. For high capacity IDMA systems, which can be heavily loaded and operate close to the channel capacity, the performance of acquisition and tracking can be severely affected by multiple access interference as well as severe drift. This thesis develops acquisition and synchronisation algorithms which can cope with heavy multiple access interference as well as high levels of drift. Once the timing points have been estimated for an IDMA receiver the detection and decoding process can proceed. An important issue with uplink systems is the alignment of frame boundaries for efficient detection. This thesis demonstrates how a fully asynchronous system can be modelled for detection. This thesis presents a model for the frame asynchronous IDMA system, and then develops a maximum likelihood receiver for the proposed system. This thesis develops tools to analyse and optimise IDMA receivers. The tools developed are general enough to be applied to other multiuser receiver techniques. The conventional EXIT chart analysis of unequal power allocated multiuser systems use an averaged EXIT chart analysis for all users to reduce the complexity of the task. This thesis presents a multidimensional analysis for power allocated IDMA, and shows how it can be utilised in power optimisation. Finally, this work develops a novel power zoning technique for multicell multiuser receivers using the optimised power levels, and illustrates a particular example where there is a 50% capacity improvement using the proposed scheme. -- provided by Candidate

Self-concatenated coding for wireless communication systems

In this thesis, we have explored self-concatenated coding schemes that are designed for transmission over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels. We designed both the symbol-based Self-ConcatenatedCodes considered using Trellis Coded Modulation (SECTCM) and bit-based Self- Concatenated Convolutional Codes (SECCC) using a Recursive Systematic Convolutional (RSC) encoder as constituent codes, respectively. The design of these codes was carried out with the aid of Extrinsic Information Transfer (EXIT) charts. The EXIT chart based design has been found an efficient tool in finding the decoding convergence threshold of the constituent codes. Additionally, in order to recover the information loss imposed by employing binary rather than non-binary schemes, a soft decision demapper was introduced in order to exchange extrinsic information withthe SECCC decoder. To analyse this information exchange 3D-EXIT chart analysis was invoked for visualizing the extrinsic information exchange between the proposed Iteratively Decoding aided SECCC and soft-decision demapper (SECCC-ID). Some of the proposed SECTCM, SECCC and SECCC-ID schemes perform within about 1 dB from the AWGN and Rayleigh fading channels’ capacity. A union bound analysis of SECCC codes was carried out to find the corresponding Bit Error Ratio (BER) floors. The union bound of SECCCs was derived for communications over both AWGN and uncorrelated Rayleigh fading channels, based on a novel interleaver concept.Application of SECCCs in both UltraWideBand (UWB) and state-of-the-art video-telephone schemes demonstrated its practical benefits.In order to further exploit the benefits of the low complexity design offered by SECCCs we explored their application in a distributed coding scheme designed for cooperative communications, where iterative detection is employed by exchanging extrinsic information between the decoders of SECCC and RSC at the destination. In the first transmission period of cooperation, the relay receives the potentially erroneous data and attempts to recover the information. The recovered information is then re-encoded at the relay using an RSC encoder. In the second transmission period this information is then retransmitted to the destination. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated encoder. At the destination a Distributed Binary Self-Concatenated Coding scheme using Iterative Decoding (DSECCC-ID) was employed, where the two decoders (SECCC and RSC) exchange their extrinsic information. It was shown that the DSECCC-ID is a low-complexity scheme, yet capable of approaching the Discrete-input Continuous-output Memoryless Channels’s (DCMC) capacity.Finally, we considered coding schemes designed for two nodes communicating with each other with the aid of a relay node, where the relay receives information from the two nodes in the first transmission period. At the relay node we combine a powerful Superposition Coding (SPC) scheme with SECCC. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second transmission period after re-encoding it, again, using a SECCC encoder. At the destination, the amalgamated block of Successive Interference Cancellation (SIC) scheme combined with SECCC then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput

Optical frequency comb source for next generation access networks

The exponential growth of converged telecommunication services and the increasing demands for video rich multimedia applications have triggered the vast development of optical access technology to resolve the capacity bottleneck at metropolitan-access aggregations. To further enhance overall performance, next generation optical access networks will require highly efficient wavelength division multiplexing (WDM) technology beyond the capability of current standard time division multiplexed (TDM) systems. The successful implementation of future-proof WDM access networks depends on advancements in high performance transmission schemes as well as economical and practical electronic/photonic devices. This thesis focuses on an investigation of the use of optical frequency comb sources, and spectrally efficient modulation formats, in high capacity WDM based optical access networks. A novel injected gain switched comb generation technique which deliver simplicity, reliability, and cost effectiveness has been proposed and verified through experimental work. In addition, a detailed characterization of the optical comb source has been undertaken with special attention on the phase noise property of the comb lines. The potential of the injected gain switched comb source is then demonstrated in a digital coherent receiver based long reach WDM access scenario, which intends to facilitate 10 - 40 Gbit/s data delivery per channel . Furthermore, an optical scalar transmission scheme enabling the direct detection of higher order modulation format signals has been proposed and experimentally investigated

Digital Processing for an Analogue Subcarrier Multiplexed Mobile Fronthaul

In order to meet the demands of the fifth generation of mobile communication networks (5G), such as very high bit-rates, very low latency and massive machine connectivity, there is a need for a flexible, dynamic, scalable and versatile mobile fronthaul. Current industry fronthaul standards employing sampled radio waveforms for digital transport suffer from spectral inefficiency, making this type of transport impractical for the wide channel bandwidths and multi-antenna systems required by 5G. On the other hand, analogue transport does not suffer from these limitations. It is, however, prone to noise, non-linearity and poor dynamic range. When combined with analogue domain signal aggregation/multiplexing, it also lacks flexibility and scalability, especially at millimetre wave frequencies. Measurements (matched in simulation) of analogue transport at millimetre wave frequencies demonstrate some of these issues. High data rates are demonstrated employing wide bandwidth channels combined using traditional subcarrier multiplexing techniques. However, only a limited number of channels can be multiplexed in this manner, with poor spectral efficiency, as analogue filter limitations do not allow narrow gaps between channels. To this end, over the last few years, there has been significant investigation of analogue transport schemes combined with digital channel aggregation/ de-aggregation (combining/ separating multiple radio waveforms in the digital domain). This work explores such a technique. Digital processing is used at the transmitter to flexibly multiplex a large number of channels in a subcarrier multiplex, without the use of combiners, mixers/ up-converters or Hilbert transforms. Orthogonal Frequency Division Multiplexing (OFDM) - derived Discrete Multi-Tone (DMT) and Single Sideband (SSB) modulated channels are integrated within a single Inverse Fast Fourier Transform (IFFT) operation. Channels or channel groups are mapped systematically into Nyquist zones by using, for example, a single IFFT (for a single 5G mobile numerology) or multiple IFFTs (for multiple 5G mobile numerologies). The analogue transport signal generated in this manner is digitally filtered and band-pass sampled at the receiver such that each corresponding channel (e.g. channels destined to the same radio frequency (RF)/ millimetre wave (mmW) frequency) in the multiplex is presented at the same intermediate frequency, due to the mapping employed at the transmitter. Analogue or digital domain mixers/ down-converters are not required with this technique. Furthermore, each corresponding channel can be readily up-converted to their respective RF/mmW channels with minimal per-signal processing. Measurement results, matched in simulation, for large signal multiplexes with both generic and 5G mobile numerologies show error-vector magnitude performance well within specifications, validating the proposed system. For even larger multiplexes and/or multiplexes residing on a higher IF exceeding the analogue bandwidth and sampling rate specifications of the ADCs at the receiver, the use of a bandwidth-extension device is proposed to extend the mapping to a mapping hierarchy and relax the analogue bandwidth and sampling rate requirements of the ADCs. This allows the receiver to still use digital processing, with only minimal analogue processing, to band-pass sample smaller blocks of channels from the larger multiplex, down to the same intermediate frequency. This ensures that each block of channels is within the analogue bandwidth specification of the ADCs. Performance predictions via simulation (based on a system model matched to the measurements) show promising results for very large multiplexes and large channel bandwidths. The multiplexing technique presented in this work thus allows reductions in per-channel processing for heterogeneous networking (or multi-radio access technologies) and multi-antenna configurations. It also creates a re-configurable and adaptable system based on available processing resources, irrespective of changes to the number of channels and channel groups, channel bandwidths and modulation formats