7 research outputs found
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
Non-orthogonal Frequency Division Multiplexing with Index Modulation
Orthogonal Frequency Division Multiplexing (OFDM) is a well-established technique in wired and wireless communications due to its high spectral efficiency compared to other multicarrier transmission schemes. However, the explosion of Internet of Things (IoT) has demanded a more spectrally-efficient technique to utilize small bandwidths, on which numerous low-power low-rate devices operate. This thesis aims to provide solutions for this problem.
First, the integration of index modulation to fast-OFDM, which is a special variant of OFDM, is investigated. The highest obtainable bit rate of this system is derived, which demonstrates enhancements compared to OFDM systems in the low-power low-rate regions. Furthermore, an improved one-dimension constellation is found to optimize the overall bit error rate (BER) of this system. Numerical results show that the proposed system exhibits enhancements in both bit rate and error performance, leading to higher spectral efficiency compared to OFDM in the low-power regions.
The second part of the thesis is concerned with reducing the bandwidth consumed by multicarrier transmissions. This results in the mutual orthogonality among subchannels being relaxed, yielding a Non-orthogonal Frequency Division Multiplexing (NFDM) system. The main contribution in this part includes a novel and feasible design for NFDM systems, which is capable of eliminating inter-channel interference (ICI), which is the major limitation of the conventional NFDM system. Because ICI is completely eliminated, the BER performance of the proposed system is the same as that of an OFDM system over additive white Gaussian noise channels. The power spectrum density (PSD) of the proposed system is also investigated, leading to design guidelines and tradeoffs between the PSD shape and the system's bit rate.
Finally, index modulation is incorporated in the proposed NFDM systems. Thanks to our ICI-free design of NFDM, this combined system (NFDM-IM) and fast-OFDM-IM share a similar simple two-stage signal detection mechanism. Improved QAM constellations are found for NFDM-IM systems to optimize their overall BER. Obtained results show that with low modulation orders such as 8-QAM (Quadrature Amplitude Modulation), NFDM-IM systems employing the improved constellation achieve BER performance close to that of NFDM in the low BER regions. With equivalent occupied bandwidth and error performance, an NFDM-IM system with optimal 8-QAM constellation produces better spectral efficiency
than the one using the conventional hexagonal constellation
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
The First 15 Years of SEFDM: A Brief Survey
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
Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing
To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation.
This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed.
The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms.
In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels
Spectrally efficient multicarrier communication systems: signal detection, mathematical modelling and optimisation
This thesis considers theoretical, analytical and engineering design issues relating
to non-orthogonal Spectrally Efficient Frequency Division Multiplexing (SEFDM)
communication systems that exhibit significant spectral merits when compared to Orthogonal
FDM (OFDM) schemes. Alas, the practical implementation of such systems
raises significant challenges, with the receivers being the bottleneck.
This research explores detection of SEFDM signals. The mathematical foundations
of such signals lead to proposals of different orthonormalisation techniques as required
at the receivers of non-orthogonal FDM systems. To address SEFDM detection, two
approaches are considered: either attempt to solve the problem optimally by taking
advantage of special cases properties or to apply sub-optimal techniques that offer reduced
complexities at the expense of error rates degradation. Initially, the application
of sub-optimal linear detection techniques, such as Zero Forcing (ZF) and Minimum
Mean Squared Error (MMSE), is examined analytically and by detailed modelling. To
improve error performance a heuristic algorithm, based on a local search around an
MMSE estimate, is designed by combining MMSE with Maximum Likelihood (ML)
detection. Yet, this new method appears to be efficient for BPSK signals only. Hence,
various variants of the sphere decoder (SD) are investigated. A Tikhonov regularised
SD variant achieves an optimal solution for the detection of medium size signals in
low noise regimes. Detailed modelling shows the SD detector to be well suited to the
SEFDM detection, however, with complexity increasing with system interference and
noise. A new design of a detector that offers a good compromise between computational
complexity and error rate performance is proposed and tested through modelling
and simulation. Standard reformulation techniques are used to relax the original optimal
detection problem to a convex Semi-Definite Program (SDP) that can be solved
in polynomial time. Although SDP performs better than other linear relaxations, such
as ZF and MMSE, its deviation from optimality also increases with the deterioration
of the system inherent interference. To improve its performance a heuristic algorithm
based on a local search around the SDP estimate is further proposed. Finally, a modified
SD is designed to implement faster than the local search SDP concept. The new
method/algorithm, termed the pruned or constrained SD, achieves the detection of
realistic SEFDM signals in noisy environments
A Vision and Framework for the High Altitude Platform Station (HAPS) Networks of the Future
A High Altitude Platform Station (HAPS) is a network node that operates in
the stratosphere at an of altitude around 20 km and is instrumental for
providing communication services. Precipitated by technological innovations in
the areas of autonomous avionics, array antennas, solar panel efficiency
levels, and battery energy densities, and fueled by flourishing industry
ecosystems, the HAPS has emerged as an indispensable component of
next-generations of wireless networks. In this article, we provide a vision and
framework for the HAPS networks of the future supported by a comprehensive and
state-of-the-art literature review. We highlight the unrealized potential of
HAPS systems and elaborate on their unique ability to serve metropolitan areas.
The latest advancements and promising technologies in the HAPS energy and
payload systems are discussed. The integration of the emerging Reconfigurable
Smart Surface (RSS) technology in the communications payload of HAPS systems
for providing a cost-effective deployment is proposed. A detailed overview of
the radio resource management in HAPS systems is presented along with
synergistic physical layer techniques, including Faster-Than-Nyquist (FTN)
signaling. Numerous aspects of handoff management in HAPS systems are
described. The notable contributions of Artificial Intelligence (AI) in HAPS,
including machine learning in the design, topology management, handoff, and
resource allocation aspects are emphasized. The extensive overview of the
literature we provide is crucial for substantiating our vision that depicts the
expected deployment opportunities and challenges in the next 10 years
(next-generation networks), as well as in the subsequent 10 years
(next-next-generation networks).Comment: To appear in IEEE Communications Surveys & Tutorial