The next generation digital subscriber line (DSL) standard G.mgfast introduces far stronger co-channel interference termed as far-end crosstalk (FEXT) than the existing ones. Given perfect transmitter-side channel state information (CSIT), it is well known that the lattice-reduction-aided ${\mathcal{K}}$-best sphere encoder (LR-KBSE) is a near-optimal transmit precoding (TPC) technique compared to the classic (LR-) depth-first sphere encoder (DFSE), albeit having significantly lower complexity than the latter. However, the decision feedback precoding (DFP) structure and the Schnorr-Euchner enumeration procedure, both perceived as state-of-the-art in the literature, are not provably optimal for solving the closest vector problem (CVP) embedded in sphere encoding. As a counterexample, this paper proposes a stochastic sphere encoder (SSE) relying on differential evolution aided random walk over lattices. The parallel processing complexity, memory efficiency and signal to noise ratio (SNR) improvement of the proposed SSE are all shown to be superior to the LR-KBSE for G.mgfast systems.

The demand for higher broadband speeds is ever increasing whereas the deployment of full fibre to the premises is slower than initially predicted and remains costly. Solutions exploiting the existing, ubiquitous, copper network and increasing its capacity would be highly beneficial in the near term. One approach is to use surface wave (SW) transmission mode to transmit signals over the existing copper cabling network. We present proof-of-concept experimental SW data transmission on twisted pair cables. A surface wave launcher for low GHz carrier frequency operation is designed and optimised. Experimentally, we demonstrate data rates in excess of 12 Gb/s in a 1.15-3.25 GHz band over a 6.1 m twisted pair cable with an average bit error rate of$2.25 \times 10 ^{-5}$, without coding or feedback implementation. Furthermore, higher frequency bands are tested with data rates up to 3.4 Gb/s displaying their potential for surface wave transmission. S-parameter measurements allow capacity estimations of SW data transmission on longer cable lengths using water-filling algorithms. Our calculations predict over 13 Gb/s capacity on a 100 m cable using a 3.5 GHz transmission bandwidth, this may be further extended by further increases to the bandwidth used for SW transmission.

This paper investigates the utilisation of classical antennas as surface wave (SW) launchers. SWs have potential to provide multiplicative factors of increase in the capacity over the existing multi-pair copper wires thanks to their low-loss and extended bandwidth compared to the well-known differential mode signalling, which is operating at sub-GHz frequencies. Although specially designed devices are required for high SW launching efficiencies, classical antennas can be also utilised for launching and receiving SWs by fixing a simple copper wire between antennas. In this way, transmitted power from an antenna is guided along the wire such that the received power of point-to-point wireless communication links can be substantially improved. To prove our claims, we investigate launching and receiving SWs with double-ridged horn antennas from cellular frequencies up to milli-meter wave spectrum. According to the experimental and numerical results, the proposed solution can achieve 30-50dB enhancement in the received power at short to medium communication ranges (under 150m) compared to wireless communication scenarios. Exploiting SWs in the future telecommunication networks may enable substantially improved data rates multi-Gbps links up to Tbps on the last mile without the need of replacing the copper infrastructure with fibre-optic cables. The proposed solution has the potential to provide a cost-effective alternative for enabling high data rate backhaul links required for 6G and beyond communication technologies.

This paper re-examines the 100 Ohm characteristic impedance assumption used in the context of Digital Subscriber Line in the very to ultra high frequency range. A novel method of measuring the characteristic impedance of a transmission line is introduced which uses time-gated measurements from a vector network analyser. The results are utilised to synthesise impedance matching circuits for the excitation of a single twisted pair and a two pair underground cable at centre frequencies of 150 MHz and 500 MHz. These circuits achieved reflections as low as -40 dB. Furthermore, we report gains in transmission increasing with frequency, ranging from few decibels below 100 MHz, to several in 100-250 MHz and many above 400 MHz when compared to a commercial reference balun. In fact, compatibility tests beyond the target cable samples demonstrated higher than 10 dB gains in 20, 40 and 60 metre underground cables at around 500 MHz indicating that sample-based matching circuits are not entirely sample-specific. Preliminary tests showed no significant change in crosstalk when using differential matching circuits.

To achieve increased capacity over legacy twisted-pair copper, standards have considered use of increasingly high frequencies. The most recent digital subscriber line (DSL) standard, G.fast, carried forward the forward error correction scheme from the previous standards, namely the concatenated Reed Solomon and multi-dimensional trellis coded modulation scheme. In this work, a novel joint code and interleaver optimisation for low-density parity-check (LDPC) coded multicarrier systems with variable bit loading is proposed. This optimisation exploits the effects of both the channel and the modulation scheme on the soft information available at the LDPC decoder, through use of extrinsic information transfer (EXIT) analysis. The performance of the proposed scheme is demonstrated for the discrete multi-tone system operating on a twisted-pair channel.

The next generation of Digital Subscriber Line (DSL) technologies seek to exploit frequencies beyond 106 MHz and up to 500 MHz where Far-End Crosstalk (FEXT) becomes excessive; for these frequencies effective crosstalk cancellation, also known as vectoring, is essential. This paper proposes a novel spatially adaptive linear precoder and explores its performance, alongside classical Zero-Forcing Precoding (ZFP) and Tomlinson-Harashima Precoding (THP) methods, under two distinct scenarios. In this paper, the objective function is set to maximise the aggregate capacity of the copper MIMO channel. All precoding methods benefit from a coordinated bitloading to maximise the spectra within a defined power spectrum density (PSD) mask. Results suggest that THP's superiority is substantial in the fixed cable length scenario whilst the proposed Spatially Adaptive Generalised ZFP (SA-GZFP) outperforms the latter marginally in the dendritic one. The paper further suggests that a spatially adaptive nonlinear precoder may have the potential of combining the gains of THP and Maximal Ratio Transmission (MRT) for greater system performance.

A new cost efficient automated planning and optimization method is proposed for OFDMA future-generation cellular networks targeting throughput maximization. The mathematical formulation is a non-linear multi-objective optimization problem subject to minimum interference, cost and similar resource constraints at each cell within a defined heterogeneous traffic environment. The fundamental objective is to maximize the individual cell throughput without deteriorating it over other cells, which results in a throughput equilibrium maximization over multiple cells. This implicitly implies traffic and co-channel interference congestion avoidance across the network whilst maintaining both cost efficiency and quality of service (QoS) policies. Optimal solution existence is subject to the network size, traffic and computational complexity constraints which converges to a throughput equilibrium or alternatively to the well known Nash Equilibrium (NE).

Throughput maximization is generally the major objective when allocating resources in orthogonal frequency division multiple access (OFDMA)networks. Traditionally, dynamic allocation methods were developed to exploit multi-user diversity in these networks. These techniques achieved significant gain in throughput by adopting relaxed convex models to define system upper bound capacity. Frequency diversity, on the other hand, is only considered to a certain extent in order to meet user service constraints. The vast majority of existing research relies on these techniques. Separately, research considering combining frequency diversity and multi-user diversity in full has been scarce. The results of our research in this paper show that using this dual diversity combining can substantially maximize system capacity and resource efficiency, and minimize outage probability whilst users' quality of service (QoS) demands are maintained.

In this paper, a new network planning framework is proposed for orthogonal frequency-division multiple access (OFDMA) cellular systems based on co-channel interference and traffic congestion avoidance. The network planning is formulated as a non-linear multi-objective optimization problem subject to minimum interference and related resource constraints at each cell under heterogeneous traffic. The multi-objective problem is represented by the throughput maximization of each single cell without penalizing the remaining cells, which results in a throughput equilibrium over the whole network. The fundamental objective is to maximize the throughput balance and, hence, traffic and co-channel interference congestions are avoided across the network. In order to maximize the equilibrium, the optimization problem is decomposed into a positioning problem and a resource allocation problem, which are solved by parallel heuristics and convex optimization. Additionally, a novel rotated polarization assignment method is proposed to minimize further the effect of the co-channel interference.

In this study, new mathematical formulations and algorithms for joint scheduling and hybrid resource allocation are derived and investigated for a multi-user downlink orthogonal frequency division multiple access system. A three-sectored multi-cellular heterogeneous traffic environment is considered where users are randomly distributed and categorised under different priority levels. Traffic consists of time delay-sensitive and time delay-insensitive services. Three practical scheduling and resource allocation methods are proposed to address the balance between throughput, outage probability and resource efficiency under varying channel conditions. The proposed methods are based on the Lagrangian duality framework, and are formulated as mixed integer programming problems constrained by the total power of the base station and users' data rate while maintaining the quality of service for each user. Both dynamic and fixed resource allocation approaches are included in the main problem formulation. The complexity of the resource allocation problem is minimised by approximating the well-known water level. Simulation results show that the total system throughput is penalised for the method that aims to minimise the outage probability of the highest priority level. This is because of the severe channel conditions experienced by some users, whereas the alternatively proposed methods maintain system efficiency under a similar amount of constrained resources and required traffic.

In this paper, a new joint scheduling and hybrid resource allocation method is derived and investigated for a multi-user downlink Orthogonal Frequency Division Multiple Access (OFDMA) system that provides Time Delay-Sensitive services (TDS) and Time Delay-Insensitive services (TDI). A three sectored multi-cellular heterogeneous traffic environment is considered where users are randomly distributed and categorised under different priority levels. The method is proposed to address the balance between throughput, outage probability, and user priorities under varying channel conditions. The proposed method is based on the Lagrangian duality framework, and have been formulated as a Mixed Integer Non Linear Problem (MINLP) constrained by the total power of the Base Station BS and users' data rate while maintaining the Quality of Service (QoS) for each user. The hybrid resource allocation includes dynamic and fixed allocations in the main problem formulation. Simulation results show that the outage probability gaps between the priority levels are reasonably balanced. This is due to the optimality conditions which restrict the resource allocation domain for each priority level to avoid sever penalisation of one priority level over the others.

In this paper, a new planning method is proposed for the next generation wireless networks that are based on Orthogonal Frequency Division Multiple Access (OFDMA). As a consequence of the wide variety service demands in terms of data rate and Quality of Service (QoS), the traffic pattern is considered to be heterogeneous. Therefore, the complexity of obtaining Base Stations (BSs) positions increases with the randomness of the traffic distribution. In addition to this challenge, the capacity of each BS is limited due to power and bandwidth constraints, propagation losses, Gaussian antenna pattern, and the Co-Channel Interference (CCI), which in turn increase the complexity measures for an efficient network design. According to Nash Equilibrium, combined efficient systems must perform equally to achieve certain performance. This implies that the traffic of a cellular system should be equally distributed over all the BSs to achieve the highest network performance. Hence, we formulate the planning problem as a non-linear multi-objective optimization problem. The optimum solution should not dominate the throughput of one BS over the others and this is referred to as Pareto optimal. However, loading all cells equally may not be possible in certain traffic distributions. Therefore, the proposed method tends to approach the optimal solution by tackling the problems of BS positioning and resource allocation simultaneously. We adopt a hybrid approach, i.e. Pareto-Metaheuristic (PMH) that achieves a balanced throughput over all cells as well as minimizing the number of the installed BSs targeting a certain service outage probability. Simulation results show that, in addition to maximizing the individual cell throughput, the network throughput variation decreases as the number of iteration increases.

Fourth generation (4G) mobile access is drawing particular attention as it promises to deliver high data rates and reliable coverage for broadband wireless access. In this paper, Orthogonal Frequency Division Multiplexing Access (OFDMA) and Multi-Carrier Code Division Multiplexing Access (MC-CDMA) are investigated to highlight their strengths and weaknesses as candidates for 4G wireless access. Using a multi-cell environment, MC-CDMA and OFDMA coverage is dimensioned based on the value of the Signal to Interference plus Noise Ratio (SINR). The results show that OFDMA system offers cell coverage of 92.5% and a maximum actual throughput of 24.2 Mbps/cell (fade margin 10 dB). Using the same assumptions for MC-CDMA, the results show better coverage only with complete orthogonal spreading codes which can guarantee 97% of user coverage and actual throughput of 28.8 Mbps. These measurements decrease as the orthogonality between the spreading codes is reduced. In the case of 94% orthogonality the MC-CDMA system achieved 89.3% coverage and 21.9 Mbps throughput while with a 60% orthogonality 47% coverage and 5.8 Mbps throughput was achieved.