On the Transport Capability of LAN Cables in All-Analog MIMO-RoC Fronthaul

Centralized Radio Access Network (C-RAN) architecture is the only viable solution to handle the complex interference scenario generated by massive antennas and small cells deployment as required by next generation (5G) mobile networks. In conventional C-RAN, the fronthaul links used to exchange the signal between Base Band Units (BBUs) and Remote Antenna Units (RAUs) are based on digital baseband (BB) signals over optical fibers due to the huge bandwidth required. In this paper we evaluate the transport capability of copper-based all-analog fronthaul architecture called Radio over Copper (RoC) that leverages on the pre-existing LAN cables that are already deployed in buildings and enterprises. In particular, the main contribution of the paper is to evaluate the number of independent BB signals for multiple antennas system that can be transported over multi-pair Cat-5/6/7 cables under a predefined fronthauling transparency condition in terms of maximum BB signal degradation. The MIMO-RoC proves to be a complementary solution to optical fiber for the last 200m toward the RAUs, mostly to reuse the existing LAN cables and to power-supply the RAUs over the same cable

Physical Layer Techniques for High Frequency Wireline Broadband Systems

This thesis collects contributions to wireline and wireless communication systems with an emphasis on multiuser and multicarrier physical layer technology. To deliver increased capacity, modern wireline access systems such as G.fast extend the signal bandwidth up from tens to hundreds of MHz. This ambitious development revealed a number of unforeseen hurdles such as the impact of impedance changes in various forms. Impedance changes have a strong effect on the performance of multi-user crosstalk mitigation techniques such as vectoring. The first part of the thesis presents papers covering the identification of one of these problems, a model describing why it occurs and a method to mitigate its effects, improving line stability for G.fast systems.A second part of the thesis deals with the effects of temperature changes on wireline channels. When a vectored (MIMO) wireline system is initialized, channel estimates need to be obtained. This thesis presents contributions on the feasibility of re-using channel coefficients to speed up the vectoring startup procedures, even after the correct coefficients have changed, e.g., due to temperature changes. We also present extensive measurement results showing the effects of temperature changes on copper channels using a temperature chamber and British cables. The last part of the thesis presents three papers on the convergence of physical layer technologies, more specifically the deployment of OFDM-based radio systems using twisted pairs in different ways. In one proposed scenario, the idea of using the access copper lines to deploy small cells inside users' homes is explored. The feasibility of the concept, the design of radio-heads and a practical scheme for crosstalk mitigation are presented in three contributions

Performance Enhancement in Copper Twisted Pair Cable Communications

The thesis focuses on the area of copper twisted pair based wireline communications. As one of the most widely deployed communication media, the copper twisted pair cable plays an important role in the communication network cabling infrastructure. This thesis looks to exploit diversity to improve twisted pair channels for data communications in two common application areas, namely Ethernet over Twisted Paris and digital subscriber line over twisted pair based telephone network. The first part of the thesis addresses new approaches to next generation Ethernet over twisted pair cable. The coming challenge for Ethernet over twisted pair cable is to realise a higher data rate beyond the 25/40GBASE-T standard, in relatively short reach scenarios. The straight-forward approaches, such as improving cable quality and extending frequency bandwidth, are unlikely to provide significant improvement in terms of data rate. However, other system diversities, such as spectrum utilization are yet to be fully exploited, so as to meet the desired data rate performance. The current balanced transmission over the structured twisted pair cable and its parallel single-in-single-out channel model is revisited and formulated as a full-duplex multiple-in-multiple-out (MIMO) channel model. With a common ground (provided by the cable shield), the balanced transmission is converted into unbalanced transmission, by replacing the differential-mode excitation with single-ended excitation. In this way, MIMO adoption may offer spectrum utilization advantages due to the doubled number of the channels. The S-parameters of the proposed MIMO channel model is obtained through the full wave electromagnetic simulation of a short CAT7A cable. The channel models are constructed from the resulting S-parameters, also the corresponding theoretical capacity is evaluated by exploiting different diversity scenarios. With higher spectrum efficiency, the orthogonal-frequency-division-multiplexing (OFDM) modulation can significantly improve the theoretical capacity compared with single-carrier modulation, where the channel frequency selectivity is aided. The MIMO can further enhance the capacity by minimising the impact of the crosstalk. When the crosstalk is properly handled under the unbalanced transmission, this thesis shows that the theoretical capacity of the EoTP cable can reach nearly 200GBit/s. In order to further extend the bandwidth capability of twisted pair cables, Phantom Mode transmission is studied, aiming at creating more channels under balanced transmission operation. The second part of the thesis focuses on the research of advanced scheduling algorithms for VDSL2 QoS enhancement. For VDSL2 broadband access networks, multi-user optimisation techniques have been developed, so as to improve the basic data rate performance. Spectrum balancing improves the network performance by optimising users transmit power spectra as the resource allocation, to mitigate the impact from the crosstalk. Aiming at enhancing the performance for the upstream VDSL2 service, where the users QoS demand is not known by all other users, a set of autonomous spectrum balancing algorithms is proposed. These optimise users transmit power spectra locally with only direct channel state information. To prevent selfish behaviour, the concept of a virtual user is introduced to represent the impact on both crosstalk interference and queueing status of other users. Moreover, novel algorithms are developed to determine the parameters and the weight of the virtual user. Another type of resource allocation in the VDSL2 network is crosstalk cancellation by centralised signal coordination. The history of the data queue is considered as a time series, on which different smooth filter characteristics are investigated in order to investigate further performance improvement. The use of filter techniques accounts for both the instantaneous queue length and also the previous data to determine the most efficient dynamic resource allocation. With the help of this smoothed dynamic resource allocation, the network will benefit from both reduced signalling communication and improved delay performance.The proposed algorithms are verified by numerical experiments

Mitigation of impulsive noise for SISO and MIMO G.fast system

To address the demand for high bandwidth data transmission over telephone transmission lines, International Telecommunication Union (ITU) has recently completed the fourth generation broadband (4GBB) copper access network technology, known as G.fast. Throughout this thesis, extensively investigates the wired broadband G.fast coding system and the novel impulsive noise reduction technique has been proposed to improve the performance of wired communications network in three different scenarios: single-line Discrete Multiple Tone (DMT)- G.fast system; a multiple input multiple-output (MIMO) DMTG.fast system, and MIMO G.fast system with different crosstalk cancellation methods. For each of these scenarios, however, Impulsive Noise (IN) is considered as the main limiting factor of performance system. In order to improve the performance of such systems, which use higher order QAM constellation such as G.fast system, this thesis examines the performance of DMT G.fast system over copper channel for six different higher signal constellations of M = 32, 128, 512, 2048, 8192 and 32768 in presence of IN modelled as the Middleton Class A (MCA) noise source. In contrast to existing work, this thesis presents and derives a novel equation of Optimal Threshold (OT) to improve the IN frequency domain mitigation methods applied to the G.fast standard over copper channel with higher QAM signal constellations. The second scenario, Multi-Line Copper Wire (MLCW) G.fast is adopted utilizing the proposed MLCW Chen model and is compared to a single line G-fast system by a comparative analysis in terms of Bit-Error-Rate(BER) performance of implementation of MLCW-DMT G.fast system. The third scenario, linear and non-linear crosstalk crosstalk interference cancellation methods are applied to MLCW G.fas and compared by a comparative analysis in terms of BER performance and the complexity of implementation.University of Technology for choosing me for their PhD scholarship and The Higher Committee For Education Development in Iraq(HCED

Energy-Efficient and Robust Hybrid Analog-Digital Precoding for Massive MIMO Systems

The fifth-generation (5G) and future cellular networks are expected to facilitate wireless communication among tens of billions of devices with enormously high data rate and ultra-high reliability. At the same time, these networks are required to embrace green technology by significantly improving the energy efficiency of wireless communication to reduce their carbon footprint. The massive multiple-input multiple-output (MIMO) systems, in which the base stations are equipped with hundreds of antenna elements, can provide immensely high data rates and support a large number of users by employing the precoding at the base stations. However, the conventional precoding techniques - which require a dedicated radio-frequency chain for each antenna element - become prohibitively expensive for massive MIMO systems. To address this shortcoming, the hybrid analog-digital precoding architecture is proposed, which requires fewer radio-frequency chains than the antenna elements. The reduced hardware costs in this novel architecture, however, comes at the expense of reduced degrees of freedom for the precoding, which deteriorates the energy efficiency of the network. In this thesis, we consider the design of energy-efficient hybrid precoding techniques in multiuser downlink massive MIMO systems. These systems are fundamentally interference limited. To mitigate the interference, we adopt two interference management strategies while designing the hybrid precoding schemes. They are, namely, interference suppression-based hybrid precoding, and interference exploitation-based hybrid precoding. The former approach results in a lower computational complexity - as the resulting precoders remain the same as long as the channel is unchanged when compared to the latter approach. On the other hand, the interference exploitation-based hybrid precoding is more energy efficient due to judicious use of transmit symbol information, as compared to the interference suppression-based hybrid precoding. In the hybrid analog-digital precoding, analog precoders are implemented in analog radio-frequency domain using a large number of phase shifters, which are relatively inexpensive. These phase shifters, however, typically suffer from artifacts; their actual values differ from their nominal values. These imperfect phase shifters can lead to symbol estimation errors at the users, which may not be tolerable in many applications of future cellular networks. To establish a high-reliable communication under the plight of imperfect phase shifters in the hybrid precoding architecture, in this thesis, we propose an energy-efficient, robust hybrid precoding technique. The designed scheme guarantees 100% robustness against the considered hardware artifacts. Moreover, the thesis demonstrates that the proposed technique can save up to 12% transmit power when compared to a conventional method. Another critically important requirement of the future cellular networks - apart from ultra-high reliability and energy efficiency - is ultra-low latency. Some envisioned extreme real-time applications of 5G, such as autonomous driving and remote surgery, demand an end-to-end latency smaller than one millisecond. To fulfill such a stringent demand, we devise an efficient implementation scheme for the proposed robust hybrid precoding technique to reduce the required computational time. The devised scheme exploits special structures present in the algorithm to reduce the computational complexity and can compute the precoders in a distributed manner on a parallel hardware architecture. The results show that the proposed implementation scheme can reduce the average computation time of the algorithm by 35% when compared to a state-of-the-art method. Finally, we consider the hybrid precoding in heterogeneous networks, where the cell edge users typically experience severe interference. We propose a coordinated hybrid precoding technique based on the interference exploitation approach. The numerical results reveal that the proposed coordinated hybrid precoding results in a significant transmit power savings when compared to the uncoordinated hybrid precoding

Signal processing for ultra fast next generation metallic access network

With the escalating demand for high speed, high reliability, low latency, low cost and ubiquitous connectivity, the telecommunications industry is entering a new era where the ultimate optimality of the current wireline-wireless access network has to be achieved.Regarding the current wireline network paradigm, dominated by the copper-based digital subscriber lines (DSL) technology, multi-Gigabit data rate is the ambitious design objective at the customer end for the forthcoming ITU-T G.mgfast standard. In order to prepare for the new challenges in the era of total network convergence, both the wireline and the wireless community must be able to think beyond their respective conventions and learn from each other if necessary. Overall, the current DSL-based wireline network architecture is prone to the mutual interference resulting in far-end crosstalk (FEXT).The recently expanded 424/848 MHz spectrum of the ambitious G.mgfast project introduces far higher FEXT than that over the current 212/30 MHz G.fast/VDSL2 band.Additionally, the coexistence of multiple standards will also cause 'alien' FEXT. In the face of these new challenges, most state-of-the-art techniques, such as linear transmit precoding or Reed-Solomon coding, fail to satisfy the escalating performance requirements. In this thesis, we conceive a general architecture for next-generation DSL networks based on recent technological advances in key areas of access networks. More specifically, we conceive a dynamic spectrum management (DSM) aided signal processing framework relying on vectored transmission, spectrum balancing and error control.Specifically, the excessive FEXT cannot be combated by low-complexity linear transmit precoding for downstream vectoring. However, as shown in the field of wireless communications, using lattice reduction as a signal space remapping technique significantly improves the performance of traditional multi-user detectors (MUD) and of the respective multi-user precoders (MUP). These promising techniques have largely remained unexploited in commercial wireless communications, due to their complexity in the face of the rapidly fluctuating wireless channels. However, they are eminently suitable for quasi-static copper channels. Hence we design powerful lattice-reduction-aided MUP (LRMUP) as well as an optimal sphere encoder and its low-complexity variants. Furthermore, we propose the concept of vectoring mapping regions (VMR) as the transmitterside dual counterpart of the classic decision regions conceived for receiver-side signal detection. Based on the VMR, we propose a near-optimal multi-level DSM algorithm relying on the family of LRMUPs, which strikes a more favourable sum rate vs. fairness trade-off than the state-of-the-art non-linear Tomlinson-Harashima precoder (THP).On the other hand, impulsive noise (IN) contamination constitutes another challenge in next-generation DSL networks. In particular, the copper loops used for transmitting DSL data may become contaminated by other high-power undesired wireless signals such as IN and radio-frequency interference (RFI). As a counter-measure, we amalgamate forward error correction (FEC) with sophisticated automatic repeat request (ARQ) techniques for conceiving hybrid-ARQ (HARQ) schemes. Given that low density parity check (LDPC) codes are likely to be used in G.mgfast, we propose a novel low-complexity HARQ protocol-based on the class of New Radio (NR) LDPC codes conceived for 5G cellular wireless systems, while exploiting the available a posteriori knowledge concerning the IN events at the receiver, in order to minimize the SNR degradation due to IN. Specifically, based on our proposed Tanner graph characterization as well as on the corresponding extrinsic information transfer (EXIT) chart, we propose an EXIT-chart-aided deferred iteration (DI) decoder switching technique, as well as a pair of MI-thresholding-aided curtailed iteration (CI) early stopping strategies, in order to minimize the potentially futile or redundant decoding operations