Millimetre-Wave Fibre-Wireless Technologies for 5G Mobile Fronthaul

The unprecedented growth in mobile data traffic, driven primarily by bandwidth rich applications and high definition video is accelerating the development of fifth generation (5G) mobile network. As mobile access network evolves towards centralisation, mobile fronthaul (MFH) architecture becomes essential in providing high capacity, ubiquitous and yet affordable services to subscribers. In order to meet the demand for high data rates in the access, Millimetre-wave (mmWave) has been highlighted as an essential technology in the development of 5G-new radio (5G-NR). In the present MFH architecture which is typically based on common public radio interface (CPRI) protocol, baseband signals are digitised before fibre transmission, featuring high overhead data and stringent synchronisation requirements. A direct application of mmWave 5G-NR to CPRI digital MFH, where signal bandwidth is expected to be up to 1GHz will be challenging, due to the increased complexity of the digitising interface and huge overhead data that will be required for such bandwidth. Alternatively, radio over fibre (RoF) technique can be employed in the transportation of mmWave wireless signals via the MFH link, thereby avoiding the expensive digitisation interface and excessive overhead associated with its implementation. Additionally, mmWave carrier can be realised with the aid of photonic components employed in the RoF link, further reducing the system complexity. However, noise and nonlinearities inherent to analog transmission presents implementation challenges, limiting the system dynamic range. Therefore, it is important to investigate the effects of these impairments in RoF based MFH architecture. This thesis presents extensive research on the impact of noise and nonlinearities on 5G candidate waveforms, in mmWave 5G fibre wireless MFH. Besides orthogonal frequency division multiplexing (OFDM), another radio access technology (RAT) that has received significant attention is filter bank multicarrier (FBMC), particularly due to its high spectral containment and excellent performance in asynchronous transmission. Hence, FBMC waveform is adopted in this work to study the impact of noise and nonlinearities on the mmWave fibre-wireless MFH architecture. Since OFDM is widely deployed and it has been adopted for 5G-NR, the performance of OFDM and FBMC based 5G mmWave RAT in fibre wireless MFH architecture is compared for several implementations and transmission scenarios. To this extent, an end to end transmission testbed is designed and implemented using industry standard VPI Transmission Maker® to investigate five mmWave upconversion techniques. Simulation results show that the impact of noise is higher in FBMC when the signal to-noise (SNR) is low, however, FBMC exhibits better performance compared to OFDM as the SNR improved. More importantly, an evaluation of the contribution of each noise component to the overall system SNR is carried out. It is observed in the investigation that noise contribution from the optical carriers employed in the heterodyne upconversion of intermediate frequency (IF) signals to mmWave frequency dominate the system noise. An adaptive modulation technique is employed to optimise the system throughput based on the received SNR. The throughput of FBMC based system reduced significantly compared to OFDM, due to laser phase noise and chromatic dispersion (CD). Additionally, it is shown that by employing frequency domain averaging technique to enhance the channel estimation (CE), the throughput of FBMC is significantly increased and consequently, a comparable performance is obtained for both waveforms. Furthermore, several coexistence scenarios for multi service transmission are studied, considering OFDM and FBMC based RATs to evaluate the impact inter band interference (IBI), due to power amplifier (PA) nonlinearity on the system performance. The low out of band (OOB) emission in FBMC plays an important role in minimising IBI to adjacent services. Therefore, FBMC requires less guardband in coexistence with multiple services in 5G fibre-wireless MFH. Conversely, OFDM introduced significant OOB to adjacent services requiring large guardband in multi-service coexistence transmission scenario. Finally, a novel transmission scheme is proposed and investigated to simultaneously generate multiple mmWave signals using laser heterodyning mmWave upconversion technique. With appropriate IF and optical frequency plan, several mmWave signals can be realised. Simulation results demonstrate successful simultaneous realisation of 28GHz, 38GHz, and 60GHz mmWave signals

Enabling High Throughput and Reliable Low Latency Communication over Vehicular Mobility in Next-Generation Cellular Networks

The fifth-generation (5G) networks and beyond need paradigm shifts to realize the exponentially increasing demands of next-generation services for high throughputs, low latencies, and reliable communication under various mobility scenarios. However, these promising features have critical gaps that need to be filled before they can be fully implemented for mobile applications in complex environments like smart cities. Although the sub-6 GHz bands can provide reliable and larger coverage, they cannot provide high data rates with low latencies due to a scarcity of spectrum available in these bands. Millimeter wave (mmWave) communication is a key enabler for a significant increase in the performance of these networks due to the availability of large bands of spectrum. However, the extremely limited transmission range of mmWave frequencies leads to poor reliability, especially for mobility scenarios. In this work, we present and evaluate the solutions in three key areas for achieving high throughput along with reliable low latency connection, especially for mobility scenarios in next-generation cellular networks. To enable the 5G networks to meet the demanding requirements of cellular networks, we look into (1) multi-connectivity for enhancing the performance of next-generation cellular networks, (2) designing a reliable network using multi-connectivity, and (3) developing a multilink scheme with efficient radio resource management. Despite the technological advances made in the design and evolution of 5G networks, emerging services impose stringent requirements which have not been fully met by 5G networks so far. The work in this dissertation aims to explore the challenges of future networks and address the needs in the three areas listed above. The results of the study open opportunities to resolve real-world 5G network issues. As 5G networks need to fulfill the rising performance demands of upcoming applications and industry verticals, we first study and evaluate multi-connectivity, which involves simultaneous connectivity with multiple radio access technologies or multiple bands, as a key enabler in improving the performance of the 5G networks. 5G networks are designed to have several small cells operating in the mmWave frequency range using ultra-dense networks (UDN) deployments to provide continuous coverage. But, such deployments not only face challenges in terms of frequent handovers, higher latency, lower reliability, and higher interference levels but also in terms of increasing complexity and cost of deployment, unbalanced load distributions, and power requirements. To address the challenges in high density base station deployments, we study and evaluate novel deployment strategies using multi-connectivity. In NR-NR Dual Connectivity (NR-DC), the user equipment (UE) is connected simultaneously to two gNBs, with one acting as the master node and the other as the secondary node to improve the performance of the 5G system. The master node operating at the sub-6 GHz bands provides high reliability, and the secondary node using the high bandwidth mmWave bands provides the high throughputs expected of 5G networks. This deployment also improves the latency as it decreases the number of handovers and link establishments. Thus, in this dissertation, we propose and evaluate novel 5G deployments with multi-connectivity, which can be used to ensure that these 5G networks are able to meet the demanding requirements of future services. The 5G networks also need to support ultra-reliable low latency communication, which refers to using the network for mission-critical communication that requires high reliability along with low latency. However, technological advancements so far have not been able to fully meet all these requirements. Thus, in this work, we design a reliable 5G network using multi-connectivity, which can simultaneously support high throughputs along with ultra-reliable low latency communication. Deployments using mmWave bands are highly susceptible to channel fluctuations and blockages. Thus, it is critical to consider new techniques and approaches that address these needs and can be implemented practically. In this work, we propose and implement a novel approach using packet duplication and its optimization in an NR-DC system to improve the performance of the system. In an NR-DC deployment with packet duplication, multiple instances of a packet are generated and transmitted simultaneously over different uncorrelated channels between the UE and the base stations, which decreases the packet failure probability. We also propose enhancements to the packet duplication feature for efficient radio resource utilization by looking into the distance of the UE from the base station, the velocity of the UE, and the received signal strength indicator (RSSI) levels. The proposed system improves the performance in terms of throughput, latency, and reliability under varying mobility scenarios. Finally, the 5G networks need to meet the increasing demands of uplink data traffic for applications such as autonomous driving, IoT applications, live video, etc. However, the uplink performance is lower compared to the downlink, and hence, it is critical for 5G to improve uplink performance. Thus, there are open research questions on what should be the network architecture with efficient radio resource utilization to meet the stringent requirements for mobility scenarios. In this work, we propose a novel uplink scheme where the UE performs only a single transmission on a common channel, and every base station that can receive this signal would accept and process it. This technique increases the probability of successful transmission and hence, increases the reliability of the network. It also removes the need to perform frequent handovers and allows high mobility with reduced latency. In this work, we propose and evaluate novel approaches for improving the performance of next-generation networks, which will be a key enabler for future applications. The proposed 5G techniques are shown to significantly improve the throughput, latency, and reliability simultaneously and are able to fulfill the stringent requirements of future services. Our work focuses on developing novel solutions for addressing the challenges involved in building next-generation cellular networks. In the future, we plan to further develop our system for real-world city-scale deployments

Capacity Enhancement Approaches for Long Term Evolution networks: Capacity Enhancement-Inspired Self-Organized Networking to Enhance Capacity and Fairness of Traffic in Long Term Evolution Networks by Utilising Dynamic Mobile Base-Stations

The long-term evolution (LTE) network has been proposed to provide better network capacity than the earlier 3G network. Driven by the market, the conventional LTE (3G) network standard could not achieve the expectations of the international mobile telecommunications advanced (IMT-Advanced) standard. To satisfy this gap, the LTE-Advanced was introduced with additional network functionalities to meet up with the IMT-Advanced Standard. In addition, due to the need to minimize operational expenditure (OPEX) and reduce human interventions, the wireless cellular networks are required to be self-aware, self-reconfigurable, self-adaptive and smart. An example of such network involves transceiver base stations (BTSs) within a self-organizing network (SON). Besides these great breakthroughs, the conventional LTE and LTE-Advanced networks have not been designed with the intelligence of scalable capacity output especially in sudden demographic changes, namely during events of football, malls, worship centres or during religious and cultural festivals. Since most of these events cannot be predicted, modern cellular networks must be scalable in terms of capacity and coverage in such unpredictable demographic surge. Thus, the use of dynamic BTSs is proposed to be used in modern and future cellular networks for crowd and demographic change managements. Dynamic BTSs are complements of the capability of SONs to search, determine and deploy less crowded/idle BTSs to densely crowded cells for scalable capacity management. The mobile BTSs will discover areas of dark coverages and fill-up the gap in terms of providing cellular services. The proposed network relieves the LTE network from overloading thus reducing packet loss, delay and improves fair load sharing. In order to trail the best (least) path, a bio-inspired optimization algorithm based on swarm-particle optimization is proposed over the dynamic BTS network. It uses the ant-colony optimization algorithm (ACOA) to find the least path. A comparison between an optimized path and the un-optimized path showed huge gain in terms of delay, fair load sharing and the percentage of packet loss

Improving Channel Estimation and Tracking Performance in Distributed MIMO Communication Systems

This dissertation develops and analyzes several techniques for improving channel estimation and tracking performance in distributed multi-input multi-output (D-MIMO) wireless communication systems. D-MIMO communication systems have been studied for the last decade and are known to offer the benefits of antenna arrays, e.g., improved range and data rates, to systems of single-antenna devices. D-MIMO communication systems are considered a promising technology for future wireless standards including advanced cellular communication systems. This dissertation considers problems related to channel estimation and tracking in D-MIMO communication systems and is focused on three related topics: (i) characterizing oscillator stability for nodes in D-MIMO systems, (ii) the development of an optimal unified tracking framework and a performance comparison to previously considered sub-optimal tracking approaches, and (iii) incorporating independent kinematics into dynamic channel models and using accelerometers to improve channel tracking performance. A key challenge of D-MIMO systems is estimating and tracking the time-varying channels present between each pair of nodes in the system. Even if the propagation channel between a pair of nodes is time-invariant, the independent local oscillators in each node cause the carrier phases and frequencies and the effective channels between the nodes to have random time-varying phase offsets. The first part of this dissertation considers the problem of characterizing the stability parameters of the oscillators used as references for the transmitted waveforms. Having good estimates of these parameters is critical to facilitate optimal tracking of the phase and frequency offsets. We develop a new method for estimating these oscillator stability parameters based on Allan deviation measurements and compare this method to several previously developed parameter estimation techniques based on innovation covariance whitening. The Allan deviation method is validated with both simulations and experimental data from low-precision and high-precision oscillators. The second part of this dissertation considers a D-MIMO scenario with $N_t$ transmitters and $N_r$ receivers. While there are $N_t imes N_r$ node-to-node pairwise channels in such a system, there are only $N_t + N_r$ independent oscillators. We develop a new unified tracking model where one Kalman filter jointly tracks all of the pairwise channels and compare the performance of unified tracking to previously developed suboptimal local tracking approaches where the channels are not jointly tracked. Numerical results show that unified tracking tends to provide similar beamforming performance to local tracking but can provide significantly better nullforming performance in some scenarios. The third part of this dissertation considers a scenario where the transmit nodes in a D-MIMO system have independent kinematics. In general, this makes the channel tracking problem more difficult since the independent kinematics make the D-MIMO channels less predictable. We develop dynamics models which incorporate the effects of acceleration on oscillator frequency and displacement on propagation time. The tracking performance of a system with conventional feedback is compared to a system with conventional feedback and local accelerometer measurements. Numerical results show that the tracking performance is significantly improved with local accelerometer measurements

Software defined virtualized cloud radio access network (SD-vCRAN) and programmable EPC for 5G

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis thesis focuses on proposing a Software Defined Network (SDN) based programmable and capacity optimized backhaul and core network which is critical for 5G network design. Cloud Radio Access networks (CRAN) which is key enabler of 5G networks can address a number of challenges that mobile operators face while trying to support ever-growing end-users’ needs towards 5th generation of mobile networks (5G). A novel layered and modular programmable CRAN architecture called Software Defined Virtualised Cloud Radio Access Network (SD-vCRAN) is introduced with Network Function Virtualization (NFV) and Software Defined Network (SDN) capabilities. The SDN-Base Band Unit (BBU) pool is shifted to the programmable core network site, where a centralised SDN controller manages the network servers and virtualised network function entities – Mobile Management Entity (MME), Serving/Packet Data Network Data plane (S/PGW-D), Serving/Packet Data Network Control plane (S/PGW-C), Software Network Defined Baseband Unit (SDN-BBU) and Local controllers (LC) via OpenFlow (OF) protocol. This approach simplifies network operations, improve traffic management, enable system-wide optimisation of Quality of Service (QoS) and network-aware application development. The control plane (excluding the preserved 3GPP standard interfaces: S1-MME, S6a, Gx) managed by the network servers provides load balancing, traffic management and optimisation tools for the data plane. The proposed work starts by reviewing the requirements of 5G networks, followed by discussion on 5G backhaul and core challenge. Then, an overview of CRAN, Evolved Programmable Core (EPC), SDN, NFV and related works. The simulation details of the proposed architecture are discussed along with the challenges faced by adopting SDN and NFV in mobile core. A thorough assessment of the interfaces and protocols that should be conserved or enhanced on both data and control plane is conducted. The result enables an architecture where the SDN-BBU pool shares a single cloud with the programmable EPC and the control plane is migrated from the network elements to a centralized controller, running on a virtual machine in the mobile core. The data and control plane separation removes overlaps and provides better signalling, as well as efficient network functioning to comply with latency demands. The proposed system performance is validated in terms of throughput, datagram loss, and packet delay variation under three scenarios: 1. single policy installation, 2. multiple policy installation and 3. load balancing. The load balancing performance of proposed system is validated comparing the performance of two different SDN controllers: Floodlight and OpenDaylight, where the later performs better in terms of throughput (no bandwidth restriction), packet loss (below 0.3%) and jitter (below 0.2ms). Furthermore, a detailed comparison of two SDN controller’s – Floodlight and OpenDaylight performances is presented, which shows that OpenDaylight performs better only for less dense networks which needs less processing of messages without being blocked, and the Floodlight performs better in ultra-dense network. Some directions and preliminary thoughts for future work and necessary information to operators for building their roadmap to the upcoming technologies is presented

LTE in unlicensed spectrum: indoor planning, performance evaluation, and coexistence with WiFi

The pursuit of more bandwidth and more efficient spectrum usage has led to consider the use of Long Term Evolution (LTE) technology in unlicensed spectrum, a concept particularly useful for indoor deployments. However, LTE must be modified in order to guarantee a fair coexistence with other systems, particularly WiFi. There exist several coexistence methods, such as listen-before-talk (LBT), advanced channel selection, duty cycle, and variations of them. Research into unlicensed spectrum has focused into LTE Licensed Assisted Access (LAA) and LTE-Unlicensed (LTE-U), expected to be specified in 2016. The contribution of this thesis is complementary to the current work, and is focused on coexistence from the perspective of network planning and radio access optimization. This is accomplished with a framework that yields optimized network topologies that maximize the benefits from the LTE deployment, fulfill coverage criteria, and minimize interference. The efficacy of the statistically optimized network topologies has also been validated by means of system level simulations

Formulation, implementation considerations, and first performance evaluation of algorithmic solutions - D4.1

Deliverable D4.1 del projecte Europeu OneFIT (ICT-2009-257385)This deliverable contains a first version of the algorithmic solutions for enabling opportunistic networks. The presented algorithms cover the full range of identified management tasks: suitability, creation, QoS control, reconfiguration and forced terminations. Preliminary evaluations complement the proposed algorithms. Implementation considerations towards the practicality of the considered algorithms are also included.Preprin