Maria A. Lema

Flexible Dual-Connectivity Spectrum Aggregation for Decoupled Uplink and Downlink Access in 5G Heterogeneous Systems

Maintaining multiple wireless connections is a promising solution to boost capacity in fifth-generation (5G) networks, where user equipment is able to consume radio resources of several serving cells simultaneously and potentially aggregate bandwidth across all of them. The emerging dual connectivity paradigm can be regarded as an attractive access mechanism in dense heterogeneous 5G networks, where bandwidth sharing and cooperative techniques are evolving to meet the increased capacity requirements. Dual connectivity in the uplink remained highly controversial, since the user device has a limited power budget to share between two different access points, especially when located close to the cell edge. On the other hand, in an attempt to enhance the uplink communications performance, the concept of uplink and downlink decoupling has recently been introduced. Leveraging these latest developments, this paper significantly advances prior art by proposing and investigating the concept of flexible cell association in dual connectivity scenarios, where users are able to aggregate resources from more than one serving cell. In this setup, the preferred association policies for the uplink may differ from those for the downlink, thereby allowing for a truly decoupled access. With the use of stochastic geometry, the dual connectivity association regions for decoupled access are derived, and the resultant performance is evaluated in terms of capacity gains over the conventional downlink received power access policies.

Improved component carrier selection considering MPR information for LTE-A uplink systems

Carrier Aggregation (CA) is one of the key features introduced in LTE Release 10 to achieve higher levels of throughput. Two or more component carriers (CCs) are aggregated and user equipments (UEs) simultaneously transmit in more than one. The use of non-contiguous resource allocation in the uplink (UL) implies higher peak to average power ratio, so power de-rating is essential to avoid inter-modulation distortion and adjacent channel leakage-power ratio. CC selection is a key radio resource management procedure by which the eNB assigns UEs to CCs. While most CC selection algorithms deal with downlink, existing literature lacks efforts on UL CA. Moreover the mechanism is determinant on the UL performance. Given the UE power limitation, different criteria must be used in each link. This work proposes a novel CC selection algorithm that distinguishes between power limited and non-power limited UEs. In particular it is proposed to introduce information on maximum power reduction in selection decisions. Besides, UEs are not directly rejected if they are power limited, an acceptance margin is defined. This contains information on throughput variations between the allocation in several or just one CCs. This novel approach is contrasted with other CC selection techniques. Results show cell edge throughput improvements and the benefit of allowing bandwidth aggregation in a subset of power limited users.

Metaheuristic Procedure to Optimize Transmission Delays in DVB-T Single Frequency Networks

The numerous advantages of single-frequency networks (SFNs) make them one of the preferred deployment options for digital video broadcasting terrestrial (DVB-T) operators. However, SFNs are exposed to self-interference that may reduce the effective coverage. This work deals with the optimal adjustment of internal delays at the transmitters to minimize areas with this problem. The use of metaheuristics is proposed to define a feasible automatic process that allows an intelligent exploration of the space of solutions. Several realistic scenarios in the northeast of Spain have been successfully solved and the quality of solutions has been quantified against other resolution methods. Details on how to adjust the parameters of the algorithms along with practical implementation issues are also addressed.

Dynamic Multi-Connectivity Performance in Ultra-Dense Urban mmWave Deployments

Leveraging multiple simultaneous small cell connections is an emerging and promising solution to enhance session continuity in millimeter-wave (mmWave) cellular systems that suffer from frequent link interruptions due to blockage in ultra-dense urban deployments. However, the available performance benefits of feasible multi-connectivity strategies as well as the tentative service quality gains that they promise remain an open research question. Addressing it requires the development of a novel performance evaluation methodology, which should consider: 1) the intricacies of mmWave radio propagation in realistic urban environments; 2) the dynamic mmWave link blockage due to human mobility; and 3) the multi-connectivity network behavior to preserve session continuity. In this paper, we construct this much needed methodology by combining the methods from queuing theory, stochastic geometry, as well as ray-based and system-level simulations. With this integrated framework, both user- and network-centric performance indicators together with their underlying scaling laws can be quantified in representative mmWave scenarios. To ensure modeling accuracy, the components of our methodology are carefully cross verified and calibrated against the current considerations in the standards. Building on this, a thorough comparison of alternative multi-connectivity strategies is conducted, as this paper reveals that even simpler multi-connectivity schemes bring notable improvements to session-level mmWave operation in realistic environments. These findings may become an important reference point for subsequent standardization in this area.

Business Case and Technology Analysis for 5G Low Latency Applications

A large number of new consumer and industrial applications are likely to change the classic operator’s business models and provide a wide range of new markets to enter. This paper analyzes the most relevant 5G use cases that require ultra-low latency, from both technical and business perspectives. Low latency services pose challenging requirements to the network, and to fulfill them, operators need to invest in costly changes in their network. In this sense, it is not clear whether such investments are going to be amortized with these new business models. In light of this, specific applications and requirements are described and the potential market benefits for operators are analyzed. Conclusions show that the operators have clear opportunities to add value and position themselves strongly with the increasing number of services to be provided by 5G.

Internet of skills, where robotics meets AI, 5G and the Tactile Internet

Capitalizing on the latest developments in 5G and ultra-low delay networking as well as Artificial Intelligence (AI) and robotics, we advocate here for the emergence of an entirely novel Internet which will enable the delivery of skills in digital form. We outline the technical challenges which need to be overcome to enable such a vision, i.e., on the development of a 5G Tactile Internet, standardized haptic codecs, and AI to enable the perception of zero delay networks. The paper is concluded with an overview on the current capabilities, and the standardization initiatives in the IEEE 5G Tactile Internet standards working group as well as the IEEE 5G Initiative.

On the Performance Evaluation of Enabling Architectures for Uplink and Downlink Decoupled Networks

The road to 5G is posing challenging requirements to the cellular network to introduce more applications from several industry verticals. Low delay, high scalability, ultra-reliability and device-centric procedures are some of these requirements. Decoupled Uplink (UL) and Downlink (DL), DUDe, is a key enabler of the device-centric network, and provides a good solution to the UL and DL imbalance problem in heterogeneous networks, improving the UL reliability and load balancing. However, the direct applicability of this technique in 4G networks is subject to either very low backhaul latency between both cooperative base stations, or assisting UL and DL connections that can carry the user plane control signals. This article does a comprehensive study of the enabling architectures for DUDe; the proposed architectures are based on two well- known techniques, Dual Connectivity and Cloud Radio Access Networks. The impact of high latency fronthaul and X2 interfaces is studied and compared to the upper bound UL reliability and throughput obtained with regular round trip time (RTT) values. Results show that even if the radio access network RTT is doubled, DUDe provides an improvement in the UL reliability compared to the classical DL received power cell association.

Adapting fractional frequency reuse to realistic OFDMA cellular networks

Effective intercell interference (ICI) mitigation has been identified as a key challenge for emerging OFDMA cellular technologies such as Long Term Evolution (LTE). In order to address this issue, mobile operators have adopted static Intercell Interference Coordination (ICIC) strategies, including Fractional Frequency Reuse (FFR), given their low complexity and easy implementation. However, recent results made evident the need for additional research efforts as the performance of FFR is poor in realistic cellular deployments. Thus, this paper presents a solution to this problem by means of a novel multiobjective optimization framework able to adapt FFR to any realistic cellular layout. By tuning the operational parameters of FFR at cell level, the proposed scheme succeeds in finding solutions outperforming reference schemes and baseline designs in terms of network capacity and cell edge performance while keeping energy consumption as low as possible.

Achieving End-to-End Reliability of Mission-Critical Traffic in Softwarized 5G Networks

Network softwarization is a major paradigm shift, which enables programmable and flexible system operation in challenging use cases. In the fifth-generation (5G) mobile networks, the more advanced scenarios envision transfer of high-rate mission-critical traffic. Achieving end-to-end reliability of these stringent sessions requires support from multiple radio access technologies and calls for dynamic orchestration of resources across both radio access and core network segments. Emerging 5G systems can already offer network slicing, multi-connectivity, and end-to-end quality provisioning mechanisms for critical data transfers within a single software-controlled network. Whereas these individual enablers are already in active development, a holistic perspective on how to construct a unified, service-ready system as well as understand the implications of critical traffic on serving other user sessions is not yet available. Against this background, this paper first introduces a softwarized 5G architecture for end-to-end reliability of the mission-critical traffic. Then, a mathematical framework is contributed to model the process of critical session transfers in a softwarized 5G access network, and the corresponding impact on other user sessions is quantified. Finally, a prototype hardware implementation is completed to investigate the practical effects of supporting mission-critical data in a softwarized 5G core network, as well as substantiate the key system design choices.

MPR-Aware Scheduler for Carrier Aggregation Transmissions in LTE Uplink

Unlike previous long term evolution releases, LTE-advanced allows the use of non-contiguous resource allocation in the uplink. This feature leads to increase the spectral efficiency thanks to link performance gains obtained from frequency diversity. At the same time, non-contiguous allocations bring higher peak to average power ratio and so potentially higher inter-modulation distortion and adjacent channel leakage-power ratio. Power de-rating has been proposed as a means to avoid this problem and thus user equipments (UEs) must reduce their maximum transmitted power. However, the additional link loss on power limited UEs partially counteracts the gain brought by multi-cluster allocation. In this sense, this paper proposes to include maximum power reduction (MPR) information in opportunistic scheduling decisions. The new scheduling proposal is able to determine whether multi-clustering leads to a net gain in instantaneous throughput or if localized allocation is preferred. The proposed method is compared to other scheduling techniques and it is also analyzed in different inter-site distance scenarios. Results show that considering MPR in opportunistic decisions can lead to overall cell performance improvements.