Javier Lorca

Towards a QoE-Driven Resource Control in LTE and LTE-A Networks

We propose a novel architecture for providing quality of experience (QoE) awareness to mobile operator networks. In particular, we describe a possible architecture for QoE-driven resource control for long-term evolution (LTE) and LTE-advanced networks, including a selection of KPIs to be monitored in different network elements. We also provide a description and numerical results of the QoE evaluation process for different data services as well as potential use cases that would benefit from the rollout of the proposed framework.

Network Slicing for 5G with SDN/NFV: Concepts, Architectures, and Challenges

The fifth generation of mobile communications is anticipated to open up innovation opportunities for new industries such as vertical markets. However, these verticals originate myriad use cases with diverging requirements that future 5G networks have to efficiently support. Network slicing may be a natural solution to simultaneously accommodate, over a common network infrastructure, the wide range of services that vertical- specific use cases will demand. In this article, we present the network slicing concept, with a particular focus on its application to 5G systems. We start by summarizing the key aspects that enable the realization of so-called network slices. Then we give a brief overview on the SDN architecture proposed by the ONF and show that it provides tools to support slicing. We argue that although such architecture paves the way for network slicing implementation, it lacks some essential capabilities that can be supplied by NFV. Hence, we analyze a proposal from ETSI to incorporate the capabilities of SDN into the NFV architecture. Additionally, we present an example scenario that combines SDN and NFV technologies to address the realization of network slices. Finally, we summarize the open research issues with the purpose of motivating new advances in this field.

YouTube QoE evaluation tool for Android wireless terminals

In this paper, we present an Android application which is able to evaluate and analyze the perceived quality of experience (QoE) for YouTube service in wireless terminals. To achieve this goal, the application carries out measurements of objective quality of service (QoS) parameters, which are then mapped onto subjective QoE (in terms of mean opinion score, MOS) by means of a utility function. Our application also informs the user about potential causes that lead to a low MOS as well as provides some hints to improve it. After each YouTube session, the users may optionally qualify the session through an online opinion survey. This information has been used in a pilot experience to correlate the theoretical QoE model with real user feedback. Results from such an experience have shown that the theoretical model (taken from the literature) provides slightly more pessimistic results compared to user feedback. Users seem to be more indulgent with wireless connections, increasing the MOS from the opinion survey in about 20% compared to the theoretical model, which was obtained from wired scenarios.

5G radio access above 6źGHz

Designing and developing a millimetre-wave mmWave-based mobile radio access technology RAT in the 6-100i¾źGHz frequency range is a fundamental component in the standardisation of the new 5G radio interface, recently kicked off by 3rd Generation Partnership Project. Such component herein called the new mmWave RAT will not only enable extreme mobile broadband services but also support ultra-high definition/three-dimensional streaming, offer immersive applications and ultra-responsive cloud services to provide an outstanding quality of experience to the mobile users. The main objective of this paper is to develop the network architectural elements and functions that will enable tight integration of mmWave technology into the overall 5G radio access network. A broad range of topics addressing mobile architecture and network functionalities will be covered-starting with the architectural facets of network slicing, multi-connectivity and cells clustering, to more functional elements of initial access, mobility, radio resource management and self-backhauling. The intention of the concepts presented here is to lay foundation for future studies towards the first commercial implementation of the mmWave RAT above 6i¾źGHz. Copyright

Increasing coverage and maximum CFO in DFT-s-OFDM for Machine-Type Communications

One of the growing fields of interest in cellular communications is Machine-Type Communications (MTC). MTC traffic can be characterized in many applications by very low bit rates while requiring a high degree of coverage and reliability. Studies on how to increase coverage and reduce device costs have been extensively performed in DFT-s-OFDM due to its lower peak-to-average power ratio. Among the drawbacks of using DFT-s-OFDM for MTC are the Carrier Frequency Offset (CFO) requirements (thus precluding the use of low-cost local oscillators) and poor performance when coverage is limited (thus precluding devices with low transmission power). A common approach for coverage enhancements is to reduce the signal bandwidth in order to increase the power spectral density, but this does not alleviate the frequency offset requirements. This paper proposes an alternative transmission scheme that increases coverage and supports larger frequency offsets compared to classical bandwidth reduction schemes in DFT-s-OFDM. Link-level simulations demonstrate the superiority of the proposed technique in terms of coverage and resilience against large frequency offsets, and put into question the traditional approach of reducing bandwidth for coverage improvements in OFDM systems.

Cyclic Prefix Overhead Reduction for Low-Latency Wireless Communications in OFDM

Mobile wireless communications are constantly struggling to reduce air interface latencies in order to make the overall systems more responsive to human interaction. Latency reductions in OFDM require substantial reductions in the OFDM symbol lengths, which are limited by the cyclic prefix length according to the maximum channel delay spread to be supported. This paper explores a new scheme that achieves significant overhead reduction by leaving only the cyclic prefix corresponding to the first OFDM symbol and removing the remaining ones in a time transmission interval, while modifying the general transmission procedure. An algorithm is proposed at the receiver for cancellation of any inter-symbol and inter-carrier interference appearing in multipath channels, which benefits from significantly low computational complexity. Link-level simulations show excellent results in terms of block error rate and achievable throughput when applied to an LTE system, therefore allowing for significant symbol length reductions and reduced air interface latencies.

5G systems: The mmMAGIC project perspective on use cases and challenges between 6–100 GHz

mmMAGIC (Millimetre-Wave Based Mobile Radio Access Network for Fifth Generation Integrated Communications) is an EU funded 5G-PPP project, whose overall objective is to design and pre-develop a mobile radio access technology (RAT) operating in the 6–100 GHz range, capable of impacting standards and other relevant fora. The focus of the project is on extreme Mobile Broadband, which is expected to drive the 5G requirements for massive increase in capacity and data-rates. This paper elaborates on some 5G key research areas such as: identification of the most compelling use-cases and Key Performance Indicators (KPIs) for future 5G systems, advantages and challenges of millimeter-wave (mmWave) technologies, channel measurements and channel modeling, network architecture; and the design of a new mobile radio interface including multi-node and multi-antenna transceiver architecture.

Resource and Mobility Management in the Network Layer of 5G Cellular Ultra-Dense Networks

The provision of very high capacity is one of the big challenges of the 5G cellular technology. This challenge will not be met using traditional approaches like increasing spectral efficiency and bandwidth, as witnessed in previous technology generations. Cell densification will play a major role thanks to its ability to increase the spatial reuse of the available resources. However, this solution is accompanied by some additional management challenges. In this article, we analyze and present the most promising solutions identified in the METIS project for the most relevant network layer challenges of cell densification: resource, interference and mobility management.

Over-The-Air Phase Synchronization Mechanism for LTE Small Cells in Interference-Limited Scenarios

Phase synchronization is one of the most important features needed in some of the techniques envisaged for LTE-Advanced, such as Cooperative Multi-Point (CoMP) or enhanced inter-cell interference coordination (eICIC), among others. Phase synchronization can be accomplished through the use of IEEE 1588v2 or GPS receivers. However when dealing with small cells deployed in an uncoordinated manner, such as Home-eNBs, the use of IEEE 1588v2 is not always feasible due to delay and jitter impairments which can be present in xDSL lines. Moreover, GPS receivers are not operative in indoors. The present paper describes an over-the-air synchronization mechanism whereby already synchronized LTE macro cells transmit a new physical signal on a subset of yet unused resource elements, so that small cells can acquire suitable phase synchronization. As the involved resources are reserved and not used for transmission, interference is much lower and signal to noise ratio can be improved compared to traditional network listening modes. Simulations employing a simple proposed receiver structure show very good results in channels where the delay spread is within the length of the cyclic prefix.

Frequency-dependent modulation and coding rates for LTE link adaptation in static conditions

OFDM wireless cellular systems rely on link adaptation in order to match the Modulation and Coding Scheme (MCS) of the transmission blocks with the dynamic channel conditions experienced at the receive side. For simplicity, Long-Term Evolution (LTE) systems consider a single MCS format per codeword, which is optimized according to the average frequency response over the users allocated bandwidth. When the channel coherence bandwidth is smaller than the user bandwidth, the constituent codeblocks experience significantly different channel responses, thus rendering link adaptation less effective. This paper proposes a frequency-dependent link adaptation mechanism whereby codeblocks are independently assigned different MCS values that can be fine-tuned to the frequency characteristics of the channel. Post-detection SINR values at the receive side are exploited (instead of CQI values), along with horizontal mapping of resources with two variants: direct mapping and diversity mapping. A suitable in-band signaling scheme for the codeblock sizes and modulations is also described. Link-level simulations show moderate increases in median throughput, but significant improvements in instantaneous throughput, for a broad range of SINR conditions. The proposed scheme can be particularly beneficial when very large signal bandwidths are used as foreseen in future 5G cellular systems.