Ramon Ferrús

Interworking in heterogeneous wireless networks: Comprehensive framework and future trends

Interworking mechanisms are of prime importance to achieve ubiquitous access and seamless mobility in heterogeneous wireless networks. In this article we develop a comprehensive framework to categorize interworking solutions by defining a generic set of interworking levels and its related key interworking mechanisms. The proposed framework is used to analyze some of the most relevant interworking solutions being considered in different standardization bodies. More specifically, I-WLAN and GAN approaches for WLAN and cellular integration, solutions for WiMAX and 3GPP LTE/SAE interworking, and the forthcoming IEEE 802.21 standard are discussed from the common point of view provided by the elaborated framework.

Towards transport-layer mobility: Evolution of SCTP multihoming

Recently, growing availability of emerging wireless technologies has pushed the demand to integrate different wireless-network technologies such as: wireless local-area networks, cellular networks, and personal and short-range networks. The inter-working of heterogeneous radio access networks poses many technical challenges, with mobility management being one of the most important. In this paper we survey the existing proposals and show that transport-layer mobility is a viable candidate for implementing seamless handover in heterogeneous wireless access networks. Since the mobile Stream Control Transmission Protocol (mSCTP) is at the core of most relevant transport-layer mobility schemes being currently studied, we identify the key scenarios where the protocol can effectively leverage the multihoming feature to enhance handover support. Moreover, to provide the reader with a complete overview of the mSCTPs application area, we also survey the situations where the use of mSCTP-based schemes is not possible or has some limitations. Then, in one of the identified key scenarios, we investigate several challenging open issues related to path management and path-transition optimization by considering bandwidth-estimation schemes and link-layer support. Finally, we consider introducing concurrent multipath transfer (CMT) into mSCTP-based mobility schemes, as a future research direction.

Design and Evaluation of a Backhaul-Aware Base Station Assignment Algorithm for OFDMA-Based Cellular Networks

Existing base station (BS) assignment methods in cellular networks are mainly driven by radio criteria since it is assumed that the only limiting resource factor is on the air interface. However, as enhanced air interfaces have been deployed, and mobile data and multimedia traffic increases, a growing concern is that the backhaul of the cellular network can become the bottleneck in certain deployment scenarios. In this paper, we extend the BS assignment problem to cope with possible backhaul congestion situations. A backhaul-aware BS assignment problem is modeled as an optimization problem using a utility-based framework, imposing constraints on both radio and backhaul resources, and mapped into a Multiple-Choice Multidimensional Knapsack Problem (MMKP). A novel heuristic BS assignment algorithm with polynomial time is formulated, evaluated and compared to classical schemes based exclusively on radio conditions. Simulation results demonstrate that the proposed algorithm can provide the same system capacity with less backhaul resources so that, under backhaul bottleneck situations, a better overall network performance is effectively achieved.

SDN/NFV-enabled satellite communications networks

In the context of next generation 5G networks, the satellite industry is clearly committed to revisit and revamp the role of satellite communications. As major drivers in the evolution of (terrestrial) fixed and mobile networks, Software Defined Networking (SDN) and Network Function Virtualisation (NFV) technologies are also being positioned as central technology enablers towards improved and more flexible integration of satellite and terrestrial segments, providing satellite network further service innovation and business agility by advanced network resources management techniques. Through the analysis of scenarios and use cases, this paper provides a description of the benefits that SDN/NFV technologies can bring into satellite communications towards 5G. Three scenarios are presented and analysed to delineate different potential improvement areas pursued through the introduction of SDN/NFV technologies in the satellite ground segment domain. Within each scenario, a number of use cases are developed to gain further insight into specific capabilities and to identify the technical challenges stemming from them.

WLAN throughput improvement via distributed queuing MAC

This paper analyzes the performance of a MAC scheme for wireless local area networks (WLANs) that makes use of distributed queues to improve radio channel utilization. Analytical values for the maximum throughput performance are derived as a function of the system parameters. The obtained results show that the proposed scheme outperforms the legacy 802.11 MAC protocol in terms of maximum stable throughput. This benefit is obtained from eliminating back-off periods and collisions in data packet transmissions while minimizing the needed control overhead. The proposal also makes performance to be independent of the number of nodes transmitting in the system and provides stability for high load conditions.

Cognitive control channels: from concept to identification of implementation options

Recent effort related to cognitive radio systems has lead to an in-depth analysis of context information management and exploitation based on a cognitive control channel for enhancement of management needed for, say, suitable link selection in a heterogeneous radio framework, dynamic radio resource management, and distributed sensing. Concerning the actual implementation of such a CCC, the focus was recently moved toward an in-band solution, where the information is transported building on existing radio access technologies. In this scope, this article illustrates relevant technical scenarios in which CCCs can be exploited and outlines a set of derived system requirements. The article provides an overview of various possible RAT independent and dependent implementation options, such as Diameter, distributed agents, 3GPP radio resource control (RRC) mechanisms, IEEE 802.21, IEEE 802.11, WiMedia UWB, and Bluetooth. The advantages and drawbacks of the various options are discussed.

Cross-layer scheduling strategy for UMTS downlink enhancement

This article describes the benefits of including cross-layer information in the scheduling mechanism of a UMTS downlink channel. In particular, the information obtained from the fast power control algorithm is used to properly schedule transmissions. A prioritization function that exploits the short-term channel variations is proposed. This strategy is shown to be a feasible approach to improve system performance in terms of capacity and delay. This enhancement is obtained as a benefit of intrinsic multi-user diversity. The proposal is applicable within the current UMTS radio resource management framework.

Learning-based coexistence for LTE operation in unlicensed bands

The use of Long Term Evolution (LTE) in the unlicensed 5 GHz band, referred to as LTE-U, is a promising enhancement to increase the capacity of LTE networks and meet the requirements foreseen for future systems. Nevertheless, coexistence among several LTE-U and/or Wi-Fi systems in the same band is a key technical challenge to be resolved. In this context, this paper focuses on the channel selection functionality for LTE-U enabled cells to decide the most appropriate channel to use for downlink traffic offloading in the unlicensed band. A distributed Q-learning mechanism that exploits prior experience is proposed to support this functionality, thus enabling coexistence with other systems in a smart and efficient way. The behavior of the proposed approach is illustrated in an indoor scenario with small cells from two different operators. A fully decentralized approach, where the channel selection decision-making is performed independently by each small cell in the scenario, is considered to initially assess the potentials of the Q-learning solution. Promising results are obtained revealing that the throughput achieved by the proposed approach can be between 96% and 99% of the optimum ideal achievable throughput.

An Analytical Estimation of the Failover Time in SCTP Multihoming Scenarios

The motivation behind this paper is a need to have a more accurate estimation of the failover time in SCTP. The traditional one, commonly used in the literature, is based on the sum of the consecutive retransmission timeouts. This is not always appropriate, especially when using the SCTP multihoming feature as a basis for achieving transport layer mobility in wireless networking scenarios, where the transition time between available paths becomes a key aspect for the optimisation. Two new factors are introduced into the proposed estimation formula to reflect the influence of the network parameters and the behaviour of the most common protocol implementations. For the proposed model, we perform a best-worst case analysis, and then illustrate it with an example of a detailed estimation. Finally, we perform simulations comparing our proposal with the traditional estimation in a typical transport layer mobility scenario including long thin networks.

A taxonomy and survey of SCTP research

The Stream Control Transmission Protocol (SCTP) is a relatively recent general-purpose transport layer protocol for IP networks that has been introduced as a complement to the well-established TCP and UDP transport protocols. Although initially conceived for the transport of PSTN signaling messages over IP networks, the introduction of key features in SCTP, such as multihoming and multistreaming, has spurred considerable research interest surrounding SCTP and its applicability to different networking scenarios. This article aims to provide a detailed survey of one of these new features—multihoming—which, as it is shown, is the subject of evaluation in more than half of all published SCTP-related articles. To this end, the article first summarizes and organizes SCTP-related research conducted so far by developing a four-dimensional taxonomy reflecting the (1) protocol feature examined, (2) application area, (3) network environment, and (4) study approach. Over 430 SCTP-related publications have been analyzed and classified according to the proposed taxonomy. As a result, a clear perspective on this research area in the decade since the first protocol standardization in 2000 is given, covering both current and future research trends. On continuation, a detailed survey of the SCTP multihoming feature is provided, examining possible applications of multihoming, such as robustness, handover support, and loadsharing.