Yoram Haddad

5G: The Convergence of Wireless Communications

As the rollout of 4G mobile communication networks takes place, representatives of industry and academia have started to look into the technological developments toward the next generation (5G). Several research projects involving key international mobile network operators, infrastructure manufacturers, and academic institutions, have been launched recently to set the technological foundations of 5G. However, the architecture of future 5G systems, their performance, and mobile services to be provided have not been clearly defined. In this paper, we put forth the vision for 5G as the convergence of evolved versions of current cellular networks with other complementary radio access technologies. Therefore, 5G may not be a single radio access interface but rather a “network of networks”. Evidently, the seamless integration of a variety of air interfaces, protocols, and frequency bands, requires paradigm shifts in the way networks cooperate and complement each other to deliver data rates of several Gigabits per second with end-to-end latency of a few milliseconds. We provide an overview of the key radio technologies that will play a key role in the realization of this vision for the next generation of mobile communication networks. We also introduce some of the research challenges that need to be addressed.

Wireless Software Defined Networks: Challenges and opportunities

Software Defined Networking (SDN) is a network paradigm that relies on the separation of the control and forwarding planes in IP networks. The interconnection devices take forwarding decisions solely based on a set of multi-criteria policy rules defined by external applications called controllers. It is possible to let multiple controllers manage each element of a given network, which allows to create independent networks on the same physical infrastructure. If the implementation of SDN in wired networks is relatively easy, it poses a lot of radio-specific problems in the wireless domain, related to link isolation or to channel estimation. Nevertheless, the wireless domain is also where SDN bears the highest potential, as it provides functions that could foster a better collaboration between access points to reduce interferences or to enhance security. This paper reviews some benefits of wireless SDN and exposes related challenges.

Can context monitoring improve QoE? A case study of video flash crowds in the internet of services

Over the last decade or so, significant research has focused on defining Quality of Experience (QoE) of Multimedia Systems and identifying the key factors that collectively determine it. Some consensus thus exists as to the role of System Factors, Human Factors and Context Factors. In this paper, the notion of context is broadened to include information gleaned from simultaneous out-of-band channels, such as social network trend analytics, that can be used if interpreted in a timely manner, to help further optimise QoE. A case study involving simulation of HTTP adaptive streaming (HAS) and load balancing in a content distribution network (CDN) in a flash crowd scenario is presented with encouraging results.

Energy efficiency in future wireless networks: Cognitive radio standardization requirements

Energy consumption of mobile and wireless networks and devices is significant, indirectly increasing greenhouse gas emissions and energy costs for operators. Cognitive radio (CR) solutions can save energy for such networks and devices; moreover, the energy consumption of CR technologies themselves have to be considered. This paper discusses ways in which standardization efforts can assist the use of CR to both save energy for mobile/wireless communications, and ensure that the energy consumption in CR networks and devices is minimized. Compelling argument for such solutions are presented.

Software-Defined Wireless Transport Networks for Flexible Mobile Backhaul in 5G Systems

Traditionally microwave backhaul has been configured and operated in a static manner by means of vendor specific management systems. This mode of operation will be difficult to adapt to the new challenges originated by 5G networks. New mechanisms for adaptation and flexibility are required also in this network segment. The usage of a signaled control plane solution (based on OpenFlow) will facilitate the operation and will provide means for automation of actions on the wireless transport network segment. In addition to that, a standard control plane helps to reach the multi-vendor approach reducing complexity and variety of current per-vendor operation. This paper presents the motivation for the introduction of programmability concepts in wireless transport networks and illustrate the applicability of such control plane with two relevant use cases for dynamically controlling wireless transport nodes in 5G networks. Extensions to OpenFlow protocol are also introduced for building Software Defined Wireless Transport Networks (SDWTNs).

A two-tier frequency reuse scheme

The race toward higher throughputs for cellular network users is getting more difficult everyday. On the one hand cellular network operators wish to increase benefits by offering new services to users, but on the other hand spare radio resource are shrinking away. The spreading of WiFi-3G dual mode devices is making this fight even harder. The new ”Femtocell” technology is expected to be the rescuer of cellular network operators. This ”mini” cellular base station will provide high indoor coverage and throughput to indoor users relying on regular home access connections to the internet. However the big challenge remaining is to efficiently allocate spectrum to this technology. As spectrum licenses are very expensive most operators do not hold enough to completely separate the femtocell and macrocell layers. Coexisting femtocells and macrocells lead to severe interference scenarios. We propose here a double frequency reuse scheme, which allows a femtocell to reuse the frequency already in use by adjacent sectors of the overlaying macrocell. We present three solutions: full, partial or mixed frequency reuse. Each has advantages and drawbacks, and may be more suitable than the others in some specific configurations. Thanks to our scheme we preserve the radio resource management efficiency without affecting the system performance.

Femtocell SINR Performance Evaluation

Indoor use of mobile phones is growing. Signal penetration into buildings induces severe attenuation which leads to poor indoor mobile coverage. Thus achieving adequate indoor signal to noise and interference ratio is challenging. If operators want to stimulate 3G usage as an alternative to the competitive WIFI solution, they will have to offer better data rates when users are at home or at work. The emerging femtocell solution may be the last step toward broadband mobile internet. Radio planning is not obvious for a plug-and-play femtocell device, which will inherently have an unpredictable deployment. In this paper we evaluate the performance that a femtocell system can achieve when coexisting with an overlaying macrocell system. We propose a double reuse frequency scheme for the assessment of the SINR at the femtocell level. We show that femtocells can definitely provide a meaningful improvement in the data rates experienced by the femtocell user equipment.

SINR diagram with interference cancellation

In this paper we study the reception zones of a wireless network in the SINR model with receivers that employ interference cancellation (IC), a technique that allows a receiver to decode interfering signals, and cancel them from the received signal in order to decode its intended message. We first derive some important topological properties of the diagram describing the reception zones and their connections to high-order Voronoi diagrams and other related geometric objects. We then discuss the computational issues that arise when seeking an efficient description of the zones. Our main fundamental result states that although potentially there are exponentially many possible cancellation orderings (and consequently reception cells), in fact there are much fewer nonempty such cells. We prove a (tight) linear bound on the number of cells and provide a polynomial time algorithm to describe the diagram. Moreover, we introduce a novel measure, referred to as the Compactness Parameter, which influences the tightness of our bounds. We then utilize the properties established for reception diagrams to devise a logarithmic time algorithm for answering point-location queries for networks with IC.

A dynamic load balancing architecture for SDN

Software-defined networking (SDN) can realize the separation between control and data planes. Relying on a single controller in future networks imposes a potential scalability problem. To tackle this problem, it has been proposed to use multiple controllers to manage the large wide-area network, where load balancing among the multiple controllers becomes the major challenge. This paper proposes a novel multi-controllers architecture for SDN. In this architecture a SuperController communicate with RegularControllers split into clusters. Thanks to our architecture which enables dynamic load balancing we improve the run time of the periodic operation and break the usual dependency between SuperController and RegularController existing in previous works.

VoIP transmission in Wi-Fi networks with partially-overlapped channels

The unprecedented cellular traffic growth caused by the ubiquitous mobile Internet access has motivated the search for solutions to cope with this explosive demand of connectivity. Mobile traffic offloading through Wi-Fi networks has emerged as an effective way of supplementing cellular services. This approach has been proven very effective to reduce the load of delay-tolerant traffic in cellular networks. Recent developments suggest that real-time traffic like VoIP could be also offloaded if Wi-Fi networks supported a reasonable number of concurrent calls. In this way, ubiquitous IEEE 802.11 networks operating in the 2.4 GHz ISM band could complement the cellular systems in indoor and rural environments. Wi-Fi networks are allocated 14 channels in this frequency band, thereof only 3 non-overlapped channels are allowed for Wi-Fi extended service sets in order to avoid interference. In this paper we investigate the use of assignment configurations with 4 partially-overlapped channels for VoIP transmissions, which may increase the network capacity in terms of concurrent users supported by Wi-Fi networks. Through computer simulations we demonstrate that 4-channel configurations are feasible at the expense of a tolerable degradation in quality of service for voice traffic with pedestrian mobility.