Marja Matinmikko

Software defined mobile networks: concept, survey, and research directions

This article provides a brief overview on the current development of software-defined mobile networks (SDMNs). Software defined networking is seen as a promising technology to manage the complexity in communication networks. The need for SDMN comes from the complexity of network management in 5G mobile networks and beyond, driven by increasing mobile traffic demand, heterogeneous wireless environments, and diverse service requirements. The need is strong to introduce new radio network architecture by taking advantage of software oriented design, the separation of the data and control planes, and network virtualization to manage complexity and offer flexibility in 5G networks. Clearly, software oriented design in mobile networks will be fundamentally different from SDN for the Internet, because mobile networks deal with the wireless access problem in complex radio environments, while the Internet mainly addresses the packet forwarding problem. Specific requirements in mobile networks shape the development of SDMN. In this article we present the needs and requirements of SDMN, with particular focus on the software-defined design for radio access networks. We analyze the fundamental problems in radio access networks that call for SDN design and present an SDMN concept. We give a brief overview on current solutions for SDMN and standardization activities. We argue that although SDN design is currently focusing on mobile core networks, extending SDN to radio access networks would naturally be the next step. We identify several research directions on SDN for radio access networks and expect more fundamental studies to release the full potential of software-defined 5G networks.

Centralized and distributed spectrum channel assignment in cognitive wireless networks: A Harmony Search approach

This paper gravitates on the spectrum channel allocation problem where each compounding node of a cognitive radio network is assigned a frequency channel for transmission over a given outgoing link, based on optimizing an overall network performance metric dependant on the level of interference among nearby nodes. In this context, genetically inspired algorithms have been extensively used so far for solving this optimization problem in a computationally efficient manner. This work extends previous preliminary research carried out by the authors on the application of the heuristic Harmony Search (HS) algorithm to this scenario by presenting further results and derivations on both HS-based centralized and distributed spectrum allocation techniques. Among such advances, a novel adaptive island-like distributed allocation procedure is presented, which dramatically decreases the transmission rate required for exchanging control traffic among nodes at a quantifiable yet negligible performance penalty. Extensive simulation results executed over networks of increasing size verify, on one hand, that our proposed technique achieves near-optimum spectral channel assignments at a low computational complexity. On the other hand, the obtained results assess that HS vastly outperforms genetically inspired allocation algorithms for the set of simulated scenarios. Finally, the proposed adaptive distributed allocation approach is shown to attain a control traffic bandwidth saving of more than 90% with respect to the naive implementation of a HS-based island allocation procedure.

Distributed and directional spectrum occupancy measurements in the 2.4 GHz ISM band

This paper presents distributed and directional spectrum occupancy measurements in the 2.4 GHz ISM band. Spectrum occupancy measurements can be used to assess how efficiently the spectrum bands are used today. Future cognitive radio systems can improve the spectrum occupancy by filling the gaps in the prevailing spectrum by opportunistically using unoccupied channels. Most of the spectrum occupancy measurements in the literature have been conducted by using a single measurement device with an omnidirectional antenna. The resulting spectrum occupancy values have presented an average of the overall situation. To characterize the influence of the spatial dimension on the spectrum occupancy in a given area, we introduce the directional spectrum occupancy metric. Directional spectrum occupancy is defined as the fraction of time that the received power in a channel exceeds a threshold in a given measurement direction. We have used two separately located measurement devices with directional antennas to measure the directional spectrum occupancy in an office area with heavy traffic load. The results indicate that the spectrum occupancy is heavily dependent on the measurement location and direction. The influence of the spatial dimension is therefore very crucial in the development of future cognitive radio systems.

Simple rules for mobile network operators' strategic choices in future cognitive spectrum sharing networks

Spectrum sharing is becoming a necessity in future cellular networks due to the increasing traffic demand and challenges of getting exclusive spectrum. This article reviews the spectrum sharing framework that consists of regulatory, technology, and business domains. For future mobile network operators, sharing of spectrum with other operators or with other radiocommunication services - especially when using cognitive radio system technologies - is a disruptive change. Building on alternative spectrum sharing scenarios, this article discusses a set of Simple Rules for mobile network operators, both dominators and challengers, regarding spectrum sharing in future cognitive cellular networks. The Simple Rules provide a dynamic framework for both dominating and challenger mobile network operators for developing their sharing-based business models.

An evolution toward cognitive cellular systems: licensed shared access for network optimization

This article reviews the application of the recent European Licensed Shared Access (LSA) concept for spectrum sharing between a mobile network operator (MNO) and an incumbent user. LSA, as a new area of application of cognitive technology, provides the MNO an opportunity to access new frequency resources on a shared basis. The article presents critical design criteria of LSA from the MNO point of view in order to allow future cognitive cellular networks to efficiently exploit shared spectrum bands. We describe the role of LSA bands in the context of heterogeneous networking, and identify the Long Term Evolution (LTE) and LTE-Advanced enabling technologies that support the introduction of LSA. Such technologies include traffic steering, carrier aggregation, and self-organizing networking. Additionally, we introduce an LSA management unit controlled by the MNO, to be implemented on top of the existing LTE/LTEAdvanced architecture, and we discuss the functionalities required for the optimization and automation of LSA resource management. We also depict the interrelations of the tasks between the LSA management unit and the supporting LTE/LTE-Advanced technologies. Based on the findings in this article, the ongoing cellular system evolution is shown to form a solid base for the introduction of new shared spectrum bands for cognitive cellular systems.

Performance of spectrum sensing using Welch's periodogram in rayleigh fading channel

In this paper we present theoretical performance evaluation of spectrum sensing with energy detection using Welchs periodogram for cognitive radio systems. We generalize the theoretical expressions for the probability of detection and the probability of false alarm of energy detection in Rayleigh fading channel to the case of Welchs periodogram. We verify the theoretical results by simulations both in single node and cooperative sensing scenarios. In particular, cooperation is crucial in fading environment. Protection of primary systems from harmful interference is the key requisite for the introduction of cognitive radio systems into the future spectrum regulatory framework if the systems are deployed on the same spectrum bands. The primary users concern is how often it could be susceptible to potential interference from the cognitive radio system, which, as we show, is dependent on the probability of detection. Therefore, performance evaluation and in particular the probability of detection is critical in assessing the potential capabilities of the future cognitive radio systems.

CogMesh: Cognitive Wireless Mesh Networks

We introduce the concept of cognitive wireless mesh network, named CogMesh, in order to meet the future needs of ubiquitous wireless communications. CogMesh is not a concept that simply applies cognitive functionalities into traditional wireless mesh networks. Instead, it aims to enable a uniform service platform by seamlessly integrating heterogenous wireless networks through the utilization of advanced cognitive and adaptive technologies under a mesh structure. The context based reasoning, policy and role based control model, and distributed trust and security mechanism are applied in CogMesh to establish a flexible, reliable, scalable and adaptive wireless network in complex wireless environments. It serves as a model to inspire the design of future wireless networks.

Overview and comparison of recent spectrum sharing approaches in regulation and research: From opportunistic unlicensed access towards licensed shared access

This paper reviews recent spectrum sharing models under study in the spectrum regulation and wireless communications research domains. An overview of different spectrum regulator forums and directions is presented and their activities related to the development of spectrum sharing models are reviewed. Special emphasis is put on the recent European and US regulatory approaches for spectrum sharing. In particular, Licensed Shared Access (LSA) and Collective Use of Spectrum (CUS) models from Europe and Three-Tier Hierarchy Model from the US are analyzed in detail. A comparison is made between these approaches to identify similarities and differences in the regulatory developments. Factors for developing a successful sharing model are also discussed. For a dynamic spectrum sharing model to be adopted, it must protect the rights of entrant users without impact to the legacy systems. It must also create a reasonable straightforward opportunity for an entity that wishes to access a shared spectrum to do so in a manner that is neither overly complex nor costly to implement. The practical implementation of dynamic spectrum sharing models is likely to require different national implementations because the regulatory approaches and the incumbent spectrum uses are different in various countries.

Business models for mobile network operators in Licensed Shared Access (LSA)

This paper presents business models for mobile network operators (MNOs) in the new Licensed Shared Access (LSA) concept. The LSA concept allows spectrum sharing between an incumbent spectrum user and an LSA licensee under the supervision of the regulator with rules and conditions that guarantee predictable quality of service (QoS) levels to all involved spectrum users. This paper summarizes the LSA concept and its application to the mobile broadband where an MNO shares spectrum from another type of incumbent spectrum user such as military or programme making and special events (PMSE) services which corresponds to the industry driven Authorised Shared Access (ASA) concept. The paper highlights the importance of developing viable business models for the new spectrum sharing concepts as they need to provide clear benefits to the key stakeholders to be adopted in real life. The paper depicts the evolution path of business model theories and focuses on a recent action-oriented business modeling approach. This approach is applied to the mobile broadband using the LSA concept to derive business models for MNOs for accessing new LSA bands. Separate business models are derived for dominating and challenger MNOs whose market shares and amounts of exclusive spectrum license differ significantly and will face different business opportunities arising from LSA. To assess the transformation coming with the LSA concept, business models are first developed for the current situation with exclusively licensed spectrum bands. New business models are then developed for the introduction of the new shared LSA bands. The developed business models indicate that the dominating MNOs could benefit significantly from the new LSA bands which would enable dynamic traffic management to offer different service levels to different customer segments. For challenger MNOs, the LSA concept could offer the opportunity to challenge the dominating MNOs and win their customers by offering tailored services to a wider customer base using the new LSA spectrum resources. Moreover, it could significantly re-shape the business ecosystem around the mobile broadband by opening the door to non-MNO entrants.

Spectrum and license flexibility for 5G networks

Spectrum sharing is a key solution facilitating availability of the necessary spectrum for 5G wireless networks. This article addresses the problem of flexible spectrum sharing by the application of adaptive licensing among interested stakeholders. In particular, it acts as a proponent of “pluralistic licensing” and verifies it in three simulation scenarios that are of strong interest from the perspective of 5G networks. The concluding analysis offers discussion of the potential benefits offered to spectrum holders and other interested players through the application of the pluralistic licensing concept.