Miia Mustonen

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.

Cooperative and noncooperative spectrum sensing techniques using Welch’s periodogram in cognitive radios

Radio spectrum deployment is growing considerably. With this respect finding unutilized frequency channels for new applications has become much more challenging. The problem can be solved by letting unlicensed systems to dynamically use unexploited licensed bands. This kind of flexible spectrum usage requires telecommunication systems to be equipped by an ability to specify unoccupied parts of radio spectrum. One method to identify temporarily unused parts of radio spectrum is spectrum sensing. In this paper, we focus on spectrum sensing using Welchs periodogram. In particular, we generalize and apply the theoretical analysis of the energy detection to the Welchs periodogram. Furthermore, we extend our study to cooperative spectrum sensing. The results indicate that the cooperation between two radios provides the highest cooperation gain.

Cooperative spectrum sensing using quantized soft decision combining

In this paper, a novel method combining cooperative spectrum sensing with quantized soft decision combining is introduced. In order to allow cognitive radios and cognitive networks to opportunistically use spectrum, it is a prerequisite that the license owner or primary user of the spectrum will not be harmfully interfered and the spectrum band will be vacated as soon as the primary user starts its own transmission. There are results indicating that the reliability of sensing information can be improved by exploiting the spatial dimension via cooperation between cognitive radios. Our approach is to further improve the reliability by sharing sensing information between cooperative radios using quantized soft decision combining. Simulations are conducted for the proposed two bit quantized soft decision combining, hard decision combining and nonquantized soft decision combining in an additive white Gaussian noise (AWGN) channel using Welchs periodogram. Hard decision combining is considered with three different decision making rules and the obtained simulation results are verified with analytical performance results for Welchs periodogram. The results show substantial improvement in the detection probability when sensing information between cooperating nodes is shared using two bits instead of one. By using an additional bit it is possible to reach detection probabilities that in hard decision combining would have required one or more additional cooperative users. The results also indicate that the increase in probability of detection is not as significant when full observation of the signal energy is shared between cooperative radios instead of two bits. Thus, almost all the achievable benefit from soft decision combining can be obtained with the proposed quantized soft decision combining.

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.

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.

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.

Fuzzy-Logic Based Framework for Spectrum Availability Assessment in Cognitive Radio Systems

This paper presents a novel decision-making system for the selection of methods to obtain knowledge of spectrum availability in future mobile communication systems equipped with cognitive radio system (CRS) capabilities. The proposed decision-making scheme selects the methods to obtain knowledge of spectrum availability between control channels, databases and spectrum sensing based on the specific requirements of the frequency band at hand. The developed decision-making system considers realistic frequency bands and spectrum sharing scenarios, including bands with primary allocation to mobile service where the operator governs the spectrum use, bands with co-primary or secondary allocation to mobile service where the primary users have to be protected from harmful interference, and finally license-exempt bands, where different systems coexist in uncontrolled interference conditions. Specifically, a novel rule-based decision-making system with a learning mechanism is developed to select among different spectrum sensing techniques including matched filtering, correlation detection, feature detection, energy detection, and cooperative sensing. The decision making system is further applied to operator-governed opportunistic networks, which are dynamically created temporary extensions of the mobile infrastructure networks. Performance evaluation is done by assuming changing operational conditions so as to elucidate the gains of the proposed decision making system with respect to the case when the sensing approach is kept fixed.

A novel Harmony Search based spectrum allocation technique for cognitive radio networks

This paper outlines the application of the heuristic Harmony Search (HS) algorithm for efficient spectrum allocation in cognitive radio networks under a minimum Bit Error Rate (BER) criterion. Our proposed algorithm provides a higher degree of diversity in the search process by virtue of its particular improvisation procedure, as opposed to evolutionary computation techniques used so far for this optimization problem. In our work both centralized and distributed implementations of our approach are proposed and detailed. The first set of simulation results made for one single HS instance running over a fixed network show, on one hand, that our approach achieves near-optimum spectral channel assignments at a very low computational complexity. On the other hand, satisfactory results obtained for a distributed implementation of our algorithm pave the way for future research aimed at comparing our approach with avantgarde genetically-inspired spectrum allocation techniques.