Today’s networked society has an unprecedented and growing demand for wireless capacity. New technological innovations both in the physical layer and on the network level are required in order to enable future wireless communication systems to scale up accordingly. However, these developments will necessarily need to be aligned with improved means to manage radio spectrum, the scarce essential resource, and limit, for wireless communications. Apart from extensions to the traditional set of tools for spectrum management, new methods for granting spectrum access on a secondary use basis have been proposed recently. They have been widely discussed in the academic, industrial, and regulatory communities, albeit with only a limited number of practical implementations so far. A presumed reason for this observed hesitance are uncertainties on the technical and economical value of operating in shared spectrum. In order to fill this gap, the main contribution of this thesis is the development of a framework that enables the unified assessment of entire secondary network deployments. This framework has been furthermore implemented as a spectrum assessment tool software that allows for a detailed integrated technology and regulatory analysis. It is a primary concern in secondary access scenarios to protect the incumbent spectrum user against a deterioration of spectrum quality due to additional interference. In this thesis, we evaluate the options and necessary tradeoffs for different prototype protection models in terms of primary service quality reduction and secondary technical operation limits. We specifically quantify the primary-secondary relationship using the German TV broadcasting network as a case study for detailed analysis. Apart from this sensitivity analysis, our work provides realistic availability figures for the underutilized TV bands of Germany, commonly known as the TV whitespaces (TVWS). Current secondary access policies that are based on geo-location databases may result in excessive interference or low system performance due to the limited precision of the propagation models that they employ. This motivates us to propose the addition of functionalities to these databases that enable them to exploit auxiliary primary signal strength information to improve their prediction performance. We analyze different model-based and model-free estimation methods for their feasibility in such hybrid setups. Our analysis is based on large-scale data sets from real measurement campaigns and synthetic spectrum data. We furthermore compare our results against the theoretical bounds of the methods.

Assessment methods for secondary wireless networks

The commercial long-term evolution (LTE) networks of today offer fast and regionally wide access to the Internet and to the commercial applications and services at a reasonable price. At the same time, public safety (PS) users are still communicating with old-fashioned, second-generation voice and data services. Recently, the commercial LTE networks have been standardized to offer capabilities to mission-critical users. However, the commercial networks do not yet fully support the coverage requirements of the PS users. Moreover, the commercial infrastructure might be out of order in critical scenarios where PS actors are needed. Thus, the PS users require, for example, rapidly deployed LTE networks to support their own communication. This thesis studies the PS use of commercial operators' LTE networks and rapidly deployed closed LTE networks. The key tasks are to find out how to connect users seamlessly together between the different networks as well as finding out how the frequency planning is implemented. This thesis provides practical design solutions to guarantee network interoperability by connecting the networks as well as radio spectrum utilization solutions by licensed shared access (LSA). While the concept of LSA has been well developed, it has not been thoroughly investigated from the point of view of the PS actors, who have special requirements and should benefit from the concept. Herein, the alternatives for spectrum sharing between PS and commercial systems are discussed. Moreover, the thesis develops a specific LSA spectrum sharing system for the PS actors deploying their own network in scenarios where the commercial networks are insufficient. The solution is a robust LSA-based spectrum sharing mechanism. Note that PS actors also need to be able to utilize the spectrum when the LSA system is not available and when the commercial system has failed. Thus, this thesis proceeds on developing sensing methods for complementing LSA, where the sensing methods guarantee spectrum information for a rapidly deployed PS network. It is shown how PS actors can utilize available spectrum with a secondary spectrum licence. This is a good alternative to reserving the spectrum completely. The work assembles missing pieces of existing methods to ensure the functionality of the commercial and of the supporting rapidly deployed networks, both in terms of spectrum usage and application services.

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Special applications and spectrum sharing with LSA

The evolution of wireless communication technology has entered a new era where the vision of vendors and researchers to move beyond connecting people to connecting everything is becoming reality. Pioneers have been working for decades to enhance the netwo

Radio access for LTE-advanced femtocells

The ongoing development of mobile cellular networks, supporting a wide range of applications and services with high data-rate and ubiquitous connectivity requirements, has resulted in a considerable increase in capacity demand. With the advent of next generation of mobile cellular networks, it is expected that the capacity demand to exceed far beyond the supply. This imminent capacity shortage has introduced impetus to identify practical solutions towards a more efficient utilisation of the spectrum. In this respect, various approaches under the umbrella of Spectrum Sharing (SS) have been explored. However, the incorporated techniques, along with some sets of strict assumptions, have imposed conservatively broad boundaries, known as Exclusion Zones (EZs) to ensure interference protection, irrespective of the actual spatial-temporal utilisation of the spectrum. This has resulted in limited achievable gains, and consequently the conventional approaches are identified as inefficient for the real-world deployment. In fact, for the SS to be efficient and practically viable, there is a need for a paradigm shift towards a more dynamic mechanisms with a level of live spectrum usage awareness in the network, which can efficiently identify interference-free Spectrum Opportunities (SOPs) for sharing, and hence, the shortcomings and constraints of the conventional SS approaches can be mitigated. In this context, the aim of this thesis is to investigate a novel and efficient SS mechanism, in which Radio Environment Map (REM) technique as an enabler is applied. The REM captures near real-time spectrum utilisation in the network in temporal and spatial domains pro-actively, resulting in increased SOPs for Sharing. A comprehensive literature survey of the SS is provided in this thesis. The concepts, various authorisation regimes, along with their specifications and requirements are discussed. Moreover, the potential sharing deployment scenarios, as well as the use cases in which the mobile cellular networks can gain benefit from SS are pointed out. Further, having a robust view of State-Of-The-Art (SOTA) coordination protocols (i.e., centralised and sensing based approaches) and enabling techniques, the associated advantages, as well as the major shortcomings and challenges are investigated. This is followed by providing an in-depth insight into the SOTA proposals, approaches, the respective achieved gains, and the necessity for the enhanced/new techniques. Consequently four techniques, namely Inter-Operator Inter-Cell Interference (IO-ICI), the Sensing, Coordinated Beamforming, and REM identified as promising dimensions that can be substantially enhanced/applied in SS. Focusing on the adoption of REM technique, a SS mechanism is proposed which exploits Received Signal Strength (RSS) along with spatial interpolation techniques to model temporal and spatial map of SOPs in the downlink of Long Term Evolution-Advanced (LTE-A), in a dynamic manner, subject to update rate in the order of LTE-A time frame. The investigation is performed over the two well-known and distinctive spectrum sharing schemes; (1) Inter-Operator Spectrum Sharing (IOSS), and (2) Licensed Shared Access (LSA) 1 . For the scheme (1), the sharing players comprise two large-scale independently deployed Mobile Network Operators (MNOs), over the two standardised multi-MNO deployment topologies; non-collocated and collocated, in urban environment. The simulations are performed with high data rate real-time video streaming traffic traces. The simulation results are compared to the two SOTA approaches (i.e., centralised and sensing based approaches), as well as the LTE-A baseline. The simulation results demonstrate that the proposed REM-based sharing mechanism results in 23% improvement in Spectrum utilisation efficiency, 37.5% average system throughput, with respect to the baseline LTE-A, where the SS is not applied. Moreover, it is observed that the REM-based approach outperforms the two considered SOTA approaches. The cost of overhead, and computational complexity of implementation are found negligible. In addition to IOSS, for the scheme (2) (i.e., the LSA), an arbitrary LSA incumbent as a worst case scenario (when no priori information is given) is considered. Through the the simulation results it is shown that the proposed approach reduces the size of EZs from considerable number of cells to a fewer numbers. The transmit power level does not need to to be reduced in majority of the cells in the network, and thus, the LSA bands can be utilised in a more dynamic manner. As a result, the overall system throughput is significantly increased with respect to the SOTA approach by 80%. However, this gain is subject to fast and reliable interface between two networks to allocate sufficient time for band evacuation.

Radio environment map-enabled spectrum sharing in mobile cellular networks.

We investigate the design of signal processing in wideband spectrum usage (SPU) measurements for efficient and smart dynamic spectrum access (DSA). In particular, we focus on spectrum usage detection (SPUD) in the experimental measurements. The detection results can be exploited to estimate statistics of the SPU. An appropriate design of the SPUD depends on the actual SPU in the target frequency band. There is a broad range of wireless systems in a considered broad measurement frequency band, such as from 60MHz to 6GHz, therefore a general design framework in the measurement frequency band is desired. In the proposed design framework, we at first define two models in terms of the SPU and the SPUD process. In addition, the proposed design procedure determines the adequate choice of parameters for the SPUD model based on given parameters of the SPU model in the target frequency band. Numerical evaluation based on computer simulations shows the validity of the design framework and design procedure. Moreover, a modified duty cycle (DC) estimation method is proposed, which can remove bias errors caused by low time resolution in the SPUD. Numerical evaluation based on experimental measurements demonstrates the practicality of the detection framework and procedure proposed in this work.

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Design of Spectrum Usage Detection in Wideband Spectrum Measurements

This paper presents a demonstration of the new Licensed Shared Access (LSA) concept using a TD-LTE access network in the 2.3 GHz spectrum band in Finland. In the demonstrated trial, the TD-LTE network shares the spectrum of an incumbent spectrum user, who is focused on programme making and special events (PMSE) services. The demonstrator implements the new LSA concept and the required new building blocks including LSA Repository for spectrum protection information and LSA Controller for controlling the mobile communication network in the same band. The trial uses commercial network components like multiband-terminals, TD-L TE base stations, network management system, and core network. Spectrum usage data of incumbents is collected to LSA Repository using two incumbent user tools and is actively updated to LSA Controller for radio network planning to protect the incumbent's activity in the area. LSA Controller uses the information from the base stations and incumbents to protect incumbent spectrum users' rights. This is demonstrated by providing different algorithms, which analyze base stations and sectors that need to be reconfigured to prevent interference from LTE to incumbent (and vice versa). The demonstration shows that the new LSA concept can be implemented with existing network elements and a minimum amount of new components.

Marko Palola

Papers

Presentation of paper (Licensed Shared Access (LSA) Trial Demonstration Using Real LTE Network)