Jonas Kronander

Sensor Selection for Cooperative Spectrum Sensing

This article considers spectrum-on-demand in a cellular system. A communication system that wants to access spectrum to which it does not own a license must perform spectrum sensing to identify spectrum opportunities, and to guarantee that it does not cause unacceptable interference to the license owner. Because a single sensor may be in a fading dip, cooperative sensing among multiple sensors which experience uncorrelated fading is required to guarantee reliable sensing performance. At the same time, as few sensors as possible should be used to reduce the battery consumption, while still employing enough many for the sensing to be reliable. Since shadow fading is correlated for closely spaced sensors, it is desired to select sensors which are sufficiently spatially separated. The present article addresses the problem of selecting appropriate sensors from a candidate set to engage in cooperative sensing, using different degrees of knowledge about the sensor positions. Three different algorithms for sensor selection are presented and evaluated by means of simulation. It is shown that all algorithms outperform random selection of the sensors.

Spectrum sharing scenarios and resulting technical requirements for 5G systems

Cellular networks today are designed for and operate in dedicated licensed spectrum. At the same time there are other spectrum usage authorization models for wireless communication, such as unlicensed spectrum or, as widely discussed currently but not yet implemented in practice, various forms of licensed shared spectrum. Hence, cellular technology as of today can only operate in a subset of the spectrum that is in principle available. Hence, a future wireless system may benefit from the ability to access also spectrum opportunities other than dedicated licensed spectrum. It is therefore important to identify which additional ways of authorizing spectrum usage are deemed to become relevant in the future and to analyze the resulting technical requirements. The implications of sharing spectrum between different technologies are analyzed in this paper, both from efficiency and technology neutrality perspective. Different known sharing techniques are outlined and their applicability to the relevant range of future spectrum regulatory regimes is discussed. Based on an assumed range of relevant (according to the views of the authors) future spectrum sharing scenarios, a toolbox of certain spectrum sharing techniques is proposed as the basis for the design of spectrum sharing related functionality in future mobile broadband systems.

On the scalability of cognitive radio: assessing the commercial viability of secondary spectrum access

We report results from the recently finished QUASAR project, which has studied overall system aspects of cognitive radio technologies and has paid attention particularly to the economic viability of different use cases. We find that successful secondary sharing goes far beyond the detection of spectrum holes. Large-scale commercial success requires that secondary systems are scalable so that a large number of users can be served in an economically viable fashion. Our key finding is that secondary spectrum use is not an attractive method for most of the commercially interesting scenarios, from neither a business nor technical perspective. Perhaps somewhat surprisingly, the likely commercial “sweet spot” for secondary sharing in the lower frequency bands is short-range indoor communications. We also find that regulation does not currently present a significant barrier in Europe or the United States.

Optimizing power limits for white space devices under a probability constraint on aggregated interference

This paper presents a solution to the problem of setting power limits for white space devices sharing a spectrum band. It is desired to utilize the available white space efficiently while also protecting the primary system from harmful interference. Power limits are set individually for each white space device by maximizing a joint utility measure, e.g., sum capacity. The aggregated interference caused by the white space devices to the primary system is controlled by constraining the probability of harmful aggregated interference to be below a defined threshold. First, the problem of single white space channel sharing is given a mathematical formulation in the form of an optimization problem. Under the common assumption of lognormal fading the distribution of the aggregate interference is unknown and the optimization problem becomes infeasible to solve. A computationally feasible approximation of the initial optimization problem is formulated in which the distribution of the aggregated interference is modeled using the Fenton-Wilkinson approximation. We derive the expressions needed for efficiently solving the simplified optimization problem with a numerical solver, including the gradients of the constraint and objective functions. We show by means of simulations that the solutions to the simplified optimization problem typically fulfill the original probability constraints with good precision. Further, the resulting sum-capacity values are higher than what can typically be obtained by using fixed margins for coping with the aggregate interference. We also discuss multi channel extensions which are able to handle not only interference to primary systems operating on adjacent channels, but also the joint problem of selecting the channels for white space operation and deciding the associated power limits.

Cooperative Detection of Programme Making Special Event Devices in Realistic Fading Environments

In this article the effect of licensed non-standardized low power transmitters, i.e., PMSE (programme making special event) devices such as wireless microphones, on secondary usage of TV white space is considered. In particular, the performance for energy detection of these devices is studied under realistic fading and interference situations. One motivation for using energy detection is that PMSE devices are not standardized and, hence, there are few common signal properties that can be exploited when trying to detect them. Further, a novel semi-analytical approach based on single sensor detection performance as a function of distance is developed and shown to accurately predict cooperative sensing performance. The conclusion from the study is that it is sometimes very challenging to accurately detect the presence of PMSE devices. Many spectrum opportunities at times needs to be sacrificed in order to guarantee a low probability of interference.

Joint power, rate, and channel allocation in multilink (cognitive) radio system

We consider multi-constrained power, rate and channel allocation crafted for low power consumption, delay tolerant traffic, and under interfering link conditions that may be used in a cognitive radio system. Specifically, an iterative distributed algorithm, based on a sum-power constrained sum-rate maximization with upper (and lower) per user and channel power and rate constraints, as well as upper per user sum-power and sum-rate constraints is developed. The feasibility and performance of the algorithm is demonstrated by simulation in a cellular system. Simulations show that the multiple constraints are handled while improving the sum-rate vs. sum-power relative an “equal power adaptive rate” RRM approach.

Coexistence between 5G and Fixed Services

This study focuses on the coexistence between 5G networks and Fixed Services (FS), where fixed links (FL) is one application. 5G is expected to require spectrum in high frequency ranges and fixed services is a highly probable candidate to share spectrum with. Most of the spectrum is co-primary allocated to both mobile and fixed. This study gives assessment on the inference to/from the fixed link, and identifies areas for further study. The results indicate that the interference that 5G radiates to the fixed link is higher than the requirement in the co- channel case. However a low traffic load at 5G together with beamforming is the best scenario with a 30\% probability of interference. One possibility to reduce the probability of interference to 6\% is to increase antenna directivity of the fixed links. This can be a valid solution to be applied for operators owning both fixed and 5G networks. The interference from fixed link to 5G downlink is below the allowed limit and it is found that at 5G downlink the main contributor to the aggregated interference is the intra network interference. The interference scenario can be improved by utilizing coordination protocols with beam- steering, and advanced antennas. Operators can also consider to deploy in a coordinated manner, or even using other deployments type like micro or indoor.