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.
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 sumcapacity 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.
Achieving end-to-end ultra-reliability and resiliency in mission critical communications is a major challenge for future wireless networks. Dual connectivity has been proposed by 3GPP as one of the viable solutions to fulfill the reliability requirements. However, the potential correlation in failures occurring over different wireless links is commonly neglected in current network design approaches. In this paper, we investigate the impact of realistic correlation among different wireless links on end-to-end reliability for two selected architectures from 3GPP. In ultrareliable use-cases, we show that even small values of correlation can increase the end-to-end error rate by orders of magnitude. This may suggest alternative feasible architecture designs and paves the way towards serving ultra-reliable communications in 5G networks.
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