@article {Simula.simula.2542,
	title = {System Level Performance of IEEE 802.22 With Sensing-Based Detection of Wireless Microphones},
	journal = {IEEE Communications Magazine},
	volume = {52},
	number = {1},
	year = {2014},
	month = {January},
	pages = {200-209},
	publisher = {IEEE},
	abstract = {We present the state-of-the-art system level evaluation of the IEEE 802.22-2011 standard using a highly detailed simulator implementation in NS-2. In the evaluation our attention is focused on the effect of spatiotemporal wireless microphone (WM) activity on the performance of the IEEE 802.22-2011 network, while considering novel spectrum sensing strategies and multimedia traffic with different prioritization in IEEE 802.22-2011. Our general finding is that the IEEE 802.22-2011 standard deals well with WMs and prioritization of simultaneous multimedia traffic using different QoS profiles, while some surprising conclusions follow.},
	doi = {10.1109/MCOM.2014.6710084},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund} and Pawe{\l}czak, Przemys{\l}aw and Park, Jihoon and Cabric, Danijela}
}
@article {gronsund-et-al-JTPO-2012,
	title = {Business Case Evaluations for LTE Network Offloading With Cognitive Femtocells},
	journal = {Telecommunications Policy Journal},
	volume = {37},
	number = {2-3},
	year = {2013},
	month = {March-April},
	pages = {140-153},
	publisher = {Elsevier},
	abstract = {Mobile networks are increasingly becoming capacity limited such that more base stations and smaller cells or more spectrum are required to serve the subscribers\&$\#$39; increasing data usage. Among several challenges, the establishment of new base station sites becomes challenging and expensive. This study proposes and analyzes critical aspects of a business case where a mobile operator offloads its mobile LTE network by deploying cognitive femtocells. When aided by a sensor network the cognitive femtocell will be able to use frequencies other than the mobile network and hence increase its power to cover outdoor areas and neighbour buildings. This cognitive femtocell strategy will be compared with an alternative strategy where an operator deploys conventional femtocells and has to build additional base stations to meet the traffic demands. The business case analysis illustrates that there is a potential for cost savings when offloading the mobile network with cognitive femtocells when compared to the alternative strategy. It must be emphasized that the studied concept is innovative and that the business case period starts in 2017, hence parameter assumptions are uncertain. Therefore, as the most important message of this work, sensitivity analysis are used to reveal the most critical aspects of the cognitive femtocell business case. It is found that that the most critical parameters regarding the cognitive femtocell are the price for backhauling, the number of users supported and the coverage. Furthermore, an optimal coverage radius for the cognitive femtocell for lowest possible costs is found. Costs related to the fixed sensor network are found to be less critical since sensors are embedded in the cognitive femtocells. Sensitivity analysis is also presented for spectral efficiency, cognitive and conventional femtocell offloading gain, sensor density and price, customer density and price for base station site establishment.},
	doi = {10.1016/j.telpol.2012.07.006},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund} and Gr{\o}ndalen, Ole and L{\"a}hteenoja, Markku}
}
@phdthesis {Simula.simula.2540,
	title = {Cognitive Radio From a Mobile Operator{\textquoteright}s Perspective: System Performance and Business Case Evaluations},
	year = {2013},
	month = {October},
	school = {University of Oslo},
	type = {phd},
	abstract = {Cognitive Radio (CR) is a promising technology to solve the spectrum scarcity problem and to increase spectrum efficiency. By using spectrum sensing and databases, one is able to obtain information about and utilize white space spectrum. Spectrum costs, which tend to be high for mobile operators, can then be reduced significantly. For mobile operators, CR technology brings threats and opportunities. Two evident threats are the risk of increased interference and competition when secondary users access white spaces in the operator\&$\#$39;s own spectrum. Considering the high level of activities on CR in research, standardization and regulation in addition to commercial activities, CR might eventually emerge in the telecommunications market. Therefore, instead of focusing on the threats only, mobile operators should focus on understanding how they can benefit from using CR. One opportunity is to use CR to get access to more spectrum to cope with the increasing wireless data demand and spectrum scarcity. Another opportunity is to use CR to access spectrum in, and to enter, new markets where there are no available spectrum licenses. The objective of this thesis is to study and understand how a mobile operator can benefit from using CR as a potential sustaining or disruptive innovation to opportunistically access white spaces. We show, by example case studies, that there are potentials for a mobile operator to use CR to access white spaces and achieve well performing technical and economic viable solutions. In particular, we study three important areas for CR with focus on the mobile operator\&$\#$39;s perspective. First, we characterize spectrum usage and analyze potential capacity for CR access in primary OFDMA networks. We show that there is a potential for CR systems to utilize white spaces. Furthermore, we propose that cooperation with the primary operator is important to maximize spectrum utilization. Second, we study the concept of a sensor network aided CR system. We propose three business cases and evaluate the economic viability. The most promising business case for an operator is that of a joint venture that gets the rights to use the {\textquoteleft}{\textquoteleft}unused\&$\#$39;\&$\#$39; spectrum resources of spectrum owners. We find that high reuse of existing base station sites by the CR system is a business critical parameter. Furthermore, it is found challenging to achieve high reuse of existing base station sites when evaluating technical performance using a simulation model. Hence, this points in the direction of shorter range and less expensive access points such as femtocells. However, we show that full reuse of base station sites can be achieved by relaxing interference requirements for the CR. Then, we propose a promising business case that uses cognitive femtocells aided by a sensor network to offload the LTE network. Third, we use simulations to evaluate performance of the first CR standard IEEE 802.22. We find that the activity of wireless microphones as the primary users should be quite high to reduce throughput and delay. Interference to the wireless microphone is found to be low in general and to occur only for short periods when using novel sensing strategies. Furthermore, we show that the guaranteed bit rate QoS service for VoIP can be prioritized. Though, the spectrum sensing strategy is important to satisfy strict QoS requirements for throughput and delay. Finally, we explore spectrum selection functions, which are used as basis for channel selection. We show that selection functions that utilize long-term spectrum usage statistics based on historic, accumulated sensing results can enhance over-all performance.},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund}}
}
@article {gronsund2011,
	title = {Analysis Framework for Opportunistic Spectrum OFDMA and Its Application to the IEEE 802.22 Standard},
	journal = {IEEE Transactions on Vehicular Technology},
	volume = {61},
	number = {5},
	year = {2012},
	month = {July},
	pages = {2271-2293},
	publisher = {IEEE},
	abstract = {We present an analytical model that enables the evaluation of opportunistic spectrum orthogonal frequency division multiple-access (OS-OFDMA) networks using metrics such as blocking probability or, most importantly, throughput. The core feature of the model, based on a discrete-time Markov chain, is the consideration of different channel and subchannel allocation strategies under different primary and secondary user types, traffic, and priority levels. The analytical model also assesses the impact of different spectrum sensing strategies on the throughput of OS-OFDMA network. In addition, we consider studies of cochannel interference. The analysis is applied to the IEEE 802.22 standard to evaluate the impact of the two-stage spectrum sensing strategy and the varying temporal activity of wireless microphones on the system throughput. In addition to the analytical model, we present a set of comprehensive simulation results using NS-2 related to the delay performance of the OS-OFDMA system considered. Our study suggests that OS-OFDMA with subchannel notching and channel bonding could provide almost ten times higher throughput compared with a design without these options when the activity and density of wireless microphones are very high. Furthermore, we confirm that OS-OFDMA implementation without subchannel notching, which is used in the IEEE 802.22, can support the real-time and non-real-time quality of service classes, provided that the temporal activity of wireless microphones is moderate (with sparse wireless microphone distribution, with light urban population density and short duty cycles). Finally, the two-stage spectrum sensing option improves the OS-OFDMA throughput, provided that the length of spectrum sensing at every stage is optimized using our model.},
	author = {Park, Jihoon and Pawe{\l}czak, Przemys{\l}aw and P{\r a}l Rolfsen {Gr{\o}nsund} and Cabric, Danijela}
}
@article {gronsundvlsi2012,
	title = {Comparison of Cell Sizes for Cost Efficient Deployment of a Sensor Network Aided Cognitive Radio System, Journal of Signal Processing Systems},
	journal = {Journal of Signal Processing Systems},
	volume = {69},
	number = {1},
	year = {2012},
	pages = {95-104},
	publisher = {Springer},
	abstract = {To exploit spectrum resources on a secondary basis, a Sensor Network Aided Cognitive Radio Network uses a wireless sensor network that assists a secondary cognitive radio network by providing information about the current primary spectrum occupancy. In this paper we determine the performance for different cell sizes when considering the costs for deployment of base stations in a secondary network that exploits spectrum holes identified by the wireless sensor network. The secondary base station is deployed co-located with a mobile primary network that uses a cellular reuse pattern with seven frequencies. Performance of the secondary system and impact on the primary system are mainly studied in terms of throughput, packet loss and coverage when using spectrum holes in the space, time and frequency domains. Especially, we find that the cell size and configured transmit powers for the secondary system are important for optimal system performance, and that smaller cell sizes and less expensive base stations for the secondary system are beneficial. The impact on primary system performance was found to be low, but that optimal tuning of the sensor network is important.},
	doi = {10.1007/s11265-011-0636-4},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund} and Gr{\o}ndalen, Ole}
}
@inproceedings {gronsund-et-al-globecom-2011,
	title = {Evaluation of Interference Requirements in a Sensor Aided Cognitive Radio System},
	journal = {54th IEEE Global Communications Conference (GLOBECOM)},
	year = {2011},
	month = {December},
	publisher = {IEEE},
	type = {Conference},
	abstract = {To better exploit the spectrum resources a wireless sensor network can be used to assists a secondary cognitive radio network by providing information about the current primary spectrum occupancy. In this paper we study the performance of the secondary network when it is co-located with and having similar cell size as a mobile primary network that uses a cellular reuse pattern with seven frequencies. Especially we study how relaxed requirements for the maximum interference generated by the cognitive radios affect the performance of the secondary and primary network in terms of throughput, packet loss, delay, coverage and connectivity. We show that it is possible to find interference limits for the cognitive radio that allow full throughput and coverage for the secondary system at the cost of a slight reduction in throughput and an increase in packet loss per user of 2\% on average for the primary system.},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund} and Gr{\o}ndalen, Ole},
	editor = {IEEE, }
}
@inproceedings {gronsund-et-al-pimrc-2011,
	title = {Performance of a Sensor Network Aided Cognitive Radio System},
	journal = {22th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)},
	year = {2011},
	month = {September},
	publisher = {IEEE},
	type = {Conference},
	abstract = {A Sensor Network Aided Cognitive Radio Network uses the concept of a wireless sensor network that assists a cognitive radio network by providing information about the current primary spectrum occupancy. In this paper we study the performance of the cognitive network for various cell sizes and transmit power levels when deployed co-located with a mobile primary system that uses a cellular reuse pattern with seven frequencies. Co-location of secondary and primary base stations has been found to be very important in order to reduce network costs. An expression for the degree of co-location of secondary and primary base stations is derived and used for identifying optimal secondary cell sizes. For these optimal secondary cell sizes, we determine the performance in terms of throughput, packet loss, delay, coverage and connectivity when using spectrum holes in the space, time and frequency domains. Especially, we {fi}nd that cell size and transmit power levels are crucial for secondary system performance, and that smaller cell sizes and less expensive base stations for the secondary system such as WiFi access points and femto-cells is beneficial.},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund} and Gr{\o}ndalen, Ole},
	editor = {IEEE, }
}
@inbook {gronsund-et-al,
	title = {System Level Analysis of OFDMA -Based Networks in TV White Spaces: IEEE 802.22 Case Study},
	booktitle = {TV White Space Spectrum Technologies: Regulations, Standards and Applications},
	year = {2011},
	pages = {209-238},
	publisher = {CRC Press},
	organization = {CRC Press},
	chapter = {8},
	author = {Pawe{\l}czak, Przemys{\l}aw and Park, Jihoon and P{\r a}l Rolfsen {Gr{\o}nsund} and Cabric, Danijela},
	editor = {R. A. {Saaed} and S. J. {Shellhammer}}
}
@inproceedings {Simula.ND.387,
	title = {A Dynamic Spectrum Access Scheme for Unlicensed Systems Coexisting With Primary OFDMA Systems},
	journal = {The 7th Annual IEEE Consumer Communications and Networking Conference (CCNC)},
	year = {2010},
	publisher = {IEEE},
	type = {Conference},
	abstract = {In this paper, we consider Mobile WiMAX and LTE as the future technologies for primary OFDMA systems and study Dynamic Spectrum Access (DSA) for unlicensed systems coexisting with primary OFDMA systems. We propose an effective DSA scheme that allows an unlicensed system to statistically and opportunistically access the whole spectrum bandwidth during the last consecutive symbols of each primary OFDMA subframe. There is a tradeoff in gaining high normalized throughput by enlarging the access duration in each subframe and keeping low interference caused to the primary system by shorten the access period. Then, we model that tradeoff by deriving the optimization problem that maximizes the normalized throughput of the unlicensed system while guaranteeing the harmful interference constraints set by the primary system. We develop and conduct our simulations in our simulator modified from the powerful WiMAX simulator developed by the WiMAX Forum in Ns-2.},
	isbn = {978-1-4244-5176-0},
	author = {Hai Ngoc {Pham} and P{\r a}l Rolfsen {Gr{\o}nsund} and Paal Einar {Engelstad} and Gr{\o}dalen, Ole},
	editor = {Ott, J{\"o}rg and Balandin, Sergey and Matuszewski, Marcin}
}
@inproceedings {Simula.ND.375,
	title = {Towards Dynamic Spectrum Access in Primary OFDMA Systems},
	journal = {The 20th Personal, Indoor and Mobile Radio Communications Symposium 2009 (PIMRC{\textquoteright}09)},
	year = {2009},
	pages = {848-852},
	type = {Conference},
	abstract = {OFDMA will be the major transmission technology in the future mobile wireless broadband systems, and is already used in Mobile WiMAX and LTE. In this paper, we use simulations to characterize the spectrum usage of such primary systems. This knowledge is useful for cognitive radio and other technologies for dynamic spectrum access that aim at improving the overall spectrum usage. We calculate the available capacity and analyze the distribution of the spectrum occupancy over time for various network scenarios and traffic models. Based on our analyses, we finally propose directions for improving the dynamic access of spectrum allocated to primary OFDMA systems.},
	author = {P{\r a}l Rolfsen {Gr{\o}nsund} and Hai Ngoc {Pham} and Paal Einar {Engelstad}}
}
