Pål Grønsund

Fixed WiMAX Field Trial Measurements and Analyses

Much hype is spread about the performance of WiMAX, and many contrary statements are put forward. A reason for the confusion is that little or no published material exists about WiMAX performance based on measurements in real life field trials. We therefore set up a test-bed using WiMAX equipment now on the marked, and did extensive, real life field trial measurements. This paper presents measured throughput and received signal strength under conditions typical for fixed WiMAX systems. Based on the results, throughput is analyzed and analytical expressions representing the measurements are derived for easy use in models.

The physical performance and path loss in a fixed WiMAX deployment

Fixed WiMAX is being deployed worldwide, and the networks are increasing in size. Measurements have been performed, but the amount of measurements are few and do therefore not demonstrate performance in a real life deployment. We have performed extensive analyses of the physical performance in a fixed WiMAX deployment which has been operative for a year and where the amount of subscribers constantly increases. The analyses presented in this paper focus on received signal strength and signal to noise ratio. Based on the measured parameters, we present a Path Loss model for fixed WiMAX which will hopefully be of great reference value due to the amount of measurements presented. Finally, our Path Loss model is compared to other well known Path Loss models and is found to approach the free space loss model.

Evaluation of business cases for a cognitive radio network based on wireless sensor network

This paper proposes and evaluates three business case scenarios for deployment of a sensor network aided cognitive radio system in a typical European city. The first and main business case is based on spectrum sharing, where several spectrum owners establish a joint venture and this joint venture gets the rights to use the “unused” spectrum resources of all those spectrum owners in a cognitive way. Then we study the business case of a spectrum broker, an entity that deploys, builds and operates a sensor network and sells either sensing information or information on spectrum opportunities to one or more cognitive radio operators. Finally we analyze the potential of a new entrant without existing infrastructure or frequency licenses, that uses a sensor network aided cognitive radio system to offer a nomadic mobile broadband service. It is found that the spectrum sharing business case is one of the best possible cases for the studied system because the joint venture operator has free access to frequency resources of the mother companies, detailed knowledge of the primary systems and good possibilities for sharing infrastructure with the owning operators. However, since the studied system is an innovative concept and some of the assumed parameters are therefore uncertain, it should be noted that the main value of the business case calculations is to identify critical aspects influencing the profitability so that future research and development work can focus on them. It is found that the most critical aspects are the fixed sensor density, the fixed sensor operational costs and the number of new cognitive base station sites required.

Towards dynamic spectrum access in primary OFDMA systems

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.

Analysis Framework for Opportunistic Spectrum OFDMA and Its Application to the IEEE 802.22 Standard

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.

Spectrum micro-trading for mobile operators

Spectrum trading is an important tool for increasing overall and local spectrum utilization, and to enable access to new and additional spectrum for mobile operators. However, the current spectrum trading regimes usually require long times to execute a trade, hence limiting the flexibility over short timescales in addition to limiting the granularity of the bandwidth and geographical units that may be traded. In this article we discuss the concept of spectrum micro-trading to enable trading of spectrum on the micro-scale in at least three dimensions: the micro-spatial, micro-temporal, and micro-frequency scales. An ecosystem for spectrum micro-trading is presented along with the most important metrics for spectrum micro-trading evaluation. Results from a simulation study for mobile operators, where spectrum is traded via auction, show that the market is viable using the proposed spectrum micro-trading model, and that spectrum utilization can be greatly improved.

Business case proposal for a cognitive radio network based on Wireless Sensor Network

This paper describes a business case scenario and gives the results of a business case analysis for deployment of a sensor network aided cognitive radio system in a typical European city. The main idea behind the business case is that several spectrum owners will establish a joint venture and this joint venture will get the right to use the “unused” spectrum resources of all the companies in a cognitive way. The joint venture will base its operation on a Wireless Sensor Network aided Cognitive Radio concept, which means that a network of fixed sensors is deployed in order to improve the systems capabilities for detecting primary users and spectrum holes. The main value of the business case calculation is to identify critical aspects influencing the profitability so that future research and development work can focus on them. It is found that the most critical aspects are the fixed sensor density, the fixed sensor operational costs and the number of new cognitive base station sites required.

System level performance of IEEE 802.22-2011 with sensing-based detection of wireless microphones

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.

A solution for SGi-LAN services virtualization using NFV and SDN

Today operators deploy functions like Deep Packet Inspection, Caches, traffic optimization, NAT and Firewall on the SGi/Gi-LAN for subscribers accessing Internet based content/services. Currently these functions are deployed on dedicated hardware components from different vendors that most often need to be managed separately. This is not cost efficient and gives long lead times for new services. The main contribution of this paper is the implementation of a solution for virtualizing the services on the SGi-LAN using NFV and SDN. The virtualized services include TCP optimization, video optimization and network analytics. In addition, a performance evaluation is presented with focus on key indicators for virtualization. It is shown that virtualizing network functions on servers using NFV adds an overhead of 20-40 μ seconds in latency per hop, but that the impact on the network function performance is negligible. It is also shown that a COTS server can support a single instance of the SDN controller programming 100K OpenFlow transactions/second and that a software switch can implement 100K rules/sec while forwarding traffic at 160 Gbps with 200M rules. To evaluate the scaling feature of NFV it is shown that the time to bring up a new virtual network function was between 90-120 seconds.

Sensing of wireless microphones in IEEE 802.22: A system level performance evaluation

We present results on the system level performance of the IEEE 802.22 standard with sensing functionality, using a highly detailed implementation of the IEEE 802.22 protocol stack in the NS-2 simulator. Our attention is focused on the effect of spatio-temporal wireless microphone (WM) activity on the performance of the IEEE 802.22 network with spectrum sensing considered. In general we find that the frequency of WM appearance and activity duration should be quite high in all channels not used by TV broadcasters to reduce IEEE 802.22 throughput, for example about 50% WM occupancy in each of total of four channels. Impact on WM performance is found to be low in general using the two-stage spectrum sensing strategy with frequent sensing stages.