Dennis Roberson

Spectral Occupancy and Interference Studies in support of Cognitive Radio Technology Deployment

This paper describes the high value of cognitive radio technology and characterizes the opportunity space in four distinct classes. A Chicago-based spectrum occupancy study illustrates the opportunity showing that 82.6% of the spectral capacity is unused. A set of spectral signatures is presented for common devices in the unlicensed frequency band with the view that this technique can be widely deployed across the spectrum. The limitations of current network simulation tools in an interference environment are identified. Finally, the paper briefly discusses several of the non-technology related issues that impact the deployment of cognitive radio techniques.

Long-term spectral occupancy findings in Chicago

This paper summarizes some of the results of measurements and related analysis efforts at the Illinois Institute of Technology (IIT) Spectrum Observatory in Chicago over the past three years. The results are unique in the sense that the spectral occupancy estimates are based on multiple years of observations, whereas previous studies produced occupancy numbers based on short term snapshot measurements, often of a few hours duration or at most spanning a few days or weeks. The measurements are also presented in a novel way: the occupancy data in a band of interest during a one year span is graphed as a 2-dimensional image that visually reveals daily, weekly, and yearly trends and anomalies. The main objective of this paper is to present year by year first-order statistics about the spectral occupancy across multiple bands, but more details are presented about radio usage in a few bands like the TV band. In particular, we examine the spectral opportunities that are seen in the newly available “TV White Space”. The results illustrate occupancy trends and notable spectral events, such as the 2009 broadcast television transition and the related vacating of the 700 MHz band, which have created significant spectrum opportunities in the 30–1000 MHz region. The trends reported are applicable to long term spectrum modeling, spectrum planning, and regulatory decision-making efforts applicable to dynamic spectrum access networks.

Spectrum Occupancy Measurements: A Survey and Use of Interference Maps

In order to provide meaningful data about spectrum use, occupancy measurements describing the utilization rate of a specific frequency band should be conducted over a specific area instead of a single location. This paper presents a comprehensive methodology for the measurement and analysis of spectrum occupancy. This paper surveys spectrum measurement campaigns and associated interference maps, introducing the latter as a tool for spectrum analysis and management based on measurement data. An interference map characterizes the spectrum use by defining the level of interference over an area of interest in a certain frequency band. Building on findings from practical measurement studies, guidelines for spectrum occupancy measurements are given. While many scientific spectrum occupancy measurement papers tend to be too optimistic about the significance and generality of the results, we propose a cautionary perspective on drawing strong conclusions based on the often limited amount of data gathered. The different phases of the spectrum occupancy measurement and analysis process are described and a thorough discussion of interpolation methods is provided. Means to improve the measurement accuracy are discussed, especially regarding spatial domain considerations and the impact of the sampling interval on the results. A practical example of an improved measurement system design covering all the phases of the measurement process and used at the Turku, Finland; Blacksburg, VA, USA; and Chicago, IL, USA, spectrum observatories is given. Using the improved design, more realistic spectrum occupancy data can be obtained to lay the foundation for spectrum management decisions.

Spectrum Utilization Study in Support of Dynamic Spectrum Access for Public Safety

Radios for public safety communication have some of the most stringent requirements for access, reliability and robustness. While wireless technology has seen tremendous strides in the past decade, large parts of the public safety infrastructure have unfortunately lagged behind. Today the majority of the Land Mobile Radios (LMR) used by police and fire departments, among others, utilize bandwidth inefficient analog FM radio systems, despite the limited available radio spectrum allocated for these applications. Additionally, numerous interoperability issues continue to exist between the various agencies, jurisdictions and disciplines; for example, radios from the state law enforcement authorities may not be able to communicate with Federal ones. This paper presents data from spectral measurements carried out over several public safety bands in the city of Chicago. Occupancy estimates over a period of several months are given and analyzed, and seasonal/event-driven variation and trends are discussed. The results demonstrate an imbalance in occupancy between public safety channels, which show high peak occupancy during normal day to day operations, and adjacent commercial LMR channels, which have much lower usage. This indicates potential opportunities for the application of dynamic spectrum access techniques to increase the capacity of public safety channels during emergencies. Furthermore, the spectrum utilization data may be useful for planning for the expansion or optimization of present-day systems.

Overview and comparison of recent spectrum sharing approaches in regulation and research: From opportunistic unlicensed access towards licensed shared access

This paper reviews recent spectrum sharing models under study in the spectrum regulation and wireless communications research domains. An overview of different spectrum regulator forums and directions is presented and their activities related to the development of spectrum sharing models are reviewed. Special emphasis is put on the recent European and US regulatory approaches for spectrum sharing. In particular, Licensed Shared Access (LSA) and Collective Use of Spectrum (CUS) models from Europe and Three-Tier Hierarchy Model from the US are analyzed in detail. A comparison is made between these approaches to identify similarities and differences in the regulatory developments. Factors for developing a successful sharing model are also discussed. For a dynamic spectrum sharing model to be adopted, it must protect the rights of entrant users without impact to the legacy systems. It must also create a reasonable straightforward opportunity for an entity that wishes to access a shared spectrum to do so in a manner that is neither overly complex nor costly to implement. The practical implementation of dynamic spectrum sharing models is likely to require different national implementations because the regulatory approaches and the incumbent spectrum uses are different in various countries.

Location Estimation of Isotropic Transmitters in Wireless Sensor Networks

There are several techniques available for determining the location of wireless transmitters in a network of receivers. The simplest technique for use in sensor networks, is to interpolate the position of the transmitter in the network using the received signal strength (RSS). In this paper we review the RSS geometric locating process. We consider the model for the propagation path to determine an optimal estimate of the location of an isotropic transmitter. We apply a location estimation algorithm to experimental data taken in the field. The experiments involved locating GSM cellular transmitters within a network of power sensors which we emulated with GSM handsets. We analyze the performance of the algorithm in light of the the field tests. We consider modifications of the model to encompass the more nuanced nature of real directional transmitters. We conclude with some remarks on applications of this process to intrusion detection and locating mobile users for emergency services

An RF spectrum observatory database based on a Hybrid Storage System

In 2007, the Wireless Network and Communications (WiNCom) Research Center at the Illinois Institute of Technology initiated a continuous RF spectrum measurement program in the frequency range 30 MHz to 6 GHz. The data measurement collection, now multiple Terabytes, was historically stored in a flat file format on multiple hard drives which was efficient and easy to deal with from a data collection perspective, but not very effective from an analysis and sharing perspective. This paper describes the data capture structure, the new database and data storage approach that has been created to enable large scale, “safe storage”, and to facilitate data queries and RF measurement analysis by researchers both inside and outside of IITs network, and some of the application that have been implemented using this new structure.

Development and Quantitative Analysis of an Adaptive Scheme for Bluetooth and Wi-Fi Co-Existence

A smart radio algorithm to supplement the Adaptive Frequency Hopping (AFH) scheme used by Bluetooth devices is developed and studied. The investigation focuses on the Media Access Control (MAC) layer of the Bluetooth. Collision detection, and Bluetooth channel hopping information are used to detect when an IEEE 802.11 wireless Access Point (AP) is operating and the APs Radio Frequency (RF) channel number (1 through 11). The algorithm then adapts the Bluetooth device to avoid the spectral region occupied by the AP. The performance of this scheme is tested via simulation, and compared with the native AFH system employed by Bluetooth devices.

Spectrum Occupancy Estimation in Wireless Channels with Asymmetric Transmitter Powers

In proposed cognitive radio schemes, channel occupancy is often offered as the metric to determine if a channel is free to open a new communication channel. Channel occupancy is the time average of detected transmissions above a certain power level. In many systems the transmission power between the uplink side and down-link side are asymmetric. If a single power threshold is used, then a system may underestimate channel occupancy on the low power down-link side. This results in an increased probability of interference in an existing channel if a listen-before-talking scheme is used. To avoid this hidden terminal problem, cognitive radios need to better understand the receiver properties of existing wireless channels.

Phone to Fridge: shut up!

When one of us (Roberson) used to live in Wheaton, Ill., his cars FM radio would blare static every time he drove near a pole-mounted electrical transformer. Now, when hes near a particular intersection in Chicago and an elevated train passes by, his mobile phone call gets dropped. The same thing happened to him in a rapid transit station in Washington, D.C., during a conference call with the other two authors of this article. One of them (Matheson) has had to train himself to wait until the commercials begin before turning on his electric toothbrush, because it always breaks up the picture and sound of the TV set in his bedroom.