Tanim M. Taher

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 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.

Microwave Oven Signal Modelling

The microwave oven (MWO) is a commonly available appliance that does not transmit data but still radiates signals in the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM) band. The MWO thus acts as an unintentional interferer for IEEE 802.11 Wireless Fidelity (Wi-Fi) communication signals. An analytic model of the MWO signal is developed and studied in this paper. The models efficacy is studied via simulation and experimental emulation.

Characterization of an Unintentional Wi-Fi Interference Device - the Residential Microwave Oven

Some devices not used for data communications radiate in the 2.4 GHz wireless-fidelity (Wi-Fi) band, thus causing unintentional interference that degrades the performance of IEEE 802.11 wireless systems. An analytical model for radio emissions from one of the most common unintentional interferers, the residential microwave oven, is developed from laboratory measurements. Simulation of the analytical model results in a power spectral density and spectrogram that are in good agreement with experimental data. An interference mitigation technique is proposed for the microwave oven emission

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.

A Two-Tiered Cognitive Radio System for Interference Identification in 2.4 GHz ISM Band

A detection module has been prototyped for cognitive radio usage in the Industrial, Scientific and Medical (ISM) band using time domain as well as frequency domain detection. Duty cycle and pulse width characteristics are used for detection in the time domain. Fast Fourier Transform (FFT) signatures and spectral occupancy information is used to confirm the detection in the frequency domain. The detection module is designed to behave dynamically. Varying the input parameters to the detector module adjusts the detection overhead. The overhead varies depending on the relative usage of a fast detection algorithm versus a slower but more accurate scheme; the number of device types to be detected; and whether frequency-selective scanning or wide-band detection is needed. The prototype is built on a software radio platform and is targeted for future Software Defined Radios (SDR), and can be adapted to current and future Orthogonal Frequency Division Multiplexed (OFDM) systems.

Symbol shaping for Barker spread Wi-Fi communications

This paper details the progressive development of symbol shaping for Barker spread IEEE 802.11 modulation used in wireless fidelity communications. Symbol shaping is used to satisfy the spectral mask requirements of the Federal Communications Commission (FCC) with minimal output filtering and inter-symbol interference. Logarithmic, sinusoidal, and sine-function shaping is investigated using analytic, simulation, and experimental methods. Power spectral densities are compared to the FCC mask to determine the effectiveness of the symbol shaping. Bit error rate is evaluated to provide a performance metric for each symbol shape. A complete experimental system has been implemented as a test bed for this research.