Kenneth J. Zdunek

Performance and Optimization of Switched Diversity Systems for the Detection of Signals with Rayleigh Fading

The performance and optimization of switched diversity systems are considered. First, the one-dimensional distribution and probability density functions of the envelope of the received signal are obtained for three different switching strategies. This information is used to obtain the average probability of bit error for the case of non-coherent detection of binary FSK signals with Rayleigh fading envelopes and additive white Gaussian noise. The optimization of two of these switching strategies is then considered, and it is shown that by proper selection of switching thresholds, the average probability of bit error during detection can be minimized. It is also shown that these optimized switching strategies yield a significant improvement in performance over non-diversity systems and can approach the performance of more complex receivers such as maximal ratio combining. Computer simulations of switched diversity systems using a practical field model are used to verify the analysis.

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.

Packet radio performance of inhibit sense multiple access with capture

Current portable and land-mobile radio systems employ frequency modulation which exhibits a distinct capture effect. Furthermore, multipath propagation, shadowing, and the spatial distribution of the terminal units create data packets with varying signal strength. We investigate the performance of nonpersistent inhibit sense multiple access (ISMA) applied to the forward channel of packet radio communication networks. We show that the aggregate capacity of ISMA substantially increases compared to the noncapture case for small capture ratios. The mean packet delay of ISMA is also reduced with capture. The effect of different signal strength distribution is explored, and the capacity and delay improvements discussed.

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.

A packet radio network using inhibit sense multiple access with capture

The throughput and delay of the mobile-to-base channel of a packet radio network employing a nonpersistent inhibit sense multiple access (ISMA) technique are investigated using analysis and discrete event simulation. Land-mobile packet radio networks typically employ frequency modulation, which exhibits a distinct capture effect. The capture phenomenon and the distribution of received packet amplitudes caused by propagation losses and multipath effects allow a packet sent on the mobile-to-base channel to be successfully received in the presence of interfering packets. It is found that, under these conditions, the capacity of ISMA can be substantially higher than that of the same protocol without capture. Furthermore, at high channel loading, the packet delivery delay of ISMA with capture is noticeably smaller than the delay of a channel without capture. The particular distribution of received packet signal strengths is a key factor in determining the throughput characteristic with capture. Reducing the capture ratio by choice of modulation technique and error control is therefore a step that system designers can take to improve the capacity of packet radio systems.<<ETX>>

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.

Multiple channel inhibit sense multiple access with capture

The throughput and delay of the uplink of a metropolitan area packet radio network employing nonpersistent, multiple-channel inhibit-sense-multiple-access (MC-ISMA) with capture are investigated using analysis and discrete event simulation. Both nonslotted and slotted MC-ISMA protocols are shown to produce improvements in throughput of up to 400% compared to the respective ISMA protocols using multiple channels independently, depending on the delay performance criteria. Land-mobile packet radio networks typically employ frequency modulation, which exhibits a distinct capture effect and allows singlechannel ISMA to deliver capacities from 8% to 37% higher than without capture. The effects of the MC-ISMA protocol and capture are shown to combine to produce larger performance improvements than either one alone.<<ETX>>