Dynamic spectrum access is a promising approach to alleviate the spectrum scarcity that wireless communications face today. In short, it aims at reusing sparsely occupied frequency bands while causing no (or insignificant) interference to the actual licensees. This article focuses on applying this concept in the time domain by exploiting idle periods between bursty transmissions of multi-access communication channels and addresses WLAN as an example of practical importance. A statistical model based on empirical data is presented, and it is shown how to use this model for deriving access strategies. The coexistence of Bluetooth and WLAN is considered as a concrete example

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COGNITIVE RADIOS FOR DYNAMIC SPECTRUM ACCESS - Dynamic Spectrum Access in the Time Domain: Modeling and Exploiting White Space

Most existing studies of spectrum usage have been performed by actively sensing the energy levels in specific RF bands including cellular bands. In this paper, we provide a unique, complementary analysis of cellular primary usage by analyzing a dataset collected inside a cellular network operator. One of the key aspects of our dataset is its scale - it consists of data collected over three weeks at hundreds of base stations. We dissect this data along different dimensions to characterize and model primary usage as well as understand its temporal and spatial variations. Our analysis reveals several results that are relevant if dynamic spectrum access (DSA) approaches are to be deployed for cellular frequency bands. For instance, we find that call durations show significant deviations from the often- used exponential distribution, which makes call-based modeling more complicated. We also show that a random walk process, which does not use call durations, can often be used for modeling the aggregate cell capacity. Furthermore, we highlight some applications of our results to improve secondary usage of licensed spectrum.

http://www.tkn.tu-berlin.de/fileadmin/fg112/Papers/dyspan08_measurement-study.pdf

Primary Users in Cellular Networks: A Large-Scale Measurement Study

Spectrum occupancy models are very useful in cognitive radio designs. They can be used to increase spectrum sensing accuracy for more reliable operation, to remove spectrum sensing for higher resource usage efficiency, or to select channels for better opportunistic access, among other applications. In this survey, various spectrum occupancy models from measurement campaigns taken around the world are investigated. These models extract different statistical properties of the spectrum occupancy from the measured data. In addition to these models, spectrum occupancy prediction is also discussed, where autoregressive and/or moving-average models are used to predict the channel status at future time instants. After comparing these different methods and models, several challenges are also summarized based on this survey.

/pdf/a-survey-of-measurement-based-spectrum-occupancy-modeling-5h1rhm2b34.pdf

A Survey of Measurement-Based Spectrum Occupancy Modeling for Cognitive Radios

Dynamic spectrum access networks and wireless spectrum policy reforms heavily rely on accurate spectrum utilization statistics, which are obtained via spectrum surveys. In this paper, we propose a generic spectrum-surveying framework that introduces both standardization and automation to this process, as well as enables a distributed approach to spectrum surveying. The proposed framework outlines procedures for the collection, analysis, and modeling of spectrum measurements. Furthermore, we propose two techniques for processing spectrum data without the need for a priori knowledge. In addition, these techniques overcome the challenges associated with spectrum data processing, such as a large dynamic range of signals and the variation of the signal-to-noise ratio across the spectrum. Finally, we present mathematical tools for the analysis and extraction of important spectrum occupancy parameters. The proposed processing techniques have been validated using empirical spectrum measurements collected from the FM, television (TV), cellular, and paging bands. Results show that the primary signals in the FM band can be classified with a miss-detection rate of about 2% at the cost of 50% false-alarm rate, while nearly 100% reliability in classification can be achieved with the other bands. However, the classification accuracy depends on the duration and the range of frequencies over which data are collected, as well as the RF characteristics of the spectrum measurement receiver.

A Spectrum Surveying Framework for Dynamic Spectrum Access Networks

While dedicated spectrum occupancy monitoring provides vital information for frequency planning and management, it usually cannot tell the common properties in spectrum occupancy. As a complement, the models approach can be used to describe and compare the occupancy situations under similar conditions. Time series analysis has been applied to modeling the radio spectrum occupancy. This paper categorizes different time series models to different occupancy patterns. Occupancy analysis of the Global System for Mobile communications (GSM) band is given as an example.

Spectrum Occupancy Statistics and Time Series Models for Cognitive Radio

A long-term joint UK-Swedish-German project has been undertaken on the measurement and analysis of HF spectral occupancy over northern Europe. This has resulted in an extensive database of spectral occupancy measurements made at four sites over a complete sunspot cycle, and mathematical models for spectral occupancy have been developed. The procedures for measuring and modelling spectral occupancy are briefly presented, with final stable-day and stable-night models for northern Europe, when using calibrated monopole antennas. Accuracy of fit and examples of extrapolation in time and in space are presented.

Models of HF spectral occupancy over a sunspot cycle

The authors examine mathematical modelling of occupancy for the entire high-frequency (HF) spectrum. The theory of modelling the experimental occupancy data is presented, and an example of the modelling procedures is given. Occupancy has been measured as congestion values for each International Telecommunications Union (ITU) frequency allocation across the entire HF spectrum. Congestion is defined as the fraction of signal-strength observations across each allocation for which the signal exceeds a defined threshold.

https://ieeexplore.ieee.org/iel1/2191/12591/00580374.pdf

Development of the Laycock-Gott occupancy model

Since 1982, the Digital Communications Group at UMIST has systematically measured and analysed the occupancy of the HF spectrum. The authors describe the measurement system and measurement procedure, and give mathematical models for solstice day and night occupancy across the whole HF spectrum.

High frequency spectral occupancy at the solstices

The paper investigates the use of differential modulation techniques to achieve high rate data transmission by near vertical incidence sky wave high frequency propagation, using a 2.7 kHz voice channel bandwidth. Channel characteristics have been measured for a range of frequencies between 2.8 and 9.4 MHz, using a transmitter power of 100 W over a distance of 160 km. These measurements are used to characterise simulated channel conditions, and the simulator is then used to determine the performances of differential modulation methods. In particular, time-differential amplitude and phase shift keying and frequency-differential amplitude and phase shift keying modulation methods are investigated. Symbol error rates are presented for data rates ranging from 4.3 to 20.6 kbit/s, where the system performances are limited by time-varying channel dispersion rather than by additive noise.

High rate data transmission in the mid-latitude NVIS HF channel

Since 1982, a long term programme has been undertaken at UMIST to measure and analyse spectral occupancy across the entire HF band 1.6-30 MHz. The aim of the work is to provide experimental data and mathematical models, showing how occupancy varies with frequency, time, bandwidth, threshold level, type of user allocation, antenna, and geographical location. From 1982 to 1989, the measurement site was RSRE, Pershore, Worcestershire, a rural site in central England which was available at the times of the solstices. In 1989, a dedicated measurement system was installed at the Radiocommunications Agency monitoring site, at Baldock, Hertfordshire. A data link between UMIST and Baldock enables system control and transfer of results. In 1990, an identical measurement system was set up by the Swedish National Defence Research Establishment at LinkSping, Sweden, and an agreement made for the simultaneous operation of the two sites, and for data exchange. In 1993 a third system was installed by UMIST and DRA at the antenna site of Rohde and Schwarz near Munich, Germany, again linked to UMIST for control and data transfer. These three sites are approximately at the corners of an equilateral triangle of side length 11000 km, and provide effective measurement of spectral occupancy over northern Europe. The introduction of automatic systems has meant that occupancy measurements are not restricted to the solstices, and this paper is based on results taken at more frequent time intervals.

https://ieeexplore.ieee.org/iel3/1166/7915/00336999.pdf

G.F. Gott

Papers

Models of HF spectral occupancy over a sunspot cycle

Development of the Laycock-Gott occupancy model

High frequency spectral occupancy at the solstices

High rate data transmission in the mid-latitude NVIS HF channel

Recent work on the measurement and analysis of spectral occupancy at HF