Advances in cognitive radio networks: A survey <s> Measurements-Based Sensing and Modeling: <s> 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. <s> BIB001 </s> Advances in cognitive radio networks: A survey <s> Measurements-Based Sensing and Modeling: <s> This paper describes the development, deployment and early results of a long-term, wide-band (30 MHz - 6 GHz) spectrum observatory system focused on downtown Chicago and the immediately surrounding areas. Previous short term studies have indicated that more than 80% of the spectral capacity may be unused, even in United States urban centers. The goals of this research effort include the validation of these early results, the understanding of trends in spectral usage over long periods (years), the observation of usage patterns and anomalies, and the detection of the positions of spectral "holes" in time and space. The current status in the attainment of these goals will be shared in this paper. This information, once obtained, vetted and appropriately analyzed will be extremely useful in the development of cognitive radios and other dynamic access network systems, and in the proper establishment of policies and regulations to govern the deployment of such systems. <s> BIB002
By collecting data over a long period of time at many base stations, BIB001 provides a unique analysis of cellular primary usage. The collected data is dissected along different dimensions to characterize the primary usage. With the aid of spectrum observatory, BIB002 extends short-term spectrum usage measurements to study the spectrum usage trend over long periods, observes spectrum usage patterns, and detects the positions of spectrum white space in time and spatial domains. Such information can be greatly helpful in developing good dynamic access protocols and governing secondary systems.