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High resolution wideband spectrum sensing

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Adnan Ahmad Cheema
added 2 research items
High time resolution spectrum occupancy measurements and analysis are presented for 2.4 GHz WLAN signals. A custom-designed wideband sensing engine records the received power of signals, and its performance is presented to select the decision threshold required to define the channel state (busy/idle). Two sets of measurements are presented where data were collected using an omni-directional and directional antenna in an indoor environment. Statistics of the idle time windows in the 2.4 GHz WLAN are analyzed using a wider set of distributions, which require fewer parameters to compute and are more practical for implementation compared to the widely-used phase type or Gaussian mixture distributions. For the omni-directional antenna, it was found that the lognormal and gamma distributions can be used to model the behavior of the idle time windows under different network traffic loads. In addition, the measurements show that the low time resolution and angle of arrival affect the statistics of the idle time windows.
An ultra-wideband (UWB) digital frequency modulated continuous wave (FMCW) sensing engine is proposed as an alternative technique for cognitive radio applications. A dual band demonstrator capable of sensing 750 MHz bandwidth in 204.8 µs is presented. Its performance is illustrated from both bench tests and from real time measurements of the GSM 900 band and the 2.4 GHz WLAN band. The measured sensitivity and noise figure values are -90 dBm for a signal-to-noise ratio margin of at least 10 dB and ~13-14 dB, respectively. Data were collected over 24 hours and were analyzed using the energy detection method. The obtained results show the time variability of occupancy and considerable sections of the spectrum are unoccupied. In addition, unlike the cyclic temporal variations of spectrum occupancy in the GSM 900 band, the detected variations in the 2.4 GHz WLAN band have an impulsive nature.