Block diagram of the proposed rapid estimation method: the first block collects information on , , geolocation, and time stamp. The second block detects Primary Users (PU) and unused channels, stochastic and mathematical information, and Receiver Operation Characteristics (ROC). The third block applies the rapid method to estimate Television White Spaces (TVWS).
TV-UHF spectrum samples were collected by using two Radio Frequency Explorer (RFE) devices in parallel, one to characterize the noise signal and another to collect the composite signal , together with a GPS receptor antenna to geolocate the readings. Each reading consisted of 112 samples for the composite signal and 112 samples for noise. The separation between two samples was 1.76 MHz, and all 112 samples covered 198 MHz, which is the TV-UHF bandwidth.
Example measurements: (a) noise of the system, ; (b) composite signal sensed, ; and (c) the presence of the PU clearly observed when ten sampled points overlapped in order to illustrate the behaviour of the UHF TV spectrum in the sensed area.
Spatiotemporal map of the spectrum sensed in our area of interest.
Different values for threshold are plotted to show that produces missed detection of real PU signals and that produces some noise signals which are be considered PUs. In both cases, there are errors in the obtained results. An adequate value for T is plotted, which maintains enough distance from the noise floor to avoid false alarms and missed detection. This equilibrium is obtained when T considers a of .
Channels detected as used are coloured in gray, whereas channels considered as TVWS are in white. Channel 37 is in yellow because it is assigned for other purposes. Panels (a–c) correspond to points 1–3, respectively.
Collected signal representation: (a) the Probability Density Function (PDF) of is represented in blue, the PDF of is plotted with a magenta dotted line, and the PDF of is plotted with red dotted line. Notice that and curves have the same means and standard deviations; (b) the normal PDF curves of , , and lines labelled as I and T delimit four areas under the curve (AUC). It is possible to identify in green, in blue, in orange, the in gray.
ROC curve where is the input and is calculated: panel (a) shows a single ROC, and panel (b) shows the overlapped ROC curves from ten different points sensed.
Two-point readings are plotted, for which panels (a,d) represent the signal sensed. In panels (b,e), the PDF representations for and are presented, and panels (c,f) illustrate their respective Receiver Operation Characteristics (ROC) curves, where we can observe different patterns.
Diagram of the rapid estimation method proposed that shows the data flow process: Data collected by the Mobil Spectrum Sensing Station (MSSS) are combined and fed into three sub-blocks, namely, the Energy Detection (ED), the Statistical Analysis (SA), and the ROC Analysis (RA). The output of these blocks is introduced in the Rapid Estimation Method (REM) block to obtain an estimation of the TVWS (E-TVWS).
Energy Detection (ED) results for points 1 and 6: (a) point 1, with 10 used channels, which are 35, 38, 40, 41, 42, 43, 44, 45, 47, and 48, means 32.25% usage and (b) point 6, with 15 used channels, which are 20, 21, 26, 31, 32, 38, 39, 40, 41, 42, 43, 44, 45, and 49, means 46.87% usage.
Statistical Analysis (SA) results for example points: (a) PDFs of ten points that are overlapped. It is easy to observe that each point corresponds to different PDF curves. The shape variation is related to the number of energy peaks detected in the ED block. (b) ROC curves overlapped for points 1 to 10, where the horizontal axis scale has been modified to observe the variation in for a , shown by the green arrows.
REM parameters were used to find the estimation of the TVWS (E-TVWS), where sensed parameters are obtained by the MSSS, whereas calculated and auxiliary parameters are obtained by the signal analysis block.
In the plot that represents the PDF of the sensed signals, we draw a reference line named , which is defined by a Z-score that separates 99% vs. 1% of the AUC of . Additionally, we observe its distance from T, I, , and , denoted as , , and , respectively.
PDFs of sensed parameters and showing calculated parameters , , and T as well as auxiliary parameters I and for points P1 (a) to P9 (i).
Extreme cases analyzed: (a) ROC curves for Scenarios 1 and 2 in full scale; (b) extreme ROC curves for Scenarios 1 and 2 vs. the curves for points P1 to P10. Green arrows indicates the upper and lower limits for corresponding to 3% to find E-TVWS.
RFE technical characteristics.
|1||Frequency Range||240 MHz to 960 MHz|
|2||Span||0.112 MHz to 300 MHz|
|3||Frequency Resolution||1 kHz|
|4||Average Noise Level||−115 dBm|
|5||Amplitude Resolution||0.5 dBm|
|6||Automatic RBW||2.6 kHz to 600 kHz|
Tabulated results obtained from the ED, SA, and RA blocks.
Distance measured from different statistical parameters.
Auxiliary parameters used in the REM.
Tabulated results obtained from simulated Scenarios 1 and 2.
Confusion Matrix results for and .
| || ||Average||93.81|
TVWS decision matrix: PU presence, channel numbers to identify them, percentage in the band of interest, and preferred order to be assigned.
|PU Presence (%)||Channels||TV-UHF Band||TVWS Preferred Order|
|19, 22, 23, 24, 27, 30, 33, 34, 36, 51||31.25%||1|
| ||28, 29, 35, 46, 47, 48||18.75%||2|
| ||20, 25|| 6.25%||3|
| ||26|| 3.13%||4|
| ||21, 31, 32, 38, 39, 49, 50||21.87%||5|
|40, 41, 42, 43, 44, 45||18.75%||6|
Results of the tested point.