Tracking short-term maximum power spectrum density for improved visibility of low duty cycle signals
A method is provided for analyzing activity in a frequency band that improves over conventional spectrum analyzers by providing the ability to visualize signals or energy with short duty cycles. During a time interval, a sequence of short-time power spectrum estimates is computed for energy received in said frequency band. Each short-time power spectrum estimate comprises data representing power of the received energy at each of a plurality of frequency bins that span a frequency sub-band at different time instants during the time interval. Data associated with the sequence of power spectrum estimates is accumulated. This process is repeated for each of a plurality of different sub-bands that span a frequency band of interest. As a result, activity can be observed in the frequency band of interest over relatively short time intervals, even if the activity has a short duty cycle.
1 . A method for analyzing wireless activity in a frequency band, comprising:
a. during a time interval, computing a sequence of short-time power spectrum estimates for energy received in said frequency band, each short-time power spectrum estimate comprising data representing power of the received energy at each of a plurality of frequency bins that span a frequency sub-band at different time instants during said time interval; and
b. accumulating data associated with said sequence of power spectrum estimates.
2 . The method of claim 1 , wherein (a) computing comprises computing a sequence of a plurality of short-time frequency transforms for energy received in said frequency band, each short-time frequency transform spanning said frequency sub-band but taken at said different time instants to produce said short-time power spectrum estimate.
3 . The method of claim 1 , and further comprising, for each frequency bin associated with the short-time power spectrum estimates, storing a value representing the maximum power that has occurred in each frequency bin in said sequence.
4 . The method of claim 1 , and further comprising generating data for displaying a trace representing the power values for each frequency bin over time.
5 . The method of claim 1 , and further comprising performing (a) computing during each of a plurality of time intervals, wherein the sequence of short-time power spectrum estimates during a time interval spans the same frequency sub-band, but the frequency sub-band is different across the plurality of time intervals.
6 . The method of claim 5 , wherein (a) computing comprises computing the sequence of short-time power spectrum estimates during the plurality of time intervals across the plurality of frequency sub-bands which are substantially contiguous and span a frequency band of interest.
7 . The method of claim 5 , wherein (b) accumulating comprises accumulating data associated with each of the sequences of short-time power spectrum estimates during each of the plurality of time intervals.
8 . The method of claim 7 , and further comprising, for each time interval, storing a value representing the maximum power that has occurred in each frequency bin over the sequence of short-time power spectrum estimates during that time interval.
9 . The method of claim 8 , and further comprising generating data for displaying a trace representing the power values for each frequency bin over time.
10 . The method of claim 1 , wherein said (a) computing comprises computing a sequence of short-time Fourier transforms.
11 . The method of claim 1 , wherein said (a) computing further comprises discarding some of the short-time power spectrum estimates.
12 . The method of claim 1 , wherein said (a) computing comprises computing said sequence of short-time power spectrum estimates such that they at least partially overlap in time.
13 . A device, comprising:
a. a radio receiver that receives wireless energy in a frequency band and produces a receive signal representative thereof;
b. an analog-to-digital converter coupled to the radio receiver that converts the receive signal to digital data;
c. a power spectrum computation circuit coupled to the analog-to-digital converter that computes short-time power spectrum estimates for energy received in said frequency band from the digital data; and
d. a control unit connected to said power spectrum computation circuit and to said radio receiver, wherein the control unit controls the power spectrum computation circuit to compute a sequence of short-time power spectrum estimates for energy received in said frequency band, each short-time power spectrum estimate comprising data representing power of the received energy at each of a plurality of frequency bins that span a frequency sub-band at different time instants during said time interval.
14 . The device of claim 13 , wherein said power spectrum computation circuit computes short-time frequency transforms for energy in said frequency sub-band of said frequency band, each short-time frequency transform spanning said frequency sub-band but taken at said different time instants to produce said short-time power spectrum estimate.
15 . The device of claim 13 , wherein said control unit stores, for each frequency bin associated with the short-time power spectra estimates, data representing the maximum power that has occurred in that frequency bin in said sequence.
16 . The device of claim 13 , wherein said control unit controls the power spectrum computation circuit to compute the sequence of short-time power spectrum estimates during each of a plurality of time intervals, wherein the sequence of short-time power spectrum data during a time interval spans the same frequency sub-band, but the frequency sub-band is different across the plurality of time intervals.
17 . The device of claim 13 , wherein said control unit controls the power spectrum computation circuit to compute the sequence of short-time power spectrum estimates during the plurality of time intervals across the plurality of frequency sub-bands which are substantially contiguous and span a frequency band of interest.
18 . The device of claim 17 , wherein said control unit stores data associated with each of the sequences of short-time power spectrum estimates during each of the plurality of time intervals.
19 . The device of claim 18 , wherein said control unit stores, for each time interval, data representing the maximum power that has occurred in each frequency bin over the sequence of short-time power spectrum estimates during that time interval.
20 . The device of claim 13 , wherein said power spectrum computation circuit computes short-time Fourier transforms to produce said short-time power spectrum estimates.
21 . A processor readable medium storing instructions, that when executed by a processor, cause the processor to perform functions of:
a. during a time interval, computing a sequence of short-time power spectrum estimates for energy received in said frequency band, each short-time power spectrum estimate comprising data representing power of the received energy at each of a plurality of frequency bins that span a frequency sub-band at different time instants during said time interval; and
b. accumulating data associated with the sequence of power spectrum estimates.
22 . The processor readable medium of claim 21 , and further comprising instructions that, when executed by a processor, cause the processor to, for each frequency bin associated with the sequence of short-time power spectrum estimates, store a value representing the maximum power that has occurred in each frequency bin in said sequence.
23 . The processor readable medium of claim 22 , and further comprising instructions that, when executed by a processor, cause the processor to generate data for displaying a trace representing the values for each frequency bin over time.
24 . The processor readable medium of claim 21 , wherein said instructions for computing comprise instructions that cause the processor to compute the sequence of short-time power spectrum estimates during each of a plurality of time intervals, wherein the sequence of short-time power spectrum estimates during a time interval spans the same frequency sub-band, but the frequency sub-band is different across the plurality of time intervals.
25 . The processor readable medium of claim 24 , wherein said instructions for computing comprise instructions that cause the processor to compute the sequence of short-time power spectrum estimates during the plurality of time intervals across the plurality of frequency sub-bands which are substantially contiguous and span a frequency band of interest.
26 . The processor readable medium of claim 25 , and further comprising instructions, that when executed by the processor, cause the processor to store a value representing the maximum power that has occurred in each frequency bin over during each of the plurality of time intervals.
27 . The processor readable medium of claim 26 , and further comprising instructions, that when executed by the processor, cause the processor to generate data for displaying a trace over time representing the maximum power at each frequency bin.
28 . The processor readable medium of claim 21 , wherein said instructions for computing comprise instructions that cause the processor to compute a sequence of short-time Fourier transforms.
29 . The processor readable medium of claim 21 , wherein said instructions for computing comprise instructions that cause the processor to discard some of the short-time power spectrum estimates.
30 . processor readable medium of claim 21 , wherein said instructions for computing comprise instructions that cause the processor to compute the sequence of short-time power spectrum estimates such that they at least partially overlap in time.