Systems and method for frequency based satellite channel scanning
A satellite signal demodulator is configured to use frequency-based channel scanning to sense the presence of a channel and to obtain the frequency profile of the channel. Once the channel is identified and the profile is obtained, channel extraction is used to identify the frequency parameters for a given channel. A coarse parameter estimation is performed to obtain a coarse estimate of the symbol rate (SR) and the center frequency (f c ) of the channel. The coarse estimation can then be followed by a fine estimation of the symbol rate and center frequency (f c ), using a bit tracking loop (BTL) lock indicator.
1. A method for frequency based channel scanning comprising:
placing a demodulator in a power scanning mode;
scanning a frequency spectrum to obtain power samples at a plurality of frequencies;
comparing the power samples to a threshold power to detect a channel, wherein the detected channel comprises a flat area, a left point of inflection, and a right point of inflection;
performing channel extraction once the channel is detected; and
obtaining a coarse estimate of the channel parameters associated with the detected channel, wherein obtaining the coarse estimate comprises measuring power at three separate frequencies for the left point of inflection for the channel.
2. The method of claim 1 , wherein the three frequencies are defined as f_center−Δf, f_center, and f_center+Δf, and wherein the associated power of these three frequencies is defined as power_left, power_center, and power_right.
3. The method of claim 2 , wherein the channel further comprises a concave cup region and a convex cap region, and wherein it is determined that the demodulator is sampling the channel in the concave cup region when power_center>0.5*(power_left+power_right).
4. The method of claim 2 , wherein it is determined that the demodulator is operating in the convex cap region when power_center<0.5*(power_left+power_right).
5. The method of claim 2 , wherein it can be determined that f_center is the left point of inflection when power_center=0.5(power_left+power_right).
6. The method of claim 2 , wherein the left inflection point is determined using multiple readings.
7. The method of claim 6 , wherein the multiple readings comprise three sets of equi-spaced points, each set containing more than one power reading in the frequency domain.
8. The method of claim 1 , wherein obtaining a coarse estimate comprises measuring the power at three separate frequencies in order to determine a right point of inflection for the channel.
9. The method of claim 8 , wherein the three frequencies are defined as f_center−Δf, f_center, and f_center+Δf, and wherein the associated power of these three frequencies is defined as power_left, power_center, and power_right.
10. The method of claim 9 , wherein the channel further comprises a concave cup region and a convex cap region, and wherein it is determined that the demodulator is sampling the channel in the concave cup region when power_center>0.5*(power_left+power_right).
11. The method of claim 9 , wherein it is determined that the demodulator is operating in the convex cap region when power_center<0.5*(power_left+power_right).
12. A receiver configured to act in a power scanning mode, comprising:
a demodulator configured to receive a satellite signal;
a power measurement circuit configured to determine frequency and power information for signals received by the demodulator and to compare the power information to a threshold power; and
a processor configured to control the demodulator and the power measurement circuit and to determine signal rate and channel center frequency parameters based on the frequency and power information determined by the power measurement circuit if the power information is equal to or greater than the threshold power, to place the demodulator in a power scanning mode, to scan a frequency spectrum to obtain power samples at a plurality of frequencies until a channel is detected by comparing the power samples to the threshold power, to perform channel extraction once the channel is detected, and to obtain a coarse estimate of the channel parameters associated with the detected channel, wherein the detected channel comprise a flat area, a left point of inflection, and a right point of inflection, and wherein obtaining the coarse estimate comprises measuring power at three separate frequencies for the left point of inflection for the channel.
13. The receiver of FIG. 12 , wherein the demodulator comprises a matched filter, and wherein the processor is configured to place the demodulator in the power scanning mode by controlling the operation of the matched filter.
14. The receiver of claim 13 , wherein the processor is configured to place the demodulator into a power scanning mode by controlling the matched filter to act as an anti-aliasing filter.
15. The receiver of claim 14 , wherein the processor is configured to place the demodulator into the power scanning mode by also setting the bandwidth of the demodulator to a maximum and causing the matched filter to be clocked at a clocking rate that is different from a symbol clocking rate.
16. The receiver of claim 13 , wherein the power measurement circuit comprises a phase rotator bank coupled with the matched filter, the phase rotator bank configured to accept a single input, both I and Q, from the output of matched filter and to produce multiple outputs corresponding to various frequency rotations.
17. The receiver of claim 16 , wherein the phase rotator bank is configured to accept data from the matched filter at a clocking rate used to clock the matched filter.
18. A receiver configured to act in a power scanning mode, comprising:
a demodulator configured to receive a satellite signal;
a power measurement circuit configured to determine frequency and power information for signals received by the demodulator; and
a processor configured to place the demodulator in a power scanning mode, to scan the frequency spectrum to obtain power samples at a plurality of frequencies, until a channel is detected by comparing the power samples to a threshold power, to perform channel extraction once a channel is detected, and to obtain a coarse estimate of the channel parameters associated with the detected channel, wherein the detected channel comprises a flat area, a left point of inflection, and a right point of inflection, and wherein obtaining the coarse estimate comprises measuring power at three separate frequencies for the left point of inflection for the channel.