Stable modulation index calibration and dynamic control
View Patent ↗Calibrating a Gaussian frequency-shift keying modulation index includes generating a training sequence of bits, shaping a pulse from the training sequence according to an initial modulation index, and converting the shaped signal to a transmission signal. The transmission signal is then either looped through a radio frequency core or processed by frequency deviation estimation hardware to determine a frequency deviation. The frequency deviation is converted to a new modulation index, and potentially a ratio between a target modulation index and a measured modulation index as a scaling factor. The process is then iteratively repeated until a threshold frequency deviation is achieved.
1. A circuit comprising:
a signal generator that produces a training bit sequence;
a pulse shaping element that produces a shaped signal from the training bit sequence and a target modulation index value;
a baseband transmitter that produces a transmission signal from the shaped signal;
a frequency deviation estimator that determines a frequency deviation of the transmission signal; and
a modulation index value estimator that determines an updated modulation index value from the frequency deviation and updates the modulation index value used by the pulse shaping element;
wherein the circuit iteratively produces updated modulation index values until the frequency deviation is within an acceptable range.
2. The circuit of claim 1 , further comprising a radio frequency core that receives the transmission signal, wherein the frequency deviation estimator receives a radio frequency signal from the radio frequency core.
3. The circuit of claim 1 , wherein the modulation index value estimator further produces a ratio of the target modulation index value to the updated modulation index value.
4. The circuit of claim 3 , wherein the ratio comprises a scaling factor for the pulse shaping element.
5. The circuit of claim 1 , wherein the circuit iteratively determines frequency deviations and the modulation index value estimator produces an average frequency deviation over two or more iterations.
6. The circuit of claim 1 , wherein the training bit sequence comprises alternating groups of uniform bits of identical length.
7. A device comprising:
a modulator comprising:
a signal generator that produces a training bit sequence;
a pulse shaping element that produces a shaped signal from the training bit sequence and a target modulation index value; and
a baseband transmitter that produces a transmission signal from the shaped signal;
a demodulator comprising:
a frequency deviation estimator that determines a frequency deviation of the transmission signal; and
a modulation index value estimator that determines an updated modulation index value from the frequency deviation and updates the modulation index value used by the pulse shaping element;
wherein the device iteratively produces updated modulation index values until the frequency deviation is within an acceptable range.
8. The device of claim 7 , further comprising a radio frequency core that receives the transmission signal, wherein the frequency deviation estimator receives a radio frequency signal from the radio frequency core.
9. The device of claim 7 , wherein the modulation index value estimator further produces a ratio of the target modulation index value to the updated modulation index value.
10. The device of claim 9 , wherein the ratio comprises a scaling factor for the pulse shaping element.
11. The device of claim 7 , wherein the device iteratively determines frequency deviations and the modulation index value estimator produces an average frequency deviation over two or more iterations.
12. The device of claim 7 , wherein the training bit sequence comprises alternating groups of uniform bits of identical length.
13. A method comprising:
producing a training bit sequence;
producing a shaped signal from the training bit sequence and a target modulation index value;
producing a transmission signal from the shaped signal;
determining a frequency deviation of the transmission signal;
determining an updated modulation index value from the frequency deviation;
updating the modulation index value used to produce the shaped signal; and
iteratively producing updated modulation index values until the frequency deviation is within an acceptable range.
14. The method of claim 13 , further comprising looping the transmission signal through a radio frequency core.
15. The method of claim 13 , further comprising producing a ratio of the target modulation index value to the updated modulation index value.
16. The method of claim 15 , wherein the ratio comprises a scaling factor for a subsequent shaped signal.
17. The method of claim 13 , further comprising iteratively determining frequency deviations and producing an average frequency deviation over two or more iterations.