Methods and apparatus for reducing the average-to-minimum magnitude ratio of communications signals in communications transmitters
View Patent ↗A communications transmitter configured to reduce the average-to-minimum magnitude ratio (AMR) of a communications signal includes a symbol mapper, a pulse-shaping filter, an AMR reduction circuit, and a modulator. The symbol mapper operates to generate a sequence of symbols from a binary-source data stream containing a message to be transmitted, and the pulse-shaping filter generates a baseband signal based on the sequence of symbols. The AMR reduction circuit is configured to compare magnitudes of samples of the baseband signal to a time-varying low-magnitude threshold, and modify the baseband signal to produce a modified baseband signal having a reduced AMR if a sample of the baseband signal is determined to have a magnitude less than the time-varying low-magnitude threshold. Finally, the modulator operates to modulate a carrier signal based on the modulation information contained in the modified baseband signal.
1. A communications transmitter, comprising:
a symbol mapper configured to generate a sequence of symbols from a binary-source data stream containing a message to be transmitted;
a pulse-shaping filter configured to generate a baseband signal based on said sequence of symbols;
an average-to-minimum magnitude ratio (AMR) reduction circuit configured to compare magnitudes of samples of said baseband signal to a time-varying low-magnitude threshold that is varied at a rate equal to or dependent on a rate at which the symbol mapper generates the sequence of symbols, and modify said baseband signal to produce a modified baseband signal having a reduced AMR if a sample of said baseband signal is determined to have a magnitude less than said time-varying low-magnitude threshold; and
a modulator configured to modulate a carrier signal based on modulation information contained in said modified baseband signal.
2. A method of reducing the average-to-minimum magnitude ratio (AMR) of a baseband signal in a communications transmitter, comprising:
generating a sequence of symbols from a binary-source data stream containing a message to be transmitted;
pulse shaping said sequence of symbols to form a baseband signal;
sampling said baseband signal;
setting a time-varying low-magnitude threshold;
varying the time-varying low-magnitude threshold at a rate equal to or dependent on a rate at which the sequence of symbols are generated;
detecting whether samples of said baseband signal have a magnitude less than said time-varying low-magnitude threshold; and
upon detecting a sample of said baseband signal having a magnitude less than said time-varying threshold, modifying said baseband signal to produce a modified baseband signal having a lower AMR than said baseband signal.
3. A baseband circuit for a communications transmitter, comprising:
a threshold setting circuit configured to generate a time-varying low-magnitude threshold at a rate equal to or dependent on a rate at which symbols representing the baseband signal are generated or received by the threshold setting circuit;
a local minimum detector configured to compare magnitudes of samples of a baseband signal to said time-varying low-magnitude threshold;
a circuit configured to generate an insertion pulse in response to said local minimum detector detecting a low-magnitude sample having a magnitude less than said time-varying low-magnitude threshold, and combine said insertion pulse with said baseband signal in the temporal vicinity of the detected low-magnitude sample to produce a modified baseband signal having a lower average-to-minimum magnitude ratio than that of said baseband signal.
4. The communications transmitter of claim 1 wherein said AMR reduction circuit includes a threshold setting circuit configured to generate said time-varying low-magnitude threshold as a function of one or more symbols in said sequence of symbols.
5. The communications transmitter of claim 4 wherein said function depends on a magnitude or magnitudes of said one or more symbols.
6. The communications transmitter of claim 4 wherein said function is a linear function of said one or more symbols.
7. The communications transmitter of claim 4 wherein said function is a non-linear function of said one or more symbols.
8. The communications transmitter of claim 1 wherein said AMR reduction circuit includes a threshold setting circuit configured to generate said time-varying low-magnitude threshold as a function of one or more samples of said baseband signal.
9. The communications transmitter of claim 8 wherein said function depends on a magnitude or magnitudes of said one or more samples.
10. The communications transmitter of claim 8 wherein said function is a linear function of said one or more samples.
11. The communications transmitter of claim 8 wherein said function is a non-linear function of said one or more samples.
12. The communications transmitter of claim 1 wherein said modulator comprises a polar modulator.
13. The communications transmitter of claim 1 wherein said modulator comprises a quadrature modulator.
14. The method of claim 2 wherein said time-varying low-magnitude threshold is a function of one or more symbols in said sequence of symbols.
15. The method of claim 14 wherein said function depends on a magnitude or magnitudes of said one or more symbols.
16. The method of claim 14 wherein said function is a linear function of said one or more symbols.
17. The method of claim 14 wherein said function is a non-linear function of said one or more symbols.
18. The method of claim 14 wherein said time-varying low-magnitude threshold is a function of one or more samples of said baseband signal.
19. The method of claim 18 wherein said function depends on a magnitude or magnitudes of said one or more samples.
20. The method of claim 18 wherein said function is a linear function of said one or more samples.
21. The method of claim 18 wherein said function is a non-linear function of said one or more samples.
22. The method of claim 2 , further comprising varying said time-varying low-magnitude threshold at a rate equal to or dependent on a rate at which said sequence of symbols are generated.
23. The method of claim 2 , further comprising varying said time-varying low-magnitude threshold at a rate equal to or dependent on a rate at which said baseband signal is sampled.
24. The method of claim 2 , further comprising upconverting said modified baseband signal using a quadrature modulator.
25. The baseband circuit of claim 3 wherein said threshold setting circuit is configured to receive symbols representing said baseband signal and vary said time-varying low-magnitude threshold according to a function that depends on one or more symbols of said symbols.
26. The baseband circuit of claim 25 wherein said function depends on a magnitude or magnitudes of said one or more symbols.
27. The baseband circuit of claim 25 wherein said function is a linear function of said one or more symbols.
28. The baseband circuit of claim 25 wherein said function is a non-linear function of said one or more symbols.
29. The baseband circuit of claim 3 wherein said threshold setting circuit is configured to vary said time-varying low-magnitude threshold according to a function that depends on one or more samples of said baseband signal.
30. The baseband circuit of claim 29 wherein said function depends on a magnitude or magnitudes of said one or more samples.
31. The baseband circuit of claim 29 wherein said function is a linear function of said one or more samples.
32. The baseband circuit of claim 29 wherein said function is a non-linear function of said one or more samples.