System and method for adapting to a change in constellation density while receiving a signal
View Patent ↗One embodiment comprises a transmitter precoder operating on an input signal to produce an output signal for modulation. The output signal is transmitted using a constellation with a constellation density. The transmitter precoder comprises scaler logic, precoder logic and selection logic. The scaler logic scales the input signal to maintain constant power on the input signal independent of the constellation density. The precoder logic precodes the scaled signal to produce a dither signal limited to a range of values. The range is inversely proportional to the constellation density. The selection logic is operable in two states. In the first state, the selection logic combines the scaled signal with the dither signal to produce the output signal. In the second state, the selection provides the scaled signal as the output signal.
1. A transmitter precoder operating on an input signal to produce an output signal for modulation, wherein the output signal is transmitted using a constellation with a constellation density, the precoder comprising:
logic configured to scale the input signal to maintain constant power on the input signal independent of the constellation density;
logic configured to precode the scaled signal to produce a dither signal limited to a range of values, wherein the range is inversely proportional to the constellation density; and
selection logic operable in a first state to combine the scaled signal with the dither signal to produce the output signal and operable in a second state to provide the scaled signal as the output signal.
2. The precoder of claim 1 , wherein the precoder logic produces a modulo count and a Trellis state for output to a Trellis encoder.
3. The precoder of claim 1 , wherein the precoder logic further comprises:
modulo logic to repeatedly add or subtract an interval to or from each dimension of the input signal until each dimension of the input signal is within the range, where the interval is inversely proportional to the constellation density.
4. The precoder of claim 3 , wherein the modulo logic is further configured to produce a modulo output that is a count of the number of times the interval was added or subtracted.
5. The precoder of claim 4 , wherein the interval is 2S b and the range is ±S b , where S b is a factor inversely proportional to the constellation density.
6. The precoder of claim 5 , wherein S b is half the distance between points in the constellation.
7. The precoder of claim 1 , wherein the scaler logic is a multiplication by S b and the dither signal is limited to the range ±S b , where S b is a factor proportional to the constellation density.
8. A method for producing an output signal for modulation in a transmitter, where the output signal is transmitted using a constellation with a constellation density, the method comprising:
scaling an input signal to maintain constant power on the input signal independent of the constellation density;
precoding the scaled signal to produce a dither signal limited to a range of values, wherein the range is inversely proportional to the constellation density; and
combining the scaled signal with the dither signal to produce the output signal when in a first state and providing the scaled signal as the output signal when in a second state.
9. The method of claim 8 , wherein the precoding produces a modulo count and a Trellis state for output to a Trellis encoder.
10. The method of claim 8 , wherein the precoding further comprises:
repeatedly adding or subtracting an interval to or from each dimension of the input signal until each dimension of the input signal is within the range, where the interval is inversely proportional to the constellation density.
11. The method of claim 10 , wherein the precoding further comprises producing a modulo output that is a count of the number of times the interval was added or subtracted.
12. The method of claim 11 , wherein the interval is 2S b and the range is ±S b , where S b is a factor inversely proportional to the constellation density.
13. The method of claim 8 , wherein the scaling is a multiplication by S b and the dither signal is limited to the range ±S b , where S b is a factor proportional to the constellation density.
14. A transmitter for transmitting a modulated output signal using a constellation with a constellation density, comprising:
means for scaling an input signal to maintain constant power on the input signal independent of the constellation density;
means for precoding the scaled signal to produce a dither signal limited to a range of values, wherein the range is inversely proportional to the constellation density; and
means for combining the scaled signal with the dither signal to produce the output signal when in a first state and providing the scaled signal as the output signal when in a second state.
15. The transmitter of claim 14 , wherein the means for precoding produces a modulo count and a Trellis state for output to a Trellis encoder.
16. The transmitter of claim 14 , wherein the means for precoding further comprises:
means for repeatedly adding or subtracting an interval to or from each dimension of the input signal until each dimension of the input signal is within the range, where the interval is inversely proportional to the constellation density.
17. The transmitter of claim 16 , wherein the means for precoding further produces a modulo output that is a count of the number of times the interval was added or subtracted.
18. The transmitter of claim 17 , wherein the interval is 2S b and the range is ±S b , where S b is a factor inversely proportional to the constellation density.
19. The transmitter of claim 14 , wherein the means for scaling the input signal comprises multiplication by S b .
20. The transmitter of claim 14 , wherein the dither signal is limited to the range ±S b , where S b is a factor proportional to the constellation density.