Leg combining by FFT selection

1. A system comprising:

a transmitter circuit configured to transmit a first downstream signal to a first device and a second downstream signal to a second device;

a first echo cancellation circuit configured to reduce a reflection of the first downstream signal superimposed on a first upstream signal transmitted by the first device to the system, to obtain a first signal;

a first frequency transformation circuit configured to transform the first signal in a time domain into a corresponding second signal in a frequency domain;

a second echo cancellation circuit configured to reduce a reflection of the second downstream signal superimposed on a second upstream signal transmitted by the second device to the system, to obtain a third signal;

a second frequency transformation circuit configured to transform the third signal in the time domain into a corresponding fourth signal in the frequency domain; and

a leg combining circuit, the first frequency transformation circuit coupled between the leg combining circuit and the first echo cancellation circuit, the second frequency transformation circuit coupled between the leg combining circuit and the second echo cancellation circuit, the leg combining circuit configured to:

select, for a group of subcarriers, one of the first frequency transformation circuit and the second frequency transformation circuit, and

cause, for the group of subcarriers, the selected one of the first frequency transformation circuit and the second frequency transformation circuit to output one of the second signal and the fourth signal, according to the selection.

2. The system of claim 1 , wherein the group of subcarriers is selected from groups of subcarriers of orthogonal frequency division multiple access (OFDMA) symbols or orthogonal frequency division multiplexing (OFDM) symbols.

3. The system of claim 1 , wherein the leg combining circuit comprises:

a power detection circuit coupled to the first frequency transformation circuit and the second frequency transformation circuit, the power detection circuit configured to detect, for the group of subcarriers, a first power level of the second signal and a second power level of the fourth signal; and

a control circuit coupled to the first frequency transformation circuit, the second frequency transformation circuit, and the power detection circuit, the control circuit configured to:

compare the first power level and the second power level, and

select, for the group of subcarriers, the one of the first frequency transformation circuit and the second frequency transformation circuit associated with a higher power level of the first power level and the second power level according to the comparison.

4. The system of claim 3 , wherein the control circuit is configured to:

offset the first power level according to a first noise associated with a first connection between the first device and the first frequency transformation circuit, and

offset the second power level according to a second noise associated with a second connection between the second device and the second frequency transformation circuit.

5. The system of claim 4 , wherein the leg combining circuit further comprises:

a noise detection circuit coupled to the first connection and the second connection, the noise detection circuit configured to detect the first noise during a first time period and the second noise during a second time period.

6. The system of claim 1 , wherein the leg combining circuit comprises:

a control circuit coupled to the first frequency transformation circuit and the second frequency transformation circuit, the control circuit configured to:

select the second signal to be output during a first time period associated with the first device, and

select the fourth signal to be output during a second time period associated with the second device.

7. The system of claim 1 , wherein the first echo cancellation circuit is (i) coupled between the first frequency transformation circuit and the transmitter circuit, and (ii) coupled between the first frequency transformation circuit and the first device, wherein the echo cancellation circuit is further configured to:

predict the reflection of the first downstream signal superimposed on the first upstream signal; and

subtract the predicted reflection of the first downstream signal from the first upstream signal to obtain the first signal.

8. The system of claim 1 , further comprising:

a frequency demodulation circuit coupled to the leg combining circuit, the leg combining circuit coupled between i) the frequency demodulation circuit and ii) the first frequency transformation circuit and coupled between i) the frequency demodulation circuit and ii) the second frequency transformation circuit, the frequency demodulation circuit configured to receive the one of the second signal and the fourth signal from the leg combining circuit, and demodulate the one of the second signal and the fourth signal.

9. The system of claim 1 , further comprising:

a frame buffer coupled to the leg combining circuit,

wherein the leg combining circuit is further configured to:

cause, during a first time period, the selected one of the first frequency transformation circuit and the second frequency transformation circuit to output a portion of the one of the second signal and the fourth signal to the frame buffer for the group of subcarriers, and

cause, during a second time period, the other of the first frequency transformation circuit and the second frequency transformation circuit to output a portion of the other of the second signal and the fourth signal to the frame buffer for another group of sub carriers.

10. A method, comprising:

transmitting, by a transmitter circuit of a system, a first downstream signal to a first device and a second downstream signal to a second device;

reducing, by a first echo cancellation circuit of the system coupled to the transmitter circuit, a reflection of the first downstream signal superimposed on a first upstream signal transmitted by the first device to the system, to obtain a first signal;

transforming, by a first frequency transformation circuit of the system, the first signal in a time domain into a corresponding second signal in a frequency domain;

reducing, by a second echo cancellation circuit of the system coupled to the transmitter circuit, a reflection of the second downstream signal superimposed on a second upstream signal transmitted by the second device to the system, to obtain a third signal;

transforming, by a second frequency transformation circuit of the system, the third signal in the time domain into a corresponding fourth signal in the frequency domain;

selecting, for a group of subcarriers by a leg combining circuit of the system, one of the second signal and the fourth signal, the first frequency transformation circuit coupled between the leg combining circuit and the first echo cancellation circuit, the second frequency transformation circuit coupled between the leg combining circuit and the second echo cancellation circuit; and

outputting, for the group of subcarriers by the leg combining circuit of the system, the selected one of the second signal and the fourth signal.

11. The method of claim 10 , wherein the group of subcarriers is selected from groups of subcarriers of orthogonal frequency division multiple access (OFDMA) symbols or orthogonal frequency division multiplexing (OFDM) symbols.

12. The method of claim 10 , wherein selecting the one of the second signal and the fourth signal further comprises:

detecting, for the group of subcarriers by the leg combining circuit of the system, a first power level of the second signal and a second power level of the fourth signal;

comparing, by the leg combining circuit of the system, the first power level and the second power level; and

selecting, by the leg combining circuit of the system, the one of the second signal and the fourth signal according to the comparison.

13. The method of claim 12 , wherein selecting the one of the second signal and the fourth signal further comprises:

offsetting, by the leg combining circuit of the system, the first power level according to a first noise associated with a first connection between the first device and the system, and

offsetting, by the leg combining circuit of the system, the second power level according to a second noise associated with a second connection between the second device and the system.

14. The method of claim 10 , wherein selecting the one of the second signal and the fourth signal further comprises:

selecting, by the leg combining circuit of the system, the second signal to be output during a first time period associated with the first device; and

selecting, by the leg combining circuit of the system, the fourth signal to be output during a second time period associated with the second device.

15. The method of claim 10 , further comprising:

predicting, by the first echo cancellation circuit of the system, the reflection of the first downstream signal superimposed on the first upstream signal; and

subtracting, by the first echo cancellation circuit of the system, the predicted reflection of the first downstream signal from the first upstream signal to obtain the first signal.

16. The method of claim 10 , further comprising:

combining, by the leg combining circuit of the system, a portion of the one of the second signal and the fourth signal received during a first time period for the group of subcarriers, and another portion of the other of the second signal and the fourth signal received during a second time period for another group of subcarriers.

17. A system comprising:

a first echo cancellation circuit configured to reduce a reflection of a first downstream signal superimposed on a first upstream signal transmitted by a first device to the system, to obtain a first signal, the first downstream signal transmitted by a transmitter circuit to the first device;

a first frequency transformation circuit configured to transform the first signal in a time domain into a corresponding second signal in a frequency domain;

a second echo cancellation circuit configured to reduce a reflection of a second downstream signal superimposed on a second upstream signal transmitted by a second device to the system, to obtain a third signal, the second downstream signal transmitted by the transmitter circuit to the second device;

a second frequency transformation circuit configured to transform the third signal in the time domain into a corresponding fourth signal in the frequency domain; and

a leg combining circuit, the first frequency transformation circuit coupled between the leg combining circuit and the first echo cancellation circuit, the second frequency transformation circuit coupled between the leg combining circuit and the second echo cancellation circuit, the leg combining circuit configured to:

detect power levels of the second signal and the fourth signal for a first group of subcarriers of orthogonal frequency division multiple access (OFDMA) symbols or orthogonal frequency division multiplexing (OFDM) symbols, and

output one of the second signal and the fourth signal for the first group of subcarriers according to the detected power level.

18. The system of claim 17 , wherein the leg combining circuit is configured to:

detect the power levels of the second signal and the fourth signal for the first group of subcarriers during a first time period;

detect the power levels of the second signal and the fourth signal for a second group of subcarriers during a second time period;

output the one of the second signal and the fourth signal for the first group of subcarriers during the first time period; and

output the other of the second signal and the fourth signal for the second group of subcarriers during the second time period.

19. The system of claim 18 , further comprising a frame buffer coupled to the leg combining circuit, the frame buffer configured to combine the one of the second signal and the fourth signal for the first group of subcarriers and the other of the second signal and the fourth signal for the second group of subcarriers.

20. The system of claim 17 , further comprising:

a frequency demodulation circuit coupled to the leg combining circuit, the leg combining circuit coupled between i) the frequency demodulation circuit and ii) the first frequency transformation circuit and coupled between i) the frequency demodulation circuit and ii) the second frequency transformation circuit, the frequency demodulation circuit configured to receive the one of the second signal and the fourth signal from the leg combining circuit, and demodulate the one of the second signal and the fourth signal.