Phase noise suppression

1. A system comprising:

a modulator circuit operable to generate a data-carrying signal based on a reference signal;

a test signal generator circuit operable to generate a test signal based on the reference signal;

a test signal insertion circuit operable to combine the data-carrying signal and the test signal to generate a combined signal; and

control circuit operable to:

determine current status of a microwave backhaul link according to a determination of a performance metric for the combined signal;

configure a nominal frequency at which the test signal generator circuit generates the test signal based on the determined current status of the microwave backhaul link;

determine an amount of whitespace to have on either side of the test signal based on the determined current status of the microwave backhaul link; and

configure the modulator circuit such that the data-carrying signal has the determined amount of whitespace surrounding the nominal frequency of the test signal.

2. The system of claim 1 , wherein the performance metric comprises one of: signal-to-noise ratio, symbol error rate, and bit error rate.

3. The system of claim 1 , wherein the performance metric is an indication of phase noise.

4. The system of claim 1 , comprising a digital-to-analog converter operable to convert the combined signal to a corresponding analog signal.

5. The system of claim 4 , comprising an analog front-end operable to upconvert the combined signal to a microwave frequency signal and transmit the microwave frequency signal.

6. The system of claim 5 , comprising:

a receive analog front-end circuit operable to receive the microwave frequency signal and convert the microwave frequency signal to an analog baseband signal;

an analog-to-digital converter operable to convert the baseband signal to a digital baseband signal;

a test signal processing circuit operable to:

select a first portion of the digital baseband signal that includes the whitespace and the test signal; and

process the first portion of the digital baseband signal to generate a signal indicative of phase of the test signal; and

a phase noise removal circuit operable to correct, based on the signal indicative of phase of the test signal, phase noise in a second portion of the digital baseband signal that does not include the whitespace or the test signal.

7. The system of claim 5 , wherein:

a bandwidth of the microwave frequency signal is at least one order of magnitude larger than the bandwidth of the whitespace; and

the bandwidth of the whitespace is at least one order of magnitude larger than the bandwidth of the test signal.

8. The system of claim 1 , wherein the modulator circuit, test signal generator circuit, and control circuit are integrated in a microwave backhaul assembly.

9. A method comprising:

generating, by a modulator circuit, a data-carrying signal based on a reference signal;

generating, by a test signal generator circuit, a test signal based on the reference signal;

combining, by a test signal insertion circuit, the data-carrying signal and the test signal to generate a combined signal;

determining, by a control circuit, current status of a microwave backhaul link by determining a performance metric for the combined signal;

configuring, by the control circuit, a nominal frequency at which the test signal generator circuit generates the test signal based on the determined current status of the microwave backhaul link;

determining, by the control circuit, an amount of whitespace to have on either side of the test signal based on the determined current status of the microwave backhaul link; and

configuring, by the control circuit, the modulator circuit such that the data-carrying signal has the determined amount of whitespace surrounding the nominal frequency of the test signal.

10. The system of claim 9 , wherein the performance metric comprises one of: signal-to-noise ratio, symbol error rate, and bit error rate.

11. The system of claim 9 , wherein the performance metric is an indication of phase noise.

12. The system of claim 9 , comprising converting, by an digital-to-analog converter circuit, the combined signal to a corresponding analog signal.

13. The system of claim 12 , comprising upconverting, by an analog front-end circuit, the combined signal to a microwave frequency signal and transmit, by the analog front-end circuit, the microwave frequency signal.

14. The system of claim 13 , comprising:

receiving, via a receive analog front-end circuit, the microwave frequency signal;

converting, via the receive analog front-end circuit, the microwave frequency signal to an analog baseband signal;

converting, by an analog-to-digital converter circuit, the baseband signal to a digital baseband signal;

selecting, by a test signal processing circuit, a first portion of the digital baseband signal that includes the whitespace and the test signal; and

processing, by the test signal processing circuit, the first portion of the digital baseband signal to generate a signal indicative of phase of the test signal; and

correcting, by a phase noise removal circuit based on the signal indicative of phase of the test signal, phase noise in a second portion of the digital baseband signal that does not include the whitespace or the test signal.

15. The system of claim 13 , wherein:

a bandwidth of the microwave frequency signal is at least one order of magnitude larger than the bandwidth of the whitespace; and

the bandwidth of the whitespace is at least one order of magnitude larger than the bandwidth of the test signal.

16. The system of claim 9 , wherein the modulator circuit, test signal generator circuit, and control circuit are integrated in a microwave backhaul assembly.