Apparatus and method for measuring nonlinear system noises
An apparatus and method to measure nonlinear system noises may include a processor to generate a bilateral notch signal, a unilateral notch signal and a multi-tone signal; to measure power of an additive Gaussian white noise of a nonlinear system by using the multi-tone signal; to measure a first power-to-noise ratio of the nonlinear system by using the bilateral notch signal; to measure a second power-to-noise ratio of the nonlinear system by using the unilateral notch signal. The processor is to calculate a nonlinear power-to-noise ratio of the nonlinear system and a power-to-noise ratio introduced by IQ imbalance according to the power of the additive Gaussian white noise, the first power-to-noise ratio and the second power-to-noise ratio.
1. An apparatus to measure nonlinear system noises, the apparatus comprising:
a memory; and
a processor coupled to the memory to control execution of a process to,
generate a bilateral notch signal and a unilateral notch signal in which notch depths of the bilateral notch signal and the unilateral notch signal are greater than or equal to a preset depth,
generate a multi-tone signal via transmitter digital signal processing, such that a frequency interval of the multi-tone signal is greater than or equal to a notch bandwidth of the unilateral notch signal or the bilateral notch signal, and the multi-tone signal is generated by adjusting initial phases of different single-tone signals so that a peak-to-average power ratio of the multi-tone signal is close to that of the unilateral notch signal or the bilateral notch signal;
measure a power of an additive Gaussian white noise of a nonlinear system by using the multi-tone signal;
measure a first power-to-noise ratio of the nonlinear system by using the bilateral notch signal;
measure a second power-to-noise ratio of the nonlinear system by using the unilateral notch signal; and
calculate a nonlinear power-to-noise ratio of the nonlinear system and a power-to-noise ratio introduced by IQ imbalance, according to the power of the additive Gaussian white noise, the first power-to-noise ratio and the second power-to-noise ratio.
2. The apparatus according to claim 1 , wherein to generate the bilateral notch signal, the process is to:
zero out a frequency component amplitude of a spectrum of a two-dimensional signal in a bilateral notch bandwidth and a mirror frequency bandwidth of the bilateral notch bandwidth via transmitter digital signal processing to generate the bilateral notch signal, or perform identical notch processing at identical frequency positions on real signals of I-path and Q-path of a two-dimensional signal to generate the bilateral notch signal.
3. The apparatus according to claim 2 , wherein when the nonlinear system is a receiver, to generate the bilateral notch signal, the process is to perform filtering processing on a broad-spectrum light source via an optical waveform editor to directly generate the bilateral notch signal in an optical domain.
4. The apparatus according to claim 1 , wherein to generate the unilateral notch signal, the process is to:
zero out a frequency component amplitude of a spectrum of a two-dimensional signal only within a bilateral notch bandwidth via transmitter digital signal processing to generate the unilateral notch signal.
5. The apparatus according to claim 4 , wherein when the nonlinear system is a receiver, to generate the unilateral notch signal, the process is to perform filtering processing on a broad-spectrum light source via an optical waveform editor to directly generate the unilateral notch signal in an optical domain.
6. The apparatus according to claim 1 , wherein to calculate the nonlinear power-to-noise ratio of the nonlinear system, the process is to:
calculate a nonlinear noise power of the nonlinear system according to a first average power, the first power-to-noise ratio and the power of the additive Gaussian white noise, the first average power being obtained by measuring the nonlinear system by using the bilateral notch signal;
calculate the nonlinear power-to-noise ratio according to the first average power and the nonlinear noise power; and
calculate the power-to-noise ratio introduced by IQ imbalance according to the first power-to-noise ratio and the second power-to-noise ratio.
7. The apparatus according to claim 1 , wherein the process is to calibrate the first power-to-noise ratio and the second power-to-noise ratio when a notch depth of the bilateral notch signal or the unilateral notch signal is less than or equal to a set threshold.
8. The apparatus according to claim 1 , wherein the bilateral notch signal and the unilateral notch signal are isospectral equiprobability signals.
9. An apparatus to estimate performance of a nonlinear system, the apparatus comprising:
a measuring apparatus to measure nonlinear system noises according to claim 1 ; and
a processor coupled to a memory to control execution of a process to,
obtain, from the measuring apparatus, the power of the additive Gaussian white noise, the nonlinear power-to-noise ratio and the power-to-noise ratio introduced by IQ imbalance of the nonlinear system, at multiple notch center frequencies,
establish an equivalent additive noise model according to the power of the additive Gaussian white noise, the nonlinear power-to-noise ratio and the power-to-noise ratio introduced by IQ imbalance of the nonlinear system at multiple center frequencies of notches, and
estimate performance of the nonlinear system according to the equivalent additive noise model.