Signal modulation method, signal demodulation method, signal modulation apparatus, signal demodulation apparatus and signal transmission system

A signal demodulation method, comprising:

• performing optical-to-electrical conversion on a received optical signal, to obtain N pairs of carrierless amplitude phase (CAP) signals by means of the conversion, wherein two sub-signals in each pair are orthogonal to each other and have a same frequency band, frequency bands of different pairs of sub-signals are different, and a spacing between center frequencies of two neighboring frequency bands is greater than or equal to an average value of baud rates of sub-signals corresponding to the two neighboring frequency bands;
• performing filtering on the N pairs of CAP signals, and performing CAP demodulation on the two sub-signals in each pair, to generate 2N sub-signals;
• and
• multiplexing the 2N sub-signals into an input signal, wherein N>1.

A signal modulation apparatus, comprising:

• a demultiplexing unit, N carrierless amplitude phase (CAP) filtering units, an addition unit, and a modulation unit, wherein the demultiplexing unit is connected to the N CAP filtering units, the N CAP filtering units are all connected to the addition unit, and the addition unit is connected to the modulation unit;
• wherein the demultiplexing unit is configured to:
• demultiplex an input signal into 2N sub-signals, group every two of the 2N sub-signals into a pair, and output each pair to one of the CAP filtering units;
• wherein the CAP filtering units are configured to:
• perform filtering on two sub-signals in each pair, perform CAP modulation on the two sub-signals in each pair, modulate the two sub-signals in each pair to a same frequency band, to generate N pairs of CAP signals, wherein frequency bands of different pairs of sub-signals are different, two sub-signals in a same pair are orthogonal to each other, and a spacing between center frequencies of two neighboring frequency bands is greater than or equal to an average value of baud rates of sub-signals corresponding to the two neighboring frequency bands, and output the N pairs of CAP signals to the addition unit;
• and
• wherein the addition unit is configured to:
• combine the N pairs of CAP signals and output a signal obtained after the combining to the modulation unit for electro-optic modulation, wherein N>1.

A signal demodulation apparatus, comprising:

• a multiplexing unit, N carrierless amplitude phase CAP filtering units and an optical-to-electrical conversion unit, wherein the optical-to-electrical conversion unit is connected to the N CAP filtering units, and the N CAP filtering units are connected to the multiplexing unit;
• and
• wherein the optical-to-electrical conversion unit is configured to:
• perform optical-to-electrical conversion on a received optical signal, to obtain N pairs of CAP signals by means of the conversion, wherein two sub-signals in each pair of CAP signals are orthogonal to each other and have a same frequency band, frequency bands of different pairs of sub-signals are different, and a spacing between center frequencies of two neighboring frequency bands is greater than or equal to an average value of baud rates of sub-signals corresponding to the two neighboring frequency bands, and output each pair of the N pairs of CAP signals to one of the CAP filtering units;
• wherein the N CAP filtering units are configured to:
• perform filtering on the N pairs of CAP signals, and perform CAP demodulation on two sub-signals in each pair, to generate 2N sub-signals;
• and
• wherein the multiplexing unit is configured to:
• multiplex the 2N sub-signals into an input signal, wherein N>1.