Signal method and apparatus

1. A method comprising:

receiving one or more input digital signals;

generating from the one or more input digital signals a plurality of analog electrical baseband signals each comprising a plurality of subcarriers spaced apart by a subcarrier spacing frequency equal to an integer multiple of a symbol rate of the baseband signals; and

up-converting each of the baseband signals to a respective up-converted radio frequency (RF) band signal, the up-converted signals also being spaced apart by an integer multiple of the symbol rate;

combining the up-converted RF band signals; and

modulating a light source with the combined up-converted RF band signals.

2. A method defined by claim 1 wherein the up-converted signals are spaced apart by an integer multiple of the subcarrier spacing frequency.

3. A method defined by claim 1 wherein each of the plurality of analog electrical baseband signals is generated by a method comprising:

mapping one or more bits of the input digital signals to respective ones of a plurality of information symbols; and

modulating each one of the plurality of information symbols onto a corresponding subcarrier of one of the analog electrical baseband signals.

4. A method defined by claim 3 wherein modulating each one of the plurality of information symbols comprises:

generating a digital time domain signal by frequency-time transformation of the plurality of information symbols; and

converting the digital time domain signal to a corresponding analog electrical baseband signal.

5. A method defined by claim 4 further comprising inserting a guard interval into the digital time domain signal.

6. A method defined by claim 4 further comprising inserting a cyclic prefix into the digital time domain signal.

7. An apparatus comprising:

a baseband generator arranged to receive one or more input digital signals, and to generate from the one or more input digital signals a plurality of analog electrical baseband signals, each baseband signal comprising a plurality of subcarriers spaced apart by a subcarrier spacing frequency equal to an integer multiple of a symbol rate of the baseband signals;

an up-converter in communication with the baseband generator, the up-converter being arranged to receive and up-convert each baseband signal to a respective up-converted radio frequency (RF) band signal, the up-converted signals also being spaced apart by an integer multiple of the symbol rate;

an RF combiner arranged to combine the up-converted RF band signals; and

an optical modulator in communication with a light source and the RF combiner, the modulator being arranged to modulate the light source with the combined up-converter RF band signals.

8. An apparatus defined by claim 7 wherein the baseband generator comprises a plurality of baseband generators, each generator being arranged to generate a respective one of the baseband signals.

9. An apparatus defined by claim 8 wherein each of the baseband generators comprises an OFDM generator.

10. An apparatus defined by claim 7 wherein the up-converter comprises a plurality of up-converters.

11. An apparatus defined by claim 10 wherein each of the up-converters comprises an IQ modulator.

12. An apparatus defined by claim 7 wherein the baseband generator comprises:

a subcarrier symbol mapper arranged to map one or more bits of the input digital signals to respective ones of a plurality of information symbols, each corresponding with a subcarrier of one of the analog electrical baseband signals;

a frequency-time transformer arranged to generate a digital time domain signal from the plurality of information signals; and

a digital-to-analog converter arranged to convert the digital time domain signal to a corresponding analog electrical baseband signal.

13. A method comprising:

receiving a modulated optical signal comprising a plurality of mutually orthogonal subcarriers constituting a plurality of bands;

detecting the modulated optical signal to produce an electrical signal comprising a plurality of radio frequency (RF) band signals, wherein each RF band signal corresponds with one of the bands of the modulated optical signal;

down-converting one or more of the RF band signals to respective one or more analog electrical baseband signals; and

converting the one or more analog electrical baseband signals to corresponding digital signals; and

processing the digital signals to reconstruct transmitted information encoded in the modulated optical signal.

14. A method defined by claim 13 wherein processing each of the digital signals comprises processing each of the digital signals as for an OFDM baseband signal.

15. An apparatus comprising:

an optical receiver arranged to detect a modulated optical signal comprising a plurality of mutually orthogonal subcarriers constituting a plurality of bands and to produce an electrical signal comprising a plurality of radio frequency (RF) band signals, wherein each RF band signal corresponds with one of the bands of the modulated optical signal;

an RF down-converter arranged to down-convert one or more of the plurality of RF band signals to respective one or more analog electrical baseband signals;

one or more analog-to-digital converters arranged to convert the one or more analog electrical baseband signals to corresponding digital signals; and

a processing module arranged to process each of the one or more digital signals to reconstruct transmitted information encoded in the modulated optical signal.