Patent ID: 11956015
Assignee: TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Field: Telecommunications (Electrical engineering)
Classification: CPC H | IPC H

Claim 4:
5. A method of multiplexing communication signals, the method comprising:
receiving an optical analog radio signal and converting the optical analog radio signal into a corresponding electrical analog radio signal having a carrier frequency;
receiving an optical digital communication signal and converting the optical digital communication signal into a corresponding electrical digital communication signal having a frequency spectrum;
low-pass filtering the electrical digital communication signal with a low-pass filter having a cut-off frequency lower than the carrier frequency of the electrical analog radio signal;
combining the low-pass filtered electrical digital communication signal with the electrical analog radio signal to form a combined electrical communication signal; and
generating an optical communication signal carrying a representation of the combined electrical communication signal;
wherein the electrical digital communication signal is low-pass filtered with a first low-pass filter having a first cut-off frequency or with the first low-pass filter followed by a second low-pass filter having a second cut-off frequency lower than the first cut-off frequency, and wherein the first low-pass filter is used when a first lobe of the frequency spectrum of the electrical digital communication signal is lower than the first cut-off frequency and the combination of the first low-pass filter followed by the second low-pass filter is used when the first lobe of the frequency spectrum of the electrical digital communication signal is lower than the second cut-off frequency.