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

Claim 0:
1. A communication signal multiplexing apparatus comprising:
a first optical receiver configured to receive an optical analog radio signal and to convert the optical analog radio signal into a corresponding electrical analog radio signal having a carrier frequency;
a second optical receiver configured to receive an optical digital communication signal and to convert the optical digital communication signal into a corresponding electrical digital communication signal having a frequency spectrum;
a first electrical filter apparatus comprising a low-pass filter having a cut-off frequency lower than the carrier frequency of the electrical analog radio signal, wherein the first electrical filter apparatus is configured to receive the electrical digital communication signal and to apply the low-pass filter to the electrical digital communication signal;
signal combining apparatus configured to combine the low-pass filtered electrical digital communication signal with the electrical analog radio signal to form a combined electrical communication signal; and
an optical transmitter configured to generate an optical communication signal carrying a representation of the combined electrical communication signal;
wherein the first electrical filter apparatus comprises:
a filter cascade comprising:
a first low-pass filter having a first cut-off frequency;
a second low-pass filter having a second cut-off frequency lower than the first cut-off frequency; and
a switch having a first state in which an output of the first low-pass filter by-passes the second low-pass filter and a second state in which the output of the first low-pass filter is coupled to an input of the second low-pass filter, wherein the switch is configurable to be set to the first state when a first lobe of the frequency spectrum of the electrical digital communication signal is lower than the first cut-off frequency and is configurable to be set to the second state when the first lobe of the frequency spectrum of the electrical digital communication signal is lower than the second cut-off frequency.