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

Claim 2:
3. A communication signal demultiplexing apparatus comprising:
an optical receiver configured to receive an optical communication signal carrying a representation of a combined electrical communication signal and configured to convert the optical communication signal into the combined electrical communication signal, the combined electrical communication signal comprising an electrical digital communication signal having a frequency spectrum and an electrical analog radio signal having a carrier frequency;
a signal splitting apparatus configured to power split the combined electrical communication signal into first and second parts;
a second 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 second electrical filter apparatus is configured to receive a first part of the combined electrical communication signal and to apply the low-pass filter to the combined electrical communication signal to obtain the electrical digital communication signal;
a first optical transmitter configured to convert the electrical digital communication signal into a corresponding optical digital communication signal; and
a second optical transmitter configured to receive a second part of the combined electrical communication signal and to convert said second part into a corresponding optical communication signal;
wherein the second 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.