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

Claim 3:
4. 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 communication signal demultiplexing apparatus further comprises a third electrical filter apparatus comprising a high-pass filter having a cut-off frequency lower than the carrier frequency of the electrical analog radio signal, wherein the third electrical filter apparatus is configured to receive said second part of the combined electrical digital communication signal and to apply the high-pass filter to said second part of the combined electrical digital communication signal to obtain the electrical analog radio signal, and wherein the second optical transmitter is configured to receive the electrical analog radio signal and to convert the electrical analog radio signal into a corresponding optical analog radio signal; and
wherein the third electrical filter apparatus comprises:
a filter cascade comprising:
a first high-pass filter having a first cut-off frequency;
a second high-pass filter having a second cut-off frequency higher than the first cut-off frequency; and
a switch having a first state in which an output of the first high-pass filter by-passes the second high-pass filter and a second state in which the output of the first high-pass filter is coupled to an input of the second high-pass filter, wherein the switch is configurable to be set to the first state when the electrical digital communication signal frequency spectrum occupies a frequency range lower than the first cut-off frequency and is configurable to be set to the second state when the electrical digital communication signal frequency spectrum occupies a frequency range higher than the first cut-off frequency and lower than the second cut-off frequency.