Method and system for eliminating echo in the reproduction of radio signals transmitted via a radio channel
A method and system eliminate echoes in the reproduction of radio signals transmitted via a radio channel. A radio signal transmitted by a transmitter is received by at least a first base station as a first audio signal and by at least a second base station as a second audio signal. The received audio signals are transmitted via an IP network to a control station for reproduction. The first and second audio signals arrive in the control station at different times or with a time shift and undergo a similarity analysis before their reproduction in the control station in order to reproduce the radio signal contained in both audio signals without echo if a similarity is established between the first audio signal and the second audio signal.
1 . A method for eliminating an echo in a reproduction of radio signals transmitted via a radio channel, which comprises the steps of:
receiving a radio signal, transmitted by a transmitter, by at least a first base station as a first audio signal and by at least a second base station as a second audio signal; and
transmitting the first and second audio signals via an Internet protocol (IP) network to a control station for reproduction, wherein the first audio signal and the second audio signal arrive in the control station at different times or with a time shift and undergo a similarity analysis before their reproduction in the control station in order to reproduce the radio signal contained in both the first and second audio signals without echo if a similarity is established between the first audio signal and the second audio signal;
calculating a time-dependent cross-correlation between the first audio signal and the second audio signal in the similarity analysis, envelopes of the first audio signal and the second audio signal being used in each case to calculate the time-dependent-cross-correlation, and establishing the similarity if a cross-correlation peak occurs with time shifts between 0 ms and 1000 ms; and
if the similarity is established between the first audio signal and the second audio signal, removing or reducing the time shifts of the radio signal contained in the audio signals so that the first audio signal and the second audio signal are reproduced in a superimposed and/or synchronized manner.
2 . The method according to claim 1 , wherein if the similarity is established between the first and second audio signals, only the first audio signal or only the second audio signal is reproduced.
3 . The method according to claim 2 , which further comprises calculating a quality value in each case from the first and second audio signals, wherein only the first audio signal or the second audio signal having a higher quality value is reproduced.
4 . The method according to claim 1 , which further comprises establishing in the similarity analysis whether receive areas of the first and second base stations overlap one another.
5 . The method according to claim 1 , wherein the cross-correlation peak occurs with the time shifts between 2 ms and 500 ms.
6 . The method according to claim 1 , wherein the cross-correlation peak occurs with the time shifts between 5 ms and 200 ms.
7 . The method according to claim 1 , wherein the envelopes are obtained by applying a low-pass filter and/or a Hilbert transform to the first and second audio signals.
8 . A system, comprising:
at least a first base station and a second base station for receiving at least one radio signal transmitted via a radio channel as a first and second audio signal respectively;
at least one control station connected to said first and second base stations via at least one Internet protocol network for the reproduction of the first and second audio signals; and
an analysis unit for performing a similarity analysis of the first and second audio signals, said analysis unit being programmed to carry out the method according to claim 1 .