Suppression of adjacent channel interference by adaptive channel filtering in mobile radio receivers
A channel filter ( 200 ) with a variable pass bandwidth has a first low-pass filter ( 200.2 ) on the input side and is driven by a means ( 30 ) for controlling the pass bandwidth as a function of the adjacent channel interference. A first input of the control means ( 30 ) is connected to the first low-pass filter ( 200.2 ), and a second input is connected to a bandpass filter ( 200.4 ) which is connected in parallel with the channel filter ( 200 ). The signal path which contains the low-pass filter ( 200.2 ) contains a means ( 37 ) for removing a DC signal component or DC component.
1 . An adaptive channel filter for a receiver unit for a mobile communications system, comprising
a channel filter with a variable pass bandwidth, which comprises a first low-pass filter on the input side,
a bandpass filter which is connected in parallel with the channel filter,
a means for controlling the pass bandwidth of the channel filter as a function of the adjacent channel interference, having a first input which is connected to an output of the first low-pass filter, and having a second input which is connected to an output of the bandpass filter, and
a means for removal of any DC signal component or DC component in the signal path which contains the first low-pass filter.
2 . The adaptive channel filter as claimed in claim 1 , wherein
the means for removal of the DC signal component is a notch filter.
3 . The adaptive channel filter as claimed in claim 1 , wherein
the means for removal of the DC signal component comprises a DC signal estimator for estimation of the DC signal from an input signal, and comprises an adder for subtraction of the estimated DC signal component from the input signal.
4 . The adaptive channel filter as claimed in claim 1 , wherein
the channel filter is a digital low-pass filter in the baseband section of the receiver unit.
5 . The adaptive channel filter as claimed in claim 1 , wherein
the means for controlling the pass bandwidth also takes account of the noise, in addition to the adjacent channel interference.
6 . The adaptive channel filter as claimed in claim 1 , wherein
the channel filter with a variable pass bandwidth comprises two or more filters which are arranged in series with one another and limit the bandwidth in steps, and comprises a selection switch, at least some of whose inputs are connected to signal taps between the filters.
7 . The adaptive channel filter as claimed in claim 1 , wherein
the means for controlling the pass bandwidth comprises:
in each case one energy estimator, which is connected to the two inputs and in each case calculates a variable which is representative of the power supplied to this input, and
a comparison means which compares the variables calculated for different inputs with one another.
8 . The adaptive channel filter as claimed in claim 1 , wherein
the means for removal of the DC signal component is arranged downstream of the first low-pass filter.
9 . A method for setting the variable pass bandwidth of a channel filter, having the following steps:
filtering of an input signal with a bandpass filter for production of a signal which is characteristic of an interference signal in an interference signal path, and having a low-pass filter for production of a signal which is characteristic of a payload signal in a payload signal path and for removal of the DC signal component in the payload signal path,
calculating two variables which are characteristic of the signal powers of the two filtered signals, and
setting of the pass bandwidth of the channel filter as a function of a comparison of the calculated variables.
10 . The method as claimed in claim 9 , wherein
the DC signal component in the payload signal path is removed by means of a notch filter.
11 . The method as claimed in claim 9 , wherein
the DC signal component in the payload signal path is removed by first of all estimating it on the basis of the input signal and then subtracting it from the input signal.
12 . An adaptive channel filter for a receiver unit for a mobile communications system, comprising
a channel filter with a variable pass bandwidth, which comprises a first low-pass filter on the input side,
a bandpass filter which is connected in parallel with the channel filter,
a pass bandwidth controller which controls the pass bandwidth as a function of the adjacent channel interference, comprising a first input connected to an output of the first low-pass filter, and a second input connected to an output of the bandpass filter, and
a DC component removal unit arranged in the signal path which contains the first low-pass filter.
13 . The adaptive channel filter as claimed in claim 12 , wherein
the DC component removal unit is a notch filter.
14 . The adaptive channel filter as claimed in claim 12 , wherein
the DC component removal unit comprises a DC signal estimator for estimation of the DC signal from an input signal, and comprises an adder for subtraction of the estimated DC signal component from the input signal.
15 . The adaptive channel filter as claimed in claim 12 , wherein
the channel filter is a digital low-pass filter in the baseband section of the receiver unit.
16 . The adaptive channel filter as claimed in claim 12 , wherein
the pass bandwidth controller also takes account of the noise, in addition to the adjacent channel interference.
17 . The adaptive channel filter as claimed in claim 12 , wherein
the channel filter with a variable pass bandwidth comprises two or more filters which are arranged in series with one another and limit the bandwidth in steps, and comprises a selection switch, at least some of whose inputs are connected to signal taps between the filters.
18 . The adaptive channel filter as claimed in claim 12 , wherein
the pass bandwidth controller comprises:
in each case one energy estimator, which is connected to the two inputs and in each case calculates a variable which is representative of the power supplied to this input, and
a comparison means which compares the variables calculated for different inputs with one another.
19 . The adaptive channel filter as claimed in claim 12 , wherein
the DC component removal unit is arranged downstream of the first low-pass filter.