Method for deriving parasitic signals from modulated digital signals
View Patent ↗A method for deriving interference signals from modulated, digital signals is provided. The receiver end reconstructs the modulated digital signals sent by a transmitter. These reconstructed modulated digital signals are then subtracted from the received modulated digital signals, and the result of the subtraction is used to estimate the interference signals without influence by prior filtering at the receiver end. By way of example, it is possible to demodulate the interference signals estimated at the receiver end in order to ascertain possible unauthorized carrier frequencies which disturb the regular carrier frequencies, even if the interference signals are not completely in the bandwidth of the regular carrier frequency or carrier frequencies.
1. A method for deriving parasitic signals from modulated digital signals, with each signal being determined from digital data to be transmitted by using a modulation schema, comprising:
receiving, at a receiver end, modulated digital signals transmitted by a transmitting end, the received signals including parasitic signals and the transmitted modulated signals;
reconstructing the transmitted modulated digital signals at a receiver end;
subtracting the reconstructed modulated digital signals from the received modulated digital signals;
estimating the parasitic signals from a result of the subtraction without influence from prior filtering at the receiver end; and
identifying sources of the parasitic signals at the receiver end based on the estimated parasitic signals,
wherein mid frequency, bandwidth and/or power is determined from the estimated parasitic signals.
2. The method as claimed in claim 1 , wherein at the receiver end, values of the digital data to be transmitted determined are used in the reconstructing.
3. The method as claimed in claim 1 , wherein at the receiver end, influencing parameters of a transmission channel are used in the reconstructing.
4. The method as claimed in claim 3 , wherein the influencing parameters include an attenuation of the transmission channel and/or a time delay through the transmission channel.
5. The method as claimed in claim 1 , wherein the transmitted modulated digital signals are shown as a time-related function and/or as a linear combination of N modulated digital signals with an index i=1, 2, . . . , N with the digital data to be transmitted as parameters.
6. The method as claimed in claim 1 , wherein a received signal is represented as
s r =As mi ( c, t−t d )+ s ′ ai ( t ), wherein
A is an attenuation of a transmission channel,
s mi is a transmitted modulated digital signal with an index i, by which values of 1 to N are assumed,
c is the digital data to be transmitted,
t d is a time delay of the transmission channel, and
s′ ai (t) is a parasitic signal, by which the i-th transmitted modulated digital signal s mi is influenced.
7. The method as claimed in claim 1 , wherein at the receiver end, the reconstruction of the transmitted modulated digital signals is represented as
Ŝ mi =Âs mi ( ĉ, t−{circumflex over (t)} d ), wherein
 is an estimation of an attenuation of a transmission channel,
s mi is a transmitted modulated digital signal with an index i, by which values from 1 to N are assumed,
ĉ is an estimation of the digital data to be transmitted, determined at the receiver end, and
{circumflex over (t)} d is an estimation of a time delay.
8. The method as claimed in claim 1 , wherein an estimation of the parasitic signals is determined according to the formula
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a
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=
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N
A
i
s
mi
(
c
i
,
t
-
t
di
)
-
A
^
i
s
mi
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c
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i
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t
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t
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s
0
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,
wherein
A is an attenuation of a transmission channel
 is an estimation of the attenuation,
s mi is a transmitted modulated digital signal with an index i, by which values from 1 to N are assumed,
c is the digital data to be transmitted,
ĉ is an estimation of the digital data to be transmitted, determined at the receiver end, and
t d is a time delay of the transmission channel,
{circumflex over (t)} d is an estimation of the time delay,
s a are the parasitic signals,
the minuend of the subtraction designating a proportion of the received modulated digital signals, and
the subtrahend of the subtraction designating
the reconstructed modulated digital signals ŝ mi and with s 0 (t) approaching zero with increasing estimation quality.