METHOD AND ARRANGEMENT FOR SIGNAL PROCESSING IN A RECEIVER THAT CAN BE TUNED TO DIFFERENT CARRIERS

• US 20090221249A1
• Filed: 01/30/2009
• Published: 09/03/2009
• Est. Priority Date: 01/31/2008
• Status: Active Grant

• Current Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Original Assignee: ST Wireless SA
• Inventors: Aue, Volker, Amiot, Sebastien
• Granted Patent: US 8,224,276 B2
• Time in Patent Office: Days
• US Class Current: 455/192.100
• CPC Class Codes: H04B 1/0028 wherein the AD/DA conversion occurs at baseband stage
• CPC Class Codes: H04B 1/0046 Decimation, i.e. data rate reduction techniques
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 25/03821 Inter-carrier interference cancellation [ICI]
• CPC Class Codes: H04L 27/2657 Carrier synchronisation

Abstract

A method and circuit for signal processing in a receiver that can be tuned to different carriers, the method determining the energy of the adjacent carriers N+1 and N−1, wherein a carrier N contains a signal of interest and the receiver is tuned to it, from the digital signal, in that the energy value of the carriers N+1 and N−1 determined are compared with a threshold value, and in the case where the threshold value is exceeded, a frequency shift of the signal by +Δf or −Δf is effected in the second method step prior to the filtering, and the frequency shift thus produced is reversed by a frequency shift by −Δf or +Δf prior to the filtering, and the signal is decoded.

Claims

1. A method for signal processing in a receiver that can be tuned to different carriers, wherein an analog signal is received via an antenna, the method comprising:

filtering and amplifying the analog signal in a first step, converting the filtered and amplified signal into a baseband frequency that is filtered in a second method step, and, in a third method step, generating a digital signal from the filtered baseband frequency signal by means of analog-to-digital conversion, and, in a fourth method step, filtering the digital signal and subsequently decoding the filtered digital signal and outputting the decoded data, and further comprising determining from the digital signal the energy of the adjacent carriers N+1 and N−

1, wherein a carrier N contains a signal of interest and the receiver is tuned to it, and comparing the energy value of the carriers N+1 and N−

1 with a threshold value, in that in the case where the threshold value is exceeded, a frequency shift of the signal by +Δ

f or −

Δ

f is effected in the second method step prior to the filtering, and in that the frequency shift thus produced is reversed by a frequency shift by −

Δ

f or +Δ

f in the fourth method step prior to the filtering and the signal is decoded.

2. The method of claim 1 wherein the energy of a carrier N, which contains a signal of interest and to which the receiver is tuned, is determined from the digital signal and is used for threshold value setting in such a way that the ratio of the energy of the carrier N and the energy of the adjacent carriers N+1 or N−

1 determines the frequency shift.

3. A circuit for implementing a method of signal processing, comprising:

a receiver having an antenna input, to which an antenna is connected and which has on the output side a low-pass filter and a baseband circuit connected downstream of the receiver and having an input-side analog-to-digital converter, which is connected to the low-pass filter, and an output for outputting the decoded data, and comprising in the baseband circuit an ACI detector that is adapted to determine the energy of the carriers and that has a first control output, which is fed back from the digital baseband circuit into the analog receiver in such a way that it is connected in controlling fashion to a frequency shifting circuit that acts upon the antenna input with a frequency shift, and which has a second control output, which, within the digital baseband circuit, is connected in controlling fashion to a circuit for correcting the frequency shift, which circuit revises the frequency shift.

4. The circuit of claim 3 wherein the frequency shifting circuit has a frequency generator, which has a control input connected to the first control output of the ACI detector, a received signal input and a frequency output, which is connected to the low-pass filter and in which a multiplier that applies the frequency shift to the received signal is arranged between the received signal input and the frequency output.

5. The circuit of claim 3 wherein the antenna input is connected to an input of a bandpass filter, an output of the bandpass filter is connected to an input of a low noise amplifier, and an output of the low noise amplifier is connected to the received signal input of the I/Q mixing circuit, the I/Q mixing circuit having a first and a second multiplier and also a phase shifting circuit, wherein the received signal input of the I/Q mixing circuit is respectively connected to a first input of the first multiplier and a first input of the second multiplier, the control input of the I/Q mixing circuit is connected to a second input of the first multiplier directly and to a second input of the second multiplier via the phase shifting circuit, the I/Q mixing circuit has a first and a second frequency output, wherein the first frequency output is connected to the output of the first multiplier and the second frequency output is connected to the output of the second multiplier, in that the frequency outputs of the I/Q mixing circuit are respectively connected to an input of a low-pass filter circuit, in that the outputs of the low-pass filter circuit respectively form the outputs of the receiver, in that the outputs of the receiver are respectively connected to an input of a baseband circuit connected downstream, in that each input of the baseband circuit is connected to an input of an analog-to-digital converter, in that outputs of the analog-to-digital converters are respectively connected to an input of a circuit for correcting the frequency shift, in that output of the circuit for correcting the frequency shift are respectively connected to an input of a first digital low-pass filter, in that outputs of the first digital low-pass filter are connected to inputs of a sampling rate converter connected downstream, in that outputs of the sampling rate converter are connected both to inputs of a second digital low-pass filter and to inputs of an ACI detector, in that outputs of the second digital low-pass filter are connected to inputs of a demodulator, in that an output of the demodulator is connected to the output of the baseband circuit for outputting the decoded data bits, in that the ACI detector has a first and a second control output, wherein the first control output is connected to an input of a frequency generator and an output of the frequency generator is connected to a second input of the I/Q mixing circuit, in that the second control output of the ACI detector is connected to a further input of the circuit for correcting the frequency shift.

6. The arrangement of claim 3 wherein the antenna input is connected to an input of a bandpass filter, in that an output of the bandpass filter is connected to an input of a low noise amplifier, in that an output of the low noise amplifier is connected to the received signal input of the I/Q mixing circuit, in that the I/Q mixing circuit has a first and a second multiplier and also a phase shifting circuit, wherein the received signal input of the I/Q mixing circuit is respectively connected to a first input of the first multiplier and a first input of the second multiplier, in that the control input of the I/Q mixing circuit is connected to a second input of the first multiplier directly and to a second input of the second multiplier via the phase shifting circuit, in that the I/Q mixing circuit has a first and a second frequency output, wherein the first frequency output is connected to the output of the first multiplier and the second frequency output is connected to the output of the second multiplier, in that the frequency outputs of the I/Q mixing circuit are respectively connected to an input of a low-pass filter circuit, in that the outputs of the low-pass filter circuits respectively form the outputs of the receiver, in that the outputs of the receiver are respectively connected to an input of a baseband circuit connected downstream, in that each input of the baseband circuit is connected to an input of an analog-to-digital converter, in that the outputs of the analog-to-digital converters are respectively connected to an input of a circuit for correcting the frequency shift, in that outputs of the circuit for correcting the frequency shift are respectively connected to an input of a first digital low-pass filter, in that the outputs of the first digital low-pass filter are connected to inputs of a sampling rate converter connected downstream, in that the outputs of the sampling rate converter are connected to the inputs of a second digital low-pass filter, in that the outputs of the second digital low-pass filter are connected to inputs of a decimation circuit, in that the outputs of the decimation circuit are connected to inputs of a circuit for removing a guard interval, in that the outputs of the circuit are connected to inputs of an FFT circuit in that the outputs of the FFT circuit are connected both to the inputs of a demodulator directly or via an interposed second digital low-pass filter and to the inputs of a ACI detector, in that an output of the demodulator is connected to the output of the baseband circuit for outputting the decoded data bits, in that the ACI detector has a first and a second control output, wherein the first control output is connected to an input of a frequency generator and an output of the frequency generator is connected to a second input of the I/Q mixing circuit, in that the second control output of the ACI detector is connected to a further input of the circuit for correcting the frequency shift.

7. A method of signal processing in a receiver adapted to be tuned to different signal carriers received on an antenna, the method comprising:

filtering and amplifying a received analog signal from the antenna;

converting the filtered and amplified analog signal into a baseband frequency signal that is filtered;

generating a digital signal from the filtered baseband frequency signal by means of an analog-to-digital conversion method, and

filtering the digital signal and decoding the filtered digital signal to output decoded data; and

determining from the digital signal the energy of adjacent carriers N+1 and N−

1, wherein a carrier N contains a signal of interest to which the receiver is tuned, and comparing energy values of adjacent carriers with a threshold value, and where the threshold value is exceeded, frequency shifting the baseband frequency prior to the filtering of the baseband frequency signal, and reversing the shifting of the baseband frequency prior to filtering of the digital signal.

8. The method of claim 7 wherein determining the energy of adjacent carriers comprises determining from the digital signal the energy of the adjacent carriers N+1 and N−

1, where the carrier N contains a signal of interest to which the receiver is tuned, and comparing the energy value comprises comparing the energy value of the carriers N+1 and N−

1 with the threshold value.

9. The method of claim 8 wherein the energy of the carrier N is determined from the digital signal and is used in setting the threshold value so that the ratio of the energy of the carrier N and the energy of the adjacent carriers N+1 or N−

1 determines the frequency shift.

10. A circuit, comprising:

a bandpass filter and low noise amplifier adapted to filter and amplify a received analog signal;

an I/Q mixing circuit adapted to receive the filtered and amplified signal and to output a baseband frequency signal that is filtered, the I/Q mixing circuit comprising first and second multipliers for phase shifting the baseband frequency signal prior to filtering; and

a baseband circuit comprising an analog-to-digital converter that receives the filtered baseband frequency signal and outputs a digital signal to a filter and decoder that output a filtered digital signal and decoded data, respectively, the baseband circuit further comprising a frequency shifting circuit that reverses the frequency shift of the first and second multipliers in the I/Q mixing circuit, a filter that filters the frequency-shifted digital signal and outputs to a sampling rate converter that converts the signal with a sampling rate, the output of which is filtered, and the filtered signal is divided by the divisor 2 in a decimation circuit, the baseband circuit further comprising an ACI detector that receives the sampled output signal from the sampling rate converter and generates a control signal to a frequency generator that outputs a control signal to the first and second multipliers in the receiver and a control signal to the frequency shift circuit.

11. The circuit of claim 10 wherein the ACI detector is adapted to determine from the sampled digital signal the energy of adjacent carriers to a carrier signal N that contains a signal of interest and to compare the energy value of the adjacent carriers with a threshold value and determine a frequency shift control signal for the frequency generator 4 and the frequency shift circuit 13.

12. The circuit of claim 11 wherein the ACI circuit compares the energy value of the adjacent carriers N+1 and N−

1 with the threshold value in determining the frequency shift.