Method and apparatus for processing signal
A signal processing method and system are provided. The method includes receiving an input signal within a first frequency range, the input signal including a desired signal and an interference signal. The method includes down-converting the input signal to a second frequency range, which is lower than the first frequency range, using an offset local oscillator signal having a frequency substantially equal to the central frequency of the desired signal. The method includes separating the interference signal from the down-converted input signal. The method includes up-converting the separated interference signal to the first frequency range. The method includes subtracting the up-converted interference signal from the input signal at the first frequency range to obtain an interference removed signal. The method includes down-converting the interference removed signal to a third frequency range, which is lower than the first frequency range, using a local oscillator signal, for demodulating. The frequency of the offset local oscillator signal is different from the frequency of the local oscillator signal.
1. A signal processing method for a receiver comprising:
receiving an input signal within a first frequency range, the input signal including a desired signal and an interference signal;
down-converting the input signal to a second frequency range using an offset local oscillator signal having a frequency substantially equal to a central frequency of the desired signal, wherein the second frequency range is lower than the first frequency range;
separating the interference signal from the down-converted input signal;
up-converting the separated interference signal to the first frequency range;
subtracting the up-converted interference signal from the input signal at the first frequency range to obtain an interference removed signal; and
down-converting the interference removed signal to a third frequency range for demodulating using a local oscillator signal, wherein the third frequency range is lower than the first frequency range and the frequency of the offset local oscillator signal is different from a frequency of the local oscillator signal.
2. The signal processing method of claim 1 , wherein the first frequency range is an RF frequency range, and the second frequency range and the third frequency range are IF frequency ranges.
3. The signal processing method of claim 1 , wherein the interference signal is from a channel adjacent to the desired signal.
4. The signal processing method of claim 1 further comprising:
phase shifting the up-converted interference signal by 180 degrees; and
adding the phase shifted interference signal to the input signal at the first frequency range to obtain the interference removed signal.
5. The signal processing method of claim 1 further comprising:
mixing the local oscillator signal and a signal having a frequency equal to the difference between the frequency of the local oscillator signal and the central frequency of the desired signal, to generate the offset local oscillator signal.
6. A signal processing method comprising:
receiving an input signal within a first frequency range, the input signal including a desired signal and an interference signal;
down-converting the input signal to a second frequency range using a zero IF method, wherein the second frequency range is lower than the first frequency range;
separating the interference signal from the down-converted input signal;
up-converting the separated interference signal to the first frequency range;
subtracting the up-converted interference signal from the input signal at the first frequency range to obtain an interference removed signal; and
down-converting the interference removed signal to a third frequency range for demodulating using a non-zero IF method, wherein the third frequency range is lower than the first frequency range.
7. The signal processing method of claim 6 , wherein the first frequency range is an RF frequency range, and the second frequency range and the third frequency range are IF frequency ranges.
8. The signal processing method of claim 6 , wherein the interference signal is from a channel adjacent to the desired signal.
9. The signal processing method of claim 6 further comprising:
phase shifting the up-converted interference signal by 180 degrees; and
adding the phase shifted interference signal to the input signal at the first frequency range to obtain the interference removed signal.
10. The signal processing method of claim 6 , wherein the non-zero IF method is selected from a group comprised of low IF methods and high IF methods.
11. A receiver comprising:
a first mixing circuit for down-converting an input signal within a first frequency range to a second frequency range using a zero IF method, wherein the second frequency range is lower than the first frequency range, and the input signal includes a desired signal and an interference signal;
a filter for separating the interference signal from the down-converted input signal;
a second mixing circuit for up-converting the separated interference signal to the first frequency range;
a subtracting circuit for subtracting the up-converted interference signal from the input signal at the first frequency range to obtain an interference removed signal; and
a third mixing circuit for down-converting the interference removed signal to a third frequency range for demodulating using a non-zero IF method, wherein the third frequency range is lower than the first frequency range.
12. The receiver of claim 11 , wherein the filter is selected from a high pass filter and a band pass filter.
13. The receiver of claim 11 , wherein the first frequency range is an RF frequency range, and the second frequency range and the third frequency range are IF frequency ranges.
14. The receiver of claim 11 , wherein the interference signal is an interference signal from a channel adjacent to the desired signal.
15. The receiver of claim 11 further comprising:
a local oscillator signal source for providing a local oscillator signal to the third mixing circuit for down-converting the interference removed signal to the third frequency range; and
an offset local oscillator signal source for providing an offset local oscillator signal to the first mixing circuit for down-converting the input signal to the second frequency range.
16. The receiver of claim 15 , wherein the offset local oscillator signal source comprises a fourth mixing circuit for mixing the local oscillator signal with a signal having a frequency equal to the difference between the frequency of the local oscillator signal and the central frequency of the desired signal, to obtain the offset local oscillator signal.
17. The receiver of claim 16 , wherein the fourth mixing circuit comprises a pair of mixers provided as quadrature mixers.
18. The receiver of claim 11 , wherein the first mixing circuit comprises a first pair of mixers provided as quadrature mixers, and the second mixing circuit comprises a second pair of mixers provided as quadrature mixers.
19. The receiver of claim 11 , wherein the third mixing circuit comprises a third pair of mixers provided as quadrature mixers.
20. The receiver of claim 11 , wherein non-zero IF method is selected from a group comprised of low IF methods and high IF methods.