Low-IF receiver
A method of selecting an intermediate frequency, IF, for use with a low-IF receiver, the method comprising determining a first frequency as the central frequency of the system bandwidth of the communication scheme used by the low-IF receiver, determining a second frequency as the central frequency of the bandwidth of the wanted signal to be received, selecting the sign of the IF to be used based on the first and second frequencies.
1. A method of selecting an intermediate frequency, IF, for use with a low-IF receiver, the method comprising:
selecting a negative IF if a second frequency is less than a first frequency;
wherein the first frequency is defined as the central frequency of the system bandwidth of an RF signal received by the low-IF receiver; and
wherein the second frequency is defined as the central frequency of the bandwidth of a wanted RF signal within the system bandwidth of the RF signal received by the low-IF receiver.
2. The method of claim 1 wherein either a negative IF or a positive IF is selected so that power of an interferer adjacent to the system bandwidth is minimized in the receive chain of the low-IF receiver.
3. The method of claim 2 wherein either a negative IF or a positive IF is selected so that an analog RF baseband filter of the low-IF receiver blocks at least a portion of the adjacent interferer.
4. The method of claim 1 wherein a positive IF is selected as positive if the second frequency is more than the first frequency in the system bandwidth.
5. The method of claim 1 wherein a negative IF is selected if (second frequency−first frequency) is negative and a positive IF is selected if (second frequency−first frequency) is positive.
6. The method of claim 1 wherein a modulus of the IF to be used is selected so as to minimize DC carrier puncturing of the wanted RF signal to be received.
7. The method of claim 1 wherein a modulus of the IF to be used is selected based on the position of a DC offset of the low-IF receiver relative to the wanted RF signal.
8. The method of claim 1 wherein a modulus of the IF to be used is selected so that the position of a DC offset of the low-IF receiver falls outside of the wanted RF signal and it is filtered by a digital front-end filter of the low-IF receiver thereby avoiding any DC carrier puncturing.
9. The method of claim 1 wherein a modulus of the IF to be used is selected so that the position of a DC offset of the low-IF receiver falls outside of the wanted RF signal and onto a guard band of an FFT module of the low-IF receiver, wherein the guard band of the FFT module and is thrown away when obtaining the result of the FFT thereby avoiding any DC carrier puncturing.
10. The method of claim 1 wherein the wanted RF signal comprises a plurality of subcarriers and wherein a modulus of the IF to be used is selected so that the position of a DC offset of the low-IF receiver falls within the wanted RF signal but in between two of the plurality of subcarriers of the wanted RF signal thereby reducing DC carrier puncturing.
11. The method of claim 1 wherein to down convert an incoming RF signal to the intermediate frequency to be used, a local oscillator of the low-IF receiver is set to provide a frequency output of the second frequency minus the intermediate frequency to be used to an input of a mixer, the mixer having a further input of the incoming RF signal and an output at the intermediate frequency to be used.
12. A non-transitory computer readable medium comprising instructions that when executed by a processor cause the processor to carry out the method of claim 1 .
13. A low-IF receiver configured to carry out the method of claim 1 .
14. The low-IF receiver of claim 13 further comprising a mixer, an analog filter, a digital filter and an FFT module.