Receiver window shaping in OFDM to mitigate narrowband interference

1. A method for receiver window shaping for symbol extraction, comprising:

receiving a wideband signal carrying a symbol spread across a plurality of sub-carriers of a frequency band; and

obtaining a first receiver window for extracting the symbol, wherein the first receiver window has a starting point before the start of the symbol, and includes:

a first decaying edge between the starting point and the start of the symbol; and

a second decaying edge in a zero padded portion of the symbol.

2. The method of claim 1 , further comprising:

determining whether the frequency band is significantly affected by narrowband interference; and

extracting the symbol using the first window if the frequency band is significantly affected by narrowband interference,

wherein the first receiver window overlaps with a previous window in the same frequency band.

3. The method of claim 2 , further comprising:

obtaining a second receiver window for extraction of the symbol in the frequency band if the frequency band is unaffected by narrowband interference; and

extracting the symbol using the second receiver window if the frequency band is unaffected by narrowband interference,

wherein the second receiver window is non-overlapping with a previous receiver window in the same frequency band.

4. The method of claim 1 , wherein the shape of the first receiver window concentrates narrowband interference energy to a center frequency of the narrowband interference to reduce narrowband interference leakage to other sub-carriers in the frequency band.

5. The method of claim 1 , wherein obtaining the first receiver window includes:

shaping the first receiver window as a trapezoid window; and

applying the first receiver window at the outer edges between the starting point and the end of a zero-padded portion of the symbol.

6. The method of claim 5 , wherein obtaining the first receiver window further includes:

overlapping and adding a channel impulse response segment from the zero-padded portion of the symbol to the beginning of the symbol; and

overlapping and adding a second portion from a previous zero-padded symbol to the end of the symbol.

7. The method of claim 1 , wherein the first receiver window overlaps a previous receiver window for the previous adjacent symbol in the frequency band.

8. The method of claim 1 , wherein the wideband signal is an orthogonal frequency division multiplexing (OFDM) signal including an OFDM symbol spread across the plurality of sub-carriers of the frequency band.

9. The method of claim 1 , wherein the frequency band includes a plurality of sequential zero-padded symbols, and the first receiver window overlaps a zero-padding portion of a previous symbol.

10. The method of claim 1 , further comprising:

determining whether a first sub-carrier of the frequency band is significantly affected by a center frequency of the narrowband interference; and

ignoring the first sub-carrier if it has been significantly affected by the narrowband interference.

11. The method of claim 1 , further comprising:

shaping the first receiver window to minimize the total energy captured therein.

12. The method of claim 1 , further comprising:

limiting the first receiver window size in the time domain so that it is zero outside the first window range.

13. The method of claim 1 , further comprising:

shaping the first receiver window to include a substantially flat region in the time domain between the symbol edges for all samples in between the edges.

14. The method of claim 1 , further comprising:

placing a stop band in the frequency domain for the first receiver window on interference side lobes below a certain level.

15. The method of claim 1 , further comprising:

keeping the total stop band energy of a sampled frequency in the frequency domain for the first receiver window below a particular threshold.

16. The method of claim 1 , wherein the first decaying edge and second decaying edge are asymmetric.

17. A receiver module, comprising:

a serial to parallel converter configured to receive a wideband signal carrying a symbol spread across a plurality of sub-carriers of a frequency band; and

a window shaping module configured to obtain a first receiver window for extracting the symbol, wherein the window shaping module is configured so that the first receiver window has:

a starting point before the start of the symbol;

a first decaying edge between the starting point and the start of the symbol; and

a second decaying edge in a zero padded portion of the symbol.

18. The receiver module of claim 17 , wherein the window shaping module is further configured to:

determine whether the frequency band is significantly affected by narrowband interference; and

extract the symbol using the first window if the frequency band is significantly affected by narrowband interference,

wherein the first receiver window overlaps with a previous window in the same frequency band.

19. The receiver module of claim 18 , wherein the window shaping module is further configured to:

obtain a second receiver window for extraction of the symbol in the frequency band if the frequency band is unaffected by narrowband interference; and

extract the symbol using the second receiver window if the frequency band is unaffected by narrowband interference,

wherein the second receiver window is non-overlapping with a previous receiver window in the same frequency band.

20. The receiver module of claim 17 , wherein the window shaping module is further configured so that the shape of the first receiver window concentrates narrowband interference energy to a center frequency of the narrowband interference to reduce narrowband interference leakage to other sub-carriers in the frequency band.

21. The receiver module of claim 17 , wherein the window shaping module is further configured to:

shape the first receiver window as a trapezoid window;

overlap and add a channel impulse response segment from a zero-padded portion of the symbol to the beginning of the symbol;

overlap and add a second portion from the previous zero-padded symbol to the end of the symbol; and

apply the first receiver window at the outer edges between the starting point and the end of the zero-padded portion of the symbol.

22. The receiver module of claim 17 , wherein obtaining the first receiver window, the window shaping module is further configured to:

shape the first receiver window to minimize the total energy captured therein;

limit the first receiver window size in the time domain so that it is zero outside the first window range;

shape the first receiver window to include a substantially flat region in the time domain between the symbol edges for all samples in between the edges;

place a stop band in the frequency domain for the first receiver window on interference side lobes below a certain level; and

keep the total stop band energy of a sampled frequency in the frequency domain for the first receiver window below a particular threshold.

23. The receiver module of claim 17 , wherein the window shaping module is further configured to:

shape the first receiver window as a trapezoid window; and

apply the first receiver window at the outer edges between the starting point and the end of a zero-padded portion of the symbol.

24. The receiver module of claim 23 , wherein the window shaping module is further configured such that obtaining the first receiver window further includes:

overlapping and adding a channel impulse response segment from the zero-padded portion of the symbol to the beginning of the symbol; and

overlapping and adding a second portion from a previous zero-padded symbol to the end of the symbol.

25. The receiver module of claim 17 , wherein the wideband signal is an orthogonal frequency division multiplexing (OFDM) signal including an OFDM symbol spread across the plurality of sub-carriers of the frequency band.

26. A receiver module, comprising:

means for receiving a wideband signal carrying a symbol spread across a plurality of sub-carriers of a frequency band;

means for obtaining a first receiver window for extracting the symbol, such that the first receiver window has:

a starting point before the start of the symbol;

a first decaying edge between the starting point and the start of the symbol; and

a second decaying edge in a zero padded portion of the symbol.

27. The receiver module of claim 26 , wherein means for obtaining a first receiver window comprises means for obtaining the first receiver window so that the shape of the first receiver window concentrates narrowband interference energy to a center frequency of the narrowband interference to reduce narrowband interference leakage to other sub-carriers in the frequency band.

28. The receiver module of claim 26 , further comprising:

means for shaping the first receiver window as a trapezoid window;

means for overlapping and adding a channel impulse response segment from a zero-padded portion of the symbol to the beginning of the symbol;

means for overlapping and adding a second portion from the previous zero-padded symbol to the end of the symbol; and

means for applying the first receiver window at the outer edges between the starting point and the end of the zero-padded portion of the symbol.

29. The receiver module of claim 26 , further comprising:

means for shaping the first receiver window to minimize the total energy captured therein;

means for limiting the first receiver window size in the time domain so that it is zero outside the first window range;

means for shaping the first receiver window to include a substantially flat region in the time domain between the symbol edges for all samples in between the edges;

means for placing a stop band in the frequency domain for the first receiver window on interference side lobes below a certain level; and

means for keeping the total stop band energy of a sampled frequency in the frequency domain for the first receiver window below a particular threshold.

30. A circuit for improving capture of a wideband signal, wherein the circuit is adapted to:

receive a wideband signal carrying a symbol spread across a plurality of sub-carriers of a frequency band; and

obtain a first receiver window for extracting the symbol, wherein the first receiver window has a starting point before the start of the symbol, and includes:

a first decaying edge between the starting point and the start of the symbol; and

a second decaying edge in a zero padded portion of the symbol.

31. The circuit of claim 30 , wherein the circuit is adapted to obtain the first receiver window such that the shape of the first receiver window concentrates narrowband interference energy to a center frequency of the narrowband interference to reduce narrowband interference leakage to other sub-carriers in the frequency band.

32. A non-transitory computer-readable medium having stored thereon processor-executable instructions for receiver window shaping for symbol extraction, which when executed by a processor causes the processor to:

receive a wideband signal carrying a symbol spread across a plurality of sub-carriers of a frequency band; and

obtain a first receiver window for extracting the symbol, wherein the first receiver window has a starting point before the start of the symbol, and includes:

a first decaying edge between the starting point and the start of the symbol; and

a second decaying edge in a zero padded portion of the symbol.

33. The non-transitory computer-readable medium of claim 32 , wherein the stored processor-executable instructions when executed by a processor causes the processor to:

determine whether a first sub-carrier of the frequency band is significantly affected by a center frequency of the narrowband interference; and

ignore the first sub-carrier if it has been significantly affected by the narrowband interference.