Cyclic prefix based opportunistic transmission/reception scheme for interference cancelation

1. A method, comprising:

forming, by a wireless system, a signal structure to match a structure of an interfering signal with repetitive time structure;

using the formed signal structure to eliminate interference caused by the interfering signal;

wherein the signal structure comprises parts that are synchronized with repeated parts of the interfering signal structure to cancel a repetition of the interference, and the signal structure further comprises another part synchronized with non-repeated parts of the interfering signal.

2. The method according to claim 1 , wherein the interfering signal results from an orthogonal frequency-division multiplexing (OFDM) symbol of another wireless system, and the repetition of the interference signal is caused by a repetition of a cyclic prefix of the OFDM symbol.

3. The method according to claim 2 , wherein the signal structure comprises a first part synchronized to cancel the cyclic prefix of the OFDM symbol and a third part synchronized to cancel a repetition of the cyclic prefix of the OFDM symbol, and the signal structure further comprises a second part synchronized with a remainder of the OFDM signal.

4. The method according to claim 3 , wherein the first part of the signal structure is represented as x 1 , the second part of the signal structure is represented as x 2 , and the third part of the signal structure is represented as x 3 , and wherein x 1 and x 3 are calculated according to the following equations:

x 1 =k 1,1 s 1 +k 1,2 s 2   Equation 1

x 3 =k 3,1 s 1 +k 3,2 s 2   Equation 2

where s 1 and s 2 are two data signals, and represents the mapping of data signal s m into transmitted signal x n .

5. The method according to claim 4 , wherein the data signals s m comprise OFDM symbols, or any other type of modulated signal with a symbol length smaller than a length of the cyclic prefix.

6. The method according to claim 4 , wherein the second data signal s 2 is ignored, and k 1,1 =1 and k 1,2 =−1, such that:

x 1 =−x 3 =s   Equation 3.

7. The method according to claim 6 , wherein observed signals at receivers y 1 and y 3 are obtained by the following equations:

y 1 =h*x 1 +g*B+n 1 =h*s+g*B+n 1   Equation 4

y 3 =h*x 3 +g*B+n 2 =−h*s+g*B+n 2   Equation 5

where h and g represent the channel impulse response for signals s and B, respectively, and the symbol “*” represents a time domain convolution.

8. The method according to claim 7 , wherein, given the observed signals at the receivers y 1 and y 3 , an effect of interference over s and B can be removed by performing the following:

r

s

=

y

1

-

y

3

2

≈

h

*

s

+

n

1

-

n

3

2

Equation

⁢

⁢

6

r

B

=

y

1

+

y

3

2

≈

g

*

B

+

n

1

+

n

3

2

.

Equation

⁢

⁢

7

9. The method according to claim 3 , wherein the first part of the signal structure is represented as x 1 , the second part of the signal structure is represented as x 2 , and the third part of the signal structure is represented as x 3 , and wherein x 1 and x 3 are calculated according to the following equations:

x 3 =−s   Equation 8

x 1 =0  Equation 9.

10. The method according to claim 9 , wherein interference over s can be removed by performing the following:

r s =y 1 −y 3 ≈h*S+n 1 −n 3   Equation 10.

11. The method according to claim 1 , wherein the using comprises transmitting the formed signal structure to cancel the interference caused by the interfering signal.

12. An apparatus, comprising:

at least one processor; and

at least one memory comprising computer program code,

the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus at least to

form a signal structure in a wireless system to match a structure of an interfering signal with repetitive time structure;

use the formed signal structure to eliminate interference caused by the interfering signal;

wherein the signal structure comprises parts that are synchronized with the repeated parts of the interfering signal structure to cancel the repetition of the interference, and the signal structure further comprises another part synchronized with the non-repeated parts of the interference signal.

13. The apparatus according to claim 12 , wherein the interfering signal results from an orthogonal frequency-division multiplexing (OFDM) symbol of another wireless system, and the repetition of the interference signal is caused by a repetition of a cyclic prefix of the OFDM symbol.

14. The apparatus according to claim 13 , wherein the signal structure comprises a first part synchronized to cancel the cyclic prefix of the OFDM symbol and a third part synchronized to cancel a repetition of the cyclic prefix of the OFDM symbol, and the signal structure further comprises a second part synchronized with a remainder of the OFDM signal.

15. The apparatus according to claim 14 , wherein the first part of the signal structure is represented as x 1 , the second part of the signal structure is represented as x 2 , and the third part of the signal structure is represented as x 3 , and wherein x 1 and x 3 are calculated according to the following equations:

x 1 =k 1,1 s 1 +k 1,2 s 2   Equation 11

x 3 =k 3,1 s 1 +k 3,2 s 2   Equation 12

where s 1 and s 2 are two data signals, and k n,m represents the mapping of data signal s m into transmitted signal x n .

16. The apparatus according to claim 15 , wherein the data signals s m comprise OFDM symbols, or any other type of modulated signal with a symbol length smaller than a length of the cyclic prefix.

17. The apparatus according to claim 16 , wherein the second data signal S 2 is ignored, and k 1,1 =1 and k 1,2 =−1, such that:

x 1 =−x 3 =s   Equation 13.

18. The apparatus according to claim 17 , wherein observed signals at receivers y 1 and y 3 are obtained by the following equations:

y 1 =h*x 1 +g*B+n 1 =h*s+g*B+n 1   Equation 14

y 3 =h*x 3 +g*B+n 2 =−h*s+g*B+n 2   Equation 15

where h and g represent the channel impulse response for signals s and B, respectively, and the symbol “*” represents a time domain convolution.

19. The apparatus according to claim 18 , wherein, given the observed signals at the receivers y 1 and y 3 , an effect of interference over s and B can be removed by performing the following:

r

s

=

y

1

-

y

3

2

≈

h

*

s

+

n

1

-

n

3

2

Equation

⁢

⁢

16

r

B

=

y

1

+

y

3

2

≈

g

*

B

+

n

1

+

n

3

2

.

Equation

⁢

⁢

17

20. The apparatus according to claim 14 , wherein the first part of the signal structure is represented as x 1 , the second part of the signal structure is represented as x 2 , and the third part of the signal structure is represented as x 3 , and wherein x 1 and x 3 are calculated according to the following equations:

x 3 =−s   Equation 18

x 1 =0  Equation 19.

21. The apparatus according to claim 20 , wherein interference over s can be removed by performing the following:

r s =y 1 −y 3 ≈h*s+n 1 −n 3   Equation 20.

22. The apparatus according to claim 12 , wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus to transmit the formed signal structure to cancel the interference caused by the interfering signal.

23. The apparatus according to claim 12 , wherein the apparatus further comprises a comb filter.

24. A non-transitory computer readable medium encoded with a computer program configured to control a processor to perform a process, comprising:

forming a signal structure in a wireless system to match a structure of an interfering signal with repetitive time structure;

using the formed signal structure to eliminate interference caused by the interfering signal;

wherein the signal structure comprises parts that are synchronized with the repeated parts of the interfering signal structure to cancel the repetition of the interference, and the signal structure further comprises another part synchronized with the non-repeated parts of the interference signal.