Avoidance mechanism for co-channel interference in a network

1. An avoidance method for co-channel interference in a network, comprising the steps of:

estimating at least one channel gain of each subcarrier respectively from received symbols;

evaluating an interference measure on each subcarrier based on said channel gains;

obtaining a peak-to-average measure ratio of interference within a received symbol based on said interference measure of each subcarrier;

if said peak-to-average measure ratio of interference is greater than a predetermined threshold, detecting a most interfered subcarrier at which the maximum of said interference measures occurs; and

setting a downgrading factor for said most interfered subcarrier.

2. The method as recited in claim 1 wherein said evaluating step comprises:

calculating said interference measure of each subcarrier based on first and second channel gains of each subcarrier respectively estimated from first and second received symbols.

3. The method as recited in claim 2 , wherein said peak-to-average measure ratio of interference is obtained by a ratio of the maximum of said interference measures to a total average interference measure over all subcarriers.

4. The method as recited in claim 3 wherein said downgrading factor of said most interfered subcarrier is set using a function of the maximum of said interference measures and another average interference measure over unaffected subcarriers, where said unaffected subcarriers do not belong to a group of affected subcarriers close to said most interfered subcarrier.

5. The method as recited in claim 4 further comprising the steps of:

setting another plurality of downgrading factors for said group of affected subcarriers by scaling said downgrading factor of said most interfered subcarrier by respective scaling factors; and

setting yet another plurality of downgrading factors to 1.0 for said unaffected subcarriers.

6. The method as recited in claim 5 wherein said scaling factors are chosen to make said another plurality of downgrading factors less than 1.0 for said group of affected subcarriers.

7. The method as recited in claim 5 further comprising the step of:

multiplying bit metrics associated with each subcarrier by said respective downgrading factors, thereby achieving interference avoidance.

8. The method as recited in claim 2 wherein said first and said second received symbols are two long OFDM training symbols.

9. The method as recited in claim 1 wherein said evaluating step comprises:

in an initial stage, calculating said interference measure of each subcarrier based on first and second channel gains of each subcarrier respectively estimated from first and second received symbols;

in a tracking stage, calculating said interference measure of each subcarrier at iteration i based on an instantaneous interference measure estimate of each subcarrier at iteration i and said interference measure of each subcarrier at iteration {tilde over ( )}i 1 , where i is a positive integer.

10. The method as recited in claim 9 wherein said peak-to-average measure ratio of interference is obtained by a ratio of the maximum of said interference measures at iteration i to a total average interference measure at iteration i over all subcarriers.

11. The method as recited in claim 10 wherein said downgrading factor of said most interfered subcarrier is set using a function of the maximum of said interference measures at iteration i and another average interference measure at iteration i over unaffected subcarriers, where said unaffected subcarriers do not belong to a group of affected subcarriers close to said most interfered subcarrier.

12. The method as recited in claim 11 further comprising the steps of:

setting another plurality of downgrading factors at iteration i for said group of affected subcarriers by scaling said downgrading factor of said most interfered subcarrier by respective scaling factors; and

setting yet another plurality of downgrading factors to 1.0 at iteration i for said unaffected subcarriers.

13. The method as recited in claim 12 wherein said scaling factors are chosen to make said another plurality of downgrading factors less than 1.0 for said group of affected subcarriers.

14. The method as recited in claim 12 further comprising the step of:

multiplying bit metrics associated with each subcarrier by said respective downgrading factors, thereby achieving interference avoidance.

15. The method as recited in claim 9 wherein said first and said second received symbols are two long OFDM training symbols.

16. A method of interference avoidance in a wireless network, comprising the steps of:

evaluating an interference measure, σ k,i , on each subcarrier, where subscripts k and i denote a subcarrier index and an iteration index, respectively;

obtaining a peak-to-average measure ratio of interference, PAMR i , by:

PAMR

i

=

N

ST

×

P

i

S

i

 where

P

i

=

max

k

⁢

{

σ

k

,

i

}

,

S

i

⁢

∑

k

⁢

⁢

σ

k

,

i

,

and N ST is the number of subcarriers;

if said peak-to-average measure ratio of interference is greater than a predetermined threshold, detecting a most interfered subcarrier at which the maximum of said interference measures occurs; and

setting a downgrading factor for said most interfered subcarrier, by the following formula:

β

k

p

,

i

=

(

∑

k

∉

W

i

⁢

⁢

σ

k

,

i

(

N

ST

-

L

W

)

/

P

i

)

2

 where

subscript k p denotes an index of said most interfered subcarrier, W i is an index window of subcarriers, which is centered at subcarrier k p and constituted by

{

k

P

-

L

W

-

1

2

,

⋯

⁢

,

k

P

-

1

,

k

P

,

k

P

+

1

,

⋯

⁢

,

k

P

+

L

W

-

1

2

}

at iteration i

L W is a length of said index window W i and L W<N ST , and

β k p ,i denotes said downgrading factor of subcarrier k p at iteration i.

17. The method as recited in claim 16 wherein said evaluating step comprises:

calculating said interference measure of each subcarrier in an initial stage from:

σ

k

,

i

=

1

2

×



H

k

(

1

)

-

H

k

(

2

)



,

for

⁢

⁢

i

=

0

 where σ k,0 denotes said interference measure of subcarrier k evaluated in said initial stage, and H k (1) and H k (2) are channel gains of subcarrier k estimated from first and second received symbols, respectively; and

calculating said interference measure of each subcarrier in a tracking stage from:

σ k,i =(1 −f g )×σ k,i−1 +f g ×e k,i , for i ≧1 and i ∈integer

 where f g is a for getting factor ranging from 0 to 1.0, e k,i denotes an instantaneous interference estimate of subcarrier k at iteration i, and σ k,i−1 , σ k,i denote said interference measure of subcarrier k at iterations {tilde over ( )}i 1 and i, respectively.

18. The method as recited in claim 17 further comprising the steps of:

setting another plurality of downgrading factors for (L W −1) subcarriers with indices included in W i except k p , as follows:

β

k

P

±

l

,

i

=

r

l

·

β

k

P

,

i

,

for

⁢

⁢

l

=

1

,

2

,

⋯

⁢

,

L

W

-

1

2

 where r 1 , r 2 , . . . , r 1 , . . . , r (L W −1)/2 denote (L W −1)/2 scaling factors greater than one, respectively; and

setting yet another plurality of downgrading factors to 1.0 for the other (N ST −L W ) subcarriers with indices not included in W i .

19. The method as recited in claim 18 further comprising the step of:

multiplying bit metrics associated with each subcarrier by said respective downgrading factors, thereby achieving interference avoidance.

20. The method as recited in claim 17 wherein said first and said second received symbols are two long OFDM training symbols.