Adaptive weighting method for orthogonal frequency division multiplexed soft symbols using channel state information estimates

1. A method for weighting orthogonal frequency division multiplexed soft symbols, said method comprising the steps of:

receiving a plurality of sub-carriers modulated by digital information;

filtering the sub-carriers to produce complex soft decision outputs;

creating a first sequence of the magnitudes of said complex soft decision outputs;

determining the differences between successive samples in said first sequence;

creating a second sequence of the differences between successive samples in said first sequence;

using said first and second sequences to determine a plurality of weights; and

applying said plurality of weights to said complex soft decision outputs.

2. The method of claim 1 , wherein said sub-carriers are modulated using quadrature phase shift keying.

3. A radio receiver comprising:

an input for receiving a plurality of sub-carriers modulated by digital information;

a filter for filtering the sub-carriers to produce complex soft decision outputs; and

a signal processor for creating a first sequence of the magnitudes of said complex soft decision outputs, for determining the differences between successive samples in said first sequence, for creating a second sequence of the differences between successive samples in said first sequence, for using said first and second sequences to determine a plurality of weights, and for applying said plurality of weights to said complex soft decision outputs.

4. The receiver of claim 3 , wherein said sub-carriers are modulated using quadrature phase shift keying.

5. The receiver of claim 3 , wherein said signal processor filters said first and second sequences to produce third and fourth sequences of magnitudes.

6. The receiver of claim 5 , wherein:

said third sequence has a time constant smaller than a reciprocal of a fading bandwidth of the plurality of sub-carriers; and

said fourth sequence has a time constant larger than the reciprocal of the fading bandwidth of the plurality of sub-carriers.

7. The receiver of claim 5 , wherein the signal processor compensates for differences in effective group delay of said first and second sequences to produce the third and fourth sequences.

8. The receiver of claim 5 , wherein said plurality of weights are determined using the formula:

w

k

,

n

=

1

filtd

k

,

n

·

(

1

+

(

filtd

k

,

n

filtv

k

,

n

-

filtd

k

,

n

)

4

)

wherein w k,n represents said plurality of weights, filtv k,n represents said third sequence, and filtd k,n represents said fourth sequence, k identifies a symbol in said digital information, and n identifies one of the said sub-carriers.

9. The receiver of claim 8 , wherein if filtv k,n >1.5·filtd k,n , then w k,n is set to zero.