Granted Patent B2

US 8,050,335 · App. 12/170,460 · Granted Nov 1, 2011

Abstract

Claims (381)

1. A method, comprising:

receiving and synchronizing, via a symbol synchronizer module of a receiver, a transmitted data packet comprising orthogonal frequency division multiplexing (OFDM) symbols having cyclic prefixes;

removing, via a cyclic prefix remover module, the cyclic prefixes from the OFDM symbols to form time domain symbols;

converting, via a fast fourier transform (FFT) module, the time domain symbols to frequency domain symbols consisting of multiple sub-carriers;

estimating, via a channel estimator, channel coefficients at the multiple sub-carriers of the frequency domain symbols through at least one known OFDM symbol of the OFDM symbols transmitted at any position of the data packet;

equalizing, via an equalizer, the multiple sub-carriers of the frequency domain symbols with complex conjugate of the estimated channel coefficients at respective sub-carrier frequencies;

combining, via a combiner, the frequency domain symbols spread over the multiple sub-carriers during transmission upon equalizing the multiple sub-carriers; and

detecting, via a detector module, phase information of the combined frequency domain symbols.

2. The method of claim 1 , further comprising:

obtaining the transmitted data packet comprising of OFDM symbols via:

mapping by phase shift keying (PSK) constellations, via a mapper, data to form data symbols;

spreading, via a spreader, the data symbols over multiple sub-carriers in OFDM symbol(s);

converting, via an inverse FFT (IFFT) module, the spread data symbols to time domain symbols through inverse FFT; and

cyclically prefixing, via a cyclic prefix module, the time domain symbols to form the OFDM symbols.

3. The method of claim 2 , further comprising:

converting, via a digital to analog converter, the OFDM symbols to an analog signal;

up-converting, via an up-conversion module, the analog signal; and

transmitting, via an antenna, the up-converted analog signal.

4. The method of claim 1 , wherein the converting, via an FFT module, the time domain symbols to frequency domain symbols is expressed as:

Y k =H k ·X k +N k ,

wherein Y k is received k th sub-carrier data, H k is a frequency domain channel transfer function at the k th sub-carrier, X k is the k th sub-carrier data transmitted, and N k is noise at the k th sub-carrier.

5. The method of claim 1 , wherein the equalizing, via an equalizer, the multiple sub-carriers of the frequency domain symbols with complex conjugate of the estimated channel coefficients at respective subcarrier frequencies comprises:

weighting the sub-carriers with the complex conjugate of the estimated channel coefficients of the sub-carrier such that less weight is given to the sub-carriers having a low signal-to-noise ratio.

6. The method of claim 1 , wherein the combining, via a combiner, the frequency domain symbols spread over the multiple sub-carriers during transmission comprises:

X

^

K

=

∑

k

i

∈

⁢

K

⁢

H

k

i

*

·

Y

k

i

,

wherein, K is a set of sub-carrier indices {k i } where the same data X K is spread, {circumflex over (X)} K is an estimate of X K , Y k i is the received k i th subcarrier data, H k i the frequency domain channel transfer function at the k i th sub-carrier, * is the complex conjugate operator.

7. The method of claim 6 , wherein the expression

X

^

K

=

∑

k

i

∈

⁢

K

⁢

H

k

i

*

·

Y

k

i

is expanded as:

X

^

K

=

∑

k

i

∈

⁢

K

⁢

(

H

k

i

*

·

H

k

i

·

X

K

+

H

k

i

*

·

N

k

i

)

;

or

X

^

K

=

∑

k

i

∈

⁢

K

⁢

(



H

k

i



2

·

X

K

+

H

k

i

*

·

N

k

i

)

,

wherein a k i th sub-carrier is weighted by a factor |H k i | 2 to give a relatively lesser weight to the k i th sub-carrier having a low signal-to-noise ratio and to give a relatively greater weight to the k i th sub-carrier having a high signal-to-noise ratio, and N k i is noise at the k i th sub-carrier.

8. A system comprising a receiver, wherein the receiver comprises:

a symbol synchronizer module to receive and synchronize a transmitted data packet comprising orthogonal frequency division multiplexing (OFDM) symbols having cyclic prefixes;

a cyclic prefix remover module to remove the cyclic prefixes from the OFDM symbols to form time domain symbols;

a fast fourier transform (FFT) module to convert the time domain symbols to frequency domain symbols consisting of multiple sub-carriers;

a channel estimator to estimate channel coefficients at the multiple sub-carriers of the frequency domain symbols through at least one known OFDM symbol of the OFDM symbols transmitted at any position of the data packet;

an equalizer to equalize the multiple sub-carriers of the frequency domain symbols with complex conjugate of the estimated channel coefficients at respective sub-carrier frequencies;

a combiner to combine the frequency domain symbols spread over the multiple sub-carriers during transmission upon equalizing the multiple sub-carriers; and

a detector module to detect phase information of the combined frequency domain symbols.

9. The system of claim 8 , further comprising a transmitter, wherein the transmitter comprises:

a mapper to map, by phase shift keying (PSK) constellations, data to form data symbols;

a spreader to spread the data symbols over multiple sub-carriers in an OFDM symbol; an inverse FFT (IFFT) module to convert the spread data symbols to time domain symbols through inverse FFT; and

a cyclic prefix module to cyclically prefix the time domain symbols to form the OFDM symbols.

10. The system of claim 9 , further comprising:

a digital to analog converter to convert the OFDM symbols to an analog signal;

an up-conversion module to up-convert the analog signal; and

an antenna to transmit the up-converted analog signal.

11. The system of claim 8 , wherein the conversion of the time domain symbols to frequency domain symbols is expressed as:

Y k =H k ·X k +N k ,

wherein, Y k is received k th sub-carrier data, H k is a frequency domain channel transfer function at the k th sub-carrier, X k is the k th sub-carrier data transmitted, and N k is noise at the k th sub-carrier.

12. The system of claim 8 , wherein the equalizer further weights the sub-carriers with the complex conjugate of the estimated channel coefficients of the sub-carrier such that less weight is given to the sub-carriers having a low signal-to-noise ratio.

13. The system of claim 8 , wherein the combiner further combines according to a formula:

X

^

K

=

∑

k

i

∈

⁢

K

⁢

H

k

i

*

·

Y

k

i

,

wherein, K is a set of sub-carrier indices {k i } where the same data X K is spread, {circumflex over (X)} K is an estimate of X K , Y k i is the received k i th subcarrier data, H k i is the frequency domain channel transfer function at the k i th sub-carrier, * is the complex conjugate operator.

14. The system of claim 13 , wherein the expression

X

^

K

=

∑

k

i

∈

⁢

K

⁢

H

k

i

*

·

Y

k

i

is expanded as:

X

^

K

=

∑

k

i

∈

⁢

K

⁢

(

H

k

i

*

·

H

k

i

·

X

K

+

H

k

i

*

·

N

k

i

)

;

or

X

^

K

=

∑

k

i

∈

⁢

K

⁢

(



H

k

i



2

·

X

K

+

H

k

i

*

·

N

k

i

)

,

wherein a k i th sub-carrier is weighted by a factor |H k i | 2 to give a relatively lesser weight to the k i th sub-carrier having a low signal-to-noise ratio and to give a relatively greater weight to the k i th sub-carrier having a high signal-to-noise ratio, and N k i is noise at the k i th sub-carrier.

15. A non-transitory computer readable storage medium having instructions, that when executed by a computing platform, result in execution of an orthogonal frequency division multiplexing (OFDM) method comprising:

receiving and synchronizing, via a symbol synchronizer module, a transmitted data packet comprising OFDM symbols having cyclic prefixes;

removing, via a cyclic prefix remover module, the cyclic prefixes from the OFDM symbols to form time domain symbols;

converting, via a fast fourier transform (FFT) module, the time domain symbols to frequency domain symbols consisting of multiple sub-carriers;

estimating, via a channel estimator, channel coefficients at the multiple sub-carriers of the frequency domain symbols through at least one known OFDM symbol of the OFDM symbols transmitted at any position of the data packet;

equalizing, via an equalizer, the multiple sub-carriers of the frequency domain symbols with complex conjugate of the estimated channel coefficients at respective sub-carrier frequencies;

combining, via a combiner, the frequency domain symbols spread over the multiple sub-carriers during transmission upon equalizing the multiple sub-carriers; and

detecting, via a detector module, phase information of the combined frequency domain symbols.

16. The non-transitory computer readable storage medium of claim 15 , further comprising:

weighting the sub-carriers with the complex conjugate of the estimated channel coefficients of the sub-carrier such that less weight is given to the sub-carriers having a low signal to noise ratio and a greater weight to the subcarriers with a high signal to noise ratio.

17. The non-transitory computer readable storage medium of claim 15 , wherein the combining, via a combiner, the frequency domain symbols spread over the multiple sub-carriers during transmission is expressed as:

X

^

K

=

∑

k

i

∈

K

⁢

H

k

i

*

·

Y

k

i

wherein K is a set of sub-carrier indices {k i } where the same data X K is spread, {circumflex over (X)} K is an estimate of X K , Y k i is the received k i th subcarrier data, H k i is the frequency domain channel transfer function at the k i th sub-carrier, * is the complex conjugate operator.

18. The non-transitory computer readable storage medium of claim 17 , wherein the expression

X

^

K

=

∑

k

i

∈

K

⁢

H

k

i

*

·

Y

k

i

is expanded as:

X

^

K

=

∑

k

i

∈

K

⁢

(

H

k

i

*

·

H

k

i

·

X

K

+

H

k

i

*

·

N

k

i

)

;

or

X

^

K

=

∑

k

i

∈

K

⁢

(



H

k

i



2

·

X

K

+

H

k

i

*

·

N

k

i

)

,

wherein a k i th sub-carrier is weighted by a factor |H k i | 2 to give a relatively lesser weight to the k i th sub-carrier having a low signal-to-noise ratio and to give a relatively greater weight to the k i th sub-carrier having a high signal-to-noise ratio, and N k i is noise at the k i th sub-carrier.

Assignments (8)