Speed detection method in communication system, receiver, network element and processor

• US 20070046527A1
• Filed: 06/08/2006
• Published: 03/01/2007
• Est. Priority Date: 07/04/2005
• Status: Active Grant

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Saily, Mikko, Jones, Eric, Sundaralingam, Sathiaseelan, Hasan, Khairul
• Granted Patent: US 7,505,864 B2
• Time in Patent Office: Days
• US Class Current: 342/88
• CPC Class Codes: G01S 11/10 using Doppler effect

Abstract

The embodiment of the invention is related to a processor comprising, for example, means for determining a predetermined number of frequency estimates, means for determining an average of the frequency estimates for obtaining an averaged frequency offset, means for unbiasing received samples and/or impulse response values using the averaged frequency offset, means for calculating Doppler frequency estimates using the unbiased received samples and/or impulse response values and means for calculating selected second order statistics of the Doppler frequency estimates over a predetermined period.

Claims

1. A speed detection method in a communication system, comprising:

determining a predetermined number of frequency estimates;

determining an average of the frequency estimates for obtaining an averaged frequency offset;

unbiasing received samples and/or impulse response values using the averaged frequency offset;

calculating Doppler frequency estimates using the unbiased received samples and/or the impulse response values;

calculating selected second order statistics of the Doppler frequency estimates over a predetermined period;

estimating a maximum Doppler frequency based on the selected second order statistics;

calculating a speed of a communication system terminal using the maximum Doppler frequency.

2. The method of claim 1, wherein the method is executed over a selected period.

3. The method of claim 1, wherein the method is executed burstwise.

4. The method of claim 1, further comprising:

determining the frequency estimates by using equation

${\widehat{\mathrm{\omega <br><br>}}}_{\mathrm{lse}}=-\frac{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n<br><br>\mathrm{Im}<br><br>\left\{a_n^{*}<br><br>z_n\right\}}{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n<br><br>{<br><br>a_n<br><br>}^2},$

wherein

z_n are received samples,

r_n≡

(n−

N/2) are constants,

n denotes current received symbols, and

a_n denotes reference values that are obtained from

$a_n=\underset{k=0}{\overset{L}{\sum <br><br>}}<br><br>h_k<br><br>s_{n-k},<br><br>n=64<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>87,$

wherein

h_k represents a current channel impulse response value,

s<sub>n−

k</sub> represents transmitted training symbols, and

L represents a number of channel impulse response values.

5. The method of claim 1, further comprising:

determining the average of the frequency estimates by using equation

ω

_k= ω

<sub>k−

1</sub>+μ

ω

_k,

wherein

ω

<sub>k−

1</sub> represents a previous frequency estimate average calculated for a previous burst,

ω

_k represents a frequency estimate over a selected period comprising a burst,

k is a period number, and

μ

is an adaptive constant, wherein the adaptive constant μ

is set between 0.008-0.04 to obtain a smooth average, and is set to a higher value when a fast adaptation is needed.

6. The method of claim 5, further comprising:

unbiasing predetermined frequency estimates by using equation

z′

_n=z_ne<sup>−

j2π

ω

k(n−

M/2)</sup>, n={0,1, . . . M−

1}

wherein

z_n represents the received samples before unbiasing,

M is a period length comprising a burst length, and

j denotes a complex value.

7. The method of claim 5, further comprising:

unbiasing impulse response values using equation

h′

_i=h_ie<sup>−

j2π

ω

k(i−

L/2)</sup>, i={0,1, . . . L−

1},

wherein

h_i represents filter taps or the impulse response values before biasing,

L denotes a number of filter taps or impulse response values, and

j is a complex value.

8. The method of claim 1, further comprising:

calculating the Doppler frequency estimates by using equation

${\widehat{\mathrm{\omega <br><br>}}}_{\mathrm{lmmse}}=-\frac{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n<br><br>\mathrm{Im}<br><br>\left\{a_n^{\mathrm{\prime <br><br>}*}<br><br>z_n^{\mathrm{\prime <br><br>}}\right\}}{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n^2<br><br>{<br><br>a_n^{\mathrm{\prime <br><br>}}<br><br>}^2},$

wherein

z′

_n are modified received samples comprising mean/average frequency offset removed,

r_n≡

(n−

N/2) are constants,

σ

_w² is an estimated noise variance,

σ

_ω

² is a variance of the frequency offset,

Σ

denotes a summing operation,

Im denotes an imaginary value,

n denotes a current received symbol,

a′

*_n represents the complex conjugate of reference values obtained after average removal, and

a′

_n represents reference values obtained after an average removal

$a_n^{\mathrm{\prime <br><br>}}=\underset{k=0}{\overset{L}{\sum <br><br>}}<br><br>h_k^{\mathrm{\prime <br><br>}}<br><br>s_{n-k},$

wherein

h′

_k represents a channel impulse response value after mean/average removal,

s<sub>n−

k</sub> denotes a transmitted training symbols, and

L represents a number of channel impulse response values.

9. The method of claim 5, further comprising calculating a selected second order statistics by using equation

$f_{\mathrm{std}}=\sqrt{\frac{1}{N}}$

∑

k = 0 N - 1 ⁢



ω

k - ω

_ k 

2 ,

wherein

N is a number of periods,

ω

_k represents the frequency estimate over a selected period comprising a burst),

ω

_k denotes the average of the frequency estimates, and

k is a period number.

10. The method of claim 1, wherein the selected second order statistics being a standard deviation.

11. The method of claim 9, further comprising:

estimating a maximum Doppler frequency by using equation

f_m=√

{square root over (−

2f_std²ln(α

) )},

wherein

α

is a confident interval or an optimum probability that captures the maximum Doppler shift from a frequency distribution, wherein a is chosen using simulations.

12. The method of claim 11, further comprising:

calculating the speed of a communication system terminal by using equation

$\hat{v}=\frac{c<br><br>\text{\hspace{1em}<br><br>}<br><br>{\hat{f}}_m}{f_c},$

wherein

f_c is a carrier frequency, and

c is speed of light, 3*10⁸ m/s.

13. A receiver comprising:

means for determining a predetermined number of frequency estimates;

means for determining an average of the frequency estimates for obtaining an averaged frequency offset;

means for unbiasing received samples and/or impulse response values using the averaged frequency offset;

means for calculating Doppler frequency estimates using the unbiased received samples and/or the impulse response values;

means for calculating a selected second order statistics of the Doppler frequency estimates over a predetermined period;

means for estimating a maximum Doppler frequency based on the selected second order statistics;

means for calculating a speed of a communication system terminal using the maximum Doppler frequency.

14. The receiver of claim 13, further comprising:

means for executing the speed calculation over a selected period.

15. The receiver of claim 13, further comprising:

means for executing the speed calculation burst-wise.

16. The receiver of claim 13, further comprising:

means for determining frequency estimates by using equation

${\widehat{\mathrm{\omega <br><br>}}}_{\mathrm{lse}}=-\frac{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n<br><br>\mathrm{Im}<br><br>\left\{a_n^{*}<br><br>z_n\right\}}{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n<br><br>{<br><br>a_n<br><br>}^2},$

wherein

z_n are received samples,

r<sub>n≡

(n−

N/</sub>2) are constants,

n denotes current received symbols, and

a_n represents reference values that are obtained

$a_n=\underset{k=0}{\overset{L}{\sum <br><br>}}<br><br>h_k<br><br>s_{n-k},<br><br>n=64<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\dots <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>87,$

wherein

h_k represents a current channel impulse response value,

s<sub>n−

k</sub> denotes a transmitted training symbols, and

L represents a number of channel impulse response values.

17. The receiver of claim 13, further comprising:

means for determining the average of the frequency estimates by using equation

ω

_k= ω

<sub>k−

1</sub>+μ

ω

_k,

wherein

ω

<sub>k−

1</sub> represents a previous frequency estimate average calculated for a previous burst,

ω

_k represents a frequency estimate over a selected period comprising a burst,

k is a period number and

μ

is an adaptive constant, wherein the adaptive constant μ

is set between 0.008-0.04 to obtain a smooth average, and is set to a higher value when a fast adaptation is needed.

18. The receiver of claim 13, further comprising:

means for unbiasing predetermined frequency estimates by using equation

z′

_n=z_ne<sup>−

j2π

ω

k(n−

M/2)</sup>, n={0,1, . . . M−

1},

wherein

z_n represents the received samples before unbiasing,

M is a period length comprising a burst length, and

j denotes a complex value.

19. The receiver of claim 13, further comprising:

means for unbiasing impulse response values using equation

h′

_i=h_ie<sup>−

j2π

ω

k(i−

L/2)</sup>, i={0,1, . . . L−

1}

wherein

h_i represents filter taps or the impulse response values before biasing,

L denotes a number of filter taps or impulse response values, and

j denotes a complex value.

20. The receiver of claim 13, further comprising:

means for calculating the Doppler frequency estimates by using equation

${\widehat{\mathrm{\omega <br><br>}}}_{\mathrm{lmmse}}=-\frac{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n<br><br>\mathrm{Im}<br><br>\left\{a_n^{\mathrm{\prime <br><br>}*}<br><br>z_n^{\mathrm{\prime <br><br>}}\right\}}{\underset{n=64}{\overset{87}{\sum <br><br>}}<br><br>r_n^2<br><br>{<br><br>a_n^{\mathrm{\prime <br><br>}}<br><br>}^2},$

wherein

z′

_n are the modified received samples comprising mean/average frequency offset removed,

r_n≡

(n−

N/2) are constants,

σ

_w² is an estimated noise variance,

σ

_ω

² is a variance of the frequency offset,

Σ

denotes a summing operation,

Im denotes an imaginary value,

n denotes a current received symbol,

a′

*_n represents a complex conjugate of reference values obtained after an average removal, and

a′

_n represents reference values obtained after average removal

$a_n^{\mathrm{\prime <br><br>}}=\underset{k=0}{\overset{L}{\sum <br><br>}}<br><br>h_k^{\mathrm{\prime <br><br>}}<br><br>s_{n-k},$

wherein

h′

_k represents a channel impulse response value after mean/average removal,

s<sub>n−

k</sub> denotes a transmitted training symbols, and

L represents a number of channel impulse response values.

21. The receiver of claim 17, further comprising:

means for calculating a selected second order statistics by using equation

$f_{\mathrm{std}}=\sqrt{\frac{1}{N}<br><br>\underset{k=0}{\overset{N-1}{\sum <br><br>}}<br><br>{<br><br>{\mathrm{\omega <br><br>}}_k-{\stackrel{\_}{\mathrm{\omega <br><br>}}}_k<br><br>}^2},$

wherein

N is a number of periods,

ω

_k represents the frequency estimate over a selected period comprising a burst),

ω

_k denotes the average of the frequency estimates, and

k is a period number.

22. The receiver of claim 13, further comprising means for calculating standard deviation as a second order statistics.

23. The receiver of claim 21, further comprising:

means for estimating a maximum Doppler frequency by using equation

{circumflex over (f)}_m=√

{square root over (−

2f_stdln(α

))},

wherein

α

denotes a confident interval or an optimum probability that captures the maximum Doppler shift from a frequency distribution, wherein a is chosen using simulations.

24. The receiver of claim 23, further comprising:

means for calculating the speed of a communication system terminal by using equation

$\hat{v}=\frac{c<br><br>\text{\hspace{1em}<br><br>}<br><br>{\hat{f}}_m}{f_c},$

wherein

f_c is a carrier frequency, and

c is speed of light, 3*10⁸ m/s.

25. A network element comprising:

means for determining a predetermined number of frequency estimates;

means for determining an average of the frequency estimates for obtaining an averaged frequency offset;

means for unbiasing received samples and/or the impulse response values using the averaged frequency offset;

means for calculating Doppler frequency estimates using the unbiased received samples and/or impulse response values;

means for calculating selected second order statistics of the Doppler frequency estimates over a predetermined period;

means for estimating a maximum Doppler frequency based on the selected second order statistics;

means for calculating a speed of a communication system terminal using the maximum Doppler frequency.

26. A processor comprising:

means for determining a predetermined number of frequency estimates;

means for determining an average of the frequency estimates for obtaining an averaged frequency offset;

means for unbiasing received samples and/or impulse response values using the averaged frequency offset;

means for calculating Doppler frequency estimates using the unbiased received samples and/or the impulse response values;

means for calculating selected second order statistics of the Doppler frequency estimates over a predetermined period;

means for estimating a maximum Doppler frequency based on the selected second order statistics;

means for calculating a speed of a communication system terminal using the maximum Doppler frequency.

27. A receiver configured to:

determine a predetermined number of frequency estimates;

determine an average of the frequency estimates for obtaining an averaged frequency offset;

unbias received samples and/or impulse response values using the averaged frequency offset;

calculate Doppler frequency estimates using the unbiased received samples and/or the impulse response values;

calculate a selected second order statistics of the Doppler frequency estimates over a predetermined period;

estimate a maximum Doppler frequency based on the selected second order statistics;

calculate a speed of a communication system terminal using the maximum Doppler frequency.

28. A processor configured to:

determine a predetermined number of frequency estimates;

determine an average of the frequency estimates for obtaining an averaged frequency offset;

unbias received samples and/or impulse response values using the averaged frequency offset;

calculate Doppler frequency estimates using the unbiased received samples and/or the impulse response values;

calculate selected second order statistics of the Doppler frequency estimates over a predetermined period;

estimate a maximum Doppler frequency based on the selected second order statistics;

calculate a speed of a communication system terminal using the maximum Doppler frequency.

29. A network element configured to:

determine a predetermined number of frequency estimates;

determine an average of the frequency estimates for obtaining an averaged frequency offset;

unbias received samples and/or impulse response values using the averaged frequency offset;

calculate Doppler frequency estimates using the unbiased received samples and/or the impulse response values;

calculate selected second order statistics of the Doppler frequency estimates over a predetermined period;

estimate a maximum Doppler frequency based on the selected second order statistics;

calculate a speed of a communication system terminal using the maximum Doppler frequency.