Method And Apparatus For Determining The Confidence Index Of The Estimated Location For A Target Device In A Wireless System

• US 20080154542A1
• Filed: 04/20/2007
• Published: 06/26/2008
• Est. Priority Date: 12/22/2006
• Status: Abandoned Application

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Hsyu, Ming-Chun, Chen, Chao-Nan, Tsuei, Wen
• Application Number:
  US11/737,756
• Publication Number:
  US 20080154542A1
• Time in Patent Office: Days
• US Class Current: 702/181
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/02527 Detecting or resolving anomalies in the radio frequency fingerprints of the radio-map

Abstract

Disclosed is a method for determining the confidence index of the estimated position for a target device in a wireless system. In the online location determining phase, after knowing the observations of the radio signal for a target device, the target device'"'"'s probability distribution of location and its motion model are combined to calculate the position uncertainty, thereby giving the confidence index of this location estimate. The invention determines the location probability distribution, and calculates the uncertainty of the location probability distribution and the possible maximum uncertainty under the current situation. Based on these uncertainties, this invention determines the confidence index of the radio signal. The confidence may be regarded as a quantity that the location uncertainty can be excluded in the location prediction. The larger the quantity is, the more confident the estimated location is.

Claims

1. A method for determining confidence index of estimated location of a target device in a wireless system, when a radio signal of said target device being known, said method comprising the steps of:

determining a location probability density function of said target device;

calculating a first uncertainty and a possible maximum uncertainty under current condition of said location probability density function; and

calculating a confidence index of said radio signal based on said first uncertainty and said maximum uncertainty.

2. The method as claimed in claim 1, wherein said location probability density function is a conditional probability density function p(q_t|o_t,q_t−

1), where o_t is the current received radio signal at current time t, and q<sub>t−

1</sub> is the previous location.

3. The method as claimed in claim 1, wherein said confidence index is a function of said first uncertainty and said possible maximum uncertainty.

4. The method as claimed in claim 2, wherein said first uncertainty U(Q_t|o_t, q_t−

1) is a self-contained information function of said location probability density function.

5. The method as claimed in claim 2, wherein said first uncertainty U(Q_t|o_t, q_t−

1) is the average of self-contained information of said location probability density function.

6. The method as claimed in claim 4, wherein said first uncertainty U(Q_t|o_t, q_t−

1) is obtained through the following expression;

$\begin{array}{c}U<br><br>\left(Q_t<br><br>\text{|}<br><br>o_t,q_{t-1}\right)=H<br><br>\left(Q_t<br><br>\text{|}<br><br>o_t,q_{t-1}\right)\\ =-\underset{q_t\in <br><br>Q_t}{\sum <br><br>}<br><br>p<br><br>\left(q_t<br><br>\text{|}<br><br>o_t,q_{t-1}\right)<br><br>{\log }_2<br><br>p<br><br>\left(q_t<br><br>\text{|}<br><br>o_t,q_{t-1}\right),\end{array}$

where Q_t is all possible locations of said target device at time t;

o_t is a specific observation received by said target device at time t;

p(q_t|o_t,q<sub>t−

1</sub>) is the probability that said target device is at location q_t at time t,

given that o_t is received and the estimated location of said target device at time t−

1 is q<sub>t−

1</sub>;

log₂p(q_t|o_t,q<sub>t−

1</sub>) is the self-contained quantity of the event that said target device is at location q_t at time t, given that o_t is received and the estimated location of said target device at time t−

1 is q<sub>t−

1</sub>; and

H(Q_t|o_t,q<sub>t−

1</sub>) is the entropy of said location probability distribution p(q_t|o_t,q<sub>t−

1</sub>).

7. The method as claimed in claim 2, wherein said conditional probability density function

$p$

( q t 

| 

o t , q t - 1 ) = p 

( q t , o t 

| 

q t - 1 ) p 

( o t 

| 

q t - 1 ) , and $p<br><br>\left(o_t<br><br>\text{|}<br><br>q_{t-1}\right)=\underset{{\tilde{q}}_t\in <br><br>Q_t}{\sum <br><br>}<br><br>p<br><br>\left(o_t<br><br>\text{|}<br><br>{\tilde{q}}_t\right)<br><br>p<br><br>\left({\tilde{q}}_t<br><br>\text{|}<br><br>q_{t-1}\right),$

where p({tilde over (q)}_t|q<sub>t−

1</sub>) is the transition probability that said target device moves from location q<sub>t−

1</sub> at previous time t−

1 to a possible location {tilde over (q)}_t at current time t.

8. The method as claimed in claim 7, wherein said p({tilde over (q)}_t|q_t−

1) is a transition probability that obeys Markov model, and

p(q_t,o_t|q<sub>t−

1)=p(ot</sub>|q_t,q<sub>t−

1</sub>)p(q_t|q<sub>t−

1</sub>)=p(o_t|q_t)p(q_t|q<sub>t−

1</sub>).

9. The method as claimed in claim 1, wherein said maximum uncertainty occurs when the probabilities of possible locations are the same under the same condition, and said maximum uncertainty has a maximum entropy.

10. The method as claimed in claim 9, wherein said maximum entropy is log₂(|Q_t|) where |Q_t| is the total number of all possible locations at time t.

11. The method as claimed in claim 1, wherein said confidence index depends on the quantity of said uncertainty of estimated location of said target device that is excluded from the location prediction of said target device.

12. The method as claimed in claim 6, wherein said confidence index is a function of H(Q_t|o_t,q_t−

1) and log₂(|Q_t|) , where |Q_t| is the total number of all possible locations at time.

13. An apparatus for determining confidence index of estimated location of a target device in a wireless system, when a radio signal of said target device being known, said apparatus comprising:

a location probability model indicating a location probability density function for said target device in the wireless system;

a module for calculating a first uncertainty and a possible maximum uncertainty under current condition of said location probability density function; and

a confidence index module for calculating a confidence index of said radio signal based on said first uncertainty and said maximum uncertainty.

14. The apparatus as claimed in claim 13, wherein said confidence index module produces said confidence index that is a function of said first uncertainty and said possible maximum uncertainty.

15. The apparatus as claimed in claim 13, wherein said location probability density function is a conditional probability density function p(q_t|o_t,q_t−

1), where o_t is the current received radio signal at current time t, and q<sub>t−

1</sub> is the previous location.

16. The apparatus as claimed in claim 13, wherein said first uncertainty U(Q_t|o_t, q_t−

1) is a self-contained information function of said location probability density function.

17. The apparatus as claimed in claim 13, wherein said possible maximum uncertainty has a maximum entropy, and said maximum entropy is log₂(|Q_t|), where |Q_t| is the total number of all possible locations at time t.