Method and apparatus for determining the location of a node in a wireless system
A location technique is utilized within a wireless communication system where power measurements from various nodes are weighted to determine a node's location. An iterative location process is executed where as more and more nodes are heard from, a node will re-locate itself in order to improve location accuracy.
1. A method for determining a location of a node in a wireless communication system, the method comprising the steps of:
receiving a first plurality of over-the-air signals from a first plurality of nodes, the first plurality of over-the-air signals each containing a location;
calculating a first plurality of weighting factors based on a ratio of received power to transmit power;
calculating a location based on the first plurality of weighting factors and the locations;
receiving a second plurality of over-the-air signals from a second plurality of nodes, the second plurality of over-the-air signals each containing a location;
calculating a second plurality of weighting factors based on transmit and receive powers of the second plurality of over-the-air signals;
calculating an updated location based on the second plurality of weighting factors and the locations within the second plurality of over-the air signals;
wherein the first plurality of nodes comprises a first plurality of reference nodes, the locations of which are known; and
wherein the second plurality of nodes comprises reference nodes, the locations of which are known, and blind nodes, the locations of which are estimate;
wherein the step of calculating the first plurality of weighting factors comprises the step of calculating a plurality of values for
β
k
,
j
=
(
P
r
,
i
,
j
P
t
,
j
)
1
/
n
1
,
j
=
1
,
2
,
3
,
…
,
Nr
,
where
k—index for a blind node wishing to locate itself,
Nr—number of reference nodes in the system,
j—index for reference nodes,
n 1 is a parameter adjustable to optimize location estimation,
P r,k,j is the received power at the kth node for the transmission initiated at the jth node; and
P t,j is the transmit power from jth reference node; and
wherein the step of calculating the location comprises the step of calculating
x
^
k
=
∑
j
β
k
,
j
x
j
∑
j
β
k
,
j
,
k
=
1
,
2
,
3
,
…
,
Nb
,
where
Nb—number of blind nodes in the system,
x j is the location of node j; and
j—index for reference nodes.
2. The method of claim 1 wherein the first plurality of over-the-air signals additionally comprises transmit power information.
3. The method of claim 1 wherein n 1 is a parameter adjustable to optimize location estimation, preferably in the range of n/1 and 3n/1, where n is the path loss exponent assuming the following path loss model,
PL (in dB)= PL 0 (in dB)+10 n log( r )+ε,
PL (in dB)=−10log 10 (β), where r is a distance between the two nodes.
4. The method of claim 1 wherein the second plurality of over-the-air signals additionally comprises transmit power information.
5. The method of claim 1 wherein the step of calculating the second plurality of weighting factors comprises the step of calculating a second plurality of weighting factors that are based on a ratio of received power to transmit power.
6. The method of claim 1 wherein the step of calculating the second plurality of weighting factors comprises the step of calculating a plurality of values for
β
i
,
j
=
(
P
r
,
i
,
j
P
t
,
j
)
1
/
n
1
and
β
i
,
k
=
(
P
r
,
i
,
k
P
t
,
k
)
1
/
n
1
,
j
=
1
,
2
,
3
,
…
,
Nr
,
where
k—an index for a blind node wishing to locate itself,
Nr—number of reference nodes in the system,
j—index for reference nodes,
n 1 is a parameter adjustable to optimize location estimation,
P r,k,j is the received power at the kth node for the transmission initiated at the jth node; and
P t,j is the transmit power from jth reference node.
7. The method of claim 6 wherein n 1 is a parameter adjustable to optimize location estimation, preferably in the range of n/1 and 3n/2, where n is the path loss exponent assuming the following path loss model,
PL (in dB)= PL 0 (in dB)+10 n log( r )+ε,
PL (in dB)=−10log 10 (β), where r is a distance between the two nodes.
8. The method of claim 6 wherein the step of calculating the updated location comprises the step of calculating
x
^
i
=
∑
j
β
i
,
j
x
j
+
∑
k
β
i
,
k
x
^
k
∑
j
β
i
,
j
+
∑
k
β
i
,
k
,
where
i=1,2, 3, . . . , Nb
k—index for blind nodes,
Nb—number of blind nodes in the system,
x j is the location of node j; and
j—index for reference nodes.