3 Range-Based Localization Scheme:

Range-Based Localization 1,2 scheme is used to calculate the distance between an anchor

node and unknown node using parameters such as angle, time and signal strength. In this method the

locality of sensor node estimation is accurate, but the hardware implementation

cost is high.

3.1

Angle of Arrival:

Angle

of Arrival(AoA) Localization Scheme 8 is based on measuring the angels of the

signal received from anchors. Antennas are used to compute the angle of arrival

of each signal at the receiver. This

scheme is an inaccuracy, and this type of measurement is inefficient due to

additional hardware cost and size of nodes. This method is not advisable for

all kinds of applications because of more cost and less accuracy. In the Fig.

2. Shows angle of arrival.

3.2

Time of Arrival Localization

Time

of Arrival(ToA) Localization Scheme 9,10 is used to determine the distance

between two sensor nodes. In this method the distance between anchor node and

unknown node is determined using the formula D=SP*T; where D is the

distance between two nodes and SP is propagation speed of signal.

Fig. 3. Indicates ToA scheme.

.3

Time Difference of Arrival method

Time Difference of Arrival method 9,10 determines the time difference

between two signals. In this method the beacon nodes should be synchronized,

the clock time must be same. In Fig. 4. T1 is the time taken to transmit

signal from anchor2 to unknown node, T2 is the time taken to

transmit signal from anchor1 to unknown node and T3 is the time

taken to transmit signal from anchor3 to unknown node.Time difference between

Anchor1 and Anchor2 is

calculated as ToDA21 = T2-T1 ; Time difference

between Anchor2 and Anchor3

is calculated as ToDA31 = T3-T1.

Received Signal Strength Indicator

Received

Signal Strength Indicator (RSSI) localization scheme is used to determine

location of unknown node with help of

signal strenght received from anchor.If received singal strenght is high then

the anchor node is near to unknown node.

If the recived signal strenght is low which indicates anchor node is

farway.RSSI is a range-based localization scheme in which the accuracy is good

but cost is high because additional hardware is required to measure the signal

send by anchor node and receiver side. In Fig. 5. three anchor nodes are

present at (x1,y1), (x2,y2) and (x3,y3) and unknow node is located at (x,y). The

received signal strenght is r1,r2

and r3.

4 Range-Free Localization Scheme:

Range-free

localization 3,4,5 method is used because of hardware equipment

confinements and power requirements and this method produces locality

information with economical manner.

4.1 Centroid Localization Scheme:

Centroid

Localization Scheme is a range-free localization scheme in which does not

requires any additional hardware and exchanging information cost when compared

with range-based localization scheme. Localization algorithm is simple and low cost the sensor

node localizes itself by calculating the centroid of position all the nearby

beacon nodes4, 6.

The algorithm works as follows: Deploy all sensor nodes in the required wireless

sensor field ,anchor nodes send is locality information periodically to all

other blind nodes, which contains the anchor node id and its 2D locality

information {ID,Loctioninfo(A(x,y))} which can be obtained with the help of GPS

device. All blind nodes collects locality information about the nearby beacon

mode.

Now all the

blind nodes {B(x1,y1),B(x2,y2),

…B(xn,yn)} ready

to calculate their geographical coordinates with the help of anchor nodes {A(x1,y1), A(x2,y2),… ,A(xn,yn)} using

centroid formula.In Fig. 6. A(x1,y1),

A(x2,y2) and A(x3,y3) represents anchor

nodes and location of the blind node b(x,y)

can be estimated using the centroid localization scheme. The equation (1) is

used to calculate the node b(x,y) position.

x=

; y=

———————————–(1)

Fig. 6. Centroid Localization Scheme