[Tinyos-help] node localization using RSSI

[Aditya Bhave]

I just completed a project on localization.

One way to create beacon nodes is to have a predefined co-ordinate system
and preprogram the beacon nodes with their x,y positions. Each beacon holds
a packet

typedef struct AnchorXY
{
    int X, Y, id;
}

If your project involves mobile non beacon nodes, have the beacon nodes
periodically broadcast an "AnchorXY" packet. Each mobile node can maintain a
link list of the AnchorXY packets it receives and when it has >= 4
triangulate to arrive at its position estimate. You can let the beacon nodes
transmit a packet as

typedef struct Beacon
{
    AnchorXY pkt;
    int hopCount;
    int ngb_id;
}

As this packet goes over multiple hops over the network, the "immediate
neighbour ID = ngb_id" field can be updated to TOS_LOCAL_ADDR at every node
and the hopCount incremented by one. In this way, an interested mobile node
can come to know how far it is from each beacon and the neighbour from which
it received the AnchorXY packet. For more details refer the paper

"Robust positionning algorithms in wireless sensor networks" by Chris
Savarese

If your network is sufficently dense and isotropic, you need not use RSSI to
calculate distance in metres. You can use distance = correction factor *
hopCount to get the distance from each beacon approximately. The correction
factor is a measure of the average hop distance in the network.

 Refer "Ad-Hoc positioning system" by Badri nath to understand the
calculation of correction factor.

On 7/4/06, Esmaeil Nadimi <Esmaeil.Nadimi at agrsci.dk> wrote:
>
> Hi all
> I am doing a project which I need to localize the nodes (Micaz motes)
> using RSSI. How can I define some nodes as beacons (the nodes which they
> know their position) in such a way that mobile nodes communicate with
> them and also with the gateway.
> Is there any application similar or any code?
> Thanks in advance
> Esmaeil
>
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-- 
regards,
Aditya Bhave
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