Does anyone have any resources or what algorithm to use for DTOA in a RTLS

I have a project whereby I need to develop an application in java to calculate an RFID tagged object using DTOA (differential time of arrival) between four readers in a room. So when the tag beacons, it will hit each of the tags at different times and from that I need to calcuate the co-ordinates of the device. I am not looking for the code but an algorithm. Does anyone have any suggestions or resources?
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jtiernan2008Asked:
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Kevin CrossConnect With a Mentor Chief Technology OfficerCommented:
And probably makes more sense for south wall to be 0, so that SW corner of your room is (0, 0) to make sense from a graph/grid perspective.  Then other distances will be expressed as positive (x, y) combinations from there.

What that changes is this:
x  = Nw * d/t
x = W - (Ne * d/t)
y = L - (Nn * d/t)
y = Ns * d/t
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Kevin CrossChief Technology OfficerCommented:
This is probably not complete thought as have to figure out how to adjust the equations for non-linear travel to sensor (i.e. diagonal - being in a corner) but at least a start if a sensor reads time to hit each wall.

Assumptions:
Location on an axis W-E or N-S is expressed as a straight line from that wall.
West wall is 0 and East wall is full width of room (W).
North wall is 0 and South wall is full length of room (L).
Amount of time (N) that it takes to get a wall/sensor is equivalent to (time received - time sent) expressed in some time interval (t).  Nw = west wall, Ne = east wall, Nn = north wall, Ns = south wall.
There is a set rate of travel for a signal in this room expressed by distance over time interval (d/t).

So each of the coordinates x (W-E axis) and y (N-S axis) have two equations each.

x  = Nw * d/t
x = W - (Ne * d/t)
y = Nn * d/t
y = L - (Ns * d/t)

Solving for x and y will give you your (x, y) coordinate.

Just some thoughts -- hopefully not totally useless :).
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jtiernan2008Author Commented:
This is pointing me in the right direction... thanks
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