Indoor geolocation systems have applications in safety, military and nursing homes. This paper is concerned with the geolocation system based upon  time of arrival technique. The success of the time of arrival technique depends largely upon the position of the reference nodes. The optimum position of the reference nodes is found. There are errors in the measurement of time of arrival. The effect of these errors is studied. The failure rate and root mean square error (RMSE) in tag position are computed.  Uncertainty in the positions of reference nodes and its effect upon failure rate and RMSE is also computed