Accurate node localization with directional pulsed infrared light for indoor ad hoc network applications

We present a localization scheme for indoor ad hoc networks which use pulsed infrared light as the communication medium. Ad hoc networks are formed when devices with wireless communications capabilities spontaneously connect and exchange information packets. Typically, in wireless ad hoc networks, nodes estimate their position relative to their neighbors by processing the location information in conjunction with the certain physical properties of the signals they receive, such as signal strength, bit error rate, or time difference of arrival. Unfortunately, widely used low-cost infrared transmitters and receivers for indoor applications do not allow measurement of these properties easily. To overcome this, we have developed a system which relies only on the reception of a data frame and is capable of estimating the angular direction of the infrared signal source within an error margin of +/- 5 degrees. Then, through the application of triangulation, a node estimates its relative position with respect to its neighbors. One effective method of translating a relative position to an absolute one is to use anchor nodes. These nodes broadcast their exact location. Each receiving node then progressively fixes its position and broadcasts the position updates, leading to the entire network localizing itself. A major drawback of this approach arises in large networks, where the average hop distance between an anchor and ordinary nodes is large, and position estimation errors inevitably start to accumulate. In order to alleviate this problem, we have developed the Anchor Hop Distance Weighted Localization (AHDWL) algorithm to selectively weigh position estimates at each hop. We found that the AHDWL algorithm is very effective in reducing propagation of positioning errors.