Method of estimating position of mobile node in wireless sensor network

A method of estimating the positions of a plurality of mobile nodes in a wireless sensor network including a small number of anchor nodes, the method comprising:

• estimating frequency offsets of the anchor nodes, the frequency offsets of the anchor nodes representing differences between a reference frequency and frequencies of the anchor nodes;
• when a new mobile node is connected, estimating a frequency offset of the mobile node, the frequency offset of the mobile node representing a difference between the reference frequency and a frequency of the mobile node;
• allowing the anchor nodes to sequentially transmit ranging frames;
• allowing the mobile node to receive the ranging frames, form node pairs, and estimate a difference in distance between the formed node pair;
• and
• applying the difference in distance between the node pair to time difference of arrival (TDOA) to estimate the position of the mobile node.

A method of estimating the position of a mobile node in a wireless sensor network including a plurality of anchor nodes, the method comprising:

• using the anchor nodes to form pairs of anchor nodes connected to each other;
• calculating frequency offsets of the anchor nodes on the basis of information on the transmission and reception times of ranging frames between the pair of anchor nodes;
• calculating the frequency offset of the mobile node on the basis of information on the transmission and reception times of ranging frames between one of the anchor nodes whose frequency tolerance has been known and a new mobile node;
• allowing the anchor nodes to sequentially transmit the ranging frames, starting from a reference anchor node, and allowing the other anchor nodes and the mobile node to receive the transmitted ranging frames;
• allowing the mobile node to calculate a difference in distance between the anchor nodes and the mobile node at a synchronization time on the basis of information on the reception time of the ranging frame, time information included in the ranging frame, the positions of the anchor nodes, and the frequency offset of each node;
• and
• applying the calculated difference in distance to time difference of arrival (TDOA) to estimate the position of the mobile node,
• wherein, in the calculation of the frequency offsets of the anchor nodes, the frequency offsets of two nodes are calculated from the distance between the two nodes, an expression to calculate time of flight (TOF) between the two nodes, and an expression obtained from the relationship in which the transmission and reception times of the ranging frames, which are generated in parallel between the two nodes, are equal to each other.

A method of estimating the position of a mobile node in a wireless sensor network having a location server, a plurality of anchor nodes, and the mobile node, the method comprising:

• estimating differences between a reference frequency and frequencies of the anchor nodes under the control of the location server and storing the estimated result in the location server;
• when a new mobile node is added to a distance estimate service, estimating differences between the reference frequency and frequencies of a reference anchor node and the mobile node under the control of the location server, and storing the estimated result in the location server;
• allowing the location server to control the reference anchor node and the other anchor nodes to transmit frames including information required for distance estimate;
• allowing the mobile node to acquire distance difference information to be applied to time difference of arrival (TDOA) from the information required for distance estimate, which is included in the transmitted frame and information on the reception time of the frame;
• and
• transmitting the frame including the acquired distance difference information to the location server to request to estimate the position of the mobile node.