Pseudo Echo Ranging

According to the characteristics of wireless sensor networks, a novel ranging method is proposed based on measuring propagation time of acoustic signal modulated with pseudo-random number through binary phase shift keying (BPSK) and flying to and fro between two sensor nodes in a wireless sensor network. A node, that launches a ranging process and is called active node, sends modulated acoustic signal to another node which demodulates the acoustic signal received from the active node, gets the pseudo-random number sequence carried by the acoustic signal, regenerates the received acoustic signal with the pseudo-random number sequence, then sends it back to the active node and is called target node. The active node measures the time delay between the acoustic signal it sends and the acoustic signal received from the target node and then, taking into account the extra time delay caused by signal demodulation and modulation executed on the target node, estimates the distance between the two nodes. Precise time synchronization is not needed. The target node does not need to know in advance the pseudo-random number sequence sent by the active node. The active node, using cross-correlation function and the pseudo-random number sequences carried by the acoustic signals, determines the scope of general time delay firstly and then computes the precise value of the time delay in this scope. So the computational complexity or workload of the algorithm of this ranging method is much smaller than usually to compute all the entire cross correlation function values.