To implement the system to solve the joint problem of packet scheduling and self-localization in an underwater acoustic sensor network with randomly distributed nodes. In terms of packet scheduling, our goal is to minimize the localization time, and to do so we consider two packet transmission schemes, namely a collision-free scheme (CFS), and a collision-tolerant scheme (CTS). The required localization time is formulated for these schemes, and through analytical results and numerical examples their performances are shown to be dependent on the circumstances. When the packet duration is short (as is the case for a localization packet), the operating area is large (above 3 km in at least one dimension), and the average probability of packet-loss is not close to zero, the collision-tolerant scheme is found to require a shorter localization time. Collision Tolerant and Collision Free Packet Scheduling for Underwater Acoustic Localization
Optimal collision-free packet scheduling in a UASN for the localization task in single-channel ( L-MAC ) and multi-channel scenarios (DMC-MAC). In these algorithms, the position information of the anchors is used to minimize the localization time. In spite of the remarkable performance of L-MAC and DMC-MAC over other algorithms (or MAC protocols), they are highly demanding. The main drawback of L-MAC or DMC-MAC is that they require a fusion center which gathers the positions of all the anchors, and decides on the time of packet transmission from each anchor. In addition, these two collision-free algorithms need the anchors to be synchronized and equipped with radio modems to exchange information fast.
An underwater acoustic sensor network consisting of M sensor nodes and N anchors. The anchor index starts from 1, whereas the sensor node index starts from N + 1. Each anchor in the network encapsulates its ID, its location, time of packet transmission, and a predetermined training sequence for the time of flight estimation. The so-obtained localization packet is broadcast to the network based on a given protocol, e.g., periodically, or upon the reception of a request from a sensor node. The system structure is specified as follows. Anchors and sensor nodes are equipped with half-duplex acoustic modems, i.e., they cannot transmit and receive simultaneously. Anchors are placed randomly on the surface, and have the ability to move within the operating area. The anchors are equipped with GPS and can determine their positions which will be broadcast to the sensor nodes. It is assumed that the probability density function (pdf) of the distance between the anchors is known, fD(z). It is further assumed that the sensor nodes are located randomly in an operating area according to some probability density function. The sensor nodes can move in the area, but within the localization process, their position is assumed to be constant. The pdf of the distance between a sensor node and an anchor is gD(z). These pdfs can be estimated from the empirical data gathered during past network operations. Consider a single-hop network where all the nodes are within the communication range of each other. The received signal strength (which is influenced by path loss, fading and shadowing) is a function of transmission distance. Consequently, the probability of a packet loss is a function of distance between any pair of nodes in the network.