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Top1. Introduction
The ONR (Office of Naval Research) Code 31developed a system designated Precise At-Sea Ship System for Indoor Outdoor Navigation (PASSION). PASSION is a shipboard interior positioning wireless navigation system which locates and tracks personnel and high value equipment aboard ships within a net-centric architecture. The PASSION algorithms presently utilize Wi-Fi along with accelerometers, gyroscopes, magnetometers when appropriate, and cameras via QR symbols. These sensors are fused with innovative vector intelligence algorithms. The existing system method has been demonstrated dockside and on land utilizing a novel hybrid federated implementation (as shown in Figure 1).
Figure 1. Simplified functional block diagram
PASSION aims at providing improved situational awareness to personnel aboard naval vessels. This improved situational awareness is particularly important for reduced manning, damage control, emergency management and ship’s security. As an ONR project it involves several innovative aspects including: a. performing interior navigation on a moving vehicle b. using MEMS sensors on a moving vehicle, c. using virtually the entire complement of available Smartphone sensors, and d. contending with the adverse RF environment of a ship.
This has worked satisfactorily with the limitation that Wi-Fi coverage (originally designed for communications but now widely used as an indoor location sensing systems (Tanju, 2009)) does not exist throughout the entire ship. Wi-Fi coverage cannot be expanded easily as its power and RF footprint are fairly large. In addition, Wi-Fi access points are not configured to provide additional situational awareness, whereas BTLE devices are designed to accommodate many different types of sensors.
1.1. Navigation and Situational Awareness Attributes
Navigation, in its most elemental representation can be categorized (May 2009), albeit not necessarily uniquely, into fixing, dead reckoning and correlation techniques. In PASSION (Tanju, 2009) all of these categories are used with the dead reckoning being implemented with accelerometers, gyroscopes, and magnetometers, and correlation navigation being implemented with Wi-Fi Fingerprinting using surveyed Wi-Fi Received Signal Strength (RSS) power.
Position fixing, in turn, in its most elemental representation, may be described as using measurements to determine loci of possible position, and then forming collections of measurements to arrive at a position fix. Position fixing sources used in PASSION include GPS (outdoors), manual “on-tops” and Quick Response codes. GPS fundamentally employs Time of Arrival measurements (in the form of pseudo ranges which may be represented as spherical or effective hyperbolic lines of position), whereas manual “on-tops” and Quick Response symbols are essentially employed as proximity sensors. Proximity sensors may be considered as a determination of the locus of points whose range is less than a threshold value from a known position. In the PASSION algorithm, QR codes can also yield a Line of Position associated with the relative orientation of the wall to which the QR code is affixed.
The utilization of BTLE sensors as a navigation aid in an integrated navigation suite is the topic of investigation for this paper. In the protocol/specifications associated with BTLE, the subject of “segregated ranging” is rather vaguely addressed. One of the parameters passed over the BTLE link is the RSS power. The implication is that the term “segregated ranging” refers to the ability to use the RSS power to determine the range from the sensor using theoretical or empirical propagation characteristics. In this paper, these BTLE RSS range associations, and therefore its utility as a navigation aid, is explored.