**1. Introduction**

Nowadays, GPS (Global Positioning System) has been widely used to position airplanes, ships, automobiles, migrating animals, and human beings, etc. However, GPS has its own limitations. Other than the user groups for whom GPS is operated, there is no service level agreement with anyone else. As more and more people become dependant on GPS in more and more countries, the political control of GPS raised doubt about its value. Moreover, in the event of system failure, equipment depending on GPS, such as airplanes or ocean-going vessels, needs alternative positioning systems. Furthermore, GPS relies on complicated infrastructure and cannot provide sufficient accuracy, stability and coverage for environments such as indoors and highly urbanized areas (known as "urban canyon") due to the lack of lineof-sight (LOS) to the satellites of GPS. As a result, most commercial and social activities taking place in such environment can not benefit from positioning services offered by GPS.

Local positioning systems (LPS) are intended to provide a back-up for applications where GPS does not perform sufficiently to the requirements of the users. As indicated by the name, LPS can only provide positioning services within a limited area. Unlike GPS, LPS provides positioning services in communities, campuses, urbanized areas and inside buildings. LPS can be categorized into two groups: indoor positioning systems and outdoor positioning systems. The former provides positioning services inside buildings while the latter provides the services outdoors.

LPS can provide positioning services in a wide range of applications, including personal guidance, people-finding, mobile information, moving object management and so on. LPS is also essential for augmented reality and ubiquitous computation. Typical applications of LPS are as follows personal navigation assistances (PNA), personal guidance (PG), LPS tags, people-rescue and intelligent transportation services (ITS).

PNA is a portable electronic device with both positioning function and navigation capability. A PNA based system is more flexible than GPS in providing optimal route descriptions for pedestrians because they only rely on the same maps for both in-vehicle and on-foot scenarios. On the other hand, as an interactive portable device, PG can help people with effective routing, or real-time reservation, and journey updating to inform the concerned parties of the latest situation on the journey. With this service, traveling will be easier and safer for people.

The Application of Magnetic Sensors in Self-Contained Local Positioning 69

reckoning and inertial positioning. In the implementation of such a technology, the

Examples of existing self-contained LPS systems include dead reckoning systems for marine navigation (McBrewster, 2009), wheel sensing systems for automobiles (Thiessen & Dales, 1983), and pedometers for human beings (Chiang, 2007). Dead reckoning is a method of estimating an object's present position by projecting its courses steered and speeds over ground from the last known position. The dead reckoning position is only a rough approximation because it does not

All dead reckoning systems compute the position of an object based on the last known position and the relative movement from that position. The relative movement is calculated according to the direction and speed of motion. This principle is employed in the aforementioned three existing self-contained LPS. Despite the advantage of independence

An inertial positioning system (IPS) indirectly obtains the speed and direction, or displacement, through integrating the measured accelerations and the angular velocity of an object over time. Accelerometers and gyroscopes are used to continuously measure and record translational and rotational motions. Thus inertial positioning and dead reckoning are different in the data acquired (acceleration v. s. speed, angular velocity v. s. course direction) and the devices used to measure these data (e. g. accelerometer v. s. speedometer). For a dead reckoning system, the distance can also be acquired through direct estimation. For example, in a pedometer, the step length is simply estimated, not measured or calculated. The distance is estimated by multiplying the estimated step length and the number of steps counted. Generally speaking, inertial positioning, or inertial navigation, is a

on complicated infrastructure, these systems normally suffer from low accuracy.

modern technology superseding the dead reckoning, a relatively older technology.

velocity, orientation and angular velocity is less complex.

As shown in Fig. 1, with the initial local velocity **v**<sup>l</sup>

geographic frame (l-frame):

A traditional inertial positioning system is gimbaled (Sarton and George, 1959). A mechanical device called gimbal-stabilized platform is used to establish a reference system in vehicles such as submarines, surface vehicles, aircrafts and space crafts. The sensors, the gyroscopes and accelerometers, or pick-ups, are mounted up on the stabilized platform to sense specific forces. The advantage of gimbaled systems is that the computation of position,

an object known respectively, we are able to track the position of the object by subtracting the acceleration due to gravity, **g**, and then integrating the remaining acceleration **a**<sup>l</sup>

once over a time period *t* to obtain velocity, and twice to obtain displacement in the local

 11 1 <sup>0</sup> ( ) (0)

 1 l 0 <sup>1</sup> ( ) (0) d

*t*

 d

 *t*

(0) and initial local displacement **s**<sup>l</sup>

**vv s g** *t* (1)

*s t v* **s** (2)

(0) of

(*t*)-**g**,

magnetic sensors take an important role in achieving acceptable performance.

consider the effect of leeway, currents, helmsman error, or gyro error.

**2.1 Dead reckoning** 

**2.2 Inertial positioning** 

LPS can find the location of people equipped with an LPS tag, such as business men traveling in urban areas, workers working on a construction site, fire fighters in operation, such that the pertinent activities can actively monitored and coordinated for better effectiveness, efficiency and safety. An important application of LPS in public services is people-rescue, such as urban search and rescue (USAR). When disasters such as earthquakes, cyclones, tornadoes and floods occur, some specialized organizations, governments and private companies will dispatch task forces immediately. The task force will firstly locate and extricate victims entrapped, then provide and conduct first aid care. Those victims may be entrapped in confined spaces such as collapsed structures and trenches, mines and transportation accidents. Obviously, the positioning of the victims is critical for an efficient rescue action.

A typical application of LPS in transportation is so-called ITS. This new technology is still being developed to control traffic jam and improve road safety. ITS also reduces vehicle wear, travel time, and fuel consumption through managing competing factors such as vehicle type, load, and routes. Other than conventional services such as electronic toll collection and emergency vehicle notification, sophisticated services are also provided to control urban traffic and to guide drivers with automatic routes for optimal performance. LPS, integrated with GPS, makes these services possible.

In the long run, both the technology and society environments will be changed greatly. Integrated circuits (IC) will be faster, smaller and cheaper according to Moore's law. The positioning will be more accurate and robust with advanced algorithms and new sensors. Building automation and indoor three-dimensional (3D) dynamic mapping will illustrate and control the whole building environment in much greater details such that both the quality of indoor environment and the operation cost-effectiveness will be significantly improved. Virtual world and real world will be merged to create new sports, games, entertainment and arts. People will have more wealth, enjoying more social networking, and receive more cares. As a result, LPS will surely have more and more applications. Personal positioning devices will be popular to every working persons and school students. Value added services will be provided through LBS (Location Based Services) and ITS. GIS (geographic information system) and LPS will be combined to provide quick emergency response and automatic rescuing. Much smarter supply chain management, traffic management, and work force management will be available to businesses. LPS may induce a commercial exploitation in the future.
