Ever since the seventies when it was invented GPS technology has been of great help to people. One of its drawbacks was that it couldn’t have been used indoors. However ithe situation has changed.
Basics:
The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver. The system imposes some technical limitations[clarification needed] which are only removed for authorized users.
The GPS program provides critical capabilities to military, civil and commercial users around the world. In addition, GPS is the backbone for modernizing the global air traffic system. [1]
Global navigation satellite systems (GPS or GNSS) are generally not suitable to establish indoor locations, since microwaves will be attenuated and scattered by roofs, walls and other objects. However, in order to make positioning signal can be obtained everywhere (ubiquitous), integration between GPS and indoor positioning can be made.
Currently, GNSS receivers are becoming more and more sensitive due to ceaseless progress in chip technology and processing power. High Sensitivity GNSS receivers are able to receive satellite signals in most indoor environments and attempts to determine the 3D position indoors have been successful. Besides increasing the sensitivity of the receivers, the technique of A-GPS is used, where the almanac and other information are transferred though a mobile phone. [2]
A Global Positioning System (GPS) that works in cell-phones, and indoors, is the key to consumer applications that will dramatically improve our quality of life. GPS applications will do this by increasing two priceless resources: our security and our time. In this paper we outline the key applications of GPS in cell-phones and similar wireless devices. Most of these applications require the GPS to work indoors, and we provide an outline of the theory of indoor GPS, showing that GPS can indeed be made to work in most places that cell-phones work. Indoor GPS, or more precisely high-sensitivity GPS, is a combination of assisted-GPS (A-GPS) and massive parallel correlation. This paper describes both these components, with examples of each, and provides test results showing the theory in practice.[3]
This paper describes the evolution of the Parthus Technologies GPS 3000 Receiver in order to track GPS signals inside buildings and provide location solutions. GPS300 is available as Intellectual Property (IP), which is integratable into cellular telephones and PDA’s. It is necessary to be able to measure the GPS signal indoors in order to understand its structure and characteristics. The development of the Indoor Signal Sensor (ISS) GPS receiver was completed for this purpose. This receiver uses two antenna’s and two RF front ends. One antenna was placed outside or in a reference position allowing GPS signals to be acquired by conventional techniques. The other antenna was placed indoors at the location where the GPS signal was to be characterized. Using the reference code and carrier from the tracked (outside) signal, the code and carrier for the indoor signal could be generated, such that long integration periods could be achieved, with coherent signal integration, relative to the outside antenna. Twelve physical channels were assigned to the indoor antenna, with variable and selectable code delays relative to the outdoor signal. This technique provided real-time measurements of indoor GPS signals, for multiple code delays, and for various coherent integration times. The fundamental “Integrate and Dump” correlation time was set to be 125 microseconds. Each code delay correlator sample of the indoor signal was normalized against the outside signal to remove the effects of the 50 bits per second GPS data message. Each channel thus produced a relative code magnitude and carrier phase measurement. Internally, samples were accumulated over periods ranging from 1 millisecond to 4 seconds. Longer integration times are simply a convenient method of measuring the indoor GPS signal relative to the outside signal. The receiver was enabled to output the results both in real-time and in a format suitable for post processing. The real-time output consisted of D/A outputs to drive a standard oscilloscope. The Y-axis was used to display signal magnitude, relative carrier phase and raw I and Q correlator counts, verses the code delay on the X-axis. Actual video clips of the oscillator display are included in the accompanying presentation of the paper. The video clips show the constitution of the GPS signal under several conditions including stationary and slow moving antenna positions. The effects of multiple signal paths, standing waves, and the corresponding carrier phase relationships can be clearly seen. For more formal data collection, suitable for postprocessing, the receiver outputs text messages containing raw correlator counts, or relative signal strength, for all code delays. This data is captured on a PC and processed by a variety of means including Matlab and Excel to produce two and three dimensional plots. To conclude, the results of several environments are illustrated and discussed. The most important characteristics of indoor GPS signals are identified. Examples of standing wave patterns, multiple signal pathways and general signal attenuation are given, and the optimum coherent and incoherent integrations times estimated.[4]
Position location (PL) has been an important and motivating criterion in position-based routing protocols which will reduce routing overhead. Several PL technologies such as Global Positioning System (GPS), the active badge system, the bat system and the cricket compass system have been proposed. GPS technology is very useful outdoor but quite ineffective indoors because walls in buildings block GPS transmissions. Other systems mentioned above are hardware-based which require additional devices for signal transmission and this will significantly incur additional cost of installation and maintenance. In this paper, the development of a GPS-free, simple self-positioning system to be implemented in MANET are presented where the node itself determines its location from hello message signals received that are being broadcast at intervals from specifically identified stationary nodes. Location of all nodes will be based on a global coordinate system which will provide a simpler routing task in any position-based routing protocol. The proposed system will be economically developed since the hardware required are laptops or PDAs with a standard IEEE 802.11 wireless LAN card which will have a relative large transmission coverage compared to Bluetooth and infrared signals. [5]
Conclusion:
With the development of GPS system and the possibility to use it indoors people felt even more benefits of using it. Its limitations have been surpassed and it is only left for us to how it will develop further.
References:
[1] http://en.wikipedia.org/wiki/Global_Positioning_System
[2] http://en.wikipedia.org/wiki/Indoor_positioning_system#Relation_to_GPS
[3] ”Indoor GPS theory & implementation”
[4] ”Understanding The Indoor GPS Signal” by T Haddrell, A R Pratt
[5] ”Development of an indoor GPS-free self-positioning system for mobile ad hoc network (MANET)” by: Latiff, L.A.; Ali, A.; Ooi Chia-Ching; Fisal, N.
Special thanks goes to http://www.rjgaragedoors.com.au/ for article “Indoor GPS technology” title suggestion.
