Global Positioning System (GPS)
One of the best known positioning systems is the Global Positioning System or GPS. The reference points are the GPS satellites high in the sky above us. The system is not perfect. In (urban) canyons and under thick foliage, it does not perform well. And inside buildings it does not function at all. But the GPS system does a tremendous job for navigation and asset/personal tracking. Our site treats a lot of different aspects of GPS, so we will not go into further details here.
ARGOS satellite system
The ARGOS system is a worldwide system used for locating and collecting data by satellite often used for wildlife telemetry. It works in the opposite direction as GPS. Animals do not wear receivers, but transmitters, that send signals to the satellites passing overhead. It also enables data transmitted by sensors connected to the transmitter to be retrieved. Contrary to GPS signals that can be used for free by anybody, the use of the ARGOS system needs approval by an Approving Authority.
There are two ARGOS satellites about 527 miles above the Earth. Both circle the planet from the North pole to the South pole fourteen times a day. They take 101 minutes to go completely around the Earth.
Each satellite sees an area of Earth more than 3,000 miles wide. However, since it is traveling so fast, it sees any one animal radio collar for only ten to fourteen minutes each time it passes overhead.
The satellite records the location of the radio signal it receives relative to itself then makes sure it knows where it is, using eleven beacons on earth. The satellite can locate an animal collar signal on the surface within about 3,000 feet. The animal information is sent by the satellite to one of three ground stations -- Fairbanks, Alaska, Wallops Island, Virginia, and Lannion, France.
ARGOS also has been used to monitor sea currents, snow stations, world weather, ships, weather balloons, river water flow, volcano activity, as well as movements of animals.
ARGOS plus GPS
The French company Elta, specializing in the manufacturing of products dedicated to the ARGOS system, has recently released a new line of ARGOS data transmitters. The new generation Argos HAL-2 (for High Accuracy Locator) transmitter has an excellent and reliable frequency stability making it possible to pinpoint to an accuracy of 1,000 to 1,300 feet. The VHAL-2 (for Very High Accuracy Locator) transmitter is fitted with an integrated GPS device. It enables even more accurate pinpointing to within a few feet, while at the same time retaining the same general features and overall performances as the HAL-2.
Owing to their very low electric power consumption (less than 50µA), an elaborate miniaturization and their sturdiness, this new line can be adapted to all environmental applications, even the most demanding and most critical.
Cell phone networks
For every cell tower on Earth the exact location is known (determined with GPS), so they can serve as reference points too. And indeed, there are many cell tower location systems. As already presented in detail on our Assisted GPS page there are: Cell-ID, AOA, TDOA, TOA, E-OTD, A-FLT and OTDOA.
More modern positioning systems, used in cell phone networks, are:
E-CID: Enhanced Cell-ID. Derives additional timing and power measurements from the wireless network. Works with any phone. Accuracy: 200 - 1000m, depending on cell site density.
U-TDOA: Uplink Time Difference of Arrival. Utilizes low-cost location measurement units, installed in the operator's base stations, to precisely calculate location, using triangulation. Works with any wireless phone. Works well in urban, suburban and obstructed environments. Accuracy: 50m.
A-GPS: Assisted Global Positioning System. Utilizes modified handsets that contain a GPS receiver and a special network server to assist in location calculation. Works well in rural and suburban areas that provide an unobstructed view of the sky. Accuracy: 10m.
TruePosition
Hybrid: Any combination of location technologies, including E-CID, A-GPS, U-TDOA or AOA to achieve optimal performance for any situation.
Situated at the core of almost every wireless location system, the Serving Mobile Location Center (SMLC) is a specialized server that computes the location of a cell phone or other wireless device. TruePosition's SMLC uniquely supports all major positioning technologies, including U-TDOA, A-GPS, E-CID, and AOA, in any combination, to produce a hybridized result that offers higher accuracy performance than individual methods. The SMLC selects and prioritizes the technologies to be used in calculating the location, based on the performance requirements of the location request.
Cambridge Positioning Systems (CPS)
CPS has developed the Matrix positioning system. It is a software-only solution and hence, very cheap. How does it work?
A small software upgrade is installed in a terminal (handset) which measures the relative receive times of the signals from surrounding network transmitters. These timings are occasionally requested by the Matrix SMLC from 'anonymous' terminals, and are used to calculate and maintain a list of network transmission time offsets (the network timings). When a position request for a specified target terminal is generated by an application, the terminal responds with its timing measurements, which the Matrix locator then uses in conjunction with the
network timings to calculate the position of the terminal. The accuracy of the timings is improved by the in-built averaging of the measurements from many terminals.
This is very smart. ALL handsets in a given region contribute to the precision of the network timings, hence to the precision of the location calculation for every individual handset.
E-GPS
GSM and W-CDMA (3G) use un-synchronized networks, i.e. ones in which the transmission time offsets of the signals transmitted by one base station relative to another are unknown. The Matrix system can provide accurate timing, which facilitates the tasks for a GPS receiver. CPS has teamed with SiGe Semiconductor and Trimble to develop Enhanced-GPS (E-GPS). The combination of Matrix and GPS technology has the potential to produce a low cost and very capable positioning solution for GSM and W-CDMA handsets.
Polaris Wireless Location Signatures (PWLS)
Most positioning technologies are rapidly loosing accuracy when confronted with obstructed lines-of-sight or shadowing by buildings. PWLS makes use of the unique shadowing properties of buildings to determine where a mobile is. Often the richness of signatures in heavy multi-path improves the accuracy of this technique.
In addition to cellular and PCS networks, the Polaris location technology can be shown to provide accurate location in WiFi and WiMax wireless networks. The solution resides on standard servers and requires no modifications to handsets or cell sites.
PWLS relies on neighbor cell signal strengths and other standard network measurements automatically reported as part of normal network operation. Reports are compared against an established geo-referenced database that models the radio environment. The system identifies the best pattern match to get an accurate fix on the location of a handset.
The Polaris WLS technology is based on the principle that every location has a unique radio frequency (RF) signature. Like a fingerprint's pattern of lines and swirls, a location can be identified by a unique set of values including measurements of neighbor cell signal strengths, time delay, and other network parameters.
Polaris relies on this network information, as well as other field measurements, to model the radio environment and create a database of predicted values (the location signature). Using its proprietary statistical algorithms for pattern matching, Polaris optimally processes this data for E911 or location-based services requests to accurately determine the location of any digital wireless handset.
PWLS can be deployed stand-alone or side-by-side with existing technologies and complements A-GPS.
TV-GPS
As with cell phone towers, the positions of TV towers are exactly known. They also can be used as reference points. TV signals are low frequency, high bandwidth and high power signals that are designed to penetrate well into buildings. Rosum Corporation developed a hybrid system of GPS and TV signal triangulation to provide coverage in areas that GPS alone would be unable to serve.
WiFi in populated areas
We already reported how Skyhook Wireless and Microsoft are creating huge databases with all WiFi points in town. See this article for more info.
SiRF has licensed Skyhook's Wi-Fi Positioning System (WPS) to integrate the two technologies so that handsets can use either location determining method for location-based applications. SiRF hopes that adding Skyhook technology to its GPS chips will bring a unique competitive advantage. By selecting the hybrid offering, the vendors can take advantage of the already purchased/selected Wi-Fi and include a top notch GPS chip from SiRF.
Skyhook Wireless and MaxMind have announced a strategic partnership and technology integration. Skyhook Wireless will utilize MaxMind's IP location technology to provide universal location coverage for Skyhook applications. Skyhook and MaxMind also will integrate their two technologies to validate and optimize IP location data in ways never before possible.
But why drive all those roads yourself?
Navizon members worldwide (membership is free) constantly drive and walk around with their WiFi and/or Cellular enabled PocketPC and an incorporated or separate GPS receiver. The Navizon software, in the background, constantly uses the GPS information to build an accurate map of the WiFi and Cellular "Landscape" around a user (it determines the exact Lat/Lon of Wireless Access Points and Cellular Towers within a city, neighborhood or territory) and then stores this positioning information locally on the user's device. The user does not make an active WiFi or Cellular connection and therefore does not pay anything for this operation.
If anytime during the drive or walk the GPS signal would be lost, the Navizon software feeds the user's favorite navigation program (TomTom, Destinator, CoPilot-Live, Mapopolis etc) with accurate positioning information, so that these applications continue functioning in tunnels and even underground.
The best part is that users, who wish so, can sync with the Navizon network and upload their database with Lat/Lon information to the Navizon servers. This way an ever growing and ever more precise database with exact locations of Wireless Access Points and Cellular Towers is created.
If a member wants to go out for a drive or a walk in a region for which he/she did not yet create database entries, the user can sync with the Navizon servers and download this information (gathered by other members) to his/her pocketPC.
There are three options to sync with Navizon:
--PDA cradle sync via a PC with active internet connection
--PDA WiFi sync via an active internet connection running on the pocketPC
--GPRS cellular sync via an active connection for the pocketPC cell phone
Intel Precision Location Technology (PLT)
Usually location detection by means of triangulation is based on signal strength readings from nearby access points. But signal strength can vary for reasons other than distance. Hence, the distance calculations are less precise and as a consequence the final position will be less precise too.
Intel has developed a Precision Location Technology (PLT), based on time of arrival (TOA). The client (handset) sends a special data packet to at least two fixed Access Points (APs). The base-station time-stamps the packet and sends it back to the client.
This way the time for the packet to travel from the base-station to the client is exactly known and the distance can be calculated with much more precision. When the client knows how far it is from two APs, it can triangulate its position.
Position could become as accurate as to within one meter. This technique requires modifications to both the access point and the client, but Intel will submit the technique to the IEEE 802.11 standards for incorporation into future WLAN products.
Incorporated into WiFi and WiMAX networks, this technology could complement GPS inside buildings and urban canyons.
WiFi in hospitals, offices, warehouses, etc
Ekahau
Ekahau has developed the Ekahau Positioning Engine (EPE), a software-only location server that features up to 1m average positioning accuracy. Ekahau's tracking technology works with all industry-standard WiFi (IEEE 802.11a/b/g) access points and most network cards without proprietary hardware. EPE is capable of pinpointing Ekahau T201 WiFi Tags, laptops, PDAs and other Wifi enabled devices, with floor, room- and door-level accuracy in existing WiFi infrastructures.
Aeroscout
The AeroScout suite of products provides Enterprise Visibility Solutions using standard Wi-Fi wireless networks as an infrastructure. AeroScout's patent-pending Wi-Fi positioning technologies use the wireless infrastructure to locate any standard 802.11b mobile unit, such as laptops, PDAs, barcode scanners and RFID readers, in addition to battery-powered AeroScout Tags attached to people or any other assets and equipment. AeroScout's MobileView provides the visibility tools for developers to create location-enabled applications.
PanGo
PanGo Locator is an asset tracking system designed to provide Enterprise Asset Visibility. It is an 802.11-based asset tracking system that allows companies to know, in real-time, the location of assets, where they've been and when they're on the move. It also seamlessly integrates with workflow automation and business process solutions to enable location-based workflow optimization and better asset utilization.
WiFi underground
AeroScout, together with NL Technologies (NLT) has also developed an advanced real-time location solution (RTLS) for the underground mining industry. Using standard wireless networking technology and the industry's leading Wi-Fi-based active RFID system, the joint solution offers immediate and accurate tracking of personnel, equipment and other assets for improved safety and efficiency. NLT has integrated AeroScout's wireless real-time location system into their Northern Light Digital Network. AeroScout's long range active RFID tag is installed into the Northern Light GII Model cap lamps, providing Wi-Fi-based location tracking capabilities, in addition to the renowned quality, innovative design and durability of the Northern Light cap lamp family. With this solution in place, the location of workers, as well as valuable mobile equipment, can be continually tracked and viewed in real-time from any Web browser, to ensure safety and improve operations.
RFID (Radio Frequency IDentification)
See this article in our GPS and Wireless News Blog for more information.
Dual Frequency RFID
The AXCESS asset and personnel tracking system combines asset and people identification with the ability to functionally link an asset to a person. AXCESS active RFID tags placed on assets and people allow strategically positioned readers to automatically track and monitor movement throughout a facility without human interaction. By linking an asset ID to an employee ID, people can carry their laptops or tools with them, allowing employees to forego physical searches. The flexibility of the system comes from the use of dual frequencies for tag wake-up and data transmission; low frequency (LF) on wake up (132 kHz) and high frequency (HF) for transmission (315 MHz or 433 MHz). Tag transmission at HF encounters minimal interference and penetrates all materials except metal, enabling reliable tag transmission. This also enables long range tag reads at distances over 35 feet using omni-directional antennas, hence no line of sight required. The AXCESS tracking system provides unique features such as multi-tag read which allows for multiple tags to be read simultaneously, and Functional Linkage™ which permits decision and control based on tying two or more tag reads together (e.g., person to laptop, driver to vehicle, trailer to cargo, etc.)
ZigBee Positioning System
The new InnerWireless RF (radio frequency) location technology will allow healthcare organizations to positively impact patient safety and hospital productivity by accurately locating and optimally utilizing clinical assets; medical equipment and care givers. The system can be rapidly adopted by hospitals because virtually no data or power cables are pulled when installing the system. A two-person team can install and make fully operational an InnerWireless system within one eight-hour-shift per hospital department. Both tags and RF infrastructure are optimized using the 802.15.4 (ZigBee) wireless communications standard, thus avoiding the IP address proliferation that piggybacking on the hospital's existing 802.11 wireless data networks would cause. The InnerWireless location system scales seamlessly without major cost breakpoints, enabling a hospital to install the system and add tags when, where, and how it wants.
UWB (Ultra Wide Band)
First we have to distinguish UWB for home networking for high speed data transmission, which has been standardized in IEEE 802.15.3a and UWB for low speed data transfer, which has been standardized in IEEE 802.15.4a. Its goal is to enable indoor positioning to be very accurate with very low power. This is possible because UWB has good multipath resolution characteristics and obstacle penetration capability in the room, compared with the existing transmission media.
UWB-based tracking systems are capable of locating objects within a building to an accuracy of 10-15cm in 3D.
Multispectral Solutions, Inc. (MSSI) is a pioneer and established industry leader in the development of ultra wideband (UWB) systems for communications, radar and precision positioning applications. The company's PAL650 Precision Asset Location system is the world's first FCC-certified, UWB-based, active RFID and tracking system for personnel and high valued assets.
Ubisense is a UK-based provider of Ultra-Wideband (UWB) location tracking systems. Ubisense UWB location systems are in use in ten countries worldwide, and Ubisense was the first non-US company to receive FCC certification for an indoor UWB device in 2004.
Thales Research and Technology (UK) Ltd (TRT (UK)) in Reading has executed trials on the comparison of two UWB positioning technologies, Pulse UWB (P-UWB) and Frequency Hopped Direct Sequence UWB (FH-UWB) and has achieved positioning accuracies generally better than 30cm in both cases, even in very cluttered environments.
Researchers at Mitsubishi Electric Corp. have developed a location finding and ranging system based on an emerging short-range wireless technology. The system is capable of determining the location of an object to an accuracy of 15 centimeters over a distance of up to 30 meters and uses the IEEE802.15.4a ultra wideband (UWB) technology that's approaching in the final stages of standardization. It could be used in a hospital, for example, where sensors continuously monitor patients and alert doctors to any problems. The doctors could be sent directly to wherever the patient is in the hospital.
TRT (UK) investigates Indoor Positioning as an Augmentation to GNSS (GPS and similar systems).
Laser Positioning System
Indoor GPS from Metris can be compared to the matrix of satellites that create the Global Positioning System. Instead of satellites, Indoor GPS uses small infrared laser transmitters that emit laser pulses to create a measurement "universe". Photo detectors pick up the signals and compute angle and positions based on the timing of the arriving light pulses. This unique approach to precision measurement solves many of the problems inherent to large-scale industrial metrology and large sub-assembly positioning. To avoid confusion, we have to add that here GPS does not stand for Global Positioning System. We even thought that IndoorGPS was registered by Global Locate, a company that develops real Global Positioning System chips. The Metris system obtains a sub-millimeter level accuracy for static measurements, millimeter for dynamic measurements. The system can be used in large production halls, like airplane or car assembly halls and works both inside and outside.
Microwave-based tracking systems
Fraunhofer IIS, Erlangen, Germany has designed and set-up on behalf of Cairos technologies AG, Munich, Germany the Cairos system to enable real-time localization and tracking of ball and players during a football match.
The system consists of 6 to 12 fixed antennas, placed around the field on various heights above the ground. These receivers are fixed at the floodlights and at different facilities inside the stadium. In the ball and in each shin pad of each player are miniature transmitters, approximately the size of a ten Euro cent coin.
The core of the miniature transmitters consists of a two-chip ASIC solution, which sends out up to 2000 brief code sequences per second in the ISM band at 2.4 GHz. At this rate one accumulator load is sufficient for about 4 hours and the accuracy of the system is within the range of few centimeters, even if an object is moving with a speed of up to 140 km/h.
In order to obtain a very precise 3D positioning for every transmitter, several reference transmitters and receivers are placed in the field, which are fed with a high precision synchronizing signal. The signals arriving at the receivers are transmitted, together with a time stamp in the Pico seconds range, to the central computer through glass-fiber cables.
System tests are currently being performed in Nuremberg's Frankenstadion, a stadium taking part in the FIFA world cup 2006, so for the first time in history we can expect some very precise statistics about important matches. In the future this system could be used to help arbiters take more correct decisions.
This system can, of course, be employed in many more high dynamic domains than only sport.
Radar/Sonar positioning
At the Linköping University doctoral student Rickard Karlsson described in his thesis this Spring (2005) how modern, simulation-based methods of treating signals can be used to monitor and, if necessary, to take over the GPS function on a vessel.
This technology requires no external infrastructure and is not susceptible to interference. Instead, the vessel's own radar is used to measure the distance to surrounding shores, and this data is then compared with a digital sea chart. In a submarine, information from sonar equipment is compared with a digital depth chart. In combination with data about the movement of the vessel, the correct position can be calculated.
Preliminary trials show that the method works just as well as GPS in navigating an archipelago.
Loran
With all those modern technologies we almost forgot the longest existing system, Loran, which stands for LOng RAnge Navigation. Loran-A was developed during World War II and Loran-C in the 1950s. It is a land-based radio navigation system operating in the 90 - 110 kHz band and provides coverage for the continental U.S. and its coastal waters, the Great Lakes, and most of Alaska.
Just when the world got accustomed to GPS and everybody thought that Loran was almost dead, a 2003 agreement between the FAA, United States Coast Guard (USCG) and Department of Transportation (DOT) acknowledges that "GPS is indeed vulnerable to intentional and unintentional interference and that backup systems are required…" and identified timing as another part of the US critical infrastructure.
Timing is essential to the secure and continued operation of telecommunications, power and financial infrastructures in all modern economies, and is frequently based solely on GPS. Importantly, Loran is a proven, high quality timing source, and it can support these infrastructure operations as well.
eLoran
Enhanced Loran or eLoran is a Loran system that incorporates the latest receiver, antenna, and transmission system technology to enable Loran to serve as a back-up to, and complement global navigation satellite systems (GNSS) for navigation and timing. This new technology provides substantially enhanced performance beyond what was possible with Loran-C.
For example, it is now possible to obtain absolute accuracies of 8-20 meters using eLoran for harbor entrance and approach. Similarly, eLoran can function as an independent, highly accurate source of Universal Time Coordinated (UTC). eLoran transmission infrastructure is now being installed (2004) in the US, and a variation of eLoran is now operational in northwest Europe.
It is expected that there will be a global evolution towards eLoran, and users can anticipate integrated eLoran/GNSS receivers in the near future for a variety of applications. Reference: Locus, Inc. (www.locusinc.com).
XNAV
Scientists and engineers at the Applied Physics Laboratory of the John Hopkins University are examining whether X-ray signals from celestial sources, such as stars and pulsars, can be used for satellite navigation in deep space. X-ray signals from pulsars can be observed from anywhere outside the Earth's atmosphere.
The pulsar signals have a remarkable stability, which can rival our best atomic clocks. However, the signals are very weak. APL engineers will develop the navigation algorithms necessary to convert the timing data from pulsars into a three-dimensional, real-time navigation fix, referenced to the center of our solar system. XNAV would free a satellite completely from the need for navigational assistance on Earth.
Acoustic Positioning Systems (APS)
Dynamic Position (DP) is the process of positioning a vessel in a fixed location, using dynamic forces (thrusters). Wind, waves, swell and current make that without countermeasures a vessel would not stay in the same position for long. For drilling vessels, diving support vessels, offshore production vessels and heavy lifting vessels, maintaining the exact position is extremely important.
To maintain the right position means that there must be a system to determine the actual position. For an Acoustic Positioning System an array of four or more electronic beacons are deployed on the seabed around the site. The beacons listen for acoustic sound signals in the water and can reply with a different, individual signal if they receive a signal they recognize.
The positions of the beacons can be calculated relative to each other by getting the beacons to acoustically measure the distance between themselves and the other beacons. They can measure their own depth and relay the information to a controlling system on the surface. The positions of the beacons can also be determined in real-world co-ordinates by combining acoustic range measurements from a surface unit on a boat with positions from a DGPS receiver.
Once calibrated the array of beacons can then be used to position a mobile unit carried on a diver. The diver unit can simultaneously interrogate the beacons and measure the distance from itself to each of the beacons. This way the position of the diver can be calculated.
Acoustic positioning systems can compute the position of a point many times a second. Systems are available which are accurate to 10mm over ranges of several hundred meters. Others are accurate to 50mm which can cover kilometers.
A book for students and professionals
The fact that you made it up till here proves that you are really interested in the subject. We would like to recommend to you one of the rare good books about Positioning Systems:
"Local Positioning Systems" by Krzysztof W. Kolodziej, Johan Hjelm. Hardcover 488 pages. ISBN: 0849333490
