K. Leo Pushpraj
Manager (GPS Technology Group), Advanced Micronic Devices Ltd.
Minneapolis officially launched its travlink “Magic Bus” advanced traveler information system to provide commuters with real time information on arrival times of GPS equipped buses.
Georesearch Inc., (Vienna, Virgina) wants to use its new generation of technology incorporating GPS hardware to expand into real time vehicle tracking and fleet management markets, including emergency 911 and military command and control.
LaSalle Ambulance Service in Buffalo, New York teamed GPS with desktop mapping software to track and monitor its fleet of 42 ambulances and three aircraft. As a result, LaSalle’s vehicles have logged response times of less than eight minutes for 96-98 percent of its emergencies.
These are some of the notable points referring to the impact that he GPS technology has made on the Vehicle tracking industry. With the kind of advantages, features and pricing of the GPS modules available today, a sluggish industry is awakening with full vigour to flood the market with reliable, low cost, compact and multi-featured equipment. The requirement in India is no less compared to the situation abroad.
This paper provides a brief overview of a tracking system developed by Advanced Micronic Devices Ltd. using GPS and GIS to track any dynamic platform.
AMDL has developed the GPs based tracking system with 50% financial contribution from Department of Electronics (DOE), under the FANS Program. DPTIS is a general purpose system that can be easily customised for a wide range of applications such as airport vehicle monitoring, cargo vehicle monitoring, ocean vessels monitoring etc.
Dynamic Platform Tracking and Information System (DPTIS) employs and combines well suited technologies for positioning, mobile communication and geographical information to bring out a flexible surveillance of mobile units on ground, water and in air, The basic function is the tracking of all mobile units on ground, water and in air. The basic function is the tracking of all mobile unit and the control center.
Exact positioning of mobile units is obtained by using Differential Global Positioning System, to an accuracy of better than 10m.
The Positioning Element
Global Positioning System (GPS) is a satellite based, all weather, worldwide precise positioning system. It basically consists of 3 segments.
The Space segment which comprises of a constellation of specific GPS satellites launched in specific orbits with orbital periods of 12 hours.
The Control segment consists of the master control station at Colorado springs along with few other stations positioned around the globe to monitor and maintain the health and orbits of the GPS satellites.
User segment Consists of the military and the commercial users who use the GPS receivers to track signals from GPS satellites and use the triangulation technique to find out their positon on the surface of the earth. A standalone GPS receiver is capable of giving accuracies of about 100m RMS.
An upgradation of the GPS is Differential GPS (DGPS) which is capable of giving acuracies better than 10m. For this a special GPS reciever known as the reference receiver is placed in a known presurveyed location and by tracking the GPS satellites is able to compute the errors in the system. Using wireless communication links the error corrections are transmitted to the mobile GPS receiver s to enable them to apply these corrections in their algorithms and enhance their position accuracy.
- DPTIS components
- The system basically consists of 2 principal elements
IN-Vehicle unit (IVU): The IVU consists of the GPS receiver, a control Display Unit (CDU) and a communication system.
Control Centre The control centre consists of high a high end PC optionally in a network environment along with the communication system and a
The communication link is a two way wireless link that caters to data exchange between the control centre and the vehicles.
In-Vehicle unit (IVU): The GPS receiver used in the vehicle will have 8 or more tracking channels with parallel satellite tracking capability. Research continues to show that such receivers provide the ideal coverage for maximum GPS performance.
The “urban canyon” creates a special problem for the automotive application. Large buildings and structures made of concrete, steel and glass from canyon-like walls which interfere with incoming signals transmitted from GPS satellites. GPS receivers operating in these heavily-structured areas are subject to signal interruption and the multipath effects of signal reflection. The degree to which a GPS receiver is able to handle these anomalies is a strong function of the receiver’s signal tracking strategy. Additional channels allow the receiver to continuously track more visible satellites, which increases overall performance and reliability.
For application which require a high update rate and operate in a hostile “urban canyon” environment it becomes necessary to add a dead reckoning sensor to IVU. This will consists of a self contained heading sensor and a speed sensor to sustain the position updates during GPS outages until such a time that GPS comes back online.
The CDU serves as a link between the GPs, the user in the vehicle and the communication system. Its functionallity includes obtaining and storing the currrent position fixes computed by the GPS receiver for eventual commanded or regular interval transfer back to the control centre. Data messages originating from the control centre are displayed on an LCD screen and if required the CDU will also generate Audio-visual alarms to attract the attention of the operator. The CDU will also allow the user in the vehicle to select and convey messages back to the control centre. Entry keys are designed depending on the type of application. The options can be to have just browse and select keys or full fledged alphanumeric keys allow access to these messages and the browse and select keys allow the required message to be picked up from the available ones for transmission back to the control centre. On the other hand alphanumeric keys allow freeform entry of messages.
At first glance Vehilce tracking marketplace may seem to offer a host of communication technologies for vehicle tracking applications. However, just by taking into account the application requirements one or two technologies mat come into focus. The requirements mainly cover aspects such as reporting rate, throughout capacity geographic coverage and cost. Through the systems currently implemented in DTPIS involve UHF transceivers, a brief overview of the different types of communication technologies is warranted in order to understand the comparative advantages and limitations.
To date, the most common type of communication system used for tracking has been the conventional radios. The frequency ranges normally used are UHF (400-500 Mhz) and VHF 25-175 Mhz, although others have been used. Conventional radios are portable and can handheld units or dashboard mountable units. They are intended to operate in defined geographical regions. Users of these radios share a common radio channel and compete for airtime. As a result, RF collisions can occur if two users transmit at the same time. To curb collisions, a radio etiquette must be established wherein the users must monitor a channel and announce a line clear before attempting a call. Alternatively the control centre can adopt the polling technique to enable a response-on-request mode of operation. Hence only a half duplex radio will suffice.
Due to its wide acceptance and coverage cellular technology has attracted significant interest in the tracking industry. Though the cellular system can guarantee a better link between the control centre and the vehicles, considerable time needs to be expended in establishing a correction hence reducing the position update rates per vehicle. Also the running cost implementing this technology is high. Considering the above points it can be said that for applications with infrequent position reporting rates and requiring voice communications, a cellular system is ideal.
In North America, trunked radio is a very popular communication technology, used in 17 different Vehicle tracking systems. In Europe, it is used by five. A trunked radio system is a two way radio communications system with a central controller that acts as an automatic switchboard, handling many users and talk groups. A trunked radio system can have as many as 28 channels, one of which is a dedicated control channel that links all users and assigns open channel automatically. When a user from a single “talk group” connects, the control channel assigns an open channel for the user automatically and lets the rest of the group know which channel is in use. All the radios in that talk group automatically change to that channel, and communication commences. Each user talk group has exclusive use of the same channel to maintain privacy.
As was the case for conventional radio, trunked systems were traditionally designed for voice communications, and can become overtaxed when dealing with data. Digital trunked radio systems that are just rolling out are much better suited for voice and data.
Worldwide, 23 Automatic Vehicle location systems now include satellite-based communications. The relatively high number is due to a significant number of open architecture-type designs that can accommodate satellite communications as well as terrestrial-based communications. Some satellite-based system manufacturers see their systems as complementing existing terrestrial-based system; for example, satellite communications can be used in remote areas not covered by cellular and specialised mobileradio (SMR) techniques (which would require a dual-equipment design). Satellite communications systems typically fall into two categories; those that utilise geostationary satellites and those that plan to incorporate low earth orbit (LEO) satellites..
To date, most satellite communication systems involve geosynchronous satellites. Orbiting at altitude of 36,000 kilometers in synchronization with the earth’s surface near the equator. Due to their vast distance above the earth, they require relatively large antennas to send and receive signals, making the equipment somewhat bulky. This technology is effective for tracking applications that require wide-area coverage like ocean going vessels. The equipment and services are relatively costly. INMARSAT is a popular Satcom link for marine communication & tracking.
The Control centre is the nerve centre of the whole system polling the vehicles for their positions and receiving and sending data message from and to the vehicles. Apart from this the control centre also transmits the DGPS error correction messages.
The main PC runs software which includes an efficient operating system, a relational data base management system, a geographical information system (GIS) software to display the positions of the vehicles over a local detailed digitised map, a communication control software and a dispatching software.
At the time of deployment of the system each vehicles information is centred into a database at the control centre. These sats can be entered in a specific format to include vehicle description, vehicle identification, in-vehicle equipment details and any pertinent information or special needs the vehicles may have. The database software is also used to keep up-to-date information on the movements of the vehicles along with their defined schedules and destinations.
The graphical software provides a host of features to enable the operator to make quick position related assessments. The software provides zooming feature to enable a close-up view of the vehicle of interest and also an overall view by zooming out to be able to see all the vehicles on the screen. Editing function on the digitised map provides demarcation of certain areas which can be hazardous to the vehicles and if a vehicle ventures into such areas an audio visual alarm is activated which the operator proceeds to convey to the specific errant vehicle. Multiple window views provide both an overall view and a close up view on the same screen.
Messages from the control centre to the vehicles can be both predefined or freeform entry since the entire resources of the powerful computer is available to the operator. Emergency messages from the vehicles generate audio visual alarms at the control centre the attract the operators attention and demand an acknowledgement to ensure that the message has been received and read.
The basic data format employed for message exchanges between the control centre and the vehicles includes predefined codes in the headers of each message to stimulate the desired response from the specific member of the system.
Polling technique is employed in DPTIS. In this technique, the control centre firs transmits the DGPS corrections which will be received by all the mobile GPS receivers via the communication links. Then the control centre will poll the vehicles for their positions using their identity codes in a sequential manner to cover all the vehicles in the database. If for reasons of communication link masking, a particular vehicle does not respond the first time, the control centre will execute retries for a finite number of attempts which can be preset by the operator depending on the need.
Among the different DPTIS components-communications, positioning, maps and computers-the communication link is the chief impediment to successful widespread implementation of DPTIS. As stated at the outset, the challenges of selecting the appropriate communication solution for a particular application still remains in view of optimising reporting rate, throughput capacity, geographic coverage and reducing cost.
Vehicle tracking systems have evolved rapidly and are being currently used in many western countries. In Japan and Singapore it has already been commercialised. The tracking option has provides a tremendous advantage in all areas involving Air, Marine and Land transport.
GPS represents one of the most significant technological developments in air navigation, for establishing more efficient routes to save on fuel costs, and for managing air corridors.
At sea, GPS along with satellite based communication links help vessels to navigate safely and efficiently-even in adverse situations-while keeping in touch with the home office.
On land the goal of a GPS based tracking system is to significantly improve the efficiency of commercial and private transportation by keeping public safety organisations, maintenance crews, and drivers informed in real time about the status of the roadways. The system has also enabled cargo companies to ensure on-time schedules. Dispatchers and switchers can use the position given by GPS to adjust the routes of the vehicles to allow optimal usage of the cargo service with maximum returns.
As mentioned earlier DPTIS is a flexible and expandable system that can be easily customised to support any configuration to suit a variety of applications.