Waiting for too long at a bus stop and not sure when the bus arrives there? You don’t have to fret any more - at least on some Volvo routes. Under BMTC’s new ‘Yelli Iddira’ (where are you?) service just send an SMS on your mobile and within a minute you will get a message telling you how many buses are heading towards your stop and where they are.
   This has been made possible because BMTC has adapted the GPS system to track its fleet on-line. 

What is GPS? 
   GPS (Global Positioning System) is an advanced navigational system which can be used to determine one’s position, velocity and time any where on the globe. Instead of using stars or planets or any other fixed object for navigation, the GPS system uses satellites as precise reference points.
   It is owned and operated by the US Department of Defense, but available for public use also. It consists of three main segments: 1) the satellite constellation, 2) the ground control network and 3) the user equipment.
   The satellite constellation is made up of 24 solar-powered satellites which revolve around the earth, in six orbits at a height of about 26,600 km from the center of the earth. Their main function is to continually broadcast ranging and navigational signals. These are in the form of pseudo random codes (PRC), radiated as low power radio waves in the L band carrying information on their position in space and time. Each satellite is identified with its unique PRC and equipped with a precise timing devise.
   The ground control network monitors the satellites and fine tune their orbital data which is transmitted back to them.
   The user equipment is a GPS receiver. Depending on the complexity of the user- an individual hiker, a ship on the high seas, an aero plane in flight or a vehicle on the road - the receiver can be as small as a hand-held device or a box mounted on the vehicle.
   They all have an antenna to receive the radio signals, a microprocessor to analyze the signal, control and display devises, data reading unit and a power supply. The GPS receiver captures the ranging and navigational signals from the satellites in view and computes its own position in terms of latitude, longitude and elevation, velocity in case it is moving and time.
   To determine the location of the receiver with sufficient precision, ranging information from at least three satellites are required.
   The argument is as follows: Suppose you tell a friend that you are at a location 2 kms from the Town Hall. Then you may be anywhere in a circle of radius 2 kms with the Town Hall as the center. That is not good enough.
   If you provide a second reference, say 3 kms from the City Market, then you must be situated at one of the two points where the two circles intersect. If you have a third reference, then one of the points can be eliminated since the three circles intersect at only one common point.
   Applying the same logic, the receiver computes its position by analyzing the ranging information from three satellites using a procedure known as “Trilateration” with a precision of about 100 meters for longitude and latitude and 150 meters for elevation.
   Ranging information from a fourth satellite gives the exact time.
   BMTC has equipped most of its Volvo buses with GPS receivers just above the driver’s seat. The antenna is fixed on top of the bus.
   Locating a road vehicle in terms of its longitude and latitude is of very little use to the commuters. To convert the information to a format the commuter understands, the BMTC has produced digitized route maps along with bus stops and major landmarks, using a technology known as Geographic Information System.

How to get info
    A commuter sends an SMS to the number 9945634666 with the message, say, “Yi V356 C U” where “Yi” means “Yelli Iddira?”. V356 C is the route number of a bus heading from Kempegowda Bus Stand to Electronic City. “U” stands for “UP”- buses from the starting point and “D” for those towards the starting point.
   The message first goes to an SMS Server who forwards it to a GPS Server, both contracted by the BMTC. The GPS Server continuously receives, every ten seconds, information on location, speed and time from all the GPS receiver equipped buses.
   The GIS maps are stored in the computer at the GPS Server which integrates it with the location information received from the bus. Within a minute a message, through the SMS Server,  goes to the commuter saying, “Singasandra; Bangalore Dairy; Maharani’s College” meaning that there are three buses on the route currently, each of them approaching the stops listed, after having left the previous stop.
   Since the BMTC has displayed the digitized route maps at nearly 2000 bus stops in the city, the commuter may then estimate how long it may take for the nearest bus to arrive at his stop.
    In addition to commuter interphasing, BMTC has also installed GPS receivers in more than 1000 other buses for real-time analyses of their journey time, routing problems, monitoring drivers for speeding and so on. In some cases the information has also been used for accident reconstruction.

Future plans
   The BMTC plans to extend the ‘Yelli Iddira’ service to more buses, removing the guess work at the bus stops. Sunil Shekar, ATM, BMTC says that it also plans to introduce Passenger Information System (PIS) inside the bus using state-of-the-art technology with Liquid Crystal Display (LCD).
   PIS uses GPS-based location announcement and estimated time of arrival at different stops in that route with dynamic updates.