Start-up sequence in the PTT project

GPS positioning is a well-known positioning system and used in severalapplications. However, these signals are sent with low power and do notpenetrate walls and have problems in urban areas with tall buildings. On theother hand, GPS shows advantages compared to other technologies when usedoutside. Since timing is one of the most important issues when it comes topositioning, some of the timing tools from the GPS can be helpful in otherpositioning systems.Using terrestrial communication such as television signal, which is designed topenetrate into people’s houses, makes it possible to positioning indoor and inurban areas as well. Still, this is not designed for positioning use, and there aremore possible positioning errors. Depending on what the positioning is used for,the accuracy with TV signals may be enough, but when used in violence alarmsand for firefighters there is a need for much higher accuracy. It is also importantthat the altitude can be decided.The Pseudo Television Transmitters (PTT) system has been designed for highaccuracy positioning indoor, where it is crucial to reduce errors. Especially thetiming and start up order is important and one of the technical things we cancontrol. The rest of the error is often caused by multipath, and bad geometry onthe transmitters. The PPT system consist of GPS receivers who give theabsolute position for the transmitter, baseband transmitters with special designedantennas which broadcast the TV signals, Software signal generator, filters, andamplifiers. There is an interface controller which connects and controls all theparts and which the communications goes through.In the system discussed and the applications developed in this paper, GPS hasbeen used as a helpful part of the system. The system needs to use GPS forabsolute positioning of the baseband receivers, and provides an in commonclock for the total system. It also provides a 1 Pulse per Second (1PPS) signalwhich is used as a reference to make the system work together in the best way.This paper has focused on the interface controller which is the communicationbetween the parts in the system. One of the most important parts is to optimizethe timing and have a start-up sequence where the accuracy errors are reducedas much as possible. This paper is written at and for Rosum Corp, anddevelopment done is used in a system which will run live, already sold to acustomer.To be able to make an optimized interface controller, a hardware unit is chosenregarding to the specification, and the start-up sequence developed,implemented and written in the programming language C.