Navigation Systems

It was already mentioned that ICT systems can be used to optimize traffic systems. This can be considered as a kind of high-level optimization by traffic management. On the other hand information technology also serves for optimizing the routes of individual participants in traffic system, and therefore enables efficiency gains in travel time, travel distances and energy needed for transportation. Such systems are for example in-car navigation systems using the GPS standard for real-time route planning, or online mapping and routing software. All these systems can be categorized as navigation systems and lead to less CO2 emissions in theory [1]. Navigation systems are used in private individual transport, as well as in commercial transport and logistics. Navigation systems using the Global Positioning System (GPS), which today are implemented as on-board features of modern cars, as discrete mobile devices or as part of many mobile phones, are based on satellite navigation. The principle of determining positions via satellites is trilateration [2]. This method allows determining positions by measuring distances to a minimum of three points with known coordinates. The method of trilateration is shown in figure 1.

Figure 1: Principle of trilateration - The measured distances to three points of reference (S1, S2, S3) determine the position of P [2]

The GPS standard uses 24 satellites, which orbit the Earth on 6 different orbital planes. These satellites are positioned in a way that allows more than 99 percent of GPS users all over the world to contact at least four satellites at any given time [2]. The GPS satellites are equipped with atomic clocks and transmit signals at a frequency of 1575.42 MHz directed to Earth [3]. A GPS signal contains the Navigation Message, consisting of it’s on-board time and orbit parameters, which can be processes by any GPS receiver to compute satellite coordinates. The atomic clocks of each of the 24 satellites are regularly synchronized from control stations on Earth, while the clocks of GPS receivers are not synchronized with the clocks of satellites and are far less precise [4]. Since the distance between a GPS receiver and a satellite is determined by measuring the time delay of the transmission and the reception of the satellite’s signal, which is moving by the speed of light, there is a certain time error influencing the measurement, due to the non-synchronized clocks of satellite and receiver. This time error is unknown, together with the coordinates of the GPS receiver, which means that there are four unknown variables that have to be determined for positioning in three-dimensional space [3]: longitude (x), latitude (y), height (z) and time error (4t). To determine four unknown variables, four independent equations are needed. For this reason the minimum number of satellites for GPS locating is four. Figure 2 illustrates the basic function of GPS, which is calculating the coordinates of a location by measuring the distances to four GPS satellites.

Figure 2: The basic function of GPS [3]

Beside the economical and environmental benefits of navigation systems in form of fuel and emissions savings, there are social and personal advantages for the users of these systems. Route planning software and GPS navigation increases the efficiency of traveling and therefore saves time. Navigation systems can ease the complex activity of way finding and therefore leave more capacity for engagement with the surroundings. On the other hand it is reasonable to argue, that navigation systems disengage the users from their environment, in case they fully rely on it.

There was a study in 2008 about how navigation systems alter the users’ experience of their environment [5]. For this reason observations and interviews where done with in-car GPS users, to determine how using a navigation system changes the behavior and the experience while driving. The findings of the study where partly claiming a trend to disengagement from the environment, due to the reduced need for orientation and keeping track of locations. Additionally some users of navigation systems are just following the instructions whether they are correct or not. On the other hand the researchers found out, that there was an enriched engagement with the environment in some cases, because of the discovery of new points of interest and the safety of not getting lost in unknown areas [5]. Due to the results of this study, navigation systems are an example for the fact that the social impact of information and communication technologies is often hard to classify.

References

[1] B. Tomlinson. Greening through IT - Information Technology for Environmental Sustainability. The MIT Press, 2010.

[2] accessscience.com. Satellite navigation systems. http://accessscience.com/content/Satellite-navigation-systems/602800. Accessed: 2013-02-12.

[3] J.-M. Zogg. Gps basics. http://faculty.ksu.edu.sa/hbilani/SE412books/GPS_basics_u_blox_en.pdf, 2002. Accessed: 2013-02-12.

[4] G. Blewitt. Basics of the gps technique: Observation equations. http://www.nbmg.unr.edu/staff/pdfs/Blewitt%20Basics%20of%20gps.pdf, 1997. Accessed: 2013-02-12.

[5] G. Leshed, T. Velden, O. Rieger, B. Kot, and P. Sengers. In-car gps navigation: engagement with and disengagement from the environment.  In Proceedings of the twenty-sixth annual SIGCHI conference on Human factors in computing systems, CHI ’08, pages 1675–1684, New York, NY, USA, 2008. ACM.