Global Positioning System Reference
In-Depth Information
Chapter 4
Current Whereness Applications
This chapter looks at what is possible to do today and in the medium term. Each
application is described and the positioning element highlighted. The benefits and
weaknesses in the application are discussed to help potential operators and users
get a balanced view of what may be possible. Most technology can be abused and
radio technology is particularly vulnerable to external interference and can suffer
from poor coverage. The basic requirements are discussed and links to other
systems are highlighted. Chapter 5 is more futuristic and concerns things still
emerging from the research phase whereas in this chapter the barriers are more
about the commercial viability of applications and systems.
4.1
Mobile Information
The first application to use position-dependent information delivery was traffic
information services for drivers. The are many ways to deliver position-
dependent information, for example, a simple approach is where a driver calls a
number on a mobile phone using a hands-free facility and the approximate
location is passed from the network to the traffic service provider to select local
traffic reports dependent on the identity (and hence approximate location) of the
local cell base station that is handling the call.
1
Another simple approach that has been used is to broadcast traffic messages
as data codes using broadcast FM local radio's RDS system (usually used for
automatic tuning, station identification, and simple spoken road information). A
message set has been standardized as the traffic message channel (TMC) that
encodes standard messages into a 16-bit code. There are 2
16
possible preset
messages and a second 16-bit code to represent location (i.e., there are 2
16
possible
preset locations in the region). A vehicle location system can then select the
location codes that are relevant and display only the local relevant messages.
1
This approach is know as Cell ID and it is explained together with more complex cellular position in
Chapter 6.
55
