Global Positioning System Reference
In-Depth Information
especially radio regulations. However, the more power the better as far as the
receiver is concerned.
Figure 6.2
Bandwidth of a radio channel.
At a receiver in addition to receiving the desired signal (S), unwelcome extra
signals are present including interference from other transmissions and an
unavoidable component of random fluctuations present in all physical systems.
Collectively, all these unwanted components are known as noise (N). Any system
seeks to maximize the signal-to-noise ratio. The S/N ratio is purely a number but
is usually expressed using the unit decibel or dB. The ranges in power in radio
systems are very large, ranging from transmitters outputting kilowatts to receivers
inputting picowatts (i.e., a range of 10
15
). The decibel is a logarithmic ratio that
helps keep the quantities manageable and allows gains and attenuations to be
treated as simple additions rather than multiplications. The implication for any
positioning system is profound: the better the signal-to-noise ratio (S/N), the more
accurate any measurement is likely to be.
P
dB
= 10 log
10
(P1/P2)
(6.2)
