Wavecom W61PC V7.5.0 - Manual (Page 104)

94  Fundamentals of Radio Data Transmission WAVECOM Decoder W61PC/LAN Manual V7.5
Fundamentals of Radio Data
Transmission
The drawing illustrates the various processing operations applied to digital information from source to
sink. The box labeled “Channel” represents the media through which data must pass (adapted from Ber-
nard Sklar, “Digital Communications – Fundamentals and Applications”, Prentice Hall, 2001).
A basic understanding of how digital information is transferred by land line or radio links is necessary to
fully exploit all of the features of the WAVECOM decoder. It is assumed that the user is familiar with the
general working of telecommunication systems, in particular radio systems. The overview below deliber-
ately avoids the mathematical descriptions and proofs which underly modern communication theory and
practice, for the sake of brevity.
We define digital information as information which is represented by discrete states of the transmission
medium. In contrast, analogue information is represented by an infinite continuum of states. For exam-
ple, live music is analogue information, whereas the same music recorded on a CD has been transformed
into digital information imprinted on the surface of the disc. Digital information or data is not only text, it
can also represent speech, music or images.
A land line, short wave link, satellite link or any other way of connecting two points for communications is
called a channel.
The tremendous development within electronics and computer science in the last few decades has led to
enormous improvements in the reliability and robustness of the wireless transmission of digital data,
which has especially benefited the HF spectrum users. The HF frequency range is an especially hostile en-
vironment to communications, as it is prone to both natural and manmade disturbances of a time-varying
nature, e.g. heavy industrial noise, fierce solar storms, interference from other spectrum users and severe
fading. The ever increasing powers of CPUs has been harnessed via digital signal processing (DSP) tech-
niques and has resulted in improved coding and modulation methods such as turbo codes, adaptive equal-
ization, m-ary modulation and powerful and innovative demodulation and decoding methods. Further im-
provements have been made in the field of automation of operations and in the size, power consumption
and features of modern integrated circuits.