A2-Radio Communication principles

=⌘ Coding and Modulation= A modulated radio signal can be written in a general form: $$ C(t) = A(t) cos(2\pi f(t) t + \varphi(t)) $$ Any of these three parameters can be varied: amplitude-, frequency- or phase-modulation.


 * Channel-coding is used to reduce bit-error-rate, e.g. through forward error correction.
 * Multiplexing is used to split the total amount of radio into smaller pieces. Typical: time, frequency or code multiplex. examples

[Source:K.E. Walter, Basics of Mobile Communications]

Comments
Figure: A frequency band consists of n channels.

Example GSM: the upload band is from 880-915 Unik/MHz, which is 35 Unik/MHz. With a carrier of 200 kHz we have 175 channels, which have to be divided between the various operators.

=⌘ Modulation types =

[Source:K.E. Walter, Basics of Mobile Communications]
 * Amplitude shift keying (ASK)
 * Frequency shift keying (FSK)
 * Phase shift keying (PSK)

=⌘ Frequency and time division multiplexing =




 * Time domain, e.g. 8 slots in GSM
 * Frequency domain, e.g. up- and downlink in specific bands
 * Code division (CDM), specific codes

[Source:K.E. Walter, Basics of Mobile Communications]

=⌘ Code division multiple access =

UMTS as an example (in one of the future lectures)