Digital Signal Processing Reference
In-Depth Information
Imaginary part
1,5
1,5
1,0
1,0
GAUSSsian plane
0,5
0,5
0,0
0,0
Real part
-0,5
-0,5
-1,0
-1,0
-1,5
-1,5
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
2-ASK
2-PSK
Volt
Volt
1,5
1,5
1,0
1,0
0,5
0,5
0,0
0,0
-0,5
-0,5
-1,0
-1,0
-1,5
-1,5
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
Volt
Volt
25 discrete states
(noise on transmission channel)
24 discrete states
Illustration 262:
Discrete signal states and signal space
The GAUSSian numerical plane is represented as a two dimensional signal space for carrier oscillations
where amplitude and phase are in a discrete state. 2-ASK and 2-PSK are positioned on the horizontal axis.
It is obvious that the number of possible discrete signal states should be increased to form a two dimen-
sional signal space.
This is possible - as shown in Illustration 98 ff - by splitting up the phase shifted sinusoidal oscillations
into a sine and cosine part. Quadrature phase shifting (QPSK) is the simplest example - described in
Illustration 263 and the following text.
• Another point which needs to be clarified is the use of several adjacent carrier frequen-
cies (frequency multiplex) each of which has a certain number of discrete states.
Different frequencies theoretically require different GAUSSian planes. If you follow
this train of thought the signal space is really
three
dimensional with the frequency as
the third dimension.
