Digital communications
Vector modulation
All TSG4100A Series generators include standard support for I/Q modulation
on RF carriers between 400 MHz and 6.075 GHz. In addition, they feature a
dual, arbitrary waveform generator operating at 125 MHz for baseband signal
generation. The generator has built-in support for the most common vector
modulation schemes: ASK, QPSK, DQPSK,
π
/4 DQPSK, 8PSK, FSK, CPM.
QAM (4 to 256), 8VSB, and 16VSB. It also includes built-in support for all the
standard pulse shaping
fi
lters used in digital communications: raised cosine,
root-raised cosine, Gaussian, rectangular, triangular, and more. Lastly, it provides
direct support for the controlled injection of Additive White Gaussian Noise
(AWGN) into the signal path.
The baseband generator supports the playback of pure digital data. It automatically
maps digital symbols into a selected IQ constellation at symbol rates of up to
6 MHz and passes the result through the selected pulse shaping
fi
lter to generate a
fi
nal waveform updated in real time at 125 MHz. This baseband signal is then
modulated onto an RF carrier using standard IQ modulation techniques.
This architecture provides a simpli
fi
ed and productive user experience. PRBS data
and simple patterns can be played back directly from the front panel. Trade-offs
in
fi
lter bandwidth versus power ef
fi
ciency can be explored from the front panel
in real time without the need to download complex new waveforms each time.
Likewise, the degradation of a signal by AWGN can be easily manipulated from
the front panel.
Your instrument comes with a number of modulation presets for demonstrating
various modulation capabilities. Sample modulation waveforms and setups are
included for communications standards such as NADC, PDC, DECT, APCO
Project 25, TETRA, GSM, GSM-EDGE, and W-CDMA.
Finally, the rear panel BNC I-Q modulation inputs and outputs enable arbitrary
vector modulation through an external source. The external signal path supports
300 MHz of RF bandwidth with a full scale range of ±0.5 V and a 50
Ω
input
impedance.
Constellations
One important characteristic of digital signals that distinguishes them from analog
signals is that they are quantized and bounded. Normally, digital signals are
represented as binary sequences of
fi
nite length. A 1-bit (binary) signal has only
two states: 0 or 1. A 2-bit signal is represented with two binary digits in sequence
and, thus, has 4 states: 00, 01, 10, and 11. A 3-bit signal will have 8 states. An
N-bit signal will have 2
N
states.
38
TSG4100A Series RF Signal Generators User Manual
