Tektronix TSG4102A, Руководство пользователя

Страница: 63 / 99

Digital communications
PSK (phase shift keying) PSK is a modulation technique in which digital symbols are encoded in the phase
of the RF. The amplitude of each constellation point is the same. In spite of this,
the modulation is not constant amplitude as it is for FSK. The pulse shaping
fi lters
create amplitude variations as the modulation traverses from symbol to symbol,
creating waveforms very similar to QAM. In fact, vector PSK modulation may be
considered a subset of QAM modulation.
Simple waveforms. Vector phase modulation with some simple waveforms is
supported. The supported waveforms are summarized in the following table.
Table 8: Vector phase modulation waveforms
Waveform Description
Sin cos Channel I is a sine wave and channel Q is a cosine wave. This combination moves the RF carrier
down in frequency by the modulation rate.
Cos sin Channel I is a cosine wave and channel Q is a sine wave. This combination moves the RF carrier
up in frequency by the modulation rate.
Phase noise Degrades the RF output with pure phase noise. The amplitude is held constant. The bandwidth and
RMS deviation of the noise may be con
fi gured.
IQ noise Degrades the RF output with IQ noise. The bandwidth of the noise may be con fi gured. The noise
power is equal to the RF carrier power when modulation is off.
Digital constellations. The generators provide four basic constellations and four
specialized constellations. Custom user constellations can also be downloaded, if
desired. The constellations are summarized in the following table. Waveforms for
digital modulations include PRBS data, simple patterns, and user data. Frequency
deviations of up to 6 MHz are supported.
NOTE. More information about basic and specialized constellations is available
here. (See page 48, Basic PSK constellations.) (See page 52, Specialized PSK
constellations.)
Table 9: PSK constellations
Display Standard acronym
Bits /
symbol
Comments
PM binary
BPSK
1
Normal binary shift keying
PM quadrature
QPSK
2
Normal quadrature shift keying
PM Quad offset OQPSK 2 Offset quadrature shift keying
PM diff quad DQPSK 2 Differential quadrature shift keying
PM π 4 diff quad π /4 DQPSK 2 DQPSK with π /4 rotation
PM 3 π 8 3 bit 3 π /8 8 PSK 3 8 PSK with 3 π /8 rotation
PM 3 bit 8 PSK 3 Normal 8 PSK
PM 4 bit 16 PSK 4 Normal 16 PSK
TSG4100A Series RF Signal Generators User Manual 47