Comtech EF Data SLM-5650A Vipersat - Manual (Page 146)

D-8 Vipersat SLM-5650A User Guide
P
PLDM Path Loss Data Message – A packet message that is sent by older Vipersat
modems (e.g., CDM-570/L) to the VMS every sixty seconds, providing status
update and operating parameter information.
PSK Phase Shift Keying – A digital modulation scheme that conveys data by chang-
ing the phase of a base reference signal, the carrier wave. Different PSKs are
used, depending on the data rate required and the signal integrity. Examples are
binary phase-shift keying (BPSK or 2-PSK) which uses two phases, and quadra-
ture phase-shift keying (QPSK or 4-PSK) which uses four phases.
PSTN Public Swithed Telephone Network – The world’s public circuit-switched tele-
phone network, digital and analog, and includes mobile as well as land-line
voice and data communications.
Q
QAM Quadrature Amplitude Modulation – A digital modulation technique in which
the amplitude of two carrier waves is changed to represent the data signal. These
two waves are 90 degrees out of phase with each other.
QoS Quality of Service
QPSK Quadrature Phase Shift Keying – Sometimes referred to as 4-PSK, or 4-QAM.
A modulation technique in which the carrier is phase shifted +/-90 or +/-180
degrees. With four phases, this modulation can encode two bits per symbol—
twice the rate of BPSK. However, it also uses twice the power. See also OQPSK
and BPSK.
R
Remote Satellite earth site that links to a central network site (Hub).
Return Path Transmission path from a Remote site to the Hub site.
RF Radio Frequency – A generic term for signals at frequencies above those used
for baseband or IF.