Quadrature Amplitude Modulation or QAM is a form of modulation which is widely used for modulating data signals onto a carrier used for radio communications. It is widely used because it offers advantages over other forms of data modulation such as PSK, although many forms of data modulation operate alongside each other.
Quadrature Amplitude Modulation, QAM is a signal in which two carriers shifted in phase by 90 degrees are modulated and the resultant output consists of both amplitude and phase variations. In view of the fact that both amplitude and phase variations are present it may also be considered as a mixture of amplitude and phase modulation.
Normally the lowest order QAM encountered is 16QAM. The reason for this being the lowest order normally encountered is that 2QAM is the same as binary phase-shift keying, BPSK, and 4QAM is the same as quadrature phase-shift keying, QPSK. Additionally 8QAM is not widely used. This is because error-rate performance of 8QAM is almost the same as that of 16QAM - it is only about 0.5 dB better and the data rate is only three-quarters that of 16QAM. This arises from the rectangular, rather than square shape of the constellation.
DIBSYS IPQ6250 is a new generation of modular & high density Edge QAM modulator combining TS-over-UDP/RTP reception, 16/32/64/128/256QAM modulation ect. It supports up to 48 QAM channels by using three external pluggable 16 QAM modules, each of QAM modules supporting up to two Gigabit copper interfaces.With the IPQ6250, cable operators can be ensured that they will have a scalable, reliable, high performance video stream services for years into the future. It can be applied to cable DTV head-ends, sub head-ends and VOD networks.