What Is A QPSK And QAM?
Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude Modulation (QAM) are two different forms of modulation techniques used with cable modem technology. Quadrature Phase Shift Keying (QPSK) is easy to implement and fairly resistant to noise. It is used primarily for sending data from the cable subscriber upstream to the Head-End, but sometimes it can also be used to send data downstream. Quadrature Amplitude Modulation (QAM) is primarily used for sending data downstream. QAM is very efficient, but QAM’s susceptibility to interfering signals makes it ill-suited to noisy upstream transmissions from the subscriber to the Head-End. There are three variations, 16QAM, 64QAM and 256QAM. A single downstream 6 MHz channel may support up to 27 Mbps of data throughput from the Head-End using 64QAM while speeds can be boosted to 36 Mbps using 256QAM. A single 6MHz upstream channel may support between 500Kbps to 10Mbps of data throughput from cable subscribers homes using 16QAM or QPSK dep
