Please tell me which is a reliable modulation to use in CATV system, QPSK or QAM? What are the advantages and disadvantages. Please discuss it in a "lay man's term" and set some examples. Thank you and more power.
QPSK or QAM on cable system
Started by ●February 6, 2008
Reply by ●February 6, 20082008-02-06
"nonahvy" <nonahvy@yahoo.com> writes:> Please tell me which is a reliable modulation to use in CATV system, QPSK > or QAM? What are the advantages and disadvantages. Please discuss it in a > "lay man's term" and set some examples. Thank you and more power.Well, more power is exactly what you have in a CATV system, and that is why higher-order modulations like QAM make more sense. In a nutshell, the closer the constellation points are, the more susceptible the modulation is to noise. That's why, for noisy systems like mobile radios, "low-order" modulations (M-ary PSK, FSK) are better. OTOH, CATV systems have a lot of power, or high SNR, so one can take advantage of that power to send more information (per bandwidth) down the "pipe." -- % Randy Yates % "So now it's getting late, %% Fuquay-Varina, NC % and those who hesitate %%% 919-577-9882 % got no one..." %%%% <yates@ieee.org> % 'Waterfall', *Face The Music*, ELO http://www.digitalsignallabs.com
