5.2 Pulse amplitude modulation 5.2.1.PAM:M-ary k bits at a time. A str of k bits is regarded as a symbol,and we have M=2k different symbols. Take k=2,then M=4,and there are 4 symbols:00,01,10,11. We need 4 signals,pulses of 4 different amps,to send them. “11” “10” “01” “00” If one symbol takes an interval of 7 seconds,the rate of signaling is R.=1/T symbols/s (also called Bauds). UESTC-Digital transmission through the AWGN channel Prof李晓峰 4