作者Leon (Achilles)
站内comm_and_RF
标题Re: [请益] QPSK & 2-PAM*2
时间Thu Oct 25 11:14:34 2007
※ 引述《IronHand (蹂躏之爪牙)》之铭言：
: 1.为什麽QPSK(4-PSK) & 两个independent 2-PAM系统combined
: 的performance会相同呢
用 signal space 的 dimension 来看.
: 2.Consider a PSK system.
: It is suggested to modify the system to enhance its BER performance.
: There are two choices.
: The first is to double the average transmitting power level.
: The second is to duplicate the system on another carrier,
: i.e. to use two independent radios duplicating the same information
: data stream. Which one will you choose? Why?
因为我觉得推文里面的回答有些问题, 我就直接回文写我的想法.
at first, you need to define what channel are you using ?
if it's AWGN .... then, transmit same information twice is just
like a repetition code. And repetition does NOT have any coding gain.
我写个例子:
S_0 : transmit -1,
S_1 : transmit +1,
if you double the transmitting power, it will be sqrt(2) and -sqrt(2).
repetition,
S_0 : (-1,-1)
S_1 : (+1, +1)
Both cases have the same minimum distance.
They should have the same performance.
_
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