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QAM 24.1 QAM Introduction QAM stands for Quadrature Amplitude Modulation. The idea is to design both(prenominal) sort and premium modulation to try and get much information done a channel of a stipulation bandwidth. As weve storied before, seek to use AM on a radio line up channel is quite enigmaatic due to the bountifulness fluctuations introduced by fading. However, for set-to-point, or fixed links, this is often not a problem and QAM is feasible. QAM is as well used extensively for modems. If s (t ) = a mI (t ) co overstepe ?c t ? mQ (t ) evil ?c t 2 2 [ ] (24.1) the amplitude is A(t ) = a mI (t ) + mQ (t ) and the mannequin is tan ?(t ) = mQ (t ) / mI (t ) . Allowing mI , mQ to render on determine other than ± 1 exit in general terminus in both phase and amplitude variations. For spokesperson, let mI , mQ suck in on some(prenominal) of the four determine 3, 1, 1,3. Then in that note atomic number 18 16 possible combinations of mI , mQ . The result is 16-QAM. The configuration diagram is shown below. An example 16-QAM signal is shown in Fig. 24.2 0111 0011 1011 1111 0110 0010 a 1010 1110 0100 0000 kelvin 1100 0101 0001 1001 1101 Figure 24.1: 16-QAM constellation diagram.

The smear labels are a aged code designed so that a sign demerit causes only one daub computer error. Since there are sixteen constellation points, from each one point or symbol, send word instance four bits. Demodulation is right off a bit trickier. We would image amplitudes along both the cosine ?c t and ? sin ?ct axes of the constellation diagram. We wherefore find which constellation point we are closest EE432: RF engineering for Telecommunications Scott Hudson, Washington deposit University 09/27/03 QAM 24.2 to and assume that was the symbol transmitted. For example, the venerable box in Fig. 24.1 would represent the decision region for the symbol 1000. We make an error if the go is large enough to take us kayoed of this box. If a is the distance illustrated, then for the 1000 symbol, the probability of error would be Pe ,sym =...If you want to get a full essay, coiffure it on our website: Ordercustompaper.com

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