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QAM 24.1 QAM Introduction QAM stands for Quadrature Amplitude Modulation. The idea is to apply both(prenominal) leg and premium conversion to try and get to a greater extent information done a channel of a apt(p) bandwidth. As weve storied before, laborious to use AM on a radio qualify channel is quite enigmaatic receivable to the bounteousness fluctuations introduced by fading. However, for come in-to-point, or fixed links, this is often non a problem and QAM is feasible. QAM is also used extensively for modems. If s (t ) = a mI (t ) co hellholee ?c t ? mQ (t ) goof ?c t 2 2 [ ] (24.1) the amplitude is A(t ) = a mI (t ) + mQ (t ) and the flesh is tan ?(t ) = mQ (t ) / mI (t ) . Allowing mI , mQ to replication on value other than ± 1 exit in general result in both phase and amplitude variations. For spokesperson, let mI , mQ number on some(prenominal) of the four value 3, 1, 1,3. Then in that find atomic number 18 16 possible combinations of mI , mQ . The result is 16-QAM. The configuration draw 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 guanine 1100 0101 0001 1001 1101 Figure 24.1: 16-QAM constellation diagram.

The piece labels atomic number 18 a colorise-haired code designed so that a symbolic representation good luck causes only one objet dart computer error. Since there are sixteen constellation points, individually point or symbol, nates set up four bits. Demodulation is directly a bit trickier. We would appear amplitudes along both the romaine ?c t and ? sin ?ct axes of the constellation diagram. We therefore find which constellation point we are closest EE432: RF plan for Telecommunications Scott Hudson, Washington deposit University 09/27/03 QAM 24.2 to and assume that was the symbol transmitted. For example, the gray box in Fig. 24.1 would represent the decision region for the symbol 1000. We make an error if the resound 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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