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QAM 24.1 QAM Introduction QAM stands for Quadrature Amplitude Modulation. The idea is to use both(prenominal) stage and gift modulation to try and drop dead more information through a channel of a given bandwidth. As weve famed before, trying to use AM on a intercommunicate set channel is quite enigmaatic due to the amplitude fluctuations introduced by fading. However, for point-to-point, or fixed links, this is often not a enigma and QAM is feasible. QAM is also used extensively for modems. If s (t ) = a mI (t ) romaine ?c t ? mQ (t ) sin ?c t 2 2 [ ] (24.1) the amplitude is A(t ) = a mI (t ) + mQ (t ) and the phase is tan ?(t ) = mQ (t ) / mI (t ) . Allowing mI , mQ to take on value other than ± 1 will in general root in both phase and amplitude variations. For spokesperson, let mI , mQ take on some(prenominal) of the four values 3, 1, 1,3. Then in that respect atomic number 18 16 mathematical combinations of mI , mQ . The result is 16- QAM. The configuration diagram is shown below. An example 16-QAM suggest is shown in Fig. 24.2 0111 0011 1011 1111 0110 0010 a 1010 1110 0100 0000 1000 1100 0101 0001 1001 1101 Figure 24.1: 16-QAM constellation diagram.

The spot labels are a Gray code designed so that a token fracture causes only one puss computer error. Since there are sixteen constellation points, from each one point or symbol, can represent four bits. Demodulation is in a flash a bit trickier. We would calculate amplitudes along both the cos ?c t and ? sin ?ct axes of the constellation diagram. We whence find which constellation point we are closest EE432: RF Engineering for Telecommunications Scott Hu! dson, 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 division for the symbol 1000. We make an error if the noise is large tolerable to take us kayoed of this box. If a is the distance illustrated, because 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: OrderEssay.net

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