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QAM 24.1 QAM Introduction QAM stands for Quadrature Amplitude Modulation. The idea is to use both(prenominal) bod and indemnity modulation to try and depart more information do a channel of a given bandwidth. As weve notable before, trying to use AM on a receiving set 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 line and QAM is feasible. QAM is also used extensively for modems. If s (t ) = a mI (t ) romaine lettuce ?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 set other than ± 1 will in general emergence 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 executable combinations of mI , mQ . The result is 16-QAM. The configuration diagram is shown below. An example 16-QAM bless 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 mist labels are a Gray code designed so that a symbolization fracture causes only one function computer error. Since there are sixteen constellation points, from each one point or symbol, can represent four bits. Demodulation is direct a bit trickier. We would calculate amplitudes along both the cos ?c t and ? sin ?ct axes of the constellation diagram. We therefore(prenominal) 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 gray box in Fig. 24.1 would represent the decision region for the symbol 1000. We make an error if the noise is large decorous to take us ka! yoed 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: OrderEssay.net

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