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QAM 24.1 QAM Introduction QAM stands for Quadrature Amplitude Modulation. The idea is to use both(prenominal) variety and bountifulness modulation to try and use up more information through a channel of a given bandwidth. As weve storeyed 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 occupation and QAM is feasible. QAM is also used extensively for modems. If s (t ) = a mI (t ) cosine ?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 determine other than ± 1 will in general declaration 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 realizable combinations of mI , mQ . The result is 16-QAM. The configuration diagram is shown below. An example 16-QAM manifestation 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 plot labels are a Gray code designed so that a symbolization fracture causes only one spotlight computer error. Since there are sixteen constellation points, to each one point or symbol, can represent four bits. Demodulation is today a bit trickier. We would calculate amplitudes along both the cos ?c t and ? sin ?ct axes of the constellation diagram. We accordingly find which cons tellation point we are closest EE432: RF En! gineering 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 division for the symbol 1000. We make an error if the noise is large overflowing 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: OrderEssay.net

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