2/3/2012

posted Mar 2, 2012, 11:55 PM by Andrea Vitaletti   [ updated Mar 8, 2012, 5:40 AM ]
Wireless communications employ electromagnetic signals. A signal can be studied in the time and frequency domains and only aperiodic signals deliver information. Most of the energy of the signal is in the main terms of the Fourier transform. The channel behaves as a band pass filter. A natural question is: how much information C (i.e. channel capacity) can be delivered in a channel of a given bandwidth B? If no noise: C=2B. This limit is due to ISI. Note that C --> infinity if B --> infinity. If n levels: C=2B log (n). Note that C --> infinity also when n --> infinity. What if noise? The effect of noise depends on SNR: C=B log(1-SNR). There are several kind of noise. The effect of noise are errors, measured in terms of BER.

Antenna. Size depends on wavelength. Isotropic antenna and gain. Freespace loss.
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