TDMA (Time Division): Users take turns on the same frequency.
Alters the starting angle (phase) of the wave cycle. Advanced Modulation: QAM
If the direct path is blocked, the receiver sees the sum of dozens of reflections. These waves add vectorially; sometimes they cancel each other out (deep fade), and sometimes they amplify each other. This phenomenon—Multipath Fading—is the primary adversary of reliable wireless links. wireless communications from the ground up pdf
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Occurs when a wave hits an object larger than its wavelength (e.g., the surface of the Earth, buildings, or walls). TDMA (Time Division): Users take turns on the same frequency
Assigns a unique time slot to each user on the same frequency (used in 2G GSM).
Changes the starting point of the wave cycle. Digital Modulation These waves add vectorially; sometimes they cancel each
A raw digital signal is a "baseband" signal, containing low-frequency components unsuitable for over-the-air transmission. By mixing this baseband signal with a high-frequency "passband" carrier wave, the information can be transmitted efficiently over long distances. Digital Modulation Schemes
If we transmitted data directly over the fading channel described in Section 2, the communication would fail constantly due to interference and noise. The "ground up" architecture requires countermeasures.
: Radiates and receives signals equally in all horizontal directions.
Focus energy into a tight beam (like a flashlight), increasing transmission distance and signal strength (gain). MIMO (Multiple-Input Multiple-Output)