Multiple Access Techniques
Multiple Access: several (2 or more) users transmit simultaneously
over the same propagation channel (medium).
Conflict-free multiple access: No collisions (hence, no lost data).
Conflicts are resolved through orthogonality amon
Bandpass Transmission Techniques
Power Spectral Density
Signal Space Interpretation and Optimal Receiver
Probability of detection Error
1 d (t )
f (t ) =
Ac cos(2f c t + c ) = Ac cos( (t )
2. Characterization of Wireless Channels
Signal strength varies heavily over small distances and/or short-time
periods small-scale fading.
Primary cause: multipaths
Objective: Need a model to describe these effects. Useful in receiver
A typical MSC handles 100,000 cellular subscribers and 5000
simultaneous conversations. It also performs all maintenance and
Fundamentals of Cellular Communications
Given limited frequency spectrum and large number of users