A B C A

Frequency

Time

Frequency

Multiple users can share single transmitters with high efficiency. Simple timing logic easily numbers of Individual users. Compatible with beam-

Pulsed carrier transmission makes peak power greater than average. Requires precise time synchronlzatioa Modulation burst rates high compared to user data rates. Requires memory buffers.

antenna. Can handle large power variations between users.

Code Division

Time

Frequency

Frequency

Relatively immune to transmitter distortion, multlpath and Interference. Inherent privacy.

Access (CDMA)

Limited to low data rates relative to transmission boundaries. Limited number of users due to mutual Interference. Limited variation in power differences between users. Needs precise time synchronization.

Multiple Access Techniques Allow Different Users to Share the Same Transmission Channel.

(Fig. 13-17D). The PN code modulation is completely removed, leaving the desired user signal "despread." At the same time, the signals from the undesired users appear at the output of the mixer as PN-coded signals with a spectrum width roughly twice the PN-code rate. Therefore, only a small portion of the undesired signal will pass through the narrow-band output BPF.

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