Code Division Multiplexing

Code Division Multiplexing

This figure shows how a single direct sequence spread spectrum communication channel can have several channels. In this example, there are 3 different code patterns that are used for communication channels. When a receiver uses the reference code, a direct sequence spread spectrum system can build a mask as shown in this figure for each conversation allowing only that information which falls within the mask to be transmitted or received.

Open Loop Power Control

This diagram shows how open loop RF power control can be used in a mobile telephone system to provide approximately the same level of RF signal received by the base station from the mobile telephone regardless of the distance the mobile telephone is located from the base station. This diagram shows that the mobile telephone's coarse (open loop) RF amplifier adjustment is controlled by feedback from its receiver section. The mobile telephone continuously measures the radio signal strength received from the base station to estimate the signal strength loss between the base station and mobile telephone. This diagram shows that as the mobile telephone moves away from the base station, the received signal level decreases. When the received signal is stronger, the mobile telephone reduces its own RF signal output; conversely, when the mobile received signal level is weaker, the mobile telephone increases the amplification of its own RF signal output. The end result is that the signal received at the base station from the mobile telephone remains at about at the same power level regardless of the mobile telephone's distance.