Download

396 AIR INTERFACE SIGNALING IN CDMA NETWORKSFigure 13.2-2. Conceptual view of Reverse CDMA Channel bit processing for IS-95 B.despreading in most of the literature, do not change the bandwidth because their chiprates are the same as those of the first and last steps.Before the initial coding step at the source, the user’s data stream is subjected toprocesses that increase the reliability of transmission as well as the bit rate, such asconvolutional encoding (a form of error correction coding), symbol repetition (alsoused in AMPS, see Section 12.2.2), and bit interleaving (in which bits are shuffled tomitigate the effects of error bursts). At the destination the processes are applied inreverse after the final decoding step.13.1.4 Other Aspects of CDMATraffic. We distinguish two types of traffic in CDMA channels: user traffic (orbearer connections) and signaling traffic (or control connections).User traffic consists of voice and/or data flows between users. User traffic is subdividedinto:. Primary traffic—typically the voice connection. Secondary traffic—additional user data flows, typically nonvoice such aspacket trafficSignaling traffic consists of message flows that are used to manage radioresources and establish, manage, and release connections.Primary, secondary, and signaling traffic flows can be time-multiplexed in thesame code channel with two techniques: blank and burst and dim and burst.With blank and burst, an individual frame (see below) is blanked for primarytraffic and used to send a burst of data with secondary or signaling traffic. Moreon blank and burst is found in Section 12.2.2.With dim and burst, some bits in a frame are stolen from primary traffic and usedto send signaling and/or secondary traffic, with little effect on voice quality.