Dim and Burst
Application: Signaling or overhead traffic is needed to adjust, control, and coordinate the IS-95 system configuration and operation. This signaling traffic is carried by the paging and Access Channels when a mobile is not in the traffic mode. However, the need for signaling traffic may well arise while a mobile is in the traffic mode. In this case, the mobile and base do not revert to their access and paging channels; but instead, time multiplex the signaling with the voice traffic. In the case of the forward link from base to mobile, the power control bits are also time multiplexed with the primary digital voice data in the traffic mode. See Puncturing for a discussion of how the power control bits are multiplexed with the primary voice traffic symbols.
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© 1999 DR. ERNEST SIMO - SPACE2000
Dim and Burst
Example: The normal IS-95 half-rate frame contains 80 Vocoder bits, 8 Frame Quality Indicator (FQI) bits, and 8 encoder-tail bits to initialize the convolutional encoder for the next frame. The total number of transmitted bits per half-rate frame is 96. With a frame duration of 20 msec or frame rate of 50 per second, the half-frame transmitted bit rate is 4800bits/second. However, if signaling traffic must be transmitted while in the traffic mode, and the Vocoder outputs a half-rate frame, the transmitted bit rate is increased to 9600 bits/sec by forming a dim-and-burst frame. This frame contains 4 bits used to indicate mixed mode, traffic type, and traffic mode; all 80 Vocoder bits, and 88 signaling bits to produce a frame containing 172 bits. This dim-and-burst frame conveys 9600 bits/sec and contains both primary digital voice bits and signaling bits. When the Vocoder produces a less-than-half-rate frame, the dim-and-burst mode sends all the voice bits and accommodates 128 signaling bits for quarter-rate frames and 152 signaling bits for eighth-rate frames.
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© 1999 DR. ERNEST SIMO - SPACE2000
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