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Blank and Burst

Definition: A time multiplexing technique used on traffic channels to send overhead signaling or (optionally) secondary traffic in which a frame of primary digital voice data is blanked, i.e., not transmitted to allow the overhead or secondary traffic to be transmitted at a 9600 bit/second rate.

Note: In the blank-and-burst format, a frame or frames of primary digital voice data are suppressed or not transmitted to make time available to send signaling traffic. The digital voice frames are lost. However, the degradation of the recovered analog voice is minimal provided not too many frames are blanked consecutively. Typically, the transmitter controllers wait for a less-than-full-rate Vocoder frame in which signaling traffic can be multiplexed with voice traffic without the loss of any voice bits. Multiplexing signaling with voice in less-than-full-rate frames is called dim and burst. See Dim and Burst for a discussion of this format.

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© 1999 DR. ERNEST SIMO - SPACE2000

Blank 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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Blank and Burst

Example: The normal 9600-bit/second frame contains 1 bit to identify mixed mode followed by 171 primary traffic bits for a total of 172 bits. The traffic bits are followed by 12 Frame Quality Indicator (FQI) bits and then by 8 encoder-tail bits to initialize the convolutional encoder for the next frame. The total number of bits per transmitted frame is 192. With a frame duration of 20 msec or frame rate of 50 per second, the full-frame transmitted bit rate is 9600 bits/second. However, if signaling traffic must be transmitted while in the traffic mode, the 172 voice-message bits are discarded. In their place, 4 bits are used to indicate mixed mode, traffic type, and traffic mode and, therefore, 168 bits are available to send signaling traffic.

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© 1999 DR. ERNEST SIMO - SPACE2000

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