SLOT SYNCHRONIZATION IN ASTRO SITE STEERED TRANSMISSIONS
Original Publication Date: 2002-Aug-02
Included in the Prior Art Database: 2002-Aug-02
Michael Petrie: AUTHOR [+3]
Astroä Simulcast systems use site steering, a method to transmit data packets from only the specified sub-site while all adjacent sub-sites remain de-keyed in order to improve packet data throughput performance. During a site steered transmission, it is desirable to shorten the transmit slot size since the transmitting station updates the busy bits and does so more quickly than the comparator in simulcast transmissions. The faster busy bit turnaround time allows faster access on the inbound channel by the subscriber radios. The transmit slot times are kept larger for simulcast transmissions in order to account for worst case throughput delay of the infrastructure.
When a site steered station resumes simulcast transmission, its transmit slots will no longer be aligned to the transmit slots of the other simulcast sub-sites as depicted in figure 1. This slot misalignment between RF transmitters corrupts the busy bits which prevents subscriber radios in the simulcast overlap area from accessing the inbound channel.
One approach to regain transmit slot synchronization is for the site steered station to de-key and re-key. However, this is not optimal since additional time is wasted to de-key and key the site steered station.
The preferred solution is to have the Astro Simulcast station DSP software maintain two transmit slot counters, each synchronized to the specified transmi...