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Astro Simulcast System Throughput Optimization via Launch Time Offset Auto Calibration

IP.com Disclosure Number: IPCOM000007352D
Original Publication Date: 2002-Mar-18
Included in the Prior Art Database: 2002-Mar-18
Document File: 2 page(s) / 49K

Publishing Venue

Motorola

Related People

Michael C. Petrie: AUTHOR [+3]

Abstract

In current Astro Simulcast Systems, the Launch Time Offset is a static configurable parameter residing in the comparator used to determine how far in the future the station will begin a simulcast transmission. In order to optimize this value, service personnel need to find the simulcast sub-site with highest expected link delay, and manually perform optimization. The link delays will change over time requiring this procedure to be repeated at regular intervals. This is a difficult procedure whose outcome directly impacts system audio throughput delays. The existing manual optimization procedure is cumbersome, time consuming, and does not automatically adapt to changing link delays. The procedure measures link delay between the comparator and the base station. The station's processing latency factor also needs to be considered in order to yield a safe Launch Time Offset value that can be stored in the comparator. As a result, conservative values have been used for the Launch Time Offset resulting in systems being fielded with higher than necessary audio throughput delays and high overall subscriber access times.

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PROBLEM

In current Astro Simulcast Systems, the Launch Time Offset is a static configurable parameter residing in the comparator used to determine how far in the future the station will begin a simulcast transmission. In order to optimize this value, service personnel need to find the simulcast sub-site with highest expected link delay, and manually perform optimization. The link delays will change over time requiring this procedure to be repeated at regular intervals. This is a difficult procedure whose outcome directly impacts system audio throughput delays. The existing manual optimization procedure is cumbersome, time consuming, and does not automatically adapt to changing link delays. The procedure measures link delay between the comparator and the base station. The station's processing latency factor also needs to be considered in order to yield a safe Launch Time Offset value that can be stored in the comparator. As a result, conservative values have been used for the Launch Time Offset resulting in systems being fielded with higher than necessary audio throughput delays and high overall subscriber access times.

PROPOSED FEATURE

This feature automates the setting of the Launch Time Offset parameter. With this feature the Launch Time Offset is automatically negotiated between base stations and the comparator. The manual link delay measurements will no longer be necessary for determining Launch Time Offset since the time left to scheduled launch (TLTL) feedback values account for true end to end delays along with box processing latencies.

                    The Launch Time Offset parameter control stays within the comparator to allow for backward compatibility, and can be automatically enabled when linking up to base stations that implement this design. Also, stations can implement this feature without impacting current site operation. The comparator could implement this design at any time to take advantage of this feature.

DESIGN DETAILS

The Astro Simulcast Infrastructure Signaling protocol provides a Base Radio Status message (BRSTAT) for reporting periodic status from the station to the comparator. This message can be mod­ified to include Launch Time Offset and frame length information. The station currently performs launch time delta calculation. The launch time delta is calculated by the station from the time stamp value inserted by comparator to the instant the time stamp is processed by the station's DSP firmware. The station would modify the launch time delta...