Browse Prior Art Database

METHOD OF OUTPUT PAYLOAD PACING IN A SIMULCAST CONTROLLER USING IMPRECISE TIME REFERENCES

IP.com Disclosure Number: IPCOM000011438D
Original Publication Date: 2003-Feb-19
Included in the Prior Art Database: 2003-Feb-19
Document File: 2 page(s) / 34K

Publishing Venue

Motorola

Related People

Nathanael P. Kuehner: AUTHOR

Abstract

A simulcast channel controller in a wireless communications system is required to continuously pace out transmit payload packets at an average rate that corresponds exactly to the downstream air interface data rate. The controller must be able to continue this indefinitely since there is no limit on the duration for which continuous channel transmission may be required.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.


Introduction

A simulcast channel controller in a wireless communications system is required to continuously pace out transmit payload packets at an average rate that corresponds exactly to the downstream air interface data rate.  The controller must be able to continue this indefinitely since there is no limit on the duration for which continuous channel transmission may be required.

In addition, in order to coordinate all of its simulcast transmitters, the controller must set a transmit ‘launch time’ for each packet.  The launch time is the absolute time at which all of the simulcast transmitters must begin to transmit the packet together.

Previous methods involve providing the controller with extremely precise time reference information.  For example, the controller may be given absolute time indications from a GPS receiver and be clocked with a GPS-disciplined oscillator.

Method of Compensation for Imprecision

This method enables the controller to operate correctly based on an arbitrarily imprecise time reference by adding enough buffering delay to compensate for the upper-bound imprecision of its time reference information.  Accordingly, it can operate with standard protocols such as NTP (Network Time Protocol), eliminating the need for the more specialized clocking signals associated with previous methods.

In this method, the controller relies on the assumption that even though it may not have precise synchronization with the time-base being used by its simulcast transmitter(s), it can determine an upper bound on the imprecision of its synchronization.  As long as the controller makes allowance for this imprecision, it can fully satisfy its payload pacing and launch time generation requirements by compensating for any possible imprecision.

Simulcast transmitters are normally able to buffer small amounts of transmit payload, but if they run out of payload, they normally end the transmission.  It is impossible to simulcast a packet that arrives at the transmitter after its scheduled transmit time has already passed.  In other words, simulcast transmitters can cope much more easily with a small amount of over-run in the payload stream from the simulcast controller than with under-run.  The controller accommodates this asymmetry by ensuring that it compensates for any time reference imprecision by erring on the side of overrun.

Thus, with this method, the controller continuously tracks both nominal current time and maximum time-value imprecision.  It paces out the simulcast payload stream assuming that the nominal time is ‘slow’ or ‘late’ by the current maximum imprecision.  This ensures that...