Browse Prior Art Database

USE OF REDUNDANT GPS RECEIVER TO IMPROVE SITE SYNCHRONIZATION

IP.com Disclosure Number: IPCOM000009624D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Sep-05
Document File: 2 page(s) / 161K

Publishing Venue

Motorola

Related People

Anatoly Agulnik: AUTHOR [+2]

Abstract

Synchronous networks such as the iDEN system use GPS to provide time synchronization of crucial network elements such as the ACG and Base Radios. The ACG contains a GPS receiver whose sole purpose is to use GPS satellites to synchronize the ACG and BRs. GPS satellites broadcast date/time to the receiver, which in turn uses this date/time information to setup its own internal clock to determine current date/time and generate a 1PPS (1 Pulse Per Second) signal that is aligned at the top of each GMT second. The ACG receives date/time information periodically from the receiver for the purposes of setting ACG and BR time. The 1PPS is then used to ensure that the date/time information received from the receiver is set and maintained cor- rectly in both the ACG and BRs.

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Technical MO-LA @ Developmems

USE OF REDUNDANT GPS RECEIVER TO IMPROVE SITE SYNCHRONIZATION

by Anatoly Agulnik and Gary Soibel

generally yield poor position estimates. This is due to the fact that position estimation involves a trian- gulation process, which is prone to bad estimates when the spread of the satellites is small. When you consider that included in the position estimate is a time estimate factor due to the fact that we are using clock based pseudo-range propagation delay esti- mates, we can easily see that time itself is subject to the sensitivity of the triangulation process, and hence to satellite configurations. This means that even after a good position estimate is known and the clock is set correctly, bad satellite configurations can cause 1PPS to be generated incorrectly.

POSlTlON HOLD MODE - DATE/TIME ESTIMATION INDEPENDENT OF SATELLITE CONFIGURATIONS

  The solution to this problem involves the use of geometric ranging for the purpose of date/tune esti- mations. Geometric ranging would involve propaga- tion delay estimation based on the known distances from the GPS receiver and satellites. In this way, clock settings would not be dependent on satellite configurations.

  However, to achieve satisfactory results using geometric ranging, we need to have a good estimate of GPS receiver position. Once we have this, we could use geometric ranging to provide a suitable timing reference independent of satellite configura- tion. In addition, if all satellites were used for the sole purpose of date/time estimation, then propaga- tion error effects on date/time estimation would in general be eliminated by the process of averaging.

  The key to solving this problem then would be to fix a position as accurate as possible and allow the GPS receiver to use all satellites for the sole pur- pose of time estimation. To do so, we change the mode of the GPS receiver to a Position Hold Mode, in which tire GPS receiver no longer uses data from

0 Motomh,l"c. 1999 308 September I999

BACKGROUND

  Synchronous networks such as the iDEN system use GPS to provide time synchronization of crucial network elements such as the ACG and Base Radios. The ACG contains a GPS receiver whose sole purpose is to use GPS satellites to synchronize the ACG and BRs. GPS satellites broadcast date/time to the receiver, which in turn uses this date/time information to setup its own internal clock to determine current date/time and generate a 1PPS (1 Pulse Per Second) signal that is aligned at the top of each GMT second. The ACG receives date/time information periodically from the receiver for the purposes of setting ACG and BR time. The 1PPS is then used to ensure that the date/time information received from the receiver is set and maintained cor- rectly in both the ACG and BRs.

PROBLEM - DEPENDENCE OF DATE/TIME ESTIMATION ON SATELLITE CONFIGURATIONS

  The single most important factor regarding the accurate interpretation of the date/time received from a GPS satellite...