Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-08-31
2001-07-03
Banks-Harold, Marsha D. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S427000
Reexamination Certificate
active
06256507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to telecommunications network and, in particular, to a system for providing synchronization within a telecommunicatings network that supports data communications services.
2. Description of Related Art
Most telecommunications networks require synchronization in order to prevent impairments in the provision of communications services. Synchronization is generally effectuated through master-slave arrangements.
As an example, some wireless telecommunications networks utilize a primary reference source (PRS) clock derived from the pulse code modulated (PCM) communications carried by the connected public switched telephone network (PSTN). When considering voice services, this master-slave PSTN derived, stratum
4
classified, clock relationship operates quite effectively, even considering the consequences of frame losses due to clock slips in the transport network.
As demand for data (as opposed to voice) services increases, however, maintenance of more stringent synchronization requirements within the transport network becomes a more significant and pressing concern to the system operator. This is because data services require much tighter timing specifications to ensure that the transport network is not lossy. A clock slip that would cause little to no discernable disruption in provided voice services may result in a significant bit/byte/word loss of transported data. Such a loss is costly as it not only degrades the data service being provided, but also introduces delays in communication necessitated by having to re-transmit lost information. As such, there is an increasing need for a stratum
1
classified synchronization for use in wireless telecommunications networks providing data services.
SUMMARY OF THE INVENTION
Stratum
1
classified synchronization within a wireless communications network is provided by installing a global positioning system (GPS) receiver at each mobile switching center of the network. A local clock maintained within each mobile switching center receives a GPS sourced stratum
1
classified clock pulse from its associated GPS receiver. By training to this clock pulse, the local clock can generate a synchronization clock pulse having a corresponding stratum
1
classification for application to the operations of the mobile switching centers. A star network type topology is thus provided for the synchronization system with synchronization information radiating from a centralized primary reference source (PRS) comprising the global positioning system to each of the network nodes. As a further enhancement, the GPS receiver may also be installed at each base station for use in training base station local clocks to generate stratum
1
classified synchronization clock pulses in an extended star network type topology.
In the event the global positioning system primary reference source fails or its accuracy unacceptably degrades, the primary reference source for the network synchronization system is changed to the local clock within each of the mobile switching centers. This change is coordinated through a synchronization manager maintained by the transport network management system of the network. Through a network supported clock distribution system, the local clock within each mobile switching center synchronizes its connected base stations. In this back-up mode of operation, a tree or linear network type topology is thus provided for the network synchronization system with synchronization information flowing downstream to the base stations from each mobile switching center.
Primary use of the star network type topology for the network synchronization system makes it possible for the wireless communications network to offer a number of value added services such as a service for geographically locating traveling mobile stations and a service for time stamping wireless communications network communications.
Provision of these services is coordinated through the synchronization manager of the transport network management system. With respect to the locating service, the highly accurate synchronization provided through the star network type topology makes it possible for the base stations to very accurately calculate propagation delays for base station handled communications to and from mobile station. If such delay information is collected from several base stations with respect to a single mobile station, a triangulation/arcuation algorithm may be executed to process the measured delays and accurately determine mobile station position relative to the base station geo-coordinate data supplied by the GPS receivers. With respect to the time stamping service, the highly accurate synchronization provided through the star network type topology and time of day information supplied by the GPS receivers provides a highly accurate system clock supporting the time stamping of information handled by pooled transcoders within each mobile switching center.
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patent: 5525999 (1996-06-01), King et al.
patent: 5548583 (1996-08-01), Bustamante
patent: 5594739 (1997-01-01), Lemieux
patent: 5930722 (1999-07-01), Han et al.
patent: 6072847 (2000-06-01), Dupuy et al.
patent: 0 450 828 (1991-03-01), None
patent: 0 668 667 (1994-07-01), None
patent: 2 310 098 (1996-02-01), None
patent: WO 94/08405 (1994-04-01), None
patent: WO 98/18206 (1998-04-01), None
PCT International Search Report, Dec. 17, 1999, PCT/SE99/01330.
“Digital Network Synchronization Plan”, Issue 2, Jun. 1993; Bell Communications Research Technical Advisory TA-NWT-000436.
Banks-Harold Marsha D.
Jenkens & Gilchrist
Telefonaktiebolaget LM Ericsson (publ)
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