Pulse or digital communications – Miscellaneous
Reexamination Certificate
1999-04-05
2003-03-04
Bocure, Tesfaldet (Department: 2631)
Pulse or digital communications
Miscellaneous
C375S354000
Reexamination Certificate
active
06529572
ABSTRACT:
The invention relates to network independent clocking in a telecommunication system, particularly in data transmission where the maximum data rate of a traffic channel is equal to one of the user data rates at a terminal interface.
DESCRIPTION OF THE RELATED ART
Mobile systems generally mean different telecommunication systems that enable private wireless data transmission for subscribers moving within the system. A typical mobile system is a Public Land Mobile Network (PLMN). The PLMN comprises fixed radio stations (base stations) located in the service area of the mobile network. The radio coverage areas (cells) of the base stations provide a uniform cellular network. A base station provides a radio interface (air interface) in the cell for communication between a mobile station and the PLMN.
Another area of mobile systems includes satellite-based mobile services. In satellite system, radio coverage is obtained by satellites instead of terrestrial base stations. The satellites orbit round the earth and transmit radio signals between mobile stations (or User Terminals (UT)) and Land Earth Stations (LES).
Subscriber mobility requires similar solutions in satellite mobile systems as in the PLMNs, i.e. subscriber data management, authentication and location management of mobile subscribers, handover, etc. The satellite systems should also support similar services as the PLMNs.
One way of meeting the above requirements in satellite mobile systems is to use existing PLMN solutions. In principle this alternative is very straightforward since a satellite system can basically be compared to a base station system of a mobile system having a different radio interface. In other words, it is possible to use conventional PLMN infrastructure, where the base station system(s) is (are) a satellite system. In such a case, the same network infrastructure could, in principle, even contain both conventional PLMN base station systems and satellite ‘base station systems’.
There are many practical problems, however, in adaptation of the PLMN infrastructure and a satellite system. A problem apparent to the Applicant is that a PLMN traffic channel and a traffic channel of a ‘radio interface’ in a satellite system differ considerably. Let us examine an example where the PLMN is the Pan-European digital mobile system GSM (Global System for Mobile Communication), and the satellite mobile system is the Inmarsat-P system that is currently being developed.
At present, a GSM traffic channel supports data transmission at user rates 2400, 4800, 7200 and 9600 bit/s. In addition to user data, status information on the terminal interface (control signals of a V.24 connection) is transmitted on the traffic channel in both directions. In transparent High Speed Circuit Switched Data (HSCSD) data service, it is also necessary to transmit synchronization information between subchannels. In synchronous transparent bearer services, the clocking information of network independent clocking (NIC) must also be transmitted through a transmission channel from transmitting terminal equipment to receiving terminal equipment via a transmission network, when the transmission network and the transmitting terminal equipment are not in sync with each other, i.e. the terminal equipment uses network independent clocking (e.g. internal clock). The above-mentioned additional information raises the bit rate at the radio interface to be higher than the actual user rate. The GSM radio interface rates corresponding to user rates 2400, 4800 and 9600 bits are 3600, 6000 and 12000 bits. These signals are subjected to different channel coding operations, which raise the final bit rate to about 22 kbit/s.
The Inmarsat-P satellite system requires that standard data rates up to 4800 bit/s (e.g. 1200, 2400, 4800 bit/s) can be transmitted on one traffic channel, and that standard data rates exceeding 4800 bit/s (e.g. 9600, 14400, 19200 bit/s, etc.) can be transmitted by using several parallel traffic channels, like in the HSCSD service of the GSM system.
In the Inmarsat-P satellite system, the data rate of one traffic channel at the radio interface is at most 4800 bits, which equals the user data rate of 4800 bits at the terminal interface. In a data service employing two traffic channels, the data rate at the radio interface equals the user data rate of 9600 bits at the terminal interface. A problem arises when not only the user data but also the above-described terminal interface status information and any inter-subchannel synchronization information should be transferred over the radio interface. Therefore the protocol data unit, i.e. frame structure, used by the satellite system at the radio interface should be defined to carry the above mentioned control and synchronization information over the radio interface.
One approach would be to use a GSM solution, i.e. a V.110-based frame structure, for the transmission of the status also at the radio interface of the satellite system. However, this would be a very complicated solution, and it would significantly reduce the user data rates available. A single traffic channel could not support the user data rate of 4800 bit/s since a V.110 frame structure and the terminal interface status information raise the actual data rate (radio interface rate) to be higher than 4800 bit/s. Therefore the highest standard user data rate on one traffic channel would be 2400 bit/s. For the same reason, a two-traffic-channel data service could not support the user rate of 9600 bit/s, but the highest standard user data rate would be 4800 bit/s (or in some systems 7200 bit/s). A corresponding decrease in the available data rates would also occur in data services employing more than two traffic channels. Such a solution, where the overhead information causes a significant loss of capacity, would not be satisfactory.
A similar problem can also arise when other types of radio interfaces, such as wireless telephone systems, are connected to the PLMNs.
A similar problem can also arise on other types of connections in which the radio interface rate is to be used as effectively as possible. For example, a new 14400 bids traffic channel has been planned for the GSM. In order that the terminal interface statuses and any other control information may be transferred over the radio path in addition to the 14400 bit/s user data, the radio interface rate, implemented on the present principles, must be higher than 14400 bit/s, about 18 kbit/s. A higher radio interface rate requires that the existing radio networks should be re-designed and the intermediate rate Transcoder/Rate Adaptor Unit (TRAU) increased so that only two subchannels could be put in a single 64 kbit/s timeslot in the HSCSD service (i.e. efficiency of a TRAU transmission link is impaired). The radio interface rate of 14400 bit/s, which does not cause such problems, can be formed, for example, from the present radio interface rate of 12000 kbit/s by enhancing the puncturing that follows channel coding. The actual user data rate, however, would then be below 14400 bit/s, if the new traffic channel were implemented on the same principles as the existing GSM traffic channels. It would thus be preferable to implement a user data rate of 14400 bids at a radio interface rate of 14400 bit/s.
The parallel Finnish patent applications 955,496 and 963,455 by the same Applicant describe a data transmission method in which the terminal interface status information and any other control or synchronization information are transmitted through a traffic channel in the redundant data elements of end-to-end protocols, such as the redundant parts of the protocol data units of user data or the start and stop bit positions of asynchronous data characters. The overhead information thus does not increase the number of the bits to be transmitted, so the transmission capacity of the traffic channel can be exactly the same as the user data rate at the terminal interface. In high-rate data transmission (HSCSD) a data link may comprise a group of two or more traffic channels, whereby the total cap
Bocure Tesfaldet
Nguyen Dung X.
Nokia Telecommunications Oy
Pillsbury Winthrop LLP Intellectual Property
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