Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1996-06-10
1998-11-17
Mullen, Jr., Thomas J.
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
370331, 455456, H04Q 700
Patent
active
058390715
DESCRIPTION:
BRIEF SUMMARY
REFERENCE TO RELATED APPLICATIONS
This application was filed under 35 U.S.C. .sctn.371 and is based upon International patent application No. PCT/AU94/00561, filed Sep. 21, 1994.
BACKGROUND OF THE INVENTION
The present invention relates to a base station for a mobile telecommunications system, a mobile telecommunications method, and an extended cell system.
Mobile telecommunications systems are generally based on cellular radio networks where the network comprises a number of base stations which each handle all communications with mobile stations that are within a respective area referred to as a cell. By placing base stations so that boundaries in the respective cells are adjacent to or overlap one another, handover protocols can be established to enable mobile stations to move between cells and continue a call without any discernible indication that the call handled by one base station has been transferred or handed over to another base station. Calls handled by the base stations are passed to associated mobile switching centres, which act as switching exchanges and connect with the exchanges of other networks, such as the public switched telephone network (PSTN).
Analogue cellular radio systems are now being replaced by more efficient and sophisticated digital systems, one of which is the groupe speciale mobile (GSM) digital cellular radio system. The GSM system was derived by a groupe speciale mobile established by the Committee of European Posts and Telecoms (CEPT), and is currently in use in Europe and Australia. The specification for the GSM system comprises over 100 recommendations administered by the European Technical Standard Institute (ETSI). A general description of the air interface of the GSM system is provided in M. R. L. Hodges, "The GSM radio interface", Br. Telecom Technology J., Vol. 8, No. 1, January 1990, pages 31 to 43.
The GSM system is based on the transmission of time division multiple access (TDMA) frames which each comprise eight 577 .mu.s timeslots (TS). To maintain the integrity of the system, communications between a base station (BS) and a mobile station (MS) must be synchronised. To maintain synchronisation as a mobile station moves within a cell, the base station must take into account the distance between it and the mobile station. The GSM system uses an adaptive time alignment system to ensure transmissions from the mobile station arrive at their destination in the correct timeslots without any overlap. By monitoring initial access transmissions, and continuing to monitor transmissions from the mobile station, the base station is able to determine the separation distance, and transmits a 6 bit timing advance (TA) number to the mobile station which represents the number of bits by which the mobile station must advance its frame transmissions to account for the delay in travel to the base station. The GSM specification imposes a 6 bit limit on the size of the TA, which restricts the distance a mobile station can travel from a base station, and therefore restricts the size of a cell which a base station can cover. Whilst this limitation imposes little difficulties in densely populated areas where a relatively large number of base stations are available to complete a cellular network, in sparsely populated rural areas it would be desirable to be able to extend a base station's coverage beyond the limits imposed by the GSM TA restriction.
One way of extending the cell coverage would be to increase the size of the TA by 1 bit so that it could represent seven bit numbers instead of six. This, however, would require significant changes at the base station and for all mobile stations which wish to take advantage of the extended cell radius. Adjusting all mobile stations is impractical, and it is also not considered prudent to depart substantially from the GSM specification.
Another method involves using only every second timeslot in a TDMA frame so as to allow transmissions to be received in or overlap a succeeding timeslot when a mobile station moves outside the normal cell
REFERENCES:
patent: 4217588 (1980-08-01), Freeny, Jr.
patent: 5448751 (1995-09-01), Takenaka et al.
patent: 5483537 (1996-01-01), Dupuy
patent: 5551060 (1996-08-01), Fujii et al.
patent: 5579373 (1996-11-01), Jang
patent: 5657487 (1997-08-01), Doner
International Search Report for PCT/AU94/00561 issued Nov. 25, 1994.
Engellenner Thomas J.
Lane, Jr. David A.
Mullen Jr. Thomas J.
Telstra Corporation Limited
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