Base station

Details Base station Base station

1998-12-28

2001-05-22

Kizou, Hassaan (Department: 2662)

Multiplex communications

Communication over free space

Combining or distributing information via time channels

C370S321000, C370S330000, C370S442000, C370S334000

Reexamination Certificate

active

06236651

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a base station for a TDMA radio system in which, the base station includes at least two transceivers adapted to communicate with terminals within the base station area. The base station being adapted to transmit information concerning itself to the terminals and the transceivers are adapted to communicate with the terminals within service areas that are at least partly different to form an inner and an outer service area.
Description of the Related Art
In digital Time Division Multiple Access (TDMA) radio systems, a plurality of mobile radio stations may utilize the same radio channel on a time division basis for communication with the base station. Communication on the radio channel takes place in a number of successive repeated timeslots, e.g., 8 time slots, allocated to the users as required. A mobile radio station is synchronized with a signal from the base station, and transmits to the base station so that the signal is received at the mobile station in a timeslot allocated to this particular mobile station. Mobile stations, however, may be located at different distances from the base station, whereby the propagation delay caused by this distance has to be taken into account in the synchronization of the time of transmission of each mobile station with the base station so that the signal will be received at the base station in the right timeslot. For this purpose, the base station measures the time difference between its own transmission and the transmission received from the mobile station station based on which it defines a suitable timing advance for the mobile station. The mobile station uses this timing advance to advance the time of its transmission relative to a basic time instant defined by the sync received from the base station. Various intrasystem features limit the highest possible timing advance to a given maximum value. This maximum value of the timing advance, in turn, dictates the maximum cell size that the base station of the system is able to serve. In the GSM mobile telephone system (Global System for Mobile Communication), for example, the timing advance is expressed by using six bits and can be given values from 0 to 63, which means a cell size with a maximum radius of 35 km. However, such a cell size of 35 km may be too small in, e.g., sparsely populated areas with a low traffic load.
To increase cell size, an “extended cell” has been developed, whereby a cell is divided into several, e.g., two, parts; an inner and outer service area. In this case, the base station serving the cell comprises two transceivers, each of which serve terminals within its own service area. Problems caused by the different propagation delays of the different service areas are solved by delaying the reception frame structure of the transceiver serving the outer service area. Some examples of such extended cells are described in, e.g., patent publications WO 9502306 and WO 9508896.
A problem in extended cells is transmission of base station broadcast channels. In a typical radio system the base station has to transmit information concerning itself to the terminals, and the terminals use this information to identify the base station and to be able, when needed, to transmit a call setup request to the base station. In the GSM system, for example, the base stations transmit the BCCH channel.
FIG. 1
illustrates a prior art manner of transmitting the BCCH channel in an extended cell.
FIG. 1
shows transmission and reception frames
100
and
102
of a transceiver (TRX1) serving an inner service area, and transmission and reception frames
104
and
106
of a transceiver (TRX2) serving an outer service area. In transmitting traffic channels, the TRX1 uses a given frequency channel X which comprises specific physical frequency bands for the different transmission directions. In transmitting traffic channels, the TRX2 uses a given frequency channel Y which comprises specific physical frequency bands for the different transmission directions. In the example of the figure the frames comprise 8 timeslots, numbered from 0 to 7. However, on the reception side the time slot numbering is different in that a certain time slot number appears three timeslots later than the corresponding timeslot number on the transmission side. The BCCH channel is transmitted in the first timeslot of the frame
100
of the transceiver serving the inner service area. The terminals transmit their call set-up bursts in a corresponding timeslot of the other transmission direction. The first timeslot of the reception frame
106
of the transceiver TRX2 serving the outer area is also reserved for call set-up bursts originating from the outer area, and this timeslot uses the frequency X. In both transmission directions the second timeslot of the transceiver TRX1 serving the inner service area has to be left unused in order not to interfere with a call set-up request from the outer area to the TRX2. The first timeslot in the transmission direction frame
104
of the transceiver TRX2 serving the outer service area is not in use because the BCCH is transmitted via the TRX1 and because the reception of the same timeslot is reserved for call set-up of the outer area.
The drawback in the above arrangement is that the transmission of the transceiver serving the inner service area has to be audible in the outer service area, too. For this reason the antennas of both transceivers have to have a narrow beam or be highly amplifying and located high up in the antenna mast. The transmission power has also to be maximized to both transmission antennas. This makes it costly to implement an extended cell.
BRIEF DESCRIPTION OF THE INVENTION
It is an object of the invention to eliminate the above problem. This is achieved by a base station having at least to translators adapted to communicate with a plurality of terminals within the base station area, wherein the base station is adapted to transmit information concerning itself to the plurality of terminals wherein the transceivers are adapted to communicate with the plurality of terminals within at least two service areas that are at least partly different to form an inner and an outer service area, and wherein the transceiver serving the outer service area is adapted to transmit information concerning the base station.
The invention also relates to a data transmission method for a TDMA radio system that includes a plurality of base stations communicating with terminals within their area, and at least two transceivers being used in the base stations to form at least two service areas which are at least partly different so as to form an inner and an outer service area, wherein each transceiver serves one service area, and the base station transmits information concerning itself to the terminals. In this method of the instant invention, only the transceiver serving the outer service area transmits information concerning the base station to the terminals.
The method and system of the invention provide many advantages. The antennas/antenna lines of only one transceiver have to be optimized in order for the audibility to cover the outer service area. This allows an extended cell to be implemented significantly more inexpensively than before.


REFERENCES:
patent: 5544171 (1996-08-01), Godecker
patent: 5615215 (1997-03-01), Utting et al.
patent: 5668804 (1997-09-01), Suonvieri
patent: 5740166 (1998-04-01), Ekemark et al.
patent: 5825764 (1998-10-01), Rudolph
patent: 5839071 (1998-11-01), Johnson
patent: 687 079 A2 (1995-12-01), None
patent: 738 052 A2 (1996-10-01), None
patent: 95/02306 (1995-01-01), None
patent: 95/08896 (1995-03-01), None
patent: 97/01254 (1997-01-01), None

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