Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-07-23
2003-06-17
Appiah, Charles N. (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S562100, C370S529000
Reexamination Certificate
active
06580918
ABSTRACT:
DESCRIPTION
The invention relates to a cellular telecommunications system in accordance with the preamble of Patent claim
1
.
Cellular telecommunications systems which are already known are generally more cost-intensive the bigger their transmission/reception range, i.e. the more cells there are in the cellular telecommunications system. This is primarily due to the fact that each individual cell is assigned its own base station. Therefore, the greater the area which is to be covered by a cellular telecommunications system, the more base stations are necessary. Consequently, in contemporary cellular telecommunications systems the base stations constitute one of the main cost factors.
The object of the invention is to provide a more cost-effective cellular telecommunications system with which a greatest possible transmission/reception range can be made available.
The means of achieving the object which has been set can be found in the characterizing part of Patent claim
1
.
A cellular telecommunications system in accordance with the invention is characterized by the fact that all n cells are assigned only one common base station with n antennas which can be switched over, the number n of cells being greater than or equal to two.
According to a preferred exemplary embodiment of the invention, the telecommunications system has precisely two cells, the assignment of the cells to the common base station being carried out by means of a switch which is contained in the base station and via which the respective antennas are connected to a RF (Radio Frequency) unit contained in the base station. In this way, it is possible to make a saving of one base station in comparison with conventional telecommunications systems, which has positive effects on the costs.
By making an appropriate selection of the number of antennas and of the switch, it is possible, as an alternative, also to assign more than two cells to one base station in each case.
According to one development of the invention, the switch is controlled by a microcontrol unit (MCU) contained in the base station. The switch can be controlled here in accordance with an algorithm which is implemented, for example, as software in the MCU. In this way, the control of the switch can be adapted relatively easily and quickly to different demands.
According to another development of the invention, information which is supplied by the MCU and which specifies in which time slot and at what frequency the RF unit has to transmit data is buffered in a BMC (Burst Mode Controller) before it is passed on to the RF unit. It is necessary to buffer the data because, depending on the position of the switch, the data can be passed on to the RF unit only in corresponding time slots.
So that the MCU can carry out the abovementioned functions, according to one development of the invention said unit is coupled to memory modules which may be designed, for example, as fixed and/or variable ROMs (Read Only Memory) and/or RAMs (Read Access Memory), the components which are contained in the base station being synchronized by means of a common clock generator. This ensures that the correct data are transmitted via the correct antenna in the corresponding time slots.
According to yet another refinement of the invention, a first antenna is arranged in a building and a second antenna is arranged outside the building. In this way, the transmission/reception range of the telecommunications system can easily be extended. Consequently, it is possible, for example, also to set up a connection between two mobile stations, one of which is located in the interior of the building and the other in the garden, for example.
Telecommunications systems of the abovementioned type can, for example, be operated according to the DECT Standard. These may be cellular or so-called cordless systems.
According to the DECT Standard, it is possible to transmit both voice and data signals. Consequently, it is possible to set up cellular data networks which are based on the DECT Standard and which permit the subscriber to move freely within various cells without, for example, the call which is currently being made being interrupted. Voice and data signals are transmitted here by means of so-called bearers (see DECT Standard for more details).
In order to prevent a call being interrupted, a call is, when necessary, transferred from one cell into another, which is customarily also referred to as handover, (changing over to another channel), specifically also as intercell handover.
A handover can also be carried out within a cell (intracell handover) if the connection quality is, for example, degraded as a result of common channel interference. Here, a change-over of the radio channel takes place within a cell with the same base station being retained. In this context, the change-over of the channel can consist in changing over between frequencies or between time slots.
In the abovementioned types of handover, a channel change is seamless, that is to say without the connection being interrupted. This is achieved by virtue of the fact that the old bearer is not released until the new one has already been set up. Consequently, two bearers must be operated in parallel for a short time, which leads to an increased loading of the system. However, in order to protect the resources in a telecommunications system, the number of handovers must, on the one hand, be kept as low as possible, while, on the other hand, any desired reduction in the number of handovers is not possible since otherwise the desired connection quality cannot be maintained.
In order, to be able to utilize fully the power of, for example, a two-cell telecommunications system according to the DECT Standard, so-called dummy bearers (DB) must be transmitted in each cell via respective antennas.
So the mobile stations know that a call has arrived for them, they must activate their receiver in a specific time slot and at a specific frequency in order to determine whether there is information for them. Customarily, they receive this information via the broadcast channel which is usually transmitted via the dummy bearer (DB).
In order to avoid the dummy bearer being subject to interference, it must be transmitted on various channels, i.e. at a different frequency and/or in another time slot.
If, for reasons of cost, a so-called low-cost synthesizer is used in a base station, it is not possible with such a synthesizer to change the frequency in two successive time slots since the synthesizer is too slow. This means that, instead of the 24 time slots defined in the DECT standard, it is possible to use only every second time slot. Consequently, when a “low-cost” synthesizer is used, only six time slots are used in the downlink (base station—mobile station) and six in the uplink (mobile station—base station), respectively.
If it is then desired to reduce the number of base stations in the abovementioned example from two to one and to transmit the respective bearers into both cells via the remaining base station in which a slow synthesizer is being used, in order to set up the bearers (traffic bearers and dummy bearers) there are therefore only six time slots left for connections from the base station to the mobile station and from the mobile station to the base station. In the case of a standard configuration of a telecommunications system it should be possible to make telephone calls to the outside (line call) from a cell using at least one mobile station, while being able at the same time to set up a connection to a mobile station of another cell (inter-call) using a different mobile station in the cell. Furthermore, a handover must also be possible in each cell, it being possible for further mobile stations to be in stand-by mode. As a result, the following number of bearers results for a telecommunications system according to the DECT Standard with two cells and “low-cost” synthesizer:
1.
Transmission of a dummy bearer
1 bearer;
in the first cell
2.
Transmission of a dummy bearer
1 bearer;
in the second cell
3.
Call between two extensi
Jakobsen Jens
Leickel Torsten
Appiah Charles N.
Nokia Mobile Phones Ltd.
Perman & Green LLP
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