Cellular radio system

The object of the invention is to provide a cellular radio system, in particular a LMDS system wherein the utilization of the transmission capacity is optimized. The cellular radio system is characterized in particular in that each cell contains a base station, that at least one cell is divided into at least two sectors, that each sector comprises one non-overlapping zone and two overlapping zones, and that each base station is suitable to allocate at least one transmission unit (time slot or orthogonal code) simultaneously to at least two different terminals located in different, non-overlapping zones of a cell.

The exemplary embodiment will firstly be explained with reference to FIG. 1 . FIG. 1 illustrates a division of a cell of a cellular radio network into sectors. The cellular radio network is designed for example as a LMDS system. The radio network is constructed from a plurality of mutually adjacent cells. Each cell has a base station which controls the radio communication within the cell. The base station is generally arranged centrally in the cell. Each cell is divided into a number of sectors, it being possible to vary the number from cell to cell. The size of the cells can likewise vary from cell to cell, for example as a function of the topology of the network. FIG. 1 schematically illustrates a cell having K sectors S 1 , S 2 to SK and a base station BS, where K is a natural number greater than one. Each sector S 1 , S 2 to SK has three zones, one non-overlapping zone and two overlapping zones. Sector S 1 comprises the non-overlapping zone B 21 and the overlapping zones B 11 and B 31 . Sector S 2 comprises the non-overlapping zone B 22 and the overlapping zones B 12 and B 32 . Sector SK comprises the non-overlapping zone B 2 K and the overlapping zones B 1 K and B 3 K. The transmitting antennae used in the base station BS to form the sectors S 1 , S 2 to SK have scatter zones in the edge regions, which project into the adjacent sector. This gives rise to the overlapping zones. Terminals situated in the overlapping zones on the one hand can receive radio signals from two different transmitting antennae of the base station. On the other hand the receiving antennae of the base station, which are assigned to the transmitting antennae, receive both radio signals transmitted by a terminal in the overlapping zone. Terminals which on the other hand are located in a non-overlapping zone on the one hand can only receive radio signals from one transmitting antenna of the base station. On the other hand only one receiving antenna of the base station receives radio signals transmitted from the terminal in the non-overlapping zone. Terminals located in a non-overlapping zone thus cannot interfere with terminals located in non-overlapping zones of other sectors. A terminal which on the other hand is located in an overlapping zone can interfere with a terminal located in the adjacent sector adjoining the overlapping zone if it is allocated the same time slot or code as said terminal. Each sector S 1 , S 2 to SK spans a specific angular range. Each sector S 1 , S 1 to SK can span a different angular range. If for example two sectors are used for a cell, each sector spans an angular range of 180° for example. If for example four sectors are used for a cell, each sector spans an angular range of 90° for example. If for example six sectors are used for a cell, four sectors each span an angular range of 80° for example and two sectors each span an angular range of 20°. The latter sectors are directed for example towards zones in which a higher terminal capacity and/or a higher communication rate exists. Within a sector the non-overlapping zone encompasses approximately 96 to 98% of the sector surface and the two overlapping zones approximately 2 to 4% thereof. The base station BS contains the usual components, such as a processor, a memory, a number of antennae, coders and decoders, detectors etc. and for example an optical link via optical glass fibre cable to an exchange, a radio link to another base station, or a radio relay link to a control centre. When TDMA is used, in each cell a number of time slots are used to transmit information from the terminals to the base station. When CDMA is used, in each cell a number of orthogonal codes are used to transmit information from the terminals to the base station. This will be explained in detail in the following for the situation in which CDMA is used. Similar applies to the transmission of information from the base station to the terminals, taking into account the point-to-multipoint Configuration, for which reason this will not be discussed in detail. In the base station BS for example a maximum number of N orthogonal codes are available at the air interface, where N is a natural number, for example 1000. These codes can now be distributed between terminals in the individual sectors as follows: If those terminals which wish to communicate are all located in the non-overlapping zones, due to the fact that the terminals cannot influence one another, all N codes can be multiply allocated. The N codes are allocated for example to a terminal in sector SI. At the same time m of the N codes are allocated to a first terminal in sector S 2 and N-m codes of the N codes are allocated to a second terminal in the sector S 2 . At the same time for example the N codes are distributed between n terminals in the sector K and allocated thereto. The base station then undertakes the forwarding of the information of all the active terminals of all the sectors, for example via an optical glass fibre line to an exchange, it being possible to employ multiplex techniques for example on the glass fibre line. In LMDS systems it is easy to determine whether the terminals are located in the non-overlapping zones as the terminals are situated at fixed positions which are previously known. The probability that all terminals are located in non-overlapping zones is high as these zones cover by far the largest area of the cell. In the event that a terminal located in an overlapping zone wishes to become active, i.e. to communicate with another terminal via the base station BS, a preprogrammed algorithm is started in the base station. If the terminal is located for example in the zone B 31 , prior to the allocation of a code it must be checked whether: 1. The code has already been allocated to a terminal in the non-overlapping zone B 21 and therefore is in use. Terminals in the zones B 21 and B 31 lie in the same sector and therefore can interfere with one another. 2. The code has already been allocated to a terminal in the non-overlapping zone B 22 and therefore is in use. A terminal in the zone B 31 lies in the edge region and therefore can interfere with terminals in the sectors S 1 and S 2 . 3. The code has already been allocated to a terminal in the overlapping zones B 11 , B 31 , B 12 , B 32 and therefore is in use. 4. If, due to the allocations specified by 1. to 3., a free code cannot be found, a redistribution of the codes in sectors S 1 and S 2 can take place in that the number of identical codes in the zones B 21 and B 22 is maximised as these do not influence one another. Of the 1000 codes, for example preferably the first 900 codes are reserved for the non-overlapping zones and the last 100 codes for the overlapping zones. A free code X which has been found is then allocated to the terminal in the zone B 31 . For all the terminals in the sectors S 1 and S 2 the code X is then in use. However for terminals outside the sectors S 1 and S 2 this code is freely available and can be simultaneously allocated to another terminal. A terminal in a non-overlapping zone can thus be allocated the maximum number N of codes. At the same time the N codes are available to the other sectors. A terminal in an overlapping zone can likewise be allocated the maximum number of N codes. At the same time the N codes are available to the other sectors with the exception of the adjacent sector. Example: A terminal in the zone B 31 is allocated N/2 codes from a number of N codes. A terminal in the zone B 12 is allocated the remaining N/2 codes. Then no further codes can be allocated in the sectors S 1 and S 2 . However all N codes are freely available to all the other sectors in the direction from the terminals to the base station. In the direction from the base station to the terminals for example the codes allocated in the sector S 1 can be reallocated in the sector S 3 ; in the sector S 4 the N/2 codes from sector S 2 are freely available. UMTS can also be used in place of a LMDS system as radio system; UMTS&equals;universal mobile telecommunication system or any other cellular radio system. It can be determined by means of the handover function whether a mobile radio device is located in the overlapping zone. The invention is not limited to CDMA. It can also be used in a similar manner in TDMA, FDMA or comparable processes. The exemplary embodiment will now be explained further with reference to FIG. 2 . FIG. 2 illustrates a topology of a cellular radio network. The illustrated extract shows nine cells. One cell is divided into four sectors, another into three sectors. Each sector comprises one non-overlapping zone and two overlapping zones. The number of sectors per cell is a function of the size of the cell, the terrain, the number of terminals, the customer requirements etc. When a LMDS system is used as cellular radio network and the position of the stationary customers prior to the commencement of the installation is also known, in the topology planning it is possible to select the sectors such that the number of terminals in the overlapping zones is minimised, and ideally is zero. In the simplest case the number of sectors for each cell can also be the same for a part of the radio network or for the entire radio network. In most cases each cell of the cellular radio network is divided into at least two sectors, each sector comprising one non-overlapping zone and two overlapping zones. This will be the case in particular in networks which have a high subscriber density, thus generally in town-centre areas. In exceptional cases sectors can also comprise only one non-overlapping zone, or one non-overlapping zone and only one overlapping zone. This is the case for example when no terminals are present in a specific angular range within a cell and therefore the transmitting- and receiving range need not compulsorily project into this angular range. This can occur particularly in areas with a low subscriber density.