WO2000070890A1

WO2000070890A1 - Resource allocation method

Info

Publication number: WO2000070890A1
Application number: PCT/FI2000/000444
Authority: WO
Inventors: Olli-Pekka MÄKINEN; Jukka Peltola; Olli Rissanen; Hannu Tuominen
Original assignee: Nokia Networks Oy
Priority date: 1999-05-17
Filing date: 2000-05-17
Publication date: 2000-11-23
Also published as: FI991118A; AU4572300A; FI991118A0

Abstract

The invention is concerned with optimization of data transfer within cellular telecommunication systems, namely between base stations and base station controllers or corresponding network elements. According to the invention, the Abis link channels are divided into at least two different types of categories: a first category comprises permanent point to point type connections between the BSC and the TRX units of the base stations, and a second category comprises logical point to multipoint type connections between the BSC and the TRX units of the base stations. In the downlink direction, i.e. from BSC to TRX units, the communication is of the broadcast type, i.e. all TRX units having connections in the second category receive the data sent by the BSC. In the uplink direction, the connections are shared between the TRX units. To avoid collisions in the uplink direction, the BSC allocates and deallocates capacity of the shared connections for each TRX unit according to the current need for transmission capacity.

Description

Resource allocation method

TECHNICAL FIELD OF THE INVENTION

The invention is concerned with optimization of data transfer within cellular tele- communication systems, namely between base stations and base station controllers or corresponding network elements. More accurately, the invention is directed to a method according to the preamble of claim 1.

BACKGROUND OF THE INVENTION

Figure 1 shows a part of a radio access network of a cellular telecommunication system such as a GSM (Global System for Mobile telecommunications) system. Figure 1 shows a base station subsystem (BSS) comprising base stations (BS) 10, which are connected to a base station controller (BSC) 20. The interface between a BSC and a BS is called the Abis interface. Similarly, the communications link between a BSC and a BS is called the Abis link. The base stations comprise one or more tranceiver units (TRX) 15. In the GSM system, one TRX can transmit and receive information on up to eight channels, the number of timeslots in a frame being eight. In conventional GSM systems, this enables speech data transfer to and from eight mobile stations (MS), each using a given timeslot of each frame transmitted by a TRX of a base station. The BSC transmits speech data and various commands to be transmitted to the mobile stations via the Abis link to the base stations, and the base stations transmit speech data and any signalling received from mobile stations via the Abis link to the BSC. The Abis link is used also for transmission of various types of control signalling between the BSC and the base stations. The BSC is in turn connected to further network elements of the cellular telecommunication system. The exemplary system shown in figure 1 can also be taken as an example of a radio access network of the UMTS system (Universal Mobile Telecommunications System).

One drawback of conventional GSM systems is that the data rates, which the GSM system is able to provide for a mobile station, are relatively low. Various schemes have been devised to overcome this limitation. EDGE or "Enhanced Datarates for GSM Evolution", where GSM stands for "Global System for Mobile telecommunications", is an international project where means are being developed for providing users with higher data rates in a telecommunications system based on known GSM technology. The raw bit rate at the GSM air interface between a base station and a mobile station is 22.8 kbit/s. Channel coding and the overheads associated thereto lower the usable data rate so that data rates from 3.6 to 14.5 kbit/s are available to connected data applications. Even these rates carry a certain overhead on top of the available user data rate. The EDGE project aims to a manyfold increase of the raw air-interface bit rate. The enhancement in data rates is effected using 8PSK (8-level Phase Shift Keying) modulation method in EDGE, in contrast to the GMSK (Gaussian Minimum Shift Keying) modulation used in GSM. A second example of a system for increasing the data rates is the HSCSD (High Speed Circuit Switched Data) system presently under development. The HSCSD system is able to provide higher data rates to a mobile station by using more than one time slot per transmission frame for data transfer to and from the mobile station. Both the EDGE and the HSCSD system are presently being introduced into existing GSM networks.

The present invention is concerned with a problem presented by the EDGE system, namely the use and capacity of an Abis link. Abis links are typically realized using bidirectional 2048 kbit/s communication links. A 2048 kbit/s communication link is a typical basic building block of fixed line telephony. A 2048 kbit/s communication link provides 32 channels having a capacity of 64 kbit/s each, of which 31 can be used for transferring of payload data. The data is transmitted in frames comprising 32 time slots, each time slot corresponding to a channel. Each time slot comprises 8 bits, and the frame is repeated 8000 times a second. In the GSM system, speech data is transferred using 16 kbit/s channels. A 16 kbit/s channel can be formed by using two bits of a time slot. Consequently, four 16 kbit/s channels can be inserted into one 64 kbit/s channel of the Abis link. One TRX needs 8 of these 16 kbit/s channels on the Abis link in order to provide full service on all eight radio channels it is able to provide. Further, one 16 kbit/s channel is needed for each TRX for transferring control signalling to and from the TRX, and one 16 kbit/s channel is needed for each BS for transferring control signalling to and from the BS. One Abis link has enough capacity for quite a large number of transceiver units. For example, one Abis link can support three base stations comprising four transceiver units each.

However, use of the EDGE system in the air interface creates a problem with the Abis link, since the EDGE system can increase the air interface data rate up to five times from that of a conventional GSM system. Consequently, one TRX may require up to 8 * 5 * 16 kbit/s capacity on the Abis link, if the maximum trans- mission rates according to the EDGE system are used in all eight channels a TRX can provide. In the example of figure 1, if all TRX units of one of the base stations 10 are upgraded to EDGE capable TRX units, the one Abis link in figure 1 does not have enough capacity to support maximum data transfer rates on all channels of the new EDGE capable TRX units. Similar problems arise from the use of new codecs being developed which support high data rates. Such codecs are being developed particularly for use with the GPRS system (General Packet Radio Service). Examples of such codecs are the AMR, CS-3, and CS-4 codecs.

This problem may naturally be solved by adding new Abis links to the system to cater for the increased need of data transfer capacity. For example, one Abis link has enough capacity to cany the maximum traffic from three EDGE capable TRX units. However, this is not a very economical solution, since new links require new hardware to be installed, which is costly. Many network operators especially among newly started operator companies are so called leased line operators, which lease the needed landline capacity for connections between the network elements of the cellular network of the operator from conventional telecommunication operators. Leasing costs form a considerable part of the operating costs of leased line operators, which strongly discourages the leasing of new links.

Furthermore, it is quite probable that all EDGE capable mobile stations will not use maximum data transfer rates all the time, since maximum data transfer rates are not needed for plain speech. The same applies also in the downlink direction. Further, the number of mobile terminals within the area controlled by one base station is highly variable. The Abis link needs to be constructed in such a way, that at the maximum predicted load, a given call blocking rate limit will not be exceeded. Therefore, a large portion of the newly installed Abis link hardware will remain unused for most of the time. A better solution is clearly needed.

Optimization of Abis links has been the subject of several patents and patent applications, which deal with the problem of a large part of fixed Abis link connections being unused, since the TRX capacity is not always in maximum use.

For example, the patent US 5708974 describes a method for dynamically allocating Abis link channels. The patent aims to avoid time delays associated with reconfiguration of Abis link channels by preconfiguring a number of channels, which can then be assigned dynamically to any BS. This solution has the drawback, that a number of channels need to be configured, even if they were idle due to a low amount of traffic. This solution is not flexible enough. The patent US 5678178 proposes the use of a SDH (Synchronous Digital Hierarchy) between the BSC and the base stations. This solution is indeed able to increase the efficiency of the Abis link, since according to the solution, idle channels are not transmitted in the SDH network and therefore consume no resources. However, installing a SDH network is evidently not a good solution for leased line operators, and does not either provide any solution for improving the efficiency of already installed Abis links.

The application WO 97/04615 presents another approach: the use of connections via a second network for providing capacity during peak traffic. They propose using ISDN connections for this purpose. Consequently, the Abis capacity does not need to be dimensioned according to the peak traffic. However, this solution brings the complicity and costs associated with the use of two landline networks instead of only one for Abis connections.

SUMMARY OF THE INVENTION

An object of the invention is to realize a method for optimizing the transmission of data over an Abis link. A further object of the invention is to realize a method for transmission of data over an Abis link, which allows support of maximum data transfer rates of EDGE capable TRX units without incurring as much waste of Abis link capacity as in the solutions according to prior art.

The objects are reached by dividing the channels of an Abis link into at least two categories. A first category provides permanent connections between TRX units and the BSC, and a second category provides shared connections between TRX units and the BSC, which shared connections may be allocated and deallocated by the BSC as needed. The Abis link may also comprise more than one category providing shared connections.The method according to the invention is characterized by that, which is specified in the characterizing part of the independent method claim. The system according to the invention is characterized by that, which is specified in the characterizing part of the independent claim directed to a system. The network element according to the invention is characterized by that, which is specified in the characterizing part of the independent claim directed to a network element. The transceiver unit according to the invention is characterized by that, which is specified in the characterizing part of the independent claim directed to a transceiver unit. The dependent claims describe further advantageous embodiments of the invention. According to the invention, the Abis link channels are divided into at least two different types of categories:

- a first category comprises permanent point to point type connections between the BSC and the TRX units of the base stations, and - a second category comprises logical point to multipoint type connections between the BSC and the TRX units of the base stations. In the downlink direction, i.e. from BSC to TRX units, the communication is of the broadcast type, i.e. all TRX units having connections in the second category receive the data sent by the BSC. In the uplink direction, the connections are shared between the TRX units. To avoid collisions in the uplink direction, the BSC allocates and deallocates capacity of the shared connections for each TRX unit according to the current need for transmission capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail in the following with reference to the accompanying drawings, of which

Figure 1 illustrates a base station subsystem according to prior art,

Figure 2 illustrates an advantageous embodiment of the invention,

Figure 3 aids in the description of an advantageous embodiment of the invention by illustrating the principle of a way to implement common channel connections,

Figure 4 illustrates a method according to an advantageous embodiment of the invention, and

Figure 5 illustrates a system, a network element and a transmission unit according to various advantageous embodiments of the invention.

Same reference numerals are used for similar entities in the figures.

DETAILED DESCRIPTION

Figure 2 illustrates an example of an advantageous embodiment of the invention. Figure 2 shows a BSC 20 and three base stations 10 BS1, BS2, and BS3. The Abis link between the BSC and the base stations is shown as a number of separate connections, each corresponding to a plurality of time slots of the Abis link. Connections are grouped into two categories Cl and C2. The first category Cl comprises permanent point to point type connections between the BSC and the TRX units of the base stations, the second category comprises shared coimections between the BSC and the TRX units of the base stations, forming a shared connections pool. In the example of figure 2, time slots 1 to 5 of the Abis link form a communication channel of the first category between the BSC and BS3, time slots 6 to 10 between the BSC and BS2, and time slots 11 to 15 between the BSC and BS1. Time slots 16 to 30 are used as a shared connection pool, which the BSC dynamically allocates to the base stations and the TRX units of the base stations. It is clear for a man skilled in the art, that the division of time slots to various connections and various categories can be different from the example of figure 2.

Connections in the first category are preferably used for speech data transfer to conventional TRX units, i.e. TRX units which do not support the inventive method of dynamic Abis allocation, and for signalling between the BSC and the base stations. Particularly, the 16 kbit/s control signalling channel OMUSIG of each BS and the 16 kbit/s control signalling channel TRXSIG of each TRX unit can be transmitted using connections in the first category.

Due to the shared nature of the connections in the shared connection pool, each TRX unit participating in this pool receives all downlink data transmitted from the BSC in all time slots in the shared connection pool. Each TRX unit participating in the shared connections pool can also receive all uplink data transmitted from other TRX units to BSC in all time slots in the shared connection pool. There is no danger of collision in the downlink direction, since BSC is the only unit transmitting data. However, in the uplink direction, care must be taken to avoid collisions, i.e. situations in which more than one TRX unit transmit in the same time slot. Due to the shared nature of the second category connections, in such a situation the data from the competing TRX units would be superposed, distorting the data. To avoid collisions, the BSC allocates the capacity of the uplink direction of the shared connections pool, allocating time slots for the base stations and TRX units participating in the shared connections pool.

The BSC grants the permissions for the TRX units to use a particular time slot or several specified time slots. For example, if lot of transmission capacity is needd at BS3, the BSC may grant permissions for a first TRX unit of BS3 to start transmitting on the Abis link in timeslots 16 and 17, for a second TRX unit of BS3 in time slots 18 and 19, and so on. Naturally, the BSC needs to remove any permissions given to other TRX units for these time slots, before granting the new permissions. In this way, the BSC can ensure that only one of the TRX units can transmit in a given time slot, whereby no collisions will happen. Further, the BSC can remove permissions given to a TRX unit, if the transmission capacity needed by the TRX unit is decreases for example due to a handover of a mobile station to another base station, or for any other reason. Thus the BSC can dynamically allocate and deallocate transmission resources in the Abis link according to the present traffic situation.

The elements 21 shown in figure 2 denote the interconnection of the communication line to and from the particular base station and the Abis communication link. Figure 3 illustrates one example of a structure of the element 21 for realizing a shared connection. Figure 3 shows how such an element can be realized using three combining elements. Figure 3 shows the terminals DIRECTION 1, DIRECTION 2 connected to the Abis link and the terminal BS BUS connected to the base station. Figure 3 also illustrates both directions of communication. As figure 3 shows, a shared connection can be realized using three combining elements, each of which has two inputs. The input of each terminal is connected to two combining elements, whose outputs are connected to the other two terminals. Consequently, each output receives all data coming in from either of the two other terminals. When a plurality of units such as base stations and the BSC are connected using elements 21, the result is that all of the units receive all data any one of the units write to a terminal of an element 21, whereby a shared communication channel is realized. The combining elements 22 can be realized, for example, using logical elements performing the AND or the OR function, depending on the sense of logic used.

Other types of structures can also be used to realize the shared connections C2. For example, there is no need for the data transmitted from BS1 to the BSC to reach the other two base stations. It is sufficient, if data transmitted from the BSC reaches all base stations connected with the shared connections, and if data transmitted from any of these base stations reaches the BSC. Consequently, other logic gate structures than that shown in figure 2 can also be used to realize the C2 connections.

According to an advantageous embodiment of the invention, the allocation of resources in the shared connections pool may be performed in steps having an other size than one time slot, i.e. 64 kbit/s. The BSC may grant a permission for a TRX unit to use a specified bit in a time slot, i.e. a 8 kbit s channel, or a multiple of bits i.e. 8 kbit/s channels. Further, the BSC may allocate shared connections pool resources also in larger units, such as multiple time slots at one time. The invention does not limit the order in which the time slots or bits of time slots are allocated; a TRX unit may be given the permission to use a number of consecutive time slots, or a number of non-consecutive time slots. The uplink and downlink directions do not need to be allocated symmetrically. For example, a connection may have a low- capacity link in the uplink direction, but a high-capacity link in the downlink direction. Such connections can be used for example for browsing databases or the Internet or for other uses, in which the mobile station only needs to send short requests but needs to receive large amounts of information.

According to a further advantageous embodiment of the invention, the BSC can also change the allocation of time slots and parts of time slots of the Abis link between the first category, the second category and any further categories. However, the size of the shared connections pool, i.e. total capacity of the second category connections should preferably be specified in 32 kbit/s steps in order to guarantee maximum compatibility with already existing, older GSM base stations.

The BSC can use the conventional signalling channels, i.e. the previously described TRXSIG and OMUSIG channels for communicating the granting or removal of permissions to the base stations and the TRX units. For this effect, specific signalling messages may be defined, which commands specify the particular TRX unit and the time slot information of the time slots or parts of time slots, for which permissions are granted or removed. In a further advantageous embodiment of the invention, the signalling is effected using already defined Abis interface messages, in which case the necessary time slot information and granting/removal information is attached as message parameters. In a still further advantageous embodiment of the invention, the control signalling is performed at least in part with in-band signalling, i.e. using resources of the shared connections pool.

In this specification and the attached claims the term transmission resource unit is intended to cover the transmission units of a communication link between a base station controller or a corresponding network element and a base station, e.g. time slots and bits of time slots, which can be allocated individually and/or in groups.

Figure 4 illustrates a method according to an advantageous embodiment of the invention. It is to be understood that the example of figure 4 shows an example only, and is not intended to limit the invention in any way. The method is used for optimization of the communication link between a network element 20 of a cellular telecommunication system and at least two transceiver units TRX1, TRX2 15 in at least one base station. The method comprises steps, in which - transmission resource units of the communication link are divided 100 into at least two categories,

- at least one point to point type channel for transmission of data between the network element and one of the at least two transceiver units is allocated 105 from a first category of said at least two categories, and

- at least one channel for transmission of data between the network element and at least two of the at least two transceiver units is allocated 110 from a second category of said at least two categories.

In step 115, a point to point type channel of the first category is used for transferring 115 transceiver unit control signalling between the network element and a transceiver unit TRXl. In step 120, a point to point type channel of the first category is used for transferring 120 transceiver unit control signalling between the network element and a transceiver unit TRXl. Preferably, the network element 20 informs the TRX units about which transmission resource units they may use for uplink data transmission and which transmission resource units they are supposed to monitor for receiving data directed to the particular TRX unit. Further, at least one channel allocated from said second category is used for transferring 125 data from the network element to at least two transceiver units. Preferably, the network element 20 transmits the data via a second category broadcast channel, which can be received by both TRX units TRXl, TRX2, 15. For receiving information addressed to the particular TRX unit, the TRX units monitor the transmission resource units assigned to them by the network element.

In step 130, the transceiver unit TRXl transfers data in the uplink direction on a channel assigned to it by the network element 20. In step 135, the transceiver unit TRX2 transfers data in the uplink direction on a channel assigned to it by the network element 20. Since both of these transceiver units TRXl and TRX2 use their own channels, both of them may transmit data during the same frame.

In step 140, at least one channel for transferring data from the transceiver unit TRX2 to the network element allocated from said second category is deallocated 140 for removing a communication channel. Next, the network element 20 transmits 145 control information to inform TRX2 about the removed allocation.

Figure 4 further illustrates, that the network element may allocate channels again

150 and inform 150 the transceiver units about the new allocation. In other words, the network element may change the allocation of transmission resource units according to the current situation. After these steps, transferring of data may continue in the allocated channels in the downlink direction 160 and in the uplink direction 165.

The inventive method can be applied in many different digital cellular telecommunication systems such as the GSM system, in which case the network element is a base station controller, or for example the UMTS system, in which case the network element is a radio network controller.

Figure 5 illustrates a system according to an advantageous embodiment of the invention. Figure 5 illustrates a system in a cellular telecommunications network having a network element 20 and at least two transceiver units 15 in at least one base station 10 and a communication link 30 between the network element and the at least two transceiver units. The system comprises means 200 for allocating transmission resource units of the communication link for forming a communication channel, means 210 for deallocating transmission resource units of the communication link for removing a communication channel, and in the network element, means 220 for transnntting to at least one of the at least two transceiver units information describing which at least one transmission resource unit corresponds to a communication channel; and in at least one of the at least two transceiver units, means 230 for receiving information directed to the transceiver unit from a commumcation channel formed of at least one transmission resource unit.

Further, according to an advantageous embodiment of the invention, the system of figure 5 is arranged to divide the transmission resource units of the commumcation link into at least two categories, allocate at least one point to point type channel between the network element and one of the at least two transceiver units from a first category of said at least two categories, and allocate at least one channel between the network element and at least two of the at least two transceiver units from a second category of said at least two categories.

Figure 5 further illustrates a network element 20 of a cellular telecommunication system, which network element is adapted to be connected to a communication link 30 for transmission of information to at least two transceiver units of at least one base station. The network element comprises means 200 for allocating transmission resource units of a communication link for forming a communication channel, means 210 for deallocating transmission resource units of a communication link for removing a communication channel, and means 220 for tiansπύtting information via a commumcation link describing which at least one transmission resource unit corresponds to a communication channel. Advantageously, the network element is arranged to divide the transmission resource units of the communication link into at least two categories, allocate at least one point to point type channel between the network element and one of the at least two transceiver units from a first category of said at least two categories, and allocate at least one channel between the network element and at least two of the at least two transceiver units from a second category of said at least two categories.

Figure 5 also illustrates a transceiver unit 15 of a base station 10 adapted to be connected to a cellular network element 20 via a communication link 30. According to an advantageous embodiment of the invention, the transceiver unit comprises means 240 for receiving information from the communication link describing which at least one transmission resource unit of the communication link corresponds to a communication channel, means 230 for receiving information directed to the transceiver unit from a communication channel formed of at least one transmission resource unit of the communication link, and means 250 for receiving information from the communication link describing which at least one transmission resource unit previously designated as corresponding to a communication channel shall not be used as a communication channel by the transceiver unit any more.

The various means 200, 210, 220, 230, 240, and 250 shown in figure 5 can advantageously be realized using processors, such as microprocessors or digital signal processors executing a program stored in a memory means.

Transmission units employing the invention can be realized and in a variety of ways. For example, completely new transmission units having the inventive capabilities may be installed in existing networks. In principle, it is also possible to retrofit existing, older TRX units with the inventive capabilities for example by replacing communication circuitry connecting the TRX unit to the Abis link by new circuitry realizing the inventive functionality.

A great advantage of the invention is, that the inventive method does not require performing of connection changes in cross connection matrices (switching matrices) in real time, since the invention uses a common channel type connection for transferring data to multiple TRX units. Therefore, connection matrixes in the various network elements such as base stations, BSCs and RNCs taking part in the transferring of information need not be changed when a transmission resource unit is deallocated from one TRX and allocated to another TRX. This is an important point, since the EDGE and particularly EGPRS systems may require very fast and very frequent changes in capacity. Such changes are necessary for optimizing data transmission in the case of for example data connections used for internet browsing, which results in very bursty transfer of data. Performing such capacity allocation by reassigning connections in the switching matrices is a very demanding requirement, which would require real time switching capabilities of the switching matrices. The present invention allows fast allocation of temporary capacity without requiring the switching matrices to be able to follow the changes in the allocations.

The invention also has several other advantages. For example, the method allows optimization of Abis link capacity. The method further allows the use of less Abis link resources than according to solutions of prior art for supporting high data rates of the EDGE system. Further, the inventive method is able to produce these benefits, while still allowing the use of conventional base stations and TRX units in the same Abis link, to which new equipment supporting the inventive method are connected to. This allows the network operators to upgrade gradually to newer equipment, without having to upgrade all TRX units and base stations connected to the same Abis link at one time. Further, the inventive method reduces the leasing costs for leased line operators.

The name of a given functional entity, such as the base station controller or the Abis link, is often different in the context of different cellular telecommunication systems. For example, in the UMTS system the functional entity corresponding to a base station controller (BSC) is the radio network controller (RNC). Therefore, the particular terminology used to denote various functional entities in this application are only examples according to the GSM system, and do not limit the invention in any way. Although the examples in the previous description refer to the GSM system, the invention may be used in other cellular telecommunication systems, particularly in the UMTS system.

In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. While a preferred embodiment of the invention has been described in detail, it should be apparent that many modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention.

Claims

1. In a cellular telecommunication system, a method for optimization of the communication link between a network element of the cellular telecommunication system and at least two transceiver units in at least one base station, characterized in that in the method

- transmission resource units of the communication link are divided into at least two categories,

- at least one point to point type channel for transmission of data between the network element and one of the at least two transceiver units is allocated from a first category of said at least two categories, and

- at least one channel for transmission of data between the network element and at least two of the at least two transceiver units is allocated from a second category of said at least two categories.

2. A method according to claim 1, characterized in that at least one channel for transferring data from one of the at least two transceiver units to the network element allocated from said second category is deallocated.

3. A method according to claim 1, characterized in that at least one of said at least one point to point type channel is used for transferring transceiver unit control signalling between the network element and a transceiver unit.

4. A method according to claim 1, characterized in that at least one channel allocated from said second category is used for transferring data from the network element to at least two transceiver units.

5. A method according to claim 1, characterized in that the method is applied in a GSM system, and that the network element is a base station controller.

6. A method according to claim 1, characterized in that the method is applied in an UMTS system, and that the network element is a radio network controller.

7. A system in a cellular telecommunications network having a network element and at least two transceiver units in at least one base station and a communication link between the network element and the at least two transceiver units, characterized in that the system comprises

- means for allocating transmission resource units of the communication link for forming a communication channel, - means for deallocating transmission resource units of the communication link for removing a communication channel,

- in the network element, means for transmitting to at least one of the at least two transceiver units information describing which at least one transmission resource unit corresponds to a commumcation channel, and

- in at least one of the at least two transceiver units, means for receiving information directed to the transceiver unit from a communication channel formed of at least one transmission resource unit.

8. A system according to claim 7, characterized in that the system is arranged to - divide the transmission resource units of the communication link into at least two categories,

- allocate at least one point to point type channel between the network element and one of the at least two transceiver units from a first category of said at least two categories, and - allocate at least one channel between the network element and at least two of the at least two transceiver units from a second category of said at least two categories.

9. A system according to claim 7, characterized in that the network element is a base station controller.

10. A system according to claim 7, characterized in that the network element is a radio network controller.

11. Network element of a cellular telecommunication system, which network element is adapted to be connected to a communication link for transmission of information to at least two transceiver units of at least one base station, characterized in that the network element comprises - means for allocating transmission resource units of a communication link for forming a communication channel,

- means for deallocating transmission resource units of a communication link for removing a commumcation channel, and

- means for ttans-mitting information via a communication link describing which at least one transmission resource unit corresponds to a communication channel.

12. A network element according to claim 11, characterized in that the network element is arranged to

- divide the transmission resource units of the communication link into at least two categories, - allocate at least one point to point type channel between the network element and one of the at least two transceiver units from a first category of said at least two categories, and

- allocate at least one channel between the network element and at least two of the at least two transceiver units from a second category of said at least two categories.

13. A network element according to claim 11, characterized in that the network element is a base station controller.

14. A network element according to claim 11, characterized in that the network element is a radio network controller.

15. Transceiver unit of a base station adapted to be connected to a cellular network element via a commumcation link, characterized in that the transceiver unit comprises

- means for receiving information from the communication link describing which at least one transmission resource unit of the communication link corresponds to a commumcation channel,

- means for receiving information directed to the transceiver unit from a communication channel formed of at least one transmission resource unit of the communication link, and

- means for receiving information from the communication link describing which at least one transmission resource unit previously designated as corresponding to a communication channel shall not be used as a commumcation channel by the transceiver unit any more.