BROADBAND CELLULAR NETWORK DEVICE

Abstract: A broadband cellular network device comprises a cellular controller means (2) adapted to control the distribution of cellular traffic consisting of asynchronous transfer mode cells in trunking mobile communication networks based on ATM technology, and an asynchronous transfer mode switching means (3) controlled by said cellular controller means and adapted to multicast said cellular traffic to downlink base transceiver stations (4) using multicast properties of the asynchronous transfer mode switching means (3).

Description: BROADBAND CELLULAR NETWORK DEVICE FIELD OF THE INVENTION The present invention relates to cellular multicasting in a mobile communication system, and in particular concerns an asynchronous transfer mode cellular network device for performing cellular multicasting in downlink direction using multicast properties of an asynchronous transfer mode switching element. BACKGROUND OF THE INVENTION In recent years, the Global System for Mobile Communications (GSM) and other cellular networks have grown rapidly all over the world. An accordingly increasing number of subscribers has led to a corresponding increase of bandwidth in trunking networks of cellular systems such as base station subsystems (BSS) in the GSM. In addition, the integration of mobile stations (MS) such as mobile phones and data communication has given rise to new data services like e.g. the Short Message Service (SMS) or access to the Internet using a mobile station. It is more and more difficult and expensive to provide the bandwidth required for these new data services by conventional PCM based trunking networks. Accordingly, there is an increasing demand for replacing these networks with broadband communication systems . As a future technology for use in broadband communication systems, Asynchronous Transfer Mode (ATM) has recently been proposed. The basic idea of ATM is to transfer data in small data packets having a fixed size. These data packets are called cells. A flow of such cells represent a virtual channel connection (VCC) between respective end users. Since the switching of the cells is performed by hardware and not by software, as in conventional software based packet switching technologies, the ATM principle provides for a very fast transfer technology. Along with the aforementioned technological changes in mobile communication systems, demand increases for cellular multicasting, in particular with respect to downlink traffic, i.e. traffic directed from a mobile communication network to mobile stations of end users. Cellular multicasting means here, that one channel is directed to more than one destination, and includes also the broadcasting of a channel to the entirety of possible destinations. Fig. 3a and 3b schematically show part of a conventional PCM mobile communication system, respectively, in which the downlink cellular multicasting of channels is performed by a centrally located switching center SC. The switching center SC multicasts an incoming channel to a plurality of remote base transceiver stations BTS . The base transceiver stations BTS communicate with the mobile station of the end user. In Fig. la, the base transceiver stations BTS transmit the multicast channel to one specific mobile station, thereby implementing e.g. a soft handover procedure for mobile stations crossing cell borders. In Fig. lb, the base transceiver stations BTS transmit the multicast channel to a plurality of mobile stations located within the respective base transceiver station cell area. In such a conventional PCM mobile communication system, however, the switching center SC on the one part represents a complex and, thus, expensive device, and on the other part is located remote from the destination mobile station. Due to the accordingly remote switching operation, valuable bandwidth between the switching center SC and the base transceiver stations BTS is occupied for each multicast channel and, thus, no longer available for other cellular traffic. Accordingly, the overall bandwidth efficiency is deteriorated. It is therefore an object of the invention to provide a low cost broadband cellular network device which is capable of improving the bandwidth efficiency in mobile communication systems . This object is achieved by a broadband cellular network device, comprising a cellular controller means adapted to con- trol the distribution of cellular traffic consisting of asynchronous transfer mode cells, and an asynchronous transfer mode switching means controlled by said cellular controller means and adapted to multicast said cellular traffic to downlink mobile communication system components. With the above configuration, the multicast properties of an inexpensive asynchronous transfer mode switching element are advantageously used to perform cellular multicasting close to the destination. Thereby, valuable bandwidth before the broadband cellular network device is saved, since the incoming channel can be distributed to several destinations at the switching element closest to the mobile stations. Further embodiments of the present invention are subject of the attached dependent claims. Preferably, the asynchronous transfer mode switching means is coupled to said downlink base transceiver stations directly. Alternatively, the asynchronous transfer mode switching means may be a higher level switching element which delivers said cellular traffic to a respective lower level switching element coupled to said downlink base transceiver stations. In the latter case, the higher level switching element may comprise an asynchronous transfer mode specific controller means providing an interface to the cellular controller means, and the lower level switching element may comprise the hardware required for switching said cellular traffic. Favorably, said asynchronous transfer mode switching element is adapted to switch an incoming asynchronous transfer mode cell to a plurality of output ports thereof. Also favorably, said asynchronous transfer mode switching element is adapted to switch an incoming virtual channel to a plurality of output virtual channels. In addition, said asynchronous transfer mode switching element may be adapted to permanently reserve a virtual channel as a multicast virtual channel and to switch an incoming re- served virtual channel to a plurality of output virtual channels. Advantageously, said cellular controller means and said asynchronous transfer mode switching means are arranged in a base station controller device located close to a destination mo- bile station. Finally, the device is capable of handling asynchronous transfer mode cells carrying voice messages, data messages, signalling messages, or a mixed content thereof. Hence, the device according to the present invention may most advantageously be used for cellular multicasting in downlink direction employing the multicast properties of an asynchronous transfer mode switching element. BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in greater detail by way of a preferred embodiment with reference to the accompanying drawings, in which: Fig. 1 shows part of a mobile communication system using a broadband cellular network device according to a preferred embodiment of the present invention; Fig. 2 schematically illustrates the broadband cellular network device according to the preferred embodiment; and Fig. 3a and 3b show part of a known mobile communication system. BEST MODE FOR CARRYING OUT THE INVENTION Fig. 1 schematically shows part of a GSM system in which an ATM based cellular network element is used as a preferred embodiment of the broadband cellular network device according to the present invention. In Fig. 1, a mobile services switching center (MSC) 1 representing a first downlink transfer stage is connected to a predetermined port of an ATM switch 3. In addition, a base station controller (BSC) 2a is connected to a further predetermined port of the ATM switch 3. The output side of the ATM switch 3 is coupled to a plurality of base transceiver stations (BTS) 4 which communicate as described above with a particular one or a plurality of respective end user mobile stations (MS) 5. Within this structure, the ATM switch 3 serves as the switching element and is controlled by the base station controller 2a. Fig. 2 schematically illustrates the ATM based cellular net- work element as the said preferred embodiment of the broadband cellular network device. The ATM based cellular network element comprises a cellular controller 2 and an ATM switch 3 and provides for the switch- ing of cellular traffic channels consisting of asynchronous transfer mode cells carrying e.g. voice messages, data messages, signalling messages, or a mixed content thereof. The cellular controller 2 thereby performs known cellular related functions such as signalling and is appropriately connected with the ATM switch 3 in order to control same. The ATM switch 3 may be arranged such that it is coupled to a respective number of base transceiver stations 4 directly, i.e. comprise the actual hardware switch and be adapted to perform the switching operation under the control of the cel- lular controller 2. Alternatively, the ATM switch 3 may be arranged in the form of a higher level switch delivering cellular traffic to a corresponding of lower level switching element. In this case, the higher level switching element then comprises an asynchronous transfer mode specific controller means providing a suitable interface to the cellular controller 2, while the lower level switching element comprises the hardware required for switching said cellular traffic. As indicated in Fig. 2 by dotted lines, the ATM switch 3 has multicast properties, i.e. is capable to arbitrarily connect cellular traffic coming in at a respective input port to one or a plurality of its output ports. In practice, an asynchro- nous transfer mode cell arriving at an input port of the ATM switch 3 is copied to one or a plurality of output ports and to one or a plurality of virtual channels VC, respectively. Several possibilities do exist for utilizing the multicast properties of the ATM switch 3 for multicast connections. For example, permanent virtual channels VC may be reserved for multicast operation. In this case, an asynchronous transfer mode cell containing e.g. speech, data or signalling information and coming in from a virtual channel to be multicast is copied to a predetermined number of output ports and virtual channels, respectively. Alternatively, ATM signalling, e.g. according to the User- Network Interface 3.1 (UNI3.1) of ATM Forum, which is the standard adopted by the ATM Forum to define connections between users or end stations and a local switch and which pro- vides an interface point between ATM end users and a private ATM switch or between a private ATM switch and the public carrier ATM network, may be used to create a new point-to- multipoint channel upon detection of a need for multicast operation. Since the actual switching is performed by a relatively inexpensive ATM switch 3 arranged in the base station controller area located close to the base transceiver stations 4 rather than in the remote mobile services switching center 1, the multicast operation is achieved with low cost. In addition, valuable bandwidth is saved, because the information to be multicast can be distributed to a plurality of destinations at the switching element located closest to an end users mobile station. It should be understood that the above description and accompanying figures are only intended to illustrate the present invention. Thus, the device according to the invention may also be used in networks other than the GSM referred to in the example. The preferred embodiment of the invention may also vary within the scope of the attached claims.

Claims: Claims 1. Broadband cellular network device, comprising a cellular controller means (2) adapted to control the distribution of cellular traffic consisting of asynchronous transfer mode cells, and an asynchronous transfer mode switching means (3) controlled by said cellular controller means and adapted to multicast said cellular traffic to base transceiver stations (4). 2. A device according to claim 1, wherein the asynchronous transfer mode switching means (3) is coupled to said base transceiver stations (4) directly. 3. A device according to claim 1, wherein the asynchronous transfer mode switching means (3) is a higher level switching element which delivers said cellular traffic to a respective lower level switching element coupled to said base transceiver stations (4). 4. A device according to claim 3, wherein the higher level switching element comprises an asynchronous transfer mode specific controller means providing an interface to the cellular controller means (2), and wherein the lower level switching element comprises hardware required for switching said cellular traffic. 5. A device according to one of claims 1 to 4, wherein said asynchronous transfer mode switching element (3) is adapted to switch an incoming asynchronous transfer mode cell to a plurality of output ports thereof. 6. A device according to one of claims 1 to 4, wherein said asynchronous transfer mode switching element (3) is adapted to switch an incoming virtual channel to a plurality of output virtual channels. 7. A device according to claim 6, wherein said asynchro- nous transfer mode switching element (3) is adapted to permanently reserve a virtual channel as a multicast virtual channel and to switch an incoming reserved virtual channel to a plurality of output virtual channels. 8. A device according to claim 1, wherein said cellular controller means (2) and said asynchronous transfer mode switching means (3) are arranged in a base station controller device (6) located close to a destination mobile station (5). 9. A device according to claim 1, wherein said asynchronous transfer mode cells are adapted to carry voice messages, data messages, signalling messages, or a mixed content thereof. 10. Use of a device according to one of the preceding claims for cellular multicasting in downlink direction employing the multicast properties of an asynchronous transfer mode switching element (3).

Inventors: RUUTU JUSSI, RUUTU, JUSSI
Applicants: NOKIA TELECOMMUNICATIONS OY, RUUTU JUSSI, RUUTU, JUSSI
Application year: 1997
Main classification: H04Q7
IPC codes: H04L12, H04Q11, H04W4, H04W88