WO1998028934A1

WO1998028934A1 - Wireless system in fixed network

Info

Publication number: WO1998028934A1
Application number: PCT/FI1997/000760
Authority: WO
Inventors: Juho Laatu; Jussi Rajala; Pekka Lahtinen
Original assignee: Nokia Telecommunications Oy
Priority date: 1996-12-05
Filing date: 1997-12-04
Publication date: 1998-07-02
Also published as: FI104607B; FI964888A; AU5223198A; FI964888A0

Abstract

The invention relates to a data tansmission system implemented by a fixed network, the data transmission system comprising subscriber stations (1A), base transceiver stations (BTS) for connecting subscriber stations (1A) to the network over the radio path, a radio system interworking unit (RSIWU) for controlling the base transceiver stations (BTS), and a fixed network (ISDN) with local exchanges (LE) for call control. In order to connect a fixed and a wireless network the radio system interworking unit (RSIWU) is hierarchically located above the local exchange (LE) and the base transceiver station (BTS) below the local exchange (LE). The invention further relates to a data transmission network to which the system of the invention can be applied.

Description

WIRELESS SYSTEM IN FIXED NETWORK

The invention relates to wireless telecommunication systems and particularly to wireless telecommunication systems implemented by a fixed network.

The invention is, in particular, associated with implementing a cellular radio system enabling wireless data transmission over an already existing fixed network but it can also be utilized for implementing an entirely new network. The fixed network can, for example, be an Integrated Service Digital Network ISDN or a Public Switched Telephone Network PSTN. The wireless data transmission can utilize the cellular radio systems already in use, such as the GSM system (Global System for Mobile Communications) or ones being developed, such as the Universal Mobile Telecommunications System UMTS and Personal Communication System PCS. The wireless data transmission can also utilize other wireless digital systems, which are not actual cellular radio systems, but offer the freedom of movement within an outlined area as, for example, the Digital European Cordless Telephone DECT.

In the cellular radio systems which are implemented over a fixed network, a Local Exchange LE of the fixed network is used instead of a Mobile Switching Centre MSC, when according to the traditional solution a base station subsystem stays under the local exchange in the network hierarchy. Thus, beginning from the lowest level, the network hierarchy is: a Base Transceiver Station BTS, a Base Station Controller BSC, a Local Exchange LE, higher exchanges of a fixed network. The local exchanges are often small and do not comprise features supporting a mobile communication network. Then the highest cellular radio system component of the network level is a base station controller, and particularly regarding mobility management, control and signalling the essential network elements, the mobile switching centre MSC and a Visitor Location Register VLR, are missing. This presents problems, for exam- pie, with the management of compatible functions, or InterWorking Functions IWF, of different networks and the management of handovers. Furthermore, the traditional network hierarchy presented above needs connections crossing the fixed network connections. Another problem with the traditional solution is the underutilization of the capacity of the base station controllers since the lo- cal exchanges are small. In the future the local exchange LE may be assumed to comprise a small set of general features supporting mobile communication connections. Then the fact that the network consists of local exchanges LE of different levels which should, however, be able to guarantee a similar service for the mobile stations will present a problem.

One way to implement a cellular radio network over a fixed network is described in the publication "Switching and Signalling Generic Requirements for Network Access Services to Personal Communication Services (PCS) Providers", GR-2801-CORE, Issue 1 , December 1993, Bellcore, Bell Communications Research, particularly chapter 2, pages 1-26. In this solution a radio interface is connected to the local exchange of a fixed network, to which an Ad- vanced Intelligent Network AIN with Service Control Points SCP is connected. The problem with the solution is that an intelligent network is not connected to the main part of the fixed exchanges of the existing network, therefore the mobile services vary from one exchange to another. Further problems are presented by the fact that a network element incompatible with a wireless access network standard is, in particular, responsible for the mobility management. The problem with the solution is that it also needs new interfaces that are currently being standardized.

The Finnish patent application 950 776 shows a solution in which in a group of two or more base station systems there is one main base station controller controlling the other base stations of the group, the main base station controller performing radio path-specific functions associated with radio path management. The solution presupposes that the local exchange LE is either connected to the service control point SCP of the advanced intelligent network AIN or that the local exchange itself comprises intelligent functions. New signalling connections are also needed in the solution. The problems with this solution, too, are the underutilization of the capacity of the normal base station controllers under small exchanges, the connections crossing the fixed network and the fact that old local exchanges, which do not have an intelligent network connection, cannot be used in constructing the network. Another problem with the solution is that new signalling connections are needed in the solution, whereby more signalling is also needed. The problem with this solution, too, is that it needs a new interface which is still under standardization.

An object of the invention is to connect fixed and wireless telecommunication networks to one access network enabling the users' freedom of movement, the connection network offering all the services of a cellular network utilizing the fixed network to the best possible effect, making the service level independent of the local exchange of the fixed network.

This objective is achieved with the wireless data transmission system of the invention implemented by a fixed network, the wireless data transmission system comprising subscriber stations, base transceiver stations to connect subscriber stations to the network over the radio path, a radio system interworking unit to control the base transceiver stations and a fixed network with local exchanges for call control, characterized in that the radio system interworking unit is hierarchically located above the local exchange and the base transceiver station below the local exchange. The invention further relates to a data transmission network to which the inventive system can be applied. The wireless data transmission network of the invention, such as a cellular radio network or a base station system, consisting of subscriber stations, base transceiver stations, radio system interworking units controlling them, characterized in that the signalling and traffic channels between the base transceiver stations and radio system interworking units are connected via local exchanges of a fixed network in such a manner that in the hierarchy the radio system interworking unit is above the local exchange and the base transceiver station below the local exchange. The invention is based on the idea to utilize the fixed network with existing elements as efficiently as possible in constructing a wireless data transmission network so that existing interfaces are used, the capacity of the standard elements of the wireless data transmission network can be used as effectively as possible and that a standard quality service can be provided re- gardless of the features of the fixed network. The most significant advantages of the invention are thus the independence of the availability of services and quality from the local exchange features of the fixed network on account of the radio system interworking unit, the effective and easy use of the fixed network connections without cross-connections enabled by a new hierarchy, and the use of standardized connection interfaces. Furthermore, in a preferred embodiment of the invention, which does not comprise base station controllers, the advantages are the smaller number of used network elements and as a result a lesser signalling need and signalling costs compared with the existing solutions and a better utilization of the capacity of the network elements in use. Moreover, in a preferred embodiment of the invention the routing of calls can be optimized by routing the calls between the local exchanges controlled by a radio system interworking unit as local calls and by reducing the need of signalling in the handover between the base transceiver stations controlled by the radio system interworking unit.

On account of the invention also different interworking functions IWF and other corresponding special functions, such as a Transcoder Rate Adapter Unit TRAU, can be located in the radio system interworking unit.

The preferred embodiments of the inventive system and the data transmission network are disclosed in the attached dependent claims 2-12 and 14-19. In the following the invention will be described in greater detail using a preferred embodiment of the invention with reference to the accompanying drawings, in which

Figure 1 is a block diagram illustrating a wireless data transmission network based on a fixed network according to the invention in the first pre- ferred embodiment,

Figure 2 illustrates the connection of interworking functions to a data connection in the network shown in Figure 1 ,

Figure 3 is a block diagram illustrating the optimization of a call routing in the first preferred embodiment, Figures 4 and 5 are block diagrams illustrating the division of a mobile switching centre MSC and a visitor location register VLR into functional units and their allocation to different network elements.

The basic principles of the invention may be applied to connecting any wireless access network to the local exchange of a fixed network. In the first preferred embodiment of the invention the access network is a radio system based on the GSM system, such as PCS1900, and the fixed network is an ISDN network. As to the details of the GSM system, reference is made to ETSI GSM recommendations and to the book "The GSM System for Mobile Communications", M. Mouly, M.B. Pautet, Palaiseau, France, 1992, ISBN:2- 9507190-0-7.

The block diagram in Figure 1 illustrates the network elements of the first preferred embodiment of the invention. Unlike a conventional GSM- based network the base transceiver stations BTS are not connected to the base station controller and this way to the mobile switching centre, but the base transceiver station BTS is connected directly to the local exchange LE of a fixed network, the local exchange being normally connected to the rest of the fixed network ISDN. Unlike the conventional, the local exchange LE is also connected to the radio system interworking unit RSIWU which is hierarchically located above the local exchange LE. Two local exchanges LE are connected to one radio system interworking unit RSIWU in order to clearly illustrate the network structure. One or more local exchanges LE can perfectly well be connected to one radio system interworking unit RSIWU. Similarly one or more base transceiver stations BTS can be connected to the local exchange LE. The radio system interworking unit RSIWU controls the base transceiver stations BTS which are connected to the local exchanges LE connected to the radio system interworking unit RSIWU and which are therefore below the local exchanges LE in the hierarchy. The base transceiver stations BTS communicate with personal stations 1A, or subscriber stations, through a conventional radio interface of the PCS1900 system. The local exchange LE provides call control and routing to the effect that a call arriving from the fixed network ISDN to the subscriber station 1A or from the subscriber station 1A to the fixed network ISDN proceeds from the local exchange LE via the radio system interworking unit RSIWU back to the same local exchange LE as shown by solid line 2 in the Figure. The call can also proceed to another local exchange controlled by the same radio system interworking unit. In handovers the radio system interworking unit RSIWU functions as an anchor mobile switching centre of the GSM system, whereby the connection after handover between the local exchanges within the radio system interworking unit can be established as a relatively short one. The connection after handover is shown in the Figure by dashed line 3. Figure 1 clearly shows that connections crossing the fixed network connections are not needed, but the necessary new connections complement the fixed network utilizing the fixed network connections as efficiently as possible. Therefore the base transceiver stations BTS and the radio system interworking unit RSIWU use only the connections of the fixed network ISDN with local exchanges LE for traffic and signalling. Thereby they do not form a physically or hierarchically logically separate transmission network from the fixed network ISDN.

The radio system interworking unit RSIWU preferably also comprises equipment performing the interworking functions IWF for data calls. When a data call is established through the radio system interworking unit RSIWU it connects a correct kind of interworking function IWF to the data con- nection as illustrated in Figure 2. Correspondingly in a speech call the radio system interworking unit RSIWU can connect for the connection a transcoder rate adapter unit TRAU which performs, for example, a conversion between pulse code modulated speech PCM and lower rate speech coding used on the radio path. Examples of interworking and transcoding functions are described in the specifications of the GSM system.

The block diagram in Figure 3 illustrates the routing optimization according to the first preferred embodiment. Here subscriber A (calling) of the wireless network has called with his/her subscriber station 1A to the fixed sub- scriber station 1 B of subscriber B (called). If a local exchange LE-A, to which the subscriber station 1A of subscriber A is connected by means of the base transceiver station BTS, is located in the domain of the same radio system interworking unit RSIWU as a local exchange LE-B, to which the subscriber station of subscriber B is connected, then the call can be routed as a local call so that the call control of both subscribers is on the local exchange LE-A of subscriber A. The call then moves via the radio system interworking unit RSIWU by means of the local exchange LE-B of subscriber B to subscriber station 1 B of subscriber B. The established connection is described in the Figure by unbroken line 2. Routing as a local call is also possible if the subscriber station of subscriber A is a fixed one and the subscriber station of subscriber B is a subscriber station of a wireless data transmission or if both subscriber stations are wireless. If the subscriber station of subscriber B is wireless the local exchange LE-B of subscriber B's subscriber station moves only the A-bis interface between the radio system interworking unit RSIWU and the base trans- ceiver station BTS.

Figures 4 and 5 show an example of how the functions of a mobile switching network can be divided into functional units which can be allocated to the ISDN-based physical network elements of the PCS network. The names of the functional units end with the letter F (function) in order not to confuse them with the physical network elements, in which functional units can be located. Each functional unit will be briefly described below.

BSCF (Base Station Controller Function) corresponds to the normal base station controller BSC functionality in the GSM network.

BSCF+ (Base Station Controller Function Additions) performs many of the functions of the mobile switching centre MSC in the GSM network (particularly the switching features associated with handover). It divides the A- interface between the GSM-type network subsystem and the base station subsystem so that the call control CC is assigned to LEF and other signalling to RSCF. BSCF+ acts as an anchor in handovers and performs the switching operations attached to it. In addition, it converts GSM call control into ISDN call control and includes other possible interworking functions IWF and the speech transcoding TRAU in the GSM network. BSCF+ can also perform checkings of the subscriber's service selection.

IWF (Interworking Function) comprises the interworking functions which may be needed in data calls to arrange the transmission protocol be- tween the subscriber stations and the radio system interworking unit RSIWU to the transmission protocol used between the radio system interworking unit and another network, such as the PSTN or ISDN, thus enabling the connections also to circuit switched and packet switched data networks. IWF also attends to other non-speech services, such as fax services. LEF (Local Exchange Function) comprises the standard functions of an ISDN local exchange LE (National ISDN 3 as default) providing, for example, call control. LEF may support non-call associated signalling NCA and/or three-party call based handover switching. No modifications are suggested to the standard LEF in the invention since an ISDN-based PCS1900 system should be able to operate with all standard-type ISDN local exchanges of the fixed network.

RSCF (Radio System Control Function) performs several functions of the mobile switching centre MSC. It controls radio resources and handover between the local exchanges LE or base station controllers BSC. In addition, RSCF is a border unit between the A-interface and MAP protocols of GSM.

HOF (Handover decision Function) is separated from RSCF in order to enable the control of the handover process from an even higher level. Only high-level control, such as overload control, is performed by HOF. The actual handover is carried out by BSCF+ and controlled by RSCF. VLRF (Visitor Location Register Function) is responsible for the functions of the visitor location register VLR in the GSM network. It is divided into two parts in order to enable, for example, the allocation of functions partly to the service control point SCP of the intelligent network and partly to the access network. The division further enables the expansions of the visitor loca- tion register VLR and home location register HLR hierarchy. The division could comply with the Bellcore division into an Access Manager AM (VLR1F) and a Bellcore visitor location register (VLR2F).

SCF (Service Control Function) is a standard SCF of the fixed network providing the standard intelligent network services. Furthermore, it has an ability to carry out location inquiries to HLRF (corresponding to the gate- way-MSC situation) and to VLRF (local location inquiries) and to co-operate with VLRF when responding to intelligent network inquiries. The invention does not require the existence of SCF since the ISDN-based PCS1900 system should be able to operate with all standard-type ISDN local exchanges of the fixed network. HLRF (Home Location Register Function) corresponds to the functionality of a normal home register in the GSM network.

In addition, an Equipment Identification Register Functions EIRF associated with the identification of the apparatus and possible Short Message Service Gateway/I nterworking Functions SMS-GIWF are connected with the functionality of the network. However, it is not here necessary to describe how the EIRF and SMS-GIWF operate since their supply depends on the operator.

Of the above listed functions BSCF, BSCF+, IWF and LEF handle the network service to the traffic channels, the other units handle signalling only. In this context traffic means transmitting speech, data and information presented in various forms, for example, as pictures.

Figures 4 and 5 illustrate how freely the functional units can be allocated in the solutions of the invention. The only restrictions being that the LEF unit always has to be located in the local exchange LE and the BSCF+ unit in the radio system interworking unit RSIWU. These functional units route con- nections.

Figure 4 shows according to the basic principle of the invention how the functional units are distributed among different network elements. The local exchange LE is by way of example assumed to be a "stupid" exchange, in which only the call control LEF is located. The local exchange LE can be con- nected to the service control point SCP of the advanced intelligent network AIN as shown by broken line 4, but the connection is unnecessary in the case shown in the Figure. Other functional units, or BSCF, BSCF+, IWF, RSCF, HOF, VLR1F and VLR2F, are located in the radio system interworking unit RSIWU. The radio system interworking unit is directly in connection with the home location register HLR, where the HLRF unit is located. The local exchange LE transparently transmits the interface between the radio system in- terworking unit RSIWU and the base transceiver station BTS, the interface being an A-bis interface in the GSM system. The interfaces and connections between the local exchange LE and the radio system interworking unit RSIWU and the local exchange LE and the base transceiver station BTS are normal interfaces and connections specified for a fixed network.

As the functions and features obtained from the network increase, they can be moved from the radio system interworking unit RSIWU elsewhere on the network. Figure 5 shows a preferred embodiment in which practically all functions handling signalling only are obtained from the fixed network. The local exchange LE is connected to the service control point

SCP of the advanced intelligent network AIN through an intelligent network connection. The SCF and VLR2F units are located in the service control point SCP. Alternatively only the SCF unit could be located therein and the VLR2F unit would be located in connection with the VLR1 F unit. If the local exchange comprises enough of intelligent functions, the intelligent network is not necessarily needed, but the units located in the service control point SCP can be entirely located in the local exchange LE.

The embodiment presented in Figure 5 comprises a separate Access Manager AM in which the VLR1F, RSCF and HOF units are located. The access manager AM can be implemented as an intelligent network service or as a separate element. If there is no access manager, then these units are located in the radio system interworking unit RSIWU. Alternatively some of said units can be located in the radio system interworking unit RSIWU and others in the service control point SCP of the intelligent network. In the embodiment presented in Figure 5 a base station controller

BTS, in which a BSCF unit is located, is connected between the base transceiver station BTS and the local exchange LE. One or more base station controllers BSC can be connected to one local exchange LE, and correspondingly one or more base transceiver stations BTS can be connected to the base sta- tion controllers. The interface and connection between the base station controller and the local exchange are normal interfaces and connections specified for a fixed network. Then the local exchange LE transparently transmits the A- interface between the radio system interworking unit RSIWU and the base station controller. The interface between the base station controller and the base transceiver station is a normal A-bis interface of a wireless network. If there were no base station controller BSC, the BSCF unit would be located in the radio system interworking unit RSIWU and the local exchange LE would transparently transmit the A-bis interface.

In the embodiment according to Figure 5 only the BSCF+ and IWF units are located in the radio system interworking unit and the LEF unit is lo- cated in the local exchange LE. Connections with the home location register

HLR, in which the HLRF unit is located, are maintained through the service control point SCP and the VLR2F unit.

It is obvious that the above description and the related figures are only intended to illustrate the present invention. A variety of modifications and variations of the invention will be apparent to those skilled in the art without deviating from the scope and spirit of the invention disclosed in the appended claims.

Claims

1. A wireless data transmission system implemented by a fixed network, the wireless data transmission system comprising subscriber stations (1A), base transceiver stations (BTS) to connect the subscriber stations (1A) to the network over the radio path, a radio system interworking unit (RSIWU) to control the base transceiver stations (BTS) and a fixed network (ISDN) with local exchanges for call control, characterized in that the radio system interworking unit (RSIWU) is hierarchically located above the local exchange (LE) and the base transceiver station (BTS) below the local exchange (LE).

2. A system as claimed in claim 1, characterized in that the call control is located in the local exchange (LE) which is arranged to transmit telecommunications arriving from the subscriber terminal (1A) through the base transceiver station (BTS) via the radio system inter- working unit (RSIWU) to the fixed network (ISDN) and telecommunications arriving from the fixed network (ISDN) through the radio system interworking unit (RSIWU) via the base transceiver station (BTS) to the subscriber terminal (1A).

3. A system as claimed in claims 1 or 2, characterized in that the division of an interface between a network subsystem of the wireless data transmission network and a base station subsystem into call control and other signalling, handover anchor functions and functions to transfer the call control from a fixed network (ISDN) control to a wireless network control and vice versa are located in the radio system interworking unit (RSIWU).

4. A system as claimed in claim 1, 2 or 3, characterized in that interworking functions (IWF) required by wireless speech or data transmission, speech transcoding functions and/or other special functions are located in the radio system interworking unit (RSIWU).

5. A system as claimed in any one of the previous claims, char- acterized in that the interface (A-bis) between the base transceiver stations (BTS) and the radio system interworking unit (RSIWU) is transparently connected through the local exchange (LE) using the connections of the fixed network.

6. A system as claimed in any one of the previous claims, char- acterized in that the radio system interworking unit (RSIWU) comprises means for dynamically connecting or reconnecting the base transceiver sta- tions (BTS) from the control of the radio system interworking unit (RSIWU).

7. A system as claimed in any one of the previous claims, characterized in that the system comprises an advanced intelligent network (AIN) having a connection (SCP) to the local exchange (LE), and that some functions (SCF, VLR2F) and features of the wireless data transmission network are located in the intelligent network.

8. A system as claimed in any one of the previous claims, characterized in that the system comprises an access manager (AM) having a connection with the radio system interworking unit (RSIWU) and that some functions (VLR1F, RSCF, HOF) and features of the wireless data transmission network are located in the access manager (AM).

9. A system as claimed in any one of the previous claims further comprising base station controllers (BSC) to control base transceiver stations (BTS) connected to them, characterized in that the base station con- trollers (BSC) are hierarchically connected below the local exchange (LE) to be controlled by the radio system interworking unit (RSIWU) and that the interface (A) between the radio system interworking unit (RSIWU) and the base station controller (BTS) is transparently connected through the local exchange (LE) using the connections of the fixed network.

10. A system as claimed in claim 9, characterized in that some functions (BSCF) of the wireless data transmission network are located in the base station controller (BSC).

11. A system as claimed in claim 1, characterized in that one or more local exchanges (LE) are connected to the radio sys- tern interworking unit (RSIWU), the call control is arranged to the local exchange (LE) whereby the subscriber station call is arranged to be connected from the local exchange (LE) through the radio system interworking unit (RSIWU) to the same or to another local exchange which is connected to the same radio system interwork- ing unit (RSIWU).

12. A system as claimed in claim 1, characterized in that the system is arranged to route a call between the subscriber stations (1A, 1B) of subscriber A and subscriber B through the radio system interworking unit (RSIWU) from the local exchange of the subscriber station of subscriber A (LE-A) to the local exchange of the subscriber station of subscriber B (LE-B) so that the call control is maintained on the local exchange of the subscriber station of subscriber A (LE-A), if both the local exchange of the subscriber station of subscriber A (LE-A) and the local exchange of the subscriber station of subscriber B (LE-B) are connected to the same radio system interworking unit (RSIWU).

13. A wireless data transmission network, such as a cellular radio network or a base station system consisting of subscriber stations (1A), base transceiver stations (BTS), radio system interworking units (RSIWU) controlling them, characterized in that the signalling and traffic channels between the base transceiver stations (BTS) and the radio system interworking unit (RSIWU) are connected via local exchanges (LE) of a fixed network in such a manner that in the hierarchy the radio system interworking unit (RSIWU) is above the local exchange (LE) and the base transceiver station (BTS) is below the local exchange (LE).

14. A data transmission network as claimed in claim 13, char- acterized in that the base transceiver stations (BTS) forming a wireless connection for the subscriber stations are connected to the local exchanges (LE) using specified connections and interfaces in the fixed network (ISDN).

15. A data transmission network as claimed in claim 13 or 14, characterized in that the local exchanges (LE) transparently transmit an interface (A-bis) between the base transceiver station (BTS) and the radio system interworking unit (RSIWU) and provide call control.

16. A data transmission network as claimed in claim 13, 14 or 15, characterized in that the radio system interworking unit (RSIWU) comprises at least one of the following functions: the division of the interface between a network subsystem of the wireless data transmission network and a base station subsystem into call control and other signalling; the handover anchor function; the transfer of the call control from a fixed network (ISDN) control to a wireless network control and vice versa; and the functions (BSCF, RSCF, HOF, VLR1F, VLR2F) and features of the wireless data transmission network which are missing from the local exchange (LE) and base transceiver station (BTS).

17. A data transmission network as claimed in claim 13, char- acterized in that the base transceiver stations (BTS) and radio system interworking units (RSIWU) are arranged to use for traffic and signalling only the connections of the fixed network (ISDN) with local exchanges (LE).

18. A data transmission network as claimed in any one of the previous claims 13-17, characterized in that the radio system interworking unit (RSIWU) is arranged to directly connect the call control of the subscriber stations (1A, 1B) of subscribers A and B to the local exchange of the subscriber station of subscriber A (LE-A), whereby the local exchange of the subscriber station of subscriber B (LE-B) only moves the interface (A-bis) of the radio system interworking unit (RSIWU) and base transceiver station (BTS), when the local exchanges of the subscriber stations of both subscriber A and B (LE-A, LE-B) are connected to the same radio system interworking unit (RSIWU).

19. A data transmission network as claimed in claim 13, characterized in that the interworking functions required by wireless speech or data transmission, the speech transcoding functions and/or other special functions are located in the radio system interworking unit (RSIWU).