EP1183886A1

EP1183886A1 - Radio communications infrastructure using a packet communication protocol

Info

Publication number: EP1183886A1
Application number: EP01915552A
Authority: EP
Inventors: Mark Wentworth Rayne
Original assignee: Simoco International Ltd
Current assignee: Simoco International Ltd
Priority date: 2000-03-28
Filing date: 2001-03-28
Publication date: 2002-03-06
Also published as: WO2001074099A1; GB2360913A; GB0007518D0; GB0107765D0; AU4263701A

Abstract

A mobile radio system includes a number of radio base stations (2, 3, 4, 5, 6, 16, 26 and 28), each connected to a radio antenna (7, 34, 8, 17, 27 and 29). It also includes plural mobile stations, such as mobile stations (1 and 18), which are in radio communication with base stations (2 and 16), respectively. The base stations of the fixed radio network are interconnected by ethernet buses (12, 14). Data, etc., is communicated around the fixed network using any suitable packet data routing method. Each base station has an associated base site interfacing controller (9, 10, 11, 15, 22, 24), which carries out the usual base station control functions, but also hosts packet data network agents which represent the mobile stations on the packet data network and act to interface and convert between the radio system communications protocol used between the mobile stations and base stations and the packet data network communications protocol used in the fixed packet data network.

Description

RADIO COMMUNICATIONS INFRASTRUCTURE USING A PACKET COMMUNICATION PROTOCOL

5 The present invention relates to a mobile radio communications system and to a method of operating a mobile radio communications system.

As is known in the art, mobile radio telecommunications systems such as the GSM (Global 0 System for Mobile communications) public cellular telephone system comprise a fixed radio network comprising plural base stations for communicating with mobile stations of the system. The base stations are linked together by a fixed radio network infrastructure 5^' which includes one or more switches which route the audio speech signals through the fixed network from one radio base station to another. The switches are usually operated and must be capable of operating in a so-called circuit-mode switching arrangement, in which the 0 switches are arranged to provide in effect a fixed circuit between the network terminals while a call is proceeding.

The switches used in such mobile radio communications systems, and the associated fixed network 5 controllers, are relatively expensive specialist equipment usually designed or adapted specifically for the particular type of radio system in question. The number and type of switches used is often also the limiting factor in determining the traffic capacity of 0 the radio system, since the switches determine how many audio channels can be handled simultaneously by the fixed radio network.

According to a first aspect of the present invention, there is provided a radio network 5 infrastructure for a mobile radio communications system, the radio network infrastructure comprising: plural interconnected base stations, the base stations being adapted to communicate with mobile stations of the radio system via a mobile radio system communications protocol; wherein: the radio network infrastructure comprises a packet data communications network interconnecting the base stations which uses a packet data network communications protocol; and the network infrastructure further comprises means for converting communications in the mobile radio system communications protocol received at a base station from a mobile station to the packet data network communications protocol for onward transmission through the network infrastructure, and means for converting communications in the packet data network communications protocol from the network for a mobile station to the mobile radio system communications protocol for onward transmission by a base station to the mobile station.

According to a second aspect of the present invention, there is provided a method of operating a mobile radio communications system, which system comprises plural mobile stations and plural base stations, which base stations are interconnected by a fixed network, the method comprising: using a mobile radio system communications protocol for radio communications between the mobile stations and base stations; using a packet data network communications protocol for communications between the base stations via the fixed network; converting communications in the mobile radio system communications protocol received at a base station from a mobile station to the packet data network communications protocol for onward transmission through the fixed network; and converting communications in the packet data network communications protocol from the fixed network for a mobile station to the mobile radio system communications protocol for onward transmission by a base station to the mobile station.

In the present invention, the fixed network of the mobile radio system comprises a packet data communications network, rather than the more usual circuit-mode switch based network.

The Applicants have recognised that packet data communications protocols such as the Internet protocol (IP) and associated protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol), which provide a means of routing and controlling the flow of packet data across networks, can be used to control communications in the fixed network part of a mobile radio communications system. Because such packet data protocols are widely used, the equipment for using them is relatively inexpensive, powerful and readily available. Thus by using such an arrangement for the fixed network part of the radio system, the need to use a centralised circuit-mode switch can be avoided and a less expensive, more flexible and fault tolerant method of interconnecting and handling communications in the fixed network infrastructure of the radio system can be used.

The present invention thus effectively combines a packet data fixed infrastructure with a mobile radio system air-interface. It thus combines the benefits of effective radio communications with the benefit of being able to interconnect and control radio base stations using inexpensive, readily available packet data network equipment and protocols.

The Applicants believe that packet data protocols, such as TCP/IP, although known to be well suited to fixed communications network use, would previously not have been thought suitable for use in mobile radio communications systems, because, for example, of the limitations in the performance of TCP in the presence of flow interruptions (which, as is known in the art, occur

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appropriate manner. Thus messages and other information received in one communications protocol should be converted appropriately to the other protocol, i.e. communications in the radio system's communications protocol used over the air (radio) -interface between the mobile stations and the base stations should be converted appropriately (e.g. placed in properly formatted data packets) to the packet data communications protocol used for the fixed infrastructure, and vice-versa. It should be noted in this regard that the communications being routed through the packet data network and converted between the packet data communications protocol and the air-interface communications protocol can comprise all forms of communication such as speech (e.g. speech frames), short data messages, etc., and not just packet data (e.g. IP packets) that is already in a packet data format but may need some modification to, e.g., be transmitted over the air interface to a packet data based device in a mobile station (e.g. an IP-based protocol within the mobile station) .

The communications protocol conversion can take place where desired in the fixed network, but preferably takes place at or near a node of the packet data network to which the relevant base station is connected.

In a particularly preferred embodiment the network infrastructure further comprises a controller associated with each base station for interfacing between the mobile radio system protocol used for communications between the base station and the mobile stations, and the packet data network communications protocol used for communications between base stations via the packet data network, where the conversion takes place. Such controllers are preferably located at the node of the network to which their associated base station (s) connect (i.e. such that each base station is connected to the packet data network via an interfacing controller) . Each interfacing controller should convert information and requests destined for and received from its associated base station or base stations appropriately for onward transmission. The number of such interfacing controllers used in the fixed network can be selected as desired. For example, a single network interfacing controller may be associated with and accessible by plural base stations (e.g. all those base stations at a single base site and/or connecting to the same network node) , or each base station may have its own individual single controller.

It is believed that the use of such interfacing controllers may be new and advantageous in its own right. Thus according to a third aspect of the present invention, there is provided a radio network infrastructure for a mobile radio communications system, comprising: plural interconnected base stations, the base stations being adapted to communicate with mobile stations of the radio system via a mobile radio system communications protocol; wherein: the radio network infrastructure comprises a packet data communications network interconnecting the base stations which uses a packet data network communications protocol; and the network infrastructure further comprises a controller associated with each base station for interfacing between the mobile radio system protocol used for communications between the base station and the mobile stations, and the packet data network communications protocol used for communications between base stations via the packet data network.

It is, of course, necessary, to ensure that any messages, etc. received at a base station for a given mobile station are routed through the packet data network to that mobile station correctly. This could be achieved, for example, by determining the current serving base station of the mobile station and then routing the data packets through the packet data networks to that base station (or, e.g., to its associated interfacing controller) .

In a particularly preferred embodiment, each mobile station is allocated a corresponding packet data network address to which communications, data, etc., intended for it can be routed. In this arrangement, each mobile station's packet data network address is preferably associated with the mobile station's allocated radio system protocol address (e.g. number), where appropriate, so that the system can convert between the packet data network and radio system addresses of the mobile stations (which will usually differ) to allow calls, etc., to be properly routed. In such an arrangement, a request from one mobile station to place a speech call to another mobile station will be converted into a request from a device with a given packet data network address to send some packets of data to another packet data network address. This could be achieved by, for example, inserting the speech frames into data packets each individually addressed to the intended destination and placing them on the packet data network.

The packet data network address for a mobile station can be selected as desired. It is preferably an address at or associated with the network node (e.g. interfacing controller) to which the base station serving the mobile station is connected. Where the packet data network comprises an Internet Protocol network, it could, for example, comprise a full Internet Protocol address, or a port number at a given Internet Protocol address (e.g. at the Internet Protocol address of the interfacing controller associated with the mobile station's current serving base station) . The use of port numbers for the mobile stations ' addresses permits larger numbers of mobile stations to be accommodated at each separate packet data network (e.g. Internet Protocol) address (since for example, in TCP or UDP a 16-bit port number is defined at each network (IP) address) , and thus allows each network address to carry very many separate mobile station connections.

The mobile stations' packet data network addresses, together with their corresponding radio system addresses, where necessary, should be stored in the packet data network infrastructure and kept updated in an appropriate manner to allow the relevant addresses to be determined (e.g. by the interfacing controllers) when a call to or from a particular mobile station arrives. Thus, for example, one or more databases storing the addresses and accessible by the interfacing controllers, etc . , could be provided throughout the packet data network, which databases are kept updated with each mobile station's current packet data network address. Each network node, interfacing controller and/or base station could also have a local data cache in which it stores the addresses of mobile stations that have recently communicated through it or its associated base station (s) .

A mobile station's packet data network address is preferably changed appropriately as the mobile station moves between base stations of the radio system in use (e.g. to an address at or associated with the new network node (e.g. interfacing controller) to which the mobile station's new serving base station is connected). This allows data packets always to be routed efficiently to the current network node the mobile station is at.

In a particularly preferred embodiment, each mobile station is represented by an agent on the packet data network to which all communications in the packet data network intended for the mobile station can be sent and which agent carries out the interfacing and conversion between the communications protocol used over the air- interface and the packet data network communications protocol used for the packet data network fixed infrastructure. The agent can thus be used to, effectively, provide and manage the link between the packet data network and its mobile station. This packet data network "link" agent is, effectively, a projection of the mobile station on to the packet data network and appears, to the packet data network, to be the mobile station. Thus messages and requests pertaining to a mobile station, such as speech calls, will be routed through the packet data network to a mobile station's packet data network agent. Each mobile station preferably has its own individual packet data network "link" agent. The use of packet data network ' agents ' is known (see, for example, Minar, M. , Kramar, K.H. , Maes, P. Cooperating Mobile agents for Dynamic Network Routing, MIT Media Lab, E15-302 20 Ames St., Cambridge MA 02139, USA.), and the mobile station agents can be arranged as would normally be the case for packet data network agents on the packet data network in question. Thus they will typically encapsulate a thread of execution along with a bundle of code and data, run independently of all other agents, be a self-contained program, be able to roam around the packet data network (i.e. be "mobile") , preserve all of their state when they move from one network node to another, and be able to identify and use resources specific to any network node on which they find themself . The agents are therefore effectively movable software capable of running at any suitable location in the packet data network that provide functions to facilitate communications between the packet data network and the mobile station which the agent represents . For example, in an Internet Protocol based packet data network, the packet data network "link" agent representing a mobile station on the packet data network could be treated as a mobile host as used in the Mobile IP protocol (see, for example, Perkins, C.E., Mobile IP - Design Principles and Practices, Addison Wesley, 1998, ISBN 0-201-63469-4) . In this arrangement, the mobile "link" agent would be effectively considered as a migrating IP unit and therefore be allocated corresponding Mobile IP Agents.

Using a packet data network agent to carry out the protocol conversion functions, etc., is believed to be a particularly convenient and efficient way of interfacing between the two communications protocols.

Thus, according to a fourth aspect of the present invention, there is provided a method of operating a mobile radio communications system, in which system communication between mobile stations and base stations of the system is carried out using a mobile radio system communications protocol, and the fixed radio network infrastructure connecting the base stations of the system comprises a packet data network which uses a packet data communications protocol, the method comprising: representing each mobile station on the packet data network by means of an agent on the packet data network to which all packet data network communications intended for the mobile station can be sent, and which agent is operable to interface between the radio system communications protocol used for communication between mobile stations and base stations of the system and the packet data communications protocol used within the fixed network. According to a fifth aspect of the present invention, there is provided a radio network infrastructure for connecting base stations of a mobile radio communications system, comprising: a packet data network which uses a packet data communications protocol; means for creating and storing agents on the packet data network for representing mobile stations on the packet data network and for interfacing between a radio system communications protocol used for communication between mobile stations and base stations of the system and the packet data communications protocol used within the network; and means for sending all packet data network communications intended for a mobile station to that mobile station's packet data network agent. The mobile station packet data network representative agents are preferably able to carry out, preferably all, functions necessary to interface between the mobile station and the packet data network and most preferably carry whatever information is necessary to allow the packet data network to communicate with their respective mobile station.

Thus each packet data network "link" agent is preferably able to convert radio network addresses into packet data network addresses, and preferably carries its corresponding mobile station's radio system protocol address, so that, for example, when a message arrives from the packet data network addressed to the mobile station's packet data network representative agent, the agent can readdress the message for transmission to the mobile station. The agents are preferably also able to convert packet data network communications for the mobile station into the radio system communications protocol and, preferably, vice-versa. Thus they can preferably take data from the radio link and insert it into individually addressed packets and post them on the packet data network. They are preferably also able to cause the fixed network (i.e. base stations) to transmit messages, data, etc., that they receive to their mobile station. Thus, for example, if a circuit mode call is in progress, the link agent preferably strips off the packet data protocol headers and tails of the packets addressed to itself that it receives, and places the content into transmission timeslots on the radio interface. If packet data is being communicated over the air interface, the link agent preferably obtains radio timeslots for its mobile station and places entire packets in the time slots.

Each mobile station's packet data network "link" agent preferably also carries other data relating to its mobile station's operation and requirements. This can include, for example, data defining the permissions and privileges of the mobile station (e.g. what type of calls it can make and what priority it can use) . The link agent could also store some quality of service information indicating the current or recent average air interface bit error rate. This could be used, for example, to agree a quality contract with another correspondent for a particular connection - e.g. it would allow an appropriate slot rate and channel protection level to be determined for a video connection. The link agent preferably also stores the IP addresses of any data terminals connected to the mobile station, and also preferably maintains call timers, etc.

In a particularly preferred arrangement, the packet data network link agents can also carry out, preferably all, call set-up and registration functions for their mobile station. Thus they can preferably, for example, establish the availability of a desired correspondent for a circuit mode call, by, for example, exchanging messages with the other party's link agent. The packet data network agent can perform these functions by for example, making use of basic services provided by a base site controller of the radio system for accessing the base station functions, and by interrogating data stores elsewhere on the packet data network by making use of packet data communication facilities.

Thus, in its preferred embodiments at least, a mobile station's packet data network agent will present a packet data network address representing the mobile station to the packet data network and receive messages from the packet data network for the mobile station. The agent will know the correct translation into the mobile station's radio communications protocol address, and act to pass the re-addressed information on to the mobile station by invoking the functions of the appropriate base station of the network to cause it to transmit the information to the mobile station (using the mobile station's true air-interface address).

The mobile stations' packet data network agents should each have an appropriate packet data network address (which will typically effectively be the mobile station's packet data network address). Thus, if, for example, mobile IP is being used, the mobile station's packet data network "link" agent would assume the IP address notionally assigned to the mobile station. Alternatively, if mobile IP is not being used, the link agent could assume the address of the network node in which it currently resides. These addresses may be arranged, selected and stored as discussed above for the mobile station's packet data network addresses. Thus, where appropriate, the packet data network agents could have Internet Protocol addresses, or port numbers at a particular Internet Protocol address (which would typically be the address of the relevant base station or base station controller, i.e. the address of the computer which currently hosts the agent) . A mobile station's agent is preferably located at, and, preferably, where appropriate, has a packet data network address associated with, the packet data network node connecting to the mobile station's serving base station. Thus it will preferably, where appropriate, be stored in the interfacing controller associated with the mobile station's serving base station and, where appropriate, have an address associated with that interfacing controller.

The packet data network agents for the mobile stations can be created as necessary by the system. For example, an agent is preferably created when a mobile station first communicates with a given base station. The agent can be created where desired in the packet data network. It is, for example, preferably created in and by the base station interfacing controller associated with the base station with which the mobile station is communicating.

The packet data network representative agent of a mobile station preferably moves within the packet data network (and, where appropriate, changes its network address as it moves) as a mobile station moves between base stations of the radio system in use. This facilitates more rapid communication with a mobile station as it moves around the radio system.

Thus when a mobile station moves to a new serving radio system base station, the mobile station's packet data network agent is preferably transferred to a network location (e.g. an interfacing controller) associated with the new base station. Thus the packet data network agents preferably move themselves and their associated data around the packet data network as their respective mobile stations move around the network.

The transfer of a packet data network agent to a new location could be achieved by creating a new agent at the new location (e.g. in the new base station's interfacing controller) . Thus, when a mobile station changes its serving base station when a packet data network agent is already in use for the mobile station (such as would be the case during a handover between base stations during an ongoing call) , a new packet data network agent is preferably created at the network location (e.g. interfacing controller) of the new base station. The new agent may be created anew at the new network location, or the existing packet data network agent could copy itself or move its program code (and data, etc.) to the network location for the new base station (e.g. as part of the handover process) . In the latter case, the new agent should be given the complete state of the old agent, except for any essential differences relating to, for example, the new location (e.g. its packet data network address (location) may have changed to one associated with the new base station), etc. In a particularly preferred embodiment of this arrangement, the mobile station's original agent used for the previous base station is left in operation for a limited period of time (e.g. 60 seconds) after the new agent is created, so that it can forward any already transmitted data packets that arrive after the change of base station to the new agent. In this arrangement, the existing agent therefore preferably notes the packet data network address of the new agent so that it can send data packets directly to the address of the new agent and, for example, avoid having to seek the new agent's address from elsewhere in the system.

In one preferred embodiment, each mobile station has two packet data network agents allocated to it, a 'home' packet data network agent having an effectively fixed packet data network address, and the above packet data network "link" agent associated with the base station currently serving the mobile station. The home agent remains at the same 'home' location and packet data network address in the packet data network, but the link agent moves and changes addresses within the packet data network as the mobile station moves between base stations of the radio system.

The home agent serves as a default location for routing communications for the mobile station to when the address of the link agent is not known. The home agent therefore preferably keeps track of and stores the mobile station's present packet data network 'location', by keeping an up-to-date record of the current location of the mobile station's link agent. The fixed network preferably therefore updates a mobile station's home agent with the new location (address) of its link agent whenever the link agent moves locations in the fixed network. The home agent could, for example, be a Mobile IP Home Agent, where Mobile IP is being used.

Thus, in such an arrangement, a message (i.e. data packets) for a particular mobile station is preferably addressed directly to the called mobile station's link agent, if its address is known. Otherwise, the address of the mobile station's home agent can be retrieved, and then the message either forwarded to the home agent (in which case the mobile station's packet data network home agent should be arranged to forward any messages it receives for the mobile station to the mobile station's link agent), or the address of the mobile station's link agent retrieved from the home agent and the message then forwarded to the mobile station's link agent. Once it receives the message, the link agent should then forward it to the mobile station. (Where Mobile IP is being used, there may be no need to retrieve the Home Agent's address, because messages sent to the Mobile Station's IP address appear on the subnet to which the Home Agent is connected, and the Home Agent will recognize the address and collect and forward the packets.)

Where home agents are used, the packet data network link agent should know and store the home agent's address. Thus, when the mobile link agent already exists but is recreated at a new base site, it should retrieve its state table from the previous copy of the mobile link agent, and will therefore automatically obtain the address of its home agent, since the home agent address is known by the mobile link agent as part of its state table. However, when the mobile station is switched on and registers, the mobile station's link agent is newly created and only knows the mobile station's radio network address. In this case the link agent can examine a data base to discover the mobile station's IP address and home agent address. It can then also obtain any permissions, information, etc., about the mobile station from the home agent, if desired. The link agent could determine the mobile station's home agent's network address, for example, by accessing a centralised store of mobile -station home agent addresses (although a local data cache that stores home agent addresses of recent visitors to the base station could also be provided to allow quicker retrieval of home agent details for mobile stations that have recently communicated via the base station) .

The link agent preferably then advises the home agent of its existence or of its new address (e.g. base station controller's IP address and a port number), e.g. so that the home agent can send any data packets addressed to the mobile station to the new link agent's location. Where Mobile IP is being used, a mobile station can also be allocated an associated Mobile IP Foreign Agent, as well as a Mobile IP Home Agent and its packet data network "link" agent. In that case the mobile link agent could at each new base station make its presence known to the local Foreign Agent and the address of the new Foreign Agent would be forwarded to the Home Agent, so that the link agent can receive packets, which would be sent to it via the Foreign Agent (which it would share with other roamed mobile stations currently using that network node) . The Foreign Agent would act to forward messages to the mobile station's link agent, which link agent would then manage the communication from the IP network to the mobile station via the radio protocols . It would be possible for a mobile station to be known by multiple packet data network (IP) addresses, thus allowing it to possess multiple applications. In this case it would be necessary to allow the mobile station's packet data network link agent to use any of these addresses, as appropriate. Each address would also have to be registered separately with the home agent or home agents (for example a mobile internet application could connect through the mobile station which has an entirely different IP address) . It would in this case be necessary for the single network link agent to handle both sets of communication, to avoid complications over which application gets the air-interface time. When the mobile station moves to a new base site, the mobile station's link agent would have to update the two (or more) home agents with its new location (or, where Mobile IP Foreign Agents are being used, with the new local Foreign Agent; in this case it would also have to present itself to the Foreign Agent twice (or more) , once for each address) .

In a preferred embodiment, the packet data network (and preferably the mobile station's packet data network link agent, where used) is arranged to store data packets (e.g. up to some predetermined time or data limit) which cannot be immediately passed on to a mobile station (e.g. because the mobile station is temporarily out of contact with the fixed radio network (which may occur relatively frequently given the relatively unreliable connection between the network and the mobile station via the air-interface) ) , for subsequent transmission to the mobile station.

Decisions concerning call control and mobile station mobility management (e.g. registration of mobile stations to base stations, call requests and handover requests) can be handled as desired in the fixed network. For example, they could be handled by a single control means in the fixed network. However, they are preferably handled by plural control means distributed throughout the network, e.g. preferably by the interfacing controllers of the network. Using plural distributed controllers to handle these decisions is believed to provide increased speed and better scalability. The mobile stations' packet data network agents, where used, could also handle some or all of these decisions.

The methods in accordance with the present invention may be implemented at least partially using software e.g. computer programs. It will thus be seen that when viewed from further aspects the present invention provides computer software specifically adapted to carry out the methods hereinabove described when installed on data processing means, and a computer program element comprising computer software code portions for performing the methods hereinabove described when the program element is run on a computer. The invention also extends to a computer software carrier comprising such software which when used to operate a radio system comprising a digital computer causes in conjunction with said computer said system to carry out the steps of the method of the present invention. Such a computer software carrier could be a physical storage medium such as a ROM chip, CD ROM or disk, or could be a signal such as an electronic signal over wires, an optical signal or a radio signal such as to a satellite or the like.

It will further be appreciated that not all steps of the method of the invention need be carried out by computer software and thus from a further broad aspect the present invention provides computer software and such software installed on a computer software carrier for carrying out at least one of the steps of the methods set out hereinabove .

A number of preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a mobile radio communications system in accordance with the present invention; and

Figure 2 is a schematic diagram of two base station controllers in accordance with the present invention. The present embodiment relates to a mobile radio communications system which uses a standard mobile radio system air-interface communications protocol, such as the GSM standard (see, e.g. Mouly, M. , Paulet, M, The GSM System for Mobile Communications, Cell & Sys . , 4 rue Elisee Reclus, F-91120 Palaiseau, France, 1992, IBSN 2-9507190-0-7), or the TETRA standard (see, e.g. Terrestrial Trunked Radio (TETRA) Voice plus DATA (V+D) ; Part 2: Air Interface (AI) , ETS 300 392-2, European Telecommunications Standards Institute, F-06921 Sophia Antipolis, CEDEX - FRANCE) , for radio communications between the base stations and mobile stations, but in which the radio base stations are interconnected by a packet data network fixed infrastructure which uses a packet data communications protocol, such as an Internet Protocol based system, such as UDP, rather than being interconnected in the traditional fashion, using circuit switches .

To facilitate interfacing and protocol conversion between the air-interface radio system and the packet data network connecting the base stations, each mobile station is represented on the packet data network by a packet data network software "link" 'agent', which agent will move with the mobile station when it moves to a new base station, and represents its respective mobile station to the packet data network.

The mobile station's link agent acts as the link between the mobile station and the packet data network. It converts between the radio system's communications protocol and the packet data network's communications protocol, and converts between the radio system's addresses and the packet data network's addresses, for its mobile station, appropriately. Thus messages (such

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agent for the mobile station, allocating a packet data network address from a range of addresses reserved for that purpose. The base station controller should also determine the mobile station's home agent's address, e.g. by making an enquiry to a server containing an address database, or by examining a local cache of recent visitor details. The link agent would then immediately register with the mobile station's home agent . To do this, the base station controller could obtain the home address of the mobile station, and its home agent by checking its local cache, or a central database, against the mobile station's radio identity, using its own (Base Station Controller's) address for the reply address. It would then create the new mobile link agent, and furnish it with these two items of information, and also its (the base station controller's) address as the address of the Foreign Agent (if it is using Mobile IP Foreign Agents - alternatively, the mobile link agent could discover the

Foreign Agent for itself using standard Mobile IP methods for finding Foreign Agents) . Alternatively, e.g. where Mobile IP Home and Foreign Agents are not being used, the base station controller could provide the mobile link agent with the base station controller's address plus a reserved port number. The mobile agent can now find the home agent itself by checking the local cache and a central data base .

When handover of a mobile station from one base station to another occurs, a link agent copies itself across to the base site controller for the new base station as part of the handover process (or it may be created from existing code at the new base station controller) . The new link agent is given the complete state of the old link agent, except that its packet data network address may be changed to one that is appropriate to the new base station's controller. As before, the new link agent will then register with the mobile station's home agent, so that all new incoming data packets can be forwarded to the new link agent address. Thus the link agents are effectively movable software that move themselves and their data around the packet data network as their respective mobile stations move around the network.

Figure 1 shows schematically a mobile radio system in accordance with the present invention. The system includes a number of radio base stations 2, 3, 4, 5, 6, 16, 26 and 28, each connected to a radio antenna 7, 34, 8, 17, 27 and 29. It also includes plural mobile stations, two of which, mobile stations 1 and 18, in radio communication with base stations 2 and 16, respectively, are shown.

The base stations of the fixed radio network are interconnected by ethernet buses 12, 14, and routers are used to interconnect separate networks (e.g. routers 13 and 19) or to connect a network to a serial link (for example router 23 interconnects ethernet 14 to PSTN gateway 20 via a serial link - where an external network link is present, the external network could have controllers and/or "agents" for interfacing between the packet data network and the external network as appropriate). Data, etc., is communicated around the fixed network using any suitable packet data routing method. (See, for example, Stevens, W. Richard, "TCP/IP Illustrated, Volume 1 - The Protocols " , Addison Wesley, 1994, ISBN 0-201-63346-9) . The packet data network also includes a home location database server 25 which keeps records of the mobile station's home agent's addresses.

Each base station has an associated base site interfacing controller 9, 10, 11, 15, 22, 24, which carries out the usual base station control functions, but also houses or hosts the home and link agents of mobile stations and thus acts to interface and convert

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the address of the called mobile station's current base site controller using the port number assigned to the called party's mobile link agent. The calling mobile link agent can, if desired, first check if the called party's mobile link agent happens to be present at the location before sending data packets all around the network - a base station controller data cache could be checked for this information.

Each base site controller also includes a data cache for storing, e.g. link and home agent addresses of mobile stations that have recently communicated through its associated base station (s) .

In the present embodiment, the base site controllers also handle all decisions concerning registration of mobile stations to base sites, call requests and handover requests (i.e. call control and mobility management) , as using distributed base site controllers to handle these functions is believed to provide benefits of speed and scalability when the methods of the present invention are employed. However, it would be possible for a single packet data network- connected server to handle these functions for the whole system.

In the present example, base site controller 9 is associated with a single base station, base station 2, but base site controller 11 is associated with plural base stations 4, 5 and 6.

Figure 2 gives a more detailed view of the base station and base site controller arrangement. Radio messages from a mobile station are received by base site antenna 7, and travel through RF feeder 42 into radio base station 2. In this example, the TETRA air- interface protocol is in use, and the messages are interpreted in TETRA protocol stack 41. Other air- interface protocols, such as the GSM (Global System for Mobile Communications) protocol, could equally be used. (The protocol stack implementation could also be split between the radio base station and the base site controller, or entirely installed in the base site controller. )

The base station 2 may be connected to its associated base site controller 9 by any suitable means such as by a serial connection using a well known protocol such as SLIP (Serial Line IP) or PPP (Point to Point Protocol) . In the present example, TETRA messages and user data (speech or data) are then sent via PPP protocol stack 39 (for example) and serial link 38 to be received at the base site controller 9 in PPP stack 37, using any suitable known method.

Each base site controller contains a software or logic module 36 which can support the execution of identical software procedures in multithreaded operation, such that they appear to execute independently and simultaneously, each at a different point in its sequence of operations. This module handles call control and mobility management, and stores the packet data network link agents of the mobile stations, as appropriate. Each base site controller can accommodate a number of concurrently running home agents and visiting link agents.

Thus, for example, base site controller 9 includes in its software module 36 one or more software 'agents' representative of mobile stations which are communicating via the base station 2, including a link agent 33 which corresponds to mobile station 1.

In a preferred embodiment of the present invention, the home and link agents for each mobile station are given as their packet data network addresses port numbers (e.g. a TCP/UDP port number) at the packet data network (IP) address of the relevant base site controller. Thus, each mobile station would have a link agent, which link agent attaches to a particular port number in the base station controller associated with the base station currently serving the mobile station and is assigned a port number on the visited base station controller for the duration of its visit, and a home agent attached, for example, to a port on the mobile station's home base station controller. Each agent in effect manages a packet data (IP) network port on behalf of its mobile station.

An example of the operation of an embodiment of the present invention which uses port numbers as addresses for the agents representing the mobile stations in the packet data network will now be considered.

Referring to Figure 1, the case where mobile station 1 has radio identity '123456', and has a home agent 32 at base site controller 22, with packet data network (IP) address 128.8.120.04 and port number 6196, will be considered. Base site controller 9 has packet data network address 128.8.128.56.

We will consider the situation where mobile station 1 is switched on when in range of base site 2. When it is first switched on, the mobile station sends a registration request to radio base station 2, using its radio system identity 123456. This is passed straight to base site controller 9 via the serial connection 38. Base site controller 9 examines its data cache records but is unable to find an entry for mobile station 123456. It therefore sends an enquiry to the home location database server 25 of the packet data network, and obtains responses of IP address 128.8.120.04 and port number 6196, for the mobile station l's home agent. The base site controller 9 now creates a new link agent 33 to act on behalf of mobile station 123456, using port number 3657, and provides it with 128.8.120.04 port 6196 as the home agent's address and 128.8.128.56 port 3657 as the link agent's address.

The newly created link agent 33 sends a registration message to the home agent at address

128.8.120.04, port 6196, quoting 128.8.128.56 port 3657 as its current address . At this stage the base site controller may attempt to authenticate the mobile station, using, e.g., the services of an authentication server connected somewhere on the packet data network (not shown in Figure 1) . If the authentication fails, the mobile station's link agent is deleted.

Now consider the situation when mobile station 18, having an established link agent 30, attempts to send a call request to mobile station 1. Its link agent 30 (which is in base site controller 15) receives a request to call mobile station 123456, and obtains the equivalent packet data network home agent address either from a local data cache (if it has called mobile station 1 recently, for example) , or by a request to home location database server 25. It then sends the call request to network address 128.8.120.04 port 6196. Home agent 32 of mobile station 1 at base site controller 22 collects the call request and forwards it to mobile station l's link agent 33 at address 128.8.128.56, port 3657 (i.e. at base site controller 9) . Base site controller 9 forwards the call request message to mobile station l's link agent 33 at port 3657. The link agent 33 endeavours to reserve the resources required to make the call, and ascertain the availability of mobile station 1 by calling on the radio protocol services provided by the base station controller. If a call is possible, it sends a call acceptance message to the link agent of mobile station 18, via mobile station 18 ' s home agent, if necessary. When the call acceptance is received by mobile station 18 's link agent 30, link agent 30 completes the call connection (in conjunction with mobile station 18) .

Now suppose that mobile station 1 decides that it needs to move on to radio base station 3 in the middle of its call. It requests the handover, and its link agent 33 sends a complete copy of its own state table to base site controller 10. (It could also send a copy of the agent code, but it may be more efficient to just transmit the state table and execute code pre-stored in the base site controller.) Base site controller 10 creates a copy 31 of mobile station l's link agent, but gives it the new address 128.8.128.57, port 2249. The new mobile link agent 31 should then register its location with the home agent 32 at 128.8.120.04 port 6196. As the call continues, data packets from mobile station 18 would now be routed to the new link agent 31 at base site controller 10, where necessary by mobile station l's home agent 32. Old link agent 33 at base site controller 9 preferably remains active for about 60 seconds to redirect any late data packets. It then terminates itself.

In an alternative embodiment of the present invention, the packet data network link agents representing the mobile stations on the packet data network could be given their own full packet data network (e.g. Internet Protocol) addresses. Where the Internet Protocol is used, the addresses could be full 8-bit number addresses, and/or subnet addresses.

Where an arrangement in accordance with the present invention is used in an Internet Protocol based packet data network, the mobile stations' packet data network link agents would take the appearance of mobile nodes as used in the Mobile IP protocol (see, for example, Perkins, C.E., Mobile IP - Design Principles and Practices, Addison Wesley, 1998, ISBN 0-201-63469-4) . In such a case each mobile station's link agent would be considered as a migrating IP unit, and a Mobile IP Foreign Agent could provide a 'care-of ' address for the migrated unit. The Mobile IP Home Agent would be connected to the migrating unit's (mobile station's) home subnet and would forward any data packets sent to the mobile station to .the foreign agent (by packing them inside data packets addressed to the Foreign Agent) . The Foreign Agent would unpack any data packets it receives and send them on to the mobile station's mobile link agent which would examine the data and determine if it is signalling information or user data. The link agent would repackage user data and ask the base site controller to transmit it to the mobile radio unit. The link agent would use signalling information to connect or modify calls, reserve radio resources or provide information, etc.

An example of the operation of such an embodiment of the present invention will now be described. Referring again to Figure 1, we will again suppose that mobile station 1 in Figure 1 has radio identity '123456'. In this case, mobile station 1 also has a home IP network address of '128.8.120.143, and a Home Agent 32 at base site controller 22, with IP address 128.8.120.04. We will further suppose that base site controller 9 has IP address 128.8.128.56.

When mobile station 1 is switched on when in range of base station 2, it will send a registration request to radio base station 2, using its identity 123456. This is passed straight to base site controller 9 via the serial connection. As before, base site controller 9 examines its cache records but is unable to find an entry for mobile station 123456. It therefore sends an enquiry to the home location database server 25, and obtains responses 128.8.120.143 for the mobile station's IP address, and 128.8.120.04 as the mobile station l's Home Agent's address. The base site controller 9 now creates a new link agent 33 to act on behalf of mobile station 123456, giving it IP address 128.8.120.143, and provides it with 128.8.120.04 as the mobile station's Home Agent's address and 128.8.128.56 as the mobile station ' s Foreign Agent ' s address .

The link agent 33 sends a registration message to the Home Agent 128.8.120.04, quoting 128.8.128.56 as its current Foreign Agent. At this stage, as in the embodiment discussed above, the base site controller may attempt to authenticate the mobile station, using the services of an authentication server connected somewhere on the IP network (not shown in Figure 1) . If the authentication fails, the link agent is deleted.

Now consider the situation where mobile station 18, having a link agent 30, attempts to send a call request to mobile station 1. Its link agent 30 (which is in base site controller 15) will receive a request to call mobile station 123456, and obtains the equivalent IP address either from a local cache (if it has called mobile station 1 recently, for example) , or by a request to home location server 25. It sends the call request to IP address 128.8.120.143. The request is collected by the Home Agent 32 at base site controller 22, and tunnelled to address 128.8.128.56 (by packing the data packets inside data packets addressed to address

128.8.128.56), which is base site controller 9. The Foreign Agent resident in base site controller 9 forwards the call request message to mobile station l's link agent 33, which endeavours to reserve the resources required to make the call, and ascertain the availability of mobile station 1. If a call is possible, link agent 33 sends a call acceptance message to the IP address of mobile station 18. If mobile station 18 is away from home, this message will go via mobile station 18' s Home Agent (not shown) and the Foreign Agent at base site controller 15 and mobile station 18 ' s link agent 30. When the call acceptance is received by mobile station 18 's link agent 30, its link agent 30 completes the call connection (in conjunction with mobile station 18) .

As the call proceeds, the network or routers deliver all 128.8.120.143 packets to the ethernet subnet corresponding to this address. The Home Agent on host 128.8.120.04 is connected to this subnet, and sees these packets. It collects all packets addressed to host 128.8.120.143 and sends each inside a larger packet addressed to the Foreign Agent at 128.8.128.56 (often referred to as "tunnelling" , as is known in the art) . When the Foreign Agent unpacks one of these packets it finds inside a packet addressed to 128.8.120.143. By checking its data base, it discovers that this is the address of a mobile station link agent executing on its own hardware, and passes the packet on to the link agent .

Now suppose that mobile station 1 decides that it needs to move on to radio base station 3 in the middle of its call. It requests the handover, and its link agent 33, as before, sends a complete copy of its own state table to base site controller 10. Base site controller creates a copy 31 of the link agent, and gives it a new address 128.8.128.57. The new link agent 31 registers its location with the Home Agent 32 at 128.8.120.04, and speech data packets from mobile station 18 are routed to the new base site controller 10 by the Home Agent 32.

As before, link agent 33 at base site controller 9 may remain active for about 60 seconds to redirect any late packets and then terminate itself.

As can be seen from the above, the present invention provides a mobile radio communications system that permits the use of relatively inexpensive, flexible and readily available packet data (e.g. IP) protocol hardware and software to interconnect base stations of the radio system, using standard packet data (e.g. IP) protocols to provide mobility management and manage the routing of data packets to a mobile station through the packet data network. However, standard radio terminal units that have no knowledge of packet data protocols may be used in the system, and the packet data network needs no knowledge of the radio system's radio protocols.

Claims

1. A radio network infrastructure for a mobile radio communications system, the network infrastructure comprising: plural interconnected base stations, the base stations being adapted to communicate with mobile stations of the radio system via a mobile radio system communications protocol; a packet data communications network interconnecting the base stations which uses a packet data network communications protocol; and means for converting communications received at a base station from a mobile station to the packet data network communications protocol for onward transmission through the network infrastructure, and means for converting communications from the network for a mobile station to the mobile radio system communications protocol for onward transmission by a base station to the mobile station.

2. The infrastructure of claim 1, wherein the packet data network interconnecting the base stations comprises an Internet Protocol based network.

3. The infrastructure of claim 1 or 2 , wherein each base station has a controller associated with it in the infrastructure for interfacing between the mobile radio system protocol used for communications between the base station and the mobile stations, and the packet data network communications protocol used for communications between base stations via the packet data network, where the communications conversion takes place.

4. The infrastructure of claim 3, wherein each controller is located at a node of the network to which their associated base station (s) connect. O LO to t μ¹

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communications protocol used over the air-interface and the packet data network communications protocol used for the packet data network fixed infrastructure .

10. The infrastructure of claim 9, wherein the packet data network is Internet Protocol based, and the packet data network agent representing a mobile station on the packet data network is a mobile host as used in the Mobile IP protocol.

11. A radio network infrastructure for connecting base stations of a mobile radio communications system, comprising: a packet data network which uses a packet data communications protocol; means for creating and storing agents on the packet data network for representing mobile stations on the packet data network and for interfacing between a radio system communications protocol used for communication between mobile stations and base stations of the system and the packet data communications protocol used within the network; and means for sending packet data network communications intended for a mobile station to a packet data network agent for that mobile station.

12. The infrastructure of claim 9, 10 or 11, wherein the mobile station packet data network representative agents are able to carry out functions necessary to interface between a mobile station and the packet data network and carry information necessary to allow the packet data network to communicate with the agent ' s respective mobile station.

13. The infrastructure of claim 9, 10, 11, or 12 , wherein the mobile station packet data network agents carry data relating to their mobile station's operation and requirements.

14. The infrastructure of any one of claims 9 to 13 , wherein the mobile station packet data network agents have a packet data network address.

15. The infrastructure of any one of claims 9 to 14, when dependent upon any one of claims 3 to 5, wherein a mobile station's packet data network agent is stored in the interfacing controller associated with the mobile station's serving base station.

16. The infrastructure of any one of claims 9 to 15, wherein the packet data network agent of a mobile station moves within the packet data network as its mobile station moves between base stations of the radio system.

17. The infrastructure of any one of claims 9 to 16, wherein each mobile station has two packet data network agents allocated to it, a home packet data network agent having a fixed packet data network address, and another packet data network agent which is associated with the base station currently serving the mobile station and which moves within the packet data network as the mobile station moves between base stations of the radio system.

18. A method of operating a mobile radio communications system, which system comprises plural mobile stations and plural base stations, which base stations are interconnected by a fixed network, the method comprising: using a mobile radio system communications protocol for radio communications between the mobile stations and base stations; using a packet data network communications protocol for communications between the base stations via the fixed network; converting communications received at a base station from a mobile station to the packet data network communications protocol for onward transmission through the fixed network; and converting communications from the fixed network for a mobile station to the mobile radio system communications protocol for onward transmission by a base station to the mobile station.

19. The method of claim 18, further comprising allocating each mobile station a corresponding packet data network address .

20. The method of claim 19, further comprising associating each mobile station's packet data network address with the mobile station's allocated radio system protocol address.

21. The method of claim 18, 19 or 20, further comprising changing a mobile station's packet data network address as the mobile station moves between base stations of the radio system.

22. The method of claim 18, 19, 20 or 21, further comprising representing each mobile station by an agent on the packet data network to which all packet data network communications intended for the mobile station can be sent and which agent can carry out the interfacing and conversion between the communications protocol used over the air-interface and the packet data network communications protocol used for the packet data network fixed infrastructure.

23. A method of operating a mobile radio communications system, in which system communication between mobile stations and base stations of the system is carried out using a mobile radio system communications protocol, and the fixed radio network infrastructure connecting the base stations of the system comprises a packet data network which uses a packet data communications protocol, the method comprising: representing a mobile station on the packet data network by means of an agent on the packet data network to which packet data network communications intended for the mobile station can be sent, and which agent is operable to interface between the radio system communications protocol used for communication between mobile stations and base stations of the system and the packet data communications protocol used within the fixed network.

24. The method of claim 22 or 23, wherein the mobile station packet data network representative agents are able to carry out functions necessary to interface between the mobile station and the packet data network and carry information necessary to allow the packet data network to communicate with the agent ' s respective mobile station.

25. The method of claim 22, 23 or 24, wherein a mobile station's packet data network agent carries data relating to its mobile station's operation and requirements .

26. The method of claim 22, 23, 24 or 25, further comprising allocating to a mobile station's packet data network agent a packet data network address .

27. The method of any one of claims 22 to 26, further comprising moving the packet data network agent of a mobile station within the packet data network as its mobile station moves between base stations of the radio system.

28. The method of any one of claims 22 to 27, further comprising allocating to a mobile station two packet data network agents , a home packet data network agent having a fixed packet data network address, and another packet data network agent which can be associated with the base station currently serving the mobile station and moves within the packet data network as the mobile station moves between base stations of the radio system.

29. A computer program element comprising computer software code portions for performing the method of any one of claims 18 to 28 when the program element is run on a data processing means.

30. A radio network infrastructure substantially as hereinbefore described with reference to any one of the accompanying drawings .

31. A method of operating a mobile radio communications system substantially as hereinbefore described with reference to any one of the accompanying drawings .