HK1087293B - Cell reselection signalling method - Google Patents

Description

Cell reselection signaling method and cellular telecommunication system

The present application is a divisional application with application number 01803214.1 entitled "cell reselection signaling method" filed on 17.1.2001 by nokia corporation.

Technical Field

The present invention relates to methods relating to cell reselection in a cellular telecommunications system, and in particular to a channel reselection signalling method in a cellular telecommunications network.

Background

To illustrate common terminology used within this document, an overview of certain cellular telecommunications system configurations is presented below.

Proposals for third generation systems include UMTS (universal mobile telecommunications system) and FPLMTS/IMT-2000 (future public land mobile telecommunications system/2000 MHZ international mobile telecommunications). Within these plans, cells are classified into pico-cells, nano-cells, micro-cells, and macro-cells according to their size and characteristics, and an example of the service level is bit rate. The bit rate is highest in pico cells and lowest in macro cells. The cells may partially or completely overlap and there may be different terminals, so that not all terminals have to be able to utilize all the service levels provided by the cells.

Fig. 1 shows a future cellular radio system which is not new compared to the known GSM system and which comprises both known and new units. In current cellular radio systems, the bottleneck preventing more advanced services from being provided to the terminal comprises the radio access network RAN, which comprises base stations as well as base station controllers. The core network of a cellular radio system comprises a mobile services switching centre (MSC), other network elements (in GSM, e.g. SGSN and GGSN, i.e. serving GPRS support nodes and gateway GPRS support nodes, GPRS standing for general packet radio service) and related transmission systems. The core network may also provide new services, for example according to the GSM + specifications developed from GSM.

In fig. 1, the core network of the cellular radio system 930 comprises a core network 931, the core network 931 having three parallel radio access networks linked thereto. Of these radio access networks, networks 932 and 933 are UMTS radio access networks, while network 934 is a GSM radio access network. The above UMTS radio access network 932 is, for example, a commercial radio access network owned by a telecommunications carrier providing mobile services, which serves equally all subscribers of the telecommunications carrier. The following UMTS radio access network 933 is, for example, dedicated, e.g., owned by a company operating within the company's building. Typically, the cells of the private radio access network 933 are nanoand/or pico cells within which only terminal parties of employees of the company are operational. The three radio access networks may each have cells of different sizes providing different types of services. In addition, the cells of all three radio access networks 932, 933, and 934 may overlap, either completely or partially. The bit rate used at a particular time depends on, among other things, the radio path conditions, the characteristics of the service used, the total capacity of the area of the cellular system, and the capacity required by other users. The new radio access network described above is referred to as a General Radio Access Network (GRAN). Such a network may cooperate with different types of fixed core networks CN, in particular with GPRS networks of the GSM system. A General Radio Access Network (GRAN) may be defined as a group of Base Stations (BSs) and Radio Network Controllers (RNCs) that are capable of communicating with each other using signaling messages. Hereinafter, the general radio access network will be simply referred to as a radio network GRAN.

The terminal 935 shown in fig. 1 is advantageously a so-called dual mode terminal, which may act as a second generation GSM terminal or a third generation UMTS terminal, depending on the type of service available at each particular location and the communication requirements of the user. It may also be a multimode terminal that can act as a terminal for several different communication systems, depending on the services required and available. The radio access networks and the services available to the user are defined in a subscriber identity module 936(SIM) connected to the terminal.

A conventional approach to treating a connection establishment request in a congested situation is to simply reject the connection establishment request. Thereafter, the Mobile Station (MS) needs to find a new cell for the new connection attempt. The problem with this approach is that there will be a large amount of failure signalling if the mobile station needs to make several connection attempts to several different cells before finding a cell to accept a new connection. This situation may arise when many cells in the surroundings are also congested. The establishment of the connection will therefore also take a long time, which may be disappointing for the user of the mobile station.

Another prior art approach to treating connection establishment requests in congested situations is to perform the connection establishment as requested by the mobile station and then immediately force a handover to a less congested cell. This approach is quite satisfactory from the mobile user's point of view, since the network quickly receives the new connection, but it causes excessive signalling in the form of handover signalling.

At the time of this patent writing, in the RRC specification of third generation cellular networks, the network has no explicit control over which cell the UE will select after the XRRC connection establishment is rejected in the serving cell. In GSM systems, cell reselection after rejection of the connection establishment request and retry actions by the mobile station are also problematic under the control of the network.

Disclosure of Invention

The object of the present invention is to achieve a cell reselection method requiring only a small amount of signaling. Other object is to achieve a cell reselection method that allows the network to have some control over the actions of the mobile station in case of connection rejection.

This object is achieved by indicating within the connection setup rejection message information affecting the determination of at least one parameter for the new connection attempt.

According to one aspect of the present invention, there is provided a channel reselection signalling method in a cellular telecommunications network, characterized in that said method comprises the steps of:

a connection establishment request is received from the mobile station,

notifying that the connection establishment request must be denied if the cellular telecommunications network cannot provide the requested connection; the cellular telecommunications network indicating to the mobile station in a connection rejection message information about the value of at least one parameter relating to connection establishment used at the time of the new connection establishment attempt;

transmitting the connection rejection message from the cellular telecommunications network to the mobile station.

According to yet another aspect of the present invention, there is provided a network element of a cellular telecommunications network, characterized in that,

the network element is configured to:

a connection establishment request is received from the mobile station,

notifying that the connection establishment request must be denied if the cellular telecommunications network cannot provide the requested connection; (ii) a

Indicating to the mobile station in a connection rejection message information about the value of at least one parameter related to connection establishment used at the time of the new connection establishment attempt;

transmitting the connection rejection message to the mobile station.

According to another aspect of the present invention, there is provided a mobile communication device in a cellular telecommunication system, wherein the mobile communication device is configured to:

transmitting a connection establishment request to the cellular telecommunications system;

receiving a connection rejection message if the cellular telecommunications system is unable to provide the requested connection;

observing at least one parameter of the connection rejection message;

setting a value of at least one parameter for a new connection establishment attempt based at least in part on information in the at least one parameter of the connection rejection message;

channel selection is performed by attempting to establish a new connection using the set value of the at least one parameter.

According to yet another aspect of the present invention, there is provided a cellular telecommunications system comprising a network element and a mobile communications device, the mobile communications device being arranged to transmit a connection establishment request to the cellular telecommunications system, the network element being arranged to notify that the connection establishment request must be denied if the cellular telecommunications system is unable to provide the requested connection;

it is characterized in that the preparation method is characterized in that,

the network element is arranged to:

indicating to the mobile communication device in a connection rejection message information about the value of at least one parameter related to connection establishment used in the new connection establishment attempt,

transmitting the connection rejection message to the mobile communication device;

the mobile communication device is configured to:

observing at least one parameter of the connection rejection message;

setting a value of at least one parameter for a new connection establishment attempt based at least in part on information in the at least one parameter of the connection rejection message;

channel selection is performed by attempting to establish a new connection using the set value of the at least one parameter.

According to the invention, the connection establishment rejection message is used to instruct the mobile communication device to attempt a new connection by means of certain parameter values, e.g. certain carrier frequencies. It is also possible to indicate within the message a number of parameter values, the message allowing the network to instruct the mobile communication device to make a connection establishment request to a particular cell. The connection setup rejection message may be, for example, a "connection setup rejection" message of the RRC protocol.

In a preferred embodiment, the network indicates the carrier frequency within the connection establishment rejection message. After receiving the message, the mobile communication device attempts to establish a new connection to the cell using the carrier frequency. There may be a plurality of such cells. For example, in a WCDMA cellular system under development, multiple cells may use the same carrier frequency. In this case, the mobile station must select one of the cells for the new attempt.

In a more preferred embodiment, the network indicates a carrier frequency and information identifying a certain one of the cells using the indicated carrier frequency. Such information identifying a certain cell may be more advantageous, for example, a scrambling code corresponding to the cell. Since these parameters define a certain cell, the mobile station does not need to select a cell among those using the carrier frequency, which shortens the time required to establish a desired connection.

In a more preferred embodiment of the invention, the network indicates a cellular network identifier within the rejection message. This embodiment is advantageous in such cases when multiple cellular networks are present in the same geographic area and the mobile communication device may use at least two different networks, or even multiple different networks. For example, the present embodiments allow a UMTS (universal mobile telecommunications system) network to instruct a mobile station to make connection attempts to a GSM (global system for mobile communications) network, a GPRS (general packet radio service) network, a network capable of operating EDGE (enhanced data rates for GSM evolution), and some other networks.

The network may also indicate other parameters within the rejection message, such as parameter values for certain timers affecting the timing of the next connection attempt, the time difference of the cell transmitting the rejection message and the cell suggested by the network, and parameter values identifying certain used transport channels. The parameter values for certain transport channels may for example be parameter values describing a certain primary common pilot channel (CPICH), if the ideal connection is an FDD (frequency division duplex) mode connection of a WCDMA system; or a parameter value describing a certain basic Common Control Physical Channel (CCPCH), if the desired connection is a TDD (time division duplex) mode connection of a WCDMA system.

In a more preferred embodiment of the invention, the mobile communication device derives at least one parameter from the system information message if the rejection message indicates some reason for rejection. For example, if the reject message indicates that the cause is congestion, the mobile communication device may derive a carrier frequency from the system information message for the next connection attempt. In a preferred embodiment of the present invention, such a System information message is a System Info Block Type 5 message of the RRC protocol according to certain specifications of the WCDMA System.

Drawings

Various embodiments of the present invention will now be described in detail with reference to the following examples, with reference to the accompanying drawings. In the attached drawings

Figure 1 shows a cellular telecommunication network according to the prior art,

FIG. 2 illustrates a method according to a preferred embodiment of the present invention, an

Fig. 3 shows a further method according to a preferred embodiment of the invention.

The description of fig. 1 has been given above together with the description of the technical situation. In the drawings, similar entities are provided with the same reference numerals.

Detailed Description

Although a congestion situation usually arises due to insufficient resources of the whole cell, a congestion situation may also arise due to insufficient radio resources of the channel. The connection rejection message may also result from channel congestion. Thus, in the following description, and in particular in the claims, the term channel is used as covering a cell as well as a specific channel according to specific frequency, coding, etc. parameters. Since a handover may indicate a change of some connection parameters, e.g. coding or frequency, and a change of connection from a first cell to a second cell, the selection of a new channel may equally indicate a change of some connection parameters, e.g. coding or frequency, and a change of cell. The channel selection may for example represent the selection of a new frequency within the same cell or a different cell, the selection of a new cell with the same or a different frequency, the selection of a different scrambling or channel code on the same or a different frequency within the same or a different cell, or even the selection of another cellular telecommunication system. In addition, the term mobile station is intended to include all mobile communication devices.

A. First group of preferred embodiments

According to a first aspect of the present invention, there is provided a channel reselection signalling method within a cellular telecommunications network. Fig. 2 illustrates this aspect of the invention. According to the method, the network 10 indicates in a connection rejection message 30 to the mobile station 20 information about the value of at least one connection establishment related parameter used in the new connection establishment attempt.

In a preferred embodiment, the connection reject message 30 is an RRC connection reject message.

In the preferred embodiment, the information includes information 100 about the preferred channel for the next connection attempt.

In a preferred embodiment, the information includes frequency information 110.

In a preferred embodiment, the information comprises information 115 about the reference time difference between the channel of the previous attempt and the preferred channel for the next connection attempt.

In a preferred embodiment, the information comprises information 120 about the primary CPICH channel (PCPICH).

In a preferred embodiment, the information includes information 125 about the primary CCPCH channel.

In a preferred embodiment, the information includes scrambling code information 130 corresponding to a certain preferred channel.

In a preferred embodiment, the information includes channel code information 135 corresponding to a preferred channel.

In a preferred embodiment, the information comprises information 140 about the second cellular telecommunication network.

B. Second group of preferred embodiments

According to a second aspect of the present invention, there is provided a channel reselection method in a mobile communication device of a cellular telecommunication system. Fig. 3 illustrates this aspect of the invention. According to a preferred embodiment of the invention, the method comprises the steps of

A connection rejection message is received 200 and,

observing 210 at least one parameter of the connection rejection message, an

Setting 220 a value of at least one parameter for a new connection attempt based at least in part on information within at least one parameter of the connection rejection message.

According to a more preferred embodiment of the present invention, the connection rejection message is an RRC connection rejection message.

In a more preferred embodiment of the invention, the value of at least one parameter for a new connection attempt is derived from a system information message if a predetermined parameter of said connection rejection message has a predetermined value.

According to a more preferred embodiment of the invention, the method further comprises the step of

Setting a reception frequency based on a value of a parameter of the connection rejection message,

selecting a channel to be transmitted at the reception frequency,

a connection establishment procedure is initiated.

According to a preferred embodiment of the invention, the reception frequency may be, for example, a UTRA (UMTS terrestrial radio access) carrier frequency. The UE selects an appropriate cell to camp on based on the frequency. The candidate cells for this selection are those on the frequency that the UE monitors before initiating the initial RRC connection establishment procedure that results in a rejection message. If no suitable cell is found, the UE may use a stored information cell selection procedure to find a suitable cell to camp on, for example. After camping on a cell, the UE may be more advantageous to restart the RRC connection establishment procedure. The stored information cell selection procedure is described, for example, in 3GPP technical specification TS 25.304 "UE Procedures in Idle Mode".

According to a more preferred embodiment of the invention, the method further comprises the step of

Setting a reception frequency based on a value of a parameter of the connection rejection message,

setting a special channel scrambling code based on a value of a parameter of the connection rejection message, an

A connection establishment procedure is initiated.

According to a more preferred embodiment of the invention, the method further comprises the step of

Setting a reception frequency based on a value of a parameter of the connection rejection message,

setting a special channel code based on a value of a parameter of the connection rejection message, an

A connection establishment procedure is initiated.

According to a more preferred embodiment of the present invention, the method further comprises the step of setting a timing value based on a value of a parameter of said connection rejection message.

According to a more preferred embodiment of the present invention, the method further comprises the step of setting a reception frequency based on a value of a parameter of the connection rejection message.

According to a more preferred embodiment of the present invention, the method further comprises the step of setting a timing value based on a value of a parameter of said connection rejection message.

According to a more preferred embodiment of the invention, the method further comprises the step of setting a scrambling code parameter based on a value of a parameter of said connection rejection message.

According to a more preferred embodiment of the present invention, the method further comprises the step of setting a channel code parameter based on a value of a parameter of said connection rejection message.

According to a more preferred embodiment of the invention the method further comprises the step of setting a parameter describing a certain primary CPICH channel based on the value of the parameter of the connection rejection message.

According to a more preferred embodiment of the invention, the method further comprises the step of setting a parameter describing a certain primary CCPCH channel based on the value of a parameter of said connection reject message.

According to a more preferred embodiment of the invention, the method further comprises the step of setting a parameter identifying the second cellular telecommunication network based on a value of a parameter of said connection rejection message.

According to a more preferred embodiment of the invention, the method further comprises the step of initiating a new connection attempt at least partly on the basis of the value of a parameter of said connection rejection message.

C. Third group of preferred embodiments

According to a third aspect of the invention, a network element of a cellular telecommunications network is provided. In a preferred embodiment of the invention, the network element is adapted to indicate within the connection rejection message to the mobile station information about the value of at least one connection establishment related parameter used in the new connection establishment attempt.

According to a more preferred embodiment with respect to the network element, the network element is a network element of a radio access network of a cellular telecommunication network.

According to a more preferred embodiment regarding the network element, the network element is a radio network controller.

According to a more preferred embodiment in respect of the network element, the connection rejection message is an RRC connection rejection message.

According to a more preferred embodiment relating to a network element, said information comprises information about a preferred channel for the next connection attempt.

According to a more preferred embodiment in respect of the network element, said information comprises frequency information.

According to a more preferred embodiment relating to a network element, said information comprises information about a reference time difference between a previously attempted channel and a preferred channel for a next attempt.

According to a more preferred embodiment in respect of the network element, said information comprises information in respect of the primary CPICH channel.

According to a more preferred embodiment in respect of the network element, said information comprises information in respect of a primary CCPCH channel.

According to a more preferred embodiment in respect of the network element, said information comprises scrambling code information corresponding to a certain preferred channel.

According to a more preferred embodiment in respect of the network element, said information comprises channel code information corresponding to a certain preferred channel.

According to a more preferred embodiment, the information comprises information about the second cellular telecommunication network.

D. Further considerations

The invention has several advantages. For example, the present invention reduces signaling between the mobile telecommunications device and the network. Handover signaling is not required since the mobile station may be informed of new information for establishing a new connection within the reject message.

The invention is applicable to many different cellular telecommunication systems, such as UMTS systems or GSM systems. The present invention is applicable to any cellular telecommunications system in which a cellular telecommunications network sends a rejection message in response to a connection establishment request from a mobile station if the network is unable to provide the required connection.

The name of a particular functional entity, such as a radio network controller, is typically different in the context of different cellular telecommunication systems. For example, in a GSM system, the functional entity corresponding to a Radio Network Controller (RNC) is a Base Station Controller (BSC). The term radio network controller in the claims is therefore intended to include all corresponding functional entities, irrespective of the entity used within a particular cellular telephone system. In addition, various message names, such as the connection setup rejection message name, are used as examples only, and the present invention is not limited to use of only the message names listed in the present specification.

From the above description it will be evident to a person skilled in the art that various modifications are possible within the scope of the invention. Although the preferred embodiments of the present invention have been described in detail, it should be apparent that modifications and variations are possible within the true spirit and scope of the invention.

Claims (24)

1. A method of channel reselection signaling in a cellular telecommunications network, said method comprising the steps of:

a connection establishment request is received from the mobile station,

notifying that the connection establishment request must be denied if the cellular telecommunications network cannot provide the requested connection;

the cellular telecommunications network indicating to the mobile station in a connection rejection message information about the value of at least one parameter relating to connection establishment used at the time of the new connection establishment attempt;

transmitting the connection rejection message from the cellular telecommunications network to the mobile station.

2. The method according to claim 1, characterized in that said connection rejection message is a radio resource control, RRC, connection rejection message.

3. A method according to claim 1, characterized in that said information comprises information about a preferred channel for the next connection attempt.

4. The method of claim 1, wherein the information comprises frequency information.

5. A method according to claim 1, characterized in that said information comprises information about a reference time difference between a previously attempted channel and a preferred channel for a next connection attempt.

6. Method according to claim 1, characterized in that said information comprises information on the primary common pilot channel CPICH.

7. A method according to claim 1, characterized in that said information comprises information on a primary common control physical channel, CCPCH.

8. A method according to claim 1, characterized in that said information comprises scrambling code information corresponding to a certain preferred channel.

9. A method according to claim 1, characterized in that said information comprises channel code information corresponding to a certain preferred channel.

10. The method of claim 1, wherein the information comprises information about the second cellular telecommunications network.

11. A network element of a cellular telecommunications network,

the network unit comprises:

means for receiving a connection establishment request from a mobile station,

means for notifying that the connection establishment request must be denied if the cellular telecommunications network is unable to provide the requested connection;

means for indicating to the mobile station in a connection rejection message information about the value of at least one parameter relating to connection establishment used at the time of the new connection establishment attempt;

means for transmitting the connection rejection message to the mobile station.

12. A network element according to claim 11, characterized in that the network element is a network element of a radio access network of a cellular telecommunication network.

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

14. A network element according to claim 11, characterized in that said connection rejection message is an RRC connection reject message.

15. A network element according to claim 11, characterized in that the network element is configured to set information about a preferred channel for the next connection attempt into the connection reject message.

16. A network element according to claim 11, characterized in that the network element is configured to set frequency information into the connection rejection message.

17. A network element according to claim 11, characterized in that the network element is configured to set information into the connection reject message about the reference time difference between the previously attempted channel and the preferred channel for the next attempt.

18. Network element according to claim 11, characterized in that the network element is configured to set information about the primary CPICH into the connection reject message.

19. A network element according to claim 11, characterized in that the network element is configured to set information about the basic CCPCH into the connection reject message.

20. A network element according to claim 11, characterized in that the network element is configured to set scrambling code information corresponding to a preferred channel into the connection reject message.

21. A network element according to claim 11, characterized in that the network element is configured to set channel code information corresponding to a preferred channel into the connection reject message.

22. A network element according to claim 11, characterized in that the network element is configured to set information about the second cellular telecommunication network into the connection rejection message.

23. A mobile communication device in a cellular telecommunication system, wherein the mobile communication device comprises:

means for transmitting a connection establishment request to the cellular telecommunications system;

means for receiving a connection reject message if the cellular telecommunications system is unable to provide the requested connection;

means for observing at least one parameter of the connection rejection message;

means for setting a value of at least one parameter for a new connection establishment attempt based at least in part on information in the at least one parameter of the connection rejection message;

means for performing channel selection by attempting to establish a new connection using the set value of the at least one parameter.

24. A cellular telecommunications system comprising a network element and a mobile communications device, the mobile communications device being arranged to communicate a connection establishment request to the cellular telecommunications system, the network element being arranged to notify that the connection establishment request must be denied if the cellular telecommunications system is unable to provide the requested connection;

it is characterized in that the preparation method is characterized in that,

the network element is arranged to comprise:

means for indicating to the mobile communication device in a connection rejection message information about the value of at least one parameter relating to connection establishment used in the new connection establishment attempt,

means for transmitting the connection rejection message to the mobile communication device;

the mobile communication device includes:

means for observing at least one parameter of the connection rejection message;

means for setting a value of at least one parameter for a new connection establishment attempt based at least in part on information in the at least one parameter of the connection rejection message;

means for performing channel selection by attempting to establish a new connection using the set value of the at least one parameter.