WO1997013385A1

WO1997013385A1 - A method for maintaining a connection in a mobile communication system during a battery change in a mobile communication device

Info

Publication number: WO1997013385A1
Application number: PCT/FI1996/000504
Authority: WO
Inventors: Esa Lauri; Matti Sangi; Jari Schroderus; Hannu Hietalahti
Original assignee: Nokia Mobile Phones Limited
Priority date: 1995-10-04
Filing date: 1996-09-25
Publication date: 1997-04-10
Also published as: AU6990596A; FI954713A; FI954713A0; FI100936B

Abstract

A method for maintaining a connection established in a communication network to or from a mobile communication device, which connection can be divided into a connection which includes a radio connection (21) between the mobile communication device and the network and a connection (22) within the network, is characterized in that the mobile communication device (MS) sends the network (MN) a first message (23) which indicates that a battery change will be performed, the connection (21) between the mobile communication device and the network is disconnected and the battery change (27) is performed, as a response to the first message (23), the connection (22) within the network is maintained, the mobile communication device (MS) sends the network (MN) a second message (28) which indicates that the batteries have been changed and starts signaling aimed at re-establishment of the connection (21) between the mobile communication device and the network.

Description

A method for maintaining a connection in a mobile communication system during a battery change in a mobile communication device

The present invention is related to maintaining a connection in a mobile communication system during a battery change in a mobile communication device.

Mobile communication devices increasingly are very small, battery-operated portable telephones. Although said devices are being developed to consume less power, and although operation of said devices has been developed to save batteries as much as possible, it is still a common occurrence for a battery to become empty during usage. Naturally, this also is affected by the fact that batteries are made as compact as possible, sacrificing their energy-storing capacity. The situation is troublesome to a user when a battery becomes empty during an important call and a battery change causes a connection to be lost.

Current mobile communication devices are designed to allow very quick battery changes, requiring only a few seconds, if a replacement battery unit is readily available. Thus, a battery change would not significantly disturb a call or data connection if the change could be performed without losing the connection. In some mobile communication systems, a rapid battery change can be performed within the framework of normal operation which maintains a connection when a radio connection is temporarily lost. One such system is the nordic NMT 900, whose operation related to maintaining a connection is examined in more detail later. In said system, a battery change is possible due to the fact that both the mobile communication device and the network incorporate time monitoring with a limit within which a connection in the network is maintained and a radio connection which is temporarily lost (due to a strong shadow region, for example) can be restored. The mobile communication device must be able to return to the radio connection or re¬ establish the connection after the interruption in power caused by the battery change.

In the situation described above, the battery change occurs without any special function having been defined in the mobile communication device for that purpose and without the network knowing why the radio connection was lost. Solutions are known in the art which have been developed especially to maintain a radio connection during a battery change, with one such solution presented in GB patent application 2 240 010. In said patent application, the connection data of the current connection are stored in the mobile communication device when an alarm indicating an empty battery is received. When the mobile communication device ceases to send a control signal during the battery change, a base station maintains a connection to the device in the network for a predetermined period of time. If the battery is changed within said period, the mobile communication device re- establishes the connection between itself and the base station, based on the connection data stored within the device. The problem with this solution is, firstly, that it requires implementation of a considerably large change in the operation of a mobile communication device. In the primary embodiment presented in the publication, the mobile communication device has a separate processor and peripheral functions for said operation. Another problem is that the network does not know in this solution, either, that a battery is being changed. Therefore, operation in the network must be defined so as to maintain the connection to the base station in the network for a certain predefined period of time after reception of the control signal from the mobile communication device has ceased. Therefore, said period must be relatively short, and there is no way to be sure that the battery will be changed within said period.

DE patent application 40 01 412 presents a solution in conjunction with a wireless telephone system which eliminates the latter of the problems mentioned above. In said patent application, the wireless telephone automatically sends a base station a certain specific information when the battery is removed. As a result, the base station maintains a connection from the base station onward and begins to send connection-establishing data to the wireless telephone via the same channel in which the connection existed. The base station does this for a certain period of time, and if the battery is changed within said period and the wireless telephone begins to function again, it will immediately receive necessary connection-establishing data and will be able to form a new connection to the base station and the connection from the base station onward which was maintained by the base station.

In the NMT 900 system, the possibility of maintaining a connection while a battery is being changed is based on a mobile communication device function which is essentially the same as the one in the above-mentioned GB-2 240 010 publication. At the beginning of a call, the mobile telephone always stores cellular-status data including communication area identification and channel identification in EPROM memory. A 5 - 6-second time monitoring period is realized in the mobile telephone, with a limit within which a connection between the mobile telephone and a base station can be disconnected and then restored, based on the data stored in the EPROM memory. By exploiting this function, the battery of the telephone can be changed within the 5 - 6-second time monitoring framework without losing the connection. This solution contains the problems stated in the above examination of the publication GB-A 2 240 010.

A method according to the present invention for maintaining a connection established in a communication network to or from a mobile communication device, which connection can be divided into a connection including a radio connection between the mobile communication device and the network and a connection within the network, while the battery of the mobile communication device is being changed, is characterized in that said method includes steps in which: a mobile communication device sends a network a first message which indicates that a battery is going to be changed, as a response to the first message, a connection within the network is maintained, a connection between the mobile communication device and the network is disconnected and the battery is changed, the mobile communication device sends the network a second message which indicates that the battery has been changed and starts signaling aimed at re- establishment of the a connection between the mobile communication device and the network.

I The method according to the present invention is based on signaling between the mobile communication device and the network. In one advantageous embodiment of the present invention, the mobile communication device first sends the network a message indicating that the battery is going to be changed. The network acknowledges the message with a reply message and thereafter the connection between the mobile communication device and the network is disconnected in a normal manner and by means of appropriate signaling. This differs from normal operation in that the network knows the connection was disconnected for the purpose of changing the battery and the connection between the network and the mobile communication device will be promptly re-established. Thus, the network intentionally continues to reserve other connection resources within the network for a longer time than the conventional time monitoring limit which is applied when a connection is lost. When the mobile communication device begins to operate again after the battery has been changed, the device informs the network of its operation and the connection between the network and the mobile communication device is re¬ established in a normal manner and by means of appropriate signaling.

In another embodiment of the present invention, the network is informed by means of a battery change message that the battery will be changed and the radio connection between the mobile communication device and the network is allowed to be lost in conjunction with the battery change. Before the connection is lost, data needed for re-establishing a radio connection are stored in the mobile communication device. As a response to the battery change message it receives, the network maintains readiness to re-establish a radio connection. After the battery has been changed, a radio connection is re- established by the mobile communication device.

In one advantageous embodiment of the present invention, messages indicating a battery change and completion of said change are realized by means of messages and signaling procedures already defined in a system. Only very little new functions and additional definitions in the messages are necessary. For example, in a GSM system, which is a primary application of the present invention, realization of the present method requires only relatively minor modifications and additions to functions in both the mobile communication device and the network.

A benefit of the method according to the present invention compared to methods of the prior art is that the whole battery change procedure is completely under control without dependency on time monitoring limits defined in a system for situations in which a connection is lost. A battery change function can be defined in a mobile communication device and the method according to the present invention is automatically performed when a user selects said function by means of a user interface. A period of time can be reserved for a battery change in which the battery can be changed easily and surely. Because realization of said method does not require implementation of major modifications in the functions of a network, it is easy to obtain the support of network operators. Because the method is based on an exchange of messages between a mobile communication device and a network, it is easy to determine whether or not the network supports the method. Moreover, realization of the method in a mobile communication device does not prevent a battery change and maintaining of a connection within the limit of a system's normal operation and time monitoring, if a network does not support the method of the present invention.

The present patent application uses the definition "a connection formed in a communication network to or from a mobile communication device, which connection can be divided into a connection including a radio connection between the mobile communication device and the network and a connection within the network" . This means that a communication connection formed in a communication network can be divided, for example, so that a connection between a mobile communication device and a network is only a radio connection between the mobile communication device and the network, that is, a base station of the network, and, on the other hand, for example, the connection between the mobile communication device and the network is a connection from the mobile communication device to a mobile telephone exchange or base station controller. A connection within a network refers in all cases to all other connection resources in the network and possibly another network, which together with the connection between the mobile communication device and the network form said communication connection. A communication connection typically is a voice connection which is established between a subscriber operating a mobile communication device and another subscriber, a subscriber of a fixed or mobile communication network. The formed connection also may be a data connection.

The present invention and its various embodiments are described in detail below, with references to the enclosed drawings.

Figure 1 is a flow chart which generally describes an embodiment of the present invention,

Figure 2 is a diagram which generally describes a method and related signaling according to the present invention,

Figure 3 (a) and 3 (b) are signaling diagrams which describe signaling used in the method according to the present invention, PCI7FI96/00504

8

Figure 4 is a signaling diagram which describes an embodiment of the method according to the present invention.

Figure 1 presents a possible realization of a method according to the present invention as a flow chart. As part of the normal operation of a mobile communication device, it gives an alarm to the user when only a small part of a battery's charge is left. If the alarm indicating an empty battery is given when a call or data connection is active, the method of the present invention can be implemented to maintain the connection while the battery is changed. In an advantageous embodiment of the present invention, a battery change function can be selected from a menu of the user interface of the mobile communication device during a call in phase 2 of the flow chart in figure 1. In such a case, the mobile communication device sends a message to the network during phase 3 informing that the battery is going to be changed. The method naturally can be initiated by something other than a menu selection, such as a certain keyboard entry, or it can happen automatically. Because the method according to the present invention is based on signaling between a mobile communication device and a network, it will only function if the network with which the mobile communication device is communicating supports said method. The message indicating the battery change and the method of sending the message are advantageously realized so that if the network does not support the method in phase 4, it nevertheless will reply with a status message in phase 5, indicating that it did not understand said message and otherwise will not react to said message. In such a case, application of the method ends in phase 12. This type of definition of operation is advantageous in that it guarantees compatibility with existing networks realizations and in that the battery change function can be realized in a network as an option. If the network supports the method in phase 4, it replies to the battery change message with an acknowledgement in phase 6. Then the connection between the mobile communication device and the network is disconnected in phase 7, advantageously by means of a normal signaling procedure. At the same time, the network, which now knows that the battery is being changed in the mobile communication device, keeps other connection resources reserved for the connection. The network can also inform the other party of the connection about the cause for the loss of communication. The user changes the battery during phase 8. After the battery has been changed, in phase 9 the mobile communication device sends the network a message which starts signaling aimed at re-establishment of the connection between the network and the mobile communication device. In phase 10 the network and mobile communication device continue signaling to re-establish the connection. The signaling of phases 9 and 10 can be normal signaling of the system which starts automatically when the mobile communication device becomes active after the battery has been changed. Alternative signaling iε examined in more detail later. In phase 11 the connection between the mobile communication device and the network has been re¬ established and operation continues normally using the maintained connection.

The signaling and connection diagram of figure 2 describes operation according to the present method. A connection has been established from the mobile communication device MS of subscriber A via a network MN to subscriber B. The connection is made up of a connection 21 between the mobile communication device MS and the network MN and a connection 22 within the network, which here means all other connection resources between the subscribers A and B. When it is necessary to change the battery, mobile communication device MS informs the network MN of the need for a battery change with a message 23 which the network MN acknowledges with a message 24. Then signaling between the mobile communication device MS and the network MN continues for the purpose of disconnecting the connection between them, ending in a message 26 which may be a message indicating that the disconnection between the network and the mobile communication device has been completed. The connection 21 has now been disconnected, but the other connection resources 22 in the network are kept reserved. A block 27 enclosed by a dotted line indicates the battery change. When the battery has been changed, the mobile communication device MS sends the network a message 28, after which signaling between the mobile communication device MS and the network MN continues for the purpose of re-establishing a connection between them, ending with a signaling message 29. The connection 21 has now been re- established and the connection between the subscribers A and B formed by said connection and the connection 22 has been maintained during the battery change.

Figures 3 (a) and 3 (b) are signaling diagrams which generally present signaling which is an essential part of the method according to the present invention. Signaling according to the present invention is started by a message 31 sent by the mobile communication device MS to the network MN indicating that the battery is going to be changed. The network MN acknowledges said message with a message 32. The network MN now knows that the battery is being changed in the mobile communication device and the mobile communication device knows that the network supports the battery change function. Then the connection between the network and the mobile communication device is disconnected or it is lost and the user changes the battery in the manner shown in block 33. After the battery has been changed, the mobile communication device MS initiates signaling for the purpose of re-establishing a connection by means of a message 34 which also informs the network MN that the battery in the mobile communication device has been changed. The message 34 indicating that the battery has been changed may be a request to re-establish a connection, and the network MN may reply with a message 35 which approves the request.

Figure 3 (b) describes signaling in a situation in which the network does not support a battery change function. In such a case, the network MN replies to the battery change message 31 with a status message 36 which indicates that it did not understand the received message. The mobile communication device and the user now know that the battery cannot be changed without a risk of losing the connection.

The following paragraph examines alternate ways of realizing the method according to the present invention in a GSM mobile communication system or PCN and DCN systems having corresponding signaling, which are primary applications of the method according to the present invention. The signal diagram of figure 4 presents one possible embodiment. In said embodiment, a battery change message 41 is a DISC message of a CC sublayer, or a call control sublayer, of an L3 layer, which message indicates a lost connection, and which differs from the specifications of the system in that the cause for the loss is defined as a battery change. This message type includes a cause field whose possible values have not all been used. A new cause, which is a battery change, is now taken into use in the cause field. The network MN replies with an acknowledgement message 42 which is a disconnect message with the same value representing a battery change in its cause field. The connection between the mobile communication device MS and the network MN are now disconnected according to normal signaling procedures in all signaling layers. When the user has changed the battery in the manner shown in block 43, the following signaling for the purpose of re-establishing a connection between the mobile communication device and the network can be initiated by means of normal location updating, for example. When the power is switched on again, which the mobile communication device MS advantageously performs automatically, the device can also automatically send a channel request message 44, which starts the location updating. When the network MN has sent a message 45 ending the location updating, the mobile communication device will have been registered in the network again by means of its subscriber identification, IMSI. The network MN, in which the other connection resources have been reserved, starts re-establishing a connection between the network and the mobile communication device by means of a message 46 whose cause field again contains a value representing a battery change. Then the connection between the network and the mobile communication device is re-established by means of normal signaling ending with a message 47 by which the mobile communication device indicates that the connection has been established, and which the network MN acknowledges with message 48.

In D-AMPS system Release message (according to specification IS-136.2, item 2.7.3.1.3.2.8) and information element Release Reason thereof may be used for disconnecting the connection between the mobile communication device and the network in accordance with the invention. Correspondingly, Registration message (according to specification IS-136-1, item 6.4.4.12 for digital control channel or IS-136.2, item 2.7.1.1 for analog control channel) may be used to indicate that the battery change has been performed and to start signaling aimed at re-establishment of the connection.

In the alternative presented above, the re-establishing of a connection between the network and the mobile communication device is performed by the network. A mobile telephone center of the communication region in question in the network knows the IMSI identification of the mobile communication device, which includes information indicating that the battery is being changed in the mobile communication device in question. When the mobile telephone exchange receives the IMSI identification of the mobile telephone in conjunction with the location updating after the battery has been changed, it begins to re-establish a connection from the connection waiting within the network to the mobile communication device. In order to make it relatively simple to re-establish a connection in the network, the mobile communication device must remain in the same mobile communication network and the same traffic area, i.e., the region of the same. obile telephone exchange, while the battery is being changed. In any case, the realization must take into account the possibility that a connection between the network and the mobile communication device cannot be re-established, and therefore, a reasonable time limit must be set for maintaining the connection within the network. If the mobile communication device has moved to another traffic area during the battery change, or if re-establishment of a connection from the network to the mobile communication device is not possible for some other reason, the connection within the network is disconnected after a specified period of time has elapsed. The realization requires of the network firstly that it links battery change data to a specific IMSI identification. The network also must ensure that the connection to the mobile communication device in question is only disconnected between the network and the mobile communication device and the other connection resources in the network are reserved for said connection. The network must also link the reserved connection resources to the IMSI identification, and when information is received indicating that the IMSI identification has been registered again, the network must establish a connection to the mobile communication device, connect the device to the reserved connection resources and then restore the relationship between the mobile communication device (IMSI identification) and said connection to normal operation. This realization requires some definition and realization of new functions in the network.

The method according to the present invention can also be realized by having the mobile communication device take care of re-establishing a connection between the network and the mobile communication device. In such a case, a user action initiating a battery change, such as a selection from a menu, results in the mobile communication device storing status data of active connections and other necessary data, such as data indicating that the battery is being changed, in permanent memory for the duration of the period of no power. Then the mobile communication device sends a battery change message to the network. The message could be an MM layer IMSI_DETACH, for example, enhanced with new information defined for this purpose, or a new L3 message. This message is needed primarily so that when the connection is lost, the network will allow the user more time to change the battery than is available within the normal time monitoring limit of the system related to a loss of a radio connection. No other operation by the network is necessarily required related to the battery change, but, based on the message indicating the battery change, the network could send a message regarding the battery change to the other party. The battery change message must be defined in such a way that if the network does not support the battery change function and does not understand the message, it will nevertheless reply to the message with a status message which indicates that it does not support the battery change function. When the power is turned on after the battery has been changed, which the mobile communication device advantageously performs automatically without any action of the user, the device detects that the battery has been changed in the middle of a call or data connection and requests re- establishment of a connection. In this manner the radio connection lost when the battery was changed is re¬ established. Except for the radio connection, all other connection resources have been kept reserved for this connection, so re-establishment of the radio connection is sufficient to restore the connection.

Embodiments of the present invention were described above, which in no way place limits on the present invention, but rather the present invention can vary within the limits of the enclosed claims.

Claims

1. A method for maintaining a connection established in a communication network to or from a mobile communication device, which connection can be divided into a connection which includes a radio connection (21) between the mobile communication device and the network, and a connection (22) within the network, while a battery change is performed in the mobile communication device, characterized by steps in which: the mobile communication device (MS) sends the network (MN) a first message (23) which indicates that the battery change will be performed, as a response to the first message (23) , the connection within the network is maintained, the connection (21) between the mobile communication device and the network is disconnected and the battery change is performed (27) , the mobile communication device (MS) sends the network (MN) a second message (28) which indicates that the battery change has been performed and starts signaling aimed at re-establishment of the connection (21) between the mobile communication device and the network.

2. The method according to claim 1, characterized in that the connection between the mobile communication device and the network is disconnected by means of normal signaling procedures.

3. The method according to claim 1, characterized in that the connection between the mobile communication device and the network is disconnected by disconnecting a radio connection between the mobile communication device and the network.

4. The method according to one of the above claims, characterized in that the second message is a message (44) initiating a location updating procedure of the mobile communication device.

5. The method according to claim 3, characterized in that the second message is a message (34) requesting re- establishment of the radio connection.

6. The method according to one of the above claims, characterized in that data required for re-establishing the connection between the mobile communication device and the network is stored in the network.

7. The method according to one of the claims 1 - 5, characterized in that data required for re-establishing the connection between the mobile communication device and the network is stored in the mobile communication device.

8. The method according to one of the above claims, characterized in that the first message is a signaling message including a cause field, the value of which field indicates a battery change.

9. The method according to one of the above claims, characterized in that the mobile communication device (MS) is a GSM system mobile communication device.

10. The method according to claim 9, characterized in that the first message is a layer L3 signaling message (41) .

11. The method according to claim 9, characterized in that the first message is an IMSI_DETACH message enhanced with additional data indicating a battery change and the second message is an IMSI_ATTACH message.

12. The method according to one of the claims 1-8, characterized in that the mobile communication device

(MS) is a D-AMPS system mobile communication device and that the first message is a Release message and the second message is the Registration message.