WO1995022870A2

WO1995022870A2 - Establishment of a prioritized telecommunication connection

Info

Publication number: WO1995022870A2
Application number: PCT/FI1995/000050
Authority: WO
Inventors: Hannu Vaitovirta
Original assignee: Nokia Telecommunications Oy
Priority date: 1994-02-08
Filing date: 1995-02-06
Publication date: 1995-08-24
Also published as: FI98033C; FI940572A0; AU1579295A; FI98033B; FI940572A7; WO1995022870A3

Abstract

The invention relates to a method and a mobile radio system for establishing a prioritized telecommunication connection between desired subscribers at least one of which is a mobile station (MS, 240) in a mobile radio system comprising a base station (1), when said base station has no unoccupied radio units (222-224) for the prioritized telecommunication connection to be established, in which method one (222) of the occupied radio units (222-224) of said base station (1) is allocated to said prioritized telecommunication connection to be established. For establishing the prioritized telecommunication connection, the radio unit (222) of the base station allocated to said prioritized telecommunication connection is directed to tune to a new channel reserved for the prioritized telecommunication connection, the mobile station (MS, 240) is directed to said new channel, and a prioritized telecommunication connection is established between the desired subscribers.

Description

Establishment of a prioritized telecommunication connection

Field of the invention The invention relates to a method for establishing a prioritized telecommunication connection between desired subscribers at least one of which is a mobile station in a mobile radio system comprising a base station, when said base station has no unoccupied radio units for the prioritized telecommunication connection to be established, in which method one of the occupied radio units of said base station is allocated to said prioritized telecommunication connection to be established.

Background of the invention

In systems according to the prior art, a prioritized call, for example an emergency call or a call with a high priority, can be established in two ways. One way is a method and a system where an ongoing call is released to give way to a prioritized call. In such a case, the system receives a request for an emergency call in response to which it searches for unoccupied traffic channels. This operation can be performed by, for example, the exchange or the base station of the mobile radio system. The system notices that the base stations where the prioritized call is to be established have no unoccupied traffic channel. Then the system selects a call to be released. The call is released in such a way that release messages are transmitted typically from the exchange to the base stations and radio channel units maintaining the call to be released. Next, the radio units of the traffic channels remove all subscribers on the channels needed for ti emergency call from the traffic channels. This is done for example by transmitting several release messages on each traffic channel to be released, whereby the receivers communicating on the particular traffic channel hopefully hear these release messages and stop their communication. Next, when all the subscribers are assumed to have left the desired traffic channel, the call is also released in the exchange of the mobile radio system. Thus the traffic channels become unoccupied also in the exchange, and they can be allocated for the use of the prioritized call. After this, the prioritized call is established on the unoccupied channel. This occurs in such a way that the subscribers are commanded to the traffic channel, and a message is then transmitted on the traffic channel instructing all subscribers not concerned with the call to leave the channel.

This arrangement according to the prior art includes the following problems.

When the method described above for releasing another call to give way to a prioritized call is utilized, it takes a long time to establish the prioritized call, since the ongoing call, i.e. the call which has reserved that particular radio unit of the base station on a previous channel, must be released first, and the mobile stations communicating on that channel must be commanded to leave the channel. Furthermore, it is not sure then whether all the subscribers of the released call have actually been removed from that traffic channel. Another drawback of the arrangement described above is that since a channel can be released regardless of whether a mobile station was transmitting simultaneously with the release of the call, an extra subscriber, which was itself transmitting at the time the exchange transmitted, through the base stations, the release messages for that call, may be left in the call. It is also possible that several subscribers remain on . the channel of the call to be released.

A further disadvantage of the arrangement according to the prior art is that the channel is possibly not taken for a new call as long as there is a transmission going on on the channel. It can thus go on until the transmission of the parties of the call to be released is over. Thus the release of the call also takes a long time. The drawback is then that a new urgent call cannot be established.

Furthermore, when it is to be insured that the release message transmitted by the base station gets through and therefore duplex radio phones which may simultaneously transmit and receive are used, the drawback of the arrangement according to the prior art is that such radio phones are expensive and large.

If simplex radios which can only receive or transmit at the same time are used instead of the duplex radios, the drawback of the arrangement according to the prior art is that the radio phone has to have breaks during the transmission and to listen to a release message transmitted by the base station. The problem in such a case is that the transmission can be disconnected and the call released only when the transmitting mobile station has a break in its transmission. If there are several breaks in an analogue system, they deteriorate the quality of speech transmission. If on the other hand, there are too few breaks, the release of the call is correspondingly slower, and thus the switching of the new urgent prior:- ized telecommunication connection will also be slower.

In the digital systems according to the prior art, it is possible to arrange breaks in the transmission without deteriorating the quality of the speech. In such a case, the breaks are utilized for establishing a signalling channel in an opposite direction. The drawback then is that the time needed for the breaks is taken from the payload data rate, which is thus diminished, or then a larger bandwidth is correspondingly needed. The bandwidth of the channel cannot usually be freely selected, wherefore any unnecessary breaks are thus taken from the payload data rate. It is also possible that even though the systems according to the prior art employ duplex mobile stations and the systems are digital, there may remain subscribers on the traffic channels in situations where they cannot hear the traffic channel for some reason or other. The subscribers remaining on the traffic channel would then possibly interfere with the prioritized telecommunication connection established on that channel according to the prior art.

Another method according to the prior art for establishing a prioritized call is a system where each base station has in reserve a spare radio unit to which a particular traffic channel is allocated for emergency calls. In such a system, it is possible to quickly establish a prioritized telecommunication connection, but a spare radio unit must be in reserve. Furthermore, in such a system each base station has to be provided with its own emergency call frequency to which that radio unit is tuned. Thus, the spare radio unit kept in reserve in the system is unused most of the time, wherefore it cannot be constantly guaranteed that when an emergency call arrives the equipment connected to this traffic channel actually works and the prioritized or emergency call can be established through that radio unit. Disclosure of the invent-on

The purpose of this. invention is to solve the above-described problems of the arrangements according the prior art by providing a method and a system for establishing prioritized calls. The purpose is to provide a method where prioritized telecommunication connections can be established quickly and reliably without the danger that subscribers of the previous call would remain in the telecommunication connection to be established and without the need for radio transmitter/receiver units reserved especially for prioritized telecommunication connections.

This new type of method for establishing a prioritized telecommunication connection between desired subscribers is achieved with the method according to the invention, which is characterized by the following steps: the radio unit of the base station allocated to said prioritized telecommunication connection is directed to tune to a new channel reserved for the prioritized telecommunication connection, the mobile station is directed to said new channel, and a prioritized telecommunication connection is established between the desired subscribers.

The invention also relates to a mobile radio system comprising a base station, the radio units of which have a radio connection with at least one mobile station, switching means for switching telecommunication connections between desired subscribers. The mobile radio system according to the invention is characterized in that the system comprises control means for directing the radio unit of the base station allocated to the prioritized telecommunication connection to tune to a new channel reserved for a prioritized telecommunication connection, for establishing a telecommunication connection. The invention is based on the idea that when a prioritized telecommunication connection is to be established, a radio transmitter/receiver of a base station is directed to change its channel, i.e. its frequency and/or the frequency of its time slot. Thus, a channel which has hardly been used previously is selected for the prioritized telecommunication connection to insure that the channel contains no traffic interfering with the prioritized call to be established.

The advantage of this invention is that it solves the problems of the prior art systems and methods.

The advantage of the invention is that it provides a method and system for establishing a prioritized telecommunication connection in a faster way than in the arrangements of the prior art, without the necessity of having in reserve radio transmitter/ receiver units for a prioritized telecommunication connection at the base stations of the system.

A further advantage of the invention is that it guarantees that there are no extra subscribers in a prioritized call, e.g. an emergency call. Also, by means of the invention a call can be established quickly in a situation where there are no unoccupied channels. Another advantage is that the method employs existing, normally used radio transmitter/receiver units, i.e. in a normal situation there is no need in the system to have any spare radio transmitter/receiver units in reserve for prioritized telecommunication connections.

Another advantage of the invention is that it enables the rapid establishment of a prioritized, or emergency, call also in a situation where all traffic channels are occupied. A further advantage of the invention is that the base station used in the realization of the invention is low in price, since there is no need to reserve spare equipment, i.e. a radio unit, for the prioritized telecommunication connection.

Furthermore, it is possible to imagine a situation where problems arise in a system where a separate radio unit is reserved for a prioritized or emergency call, if another emergency call arrives and all traffic channels are occupied. By means of the arrangement according to the invention, the "extra" subscribers who have previously reserved the radio units can be effectively removed from the call or from the telecommunication connection. Another advantage of the invention is that the emergency call frequencies, i.e. the frequencies reserved for the prioritized telecommunication connections, are used effectively. In the system according to the invention, it is enough when a group of channels reserved for the use of prioritized calls are allocated to a large number of base stations. Thus, it is possible to reserve far fewer prioritized channels than there are base stations, since all base stations do not necessarily need their own prioritized channel.

List of figures

In the following, the invention will be described in greater detail with reference to the accompanying drawings, in which Figure 1 shows an exchange of a mobile radio system according to the invention,

Figure 2 shows a base station in the mobile radio system according to the invention,

Figures 3 to 8 show the contents of databases comprised by the memory means of the mobile radio systeir according to the invention during the establishment of a prioritized telecommunication connection according to . the invention.

Detailed description of the invention

Figure 1 shows an exchange 100 in the mobile radio system according to the invention. An interface unit 108 in the exchange connects the speech and other telecommunication connections arriving from base stations 101, 102 to a switching matrix 107 by means of a telecommunication connection 111, and it connects the signalling 109 to the controller 105 of the exchange 100. Besides the base stations 101, 102, other units, such as "fixed" control points or dispatchers, private automatic branch exchanges (PABX), or the exchanges of a fixed network, may be connected to the interface unit 108.

The exchange 100 also comprises a switching matrix 107, where the speech or other telecommunication of the mobile stations is connected from base stations to other base stations and, through them, to the receiving mobile stations or also to other parts ( 103, 104) through the interface unit 108.

The exchange 100 also comprises a controller 105, which makes the decisions concerning the establishment and release of calls and the allocation of resources used for a call, i.e. the use of e.g. radio frequencies and time slots, and base station channels.

The controller 105 of the exchange 100 is connected to the interface unit 108 via a data link 109, by means of which the controller 105 for example transmits data messages to the base station controller (reference numerals 211 - 214, shown in Figure 2). The controller 105 is also connected to the switching matrix 107 by means of for example logic signals through which the switchings in the switching matrix are changed to correspond to each particular call or other telecommunication connection.

The exchange 100 according to the invention comprises control means 112 for directing the base station radio unit (Figure 2, 222) allocated to the prioritized telecommunication connection to tune to a new channel reserved for the prioritized telecommunication connection, for establishing a telecommunication connection between desired subscribers. It must be noted that the aforementioned control means may be situated anywhere in the area of the mobile radio system; one possible place is the base station, another is the exchange 100. It must be noted that the channel to which the control means 112 direct the radio unit allocated to the telecommunication connection is a channel reserved for prioritized calls. The identifier of this prioritized channel is stored somewhere in the mobile radio system, for example in the memory means from where this identifier of the channel can be retrieved.

In the mobile radio system according to the invention, the aforementioned control means 112 are arranged to form and transmit a channel control message to the radio unit of the base station (Figure 2) allocated to the prioritized telecommunication. connection, the radio unit tuning to a new channel reserved for the prioritized telecommunication connection in response to the aforementioned channel control message. This occurs thus in such a way that the control -v.eans 112, which may have been placed in the controller 105, transmit a message to the base station channel controller (Figure 2, 212), the message commanding the base station controller 212 to change 231 the frequency of its transmitter/receiver 222 or the frequency of the time slot of its transmitter/receiver 222 on which the transmitter/receiver communicates.

The exchange 100 also comprises a memory means which has tables by means of which the controller 105 selects the base station channel/s and the frequency for each prioritized telecommunication connection, i.e. for example for an emergency call or a high-priority call, and after that connection is over, restores the frequency of the base station channel to the original. Figure 2 shows a base station 1 in the mobile radio system according to the invention. The base station is connected to the rest of the mobile radio system by an interface block 201 which connects the channel-specific speech and signalling arriving 101 from the exchange to the controllers 211 to 214 of the base station channel. Controller 211 is for a control or calling channel, and the other controllers 212 to 214 are for traffic channels. Naturally, the controllers may also be provided as one integrated controller. In this invention, only the traffic channel controllers 212 to 214 are important, since it is worthwhile to change the channel of a traffic channel only, i.e. to change the frequency or the frequency of the slot of the traffic channel. Naturally, it is also possible to change the frequency of a control, or calling, channel. This could be done in the case of decentralized and dynamically allocated calling channel arrangements. The base station 1 also comprises radio units, i.e. radio transmitter/ receivers. The radio units are connected to a combiner, 202, which directs the radio-frequency signals to an antenna 203. The antenna is connected via a radio path to a mobile station MS, 240 within the coverage area of the base station. The base station 1 of the mobile radio system according to the invention comprises means 210, responsive to the aforementioned control means (Figure 1, 112), for directing 231, 232, 233 a previously occupied_. radio unit 222 to 224 of the base station to tune to a new channel reserved for a prioritized telecommunication connection, for establishing a prioritized telecommunication connection.

Figures 3 to 8 show a case where all the channels, i.e. in fact radio units, of the base station 1 are occupied, when a request for a prioritized call, for example an emergency call, arrives at the controller 105 of the exchange 100 (Figure 1). The prioritized call must be established at the base station 1, whereupon the following occurs:

The controller 105 of the exchange 100 examines in its memory means 106, one database of which is shown in Figure 3, whether the base station 1 has an unoccupied traffic channel.

After this, the controller 105 notices that all radio units 222 to 224 or channels of the base station 1 are occupied, whereupon the controller 105 selects from the base station 1 channel number 2, i.e. a traffic channel, for the prioritized call, from the database, shown in Figure 3, comprised in the memory means of the exchange. That channel is used in the base station 1 by radio unit 222. After this, the controller 105 selects from Figure 4 the next unoccupied emergency call frequency, in this case frequency 031, which it allocates to the prioritized telecommunication connection to be established.

After this the control means 112 of the mobile radio system transmit a channel control message to the controller 212 of the channel 2 of the base station 1 via the interface unit 108, a transmission path and the interface block 201, the message commanding the controller to change 231 the frequency of its radio 222 to a new one, i.e. to frequency 031. Thus the mobile stations, for example radio phone subscribers, which were having a call on that channel 2 lose their telecommunication connection.

After this, the controller 105 establishes the prioritized telecommunication connection through the radio unit 222 on the new traffic channel 031, which may be a new frequency or a new frequency and a time slot.

Next, the controller 112 of the exchange 100 updates the databases in the memory means 106 to the spaces shown in Figures 5 and 6.

When the established prioritized tele¬ communication connection is over, the following occurs:

The controller 112 of the exchange 100 receives information about the release of the connection, and the traffic channel is cleared.

The controller 112 examines from the database of the memory means 106, shown in Figure 6, to which frequency the traffic channel taken to the emergency call is restored, i.e. in this case to frequency 007. After this, the controller 112 transmits, via the interface unit and block, a message to the controller 212 of the channel 2 of the base station 1, the message commanding the controller 212 to change the frequency or channel of its radio 222 to the original, i.e. to frequency or channel 007.

Next, the controller 112 of the exchange 100 updates the databases in the memory means to the spaces shown in Figures 7 and 8.

The operation of the invention can also be described in the following way. First, a request for a prioritized telecommunication connection, for example an emergency call, arrives at the exchange 100. The exchange notices that there is no unoccupied traffic channel for the emergency call to be established. Thus the exchange 100 selects the call to be released, i.e. channel 007. A channel control message is transmitted to the controller 212 (which is at the base station 1) of that particular traffic channel unit, the message commanding the controller to tune its radio unit 222 to a new frequency 031. After this, the prioritized telecommunication connection, e.g. an emergency call, is established on this traffic channel 031. Thus, the call which was maintained on the channel 007 by the radio unit 222 is disconnected in the exchange 100. The frequency or channel 007 used in the disconnected call can be marked as a frequency that can be used for a possible new emergency call.

The drawings and the description related thereto are only meant to illustrate the idea of the invention. The details of the method and the mobile radio system according to the invention for establishing a prioritized telecommunication connection may vary within the scope of the claims.

Claims

Claims :

1. A method for establishing a prioritized telecommunication connection between desired subscribers at least one of which is a mobile station (MS, 240) in a mobile radio system comprising a base station ( 1 ) , when said base station has no unoccupied radio units (222-224) for the prioritized telecommunication connection to be established, in which method one (222) of the occupied radio units (222-224) of said base station (1) is allocated to said prioritized telecommunication connection to be established, the method being c h a r a c t e r i z e d by the following steps: the radio unit (222) of the base station allocated to said prioritized telecommunication connection is directed to tune to a new channel (031) reserved for the prioritized telecommunication connection, the mobile station (MS, 240) is directed to said new channel, and a prioritized telecommunication connection is established between the desired subscribers.

2. A method according to claim 1, c h a r a c t e r i z e d in that said step, where the radio unit (222) of the base station is directed to tune to the new channel (031), comprises the following steps: a channel control message is transmitted to the base station. in response to said channel control message, the base station tunes (231) the radio unit (222) allocated to said prioritized telecommunication connection to the channel (031) defined in the channel control message.

3. A method according to claim 2, c h a r a c t e r i z e d in that said channel control message is transmitted from the mobile switching exchange ( 100) to the base station ( 1 ) of the mobile radio system.

4. A method according to claim 1, 2 or 3, c h a r a c t e r i z e d in that after said prioritized telecommunication connection is over, said radio unit (222) tuned to the channel reserved for the prioritized telecommunication connection is tuned back to its previous channel (007) .

5. A method according to claim 1, 2, 3 or 4, c h a r a c t e r i z e d in that the channel of the telecommunication connection previously maintained by the reserved radio unit (222) is allocated to a channel to be used for a new prioritized telecommunication connection.

6. A method according to claim 1, 2, 3, 4 or 5, c h a r a c t e r i z e d in that said prioritized telecommunication connection is an emergency call.

7. A method according to claim 1, 2, 3, 4, or 5, c h a r a c t e r i z e d in that said prioritized telecommunication connection is a call with a high priority.

8. A mobile radio system comprising a base station (1), the radio units (221-224) of which have a radio connection with at least one mobile station (MS, 240), switching means ( 107) for switching telecommunication connections between desired subscribers ( 240, 102, 103 , 104 ) , c h a r a c t e r i z e d in that the system comprises control means (112) for directing (231) the radio unit (222) of the base station allocated to the prioritized telecommunication connection to tune to a new channel (031) reserved for a prioritized telecommunication connection, for establishing a telecommunication connection.

9. A mobile radio system according to claim 8, c h a r a c t e r i z e d in that the channel (031) to which the control means direct the radio unit (222) allocated to the telecommunication connection is a channel reserved for prioritized calls.

10. A mobile radio system according to claim 8, c h a r a c t e r i z e d in that said control means (112) are arranged to form and transmit a channel control message to the radio unit (212, 222) of the base station ( 1) allocated to the prioritized tele¬ communication connection, the radio unit tuning to a new channel (031) reserved for the prioritized telecommunication connection in response to said channel control message.

11. A mobile radio system according to claim 8, 9 or 10, c h a r a c t e r i z e d in that said base station (1) of the mobile radio system comprises means (210), responsive to said control means (112), for directing the previously reserved radio unit (222) of the base station (1) to tune to a new channel (031) reserved for a prioritized telecommunication connection, for establishing a prioritized telecommunication connection.