METHOD FOR REALIZING AMBIENCE LISTENING, AND RADIO UNIT

Abstract: The invention relates to a method and radio unit for activating ambience listening in which a first radio unit (RU1) transmits (103) ambient sounds and voice to a second radio unit (RU2) over a radio path. To check that the second radio unit (RU2) has listening authority, the second radio unit (RU2) commands (101) the first radio unit (RU1) to transmit (103) ambient sounds and voice to the second radio unit (RU2); in response to the command (101) given by the second radio unit (RU2), the first radio unit (RU1) checks (102) the listening authority of the second radio unit (RU2); and if the second radio unit (RU2) has the listening authority, the first radio unit (RU1) starts transmitting (103) ambient sounds and voice to the second radio unit (RU2).

Description: 1 Method for realizing ambience listening, and radio unit Field of the invention The invention relates to a method for activating ambience listening in which a first radio unit transmits ambient sounds and voice to a second radio unit over a radio path. Background of the invention The invention relates to radio tele¬ communications systems. A subscriber of a radio telecommunications system, i.e. a radio unit or a subscriber station, such as a mobile phone or some other means of communication, may be registered in a radio network or radio system through system or traffic channels maintained by the base stations of the radio network. Apart from system channels of radio tele¬ communications systems, direct mode channels can also be used, i.e. direct mode operation can be applied. Radio units or subscriber stations using direct mode operation do not communicate with a radio network or its base stations. Direct mode channels are frequencies or channels at which mobile phones or other means of communication are able to communicate directly with one another without the system. Direct mode channels are typically used in cases where e.g. a plural number of hand-portable mobile phones communicate with one another at such a distance from the base station that system channels cannot be used. Another important use of direct mode channels is in the addition of capacity when traffic increases rapidly in one part of the service area of the system, e.g. at one point of the radio network. A direct mode channel is also called a direct or simplex channel, or a simplex connection. A direct mode channel is a channel that is typically not at all used by the system. It may be, for example, a channel with the same channel spacing as the channels of the system, e.g. 12.5 kHz or 25 kHz. Of the mobile phones operating on the direct mode channel, the transmitting station has tuned its transmitter to the channel and transmits speech or data information. The other mobile phones set to direct mode operation have tuned their receivers to the same channel, whereby they are able to directly hear the transmission. On a direct mode channel, both analogue modulation and digital modulation can be used. The mobile phone transmitting on the channel can also send signalling information, such as information about access rights and priorities or a group operating on the channel. On a direct mode channel, messages can be encrypted, or speech can be transmitted in clear form. Radio units, i.e. subscriber stations, operating in direct mode communicate with other radio units on a direct mode channel, without necessarily being in direct contact with the base stations of the radio network. In private mobile radio systems PMR, it is conventional to use an ambience listening function, in which the speech paths of a radio unit, such as a mobile phone, are opened and the transmitter is activated without any indication to the user interface of the mobile phone. In prior art solutions, it has been possible to activate ambience listening either from the mobile phone listened to or through the system from another terminal equipment. When the ambience listening function is activated from the mobile phone listened to, the call is forwarded to a predetermined number, usually to a dispatcher or a station on duty. The direct mode channels of the prior art operate on a so-called open channel principle. This means that a mobile station can call another mobile station or other mobile stations using selective calls. Actual signalling is not used in the prior art systems. On a direct mode channel of the prior art, ambience listening has not been realized. It is impossible to activate the ambience listening function from another mobile phone that operates on the direct mode channel. Yet this would be an important characteristic precisely in the PMR systems, since PMR systems are often used by the authorities, e.g. by the police and in rescue operations, where it is of great advantage if a radio unit can be activated by remote control to transmit ambient sounds and voice. An example for a situation where this characteristic is needed is a situation where a first radio unit, i.e. mobile station, has fallen into the wrong hands and a second radio unit wants to secretly listen to what is spoken near the first radio unit. Description of the invention It is an object of the present invention to provide a method and radio units by which ambience listening can be realized on a direct mode channel. Another object of the invention is to solve the problems of the prior art solutions, i.e. to make it possible to use the ambience listening function in radio units communicating on a direct mode channel. Yet another object of the invention is to provide a method and a radio unit by which ambience listening can be conducted safely, e.g. on a direct mode channel. The object of the invention is thus that not anybody can listen to just anyone by using the ambience listening function, but the ambience listening function can be activated from specified entities only. This new kind of method for activating ambience listening is achieved with the present invention, the method being characterized in that the second radio unit commands the first radio unit to transmit to the second radio unit the ambient sounds and voice; in response to the command given by the second radio unit, the first radio unit checks the listening authority of the second radio unit; and if the second radio unit has the listening authority, the first radio unit starts transmitting ambient sounds and voice to the second radio unit. The invention also relates to a radio unit for ambience listening in which the radio unit transmits ambient sounds and voice to a second radio unit over a radio path, the radio unit comprising a transceiver unit and means for transmitting the ambient sounds and voice through the transceiver. An inventive radio unit according to a first embodiment of the invention further comprises memory means for storing the identifiers of the other radio units that are authorized to activate ambience listening at said radio unit, and comparison means for comparing the identifiers contained in the activate-ambience- listening messages transmitted by said other radio units with the identifiers stored in the memory means and, if it appears in the comparison that the same identifier is found in the memory means and in the activate- ambience-listening message, for activating ambience listening at said radio unit. An inventive radio unit according to a second embodiment of the invention is characterized by further comprising means for generating a random number and transmitting it to a radio unit that has commanded the first radio unit to start ambience listening; memory means for storing a key number characteristic of the radio unit; means for computing a reference number from said random number and said key number and for storing that reference number; means for comparing the reference number with a response number received by the radio unit and computed by some other radio unit and, if the numbers are identical, for activating the ambience listening function at the radio unit. The invention also relates to a radio unit for ambience listening in which the radio unit transmits ambient sounds and voice to a second radio unit over a radio path, the radio unit comprising a transceiver unit. This radio unit of the invention is characterized by further comprising memory means for storing the random number received by the radio unit and the key numbers of such radio units whose ambience listening function said radio unit is authorized to activate; and means for computing a response number from the random number and the key number of the other radio unit that has sent the random number, and for sending the response number to said other radio unit. The invention is based on the idea that the second radio unit can activate the ambience listening function at the first radio unit by remote control without any indication to the user of the first radio unit that ambient sounds and voice is being transmitted to the second radio unit. The first embodiment of the invention is based on the idea that a first radio unit contains a list of the identifiers of the radio units that are authorized to activate that radio unit, and the list is used for ensuring that only authorized radio units can activate the ambience listening function. The second embodiment of the invention is based on the idea that a first radio unit generates a random number and transmits it to a second radio unit that attempts to activate the ambience listening function, and computes a reference number from the random number and the key number characteristic of the radio unit. The second radio unit computes a response number from the same random number and the key number - stored in its memory - that is characteristic of the first radio unit, comparing it with the reference number. If the numbers are identical, the first radio unit starts ambience listening and transmits the ambient sounds and voice to the second radio unit. The advantage of this kind of method for ambience listening and of this kind of radio unit is that they make it possible to realize ambience listening between radio units, such as mobile stations, communicating on a radio channel, such as a direct mode channel. The advantage of the invention is that with the invention it is possible to specify the radio units that are authorized to activate ambience listening at some other radio unit. This is checked by identifying and approving the listening radio unit even if only two radio units communicating e.g. on a direct mode channel are involved. Ambience listening or any attempts thereof by unauthorized listeners are hereby prevented. Brief description of the figures In the following the invention will be described in greater detail with reference to the attached drawings, wherein fig. 1 is a signal flow diagram illustrating the operation of the method and radio unit of the invention, fig. 2 is a scheme illustrating a message according to a first embodiment of the invention for activating ambience listening, fig. 3 is a scheme illustrating the operation of a second embodiment of the invention, fig. 4 is a block diagram showing a radio unit according to the invention. Detailed description of the invention Fig. 1 is a signal flow diagram illustrating the operation of the method and radio unit according to the invention. The invention is a method for activating the ambience listening function through a direct mode channel from a second radio unit RU2 such that a first radio unit RUl starts transmitting ambient sounds and voice to the second radio unit RU2. In the invention, the radio unit activating the ambience listening, e.g. radio unit RU2, sends an ambience listening message 101 to the mobile phone RUl listened to. In response to the message, the first radio unit RUl checks 102 whether the second radio unit RU2 is authorized to activate the ambience listening function at the first radio unit RUl and, if the second radio unit is authorized to listen, the first radio unit RUl starts to transmit ambient sounds and voice to the second radio unit RU2. Fig. 2 is a scheme illustrating a message according to the first embodiment of the invention for activating ambience listening. In the invention, the radio unit RU2 activating the ambience listening function sends the radio unit RUl listened to an activate-ambience-listening message. The message contains the fields shown in fig. 2. Field 201 contains the address of the first radio unit RUl, i.e. the radio unit listened to. Field 202 contains the identifier of the message, i.e. the identifier of the activate- ambience-listening message. Field 203 contains the address of the second radio unit RU2, i.e. the radio unit activating the ambience listening function. Field 204, which is an optional field, can contain the priority of the message. Field 205 in fig. 2 determines for how long the ambience listening function is activated. If the direct mode channel has a reverse channel in use, the ambience listening function can be deactivated by using it, so the listening time field 205 or its contents are not needed. If reverse signalling cannot be transmitted, the listening time field 205 must be used. In the basic embodiments of the invention, the ambience listening function takes up the whole capacity of a direct mode channel. If one wants the ambience listening function to use some other direct mode channel, the channel to be used can be indicated in field 206 of the ambience listening message. In the first embodiment of the invention, a list of mobile phones, i.e. second radio units RU2, that are authorized to receive ambient sounds and voice of the radio unit RUl listened to is programmed in the radio unit RUl listened to or more particularly in its memory means. The authority of the listener RU2 is thus programmed in the radio unit RUl listened to. Fig. 3 is a scheme illustrating the operation of a second embodiment of the invention. In the invention, each radio unit or mobile phone RUl listened to has an individual ambience listening key 305, Kamb. The operation starts as the second radio unit RU2 commands 301 the first radio unit RUl to shift to an ambience listening state. Having received the command 301 to shift to the ambience listening state, i.e. having received e.g. an activate-ambience-listening message or command 301, the radio unit RUl listened to, i.e. the first radio unit RUl, generates 302 and transmits 303 a random number to the listening radio unit RU2, i.e. the second radio unit, stores the random number in the memory or sends it for further processing. The second radio unit RU2 computes 309 by an algorithm a response number from the random number and the key number Kamb characteristic of the first radio unit RUl, and sends 310 the response number to the first radio unit RUl. Correspondingly, the first radio unit computes 306 by a similar algorithm a reference number 307 from the previously generated 302 random number 304, and compares 311 the response number 310 obtained from the second radio unit RU2 with this reference number. If the response number 310 is the same as the reference number 307, the first radio unit RUl will be convinced that the second radio unit is authorized to listen to the ambient sounds and voice of the first radio unit. The first radio unit RUl then activates the ambience listening function. If, on the other hand, the response number 310 and the reference number 307 are different, the ambience listening function is not activated. Thus, the key numbers, i.e. the ambience listening keys, of all those first radio units RUl, i.e mobile phones, which the second radio unit RU2 is authorized to listen to are programmed in the second radio unit RU2, i.e. the listening mobile phone. Fig. 4 is a block diagram of a radio unit of the invention. The figure shows a typical radio unit 500 communicating on a traffic channel, i.e. a mobile phone, mobile station or e.g. a subscriber station used by the subscriber. The function of a transceiver (TX/RX) 501 is to tune to the channel used. With the transceiver 501 is connected an antenna 502, which is connected with the radio path RP. Usually, radio frequencies in the range of 60 to 1000 MHz (VHF and UHF ranges) are used, but other frequencies are also possible. On the radio path RP, analogue modulation can be used, the modulation being then usually phase modulation. Other kinds of modulation can also be used. Signalling can be transmitted e.g. by a voice-frequency subcarrier wave (FFSK). Transmission over a radio path can also be digital. A user interface 505 may comprise electro- acoustic transducers, typically a headphone 506 and a microphone 507, and optionally buttons for starting and ending a call, and for dialling. Since in a trunking system, and especially on a direct mode channel, transmission over a radio path RP is advantageously unidirectional, the subscriber station usually also has a push-to-talk button that must be depressed during the transmission. The push-to-talk button is not shown in fig. 4. In ambience listening, a push-to-talk button is naturally not depressed at the radio unit whose ambient sounds and voice is being transmitted to a second radio unit. The function of a controller 503 is to control the operation of the subscriber station. The controller 503 is connected with the user interface 505, from which it receives signals e.g. for starting and ending a call. In the invention, the signals may also be received from the radio path RP. The controller 503 may also give the user, via the user interface 505, voice or visual signals that relate to the operation of the mobile phone and/or the radio telecommunications system. The con¬ troller 503 is connected to the transceiver TX/RX 501. The channel used by the transceiver is allocated by the controller 503, i.e. the transceiver 501 tunes to the channel, i.e. radio frequency and a suitable time slot, allocated by the controller 503. The radio unit of the invention is able to tune to a direct mode channel. The transceiver 501 is also activated by the controller 503. The controller 503 receives and transmits signalling messages through the transceiver 501. A radio unit 500, RUl, RU2 (figs. 1 and 2) of the invention communicating on a direct mode channel can be used e.g. in a radio system that comprises a radio network with at least one base station and mobile stations and optionally one or more repeater stations that transmit traffic between at least one base station and subscriber stations communicating on a direct mode channel. The radio unit then comprises a transceiver unit 501 for receiving transmissions sent by other radio units, for sending transmissions to these other radio units, and for controlling the functions of the radio unit of a control unit 503, and a user interface 505. The radio unit 500, RUl of the first embodiment of the invention further comprises memory means 509 for storing the identifiers of the other radio units RU2 that are authorized to activate ambience listening at the radio unit concerned. The radio unit 500, RUl of the first embodiment also comprises means 510 for comparing the identifiers contained in the messages 101 (fig. 2) transmitted by the other radio units RU2 for activating ambience listening with the identifiers contained in the memory means 509 and, upon detecting the same identifier in the memory means and the ambience listening message 101 (fig. 2), activating the ambience listening function at the first radio unit RUl. A radio unit RUl (fig. 3) of the second embodiment of the invention comprises means 511 for generating a random number and transmitting it to a radio unit RU2 that has commanded radio unit RUl to activate the ambience listening function. The radio unit 500 (fig. 3) further comprises memory means 512 for storing a key number characteristic of the radio unit, and means 513 for computing a reference number from the random number and the key number and for storing the reference number, and means 514 for comparing the reference number with a response number received by the radio unit and computed by some other radio unit and, if the numbers are identical, for activating ambience listening at the radio unit. The second radio unit for ambience listening according to the second embodiment of the invention, i.e. the radio unit that sets, if possible, the first radio unit to the ambience listening state by remote control, further comprises a transceiver unit and memory means 515 for storing the random number received by the radio unit, and for storing the key numbers of radio units whose ambience listening function the radio unit is authorized to activate. The radio unit further comprises means 516 for computing a response number from the random number and the key number of the other radio unit that has transmitted the random number, and for transmitting the response number to said other radio unit. The radio units of the invention may naturally communicate on direct mode channels. The drawings and the description associated therewith are intended only to illustrate the idea of the invention. The method of the invention for realizing ambience listening and the radio unit of the invention may vary in their details within the scope of the claims. Although the invention is described above mainly in connection with radio units communicating on a direct mode channel, the invention can also be used with other kinds of mobile stations and mobile phones.

Claims: Claims 1. A method for activating ambience listening, in which a first radio unit (RUl; 500) transmits (103) ambient sounds and voice to a second radio unit over a radio path (RP), c h a r a c t e r i z e d in that the second radio unit (RU2) commands (101; fig. 2, 301) the first radio unit (RUl) to transmit (103) to the second radio unit (RU2) the ambient sounds and voice; in response to the command (101; fig. 2, 301) given by the second radio unit (RU2), the first radio unit (RUl) checks (102) the listening authority of the second radio unit (RU2), and if the second radio unit (RU2) has the listening authority, the first radio unit (RUl) starts transmitting (103 ) ambient sounds and voice to the second radio unit (RU2) . 2. A method of claim 1 , further c h a r a c - t e r i z e d in that the second radio unit (RU2) sends the first radio unit (RUl) an activate-ambience-listening message (fig. 2) that contains an identifier (203) of the second radio unit (RU2), in response to said activate-ambience-listening message (fig. 2), the first radio unit (RUl) compares the identifier (203) of the second radio unit (RU2) with the identifiers, stored (509) in the first radio unit (RUl), of those radio units (RU2) which are authorized to activate the ambience listening function at the first radio unit (RUl) and, if the identifier of the second radio unit (RU2) is stored in the first radio unit (RUl ) , the first radio unit (RUl ) starts ambience listening and transmits (103) the ambient sounds and voice to the second radio unit (RU2). 3 . A method ( fig . 3 ) of claim 1 , further c h a r a c t e r i z e d in that the step (102) where the first radio unit (RUl) checks (102) the listening authority of the second radio unit (RU2) comprises the following steps: in response to the command (301 ) given by the second radio unit (RU2) by which the second radio unit (RU2) commands the first radio unit (RUl) to activate ambience listening (103), the first radio unit (RUl) generates (302) a random number and transmits (303) it to the second radio unit (RU2), the first radio unit (RUl) computes (306) a reference number (307) from said random number (304) and the key number (305, Kamb) characteristic of the first radio unit (RUl), and stores it in the memory, in response to the random number (303) transmitted by the first radio unit (RUl), the second radio unit (RU2) searches the memory (515) for the key number (308 ) characteristic of the first radio unit (RUl) and computes (309; 516) a response number (310) from the key number and the random number (303) it has received, transmitting it then to the first radio unit (RUl), in response to the response number (310) transmitted by the second radio unit (RU2) , the first radio unit (RUl) compares (311; 514) the response number (310) transmitted by the second radio unit (RU2) with the reference number (307) stored in the first radio unit (RUl) , and if the numbers (310, 307) are identical, the first radio unit (RUl) acknowledges that the second radio unit (RU2) has listening authority. 4. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that the first (RUl ) and second (RU2) radio units communicate with each other on a direct mode channel. 5. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that as the second radio unit (RU2) commands (101; fig. 2; 301) the first radio unit (RUl) to transmit (103) the ambient sounds and voice to the second radio unit (RU2), the second radio unit (RU2) transmits the identifier (206) of the channel on which it wants the first radio unit (RUl) to transmit the ambient sounds and voice. 6. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that the second radio unit (RU2) commands the first radio unit (RUl) to stop transmitting (103) ambient sounds and voice to the second radio unit (RU2) by sending the first radio unit (RUl) a deactivate-ambience-listening message on a reverse signalling channel. 7. A method according to claim 2, c h a r a c ¬ t e r i z e d in that the second radio unit (RU2) commands (101; fig. 2) the first radio unit (RUl) to stop transmitting ambient sounds and voice (103) to the second radio unit (RU2) at the moment determined by the second radio unit by placing in the activate-ambience- listening message (101; fig. 2) that it transmits information (205) indicating when the first radio unit (RUl ) should stop transmitting ambient sounds and voice to the second radio unit ( U2) . 8. A radio unit (RUl; 500) for ambience listening in which the radio unit transmits ( 103) ambient sounds and voice to a second radio unit (RU2) over a radio path (RP), the radio unit comprising a transceiver unit ( 501 ) , and means (507, 505) for transmitting ambient sounds and voice through said transceiver, c h a r a c t e r i z e d in that said radio unit (RUl; 500) further comprises memory means (509) for storing the identifiers of the other radio units (RU2) that are authorized to activate ambience listening at said radio unit (RUl), means (510) for comparing the identifiers (203) contained in the activate-ambience-listening messages (101; fig. 2) transmitted by said other radio units with the identifiers stored in the memory means (509), and if it appears in the comparison that the same identifier is found in the memory means ( 509 ) and in the activate- ambience-listening message (101; fig. 2), for activating ambience listening at said radio unit (RUl; 500). 9. A radio unit (RUl, 500; fig. 3) for ambience listening in which the radio unit (RUl; 500) transmits (103) ambient sounds and voice to a second radio unit (RU2) over a radio path (RP), the radio unit (RUl; 500) comprising a transceiver unit (501), and means (507, 505) for transmitting ambient sounds and voice through said transceiver, c h a r a c t e r i z e d in that said radio unit (RUl; 500) further comprises means (511) for generating (302) a random number and transmitting (303) it to a radio unit (RU2) that has commanded said radio unit to activate the ambience listening function; memory means (512) for storing a key number (305; Kamb) characteristic of the radio unit (RUl; 500); means (513) for computing (306) a reference number (307) from said random number (304) and said key number (305; Kamb) and for storing that reference number (307); means (514) for comparing (311) said reference number (307) with a response number (310) received by the radio unit (RUl) and computed by some other radio unit (RU2) and, if the numbers (310, 307) are identical, for activating the ambience listening function at the radio unit (RUl ) . 10. A radio unit (RU2; fig. 3; 500) for ambience listening in which a radio unit (RUl) transmits (103) ambient sounds and voice to a second radio unit (RU2) over a radio path (RP), the radio unit (RU2; 500) comprising a transceiver unit (501 ), c h a r a c t e r i z e d in that said radio unit (RU2; 500) further comprises memory means (515) for storing the random number (303) received by the radio unit (RU2; 500) and the key numbers (308, Kamb) of such radio units (RUl) whose ambience listening function said radio unit (RU2; 500) is authorized to activate; and means (516) for computing (309) a response number (310) from the random number (303) and the key number (308, Kamb) of the other radio unit (RUl) that has sent the random number, and for sending (310) the response number to said other radio unit (RUl). 11. A radio unit of claim 8, 9 or 10, c h a r ¬ a c t e r i z e d in that said radio units (RUl, RU2) are arranged to communicate on direct mode channels.

Inventors: HEISKARI MIKA, LEHMUSTO MIKA, HEISKARI, MIKA, LEHMUSTO, MIKA
Applicants: HEISKARI MIKA, LEHMUSTO MIKA, NOKIA TELECOMMUNICATIONS OY, HEISKARI, MIKA, LEHMUSTO, MIKA
Application year: 1995
Main classification: H04Q7
IPC codes: H04B1, H04W88