WO2006007546A1

WO2006007546A1 - A method and a system for operating an ambiance listening mode in a wireless communication system

Info

Publication number: WO2006007546A1
Application number: PCT/US2005/023473
Authority: WO
Inventors: Michael Cherniak; Boaz Or-Shraga; Arieh Vered
Original assignee: Motorola, Inc.
Priority date: 2004-07-01
Filing date: 2005-06-30
Publication date: 2006-01-19
Also published as: EP1779534A1; GB2415862A; AU2005262336B2; GB0414746D0; CN1981452A; CN1981452B; AU2005262336A1; EP1779534A4; GB2415862B

Abstract

A system comprises a monitoring communication unit (107) performing an ambiance listening service for a monitored communication unit (101). The monitored communication unit (101) comprises a transmitter (109) for transmitting the ambiance listening mode transmissions to the monitoring communication unit (107) which comprises a receiver (117) for receiving these. In addition, the monitoring communication unit (107) comprises a command controller (119, 121) which determines and transmits transmission parameter commands to the monitored communication unit (101) where they are received by a receiver (113). The monitored communication unit (101) comprises a transmission controller (115) which sets at least one transmission parameter of the ambiance listening mode transmissions in response to the transmission parameter commands. The monitoring communication unit (107) may accordingly control aspects of the transmission from the monitored communication unit (101) and may in particular reduce the transmit power or the transmit time thereby reducing power consumption, heating and interference.

Description

A METHOD AND A SYSTEM FOR OPERATING AN AMBIANCE LISTENING MODE IN A WIRELESS COMMUNICATION SYSTEM

Field of the invention

The invention relates to a method and system for operating an ambiance listening mode in a wireless communication system and in particular, but not exclusively, to operating an ambiance listening mode in a cellular communication system, such as a TETRA (TErrestrial Trunked RAdio) communication system.

Background of the Invention

In a cellular communication system, a geographical region is divided into a number of cells each of which is served by base station. The base stations are interconnected by a fixed network which can communicate data between the base stations. A remote unit is served via a radio communication link by the base station of the cell within which the remote unit is situated.

As a remote unit moves, it may move from the coverage of one base station to the coverage of another, i.e. from one cell to another. As the remote unit moves towards a new base station, it enters a region of overlapping coverage of two base stations and within this overlap region it changes to be supported by the new base station. As the remote unit moves further into the new cell, it continues to be supported by the new base station. This is known as cell reselection or handover.

Communication from a remote unit to a base station is known as uplink, and communication from a base station to a remote unit is known as downlink.

The fixed network interconnecting the base stations is operable to route data between any two base stations, thereby enabling a remote unit in a cell to communicate with a mobile station in any other cell. In addition, the fixed network may comprise gateway functions for interconnecting to external networks such as the Public Switched Telephone Network (PSTN), thereby allowing remote units to communicate with landline telephones and other communication terminals connected by a landline. Furthermore, the fixed network comprises much of the functionality required for managing a conventional cellular communication network including functionality for routing data, admission control, resource allocation, subscriber billing, mobile station authentication etc.

Examples of cellular communication systems include both public cellular communication system such as the Global System for Mobile communication (GSM) and Professional Mobile Radio (PMR) systems such as TETRA (TErrestrial Trunked RAdio) .

Specifically, although TETRA may be used as a public cellular communication system, it is designed to provide a number of features and services that are particularly suitable for private organisations or groups such as for example the emergency services.

For example TETRA provides a number of features and services for managing and controlling group calls as well as for managing the membership of these groups. Thus, TETRA provides services for making group calls wherein e.g. a voice message is quickly and efficiently relayed to a specific group of remote units. TETRA furthermore provides features for managing the membership of different groups, priorities of different groups etc. Also, TETRA provides for both acknowledged and non- acknowledged communication. For acknowledged services, the call setup comprises the call originator receiving an acknowledgement indicating that the destination (s) has been reached. However, for non-acknowledged services, no acknowledgement is received from the destination.

Other features and services provided by TETRA include a high level of security which may be optimised for specific purposes, push-to-talk channel allocation, broadcast calls, Direct Mode Operation (DMO) wherein remote units may communicate directly without the involvement of a base station etc.

One supplementary service that has been proposed for TETRA is an Ambience Listening service. Ambience listening allows an authorized user to establish a call with a specific remote unit for the purpose of monitoring sound activity in the vicinity of that remote unit without causing any indication that such activation is taking place. The ambience listening service allows the authorized user to listen to the sound environment of the remote unit without this being apparent to the user or people in the vicinity of the remote unit.

Ambience listening is typically intended to increase security and safety for users. The authorized user will typically be a control centre for the organisation operating the TETRA network. For example, for a TETRA system operated by a law enforcement organisation, such as the police, a central control centre will typically be assigned authorized user status allowing it to listen to the remote units of the individual law enforcers. In e.g. situations where the central control centre has received an alarm from the remote unit, or otherwise has a suspicion that a critical situation may be arising, ambiance listening may assist the central control centre in determining what the situation is and to select an appropriate cause of action.

Typically, the individual user of the remote units may prohibit the use of ambience listening. However, if ambiance listening is allowed by the remote unit, the ambience listening is normally activated or ceased by the authorized user by transmitting an activation command to the remote unit.

Although, the ambiance listening service provides a number of advantages and may increase the safety and security of users of remote units, there are also some disadvantages associated with supporting ambiance listening services.

For example, in order to receive the ambience sound signals from the remote units, these continuously transmit to the authorized user. Hence, a traffic channel is continuously occupied by this transmission. This not only causes interference and reduces the overall capacity of the communication system but also affects the remote unit itself. One effect is that the transmission is associated with a very significant power consumption resulting in a significant battery drain. The use of ambience listening may accordingly reduce the battery life and will be further inconvenient to the user since this power drain typically occurs without his knowledge. This could result in the battery being discharged without the user noting it thereby possibly preventing him from using the remote unit in an emergency situation.

Also, the transmission in the ambience listening results in increased power loss which results in a heating of the remote unit. Although, this increase in temperature is not necessarily large, it may allow a person to determine that transmissions are taking place. Therefore, the heating may enable a person to detect that the ambience listening service is activated which is undesirable in many situations.

Hence, an improved system for operating an ambience listening mode would be advantageous and in particular a system allowing increased flexibility, increased control, reduced power consumption, increased stealth and/or improved performance would be advantageous.

Summary of the Invention Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to a first aspect of the invention there is provided a system for operating an ambiance listening mode associated with a monitoring communication unit and a monitored communication unit in a wireless communication system; the system comprising: the monitoring communication unit having: means for receiving ambiance listening mode transmissions from the monitored communication unit, and means for transmitting at least one transmission parameter command to the monitored communication unit; and the monitored communication unit comprising: means for transmitting the ambiance listening mode transmissions to the monitoring communication unit, means for receiving the at least one transmission parameter command from the monitoring communication unit, and means for setting at least one transmission parameter of the ambiance listening mode transmissions in response to the at least one transmission parameter command.

The invention may provide an improved performance when operating an ambiance listening service. The monitoring communication unit may be associated with an authorized user that may monitor the sound environment of the monitored communication unit without the user being aware of this activity. The monitoring communication unit, and thus the authorized user, may control the at least one transmission parameter of the monitored communication unit thereby allowing remote control of the transmission characteristics. The monitoring communication unit may control the transmission parameters to be suitable for the current operating conditions, propagation environment and/or perceived importance or criticality of the monitoring. For example, the transmission parameter may be adjusted by the monitoring communication unit to dynamically optimise a trade off between resource usage and quality of the monitoring. The transmission parameter may in suitable situations be varied to reduce power consumption and heating of the remote unit while allowing a reduced quality. This may improve battery life and/or may reduce the probability of the monitoring activity being detected at the monitored remote unit. In some embodiments of the invention, the at least one transmission parameter may cause a reduced interference level and an increased capacity of the communication system as a whole.

According to an optional feature of the invention, the at least one transmission parameter comprises a continuity parameter of the ambiance listening mode transmissions.

The monitored communication unit may switch between a continuous transmission mode and a discontinuous transmission mode in response to the transmission parameter command. In the continuous mode, the traffic channel assigned to the ambience listening may be fully utilised, for example by all appropriate time slots of the channel being used for transmission of data from the monitored communication unit to the monitoring communication unit. In the discontinuous mode, the traffic channel assigned to the ambience listening may only be partially utilised, for example by only some of the appropriate time slots of the channel being used for transmission of data from the monitored communication unit to the monitoring communication unit. This may provide an effective and simple to implement means of reducing power consumption, temperature increase and interference for an ambience listening service.

According to an optional feature of the invention, the at least one transmission parameter comprises a transmit power parameter. For example, the transmit power may be reduced when the quality of the ambience listening is less critical, e.g. because the monitored sound does not indicate a critical situation. The feature may provide an effective and simple to implement way of reducing power consumption, temperature increase and interference for an ambience listening service.

According to an optional feature of the invention, the means for transmitting the ambiance listening mode transmissions is operable to transmit discontinuously and the at least one transmission parameter comprises a temporal characteristic of at least one discontinuous transmission. Variation of temporal characteristics for discontinuous transmissions provides a particularly suitable way of optimising the transmission characteristics of the ambiance listening mode transmissions. Typically variations of temporal characteristics provide significant results and are uncomplicated to implement.

According to an optional feature of the invention, the temporal characteristic comprises a duration of the at least one discontinuous transmission. This provides for a particularly simple and effective implementation suitable for many embodiments .

According to an optional feature of the invention, the temporal characteristic comprises an interval between discontinuous transmissions. This provides for a particularly simple and effective implementation suitable for many embodiments. For example, modifying the time interval between consecutive discontinuous transmissions is uncomplicated and provides for efficient control. As an example, in a TETRA communication system, the means for setting at least one transmission parameter may cause one or more time slots to be skipped in response to receiving a transmission parameter command. The transmission parameter command may specifically indicate how many frames should be skipped between transmissions from the monitored communication unit.

According to an optional feature of the invention, the monitored communication unit comprises means for transmitting operating parameter information to the monitoring communication unit. This may provide additional information to the monitoring communication unit and/or the authorized user thereby allowing the authorized user to control the operation of the monitoring communication unit and/or the monitored communication unit in response thereto.

According to an optional feature of the invention, the monitoring communication unit comprises means for generating the at least one transmission parameter command in response to the operating parameter information. This may allow an improved setting of the at least one transmission parameter as the transmission parameter command may be selected to reflect the current operating conditions of the monitored communication unit. The transmission parameter command may for example be selected automatically or semi-automatically in the monitored communication unit.

According to an optional feature of the invention, the operating parameter information comprises an operating temperature indication of the monitored communication unit. This may allow the at least one transmission parameter to be controlled by the monitoring communication unit in response to the operating temperature of the monitored communication unit thereby improving control of the characteristics of the monitored communication unit. For example, if the temperature of the monitored communication unit increases above a given threshold, the transmission power may be reduced.

According to an optional feature of the invention, the operating parameter information comprises a battery charge indication of the monitored communication unit. This may allow the at least one transmission parameter to be controlled by the monitoring communication unit in response to the battery charge of the monitored communication unit thereby improving control of the characteristics of the monitored communication unit. For example, if the battery charge is below a given threshold, the transmission power may be reduced and/or an increased interval between transmissions may be applied. The battery charge indication may for example be an indication of the charge left in the battery powering the monitored communication unit. According to an optional feature of the invention, the operating parameter information comprises an external power connection indication for the monitored communication unit. For example, the external power connection indication may indicate whether the monitored communication unit is coupled to an external power source or whether it is powered by an internal battery. An improved regulation of the transmission characteristics of the monitored communication unit may be achieved and in particular the transmission characteristics may be optimised to reflect whether a limited battery power source or a typically unlimited external power source is powering the monitored communication unit.

According to an optional feature of the invention, the operating parameter information comprises an operating mode indication for the monitored communication unit. This may allow an optimisation of the at least one transmission parameter in response to the current operating mode of the monitored communication unit. For example, ambiance listening may be performed despite the monitored communication unit being switched of and the transmissions characteristics may accordingly be modified to reflect whether the monitored communication unit is in an on-operating mode or an off-operating mode.

According to an optional feature of the invention, the monitoring communication unit comprises means for transmitting an operating parameter information request message to the monitored communication unit and the monitored communication unit is operable to transmit the operating parameter information in response to receiving the operating parameter information request message. This provides an efficient system for communicating operating parameter information and allows the monitoring communication unit to control when this information is provided.

According to an optional feature of the invention, the monitored communication unit is operable to operate in a first operating mode and a second operating mode wherein the at least one transmission parameter is applied to transmissions in the second operating mode but not in the first operating mode. In particular, the first operating mode may be a full monitoring operating mode and the second operating mode may be a reduced monitoring mode. The monitored communication unit may operate in a first operating mode wherein e.g. conventional ambience listening is provided but may also be able to switch to a second operating mode wherein e.g. the temperature increase, the power consumption and/or the interference is reduced.

According to an optional feature of the invention, the monitoring communication unit is operable to transmit a modified monitoring operating mode request to the monitored communication unit and the monitored communication unit is operable to enter the second operating mode in response to receiving the modified monitoring operating mode request. This provides for an efficient way of allowing the monitoring communication unit and the authorized user to control the operation of the monitored communication unit. The monitored communication unit may transmit operating parameter information in response to receiving the operating mode request thereby providing an acknowledgement and information of the operating conditions of the monitored communication unit when entering the second operating mode.

According to an optional feature of the invention, wherein the monitored communication unit comprises means for switching between the first operating mode and the second operating mode in response to a monitored ambient sound characteristic. This may allow an efficient and convenient way of modifying the transmissions characteristics to suit the current conditions. In particular, the second operating mode may be entered when the ambient sound characteristic indicates relative silence and exited when this silence ends.

According to an optional feature of the invention, the monitored ambient sound characteristic is a voice detection characteristic. This provides a particularly suitable ambient sound characteristic as it may allow full ambience listening when there is voice activity in the environment of the monitored communication unit while reducing power consumption and interference when there is no voice activity. Hence, improved ambience listening quality is achieved when this is likely to be of importance while allowing reduced resource consumption when ambience listening is likely to be of less importance.

According to an optional feature of the invention, the means for switching is operable to activate the second operating mode if the monitored ambient sound characteristic indicates a sound level below a volume threshold for a given duration. This provides for an efficient and simple way of determining a suitable ambient sound characteristic for switching to the second operating mode.

According to an optional feature of the invention, the means for switching is operable to set the duration in response to the at least one transmission parameter command. This allows the monitoring communication unit and the authorized user improved control over the operation of the monitored communication unit when in an ambience listening mode.

According to an optional feature of the invention, the monitored communication unit comprises means for transmitting status indication messages in the second operating mode but not in the first operating mode. This allows for status indication messages to be transmitted when this is likely to be most suitable. For example, in the second operating mode, some or all of the ambiance listening mode transmissions may be substituted by status indication messages without this being critical for the authorized user.

The wireless communication system may be a cellular communication system and may in particular be a TETRA (TErrestrial Trunked RAdio) system.

According to a second aspect of the invention, there is provided an apparatus for operating an ambiance listening mode associated with a remote communication unit in a wireless communication system; the apparatus comprising: means for receiving ambiance listening mode transmissions from the remote communication unit; and means for at least one transmitting transmission parameter command to the remote unit, the at least one transmission parameter command indicating a transmission parameter setting to be used by the remote command when transmitting the ambiance listening mode transmissions.

According to a third aspect of the invention, there is provided an apparatus for operating an ambiance listening mode associated with a monitoring communication unit in a wireless communication system; the apparatus comprising: means for transmitting ambiance listening mode transmissions to the monitoring communication unit; means for receiving at least one transmission parameter command from the monitoring communication unit; and means for setting at least one transmission parameter of the ambiance listening mode transmissions in response to the at least one transmission parameter command.

According to a fourth aspect of the invention, there is provided a method of operating an ambiance listening mode associated with a monitoring communication unit and a monitored communication unit in a wireless communication system; the method comprising the steps of: at the monitoring communication unit: receiving ambiance listening mode transmissions from the monitored communication unit, and transmitting at least one transmission parameter command to the monitored communication unit; and at the monitored communication unit: transmitting the ambiance listening mode transmissions to the monitoring communication unit, receiving the at least one transmission parameter command from the monitoring communication unit, and setting at least one transmission parameter of the ambiance listening mode transmissions in response to the at least one transmission parameter command.

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment (s) described hereinafter.

Brief Description of the Drawings

An embodiment of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 illustrates an example of a TETRA cellular communication system incorporating an embodiment of the Invention.

FIG. 2 illustrates an example signal flow diagram in accordance with an embodiment of the Invention.

Detailed Description of a Preferred Embodiment of the Invention

The following description focuses on embodiments of the invention applicable to an ambiance listening service of a TETRA (TErrestrial Trunked Radio) cellular communication system. However, it will be appreciated that the invention is not limited to this application but may be applied to many other wireless communication systems. FIG. 1 illustrates an example of a TETRA cellular communication system incorporating an embodiment of the Invention.

TETRA is a Time Division Multiple Access (TDMA) system wherein 25 kHz wide carriers are further divided into four time slots that are individually assignable. Each time slot has a duration of 14.167 msecs and four timeslots are combined into a time frame having a duration of 56.67 msecs. Each of the four time slots in a time frame may be individually allocated to the same or different remote units. Furthermore, the time frames are combined into multiϋrames comprising 18 time frames. Frame number 18 is reserved as a control frame wherein control information may be communicated during an active call.

In the system of FIG. 1, a TETRA remote unit 101 is communicating with a TETRA base station 103 over a TETRA radio air interface. The base station 103 is coupled to a fixed network 105 which interfaces to other base stations (not shown) and other networks (not shown) . The fixed network 105 is coupled to a control unit 107. The control unit 107 is in the embodiment of FIG. 1, a control unit of a central dispatch centre of an organisation using the TETRA communication system for communication services between a large number of individual users. For example, the central control centre may be a central control centre for a law enforcement organisation such as the police.

In the embodiment, the central control centre may advantageously use a TETRA ambiance listening service in some situations. For example, if an alarm is received from the remote unit 101, an operator in the central control centre may set up an ambience licensing operation for the remote unit 101 in order obtain further information of the situation giving rise to the alarm. The operator may in this way obtain further information without requiring the user to operate the remote unit. When an ambiance listening service is set up, both the remote unit 101 and the control unit 107 enters an ambiance listening mode.

In accordance with the embodiment of FIG. 1, the operation of the remote unit 101 is influenced or controlled by the control unit 107 when operating in the ambiance listening mode. In particular, the control unit 107 may control one or more parameters of the transmissions from the remote unit 101 to the base station 103.

In accordance with the embodiment of FIG. 1, the remote unit 101 comprises a transmitter 109 for transmitting the ambiance listening mode transmissions to the monitoring communication unit. In the embodiment, the transmitter 109 receives an input from a microphone 111 of the remote unit 101, encodes the signal and transmits the resulting ambiance listening data over the TETRA air interface to the base station 103. The ambiance sound data is then routed from the base station 103 to the control unit 107 through the fixed network 105. Hence, in the embodiment, the ambiance sound data is not transmitted directly over the air interface to the control unit 107 but is transmitted indirectly via the base station 103 and the fixed network 105. It will be appreciated that in some embodiments, the control unit 107 and the base station 103 may be integrated, and the transmission of ambiance sound data may be directly to the control unit 107 over the air interface without involving the fixed network 107.

The encoding of the ambient sound and the transmission of the resulting data is in the embodiment of FIG. 1 performed in accordance with the TETRA Technical Specifications as is well known in the art and which for brevity and clarity will not be described further here.

The remote unit 101 further comprises a receiver which is operable to receive transmission parameter commands from the control unit 107. The transmission parameter commands are transmitted from the control unit 107 via the fixed network 105 and the base station 103. The remote unit 101 furthermore comprises a transmission controller 115 which is coupled to the receiver 113 and the transmitter 109. The transmission controller 115 receives the transmission parameter commands from the receiver 113 and is operable to control one or more transmission parameters of the transmissions of the ambiance sound data in response to the transmission parameter commands.

The control unit 107 comprises a receiver 117 which receives the ambiance sound data transmissions from the remote unit 101 via the base station 103 and the fixed network 105.

The receiver 107 receives the ambiance sound data and generates a sound signal which is presented to the operator for example through a speaker, headset or other suitable user interface means .

The receiver 117 is also coupled to an ambiance listening controller 119 which in the embodiment of FIG. 1 is fed operating information related to the ambiance listening service, the ambiance sound data and/or the remote unit 101 as will be described later. The ambiance listening controller 119 is operable to determine a desired remote transmission characteristic or parameter of the transmissions of the ambiance sound data from the remote unit 101.

The control unit 107 further comprises a command controller 121 which is fed the desired remote transmission characteristic from the ambiance listening controller 119. In response the command controller 121 generates one or more transmission parameter commands which are transmitted to the remote unit 101 via the fixed network 105 and the base station 103.

In accordance with the embodiment of FIG. 1, the control unit 107 thus forms a monitoring communication unit for an ambiance listening service of which the remote unit 101 forms a monitored communication unit. Furthermore, in addition to instigating and terminating the ambiance listening operation, the Control unit 107 can also modify the call transmitting method of the monitored remote unit 101. Thus, the control unit 107 can generate transmission parameter commands which when received by the remote unit 101 will result in a transmission parameter being set accordingly. Thus, the control unit is provided with additional control allowing improved performance and increased flexibility. In particular, the control unit 107 may generate the transmission parameter command to result in the transmission parameters being modified to match the current conditions.

In some embodiments the determination of transmission parameter commands and/or the desired transmission parameters may be determined automatically by the control unit 107 in accordance with a suitable algorithm. However, in other embodiments the transmission parameter commands and/or the desired transmission parameters may be determined semi-automatically or may be determined manually. For example, the ambiance listening controller 119 may implement user interface means allowing an operator to directly input a desired absolute or relative transmission parameter and/or transmission parameter command. In some such embodiments, the user interface may also present information on the status or characteristics of the ambiance listening service or the remote unit 101 to the user thereby enabling the user to select a suitable transmission parameter or transmission parameter command in response to these parameters. The user interface may for example comprise a display, a keyboard and/or pointing device.

It will be appreciated that the transmission parameters that can be and are modified in different embodiments may depend on the specific characteristics and requirements associated with the individual embodiment. In the following, examples of transmission parameters that may individually or in combination be influenced or controlled from a monitoring communication unit are described with specific reference to the embodiment of FIG. 1.

In some embodiments, the control unit 107 may remotely control or influence a transmit power parameter. In particular, the transmit power of the ambiance listening sound data transmissions may be controlled by the control unit 107 transmitting transmission parameter commands in response to which the transmission controller 115 determines a suitable transmit power. The transmission parameter command may directly instruct the transmission controller 115 to set the transmission power to a given level or to increase or decrease the transmit power by a given amount .

This may allow the control unit 107 to reduce the transmit power in situations where a reduced quality of the ambiance listening signal is acceptable. For example, if no ambient sound is heard, the transmit power may be reduced temporarily thereby reducing the power consumption and the temperature of the remote unit 101 as well as the generated interference. Although increased noise may be introduced this will typically be acceptable during quiet periods.

In some embodiments, the control unit 107 may remotely control or influence a data rate of the ambiance listening data. The data rate may be varied by varying the source encoding rate and/or a channel encoding rate. For example, the data rate may be reduced during quiet periods resulting in a reduced quality but acceptable signal. For example, the remote unit 101 may comprise a high data rate sound (voice) encoder and a low rate sound encoder and the transmission controller may switch between these in response to the transmission parameter commands received from the control unit 107. Similarly, the remote unit 101 may comprise a high rate channel encoder and a low rate channel encoder and the transmission controller may switch between these in response to the transmission parameter commands.

It will be appreciated that in some embodiments, the transmission controller may modify a number of these parameters in combination and in dependence on each other. For example, the transmission parameter commands may comprise a command instructing the remote unit 101 to switch to a silent operating mode. When this command is received, the transmission controller 115 may control the transmitter 109 to switch to a low data rate source encoder and a high rate channel encoder (preferably resulting in the same channel data rate as previously) . The increased channel encoding allows the transmission to be performed at a much lower transmit power thereby resulting in significantly reduced power consumption, temperature increase and interference. Furthermore, a reliable ambient sound signal is received at the control unit 107 albeit at a lower quality due to the reduced source data rate.

In some embodiments, a continuity parameter of the transmission of the ambiance listening data may be controlled in response to the transmission parameter commands. For example, the transmission controller 115 may switch between a continuous transmission of ambiance listening data to an intermittent transmission of ambiance listening data in response to receiving an appropriate transmission parameter command.

In some embodiments where the ambiance listening data may be transmitted discontinuously or intermittently, a temporal characteristic of the discontinuous transmissions may be modified. For example, the duration of the transmissions may be increased or decreased by the control unit 107 transmitting suitable transmission parameter commands to the remote unit 101. In some such embodiments, a source encoder may generate data which is organised in order of decreasing importance. Within each sound encoding frame, a first group of data bits may be generated which are essential to regenerating the encoded sound, a second group of data bits may be encoded which are important for regenerating the sound without significant quality degradation and a third group of data bits may be encoded which provides only a relatively minor quality improvement. In this embodiment, a transmission parameter command may be transmitted from the control unit 107 which results in a duration of the transmissions of the ambiance listening data which allows only the first group of data to be transmitted. This will allow a low quality sound to be reproduced at the control unit 107 while resulting in low power consumption, temperature increase and interference and may for example be suitable for quiet periods. Another transmission parameter command may be sent if improved quality is required. This command may result in the duration being increased to also include the second group of data bits. Finally, a third transmission parameter command may be sent setting the duration to allow all data bits to be transmitted resulting in the best quality but at the expense of an increased power consumption and interference.

Alternatively or additionally, an interval between discontinuous transmissions may be controlled or influenced by the control unit 107. For example, the duration of the individual data transmissions may be kept substantially constant while the effective data rate of the ambiance listening data may be varied by varying the interval between consecutive data transmissions.

In TETRA embodiments where an ambiance listening traffic channel is formed by repeating time slots, the interval between transmissions of ambiance listening data may be achieved by omitting to transmit data in some time slots. For example, transmission parameter commands may be used by the control unit 107 to cause ambiance listening data transmissions to use every time slot, to use every second time slot or to use every fourth time slot. In this way, the control unit 107 may control the effective data rate of the transmission of ambiance listening data from the remote unit 101 and thereby may control the trade off between ambiance listening quality and power consumption, heating and interference.

It will be appreciated that whereas these parameters in some embodiments may be completely controlled by the control unit 107, the transmission parameter commands are in other embodiments merely included as a parameter in the determination of the transmission parameters.

Specifically, the transmission controller 115 may operate an algorithm for determining a suitable transmission parameter which includes consideration of a number of characteristics, parameters and commands. Thus, the transmission parameter command may simply be one of a plurality of input parameters used by the algorithm to select and set a suitable parameter value.

The control unit 107 may accordingly control or influence a number of parameters which may result in a reduction of resource consumption associated with the transmission of ambiance listening data. In particular, by reducing the transmit power or effective transmission time (or transmission duty cycle) of the ambiance listening data transmissions the power consumption and thus the battery drain and temperature increase may be reduced. In addition, the average interference caused by the transmissions is reduced thereby increasing the capacity of the communication system as a whole. Furthermore, the ambience listening service is still supported at the reduced resource consumption. Also, by allowing the control unit to control the trade off between the resource usage and the ambiance listening quality, this can be optimised to provide the ambiance listening performance deemed necessary by the authorized user for the current situation. In particular, the approach allows an authorized user to reduce the resource usage when the ambiance listening is not considered critical while allowing uncompromised quality when this is considered essential. Thus, the authorized user may fulfil the ambience listening task without significantly heating or draining the battery of the remote unit 101.

In some embodiments, the remote unit 101 is operable to operate in two ambiance listening transmission modes under the control of the transmission controller 115. In some such embodiments, a received transmission parameter command may adjust the operation of one operating mode but not of another. For example, the remote unit 101 may be capable of operating in a normal full ambiance listening mode wherein all available resource is used or may operate in a reduced ambiance listening mode wherein the remote unit 101 is operated in a less resource demanding mode, for example by only transmitting in a subset of available time slots and/or with reduced transmit power.

In some such embodiments, a given transmission parameter command may apply only to one of the operating modes. For example, a transmission parameter command may be transmitted indicating that the remote unit 101 should skip every other time slot when transmitting in the reduced operating mode. The transmission parameter command may optionally be combined with a command that enters the remote unit 101 into the reduced operating mode.

It will be appreciated that in some such embodiments, some transmission parameter commands may relate only to the first operating mode, some transmission parameter commands may relate only to the second operating mode and some transmission parameter commands may relate to both the first and the second operating mode.

In some such embodiments, the transmission controller 115 is operable to control the operating mode of the remote unit 101 in response to local characteristics. For example, transmission parameter commands may have been received which enables the use of the reduced operating mode and which optionally specifies characteristics to be used'in the operating mode. However, the transmission controller 115 may switch between the first and second operating mode based on local characteristics and without a specific transmission parameter command being received. Thus, the transmission parameter command sets the applied transmission characters by enabling the reduced mode thereby causing the remote unit 101 to use less resource demanding transmission parameters when this is feasible.

As an example, the transmission controller 115 may comprise a sound detection element which detects if the microphone is picking up any sound or whether the sound environment of the remote unit 101 is quiet. In some such embodiments, the transmission controller 115 may operate the remote unit 101 in the full ambiance listening operating mode when sound is detected and in the reduced operating mode when relative silence is detected. This may allow the remote unit 101 to automatically and quickly adapt to the local sound environment and may result in a significant reduction in power consumption, heating and interference without unacceptably degrading the ambiance listening service.

In some embodiments, the sound detection element may consist in or comprise a voice detector which generates a voice detection characteristic. The voice detection characteristic is an indication of whether the microphone is picking up speech and if so, the transmission controller may enter the full ambiance listening operating mode and otherwise it may enter the reduced operating mode. A possible algorithm for the sound detection element may simply be to determine an (averaged) sound level. For example, an amplified signal from the microphone may be filtered in a suitable filter. The filtered signal may be compared to a predetermined volume level and if this is exceeded for a given duration, the transmission controller 115 may enter the full ambiance listening operating mode. Similarly, if the filtered signal falls below the predetermined threshold for a given duration, the transmission controller 115 may enter the remote unit 101 in the reduced operating mode.

It will be appreciated that in some embodiments, the characteristics and parameters of the operating mode algorithm used by the transmission controller may be determined in response to transmission parameter commands received from the control unit 107. For example, the duration for which the volume threshold must be crossed before a mode transition is performed may be set by a transmission parameter command from the control unit 107.

In some embodiments, the monitored communication unit (such as the remote unit 101) may transmit operating parameter information to the monitoring communication unit (such as the control unit 107) .

For example, instead of transmitting ambiance listening data a monitored communication unit may transmit parameter information when in the reduced operating mode but not when in the full ambiance listening operating mode. The operating parameter information may provide the monitoring communication unit with additional information that allows it to more accurately control the operation of the monitored communication unit to suit the current conditions. Accordingly, in some embodiments the ambiance listening controller 119 and/or the command controller 121 utilise the operating parameter information in determining the desired transmission parameters and/or the transmission parameter commands.

The operating parameter information may for example be information related to characteristics of the monitored communication unit or of the ambiance listening performance. In particular, the operating parameter information may comprise one or more of the parameters described in the following.

It is desirable to reduce the heating of the monitored communication unit in order to reduce the likelihood of the ambiance listening operation being detected. For example, it may be acceptable that the temperature increases by 3-4 degrees but preferably no further. Accordingly, the monitored communication unit may transmit operating parameter information comprising an operating temperature indication of the monitored communication unit. This operating temperature may be compared to a desired value and if it increases beyond this value, the monitoring communication unit may instigate a reduced ambiance listening operation as previously described.

As described previously, the power consumption of the monitored communication unit may be reduced by the monitoring communication unit controlling one or more transmission parameters of the monitored communication unit. However, the advantage and criticality of such an operation may depend on the power resource available at the monitored communication unit.

For example, if the monitored communication unit is connected to an external power source, such as a charger or a mains supply adapter, the monitored communication unit may have sufficient power resource, and the power reduction achievable by modifying the transmission parameters is unimportant. Thus, the operating parameter information may comprise an external power connection indication for the monitored communication unit. The external power connection indication may specifically reflect whether the monitored communication unit is coupled to an external power source or not. If the monitored communication unit is connected to an external power source, the monitoring communication unit may allow the monitoring communication unit to continue with the full ambiance listening operation whereas it will at least partially use the reduced ambiance listening operation if the monitored communication unit relies only on internal power resources (the batteries) .

Furthermore, the operating parameter information may additionally or alternatively comprise a battery charge indication for the monitored communication unit. The battery charge indication may specifically indicate the charge remaining in the battery. For example, an estimated remaining battery life or a percentage charge may be transmitted to the monitoring communication unit. The monitoring communication unit may utilise this information in controlling the ambiance listening operation. For example, high quality ambiance listening with associated high power consumption may be utilised when the battery still has a high charge whereas increasingly significant power consumption reduction is introduced as the battery charge reduces.

The preferred transmission parameters may depend on the operating mode of the monitored communication unit and accordingly the operating parameter information may comprise an operating mode indication for the monitored communication unit. The operating mode may be used by the monitoring communication unit to determine a suitable transmission parameter command.

For example, in TETRA communication systems, ambiance^{^} listening may be performed even if the monitored communication unit is switched off by a user. The preferred transmission parameters may depend on whether the monitored communication unit is switched on and accordingly an on/off indication may be comprised in the operating parameter information transmitted to the monitoring communication unit.

The operating parameter information may be sent at any suitable time. In some embodiments, the operating parameter information may be transmitted by the monitored communication unit without any interaction of the monitoring communication unit. However, in other embodiments, the operating parameter information may additionally or alternatively be transmitted in response to a request from the monitoring communication unit. Thus, the monitoring communication unit may transmit an operating parameter information request message to the monitored communication unit. When receiving this request message, the monitored communication unit accordingly transmits the operating parameter information to the monitoring communication unit. This may allow the monitoring communication unit to determine when new information is required and may allow for transmissions of operating parameter information to only be performed when necessary or desired.

In the following an embodiment of the invention suitable for a TETRA cellular communication system is described in more detail. In the embodiment, the ambiance listening operation is controlled by transmission of various messages between the monitored communication unit and the monitoring communication unit.

In accordance with this example, the TETRA standard may be enhanced to allow a monitoring communication unit to modify the transmission parameters such that in situations when high quality ambiance listening is not required, the monitoring communication unit may decrease the total transmission time or/and the transmit power level.

In this embodiment, dedicated Ambience Listening Messages are exchanged in Packet Data Units (PDUs) between the monitored communication unit and the monitoring communication unit in order to control the ambience listening transmissions.

The following PDUs are used: • CTXQ REQUEST PDU issued by the monitoring communication unit to the monitored communication unit for configuring the call transmitting method.

• CTXQ RESPONSE PDU issued by the monitored communication unit to the monitoring communication unit as a response to a CTXQ REQUEST^* PDU. This response will indicate whether the configuring was successful or failed.

• CTXQ INTERROGATION PDU issued by the monitoring communication unit to the monitored communication unit to request operating parameter information.

• CTXQ INDICATION PDU issued by the monitored communication unit to the monitoring communication unit a response to a CTXQ INTERROGATION PDU. THE CTXQ INDICATION PDU comprises operating parameter information and may also be sent instead of traffic data without receiving a CTXQ INTERROGATION PDU.

The transmission parameter commands will be transmitted in CTXQ REQUEST PDUs and CTXQ INTERROGATION PDUs and will comprise the following parameters:

• Transmit skip (in transmit (TX) frames) : Instructs the monitored communication unit of how many time slots should be skipped

• Transmit power change:

Instructs the monitored communication unit of an increase or decrease of the transmit power.

• Call inactivity timer (in multiframes) : Indicates an interval in which a monitored communication unit which is not transmitting voice should wait prior to activating a reduced ambiance listening mode.

The PDUs may specifically comprise the following data fields:

FIG. 2 illustrates a signal flow diagram in accordance with an embodiment of the invention. The signal flow diagram shows an example of the PDU message exchange that may be performed when instigating and supporting a reduced ambiance listening mode.

If the monitoring communication unit determines that there is currently no voice activity in the vicinity of the remote unit (or that ambiance listening for other reasons is not critical), a CTXQ REQUEST PDU 201 is transmitted to the monitored communication unit. For example, a CTXQ REQUEST PDU comprising the following data values may be sent:

When the monitored communication unit receives this message, it initialises a reduced ambiance listening mode operation with the specified parameters. It then transmits a CTXQ RESPONSE PDU 203 to the monitoring communication unit to acknowledge successful receipt of the data. In addition, the operating parameter information is included in the message. A CTXQ RESPONSE PDU with the following data may for example be sent:

From then on, the monitored communication unit performs a sound detection and if it is detected that no sound has been detected for a duration corresponding to the call inactivity timer value, the monitored communication unit enters the reduced transmission mode. In this mode, the monitored communication unit will transmit CTXQ INDICATION PDUs 205 either at periodic intervals defined by the TX skip value or in response to receiving a CTXQ INTERROGATION PDU 207.

If the monitored communication unit detects sound or voice activity it will exit the reduced transmission mode and return to normal transmission operation.

The monitoring communication unit may furthermore modify transmission parameters for the monitored communication unit during normal operation or the reduced ambiance listening mode operation by transmitting further CTXQ REQUEST PDUs. Specifically, any data from later CTXQ REQUEST PDUs may overwrite data received in previous CTXQ REQUEST PDUs

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. However, preferably, the invention is implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors. Although the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the term comprising does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality.

Claims

CIiAIMS

1. A system for operating an ambiance listening mode associated with a monitoring communication unit and a monitored communication unit in a wireless communication system; the system comprising: the monitoring communication unit having: means for receiving ambiance listening mode transmissions from the monitored communication unit, and means for transmitting at least one transmission parameter command to the monitored communication unit; and the monitored communication unit comprising: means for transmitting the ambiance listening mode transmissions to the monitoring communication unit, means for receiving the at least one transmission parameter command from the monitoring communication unit, and means for setting at least one transmission parameter of the ambiance listening mode transmissions in response to the at least one transmission parameter command.

2. A system as claimed in claim 1 wherein the at least one transmission parameter comprises at least one of a) a continuity parameter of the ambiance listening mode transmissions and b) a transmit power parameter.

3. A system as claimed in claim 1 wherein the means for transmitting the ambiance listening mode transmissions is operable to transmit discontinuously and the at least one transmission parameter comprises a temporal characteristic of at least one discontinuous transmission.

4. A system as claimed in claim 3 wherein the temporal characteristic comprises at least one of a) a duration of the at least one discontinuous transmission and b) an interval between discontinuous transmissions.

5. A system as claimed in claim 1 wherein the monitored communication unit comprises means for transmitting operating parameter information to the monitoring communication unit.

6. A system as claimed in claim 5 wherein the operating parameter information comprises at least one of a) an operating temperature indication of the monitored communication unit, b) a battery charge indication of the monitored communication unit, c) an external power connection indication for the monitored communication unit, and d) an operating mode indication for the monitored communication unit.

7. A system as claimed in claim 1 wherein the monitored communication unit is operable to operate in a first operating mode and a second operating mode wherein the at least one transmission parameter is applied to transmissions in the second operating mode but not in the first operating mode.

8. A system as claimed in claim 7 wherein the monitored communication unit comprises means for switching between the first operating mode and the second operating mode in response to a monitored ambient sound characteristic.

5

9. A system as claimed in claim 8 wherein the monitored ambient sound characteristic is a voice detection characteristic.

10 10. A system as claimed in claim 7 wherein the first operating mode is a full monitoring operating mode and the second operating mode is a reduced monitoring mode.