Method and apparatus for a talkgroup call in a wireless communication system

(54) (56) (57)

PATENTHAVARE Motorola Inc., 1303 East Algonquin Road Schaumburg 60196 IL US

Rich Comroe, South Barrington IL US, Shaowei Pan, Lake Zurich IL US, Bruce A Oltman, Schaumburg IL US, Shmuel Silverman, Buffalo Grove IL US, Mark O'Beirne, Lake Barrington IL US

Ehrner & Delmar Patentbyrå AB

Method and arrangement for a group call in a wireless communication system

CALLED PUBLICATIONS:

US A 6 005 848 (370/266), US A 4 360 910 (370/62),

US A 5,436,896 (370/62)

SUMMARY. _{χ one} code split multiple access (CDMA) system (100), a call group (101) is provided with subscriber HEBUD

NAME ter. A sub-speaker group (102) with subscriber units forming part of the call group is assigned at least one input channel (416-417) in the form of a time slot in a frequency channel. The call group is assigned to outgoing channels (415) in the form of time slots in a frequency channel. The members of the sub-speaker group can simultaneously send voice information (410-411) using the at least one incoming channel, whose speech information is summed (412) and returned to the call group using the outgoing channels. The speech information is summed up so that an individual speaker receives summed speech information without the speech content of the individual subscriber. Subscriber units in the sub-listening group are allowed to send voice information only upon request, and reception, of an additional incoming channel.

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The numbers in brackets indicate international identification code, INID code. Letters in clamps indicate international document code.

* ,

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SAMMÄHDRAS

In a wireless code split multiple access (CDMA) system (100), a call group (101) is provided with subscriber units. A sub-speaker group (102) with subscriber units forming part of the call group is assigned at least one input channel (416-417) in the form of a time slot in a frequency channel. The call group is assigned to outgoing channels (415) in the form of time slots in a frequency channel. The members of the sub-speaker group can simultaneously send voice information (410-411) using the at least one incoming channel, whose speech information is summed (412) and returned to the call group using the outgoing channels. The speech information is summed up so that an individual speaker receives summed speech information without the speech content of the individual subscriber. Subscriber units in the sub-listener group are allowed to send voice information only upon request, and reception, of an additional incoming channel.

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Cross-reference to related patent applications

The present application is related to a simultaneously filed application, also referred to as the method and arrangement for a group call in a wireless communication system, based on the international application PCT / US01 / 05211 with the same priority date and the applicant.

Field of the Invention

The present invention relates generally to wireless code division multiple access systems, and more specifically to a method and apparatus for group calls within such systems.

Background of the invention

Two-way wireless communication systems that include group dispatch services are known in the art. Group messaging services typically provide communication within a call group. A call group is a plurality of logically connected subscriber units (e.g., mobiles in vehicles and / or handheld portable radios) capable of engaging in group-wide communications. In normal call group communication, a single subscriber unit in the call group transmits voice information received by a fixed infrastructure and is returned to other subscriber units in the call group. Typically, such systems use frequency-division multiple access (FDMA) »

• 25 and / or time-division multiple access (TDMA) methods for receiving, receiving and broadcasting the broadcast. In FDMA systems, the input channel is normally paired with an output channel,. and the incoming channel can only be used by one subscriber at a time. Similarly, in TDMA systems inbound and outbound time slots are paired, and only one subscriber unit at a time ... can send one inbound message for retransmission.

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While these systems provide useful group communication, they force the communication to be somewhat rectified in that only one subscriber owns the call at any given time. That is, more natural group communication in which there are multiple simultaneous speakers and multiple listeners is not possible, since only one subscriber unit can send at any time. Although a number of prioritization methods exist today to allow high-priority users, or users with high-priority traffic (ie emergency calls), to be declared the owner of a group call, communication is still limited to configurations with a single speaker / multiple listeners.

Current telephony services provide conference calls in which several speakers and multiple listeners can simultaneously participate in a call. Conference calls can be extended to current wired systems by allocating a separate incoming channel or time slot to each potential speaker and a separate outgoing channel or time slot for potential listeners. Furthermore, separate full duplex channels (inbound and outbound resources) could be allocated to each subscriber unit in the call group.

While these approaches work, they are highly inefficient when it comes to resource use. E.g. it is not uncommon for public safety organizations to have call groups that include up to one hundred subscriber units. Obviously, setting up a group conference call using 25 separate and incoming resources for up to 100 separate subscriber units would require communication resources beyond the capabilities of most communication systems.

; A solution to the above problems is provided by Grube et al. in U.S. Patent No. 6005848 entitled METHOD AND APPARATUS; 30 FOR A TALKGROUP CALL IN A WIRELESS CDMA SYSTEM, assigned to; the proprietor of the present invention and incorporated by; reference herein. As described in Grube et al., One is assigned

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523 722 sub-call group in the call group at least one incoming code, with the entire call group assigned an outgoing code. Members of the sub-call group can simultaneously send voice information using the incoming code (s). The voice information from the speakers is summed up and transmitted to all users in the call group. While the aforementioned technology provides a more natural conversation between users, one disadvantage of this approach is that the individuals who actively speak get their voices emitted to them, which can be annoying to the speaker.

Thus, there is a need for duplex communication between members of a call group in wireless communication systems that allows multiple users to simultaneously broadcast to the call group, and yet does not allow an active speaker to hear their voice broadcast.

Brief description of the drawings

Figure 1 shows a block diagram of a wireless communication system in accordance with the present invention.

Figure 2 shows a flow chart of the method of using a fixed infrastructure in accordance with the present invention.

Figure 3 shows a table which can be incorporated in the preparation of a group call in accordance with the present invention.

Figure 4 is a block diagram of the operation of the wireless communication system of Figure 1 in accordance with the present invention.

Figure 5 shows a flow chart of a method of using a subscriber unit in accordance with the present invention.

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Figure 6 shows a block diagram of the wireless communication system operating mode of Figure 1 in accordance with an alternative embodiment of the present invention.

Figure 7 is a block diagram of the time slot distribution in the TDMA wireless communication system of Figure 6.

Description of a preferred embodiment

The present invention generally provides duplex communication within the call group where a speaker's voice is not broadcast to the speaker. A sub-call group with subscriber units, which make up part of the call group, is assigned at least one incoming code. The call group is assigned outgoing codes. At the same time, members of the sub-call group can send voice information by using at least one input code, which voice information is summed and returned to the call group by using the outgoing codes. Voice information is summed up so that an individual speaker receives summed voice information without the individual subscriber's voice content. Subscriber units in the call group, but not included in the sub-call group, (sub-listener group), are allowed to send voice information only after requesting, and receiving, an additional incoming code.

The present invention encompasses a method for the fixed infrastructure to establish a group call. The method comprises the steps of receiving from a first subscriber unit of a plurality of subscriber units a request for a group call, which request includes an identity of the first subscriber unit and an identity of a call group, identifying, based on the identity of the call group, a call group with subscribers, units comprising at least two subscriber units of the plurality of subscriber units, identifying, based on the identity of * ', the first subscriber unit, a sub-speaker group with subscriber units in the call group, and assign an outgoing time slot in one

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523 722 frequency channel to the subscribers in the sub-listener group. In the preferred embodiment of the present invention, a plurality of output time slots in a frequency channel are uniquely assigned to subscribers in the sub-speaker group if there are more than one speaker, and at least one input time slot in the frequency channel is uniquely assigned to the sub-speaker group.

The present invention further comprises a method for the fixed infrastructure to establish a group call. The method comprises the steps of receiving incoming voice data from a plurality of subscriber units within a call group, the incoming voice data comprising voice data of a first subscriber. The input voice data is summed to produce a first summed voice data. Finally, the summed voice data is sent to subscribers within the call group without sending the summed voice data to the first subscriber.

The present invention further comprises a method comprising the steps of receiving incoming voice data from a plurality of subscriber units within a call group, wherein the incoming voice data comprises voice data of a first subscriber, sending the first summed voice data to the sub-listener group, wherein the first summed voice data comprises a summation. of a number of subscriber units that are actively sending incoming speech, and finally cease sending voice data to subscribers in the sub-speaker group.

The present invention can be further described with reference to Figures 1-5. Figure 1 shows a block diagram of a wireless communication system 100 in accordance with the present invention. In the preferred embodiment of the present invention, the communication system 100 utilizes the next generation CDMA architecture as described in cdma2000 International Telecommunication Union-Radio communication (ITU-R) Radio

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Transmission Technology (RTT) Candidate Submission document, but in alternative embodiments, the communication system may

100 utilize other analog or digital cellular communication system protocols such as, but not limited to, the next generation Global System for Mobile Communications (GSM) protocols, or the CDMA system protocol as described in the Personal Station-Base Station Compatibility Requirements for 1.8 to 2.0 GHz Code Division Multiple Access (CDMA) Personal Communication Systems (American National Standards Institute (ANSI) J-STD-008).

The wireless communication system 100 comprises a plurality of subscriber units 104-109 arranged in at least one call group.

101 in wireless communication with a fixed infrastructure 103. The call group 101 further comprises a sub-speaker group 102 and a sub-listener group 130. In the example shown, the subscriber units identified by the reference numerals 104-106 are included in the call group 101 and the sub-speaker group 102, while the subscriber units identified by the reference numerals 107-109 included in the sub-listener group. In the preferred embodiment, each subscriber unit 104-109 is physically capable of duplex communication. However, as described in more detail below, only those subscriber units included in the sub-speaker group are logically allowed to engage in duplex communication relative to the call group 101.

As is known in CDMA systems, communication channels 117-125 are effectively provided by the use of spreading codes. As described in more detail below, outgoing codes are used to efficiently provide outbound communication channels 117-122 to each subscriber unit in the call group 101.

In addition, input codes (three are used in the example shown in Figure 1) to effectively provide input

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523 722 communication channels 123-125 to each subscriber unit in the sub-speaker group 102.

The fixed infrastructure 103 includes the elements normally required to support communication within the wireless system 100 and, in the preferred embodiment, conforms to a packet-based CDMA architecture. More specifically, fixed infrastructure 103 includes a switch 110 in communication with a controller 111, which in turn is in communication with base transceiver stations (BTSs) 112-113. The switch 110 (often referred to as a Mobile Switching Center or MSC), controls (often referred to as a Base Station Controller or BSC) 111 and BTSs 112-113 are all well known in the art. In practice, gear 110 typically communicates with more than one controller and can communicate with other equipment not shown. For simplicity, fixed infrastructure 103 has been limited as shown in Figure 1. The fixed infrastructure 103 may also optionally comprise a dispatch controller 114 which is in communication with the BTS 112-113. A suitable message controller 114 is the Dispatch Application Processor used in iDEN wireless communication systems manufactured by Motorola, Inc. The administration of group call processing is preferably handled by check 111 or message controller 114 if used. In addition, the function of group call management can be distributed through the fixed infrastructure 103, as described below.

Figure 2 shows a flow chart of a method that can be used in the fixed infrastructure 103. Although the method described in Figure 2 is generally implemented through the fixed infrastructure 103, the method is preferably performed by check 111 or the message processor 114 if used. In addition, the functionality shown in Figure 2 may be distributed over the entire fixed infrastructure 103. Generally, implement11194; 01-11-23

523 722, the method illustrated in Figure 2 is run by stored software routines executed by the platforms on which the software is stored.

In step 202, the fixed infrastructure 103 receives a request for a group call from a subscriber unit in the call group 101.

The requesting subscriber unit may be one of the subscriber units 104-106 included in the subtalar group 102, or it may be one of the subscriber units 107-109 which is not a member of the subtalar group 102. Either way, the request includes an identification of the requesting subscriber unit and an identification of the subscriber unit 102. the call group to which communication is to be established. In step 204, the fixed infrastructure 103 determines using a table and the identifications of the call group and the requesting subscriber unit, which subscriber units within the call group 101 to be established as duplex participants in the group call, i.e. the subscriber units included in the subtalar group 102. The table used for this purpose is further described with reference to Figure 3.

Figure 3 shows a table 300 that can be used by the fixed infrastructure 103 when establishing a group call. Table 300 includes a series of inputs 301-303 which correlate the identifiers of the call groups 301 with the identifications of the requesting subscriber units 302 and the sub-speaker groups corresponding to each requesting subscriber unit 303. An advantage of this structure is that by changing the inputs in Table 300, a plurality of subtalar group configurations can be provided on a dynamic basis. Referring to the example shown in Figure 3, the call group identified as TG 001 includes subscriber units identified as SU 001, SU 002, SU

003, SU 004, SU 008 and SU 009. Thus, when the subscriber unit SU; 003 requests a group call, the subscriber units SU 001 are included,

SU 002, SU 003, SU 004, SU 008 and SU 009 in the call group and

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523 The 722 subscriber units SU 001 and SU 008 are established as duplex subgroup group members. Alternatively, when any of the subscriber units SU 002, SU 004 or SU 009 requests a group call, the subscriber units SU 001, SU 002, SU 003, SU 004, SU 008 and SU 009 are included in the call group, and only the subscriber unit SU 001 is established as a duplex subgroup group member.

Data that is input to the duplex speaker group inputs 303 can be entered by a system administrator, or they can be entered automatically as a dynamic function of various events. One way to perform dynamic updates of subgroup inputs 303 is to continuously store subscriber unit identities that have recently been engaged in communication with the requesting subscriber unit. That is, when one-to-one communication with a given device is established, sub-speaker group inputs can be updated to include the identity or identities of the subscriber units that participated in such one-to-one communication. Alternatively, any subscriber unit requesting to be added to a group call initiated by the requesting unit (as described in more detail below) may be added to the appropriate sub-speaker group input. The time window for such recent communication is a matter of design choice and can be based on an absolute time (eg, only subscriber units that have communicated in the last X minutes) or sequence (eg, only the latest X subscriber units in communication). Another method is to update the sub-speaker group inputs 303 based on the relative priorities of subscriber units within the call group. Thus, for each given subscriber unit, the subtalar group includes only those subscriber units within the call group that have a priority at least as high as the given unit. As subscriber unit priorities are changed, sub-speaker group inputs 303 can be updated accordingly. Yet another method is to update the subtalar array inputs 303

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523 722 based on locations of subscriber units relative to each other. Thus, when a given subscriber unit updates its current location, the sub-speaker group corresponding to that subscriber unit is updated to include only those subscriber units that are within a predetermined distance (e.g., one mile) from the given subscriber unit. Of course, other methods may be apparent to one skilled in the art. In addition, other embodiments which produce the same results as Table 300 may also be used.

A subscriber can dynamically switch between the sub-speaker group and the sub-listener group. If a subscriber requests to join the sub-listener group, a new incoming and outgoing channel is assigned to that subscriber. The subscriber then switches from the sub-listener group to the sub-speaker group. In order to save RF resources, if a subscriber who is in the sub-speaker group requests only listening, the incoming and outgoing channel for that subscriber and the outgoing channel in the sub-listener group is released to the subscriber. The subscriber then switches from the sub-speaker group to the sub-listener group.

Referring to Figure 2, fixed infrastructure 103 assigns a plurality of outgoing and incoming codes to the sub-listener group and sub-speaker group, respectively, when the sub-listener group 130 and sub-speaker group 102 have been determined. In the preferred embodiment of the present invention, the users of the sub-listener group 130 are assigned a single multicast outgoing channel. However, the users in the subtalar group 102 are each assigned a unique outgoing broadcast channel. If there is only one subscriber / speaker in the sub-group there is no need to assign an outgoing channel

0 to this subscriber / speaker. To this end, the fixed infrastructure 103 in step 206 determines a plurality of outgoing codes for use in the call group 101 and at least one input code

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for use in the subtalar group 102. The fixed infrastructure 103 may determine a single input code to be used by the subtalar group 102 or, preferably, separate input codes assigned to each member of the subtalar group 102. The outgoing codes are used to create outgoing channels 117-122 (often referred to as a downlink or forward channel) to each subscriber unit in the call group 101. The at least one input channel is used (often referred to as an uplink or down channel) for the members of the subtalar group 102. The outgoing code and at least one input code are communicated. the call group 101 in step 208. This message can be obtained by using a control channel based on a PN code known by each subscriber unit, which control channel is monitored by the subscriber units.

In the preferred embodiment of the present invention, the group call is similar to an iDEN message call if the maximum subscriber number in the sub-speaker group is 1. This requires only one input channel and one output channel. If the maximum subscriber number in the sub-speaker group is equal to the number in the call group, the group call is similar to the full duplex conference call. This requires N incoming channels and N outgoing channels, where N is the subscriber number in the call group. However, if the maximum subscriber number, M, in the sub-speaker group is between 1 and N, the group call is identified as an M-master message message. This design requires M inbound and M + l outbound channels.

When the code assignment has been made, only the subscriber units 7 included in the sub-speaker group 102 can make incoming broadcasts': to the group call. Accordingly, in step 210, the message controller 114 receives streams of speech information from one or ·; several subscriber units in the sub-speaker group 102. The speech streams: are sent to the message controller via the base stations 112-113.

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Assuming that the at least two subscriber units within the subtalar group 102 were assigned unique input codes, the stream of speech information received by the fixed infrastructure 103 may arrive simultaneously, i.e. in a way representative of normal group-like communication. The units within the subtalar group 102 that do not currently transmit speech will transmit a blank pattern, as is known in the art. In step 212, fixed infrastructure 103 (message controller 114) sums up the streams of speech information to produce summed speech information. Various summing techniques can be used including, but not limited to, conference bridges or arithmetic adding within a signal processor. If the streams with speech information are in a form that is not suitable for summation, e.g. compressed digital speech, at least one interim code converter may be required to convert the stream of speech information into a format that can be easily summed, as is known in the art. It should be noted that when using an Enhanced Variable Rate Coder (EVRC), only two signals are combined, since an EVRC speech encoder can only encode a maximum of two people's numbers. If more than two people's numbers are summed together, the patch information is beyond the limitations of the EVRC speech encoder. Thus, when an EVRC speech encoder is used, only the two highest speech signals are summed. In the preferred embodiment of the present invention, a determination is made as to where the resulting summed signal is to be sent, and if the resulting signal is to be sent to a current speaker within subgroup 102, the speech of the individual speaker is removed from the resulting summed signal (step 213). If the resulting signal is to be sent to a subscriber unit that is not currently speaking, in step 213 no speech signal is removed from the summed signal.

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Regardless of which summation method is used, the summed speech information is then transmitted by the fixed infrastructure 103 using an outgoing code. Since the outgoing code is used, only the subscriber unit that uses the specific code may be able to receive and reproduce the summed speech information. Since the summed speech information is representative of a number of speakers, more realistic group communications are achieved. In addition, each individual user's voice is removed from their outgoing signal, which prevents the user's voice from being transmitted to them.

The present invention anticipates that it may be necessary for subscriber units that are not currently members of the sub-speaker group 102, and therefore unable to send voice information, to request the ability to transmit. Thus, the fixed infrastructure 103, in step 214, determines whether any subscriber units in the sub-listener group have sent a request to speak. The request to speak is transmitted on a channel based on a code other than the subtalar group 102 assigned to the input codes (i.e., a control channel). The request to speak includes identification of the call group 101 and an identification of the subscriber unit requesting to speak. If such a request is received, the fixed infrastructure determines an additional input code, which is preferably unique from the previously assigned input code (s) in step 216. It further.

; The input code is then notified to the requesting unit in; step 208, and the group call continues as before, but with¹ 'the addition that the requesting entity is a speaker in the call.

As described above, the table discussed with reference (1 to FIG. 3) can be updated to include the^; '30 unit (i.e. the unit assigned to the additional incoming code) in the sub-speaker group input used to establish the current group call. The mode of operation of a subscriber; 01-11-23

523 722 unit, in addition to steps 214 and 216, are discussed with reference to Figure 5 below.

Assuming that no request to speak has been received in step 214, the fixed infrastructure 103 determines in step

218 whether a subscriber / speaker in the sub-speaker group requires only listening instead of speaking. If a subscriber / speaker in the sub-speaker group requires only listening, the incoming and outgoing channels for that subscriber are released, and the outgoing channel for the sub-listener group is assigned to the subscriber in steps

220. The subscriber is moved from the sub-speaker group to the sub-listener group.

Fixed infrastructure 103 then determines (step 222) whether the group call has ended. It will be appreciated that various techniques can be used to detect the end of a group call.

E.g. a time-out timer can be used after all units have stopped transmitting either empty patterns or speech information. Alternatively, a detection that all the subscriber units of the subtalar group 102 have terminated can be used. Regardless, assuming that the group call has ended, fixed infrastructure 103 assigns the outgoing code and incoming codes in step 224. Similar to step 208, the allocation of the incoming and outgoing codes can be performed over a control access channel using known PN codes.

The method of the present invention can be further described with reference to Figure 4. In Figure 4, the fixed infrastructure 103 includes a receiver 409 providing separate streams of speech information 410-411 based on broadcasts from the members of the sub-speaker group 102, summers 412 and 415 · which summarize the streams with speech information 410-411, and a transmitter 414 which sends summed speech information 413 to the sam ··, voice group 101 using outgoing codes 415 (referred to as

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523 722 code A, D and E). The transmissions from the members of the subtalar group 102 are based on input codes 416-417 (designated code B and code C). In the preferred embodiment of the present invention, summers 412 and 415 are part of message controller 114 located externally to base stations 112113.

As shown in Figure 4, each of the subscriber units 104109 has a plurality of common elements. More specifically, a control and processor element 401, which typically comprises one or more processor devices (e.g., microprocessors, digital signal processors, etc.), is coupled to a memory 402. The control and processor element 401 is coupled to a transmitter 403, a receiver 404, a speaker 405, a microphone 406, and an input device 407. Each of these elements is well known in the art. Under the control of software algorithms stored in memory 402, the control and processor element 401 performs the data required for the operation of the subscriber unit. Receiver 404 is used to receive assignments of outgoing and / or incoming codes for use in group 20 calls, and then to receive allocations of outgoing and / or incoming codes. In addition, in all the subscriber units included in the call group 101, summed speech information 413, modulated in accordance with outgoing codes 415 and received via receiver 404, is processed and provided to the loudspeaker 405. In this way, subscriber units included in the call group 101, monitor the outgoing communication corresponding to the group call. The input device 407, which may include a keyboard, menu-driven monitor or similar device, allows users to send the request to speak.

In duplex subscriber units (i.e., members of the subtalar group 102), numbers input through microphone 406 are processed and provided as a stream of speech information to transmitter 403 for

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523 722 transmission based on an input code 416-417. The duplex subscriber units also use a voice-activated switching element (VOX) 408 so that a continuous stream of speech information (when speech is captured by microphone 406) or an empty pattern (when speech is not captured by microphone 406).

In the example of Figure 4, two unique input codes, code B and code C, are used by the subscriber unit in the sub-speaker group 102 to send streams of speech information 410-411. In practice, the input codes, code B and / or code C, are used not only to send incoming voice information but can also be used to send transmission power control information so that the fixed infrastructure 103 knows the status of the outgoing code. Ie the fixed infrastructure 103 can adjust the output transmitted power relative to the outgoing codes in order to maintain communication. In addition, a plurality of outgoing codes 425-427 (codes A, D and E) are used to send the resulting summed speech information. In practice, the outgoing codes are not only used to send summed speech information 413, but can also be used to send control information such as input code assignments and power control information to members of the sub-speaker group 102.

As described above, several subscriber units that are members of the subtalar group 102 can send speech simultaneously to the fixed infrastructure 103. In the preferred embodiment of the present invention, the speech signals are received by the receiver 404 and ··; is sent to processor 418. Processor 418 can send any cow ;; to an encoder 412, however, when an EVRC speech encoder is used, only the two highest-energy speech signals are sent from processor 418 to be summed by the encoder 412. The resulting summed number is then sent to a second encoder.

415, where an individual speech signal is removed from the summed signal 413. In the preferred embodiment of the present invention,

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523 722 invention, the control and processor unit 418 sends an individual speech signal to the summator 415 so that it can be removed from the summed signal 413 even if the individual speech signal has the highest speech energy. The individual speech signal sent to the buzzer 415 is determined by each resulting signal 419 being sent. For example, a signal utilizing a specific code (code D) is sent to the subscriber 104, then the speech signal is sent from the subscriber 104 to the buzzer 415 and is removed from the signal 413. The resulting signal (signal

419) is then propagated with a specific code (code D) and sent to subscriber 104. The result is a signal received by subscriber 104 which is a combined signal of all simultaneous speakers (or the two highest ones) without sending a signal from the incoming channel in the subscriber unit 104.

Thus, in accordance with the preferred embodiment of the present invention, a specific speaker in subgroup 102 receives an output signal comprising the combined speech of all speakers in the sub-speaker group 102, however, the voice of the specific speaker is removed from the output signal. The units 107-109 in the sub-listener group will receive a combined signal with all speakers without any number being removed from signal 413. This is accomplished by the processor unit 418 not sending any signal to the buzzer 415 when a transmission to the units 107-109 is desired.

As described above, a subscriber unit in the sub-listener group can: send a request to talk to the fixed infrastructure

103 in order to participate in the group conversation. The operation of a: subscriber unit for this purpose is shown in more detail in Figure 5. In step: 502, a subscriber unit receives an assignment of an outgoing code relative to a group call. As described above, such an assignment is typically sent over a control access channel created by the use of a known code.

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In step 504, the subscriber unit may optionally monitor outbound communications related to the group call. This step is optional in that a user of a subscriber unit may choose not to monitor the group call, or in that outbound communication need not be immediately imminent upon receipt of the outbound code assignment. Regardless, the subscriber unit detects, in step 506, the need to send a request to speak, which request is addressed to the group call. After sending the request to speak to fixed infrastructure 103 in step 508, the subscriber unit then receives an assignment of an additional input code from fixed infrastructure 103, and an additional output code if there is more than one speaker in the sub-speaker group, in step 510 . Once it has received the assignment, the subscriber unit, in step 512, may begin to send an additional stream of speech information using the input code, and receive an additional stream of speech information using the outgoing code if there is more than one speaker. In this way, any given subscriber unit can remain a listening participant only or, if desired, change its status to become an active participant (ie a speaker) in the group conversation.

Figure 6 shows a block diagram of the operation of the wireless communication system of Figure 1 in accordance with an alternative embodiment of the present invention. In the alternative embodiment of the present invention, the communication system 100 utilizes a system protocol for a time-division multiple access (TDMA). The alternative embodiment will be described below with communication system 100, which is preferably an iDEN® system commercially available; * 30 from Motorola, Inc. Base stations 112-113 preferably comprise iDEN Enhanced Base Transceiver Sites (EBTS) commercially available from Motorola, Inc. and provided 71194; 01-11-23

523 722 provides at least message communication services to subscriber units 104-109. The communication units 104-109 preferably include two-way radio or radio telephone devices, such as the Motorola iDEN mobile or portable radio.

In Figure 6, the fixed infrastructure 103 comprises a receiver 609 providing separate streams of speech information 610-611 based on transmissions from the members of the sub-speaker group 102, summers 612 which summarizes the streams of speech information 610-611, a switch 615 and a transmitter 614 as transmitters. summed speech information 613 to call group 101 using outgoing channels 615 (referred to as channels A, D and E). Unlike the preferred embodiment where a CDMA system architecture is used, channels in the alternative embodiment include a specific frequency / time slot combination. The broadcasts of the members of the subtalar group 102 are based on the input channels 616-617 (designated channel B and channel C).

As shown in Figure 6, each of the subscriber units 104109 has a plurality of common elements. More specifically, a control and processor element 601, which typically includes one or more processor devices (e.g., microprocessors, digital signal processors, etc.), is coupled to a memory 602. The control and processor element 601 is coupled to a transmitter 603, a receiver 604, a speaker 605, a microphone 606, an input device 607, and time-division switches 608 and 609.

Each of these elements is well known in the art. Under the control of software algorithms stored in memory 602, the control and processor element 601 performs the data required for the operation of the subscriber unit. Receiver 604 is used to receive assignments of outgoing and / or incoming channels for use in group calls and thereafter to receive allocations of the outgoing and / or incoming channels.

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In addition, in all of the subscriber units included in the call group 101, summed speech information 613 is modulated in accordance with the outgoing channels 615 and received via the receiver 604, and is provided to the speaker 605. In this way, subscriber units included in the call group 101 can monitor the outgoing communication corresponding to the group call. The input device 607, which may include a keyboard, menu driven monitor or similar device, allows the user to send a request to speak. In the duplex subscriber units (i.e., members of the subtalar group 102), numbers input through microphone 606 are processed and provided as a stream of speech information to transmitter 603 for transmission based on an input channel 616-617. The duplex subscriber units also use a voice-activated switching element (VOX) 608 so that a continuous stream of speech information (when speech is captured by microphone 606) or a blank pattern (when speech is not captured by microphone 606).

In the example of Figure 6, two unique input channels, channel B and channel C, are used by the subscriber units in the sub-speaker group 102 to send streams of speech information 610-611. In practice, the input channels, channel B and / or channel C, are used not only to send incoming voice information but can also be used to send power control information so that the fixed infrastructure 103 knows the status of the outgoing channel. That is, fixed infrastructure 103 can adjust outbound transmit power relative to outbound channels for the purpose of retaining communications. In addition, a plurality of numbers of outgoing channels 625-627 (channels A, D and E) are used to send the resulting summed speech information.

As described above, several subscriber units which are members of the sub-speaker group 102 can simultaneously send speech to it: fixed infrastructure 103. In the preferred embodiment of

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523 722 of the present invention, voice signals are received from receiver 604 and sent to processor 618. Processor 618 can send all the channels to sumer 612, but when an EVRC speech encoder is used, only the two highest energy speech signals can be sent from processor 618 to be summed in sumer 612. The resulting summed number is then sent to switch 615 where the summed signal 613 is either sent to the transmitter 414 or not, based on the current speaker and where the resulting signal 619 is sent. For example,

a signal utilizing a specific channel (channel D) is sent to subscriber 104, so the speech signal is not sent from subscriber 104 through switch 615 to transmitter 614. The result is a signal received by subscriber 104 which does not have audio components when subscriber 104 speaks.

Thus, in accordance with the preferred embodiment of the present invention, a specific subscriber in the subgroup 102 receives an output signal comprising the combined speech of all speakers in the sub-speaker group 102, however, when a specific subscriber speaks, the switch 615 does not send the combined signal 413 , which results in no audible signals being received by the subscriber. The units 107-109 in the sub-listener group will receive a combined signal from all speakers, where switch 615 sends the combined signal 613.

In order to save RF resources, the transmitting and receiving operations use different time slots. For example, with reference to Figure 7, when an iDEN system makes a call, a mobile input frame 702 uses a time (e.g., time slot 3), and its outgoing frame 701 also uses the same time slot (e.g. time slot 3). In the preferred embodiment of the present invention, the output time slot (slot 3) in the input frame 702 is assigned a time slot delayed after the input time slot (701) (slot 3). Because they are inbound and outbound

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523 722 time slots differentiate in time, RF duplexers in the mobiles are avoided by using the time switches 608 and 609.

When a mobile makes a 2-master (more than one speaker) message telephone call, the caller belongs to the sub-speaker group 102 initiator (the caller is defined as the first master). The caller is assigned to one of the incoming time slots (e.g. time slot 3) from the fixed infrastructure 103. The outgoing time slot (slot 3) with the same incoming slot number as other dialers belonging to the sub-listener group 103 is also assigned by the fixed infrastructure 103. When one of the listeners in the sub-listener group 130 requires to be allowed to speak and its request is granted from the fixed infrastructure 103, the listener is moved from the sub-listener group 130 to the sub-speaker group 101. In the preferred embodiment of the present invention, a pair of incoming and outgoing slots is assigned (e.g. time slot 4) for the new speaker (the second speaker is defined as the second master). In order to provide the first speaker (first master) listening capabilities, the same output time slot (slot 3) as the input time slot is assigned to the first speaker (first master). A new outgoing time slot (time slot 2) other than the same output time slot (time slot 3) must be assigned to the sub-listener group 130.

If the first speaker (first master) stops speaking, its incoming and outgoing slots are released (Tx / Rx time slot 3). The outgoing time slot (Rx time slot 4) for the second speaker (second master) is also released. In order to save resources for other calls, the incoming time slot number (Tx time slot # 4) of the other speaker is changed to the same outgoing time slot number (here time slot number 2) for the sub-listener group 130. Then the second speaker (second master) is referred to as the first speaker (first master).

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523 722

If N participants wish to speak, N pairs are required with transmission and reception time slots plus one or more reception time slots, where N is the number of members in the sub-speaker group 103. In the iDEN system, there are only six time slots in a frequency channel.

If N is greater than 5, some of the participants in the sub-speaker group 103 must be relocated to other frequency channels, since an outgoing time slot must be reserved for the sub-listener group 130.

In the traditional iDEN message group call there is a monitoring mode. If a participant has the priority of a monitor, its speech from one of the included slots can be exchanged for the current message speaker's number to be sent to the listeners in the sub-listener group 130. In the present invention, the monitor's speech and the current speakers' speech are summed to all listeners in the sub-listener group.

The present invention generally provides a method and apparatus for duplex communication within call groups. By using an effective CDMA or TDMA system resource allocation method, the present invention allows a subscriber unit with subscriber units to speak in a wireless duplex conference call while other members, potentially in a very large call group, can listen and, if desired, participate in the call. In this way, a more natural group-like communication can be achieved without putting an unnecessary burden on use: one of the wireless communication resources.

Although the present invention has been described with reference to certain preferred embodiments, a number of modifications and variations may be made by one of ordinary skill in the art within the scope of the present invention. For example, although a preferred embodiment was described above by subtracting an individual user's voice signal from a summed signal, other techniques can be used to construct a summed signal without

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523 722 the number of the individual user. For example, instead of subtracting a subscriber's speech signal in summer 415, in an alternative embodiment, the summator 415 can be eliminated and the processor unit 418 simply does not send the subscriber's speech signal to the summator 412 when the resulting summed signal is to be sent to the subscriber.

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