Abstract:
Disclosed is a method and system for interrupting a transmitting subscriber where the transmitting subscriber communicates on a forward channel of a wireless communications system while listening to a reverse channel for reverse channel signaling. The transmitting subscriber receives reverse channel signaling on the reverse channel from a second subscriber, wherein the message is received either directly from the second subscriber or through at least one base radio and terminates the communication on the forward channel in response to the received reverse channel signaling.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. provisional application No. 60/778,737 filed Mar. 3, 2006, which is incorporated by reference as if fully set forth. The present application is also related to co-pending U.S. patent application Ser. No. 10/799,035, entitled “Method of Signaling Reverse Channel Information with Minimal Voice/Data Delay,” filed on 12 Mar. 2004 and assigned to Motorola, Inc. which is hereby incorporated by reference as if fully set forth. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to wireless communications systems and more specifically to interrupting a transmitting subscriber in a wireless communications system. 
       BACKGROUND 
       [0003]    A wireless communications system may generally comprise a set of “subscribers,” typically subscribers are the endpoints of a communication path, and a set of “base radios,” typically stationary and the intermediaries by which a communication path to a subscriber may be established or maintained. One such type of system is a time division multiple access (TDMA) communications system where the radio medium is divided into time slots to carry the communications of the system. 
         [0004]    When a subscriber is transmitting communications, there may be instances when interrupting the transmitting subscriber may be important. For example, a first police officer needing back up may need to interrupt a second police officer that is engaged in a call. In such an instance, it would be important to have a mechanism to interrupt the second police officer to notify the second officer that the first police officer requires assistance. 
         [0005]    Accordingly, there is a need for interrupting a transmitting subscriber in a wireless communications system. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    An illustrative embodiment of the invention is now described, by way of example only, with reference to the accompanying figures in which: 
           [0007]      FIG. 1  is a block diagram of an example wireless communications system in accordance with an embodiment of the invention. 
           [0008]      FIG. 2  is a block diagram of an example reverse channel burst on the outbound channel in accordance with an embodiment of the invention. 
           [0009]      FIG. 3  is a block diagram of an example of a reverse channel burst on the inbound channel in accordance with an embodiment of the invention. 
           [0010]      FIG. 4  is a flow diagram of an example operation of a subscriber transmitting in the wireless communications system of  FIG. 1  in accordance with an embodiment of the invention. 
           [0011]      FIG. 5  is a flow diagram of an example operation of a subscriber initiating an interrupt in the wireless communications system of  FIG. 1  in accordance with an embodiment of the invention. 
           [0012]      FIG. 6  is a block diagram of an example remote control request message in accordance with an embodiment of the invention. 
       
    
    
       [0013]    It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to each other. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate identical elements. 
       DETAILED DESCRIPTION 
       [0014]    Referring now to  FIG. 1 , there is shown an example wireless communications system  100  where wireless communications take place between subscribers, namely subscriber  102  and subscriber  104 , either directly or via a base radio, namely base radio  106 . The subscribers and base radio are communicating with each other via an RF medium assigned to the wireless communications system  100 . 
         [0015]    In the wireless communications system  100 , an air interface protocol is used to manage access to the RF medium. In one example, the RF medium is divided into slots (also known in the art as “channels”) so that the various slots carry different information, e.g. carrying control information common to channels, carrying voice or data payload, and carrying signaling information (e.g., synchronization and embedded signaling). In one example, the wireless communications system  100  is a time division multiple access (TDMA) communications system having time slots. In another example, the wireless communications system  100  adheres to ETSI standard TS 102 361. 
         [0016]    The wireless communications system  100  may be configured so that a subscriber may receive signaling information while transmitting. As is known to one of ordinary skill in the art, the channel that carries signaling while the subscriber is transmitting payload (e.g. as a part of a call) is termed the “reverse channel” and the control information sent on the reverse channel is termed “reverse channel signaling.” Likewise, the channel that the subscriber is utilizing for transmitting payload is termed the “forward channel.” 
         [0017]    In any case, regardless of whether the channel is a “forward channel” or a “reverse channel,” the communication may be of an inbound direction, which means that the communication is from the subscriber to a base radio, e.g. as shown in  FIG. 1  as  108 . The communication may be of an outbound direction, which means that the communication is from the base radio to the subscriber, e.g. as shown in  FIG. 1  as  110 . Even though the inbound and outbound directions are shown with respect to a base radio (termed “indirect mode”), the same definitions can be applied to communications directly between subscribers (termed “direct mode”). That is, signaling from subscriber  102  to subscriber  104  may be termed inbound and signaling from subscriber  104  to subscriber  102  may be termed outbound. 
         [0018]    In one embodiment, the wireless communications system  100  is a two-slot TDMA communications system that has two 6.25 kHz equivalent logical channels which share a single 12.5 kHz physical channel. The two slots allow a subscriber to alternately transmit on one channel and receive control information, e.g. the reverse channel signaling, on the other channel. In one example of the two-slot TDMA communications system, an entire slot does not carry control information, but only a center portion of the slot carries the control information. In another example of the two-slot TDMA communications system, an entire slot does not carry information, but only a center portion of the slot carries synchronization and/or control information. For the outbound channel (e.g. as shown in  FIG. 2 ), only the center 5 msec portion of the slot carries control information whereas for the inbound channel (e.g. as shown in  FIG. 3 ), the center 10 msec portion of the slot carries control information. By confining the control information to the center of the time slot, subscribers that are slower to change frequencies may be used. As is known in the art, described in the figures is only one embodiment of the invention. Alternatives such as the center portions of the burst carry either control and/or synchronization are well known and considered to be equivalent. Further known, even though the term “inbound channel” is used, the inbound channel may be used for subscriber to subscriber communications (also termed “direct mode” as described above). 
         [0019]    In one embodiment, the format of the reverse channel signaling in an outbound direction, e.g.  110 , is a part of the outbound channel burst  200  as shown in  FIG. 2 . In one embodiment, the outbound channel burst  200  has duration  204  of 27.5 msec and the slot that carries the outbound channel burst  200  is of 30 msec. In any case, the center  206  of the outbound channel burst  200  having duration of 5 msec carries the reverse channel signaling  206  and is between payload. In one embodiment, the reverse channel signaling  206  is 32 bits of reverse channel information  202  and 16 bits of embedded information  208 . In one example, the 32 bits of reverse channel information  202  comprises 11 bits of RC info and 21 bits of FEC Parity. 
         [0020]    In one embodiment, the format of the reverse channel signaling in the inbound direction, e.g.  108 , is called a reverse channel burst  300  as shown in  FIG. 3 . In one embodiment, the reverse channel burst  300  has duration  310  of 10 msec and the slot that carries the reverse channel burst  300  is of 30 msec in duration  304 . In any case, the center of the reverse channel burst  300  carries the synchronization (e.g. a 48-bit synchronization word) and the rest of the reverse channel burst  300  carries the reverse channel signaling  306 . Notice, that shown in  FIG. 3  is reverse channel signaling  306  having a noncontiguous 32-bit field, but in other embodiments, the reverse channel signaling  306  may be contiguous. In any case, in one example, the reverse channel signaling  306  is 32 bits of reverse channel information  302  and 16 bits of embedded information  308 . In one example, the 32 bits of reverse channel information  302  comprises 11 bits of RC info and 21 bits of FEC Parity. In any case, the inbound reverse channel burst shown in  FIG. 3  allows a subscriber to send reverse channel signaling on an inbound channel whether directly to another subscriber or via a base radio. 
         [0021]    In one embodiment, the 11 bits of RC info in either 32 bit fields  202  or  302  are defined as 3 bits for conveying format or opcode information, 5 bits for conveying message dependent information, and 3 bits for a cyclic redundancy check (CRC) which can be used for error detection. 
         [0022]    As is known to one of ordinary skill in the art, the information contained in the bursts, the length of fields, and the order of information as shown in the figures is representative and is not meant to be a limitation on an embodiment of the present invention. 
         [0023]    Further used herein, the terms “communication” and “transmission” are used interchangeably and refer to contiguous TDMA bursts emanating from one subscriber in one slot. As such, transmissions may generically refer to voice, data or control information relating to the wireless communications system  100 . The term “call” refers to related voice transmissions between subscribers in the wireless communications system  100 . 
         [0024]    Referring to  FIG. 4 , shown is a flow diagram  400  of an operation of a subscriber, e.g. a first subscriber  102 , transmitting in a forward channel (step  402 ). As mentioned above, the transmission may be voice, data, or control. In an embodiment, the subscriber is engaged in a call with another subscriber, e.g. a second subscriber  104 . While the subscriber is transmitting on the forward channel (e.g. while engaged in a call with the second subscriber), the subscriber receives a message on the reverse channel (step  404 ). If the subscriber determines that the received message is an interrupt message (step  406 ), then the subscriber determines the type of interrupt (step  408 ). If the subscriber determines that the received message is not an interrupt message (step  406 ), then the subscriber returns to transmitting on the forward channel (step  402 ). 
         [0025]    In one embodiment, determining that the received message is an interrupt message requires checking that the 3 bit opcode field of the RC info in the outbound channel burst (shown as  200  in  FIG. 2 ) is 001, where the opcode 001 means to interrupt the transmitting subscriber. 
         [0026]    In one embodiment, the subscriber is provisioned so that the subscriber can be interrupted during transmissions. As is known to one of ordinary skill in the art, “provisioned” means that the subscriber is programmed with an attribute or feature which instructs the subscriber how to operate. In an illustrative embodiment, Customer Provisioning Software (CPS) (also known as Radio Service Software (RSS)), manufactured by Motorola, Inc., is used for assigning the subscriber a provisioned characteristic, e.g. enabling interruptions and/or enabling reverse channel signaling. In such an embodiment, the subscriber determines that it is provisioned for being allowed to be interrupted and performs the steps of  FIG. 4 . 
         [0027]    In any case, if reverse channel signaling is enabled in a subscriber to be interrupted, a user of a subscriber performing the interrupting should not be able to notice that such a feature is enabled. For example, if the user of the subscriber performing the interrupting pushes push-to-talk (PTT), the subscriber clears the channel and enables the user to transmit, without additional steps that the user has to take to normally place a call. Thus, from a user&#39;s perspective, the operation of the subscriber remains the same. 
         [0028]    Returning to  FIG. 4 , if the subscriber can be interrupted and the received message is an interrupt message, then in one embodiment, the subscriber determines the type of interrupt (step  408 ). In such an embodiment, the subscriber may be interrupted for a number of reasons. Some examples of such reasons include because another subscriber needs to use the channel immediately (called “transmitter interrupt”), another subscriber in an emergency mode needs to use the channel immediately (called “emergency preemption”), another subscriber in remote control mode is requesting the channel immediately (called “control of remote monitor”). 
         [0029]    In one embodiment, the subscriber determines the type of interrupt (step  408 ), by decoding the RC info of the outbound channel burst  200  (shown in  FIG. 2 ). In one embodiment, 5-bits of the RC Info are used to indicate the interrupt type. For example, in one embodiment, “transmitter interrupt” is indicated by the 5-bits 00001, “emergency preemption” is indicated by the 5-bits 00010, and “control of remote monitor” is indicated by the 5-bits 00011. As is known to one of ordinary skill in the art, the subscriber can be interrupted for many reasons and new types of interrupts may be created. As such, the message may be identified utilizing the 5-bit information field of the reverse channel signaling burst. 
         [0030]    Returning to  FIG. 4 , if the subscriber determined that the interrupt message is of type “transmitter interrupt” (step  410 ), then the subscriber stops transmitting (step  420 ) if the subscriber is presently transmitting voice on the forward channel (step  416 ). Thus, the “transmitter interrupt” message is used to interrupt (also called pre-empt) a subscriber that is engaged in a call, e.g. a group call, a private call, an “all” call, or an emergency voice call. By doing so, the wireless communications system provides priority call control. If the subscriber is not presently transmitting voice on the forward channel (step  416 ), the subscriber continues to transmit (e.g., non-voice) on the forward channel (step  402 ) and the received interrupt message does not affect the operation of the subscriber. 
         [0031]    If the subscriber determined that the interrupt message is of type “emergency preemption” (step  412 ), then the subscriber immediately stops transmitting regardless of whether the subscriber was engaged in a call or non-voice communication (e.g. a data or control communication) (step  420 ). In one embodiment, the subscriber additionally emits a tone denoting that the subscriber has been preempted. Emergency preemption stops any ongoing transmission and, in one embodiment, starts a new call for the subscriber performing the interrupting. 
         [0032]    If the subscriber determined that the interrupt message is of type “control of remote monitor” (step  414 ), then the subscriber stops transmitting (step  420 ) if the subscriber is presently being monitored (step  418 ). Thus, the “control of remote monitor” message is used to interrupt a subscriber that has been previously set to a remote control mode, e.g. by receiving a remote control request message  600  (also called a control signaling block CSBK) as shown in  FIG. 6  where the remote control request message  600  identifies the subscriber being monitored via source and target addresses  602 ,  604 . If the subscriber is not presently in a remote control mode (step  418 ), the subscriber continues to transmit on the forward channel (step  402 ) and the received interrupt message does not affect the operation of the subscriber. In one embodiment, the remote control mode allows another subscriber to remotely activate the subscriber&#39;s microphone without providing any indication to the user of the monitored subscriber. It also allows the subscriber to be keyed up and/or de-keyed. 
         [0033]    Referring to  FIG. 5 , shown is a flow diagram  500  of an operation of a subscriber, e.g. a second subscriber  104 , initiating an interrupt of a transmitting subscriber (e.g. a first subscriber  102 ) (step  502 ). In one embodiment, the subscriber that initiates the interrupt, e.g. by sending an interrupt message, may initiate the interrupt message by a user of the subscriber pressing a PTT button, navigations buttons, a programmable button, or a button on an accessory that is mapped to interrupt a call. 
         [0034]    If the subscriber determines that the channel is busy (step  504 ), then the subscriber continues to determine whether the subscriber may interrupt the transmitting subscriber (steps  506 - 520 ). Otherwise, the subscriber transmits in a forward channel (step  522 ). As mentioned above, the transmission may be voice, data, or control. 
         [0035]    If, however, the channel is busy (step  504 ), then the subscriber determines if a remote control request message was previously sent (step  506 ). If a remote control request message was sent, then the subscriber being controlled is transmitting to the subscriber and the subscriber initiating an interrupt sends an interrupt message on the reverse channel to the subscriber being controlled (step  508 ). In one embodiment, the interrupt message is a specific remote of control message interrupt message. 
         [0036]    If, however, a remote control request message was not previously sent (step  506 ), then the subscriber determines whether it is in an emergency mode (step  510 ). If the subscriber is in an emergency mode (step  510 ), then the subscriber transmits an emergency preemption on the reverse channel (step  512 ). 
         [0037]    If, however, the subscriber is not in an emergency mode (step  510 ), then the subscriber determines whether there is a call on the forward channel (step  514 ). If there is not a call on the forward channel, then the subscriber can not interrupt the busy channel. If there is a call on the forward channel, the subscriber determines whether the subscriber is provisioned for polite channel access (step  516 ). If the subscriber is not provisioned for polite channel access (step  516 ), then the subscriber sends an interrupt message on the reverse channel (step  520 ). 
         [0038]    As used herein, polite channel access means that the subscriber considers what type of communications are currently on the forward channel before accessing the forward channel for its own communication. A subscriber provisioned for polite channel access may be defined with rules governing access to the channel. For example, the subscriber may be polite to all voice communications on the channel, may be polite to only specific voice communications satisfying a criteria (e.g. color code), etc. 
         [0039]    If, however, the subscriber is provisioned for polite channel access (step  516 ), then the subscriber determines whether it is a party to the voice, e.g. a call (step  518 )? As used herein, being a party to the voice means that the subscriber is participating in the call. If the subscriber is not a party to the voice and the subscriber is provisioned for police channel access (step  518 ), then the subscriber can not interrupt the busy channel. Otherwise, the subscriber sends an interrupt message on the reverse channel (step  520 ). 
         [0040]    While the invention has been described in conjunction with specific embodiments thereof, additional advantages and modifications will readily occur to those skilled in the art. The invention, in its broader aspects, is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. Various alterations, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Thus, it should be understood that the invention is not limited by the foregoing description, but embraces all such alterations, modifications and variations in accordance with the spirit and scope of the appended claims.