Abstract:
A method and apparatus for receiving dispatch messages in a broadcast radio receiver. In one embodiment, audio dispatch messages can be received, in another embodiment, data dispatch messages can be received. In either embodiment, a previously selected broadcast channel is received until a dispatch alert message is simultaneously received. The dispatch alert message includes a dispatch ID codes which is compared by the receiver with a previously stored dispatch ID code. If equality is found, the receiver switches from the previously selected broadcast channel to a dispatch broadcast channel to receive the dispatch message. Upon completion of the dispatch message, the receiver automatically switches back to the previously selected broadcast channel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to dispatch radio communications. More specifically, the present invention relates to dispatch communications in broadcast radio receivers adapted to receive dispatch messages during the reception of conventional program signals in a broadcast radio system. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     2. Description of the Related Art 
     Satellite radio operators will soon provide digital quality radio broadcast services covering the entire continental United States. These services intend to offer approximately 100 channels, of which nearly 50 channels will provide music with the remaining stations offering news, sports, talk and data channels. According to C. E. Unterberg, Towbin, satellite radio has the capability to revolutionize the radio industry, in the same manner that cable and satellite television revolutionized the television industry. 
     Satellite radio has the ability to improve terrestrial radio&#39;s potential by offering a better audio quality, greater coverage and fewer commercials. Accordingly, in October of 1997, the Federal Communications Commission (FCC) granted two national satellite radio broadcast licenses. The FCC allocated 25 megahertz (MHz) of the electromagnetic spectrum for satellite digital broadcasting, 12.5 MHz of which are owned by CD Radio and 12.5 MHz of which are owned by the assignee of the present application “XM Satellite Radio Inc.” The system plan for each licensee presently includes transmission of substantially the same program content from two or more geosynchronous satellites to both mobile and fixed receivers on the ground. In urban canyons and other high population density areas with limited line-of-sight satellite coverage, terrestrial repeaters will simultaneously broadcast the same program content in order to improve coverage reliability. 
     In accordance with the XM frequency plan, each of two geosynchronous Hughes 702 satellites will transmit identical or at least similar program content. The signals will be transmitted with QPSK digital modulation. The assigned 12.5 MHz bandwidth is called the “XM” band. The modulation scheme allows up to 4096 Mbits/s of total user data to be distributed across the available bandwidth. The data transmission will be multiplexed according to a TDM interleaving scheme, multiplexing that various channels of program content together, which provides for the simultaneous transmission and simultaneous reception of the various channels. Receivers will receive and de-interleave, or demultiplex, the channels for reception of the desired program content by end users. 
     The new XM band broadcast system will deliver a large volume of digital quality audio, including music and other program content to end users. While broadcasts which closely mimic convention commercial analog broadcast will be provided, the inherent capability to simultaneously broadcast and simultaneously receive the various channels makes it possible to provide advanced program content and messaging capabilities will be possible. It is anticipated that end users may desire special services that meet their particular needs. For example, in a fleet environment, where multiple end users are related in a personal or business nature, specialty messaging, otherwise known as dispatch messages, may be desired so that a particular fleet of users can be advised with information conforming to their needs. In a similar vein, individual users may desire to receive specialty, or dispatch messages, directed to them personally. However, since users in a fleet environment, or individual users, may be monitoring conventional broadcast program content, they may not be ‘tuned’ to an alternate channel comprising the specialty information. 
     Thus there is a need in the art for a method and device to deliver dispatch messages which are transmitted, received, and recognized notwithstanding the fact that the users are monitoring program content broadcast to a general audience. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the apparatus and methods of the present invention. The inventive method operates in a satellite digital radio broadcast system in which dispatch radio signals are provided to a receiver in the system which transmits dispatch alert messages on broadcast information channels, transmits dispatch messages on dispatch broadcast channels, and transmits program content on broadcast channels. The receiver simultaneously monitors a broadcast information channel TDM slot to receive dispatch alert messages while receiving program content on a broadcast channel TDM slot. When a dispatch alert message is sent, and upon receiving the dispatch alert message on the broadcast information channel, which identifies a dispatch broadcast channel and a dispatch message ID code, the radio compares the dispatch message ID code to another previously stored dispatch ID code in the receiver. If the two are found to be equal, the receiver recognizes the message as being addressed to that particular receiver and demultiplexes a dispatch message identified by the dispatch ID code on the dispatch broadcast channel. The receiver then provides the dispatch message to an audio output circuit, if it is an audio message, and upon completion of the dispatch message, subsequently reverts to receiving the broadcast channel. On the other hand, if the dispatch message is a data message, the receiver stores the message in a memory and utilizes it in another appropriate fashion, such as displaying it on a display or delivering it to another computing device or function. In this fashion, the user can monitor program content on a convention broadcast channel, yet still receive dispatch message as they occur, then revert to the previously selected program content. 
     In the illustrative embodiment, each radio in the system has a unique dispatch ID code previously stored within a memory which allows dispatch messages to be uniquely addressed to that particular radio. All radios compatible with the system also have a common dispatch ID code previously stored within the memory. In this way, dispatch messages may be sent to all radios simultaneously. This is useful for emergency situations and situations where the system operator, or others, desire to address a dispatch message to all users within a system. 
     In the situation where a fleet of receivers share a common interest, such as in a business environment, the system and receivers are adapted to be organized so that all members of the fleet receive the same dispatch message, but no other users in the system receive it. The system broadcasts ID code assignment messages on the broadcast information channels, and the ID code assignment messages include assigned dispatch ID codes related to unique dispatch ID codes of the receivers in the targeted fleet or other grouping of receivers. The receivers receive an ID code assignment message on the broadcast information channel. The ID code assignment message has within it an assigned dispatch ID code and a unique dispatch ID code. The receiver compares the unique dispatch ID code in the message to the unique previously stored dispatch ID code in the receiver. If they are found to be equal, the receiver stores the assigned dispatch ID code in its memory so that subsequently received dispatch message can be compared with the, now stored, assigned dispatch ID code. This allows the receiver to receive messages addressed to the assigned dispatch ID code as well as the unique dispatch ID code and the common dispatch ID code. In the case of a fleet, each of the receivers in the fleet are programmed with the same assigned dispatch ID code so that each is enabled to receive messages common to that fleet. 
     Each dispatch message in the preferred embodiment also includes a termination field. This field of data notifies the receiver that the dispatch message has been completely received and causes the receiver to revert to the previously selected broadcast channel program content. Of course, the dispatch broadcast channel is used from time to time by various users in the system. Therefore, on completion of a message, a subsequent message to another user is likely to follow. It is possible that a receiver may not receive an entire dispatch message. This creates a potential problem in that the termination field may not be received and the receiver will continue to receive the next subsequent dispatch message that is intended for another user. To alleviate this problem, the receiver is adapted to terminate the reception of the dispatch message on the occurrence of some other event. A time-out timer may be employed to end the reception of dispatch messages or the receiver may monitor the message for other dispatch ID codes that are not present in the receiver&#39;s memory thereby causing the termination of the reception of dispatch message. In an illustrative embodiment, the current dispatch ID code for the dispatch message being transmitted is encoded into the message periodically and is interpreted by the receiver as indicating that the current message is for that receiver. In the event that dispatch ID code ceases to be present in the message, the receiver terminates reception of that message and reverts to the previously selected broadcast channel. Other methods for such termination are obvious to those skilled in the art, including but not limited to, error detection, recognizable bit patterns, or stop bits. In any event, the recognition of the termination of a dispatch message causes the receiver to return to the previously selected broadcast channel. 
     The receiver in the preferred embodiment, which generally includes all of the circuits needed to accomplish the reception of broadcast and dispatch messages, includes a radio receiver, in the preferred embodiment, an XM radio receiver, adapted to receive broadcast and dispatch messages through an antenna in the previously described system. 
     The radio receiver outputs the multiplexed data signals including the broadcast information signals, broadcast signals, and dispatch broadcast signals. This output is coupled to a data demultiplexer that receives the multiplexed data signals. The demultiplexer has a first output for providing demultiplexed broadcast information channel signals and a second output for selectively outputting broadcast channel signals or dispatch channel signals, or simply dispatch messages, in accordance with control commands it receives. The second output is coupled to an output circuit which converts the broadcast channel signals or dispatch messages to analog audio signals for output to an audio transducer or to a memory in the case of data dispatch messages. It may also store the audio content in a memory for later recall by the user. The broadcast information signals output through the first output are coupled to an address correlator. The address correlator continuously compares the flow of data in the broadcast information signals to the previously stored dispatch ID codes stored in the receiver&#39;s memory. 
     In the event there is determined to be an equality between an ID code transmitted in a dispatch alert signal, that is transmitted in the broadcast information signals, and one of the previously stored dispatch ID codes, the address correlator activates a dispatch alert output which indicates the existence of the equality. A controller, coupled to the data demultiplexer, receives the dispatch alert signal and causes an audio channel demultiplexer to change states from demultiplexing the broadcast channel signals to demultiplexing the dispatch signals. On receipt of the termination field, or other events described above, the controller causes the audio channel demultiplexer to revert to demultiplexing the broadcast channel signals. 
     With respect to the transmission of dispatch messages, assignment of fleet ID codes and so forth at the uplink site, the insertion of such information differs little from the broadcast of any other information in the system. The data is gathered by a controller at the uplink site and is inserted onto the broadcast information channel or dispatch channel. The information may be fed to the controller by keying the data into a terminal or it may be communicated electronically locally or remotely through a data network. Those skilled in the art will realize various methods and devices can be used to assemble such data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a preferred embodiment of the system of the present invention. 
     FIG. 2 is a diagram of the TDM data frame received by the receiver of the preferred embodiment. 
     FIG. 3 is a diagram of the dispatch message. 
     FIG. 4 is a diagram of the timing relationship between the broadcast information channel, broadcast channels, and the dispatch broadcast channel as dispatch messages are transmitted. 
     FIG. 5 is a flow chart of the preferred embodiment of the method of the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
     Reference is directed to FIG. 1 which is a block diagram of the preferred embodiment receiver  2 . The XM radio uplink site  1 , which includes satellite links and terrestrial repeaters (not shown), transmits radio signals which are intercepted by antenna  4  and coupled to radio receiver  6 , also known as an XM radio receiver The uplink site and related equipment as well as the XM radio receiver are disclosed in detail in co-pending U.S. patent application Ser. No. 09/318,296, filed by Marko et al. on May 25, 1999 (Atty. Docket No. XM 0006) the teachings of which are incorporated herein by reference. 
     The radio receiver  6  demodulates the radio signals to a TDM multiplexed data signal that comprises dispatch alert messages on broadcast information channel TDM slots, dispatch messages on dispatch broadcast channel TDM slots, and program content on broadcast channel TDM slots. The TDM multiplexed data signals are coupled to data channel demultiplexer  8  and audio channel demultiplexer  10 . The data channel demultiplexer  8  serves the function of demultiplexing the broadcast information channel and other data service channels that may be in operation in the system, in accordance with commands received by controller  20 . The design and operation of TDM slot demultiplexer are well known to those skilled in the art. 
     In normal receive operation, the user activates a control within user interface  22  to select a broadcast channel to receive program content that is desired. The demultiplexed broadcast channel data signal is coupled from audio channel demultiplexer  10  to channel select switch  12 . Channel select switch  12 , under control of controller  20 , decodes the selected broadcast channel and provides that channel&#39;s data signal to output circuit  14 . Output circuit  14  converts the digitally encoded broadcast channel signal to an analog audio signal which drives audio transducer  16 . The digital to analog conversion of the output circuit  14  is well known to those skilled in the art. The audio transducer  16  may be a stereo or monaural audio transducer such as a loudspeaker or headphone. 
     Simultaneous with the reception and playing of the audio broadcast channel, address correlator  18  monitors the output of data channel demultiplexer  8 . In the preferred embodiment, controller  20  controls the data channel demultiplexer  8  to select and demultiplex a broadcast information channel The system transmits dispatch alert message on the broadcast information channel and within the dispatch alert messages are dispatch ID codes which identify the radio or radios that are targeted to receive an upcoming dispatch message. Address correlator  18  continuously monitors the data flow of the broadcast information channel and compares the bit pattern with previously stored dispatch ID codes, which are stored in a memory (not shown). The memory may be an external memory device or may be internal to controller  20 . 
     In an illustrative embodiment, the address correlator  18  comprises a fixed register loaded with one or more previously stored dispatch ID codes and a serially load shifted register which is sequentially loaded with the broadcast information channel data flow in a first-in, first-put fashion. As each bit of data in loaded into the shift register, the register content is compared with the dispatch ID code. When they are found to be equal, a dispatch ID code on the broadcast information channel data flow has been found for the particular radio. When address correlator  18  finds equality between a dispatch ID code in the dispatch alert message and one of those previously stored in the memory, a signal is coupled to controller  20  indicating such equality. 
     The dispatch alert message may also comprise a designation of a dispatch broadcast channel and this information is coupled to controller  20  as well. Since the controller  20  has identified the presence of a dispatch message and the appropriate dispatch broadcast channel, the controller  20  directs the channel select switch  12  to decode the appropriate dispatch broadcast signal from audio channel demultiplexer  10 . The signal is subsequently coupled through output circuit  14  to audio transducer  16  for listening by the user. In the case that the dispatch message is a data message, as indicated in the dispatch alert message, the controller directs data channel demultiplexer  8  to demultiplex the data dispatch message and couple it to controller  20 . The data dispatch message is stored in the memory and may be presented to a display in user interface  22 , or coupled to an external computing device through a communications port coupled to controller  20  (not shown). The implementation and utilization of such data messages are well known to those skilled in the art. 
     The dispatch message received, whether an audio message or a data message may contain an associated “dispatch ID” or may be terminated by a termination field in the preferred embodiment. The absence of the dispatch ID code or receipt of the termination field, and its coupling to controller  20  causes the controller  20  to redirect the data channel demultiplexer  8  or audio channel demultiplexer  10 , in the case of data messages and audio messages respectively, to revert to the previously selected broadcast channel for resumption of the program originally selected by the user. 
     Reference is directed to FIG. 2 which is a diagram of the TDM data frame output by radio receiver  6 . The TDM data frame  24  comprises a synchronization field  26 , as is typically used in TDM communications systems. A control field  28  follows which includes the broadcast information channel in an illustrative embodiment where there is only one broadcast information channel in the system. Alternatively, the broadcast information channel may be assigned to one of the regular TDM frame slots  30 . In the preferred embodiment, there are 256 TDM frame slots in FIG.  30 . Each typically has 8 kilobits of data per second, however, the control field  28  may direct other arrangements of TDM frame slots so that higher data and audio rates may be achieved. Each of the TDM frames slots in  30  comprises an error detection and/or error correction fields. Error correction may be achieved if desired by the system designers. Such uses of error detection and correction are well known to those skilled in the art. 
     Reference is directed to FIG. 3, which is a diagram of the dispatch broadcast message  34  in the preferred embodiment. A header field  36  may include the dispatch ID code to which the dispatch message  34  is directed, a command and associated dispatch ID code, or other information necessary to synchronize the receiver and demultiplexers. A length field  38  follows which indicates the length of the dispatch message. In addition, this field may be used as a reference for the controller to determine that the termination field has not been received to terminate the reception of the dispatch broadcast channel. The dispatch message data field  40  follows. This field may comprise digital data or audio data. At the end of this field is a termination field (not shown) which indicates the end of the dispatch message broadcast. 
     Reference is directed to FIG. 4, which is a diagram of the timing relationship between the broadcast information channel, broadcast channels and the dispatch broadcast channel as dispatch messages are transmitted within the system and received by the receiver. Since the system receives multiplexed broadcast signals, there exists a plurality of broadcast channel signals  44 ,  46 ,  48  and so on to  50 , which may be selected by the user. In addition, there is at least one broadcast information channel signal  42 . As the receiver monitors the broadcast information channel signals  42 , it may receive a dispatch alert signal  54  that includes a dispatch ID code equaling one of the aforementioned previously stored dispatch ID codes. This causes the controller to direct the receiver to switch from receiving the selected broadcast channel to receiving the dispatch broadcast channel  52 . At that time, the dispatch message  56  is received. The end of the dispatch message is followed by the termination field  58  which causes the receiver to revert to the previously selected broadcast channel. 
     Reference is directed to FIG. 5, which is a flow diagram of the preferred embodiment. The process begins at start  60  and proceeds to initialization of the radio at step  62 . Essentially this is the turning on of the radio and setting it for operation by the user through interaction with the user interface. At step  64 , the user selects a broadcast channel for routine monitoring of the desired program content. Once a broadcast channel is selected at step  64 , flow proceeds to step  66  where the receiver tests to determine if the dispatch function has been enabled. If it has not, the receiver ignores dispatch ID codes, or dispatch address fields, in the dispatch alert message fields, at step  68 . On the other hand, at step  66 , if the dispatch function has been enabled, the flow proceeds to step  70  where the address correlator is loaded with the previously stored dispatch ID codes. 
     If equality of the received dispatch ID code with any of the previously stored dispatch ID codes occurs at step  72 , flow proceeds to step  74  where the dispatch alert message is decoded and the dispatch broadcast channel is identified, causing the receiver to switch to the designated dispatch broadcast channel to received the dispatch message addressed by the dispatch ID code. At step  76 , the receiver tests to determine if the termination field has been received, thus indicating the end of the dispatch message. As mentioned earlier, the end of the dispatch message can be determined at step  76  by a number of means. Having determined that the dispatch message has ended at step  76  flow continues to step  78  where the receiver returns to the previously selected broadcast channel to continue receiving the selected program content. 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
     Accordingly,