Abstract:
A method and system is disclosed that allows for the designation of over 1,000,000 individual users in a communication system, such as an EDACS system, using the existing five-digit portion of command message utilized for specifying the destination address. This is accomplished by using an Extended Addressing Digital Interface (EADI) protocol using hexadecimal characters in the command message rather than decimal characters, thereby creating an “extended addressing” (EA) capability. The largest five-digit hexadecimal number, FFFFF, corresponds to the decimal number 1,048,575, thereby realizing the ability to exceed one million users, without having to change the size (number of digits) in the command message. Backward compatibility is assured by adding new mode commands that identify a particular command message as being generated by EA compatible equipment.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is generally related to the field of two-way radio communications and, more particularly, relates to trunked two-way radio systems using digital control signals transmitted over a dedicated control channel.  
         BACKGROUND OF THE INVENTION  
         [0002]    Two-way radio communication systems such as land mobile radio (LMR) have been in use for many years. With conventional LMR, users typically communicate with each other using hardware devices comprising at least one base station or dispatching unit and one or more transmitting/receiving (TR) devices, such as mobile radios (MR&#39;s). MR&#39;s typically comprise hand-held portables, vehicle-installed radios, and the like, and to communicate with each other, users of the system select a predetermined frequency over which to transmit and receive messages via the base station.  
           [0003]    LMR&#39;s are frequently used by police and fire departments, rescue workers, paramedics, power and telephone company field technicians, municipalities, and other mobile groups that require immediate communication with other members of their respective groups. Communication between the various members can also include visual information, which may be displayed on another TR device called a mobile data terminal (MDT). MDT&#39;s include portable devices such as a laptop computer, a personal digital assistant (PDA), or other portable data device that is associated with an MR. For example, a police officer may request and receive information from a computer located at the police station about a stopped motorist, which is displayed on an MDT in the officer&#39;s patrol car via the officer&#39;s MR.  
           [0004]    [0004]FIG. 1 illustrates a typical LMR environment. Referring to FIG. 1, individual units of various groups (e.g., emergency vehicles, fire vehicles, police vehicles, and handheld users) communicate with each other (both within and possibly outside of their own group) using MR&#39;s (e.g., a vehicle mounted MR  120  and a handheld MR  124  in FIG. 1) over shared radio channels coordinated by a central controller  100 . If desired, MDT&#39;s can be paired with any of the MR&#39;s so that visual information can be transmitted and received over the LMR system. In FIG. 1, MR  120  is paired with MDT  122 , and MR  124  is paired with MDT  126 .  
           [0005]    Central controller  100  can comprise a dispatch console housed directly at a base station or may be remotely located via other communication facilities (e.g., landline connections) as will be appreciated by those in the art. There may also be multiple dispatch consoles (e.g., one for each separate fleet) and a master or supervisory dispatch console for the entire system as will also be appreciated by those in the art. The details of the operation of such a system, as well as the hardware and/or software for building such a system are well known and are not discussed in detail herein.  
           [0006]    In early systems, each channel was assigned a dedicated frequency. Thus, for example, all persons utilizing channel  10  in the system would transmit and receive messages on the same frequency. While this functioned adequately when a small number of users used the system, as the popularity of two-way radio systems grew, the pre-assigned channels became congested and difficult to use, and privacy was limited so that anyone could easily listen in on communications over the channels.  
           [0007]    The spectral inefficiency of conventional two-way radio systems led to the development of “trunked” systems. Trunking is a method of using relatively few communication paths for a large number of potential users. Trunking systems allow for the automatic sharing of a “pool” of frequencies assignable to multiple radio channels among a group of users.  
           [0008]    In a typical trunking system, each MR has a unique identifier (“logical ID” or “LID”), and multiple MR&#39;s may be designated as being part of a group (e.g., all firefighters) with a corresponding group identifier (group ID or GID). A user of an MR wishing to transmit a voice communication to another MR or group of MR&#39;s inputs a LID (for an individual MR) or a GID (for a group of MR&#39;s) for the target (i.e., receiving) radio(s), e.g., via a keypad on the MR or any other known means for inputting an ID. In a known manner, the central controller assigns a frequency from the frequency pool for the transmission, and when the transmission is complete, the frequency is “returned” to the pool.  
           [0009]    A control frequency (also referred to as a “control channel”) is allocated to send signals that coordinate the use of the MR&#39;s within the system. In FIG. 1, control channel  130  performs this function for MR  120 , and control channel  136  performs this function for MR  124 . The MR&#39;s constantly monitor the control channel for instructions from the central controller  100 . When a voice call is initiated from a radio in the system (e.g., by pressing the “push-to-talk” (PTT) button on the MR) the LID&#39;s of the transmitting and target radios are transmitted on the control frequency to the central controller. The central controller uses the LID information to assign a voice “working” frequency (also called a “working channel”) for the voice transmission between the transmitting and target radios. In FIG. 1, the working channel for a voice transmission from MR  120  to central controller is illustrated by transmit (TX) and receive (RX) lines  132 . Likewise, the working channel for voice communications between MR  124  and central controller  100  is illustrated by TX and RX lines  138 . The concept of trunking radio systems and their use of LID&#39;s and GID&#39;s is well known. The focus of the present application is on the manner in which the LID&#39;s and GID&#39;s are assigned, and in particular, how they are assigned in a well-known system called the Enhanced Digital Access Communications System (EDACS).  
           [0010]    EDACS is a well known, extremely flexible trunked communication system designed to provide secure, reliable two-way radio communications for public safety, utility, government, military, and business and industrial organizations. EDACS allows the transmission and receiving of voice and data communications and allows users to make and receive telephone calls over the system via fixed handsets or cordless telephones. An interface between MR&#39;s in an EDACS system and their associated MDT&#39;s is necessary for flow control. Key to the operation of EDACS is the Radio Digital Interface (RDI) and the RDI protocol. The RDI protocol is a protocol that functions with the RDI (a known hardware device) to facilitate the flow of data between an MR and its associated MDT. The RDI protocol functions with RDI hardware to maximize data throughput in the EDACS system by handling all system acknowledgments and message retries necessary to ensure that data is transported correctly and without errors. Typically, the MDT uses a 9600 bps serial interface of the RDI hardware to connect to the MR. The MR&#39;s can contain an internal RDI or an external RDI. The RDI protocol is simply a flow control protocol and, as such, has no effect on the content of the message.  
           [0011]    Under the RDI protocol, a request to send a block of data from the MDT to the MR, or vice versa, is referred to as an “XFERB command”. The RDI-protocol-specific information is not transmitted over the RF interface (the RF coupling between the MR and the central controller), rather, the RDI protocol serves only to transfer the block of data and associated call information between the MR and the MDT. In an outgoing data transfer from an MDT to an MR, the LID sent via the RDI protocol identifies the target MR that will receive the data and transfer the data to its MDT. It is subsequently included by the transmitting MR, along with its own LID, in a call request over the control channel. The processor that manages the control channel (not shown) assigns a data working channel for the data transmission, and the block of data that was sent to the transmitting MR from the transmitting MDT, via the RDI protocol, is then sent over the data working channel to the central controller.  
           [0012]    In FIG. 1, if we assume a data transmission from MDT  122  to MDT  126 , the LID of receiving MDT  122  would be sent over the RDI interface to transmitting MR  120 . Transmitting MR  120  would then add its own LID and transmit both LID&#39;s over the control channel  130  to central controller  100 . Central controller  100  would then establish a data working channel, illustrated by TX and RX lines  134 , over which MR  120  would send the data. In a similar (but reverse) manner, central controller  100  then sets up a data working channel  140  to receiving MR/MDT pair  124 / 125 . When received by receiving MR  124 , the LID of the transmitting MR  120  is also received as part of the transmission, so that the receiving MR/MDT pair  124 / 125  knows the origin of the transmission.  
           [0013]    An example of a typical XFERB command is illustrated in FIG. 2 and is described in more detail below. An XFERB command under the RDI protocol comprises a sequence of fifteen (15) decimal (0-9) numbers divided into command “fields,” with each field in the sequence having a predetermined “role” in the command. The XFERB command follows the structure “mc00tgggggnnnnn” where “m” refers to the “mode” field; “c” refers to the “ACK2” field (a request that the receiver respond with a positive acknowledgment upon receipt of the data); “00” (reserved placeholders); “t” refers to the “call type” field; “g” refers to one of the five numbers of the LID or GID field; and “n” refers to one of the four numbers in the “data binary bytes” field (indicating the size of the data block to be sent). Thus, in the example XFERB command of FIG. 2, the mode field  202  is “Standard XFERB” (1); the ACK2 field  204  is “Standard Sequence Implemented” (0); the placeholders (00) are in field  206 ; the call type field  208  is “Individual Call” (2); the LID field  210  is “16238”; and the data binary bytes field  212  are “0032”. The complete sequence is thus 10002162380032.  
           [0014]    Because each radio has a unique LID number, it is possible to address any individual radio from the dispatch center or from another radio unit that has the authority to do so. In the standard configuration, EDACS allows 16384 (2 14 ) individual users (LID Nos. 0-16383) to be defined in the system. Since five decimal digits (ggggg) are allocated to the ID numbers, theoretically a maximum number of 100,000 individual users (LID Nos. 00000 to 99999) could be defined in an EDACS system, if the RDI protocol were modified to allow the user ID numbers to exceed 16383.  
           [0015]    A problem exists if it is desired to configure a system to be able to define more than 100,000 users. The XFERB command message used by the RDI protocol identifies a fixed-length and format (five decimal digits) for ID numbers, and many systems are now in place throughout the world that utilize this protocol. While the RDI protocol could be modified so that more than five decimal digits are available to specify the LID destination address, there would not be compatibility between the current system and a more-than-five-decimal-digit system. For example, a system using the current protocol would register an error condition upon receipt of a LID segment of more than 5 digits in size.  
           [0016]    Accordingly, there is a need for a method and system for designating more than 100,000 LID&#39;s without changing the structure of the command message containing the LID.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention introduces a new protocol, called the Extended Addressing Digital Interface (EADI) protocol. The EADI protocol allows for the designation of over 1,000,000 individual users in an EDACS system using the existing five-digit portion of the XFERB command message utilized for specifying the LID destination address. This is accomplished by using hexadecimal characters in the XFERB command message rather than decimal characters, thereby creating an “extended addressing” (EA) capability. The largest five-digit hexadecimal number, FFFFF, corresponds to the decimal number 1,048,575, thereby realizing the ability to exceed one million users, without having to change the size (number of digits) in the XFERB command message. Backward compatibility is assured by adding new mode commands that identify a particular XFERB command message as being generated by EA compatible equipment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 illustrates a typical LMR environment of the prior art;  
         [0019]    [0019]FIG. 2 is an example of a typical XFERB command message of the prior art;  
         [0020]    [0020]FIG. 3 illustrates the structure of a command message in accordance with the present invention; and  
         [0021]    [0021]FIG. 4 is a flowchart illustrating an example of the basic steps performed during operation of a system in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    [0022]FIG. 3 illustrates an example of the structure of a command message in accordance with the present invention. Referring to FIG. 3, the XFERB command used in the EADI protocol of the present invention includes a “mode” field  302 , “ACK2” field  304 , placeholder field  306 , “call type” field  308 , “ID” field  310 , and “data binary bytes” field  312 , similar to the command message of an RDI protocol XFERB command illustrated in FIG. 2. However, in accordance with the present invention, hexadecimal numbers are used in the ID command field (“ggggg”) of the command message. Use of hexadecimal characters in the ID field is referred to herein as “extended addressing” and when used with an MR, provides the MR with what is referred to herein as “EA capability.” For example, in the example of FIG. 3, the five-digit hexadecimal number F112A corresponds to the six-digit decimal number 987434. By using hexadecimal numbering in the existing 5-digit ID field of the command message, up to 1,048,575 (hexadecimal FFFFF) ID&#39;s are available for use in a command message, without changing the number of digits in the ID field.  
         [0023]    If both the MR and MDT have EA capability, when an XFERB command message using extended addressing is sent/received across the EADI interface, the system functions normally since both the sending device and the receiving device are compatible with the new addressing scheme. However, a problem could arise if, for example, an EA capable MR attempts to send an XFERB command message using extended addressing to a non-EA capable MDT. The incompatible MDT would receive the hexidecimal address and return an error message, and the two devices could not communicate with each other. Upgrading equipment on an incremental basis (e.g., purchasing dual-mode MDT&#39;s capable of operating in either EA or Non-EA modes at the beginning or end of a fiscal year and not upgrading the MR&#39;s until a later date) is a common mode of operation and thus such incompatibility is likely.  
         [0024]    To solve this potential problem and ensure compatibility between systems using the standard addressing and systems having EA capability, in accordance with the present invention, two new values for the “mode” field of the XFERB command are utilized. As can be seen in the legend portion of FIG. 3, the mode field includes “Mode 1” and “Mode 2” as used by the prior art. In addition, in accordance with the present invention, a “Mode 3” for “standard extended address (EA) XFERB” and “Mode 4” for “profile EA message” are provided. These modes allow the receiver of the XFERB command to tell how to interpret the LID/GID field of the XFERB command, that is, either as decimal or hexadecimal coded digits.  
         [0025]    As an example, assume a typical EDACS system that includes an MR/MDT pair, neither of which are EA compatible. Since both the MR and MDT are non-EA compatible, any XFERB commands sent between the two will only utilize Mode  1  or Mode  2  in the mode field, and everything will operate normally.  
         [0026]    Now assume that as part of an initial upgrade, the operator of the system switches the MDT&#39;s in the system to dual-mode MDT&#39;s, meaning that they can operate in either EA or non-EA mode. When the dual-mode MDT attempts to send an XFERB command across the EADI to its associated non-EA capable MR using Mode  3  or Mode  4  in the mode field, the MR will send an error code back to the MDT (e.g., an ACK-A with the error code “DATERR_BAD_CALLTYPE”) indicating that the MR is not EA compatible. This will cause the dual-mode MDT to switch to the non-EA mode and send the XFERB command message with the appropriate non-EA mode field (“Mode 1” or “Mode 2”). Thus, the system is backward compatible allowing users to upgrade on an “as-you-go” basis instead of requiring the entire upgrade to be performed at one time.  
         [0027]    When the system operator takes the next step and upgrades the MR&#39;s to dual mode (i.e., EA compatible) equipment, when the new MR attempts to send its first message in the EA mode (i.e., using Mode  3  or Mode  4  in the mode field), the dual-mode MDT, at that point operating in non-EA mode, automatically switches to EA mode and receives the XFERB command properly. It is understood that the same action will occur (but in reverse) if the MR&#39;s are upgraded first, instead of the MDT&#39;s being upgraded first.  
         [0028]    [0028]FIG. 4 is a flowchart illustrating an example of the basic steps performed during operation of a system in accordance with the present invention. At step  402 , a transmitting device (e.g., an MDT or MR) sends an XFERB command across the EADI to its associated receiving device (MDT or MR). At step  404 , a determination is made as to whether or not the XFERB command contains a Mode  3  or Mode  4  in the Mode field. If not, the XFERB command is known to be in non-EA format. Thus, since both non-EA-compatible and EA-compatible devices can process an XFERB command in non-EA-format, the process proceeds directly to step  412  where the XFERB command is received and processed.  
         [0029]    If at step  404 , a determination is made that the XFERB command does include a Mode  3  or Mode  4  in the Mode field, then at step  406 , a determination is made as to whether or not the receiving device is EA-capable. If the receiving device is EA-capable, then the process proceeds to step  412  where the XFERB command is received and processed. If, however, a determination is made at step  406  that the receiving device is not EA-capable, then at step  408  an error message is returned to the transmitting device, and at step  410 , the transmitting device switches to non-EA mode and retransmits the XFERB command in non-EA mode. At step  412 , the XFERB command is received and processed.  
         [0030]    Use of the present invention allows the expansion of the number of addresses that can be utilized in LMR&#39;s while ensuring backward compatibility with systems and hardware that are not yet EA compatible. The overall structure of the XFERB command remains the same while the capabilities that can be achieved are increased substantially.  
         [0031]    The above-described steps can be implemented using standard well-known programming techniques. The novelty of the above-described embodiment lies not in the specific programming techniques but in the use of the steps described to achieve the described results. Software programming code which embodies the present invention is typically stored in permanent storage of some type, such as permanent storage of a workstation located, for example, in central controller  100 . In a client/server environment, such software programming code may be stored with storage associated with a server. The software programming code may be embodied on any of a variety of known media for use with a data processing system, such as a diskette, or hard drive, or CD-ROM. The code may be distributed on such media, or may be distributed to users from the memory or storage of one computer system over a network of some type to other computer systems for use by users of such other systems. The techniques and methods for embodying software program code on physical media and/or distributing software code via networks are well known and will not be further discussed herein.  
         [0032]    It should be understood that the foregoing is illustrative and not limiting and that obvious modifications may be made by those skilled in the art without departing from the spirit of the invention. For example, while the above-described embodiment is described in connection with an EDACS system, it is understood that the present invention will find application in any system in which a limited number of decimal digits are available as command characters in a command string, regardless of the type of system. Using hexadecimal characters instead of decimal characters, and designating additional control codes to designate the use of extended addressing, can find applicability in many other systems, communications systems or otherwise, and thus such uses fall within the scope of the claimed invention. Accordingly, the specification is intended to cover such alternatives, modifications, and equivalence as may be included within the spirit and scope of the invention as defined in the following claims.