Method for dynamically allocating data channels on a trunked communication system.

Description: TECHNICAL FIELD [Detailed description of the invention]

Technical field The present invention generally relates to a trunked communications system, and more specifically to a trunked communications system that transmits and receives both voice and data. Background technology In a basic RF trunk system, there is a high degree of flexibility in separating voice conversations between different groups so that no group of users is specifically aware when other groups of users are using the system. have. Typically, these groups are subdivided into subgroups, which can generate calls on a group, subgroup or individual basis, depending on the type of communication desired by the calling subscriber. To establish voice communication between groups of units operating in a trunk system, the subscriber unit maintains a data packet called an "inbound signaling word" (ISW) for that purpose. Send with. ISW is the current calling group (talk) of the requesting subscriber Contains at least the unique ID code of the requesting unit that can be used to include or obtain group). The request is sent to the central controller, which decodes the request and "outputs" to all subscriber units that are constantly monitoring the control channel when not participating in a voice conversation by the control channel. Sends a data packet called "outbound signaling word" (OSW). The OSW is a channel grant that includes the call group code of the requesting unit and the voice channel number assigned to the conversation. The OSW makes the request unit move to the voice channel and initiate transmission, while simultaneously moving all other subscriber units in the same calling group to the voice channel as listening units. The group call is set in this way. However, if all voice channels are in use when a subscriber unit sends an ISW, the central controller typically sends a "visit-OSW" to the requesting subscriber. In addition to voice messages, it is desirable to transmit data information via trunk wireless channels. In some data systems, the subscriber unit obtains a trunk data communication channel by the same procedure used to obtain a voice channel. However, this method is inefficient and wastes the spectrum, which is necessary for the requesting subscriber to set and resolve the call in the time required to send the ISW and receive the channel-approved OSW from the center and in the voice channel. For a good time. At modern data transmission rates, it is expected that a typical entire data message will take significantly less time to send than it takes to get a channel (about 0.5 seconds). Therefore, allocating a data channel by the same procedure as allocating a voice channel is a waste of spectrum and consumes valuable system time that would be better available for sending data messages. Other trunk communication systems that want to accommodate data traffic have one or more permanent, dedicated channels for handling data traffic. While this avoids the access time issues described above, this technique violates the basic principles of trunk communication systems that strive to allocate channel resources to multiple users on demand. Therefore, having a dedicated data channel, i.e. permanently disconnected from the frequency channel allocation "pool", is a waste of spectral resources and leads to inefficient system operation. Moreover, systems with dedicated data channels lack the ability to dynamically redistribute or allocate data traffic loads to available data channels. Such systems typically assign subscriber units permanently to data channels, thereby incorporating future issues as the number of data subscribers increases on a particular channel. Therefore, there is a need for a trunk communication system that can accommodate both voice and data signals and operates in a true trunk way that efficiently utilizes spectral resources. Outline of the invention Therefore, an object of the present invention is to provide an improved trunk communication system. Another object of the present invention is to provide a procedure for dynamically allocating a data channel in a trunk radio system. Yet another object of the present invention is to redistribute or balance the data traffic load on a particular number of currently available data channels. Yet another object of the present invention is to provide a fast and convenient way to broadcast system-wide data messages to all data subscribers. Therefore, these and other objectives are achieved by the dynamic allocation of data channels in the trunk radio system of the present invention. In summary, the present invention discloses a method for dynamically allocating a large number of data channels in a trunk radio system. Data activity is monitored for a given time interval. If there is more activity than a given maximum, additional channels are reserved for data use. Conversely, if data traffic is low, the data channel will be reassigned for use with voice messages. Moreover, if the amount of data traffic among the available data channels is unbalanced, the invention reallocates the subscriber unit to the available data channels, thereby providing better access time and system performance. Intended to provide. A brief description of the drawing Features of the invention believed to be novel are specifically described in the appended claims. The present invention, along with yet another object and advantage thereof, can be understood by incorporating the accompanying drawings and referring to the following description, and similar reference numbers are similar in some of the figures in the accompanying drawings. Represents an element. In these figures, FIG. 1 is a block diagram showing a trunk type wireless system in which the present invention can be incorporated. FIG. 2 is an explanatory diagram of the preferred signal format for the main data channel. FIG. 3 is an explanatory diagram showing a preferred signal format for other data channels. FIG. 4 is a flow chart showing steps performed by the fixed end device of FIG. 1 according to the present invention. FIG. 5A is a flow chart showing steps performed by the fixed end device of FIG. 1 to load average subscriber units to available data channels according to the present invention. FIG. 5B is a flow chart showing the steps performed by the fixed end device of FIG. 1 to send a system message to the subscriber unit in accordance with the present invention, and FIG. 6 is a flowchart showing the steps performed by the data subscriber of FIG. Detailed description of preferred embodiments Next, referring to the drawings, especially in FIG. 1, a block diagram of a trunk type voice / data communication system (100) to which the present invention can be applied is shown. The central or fixed-end device comprises a central controller 102, which is tasked with allocating channel resources (represented here by repeaters 104A-104N) among many subscriber units. Of the available communication channels, one (repeater 104A) is selected as the voice control channel, which communicates with any trunk subscriber capable of transmitting voice traffic. Preferably, each of the repeaters 104A through 104N can operate as a voice channel, control channel, or data channel. Such repeaters are provided with a data interface 122 to accommodate data traffic. Data interface 122 is tasked with encoding outbound data, decoding inbound data and correcting errors, performing repeater control, and providing an interface between the repeater and the network controller 108. ing. Alternatively, a predetermined subset of all repeaters is equipped for data or can be used as a control channel. Typically, the particular repeater selected to be the control channel (104A) is periodically modified as a control measure. The data network comprises at least one host computer 106, which is coupled (ie, wired) to the network controller 108. Network controller 108 is tasked with communicating with central controller 102 to request data traffic routing and data channel allocation. Those skilled in the art will appreciate that if the host computer 106, network controller 108 and central controller 102 are placed together, the interconnect (124-128) may be direct. However, if remote locations are desired, such communication could be maintained by the use of technically known data modems. Optionally, or additionally, the trunk voice / data communication system 100 can use one or more radio frequencies (RF) coupled to the host computer 118. The RF host 118 communicates as a trunk control station via any suitable data transmitter / receiver 120. The main difference between the wired host 106 and the RF host 118 is that the data subscriber communicates directly with the RF host (ie, via both the incoming and outgoing frequencies of the data-equipped repeater), while the wired host 106 is all. The point is that information is transmitted and received via the input and output frequencies of the data-equipped repeater. Therefore, the data network according to the present invention can use several computers having a centralized or distributed processing configuration. In general, it includes a system manager console 110 that allows the administrator of a fixed-end device or communication service provider to set a number of operating parameters that control the operation of the trunk communication system. Typical examples of such parameters are the maximum number of data channels that can be allocated (if any), whether voice or data is preferred traffic, and data channels are added or reassigned to voice traffic. Includes various thresholds for controlling when. Therefore, at any particular time, the trunk communication system of the present invention does not need to have any channel assigned to data traffic. Conversely, if voice traffic is low, or if data traffic remains preferred or particularly high, one or more channels could be allocated for data communication. According to the present invention, a given channel is usually the first channel to be assigned to data. Preferably, this initially assigned data channel (hereinafter referred to as the "main data channel") has the same frequency as any single frequency data-only subscriber (116) for maximum compatibility with existing data equipment. Has. Alternatively, any channel can be the first data channel to be assigned, but data-only subscribers must scan the available channels to find it. Therefore, it is preferred that the present invention allocates a selected channel first, and then any other data equipment (122) channel as an additional data channel. The present invention allocates data channels for a time interval determined by the system administrator or the default parameter. The length of the allocation period will vary depending on the date and time, system load or other such parameters. Reserving channels for data over a period of time minimizes data channel requirements and maximizes spectral efficiency, which allows data subscribers to request data channels for each separate data transmission. Because there is no need to do it. As a general principle, the goal of any trunk communication system is to effectively allocate limited channel resources among multiple subscriber units. The present invention considers three classes of subscriber units. That is, voice-only subscriber 112, voice / data subscriber 114, and data-only subscriber 116. The voice-only subscriber 112 is intended to be any existing trunk subscriber unit with a compatible signaling protocol capable of interacting with the system (100). Data-only subscriber (116) is KDT800 manufactured by Motorola^TMIt is intended to be any multiplex or single channel data transmitter / receiver, such as type, or functionally equivalent. Of course, receive-only data devices, such as any of the Motorola family of display pagers, can also operate to receive paging data on the assigned data channel. In this way, the trunk system according to the present invention accommodates existing equipment while providing enhanced communication capabilities. Subscriber units are typically mobile, portable or control stations. Typically, the mobile unit is understood to be a transmitter / receiver designed to operate in the vehicle. A portable unit is typically understood to be a transmit / receive or receive-only device designed primarily to be carried by or around humans. Control stations are usually permanent or semi-permanent equipment in buildings or other such fixed locations. These are collectively referred to herein as subscriber units that communicate with each other through fixed-end equipment. As mentioned earlier, the first assigned data channel is defined as the primary data channel, and its identity is periodically transmitted by the control channel to all subscribers. Additional or optionally, the identification information of all other assigned data channels is periodically transmitted by both the voice control channel and the main data channel. Those skilled in the art will appreciate that certain criteria are needed to determine how to distribute data users when multiple data channels are present. According to the present invention, data subscribers (114 and 116) each determine their own assigned data channel by randomly selecting one of the available data channels. Other criteria are also available and the particular criteria used in any particular embodiment are not critical to the practice of the present invention. Random number (selection) generators are well known in the art, and the particular algorithms used are not critical to the practice and understanding of the methods of the invention. Of course, the particular data channel allocation will depend on the actual number of data channels currently available. For example, a particular subscriber unit may choose data channel 1 if the current number of data channels is 2. If the number of channels is 3, channel 2 may be selected, and so on. Of course, if only one channel is available, all data subscribers will use that channel. In this way, the data subscriber can select a data channel and upload (up-load) or download (down-load) information to or from the host computer 106 (or 118). As used herein, "upload" means transferring data or executable code from a subscriber unit to a host computer. The term "download" means sending data or executable code from the host computer to the subscriber unit. When a certain number of data channels are assigned, the central 102 monitors voice activity, while the network controller 108 monitors activity in the data channels. Monitoring of this activity is preferably carried out over a predetermined period of time. For example, activity monitoring is done over time (or half an hour), which allows the trunk system (100) to quickly reallocate channel resources during peak load hours. If the network controller determines that the data activity in the assigned data channel exceeds the threshold selected by a given administrator, the network controller 108 centrally requests the data traffic to allocate another channel. Conversely, if the center determines that voice activity has exceeded a predetermined threshold, the center 102 requests the network controller to let go of the data channel. In this way, the trunk system 100 is configured to reallocate channel resources. According to the present invention, reassignment is initiated by sending a "return to master" command across all currently assigned data channels. When the subscriber units receive this command, they all return to the master data channel and listen for new data channel assignments. The assigned data channels are incremented or decremented by a predetermined number (one of the preferred embodiments), and the number of new allocations or data channels is broadcast with the identification information for each data channel. The subscriber unit receiving this information determines the number of available data channels and randomly selects an allocation. In this way, the number of data channels can be conveniently incremented or decremented depending on the data traffic. In addition to monitoring the overall data traffic, the network controller 108 can determine that the data traffic load on a particular data channel is overloaded. Therefore, the present invention considers a method for balancing data traffic in available data channels. Load averaging can be achieved simply by sending a "return to master" command over all currently assigned data channels. When the subscriber units receive this command, they all return to the primary data channel and listen for a new data channel allocation. Due to load averaging, the actual number of allocated data channels has not changed. Data subscribers are simply forced to randomly reselect data channel assignments. However, it is possible that data subscribers may not be able to effectively redistribute data traffic using this simple method. Therefore, the present invention is intended to transmit an offset "seed" to some or all subscribers for a random selection algorithm. In this way, there is a statistical possibility that the load will be distributed across the available data channels, as opposed to being crowded on a particular data channel. Data traffic will then be monitored over the next operating period, and if the load is still unbalanced, a different offset seed will be sent to redistribute the data load. Those skilled in the art will appreciate that it is often desirable to communicate with all subscriber units at once in response to emergencies or to distribute messages of general interest. For example, a message that broadcasts some emergency, or that host computer 106 (or 118) is shut down for repair is an example of a message that is convenient to send to all subscribers at once. Therefore, the present invention achieves this operation by sending a command back to the master through all assigned data channels. All subscribers respond to this command by listening to the master data channel. Before retransmitting the current number of data channels and their identification information (although these do not change), a system broadcast message is sent so that all subscribers can receive the message before receiving the data channel information. To do so. In this way, rapid system-wide data communication is provided by the methods of the invention. After receiving such system messages, data subscribers can return to their assigned data channels. Next, with reference to FIG. 2, a diagram of the preferred signal format for the main (master) data channel is shown. Signal format 200 begins with preamble section 202, which contains synchronization or frame information for the data subscriber unit. Following the preamble 202 is an optional block 204 where a system message or offset seed is sent to accomplish the system message operation or the load averaging procedure described above. Of course, during normal operation the format block 204 is not used and the preamble 202 directly precedes the block 206. Basically, block 206 transmits the total number of currently available data channels (which can be 1, 2, 5, etc.) in any suitable format. Following block 206, there are multiple blocks (208A-208N) that transmit data channel identification information. In a preferred embodiment, the transmitted identity of the data channel is the actual frequency of the channel. Alternatively, the channel can be assigned a designated number and the selected one available for data is transmitted. For example, if a particular system has 5 channels, it is convenient to label them 1-5. In this case, assuming the subscriber knows the frequency, the numbers "4" and "5" can be transmitted to indicate that channels 4 and 5 are data channels. However, in a preferred embodiment, the actual frequency is transmitted, as this allows for simple expansion of the system and limits the amount of information required to be present in the subscriber unit. Therefore, if there is one data channel (ie, the main data channel), that frequency will be transmitted in block 208A. If there are 5 currently available data channels (4 other data channels in addition to the main data channel), these frequencies will be transmitted (eg in blocks 208A-208E), and so on. After transmission of the last available data channel identification, the main data channel is available as a data channel by the subscriber unit as illustrated by block 210. When any particular subscriber unit should temporarily lose its data channel allocation to achieve recovery processing, the central 102 and network controller 108 periodically signal format 200 by voice control channel and main data channel, respectively. To send. If the data channel allocation is lost due to some error, the present invention causes the subscriber units in all data modes to automatically return to the primary data channel. In this way, the subscriber unit can receive periodic channel allocation transmissions from the main data channel and return to the proper data channel allocation. If the subscriber unit loses the identification information of the main data channel, the present invention further causes the subscriber unit to return to the voice control channel to receive the data channel allocation information. Next, with reference to FIG. 3, the preferred formats of other (ie, non-main) data channels are shown. Basically, the format of data channel 300 begins with preamble 302, which can include synchronization and framing information. The preamble 302 is followed by a plurality of variable length data messages 304-308. As mentioned earlier, data channel allocation requests are extremely long compared to typical data message transmission times. Therefore, the present invention is intended for a subscriber unit to proceed to its assigned data channel and transmit data information without reclaiming the channel. Working in this way eliminates the need to require a data channel and ensures spectral and high speed transmission. Of course, data conflicts can occur in the data channel. However, the mechanisms and methods for avoiding data collisions are well known in the art and any suitable data collision avoidance and recovery method is suitable for use in the present invention. As shown in FIG. 3, the lengths of data messages 1, 2 and 3 (304, 306 and 308) are all of varying lengths depending on the amount of information to be transmitted. Thus, once a subscriber unit gains access to a data channel, the subscriber unit can transmit data as long as necessary to complete a data message. Of course, the second subscriber unit attempting to transmit the data will be required to wait for the first subscriber unit to complete the transmission. Therefore, the data channel is in constant or near use. The preamble portion 302 does not need to be transmitted during periods of high data channel usage, as the subscriber is still in sync with the incoming data. However, if the data channel is underutilized, the network coctoroller 108 or datate subscriber will transmit the preamble portion 302 prior to transmission. Next, with reference to FIG. 4, a flowchart illustrating the steps performed to carry out the present invention by the fixed end device is shown. This routine begins at initialization step 400, where the central controller 102 and network controller 108 allocate memory space or perform other such functions as required by any particular system. The routine then proceeds to step 402, where the central controller 102 monitors voice activity and the network controller initiates a period timer for monitoring data activity. In step 404, these measurements are made by calculating air-time billing information or by other such appropriate means. Following step 404, determination 406 determines whether the timer has expired. If the timer has not expired, a loop is formed with step 404 until decision 406 determines that the timer has expired. Judgment 408 determines if voice activity is higher than a selected threshold that can be identified by the system administrator. If the decision of Judgment 408 is voice-intensive, then Judgment 410 is the current number of data channels minus a given offset (1 in the preferred embodiment) of the data identified by the system administrator. Determine if it is less than the minimum number of channels (if any). If so, decision 410 returns control to reference letter A, where it resets the timer and the routine starts again. However, if decision 410 determines that the removal of one channel is not less than the minimum allowed data channel, or if there is no minimum, the routine proceeds to step 412, where it returns the channel from the data traffic (de-). allocates) and returns it to voice traffic. The routine then proceeds to reference letter A in Figure 4. If the decision of decision 408 is that there is not much voice activity, the routine proceeds to decision 414, where it determines if the data activity is high compared to a given threshold selected by the system administrator. To do. If the judgment of judgment 414 is that there is a lot of data activity, the routine proceeds to judgment 416, where the current number of channels plus 1 (in the preferred embodiment) is the maximum determined by the system administrator. Determine if it is greater than the number (if any). If the judgment of judgment 416 indicates that the additional channel exceeds the maximum value, the routine returns control to reference character A. However, if the decision 416 indicates that the data channel addition does not exceed the maximum value, the routine proceeds to step 418, where it allocates additional channels from voice traffic to data traffic. The routine then returns control to the reference letter A in Figure 4. In addition, fixed-end equipment can consider traffic priority prior to allocation step 418 and de-allocation step 412. If, for example, a particular system prefers voice traffic, it can avoid allocating additional data channels if voice traffic is above a predetermined minimum. Alternatively, for systems with a preference for data traffic, the data channel can be prevented from being reassigned for voice traffic if the data traffic is greater than a predetermined threshold. If you do not like voice or data traffic, the absolute allocation and rebate procedure in Figure 4 is preferred. Further referring to Figure 4, if the decision of 414 is that there is not much data activity as a whole, the routine goes to decision 420 and the data traffic for all available data channels is balanced or unbalanced. Determine if it is balanced. If the decision of decision 420 means that the traffic is essentially balanced, the routine returns control to reference letter A, where the timer of step 402 is reset. However, if Judgment 420 determines that the data traffic is unbalanced, the routine proceeds to the load averaging routine of FIG. Then, with reference to FIG. 5A, the steps taken to achieve data traffic load averaging over the data channels available by the network controller 108 are shown. The routine begins at step 500, where all data channels return to the master and send commands. Upon receiving this command, the data subscriber listens to the main data channel and receives an offset seed parameter or load averaging command sent as block 204 in Figure 2 (502 in Figure 5A). The load averaging routine then proceeds to step 504, where the number of data channels available and their identification information are transmitted by the main data channel. Of course, the total number may not change, but instead an offset seed parameter may be added to statistically redistribute groups (or subgroups) to the available data channels. After receiving this information, each subscriber randomly reselects the data channel allocation. Of course, as mentioned earlier, if the data traffic load remains unbalanced after monitoring the next transmission period, then there is an acceptable balance between the data traffic and the available data channel resources. Different offset seeds will be sent until Next, with reference to FIG. 5B, the steps taken by the network controller 108 to send a system-wide data message are shown. This routine begins at step 506, where it returns to the master and the command joins all the data. sent to . Then, in step 508, a system message is sent by the main data channel to the subscriber unit (block 204 in Figure 2). Following step 508, the current number of data channels and their identification information (although this may not change) are transmitted in step 510. In this way, messages of general concern are sent quickly and efficiently to all data subscriber units. Finally, after step 510, the routine returns to reference letter A in FIG. Next, with reference to FIG. 6, a flowchart illustrating the steps performed by the data subscriber unit (114 or 116) according to the present invention is shown. The routine begins at step 600, where the data subscriber accomplishes some initialization step required in any particular embodiment. In step 602, the data subscriber receives data channel allocation information from either the voice control channel or the main data channel. Additionally, subscribers monitoring the primary data channel may receive system messages (see Figure 2). In step 604, the data subscriber selects a data channel from randomly available data channels. In step 608, the data subscriber operates to receive and transmit data information on the assigned data channel. Judgment 610 determines whether or not the "return to master" command has been received. If so, the subscriber transitions to the main control channel and receives the data channel allocation information in step 612, otherwise the routine returns to reference letter B and continues data operation. Judgment 614 determines whether the data allocation information contains system messages. If so, the data subscriber stores or plays the message by any appropriate means. For example, the subscriber displays the message by any appropriate display means (step 616). Optionally, the data subscriber can generate a "hard copy" on the printer or use speech synthesis to obtain an audible message. If the decision of decision 614 does not include the data channel allocation information, the routine proceeds to decision 618. Judgment 618 determines whether the data channel allocation information contains a load averaging command or a new offset seed. If included, the data subscriber again randomly selects a data channel assignment at 620, which may be different from the data channel assignments that follow, and the routine goes to reference letter B where the subscriber Returns to normal data communication. Although specific embodiments of the present invention have been described and presented, it should be understood that the present invention is not limited thereto as many modifications are possible. The application is therefore intended to include any and all such modifications within the true spirit and scope of the underlying principles disclosed and claimed herein.