MXPA97001650A

MXPA97001650A - Method and apparatus for selection of channels of entry in communication systems

Info

Publication number: MXPA97001650A
Application number: MXPA/A/1997/001650A
Authority: MX
Inventors: I Ayerst Douglas; J Khan Malik; Alan Hill Richard; Connon Gregory
Original assignee: Motorola Inc
Priority date: 1995-07-05
Filing date: 1997-03-04
Publication date: 1997-06-01

Abstract

A system controller (102) is used in a communication system (100) which has a set of input channels, the system controller (102) includes a processing system (204) to generate a first message which is transmitted to selective calling devices (106). The first message includes a subset identifier identifying an ALOHA subset of the set of input channels for use by a set of selective calling devices (106). A selective calling device (106) includes a transmitter (708) and a processing system (710) the processing system (710) identifies the ALOHA subset of the set of input channels, and generates a second message and couples the second message to the transmitter (708) using an ALOHA protocol in an input channel which is in the ALOHA subset of the set of input channels when the second message is a first type the transmitter (708) transmits the second message

Description

METHOD T APPARATUS FOR SELECTION OF ENTRY CHANNELS COMMUNICATIONS SYSTEMS APPLICATIONS PE REFERENCE Application N °: 08 / 397,322 filed on February 28, 1995, by Gorday et al, entitled "Method and Apparatus for Determining the Quality Level of a Analog Signal in Systems ^ Radial Communications ".

The invention relates generally to communication systems with multichannels and, in particular, to the input of radial input channels for transmission of a message using a containment prot.

BACKGROUND OF THE INVENTION [0002] Known techniques for transmitting incoming messages in communication systems, channels that include a plurality of call screening devices and having a μ, multiple input channels are techniques used to synchronize the protocol of the input transmission and techniques that are used in a containment input transmission protocol (not synchronized). An example of a synchronized transmission protocol is a transmission protocol in which at least a predetermined time period was reserved in at least one predetermined input channel for each call selection device that are active in the communication system . Another example of a synchronized input transmission protocol is a transmission protocol in which the selective calling device is notified in response to a time request that is used to transmit an extended input message. The notification is given within the output message that is sent in response to a short input message sent by the call selection device informing the communication system of the existence of a long input message. An example of a data contention protocol. input transmission is an ALOHA protocol, which is well known in the art by specialists. The input messages sent by an ALOHA protocol are typically transmitted as soon as they are generated. When two messages like that are transmitted on a channel that portions are transmitted to the ALOHA protocol. same time simultaneously, one or both messages may not be received correctly. In this case, the messages are not recognized by the communication system, and each call selection device repeats the message after each delay. The communication system may be a cable, optical or radio communication system In a cable communication system e, the input channels may be separated by wires, or they may be separated (particularly in the case of high-speed cable systems) by limited band channels, or by both In the optical or radio communication systems, the channels are typically separated by limited band channels, but alternatively they can be additionally separated by a time-counting system. Some systems that have signal output protocol, which are synchronous, are designed in such a way that the call selection devices acquire a smithism of the signal output protocol, and use a synchronized protocol of input transmissions, because the synchronized input transmission protocol is typically more efficient than the incoming transmission containment protocol, for different types of input messages, such as some answers and recognitions However, a protocol of content Transmission ion can typically be more efficient for other input messages, such as some unsolicited input messages. Prior art systems provide a mix of contention protocols for input transmissions by designing some types of messages to be transmitted. using an ALOHA protocol and other types of messages transmitted using a synchronized transmission protocol A call screening device then uses an appropriate technique on an authorized input channel The authorized input channel is typically any of the input channels that are designed to use in a call selection device. Nevertheless, in some communication systems, some input channels are not enough when they are used for incoming messages when using an ALO protocol! 1A For example, in some radio communication systems, some radio input channels (hereinafter referred to as "restricted channels"), are geographically restricted to areas smaller than the area covered by the radio output channels while the radio input channels have a coverage substantially equivalent to the external radio channels. Restricted channels are not efficient for transmitting incoming messages using an ALOHA protocol, because the call selection device can not be in the covered area of the restricted channel. What is needed, then, is an improved technique of channel selection. input that is used to transmit input messages using an ALOHA protocol in a communication system SUMMARY OF THE INVENTION Accordingly, the first aspect of the present invention is a method for use in a call screening device. The call selection device is used in a communication system having a set of input channels. The method includes the steps of identifying an ALOHA subset of a set of input channels, and of transmitting a first message using an ALOHA protocol on an input channel, which has an ALOHA subset. Accordingly, in a second aspect of the present invention a call selection device is used in a communication system. The communication system has a set of input channels The call selection device includes a transmitter and a processing system The transmitter transmits a first message The processing system is coupled to the transmitter The processing system identifies an ALOHA subset of a set of input channels, and generates a first message and couples with the first message to the transmitter using an ALOHA protocol in an input channel that is in the ALOHA subset. Accordingly, in a third aspect of the present invention, a device is used call selection in a radio communication system The call screening device has a set of input channels The call selection device includes a transmitter and a processing system The transmitter transmits a first message The processing system is coupled to the transmitter The processing system identifies a subset to the OHA of a set of input channels and a position of a portion of ALOHA of each subset of ALOHA of the set of input channels, identifies an input channel that is in the subset of ALOHA Accordingly, in a fourth aspect of the present invention, a control system is used in a communication system. The communication system includes call screening devices and a control system. The communication system has a set of input channels. The control system includes a processing system for generating a first message that is transmitted to the call selection device. The first message includes an identified subset that identifies an ALOHA subset of a set of input channels for use by a set of communication devices. call selection BRIEF DESCRIPTION OF THE DRAWINGS Figure I is a block electrical diagram of a radial communication system, according to the preferred configuration of the present invention. Figure 2 is a block electrical diagram of a controller system used in a radial communication system, according to the preferred configuration and Alternatives of the present invention Figure 3 is a timing diagram illustrating characteristics of a transmission format of an input signal protocol used by the radial communication system, according to the preferred or alternative configurations of the present invention. Figure 4 is a diagram of synchronization of radio signals of input and output channels for a first type of radial communication system, according to the preferred configuration of the present invention. FIG. 5 is a diagram of synchronization of radial signals of input and output channels. output, for a second type of radial communication system, depending on the n the preferred configuration of the present invention Figure 6 is a diagram of a method used in the controller system to identify a subset of input channels by a call pickup radio to transmit an input message using an ALOHA technique, according to a configuration Preferred or alternative of the present invention Figure 7 is a block electrical diagram of a multi-channel radio call selection according to the preferred configuration or alternatives of the present invention. Figure 8 is a flow chart of a method used in a radio call picker, according to the preferred configuration or alternatives of the present invention DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, an electrical block diagram of a radial communication system 100 according to the preferred or alternative configurations of the present invention is shown. The communication system comprises 100 such a message entry device. as a conventional telephone 101, a 1 0 fax machine or an answering machine 122, connected through a telephone terminal 108, by means of conventional telephone lines 1 10 to a controller system 102. The controller system 102 controls the operation of a plurality of radial frequency receivers / transmitters 103 through one or more communication lines I! 6 which typically are telephone cables doubled in pairs. The controller system 102 decodes and encodes the incoming and outgoing telephone messages in formats that are compatible with the computers. The controller system 102 also functions to encode and synchronize outgoing messages. Alphanumeric output is an alphanumeric page message that is recorded from the message terminal 122 It should be emphasized that the control system 102 is capable of operating in distributed control environments of the transmissions that allow the mixing of cellular coverage schemes. satellites, and others involving a plurality of radio frequency receivers / transmitters 103, conventional antennas 104, to provide reliable radio signals within a geographical area as large as the worldwide network. Each of the so called selector radios 106 assigned to use in the 0 radio communication system 100 has at least one assigned destination that is unique. The call selection destination allows transmission of the message from the controller 102 only to the intended radio selector radio. It will be appreciated that the radio selector call 106 is one of several types of radios, including conventional mobile radios, which have a data terminal, or which optionally have a designated data terminal capacity. Each one of the call pickup radios 106 assigned to use in the communication system radial 100, has an assigned destination that is unique A list of selected destinations and assigns two and the corresponding telephone numbers are stored in the call pickup radios in the controller system 102 in the form of a base of - data Referring to Figure 2, a block electrical diagram of the controller system 102 is shown, according to the preferred or alternative configurations of the present invention. The controller system 102 stores data and voice messages, for transmitting to call pickup radios 106. , connects phone calls to transmit to radios 106, and receives 5 acknowledgments, answers, unsolicited data and stores audio messages, and telephone calls from radio selectors The controlled system! 102 comprises a cellular controller 202 a processing system 204, a memory for outgoing messages 208, a database 202, and a telephone interface 206 0 The cellular controller 202 transmits outgoing messages that include call selectors to receivers / transmitters 103 and controls that the receiver / transmitter 103 transmits the radio cycles that include the outgoing messages The cellular controller 202 also processes incoming messages of the selector radios 1 6 The processing system 204 is coupled to the cellular controller 202. to the telephone interface 206, to the data base 220 and to the output message memory 208 The database 220 which is coupled to the processing system 204, stores information for each subscriber, including a correlation between a call pickup destination assigned to each radio selector and called 106, and the telephone number used with the telephone connection l or K to direct and drive the messages The message memory of exit 208, is to store a list of messages that are waiting to be delivered. Analogue messages are converted to digital form by the processing system 204. before being stored in the outgoing message memory 208 As described above, the messages they can be digital information, such as alphanumeric messages or analogous information, such as voices. The digital portion of the cycle is in one or more frames, it is prepared to be transmitted by the manual messaging function The analog message is included in one or more frames The controller system 102. synchronizes transmission of responses demands and knowledge from radio selector called 106 The synchronization of input messages under certain circumstances improves the connection of the input channel compared to the unsynchronized organization scheme that is used in an ALOHA system. Alternatively, the synchronized input channel may be a portion or all the time available in a channel that has a radial conveyor frequency that is different from the frequency of output channels. The methods of identifying the synchronized times will be described next.

Preferred is the system made by Motorola, model PS 2000, registered trademark, by Motoiola Inc. of Schaumburg, Illinois. The processing system preferably includes a conventional computer system 212, and a conventional mass storage medium. 214 The computer system 212 it preferably comprises a plurality of processors such as VME Sparc, manufactured by Sun Microsystems, lnc. These processors include a dynamic access memory, which serves as temporary storage. The conventional mass storage means 214 that is preferred is a hard disk storage device. that other types of conventional computing systems 2 1 2 can be used, and that additional computing systems 2 12 \ massive storage means 214 of the same or different type can be added as required to handle the process The radial communication system 100 of the present invention preferable you use a frame structure similar to the FLEX, registered trademark, in the cinnamon output to allocate, the digital or voice message As described above there are two types of frames the voice and the control The control frames preferably, they are used to control, allocate, and distribute the digital messages of the call pickup radios. The voice frames are used to deliver analog messages to the call pickup radio. Both types of frames start with a standard FLUX synchronization. 3 shows a synchronization diagram illustrating the characteristics of the transmission format of an output signaling protocol used by the communication system 100 of FIG. I, which includes details of the control frame 330. The output signaling protocol is divided into a now 310, a cycle 320, a frame 330, 345, a block 340 and a word 350 Information is included in each control panel 330 in camp Information panel, comprising information in each word panel 338 or block 332 One aspect of the information system is that the word information panel 338 includes a panel number and cycle number The cycle is a number between 0 to 15 The panel number is a number from zero to 127 The block information field 332 includes all the active call selector radios that are decoded during control panel 330. This is called global information. The block information field includes year, month, day, date, hour, minute, and an eighth of a minute. The vectors contain information that specifies the initial word of the long message, in terms of protocol divisions described above, and additionally radial information, such as radial frequency, can be rectified. When the calling radio selector 106 detects its destination within the panel 330, it processes the associated vector packet or the short message packet within the panel 330. When the calling radio selector 106 decodes the vector packet in the corresponding panel 330 with its destination, the selector radio 106 is directed in order to receive and decode the long message or the analogous message. Referring to FIG. 4, a synchronization diagram 400 shows signals of input and output radio channels for the first type of communication system according to the preterred configuration of the present invention. During the output portion 420, the radio signal output channel is transmitted from the transmitter / receiver 103 to one or more selective calls 106. A plurality of output messages 404, 405 are transmitted within the output portion 420 of the panel control 330 Output portion 420 starts at the beginning of control panel 330 and ends at the output / input limit 402 A plurality of synchronized responses 406, 440, 412, 413, 414 are transmitted as data units, each data unit is extended about one and more time slots 440 Each of the synchronized responses 406, 410,412,413,414 is a radio signal transmitted from one of the call picking radios 106, in response to a command 455 which is completed in one of the output messages 404,405 A synchronized response 410 is transmitted by one of the selector radios 106 TIME initial of each external message 404 is defined as panel number, block number and word number A command 455 is included in one or more of the output messages 404. identifying one of the selector radios 106. by a call selection destination of that radio 106 Command 455 includes a determined length of the data unit. The output messages 404 may further include data 457, such as alphanumeric information messages. Each segment 403 includes the synchronization signal 331, which marks the output panel 401 and includes the information described at offset 525. The output messages may include 504, 505, one or more commands 455. each command 455 identifies one of the call picking radios. With respect to Figure 6, a flow diagram of the method used in the control system 102, to identify a subset of satellite input channels by means of call-picking radios. With respect to figure 7. an electrical block diagram of multi-channel call selector radio, 106 The selector radio includes an antenna 702, to intercept and transmit radio signals the antenna is coupled to the conventional receiver 704, where the intercepted signal 703, it is received.

The receiver 704 generates a demodulated signal 705, which is coupled to the processing section 310 The processing system 710 performs works includes at least portions of recovery of the bits, synchronization, decoding of words, processing of messages, sample, generation of incoming messages, etc. It can be appreciated that the processing system may optionally be supplemented and improved without the microprocessor 716. It will be appreciated that the microprocessor 716 may be a conventional microprocessor, such as type 68 HC1 1 microprocessor manufactured by Motorola, Inc. of Schaumburg, Illinois.

With reference to the F1G 8, a flow diagram of a method used in the selective calling radio 106 is shown, in accordance with the preferred and alternative embodiments of the present invention. This method includes unique ALOHA channel selection (ACS) functions programmed into the selective call radio processing system 710. The unique ACS functions are controlled by a unique combination of conventional program instructions stored in the processing system 710. In step 805, the processing system 710 retrieves a ALOHA subset of the set of input channels and a missing set of ALOHA portions of memory input channels in the selective calling device 106, and initializes a subset ALOHA of the / o set of input channels and a set of Al.OHA portions of input channels The subset of the initialized ORA of the input channels identifies the input channels in the set of input channels to be used by the radio. selective call 106 for transmitting incoming messages that are to be transmitted using the ALOHA technique until the selective calling radio 106 receives newer information that defines or add to the ALOHA subset of input channels. The technique for determining the initialized ALOHA subset of the stored subset is conventional, but the use of the missing ALOHA subset is unique. The missing ALOHA subset can be anything from an empty set, i.e. no channel is designated for ALOH transmissions. to a complete set of input channels Typically, the set Z 0 missing includes at least one channel, thus allowing a non-registered selective call radio 1 6 to transmit a non-required registration request using the ALOHA technique. The initialized set of ALOHA portions of input channels identifies programmed limit positions / .ALOHA (and consequently ALOHA portions) for each input channel that is usable in the system for ALOHA transmissions. The missing set of ALOHA portions 5 of input channels may be a programmed position / ALOHA commonly used for all input channels, or several values that define different programmed positions / Al. OHA for each input channel or groups of input channels . The technique for determining the initialized set of ALOHA portions of input channels from the stored missing set is conventional, but the use of the set or missing ALOHA portions of input channels is unique In step 10. the selective calling radio receives an output message that includes an identifier of the ALOHA subset, which identifies a new ALOHA subset of the set of input channels for use by all selective call radios 106 active in the system The identifier of the ALOH.A subset comprises bits in block information field 332 arranged conventionally to identify one or more input channels. The message is either a global message identifying a new sub-location Al. KA for its support part of all the selective call radios 106 active in the system, or a selective call message, of individual type or of all call, which identifies the new ALOHA subset of the set of restricted input channels 1 rj for use by an identified group of selective calling radios 106 or by only a selective calling radio 106 addressed In step 813, the processing system 71 updates the ALOHA subset stored therein by replacing the old subset by the new subset It will be appreciated that alternative methods are also usable for identifying the subset input channels which may be 1 5 used by a selective calling radio 106 for ALOHA transmissions For example, the subset of channels to which ALOHA can not be used can be identified, since each channel is usable or unusable by each selective calling radio 106 for transmission purposes. n A! 011 A In another alternative, an outgoing message that is identifying channels that are (or channels that are not) usable for ALOHA transmissions can indicate only changes to the ALOHA subset, such as when adding or removing a channel or channels from the ALOHA subset In step 815, the selective call radio 106 receives a global output message that includes a programmed limit identifier / ALOHA (separation identifier). protocol) for an input channel The programmed limit identifier / AI OH A identifies the position of the programmed limit / ALOHA 431 FIG 4), > | 1 or (Fl (5) e an input channel The programmed limit identifier / ALOHA comprises bits in the block information field 332 conventionally arranged to identify a channel, and a programmed limit position / ALOHA 431 (FIG 4) , 510 (FIG 5) of an input channel The position of the programmed limit / ALOHA 431, 510, which is stored in the selective calling radio 106, is updated by the processing system 710 in step 820 by means of the information in the global message, in a similar way to the one described in the case of the subco? together ALOHA of the set of input channels.It will be appreciated that the programmed limits / ALOHA 431, 510, for all the input channels that are in all subco? together ALOHA for all selective calling radio 5 106 are determined by the missing set of ALOHA portions or by the transmission (s) of one or more programmed limit identifiers / ALOHA.

In step 825, the processing system 710 generates an input message. The input message is typically one of the following types: an incoming or outgoing message, an immediate ALOHA response message, a scheduled acknowledgment or a programmed response. The input messages not required and the immediate ALOHA response messages are a first type, "ALOHA", which are generated by the processing system 710 and transmitted by the transmitter 708 in time segments and in input channels as determined by the 710 processing system using the 5 ALOHA technique, while the programmed acknowledgments and the programmed ones are a second type, "programmed", that are transmitted in accordance with a program received in an output message that includes information of necessary programming such as input channel identification, initial time segment and data transfer rate. The synchronization, modulation and selection of channels are controlled by the 0 processing system 710. When the type is "programmed" in step 830, the input message is transmitted in step 855 using the input channel programmed in the segment of programmed time, which is during the programmed portion of the input channel. When the type is not "programmed" in step 830, and when the radio communication system 100 is a frequency division multiplex system as described with reference to FIG. 5, the processing system 710 further determines whether the output frame 330 in which the identifier of the last ALOHA channel or protocol separation identifier has the same frame number as the input frame in which the input message is generated for transmission in step 835. When it is determined that the output box 330 in which the identifier of the last ALOHA channel or protocol separation or identifier is received has the same frame number as the input frame in which the input message is generated in step 830, the transmission of the input message is delayed by the processing system 710 in step 840 to the next input frame 530. When it is determined that the output frame 330 in which the identifier of the last ALOHA channel or identifier was received was received. protocol separation does not have the same frame number as the input frame in which the input message is generated in step 835, or when the message has been delayed in step 840, one of the input channels in the subcoding ? together ALOHA is chosen randomly in step 845 by the processing system 710, and the input message is then transmitted in a time segment determined by the processing system 710 in the ALOHA 450, 518 portion of the randomly chosen channel, using an ALOHA technique in step 850. For example, using the ALOHA technique, the input message is transmitted starting at a time segment with respect to the programmed limit / ALOHA 431, 510, which is chosen at random in a predetermined range of ALOHA time segments, in a manner well known to one skilled in the art.

When the radio communication system 100 is a time division duplex system such as that described with reference to FIG. 4, steps 835 and 840 are eliminated.

Steps 835 and 840 are also eliminated in accordance with an alternative embodiment of the present invention used in a time division duplex system as described with reference to FIG. 5. In the case of the alternative embodiment, an input message that is being transmitted using an ALOHA protocol is typically transmitted by a selective calling radio 106 in the ALOHA portion of the frame 330 in which the message is generated. In the alternative embodiment of the present invention, an input message is transmitted using an ALOHA protocol in the input box 530 in which the message is generated. The alternative embodiment has a deficiency in that, in a frequency division multiplex system as described with reference to FIG. 5, when the offset time 525 is less than the duration of a frame 330, 520, 530, a predetermined maximum ALOHA portion of the input message is defined, during which a limit or subset change will not be transmitted in a message of output, and before which a selective calling radio 106 will not transmit an ALOHA message. This avoids problems with an ALOHA message that is being transmitted in a non-ALOHA portion of a message during the frame in which the change is transmitted, but restricts the ALOHA portion to being less than a complete input frame.

It will be appreciated that the unique method and apparatus described above, which provides an improved channel selection technique for channels to be used for ALOHA transmission of input messages in a radio communication system 100 having multiple input channels, provides improvements Similar when used in systems that share some similarities with the system described, but can be quite different in other respects. In particular, the system does not need to be radio or even wireless. For example, in a point-to-multipoint wireline system that has several selective call devices and several input channels (for example, several wire pairs), some input channels may be designed so that all selective call devices are for ALOHA transmissions and others for programmed transmissions, using the technique described above. For example, messages shorter than a fixed length can be designated for ALOHA transmission or an ALOHA channel.

Furthermore, when the communication system is a radiocommunication system, it does not need to be a radiocommunication system that uses a FLEX1 ^ family protocol such as the ReFLEX1 ^ or InFLEXionMR protocol. Other protocols such as the protocol used in the ARDIS ^ system could be modified to provide the functions described herein.

It should be appreciated at this point that a method and apparatus for improving the performance of the input message has been provided by controlling the selection of an ALOHA subset of input channels used by a selective calling device in a communication system having multiple input channels. .

Claims

1 A selective calling device used in a communication system, wherein the communication system has a set of output channels for transmitting messages to various selective calling devices from a system controller, and a set of input channels for receiving messages in the system controller from several selective calling devices, said selective calling device being characterized by comprising: a transmitter for transmitting a first message; Y a processing system, coupled to said transmitter, where said processing system: receives a subset identifier transmitted by the system controller in a channel of the set of output channels; identifies from the identifier of subco? together a subco? together ALOHA of the set of input channels; Y generates the first message and couples the first message to said transmitter for transmission to the system controller using an ALOHA protocol on an input channel which is in the ALOHA subset of the set of input channels when the first message is a first type of message.

2. The selective calling device according to Claim 1, characterized in that the processing system selects the input channel randomly from the ALOHA subset of the set of input channels, when it generates the first message.

3. The selective calling device according to Claim 1, characterized in that the first type of message is one of a non-required input message and an immediate ALOHA response message.

4. The selective calling device according to Claim 1, characterized in that the processing system generates a second message and couples the second message to said transmitter using one of the set of input channels that is not one of the ALOHA subset when the second message is a second type of message.

The selective calling device according to claim 1, characterized in that the processing system couples the first message to the transmitter during an input frame which is the following after an input frame having the same frame number as the number of an output box in which the subset identifier was received.

The selective calling device according to Claim 1, characterized in that said input channel has an ALOHA portion, and wherein said processing system couples the first message during the ALOHA portion of the input channel.

7. A selective calling device used in a communication system, wherein the communication system has a set of output channels for transmitting messages to various selective calling devices from a system controller, and a set of input channels for receiving messages in the system controller from several selective calling devices, said selective calling device being characterized by comprising. a receiver for receiving a subset identifier and an output / input identifier transmitted by the system controller on a channel of the set of output channels; a transmitter for transmitting a first message; Y a processing system, coupled to said transmitter, where said processing system: identifies from the subset identifier an ALOHA subset of the set of input channels, and identifies from the output / entry identifier a position of an ALOHA portion of each ALOHA subset of the set of input channels, identifies an input channel that is in the ALOHA subset of the set of input channels; Y generates the first message and couples the first message to said transmitter for transmission to the system controller using an ALOHA protocol for a portion ALOHA of the input channel identified when the first message is a first type of message. 8 A system controller used in a communication system, characterized in that the communication system comprises selective calling device and the system controller; and wherein the communication system has a set of output channels for transmitting messages to various selective calling devices from a system controller, and a set of input channels for receiving messages in the system controller from various selective calling devices, said selective calling device being characterized by comprising: a processing system for generating a subset identifier that identifies an ALOHA subset of the set of input channels for use by a set of selective calling devices; Y a local cellular controller for coupling the identifier of subsets to a transmitter that transmits the identifier of subsets in a channel of a set of output channels to the set of selective call devices The system controller according to claim 8, characterized in that said processing system generates a protocol separation identifier that is included in a second message which is transmitted to the selective calling devices, where said protocol separation identifier identifies a position of an ALOHA portion and a programmed portion of each ALOH.A subset of the set of input channels The system controller according to claim 8, characterized in that said system controller further comprises a radio receiver and wherein the transmitter is a radio transmitter. SYNTHESIS OF THE INVENTION A system controller (102) is used in a communication system (100) which has a set of input channels the system controller (102) includes a processing system (204) to generate a first message which is transmitted to selective calling devices (106). The first message includes a subset identifier identifying an ALOHA subset of the set of input channels for use by a set of selective calling devices (106). A selective calling device (106) includes a transmitter (708) and a processing system (710). the processing system (710) identifies the ALOHA subset of the set of input channels, and generates a second message and couples the second message to the transmitter (708) using an ALOHA protocol on an input channel which is in the ALOHA subset of the set of input channels when the second message is a first type the transmitter (708) transmits the second message.