WO1996027993A1

WO1996027993A1 - A subscriber unit having a sleep mode and a dormant mode

Info

Publication number: WO1996027993A1
Application number: PCT/US1996/003150
Authority: WO
Inventors: Ido Ein-Dor
Original assignee: Geotek Communications, Inc.; Powerspectrum Technology Ltd.
Priority date: 1995-03-08
Filing date: 1996-03-08
Publication date: 1996-09-12
Also published as: CA2214768A1; IL112939A0; EP0872136A4; IL112939A; KR19980702771A; AU5304396A; EP0872136A1

Abstract

A method for providing communication services between a base station (2) and a subscriber unit (6), including the steps of placing the subscriber unit in a dormant mode wherein the subscriber unit consumes limited power, transmitting communication signals from the base station when the subscriber unit is in the dormant mode, at the base station, determining that the subscriber unit is not responsive to the transmitted communication signals and storing the communication and the identity of the subscriber unit to which the communication was directed in a buffer at the base station, after a predetermined time, taking the subscriber unit out of the dormant mode and causing the subscriber unit to communicate with the base station to inquire about communications messages, and if there are buffered communications for the subscriber unit, transmitting the buffered communications from the base station to the subscriber unit.

Description

A SUBSCRIBER UNIT HAVING A SLEEP MODE AND A DORMANT MODE Background of the Invention

The present invention relates to wireless communication systems. More specifically, it relates to the subscriber units used by subscribers to the wireless communication systems.

Wireless communication systems are used to provide communications capabilities to businesses having fleets of vehicles operating in the field -- for example, taxi companies or limousine companies. Typically, wireless communication systems include a base station, one or more dispatch stations and a plurality of subscriber units. All communications are routed through the base station. The subscriber units are mounted in the vehicles operating in the field to provide communication capabilities to the vehicle's occupants. The dispatch stations allow a dispatcher to send dispatch communications to one or more of the subscriber units through the base station.

Today's dispatch communication systems, however, provide limited communication capabilities. For example, deliverymen working the eight-to-five shift turn their subscriber units off at 5:00 P.M. The next day, when they start their new workshift, they turn their subscriber units on a short time before 8:00 A.M. Communications from the dispatch station are not transmitted until the subscriber units are turned on. If too many subscriber units are turned on at the same time, the communication system can be overloaded, thereby creating delays in the transmissions of messages.

In view of these and other limitations, new systems and methods that provide improved communications between a dispatch station and a fleet of subscriber units are needed.

Summary of the Invention

The present invention provides apparatus and method of providing dispatch communications in a system that includes a base station, a dispatch station and one or more subscriber units, in accordance one aspect of the present invention, the subscriber unit has four modes of operation that consume various amounts of power. The modes include a sleep mode, a dormant mode, a power off mode and a power on mode. In the sleep mode, limited power is consumed while the subscriber unit listens for

communications from the base station. In the dormant mode, the subscriber unit is essentially shut down and, therefore, consumes minimal power.

During the dormant mode, communication signals transmitted to the

subscriber unit, including dispatches from a dispatch station, are stored in a buffer at the base station. After a predetermined time, which is preset by the dispatch station or by the subscriber, an Internal alarm clock in the subscriber unit causes the subscriber unit to come out of the dormant mode to initiate a call to the base station to inquire about messages which were directed to ths subscriber unit during the time it was in the dormant mode. If there are buffered communications for the subscriber unit, the base station transmits the buffered communications from the base station to the subscriber unit. The subscriber unit then returns to the dormant mode.

The invention will now be described in connection with certain illustrated embodiments; however, it should be clear to those skilled in the art that various modifications, additions and subtractions can be made without departing from the spirit and scope of the claims.

Description of the Drawings

FIG. 1 illustrates a communication system;

FIG. 2 illustrates a common air interface for providing communications between the various components of the communication system of FIG. 1 ;

FIG. 3 illustrates a base station in the communication system;

FIGS. 4 and 5 illustrate a subscriber unit in the communication system;

FIG. 6 illustrates a dispatch station in the communication system;

FIG. 7 illustrates a billing station in the communication system;

FIG. 8 illustrates the on/off power control of the subscriber unit;

FIG. 9 illustrates the power control of the subscriber unit during the sleep mode;

FIGS. 1 0 and 1 1 illustrate the steps taken by the subscriber unit in the dormant mode; and

FIGS. 1 2 and 1 3 illustrate the organization of memory in the base station which is used to buffer messages to dormant subscriber units.

Description of the Preferred Embodiment

Referring to FIG. 1 , a communication system 1 is illustrated. The system 1 includes a base station 2, a dispatch station 4 and a plurality of subscriber units 6. A billing station, not shown in FIG. 1 , is preferably also provided to process billing information from a plurality of communication systems 1 .

The communication system 1 may be a frequency hopping system which is divided into sectors 8 to 10 wherein sets of frequencies are reused in each sector to provide wireless communications. Note, however, that the present invention may be used on other types of communication systems, including TDMA systems, CDMA systems and even analog based systems.

The base station 2 includes the communication equipment necessary to provide the multiple access communications for the plurality of

subscribers units 6 and for the dispatch station 4. The base station 2 also includes the communication equipment needed to provide communications through the Public Switched Telephone Network (PSTN).

The dispatch station 4 includes equipment necessary to dispatch communications from the dispatch station 4 to a number of subscriber units 6, commonly referred to as point-to-multipoint communications. It also includes equipment needed to communicate with individual subscriber units. The subscriber units 6 generally consist of mobile or portable equipment necessary to transmit, receive and process communication signals.

Referring to FIG. 2, the communication links between the base station 2, the dispatch station 4 and the subscriber units 6 - - referred to as the common air interface - - are illustrated. The communication channels in FIG. 2 include a plurality of traffic channels (TCHs), at least one control channel

(CCH) and at least one access channel (ACH). In the communication system 1 of FIG. 1 , all of these channels are present in each sector 8 to 1 0. The TCHs operate in the uplink (transmissions from subscriber units 6 to the base station 2) and in the downlink (transmissions from the base station 2 to the subscriber units 6) . The CCH and the ACH, however, operate only in one direction - - the CCH in the downlink and the ACH in the uplink.

In the illustrated embodiment of FIGS. 1 and 2, ten 25 kHz frequency channels are used to define ten uplink channels and ten 25 kHz frequency channels are used to define ten downlink channels. In each sector 8 to 1 0, nine of the frequency channels are used to implement nine uplink TCHs and nine of the frequency channels are used to implement nine downlink TCHs. In each sector 8 to 10, the remaining frequency channels are used to transmit one ACH and one CCH. Voice information, data information and inband overhead control signals between the base station 2 and the

subscriber units 6 are transmitted over the TCHs, preferably using frequency hopping and time hopping communication methodology. Timing and control signals from the base station 2 to the subscriber unit 6 are transmitted on the CCH. Status and operational requests from the subscriber unit 6 to the base station 2 are transmitted on the ACH. Transmissions between the base station 2 and the dispatch station 4 are treated in the same fashion as transmissions between the base station 2 and the subscriber units 6. Note that this description is illustrative of one communication method and one air interface that can be used in connection with the present invention - - many others are possible.

Referring to FIG. 3, the base station 2 is illustrated. The base station 2 includes a first sector unit 1 6, a second sector unit 1 7, a third sector unit 1 8, a microsector unit 20, a redundant sector 21 , a PABX 22, a voice mail unit 24, a central frequency source unit 26, an administration computer 28, a central controller 30, a database server 32, a local administrative computer 34 a terminal server 36, a local area network 38, a power supply 39, data computers 40 and a modem pool 41 . The base station 2 may also include a billing station, but where the communication system 1 is part of a regional or national system having numerous base stations, it is preferred to provide a central billing system that serves all of the base stations. The base station 2 of FIG. 3 does not include a billing station.

The sector units 1 6 to 1 8 establish the communication channels illustrated in FIG. 2 in the sectors 8 to 1 0, respectively. The microsector unit 20 establishes communications with additional communication

equipment in trouble spots in the communication system 1 . The redundant sector 21 provides redundant communication channels for the sector units 1 6 to 1 3. The base station 2 provides communications with the PSTN via the PABX 22. The PABX 22 also provides three way conferencing, routing, least cost routing of long distance calls, voice mail interfacing, dispatch bridging, user services support and metering functions.

The voice mail unit 24 provides voice mail capability to the

communication system 1 . The central frequency source unit 26 provides timing references throughout the system. The administrative computer 28 tracks subscriber unit 6 configurations, tracks administrative activities, performs network management, performs built-in-test management and performs system initialization. The central controller 30 provides various functions, including call management, dispatch management, control of the PABX 22, voice mail interfacing, operational mode management, subscriber management, call management, supplies billing information, and generates reports. The data base server 32 stores user data concerning user rights, status, calls and airtime. It also provides basic data base management and services to all data base clients, such as the local operator, fleet

administrators and remote operators. The local administration computer 34 provides maintenance and operational control of the base station 2. The local area network 38 enables communications between the various components connected to the network.

Two pieces of equipment form a subscriber unit - - a subscriber terminal 14 illustrated in FIG. 4 and a radio unit 1 2 illustrated in FIG. 5. In general, the radio unit 12 provides the equipment needed to transmit, receive and process signals over the common air interface of FIG. 2 while the subscriber terminal 14 provides an interface to a subscriber.

Referring to FIG. 4, the subscriber terminal 14 includes a

microprocessor 50, an oscillator circuit 52, a power supply circuit 54, a serial interface circuit 56, a display driver circuit 58, a memory circuit 60, a keyboard interface circuit 62, an I/O decoder circuit 64, a LED driver 66 and an interface circuit 68. The subscriber terminal 14 can also include a real time clock 70 or, alternatively, the base station 2 can distribute real time clock information to each of the subscriber units 6.

The memory circuit 60 includes a decoder circuit 76, an address latch 78. a boot ROM 80, a flash memory 82 and a static RAM 84. The boot ROM 80 stores the code necessary to initialize the microprocessor 50 and the circuitry of the subscriber terminal 14 as well as code necessary to download future software versions for the subscriber terminal 14. The flash memory 82 is non-volatile re-writable memory which is utilized to store information which must be maintained even during a loss of power. The static RAM 84 is utilized as a working memory as needed.

The display driver circuit 58 includes the LCD display 24, a power supply 86, a LCD controller 88, a memory circuit 90 and an address

controller 92. The display driver circuit 53 is accessed by the microcontroller 50 via the I/O decoder 64. The information to be displayed is downloaded from the microprocessor 50 to the memory circuit 90. The display of the information on the display 24 is then controlled in a

conventional manner by the LCD controller 88.

The microprocessor 50 is responsive to the selection of the keys 30 to

34 and 36 to 43, as well as to the selection of the keys on the handset 28. When the keys are selected, selection signals are processed through the ke yboard interface circuit 62 to the microprocessor 50. The microprocessor 50 also controls the LEDs 44 through the LED driver circuit 66. The RS-232 interface 94 provides communications between the subscriber terminal 1 4 and external devices, such as notebook computers, magnetic swipe devices used to read magnetic strips, printers, bar code readers and serial keyboards. The RS-485 interface 96 and the interface circuitry 68 provides

communications between the subscriber terminal 14 and the receiver and transmitter circuitry of the radio unit 12 (shown in FIG. 5).

In FIG. 5, the circuitry of the radio unit 1 2 is illustrated. The radio unit 1 2 includes antennas 102 and 104, a radio board 106, a baseband unit 1 08, a service board 1 1 0, and a GPS interface 1 1 1 . The radio unit circuitry illustrated in FIG . 5, except the antennas 102 and 1 04, is preferably housed separately from the subscriber terminal 14, for example, inside the trunk of an automobile. The antennas 1 02 and 1 04 are preferably mounted

externally on the automobile. The radio board 1 06 includes transmitter and receiver circuitry. More particularly, it includes a transmitter 1 12, two receiver channels 1 14 and 1 16, a duplexer 1 1 8, a frequency synthesizer 1 20, gain and frequency control circuitry 122 and transmitter gain control circuitry 124. As previously described, the circuitry of the radio board 1 06 preferably provides communication via frequency hopping, that is, a communication signal is transmitted and received by hopping the signal over several different frequency channels.

The radio board 106 is interfaced with the baseband unit 108. The baseband unit 108 includes a modem 126, a controller 1 28, a voice processing package 130 and an interface circuit 132 to the subscriber terminal's 1 4 circuitry. This baseband unit 108 receives the signals to be transmitted to the base station 2 from the subscriber terminal 14 processes those signals and then sends the signals to the transmitter 1 12 in the radio board 106 for transmission. This baseband unit 108 also receives the signals that the radio board 106 receives from the base station 2, processes the received signals and sends them to the subscriber terminal 14 through the interface 1 32.

Referring to FIG. 6, the dispatch station 4 is illustrated. The dispatch station 4 includes a personal computer 1 50, a modem 1 52, a radio unit 1 2, a microphone 1 54, a speaker 1 56 and an antenna 1 58. When the base station transmits to the dispatch station 4, the communication signals are received on the antenna 1 58, processed by the radio unit 1 2 and sent to the computer 1 50 through a serial port 1 60. The computer 1 50 determines whether the communication is voice or data communications. If the communication is a voice communication, then the signals are sent to a sound card in the computer 1 50 for voice processing. The voice signals are eventually sent to the speaker 1 56 through a port 1 62 on the sound card so that they can be heard by a dispatcher. If the communication is a data communication, then the computer 1 50 processes the data so that it can be presented to the dispatcher in a desired format.

When the dispatcher sends a voice or data communication signal from the dispatch station 4 to the base station 2, the signal is generated from the microphone 1 54, in the case of voice signals, or from a data file in the computer 1 50, in the case of data signals. The voice signals are preferably processed through the sound card in the computer 1 50. Then, the voice or data signals are sent through the port 160 to the radio unit 12 for

transmission by the antenna 1 58.

In addition to voice and data, the dispatcher can send fleet

administration information to the subscriber units in the dispatcher's fleet to control the configuration and capabilities of those subscriber units. To do this, the dispatcher accesses the computer 1 50 to set the desired fleet administration information. The fleet administration information, once configured by the dispatcher, is then sent through a port 1 64 to the modem 1 52. The modem 1 52 transmits the fleet administration information to either a central billing station or to the base station 2 over a land line.

Alternatively, the fleet administration information is transmitted over-the-air to the base station 2 through the dispatch station radio unit 12. The fleet administration information can then be forwarded to the billing station, whether the billing station is part of the base station 2 or off-site in a central location.

Referring to FIG. 7, a central billing station 1 70 is illustrated. The billing station 170 includes a server 172, a gateway 1 74, a local area network 1 76 and a router 178 to a wide area network. The server 172 has a database that keeps track of information concerning all users of the communication system 1 , including all of the dispatchers and all of the subscribers. The information tracked includes the services that the users have signed up to use, the payment histories of the users, the configurations of the users of the system 1 and current billing information. The gateway

1 74 's a switch that provides a signal path to and from the local area network 1 76. A router 178 then routes these signals to a wide area network for distribution to and from the focal area network 38 of the base station 2.

In accordance with the present invention, the subscriber unit 6 preferably has four different modes of operation, each of which consume differing amounts cf power. In the first mode, power off, all components in the subscriber unit 6 are turned off and no power is consumed. In the second mode of operation, power on, all components in the subscriber unit 6 are turned on and maximum power is consumed. In the third mode, the dormant mode, all components except those responsible for "waking up" the subscriber unit 6 at a preset time are turned off. The subscriber unit 6 wakes up at a preselected time to query the base station 2 for messages. Once in the dormant mode, however, the subscriber unit 6 will not resume normal operation until the unit is turned on by the subscriber. In the fourth mode, the sleep mode, subscriber unit 6 turns power off to all components except those necessary to receive signals from the base station 2. Then, when signals are received, the subscriber unit 6 again wakes up to process those signals. The subscriber unit 6 exits the sleep mode whenever any key on the keypad 24 is touched.

These modes of operation are illustrated in FIGS. 8 to 1 1. Referring to FIG . 8, the steps taken by the subscriber unit 6 when turning power on and off are illustrated. In step 200, the microprocessor 50 in the subscriber terminal 1 4 determines that the power control key on the subscriber terminal 1 4 has been selected. If the power is being turned on, then in steps 202 and 204, the controller 123 and the microprocessor 50 cause the power to the radio unit 1 2 and to the subscriber terminal 14, respectively, to be turned on. If the power is being turned off, then in steps 206 and 208, the controller 1 28 and the microprocessor 50 cause the power to the radio unit 12 and to the subscriber terminal 1 4, respectively, to be turned off.

Referring to FIG. 9, the steps taken by the subscriber unit 6 :n the sieep mode are illustrated. In step 220, the microprocessor 50 receives an instruction from a subscriber that causes the subscriber unit 6 to enter the sleep mode. In step 222, the microprocessor 50 sends an instruction to the controller 1 28 in the radio unit 1 2 that tells the radio unit 12 to enter the sleep mode. Then, in step 224, the processor 50 causes power to the subscriber terminal 14 to be turned off. In step 226, the controller 1 23 causes power to be turned off to selected components but allows power to supplied to other components. The controller 128 turns power off to all components not needed to receive communication signals from the base station 2. Therefore, in the radio unit 1 2 (FIG. 5), the receivers 1 14 and 1 16, the synthesizer 120, the frequency and gain control circuit 122, the modem 1 26 and the controller 1 28 remain powered during the sleep mode. Thus, the subscriber unit 6 can receive signals when in the sleep mode.

When signals are received or when a subscriber touches a key on the keypad 26, the subscriber unit 6 returns to normal operation and processes any received or transmitted communications.

Referring to FIG. 10, the steps taken to enter the dormant mode are illustrated . In step 300, the subscriber depresses keys on the keyboard 26 on the subscriber terminal 1 4 to instruct the subscriber unit 6 to enter a dormant m ode of operation. The microprocessor 50 reads the depressed keys, interprets the dormant mode instructions and notifies the controller 1 28 in the radio unit 1 2 that the subscriber unit 6 has been instructed to enter the dormant mode of operation.

Then, in step 302, in one embodiment of the present invention, the controller 1 28 causes a communication signal to be sent by the subscriber unit's transmitter 1 1 2 to the base station 2. The communication signal is preferably sent on the ACH, but may also be sent on the uplink TCH as well. It is received and processed by the appropriate sector unit 1 6 to 18 or 20. The sector unit 16 to 1 8 or 20 processes the signal by examining a control field in the communication signal to determine what type of communication was received. In this case, the control field indicates that the

communication signal is from a particular subscriber unit that is entering the dormant mode.

The sector unit 1 6 to 1 8 or 20, from the received communication signals, determines which subscriber unit is entering the dormant mode.

This information is transmitted to the database 32 and the administrative computer 28 under the control of the central controller 30. The information concerning the status of the subscriber unit 6 in the database 32 and the administrative computer 28 is updated to reflect the dormant status. Thus, the base station 2 knows which subscriber units 6 are in the dormant state.

In an alternate embodiment of the present invention, step 302 is skipped. Then, the base station 2 is not notified that the subscriber unit 6 is entering the dormant mode of operation. Thus, upon attempting a

communication with a dormant subscriber unit 6, the base station 2 will only know that the subscriber unit 6 is not receiving the communication.

In response to the dormancy message, the base station 2 can send a message to the subscriber unit 6 instructing the subscriber unit 6 to stay awake for a preselected or an instructed period of time. The base station 2 can issue this instruction if it wants to broadcast a message to many subscriber units 6 or for any other reason.

In step 304 , the subscriber unit 6 checks its controller 1 23 memory to determine how long the subscriber unit 6 should enter the dormant mode. In one embodiment, the length of time is set in the controller 123 memory so that every subscriber unit 6 enters the dormant mode for the same length of time. In an alternate embodiment, the subscriber can enter the length of time that the subscriber unit 6 should stay in the dormant mode through the keyboard 26 on the subscriber terminal 14. In this case, the microprocessor

50 reads this information (the length of time) from the keyboard and transmits it to the controller 1 28, where it is stored in memory.

In another embodiment, however, the length of time that a subscriber unit 6 stays in the dormant mode is programmable by a dispatcher at the dispatch station 4. To do this, the dispatcher accesses the computer 1 50.

One of the options the computer 1 50 offers as part of a fleet administration package is to allow the dispatcher to select the length of time the subscriber unit remains dormant once the subscriber places the unit in the dormant mode. When the dispatcher selects this option, the computer 1 50 prompts the dispatcher to enter the length of time. Once the dispatcher enters the length of time, the computer 1 50 stores this parameter in its memory.

When the dispatcher completes the entry, the dispatcher enters an instruction that causes the computer 1 50 to send this information to the base station 2. This information is preferably sent to the base static n with the other dispatcher controlled fleet administration information that

configures and controls the subscriber units 6. Examples of the information that can be controlled include groupings of subscriber units, PSTN

assignments to subscriber units, and subscriber unit telephony configurations and quick dial lists,

Referring to FIG. 6, when the dispatcher instructs the computer 1 50 to send the fleet administration information, including the dormancy time in accordance with the present invention, the computer 1 50 sends the information through a port 1 64 to a modem 152 in the dispatch station 4. The modem 1 52 preferably transmits the fleet administration information over a land line to the modem pool 41 in the base station 2. Alternatively, the computer 1 50 can route the fleet administration information through the radio unit 1 2 so that the transmission is over-the-air, via the TCH or the

ACH, to one of the sectors 1 6 to 1 8 in the base station 2.

Once the length of dormancy has been determined, in step 306, a power off timer is set. The timer determines the time that the subscriber unit 6 spends in the dormant mode and in waking up from the dormant mode. Then, in step 308, the power to the components in the subscriber terminal T4 and the radio unit 1 2 are turned off, except power is supplied to the microprocessor 50 in the subscriber terminal 14 and to the controller

1 28 in the radio unit 12. This allows the subscriber unit to "wake up" at a later time and then, in turn, to wake up other components needed to receive messages. It also allows the controller 128 to maintain the power off timer.

Referring now to FiG. 1 1 , during the dormancy time, the controller 1 28, in step 310, keeps checking to see whether the dormancy time has elapsed. During this time, the base station 2 can be attempting to transmit communication signals to the subscriber unit 6 while it is in the dormant state. If step 302 has been skipped, the base station 2 attempts to communicate with the dormant subscriber unit 6 and determines that the subscriber unit 6 is not responding. If step 302 is performed, the base station 2 will know that the subscriber unit 6 is in the dormant mode by checking its database.

When the base station 2 determines that the subscriber unit 6 to which the communication is directed is not available, either by attempting to communicate or by checking the database or both, the base station 2 buffers the message in the communication signal. FIGS. 1 2 and 1 3, illustrate the buffering of these messages. In FIG. 1 2, the database 32 maintains a table of subscriber unit identification numbers, an indication of whether there are buffered messages and the locations of those buffered messages. Whenever a message cannot be delivered by the base station 2 to the subscriber unit 6, the table of FIG. 1 2 is updated to indicate that the subscriber unit has a buffered message and the location of the message. In FIG. 13, the buffering of the message is indicated. For example, in FIG. 1 2, the database indicates that subscriber unit having identification number SU002 has a buffered message starting at memory location 0000. Referring to memory location 0000, in FIG. 1 3, the buffered message is found. In this case, the buffered message is the next days itinerary.

Referring now back to FIG. 1 1 , once the dormancy time has elapsed, the controller 128 checks the power off timer. The power off timer keeps track of how long the subscriber unit 6 has been in the dormant mode, including the times that the subscriber unit 6 wakes up and then returns to the dormant mode. If the power off timer is less than a predetermined amount, preferably fourteen ( 14) hours, in step 31 2, the microprocessor 50 and the controller 1 28 cause power to be turned on to the subscriber terminal 1 4 and to the radio unit 12, respectively. If the power off timer exceeds the predetermined amount, then the subscriber unit 6 does not wake up. Thus, the power off timer stops the subscriber unit 6 from

repeatedly waking up from the dormant mode, thereby preventing the draining of the battery of the vehicle in which the subscriber unit 6 is installed.

Once awake, in step 31 4, the controller 1 28 causes a communication signal to be transmitted to the base station 2 indicating that the subscriber unit 6 is no longer in the dormant mode. Then the base station 2 accesses its memory as illustrated in FIGS. 1 2 and 1 3 to determine whether there are buffered messages. If any are found, the base station 2, in step 31 6, transmits these messages to the subscriber unit 6.

Any message which has been directed to the dormant subscriber unit 6 can be buffered and then transmitted. The present invention, however, is particularly useful in transmitting the next day's work orders to a subscriber, to transmit new user databases and to download new software versions to subscriber units.

Once all of the buffered messages have been transmitted, the subscriber unit 6 returns to the dormant mode. The subscriber unit 6 is removed from the dormant mode by power being turned on or, in an alternative embodiment, by the selection of one of the keys on the keypad 24.

It is understood that changes may be made in the above description without departing from the scope of the invention. It is accordingly intended that all matter contained in the above description and in the drawings be interpreted as illustrative rather than limiting.

Claims

We claim:

1 . A method of providing communication services between a base station and a subscriber unit, comprising the steps of:

placing the subscriber unit in a dormant mode wherein the subscriber unit consumes limited power;

transmitting communication signals from the base station when the subscriber unit is in the dormant mode;

at the base station, determining that the subscriber unit is not responsive to the transmitted communication signals and storing the communication and the identity of the subscriber unit to which the communication was directed in a buffer at the base station;

after a predetermined time, taking the subscriber unit out of the dormant mode and causing the subscriber unit to communicate with the base station to inquire about communications messages; and

if there are buffered communications for the subscriber unit, transmitting the buffered communications from the base station to the subscriber unit.

2. The method of claim 1 , further comprising the step of:

from the dispatch station, transmitting a communication to the subscriber unit containing the length of the dormant mode.

3. The method of claim 2, further comprising the step of:

transmitting a communication containing the length of the dormant mode from the dispatch station to the base station and then to the subscriber unit.