KR20000016550A - Method and apparatus of preserving power of remote unit in dispatch system - Google Patents

Abstract

PURPOSE: A method and an apparatus for remote unit operation in a multiple access system and for power conservation in a remote unit are provided. CONSTITUTION: To reduce the power consumption of a remote unit in a dispatch system the remote unit enters a dormant state. A base station transmits a forward link broadcast signal and monitors a common access channel. A first remote unit continually receives and decodes the forward link broadcast signal and determines whether said forward link broadcast signal comprises active signals. If the remote unit determines that the forward link broadcast signal comprises no active signals for some a duration T1, the first remote unit enters a dormant mode. In the dormant mode the remote unit sporadically receives and decodes said forward link broadcast signal. If this remote unit or any other remote unit on the same net presses a push to talk button, it transmits a message on the common access channel. In response, every remote unit on the net which is in a dormant state exits the dormant state and continually monitors the forward link broadcast signal.

Description

Method and apparatus for conserving power of a remote unit in a dispatch system

In wireless telephony systems, many users connect and communicate with other wireless or wireline telephone systems through wireless channels. Communication over a wireless channel may be accomplished by one of several multiple access technologies. These multiple access techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA). CDMA technology has many advantages. Examples of CDMA are disclosed in K. Kilhausen et al., U.S. Patent No. 4,901,307, Spectrum Spread Multiple Access Communication System Using Satellite or Terrestrial Repeater, which is assigned to the assignee of the present invention and incorporated herein by reference.

In the foregoing patents, multiple access technologies are disclosed in which a large number of mobile telephone system users, each having a transceiver, communicate via satellite repeaters, air repeaters, or terrestrial base stations using CDMA spread spectrum communication signals. When using CDMA communication, the frequency spectrum can be reused many times to increase system user capacity.

In a CDMA cellular system, each base station provides a coverage area for a restricted area and connects the remote unit to a public switched telephone network through a cellular system switch within that coverage area. When the remote unit moves to the coverage area of the new base station, routing of the remote unit call is transferred to the new base station. The base station to remote unit signal transmission path is called the forward link, and the remote unit to base station signal transmission is called the reverse link.

In an example of a CDMA system, each base station transmits a pilot signal having a common pseudo noise (PN) spreading code that is an offset of the code phase from the pilot signal of the other base station. During system operation, the remote unit is provided with a list of code phase offsets corresponding to neighboring base stations surrounding the established base station. The remote unit is arranged with a search element, which tracks the signal strength of the pilot signal from the base station group including the neighbor base station by the search element.

A method and system for communicating with a remote unit via one or more base stations during the handoff process is disclosed in US Pat. No. 5,267,261, "Mobility Assisted Soft Handoff in CDMA Cellular Communication Systems," issued Nov. 30, 1993. This was assigned to the assignee of the present invention. Using this system, communication between the remote unit and the end user is not interrupted by handoff from the original base station to the next base station. This kind of handoff is considered a "soft handoff" in which communication with the next base station is established before communication with the original base station ends. When the remote unit is communicating with two base stations, the remote unit combines the signals received from each base station in the same way that the multipath signals from the common base station are combined.

In a typical microcellular system, a system controller is used to generate a single signal for the end user from the signals received at each base station. Within each base station, the signals received from the common remote unit are combined before they are decoded to get all the advantages of the multiple signals received. The decoded result from each base station is provided to the system controller. When a signal is decoded, it cannot be combined with other signals. Thus, the system controller must select from a plurality of decoded signals formed by each base station where communication is established by a single remote unit. The most preferred decoded signal is selected from the signal set from the base station and the unselected signal is simply ignored.

Remote unit support soft handoff operates based on the pilot signal strength of several base station sets measured by the remote unit. The active set is a base station set in which active communication is established. The candidate set is a set of base stations selected from a contiguous set or the remaining set with a pilot signal strength of a signal level sufficient to establish communication. The contiguous set is a base station set around an active base station that includes a high likelihood base station with a level of signal strength sufficient to establish communication. The remaining set includes all base stations in the system that are not active sets, candidate sets or adjacent sets.

When communication is initially established, the remote unit communicates through the first base station and the active set includes only the first base station. The remote unit monitors the pilot signal strength of the base station of the active set, the candidate set, the neighbor set, and the rest of the set. If the pilot signal of the neighboring set or the remaining set of base stations exceeds a predetermined threshold level, the base station is added to the candidate set. The remote unit communicates a message identifying the new base station to the first base station. The system controller decides whether to establish communication between the new base station and the remote unit. If determined by the system controller, the system controller identifies the information about the remote unit, sends a message to the new base station, and also sends a command to establish communication with the new base station. The message is also sent to the remote unit via the first base station. The message identifies a new active set that includes the first base station and a new base station. The remote unit retrieves the transmitted information of the new base station and establishes communication with the new base station without interrupting communication with the first base station.

As the remote unit communicates through multiple base stations, the remote unit continuously monitors the base station signal strengths of the active set, the candidate set, the neighbor set, and the rest of the set. If the signal strength corresponding to the base station of the active set falls below a predetermined threshold for a predetermined period of time, the remote unit generates and sends a message reporting an event. The system controller receives the message via at least one of the base stations with which the remote unit communicates. The system controller may determine to terminate communication via the base station with weak pilot signal strength.

The system controller determines to terminate communication through the base station and generates a mesh that identifies a new active set of base stations. The new active set does not include the base station from which communication was terminated. The established base station sends a message to the remote unit. The system controller also communicates information to the base station to terminate communication with the remote unit. Thus, remote unit communication is only through the base station identified in the new active set.

Since the remote unit communicates with the end user through at least one base station at a time through a soft handoff process, no interruption occurs in communication between the remote unit and the end user. Soft handoff offers significant advantages because it utilizes a "make before break" technique that is inherently superior to the conventional "break before make" used in other cellular communication systems.

In wireless telephone systems, it is extremely important to maximize the capacity of the system in terms of the number of instantaneous phone calls that can be handled. If the transmit power of each remote unit is controlled such that each transmitted signal reaches the base station receiver at the same level, the system capacity in the spread spectrum system can be maximized. In an active system, each remote unit can transmit a minimum signal level that generates a signal to noise ratio that allows for acceptable data recovery. If the signal sent by the remote unit reaches the base station receiver at a power level that is too low, the bit-error rate is too high to allow good communication due to interference from other remote units. On the other hand, when the remote unit transmission signal is received at the base station, it is too high power level, and communication with a specific remote unit is possible, but such a high power signal interferes with other remote units. Such interference can adversely affect communication with other remote units.

Thus, in order to maximize capacity in the example of a CDMA spread spectrum system, the transmit power of each remote unit within the coverage area of the base station is controlled by the base station to generate the same normal received signal power at the base station. In an ideal case, the total signal power received at the base station is received by the base station from the remote unit within the coverage area of the neighboring base station times the number of remote units transmitted within the service range of the base station times the normal power received from each remote unit. Same as the added power.

Path loss within a radio channel is two separate phenomena; Ie characterized by average path loss and fading. The forward link from the base station to the remote unit operates at a different frequency than the reverse link from the remote unit to the base station. However, since the forward link and reverse link frequencies are within the same general frequency band, there is a significant correlation between the average path loss of the two links. Fading, on the other hand, is a phenomenon independent of the forward and reverse links and varies as a function of time.

In the example of a CDMA system, each remote unit estimates the path loss of the forward link based on the total power at the input to the remote unit. The total power is the sum of the powers from all base stations operating at the same assigned frequency as recognized by the remote unit. From the estimate of the average path loss of the forward link, the remote unit sets the transmission level of the reverse link signal. If the reverse link channel for one remote unit suddenly improves compared to the forward link for the same remote unit due to the independent fading of the two channels, the signal received from the remote unit to the base station increases in power. This increase in power causes additional interference to all signals sharing the same assigned frequency. Thus, the quick response of the remote unit transmit power to the sudden improvement in the channel improves the system performance. It is therefore desirable for the base station to continuously control the power control mechanism of the remote unit.

Remote unit transmit power may also be controlled by one or more base stations. Each base station with which the remote unit is communicating measures the signal strength received from the remote unit. The measured signal strength is compared with the appropriate signal strength level for the particular remote unit. Power adjustment commands are generated by each base station and sent to the remote unit via the forward link. In response to the base station power adjustment command, the remote unit increases or decreases the remote unit transmit power by a predetermined amount. In this way, a quick response to changes in the channel is possible and the average system performance is improved. In a typical cellular system, the base stations are not directly connected and each base station in the system does not know the power level at which other base stations receive signals of remote units.

When the remote unit communicates with one or more base stations, power adjustment commands are provided from each base station. The remote unit operates upon receiving these multiple base station power adjustment commands to avoid transmission power levels that interfere with other remote unit communications and provide sufficient power to support communication of the remote unit and at least one base station. The power control mechanism is achieved by causing the remote unit to increase its transmit power level only when all base stations communicating with the remote unit require an increase in power level. The remote unit reduces the transmission signal level if the base station communicating with the remote unit requires a power reduction. A system for base station and remote unit power control is disclosed in U.S. Patent No. 5,056,109, entitled "Method and Apparatus for Correlating Transmit Power in a CDMA Cellular Mobile Phone System," issued Oct. 8, 1991, which is a subject matter of the present invention. It was transferred to the assignee.

It is also necessary to control the perennial power used for each data signal transmitted by the base station in response to the control information sent by each remote unit. The primary reason for providing such control is to remedy that the forward channel link may be significantly damaged at a given location. If the power transmitted to the damaged remote unit is not increased, the signal quality becomes unacceptable. An example of such a location is that the path loss for one or two neighboring base stations is approximately equal to the path loss for the base station communicating with the remote unit. At such a location, the total interference is increased three times than the interference by the remote unit at a point relatively close to the base station. Also, as in the case of interference from an active base station, interference from adjacent base stations does not fade in line with signals from the active base station. The remote unit in such a location may require 3 to 4 dB of additional signal power from the active base station to obtain adequate performance.

At other times, the remote unit may be located where the signal-to-interference ratio suddenly improves. In such a case, the base station can transmit the appropriate signal using a transmitter power lower than the normal transmitter power, thereby reducing interference to other signals transmitted by the system.

In order to achieve the above object, a signal-to-interference measurement function can be provided in the remote unit receiver. This measurement is made by comparing the appropriate signal power to the total interference and noise power. If the measured ratio is less than the predetermined value, the remote unit requires additional power from the base station via the forward link signal. If the measurement ratio exceeds a predetermined value, the remote unit requires a power reduction. One way to allow the remote unit receiver to monitor the signal to interference ratio is to monitor the frame error ratio (FER) of the final signal. Another method is to measure the erased number.

The base station is requested to adjust power from each remote unit and responds by adjusting the power allocated to the corresponding forward link signal by a predetermined amount. The adjustment is generally small amounts of about 0.5 to 1.0 dB or about 12%. The power change rate may be slightly slower than that used for the reverse link approximately once per second. In this form, the power reduction requirement would normally be accepted at a 12% change.

When cellular telephone licenses were originally permitted by the government, one of the limitations in spectrum use is that carriers cannot provide dispatching system services. However, because of the enormous advantages of CDMA systems and the inherent high costs and problems of developing and maintaining private dispatch systems, the government is rechecking these permits.

While traditional wireless and landline telephone services provide point-to-point services, dispatching services provide one-to-many services. Common uses of dispatch services are local police radio systems, taxi dispatch systems, information and secret services federal offices, and general military communications systems.

The basic model of the dispatch system consists of user broadcast nets. Each broadcast net user monitors a common broadcast forward link signal. If the net user wants to talk, he presses a push to talk (PTT) button. In general, the user voice being talked is routed from the reverse link via the broadcast forward link. Ideally the dispatch system would allow landline and wireless access to the system.

The power control mechanism for remote units operating as point-to-point units described above is not directly available to dispatch systems. In a dispatch system, many remote units listen to some forward link signal. In a dispatch system, most remote units are passive (ie listening) at any one time. In addition, a long time period may be passed in which the forward link broadcast channel does not transmit any voice information. The present invention has the advantage of significantly reducing the power consumption of the remote unit.

FIELD OF THE INVENTION The present invention relates to remote unit operation in multiple access systems, and more particularly to power conservation in remote units.

1 illustrates a typical dispatch system.

2 is a flow diagram illustrating forward link broadcast channel power control in accordance with the present invention.

3 is a state diagram illustrating a stimulus in which a transition can occur between a remote unit state and a remote unit.

4 is a state diagram illustrating a stimulus in which a transition can occur between a remote unit state and a remote unit, where the idle state is controlled by the base station.

In a push torque system, the ability of the remote unit to remain active in the field without replacing the battery is of great importance. It is also important, however, that the latency between the pressing of the pushed torque in one remote unit and the reception of the corresponding audio signal in the other remote unit is maintained to an acceptable limit. Thus, the remote unit travels a number of areas during operation. When a period of time in which no voice information is transmitted over the forward link broadcast channel passes, the remote unit enters a dormant state. In the dormant state, the remote unit reduces power consumption by limiting the time to monitor the forward link broadcast channel. The idle state can have multiple substates with different slot cycles for each different power consumption level and pressed torque latency. When the remote unit on the net presses the push torque button, the whole system is reactivated. Power control is continuously activated in idle mode to start normal operation when the system is powered up again.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

1 illustrates a typical dispatch system. In the preferred embodiment, the remote units 10, 20, 22, 24 can function as dispatch units and point-to-point telephones. In FIG. 1, the remote unit 10 is generally an active talker and the remote units 20, 22, 24 are generally passive listeners. Base stations 30, 32, and 34 provide forward link broadcast channels to remote units 20, 22, and 24. Base station 30 provides a dedicated traffic channel to remote unit 10. The dedicated traffic channel is similar to the forward link broadcast channel except that the remote unit 10 cannot receive its own voice signal. Base station 30 receives a reverse link signal from active remote unit 10. Mobile switching center (MSC) 38 coordinates signaling from and to the base station. The communication manager 40 controls the net as the priority of the request when two of the remote units simultaneously push-to-talk (PTT). In a preferred embodiment, broadcast interface signaling and modulation is simply in accordance with the code division multiple access (CDMA) described in the "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systems" referred to simply as IS-95.

It is known that the base station is divided into three sectors. The term base station will be referred to as a single sector of an entire base station or a multisector base station.

In FIG. 1, the active remote unit 10 has a bidirectional link with a base station. To be active, the remote unit 10 sends an access channel message requesting a traffic channel to the base station 30. The access message is sent over the access channel. An access channel is a reverse link channel used by a remote unit that communicates to a base station. Access channels are used for short signaling message exchanges such as call initiation, response to a page, and registration. The access attempt is sent by the remote unit in a series of access probes. Each access probe transmits the same information but at a higher power level than the previous level. The access probe continues until a base station response is received at the remote unit.

The access channel is a shared slot random access channel. Only one remote unit can successfully use the access channel in one hour. In addition, since each successful access probe is transmitted at an increased power level compared to the previous level and the power of the access channel is not controlled, the access channel acts as an interference to other reverse link signals. For this reason it is advantageous to keep the number of access attempts to a minimum.

When the remote unit 10 establishes a communication link, the remote unit 10 receives signaling of a forward broadcast channel over a typical forward link traffic channel. In the meantime, the remote unit 10 does not monitor the forward broadcast channel and receives all dispatch system information over its own dedicated forward link traffic channel. The remote unit 10 communicates back to the base station 30 via a dedicated reverse channel. In a preferred embodiment, power control of the forward and reverse links is performed as described above in accordance with IS-95. Since the remote unit 10 has its own dedicated forward link signaling path, remote unit specific messaging can be included in the signaling. For example, if the remote unit 10 can operate as a dispatch system remote unit and point-to-point telephone, the remote unit 10 may forward the input point-to-point call to the remote unit 10. Link traffic can be known through the channel.

On the other hand, in FIG. 1, the passive remote units 20, 22, 24 do not have reverse link signals established at some of the base stations. If the remote units 20, 22, 24 are fully passive units, then each base station does not know whether the remote units are in their corresponding effective area. Although the remote unit is registered with the base station when the remote unit enters the base area, the base station never knows when the remote unit leaves the base area.

Although the remote units 20, 22, 24 may be passive units, the remote unit may continue to use the access channel to communicate with the base station. In the preferred embodiment, the passive remote units 20, 22, 24 use an access channel to send signals to the base station if they need high power from the forward link broadcast channel. Several signal level or quality indications may be included in the power request access message. For example, there may be a field indicating the strength at which the remote unit recognizes the pilot signal from the base station. In addition, there may be a field indicating the strength or quality at which the remote unit recognizes the forward link broadcast channel. There may be a field indicating the signal strength or quality of the pilot channel and the forward link broadcast channel. There may be a field indicating the ratio of pilot signal strength to forward link broadcast channel strength or the difference between these strengths.

A standard cellular system includes a number of base stations, each of which provides communication to a remote unit located within a limited effective area. Many base stations provide an effective area for the entire service area. When the dispatch system is leased by the leasing party, the leasing party may wish to provide coverage across the entire service area. However, if the forward link broadcast signal is transmitted from all base stations in the system all the time. An efficient and economical way of providing large capacity to the system is to provide the forward link broadcast channel at the minimum level necessary to transmit the forward link broadcast channel only in a base station where the remote unit is deployed and to provide reliable communication.

If a forward link broadcast channel is not transmitted, the corresponding resource may be available to other point-to-point or broadcast users. Moreover, other users in the effective area of the base station not transmitting the forward link broadcast channel are not affected by the interference. The pilot signal is transmitted continuously from each base station whether or not a forward link broadcast channel is transmitted.

The handoff of communication between base stations is in a different broadcast mode than when the remote unit is operating as a point-to-point unit. As described in detail above, when the remote unit operates as a point-to-point unit, the handoff is controlled in conjunction with the measurement of the set of pilot signal strengths performed by the remote unit. An active set is a set of base stations for which active communication is established. The candidate set is a set of base stations selected from an adjacent set or the remaining set with pilot signal strengths of sufficient signal level to establish communication. The contiguous set is a set of base stations surrounding an active base station that includes a base station with a high probability of having a signal level of sufficient level to establish communication. The remaining set includes all base stations in the system that are not part of an active, candidate or adjacent set.

When the remote unit operates point-to-point, the base station of the adjacent set is preferred for the remaining set where the pilot signal corresponding to the base station of the adjacent set is searched at a higher frequency than the pilot signal corresponding to the remaining set. For example, in the preferred embodiment, the first entire contiguous set is searched and then a portion of the remaining set is searched. Second, the entire contiguous set is searched again and the next consecutive part of the rest of the set is searched. The operation continues circularly.

When the remote unit has an active point-to-point communication link established, the system controller located in the mobile switching center sends to each mobile unit a list of base stations containing adjacent sets. The adjacent set depends on the location of the remote unit. For this reason, the neighboring set includes another set of base stations in the remote unit. The system controller may send a separate list of base stations for the adjacent set to the corresponding remote unit over the established forward link traffic channel.

However, in the broadcast mode, the forward link broadcast channel is the same for all remote units, so transmission of adjacent set information to each remote unit is not accurate in the broadcast mode. In addition, since the reverse link is not established to the remote unit in broadcast mode, the system controller does not know the location of the remote unit to determine the adjacent set. In a preferred embodiment of the broadcast mode, an adjacent set of each remote unit operating in the broadcast mode is empty. Because of this, the remote unit operating in broadcast mode is continuously searched directly from the remaining set as it monitors the forward link broadcast channel. If the pilot signal strength for a portion of the active set falls below the threshold, i.e., T_DROP for a sufficient time, the corresponding entry in the active set is deleted and the corresponding entry is added to the remaining set. The remote unit no longer monitors the forward link broadcast channel from the corresponding base station. Because of this, no candidate set is used.

When the pilot signal of a base station that is part of the remaining set exceeds an arbitrary threshold, T_ADD, the remote unit may add an entry corresponding to the active set. The remote unit demodulates the forward link broadcast channel from the base station. The remote unit starts to perform diversity combining the signal from the other base station it is receiving with the signal from the newly added base station. If the remote unit cannot demodulate the forward link broadcast channel, the remote unit sends a power request access message to the base station.

When the base station receives the power request access message and the forward link broadcast channel is not established, the remote unit informs the system controller controlling the base station to transmit the forward link broadcast channel at the initially set level. The base station begins to execute power control in accordance with FIG. 2 starting from the start block 50. Block 52 of Figure 2 is executed at predetermined intervals. The interval at which block 50 is executed sets the power control operating speed. In block 52, the base station determines whether a power request access message is received. If not, block 54 is executed that reduces the current transmit power by a predetermined amount δ and if so does not reduce the transmit power by less than a predetermined minimum value MIN. Flow continues to block 56. In block 56, if the base station transmit power is minimum for more than a predetermined time interval T, the transmission of the forward link broadcast channel ends as indicated in block 58 and the execution of FIG. 2 is indicated in block 60. It ends as one. Because of this, if all passive remote units leave the effective area of the base station, the base station eliminates transmission of the forward link broadcast channel by reducing the transmission level to the minimum and transmitting at the minimum level for a predetermined period T. Referring back to block 56, if the transmission level is not equal to the minimum value for a predetermined period T or more, the flow continues to block 52 again.

Execution continues from block 52 to block 66 if a power request access message is received. If the transmit power is increased (eg within the last X frame), the flow continues back to block 52 and the request is ignored. Because of this, if two remote units require power increase from each other, the power is increased only once. If one remote unit does not yet require high power, the unit can send another request. Thus, the system excessively inappropriately increases the forward link broadcast channel power until another system user is compromised.

If the transmit power level has not been increased in the last X frame, the base station determines the amount Δ that increases power based on the strength with which the remote unit receives the base station pilot signal (block 68). If the remote unit is near the edge of the effective area, the remote unit sends a power request access message to the base station to increase power. If the remote unit moves out of the service area, the base station no longer needs to provide a signal to the remote unit. The amount Δ is selected between Δ ₁ and Δ ₂ based on the signal strength message sent by the remote unit. For example, if the remote unit requires an increase in power and the difference in power level between the pilot signal and the forward link broadcast channel measured by the remote unit is small, then the magnitude of Δ is smaller than the difference in power level is high. In block 70, the transmit power is increased by an amount Δ or up to a maximum transmit value MAX that yields a lower transmit power level. For this reason, the maximum transmission power of the base station is limited. From block 70, the flow continues back to block 52. The case where the value of Δ is fixed is within the scope of the present invention.

The system parameters, T, MIN and MAX, can be set by the leasing party according to their needs and payability. For example, if the central intelligence agency CIA implements high secrecy and dangerous transmission, the CIA may perform passive remote unit operations in which no power request access messages are sent. In this case, the parameters MIN and MAX are set equal to the maximum power and T is set to infinity. Because of this, all base stations in the system continue to be transmitted at full power and remote units in the effective area do not need to send a power request access message.

The manner in which the remote unit determines that higher power is required is similar to that used for remote units operating in accordance with IS-95. For example, the remote unit can compare the frame erase rate to a threshold. The remote unit can count the number of erases in the sliding window of the frame. The remote unit can count consecutive erases. Any other link quality measurement, such as signal to noise ratio, can be used to determine if the remote unit requires high power. If the strength of the corresponding pilot signal is less than or equal to T_DROP, the remote unit does not send a power request access message.

While protection of base station resources is important, protection of remote unit power is also very important. When the remote unit is in the field, the remote unit is typically powered by a battery. One way to protect battery power is to limit the amount of time the remote unit monitors the forward link broadcast channel. For example, FIG. 3 is a state diagram illustrating a remote unit state and a diagram in which a transition occurs.

When the net is initially set up, the possible units are to dial the net number. Each remote unit participating in the net calls the same number. Dialing of numbers may not be manual. Dialing of numbers can be done automatically by simply powering the unit. It can also be dialed by pressing a limited number of key strokes. In FIG. 3, block 100 shows the status of the remote unit before the number of the net is dialed. The service is an activated 116 indication that the remote unit sends the dialed number and the remote unit is in its initial state 102. In the initial state 102, the remote unit is registered and executes another initial procedure according to section 6.6.5.5.2 of IS-95.

From the initial state 102, the remote unit goes to the initial idle state 104 if the net is still not set up via broadcast deactivation 118. The remote unit maintains the initial idle state 104 until the net is established. When the remote unit notifies that the net has been established, the remote unit enters a listening state 106 via the remote unit page 122. The remote unit may go directly from the initial state 102 to the listening state 106 via broadcast activation 120 when the net is established.

In listening state 106, the remote unit continuously monitors the forward link broadcast channel. If the remote unit in the net has not pressed the PTT button for a period of more than T ₁ , the remote unit is put to idle 108 via timeout 124. In the preferred embodiment, the idle state 108 consists of a number of states. For example, the idle state 108 consists of two slot mode states D ₁ 134 and D ₂ 136. From the initial timeout 124, the remote unit goes to D ₁ 134 where the remote unit no longer continuously monitors the forward link broadcast channel. Instead, the remote unit monitors the forward link broadcast channel only for some time. Using periodic slot cycles, the remote unit monitors the forward link broadcast channel for a short time of T _D1 seconds. When the remote unit does not monitor the forward link broadcast channel, the remote unit supplies power underneath a portion of the circuit that reduces power consumption. Typical slot cycles for state D ₁ 134 are 2-3 seconds. Since the remote unit monitors only the forward link broadcast channel every 2 to 3 seconds, in the effective area there is a potential of 1 to 1.5 seconds between the time used to transmit the signal over the forward link broadcast channel when the remote unit knows to receive the signal. Delay is present.

If a broadcast alert is received by the remote unit during the time that the remote unit is in D ₁ 134, the remote unit goes back to the listening state 106 via the broadcast alert 126. A broadcast alert is generated when any number on the net presses the PTT button. The remote unit goes to D ₂ via timeout 138 if a broadcast alert is not received after any time T ₂ during the time the remote unit is at D ₁ 134. At D ₂ 136, the remote unit monitors the forward link broadcast channel for some short time. For example, using periodic slot cycles, the remote unit monitors the forward link broadcast channel for a brief period of T _D2 seconds. Typical slot cycles for state D ₁ 134 are 5-10 seconds, resulting in more remote unit power at a much larger potential average time. In a preferred embodiment, T ₁ , T _D1 , T ₂ and T _D2 can be programmed so that each net user saves potential time individually and dynamically.

In the preferred embodiment, each remote unit determines the slot cycle index, for example, by using the remote unit identification number and hash function. The remote unit uses the slot cycle index to select during the timeslot it will monitor the forward link broadcast channel. Because of this, different remote units monitor the forward link broadcast channel at different times. Similarly, the base station must repeat the broadcast path for a sufficient time until all remote units monitor the forward link broadcast channel in idle mode.

In idle state 108, the remote unit still performs power control as described above. For example, if the remote unit is a remote unit determines the level at which the received forward-link broadcast channel to monitor the forward link broadcast channel during a slot in D ₂ (136), the remote unit is beyond the D ₂ (136) state You can use the power request access message to request higher power without. Further, although the preferred embodiment is described in two different states within the idle state 108, fewer or more different states can be applied to the present invention.

If the user of the remote unit presses the PTT button while in the dormant state 108, the remote unit enters the PTT access state 110 via the pressed PTT 128. In PTT access state 110, the remote unit begins to allow gain to become an active talking remote unit using the access channel. When this remote unit enters the PTT access state 110 and begins to access the system, other remote units in the same net receive a broadcast alert message. If the user releases the PTT button before the PTT is rejected or a traffic channel can be allocated, the remote unit is put into listening state 106 via the rejected PTT / released PTT 132. From the listening state 106, the remote unit can be placed directly into the PTT access state 110 via the pressed PTT 130 by pressing the PTT button.

Note what happens if the remote unit user quickly presses and releases the PTT button while at rest 108. The user is placed in the listening state 106 by himself, and the broadcast alert generated because the user releases it by pressing the PTT button causes all remote units on the communication network to transition to the listening state. In this way, the entire idle system is activated by the operation of a single remote unit. Operators who are accustomed to using the system can use this method to run the system. For example, if a series of network users are monitored for several days, the system may be idle because there is no reason for the net user to communicate when no activity occurs. As soon as an operator sees a signal that the suspect is approaching the car, the operator simply presses the PTT button to release and the entire network is taken out of idle state. When a network user continues to press the PTT button to send a message, the network responds immediately.

Returning to the PTT access state 110 again, if the user continues to press the PTT button to approve the PTT request, the remote unit enters the talk state 112 via the PTT approved state 140. Note that if some of the remote units are in D ₂ 136, they may not be able to immediately begin receiving signals. The remote unit operator will be accustomed to pressing and releasing the PTT button or waiting for a few seconds after pressing the PTT button before speaking threshold information. Another way to handle this situation is to delay the initial transmission of voice information at the facility. The remote unit remains in torque state 112 until the user releases the PTT button or until the user's transmission is occupied by another network user, in which case the remote unit passes through the PTT release / PTT occupancy 142. The listening state 106 is entered again.

Another embodiment of FIG. 3 is shown in FIG. 4. In FIG. 4, timeout 124, timeout 138, D ₁ 134, D ₂ 136 and the idle state 108 of FIG. 3 have been replaced. In FIG. 4, the remote unit exits to the listening state 106 for the dormant state 148 when a command to enter the dormant mode is received by the remote unit via the dormant command from the base station 144. The idle command from the base station includes the slot time duration that the remote unit uses to determine how to monitor the forward link broadcast channel. In this way, all remote units can be commanded to be idle at the same time. If the system wants to change the idle mode, the base station sends the next idle command with a larger or smaller slot time duration. The remote unit in idle state 148 responds by changing the interval for monitoring the forward link broadcast channel while remaining in idle state 148 via the idle command from base station 146. Typically the base station starts a first timer when a PTT release indication is received from the last remaining talker. If the first timer expires before the next PTT indication is received, the base station may command the idle mode in a very short slot cycle. After the second timer expires before the PTT indication is received, the base station may command the idle mode in a long slot cycle. If a case occurs that the system believes that the PTT indication is coming soon, the slot cycle duration will be reduced. Examples of such cases are the landing of large computer planes for land movement or daybreaks for army applications.

The foregoing description of the preferred embodiment is provided to enable any person skilled in the art to practice the invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of progressive functionality. Therefore, the present invention is not limited to the embodiments shown herein but provides a wide range consistent with the principles and novel features disclosed herein.

Claims (20)

A method for reducing power consumption of a remote unit in a dispatch system, the method comprising: Transmitting a forward link broadcast signal from a base station; Continuously receiving and decoding the forward link broadcast signal at a first remote unit, and determining whether the forward link broadcast signal includes an operation signal; By the remote unit if the remote unit determines that the forward link broadcast signal does not contain any operation signal for the duration T ₁ of receiving and decoding the forward link broadcast signal sporadically at the _first remote unit. Entering a first dormant state; And Reducing power consumption of the remote unit in the first idle state. A method for conserving power of a remote unit in a dispatch system, the method comprising: Entering a listening state by a first remote unit, wherein the first remote unit continuously monitors the forward link broadcast channel and sends a request for increased broadcast power if necessary; And When the operating level on the forward link broadcast channel falls below a predetermined operating level, entering the first idle state by the first remote unit, wherein the first remote unit is in an appropriate time period. Monitoring the forward link broadcast channel only during a first predetermined set of time slots set at intervals and transmitting a request for increased broadcast power if necessary. The method of claim 2, Exiting the first idle state and entering a second idle state, wherein the first remote unit monitors the forward link broadcast channel only during a second predetermined set of time slots set at larger time intervals; If necessary, transmitting a request for increased broadcast power. The method of claim 2, Exiting the first idle state and reentering the listening state when a broadcast alert is transmitted on the forward link broadcast channel. The method of claim 4, wherein And a base station generates said broadcast alert in response to receiving a push-to-talk access message from a second remote unit. The method of claim 2, Exiting the first dormant state and entering an access state in response to a push-to-talk instruction generated by the first remote unit. The method of claim 6, And reentering the listening state from the access state in response to the release of the push-to-talk indication. The method of claim 6, Sending a broadcast alert on the forward link broadcast channel in response to the push-to-talk indication to cause the second remote unit to exit the second unit dormant state and enter a second unit listening state; Characterized in that the method. The method of claim 2, And the first remote unit spontaneously enters the first idle state. The method of claim 2, And wherein the first remote unit enters the first dormant state in response to a command on the forward link broadcast channel. The method of claim 3, And wherein the first remote unit enters the second dormant state in response to a command on the forward link broadcast channel. The method of claim 2, Initiating a communication by dialing a network number and transmitting a signal to a base station. The method of claim 12, Entering an idle state if a broadcast communication network is not formed, wherein entering the listening state is performed in response to a page from the base station indicating that the broadcast communication network is formed. . The method of claim 12, And the forward link broadcast channel uses code division multiple access signaling. 3. The method of claim 2, wherein the first remote unit is used as a push-to-talk dispatch unit and a point-to-point telephone. The method of claim 12, The base station functions as a point-to-point base station and a dispatch base station. A system for conserving power of a remote unit in a dispatch system, And a plurality of remote units, each configured to receive a forward link broadcast channel continuously in a listening state and to monitor link operation on the forward link broadcast channel, wherein the remote unit is further configured when the link operation falls below a predetermined threshold. 1 go into a dormant state; And A base station configured to generate a broadcast alert on the forward link broadcast channel in response to a push-to-talk indication received from one of the plurality of remote units on an access channel, the broadcast alert being the first dormant. Instruct the plurality of remote units to exit a state. An apparatus for controlling a remote unit operating in a dispatch system, the apparatus comprising: Means for continuously receiving a forward link broadcast channel; Means for determining a level of the forward link broadcast channel; And Means for receiving the forward link broadcast channel during a first predetermined set of time slots set at appropriate time intervals when the level of operation on the forward link broadcast channel falls below a predetermined level of operation. The method of claim 18, Means for reducing the amount of power consumed by the remote unit when the remote unit receives the forward link broadcast channel during the predetermined set of time slots. The method of claim 19, Receiving the forward link broadcast channel during a second predetermined set of time slots set to a larger time interval than the first predetermined set of time slots only when the operating level on the forward link broadcast channel drops below a predetermined operating level. The apparatus further comprises means for.