Abstract:
A method and system for controlling the level of subscriber unit transmission power in a two-way paging network. The ability to adjust the transmission power of individual subscriber units saves critical subscriber unit resources while still ensuring that a subscriber unit&#39;s transmissions are received at a base station in a paging network system. Transmission power-level control further facilitates eliminating interference among subscriber units that transmit to the same base station.

Description:
STATEMENT OF RELATED APPLICATIONS 
     The present application relates to the subject matter of five coassigned applications: VERSATILE ANTENNA ARRAY FOR MULTIPLE PENCIL BEAMS AND EFFICIENT BEAM COMBINATION, application Ser. No. 08/808,347; MULTI-CHANNEL MULTI-BEAM ENCODING SYSTEM, filed on May 22, 1997; METHOD AND APPARATUS FOR ADAPTING OMNIDIRECTIONAL SYNCHRONOUS WIRELESS COMMUNICATIONS PROTOCOL TO SECTORIAL ENVIRONMENTS, filed on May 22, 1997; IMPROVED TWO-WAY PAGING UPLINK INFRASTRUCTURE, filed on Aug. 19, 1997; and CONFLICT RESOLUTION IN A MULTI-BEAM MULTI-SITE PAGING SYSTEM, filed on Nov. 17, 1997. The contents of these co-assigned applications are herein incorporated by reference for all purposes. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to two-way paging networks and more particularly to subscriber unit transmission power control in two-way paging networks. 
     Two-way paging systems that allow individual subscriber units (SUs), or pagers, to both receive paging information and transmit responses are becoming more prevalent. An SU may either be mobile, such as with portable pagers, or stationary, such as an SU in a vending machine for status reporting. It will be recognized that the invention has a wide range of applicability; it can also be applied to any type of individual wireless receiver/transmitter used in a two-way pager network. In prior art two-way pager networks, the transmission power used by individual SUs to transmit responses is not controlled. An SU transmits information using a constant power level, regardless of either the physical distance to a base station within the paging network, or the clarity of the inbound signal received at the base station. 
     Several problems arise in this situation, which can be explained with reference to FIG.  1 . FIG. 1 depicts a two-way paging network  100 . This network is not represented to be prior art, but relates to paging infrastructure as disclosed in co-assigned applications listed above, which are herein incorporated by reference. Network  100  includes a regional controller  101 , a plurality of base stations  105 , and a plurality of subscriber units (SUs)  110 . 
     Base station  105  utilizes a multi-beam concept by sending signals to the SUs  110  on outbound beams  115 , and receiving signals from SUs  110  on inbound beams  120 . Preferably, inbound beams  120  and outbound beams  115  are coincident, but in practice they may be skewed from each other as displayed in FIG.  1 . Base station  105  may also utilize an omni-directional antenna, which is also disclosed in the co-assigned applications listed above, and herein incorporated by reference. 
     On occasion, different SUs will send data at the same frequency at the same time. This gives rise to a possibility that SU transmissions will interfere with one another. Compounding the interference problem is an inability of current two-way pager networks to control or vary the level of SU transmission power. 
     Other problems arise where SU transmission power levels are uncontrolled. First, when the range, or distance, from the SU to the base station is short, a SU may expend excessive energy in transmitting responses. This negatively effects the efficiency and lifetime of the SU&#39;s power source. Second, an SU that transmits at excessive power levels at any distance from the base station may interfere with the transmission of another SU that transmits on the same frequency at the same time. Because of its distance from the base station or due to other transmission propagation conditions, the transmissions from the other SUs may hardly be received at a base station or possibly cancelled out by an SU transmitting at an excessive power level. 
     What is needed is a two-way paging system that supports the capability of controlling transmission power level of individual subscriber units. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and system for controlling subscriber unit transmission power levels in a two-way paging network. The ability to adjust the power level of individual SUs saves critical power resources yet ensures that the SU&#39;s transmissions are received at a base station in a paging network. Power control in a two-way paging network further lessens the possibility of interference among multiple SUs transmitting at the same time. 
     In accordance with a first aspect of the present invention, a method is provided for receiving at a subscriber unit a communication containing a power control command. In response to the power control command, the subscriber unit adjusts its transmission power. 
     In accordance with a second aspect of the present invention, a method is provided for controlling subscriber unit transmission power in subscriber unit-initiated communication sessions using ReFLEX protocol standards developed by Motorola Inc. of Schaumburg, Ill. 
     In accordance with a third aspect of the present invention, a method is provided for controlling subscriber unit transmission power levels in base station-initiated communication sessions using the ReFLEX protocol standard. 
     In accordance with a fourth aspect of the present invention, a two-way paging network is provided for allowing a SU&#39;s transmission power to be controlled. The paging network. includes: a plurality of subscriber units having a receiver and a transmitter, a plurality of base stations for sending and receiving data and for sending to selected subscriber units a power control command, and a regional controller for directing communication between individual subscriber units and individual base stations. Further, selected subscriber units include a power control system for controlling transmission power levels of data signals sent to a selected base station. 
     In accordance with still a fifth aspect of the present invention, a subscriber units apparatus for use in a two-way paging network includes: a receiver, a transmitter, and a power level controller. The power level controller responds to a power control command received from a paging network to adjust the power level of the transmitter for subsequent transmissions. The power control command sets a power level of a subscriber units&#39;s transmissions to ensure that a subscriber units apparatus&#39;s successful transmission to a base station, while decreasing the such transmission&#39;s interference with other subscriber units&#39; transmissions. 
     The above discussion has been in terms of pager systems, but the invention applies the same principle to cellular communications in general. For example, the present invention could be adapted for use with multiple stationary subscriber units that transmit large amounts of data on a reverse channel to paging network. A further understanding of the nature and advantages of the invention herein may be realized by reference to the remaining portions of the specification and the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a two-way paging network including a regional controller, a plurality of base stations and a plurality of subscriber units, for use with the present invention. 
     FIG.  2 ( a ) depicts a two-way subscriber unit according to the present invention. 
     FIG.  2 ( b ) depicts a power level controller system in a two-way subscriber unit in accordance with the present invention. 
     FIG. 3 depicts a flowchart describing steps of operating a subscriber unit network in accordance with one embodiment of the present invention. 
     FIG. 4 depicts a flowchart describing steps of operating a subscriber unit network in accordance with an alternative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG.  2 ( a ) depicts a subscriber unit (SU) apparatus  200  according to the present invention. Subscriber unit  200  includes an antenna  225  and a receiver  215  for receiving signals from a paging network, such as from a base station  105  in FIG.  1 . Subscriber unit  200  also includes a transmitter  220  for sending data back to the paging network  100  in which it resides, such as responses to the base station  105  from which it receives messages. Subscriber unit  200  also contains a power level controller  210 , which controls the transmission power level of transmitter  220 . 
     Power level controller  210  receives a signal from the paging network  100  containing a unique power level command message  226 . The signal is received at receiver  215  and sent to the power level controller  210 , which processes the signal and the power level command message  226 . The outcome of the power level controller&#39;s is a power control signal  227  which influences the power level of transmitter  220 . In response to signals received from the paging network  100 , the transmission power level of SU apparatus  210  may be controlled to avoid excessive levels of transmission power and reduce interference with other SUs. 
     FIG.  2 ( b ) depicts a more detailed view of power level controller  210 , according to another aspect of the present invention. A protocol specifies the interaction between SU apparatus  200  and paging network  100 . The preferred embodiment uses the ReFLEX protocol but other interactive protocols for use in two-way cellular communications may be suitably employed. The signal  226  received from the paging network  100  is first sent to a ReFLEX decoder  230  where the signal  226  is decoded. Decoded signal  226  includes vectors and messages  250  which are sent to a microcontroller  240 . Microcontroller  240  may be any type of computer processor device operable according to the algorithmic flowcharts described below. 
     Microcontroller  240  receives the decoded signal  250  from ReFLEX decoder  230  and processes it. Power control signal  245  is extracted from decoded signal  250  by microcontroller  240  and sent to power controller  235 . The power controller  235  adjusts a power level signal  227  sent to the transmitter  220 . In the preferred embodiment, transmitter  220  is supplied power by a battery, but any power storage supply may be employed. The power level signal  227  adjusts the power level at which transmitter  220  sends out data signals. 
     In communication sessions initiated by SU apparatus  200 , the first transmission will be controlled to transmit at an initial power level. The initial power level is approximately midway between the maximum transmitter power level and the minimum transmitter power level, as measured in dBm. If in response to its initial transmission, the SU apparatus  200  does not receive an acknowledgement, it will retransmit the initial transmission at its maximum power level. Among all of the base stations  105  that receive the SU&#39;s initial transmission, the regional controller  101  will select the base station having a high enough signal to noise ratio of the received transmission. Communication sessions using a specific two-way protocol are described below. 
     FIG. 3 depicts a flowchart  300  describing further steps of operating a paging network in accordance with one embodiment of the present invention. Flowchart  300  describes a ReFLEX communication session initiated by a SU  110  in paging network  100 . At step  305 , SU  110  is synchronized in time and frequency with the paging network  100 . Specifically, SU  110  synchronizes its receiver/transmitter to a selected base station  105  within the paging network  100 . 
     At step  310 , the SU  110  wishes to send data on the reverse channel. To accomplish this, SU  110  receives and decodes Block Information Words (BIW) sent by base station  105 . The SU  110  uses the BIWs to select a time slot for transmission at step  315  by updating channel and time-slot parameters in its internal processor. At step  320 , SU  110  sends an Inbound Message Request (IMR) on the reverse channel  120 . The paging network  100  will select for the SU  110  the optimal outbound beam  115  and inbound beam  120  at the base station  105  for subsequent communication, as shown in the following steps. 
     At step  325  SU  110  receives a Short Message (SM) from the paging network  100 . The SM uses a “numeric characters” option and data bits which can only be interpreted. by SUs having power control capability of the present invention. The SM contains a custom data structure called the power level command, instructing the SU  110  to transmit at a power level desired by the paging network  100 . The desired transmission power level is set so as to guarantee reception at the base station  105 , yet takes account of possible interference of other SU communications. At step  330 , the SU  105  responds to the SM by transmitting to the base station a standard acknowledgment (ACK) at the power level specified in the SM. 
     At step  335 , the SU  110  receives a Standard Inbound Message (SIM) command, which also includes a power level command. The SIM received at step  335  tells the SU  105  when and how to send its data, and specifies a power level at which to transmit. The specified power level from the SIM may be higher if necessary. In response to the SIM, at step  340  SU  110  sends its data at the transmission power level specified by the SIM. Data is sent on Multi-Packet Scheduled Inbound (MPSI) messages, preceded by a Start Address Unit (SAU). After each packet or groups of packets sent by the SU  110  at step  340 , the SU expects an ACK from the base station  105 . If there is no ACK, the SU will retransmit at an incremental higher power level. Included in an ACK from the base station  105  can be another SIM specifying the same power level or a higher power level. Steps  335 ,  340  and  345  are repeated until the session ends. 
     FIG. 4 depicts a flowchart  400  describing still further steps of operating a paging network in accordance with the present invention. Flowchart  400  describes a ReFLEX communication session initiated by the paging network  100 , and specifically a base station  105  within the paging network  100 . At step  405 , the regional controller  101  in the paging network  100  selects a base station  105  and broadcast frames (BFs) for broadcast messages and initiation signals. It is assumed that the targeted SU  110  is already synchronized with the paging network in time and frequency. 
     Wishing to send a data message to a particular, selected SU  110 , at step  410  the regional controller  101  sends a “Where aRe yoU” (WRU) query on the next BF. The WRU query instructs the SU&#39;s  110  how to respond by containing signals indicating a specific channel, frame and time slot. At step  415 , the SU  110  responds to the WRU and reports to the regional controller with a message containing “quality bits” to report the quality of the WRU the SU received. The base station  105  receives the WRU response. Detecting the base station&#39;s receipt of the WRU response at step  420 , the regional controller selects the best inbound beam  120  and outbound beam  115  from the inbound beams at base station  105  which received the WRU response. 
     At step  430 , the base station  105  sends a SM to the SU  110  indicating a desired power level on which to transmit. At step  435 , the base station  105  receives an ACK from the SU  110 , sent at the transmission power level specified in the SM. After step  435 , the communication session can progress according to steps  335 - 350  in FIG.  3 . 
     Alternatively, the regional controller at step  440  may send a Binary Vector (BV) to the SU  110  specifying to the SU the channels and frames on which the paging network expects the SU&#39;s data, and when to send the MPSI messages. The BV specifies channel, frame, and slot for subsequent SU communications. At step  445  the base station  105  sends a SIM to the SU, specifying if needed a new power level for SU transmissions. The SU responds at step  450  by sending data at the power level designated in the SIM. Steps  440  through  450  are repeated until the communication session ends. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims and their full scope of equivalents.