Abstract:
A power management system for a mobile unit wherein the base station detects the quality of the signals transmitted by the mobile unit. Based on this signal quality, the base station determines if the mobile unit should increase the transmission power level. If an increase in transmission power is indicated, the base station sends a signal to the mobile unit to cause the mobile unit to increase transmission power. However, to save battery power, the mobile unit only transmits at the increased power level for a limited amount of time, and then automatically returns to transmitting at the lower power level. Further, a slightly decreased high power level is established to allow the mobile unit to function when it is located away from the base station, yet not near the outer transmission boundary.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates to the field of wireless communication systems. More specifically, the present invention relates to power management by dynamically adjusting the transmission power of mobile stations based upon the quality of received signals by the base station. 
     2. Background 
     The use of wireless communication systems is growing with users now numbering well into the millions. One of the most popular wireless communications systems is the cordless telephone, consisting of a mobile unit (or handset) and a base station. Cordless telephones allow a user to talk over the telephone without having to remain in a fixed location. This allows users to, for example, move freely about a house while talking on the phone. However, one inconvenience associated with routine use of a cordless telephone is the constant need to recharge and replace depleted batteries in the handset. 
     As with any transmitted signal, the quality of the received signals varies based upon a number of factors, including atmospheric conditions, location of the mobile unit, or interference by walls or buildings. If a signal transmitted by the mobile unit has degraded, the base station may be unable to decode and process the signal. This may occur, for example, if the mobile unit is at the outer transmission boundary of the base station. 
     The power required by the mobile unit to transmit signals to the base station is one of the largest drains on battery power. In an attempt to extend battery life, mobile units are designed to vary the amount of transmission power based upon current needs. For example, a mobile unit located a long distance from the base station needs to transmit signals at a higher power level than a mobile unit near the base station. Current systems adjust the transmission power of the mobile unit based upon signal quality measurements taken over an extended period of time. Once the average signal quality diminishes below a set level, the mobile unit begins transmitting signals at a higher power level. After switching to the higher power level, the signal quality is again measured. If these signal quality measurements are above a threshold for an extended period of time, the base station instructs the mobile unit to switch to a lower power level to conserve battery power. While adjusting the transmission power levels of the mobile unit over extended periods of time has improved battery life, there is always a desire to further extend the useful life of the battery. 
     Improvements in battery technology, while helpful, have done little to avoid the seemingly ever-present need to recharge and replace mobile unit batteries. What is needed is a system to further conserve battery power by reducing the power consumed by the mobile unit. 
     SUMMARY 
     The present invention is directed to reducing power consumed by a mobile unit. The present invention recognizes the largest amount of battery power is consumed during the highest transmission power level of the mobile unit. Therefore, the present invention is directed to minimizing the amount of time the mobile unit transmits at the highest power level. 
     In one embodiment of the present invention, the base station detects the quality of the signals transmitted by the mobile unit. Based on this signal quality, the base station determines if the mobile unit should increase the transmission power level. If an increase in transmission power is indicated, the base station sends a signal to the mobile unit causing the mobile unit to increase transmission power. However, to save battery power, the mobile unit transmits at the increased power level for a limited amount of time, and then automatically returns to transmitting at the lower power level. 
     The present invention also recognizes that in certain circumstances, mobile units can transmit at a high power level for long periods of time. By transmitting at a high power level, the mobile unit can function at the outer transmission boundary of the base station. However, the mobile unit often transmits at a high power level without being at the outer transmission boundary. In these situations, where the mobile unit is located away from the base station, yet not near the outer transmission boundary, the highest power level is not necessary. Therefore, the present invention allows the mobile unit to operate at a reduced high power level during these periods. 
     One embodiment of the invention is a wireless communication system comprising a base station which transmits a first plurality of signals and receives a second plurality of signals. A signal strength detector in the base station determines the quality of at least some of the second plurality of signals received by the base station. When the quality of the signals is below a predetermined threshold, the base station inserts a low power indicator in at least one of the first plurality of signals transmitted by the base station. A mobile unit receives the first plurality of signals transmitted by the base station. The mobile unit is configured to operate at either a first power level or a second power level, where the first power level is higher than the second power level. When the mobile unit receives the low power indicator from the base station, the mobile unit operates at the first power level and after the transmission of a signal, the mobile unit resets to operate at the second power level. 
     Another embodiment of the invention is a wireless communication unit comprising a receiver configured to receive a first plurality of signals, at least one of the first plurality of signals having a power level command. A transmitter is configured to transmit a second plurality of signals over at least two power levels, where a first power level is greater than a second power level. A processor is connected to the receiver and the transmitter. The processor is configured to control the transmitter so as to vary the power levels of the second plurality of signals. The processor is further configured to select the first power level in response to the power level command and then select the second power level after the transmission of the second plurality of signals. 
     Another embodiment of the invention is a method of conserving power in a wireless communication system comprising the acts of determining the quality of a first signal received from the mobile unit and comparing the received signal quality to a predetermined value. A second signal is then transmitted from the mobile unit at a first power level when the received signal quality is below the predetermined value. The mobile unit automatically resets to transmit at a second power level following a transmission at a first power level, where the first power level is higher than the second power level. 
     Another embodiment of the invention is a wireless communication system comprising a signal strength indicator which determines the quality of a signal received from a mobile unit and a power level adjustor which increases the power level of a signal transmitted by the mobile unit for only a predetermined number of transmissions when the signal quality is below a set value. 
     Another embodiment of the invention is a method of saving power in a communications system which provides for the repeated exchange of signals between a first location and a second location. The method comprises the acts of determining the quality of a first signal transmitted by the first location and transmitting information instructing the first location to increase the transmission power for a second signal to a first power level if the quality of the first signal falls below a predetermined level. The method then resets the transmission power of the first location to a second power level after transmission of the second signal, where the first power level is higher than the second power level. The method then determines the quality of the second signal transmitted by the first location and transmits information instructing the first location to increase the transmission power for a third signal to a first power level if the quality of the second signal falls below a predetermined level. 
     Another embodiment of the invention is a wireless communication system comprising means for determining the quality of a signal received, means for indicating when the quality of the signal falls below a threshold, and means for increasing the signal transmission power for only a predetermined number of transmissions when the indication means is detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the invention will become more apparent upon reading the following detailed description and upon reference to the accompanying drawings. 
     FIG. 1 illustrates components of a remote telephone system appropriate for use with one embodiment of the present invention. 
     FIG. 2 illustrates a block diagram of a mobile unit according to one embodiment of the present invention. 
     FIG. 3 illustrates an example of wireless communication signal data transmitted by a base station and a mobile unit. 
     FIG. 4A illustrates a block diagram of the slow power control used by existing wireless communication systems. 
     FIG. 4B illustrates a block diagram of the fast power control of one embodiment of the present invention. 
     FIG. 5 illustrates acts performed by a base station to determine the transmission power required by the mobile unit. 
     FIG. 6 illustrates acts performed by a mobile unit to determine transmission power level. 
     FIG. 7A illustrates an example of the transmission power levels generated by a mobile unit using the slow power control in existing wireless communication systems. 
     FIG. 7B illustrates an example of the transmission power levels generated by a mobile unit using the fast power control of the present invention. 
     FIG. 8 illustrates a graph depicting the amount of talk time available over a range of distances using both the slow power control in existing wireless communication systems and the fast power control of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A remote telephone system  100  appropriate for use with one embodiment of the invention is shown in FIG.  1 . The remote telephone system  100  contains a base station  104  and a mobile unit  106 . An antenna  108  on the base station  104  transmits signals  110  to and from an antenna  107  on the mobile unit  106 . The base station  104  is connected to a land-base telephone network  114  via a connection  112 . Of course, other methods of connecting the base station  104  to the land-base telephone network  114 , such as wireless connections, may be used. 
     In operation, the mobile unit  106  monitors signals  110  from the base station  104  to determine if a call is pending. If a call is pending, the mobile unit  106  switches to a communications mode. In the communications mode, a user speaks into a microphone  105 . The speaking is then encoded at the mobile unit  106  and transmitted to the base station  104 . This data is eventually transmitted over the telephone network  114 . Information received via the telephone network  114  is transmitted along the connection  112  to the base station  104  for transmission to the mobile unit  106 . At the mobile unit  106 , the signal  110  is received, decoded and played to the user through a speaker  109 . 
     FIG. 2 illustrates one embodiment of a mobile unit  106  according to one embodiment of the present invention. The mobile unit  106  downlinks the signals from the base station  104  at a transceiver  120  via an antenna  107 . The transceiver  120  may also uplink information to the base station  104 . Alternatively, a separate receiver and transmitter may be used in place of the transceiver  120 . After receiving the signals, the transceiver  120  relays the signals to a processor  125 . In one embodiment, a microprocessor performs the function of the processor  125 . Of course, other types of processors may be used including conventional general purpose single-chip or multi-chip microprocessors, digital signal processors, embedded microprocessors, microcontrollers and the like. 
     The processor  125  converts the signals into data and performs the functions requested by the signal. This may include an indication that a call is pending. The mobile unit  106  may inform the user of a pending call by a variety of methods, including ringing, vibrating or flashing lights. During the pendency of a call, the data transmitted and received by the mobile unit  106  may include voice and data. 
     The data created by the processor  125  may be temporarily or permanently stored in a storage medium  130 . The storage medium  130  may comprise any method of storing information. For example, the storage medium  130  may comprise an electrically erasable programmable read-only memory (EEPROM), read-only memory (ROM), random access memory (RAM), hard disks, floppy disks, laser disc players, digital video devices, compact discs, video tapes, audio tapes, magnetic recording tracks, and other techniques to store data. 
     The data from the storage medium  130  may be transmitted through a codec (coder/decoder)  135  to the speaker  109 . The codec  135  may comprise a digital-to-analog converter or the like. The decoded data may then be played through the speaker  109  to be heard by the user. 
     The user may also direct voice into the microphone  105  of the mobile unit  106 . The voice data passes through the codec  135  and may be stored by the storage medium  130  prior to processing by the processor  125 . The codec  135  may comprise an analog-to-digital converter or the like. The processor  125  maintains two-way communication with the transceiver  120 , and therefore the voice data may be sent from the mobile unit  106  to the base station  104 . 
     FIG. 3 illustrates wireless communication signal data transmitted by a base station  104  in structural data frames, sometimes called time division duplex (TDD) frames. Time division duplex is a type of multiplexing where two or more transceivers transmit and receive on the same frequency, but never at the same time. This kind of duplex operation is called half-duplex operation. Of course, the invention is not limited to time division duplex systems or time division duplex frames, and may include systems using code division multiple access, statistical time division multiplexing, spread spectrum, single communication channels, global system for mobile communications standards, or the like. For ease of understanding, the present invention will be described with reference to a time division duplex base system. 
     The time division duplex system provides for a series of data frames  300  divided into transmission frames  304  and receiving frames  308  sent between the base station  104  and mobile unit  106 . Each of the transmission frames  304  and receiving frames  308  has a duration of approximately one millisecond. Although the time division duplex system operates in a half-duplex mode, the one millisecond frame length allows the time division duplex system to appear to be a full duplex operation to the user. The time division duplex operations are performed by the transceiver  120  and the processor  125 , according to common techniques known to those of skill in the art. 
     Each of the transmission frames  304  and the receiving frames  308  contains 100 bits of data. In one embodiment, the composition of the bits of data are the same in both the transmission frames  304  and receiving frames  308 . Thus, the composition of the bits will be described in reference to one of the transmission frames  304 . The 100 bits of data in a single transmission frame  304  are allocated as follows: 5 guard bits  312 , 10 settling bits  316 , 1 differential decoder start bit  318 , 80 voice data bits  320 , and 4 control bits  324 . 
     The guard bits  312  are divided into two sets of bits, one bit at the beginning of the data frame and 4 bits at the end of the data frame. The guard bits  312  at each end of the data frame allow for an isolation of each frame in time to ensure proper reading of the bits in case of frame overlap. The settling bits  316  represents a period of time during which the mobile unit  106  ramps up radio frequency (RF) power. The decoder start bit  318  initializes the codec  135 . 
     The actual conversation or speaking is contained in the 80 voice data bits  320 . These are the data bits that have been encoded by the codec  135  of FIG.  2 . The actual coding and decoding of the voice data bits  320  use techniques which are well known to one of skill in the art. The 80 voice data bits  320  are decoded by the codec  135  of the receiving unit to be played through the speaker  109 . 
     The remaining 4 bits of data in the transmission frame  304  are control bits  324 . Two of these bits comprise the supervisory control bits  328  which contain basic controlling information, including, among other things, the slow power control data, channel hopping sequences, ring requests, and other control information. In one embodiment, the remaining two bits are the fast power control bits  332 . The fast power control bits  332  convey information to the mobile unit  106  as to what power level to transmit in. Further details of the operation and identification of the fast power control bits  332  will be discussed below. 
     In one embodiment, the fast power control bits  332  have four possible values which are shown in FIG.  3 . Of course, it is possible to use one bit, having two possible values, for the fast power control. However, two bits are used in one embodiment to ensure a single bit error does not thwart an instruction to increase power. Using two fast power control bits  322 , when both bits have a value of zero, the mobile unit  106  is instructed to transmit at the medium/high power level. When bit  1  has a value of 1 and bit  2  has a value of 0, or bit  1  has a value of 0 and bit  2  has a value of 1, or both bits  1  and  2  have a value of 0, the mobile unit  106  is instructed to transmit at the high power level. Therefore, if either bit  1  or bit  2  is set to 1, the mobile unit  106  operates at the high power level. 
     FIG. 4A is a block diagram  400  showing the operation of a slow power control  405  used in some current wireless systems. The slow power control  405  is a software control system operated by the base station  104 . The block diagram  400  of FIG. 4A is an illustration of the slow power control  405  as it functions in the base station  104 . The slow power control  405  instructs the transceiver  120  of the mobile unit  106  at which power level to transmit the transmission frames  304 . 
     Using a software switch  410 , the slow power control  405  selects between a low power level  415 , a medium power level  420 , or a high power level  425 . In selecting between the power levels, the slow power control  405  measures the quality of signals over a broad range of time, generally in the hundreds of millisecond range. Of course, the switch  410  is merely representative of how the slow power control  405  selects between power levels. The selection may be accomplished in a variety of manners, including running a separate subroutine for each power level, setting a flag indicating at which power level to transmit, or using a logic sequence to identify the proper power level. 
     The quality of signals are determined from a variety of metrics, including among others the bit error rate, the received signal strength indicator, and the signal quality. The signal quality metrics are discussed in further detail below. Because the transmission frames  304  and the receiving frames  308  are approximately one millisecond long, the slow power control  405  only switches between power levels at a minimum of every 100 data frames. 
     When the slow power control  405  indicates the signal level is very strong, the base station  104  instructs the mobile unit  106  to transmit the transmission frames  304  at the low power level  415 . As a user walks away from a base station  104 , the quality of the signal may decrease. When the average signal quality over a period of time falls below a preset threshold, the slow power control  405  in the base station  104  sets the mobile unit  106  to the medium power level  420 . This increases the amount of power at which the mobile unit  106  transmits the transmission frames  304 . 
     As the user moves yet further away from the base station  104 , or atmospheric conditions degrade the signal from the mobile unit  106  to the base station  104 , the average signal quality measured over a period of time may diminish below a second threshold. If the average signal quality diminishes below the second threshold, the slow power control  405  in the base station  104  directs the mobile unit  106  to the high power level  425 . The mobile unit  106  then transmits the transmission frames  304  at the high power level  425 . 
     The mobile unit  106  transmits at each power level until the average signal quality over a period of time moves above or below the thresholds. For example, the mobile unit  106  transmits at the high power level  425  until the average signal quality over a period of time improves beyond the second threshold. At this point, the slow power control  405  in the base station  104  instructs the mobile unit  106  to transmit at the medium power level  420 . In one embodiment, the power levels are measured as the ratio of a quantity of power to 1 milliwatt (dBm). In an embodiment of the slow power control  405 , the low power level transmits at 3 measured decibels (dBm), the medium power level  420  transmits at 7 dBm, and the high power level  425  transmits at 20 dBm. 
     FIG. 4B illustrates a block diagram  440  showing the fast power control  450  according to one embodiment of the present invention. The slow power control  405  operates with respect to the low power level  415  and the medium power level  420  in the same manner as described with reference to FIG.  4 A. However, when the slow power control  405  determines the signal quality has reached the second threshold, the slow power control  405  through the switch  410  activates the fast power control  450 . The fast power control  450  has a switch  455  which selects between the high power level  425  and a medium/high power level  460 . 
     As with the switch  410 , the switch  455  is merely representative of how the fast power control  450  selects between power levels. The selection may be accomplished in a variety of manners, including running a separate subroutine for each power level, setting a flag indicating at which power level to transmit, or using a logic sequence to identify the proper power level. The medium/high power level  460  is a level between the medium power level  420  and the high power level  425 . In one embodiment of the invention, the medium/high power level  460  is 13 dBm. 
     In operation, the switch  455  of the fast power control  450  defaults to the medium/high power level  460 . As will be described below in greater detail, the fast power control  450  measures the signal quality during every data frame. If, during any data frame, the signal quality falls below a preset threshold, the switch  455  of the fast power control  450  will activate the high power level  425  and instruct the mobile unit  106  to transmit at the high power level  425 . After the mobile unit  106  transmits at the high power level  425 , the mobile unit  106  automatically resets the switch  455  to transmit at the medium/high power level  460 . Only another instruction by the fast power control  450  causes the mobile unit  106  to transmit at the high power level  425 . 
     FIG. 5 illustrates the process  500  performed by the base station  104  to set the transmission power of the mobile unit  106 . The base station  104  initializes as indicated by start block  505 . Proceeding to state  510 , the slow power control  405  in the base station  104  directs the mobile unit  106  to operate at either the low power level  415 , the medium power level  420 , or the high power level  425 . 
     Proceeding to state  515 , if the slow power control  405  in the base station  104  directs the mobile unit  106  to operate at either the low power level  415  or the medium power level  420 , the base station  104  proceeds along the NO branch to an end state  545 . 
     Returning to state  515 , if the high power level  425  is selected by the slow power control  405 , the base station  104  proceeds along the YES branch to state  520 . In state  520 , the base station  104  determines the quality of the signals received from the mobile unit  106 . 
     The base station  104  uses a variety of indicators to determine signal quality. Among these indicators is a bit error rate, a receiver quality indicator (RX Quality), a signal quality indicator, and a receive signal strength indicator (RSSI). The base station  104  uses these indicators to determine the quality of the signals received from the mobile unit  106 . These indicators are well known and presently monitored by the base station  104 . 
     In particular, the bit error rate is the number of erroneous bits in a data transmission. The RX Quality is a value assigned by the network indicating the quality of the received signal based upon the bit error rate. The RX Quality figure provides a base station  104  with an expected measurement accuracy. The base station  104  uses the RX Quality to determine the overall potential for error. 
     The base station  104  may also use the signal quality indicator to determine the strength of the signals received from the mobile unit  106 . The signal quality indicator is an estimate of the signal to noise ratio of the received signal. The signal quality indicator is calculated from the signal received at the base station  104 . 
     Another measurement that may be used by the base station  104  is RSSI. RSSI provides a known value based upon the measured strength of the signal at the base station  104 . A strong signal at the base station  104  indicates less likelihood for error. Table 1 provides examples of potential values for RSSI based upon the signal strength received at the base station  104 . Each specific value for RSSI correlates to the strength of the signal (in measured decibels (dBm)) at the base station  104 . 
     
       
         
               
               
             
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 RSSI 
                 Level at Base Station (dBm) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 Less than −110 
               
               
                 1 
                 −110 to −109 
               
               
                 2 
                 −109 to −108 
               
               
                 . 
                 . 
               
               
                 . 
                 . 
               
               
                 . 
                 . 
               
               
                 62 
                 −49 to −48 
               
               
                 63 
                 above −48 
               
               
                   
               
             
          
         
       
     
     Using the above indications of signal quality, the base station  104  can determine the probability of receiving a usable signal if the mobile unit  106  continues transmission at the same power level. If the signal quality is poor, the mobile unit  106  must increase the transmission power level to ensure a usable signal is received by the base station  104 . Any technique known to one skilled in the art to measure signal quality may be used without departing from the spirit of the invention. 
     Proceeding the state  525 , the base station  104  compares the measured signal quality to a preset threshold. The preset threshold may vary but is generally chosen to ensure adequate reception of the signals transmitted by the mobile unit  106  to the base station  104 . For example, it may be known an RSSI of less than 30 results in an unusable signal. When this RSSI is detected, the mobile unit  106  needs to boost transmission power to ensure proper reception. 
     To communicate with the mobile unit  106 , the base station  104  constructs the receiving frame  308 . As described above, the receiving frame  308  contains guard bits  312 , DC settling bits  316 , a decoder start bit  318 , voice data bits  320 , and control bits  324 . The fast power control  450  information is included in the control bits  324 . The base station  104  includes fast power control bits  332  in the control bits  324  of the receiving frame  308 . 
     Proceeding the state  530 , the base station  104  determines if the measured signal quality is below the preset threshold. If the signal quality is not below the threshold, the signal quality is adequate and the base station  104  proceeds along the NO branch to state  540 . In state  540 , the fast power control bits  332  are set to indicate the medium/high power level  460 . As described above with reference to FIG. 3, this sets both of the fast power control bits  332  to 0. The base station  104  then proceeds to the end state  545 . 
     Returning to state  530 , if the signal quality is below the preset threshold, the mobile unit  106  needs to increase the transmission power. As a result, the base station  104  proceeds along the YES branch to state  535 . In state  535 , the base station  104  sets the fast power control bits  332  to select the high power level  425 . As described above with reference to FIG. 3, the high power level  425  is selected when either of the fast power control bits  332  are set to 1. To ensure that a single bit error does not thwart an instruction to increase power, the fast power control bits  332  also sets high power if either bit  1  or bit  2  is set to 1. The base station  104  then concludes the process by proceeding to the end state  545 . 
     FIG. 6 illustrates a process  600  according to one embodiment used by the mobile unit  106  to determine the proper transmission power level. The process  600  begins at start state  605 . Proceeding to state  610 , the mobile unit  106  receives a receiving frame  308  from the base station  104 . As described above with reference to FIG. 3, the receiving frame  308  contains a variety of information including guard bits  312 , settling bits  316 , voice data bits  320 , and control bits  324 . 
     After obtaining the receiving frames  308 , the mobile unit  106  processes the information in the receiving frame  308 . The codec  135  decodes the voice data bits  320  to play the voice to the user. The control bits  324  are processed by the processor in the mobile unit  106 . After processing the control bits  324 , the mobile unit  106  proceeds to state  615  to determine the power level selected by the slow power control  405  in the base station  104 . This information is embedded in the supervisory control bits  328  as described above in FIG.  3 . The slow power control  405  either selects the low power level  415 , the medium power level  420 , or the high power level  425 . 
     Proceeding to state  620 , the mobile unit  106  determines if the high power level  425  is selected by the slow power control  405  existing in the base station  104 . If the high power level  425  is not selected, the mobile unit  106  proceeds along the NO branch to state  630 . In state  630 , the mobile unit  106  initializes to transmit at the power level selected by the slow power control  405 . This is either the lower power level  415  or the medium power level  420 . The mobile unit  106  then proceeds to an end state  655 . 
     Returning to state  620 , if the high power level  425  is selected by the slow power control  405 , the mobile unit  106  proceeds along the YES branch to state  625 . In state  625 , the mobile unit  106  processes the fast power control bits  332 . As stated above, the fast power control bits  332  have four potential settings. If both bits are set to 0, the medium/high power level  460  is selected. However, if any bit is set to 1, the high power level  425  is selected. 
     Proceeding to state  635 , the mobile unit  106  determines if the high power level  425  is selected by the fast power control bits  332 . If the fast power control bits  332  are not set to select the high power level  425 , the mobile unit  106  proceeds along the NO branch to state  640 . At state  640 , the mobile unit  106  initializes to transmit at the medium/high power level  460 . The mobile unit  106  then proceeds to the end state  655 . 
     Returning to state  635 , if the fast power control bits  332  are set to select the high power level  425 , the mobile unit  106  proceeds along the YES branch to state  645 . In state  645 , the mobile unit  106  initializes and transmits at the high power level  425 . After the transmission, the mobile unit  106  proceeds to state  650 . 
     In state  650 , the mobile unit  106  independently resets the transmission power level to the medium/high power level  460 . This ensures the mobile unit  106  does not waste battery power by operating at the high power level  425  for an extended period of time, unless repeatedly instructed to do so by the base station  104 . The mobile unit may reset the transmission power level following detection of any of a number of activities. Some examples include passage of a predetermined period of time, the end of a transmission of a frame or a preset number of frames, or an end of send detection. In one embodiment, the number of frames is a system parameter which can be set to a desired value. The process  600  then proceeds to the end state  655 . 
     The mobile unit  106  performs the process shown in flowchart  600  for each of the transmission frames  304 . Therefore, the fast power control  450  resets the power level to be transmitted for each of the transmission frames  304 . Under the slow power control  405 , the power level selected is only changed on the order of hundreds of data frames. Also, under the slow power control  405 , signal qualities which exceed the second threshold automatically cause the mobile unit  106  to transmit at the high power level  425 , and the medium/high power level  460  is not available. 
     FIG. 7A illustrates an example of transmission power levels by the mobile unit  106  under the slow power control  405  system used in existing wireless communication systems. The graph  700  in FIG. 7A depicts the transmission power level in dBm, either 3, 10, or 20, corresponding to the low power level  415 , the medium power level  420 , and the high power level  425 . The transmission power levels are charted against the distance the mobile unit  106  is from the base station  104 . As can be seen by the graph  700 , when the mobile unit  106  is at a distance close to the base station  104 , the low power level  415  is selected and the transmission occurs at 3 dBm as indicated by section  705  of the graph  700 . As the user moves further from the base station  104 , the slow power control  405  activates the mobile unit  106  to transmit at the medium power level  420  and the mobile unit  106  transmits at 10 dBm as indicated by section  710  of graph  700 . As the mobile unit  106  is moved yet further from the base station  104 , the slow power control  405  selects the high power level  425  and the mobile unit  106  transmits at 20 dBm as indicated by the section  715  of the graph  700 . Switching between the power levels can only occur on the order of hundreds of milliseconds because of the slow power control  405  switching time constraints. 
     FIG. 7B illustrates the transmission levels by the same mobile unit  106  with an active fast power control  450 . Because, as described above, the fast power control  450  is only activated when the slow power control  405  selects the high power level  425 , the graph  730  is identical for the low power level  415  and the medium power level  420  as indicated by sections  705  and  710  of graph  730 . Thus, if the mobile unit  106  is close to the base station  104 , the mobile unit  106  transmits at the low power level  415 , and as it moves further away or the signal quality degrades, the mobile unit  106  transmits at a medium power level  420 . However, when the slow power control  405  selects the high power level  425 , the fast power control  450  activates causing the medium/high power level  460  to be used. In this embodiment of the invention, the medium/high power level is 13 dBm as indicated by section  735  of graph  730 . 
     Under the fast power control  450 , the mobile unit  106  reads the receiving frames  308  to determine whether to transmit at the medium/high power level  460  or the high power level  425 . As described above, when the signal quality degrades below a preset threshold, the fast power control  450  switches the mobile unit  106  to transmit at a high power level  425 , indicated by section  715  of the graph  730 . After transmitting at the high power level  425 , the fast power control  450  resets the transmission power level back to the medium/high power level  460 , indicated by section  735  of the graph  730 . The mobile unit  106  alternates between the medium/high power level  460  and the high power level  425  only as indicated by the fast power control  450  on a frame-by-frame basis. 
     Therefore, in one embodiment, the fast power control  450  causes the mobile unit  106  to automatically reset to the medium/high power level  460  independently of instructions from the base station  104 . If the base station  104  then determines the signal quality of the transmission frames  304  are below an established standard, the base station  104  instructs the mobile unit  106  to increase to the high power level  425 . By constantly resetting to the medium/high power level  460 , the fast power control  450  ensures the mobile unit  106  only operates at the high power level  425  when necessary. 
     FIG. 8 illustrates a graph  800  depicting the amount of talk time available over a range of distances for both systems having only the slow power control  405 , indicated by line  805 , and systems equipped with the fast power control  450 , indicated by line  810 . The graph  800  shows that when the mobile unit  106  is in the close proximity to the base station  104  (approximately less than ten meters in this example), the talk time of systems with and without the fast power control  450  are nearly identical. However, as the mobile unit  106  moves further from the base station  104 , the amount of talk time available in the system with the fast power control  450  is greatly enhanced. This is due to the battery power saved by transmitting at the medium/high power level  460  for an extended period of time. 
     The power savings can be exemplified by viewing the amount of talk time available at the 30 meter point of graph  800  for both systems. The talk time available on the system having the fast power control  450  at a distance of 30 meters is approximately 6.3 hours, as indicated by a point  820  on the line  810 . In the system having only the slow power control  405 , the amount of talk time available at a distance of 30 meters is approximately 5.3 hours, indicated by a point  825  on the line  805  of the graph  800 . Therefore, allowing the use of the medium/high power level  460  and the constant switching between the medium/high power level  460  and the high power level  425 , when necessary, will conserve enough battery power in this example to increase the talk time of the mobile unit  106  approximately 1 hour before battery failure. 
     Numerous variations and modifications of the invention will become readily apparent to those skilled in the art. Accordingly, the invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The detailed embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.