Abstract:
Methods and systems are provided for dynamic adjustment of the reverse-link frame-error-rate (RFER) target based on reverse-link RF conditions. In an embodiment, a base station provides service to at least one mobile station on a carrier in a wireless coverage area using a first RFER target. The base station calculates a reverse noise rise (RNR) value for the carrier, and then selects a second RFER target based at least in part on the calculated RNR value. The base station then provides service to at least one mobile station on the carrier in the wireless coverage area using the second RFER target.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to wireless networks, and, more particularly, to managing transmission power between mobile stations and base stations. 
     2. Description of Related Art 
     a. CDMA Networks Generally 
     Many people use mobile stations, such as cell phones and personal digital assistants (PDAs), to communicate with cellular wireless networks. These mobile stations and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1×RTT networks” (or “1× networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication. 
     Typical CDMA networks include a plurality of base stations, each of which provide one or more wireless coverage areas, such as cells and sectors. When a mobile station is positioned in one of these coverage areas, it can communicate over the air interface with the base station, and in turn over one or more circuit-switched and/or packet-switched signaling and/or transport networks to which the base station provides access. The base station and the mobile station conduct these communications over a frequency known as a carrier, which may actually be a pair of frequencies, with the base station transmitting to the mobile station on one of the frequencies, and the mobile station transmitting to the base station on the other. This is known as frequency division duplex (FDD). The base-station-to-mobile-station link is known as the forward link, while the mobile-station-to-base-station link is known as the reverse link. 
     Furthermore, using a sector as an example of a wireless coverage area, base stations may provide service in a given sector on one carrier, or on more than one. An instance of a particular carrier in a particular sector is referred to herein as a sector/carrier. In a typical CDMA system, using a configuration known as radio configuration 3 (RC3), a base station can, on a given sector/carrier, transmit forward-link data on a maximum of 64 distinct channels at any given time, each channel corresponding to a unique 64-bit code known as a Walsh code. Of these channels, typically, 61 of them are available as traffic channels (for user data), while the other 3 are reserved for administrative channels known as the pilot, paging, and sync channels. 
     When a base station instructs a mobile station—operating on a particular sector/carrier—to use a particular traffic channel for a communication session, such as a voice call or a data session, the base station does so by instructing the mobile station to tune to a particular one of the 61 Walsh-coded traffic channels on that sector/carrier. It is over that assigned traffic channel that the base station will transmit forward-link data to the mobile station during the ensuing communication session. And, in addition to that Walsh-coded forward-link channel, the traffic channel also includes a corresponding Walsh-coded reverse-link channel, over which the mobile station transmits data to the base station. 
     b. Reverse-Link Transmission-Power Management 
     i. The Power Control Bit (PCB) and the Ratio E b /N t    
     In CDMA networks, the transmitting power of a mobile station on the reverse link of a traffic channel at any given moment is based on a number of factors, two of which are known as the power control bit (PCB) and the ratio E b /N t . The PCB is a bit ( 0  or  1 ) that the base station sends to the mobile station on the forward link at a high frequency, on the order of 800 times per second (i.e. once every 1.25 milliseconds (ms)). The mobile station repeatedly responsively adjusts its transmission power to the base station on the reverse link. Typically, if the base station sends a 0, the mobile station will decrease the power by a set decrement, such as 1 dB, whereas, if the base station sends a 1, the mobile station will increase the power by a set increment, which may also be 1 dB. Thus, using these numbers, the mobile station&#39;s reverse-link transmission power would change by plus or minus 1 dB every 1.25 ms. 
     Each such 1.25-ms cycle, a typical base station determines whether to transmit a PCB equal to 0 or 1 to a given mobile station by comparing (i) a signal-to-noise ratio that the base station computes for that mobile station with (ii) a stored threshold value for that signal-to-noise ratio that the base station maintains on a per-mobile-station basis. This ratio is generally known and referred to herein as E b /N t , while the threshold is referred to herein as the E b /N t  threshold. E b /N t  compares the strength at which the base station is receiving the reverse-link signal from the mobile station (E b  for “energy per bit”) with the strength at which the base station is receiving signals from all other sources on the frequency of the sector/carrier on which that mobile station is operating (N t  for “noise”). E b /N t , then, is a signal-to-noise ratio for the reverse-link part of the traffic channel. As stated, the base station typically computes E b /N t  at the same frequency at which it transmits the PCB, which again may be once every 1.25 ms. 
     Thus, in typical operation, for a given mobile station (and in fact for each mobile station that the base station is serving), every 1.25 ms, the base station compares the most recent computation of E b /N t  for that mobile station with the E b /N t  threshold for that mobile station. If E b /N t  exceeds the threshold, then the base station is receiving a strong enough signal from the mobile station, and thus it transmits a PCB of 0, causing the mobile station to reduce its reverse-link transmission power. If, on the other hand, the computed E b /N t  is less than the threshold, the base station is not receiving a strong enough signal, and thus it transmits a PCB of 1, causing the mobile station to increase its reverse-link power. Thus, the reverse-link power on the traffic channel typically stabilizes to a point that achieves an E b /N t  value (as measured at the base station) that is near the E b /N t  threshold. And this threshold can be changed during operation. 
     ii. Reverse-Link Frame Error Rate (RFER) 
     In CDMA networks, data is transmitted from the mobile station to the base station (and vice versa) in data units known as frames, which typically last 20 ms. Some frames received by the base station contain errors as a result of imperfect transfer from the mobile station, while some do not. The reverse-link frame error rate (RFER) is a ratio, computed on a per-mobile-station basis by the base station, of the number of error-containing frames that the base station receives from a given mobile station to the total number of frames that the base station receives from the given mobile station, over a given time period. Note that the RFER often also takes into account frames that are not received at all by the base station. And other things being more or less equal, the more power the mobile station uses to transmit to the base station, the lower the mobile station&#39;s RFER will be. 
     More particularly, at approximately the same frequency at which the base station is receiving reverse-link frames (i.e. once every 20 ms) from a given mobile station, the base station computes a RFER for that mobile station over some previous number of frames, which may be 20, 100, 200, or some other number. Thus, the base station essentially computes a RFER for some rolling window of previous frames. And each time the base station computes the RFER for that mobile station, the base station compares that computed value with a threshold: a sector/carrier-level parameter often referred to as the “RFER target,” which may be around 2%. 
     If the RFER for that mobile station exceeds the RFER target for the sector/carrier, the base station is receiving too many error-containing frames and/or missing too many frames from that mobile station, and thus the base station will responsively increase its E b /N t  threshold related to that mobile station. In the short term, this will result in the base station&#39;s computed E b /N t  for that mobile station falling below the increased threshold, which in turn will result in the base station repeatedly sending PCBs equal to 1 to the mobile station. This, in turn, will result in the mobile station increasing its reverse-link transmission power, which will then typically stabilize at a level that will result in the base station computing an E b /N t  for that mobile station that is close to the new, increased E b /N t  threshold that the base station is maintaining for that mobile station, and perhaps result in an acceptable RFER for that mobile station. 
     If, on the other hand, the RFER falls below the RFER target, the mobile station may be using excessive power for transmitting on the reverse-link—in essence, the base station may be receiving a signal from that mobile station that may be considered too strong, perhaps at the expense of that mobile station&#39;s battery life, and perhaps creating excessive noise from a single mobile station on the sector/carrier. If that situation holds for a specified period of time, the base station may decrease the E b /N t  threshold that the base station is maintaining for that mobile station, resulting in the base station&#39;s computed E b /N t  repeatedly exceeding the decreased threshold. This, in turn, will result in the base station repeatedly sending PCBs equal to 0 to the mobile station, which will result in the mobile station decreasing its reverse-link transmission power, which will then typically stabilize at a level that will result in the base station computing an E b /N t  that is very close to the new, decreased E b /N t  threshold. 
     Thus, the base station&#39;s repeated RFER calculation for the mobile station and comparison with the RFER target for the sector/carrier causes the base station to iteratively adjust its E b /N t  threshold corresponding to the mobile station. In turn, the base station&#39;s even-more-frequent calculation of E b /N t  and comparison with its current E b /N t  threshold for the mobile station causes the base station to iteratively send PCBs of 0 (for less power) or 1 (for more power) to the mobile station, which then causes the mobile station to adjust its reverse-link transmission power on the traffic channel. This entire back-and-forth calibration process is conducted in an attempt to keep the RFER calculated by the base station and associated with the mobile station at or below what is deemed to be an acceptable threshold, which again may be around 2%. 
     Note that different situations may present themselves on a given sector/carrier at different times. For one, the number of mobile stations using traffic channels can vary between just a few, such as 10, to a larger number, such as 30, and perhaps approach the upper bound of 61 (assuming RC3). And, as stated, the power that the mobile stations use for transmission to the base station can vary. In particular, variables such as terrain, weather, buildings, other mobile stations, other interference, and distance from the base station can affect the RFER that the base station experiences for a given mobile station, and thus the amount of power the mobile station uses on the reverse link. Using too much power can drain battery life, and it may sometimes be the case that a mobile station reaches its maximum transmission power and still cannot achieve an acceptable RFER, in which case it may not be able to communicate with the base station. 
     Note that, in some implementations, a ratio other than E b /N t  may be used. In particular, each mobile station, when operating on a traffic channel, may also transmit on the reverse-link on what is known as a reverse pilot channel. The base station may then compute a ratio known as E c /I o  for that mobile station, which would be a ratio comparing (a) the power level at which the base station is receiving the reverse pilot channel (“E c ” for “energy per chip”) and (b) the power level at which the base station is receiving all transmissions (“I o ”) on the frequency (sector/carrier) on which the mobile station is operating (including the reverse pilot channel). 
     The base station would then operate with respect to E c /I o  as described above with respect to E b /N t . That is, the base station would maintain an E c /I o  threshold for each mobile station, and repeatedly compare the measured E c /I o  with the E c /I o  threshold, and send PCBs equal to 0 or 1, causing the mobile station to either decrease or increase its reverse-link transmission power. The base station would also adjust the E c /I o  threshold as described above with respect to the E b /N t  threshold, in an effort to keep each mobile station at or just below the RFER target. 
     iii. Reverse Noise Rise (RNR) 
     As stated, in general, interference can be—and often is—present on the reverse link of a given sector/carrier. That is, on the given sector/carrier, a base station will receive transmissions not only from mobile stations that are operating on that sector/carrier, but will also often receive transmissions on that frequency from other mobile stations, other transmitting devices, and/or any other sources of interference on that frequency in that area. At a given moment, the sum total of what a base station is receiving on a given sector/carrier (i.e. a given frequency)—including transmissions from mobile stations operating on that sector/carrier, as well as from all other sources—is known as the “reverse noise” on that sector/carrier. 
     Quite frequently (e.g., once per frame (i.e. once every 20 ms)), base stations compute a value known as “reverse noise rise” (RNR) for a given sector/carrier, which is the difference between (i) the reverse noise that the base station is currently detecting on the sector/carrier and (ii) a baseline level of reverse noise for the sector/carrier. Thus, the base station computes how far the reverse noise has risen above that baseline. 
     For the baseline level, CDMA networks may use a value such as the lowest measurement of reverse noise on the sector/carrier in the previous 24 hours, or perhaps an average of the 24-hour lows over the previous week, or some other value. Incidentally, some networks, including Evolution Data Optimized (EV-DO) networks, may periodically use what is known as a silent interval, which is a coordinated time period during which mobile stations know not to transmit anything to the base station. The base station can then measure whatever else is out there. In that case, the baseline level would correspond to the amount of reverse noise when the sector/carrier is unloaded. And other reverse-link-noise levels could be used as a baseline. 
     Other things being more or less equal, the lower the RNR is at a given moment, the more favorable the RF environment is for communication between mobile stations and the base station at that time. Correspondingly, the higher the RNR, the less favorable the RF environment is. Also, a low RNR generally corresponds to a sector/carrier being lightly loaded, in other words that is supporting communications for a relatively low number of mobile stations. A high RNR, as one might expect, generally corresponds to a sector/carrier being heavily loaded, in other words that is supporting communications for a relatively high number of mobile stations. 
     SUMMARY 
     Methods and systems are provided for dynamic adjustment of the reverse-link frame-error-rate (RFER) target based on reverse-link RF conditions. In one aspect, an exemplary embodiment of the present invention may take the form of a method. In accordance with the method, a base station provides service to at least one mobile station on a carrier in a wireless coverage area using a first RFER target. The base station calculates a reverse noise rise (RNR) value for the carrier in the wireless coverage area, and then selects a second RFER target based at least in part on the calculated RNR value. The base station then provides service to at least one mobile station on the carrier in the wireless coverage area using the second RFER target. 
     These as well as other aspects and advantages will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments are described herein with reference to the following drawings, wherein like numerals denote like entities. 
         FIG. 1  is a simplified block diagram of a communication system, in accordance with exemplary embodiments; 
         FIG. 2  is a simplified block diagram of an example of correlation data, in accordance with exemplary embodiments; 
         FIG. 3  is a flowchart of a method, in accordance with exemplary embodiments; 
         FIG. 4  is a flowchart of a method, in accordance with exemplary embodiments; and 
         FIG. 5  is a table showing several exemplary situations, in accordance with exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     1. Overview 
     As presently contemplated, in exemplary embodiments, a base station will, on a given sector/carrier, dynamically adjust the RFER target in response to periodic calculations of RNR. Thus, if the base station determines that the sector/carrier has a relatively high RNR, the base station will increase (i.e. relax) the RFER target for that sector/carrier. This will tend to result in mobile stations decreasing transmission power on the reverse link. That, in turn, will tend to result in the sector/carrier having more capacity, albeit perhaps at a lesser quality of service. If, however, the base station determines that the sector/carrier has a relatively low RNR, the base station will decrease (i.e. make more strict) the RFER target. This will tend to result in mobile stations increasing transmission power on the reverse link. That, in turn, will tend to result in a higher quality of service (e.g. better voice quality), albeit perhaps at a lower capacity. 
     As explained, a relatively low RNR may correspond to a sector/carrier being lightly loaded with mobile stations, while a relatively high RNR may correspond to a sector/carrier being heavily loaded with mobile stations. Thus, one way to characterize the present invention is that the RFER target is being made dynamically responsive to loading conditions. And metrics of sector/carrier load other than RNR can be used—alone or in combination with RNR or each other—to dynamically adjust the RFER target for the sector/carrier. Some load-metric candidates include Walsh-code occupancy and paging-channel-timeslot occupancy, which are explained herein, any other load metrics, and any combination of these. Using RNR is preferred, however, since both it and RFER are related to reverse-link transmission power. 
     As also explained, a relatively low RNR could correspond to favorable RF conditions on a sector/carrier, while a relatively high RNR could correspond to unfavorable RF conditions. As such, another way to characterize the present invention is that the RFER target is being made dynamically responsive to RF conditions. And the loading-conditions and RF-conditions views are not mutually exclusive. That is, RNR generally reflects some of each, and each can certainly contribute to situations where it would be advantageous to adjust the RFER target. 
     In some embodiments, a threshold value of RNR may be used to dynamically adjust the RFER target. If the base station determines that RNR is above the threshold, the base station may increase (relax) the RFER target for the sector/carrier, such that mobile stations will likely then reduce their transmission power on the sector/carrier, bringing RNR back down. If, on the other hand, the base station determines that RNR is below the threshold, the base station may decrease (make more strict) the RFER target for the sector/carrier, such that mobile stations will likely then increase their transmission power on the sector/carrier, which will provide a higher quality of service, but may reduce capacity and eventually push RNR back up. 
     In other embodiments, more than two ranges—or more than one threshold value—of RNR may be used. For example, the base station may maintain a table of RNR ranges correlated with various values for the RFER target. Upon calculating RNR on the sector/carrier, the base station may determine into which range the calculated value falls, and set the RFER target for the sector/carrier equal to the RFER-target value corresponding to that range. In other embodiments, two RNR thresholds may be used: if RNR is below the lesser of the two thresholds, the base station may decrease the RFER target; if RNR is above the greater of the two thresholds, the base station may increase the RFER target; if RNR is between the thresholds, the base station may leave the RFER target unmodified. And other examples are possible. 
     Furthermore, it may be taken into consideration how frequently it would be advisable to change the RFER target for a given sector/carrier. Generally stated, the base station should change the RFER target often enough to be dynamically responsive to RNR conditions on the sector/carrier, but not so often so as to inefficiently consume resources such as processing power, memory, battery power, time, and/or other resources of the base station and/or the mobile stations. For example, in a situation where RNR is hovering near a threshold value or boundary between RNR ranges, the base station could guard against switching the RFER target every time RNR crosses the threshold or boundary value. 
     Thus, the base station could have a limit as to how often it would change the RFER target, such as once every 10 seconds, 30 seconds, minute, etc. If one of those time periods—or some other time period—were used as the interval, then the base station could, once per interval, base its decision on the most recent measurement of RNR, a measurement near the halfway point of such an interval, an average of several samples taken over the interval, or perhaps an average of all measurements taken over the interval. And other possibilities exist as well, without deviating from the scope and spirit of the present invention. 
     Moreover, while embodiments of the invention are described herein for the most part with respect to a single base station and, more particularly, with respect to a single sector/carrier, this mode of explanation is for clarity and not by way of limitation. Thus, the present invention could be implemented in all or any subset of the base stations of a given wireless network, and in all or any subset of the sectors and carriers of a given wireless network as well. 
     The present invention, then, makes the RFER target dynamically responsive to loading and RF conditions on a sector/carrier. Preferably, the RFER target is dynamically responsive to periodic calculations of RNR. Among other advantages, the invention improves service quality at the expense of capacity in situations where capacity is less of a concern, and improves capacity at the expense of service quality in situations where capacity is more of a concern. 
     2. Exemplary Architecture 
     a. Exemplary Communication System 
       FIG. 1  is a simplified block diagram of a communication system, in accordance with exemplary embodiments. It should be understood that this and other arrangements described herein are set forth only as examples. Those skilled in the art will appreciate that other arrangements and elements (e.g., machines, interfaces, functions, orders, and groupings of functions, etc.) can be used instead, and that some elements may be omitted altogether. Further, many of the elements described herein are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, and in any suitable combination and location. Various functions described herein as being performed by one or more entities may be carried out by hardware, firmware, and/or software. Various functions may be carried out by a processor executing instructions stored in memory. 
     As shown in  FIG. 1 , a communication system  100  includes a mobile station (MS)  102 , a base transceiver station (BTS)  104 , a base station controller (BSC)  106 , a mobile switching center (MSC)  108 , a public switched telephone network (PSTN)  110 , a packet data serving node (PDSN)  112 , and a packet-data network (PDN)  114 . And additional entities could be present as well. For example, there could be additional mobile stations in communication with BTS  104 ; furthermore, there could be additional entities in communication with PSTN  110  and/or PDN  114 . Also, there could be one or more devices and/or networks making up at least part of one or more of the communication links. For example, there could be one or more routers, switches, or other devices or networks on the link between PDSN  112  and PDN  114 . 
     Mobile station  102  may be any mobile device arranged to carry out the mobile-station functions described herein. As such, mobile station  102  may include a user interface, a wireless-communication interface, a processor, and data storage comprising instructions executable by the processor for carrying out those mobile-station functions. The user interface may include buttons, a touch-screen, a microphone, and/or any other elements for receiving inputs, as well as a speaker, one or more displays, and/or any other elements for communicating outputs. 
     The wireless-communication interface may comprise an antenna and a chipset for communicating with one or more base stations over an air interface. As an example, the chipset could be one that is suitable for CDMA communication. The chipset or wireless-communication interface in general may also be able to communicate with other types of networks and devices, such as IS-856 Evolution Data Optimized (EV-DO) networks, Wi-Fi (IEEE 802.11) networks, Bluetooth devices, and/or one or more additional types of wireless networks. The processor and data storage may be any suitable components known to those of skill in the art. As examples, mobile station  102  could be or include a cell phone, a PDA, a computer, a laptop computer, a hybrid CDMA/EV-DO device, and/or a multi-mode cellular/Wi-Fi device. 
     BTS  104  may be any network element arranged to carry out the BTS functions described herein. As such, BTS  104  may include a communication interface, a processor, and data storage comprising instructions executable by the processor to carry out those BTS functions. The communication interface may include one or more antennas, chipsets, and/or other components for providing one or more CDMA coverage areas such as cells and sectors, for communicating with mobile stations, such as mobile station  102 , over an air interface. The communication interface may also include one or more wired and/or wireless interfaces for communicating with at least BSC  106 . As an example, a wired Ethernet interface may be included. 
     BSC  106  may be any network element arranged to carry out the BSC functions described herein. As such, BSC  106  may include a communication interface, a processor, and data storage comprising instructions executable by the processor to carry out those BSC functions. The communication interface may include one or more wired and/or wireless interfaces for communicating with at least BTS  104 , MSC  108 , and PDSN  112 . In general, BSC  106  functions to control one or more BTSs such as BTS  104 , and to provide one or more BTSs such as BTS  104  with connections to devices such as MSC  108  and PDSN  112 . Note that the combination of BTS  104  and BSC  106  may be considered a base station. 
     However, BTS  104  or BSC  106  could, taken alone, be considered a base station as well. Furthermore, a base station may be considered to be either or both of those devices, and perhaps make use of one or more functions provided by MSC  108 , PDSN  112 , and/or any other entity, without departing from the scope or spirit of the present invention. 
     Referring to BTS  104  as a base station for illustration, BTS  104  may maintain one or more sets of data for use in carrying out exemplary embodiments.  FIG. 2  depicts one possible set of such data. In particular,  FIG. 2  depicts correlation data  200 , which generally (i.e. in each row of the table) correlates ranges of RNR values with RFER-target values. Thus, a low range of RNR is correlated with a RFER_TARGET_ 1 , a moderate range of RNR is correlated with a RFER_TARGET_ 2 , and a high range of RNR is correlated with a RFER_TARGET_ 3 . 
     Note that, while three RNR ranges and associated RFER-target values are depicted in  FIG. 2 , any number of correlations could be used. Furthermore, these ranges and RFER targets could take on any values deemed suitable for a particular implementation. As one example, the low range could be RNR values that are less than 3 dB, the moderate range could be RNR values between 3 dB and 5 dB, and the high range could be RNR values greater than 5 dB. Further to this example, RFER_TARGET_ 1  could be 1%, RFER_TARGET_ 2  could be 2%, and RFER_TARGET_ 3  could be 3%. And many other examples are possible as well. 
     Returning to  FIG. 1 , MSC  108  may be any networking element arranged to carry out the MSC functions described herein. As such, MSC  108  may include a communication interface, a processor, and data storage comprising instructions executable by the processor to carry out those MSC functions. The communication interface may include one or more wired and/or wireless interfaces for communicating with at least BSC  106  and PSTN  110 . In general, MSC  108  functions as a switching element between PSTN  110  and one or more BSCs such as BSC  106 , facilitating communication between mobile stations and PSTN  110 , which may be the well-known public switched telephone network. 
     PDSN  112  may be any networking element arranged to carry out the PDSN functions described herein. As such, PDSN  112  may include a communication interface, a processor, and data storage comprising instructions executable by the processor for carrying out those PDSN functions. The communication interface may include one or more wired and/or wireless interfaces for communicating with at least BSC  106  and PDN  114 . In general, PDSN  112  functions as a network access server between PDN  114  and BSCs such as BSC  106 , facilitating packet-data communication between mobile stations and PDN  114 . 
     PDN  114  may include one or more wide area networks, one or more local area networks, one or more public networks such as the Internet, one or more private networks, one or more wired networks, one or more wireless networks, and/or one or more networks of any other type. Devices in communication with PDN  114  may exchange data using a packet-switched protocol such as the Internet Protocol (IP), and may be identified by an address such as an IP address. 
     3. Exemplary Operation 
     a. A First Exemplary Method 
       FIG. 3  depicts a flowchart of an exemplary method, in accordance with an exemplary embodiment. As shown in  FIG. 3 , method  300  begins at step  302 , when BTS  104  provides service to at least one mobile station on a carrier in a wireless coverage area using a first RFER target. At step  304 , BTS  104  calculates an RNR value for the carrier in the wireless coverage area. At step  306 , BTS  104  selects a second RFER target based at least in part on the calculated RNR value. At step  308 , BTS  104  provides service to at least one mobile station on the carrier in the wireless coverage area using the second RFER target. 
     These steps are explained in the following subsections. And it should be noted that, although method  300  is described as being carried out by BTS  104 , this is not required. In some embodiments, method  300  may be carried out by BSC  106 , or perhaps by a combination of BTS  104  and BSC  106 . In general, method  300  could be carried out by any one or any combination of the network elements described herein, or any other network element(s). 
     i. Provide Service to Mobile Stations Using First RFER Target 
     At step  302 , BTS  104  provides service to mobile station  102  on a carrier in a wireless coverage area using a first RFER target. Note that, typically, BTS  104  will provide service to multiple mobile stations, perhaps on multiple carriers, in the given wireless coverage area (and, for that matter, in multiple coverage areas), and that mobile station  102  would simply be an exemplary one of these mobile stations. Furthermore, the service provided by BTS  104  may be or include CDMA service, perhaps in conformance with one or more well-known industry standards such as IS-95 and IS-2000, both of which are incorporated by reference herein. 
     And the coverage area could be a cell or sector. For the balance of the description of method  300 , for purposes of illustration only, one exemplary carrier in one exemplary sector will be described, and referred to, as above, as a sector/carrier. Furthermore, as an example, the first RFER target could be 2%, though other values could be used. And, in general, providing service to at least one mobile station on the carrier in the wireless coverage area using a given RFER target may involve calculating various RFERs for various mobile stations, and comparing those RFERs with the given RFER target. 
     If BTS  104  calculates a RFER for a given mobile station that is higher than the given RFER target, BTS  104  will typically instruct that given mobile station to increase transmission power on the reverse link (such as by increasing an E b /N t  threshold or E c /I o  threshold and by sending PCBs equal to 1), in an effort to bring its RFER back down to an acceptable level. In some implementations, if BTS  104  calculates a RFER for a given mobile station that is lower than the given RFER target, BTS  104  will instruct that mobile station to decrease transmission power on the reverse link (such as by decreasing an E b /N t  threshold or E c /I o  threshold and by sending PCBs equal to 0), which will tend to allow that mobile station&#39;s RFER to go back up. 
     ii. Calculate RNR 
     At step  304 , BTS  104  calculates an RNR value for the sector/carrier. This may involve, as explained above, BTS  104  measuring a current level of noise on the reverse link of the sector/carrier, and then calculating the RNR value as the difference between that current level of noise on the reverse link and a baseline level of noise on the reverse link. And, as also explained above, this baseline level could correspond to a minimum amount of reverse noise measured in the previous 24 hours, an average of 24-hour-minimum levels of reverse noise over a previous 7-day period, an amount of noise present when the wireless coverage area is unloaded, or some other value. As a general matter, step  304  could involve calculating an average of multiple RNR values calculated during a preceding time interval. 
     iii. Select Second RFER Target Based at Least in Part on RNR 
     At step  306 , BTS  104  selects a second RFER target based at least in part on the calculated RNR value from step  304 . In one embodiment, step  306  may involve BTS  104  comparing the calculated RNR with a threshold value for RNR. As one example, the threshold value could be 5 dB or thereabouts. If the calculated RNR is less than the threshold RNR, BTS  104  may select the second RFER target to be less than the first RFER target. This will tend to increase mobile stations&#39; reverse-link transmission power and drive RNR back up. If, on the other hand, the calculated RNR is greater than or equal to the threshold RNR, BTS  104  may select the second RFER target to be greater than the first RFER target. This will tend to decrease mobile stations&#39; transmission power on the reverse link, and drive RNR back down. 
     And BTS  104  may have particular increments that it uses in selecting the second RFER target, depending on the comparison of the calculated RNR to the threshold RNR. Thus, if the calculated RNR is less than the threshold RNR, BTS  104  may select the second RFER target to be 1% less than the first RFER target. If, on the other hand, the calculated RNR is greater than or equal to the threshold RNR, BTS  104  may select the second RFER target to be 1% greater than the first RFER target. Thus, if the first RFER target were 2%, the second may end up being either 1% or 3%. And other increments are certainly possible as well. And, obviously, certain limitations may be accounted for as well, such as not going to or below 0%, and perhaps not going above a certain upper bound as well. 
     In other embodiments, multiple RNR thresholds may be considered. For example, BTS  104  may compare the calculated RNR with both a lower RNR threshold and an upper RNR threshold, where the lower threshold is less than the upper threshold. If the calculated RNR is less than the lower threshold, BTS  104  may select the second RFER target to be less than the first RFER target. This is depicted in situation  508  in  FIG. 5 , which in general depicts three exemplary scenarios  506 ,  508 , and  510  in accordance with exemplary embodiments. Each scenario has an input  502  (to the left of dashed line  512 ) that pertains to the comparison of a calculated RNR value with one or more RNR thresholds. Each scenario further has an output  504  (to the right of the dashed line  512 ) that provides an exemplary decision with respect to how to adjust the RFER target for the sector carrier. 
     If, however, the calculated RNR is both (i) greater than or equal to the lower threshold and (ii) less than or equal to the upper threshold (situation  510  in  FIG. 5 ), then BTS  104  may select the second RFER target to be equal to the first RFER target. That is, BTS  104  may leave the RFER target for the sector/carrier unmodified. Finally, if the calculated value of RNR is greater than the upper threshold (situation  506  in  FIG. 5 ), BTS  104  may select the second RFER target to be a value that is greater than the first RFER target. 
     Note that explicit comparison with one of the thresholds could include implicit comparison with the other. That is, for example, a determination that the calculated RNR is less than the lower threshold obviates the need to explicitly compare the calculated RNR with the upper threshold. Again, any RFER-target increments could be used. And, as examples, the lower threshold could be approximately 3 dB, while the upper threshold could be approximately 5 dB, though other values could clearly be used. 
     In other embodiments, BTS  104  may maintain data that correlates each of multiple RNR ranges with a respective RFER-target value. For example, BTS  104  may maintain (which may encompass storing and/or having access to) data such as correlation data  200  of  FIG. 2 . BTS  104  may thus determine that the calculated RNR falls within a particular one of the RNR ranges, and responsively select the second RFER target to be equal to whichever RFER-target value is associated with that particular RNR range. As one example, BTS  104  may determine that the calculated RNR falls within the low range, and responsively select RFER_TARGET_ 1 . 
     iv. Provide Service to Mobile Stations Using Second RFER Target 
     At step  308 , BTS  104  provides service to mobile stations, such as mobile station  102 , on the sector/carrier using the second RFER target, which was selected in step  306 . As described herein, this may involve determining various RFERs for mobile stations such as mobile station  102 , comparing those RFERs with the second RFER target, and instructing the mobile stations to adjust their reverse-link transmission power accordingly. 
     v. Generally 
     In general, it is contemplated that method  300  will be carried out repeatedly, so as to make the sector/carrier&#39;s RFER target dynamically responsive to RNR on the sector/carrier. Thus, method  300  may be carried out once every 10 seconds, 30 seconds, minute, or any other suitable time interval, on substantially a continuous basis. As such, starting with the second such time interval, the first RFER target of step  302  would be equal to the second RFER target of the previous time interval, and operation would continue iteratively from there. 
     And for a given time interval, step  304  may involve calculating RNR at the end of the time interval. In other embodiments, step  304  may involve calculating RNR approximately halfway through the time interval. And in still other embodiments, step  304  may involve calculating an average of multiple RNR values calculated during the time interval. And other possibilities exist as well. 
     b. A Second Exemplary Method 
       FIG. 4  is a flowchart of an exemplary method, in accordance with an exemplary embodiment. As with method  300  of  FIG. 3 , method  400  of  FIG. 4  is described as being carried out by a BTS, and by BTS  104  in particular, though this is not required. Method  400  could be carried out by any one or any combination of the entities described as possibilities for carrying out method  300 , and/or any other entity or entities. And method  400  is similar to method  300 , and thus is not described in as great of detail. 
     As shown in  FIG. 4 , method  400  begins at step  402 , when BTS  104  provides service to one or more mobile stations on a carrier in a wireless coverage area. At step  404 , BTS  104  determines whether the current level of load on the carrier is low or high. At step  406 , if the current level of load is low, BTS  104  decreases the RFER target for the carrier. At step  408 , if the current level of load is high, BTS  104  increases the RFER target for the carrier. 
     Note that, in step  404 , the determination as to whether the current level of load is low or high may involve consideration of any one or any combination of sector/carrier-load metrics. One such metric is RNR, as discussed herein. In particular, BTS  104  may calculate an RNR value and compare that calculated value with a threshold value. If the calculated RNR value is less than the threshold RNR value, BTS  104  may determine that the current level of load on the carrier is low. If, on the other hand, the calculated RNR value is greater than or equal to the threshold RNR value, BTS  104  may determine that the current level of load is high. And, as described herein, comparison with more than one threshold could be carried out as well. 
     Another load metric that could be used is Walsh-code occupancy, which may be computed as a ratio of (i) the number of Walsh codes currently assigned to mobile stations for traffic channels and (ii) the total number of Walsh codes generally available for traffic channels on the sector/carrier. Another possible metric is paging-channel-timeslot occupancy, which would be a similar ratio, though specifically pertaining to the finite number of timeslots available each time BTS  104  transmits the paging channel, as is known in the relevant art. And any other load metric or combination of load metrics could be used as well. 
     4. Conclusion 
     Various exemplary embodiments have been described above. Those skilled in the art will understand, however, that changes and modifications may be made to those examples without departing from the scope of the claims.