Abstract:
This description describes examples of performing reverse link power control in a mobile network having a plurality of first modem devices that receive and transmit signals to wireless access terminals (ATs) and a second device in communication with the plurality of first devices. One of the first devices derives a first power control threshold (PCT) value for reverse link power of one of the access terminals (ATs) and the second device derives a second power control threshold (PCT) value for reverse link power of the one of the ATs. The second power control threshold (PCT) value is transmitted using a data traffic path and either the first PCT value or the second PCT value is selected.

Description:
BACKGROUND  
       [0001]     This description relates to reverse link power control.  
                                         ACRONYMS AND ABBREVIATIONS                                1x-EVDO   Evolution Data only, CDMA2000 family standard           for high speed data only wireless internet access       AN   Access Network       API   Application Programmable Interface       ASIC   Application Specific Integrated Circuit       AT   Access Terminal       BIO-SC   Basic Input/Output - System Controller       CDMA   Code-Division Multiple Access       CPU   Central Processing Unit       CSM5500 ASIC   Qualcomm Inc. modem ASIC       CSM5500 Drivers   Qualcomm Inc. modem ASIC Driver and API       FCS   Frame Check Sequence       FER   Frame Error Rate       FLM   Forward Link Modem       IP   Internet Protocol       PCT   Power Control Threshold       PCT RNi     Power Control Threshold computed at ith RN       PCT RNC     Power Control Threshold computed at RNC       RAN   Radio Access Network       RL   Reverse Link or uplink - from mobile to base station.       RLILPC   Reverse Link Inner-Loop Power Control       RLM   Reverse Link Modem       RLOLPC   Reverse Link Outer-Loop Power Control       RLOLPC-RN   Power Control Algorithm running on RN       RLOLPC-RNC   Power Control Algorithm running on RNC       RN   Radio Node or Base Station       RN-BIO-SC   Radio Node BIO-SC Card or module       RNC   Radio Network Controller       RNSM   Radio Network Serving Module       RPC   Reverse Power Control       RTCHMO   Reverse Traffic Channel MAC Object       SDU   Selection and Distribution Unit       SINR   Signal-to-Interference Ratio (E b /I t )                  
 
         [0002]     Capacity of a cellular system represents the total number of mobile users (access terminals or ATs) that can be supported by the system. Capacity can be an important factor for cellular service providers, since it directly impacts revenue. CDMA wireless communications systems offer improved capacity and reliable communications for cellular and PCS systems.  
         [0003]     In a CDMA system, each AT transmit signal utilizes a different pseudo random sequence signal that appears as noise to other ATs. This enables many ATs to transmit on the same frequency. However, each AT&#39;s transmitted signal contributes to interference to the transmitted signal of all other users. Thus, the total number of users supported by the system is limited by interference. Therefore, reducing the amount of interference in a CDMA wireless communications system increases capacity.  
         [0004]     A typical problem in a CDMA cellular environment is the near/far problem. This entails the scenario where the transmit power of an AT near the RN may drown out an AT which is far from the RN. This is effectively mitigated by controlling the transmit power of each AT via power control scheme implemented by the access network (AN). AN continuously commands each AT to increase or decrease its transmit power to keep them all transmitting at the minimal power required to achieved the configured error rate for the operating data rate and maintain the overall balance of the power while reducing the interference in the area of coverage.  
         [0005]     In a CDMA 1x-EVDO system (see e.g., CDMA2000 High Data Rate Packet Data Air Interface Specification, 3GPP2 C.S0024, Version 4.0, Oct. 25, 2002), the reverse link operates in CDMA and hence reverse link power control is needed. The reverse link power control comprises of an open-loop power control (also called autonomous power control) and closed-loop power control. Open-loop power control is implemented in an AT, based on the received pilot-power of an RN. Closed-loop power control includes inner loop power control and outer loop power control, both of which are performed by the access network. Typical operation of a closed loop power control can be found in textbooks (see e.g., Vijay K. Garg, IS-95 CDMA and CDMA2000 Cellular/PCS Systems Implementation, Chapter 10, Prentice Hall, 1999, R. Steele. Mobile Radio Communications. Pentech Press, London, England, 1992, and Rashid A. Attar and Eduardo Esteves, A Reverse Link Outer-Loop Power Control Algorithm for CDMA2000 1xEV Systems, Proceedings of ICC, April 2002). Also, additional details can be found in e.g., U.S. Pat. No. 6,633,552, titled Method And Apparatus For Determining The Closed Loop Power Control Set Point In A Wireless Packet Data Communication System, and issued on Oct. 14, 2003, U.S. Pat. No. 6,507,744, titled Outer Loop Power Control Method During A Soft Handoff Operation, and issued on Jan. 14, 2003, and U.S. Pat. No. 5,884,187, titled Outer Loop Power Control Method During A Soft Handoff Operation, and issued on Mar. 16, 1999. A typical implementation is now described.  
         [0006]      FIG. 1  illustrates a system  100  implementing the basic closed loop power control operation. In closed loop power control, power adjustment is done at an AT  105  in accordance with the power control commands received from an RN  110  (also referred to as a base station  110 ). RN  110  sends up/down commands to each active AT (e.g.,  105 ) to ensure that the AT transmit signal is received at the RN  110  at the lowest possible power required for the RN  110  to receive the data correctly at the operating rate.  
         [0007]     In a reverse link inner-loop power control (RLILPC) mechanism  115 , the reverse link signal to the interference-noise ratio (SINR) is continuously and frequently measured at a modem receiver of RN 110 . These frequent measurements track rapid channel variations of the link between the AT  105  and the RN  110  and facilitate accurate power control even when the AT 105 is in a deep fade. This measured of SINR is compared to a threshold value called ‘power control threshold’ (PCT). If the measured value is greater than PCTmax (=PCT+PCTDelta), the RPC bit is cleared. If the measured value is less than PCTmin (=PCT-PCTDelta), RPC bit is set. PCTDelta is a small value that provides an interval around the PCT. If the PCT is within this interval, the RPC bit status is unchanged from the previous value. Setting the RPC bits (‘up decisions’) commands AT  105  to increase its transmit power by a pre-determined step size, say ‘x’ dB. Clearing RPC bits (‘down decisions’) commands the AT  105  to decrease its transmit power by ‘x’ dB. The step size is negotiated a priori between RN  110  and AT  105 .  
         [0008]     Frame Error Rate (FER) is defined as a ratio of the bad frames to the total number of frames received by the RN  110 . A frame with correct physical layer frame check sequence (FCS) is defined to be a good frame. In 1x-EVDO, the physical layer cyclic redundancy code (CRC) can be used to determine good or bad frames. In a reverse link closed outer-loop power control (RLOLPC) algorithm  120 , the PCT is adaptively adjusted such that the configured target FER is achieved and maintained for the duration of the connection. (A target reverse link FER of 1% is considered typical for wireless networks). The RLOLPC algorithm  120  is implemented in a RNC  125 .  
         [0009]     It should be noted that there is another parameter beside FCS that is used in the voice application in CDMA system. This parameter is called the quality metric, which is an indication of how “bad” the bad frame is. For voice, it may be beneficial to play out a bad packet in order to maintain the perception of a good voice quality. Therefore, even the bad packets are still sent to the RNC  125  from the RN  110  with the marking for a correct FCS and a quality metric. It&#39;s up to the RNC  125  to determine if the quality metric meets the criteria for the packet to be used even when the FCS is incorrect.  
         [0010]     Typical operation of the RLOLPC algorithm  120  is described now. Upon reception of a RL frame with bad FCS, PCT is increased by a pre-set large value (e.g., 0.5 dB), which is termed a good frame PCT Delta. Upon reception of a RL frame with good FCS, PCT is decreased by a pre-set small value (e.g., 0.5 dB), which is termed a bad frame PCT Delta. Given the values of RL FER and the good frame PCT Delta, the bad frame PCT Delta value is computed as follows:  
         [0011]     Bad Frame PCT Delta=Good Frame PCT Delta (1−RL FER)/RL FER (Note that this same equation can be used to compute the good frame PCT Delta given the values of RL FER and the bad frame PCT Delta.) Before a connection establishment, or if there is no data on a RL, the PCT is set to a pre-set high value to facilitate rapid reverse link acquisition. A new value of the PCT is computed upon reception of each good/bad RL frame and an updated PCT is input into the RN modem receiver and to the RLILPC algorithm  115 .  
         [0012]      FIG. 2  illustrates an example system  200 , in which AT  105  is in a L-way soft hand-off (i.e., AT  105  is communicating with L RNs, e.g., RN 1 ,  110 , RN 2    205 , and RN L    210 , at the same time). The selection and distribution unit (SDU) (not shown) at the RNC  125  determines which received frame from all the different ‘legs’ should be used. In addition it determines if correct or incorrect received frame indication needs to be send to the RLOLPC algorithm  120  on each frame boundary. The RLOLPC algorithm  120  uses this information to compute the overall PCT for the AT  105 . This PCT value is sent to all L RNs involved in the soft hand-off.  
       SUMMARY OF INVENTION  
       [0013]     In one aspect, there is a method of performing reverse link power control in a mobile network having a plurality of first modem devices that receive and transmit signals to wireless access terminals (ATs) and a second device in communication with the plurality of first devices. The method includes transitioning execution between a first and a second loop to control reverse link power of one of the ATs, the transition being based on a state of a connection. The first control loop executes at one of the first devices and the second loop executes at the second device.  
         [0014]     Other examples can include one or more of the following features. The transitioning can include synchronizing between the first control loop and the control loop based on a change of the state. The change of the state of the connection can include transitioning from the connection not in handoff to the connection in soft handoff. The method can include transmitting to the second control loop a value for a power control threshold calculated by the first control loop. The transmitting can include transmitting the value for the power control threshold during transmission of handoff-related data. The method can include deriving a power control threshold using the first or second control loop.  
         [0015]     The method can include generating, by the one of the first devices, an indicator representing quality of a signal received from the one of the ATs, and calculating a power control threshold using the indicator. The method can include preventing transmission of a packet from the one of the first devices to the second device if the packet is associated with a bad indication. The method can include transmitting the bad indication to the second device. The method can include determining good or bad indication of a packet using a cyclic redundancy code (CRC) associated with the packet. The state of the connection can include the connection not in handoff, the connection in softer handoff, or the connection in soft handoff. The method can include communicating between the first devices and the second device using Internet Protocol (IP) or asynchronous transfer mode (ATM).  
         [0016]     In another aspect, there is a method of performing reverse link power control in a mobile network having a plurality of first modem devices that receive and transmit signals to wireless access terminals (ATs) and a second device in communication with the plurality of first devices. The method includes deriving, by one of the first devices, a first power control threshold (PCT) value for reverse link power of one of the access terminals (ATs) and deriving, by the second device, a second power control threshold (PCT) value for reverse link power of the one of the ATs. The method also includes transmitting the second power control threshold (PCT) value using a data traffic path and selecting the first PCT value or the second PCT value.  
         [0017]     Other examples can include one or more of the following features. The transmitting can include transmitting using User Datagram Protocol or Generic Route Encapsulation protocol. The transmitting can include transmitting the second power control threshold (PCT) value based on a state of a connection. The state of the connection can include the connection in soft handoff. The second PCT value can be selected when the second PCT value is received at the one of the first devices. The first PCT value can be selected when a connection is not in handoff or a connection is in softer handoff. The second PCT value can be selected when a connection is in soft handoff.  
         [0018]     The method can include generating, by the one of the first devices, an indicator representing quality of a signal received from the one of the ATs, and calculating the first PCT and the second PCT using the indicator. The method can include preventing transmission of a packet from the one of the first devices to the second device if the packet is associated with a bad indication; and transmitting the bad indication to the second device. The method can include determining good or bad indication of a packet using a cyclic redundancy code (CRC) associated with the packet. The method can include communicating between the first devices and the second device using Internet Protocol (IP) or asynchronous transfer mode (ATM).  
         [0019]     In another aspect, there is a system for performing reverse link power control in a radio access network (RAN). The system includes a first modem device and a second device in communication with the first device over a network. The first modem device receives and transmits signals to a wireless access terminal (AT). The first device is configured to execute a first loop to control reverse link power of the AT based on a first state of a connection. The second device is configured to execute a second loop to control reverse link power of the AT based on a second state of the connection and to synchronize the second loop with the first loop during a transition from the first state to the second state.  
         [0020]     Other examples can include one or more of the following features. The first state of the connection can include the connection not in handoff or the connection in softer handoff. The second state of the connection can include the connection in soft handoff. The second device can be configured to obtain a power control threshold calculated by the first control loop. The second device can be configured to obtain a power control threshold calculated by the first control loop during transmission of handoff-related data. The first device can be configured to derive a power control threshold using the first control loop.  
         [0021]     The first device can be configured to generate an indicator representing quality of a signal received from the AT and to calculate a power control threshold using the indicator. The first device can be configured to prevent transmission of a packet from the first device to the second device if the packet is associated with a bad indication and to transmit the bad indication to the second device in place of the packet. The first device can be configured to determine good or bad indication of a packet using a cyclic redundancy code (CRC) associated with the packet. The first device and the second device can communicate using Internet Protocol (IP) or asynchronous transfer mode (ATM).  
         [0022]     In another aspect, there is a system for performing reverse link power control. The system includes a first modem device and a second device in communication with the first device over a network. The first modem device receives and transmits signals to a wireless access terminal (AT). The first device is configured to derive a first power control threshold (PCT) value for reverse link power of an AT. The second device is configured to derive a second power control threshold (PCT) value for reverse link power of the AT and to transmit the second power control threshold (PCT) value to the first device using a data traffic path.  
         [0023]     Other examples can include one or more of the following features. The first device can be configured to transmit the second power control threshold (PCT) value to the first device over the data traffic path using User Datagram Protocol or Generic Route Encapsulation protocol. The first device can be configured to select the first PCT value or the second PCT value. The first device can be configured to select the second PCT value when the second PCT value is received at the first device. The first device can be configured to select the first PCT when the connection is not in handoff or the connection is in softer handoff. The first device can be configured to select the second PCT value when the connection is in soft handoff.  
         [0024]     The first device can be configured to generate an indicator representing quality of a signal received from the AT and to calculate the first PCT using the indicator. The first device can be configured to prevent transmission of a packet from the one of the first devices to the second device if the packet is associated with a bad indication and to transmit the bad indication to the second device. The first device can be configured to determine good or bad indication of a packet using a cyclic redundancy code (CRC) associated with the packet. The first device and the second device can communicate using Internet Protocol (IP) or asynchronous transfer mode (ATM).  
         [0025]     In another aspect, there is a computer program product, tangibly embodied in an information carrier, for performing reverse link power control in a mobile network having a plurality of first modem devices that receive and transmit signals to wireless access terminals (ATs) and a second device in communication with the plurality of first devices. The computer program product includes instructions being operable to cause data processing apparatus to transition execution between a first and a second loop to control reverse link power of one of the ATs, where the transition is based on a state of a connection, and the first control loop executes at one of the first devices and the second loop executes at the second device.  
         [0026]     Other examples can include one or more of the following features. The computer program product of can include instructions operable to cause the data processing apparatus to synchronize between the first control loop and the control loop based on a change of the state. The change of state of the connection can include transitioning from the connection not in handoff to the connection in soft handoff.  
         [0027]     The computer program product can include instructions operable to cause the data processing apparatus to transmit to the second control loop a value for a power control threshold calculated by the first control loop. The computer program product can include instructions operable to cause the data processing apparatus to transmit the value for the power control threshold during transmission of handoff-related data.  
         [0028]     The computer program product can include instructions operable to cause the data processing apparatus to derive a power control threshold using the first or second control loop. The computer program product can include instructions operable to cause the data processing apparatus to generate, by the one of the first devices, an indicator representing quality of a signal received from the one of the ATs, and calculate a power control threshold using the indicator. The computer program product can include instructions operable to cause the data processing apparatus to prevent transmission of a packet from the one of the first devices to the second device if the packet is associated with a bad indication, and transmit the bad indication to the second device. The computer program product can include instructions operable to cause the data processing apparatus to determine good or bad indication of a packet using a cyclic redundancy code (CRC) associated with the packet. The state of the connection can include the connection not in handoff, the connection in softer handoff, or the connection in soft handoff. The computer program product can include instructions operable to cause the data processing apparatus to communicate between the first devices and the second device using Internet Protocol (IP) or asynchronous transfer mode (ATM).  
         [0029]     In another aspect, there is a computer program product, tangibly embodied in an information carrier, for performing reverse link power control in a mobile network having a plurality of first modem devices that receive and transmit signals to wireless access terminals (ATs) and a second device in communication with the plurality of first devices. The computer program product includes instructions being operable to cause data processing apparatus to derive, by one of the first devices, a first power control threshold (PCT) value for reverse link power of one of the access terminals (ATs), derive, by the second device, a second power control threshold (PCT) value for reverse link power of the one of the ATs, transmit the second power control threshold (PCT) value using a data traffic path, and select the first PCT value or the second PCT value.  
         [0030]     Other examples can include one or more of the following features. The computer program product can include instructions operable to cause the data processing apparatus to transmit using User Datagram Protocol or Generic Route Encapsulation protocol. The computer program product can include instructions operable to cause the data processing apparatus to select the second PCT value when the second PCT value is received at the one of the first devices. The computer program product can include instructions operable to cause the data processing apparatus to select the first PCT value when a connection is not in handoff or a connection is in softer handoff. The computer program product can include instructions operable to cause the data processing apparatus to select the second PCT value when a connection is in soft handoff. The computer program product can include instructions operable to cause the data processing apparatus to generate, by the one of the first devices, an indicator representing quality of a signal received from the one of the ATs, and calculate the first PCT and the second PCT using the indicator.  
         [0031]     The computer program product can include instructions operable to cause the data processing apparatus to prevent transmission of a packet from the one of the first devices to the second device if the packet is associated with a bad indication and transmit the bad indication to the second device. The computer program product can include instructions operable to cause the data processing apparatus to determine good or bad indication of a packet using a cyclic redundancy code (CRC) associated with the packet. The computer program product can include instructions operable to cause the data processing apparatus to communicate between the first devices and the second device using Internet Protocol (IP) or asynchronous transfer mode (ATM).  
         [0032]     Among the advantages of the system are one or more of the following. By reducing RNC-RN signaling (e.g., sending PCT only for connections in handoff), there is a reduced backhaul bandwidth consumption. Similarly, by reducing RN-RNC data traffic (e.g., sending only an indication of bad frames to a RNC, excluding the payload), there is a reduced backhaul bandwidth consumption. Other features and advantages will become apparent from the following description and from the claims. 
     
    
     DESCRIPTION  
       [0033]      FIG. 1  is a block diagram illustrating reverse link power control in an example CDMA System.  
         [0034]      FIG. 2  is a block diagram illustrating reverse link power control in another example CDMA System.  
         [0035]      FIG. 3  is a block diagram illustrating a system for distributed reverse link power control.  
         [0036]      FIG. 4  is a block diagram depicting an example system for reverse link power control on the RN.  
         [0037]      FIG. 5  is a block diagram depicting an example system for reverse link power control on the RNC.  
         [0038]      FIG. 6 ( a ) depicts an example data structure of a message from RNC to RN.  
         [0039]      FIG. 6 ( b ) depicts an example data structure of a message from RN-BIO-SC to RLM. 
     
    
       [0040]      FIG. 3  illustrates a 1xEV-DO Radio Access Network (RAN)  300 . The RAN  300  can be built entirely on IP technology, all the way from an AT  305  to a network connection to the Internet (e.g., via a RNC  310 ), thus taking full advantage of the scalability, redundancy, and low-cost of IP networks. The entire service area of a wireless access provider may comprise one or more IP RANs  300 . Each IP RAN  300  can include many radio nodes (RNs), e.g., RN  315  and RN  320 , and one or more radio network controllers (RNC), e.g.,  310 . The RNs  315  and  320  and the RNC  310  are connected over an IP (backhaul) network  330 , which supports many-to-many connectivity between RNs  315  and  320  and RNC  310 , and any other RNs and RNCs that may be part of RAN  300 .  
         [0041]     In presence of an IP connectivity between RNs  315  and  320  and RNC  310 , transmission of PCT values as IP packets over IP backhaul  330  to connections on all RNs can generate a high amount of signaling message transmission. Each RNC could potentially support  100 s of RNs and the signaling message overhead for PCT message transmission could be a significant portion of the overall backhaul traffic. System  300  implements a distributed approach to reduce the signaling messaging over IP backhaul  330 , as described in more detail below, since signaling messaging has priority over data, which can cause significant reduction of data throughput to the end user.  
         [0042]     In system  300 , the RLOLPC functionality (e.g., updating the PCT) is distributed across RNs  315  and  320  and RNC  310 . This distribution is accomplished by using a RLOLPC-RNC module  335  for RLOLPC functionality in RNC  310  and a RLOLPC-RN module  340  for RLOLPC functionality in RNs  315  and  320 .  
         [0043]     In a general overview, system  300  uses RLOLPC-RNC module  335  or RLOLPC-RN module  340  based on the handoff state of AT  305 . In general, handoff represents the migration of a connection of AT  305  from one RN to another RN. When AT  305  is in communication with only one RN, for example RN  315 , then AT  305  is not in handoff. When AT  305  migrates, for example, from RN  315  to RN  320 , then AT  305  is in handoff. Soft handoff represents the overlapping coverage area of RNs  315  and  320 , where AT  305  can communicate with both RN  315  and RN  320  at the same time. A soft handoff is sometimes referred to as a make before break connection. Softer handoff represents the overlapping coverage area between different sectors for the same RN.  
         [0044]     If the AT  305  is not in handoff or is in softer handoff, the RLOLPC-RN module  340  of the serving RN handles the RLOLPC functionality. For example, if AT  305  is in communication only with RN  315  or is in a coverage area of RN  315  where AT  305  can communicate with multiple sectors of RN  315 , then the RLOLPC-RN module  340  of the RN  315  handles the RLOLPC functionality. As described above, the RLOLPC algorithm increases or decreases the PCT value based on whether the reverse link receives good or bad frame input. The RLOLPC-RN module  340  can determine bad or good frame input locally at the RN  315  by using the CRC state. Because system  300  is a 1xEV-DO system, there is no quality metric assigned to each received packet. Since the packet of data is either good or bad, the CRC state indicates the usefulness of the packet. In this scenario, the RLILPC  350  receives the PCT locally (shown by arrow  355 ) and not from the RNC  310  (shown by arrow  360 ). Because no information has to be transferred between RN  315  and RNC  310 , this local PCT calculation advantageously generates bandwidth savings on both reverse and forward links in backhaul  330 . Also, there is a saving of processor bandwidth in RNC  310 , since it does not have to execute an RLOLPC algorithm for this connection.  
         [0045]     If the AT  305  is in soft handoff, the RLOLPC-RNC module  335  of the serving RNC handles the RLOLPC functionality. For example, if AT  305  is in communication with both RN  315  and RN  320 , then the RLOLPC-RNC module  335  of the RNC  310  handles the RLOLPC functionality. In this scenario, like the scenario above, the RN (e.g.,  315  and/or  320 ) receiving the packet determines whether it is a good or bad frame using the CRC state. If the RN (e.g.,  315  and/or  320 ) determines the packet is a good frame, the RN forwards the packet to RNC  310 . If the RN (e.g.,  315  and/or  320 ) determines the packet is a bad frame, the RN does not forward the packet to RNC  310 . Instead, the packet is dropped at the RN and an indication of a bad frame is sent to RNC  310 . This indication is smaller than sending the entire received packet, hence less traffic is generated on the backhaul  330 .  
         [0046]     An SDU in RNC  310  determines which leg (e.g., the communication between AT  305  and RN  315  or the communication between AT  305  and RN  320 ) is providing the good frame, if any, and inputs the RLOLPC-RNC module  335  accordingly. The RLOLPC-RNC module  335  generates the PCT and sends it to the applicable RNs using, for example, a packet. The PCT packet may be treated as a signaling packet and sent using a signaling path, (e.g., using Transmission Control Protocol (TCP)). This signaling path can be slower but more reliable than the data traffic path. In another example, the PCT packet can be treated as a data packet and sent using a data traffic path (e.g., using User Datagram Protocol (UDP) or Generic Route Encapsulation (GRE) protocol). This data traffic path can be faster but less reliable than the signaling path. For each RN, the PCT for all connections on each carrier in that RN can be multiplexed into one packet and sent to the respective RN. Also, the PCT values for all of the RNs can be multiplexed into one packet and multicast to all of the RNs. These examples of using a single packet advantageously saves bandwidth on the forward link of the backhaul  330 . Sending only a bad frame indication instead of the entire bad frame with appropriate markings advantageously generates bandwidth savings on the backhaul  330 . Also, there is a saving of processor bandwidth in the RNs since the RLOLPC-RN module  340  is not run for this connection.  
         [0047]     System  300  coordinates RLOLPC between the RLOLPC-RNC module  335  and the RLOLPC-RN module  340  for PCT input into the RLILPC  350  as the connection (with AT  305 ) enters handoff or exits handoff. System  300  coordinates RLOLPC in a number of ways. One way to coordinate RLOLPC is to transition the RLOLPC from RN to RNC and back to RN as connection (with AT  305 ) enters and exists handoff and to synchronize the RLOLPC to generate the same PCT while RLOLPC is transitioned.  
         [0048]     To start the description of this process, the AT  305  is not in handoff and is communicating with RNC  310  only through RN  315 . At some point, as AT  305  moves closer to RN  320 , AT  305  enters an area where AT  305  can communicate with RNC  310  through both RN  315  and RN  320  (a soft handoff condition). Once RNC  310  detects this condition, which requires the connection to enter into handoff, the RNC  310  requests the channel-element resources from target RN  320  and has to update the source RN  315  with the number of legs in the handoff (in this case 2). During these transactions, source RN  315  responds with the latest value of PCT to initialize the RLOLPC-RNC module  335  in RNC  335 . During resource allocation on target RN, the RNC  335  uses this PCT value to prime the target RN RLILPC  350 . Once initialized, the RLOLPC-RNC module  335  determines the PCT and transmits the value to the RNs  315  and  320  s described above. This transmission of the PCT from the RLOLPC-RN  340  to the RLOLPC-RNC  335  enables the RLOLPC-RNC  335  to become synchronized with the RLOLPC-RN  340 . The RLOLPC-RNC  335  can then take over the RLOLPC functionality seamlessly from the RLOLPC-RN  340 . Once RNC detects the condition that AT needs to leave the handoff state, it has to update the last remaining leg with the number of handoff legs.  
         [0049]     The latest value of PCT can be also sent to RN at this time, before the periodic update time. Once the RN receives the above message, the RN switches to run RLOLPC (using the RLOLPC-RN  340 ) and generates the PCT locally (e.g., at the RN) for this connection.  
         [0050]     Another way to coordinate RLOLPC is to simultaneously run RLOLPC in both RLOLPC-RN  340  and RLOLPC-RNC  335 . Unlike the above examples, in this scenario, the RNs send a bad frame indication to the RNC  310 , even when in a no handoff state, because RLOLPC-RNC  335  continuously calculates PCT, regardless of the handoff state. In this way, both RLOLPC-RN  340  and RLOLPC-RNC  335  are synchronized with each other. When, however, the AT  305  is in a no handoff or softer handoff state, RNC  310  does not transmit its PCT value to the RNs. RNs  315  and  320  are configured such that when they do not receive a PCT value from the RNC  310  they use the PCT value calculated by the RLOLPC-RN module  340 . When the AT  305  moves into a soft handoff state, RNC  310  starts transmitting the PCT value calculated by RLOPC-RNC module  335 . When the RNs  315  and  320  receive a PCT value from the RNC  310 , they use that received PCT value instead of their locally calculated value. In other words, a PCT value received from the RNC  310  overwrites, or has higher priority than, the PCT value calculated by the local RLOLPC-RN module  340 .  
         [0051]     In some examples, the updated PCT is computed immediately after reception of the FCS information. However, since RLOLPC is a slow control loop, other examples input the PCT value to a RN modem receiver only once every ‘N’ RL frames. N represents a configurable parameter. In one example, N is set to 4 RL frames. Typically, each 1x-EVDO RL frame duration is 26.66 ms (see e.g., CDMA2000 High Data Rate Packet Data Air Interface Specification, 3GPP2 C.S0024, Version 4.0, Oct. 25, 2002) and hence an update period where N is set to 4 is 106.64 ms. This characteristic of the RLOLPC algorithm also facilitates transmission of consolidated PCT messages as opposed to individual PCT messages from RNC  310  (e.g., single PCT packets described above).  
         [0052]      FIGS. 4 and 5  illustrate the modules of RN  315  and RNC  310  in more detail. The modules that are running on RN  315  are shown in  FIG. 4 . The modules that are running on RNC  310  are shown in  FIG. 5 . In one example, the power control function at RN  315  is distributed across a BIO-SC  515  and modem line cards. The modem line card contains both a FLM module  440  and a RLM module  435 . In one example, the power control function at the RNC  310  resides on a RNSM card  540 .  
         [0053]     In the illustrated example, the inner loop power control module (RLILPC)  405  exists in a modem receiver  410  of the RN  315 . In the distributed approach for reverse link power control described above, the RLOLPC functionality is distributed across RNs and RNC based on all different handoff scenarios of the mobile (e.g., AT  305 ). In describing  FIGS. 4-6 , the following handoff scenarios will be used, and referred to using its respective preceding letter. 
        (a) Connection (AT) is not in hand-off.     (b) Connection (AT) is in softer hand-off but not in soft hand-off.     (c) Connection (AT) is in softer and soft hand-off.     (d) Connection (AT) is in soft hand-off.        
 
         [0058]     Handoff areas are located at the cell site boundaries. As described above, an AT  305  is said to be in ‘soft’ handoff if the AT  305  is able to see pilot signals from multiple RNs (e.g., both RN  315  and RN  320 ). An AT  305  is said to be in ‘softer’ handoff if the AT is able to see pilot signals from multiple sectors of a single RN. The AT  305  reports the pilots seen to the AN (e.g., RAN  300 ) as part of the route update message (see e.g., CDMA2000 High Data Rate Packet Data Air Interface Specification, 3GPP2 C.S0024, Version 4.0, Oct. 25, 2002). At the AN, a determination of whether the AT  305  is in no/soft/softer handoff is made based on the number of pilots and corresponding PN offsets. For example: An AT is said to be in ‘three-way’ soft handoff if the AN resolves PN offsets of the three pilots reported in the route update message that corresponds to the three different RNs. For example, if the system is compliant with CDMA2000 High Data Rate Packet Data Air Interface Specification, 3GPP2 C.S0024, Version  4 . 0 , dated Oct. 25, 2002, the maximum number of pilots allowed in soft/softer handoff is  6 . The number of pilots in soft handoff is referred to as the “soft handoff count”. During connection establishment, the RNC call control module  505  passes Soft Handoff count down to its peer, a call control agent (CCA) module  510  on each RN in the handoff. This facilitates connection resource allocation at RNs.  
         [0059]     As described above, the power control for softer handoff can be identical to the no hand-off since the received signals of a specific AT  305  from different sectors on the specific RN are combined before generating FCS on that specific RN. Hence, there is no RNC involvement for softer handoff.  
         [0060]     The techniques described herein distinguish the fact that for situations (a) and (b), the updated PCT provided by RLOLPC-RN module  340  is sufficient without any necessity of RNC  310  communicating with a RN (e.g., RN  315 ). For situations (c) and (d), updated PCT from RLOLPC-RNC module  335  is sent to all RNs in the handoff (e.g., RN  315  and RN  320 ) and this overrides the updated PCT from the RLOLPC-RN  340 .  
         [0000]     Power Control when AT is not in Soft Handoff  
         [0061]      FIG. 4  illustrates portions of RN  315 , highlighting power control operation for scenarios (a) and (b). A reverse link modem  435  receives signals transmitted by the AT  305 . A received signal from the AT  305  is decoded and MAC packets are generated by the modem receiver. This is represented by a RL Decoder block  415 . A RTCHMO block  420  receives FCS and reverse rate indication of the received RL frame. The FCS information is input to the RLOLPC-RN module  340  and the updated PCT is computed. Updated PCT is input to a Decision Module  425 . Soft Handoff Count is a key parameter that is used by the Decision Module  425  to determine whether the AT  305  is in soft handoff. For no handoff or softer handoff, the value of Soft Handoff Count=1. In one example, this soft handoff count parameter is sent from the CCA  510  to a power control connection object module  430  at the RLM  435  during power control connection resource allocation.  
         [0062]     A connection list scanner module  435  scans a linked list of all active connections on the RN  315 . Entries to this list are added/deleted when a connection is opened/closed with an AT. The scan list is updated from interaction with the RN call control agent module  510 . Updates from the call control agent  510  are based on messages from its peer RNC call control  505 .  
         [0063]     In one example, upon reception of a timing callbacks (e.g., 4 RL frames detected by RL frame timing callback module  440 ) the entire active connection list is scanned. For each connection, the decision module  425  chooses appropriate PCT depending on the soft handoff count value. In cases (a) and (b), Soft Handoff Count=1 and hence PCT RN  is chosen (e.g., the PCT value calculated by the RLOLPC-RN module  340 ). This value is used as the current input to RLILPC  405 .  
         [0064]     Using the latest PCT value, the RLILPC algorithm  405  determines RPC bits and transmits them to the mobile  305  on a forward link MAC channel. Since there is no involvement of RNC signaling, delays on the backhaul  330  are minimized and bandwidth conserved, as described above. Minimization of delay from the time the updated PCT is determined to the time it is used by RLILPC advantageously offers better power control on the reverse link. This can also help improve capacity on the forward link for high data rate wireless systems.  
         [0000]     Power Control when AT is in Soft Handoff  
         [0065]      FIG. 5  illustrates portions of RNC  310  and RN  315 , highlighting power control operation for scenarios (c) and (d). In these scenarios, the AT is power controlled from the RNC  310 . An SDU algorithm  515  running on the RNC  310  processes FCS information received from all RNs that are involved in the soft hand-off and generates the consolidated FCS. If a good frame is received from at least one RN, then consolidated FCS is considered good. Bad FCS indication is generated if bad frames are received from all RNs.  
         [0066]     The RLOLPC-RNC module  335  gets FCS information from the SDU  515  and determines adaptive PCT that satisfies the FER criterion (RL FER is a configurable parameter. See the description above about the soft handoff count parameter). This value is stored in the power control connection object  520  for the specific connection.  
         [0067]     A connection list scanner module  525  scans the linked list of active connections that are in soft handoff. Entries to this list are added/deleted when an AT moves in and out of soft handoff. The scan list is updated from an interaction with the RNC call control module  505 . Updates from the call control  505  are based on soft handoff count information.  
         [0068]     Upon firing of a power control timer  530  (e.g., period=4 RL frames), the connection list is scanned. The RN-IP address and channel record 2-tuple uniquely identifies each RN. For each soft handoff leg (RN) in that connection, a PCT multiplexer  535  updates a consolidated PCT message with a new PCT. The structure of the consolidated PCT message is given in  FIG. 6 ( a ).  
         [0069]     Once all connections in the list are scanned, PCT messages are transmitted to all RNs. In one example, for load balancing amongst competing tasks on the RNSM  540 , the connection list scanner  525  scans only a subset of connections in the connection list. This scanning size can be a configurable parameter on the RNC  310  and in one example is set to 960.  
         [0070]     In one example, the signaling PCT messages are sent to the RN  315  over the IP backhaul  330  using proprietary ABIS signaling protocol. In this example, there is no acknowledgement provided by RN  315  to RNC  310 . PCT values are quasi real-time and hence acknowledgements/retransmissions are redundant if messages are lost or dropped on the backhaul  330 .  
         [0071]     For a received message at RN-BIO-SC  515 , the PCT message remapper  545  strips out the BSCConnectionId and sends the received message to the appropriate RLM card  435 . Contents of this message are illustrated in  FIG. 6 ( b ). PCT demultiplexer  445  located on the RLM  435  populates the appropriate power control connection object  430  with PCT RNC . For each connection, the decision module  425  chooses an appropriate PCT depending on the soft handoff count value. In scenarios (c) and (d), the soft handoff count&gt;1 and hence PCT RNC  is chosen. This value is written into the modem receiver and serves as current input to RLILPC  405 .