Abstract:
In a radio access network, techniques for controlling relative usages, by different groups of access terminals in communication with a radio access network, of available power handling capacity of the radio access network, based on information about usages by different groups of access terminals in communication with the radio access network.

Description:
TECHNICAL FIELD 
     This disclosure relates to controlling usage capacity in a radio access network. 
     BACKGROUND 
     Cellular wireless communications systems are designed to serve many access terminals distributed in a large geographic area by dividing the area into cells. At the center of each cell, a base transceiver station is located to serve access terminals (e.g., cellular telephones, laptops, PDAs) located in the cell. Each cell is often further divided into sectors by using multiple sectorized antennas (the term “sector” is used both conventionally and in this document, however, even when there is only one sector per cell). In each cell, a base transceiver station serves one or more sectors and communicates with multiple access terminals in its cell. A base transceiver station can generally support a certain amount of traffic in each sector for a particular bandwidth and it is often desirable to monitor the level of traffic in a sector in order to ensure that the sector is not becoming overloaded. 
     SUMMARY 
     In general, this disclosure relates to controlling usage capacity in a radio access network based on load information feedback so as to allocate limited radio resources amongst competing groups of access terminals with different performance requirements and priorities. 
     In one aspect, the invention features a method for controlling relative usages, by different groups of access terminals in communication with a radio access network, of available power handling capacity of the radio access network, based on information about usages by different groups of access terminals in communication with the radio access network. 
     Implementations of the invention may include one or more of the following. The method for controlling relative usages includes controlling levels of transmission power used by different groups of access terminals in communication with the radio access network, based on information about levels of transmission power associated with different groups of access terminals in communication with the radio access network. The method for controlling relative usages also includes controlling the level of transmission power used by one or more of the groups of access terminals to enable differentiated performance amongst groups of access terminals in communication with the radio access network. The performance can include temporal factors. Further, the performance can be measured by uplink data rate, uplink latency, or both. The method for controlling relative usages can be performed at a base station transceiver or a base station controller. The radio access network can include a code division multiple access network. For example, the radio access network can include a first evolution-data optimized or a first evolution-data/voice compliant network. 
     The method for controlling relative usages also includes at least one access terminal in communication with the radio access network. The method further includes information about usages by different groups of access terminals in communication with the radio access network such as relative levels of transmission power used by the groups of access terminals. The information can be exchanged between base transceiver stations in the radio access network. The information can also be sent from a base transceiver station to a base station controller for processing at the base station controller. 
     The method further includes determining a relative level of transmission power used by a group of access terminals. Such a determination can include comparing a decodable signal power received by a base transceiver station in the radio access network, transmitted by the group of access terminals, with a total power received by the base transceiver station in the radio access network. The determination can include determining a decodable signal power transmitted by the group of access terminals and received by a base transceiver station in the radio access network. The determination can also include determining a total power received by a base transceiver station in the radio access network. 
     Further, the method for controlling relative usages can include comparing an actual load associated with levels of transmission power used by a group of access terminals to a target load associated with the group of access terminals. 
     The method also includes controlling relative usages by setting transmission rate limits for different access terminals in communication with the radio access network. Setting a rate limit for an access terminal in the radio access network can include transmitting a rate limit to the access terminal. Transmitting the rate limit can involve broadcasting a rate limit message to the access terminal in one or more of the sectors in which the access terminal has a connection. Transmitting the rate limit can also involve unicasting a rate limit message to the access terminal in one or more of the sectors in which the access terminal has a connection. 
     In other aspects, corresponding computer programs and apparatus are also provided. 
     Advantages that can be seen in particular implementations of the invention include one or more of the following. Load assisted performance differentiation provides various levels of service, including premium performance for users demanding greater transmission throughput. Also, differentiated performance supports rate and latency sensitive services and multimedia applications such as high-quality audio, imaging, and real-time video. Further, differentiated performance based on load accounts for actual resource usage under varying transmission rates and traffic demands, whereas connection-count based loading fails to account for such conditions. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram of a radio access network. 
         FIG. 2  is a diagram of cells in a radio access network. 
         FIG. 3  is a diagram of a power adjustment between sectors. 
         FIG. 4   a  is a diagram of a radio access network. 
         FIG. 4   b  is a diagram of a radio access network. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a radio access network (RAN)  100  uses the first evolution data-only (1x EV-DO) protocol to transmit data packets between an access terminal  118 , such as laptop or personal data assistant (PDA), and an external network such as the Internet  114 . The 1xEV-DO protocol has been standardized by the Telecommunication Industry Association (TIA) as TIA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-0, Version 4.0, Oct. 25, 2002, which is incorporated herein by reference. Revision A to this specification has been published as TIA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-A, Version 1.0, March 2004, Ballot Resolution, but has yet not been adopted. Revision A is also incorporated herein by reference. 
     The radio access network  100 , which may cover a large service area, includes one or more Access Sub-Networks (ASNs), e.g., ASN  102 , each anchored by a Base Station Controller (BSC)  108  communicating with several Base Transceiver Stations (BTSs)  104   a - 104   c  using a private or public IP backhaul network  106 . Each base transceiver station  104   a - 104   c  may support multiple sectors, with each sector covering a certain cell area around the base transceiver station  104   a - 104   c.    
     An access sub-network  102  is connected over a public or private IP network  110  to one or more Packet Data Serving Nodes (PDSNs), e.g., PDSN  112 . The packet data serving node  112 , in turn, receives and transmits data packets (e.g., voice over IP packets) to a server  116  via the Internet  114 . In some implementations, the functions of a packet data serving node  112  and a base station controller  108  are combined into a single device. 
     Each access terminal  118  is in communication with a base transceiver station, e.g., BTS  104   a , via an air link  120   a ,  120   b . An air link comprises a forward link, which carries data transmitted from a base transceiver station  104   a - 104   c  to an access terminal  118 , and a reverse link, which carries data transmitted from an access terminal  118  to a base transceiver station  104   a - 104   c . As an access terminal  118  moves from one sector to another sector serviced by different base transceiver stations  104   a - 104   c , it undergoes a “soft handoff” between the base transceiver stations  104   a - 104   c . Similarly, when an access terminal  118  moves from one sector to another sector serviced by the same base transceiver station  104   a - 104   c , it undergoes a “softer handoff” between the sectors. When an access terminal  118  is in soft or softer handoff, it will have connections in multiple sectors. 
     As shown in  FIG. 2 , a geographic area covered by a radio access network  100  (shown in  FIG. 1 ) is divided into multiple cells A, B, and C, which may be further structured as one or more sectors. Each cell includes a base transceiver station  104   a - 104   c  that communicates with access terminals (e.g., cellular telephones)  118  located within the cell. Each base transceiver station  104   a - 104   c  uses a directional antenna (not shown) appropriately positioned in each sector to send data to and receive data from access terminals  118  located in the sectors. 
     In practice, a base transceiver station  104   a - 104   c  will often include a main receiver plus one or more identical diversity receivers. The antennae of each receiver are spaced apart from each other by a distance of several (e.g., 10) wavelengths of the radio frequency (RF) carrier (e.g., 0.153 meters for 1900 MHz Personal Communications Service (PCS) band). This spatial diversity mitigates against RF fading and multi-path effects incurred by destructively combining RF waves due to multiple RF receive paths between the access terminal  118  and the base transceiver station  104   a - 104   c  caused by, for example, terrain and obstacle reflections. Generally, the more diversity receivers employed, the better the performance of the uplink signal reception. 
     A base transceiver station, such as BTS  104   a  shown in  FIGS. 1-2 , can generally support a certain amount of data traffic. The amount of data traffic supported by a base transceiver station  104   a - 104   c  in a given sector is referred to as the pole capacity. However, pole capacity is a theoretical maximum that is limited by radio frequency (RF) interference present in the sector, which may be caused by access terminals  118  transmitting in the sector, access terminals  118  from adjacent sectors, access terminals  118  from other networks, or other RF sources such as microwave ovens. In some radio access networks, the data traffic within a sector is limited using a connection-based loading approach that limits the number of concurrent transmitting access terminals  118 . 
     Network designers can design radio access networks  100  to limit the data traffic in a sector to maintain usage of the sector at some percentage of pole capacity, for example, 50% or 75% of the pole capacity. This limitation corresponds to some rise of total power over the baseline thermal noise of a receiver for a sector (referred to as “rise-over-thermal” or simply ROT). The total power received by a base transceiver station  104   a - 104   c  servicing a sector may be represented by the following time-varying function:
 
Total Power( t )= S ( t )+ I ( t )+ N ( t )
 
where, S(t) is the total useful, decodable signal power received over time at the base transceiver station  104   a - 104   c  from all access terminals  118  in the sector, I(t) is the total undecodable signal power received over time at the base transceiver station  104   a - 104   c  from interference sources (e.g., access terminals in adjacent sectors, access terminals from another radio network, microwave ovens, etc.), and N(t) is the baseline noise power of the base transceiver station&#39;s  104   a - 104   c  receiver. Noise power, or thermal noise, results from thermally induced random fluctuation in current in the receiver&#39;s load resistance. Thus, since ROT represents total power over thermal noise, ROT may be calculated as a dimensionless quantity using the following equation:
 
 ROT ( t )=[ S ( t )+ I ( t )+ N ( t )]/ N ( t )
 
     To ensure that a sector does not become overloaded, a radio access network  100  can manage the rise in thermal noise (ROT) at the radio receiver for each sector using a Common Rate Control mechanism that utilizes a predetermined target ROT to control transmissions in the radio access network  100 . Under this Common Rate Control mechanism, if the ROT reaches the target, indicating that the sector is becoming overloaded, the radio access network  100  commands the access terminals  118  in the sector to reduce or hold their current transmission data rates. On the other hand, if the ROT falls below the target, the network  100  commands the access terminals  118  to increase or hold their current transmission rates. 
     In some examples, a 1xEV-DO-compliant network  100  implements Common Rate Control of access terminals  118  in a sector by setting (or clearing) the reverse activity (RA) bit in the reverse activity channel on the forward link. For example, if the current ROT value is at or above its target, then the base transceiver station  104   a - 104   c  for the affected sector sets the RA bit. If the ROT value is below the target, the RA bit is cleared. When an access terminal  118  receives data on a MAC channel with the RA bit set, the access terminal  118  becomes aware that the sector is over-loaded and executes a “coin-flip” algorithm to determine whether to freeze or reduce its transmit rate. If the coin-flip has a first outcome, the access terminal  118  holds its transmit rate, if the coin-flip has a second outcome, the access terminal  118  decreases its rate from its current rate to the next lowest rate defined by the 1xEV-DO standard. By reducing the rate at which access terminals  118  transmit on the reverse link, access terminals  118  transmit at less power, which decreases the access terminals&#39;  118  usage of the base transceiver&#39;s  104   a - 104   c  power reception capacity for that sector. Thus, the Common Rate Control mechanism maintains a constant balance between the transmission rates of the access terminals  118  in the sector and the power received by the base transceiver station  104   a - 104   c.    
     In a radio access network  100 , the ROT value for each sector interrelates to the ROT value for other sectors, including those in other cells. This is due to the nature of the signal power, S, and interference, I, components of ROT. Signal power, S, is the useful, decodable signal received by a base transceiver station  104   a - 104   c  from an access terminal  118  in the sector. Interference, I, or the undecodable signal received by a base transceiver station  104   a - 104   c , may originate from many sources, one of which is the decodable signal, S, transmitted from an access terminal  118  in a neighboring sector. Thus, while a transmission in one sector represents a source of decodable signal power in that sector, it represents a source of interference power in neighboring sectors. 
       FIG. 2  illustrates this relationship. The total power received at BTS A    104   a  for Sector 3  equals S A3 +I A3 +N A3  and the total power received at BTS B    104   b  for Sector 1  equals S B1 +I B1 +N B1 . An access terminal  118  in Cell A -Sector 3  contributes to the ROT value for every sector served by the BTSs in the network  100 . For example, a transmission from an access terminal  118  in Cell A -Sector 3  increases S A3  in Cell A -Sector 3  and I B1  in Cell B -Sector 1 . Since ROT is a measurement related to total power, corresponding increases in both ROT A3  and ROT B1  result. Due to the increase in ROT values, the Common Rate Control mechanism in each sector may adjust the transmission rates of some or all of the access terminals  118  in that sector to maintain the balance between the transmission rates of the access terminals  118  in the sector and the power received by the base transceiver station  104   a - 104   c  servicing the sector. 
     Just as an increase in signal power, S, in one sector results in an increase in interference power, I, in another sector, a decrease of signal power, S, in one sector results in a decrease of interference power, I, in another sector. When there is a decrease of interference power, I, received by a base transceiver station  104   a - 104   c , that base transceiver station  104   a - 104   c  is able to handle more signal power, S, because of the balance maintained by the Common Rate Control mechanism. As a base transceiver station  104   a - 104   c  receiving less power than expected will inform access terminals  118  in the sector to increase their transmission rates, the access terminals  118  in that sector will exhibit increased performance when there is less signal usage in a neighboring sector. 
       FIG. 3  provides an example of this re-adjustment of resources. At some initial time, t=0, the power allocation in the sectors served by BTS A    104   a  and BTS B    104   b  may be approximately equal. However, at a later time, t=1, if the decodable signal power, S, received by BTS B    104   b  decreases, there is a corresponding decrease of interference power, I, received by BTS A    104   a . The decrease in interference power, I, received by BTS A    104   a  results in increased signal power, S, resources for BTS A    104   a . The Common Rate Control mechanism will allocate these resources to access terminals  118  in the appropriate sector. As a result, the decodable signal power received by BTS A    104   a  increases. Finally, this increase creates a corresponding increase of interference power, I, received by BTS B    104   b.    
     This interrelationship of total power between sectors may be used to the advantage of service providers. While the Common Rate Control mechanism may naturally create varying performance rates depending upon usage in neighboring sectors, the radio access network  100  can also systematically create differentiated performance amongst sectors. Performance may be quantified by the throughput and delay associated with services offered by the cellular network to an access terminal  118 . 
     A measure known in the CDMA 1x EV-DO and 1x EV-DV literature as load indicates how much of the total power received by a base transceiver station  104   a - 104   c  is decodable signal power, S. Each access terminal  118  in a sector contributes some portion of signal power, S, to the total load for the sector. Thus, the load of a group of access terminals  118  at a particular base transceiver station  104   a - 104   c  represents the ratio of total decodable signal power, S, received by that base transceiver station  104   a - 104   c , for that group of access terminals  118 , to the total power received at the same base transceiver station  104   a - 104   c . Applying this concept to the relationship described above, a decrease in the load, or aggregate decodable signal power, of one sector will decrease the interference power, I, received by the base transceiver station  104   a - 104   c  in a neighboring sector. Following the decrease in interference power, I, the base transceiver station  104   a - 104   c  in the neighboring sector can notify a group of access terminals  118  to increase their transmission rates. The increase in transmission rates results in an increase in performance. Therefore, using load, the performance of one group of access terminals  118  can be differentiated from that of another group of access terminals  118 . This concept can be applied to access terminals  118  in sectors in different cells as well as to access terminals  118  in sectors within the same cell. 
     In some examples, differentiated throughput performance is achieved by using load information feedback from base transceiver stations  104   a - 104   c . Access terminal  118  groups are defined by preferred service sectors. A particular group may, then, receive increased performance at the expense of allocable power resources for other groups of access terminals  118  as dictated by the radio access network  100 . To achieve this, load and group status information is shared between multiple sectors in the system. One way to implement this is through decentralized BTS-to-BTS communications, as seen in  FIG. 4   a . Another implementation may use the centralized Base Station Controller (BSC)  108  shown in  FIG. 4   b . The information conveyed by the base transceiver stations  104   a - 104   c  in either example may contain the target and actual load data, the difference between those measurements, or even a quantized value of the difference. 
     In some examples, differentiated rate control is based on geography. In this implementation, the system improves throughput performance for access terminals  118  grouped by geographic area. First, the base transceiver station  104   a - 104   c  is configured with a target throughput performance for the group of access terminals  118  in a predefined geographic area. Since throughput performance is directly related to the transmission power of an access terminal  118 , and load is a measure of decodable signal power received by the base transceiver station  104   a - 104   c , then, in this example, load is treated as a measure of throughput performance. Therefore, the target throughput performance, or group-load target, is used by the system to prompt increased or decreased transmission rates. Thus, as access terminals  118  in the group attempt to increase their transmission power toward the group-load target, such that the Common Rate Control mechanism would normally decrease their transmission rates, the system would instead decrease transmission rates for non-group access terminals  118  to free power resources for the group. 
     In some examples, differentiated latency control is achieved by using load information feedback from base transceiver stations  104   a - 104   c . CDMA architectures such as 1x EV-DO and 1x EV-DV may use interlaced Hybrid ARQ error detection and correction. Under this method, high transmission rates support early decoding and, hence, lower latency of transmitted data packets. High transmission rates relate directly to increased power received by base transceiver stations  104   a - 104   c . Thus, differentiated latency control may be achieved using a load-based feedback mechanism. Multimedia applications require very low bit-error-rates and perform best in reliable communications conditions with low delays. In such cases, the network  100  provides preferred service to a group in order to deliver lower latency. Similar to the previous example, a group-load target is set and the system allocates resources so as to meet that target. 
     Although the techniques described above employ the 1xEV-DO air interface standard, the techniques are also applicable to other CDMA and non-CDMA interference limited multi-user communications systems in which a control system based on load information feedback is used to allocate limited radio resources within a network to achieve differentiated performance amongst competing groups of access terminals. 
     The techniques described above can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The techniques can be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. 
     Method steps of the techniques described herein can be performed by one or more programmable processors executing a computer program to perform functions of the invention by operating on input data and generating output. Method steps can also be performed by, and apparatus of the invention can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). Modules can refer to portions of the computer program and/or the processor/special circuitry that implements that functionality. 
     Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry. 
     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention, and, accordingly, other implementations are within the scope of the following claims.