Abstract:
A throughput of an air interface is recorded during a plurality of intervals to produce a set of recorded throughputs. A slot utilization is also recorded during each of the plurality of intervals to produce a set of recorded slot utilizations. A slot is an allocation of time and frequency. A linear regression on the data points of the set of recorded throughputs and the set of recorded slot utilizations is performed to produce a regression line of throughput versus slot utilization. An indicator of air interface quality is calculated based on the slope of the regression line.

Description:
TECHNICAL BACKGROUND 
     Wireless communication may be used as a means of accessing a communication network and has certain advantages over wired communications for accessing a communication network. One of those advantages is a low cost of infrastructure to provide access to many separate mobile devices. To use wireless communication to access a network, a customer device needs to have at least one transceiver in active communication with another transceiver that is connected to the network. 
     To facilitate wireless communication, the Institute of Electrical and Electronics Engineers (IEEE) has promulgated a number of wireless standards. These include the 802.11 (WiFi) standards and the 802.16 (WiMAX) standards. Likewise, the International Telecommunication Union (ITU) has promulgated standards to facilitate wireless communications. This includes TIA-856, which is also known as evolution-data optimized (EV-DO). The European Telecommunications Standards Institute (ETSI) has also promulgated a standard known a long term evolution (LTE). All of these standards may include specifications for various aspects of wireless communication with a network. This includes processes for registering on the network, carrier modulation, frequency bands of operation, and message formats. 
     OVERVIEW 
     A method of determining an indicator of air interface quality is disclosed. A throughput of an air interface is recorded during a plurality of intervals to produce a set of recorded throughputs. A slot utilization is also recorded during each of the plurality of intervals to produce a set of recorded slot utilizations. A slot is an allocation of time and frequency. A linear regression on the data points of the set of recorded throughputs and the set of recorded slot utilizations is performed to produce a regression line of throughput versus slot utilization. An indicator of air interface quality is determined based on the slope of the regression line. 
     A method of analyzing a communication system is disclosed. A slot utilization is measured during a first interval to determine if the slot utilization satisfies a first utilization criteria. A packet drop rate is measured during a second interval to determine if the packet drop rate satisfies a first packet drop criteria. An uplink air interface quality indicator is determined. A downlink air interface quality indicator is determined. An air interface problem is diagnosed based on the slot utilization, the packet drop rate, the uplink air interface quality indicator, and the downlink air interface quality indicator. 
     A slot utilization is measured during a first interval to determine if the slot utilization satisfies a first utilization criteria. A packet drop rate is measured during a second interval to determine if the packet drop rate satisfies a first packet drop criteria. In response to the slot utilization satisfying the first utilization criteria and the packet drop rate satisfying the first packet drop criteria, a first linear regression is performed on data points of a first set of recorded throughputs and a first set of recorded slot utilizations. This produces a first regression line of throughput versus slot utilization. A first air interface quality indicator is based on the slope of the first regression line. An air interface quality problem is diagnosed based on the slot utilization, packet drop rate, and the first air interface quality indicator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a communication system. 
         FIG. 2  is a flowchart illustrating a method of determining an air interface quality indicator. 
         FIG. 3  is a flowchart illustrating a method of analyzing a communication system. 
         FIG. 4  is a flowchart illustrating a method of analyzing a communication system. 
         FIG. 5  is a block diagram of a computer system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram illustrating a communication system. In  FIG. 1 , communication system  100  comprises base station  110 , network  120 , wireless device  130 , wireless device  131 , wireless link  140 , and wireless link  141 . 
     Wireless devices  130  and  131  may be operatively coupled to base station  110  by wireless links  140  and  141 , respectively. Base station  110  is operatively coupled to network  120 . Thus, wireless devices  130  and  131  may be operatively coupled to network  120 . 
     Wireless device  130  or wireless device  131  may be any device, system, combination of devices, or other such communication platform capable of communicating with base station  110  via wireless links. Wireless device  130  and wireless device  131  may be, for example, a mobile phone, a wireless phone, a wireless modem, a personal digital assistant (PDA), a voice over internet protocol (VoIP) phone, a voice over packet (VOP) phone, or a soft phone, as well as other types of devices or systems that can exchange data with base station  110  via wireless links. Other types of communication platforms are possible. 
     Base station  110  may be any wireless system that provides the air interface to wireless device  130  and wireless device  131  and communication connectivity to network  120 . Examples of base stations that may be utilized include, base transceiver stations (BTSs), radio base stations (RBSs), Node B, enhanced Node B (eNBs) and others. Base stations may include a number of elements known to those skilled in the art comprising a transceiver, power amplifier, combiner, duplexer, antenna and control function. 
     Network  120  may comprise a computer, a network, or a collection of computers and networks that couple, link, or otherwise operatively provide wireless device  130  or wireless device  131  with communication service. It should be understood that network  120  may comprise secondary data networks. For example, network  120  may include a backhaul network, a local network, a long distance network, a packet network, or any combination thereof, as well as other types of networks. Network  120  may be or include an access service network (ASN), an access service network gateway (ASN-GW), wireless local access network access gateway (WAG), packet data gateway (PDG), mobile switching center (MSC) and packet data serving node (PDSN). 
     Wireless device  130  and wireless device  131  may establish communication sessions with base station  110  in order to receive communication services via network  120  and wireless links  140  and  141 , respectively. These services may include voice services and data services. These services may include but are not limited to telephone services, long distance services, mobile voice services, mobile data services, push-to-talk services, internet services, web browsing, email, pictures, picture messaging, video, video messaging, audio, voicemail, music, MP3&#39;s, ring tones, stock tickers, news alerts, and so on. 
     The amount of information that can be exchanged via wireless links  140  and  141  depends upon air interface factors such as the number of wireless devices communicating via base station  110 , interference, clutter, morphology, wireless device location, and wireless device mobility. To address user performance expectations, additional base stations may be added to improve one or more of these air interface factors. However, simply adding base stations may be expensive, and may not improve the user experience. 
     An air interface quality indicator may be determined for communication system  100  to help detect or diagnose problems. The air interface quality indicator may also be used to help determine an appropriate course of action to improve the user experience. 
     Communication system  100  may measure physical layer throughput. Physical layer throughput is the number of bits per a unit of time carried through the physical layer (e.g., wireless links  140  and  141 ) for all of the wireless devices communicating with base station  110 . 
     Communication system  100  may measure physical layer throughput in a downlink direction (e.g., traffic flowing from base station  110  to wireless device  130  and wireless device  131 ). Communication system  100  may measure physical layer throughput in an uplink direction (e.g., traffic flowing to base station  110  from wireless device  130  and wireless device  131 ). Communication system  100  may use base station  110  to measure and record physical layer throughput. Communication system  100  may use other devices to measure physical layer throughput. 
     Communication system  100  may measure a media access control (MAC) layer throughput. MAC layer throughput is the amount of information carried by the MAC layer. MAC layer throughput is the throughput of the air interface seen by the transport layers. MAC throughput depends on at least: (1) the configuration of communication system  100 ; (2) the number of wireless devices transferring data; (3) the amount of data transferred by each user; (4) the radio frequency (RF) conditions; and, (5) MAC layer overhead packets. 
     Communication system  100  may measure MAC layer throughput in a downlink direction. Communication system  100  may measure MAC layer throughput in an uplink direction. Communication system  100  may use base station  110  to measure and record MAC layer throughput. Communication system  100  may use other devices to measure MAC layer throughput. 
     Communication system  100  may measure slot utilization. A slot is a particular allocation of time (or symbol) and frequency used to transfer information between base station  110  and wireless device  130  or wireless device  131 . Slot utilization may be expressed as a percentage (or ratio) of slots that are allocated to transmit information out of a total number of available slots. Slot utilization depends on at least: (1) MAC layer throughput, and (2) RF conditions. Poor RF conditions result higher slot utilization because communication system  100  needs to use lower order modulation schemes, higher redundancy codes, and packet retransmission on wireless links  140  or  141  when RF conditions degrade. 
     Communication system  100  may measure slot utilization in a downlink direction. Communication system  100  may measure slot utilization in an uplink direction. Communication system  100  may use base station  110  to measure and record slot utilization. Communication system  100  may use other devices to measure slot utilization. 
     Communication system  100  may measure packet drop rate. Communication system  100  may measure packet drop rate in a downlink direction. Communication system  100  may measure packet drop rate in an uplink direction. Communication system  100  may use base station  110  to measure and record packet drop rate. Communication system  100  may use other devices to measure packet drop rate. 
     Communication system  100  may measure physical layer throughput, MAC layer throughput, slot utilization, a number of users (i.e., the number of wireless devices transferring data), or packet drop rate over multiple time intervals. For example, communication system  100  may measure MAC layer throughput and slot utilization over a period of 15 minutes. Communication system may average the slot utilization or MAC layer throughput to produce an average slot utilization or MAC layer throughput for the interval. Communication system may record these 15-minute averages for a period of time such as 24 hours, or 30 days. 
     The data points for these 15-minute averages may be used as the basis for determining an air interface quality indicator. The data points for slot utilization and MAC layer throughput for each 15-minute interval may be the input variables for a linear regression analysis. This linear regression analysis may produce a regression line that relates MAC layer throughput to slot utilization. The slope of the regression line may be used as a basis for an air interface quality indicator. 
     In an example, the slope of the regression line for the downlink MAC layer throughput and the downlink slot utilization may be divided by 17.28 Mbps to produce an uplink air interface quality (AIQ) factor. The number 17.28 Mbps is chosen to normalize the AIQ factor to the range of between zero (0.0) and one (1.0) for a 10 MHz WiMAX downlink channel which has a 17.28 Mbps maximum throughput. Other numbers can be chosen according the maximum MAC layer throughput and most efficient modulation and coding schemes that may be utilized by communication system  100 . 
     In another example, the slope of the regression line for the uplink MAC layer throughput and uplink slot utilization may be divided by 8.4 Mbps to produce an uplink AIQ factor. The number 8.4 Mbps is chosen to normalize the AIQ factor to the range of between 0.0 and 1.0 for a 10 MHz WiMAX uplink channel which has an 8.4 Mbps maximum throughput. Other numbers can be chosen according the maximum MAC layer throughput and most efficient modulation and coding schemes that may be utilized by communication system  100 . 
     The AIQ factor may be used to determine certain information about the functioning of communication system  100 . The following examples are based on the 10 MHz WiMAX channel discussed, above. Other communication systems may have other coefficients and formulas. 
     In an example, the number of bits transferred in a slot is equal to the AIQ factor multiplied by 240 (i.e., # bits per slot=240*AIQ). The maximum number of bytes transmitted in the downlink direction is: 2.16*AIQ bytes/s. The maximum number of bytes transmitted in the uplink direction is: 1.05*AIQ bytes/s. The maximum downlink capacity of base station  110  in terms of bytes per hour can be calculated as: 7776*AIQ bytes/hr. The maximum uplink capacity of base station  110  in terms of bytes per hour can be calculated as: 3780*AIQ bytes/hr 
     The AIQ factor may also be used with other recorded data to diagnose a problem with communication system  100 . For example, problems with system optimization, coverage, or capacity of communication system  100  may be diagnosed based on slot utilization, packet drop rate, and an AIQ factor. A coverage problem may indicate that adjustments to a base station&#39;s antenna are needed to better cover a highly used area with bad air interface conditions. An optimization problem may indicate that there is a bottleneck somewhere in the system, such as a low bandwidth backhaul link. A capacity issue may indicate that additional equipment is needed at a base station to handle the traffic passing through that base station. An example decision table is given in Table 1. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 AIQ factors 
               
               
                   
                 Slot Utilization and Packet 
                 DL = downlink 
               
               
                 Problem 
                 Drop Rate 
                 UL = uplink 
               
               
                   
               
             
             
               
                 No Problem 
                 Utilization &lt; 50% 
                 N/A 
               
               
                   
                 and 
                   
               
               
                   
                 Drop Rate &lt; 1% 
                   
               
               
                 Capacity 
                 50% &lt; Utilization &lt; 55% 
                 DL AIQ &gt; 0.3 
               
               
                   
                 or 
                 or 
               
               
                   
                 1% &lt; Drop Rate &lt; 1.3% 
                 UL AIQ &gt; 0.2 
               
               
                 Coverage or 
                 50% &lt; Utilization &lt; 55% 
                 DL AIQ &lt; 0.3 
               
               
                 Optimization 
                 or 
                 or 
               
               
                   
                 1% &lt; Drop Rate &lt; 1.3% 
                 UL AIQ &lt; 0.2 
               
               
                 Coverage, 
                 50% &lt; Utilization &lt; 55% 
                 0.2 ≦ DL AIQ ≦ 0.3 
               
               
                 Optimization, 
                 or 
                 or 
               
               
                 or Capacity 
                 1% &lt; Drop Rate &lt; 1.3% 
                 0.15 ≦ UL AIQ ≦ 0.2 
               
               
                 Capacity 
                 Utilization &gt; 55% 
                 DL AIQ &gt; 0.3 
               
               
                   
                 or 
                 and 
               
               
                   
                 Drop Rate &gt; 1.3% 
                 UL AIQ &gt; 0.2 
               
               
                 Coverage or 
                 Utilization &gt; 55% 
                 DL AIQ &lt; 0.3 
               
               
                 Optimization 
                 or 
                 or 
               
               
                   
                 Drop Rate &gt; 1.3% 
                 UL AIQ &lt; 0.2 
               
               
                 Coverage, 
                 Utilization &gt; 55% 
                 0.2 ≦ DL AIQ ≦ 0.3 
               
               
                 Optimization, 
                 or 
                 or 
               
               
                 or Capacity 
                 Drop Rate &gt; 1.3% 
                 0.15 ≦ UL AIQ ≦ 0.2 
               
               
                   
               
             
          
         
       
     
       FIG. 2  is a flowchart illustrating a method of determining an air interface quality indicator. The steps illustrated in  FIG. 2  may be performed by one or more elements of communication system  100 . 
     An air interface throughput is recorded ( 202 ). For example, base station  110  may measure and record an average throughput exchanged in either the uplink direction, downlink direction, or both, with all of the wireless devices it is communicating with. The average throughput may be measured at the physical layer or the MAC layer. The average throughput may be measured over a time interval such as 15 minutes. The average throughput may be measured over multiple of time intervals. For example, base station  110  may measure and record an average air interface throughput for each 15-minute interval over a period of approximately one month. 
     An air interface slot utilization is recorded ( 204 ). For example, base station  110  may measure and record an average slot utilization in either the uplink or downlink direction. The average slot utilization may be measured at the physical layer or the MAC layer. The slot utilization may be measured for only the downlink or uplink burst zones of a frame. The average slot utilization may be measured over a time interval such as 15 minutes. The average slot utilization may be measured over multiple of time intervals. For example, base station  110  may measure an average air interface slot utilization for each 15-minute interval over a period of approximately one month. These time intervals may be the same as, or overlap, the time intervals used to measure average throughput. 
     A regression line is produced ( 206 ). For example, linear regression may be applied to the throughput and slot utilization data points recorded in steps  202  and  204  to produce slope and intercept coefficients for a regression line that relates throughput to slot utilization. 
     An air interface quality indicator is determined ( 208 ). For example, an air interface quality indicator may be determined based on a slope coefficient calculated in step  206 . In an embodiment, an air interface quality indicator is determined by dividing a slope coefficient that relates throughput to slot utilization by the maximum throughput of an air interface. The maximum throughput of an air interface may be determined by the characteristics of the air interface. In an example, the maximum throughput of a 10 MHz per channel WiMAX system is 17.28 Mbps in the downlink direction and 8.4 Mbps in the uplink direction. 
       FIG. 3  is a flowchart illustrating a method of analyzing a communication system. The steps illustrated in  FIG. 3  may be performed by one or more elements of communication system  100 . 
     A slot utilization is measured ( 302 ). For example, base station  110  may measure and record an average slot utilization in either the uplink direction, downlink direction, or both. The average slot utilization may be measured at the physical layer or the MAC layer. The slot utilization may be measured for only the downlink or uplink burst zones of a frame. The average slot utilization may be measured over a time interval such as 15 minutes. The average slot utilization may be measure over a long-term time interval such as a week or month. The average slot utilization may be measured over multiple of time intervals. For example, base station  110  may measure an average air interface slot utilization for each 15-minute interval over a period of approximately one month. 
     A packet drop rate is measured ( 304 ). For example, base station  110  may measure and record a packet drop rate in either the uplink direction, downlink direction, or both. The packet drop rate may be measured at the MAC layer or at a transport layer. The packet drop rate may be measured over a time interval such as 15 minutes. The packet drop rate may be measure over a long-term time interval such as a week or month. The packet drop rate may be measured over multiple time intervals. For example, base station  110  may measure the packet drop rate for each 15-minute interval over a period of approximately one month. These time intervals may be the same as, or overlap, the time intervals used to measure slot utilization. 
     An uplink air interface quality indicator is determined ( 306 ). For example, the method illustrated in  FIG. 2  may be used by communication system  100  to determine an uplink air interface quality indicator. A downlink air interface quality indicator is determined ( 308 ). For example, the method illustrated in  FIG. 2  may be used by communication system  100  to determine a downlink air interface quality indicator. 
     An air interface problem is diagnosed ( 310 ). For example, the uplink and downlink air interface quality indicators determined in steps  306  and  308 , respectively, may be used in conjunction with the slot utilization and packet drop rate measured in steps  302  and  304 , respectively, to determine if there is an air interface problem. It may also be determined whether the problem may be with capacity, coverage, or system optimization. In an embodiment, Table 1 may be used as a decision table to help diagnose an air interface problem using an uplink air interface quality indicator, a downlink air interface quality indicator, a slot utilization, and a packet drop rate. 
       FIG. 4  is a flowchart illustrating a method of analyzing a communication system. The steps illustrated in  FIG. 4  may be performed by one or more elements of communication system  100 . 
     A slot utilization is measured ( 402 ). For example, base station  110  may measure and record an average slot utilization in the uplink direction, the downlink direction, or both. The average slot utilization may be measured at the physical layer or the MAC layer. The slot utilization may be measured for only the burst zones of a frame. The average slot utilization may be measured over a time interval such as 15 minutes. The average slot utilization may be measure over a long-term time interval such as a week or month. The average slot utilization may be measured over multiple time intervals. For example, base station  110  may measure an average air interface slot utilization for each 15-minute interval over the period of approximately one month. 
     A packet drop rate is measured ( 404 ). For example, base station  110  may measure and record a packet drop rate in either the uplink direction, downlink direction, or both. The packet drop rate may be measured at the MAC layer or at a transport layer. The packet drop rate may be measured over a time interval such as 15 minutes. The packet drop rate may be measured over a long-term time interval such as a week or month. The packet drop rate may be measured over multiple time intervals. For example, base station  110  may measure the packet drop rate for each 15-minute interval over a period of approximately one month. These time intervals may be the same as, or overlap, the time intervals used to measure slot utilization. 
     A criteria is checked ( 406 ). For example, the slot utilization measured in step  402  may be checked to determine if it satisfies a threshold. In an embodiment, the slot utilization may be checked to determine if it exceeds a threshold of 50%. In an embodiment, the slot utilization may be checked to determine if it exceeds a threshold of 55%. In an embodiment, the slot utilization may be checked to determine if it satisfies one or more criteria shown in Table 1. 
     In another embodiment, the criteria may involve multiple checks or thresholds such as the average number of users exceeding a threshold when the slot utilization satisfies a criteria. For example, the criteria may be that the slot utilization exceed a threshold and the packet drop rate also satisfy another criteria. In another example, the criteria may be that the slot utilization exceed a threshold percentage when there are more than a threshold number of users. In another example, the criteria may be that the slot utilization exceed a first threshold percentage when there are more than a second threshold number of users more than a third threshold number times in a month. 
     In another example, the packet drop rate measured in step  404  may be checked to determine if it satisfies a threshold. In an embodiment, the packet drop rate may be checked to determine if it exceeds a threshold of 1%. In an embodiment, the packet drop rate may be checked to determine if it exceeds a threshold of 1.3%. In an embodiment, the packet drop rate may be checked to determine if it satisfies a criteria shown in Table 1. 
     In another embodiment, the criteria may involve multiple checks or thresholds such as the packet drop rate exceeding a threshold when the slot utilization satisfies a criteria. For example, the criteria may be that the slot utilization exceeds a first threshold and the packet drop rate exceeds a second threshold criteria. In an embodiment, the criteria may be that the slot utilization exceeds a first threshold or the packet drop rate exceeds a second threshold when there are more than a third threshold number of users more than a fourth threshold number times in a month. For example, the criteria may be that the slot utilization exceeds 50% or the packet drop rate exceeds 1% when the number of users is greater than three more than 144 times in a month. 
     In an embodiment, an AIQ may be determined and used as a basis to trigger a diagnosis according to the steps illustrated in  FIG. 2 . The steps illustrated in  FIG. 2  may include determining a second AIQ. 
     Steps  408 ,  410 , and  412  may be performed in response to the result of the criteria check in step  406 . A linear regression is performed ( 408 ). For example, linear regression may be performed on data points that relate slot utilization to a throughput. This linear regression may produce slope and intercept coefficients that describe a regression line. 
     An air interface quality indicator is determined ( 410 ). For example, an air interface quality indicator may be determined based on the slope of a regression line produced in step  408 . In an embodiment, an air interface quality indicator is determined by dividing a slope coefficient that relates throughput to slot utilization by the maximum throughput of an air interface. The maximum throughput of an air interface may be determined by the characteristics of the air interface. In an example, the maximum throughput of a 10 MHz per channel WiMAX system is 17.28 Mbps in the downlink direction and 8.4 Mbps in the uplink direction. 
     An air interface quality problem is diagnosed ( 412 ). For example, an uplink or a downlink air interface quality indicator, or both, as determined in step  408  may be used in conjunction with the slot utilization and packet drop rate measured in steps  402  and  404 , respectively, to determine if there is an air interface quality problem. It may also be determined whether the problem may be with capacity, coverage, or system optimization. In an embodiment, Table 1 may be used as a decision table to help diagnose an air interface quality problem using an uplink air interface quality indicator, a downlink air interface quality indicator, a slot utilization, and a packet drop rate. 
     The methods, systems, networks, devices, and base stations described above may be implemented with, contain, or be executed by one or more computer systems. The methods described above may also be stored on a computer readable medium. The elements of communication network  100  may comprise, or include computers systems. This includes, but is not limited to base station  110 , network  120 , wireless device  130  and wireless device  131 . 
       FIG. 5  illustrates a block diagram of a computer system. Computer system  500  includes communication interface  520 , processing system  530 , and user interface  560 . Processing system  530  includes storage system  540 . Storage system  540  stores software  550 . Processing system  530  is linked to communication interface  520  and user interface  560 . Computer system  500  could be comprised of a programmed general-purpose computer, although those skilled in the art will appreciate that programmable or special purpose circuitry and equipment may be used. Computer system  500  may be distributed among multiple devices that together comprise elements  520 - 560 . 
     Communication interface  520  could comprise a network interface, modem, port, transceiver, or some other communication device. Communication interface  520  may be distributed among multiple communication devices. Processing system  530  could comprise a computer microprocessor, logic circuit, or some other processing device. Processing system  530  may be distributed among multiple processing devices. User interface  560  could comprise a keyboard, mouse, voice recognition interface, microphone and speakers, graphical display, touch screen, or some other type of user device. User interface  560  may be distributed among multiple user devices. Storage system  540  could comprise a disk, tape, integrated circuit, server, or some other memory device. Storage system  540  may be distributed among multiple memory devices. 
     Processing system  530  retrieves and executes software  550  from storage system  540 . Software  550  may comprise an operating system, utilities, drivers, networking software, and other software typically loaded onto a computer system. Software  550  could comprise an application program, firmware, or some other form of machine-readable processing instructions. When executed by processing system  530 , software  550  directs processing system  530  to operate as described herein. 
     The above description and associated figures teach the best mode of the invention. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Those skilled in the art will appreciate that the features described above can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described above, but only by the following claims and their equivalents.