Abstract:
An automatic meter reading fixed communication network for collecting data generated by a plurality of metering devices located within a geographic area, and a method for collecting data generated by a plurality of metering devices located within a geographic area. The network includes a plurality of endpoint devices, at least one relay device, a central radio device, and a head-end station for effecting wirelessly collection and communication of consumption data. A method of optimizing communications between network devices is also disclosed.

Description:
RELATED APPLICATIONS AND CLAIM TO PRIORITY  
       [0001]     This application claims priority to U.S. Provisional Patent Application No. 60/565,289, filed on Apr. 26, 2004, and entitled “SYSTEM AND METHOD FOR UTLITY DATA COLLECTION,” which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to radio frequency (RF) communication systems, and more particularly to RF communication architectures used in advanced automatic meter reading (AMR) devices.  
       BACKGROUND OF THE INVENTION  
       [0003]     Automatic meter reading (AMR) systems are generally known in the art. Utility companies, for example, use AMR systems to read and monitor customer meters remotely, typically using radio frequency (RF) and other wireless communications. AMR systems are favored by utility companies and others who use them because they increase the efficiency and accuracy of collecting readings and managing customer billing. For example, utilizing an AMR system for the monthly reading of residential gas, electric, or water meters eliminates the need for a utility employee to physically enter each residence or business where a meter is located to transcribe a meter reading by hand.  
         [0004]     There are two general ways in which current AMR systems are configured, fixed networks and mobile networks. In a fixed network, endpoint devices at meter locations communicate with readers that collect readings and data using RF communication. There may be multiple fixed intermediate readers, or relays, located throughout a larger geographic area on utility poles, for example, with each endpoint device associated with a particular reader and each reader in turn communicating with a central system. Other fixed systems utilize only one central reader with which all endpoint devices communicate. In a mobile network, a handheld unit or otherwise mobile reader with RF communication capabilities is used to collect data from endpoint devices as the mobile reader moves from place to place. The differences in how data is reported up through the system and the impact that has on number of units, data transmission collisions, frequency and bandwidth utilization has resulted in fixed network AMR systems having different communication architectures than mobile network AMR systems.  
         [0005]     AMR systems can include one-way, one-and-a-half-way, or two-way communications capabilities. In a one-way system, an endpoint device typically uses a low power count down timer to periodically turn on, or “bubble up,” in order to send data to a receiver. One-and-a-half-way AMR systems include low power receivers in the endpoint devices that listen for a wake-up signal which then turns the endpoint device on for sending data to a receiver. Two-way systems enable two way command and control between the endpoint device and a receiver/transmitter. Because of the higher power requirements associated with two-way systems, two-way systems have not been favored for residential endpoint devices where the need for a long battery life is critical to the economics of periodically changing out batteries in these devices.  
         [0006]     It would be desirable to provide for a fixed AMR system that had a communication architecture capable of efficiently supporting two way communications, while also permitting the flexibility of configuring the mobile AMR system to utilize different initiation protocols and to provide the capability of working in both a fixed network and a mobile network AMR system.  
       SUMMARY OF THE INVENTION  
       [0007]     The invention substantially meets the aforementioned needs of the industry, in particular by providing a system and method of collecting data by an AMR system that allow for the storage and transfer of meter readings and other data to eliminate the need to physically visit a remote endpoint device and connect directly to the endpoint device for the collection of data.  
         [0008]     In one embodiment, a ring network for an automatic meter reading fixed communication network for collecting data generated by a plurality of metering devices located within a geographic area comprises a plurality of fixed-location endpoint devices, a fixed central radio device and a plurality of fixed relay devices. The plurality of fixed-location endpoint devices are positioned in the geographic area, each endpoint device coupled to a respective metering device and comprising a regenerative receiver to receive wake-up signals, a second receiver, and a transmitter to transmit signals representative of at least a portion of the data generated by the metering device and signals representative of a state of the endpoint device in an assigned time slot. The fixed central radio device is generally centrally located within the geographic area and operably connected to a head end station and has at least one transceiver to receive signals transmitted by at least one of an endpoint device and a relay device and to transmit signals representative of data generated by a metering device, status of at least one endpoint device, status of at least one relay device, wake-up signals, or any combination thereof. The fixed central radio device has an effective radio transmission inner radius in the ring network. The plurality of fixed relay devices are generally peripherally located within the geographic area and within the effective radio transmission radius of the fixed central radio device. There are fewer relay devices than endpoint devices. Each relay device has a regenerative receiver to receive wake-up signals, a second receiver to receive signals transmitted from at least one endpoint device, and a transmitter to transmit signals representative of the data generated by the metering device, a state of the endpoint device, and wake-up signals. The fixed relay devices has an effective radio transmission outer radius, such that the inner radius of the fixed central radio device and the outer radii of the plurality of fixed relay devices combine to provide an effective radio frequency coverage for the geographic area of the ring network. In another embodiment, the endpoint device is integrated into the metering device as a single device.  
         [0009]     In one embodiment of an automatic meter reading communication network, a method for collecting data generated by a plurality of metering devices located within a geographic area comprises the steps of, for each of a plurality of fixed endpoint device coupled to a respective metering device, transitioning from a low-consumption mode to an active mode in an assigned time slot and wirelessly transmitting signals representative of at least a portion of the data generated by the metering device for that endpoint device in an assigned time slot; for at least one of a plurality of relay devices, transitioning from a low-consumption mode to an active mode in an assigned time slot and wirelessly receiving signals transmitted by at least one endpoint device; for a central radio device, wirelessly receiving the signals transmitted by at least one relay device and the signals transmitted by at least one endpoint device, and wirelessly transmitting signals representative of at least a portion of the data generated by the metering device for that endpoint device to a head-end station; and for a head-end station, wirelessly receiving the signals transmitted by the central radio device, decoding the signals, and storing data representative of at least a portion of the decoded signals in a database. The method can also comprise steps for optimizing a communication path to an endpoint device.  
         [0010]     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description that follow more particularly exemplify these embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:  
         [0012]      FIG. 1  is an exemplary diagram of a coverage cell of a fixed AMR system in accordance with an embodiment of the present invention.  
         [0013]      FIG. 2  is an exemplary timing diagram of communications in a fixed AMR system in accordance with an embodiment of the present invention.  
         [0014]      FIG. 3  is an exemplary slot timing diagram in accordance with one embodiment of the present invention.  
         [0015]      FIG. 4  is a flowchart of an installation process according to one embodiment of the invention.  
         [0016]      FIG. 5  is a flowchart of a path determination process according to one embodiment of the invention.  
         [0017]      FIG. 6  is a flowchart of endpoint programming according to one embodiment of the invention.  
         [0018]      FIG. 7  is a flowchart of endpoint programming according to one embodiment of the invention.  
         [0019]      FIG. 8  is an exemplary automatic frequency control block diagram in accordance with one embodiment of the present invention. 
     
    
       [0020]     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Preferred embodiments of the fixed network AMR system and method of the invention provide two-way communication capabilities in a locally geographically distributed environment. The invention can be more readily understood by reference to  FIGS. 1-8 , the appendices, and the following description. While the present invention is not necessarily limited to such an application, the invention will be better appreciated using a discussion of example embodiments in such a specific context.  
         [0022]      FIG. 1  is an exemplary diagram of a coverage cell  10  of a fixed AMR system. Coverage cell  10  includes a central device  20  having an associated RF coverage radius  22 . At an outer communicative edge of radius  22  are a plurality of relay devices  30 , each having associated relay coverage radii  32 . The combination of radii  22  and  32  blankets cell  10  with a predictable probability of wireless communicative success with any endpoint device located within radii  22  and  32 .  
         [0023]     Radii  22  and  32  can vary according to geographic and physical features and other factors affecting wireless communications, as will be appreciated by those skilled in the art. A typical area in which the system can be implemented will comprise areas of varied densities, including single- and multi-family homes, apartment complexes, residential medical facilities, educational centers, and areas of commercial and industrial zoning. These densities and uses will affect communication between the various devices  20  and  30  and the endpoint devices.  
         [0024]     For example, an endpoint device located in close geographic proximity to central device  20  and within associated coverage radius  22  communicates directly with central device  20 . An endpoint device located at the geographic periphery of coverage cell  10  yet within one of coverage radii  32  associated with a particular relay device  30  can communicate with central device  20  via associated relay device  30 . An endpoint device located in an area of overlapping coverage  34  can communicate with either of the relevant relay devices  30   a  and  30   b , or directly with central device  20 , depending upon, for example, which device  30   a ,  30   b , or  20  provided the clearest communication; which device  30   a ,  30   b , or  20  had the fewest number of endpoint devices already associated with it; or some other factor.  
         [0025]     As depicted in  FIG. 1 , coverage cell  10  is configured as an approximate hexagon for exemplary determinations of area and endpoint device density. RF coverage and hopping analyses will use circles. It can be shown that the area of a hexagon is: 
        Area=12*(r*cos 30*r*sin 30)/2     Area=3*cos 30*r{circumflex over ( )}2, where r is the radius of cell  10      Area=2.598*r{circumflex over ( )}2        
 
         [0029]     For example, assume for purposes of this exemplary analysis that there is one residential endpoint device for each approximately 33,508 square feet. While this number can and will vary in specific implementations and installations of the system, it serves here as a starting point of one example. TABLE 1 below shows the correlation between the number of meters in one cell  10  and the radius of cell  10 .  
                                             TABLE 1                       RADIUS IN   AREA IN   AREA IN   NUMBER OF       FEET   SQUARE FEET   SQUARE MILES   METERS/CELL                                200   103,920   0.0037   3       300   233,820   0.0084   7       400   415,680   0.0149   12       500   649,500   0.0233   19       600   935,280   0.0335   28       700   1,273,020   0.0457   38       800   1,662,720   0.0596   50       900   2,104,380   0.0755   63       1000   2,598,000   0.0932   78       1100   3,143,580   0.1128   94       1200   3,741,120   0.1342   112       1300   4,390,620   0.1575   131       1400   5,092,080   0.1827   152       1500   5,845,500   0.2097   174       1600   6,650,880   0.2386   198       1700   7,508,220   0.2693   224       1800   8,417,520   0.3019   251       1900   9,378,780   0.3364   280       2000   10,392,000   0.3728   310       2100   11,457,180   0.4110   342       2200   12,574,320   0.4510   375                  
 
         [0030]     Within a particular fixed network system, variations introduced related to geography, density, and types of meters should be considered with respect to signal propagation. Exemplary path loss equations are used for the loss between different types of environments. The equations each have a respective breakpoint at which the loss changes from a free space loss to a higher exponent loss.  
         [0031]     Shown below are basic loss equations and a table showing the amount of loss for a given distance at a frequency of about 1430 MHz rounded to the nearest approximately 0.1 dB. The heights of antennas for the various endpoint devices, relay devices  30 , and central device  20  used for these exemplary calculations include about twenty-five (25) feet to about 1.5 feet, about twelve (12) feet to about 1.5 feet, about six (6) feet to about 1.5 feet, about twenty-five (25) feet to about five (5) feet, about twelve (12) to about five (5) feet, and about six (6) to about five (5) feet. The heights of 1.5 feet and five (5) feet are used to simulate the actual heights of gas and electric meter endpoint devices and the twelve (12) and six (6) foot heights are used to simulate the heights of relay devices  30 . These heights are only approximate and exemplary of one embodiment of the system of the invention. The heights can vary in actual system implementations according to a variety of factors recognized by those skilled in the art.  
         [0032]     The following equations primarily describe the path losses (PL) after the breakpoint: 
 
 PL= 10*Loss Exp*log(Distance in feet)+loss intercept (for distance&gt;break point) 
 
         [0033]     Path Loss Equations for Exemplary Gas Meters 
 
 PL= 10*4.7917*log(Distance)−28.0 for distance&gt;100 feet and 25-1.5 antennas 
 
 PL= 10*5.6252*log(Distance)−49.228 for distance&gt;150 feet and 12-1.5 antennas 
 
 PL= 10*5.5619*log(Distance)−45.999 for distance&gt;150 feet and 6-1.5 antennas 
 
         [0034]     Path Loss Equations for Electric Meters 
 
 PL= 10*4.3468*log(Distance)−17.346 for distance&gt;200 feet and 25-5 antennas 
 
 PL= 10*5.2635*log(Distance)−40.691 for distance&gt;180 feet and 12-5 antennas 
 
 PL= 10*5.3915*log(Distance)−42.678 for distance&gt;180 feet and 6-5 antennas 
 
         [0035]    
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
               
             
             
               
                   
                 FREE 
                 GAS 
                 GAS 
                 GAS 
                 ELECTRIC 
                 ELECTRIC 
                 ELECTRIC 
               
               
                   
                 SPACE 
                 25-1.5 
                 12-1.5 
                 6-1.5 
                 25-5 
                 12-5 
                 6-5 
               
               
                   
               
               
                 BREAKPOINT 
                 1 
                 100 
                 150 
                 150 
                 200 
                 180 
                 180 
               
               
                 IN FEET 
               
               
                 Loss 
                 2 
                 4.7917 
                 5.6252 
                 5.5619 
                 4.3468 
                 5.2635 
                 5.3915 
               
               
                 EXPONENT 
               
               
                 Loss INTER. 
                   
                 −28.000 
                 −49.228 
                 −45.999 
                 −17.346 
                 −40.691 
                 −42.678 
               
               
                   
               
               
                 DISTANCE IN 
                 PL 
                 PL 
                 PL 
                 PL 
                 PL 
                 PL 
                 PL 
               
               
                 FEET 
                 IN DB 
                 IN DB 
                 IN DB 
                 IN DB 
                 IN DB 
                 IN DB 
                 IN DB 
               
               
                   
               
               
                  100 
                 65.0 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                  200 
                 71.0 
                 82.3 
                 80.3 
                 82.0 
                 NA 
                 80.4 
                 81.4 
               
               
                  300 
                 74.5 
                 90.7 
                 90.3 
                 91.8 
                 90.3 
                 89.7 
                 90.9 
               
               
                  400 
                 77.0 
                 96.7 
                 97.3 
                 98.7 
                 95.8 
                 96.3 
                 97.6 
               
               
                  500 
                 79.0 
                 101.3 
                 102.8 
                 104.1 
                 100.0 
                 101.4 
                 102.8 
               
               
                  600 
                 80.6 
                 105.1 
                 107.2 
                 108.5 
                 103.4 
                 105.5 
                 107.1 
               
               
                  700 
                 81.9 
                 108.3 
                 111.0 
                 112.2 
                 106.3 
                 109.1 
                 110.7 
               
               
                  800 
                 83.1 
                 111.1 
                 114.2 
                 115.5 
                 108.8 
                 112.1 
                 113.8 
               
               
                  900 
                 84.1 
                 113.6 
                 117.1 
                 118.3 
                 111.1 
                 114.8 
                 116.6 
               
               
                 1000 
                 85.0 
                 115.8 
                 119.7 
                 120.9 
                 113.1 
                 117.2 
                 119.1 
               
               
                 1100 
                 85.8 
                 117.7 
                 122.0 
                 123.2 
                 114.9 
                 119.4 
                 121.3 
               
               
                 1200 
                 86.6 
                 119.5 
                 124.2 
                 125.3 
                 116.5 
                 121.4 
                 123.3 
               
               
                 1300 
                 87.3 
                 121.2 
                 126.1 
                 127.2 
                 118.0 
                 123.2 
                 125.2 
               
               
                 1400 
                 87.9 
                 122.8 
                 127.9 
                 129.0 
                 119.4 
                 124.9 
                 126.9 
               
               
                 1500 
                 88.5 
                 124.2 
                 129.6 
                 130.7 
                 120.7 
                 126.5 
                 128.6 
               
               
                 1600 
                 89.1 
                 125.5 
                 131.2 
                 132.2 
                 121.9 
                 128.0 
                 130.1 
               
               
                 1700 
                 89.6 
                 126.8 
                 132.7 
                 133.7 
                 123.1 
                 129.3 
                 131.5 
               
               
                 1800 
                 90.1 
                 128.0 
                 134.1 
                 135.1 
                 124.2 
                 130.7 
                 132.8 
               
               
                 1900 
                 90.6 
                 129.1 
                 135.4 
                 136.4 
                 125.2 
                 131.9 
                 134.1 
               
               
                 2000 
                 91.0 
                 130.2 
                 136.6 
                 137.6 
                 126.1 
                 133.1 
                 135.3 
               
               
                 2100 
                 91.4 
                 131.2 
                 137.8 
                 138.8 
                 127.1 
                 134.2 
                 136.4 
               
               
                 2200 
                 91.8 
                 132.2 
                 139.0 
                 139.9 
                 127.9 
                 135.2 
                 137.5 
               
               
                 2300 
                 92.2 
                 133.1 
                 140.1 
                 141.0 
                 128.8 
                 136.3 
                 138.6 
               
               
                 2400 
                 92.6 
                 134.0 
                 141.1 
                 142.0 
                 129.6 
                 137.2 
                 139.6 
               
               
                 2500 
                 93.0 
                 134.8 
                 142.1 
                 143.0 
                 130.4 
                 138.2 
                 140.5 
               
               
                   
               
             
          
         
       
     
         [0036]     The above path loss numbers calculated are only statistical. Variation in these numbers should also be considered. Three forms of variation include: 
        σ LN =log normal variance in the path due to buildings, cars, etc.=about 8 dB     σ R =variance in the path due to Ricean fading=about 3.3 dB     σ F =variance in the path loss due to foliage=about 2.5 dB     σ t =total variance in the path loss=(σ LN   2 +σ R   2 +σ F   2 ) 1/2 =about 9.0 dB        
 
         [0041]     The variance is used to calculate a link margin necessary to achieve a particular probability of success in communications between devices within cell  10 . Two exemplary probabilities will be used, 80% and 95%. Using a table of Standard Normal Distribution, the 80% and 95% probability occur at z=0.84 and z=1.645, respectively. Link margin for any path can thus be found by multiplying σ t =9.0 dB by z. 
 
Link Margin (80%)=9.0*0.84=7.6 dB 
 
Link Margin (95%)=9.0*1.645=14.8 dB 
 
         [0042]     To determine cell coverage, several RF signal factors should be considered. Assume for purposes of this exemplary analysis that devices  30  and  20  and the endpoint devices use frequency-shift keying (FSK) modulation to transmit and receive in one mode of operation. This can vary in other modes, for example a two-step regenerative receiver mode, as shown below: 
        Sensitivity for central device  20 : 
            about −115 dBm for 0.01 frame error rate (FER)    
            Sensitivity for endpoint device/relay device  30 : 
            about −108 dBm for 0.01 FER    
            Sensitivity for regenerative mode for endpoint device/relay device  30 : 
            about −100 dBm for tone detect    
            Link Margin (80%): about 7.6 dB above PL     Link Margin (95%): about 14.8 dB above PL     Transmit Power for central device  20 : about +30 dBm     Transmit Power for endpoint device/relay device  30 : about +14 dBm     Antenna Gain of central device  20 : about 3 dBi     Antenna Gain of endpoint device: about −3 dBi     Antenna Gain of relay device  30 : about 0 dBi        
 
         [0056]     Outbound Regenerative Mode (Values are Approximate) 
        Path Loss for 80% (7.6 dB) central device  20  to endpoint device=+30+3−(−100)−3-7.6=122.4 dB     Path Loss for 80% (7.6 dB) central device  20  to relay device  30 =+30+3−(−100)+0-7.6=125.4 dB     Path Loss for 80% (7.6 dB) relay device  30  to endpoint device=+14+0−(−100)−3-7.6=103.4 dB        
 
         [0060]     Outbound FSK (Values are Approximate) 
        Path Loss for 80% (7.6 dB) central device  20  to endpoint device=+30+3−(−108)−3-7.6=130.4 dB     Path Loss for 95% (14.8 dB) central device  20  to endpoint device=+30+3−(−108)-3-14.8=123.2 dB     Path Loss for 95% (14.8 dB) central device  20  to relay device  30 =+30+3−(−108)+0-14.8=126.2 dB     Path Loss for 80% (7.6 dB) relay device  30  to endpoint device=+14+0−(−108)−3-7.6=111.4 dB     Path Loss for 95% (14.8 dB) relay device  30  to endpoint device=+14+0−(−108)−3-14.8=104.2 dB        
 
         [0066]     Inbound FSK (Values are Approximate) 
        Path Loss for 80% (7.6 dB) endpoint device to central device  20 =+14−3−(−115)+3-7.6=121.4 dB     Path Loss for 95% (14.8 dB) endpoint device to central device  20 =+14−3−(−115)+3-14.8=114.2 dB     Path Loss for 95% (14.8 dB) relay device  30  to central device  20 =+14+0−(−115)+3-14.8=117.2 dB     Path Loss for 80% (7.6 dB) endpoint device to relay device  30 =+14−3−(−108)+0-7.6=111.4dB     Path Loss for 95% (14.8 dB) endpoint device to relay device  30 =+14−3−(−108)+0-14.8=104.2 dB        
 
         [0072]     Observations relevant to system design and implementation, in particular how large cell  10  can or should be, can be made from the path loss table and link margin calculations. By way of example, assume that the antenna of central device  20  is about twenty-five (25) feet, the antenna of relay device  30  is about twelve (12) feet, a gas antenna is about 1.5 feet, and an electric antenna is about five (5) feet. See TABLE 3 below:  
                                                     TABLE 3                                   Distance   Distance for           Coverage   Path Loss   for Gas   Electric           In %   In dB   In Feet   In Feet                                Outbound central device 20 to endpoint   80   122.4   1375   1640       device WUT       Outbound central device 20 to relay   80   125.4   2380   2380       device 30 WUT           (est.)   (est.)       Outbound relay device 30 to endpoint   80   103.4   517   547       device WUT       Outbound central device 20 to endpoint   80   130.4   2020   2500       device FSK       Outbound central device 20 to endpoint   95   123.2   1430   1710       device FSK       Outbound central device 20 to relay   95   126.2   2480   2480       device 30 FSK           (est.)   (est.)       Outbound relay device 30 to endpoint   80   111.4   717   775       device FSK       Outbound relay device 30 to endpoint   95   104.2   535   565       device FSK       Inbound endpoint device to central device   80   121.4   1315   1555       20 FSK       Inbound endpoint device to central device   95   114.2   927   1060       20 FSK       Inbound relay device 30 to central device   95   117.2   1500   1500       20 FSK           (est.)   (est.)       Inbound endpoint device to relay device   80   111.4   717   775       30 FSK       Inbound endpoint device to relay device   95   104.2   535   565       30 FSK                  
 
         [0073]     Note from the above that the inbound FSK data from the endpoint device to central device  20  is the weakest link in this example. Note also that gas meter coverage area is smaller because the antenna is only about 1.5 feet above the ground versus the electric meter&#39;s approximately five (5) feet. Therefore, if cell  10  is designed for the worst-case gas meter coverage area, the electric meters will also be incorporated.  
         [0074]     In this example, relay devices  30  are placed about 1500 feet from the center of cell  10 . The outbound WUT/data from central device  20  will talk for approximately 1500 feet directly to endpoint devices or relay devices  30 . Relay devices  30  will extend that information another 500 feet or more to endpoint devices at the outer edges of cell  10 . For endpoint devices that are RF shadowed, another relay device  30  can be added as needed. The combination of central device  20  to endpoint device or central device  20  to the relay device  30  to endpoint device will be extended out to about 2000 feet or more. This process is repeated in reverse during the in-bound portion of a read cycle. Because endpoint devices can talk directly to central device  20  or a relay device  30 , the probability that the endpoint devices at the cell&#39;s  10  outer limits can talk back successfully to at least one device  20  or  30  is greatly increased. Thus, coverage in a 2000-foot cell  10  could include about 310 gas or electric meters under the umbrella of central device  20 .  
         [0075]     When central device  20 , a plurality of relay devices  30 , and a plurality of endpoint devices have been installed in a cell  10  and that all relay devices  30  are able to communicate with central device  20 . Each endpoint device and relay device  30  includes a regenerative receiver, a FSK receiver, and a FSK transmitter tuned to cell  10 &#39;s channel.  
         [0076]     Referring to  FIGS. 1 and 2 , central device  20  receives a command from the Head-End (HE), which will typically be a utility control or management center, through a Wide Area Network (WAN). Central device  20  then sends out an approximately two-second WUT (wake-up tone)  102  on cell  10 &#39;s channel to the regenerative receivers. This wakes up relay devices  30  and some or all of the endpoint devices, which in turn activate their FSK receivers. During the “on” portion of the WUT, FSK data is sent out with the number of WUT “on” periods left before sync and control information, plus the cell number. The endpoint device and relay devices  30  then go into sleep mode until the sync and control slot  104  to conserve current. Central device  20  then sends FSK sync and control data to relay devices  30  and the endpoint devices after the devices wake up again. The sync information is used to reset the real time clock (RTC) of each device to enable each device to transmit and receive with only a small error in specific time slots that follow.  
         [0077]     After sync and control sequence  104 , the endpoint devices and relay devices  30  go into sleep mode again until their assigned time slots.  FIG. 1  depicts only eight relay devices  30  ( 30   a - 30   h ), but a larger number, for example up to about thirty-one (31) relay devices  30  in one preferred embodiment, can be handled in the protocol and cell  10  with appropriate extension of the time sequence.  
         [0078]     After the WUT and sync time periods  102  and  104 , relay device  30  sends out the same WUT/sync sequence, such as sequences  106  and  108  by relay device  30   a  and sequences  110  and  112  for relay device  30   h , and wakes up the endpoint devices in its coverage area to establish a better communicative path to the endpoint devices than that directly from central device  20  (refer to  FIG. 1 ). This process repeats until all eight relay devices  30  have transmitted WUT sequences.  
         [0079]     The endpoint devices then begin responding to central device  20  or relay devices  30  in assigned time slots. If an endpoint device is assigned to a particular relay device  30 , that relay device  30  will wake up during that endpoint device&#39;s time slot, receive data transmitted by the endpoint device, and relay the data to central device  20  in a later assigned time slot. This sequence continues until all endpoint devices have transmitted. In one example embodiment, up to about 1790 time slots of about 100 milliseconds each are available for data. At the end of the data slots are 256 slots for Unsolicited Messages (UM). UMs can be global, central device  20 , relay device  30 , or reserved, and will be described in a later section. This total sequence takes about 223.7 seconds for cell  10  having eight (8) relay devices  30   a - 30   h . A similar sequence will take about 272 seconds for a cell with thirty-one (31) relay devices  30 . It is estimated that approximately 1000 or more endpoint devices could be read during this time. If needed, additional data slots could be added.  
         [0080]     Several wake-up tones can be set as default as shown below to accommodate a variety of data collection devices and create selectively hybrid systems. In one exemplary embodiment, some or all of the following wake-up tones can be set to increase the communicative options available for collecting data, although the wake-up tones and collection devices can vary in other preferred embodiments of the invention: 
         0 —Mobile Vehicle System      1 —Mobile Hand-Held System      2 —Relay Device  30  Wake-Up      3 —Endpoint Device Wake-Up Group A      4 —Endpoint Device Wake-Up Group B      5 —Endpoint Device Wake-Up Group C        
 
         [0087]     A mobile vehicle system tone ( 0 ) causes the endpoint devices, and preferably not relay devices  30 , to wake up and transmit a consumptive data message in a slot assigned to the device by a mobile collector, for example a data collection unit mounted or housed in a van or other vehicle. The mobile collector can therefore be used as needed or desired to conveniently collect supplementary, missed, or other data readings from a particular endpoint device or a plurality of endpoint devices.  
         [0088]     A hand-held tone ( 1 ) causes the endpoint devices, but not relay devices  30 , to wake up and transmit a consumptive data message in a slot assigned to it by a hand-held collector. Similar to the previously described mobile collector, a hand-held collector can be used as needed or desired to collect readings in a variety of situations, such as when an endpoint device reading by central device  20  or relay device  30  was missed or failed, or when a mid-cycle reading is needed. A user, whom may be a utility employee, walks or otherwise brings the hand-held collector within communicative range of the endpoint device to collect data.  
         [0089]     In one embodiment, a relay device ( 2 ) wake-up tone wakes up only a relay device  30 , not an endpoint device. Relay device  30  is then active to receive a command.  
         [0090]     The endpoint device wake-up group tones ( 3 - 5 ) wake up both relay devices  30  and endpoint devices to receive a communication. The communication can be a read command; a communication to register a newly installed device when building a cell; a communication or command to register, initiate, or test a replaced or serviced device; a device programming command; an instruction to a device to turn on a switch, for example in telemetry applications; and other similar commands, communications, requests, and instructions. In one embodiment, the endpoint device or relay device  30  comprises an application-specific integrated circuit (ASIC) RF detect/tone detect chip that can be programmed to accept up to eight tones. In other embodiments, chips capable of accepting more or fewer tones can be used.  
         [0091]     A synchronization and control communication between central device  20  and endpoint devices, central device  20  and relay devices  30 , and relay devices  30  and endpoint devices is preferably 100 milliseconds long at about 4.8 kbps in one embodiment of the invention. The communication begins with five (5) milliseconds of “dead” time, followed by 10 milliseconds of synchronization, start/calibrate RTC, in one embodiment. Frame ID and the number of relay devices  30  in cell  10  comprise ten (10) bits and are followed by a 32-bit time stamp. Next, global flags and commands comprise 24 bits in this exemplary embodiment, with fifty-six (56) bits held in reserve, to be assigned later. A 32-bit ID and 16-bit vector can be sent to up to four (4) devices in one embodiment to tell the devices to which transmit/receive slot to go for downloaded data. A 16-bit cyclic redundancy check (CRC16) preferably ends the data string, with 15 milliseconds of synchronization information sent to complete the start/calibration of the RTC.  
         [0092]     Referring to  FIG. 3 , UM slots  114  are slots  1791  to  2046 , with slots  1791  and  1792  as global UM slots in normal mode, in one preferred embodiment. Global UM slots are used most frequently during the installation and building of cell  10 , although the slots can also be used at other times and for other purposes. During installation and building, global UM slots may be expanded to sixteen (16) slots. Both central device  20  and relay devices  30  listen during global UM slots.  
         [0093]     Central device  20  UM slots are slots  1793  to  1825  in one preferred embodiment. The endpoint devices in cell  10  transmit to central device  20  on the odd slots in this range in a random fashion. If central device  20  hears a particular endpoint device, device  20  transmits a confirmation in the next slot back to the listening endpoint device. Up to sixteen (16) Ums can be received by central device  20  during any read sequence in one embodiment.  
         [0094]     Relay device  30  UM slots are preferably slots  1826  to  1981 . These slots are divided into thirty-one (31) blocks of five slots each. An endpoint device transmits in a random fashion in one of the first two slots to a relay device  30  to which the endpoint device is assigned. If relay device  30  receives the transmission, relay device  30  simultaneously sends the UM to central device  20  and back to the endpoint device sending the UM. Central device  20  sends a confirmation message back to relay device  30  in the fifth slot. This continues for the total number of relay devices  30  in cell  10 . Reserved slots are assigned from slot  1982  to slot  2046  in one embodiment, with slots  0  and  2047  reserved for quiet time and to listen to the noise floor of the system.  
         [0095]     An installation and general configuration process for a fixed AMR system according to one embodiment of the invention is depicted in  FIG. 4 . After an initial propagation study and pole location determination at step  120 , central device  20  is mounted and connected to the WAN at step  122 . At step  124 , relay devices  30  are mounted, although these devices  30  can also be added as needed as cell  10  is built. At step  126 , central device  20  to relay device  30  communication margins are tested. Endpoint devices can then be installed and associated data, including latitude and longitude location and other information, recorded at step  128 , then tested on-site at step  130  using a hand-held reader or other mobile device. Each endpoint device is sent a unique WUT at step  132  and in response activates its FSK receiver at step  134 . At step  134 , the WUT is followed by an install command from the reader to the endpoint device. If the endpoint acknowledges the command by transmitting its identification on the cell channel at step  138 , the endpoint is successfully installed and initialized.  
         [0096]     A preferred or optimal path to any endpoint device can be determined and set during the installation process, as depicted in  FIG. 5 . During a normal read cycle, the endpoint device hears a WUT from either central device  20  or a relay device  30 . For example, in one embodiment after a head-end initiates a command to central device  20  at step  140 , central device  20  transmits a WUT to endpoint devices and relay devices  30  within cell  10  at step  142 . The endpoint device receives synchronization, and command and control information, and then goes into low current sleep mode at step  144 . If the endpoint device is registered, the device will later respond according to command at step  146 . If the device is unregistered, at step  148  the device will remain in sleep mode until the global UM slots. Upon wake-up in either situation, the endpoint device transmits a “Who Can Hear Me?” message. Central device  20  and each relay device  30  listen during these slots. If relay device  30  hears an endpoint device, device  30  transmits endpoint device information to central device  20  at step  150 . These devices  20  and  30  record endpoint device identification and received signal strength indicator (RSSI) information that is sent to the head-end at step  152  for determination of the optimal route at step  154 . This information can be sent directly from central device  20  or through one of the relay devices  30 . This relieves central device  20  of the task of solely determining optimum routes.  
         [0097]     Referring to  FIG. 6 , during the next read cycle, the endpoint device just heard is called up in the identification vector of the system sync and control slots. At step  160 , central device  20  sends WUT and system synch and command and control information to the endpoint device. The endpoint device then sets its RTC during the synch pattern at step  162  and goes into low current sleep mode, wakes up during the proper slot called out by the vector, and listens for its assigned transmit slot at step  164 . Alternatively, the endpoint device can send back a confirmation in one of the later slots or wait for the next read cycle and transmit data as confirmation.  
         [0098]     Referring to  FIG. 7 , the endpoint device receives information from relay device  30 , rather than directly from central device  20 . At step  170 , central device  20  sends a WUT, system synchronization and control information, and endpoint slot information to relay device  30 . Relay device  30  passes the information to the endpoint device at step  172  and the endpoint device transmits a confirmation in its assigned time slot at step  174 . Relay device then transmits the confirmation to central device  20  at step  176 .  
         [0099]     There may be occasions when an endpoint device will lose synchronization with central device  20 . In one embodiment, the endpoint device will wait for the next read cycle, wake up, have its RTC set, and respond in the proper slot to regain synchronization. An advantage of the system is that it is automatically synchronized during each read cycle by simply waking up and listening to the system sync and control time period.  
         [0100]     Data packet speeds will depend primarily upon the endpoint device receive detection scheme, controller power, and current. In one embodiment, 4.8 kbps Manchester encoded data can be decoded in a relatively inexpensive controller. At this speed, about 480 bits or about 60 bytes of data could be sent during the 100 millisecond transmit and receive data slots. Data sent at about 4.8 kbps will also be decoded at an improved receive sensitivity than that sent at 9.6, 16.384, 19.2, or 38.4 kbps. This will help to enlarge cell  10  and improve the link margin.  
         [0101]     Data packet sizes will dictate much of the system and communication timing. In one embodiment, and allowing about five (5) milliseconds at the beginning and end of the packet as dead time for RTC drift or some other minor error, the nominal size of the packet is about fifty-four (54) bytes. The packet preferably comprises three (3) bytes of bit/frame synchronization, four (4) bytes central device  20  identification, four (4) bytes of relay device identification, four (4) bytes endpoint device identification, three (3) bytes of command protocol, thirty-four (34) bytes of data, and two (2) bytes of CRC in one preferred embodiment. The thirty-four (34) bytes of data allow for seventeen (17) buckets of data at two (2) bytes/bucket in one embodiment. This enables one (1) hour and twenty-five (25) minutes worth of reads with a five (5) minute interval; four (4) hours and fifteen (15) minutes worth of reads with a fifteen (15) minute interval, and seventeen (17) hours worth of reads with a one (1) hour interval.  
         [0102]     The bandwidth of the transmitters is a function of various factors, for example, the data rate, encoding technique, deviation, data wave shape generation, and base-band filtering, among others. Outbound and inbound data packets will preferably use a form of FSK modulation, such as minimum shift keying (MSK), Gaussian MSK (GMSK), or compatible four-level frequency modulation (C4FM), among others, with 4.8 kbps Manchester encoded data. Deviation can be about ±4.8 kHz in one embodiment.  
         [0103]     Using Carson&#39;s rule, the approximate bandwidth (BW) is as follows: 
        BW=2*Peak Deviation+2*Base-band bandwidth     BW=2*4.8 kHz+2*4.8 kHz     BW=about 19.2 kHz        
 
         [0107]     The bandwidth of the receivers is preferably as narrow as possible, consistent with phase-locked loop (PLL) reference crystal drift, range of automatic frequency control (AFC), and temperature drift of the IF filters, to provide the best sensitivity and range for the system. In one embodiment, receiver bandwidth may be about 20 kHz to about 25 kHz. To address adjacent channel rejection in all system devices, the channels are preferably spaced about 50 kHz apart. While potential exists for interference from another system in the local area of cell  10 , the time and frequency of the reads should minimize the data packets lost.  
         [0108]     Cell timing is important, as each endpoint device and relay device  30  in cell  10  needs to know when to come out of sleep mode and either transmit or receive in a specific time slot. The RTC is preferably running all the time, even during an endpoint device&#39;s low current sleep mode. The RTC and a counter in the device controller will instruct the FSK receiver when to turn on. Because the RTC clock must be relatively low frequency to keep the sleep mode current low and reduce battery consumption, a 32-kHz crystal will be used in one embodiment. The 32-kHz crystal can be a “BT” cut with parabolic TC curve having a reference setting at +25C in one preferred embodiment, although other crystals can also be used.  
         [0109]     Over a temperature range of about −40C to about +85C, however, the crystal could move up to about −150 ppm. This translates to about −45 milliseconds in a 5-minute read period. This amount of time is about half of the 100 millisecond transmit and receive data slot and is therefore unacceptable. A proposed correction scheme is to use the synchronization at the beginning and end of the system sync and control slot is transmitted after the WUT as described above. The time between these two (2) synchronization bursts would calibrate the 32-kHz crystal and counter in the controller within about 15 ppm, reducing error in the Sminute read cycle wake-up error to less than five (5) milliseconds.  
         [0110]     A combination of a special specification for the crystal and AFC in the receiver may be required in some embodiments. If the crystal of the PLL is called out to be ±10 ppm in a range of about −20C to about +70C, the crystal can then be about −30 ppm at about −40C and about +25 ppm at about +85C. Taking the worst case of −30ppm, the LO would be about −43kHz from the desired frequency. This is approaching two (2) channel bandwidths away. Accordingly, a tighter crystal could be called out and AFC used in the receiver.  
         [0111]     Referring to  FIG. 8 , an AFC loop  120  preferably starts during the WUT detection period. After the WUT is detected, the FSK receiver turns on. Since detector  122  has a component at DC that is representative of the carrier, the modulation is stripped away in a low pass filter (LPF)  124 . This leaves the DC component, which is fed to a controller  126  A/D port where a voltage offset between the incoming carrier and a perfect carrier is measured. This differential is converted to a frequency error and then new numbers in the PLL fractional N divider  128 . The new numbers are loaded, VCO  130  changes frequency in the LO, and the new IF is fed to detector  122  for another sampling. Because the fractional N divider resolution is about 500 Hz, the overall LO should be correctable to this level in a preferred embodiment.  
         [0112]     The above preferably occurs during the WUT period before the system sync and control begins. This will center the IF and ensure the receiver has the best possible sensitivity. The offset in the fractional N dividers is also transferred to the transmit signal. This will ensure that the endpoint device is transmitting on the correct frequency, or within about 500 Hz. AFC loop  120  is used in relay device  30  to ensure that device  30  transmits on the correct frequency to the endpoint device.  
         [0113]     Battery-powered devices within cell  10  can present power consumption issues that should be addressed to improve the efficiency of the system. For example, the overall costs associated with the system are greatly increased if system devices need to be frequently serviced in person in order to check and change out battery power supplies. In one preferred embodiment according to exemplary calculations and estimations, system devices are optimized to reduce current drain, providing a battery power source life of at least seven (7) years or more for a SAFT D LS 33600 cell in relay device  30 . For relay devices  30  having less than ten (10) endpoint devices in a communicative umbrella, which infrequently send UMs, and with a cell read every approximately half-hour or hour, the same D-cell could last ten (10) years or more.  
         [0114]     Therefore, the invention substantially meets the aforementioned needs of the industry, in particular by providing a system and method of operating AMR systems that allow for the storage and transfer of meter readings and other data to eliminate the need to physically visit a remote endpoint device and connect directly to the endpoint device for the collection of data.  
         [0115]     In one preferred embodiment, the invention is directed to a system and method for meter reading of a fixed network that provides two-way communication between an endpoint device and a reader. The fixed network meter reading system and method of the present invention provide larger cell sizes than in previous fixed network meter reading systems, partly through the use of intermediate relay devices and cost-effective endpoint devices that consume less power.  
         [0116]     In a related embodiment, the invention enables two-way communication in a fixed network meter reading system. In a series of communications between a central reader, a plurality of relays, and a plurality of endpoint devices associated with each of the plurality of relays, data requests and responses are exchanged between the endpoint devices and the relays, and subsequently the relays and the central reader. The central reader, plurality of relays, and plurality of endpoint devices are part of a fixed “ring” system distributed throughout a geographic area.  
         [0117]     The invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.