Abstract:
A radial-shaped wireless fence system is provided that contains one or more dogs in a user-defined area without the need for a physical fence or underground wire. The system includes a base unit and at least one collar, and is easy to set up and use. Through improved filtering of consecutive distance measurement values taken between the base unit and the collar, errant measurement values are discounted in terms of their contribution to the current estimate of the dog&#39;s distance from the base unit. These filtering techniques, in combination with improved signal strength and antenna diversity in the communication between the base unit and the collar, improve the accuracy and consistency with which the dog&#39;s distance from the base unit is tracked so that unwanted corrections are not administered to the dog.

Description:
[0001]    This application is entitled to and hereby claims the priority of co-pending U.S. Provisional application Ser. No. 61/282,727, filed Mar. 23, 2010. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related to the field of animal containment and, more particularly, to a system and method for defining a wireless dog fence that surrounds a user-defined area and for using the fence to contain one or more dogs within the user-defined area. 
         [0004]    2. Description of the Related Art 
         [0005]    Containing one or more dogs within a prescribed area has been achieved in many different ways, most traditionally through the construction of a fenced enclosure that is high enough to prevent the dog from escaping the enclosure by going over the fence. Since some consider above-ground fencing to be unattractive or otherwise undesirable, “invisible” fence products have been developed that rely on a wire buried underground that defines a desired “fence” border for the dog or dogs. The wire transmits a signal that activates a specially designed collar worn by the dog when the dog comes within a certain proximity of the border. The collar, once activated, can issue an audible warning and/or an electric shock to the dog to ensure that the dog does not leave the “fenced-in” area. Buried wire systems are labor intensive to install. Further, since the wire may be unintentionally cut, or otherwise damaged, such as by digging or tilling during lawn maintenance or the like, such buried wire fence systems are also labor intensive when attempting to find the location of the broken wire or other difficulty. 
         [0006]    More recently, wireless fence products have been developed that radiate a low frequency signal to saturate a spherical volume which translates to a generally circular area on the ground plane. The radius of the circle is user-definable and, according to one such product manufactured by PetSafe, generally extends radially from about 5 feet to about 90 feet. When the dog, while wearing a specially designed collar, is “inside” the signal saturated area, the collar receives a signal and no action is taken. When the dog moves outside the signal area, however, the collar delivers a correction signal. 
         [0007]    Another wireless system is that marketed by Perimeter Technologies, Inc. which, rather than creating a signal-saturated area, uses a distance measuring technology between the collar and a base unit to determine the range of the dog from the base unit. However, interference created by objects often found within a household environment can cause the collar and base to lose communication with one another, resulting in artificially high range values caused by attenuation or reflection, and/or undesired corrections being delivered to the dog, i.e., corrections when the animal is within the defined containment radius. 
         [0008]    Accordingly, a need exists for an improved wireless fencing system that is easy for the consumer to set up and use and that overcomes the problems encountered with prior art systems. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the foregoing, one object of the present invention is to overcome the difficulties of containing a dog within a wireless fence boundary without administering unwanted corrections to the animal. 
         [0010]    Another object of the present invention is to provide a wireless fence system having a dual-antenna base unit and a dual-antenna collar to improve the ratio of successfully received signal transmissions to lost signals. 
         [0011]    A further object of the present invention is to provide a wireless fence system in accordance with the preceding objects in which distance values are repeatedly obtained between the base unit and the collar and then weighted and filtered to discount those distance values likely to be errant and to track more accurately the range of the dog from the base unit. 
         [0012]    A still further object of the present invention is to provide a wireless fence system in accordance with the preceding objects in which NANOLOC™ chipsets are used in conjunction with a power amplification circuitry to provide greater signal strength for improved reliability in tracking the dog within the fence boundary. 
         [0013]    Yet another object of the present invention is to provide a wireless fence system in accordance with the preceding objects in which the tracking process of the system includes a normal battery conservation mode and an accelerated mode during which the distance value sampling rate is increased in response to the dog&#39;s proximity to the fence boundary. 
         [0014]    It is yet another object of the invention to provide a wireless pet containment product that is user friendly and robust in operation and which effectively tracks the distance between a base unit and the dog to reduce the number of inappropriate corrections administered to the dog. 
         [0015]    In accordance with these and other objects, the present invention is directed to a radial-shape wireless fence system for containing one or more dogs in a user-defined area without the need for a physical fence or underground buried wire. As used herein, “radial-shape” refers to a generally circular area defined by a border that encircles a center point defined by the location of the base unit. The border represents an approximate area within which the collar will begin to initiate a correction to the dog. This border area marks the start of a trigger zone which extends outwardly from the border in all directions to a distance at which the collar can no longer receive input from the base unit. This distance, and hence the “size” of the trigger zone, will vary depending upon the terrain and objects between the dog and the base unit, but can be as much as about a mile and a half from the base unit in open flat country. The fence radius, which is set by the user, is the distance between the base unit and the border and defines a roaming area. As long as the dog remains within the roaming area, signal transmissions are effectively sent and received between the base unit and the collar to monitor the dog&#39;s range from the base unit in real time, and no corrections are issued to the dog. Under these conditions, the collar may be configured to go to sleep to conserve battery power. In addition, the system may be configured to filter out errant values and/or to take no action if communication is suddenly blocked, such as due to loss of power to the base or collar, or the introduction of a physical signal-blocking element to the system environment. 
         [0016]    Also as used herein, the “fence” is an estimated line that runs concentrically with the border of the trigger zone. In the absence of any interference or signal attenuation, the fence would be circular, representing the circumference of a circle defined by the radius. Due to real-world conditions, however, in which signal interference is caused by various objects within the encircled area, or objects anywhere that cause multipath effects, the generally circular roaming area may have segments in which the border or “fence” is closer to the base unit than at other segments, i.e., segments in which the distance between the border/fence and the base unit is less than the fence radius. 
         [0017]    The system includes a base unit and at least one collar for a dog, with multiple collars also being supported for additional dogs, which is easy to set up and use. Both the base unit and the collar have two antennas each, providing diversity to improve the ratio of successfully received signal transmissions to lost signals. 
         [0018]    The base unit is mounted inside the user&#39;s house or other desired indoor location. By following a set-up menu on a display screen and using input elements on the base unit, the user enters a desired fence radius. The user then verifies the desired fence radius by walking outwardly from the base unit with the collar, noting when the collar outputs a signal indicating proximity to the trigger zone and placing a flag or other marker at that location. The user then walks back into the roaming area, moves laterally, and then walks back outwardly until the collar again signals proximity to the trigger zone at which point the user sets another flag or marker. This process is continued until the complete border has been marked with the flags or markers. Using these flags as visual cues of the location of the “fence”, and with the collar on the dog, the user can then train the dog where the fence border is so that the dog can be effectively contained therein. 
         [0019]    Once the fence has been set up and the dog trained, the system operates by continuously obtaining distance values between the base unit and the collar in order to track the distance of the dog from the base unit on a real time basis. These distance values are weighted and filtered to discount those distance values likely to be errant due to their disparity with previously measured values and previous calculated estimates of the dog&#39;s position. More particularly, through weighting and filtering of a plurality of continuously obtained distance measurement values taken between the base unit and the collar, anomalous measurement values are discounted in terms of their contribution to the current estimate of the dog&#39;s location. These filtering techniques in combination with improved signal strength and antenna diversity in the communication between the base unit and the collar improve the accuracy with which the dog&#39;s range from the base unit is tracked so that unwanted corrections are not administered to the dog. 
         [0020]    These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  shows the components of a radial-shape wireless fence system in accordance with the present invention. 
           [0022]      FIG. 2  illustrates the base unit shown in  FIG. 1  as mounted inside a house to define a roaming area and the trigger zone. 
           [0023]      FIG. 3  illustrates the fence border and outlying trigger zone of the system set-up shown in  FIG. 2 . 
           [0024]      FIG. 4  is a flowchart showing the steps taken during the fence setting mode of the system shown in  FIG. 1 . 
           [0025]      FIG. 5A  is an isolated view of the assembled collar shown in  FIG. 1 . 
           [0026]      FIG. 5B  is an exploded view of the components of the collar shown in  FIG. 5A . 
           [0027]      FIG. 5C  is a photograph of the first strap part of the collar strap as shown in  FIGS. 5A and 5B , and the antenna to be inserted into the hole in an interior end of the strap part. 
           [0028]      FIG. 5D  is a photograph of the components shown in  FIG. 5C  after the antenna has been inserted into the hole in the strap. 
           [0029]      FIG. 5E  is a photograph of the printed circuit board shown in  FIG. 5B , as mounted in the lower housing and with the collar straps connected thereto. 
           [0030]      FIG. 5F  is a photograph of the collar components shown in  FIG. 5B , without the battery, as the upper housing is brought into alignment with the lower housing. 
           [0031]      FIG. 5G  is a photograph of the collar components shown in  FIG. 5F , as the upper housing is brought into engagement with the lower housing to seal the correction unit compartment. 
           [0032]      FIG. 5H  is a photograph of the collar components shown in  FIGS. 5F and 5G  with the correction unit compartment positioned for sealing in an ultrasonic welding machine. 
           [0033]      FIG. 6  is a flowchart showing the steps taken during the collar setting mode of the system shown in  FIG. 1 . 
           [0034]      FIG. 7  is a flowchart showing the steps taken during the ranging process of the system shown in  FIG. 1 . 
           [0035]      FIG. 8  is a flowchart showing the steps taken during the system monitoring mode of the system shown in  FIG. 1 . 
           [0036]      FIG. 9  is a flowchart showing the steps taken during the tracking process of the system shown in  FIG. 1 . 
           [0037]      FIG. 10  is a flowchart showing the steps taken during the correction process of the system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
         [0039]    According to the present invention generally designated by reference numeral  10 , a radial-shape wireless fence system is provided that includes a base controller unit  12  and a remote unit, generally embodied as a collar  14 , as shown in  FIG. 1 . For the purposes of training the dog and to provide visual markers for both the dog and the user that generally correspond with the fence border, a set of flags  16  is also preferably provided with the system. The number of flags may be variable, but it is preferred to have from about 25 to about 100 flags, depending upon the radius of the containment or roaming area  32  to be defined. 
         [0040]    As shown in  FIG. 2 , the base unit  12  is intended to be positioned within the user&#39;s home  18 , garage, or other environmentally controlled, indoor area, and is preferably configured to be mounted on a wall. While it is possible to power the base unit with batteries, it is preferably plugged into a properly grounded 120V AC outlet. The base unit has two antennas  20 ,  21  for diversity when communicating with the collar  14 , a display screen  24  (preferably LCD) and input elements or buttons, generally designated by reference numeral  26 , for inputting information to set up and control the system. According to a preferred embodiment, the input elements include up and down arrow keys  28 ,  29  and an enter button  30 . 
         [0041]    The base unit communicates with the collar using an integrated circuit (IC) chip contained within the base unit. According to a preferred embodiment, the chipset is a NANOLOC™ TRX 2.4 GHz transceiver chipset sold by Nanotron Technologies of Berlin, Germany. The NANOLOC™ TRX 2.4 GHz transceiver chipset is an IEEE 802.15.4a chirp spread spectrum radio module with indoor and outdoor ranging capabilities. Other chipsets that use the IEEE 802.15.4a chirping technique for radio frequency distance measurement could also be used. 
         [0042]    The base unit  12  is configured to enable the user to set up a custom-sized fence radius of from about 40 to about 400 feet. As noted previously, the radius establishes the distance to the “fence”  31  which encloses the inner roaming area  32  and establishes the border at which the trigger zone  34  begins. While the trigger zone appears to be an annular area or ring  33  as shown in  FIG. 3 , the ring  33  actually represents the fact that there is generally some leeway or cushion in the exact location of the border  31  as compared to the fence radius set by the user, due to signal interference and attenuation caused by real-world conditions as already noted. Hence, the point at which a correction is actually initiated could be within or on either the inner or outer edges of the annular area  33 . 
         [0043]    As summarized in  FIG. 4 , during the fence setting mode, the base unit is located at the center of the desired radial-shaped area to be set up, step  40 . The user enters the desired fence radius into the base unit, step  40 , following a set-up menu displayed on the display screen and using the input elements or buttons  26  to select the desired parameters. Once the radius has been entered, the user walks to the border with the collar to verify that the desired radius has been set by noting where the collar reacts indicating proximity to the trigger zone  34  and places a training flag at that location to define the fence  31 , step  42 . The remainder of the border or fence  31  is flagged off by the user as described in step  44 . A more complete description of the process by which the user enters the fence radius and verifies the location of the fence  31  is set forth in the document entitled “Radial-Shape Wireless Dog Fence Instruction Manual” which is attached hereto as Appendix A and is considered part of the instant disclosure as if fully set forth herein in its entirety. 
         [0044]    As shown in  FIGS. 5A and 5B , the collar  14  includes a strap generally designated by reference numeral  50  that is fitted around the dog&#39;s neck and a correction unit  52  mounted to the strap  50 . The strap  50  includes a first part  49  having holes therein that is coupled to one side of the correction unit  52 , and a second part  51  connected to the other side of the correction unit  52  which has a buckle assembly  53  that can be engaged with the holes to secure the collar  14  around the dog&#39;s neck. 
         [0045]    The correction unit  52  includes a compartment  29  having a lower housing  66  and an upper housing  54  with a cover  55  through which a CR123A battery  56 , for example, may be inserted into the compartment  29  for providing power to the unit  52 . The correction unit further preferably includes an indicator light  58 , preferably an LED post  59  joined to the upper housing  54  with a waterproof adhesive, that is visible from the outer side of the correction unit and, like the base unit, the collar has two antennas  60 ,  61  to provide diversity when communicating with the base unit. 
         [0046]    As shown in  FIGS. 5C and 5D , the antenna  61  is preferably inserted through an opening  46  and into a blind channel  47  in the collar strap part  49  prior to final assembly of the collar and is secured with silicone or similar material at the strap antenna insertion points. Insertion of antenna  60  into a corresponding hole and channel in strap part  51  is accomplished in like manner. 
         [0047]    Housed within the compartment  29  of the collar correction unit  52  is a printed circuit board (PCB) assembly  65  as shown in FIGS.  5 B and  5 E- 5 G. A NANOLOC™ TRX 2.4 GHz transceiver chipset like that in the base controller is integrated with the PCB assembly  65  under RF shield  39  (see  FIG. 5E ). The collar and base unit NANOLOC™ chipsets send and receive radio transmissions from one another like 2-way radios. The NANOLOC™ chipsets are preferably enhanced in operation with power amplification circuitry to provide greater signal strength. When radio signals are sent from the antennas of either the base unit or the collar to the other of the two components, these signals propagate in an omni-directional or spherical manner. Using these signals, the enhanced NANOLOC™ chipsets perform a ranging process with their associated antenna pairs which continuously captures, filters and refines the data to yield the distance between the base unit and the collar at any given time, as will be described further hereinafter. 
         [0048]    Two probes  64  extend laterally from the lower housing  66  of the compartment  29  that is against the dog&#39;s neck and are insulated from the housing  66  by electrode grommets  63 . Shorter probes  67  can be interchangeably mounted to the lower housing  66  to better suit short-haired dogs. Depending upon the setting of the collar, the probes  64 ,  67  provide a physical correction signal to the dog upon reaching the trigger zone. Alternatively, the collar can be set to provide only an auditory correction signal to the dog. The physical correction signal is preferably adjustable between a plurality of levels to suit the size, age and temperament of the dog. In a preferred embodiment, the collar defaults to a tone-only correction signal. 
         [0049]    To assemble the collar, the ends of the antennas  60 ,  61  that extend out of the channels  47  are coupled to connectors on the PCB assembly  65 , preferably with a snap-on or push-on fit. The PCB assembly is received within the lower housing  66  with the collar strap parts  49 ,  51  on either side of the lower housing as shown in  FIG. 5E . The upper housing  54  is then brought into alignment with the lower housing as shown in  FIG. 5F , and then brought closer to engage with the lower housing as shown in  FIG. 5G . Once the upper and lower housing are engaged with one another to ultimately close the compartment  29 , the correction unit  52  is sealed, preferably using an ultrasonic welding machine  81  as shown in  FIG. 5H . Once fully assembled and welded as shown in  FIG. 5A , the collar and correction unit  52  are sufficiently waterproof so as to be able to be submerged for a period of about one minute and thereafter operate at or above 75% of accepted specifications for collar performance. 
         [0050]    The collar  14  is set up for use with the fence system of the present invention using the base unit  12  as summarized in  FIG. 6 . The consumer can use the base unit to add, delete or change settings for the collar, step  70 . To add another collar for another dog, step  72 , the user presses one of the input buttons  26  on the base unit to place the base unit into a seek mode. When powered on, the collar is programmed to listen for and respond to a signal from an appropriate enabled device such as the base unit. Upon receiving the collar&#39;s response signal, the base unit identifies the unique media access control (MAC) address associated with the collar and stores its identity. Collar correction levels and the on/off status of the collar can also be changed using the base unit, step  74 . In addition, collars can be deleted using the base unit, step  76 . A more detailed description of the process by which the user sets up, activates and deletes one or more collars is set forth in Appendix A, previously referenced and attached hereto. 
         [0051]    Once the collar has been set up and activated, the NANOLOC™ chipsets perform their ranging function to determine the distance between the base unit and the collar at any given time. The ranging process is as described in connection with the NANOLOC™ chipset on the NANOLOC™ website, and is summarized in  FIG. 7 . Ranging occurs on an ongoing basis unless the collar is asleep. The collar sleeps on lack of motion and wakes up when motion is detected by a motion sensor, such as an accelerometer, integrated with the collar. 
         [0052]    In brief, the first antenna at the base unit determines a first distance value between itself and the first antenna on the collar, and then determines a second distance value between itself and the second antenna on the collar. The second antenna at the base unit then determines a third distance value between itself and the first antenna on the collar, and then determines a fourth distance value between itself and the second antenna on the collar. If all four distance values are successfully determined, the actual distance value used in terms of obtaining the current estimate of the dog&#39;s location is the shortest of the four measured values. This ranging process is more fully described in co-pending application Ser. No. 12/539,404, published as U.S. Publ. No. US 2010/0033339 on Feb. 11, 2010 (“the &#39;339 application”). The &#39;339 application is hereby incorporated by reference and considered part of the instant disclosure as if fully set forth herein in its entirety. 
         [0053]    Having two antennas at each of the base unit and the collar improves the ratio of successfully received signal transmissions to lost signals as compared with single antenna systems. This improved ratio is particularly helpful in a household environment in which buildings, shrubs, vehicles and other objects can act to interfere with and/or block signal transmissions. Blocked signals can result in the unwanted issuance of a correction to the dog, i.e., the dog is corrected even though still within the prescribed boundary, or in escapes from the boundary if communication is sufficiently blocked. 
         [0054]    The double antenna system also provides for dead zone detection and accommodation. A dead zone is defined as an area in which signal transmission may be lost or compromised. If such dead zones are not detected or otherwise taken into account, this omission can result in an unwanted correction being issued to the dog as the system may conclude from the lack of signal transmission that the dog is outside the boundary. A fuller discussion of the dead zone feature is set forth in the &#39;339 application. 
         [0055]    As summarized in  FIG. 8 , once set up, the wireless fence system  10  maintains a monitoring mode during which the base unit  12  displays information relating to the status of the battery charge level of the collar  14 , the current distance value between the collar and the base, and whether a breach is detected, step  80 . The base unit  12  may be configured during set-up to sound an alarm when a breach occurs. A breach is defined as having occurred when the distance value between the collar and the base unit is greater than or equal to the radius set up for the fence border, step  82 . When a breach occurs, the system enters a correction mode as will be described further hereinafter. 
         [0056]    To reduce the likelihood of an unwanted correction being administered to the dog, the system according to the present invention includes a tracking process which is summarized in  FIG. 9 . When performing the tracking process, a valid distance value is stored in flash memory at the base unit, step  90 . However, the base and collar continually transmit and receive signals to calculate updated distance values on an on-going basis to track the dog in real time. During this ongoing process, particular distance values taken at any given time may be slightly inaccurate with respect to the actual location of the dog, indicating the dog to be in the trigger zone when, in fact, the dog is still inside the roaming area. These errant values, if taken on face value, would result in an unwanted correction being administered to the dog. Hence, the tracking process uses an improved Kalman filtering technique with hysteresis to “smooth out” consecutive distance values so that errant values caused by tolerances and attenuation will be ignored, step  92 , and a more accurate tracking distance value obtained, step  100 , as will be described more fully hereinafter. 
         [0057]    The tracking process includes a normal battery conservation mode and an accelerated mode for the battery  56  of the collar  14 . Whether the battery conservation mode is appropriate depends upon the difference between the distance value and the fence radius, step  93 . If the difference between the distance value and the fence radius is greater than a threshold value, the tracking mode remains in the normal battery conservation mode in which the current range to the collar is checked every 500 ms, step  95 . If, however, the difference between the distance value and the fence radius is less than the threshold value, indicating the dog to be nearing the fence or border, the system enters a fast range mode in which the range is checked every 100 ms, step  97 . This use of different sampling rates allows for greater battery conservation through less frequent sampling when warranted by the dog&#39;s position without sacrificing accurate tracking obtained through accelerated sampling as the dog approaches the fence  31  and trigger zone  34 . 
         [0058]    As already described, the tracking process also continually compares the distance value associated with the collar with the fence radius, step  94 , and, if the distance value is less than the fence radius, no action is taken, step  96 . If the distance value is greater than the fence radius, however, a correction sequence is commenced, step  98 . 
         [0059]    As summarized in  FIG. 10 , the correction process begins when the base unit sends a command to the collar to correct, step  110 . Upon receipt of this command, the collar is activated and issues a correction in the form of a tone and/or physical correction, step  112 . The correction continues until a set time-out period has been reached, step  114 , or until the dog returns approximately 10 feet within the roaming area, step  116 . If the time-out period has been reached, step  114 , the correction stops, step  118 . If the time-out period has not been reached, step  114 , and the dog has returned within the roaming area, step  118 , the correction also stops. If, however, the time-out period has not been reached and the dog has not returned, step  116 , the correction continues, step  112 . The length of the time out period can be varied, but according to one preferred embodiment the time out period is about 30 seconds. The extent to which the dog must return within the roaming area before the correction is stopped could also be more or less than 10 feet according to system design and settings. 
         [0060]    To perform the “smoothing out” of consecutive distance values to avoid inadvertent correction of the dog, various types of filtering algorithms may be employed to filter the distance values. In a preferred embodiment, the system according to the present invention uses an enhanced Kalman filtering technique as described in Appendix B, attached hereto and considered part of the instant disclosure as if fully set forth herein in its entirety. Appendix B is an excerpt of a paper entitled, “An Introduction to the Kalman Filter” by Greg Welch and Gary Bishop in the Department of Computer Science at the University of North Carolina at Chapel Hill. 
         [0061]    As a means of further smoothing out consecutive distance values and of detecting and ignoring anomalous values, the Kalman filtering algorithm used according to the present invention assigns a weight to each measured distance value according to the apparent reliability or confidence of the measurement sample. The confidence of the measurement sample is determined on the basis of a comparison made between the currently measured distance value and the previously estimated distance value as determined by the Kalman filtering algorithm. If the difference between the currently measured distance value and the previously estimated distance value is greater than a predetermined threshold, then the currently measured distance value is considered to be suspect, i.e., to have limited confidence, and is given little weight. This situation may be illustrated by the following example. The previously estimated distance value between the dog and the base unit was 10 feet and the currently measured distance value, taken a second later, indicates the dog to be 30 feet away from the base unit. The currently measured distance value would appear to be errant since, clearly, the dog could not have covered that much distance in the time that elapsed. A currently measured distance value that represents a realistic movement change, i.e., that shows a position change less than the threshold, is given greater weight when used to calculate an updated estimated distance value from the base unit to the dog. A more detailed description of the weighting process used by the Kalman filtering algorithm according to the present invention is set forth in Appendix B and is also described in the &#39;339 application. 
         [0062]    The confidence of the measurement sample may also be evaluated using both a comparison between the currently measured distance value and the previously estimated distance value, and an output of an accelerometer on the collar. If the delta between the currently measured distance value and the previously estimated distance value is large and “high” acceleration is also reported, then the value is given greater weight, i.e., is considered more reliable. If, on the other hand, a large range delta is accompanied by little or no acceleration, then the value is given little weight or ignored as likely representing a bad range value. 
         [0063]    It should be noted that the converse of the above identified relationship does not necessarily hold true. For example, a low delta in range values does not become more or less reliable when accompanied by low acceleration reporting due to the incidence of tangential motion under high acceleration. But including the input of the accelerometer may be beneficial when evaluating motion radiating toward or away from the base unit. 
         [0064]    The present invention further achieves enhanced robustness in adverse conditions through strength enhancement of the signals being exchanged between the collar and the base unit. This strength enhancement, or signal amplification, allows the base unit and collar to conduct the ranging and tracking processes more accurately than is possible with just the conventionally configured NANOLOC™ chipsets when operating in a household environment where buildings, shrubs, vehicles, etc., can interfere with signal receipt and transmission. According to a preferred embodiment, power amplification circuitry is integrated to work with the NANOLOC™ chipsets to provide greater signal strength. 
         [0065]    The present invention may also be adapted to track the location of children, as well as other types of animals, through appropriate modification of the remote unit. For example, rather than a collar, a child could wear a wrist bracelet as the remote unit. The wrist bracelet is configured with a NANOLOC™ chipset like that in the collar already described herein. The wrist bracelet would not have a correction capability, however, but would provide continuous location information to the base unit, including the boundary breach alert signal, for use by the parent or other supervising adult as may be appropriate. Similarly, a harness or collar arrangement could be configured for other animals that, by providing distance information to the base station, would allow the owner to track the animal&#39;s location, with or without a correction capability as appropriate. 
         [0066]    The foregoing descriptions and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of ways and is not limited by the dimensions of the preferred embodiment. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.