in the following detailed description , reference is made to the accompanying drawings that form a part hereof , and in which is shown by way of illustration specific embodiments that may be practiced . these embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments , and it is to be understood that other embodiments may be utilized and that logical , mechanical , electrical and other changes may be made without departing from the scope of the embodiments . the following detailed description is , therefore , not to be taken as limiting the scope of the invention . referring to fig1 , a telemetry system 10 is shown in accordance with an embodiment . the telemetry system 10 includes one or more transmitter / monitors 12 ; one or more receivers 14 ; and a central server 16 comprising a processor 18 . the telemetry system 10 may also optionally include a display 20 ; and an alarm 22 . those skilled in the art will appreciate that the telemetry system 10 is configured to track the relative location of the transmitter / monitors 12 , and that a transmitter / monitor 12 can be assigned to a specific patient in order to track and / or monitor that patient . for illustrative purposes assume that three patients 30 - 34 are being tracked and monitored by the telemetry system 10 . it should , however , be appreciated that the telemetry system 10 may be implemented to track and / or monitor a much larger number of patients . the transmitter / monitors 12 will be described in accordance with an embodiment as a portable device comprising an electrocardiograph and a plurality of electrograph sensors 36 configured to monitor cardiac electrical activity . for purposes of this disclosure , a portable device should be defined to include any device that is sufficiently compact and lightweight such that a typical patient can conveniently carry the device wherever they go . a separate transmitter / monitor 12 is assigned to each of the patients 30 - 34 , and thereafter the assigned transmitter / monitor 12 generates patient monitoring data and / or patient tracking data . the patient monitoring data and / or patient tracking data from the transmitter / monitors 12 is transferred to the receivers 14 via the wireless connections 38 represented by a dashed line . the receiver 14 will be described in accordance with an embodiment as comprising a network of receivers 14 that are uniformly distributed throughout a region of interest in order to define a coverage area . the region of interest may include a relatively small area with a high - patient density such as a patient ward . the region of interest generally does not include areas such as the cafeteria ; areas with low - risk patients ; areas designated exclusively for hospital staff ; areas immediately outside the hospital ; etc ., due to economic considerations associated with the requisite infrastructure . the network of receivers 14 transfers the patient monitoring data and / or patient tracking data to the central server 16 via connection 40 . the central server 16 comprises the processor 18 configured to process the patient monitoring data and / or patient tracking data in a known manner . for example , the processor 18 may convert raw patient monitoring data acquired by the sensors 36 into more conveniently readable electrocardiogram ( ecg ) data comprising a p - wave , a qrs complex and a t - wave . the processor 18 may also be implemented to predict the location of a patient ( or a transmitter / monitor 12 associated therewith ) that has recently left a coverage area as will be described in detail hereinafter . the display 20 may optionally be implemented to graphically convey patient monitoring data and / or patient tracking data from the central server 16 in a conveniently readable manner . as one example , the patient monitoring data may be graphically conveyed as a conventional ecg plot comprising a sequence of p - waves , a qrs complexes and a t - waves . as another example , the patient tracking data may be graphically conveyed as an icon superimposed onto a map to indicate the patient &# 39 ; s relative location . the alarm 22 may optionally be implemented to alert hospital personnel when a patient has exited or is about to exit a given coverage area . the alarm 22 may comprise an audible device ( e . g ., a loudspeaker ) and / or a visual device ( e . g ., a flashing light ). as one example , patient position may be tracked and the alarm 22 may be sounded when the patient approaches the periphery of a given coverage area . as another example , the alarm 22 may be sounded based on the patient &# 39 ; s trajectory such that a patient walking in a direction that is generally perpendicular to the peripheral edge of a coverage area would generate an alarm while a patient walking in a direction that is generally parallel to the peripheral edge of the coverage area would not generate an alarm . as yet another example , the alarm 22 may be sounded based on the strength of a patient tracking signal from a transmitter / monitor 12 as an indication that the patient is approaching the limits of a given coverage area . as yet another example , the alarm 22 may be sounded only when the patient actually leaves a given coverage area . having described the components of the telemetry system 10 in detail , a method 100 ( shown in fig3 ) for predicting the location of a patient ( or a transmitter / monitor 12 associated therewith ) outside a coverage area will now be described with respect to fig2 and 3 . referring to fig2 , a schematic representation of a hospital map 50 is shown in accordance with an embodiment . the region circumscribed by the dashed line 52 represents a coverage area 53 that may be defined by the receiver network 14 ( shown in fig1 ). as previously described , any patient having a transmitter / monitor 12 ( shown in fig1 ) can be tracked and monitored as long as they remain within the coverage area 53 . as soon as a patient exits the coverage area 53 , the signal from their transmitter / monitor 12 is lost and they can no longer be monitored or tracked in a conventional manner . a solid line represents the path 54 of the patient 30 walking from a known position within the coverage area 53 to an unknown position outside the coverage area 53 . positions 56 - 62 are known positions along the patient &# 39 ; s path 54 and within the coverage area 53 . the cross - hatched region 64 of the map 50 represents a first region outside the coverage area 53 , and the stippled region 66 of the map 50 represents a second region outside the coverage area 53 . reference numbers 70 - 76 identify specific hallways of the map 50 . referring to fig3 , the method 100 for predicting the location of a patient ( or a transmitter / monitor 12 associated therewith ) that is disposed outside a coverage area will now be described in accordance with an embodiment . the method 100 comprises a plurality of steps 102 - 110 . one or more of the steps 102 - 110 may be performed by the processor 18 ( shown in fig1 ). referring now to both fig2 and 3 , the method 100 will be described as it applies to the exemplary embodiment of fig2 in order to more clearly illustrate the steps 102 - 110 . at step 102 the method 100 identifies two or more patient positions within the coverage area 53 . for illustrative purposes , the two or more patient positions will be described as including the positions 56 - 62 . according to one embodiment , the positions 56 - 62 are established by the processor 18 ( shown in fig1 ) based on patient tracking data acquired from the specific transmitter / monitor 12 ( shown in fig1 ) assigned to patient 30 . at step 104 the method 100 estimates patient speed based on the patient positions acquired at step 102 . patient speed may be estimated by the processor 18 ( shown in fig1 ) by calculating the patient &# 39 ; s change in position divided by the change in time . at step 106 the method 100 estimates patient trajectory based on the patient positions acquired at step 102 . patient trajectory may be estimated by the processor 18 ( shown in fig1 ) by generating a line or curve based on two or more of the positions acquired at step 102 . according to one embodiment , patient trajectory may be defined by a straight line passing through both of the two most recent patient positions acquired just prior to the patient 30 leaving the coverage area 53 . according to another embodiment , patient trajectory may be defined by a best - fit curve passing through three or more patient positions acquired at step 102 . at step 108 the method 100 measures the time elapsed after the patient 30 leaves the coverage area 53 . at step 110 the method 100 estimates the current patient position outside the coverage area 53 based on patient speed ( acquired at step 104 ); patient trajectory ( acquired at step 106 ); and elapsed time ( acquired at step 108 ). to further illustrate step 10 , assume first that only a relatively short time has passed after the patient 30 left the coverage area 53 . based on this assumption and the patient &# 39 ; s speed ( acquired at step 104 ), it can be estimated that the patient 30 is somewhere in the cross - hatched area 64 . additionally , based on the patient &# 39 ; s trajectory in combination with the relatively short elapsed time , it can be estimated that the patient 30 is most likely in hallway 70 . if a relatively longer time has passed after the patient 30 left the coverage area 53 , it can be estimated based on the patients speed ( acquired at step 104 ) that the patient 30 is somewhere in the stippled area 66 . additionally , based on the patient &# 39 ; s trajectory in combination with the relatively longer elapsed time , it can be estimated that the patient 30 is most likely in hallway 74 . this written description uses examples to disclose the invention , including the best mode , and also to enable any person skilled in the art to practice the invention , including making and using any devices or systems and performing any incorporated methods . the patentable scope of the invention is defined by the claims , and may include other examples that occur to those skilled in the art . such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims , or if they include equivalent structural elements with insubstantial differences from the literal language of the claims .
a telemetry system is disclosed herein . the telemetry system includes a transmitter configured to provide tracking data , and a receiver adapted to define a coverage area . the receiver is configured to receive the tracking data from the transmitter only when the transmitter is within the coverage area . the telemetry system also includes a processor configured to receive the tracking data from the receiver . the processor is configured to estimate the location of the transmitter when the transmitter is outside the coverage area based on the tracking data .