Abstract:
The present invention provides a system for identifying and locating an acoustic event. In a preferred embodiment a gunshot detection sensor includes an audio sensor which detects gunshots in combination with a GPS engine which provides location and timing in conjunction with a host system. This allows an acoustic sensing weapon locator which is integrated for size and portability. The inventive mobile military gunshot detector requires a battery or fuel cell at its heart to operate. By managing the power consumption, batteries can be down-sized and the time between changes or recharges can be dramatically extended allowing soldiers to carry less weight and transport fewer replacement batteries into a hostile environment.

Description:
This application hereby claims priority back to U.S. Provisional Application Ser. No. 60/481,921, filed on Jan. 20, 2004, and is hereby incorporated by reference as if set forth fully herein. 

   BACKGROUND OF THE INVENTION 
   1. Priority and Field of the Invention 
   The present invention relates to a system and method for detecting and locating an acoustic event. More particularly, but not by way of limitation, in a system for identifying and locating an acoustic event, the present invention provides an acoustic sensor which operated with improved electrical efficiency. 
   2. Background of the Invention 
   Gunfire and sniper detection systems are generally known in the art. Such systems can be broadly grouped into three categories: systems which pinpoint the precise location of the source of gunfire; azimuthal sensors which provide an indication of the radial direction to the source of gunfire; and proximity sensors which merely provide an indication that nearby gunfire was detected. While such systems have been demonstrated to perform well in both law enforcement and military applications, the entire field is presently an emerging technology. 
   In many large cities, gun-related violence has become a plague of epidemic proportions. Urban gunfire, whether crime-related or celebratory in nature, results in thousands of deaths per year in the United States alone. Gunfire location systems, such as those installed in the Redwood City, Calif., Glendale, Ariz., Willowbrook, Calif., City of Industry, Calif., and Charleston, S.C. areas, have proven to be effective in reducing law enforcement response time to detected gunfire, apprehending criminals, collecting evidence, and reducing the occurrence of celebratory gunfire. One such system is described in U.S. Pat. No. 5,973,998, issued to Showen, et al., which is incorporated herein by reference. 
   Showen, et al. discloses a system wherein sensors are placed at a density of roughly six to ten sensors per square mile. Audio information is sent to a computer at a central location and processed to: detect a gunshot; determine a time of arrival for the gunshot at each sensor; and calculate a location of the shooter from the differences in the times of arrival at three or more sensors. Showen, et al. takes advantage of the long propagation distance of gunfire to place sensors in a relatively sparse array so that only a few of the sensors can detect the gunfire. This permits the processor to ignore impulsive events which only reach one sensor—a concept called “spatial filtering.” This concept of spatial filtering radically reduces the sensor density compared to predecessor systems, which require as many as 80 sensors per square mile. 
   Another gunshot location system is described in co-pending U.S. patent application Ser. No. 10/248,511 by Patterson, et al., filed Jan. 24, 2003, nw U.S. Pat. No. 6,847,587 which is incorporated herein by reference. Patterson, et al., discloses a system wherein audio information is processed within each sensor to detect a gunshot and determine a time of arrival at the sensor. Time of arrival information, as determined from a synchronized clock, is then transmitted wirelessly by each sensor to a computer at a centralized location where a location of the shooter is calculated in the same manner as in the Showen, et al. system. 
   As yet, azimuthal systems have not been as widely accepted as, for example, the Showen, et al. system. Azimuthal sensors typically employ one or more closely-spaced sensors, where each sensor includes several microphones arranged in a small geometric array. A radial direction can be determined by measuring the differences in arrival times at the various microphones at a particular sensor. Presently such systems suffer from somewhat limited accuracy in the determination of the radial angle, which in turn, translates into significant errors in the positional accuracy when a location is found by finding the intersection of two or more radial lines, from corresponding sensors, directed toward the shooter. Since errors in the radial angle result in ever increasing positional error as the distance from the sensor to the source increases, the reported position will be especially suspect toward the outer limits of the sensors&#39; range. 
   Under certain conditions, power consumption of an acoustic sensor is of concern. For example, in a military application it may be desirable to provide a soldier-worn sensor to identify sniper locations. Such a sensor would obviously require a portable supply of electrical power, most likely batteries. Since size and weight are major considerations in a wearable, or carryable, device, the electrical efficiency of the sensor dictates the size and weight of the required batteries. 
   Power consumption may be of major concern in fixed sensor as well. In general, anywhere that AC power from an electric utility is not available, the alternatives for electrical power, i.e. solar, battery, etc., dictate a need to maintain an awareness of electrical efficiency. It is known in the art to use telephone lines to return acoustic information to a host computer and to use electrical power available over the phone line to power a sensor. As will be appreciated by those skilled in the art, only a few milliamps of electrical current are available from a telephone line to power circuitry. 
   It is thus an object of the present invention to provide a system and method for improving the electrical efficiency of a remote acoustic gunshot detection sensor. 
   SUMMARY OF THE INVENTION 
   The present invention provides an electrically efficient sensor for identifying and locating an acoustic event and a method for reducing the power consumption in an acoustic sensor. In a preferred embodiment, the inventive sensor includes: an audio circuit for delivering acoustic signals to a processor; a global positioning system (“GPS”) receiver for providing positional information and an accurate real time clock; a processor for processing acoustic signals to detect an acoustic event and determine a time of arrival; and a network interface for transmitting position and time of arrival information to a host computer. In the sensor, processor clock rates are managed, or throttled, to minimize the number of processor cycles executed per second in light of the workload. 
   In another preferred embodiment, the inventive sensor incorporates one or more switching regulators to reduce power consumption thus reducing losses attributable to dissipation in the regulators. 
   In still another preferred embodiment, the host further conserves electrical power through a series of sleep levels wherein at each level, only the circuitry needed to support active functions receives electrical power. Circuitry may be powered directly from processor digital outputs or through solid state switches, as electrical current demands dictate. Modules which provide power down, or sleep, inputs are manipulated through such inputs. Circuitry awakens on: acoustic events; inbound network traffic; or on predetermined intervals. 
   Further objects, features, and advantages of the present invention will be apparent to those skilled in the art upon examining the accompanying drawings and upon reading the following description of the preferred embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a preferred configuration of the inventive gunshot detection sensor in its general environment. 
       FIG. 2  provides a block diagram of the inventive sensor wherein a separate, switchable voltage regulate provide power to the GPS receiver. 
       FIG. 3  provides a block diagram of the inventive sensor wherein a window comparator is used to awaken the processor upon an acoustic event of interest. 
       FIG. 4  provides a block diagram for the inventive sensor wherein each subsystem is switchable. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the construction illustrated and the steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. 
   Referring now to the drawings, wherein like reference numerals indicate the same parts throughout the several views, a representative gunshot detection system  100  is shown in its general environment in  FIG. 1 . In a preferred embodiment, a plurality of sensors  102 - 106  are dispersed over a monitored area. Preferably, each sensor is placed such that it has a relatively unobstructed acoustic view around its immediate area. By way of example and not limitation, suitable sites include: placed atop a building; placed atop utility or light poles; on towers, etc. Typically sensors  102 - 106  communicate through a communication network  108  with a centralized processor  110  wherein information concerning acoustic events is processed to provide details of the event, such as the source location of a gunshot, time of the gunshot, the number of detected gunshots, the type of event, and the like. It should be noted that sensors  102 - 106  may be any combination of wired or wireless sensors, that communications paths  112 - 116  may carry either analog or digital signals, and that network  108  may comprise any combination of sub-networks, such as, by way of example and not limitation: a telephone network; the internet; a private computer network; a wireless network, or even a collection of dedicated wires routed to the sensor array. 
   It should be noted that the present invention resides in a novel combination of circuitry and software, and not in the particular detailed configuration which is the preferred embodiment. The structure, control, and arrangement of these circuits and software routines have been illustrated in the drawings by readily understandable block diagrams which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with structural details which will be readily apparent to one of ordinary skill in the art having benefit of the disclosure herein. For the sake of clarity, individual blocks illustrate the major structural components of the inventive system as convenient functional groups. 
   With reference to  FIG. 2 , in a preferred embodiment, an inventive sensor  200  includes: a microphone  202  for receiving acoustic information; an amplifier  206 , or other signal conditioning; an analog to digital converter  210  for converting the analog signal into its digital form; a processor for processing the acoustic signal to detect an acoustic event and determine a time of arrival for the event; a GPS receiver  226  and its associated antenna  228  for providing a sensor position and exceptionally accurate time information; and a communication interface for transmitting position information and time of arrival to a host computer. It should be noted that the communication network through which the information is transmitted may be any combination of wired or wireless connections. 
   In addition, sensor  200  includes a number of features for power management. Electrical power is provided by a DC source  246 , whether a battery, solar panel, fuel cell, telephone line, rectified from an AC source, or the like. A power supply  232  provides continuous power on a power bus  280 . It should be noted that for purposes of this disclosure, the term “bus” may encompass several different voltages, or more than one actual regulated source and separate conductors for a common voltage where current requirements require. From bus  280 , switched power is provided to various parts of the circuitry of sensor  200 . Thus, switch  278  selectively provides power through output  308  to microphone  202  as directed by processor output  298 ; switch  276  selectively provides power through output  306  to amplifier  206  as directed by processor output  296 ; switch  274  selectively provides power to analog to digital converter  210  through output  304  as directed by processor output  294 ; switch  272  selective provides power through output  302  to GPS receiver  226  as directed by processor output  292 ; and switch  270  provides power through output  300  to network interface  222  as directed processor output  290 . Switches are preferably MOSFET devices but may be any solid state type switch such as, by way of example and not limitation, bipolar transistors, IGBT devices, solid state relays, thyristors, etc. 
   Although not every subsystem will likely require continuous power, sensor  200  includes a provision for keep alive circuits which either consume so little electrical power that switching is unnecessary or which require continuous operation to ensure the circuitry will be fully functional in an appropriate time frame when needed. Thus, power supply  232  provides continuous power on outputs  268 ,  266 ,  214 ,  262 , and  258  for microphone  202 , amplifier  206 , A/D converter  210 , GPS receiver  226 , and network interface  222 , respectively. It should be noted that keep alive power may be of a lower voltage than the primary power is switched under processor  214  control. 
   It should also be noted that continuous, or switched, power is provided to processor  214  through power supply output  260  and that individual regulators of power supply  232  may be selectively enabled or disabled through processor output  250 . Further, to conserve power which would be lost through switching regulator losses, even though such regulators are normally on the order of 85%-95% efficient, power may be directed directly from DC source  246 , possibly through a low quiescent current regulator  252  to processor  214 . This may be particularly useful when processor  214  can operate from a wide supply range and thus avoid regulation, or when internal ram may be preserved through a low standby voltage. 
   In operation, with sensor  200  receiving full power, when a gunshot is received at microphone  202 , the signal is amplified by amplifier  206 , and converted to a digital form by A/D converter  210 . Processor  214  processes the signal to detect the gunshot and determine a time of arrival using the real time feature of GPS  226 . The time of arrival and sensor position are transmitted through interface  222  to network  230 . During this process, oscillator  310  would likely be programmed to operate at its maximum speed. After the gunshot is processed, oscillator  310  is programmed to operate at a speed substantially less than its full speed to reduce the power consumption of processor  214 . 
   As may be triggered by a sensor position, lack of gunshots, time of day, or other event, portions of sensor  200  may be put to sleep. For example, if GPS receiver  226  indicates that a man-wearable sensor is at a predetermined safe location, such as a police station, military headquarters, etc., the processor may direct the appropriate switches to turn off the microphone  202 , amplifier  206 , A/D converter  210 , and GPS receiver  226 . Network interface  222  may be left active so that the host computer could awaken the circuitry of sensor  200  in an emergency. Power may be reapplied to GPS receiver  226  periodically to determine if sensor  200  is removed from the safe location at which time power may be restored to all of the circuitry. While the circuitry of sensor  200  is thus asleep, processor  214  may execute a sleep instruction and awaken on periodic intervals to determine if its services are needed. 
   While in the field, if sensor  200  goes a long period of time without detecting any events, power may be removed from A/D converter  210  and clock oscillator  310  slowed to its lowest rate. If a loud sound is received at microphone  202 , window detector  314  will detect the voltage from amplifier  206  and awaken processor  214  thorough interrupt input  316 . Processor  214  can then restore the clock  310  to full speed and restore power to A/D converter  210 . As will be appreciated by those skilled in the art, if processor  214  executes a sleep instruction but is programmed to awaken once per millisecond, and if processor  214  can perform its administrative duties during non-peak use in ten microseconds, its power consumption will be reduced by approximately 99%. 
   As will be appreciated by those skilled in the art, during a period of low activity, the GPS receiver  226  may be powered, by way of example, once per minute to determine if activity has increased. Under such conditions, and with battery backup, many GPS receivers are able to reacquire a position fix in under 10 seconds. Such operation would reduce power consumption of GPS receiver  226  by approximately 84%. It should be noted that, assuming oscillator  310  is stable and accurate to 0.05%, a readily achievable value for crystal based oscillators, processor  214  can maintain relatively accurate time in the absence of GPS receiver  226  for a sufficient period of time to still determine an accurate time of arrival if a gunshot is received during the off time of the GPS. After processing the gunshot, GPS  226  be immediately powered to determine the sensor position. 
   Turning to  FIG. 3 , not all of the features of the embodiment of  FIG. 2  need to be incorporated to achieve significant improvements in power consumption. Sensor  300  comprises: microphone  302 ; amplifier  304 ; A/D converter  306 ; processor  308 ; communication interface  310 ; and GPS receiver  312 , which process audio to detect gunshots and determine a time of arrival as discussed with reference to the previous embodiment  200 . Since microphone  302  and amplifier  304  consume negligible amounts of power. In addition, GPS  312  may be put to sleep through a command issued from processor  308  and the power consumption of A/D converter  306  can be managed simply through the rate conversions are executed. Processor clock  316  can be throttled as needed for processing speed of processor  308  and regulator  315  can be of a highly efficient switching type. Under such conditions, sensor  300  can achieve substantial improvements in battery life over prior art devices. 
   With reference to  FIG. 4 , in a similar manner, significant savings can be realized with sensor  400 . Again, audio is input and processed through microphone  402 , amplifier  406 , A/D converter  410 , processor  414 , and interface  422  as discussed with regard to embodiment  300 . Clock  416  can be throttled to achieve maximum efficiency of processor  414 , while running. In addition, processor  414  can execute a sleep instruction and be awaken by load noises as detected by window comparator  432 . Another feature of sensor  400  allows for the use of an external GPS  426  located outside of a sensor housing  418 . Preferably, GPS receiver  426  communicates with sensor  400  through a serial link  424 . 
   It should be noted that, while preferred embodiments of the inventive sensor have been discussed with reference to GPS based sensors, the invention is not so limited. The techniques for conserving electrical power are applicable to all types of gunshot detection acoustic sensors and whether a GPS is employed or not. 
   Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the scope and spirit of this invention.