Patent Publication Number: US-2002008633-A1

Title: Location, identification and telemetry system using strobed signals at predetermined intervals

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to identification, location, and telemetry systems, and more particularly, to a system for positively identifying and receiving telemetry from devices on assets and individuals using reduced power and reduced channel occupancy.  
       [0003] 2. Description of the Related Art  
       [0004] Identification, location and tracking systems identify the presence, the absence, or movement of unique devices affixed to people and objects within a predefined area. These systems find increasing application in all areas of automation, accounting, manufacturing, and materials handling areas as well as medical facilities and other areas where real time location and identification can be critical.  
       [0005] In a typical system, one or more objects or individuals are provided with transmitting devices, commonly known as “TAGs,” which can be tracked by an array of receivers in a given tracking area. Each TAG periodically transmits a unique digital identification number which is sensed by one or more receivers. The receiver information is then forwarded to a data processing system for storage and tracking. A number of systems have been developed using various techniques, such as radio frequency (RF), and ultrasound for continuously tracking location.  
       [0006] Such systems typically employ radio frequency or ultrasonic based transmitters and sensors. RF systems can provide a high degree of accuracy while maintaining a comparably favorable ratio of range per watt of power. A system using RF tracking methods is disclosed in U.S. Pat. No. 5,119,104 to Heller, which is hereby incorporated by reference. The Heller patent discloses a system which addresses some of the issues associated with RF tracking systems. As disclosed, radio frequency transmissions can be susceptible to interference from multipath reflections, as well as signal attenuation through certain objects which tends to distort the accuracy of the location data. The Heller patent offers a method for incorporating a plurality of receivers and time-of-arrival data to more accurately identify target location.  
       [0007] The Heller patent also offers power conservation by including a motion detector with each TAG transmitter. By transmitting identification information when the target is in motion, but reducing transmissions when motionless, the system can conserve power during motionless periods. The receiving system simply uses the last recorded transmission to identify location. However, one power consumption issue of that system is that if the object is moving, the system of the Heller patent does require higher power consumption for more frequent transmissions.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008] The technique according to the invention provides for an abundance of devices present in the same area, with real time supervision for presence and for changes in sensory telemetry. The technique employs transmitters, which use the same carrier frequency, but having a unique identification. The system reduces transmitter power consumption by only transmitting a portion of that identification in any one burst. Thus, the transmitters use miniscule amounts of power but can be detected at long ranges. The system also provides for an antenna that receive signals at the transmit frequency and a signal processor that supervises the devices for presence and for telemetry. The system also provides for antennae that are located at similar points in space that can measure the signal strength of the incident signals in such a way as to determine their approximate sector or angle of reception of the incident signal. Hand-held antennae can be used as “finders”, and systems of antennas can be constructed as location grids.  
       [0009] A technique according to the invention provides for transmitting identification, location, and telemetry data while conserving power and increasing available bandwidth. According to the invention, each transmitter identification is split into multiple, smaller, timed transmission packets. The transmitter then transmits a portion of that identification (such as a single bit) periodically, such as once per second. The period of time between transmissions is precise, such that once the system identifies a transmitter, it can then accurately identify the transmitter based upon the next transmission packet&#39;s time of arrival. Because of the small bandwidth occupied by and the limited energy used in each single transmission bot the individual transmissions and resulting identifications are resistant to collisions from other transmitters, as well as from noise.  
       [0010] The receiver receives and accurately time-stamps each transmission. This information is then transmitted over a network by sending a map of the received transmission. The received transmission is then processed to identify the device that transmitted and any other data that may have been sent. In one embodiment, the packet is sent over a network that may accommodate other receivers, all feeding a signal processor used for device identification, storage, and/or forwarding of the further processed information.  
       [0011] A signal processor, (currently, a server over an RS-485 bus) receives such packets from all receivers, recognizes identifications from previously “unacquired” transmitters, and maintains information on previously acquired transmitters. From the start of receiving transmissions (or “symbols”) that are unexpected or unscheduled, the signal processor establishes an interval from the periodicity of the transmitted symbols. The signal processor attempts to lock onto a transmitter that was newly introduced into the field of the receiver based on the transmission interval. The signal processor does so by correlating the unexpected and unscheduled symbols and calculates a transmission period, or interval. It then predicts times to expect future symbols. As future symbols are received, their additional identification information is accumulated into the system, which both reinforces the algorithm&#39;s assurance that future receptions are from a given transmitter and more positively identifies that transmitter. Though the average delay between symbols may vary randomly somewhat, or drift, the repeatability of symbols each second (i.e., jitter) is highly accurate. This repeatability allows the system to identify, and infer with an increasingly higher degree of certainty, the presence of a particular transmitter based on its transmission&#39;s time of arrival at the receiver.  
       [0012] When an unexpected symbol is first received, the system holds that uncorrelated symbol in a queue, and waits for the transmission of subsequent, associated symbols to establish an interval. Once that interval is established, the signal processor accumulates subsequent transmissions to establish the transmitter&#39;s identity. Partial identifications may be used to establish a probable identity. Once associated, approximately or exactly, the signal processor expects subsequent symbols at the predetermined interval. Lack of arrival of expected symbols is tolerated, but with locking lost after a certain number of “missed” symbols. As information packets reflecting subsequent receipts of symbols are detected, the information is added to the identification within the system. If no matching identification appears in the database, the new transmitter data is then added to the database. Once all data bits have been received, the identification of the transmitter is positively known. Successive transmissions of symbols received at known transmission periods allow for the continuous supervision of the device without the device transmitting the entire identification on every transmission, unnecessarily using the energy and unnecessarily occupying channel space by continuously transmitting that complete identification code.  
       [0013] One advantage of the technique is that once an interval is acquired, the transmitter can be identified based primarily when it transmits, with the actual transmitted symbol verifying the identity of the transmitter. The transmission of a symbol, however, which is only a portion of the identification code, takes a proportionally low amount of power to transmit. For example, assume a system which transmits an identification code once every second requires some predetermined power to transmit. By dividing the identification code into some number of portions and transmitting only one portion every second or so, the disclosed transmitter could require over an order of magnitude less power than the prior system, while maintaining the same transmission, and thus tracking, rate. Particularly advantageous is the immunity of a device&#39;s identification to various kinds of noises. A smaller packet containing the “same data” will have a smaller possibility of being lost to noise. Losing data to noise is a function of the time that the data occupies the channel. Therefore, the smaller the data packet, for the same amount of data, the greater the noise immunity. Assume a typical system would take 64 milliseconds to transmit a 64 bit identification packet. Since the disclosed embodiment takes approximately 600 microseconds for each bit, then the noise immunity of transmitting a single bit, rather than 64 bits is increased over 100 times, providing 20 db more noise immune.  
       [0014] Prior systems could reduce power by transmitting less frequently, but that would cut down on the ability of the system to supervise the presence of a “TAG”, or device, in real time, as well as obviating the practical use of an antenna for “finding” the device. Once again, by using the disclosed techniques, the present system has longer life on the same battery, has an abundance of devices that can exist in the same area, provides a high tracking rate, and has greatly increased immunity to noise. Noise immunity occurs for all forms of noise, including other like devices&#39; transmissions, other same frequency but dissimilar transmissions, and man-made and more natural Gaussian, Schott and impulse noise.  
       [0015] Further, when an antenna receives a transmission by a particular device, it encodes the received data in such a way that future changes in both transmission format and system parameter do not require modifications of the antenna. Specifically, rather than deciphering the meaning of a particular transmission, a receiver encodes the received transmission as a “pulse map” of energy received in distinct packets of time. This pulse map can be set to a variety of lengths depending on the particular data transmission formats used. For example, a startup transmission “symbol” may be a pulse followed by a particular silent period followed by a second pulse; a “1” identification bit could be a start pulse followed by a second interval and then a second pulse; and a “0” bit could be a start pulse followed by yet a third interval and then a second pulse. If it is desired to have multiple identification bits, or additional data to be appended to that initial data, the pulse map could be extended until data is not received, or multiple pulse maps could be sent for a string of data. But by mapping the received pulses as a map, rather than deciphering their meaning them at the antenna, the antenna maintains a great deal of flexibility without having to know the exact protocols of a particular implementation. The received data is transmitted in the form of pulse maps along with time stamps and other information over the network to the signal processor, which processes the maps, identifies transmitters, accumulates data associated with the transmissions, and otherwise monitors all transmitters within the range of the system. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
     [0016]FIG. 1 is a block diagram illustrating a tracking system implemented according to the invention;  
     [0017] FIGS.  2 A- 2 C are illustrations of transmissions of identifying data according to one embodiment of the invention;  
     [0018]FIG. 3 is a diagram illustrating potential antenna reception patterns according to the invention;  
     [0019]FIG. 4 is a diagram illustrating the timing of transmitted and received signals according to one embodiment of the invention;  
     [0020]FIG. 5 is a block diagram illustrating a multi-directional antenna implemented according to the invention;  
     [0021]FIG. 6 is a block diagram of a room illustrating antenna reception patterns according to the invention;  
     [0022]FIG. 7 is a flow diagram illustrating the transmission of data from a transmitter to an antenna over a network and to a central server to process the data;  
     [0023]FIG. 8 is a block diagram illustrating the encryption and authentication of data transmitted by a transmitter according to the invention;  
     [0024] FIGS.  9 A- 9 G are illustrations of data structures used in the signal processor according to the invention;  
     [0025] FIGS.  10 A- 10 B are flow charts illustrating transmitter identification according to the invention;  
     [0026]FIGS. 11 and 12 are timing diagrams illustrating a transmission format of another embodiment according to the invention;  
     [0027]FIGS. 13A and 13B are timing diagrams illustrating received data according to the invention;  
     [0028]FIG. 14 is a block diagram illustrating pulse mapping interpretation according to the invention;  
     [0029]FIGS. 15A and 15B are tables illustrating the interpretation of data by the signal processor according to the invention;  
     [0030]FIG. 16 is a block diagram illustrating transmitter circuitry according to the invention;  
     [0031]FIG. 17 is a schematic illustration of a transmitter according to the invention; and  
     [0032]FIG. 18 is a schematic illustration of a receiver according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0033] System Overview  
     [0034] Turning to FIG. 1, shown is a block diagram illustrating a presence detection and identification system S according to the invention. In the shown system S, a wireless transmitter W A    100  and a wireless transmitter W B    102  each transmit identification information along with data. As is further described in detail below, the identification information is generally not transmitted as a single periodic burst of data. Instead, the transmitters W A    100  and W B    102  separate their identification data into a series of components, which are individually transmitted periodically over time.  
     [0035] These transmissions are received by one or more directional or nondirectional antennas A 1    104 , A 2    106  and A 3    108 . These antennas  104 ,  106  and  108  are preferably coupled to a network  110  and timestamp each received transmission from one of the transmitters W A    100  or W B    102 . The antennas  104 ,  106  and  108  transmit both the timestamp and the corresponding received data to a signal processor or other controller  112 . The signal processor  112  is connected to a second network  114 , which provides the information gathered by the signal processor  112  to various work stations  116   a  and  116   b , or to other devices  118 , such as a phone system controller Alternatively, or in connection with the system S of FIG. 1, work stations and devices  120  can be connected to the network  110 , where the network  110  could be a standard Ethernet or other type of local operating network (LON), local area network (LAN), or wide area network (WAN).  
     [0036] The transmissions from the wireless transmitters W A    100  and W B    102  are of a particularly advantageous format. Specifically, these transmitters W A    100  and W B    102  can have 64-bit identification values that uniquely identify each transmitter  100  or  102 . In typical previous systems, this identification was transmitted in a single burst, alone or along with telemetry (such as a button push), which was then received by antennas. The transmitter identification was then immediately known if the packet was received without a collision. The packet may have contained error detection logic, such as parity, CRC, or forward correcting codes, but even so, a collision could prevent positive identification.  
     [0037] For real-time location purposes, there is a tradeoff between the frequency of transmission and bandwidth of the area (the number of devices in the area). For applications where an increase in the real-time location capability was desired, system tradeoffs included:  
     [0038] 1. an increase in cost and size of battery,  
     [0039] 2. an increase in cost of receiver to increase the bandwidth (hence reducing the time of transmission),  
     [0040] 3. a limit to the number of devices in the area,  
     [0041] 4. a reduced number of unique identification numbers (because fewer bits of identification data reduced power requirements), or  
     [0042] 5. addition of a receiver to the tag so that the device will only “transmit” when commanded.  
     [0043] These tradeoffs increase the devices complexity and cost, so previously the periodic transmission interval would be increased until all the design requirements could be satisfied. Often marketing research and prototype testing could lead to a reasonable solution, but the system would be limited by these parameters in future applications. With these settled parameters, the manufacturer would be required to make products according to those predefined parameters.  
     [0044] As further demonstration of the tradeoffs regarding real time location capability, if a transmitter transmitted ten times a second, for most applications the real time location of the transmitter would be considered excellent. However, with similar devices passing under the same sensor, the increased transmission rate would lead to a greater number of collisions. A 50 millisecond identification transmitted every 100 milliseconds would occupy 50% of the bandwidth of a receiver. To the receiver trying to capture one of the transmitters, another would appear as noise and hence create havoc for the reception of the other TAGs identification. By decreasing the number of unique identification numbers (less bits to transmit) the system would occupy less bandwidth, but with reduced flexibility and future expansion capabilities.  
     [0045] To improve battery life, prior systems have implemented techniques such as motion sensors for adjusting the period between transmissions up for less active or nonmoving TAGs. According to the invention, however, the transmitter can transmit at relatively high powers, relatively frequently, and with extended battery life. This is achieved by transmitting only a portion of the identification from each transmitter W A    100  or W B    102  at a periodic interval. Thus, instead of transmitting the entire identification in one burst, the transmission of the identification is spread out over, for example, a period of thirty seconds to one minute.  
     [0046] The transmission of symbols (a portion of the identification data), however, occurs once a second, for example. Further, the period between each transmission is repeatable over several seconds such that the intelligent signal processor  112  can predict and schedule the next expected transmission. When received within the predicted scheduled time, the system then knows with a high degree of confidence which device transmitted that information. Following the collection of some or all of the identification code, the signal processor  112  can then associate that identification with each single symbol it predictably receives.  
     [0047] Using this protocol, the system may take several symbols to initially determine that a unique device is responsible for repeatable intervals of symbols and begin to accumulate the full identification. Algorithms discussed below match “recently seen TAGs” to fragments of identifications that the signal processor receives. From this information, the signal processor infer the actual identification prior to the identification number&#39;s complete.  
     [0048] The Transmission Protocol  
     [0049] Turning to FIGS. 2A and 2B, various details of one data format transmitted by the wireless transmitters W A    100  and W B    102  are shown. FIG. 2A illustrates a wireless identification number (WIN) that is associated with each of the transmitters W A    100  and W B    102 . Specifically, a WIN A    150  is shown to be a 64-bit hexadecimal value 64′h02468ACE02468ACE, while a WIN B    152  is shown to be a hexadecimal value 64′h13579BDF13579BDF. The WIN A    150  is transmitted as the identification of the wireless transmitter W A    100 , while the WIN B    152  is transmitted as the wireless identification number of the transmitter W B    102 . Although the WIN A    150  and the WIN B    152  are shown to be repeating numbers, generally they will be seemingly random to one another as a function of their manufacture date and other parameters, and are unlikely to have consecutive identical values.  
     [0050] Concerning how these identification values are transmitted, referring to FIG. 2B, a typical transmission sequence for the 64-bit WIN A    150  is shown. For example, the 64-bit identification value is divided into a series of sixteen, 4-bit nibbles. These nibbles are then transmitted in the intervals approximately one second apart. Referring to FIG. 2B, in a first period  154 , for example, the first nibble (4′h0) is transmitted in a burst over a period of time t A1    154  then, a second nibble is transmitted during a period t A2    156 , which begins T A1  period of time later.  
     [0051] Preferably, the period t A1  is orders of magnitude less than the length of time T A1 . For example, the period t A1  could be 500 microseconds, while T A1  is one second, yielding a duty cycle and a same channel occupancy of less than 0.05%. Further, the first nibble is transmitted using a symbol  164 , of which there are seventeen in the disclosed embodiment, sixteen for the four nibbles and one for a header value. Symbols are discussed further below in conjunction with the transmission format of the transmitters W A    100  and W B    102 .  
     [0052] The period between transmissions T An  tends to be much larger than the transmission period t An  itself. Further, while the symbol  164  is transmitted as a portion of the WIN A    150 , data  166  can also be appended to the transmission. Thus, some transmissions may be longer than others because of this additional data  166 , having a period t d . The reception of symbols and data is the domain of the receiver. Both symbols and data are short as compared to T An  and entirely detected by the receiver. The symbol and data are time stamped and sent the signal processor  116  for its determination of:  
     [0053] 1. which device transmitted it,  
     [0054] 2. an accumulation of the new data with prior data from the same device,  
     [0055] 3. a predication or scheduling of the next symbol that it may receive and forwarded as programmed by the user or an applications program based on the event of a symbol arriving, and  
     [0056] 4. the newly obtained TAG identification in the area or a change in the telemetry that came in as data.  
     [0057] Turning to FIG. 2C, it will be appreciated that the amount of energy necessary to transmit the WIN A    150  according to the disclosed embodiment is lower than if the WIN A    150  were transmitted in its entirety at each of the periodic transmissions  154 - 162 . Shown in FIG. 2C is a series of transmissions  168  by the wireless transmitter W A    100  and a series of a transmissions  170  by the wireless transmission W B    102 . The series of transmissions  168  are continuous transmissions separated by the period T A1 , with a header symbol being transmitted followed by a transmission of a symbol for (0), then (0), then (1), etc. making up the WIN A    150 . In this disclosed embodiment, each symbol is repeated twice to assist the system of FIG. 1 in determining which transmitter is transmitting a particular sequence of symbols. According to the invention, however, this is not necessary—instead, the WIN A    150  can be transmitted as a sequence of changing symbols making up the entirety of the WIN A    150 , without repeating each symbol. Such an embodiment is discussed below in conjunction with FIGS.  11 - 15 B.  
     [0058] It can be assumed that a certain amount of energy is necessary to transmit a certain amount of data. Because during each of the periods T An  only 4 bits of data are being transmitted rather than 64 bits, the energy used for such a transmission is thus reduced. At the same time, the period T A  is sufficiently short to provide suitable tracking of an object or person that is moving. In this way, and by transmitting only portions of the WIN A    150  in each period, power consumption is reduced without reducing the periodicity of the transmission, and thus without reducing the real time detectability of the wireless transmitter W A    100 .  
     [0059] Reception of WINs  
     [0060] Turning to FIGS. 3 and 4, illustrated are an antenna system employing the antennas A 1    104 , A 2    106  and A 3    108  to track the presence and location of wireless transmitters W A    100  and W B    102 . It is assumed that A 2    106  is an omni-directional antenna while A 1    104  is a directional antenna. The transmitter W A    100  is shown to be within an extended range  200  of the omnidirectional antenna A 2    106 , as well as within an angular range  202  of the directional antenna A 1    104 . W B    102 , in contrast, is only within the range of the omnidirectional antenna A 2    106 . The omnidirectional A 2    106  is also shown to have a reduced range  204 , which by employing signal strength monitoring can further be used to locate the transmitters W A    100  and W B    102 . Turning to FIG. 4, shown are a transmission sequence  206  that is transmitted by the wireless transmitter W A    100 , and a transmission sequence  208  that is transmitted by the wireless transmitter W B    102 . The transmission  206 , as discussed above in conjunction with FIG. 2C, can include a series of nibbles of data in the form of symbols, with each once repeated for ease of identification and matching of subsequent symbols with a previous symbol. Alternatively, the data can be single bits, as discussed below, in conjunction with FIGS.  11 - 15 B. In the transmission  206 , a header symbol is transmitted twice, followed by the symbol reflective of the first nibble of the WIN A    150 , then the second nibble of the WIN A    150 , followed by the third nibble of the WIN A    150 , etc. The transmitter W B    102  transmits a header symbol twice, again followed by a symbol reflected with the first nibble of the WIN B    152 , then the second nibble of the WIN B    152 , etc.  
     [0061] It should be remembered that the transmission  206  by the transmitter W A    100  and the transmission  208  by the transmitter W B    102  are in general decoupled from each other. Although they are shown being interleaved, and both starting with a header symbol, in general the transmissions  206  and  208  will be randomly related, drift with respect to each other, and may even collide at particular times. The interrelationships of FIG. 4 are simply shown for illustrative purposes of what a particular antenna would receive.  
     [0062] The antennas A 1    104  and A 2    106  receive these transmissions  206  and  208 , or some portion of these transmissions  206  and  208 . The antenna A 1    104  receives a series of transmissions  210 , which are simply the transmitted symbols of the wireless transmitter W A    100  transmitted in the transmission sequence  206 . The transmission sequence  208  is not received because the transmitter W B    102  is not within the range of the antenna A 1    104 . In contrast, the antenna A 2    106 , which is omnidirectional, receives a transmission sequence  212 , which is shown to be the combined transmissions  206  and  208  of the transmitter W A    100  and W B    102 . The header symbol of the transmitter W A    100  is received, followed by the header symbol of the transmitter W B    102 , and the sequence continues to alternate. As illustrated by the transmission sequence  212 , it will be appreciated that because of the very low duty cycle of the transmissions (200 microseconds on, 1 second off), the chances of a collision are very low.  
     [0063] Referring back to FIG. 3, it will be appreciated that the antenna A 1    104  sends data packets over the network  110  indicating the time of arrival of each of the transmissions from transmitter W A    100 . Those data packets can include data indicative of the signal strength of the transmitter W A    100 . If such is the case, the system S of FIG. 1 can determine not only that the transmitter W A    100  is within the angle of reception  202  of the antenna A 1    104 , but also a particular area  214  within which that particular signal strength would be present. This would be determined by a signal strength indication added to the packet of data transmitted over the network  110  by the antenna A 1    104  and by the antenna A 2    106 .  
     [0064] Further, it will be appreciated that rather than simply having an angled antenna A 1    104 , a multi-directional antenna can be provided which include six independent antennas as illustrated in FIG. 5. As illustrated in FIG. 5, the antenna is provided with six independent antennas, A 4    216  through A 9    226 . Using such a sectored antenna, the entire periphery as illustrated in FIG. 3 can be divided up into sectors. If an antenna is located in a corner of a room, one could instead sector the room into multiple subsectors without having a full 360° angle of reception.  
     [0065] A wide variety of antenna configurations is possible, and by suitably selecting the configuration, objects can be located by the intersection of the reception areas of the various antennas. Referring to FIG. 6 for example, shown is a room with four antennas A 10    228 , A 11    230 , A 12    232  and A 13    234  in each of the comers of the room. Each antenna includes three sub-antennas, thus effectively dividing the room into three regions for each antenna. Employing these four antennas A 10    228  through A 13    234 , the room can be broken up into twenty-five regions R 1  through R 25 . In this way, by employing intersections of the regions covered by each of the antennas  228  through  234 , the location of a transmitter W A    100  or W B    102  can be precisely determined based on which antennas are receiving a signal from those transmitters  100  or  102  and which are not. Note that even further accuracy in identifying the locations of each of the transmitters W A    100  or W B    102  can be achieved by employing signal strength to determine the distance of the transmitter from a particular antenna A 10    228  through A  234 .  
     [0066] Data Flow  
     [0067] Turning to FIG. 7, a sample of the data flow in the system S of FIG. 1 is illustrated. Specifically, shown is exemplary data flow from the wireless transmitter W A    100  to one of the antennas A 2    106 , then over the network  110  to the signal processing server  112 . Over a period of time, the wireless transmitter W A    100  periodically transmits identification WIN A    150 , along with any additional data that may be desired, such as motion status or temperature. This results in a series of data packages  300  transmitted in short bursts, together forming WIN A  [0 . . . 15], which is 16, 4-bit nibbles forming WIN A    150 .  
     [0068] The first of these pulses containing WIN A [0] is received by the antenna A 2    106 . This antenna is a smart networked antenna. It includes a relatively stable clock to provide a timestamp for time of arrival. It also includes its own identification A 2ID  and, preferably, can determine the signal strength of the data  300  transmitted by the wireless transmitter W A    100 . After receiving the first pulse from W A    100 , the antenna A 2    106  forms a packet of data  302 , which includes the portion of the WIN A    150  transmitted in the first burst by the transmitter W A    100 , includes the antenna identification A 2ID , includes any associated data, includes the timestamp of TOA (i.e., time of arrival), and includes an indication of transmit strength. The format of this data can be varied, and items such as the antenna ID A 2ID  could be in an object ID format as described in U.S. Pat. No. 5,572,195, issued Nov. 5, 1996, entitled Sensougard Control System for Local Area Networks, which is hereby incorporated by reference.  
     [0069] Further, rather than transmitting deciphered data as the packet of data  302 , the antenna A 2   106  can instead transmit a “pulse map” of the received data as is discussed below in conjunction with FIGS.  11 - 15 B. This allows for different transmitters to be provided in the system with different transmission formats without the need to modify the software, the antenna A 2    106 . The received data and transmit strength could also be similarly “pulse” and “amplitude” mapped.  
     [0070] Such a package of data  302  is transmitted by the antenna A 2    106  for each burst of data received from the wireless antenna W A    100 . The package of data  302  is transmitted over the network  110  to the server  112 . Because the antenna A 2    106  stamps the data with a time of arrival, transmission latency over network  110 , as long as it is not highly excessive, will have little effect on the operation of the system. The server  112  is then running software  304  which receives the packets from the various antennas A 1    104 , A 2    106 , and A 3    108 , as well as other antennas and potentially touch-sensitive receivers as well. The software  304  employs a digital signal processing algorithm described below to identify, locate, and track the various wireless transmitters. Specifically, a data table is created containing, for each transmitter such as W A    100 , the identification number (WIN), a calculated transmit interval, and an expected time of arrival of the next transmission. Then, when the server  112  receives a packet such as the packet  302  that has a time of arrival stamp that falls within an expected time of arrival, the server  112  can compare the portion of the WIN within that packet to the expected next portion of the WIN as defined by the data item  306 . If they match, it can be deduced with a high degree of certainty that the packet was in fact transmitted by the transmitter W A    100 .  
     [0071] At this point, it is instructive to understand that the data formats and transmission intervals can be varied in different embodiments. For example, although FIG. 2C illustrates a transmission format in which each nibble of the transmission is repeated, that is done to assist the software within the server  112  to determine when two successive nibbles are being transmitted by the same transmitter W A    100  or W B    102 . Instead, by employing an intelligent algorithm (described below) within the server  112 , the nibbles need not be repeated as shown in FIG. 2C, but instead the software  304  within the server  112  can determine when successive symbols are transmitted by the same transmitter W A    100  or W B    102  based on the intervals between transmissions. If the intervals are fixed, for example, if a sequence of three transmitted symbols has two identical periods TN between the transmissions, it can be determined with a high degree of certainty that the same transmitter W A    100  or W B    102  is transmitting the symbol. This is because the jitter between consecutive transmission periods is preferably very low.  
     [0072] Further, although as shown in FIGS.  2 A- 2 C the WIN A    150  or WIN B    152  is broken up into a sequence of nibbles, it could instead be encoded, encrypted, digitally signed, or otherwise re-arranged. This is illustrated in FIG. 8, where a WIN  400  is combined with a random value  402  (which could instead be a sequential counter to eliminate the transmission of unneeded, random data). This yields combined data  404 , which is then passed both through a public key and a private key algorithm  406 . This algorithm encrypts the data  404  with a public key known to the server  112 , and encrypts the data  404  with a private key unique to the transmitter W A    100  or W B    102 . As is known in the encryption arts, this has the effect of both digitally signing and digitally encrypting the data  404 . This results in signed and encrypted data  408 , which is transmitted through the antenna such as the antenna A 2    106 , over the network  110 , and to the server  112 . Within the server software  304 , a public key and private key corresponding to the private key and public key used in the algorithm  406 , are employed in a step  410 , where the private key encryption of step  406  is reversed using the public key associated with the transmitter W A    100 , and the public key encryption of step  406  is decrypted with a private key associated with the server  112 . In this way, the data is authenticated by the private key/public key combination and decrypted with the public key/private key combination. This decrypted authenticated data  412 , once fully gathered in a sequence of transmissions, is then stored as the data  306  within the server  112 , yielding a wireless identification number WIN  414  But again, even though the data  404  is encrypted and signed in a step  406 , that encrypted signed data  408  is still divided into a sequence of symbols which are transmitted in a series of bursts as illustrated in FIG. 2C. That is, all of the data forming the encrypted data  408  is in general transmitted in a series of descrete transmissions, such that the server  112  first receives a series of packets  302  over a period of time before it can identify the transmitter W A    100  or W B    102  with certainty.  
     [0073] Preferably, the “random” number  402  is actually a sequential counter that is incremented for each series of packets containing a WIN. By employing a sequential counter, it is ensured that over time, encrypted data item  408  will be different. This way, an eavesdropper cannot capture a series of bursts that together form all of the identification data of a transmitter and then retransmit that, “spoofing” the transmitter. This is because the software  304  will expect a next sequential number  402 , rather than a previously transmitted number, and will thus know that the “spoofed” transmission is invalid.  
     [0074] Referring back to FIG. 7, many variations are possible. For example, within the data  306 , an interval is stored which corresponds with a particular transmitter s interval T N  as is illustrated in FIG. 2B. Although this interval is shown as being fixed, it will be appreciated that the interval is more generally arbitrary, rather than necessarily fixed. For example, a known, pseudo-random offset can be added to each succeeding interval TN so that two transmitters will not become in lock step and continuously collide. This pseudo-random offset could be based on a variety of values. For example, the offset of the interval for the next transmission could be a hash function or other function of the random (or counter) number  402  as illustrated in FIG. 8. Then, when the server software  304  receives both the WIN  400  and the random number (or counter)  402  as illustrated in FIG. 8, it can calculate a series of next intervals TN for the next sequence of transmissions of the encrypted WIN. Alternatively, it is possible to base the random offset on the symbol that was last transmitted by the transmitter W A    100 . Because each transmitter has its own unique WIN, such as the WIN A    150  or the WIN B    152 , and because the succeeding symbols in general differ among the transmitters, by providing that the next interval will have an offset based on the particular symbol transmitted in the current transmit period (such as the transmit period  154 , FIG. 2B), a pseudorandom interval can be determined to adjust the expected time of arrival of the next transmitted symbol. Although “pseudo-random,” the offset is both arbitrary and deterministic, in that the server  112  can calculate based on previous transmissions what that next pseudo-random offset will be.  
     [0075] Further, it will be appreciated that although the wireless transmitters W A    100  and W B    0102  should have low unanticipated jitter between subsequent transmission periods (such as the period T A1  and T A2 , see FIG. 2B), it will not adversely affect the operation of the systems if over time period T N  drifts. This is because the server  112  can compensate for slight drifts over time by adjusting the determined interval within the data  306 . This is particularly advantageous, because it is fairly simple to construct a transmitter that has little jitter between subsequent transmissions, but a change in temperature or operational characteristics of components will often cause drift of transmission periods over time.  
     [0076] Also, while it might be difficult to synchronize the clocks within the antennas A 1    104 , A 2    106  and A 3    108 , this is not strictly necessary as long as the clocks do not have much jitter themselves. This is true because the server  112  and its software  304  can normalize all the antennas A 1    104 , A 2    106  and A 3    108  to a single time base. This is done when two of the antennas, such as A 1    104  and A 2    106  both receive a transmission by a single transmitter such as W A    100 . In that case, that transmission can be used as a reference point for the clocks for both of the antennas, with an offset between the two antenna clocks calculated by the server  112 . Over time, the clocks speeds can similarly be scaled, such that the relationship of the clocks within the antennas A 1    104 , A 2    106  and A 3    108  are ultimately correlated to a high degree of precision within the server  112 .  
     [0077] Server Software  
     [0078] Referring to FIGS.  9 A- 9 F, shown are various data items employed by the server software  304  discussed below in conjunction with FIG. 10. Turning to FIG. 9A, shown is an EVENT data item  500 , which is transmitted over the network  110 . This data item  500  is essentially a packet of data transmitted by an antenna that has received a transmission from a transmitter. As illustrated, the EVENT data item  500  includes five elements in the disclosed embodiment, a SYMBOL item, an ANTENNA_ID item, a DATA item, a TOA (time of arrival) item, and a SIGNAL_STRENGTH item. As discussed previously and below, this data item could instead include pulse maps rather than the SYMBOL item and the DATA item, and then the pulse maps can be deciphered by the signal processing server  112  rather than at one of the antennas.  
     [0079] The SYMBOL item is the nibble that has been received as a symbol by one of the antennas, such as the symbol  164  of FIG. 2B. It is indicated that the SYMBOL can be up to 64 bits, however. This would be for implementations in which it is desired to at some times transmit an entire identification at one time. For example, the wireless transmitter W A    100  could employ the low power, split transmission of the WIN A    150  in normal operation, but could also include a physical touch port that would allow the wireless transmitter W A    100  to actually be used as a key . By touching the physical touch port of the wireless transmitter W A    100  to a receiver port, it would then be desirable to immediately transmit the entire ID. In such an instance, the SYMBOL data item would actually include all 64 bits (i.e., 16 symbols worth) of the identification data, or WIN, of the wireless transmitter. In such a circumstance, the ANTENNA_ID field would include a sensor identification value.  
     [0080] The ANTENNA_ID field is shown to be a 16-bit value. It could be more or less, however, an it could employ an object ID technology as described in the previously incorporated U.S. patent entitled Sensory and Control System for Local Area Networks. In any case, the ANTENNA_ID field identifies the particular antenna or sensor which has received the data, such as the antennas A 1    104 , A 2    106  and A 3    108  of FIG. 1.  
     [0081] The DATA field could include any associated data (such as the data  166  of FIG. 2B) transmitted on the particular transmission, here shown to be between 0 and 256 bytes. Typically, a data transmission associated with a symbol transmission would include a header value that indicates the amount of data to be transmitted, followed by the data itself. Preferably, large amounts of data that are transmitted via wireless transmission would be split up among transmission periods such as the transmission periods  154 - 162  of FIG. 2B, so that if there is a collision involving any particular packet of data, only a portion of the transmitted data is invalid.  
     [0082] The TOA field is shown to be 32 bits. It again could be larger or smaller. Further, the time of arrival field is preferably the value transmitted by the antenna/sensor, but could be normalized upon receipt to a common time-base before it is stored as discussed above. In any case, because the antenna/sensor is known, the TOA can at some point be normalized to a common time base for the server  112  in the systems as discussed above.  
     [0083] A SIGNAL_STRENGTH field shown to be 8 bits to indicate relative minimal and maximal strength between 256 values. The SIGNAL_STRENGTH field is preferably set within an antenna by sensing the signal level of the received transmission.  
     [0084] While the EVENT item  500  preferably reflects each received burst transmission by an antenna, this could mean that multiple EVENT items will be received for each signal transmission if more than one antenna has received that item. For example, if the three of the antennas A 1    104 , A 2    106  and A 3    108  all receive a transmitted symbol, three EVENT items will be generated from three packets of data. These three EVENT items are then stored in a queue until they can be processed by the software  304 . The software  304  will either normalize the TOA field of the received EVENT item based on the ANTENNA_ID field, or can wait to normalize the TOA field when the EVENT item is processed.  
     [0085] In either case, for purposes of identifying a particular transmitter such as the transmitter W A    100  or W B    102 , the software  304  normalizes the three EVENT items to a single time of arrival and a single symbol, which are stored as a SINGLE item  502  within a SINGLES_TABLE  504 . Alternatively, the software  304  can normalize the three EVENT items to three SINGLE items  502 , each reflecting a different received packet. In that case, it is preferable that the SINGLES item  502  farther include an ANTENNA_ID item (not shown) so that the software  304  can appropriately determine which antenna a particular SINGLES item  502  is associated with.  
     [0086] The SINGLES item  502  includes a 4-bit SYMBOL item, which reflects the particular symbol transmitted by a particular transmitter in the system, and its associated time of arrival (TOA), the 32-bit value normalized to a common server  112  time base.  
     [0087] These SINGLES items  502  are stored in a SINGLES_TABLE  504  of FIG. 9C. The SINGLES_TABLE  504  is an array of SINGLE items  502 . Although shown to contain 16 data items, this is more of a function of how many transmitters are expected within the system S, how widespread the system S is intended to be, and the processing power of the server  112 . The SINGLES_TABLE  504  is employed by the software  304  to determine when subsequent symbols are being received from the same wireless transmitter such as W A    100 , and then to positively identify that transmitter such as W A    100 .  
     [0088] Specifically, for the various single transmissions in the SINGLES_TABLE  504 , a list of possible pairs of symbols is generated and formed into a data table SINGLE_INTERVAL_TABLE  506 , illustrated in FIG. 9D. The SINGLE_INTERVAL_TABLE  506  is an array of POSSIBLE_PAIR data items, which are of a type PAIRS  508 , illustrated in FIG. 9E. Each of the PAIRS data items  508  includes a FIRST_SINGLE and a SECOND_SINGLE data item, which are each a pointer to a particular SINGLE data item  502  within the SINGLES_TABLE  504 . Each PAIRS data item  508  further includes a 16-bit value which indicates the time interval between the two SINGLE data items  502  TOA value. Thus, each of the PAIRS data items  508  effectively points to a received transmission and denotes the interval of that transmission.  
     [0089] As is further discussed below in conjunction with FIGS. 10A and 10B, when three symbols are successfully received from a transmitter such as the wireless transmitter W A    100 , those three transmissions could be matched up as follows. First, the interval between the first transmission and the second transmission, as compared to the interval between the second transmission and the third transmission will be the same (or of a known relationship). Thus, the software  304  can examine the SINGLE_TABLE  506 , and the INTERVAL values within that table  506 , to determine if a previous possible pair had an interval that matched the interval between the present received data item under investigation and the second data item of the possible pair. This will be further understood in the discussion of the software and FIGS. 10A and 10B, but to summarize, when three data items have intervals that are the same or related in a known way, and the middle data item is the same for both potential pairs, then it is determined that the three data items were transmitted from the same transmitter W A    100 .  
     [0090] Once a particular transmitter, such as the transmitter W A    100 , has been either partially or fully identified, it is placed into an IDENTITY_TABLE  510 , illustrated in FIG. 9F. This IDENTITY includes a WIN field of 64 bits, which stores a wireless identification number. Although the WIN field is 64 bits, it will be understood that when a transmitter such as the W A    100  is first partially identified, not all 64 bits stored in the WIN field will be valid. The number of bits that are presently valid within the WIN field is indicated by an IDENTIFIED field, which is a 4-bit counter of the number of valid nibbles in the WIN field. As additional symbols are received via the antennas and identified based on time of arrival, that identity is added to the WIN field and the IDENTIFIED variable is incremented until it reaches a value of 15, including all 16 nibbles have been identified.  
     [0091] Further, a SYMBOL_INDEX value is an index into the WIN field to indicate what the next expected symbol is going to be. Of note, if the SYMBOL_INDEX value exceeds the IDENTIFY value, the next symbol is still unknown because the WIN has not yet been fully received.  
     [0092] Two values, a LAST_TOA and a NEXT_TOA value, indicate the normalized 32-bit time of arrival of the last received symbol for this transmitter, and the normalized next expected time of arrival for this transmitter. This next expected time of arrival in NEXT_TOA is in part determined based on an INTERVAL field, which indicates the basic determined interval for the transmitter. As previously discussed, generally the interval will be constant, but it could be arbitrarily altered to reduce collisions.  
     [0093] Finally, a SYMBOL_COUNTER field is a counter of the number of times a particular transmitter has transmitted. This counter is preferably included in a portion of the data transmitted by the transmitter itself. Specifically, the SYMBOL_COUNTER field would preferably correspond to the data  402  of FIG. 8.  
     [0094] These various identities are stored in an IDENTITY_TABLE  512 , illustrated in FIG. 9G, which is simply an array of types of IDENTITY  510 .  
     [0095] It will be appreciated that variety of other data items can be associated with the structures of FIGS.  9 A- 9 G. Specifically, the structures of FIGS.  9 A- 9 G are principally directed to identifying transmitters, rather than the accumulation of data and the processing of data. Other structures could be employed for data processing and accumulation, as well as identifying a particular location for a transmitter. Further, a variety of other data items could be employed for the acquisition of telemetry data from a transmitter.  
     [0096] Turning to FIGS. 10A and 10B, illustrated is a flow chart of a typical routine used by the software  304  of the server  112  to identify particular transmitters within the system S. The routine begins at a step  600  when a packet of data has been received from one of the antennas A 1    104 , A 2    106 , or A 3    108 . This packet is in the form of an EVENT structure  500 . Beginning at a step  602 , the EVENT structure  500  is received, and it is assumed in this embodiment that the TOA field is normalized to the time base of the server  112 .  
     [0097] Proceeding to a step  604 , it is determined whether the TOA within the EVENT structure  500  is found within the IDENTITY_TABLE  512 . Specifically, it is determined whether one of the IDENTITY structures  510  includes a NEXT_TOA field that matches the TOA of the EVENT, plus or minus certain error tolerance If so, in the disclosed embodiment it is presumed that the received symbol is in fact part of an already identified transmitter, such as the transmitter W A    100 . So, control proceeds to step  606 , where it is determined whether the SYMBOL field of the received EVENT  500  matches the corresponding symbol within the IDENTITY structure  510  with the matching NEXT TOA field. This would not be true if the IDENTITY  510  has not been filly established, and the SYMBOL_INDEX field is greater than the IDENTIFIED field of the matched IDENTITY  510 .  
     [0098] If the SYMBOL value of the EVENT  500  is not known at step  606 , control proceeds to step  608 , where the SYMBOL value of the EVENT  500  is stored within the WIN field of the IDENTITY structure  510  at a location specified by the SYMBOL_INDEX value of the matched IDENTITY  510 .  
     [0099] If at step  606 , however, the SYMBOL is known within the matched IDENTITY structure  510 , control proceeds to step  610 , where it is determined whether the SYMBOL value of the present EVENT  500  matches the symbol within the IDENTITY  510  as specified by the SYMBOL_INDEX value into the WIN. These values should match, indicating that the received symbol is in fact from the identified transmitter such as W A    100 . If not, control proceeds to step  612 , where in the present embodiment, the packet is discarded. There are other potential approaches to handling an “incorrect” received symbol, such as reverting a previously identified transmitter to a non-identified status, but for the simplicity they are not shown here.  
     [0100] From step  608 , from step  612 , and from step  610  if the SYMBOL does match the expected value, control proceeds to step  614 , where various aspects of the matched IDENTITY structure  510  are updated. For example, the SYMBOL_INDEX value is incremented if a valid symbol was received, the IDENTIFIED value is incremented if it is not yet equal to 15, the NEXT_TOA value and LAST_TOA value are calculated and stored, the SYMBOL_COUNTER is incremented if the received value is a header value, and various other housekeeping is performed.  
     [0101] In this regard, it should be noted that a header symbol, when received, is used to align the WIN of an identity. For example, a new transmitter may enter the omnidirectional antenna A 2    106  range, but the first values received would generally not be a header value. But the system can continue to receive and store nibbles of the WIN until a header value is received, at which point, the SYMBOL_INDEX and the values stored in the WIN are adjusted so that the first nibble is in the appropriate position. From step  614 , control proceeds to step  616 , with processing of the received packet begun at step  600  complete. The routine will be reentered when another packet is received.  
     [0102] From step  604 , if the TOA is not present in the IDENTITY_TABLE  512 , the received symbol is not a part of a previously identified transmitter. Control in this case proceeds to step  618 , where it is determined whether the SYMBOL portion of the received EVENT  500  is present in the SINGLES_TABLE  504 . If so, this means another antenna has already transmitted and the server  112  has already stored this particular symbol with its corresponding TOA as a SINGLE item  502  within the SINGLES_TABLE  504 . So, this particular received symbol does not need to again be stored in the SINGLES_TABLE  504 . Therefore, control proceeds to step  620 , where any additional antenna information is stored if desired. This may be desired because at this point, it is clear that more than one antenna, such as the antennas A 1    104 , A 2    106  and A 3    108 , has received this particular transmitted symbol from a particular transmitter such as W A    100  or W B    102 . By storing additional antenna information, the particular location of the transmitter can ultimately be determined. Control proceeds from step  620  to step  616 , where the routine is complete.  
     [0103] From step  618 , if the received SYMBOL and the EVENT  500  are not in the SINGLES_TABLE  504 , control instead proceeds to step  622 . In this step, potential intervals are calculated between the symbol and TOA within the current EVENT  500  and previously stored SINGLES data items  502  within the SINGLES_TABLE  504 . This process generally involves matching a symbol and TOA within the current EVENT  500  with any SINGLE data items  502  that occurred a certain amount of time earlier. For example, assume it is known that all transmitters in the system transmit with a periodicity of one second plus or minus ten percent. Then, any SINGLES data items  502  that occurred outside that window earlier cannot be from the same transmitter, with such appearing with the current symbol and TOA within the current EVENT  500  is impossible. Thus, such “out of range” previous SINGLES data items  502  are not stored with the current EVENT  500  as a potential interval. Only those intervals which are permissible are actually calculated to be potential intervals.  
     [0104] Proceeding to step  624 , the calculated intervals are looked up in the SINGLES_INTERVAL_TABLE  506 . Specifically, the interval calculated in step  622  is looked up in the various PAIRS data items  508  within the SINGLE_INTERVAL_TABLE  506 . If the interval is the same as a previous interval, control proceeds from a step  626  to step  628 , where it is determined whether the stored INTERVAL item of the PAIRS item  508  which is a match can be the correct pair. Specifically, even if the two intervals match, the SECOND_SINGLE must correspond to the SINGLE with which the present events symbol has been used to calculate the present interval. That is, the series of symbols must be FIRST_SINGLE and then SECOND_SINGLE of a particular pair, followed by the SYMBOL within the present EVENT  500 . If so, as determined at a step  630 , control proceeds to step  632 .  
     [0105] At step  632 , a partial identity is stored as an IDENTITY item  510  within the IDENTITY_TABLE  512 . Further, the SINGLES_TABLE  504  and the SINGLE_INTERVAL_TABLE  506  is “cleaned up” by removing any corresponding singles, intervals, and possible pairs corresponding to the identified items. From step  632 , control proceeds to step  634 , where the routine is complete.  
     [0106] At this point, it should be appreciated that this disclosed technique is illustrative only. For example, it may be required that more than three consecutive received symbols be identified as having the same intervals to positively identify a particular transmitter.  
     [0107] At step  626 , if calculated intervals are not found in the SINGLE_INTERVAL_TABLE  506 , and at step  630 , if the interval is not positively identified, control instead proceeds to step  636 , where the SYMBOL and the TOA of the present EVENT  500  is added to the SINGLES_TABLE  504  as a SINGLE item  502 . Control then proceeds to step  638 , where the calculated possible intervals are added to the SINGLE_INTERVAL_TABLE  506  possible pairs. From step  638 , control proceeds to step  634 , where the routine is complete.  
     [0108] Other software would also typically be involved in the identification and tracking system according to the invention. For example, background “watch dog” software would monitor the SINGLES_TABLE  504  and the SINGLES_TABLE  506  and eliminate any stale data. Further, error checking and handling software can process spurious or out of tolerance data.  
     [0109] Further, once a particular transmitter is identified, error handling and monitoring software, including portions of the routine of FIGS. 10A and 10B, can remove an item as identified once symbols are no longer being received from that transmitter.  
     [0110] Exemplary code for acquiring the various transmitters is attached as Appendix A.  
     [0111] Further, the particular code used for location tracking is not shown. Once a transmitter is identified, however, it is tracked and its presence located based on each symbol received. For example, the IDENTITY data item  510  within the IDENTITY_TABLE data item  512 , would typically include further data items corresponding to which antennas had most recently received data from that particular transmitter. Then, tracking software can determine the location of the transmitter based on that data. This is further understood in conjunction with U.S. Pat. No. 5,119,104, entitled Location System Adapted for use in Multipath Environments, issued Jun. 2, 1992; U.S. Pat. No. 5,276,496, entitled Optical Receiver for Area Location System, issued Jan. 4, 1994; U.S. Pat. No. 5,387,993, entitled Method for Receiving and Transmitting Optical Data and Control Information to and from Remotely Located Receivers and Transmitters in an Optical Locator System, issued Feb. 7, 1995; U.S. Pat. No. 5,355,222, entitled Optical Receiver for Area Location System, issued Oct. 11, 1994; and U.S. Pat. No. 5,548,637, entitled Method and Apparatus for Locating Personnel and Objects in Response to Telephone Inquiries, issued Aug. 20, 1996.  
     [0112] Alternative, One Bit Per Symbol Technique  
     [0113] Turning to FIGS.  11 - 15 B, illustrated is a simplified embodiment in which each transmitter has a 9-bit identification value. This simplified system is useful for demonstration purposes, both in illustrating the acquisition of the identification, the tracking by multiple antennas, the bandwidth occupation, the protocol of particular symbols, and how those particular symbols are transmitted from an antenna to the signal processor. This alternative embodiment is also exemplary of the variety of actual implementations available while using the techniques according to the invention. The embodiment of FIGS.  11 - 15 B could be used in a 64-bit identification value technique while only transmitting one bit per second, and could be used in a variety of other transmit rates using a variety of pulse mapping techniques.  
     [0114] Referring to FIG. 11, transmissions from two transmitters are shown. A first transmission  800  from a first transmitter illustrates the periodic transmission of a 9-bit identification value “9′6010000001”. Slightly offset and asynchronous to that transmission  800  is a transmission  802 , which is a transmission by a second transmitter of a identification 9′b 000111010. The transmission format is a start of transmission, or STX, symbol followed by nine either 0 or 1 symbols. The format of these symbols are discussed in more detail below in conjunction with FIGS. 13A and 13B. Referring to the details of the transmission  800 , however, FIG. 12 shows the timing of these symbols. The STX symbol, as well as the various 0 and 1 symbols, are each transmitted in this embodiment in approximately one millisecond or less. The time between symbols is approximately one second. Thus, the bandwidth is around 0.1 percent per transmitter. The bandwidth could be reduced to much less by reducing the amount of time used to transmit a particular symbol. This can be done in a variety of ways, and again is discussed below in conjunction with FIGS. 13A and 13B.  
     [0115] In this particular embodiment, the amount of time between an initial and a second pulse establishes what type of symbol is being transmitted. In this particular embodiment, additional telemetry data, ranging pulses, and the like are not employed. They could, however, be appended to each transmission. Further, a single bit is transmitted during each transmission. Again, this can be modified as desired, allowing some other multiple of bits to be transmitted during each transmission period, such as 4 bits as is disclosed in FIGS.  2 A- 2 C.  
     [0116] Turning to FIGS. 13A and 13B, details of the particular transmission format as well as how the transmitted pulses are received and then transmitted on to the signal processor  112  is shown. Referring to FIG. 13A, shown is a timing diagram with the timing of a 0 symbol  804 , a 1 symbol  806 , and a STX symbol  808 . The transmission of the 0 symbol  804  is addressed first. In this embodiment, a 100 microsecond start bit  810  is first transmitted, followed by a 300 microsecond silent period  812 , and then a 100 microsecond pulse  814 . The start and end pulses  810  and  814  are preferably formed by turning on a 900 megahertz carrier transmitter for 100 microseconds. The 1 symbol  806  and the STX symbol  808  are similarly formed with start and end bits  816 ,  818 ,  820 , and  822 , but the 1 bit includes a 700 microsecond off period  824  and the STX symbol has a 1000 microsecond off period  826 .  
     [0117] The timing of these symbols can be greatly reduced. For example, the 100 microsecond pulses could be reduced to 10 microseconds, and the off periods could similarly be reduced by an order of magnitude. Doing so, however, requires the receiver to have a higher “pulse map” resolution, as is now discussed. In the disclosed embodiment of FIG. 1, it would be possible for the antenna A 1   104 , for example, to itself detect the 100 microsecond pulse  810 , the 300 microsecond off period  812 , and then the 100 microsecond on  814  forms a 0 symbol  804 . It could then transmit that 0 symbol on to the signal processor  112 . According to the present embodiment of the invention, however, the antenna does not decipher the meaning of the transmitted signals and then forward the deciphered information on to the server  112 . Instead, the antenna creates a “pulse map” which effectively is a time slot mapping showing when the carrier is being received. The server  112  then deciphers the meaning of that pulse map. Using this technique, the “intelligence” can be embedded in the server  112 , and as different transmitters are introduced into the system which may have different transmission formats, it is unnecessary to alter the antennas.  
     [0118] To this end, each antenna includes an internal clock that counts at a high rate of speed. Here, a first interval  828  is shown during which each of the three exemplary symbols starts transmitting its first pulse. This interval  828  in the illustrated embodiment is approximately 70 microseconds. When a 900 megahertz transmission is received during a particular interval, the antenna recognizes this as the start of a symbol transmission. It waits for three 70 microsecond intervals  830 , and then begins acquiring data which will become the pulse map. Specifically, in this embodiment, the following 16 intervals  832  are monitored, and whenever a 900 megahertz transmission is received during any portion of an interval, a 1-bit is assigned in the pulse map corresponding to that interval. Otherwise, a 0-bit is assigned corresponding to that interval. This pulse map could be extended indefinitely, such as until no 900 megahertz transmission is received for at least a predetermined number of 70 microsecond intervals. In any case, referring to the symbol 0  804 , it is seen that during the first two intervals of the pulse map  834  and  836 , no 900 megahertz transmission is received from the transmitter, so these are mapped as 0 bits. During the following two intervals  838  and  840 , however the pulse arrives, so these two intervals are mapped as binary 1 bits. The following 12 intervals  842  receive no transmission, and are thus assigned a value of binary 0. Thus, when the 0 symbol  804  is sent by a transmitter, the antenna receives it in FIG. 13A as a 16′h 3000 value, which is transmitted over the network  110  to the signal processor  112 . Similarly, a 1 symbol maps to 16′h01C0 and the STX symbol  808  maps as a 16′h000C.  
     [0119] Turning to FIG. 13B, it is seen that different pulse maps can be generated for the same symbol. Specifically, in FIG. 13B, three start pulses  843 A,  843 B, and  843 C occur early in a first interval  844 . This results in corresponding end pulses  845 A,  845 B, and  845 C falling into slightly different intervals within the pulse map. Therefore, in this case the 0 symbol maps as 16′h0700, the 1 symbol maps as 16′h180, and the STX symbol maps as 16′h100C.  
     [0120] These slightly different exceptions can occur both because of the transmission rate of the transmitters, the fact that the transmitters and the antennas clocks are not synchronized, and spreading that can result from reflections and noise during the transmission of the pulse.  
     [0121] Using intelligence algorithms, the variation in the pulse maps is readily accommodated by the signal processor  112 . Referring to FIG. 14, the particular decoding for these pulse maps is shown. Specifically, an STX symbol is determined to have occurred whenever a pulse map  846  occurs—specifically, when one of the final 7 values is a 1. Similarly, a 1 is decoded when a pulse map  848  occurs again where one of the middle three values is a 1. Finally, a 0 is decoded when a pulse map such as  850  occurs—that is, when one of the initial six intervals mapping as a 1.  
     [0122] But the particular deciphering of the pulse map is not critical—the point is the deciphering occurs not at one of the antennas, such as the antenna A 1    104 , A 2    106 , or A 3    108 , but instead at the signal processor  112 . Therefore, if different transmitters are used employing a different protocol, the older antennas can still be used, as long as software within the signal processor  112  is updated. That is, employing pulse mapping allows the decoding of symbols and transmissions into their particular meaning to occur at the signal processor  112  rather than within one of the intelligent antennas.  
     [0123] Turning to FIGS. 15A and 15B, shown are both the data packets transmitted by a particular antenna or receiver, as well as that data as decoded by the signal processor  112 . Whenever a receiver receives a transmission such as illustrated in FIGS.  11 - 14 , that receiver then transmits a data packet over the network  110  as illustrated in FIG. 15. First, it transmits a header symbol  852 . It then transmits a sequence number  854 . This is simply a incrementing value between 0 and 256 which allows the signal processor  112  to ensure it has not missed any data packets from a particular receiver. Next included in the data packet is a packet type  858 . This is normally a space character, or “ ”, but would be an exclamation point, or “!” for a data packet intended to indicate to the signal processor  112  that the receiver is “still alive”. The next data item in a data packet is a receiver number  860 . This is preferably a 16-bit value that represents a unique receiver identification within the system. Next is a time of arrival  862 , which in the disclosed embodiment is a 32-bit value that, represents 70 microsecond tics of the receiver&#39;s counter. Similarly, the pulse map is a 16-bit value representing the pulse map as discussed in FIGS.  11 - 14  previously.  
     [0124] In FIG. 1A, two packets of data  864  and  866  are shown transmitted to the signal processor  112  by a receiver EC 03  and a receiver EC 05 . It is seen that the time of arrival  862  of these packets is slightly different, perhaps because the clocks of the two receivers are not synchronized. But, these represent the same received pulse by the two separate receivers. In this case, these packets represent a “1” symbol.  
     [0125] Turning to FIG. 15B, it is appreciated how the signal processor  112  decodes the packets transmitted by the various receivers and antennas here has corresponded packets sent over the network by a first receiver  868  with packets received by a second receiver  870 . By corresponding various transmissions, such as the STX  872 , the “TOA” of the first receiver and the second receiver can be correlated. That is, using a variety of transmissions, the 70 microsecond clock of the first receiver  868  and the second receiver  870  can be synchronized. In any case, it is seen that a sequence of symbols  874  and  876  have been received by the first and second receivers  868  and  870  which correspond to a transmitter that is transmitting an STX symbol followed by a sequence of identification bits that map to 9′b10000001. (One transmitted packet  878  is discarded because it is a “keep alive” packet transmitted by the receivers  868  and  870 ). Referring back to FIG. 15A, the packets  864  and  866  are seen to correspond to the received 1 symbol  880  in FIG. 15B. It will be further appreciated that additional antennas or receivers could be added to the system, and that the presence of a transmitter to one receiver but its absence to another can be used for location of the transmitter.  
     [0126] Sample Transmitter  
     [0127] Turning to FIGS. 16 and 17, the construction of a transmitter within the wireless transmitter W A    100  is shown. Preferably, the transmitter transmits a 900 megahertz signal generated by Colpitts oscillator. That oscillator is turned on and off to generate an appropriate sequence of pulses. Block and schematic diagrams of the wireless transmitter W A    100  is shown in FIGS. 16 and 17. As illustrated, a logic sense and control unit  700  can have an input from a motion switch  702  and a push button  704  as optional features. Further, a watchdog timer  706  periodically wakes up the logic sense and control unit  700  at appropriate times for transmission. This reduces overall power consumption. An external serial port  708  can be provided which can provide an external ID, or include memory, temperature, or addressable transistor inputs, as well as a binary switch close sense input. The logic sense and control unit uses all of these inputs to create appropriate strobes via transmission circuitry  710 . Turning to FIG. 17, shown as typical transmitter circuitry that would be used according to the invention. The motion sensor  702  and push button switch  704  both have direct inputs to logic sense and control circuit  700 , which in the disclosed embodiment is a PIC 12C508 processor. This is controlled by the watchdog timer  706 , which in the disclosed embodiment is an MN1381-E. The logic sense and control circuit  700  controls the RF transmitter block  710 , which is effectively a Colpitts oscillator. A battery circuit  712  powers the entire system. Exemplary software for execution by a logic sense and control circuit  700  is illustrated in the attached Appendix B.  
     [0128] Sample Receiver  
     [0129] Turning to FIGS. 18A and 18B, shown is a sample receiver section for the antenna such as the antenna A 1    104 , A 2    106 , or A 3    108 , that is connected to the server  112 . Circuitry block  900  is simply a standard receiver section for receiving a signal of around 900 megahertz. It includes various components such as a mixer  902 , an antenna  904 , a crystal  906 , and provides an output signal  908 . This is fed into processing section  910 , shown in FIG. 18B. This processing section further processes received data that has been received from the mixer section  900 , and provides output data on a data signal  912 . This data signal is provided to a microcontroller section  914 . This microcontroller section  914  includes a microcontroller  916 , here a PIC12C508 microcontroller. It processes data, and then provides signals to the server  112  over a network via connectors  918  and  920 .  
     [0130] Exemplary software for execution by the microcontroller  916  is illustrated in Appendix C.  
     [0131] Conclusion  
     [0132] Therefore, according to the invention, a transmission and reception system is provided in which identification data is distributed over a number of discreet transmission periods. After acquiring enough identification data to either tentatively or affirmatively identify a particular transmitter, the receiving system can identify a particular transmitter based not on the data transmitted, but instead on when it is transmitting a particular discreet burst. This can be used in either a wireless or a wired system.  
     [0133] Further, using smart receivers, the receivers can pulse map the received data rather than actually interpret the meaning of the data itself. By transmitting these pulse map and then time stamped received transmissions over a network, a server can process packets received by a number of antennas or receivers, and positively identify both the identity and the location of a particular transmitter.  
     [0134] Further, various security features can be embedded, such as encrypting the actual identification transmitted by the transmitters, and by providing an arbitrary interval between various transmission which is not necessarily the same from transmission to transmission, but is determinable at the receivers.  
     [0135] Using this system, a large amount of identification data can be transmitted, with a relatively high transmission frequency, but with greatly reduced power consumption. This is desirable in battery powered transmitter for both identification, location, and transmission of telemetry data in a system.  
     [0136] The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, materials, components, circuit elements, wiring connections and contacts, as well as in the details of the illustrated circuitry and construction and method of operation may be made without departing from the spirit of the invention.