Abstract:
A battery-powered two-way long range automatic meter reading system and method that increases battery longevity. The system includes a meter side unit (MSU) transceiver that acquires utility data, a centralized data collector (Collector) that gathers data from the MSU, and a repeater to facilitate long-range transmission by shuttling radio signals around physical or geographic transmission barriers. The MSU includes a circuit to monitor the passage of time and apply power to a transmitter in response to a predetermined elapsed period of time. The MSU transceiver monitors a predetermined radio channel for traffic. In response to the predetermined radio channel being essentially clear of signal traffic, the MSU sends utility data to the collector. The MSU scans for a reply from the collector. In response to the collector having control data to transmit to the MSU, the collector transmits this control data in response to receiving a transmission from the MSU. The MSU is configured to enter a sleep mode. In response to receiving commands from the collector, the MSU is configured to perform the commands.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/712,898, filed on Sep. 1, 2005, titled “BATTERY SAVING TWO-WAY COMMUNICATION CIRCUIT AND SYSTEM AND METHOD FOR AUTOMATIC METER READING,” the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to a transmitting circuit. More particularly, the present invention relates to a battery saving two way communication circuit for use in an automatic meter reading system and a method of use.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is generally known that metering systems are utilized to collect or display utility data so that a utility company can determine utility usage of its customers and assess appropriate fees for those customers. To collect the utility data, utility companies have conventionally employed people as meter readers to visit each meter individually and record the displayed data.  
         [0004]     Initial efforts to improve this process focused upon eliminating transcription errors and automating the process of moving meter reading data from the human meter reader into a utility billing system. Systems where developed that allowed the meter reader to record meter readings in a portable electronic device. These devices allowed the meter reader to download meter data from a billing system, and upload meter reading data back into the billing system.  
         [0005]     Other conventional method of improving the system included attaching short-range transmitters or transceivers to the meters. These transceivers allowed receivers mounted in vehicles to collect meter reading data as the vehicle passed into near proximity of the meters. These conventional systems were generally configured so that the meter side unit regularly transmitted meter information every few seconds. In this manner, a passing vehicle and data receiver is typically in range when the meter side unit is transmitting. Another conventional method utilizes “vigilant” meter side units that constantly listen for a “wake-up call” and transmit the utility data in response to receiving this wake-up call from a passing vehicle and data receiver.  
         [0006]     Unfortunately, these and other conventional devices draw too much power to be economically operated with a battery at a longer range. That is, due to the frequency of battery replacement, these conventional systems are not cost effective when their technology is extended to long range operation.  
         [0007]     Accordingly, it is desirable to provide a battery saving two way communication circuit for use in an automatic meter reading system and a method of use that is capable of overcoming the disadvantages described herein at least to some extent.  
       SUMMARY OF THE INVENTION  
       [0008]     The foregoing needs are met, to a great extent, by the present invention, wherein in some embodiments a battery saving two way communication circuit for use in an automatic meter reading system and a method of use are provided.  
         [0009]     An embodiment of the present invention relates to an automatic meter reading system. The system includes a meter-side unit and a collector. The meter-side unit is configured to receive a meter signal from a meter. The collector is configured to receive meter signals from the meter-side unit. The meter-side unit is configured to remain in a sleep mode for a predetermined amount of time. The meter-side unit being configured to enter a wake mode after the predetermined amount of time and forward the meter signal to the collector in response to waking.  
         [0010]     Another embodiment of the present invention pertains to a method of automatically reading a meter. In this method, a meter-side unit remains in a sleep mode for a predetermined sleep cycle to conserve a supply of power in the meter-side unit, the meter-side unit enters a wake mode in response to an elapse of the sleep cycle, and a meter signal is transmitted from the meter-side unit to a collector in response to entering the wake mode. The meter-side unit is operably attached to the meter and the meter-side unit is remote from the collector.  
         [0011]     Yet another embodiment of the present invention relates to a computer readable medium on which is embedded computer software comprising a set of instructions for executing a method of automatically reading a meter. In this method, a meter-side units remains in a sleep mode for a predetermined sleep cycle to conserve a supply of power in the meter-side unit, the meter-side unit enters a wake mode in response to an elapse of the sleep cycle, and a meter signal is transmitted from the meter-side unit to a collector in response to waking. The meter-side unit is operably attached to the meter and the meter-side unit is remote from the collector.  
         [0012]     There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.  
         [0013]     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.  
         [0014]     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a block diagram of a system architecture for an automatic meter reading (AMR) system according to an embodiment of the invention.  
         [0016]      FIG. 2  is a block diagram of a system architecture for a meter-side unit (MSU) suitable for use with the AMR system according to  FIG. 1 .  
         [0017]      FIG. 3  is a block diagram of a system architecture for the collector suitable for use with the AMR system according to  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The present invention provides, in some embodiments, a battery saving two way communication circuit for use in an automatic meter reading (AMR) system and a method of use.  
         [0019]      FIG. 1  is a block diagram of a system architecture for an AMR system  10  according to an embodiment of the invention. As shown in  FIG. 1 , the AMR system  10  includes a meter-side unit (MSU)  12  configured to communicate with a meter  14 . The MSU  12  is configured for direct and/or indirect two-way communication with a collector  16 . To facilitate indirect communication, the AMR system  10  optionally includes a repeater  18  and/or a communication network  20 . In an embodiment, the MSU  12  collects utility usage data from the meter  14  and stores this usage data to a file  22 . The file  22  is transmitted from the MSU  12  to the collector  16 . The file  22  may be forwarded to a central collector  24  and stored to a database  26  for example. The file  22  may further be accessed by a utility  28  to determine utility usage of a customer.  
         [0020]     In an embodiment, the MSU  12  is configured to control the meter  14 . For example, in response to a signal from the utility  28  via the central collector  24  and/or the collector  16 , the MSU  12  is configured to control or modulate the meter  14 . In a particular example, in response to a “shut off” signal, the MSU  12  is configured to modulate a valve connected in series with the meter  14  to move to a closed position.  
         [0021]     In contrast to conventional battery saving techniques which depend upon controlling or regulating the period of time that a receiver remains in a vigilant mode and is scanning or otherwise operable to receive control commands from a central station, embodiments of the present invention improves the battery life by initiating communications from the MSU  12  rather than the central station. Using this communications method, the MSU  12  transmits the file  22  to the collector  16 , and then scans for a response from the collector  16  during a relatively brief period of time after the MSU  12  has transmitted its data. This approach reduces the period of time that a receiver is in a vigilant mode to, for example, a few seconds per reporting period, and allows the MSU  12  to operate on battery power for many years.  
         [0022]     In an embodiment, the collector  16  remains in a vigilant mode and the MSU  12  scans for signals from the collector  16  for a relatively brief period of time following a transmission from the MSU  12 . This new approach reduces a duty cycle for the MSU  12  as compared to conventional systems, and therefore prolonges battery life at the MSU  12  for a two-way long-range fixed-network AMR system  10 .  
         [0023]     Embodiments of the present invention facilitate a point to multi-point communication system, where the central collector  24  is located at a place that is configured to reduce close proximity with people on a regular basis. The MSUs  12  are located in close proximity to utility meters  14 , with one, two, or more meters  14  to the MSU  12 . The MSUs  12  so installed is configured to be distributed throughout the service area of the utility  28 . The MSUs  12  may typically be installed on top of or inside utility meter  14  boxes or on the sides of buildings. In a specific example, the MSUs  12  are configured to transmit their utility data, by default, 6 (six) times per day. Each transmission is configured to last, on average for less than 0.4 seconds, (but may be made up of multiple transmissions configured to last an average no more than, for example, 0.8 seconds). Therefore, possible exposure to signals for individuals who happen to be in the proximity of the MSU  12  is reduced.  
         [0024]      FIG. 2  is a block diagram of a system architecture for the MSU  12  according to an embodiment of the invention. As shown in  FIG. 2 , the MSU  12  includes a process manager  200 , power supply  202 , digital signal processing unit (DSPU)  204 , and a radio  206 . In general, the MSU  12  is a transceiver designed to gather meter and utility data from a data device (such as the utility meter  14 ) in the field and transfer that data to the central collector  24 , and receive control data from the central collector  24 . In addition to meter and utility data, the MSU  12  may be configured to receive signals from any suitable sensor. Examples of suitable sensors include telemetry devices, pressure gauges, rain gauges, temperature sensors, and the like. In a particular example, the MSU  12  is configured to receive, store, and transmit signals from a pressure sensor. The pressure sensor may be configured to sense fluid pressure within a pipe or supply line. In this manner, a supplier of the fluid in the supply line may monitor attributes of the fluid.  
         [0025]     In a particular embodiment, the MSU  12  uses frequency modulation in the industrial, scientific and medical (ISM) band (902-928 MHz). The MSU  12  uses frequency hopping spread spectrum techniques to create a dynamic, interference resistant and jam resistant communications channel between the MSU  12  and the central collector  24 . Due to government restrictions, the maximum allowed power in the transmitted signal is 1 watt. Power management techniques between the MSU  12  and collector  16  may step down the transmission power should the signal strength at the receiving end justifies a reduced transmission power.  
         [0026]     Encryption techniques may be utilized to secure the communications channel between the MSU  12  and the central collector  24 , in order to mask utility data from inquisitive listeners, and to prevent the spoofing of commands from the central collector  24  to the MSU  12 . According to various embodiments, any suitable encryption technique may be utilized.  
         [0027]     The process manager  200  is configured to determine sleep and/or wake modes or cycles and provide the various components with power from the power supply  202  in response to the determination that a wake cycle has occurred. The process manager  200  includes a switched mode power supply unit  208 , microprocessor  210 , and low power oscillator  212 . The switched mode power supply unit  208  includes an oscillator  214  such as a 350 kilohertz (kHz) to 1.2 Mega hertz (MHz) oscillator, for example. The microprocessor  210  includes a memory  216  and calibrated resistor and capacitor (RC) oscillator  218  such as a 4 MHz oscillator, for example. The microprocessor  210  includes any suitable processor. Examples of suitable processors include relatively low power and/or low frequency integrated circuits or chips. The memory  216  is configured to store the file  22  and/or a code  220 . The code  220  includes a set of computer executable instructions configured to control the MSU  12 . The low power oscillator  212  may include a 32.768 kHz oscillator for example.  
         [0028]     The power supply  202  is configured to supply power to the various components of the MSU  12 . In various embodiments, the power supply  202  includes one or more of a battery, capacitor, fuel cell, photovoltaic device, and the like. In addition, the power supply  202  may include a power inlet to receive power from an external source. In a particular example, the power supply  202  includes a battery  222 .  
         [0029]     The DSPU  204  is configured to gather utility usage data from the meter  14  and process this data. The DSPU  204  includes a digital signal processor (DSP)  224 , interface control electronics  226 , physical interface  228 , and battery monitor  230 .  
         [0030]     The DSP  224  is configured to receive utility usage data from the meter  14  via the physical interface  228  and/or the interface control electronics  226 , process the data and forward the processed data to the microprocessor  210  and or the radio  206 . In addition to the meter  14 , the DSP  224  may receive data from remote telemetry devices. Examples of remote telemetry devices include, at least, pressure transducers, rain gauges, temperature sensors, and the like. The DSP  224  is optionally configured to forward controlling signals from the microprocessor  210  to the meter  14 . In this manner, the meter  14  may be modulated by the MSU  12  in response to signals received by the MSU  12  from the collector  16 . For example, the MSU  12  may turn the meter  14  on or off or otherwise modulate a flow of fluid therethrough in response to received signals. The DSP  224  may include one or more clocks or oscillators. For example, the DSP  224  may include a relatively low power usage clock that is utilized during a sleep cycle and a relatively higher power usage clock to control processor cycle times and the like. In a particular example, the DSP  224  includes a master oscillator  232  and system oscillator  234 . The master oscillator  232  may include a relatively low power output 8 MHZ, calibrated RC master oscillator for example. The master oscillator  234  may include a 120 MHz oscillator.  
         [0031]     The interface control electronics  226  is configured to forward signals from the physical interface  228  to the DSP  224 . In addition, the interface control electronics  226  may be configured to forward signals from the DSP  224  to the physical interface  228 . Furthermore, the interface control electronics  226  may be configured to convert analog signals to digital signals and/or vice versa.  
         [0032]     The physical interface  228  is configured to receive signals from one or more devices such as the meters  14  and forward these signals to the interface control electronics  226 . In addition, the physical interface  228  may be configured to receive signals from the interface control electronics  226  and forward these signals to one or more devices such as the meters  14 . In various embodiments, the physical interface  228  is configured to interface with one, two, three, or more of the meters  14 . For example, the MSU  12  may be located in or near an apartment complex or other such structure with multiple users. In this or other such situations, the MSU  12  may be configured to interface with some or all the meters  14 . Accordingly, the physical interface  228  may be configured to interface with  100  or more of the meters  14 .  
         [0033]     The battery monitor  230  is configured to perform and/or record the result of a battery load test on a regular basis. This load test data, along with data that indicates the power of the transmission, is transmitted to the central collector  24  along with the other raw data collected by the MSU  12 . The load test data is deposited into the database  26 . The database  26  may be utilized to develop techniques to predict a failing battery or otherwise identify battery or load test trends.  
         [0034]     The radio  206  is configured to generate and receive signals. In a particular example, the radio  206  operates in the industrial, scientific and medical (ISM) band (902-928 MHz). The radio  206  may be configured to operate in the FCC Part  15  rules, with particular attention paid to Part  247 . For example, the ISM band may be divided into 25 KHz channels, with the first channel occurring at 902.025 MHz, the second channel at 902.050 MHz, and so on.  
         [0035]     The MSUs  12  are allocated to a frequency hop set containing  61  frequencies. If density of the MSUs  12  (e.g., the number of MSUs  12  per a given area) or terrain features (which create multi-path noise or collision issues) require more than one frequency hop set for a utility, then 3 or more such hop sets may be established, with each MSU  12  may be assigned to a single set of hop frequencies.  
         [0036]     If more than one frequency hop set is used, the frequencies of the hop sets are interleaved, such that the first hop set utilizes channel  0 ,  3 ,  6 ,  9  . . . the second hop set utilizes channel  1 , 4 , 7 , 10  . . . and the third hop set utilizes channel  2 , 5 , 8 , 11  . . .  
         [0037]     A maximum length sequence (MLS) or M sequence is a pseudorandom binary sequence used as a basis for deriving pseudo-random sequences in digital communication systems that employ direct-sequence spread spectrum and frequency-hopping spread spectrum transmission systems. M sequences generally employ polynomial rings generated using maximal linear feedback shift registers and are so called because they are periodic and reproduce every binary sequence that can be reproduced by the shift registers (i.e., for m registers they produce a sequence of length 2 m −1). Each MSU  12  may be configured to use the frequencies of the hop set to which it is assigned. In various embodiments, random selection of frequency may use the wake-up time of the MSU  12  as input into the M sequence, or simply take the next value off of the top of the M sequence. For example, in an embodiment, each MSU, before initiating a transmission, may query a clock or oscillator to determine the time and select a frequency from its hop set based on the determined time. Similarly, the collector  12  may be configured to receive signals based upon the time. In this manner, communication between the MSU  12  and the collector  12  may be facilitated. In another embodiment, each MSU, before initiating a transmission, may randomly select a frequency from its hop set using a simple M sequence approach. In this regard, the MSU may include a table stored in the code  220  or otherwise in the memory  216  that is configured to cause the M-sequence to work around frequencies that may contain interference, or those that may be forced to be not used if interference to outside receivers is prevalent. The tables may cause the transmitters to increase power, or to skip certain channels. These tables are dynamic, and may be arranged so that the 50-channel minimum is configured to be observed, if frequencies are skipped.  
         [0038]     The radio  206  may be configured to send signals associated with the file  22  in response to commands from the microprocessor  210  and/or the DSP  224 . In another example, the radio  206  is configured to receive signals from the collector  16  and forward the received signals to the microprocessor  210  and/or the DSP  224 . The radio  206  may be configured to send signals at a predetermined power level and/or duration. For example, the radio  206  may send a signal for a period of less than 0.4 seconds, at a signal strength of at, or less than, 1 watt. The MSUs  12 , repeaters  18 , and collectors  16  are configured to relay signal-strength information during the initial packets of communications. Based upon the signal-strength information, the MSUs  12  may reduce transmission power output and thereby avoid unnecessary power levels. In this manner, the transmitter may be controlled to reduce power output. This reduces interference and prolongs battery life. Also, the maximum amount of power utilized to transmit may be set to any suitable value. For example a maximum transmitter power level may include 1 watt. On frequencies where power may be upped to establish communications, power level may be determined as a side-effect of automatic repeat request (ARQ) negotiation.  
         [0039]     The radio  206  is controlled via the microprocessor  210  to, within a packet, for a given period of less than 0.4 seconds, emit a signal that is non-coherent frequency shift keying (“FSK”) modulated at two levels at an 1831-baud rate using Manchester as the signaling method. The deviation of the signal is configured to be at or within 1800 Hz to 1000 Hz, resulting in a modulation index from ˜0.55 to ˜1.0. Carson&#39;s rule is configured to place the bandwidth between ˜5600 Hz and ˜7200 Hz. The receive filter is configured to handle a 7500 Hz bandwidth signal. The modulation signal is shaped (through a simple lowpass filter and a rubbered crystal) to have its harmonics limited. The passband is about between a raised-cosine and Gaussian function. This keeps adjacent-channel interference down and increases the receiver&#39;s extraction capabilities by reducing the effects of the intermediate frequency (“IF”) filter upon the signal. The choice of narrowband emission is partly from channel gain/noise capability, and part rejection capability of digital-modulation spread-spectrum emissions.  
         [0040]     The antenna  236  is configured to generate and receive signals. In a particular embodiment, the antenna  236  includes a 4 decibel (dB) antenna. With 4 dB antennas, data communications range is approximately 2 miles. This allows the MSU  12  connected to the AMR system  10  to send meter reading data through a fixed network back to the utility  28 . It is an advantage of this and other embodiments that there is no need to walk or drive-by the MSU  12  to read the meters  14  change the behavior of the MSU  12 , or send commands to the meters  14 . The radio  206  may also include an amplifier  238 , and transceiver  240 .  
         [0041]     The amplifier  238  is preferably configured to amplify signals received by the antenna  236  and/or amplify signals that are forwarded to the antenna  236 . The transceiver  240  preferably is configured to generate signals based on signals received from the microprocessor  210  and/or the DSP  224  and forward these signals via the amplifier  238  to the antenna  236 . The transceiver  240  may also configured to forward signals received by the antenna  236  to the microprocessor  210  and/or the DSP  224 . The transceiver  240  includes a main crystal oscillator  242  and a main carrier oscillator  244 . The main crystal oscillator  242  may include a 24.576 MHz oscillator for example.  
         [0042]     To intercommunicate between the various components of the MSU  12 , the MSU  12  may include one or more busses such as an internal control bus  246 , an input/output (I/O) bus  248 , and an external data bus  250 . The internal control bus  246  may be configured to facilitate intercommunication between the microprocessor  210 , the DSP  224 , and the transceiver  240 . The I/O bus  248  may be configured to facilitate intercommunication between the microprocessor  210  and the DSP  224 . The external data bus  250  may be configured to facilitate intercommunication between the microprocessor  210 , the DSP  224 , and the interface control electronics  226 .  
         [0043]      FIG. 3  is a block diagram of a system architecture for the collector  16  according to an embodiment of the invention. As shown in  FIG. 3 , system architecture of the collector  16  is similar to the system architecture of the MSU  12 , and thus, only those items that differ are discussed hereinbelow.  
         [0044]     The collector  16  is optionally hard wired to a line power  360  to facilitate remaining in a vigilant mode and scanning for signals from the MSU  12 .  
         [0045]     In an embodiment, the radio  206  is intermittently powered through the switched mode power supply unit  208  so as to reduce the use of electrical power consumption. When powered, the MSU  12  scans the communications channel for traffic, and transmits collected data to the central collector  24  when the communications channel is clear. The central collector  24  is preferably configured to receive transmitted data and, upon receiving the transmission, responds to the MSU  12 . The MSU  12 , upon receiving the response from the central collector  24 , or after waiting for a brief period after transmission, returns to a sleep mode. It is an advantage of this and other embodiments that this approach reduces the period of time that power is applied to the radio transceiver, and so increases battery life in the MSU  12 .  
         [0046]     To reduce collisions on the communications channels, the MSU  12  according to various embodiments is configured to perform a variety of protocols. For example, the MSU  12  may be configured to scan the communications channel prior to beginning its transmission. In another example, multiple channels may be assigned to each MSU  12  in order to reduce collisions on a given radio frequency. In another example, the same frequency hop set can be shifted in time between two different collectors in order to prevent collisions. In yet another example, groups of MSUs  12  may be assigned different frequency hop channel sets in order to prevent collisions between collectors that are in close proximity to one another. In this manner, multiple central collectors may operate near one another without interfering with one another, and so increases the available density of MSUs  12 . In the event that buildings, trees or geographic features interfere with the line-of-site of MSUs  12  to the central station, repeaters may be used to route the signal around the obstructions.  
         [0047]     According to an embodiment, each MSU  12  may be programmed to initiate a wake-mode and transmit data in response to specific external stimulus in addition to its regularly scheduled wake cycle. For instance, when attached to the AMR system  10 , the MSU  12  may transmit a report to the central collector  24  in response to a suitable event. Examples of suitable events include one or more of: detecting meter tampering, reverse flow event, and the like.  
         [0048]     The central collector  24  may be configured to essentially constantly scan a range of frequencies or super-scan the frequencies of a single hop-set. Upon detecting the MSU  12  transmission, the central collector  24  may respond to the MSU  12  on a channel exactly 21.4 MHz above the frequency used by the MSU  12 . The MSU  12  is configured to listen to that channel for a response from the central collector  24 .  
         [0049]     If the MSU  12  does not receive a response from the central collector  24  or collector  16 , or if the collector  16  response is one that indicates that the collector  16  received an incomplete transmission from the MSU  12 , then the MSU  12  is configured to select another frequency randomly from its hop set and resend the transmission. The MSU  12  may be configured to resend the communication a predetermined number of times. For example the MSU  12  may be configured to perform 5 such transmission before entering a sleep mode. Once in sleep mode after 5 tries, it is configured to enter the wake-mode at a later time and repeat the transmission to the central collector  24 .  
         [0050]     The communications approach is such that, under normal circumstances, a single transmission from the MSU  12  is configured to contain all of the needed transmission data. A single transmission may contain multiple meter readings and the times of those meter readings. As a result, under normal circumstances, the MSU  12  is configured to only need a single transmission of less than, for example, 0.4 seconds in order to meet its data transmission goals.  
         [0051]     If control data is passed back from the central collector  24  to the MSU  12 , then the transmission is configured to proceed approximately as follows: 
        MSU: Scan the radio channel to avoid collisions     MSU: Transmits meter data to Collector     Collector: Transmits received meter data, control data to follow     MSU Transmits ready to receive control data     Collector: Transmits first bit of control data     MSU Transmits received first bit, ready for next . . . .     Collector Transmits next bit of control data . . . Loop through the last two messages until . . .     Collector Transmits last bit of control data. End Conversation.        
 
         [0060]     Each packet of data may include a 32 bit MSU ID and the data from the last data collection effort (usually a meter reading). The 32 bit MSU ID is, preferably, not encrypted. The data is, preferably, encrypted. Each data packet is aligned, with the header containing an operation (OP) code of the message.  
         [0061]     In a particular example, data is organized into packets in a frame, with the end of each frame containing error correction code. The packet ends with 1 word of cyclic redundancy codes (CRC) and 4 more words that make up a check sum that is derived from the rest of the message.  
         [0062]     The purpose of the CRC is to further qualify the data after it runs through the parity correction system. The parity correction system has a strength of four octets (1 in 4 billion.) This adds two more octets to the error-detecting strength (1 in 2.8e14.) The CRC is calculated by running the body first-bit-first through a 16-bit shift register with generator polynomial xˆ15+xˆ13+xˆ0 (0xA001 XOR value) and then taking the resulting 16-bit number and placing it in the Post CRC position (highest order octet first.) In receive, the CRC value is generated the same way with the 70-octet body, and then compared with the Post CRC value (same octet order.) If they match, the data is considered valid.  
         [0063]     The check sums are computed from the data in the rest of the frame (not including the preamble). The check-sum data uses the Reed Solomon Code  247 / 255  approach. The raw data has a single word put on top of it for CRC purposes. The raw data and CRC word are subjected to a Reed Solomon generator.  
         [0064]     The transmitter attempts to transmit the entire data packet.  
         [0065]     The receiver attempts to receive the entire packet. If the receiver bit counter indicates that the entire packet has been received, the packet is passed to a Reed Solomon decoder which uses the last 4 words to perform error correction. In this manner, up to 4 errors may be corrected.  
         [0066]     If the Reed Solomon decoder cannot accurately decode the packet (including using the 4 words of error correction) then the entire packet may be rejected.  
         [0067]     If the decoder can decode the message, then the Reed Solomon polynomials are applied to the packet and it goes through CRC for correction. In this manner, the raw data is extracted from the packet.  
         [0068]     If the signal gets near the noise threshold, then sputter interference becomes a problem. Reed Solomon decoding facilitates extracting data from packets in the presence of sputter interference. It is an advantage of this and other embodiments that without Reed Solomon, the data runs into problems 9 or 10 dB above the noise. With Reed Solomon, the data is usable at 3 or 4 dB above the noise.  
         [0069]     In the event that two or more collectors  16  can receive the transmission of a particular MSU  12 , in an embodiment, only one collector  16  is configured to respond. To avoid multiple responses to the MSU  12 , and to make it more difficult to duplicate, copy, spoof, or otherwise emulate a MSU  12  transmission to the collector  16 , the collector  16  is configured to only respond to MSUs  12  that are entered into the collector&#39;s list of valid MSUs  12 . This list may include an identification (ID) for the MSU  12 . For example, the ID may include a 32 bit ID, and optionally a corresponding matched encryption key pair for the given MSU  12 .  
         [0070]     The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.