Abstract:
In one aspect, a wireless communications device includes a processing unit; memory communicatively coupled to the processing unit; at least one antenna; a cellular receiver communicatively coupled to the processing unit and the at least one antenna to perform wireless communications using a first protocol; and an identification device communicatively coupled to the processing unit and the at least one antenna to perform wireless communications by modulating a received signal using a second protocol different than the first protocol. The wireless communications device may further include a location-determining system communicatively coupled to the processing unit to determine a current location of the wireless communications device using a global positioning system (GPS), to allow the processing unit to perform a control operation based on the current location of the wireless communications device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 11/890,051, filed Aug. 3, 2007, which in turn is a continuation of U.S. patent application Ser. No. 11/037,774, filed Jan. 18, 2005, now U.S. Pat. No. 7,253,715, which in turn is a continuation of U.S. patent application Ser. No. 10/903,851, filed Jul. 30, 2004, now U.S. Pat. No. 7,005,961, which in turn is a continuation of U.S. patent application Ser. No. 10/452,969, filed Jun. 2, 2003, now U.S. Pat. No. 6,774,762, which in turn is a continuation of U.S. patent application Ser. No. 09/516,634, filed Mar. 1, 2000, now U.S. Pat. No. 6,583,713, which in turn is a continuation of U.S. patent application Ser. No. 08/911,303, filed Aug. 14, 1997, now U.S. Pat. No. 6,057,779, all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to transportation systems. The invention also relates to security systems, lock systems, and access control. 
     BACKGROUND OF THE INVENTION 
     Valuable cargo is transported on a daily basis. It is desirable to secure the cargo against unauthorized access, so as to prevent tampering, theft of some cargo, or theft of all cargo. 
     Cargo is typically secured using conventional locks, such as padlocks, which are opened using a metal key. For example, for cargo transported by semi-trailers, the cargo is typically secured by locking the trailer door with a padlock. The driver then carries the key. 
     A problem with conventional methods of securing cargo is that the driver has access to the cargo and has the opportunity to steal some or all of the cargo. Further, there is the possibility of the driver being hijacked, and the key taken from the driver. There is also the possibility of the driver diverging from the intended course and taking the cargo to a non-approved area, such as to a competitor, to another state or country, or through an area where the risk of theft is greater. 
     While the invention was motivated in addressing the above issues, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents. 
     SUMMARY 
     In a first aspect of the invention, a wireless communications device is disclosed. In one embodiment, the wireless communications device includes a processing unit and memory communicatively coupled to the processing unit. The device also includes a location system communicatively coupled to the processing unit configured to provide data enabling determination of a current location of the wireless communications device using a global positioning system (GPS). An antenna and an electronic identification device configured to perform wireless communications via the antenna by modulating a radio frequency (RF) field generated by an interrogating device is also included along with a cellular receiver communicatively coupled to the processing unit. The processing unit is configured to perform a control operation based on the current location of the wireless communications device and information received from the identification device. 
     In another embodiment, the wireless communication device includes a cellular receiver communicatively coupled to the processing unit and the first antenna to perform wireless communications via the first antenna using a first protocol. A second antenna and an identification device communicatively coupled to the second antenna and the processing unit to perform wireless communications via the second antenna by modulating a radio frequency (RF) field using a second protocol, the second protocol being different than the first protocol is also included. The device also includes a communication port that provides a control signal to a second device via a wired connection. In addition, the identification device uses a random number as an identifier of the identification device. 
     In a variant, the identification device communicates via magnetic field modulation. 
     In another variant, the identification device communicates via backscattering radio frequency signals from an interrogation apparatus. 
     In yet another variant, the second antenna comprises a microstrip. 
     In yet another variant, the second antenna has at least one loop. 
     In yet another variant, the identification device comprises a transmitter switchable between a first mode in which the transmitter modulates an RF field generated by a remote interrogation apparatus and a second mode in which the transmitter modulates an RF field generated by the identification device. 
     In yet another variant, the identification device is further configured to store a unique identifier corresponding to a person associated with the identification device. 
     In a second aspect of the invention, a device is disclosed. In one embodiment, the device includes a processing unit, a location-determining system configured to provide data useful in determining a current location of the wireless communications device using a global positioning system (GPS), a first wireless communication subsystem comprising a cellular receiver to perform wireless communications and a second wireless communication subsystem configured to generate a random number and to provide the random number as an identifier of the device by modulating a radio frequency (RF) field provided by a remote interrogation device. The first subsystem comprises a first antenna for wireless communications using the cellular communications system and the second subsystem comprises a second antenna to provide the random number, with the second subsystem being switchable between transmitting in a passive mode and transmitting in an active mode. 
     In a variant, the second subsystem is further configured to provide a unique identification code corresponding to a person associated with the identification device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
         FIG. 1  is a perspective view illustrating a secure cargo transportation system and a method for controlling access to a movable container. 
         FIG. 2  is a diagrammatical perspective view illustrating a lock, controller, and key included in the system of  FIG. 1 . 
         FIG. 3  is a block diagram illustrating the system of  FIG. 1  in communication with a central communications station. 
         FIG. 4  is a block diagram of an interrogator or transmitter included in the central station of  FIG. 3 . 
         FIG. 5  is a block diagram showing details of DPSK circuitry included in the interrogator of  FIG. 4 . 
         FIG. 6  is a block diagram showing details of RF circuitry included in the interrogator of  FIG. 4 . 
         FIGS. 7 and 8  together define a flowchart illustrating operation of the secure cargo transportation system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
       FIG. 1  shows a secure cargo transportation system  10  embodying the invention. The secure cargo transportation system  10  comprises a movable container or vehicle  12  including an enclosure  14  having an opening  16 . In the illustrated embodiment, the vehicle  12  is a semi trailer. In alternative embodiments, the movable container is defined by a train boxcar, a safe, a compartment in a boat or plane, or any other movable container. The vehicle  12  includes a door  18  movable relative to the opening  16  between a closed position, wherein the door  18  restricts access to the enclosure, and an open position ( FIG. 2 ). In some embodiments, the vehicle includes multiple doors  18 ,  20 . The vehicle  12  includes an electronically actuable lock  22  to selectively lock or unlock the door relative to the enclosure. In embodiments having two doors, the primary door is locked with an electronically enabled or actuable lock  22 , or both doors are locked with an electronically enabled or actuable lock  22  such that access to the enclosure requires unlocking at least one electronically actuable lock  22 . 
     More particularly, in the preferred embodiment, the doors  18  and  20  are fitted with an intelligent lock controller such as the lock controller sold by Intellikey Corporation, 551 S. Apollo Blvd., #204, Melbourne, Fla. 32901. In one embodiment, pre-existing mechanical cylinders can be replaced with electronic cylinders of the type sold by Intellikey, or the electronic cylinders can be installed initially. An electronic controller  24  is supported by the back of the door, inside the enclosure  14 , or in other appropriate (preferably secure) location. In the illustrated embodiment, the lock  22  requires both an electronic key or signal and a mechanical key to open the lock. More particularly, a key  26  has a mechanical portion  28  as well as circuitry  30  supported therefrom (e.g., in the handle for the key) which communicates electronically with the lock (e.g., by radio frequency or magnetic coupling). In alternative embodiments, only an electronic key or signal is required to open the lock. Data communicated between the key and lock is encrypted, in the illustrated embodiment. In the illustrated embodiment, the key and lock provide multiple levels of access. For example, in the illustrated embodiment, seven masterkeying levels are available. The electronic controller  24  can be programmed to change whose key will open the lock and when. The circuitry  30  of the key  26  includes memory which carries access control information and identifying information for the user of the key. The controller  24  reads this information and determines whether the user of the key should be granted access. The controller  24  is programmable to grant access to the user of the key based on factors such as location and time. The memory of the circuitry  30  records an audit trail of in which lock the associated key  26  has been used. In addition to the electronic controller  24  being programmable, the circuitry  30  of the key  26  is also programmable, and access control and feature information can be changed for each key using a key programming unit available from Intellikey Corporation. 
     The system  10  further includes a remote intelligent communications device  32  ( FIG. 3 ) supported by the vehicle  12  and in communication with the lock  22 . More particularly, in the illustrated embodiment, the remote intelligent communications device  32  has an RS-232 port, and communicates with the lock controller  24  via a RS-232 cable connected between the RS-232 port of the device  32  and the lock controller  24 . The remote intelligent communications device  32  includes a processor  33 , a memory  34  coupled to the processor  33 , and a global positioning system receiver  36  in communications with the processor  33 , and thus with the memory  34 . The global positioning system receiver  36  communicates with a global positioning satellite  37  to determine the position of the receiver  36 . While other embodiments are possible, in the illustrated embodiment, the global positioning system receiver  36  is an Encore™ GPS receiver manufactured by or available from Motorola Inc., Schaumburg, Ill. The remote intelligent communications device  32  periodically or at various times logs in the memory  34  the position of the device  32  (and therefore the position of the vehicle  12 ) with respect to time. The remote intelligent communications device  32  uses UTC time obtained from GPS satellite data to provide time of day information for use with the logging of the position information. 
     An exemplary remote intelligent communications device  32  that can be employed is described in commonly assigned U.S. patent application Ser. No. 08/656,530, titled “A Method And Apparatus For Remote Monitoring,” (now U.S. Pat. No. 5,894,266) incorporated herein by reference. In the preferred embodiment, the remote intelligent communications device  32  is an Ambit™ remote intelligent communications device available from Micron Communications, Boise, Id. The Ambit™ device is a board level device which is similar in design and operation to an integrated circuit described in commonly assigned U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996 (now U.S. Pat. No. 6,130,602), and incorporated herein by reference, except that it further includes the global positioning system receiver. 
     The remote intelligent communications device  32  further includes a radio frequency (RF) communications receiver  38  coupled to the processor  33 , which receives a desired location coordinate at which access to the contents of the enclosure  14  is permitted. The remote intelligent communications device  32  further includes a radio frequency (RF) communications transmitter  39  coupled to the processor  33 . In the illustrated embodiment, the remote intelligent communications device receives and transmits data at microwave frequencies. The remote intelligent communications device includes indicia for uniquely identifying the vehicle  12  with respect to other vehicles  12 . A central station  46  can communicate with a specified vehicle  12  out of a fleet of vehicles  12 ,  12   b . More particularly, in the illustrated embodiment, multiple vehicles are equipped with the remote intelligent communications device  32  and lock  22 , and the central station  46  can communicate with any desired vehicles to control access to enclosure  14  of a specified vehicle. 
     Desired access locations, such as docking bays  42  at final destinations are determined by a responsible person  44  at a central station  46  and communicated to the vehicle  12 , such as by using a transmitter  49  (described below) located at or controlled at the central station  46 . 
     When the vehicle  12  enters into a specified area, as determined by the GPS receiver  36 , the remote intelligent communications device  32  sends a digital message to the controller  24  enabling the lock  22  to be opened with the key  26 . The GPS area is defined so as to take into account the error possible with the GPS receiver  36  being used. The receiver  38  receives commands from the transmitter  49  when in communications range with a transmitter. 
     A desired or specified location  48  received by the receiver  38  is stored in memory. For example, the receiver receives a point and a radius, or three geographic points to define a desired area or location, or two points to define a line and an offset distance to the left and right of the line. In one embodiment, the processor  33  provides a signal to the controller  24  of the lock to enable unlocking using the key  26  if the vehicle  12  is within a predetermined distance of the desired location. Multiple locations can be specified where access is permitted. In another embodiment, the processor  33  provides for exception logic, enabling unlocking in all areas except a specified location  48 . 
     Other methods of receiving and storing location coordinates can be employed. For example, some coordinates can be pre-programmed. For example, weigh stations at state lines have known coordinates which can be stored in memory so unlocking is enabled at these locations. 
     Further, new location coordinates where access is permitted can be communicated to the device  32  by a paging network or system  50 . To this end, the device  32  further includes a paging receiver  52  coupled to the processor  33 . Emergency access to the contents of the enclosure  14  can be granted by the operator  44  using the paging system. For example, if the vehicle is stopped by police who want to inspect cargo in the enclosure  14 , the driver of the vehicle, using a telephone  54 , can call a telephone  56  manned by the operator  44  at the central station  46 . The operator  44  can then authorize access, regardless of the vehicle&#39;s location, using the same or a different telephone  58  to access the paging system  50 . The telephone  54  used by the driver can be a cellular phone on board the vehicle, or a pay phone or other phone located outside the vehicle  12 . 
     Alternatively, a cellular receiver can be employed instead of the paging receiver. 
     In one embodiment, a plurality of geographical areas  60  through which it is desired that the vehicle  12  travel are stored in memory  34 . The geographical location of the container at each of a plurality of different times is logged, and the locking mechanism  22  is enabled to permit unlocking if the vehicle  12  passed through all of the geographical areas stored in memory  34 . 
     In another embodiment of the invention, an order of geographical areas is defined, and the locking mechanism  22  is enabled to permit unlocking if the vehicle passed through the geographical areas in the defined order. 
     In another embodiment, an order of geographical areas is defined, including a final destination geographical area (e.g., area  48 ), and the locking mechanism  22  is enabled to unlock if the vehicle  12  passed through each of the geographical areas  60  in the defined order and is in the final destination geographical area. 
     In another embodiment of the invention, data defining a desired path of travel through which it is desired that the container travel is stored in memory  34 . A geographical area defining a desired final destination (e.g., area  48 ) is also stored in memory  34 . An alert signal is produced if the vehicle  12  deviates from the desired path of travel. In one aspect of the invention, data is stored defining a plurality of overlapping geographical areas. In one embodiment, the device  32  is coupled to the electrical system of the vehicle  12 , or to an engine controller of the vehicle  12 , and cuts off the engine if the vehicle deviates from the desired path of travel by more than a programmed amount. For example, the device  32  can be coupled to the engine controller in the manner disclosed in commonly assigned U.S. patent application Ser. No. 08/759,737, filed Dec. 6, 1996 (now U.S. Pat. No. 5,995,898) and incorporated herein by reference. 
     As previously mentioned, the central station  46  includes the transmitter  49 . More particularly, in the illustrated embodiment, the central station  46  includes an interrogator  47  comprising the transmitter  49 , and further comprising a receiver  51 . The remote intelligent communications device  32  transmits and receives radio frequency communications to and from the interrogator  47 . The central station  46  further includes one or more send/receive antenna pairs  62  coupled to the interrogator  47 . In an alternative embodiment, the interrogator  47  uses an antenna both for transmitting and receiving by the interrogator  47 . The interrogator  47  includes transmitting and receiving circuitry, similar to that implemented in the remote intelligent communication device  32 . In one embodiment, the system central station  46  further includes a controller  64 . In the illustrated embodiment, the controller  64  is a computer. The controller  64  acts as a master in a master-slave relationship with the interrogator  47 . The controller  64  includes an applications program for controlling the interrogator  47  and interpreting responses, and a library of radio frequency identification device applications or functions as described in the above-incorporated patent applications. Most of the functions communicate with the interrogator  47 . These functions effect radio frequency communication between the interrogator  47  and the remote intelligent communications device  32 . In one embodiment, the controller  64  and the interrogator  47  are combined together (e.g., in a common housing), or functions of the host computer are implemented in hard wired digital logic circuitry. 
     Generally, the interrogator  47  transmits an interrogation signal or command, such as a command to add geographical locations where opening of the lock  22  is enabled, (“forward link”) via one of the antennas  62 . The remote intelligent communications device  32  receives the incoming interrogation signal via its antenna, if it is within receiving range. Upon receiving the signal, the remote intelligent communications device  32  responds by generating and transmitting a responsive signal or reply (“return link”). The interrogator  47  is described in greater detail below. 
     In the illustrated embodiment, signals transmitted and received by the interrogator  47 , and signals transmitted and received by the remote intelligent communications device  32  are modulated spread spectrum signals. Many modulation techniques minimize required transmission bandwidth. However, the spread spectrum modulation technique employed in the illustrated embodiment requires a transmission bandwidth that is up to several orders of magnitude greater than the minimum required signal bandwidth. Although spread spectrum modulation techniques are bandwidth inefficient in single user applications, they are advantageous where there are multiple users (e.g., multiple vehicles  12 ,  12   b ). The spread spectrum modulation technique of the illustrated embodiment is advantageous because the interrogator signal can be distinguished from other signals (e.g., radar, microwave ovens, etc.) operating at the same frequency. The spread spectrum signals transmitted by the device  32  and by the interrogator  47  are pseudo random and have noise-like properties. A spreading waveform is controlled by a pseudo-noise or pseudo random number (PN) sequence or code. The PN code is a binary sequence that appears random but can be reproduced in a predetermined manner by the device  32 . More particularly, incoming spread spectrum received by the device  32  or interrogator  47  are demodulated through cross correlation with a version of the pseudo random carrier that is generated by the device  32  itself or the interrogator  47  itself, respectfully. Cross correlation with the correct PN sequence unspreads the spread spectrum signal and restores the modulated message in the same narrow band as the original data. 
     A pseudo-noise or pseudo random sequence (PN sequence) is a binary sequence with an autocorrelation that resembles, over a period, the autocorrelation of a random binary sequence. The autocorrelation of a pseudo-noise sequence also roughly resembles the autocorrelation of band-limited white noise. A pseudo-noise sequence has many characteristics that are similar to those of random binary sequences. For example, a pseudo-noise sequence has a nearly equal number of zeros and ones, very low correlation between shifted versions of the sequence, and very low cross correlation between any two sequences. A pseudo-noise sequence is usually generated using sequential logic circuits. For example, a pseudo-noise sequence can be generated using a feedback shift register. 
     A feedback shift register comprises consecutive stages of two state memory devices, and feedback logic. Binary sequences are shifted through the shift registers in response to clock pulses, and the output of the various stages are logically combined and fed back as the input to the first stage. The initial contents of the memory stages and the feedback logic circuit determine the successive contents of the memory. 
     The illustrated embodiment employs direct sequence spread spectrum modulation. A direct sequence spread spectrum (DSSS) system spreads the baseband data by directly multiplying the baseband data pulses with a pseudo-noise sequence that is produced by a pseudo-noise generator. A single pulse or symbol of the PN waveform is called a “chip.” Synchronized data symbols, which may be information bits or binary channel code symbols, are added in modulo-2 fashion to the chips before being modulated. The receiver performs demodulation. For example, in one embodiment the data is phase modulated, and the receiver performs coherent or differentially coherent phase-shift keying (PSK) demodulation. In another embodiment, the data is amplitude modulated. Assuming that code synchronization has been achieved at the receiver, the received signal passes through a wideband filter and is multiplied by a local replica of the PN code sequence. This multiplication yields the unspread signal. 
     A pseudo-noise sequence is usually an odd number of chips long. 
     Spread spectrum techniques are also disclosed in the following patent applications and patent, which are incorporated herein by reference: U.S. patent application Ser. No. 08/092,147 (now abandoned); U.S. patent application Ser. No. 08/424,827, filed Apr. 19, 1995 (now U.S. Pat. No. 5,790,946); and U.S. Pat. No. 5,121,407 to Partyka et al. They are also disclosed, for example, in “Spread Spectrum Systems,” by R. C. Dixon, published by John Wiley and Sons, Inc. 
     In one embodiment, the interrogator  47  is coupled to the controller  64  via an IEEE-1284 enhanced parallel port (EPP). 
     In one embodiment, communications from the interrogator  47  to the device  32 , and communications from the device  32  to the interrogator  47  use different physical protocols. 
     The physical communications protocol for communications from the interrogator  47  to the device  32  is referred to as the “forward link” protocol. In the illustrated embodiment, the forward link data is sent in the following order: 
     Preamble 
     Barker Code 
     Command Packet 
     Check Sum 
     A Maximal Length Pseudo Noise (PN) Sequence is used in the Direct Sequence Spread Spectrum (DSSS) communications scheme in the forward link. In one embodiment, the sequence is generated by a linear feedback shift register of a specified form. In the illustrated embodiment, there are multiple registers, the output of one of the registers is X-ORed with the output of another register, and the result is fed into the input of the first register. This produces a repeating 31 “chip” sequence. The sequence ends with all registers set to one. The sequence is taken from the output of the first register. This code is synchronous with the data in that each data bit comprises one and only one full PN sequence. 
     In one embodiment, a zero bit is transmitted as one inverted full cycle of the PN sequence. A one bit is transmitted as one full non-inverted cycle of the PN sequence. 
     The preamble precedes the data. In one embodiment, the preamble includes a series of zeros, followed by a start or Barker code. 
     In one embodiment, the Barker code is defined by the following bit string: 1111 1001 1010 1. Other embodiments are of course possible. 
     In the illustrated embodiment, command data is grouped into 13-bit words. Each word includes eight data bits (D 7 , D 6 , D 5 , D 4 , D 3 , D 2 , D 1 , DO) and five ECC (Error Correction Code) bits (P 4 , P 3 , P 2 , P 1 , and PO). In one embodiment, the bit transmission order is (with D 7  transmitted first): 
     D 7 , D 6 , D 5 , D 4 , D 3 , D 2 , D 1 , D 0 , P 4 , P 3 , P 2 , P 1 , PO . . . 
     In one embodiment, the ECC bits (P 4 -PO) are generated using the following equations:
 
 PO =( D 1+ D 2+ D 5+ D 7)modulo 2
 
 P 1=[( D 1+ D 3+ D 4+ D 6)modulo 2]Complement
 
 P 2=( D 0+ D 2+ D 3+ D 6+ D 7)modulo 2
 
 P 3=[( D 0+ D 4+ D 5+ D 6+ D 7)modulo 2]Complement
 
 P 4=( DO+D 1+ D 2+ D 3+ D 4+ D 5)modulo 2.
 
     Other methods of generating the error correction code bits are of course possible. 
     In the illustrated embodiment, a 16-bit check sum is provided to detect bit errors on the packet level. The device  32  can be programmed to either return a reply if a bad check sum is found in the forward link, or to simply halt execution and send no replies. In one embodiment, a 16 bit CRC is employed in the forward link, the return link, or both, instead of or in addition to the check sum. 
     The physical communications protocol for communications from the device  32  to the interrogator  47  is referred to as the “return link” protocol. In the illustrated embodiment, the return link messages are sent in the following order: 
     Preamble, 
     Barker Code, 
     Reply Packet 
     Check Sum 
     After sending a command, the interrogator  47  sends a continuous unmodulated RF signal with a specified frequency, such as 2.44 GHz, 915 MHz, or other frequencies. In the illustrated embodiment, return link data is Differential Phase Shift Key (DPSK) modulated onto a square wave subcarrier with a frequency of 596.1 kHz. A data  0  corresponds to one phase and data  1  corresponds to another, shifted 180 degrees from the first phase. For a simple dipole, a switch between the two halves of the dipole antenna is opened and closed. When the switch is closed, the antenna becomes the electrical equivalent of a single half-wavelength antenna that reflects a portion of the power being transmitted by the interrogator. When the switch is open, the antenna becomes the electrical equivalent of two quarter-wavelength antennas that reflect very little of the power transmitted by the interrogator. 
     The preamble for the return link includes 2000 bits, alternating 2 zeros then 2 ones, etc., and a 13-bit start (Barker) code. Alternative preambles are possible. 
     In the illustrated embodiment, the start code or Barker Code is defined by the following bit string: 1111 1001 1010 1. 
     The reply link data is grouped in 13 bit words. Each word is composed of 8 data bits (D 7 , D 6 , D 5 , D 4 , D 3 , D 2 , D 1 , DO) and 5 ECC bits (P 4 , P 3 , P 2 , P 1 , PO). 
     The Block Encoded Sequence is D 7 , D 6 , D 5 , D 4 , D 3 , D 2 , D 1 , D 0 , P 4 , P 3 , P 2 , P 1 , PO. 
     The Block ECC Bits (P 4 -PO) are generated using the following equations:
 
 PO =( D 1+ D 2+ D 5+ D 7)modulo 2
 
 P 1=[( D 1+ D 3+ D 4+ D 6)modulo 2]Complement
 
 P 2=( D 0+ D 2+ D 3+ D 6+ D 7)modulo 2
 
 P 3=[( D 0+ D 4+ D 5+ D 6+ D 7)modulo 2]Complement
 
 P 4=( DO+D 1+ D 2+ D 3+ D 4+ D 5)modulo 2.
 
     Other methods of generating error correction code bits can, of course, be employed. 
     In the illustrated embodiment, a 16-bit check sum is provided to detect bit errors on the packet level. In one embodiment, a 16 bit CRC is employed in addition to or instead of the check sum. 
     Each pair of data words is interleaved, starting with the Barker code and the first data word. The transmitted bit order for two sequential words, A and B, is D 7 A, D 7 B, D 6 A, D 6 B, D 5 A, D 5 B, D 4 A, D 4 B, D 3 A, D 3 B, D 2 A, D 2 B, D 1 A, D 1 B, DOA, DOB, P 4 A, P 4 B, P 3 A, P 3 B, P 2 A, P 2 B, P 1 A, P 1 B, POA, POB. 
     D 7 A is the first transmitted bit. In the illustrated embodiment, DPSK is applied to the interleaved data. 
     Other communications protocols are of course possible for the forward link and return link. 
     Details of construction of the interrogator  47  will now be provided, reference being made to  FIG. 4 . The interrogator  47  includes enhanced parallel port (EPP) circuitry  70 , DPSK (differential phase shift keyed) circuitry  72 , and RF (radio frequency) circuitry  74 , as well as a power supply (not shown) and a housing or chassis (not shown). In the illustrated embodiment, the enhanced parallel port circuitry  70 , the DPSK circuitry  72 , and the RF circuitry  74  respectively define circuit card assemblies (CCAs). The interrogator  47  uses an IEEE-1284 compatible port in EPP mode to communicate with the controller  64 . The EPP circuitry  70  provides all the digital logic required to coordinate sending and receiving a message to and from a remote intelligent communications device  32  of a vehicle  12 . The EPP circuitry  70  buffers data to transmit from the controller  64 , converts the data to serial data, and encodes it. The EPP circuitry  70  then waits for data from the device  32 , converts it to parallel data, and transfers it to the controller  64 . In one embodiment, messages include a programmable number of bytes of data. 
     The EPP mode interface provides an asynchronous, interlocked, byte wide, bi-directional channel controlled by the controller  64 . The EPP mode allows the controller  64  to transfer, at high speed, a data byte to/from the interrogator within a single host computer CPU I/O cycle (typically 0.5 microseconds per byte). 
     The DPSK circuitry  72  (see  FIG. 5 ) receives signals I and Q from the RF circuitry  74  (described below), which signals contain the DPSK modulated sub-carrier. The DPSK circuitry  72  includes anti-aliasing filters  76  and  78  filtering the I and Q signals, respectively, and analog to digital (A/D) converters  80  and  82  respectively coupled to the filters  76  and  78  and respectively converting the filtered signals from analog to digital signals. The DPSK circuitry  72  further includes a combiner  84 , coupled to the A/D converters  80  and  82 , combining the digital signals. The DPSK circuitry  72  further includes a FIR matched filter  86 , coupled to the combiner  84 , which filters the combined signals. The DPSK circuitry  72  further includes delay circuitry  88  and multiplier circuitry  90  coupled to the FIR matched filter  86  for delaying the signal and multiplying the signal with the delayed signal to remove the sub-carrier. The DPSK circuitry  72  further includes low pass filter circuitry  92 , coupled to the multiplier  90 , filtering the output of the multiplier  90  to remove the X2 component. The DPSK circuitry  72  further includes a bit synchronizer  94  coupled to the filter  92  for regeneration of the data clock. The DPSK circuitry  72  further includes lock detect circuitry  96  coupled to the low pass filter  92  and generating a lock detect signal. The data, clock, and lock detect signal are sent to the EPP circuitry  70 . 
     The RF circuitry  74  (see  FIG. 6 ) interfaces with the transmit and receive antennas  62 . The RF circuitry modulates the data for transmission to a device  32  of a vehicle  12 , provides a continuous wave (CW) carrier for backscatter communications with a device  32  (if backscatter communications are employed), and receives and downconverts the signal received from the transponder unit (which is a backscatter signal in one embodiment). 
     The RF circuitry  74  also includes a power divider  98 , and a frequency synthesizer  100  coupled to the power divider  98 . The frequency synthesizer  100  tunes the RF continuous waver carrier for frequency hopping and band selection. The RF circuitry defines a transmitter, and receives data from the EPP circuitry  70 . The RF circuitry  74  includes an amplitude modulation (AM) switch  102  that receives the data from the EPP circuitry  70  and amplitude modulates the data onto a carrier. More particularly, the AM switch  102  turns the RF on and off (ON OFF KEY). The RF circuitry  74  further includes a power amplifier  104 , coupled to the AM switch  102 , to amplify the signal. The RF circuitry  74  further includes a switch  106 , coupled to the power amplifier  104 , for transmission of the amplified signal through a selected transmit antenna  62 . 
     During continuous wave (CW) transmission for the backscatter mode, the AM switch  102  is left in a closed position. When the interrogator  50  is transmitting in the CW mode, the device  32  backscatters the signal with a DPSK modulated sub carrier. This signal is received via one of the receive antennas  62 . More particularly, the RF circuitry  74  further includes a switch  108  coupled to the receive antennas. In another alternative embodiment, such as when backscatter communications are not employed, the RF circuitry uses common antennas for both transmission and reception. The RF circuitry  74  further includes a low noise amplifier (LNA)  110  coupled to the switch  108  and amplifying the received signal. The RF circuitry  74  further includes a quadrature downconverter  112 , coupled to the LNA  110 , coherently downconverting the received signal. The RF circuitry  74  further includes automatic gain controls (AGCs)  114  and  116  coupled to the quadrature down converter  112 . The amplitude of the signals are set using the automatic gain controls  114  and  116  to provide the signals I and Q. The I and Q signals, which contain the DPSK modulated sub-carrier, are passed on to the DPSK circuitry  72  ( FIG. 5 ) for demodulation. 
     Although one interrogator  47  has been described, it may be desirable to provide multiple interrogators along a route, or interrogators at each of various facilities. 
     In one embodiment, communications between the central station  46  and a device  32  may be via the paging system  50  and paging receiver  52  or via the cellular system when the vehicle  12  is not within communications range of an interrogator  47 . 
       FIGS. 7 and 8  together define a flowchart illustrating operation of the secure cargo transportation system. 
     In a step  120 , a determination is made (e.g., by the processor  33  of the remote intelligent communications device  32 ) as to whether a command has been received (e.g., from an interrogator  47  or paging receiver  52 ) to add desired geographical areas. If so, the processor proceeds to step  122 ; if not, the processor proceeds to step  128 . 
     In step  122 , a desired geographical area (e.g., a point and a radius, or three or more points) is received by the device  32 . After performing step  122 , the processor proceeds to step  124 . 
     In step  124 , the desired geographical areas are stored in memory  34 . After performing step  124 , the processor proceeds to step  126 . 
     In step  126 , a determination is made as to whether there are additional desired geographical areas to be stored in memory. If so, the processor proceeds to step  122 ; if not, the processor proceeds to step  128 . 
     In step  128 , a determination is made as to whether a command has been received to change geographical areas. If so, the processor proceeds to step  130 ; if not, the processor proceeds to step  136 . 
     In step  130 , the desired change is received. After performing step  130 , the processor proceeds to step  132 . 
     In step  132 , the processor accesses the memory location of the geographic area which is to be changed (or deleted). After performing step  132 , the processor proceeds to step  134 . 
     In step  134 , the processor changes (or deletes) data in the accessed memory location, as desired. After performing step  134 , the processor proceeds to step  136 . 
     In step  136 , a determination is made as to whether a command has been received to change a user&#39;s ability to access the container or vehicle  12 . If so, the processor proceeds to step  138 ; if not, the processor proceeds to step  140 . 
     In step  138 , the device  32  communicates with the lock controller to change a user&#39;s ability to access the container. After performing step  138 , the processor proceeds to step  140 . 
     In step  140 , the present location of the container is logged using the GPS receiver  36 . After performing step  140 , the processor proceeds to step  142 . 
     In step  142 , a determination is made as to whether the vehicle  12  or container is off course. If so, the processor proceeds to step  144 ; if not, the processor proceeds to step  146 . 
     In step  144 , an alarm signal is sent (e.g., an audible or visible alarm is sent to the driver and/or to the central station  46 ). After performing step  144 , the processor proceeds to step  146 . 
     In step  146 , a determination is made as to whether the vehicle or container is in a desired geographical area (e.g., the desired final destination area). If so, the processor proceeds to step  148 ; if not, the processor proceeds to step  150 . 
     In step  148 , a determination is made as to whether other requirements for access are met (e.g., the vehicle or container is in the desired geographic area at a specified time; the vehicle passed through a specified sequence of desired areas; the holder of the key  26  is a person authorized to open the lock in this area and at this time; any other conditions imposed by the central station  46 ). After performing step  148 , the processor proceeds to step  152 . 
     In step  150 , a determination is made as to whether an override authorization has been received from the central station  46  (e.g., the vehicle is not in the desired area, but there is an emergency situation). If so, the processor proceeds to step  152 ; if not, the processor proceeds to step  120  (possibly after a time delay). 
     In step  152 , the device  32  sends a signal to the lock  22  enabling the lock to be opened (e.g., effecting unlocking, or permitting unlocking using the key  26 ). 
     Thus, a method of controlling access to a movable container is provided. As a mobile asset, such as a container, truck or some other thing travels, its movement is recorded into the memory of the device, with the location and movement being determined by GPS. 
     The location of the vehicle will be utilized to determine authorization keyed access to a truck. The keyed system, as tied into the GPS, would be such that opening would be authorized when the vehicle is within the confines of a specific location. Further, different parts of the vehicle or container may be subjected to different keyed openings, such that some enclosure of the vehicle can be opened at one location, but not others. 
     In one embodiment, the system is programmed in a “fail safe” manner, for example tying the ultimate access to some specific route over which the vehicle is expected to travel. Therefore if the truck is hijacked or the driver deviates from a prescribed course, no opening whatsoever of the vehicle would be allowed, absent obtaining some authorization or some other code. In other words, the proximity within a desired route and ending locations can be programmed into the device. 
     In one embodiment, when the container, truck, etc. moves in the proximity of some general RF station, the data from the memory is downloaded or transmitted via RF to the base unit, such that the information is obtained and recorded remotely of the AMBIT unit on the vehicle. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.