Abstract:
Dual-mode communication devices, methods, and systems are provided. Embodiments of the present invention include devices, method, and systems enabling communication in a spread-spectrum communication protocol, comprising: receiving a first portion of a communication frame at a first frequency channel, wherein the first portion of the communication frame comprises a data channel index that indicates a second frequency channel for receiving a second portion of the communication frame; switching to the second frequency channel; and receiving the second portion of the communication frame at the second frequency channel. Other aspects, embodiments, and features are claimed and disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS &amp; PRIORITY CLAIMS 
     This application is a continuation of U.S. patent application Ser. No. 10/792,464, filed 3 Mar. 2004, now U.S. Pat. No. 7,756,086, which is incorporated herein by reference as if fully set forth below in its entirety. 
    
    
     BACKGROUND 
     Prior art monitoring and controlling systems for various applications, such as automated meter reading, prognostics, vending machines, and fire alarm and sprinkler systems utilize various communication protocols. Generally, these protocols utilize wireless RF communications either between transceivers or between a plurality of transceivers and a remote interrogator. The remote interrogator may then be coupled to a wide area network (WAN) which enables access to the transceivers by backend servers, workstations, etc. 
     In some instances, the RF transceivers may utilize a single-channel, substantially low-power communications protocol and, thus, have a limited range. The low-power applications are advantageous in certain remote applications, where a constant power supply is not available. For example, a transceiver coupled to a water meter cannot tap into any local power at the water meter, because typically there is no power. In this case, a battery is typically used. In order to maximize the life span of the battery, low-power transmissions are used. Low-power transmissions may also be advantageous because at certain frequency bands, a license from the Federal Communication Commission (FCC) is not required. The FCC requires certain devices to be licensed and/or comply with certain provisions if the devices radiate enough power within a given frequency spectrum over a given period. 
     Unfortunately, there are drawbacks to a low-power, single-channel communication protocol. In particular, the range of communication is directly proportional to the level of radiated power. Therefore, low power implies shorter communication range. Shorter communication range generally requires more infrastructure in a wireless system. Furthermore, single-channel communications (e.g., communications within one frequency channel, or on one carrier frequency) can be a problem if there is other electromagnetic radiation in a given area. Interference from other devices may cause noise at or near the specific single channel in which the RF transceivers are attempting to communicate, thus making communication unreliable, if not unfeasible. 
     Considering these drawbacks, it would be desirable to have a communication protocol that overcomes the disadvantages illustrated above. Furthermore, it would be advantageous for a systems provider for the communication devices (i.e., the RF transceivers and gateways) to be compatible with both communications protocols so that a communication upgrade would not require existing devices to be replaced. Instead, the existing devices could be upgraded remotely through the system. 
     BRIEF SUMMARY OF EXEMPLARY EMBODIMENTS 
     Various embodiments of a dual-mode communication protocol, and corresponding systems, devices, methods, and computer programs, are provided. One embodiment is a method of communicating with a dual-mode communication protocol in a given frequency band composed of a plurality of channels. A first set of the plurality of channels is designated fixed-frequency channels and a second set of the plurality of channels is designated spread-spectrum channels. The spread-spectrum channels comprise a first subset of acquisition channels and a second subset of data channels. One such method comprises: enabling communication in a spread-spectrum communication mode; attempting to receive a communication packet by traversing through the subset of acquisition channels; upon receiving a communication packet, switching to a data channel designated by the communication packet; and receiving and verifying a data portion of the communication packet by communicating in the designated data channel. Upon not receiving a communication packet after traversing through the subset of acquisition channels, the method continues with: enabling communication in a fixed-frequency communication mode; attempting to receive a communication packet by traversing through the designated fixed-frequency channels; and, upon receiving a communication packet, receiving and verifying a data portion of the communication packet by maintaining communication in the current fixed-frequency channel. 
     Another embodiment is a method for communicating in a dual-mode communication protocol. The method comprises: enabling communication in a spread-spectrum communication protocol, comprising: receiving a first portion of a communication frame at a first frequency channel, the first portion of the communication frame comprising a data channel index that indicates a second frequency channel for receiving a second portion of the communication frame; switching to the second frequency channel; and receiving the second portion of the communication frame at the second frequency channel. 
     Yet another embodiment is a method for communicating data. The method comprises: enabling communication in a spread-spectrum communication protocol, the spread spectrum communication protocol, comprising: transmitting a first portion of a communication frame at a first frequency channel, the first portion of the communication frame comprising a data channel index that indicates a second frequency channel for communicating a second portion of the communication frame; switching to the second frequency channel; and transmitting the second portion of the communication frame at the second frequency channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a block diagram illustrating an embodiment of a dual-mode monitoring/control system. 
         FIG. 2  is a block diagram illustrating the functional components of an embodiment of a dual-mode transceiver of the system of  FIG. 1 . 
         FIG. 3  is an illustration of an exemplary frequency band implemented in the system of  FIG. 1 . 
         FIG. 4A  is a data structure illustrating an embodiment of a fixed-frequency communication packet for the system of  FIG. 1 . 
         FIG. 4B  is a data structure illustrating an embodiment of a spread-spectrum communication packet for the system of  FIG. 1 . 
         FIG. 5  is a flow chart illustrating an embodiment of a method for transmitting in a dual-mode communication protocol. 
         FIG. 6  is a flow chart illustrating an embodiment of a method for transmitting in a spread-spectrum communication protocol. 
         FIG. 7  is a flow chart illustrating an embodiment of a method for receiving in the dual-mode communication protocol. 
         FIG. 8  is a flow chart illustrating an embodiment of a method for receiving in the spread-spectrum communication protocol. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments illustrated in further detail below illustrate various systems, methods, devices, and programs for communicating in a dual-mode communication protocol. A first communication protocol may generally be considered a fixed-frequency communication protocol and a second communication protocol may generally be considered a spread-spectrum communication protocol. 
     An embodiment of a transceiver communicating in a fixed-frequency communication protocol is generally configured to communicate a communication packet at a single frequency channel, with a first modulation scheme, at a given radiating power level. 
     An embodiment of a transceiver communicating in a spread-spectrum communication protocol is generally configured to communicate a first portion of a communication packet at a first frequency channel, and then communicate a second portion of the communication packet at a second frequency channel. The spread-spectrum communication protocol may employ a second modulation scheme, at a given radiating power level. 
     An embodiment of a transceiver communicating in the dual-mode communication protocol can generally communicate in both communication protocols. By providing for both communication protocols, the disadvantages of utilizing one singular protocol may be avoided. The accompanied figures and description illustrate embodiments of the dual-mode communication protocol in further detail. 
     Turning now to  FIG. 1 , illustrated is a block diagram of an embodiment of a dual-mode monitoring/control system  1 . Dual-mode system  1  comprises one or more external devices to be monitored and/or controlled (e.g., sensor/actuators  10 ) as illustrated in  FIG. 1 . Each sensor/actuator may be integrated with a transceiver  30 ,  31 , or  32 . The transceivers  30 - 32  are preferably RF (radio frequency) transceivers that are relatively small in size. Depending on the communication mode utilized, the transceivers  30 - 32  transmit either a relatively low-power RF signal, or a higher-power RF signal. As a result, in some applications, the transmission range of a given transceiver may be relatively limited. Although the transceivers  30 - 32  are depicted without a user interface such as a keypad, in certain embodiments, the transceivers  30 - 32  may be configured with user selectable buttons or an alphanumeric keypad. The transceivers  30 - 32  may be electrically interfaced with the device to be monitored and/or controlled, such as a smoke detector, a thermostat, a security system, etc., where external buttons are not needed. 
     Dual-mode system  1  also includes a plurality of stand-alone transceivers  33 - 35 , which may be fixed or mobile. Each stand-alone transceiver  33 - 35  and each of the integrated transceivers  30 - 32  may be configured to receive an incoming RF transmission (transmitted by a remote transceiver) and to transmit an outgoing signal. The transceivers depicted in  FIG. 1  may include different functionality depending on whether the transceiver communicates in a fixed-frequency communication mode, a spread-spectrum communication mode, or both. These communication modes, or protocols, will be discussed in further detail in subsequent figures. All transceivers may include the hardware and/or software to communicate in either of the protocols, but may be programmed or configured to communicate in only one or the other, or both. 
     Fixed-frequency transceiver  30  is an integrated transceiver that is configured to communicate only with the fixed-frequency communication protocol. In general, the fixed-frequency communication protocol is any protocol in which a packet or frame of data is communicated within a single frequency channel. Transceiver  35  is the stand-alone counterpart to transceiver  30 . A fixed-frequency communication link is illustrated in  FIG. 1  with a thin communication bolt designated with numeral  40 . 
     Spread-spectrum transceiver  31  is an integrated transceiver that is configured to communicate only with the spread-spectrum communication protocol. The spread-spectrum communication protocol will be discussed in further detail, but in short, is a protocol that facilitates frequency-channel hopping within a given frequency band. Transceiver  34  is the stand-alone counterpart to transceiver  31 . A spread-spectrum communication link is denoted in  FIG. 1  with a wide communication bolt and given numeral  45 . 
     Dual-mode transceiver  32  is an integrated transceiver that is configured to communicate with either of the two aforementioned protocols. Transceiver  33  is the stand-alone counterpart to the dual-mode transceiver  32 . 
     Notably, each transceiver can communicate only with another transceiver configured for similar protocols. In other words, a fixed-frequency transceiver  30 ,  35  cannot communicate with a spread-spectrum transceiver  31 ,  34 . This, however, can be reasonably obviated by deploying dual-mode transceivers  32 ,  33  into the wireless infrastructure. 
     The specifics of a fixed-frequency communication  40  will be discussed in further detail in  FIG. 4A  and the specifics of a spread-spectrum communication  45  will be discussed in further detail in  FIG. 4B . Both communications, however, are preferably wireless, RF transmissions, and more preferably, in the 902-928 MHz frequency range. Although this is preferable, in other embodiments, alternative frequency ranges may be employed. Furthermore, each communication may be transmitted over a conductive wire, fiber optic cable, or other transmission media. 
     The internal architecture of a transceiver  30 - 32  integrated with a sensor/actuator  10  and a stand-alone transceiver  33 - 35  will be discussed in more detail in connection with  FIG. 2 . It will be appreciated by those skilled in the art that integrated transceivers  30 - 32  can be replaced by RF transmitters (not shown) for client specific applications that only require data collection only. 
     Local gateways  15  are configured and disposed to receive remote data transmissions from the various stand-alone transceivers  33 - 35  or integrated transceivers  30 - 32  having an RF signal output level sufficient to adequately transmit a formatted data signal to the gateways. Local gateways  15  can communicate in either of the two aforementioned communication protocols. Thus, for the purpose of this document, they will be considered dual-mode gateways  15 . In other embodiments, local gateways  15  may be capable of communicating in only one of the aforementioned protocols. 
     Local gateways  15  analyze the transmissions received, convert the transmissions into TCP/IP format (or other protocol), and further communicate the remote data signal transmissions to back-end system  21  via WAN  20 . In this regard, and as will be further described below, local gateways  15  may communicate information, service requests, control signals, etc., to integrated transceivers  30 - 32  from server  25 , laptop computer  28 , and workstation  27  across WAN  20 . Server  25  can be further networked with database server  26  to record client specific data. Server  25 , laptop computer  28 , and workstation  27  are capable of remotely controlling and/or configuring various functions of the transceivers. For instance, server  26  is capable of remotely controlling the communication protocol in which each transceiver can communicate. This can be accomplished by sending a downstream control signal and/or by sending a software/firmware upgrade downstream. 
     It will be appreciated by those skilled in the art that if an integrated transceiver (either of  30 - 32 ) is located sufficiently close to dual-mode local gateways  15  to receive RF data signals, the RF data signal need not be processed and repeated through stand-alone transceivers  33 - 35 . It will be further appreciated that the system  1  may be used in a variety of environments. In one embodiment, system  1  may be employed to monitor and record utility usage of residential and industrial customers. In another embodiment, system  1  may be configured for the transfer of vehicle diagnostics from an automobile via an RF transceiver integrated with the vehicle diagnostics bus to a local transceiver that further transmits the vehicle information through a local gateway onto a WAN. 
     Generally, transceivers  30 - 32  may have similar construction (particularly with regard to their internal electronics) where appropriate, which provides a cost-effective implementation at the system level. Alternatively, fixed-frequency transceiver  30  may include some different internal electronics then spread-spectrum transceiver  31 . Furthermore, dual-mode transceiver  32  may include different internal electronics as transceivers  30  and  31 . Stand-alone transceivers  33 - 35  may include similar communication components as their integrated counterparts. The necessary hardware and software to integrate with a sensor/actuator  10  may, however, be excluded. 
     As illustrated in  FIG. 1 , stand-alone transceivers  33 - 35  are disposed to provide adequate coverage in a desired geographic area (e.g., an industrial plant or community), which is based on the particular system application. Preferably, stand-alone transceivers  33 - 35  may be dispersed so that at least one stand-alone transceiver will pick up a transmission from a given integrated transceiver  30 - 32 . However, in certain instances, two or more stand-alone transceivers may pick up a single transmission. Thus, local gateways  15  may receive multiple versions of the same data transmission signal from an integrated transceiver, but from different stand-alone transceivers. Local gateways  15  may utilize this information to triangulate, or otherwise more particularly assess the location from which the transmission is originating. Due to the transmitting device identification that is incorporated into the transmitted signal, duplicative transmissions (e.g., transmissions duplicated to more than one gateway, or to the same gateway, more than once) may be ignored or otherwise appropriately handled. 
     Integrated transceivers  30 - 32  may be implemented in a variety of devices. For example, integrated transceivers  30 - 32  may be disposed within automobiles, a rainfall gauge, a parking lot access gate, and utility meters to monitor vehicle diagnostics, total rainfall and sprinkler supplied water, access gate position, and utility consumption, to name a few. The advantage of integrating a transceiver, as opposed to a one-way transmitter, into a monitoring device relates to the ability of the transceiver to receive incoming control signals, as opposed to merely transmitting data signals. Significantly, local gateways  15  may communicate with all system transceivers. Since local gateways  15  are integrated with WAN  20 , server  25  can host application specific software that is typically hosted in an application specific local controller. Of further significance, the data monitoring and control devices need not be disposed in a permanent location. Provided the monitoring and control devices remain within signal range of a system compatible transceiver, which is within signal range of local gateway  15  interconnected through one or more transceiver networks to server  25 . In this regard, small application specific transmitters compatible with system  1  can be worn or carried about one&#39;s person or coupled to an asset to be tracked and monitored. 
     In one embodiment, server  25  collects, formats, and stores client specific data from each of the integrated transceivers  30 - 32  for later retrieval or access from workstation  27  or laptop  28 . In this regard, workstation  27  or laptop  28  can be used to access the stored information through a Web browser in a manner that is well known in the art. In another embodiment, server  25  may perform the additional functions of hosting application specific control system functions and replacing the local controller by generating required control signals for appropriate distribution via WAN  20  and local gateways  15  to the system sensors/actuators. In a third embodiment, clients may elect for proprietary reasons to host control applications on their own WAN connected workstation. In this regard, database  26  and server  25  may act solely as a data collection and reporting device with client workstation  27  generating control signals for the system  1 . 
     It will be appreciated by those skilled in the art that the information communicated by the transceivers  30 - 35  may be further integrated with other data transmission protocols for transmission across telecommunications and computer networks other than the Internet. In addition, it should be further appreciated that telecommunications and computer networks other than the Internet can function as a transmission path between the transceivers, the local gateways, and the central server. For example, an integrated transceiver may communicate with a stand-alone transceiver in a RF communication scheme. The stand-alone transceiver may communicate with the gateway  15  in a cellular communication scheme, such as GSM or PCS. The gateway  15  may communicate with the back-end system  21  via satellite, POTS, or the Internet. 
     Reference is now made to  FIG. 2 , which is a block diagram that illustrates functional components of an embodiment of a dual-mode transceiver  32 ,  33 . Dual-mode transceiver  32 ,  33  may communicate with another transceiver  30 ,  32 ,  33 , and  35  or gateway  15  with the fixed-frequency communication protocol, or may communicate with another transceiver  31 - 34  or gateway  15  with the spread-spectrum communication protocol. 
     The integrated dual-mode transceiver  32  is coupled to external devices  10 , for example, sensor  11  and actuator  12 , by way of data interface  70 . Data interface  70  is configured to receive electrical signals from sensor  11  and provide electrical signals to actuator  12 , and ultimately convey such information to and from a data controller  50 . In one embodiment, data interface  70  may simply comprise an addressable port that may be read by the data controller  50 . Dual-mode transceiver  33  is a stand-alone transceiver, thus may not include the data interface  70  for coupling to external components  10 , such as sensor  11  and actuator  12 . 
     Data controller  50  is coupled to memory  100  which stores various software, firmware, and other logic. Further coupled with data controller  50  is an RF transceiver  80  which is used to convert information received from data controller  50  in digital electronic form into a format, frequency, and voltage level suitable for transmission from antenna  60  via an RF transmission medium. RF transceiver  80  also converts a received electromagnetic signal from antenna  60  into digital electronic form for data controller  50  to process. 
     Data controller  50  may be considered a micro-controller or micro-processor and, as such, is configured for performing the data processing for the transceiver  32 ,  33 . Data controller  50  is configured to perform operations as directed by firmware  102  stored in memory  100 . These operations include data formatting for communication in both modes of communication, as well as data formatting for communication with sensor  11  and actuator  12  (if so equipped). 
     RF transceiver  80  of dual-mode transceiver  32 ,  33  may include distinct chipsets for each communication protocol: a fixed-frequency communication protocol chipset (FF chipset)  81  and a spread-spectrum communication protocol chipset (SS chipset  82 ). Chipsets  81  and  82  include the necessary components for transmitting and receiving in the particular communication protocols. For example, FF chipset  81  includes the components for communicating in a first modulation scheme, at a given power level, and in a particular frequency band in accordance with the fixed-frequency communication protocol. SS chipset  82  includes the components for communicating in a second modulation scheme, at a given power level, and in another particular frequency band in accordance with the spread-spectrum communication protocol. In other embodiments, the chipsets may be fully integrated. 
     Fixed-frequency transceivers  30  and  35  may differ from dual-mode transceivers  32  and  33  because they may not include SS chipset  82 . Alternatively, data controller  50  for fixed-frequency transceivers  30  and  35  may not be programmed, by firmware  102 , for communicating in the spread-spectrum communication protocol. As will be discussed shortly, certain modules of memory  100  which are included in dual-mode transceivers  32  and  35  may not be included in fixed-frequency transceivers  30  and  35 . 
     Likewise, spread-spectrum transceivers  31  and  34  may differ from dual-mode transceivers  32  and  33  because they may not include FF chipset  81 . Alternatively, data controller  50  for the spread-spectrum transceivers  31  and  34  may not be programmed, by firmware  102 , to communicate in the fixed-frequency communication protocol. 
     Memory  100  can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, etc.)) and nonvolatile memory elements (e.g., ROM, hard drive, tape, CDROM, etc.). Moreover, the memory  100  may incorporate electronic, magnetic, optical, and/or other types of storage media. Memory  100  can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the data controller  50 . Modules included in the memory  100  of a dual-mode transceiver  32  and  33  are a data channel index table  103 , an acquisition channels table  105 , a fixed-frequency channels table  106 , a receiver (Rx) address table  104 , firmware  102 , RAM  101 , and a transceiver identification (Tx ID)  107 . 
     The data channel index table  103  is utilized for communication in the spread-spectrum communication protocol. The contents of the data channel index table  103  will become clearer as the spread-spectrum communication protocol is laid out in subsequent figures. In short, the data channel index table  103  includes a list of data channel frequencies in which a data portion of a communication packet may be communicated. Each data channel is given an index that RF transceiver  80  will recognize, and furthermore can be communicated in a preamble of a communication packet. A receiving transceiver  31 - 34  or gateway  15  will need to recover the data channel index from the preamble to properly receive the remainder of a communication packet. In the preferred embodiment, there are 40 frequency channels dedicated for data communication each channel designated by a unique data channel index. One will appreciate that the number of channels is not relevant. Accordingly, in other embodiments, the number of channels may vary. 
     The acquisition channels table  105  is utilized for communication in the spread-spectrum communication protocol. The acquisition channels table  105  includes a list of frequency channels designated for synchronizing communication with another transceiver and for communicating a preamble of a communication packet. In the preferred embodiment there are ten designated acquisition channels, although this number can vary. An understanding of the acquisition channels table  105  will become clearer upon further explanation of the spread-spectrum communication protocol. 
     The fixed-frequency channels table  106  is utilized for communication in the fixed-frequency communication protocol. The fixed-frequency channels table  106  includes a list of frequency channels designated for synchronizing communication and subsequently communicating the data portion of a communication packet. In the preferred embodiment, there are eight fixed-frequency channels. An understanding of the fixed-frequency channels table  106  and its associated fixed-frequency channels will become clearer upon further explanation of the dual-mode communication protocol. 
     Each transceiver is configured to have a unique identification code  107  (e.g., transceiver identification number—Tx ID), that uniquely identifies the transceiver to the functional blocks of control system  1  (see  FIG. 1 ). This transceiver identification number  107  may be electrically programmable, and implemented in the form of, for example, an EPROM. Alternatively, the transceiver identification number  107  may be set/configured through a series of DIP switches, or stored in RAM. Alternative methods of setting and configuring the transceiver identification number  107  may be implemented. 
     Rx address table  104  is generally a look-up table of transceiver identification numbers (Tx IDs), or addresses, of other transceivers in a given network in the system  1  and is called upon when preparing a communication packet to be transmitted. Each communication packet transmitted by any transceiver  30 - 35 , or gateway  15 , is destined for a particular transceiver as designated by the transceiver identification number  107  embedded within the communication packet for either communication protocol (to be illustrated in  FIG. 4 ). As a transceiver receives various packets, it can distinguish, by the transceiver identification number embedded in the communication packet, whether that packet is destined for that transceiver. Otherwise, the transceiver may disregard the packet and/or relay the packet along to another transceiver. The specifics of how a communication packet is processed upon reception, including relaying the packet, is generally beyond the scope of the present invention. 
     The Rx address table  104  may also include more information about other transceivers, such as the communication protocol with which the other transceivers communicate. Furthermore, the desired modulation scheme(s) with which the other transceivers communicate as well as a necessary radiating-power level. Importantly some or all of the contents of the Rx address table  104  can be updated remotely, for instance, by server  26 . 
     Firmware  102  includes the logic for operating data controller  50  in accordance with embodiments of the present invention. Logic configured to perform operations as laid out in flow charts illustrated in subsequent figures is found in firmware  102 , along with programming logic for communicating with data interface  70  and its coupled components  10 . Other programming logic may be incorporated in the firmware  102  as known by those of ordinary skill in the art, such as power conservation sequences, power-up and power-down sequences, and operating system upgrade sequences. 
     Sensor  11 , in its simplest form, could be a two-state device such as a smoke alarm. Alternatively, the sensor  11  may output a continuous range of values to the data interface  70 . If the signal output from the sensor  11  is an analog signal, the data interface  70  may include an analog-to-digital converter (not shown) to convert signals output to the actuator  12 . Alternatively, a digital interface (communicating digital signals) may exist between the data interface  70  and each sensor  11 . In  FIG. 2 , data interface  70  is shown with a single input from sensor  11 . It is easy to envision a system that may include multiple sensor inputs. By way of example, a common home heating and cooling system might be integrated with the present invention. The home heating system may include multiple data interface inputs from multiple sensors. A home thermostat control connected with the home heating system could be integrated with a sensor that reports the position of a manually adjusted temperature control (i.e., temperature set value), as well as, a sensor integrated with a thermostat to report an ambient temperature. The condition of related parameters can be input to data interface  70  as well, including the condition of the system on/off switch, and the climate control mode selected (i.e., heat, fan, or AC). In addition, depending upon the specific implementation, other system parameters may be provided to data interface  70  as well. 
     The integration with an actuator  12  permits data interface  70  to apply control signals to a manual temperature control for the temperature set point, a climate control mode switch, and a system on/off switch. In this way, a remote workstation  27  or laptop  28  with WAN access (see  FIG. 1 ) could control a home heating system from a remote location. 
     The operation of an embodiment of transceiver  32 ,  33  is best illustrated in the flow charts of  FIGS. 5-8 . However, a brief explanation of the operation should be made with reference to the particular components illustrated in the block diagram of  FIG. 2 . The dual-mode transceiver  32 ,  33 , as its name implies, can communicate in any one of two modes or protocols: the fixed-frequency communication protocol and the spread-spectrum communication protocol. 
     When transmitting in the fixed-frequency communication protocol, data controller  50  will build a fixed-frequency communication packet (described in  FIG. 4A ) and pass that along to the RF transceiver  80  for communication. A communication packet is transmitted in the fixed-frequency communication protocol by transmitting at a dedicated channel, where the dedicated channel is one of the fixed-frequency channels (as illustrated in  FIG. 3 ). Preferably, the dedicated channel for transmission is the center channel of the fixed-frequency band, which, in the case of  FIG. 3 , is the 916.5 MHz channel. Alternatively, building the fixed-frequency communication packet may involve querying the fixed-frequency channels table  106  to find the next fixed-frequency channel in which to communicate. The selected frequency channel is communicated to the FF chipset  81  along with the communication packet. In another alternative, the FF chipset  81  may be configured to cycle through the designated fixed-frequency channels without having to receive an index or pointer to a channel from the memory  100 . In this alternative embodiment, the fixed-frequency channel table  106  may be excluded from the memory  100  and stored in memory integrated in with the FF chipset  81 . The payload portion of the communication packet is populated with the relevant information to be communicated, which may include information received from the data interface  70 . The data controller  50  may query the Rx address table  104  to make sure the destined transceiver can communicate in the fixed-frequency communication mode. After the packet is assembled it is passed along to the transceiver  80  for transmission. 
     FF chipset may receive in the fixed-frequency communication mode by cycling through the fixed-frequency channels to look for a carrier signal. Once found and synchronized, the packet communicated at that carrier channel is received and passed along to the data controller  50  for processing. Processing of the data may include preparing a reply signal, updating information in memory  100 , and/or controlling actuator  12  or other external component  10 . 
     When transmitting in the spread-spectrum communication protocol, the data controller  50  will build a spread-spectrum communication packet (as illustrated in  FIG. 4B ). The spread-spectrum communication protocol is built by querying the acquisition channels table  105  to find the next acquisition channel in which to send a preamble of the communication packet. Alternatively, the SS chipset  82  may be configured to cycle through the designated acquisition channels without having to receive an index or pointer to a channel from the memory  100 . In this alternative embodiment, the acquisition channel table  105  may be excluded from the memory  100  and stored instead in memory integrated with the SS chipset  82 . The preamble of the communication packet may also be prepared by querying the data channel index table  103  to find which data channel to communicate the payload portion of the packet. The index to the designated data channel is populated within the preamble. The payload portion of the communication packet is populated and formatted in a similar manner as the fixed-frequency communication protocol calls for. The communication packet is then passed along to RF transceiver  80  for transmission. 
     SS chipset  82  prepares the preamble of the communication packet for transmission at the designated acquisition channel frequency. Upon completing transmission of the preamble, SS chipset  82  then transmits the remainder of the communication packet at the frequency designated by the data channel index. Typically, this requires SS chipset  82  to change frequency channels mid-communication packet. In some special cases, however, the designated data-channel may be the same as the acquisition channel, which is essentially equivalent to the fixed-frequency communication protocol. 
     Importantly, communicating with the two communication protocols also provides the opportunity to communicate in two different modulation schemes. This is beneficial because the drawbacks of each can be countered with the advantages of the other. In one embodiment, the fixed-frequency communication protocol uses an amplitude modulation scheme, such as on-off keying (OOK). The spread-spread communication protocol uses a frequency modulation scheme, such as frequency shift-keying (FSK). These are merely exemplary modulation schemes that can be utilized. Those of skill in the art will appreciate that various modulation schemes may be utilized. Furthermore, in some embodiments, the two communication protocols may utilize the same modulation scheme. The particular modulation scheme used for each communication protocol by each transceiver can be remotely controlled by devices in the back-end system  21 . Control commands can be received downstream to change the particular modulation scheme to be utilized. 
       FIG. 3  is an illustration of an embodiment of a preferred frequency band  200  at which the dual-mode transceivers communicate. The illustrated frequency band  200  is the 902-928 MHz band, which falls in the ultra high-frequency (UHF) radio band. Other frequency bands may be utilized. The 902-928 MHz band may be advantageous in certain situations because communication ion this band may not require licensing by the FCC, provided signal radiations remain below a given power threshold. 
     In the embodiment illustrated in  FIG. 3 , the 902-928 MHz frequency band is divided into a first set of channels designated as spread-spectrum communication channels and a second set of channels designated as fixed-frequency communication channels. The spread-spectrum communication channels are further divided into subsets of acquisition channels  220  and data channels  210 . In the embodiment illustrated in  FIG. 3 , there are fifty spread-spectrum communication channels, of which ten are designated as acquisition channels  220  and forty are designated as data channels  210 . Each channel comprises 500 kHz, with the carrier frequency being centered within the 500 kHz. 
     In other embodiments, the number of spread-spectrum communication channels, as well as the number of acquisition channels  220  and data channels  210  may be different. Furthermore, in some embodiments, the acquisition channels  220  and data channels  210  may overlap. In order to comply with certain provisions of Part  15  of the FCC&#39;s Guidelines for Operation (which is hereby incorporated by reference in its entirety), fifty channels are necessary for spread-spectrum communication. Embodiments of the present invention comply with the FCC&#39;s guidelines for communicating at a higher power level. By communicating at a higher power level, longer range communications and/or greater signal penetrations are possible, which is very advantageous for many applications in which system  1  may be utilized. 
     In one embodiment, the acquisition channels  220  are separated from each other by four data channels  210 , thus providing 2 MHz of bandwidth between acquisition channels  220 . The acquisition channels  220  are spread evenly across the entire frequency band  200  to spread the power spectral density across the entire frequency band. Again, this pattern can vary greatly, and should not be limited the embodiments illustrated in  FIG. 3 . For example, the acquisition channels  220  can be grouped together at various sections of the frequency band  200 . One must consider, however, complying with the FCC&#39;s guidelines when designating the acquisition channels. The acquisition channels  220  may be evenly utilized because each transceiver is configured to cycle through the acquisition channels  220 , upon transmission, in either a predetermined and/or pseudorandom pattern. The data channels  210  may also be evenly utilized because each transceiver is configured to cycle through the data channels  210  upon transmission in either a predetermined and/or pseudorandom pattern. 
     The current FCC guidelines require even usage of channels across an entire bandwidth. In one embodiment, it would appear that the acquisition channels  220  would get 4.times. more usage then the data channels  210 . This may be accounted for, however, by limiting the data throughput at each acquisition channel  220 . The total number of data bits communicated in the acquisition channels  220  is about equal to or less than the total number of data bits communicated across the many data channels  210 . 
     Spread-spectrum communication may also be advantageous because it provides for communication from more devices using a given frequency band and greatly reduces the effects of interference. If one channel is currently in use or has some external interference, the transceivers can simply switch to another frequency channel. In one embodiment, the transmitter dictates what the next frequency channel will be by communicating the data channel index in the preamble of a communication packet. Frequency hopping is often used in spread-spectrum communication, which, as its name implies, is generally the process of changing frequency channels in which a transceiver communicates during operation. 
     As briefly discussed above with respect to  FIG. 2 , several embodiments of the spread-spectrum communication protocol work by communicating a preamble portion of a communication packet in one of the designated acquisition channels  220 . A receiver can cycle through the designated acquisition channels  220  and lock onto a carrier signal at the acquisition channel  220  in which a transmitter is communicating. The receiver then receives the remainder of the preamble, which includes a data channel index field. The receiver then switches to the data channel  210  as designated by the data channel index and prepares to receive the remainder (the data portion) of the communication packet. This will be discussed in further detail in subsequent figures. 
     The fixed-frequency communication protocol is designated to communicate within another frequency band. In the embodiment illustrated in  FIG. 3 , the fixed-frequency channel band  230  is confined within one of the channels designated for the spread-spectrum communication protocol. For example, as  FIG. 3  illustrates, the fixed-frequency channel band  230  is allotted the 916.3-916.7 MHz frequency band which is slightly smaller then one of the spread-spectrum communication channels of 500 kHz. It should be noted that the frequency band selected for the fixed-frequency communication protocol is merely a preferred frequency band and other frequency bands, including those outside the band dedicated for spread-spectrum communication, could be utilized. Importantly, other components of the dual-mode transceivers are a function of the selected frequency band. For example, antenna  60  may be a dual-frequency antenna for operating in two different frequency bands. 
     In one embodiment, eight channels  235  (each 50 kHz) are dedicated for fixed-frequency communication with the carrier frequency being centered in each channel  235 . Of course, the number of fixed-frequency channels  235  and the allotted bandwidth for each channel  235  can vary. 
     Important to note is the relatively narrow bandwidth provided for the fixed-frequency channels  235 . This is because the illustrated embodiment of the fixed-frequency communication protocol calls for lower power communication and also amplitude modulation. First, with lower power communications, the power spectral density at each carrier frequency is much more focussed at the carrier frequency than higher power communications. Thus, with higher-power communications, more bandwidth is required to allow sufficient separation between the also-wider frequency responses. Second, amplitude modulation, such as OOK, does not require deviation from the carrier frequency, as only the amplitude of the carrier frequency (or a nearby secondary frequency) is being modulated. 
     A receiving device operating within the fixed-frequency communication protocol, will search for a carrier frequency by cycling through the fixed-frequency channels  235  searching for a carrier frequency. Once locked on to a carrier frequency, the receiver will begin receiving the preamble and also the data portion of a communication packet. Unlike in the spread-spectrum communication protocol, the receiver will not be required to switch to another channel to receive the data portion of the communication packet. 
       FIG. 4A  illustrates an embodiment of a fixed-frequency communication packet, or frame,  300  and  FIG. 4B  illustrates an embodiment of a spread-spectrum communication packet  400 . Both embodiments preferably implement the Manchester encoding scheme. Nonetheless, one of ordinary skill in the art will appreciate that other embodiments may employ other encoding schemes. The Manchester encoding scheme is a bit-level encoding scheme well known in the art for its reliability and ease of timing synchronization. The Manchester encoding scheme translates a binary 1 data bit into a low-to-high transition, at the physical layer level. A binary 0 data bit is thus a high-to-low transition, at the physical layer level. Thus, for each data bit to be transmitted, a full data cycle is required with a 50% duty cycle. Although this cuts the data throughput in half, timing and synchronization is easily accomplished because synchronization can be done at each clock cycle. 
     Referring to  FIG. 4A , the fixed-frequency communication packet  300  includes a preamble portion  301  and a data portion  302 , both of which are communicated while at the same frequency channel. The preamble portion  301  includes a training sequence  310 , which is composed of a predefined sequence of bits. In one embodiment, the sequence  310  is a series of binary 1s. The length of sequence  310  should be suitable for a receiver to cycle through the designated fixed-frequency channels  235  and look for the sequence. The receiver is configured to look for a subset, such as six or eight consecutive binary 1s. If the receiver receives this subset, the receiver remains at the current fixed-frequency channel  235 . Otherwise, the receiver will move on to the next channel. In one embodiment, the training sequence  310  is 24 bits in length. Furthermore, the training sequence  310  could be another sequence besides consecutive binary 1s. Consecutive binary 0s or alternating binary is or 0s could be utilized. 
     As discussed earlier, the Manchester encoding scheme makes timing and synchronization relatively easy. A string of consecutive binary is appears to a receiver to be a square wave with a 50% duty cycle (as would a string of consecutive 0s, 180 degrees out of phase). If a receiver receives this square wave for a predefined period (equivalent to the prescribed period of time for the synchronization subset), the receiver will recognize that this data is the start of a communication packet, and timing and synchronization can then be performed with a standard phase lock loop. 
     As illustrated in  FIG. 4A , a start marker  320  is composed of two bits and used to signify the end of the training sequence  310  and the start of the data portion  302  of the communication packet  300 . The start marker  320  breaks away from the standard Manchester encoding scheme and is made up of two full clock cycles (thus two bits) of an all high (or on, for OOK) signal. Certainly, other configurations could be utilized. 
     The data portion  302  of the fixed-frequency communication packet  300  is composed of a variable length payload  330 . In one embodiment, the variable length payload  330  is similar to the variable length payload  430  of the spread-spectrum communication packet  400  of  FIG. 4B  and will be discussed in further detail below. 
     Turning now to  FIG. 4B , the spread-spectrum communication packet  400  is made up of a preamble portion  401  and a data portion  402 . In one embodiment, the preamble portion  401  of the spread-spectrum communication packet  400  is communicated at one of the acquisition channels  220  (See  FIG. 3 ). The preamble portion  401  includes a training sequence  410  similar to training sequence  310  and also a data channel index field  415 . In the one embodiment, the training sequence  410  is composed of 48 bits, but this may greatly vary in other embodiments. The length of the training sequence  410  should be suitable for a receiver to cycle through all of the acquisition channels  220 . 
     The preamble  401  also includes a data channel index field  415 , which communicates to a receiver the data channel at which the data portion  402  of the communication packet  400  will be communicated. In one embodiment, the data channel index field  415  is composed of eight bits. The two most significant bits  415  are binary 0s and the remaining six bits are used to communicate the data channel. The data channel index field  415  also serves to notify a receiver that the communication packet is a spread-spectrum communication packet and not a fixed-frequency communication packet. 
     A start marker  420  similar to start marker  320  is then included in the communication packet  400 . In the embodiment of  FIG. 4B , the start marker  420  is composed of four bits and used to signify the end of the preamble  401 . 
     The data portion  402  of the communication packet  400  is composed of a variable length payload  430 . Briefly, the variable length payload  430  may include fields, such as a start-of-packet, or header,  431 , receiver (Rx) address  432 , and transmitter (Tx) address  433 . A checksum, cyclic-redundancy check (CRC)  434  or other equivalent error detection scheme could be included in the variable length payload  430 . Next, the actual data is transmitted in a variable length payload  435  followed by a footer  436 . In one embodiment, the variable length payload  430  can vary from 112 to 1024 bits. The upper limit is defined by the data rate and a maximum dwell time at a particular channel. These parameters may be different in other embodiments, thus varying the length of the data portions of the communication packets. However, the length of the total communication packet should provide for continuous communication at a particular channel, at a given data rate, that is less then the maximum dwell time allotted by the FCC&#39;s guidelines. In one embodiment, 400 ms is the maximum dwell time allotted for communication on any frequency channel in the UHF band. The communication packet has a variable length (but not to exceed a given length) and the preferred data rate is 2400 bits per second (bps). This may vary in other embodiments. 
     The discussion that follows is directed toward the flow charts of  FIGS. 5-8 . The flow charts of  FIGS. 5-8  are intended to illustrate embodiments of methods for communicating in a dual-mode communication protocol. In general, the methods may be embodied in software, hardware, firmware, or any combination thereof, and may be executed by devices, such as those illustrated in the embodiments of  FIGS. 1-2 . 
       FIG. 5  is a flow chart illustrating an embodiment of a method  500  for transmitting in the dual-mode communication mode. Initially, the method  500  begins by receiving a command to transmit a particular communication packet. The communication packet may be generated by the device preparing to transmit, or it may be from another device having just sent the communication packet. In the latter case, the current device serves as a relay or repeater. 
     The method  500  proceeds by first searching for the communication mode of the intended receiver (step  510 ). This may be accomplished by examining the Rx address of the intended receiver, where information conveying the communication mode may be found. For example, the two MSBs of the Rx address may be reserved for conveying whether the receiver can communicate in the fixed-frequency communication protocol, the spread-spectrum communication protocol, or both. This may require querying the Rx address table  104  found in memory  100  of a transceiver (see  FIG. 2 ). Alternatively, this information may be found in another table, which is not fully integrated with the Rx address. 
     If it is determined that the receiver communicates in the fixed-frequency communication protocol (step  515 ), the transmitter then begins transmission of the communication packet in the fixed-frequency communication protocol (step  520 ). The fixed-frequency communication protocol operates by communicating the entire communication packet, including the preamble and data portion, while at one frequency channel. Furthermore, the fixed-frequency communication protocol may utilize a particular modulation scheme, such as a particular amplitude modulation scheme Likewise, the fixed-frequency communication protocol may transmit at a given power level. In the preferred embodiment, the fixed-frequency communication protocol operates at a substantially low-power radiation level. Other modulation schemes and/or power radiation levels could be utilized without departing from the scope of the present invention. 
     The transmitter may determine whether the transmission was a success (step  525 ) by receiving a response from the intended receiver. In certain instances, a response may not be required, thus the transmitter may not expect such a response. In these instances, success verification is not necessary and this step may be omitted. 
     Upon a success, or upon completing transmission of the communication packet if success verification is not necessary, the communication mode of the intended receiver may be updated (step  550 ), if necessary, and the response communication packet can be processed (step  560 ). Upon a failure, the method  500  proceeds by attempting to communicate in the spread-spectrum communication protocol (step  530 ). 
     Returning back to step  515 , if it is determined that the intended receiver does not communicate in the fixed-frequency communication protocol, the transmitter will then begin transmission in the spread-spectrum communication protocol (step  530 ). This step will be discussed in further detail with relation to  FIG. 6 . 
     Upon transmitting the communication packet in the spread-spectrum communication protocol, the transmitting device may then verify whether the transmission was successful by receiving a response from the intended receiver (step  540 ). If successful, the method  500  proceeds to step  550  where the communication mode of the intended receiver may be updated. The transmitter can then process the response, if necessary (step  560 ). If not successful, the method  500  proceeds by attempting to transmit the communication packet in the fixed-frequency communication protocol (step  520 ). 
     A simple counter can be applied to count the number of failures or attempts at communicating in the two protocols (step  570 ). After a prescribed number of failures, a failure mode may be initialized, which may include a recalibration feature. 
     In some situations, the transmitting device may not have knowledge of the communication mode in which the intended receiver operates. In this case, the default procedure is to first attempt communication in the spread-spectrum communication protocol (step  530 ). If this is successful, the communication mode related to the intended receiver may be updated. If not successful, transmission can be attempted in the fixed-frequency communication protocol. If successful, the communication mode related to the intended receiver can be updated accordingly. Alternatively, the default may be to attempt communication first in the fixed-frequency communication protocol, and then the spread-spectrum communication protocol. 
       FIG. 6  is a flow chart illustrating an embodiment of a method  530  for transmitting in the spread-spectrum communication protocol. The method  530  begins by placing the transmitting device in the spread-spectrum modulation mode (step  531 ). In one embodiment, the spread-spectrum modulation mode utilizes a frequency modulation scheme, such as frequency shift keying (FSK) modulation. In other embodiments, other modulation schemes could be utilized, including those other then frequency modulation schemes. Furthermore, the spread-spectrum communication protocol calls for transmitting at a relatively higher-power radiation power then the fixed-frequency communication protocol. In this manner, the spread-spectrum communication protocol facilitates greater range and signal penetration. 
     The method  530  proceeds by setting the transmitting channel to the desired acquisition channel (step  532 ). The desired acquisition channel may be chosen in a predetermined pattern, or randomly. 
     Once the transmitting channel is set, the preamble of the communication packet can be sent (step  533 ). This step includes sending the training sequence (step  534 ) and the data channel index (step  535 ). 
     Upon sending the preamble, the transmitting device then switches the transmitting channel to the data channel as designated by the data channel index (step  536 ). The designated data channel may be selected in a predetermined pattern, or randomly. Subsequently, the data portion of the communication packet (step  537 ) is sent. 
     Once the entire communication packet is sent, the transmitting device may then switch to receive mode and await a response acknowledging reception of the communication packet by the intended receiver (step  538 ). This step may be omitted if no response is necessary. Receive mode is described in further detail in subsequent figures. 
       FIG. 7  is a flow chart illustrating one embodiment of a method  600  for receiving in the dual-mode communication protocol. The method  600  begins by placing the receiving device in one of the communication modes, in this case the spread-spectrum communication mode, which includes setting the demodulation mode to the chosen spread-spectrum modulation/demodulation scheme, as discussed in  FIGS. 5 &amp; 6  (step  605 ). 
     Next, the receiving channel is set for the next acquisition channel in the sequence or series of acquisition channels (step  610 ). The sequence or series of acquisition channels may be predetermined and preprogrammed into the firmware of the receiving devices, or may be done in a random or pseudorandom fashion. If it is determined that all of the acquisition channels have been used without detecting a carrier signal (step  615 ) the method  600  then proceeds with switching to fixed-frequency communication mode, which will be discussed shortly. 
     At each acquisition channel, a carrier signal is checked for using standard carrier detection techniques as known in the art (step  620 ). If one is not found at the current acquisition channel, the method  600  returns to step  610 , where the receiving channel moves on to the next acquisition channel. 
     If a carrier signal is detected, the method  600  proceeds with receiving the communication packet in the spread-spectrum communication protocol (step  630 ), which is discussed in further detail in  FIG. 8 . 
     Next, the receiving device transmits a response back to the originating transmitter verifying a successful communication (step  640 ). Transmitting a successful response may require communicating by way of the methods illustrated in  FIGS. 5 &amp; 6 . Upon transmitting a response, the receiving device can then return back to the start of the method  600  and prepare for the next communication packet. 
     As mentioned above, if all of the acquisition channels are cycled through and a carrier signal is not detected (at step  615 ), the method  600  proceeds to the fixed-frequency communication mode. In this case, the receiving device switches (if necessary) to the fixed-frequency demodulation scheme (step  645 ). In one embodiment, the fixed-frequency modulation/demodulation scheme is different from the spread-spectrum modulation scheme, thus requiring a switch. Alternatively, however, the two modulation/demodulation schemes may be the same. 
     Next, the receiving channel is set to the next fixed-frequency channel (step  650 ). The next fixed-frequency channel may be selected among the designated fixed-frequency channels at random or in a predetermined manner. If it is determined that all of the fixed-frequency channels have been traversed without detecting a carrier signal (step  655 ), a recalibration procedure may be initiated (step  685 ). The recalibration procedure may not, however, be initiated until after a significant number of traversals of the acquisition channels and fixed-frequency channels without a carrier signal detection. 
     If a carrier signal is detected at step  660 , the receiving device locks on and synchronizes communication by receiving the training sequence in the preamble of the communication packet. The remainder of the communication packet, including the data portion is then received at the current receiving channel (step  670 ). 
     Included within the step of receiving the entire communication packet (step  670 ) are several points at which the integrity of the data is verified. First, the receiving device receives the preamble of the communication packet (step  671 ). Next, the preamble is verified to determine whether it is a valid preamble (step  672 ). If not, the method  600  may return to step  650  where a new fixed-frequency channel is selected. If a valid preamble is detected, the receiving device receives and verifies the remainder of the communication packet (step  673 ). If the communication packet is invalid, it may be ignored and the method resumes back to step  650 . If the communication packet is valid, the receiving device may then switch to transmission mode and transmit a response (step  680 ). 
     The recalibration procedure (step  685 ) may greatly vary with other embodiments. In one embodiment, particular environment conditions can be verified to determine whether drastic changes have occurred which could result in device malfunctions (step  686 ). For example, drastic operating temperature changes or ambient temperature changes could be verified to determine whether they are the cause of a possible device malfunction. In practice, environmental conditions such as these take time to change, thus the recalibration procedure may be performed at certain intervals of time, perhaps every 1000 fixed-frequency channel cycles, as an example. If recalibration is necessary (step  687 ), a recalibration protocol could be enabled (step  688 ). 
     The method  600  may return back to the spread-spectrum communication mode at step  605 . In other embodiments, it is entirely foreseeable that the fixed-frequency communication mode is the first mode chosen, as opposed to the spread-spectrum communication mode. In this case, a receiving device would first attempt to receive in the fixed-frequency communication mode and then switch to the spread-spectrum communication mode after cycling through all of the fixed-frequency channels. 
       FIG. 8  is a flow chart illustrating an embodiment of a method  630  for receiving in the spread-spectrum communication protocol. The method  630  begins once a carrier signal has been detected at a particular acquisition channel. A receiving device then receives a preamble portion of a communication packet, which includes a training sequence and data channel index (step  631 ). The training sequence, as discussed earlier, is used to synchronize the timing for the receiving device. 
     Once the preamble is received, the receiving device may verify whether the preamble is valid (step  632 ). If not, the receiving device may return back to step  610  and switch to the next acquisition channel. 
     If the preamble is valid, the method  630  proceeds with looking up the data channel corresponding to the received data channel index in the preamble (step  633 ). Once established, the receiving device switches to the designated data channel, if necessary (step  634 ). In certain instances, where the acquisition channels and data channels overlap, it may be possible for the data channel index to indicate to the receiving device to remain at the current channel for data reception. For example, the special case of six binary is may indicate to the receiving device to remain at the current acquisition channel for data reception. 
     The data portion of the communication packet is then received and verified for integrity (step  635 ). If the communication packet is found to be invalid, the receiving device may revert back to step  610  where the next acquisition channel is selected. If the communication packet is found to be valid, method  630  ends, and the receiving device prepares to transmit a response, if necessary. 
     The embodiment or embodiments discussed were chosen and described to illustrate the principles of the invention and its practical application to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.