Patent Publication Number: US-2007124306-A1

Title: Method and system for transmitting data to vehicles over limited data links

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method and system for transferring data over a limited data link between a transmitter and a receiver. More specifically, the present invention relates to a communication system for exchanging data between an onboard device and a remote center, wherein the onboard device and remote center each have copies of one or more dictionaries.  
      2. Description of Related Art  
      Limited-bandwidth and small-packet wireless data networks provide cost-effective, ubiquitous coverage and access to mobile applications, such as those present in vehicles. Such data networks, sometimes referred to as limited data links, make it possible to efficiently convey tens of bytes to a few hundred bytes of information, but put practical limits on the amount and richness of data that can be transferred and the applications that rely upon the data. Problems associated with limited data links include the fact that only a small number of bytes can be transmitted at a time, combined with the fact that the bit transfer rate can be slow. The high cost of data transfer puts practical limits on the volume of data that can be transmitted over the limited data links.  
      For example, if there is a 200 byte limit for user data (disregarding lower-level protocol information), 200 bytes is enough to transmit 228 English language clear-text characters, if those characters are encoded in 7-bit ASCII. This may be sufficient for a short text message consisting of a few sentences. Due to overhead, most protocols that carry text will use up a portion of the 200 bytes. Assuming (conservatively) there is 15% overhead, this leaves approximately 170 bytes of data that can be transferred. By using the available 170 bytes efficiently, it is possible to reduce both the load on transmission systems and networks and the costs of transmitting data. It is desirable to utilize the limited data links in a manner that increases the richness of communications by conveying more information in the same bandwidth, while reducing processing overhead. It is also desirable to reduce the frequency with which data messages are transmitted and to simplify system operation by reducing the need to segment and reassemble multiple messages.  
      Compression algorithms for reducing bandwidth consumption by data transmitted over limited data links are known in the art, but are limited in effectiveness. A typical compression ratio for text is typically only about 15%, which is hardly worth the embedded processing and memory costs. Algorithms that achieve higher than 15% compression ratio typically rely upon large internal or external dictionaries that replace words with shorter placeholders or symbols.  
      While compression algorithms can be effective on text or sources that are not dense with binary information, but are less effective for other applications. For example, if bitmapped information is transmitted over a link, and each bit conveys a meaning (e.g., a pixel in an image), compression techniques are limited in reducing bandwidth consumption. Referencing a large dictionary is a viable option if the computing platform has vast resources and fast network connectivity, such as with a desktop personal computer. However, referencing a large dictionary places high demands on the communication system&#39;s resources (e.g., memory) and can reduce overall performance in an embedded or mobile platform.  
      The Backus-Naur Form (“BNF”) technique, often referred to as a “metasyntax” or “metalanguage”, is well known in the fields of computer languages and programming, and is a form of notation and syntactical method that involves notating, assembling, and disassembling of languages. Extended BNF (“EBNF”) has emerged as an ISO standard. Similarly, Lempel-Ziv-Welch (“LZW”) is a data compression technique known in the art, frequently used for GIF graphics file formatting, one of the standard graphic formats used on the World Wide Web. However, such concepts deal inherently with compressing data at a source with decompression or storage done at the destination. Both endpoints must implement compression/decompression algorithms.  
      Certain advanced compression technologies focus on a particular language (e.g., English) and implement an internal dictionary or rely upon an external dictionary and perform word replacement. For example, the European Computer Manufacturers Association (ECMA) has published a standard of lossless data compression, known as Data Compression according to Lempel and Ziv (DCLZ). The ECMA protocol essentially builds a dictionary based upon the candidate target compression text by replacing redundant sequences with references placed into the dictionary. The ECMA protocol can be useful for compressing text; however, the concept of using string replacements is not effective where there is little repetition of byte sequences within a data stream.  
      There remains a need to efficiently and flexibly convey rich information over a limited data link, wherein the sender and/or receiver are restricted in terms of the memory and performance available for sending/receiving data over the limited data link. Pure compression systems are not up to the task. What is needed is an alternative method and system that facilitates communication of data over a limited data link between an in-vehicle user and a remote services resource (e.g., a response center).  
      The communication system for conveying data is preferably sufficiently flexible and adaptable to the language, symbolic, and cues utilized by a vehicle telematics system. For example, if the system does not have the desired symbol in its knowledge base, the system can be configured to be flexible enough to switch from the default method of transmitting information (e.g., predetermined identifiers, symbols or tokens in a dictionary) to a free-symbol mode. The system can be configured to be able to convey spoken and written information, as well as other symbolic representations (e.g., haptic cues). The system is preferably not hard-tied to any one language, but instead is able to toggle between language and symbolic sets. The system can employ a protocol that is flexible enough to mix and match token sizes. The system can allow for optimization of length of symbol identifiers rather than being restricted to fixed-length identifiers. Such a communication system can be used to supplement or enhance the performance of vehicle navigation systems, which allow users to determine a route from a start point to a destination point. Navigation systems having capabilities for determining the geographic position of a reference point are also well known in the art, such as Global Positioning Systems (GPS) or self-contained systems having distance and bearing sensors.  
      Accordingly, it would be very desirable to provide a system and method for communicating vehicle-relevant data over low bandwidth or limited data links that overcomes the above-described shortcomings of the prior art while retaining their advantages.  
     SUMMARY OF THE INVENTION  
      The present invention addresses the shortcomings of the prior art systems and methods. In particular, the present invention is directed to a method and system for communicating messages over narrow bandwidth data links by converting the messages into protocol streams that comprise message tokens.  
      In accordance with one aspect of the embodiments described herein, there is provided a method and system for communicating a message over a data link. The method generally involves receiving a message that comprises one or more message objects, and referencing at least one dictionary to identify those message objects for which translations to the at least one dictionary tokens are available. The method further comprises converting each identified message object into a message token, and associating each non-identified message object with a free symbol indicator to generate a free symbol segment. The message tokens and the free symbol segments are then concatenated to generate a protocol stream that is sent over the narrow bandwidth data link to a receiver unit or location.  
      In accordance with another aspect of the embodiments described herein, there is provided a method and system for recovering a message received over a data link. The method generally involves receiving a protocol stream that comprises a dictionary identifier, message tokens, and at least one free symbol. The method further comprises verifying that each dictionary identified by the dictionary identifier is accessible, and selecting each dictionary identified by the dictionary identifier. Each selected dictionary is referenced to translate the message tokens into message objects. The method also comprises reassembling the message from the message objects and the at least one free symbol.  
      A more complete understanding of the disclosed bandwidth conservation system and method will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1   a  is a schematic diagram of a first embodiment of a communication system pursuant to aspects of the invention;  
       FIG. 1   b  is a schematic diagram of a broadcast communication network;  
       FIG. 1   c  is a schematic diagram of a navigation device in communication with a mobile unit;  
       FIG. 2  is a schematic diagram of an alternate embodiment of a communication system;  
       FIG. 3  illustrates an embodiment of a token/symbolic dictionary and some of the types of data contained by the dictionary;  
       FIG. 4  is a schematic diagram of an embodiment of a data communication system wherein the sender and receiver each comprise the same token/symbolic dictionaries;  
       FIG. 5   a  is a schematic diagram of an embodiment of a protocol stream for both predetermined identifiers and free symbols; and  
       FIG. 5   b  illustrates an exemplary protocol stream that comprises free symbols.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The present invention is directed to a system and method for sending data over a low bandwidth data communications link. In particular, the present invention is directed to a system and method for utilizing token or symbolic dictionaries at the transmitting and receiving ends of the low bandwidth data link to facilitate the efficient transfer of data over the data link, sometimes referred to as a data pipe or channel. In the detailed description that follows, like element numerals are used to describe like elements illustrated in one or more of the figures.  
      With reference to  FIG. 1   a,  there is provided a first embodiment of a system for the exchange of information between a remote location  10  and a vehicle  12  pursuant to aspects of the invention. The vehicle  12  includes a navigation device  14 . Referring now also to  FIG. 1   c,  the navigation device  14  may include an output unit  21 , a receiver unit  22 , an input unit  23 , a position detection unit  24 , a navigation memory unit  30 , a navigation processor unit  26 , and an RF transceiver unit  52  that are all in electrical communication with one another. The navigation memory unit  30  includes at least a portion of a user profile and in some embodiments may include the entire user profile. In addition, the navigation memory unit  30  includes a road map database portion and, in some embodiments, includes a disk reading unit for reading road map information not built into the navigation device  14 . As is provided in greater detail below, the user profile and/or the road map database stored in the memory  30  may be updated in the vehicle by way of the input unit  23 , which can include at least one of a keyboard, a touch sensitive display, and a microphone. The user profile and/or the road map. database may also be updated by way of information received through the receiver unit  22  and/or the RF transceiver unit  52 .  
      The receiver unit  22  receives information from the remote location  10  and, in one embodiment, is in communication with the remote location by way of a one-to-many communication system. One-to-many communication systems include systems that can send information from one source to a plurality of receivers, such as a broadcast network  31 . Broadcast networks include television, radio, and satellite networks. Referring now to  FIG. 1   b,  in one embodiment, the broadcast network  31  is the XM Radio satellite network  40 , which comprises broadcast towers  42 , satellite servers (not shown), and satellites  43 . The broadcast towers  42  transmit information to the satellites  43 , which bounce the information back down to the receiver unit  22  of the navigation device  14 .  
      Referring now back to  FIG. 1   c,  the information received by the receiver  22  may be processed by the navigation processor unit  26 . The processed information may then be displayed by way of the output unit  21 , which includes at least one of a display and a speaker. In one embodiment, the receiver unit  22 , the navigation processor unit  26  and the output unit  21  are provided access to only subsets of the received broadcast information based on user preferences and/or traffic information demands. The user preferences, as well as user identity information and traffic-related information, can be part of the user profile.  
      The position detection unit  24  may include a GPS receiver that communicates with a plurality of GPS satellites (separate from the XM satellites) to determine the position of the vehicle  12 . For example, the GPS receiver searches for and collects GPS information (or signals) broadcast from four or more GPS satellites that are in view of the GPS receiver. Next, using the time interval between the broadcast time and reception time of each broadcast signal, the GPS receiver calculates the distance between the GPS receiver and each of the four or more GPS satellites. These distance measurements, along with the position and time information received in the broadcast signals, allow the GPS receiver to calculate the geographic position of the vehicle  12 .  
      In the embodiment shown in  FIG. 1   a,  the mobile unit  18  is used to receive and transmit information from and to the remote location  10 ; and, in an alternate embodiment shown in  FIG. 2 , an RF transceiver  152  is used to receive and transmit information from and to the remote location  110 . The mobile unit  18  may be a wireless phone or any other device that communicates with other devices by way of the wireless communication network  46 . As shown in  FIG. 1   c,  in one embodiment, the mobile unit  18  includes a wireless receiver  32 , a wireless transmitter  34 , a mobile unit processor  40 , and an RF transceiver unit  54  that are in communication with one another. The mobile unit  18  is in two-way communication with the remote location  10  by way of the receiver  32 , the transmitter  34 , and the wireless communication network  46 , which comprises numerous base stations. In one embodiment, information is transmitted from or to the vehicle or remote location over a high bandwidth packet data (e.g., GPRS, EDGE, 1xRTT, 1xEV, HSDPA, Flash-OFDM, etc.) channel of the wireless communication network  46 . If the high bandwidth channel is unavailable, a low bandwidth DTMF channel can be used. The receiver  32  receives information from the remote location  10 , and the transmitter  34  transmits information to the remote location  10 . In other embodiments, the transmitter  34  also transmits information to suppliers of traffic or other information  48 ,  50 .  
      In one embodiment, the information received from and transmitted to the remote location  10  by way of the mobile unit  18  is accessed by the user through the navigation device  14 , which is in communication with the mobile unit  18 . The mobile unit  18  may be embedded in the vehicle  12  and be in communication with the navigation device  14  by, for example, a cable (not shown).  
      In another embodiment, the navigation device  14  and mobile unit  18  are in communication with one another by way of RF transceiver units  54  and  52 . Both the navigation device  14  and the mobile unit  18  include RF transceiver units  52 ,  54 , which, in one embodiment, comply with the Bluetooth® wireless data communication format or the like. The RF transceiver units  52 ,  54  allow the navigation device  14  and the mobile unit  18  to communicate with one another. In other embodiments not shown, the receiver  32  and transmitter  14  of the mobile unit  18  and the receiver unit  20  of the navigation device  14  allow the navigation device  14  and mobile unit  18  to communicate with one another. In yet other embodiments, there may be an RF transceiver that is separate from the navigation device  14  and the mobile unit  18  and that allows the navigation device  14  and mobile unit  18  to communicate with one another.  
      In the alternate embodiment shown in  FIG. 2 , the navigation device  114  transmits and receives information to and from the remote location  110  by way of the RF transceiver  152 , access points.  170 ,  172 , and gateways  174 ,  176  that are in communication with the network  162 . In one embodiment, the RF transceiver  152  and the access points  170 ,  172  are compliant with the IEEE 802.11 specification, and such transceivers and access points include Wi-Fi®—certified equipment. The access points  170 ,  172  are typically in communication with the gateways  174 ,  176  by way of a cable, and the gateways are in communication with the remote location  110  by way of the network  162 . The access points  170 ,  172  are in communication with the RF transceiver  152  and have a limited range over which they can communicate with the RF transceiver  152 . Thus, it is preferable that there be numerous access points  170 ,  172  positioned so that the distance between the access points and the areas through which a vehicle  12  might pass is less than or equal to the limited range of the access points. When the access points  170 ,  172  are so positioned, the RF transceiver  152  effectively exchanges information with the access points  170 ,  172  and, thus, the remote location  110 .  
      Note that in the alternate embodiment of  FIG. 2 , the navigation device  114  also includes input and output units, a receiver unit, a memory unit, and a processor unit, none of which are shown. The components of the alternate navigation device embodiment  114  have the same functionality as do the corresponding components of the navigation device  14  of the first embodiment.  
      Referring now to  FIGS. 1   a  and  2 , the remote location  10 ,  110  includes a remote server  44 ,  144 , a remote transmitter  56 ,  156  and receiver  58 ,  158 , and a remote memory  60 ,  160  that are in communication with one another. As provided above, in the first embodiment, the remote transmitter and receiver  56 ,  58  communicate with the navigation device  14  and mobile unit  100  by way of the broadcast  31  and wireless  46  communication networks, respectively. In the alternate embodiment, the remote transmitter and receiver  156 ,  158  communicate with the navigation device  114 , including the RF transceiver  152 , by way of the broadcast communication network  131  and a network  162 . The remote location  10 ,  110  is also in communication with suppliers of traffic and/or other information  48 ,  50 ,  148 ,  150  such as government traffic information suppliers, private traffic information suppliers, and users of other vehicles, by way of the network  62 , 162 .  
      In both the first and alternate embodiments shown in  FIGS. 1   a - 1   c  and  2 , the network  62 ,  162  is typically a wide area network (WAN) such as the Internet. In other embodiments, some of the information suppliers  48 ,  50 ,  148 ,  150 , such as the government and private traffic information suppliers, may be in communication with the remote location  10 ,  110  by way of a local area network (LAN), while other information providers  48 ,  50 ,  148 ,  150  such as the vehicle users, are in communication with the remote location by way of the Internet. In yet other embodiments, the RF transceiver  152  is in communication with the remote location  110  and/or the information providers  148 ,  150  by way of a network  162  that is a LAN. In these other embodiments, the LAN  162  is compliant with the IEEE 802.3 specification or is an Ethernet network.  
      As provided in greater detail below, the information suppliers  48 ,  50 ,  148 ,  150  may transmit updated user profiles and traffic-related information to the remote location  10 ,  110 . A plurality of user profiles are in a user profile database, which, along with traffic-related information, is stored in the remote memory  60 ,  160 . The updated user profiles and new traffic-related information are transmitted from the remote location  10 ,  110  to the navigation device  14 ,  114  by way of the broadcast network  31 ,  131 . In other embodiments, the new traffic-related information and updated user profiles may be transmitted to the vehicles  12 ,  112  by way of the wireless network  46  or the network  162 . At the vehicle:, the user profile stored in the memory  30  of the navigation device  14  is updated, and the vehicle-related information is made accessible to the user by way of the output unit  26  of the navigation device  14 . In other embodiments, the information providers may communicate directly with the mobile unit  18  or RF transceiver  152  by way of the wireless communication network  46  or the network  162 .  
      As explained above, in accordance with one aspect of the embodiments described herein, there is provided a system and method for transmitting data over a limited data link between a sender/transmitter and a receiver, wherein the transmitter and receiver each have identical copies of one or more token/symbol dictionaries. The transmitter and receiver typically each hold at least one copy of identical fixed-length dictionaries. For example, in one embodiment, the fixed-length dictionaries each comprise about  300  words or tokens. In order for the transmitter and receiver to communicate and understand one another, the transmitter and receiver must hold the same dictionary. If the receiver and sender want to communicate emergency information, they will each refer to their “emergency” dictionary. Alternatively, under an extension of the protocol, the sender can download one or more new dictionaries to the receiver.  
      In one embodiment, the transmitter/sender is a provider of remote services while the receiver is an in-vehicle client device, such as a telematics device. In another embodiment, the vehicle comprises the transmitter while the remote location comprises the receiver. In yet another embodiment, the vehicle comprises a first transmitter and a first receiver, while the remote location comprises a second transmitter and a second receiver.  
      As explained above, each dictionary will contain tokens or symbols for efficient, low-bandwidth communication between a sender and a receiver. The dictionary can contain a set of English words and basic punctuation. However, dictionary entries could symbolize almost anything as long as there is an agreement or understanding between the end parties as to what reference an entry represents. Each dictionary&#39;s content can be homogeneous or can comprise heterogeneous collections (“objects”) depending on the particular application. As shown in  FIG. 3 , the dictionary  200  can comprise characters, sentences, posffixes, numbers, phrases, haptic cues, paragraphs, words, punctuation, icons, prefixes, symbols, etc.  
      With reference to  FIG. 4 , in one embodiment, the data transmission system  199  comprises a remote response center  210  and a client device  220  (e.g., a telematics device in a car) that are in communication with each other via a communication or data link  212 . The data link  212  typically has bandwidth, packet size, and usage restrictions. In one embodiment, the data link  212  is a narrowband transmission link, channel, pipe, or the like, over a wireless network. The remote response center  210  and the client device  220  typically have one or more dictionaries, each with a plurality of words and symbols, according to the needs or demands of a particular application. For example, the center  210  and the device  220  each comprise n different dictionaries ( 200   1  through  200   n ). In one embodiment, the transmitter unit comprises a remote response center or the like. In another embodiment, the receiver unit comprises a vehicle onboard computer, client device, or the like.  
      The dictionaries ( 200   1  through  200   n ) are typically in memory units/devices that are in communication with the transmitter/receivers units. The transmitter/sender unit and the receiver unit have identical copies of the dictionaries ( 200   1  through  200   n ). The dictionaries are typically relatively small or limited in size. This can be achieved by utilizing dictionaries that are application or task specific, thereby avoiding the use of unnecessarily large dictionaries that fill memory units/devices with content that is not needed. The dictionaries can be modular in nature to facilitate efficient transfer of dictionary data to or from the memory units that are in communication with the transmitter/receivers units. In one exemplary embodiment, the data transmission system  199  comprises modular, relatively small dictionaries ( 200   1  through  200   n ) that make it easier to add, change, or replace the dictionaries ( 200   1  through  200   n ) according to the application or task at hand.  
      In producing the translated version of the message to be sent over the limited data link, the sender typically assembles a protocol stream containing a chain of identifiers that represent the dictionary entries or tokens to convey. Other information can be encoded, such as protocol mode, length information, characterization of token lengths, and information to the receiver regarding which dictionary to use in translating the received tokens/symbols. Upon receiving the stream of tokens, the receiver will refer to the correct dictionary and translate the stream into the correct sequence of objects. The receiver can then use these objects to convey richer information to the user that otherwise would not have been possible.  
      With continued reference to the embodiment of  FIG. 4 , the sender/transmitter unit or location (e.g., remote response center  210 ) is in electronic communication with a memory unit that stores one or more dictionaries (e.g.,  200   1  through  200   n ). The transmitter unit receives the message to be communicated (e.g., “The police car is blue.”), wherein each word and punctuation mark is a message object. The transmitter unit references at least one dictionary to identify those message objects for which translation to dictionary tokens or identifiers are available, and converts each identified message object into a message token. For example, the center  210  retrieves the appropriate dictionary based upon service needs, user input, etc., and assembles a protocol stream  214  containing multiple identifiers (e.g., 3, 6, 4, 2, 5, and 1). The protocol stream  214 , which comprises the IDs of dictionary tokens, is transmitted to one or more receiver units or devices.  
      The receiver unit (e.g., client device  220 ) is typically in wireless communication with the transmitter unit or location (e.g., remote response center  210 ). More specifically, in the present embodiment, the receiver and transmitter units are in RF wireless communication with each other over a limited data link having narrow bandwidth. The receiver unit typically receives the protocol stream, verifies that the memory unit comprises each dictionary identified by the dictionary identifier, and then selects each dictionary identified by the dictionary identifier. The receiver unit references each selected dictionary to translate the message tokens into message objects, and reassembles the message from the message objects and the at least one free symbol, explained in further detail below. For example, upon receiving the protocol stream  214 , the device  220  refers to the correct dictionary (i.e., the same dictionary utilized by the center  210 ) and translates the protocol stream into objects (e.g., 3=“the”; 6=“police”; 4=“car”; 2=“is”; 5=“blue”; 1=“.”). In other words, the phrase is reassembled at the receiving client device  220  and conveyed to the user. The reassembled phrase (e.g., “the police car is blue.”) can be conveyed to the user via a display device  222 , a speaker  224 , or the like, or combinations thereof.  
      The transmitting and receiving roles of the remote response center  210  and the client device  220 , respectively, can be reversed (i.e., the device  220  can transmit the protocol stream  214  to the center  210 ) depending on the particular application. Also, the device  220  and center  210  can utilize a plurality of dictionaries to convey protocol streams  214  to each other.  
      The dictionary  200  utilized by the sender and receiver may not always contain a token for the object that the sender wishes to convey. In one embodiment, the protocol allows escapement into free-symbol mode, wherein an encoding (e.g., ASCII characters) can be used to convey items that are not in the dictionary  200 . As shown in  FIGS. 5   a  and  5   b  , dictionary symbols can be mixed with free symbols—words, phrases, etc. that are not located in the limited dictionaries—when the dictionary  200  does not contain the desired token(s). For example, suppose the center  210  intends to send the message “the police car is on Washington” to a user near the device  220 . All of the words in this sentence are located in one of the limited dictionaries except for “Washington.” The transmitter assembles a protocol stream  214  containing multiple identifiers (e.g., 36427) and a free symbol (e.g., “Washington”).  
      With reference to  FIGS. 5   a  and  5   b  , in one exemplary embodiment, the protocol stream  214  comprises a control information area or segment  230  that can include information regarding the protocol mode, which dictionary to use, token lengths, etc. The stream  214  further comprises an identifier segment  231 , which is made up of one or more dictionary tokens. The stream  214  further comprises an escape marker or free symbol indicator  232  indicating that a free symbol area  235  will follow. The escape marker  232  is followed by an area  234  that includes information regarding the length of the proceeding free symbol area  235 . Marker  236  indicates where the free symbol area  235  ends. The marker  236  also indicates the beginning of another identifier segment comprising one or more dictionary tokens. Upon receiving the protocol stream  214 , the receiver refers to the correct dictionary (based on the information in area  230 ) and translates the protocol stream into objects (e.g., 3=“the”; 6=“police”; 4=“car”; 2=“is”; 7=“on”; free symbol=“Washington”). The phrase “the police car is on Washington” is reassembled at the receiver and conveyed to the user.  
      The transmitter typically converts each identified message object into a message token, and also associates each non-identified message object with a free symbol indicator to generate a free symbol segment from each non-identified message object. In one embodiment, the transmitter associates each non-identified message object with the free symbol indicator by prefixing each non-identified message with the free symbol indicator. The transmitter then concatenates the message tokens and the free symbol segments to generate the protocol stream that is sent over the narrow bandwidth data link to a receiver.  
      Upon receiving the protocol stream, the receiver typically verifies that the memory unit it is in communication with comprises each dictionary identified by the dictionary identifier, and then selects each dictionary identified by the dictionary identifier. The receiver references each selected dictionary to translate the message tokens into message objects, and reassembles the message from the message objects and any free symbols, as explained above. The receiver unit preferably alerts the user if it is not able to access one or more dictionaries identified by the protocol stream&#39;s dictionary identifier and/or obtains copies of the missing dictionaries to be stored in a local or internal memory.  
      Having thus described a preferred embodiment of a method and system for traffic management between a vehicle and a remote location, it should be apparent to those skilled in the art that certain advantages of the within system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. For example, the use of broadcast communication networks has been illustrated, but it should be apparent that many of the inventive concepts described above would be equally applicable to the use of other non-broadcast communication networks.