Abstract:
A wireless telecommunications system is disclosed that provides both telecommunications service and navigational assistance to travelers. In particular, the present invention addresses three common navigation problems. First, to aid a traveler who takes the same trip infrequently, the present invention records the movement of the traveler during one trip and, thereafter, provides navigational assistance on how to recreate the trip again at a later time. Second, to aid a traveler in making the homeward portion of a trip, the present invention records the outward-bound portion of the trip and, thereafter, provides navigational assistance on how to get home. And third, to aid a traveler who is trying to recreate the trip of another traveler, the present invention records the movement of one traveler when taking a trip and, thereafter, provides navigational assistance to other travelers on how to recreate the trip taken by the first. In general, the present invention performs two distinct steps. In accordance with the first step, the present invention records the movement of a wireless terminal associated with a traveler as the traveler makes a trip. In accordance with the second step, the present invention generates a set of navigational directions based on a previously recorded trip, which directions indicate either how to recreate the trip or how to backtrack the trip. Those directions are then transmitted to a wireless terminal that is associated with a traveler who desires the directions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to telecommunications in general, and, more particularly, to a wireless telecommunications system that provides both telecommunications service and navigational assistance to travelers. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 depicts a schematic diagram of a portion of a wireless telecommunications system in the prior art, which system provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals  101 - 1  through  101 - 3 ) that are situated within a geographic region. The heart of a typical wireless telecommunications system is a wireless switching center (“WSC”), which also may be known as a mobile switching center or mobile telephone switching office. Typically, a wireless switching center (e.g., WSC  120 ) is connected to a plurality of base stations (e.g., base stations  103 - 1  through  103 - 5 ) that are dispersed throughout the geographic region serviced by the system and to the local and long-distance telephone and data networks (e.g., local-office  130 , local-office  138  and toll-office  140 ). A wireless switching center is responsible for, among other things, establishing and maintaining a call between a first wireless terminal and a second wireless terminal or, alternatively, between a wireless terminal and a wireline terminal (e.g., wireline terminal  150 ), which is connected to the system via the local and/or long-distance networks. 
     The geographic region serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called “cells.” As depicted in FIG. 1, each cell is schematically represented by a hexagon. In practice, however, each cell has an irregular shape that depends on the topography of the terrain surrounding the cell. Typically, each cell contains a base station, which comprises: (1) the radios and antennas that the base station uses to communicate with wireless terminals in that cell; and (2) the transmission equipment that the base station uses to communicate with the wireless switching center. 
     For example, when a user of wireless terminal  101 - 1  desires to transmit information to a user of wireless terminal  101 - 2 , wireless terminal  101 - 1  transmits a data message bearing the user&#39;s information to base station  103 - 1 . The data message is then relayed by base station  103 - 1  to wireless switching center  120  via wireline  102 - 1 . Because wireless terminal  101 - 2  is in the cell serviced by base station  103 - 1 , wireless switching center  120  returns the data message back to base station  103 - 1 , which relays it to wireless terminal  101 - 2 . 
     Because people can require emergency assistance (e.g., first aid, police, fire, etc.) when they travel, a wireless telecommunications system must be capable of processing an emergency call (e.g., a “911” call in the United States, a “999” call in Europe, etc.) that is initiated from a wireless terminal. In particular, a wireless telecommunications system must perform three main steps when processing an emergency call from a wireless terminal: 
     1. the system must ascertain the precise location of the wireless terminal (e.g., its latitude and longitude to within 100 feet); 
     2. the system must route the emergency call to whichever emergency facility (e.g., police station, hospital, etc.) is closest to the location of the wireless terminal; and 
     3. the system must provide the authorities at the emergency facility with the location of the wireless terminal. 
     This last step is necessary because a person who places an emergency call from a wireless telephone might not know his or her precise location or might be injured or otherwise incapable of providing his or her location even if he or she knew it. 
     There are several techniques in the prior art for enabling a wireless telecommunications system to ascertain the precise location of a wireless terminal, and each requires the addition of specialized location equipment to the telecommunications system. Sometimes the location equipment is added to the base stations or other parts of the network, sometimes it is added to the wireless terminals, and sometimes it is added to both. In any case, the equipment for locating a wireless terminal is typically expensive. 
     Furthermore, although it is very important that a wireless telecommunications system be capable of processing an emergency call, the number of emergency calls actually placed is very small in comparison to the number of non-emergency calls. This has two significant implications. First, because the cost of the location equipment is expensive, the cost of the location equipment per emergency call is very high and, therefore, difficult to justify. Second, because emergency calls are infrequent, the location equipment is seldom used, which is an apparent waste of its unique capability. 
     Therefore, the need exists for a secondary use of the location equipment in a wireless telecommunications system, which secondary use does not interfere with its primary use in processing emergency calls and which helps to defray the cost of the location equipment. 
     SUMMARY OF THE INVENTION 
     The present invention is a wireless telecommunications system that uses its location equipment to provide navigational assistance to travelers when the location equipment is not processing emergency calls. Because navigational assistance is a valuable service, a wireless service provider can charge for the service, which helps the wireless service provider pay for the location equipment. 
     The present invention is particularly well-suited for providing navigation assistance to travelers because it has both a telecommunications capability and a location-finding capability. This means that the present invention can use its location-finding capability to track the movements of a wireless terminal carried by a traveler and its telecommunications capability to transmit information to the traveler based on the location of the wireless terminal (e.g., “You just missed the left turn onto Maple Street needed to reach your Grandmother&#39;s house,” etc). 
     The illustrative embodiment of the present invention addresses three common navigation problems and provides various forms of navigational assistance to travelers in solving those problems. 
     The first navigation problem involves a traveler who takes the same trip infrequently. For example, when a traveler takes a short trip frequently (e.g., drive every day to work, drive once a week to the grocery store, etc.), the frequent repetition of making the trip is likely to ingrain the directions into the traveler&#39;s mind such that the traveler has no difficulty in remembering them. In contrast, when a traveler takes a long trip infrequently (e.g., drive once a year from home to Niagara Falls, etc.), the traveler is less likely to remember from past experience how to navigate to make the trip. This is particularly true when the route is convoluted. Therefore, to aid a traveler who takes the same trip infrequently, the illustrative embodiment tracks the movement of the traveler during one trip, records his or her movements, and, thereafter, provides navigational directions to the traveler (e.g., “turn left ahead at Maple Street,” etc.) at a later time on how to make the trip again. 
     The second navigation problem involves a traveler who needs to navigate homeward after completing the outward-bound portion of a trip. Even when a traveler has successfully navigated the outward-bound portion of a trip, the directions for navigating homeward are not necessarily obvious. This is particularly true when the outward-bound portion of the trip is particularly circuitous or involves backtracking. Therefore, to aid a traveler in making the homeward portion of a trip, the illustrative embodiment tracks the movement of the traveler on the outward-bound portion of the trip, records his or her movements, and, thereafter, provides navigational directions to the traveler on how to get home. 
     The third navigation problem involves multiple travelers who desire to take the same trip to the same destination in separate vehicles (e.g., the members of a caravan or convoy, etc.). When two or more travelers desire to take the same trip, all of the travelers must agree in advance: 
     1) to follow a predetermined route, 
     2) to remain in visual contact and play follow-the-leader, or 
     3) to maintain an open telecommunications channel so that they can coordinate their movement on an ad hoc basis. 
     In some cases, these may not be feasible. For example, it is not possible for a group of travelers to follow a predetermined route when the ultimate destination is not known in advance. Furthermore, if the travelers desire to travel at different times or don&#39;t know each other, it is not feasible for them to maintain visual contact or ongoing communications. Therefore, to aid a traveler in recreating the trip taken by another traveler, the illustrative embodiment tracks the movement of one traveler when taking a trip, records his or her movements, and, thereafter, provides navigational assistance to other travelers on how to recreate the trip taken by the first traveler. 
     The illustrative embodiment of the present invention addresses all three problems by using both its telecommunications capability and its location-finding capability. 
     In general, the illustrative embodiment performs two fundamentally distinct steps. In accordance with the first step, the illustrative embodiment tracks and records the movement of a wireless terminal associated with a traveler as he or she makes a trip. In accordance with the second step, the illustrative embodiment generates a set of navigational directions based on a previously recorded trip, which directions indicate either how to recreate the trip or how to backtrack the trip. The navigational directions are then transmitted, via the telecommunications capability of the illustrative embodiment, to a wireless terminal associated with the traveler who desires them. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a schematic diagram of a wireless telecommunications system in the prior art. 
     FIG. 2 depicts a schematic diagram of the illustrative embodiment of the present invention. 
     FIG. 3 depicts a block diagram of the salient components of navigational service center  221  in FIG.  2 . 
     FIG. 4 depicts a flowchart of the operation of an illustrative embodiment of the present invention. 
     FIG. 5 depicts a flowchart of the salient steps involved in the first step of the flowchart in FIG.  4 . 
     FIG. 6 depicts a map of an illustrative geographic region that is serviced by the illustrative embodiment. 
     FIG. 7 depicts a flowchart of the salient steps involved in the second step of the flowchart in FIG.  4 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 depicts a schematic diagram of the illustrative embodiment of the present invention, which comprises: wireless switching center  220 , base stations  203 - 1  through  203 - 4 , and navigational service center  221 . The illustrative embodiment is capable of: 
     1) providing wireless telecommunications service, including emergency service, to wireless terminal  201 , 
     2) recording the movement of wireless terminal  201  as it makes a trip, and 
     3) providing navigational assistance to wireless terminal  201  or another wireless terminal based on a prior trip by wireless terminal  201 . 
     It will be clear to those skilled in the art how to make and use wireless switching center  220  and base stations  203 - 1  through  203 - 4 , in accordance with the present invention. 
     Navigational service center  221  is responsible for providing all facets of both emergency service and navigational assistance to wireless terminal  201 . FIG. 3 depicts a block diagram of the salient components of navigational service center  221 , which comprises: location service controller  301 , location service database  302 , location determining server  303 , and operator&#39;s console  304 . Location service controller  301 is advantageously a general purpose computer that is programmed to orchestrate both emergency service and navigational assistance and to control the operation of the other elements in navigational service center  221 . 
     Location service database  302  advantageously contains, among other things, digitized road maps of the area serviced by the illustrative embodiment, personal preference files for those travelers who use the navigational assistance, and the data for all previously recorded trips. 
     Location determining server  303  advantageously determines the location of wireless terminal  201  when requested to do so by location service controller  301 , and provides location service controller  301  with that information when it is obtained. Operator&#39;s console  304  enables a traveler to call navigation service center  221  and to speak to an operator and thus request a service or change a preference in the traveler&#39;s personal preference file. Alternatively, it will be clear to those skilled in the art that the operator&#39;s console could be replaced by automated processes within location service controller  301   
     FIG. 4 depicts a flowchart of the operation of the illustrative embodiment of the present invention, which records the movement of a wireless terminal as it travels during a trip and then uses that information at a later time to provide navigational assistance. In doing so, the illustrative embodiment performs two fundamentally distinct steps: (1) the recording of a trip, and (2) the provision of navigational assistance based on the trip. 
     Recording a Trip 
     Prior to step  401  in FIG. 4, a traveler with a wireless terminal decides to take a trip. The traveler can have a specific destination in mind (e.g. Grandma&#39;s house, Niagara Falls, etc.) or a generic destination (e.g., a secluded lake, a grocery store, etc.) or no destination in mind at all (e.g., a Sunday drive to see the autumn foliage in Vermont, etc.). Furthermore, the traveler can use any means of transportation (e.g., automobile, boat, bicycle, airplane, walking, etc.) or any combination of means. 
     It will be clear to those skilled in the art that the illustrative embodiment does not literally track the movement of the traveler, but tracks the movement of a wireless terminal that the traveler keeps with him or her during the trip. In this way, the movement of the wireless terminal is treated as a proxy for the movement of the traveler. Therefore, a traveler using an embodiment of the present invention should be advised to keep to his or her wireless terminal close at hand during the entire trip. 
     Step  401  begins when the traveler is ready to start the trip, and FIG. 5 depicts a flowchart of the salient aspects of step  401 . 
     At step  501 , a request is transmitted to navigational service center  221  (in FIG. 2) to begin recording the movement of wireless terminal  201  during the trip on which the traveler is about to embark. The request can be made, for example, by calling a telephone number associated with navigational service center  221  and by speaking to an operator or by pushing the buttons on wireless terminal  201 &#39;s keypad. Alternatively, the request can be made over the Internet. The traveler can make the request for himself or herself, or another person can make the request for the traveler. Furthermore, the request can be transmitted to navigational service center  221  via wireless terminal  201  or via another wireless terminal or via a wireline terminal. It will be clear to those skilled in the art how to communicate a request to navigational service center  221 . 
     In addition to the request itself, a trip identifier is also transmitted to navigational service center  221 . The trip identifier is analogous to a filename in a computer that an enables the traveler, another traveler, or other processes to identify that trip at a later time. For example, the identifier can be a mnemonic that is descriptive and easily remembered (e.g., “Trip to Grandma&#39;s house from home,” “To Niagara Falls from Santa Fe,” etc.) or it can be more cryptic (e.g., “Trip 38A-S,” etc.). The salient characteristic of the trip identifier is that it must enable a traveler to unambiguously distinguish that trip from other trips. 
     At step  506 , navigational service center  221  receives both the request to record the trip and the trip identifier. From step  506 , control passes to step  507  at which navigational service center  221  begins recording and advantageously transmits an acknowledgement to wireless terminal  201  that recording has begun. From step  507 , control passes to step  508 . 
     At step  508 , the illustrative embodiment locates wireless terminal  201 . Although the illustrative embodiment could locate and record the movement of wireless terminal  201  continuously, such an approach could monopolize the location equipment and interfere with the processing of emergency calls. Therefore, the illustrative embodiment instead locates and records the movement of wireless terminal  201  at intermittent points, called “waypoints,” during a trip. For the purpose of this specification, the term “waypoint” is defined as a point in geometric space. When the movement of a wireless terminal is restricted to the surface of the Earth, a waypoint is advantageously recorded in terms of latitude and longitude. If the altitude of a waypoint is, for some reason, deemed advantageous, it too can be recorded. 
     Because the illustrative embodiment locates and records waypoints for wireless terminal  201  intermittently, there must be a systematic plan for determining when waypoints are chosen for recordation. In general, the systematic plan must balance three factors: 
     1. The waypoints should be recorded with sufficient frequency so that unambiguous navigational directions can be generated from the waypoints at a later time. For example, enough waypoints should be recorded near an intersection to be capable of determining at a later time how to traverse the intersection. 
     2. If the waypoints are recorded too frequently, the number of waypoints to be stored and processed will be excessive. For example, if a waypoint is recorded every 2 inches during a 3000 mile cross-country trip, it would generate over 95 million waypoints. 
     3. Furthermore, if the waypoints are recorded too frequently, the location equipment in the illustrative embodiment could be monopolized, which could prevent the processing of emergency calls or the locating of other wireless terminals. 
     Therefore, the illustrative embodiment balances these three factors by choosing the frequency with waypoints are recorded based on the following criteria. 
     1) Fixed-Time Intervals—the illustrative embodiment records a waypoint at least every n seconds (e.g., one waypoint every 15 seconds, etc.). This criterion provides a minimum frequency for the recordation of waypoints. 
     2) Geographical Factors—the illustrative embodiment also records waypoints more frequently (e.g., one waypoint every 1 second, etc.) when the traveler is near an intersection or on a local street than when the traveler is on an open highway. For example, because location service database  302  (in FIG. 3) contains detailed road maps and knows the location of streets, highways, and intersections, the illustrative embodiment can temporarily increase the frequency of recording waypoints when the traveler is near certain geographical features. 
     3) Command-Based—the illustrative embodiment also records waypoints more frequently (e.g., one waypoint every 1 second, etc.) when requested to do by the traveler. For example, the traveler may be in the best position to judge when the geography suggests that detailed directions will be helpful at a later time. Therefore, at step  504 , the traveler can transmit a request to navigational service center  221 , via wireless terminal  201 , to increase the frequency of recording waypoints. In general, such a request will be remain in effect for only a fixed duration (e.g., 5 minutes, etc.). 
     Therefore, the illustrative embodiment records a waypoint when any of the above three criteria indicates that it is appropriate to do so until a request is received (step  505 ) to cease recording. In other words, the illustrative embodiment iterates between steps  507 ,  508 ,  509 , and  510  until a request is received at step  510  to cease recording. 
     When the illustrative embodiment determines that it is appropriate to record a waypoint, it must (at step  508 ) locate wireless terminal  201  so that it has the data needed to record the waypoint. 
     It will be clear to those skilled in the art that there are various ways in which the illustrative embodiment can ascertain the location of wireless terminal  201 . For example, wireless terminal  201  can comprise a satellite position system receiver (e.g., a Global Positioning System receiver, etc.) so that wireless terminal  201  can determine its own latitude and longitude. In such case, wireless terminal  201  provides its location to navigational service center  221  when requested, as shown in step  503 . An example of such an arrangement is taught by G. J. Grimes, U.S. Pat. No. 5,479,482, entitled “Cellular Terminal For Providing Public Emergency Call Location Information,” issued Dec. 26, 1995, which is incorporated by reference. In accordance with another technique, wireless terminal  201  and location determining server  303  share the task of computing the latitude and longitude of wireless terminal  201 . In such case, wireless terminal  201  provides an indicium of its location to navigational service center  221  when requested, also at step  503 . An example of such an arrangement is taught by G. Vannucci and R. E. Richton in U.S. patent applications Ser. Nos. 08/927,432, and 08/927,434, both of which are pending and both of which are incorporated by reference. 
     In accordance with other techniques, either wireless terminal  201  or base stations  203 - 1  through  203 - 4  use terrestrial triangulation techniques, in well-known fashion, to determine the location of wireless terminal  201  based on the time-of-arrival or direction-of-arrival of signals transmitted from the other. It will be clear to those skilled in the art how to determine the location of wireless terminal  201  for the purposes of the present invention. 
     At step  509 , navigational service center  221  records the most recently ascertained waypoint into location service database  302  in a data structure such as that shown in Table  1 , which has the identifier “From Home to Grandma&#39;s House.” 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 From Home to Grandma&#39;s House 
               
             
          
           
               
                 Waypoint 
                 Latitude 
                 Longitude 
               
               
                   
               
               
                 603-1 
                 40° 36′ 00″ N 
                 72° 47′ 30″ W 
               
               
                 603-2 
                 40° 36′ 00″ N 
                 72° 47′ 20″ W 
               
               
                 603-3 
                 40° 36′ 20″ N 
                 72° 47′ 00″ W 
               
               
                 603-4 
                 40° 36′ 40″ N 
                 72° 47′ 00″ W 
               
               
                 603-5 
                 40° 37′ 20″ N 
                 72° 47′ 00″ W 
               
               
                 603-6 
                 40° 37′ 40″ N 
                 72° 47′ 00″ W 
               
               
                 603-7 
                 40° 38′ 00″ N 
                 72° 46′ 40″ W 
               
               
                 603-8 
                 40° 38′ 00″ N 
                 72° 46′ 20″ W 
               
               
                 603-9 
                 40° 38′ 30″ N 
                 72° 46′ 00″ W 
               
               
                   
               
             
          
         
       
     
     FIG. 6 depicts an example of a map of a geographic region that can be serviced by the illustrative embodiment. The map depicts Home  601 , Grandma&#39;s House  602 , several streets and the nine waypoints,  603 - 1  through  603 - 9 , in Table 1 that were recorded as a traveler made a trip from Home  601  to Grandma&#39;s House  602 . 
     At the end of the trip, which is step  505 , a request is transmitted to navigational service center  221  (in FIG. 2) to cease recording the movement of wireless terminal  201 . Like the request to begin recording, the request to cease recording can be made, for example, by calling a telephone number associated with navigational service center  221  and by speaking to an operator or by pushing the buttons on wireless terminal  201 &#39;s keypad. Alternatively, the request can be made over the Internet. Analogously, the traveler can make the request himself or another person can make the request for the traveler. Furthermore, the request can be transmitted to navigational service center  221  via wireless terminal  201  or via another wireless terminal or via a wireline terminal. It will be clear to those skilled in the art how to communicate a request cease recording to navigational service center  221 . 
     At this point, the step of recording a trip is complete and the result is a table of waypoints as shown in Table 1 and stored in location services database  302 . After the step of recording is complete, the step of providing navigational assistance, step  402 , begins. 
     Providing Navigational Assistance 
     Prior to step  402 , but after step  401 , a traveler with a wireless terminal decides to take a trip and decides to have the illustrative embodiment provide navigational assistance for that trip, which navigational assistance is based on a previously recorded trip. This traveler can be same as that in step  401 , or another traveler. The traveler can use any means of transportation (e.g., automobile, boat, bicycle, airplane, walking, etc.) or any combination of means, and need not use the same means as were used for the previously recorded trip. When the traveler wants the navigational assistance to begin, the illustrative embodiment begins performing step  402 . FIG. 7 depicts a flowchart of the salient aspects of step  402 . 
     At step  701 , a request is transmitted to navigational service center  221  (in FIG. 2) to provide navigational assistance. As with the request in step  501 , the request in step  701  can be made, for example, by calling a telephone number associated with navigational service center  221  and by speaking to an operator or by pushing the buttons on wireless terminal  201 &#39;s keypad. Alternatively, the request can be made over the Internet. The traveler can make the request himself or another person can make the request for the traveler. Furthermore, the request can be transmitted to navigational service center  221  via wireless terminal  201  or via another wireless terminal or via a wireline terminal. It will be clear to those skilled in the art how to communicate the request to navigational service center  221 . 
     In addition to the request itself, five other pieces of information are advantageously transmitted to navigational service center  221  or are located in the traveler&#39;s personal preference file in location services database  302 . The traveler&#39;s personal preference file can be associated with the traveler by, for example, intelligent agent software that is operating within location service controller  301  and that knows the traveler&#39;s preferences in obtaining certain services. The other five piece of information are: 
     1) the trip identifier—The trip identifier identifies the trip for which the traveler is requesting navigational assistance (e.g. “Trip to Grandma&#39;s house from home,” “To Niagara Falls from Santa Fe,” etc.); 
     2) the playback mode—the playback mode indicates whether the traveler desires to recreate the identified trip or to backtrack the identified trip. 
     3) the playback style—the playback style indicates whether the traveler prefers the navigational assistance in the form of: 
     magnetic directions (e.g., turn north onto Main Street and go for 2 miles ), 
     relative directions (e.g., turn left onto Main Street and go for 2 miles ), or 
     landmark directions (e.g., turn left at the gas station and go for 2 miles ), etc. 
     4) the playback format—the playback format indicates whether the traveler prefers the navigational assistance in the form of: 
     spoken directions (i.e. speech synthesis), 
     data for a visual display in the form of text or maps, or 
     data for an onboard autonomous navigation system, etc. 
     5) the delivery mechanism—the delivery system enables the traveler to have all of the information downloaded at once, or to have the illustrative embodiment monitor the traveler&#39;s progress on the trip and to provide directions in real time as needed. When the navigational assistance is provided in real time, the illustrative embodiment can notify the traveler if he or she inadvertently deviates from the directions. 
     At step  702 , navigational service center  221  receives the request for navigational assistance and any ancillary information. From step  702 , control proceeds to step  703  at which the requested navigational directions are generated in accordance with the preferred playback mode, style and format. 
     For example, if a traveler requests assistance in recreating the trip “From Home to Grandma&#39;s House,” whose recorded waypoints are listed in Table 1, with relative directions for a visual display, the illustrative embodiment might produce the directions: 
     1. Go east on Landis Avenue for ½ mile to Chestnut Avenue; 
     2. Turn left onto Chestnut Avenue; 
     3. Go north on Chestnut Avenue for 2 miles to Oak Street; 
     4. Turn right onto Oak Street; 
     5. Go east on Oak Street for 1 mile to Lincoln Drive; 
     6. Turn left onto Lincoln Drive; and 
     7. Go north on Lincoln Drive for ½ mile to your destination. 
     Alternatively, if the traveler requests assistance for backtracking the trip “From Home to Grandma&#39;s House,” with magnetic directions, the illustrative embodiment might produce: 
     1. Go south on Lincoln Drive for ½ mile to Oak Street; 
     2. Turn west onto Oak Street; 
     3. Go west on Oak Street for 1 mile to Chestnut Avenue; 
     4. Turn south onto Chestnut Avenue 
     5. Go south on Chestnut Avenue for 2 miles to Landis Avenue; 
     6. Turn west onto Landis Avenue; and 
     7. Go west on Landis Avenue for ½ mile to your destination. 
     It will be clear to those skilled in the art how to turn a succession of waypoints, such as those listed in Table 1, into a series of directions, such as those described above, for either recreating a trip or for backtracking a trip. 
     At step  704 , navigational service center  221  determines if the traveler desires all of the navigation directions to be transmitted at once in a batch. If the traveler does, then control passes to step  705 ; otherwise control passes to step  707 . 
     At step  705 , navigational service center  221  transmits all of the directions to a wireless terminal associated with the traveler. At step  706 , the traveler outputs all of the directions on an appropriate output device (e.g., visual display, speaker, etc.) depending on the format of the directions. Alternatively, if the vehicle associated with the traveler has an autonomous navigation system, like those that are beginning to appear on some cars, then the directions can be downloaded directly into the navigation system via the wireless terminal. 
     At step  707 , navigational service center  221  begins the process of providing the directions, in real time, to the wireless terminal. At step  708 , the traveler requests that he or she be given the next step in the directions and at step  707 , navigational service center  221  provides the next direction. It should be made clear that the traveler will be given the same direction each time a request is made, until navigational service center  221  determines that the direction has been completed. This is advantageous because it allows the traveler to refresh his or her memory with the next direction as many times as he or she desires until the direction is completed. It will be clear to those skilled in the art that the traveler can make the request by, for example, calling navigational service center  221  and speaking to an operator or, alternatively, by pushing a key on the wireless terminal&#39;s keypad. 
     At step  709 , navigational service center  221  locates the wireless terminal, in well-known fashion, for the purpose of determining whether the wireless terminal has completed the trip or has deviated from the directions. 
     At step  710 , navigational service center  221  determines if the wireless terminal has reached its destination. If it has, then the illustrative embodiment stops; otherwise, control passes to step  711 . 
     At step  711 , navigational service center  221  determines if the wireless terminal has deviated from the route on which it is being directed. If the wireless terminal has deviated from the route, which suggests that it might have missed a turn or otherwise become lost, then control passes to step  712  and navigational service center  221  transmits a warning message to the wireless terminal. Otherwise, control returns to step  707 . 
     At step  713 , the wireless terminal receives the warning message, which alerts the traveler to the possibility that he or she is lost and should take remedial action. 
     It is to be understood that the above-described embodiments are merely illustrative of the invention and that many variations may be devised by those skilled in the art without departing from the scope of the invention. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.