Abstract:
A method, system, and apparatus for handing-off data receivers in a broadcast-based data dissemination environment. Data receiver hand-off is carried out between data sources in different data cells broadcasting information of the same category. Furthermore, data cell ranges are based on geographic regions rather than signal strength coverage. Generally, the hand-off process involves acquiring the current receiver location of the data receiver and comparing the receiver location with a current data cell range. If the current receiver location is outside the current data cell range, a hand-off controller searches for a new data source encompassing the current receiver location coordinates and having an associated data topic matching the current topic. Once a new data source is found, the hand-off controller subscribes the data receiver to the new data source.

Description:
FIELD OF THE INVENTION 
     The present invention relates to information dissemination systems, and more specifically to data source hand-off in broadcast-based data dissemination environments. 
     BACKGROUND 
     Nearly everyone uses broadcast-based information systems to receive information and entertainment in their day-to-day lives. For example, radio and television stations broadcast music, pictures, and news programs across the country to radios and television sets. Broadcast-based systems are typically characterized by a single data source disseminating information to many data receivers. Unlike many request-response type information systems, information in a broadcast-based system, in general, travels in one direction from a data source to a data receiver. In other words, the data source of a broadcast-based information system does not wait for a response from the data receiver before sending more information. 
     The “one-way” path of information from the data source to the data receiver of a broadcast-based system enables information to be sent to many subscribers in a relatively quick and inexpensive manner. Although this attribute enables efficient transfer of information, subscribers within the system give up the flexibility of choosing the arrival time and the individual content delivered over the broadcast channel. Because of this tradeoff between efficiency and flexibility, broadcast systems are generally arranged to provide different data on different data channels to meet the varied needs and preferences of its audience. For instance, many radio stations focus their broadcast on a specific area of interest, such as news, sports, or country music. Depending on individual tastes and interests, radio listeners choose the type of program to receive by tuning their radio receivers to their preferred stations. Thus, radio listeners do not have direct control over the content of each data channel, only the freedom to choose another data channel to listen to. 
     In general, data signals of traditional broadcast-based information systems have a limited geographic broadcast range. When a subscriber travels beyond the data signal&#39;s broadcast range, a new data source covering the local geographic area must be selected in order to maintain data reception. Moreover, if a subscriber wishes to continue receiving similar data content, the broadcast system must be searched to find a local data source providing such content. For example, if a radio tuned to a country radio station moves too far from the radio station, the signal will become too weak and a new radio station must be selected to maintain radio reception. Furthermore, if the listener wishes to continue listening to a country station, he or she may have to search the radio band to find another country station. Thus, a shortcoming of traditional broadcast-based information systems is the difficulty in receiving consistent data from one geographic region to another. 
     One known method of continuously carrying on a communication link from region to region is called hand-off. Hand-off is typically associated with cellular telephone communication. A cellular telephone network typically divides a geographic area into a cellular grid. A base station controls telephone communications within each cell in the grid, and wireless phones within a cell transmit and receive data to and from the cell&#39;s base station. When a wireless phone physically crosses a cell boundary and moves to a new cell in the grid, the base station in the old cell disconnects from the phone and a base station in the new cell takes over communications with the phone. This process is referred to as “handing-off” and, if all goes well, occurs without the phone user ever knowing that it is happening. To the user, the phone call appears as a continuous connection to the party at the other end of the line. 
     The type of hand-off described above is generally referred to as a horizontal hand-off. Another type of communication hand-off called vertical hand-off has emerged in recent years. The concept of vertical hand-off is similar to horizontal hand-off, except that communication cells are configured to overlap on top of each other, as opposed to being placed adjacent to each other. Typically, a small cell is used to cover the area of buildings, and a larger overlapping umbrella cell is used to cover the distances between buildings. When a mobile user enters or leaves a building, the connection between the user&#39;s wireless phone is switched over to the area&#39;s base station without dropping the voice conversation. 
     Another drawback of traditional broadcasting-based information systems is their inability to provide specific information tailored to the particular area around the listener&#39;s location. Returning to the example of a radio listener traveling across a broadcast area, the listener may be interested in listening to advertising or traffic conditions within ten square blocks of his or her location. With current radio broadcasting methods, the listener must listen to all information broadcast by the radio station, no matter how irrelevant it is to the listener. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above-mentioned limitations of traditional broadcast-based data dissemination systems by teaching a method, system, and apparatus for handing-off data receivers in a broadcast-based environment. Data receiver hand-off is carried out between data sources in different data cells broadcasting information of the same category. Furthermore, data cell ranges are based on geographic regions rather than signal strength coverage. Briefly stated, the hand-off process involves acquiring the current receiver location of the data receiver and comparing the receiver location with a current data cell range. If the current receiver location is outside the current data cell range, a hand-off controller searches for a new data source encompassing the current receiver location coordinates and having an associated data topic matching the current topic. Once a new data source is found, the hand-off controller subscribes the data receiver to the new data source. 
     Thus, an aspect of the present invention involves a method for delivering data streams categorized by topic to at least one data receiver in a broadcast-based data dissemination environment. The method includes defining a first data cell range based on a first geographic region and defining a second data cell range based on a second geographic region. A subscribing step subscribes the data receiver to a first data source when the data receiver is located at a first receiver position within the first data cell range. The first data source broadcasts a first data stream across a first data channel, and a topic categorizes the first data stream. A detecting step detects when the data receiver is located at a second receiver position outside the first data cell range and within the second data cell range. Another subscribing step subscribes the data receiver to a second data source when the data receiver is located at the second receiver position. The second data source broadcasts a second data stream across a second data channel, with the second data stream having the same topic subject as the first data stream. 
     Another aspect of the invention is a broadcast-based data dissemination system. The system includes a first data source having an associated first data cell range. The first data cell range is defined by a first geographic region and is associated to a first data topic. The first data source is further configured to broadcast a first data stream across a first data channel. The system additionally includes a data receiver having a current receiver location and subscribing to the first data source. A second data cell range defined by a second geographic region is associated to a second data source. The second data source is also associated to a second data topic matching the first data topic and is configured to broadcast a second data stream across a second data channel. A hand-off controller is configured to subscribe the data receiver to the second data source if the current receiver position changes from the first data cell range to the second data cell range. 
     Another aspect of the invention is a data structure stored in a computer-readable medium. The data structure includes a primary data source identifier field identifying data sources within a broadcast-based data dissemination environment. A data cell range field is coupled to the data source identifier field and describes geographical ranges of data cells controlled by the data sources. A communication link field is also coupled to the data source identifier field and describes data channels for receiving data streams from the data sources. 
     The data structure may further include a topics field which identifies data sources broadcasting data with a common topic. Furthermore, the data structure may be configured with a data receiver identifier field, a location information field, and a secondary data source identifier field. The data receiver identifier field identifies data receivers within the broadcast-based data dissemination environment. The location information field is coupled to the data receiver identifier field, and describes geographical locations of the data receivers. Finally, the secondary data source identifier field is also coupled to the location information field and identifies data sources subscribed to by the data receivers. 
     Another implementation of the present invention is a method for handing-off a data receiver to a data source in a broadcast-based data dissemination environment. The data receiver is positioned at a current receiver location and receives a current data stream from a current data source. The current data source has a current topic and a current data cell range, with a geographic region defining the current data cell range. The method includes acquiring the current receiver location of the data receiver. A comparing step compares the current receiver location with the current data cell range. If the current receiver location is outside the current data cell range, a searching step searches for a new data source having an associated new data cell range encompassing the current location coordinates and an associated data topic matching the current topic. A subscribing step then subscribes the data receiver to the new data source. 
     Yet another aspect of the invention is a data receiver configured to present a data stream from a data source in a broadcast-based data dissemination environment to a user. The data receiver includes a position sensor configured to sense the current geographical location of the data receiver. A broadcast receiver is configured to receive a current data stream from a current data source. The current data source has a current topic and a current data cell range, with the current data cell range defined by a current geographic region. The data receiver also includes a data source table identifying data sources, data cell ranges, and data channels within the broadcast-based data dissemination environment. In addition, a hand-off controller configured to subscribe the data receiver to a new data source listed in the data source table is used when the current geographical location of the data receiver falls outside the current data cell range. The new data source has an associated new data cell range encompassing the current geographical location of the data receiver and an associated data topic matching the current topic. 
     The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of various embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an example of a suitable broadcast-based data dissemination environment in which the invention may be implemented. 
     FIG. 2 shows the broadcast-based data dissemination environment with a hand-off controller. 
     FIG. 3 shows exemplary data structures used by the hand-off controller to perform a hand-off process. 
     FIG. 4 shows a flow chart of an exemplary data channel hand-off algorithm. 
     FIG. 5 shows another embodiment of the broadcast-based data dissemination environment contemplated by the present invention. 
     FIG. 6 shows a flow chart of an exemplary algorithm used by the data channel proxy controller to switch data channels. 
     FIG. 7 shows exemplary data receiver contemplated by the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described in detail below with reference to FIGS. 1-7. When referring to the figures, like structures and elements shown throughout are indicated with like reference numerals. 
     FIG. 1 illustrates an example of a suitable broadcast-based data dissemination environment  102  in which the invention may be implemented. It should be mentioned that the depicted broadcast-based data dissemination environment  102  is only one example of a suitable environment of the present invention and is not intended to suggest any limitation as to the scope of use or functionality of the invention. The present invention may utilize various broadcast-based data dissemination systems, environments, and/or configurations, including, but not limited to, radio, television, and satellite networks, digital radio systems, broadcast disk systems, publish/subscribe systems, Internet-based broadcasting systems, and the like. 
     The environment  102  contains data sources  104  and data receivers  106 . Each data source  104  is configured to broadcast information of common interest to receivers  106  that subscribe to the data source  104 . As used herein, the term “subscribe” encompasses connecting, logging on, tuning, demodulating, decoding, and/or other known broadcast-based data reception methods used by data receivers  106 . Thus, all data receivers  106  that subscribe to the same data source  104  receive the same categorized information at the same time. 
     Typically, each data source  104  is uniquely identifiable within the environment  102 . A data source  104  may be identified by a network address, a station name, a carrier frequency, or other distinct designation. For example, a data source  104  providing local traffic conditions may be identified by a broadcast carrier frequency, such as 88 MHz, or an Internet Protocol (IP) address, such as 128.128.80. 
     Communication from a data source  104  to data receivers  106  is effectuated over a data channel  108 . A data channel  108  may be a wired connection from a data source  104  to data receivers  106 , a wireless connection from a data source  104  to data receivers  106 , or a combination thereof. As an example, a data channel  108  may consist of a wired network of base stations  110  transmitting content to wireless data receivers  106 . The transmitted content can include various forms of data (i.e., text, audio, or video data), as well as control signals, (i.e., receiver instructions). 
     A data cell  112  is defined as a geographical region in which a data source  104  provides valid data. Data cells  112  may partially or completely overlap one another. For example, in FIG. 1, data cell  114  is completely overlapped by data cell  112 , and is partially overlapped by data cells  116  and  118 . Furthermore, a data cell&#39;s boundary is drawn arbitrarily over a geographic region, and is not limited by the signal strength of any individual base station  110  or data source  104 . Thus, unlike conventional wireless communication systems, a data cell  112  of the present invention may be larger or smaller than traditional wireless cells. For instance, a data cell  112  may span many. conventional wireless cells and a conventional wireless cell may encompass multiple data cells  112 . Therefore, rather than using signal strength as the determining factor of cell boundary, the present invention uses geographic location as the determining factor of a cell boundary. In other words, a data cell&#39;s boundary is dependent on geographic location, not signal strength. 
     Each data cell  112  is owned by a data source  104 . As discussed in detail below, when a data receiver  106  enters a new data cell, a hand-off controller (not shown in FIG. 1) determines if the data receiver  106  should begin receiving data from the new data cell&#39;s owner. For instance, if data cell  114  is owned by data source  120  and a data receiver  106  enters data cell  114 , a hand-off controller decides whether the data receiver  106  should switch data channels  108  and begin receiving content from data source  120 . 
     In FIG. 2, the broadcast-based data dissemination environment  102  is shown with a hand-off controller  202 . As mentioned above, the hand-off controller  202  is used to determine whether the data receiver  106  should switch data channels  108  and begin communicating with a new data source  104  when a data cell  112  is entered or exited. 
     As depicted in FIG. 2, a data receiver  203  in data cell  204  is traveling toward data cell  206  at time t 0 . Furthermore, at time t 0 , the data receiver  203  is subscribing to data source  208  on data channel  210  and is located at geographic position (x 0 , y 0 ). At a later time t 1 , the data receiver  203  has moved to geographic position (x 1 , y 1 ) within data cell  206  and is subscribing to data source  212  on data channel  214 . This process of switching the data receiver  203  from data source  208  to data source  212  is referred to herein as a hand-off process or as handing-off, and is coordinated by the hand-off controller  202 . 
     Hand-off occurs when a data receiver subscribing to a data source moves outside the data cell belonging to the data source and/or into a new data cell belonging to a new data source broadcasting data with the same topic. For example, assume that both data source  208  and data source  212  are broadcasting local traffic information. Also assume that each data cell  204  and data cell  206  belonging to data source  208  and data source  212  respectively encompasses ten city blocks. When the data receiver  203  subscribing to “local traffic” moves beyond data cell  204 , then, by definition, data from data source  208  is no longer valid. The hand-off controller  202  must search for a new data source broadcasting “local traffic” with a data cell range that includes the data receiver&#39;s new location. Since data source  212  meets these requirements, the hand-off controller  202  hands-off data receiver  203  to data source  212 . 
     Thus, the hand-off process of the present invention beneficially relieves users from the tasks of disconnecting data receivers from an old data source with invalid data, searching for a new data source with similar data, and connecting to the new data source in a broadcast-based data dissemination environment. In addition, the invention provides a hand-off process which automatically performs these tasks in a fast and seamless manner. As such, the present invention preserves the efficiency of broadcast environments while making such environments more convenient to use. 
     The hand-off process itself begins when the data receiver  203  provides the hand-off controller  202  its spatial coordinates. The spatial coordinates used can be derived from a variety of location determination techniques and technologies, such as, but not limited to, cell/sector, micro-cell, global positioning satellites (GPS), time difference or arrival (TDOA), angle of arrival (AOA), and hybrid location methods and technologies known to those skilled in the art. In addition, the data receiver  203  may prompt the user for location information. When the hand-off controller  202  detects that the data receiver  203  is about to leave the current data cell  204  and. enter a new data cell  206 , it opens a new data channel  214  to the new data source  212 . Once the data receiver  203  reaches the new data cell  206 , the hand-off controller  202  disconnects the data receiver  203  from the previous data channel  210  and connects it to the new data channel  214 . 
     It is contemplated that the spatial coordinates of the data receiver may be user configurable to values other than the receiver&#39;s current location. For example, a user may be interested in local advertisements from a particular location, regardless of the present location of the data receiver. In such a case, the data receiver may be subscribed to a “local advertising” data channel and the coordinates of the data receiver could be fixed to the location of interest. In a further embodiment of the invention, the data receiver may be programmed to automatically choose from a list of coordinates the coordinate closest to the actual location of the receiver. 
     In a particular embodiment of the invention, a position offset may be added to the spatial coordinates of the data receiver. For example, a user traveling east and subscribing to “local traffic” may be interested in traffic conditions five miles ahead of his or her present location. Thus, the user can specify a five-mile eastern position offset from the present location and receive traffic information from data cells in advance of the current position. It is additionally contemplated that the position offset value may be based on the on the travel velocity of the data receiver and/or user&#39;s historical travel patterns. 
     In FIG. 3, exemplary data structures used by a hand-off controller to perform the hand-off process are shown. The data structures include a current location table  302  that stores each data receiver&#39;s identity and current spatial coordinates in a data receiver identification field  304  and a location information field  306  respectively. Generally, the current location table  302  is used when the data structures reside in a hand-off controller  202  managing multiple data receivers. The location information field  306  is continuously updated as new receiver location coordinates are provided to the hand-off controller. Additionally, the current location table  302  provides a current data source identification field  308  which identifies the data source each data receiver is subscribing to. 
     A topics table  310  includes a topics field  312  containing a list of categorized subjects available to the data receivers in the broadcast-based environment. Each topic entry is associated with a particular data source table  314 . For example, the “local traffic” topic entry  318  references data source table  314  and the “local advertisement” topic entry  320  references another data source table  316 . 
     Each data source table  314  contains a data source identification field  322 . The data source identification field  322  lists data sources broadcasting the topic referenced in the topics table  310 . Each data source identification field entry has a corresponding data cell range entry in the data cell range field  324 . The data cell range field  324  describes the boundary coordinates of the data cell associated with the data source. In a particular embodiment of the invention, the cell range is expressed as an X-coordinate, a Y-coordinate, and a circle radius. It is contemplated that other representations of the data cell range may be used for the data cell. Each data source listed in the data source table  314  is also associated with a communication link field  326  describing the communication mechanism by which a data receiver communicates with the data source. The communication link field  326 , for example, may contain the carrier frequency or the computer network address for the corresponding data source in the data source identification field  322 . It is contemplated that multiple data sources may share the same communication mechanism. 
     In accordance with the present invention, the data structures described above can be any available media that can be accessed by the hand-off controller. In a particular embodiment of the invention, the data structures are embodied as computer readable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the hand-off controller. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer readable media. 
     In FIG. 4, a flow chart of an exemplary data channel hand-off algorithm is shown. The logical operations of the algorithm are implemented (1) as a sequence of computer implemented steps running on a computing system and/or (2) as interconnected machine modules within the computing system. The implementation is a matter of choice dependent on the performance requirements of the system implementing the invention. Accordingly, the logical operations making up the embodiments of the present invention described herein are referred to alternatively as operations, steps, or modules. 
     In receiver location operation  402 , the current location of the data receiver is obtained. The receiver position may be obtained by searching the current location table  302 , as discussed above. Alternatively, the receiver position may be obtained by querying the data receiver directly. After receiver location operation  402  is completed, control passes to data cell range operation  404 . 
     In data cell range operation  404 , the data cell range of the data source subscribed to by the data receiver is obtained. The data cell range operation  404  may be performed by looking up the data cell range information in the data source table  314 . Alternatively, a data source may be queried directly by the hand-off controller for its data cell range. Next, control passes to conditional operation  406 . 
     At conditional operation  406 , the current location of the data receiver is compared to the current data cell range. If the current location falls within the range of the current data cell, then no hand-off action is taken and, at some later point, control returns to receiver location operation  402 . If, however, the receiver&#39;s current location falls outside the range of the current data cell, then hand-off is initiated by passing control to searching operation  408 . 
     In searching operation  408 , a new data source with the same broadcasted topic and with a data cell range covering the current location of the data receiver is retrieved from the data source table  314 . It is contemplated that if no data source is available for the current receiver location, a message to this effect may be presented to the user, and the user may be prompted to choose a new broadcast topic from the topics table  310 . In addition, if more than one data source is available for the current receiver location, it is contemplated that the user may be prompted to select one of the available data sources. After the searching operation  408  is completed control passes to sending operation  410 . 
     During sending operation  410 , a request to connect to the new data source is sent to a data channel proxy controller. As described below, the data channel proxy controller manages data channel connections between data sources and a data receiver. The new data channel is obtained by referring to the communication link field  326  in the data source table  314 . Once the data channel is connected, the receiver subscribes to the data source and data is received. After the sending operation  410  is completed control is passed to setting operation  412 . 
     In setting operation  412 , the current location table  302  is updated and the new data source is recorded in the data source identification field  308 . Once setting operation  412  completes control is returned to conditional operation  406 . 
     With reference now to FIG. 5, another embodiment of the broadcast-based data dissemination environment  102  is shown. In this embodiment, data sources are arranged in a tree distribution network, with a parent data source  502  transmitting common data content  504  to other child data sources  506 . The child data sources  506  insert or replace data within parts of the common data content. The modified content  508  from the child data sources  506  is then retransmitted (broadcasted) to the data receivers  106 . This arrangement is similar to a syndicated radio or television network, where programs are transmitted centrally from a parent station and local broadcast stations insert local content (i.e., advertisements) during commercial breaks. 
     The data sources  506  are coupled to a data channel proxy controller  510 . The data channel proxy controller  510  is used to smoothly switch data sources  506  when hand-off between two data channels is required. As shown, the data channel proxy controller  510  can connect to multiple data sources  506 , but only the content of one data source  506  is passed to the data receiver  106 . The hand-off controller  202 , also coupled to the data channel proxy controller  510 , notifies the data channel proxy controller  510  when a data source switch is necessary. During a hand-off process between two data channels, the data channel proxy controller  510 -chooses a point in the data streams to switch data sources  508  so that the user does not experience any temporary ill effects caused by switching. 
     In one embodiment of the present invention, markers or cues are inserted in the data streams of data channels to indicate where in the data stream a data source switch would be appropriate. The data channel proxy controller  510  adds a time delay to one or both of the data streams, thereby synchronizing the markers in time between the two data streams. Once the data streams are aligned, the data channel proxy controller  510  switches the output data channel to the new data source. 
     A further embodiment of the present invention uses a speculative data channel connection controller  512  to preemptively open data channels in the data channel proxy controller  510  in anticipation of the possibility that a data channel hand-off will be soon occur. In doing so, the speculative data channel connection controller  512  helps reduce the latency costs associated with opening, aligning, and switching data channels during hand-off. 
     The number of data channels opened by the speculative data channel connection controller  512  may be dependent on the position sampling rate and the velocity of a particular data receiver. When the sampling rate of a data receiver&#39;s position is much less than the rate of change in the data receiver&#39;s location, there is greater uncertainty about the data receiver&#39;s position between location samples. Moreover, the greater the uncertainty about the data receiver&#39;s position, the more data channels need to be opened by the data channel proxy controller  510 . Thus, there is an inverse relation between the sample rate of the current location and the number of open data channels needed. The higher the sampling rate, the fewer data channels need to be opened, and similarly, there is a direct relation between the velocity and the number of open channels needed. In other words, the more uncertainty there is about the location of a data receiver, the more data channels may need to be opened in anticipation that the data receiver can suddenly appear in a new data cell after the next position sampling. The actual opening of the data channels and management of these data channels is carried out by the data channel proxy controller  510 . For this reason, the data channel proxy controller  510  includes multiple input data channels from different data sources  506  and only one output data channel to the data receiver  106 . 
     The present invention may also include a data filter  514  coupled between the data channel proxy controller  510  and the data receiver  106 . The data filter  514  is used to selectively filter output data  516  (A,B,C,D) from the data channel proxy controller  510  and passes only a data subset  518  (A,C) to the data receiver  106 . In one embodiment of the present invention the data filter  514  is programmable by the hand-off controller  202 . This is achieved by the hand-off controller  202  introducing data filer instructions into the output data  516 . The data filter  514  detects and decodes these instructions, and filters the output data  516  accordingly. At this point, it should be noted that the data channel proxy controller  510 , the speculative data channel connection controller  512 , and the data filter  514  may be embodied in either the network infrastructure as shown, or in the data receiver  106  as shown in FIG.  7  and discussed below. 
     Data filters  514  may be used to create data sub-cells within the broadcast-based data dissemination environment  102 . With reference again to FIG. 1, each data cell  112  may include one or more data sub-cells. In such an embodiment, a subscribing data receiver  106  within a data sub-cell may present only a portion of the information broadcasted by the data source  104  to the user. A data sub-cell is owned by the same data source  104  that owns the parent data cell  112 , and is located within the data cell  112 . For example, assume that data cell  118  is a data sub-cell of data cell  112 , and that both data sub-cell  118  and data cell  112  are owned by data source  122 . A data receiver  106  moving from data cell  112  to data sub-cell  118  may provide only a subset of the information broadcasted by data source  122  to its user. Thus, when the hand-off controller  202  determines that the data receiver  106  is entering a data sub-cell  118 , a control signal is sent to the data filter  514  and only that portion of the data transmitted from the data source  204  pertaining to the data sub-cell  118  is presented to the user. 
     In one application of such a configuration, a data source  104  may continuously broadcast traffic conditions for the entire geographic region delineated by its data cell  112 . Each individual traffic condition is further tagged with control data indicating which data sub-cell or sub-cells are affected by the information. Data receivers  106  within various data sub-cells then display only relevant traffic conditions by filtering out all traffic information from the data source  104  except for traffic information relevant to the data sub-cell  118  they are in. The hand-off controller  202  is used to program the data filters  514  when a data sub-cell  118  is entered or exited. 
     In FIG. 6, a flow chart of an exemplary algorithm used-by the data channel proxy controller  510  to switch data channels is shown. As before, this algorithm may be implemented (1) as a sequence of computer implemented steps running on a computing system and/or (2) as interconnected machine modules within the computing system. Accordingly, the logical operations making up the embodiments of the present invention described herein are referred to alternatively as operations, steps, or modules. 
     The algorithm begins with receiving operation  602 . During this operation, the data channel proxy controller  510  is instructed to change the data channel being output to the data receiver  106 . This instruction is issued by the hand-off controller  202 , which determines when the data receiver  106  travels outside the current data cell  112 . After the receiving operation  602  is completed, control is passed to conditional operation  604 . 
     In conditional operation  604 , the data channel proxy controller  510  determines if the data channel requested is already opened. As discussed above, the data channel proxy controller  510  may open several data channels in anticipation of a hand-off procedure. If the data channel has not been opened, then control is passed to opening operation  606 . 
     In opening operation  606 , the data channel is opened by the data channel proxy controller  510 . That is, a connection between the data channel and the data channel proxy controller  510  is established. At this point, however, the data is not yet delivered to the data receiver  106 . The opening operation  606  may require the execution of various subscription methods mentioned above to establish a connection between the data channel and the data channel proxy controller  510 . These methods include, but are not limited to, connecting, tuning, demodulating, decoding, and/or other known broadcast-based data reception methods. After the opening operation  606  is completed, or if the data channel was determined already opened at conditional operation  604 , control is passed to decision operation  608 . 
     In decision operation  608 , the data channel proxy controller  512  checks if the data channel is being output to the data receiver  106 . If the data channel is already being output to the data receiver  106 , the data channel proxy controller  510  requires no action and the routine returns to the caller at return operation  612 . 
     If the data channel is not is being output to the data receiver  106 , the output is switched to the new data channel in switching operation  610 . The switching operation  610  may involve synchronizing old and new data streams, as described above. After the switching operation  610  is completed, the data receiver  106  beings to receive data from the new data channel and the routine returns to the caller at return operation  612 . 
     In FIG. 7, an exemplary data receiver  106  contemplated by the present invention is shown. The data receiver  106  includes a micro controller  702  having a processor  704 , program memory  706 , data memory  708 , and I/O memory  710 . The I/O memory  710  is connected to one or more input devices  712  (such as a keyboard, mouse, pen, etc.), one or more output devices  714  (such as a display, speaker, etc.), and a position sensor  716 . As mentioned earlier, the position sensor  716  may use a variety of locating techniques and technologies, such as, but not limited to, cell/sector, micro-cell, global positioning satellites (GPS), time difference or arrival (TDOA), angle of arrival (AOA), and hybrid locating methods and technologies known to those skilled in the art. 
     The program memory  706  includes computer readable media for executing the hand-off controller module  202 , the data channel proxy controller module  510 , and the speculative data channel connection controller  512 . Furthermore, the data memory  708  includes computer readable media for storing the current location table  302 , the topics table  312 , and the data source table  314 . Depending on the exact configuration of the data receiver  106 , the program memory  706  and data memory  708  may be volatile (such as RAM), non-volatile (such as ROM, flash memory, magnetic memory, optical memory, etc.) or some combination of the two. 
     The data receiver  106  includes a broadcast receiver  718  (such as a satellite dish, RF receiver, microwave receiver, multicast listener, etc.), and one or more tuners  720  which tune to appropriate frequencies or addresses of data sources  104  in the broadcast-based data dissemination environment  102 . The tuners  720  may be configured to receive broadcast data in a particularized format, such as MPEG-encoded digital video and audio data, as well as digital data in many different forms, including software programs and programming information in the form of data files. The data receiver  106  may also include a modem  722  which provides wire-based access to the data sources. In other implementations of the data receiver  106 , the modem  722  might be replaced by a network card or other type of port/receiver which provides wire-based access to the data sources. The data receiver  106  also includes a data filter  512 . 
     The hand-off controller  202  in the data receiver  106  carries out a hand-off process in much the same manner as discussed above. Using the position sensor  716 , the receiver&#39;s location is compared to the current data cell range stored in the-data source table  314 . If the receiver&#39;s location moves outside the current data cell range, the data receiver subscribes to a new data source found in the data source table  314 . It is contemplated that information about the broadcast-based environment, such as data entries in the topics table  312  and data source table  314 , may be pre-stored in memory or encoded into data streams received by the data receiver  106 . The data filter  514  may also be programmed by the hand-off controller  202  using data sub-cell information stored in memory or received in data streams. 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiments disclosed were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.