Thus, the present invention is more robust than an "all or nothing" approach to broadcasting of geographic information.
解答例
With independence between data elements during transmission, there is no constraint on the order in which data elements are received.
A preferred embodiment of the invention broadcasts the geographic data as a data carousel, with each data element being retransmitted periodically (i.e. similar to broadcast of TeleText information).
This supports filling in of gaps in a map.
Geographic information within a data element for which receipt initially fails but which is successfully received on retransmission can be inserted into the appropriate place in the map.
In a first aspect, the invention provides a method of distribution of geographic information to mobile devices via a wireless communications network, the method including: generating a plurality of data elements to contain the geographic information, each data element relating to and including an identifier of a specific single segment of a segmented map; and broadcasting the data elements via the wireless communications network for receipt by the mobile devices.
In a second aspect, the invention provides a data processing system for generation of data elements containing geographic information, for distribution to mobile devices, the data processing system including a data processing component for separating input geographic information into data components which are each related to a single segment of a map, in accordance with a defined map segmentation, and combining one or more of the data components related to a specific map segment with an identifier of the specific map segment to create a data element.
In a third aspect, the invention provides a wireless data communications network for transmission of geographic information from a first data processing system to mobile devices, the network comprising: a first data processing system including means for generating a plurality of data elements to contain the geographic information, each data element relating to and including an identifier of a specific single segment of a segmented map, and means for distributing the data elements via the network to a plurality of geographically distributed transmitters; and a plurality of transmitters for broadcasting the data elements via wireless communications for receipt by the mobile devices.
In a fourth aspect, the invention provides a mobile data communication and data processing device including: a receiver for receiving wireless broadcast transmissions including receiving data elements which each include geographic information related to a specific single segment of a segmented map and an identifier of said map segment; a memory for storing a representation of the segmented map; a processing component implementing functions to process the map segment identifier of a received data element to determine which segment of a map the geographic information included in the data element relates to, and for adding the geographic information of the data element to the respective segment of the segmented map representation within the mobile data receiver device.
The functions implemented by the processing component provide the capability to process a plurality of received data elements which may be received in any order, and to add the geographic information of the received data elements to the respective segments of the segmented map representation to build up a map over time.
In a fifth aspect, the invention provides a method for building a map representation on a mobile communication device, including the steps of: receiving broadcast wireless transmissions including receiving data elements which each include geographic information related to a specific single segment of a segmented map and an identifier of said map segment; storing a representation of the segmented map; processing the map segment identifier of a received data element to determine which segment of a map the geographic information included in the data element relates to; and adding the geographic information of the data element to the respective segment of the segmented map representation within the mobile device.
In the presentation of received data elements, a visual indication may be provided of whether all data elements relevant to a particular map segment have been successfully received, such as by showing incomplete segments in "greyed out" style or with some other visual emphasis.
This can be implemented simply, for example by recording at the transmission apparatus how many data elements are relevant to each segment and then checking at the receiving device how many received data elements include the map reference for that segment--where there is a mismatch, the displayed information is greyed out.
In a preferred embodiment of the invention, data is transmitted for receipt by the mobile devices as a plurality of separate broadcast data streams, such as on a plurality of different communication channels.
A channel in this context is a particular operating frequency band and associated transmission parameters, or a timeslot within a frequency band).
The plurality of channels preferably include a low level of detail (LLoD) channel and one or more high level of detail (HLoD) channels.
The data elements sent via the LLoD channel provide a basic map outline and major features, whereas the data elements of the HLoD channels provide finer resolution information supplementary to the LLoD channel.
The data elements sent via the LLoD channel typically include only a small number of bytes of information (for example, 5 or 10 bytes).
This enables an overall picture to be built up quickly.
The HLoD data elements may be considerably larger (for example, 50 bytes), with successful receipt of the HLoD data elements enabling a detailed picture to be built up.
Alternatively, the HLoD data elements may be small but the map segment size relevant to their information content may be smaller than for LLoD data elements.
As noted above, in certain embodiments of the invention the geographic data is transmitted as a data carousel with periodic retransmission of each data element.
In such an embodiment, the LLoD data elements may be retransmitted more frequently than HLoD data elements, so that there is a higher likelihood of LLoD data elements being received within a time period acceptable to users.
This can be independent of whether or not the LLoD and HLoD data elements differ in size or map segment size, but a smaller number or smaller size of data elements on a LLoD channel further improves the likelihood of successful receipt within an acceptable timescale.
According to the preferred embodiment of the invention, when a receiving device starts to receive it will receive data elements related to the local area of its current location, identify the relevant map segments of its internal map structure and start to fill in the segments to build up a map.
In one embodiment of the invention, a receiving device is able to identify when a data element has failed to arrive which is relevant to the map segment in which the receiving device is currently located.
For example, this may use GPS or an alternative to determine the location of the receiving device and could use the previously described check of expected numbers of data elements.
Alternatively, the check may comprise simply identifying data segments for which no data element has been received.
Having identified failure of one or more local data elements, the receiving device concentrates its resources on the communication channel relevant to the missing data element or on the LLoD channel to try to obtain at least the LLoD data element or elements for that segment.
It should be noted that a receiving device may receive on multiple channels simultaneously or alternately, and may be receiving from one or a plurality of transmitters.
