GB2407004A

GB2407004A - Handover of a wireless download to a mobile terminal

Info

Publication number: GB2407004A
Application number: GB0323819A
Authority: GB
Inventors: Russell John Haines
Original assignee: Toshiba Research Europe Ltd
Current assignee: Toshiba Europe Ltd
Priority date: 2003-10-10
Filing date: 2003-10-10
Publication date: 2005-04-13
Anticipated expiration: 2023-10-10
Also published as: GB2407004B; GB0323819D0

Abstract

The wireless download of data to a mobile terminal 5 across a link with a relatively low data rate, i.e. a wireless personal access network (WPAN) such as Bluetooth<(RTM)>, is performed whilst the mobile terminal 5 is in motion. Two or more access points 1, 2, 3 are used to download the data sequentially to the mobile terminal 5. A wireless link is first set up between a first access point 1 and the mobile terminal 5 using a connection protocol, i.e. Bluetooth<(RTM)>. Subsequently, one or more further wireless links are set up between further access points 2, 3 and the mobile terminal 5 on the basis of the connection already established between the first access point 1 and the mobile terminal 5 to enable the subsequent sequential transfer of data. This arrangement may find application in an airport transfer corridor or in shopping malls and streets for location based services and the download of commercial application software.

Description

Wireless Download to a Mobile Terminal This invention relates to the

wireless download of data, such as software modules, patches or other configuration data, to a mobile terminal across a link with a relatively low data rate whilst that terminal is in motion, for example whilst being carried through an airport transfer corridor or concourse.

Software download is a well accepted method of configuring a softwaredefined or reconfigurable radio, as well as being used in a wide variety of other applications. A common application requiring software download occurs when a person arrives in a foreign country by air, and requires the downloading of local information to a mobile terminal. A similar application arises in shopping malls and along streets for location based services and the download of commercial application software to a mobile terminal.

Various prior references describe techniques for software download and many specific solutions, including the use of short-range wireless personal area networks (WPANs) for the transfer of the software modules and configuration information. Such prior references include JP 2002077030, US 5909437 and EP 0459344A1 which describe general over the air software download systems, and KR 2001026519 which describes the use of WPAN (specifically using a Bluetooth wireless link, where Bluetooth is a Registered Trade Mark) for software download.

There are issues associated with WPANs that have not been properly addressed; namely the low data rate, and therefore the slow rate of download, coupled with the short range of any connection. Taking a Bluetooth wireless link as an example, the often quoted Bluetooth data rate of 1 Mbps is in fact the aggregate gross data rate for the whole piconet. In reality, the best throughput rate (taking an asymmetric data connection as appropriate for software download) is about 721 Kbps, and this assumes that the terminal has the undivided attention of the entire piconet (not a valid assumption is a busy public location such as an airport).

A Bluetooth wireless link is also a short-range system as a consequence of offering low power consumption. A standard Bluetooth wireless link offers a range of approximately tom (high powered Bluetooth wireless link offers greater range, but is precluded because all of the terminals would also have to be high powered in order to acknowledge receipt of the data to the access point), so that a moving terminal can be reasonably be expected to be within range of a Bluetooth access point for a 20m stretch, as shown diagrammatically in Figure 1.

It is an object of the invention to provide a method of effecting the wireless download of data to a mobile terminal across a link with a relatively low data rate in a manner that largely overcomes these problems.

According to one aspect of the present there is provided a method for performing the wireless download of data to a mobile terminal across a link with a relatively low data rate whilst the mobile terminal is in motion, the method comprising: setting up a wireless link between a first access point and the mobile terminal including detection of the mobile terminal by the first access point and establishing of a connection using a connection protocol; and subsequent to the establishment of the connection between the first access point and the mobile terminal, setting up a wireless link between at least one further access point and the mobile terminal on the basis of the connection already established between the first access point and the mobile terminal to enable the subsequent transfer of data from the or each further access point to the mobile terminal.

According to another aspect of the present there is provided a data download system for performing the wireless download of data to a mobile terminal across a link with a relatively low data rate whilst the mobile terminal is in motion, the system comprising: a plurality of access points spaced along a path along which the mobile terminal is movable so that the mobile terminal comes within the transmitting range of each access point in sequence as the mobile terminal is moved along the path, and control means for setting up a wireless link between a first of the access points and the mobile terminal including detection of the mobile terminal by the first access point and establishing of a connection using a connection protocol, and for subsequently setting up a wireless link between at least one further access point and the mobile terminal on the basis of the connection already established between the first access point and the mobile terminal to enable the subsequent transfer of data from the or each further access point to the mobile terminal.

This method is effectively a way of extending the range of WPAN download to compensate for the short range and relatively low data rates of WPANs (such as Bluetooth). It not only applies to software download for reconfigurable terminals, but also any other kind of download.

The method will work in any situation where users follow a common route through an area, for example, along corridors in an airport when boarding or disembarking, through a shopping mall or along a street.

Typically the system comprises a series of WPAN access points along the route, such that a user passes in range of each access point in turn. Each access point may than download modules in a piecemeal fashion as the terminal moves in to and out of range of each access point in turn. Large downloads then become possible without having to increase transmission power (to increase range) with all of the reductions in battery life and user density that that would entail.

This cascaded approach also means that retransmission of modules corrupted due to propagation losses (for example) becomes possible long after the user has passed beyond the range of the access point that made the original transmission.

In order that the invention may be more fully understood, a data download system in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram of a conventional data download system utilizing a Bluetooth access point; Figures 2 and 3 are diagrams of data download systems in accordance with the invention utilizing a plurality of Bluetooth access points; Figures 4, 5, 6 and 7 are diagrams illustrating different control methods for such data download systems in accordance with the invention; and Figure 8 is a diagram illustrating a mechanism for establishing the required connections and effecting the required downloads.

The following description is concerned with a method in accordance with the invention for effecting the wireless download of data to a mobile terminal across a WEAN link with a relatively low data rate whilst the mobile terminal is being carried through an airport transfer corridor or concourse. This is achieved by having a series of Bluetooth access points spaced along the corridor which download the data piece by piece as the terminal moves in to and out of range of each access point in turn.

In the case of a user carrying a mobile terminal along an airport connection corridor, the user can be walking along a fixed floor (speed of the order of 1.3m/s), walking along a travelator (overall speed of the order of 3m/s taking account of the speed of the travelator) or possibly travelling on an electric cart (speed comparable to the case of the user walking along a travelator). If the user is walking slowly (say lm/s) along a fixed floor, this would mean that the terminal would be in range of an access point for about twenty seconds, whereas, if the user is walking at this speed along a travelator, the terminal would only be in range for less than seven seconds.

Assuming that a wireless link is established between the access point and the terminal during this time, a significant proportion of the time will be expended on connection setup to the access point (that is the amount of time taken for two Bluetooth devices to detect each other, handshake and establish a connection for data transfer).

Current Bluetooth (BT1. 1) specifications result in a connection setup time of up to nine seconds. The impending improved Bluetooth specification (BT1.2) will offer a faster connection setup time of the order of 1 to 2 seconds, but this new version of the specification will take some time to penetrate the market. With the BT1.1 connection setup time, up to half of the time that the terminal spends in range of the access point-if the user is walking slowly along a fixed floor may be spent establishing a link, whereas, if the user is walking along a travelator, there may be insufficient time for any data at all to be transferred to the terminal.

At the maximum transfer rate of 721 Kbps, even the full twenty second transfer time would only enable 14Mb of data to be downloaded. Current terminal designs have protocol stacks of the order of one or two Mb and applications that are larger still, and even this transfer time may not be sufficient for the downloading of the necessary data in some cases. Furthermore, with increasing terminal complexity (multiple standards and multimedia applications), it can be anticipated that such a transfer time will become insufficient for the downloading of the necessary data in many more cases. In more realistic scenarios, with transfer times of ten seconds or less, the limit will be reached even sooner.

This invention addresses the issue of limited data transfer time by providing multiple, connected Bluetooth access points in sequence, taking advantage of the predictable routes that users take through public places. In use of such a system users "run the gauntlet" of the sequence of access points as they traverse the building whilst carrying the terminals, for example on disembarking from the aeroplane and walking through baggage recovery to customs and passport control.

Such a gauntlet system comprising three Bluetooth access points 1, 2 and 3 spaced apart at 20 m intervals is shown diagrammatically in Figure 2. The access points 1, 2 and 3 are controlled by a central controller 4 and have a range such that the mobile terminal 5 whilst travelling along a path 6 remains within range of each access point for a distance of approximately 20m along its path, as indicated by the range lines 1', 2' and 3'. It will be appreciated that, although only three access points are shown in this diagram for simplicity, the number of access points used in any system in accordance with the invention is only limited by space and budget constraints. Furthermore, although the following description will be given with reference to a system using Bluetooth technology, it will be appreciated the system can also be produced in accordance with the invention using other wireless technologies.

In an alternative embodiment shown in Figure 3, the access points 1, 2 and 3 are interconnected and have a distributed control function coordinating them, rather than being controlled by a central controller 4 controlling them as in the arrangement of Figure 2.

If required the first access point 1 (or even the first two or more access points) in the system may be predominately used in a broadcast or multicast mode of operation (as all terminals will probably require some similar downloads with similar content).

Subsequent access points may then be used specifically for the transmission of bespoke downloads and content, or specific retransmissions for particular terminals that have reported problems in receiving an earlier transmitted download.

By transmitting the required data download using multiple Bluetooth access points in sequence, two major advantages are conferred.

Firstly, a quantity of data of arbitrary size can be downloaded to the terminal by subdividing it into a series of smaller modules with the modules being downloaded in turn by successive access points 1, 2 and 3, and the modules being re-assembled by the terminal 5. With modular software design, this subdivision may have already been performed prior to supply of the software to the controller 4, although it is also possible for the subdivision to be effected by the controller 4.

Secondly, because the access points 1, 2 and 3 are interconnected and perhaps linked to a central controller 4 or have a distributed control function coordinating them, it is possible to implement a limited "handover/handoff" function (as with cellular technologies) where key information, such as the hopping sequence and the current position in that hopping sequence in the case of a Bluetooth system, can be passed along the chain of access points 1, 2 and 3 to minimise connection setup time and therefore maximise the amount of time available for data transfer.

Additionally, there is an advantage gained as a result of the system using a WPAN, in that there is an inherent location dependence which results in the software downloads being able to be targeted to the audience. Because the WPAN represents a short-range solution in a specific geographical area, this means that it is possible to offer for download only the software that is required in that specific location and its environs.

In a WLAN solution covering a greater area (e.g. a cellular download system), there is a need to determine the user's location and send that data to the network to enable the software specific to that location to be downloaded, whereas in the WPAN solution that location information is implicit. For example, if a user is entering a WLAN coverage area, the terminal needs to be able to communicate what software is required (or it's location to enable the required software to be determined) to the current serving network to get the right software downloaded, whereas the WPAN gauntlet system in accordance with the invention already knows where the user is and, consequently, what software is needed.

The "handover" (or "handoff") arrangement used may be of a type used in cellular mobile telephony systems, and enables the communication node of the terminal to move from one access point or access point to another without dropping the call.

Possible minor variations on the hand-over arrangement that can be used mainly concern the way in which the radio resources are allocated. In one arrangement, in accordance with the DECT standard, the terminal performs a "make then break" sequence, that is it obtains a radio channel (where the channel could be a logical channel, such as a particular time-slot on a given frequency, rather than an entire radio frequency channel) from the new access point before ceasing communication with the old access point and starts transmitting on the new channel, thus making the transition as seamless as possible.

In another possible arrangement, in accordance with the GSM standard, the terminal performs a "break then make" sequence, that is, the currently used access point tells the terminal what frequency to use (or, in the case of Bluetooth, the hopping sequence and the current position in the hopping sequence) at the new access point, and the terminal then releases the channel that it is currently communicating on before starting to use a new channel with the next access point. Such an arrangement optimises the use of radio resources (as it is wasteful to hold two channels simultaneously as required by the DECT standard). Where such an arrangement is used for a voice call, users may notice a (hopefully brief) discontinuity in speech whilst the channel is changed and the speech paths rerouted from one access point to the next.

In the case of software download, there needs to be some mechanism for pausing the download during the brief discontinuity in communications since, although a gap in speech can be ignored, a gap in a downloaded software module or data could be catastrophic. Several alternative mechanisms can be used to this end.

In a first such mechanism diagrammatically illustrated in Figure 4, the first access point 1 acts as a "receptionist" in that it finds out what data the terminal 5 wants and then schedules the later access points 2 and 3 (and possibly the first access point 1 itself) to deliver the data as the terminal 5 passes them. This could be achieved by fragmenting the software/data into small modules A, B. C and D for example of a size that can be guaranteed to be downloaded to the terminal in the time available, and then controlling the access points so that, for example, the module A is downloaded by the access point 1, the modules B and C are downloaded by the access point 2, and the module D is downloaded by the access point 3 under the control of scheduling signals from the access point 1.

In order to ensure optimal reuse of radio resources with this arrangement, profiling and loading of the access points 1, 2 and 3 is required to provide optimal capacity. Figure 8 diagrammatically illustrates a possible mechanism involving the passing of a sequence of messages between the first access point 1, the terminal 5 and the second access point 2, the time sequence of the messages proceeding from top to bottom of the diagram. It will be noted that, prior to the establishment of the connection between the second access point 2 and the terminal 5, "backplane" messages are transmitted between the access points 1 and 2, these messages being sent not by way of the air interface being used for the downloads but by way of a wired backplane, such an IEEE802.3/Ethernet LAN, or even by way of another wireless system, such as an IEEE802. 11 wireless LAN, depending on the deployment of the access points and their associated infrastructure. A brief registration process is utilised to establish the connection between the second access point 2 and the terminal 5, this being assisted by a unique "password" communicated to the terminal 5 (in a secure fashion) by way of the wired backplane and the wireless link from the first access point 1 to the terminal 5, in order to allow the second access point 2 to verify that the terminal attempting to resume the download is indeed the terminal that is expected, rather than another device attempting to gain access. This mechanism relegates the role of the central controller to that of a file server (if the controller is provided at all, as the required downloadable modules could be held locally on the access points), with the control of the download process and associated handovers being located at the access points, although of course it is possible to conceive of other mechanisms in which the central controller manages such control directly.

In a second such mechanism diagrammatically illustrated in Figure 5, the software download or data is again into small modules that can be downloaded sufficiently quickly. However, in this arrangement, the first access point 1 passed by the terminal 5 begins to download the sequence of modules A, B. C and D and, only when the terminal 5 moves out of range of the first access point 1, is the download of the sequence of modules A, B. C and D continued by the next access point 2. Any modules that straddled the changeover from the first access point 1 to the second access point 2 could be retransmitted at the next access point in response to receipt of a negative acknowledgement signal NAK from the mobile terminal indicating that the whole of a particular module had not been received by the terminal correctly.

In a third such mechanism (in effect, a continuous version of the mechanism involving division in advance into discrete blocks as described in the previous paragraph) diagrammatically illustrated in Figure 6, the data is downloaded continuously as the first access point 1 is passed by the terminal 5, and a counter within the mobile terminal 5 maintains a count of (say) how many bytes of data have been received by the terminal up to the time when the transmission from the first access point 1 to the terminal 5 is lost, so that, at the end of this period, the counter may register 1048499 bytes received for example. The terminal 5 then transmits a signal to the next access point 2 requesting that the download of data by the next access point 2 should begin from the point indicated by the count of bytes received held in the counter, so as to begin wim the next byte, that is byte 1048500, in the data download.

In a fourth such mechanism diagrammatically illustrated in Figure 7, the data is downloaded continuously as the first access point 1 is passed by the terminal 5, and a control signal is transmitted from the access point 1 to the controller 4 as the strength of the signal transmitted from the access point 1 to the terminal 5 is seen to be dropping in order to suspend the supply of data from the central downloading server to the access point 1. When the connection from the next access point 2 to the terminal has been established, a control signal is transmitted from the access point 2 to the controller 4 to cause the central downloading server to resume the supply of data to the terminal, but by way of the next access point 2 rather than the previous access point 1.

These different mechanisms have been described as involving control from a central controller 4, although it would be possible to use similar mechanisms in a distributed architecture arranged as described with reference to Figure 3 above with (say) each access point passing responsibility for the terminal's download (in effect, a virtual token) to the next access point on handover.

It should be noted that, whilst this description has been predominately concerned with software downloads, the system in accordance with the invention is equally applicable to the download of other content, especially content with a location-based theme, such as advertisement or provision of local services, guidebooks, maps, etc., that users may want in the same locations.

A similar system can be applied at the departures side of the airport (as users board aeroplanes) so that users can download, for example, films and software specific to whatever networks are available for use during their flight.

The primary advantages of the above described systems in accordance with the invention described above are as follows. Users are able to behave normally (as opposed to having to stop and wait at a particular location, such as a download kiosk) whilst their terminal is upgraded. By adopting WPAN download (as opposed to using a common cellular technology such as GSM), there is less drain on network resources.

By adopting WPAN download and avoiding the cellular network, the act of download is cheaper for the user (the cost savings in network resources can be passed on to the consumer). The use of low-power WPAN technology in a series of short-range links results in longer battery life.

Additional advantages of the above described systems in accordance with the invention described above are as follows. This method is applicable to technologies offering higher data rates for which other considerations, such as user prompts, authentication, and financial transactions, may extend the session duration beyond the length that could be supported by a single access point. The whole system is also more robust to interference than a single access point solution, as there are opportunities for data retransmissions in different locations that may have better signal propagation as the user moves around.

Claims

CLAIMS: 1. A method for performing the wireless download of data to a

mobile terminal across a link with a relatively low data rate whilst the mobile terminal is in motion, the method comprising: setting up a wireless link between a first access point and the mobile terminal including detection of the mobile terminal by the first access point and establishing of a connection using a connection protocol; and subsequent to the establishment of the connection between the first access point and the mobile terminal, setting up a wireless link between at least one further access point and the mobile terminal on the basis of the connection already established between the first access point and the mobile terminal to enable the subsequent transfer of data from the or each further access point to the mobile terminal.
2. A method according to Claim 1, wherein, subsequent to the establishment of the connection between the first access point and the mobile terminal and on the basis of the connection already established between the first access point and the mobile terminal, a wireless link is set up between a second access point and the mobile terminal to enable the transfer of data from the second access point to the mobile terminal, and a wireless link is set up between a third access point and the mobile terminal to enable the transfer of further data from the third access point to the mobile terminal.
3. A method according to Claim 2, wherein the transfer of further data from the third access point to the mobile terminal is effected after the transfer of data from the second access point to the mobile terminal.
4. A method according to Claim 1, 2 or 3, wherein successive fractions of download data supplied to the access points from a controller are transferred to the mobile terminal by way of different access points so that substantially the whole of the download data is received by the mobile terminal.
5. A method according to any preceding claim, wherein a handover protocol is applied by which, when transfer of data to the mobile terminal from one of the access points ceases, the transfer of data to the mobile terminal from a further one of the access points is initiated.
6. A method according to Claim 5, wherein, during transfer of data to the mobile terminal from said one of the access points, a connection is established between the mobile terminal and said further one of the access points prior to initiation of the transfer of data to the mobile terminal from said further one of the access points.
7. A method according to Claim 5 or 6, wherein the data is transferred to the mobile terminal discontinuously in a series of blocks according to a schedule, determined on detection of the mobile terminal by the first access point, allotting subsequent transfer of a respective block of the data to each of a plurality of the access points.
8. A method according to Claim 5 or 6, wherein the data is transferred to the mobile terminal discontinuously in a series of regularly transmitted blocks, and the handover of the data transfer to said further one of the access points is initiated in response to the mobile terminal reaching the limit of the transmission range of said one of the access points.
9. A method according to any Claim 5 or 6, wherein the data is transferred to the mobile terminal substantially continuously during monitoring of the progress of the transfer by counting of the number of units of data transferred, and data transfer to said further one of the access points is initiated from the point at which the mobile terminal reached the limit of the transmission range of said one of the access points as determined by counting of the number of units of data transferred up to that point.
10. A method according to Claim 5 or 6, wherein the data is transferred to the mobile terminal substantially continuously but with the supply of data being suspended in response to a signal indicating that the mobile terminal has reached a predetermined limit of the transmission range of said one of the access points and with the supply of data being resumed in response to a signal indicating that said further one of the access points is available for further transfer of data to the mobile terminal.
11. A method according to any preceding claim, wherein the access points are fixed at intervals along a path along which the mobile terminal is movable so that the mobile terminal comes within the transmitting range of each access point in sequence as the mobile terminal is moved along the path.
12. A data download system for performing the wireless download of data to a mobile terminal across a link with a relatively low data rate whilst the mobile terminal is in motion, the system comprising: a plurality of access points spaced along a path along which the mobile terminal is movable so that the mobile terminal comes within the transmitting range of each access point in sequence as the mobile terminal is moved along the path, and control means for setting up a wireless link between a first of the access points and the mobile terminal including detection of the mobile terminal by the first access point and establishing of a connection using a connection protocol, and for subsequently setting up a wireless link between at least one further access point and the mobile terminal on the basis of the connection already established between the first access point and the mobile terminal to enable the subsequent transfer of data from the or each further access point to the mobile terminal.
13. A data download system according to Claim 12, wherein the control means is arranged to set up a second wireless link between a second of the access points and the mobile terminal to enable the transfer of data from the second access point to the mobile terminal, and to set up a third wireless link between a third of the access points and the mobile terminal to enable the transfer of further data from the third access point to the mobile terminal, the second and third links being set up subsequent to the establishment of the connection between the first access point and the mobile terminal and on the basis of the connection already established between the first access point and the mobile terminal.
14. A data download system according to Claim 12 or 13, wherein the control means includes handover means for providing that, when transfer of data to the mobile terminal from one of the access points ceases, the transfer of data to the mobile terminal from a further one of the access points is initiated.
15. A data download system according to Claim 14, wherein the control means is arranged to establish a connection between the mobile terminal and said further one of the access points during transfer of data to the mobile terminal from said one of the access points and prior to initiation of the transfer of data to the mobile terminal from said further one of the access points.
16. A data download system according to Claim 14 or 15, wherein the control means is arranged to transfer the data to the mobile terminal discontinuously in a series of blocks according to a schedule, determined on detection of the mobile terminal by the first access point, allotting subsequent transfer of a respective block of the data to each of a plurality of the access points.
17. A data download system according to Claim 14 or IS, wherein the control means is arranged to transfer the data to the mobile terminal discontinuously in a series of regularly transmitted blocks, and the handover of the data transfer to said further one of the access points is initiated in response to the mobile terminal reaching the limit of the transmission range of said one of the access points.
18. A data download system according to Claim 14 or 15, wherein the control means is arranged to transfer the data to the mobile terminal substantially continuously during monitoring of the progress of the transfer by counting of the number of units of data transferred, and data transfer to said further one of the access points is initiated from the point at which the mobile terminal reached the limit of the transmission range of said one of the access points as determined by counting of the number of units of data transferred up to that point.
19. A data download system according to Claim 14 or 15, wherein the control means is arranged to transfer the data to the mobile terminal substantially continuously but with the supply of data being suspended in response to a signal indicating that the mobile terminal has reached a predetermined limit of the transmission range of said one of the access points and with the supply of data being resumed in response to a signal indicating that said further one of the access points is available for further transfer of data to the mobile terminal.
20. A data download system according to any one of Claims 12 to 19, wherein the access points are fixed at intervals along a path along which the mobile terminal is movable so that the mobile terminal comes within the transmitting range of each access point in sequence as the mobile terminal is moved along the path.
21. A method for performing the wireless download of data to a mobile terminal, substantially as hereinbefore described with reference to the accompanying drawings.
22. A data download system for performing the wireless download of data to a mobile terminal, substantially as hereinbefore described with reference to the accompanying drawings.