GB2371450A

GB2371450A - Connecting a device to the Bluetooth network

Info

Publication number: GB2371450A
Application number: GB0101571A
Authority: GB
Inventors: Rolf Gopffarth; Carmen Kuhl; Wolfgang Hansmann
Original assignee: Nokia Mobile Phones Ltd; Nokia Oyj
Current assignee: Nokia Oyj
Priority date: 2001-01-22
Filing date: 2001-01-22
Publication date: 2002-07-24
Also published as: AU2002226416A1; WO2002058328A2; GB0101571D0; WO2002058328A3

Abstract

A bluetooth device 200 and method of establishing a connection between the new device and one of a plurality of available wireless devices, wherein the latter devices have time windows during which each device is receptive to messages transmitted from the new device, i.e. in a Time division duplex (TDD) arrangement, wherein the method comprises obtaining information on the plurality of available wireless devices, determining from the obtained information, the start time of the window for each of the plurality of available devices; sending messages (paging) from the new device during the next available time window to establish a connection with the corresponding device. The bluetooth device is initially connected to BSS 206. As the device moves out of the range of BBS 206 and into the range of BBS 200, it reestablishes a connection by obtaining relevant details regarding the other neighbouring BBS's according to the Handoff Enhancement Protocol (HEP), which includes a clock reference and the address of the device.

Description

PAGING

The present invention relates to networks, and more particularly to the connection of a device to a network.

Conventional networks, for example, a network of microprocessor controlled devices such as computer, printers, etc. , have relied upon physical wire connections between each device on the network. Due to the physical nature of the connection required, conventional networks are generally perceived to be fairly rigid in nature. For example, in order to add in an additional device on the network, the additional device must be physically connected to the network, and the network server may have to be informed that the additional device has been connected.

Recently, however, has seen the emergence of wireless networks, in which the network connections are provided, typically, by a wireless radio link. One of these such networks is described in the Specification of the Bluetooth System v1. 0 B. Those skilled in the art will appreciate that other wireless networks also exist, and reference herein to Bluetooth is not intended to be limited thereto.

Bluetooth wireless technology allows users to make effortless and wireless connections between various communications devices, such as mobile phones, computers, printers etc. Bluetooth provides short-range wireless connectivity and supports both point-to-point and point-to-multipoint connections. Currently, up to seven active'slave'devices can communicate with a'master'device, to form a'piconet'. Several of these piconets can be established and linked together in ad hoc'scatternets', to allow communication among continually flexible configurations.

Bluetooth operates in the 2. 4 GHz ISM band, which is globally available although the exact width and location of the band does vary from country to country. For example, in the US and Europe, a band of 83.5 MHz width is available ; in this band, 79 RF channels spaced 1 MHz apart are defined. In some other countries, for example France, a smaller band is available having only 23 channels spaced 1 MHz apart. The channel is represented by a pseudo-random hopping sequence through available channels. The hopping sequence is unique for the piconet and is determined by the Bluetooth device address of the master device. The phase in the hopping sequence is determined by the Bluetooth clock of the master. The channel is divided into time slots where each slot corresponds to an RF hop frequency. Consecutive hops correspond to different RF hopping frequencies. The nominal hop rate is 1600 hops per second. All Bluetooth devices in a given piconet are time and frequency hop synchronised to the channel.

The master device, of which there can be only one in a piconet, initiates the connection of a slave device to the piconet. The piconet operates in a time division duplex (TDD) arrangement. In a TDD network a single packet of information is transmitted in the network at a time and the slave devices are synchronised to a common time frame by the master device. This time frame consists of a series of time slots of equal length. Normally, each data packet transmitted in the piconet has its start aligned with the start of a time slot, and (in case of single slot packets) adjacent time slots are assigned for respectively transmission and reception by the master device. When the master device is performing point-to-point communication a transmitted data packet is addressed to a particular slave device which replies to the master device by transmitting a data packet addressed to the master device in the time slot immediately following the packet sent by the master device..

A Bluetooth device may connect to an existing Bluetooth device or piconet in a number of ways. For example, the existing Bluetooth device may perform an inquiry procedure in order to identify any compatible devices within range of

the existing device. An inquiry procedure typically involves transmitting an inquiry message and waiting for any compatible devices to respond. The response from a compatible device is typically a message containing information including the device address and clock information. Once information has been gathered from compatible devices within range, the existing device may establish a connection to any suitable devices by performing a page procedure directed towards a previously identified device.

Further details regarding page and inquiry procedures can be found in the Bluetooth standards.

The inquiry and paging procedures takes a finite length of time to perform, and thus the speed in which a device can be connected to an existing device is determined by the speed at which the inquiry and paging procedures can be performed.

In static configurations, the current arrangements provide adequate performance. For example, when a laptop computer wirelessly connects to a printer it is usual for both the printer and the laptop computer to be static. The inquiry and page procedure takes a short amount of time to perform, and once connected the connection remains in place as long the printer and laptop computer remain in range of one another. In this example, the length of time taken to establish a connection is very short compared to the length of time the connection is maintained.

Handover functionality for already established links has to be supported when providing connections to backbone networks via access points. Due to the limited range of Bluetooth devices and a high mobility among the connected devices, handovers will occur quite frequently. As a result, mechanisms for providing fast connection re-establishment are required.

Accordingly, one aim of the present invention is to improve connection times of wireless devices.

According to a first aspect of the present invention there is provided a method of connecting a new device to one of a plurality of available wireless devices, wherein each of the plurality of wireless devices has a time window during which each device is receptive to messages transmitted from the new device, the method comprising: obtaining information on the plurality of available wireless devices; determining, from the obtained information, the start time of the window for each of the plurality of available devices; sending messages from the new device during the next available time window to establish a connection with the corresponding device.

According to a second aspect of the present invention there is provided 9. a device for connecting to one of a plurality of available wireless devices, wherein each of the plurality of wireless devices has a time window during which each device is receptive to messages transmitted from the new device, comprising: a receiver for receiving information on the plurality of available wireless devices; a processor for determining, from the obtained information, the start time of the window for each of the plurality of available devices; a transmitter for sending messages from the new device during the next available time window to establish a connection with the corresponding device.

In our, as yet, unpublished co-pending patent application number US 09/396691 annexed hereto and incorporated herein by reference, proposals have been made to attempt to speed up connection times. For example, the annex describes techniques, herein referred to as Handoff Enhancement Protocol (HEP), in which information is gathered regarding address and timing from other nearby access points and compatible devices. Since the information regarding available devices has already been obtained, connection times can be reduced since it is not necessary to perform an inquiry procedure prior to performing a page procedure.

The invention will now be described, by way of example only, with reference to the accompanying diagrams, in which : Figure 1 is a diagram showing a Bluetooth device connected, according to the prior art, to a base station; Figure 2 shows an embodiment according to the present invention; Figure 3 shows an example paging sequence; Figure 4 is a flow diagram showing a paging procedure carried out according to the present invention; Figure 5 is a block diagram of an embodiment of a device in accordance with the present invention.

Figure 1 is a diagram showing a Bluetooth device 100 which is connected, according to the prior art, to a Bluetooth Base Station (BBS) 102. The BBS is effective substantially within the range 104 indicated and, for example, may act as an access point to a backbone network (not shown). According to the prior art, the device 100 has no knowledge of the existence or whereabouts of the other BBS devices 106 and 110. As the device moves towards the range 108 of BBS 106, the device 100 will lose contact with BBS 102. As previously indicated, the device 100 then has to establish a connection with BBS 106 by performing both an inquiry and a page procedure. This can be quite time consuming.

As previously mentioned, connection times can be improved using the techniques described in the Handoff Enhancement Protocol (HEP). Referring to Figure 1, BBS 102 would also gather information relating to neighbouring devices, such as BBS 106. By passing this information on to the device 100, when the device 100 moves out of range of BBS 102 it can simple perform a paging procedure using the already known address of BBS 106. In this way, connection time is reduced since only a paging procedure is required to be performed. However, the paging procedure can still be a lengthy procedure.

When a master device performs a page procedure, in order to initiate a connection, the master device pages the device to which it wishes to establish a connection. Paging consists of transmitting a recognised message to the device and waiting for an acknowledgement to be transmitted from the device to the master device. The device being paged, however, is only receptive to the paging message at certain times. Therefore, the master device typically transmits a series of paging messages, over a number of different frequencies, such that the device being paged will receive at least one of the paging messages. Typically devices are receptive to paging messages only at certain times. In Bluetooth this period is referred to as a'page scan window', and further information can be found in the Bluetooth standard.

Depending on when the page scan occurs in the device being paged, the master device may have to transmit many paging messages before the device being paged enters the page scan period and is receptive to paging messages. This can add considerable delay to the connection process. In addition to this, a time-out period is defined after which time, if no response is made by the device being paged, it is assumed that the device being paged is out of range of the master device. If a page procedure times out (currently 5.2 seconds according to the Bluetooth standards), the master device attempts to establish a connection with an alternative device, either by performing a new inquiry procedure and a new paging procedure, of by attempting to page a device the address of which was previously obtained by an inquiry or HEP procedure.

As previously mentioned, the inquiry procedure to retrieve nearby Bluetooth base station device addresses contributes to the delay experienced in the connection set-up process. The information obtained using the above described HEP removes the requirement to perform an inquiry procedure, since the HEP provides a list of nearby base stations.

Figure 2 shows an embodiment according to the present invention. A Bluetooth device 200 is initially connected to BBS 206. As the device 200 moves out of the range of BBS 206 and into the range of BBS 202, the device 200 must re-establish a connection. As previously described, the device 200 obtains the relevant details regarding the other neighbouring BBS's according to the HEP.

The information obtained from according to the HEP includes a clock reference and the address of the device. The present invention determines the time of the next page scan for each of the available devices based on the clock reference for that device and the particular page scan window parameters. The list of available devices is then sorted into order of the available page scans, as shown in Table 1 below.

BBS-device Time of next Index Duration of Clock number page scan time scan reference 2 t2 i2 d2 Ox68a326 1 ti1i di0x21 fe98 3 t3 i3 d3 0x4703dc TABLE 1-Sorted details list The duration of the time scan is used to determine if any of the time scan periods overlap, and any overlapping page scans are removed from the list, leaving the page scan with the earliest start time.

This procedure can be performed by an internal microprocessor (not shown) of the paging device.

Once the table is produced, a paging procedure can be carried out according to the flow diagram shown in Figure 4. Initially, according to a first step 400,

the first device in the sorted list is paged. As the time of the next page scan has been determined this greatly improves the chance that the page procedure will coincide with the page scan procedure of the device being paged, greatly improving the chance of a connection being made (assuming the paged device is within range). If the page is successful (step 402) a connection with the device is established (step 406). If the page is unsuccessful, the next device in the list is paged (step 404). If after all the devices in the list have been unsuccessfully paged, the whole algorithm is repeated. It should be noted that the frequency at which paging messages are transmitted are readily derivable, as will be appreciated by those skilled in the art, from the clock information.

The paging sequence based on the sorted HEP information is shown in Figure 3. The first available page scan is for BBS 202 of Figure 2. Although the first available page scan is actually for BBS 206, this device is not paged since it is the device with which the device 200 has just lost contact. The next device to be paged, in the event that BBS 202 does not respond, is therefore BB 210.

Figure 5 is a block diagram of an embodiment of a device in accordance with the present invention. A device 500, such as a Bluetooth device, is shown with a transceiver, for example a Bluetooth transceiver, for communicating with other Bluetooth devices in a manner as described above. Such a transceiver is capable of performing all the functions necessary to communicate with other, for example, Bluetooth devices, as will be appreciated by those skilled in the art. The transceiver 502 also performs the functionality of both a receiver and a transmitter. Additionally, a microprocessor 504 may communicate with the Bluetooth transceiver 502 in order to control the Bluetooth transceiver in accordance with the present invention. Alternatively, the functionality of the microprocessor 504 may be incorporated into the Bluetooth transceiver 502. The microprocessor 504

performs the steps as shown in Figure 4 in order to control the Bluetooth transceiver 502, thereby providing advantageously quicker connection times. The present invention therefore allows the connection time to be greatly reduced compared to the previous techniques. By actively determining the order in which page scans occur removes the delays incurred by performing a page procedure outside of the page scan window. As Bluetooth devices become increasingly mobile, reductions in connection times become increasingly important.

Claims

CLAIMS :

1. A method of connecting a new device to one of a plurality of available wireless devices, wherein each of the plurality of wireless devices has a time window during which each device is receptive to messages transmitted from the new device, the method comprising: obtaining information on the plurality of available wireless devices; determining, from the obtained information, the start time of the window for each of the plurality of available devices; sending messages from the new device during the next available time window to establish a connection with the corresponding device.

2. The method of claim 1, wherein the step of obtaining information further comprises obtaining clock information.

3. The method of claim 1 or 2, wherein the step of obtaining information further comprises obtaining address information.

4. The method of any preceding claim, further comprising creating a list of start times for each device from the obtained information, wherein the list is sorted according to earliest start time.

5. The method of claim 4, further comprising removing any start times which overlap with an earlier window.

6. The method of any preceding claim, wherein the step of sending messages comprises sending paging messages.

7. The method of claim 4,5 or 6, wherein the sending messages is schduled in accordance with the created list, and where connection is not established

with a device, sending messages to the device having the next available start time.

8. The method of any preceding claim, wherein the devices are Bluetooth devices.

9. A device for connecting to one of a plurality of available wireless devices, wherein each of the plurality of wireless devices has a time window during which each device is receptive to messages transmitted from the new device, comprising: a receiver for receiving information on the plurality of available wireless devices; a processor for determining, from the obtained information, the start time of the window for each of the plurality of available devices; a transmitter for sending messages from the new device during the next available time window to establish a connection with the corresponding device.

10. The device of claim 9, wherein the receiver is adapted to receive clock information.

11. The device of claim 9 or 10, wherein the receiver is further adapted to receive address information.

12. The device of any of claims 9 to 11, wherein the processor creates a sorted list of start times for each device from the obtained information, wherein the list is sorted according to earliest start time.

13. The device of claim 12, wherein the processor removes any start times which overlap with an earlier window.

14. The device of any of claims 9 to 13, wherein the transmitter transmits paging messages.

15. The device of claim 12,13 or 14, wherein the transmitter transmits messages in accordance with the created list, and wherein where connection is not established with a device, transmitting messages to the device having the next available start time

16. The device of any of claims 9 to 15, wherein the devices are Bluetooth devices.

17. A device for connecting to a plurality of available wireless devices operating in accordance with the method of claims 1 to 8.

18. The device of claim 17, wherein the device is a Bluetooth device.

19. The device of any of claims 9 to 18, operating according to the method of any of claims 1 to 8.

20. A system for connecting a new device to one of a plurality of available wireless devices, comprising a device of any of claims 9 to 19.

21. A system for connecting a new device to one of a plurality of available wireless devices, substantially as hereinbefore described with reference to any one or combination of Figures 2,3 and 4.

22. A method of connecting a new device to one of a plurality of available wireless devices, substantially as hereinbefore described with reference to any one or combination of Figures 2,3 and 4.

23. A device for connecting to one of a plurality of available wireless devices, substantially as hereinbefore described with reference to any one or combination of Figures 2,3 and 4.