WO2005050930A1

WO2005050930A1 - Method and device for connection of devices by means of a wireless ad-hoc communication network

Info

Publication number: WO2005050930A1
Application number: PCT/EP2004/053050
Authority: WO
Inventors: Michael Finkenzeller; Matthias Kutschenreuter
Original assignee: Siemens Aktiengesellschaft
Priority date: 2003-11-24
Filing date: 2004-11-23
Publication date: 2005-06-02

Abstract

The invention relates to a method for the connection of two or more devices by means of a wireless communication channel. In one embodiment the method comprises the steps: arbitrary allocation of a first state (INQUIRY), or a second state (INQUIRY SCAN) to the first device (1), in the first state, the first device (1) attempts to establish a connection to the second device (2) and in the second state, the first device (1) itself remains in a state of readiness for connection to the second device (2) with exchange of the present state of the first device (1) between the first and the second states, said exchange between the first and the second states occurring at fixed time separations, either until a particular period of time has expired, or until a connection to the second device is established, the time periods in which the first device (1) remains in the first or the second states being fixed. In a second embodiment a method for incorporation of a number of devices in a communication network is given.

Description

description

Method and device for connecting devices via an ad hoc wireless communication network

The invention relates generally to communication networks and, more particularly, to a method for connecting two or more devices in an ad hoc wireless communication network.

Bluetooth is a well-known technology used to connect portable electronic devices, e.g. Mobile phones, headsets, PDAs and laptop computers over short distances (approx. 10 m) were developed. However, it can also be used in fax machines, printers, toys, digital cameras, household appliances and almost all other digital devices or applications. The technology essentially represents a mechanism for forming small wireless networks between devices equipped with Bluetooth technology on an ad hoc basis. It can also serve as a wireless communication bridge to existing data networks. In conventional implementations, devices equipped with Bluetooth technology automatically search for one another and configure themselves in the networks, which often consist of just two nodes.

At present, up to eight devices with Bluetooth technology can automatically configure themselves in a so-called "piconet". Each piconet has a so-called "master", which imposes a frequency hopping pattern on the other nodes or devices that act as so-called slaves. A piconet differs from other similar networks in the vicinity by its unique frequency hopping sequence. Since each piconet executes a different frequency hopping sequence, several piconets can co-exist side by side in a common area. The Bluetooth specification, as set out in "Specification on Bluetooth System, Version 1.1, February 22, 2001 core", and the content of which is incorporated by reference in this description, defines the Bluetooth point-to-point connection establishment as a two-step process. If Bluetooth devices have no knowledge of their neighbors, they first have to carry out a so-called inquiry procedure to determine the neighborhood information, such as nodes and synchronization information. If neighborhood information is available, a so-called paging procedure is subsequently carried out in order to establish the actual connection between the devices.

The inquiry and paging procedures have an asymmetrical connection establishment protocol, which essentially comprises two types of units or devices:

- Inquiring units, which try to find neighboring units and to connect with them and

- Inquired units that are available to be found and make themselves available for connection to an Inquiring unit.

After Bluetooth, the following basic states for locating neighbors and establishing a connection are supported.

- Inquiry: The inquiry state is used to determine the identity of Bluetooth devices within the radio range. The tracking device or device collects addresses of Bluetooth devices from all devices that respond to an inquiry message.

- Inquiry scan: In this state, the Bluetooth devices "listen" for inquiries from other devices. - Page: This state is used by an inquiring unit or an inquiring device that has found other devices through the inquiry procedure.

- Page scan: In this state, a unit listens for its own "Device Access Code (DAC)" for the duration of a specified scan period.

- Connection: As soon as this state is reached, one device is the master and the other device is the slave. In this

The devices can exchange data packets.

- Standby: Standby is a state in a Bluetooth device with low power consumption. In this state there is no interaction with other devices.

The establishment of a connection between two Bluetooth devices and its timing according to the Bluetooth specification can be found, for example, in the description of FIG. 1 of US 2003/0096576 AI.

According to the Bluetooth specification, it is not clearly defined according to which scheme a Bluetooth device switches to an inquiry or an inquiry scan mode. So that two devices can find each other and establish a connection, one of the two devices must be in inquiry mode and the other in inquiry scan mode at the same time. In the case of an existing Piconet (or a so-called Scatternet) with one (or more) masters, the master occasionally switches to inquiry mode in order to connect new devices to the existing network. A random shift in the time after which the master changes to inquiry mode prevents a potential slave from switching between inquiry and inquiry scan synchronously with the searching master. In the event that there is no network and there is still no master, the device that is currently in inquiry mode when the connection is established is first set to page mode and then sets the master after the connection has been established Along with this, the device, which is in the inquiry scan mode, takes over the page scan mode and then becomes a slave of the network.

A fundamental endeavor when establishing a Bluetooth network is to establish the connection between two devices as quickly as possible. In principle there are two methods for finding Bluetooth devices.

According to the first variant, a master is statically configured, while all other devices are slaves. When starting a device, it must be specified whether it is a master or a slave. This procedure is not desirable in itself, since a user needs information about the network to be set up for the decision. For example, configuration as a slave only makes sense if there is already a master that can connect to this slave. The goal, however, is for Bluetooth devices to connect completely autonomously, while the user does not have to make any configuration.

In another variant of the connection establishment, there is a dynamic change between inquiry mode and inquiry scan mode, the change between these two modes occurring at random. Such a procedure is carried out, for example, in the already mentioned US 2003/0096576 AI. Free nodes, that is, Bluetooth devices, try to establish a connection alternately by means of inquiry and inquiry scan. This change occurs with a probability distribution, either until a predetermined time period has elapsed or until a connection to a device has been established. A similar procedure is described in the article "Efficient Pattern Formation Algorithm ^' for Dynamic Environments, G. Tan, A. Miu, J. Guttag and H. Balakrishnan, MIT Laboratory for Computer Science". Free nodes or Bluetooth devices try to establish a connection alternately using the inquiry and inquiry scan mode. The time periods are equally distributed in an interval between an average connection establishment time E (t) and a multiple thereof, preferably 3.8 E (t). A value that is greater than E (t) and less than or equal to 3.8 E (t) is selected at random.

It is an object of the present invention to provide a method and a device which enable the autonomous construction of a Bluetooth network in a shorter period of time than in the prior art.

These objects are achieved with the methods of claims 1 and 2 and the devices with claims 13 and 14. Advantageous refinements result from the dependent claims.

The methods and devices of the present inventions provide a protocol for locating and establishing a connection between two or more devices, in particular devices suitable for Bluetooth, which are improved compared to conventional procedures. With the present invention, a plurality of Bluetooth devices can select one another and automatically configure themselves in complex network structures. The process starts with nodes or Bluetooth devices that have no knowledge of theirs

Environment have and ultimately results in the formation of a network that meets the requirements specified in the Bluetooth specification.

In a first variant, the method according to the invention for connecting a first device to a second device via a communication channel comprises the steps of arbitrary assigning a first state or a second state to the first device, the first device in the first state trying to establish a connection with the second device and the first device in the second state itself for a connection to the second "Device provides; switching a current state of the first device between the first and second states; and switching between the first and second states occurs at fixed time intervals, either until a certain period of time has expired or until a connection to the second The method for establishing a connection between a plurality of devices via at least one wireless communication channel comprises an arbitrary assignment of a device to the device, the time periods within which the first device remains in the first or second state being fixed first state or a second n state of each of the devices, one device in the first state trying to connect to one of the other devices, and one device in the second state making itself available for connection to one of the other devices; Switching a current state of one of the devices between the first and second states; and the switching between the first and the second state occurs at fixed time intervals, either until a predetermined time period has expired or until a connection is established with one of the other devices, the periods of time within which the devices remain in the first or second state, are fixed.

In this way, a connection or a connection can be established without explicitly assigning an initial state to one of the participating Bluetooth devices.

As will become clear from the following description, the connection establishment between two nodes can It takes place at random time intervals compared to a change between the first and the second state. It is particularly advantageous here if the first state and the second state each last a first time period or a second time period. The second time period is preferably the product of the first time period with a first factor. The first factor must be greater than 1 so that the second period is longer than the first period. The first factor preferably takes on values between 2.5 and 7.5 inclusive, and is in particular equal to 3.

It is further preferred if the first time period is the maximum time period necessary to establish a connection between the first device and the second device. If two Bluetooth devices are in range, one of which is in inquiry mode and the other is in inquiry scan mode, then it takes a certain time for the device to respond to the inquiry due to the specified Bluetooth protocol. Mode has collected enough information about the other device and a connection is being established securely. This time represents the maximum time required to establish a connection between the first and the second device.

According to the Bluetooth standard, this time is a maximum of 10.24 seconds if no transmission errors occur. This value results from the fact that a Bluetooth device in inquiry scan mode must carry out an inquiry scan at least every 2.56 seconds in accordance with the standard. If inquiry scans are carried out at shorter time intervals, the first time period could also be shorter than the maximum time required to establish a connection between the first and the second device. According to the Bluetooth specification, an inquiry mode can also be terminated prematurely if enough Bluetooth devices are found.

The statistically shortest time for establishing a connection can be realized if the first factor is 3, the second time period therefore corresponds to three times the maximum time required to establish a connection between the first and the second device. This is the minimum amount of time that is necessary to securely connect to another Bluetooth device that switches between the first and the second state with a time period that corresponds to the first time period. If the second time period were slightly shorter, a connection establishment would no longer be guaranteed in any case, so that the time for the connection establishment would be statistically extended.

Within the specified range of the first factor between 2.5 and 7.5 inclusive, times for the connection establishment can nevertheless be realized, which are considerably better than in the random procedures known from the prior art.

A further improvement in the speed of the connection setup can be achieved if the probability with which the first state and / or the second state lasts for the first time period is a second factor. The second factor represents a probability value and preferably takes values between 0.2 and 0.8 inclusive. The probability factor only determines whether, with a certain probability, the first state lasts for a first time period or a second time period. The same applies to the second state.

This procedure is advantageous in the case where there is no network yet. This procedure therefore has a particularly advantageous effect on the first step in setting up a Pico or Scatternet. If one were to change only in a fixed rhythm, it could happen that two (or even more) Bluetooth devices are within range and the respective slave and master phases are synchronous. Since only a master can connect to a slave, not a slave with a slave or a master with a master, the devices could not connect in such a situation. The method would not create a network in such a case.

It has proven to be particularly advantageous if the second factor assumes the value 0.5.

According to the invention, the first state represents an inquiry mode and the second state represents an inquiry scan mode. The latter is a mode in which inquiry scans are carried out periodically. An inquiry scan takes just a few milliseconds.

The invention further comprises devices for setting up a connection of a first device to a second device or between a plurality of devices via a wireless communication channel, with at least one processor, which is each set up to carry out the methods described above. These devices have the same advantages as described above in connection with the method.

The invention also proposes respective computer program products which can be loaded directly into a memory of a processor of a device for establishing a connection between a first device and a second device or between a plurality of devices via a wireless communication channel and which each comprise software code sections, with which the procedures described above can be carried out when the product is running on one of the devices.

The invention and its advantages are described below with reference to the following figures. Show it:

FIG. 1 shows a flow chart for establishing a connection between a plurality of Bluetooth-compatible devices according to the invention, FIG. 2 shows a representation in which two Bluetooth devices switch between the first and the second state synchronously,

FIGS. 3 and 4 representations on the basis of which the interpretation of a preferred time period of a state can be recognized, and

Figure 5 is a schematic representation of a typical Bluetooth-enabled device, including a processor and other components.

The flowchart in FIG. 1 shows the method according to the invention for connecting a first device to a second device via a wireless communication channel. If a first Bluetooth-enabled device is switched on, it either assumes an inquiry or an inquiry scan mode. In the present exemplary embodiment, the first device is in inquiry scan mode, reference number 10. In this, it tries to connect to another, second device in its range, which is in inquiry mode. This second device could be a master of a Pico or Scatternet. The duration of this first inquire scan phase is T _ma χ_in _q . During this time, the device carries out an inquiry scan periodically, at the latest every 2.56 seconds. The time period T _max _i _n q is the maximum time required to establish a connection between two Bluetooth devices in a fault-free environment in accordance with the Bluetooth specification. If two Bluetooth devices are in range, one of which carries out an inquiry and the other carries out an inquiry scan, then it takes a certain time for the device to collect enough information about the other device in inquiry mode due to the Bluetooth protocol has and a connection is established securely. This time is called T _max _i _nq . If none According to the Bluetooth standard, transmission errors occur at most 10.24 seconds.

If another, second device is within range of the first 5 device, the second device being in inquiry mode, a connection is established between them, reference numerals 12 and 14. The method ends at this point, reference number 16.

10 If there is no device within range of the first Bluetooth-enabled device, the latter changes its state and, in the present exemplary embodiment, switches to inquiry mode, reference number 18. In this inquiry mode, the first device tries to contact a further, third device.

15 carries out periodic inquiry scans during the same period. This further, third device can be, for example, the slave of a Pico or Scatternet. The duration of this inquiry phase has the value T _max _ _inq with a probability p and the value with the probability 1-p

Z u X ^• 1max_inq •

The random decision between T _max _i _nq and x * T _max _ _inq is important for the case in which there is no Bluetooth network yet, _i.e. for the first step in setting up a Pi

25 co or scatternets. If one only changed in the rhythm T _max _ _inq , the case could _arise that two (or more) devices are within range of one another, but their slave and master phases are synchronous. This case is shown in FIG. 2, in which constellation a connection establishment between device 1 and device 2 is not possible. This is because only one device in inquiry mode can connect to one device in inquiry scan mode, but a connection between devices in inquiry scan mode or devices in inquiry mode is not possible. The algorithm would not create a network in this case. The change in the time periods between T _max _ _inq and xT _raax _ _inq based on a random decision thus prevents such a situation.

The probability value p can be set once for the duration of the entire method and then retained. The second factor (probability factor) p preferably takes on values between 0.2 and 0.8 inclusive. The second factor p = 0.5 is particularly preferred.

In the case of the proposed method, it can happen that two potentially connectable devices change randomly into the same phases of the same lengths. As long as this happens, the devices cannot connect. The probability with which this happens and the probable duration of this state depends on the probability p with which a phase of length xT _max _inq is selected. The probability for a phase of length x * Tmax_inq is then 1-p. This can be used to determine the probability that the two devices are not yet connected after n phase changes:

This value becomes minimal for p = 0.5 and is -. With this probability value, the fastest way to establish a connection is on average. In the proposed method, therefore, there is preferably a switch between the long and the short phase with a probability of 0.5.

Returning to FIG. 1, a decision is made in the next method step (reference number 20) whether a device in inquiry scan mode is within range of the first device which is currently in inquiry mode (reference number 18). If this is the case, a connection is established again (Reference number 14) and the method ends at this point (reference number 16).

If there was no device in the inquiry scan mode in the vicinity of the first device, this in turn changes back to the inquiry scan mode, reference number 22. The duration of this phase is, with a probability p T _max _j_ _nq and with a probability 1 -ρ xT _raax _ _irιq .

If another device is found that is currently in inquiry mode, a connection is set up and the method ends, reference numerals 14 and 16. In the other case, there is again a change to inquiry mode, reference number 18. From this point onwards, inquiry and inquiry scan phases are alternated continuously until a connection is established. The phases either last for each J-max_inq O er X ^• T _max _i _nq .

In order to enable the fastest possible construction of the invention between two Bluetooth-compatible devices, it is preferred if the first factor x is greater than 1, more preferably between 2.5 and 7.5 inclusive and in particular x = 3.

The selection of this preferred value x = 3 can be illustrated with reference to FIGS. 3 and 4. During a period of length 3-T _max _ _inq , one device securely connects to another that changes in the T _max _i _nq rhythm, see FIG. 3. If the phase is only slightly shorter, a connection establishment is not guaranteed at this time. as can be seen from Figure 4. In this representation it follows that the slave phases of the second device, designated t _v ι and t _v2 , are not completely in the 2, 8 • t _max _j. _n q overlap the permanent master phase of device 1. A connection establishment is therefore not secured.

If a Piconet or a Scatternet exists and a master is currently carrying out an inquiry, it takes T _max _ _inq to a connection is established safely. If no master, but a slave is ready to establish a connection, it takes 2'T _max _ _inq until the connection is established. If there is no network, but two devices try to establish a connection according to the above algorithm, the connection is established on average 3, 3 • T _max _ _inq after the second device has switched on.

FIG. 5 shows a schematic representation of a general hardware architecture of a typical Bluetooth-capable device 1, 2, 3 for executing various functional component modules in accordance with the Bluetooth protocol. The device 1, 2, 3 can have a processor 5, a memory 6 and, for example, input / output device 7. The term processor, as used in this description, is intended to refer to all types of processors, e.g. digital signal processors, microcontrollers and other circuits. The term memory as used in this description includes memory that is made available to the processor 5, such as e.g. a random access memory (RAM), read-only memory (ROM), a permanent storage device (eg a hard disk), a removable storage device (eg a floppy disk or a memory chip), flash memory, etc. The term input / Output device may include a keyboard, mouse or other for inputting data into the processor 5. It can also include a display device or a printing device for displaying results of the processor.

In the memory 6, portions of software code, including instructions or codes for performing the method of the invention as described, may be stored in one or more of the attached memory devices and may be executed in whole or in part by the processor. The method according to the invention has the advantage that possible connections are established securely. The time until a connection is established can vary statistically, but a fixed probability value, which is preferably p = 0.5, but minimizes the expected value of this distribution and thus the time until the connections are established. The procedure is completely distributed, which means that each device follows the same algorithm and starts without information about any neighboring devices. There is therefore no outstanding device that takes on the function of a coordinator.

Claims

claims

1. Method for connecting a first device (1) to a second device (2) via a wireless communication card

^■ 5 nal (4), with the steps: ^■ arbitrarily assigning a first state or a second state to the first device (1), the first device (1) in the first state trying to establish a connection with the second device ( 2) build, and being the first

10 device (1) in the second state itself for a connection to the second device (2); Switching a current state of the first device (1) between the first and the second state, that is to say, that

15 the switching between the first and the second state takes place at fixed time intervals, either until a predetermined time period has expired or until a connection is established with the second device (2), the periods of time within which the first device (1) in which first or

20 second state remains, are fixed.

2. A method for establishing a connection between a plurality of devices (1, 2, 3) via at least one wireless communication channel (4), comprising the steps: 5 arbitrarily assigning a first state or a second state to each of the devices (1, 2 , 3), wherein a device in the first state tries to establish a connection with one of the other devices, and wherein a device (1, 2, 3) in the second state tries to connect itself to one of the other devices (1 , 2,3) is available; Changing a current state of one of the devices (1, 2, 3) between the first and the second state, characterized in that the switching between the first and the second state takes place at fixed time intervals, either until a predetermined time period has expired or until a connection is established with one of the other devices (1,2,3), the Time periods within which the devices (1, 2, 3) remain in the first or second state are predefined.

3. The method of claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the first state and the second state each last a first time period (tl) or a second time period (t2).

4. The method according to claim 3, so that the second period (t2) is the product of the first period (tl) with a first factor (x).

5. The method of claim 3 or 4, d a d u r c h g e k e n n z e i c h n e t that the first factor (x) is greater than 1.

6. The method according to any one of claims 3 to 5, so that the first factor (x) assumes values between 2.5 and 7.5 inclusive.

7. The method according to any one of claims 3 to 6, d a d u r c h g e k e n n z e i c h n e t that the first factor x = 3.

8. The method according to any one of claims 3 to 7, so that the first time period is the maximum time required to establish a connection between the first device (1) and the second device (2).

9. The method according to any one of the preceding claims, characterized in that the probability with which the first state and / or the second state lasts the first time period (tl) is a second factor (p). IS

10. The method of claim 9, d a d u r c h g e k e n n z e i c h n e t that the second factor (p) assumes values between 0.2 and 0.8 inclusive.

11. The method according to claim 9 or 10, d a d u r c h g e k e n n z e i c h n e t that the second factor p = 0.5.

12. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the first state is an inquiry state and the second state is an inquiry scan state.

13. Device for setting up a connection of a first device to a second device via a wireless communication channel (4), with at least one processor (5), which is set up (i) arbitrarily a first state or a second state to the first device assign (1), wherein the first device (1) attempts in the first state, a Verbin ^¬ dung with the second device to establish (2), and wherein the first device (1) binding in the second state even for a comparison with the second device (2); (ii) to change a current state of the first device (1) between the first and second states; and (iii) alternate between the first and second states at fixed intervals, either until a predetermined period of time has elapsed or until a connection is established with the second device (2), the periods of time within which the first device in the first or second state remains, are fixed.

14. Device for establishing a connection between a plurality of devices (1, 2, 3) via at least one wireless sen communication channel (4), with at least one processor (5) which is set up to (i) arbitrarily assign a first state or a second state to each of the devices (1, 2, 3), a device (1, 2 , 3) in the first state tries to establish a connection with one of the other devices (1, 2, 3), and one device (1, 2, 3) in the second state tries to connect itself to one of the other devices (1,2,3) provides; (ii) to change a current state of one of the devices (1, 2, 3) between the first and the second state; and (iii) to switch between the first and the second state at fixed time intervals, either until a predetermined time period has expired or until a connection is established with one of the other devices (1, 2, 3), the time periods being within to which the devices (1, 2, 3) remain in the first or second state are predefined.

15. A computer program product which can be loaded directly into a memory of a processor of a device for establishing a connection between a first device and a second device via a wireless communication channel (4) and comprises software code sections with which the steps according to claim 1 can be carried out if the product runs on one of the devices.

16. Computer program product which can be loaded directly into a memory of a processor of a device for establishing a connection between a plurality of devices (1, 2, 3) via at least one wireless communication channel (4) and comprises software code sections with which the steps can be executed according to claim 2 when the product runs on one of the devices.