GB2354386A - Distance measurement in a communication network - Google Patents

Abstract

The distance between the user of an electronic device (for example, a mobile telephone) at point A and a target destination at point H, is determined using a network of electronic devices (C to G), each provided with short range radio communication means. The method comprises transferring data packets from one device to the next from point A to a transceiver 210 located at point H, then determining the number of 'hops' of the signal, each hop defining a distance value, and summing the distance values to obtain an estimated value of the total distance between the points. The method may be repeated using different routes, with either a mean value or the smallest value being used as the distance determination. The network of devices may comprise static beacons or mobile devices. The method may be used to provide a low-cost system which can be used indoors, and may be particularly useful as a tool for blind or visually impaired people moving around unfamiliar locations.

Description

2354386 METHODS AND ARRARGE24ENTS IN A TELECOMWNICATIONS SYSTEM

FIELD OF INVENTION

The present invention relates to location positioning systems. More specifically, the present invention relates to a method and arrangement providing a user of an electronic device, such as a mobile telephone or a handheld computer having a short-range radio device, with an approximate estimate of the distance to certain points in the environment.

DESCRIPTION OF RELATED ART

Today, distance measurement using radio is performed by using system for navigation and positioning such as GPS (Global Positioning System). The measurement is also performed by checking cell identities in cellular radio networks, and by measuring positions in such cells.

According to US 5,525, 999, the Global Positioning System (GPS) includes 24 satellites orbiting the earth at a-round 20,000)an. The 24 satellites are distributed so that four satellites reside in each of six orbital planes which roughly form north-south orbits at around 55 degrees inclination from the equator. Each satellite traverses its orbit in approximately 12 sidereal hours. The satellites use spread spectrum techniques to repetitively transmit their versions of the current time, their current ephemeris data, and their identification numbers (SVIDs).

A problem with the existing GPS-systems is that the user must be provided with a receiver, specially constructed for this purpose and expensive.

2 Another problem with the existing GPS-system is that it requires free sight. Thus, GPS is not suitable for usage in urban areas and cannot be used indoors.

Furthermore, a mobile using the GPS-system. must contact at least thrie satellites in order to provide an accurate 2D position.

According to US 4,701,934, any user of GPS, anywhere on the globe, can derive precise navigation information including 3-dimensional position, velocity and time of the day.

Navigation fixes using GPS are based on measurements of propagation delay times of GPS signals broadcast from the orbiting satellites to the user. Normally, reception of signals from 4 satellites is required for precise location determination in 4 dimensions (latitude, longitude, altitude, and time). Once the receiver has measured the receptive signal propagation delays, the range to each satellite is calculated by multiplying each delay by the speed of light. Then the location and time are found by solving a set of four equations incorporating the measured ranges and the known locations of the sa ' tellites. The highly precise capabilities of the system are maintained by means of on-board atomic clocks for each satellite and by ground tracking stations, which continuously monitor and correct satellite clock and orbit parameters.

GSM based positioning is used to geographically locate mobile phones and to distribute the positioning information to different applications. All existing mobile p hones can potentially be positioned since no changes are needed in the telephone itself. Positioning is currently undergoing standardization. Activities are taking place within ETSI, and derived by TlPl. It will be applicable for GSM 900, DCS 3 1800 as well as the PCS 1900. Positioning is likely to be implemented in other standards.-as well in the future.

In WO 98/15150, filed September 1996, by applicant, is disclosed a method and an apparatus in a cellular mobile telecommunication system, primarily the GSM system, to determine the geographical position of a mobile station. The distance between the mobile station and a radio base station is estimated from the propagation delay. The propagation delay is determined according to the method according to WO 98/15150, wherein the mobile station is sending access bursts to the base station which measures the access delay of the arrived bursts in the same way as an ordinary handover. The access signal is received at the base station delayed in relation to the internal signal burst arrival schedule of said base station. The time delay is measured and recorded in said base station. The recorded time delay corresponds to the wave propagation time of a signal that reciprocates between the base station and the mobile station. No confirmation on received access bursts is sent from the base station to the mobile station and therefor the handover attempt is terminated. The connection between the mobile station and the previous base station is reestablished. The measured access delay is proportional to the propagation delay and thereby also to the distance to the mobile station. The mobile position can be determined with good accuracy if values from at least three base stations are obtained, although with less accuracy if only two values are obtained. In addition, an access delay measured by earlier known methods can be used together with measurement achieved with the method according to W98/15150 to determine the mobile position.

in WO 98/36590, filed January 30, 1998 assigned to Telefonaktiebolaget LM Ericsson (publ) by Bergkvist et al., is disclosed an arrangement and a method for transferring 4 information in a telecommunication system including a mobile telecommunication system. The method according to wo 98/36590 relates to sending to an unknown switching center that serves a given mobile station a command concerning said mobile station. The command is sent by using previously known short message service, e.g. SMS in the GSM-system. The comaiand may constitute a request for the switching center to determine the position of the mobile station, and is sent from a positioning node outside the mobile communication system. WO 98/36590 also relates to a method of sending data from the switching center to the positioning node. The invention also relates to a switching center and to a system for carrying out the method.

In US 5,187,485, filed May 6, 1992 assigned to the United States of America by James et al, is disclosed a method for passively measuring the range to a target, using four GPS satellites -as radiation sources, and a GPS receiver at the observation station to form a bistatic radar system, wherein an angle of arrival of the target to the observation station has been measured first and wherein the delay times from the reflected signal of the target can be measured, the position of the target can be calculated. Four simultaneous nonlinear equations from the four 'satellites are used. The trace of the position of the target forms ellipsoidal surfaces with respect to the four satellites and the observation station. The point where the ellipsoidal surfaces intercept represent the position of the target. If only the distance between the target and the observation station is of interest, this distance can be estimated easily.

SUMiARY OF THE INVENTION The term -comprises/comprisingff when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The problem solved as disclosed in this disclosure is to 5 provide a system that is able to determine the distance between a user of an electronic device and a target.

Another problem solved as disclosed in this disclosure is to define the actual position of a user.

A further problem solved as disclosed in this disclosure is 10 to provide a low cost system solving the above mentioned problems.

in the inventive solution to the above mentioned problems, the user of the electronic device and the target are each provided with a short range radio transceiver. Between the user and the target, there is a set of devices, each device being provided with a short range radio transceiver. The items provided with a short range radio transceiver form a communication network to be used by the user. The user uses said cormumication network in order to estimate the distance to the target by calculating the amount of hops. As an alternative, the delay time between the dev2.CeS 3-S determined, and may thereafter be used to estimate the distance between the user and the target or the distance to a transceiver having an absolute (fixed) position.

in more detail, the user that is provided with a short range radio transceiver, SR T, transmits a request concerning a target also being provided with a SRT. Said request is received by nearby transceivers retransmitting the request until the target answers. The target transmits an answer to the user by means of the devices provided with nearby shortrange radio transceivers. The distance is determined by means of a counter counting the number of 6 hops between devices between the user and the target. Then, the user may estimate the- distance by means of a predetermined distance for each hop. The method using time delay may also be used when determining the distance to the target. The delay time for a signal to the target or/and a beacon having an absolute position determined by GPS or GSM, or by any other means, may also be used.

The term "Bluetootho is a specific Ericsson denomination of a small shortrange transceiver.

In one embodiment of the method and arrangement disclosed here, Bluetooth may be used to transmit messages between the user and the target, devices between the user and the target also being provided with Bluetooth transceivers.

In one embodiment of the method and arrangement disclosed here, infrared light may be used to transmit messages between the user and the target, devices between the user and the target being provided with means for communication with infrared light.

The method and system according to the invention may be used in the same way as a GPS system or a GSM system for positioning, in combination with fix transceivers being previously identified and having an absolute position.

A purpose of the method, system and arrangement as disclosed is to provide a low-cost system for estimating the distance between a user and a target.

Another purpose of the method, system and arrangement disclosed herein is to provide a system for estimating a distance between a user and a target, which may be used indoors.

7 A further purpose of the method, system and arrangement disclosed herein is to provide a system that does only require that the user is provided with an electronic device and a short range transceiver.

The main advantage of the method, system and arrangement as disclosed is that ordinary mobile stations provided with a short range radio device may be used.

one advantage of the method, system and arrangement as disclosed is that it can be used indoors.

A further advantage of the method, system and arrangement as disclosed is that it is less costly f or the user.

The system according to the invention may be used to provide blind people with inf ormation concerning products in their vicinity in a store.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS 25

Figure 1 is a schematic view illustrating a communication system of bluetooth cells.

Figure 2 is a schematic view illustrating a bluetoothtransceiver.

8 Figure 3a,b,c shows a schematic view of three electronic devices provided wi-th a bluetooth- transceiver.

Figure 4a is a schematic view of two networks interconnected by G, a gateway (router).

Figure 4b is a schematic view of three networks interconnected by two gateways.

Figure 5 is a diagram showing the relationship between time slots and frequency hops in a system using Bluetooth.

Figure 6a is a schematic block diagram of a signal from a mobile device requesting distance information.

Figure 6b is a schematic block diagram of a signal from the target provided with distance information.

Figure 7 is a f low chart of the method according to the invention.

Figure 8 is a schematic view of two piconets in a scatternet.

Figure 9 is a diagram illustrating the usage of TTL.

Figure 10 is a diagram illustrating the two levels of 20 encapsulation of the ICMP message. Figure 11 is a diagram illustrating the ICMP echo request or reply message format. Figure 12 is a diagram illustrating the ICMP time exceeded message format.

The invention will now be described in more detail with reference to preferred exemplifying embodiments thereof and with reference to the accompanying drawings.

DETAILED DESCRIPTION

In fig. I is depicted a network comprising short-range radio cells including cells 100, 110, 120, 130, 140, 150, 160. Of course, a short-range radio network may include only two cells or much more than seven cells. However, in 9 the case of Bluetooth transceivers, a maximum of seven devices may be connected simultaneously to each other. A short-range radio-cell is created by a device, such as a mobile, provided with a short-range radio- transceiver or by 5 a fix transceiver. A mobile A creates a cell 100, a mobile C creates- a cell 110, a mobile D creates a cell 120, a mobile E creates a cell 140, a mobile F creates a cell 150, and a mobile G creates a cell 160. A device B indicates a short-range radio-beacon having a GPS- receiver or a GSM- receiver. The position may also be previously known in the case of a fix installation. By means of said receiver, the position of the device B can be established. The cell around B is numbered 130. A short-range radio- cell is much smaller than a cell created by a base station (BS) in a normal mobile telephone system. The radius of a short-range radio cell is between 10 and 100 meter. As a considered mobile, provided with a short- range radio- transceiver, moves, said short-range radio cell moves. A person provided with the mobile A would like to know the distance to a considered restaurant 200 at a location H provided with a short-range radio transceiver 210. The arrows in figure I indicate an exemplary path of radio signals between the mobiles to the target H. It is established that the distance from the restaurant to the mobile A does not have to be the same as the way there, as some of the cells may have moved away. In a case, where the device B does not have a defined position and is an ordinary short-range radio cell, the maximal distance from A to the restaurant is d = 6 X 10 meter = 60 meters (6 hops). In the case, where the device B is a beacon, the distance to the device B can be established to d'= 5 hops = 50 meter. The restaurant is located within 10 meters from the beacon and the distance d is established to 60 meters. In this case, the exact position of the beacon is known, a fact that may be of interest. A better estimate of the distance on each hop can be provided using the "time-delay" method. The delay time method according to the above mentioned patent US 5, 187, 485 may be modified and used in a piconet comprising short-range radio devices. The method according to US 5,187,485 uses GPS signals, which are scattered by a target, t-o determine the distance from the target to an observation station. The distance Rt between the target and the observation station can be estimated as Rt - C(tit, -tio) (1) wherein C is the speed of the light, ti. is the time for the satellite signal to travel from a satellite i to the observation point, which is already known from the conventional GPS approach. In eq. (1), only the reflection from one satellite is required. The method according to US 5,187,485 may be used in a system comprising transceivers provided with short-range radio cormn=ication. In this case, tiO is the time for the short-range radio signals to travel between two transceivers.

The so-called Bluetooth interface is an example of a modern small short-range radio interface, which was originally intended as a replacement for cables between units. The term Bluetooth is in this disclosure used as an example of usage of short-range radio communication. However, the area of applicability has proven to be much wider. Printers, electronic calendars (PDA), desktops, fax machines, keyboards, -joysticks and virtually any other digital device can be part of the short-range radio system. But beyond untethering devices by replacing the cables, the short range radio technology provides a universal bridge to existing data networks, a peripheral interface, and a mechanism to form small private ad hoc groupings of connected devices away from fixed network infrastructures. Designed to operate in a noisy radio frequency environment, the Bluetooth radio uses a fast acknowledgement and frequency hopping scheme to make the link robust. Bluetooth radio modules avoid interference from other signals by hopping to a new frequency after transmitting or receiving a data packet, as is shown in f ig. 5. Compared with other systems operating in the same frequency band, the Bluetooth radio typically hops faster and uses shorter data packets. This makes the Bluetooth radio more robust than other systems. Use of Forward Error Correction (FEC) limits the impact of random noise on long-distance links.

Bluetooth radios operate in the unlicensed ISM band at 2,4 GHz. A frequency hop transceiver is applied to combat interference and fading. A shaped, binary FM modulation is applied to minimise transceiver complexity. The gross data rate is 1Nb1s and a TDD (Time-Division Duplex) scheme is used for full-duplex transmission.

The Bluetooth base band protocol is a combination of circuit and packet switching, as is shown in fig. 5. In fig. 5 sl denotes one time slot, and pl denotes a packet covering three time slots. Time slots can be reserved for synchronous packets. Each packet is normally transmitted in a different hop frequency. A packet nominally covers a single slot, but can be extended to cover up to five slots. Bluetooth can support an asynchronous data channel, up to three simultaneous synchronous voice channels, or a channel with simultaneously supports asynchronous data and synchronous voice. - Each voice channel supports 64 kb/s synchronous (voice). link. The asynchronous channel can support an asymmetric link of maximally 721 kb/s in either direction while permitting 57,6 kb/s in the return direction, or a 432,6 kb/s symmetric link.

In figure 2, the different function blocks of a system using short-range radio transceivers, such as Bluetooth are shown. A radio unit 300 is connected to a link control unit 12 310 providing the base band. The link control unit 310 is connected to the Central Processing Unit, called CPU, 320 providing the link management. The CPU is connected to the memory 360 providing software functions and consisting of two memory units: a SRAM 330 and a FLASH 340. The CPU 320 is connected to a host interface 350. A SRAM is a fast temporary memory. SRAM is programmable ROM.

Fig. 8 shows two piconets Al and Bl in a scatternet.

Piconet Al comprises four radio devices 10, 20, 30, 40; and piconet Bl comprises two devices 50 and 60. In piconet Al, device 10 is a master device. A piconet is a collection of devices connected via Bluetooth technology in an ad hoc fashion. A piconet starts with two connected devices, such as portable PC and a cellular telephone, and may grow to is eight connected devices. All Bluetooth devices are peer units and have identical implementations. However, when establishing a piconet, one unit will act as a master and the other(s) as slave(s) for the duration of the piconet connection. A scatternet, or an ad hoc network, is a network comprising multiple independent and nonsynchronised piconets. In this disclosure, a master unit is the device in a piconet whose clock and hopping sequence are used to synchronise all other devices in the piconet. In this disclosure, a slave unit is every device in a piconet that is not the master.

The Bluetooth system supports both point-to-point and point- to-multi point connections. Several piconets can be established and linked together ad hoc, where each piconet is identified by a different frequency hopping sequence.

All users participating on the same piconet are synchronised to this hopping sequence. The topology can best be described as a multiple piconet structure, see figure B. However, ad hoc nets, also called scatternet, are not yet conmercially available.

13 The Bluetooth technology originates from Ericsson. It eliminates the need f or wires-, cables and connectors f or and between cordless or mobile phones, modems, headsets, PDAs (Personal Digital Assistants), computers, printers, projectors, local area networks, and so on, and paves the way for - new and completely different devices and applications.

An ad hoc network might be constructed having Bluetooth devices as "cellsm. An ad hoc network is a network that is built dynamically with an unlimited number of points, i.e. a new device can be attached to the network to make it grow. other techniques than Bluetooth may be used to construct an ad hoc network, such as infra red light. When Bluetooth devices are used to comprise a network, each user that has (Bluetooth-) contact with another user, is part of the network. Bluetooth devices can have different ranges. one may have a range of 1-10 meter, and another may have a range of around 2-100 meters. By implementing a router, disclosed in more detail below, in each Bluetooth device, so that a session could be forwarded between devices, an ad hoc network could be constructed. A man skilled in the art understands that other short-range radio techniques may be used.

In the system herein disclosed, every Bluetooth- transceiver is provided with a router having a routing protocol. The routers are gateways used to pass packets from one Bluetooth transceiver to the next. In a packet switching system, routing refers to the process of choosing a path over which to send packets, i.e. routing is the method by which the host or gateway decides where to send the datagram. Router refers to any computer making such a choice. The gateways make routing decisions; that is their primary purpose and the motivation for calling them routers. The goal of a routing protocol is to supply the 14 information required to provide the routing. In the system herein disclosed, the routers:are similar to those used in a TCP/IP internet. The routers are provided with a protocol for handling address information. In the Internet, Routing 5 Information Protocol (RIP) is a widely used protocol. Routers and RIP will be described in more detail below. A man skilled in the art of TCP/IP and the Internet is able to construct, without undue burden, a simple router having a suitable protocol for an ad hoc network, e.g. based on bluetooth transceivers.

In the Internet, IP routing consists of deciding where to send a datagram. based on its destination IP address. The route is direct if the destination machine lies on a network (in this case within the same piconet, within the same cell) to which the sending machine attaches; we think of this as the final delivery step in datagram. transmission. The route is indirect if the datagram must be sent to a gateway for delivery. The general paradigm is that hosts send indirectly routed datagrams to the nearest gateway; the datagrams travel through the Internet from gateway to gateway until they can be delivered directly across one (fixed or mobile) network.

In fig. 4a, an example consisting of two physical networks is shown. In f ig. 4a, a machine G12 is connected to both a network Net 1 and a network Net 2. In order to act as a gateway, the machine G1.2 Must capture packets on network Net I that are destined f or machines on network Net 2 and transfer them. Similarly, machine G3.2 Must capture packets on network Net 2 that are destined for machines on network Net 1 and transfer them.

In the system depicted in fig. 4b, a gateway G34 must transfer, from a network Net 3 to a network Net 4, all packets destined for machines on either network Net 4 or is network Net 5. As the size of the Internet expands, the gateways task of making decisions about where to send packets becomes more complex.

Gateways in a network, e.g. a TCP/IP Internet or an ad hoc network, -form a cooperative, interconnected structure.

Datagrams pass from gateway to gateway until they reach a gateway that can deliver the datagram directly to the addressee.

In the Internet, the usual IP routing algorithm employs an "Internet routing tableff on each machine that stores information about possible destinations and how to reach them. Because both hosts and gateways route diagrams, both have IP routing tables. Whenever the IP routing software in a host or gateway needs to transmit a datagram, it consults the routing table to decide where to send the datagram.

In an Internet, there exist several solutions for finding and selecting the intermediary gateways. Gateways in a TCP/IP Internet form a cooperative, interconnected structure. Datagrams pass from gateway to gateway until they reach a gateway that can deliver the datagrams directly. In order to hide information to keep routing tables small, and make routing decisions efficient, IP routing software only keeps information about destination network addresses, not about individual host addresses.

Software called "routed" implementing the Routing Information Protocol (RIP) was originally designed at the University of California at Berkeley. The underlying RIP protocol is a straightforward implementation of vectordistance routing for local networks. The protocol RIP is one of a class of algorithms known as "distance vector algorithmso, a distance vector protocol. The protocol RIP is intended to allow hosts and gateways to exchange information 16 f or computing routes through an IP-based network. RIP is used to convey information about routes to "'destinations", which may be individual hosts, networks, or a special destination used to convey a default route.

RIP partitions into active and passive (silent) machines. Active gateways advertise their routes to others; passive machines listen and update their routes based on advertisements, but do not advertise. Typically, gateways run the protocol RIP in active mode, while hosts use passive mode.

A gateway running RIP in active mode broadcasts a message every 30 seconds. The message contains information taken from the gateway's current routing database. Each message consists of pairs, where each pair contains an IP network address and an integer distance to that network. RIP uses "hop count metric" to measure the distance to a destination. In the RIP metric, a gateway is defined to be one hop from directly connected networks, two hops from networks that are reachable through one other gateway, and so on. Thus, the number of hops or the hop count along a path f rom a given source to a given destination refers to the number of gateways that a datagram encounters along the path. It should be obvious that using hop counts to calculate shortest paths does not always produce optimal results.

The generality of the protocol RIP is also evident in the way it transmits network addresses. The address f ormat is not limited to use by TCP/IP; it can be used with multiple network protocol suites. In addition to normal IP addresses, RIP uses the convention that address 0.0.0.0 denotes a default route. RIP attaches a distance metric to every route it advertises, including default routes. Thus, it is possible to arrange for two gateways to advertise a default route. The final field of each entry in a RIP message,

17 DISTANCE TO NET contains an integer count of the distance to the specified network. Distances are measured in number of gateway hops, but values are limited to the range 1 through 15, with distance 16 used to simplify infinity, i.e., no route exists.

Each host that implements RIP 'is assumed to have a routing table. This table has one entry for every destination that is reachable through thesystem described by RIP. Each entry contains at least the following information:

- the IP address of the destination - a metric, which represents the total cost of getting a datagram from the host to that destination. This metric is the sum of the costs associated with the networks 15 that would be traversed in getting to the destination. - The IP address of the next gateway along with the path to the destination. If the destination is one of the di rectly- connected networks, this item is not needed. - A flag to indicate that information about the route has 20 changed recently. This will be referred to as the "route change flag,. - Various timers associated with the route. Above the IP-layer, there is no difference between an ad hoc network and the Internet. A protocol f or an ad hoc network, based on e.g. bluetooth-transceiver can in principle be constructed as an internet protocol. However, the implementation is different. The main difference between a router in an ad hoc network and a router in the internet is that the tables in an ad hoc net must be reconstructed much more often than in an internet. There exist already several algorithms for ad hoc networks. The choice of algorithms has no importance for the present invention. However, it is of importance for the present 18 invention that there is an existing functioning ad hoc network.

As an effect of the scope of Bluetooth, we know that each hop between devices is maximum 100 meters in a normal case without e.g. walls in its way. By using, for example, a time delay measuring method, we can measure a much more dxact distance for each hop (see below). The time delay is a measurement of the propagation delay between two transceivers. A man skilled in the art of telecommunication understands that other methods could be used. If a command similar to the UNIX command "'Itraceroute" is implemented, the number of hops between a user and a target may be calculated.

A modified traceroute command will now be disclosed with reference to fig9. The system according to fig. 1 is here used as an example. A man skilled in the art understands that the traceroute command may be used for other systems comprising a set of short range radio receivers. In contrast to the standard Internet traceroute command, the disclosed traceroute command calculates an estimate of the distance between a device and the user.

The traceroute command serves as a valuable network debugging tool. The way in which it is currently implemented has the advantage of being automatically supported by all of the routers. The existing traceroute command operates by sending out packets with Time-To-Live (TTL) of one. TTL is a technique used in best-effort delivery systems to avoid endlessly looping packets. For example, each IP datagram is assigned an integer Time-To- Live when it is created. IP gateways decrement the TTL field when they process a datagram and discard the datagram if the TTL counter reaches zero. The TTL method calculates the number of hops and estimates a maximal distance. in

19 order to provide a better estimate of the distance, the time delay must be measured f or each hop and be include in the "packet expiredff that is sent back to the user. Thus, a feature must be added in comparison to the existing Internet. This is easily understood by a man skilled in the art.

In the disclosed example, the requesting mobile A sends a signal with the parameter TTL set to 1, TTL1=1. At the first hop, the mobile C sends back an ICMP(l] error message indicating that the packet could not be forwarded, because the TTL expired. The term ICMP will be disclosed in more details further below. The distance between the mobile A and C is calculated to 32 meters, using a time delay method. Said packet is then resent with the parameter TTL set to 2, TTL2=2, and the second hop, at the mobile D, returns the TTL expired. The distance between C and D is estimated to 10 meters, and the distance between the mobiles A and D is thus estimated to 32 + 10 = 42 meters. This process continues until the destination is reached.

Thus, the packet is again resent with the parameter TTL set to 3, TTL3=3, and the third hop, at the mobile E, returns the TTL expired. The distance between the mobile A and E is estimated to 42 + 27 = '69 meters. Finally, the packet is once again resent with the parameter TTL set to 4, TTL4=4, and the fourth hop, at the target mobile B, returns that the signal has reached the target B. The distance between the mobiles A and B is in this case estimated to 69 + 16 meters.

Here follows another example with reference to fig. I of the usage of the traceroute command. If the user A would like to visit the nice restaurant H, and he wants to know the maximum distance to it, he could run said "traceroutem command, and count the number of hops, as described above.

It is easy to determine the maximum distance with said information.

Distance = <number of hops> x meter, where x is a real number between 10 and 100, depending on the device.

The distahce will probably be much less than this value, but it is a first rough estimate. In order to obtain a better estimate, e.g. the time delay of the transmission could be measured f or each hop. In this way, a much better result would be obtained. The following formula could be used:

Distance = X, + X2 + X3 ±- + X., where Xj, j=l,-, n, is the distance given by the time delay for each of the n hops.

A man skilled in the art understands that the distance could be calculated at real time. The distance can also be pre-calculated or interpolated from pre-calculated values. The distance measurement application could of course check for several parameters to improve the distance estimation. There could be stationary Bluetooth devices (beacons) in the ad hoc networks that could be used as references. It would also be possible to let the Bluetooth device setup a couple of connections, with different routes to the destination each time. The distance could then be computed as the average distance of those routes, or the shortest distance of those routes.

According to a further embodiment, a request is sent over Bluetooth transceiver to a device in a "radiuso of e.g. two hops in order to determine the position of the device. If any device in that radius knows its own position, e.g. the device being equipped with GPS or differentiated GPS, or a fixed transceiver, it may report its position to the requesting device.

21 According to a yet further embodiment, the above-described beacons may be used to determine the position of a device. It may also include its margin of error, which differs depending on the method for determining the position.

In f igure- 6a is shown a diagram of a signal from a mobile requesting information concerning the distance to a specific target. The Header includes an identification of the sender (the id of the requesting mobile), the receiver (the id of the target) and other relevant information, The Payload comprises the request for information.

In f igure 6b is shown a diagram of a signal f rom target information comprising, in the payload part, an estimation of the distance between the target and the requesting mobile. The Header includes an identification of the sender (the id of the target), the receiver (the id of the requesting mobile) and other relevant information.

Internet Control Message Protocol, ICMP, will now be disclosed in more details. ICMP allows gateways to send error or control messages to other gateways or hosts; ICMP provides communication between the Internet Protocol software on one machine and the Internet Protocol software on another. An arbitrary machine can send ICMP messages to any other machine. Thus, a host can use ICMP to correspond with a gateway or another host. The chief advantage of a.1lowing hosts to use ICMP is that i ' t provides a single mechanism used for all control and information messages.

Technically, ICMP is an error reporting mechanism. It provides a way for gateways that encounter an error to report the error to the original source. ICMP only reports error conditions to the original source; the source must relate errors to individual application programs and act to correct the problem.

22 ICMP messages require two levels of encapsulation according to fig. 10. The ICMP message is encapsulated in an IP datagram, which is further encapsulated in a frame for transmission. To identify ICMP, the datagram protocol field 5 contains the value 1.

The ICMP echo request or reply message format will now be disclosed with reference to fig. 11. Although each ICMP message has its own format, they all begin with the same three fields: an 8-bit integer message TYPE field that identifies the message, an 8 bit CODE field that provides further information about the message type, and a 16 bit CHECKSUM field (ICMP uses the same additive checksum, algorithms as IP, but the ICMP checksum only covers the ICMP message) In addition, ICMP messages that report errors always include the header and first 64 data bits of the datagram causing the problem.

The ICMP message may also be used to detect circular or excessively long routes, as will be explained below. Because internet gateways compute a next hop using local tables, errors in routing tables can produce a routing cycle for some destination, D. A routing cycle can consist of two gateways that each route a datagram for destination D to the other, or it consist of several gateways. When several gateways form a routing cycle, they each route a datagram for destination D to the next gateway in the cycle. If a datagram enters a routing cycle, it- will pass around the cycle endlessly. Each IP datagram comprises a time-to-live counter, sometimes called a hop count, in order to prevent datagram from circling forever in the TCP/IP Internet. A gateway decrement the time-to-live counter whenever it processes the datagram and discard the datagram when the count reaches zero.

23 Whenever a gateway discard a datagram because its hop count has reached zero or because a timeout occurred while waiting for fragments of a datagram, it sends an ICMP time exceeded message back to the datagram's source, using the format shown in fig. 12. The CODE field explains the nature of the timeout. When the Code value is zero, it means that the time-to-live count has exceeded. When the Code value is "ll', it means that the fragment reassembly time has exceeded. Fragment reassembly refers to the task of collecting all the fragments from a datagram. When the the first fragment of a datagram arrives, the receiving host starts a timer and considers it an error if the timer expires before all the pieces of the datagram arrive. Code value "10 is used to report such error to the sender; one message is sent for each such error.

Fig. 3a shows a PDA 500 utilizing an "add-on" bluetooth communication device 510. The bluetooth communication device, provided with an antenna, is inserted in a slot in the PDA. The bluetooth communication device may be a PC- card or a compact flashcard provided with the bluetooth chipset.

Fig. 3b shows a PDA utilizing a bluetooth communication device. Here, the PDA is provided with an antenna.

Fig. 3c shows a mobile telephone utilizing a "built-in" bluetooth cormnunication device, the mobile telephone and the bluetooth transceiver having different antennas.

The method disclosed herein may be used in a farm or a kindergarten in order to keep track of the children/ cattle.

Every cattle may be equipped with a device disclosed herein, and an alarm is sent to a central device, informing 24 the proprietor that a child/cattle is running away from the group of children/cattle.

The method disclosed herein may also be used to construct an information system, based on a bluetooth network, wherein the distance and direction to different targets are estimated. Said information may be used, using a c,omputerized voice system to help blind people to orient themselves at home or in a supermarket. A map of the supermarket may be stored in the users, device. A number of fix Bluetooth- transceivers may be located at predetermined locations in the building. Thus, when the user arrive at the vicinity of certain predetermined locations in the store, the user may be informed, by means of e.g. a voice message to his mobile, the type of products that are arranged in the vicinity of the user.

In a fix network, e.g. an Ethernet, the disclosed herein method may be used for error detection and error localization. When an error in a cable is detected, it is today difficult to locate the error. Today, the only information available states that the error is located between two fixed electronic devices. In order to find the error, the repairman has -to manually check every connection between said electronic devices, he must manually check every part of every cable between said devices. Using the method as disclosed herein it may be possible to find where the fault is located, i.e. in- which room to look for a faulty device, e.g. a cable. A man skilled in the art understands how to locate an error using the method herein disclosed.

Figure 7 shows a flow chart illustrating the method herein disclosed. In block 710, the user requests by means of e.g. a PDA the distance to a restaurant H. Said PDA is provided with a bluetooth-transceiver and sends in block 720 a signal to adjacent devices. When the signal reaches an adjacent device, a counter isr set to 1. In block 740, the signal is sent to a following device, until it reaches the target having a predefined address. Each time the signal reaches a new device said counter is incremented by one, as described- in connection with fig. 7. If the signal has reached the target by means of several paths, block 745, an optimized value of the different paths is calculated, e.g. a mean value or the smallest value, in block 750, and the result is calculated. Thereafter, in block 760, the result is shown for the user by means of a display or a synthesized voice message. If the signal has reached the target by means of only one path, the result is calculated by means of an algorithm using the amount of hops stored in the counter, and thereafter displayed in block 760.

The invention as disclosed may be used with analogous technology. However, a modem has to be added between TCP and the analogous radio.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from ' the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims (13)

1. 26 CLAIMS

   T - 1. Method in a communication network for determining a distance between a f irst point (A) and a second point (H, B), each provided with an electronic device, where the network comprises at least said two electronic devices provided with short range radio communication, the method comprising starting the communication by a requesting party in the first point (A), and 9 transferring data packets from one electronic device to the next by means of routers, characterized in that the method comprises the steps of Sending a signal to at least one adjacent of said devices, the signal including an identification of said second point (H, B), Routing the signal to the second point (H, B) utilizing said identification, Utilizing a traceroute command to determine a number of hops for the signal between said first point (A) and for said second point (H, B), each hop defining a distance value, and Generating a sum of said distance values for each hop, as an estimate value of the total distance from the first point (A) to the second point (H, B).
2. 2. A method according to claim 1, characterized in that said method is repeated using different routes, and in that a mean value of the estimated distances is generated.
3. 3. A method according to claim 1, characterized in that said method is repeated using dif f erent routes, and in that the smallest value of the estimated distances is selected.
4. 4. A method according to claim 1, characterized in that a method f or detecting hops in a ring like path is also used.
5. 5. A method according to claim I or claim 2, characterized in that the devices with short range radio transceivers comprise static placed beacons
6. 6. A method for determining the position of the first device (A) utilizing a method according to one of claims 1-4 f or reguesting the position f rom. a nearby position aware device, where the position-aware device could either be a statically positioned device, or a mobile device with position awareness.
7. 7. Arrangement in a communication network for determining a distance between two points, a f irst point (A) and a second point (H, B) in a network, each provided with an electronic device, where the network comprises short range radio comrmmication and ad hoc technology, and wherein The communication is started by a requesting party in the first point (A), and Packets are transferred from one electronic device to the next by means of routers, characterized in that the arrangement comprises An electronic device f or sending a signal to at least one adjacent device provided with short range radio 28 communication, the signal including a identification of said second point (H, B), - Means f or routing the signal to the second point (H, B) utilizing said identification, Means for utilizing a traceroute cormnand to determine the number of hops between said first point (A) and said second point (H, B), each defining a distance value, Means for generating the sum of said distance values for each hop, as an estimate value of the total distance from the f irst point (A) and the second point (H, B), and A display, visual or audio, for showing the user said estimated distance.
8. 8. Arrangement according to claim 7, characterized in that said arrangement generates the estimated distance between point (A) and point (H, B) several times using different routes, and that the mean value of the estimated distances generated, is computed and displayed.
9. 9. Arrangement according to claim 7, characterized in that said arrangement generates the estimated distance between point (A) and point (H, B) several times using different routes, and that the smallest value of the distances generated, is computed and displayed.
10. 10.A-rrangement according to claim 7, characterized in that a trac eroutecommand is used in order to detect and avoid hops in a ringlike path.
11. ll.A-rrangement according to claim 7 or 8, characterized in that in that the network is provided with static placed 29 beacons, which are used together with movable devices provided with short range radio communication.
12. 12.Arrangement in a communication system for determining the position of a device utilizing a method according to one of claims 1-4 for requesting the position from a nearby position-aware device, where the position-aware device could either be a statically positioned device, or a mobile device with position awareness.
13. 13.System in a communication network for determining a distance between a first point (A) and a second point (H, B), each provided with an electronic device, where the network comprises at least said two electronic devices provided with short range radio communication, the system comprising 0 Means for starting the communication by a requesting party in the f irst point (A), and 0 Means for transferring data packets from one electronic device to the next by means of routers, characterized in that the system comprises means for e Sending a signal to at least one adjacent of said devices, the signal including an identification of said second point (H, B), 0 Routing the signal to the second point (B) utilizing said identification, 0 Utilizing a traceroute command to determine a number of hops for the signal between said f irst point A and for said second point (H, B), each hop defining a distance value, and 0 Generating a sum of said distance values f or each hop, as an estimate value of the total distance from the first point (A) to the second point (H, B).