GB2424544A

GB2424544A - Wireless Relay

Info

Publication number: GB2424544A
Application number: GB0505924A
Authority: GB
Inventors: Russell John Haines; Gary Clemo
Original assignee: Toshiba Research Europe Ltd
Current assignee: Toshiba Europe Ltd
Priority date: 2005-03-23
Filing date: 2005-03-23
Publication date: 2006-09-27
Anticipated expiration: 2025-03-23
Also published as: GB0505924D0; GB2424544B

Abstract

The present invention relates to wireless relay devices which allow a number of separate wireless networks to operate as a single network by linking the separate wireless networks using relays communicating over a power line. This allows the communication power and range of devices in the network to be reduced whilst still allowing distant devices to communicate with each other. This helps to improve throughput and security of the system as well as allowing greater frequency reuse within a given area whilst reducing power consumption of individual devices. The system also provides a method for assisting a user in locating a relay device to maximise the benefit of the invention.

Description

0 1 2424544 Wireless Relay

Field of the Invention

The present invention relates to wireless relays, in particular but not exclusively for home network systems.

Background of the Invention

Wireless networking is becoming increasingly popular as a way of minimising cabling requirements and maximising the portability and flexibility of a networked system.

Various applications exist, including wireless networking for home entertainment equipment such as hi-fl and home cinema systems. Such systems include various "centralised" components such as CD or digital media file (e.g. "MP3" format) players, DVD or video players, satellite, cable or terrestrial wireless set-top boxes, as well as other equipment such as TV sets or other display equipment such as plasma screens, speakers, remote control units and computer systems. Various connections between these components are required in order for the system to operate properly. Traditionally this has been achieved using cabling and infra-red (IR) beam links for remote controllers.

By integrating a wireless network into such a home entertainment system, the level of cabling required is reduced, and the system itself may be vastly expanded, for example extending into multiple rooms throughout a home. The lack of cables also leads to increased flexibility and cabling is not required to be re-installed with each re-location of certain system components.

Figure 1 illustrates a home network system using a number of wirelessly coupled items of home entertainment equipment as shown. Each item of equipment 1, such as an amplifier which is part of the larger home entertainment system, may be coupled to a WLAN terminal or transceiver module 4 which couples the equipment to the wireless

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LAN associated with the home network system. The modules 1 interface with the WLAN of the home network system in order to receive for example streams of music from a CD player, and/or to send streams of audio to speakers or other components 1 of the system.

Alternatively, the devices in the house may form an ad-hoc wireless network with no central access point. In this way, a device can communicate directly with any other device in range of its radio transmission/reception abilities.

In order for the system to extend throughout a household, the communication range of a device needs to be sufficient to reach all the devices with which it needs to communicate. Even if the devices all communicate via an access point such as the module 4, the range of the devices and the module 4 must encompass all the devices with which to communicate. Thus, generally the range associated with a device must extend around the entire house. However depending on the location of the device, this can result in the range of the device extending well beyond the perimeter of the house.

For example, the PC 2 has a range 3 as shown in figure 1 in order to encompass all the devices of the house with which it needs to communicate. This range extends far outside the boundary of the house and so covers areas where no coverage is needed.

This has a number of drawbacks. Additional power is needed to provide the required range. Extending the range means that interference of the device; possibly in a neighbouring property is a problem that can reduce throughput. Extending the range beyond the perimeter of the property leads to the problem of third parties being able to access the wireless network, thereby risking the security of the network. It is therefore desirable to reduce the range of transmission to avoid interference, reduce power of transmission and also allow spatial reuse of frequencies.

One solution is to utilise a number of smaller localised WLANs coupled together, each WLAN in a different room of the house. Typically, the WLANs will be coupled together with cabling. Whilst this is still not ideal, the cabling is reduced compared with legacy "all-cabling" systems.

In the Applicant's co-pending application no. 0416822.5 (jublication no. ) , a solution is proposed in which a number of wireless relay units are provided around the house. Each unit can receive a message from a sending device and relay it onto the destination device or to another relay device, which in turn passes the message on until the message fmally reaches the destination device. However, this arrangement does require a continuous chain of relays to ensure full coverage. In a large house, this may require a significant number of relays if each of the relays only has a limited range. It also means that for coverage in two spatially separated areas, many relays may be needed.

There is therefore a need to provide a solution to the above problems without the need for installing cabling systems or having many, or long range, transmitters.

Summary of the Invention

Therefore, according to the present invention there is provided a wireless network relay for use in linking two wireless networks, the relay comprising: wireless communication means for communicating over a local wireless network; power line communication means for communicating with a remote relay over a common power line; and router means adapted to receive messages transmitted over the local wireless network and to transmit the message for reception by the remote relay over said common power line and further adapted to receive messages transmitted by a remote relay over the power line and to retransmit said message over said local wireless network.

The present invention allows a distributed wireless network to be constructed that operates like a single wireless network but in which the separate sub networks are located out of normal transmission range of each other. This means that the subnetworks can be optimised in terms of transmission power and channel reuse because each subnetwork will generally be smaller than the equivalent traditional network since each device does not need to transmit with sufficient power to reach all the devices on the network. The present invention provides a relay that provides a seamless link between the subnetworks so that a device transmitting a wireless signal does not need to be modified to utilise the relay. The relay simply retransmits the broadcast signal over the power line to another relay. The relay then retransmits the signal into the other network location for reception by the destination device. Again, the receiving device does not need to be modified since it simply receives the signal as if it had been sent directly from the original sender.

The relays preferably comprise storage means for maintaining a list of devices on the local wireless network. In this way, the relay can determine whether a message it receives is intended for a local device of not. When it receives a message over the wireless network, it can determine if the message is for a local device. If so, it can ignore the message and allow the message to be received by the destination device, which should be in range. In contrast, if the message is addressed to a device that is not local, then the relay can pass the message on to the power line for distribution to the relay hosting the device. Preferably, messages intended to be broadcast across the entire network would always be forwarded. This would allow solicitation messages to be distributed around the network.

By retaining a list of the local devices, when a relay receives a message over the power line, it can determine if the message is for a local device or not. Only if the message is destined for a local device does the relay transmit it over the local wireless network.

This avoids messages being needlessly transmitted to the entire network.

Preferably, the relay also includes a memory for storing information about which relay is in wireless contact with which device. In this way, when a message is sent across the power line, it can include an address or other information identifying the destination relay. In this way, the relays only have to monitor the messages broadcast across the power line for this address information rather than having to receive all messages and decode them to determine if the message is intended for a device that is on its local The router means in the relay preferably retransmits messages over the local wireless network in a form identical to the message originally transmitted by the originating device. In this way, the recipient device is not aware that there is any difference between the message received from the relay and that of the original device. However, it may be beneficial to modify the messages slightly from the original. The relay may simulate a virtual replica of the destination device and modify messages accordingly.

For example, if two sub networks (X & Y) are close enough that a device Xl in subnetwork X is in direct wireless communication range with a device Yl of the other subnetwork Y, then this could lead to operating difficulties. A message sent by device Xl would be received by the local relay and sent to the local relay of subnetwork Y and re-transmitted. Device Yl would therefore receive the original signal and the retransmitted signal nearly simultaneously. The relay X may therefore set up a unique substitute address, say Y2, for the purposes of network X. Thus when device Xl wants to communicate with Yl, it knows device Yl by the address Y2 and addresses the message to address Y2. Relay X readdresses the message to Yl. In this way, if Yl receives a message from Xl directly, it would be addressed to Y2 and so would ignore it and thus only receive the message forwarded via the relay X and Y, which would then be correctly addressed.

There may be other instances where it is desirable for portions of the retransmitted message to be different to the original. For example, if a power control mechanism was employed to control to transmission power of devices then the messages may need to be different for the two parts of the transmission path. Using the arrangement of the above example, device Xl is communicating with device Yl via relay X and relay Y. Xl receives messages from relay X and sends back information regarding the received power in its next message to Y 1. If Xl is close to relay X then the received power will be high and Xl may include this information in messages sent to relay X to inform relay X to reduce its transmission power. This information is clearly only related to the link between relay X and Xl and so does not need or want to be transferred to relay Y to be included in the message sent to device Yl. Consequently, relay X can strip out this data and send the remaining message to relay Y or relay Y may strip out the data. Relay Y may then include information about the power of messages received from Yl to allow power control in the wireless link between relay Y and Yl. In other words, the message from Xl to relay X will differ from the message from relay Y to Yl in terms of the power control information.

Similarly, timing information may be transmitted between wireless devices to provide timing control, such as in TDMA systems. Again, this information relates to a local link say between relay X and Xl and so the information would not be relevant to the link between relay Y and Yl. hi order to deal with this, a message from Xl to relay X can have the timing information stripped out by relay X and the rest of the message forwarded on to relay Y. Relay X can use the extracted infonnation for timing control of its wireless link to Xl. When relay Y receives the stripped message, it may have previous information on timing control to send to Yl relating to the link between it and Yl. This information can be packed into the retransmitted message.

The important aspect is that a forwarded message received by a device appears to the recipient to have come directly from the sender and the recipient device does not need to be modified to deal with the multi-hop nature of transmission between it and the distant device. The device receives the message and information about the local link as if the ultimate sender was the local relay. This avoids the need for devices to be modified to work with the relay device.

The relay according to present invention preferably operates on a wireless network according to one of the IEEE8O2.ll protocols (e.g. IEEE8O2.1 1 a; b; e; g; n, etc.).

The present invention also provides a communication system for providing a distributed wireless network formed of a plurality of separate local wireless networks, each formed of one or more wireless conmiunication devices, each local wireless network comprising a wireless network relay described above.

The present invention further provides a communication system for providing a distributed wireless network formed of a plurality of remote wireless networks, the system comprising: a first relay device for wireless communication with a first group of devices forming a first wireless network; and a second relay device for wireless communication with a second group of devices forming a second wireless network, wherein each relay device includes: a power line communication means for communicating with the other relay device over a common power line; and router means adapted to receive messages transmitted over the respective wireless network and to to transmit the message for reception by the remote relay over said common power line and further adapted to receive messages transmitted by the remote relay over the power line and to retransmit said message over said respective wireless network.

With the devices of the present invention, the positioning of the relay device is important. It is therefore advantageous to determine a prime location to maximise the effects of the invention. Consequently, the invention also provides a method of generating location information for positioning a wireless communication device in a room, the method comprising: obtaining a panoramic image of at least a portion of the room; edge processing said panoramic image to identify edges of features within the panoramic image defining the edges of objects shown in the panoramic image; processing the panoramic image to identify the position of vertices of the room in the panoramic image; generating a room plan by determining the location of the vertices of the room based upon the identified position of vertices in the panoramic image and populating the room plan with the features of the room based upon the objects identified by said edge processing; carrying out ray tracing to determine the transmission power of a transmitter located in some or all of the objects identified at a plurality of positions within the room; combining the calculated transmission powers for the objects for each of said plurality of positions to generate said location information.

The panoramic image may be formed by using a sequence of images that show contiguous or overlapping portions of said portion of the room. The images may be provided as a series of stills or from a sequence of video images.

The invention advantageously includes generating a graphical representation of the room based upon the room plan and the location information. This allows a user to easily see how the room is laid out and the most suitable sites within the room for positioning the relay.

Preferably, the method includes steps allowing a user to review and modify the data extracted from the panoramic image. The user may be presented with the information determined and can then select, using a suitable interface, those edges which are incorrect. For example, this may be due to processing anomalies caused by features such as the edge of one of the still images forming the panoramic image or a part of a wall decoration. Similarly, features that have been omitted or were obscured in the image may be selectively added.

Preferably, the user may similarly be able to review and modifr the vertices identified to remove incorrect vertices or add omitted ones. This could be done simultaneously with reviewing the detected edges.

The resulting information is preferably based upon the determined power at the plurality of positions in the room. The power is preferably based upon the sum of the power from each transmitter at that point. However, if weak transmitters are present, the average power at a point may be good but the weak transmitter may be out of range.

The information provided may be further moderated to take account of this by excluding regions that are out of range of any transmitters. Thus, only regions that would allow communication with all transmitters are presented and quantified, for example, by their total power from all transmitters.

The present invention is ideally suited to locations where a number of separate locations require wireless coverage but where long-range communication is undesirable such as in a domestic environment. The invention is therefore ideally suited for home use such as for transmission of data around a house for Internet data traffic as well as audio and video distribution.

The present invention can be implemented either in hardware or on software operating on a general-purpose programmable device. Further, the present invention can be implemented in a combination of hardware and software. The present invention can also be implemented by a single processing apparatus or a distributed network of processing apparatuses.

Embodiments of the invention may be implemented on a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). Thus, the code may comprise conventional program code or microcode or, for example, code for setting up or controlling an ASIC or FPGA. The code may also comprise code for dynamically configuring re-configurable apparatus such as re-programmable logic gate arrays. Similarly, the code may comprise code for a hardware description language such as Verilog or VHDL (Very high speed integrated circuit Hardware Description Language). As the skilled person will appreciate, the code may be distributed between a plurality of coupled components in communication with one another. Where appropriate, the embodiments may also be implemented using code running on a field-(re) programmable analogue array or similar device in order to configure analogue hardware.

Since the present invention can be implemented by software, the present invention encompasses computer code provided to a general purpose programmable device on any suitable carrier medium. The carrier medium can comprise any storage medium such as a floppy disk, a CD ROM, a magnetic device or a programmable memory device, or any transient medium such as any signal e.g. an electrical, optical or microwave signal.

Brief Description of the Drawings

The present invention will now be described in more detail by reference to the following specific embodiment, in which: Figure 1 shows a typical home system having equipment distributed throughout it; Figure 2 shows a relay according to the present invention in use; Figure 3 is a flow diagram for a method of modelling a room and positioning a relay; Figure 4 shows a collection of images formed into a panoramic montage; Figure 5 shows a cropped panoramic image; Figure 6 shows an image after edge detection; Figure 7 shows an image after initial filtering; Figure 8 shows an image after additional filtering; Figure 9 shows an image after additional features have been included; Figure 10 is an initial determination of the layout of the room based on the panoramic view; Figure 11 is an initial determination of the plan of the room; Figure 12 shows an example of the ray tracing process; Figure 13 shows an example of the result of ray tracing analysis; Figure 14 shows a further example of the result of ray tracing analysis; and Figure 15 shows a schematic graph for showing the effect of transmission range on devices.

Detailed Description

The embodiment of the present invention described below alms to overcome the problems described above. In the arrangement shown in Figure 1, the PC 2 is located in a position that is convenient for the user. The theoretical practical range of the wireless transmitter in the PC is shown by the circle 3. However, in the arrangement shown in Figure 1, the theoretical practical range means that parts of the property are out of range of the PC. In practice, the range would not be circular, as shown, due to the effect of the different absorbing and reflecting properties of the structure and contents of the property. The theoretical range of the PC also extends a long way outside of the property. The situation might be improved by moving it to a position more central in the property. This would help to ensure more effective coverage of the entire property whilst reducing the possibility of a third party accessing the device from outside the property. However, in a domestic environment, it may not be convenient to position a device in the ideal location that may be in a corridor or in a doorway. Even if a central access point is used, it may not be convenient to locate it in the ideal position without leaving areas out of range or extending the range out of the property.

Figure 2 shows an alternative arrangement in accordance with the present invention. In this arrangement, a number of relay units 20, 21, 22 are provided at convenient locations distributed around the property. In the example shown, the three main rooms each have a relay to provide local access points. Each of these relays only needs to have a range sufficient to cover the devices within the room. Consequently, the effective range for each relay can be reduced and so the power of the transmitter can be reduced.

This helps to avoid leakage of the signal outside the boundary of the property, which in turn helps to avoid the possibility of third parties having access to the access point.

The operation of this embodiment of the present invention will now be described. By way of example, the following description will describe a situation where a user wishes to watch a film that is being provided from PC 23. The user desires to view the film on the television 24 and also to use the hi-fl 25 to provide the sound using the speakers 26a and 26b. Because the PC 23 and the television 24 are not in direct wireless range of each other, they cannot communicate directly. However, the relay unit 20 is within wireless range of the PC 23. Similarly, the relay 21 is also within range of the television 24 and the hi-fl 25. Therefore, when the PC 23 wishes to transmit data to the television 24, it transmits its signal identifying the destination device of the television 24. When the relay 20 receives a message from the PC 23, it re-transmits the signal over the mains power line 27 for the property. The signal is received by relays 21 and 22 that are also connected to the mains power line. The relay 21 extracts the signal and then re-transmits it over the local wireless network. The signal is then received by the television 24.

Messages from the television 24 to the PC 23 are handled in a similar manner. The television 24 transmits the message containing a destination address identifying the PC.

This is received by the relay 21. The relay 21 then re-transmits the signal over the domestic mains power supply. The signal propagates through the domestic supply such *0 as shown by arrow 28 where it can be received by the relay 20. The relay 20 re-transmits the signal over the local wireless network where it is received by the PC 23.

Again, the PC can communicate with the hi-fl unit 25 in a similar way. In the above- described arrangement, the relay receives a signal identifying the destination device.

The relay can be provided with various levels of functionality. In a basic construction, the relay device simply receives messages broadcast on the wireless network and retransmits them over the power line. Again, all the relays that are connected for communicating over the power line would receive this retransmitted signal and retransmit the received signals over the wireless network in their local area.

In an alternative arrangement, the relay may be provided with an improved level of functionality. When the relay is activated, it would join the local wireless network. If it were acting as an access point, then devices would register with it. It would then be able to develop a list of the wireless devices on the local wireless network, in other words, all the wireless devices within its range of wireless communication. Having obtained this list, when the relay receives a message, it will know whether the message is destined for a device on the local wireless network or another device outside of the local network. In the case of the former, the relay knows that as the message is destined for a local device, it need not forward the message over the power line. Conversely, where the message is destined for a device not in the local message, the relay device can forward the message over the power line.

For example, if the 1'V 24 sends a message containing data intended for the speakers 26a, 26b, the relay would know that the speakers were on local network and know not to retransmit the message over the power line.

Similarly, when a relay receives a message broadcast over the power line, the relays receive the message and determine whom the message is addressed to. If the message is for a device on a relay's local network then it retransmits the message over the local wireless network. This ensures that only messages intended for a remote device are passed over the power line network and messages are not retransmitted by all relays, only the one which is on the network where the destination device is located.

In a further development, the relay device may provide a further level of addressing functionality. The relay may further gather information about which other relays are connected to the power line and also which wireless devices are in wireless communication with each of those relays. In this way, each relay retains a list of all wireless devices and which relay is able to communicate with them. Thus if a device 25, which is in wireless conmiunication with a relay 21, wants to send a message to device 23, which is in wireless communication with a relay 20, then device 25 initially transmits a message over the wireless network to be received by relay 21. Relay 21 identifies the destination device as device 23 and looks up which relay it needs to get the message to. It then retransmits the message over the power line and addresses this message to the destination relay 20. Although all relays receive the message, only the destination relay, relay 20, needs to react to it. Other relays simply note that the message is not addressed to them and take no further action. When relay 20 receives the message, it notes that the message is addressed to it and so retransmits it over the wireless network for reception by device 23.

This means that relay 22 only needs to look at the relay address information in the message, rather than receiving the message extracting the destination device information and looking it up in its own database, only to discover that it does not serve that device. With this arrangement, unnecessary processing of messages is avoided as only the appropriate relay responds to the message. Other relays do not need to process the message to determine which device the message is addressed to and then determine whether the device is one on its own network. This arrangement is particularly convenient where the number of devices may be large or where the extent of the network is not defined.

In most domestic applications, it can be assumed that the power line is contained within the house and so the network is limited to the relays within the house. In particular, if it is only the relay devices that are in communication over the power line then the additional routing function is not essential. It is therefore realistic to simply broadcast all messages over the power line network rather than addressing them to a specific relay device.

Although the network may be made up of a number of separate wirelessnetworks, it can operate as a unified network with the relays effectively bridging the gap between the separate networks. Reservation of resources to ensure reliable levels and quality of service can be achieved through a distributed management scheme, for example an admission-control and resource-reservation based approach could be applied to the power line network portion. This could be used to control admission to the power line network according to the overall system profile.

The embodiments described above provide a system for allowing distributed clusters of devices which connect over separate local wireless networks, to communicate with other devices as if they were connecting over one unified wireless network, even though they are out of range of the local network. This allows each of the local networks to be smaller as they only need to cover a shorter range. For example, the devices in room 30 in figure 2 need only conununicate with the other devices in that room which may be only 3 or 4 metres apart as compared to the unitary network of figure 1, where the required range may need to be tens of metres to ensure all devices are in range. This range requirement applies to all devices in an ad hoc network with no central access point Consequently, in the present invention, the power needed to provide the reduced range is less and leakage of signal into uncontrolled areas is much more limited.

Furthermore, since there may only be few devices transmitting over each local network, the available spectrum is likely to be greater allowing greater frequency reuse within a given area and less interference.

The collective group of local networks can still operate as if it were one unified wireless network even though parts may be widely distributed. For example, the network may be formed of a local network in a bedroom, a living room and a home office located in a separate annex to the property but sharing a common power line. The wireless devices would not need to know of the arrangement of the network as the retransmission of the signals to the distant local networks is seamless.

When installing a system such as the present invention, in order to maximise the benefit of the reduced size of each local network and hence the reduced power, interference and improved security, the relay needs to be located so that it can communicate with all the devices forming the local network. This can be done by physically locating the relay close to all the devices but this may not be practical. It is therefore useful if the relay can be positioned so that it can easily communicate with all the devices but without having to increase transmission power unnecessarily (and implicitly, each of the communicating devices having to increase power to conmiunicate with the relay).

The relays will need to be connected to a mains power source to allow communication and preferably to power the device. However, in modem homes most rooms are provided with several power sockets and so the user needs to identify the most appropriate, in order to maximise communication capability. Whilst it is desirable to integrate the unit into a plug-in unit, the relay may be provided with a conventional power lead, allowing it to be located away from the socket itself. However, this leads to even greater flexibility in the locating of the relay. It is therefore desirable to be able to guide a user as to the most suitable location in any given scenario. As no arrangement is likely to be like any other because of differences in room shapes, furniture, furnishing material, decorative materials and structural materials, this determination needs to be done on a bespoke basis for each relay.

The invention further provides a method for identifying suitable locations for relay devices to maximise the benefit of the invention. In order to assess the ideal location, it is necessary to firstly determine the environmental factors that affect the ideal location.

This in turn means generating a model of the room in which the relay is to be located.

Figure 3 shows the sequence of steps carried out to generate a model of the room which is suitable for analysis and then the calculation of the propagation properties of the modelled room.

Initially, the user uploads a series of images or photographs, which are then combined into a unified panorama. This image is then processed to identify the edges in the image to assist in identifying the features of the room. The generated edge data and room images are compared by the user to remove insignificant features and to add missed or hidden features. The user is again prompted to provide dimensional information to allow a scaled plan model of the room to be generated. The generated model is then used to carry out an analysis of the room based upon the identified features that allows a model of the propagation properties of the room to be developed. This can then be used to assist the user in identifying the prime location of the relay in the room.

In order to generate a basic plan of the room, a series of contiguous or overlapping images of the room are obtained. These can be obtained by the user taking a series of still images or a video sequence. These are then entered (Si) into a processing system such as a personal computer. The sequence of images allows a montage to be generated (S2) that effectively provides a panoramic view of some or all of the room. An example montage is shown in Figure 4. The montage can be generated automatically by the computer using known techniques or manually constructed on the screen by the user.

Many modem digital cameras have a built-in panorama function that assists the user in aligning the images more accurately.

Having generated the montage, the panoramic image can be cropped, as shown in Figure 5, both to reduce the number of edges and to minimise complexity and requirements imposed on the image processing. The cropped image is then processed (S3) to analyse the features of the image to identify edges within the image and thereby identify real objects in the room. Again, edge detection algorithms for processing images are well known in the art. The Canny edge detection algorithm is commonly cited. A typical approach is to look for abrupt changes in the gradient (i.e. the differential of brightness or hue of the image). In figure 6, a pictorial representation of the output of such an algorithm is shown overlaid onto the image of figure 5.

The edge detection results in many false positives, i.e. edges which are not required for the purposes of developing a model of a room. In figure 6, the edge 61 is part of a window-frame and edge 62 is a discontinuity resulting from the way in which the images were "stitched" together. As these edges are not required for formulating the room plan, it is preferable to remove them (S4). This can be done by displaying the processed image to a user and allowing them to select those edges that are not relevant.

A simple point-and-click interface could be used to allow the user to do this. In this way, the user can deselect edges representing features that do not relate to objects that will interfere with the communication in the room. The window frame and the discontinuity will clearly have little or no effect on the propagation of signals within the room. Similarly, surface features such as wallpaper may present an edge from the processed image and these can be identified as features to be disregarded by the user.

Following this filtering exercise, the user interface can also be used to receive user input identifying the parts of the image where the corners in the room are located (S5). The user would be asked to highlight edges that form vertices or corners in the room. The user would also have the opportunity to add corners or other features that have been missed. For example, in figure 6, the corner of the room on the left hand side has not been identified because it is located out of sight behind the unit. The user may note this and can manually indicate where the corner should be.

The system then uses a mapping algorithm to assess the information gathered from the images and as edited and supplemented by the user. The mapping algorithm then attempts to generate a model of the room from this information. If the necessary basic features have been found in the edge feature data then an initial model can be produced.

For example, the system needs at least two corners to determine where a wall is. If sufficient information is not available after it carries out the mapping algorithm (S 6), the system can prompt the user (S7) to provide additional information. Alternatively, if the model can be generated, the user can be presented with the initial model. If the model is an accurate representation, then the user can indicate their approval and the process moves on to step S8. If the model is not correct then the user can indicate this (S 7). The user can identify the error and if necessary provide additional information to allow the algorithm to be rerun to produce a revised model.

The fireplace shown in this example could be included in the analysis, particularly if it encroaches into the room substantially. However, it has been ignored in the following explanation for clarity.

Having filtered out the edge features and identified the corners (as shown in figure 7), the system can apply a scale to the image data. The system would therefore identify key features and distance for which dimensional data is required (S8). The user interface can be arranged to identify these dimensions superimposed on the image data to allow the user to identify what is needed and then provide the appropriate values. For example, the user would then be asked to provide the distances between the vertices labelled A - C in Figure 9. The application then analyses the edge features in isolation, i.e. without the other image data, to generate an initial flat view of the room. This is shown in Figure 10.

The system could infer that the room has four walls despite only three being shown in the provided images. The application can assume basic parameters of the room such as four walls, rectangular shape, etc as a default. However, the specific parameters such as actual number of walls, number of walls shown in the montage, shape of room, etc. can be provided manually by the user to allow more complex room layouts to be catered for.

The system is thus able to build up (S9) the plan-view model shown in Figure 11 from the user-provided distances, the relative distances of the home entertainment equipment units between the vertices, and basic assumptions such as rooms being generally rectangular. This plan can then be presented to a user and any errors or corrections can be indicated through the user interface. This preferably includes identifying items or locations in the room where a wireless device is located.

With knowledge of the location of devices, the system can identify "hot spots" where good radio coverage would be needed based on where the greatest numbers of items of home entertainment equipment are found. This has the added benefit that it can be inferred from the presence of home entertainment equipment that there are mains power outlet sockets at those locations.

However, a preferred approach is to use ray tracing (e.g. the paper entitled "Hotspot wireless LANs to enhance the performance of 3G and beyond cellular networks" by Doufexi et al, Communications Magazine, IEEE, Volume: 41, Issue: 7, July 2003, Pages: 58 - 65, describes a ray tracing system) to analyse the room to identify prime positions for the relay. l'his provides a much more reliable solution than simply looking for clusters of devices. If a room contains a cluster of devices and one additional device at the opposite side of the room then that device may be the limiting factor. One of the aims of the invention is to minimise transmission power of devices to avoid excessive power consumption and leakage of signal into uncontrolled areas. If the relay and the single device are widely spaced then this may require the device and the relay to increase their transmission power. It may therefore be better to locate the relay a little further away from the cluster of devices in order to improve communication with the remote device.

Similar problems can arise where the room is not uniform. In the example shown in figures 4 to 9, the room contains a chiinneybreast between the two sides of the room. In that example, several of the devices are located at either side of the chimneybreast. If the relay was collocated with one of the groups of devices then the other group would be located at the other side of the chimney, which represents a substantial obstruction and again requiring increased transmission power to ensure signals pass through or around the chimney.

The indoor radio environment is a very hostile one, in terms of both multi-path reflections and general signal propagation. Unlike outdoor environments where one field or one urban canyon is generally much like another, there is a wide variety of indoor environments, where the variations have significant impacts on the radio environment. These variations include differences in the building materials used (brick, cinder-blocks, breeze-blocks, stud/partitions walls, plasterboard, glass windows, suspended ceilings), the furnishings (soft upholstery, carpets and curtains, hard wooden or metal furniture) and the propagation complexity caused by both the enclosed space with significant reflections and refractions causing complicated multipath scenarios. In addition, the general clutter results in a reduced likelihood of line-of-sight (LOS) paths between the transmitter and receiver.

Consequently, very detailed, specific and complex models usually have to be employed in order to achieve accurate predictions of the ideal location. However, in a realistic environment such as a home, the ideal location is not essential and may be impractical if it suggests locating the relay 1 metre in the air in the middle of the room. The aim of this invention is to provide the user with information to assist in selecting a practical but effective place to locate a relay point.

Many models are available for calculating signal propagation. However, the invention starts with the application of the classic "inverse square" law for free-space propagation and the application of environment specific path-loss exponents (PLE).

The averaged (area mean) power (pa) comes from large transmitter/receiver separations in the range of hundreds to thousands of metres. It is a monotonically decreasing function of the distance, d, from the transmitter to the receiver. It depends on the path loss characteristics between the transmitter and receiver. The area mean power may be calculated as follows: Equation 1: Area Mean Power Where: Pa is the area mean power, C is an arbitrary constant that takes into account the transmitter power, gain of receiver & transmitter, and the wavelength, d is the distance from transmitter to receiver, d0 is the reference distance, y is the path loss exponent.

If the path-loss exponent (PLE), y, is given a value of 2, this equation reflects the theoretical free space propagation model. However, experimental results offer different PLEs for different environments and depending on whether the receiver is in direct line- of-sight (LOS) or non line-of-sight (NLOS) of the transmitter, resulting in semi- empirical models that more closely model reality. The spread of measured path losses about the mean are characterised by standard deviations ranging from 2.5 dB to 16.3 dB, low values being typical when a LOS path is present. PLEs typically range from about 1 to 6. Low values result from transmitters positioned close to a reflecting surface such that most of the signal going away from the receiver is reflected back towards it. The higher values tend to result from cluttered environments with poor line of sight communication and interposing walls, such as in office environments.

Therefore, it is important to select a suitable PLE value for the environment. This can be selected automatically or tailored for each application such as by providing the user with a selection of environmental scenarios, e.g. heavily cluttered room, which can then be used to select a suitable approximation of the PLE.

Taking each transmitter in turn, the field strength at increasing distances can be calculated using Equation 1 above with an appropriate selection of PLE. The total number of sample points calculated can be determined according to the processing power of the device doing the calculations and the time within which a result is required.

Figure 12 shows the modelled room plan with the chimney and fireplace features included. In this case, the two clusters of devices on either side of the obstruction are separated by an object that will largely prevent direct communication. Consequently, the optimum position for a PLAP to cover the whole room is actually on the other side of the room (as shown by the circle in Figure 13).

The ray tracing process involves considering rays from each of the devices within a room. Figure 12 shows an example of some of the rays considered as part of the process. Firstly, the system goes through the process of projecting a number of "rays" from each transmitter antenna. Whilst the total number of rays used can be selected according to desired processing time and processor power, the rays should have an even angular spread in directions. Although it is not shown in figure 12, the rays should be projected over 3600 because the effects of rays reflected from the wall behind the device can be significant. As mentioned above reflections from a wall close to the antenna can have a significant effect on the field strength, which is why experimentally PLEs can be better than the theoretical free-space value of 2.

By considering the paths of the rays and the decrease in signal strength with distance and due to reflection, a model of the room can be developed. Each reflection degrades the signal strength of the ray through a number of factors (including scattering, because the surface will not be a perfect reflector, absorption as heat into the surface, and the dielectric properties of the material). In addition, as the ray propagates around the room, it is governed by the path-loss equation, Equation 1 above. Different factors affect the amount of energy reflected when a ray meets a surface. These include the material that the surface is made from, the frequency of the signal and the angle of incidence. Again, if the information about the types of surface is provided by the user and with the advance knowledge of the operating frequency, the approximations can be improved. However, for simplicity, a benchmark value for all reflections could be used which would still give a sufficiently accurate picture of the radio environment for a typical home.

This process is repeated for each device to produce a plan of signal strengths for the room such as that shown in figure 14. By considering this plan of signal strengths, it can be determined where in the room the strongest signals from the collection of devices are and, by implication, where the devices would receive the strongest signals broadcast by the relay.

Figure 14 shows a representation of the resultant signal plan. Darker areas show stronger signals. They may be more than one good location based on a simple analysis but it may be necessary to review this information to fmd practical locations. By developing a signal strength plan such as that shown in figure 14, the user can determine where in the room to place the relay that is both efficient in terms of the communication with the devices in the room but also practical in terms of not being inconveniently located and positioned in or near a mains socket.

Whilst the signal plan can be used to display to the user to allow manual selection of the location of the relay, the process can be further automated. The signal plan indicates the signal strength at every point in the room and where the rays that make up that signal strength came from. This information may not be that easy for a user to identify from an image. Consequently, in a room with a number of strong transmitters but one weak short range device, a user may see an area of strong signal but not note that the signal from the short range device is insufficient as it is masked by the other devices.

Using the information available to it, the system can calculate the region in which the greatest number of transmitters' rays is represented. This may still be a fairly nebulous region covering most of the room. The system can then quantify that region to a degree by identifying an area in which these rays are all at their strongest (the point at which their field strength curves meet). In a one-dimensional room, this could be represented as shown in Figure 15, which shows an extreme example where you have a high power short-range device to contend with. Looking only at total signal strength, the user may place the relay at a position corresponding to arrow A. However, reception of the signal from the shortrange transmitter, shown in solid line, would not be possible. Instead, the system can take that into account and determine instead to propose a position such as at arrow B. Again, to give a qualitative picture to the user, the system could add additional information to the signal strength plan to weight the colours so that the area around position B is darkest. This means that the user still has a pictorial guide to use in finding the prime location. This ensures that regions that are highlighted represent points at which communication with all devices can be achieved.

The above method provides a way of identifying a suitable location fro the relay devices of the present invention. However, the technique can be applied to the location of any wireless device that needs to communicate with a plurality of other devices.

In the above embodiments, the relays simply pass signals from the wireless network to the power line. However, the relays could be arranged to adopt a store-and-forward approach to bridge between areas in the local wireless network (e.g. between the two clusters on either side of the chimney breast in Figure 13). This may further help to reduce transmission power from the devices when communicating with each other. In the example shown in figure 2, the Hi-Fi unit 25 may want to send an audio signal to the speakers 26a and 26b for reproducing sound. However, the speaker 26b is in the shadow of the chinineybreast 33. In order for the devices to communicate, they must increase their transmission power to try to penetrate the chimney or more likely rely upon reflected signals from the other walls and objects in the room. By providing the relay 21 with a bridging function, it could receive signals broadcast by the Hi-Fi unit 25 and retransmit them to the speaker unit 26b. Because both paths are line of sight and each is only half the distance of a reflective path, the power can be much lower.

Whilst the above invention has been described in a home environment, it is equally applicable for use in other environments such as offices, where it may be useful for extending a wireless network to a remote location, such as a warehouse.

The present invention allows existing wireless networks to be easily expanded by simply plugging a relay in a socket in one location in range of the current WLAN and then plugging a second or further relay into a socket in another location where a WLAN access is needed. The existing devices do not require modifing, as they would simply operate in their normal way to establish a communication link with the remote device.

The remote device would send out a solicitation message that would be received by one relay and passed to the other for retransmission. Other devices would then receive the message as if it had been received directly from the original sender and when responding would send a message that would be received by the local relay. The local relay would now know that the destination device was remote and therefore send the message over the power line to be received and retransmitted by the distant relay to the originating device. This would again assume that the message was received from the responding device directly. In this way, the extension of the WLAN can be seamless from the perspective of the devices connected to it.

The network described above is particularly suited to a home entertainment equipment that may include for example television, video player/recorder, DVD player/recorder, home cinema system, audio amplifier, CD player/recorder, record player, tape deck, digital/analogue radio, speakers, headphones, remote controls, and computer.

The skilled person will appreciate that the various embodiments and specific features described with respect to them could be freely combined with the other embodiments or their specifically described features in general accordance with the above teaching. The skilled person will also recognise that various alterations and modifications can be made to specific examples described without departing from the scope of the appended claims.

Claims

1. A wireless network relay for use in linking two wireless networks, the relay comprising: wireless communication means for communicating over a local wireless network; power line communication means for communicating with a remote relay over a common power line; and router means adapted to receive messages transmitted over the local wireless network and to transmit the message for reception by the remote relay over said common power line and further adapted to receive messages transmitted by a remote relay over the power line and to retransmit said message over said local wireless network.

2. A wireless network relay according to claim 1, further comprising storage means for maintaining a list of devices on the local wireless network.

3. A wireless network relay according to claim 2, further comprising first address detecting means arranged to determine if a message received over the local wireless network is intended for a device which is not included in said list, wherein said router is adapted to only transmit messages over said common power line means for reception by the remote relay when said address detecting means determines that a message is not included in said list.

4. A wireless network relay according to claim 2 or 3, further comprising: second address detecting means arranged to determine if a message received over the power line is intended for a device which is included in said list, wherein said router is adapted to only retransmit said message over said local wireless network when said second address detecting means determines that a message is included in said list.

5. A wireless network relay according to any one of the preceding claims further comprising second storage means for maintaining a list of devices on local wireless networks associated with other relay devices which the wireless network relay is in communication with over said power line, and for each device, storing information identifying the relay which is in wireless communication with the device.

6. A wireless network relay according to claim 5, wherein said router is adapted to transmit messages over said power line including routing information identifying the relay corresponding to the destination device identified by the message based upon the information in the second storage means.

7. A wireless network relay according to claim 5 or 6, wherein said router means is adapted to only retransmit, over said local wireless network, messages received from a remote relay over the power line which include information identifying the relay.

8. A wireless network relay according to any one of the preceding claims wherein the router means retransmits messages over said local wireless network in a form identical to the message originally transmitted by the originating device.

9. A relay according to any one preceding claim wherein the network is a WLAN according to one or more of the following IEEE8O2.l 1 protocols: a; b; e; g; n.

10. A communication system for providing a distributed wireless network formed of a plurality of separate local wireless networks, each formed of one or more wireless communication devices, and each local wireless network further comprising a wireless network relay according to any one of the preceding claims.

11. A communication system for providing a distributed wireless network formed of a plurality of remote wireless networks, the system comprising: a first relay device for wireless communication with a first group of devices forming a first wireless network; and a second relay device for wireless communication with a second group of devices forming a second wireless network, wherein each relay device includes: a power line communication means for communicating with the other relay device over a common power line; and router means adapted to receive messages transmitted over the respective wireless network and to transmit the message for reception by the remote relay over said common power line and further adapted to receive messages transmitted by the remote relay over the power line and to retransmit said message over said respective wireless network.

12. A method of generating location information for positioning a wireless communication device in a room, the method comprising: obtaining a panoramic image of at least a portion of the room; edge processing said panoramic image to identify edges of features within the panoramic image defining the edges of objects shown in the panoramic image; processing the panoramic image to identify the position of vertices of the room in the panoramic image; generating a room plan by determining the location of the vertices of the room based upon the identified position of vertices in the panoramic image and populating the room plan with the features of the room based upon the objects identified by said edge processing; carrying out ray tracing to determine the transmission power of a transmitter located in some or all of the objects identified at a plurality of positions within the room; combining the calculated transmission powers for the objects for each of said plurality of positions to generate said location information.

13. A method according to claim 12, further comprising forming said panoramic image using a sequence of images showing contiguous or overlapping portions of said portion of the room.

14. A method according to claim 12 or 13, further comprising generating a graphical representation of the room based upon the room plan and the location information.

15. A method according to claim 12, 13 or 14 further comprising: generating a first composite panoramic image including the panoramic image and the identified edges; displaying the first composite image on a display; inputting user selections of the displayed edges; and removing the selected edges from those identified.

16. A method according to any one of claims 12 to 15 further comprising: generating a second composite panoramic image including the panoramic image and the identified vertices; displaying the second composite image on a display; inputting user selections of the displayed vertices; removing the determined vertices from those identified; inputting information identifing additional vertices; and adding the additional vertices to those previously identified.

17. A method according to any one of claims 12 to 16, wherein said location information is based upon the summed calculated transmission powers for each of the transmitters at each of said plurality of positions.

18. A method according to any one of claims 12 to 16, wherein said location information is based upon the sum of the calculated transmission power of the transmitters for those of said plurality of positions where the calculated transmission power from each of the transmitters at that position is above a predetermined level.

19. A method according to any one of claims 12 to 18 wherein the wireless communication device is a relay device according to any one of claims 1 to 9 or a relay device of the communication system of claim 10 or 11.

20. A carrier medium carrying computer readable instructions for controlling a programmable device to carry out the method of any one claims 12 to 19

21. A relay device substantially as hereinbefore described with reference to the drawings.

22. A method of generating location information for positioning a wireless communication device substantially as hereinbefore described with reference to the drawings.