GB2455794A - Establishing a multi-hop route in wireless network - Google Patents

Abstract

A transmitter initiates multi-hop route discovery when a direct link between a source transmitter and a destination receiver is unavailable. The transmitter initially transmits RREQs to candidate nodes that are identified as being in substantially the same direction as the destination node. The transmitter, and also any intermediate nodes that route the RREQ, may delete, insert and/or modify channel quality information from and in the RREQ. The channel quality information may be derived from signal quality measurements monitored over time. In this way, a receiver may select one of the multi-hop routes based on signal quality.

Description

1 2455794 Multi-hop routing method and apparatus The invention is concerned with a method and apparatus for multi-hop routing in networks using directional antennas. The invention can be employed particularly, but not exclusively in 60 GHz wireless personal area networks.

High data rate communications in the 60 GHz band have received considerable interest, especially for use in the home network area. Ongoing standards development efforts in this area include proposals by the IEEE 802.1 5.3c Millimeter Wave Alternative PHY Task Group (TG3c) (http://www.ieee802.org/l5/pub/TG3c.html) and the Wirelessl-IDTM Special Interest Group (http://www.wirelesshd.org).

In addition to the potential of extremely high data rate (several Gbps) to support applications such as uncompressed High-definition television (HDTV) and video-on-demand, one advantage of 60 0Hz systems is that directional antennas are much easier to implement than at 5 GHz. This is because of the smaller wavelength and smaller fractional bandwidth (see, for example, N. Guo et a!., "60 GHz millimetre-wave radio: principle, technology, and new results", Journal on Wireless Corn. and Networking, 2007).

Past work has shown that, in terms of signal-to-noise ratio (SNR) at a receiver, directional antennas bring two major benefits, namely increased spatial reuse and improved signal quality. A study by Li eta! (G. Li et a!., "Opportunities and challenges for mesh networks using directional antennas", IEEE WiMesh, 2005) suggests that, as a result, directional antenna technology can lead to a capacity/throughput improvement of two or four times depending on the topology. Moreover, directional antennas have higher gains than omni-directional antennas and hence have a longer transmission range. Therefore, networks using directional antennas are expected to have improved routing performance and better network connectivity.

On the other hand, the 60 GHz band currently requires line of sight (LOS) between transmitter and receiver. Furthermore, the capability of 60 GHz transmissions to diffract around obstacles is much less than that of 5 GHz, for example, thus limiting its range.

Moreover, higher frequency results in higher path loss.

It is envisaged that nodes operating in accordance with high data rate communications in the 60 GHz band can be equipped with a directional antenna consisting of N antenna elements, where each antenna element has an azimuthal radiation pattern spanning an angle of 27tfN radians. An exemplary antenna system of six elements, which collectively cover the entire plane (360 degrees), is shown in Figure 1.

Such nodes could further be expected to exhibit at least some of the following features: the ability to maintain the orientation of the antenna elements at all times, irrespective of node movement; the use of a Medium Access Control (MAC) protocol able to select electronically any one or all of the antenna elements for transmitting a signal; when receiving a signal, a node can use the signal from the antenna element that has the maximum power of the desired signal; and, the use of only one transceiver (radio interface) at each node. The latter feature is considered to constitute a bottom-line' scenario, since multiple radios enable much simpler protocols, in part because problems such as deafness and hidden nodes can be solved more easily.

As the MAC protocol for 60 GHz networks has not yet been standardized, networks described hereinafter are discussed with reference to existing MAC protocols, such as 802.11, 802.15.3, or WiMedia, though the present invention is not limited thereto.

Furthermore, it will be appreciated that network codes can be fully distributed (as in 802.11 ad hoc mode or WiMedia), or there can be a central node (e.g. an Access Point, AP).

In conventional 802.11 or 802.15.3 networks, omni-directional transmission and reception of beacons or HELLO messages are used to identify neighbours. In a network with directional antennas, these messages are still transmitted (e.g., by an AP) omni-directionally (i.e. on all antenna elements). Upon receiving such a message, a station records the direction of the sender by noting the antenna element that received the maximum power. It then uses the antenna element towards that specific direction to send back a response message. After the discovery process, each node has built up a topology lookup table containing two fields: NodelD and Antenna, the latter being the antenna element used to beamform towards the node with the NodelD.

For contention-based MAC protocols in networks implementing directional communications, proposals in the art are similar to basic IEEE 802.11 DCF or 802.1 le EDCA, with adaptations for directional antennas (R. Choudhury et a!., "Using directional antennas for medium access control in ad hoc networks", ACM Mobicom, 2002). Channel reservation is performed using a Request-to-SendlClear-tO-Send (RTS/CTS) handshake between a sender S and a receiver D. When S wants to send a data packet to D for the first time there are two options: if S already knows the direction of D (from the lookup table), it transmits a RTS directionally to D; otherwise, it transmits a RTS to D on all antenna elements. Node D receives the RTS intended for it and estimates the direction from which it received the RTS. It checks its lookup table to see if there is an entry of S. If not, it records NodelD and Antenna of S. On the other hand, if there is already an entry of S but with a different direction (antenna), it updates the entry with the new direction since relative positions between nodes may change due to mobility. D then uses the same antenna element with which it received the RTS to send back a CTS. Similarly, S estimates the direction of D while receiving the CTS packet, and updates this information in its own lookup table. After the RTS-CTS handshake is performed successfully, S starts transmitting data packets using the antenna element pointing towards D. In the case of 802.lle EDCA (enhanced distributed channel access), S can send multiple frames within a TXOP (transmission opportunity).

Nodes in the neighbourhood of S and D which overhear the RTS-CTS dialogue defer transmission for the proposed duration of transfer using a NAV (network allocation vector) table, similar to 802.11. An enhancement for directional antennas is that these nodes defer transmission only for the antenna element with which RTS or CTS is overheard (R. Choudhury et al., "Using directional antennas for medium access control in ad hoc networks", ACM Mobicom, 2002). In this case, each node maintains a directional NAV table comprising of the fields Antenna and Blocked. On overhearing a RTS or CTS on antenna element i, a node sets the Blocked flag for element i, for the proposed duration. Subsequently, this node defers transmissions which requires use of element 1. After the proposed duration is over, the Blocked flag is reset.

One of the problems in 60 GHz systems is that obstacles in the LOS path between the transmitter and receiver can attenuate the signal by 20-30 dB, resulting in link outage (C. Leong el al., "A robust 60 GHz wireless network with parallel relaying, IEEE ICC'04"). In other words, the one-hop link between two nodes can be easily blocked or broken by obstacles. Given the appropriate network infrastructure, connectivity can be established through a multi-hop link.

In standard multi-hop routing protocols such as Dynamic Source Routing (DSR) or Ad-Hoc On-demand Distance Vector Routing (AODV) using omni-directional antennas, route discovery is accomplished by the source sending out route request (RREQ) packets to all the neighbours. These RREQs will then be forwarded all the way to the destination, which in turn replies with a route reply (RREP) packet to the source. When nodes use directional antennas with N elements, RREQs have to be transmitted to the neighbours over all the N antenna elements, a process known as sweeping'. It is also possible to employ a splitter' to transmit the same message over multiple antennas simultaneously. However, such multi-directional transmissions generate an excessive amount of redundant traffic and exaggerate interference in the shared medium among the neighbouring nodes.

Aspects of the invention seek to mitigate or eliminate at least some of the above mentioned problems or disadvantages.

Broadly speaking the present invention provides that, when a direct link between a transmitter and a receiver is unavailable, the transmitter initiates a route discovery process by transmitting RREQs to nodes that the transmitter identifies as candidates for a first hop in a mul ti-hop route to the receiver. Initially, these candidate nodes comprise nodes that are in substantially the same direction as the receiver relative to the transmitter, thereby reducing network flooding. If required, however, the transmitter may also transmit RREQs to nodes in other directions. These directions are sequentially selected. The transmitter, and each intermediate node, may delete, insert and/or modify channel quality information from and in the RREQ, such that the RREQ accumulates information about the quality of the multi-hop route as it travels the network. The channel quality information may be derived from signal quality measurements monitored over time. In this way, a receiver may select one of the multi-hop routes based on signal quality. The decision of multi-hop route selection based on signal quality (rather than other factors such as load) is due to the fact that in 60 GHz systems signal quality is a determining factor in network connectivity, especially in the case of obstacle blockage.

According to a first aspect of the invention, there is provided a transmitter for use in a wireless communications network, the transmitter comprising: means for transmitting signals in any one of a plurality of directions; means for storing information about nodes in the network, the information about a node comprising information indicative of a direction to or a location of the node relative to the transmitter; and means for identifying one or more neighbouring nodes as candidates for a first hop in a multi-hop route from the transmitter to a destination node, in response to detecting an impairment in a direct communication link between the transmitter and the destination node, wherein said one or more nodes are in substantially the same direction as the destination node relative to the transmitter.

According to a second aspect of the invention, there is provided a transceiver for use in a wireless communications network, the transceiver comprising: means for transmitting and receiving signals in any one of a plurality of directions; means for monitoring a channel quality of a communication link between the transceiver and neighbouring nodes; and means for deleting, modifying and/or inserting channel quality information from or in a received route request packet.

According to a third aspect of the invention, there is provided a receiver for use in a wireless communications network, the receiver comprising: means for receiving signals from any one of a plurality of directions; means for processing received route request packets, a route request packet being associated with a particular multi-hop route between a source node and the receiver, a received route request packet containing information about a channel quality of the multi-hop route; and means for selecting a multi-hop route based on said channel quality information.

According to a fourth aspect of the invention, there is provided a wireless communication network comprising: a transmitter according to the first aspect of the invention; at least one transceiver according to the second aspect of the invention; and a receiver according to the third aspect of the invention.

According to a fifth aspect of the invention, there is provided a route request packet indicative of a request to establish a multi-hop route between a source node and a destination node, the packet comprising: a packet structure field for storing information about a channel quality of the multi-hop route, wherein said information comprises a set of one or more deletable, modifiable and/or insertable channel quality indicators, each indicator being indicative of the channel quality of one or more communication links traversed by and/or to be traversed by the packet.

According to a sixth aspect of the invention, there is provided a method of identifying candidate nodes in a wireless communications network at a transmitter having means for transmitting signals in any one of a plurality of directions, the method comprising: storing information about nodes in the network, the information about a node comprising information indicative of a direction to or a location of the node relative to the transmitter; detecting an impairment in a direct communication link between the transmitter and a destination node; and identifying one or more nodes as candidates for a first hop in a multi- hop route from the transmitter to a destination node in response to said detecting, wherein said one or more nodes are in substantially the same direction as the destination node relative to the transmitter.

According to a seventh aspect of the invention, there is provided a method of routing a received route request packet at a transceiver in a wireless communications network, the route request packet originating from a source node and intended for delivery to a destination node, the method comprising: monitoring a channel quality of a communication link between the transceiver and neighbouring nodes; and deleting, modifying andlor inserting channel quality information from or in a received route request packet prior to transmitting said packet.

According to an eighth aspect of the invention, there is provided a method of selecting a multi-hop route in a wireless communications network at a receiver, the receiver having means for receiving signals from any one of a plurality of directions, the method comprising: processing one or more received route request packets, a route request packet being associated with a particular multi-hop route between a source node and the receiver, a received route request packet containing information about a channel quality of the multi-hop route; and selecting a multi-hop route based on said channel quality information.

According to a ninth aspect of the invention, there is provided a method of establishing a multi-hop route between a source node and a destination node in a wireless communications network, the method comprising: identifying first hop candidate nodes in accordance with the sixth aspect of the invention, and transmitting a route request packet to the destination node via said candidate nodes; routing said route request packet in accordance with the seventh aspect of the invention; and selecting a multi-hop route at the destination node in accordance with the eighth aspect of the invention, and transmitting a route reply packet to the source node via the selected multi-hop route.

According to a tenth aspect of the invention, there is provided a computer program for implementing apparatus according to any one of the first, second or third aspect of the invention.

According to an eleventh aspect of the invention, there is provided a carrier medium carrying processor executable code for controlling a processor to carry out the method of any of the sixth, seventh or eight aspect of the invention.

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures, in which: Figure 1 depicts the azimuthal radiation pattern of node having six antenna elements; Figure 2 depicts the azimuthal radiation pattern of a node having four antenna elements; Figure 3 shows a schematic of a node according to the present invention; Figure 4 schematically illustrates route discovery in a network of nodes; Figure 5 is a flow diagram showing the operation of a source node; Figure 6 is a flow diagram showing the route discovery initiation process of figure 5; Figure 7 shows a route request packet as known in the art; Figure 8 shows a route request packet according to the present invention; Figure 9 is a flow diagram showing operation of a destination node; Figure 10 illustrates handover in a network of nodes.

An exemplary wireless network according to the present invention comprises a set of wireless stations (hereinafter, referred to as wireless stations' or just stations') operating under the auspices of an access point (AP'). Entities in a network, such as the AP and the stations, may also be referred to as nodes', which is a generic term referring to a point of communication in a network. The AP may include an 802.11 access point or 802.15.3 piconet controller in a home network. In these protocols, the AP knows the direction (or position) of all the nodes in its cell. More specifically, the AP maintains a lookup table (or topology map) that includes NodelD and Antenna for all the nodes.

This table is updated regularly by using beacons or HELLO messages to take into account changes, such as an antenna element change caused by node movement.

Depicted in figure 2 is an exemplary node 200 equipped with a multi-directional antenna consisting of four antenna elements (not shown). Each antenna element of the node covers one of four 90 degree sectors in the azimuth direction, such that they collectively cover the entire plane (360 degrees). For convenience, antenna elements are referred to in the context of the sector in which the main lobe of their transmission pattern 201, 202, 203, 204 extends.

Referring now to figure 3, in an embodiment of the present invention, a node 300 comprises a processor 302 operable to execute machine code instructions stored in a working memory 304 and/or retrievable from a mass storage device 306. By means of a general-purpose bus 308, user operable input devices 310 are in communication with the processor 302. The user operable input devices 310 comprise any means by which an input action can be interpreted and converted into data signals, for example, DIP switches.

Audio/video output devices 312 are further connected to the general-purpose bus 308, for the output of information to a user. Audio/video output devices 312 include any device capable of presenting information to a user, for example, status LEDs.

A communications unit 314 is connected to the general-purpose bus 308, and further connected to an antenna or set of antennas 316. By means of the communications unit 314 and said antenna 316, the node 300 is capable of establishing wireless communication with other nodes. The communications unit 314 is operable to convert data passed thereto on the bus 308 to an RF signal carrier in accordance with a communications protocol previously established for use by a system in which the node 300 is appropriate for use, for example WirelessHD.

In the node 300 of figure 3, the working memory 304 stores applications 318 which, when executed by the processor 302, cause the establishment of an interface to enable communication of data to and from other nodes. The applications 318 thus establish general purpose or specific computer implemented utilities and facilities that are used in linking nodes.

As shown in figure 4, and referring also to the flow diagram illustrated in figure 5, when an AP 400 in a network 402 detects impairment (step S502) in a link 406 between itself and a destination node 408, it initiates a multi-hop route discovery process (step S504).

Link 406 comprises an established or a prospective wireless path over which information can be communicated.

Impairment is an adverse effect that could be caused by factors such as, but not limited to, interference and environmental conditions, including when an obstacle 410 moves and completely blocks the LOS path between the access point 400 and the destination node 408. Detection could be implemented by detection of received signal measurements or MAC layer timeout, for example.

Referring now also to figure 6, the route discovery process comprises the steps of: S602 the AP 400 determining the direction to or location of the destination node 408; S604 the AP 400 identifying one or more first-hop candidate nodes, initially in the same direction to or location of the destination node; S606 the AP 400 sending RREQs to identified candidate nodes; S608 the AP 400 waiting for a RREP originating from the destination node 408; and S610 the AP 400 deciding whether steps S604-S608 need to be carried out again, but in respect of an alternative direction.

Step S602 could be based on signal strength ratios between antenna elements, Global Positioning System (GPS) searches, or other direction finding methods known in the art.

Furthermore, it will be appreciated that such techniques need not be performed at the time of route discovery, so that step S602 may simply comprise checking for information in a lookup table stored at the AP 400.

Instead of using a sweeping route discovery in step S604, which has high overhead, the AP 400 initially tries to find a relay node in a similar direction or location to node 408.

Thus, if the destination node 408 was originally reachable via antenna element 1, the AP will first identify and send RREQs to nodes reachable with element 1, that is nodes 412, 413, and wait for a RREP response originating from the destination node 408.

If the relay search and route reply in sector I fails after a timeout period (S610, No'), the access point will search the neighbouring sectors for a node with respective antenna elements i+l (mod N) and i-I (mod N) sequentially (i.e. sectors 2 and 4). For clarity, only one node 414 in one sector 4 is depicted. This process continues until a path to an

II

available neighbouring node is found and a RREP originating from the destination node is received (S610, Yes'), or all the antenna elements have been tried.

Turning now to figure 7, RREQs 700 in the art, such as those of the standard Ad-Hoc On-demand Distance Vector Routing (AODV) protocol (RFC 3561, http://www.faqs.org/rfcs/rfc3561.html), contain, among other things: source, destination and broadcaster ID fields (702, 704, 706). This enables identification of the source node, the destination node, and any intermediate node that elects to forward the RREQ.

In addition, they also include sequence number and hop count fields (not shown). A sequence number is implemented to determine unique RREQs and maintain freshness, while a hop count, which is incremented at each node that processes the RREQ, indicates the number of proxy hops the packet has traversed.

In the present invention, and with reference to figure 8, each RREQ 800 may include a channel quality field 808 for incorporating information 810, 812, 814 indicating a quality of a link between a RREQ broadcasting node and a RREQ receiving node. The information may comprise a signal quality of that link. Thus, as the RREQ 800 travels the network, it accumulates information about the signal quality of each link that it traverses and, by extension, about the quality of a multi-hop route between a source node and a destination node.

In this way, a route can be selected by the destination node based on signal quality. The decision of multi-hop route selection based on signal quality (rather than other factors such as load) is due to the fact that in 60 0Hz systems signal quality is a determining factor in network connectivity, especially in the case of obstacle blockage.

Preferably, a RREQ broadcaster inserts channel quality information corresponding to a local signal measurement of the next hop link, though a RREQ receiver could also insert information corresponding to a local signal measurement of the preceding hop link prior to re-broadcasting the RREQ.

It will be apparent that, as the route hop count increases, the amount of information included in the channel quality field 808 of the RREQ packet 800 increases accordingly.

While for shorter routes the additional overhead associated with such an increase may not be significant, this may prove burdensome for extended routes or where packet size is limited or fixed. In such circumstances, the information about links may be combined, for example to generate a single average link quality value 816, rather than merely adding to an existing set of qualities 810, 812, 814.

Each node can use instantaneous signal strength measurement, e.g. SNR or received signal strength indicator (RSSI) measured by a wireless card and reported to the network interface driver. However, because the original measurements of signal quality are very bursty with multiple spikes and drops, it could lead to oscillation in route selection (and handover as discussed later). One solution is to incorporate historical information and use a smoothing filter, e.g. exponential weighted moving average: SO) = aS(j-l) + (1-a)x(j), where SO) is the value of the filter at time j, x(j) is the measured signal quality at time i' and a is the smoothing factor. This approach requires the nodes continuously monitoring wireless links.

There are two options in using channel quality for route selection.

Firstly, route discovery can avoid a "bad" path by letting intermediate nodes drop (i.e. not forward) a RREQ if the SNR of the link in question falls below some fixed threshold. It should be noted that the threshold should be properly chosen so that at least basic network connectivity is maintained. The destination node chooses the route recorded in the first arriving route request and replies with a RREP (route reply), as it is the shortest path (with minimum hop count) that consists of links with sufficient signal quality.

Secondly, each node along a prospective route forwards RREQs as in standard routing, but includes its local measurement of SNR in the RREQs, as discussed above. For example, a RREQ for prospective route 416 (400-4 1 2-'408) depicted in figure 4 will incorporate the SNR of link 41 6a, as measured by node 400, and the SNR of link 41 6b, as measured by node 412. Similarly, a RREQ for route 418 (400-*4 1 3-408) will include the SNRs of links 418a, 418b. If, for example, the quality of link 416a is below a predetermined threshold the access point drops the RREQ corresponding to that node.

Intermediate nodes 412, 413 may know the direction or location of the destination node 408 from overhearing destination node transmissions, estimating a direction and updating their lookup tables. On the other hand, if intermediate nodes do not know the direction of the destination node, they transmit the RREQ omni-directionally.

An exemplary method of selecting a multi-path route at the destination node will now be described with reference to figure 9. After receiving the first RREQ packet (step S902) the destination node 408 waits for a certain amount of time to learn all the possible routes (step S904). In order to learn all the routes and their quality, the destination node accepts RREQs received from different previous nodes. The destination then chooses the route with the best quality (step S906), e.g. the route with the maximum SNR, SNR= min(SNR1), where SNRI is the signal quality of link i. It then sends a RREP packet back to the source along the reverse selected route (step S908).

Furthermore, and unlike AODV, only the destination node can answer RREQs in the present invention; intermediate nodes cannot respond with a RREP. This ensures that the most up-to-date information is used when selecting routes and the complete route is taken into account in the route cost computation. The relationship between the route cost and the individual link cost depends on the parameter(s) characterizing the signal quality. This falls into the standard Q0S routing problem, possible solutions to which have been proposed in previous work (UK Granted Patent 2409600).

The inventors envisage that in a small network such as a home network, most of the time two-hop paths are sufficient to maintain connectivity.

Due to the small coverage in 60 GHz home network systems each indoor area, such as a room, may have to be covered by a cell; that is, an access point node, a hub node or a bridge node (hereinafter generally referred to as a serving node). When multiple cells are deployed in a home or office, stations can maintain connectivity via handover in case of movement or obstacles.

Normally a handover decision is based on signal strength. However, this process has to take into account the use of directional antennas: the signal strength of beacons sent omni-directionally from serving nodes is smaller compared to that of packets sent out directionally (assuming the transmit power remains the same). In one handover approach according to the present invention, beacon signal strength (RSSI) is used for triggering handover. In other words, handover is triggered when the RSSI value of the associated control node falls below a fixed threshold. The station then starts a scan and chooses a new serving node based on the highest received RSSI in the scan response. In another fast handover approach according to the present invention, handover is triggered when the RSSI of a new serving node exceeds the RSSI of the current control node, taking into account an additional hysteresis factor.

As shown in figure 10, station 1002 is originally served by node 1004 with antenna element 2. It then moves away from cell 1008 towards cell 1010, so the signal strength of serving node 1004 decreases until it drops below a certain threshold. In the meantime the signal strength of serving node 1006 increases, so station 1002 decides to handover to serving node 1006. Serving node 1006 is operable to send out beacons omni-directionally, and station 1002 notes the direction from which it receives the beacons.

Similarly, from the re-association message station 1002 sends to serving node 1006, node 1006 notes the direction of station 1002 and subsequently uses an appropriate antenna element (in this case element 3) for communication with station 1002.

In a multi-cell environment, when the quality of a one-hop link deteriorates, there are two options to maintain connectivity: from the serving node side, it can try to find an alternative, multi-hop route; from the station side, it can scan for other serving nodes and initiate a handover. Which option to choose depends on many factors. For example, when the traffic flow is from the station to the Internet via the serviced node, handover seems to be a good choice using the signal quality as a criterion. On the other hand, if the traffic flow is between two serviced nodes in the same cell, staying in the same cell and connecting via a multi-hop route is better.

While the invention has been described in the context of a home network where a plurality of nodes operate in the 60 GHz band, those skilled in the art will appreciate that its teachings are applicable to other communication networks operating in other frequencies.

Furthermore, it will be understood that, although antennas according to embodiments of the present invention are described as being 600 or 900 angularly sectorised antennas, embodiments of the present invention are not limited to such a configurations. For example, antennas according to embodiments of the present invention may utilise one or more antenna elements to beamform towards a target node, such that the transmission patterns are not necessarily fixed or rigidly determined.

The skilled person will recognise that the above-described apparatus and method may be embodied as processor control code, for example on a carrier medium such as a disk, CD-or DVD-ROM, programmed memory such as read only memory (Firmware), or on a data carrier such as a n optical or electrical signal carrier. For many applications embodiments of the invention will 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 programme code or microcode or, for example code for setting up pr 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. 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.

Claims (20)

1. CLAIMS: 1. A transmitter for use in a wireless communications network, the transmitter comprising: means for transmitting signals in any one of a plurality of directions; means for storing information about nodes in the network, the information about a node comprising information indicative of a direction to or a location of the node relative to the transmitter; and means for identifying one or more neighbouring nodes as candidates for a first hop in a multi-hop route from the transmitter to a destination node, in response to detecting an impairment in a direct communication link between the transmitter and the destination node, wherein said one or more nodes are in substantially the same direction as the destination node relative to the transmitter.
2. 2. A transmitter according to claim 1, further comprising means for monitoring a channel quality of a communication link between the transmitter and neighbouring nodes, and means for inserting in a route request packet information about the channel quality of a communication link between the transmitter and the neighbouring node to which said packet is transmitted.
3. 3. A transmitter according to claim 2, wherein said channel quality information comprises a signal quality measurement indicative of signal quality variations over time.
4. 4. A transmitter according to any one of claims I to 3, and comprising means for iteratively selecting another direction from among said plurality of directions in which to perform said identifying, said means being further adapted to sequentially select said another direction such that a selected direction is adjacent to a direction in which node identification has already been performed, each iteration being in response to a failure to receive a route reply packet within a given time period and continuing until a route reply packet is received or all of said plurality of directions are exhausted.
5. 5. A transceiver for use in a wireless communications network, the transceiver comprising: means for transmitting and receiving signals in any one of a plurality of directions; means for monitoring a channel quality of a communication link between the transceiver and neighbouring nodes; and means for deleting, modifying andlor inserting channel quality information from or in a received route request packet.
6. 6. A receiver for use in a wireless communications network, the receiver comprising: means for receiving signals from any one of a plurality of directions; means for processing received route request packets, a route request packet being associated with a particular multi-hop route between a source node and the receiver, a received route request packet containing information about a channel quality of the multi-hop route; and means for selecting a multi-hop route based on said channel quality information.
7. 7. A receiver according to claim 6, wherein the channel quality information contained in each received route request packet comprises a set of one or more channel quality indicators, each indicator of a set being indicative of a channel quality of one or more communication links traversed by the packet such that the set is indicative of the quality of the multi-hop route, the means for processing being operable to identify, for each set, the indicator associated with the lowest channel quality, the means for selecting being operable to select the multi-hop route associated with the set having the highest of the identified lowest channel quality.
8. 8. A receiver according to claim 6 or 7, wherein said channel quality information comprises a signal quality measurement indicative of signal quality variations over time.
9. 9. A wireless communication network comprising: a transmitter according to any one of claims 1 to 4; at least one transceiver according to claim 5; and a receiver according to any one of claims 6 to 8.
10. 10. A wireless communication network according to claim 9, wherein the network comprises a wireless personal area network operating substantially in the 60 0Hz band.
11. 11. A route request packet indicative of a request to establish a multi-hop route between a source node and a destination node, the packet comprising: a packet structure field for storing information about a channel quality of the multi-hop route, wherein said information comprises a set of one or more deletable, modifiable and/or insertable channel quality indicators, each indicator being indicative of the channel quality of one or more communication links traversed by and/or to be traversed by the packet.
12. 12. A method of identifying candidate nodes in a wireless communications network at a transmitter having means for transmitting signals in any one of a plurality of directions, the method comprising: storing information about nodes in the network, the information about a node comprising information indicative of a direction to or a location of the node relative to the transmitter; detecting an impairment in a direct communication link between the transmitter and a destination node; and identifying one or more nodes as candidates for a first hop in a multi- hop route from the transmitter to a destination node in response to said detecting, wherein said one or more nodes are in substantially the same direction as the destination node relative to the transmitter.
13. 13. A method according to claim 12, further comprising monitoring a channel quality of a communication link between the transmitter and neighbouring nodes, and inserting in a route request packet information about the channel quality of a communication link between the transmitter and the neighbouring node to which the control packet is transmitted.
14. 14. A method according to claim 12 or claim 13, and iteratively selecting another direction from among said plurality of directions in which to perform said identifying, said selecting being a sequential selecting such that a selected direction is adjacent to a direction in which node identification has already been performed, each iteration being in response to a failure to receive a route reply packet within a given time period and continuing until a route reply packet is received or all of said plurality of directions are exhausted
15. 15. A method of routing a received route request packet at a transceiver in a wireless communications network, the route request packet originating from a source node and intended for delivery to a destination node, the method comprising: monitoring a channel quality of a communication link between the transceiver and neighbouring nodes; and deleting, modifying and/or inserting channel quality information from or in a received route request packet prior to transmitting said packet.
16. 16. A method of selecting a multi-hop route in a wireless communications network at a receiver, the receiver having means for receiving signals from any one of a plurality of directions, the method comprising: processing one or more received route request packets, a route request packet being associated with a particular multi-hop route between a source node and the receiver, a received route request packet containing information about a channel quality of the multi-hop route; and selecting a multi-hop route based on said channel quality information.
17. 17. A method according to claim 16, wherein the channel quality information contained in each received route request packet comprises a set of one or more channel quality indicators, each indicator of a set being indicative of a channel quality of one or more communication links traversed by the packet such that the set is indicative of the quality of the multi-hop route, the method further comprising: identifying, for each set, the indicator associated with the lowest channel quality; and selecting the multi-hop route associated with the set having the highest of the identified lowest channel quality.
18. 18. A method of establishing a multi-hop route between a source node and a destination node in a wireless communications network, the method comprising: identifying first hop candidate nodes in accordance with any one of claims 12 to 14, and transmitting a route request packet to the destination node via said candidate nodes; routing said route request packet in accordance with claim 15; and selecting a multi-hop route at the destination node in accordance with claim 16 or 17, and transmitting a route reply packet to the source node via the selected multi-hop route.
19. 19. A computer program for implementing apparatus according to any one of claims 1 to 8.
20. 20. A carrier medium carrying processor executable code for controlling a processor to carry out the method of any of claims 12 to 17.