WO2004075599A1

WO2004075599A1 - Free-space optical communication network

Info

Publication number: WO2004075599A1
Application number: PCT/GB2004/000666
Authority: WO
Inventors: Jamieson Leigh Christmas
Original assignee: Alps Electric (Uk) Ltd
Priority date: 2003-02-22
Filing date: 2004-02-18
Publication date: 2004-09-02
Also published as: GB0304043D0; EP1595426A1; GB2398684A

Abstract

A data transmission network comprising a mesh of nodes having optical transmitters and receivers is disclosed. The transmission is preferably by modulated optical carriers, using laser diodes to transmit between nodes. High bandwidths are obtainable for local optical mesh networks. Intelligent self-healing techniques are further disclosed.

Description

FREE-SPACE OPTICAL COMMUNICATION NETWORK

This invention relates to networks. In particularly, but not exclusively, it relates to data or communications networks such as local area networks or wider networks. It may relate to networks in local neighbourhood or dwellings or workplaces which require connections to a wider network such as the Internet, television transmission network or other systems.

Conventionally, telephone lines have been used for such connections, or wire connections such Ethernet connections, and so on. More recently, wireless connections have begun to be used. These generally are of limited bandwidth and either require a physically separate line or connection from each access point (ie each house, office, etc) to a main point of connection such as a main Internet backbone.

The present invention arose in an attempt to provide an improved network.

According to the present invention there is provided a data or communication network, comprising a plurality of nodes each equipped with at least one optical transmitter and at least one optical receiver, the transmitter being adapted to transmit data optically to a receiver on another node and means at each node for receiving and/or transmitting data to or from its associated transmitter and receiver to a display or processing unit.

According to the present invention there is further provided a data network comprising a mesh of optical transmitters and receivers.

Preferably, each node is provided with two or more transmitters and two or more receivers.

Preferably, a router is associated with each node and data is passed through the router and routed out to a transmitter if the data is not intended for use at that node and to a data terminal at that node if the data is intended for that node.

Preferably, one or more of the nodes are connected to a remote communications system, for example, an Internet backbone.

The invention enables singles intended for any one node to be transmitted across any combination of nodes to be transmitted from the backbone to that particular node, or from one node to another, via one or more intermediate notes.

The apparatus further includes a self-healing routing mechanism which enables a transmitter at each node to transmit data to a desired receiver depending upon the ultimate route of the message and for dynamically altering the path in the event of node failures or alterations in node topology.

Preferably, each transmitter and/or receiver is steerable in order firstly that it may receive an optimum quality signal or transmitter optimum quality signal and also so that in the event that a link or node is functional, a transmitter or receiver can be steered so as to transmit or receive signals from an alternative node.

The self healing and or steering functions of the transmitters and receivers may apply to systems using other than optical transmission.

The invention further provides a data transmission system comprising a mesh of nodes, and means for transmitting data between the nodes, including a routing mechanism which enables a transmitter at each node to transmit data to a desired receiver depending upon the ultimate route of the message and for dynamically altering the path in the event of node failures or alterations in node topology.

The invention further provides a data transmission system, or network, comprising any one or more of the novel features described herein.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 shows an arrangement of nodes in a data transmission system;

Figure 2 shows a transmitter/receiver assembly; Figure 3 shows a routing apparatus at a node;

Figure 4 shows a node arrangement; and

Figure 5 shows a network. The present invention relates, in part, to a network, in particular an optical network, for use in transmitting data. The network may be used to transmit electronic data and information to or from users terminal which is intended for, or arrives from, the Internet or may be used for the transmission of other types of signal such as television signals, or even closed circuit signal or telephone/video phone calls.

Figure 1 shows a network of nodes la, lb, lc ... lh. These are houses or other dwellings or any other type of node at which Internet access is required for example. At each of these nodes will be a data terminal which could be a computer, digital television set or other terminals. This is connected to at least one receiver and transmitter, preferably at least two receivers and transmitters of optical signal at the node. The transmitters and receivers are adapted to transmit and receiver modulated optical radiation. Most preferably, the radiation is in the infrared band and may typically be of carrier frequency about 1550 to 1570 nm. They are mounted on the side, roof or other position on each building which forms a node so that communication transmitters and receivers are in direct line of site. By using wavelength such as those described, the optical transmission is substantially unaffected by weather conditions such as rain or fog. Data transmission between the receivers and transmitters is effected by modulating a carrier signal and preferred examples of modulation are described further below.

As shown in Figure 1, the nodes are arranged in a mesh network so that signals passing between one of them and any other them passes through the mesh between the two nodes. For instance, a message from node la to node lh will pass through node lb, lc and then lh. Note that in the event that any of these transmission paths are blocked or not functioning at any time, there is an alternative path from node la to Id to le to lc, lb and then to lh. In the example shown, the transmission and reception paths are not necessarily bi-directional. That is, a signal passes from la to lb in just one step. However, a return signal from lb to la must through lh, lg, If, Id, le and then back to la. It should be noted, however, that a system, in which the transmitters and receivers on adjacent nodes is actually communicating bi-directionally may of course be used in embodiments of the invention but then, if the transmission path is blocked for any reason, eg by a physical obstruction then both directions of transmission will be blocked whereas if the transmission and reception path are different, then only one of these is likely to be blocked.

Because the data is being transmitted by modulated optical radiation, the likely bandwidth is very high. Indeed, a bandwidth at least 600 Mb/sec, for example 622 Mb/sec is quite possible.

Generally, one of the nodes, in this case node lh is provided with a connection 2 to an external data network, ie typically the Internet, a digital television feed, or so on.

Figure 2 shows schematically a module which may house the transmitters and receivers at each node. In this example, two transmitters 3 and 4 are provided and two receivers 5 and 6. They are mounted within a housing 7 which is secured in this case to the side of a building at a position where it is in direct line of sight with other associated receivers and transmitters from other nodes. Most preferably, as discussed, the transmitters at least, and preferably also the receivers are steerable. The transmitter may be any sort of optical transmitter capable of producing a powerful enough signal to be received at a transmitter that may be situated from a few meters to a few hundred meters or even further. Plus, preferably, the transmitter comprise laser diodes and, as discussed, the preferred wavelength is roundabout 1550 nanometers. The advantage of this wavelength is that it substantially unaffected by weather conditions such as fog, mist, rain and also the radiation is absorbed by the human retina and so does not reach the back of the eye. Therefore, if the output from a laser is inadvertently directed at a person, it will not be dangerous. As discussed, with this type of optical radiation, a modulation rate and therefore data rate or bandwidth of at least 600 Mb is possible.

By arranging for the transmitter and/or receiver to have as wide an area of transmission, (divergence) as possible, the effects of physical obstructions between a respective transmitter and receiver is reduced. For example, with a very narrow directional beam, a bird flying between the two may temporarily block transmission. With a more divergent beam, however, as long as a bird does not fill the entire transmission area, the signal should still be passed.

Even if a transmission/reception path is temporarily blocked, reception can of course continue immediately after the obstruction has gone.

Figure 3 shows part of the transmitting/receiving arrangement at each node. A PC (personal computer) 12 or other terminal is situated at the node. This has an input 13 and output capable of receiving signals from and transmitting signals to the optical mesh. As described, each node in this example is provided with two receivers 3 and 4 and two transmitters 5 and 6. Each of these, together with a respective input and output from the PC out 14 and PC in 13 are provided to a router 16.

The router is able to transmit signals from any one of the three inputs 5, 6 and 14 to any of the three outputs. The router includes look-up-table means 17 to enable it to do this. More details of a router are described in a co-pending application, filed concurrently.

As is well known, Internet communication works by transmitting data as a series of packets and layers. One of which is the TCP/IP layer. Each packet is provided with the Internet address (IP address) of that package. The PC is provided with its own unique IP address. When a signal is received at a receiver and onto the router, the look-up-table 17 at the router looks to see initially whether the package is intended for that node itself, ie for that IP address. If it is, then this packet is transmitted to the PC in port 13 and onto the PC for displaying or processing. If the packet is not destined for the PC, then it is routed to one of the two transmitters 3 and 4. The look-up-table is provided with lists of the IP addresses of the remaining nodes in the local optical mesh (ie nodes la to lh in the example of Figure 1) and at any time contains details of the best route through the mesh to get to any one of the nodes. Thus, if transmitter Tx3 is considered to be the transmitter on the path between node la and lb and transmitter Tx4 is that which is directed towards node Id, then if the ultimate destination of the packet is node lb, the signal will be routed through to TX3. If the ultimate destination is node Id, then the look-up-table provides an indication of this and the packet is routed through to TX4. Similarly, if the ultimate destination is node lc then, referring to Figure 1, the transmission pass for this could either be via Id, le to lc or through lb, lh to lc. Thus, in this case three steps are necessary and so it could be routed through to either of these, although usually one of them will be given preference by the software or above the router 16. If, however, the packet is destined for an external address on the Internet, ie has to go out through the Internet backbone or other Internet connection 2, then it has to reach node lh. As seen in the example of Figure 1, the easiest method in this case would be to transmit it through node lb and therefore the signal will be sent to transmitter 3.

Alternate methods for more efficient routing are described in a co-pending patent application.

In one embodiment, the system periodically sends test signals out over the mesh and monitors the way that the signals are passed round the mesh so that if there are any changes to the mesh, eg one node goes down for any time or is blocked, then the system can generate a new look-up-table. This may be done at any desired interval. For example, if at any one time node lb is out of action then an alternative path to node lb must be found. This will, for example, be the path la to Id to le to lc to lb and so in this case the look-up- table and associated software in the route reprograms itself so that a packet intended lb is routed to Tx4, onto Id and through accordingly. Similarly, if new nodes are added to the system, the system can be made aware of these in a similar manner.

Possible network methods are as follows, although other may be used. In a first method illustrated in Figure 5, a mesh network includes sub-nodes Ni and N of an Internet network. Other nodes Na - Nn represent other addresses in the mesh. Each sub-node Ni and N₂ is provided with details of all addresses between it and the next sub-node and only Ni and N₂ communicate externally.

In an alternative, each node 'knows' a map of the local area (mesh). A node, upon connection, downloads a connection map. It then decides upon the best route, and may also consider data loading at the various addresses. A router in the system may periodically check connections and update the maps. Thus, all nodes may be provided with updatable maps.

In a further modification, only one or more 'master' nodes are provided with a map. All data is then sent to this node which then decides upon the best route.

A system it may further comprise steerable receivers and/or transmitters, as shown in Figure 2. In this case, if, for example, node lb is out of action, then there is no point transmitter 3 sending information to it. It is therefore preferable that the transmitter is able to be steered so that it can then lock on to a receiver at another node.

Referring to Figure 4, there is shown a situation in which a node In is 'connected' initially to receive signals from two nodes lo and lp and to transmit to two nodes lq and lr. If lq is out of action, or the path between In and lq is broken for any reason, then the transmitter at one end may be steered to try to find a further receiver. It may find a new receiver at node Is and thus set up the new directional path P shown in the figure. This same method can be used if a new node is added to an existing mesh. Of course, the transmitter at In may also be rotated further so it can communicate with a receiver at any other node or even with nodes lo or lp with which it receives signals, and so on. This may be termed 'self-healing'.

If a node is blocked for a very short time, then this may only be a temporary obstruction. If for a longer time period, then the system may be arranged to try to steer one or more of its transmitters after a predetermined time period has elapsed in order to try to find an alternative receiver. Once an alternative mesh pattern has been established, then a series of test signals may be passed around the mesh to determine the paths by which signals are transmitted and therefore to establish a new look-up-table which establishes the desired and most effective route from any one node to any other node, or from the Internet connection point 2 to and from any node. The methods for software or hardware based self-routing may be done with systems other than optical ones. Steering can also be useful to gain the best quality signal. In this case, a transmitter can be rotated slightly to obtain the best quality signal from a receiver.

The use of optical means to transmit data is well-known in itself and involves modulation of an optical carrier frequency. In embodiments of the present invention, many different modulation methods may be used. This may be amplitude modulation, frequency modulation, phase modulation or many others. Preferably, a bandwidth of at least 600 MB is obtained in embodiments of the invention.

Claims

CLAΓMS

1. A data transmission network comprising a mesh of nodes having optical transmitters and receivers.

2. A data transmission network as claimed in Claim 1, wherein each node comprises two or more transmitters and two or more receivers.

3. A data transmission network as claimed in Claim 1 or 2, wherein a router is associated with each node and data is passed through the router and routed out to a transmitter if the data is not intended for use at that node and to a data terminal at that node if the data is intended for that node.

4. A data transmission network as claimed in any preceding claim, wherein at least one of the nodes is connected to an external data transmission system.

5. A data transmission network as claimed in any preceding claim, using modulated optical radiation of carrier frequency around 1500-1600 nm, preferably 1550-1570 nm.

6. A data transmission network as claimed in any preceding claim, including a self- healing routing mechanism.

7. A data transmission system as claimed in Claim 6, wherein the self-healing routing mechanism enables a transmitter at each node to transmit data to a desired receiver depending upon the ultimate route of the message and for dynamically altering the path in the event of node failures or alterations in node topology.

8. A data transmission network as claimed in Claim 6 or 7, wherein the routing mechanism includes an updatable map.

9. A data transmission network as claimed in any preceding claim, wherein at least one transmitter or receiver is physically steerable.

10. A data transmission system comprising a mesh of nodes, and means for transmitting data between the nodes, including a routing mechanism which enables a transmitter at each node to transmit data to a desired receiver depending upon the ultimate route of the message and for dynamically altering the path in the event of node failures or alterations in node topology.

11. A data transmission system as claimed in Claim 9, including an updatable map.

12. A data transmission system as claimed in Claim 10 or 11, including steerable data transmission and/or reception means at each node.

13. A data transmission system comprising a mesh of nodes, including a self-healing mechanism.

4. A data transmission system substantially as hereinbefore described, with reference o, and as illustrated by, any of the accompanying drawings.