RADIO NETWORK

Abstract: A communication system is provided which can provide a broadband communications link into a number of homes and/or businesses. The communication system provides this broadband communications link by broadcasting the data using a network of radio nodes. The network of radio nodes is preferably arranged so that there are a plurality of independent data paths which can be used to transmit data through the network from a source node to a destination node. The radio nodes can communicate with each other using, for example, microwave or optical carrier signals.

Description: Radio Network The present invention relates to the broadcasting of signals between a number of users in a radio network. The invention has particular although not exclusive relevance to the communication of broadband data using broadcast line of sight communication techniques between a number of users in a communications network. There is an increasing demand for providing a broadband communication link into homes and businesses , for the provision of services such as video on demand, high speed internet, video telephony, on-line multiplayer gaming etc . At present , the communications link into homes and businesses is predominately twisted pair telephone lines which may be used to carry analogue telephone and modem signals, and ISDN. The bandwidth provided by such technology is, however, limited and may be described as narrowband . Some technologies have been proposed which will provide a broadband communications link into homes and businesses . Some of these employ the same twisted pair copper or the coaxial cable used for television distribution. It has also been suggested to run fibre optic cable into homes and businesses. However, this solution is not practical due to the cost of installing the fibre optic cable. It has been proposed to provide this broadband communications link by broadcasting the data using microwave frequencies and above. However, the problem of using such frequencies is that their propagation is severely attenuated by oxygen and rain absorbtion and the propagation is strictly line of sight. The attenuation characteristics of such high frequency signals means that transmission distances are relatively short. Using practical and safe power levels, a maximum distance of the order of 5km is achieved in real deployment. The line of sight characteristics mean that the communications link between the transmitter and receiver needs to be over a path without any obstructions . Buildings form completely opaque obstructions and even trees with dense foliage can constitute a fairly significant obstruction. Some over- the-horizon propagation has been shown to be possible, and it is also possible to bend the signal by bouncing it off fairly small reflective surfaces. However, for levels of reliability comparable to those required in a telecommunications network and offered by twisted pair copper or optical fibre, a practical installation using such high frequency radio signals will preferably need to ensure that a clear line-off-sight path is available between the transmitter and the receiver. The present invention addresses at least some of these problems and provides a way of providing broadband communications between a plurality of users located at separate locations . In accordance with the present invention, there is provided a communication system comprising: a network of nodes each comprising a transmitter for broadcasting signals to one or more other nodes in the network and a receiver for receiving broadcast signals broadcast by one or more other nodes in the network; wherein the network of nodes is arranged so that each node in the network can communicate with each other node in the network either directly or via one or more other nodes; and wherein the network of nodes is arranged so that at least two independent communication links can be formed between two of said nodes , with at least one communication link passing via one or more nodes in the network. According to one aspect, the present invention provides a communication system which employs a multi-hop network architecture in which communications from one user to another user are typically achieved by transmitting via a number of users located between the source user and the destination user. The system thereby avoids the need for a large central transmitter tower which is arranged to transmit the data to each user or the requirement for every user to be able to see every other user. According to another aspect, the present invention provides a communication system for providing radio communication between a plurality of users in a communication network, the communication system comprising a network of nodes and radio links interconnecting said nodes, the system being characterised in that a plurality of nodes are arranged to receive data from a plurality of other nodes in the network and to transmit data to a plurality of different nodes in the network. Preferably, each individual radio link between the nodes is uni-directional and therefore, the output link of one node becomes the input link of the node to which it transmits, since this allows a single transmitter and receiver to be used in each node. To avoid interference between the transmission and reception at each node, it is preferred that at each node, the frequency or frequencies of transmission of the output links is different from the frequency or frequencies of reception of the input links. Preferably a single frequency is used for reception and a single but different frequency is used for transmission at each node. In other words, each of the input links operates at a first frequency and each of the output links at a second frequency, different from the first. In this case, the plural received and transmitted signals can be discriminated, for example on a time division multiplex basis. Preferably, each node in the radio network receives data from V nodes and transmits to V nodes, where V is greater than 1. With this configuration, it can be shown, that if any one link fails between any two nodes in the network, then there will be at least one other independent data path which can be used in its place. In such an embodiment, if the nodes transmit and receive on different frequencies, then it will been seen that the nodes making up the network can be grouped into clusters which share a particular frequency either for transmitting or for receiving and that therefore any one node will belong to two clusters: one at its receiving frequency and one at its transmitting frequency. Further, each frequency which is used will be shared amongst 2V nodes : V transmitting nodes and V receiving nodes. It is possible that a particular frequency, having been used within a cluster in the manner described above, could be used for another cluster within the same network. However, the extent to which this is possible will depend primarily on local circumstances such as the physical size of the network and the actual geographical features within the network. The nodes will usually be geographically situated at convenient locations to suit the local circumstances and the requirement to be in radio range of other nodes in the network belonging to the same cluster. Nodes may simply be repeater nodes, but most will be linked to a user located within the premises . In preferred embodiments, the communication links between nodes will be line-of-sight , but it is possible that a node to node link may be made via a reflector arrangement of some type, should geographical or other constraints dictate this . A typical node might therefore be situated at a domestic user premises, with the physical component making up the node being located on or in the premises . The line of sight requirement between nodes means that at least the aerials associated with each node will need to be placed as high as conveniently possible, which means, in practice, at or above roof height. Where a node is linked into a user premises, the individual user may or may not desire to use the broadband communication services provided by the network. If the user wishes to connect to the system, then the node functions will include the routing of the broadband signals into and out of the users premises where they will connect to suitable apparatus such as a decoder, set top box, VCR, television and/or computer or computer network . A network manager is preferably provided for controlling the communication links which are actually used at any one time, thereby providing flexibility in network configuration and network up gradability. A plurality of separate radio networks can be linked together via a broadband communication link such as an optical fibre cable, thereby allowing a wide geographical area to be covered by using a plurality of radio networks embodying the present invention. In order to reduce the frequency spectrum required, frequencies can be re-used within each radio network, depending on the geographical layout of the nodes in the network . The present invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a schematic overview of a radio network which comprises twelve nodes which communicate with each other; Figure 2 shows a typical configuration of a roof mounted receiving antenna and transmitting antenna which from part of one of the nodes shown in Figure 1. Figure 3 is a schematic block diagram illustrating the components of one of the nodes shown in Figure 1 ; Figure 4 is a schematic block diagram of a second different node forming part of the radio network shown in Figure 1; Figure 5 is a schematic block diagram of a repeater node forming part of the radio network shown in Figure 1 ; Figure 6 is a schematic block diagram illustrating the form of a network manager node forming part of the radio network shown in Figure 1 ; Figure 7 is a schematic diagram illustrating the data format used in the transmission of data between the nodes in the radio network shown in Figure 1 ; Figure 8 is a schematic block diagram illustrating the form of a node forming part of a radio network which connects the radio network to the internet; Figure 9 is a schematic block diagram illustrating an alternative radio network in which three separate nodes are connected to the internet; Figure 10 is a schematic overview of a radio network having twelve nodes which are configured in a different topology to the radio network shown in Figure 1 ; Figure 11 is a schematic overview of a radio network having twelve nodes which are connected in a topology different from the radio networks shown in Figures 1 and 10; Figure 12 is a schematic overview of a radio network having eight nodes; Figure 13 is a schematic overview of a radio network having eighteen nodes which illustrates the way in which additional nodes can be added to the radio network shown in Figure 1; Figure 14 is a schematic overview of a broadband communications system which employs a plurality of separate radio networks ; Figure 15 schematically illustrates the way in which a plurality of radio networks can be logically arranged in a cellular type structure; and Figure 16 is a schematic block diagram illustrating an alternative network topology. Figure 1 illustrates a schematic overview of a radio network 1 which, in this embodiment, comprises twelve nodes (N 0 to N u ) which communicate with each other in a predetermined manner. More specifically, each node is arranged to receive broadcast data from three different nodes and is arranged to broadcast data itself to three different nodes. For example, nodes N 3 , N ή and N 5 are arranged to receive broadcast data B 0 , B t and B 2 from nodes N 0 , Nj and N 2 respectively and are arranged themselves to broadcast data B 3 , B 4 and B 5 respectively to nodes N 6 , N 7 and N 8 . For clarity, the nodes shown in Figure 1 have been arranged in a geometrically symmetric manner, wherein there are three orbital levels with four nodes in each orbit (e.g. nodes N 0 , N 3 , N 6 and N 9 being the nodes in the first orbit). As those skilled in the art will appreciate, this is a purely logical layout and will not reflect the actual geographic layout of the network in practice . The nodes have also been grouped into four radial groups RG 0 , RGi, RG 2 and RG 3 . In this embodiment, the nodes in radial group RG 0 transmit to the nodes in radial group RGx using a first frequency, the nodes in radial group RG X transmit to the nodes in radial group RG 2 using a second frequency, the nodes in radial group RG 2 transmit to the nodes in radial group RG 3 using a third frequency and the nodes in radial group RG 3 transmit to the nodes in radial group RG 0 using a fourth frequency. Therefore as can be seen from Figure 1, in this embodiment, the transmission between nodes is unidirectional so that transmission only takes place in a clockwise direction. In order to avoid interference between the data being transmitted from the nodes in each radial group, the nodes in each radial group are arranged to transmit their data in a time multiplexed manner. Therefore, in this embodiment, each node broadcasts its data for one third of the systems cycle time, which, in this embodiment, is 25 microseconds. The table below provides a time slot- frequency map for the radio network 1 shown in Figure 1. The rows represent the different frequencies f 0 , f,, f 2 and f 3 , the columns the time slots TS 0 , TS X and TS 2 and the table entries indicate the possible data flows between transmitting nodes to the receiving nodes . The length of the cycle time and which nodes transmit in which time slot is determined by a network manager (not shown) which also controls the general operation, timing and synchronisation of each of the nodes in the radio network 1. More details of the network manager will be described below. As those skilled in the art will appreciate, since each node can receive data from three separate nodes and can only transmit data during one third of the system's cycle time, each node can only pass on data which it receives from one node onto another node. The data received from the other two nodes must either be passed down into the node or must be discarded. Additionally, in this embodiment, the nodes are arranged to broadcast the data to the adjacent nodes using a microwave frequency band. In particular, in this embodiment, each node transmits data in the frequency range of 2 to 70 GHz. Since microwave frequencies have a low penetration, i.e. they will not pass through trees, buildings or the like, there must be a clear line of sight between the nodes to be able to ensure a reliable communications link between the nodes. Therefore, in this embodiment, the nodes in each radial group are expected to be in line of sight with the nodes in the radial groups from which they receive data and to which they transmit data. In this embodiment, nodes which receive data are arranged to be within 5 kilometres of the transmitting nodes and those nodes which receive from the same transmitting node are located within the beam of the transmit antenna which, in this embodiment, have a beamwidth of approximately 30 degrees. In this embodiment, the radio network 1 is used to link together computer equipment located in a number of homes and businesses to form a computer network. In particular, in this embodiment, some of the nodes represent homes which have a personal computer and some of the nodes represent businesses which have an existing local area network operating throughout the premises of the business. Since some of the user homes may not be in line of sight with other nodes in the network, some of the nodes will be repeater nodes which simply pass data from one node to another. In order to try to maintain a line of sight link between nodes, in this embodiment, the transmit and receive antenna of each node are mounted on the roof of the respective homes and businesses. Figure 2 shows a typical configuration of the roof mounted receive antenna 10 and transmit antenna 20. Broadcast transmissions received by the receive antenna 10 are processed by processing electronics 30 which is connected to the receive antenna 10 by a microwave link (not shown) . As will be described in more detail below, the processing electronics 30 processes the received broadcast data and, in this embodiment, either discards it, passes it down into the premises via cable 31 or passes it to the transmit antenna 20, via cable 32, for onward transmission . A more detailed description of a node which connects a single user from his home to the radio network 1 will now be described with reference to Figure 3. As shown, the user has a personal computer 100 which displays information to the user on a display 101 and which receives user input via the user input device 102. As shown, the personal computer 100 is connected to the processing electronics 30 via the cable 31 so that the user can receive data from the microwave receive antenna 10 and so that the user can transmit data from the microwave transmit antenna 20 to other users in the network . The way in which the personal computer 100 transmits data into the radio network 1 will now be described in more detail. In particular, in response to user input via the user input device 102, the personal computer 100 generates data to be transmitted and outputs it to cable 31 which carries the data up to the data conversion unit 35 located on the roof of the user's house. The data conversion unit 35 converts the data, under control of the control unit 37, from a format output by the personal computer 100 into a data format which complies with the protocol used by the radio network 1. This converted data is then passed to a router 39 which passes the data to an encoder 41 which encodes the data so as to try to reduce errors caused by interference in the broadcast communications channel and to introduce redundancy for error correction purposes . The encoded data is then passed to a buffer 43 where the data is buffered until it can be transmitted in the appropriate time slot of the system's cycle time. As illustrated by the control line 45, the control unit 37 controls the timing of the reading of data out from the buffer 43 so that the data is transmitted in the appropriate time slot for the node. The data read out from the buffer is then modulated in a modulator 47 using a quadrature phase shift keying (QPSK) technique. The modulated data is then passed to an up-converter 49 which converts the modulated data up to an intermediate frequency in the range of 1 to 4 GHz . The intermediate frequency signal is then passed, via cable 32, to the transmit antenna 20 where the intermediate frequency signal is up-converted to a microwave frequency in the range of 2 to 70 GHz and amplified by a power amplifier (not shown) . In a similar manner, microwave data signals received by the receive antenna 10 are amplified by a low noise amplifier (not shown) and down-converted to an intermediate frequency in the range of 1 to 4 GHz by a down-converter (not shown) both of which are located in the receive antenna 10. The intermediate signal is then passed, via cable 33, to a down-converter 57 in the processing electronics 30, which down-converts the intermediate frequency data signals to regenerate the QPSK modulated data . The QPSK modulated data is then demodulated by the demodulator 59 and the demodulated data is then passed to the decoder 61 which decodes the received data and corrects any errors caused by interference in the communications channel. The decoded data is then passed to the router 39 where a decision is made, under control of the control unit 37, as to whether the data should be forwarded to the encoder 41 for subsequent transmission to another node, whether it should be discarded or whether it should be passed to the data conversion unit 35 for transmission to the personal computer 100. Figure 4 illustrates the general layout of a node which connects a local area network 110 which is located within the premises of a building to the radio network 1. As shown, the components of the processing electronics 30 are the same as the processing electronics shown in Figure 3 and will not therefore be described again. The only difference between the node shown in Figure 3 and the node shown in Figure 4 is that the data conversion unit 35 is connected to the local area network 110 which connects a plurality of work stations 114 and personal computers 116 together, thereby allowing a plurality of different users located in the same building the ability to transmit and receive data via the radio network 1. As shown in Figure 4, a printer 118, a scanner 120, a facsimile unit 122 and a modem 124 are also attached to the local area network 110 so that they can be used by the work stations 114 and the personal computers 116. A server 126 is also provided on the network 110 to control the usage of the peripheral devices and to centrally hold data files and the like. In this embodiment, the local area network 110 operates using an ethernet type communications protocol and accordingly, the data conversion unit 35 will operate to convert the ethernet type data into the appropriate protocol for the radio network 1 and vice versa. As mentioned above, since some user nodes may not be able to have a direct line of sight link with other user nodes, some of the nodes shown in Figure 1 will be repeater nodes. Figure 5 schematically illustrates the form of such a repeater node. As shown, the processing electronics 30 of the repeater node are almost the same as the processing electronics shown in Figures 3 and 4. The only difference being that no data is passed down into the premises and therefore there is no need for a data conversion unit 35. Therefore, the router 39 will simply discard the data or pass it forward to the encoder 41 for subsequent transmission to another node, under control of the control unit 37. As mentioned above, in order to maintain synchronisation and in order to control the data communication in the radio network 1, a network manager is provided. In this embodiment, the network manager is attached directly to node N 0 shown in Figure 1. The network manager node is shown in more detail in Figure 6. As shown, the processing electronics 30 of the network manager node N 0 are the same as the processing electronics in the other nodes in the network, except for the processing electronics in the repeater nodes. As shown, the output from the data conversion unit 35 passes directly to the network manager 150 which, in this embodiment, comprises a personal computer. The way in which the network manager 150 controls the data communications in the radio network 1 will now be described in more detail with reference to Figure 7. Figure 7 generally illustrates the form of the data stream 200 received by a node. As illustrated, the node receives data in three separate time slots TS 0 , TSx and TS 2 during one system cycle T, with the data received in each time slot being from a respective one of the three nodes which broadcasts data to the receiving node. The data received (or transmitted) in each time slot will be referred to hereinafter as a network data packet. As shown, in this embodiment the network data packet received in each time slot has the same length T p and is separated by a fixed period t d from the next network data packet. In this embodiment, each network data packet has 1000 bits, thereby providing, for a cycle time of 25 μs , a maximum of 40 Mbits per second to the user at each node (As compared with 64 kbits per second with an ISDN line) . Figure 7 also shows an exploded view 210 of the network data packet received in time slot TS 2 , after it has been decoded by the decoder 61 in the processing electronics 30 of the receiving node. As shown, the network data packet received in time slot TS 2 comprises a number of control bits 212, a number of data bits 214 and error checking bits 216. The data bits 214 comprise either actual data transmitted from another node or idle data which is used to fill the network data packets when no actual data is being transmitted. The error check bits 216 are used to provide forward error correction. The network data packets received in the other time slots TS 0 and TSi have the same format. As shown, the control data 212 is provided at the beginning of the network data packet and is the first data to be passed to the router 39. As shown in Figure 7, the control data 212 comprises synchronisation bits 220 which enable the router to maintain synchronism between the network data packets and to maintain synchronisation with the radio network's system clock (not shown). The techniques for achieving this synchronisation are well known in the art of data communications and will not be described in more detail here. The control data 212 also comprises time slot information 224 which is inserted by the transmitting node and which, in this embodiment, requires two bits to encode since there are three possible time slots in each system cycle T. This time slot information 224 is extracted by the router 39 and passed to the control unit 37. On the basis of which time slot the current network data packet is in, the control unit 37 instructs the router 39 to either discard the data bits 214, to pass the network data packet on to the encoder 41 for onward transmission or, if appropriate, to pass the network data packet to the data conversion unit 35 so that the data bits 214 can be extracted from the network data packet and passed to the user or users located at that node. In this embodiment, the control actions output by the control unit 37 of a node are determined from a look up table (LUT) (not shown) stored in the control unit which is addressed by the time slot information bits 224. The control data 212 also comprises management data 226 which is used by the network manager 150 to control and to re-configure the control units 37 in each of the nodes of the radio network 1. In this embodiment, the radio network 1 operates like a telephone network. In particular, if a user at a node wishes to transmit data to another user located at another node, then a request for an appropriate data link to be set up is firstly sent to the network manager 150. This is achieved by the user sending the request to the data conversion unit 35 located on the roof of the user's premises. In response, the data conversion unit 35 generates the appropriate management data and inserts it into one or more network data packets and sends it or them to the router 39 for onward transmission to the network manager 150. Once the network manager receives the request, it determines an appropriate data path from the user's node to the desired destination node and sends management data to the appropriate nodes in the network 1 so as to set up the appropriate communications link so that the data, in passing to the destination node, will arrive there via only a single route. If, for example, the network manager 150 receives a request from a user located at node N, that he wishes to transmit data to a user located at node N 6 , then the network manager considers the current configuration of the network and re-configures the control units 37 in the appropriate nodes where necessary. This can be achieved by, for example, configuring the control units 37 in nodes N 3 , N , N 5 and N 6 so that (i) network data packets received by node N 3 from node j are transmitted on to the nodes in radial group RG 2 ; (ϋ) network data packets received by nodes N A and N 5 from node N 3 are discarded; and so that (iii) network data packets received by node N 6 from node N 3 are passed down to the user located at node N 6 . Depending on whether or not the network is also configured so as to form a communications link between other nodes in the radio network 1 , the network data packets received by node N 6 from node N 4 or from node N 5 may be transmitted on to the nodes in radial group RG 3 . Therefore, as will be appreciated by those skilled in the art, the radio network 1 is capable of sustaining simultaneous data communications between a plurality of different nodes in the radio network 1. As mentioned above, the network manager 150 configures the network so that there is only a single route from the source node to the destination node. This is because, in this embodiment, it is undesirable to have all of the data passed down each possible path from the source to the designation. Apart from the lack of efficiency, different path lengths would ensure that the packets of data arriving by different routes would be slightly out of phase, resulting in unnecessarily complexity at the destination node. However, because each node in the radio network 1 can transmit to three different nodes and can receive from three different nodes, it can be shown that three completely independent communication links can be set up between any two nodes in the network . Therefore, should a communication link between any two nodes fail, or if a node fails, then, in this embodiment, there are always at least two other communication paths which can be used to transmit data from any source node to any destination node. As will be appreciated by those skilled in the art, it is possible to determine if a failure has occurred, since a node will not receive data in a particular time slot if the node which transmits during that time slot has failed or if the communication link between that node and the receiving node is obstructed. Therefore, the receiving node can immediately notify the network manager 150 which will then take any necessary steps to change the route taken from the source node to the destination node. In this embodiment, the network is arranged so that each node can communicate with the network manager 150 at all times. This is achieved, in this embodiment, by extracting the management data in each network data packet from any packet that will be discarded by a node and then passing it onto the next node. This therefore ensures that all management data will eventually reach the processing electronics of the management node N 0 which is arranged to extract all management data from all received network data packets and to forward this to the network manager 150. In this embodiment, the control unit 37 of each node is re-configured by simply changing the look-up table (LUT) which is stored in the control unit 37. An example of which is stored in the control unit 37. An example of this look-up table for node N 6 in the above described example is shown below, with the two bits of the time slot information 224 in the left hand column and the control action output by the control unit 37 in the right hand column: As shown, in this example, if the time slot information bits are "00" (indicating that the current network data packet was received in time slot TS 0 and hence that it was transmitted by node N 3 ), then the control unit 37 instructs the router 39 to pass the current network data packet to the data conversion unit 35 so that it can be passed on to the user located at node N 6 . Similarly, if the time slot information bits are "01" (indicating that the current network data packet was received in time slot Sj and hence that it was transmitted by node N A ), then the control unit 37 instructs the router 39 to pass the current network data packet to the encoder 41 for subsequent transmission to the nodes in radial group RG 3 . Finally, if the time slot information bits are "10" ( indicating that the current network data packet was received in time slot TS 2 and hence that it was transmitted by node N 5 ), then the control unit 37 instructs the router 39 to discard the data bits 214 of the current data packet. If the time slot information bits are "11" then this indicates that there has been an error in the transmission of the packet and the packet is discarded. As those skilled in the art will appreciate, the radio network described above has the following advantages: 1. Data circulates in the manner of a ring, keeping individual radio links short and predominantly between neighbouring nodes. 2. Each node acts as a mini-broadcaster in that the data it transmits goes to three receiving nodes at the same time. 3. All the nodes have the same peer level in the network and can originate transmissions for any other node in the network. 4. Each node requires only one transmitter and one receiver since the data circulates in a circular manner in one direction. 5. Once operating, the transmitter and receiver always operate on the same frequencies and therefore frequency agile transmitters and/or receivers are not required. 6. The radio signals propagate around the network in such a way that the receive and transmit antenna of each node point approximately in opposite directions, thus facilitating improved signal discrimination. 7. Only elementary data routing is required at each node. However, this is limited to pass through, decode or discard. No knowledge of the final destination, nor the network topology is required in the node. However, a network manager is required in order to set up and destroy the data paths ; 8. There are three independent data paths available between any two nodes in the network. This provides path diversity within the network. Therefore, the failure of a radio link, or a node, need not prevent data from being delivered from a source node to a destination node, although network capacity will be degraded, but failure is gradual with complete failure at a node only occurring when all the input or output links to a node fail, and even then, the rest of the network will remain operational . 9. Radio links between the nodes are kept relatively short and can be tailored to the geographical location of the transmit and receive nodes. Therefore, the nodes may be mounted at just sufficient height to see the nodes which it has to receive from and to see the nodes which it has to transmit to. This typically only requires antennas to be mounted at roof height and therefore, no tall antenna/masts are required and installation is therefore eased. 10. The low cost and universal nature of the radio node means that the same device can be used as a repeater in the network where areas of poor coverage are encountered. In the above embodiment, a radio network has been described which connects together computer equipment located in a number of different user premises. As those skilled in the art will appreciate, it is possible to connect the radio network shown in Figure 1 to the internet, thereby giving each user connected to the radio network 1 a broadband access to the internet. This can be achieved, for example, by directly connecting one or more of the nodes shown in Figure 1 to the internet. The configuration of a node which connects the radio network to the internet is illustrated in Figure 8. As shown, the processing electronics is the same as for the nodes shown in Figures 3 and 4. In this node, however, the data conversion unit 31 is connected to an internet gateway access point 234 which connects the node shown in Figure 13 to the internet 237 via a fibre optic link 239. In this embodiment, the data conversion unit 35 must therefore convert the data which is in the radio network data format into a format suitable for transmitting data to and for receiving data from internet routers (not shown) located in the internet 237. Advantageously, since the access point to the internet can be achieved using a typical node structure within the radio network, it is not necessary to build a tall or complex base transmitter station. In order to provide flexibility, preferably more than one node in the radio network will be connected to a gateway access point of the internet. Figure 9 schematically illustrates the form of an embodiment where the radio network 1 is connected to the internet 237 via three gateway access points 234-1, 234-2 and 234-3, thereby giving users in the radio network 1 access to information and service providers 239 and 241 respectively which are also connected to the internet 237. As those skilled in the art will appreciate, by providing three separate access points from the radio network 1 to the internet 237, access to the internet can still be maintained even if the two of the internet access nodes fail. Further, since the access points to the internet are formed from a group of standard radio network nodes, they can, in principle, be located anywhere within the radio network. Therefore, the connection point to the internet can be conveniently placed close to or at an existing internet router . In the above embodiments , twelve nodes were connected in the radio network 1 so that each node received from three nodes in the network and transmitted to three different nodes in the network. It can be shown, that with the network topology shown in Figure 1, that the number of independent paths between any two nodes in the network is equal to the number of inputs into the nodes and the number of outputs from the node. Therefore, as mentioned above, for the network shown in Figure 1, there are three independent data paths which can be set up between any two of the nodes shown in Figure 1. Figure 10 schematically illustrates the form of a radio network having twelve nodes N 0 to N π in which each node receives from two nodes and transmits to two different nodes. In order to ease illustration, communication links which can be formed between the nodes in the network are represented by the curved arrows 2 , with the direction of data transfer being in the direction of the arrow. In the network topology shown in Figure 10, there are two orbital levels with six nodes in each orbit. It can be shown that there are two independent data paths which can be set up to connect any one node in the network with any other node in the network. The advantage of using the network with the topology shown in Figure 10 is that each node can transmit for half the system's cycle time. However, the disadvantages include that there will usually be more "hops" (and hence more delay) in order to transmit from a source node to a destination node and the number of transmission the FDM-TDM access technique described above, the number of different frequencies required is given by the number of nodes in the network divided by the number of input/outputs from each node. Therefore, in the first embodiment, with twelve nodes and three inputs/outputs to each node, four different frequencies are required. In the network topology shown in Figure 10, there are twelve nodes and only two inputs/outputs to each node and therefore six different frequencies will be required. Figure 11 illustrates an alternative network topology for a network having twelve nodes and with each node receiving from two nodes and transmitting to two different nodes. Again, to ease illustration communication links are illustrated by curved arrows. In the network topology shown in Figure 11 there are four orbital levels, with three nodes in each orbit. The advantage of the topology shown in Figure 11 is that fewer "hops" are usually required in order to transmit from a source node to a destination node, as compared with the network topology shown in Figure 10. As those skilled in the art will appreciate, six different transmission frequencies will still, however, be required. There are still two independent paths which can be used in order to transmit data from a source node to a destination node. However, with the topology shown in Figure 11, one path requires far less hops than the other. For example, to pass data from node N 9 to node N 4 , the two independent paths are N 9 -N 2 -N A and N 9 -N 3 -N 6 -N 8 - N 0 -Nή. Therefore, whilst the network manager may try to route data via node N 2 in this example, it may not be possible to do so because, for example, the link between node N 2 and N 4 is temporarily blocked. Therefore, with this topology, if the shortest independent path is blocked then a longer path will have to be used. this topology, if the shortest independent path is blocked then a longer path will have to be used. Figures 10 and 11 illustrate the form of two different network topologies which can be implemented with a network having twelve nodes . As those skilled in the art will appreciate, there are many other network topologies which can be implemented with a network having twelve nodes. As those skilled in the art will appreciate, the present invention can be applied to radio networks having more or less than twelve nodes and to networks having nodes with more or less then three input links and three output links. It can be shown, however, that the networks which provide the largest number of topological options are those having a large number of small prime factors of the number of nodes in the network. Figure 12 illustrates an embodiment in which there are eight nodes N 0 to N 7 in the radio network. As shown, in this embodiment, each node receives from two nodes and transmits to two different nodes. The network is arranged to have two orbital levels, with each orbit having four nodes. In this embodiment, four separate transmitting frequencies are required. In addition to the network configurations shown in Figures 1, 10, 11 and 12, where each node receives from the same number of nodes as it transmits to, other "mixed" topologies can be built where the number of inputs to and outputs from each node in the network is different. As will be explained below, this makes the network highly flexible and makes it upgradable by the subsequent addition of further nodes to the radio network . Figure 13 shows the form of a network having eighteen nodes. The network originally had twelve nodes arranged in the same configuration as the network shown in Figure 1. However, nodes Ni, N 2 and N 8 have been expanded by the addition of further nodes to create sub-networks 230 and 231. More specifically, nodes N x and N 2 have been replaced by a network of six nodes Nι.o-Nχ. 2 and N 2-0 -N 2 . 2 - Similarly, node eight has been replaced by a network of three nodes N 8-0 -N 8 . 2' The sub-network 230 therefore replaces two nodes of the basic network shown in Figure 1. Nodes N 1-2 and N 22 each have two reception inputs and three transmission outputs, while nodes N 1-0 and N 2 . 0 have three reception inputs and two transmission outputs. As shown, nodes N K1 and N 2<1 have two reception inputs and two transmission outputs. Similarly, the sub-network 231 replaces node N 8 of the basic network shown in Figure 1. As shown, node N 8-0 has three transmission outputs and one reception input, while node N 8-2 has three reception inputs and one transmission output. As shown node N 8-1 has one reception input and one reception output. The general operation of the radio network illustrated in Figure 13 is substantially the same as that of the radio network illustrated in Figure 1, and will not therefore be described again. Therefore, as those skilled in the art will appreciate, a basic radio network can be built and nodes can be added later without affecting the overall operation of the network. Additionally, once the network has expanded from, for example, twelve nodes to, for example, forty eight nodes, the network manager can simply re-configure the network into an appropriate topology for a forty eight node network. This is possible, because the network manager can configure each node by telling it when and for how long it should broadcast data, how many time slots there are in the received data and what to do with the data received in each time slot. Therefore, in theory at least, the radio network can be infinitely expanded. In practice, however, as the number of nodes increases, the delay in transmitting data from a source node to a destination node increases because a greater number of hops are required. Additionally, as the number of nodes increases, the required number of different transmission frequencies will increase. Therefore, in the situation where a large number of nodes are required, which can extend over a relatively wide geographical area, such as over a suburban area, the use of a plurality of separate radio networks are preferably used, with nodes in each network communicating with nodes in other networks via a common broadband communication link. Such an embodiment is illustrated in Figure 13. As shown, there are nine separate radio networks RN 0 to RN 8 , each of which is connected to an optical fibre link 251. As shown, in this embodiment, in order to provide flexibility, each of the radio networks, except for radio network RN 2 , is connected to the optical fibre link 251 via more than one gateway access point 235. Additionally, in this embodiment, some of the radio networks , such as radio networks RN 0 and RN, share a gateway access point 235'. In this case, the shared gateway access point 235' shares the access to the optical fibre link 251 between the two networks in a time division multiplexed manner. As those skilled in the art will appreciate, in order that the two networks can share an access point two nodes will have to be provided on the same premises, with the output from each data conversion unit being switched into the gateway access point. As shown in Figure 13, a radio network manager 253 is also connected to the fibre optic link 251 and is used to control each of the radio networks RNi in a similar manner to the way in which the network manager 150 managed the network shown in Figure 1. Additionally, as shown, the fibre optic link 251 is also connected to the internet 237, thereby allowing users in each of the radio networks access to information from, for example, the information provider 239. As those skilled in the art will appreciate, in addition to the nodes in each network RNi being able to communication with other nodes in the same radio network RN if the nodes in any one network RN can also communicate with any node in any other radio network RN j via the fibre optic link 251. As those skilled in the art will appreciate, each of the radio networks RNi in Figure 13 can be relatively small and the transmission frequencies used in one network can also be used by another network, provided that the network is sufficiently far away physically from the other radio network. Further, the actual physical location of the nodes in one radio network may be such as to allow the re-use of frequencies in the same radio network. Rather than having the generally arrangement of the radio networks shown in Figure 13, a more structured cellular type arrangement of radio networks may be provided. Such an embodiment is schematically illustrated in Figure 14. As shown in Figure 14, there are nineteen separate radio networks RN 0 to RN 18 , with three gateway access points (represented by the black dots) per radio network RN if for connecting the radio network to an outside backbone infra-structure (not shown), such as the fibre optic link 251 shown in Figure 13. As shown, the gateway access points are shared between ad acent radio networks . In practice, regular cell structures, such as the one shown in Figure 14, are unlikely to be realised. However, it is useful to view the networks in this way, since it illustrates that the network can be built up to cover almost any geographical area required, like existing cellular mobile phone networks. A number of modifications which can be made to the above embodiments will now be described. In the above embodiments , data was transmitted between nodes in one direction only. In an alternative embodiment, the communication links between one or more adjacent nodes may be bi-directional. In this case, each of the transmit and receiving antennas for a bidirectional links will receive and transmit data. However, this embodiment is not preferred, because it complicates the processing electronics required at the bi-directional nodes. In the above embodiments, a number of different frequency sets were used to transmit the data around the network. Provided that signal to noise ratios and interference criteria are met, and as mentioned above, frequency sets may be shared around the same network. This is facilitated by the fact that transmissions always tend to be focused in direction and are directed to small numbers of receiving nodes. In the extreme case of using infinitely narrow focused beams , the whole network could be served with just two frequency sets, or just one if simultaneous receive and transmit on the same frequency is possible. In the case where different radial groups transmit on the same frequency, interference can be reduced by allowing the nodes in each radial group to transmit at different times. In other words, increasing the number of time slots in the system's cycle time. In the above embodiments, a mixed frequency division multiplexing and time division multiplexing access technique has been used in order to allow each node in the radio network to be able to transmit and receive data. Other access techniques could be used. For example, a pure frequency division multiplexing technique or a pure time division multiplexing technique could be used. In a pure time division multiplexed embodiment, each node would be allocated a specific time slot for receiving data and for transmitting data and in a pure frequency division multiplexed embodiment, each node would be allocated a specific frequency for receiving data and for transmitting data. However, these techniques are not preferred because either the required spectrum is less efficiently used or the delay in transmitting data through the network is increased. Additionally, other access techniques such as code division multiple access (CDMA) or contention schemes common in computer networks , may be used . In the above embodiments a network manager was used to set up and destroy data paths through the network in order to allow a user to transmit to a desired destination. This type of control is preferred, because it reduces the complexity of each of the nodes because they do not need to know the source of the data nor the destination and they need no knowledge of the network topology. Alternatively, however, distributed routing functionality in each of the nodes, such as those commonly employed to route data through the internet using the TCP/IP protocol, can be used. In the above embodiments, microwave frequency links were provided between each of the nodes in the networks . A similar network can be configured using, for example, other electromagnetic frequencies, such as visible or infrared. Whilst these frequencies also allow broadband communications to be provided to each of the user premises, it is also possible to use lower frequency bands, such as RF frequency bands. However, at present, these frequency bands are heavily regulated and it is difficult to obtain licensing for large bandwidths . However, as those skilled in the art will appreciate the present invention should not be construed as being restricted to being for use in any particular frequency band nor that it is restricted to providing a broadband communications link, although it is ideally suited for doing so . In the above embodiments, the radio networks were provided in order to link together computer equipment located in a number of user premises . Other data services, such as video distribution, video telephony, on-line multiplayer gaming etc may be provided using these radio networks. As those skilled in the art will appreciate, in some of these alternative applications, some nodes will be attached to a user that only transmits data into the network, whilst others will be attached to users that only receive data from the network. For example, in the video distribution application, the same data may be passed from a single source to multiple destination nodes. As will be appreciated by those skilled in the art, the inherent fan-out nature of the network architecture is ideal for this type of application. In the above embodiments, the nodes in each radio network are connected in a generally ring-like manner. This is not essential. Figure 16 illustrates the form of a radio network embodying the present invention. As shown, the radio network comprises eleven nodes N 0 to N 10 , and wherein the number of inputs to each node and the number of outputs from each node are different. In this network, if, for example, node N 5 wishes to transmit data to node N,, then it transmit data to node N 7 which in turn passes the data to node N g which in turn transmits the data to a broadband fibre optic link 251. The data then passes along the fibre optic link 251 and transmitted to node N 0 which then passes the data onto node H x . Therefore, provided there are at least two connections to a backbone structure, such as the fibre optic link 251, each node in the radio network will be able to communication with each other node in the network. Figure 16 also illustrates that there may be some nodes, such as node N 10 which receives and transmits data to the same node, i.e. node N 9 . This is because some premises may be in remote or difficult to reach locations and can only be seen from one other node in the network. In this case, the same aerial is used to transmit and receive data between nodes N 9 and N 10 .

Claims: Claims : 1. A communication system comprising: a network of nodes each comprising a transmitter for broadcasting signals to one or more other nodes in the network and a receiver for receiving broadcast signals broadcast by one or more other nodes in the network; wherein the network of nodes is arranged so that each node in the network can communicate directly with one or more neighbouring nodes and can communicate with each other node in the network via the one or more neighbouring nodes ; and wherein the network of nodes is arranged so that at least two independent communication links can be formed between at least one source node and at least one destination node, with at least one of said communication links passing via one or more other nodes in the network. 2. A communication system according to claim 1, wherein each node in the network is arranged to communicate with each other node in the network via a broadband communications link. 3. A communication system according to claim 1 or 2, wherein the transmitter of each node is arranged to broadcast signals using an electromagnetic carrier frequency which requires a substantially line of sight communications link between the transmitter and receiver. 4. A communication system according to any preceding claim, wherein each transmitter is operable to broadcast signals in the microwave frequency band. 5. A communication system according to any preceding claim, wherein each transmitter is operable to transmit an optical frequency signal. 6. A signalling system according to any preceding claim, wherein one or more nodes in said network are associated with a data input device, a data output device or a data input and data output device . 7. A communication system according to claim 6, wherein said data input device, data output device or data input and output device comprises at least one of: a computer, a computer network, a video recorder, a television system, the Internet, a video distribution system, a multi-media data distribution system or the like. 8. A communication system according to any preceding claim, wherein each node is arranged to receive signals on one or more frequencies and to transmit signals on one or more different frequencies. 9. A communication system according to any preceding claim, wherein said network of nodes is arranged so that it is possible to form at least two independent communication links between a plurality of source and destination nodes in the network. 10. A communications system according to any preceding claim, wherein said network of nodes is arranged so that communications from a source node can be communicated to a plurality of destination nodes in the network. 11. A communication system according to any preceding claim, wherein the receiver of a plurality of nodes is arranged to receive communications from a plurality of different nodes and wherein the transmitter of each of said plurality of nodes is arranged to broadcast the communication received from at least one of said nodes for reception by one or more other nodes . 12. A communication system according to claim 11, wherein the receiver of each of said plurality of nodes is operable to receive communications from said plurality of different nodes using the same frequency but in a time multiplexed manner. 13. A communication system according to claim 11 or 12, wherein each of said plurality of nodes can be arranged to pass at least one of the communications received from said plurality different nodes to a user located at the node. 14. A communication system according to any of claims 11 to 13, wherein each node is configurable so that it can take different actions with regard to each communication received from said plurality of nodes. 15. A communication system according to claim 14, further comprising a network manager for configuring or re-configuring each of said nodes to thereby set up a desired communication link between a source node and a destination node. 16. A communication system according to claim 15, wherein said network manager is operable to configure the nodes in the network so that a single data path is provided between the or each source node and the or each destination node. 17. A communication system according to claim 16, wherein each node is arranged to monitor communications received from neighbouring nodes and arranged to inform said network manager in the event that communications are not received by one or more of said neighbouring nodes . 18. A communication system according to claim 17, wherein said network manager is arranged to reconfigure said nodes so that a different data path is provided between a source node and a destination node in the event that a link or a node in the first data path fails. 19. A communication system according to any of claims 15 to 18, wherein the nodes which transmit to the same node are arranged to transmit their communications in a respective time slot, and wherein the receiving node is operable to perform routing of the signals received from said plurality of nodes in dependence upon the current time slot and pre-stored instructions received from said network manager. 20. A communication system according to claim 19, wherein said instructions are in the form of a look-up table . 21. A communication system according to any of claims 15 to 20, wherein said network manager is arranged to assign a time slot for each node in the network during which that node can transmit communications to its neighbouring nodes . 22. A communication system according to claim 21 when dependent from claim 20, wherein each node is arranged to broadcast time slot information and wherein each receiver is operable to extract the time slot information from the received communication and use this extracted time slot information to address said look-up table. 23. A communication system according to any preceding claim, wherein at least two of said nodes are connected to a broadband cable communications link. 24. A communication system according to any preceding claim, wherein the nodes are arranged so that communications between each neighbouring node is unidirectional. 25. A communication system according to any preceding claim, wherein the communication links between nodes are such as to form a generally ring like network topology. 26. A communication system according to any preceding claim, wherein each node is at a separate fixed location relative to the other nodes in the network. 27. A communication system according to claim 26, wherein a plurality of said nodes are mounted on or in a respective user building. 28. A communication system according to claim 27, wherein the transmitter and receiver of said plurality of nodes are mounted on the roof of the respective user buildings. 29. A communication system according to any preceding claim, wherein a plurality of nodes are arranged to either (i) pass communications received from a neighbouring node to another neighbouring node; (ii) to pass communications received from a neighbouring node to a user located at that node; and/or (iii) to discard one or more of the received communications . 30. A communications system according to claim 29, wherein each of said plurality of nodes is configurable by a network manager which decides which communications received by a node will be passed to a neighbouring node, which will be passed to the user located at that node and which will be discarded. 31. A communication system according to any preceding claim, wherein one or more of said nodes comprises one or more sub nodes . 32. A communication system according to any preceding claim, wherein one or more of said nodes is connected by a broadband cable communications link to the Internet. 33. A communications node for use in a system according to any preceding claim, the node comprising: a receiver circuit for receiving signals broadcast from one or more other nodes; a transmitter for broadcasting signals to one or more other nodes; and means for controlling the reception and transmission of communications from the node such that received communications are either (i) passed to said transmitter for broadcasting to other nodes; (ii) passed to a user associated with the node; and/or (iii) discarded. 34. A communications node comprising the technical communication node features according to any of claims 1 to 32. 35. A method of communicating data from a source node to a destination node comprising the step of using a communication system according to any of claims 1 to 32. 36. A communication method comprising the steps of: providing a network of nodes each comprising a transmitter for broadcasting signals to one or more other nodes in the network and a receiver for receiving broadcast signals broadcast by one or more other nodes in the network; arranging the network of nodes so that each node in the network can communicate directly with one or more neighbouring nodes and can communicate with each other node in the network via the one or more neighbouring nodes; arranging the network of nodes so that at least two independent communication links can be formed between at least one source node and at least one destination node, with at least one of said communication links passing via one or more other nodes in the network; and transmitting a communication from said source node to said destination node using at least one of said communication links . 37. A video distribution system comprising: a video distribution unit for distributing video signals; and a communication system according to any of claims 1 to 32 for distributing the video signals to a plurality of users located at a respective one of said nodes. 38. A broadband communication system for providing radio communications, the system comprising a network of nodes and radio links connecting said nodes , the system being characterised in that any one node has a number of output links each output link providing a direct radio transmission link from said one node to a further node on the system, and a number of input links, each input link providing a direct radio reception link from a still further node on the system to said one node and wherein said nodes and said links are such that for at least one source node and one destination node, there are at least two independent communication links , with one link passing via one more nodes in the network. 39. A communication system according to claim 38, wherein each node comprises a transceiver. 40. A communication system according to claim 39, wherein each of said communication links is unidirectional and wherein each node comprises a single transceiver. 41. A communication system comprising: a network of transceivers for broadcasting signals to and for receiving signals from a plurality of further transceivers in the network; wherein the network of transceivers is arranged so that each transceiver in the network communicates directly with one or more neighbouring transceivers and can communicate with each other transceiver in the network via the one or more neighbouring transceivers; and wherein the network of transceivers is arranged so that at least two independent communication links can be formed between at least one source transceiver and at least one destination transceiver. 42. A radio network for the broadcast of data between a plurality of nodes, the network being configured such that each of said nodes is a member of both a logical orbital group of nodes and a logical radial group of nodes , wherein each node in a radial group comprises: means for broadcasting data to nodes in a second, different, radial group; and means for receiving broadcast data from nodes in a third radial group different from that of which the node is a member and from that to which the node transmits ; wherein the radial group broadcast to and the radial group received from are common to all nodes which are members of the radial group.

Inventors: BARTLETT DAVID WILLIAM, BARTLETT, DAVID, WILLIAM
Applicants: BARTLETT DAVID WILLIAM, WORLDPIPE LIMITED, BARTLETT, DAVID, WILLIAM
Application year: 1998
Main classification: H04L12
IPC codes: H04L12