MXPA00000317A - Rebroadcasting communication system - Google Patents

Abstract

A communication system is provided which can provide a broadband communications link into a number of homes and business. The communication system comprises a base station for broadcasting communications in the microwave frequency to a number of user stations within a cell. Some of the user stations can communicate directly with the base station while others communicate with the base station via intermediate user stations. To achieve this and to provide robustness for changing channel characteristics, each user station is adapted to re-transmit the communications which it receives. Most user stations and the base station therefore receive multipath signals and an orthogonol frequency division multiplexing technique is used to overcome the problems caused by the reception of multipath signals.

Description

BROADCASTING COMMUNICATION SYSTEM DESCRIPTION OF THE INVENTION The present invention relates to a method and an apparatus for communicating signals among a number of users. The invention has particular relevance although not exclusive for the communication of broadband data using the techniques of direct communication by broadcasting. There is a growing demand for providing a broadband communication link to homes and businesses, for the provision of services such as video on demand, high-speed internet, video telephony, online multiplayer games, etc. So far, the communications link to homes and businesses is predominantly twisted pair telephone lines, which can be used to carry analog telephone and modem signals and ISDN. The bandwidth that IS provided by such technology is, however, limited and can be described as narrowband. Some technologies have been proposed which will provide broadband communications links to homes and businesses. Some of those are the same twisted pair of copper or the coaxial cable that has been used for telephone distribution. It has also been suggested to run an optic fiber cable to homes and businesses. However, this last solution is not practical due to the cost of installing the fiber optic cable. It has also been proposed to provide this broadband communications link by broadcasting the data using microwave frequencies and higher. However, the problem of using such frequencies until their propagation is severely attenuated by the absorption of oxygen and rain and the propagation is strictly in a straight line. The attenuation characteristics of such high frequency signals make the transmission distances relatively short. Using practical and safe energy or power levels, a maximum distance of the order of 5 km is reached in a real deployment. The characteristics of the direct line make the communication link between the transmitter and the receiver necessarily on an unobstructed path. The buildings form completely opaque obstructions and even the trees with dense foliage can constitute a very significant obstruction. It has been shown that some propagation over the horizon is possible, and it is also possible to bend the signal by wobbling it away from small reflecting surfaces. However, for levels of reliability comparable to those required in a telecommunications network and offered by the twisted pair of copper or fiber optic, a practical installation using such high frequency radio signals will preferably need to ensure that a clear straight path is available. between the transmitter and the receiver. In some implementations, a central base station will be provided, which broadcasts the microwave data signals to a number of users located within the broadcasting region. The problem solved by the present invention is that in this case, not all users may be able to "see and hear" the central base station. According to one aspect, the present invention provides a communication system comprising: a base station for broadcasting communications; one or more of first user stations which are in direct communication with the base station, each of which comprises a receiving antenna for receiving broadcasting communications from the base station, a transmitting antenna for re-broadcasting the received communications and a unit repeater that operates to receive communications from the receiving antenna to pass the received communications to the transmitting antenna and one or more second user stations which are not in direct communication with the base station and which comprise a receiving antenna that operates to receive the reradio-broadcast communications of one or more of the first user stations. Providing first user stations which simply retransmit broadcast communications, users who are not in direct communication with the base station can still receive communications transmitted by the base station. Additionally, if each of the second user stations receives reradio-broadcast signals from a plurality of first user stations, or other second user stations, then a more robust communication system may be provided. The communications system described above can provide a broadband communication link to homes and businesses. Since some users can receive the same signal from a plurality of different intermediate user stations, the base station preferably modulates the data on a plurality of separate carrier frequencies to reduce the speed of transmitted symbols which reduces the problems associated with the reception of multiple path signals. This makes it easier for the user stations, which are not in direct communication with the base station, to be able to recover the signals transmitted from the multipath signals without equalization or compensation. Preferably, the carrier frequencies that are used are separated by means of a whole number of the symbol rate of the transmitted data, since this reduces the intersymbol interference. By deliberately generating multiple path signals, the system becomes more robust to changes in the physical channel and by using orthogonal frequency division multiplexing techniques, the problems caused by such multiple path signals can be mitigated. The communication system can operate to provide broadband services such as video on demand, high speed internet access and similar to homes and businesses. Now exemplary embodiments of the present invention will be described with reference to the accompanying drawings in which: Figure 1 is a general schematic view of a video distribution system for providing video on demand to a plurality of users; Figure 2 is a block diagram illustrating communication links established between a base station and a plurality of user stations that are part of the video distribution system shown in Figure 1; Figure 3 is a block diagram illustrating the components of the base station shown in Figure 2; Figure 4 shows a typical configuration of a pair of microwave antennas mounted on the roof, which are part of one of the user stations shown in Figure 2; Figure 5 is a block diagram, schematic, illustrating the components of one of the user stations shown in Figure 2; Figure 6 is a schematic block diagram showing the components of a repeater unit that is part of the user station shown in Figure 5; Figure 7 is a signal diagram illustrating the effect of multipath signals arriving at a user station; Figure 8 is a signal diagram illustrating the form of a data stream to be transmitted to a user station and the form of a stream of symbols in phase and quadrature phase derived from the illustrated data stream; Figure 9 is a frequency chart illustrating the manner in which the video distribution system shown in Figure 1 divides the available bandwidth into a plurality of frequency channels; Figure 10 is a frequency graph illustrating the carrier frequencies used within the frequency channels used in Figure 9; and Figure 11 illustrates a general schematic view of a multi-point verification system at a point at which a number of verification stations communicate with a central verification station. Figure 1 illustrates a general schematic view of a video on demand distribution system for distributing digital video signals to a plurality of user stations, some of which are referred to as 1. The video distribution system comprises a video server. central video 3, a switching circuit 5 and a plurality of base stations 7. As illustrated in Figure 1, each user station 1 is served by a single base station 7 with which the user station communicates, either directly or indirectly, via one or more other user stations. In this mode the communication link between two user stations or between a user station and a base station is in the microwave frequency band between two 2 GHz and 70 GHz, and therefore is predominantly, only direct. In this embodiment, each base station 7 comprises a directional antenna (not shown), which can operate to broadcast signals and receive signals from user stations located within a predetermined geographic area or cell. This geographical area or cell is illustrated in Figure 1 by the sector-shaped area 9 enclosed by dashed line 11. In this mode the transmitter power of the base station is such that it can communicate directly with user stations that are remote up to 3 km from the base station 7. In operation, in response to a request for a particular video received from a user station 1, the base station 7, which serves that user station 1 passes the request to the circuit switching 5 via a fiber-optic link 13. The switching circuit 5 then routes a request to the video server 3 via the fiber-optic link 15. After receiving the user's request, the video server 3 retrieves the appropriate video data from a high capacity storage device (not shown) and passes the recovered data back to the corresponding base station 7 via the fiber optic link 15, the switching point 5 and the fiber optic link 13. The base station 7 then broadcasts the video data to the cell 9 for reception by the user station 1. Since the video data signals are broadcast to the entire cell 9, and in this way can be received by all the user stations in the cell, the broadcast data is coded so that only the user who requested the video can decode and recover the video image. In this mode, since the communication link between the base station and the user stations is direct, some stations will not be able to "see and hear" the base station because the path between them and the base station is blocked . This is illustrated in Figure 1 by means of block 17 which represents a building, which is located between base station 7 and user stations 1-A and 1-E. As illustrated by the striped area 19, the building 17 casts a shadow in the area 9 in which direct line communications with the base station 7 can not be achieved. In this preferred embodiment to ensure that each station 1 can receive a signal from and can transmit a signal to the base station 7, each of the user stations 1 can be operated to broadcast any signals it receives for reception by other user stations in its vicinity. In this embodiment, the broadcasting power of each user station for re-broadcasting the received signals from the base station 7 is limited so as to preserve the power consumed at each user station. In this embodiment, the user stations comprise a solar cell (not shown) and a backup battery (not shown) to provide power to the broadcasting antenna. As illustrated in Figure 1 by the dashed circle 20, a user station 1-c broadcasts all the data which it receives from the base station 7 in all directions. As shown in Figure 1, the user station 1-b is located within the striped circle 20 and can therefore receive signals and transmit signals to the base station 7 via the user station 1-c. Similarly, the user station 1-a is located within the broadcasting range of the user stations 1-d and 1-e and can therefore receive signals from and transmit signals to the base station 7 via the 1-d stations 1-e. It should be noted that, in this mode, since the user station 1-e is located near the boundary of cell 9, it uses a directional antenna to broadcast the data it receives from the base station, so as not to broadcast the data outside the cell 9. This allows adjacent cells that are served by different base stations 7 to use the same transmission frequencies.

However, since the user station 1-a can receive signals from and transmit signals to the base station 7 via two different user stations, the communication link between the base station and the user station 1-a is more robust since the communication link between the user station 1-do 1-e is temporarily blocked, then the user station 1-a can still communicate with the base station via the other user station. To provide greater robustness, each of the two user stations are arranged to receive the broadcasting of signals from as many other user stations as practical, given the geographical distribution of the user stations in cell 9. Figure 2 is a schematic block diagram illustrating the communication links formed between the base station 7 and the user stations 1. As shown, some of the user stations 1 receive data directly from and transmit data directly to the base station 7, while other user stations receive data from and transmit data to the base station 7 via other user stations. As shown, some of the last type of user stations, such as station 1-f, receive signals from a number of different intermediate user stations. In this embodiment, To avoid interference between the signals transmitted from the base station for reception by the user stations and the signals transmitted by the user stations for the reception of the base station, different carrier frequencies are used. Figure 3 shows in more detail the components of the base station 7. As shown, the base station 7 comprises an antenna 21 which operates to transmit data to and receive data from the user stations located within the cell 9. After the reception of a request from a user station 1, the received microwave signal is passed to a circulator 23 via a microwave waveguide 25. The circulator 23 passes the received microwave signal to a microwave amplifier 27 which amplifies the received microwave signal and then pass it to a down converter 29 for the downward conversion of the microwave frequency band. The downconverted signal is then demodulated by a demodulator 31 and then passed to an encoder 33 where the user requests that it be encoded. The decoded request is then passed to an auxiliary transceiver 35 which transmits an optical signal corresponding to the communication circuit 5 for forward transmission to the video server 3.

After receiving the user's request, the video server 3 retrieves the necessary digital video data and passes it to the switching circuit 5 to transmit it back to the base station 7 via the optical fiber 13. The optical transceiver 35 receives the optical digital video data of the optical fiber 13 and converts these into a corresponding electrical data signal which is passed to an encoder 37 where the data is encoded. The encoded data is then passed to a modulator 39 where they are modulated and then passed to an upconverter where the modulated data has been converted upwardly to a microwave frequency. The microwave data signals are then amplified by the amplifier 43 and then fed, via the circulator 23 and the waveguide 25, to the antenna 21 where the data is broadcasted to the cell 9. In the remaining description, the transmitted data of the user stations to a base station will be referred to as an uplink point and transmitted from the base station to the user stations referred to as downlink data. As mentioned above, in this modality, the video distribution system is to provide video on demand to the homes of a number of different users. To try to maintain a direct link between the user stations 1 and the base station 7, in this mode, the transmitting antenna and the receiving antenna of each user station are mounted on the roof of the corresponding user's home. Figure 4 illustrates a typical configuration of the ceiling mounted transmitter and receiver antennas for a user station. As shown the user station has two microwave antennas 45 and 47. The microwave antenna 45 is for receiving downlink data and for transmitting uplink data and the microwave antenna 47 is for transmitting downlink data and for receive uplink data. The microwave antenna 45 is directional in nature and has, in this embodiment, a bandwidth of approximately 30 ° within which it can receive microwave signals. The directional antenna 45 is for receiving signals from or to transmit signals to either the base station 7 or the intermediary user station via which it communicates with the base station 7. Therefore, in this mode, in some cases the antenna Directional 45 will have to transmit signals over a space of up to 3 km. For the user stations which communicate with the base station 7 via intermediate user stations, the power of the signal transmitted from the directional antenna 45 will have to be so that it can be received by the intermediate user station. The other antenna 47 is omnidirectional, ie, it is arranged to be capable of receiving microwave signals and to transmit microwave signals through 360 °. The radio diffusion power of the omnidirectional antenna 47 can be varied, but in this mode, it will typically be such that the user stations within a range of about 500 m can receive the reradio-broadcast data signals. In this embodiment, the omnidirectional antenna 47 comprises six horn-shaped antennas 47-1 to 47-6 each of which have a bandwidth of approximately 60 ° and which are arranged close to one another in a circle to provide a 360 ° operating interval. As mentioned above, the downlink microwave data signals of the base station 7 are received by the directional antenna 45 either directly or via one or more intermediate user stations 1. The received downlink microwave signals are made then passing a waveguide 49 to a microwave processing unit 51 which (i) sends the downlink microwave signals via the waveguide 53 to the omnidirectional antenna 47 for forward transmission; (ii) the descending method of microwave signals of the downward base and these are passed through the coaxial cable 55 to the user's home; (iii) receiving and upconverting the uplink data received from the user via cable 55, and passing those to the antenna 45 to transmit it back to station 7; and (iv) receives the microwave signals from the uplink via the waveguide 53 and then passes them via the waveguide 49 to the directional antenna 45 to transmit it back to the base station 7. To make the more detailed description of a typical user station of this embodiment with reference to Figures 5 and 6. Figure 5 is a schematic block diagram illustrating the components of the user station. In operation, the downlink microwave signals received by the directional microwave antenna 45 are passed via a waveguide 49 to a repeater unit 57 located within the processing unit 51. The repeater unit amplifies the downlink signals received and passes them via the waveguide 53 to the omnidirectional antenna 47 for forward transmission to the other user stations. The repeater unit 57 is also arranged to pass the downlink signals received, amplified, via the waveguide 59 to a downconversion unit 61 which is arranged to downwardly convert the received microwave signals to an intermediate frequency in an interval of 1 to 4 Ghz. This downwardly converted intermediate frequency signal is then passed to the coaxial cable 55 via a circulator 63. A signal of the intermediate frequency downlink is passed downward to the coaxial cable 55 from the processing unit 51 mounted on the ceiling in a set of decoding boxes 65 located within the user's home. The downlink signals received by the upper case 65 with the coaxial cable 55 are passed to a circulator 67 which routes them to a down converter 69 which down-converts the lower frequency signals to recover the downlink data Modulated The modulated downlink data is then demodulated by a demodulator 71 and then passed to an encoder 73 which decodes the digital video data and generates appropriate video signals to be sent to a television system 75. As shown in FIG. Figure 5, the user station also comprises a user input device 77 for inputting user requests to the fixed upper decoder box 65. In this embodiment, the user input device 77 comprises an infrared remote controlling unit. The user requests that are to be transmitted back to the base station 7 (as uplink data) are passed to an encoder 79 where they are coded. The coded uplink data is then modulated by the modulator 81 and then up-converted to an intermediate frequency in the range of 1 to 4 GHz by the up-converter 83. The intermediate frequency uplink data is then passed via the circulator 67 outside the fixed upper case 65 on the coaxial cable 55 to be transmitted to the microwave processing unit 51 located on the roof of the user's home. The uplink data received by the processing unit 51 is passed via the circulator 63 to a second up converter 85 which upconverts the intermediate frequency uplink data to microwave frequency signals in the range of 2 to 70 GHz. The microwave signals of the uplink are then passed to the repeater unit 57 which amplifies them and then passes them to the directional microwave antenna 45 for transmission back to the base station 7 either directly or via one or more intermediate user stations 1. Similarly, the microwave uplink signals received by the omnidirectional antenna 47 of the other user stations are roasted via the waveguide 53 to the repeater unit 57 which amplifies the received uplink signals and passes them to the microwave antenna directional signal 45 for forward transmission, back to the base station 7. Figure 6 illustrates in more detail the components of the repeater unit 57 shown in Figure 5. As shown, the downlink microwave signals received by the antenna directional 45 are passed via waveguide 49 to a microwave circulator 89 which routes microwave signals from the downlink to amplifier 91. Amplifier 91 amplifies downlink signals and passes them, via waveguide 59 to the down converter 61 shown in Figure 5. The amplified downlink signals are also passed to the microwave filter. 93 which filters the signal so that only the microwave signals from the downlink to the circulator 95 pass. The circulator 95 for the microwave signals in the downlink to the waveguide 53 for the transmission of the omnidirectional antenna 47 which reradio outputs the downlink signals for reception by other user stations. Similarly, the repeater unit 57 is arranged to receive from the waveguide 53 the microwave signals of the uplink received by the omnidirectional antenna 47 which are passed, via the circulator 95 to a microwave amplifier of ba or noise 97 which amplifies them. The amplified uplink signals are then filtered by the microwave filter 99 to pass only the uplink data signals to the circulator 89 for sending them to the directional antenna 45 via the waveguide 49. The repeater unit 57 is also arranged to receiving, via the waveguide 87, the uplink data originating from the user located within the user station. As shown, these uplink data are also amplified by the amplifier 97 and filtered by the filter 99 before being passed to the directional antenna 45 via the circulator 89 and the waveguide 49. Filters 93 and 99 are necessary because to which, in practice, Circulators 89 and 95 are not perfect and some "leak" or feedback will occur. Filters 93 and 99 therefore act to attenuate these feedback signals.

Since some on-demand video system subscribers may have difficulty in reaching the location, some of the user stations not shown in Figure 1 will simply be relay stations and will not serve a user located at that station. Those relay stations will therefore only comprise the two antennas 45 and 47 and the repeater unit 57 shown in Figures 5 and 6. In practice, the relay stations will typically employ the same processing unit 51 as a typical user station, but they will not be connected in the building on which the relay station is mounted. As mentioned above, in this embodiment, most user stations 1 are arranged to re-broadcast any downlink signals they receive for reception by other user stations to provide multiple signal paths between the base station 7 and each station of user. Therefore, most user stations will receive multiple copies of the downlink data signals and the base station 7 will receive multiple copies of the uplink data signals. Since multiple signals will have to travel via different trajectories, they will be deviated in time one in relation to the other. Figure 7 illustrates the shape of a received signal 101 formed by the superposition of two versions 103-1 and 103-2 of the same signal having a phase delay td between them. As a general rule, the maximum delay td between multipath signals should not be more than one tenth of the duration of Ts of the data symbols, otherwise an equalization or compensation is necessary to be able to extract the flow of symbols from the received signal. This is an important consideration in high data rate applications such as the video on demand system of the present embodiment. In particular, to provide video on demand, a downlink bandwidth of 4 M bits per second per user station is required. In a practical system, each base station 7 will supply video on demand to approximately 1000 separate users. Therefore, a downlink data rate of 4 G bits per second is required. If this downlink data is modulated and broadcast using a modulation scheme which gives 1 bit per Hz, then the general rule means that the maximum delay between the multipath signals would be 25 picoseconds. With the microwave signals traveling at the speed of light, this represents a permissible difference in the lengths of the multiple path signals of about 7 mm, which is clearly not practical. The present method solves this problem using, among other things, an orthogonal frequency division multiplexing (OFDM) technique which increases the period of symbols Ts of the transmitted data and therefore increases the maximum allowable delay td between the signals of multiple trajectory A more detailed description will now be given of the manner in which the present invention solves this multi-path signal problem. In this mode, a QPSK modulation technique is used, which provides 2 bits per Hz of bandwidth. Figure 8 shows part of the ordered sequence of video data 105 which is used to generate a stream of symbols in phase 107 and a stream of symbols in quadrature phase 109. In particular, if the transmitted signal is in terms of the sum of two quadrature carrier signals, ie: Fc (t) = a cos 2pfct + b sin 2pfct (1) then a and b are in phase and the flow of symbols in quadrature phase 107 and 109 whose values are generated by successive pairs of video data bits of the data stream of video 105 is according to, for example, the following table: Therefore, as shown in Figure 8, since the 2 bits of the video data stream 105 are used to generate each symbol of the symbol streams 107 and 109, the period of symbols Ts is twice the period of time. the video data Td. To increase the symbol period Ts of the transmitted signal even further, instead of using the video data stream 105 directly to generate symbol flows 107 and 109, in this mode, multiple carrier frequencies are employed, with each carrying a portion of the video data 105. More specifically, in this embodiment, a channel data capacity of 5 G bits per second is provided for the downlink data, which, (using the previous QPSK modulation technique) ) require a speed of 2.5 G symbols per second. In this mode, these 2.5 G symbols per second are modulated over 100,000 different carrier signals, giving a transmitted symbol speed (1 / TS) per carrier signal of 25 K symbols per second. In this embodiment, both horizontal and vertical polarization components of the transmitted microwave signals are used to carry data. To reduce intersymbol interference (ISI), the carrier frequencies are separated by 1 / TS, ie by 25 KHz, which is known in the art as orthogonal frequency division multiplexing. To provide 100,000 separate carrier frequencies using the vertical and horizontal polarization components, this requires a total channel bandwidth of approximately 1.25 GHz. In this mode, a 2 GHz channel bandwidth is provided and the carrier signals are divided in 50 frequency channels for the horizontally polarized components and 50 frequency channels for the vertically polarized component, with each channel extending over 40 Hz and with a 15 MHz separation between the carrier frequencies used in adjacent channels. This is illustrated in Figures 9 and 10. In particular, Figure 9 shows the 2 GHz bandwidth used in this mode, which is divided into 50 frequency channels C0H-C49H for the horizontal polarization component and 50 channels of frequency C0V - C49v for the vertical polarization component. Figure 10 shows the 10000 separate carrier frequencies provided in each Cx channel shown in Figure 9. As shown, the carrier frequencies f0-fg99 are equally spaced on the channel, with the spacing between the adjacent carrier frequencies being 1 / TS, that is, 25 KHz. Leaving in this way a bandwidth of 15 MHz between the carrier frequencies in the adjacent channels. Therefore, by transmitting the data on separate carrier frequencies, the symbol period Ts of the transmitted data has been increased to 40 microseconds, thereby providing a maxiallowed delay between the multipath signals (to allow the flow of symbols to be extracted transmitted without equalization or compensation) of 4 microseconds, which is equivalent to a more achievable difference in trajectory lengths of approximately 1.2 km.

As will be appreciated by those skilled in the art, in order to provide the required 4 M bits per second to each user station, each user station must retrieve the modulated data of 80 of the carrier signals. In this embodiment, this is achieved by assigning 80 separate frequencies for a given polarization in a given channel to each of the user stations 1. In other words, for 1000 user stations, 500 will use the horizontal polarization component of the signal of transmitted microwave and the other 500 will use the vertical polarization component and the 500 users of each polarization component will share the carrier signals on the respective 50 channels. In this mode, the user stations are shared equally on the 50 channels, so that 10 user stations will share each frequency channel, with each of the 10 users per channel receiving data from 80 different carrier frequencies within the channel. As those skilled in the art will appreciate, to simultaneously receive modulated data over 80 different carrier signals, the modulator 71 at the user station will have to simultaneously demodulate each of the eighty carrier frequencies. This is achieved by using a digital signal processor which is arranged to perform the Fourier analysis of the assigned frequency channel to extract the data that is modulated on the eighty carrier frequencies assigned to that user. In this mode, the majority of the system's data capacity is required for the downlink data. In this mode, each user station is allowed to transmit 400 k bits per second back to the base station using a carrier frequency specifically assigned to that station. user As will be appreciated by those skilled in the art, the carrier frequencies used by all user stations in the cell for uplink data communications with the base station are located in a frequency band separated from the band. assigned frequency for the communication of the downlink signals. Now we will describe a number of modifications that can be made to the previous modality. In the previous modality, the stations of The user uses the horizontal or vertical polarization component of the received microwave signal for downlink communications. This is not essential. In an alternative mode, some of the user stations can use both polarization components horizontal and vertical of the received microwave signal.

Additionally, in the above embodiment, each user station was operable to use carrier frequencies within a designated frequency channel. This is not essential either. Some user stations may use carrier frequencies in one or more frequency channels. However, this increases the complexity of the electronic processing devices used in those user stations. In the previous mode, each user station used the same carrier signals in the assigned frequency channel. In an alternative mode, each user may perform "frequency jumps" around the carrier frequencies within the frequency channel or even within other frequency channels. However, in such a mode a more complex user station is required. In the previous embodiment, a QPSK modulation technique was used to modulate the uplink and downlink data on each of the carrier frequencies. In an alternative embodiment, different modulation techniques can be employed to modulate the different carrier signals. This allows the use of more efficient modulation techniques at certain frequencies. For example, if a user station establishes that there is a good communication link between the base station and the user station over a particular frequency, then it can signal the base station to use a more efficient modulation technique that provides more bits per Hz for that carrier frequency. The above embodiments describe a video distribution system for providing video signals to a plurality of users according to the user's demand. As those skilled in the art will appreciate, the data distribution system described above can be used in other applications. For example, the data distribution system can be used to provide a broadband communications link between the users and, for example, the internet. It can also be used to connect computer equipment located in the respective user stations. In the above embodiments, the data is passed in both directions between the base station and the user stations. As those skilled in the art will appreciate, the communication link between the base station and the user stations may be unidirectional. For example, each of the user stations can operate to collect data and to transmit the data to a central verification system located at the base station. This type of verification systems is illustrated in Figure 11. As shown, the system comprises a number of verification stations 111 which either communicate directly with a central verification station 113 or indirectly via intermediate verification stations. As with the first mode, some of the intermediate verification stations and the central verification stations will receive multiple copies of the transmitted data, and preferably the same orthogonal frequency division multiplexing technique is used to overcome the problem of the multipath signal. This type of verification systems can be incorporated, for example, into a monitoring system, in which each verification station 111 comprises a video camera and transmits video data signals back to the central verification system 113 either directly or indirectly via an intermediate verification station. In the above embodiments, microwave frequency links were provided between the communication stations. A similar communication system can be provided using, for example, visible or infrared frequency carrier signals. In the above modalities, each of the user stations was arranged to re-broadcast the signals it receives. As one skilled in the art will appreciate, this is not essential for all user stations within the cell. In particular, some user stations may simply receive the multipath signals and extract the necessary video data, without retransmitting the signals for reception by other user stations. In the previous modalities, the user stations were associated with homes or businesses. The communication system described above can also be used for mobile user stations. In such modality, user stations are allowed to move between adjacent cells, then "intervention" procedures similar to those used in mobile telephone communication systems will be required.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (33)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. A communication system, characterized in that it comprises: a broadcasting station for broadcasting signals carrying information in the microwave frequency band or higher; a plurality of relay stations which are located to be in direct line communication with the broadcasting station and each one comprises: i) a receiving antenna for receiving signals containing information broadcast by the broadcasting station; ii) a repeater unit which is arranged to amplify the signals that contain or carry information received by the receiving antenna and to produce the amplified information-containing signals; and iii) a transmitting antenna which is arranged to broadcast the signals containing amplified information received by the relay unit; where at least two of the relay stations are arranged to broadcast the signals containing amplified information to a common area; and at least one receiving station which is located within the common area and which is not in direct communication with the broadcasting station, or each receiving station comprises: i) a receiving antenna arranged to receive the amplified broadcast information signals from minus two relay stations; and ii) means for processing the received signals to retrieve the information transmitted by the broadcasting station.
2. 2. A communication system according to claim 1, characterized in that the broadcasting station operates to broadcast modulated data on a plurality of different carrier frequencies.
3. 3. A communication system according to claim 2, characterized in that the difference in frequency between the adjacent carrier frequencies is an integer multiple of the symbol rate of the transmitted data signals.
4. The communication system according to claim 2, characterized in that the carrier frequencies are grouped into a plurality of groups, and where the difference in frequency between the adjacent carrier frequencies in each group is an integral multiple of the symbol rate. of the transmitted data signals.
5. The communication system according to claim 2, 3 6 4, characterized in that the processing means operate to perform a Fourier analysis of the received signals to recover the information.
6. The communication system according to any of the preceding claims, characterized in that the receiving antenna of one or more of the relay stations are of a directional nature and are aligned with a broadcasting station.
7. The communication system according to any of the preceding claims, characterized in that the receiving antenna of one or more of the receiving stations is directional in nature and is aligned with the relay stations of which it is arranged to receive the signals containing information of amplified signals.
8. The communication system according to any of the preceding claims, characterized in that the transmitting antenna of at least one of the repeater stations is omnidirectional in nature.
9. The communication system according to any of the preceding claims, characterized in that one or more of the relay stations also operate to transmit signals containing information back to the broadcasting station to the receiving antenna.
10. The communication system according to claim 9, characterized in that one or more receiving stations operate to transmit signals containing information back to at least two relay stations from their receiving antenna and where at least one of at least two relay stations is arranged to receive the signals containing information transmitted from the receiving station through its transmitting antenna.
11. 11. The communication system according to claim 10, characterized in that the repeater unit comprises at least two circulators that operate to separate the information-receiving signals received from the broadcasting station from the information-containing signals received by the transmitting antenna to transmit it back to the broadcasting station.
12. 12. The communication system according to claim 11, characterized in that the repeater unit comprises at least two filters for filtering the signals between the circulators so as to reduce any feedback signals produced by the circulators.
13. The communication system according to any of the preceding claims, characterized in that one or more of the repeater stations further comprises means for downwardly converting the frequency of the signals containing received information and means for passing the signals containing information converted in a descending manner for a user terminal located in the relay station.
14. The communication system according to any of the preceding claims, characterized in that each of the relay stations are set in relation to the broadcasting station.
15. 15. The communication system according to any of the preceding claims, characterized in that each of the receiving stations are fixed in relation to the broadcasting station.
16. 16. The communication system according to any of the preceding claims, characterized in that "the broadcasting station is operable to broadcast broadband communications to the relay stations 17.
17. The communication system according to any of the preceding claims, characterized in that one or more of the receiving stations are associated with a data input device, a data output device or a data input and output device 18.
18. The communication system according to claim 17, characterized in that the data input device, the data output device or the data input and output device comprises at least one of: a computer, a computer network, a video recorder, or a television system 19.
19. The communication system according to any of the preceding claims, char bristling because the broadcasting station is. { to associated with at least one of the internet, a video distribution system, or a multi-media data distribution system.
20. The communication system according to any of the preceding claims, characterized in that each receiving station further comprises a relay unit and a transmitting antenna for amplifying and re-broadcasting the information-containing signals received for reception by other receiving stations.
21. The communication system according to any of the preceding claims, characterized in that the broadcasting station operates to broadcast data on the horizontal and vertical components of the microwave signal.
22. 22. The communication system according to any of the preceding claims, characterized in that the broadcasting station is a base station which operates to transmite the signals containing information for a plurality of receiving stations.
23. The communication system according to claim 1, characterized in that it comprises a plurality of broadcasting stations each associated with a user terminal and each of which operates to transmit the signals containing information directly or indirectly to the station receiver
24. 24. A method of communication between the broadcasting station and one or more receiving stations, characterized in that it comprises the steps of: broadcasting signals containing information in the microwave frequency band or above the broadcasting station; receiving the signals containing information in each of the plurality of relay stations which are in direct communication with the broadcasting station; amplify the signals containing information received in the plurality of repeater stations; broadcasting the amplified information-containing signals of each of the plurality of repeater stations, so that at least two of the relay stations broadcast the signals containing amplified information to a common area; locate at least one receiving station within the common area which is not in direct communication with the base station; receiving at least one receiving station the amplified broadcast information signals from at least two relay stations; and processing at least one receiving station the received signals to recover the information transmitted to the broadcasting station.
25. 25. The method according to claim 24, characterized in that before the step of broadcasting the signals of the broadcasting station, the method further comprises the step of modulating the information data on a plurality of different carrier frequencies.
26. 26. The method according to claim 25, characterized in that the difference in frequency between the adjacent carrier frequencies is an integer multiple of the symbol rate of the transmitted data signals.
27. 27. The method according to claim 25, characterized in that the carrier frequencies are grouped into a plurality of groups and where the difference in frequency between the adjacent carrier frequencies in each group is an integer multiple of the signal rate of the signals of transmitted data.
28. 28. The method according to claim 25, 26 or 27, characterized in that the processing steps perform a Fourier analysis of the received signals to retrieve the information.
29. 29. The method according to any of claims 24 or 28, characterized in that it further comprises the step of transmitting the signals containing information from one or more of the relay stations back to the broadcasting station.
30. The method according to claim 29, characterized in that it further comprises the step of transmitting the signals comprising the step of transmitting signals containing information from one or more receiving stations back to one or more repeater stations and the step of transmitting, of the relay stations, the signals containing information received from the receiving station again to the broadcasting station.
31. 31. The method according to any of claims 24 or 30, characterized in that it further comprises the steps of downwardly converting one or more of the frequency repeating stations of the signal containing received information and passing the signals containing a information converted downwards to a user terminal located in the relay station.
32. 32. The method according to any of claims 24 or 31, characterized in that it further comprises the step of amplifying and re-broadcasting the information-containing signals received at the receiving station for reception by other stations.
33. 33. The method according to any of claims 24 to 32, characterized in that the broadcasting step operates to broadcast data on the horizontal and vertical components of the microwave signal.