WO2000079688A2

WO2000079688A2 - Radio communication systems to passive terminals

Info

Publication number: WO2000079688A2
Application number: PCT/FR2000/001673
Authority: WO
Inventors: Jean-Yves Charron; Gérard Panhelleux
Original assignee: Compagnie Des Inventions De L'atelier De L'innovation
Priority date: 1999-06-18
Filing date: 2000-06-16
Publication date: 2000-12-28
Also published as: FR2795258B1; FR2795258A1; WO2000079688A3

Abstract

The invention concerns a digital radio communication system to passive user terminals, comprising a base station (10) provided with omnidirectional broadcasting means to the user terminals, in frequency diversity and/or with time interleaving, in a frequency range and at a power not involving authorisation, a least a secondary station (12) and user terminals (14). Each secondary station (12) comprises broadcasting means to the user terminals according to a mode identical to that of the base station, and linking means with the base station enabling the latter to authorise broadcasting by the secondary base by stopping its own broadcast. Each miniature user terminal can be used only once and has a limited and predetermined life span, with incorporated source, and is capable of receiving and using the signals coming from the base station or the secondary stations.

Description

RADIOCOMMUNICATION SYSTEM TO PASSIVE TERMINALS

The invention relates to radio communication systems making it possible to provide users with terminals with comments concerning events localized in time and space and possibly music; it also relates to a method capable of being implemented in such systems and to consumable terminals, with a limited lifetime, for such systems. The invention is applicable in very diverse situations, whenever there is an interest in providing, to a terminal holder, information on the development of an event as he sees it or likely to interest him. . A particularly important application is the dissemination, at a sporting, cultural or sporting event, of information of a general nature as well as comments on what is happening in the field of vision and outside the field of vision. Athletic competitions, car races, cycling events are particularly representative examples. However, the invention finds many other applications, for example for broadcasting radio alert messages in the mountains, information on activities in a holiday resort or an amusement park, for indicating points of interest in fairs or exhibitions.

At present, the diffusion of information is generally carried out by the use of a system of announcements by loudspeaker, noisy, requiring a heavy installation and not uniformly covering the space in which is find potential users. The use of radio telephones has also been proposed, the disadvantage of which is a high price and an important infrastructure.

The present invention aims in particular to provide a system and a method of low cost, easy to use and great flexibility of use. The invention notably proposes for this purpose a radio communication system in general to passive user terminals comprising: - a base station provided with omni-directional broadcasting means towards user terminals, in frequency diversity and / or with time interleaving, in the case of digital communication,

at least one secondary station, comprising means for broadcasting to the user terminals, advantageously in a mode identical to that of the base station, having means of connection with the base station allowing the latter to authorize the broadcast by the secondary station by stopping its own broadcast, and

- miniature user terminals, for single use and of limited and predetermined lifespan, with incorporated source, capable of receiving and using the signals coming from the base station or the secondary stations.

The system is essentially usable at present for the transmission of speech and music, to which can be added data intended for a complementary use, because the available components do not make it possible to economically receive a good quality image. However, the system may in the future be extended to this area.

Frequency diversity and time interleaving can be achieved by a technology now implemented in relatively low cost circuits, similar to those intended for the digital broadcasting system to mobiles or DAB but simplified. For the broadcasting of speech or music, the frequency diversity can be by alternating transmission at frequencies distributed in a pseudo-random manner according to an algorithm stored in the stations and in the terminals. The temporal interleaving can be carried out at the level of the transmitted bits, within frames having a duration of 40 milliseconds, which is compatible with the tolerable diffusion delays. Transmission security in a noisy environment can be ensured by block coding having an efficiency of less than 1, therefore redundant and allowing error correction. To avoid piracy and reserve reception for authorized users, the messages transmitted can be scrambled or encrypted, in particular by combination of the binary sequence to be transmitted with a pseudo-random sequence, according to a commonly used technology. To allow easy configuration of scrambling, it is preferable to use a pseudo-random scrambling sequence formed by a shift register having as many steps as the order of the desired generator polynomial and a number of gates " or exclusive or XOR equal to the number of additions in the polynomial, minus one. Thus, all logical XOR operations are performed in a single pass.

The following set of XOR operations has proved to be particularly interesting, bo designating the input of the shift register and b32 the output: b7 = b7 ^Λ b32 b5 = b5 ^Λ b32 b3 = b3 ^Λ b32 b2 = b2 ^Λ b 32 b1 = b1 ^Λ b32

This scrambling can implement means already widely used, for example for the implementation of the D2-MAC standard which also uses 32-stage shift registers. The use of frequency diversity, with a typical distribution over

380 carriers, and / or a temporal interleaving makes it possible to carry out the diffusion in the frequency bands UHF and SHF, ranging between 200 MHz and 3 GHz by tolerating jammers working in the same band. In practice, the transmission frequencies chosen will typically be between 400 MHz and 2.6 GHz, for free use.

The invention also proposes a consumable user terminal for a digital communication network; this terminal, devoid of transmission means, comprises a portable object (generally a flat card) containing a radio frequency receiver (often in UHF band) and deinterlacing and decoding means, as well as an integrated non-rechargeable power source allowing operation of predetermined duration and means making it possible to configure at least the means for adapting to diversity, the interleaving and possibly descrambling of the received signal. If necessary, the receiver will include frequency tracking means according to a stored algorithm. It is possible to constitute the portable object by a card of dimension comparable to that of a credit card, containing an antenna and at least one battery which is put out of service at the end of a predetermined duration, the beginning of which can be marked either by putting the terminal into service using a switch, or by receiving a specific code from the base station. It is also possible to provide two different batteries, one whose commissioning is controlled by a switch and which supplies the UHF part, the other which is commissioned by a signal from the base station and which supplies the low frequency part. Decommissioning can be done by destroying a fuse on the ground return of the low frequency battery or batteries.

The above characteristics as well as others will appear more clearly on reading the following description of a particular embodiment, given by way of nonlimiting example. The description refers to the accompanying drawings, in which: - Figure 1 is an overall diagram of the system;

- Figure 2 is a simplified block diagram of a receiving terminal;

- Figure 3 shows a possible hardware constitution of a receiving terminal;

- Figure 4 is a diagram of the broadcasting antenna. The system shown in FIG. 1 comprises a base station 10, one or more portable secondary stations 12 and user terminals 14; the particular system shown is designed to allow a bidirectional link between stations.

The base station 10 can be viewed as having a fixed broadcast transmitter 16 connected to a control desk 18 allowing control by a host or "dis jockey" and a remote antenna 20, connected to the transmitter by a coaxial cable 22. To the broadcasting transmitter is associated a transceiver for connection with the secondary stations, at a different frequency. The latter can be omitted if the links between the base station and the secondary stations are made by separate means. In general, the base station will be placed inside the site where the information is to be broadcast. It is therefore desirable that the antenna lobe is omnidirectional in azimuth. On the other hand, it is desirable to concentrate the radiated energy in the horizontal direction. This can be achieved by using an E-type antenna 20 having a substantially cardioid radiation lobe, having a high gain. Such an antenna provides vertical polarization, which lends itself well to reception. The power of the transmitter will be adjusted and the antenna will be provided not to exceed the radiated power beyond which an authorization to transmit is necessary and to have an adequate coverage area.

Each secondary station 12 includes a transmitter implementing the same modulation, diversity and interleaving mode as the base station, since only one of the stations will transmit at a given time. In the illustrated case, the communications between each secondary station and the base station are carried out by a transceiver distinct from the transmitter which serves the broadcasting. The separate transceiver uses an antenna 24, the gain of which need not be as great as that of the antenna 20, since the processing of the signals received can be carried out by more complex and efficient means than by those of the receiver contained in the terminals 14. Since the most original aspects of the invention relate to the terminals 14, these will be described first, the transmitter 10 mainly performing operations dual to those carried out in the terminal .

The terminal comprises a portable object and a listening earpiece 28, connected by a wire which, unlike what happens for many current portable devices, does not constitute the antenna. The antenna 30 is incorporated into the card, as will be seen below. The UHF signal collected by the antenna 30 is applied to a band filter 32 (surface wave filter in general) which selects the frequency band in which the diversity distribution takes place. The UHF signal is amplified by a low noise amplifier 34 and applied to a transposition mixer 36 which also receives a signal from a local oscillator 38, generally controlled by a phase locked loop. To reduce consumption, phase tracking is advantageously performed using a soft logic criterion (maximum likelihood). The transposed signal is selected by a second band filter 40, amplified by a voltage gain amplifier 42 and applied to a sampler 44. A clock 46, provided with a timing input not shown, provides a timing signal to the sampler 44 and to the entire digital part of the circuit. This digital part comprises an analog-digital converter 48 followed by two channels when the signal has an amplitude modulation in quadrature, called QAM. Each channel includes a demodulation element 50. The two demodulators 50 receive the clock signal in phase quadrature. They can also perform descrambling using the pseudo-random sequence supplied by a generator or PRBS 51. The recovered modulating signal is applied to a processor 54 and the recovered speech signal is applied to a digital-analog converter 56 which supplies the signal at voice frequency to an output amplifier 58.

The input element 60 of the processor 54 provides the deinterlacing and supplies the symbols in their normal order to the output element 62. The processor can be provided to carry out a gain control by modifying the adjustment voltage applied to the amplifier 42, in order to obtain a substantially constant output level.

The sound level is advantageously adjustable using a circuit 64 associated with pushers 66 providing one of the rising pulses, the other of the falling pulses. A switch 68 makes it possible to start the terminal by sending an impulse to a circuit 70 which fulfills two functions. On the one hand it applies to the various components, the voltage supplied by a battery 72. On the other hand, it definitively renders the terminal inoperative after a fixed period which can be counted from:

- pressing the switch 68 and / or - the moment when the output element 62 provides a level above a determined threshold, indicating that the event to which the terminal is assigned has started.

The portable object of the terminal can have the general constitution shown in FIG. 3. It can be constituted by a card having a bottom 74 and a cover 76, the external faces of which can carry an advertisement, an illustration of the event, etc. bonded to a frame 78 containing the active components and the edge of which carries the switch pushbuttons

66 and 68. The antenna 80 can be screen printed on the frame and advantageously has the folded hairpin shape which is shown and does not have the silent orientations of a closed loop. The components are advantageously mounted on a support by a technology with legs avoiding an expensive multi-layer substrate.

In the case where the terminal is designed to supply a short message recorded after the end of the event, a second battery 82, started up by an additional switch or by pressing the switch 68 again, can be provided.

During manufacture, the components are configured definitively, using inputs not shown, before inserting by fitting the bottom and the cover. The antenna 80 can be tuned at the same time to the planned central frequency, by placing a bar 8 on the hairpin.

The sequence of use of the system which has just been described may be as follows, after distribution of the appropriate terminals.

The user arriving on the site activates the battery by pressing the switch 68. The switches can be protected, when they are distributed or sold, by placing the card and the headset in a pocket plastic or by blocking the switches with a tab which must be removed. The presenter at the master station activates its transmitter, which allows it to broadcast messages using a microphone, possibly recorded advertisements, recorded music, etc. As soon as the user terminal detects the presence of a low frequency signal originating from the demodulation of the broadcast signal, it starts counting the allocated time. The console 18 constitutes a BF control room which includes a high frequency dynamic mixer allowing the dosing and mixing of all sources. It can be fitted with the usual red light 86 indicating that a transmission is in progress (on the air). The users as well as the reporters in charge of the secondary stations receive the broadcast.

When a reporter wishes to comment on a particular event, he asks the host to take the antenna, for example by activating a command on his microphone. The presenter can be alerted by lighting an orange lamp 90. The secondary station can be provided to also address an identification which appears on a display 92. To give the reporter a hand, the presenter cuts off his program. At the same time, he informs the reporter. The latter can then comment on the particular event and broadcast in place of the master station. The presenter can follow the event, like the users of the terminals and resume the antenna by asking the reporter to stop broadcasting.

The duration allocated by the component 70 is chosen so as to slightly exceed the maximum duration planned for the event. At the end of this period, the terminal is permanently deactivated, whatever the maneuvers performed by the user.

The antenna 20 may have the structure shown schematically in FIG. 4. It is a double collinear antenna with 5λ / 8 strands, in high impedance flat lines. It has a central branch for connection to the transmitter via a coaxial and an impedance transformer and two lateral dipole branches. The length 5λ / 8 represents an optimum in terms of radiation resistance. It will be possible to deviate from it. A such an antenna has an isotropic grain which makes it possible to have an increased effective radiated power at HF power supplied to the equal antenna.

Claims

1. Radio communication system towards passive user terminals, comprising: - a base station (10) provided with omni-directional broadcasting means towards the user terminals, in frequency diversity and / or with time interleaving in the event of digital communication,

- at least one secondary station (12), comprising means of broadcasting to the user terminals having means of connection with the base station allowing the latter to authorize the broadcasting by the secondary station by stopping its own broadcasting, and

- miniature user terminals (14) with single use and of limited and predetermined lifespan, with incorporated source, suitable for receiving and using the signals originating from the base station or the secondary stations.

2. The system as claimed in claim 1, the base station of which comprises means for generating signals representative of speech or of the image, using in diffusion a diversity of frequencies by transmission at frequencies distributed pseudo-randomly according to a algorithm stored in stations and terminals.

3. System according to claim 1 or 2, characterized in that the transmitted bits are grouped in frames with redundant block coding, each passive terminal using a decoder allowing error correction.

4. Consumable user terminal for digital communication network, devoid of transmission means, comprising a card containing a radio frequency receiver, deinterlacing means, and an integrated non-rechargeable power source allowing operation of predetermined duration, means making it possible to configure at least the means for adapting to the frequency diversity, the interleaving and possibly descrambling of the received signal.

5. Terminal according to claim 4, characterized in that the card contains an antenna and at least one battery constituting said source and in that the terminal further comprises a headset connected to the card.

6. Terminal according to claim 4 or 5, characterized by means putting the terminal out of service after a fixed period after manual start-up and / or the start of reception.

7. Terminal according to claim 4, 5 or 6, characterized in that it comprises means for restoring a recorded message after the terminal has been deactivated.

8. Base station for system according to claim 1, characterized in that it comprises a broadcast transmitter connected to a remote antenna, and possibly a transmitter receiver for connection with the secondary stations.

9. Base station according to claim 8, characterized in that it comprises a remote antenna (20) in E having a substantially cardioid radiation lobe.

10. Base station according to claim 9, characterized in that the antenna at E is a double collinear antenna with 5λ / 8 strands in high impedance flat lines.