EP2928092A1

EP2928092A1 - Transmitter for transmitting an information signal, preferably a warning announcement signal, via substantially all channels of a frequency range

Info

Publication number: EP2928092A1
Application number: EP15248021.6A
Authority: EP
Inventors: Stefan Teuscher
Original assignee: Institut fuer Rundfunktechnik GmbH
Current assignee: Institut fuer Rundfunktechnik GmbH
Priority date: 2014-04-04
Filing date: 2015-04-03
Publication date: 2015-10-07

Abstract

The invention relates to a transmitter for transmitting an information signal, in particular a warning announcement signal, via substantially all those channels in the frequency range. For this purpose, the transmitter is provided with a delay unit (110) for delaying with respect to each other the information signals in two adjacent channels in each case. (Fig. 1)

Description

Background of the invention

The invention relates to a transmitter according to the pre-characterizing clause of claim 1, to a tunnel transmission system provided with the transmitter, and to an information signal generating unit which can be used in the transmitter. A transmitter according to the pre-characterizing clause of claim 1 is disclosed, for example, in EP1816764A . The known transmitter is set up to transmit an information signal, in particular a warning announcement signal, in a tunnel.
To increase safety in road tunnels, at least one VHF-FM radio program is fed into the tunnel broadcasting cable which is also installed for wireless communication in road tunnels or enclosures. In an emergency (accident or similar), the current VHF-FM radio program can be interrupted from the tunnel control center and used to make an announcement to the vehicle occupants in the tunnel via the car radio receiver.

Brief description of the invention

Although the invention is not restricted to warning announcement signals in a tunnel or to broadcasting in the VHF-FM range, the invention intends to propose an improved transmitter which is able to reliably transmit information signals, in particular warning announcement signals, to vehicle occupants.
For this purpose, the transmitter according to the pre-characterizing clause of claim 1 is characterized according to the characterizing portion of claim 1. The tunnel transmission system is characterized according to claim 8. The information signal generating unit is characterized according to claim 11.
Preferred exemplary embodiments of the transmitter are characterized by claims 2 to 7. Preferred exemplary embodiments of the tunnel transmission system are characterized by claims 9 and 10.
The invention is based on the following knowledge.
In known tunnel transmission systems, up to now, a dedicated transmitter with associated modulation has been required for these announcements for each broadcast program which is fed into the tunnel and is broadcast on a channel in the (VHF-FM) frequency range.
A receiver (car radio) in the tunnel will reproduce the announcement when 1. the car radio is switched on, 2. this car radio is tuned to a frequency which is fed into the tunnel transmission system, and 3. the field strength of the tunnel overdubbing from the broadcasting cable is greater than the field strength transmitted from outside via the tunnel portals or other openings.
In reality, this has the following problems:

1. Radio frequencies f1 and f2 are fed into the tunnel. However, the receiver is tuned to frequency f3 which is not fed into the tunnel transmission system. On account of the missing signal, the receiver receives noise which is suppressed by the noise blocking system or tolerated by the driver for the duration of the journey through the tunnel. In the event of an announcement on f1 and f2, the receiver receives nothing as it is tuned to f3.
2. Frequencies f1 and f2 are fed into the tunnel. The receiver is again tuned to frequency f3, which is not fed into the tunnel system, but can be received in the tunnel sufficiently well that there is no reason for the driver to switch to one of the two frequencies f1 or f2. The driver therefore does not catch anything of the announcement on f1 and f2. (This situation can occur when the transmitter of the frequency f3, for example, is very close to the tunnel portal, e.g. the Olympia Tower in Munich by the 1.5 km long Petuel Tunnel, or when the tunnel has many entrance and exit slip roads or skylights, such as the 2.1 km long Hosbach East and West enclosures).
3. Frequencies f1 and f2 are fed into the tunnel. As in case No. 2, the receiver is tuned to frequency f3 which, although it is not fed into the tunnel transmission system, can be received throughout the tunnel. However, the driver is listening to music from a CD. The car radio is only running in the background in order to interrupt the CD in the event of traffic announcements. As the set frequency f3 can still be received sufficiently well in the tunnel that there is no need for the car radio to automatically switch in the background to one of the two frequencies f1 or f2, the driver catches nothing of an announcement on f1 and f2. In the cases depicted, car drivers cannot be reached by an announcement in the quickest way, which reduces tunnel safety. The object of an announcement should, however, be to reach as many car drivers in the tunnel as possible as quickly as possible. Exactly this can be achieved when as many broadcast programs that can be received outside the tunnel as possible can also be received inside the tunnel and the announcement reaches the car driver by as many communications paths as possible.

Today's signal conditioning in transmission technology (SDR = software defined radio) enables a signal with the same announcement to be generated not only on one but on as many available radio and transmission channels as possible. These frequencies are then amplified collectively and, in the event of an announcement, fed into the tunnel transmission system instead of the broadcast programs.
It has already been proposed earlier to broadcast a warning announcement signal on as many channels of a frequency range as possible. In this regard, reference is made, for example, to WO02/103653A . However, it has been established by the inventor that the known warning announcement signal transmission is still always subject to interference.
It has been established by the inventor that this interference is caused by interference between information signals (warning announcement signals) in adjacent channels, in particular in cases where the adjacent channels are spaced apart from one another by a relatively small frequency. In order to eliminate this interference, according to the invention, it is proposed to delay with respect to one another the information signals in two adjacent channels by a small amount.
In doing so, time delays in the range from 0 to 2 seconds, preferably however in the range from 0.5 to 1 second, can be considered.
Further, in the event that a warning announcement is required in the CB range, which is both frequency-modulated and amplitude-modulated (both types of modulation are used in channels 1 to 40 in CB radio), in a second exemplary embodiment of the transmitter, a mixed AM and FM modulation method is to be used (that is to say in these channels 1 to 40 in the CB radio example).
In addition, it must be pointed out that DE19644430A shows a wireless transmitter, in which an information signal is broadcast in different broadcasting directions with a different delay. The transmitter concerned is incorporated in a transmitter network which is operated using common wave broadcasting technology. However, there is no mention here of transmitting an information signal, such as a warning announcement on all channels in a frequency range.

Brief description of the figures

The invention is explained further in the following description of the figures based on some exemplary embodiments. In the drawings

Fig. 1 shows a first exemplary embodiment of the transmitter,
Fig. 2 shows an exemplary embodiment of a mixed modulation method, and
Fig. 3 shows an exemplary embodiment of a broadband amplifier for feeding VHF-FM channels into the tunnel.

Detailed description of the figures

Fig. 1 shows a first exemplary embodiment of the transmitter according to the invention. In this exemplary embodiment, the transmitter is also able to broadcast different broadcast programs on different channels. However, this is not necessary for the invention. It would be very easy to imagine a tunnel transmission system wherein it was only necessary to broadcast a warning announcement signal in the tunnel and dispense with the transmission of broadcast programs in the tunnel.
The information signal generator unit in the transmitter, which is formed mainly by block 102 (and if necessary also block 104 and 114), is described first. A source of the information signal or warning announcement signal is indicated by the reference number 100. This source 100 is arranged in a tunnel control center and can be designed as a microphone for overdubbing a warning announcement, or as a tape recorder with the recorded warning announcement, or as some other form of storage device such as a hard disk drive or optical recording medium on which the warning announcement is stored. The source 100 is coupled to an input 101 of the information signal generator unit.
A first modulation block is indicated by the reference number 102. The information signal/warning announcement signal is conditioned for feeding into the VHF-FM channels in this modulation block 102.
The frequencies 87.6 to 107.9 MHz (in each case inclusive) are used in analog FM radio, which continues to prevail. In practically all car radios, it is also possible to tune to frequencies 87.5 MHz and 108.0 MHz, which are currently likewise used for terrestrial reception in other countries. This results in 206 frequencies in steps of 100 kHz.
The warning announcement from the source 100 is now conditioned by means of a digital signal generator and modulated by means of the modulator circuits 106(1) to 106(n) onto all 206 frequencies in an identical manner with the exception of a time delay which is described below. At the same time, an RDS signal, which can likewise be identical on all frequencies, must also be modulated in each case (block 108). It is only important that the so-called alarm bit (PTY31) is set in all RDS data streams. By this means, every receiver in the tunnel, regardless of which frequency it is receiving, is signaled that the announcement is an emergency warning announcement and, for example, CD playback is to be interrupted.
It is entirely sufficient to transmit the announcement in mono. This is particularly advantageous, as this reduces the mutual interference between adjacent receiving frequencies. Trials have shown that, with such a close frequency assignment, interference can occur between the identically modulated adjacent frequencies, which negatively influences the reception of the warning announcement.
It has been shown that, in any event, the interference can be suppressed to a great extent when its modulation content is slightly offset by an order of magnitude between 0 and 2 seconds, preferably between 0.5 and 1 second. This delay is realized by the blocks 110(1) to 110(n). The delay times t1 to tn can all be different. Another possibility would be to make the odd delay times t1, t3, t5, ... , for example, equal to one another, equal to t(u), where, e.g. t(u) = 0, and the even delay times t2, t4, t6, .. equal to one another, equal to t(g), where the delay time difference t(g) - t(u) again lies between 0 and 2 seconds, preferably between 0.5 and 1 second.
It must be mentioned here that, when a delay time t(i) of a delay block 110(i) is equal to 0, the delay block 110(i) can of course be omitted.
All channels of the VHF-FM frequency range are combined in a signal combining unit 112 (in the form of a summer which can be realized both from a circuit point of view and also advantageously in conjunction with the overall arithmetic unit for generating the signal (Software Defined Radio)) and fed to a second signal combining unit 114. The output signal of the second signal combining unit 114 is fed to a first terminal of a switch 116. The switch 116 is coupled to an antenna arranged in the tunnel or to a tunnel broadcasting cable 124. Although not part of the invention, the transmitter in Fig. 1 is provided with a wireless reception antenna 118 which is arranged outside the tunnel and receives the different broadcast programs to pass on to the tunnel. By way of example, several channel-selective amplifiers 120(1), 120(2), ...120(m) are provided for this purpose. The broadcast programs received in this way are combined in a third signal combining unit 122 and fed to a second terminal of the switch 116.
Normally, the switch is in the position shown, thus enabling the broadcast programs to be broadcast in the tunnel. In an emergency, the switch 116 is switched to the other position, as a result of which the warning announcement signal can be broadcast on all VHF-FM channels in the tunnel.
The transmitter is further provided with a second modulation block 104 for the CB radio frequency range, which is very similar to the block 102 with regard to its circuit design. Truck drivers in particular are very often continuously on standby on a CB radio channel by means of CB radios in the vehicle. The usual channels on which truck drivers are continuously on standby via CB radio differ depending on the country of origin. If, now, a truck driver has not switched on the radio, because he has just made a telephone call for example, but is on standby via CB radio, then this target group can also be reached very quickly by transmitting the announcement on every CB radio channel. Because of the inertia and size of a truck, this is certainly at least as important as reaching passenger car occupants quickly.
In Germany and other countries, operation in AM (amplitude modulation), FM (frequency modulation) and SSB (single sideband) modulation modes is allowed on the CB radio channels 1 to 40 agreed within the CEPT (48 European states of the Conference Europeenne des Administrations des Postes et des Telecommunications). However, operation in AM or FM is usual in vehicles. However, a receiver tuned to AM cannot receive FM broadcasts. Conversely, a receiver tuned to FM cannot receive AM broadcasts.
(In reality, pure frequency modulation is not used either in CB radio or in FM radio, but a combination of frequency modulation (FM) and phase modulation (PM). This is usually generated by connecting a pre-emphasis circuit with a time constant of 750 µs or 50 µs or 75 µs before the frequency modulator. As this is merely a circuit detail, the terms frequency modulation (FM) and phase modulation (PM) are equivalent.)
In Germany, CB radio channels 41 to 80, on which only FM is allowed, are also available. In other countries, other channels, which are likewise only approved nationally and also may only be used in these countries, are sometimes available.
To now reach all receivers on all channels, it is advantageous to use a combined modulation process at least on channels 1 to 40. For this purpose, the carrier frequency is modulated with a frequency swing of e.g. approx. 2.5 kHz in FM and also with e.g. approx. 50% to 60% modulation factor in AM. (A modulation factor of 100% would be optimal for pure AM transmission; however, trials have shown that the simultaneous FM transmission suffers greatly as a result. Here, a modulation factor of 50% to 60% represents a good compromise between adequate modulation factor and resulting adequate volume in an AM receiver and still good articulation in an FM receiver. Conversely, the FM swing does not significantly impair AM reception.)
Pure FM transmission is sufficient in the German CB radio channels 41 to 80. However, combined AM-FM transmission is also possible and harmless here, as although amplitude modulation is currently not allowed on these channels in Germany, the tunnel broadcasting cable does not broadcast to the outside. Advantageously, signal conditioning can be carried out in the same way as in the channels 1 to 40. However, it can also take place in pure FM. These considerations lead to a block 104 which is provided with a block 126, in which the warning announcement signal is either FM-modulated or a mixed AM-FM modulation process is carried out on the warning announcement signal for the different channels. In turn, modulator circuits 128(1) to 128(80) are provided for modulating the warning announcement in the 80 different CB channels. In turn, delay blocks 130(1) to 130(80) are provided to delay the warning announcement signals with respect to one another on the different channels.
All channels of the CB frequency range are combined in a single combining unit 132 (in the form of a summer, see also above in conjunction with block 112) and are likewise fed to the second signal combining unit 114.
The same applies to the different delay times t1 to t80 in block 104 as has already been discussed above for the delay times t1 to tn in block 102. This makes a further detailed description unnecessary.
Fig. 2 shows an exemplary embodiment of mixed AM-FM modulation of the information signal/warning announcement signal as can be contained in block 126. The warning announcement signal is provided by the source 100 and fed to an audio frequency amplifier 202 (AF amplifier). The amplifier 202 amplifies the warning announcement signal in a speech frequency range of e.g. 300 Hz to 3 kHz. The thus amplified signal is fed to an FM modulator stage 204. The warning announcement signal is frequency-modulated by means of a voltage controlled oscillator in the FM modulator stage 204, wherein the carrier frequency of the channel in which the warning announcement signal is to be broadcast is frequency-modulated with a frequency swing of e.g. approx. 2.5 kHz. The FM-modulated signal is fed to an amplitude modulator stage 206.
The FM-modulated warning announcement signal is additionally amplitude-modulated in the amplitude modulator stage 206 with a modulation factor of e.g. approx. 50% to 60%. The thus generated signal is then amplified once more in a high-frequency amplifier 208, after which it can be fed to the tunnel antenna or into the tunnel broadcasting cable.
In general, it must be noted that, due to the non-linearities of an amplifier which are necessarily always present, intermodulation products outside the actual transmission range also always occur with collective amplification of 206 or 80 individual signals. These must be appropriately filtered at the amplifier output.
Previously, a separate VHF overdubbing transmitter had to be made available for every radio signal fed into the tunnel. For this reason, a broadband infeed of the whole radio band into the tunnel was rejected, as overdubbing transmitters could not be provided on all VHF frequencies with broadband feed.
With the proposed technique of conditioning by means of an SDR overdubbing transmitter, the whole VHF band can be amplified on a broadband basis and fed into the tunnel, as, in every case, it is guaranteed that in the event of overdubbing, the car driver is reached on every conceivable set frequency. This is made clear in Fig. 3, wherein a broadband amplifier 300 is provided between the radio receiving antenna 118 and the switch 116 for feeding in the broadcast programs. The amplifier 300 is provided with a bandpass filter 304 with a pass frequency band of 87.5 to 108 MHz, a broadband linear amplifier 306, and a bandpass filter 308 with a pass frequency band of 87.5 to 108 MHz.
The transmitter according to the invention is indicated by the block 302 and contains the blocks 102 and/or 104 and, if necessary, also the block 114 (assuming that the transmitter according to the invention generates a warning announcement signal both for the FM radio frequency band and for the CB frequency band.)
It must be mentioned that, although the invention has been described based on an exemplary embodiment for warning announcement signals in tunnels, the invention is also to be used in other applications such as in road traffic.
The invention can therefore also be used in its own right in the event of an emergency for announcements on all frequencies, that is to say also without the normal feeding of broadcast programs into a tunnel (120(1) - 120(m)). For example, this would be conceivable in short tunnels in which a normal radio infeed is dispensed with for economic reasons. The warning announcements would then only be transmitted on all 206 FM frequencies and/or on all CB radio channels in an actual emergency.

Claims

Transmitter for transmitting an information signal via substantially all neighboring frequency channels (106(1) to 106(n)) in a frequency range, characterized in that, the transmitter is provided with a delay unit (110(i)) for delaying with respect to each other the information signals for any two adjacent frequency channels in the frequency range.
Transmitter as claimed in claim 1, characterized in that, the delay unit is adapted to realize a delay between the information signals in adjacent channels which is between 0 and 2 seconds, preferably between 0.5 and 1 second.
Transmitter as claimed in claim 1 or 2, characterized in that, the frequency range is the FM Frequency range and/or the CB Frequency range.
Transmitter as claimed in claim 1, 2 or 3, characterized in that, the transmitter is adapted to transmit an information signal in all of the channels in the frequency range.
Transmitter as claimed in one of the preceding claims 1 to 4, characterized in that, the information signal is a warning announcement signal.
Transmitter as claimed in one of the preceding 1 to 5, characterized in that the transmitter is adapted to modulate the information signal to be transmitted in a channel by a combination of two modulation methods.
Transmitter as claimed in claim 6, characterized in that, the combination of the two modulation methods is in the form of a combination of an AM modulation method and an FM modulation method.
Tunnel transmission system, provided with the transmitter as claimed in one of the preceding claims.
Tunnel transmission system as claimed in claim 8, characterized in that the transmitter is in the form of a broadcast transmitter and is additionally adapted to broadcast different broadcast programs via different channels in the frequency range.
Tunnel transmission system as claimed in claim 9, characterized in that, the transmitter is provided with a switch-over unit (116) for switching the transmitter between a first mode for transmitting the different broadcast programs via the different channels in the frequency range, and a second mode for transmitting the warning announcement signal via substantially all those channels in the frequency range.
Information signal generator unit, for use in a transmitter as claimed in one of the claims 1 to 7, characterized in that it is provided with an input (101) for receiving an information signal, a modulator unit (102) for modulating the information signal in substantially all the channels in the frequency range, and is provided with a delay unit (110(i)) for delaying with respect to each other the information signals for any two adjacent channels.