EP0568143A1 - Verbessertes Sendernetzwerk mit nur einer Sendefrequenz - Google Patents

Verbessertes Sendernetzwerk mit nur einer Sendefrequenz Download PDF

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Publication number
EP0568143A1
EP0568143A1 EP93201154A EP93201154A EP0568143A1 EP 0568143 A1 EP0568143 A1 EP 0568143A1 EP 93201154 A EP93201154 A EP 93201154A EP 93201154 A EP93201154 A EP 93201154A EP 0568143 A1 EP0568143 A1 EP 0568143A1
Authority
EP
European Patent Office
Prior art keywords
transmitter
transmitters
auxiliary
signal
network
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93201154A
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English (en)
French (fr)
Inventor
Paulus G.M. c/o INT. OCTROOIBUREAU B.V. De Bot
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics NV, Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP93201154A priority Critical patent/EP0568143A1/de
Publication of EP0568143A1 publication Critical patent/EP0568143A1/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/65—Arrangements characterised by transmission systems for broadcast
    • H04H20/67—Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency

Definitions

  • the invention relates to a transmitter network comprising at least two transmitters having a like transmitter frequency which transmit a like signal.
  • the invention likewise relates to a transmitter to be used in such a network.
  • Such a transmitter network is known from the journal article entitled "DAB - A new sound broadcasting system, Status of the development - Routes to its introduction” by G. Plenge in EBU Review no. 246, April 1991, Chapter 5.2.2, pp. 87-112.
  • a signal is transmitted with a like transmitter frequency via a plurality of transmitters, whereas a receiver can receive signals from different transmitters.
  • a disturbance signal is developed having a characteristic corresponding to an echo signal.
  • This (undesired) echo signal is suppressed in the receiver by means of an echo canceller or by using a what is commonly referred to as guard band in the time domain when the signal to be transmitted is actually transmitted. Consequently, it is possible that this received signal is discarded in the receiver for a specific period of time during which the received signal is disturbed by the echo signals.
  • transmitter networks in which no more than a single transmitter frequency is used, is that much fewer channels need to be available than when conventional transmitter networks are used.
  • transmitter networks employing no more than a single transmitter frequency there will be no additional disturbance even under special propagation conditions, because such disturbing signals are already taken into account in the receivers.
  • a problem for the prior-art transmitter network is that the difference in time between the arrival at the receiver of signals coming from different transmitters may be relatively large. For example, in a situation where a first and a second transmitter are 50 km apart and a receiver is positioned between the first and the second transmitter at a distance of 10 km from the second transmitter, the difference between the distance from the first transmitter to the receiver and the distance from the second transmitter to the receiver is 30 km. If it is assumed that the transmitters transmit their information simultaneously, a 100 ⁇ s delay difference is found based on a light velocity of 300,000 km/s.
  • the transmitter network is characterized, in that one of the transmitters comprises delay means for delaying the signal transmitted by this transmitter, so that the signals transmitted by the transmitters arrive substantially simultaneously in an area of overlap of the coverage of the two transmitters.
  • the required complexity of the receiver may be further reduced by means of a further embodiment of the invention, characterized in that at least one of the transmitters is an auxiliary transmitter installed amongst a plurality of main transmitters.
  • the transmitter network solely consists of main transmitters having substantially equal coverage areas, there will be relatively large regions among these transmitters in which the echo signals received from other transmitters are significant and thus are to be suppressed. Significant echo signals occur if the received signal strength of a plurality of transmitters are of a like order. As it is possible only in a small area to provide a substantially complete compensation of the delay difference, there are still non-negligible delay differences in part of the relatively large region in which significant echo signals occur.
  • a further embodiment of the invention is characterized, in that one of the transmitters is a main transmitter and one of the transmitters an auxiliary transmitter, the auxiliary transmitter having a lower aerial height than the main transmitter, and in that the auxiliary transmitter is installed on the boundary of the coverage area of the main transmitter.
  • the field strength received from an auxiliary transmitter with a smaller aerial height than that of the main transmitter diminishes more rapidly as a function of the distance from the receiver to this auxiliary transmitter than does the field strength received from a main transmitter as a function of the distance from the receiver to the main transmitter.
  • Fig. 1 shows the field strength of a first transmitter A and a second transmitter B as a function of the position of a receiver on an imaginary line between these transmitters.
  • the variation of the field strength as a function of the distance is determined on the basis of formulas for the received field strength as a function of the distance of a transmitter as stated in the title "Microwave Mobile Communications" by W.C. Jakes, Wiley, 1974.
  • the distance between the first transmitter and the second transmitter is 80 km in the example of Fig. 1.
  • Fig. 1 also shows the echo region E in which significant echoes occur.
  • the echo region is defined here as the area in which the field strength of the received signal of both transmitters differs less than 10 dB ( ⁇ ).
  • the delay difference may be determined if it is assumed that the two transmitters simultaneously transmit the signal to be transmitted.
  • the large 133 ⁇ s delay requires a relatively large complexity of the receiver.
  • the signal transmitted by transmitter B is delayed by the average of the delay difference between the points P and Q (59.15 ⁇ s)
  • the signal from transmitter A arrives at point P 72.45 ⁇ s earlier than the signal from transmitter B.
  • the signal from transmitter A arrives at point Q 72.45 ⁇ s later than the signal from transmitter B. It appears that when this invention is implemented, in the echo region one only needs to take an echo signal into account having a delay of 72.45 ⁇ s.
  • Fig. 2 shows the field strength of a main transmitter A, a main transmitter C and an auxiliary transmitter B as a function of the position of the receiver on an imaginary line between the two transmitters.
  • the distance between the main transmitters A and C is equal to 100 km and the auxiliary transmitter B is 50 km remote from the two main transmitters.
  • the echo region E1 is shown if no more than two main transmitters are included in the transmitter network.
  • the echo region E1 then has a size of about 44 km. This results in a delay difference which may lie between -147 ⁇ s and + 147 ⁇ s in the echo region.
  • auxiliary transmitter B If an auxiliary transmitter B is inserted between the two main transmitters, there are two echo regions E2 and E3 having a size which is considerably smaller than that of the echo region E1.
  • the size of the echo regions in the situation as shown in Fig. 2 is equal to 16 km. From Fig. 2 it appears that the centre of the echo regions E2 and E3 is installed 28 km remote from the nearest main transmitter and that this centre is installed 32 km remote from the auxiliary transmitter.
  • the delay difference in the echo region may now lie between -53 ⁇ s and +53 ⁇ s. This delay difference is considerably smaller than the 147 ⁇ s delay difference that may occur in the echo region E1.
  • Fig. 3 gives a two-dimensional representation of a transmitter network comprising equal (main) transmitters 1 to 7, installed equidistantly. The echo regions are shaded and cover a considerable area.
  • Fig. 4 gives a two-dimensional representation of a transmitter network comprising mutually equal main transmitters 1 to 7 and a larger number of auxiliary transmitters s among the main transmitters 1 to 7.
  • the main transmitters 1 to 7 exactly simultaneously transmit the signal to be transmitted, whereas all the auxiliary transmitters s transmit the signal to be transmitted, delayed by a same period of time.
  • the echo regions are also shaded.
  • a comparison of Fig. 4 to Fig. 3 shows that the size of the echo regions and hence the size of the possible delay difference in the transmitter network as shown in Fig. 4 is considerably smaller than the size of the echo regions in Fig. 3.
  • the dashed line a in Fig. 5 shows the field strength of the received signal as a function of the position of a receiver whilst assuming that no more than a single main transmitter is used.
  • the coverage area is to have the size as denoted by the letter D and that the relative field strength within the coverage area is to be at least -90 dB.
  • This -90 dB value may be determined, for example, by disturbance caused by transmitters from a neighbouring area.
  • the solid lines show the received signal coming from the main transmitter A and the auxiliary transmitters B1, B2 if a plurality of auxiliary transmitters B1, B2 are positioned 30 km apart around the main transmitter A.
  • auxiliary transmitters B1 to B4 having a smaller aerial height are present increasing the overall coverage area.
  • further auxiliary transmitters D3, D5 and D6 and D1, D2 and D4 respectively are present on part of the boundary of the coverage area of the main transmitter A and on the boundary of the coverage area of the auxiliary transmitters B1 to B3, the further auxiliary transmitters having an aerial height again smaller than that of the auxiliary transmitters B1 to B4.
  • auxiliary transmitters E having an even smaller aerial height are present for completely covering the desired coverage area.
  • the output of a receiver aerial 10 is connected to a receiver 12.
  • the output of the receiver 12 is connected to an input of a demodulator 14.
  • An output of the demodulator 14 carrying output signal a r is connected to an input of the transmitter 15.
  • the output of the transmitter 15 is connected to the delay means 16 in accordance with the inventive idea.
  • the output of the delay means 16 carrying output signal a d is connected to an input of a modulator 17.
  • the output of the modulator 17 is connected to an input of a power amplifier 18, the output of the power amplifier 18 being connected to a transmitter aerial 19.
  • transmitter networks having a transmitter frequency for all transmitters are preferably used for transmitting digital signals, because the measures necessary for suppressing echo signals are harder to realise when analog signals are transmitted, although the application to analog signal transmission is highly conceivable.
  • the system as shown in Fig. 7 is arranged for processing such digital signals.
  • the signal to be transmitted is received through an aerial 10.
  • This may be an aerial for a radio link but this may also be an aerial for satellite reception.
  • the output signal of aerial 10 is processed in receiver 12 to an intermediate frequency signal and then demodulated in the digital demodulator 14 and detected, so that a sequence of digital symbols a r is available at the output of the demodulator.
  • This may be a single sequence of digital symbols but this may also be a large number of symbol sequences as occur in OFDM signals for digital broadcasting as this has been proposed in aforementioned journal article by G. Plenge.
  • the digital symbols a r are delayed by the desired period of time by the delay means 16.
  • the delay means 16 For determining the delay of the delay means 16, one not only has to take the delay into consideration necessary for simultaneously receiving in the middle of an echo region signals transmitted by two transmitters, but also the delay difference occurring in the transmission links between the studio and the various transmitters.
  • the delayed symbols a d are modulated on a carrier having the desired frequency by the modulator 17, and this modulated signal is amplified by the power amplifier 18 to a signal having the desired power.
  • Fig. 7 It is likewise conceivable that the system as shown in Fig. 7 is arranged without a demodulator 14 and a modulator 17. As a result, however, the delay means are then to be arranged in an analog form, or the signals are to be sampled at a high rate if the delay means are arranged in a digital form.
  • the signal is to be delayed in the main transmitter because the transmission link from main transmitter to auxiliary transmitter already realises a delay larger than the required delay.
  • the symbols a r to be delayed are applied to an input port of a dual port RAM 20, whereas the delayed symbols a d are available at an output port of the dual port RAM 20.
  • a clock signal CLK is applied to a clock input of a counter 26, to a control input of the multiplexer 22 and to a read/write control input of the dual port RAM 20.
  • An output of the counter is connected to a first input of the multiplexer 22 and to a first input of an adder 24.
  • the digital representation of the desired delay time D is fed to a second input of the adder 24.
  • the output of the adder 24 is connected to a second input of the multiplexer 22, whereas the output of the multiplexer is connected to the address input of the dual port RAM 20.
  • the symbols a r to be delayed are written in the dual port RAM 20 when the clock signal is a logic "0".
  • the clock signal activates the write mode of the dual port RAM 20 and likewise provides that the multiplexer 22 applies the sum of the count of the counter 26 and the value D to the address input of the dual port RAM 20.
  • the delayed symbols a d are read from the dual port RAM 20 when the clock signal is a logic "1".
  • the read mode of the dual port RAM 20 is selected when the clock signal gets the logic "1" value and the count is applied to the address input of the dual port RAM via the multiplexer 22.
  • the write address is always a value D larger than the read address, at a specific address first the symbols a r will be written and these symbols will be read out at an instant which is D.T clk later. If the adder 24 generates a carry, this carry may be ignored as a result of which the writing in the dual port RAM 20 again starts at address 0.
  • delay means as shown in Fig. 7 are advantageous relative to the use of a shift register for delay means, in that the delay can be set very simply and very rapidly by the selection of the value D.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Radio Relay Systems (AREA)
EP93201154A 1992-04-28 1993-04-21 Verbessertes Sendernetzwerk mit nur einer Sendefrequenz Withdrawn EP0568143A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP93201154A EP0568143A1 (de) 1992-04-28 1993-04-21 Verbessertes Sendernetzwerk mit nur einer Sendefrequenz

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP92201190 1992-04-28
EP92201190 1992-04-28
EP93201154A EP0568143A1 (de) 1992-04-28 1993-04-21 Verbessertes Sendernetzwerk mit nur einer Sendefrequenz

Publications (1)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0823794A1 (de) * 1996-01-10 1998-02-11 Advanced Digital Television Broadcasting Laboratory Ofdm-system und ofdm-vorrichtung
EP1037441A3 (de) * 1999-03-18 2004-01-28 Kabushiki Kaisha Toshiba Digitale Verzögerung ausführender OFDM-Signalprozessor

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4255814A (en) * 1977-07-15 1981-03-10 Motorola, Inc. Simulcast transmission system
WO1991008620A1 (en) * 1989-12-04 1991-06-13 Motorola, Inc. Simulcast communication system
US5038403A (en) * 1990-01-08 1991-08-06 Motorola, Inc. Simulcast system with minimal delay dispersion and optimal power contouring

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4255814A (en) * 1977-07-15 1981-03-10 Motorola, Inc. Simulcast transmission system
WO1991008620A1 (en) * 1989-12-04 1991-06-13 Motorola, Inc. Simulcast communication system
US5038403A (en) * 1990-01-08 1991-08-06 Motorola, Inc. Simulcast system with minimal delay dispersion and optimal power contouring

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0823794A1 (de) * 1996-01-10 1998-02-11 Advanced Digital Television Broadcasting Laboratory Ofdm-system und ofdm-vorrichtung
EP0823794A4 (de) * 1996-01-10 2002-03-20 Advanced Digital Television Br Ofdm-system und ofdm-vorrichtung
EP1037441A3 (de) * 1999-03-18 2004-01-28 Kabushiki Kaisha Toshiba Digitale Verzögerung ausführender OFDM-Signalprozessor

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