Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/06—Receivers
  • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
  • H04B1/12—Neutralising, balancing, or compensation arrangements
  • H04B1/123—Neutralising, balancing, or compensation arrangements using adaptive balancing or compensation means
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/24—Testing correct operation
  • H04L1/241—Testing correct operation using pseudo-errors
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/24—Testing correct operation
  • H04L1/242—Testing correct operation by comparing a transmitted test signal with a locally generated replica

Definitions

• the invention relates to a method for transmitting digital signals, in particular in the AM bands, a high-level modulation, preferably 32 APSK or 64 APSK, being used for data blocks to be transmitted.
• This interference suppression system has the disadvantage that a complex and thus expensive adaptive filter must be used. In addition, it is necessary that the interference signal alone can be measured continuously. This system is not applicable for broadcasting.
• the object of the present invention is therefore to specify a method for transmitting digital signals in which interference signal suppression is possible with simple means.
• test sequence a sequence of binary data, referred to as a test sequence, which are modulated in a low-level manner, for example by means of 2PSK modulation.
• the test sequence is preferably selected as a pseudo-random sequence which is sufficiently long and free of direct components.
• An interval of the test sequence is preferably selected and averaged to determine an interference signal. Because the actual binary data are canceled during averaging, only the interference signal remains, which is then subtracted from the received data signal.
• the transmitted signal sequence has so-called gaps in which the transmitter does not transmit anything. These gaps are repeated periodically and are used by the receiver to measure interference signals.
• FIG. 1a shows a functional block diagram of a transmitter
• Figure 1b is a functional block diagram of a receiver
• FIG. 2 shows several diagrams to explain the method.
• the receiver takes the information, for example, about the bandwidth used, from a specific section of the transmitted data, for example from a test sequence.
• a data stream is transmitted which has different, alternating sequences, as shown in FIG. 2.
• data block within which the digitized useful signal is transmitted.
• the binary data of the useful signal are subjected to high-level modulation, for example 64 APSK modulation.
• the data block is preceded by the test sequence, which has likewise already been mentioned and whose binary data contain different information which is necessary for the recovery of the useful signal on the receiver side are.
• the data of the test sequence are modulated in low levels, for example by means of the 2PSK method.
• test sequence and data block is repeated periodically, the test sequence preferably being sent 25 times per second.
• the data block is replaced by a sequence called a "gap".
• the transmitter does not send any information within this period of time, so that the receiver only receives a possible interference signal.
• the test sequence itself has several functions in the receiver. For example, it contains information as to whether there is an analog or a digital transmission. In the case of digital transmission, the receiver takes the channel bandwidth with the associated settings. In addition to the exact amplitude of the signal, the exact carrier frequency and its exact phase as well as the exact timing of the clock can be determined from the test sequence. This information is necessary for demodulation. This saves a previously used phase-locked loop. In addition, the impulse response of the transmission channel and the transmission function of the channel can be determined, which makes it possible to set an adaptive equalizer to equalize the received data. This achieves the "single frequency network" capability of digital transmission in the single carrier process, because the receiver does not distinguish between an echo and the signal from another transmitter.
• An interference signal that comes from an AM transmitter that works in the same channel is intended as an interference signal.
• the frequency of this interference carrier is almost in the middle of the channel bandwidth, since radio transmitters usually transmit with a very high frequency accuracy.
• the interference carrier according to amount and phase is now determined as follows:
• a pseudo-random sequence is generated in the (digital) transmitter and processed and transmitted using a low-level modulation method, here the 2PSK.
• a pseudo-random sequence is a sequence of binary data that is not repeated and results in an average of zero, that is, it is free of direct components. Such a sequence is shown schematically in FIG. 2 with the values 1, -1, which result in zero on average, so that the sequence is free of direct components.
• the date -1 is described as a left-hand pointer and the date +1 as a right-hand pointer on the X axis. In the present case, the so-called decision threshold coincides with the Y axis.
• This signal which only ideally arrives at the receiver, is superimposed on the interference carrier signal, which is entered in the 2PSK diagram as an arrow shown in broken lines and marked with an S.
• the signals marked with R for data -1 and 1 are thus received at the receiver.
• the received signals R are now averaged over a sufficiently long period in the receiver. Since, as mentioned, the binary data 1, -1 cancel each other out, the interference carrier S is obtained after averaging. When the data block is received, this interference carrier is then subtracted from the received data, so that the result is that of the interference carrier released useful signal is present.
• the interference carrier itself changes very little with regard to frequency and phase, it is possible in the present case to use the measured interference carrier signal with data received later in time.
• a difference angle can be calculated from two successive measurements of the interference carrier signal S. This difference angle is then divided by the number of cycles between the two measurements, so that the result is the change in angle per cycle.
• an interference carrier signal can be calculated for each date in the data block. According to the sampling theorem, this method leads to a difference frequency that corresponds to half the value resulting from the sequence frequency of the test sequences. At 25 test sequences per second, this results in a differential frequency to be corrected of ⁇ 12.5 Hz. Because of the low frequency fluctuations of the carrier signals from radio transmitters, this method can be used without any problems for such interference. If the difference frequencies exceed this value, as is the case, for example, with interference from monitors or power supplies, the interference suppression is carried out as follows:
• interference lines can be up to ⁇ 4.5 kHz away from the carrier. These limits correspond to those of the aforementioned bandwidth of the digital signal. If such an interference line influences the transmitted signals of a data block, it can be assumed that the interference line can also be measured in the transmission gap. To determine the interference line, interference signal measurements are therefore carried out in the periodic gaps and the period of the interference line is determined using a correlation. Then the determined sample of the interference line can be continued periodically. The correlation must be carried out separately for the I and Q components so that phase shifts are recorded. In order to determine the exact position and size of the interference line with respect to an associated data block, a new correlation is then carried out within each test sequence. The associated value of the disturbance determined by interpolation can then be subtracted from the respective data of the transmitted data block. This also frees the useful signal from disturbances that, for example, generate screens or power supplies.
• FIG. 1 shows a functional block diagram for the described method for clarification, the transmitter being shown in FIG. 1a and the receiver being shown in FIG. 1b.
• the transmitter will be S. the binary data of the useful signal digitized, for example, by an analog / digital converter, where it is converted into the corresponding modulated form by a 64 APSK modulator.
• the test sequence is generated by a 2PSK modulator which, in addition to the receiver-relevant information, modulates a binary data sequence generated by a pseudo-random generator. This data sequence is selected to be sufficiently long and, moreover, is free of direct components, so that averaging these binary data results in a predetermined value, preferably zero.
• the two modulators transmit their signals to a multiplexer which generates the sequence of the sequences shown in FIG. 2, a gap being generated between the data block sequence and the test sequence.
• this data stream which is subjected to a disturbance during the transmission, is then fed to a demultiplexer, which separates the individual sequences from one another and feeds the data or test sequence to a corresponding demodulator.
• An evaluation device derives from the test sequence the exact carrier frequency and its phase as well as the exact clock and the phase position of the clock, which is necessary for the recovery of the transmitted digital data. In order to be able to carry out this evaluation, the evaluation device is supplied with an identical pseudo-random data sequence as at the transmitter.
• the evaluation device also takes over the averaging of a certain section of the test sequence to determine the interference signal. This interference signal is then fed to a subtraction device, which subtracts it from the disturbed data signal.
• the interference signal received by the receiver during the gap is detected by a measuring device.
• the measurement signal is then fed to a correlation device which determines the interference signal from the measurement signals from previous measurements and feeds it to the subtraction device.
• the useful signal freed from interference is then available at the output of the subtraction device.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
• Monitoring And Testing Of Transmission In General (AREA)
• Noise Elimination (AREA)
• Time-Division Multiplex Systems (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)
• Optical Communication System (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (1)

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Citations (4)

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• 1996
  • 1996-11-08 DE DE19646164A patent/DE19646164A1/de not_active Withdrawn
• 1997
  • 1997-11-03 WO PCT/EP1997/006042 patent/WO1998021849A1/de not_active Ceased
  • 1997-11-03 CN CNB971995222A patent/CN1146182C/zh not_active Expired - Fee Related
  • 1997-11-03 DE DE59712149T patent/DE59712149D1/de not_active Expired - Lifetime
  • 1997-11-03 CA CA002269055A patent/CA2269055C/en not_active Expired - Fee Related
  • 1997-11-03 AT AT97948858T patent/ATE286332T1/de active
  • 1997-11-03 JP JP52210698A patent/JP3892911B2/ja not_active Expired - Fee Related
  • 1997-11-03 US US09/297,859 patent/US6501804B1/en not_active Expired - Fee Related
  • 1997-11-03 EP EP97948858A patent/EP0944973B1/de not_active Expired - Lifetime

Patent Citations (4)

Non-Patent Citations (1)

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