Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04H—BROADCAST COMMUNICATION
  • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
  • H04H20/12—Arrangements for observation, testing or troubleshooting
• • 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 present invention relates to a method and a receiver for identifying transmitters which transmit digital terrestrial radio-television signals receivable in a given geographic point of a single-frequency DVB-T broadcasting network.
• DVB-T Digital Video Broadcasting - Terrestrial
• ETS300744 Digital Video Broadcasting; Framing structure, channel coding and modulation for digital terrestrial television (DVB-T)", ETSI, 1997.
• Said system is based on OFDM (Orthogonal Frequency Division Multiplex) multi-carrier modulation.
• the number of carriers in the OFDM symbol can be 2048 or 8192; these two modes are commonly referred to as 2k mode and 8k mode.
• single frequency networks also known as SFN, wherein all network transmitters transmit on a single frequency signals that must be perfectly equal and synchronous, so that every receiver will pick up a series of echoes of the same signal (at worst with different power levels and different propagation delays).
• the frame structure of the OFDM signal consists of a sequence of OFDM symbols within which the modulated data carriers, in accordance with the chosen scheme (QPSK, 16QAM or 64QAM), and a few service carriers are located.
• Service carriers can be divided into two categories:
• pilot carriers they are transmitted at a higher power level (+2.5 dB) and are used in reception for estimating the channel response. They can be further subdivided into:
• Continual pilot carriers (Continual Pilots): they take fixed positions, i.e. they are repeated at the same frequencies in each symbol;
• TPS Transmission Parameters Signalling
• TPS carriers are used for carrying the parameters relating to the transmission systems, i.e. for channel coding and modulation. 17 and 68 TPS carriers are transmitted in 2k mode and in 8k mode, respectively.
• TPS carriers In a given OFDM symbol, all TPS carriers transmit the same bit, with differential coding.
• the position of the TPS carriers within the symbol is static and has been chosen according to a pseudo-random rule, so as to avoid frequency periodicity. Consequently, the exact position of the TPS carriers is specified in a table defined in the ETS 300744 specification.
• TPS carriers contain service information, including:
• TPS carriers are transmitted on 68 consecutive OFDM symbols, thus defining the so-called "OFDM frame".
• the reference sequence corresponding to the TPS carrier of the first symbol of each OFDM frame is used for initializing the differential modulation.
• Each OFDM symbol transmits one TPS bit.
• the group of 68 TPS bits contained in one OFDM frame is defined as follows: - 1 initialization bit;
• DVB-H Digital Video Brodcasting - Handheld
• ETSI ETS300744 Digital Video Broadcasting; Framing structure, channel coding and modulation for digital terrestrial television (DVB-T)", ETSI, 2009.
• Bits S40- S47 transport the information relating to the cell identifier (Cell-Id) used for identifying which cell the signal is received from.
• the most significant byte of the cell identifier is transmitted in the odd frames of the superframe, whereas the least significant byte of the cell identifier is transmitted in the even frames.
• bit mapping is shown in Figure 3. If the cell identifier is not enabled, the eight bits must be set to zero.
• the cell identifier (which in said standard identifies a group of transmitters of the telephone signal) is mandatory, in the case of the DVB-T standard the cell identifier is an optional parameter. At any rate, even though not expressly specified in the DVB-T specification, it is understood that all transmitters in an SFN network have the same cell identifier value.
• the measuring instruments used for this purpose can only identify the most robust signal received and can only provide delay and intensity indications about the other contributions.
• the OFDM receiver incorporates an echo equalization block based on the estimation of the channel frequency response, obtained through the pilot carriers.
• the inverse Fourier transform of the channel frequency response is the impulse response: this property is exploited in some measuring instruments in order to provide indications about the received echoes (delay with respect to the direct signal and level).
• It is an object of the present invention is therefore to provide a method and a receiver for identifying transmitters of digital terrestrial radio-television signals, which are adapted to identify all the transmitters of digital terrestrial radio-television signals receivable in a given geographic point of a single-frequency DVB-T broadcasting network.
• the method of the present invention provides for entering a univocal identifier for each transmitter into the TPS carriers of each digital terrestrial radio-television signal.
• said identifier Since it is entered into the TPS carriers, said identifier does not affect the proper demodulation by the receiver of the audio/video/data streams contained in the signal. Thanks to the presence of different signals transmitted by different transmitters, it is possible to go back to the single frequency responses of the transmission channels on the routes defined between each transmitter and the receiver.
• FIG. 1 shows a time/frequency map of a frame of an OFDM signal
• FIG. 3 shows a mapping of the TPS carriers which is useful for coding a transmitter's identifier
• FIG. 4 shows a geographic area comprising a plurality of transmitters of digital terrestrial radio-television signals belonging to a single frequency network
• FIG. 5 shows an example of the result obtained from a receiver implementing the method according to the present invention.
• a geographic area 1 in particular the Italian region Piedmont, which comprises a plurality of transmitters 5-8 of digital terrestrial radio- television signals belonging to a single frequency network.
• each transmitter 5-8 In a geographic point 3 of the geographic area 1 , it is desirable to know the intensity of each digital terrestrial radio-television signal receivable from each transmitter 5-8.
• the transmitters 5-8 are called “Mottarone”, “Trivero”, “Eremo” and “Penice”.
• the transmitters 5-8 that cover the geographic area 1 are so configured as to transmit each an identifier of its own, which is coded into the TPS service carriers (see Fig. 2) of a plurality of OFDM symbols of a frame of the respective digital terrestrial radio-television signal being transmitted.
• the identification code may advantageously be transmitted in the symbols S40-S47.
• the OFDM signal thus generated is perfectly coherent in the symbols wherein the bits of the TPS service carriers are identical, e.g. the symbols S0-S39 and S48-S53, whereas in the symbols S40-S47, wherein different bits are transmitted which relate to the identification codes of different transmitters, the OFDM signal is not perfectly coherent. More precisely, the OFDM signal is coherent in the cells that transport data (video, audio, etc.), thus ensuring perfect reception, but it is not coherent in the TPS cells, in which collisions may occur.
• a receiver 13 located in the geographic point 3 receives digital terrestrial radio-television signals from the transmitters 5-8.
• the signals transmitted by the transmitters 5-8 are signals x(t) in the time domain, just like the signal y(t) received by a receiver 13, which is ideally shown inside a transport means used for measurement campaigns.
• the signals x(t) and y(t) can be represented in the frequency domain, by applying the Fourier transform, respectively as ⁇ ( ⁇ ) and Y(co).
• the transmission channel on which the signals x(t) travel from the transmitters 5-8 to the receiver 13 is affected by multipath propagation, it may be characterized by the impulse response h(t) or by the Fourier transform H(co) of the latter, also referred to as channel frequency response.
• OFDM modulation uses a sampled data processing, with a fast Fourier transform FFT in the demodulator and the inverse thereof IFFT in the modulator, the above-mentioned variables are expressed by using a first index k for the frequency position and a second index n for the position of the symbol within the frame.
• the signals Y(40,k) ... Y(47,k), received by the receiver 13 on the TPS cells of first index k during the symbols S40-S47 of the frame of the OFDM signal are due to superimposition of all the signals of the plurality of transmitters of the single frequency network which arrive at the reception area of the geographic point 3. Each contribution turns out to be multiplied by its own channel frequency response.
• Y(40,k) Xi(40,k) ⁇ Hi(40,k) + X 2 (40,k) ⁇ H 2 (40,k) + X 3 (40,k) ⁇ H 3 (40,k) + ... + X 8 (40,k)
• Y(41 ,k) Xi(41,k) ⁇ H 1 (41,k) + X 2 (41,k) ⁇ H 2 (41,k) + X 3 (41 ,k) ⁇ H 3 (41,k) + ... + X 8 (41,k) • 3 ⁇ 4(41,k)
• Y(47,k) X ! (47,k) ⁇ Hi(47,k) + X 2 (47,k) ⁇ H 2 (47,k) + X 3 (47,k) ⁇ H 3 (47,k) + ... + X 8 (47,k)
• - Y is a vector of N elements, wherein one element Y j of the vector Y represents a digital terrestrial radio-television signal acquired through the receiver 13 and relating to the j-th symbol S40-S47 of the plurality of N symbols S40-S47 of the frame of the OFDM signal;
• - X is a matrix having NxN size, wherein one element X j j of the matrix X represents a signal contribution that the receiver 13 would receive if the i-th transmitter were the only one to transmit on an ideal transmission channel the digital terrestrial radio-television signal relating to the j-th symbol;
• - H is a vector of N elements, wherein the element Hi of the vector H represents the channel frequency response relating to the i-th transmitter.
• the linear system Y ⁇ admits of a univocal solution, provided that the determinant of the matrix X is different from zero.
• the frequency responses of each one of the N transmission channels of each transmitter 5-8 are obtained; the module of each frequency response represents the level information, relating to the strongest signal, at which the corresponding transmitter 5-8 is being received.
• the result therefore, is a list of the individual levels of the received signal (with values normalized to 1), each individual level being associated with its own transmitter 5-8 by means of the respective identifier.
• the linear system as shown above is of eight equations in eight unknowns. Therefore, by solving said system one can identify, through the respective identifier, up to eight transmitters received in a geographic point 3.
• the method can be extended by having other received signals participate in the equation system, e.g. the symbols S48-S67, and/or the symbols of the frames that carry the other eight bits of the sixteen bits that make up the identification code of each transmitter 5-8.
• the transmitter identifier consists of a 16-bit binary word, and therefore admits of 65,535 values plus the value zero, it is possible to proceed by trial and error, at each attempt building the matrix X by using the method as described above, but each time assuming a set of N new and different identification code values, different from those of the previous case.
• the method according to the present invention can be applied even by using only one carrier, and therefore only one value of the first index k. If, however, one wants to increase the already high robustness to noise of the method of the present invention, it is possible to repeat the process for more than one value of the first index k and, preferably after equalization, to calculate a mean of the results thus obtained.
• the method according to the present invention includes the following steps: -
• each column consists of the signal [Xj(40,k), ... Xj(47,k)] T that the receiver 13 would receive if only the i-th transmitter were transmitting on an ideal channel;
• each element of the vector H represents the channel response of each transmitter 5-8, in the same order as the columns of the matrix X;
• said values are the levels, relative to that of the most intense signal, i.e. normalized to 1, of the various transmitters 5-8 in the order specified above;
• the receiver 13 comprises at least one antenna adapted to receive a digital terrestrial radio-television signal, a demodulator DVB-T, a processor and memory means.
• the identifier of the transmitter of the strongest signal in this case the signal of the transmitter 7 "Eremo”
• the identifiers of the weaker signals indicating for each of them, for example, the power of the signal, relative to that of the strongest signal, and the delay.
• a first advantage of the present invention is that all the transmitters of digital terrestrial radio-television signals receivable in a given geographic point of a single frequency network are identified.
• a second advantage is that the application of the method according to the present invention does not affect the robustness of the signal being transmitted.
• the present invention is not limited to a method and a receiver for identifying transmitters of digital terrestrial radio-television signals, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Circuits Of Receivers In General (AREA)
• Television Systems (AREA)

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Citations (3)

• 2011
  • 2011-06-20 IT IT000538A patent/ITTO20110538A1/it unknown
• 2012
  • 2012-06-18 WO PCT/IB2012/053058 patent/WO2012176108A1/en not_active Ceased
  • 2012-06-18 EP EP12745530.1A patent/EP2721750B1/en active Active
  • 2012-06-18 ES ES12745530.1T patent/ES2615807T3/es active Active

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