Classifications

• • 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 method for monitoring the stability of the carrier frequency of several transmitters in a single-frequency network.
• a method for monitoring the phase synchronism of the individual transmitters of a single-wave network is presented in DE 199 37 457 AI. Any phase asynchrony that occurs between two transmitters is recorded via a transit time difference measurement by determining the channel impulse responses of the two transmitters. If there is a large difference between the measured transit time difference of the two transmitters and a reference transit time difference for the synchronous operation of the two transmitters, the two transmitters emit asynchronously. This deviation in the transit time difference is determined by a receiving station in the transmission area of the single-frequency network by evaluating the channel impulse responses and transmitted to the two phase-asynchronous transmitters for subsequent synchronization.
• a method for monitoring identical carrier frequencies for two transmitters in one Commonwave network cannot be found in DE 199 37 457 AI.
• a control center transmits a frequency reference symbol to the individual transmitters of the single-frequency network in addition to the transmission data. This frequency reference symbol is evaluated by each transmitter in the single-wave network and used to synchronize the carrier frequency with the frequency reference.
• a disadvantage of this method is the fact that the evaluation of the synchronicity of the carrier frequency of. each transmitter is carried out individually. This transmitter-specific evaluation of the frequency synchronism of the carrier frequency can consequently involve a certain transmitter-specific measurement and evaluation error, which can lead to inconsistent monitoring of the carrier frequency of all transmitters involved in the single-frequency network.
• the monitoring of the carrier frequency at each individual transmitter requires synchronization of the individual transmitters by means of a time reference, which is received by the individual transmitter, for example via GPS.
• the frequency synchronization takes place in the circuit arrangement of DE 43 41 211 Cl before the modulation, so that a subsequent frequency shift of the carrier frequency by subsequent functional units of the transmitter is not excluded. All these weak points can lead to undesired reception of different carrier frequencies of the individual transmitters in a receiver positioned at any location in the transmission area of the single-frequency network.
• the invention is therefore based on the object of specifying a method and a device for monitoring the carrier frequency stability of transmitters in a single-frequency network in which the synchronism of the carrier frequencies of the individual transmitters is uniformly ensured a single measuring arrangement, which can be positioned anywhere in the transmission area of the single-frequency network, is monitored without synchronization of the measuring arrangement by means of a time reference.
• the object of the invention is achieved by a method for monitoring the carrier frequency stability of transmitters in a single-frequency network with the features of claim 1 and a device with the features of claim 12 or 13.
• Advantageous embodiments of the inventions are specified in the dependent claims.
• the monitoring of the carrier frequency stability of the transmitters belonging to a single-frequency network is carried out via a single receiving device, which is positioned at any location in the transmission area of the single-frequency network.
• the receiving device From the transmission function of the transmission channel, the receiving device preferably determines the course of the sum impulse response of all transmitters at two different times by means of the inverse complex Fourier transformation.
• the impulse responses belonging to the respective transmitter are masked out from the two sum impulse responses after their phase relationship has been set in relation to the phase position of the two impulse responses of a reference transmitter of the single-frequency network.
• phase profiles of the two impulse responses belonging to the respective transmitter are then determined, from which in turn the phase shift difference of the impulse response of the respective transmitter to the phase position of the impulse response of the reference transmitter between two observation times is derived for each transmitter.
• the carrier frequency shift of each transmitter relative to the carrier frequency of a reference transmitter of the single-frequency network can be calculated from the course of the phase shift difference.
• the sum impulse responses of all transmitters from the transmission function of the transmission channel are carried out repeatedly using the inverse complex Fourier transformation at several different times and, based on this, the carrier frequency shift of each transmitter to the carrier frequency of a reference transmitter of the single-frequency network is repeatedly calculated and fed to a subsequent averaging.
• phase shift difference of a transmitter falls between two times to a value less than - ⁇ or if the phase shift difference of a transmitter between two times increases to a value greater than + ⁇ , the value of the phase shift difference of the respective transmitter between two times in this time period becomes + 2 * ⁇ increased or reduced by 2 * ⁇ . In this way, the phase shift difference is limited to values between - ⁇ and + ⁇ .
• the impulse response of each transmitter of the single-frequency network is obtained by determining the coefficients of the transmission function of the transmission channel from the coefficients of the equalizer in the receiving device, which is matched to the transmission channel, and then calculating the inverse Fourier transform.
• the impulse response for each transmitter can alternatively be derived from the inverse Fourier transform of the transmission function of the transmission channel by evaluating the OFDM-modulated transmission signals belonging to the scattered pilot carriers.
• Fig. 1 is a functional representation of an inventive device for monitoring the Carrier frequency stability of transmitters in one. Single wave network
• FIG. 3 shows an example of a graphical representation for a change in the course of the transfer function of the transfer channel
• 4A is a flowchart to explain the first embodiment of the method according to the invention for monitoring the carrier frequency stability of transmitters in a single-frequency network;
• 4B is a flow chart to explain the second embodiment of the method according to the invention for monitoring the carrier frequency stability of transmitters in a single-frequency network;
• 5A shows an exemplary representation of the results of the first embodiment of the invention.
• 5B shows an exemplary representation of the results of the second embodiment of the method according to the invention for monitoring the carrier frequency — stability of transmitters in a single-wave network
• 6A shows an exemplary three-dimensional graphic representation of the amplitude and carrier frequency deviation
• FIG. 6B shows an exemplary two-dimensional graphical representation of the amplitude and carrier frequency deviation.
• the method according to the invention for monitoring the carrier frequency stability of transmitters in a single-frequency network is described in its two embodiments below with reference to FIGS. 1 to 5.
• the transmitters S 0 , ..., S ⁇ Positioned in a single-wave network. , , 1, S n , for example according to FIG. 1, the transmitters S 1 , S 2 , S 3 , S 4 and S 5 , each radiate an identical phase and frequency-synchronous signal s (t) in the context of digital radio and TV broadcasting. out.
• a receiving device E which is positioned in the transmission area of the single-wave network, receives a reception signal e (t) as a superimposition of all reception signals e x (t) belonging to the individual transmitters S 0 , ..., S 17 ..., S n .
• transmitter S 0 is defined, for example, as the reference transmitter of the single-frequency network.
• the attenuation and phase distortions as well as the transit times that the transmit signals s (t) of the individual transmitters S 0 , ..., S 1 # ..., S n experience in the transmission channel to the receiving device E are in relation to the attenuation and Phase distortion and set at runtime of the reference transmitter S 0 .
• the signal e 0 (t) of the reference transmitter S 0 in equation (1) received in the receiving device E therefore corresponds to its transmission signal s (t).
• the transit time differences ⁇ . of the individual transmitters S ⁇ "to S" are based on the following effects:
• An additional phase shift A ⁇ between a transmitter S i and the reference transmitter S 0 can occur in the phase normalization of the received signal e (t) if, according to equation (4), there is a difference in the carrier frequency ⁇ . of the respective transmitter S L to the carrier frequency ⁇ 0 of the reference transmitter S 0 occurs:
• equation (1) for the time course of the received signal e (t) is converted to equation (5).
• e ( t ) s ( t ) + 2 v . * e / ⁇ , ( ' ) * J ( f _' r « (5)
• Equation (5) for the time profile of the received signal e (t) merges into equation (7) for the time range of the time slot ⁇ t B.
• ne (t) s (t) + ⁇ v, * e j ⁇ , * s (t- ⁇ ,) (7)
• ⁇ l
• the frequency spectrum E ( ⁇ ) of the received signal e (t) in equation (9) results from the Fourier transform of the received signal h SFW (t) according to equation (8) multiplied by the transfer function S ( ⁇ ) of the transmission channel of the single-frequency network :
• the bracketed term of the frequency spectrum E ( ⁇ ) of the E pfangs- signal e (t) in equation (9) corresponds to the transfer function H SFN ( ⁇ ) of the transmission channel of the single-frequency network. It consists of a sum of hands, the phase of which coincides with the ter change and have a constant phase shift ⁇ ⁇ ⁇ ⁇ t for a specific time t.
• for a single-wave network with a reference transmitter S 0 and a second transmitter S x is shown above the frequency f in FIG. 3.
• has a periodic curve with a period of l / ⁇ x .
• is determined by the carrier frequency shift ⁇ x of the transmitter S x to the carrier frequency ü) 0 of the reference transmitter S 0 .
• the course of the impulse response h SFNi (t) of the transmitter S i also changes Carrier frequency ⁇ £ has shifted to the carrier frequency ⁇ o of the reference transmitter S 0 .
• the phase angle shift ⁇ ⁇ t) of the impulse response h SFNi (t) belonging to the transmitter Si from the time t B1 of the time slot ⁇ t B1 to the time t B2 of the time slot ⁇ t B2 is consequently proportional to the course of the carrier frequency shift ⁇ according to equation (11). (t) of the transmitter S at the carrier frequency ⁇ 0 of the reference transmitter S 0 .
• the first embodiment of the method according to the invention for monitoring the carrier frequency stability of transmitters in a single-frequency network consequently results from the following method steps, as shown in FIG. 4A:
• step S1 the transfer function H SFN (f) of the transfer channel from the individual transmitters S 0 , ..., S. ; ..., S n of the single-wave network to the receiving device E is determined.
• the course of the transfer function H SPH (f) can be determined from the coefficients of the equalizer integrated in the receiving device E, which correspond to the coefficients of the transfer function H SPN (f) when the equalizer is adapted to the transmission channel.
• step S20 the curves of the associated complex sum impulse responses h SFN1 (t) and h SFN2 (t) at the two times t B1 of the time slot ⁇ t B1 and t B2 become from the transfer function H SFN (f) of the transmission channel by means of discrete inverse Fourier transformation of the time slot ⁇ t B2 is calculated.
• H SFN (f) the transfer function of the transmission channel by means of discrete inverse Fourier transformation of the time slot ⁇ t B2 is calculated.
• step S30 the two time-discrete courses of the complex sum impulse responses h SFN1 (t) and h SPN2 (t) are used to convert the complex impulse responses h SFNli (t) and to the transmitters Si involved in the single-frequency network filtered out at times t B1 and t B2 .
• the transmission function H SFN (f) of the transmission channel can be determined from the DVB-T symbols of the scattered carrier pilots.
• time-discrete courses of the impulse responses h SFNli (t) and h SFN2i (t) of the respective transmitter S. at times t B1 and t B2 are respectively complex sequences of numbers. From these complex courses of the impulse responses h SPNli (t) and h SFN2i (t), the associated time-discrete phase courses arg (h SFN1 . (T)) and arg (h SPN2 . (T)) of the respective transmitter S £ become in step S40 the times t B1 and t B2 determined. Alternatively, the impulse response cannot be assigned to the transmitters at this point in time, and for the time being only total impulse responses h SFN1 (t) and h SFN2 (t) can be calculated.
• phase shift difference ⁇ £ (t B2 -t E1 ) of the phase shift of the transmitter S j ⁇ to the reference transmitter S 0 between the times t B1 and t B2 can under certain circumstances take on values smaller than - ⁇ , which lie outside the permissible value range. Therefore, in step S60 in time periods in which the phase shift difference ⁇ ⁇ t ⁇ -t ⁇ ) the phase shift of the transmitter S L to Reference transmitter S 0 between the times t BX and t B2 assumes values smaller than - ⁇ , the phase shift difference ⁇ . (t B2 -t B1 ) of the phase shift according to equation (14) increased by the value 2 * ⁇ .
• phase shift difference ⁇ (t B2 -t B1 ) of the phase shift of the transmitter S £ to the reference transmitter S 0 between times t B1 and t B2 values greater than + ⁇ , which lie outside the permissible value range
• the phase shift difference ⁇ A (t B2 -t B1 ) the phase shift in method step S65 is reduced according to equation (15) by the value 2 * ⁇ .
• phase shift difference ⁇ i (t B2 -t B1 ) of the phase shift of the transmitter S carried out in the method steps S60 and S65 to the reference transmitter S 0 between the times t B1 and t B2 according to equations (13) and (14) ensure one unique phase value in the range from - ⁇ to + ⁇ .
• step S70 the course of the carrier frequency shift ⁇ is calculated according to equation (16). of the transmitter S £ to the carrier frequency ⁇ 0 of the reference transmitter S 0 between the times t B1 and t B2 resulting from equations (12) and (13) from the phase shift difference ⁇ i (t B2 -t B1 ) of the phase shift of the transmitter S. to the reference transmitter S 0 is calculated between times t B1 and t B2 .
• phase shift ⁇ Phasen £ (t) of the received signal e. (t) of the transmitter S due to a carrier frequency shift ⁇ otl of the transmitter S L to the reference transmitter S 0 can superimpose additional phase changes, for example due to phase noise, as shown in FIG. 5A, is a corresponding adjustment of the phase shift difference ⁇ . (t E2 -t B1 ) of the phase shift of the transmitter S to the reference transmitter S 0 between two observation times t E1 and t B2 of such phase disturbances.
• This cleanup takes place in the second embodiment of the method according to the invention for monitoring the carrier frequency stability of transmitters in a single-frequency network according to FIG. 4B.
• the phase shift difference ⁇ d in method step S50 In contrast to the first embodiment in FIG. 4A, in the second embodiment in FIG. 4B, the phase shift difference ⁇ d in method step S50. ( ⁇ t B ) of the phase shift of the transmitter S £ to the reference transmitter S 0 within a time interval ⁇ t B not only determined between the observation times t B1 and t B2 , but also at several other observation times t B and t B (d + 1) ⁇ die are separated from one another by a time interval ⁇ t B in accordance with equation (17).
• the time-discrete course of the complex sum impulse response h SPN .. (t) and h SFN (; i + 1) (t) is determined in each of the observation times t .. and t j + 1 in method step S20.
• step S30 the time-discrete courses of the complex sum impulse responses h SPN .. (t) and il sFn + D (t) become the time-discrete courses of the complex impulse responses h SFN; ii (t) and h SFN (; i + 1) i (t) of the respective transmitter S. at times t d and t. +1 hidden.
• phase profiles are arg (h SFN .. (t)) and. From the time-discrete courses of the complex impulse responses il SPNji (t) and h SPN (: i + (t) arg (h SFN ( . +1) i (t)) of transmitter S, determined at times t d and t d + 1 .
• phase shift difference ⁇ (t B (d + 1) -t Bd ) of the phase shift of the respective transmitter S, to the reference transmitter S 0 between the times t B (d + 1) and t Bd _ that of the difference in the phase shift ⁇ , (t B (d + 1) ) at time t B (d + 1) and the phase shift ⁇ . (t Bd ) at the time t Bd of the transmitter S. corresponds to the reference transmitter S 0 .
• the phase shift difference ⁇ , (t B (d + 1) -t B. ) The phase shift of the respective transmitter S, becomes the reference transmitter S 0 between the times t B ( . +1) and t B the carrier frequency shift ⁇ id of the transmitter S. based on the phase shift difference ⁇ . (t B (d + 1) -t Bd ) of the phase shift at the observation times t d and t. +1 calculated.
• the carrier frequency shift ⁇ id of the transmitter S. to the reference transmitter S 0 on the basis of the phase shift difference ⁇ . (t B (d + 1) -t B.) of the phase shift to the observation times t d and t d + 1 is at different observation times t d and t d + 1 j max total times repeatedly determined and calculated.
• the total j max calculated carrier frequency shifts ⁇ id of the transmitter S to the reference transmitter S 0 are then averaged in method step S80 in order to determine the influence of the above-mentioned phase interference, for example due to phase noise Carrier frequency shift ⁇ to eliminate or minimize.
• the averaging can also take the form of a pipeline structure in which the oldest value is rejected.
• a memory-saving variant is a recursive averaging.
• FIG. 5B An exemplary course of a carrier frequency shift .DELTA..omega., Of a transmitter S, which has been cleaned of phase interference to a reference transmitter S 0 is shown in FIG. 5B.
• FIG. 1 A device for monitoring the carrier frequency stability of several transmitters in a single-frequency network is shown in FIG. 1.
• the transmission signals from the transmitters S to S 5 are received by a receiving device E.
• the receiving device E is connected to an electronic data processing unit 1.
• the transmission function H SFN (f) of the transmission channel from the transmitters S to S 5 to the receiving device E is determined on the basis of the transmission signals of the transmitters S j ⁇ to S 5 received by the receiving device E.
• the coefficients of the equalizer integrated in the receiving device E are used, which correspond to the coefficients of the transfer function of the transmission channel in the case of an equalizer adjusted to the transmission channel.
• the transmission function H SFN (f) of the transmission channel from the transmitters S, to S 5 to the receiving device E can be determined from the scattered pilot carriers of a DVB-T signal in digital terrestrial TV broadcasting, bypassing the unit 11.
• the time-discrete courses of the complex sum impulse responses h SFNd (t) and h SFN (d + 1) (t) at the observation times t are converted from the transfer function H SFN (f) of the transfer channel Bd and t E (d + 1) calculated.
• the time-discrete profiles of the complex sum impulse responses h SPNj (t) and h SFN (d + 1) (t) are used to discrete time as the complex impulse responses and faded out for each transmitter S, the single-frequency network at times t Bd and t B (d + 1) .
• the discrete-time profiles of the complex impulse responses h SFNdi (t) and h SPH (d + 1) i (t) become the time-discrete phase profiles arg (h SFNd , (t)) and arg (h SPM ( . +1) , (t)) of the impulse responses h SFN ., (t) and h SFN ( . +1) , (t) at times t Bd and t B (d + 1) .
• arg (h SFN ., (T)) and arg (h SPN ( . +1) , ( t)) of the impulse responses h SFN ., (t) and t- sFNij + ui (t) at times t d and t j + 1 the phase shift difference ⁇ , (t B (d + 1) -t B ;.) of the phase shifts of a transmitter S, to a reference transmitter S 0 at the observation times t Bd and t B (d + 1) , which is the difference in the phase shift ⁇ , (t Bd ) and ⁇ , (t B (d + 1) ) of the transmitter S corresponds to the reference transmitter S 0 at the times t Bd and t B (d + 1) , and based on this the carrier frequency shift ⁇ ,. for each transmitter S, to a reference transmitter S
• the carrier frequency shifts ⁇ , of each transmitter S become a reference transmitter S 0 of the single-frequency network either in tabular form or represented graphically.
• the time t in the abscissa and the amplitude deviation ⁇ A, of the respective transmitter S, for the amplitude A 0 of the reference transmitter S 0 are plotted on the ordinate, while the carrier frequency deviation ⁇ , of the respective transmitter S, for Carrier frequency ⁇ o of the reference transmitter S 0 is characterized by a symbol corresponding to the carrier frequency deviation ⁇ of the point belonging to the respective transmitter S.
• the invention is not restricted to the exemplary embodiments shown and described. In particular, all of the described features can be combined with one another as desired.
• the method described is also suitable not only for signals of the DAB or DVB-T standard, but also for all standards which enable SFN, in particular also for signals of the American ATSC standard.

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