ES2569457A2 - Transmitter for transmitting a digital transmission signal in a partial reception area of a reception area of a signal frequency network (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Transmitter for transmitting a digital transmission signal in a partial reception area of a reception area of a signal frequency network. The digital transmission signal contains a broadcast program and is broadcasted as an ofdm modulated signal. The digital transmission signal contains successive ofdm frames, in which each frame contains a null symbol and a program symbol. The transmitter is configured to generate an empty symbol in a way that is equivalent or identical to the execution of the following steps: To. Generate a frequency spectrum for a program symbol that matches the broadcast program of the adjacent transmitter, B. Delete some carriers in the frequency spectrum of the program symbol, and C. Include the program symbol with a frequency spectrum suppressed of this type as an empty symbol in the ofdm frame. (Machine-translation by Google Translate, not legally binding)

Description

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DESCRIPTION

Transmitter for transmitting a digital transmission signal in a partial reception area of a reception area of a signal frequency network.

Background of the invention

The invention relates to a transmitter according to the preamble of claim 1. A transmitter of this type is known from EP-B 749649.

Single frequency networks (RFUs), as stipulated in ETSI EN 300 401, are particularly suitable for supplying the same broadcasting programs to a large area. For this purpose, the individual data streams (for example individual radio programs) compiled in a central multiplexer are supplied to one or more transmitters distributed in the supply area and are broadcast synchronously on the same transmission frequency (network of transmission). unique frequency).

At present, such single frequency networks operate widely according to ETSI standards EN 300 401 (T-DAB) and EN 300 744 (DVB-T) in the broadcasting sector.

Although OFDM single frequency networks are particularly suitable for the extensive supply (for example throughout the country) of a number N of broadcasting programs in a common multiplex, the supply of each of these N programs throughout the supply area It is mainly the same. Using DAB or DAB + for example, between 6 and 18 broadcast programs can usually be incorporated into a multiplex. (The terms DAB and DAB + are considered synonymous with T-DAB below in this report since in this case the differences with respect to frequency planning can be ignored.)

However, if an area is going to be provided substantially less programs using DAB, in the multiplex some program locations will necessarily remain empty. This results in an inefficient use of the higher frequencies and costs for the new broadcasting programs transmitted in this multiplex because the costs to configure and operate the transmitter network are the same regardless of whether only one program or 18 programs are broadcast in this single frequency network.

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It is often not desirable at all, even for reasons of media policy or competition reasons, that the competitor necessarily reaches the same supply area and therefore the same broadcasting subscribers in the same multiplex (and therefore in the same network of unique frequency). Often, local broadcasting is based on the fact that no additional competitors are present, or there are only a limited number of additional competitors, in their supply area.

In summary: the existing VHF local radio structure in many German federal states with small, politically fixed supply areas is extremely difficult to map with previous single frequency networks. Similar conditions are also present in other European countries, such as Austria and Switzerland.

EP-B 749649 mentioned above proposes a solution that allows the broadcasting of a local broadcasting program in a single frequency network thanks to the fact that OFDM symbols are not broadcast (carrier powers are nil). To prevent an OFDM symbol of this type from being mistakenly recognized by a receiver as a null symbol, individual carriers distributed on this OFDM symbol (or so-called empty symbol) are broadcast, and therefore the summed power then corresponds to the total power .

Brief Description of the Invention

The aim of the invention is to propose an improved transmitter. The transmitter according to the preamble of claim 1 is characterized by the characterizing part of claim 1. Advantageous embodiments of the transmitter according to the invention are defined in the dependent claims.

The invention is based on the following knowledge. Research on the single frequency network known from EP-B 749649 has shown that interference still occurs when local broadcast programs are received that are broadcast by an adjacent transmitter in an adjacent partial broadcast area. This interference occurs because in the transmitter known in a symbol that should actually be ignored, arbitrary fictitious signals (carriers without modulation) are emitted that necessarily result in interference in the single frequency network.

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According to the invention, for example every second or third carrier of OFDM is issued with the correct modulation while the remaining carriers of OFDM are missing. This guarantees a maximum power reduction of 3 dB or 4.8 dB that prevents this symbol from being detected as a null symbol and also produces no interference at all in the neighboring area because the correct information is actually issued. This can result in a slight improvement in reception because the single frequency gain actually occurs in every second or third carrier of OFDM. It is also possible that these remaining OFDM carriers are emitted with double or triple power. So, although this time the transmission occurs with the full summed power, the information to decode the signal in the dedicated reception area of the transmitter is missing, due to the missing carriers, which is precisely what is intended. Therefore, an empty symbol according to the invention is a symbol that may have been derived by the process of carrying out steps (a), (b) and (c) as claimed. This is the claimed way to derive the ford symbol ‘in a manner equal to stages (a), (b) and (c)’. However, there may be other ways to generate the empty symbol, other ways that may not be exactly the same as the way in which steps (a), (b) and (c) are carried out. Those other ways, which generate the same empty symbol as when steps (a), (b) and (c) are carried out, are defined (and claimed) as (other) ways 'equivalent to' the way of carrying perform steps (a), (b) and (c).

Preferably, the transmitter is adapted to derive an empty symbol in a manner that is equivalent to or equal to the following steps:

to. derive a frequency spectrum for a program symbol corresponding to the broadcasting program of the neighboring transmitter (figure 4a),

b. delete some of the carriers in the frequency spectrum of the program symbol, and

C. include the program symbols with the frequency spectrum suppressed in this way as an empty symbol in an OFDM frame (figure 5).

Preferably, the transmitter is adapted to derive the empty symbols in a manner that is equivalent to or equal to steps (a), (b) and (c), in which, in step (a), the transmitter is adapted to deriving a frequency spectrum for a program symbol corresponding to the broadcasting program protected against errors of the neighboring transmitter, and in step (b), at least so many carriers are suppressed that despite a correction of errors it is not possible to decoding of the broadcast program protected against local errors of the neighboring transmitter in the area of

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partial reception of the transmitter.

Preferably, the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in step (b), at least half of the number of carriers.

Preferably, the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in step (b), each second carrier is suppressed.

Preferably, the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in step (b) each time successive carriers of m are suppressed successive carriers, in which n and m are integers for which it applies: n> 1 and m = 2 * n.

Preferably, the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in step (b), each time m carriers are suppressed successive carriers, in which n and m are integers for which it applies: m> 2 and n = m-1.

Preferably, the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which additionally in a stage (d) the amplitudes of the remaining carriers are amplified in the frequency spectrum of the empty symbol.

Preferably, the transmitter is provided with an empty symbol generation circuit to directly derive the empty symbols.

Preferably, the transmitter is provided with a suppression circuit for suppressing carriers in an OFDM symbol.

Preferably, broadcasting programs are DAB broadcasting programs.

Preferably, the amplitudes of the bearers of the program symbols of a broadcasting program that is transmitted in the reception area of the transmitter have been reduced.

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Brief description of the drawings

The invention is explained in more detail below in the present specification with the help of some exemplary embodiments of the transmitter according to the invention in the following description of the figures. In the drawings:

Figure 1 shows an exemplary embodiment of a single frequency network equipped with some transmitters that broadcast both broadcasting programs in the entire broadcasting area of the single frequency network and local broadcasting programs only in partial areas of the broadcasting area of the single frequency network,

Figure 2 schematically shows the content of an OFDM frame in a transmission signal in a single frequency network,

Figure 3 schematically shows the content of OFDM frames in the broadcast signals broadcast by the transmitters in the broadcasting area of the single frequency network,

Figure 4 schematically shows the frequency spectrum of an OFDM searched symbol and some exemplary embodiments of the frequency spectrum of an empty OFDM symbol,

Figure 5 schematically shows an exemplary embodiment of a transmitter according to the invention, and

Figure 6 schematically shows a second exemplary embodiment of the transmitter according to the invention.

Detailed description of the figures

Figure 1 shows an exemplary embodiment of a broadcasting network equipped with five transmitters T1 to T5. These five transmitters together form a single frequency network (RFU) and broadcast, in the broadcasting area 100 of the

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single frequency network, broadcasting programs to be received throughout the broadcasting area 100. In addition, the transmitters T1, T2 and T3 broadcast local programs and will be received only in a partial area of the broadcasting area 100 of the frequency network only, specifically in the partial areas 102, 104 and 108 of the transmitters T1, T2 and T3 respectively which are indicated by shading from top to right to bottom left in Figure 1. In addition, local programs are broadcast by means of transmitters T2 and T3 and will be received only in another partial area of the broadcasting area 100 of the single frequency network, specifically in the partial areas 104 and 108 indicated by shading from top to left to bottom right in the figure 1. In addition, local programs are broadcast via transmitters T2 to T5 and will be received only in yet another partial area of the broadcasting area 100 of the single frequency network, concr In the partial areas 104, 106, 108, 110, which are indicated by vertical shading in Figure 1. The circular rings around a transmitter in Figure 1 schematically show the broadcasting areas (supply areas) of the individual transmitters. However, it will be mentioned in this case that broadcasting areas can actually be much more complicated depending on the geographical area.

Figure 2 schematically shows the content of OFDM frames in the broadcast signals broadcast by transmitters T1 to T5 in the broadcasting area 100 of the single frequency RFU network.

An OFDM frame is composed of a sequence of OFDM symbols. In DAB, the first symbol is a null symbol. An OFDM frame also contains some symbols that are indicated as the phase reference symbol and FIC symbol (fast information channel). These are followed by the program symbols (MSC symbols or main service channel).

The program symbols are indicated in Figure 2 by A to R. This series of program symbols A to R is repeated three more times in the OFDM frame. In this illustration, a maximum of 18 different broadcasting programs A to R can be broadcast. However, in general, this number of 18 will not be considered as an absolute upper limit.

Program symbols containing the information of a broadcasting program are transmitted by means of 1536 OFDM carriers (equal to 48 CU in Figure 2) in

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this example, as will be explained in more detail below in the present specification. It will be mentioned in this phase that if broadcasting programs must be broadcast to a higher quality then more CUs are required per program that must then be transmitted in different OFDM symbols. Obviously, then, less broadcasting programs can be correspondingly broadcast in the multiplex.

Figure 3 schematically shows the content of the OFDM frames of the broadcast signals broadcast by transmitters T1 to T5 in the broadcasting area of the single frequency network. Figure 3a shows the content of an OFDM frame of the transmission signal that is broadcast by the transmitter T1. Only symbols A to R are indicated in the frame. As can be seen in Figure 3a, transmitter T1 issues programs A to H, P and R. Symbols I to O and Q are empty symbols that will be explained in more detail below in the present specification. As can be seen in figure 3b, transmitter T2 broadcasts all programs A to R. This is also the case for transmitter T3, as can be seen in figure 3c. As can be seen from figure 3d, the transmitter T4 broadcasts programs A to E, M, N, P and Q. The symbols F to L, O and R are empty symbols. This is also the case for the T5 transmitter, as can be seen in Figure 3e.

Therefore, it is evident from Figure 3 that programs A to E and P can be broadcast, and received, throughout the broadcasting area 100, specifically because the program symbols A, B, C, D, E and P that are generate and broadcast through the different transmitters T1 to T5 are identical. Programs F to H and R are broadcast only in partial areas 102, 104 and 108 and can only be received in these partial areas, specifically because program symbols F, G, H and R are identical for transmitters T1, T2 and T3 and, instead of these program symbols, the T4 and T5 transmitters broadcast empty symbols. Programs I to L and O are broadcast only in partial areas 104 and 108 and can only be received in these partial areas, specifically because program symbols I, J, K, L and O are identical for transmitters T2 and T3 and Instead of these program symbols, the transmitters T1, T4 and T5 broadcast empty symbols. Programs M, N and Q are broadcast only in partial areas 104, 106, 108 and 110 and can only be received in these partial areas, specifically because the program symbols M, N and Q are identical for transmitters T2 to T5 and , instead of these program symbols, the transmitter T1 broadcasts empty symbols.

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OFDM program symbols, also called OFDM symbols, because they contain information related to a broadcasting program, are transmitted through 1536 OFDM carriers (in the case of DAB I mode for the VHF range). 2 bits (= 1 dibit) are transmitted per OFDM carrier (quadrature phase shift modulation (QPSK)) during a searched symbol. Therefore, for 1536 OFDM carriers, 1536 carriers * 2 bits / carrier = 3072 bits of the broadcasting program are transmitted. This is shown schematically using the frequency spectrum of a symbol of OFDM sought, as shown in Figure 4a, in which carrier frequencies cf1 to cf1536 are shown as a function of frequency.

The empty symbols, also called OFDM empty symbols, as they are present instead of programs I to O and Q in the transmission signal of transmitter T1 (see Figure 3a) and instead of programs F to L, O and R in the transmission signals of the transmitters T4 and T5 (see Figure 3d and Figure 3e), are formed as follows.

Figure 4b shows a first exemplary embodiment of a frequency spectrum of an empty OFDM symbol. It is similar to the frequency spectrum in Figure 4a but every second carrier cf2, cf4, ..., cf1534 and cf1536 is omitted or suppressed.

Figure 4c shows a second exemplary embodiment of a frequency spectrum of an empty OFDM symbol. It is also similar to the frequency spectrum in Figure 4a but in this case every second group of two successive carriers cf3, cf4 is omitted or deleted; cf7, cf8; ... and cf1535, cf1536.

Figure 4d shows a third exemplary embodiment of a frequency spectrum of an empty OFDM symbol. It is similar to the frequency spectrum in Figure 4a in which in this case two carriers are always omitted or deleted cf2, cf3; cf5, cf6; ... and cf1535, cf1536 of successive groups of three successive carriers.

The general teaching of the invention is that at least half of the carriers are suppressed.

In particular, this means the following for the empty OFDM symbols in the OFDM frames of the transmission signal of the T1 transmitter.

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To generate the empty I symbol (see Figure 3a), the transmitter T1 requires the broadcasting program I and derives the empty symbols of this broadcasting program I as follows. The transmitter T1, like the adjacent transmitters T2 and T3, derives the program / symbols sought I as can be seen in Figure 3b and Figure 3c and its frequency spectrum appears as shown in Figure 4a. Then, some carriers are suppressed in the frequency spectrum of the program / symbols sought in a manner shown for example by Figures 4b to 4d. The empty symbols I having a suppressed frequency spectrum of this type are received and broadcast as an empty symbol I in the OFDM frame of Figure 3a. Thanks to the fact that the empty symbols I do not contain all the carriers required to receive the broadcasting program I, the broadcasting program I cannot be received in the receiving area 102 of the transmitter T1. Thanks to the fact that the carriers (carrier signals) derived from the broadcasting program I are present in the empty symbols I of the transmitter T1, these empty symbols I of the transmitter T1 do not interfere with the reception of the broadcasting program in the reception areas 104 and 108 of the transmitters T2 and T3 respectively. In addition, this empty symbol I cannot be detected as a false null symbol by the receivers in the dedicated reception area 102 of the transmitter T1.

It will be mentioned in this case that instead of deriving the empty symbols I, as indicated above, specifically by first deriving the program symbols I in the transmitter T1 and then deleting the carriers in the program symbols, it is also possible to derive directly empty symbols with fewer carriers of the broadcasting program. It is also worth mentioning that the remaining carriers in the empty symbols I can also be broadcast with increased power to ensure that these empty symbols are not erroneously detected as null symbols by the receiver.

It is clear that the empty symbols I are derived by means of the transmitters T4 and T5 in a manner identical to that described above for the transmitter T1.

The empty symbols J, K, L and O are derived on the transmitters T1, T4 and T5 in the same manner described above for the empty symbols I. For that reason, an additional explanation will be superfluous.

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Obviously, one of the empty symbols F, G, H or R is derived in transmitters T4 and T5 in an equivalent manner. This is explained in more detail merely for a situation. In this case, the T4 transmitter will be used as an example. To generate, for example, the empty G symbol (see Figure 3d), the transmitter T4 requires the broadcasting program G and derives the empty symbols of this broadcasting program G in the following manner. The transmitter T4, like the adjacent transmitters T1, T2 and T3, derives the program / symbols sought G as can be seen in Figures 3a, 3b and Figure 3c and its frequency spectrum appears as shown in Figure 4a. Then, some carriers are suppressed in the frequency spectrum of the program / symbols sought in a manner shown for example by Figures 4b to 4d. The empty symbols G presenting a suppressed frequency spectrum of this type are received and broadcast as the empty symbol G in the OFDM frames of Figure 3d. Thanks to the fact that the empty symbols G do not contain all the carriers required to receive the broadcasting program G, the broadcasting program G cannot be received in the receiving area 110 of the transmitter T4. Thanks to the fact that the carriers (carrier signals) derived from the broadcasting program G are present in the empty symbols G of the transmitter T4, these empty symbols G of the transmitter T4 do not interfere with the reception of the broadcasting program in the reception areas 102 , 104 and 108 of the transmitters T1, T2 and T3 respectively. In addition, this empty symbol G cannot be erroneously detected as a null symbol by the receivers in the reception area 110 of the transmitter T4.

A description of how empty symbols are derived is superfluous because they are always derived in a manner equivalent to that described above.

Additionally, it should be noted that in the event that broadcast signals are encoded using differential coding before broadcasting, an additional stage should be performed, specifically on transmitter T1 for broadcasting program O and on transmitters T4 and T5 for the program of broadcasting L. It occurs specifically that when the broadcasting program is not fully present on the O channel (ie the OFDM symbol O in the OFDM frames of Figure 3a) of the broadcasting signal broadcast by the transmitter T1 (is In other words, not all 1536 carriers are present in the OFDM symbol O), a receiver in the broadcasting area 102 of the transmitter T1 cannot correctly receive the broadcasting program P. Due to the differential coding, the receiver specifically also requires all OFDM carriers of the program

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broadcasting O to receive the broadcasting program P. Therefore, this means that the transmitter T1 must in fact completely broadcast the broadcasting program O. However, as the OFDM symbol N in the OFDM frame of the transmitter T1 is a symbol However, a receiver in the broadcasting area 102 of the transmitter T1, however, cannot correctly decode the broadcasting program O which was also planned (because the broadcasting program O is a local broadcasting program that should only be received in the areas of broadcasting 104 and 108 of transmitters T2 and T3 respectively).

The same procedure as described above should also be performed for broadcast programs L on the broadcast signals broadcast by transmitters T4 and T5. This means that the broadcasting program L (ie the OFDM symbol L in the frames of figures 3d and 3d) of the broadcasting signals broadcast by the transmitters T4 and T5 must be fully present in order for a receiver to correctly decode the program M. However, the broadcasting program L will not be received in the broadcasting areas 110 and 106 of the transmitters T4 and T5 respectively because the OFDM K symbols are empty symbols.

There will still be a problem for the Q broadcast program for the T1 transmitter and the O broadcast program for the T4 and T5 transmitters. In this case, for differentially encoded broadcast signals, it would not be possible to suppress program Q in broadcast area 102 of transmitter T1 and program O in broadcast areas 110 and 106 of transmitters T4 and T5. However, in order to achieve this, it is necessary to restructure the broadcasting programs to form the OFDM symbols. A solution for the exemplary embodiment in Figure 3 could be to change the sequence of the last four broadcast programs (OFDM symbols) in an OFDM frame (currently O-P-Q-R) to Q-P-R-O.

Figure 5 schematically shows an exemplary embodiment of a transmitter according to the invention. The transmitter could for example be the transmitter T1 of Figure 1 that produces OFDM frames as shown in Figure 3a. Next, the manner in which the transmitter T1 generates the OFDM symbols for the broadcasting program C and the empty symbols for the broadcasting program J. The transmitter is provided with inputs 500 and 502 for the supply of the transmitters will be described.

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C and J broadcasting programs that offer the SC and Sj program sources respectively. It is evident that the transmitter T1 has more inputs for the supply of all the broadcasting programs that are going to be broadcast and for the generation of all the empty symbols for the programs that are not going to broadcast in the broadcasting area of the transmitter T1. However, the generation of the OFDM symbols in the transmitter T1 will be described only using the broadcasting programs C and J.

The transmitter in Figure 5 is equipped with OFDM symbol generating circuits for each of the broadcasting programs to be broadcast, such as the generating circuit 506 for the broadcasting program C in Figure 5. The transmitter is also equipped OFDM symbol generating circuits for each of the broadcasting programs that are not going to broadcast in the broadcasting area 102 of the transmitter T1, such as the generating circuit 508 for the broadcasting program J in Figure 5. In addition, a suppressor circuit, such as suppressor circuit 510 for the broadcasting program J, is connected downstream of the OFDM symbol generating circuits for broadcasting programs that are not going to broadcast. The suppressor circuit suppresses carriers in OFDM symbols for broadcasting programs that are not going to broadcast, as described above.

The empty OFDM symbols obtained in this way and the OFDM program symbols are combined in a combiner circuit 512 to obtain the OFDM frames, as indicated in Figure 3a for the transmitter T1, and are provided at an output 514 .

The exemplary embodiment of the transmitter in Figure 6 shows similarities with the transmitter in Figure 5 with the difference that in this exemplary embodiment the empty symbols are derived directly, without first of all the program symbols are derived for program J. For this purpose, the transmitter in figure 6 is provided with an empty symbol generating circuit 618 that directly derives these empty symbols and supplies them to the combiner circuit 612.

It will be mentioned in this case that the invention is not limited to the exemplary embodiments described above in the description of the figures. The invention alone

It is limited by the claims. It is evident to the person skilled in the art that different modifications of the described transmitters are possible without deviating from the invention. In this regard, it will be indicated that, for example, not only can the power in the empty symbols be increased but the power of 5 particular program symbols can also be decreased. Transmitter energy can be saved when the power reduction for an empty symbol is not too important. In any case, the power reduction does not have to be large enough to cause the recipients to change this symbol to the null symbol.

10 In addition, in some circumstances, a transmitter will broadcast only a single local broadcasting program in its dedicated broadcasting area. In this case, therefore, an OFDM frame contains only one OFDM symbol (or a plurality of OFDM symbols) for this broadcast program and contains only empty symbols instead of the remaining broadcast programs when no other programs are to be received. of 15 broadcasting in this broadcasting area.

Claims (11)

5 10 fifteen twenty 25 30 35 1. Transmitter for transmitting a digital transmission signal in a partial reception area of a reception area of a signal frequency network (RFU), the digital transmission signal comprising at least one broadcasting program and being transmitted as a signal OFDM (orthogonal frequency division multiplexing), the digital transmission signal comprising successive OFDM frames in time, each frame comprising at least one program symbol, each program symbol being assigned to at least one program of broadcasting, and comprising at least one empty symbol, said empty symbol being structured in such a way as to avoid, in the partial reception area of the transmitter, the reception of a broadcasting program that is transmitted by a neighboring transmitter in an area of neighboring partial reception, characterized in that the transmitter is adapted to derive an empty symbol in a manner that is equivalent to or equal to the following stages: to. derive a frequency spectrum for a program symbol corresponding to the broadcasting program of the neighboring transmitter (figure 4a), b. delete some of the carriers in the frequency spectrum of the program symbol, and C. include the program symbols with the frequency spectrum suppressed in this way as an empty symbol in an OFDM frame (figure 5). 2. Transmitter according to claim 1, the broadcasting program being a broadcasting program protected against errors that is transmitted by the neighboring transmitter in the neighboring partial reception area, characterized in that the transmitter is adapted to derive the empty symbols from a such that it is equivalent to or equal to steps (a), (b) and (c), in which, in step (a), the transmitter is adapted to derive a frequency spectrum for a program symbol corresponding to the program of broadcasting protected against errors of the neighboring transmitter, and in step (b), at least so many carriers are suppressed that despite a correction of errors it is not possible to decode the broadcasting program protected against local errors of the neighboring transmitter in the area of partial reception of the transmitter. 5 10 fifteen twenty 25 30 35 3. Transmitter according to claim 1 or 2, characterized in that the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in step ( b), at least half of the number of carriers is suppressed. 4. Transmitter according to claim 1, or 3, characterized in that the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in the step (b), each second carrier is deleted. 5. Transmitter according to claim 1 or 2, characterized in that the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which in step ( b) every time n successive carriers of successive carriers are deleted, in which n and m are integers for which it applies: n> 1 and m = 2 * n. 6. Transmitter according to claim 1 or 2, characterized in that the transmitter is adapted to derive the empty symbol in an equivalent or equal way to stages (a), (b) and (c), in which in step ( b), each time n bearers of successive carriers are suppressed, in which n and m are integers for which it applies: m> 2 and n = m-1. 7. Transmitter according to one of claims 1 to 6, characterized in that the transmitter is adapted to derive the empty symbol in an equivalent or equal way to steps (a), (b) and (c), in which additionally in A step (d) amplifies the amplitudes of the remaining carriers in the frequency spectrum of the ford symbol. 8. Transmitter according to one of the preceding claims, characterized in that the transmitter is provided with a circuit for generating empty symbols to directly derive empty symbols. 9. Transmitter according to one of claims 1 to 7, characterized in that the transmitter is provided with a suppression circuit for suppressing carriers in an OFDM symbol. 10. Transmitter according to one of claims 1 to 9, characterized in that the Broadcasting programs are DAB broadcasting programs. 11. Transmitter according to one of claims 1 to 10, characterized in that the amplitudes of the bearers of the program symbols of a broadcasting program 5 transmitted in the reception area of the transmitter have been reduced.