Title of Invention	METHOD AND APPARATUS FOR TRANSMISSION OF COMMAND COMBINATIONS BY MEANS OF CODED FREQUENCY-SHIFT KEYING
Abstract	Abstract A method (10) is used for transmission of commands or command combinations via a communication link by means of coded frequncy-shift keying, with a command or command combination in each case being associated with one frequncy pair. In this case, when a command changes from a preceding command or command combination to a subsequent command or command combination, one frequency (which will be the first to be transmitted) in the frequency pair of the subsequent command or command combination is chosen as a function of at least one other associated frequency pair (20) . (Figure 2)

Title of Invention

METHOD AND APPARATUS FOR TRANSMISSION OF COMMAND COMBINATIONS BY MEANS OF CODED FREQUENCY-SHIFT KEYING

Abstract

Abstract A method (10) is used for transmission of commands or command combinations via a communication link by means of coded frequncy-shift keying, with a command or command combination in each case being associated with one frequncy pair. In this case, when a command changes from a preceding command or command combination to a subsequent command or command combination, one frequency (which will be the first to be transmitted) in the frequency pair of the subsequent command or command combination is chosen as a function of at least one other associated frequency pair (20) . (Figure 2)

Full Text	Method and apparatus for transmission of command combinations by means of coded frequency-shift keying Technical Field of the Invention The present invention relates to a method and an apparatus for transmission of command combinations by means of coded frequency-shift keying. In particular, the present invention relates to a method for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying. Prior Art For protection signal transmission by means of coded frequency-shift keying, two frequencies, for example fi, f2 are allocated to each command to be transmitted or to each command combination to be transmitted. The two frequencies are then transmitted for a specific time period T: ..,f1,f2,f1,f2,f1,f2,f1,f2,f1 ..., A first problem occurs, for example, when a command change is intended to be carried out from a command A which is associated with the frequencies fi, f2 to a command combination A+B which is associated with the frequencies f3, f4. This can be done as follows: ...,f1,f2,f1,f2,f3,f4,f3,f4,... If the frequencies f2 and f3 were now to be allocated to a command C, the command sequence would accordingly be A, C, A+B and not, as desired, A, A+B. This leads to errors, for example in the form of spurious initiations. There are various variants or options for a command change for the command changes as described above. A first variant or option for a command change is referred to as a single frequency change. In the case of a single frequency change, a first frequency f1,BKi or a second frequency f2,BKi in the preceding command combination BKi in^ the preceding command combination BKi matches a first frequency f1,BK2 or a second frequency f2,BK2 in the subsequent command combination BK2. By way of example, the following frequency chain which represents a sequence of commands exhibits a single frequency change such as this from a preceding command combination BKi with a frequency pair (flf f2) to a subsequent command combination BK2 with a frequency pair (f2,f3): ...f1,f2,f1,f2,f3,f2,f3,f2 •••• A single frequency change is applied analogously for a command B. A second option is referred to as a double frequency change. In the case of a double frequency change, both the first frequency fi,BKi and the second frequency f2,BKi change to the subsequent command combination BK2 when a command change takes place from the preceding command combination BKi. This double frequency change can be carried out only via an intermediate step. By way of example, the following frequency chain, which represents a sequence of commands, exhibits a double frequency change such as this from a preceding command combination BKi with a frequency pair (fx, f2) to a subsequent command combination BK2 with a frequency pair (f3,f4) via an intermediate step (f2,f3): ...f 1,f2,f1,f2,f3,f4,f3,f4,f3,f4,.. - A double frequency change is applied analogously for a command B. The change process described above could also be carried out via the frequency pairs (fi,f3) ; (fi,f4) ; (f2/f4). This means that four intermediate steps are possible on the basis of the combination for a double frequency change. In order to maintain the correct command sequence, it would be possible not to allocate any command combinations to specific frequency pairs. In this specific example, this means that no command or command combination is allocated to the frequency pairs (fi,f3); (fi,f4); (f2/f4). However, this is disadvantageous if there are a large number of commands, since the frequency range must then be very wide in order to cover the large number of different combinations. Another solution from the prior art is to insert a pause between the individual command combinations. However, this is disadvantageous because the total time for transmission of command combinations in consequence rises considerably, and rapid transmission of command combinations is no longer guaranteed. Description of the Invention Against the background of this prior art, the invention is based on the object of specifying a method and an apparatus which allow reliable and unambiguous transmission of commands or command combinations, and which overcomes the problems from the prior art. This object is achieved by a method and an apparatus for transmission of commands having the features of patent claims 1 and 7 respectively. Advantageous refinements of the invention are specified in the dependent claims. A method is accordingly used for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying. A command or command combination is in each case associated with one frequency pair. In this case, when a command change takes place from a preceding command or command combination to a subsequent command or command combination, one frequency (which will be the first to be transmitted) in the frequency pair of the subsequent command or command combination is chosen as a function of at least one other associated frequency pair. The choice of the first frequency to be transmitted results in the advantage that undesirable command combinations no longer occur or are even transmitted. Furthermore, the width of the frequency band can be chosen to be narrower since this narrow frequency band is used more efficiently. The said first frequency to be transmitted is chosen in particular as a function of the frequency pair of the preceding command or command combination. This is advantageous because this leads to the number of possible combinations being limited, since the choice is thus restricted to the first frequency to be transmitted. By way of example, a command or command combination is an independent protection command to be transmitted. This independent protection command is preferably transmitted by means of an electrical power line. The frequencies of the command or of the command combination are preferably in a limited frequency band. The frequency band preferably has a width of 4 kHz. Furthermore, in the case of the method according to the invention, an insert frequency and/or a pause are/is inserted on changing from the preceding command or command combination to the subsequent command or command combination. The insertion of an insert frequency or of a pause makes it possible to increase the number of commands or command combinations to be transmitted, while the frequency band remains the same. In addition to a method for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, the present invention also relates to an apparatus for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, as well as a computer program product comprising computer program code means for controlling the apparatus, in particular a computer program product having a data storage medium which contains the computer program code means. Brief Description of the Drawing The invention will be described in more detail in the following text with reference to the drawing, in which: Figure 1 shows a schematic illustration of an apparatus for transmission of commands or command combinations using a method according to the present invention; and Figure 2 shows a flowchart with method steps based on a method according to the present invention. Description of one Exemplary Embodiment As illustrated schematically in figure 1, the apparatus 1 has a selection module 11, a command Table 12 and a communication module 13. The communication module 13 is designed to transmit commands and/or command combinations by means of coded frequency-shift keying (FSK) via a communication line 2 to a receiving apparatus 3. The communication module 13 preferably has a modem for communication via an electrical power line (PLC, Powerline Communications). The selection module 11 is preferably in the form of a programmed software module, which controls one or more processors for the apparatus 1, as will be described in the following text with reference to f1gure 2. The command Table 12 comprises commands and/or command combinations, each of which has an associated frequency pair. The command Table 12 is stored as a separate data table, or is integrated in the selection module 11. Furthermore, the command Table 12 may also comprise a command change table. A command B which is stored in the command Table 12 is associated with a frequency pair which has a f1rst frequency f1,B and a second frequency f2/B- The first frequency f1,B and the second frequency f2,B have different period lengths. A command combination BK which is stored in the command Table 12 has an associated frequency pair which has a f1rst frequency f1,BK and a second frequency f2/BK- The expression "an associated frequency pair" accordingly means a frequency pair which represents one command or one command combination. The expression "a command change" means a change from a preceding command Bi to a subsequent command B2 or from preceding command combinations BKi to subsequent command combinations BK2. The expression "a command change" is also used to mean a change from a preceding command Bi to a subsequent command combination BK2 or from a preceding command combination BK1 to a subsequent command B2. The commands B or command combinations BK to be transmitted may, for example, be subdivided into three categories. The subdivision into categories is used to def1ne different commands B or command combinations BK. Commands or command combinations in the f1rst category-are commands or command combinations for which the f1rst frequency f1,B2 or f1,BK2 of a command or of a command combination is predetermined in a f1xed manner for a specif1c command table, following a change in the command or the command combination. Commands or command combinations in the second category are commands or command combinations for which a dependent frequency of the frequency pair is predetermined for a specif1c command table after a change from a preceding command B1 or a preceding command combination BK1 to a subsequent command B2 or a subsequent command combination BK2 as a function of the preceding command B1 or the preceding command combination BK1. Commands or command combinations in the third category are commands for which the change from a preceding command combination to a subsequent command combination for a specif1c command table is made via an intermediate step. The intermediate step may be an insert frequency E or a pause P. If suff1cient individual frequencies are available, it is always possible to f1nd frequency associations so that all commands and command combinations fall in the f1rst category. If frequencies are short, that is to say when a large number of different command combinations or commands have to be transmitted in a narrow frequency band, it is necessary, however, to also allow commands and command combinations in the second category and in the third category. This is because use of these command combinations and/or commands allows optimized use of the available frequencies. As is illustrated in f1gure 2, the selection module 11 in a f1rst method step 10 allocates one frequency pair to a command to be transmitted or to a command combination to be transmitted, with the assistance of the command Table 12. A command Table 12 as described above may be conf1gured, for example, as shown in Table 1. In this case, four commands A, B, C, D and possible command combinations which are stored in the command table are shown. According to Table 1, the frequency pair (f1, f6) is allocated to the command D. According to Table 1, the frequency pair (f3, fe) is allocated to the command combination B+D. If now, for example, a preceding command A is transmitted and it is intended to transmit a subsequent command combination A+B, then this can be done by a single frequency change: ...f2,f5,f2,f5,f2,f4,f2,f4,... A -+ A+B •i. If, for example, a command A is then transmitted and it is intended to transmit a command combination A+B+D, this is done by a double frequency change via the command combination A+D: ...f2/f5,f2/f5,f6,f5, f6/.-. A -> A+D ...f5,f6,f5/f6,f4, f6,f4,- A+D -+ A+B+D Table 2 shows a further example of a command Table 12 with three independent commands A, B, C and a test command T. In this example, the commands T, A, B, C each have a common frequency f5. Eight different frequency combinations or frequency pairs are required to represent these three independent commands A, B, C and the test command T, as well as the command combinations A+C, A+B, B+C, A+B+C that result from the commands A, B, C. As can be seen from Table 2, f1ve single frequencies are suff1cient to form ten different frequency pairs. The frequency pairs in Table 2 have been allocated such that all commands and command combinations with the exception of the command A are included in the f1rst category. The frequency pairs (f 1, f 4 and f1, f3) have not been used in this case. In a second method step 20, the f1rst frequency to be transmitted is chosen with the assistance of the selection module 11. In this case, the selection module 11 chooses the frequency which is intended to be the f1rst to be transmitted for a command change from a preceding command Bi to a subsequent command B2. In this case, this f1rst frequency to be transmitted is chosen as a function of at least one other associated frequency pair. This frequency which is the f1rst to be transmitted can also be referred to as the frequency to be predetermined. The same applies to the transmission of command combinations BK: in the case of a command change from a preceding command combination BK1 to a subsequent command combination BK2, a frequency which is the f1rst to be transmitted in the frequency pair of the subsequent command combination BK2 is chosen as a function of at least one other associated frequency pair by the selection module 11. This also applies, of course, to a command change from a preceding command to a subsequent command combination or from a preceding command combination to a subsequent command. The selection module 11 preferably chooses the said f1rst frequency to be transmitted as a function of the frequency pair of the directly preceding command or command combination. In this case, the preceding command is the command which is transmitted immediately before the subsequent command. In the case of a command sequence Bi,B2 or Bi,BK2 or BKi,BK2 or BKi,B2, this therefore means that a f1rst frequency f1,B2 or f1,BK2 of the subsequent command B2 or command combination BK2 is chosen as a function of the frequency pair of a preceding command Bi or command combination BKi. In,particular, the f1rst frequency f2/B2 of the subsequent command B2 or command.combination BK2 is dependent on the f1rst frequency fx, B1 or f1,BK1 and/or on the second frequency f2/B2 or f2,BK2 of the preceding command B1 or command combination BKi. The selection module 11 preferably chooses the f1rst frequency to be transmitted as a function of the directly preceding command or command combination. For example, the selection module 12 may be designed in such a manner that it can check a command change table contained in the command table. Table 3 is one example of a command change table such as this, which def1nes the choice of the f1rst frequency to be transmitted. Table 3 shows the changes in the commands or command combinations def1ned in Table 2 for which there are restrictions. For these changes, the said f1rst frequencies to be transmitted are identif1ed by the frequency indexes that are underscored and printed in bold text. Three examples of command changes are intended to describe in more detail the f1rst frequency to be transmitted in the frequency pair of the subsequent command or command combination: f1rst example (A -> A+B+C) : A change from the command A (f2, fs) to the command combination A+B+C (f1,f2) is carried out as follows: .»f2,f5,f2,f5,f2,f5,f2,fl,f2,fl,f2.» A -> A+B+C In this case, the frequency f2 is the f1rst frequency to be transmitted in the frequency pair f1,f2 of the subsequent command combination A+B+C. This is because, if the frequency f1 were to be the f1rst to be transmitted after the frequency f5, instead of the frequency f2, the command T would be transmitted: •»f2 f5 f2 f5 f2 f5 fl.. A -> T Second example (A —> T) : This problem also occurs, of course, in the case of the desired command chanqe from A (f2,f5) to T (f1,fs) and T (f1,f5) to A (f2,f5) : ...f2, fs, f2, f5, f2, f5, fl, f5, fl, f5... A -> T In this case, the frequency f5 is the f1rst frequency to be transmitted in the frequency pair f1,fs of the subsequent command T. This is because, if the frequency fa were to be transmitted instead of the frequency f5, the command A+B+C would incorrectly be transmitted: ...f2,f5,f2,f5,f2,f5,f2,fl,... A -> A+B+C Third example (T -> A+C) : The following frequencies are transmitted for a command change from T (f1,f5) to A+C (f2,f4): ...f1,f5,fl,f5,f4,f2,f4 f2... T -> A+C In this case, the f1rst frequency to be transmitted is the frequency f4. If other frequencies were to be transmitted during the change, then the following undesirable change could occur: ...f1, f5, f i, f 5, f i, £2/ f Ar f2— T -»• A+B+C As they are illustrated in the command change table, the f1rst frequencies to be transmitted can be determined in various ways. For example, they can be determined on a control basis. It has been found to be particularly advantageous for a common frequency to occur in all of the commands in the association of the frequency pairs with the commands. By way of example, this is the frequency f5 in Table 2, which occurs in all of the commands A, B, C, T. These frequencies determined in this way can then be stored in a command Table 12. A further rule, which is not implemented completely in Table 2 because of the combination A+B+C, for good frequency associations states that the two frequencies used for T should occur only in those frequency pairs which are associated with single commands. In the case of commands or command combinations in the f1rst category, the f1rst frequencies to be transmitted are determined statically. In this case, the f1rst frequencies to be transmitted are determined before the method is carried out, for example during its implementation, that is to say during the def1nition of the command table. These statically determined f1rst frequencies to be transmitted can be stored in the command change table. In the case of commands or command combinations in the second category, the f1rst frequencies to be transmitted must be determined dynamically as a function of the preceding command or command combination while the method is being carried out. Suitable algorithms or processing rules must be provided for this purpose. The corresponding algorithms or processing rules are then processed by one or more processors. In a third method step 30, the frequency pair which corresponds to the command or the command combination on the basis of the sequence def1ned in step 30 is transmitted by means of the communication module 13. A fourth method step 40 is applied when a further command is intended to be transmitted. In this case, the method starts again with method step 10. Four independent commands A, B, C, D plus a test command T require 16 frequency combinations. Command Table 4 illustrates one preferred frequency allocation with 8 individual frequencies, in which case all of the commands and command combinations in category 1 can be allocated: The frequencies to be predetermined, that is to say the f1rst frequencies to be transmitted, are summarized in Table 5 for all commands or command combinations for which there are restrictions for specif1c changes. Command Frequency to be predetermined _C f8 _D f8 A+C f2 B+D f3 C+D f8 A+C+D f5 B+C+D \JA Table 5 Command Frequency to be predetermined _C f8 _D f8 A+C f2 B+D f3 C+D f8 A+C+D f5 B+C+D \JA Table 5 The commands B or command combinations BK to be transmitted may be of very different types. In particular, however, the commands are independent protection commands for use in electrical power supply systems. In this case, the commands are transmitted via communication channels. If the commands or command combinations are used for protection of devices in the electrical power supply system, an electrical power line is used as a communication channel for transmission of the protection commands. The commands B or the command combinations BK are preferably in a limited frequency band. This allows particularly effective and eff1cient conf1guration of the appropriate apparatuses. The frequency band preferably has a width of 4 kHz. Patent Claims 1. A method for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, with a command or command combination in each case being associated with one frequency pair, characterized in that, when a command changes from a preceding command or command combination to a subsequent command or command combination, the frequency which will be the first to be transmitted in the frequency pair of the subsequent command or command combination is chosen as a function of at least one other associated frequency pair. 2. The method as claimed in claim 1, characterized in that said first frequency to be transmitted is chosen as a function of the frequency pair of the preceding command or command combination. 3. The method as claimed in one of claims 1 or 2, characterized in that the command or the command combination is a protection command to be transmitted, and in that this protection command is transmitted by means of an electrical power line. 4. The method as claimed in one of claims 1 to 3, characterized in that the frequencies of the command or of the command combination are in a limited frequency band. 5. The method as claimed in claim 4, characterized in that the limited frequency band has a width of 4 kHz. 6. The method as claimed in one of claims 1 to 5, characterized in that an insert frequency and/or a pause are/is inserted on changing from the preceding command or command combination to the subsequent command or command combination. 7. An apparatus for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, with a command or command combination in each case being associated with one frequency pair, characterized in that the apparatus is designed such that when a command changes from a preceding command or command combination to a subsequent command or command combination, the frequency which will be the first to be transmitted in the frequency pair of the subsequent command or command combination can be chosen as a function of at least one other associated frequency pair. 8. The apparatus as claimed in claim 7, characterized in that the apparatus is designed to choose the said first frequency to be transmitted as a function of the frequency pair of the preceding command or command combination. 9. A computer program product having computer program code means for controlling one or more processors of an apparatus for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, with a command or a command combination in each case being associated with one frequency pair, in such a manner that the apparatus chooses, when a command changes from a preceding command or command combination to a subsequent command or command combination, the frequency which will be the first to be transmitted in the frequency pair of the subsequent command or command combination as a function of at least one other associated frequency pair. 10. The computer program product as claimed in claim 9, characterized by further computer program code means for controlling the processors in such a manner that the apparatus chooses the said first frequency to be transmitted as a function of the frequency pair of the preceding command or command combination. Dated this 10 day of April 2007

Full Text

Method and apparatus for transmission of command combinations by means of coded frequency-shift keying
Technical Field of the Invention
The present invention relates to a method and an apparatus for transmission of command combinations by means of coded frequency-shift keying. In particular, the present invention relates to a method for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying.
Prior Art
For protection signal transmission by means of coded frequency-shift keying, two frequencies, for example fi, f2 are allocated to each command to be transmitted or to each command combination to be transmitted. The two frequencies are then transmitted for a specific time period T:

..,f1,f2,f1,f2,f1,f2,f1,f2,f1
..., A first problem occurs, for example, when a command change is intended to be carried out from a command A which is associated with the frequencies fi, f2 to a command combination A+B which is associated with the frequencies f3, f4. This can be done as follows:
...,f1,f2,f1,f2,f3,f4,f3,f4,...
If the frequencies f2 and f3 were now to be allocated to a command C, the command sequence would accordingly be A, C, A+B and not, as desired, A, A+B. This leads to errors, for example in the form of spurious initiations.
There are various variants or options for a command change for the command changes as described above.

A first variant or option for a command change is referred to as a single frequency change. In the case of a single frequency change, a first frequency f1,BKi or a second frequency f2,BKi in the preceding command combination BKi in^ the preceding command combination BKi matches a first frequency f1,BK2 or a second frequency f2,BK2 in the subsequent command combination BK2. By way of example, the following frequency chain which represents a sequence of commands exhibits a single frequency change such as this from a preceding command combination BKi with a frequency pair (flf f2) to a subsequent command combination BK2 with a frequency pair (f2,f3):

...f1,f2,f1,f2,f3,f2,f3,f2 ••••
A single frequency change is applied analogously for a command B.
A second option is referred to as a double frequency change. In the case of a double frequency change, both the first frequency fi,BKi and the second frequency f2,BKi change to the subsequent command combination BK2 when a command change takes place from the preceding command combination BKi. This double frequency change can be carried out only via an intermediate step. By way of example, the following frequency chain, which represents a sequence of commands, exhibits a double frequency change such as this from a preceding command combination BKi with a frequency pair (fx, f2) to a subsequent command combination BK2 with a frequency pair (f3,f4) via an intermediate step (f2,f3):
...f 1,f2,f1,f2,f3,f4,f3,f4,f3,f4,.. -
A double frequency change is applied analogously for a command B.

The change process described above could also be carried out via the frequency pairs (fi,f3) ; (fi,f4) ; (f2/f4). This means that four intermediate steps are possible on the basis of the combination for a double frequency change.
In order to maintain the correct command sequence, it would be possible not to allocate any command combinations to specific frequency pairs. In this specific example, this means that no command or command combination is allocated to the frequency pairs (fi,f3); (fi,f4); (f2/f4). However, this is disadvantageous if there are a large number of commands, since the frequency range must then be very wide in order to cover the large number of different combinations.
Another solution from the prior art is to insert a pause between the individual command combinations. However, this is disadvantageous because the total time for transmission of command combinations in consequence rises considerably, and rapid transmission of command combinations is no longer guaranteed.
Description of the Invention
Against the background of this prior art, the invention is based on the object of specifying a method and an apparatus which allow reliable and unambiguous transmission of commands or command combinations, and which overcomes the problems from the prior art.
This object is achieved by a method and an apparatus for transmission of commands having the features of patent claims 1 and 7 respectively. Advantageous refinements of the invention are specified in the dependent claims.
A method is accordingly used for transmission of

commands or command combinations via a communication link by means of coded frequency-shift keying. A command or command combination is in each case associated with one frequency pair. In this case, when a command change takes place from a preceding command or command combination to a subsequent command or command combination, one frequency (which will be the first to be transmitted) in the frequency pair of the subsequent command or command combination is chosen as a function of at least one other associated frequency pair.
The choice of the first frequency to be transmitted results in the advantage that undesirable command combinations no longer occur or are even transmitted. Furthermore, the width of the frequency band can be chosen to be narrower since this narrow frequency band is used more efficiently.
The said first frequency to be transmitted is chosen in particular as a function of the frequency pair of the preceding command or command combination.
This is advantageous because this leads to the number of possible combinations being limited, since the choice is thus restricted to the first frequency to be transmitted.
By way of example, a command or command combination is an independent protection command to be transmitted. This independent protection command is preferably transmitted by means of an electrical power line.
The frequencies of the command or of the command combination are preferably in a limited frequency band. The frequency band preferably has a width of 4 kHz.
Furthermore, in the case of the method according to the

invention, an insert frequency and/or a pause are/is inserted on changing from the preceding command or command combination to the subsequent command or command combination.
The insertion of an insert frequency or of a pause makes it possible to increase the number of commands or command combinations to be transmitted, while the frequency band remains the same.
In addition to a method for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, the present invention also relates to an apparatus for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, as well as a computer program product comprising computer program code means for controlling the apparatus, in particular a computer program product having a data storage medium which contains the computer program code means.
Brief Description of the Drawing
The invention will be described in more detail in the
following text with reference to the drawing, in which:
Figure 1 shows a schematic illustration of an
apparatus for transmission of commands or command combinations using a method according to the present invention; and
Figure 2 shows a flowchart with method steps based on
a method according to the present invention.
Description of one Exemplary Embodiment
As illustrated schematically in figure 1, the apparatus 1 has a selection module 11, a command Table 12 and a communication module 13. The communication module 13 is designed to transmit commands and/or command

combinations by means of coded frequency-shift keying (FSK) via a communication line 2 to a receiving apparatus 3.
The communication module 13 preferably has a modem for communication via an electrical power line (PLC, Powerline Communications).
The selection module 11 is preferably in the form of a programmed software module, which controls one or more processors for the apparatus 1, as will be described in the following text with reference to f1gure 2.
The command Table 12 comprises commands and/or command combinations, each of which has an associated frequency pair. The command Table 12 is stored as a separate data table, or is integrated in the selection module 11. Furthermore, the command Table 12 may also comprise a command change table.
A command B which is stored in the command Table 12 is associated with a frequency pair which has a f1rst frequency f1,B and a second frequency f2/B- The first frequency f1,B and the second frequency f2,B have different period lengths. A command combination BK which is stored in the command Table 12 has an associated frequency pair which has a f1rst frequency f1,BK and a second frequency f2/BK- The expression "an associated frequency pair" accordingly means a frequency pair which represents one command or one command combination.
The expression "a command change" means a change from a preceding command Bi to a subsequent command B2 or from preceding command combinations BKi to subsequent command combinations BK2. The expression "a command change" is also used to mean a change from a preceding command Bi to a subsequent command combination BK2 or from a

preceding command combination BK1 to a subsequent command B2.
The commands B or command combinations BK to be transmitted may, for example, be subdivided into three categories. The subdivision into categories is used to def1ne different commands B or command combinations BK.
Commands or command combinations in the f1rst category-are commands or command combinations for which the f1rst frequency f1,B2 or f1,BK2 of a command or of a command combination is predetermined in a f1xed manner for a specif1c command table, following a change in the command or the command combination.
Commands or command combinations in the second category are commands or command combinations for which a dependent frequency of the frequency pair is predetermined for a specif1c command table after a change from a preceding command B1 or a preceding command combination BK1 to a subsequent command B2 or a subsequent command combination BK2 as a function of the preceding command B1 or the preceding command combination BK1.
Commands or command combinations in the third category are commands for which the change from a preceding command combination to a subsequent command combination for a specif1c command table is made via an intermediate step. The intermediate step may be an insert frequency E or a pause P.
If suff1cient individual frequencies are available, it is always possible to f1nd frequency associations so that all commands and command combinations fall in the f1rst category. If frequencies are short, that is to say when a large number of different command combinations or commands have to be transmitted in a

narrow frequency band, it is necessary, however, to also allow commands and command combinations in the second category and in the third category. This is because use of these command combinations and/or commands allows optimized use of the available frequencies.
As is illustrated in f1gure 2, the selection module 11 in a f1rst method step 10 allocates one frequency pair to a command to be transmitted or to a command combination to be transmitted, with the assistance of the command Table 12.
A command Table 12 as described above may be conf1gured, for example, as shown in Table 1. In this case, four commands A, B, C, D and possible command combinations which are stored in the command table are shown.

According to Table 1, the frequency pair (f1, f6) is allocated to the command D. According to Table 1, the frequency pair (f3, fe) is allocated to the command combination B+D.
If now, for example, a preceding command A is transmitted and it is intended to transmit a subsequent command combination A+B, then this can be done by a single frequency change:
...f2,f5,f2,f5,f2,f4,f2,f4,... A -+ A+B

•i. If, for example, a command A is then transmitted and it is intended to transmit a command combination A+B+D, this is done by a double frequency change via the command combination A+D:
...f2/f5,f2/f5,f6,f5, f6/.-. A -> A+D
...f5,f6,f5/f6,f4, f6,f4,- A+D -+ A+B+D
Table 2 shows a further example of a command Table 12 with three independent commands A, B, C and a test command T. In this example, the commands T, A, B, C each have a common frequency f5.

Eight different frequency combinations or frequency pairs are required to represent these three independent commands A, B, C and the test command T, as well as the command combinations A+C, A+B, B+C, A+B+C that result from the commands A, B, C.
As can be seen from Table 2, f1ve single frequencies are suff1cient to form ten different frequency pairs. The frequency pairs in Table 2 have been allocated such that all commands and command combinations with the exception of the command A are included in the f1rst category. The frequency pairs (f 1, f 4 and f1, f3) have not been used in this case.
In a second method step 20, the f1rst frequency to be transmitted is chosen with the assistance of the selection module 11.

In this case, the selection module 11 chooses the frequency which is intended to be the f1rst to be transmitted for a command change from a preceding command Bi to a subsequent command B2. In this case, this f1rst frequency to be transmitted is chosen as a function of at least one other associated frequency pair. This frequency which is the f1rst to be transmitted can also be referred to as the frequency to be predetermined.
The same applies to the transmission of command combinations BK: in the case of a command change from a preceding command combination BK1 to a subsequent command combination BK2, a frequency which is the f1rst to be transmitted in the frequency pair of the subsequent command combination BK2 is chosen as a function of at least one other associated frequency pair by the selection module 11.
This also applies, of course, to a command change from a preceding command to a subsequent command combination or from a preceding command combination to a subsequent command.
The selection module 11 preferably chooses the said f1rst frequency to be transmitted as a function of the frequency pair of the directly preceding command or command combination. In this case, the preceding command is the command which is transmitted immediately before the subsequent command.
In the case of a command sequence Bi,B2 or Bi,BK2 or BKi,BK2 or BKi,B2, this therefore means that a f1rst frequency f1,B2 or f1,BK2 of the subsequent command B2 or command combination BK2 is chosen as a function of the frequency pair of a preceding command Bi or command combination BKi. In,particular, the f1rst frequency f2/B2

of the subsequent command B2 or command.combination BK2 is dependent on the f1rst frequency fx, B1 or f1,BK1 and/or on the second frequency f2/B2 or f2,BK2 of the preceding command B1 or command combination BKi.
The selection module 11 preferably chooses the f1rst frequency to be transmitted as a function of the directly preceding command or command combination.
For example, the selection module 12 may be designed in such a manner that it can check a command change table contained in the command table. Table 3 is one example of a command change table such as this, which def1nes the choice of the f1rst frequency to be transmitted. Table 3 shows the changes in the commands or command combinations def1ned in Table 2 for which there are restrictions. For these changes, the said f1rst frequencies to be transmitted are identif1ed by the frequency indexes that are underscored and printed in bold text.

Three examples of command changes are intended to describe in more detail the f1rst frequency to be transmitted in the frequency pair of the subsequent command or command combination:
f1rst example (A -> A+B+C) :
A change from the command A (f2, fs) to the command

combination A+B+C (f1,f2) is carried out as follows:
.»f2,f5,f2,f5,f2,f5,f2,fl,f2,fl,f2.» A -> A+B+C
In this case, the frequency f2 is the f1rst frequency to be transmitted in the frequency pair f1,f2 of the subsequent command combination A+B+C. This is because, if the frequency f1 were to be the f1rst to be transmitted after the frequency f5, instead of the frequency f2, the command T would be transmitted:
•»f2 f5 f2 f5 f2 f5 fl.. A -> T
Second example (A —> T) :
This problem also occurs, of course, in the case of the desired command chanqe from A (f2,f5) to T (f1,fs) and T (f1,f5) to A (f2,f5) :
...f2, fs, f2, f5, f2, f5, fl, f5, fl, f5... A -> T
In this case, the frequency f5 is the f1rst frequency to be transmitted in the frequency pair f1,fs of the subsequent command T. This is because, if the frequency fa were to be transmitted instead of the frequency f5, the command A+B+C would incorrectly be transmitted:
...f2,f5,f2,f5,f2,f5,f2,fl,... A -> A+B+C
Third example (T -> A+C) :
The following frequencies are transmitted for a command
change from T (f1,f5) to A+C (f2,f4):
...f1,f5,fl,f5,f4,f2,f4 f2... T -> A+C
In this case, the f1rst frequency to be transmitted is the frequency f4. If other frequencies were to be transmitted during the change, then the following undesirable change could occur:

...f1, f5, f i, f 5, f i, £2/ f Ar f2— T -»• A+B+C
As they are illustrated in the command change table, the f1rst frequencies to be transmitted can be determined in various ways. For example, they can be determined on a control basis. It has been found to be particularly advantageous for a common frequency to occur in all of the commands in the association of the frequency pairs with the commands. By way of example, this is the frequency f5 in Table 2, which occurs in all of the commands A, B, C, T. These frequencies determined in this way can then be stored in a command Table 12.
A further rule, which is not implemented completely in Table 2 because of the combination A+B+C, for good frequency associations states that the two frequencies used for T should occur only in those frequency pairs which are associated with single commands.
In the case of commands or command combinations in the f1rst category, the f1rst frequencies to be transmitted are determined statically. In this case, the f1rst frequencies to be transmitted are determined before the method is carried out, for example during its implementation, that is to say during the def1nition of the command table. These statically determined f1rst frequencies to be transmitted can be stored in the command change table.
In the case of commands or command combinations in the second category, the f1rst frequencies to be transmitted must be determined dynamically as a function of the preceding command or command combination while the method is being carried out. Suitable algorithms or processing rules must be provided for this purpose. The corresponding algorithms

or processing rules are then processed by one or more processors.
In a third method step 30, the frequency pair which corresponds to the command or the command combination on the basis of the sequence def1ned in step 30 is transmitted by means of the communication module 13.
A fourth method step 40 is applied when a further command is intended to be transmitted. In this case, the method starts again with method step 10.
Four independent commands A, B, C, D plus a test command T require 16 frequency combinations. Command Table 4 illustrates one preferred frequency allocation with 8 individual frequencies, in which case all of the commands and command combinations in category 1 can be allocated:

The frequencies to be predetermined, that is to say the

f1rst frequencies to be transmitted, are summarized in Table 5 for all commands or command combinations for which there are restrictions for specif1c changes.
Command Frequency to be
predetermined
_C f8
_D f8
A+C f2
B+D f3
C+D f8
A+C+D f5
B+C+D \JA
Table 5
Command Frequency to be
predetermined
_C f8
_D f8
A+C f2
B+D f3
C+D f8
A+C+D f5
B+C+D \JA
Table 5
The commands B or command combinations BK to be transmitted may be of very different types. In particular, however, the commands are independent protection commands for use in electrical power supply systems. In this case, the commands are transmitted via communication channels. If the commands or command combinations are used for protection of devices in the electrical power supply system, an electrical power line is used as a communication channel for transmission of the protection commands.
The commands B or the command combinations BK are preferably in a limited frequency band. This allows particularly effective and eff1cient conf1guration of the appropriate apparatuses. The frequency band preferably has a width of 4 kHz.

Patent Claims
1. A method for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, with a command or command combination in each case being associated with one frequency pair, characterized in that, when a command changes from a preceding command or command combination to a subsequent command or command combination, the frequency which will be the first to be transmitted in the frequency pair of the subsequent command or command combination is chosen as a function of at least one other associated frequency pair.
2. The method as claimed in claim 1, characterized in that said first frequency to be transmitted is chosen as a function of the frequency pair of the preceding command or command combination.
3. The method as claimed in one of claims 1 or 2, characterized in that the command or the command combination is a protection command to be transmitted, and in that this protection command is transmitted by means of an electrical power line.
4. The method as claimed in one of claims 1 to 3, characterized in that the frequencies of the command or of the command combination are in a limited frequency band.
5. The method as claimed in claim 4, characterized in that the limited frequency band has a width of 4 kHz.
6. The method as claimed in one of claims 1 to 5, characterized in that an insert frequency and/or a pause are/is inserted on changing from the preceding command or command combination to the subsequent command or command combination.

7. An apparatus for transmission of commands or
command combinations via a communication link by means
of coded frequency-shift keying, with a command or
command combination in each case being associated with one frequency pair, characterized in that the apparatus is designed such that when a command changes from a preceding command or command combination to a subsequent command or command combination, the frequency which will be the first to be transmitted in the frequency pair of the subsequent command or command combination can be chosen as a function of at least one other associated frequency pair.
8. The apparatus as claimed in claim 7, characterized in that the apparatus is designed to choose the said first frequency to be transmitted as a function of the frequency pair of the preceding command or command combination.
9. A computer program product having computer program code means for controlling one or more processors of an apparatus for transmission of commands or command combinations via a communication link by means of coded frequency-shift keying, with a command or a command combination in each case being associated with one frequency pair, in such a manner that the apparatus chooses, when a command changes from a preceding command or command combination to a subsequent command or command combination, the frequency which will be the first to be transmitted in the frequency pair of the subsequent command or command combination as a function of at least one other associated frequency pair.
10. The computer program product as claimed in claim 9, characterized by further computer program code means for controlling the processors in such a manner that the apparatus chooses the said first frequency to be

transmitted as a function of the frequency pair of the preceding command or command combination.
Dated this 10 day of April 2007

Documents:

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Patent Number

279508

Indian Patent Application Number

751/CHE/2007

PG Journal Number

04/2017

Publication Date

27-Jan-2017

Grant Date

24-Jan-2017

Date of Filing

10-Apr-2007

Name of Patentee

ABB TECHNOLOGY AG

Applicant Address

AFFOLTERNSTRASSE 44, CH-8050 ZURICH, SWITZERLAND

Inventors:

#	Inventor's Name	Inventor's Address
1	BENNINGER, HANS	LIMMATHOEFLI 2, CH-5300 TURGI, SWITERLAND

PCT International Classification Number

H04B1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	060405155.0	2006-04-10	Argentina