CA2300064A1 - Method and device for generating a random number sequence for carrier frequencies of a mobile radio transmission - Google Patents
Method and device for generating a random number sequence for carrier frequencies of a mobile radio transmission Download PDFInfo
- Publication number
- CA2300064A1 CA2300064A1 CA002300064A CA2300064A CA2300064A1 CA 2300064 A1 CA2300064 A1 CA 2300064A1 CA 002300064 A CA002300064 A CA 002300064A CA 2300064 A CA2300064 A CA 2300064A CA 2300064 A1 CA2300064 A1 CA 2300064A1
- Authority
- CA
- Canada
- Prior art keywords
- shift register
- bit
- addition
- carrier frequencies
- content
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2628—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
- H04B1/7143—Arrangements for generation of hop patterns
Abstract
The invention concerns a method and a device for producing a sequence of random numbers, for transformation into carrier frequencies (fx) for a mobile radiotelephone transmission, using an algorithm, based on a shifting register (25) with feedback (27)with n bits. A bit of the shifting register (25) with feedback (27) is added by modulo2 addition to another bit of the shifting register (25). The shifting register (25) content is shifted, time pulsed, by a bit to the right. The modulo2 addition result is input in the site of the left bit cleared by the shift. Then, the shifting register (25) content is transformed (23) into a carrier frequency (fx) for a mobile radiotelephone transmission. For said transformation (23) an algorithm in the form of an endless loop is used.
Description
Description Method and device for generating a random number. sequence for carrier frequencies of a mobile radio transmission The present invention relates to a method and a device for generating a random number sequence which is converted into carrier frequencies for a mobile radio transmission.
The so-called frequency hopping spread spectrum is a known method for transmitting data on a plurality of carrier frequencies. A frequency hopping spread spectrum system is in this case to be understood as meaning a system in which, for the purpose of radio transmission of data, a multiplicity of carrier frequencies are provided and the currently used carrier frequency is periodically changed. In a time division multiplex (TDMA) system, in particular, the carrier frequency may be changed after each time slot or time frame of the time division multi-plex transmission (or multiples thereof). Such a fre-quency hopping spread spectrum system has advantages to the extant that the energy of the entire radio trans-mission is distributed over all the carrier frequencies.
This is important particularly when a generally available frequency band, such as the 2.4 Gfiz ISM (Industrial, Scientific, Medical) band, for example, is used. For the use of this frequency band, an upper limit for the maximum energy occurring per carrier frequency is defined in accordance with the relevant specifications ("FCC part 15", Federal Communications Commission), in order to minimize interference of other subscribers. Furthermore, it is prescribed by the specification "FCC part:l5" that at least 75 different carrier frequencies must be pro-vided.
A further advantage of the frequency hopping spread spectrum system that may be mentioned is that the system becomes more insensitive to interference as a result of the provision of a large number of carrier frequencies. Furthermore, the security of the system against eavesdropping by third parties is increased since the third party generally does not know the carrier frequency to which a change is made after a certain period of time.
The sequence of carrier .frequencies which are used one after the other for transmission is determined by an algorithm. Such an algorithm is implemented in an identical manner in the fixed station and also in each mobile station of the mobile radio transmission.
Consequently, if a mobile part is synchronized with the associated fixed station, the mobile part and the fixed station will perform the carrier frequency change pre-determined by the sequence of the (identical) algorithm.
in synchronism with one another.
The algorithm should ensure that each carrier frequency is used in the same number of instances and for the same length in a certain period of time.
The present invention therefore has the object of providing a method and a device for generating a random number sequence for carrier frequencies of a mobile radio transmission which make it possible to realize a random number algorithm in a simple manner.
This object is achieved by means of the features of the independent claims. The dependent claims develop the central concept of the invention in a particularly advantageous manner.
The invention, then, provides a method for generating. a random number sequence, the random number sequence being converted into carrier frequencies for a mobile radio transmission. In this case, first of all a shift register with n bits is provided. This is followed by feedback modulo-2 addition of one bit of the shift register with one or more other bits of the shift regis-ter. The register content of the shift register is then shifted cyclically by one bit. The result of the modulo-2 addition is then inserted into the bit position freed by the shifting operation. The content of the shift register is cyclically converted into a~carrier frequency fx for a mobile radio transmission. Consequently, as a result of the feedback of the shift register, a random number sequence having a maximum periodicity (depending on the type of feedback) of 2n-1, where n is the number of bits of the shift register, is created in a particularly simple manner.
Different sequences can be generated by altering the feedback, that is to say by altering the shift register bits which are used for the modulo-2 addition.
For example, 2048 different sequences having a maximum length of (2n-1) can be generated given a shift register with 16 bits.
The step of converting the content of the shift register into carrier frequencies for a mobile radio.
transmission has the addition of the content of the shift register to the current carrier frequency. Afterwards, it is decided whether the result of the addition is greater than the number of carrier frequencies that are present.
If the decision is positive, the result of the addition is then decremented by the number of carrier frequencies that are present until the decision turns out negative, that is to say until the result of the addition is no longer greater than the number of carrier frequencies that are present. If the decision turns out negative, the result of the addition is used as the next carrier frequency. Subsequently, the shift register is shifted by one bit and the sequence starts afresh.
The invention furthermore provides a device for converting a random number sequence into carrier fre-quencies fx for a mobile radio transmission. This device has a shift register with n bits. An addition device fo;~.~
the modulo-2 addition of one bit of the shift register with one or more other bits of the shift register after the manner of a feedback is furthermore provided. After the addition, the register content is shifted cyclically by one bit, preferably to the right. The result of the addition device is then inserted into the bit position freed by the shifting operation. A device for converting the content of the shift register cyclically into a carrier frequency for a mobile radio transmission is furthermore provided.
The nature of the feedback, that is to say the bits used for the modulo-2 addition and also the number of these bits, can be altered in order to generate different sequences.
The device for converting the content of the shift register into carrier frequencies furthermore has means for adding the content of the shift register to the current carrier frequency. Furthermore, means for decid-ing whether the result of the addition is greater than the number of carrier frequencies that are present are provided. In this case, if the decision is positive, the result of the addition is decreased by the number of.
carrier frequencies that are present until the decision turns out negative, that is to say until the result of the addition is no longer greater than the number of carrier frequencies that are present. If the decision turns out negative, the result of the addition is used as the next carrier frequency and the shift register is then shifted cyclically by one position to the right.
The shift register preferably has 16 bits.
The shift register can be implemented in an 8-bit or 16-bit processor.
The invention furthermore relates to a mobile radio transceiver having a device of the abovementioned type.
The invention will now be explained in more detail using an exemplary embodiment and with reference to the accompanying drawings, in which:
Figure 1 shows a mobile radio transmission system having a fixed station according to the inven-tion, Figure 2 shows a time frame of a data trans mission standard of the kind that can be employed in the case of the present invention, Figure 3 shows, in detail, the internal structure of a fixed station according to the invention, and Figure 4a shows a shift register of the kind used in the present invention.
Figure 4b shows the content of the shift register for the various clock cycles of a period, and Figure 5 shows a flow diagram for the conversion of the random number sequence into carrier fre-quencies.
Referring to Figure 1, it is intended first of all to give an explanation of the general structure of a mobile radio transmission. As is generally customary, the arrangement for the radio transmission of data has a fixed station 1 and a plurality of mobile parts (mobile stations), cordless telephones 2, 3 ... The fixed station 1 is connected by a terminal line 10 to the fixed net-work. For the purpose of communication, it is possible to provide an interface device (not illustrated) between the fixed station 1 and the terminal line 10. The fixed station 1 has an antenna 6 by means of which, for example, a communication with the mobile part 2 takes place via a first radio transmission path 8 or a communi-cation with the mobile part 3 takes place via a second radio transmission path 9. The mobile parts 2, 3 ... each have an antenna 7 for receiving and/or for transmitting data. Figure 1 diagrammatically illustrates the state in which the fixed station 1 is actively communicating with the mobile part 2 and, consequently, is exchanging data.
The mobile part 3, on the other hand, is in the so-called idle locked mode, in which it Waits in standby-like fashion for a call from the fixed station 1. In this state, the mobile part 3 is not communicating with the fixed station 1, but rather it receives only periodically the data for example of a time slot from the fixed station, in order to be able to be resynchronized with the carrier frequencies fx.
The internal structure of the fixed station 1 is illustrated diagrammatically in Figure 1. The voice information data are fed to an RF module 4, which is driven by a carrier frequency sequence unit. The exact structure of a fixed station 1 according to the invention will be described later.
Referring to Figure 2, it is now intended to give an explanation of a transmission standard of the kind that can be used in the case of the present invention. As is evident from Figure 2, data are transmitted chronologically successively on a plurality of carrier frequencies fx, ten of which are illustrated, in a plurality of time slots, 24 time slots Zx in the case illustrated, using a time division multiplex method TDMA
(Time Division Multiple Access) . In the case illustrated, operation is in the duplex mode, that is to say after the first twelve time slots Zx have been transmitted from the fixed station l, a switch is made to reception, and the fixed station 1 receives, in the opposite direction, the -second twelve time slots (Z13 to Z24) from one or more mobile stations.
If the so-called DECT standard is used for the transmission, the time duration of a time frame is 10 ms, and 24 time slots Zx are provided, namely twelve time slots for transmission from the fixed station to mobile parts and a further twelve time slots Zx for transmission from the mobile parts to the fixed statiori. According to the DECT standard, ten carrier frequencies fx between 1.88 GHz and 1.90 GHz are provided.
Of course, other frame structures can also be used in the present invention, for example those having a number of time slots that is halved in comparison with the DECT standard.
However, the present invention is also used in particular for transmissions in the so-called 2.4 GHz ISM
(Industrial, Scientific, Medical) frequency band. The generally accessible ISM frequency band has a bandwidth of 83.5 MHz. In accordance with the FCC part 15, at least 75 carrier frequencies fx must be distributed over these 83.5 MHz. What is particularly advantageous is a division of the bandwidth of 83.5 MHz between 96 carrier fre-quencies, i.e. a channel spacing of 864 kHz. The above-mentioned frequency bands and standards are cited purely as an example. The only fundamental precondition for applicability of the present invention is that a so-called frequency hopping spread spectrum is used, i.e.
that a plurality of carrier frequencies are available, and that the carrier frequency selected for transmission is periodically changed. For such a change, it is advan-tageous if the data are transmitted in time slots Zx (time division multiplex method). The DECT standard is therefore suitable, for example, as well as any other modified standard based on this DECT staadard.
Referring to Figure 3, it is now intended to give a more detailed explanation of the internal structure of a fixed station 1 according to the invention. As can be seen in Figure 3. information data are fed to the RF
module 4 when transmission is to be effected from the -fixed station 1 to a mobile part 2, 3 ... by means of the antenna 6, and information data are output from the RF
module 4 when data from mobile parts are received. The RF
module 4 modulates the digital encoded information data onto a carrier frequency fx. The carrier frequency fx that is currently to be used is in this case predeter-mined by a carrier frequency sequence unit, which is designated in general by 20. Provided in the carrier frequency sequence unit 20 is a detection device 24, to which the demodulated signal from the RF module 4 is fed.
Interference in this context means that either inter-ference in the actual sense or seizure by another trans-mitter is present. Interference in the sense of the present description can therefore be detected by demodulating a received signal on a carrier frequency and detecting whether or not a signal level is present on this carrier frequency. In this case, a carrier frequency which is subjected to interference is therefore a carrier frequency onto which a signal which exceeds a specific threshold value is modulated.
Interference in the actual sense can be detected by the occurrence of CRC errors or burst losses.
The detection device 24 therefore uses the demodulated signal from the RF module 4 to determine how high the signal component modulated onto a specific carrier frequency fx is. If the signal component detected lies above a predetermined limit value or if one of the abovementioned errors has occurred, the detection device 24 passes an interference detection signal to an inhibit/enable unit 21. Depending on the interference-source detection signal from the detection device 24, the inhibit/enable unit 21 passes an inhibit/enable informa-tion item to a processor 23. This inhibit/enable informs-tion item indicates which of the carrier frequencies fx are inhibited or enabled again on account of the detec-tion of interference by the detection device 24, as will be explained later.
In other words, the detection device 24 and the inhibit/enable device 21 provide an independent procedure by means of which frequencies subjected to interference can be inhibited and enabled again. In addition to the inhibit/enable information items from the inhibit/enable unit 21, a sequence from a random number generator 22 is fed to the processor 23. On the basis of a random algorithm implicit in it, the random number generator 22 generates a randomly distributed sequence of carrier frequency values within the predetermined frequency band.
The random number generator 22 consequently carries out a procedure which is independent of the procedure of frequency inhibition for the case of interference.
Finally, the processor 23 passes to the RF module 4 a drive signal which predetermines for the RF module 4 the carrier frequency value that is to be used.
As is illustrated in Figure 3 by an arrow from the processor 23 to the random number generator 22, the processor 23 predetermines how many different values the said random number generator is to generate. This number of values to be generated corresponds- to the number of carrier frequencies to be generated, which, for example in accordance with the US specification "FCC part 15", must be at least 75.
In particular in a mobile part, the processor 23 furthermore predetermines for the random number generator 22 a start value for the algorithm thereof . This start value is communicated to the mobile station by the fixed station for the purpose of synchronization, which is achieved by virtue of the fact that the same start value and the same algorithm are used. Given the same start value and the same algorithm, the same sequences are compulsorily generated by the fixed station and the mobile part.
The fixed station 1 is the master during fre-quency allocation, i.e. at the beginning of a connection set-up, the random number generator in a mobile part is initialized with the state of the random number generator 22 of the fixed station 1. The random number generators in the mobile part 2, 3 ... and in the fixed station 1 then generate the same carrier frequency values.
synchronously in timing and autonomously of one another.
The procedure for frequency inhibition which is carried out by the detection device 24 and the inhibit/enable unit 21 uses a unidirectional protocol on the radio interface during the entire connection time between the fixed station 1 and a mobile part 2, 3 ... If the detection device 24 finds one of the possible fre-quencies fx from the fixed station 1 to be subjected to interference, then the fixed station 1 therefore coa~uni-cates to all mobile parts with which it is operating connections that this frequency which is subjected to interference, if it is generated by the sequence of the random number generator, must be replaced by a different carrier frequency that is not detected as being subjected to interference. The random number generator 22 is not influenced by the frequency inhibition. This frequency inhibition is cancelled again by the inhibit/enable unit 21 when the inhibited carrier frequency is again suitable for transmission, or when it has been inhibited for longer than a previously defined time.
Referring to Figures 4a and 4b, it is now intended to give an explanation of how the random numbers can be generated by an algorithm which can be implemented in a simple manner in a processor, and, at the same time, how the computing time required can be kept short.
As is evident in Figure 4a, the basis of the algorithm is a feedback shift register 25 having the length x, where the length x is equal to 4 in the example illustrated. The feedback structure of the register is I==f1,4~. In accordance with the example illustrated, this means that in the sense of a feedback, the first bit is combined with the fourth bit by modulo-2 addition 26 and the result of this modulo-2 addition 26 is inserted at the position of the most significant bit, this posi-tion becoming free as a result of the register content being shifted by one bit to the right.
At the beginning, the shift register 25 is loaded with the value 0001, as illustrated. For each new value, the contents of the shift register 25 are shifted by one bit to the right, the left-hand bit being recalculated each time in the manner illustrated. The aature of the feedback, that is to say the modulo-2 addition of the left-hand bit with the extreme right-hand bit of the shift register 25 in the present example, can be altered.
Consequently, different sequences of varying length can be generated by altering the nature of the feedback 27 and the number of bits that are fed back. Depending on the feedback, the sequence length, that is to say the periodicity according to which the sequence generated is periodically repeated, is a maximum of 2n-l, where n is the number of bits of the shift register 25. In the case of the arrangement illustrated (n=4, Ir~l,4~), the sequence length is thus equal to 15 (and thus a maximum for a four-bit register), that is to say after 15 gener-ated values, the generated values are repeated period-ically. The value 0 is not generated in feedback shift registers. Figure 4b illustrates the content of the shift register 25 for the corresponding clock cycles of a period for the example illustrated in Figure 4a.
Figure 4a should be understood in particular as being an example of the generation of random numbers by a feedback shift register. In practice, a shift register with 16 bits can be used, for example. Such a shift register can be easily implemented in 8- and 16-bit processors. As a result of the various possible options for the feedback 27, it is possible to generate 2048 different sequences given a 16-bit shift register. The sequence length is a maximum of 216-1=65535 given a 16-bit shift register. Consequently, if a carrier frequency corresponding to a value of the random number sequence generated is maintained for the duration of a frame of ms, for example, the time duration of the period is 65535 x 10 ms = 10.9 min. This means that a sequence of maximum leagth is repeated only every 10.9 min given a 10 16-bit register.
The use of a random number generator having the algorithm illustrated furthermore has the advantage that it is possible to generate different carrier frequency.
hopping sequences by means of feedbacks which can be defined in a simple manner.
In the case of a shift register with 16 bits, the number of possible values of the sequence of carrier frequencies is 65535, as explained. However, the number of actually used carrier frequencies may be significantly smaller and, furthermore, variable. Consequently, the carrier frequency cannot be obtained directly by a conversion of the values of the random number sequence.
Figure 5 illustrates how the actually used frequencies are obtained in an endless loop from the content of the shift register 25. As is evident in Figure 5, first of all the frequency fxn_1 is set to 0. The current content of the shift register 25 is then added (28) to this value. Subsequently, a calculation is made and it is decided whether the result of the addition calculated in step 28 is greater than the number y of useable carrier frequencies fx. If the result of this decision 29 is positive, that is to say if the result of the addition in step 28 is greater than the number y of actually useable carrier frequencies fx, then this value is decreased (30) by the value of the number y of useable carrier frequencies. This decrease in the result of the addition 28 by the number y of useable carrier fre-quencies fx is carried out until the decision in step 29 yields a negative result, that is to say until the value fxn_1 is used as the carrier frequency of the next time slot or time frame fx. Subsequently, the shift register 25 is shifted (32) further by one bit, for example to the right. The procedure is thus ended and the sequence returns to step 28.
The maximum number of used frequencies can be adapted by altering the variable y.
Consequently, the invention enables the gener ation of random numbers by means of an algorithm which can be implemented in a simple manner in a processor. At the same time, the computing time required is kept short.
List of reference symbols 1: Fixed station 2: Mobile part 3: Mobile part 4: RF module 6: Antenna fixed station 7: Antenna mobile part 8: First radio transmission path 9: Second radio transmission path 10: Terminal line 20: Carrier frequency sequence unit 21: Inhibit/enable unit 22: Random number generator 23: Processor 24: Detection device 25: Shift register 26: Adder 27: Feedback 28: Addition 29: Decision 30: Decrease 31: Conversion 32: Shifting fx: Carrier frequency Rx: Frame Zx: Time slot
The so-called frequency hopping spread spectrum is a known method for transmitting data on a plurality of carrier frequencies. A frequency hopping spread spectrum system is in this case to be understood as meaning a system in which, for the purpose of radio transmission of data, a multiplicity of carrier frequencies are provided and the currently used carrier frequency is periodically changed. In a time division multiplex (TDMA) system, in particular, the carrier frequency may be changed after each time slot or time frame of the time division multi-plex transmission (or multiples thereof). Such a fre-quency hopping spread spectrum system has advantages to the extant that the energy of the entire radio trans-mission is distributed over all the carrier frequencies.
This is important particularly when a generally available frequency band, such as the 2.4 Gfiz ISM (Industrial, Scientific, Medical) band, for example, is used. For the use of this frequency band, an upper limit for the maximum energy occurring per carrier frequency is defined in accordance with the relevant specifications ("FCC part 15", Federal Communications Commission), in order to minimize interference of other subscribers. Furthermore, it is prescribed by the specification "FCC part:l5" that at least 75 different carrier frequencies must be pro-vided.
A further advantage of the frequency hopping spread spectrum system that may be mentioned is that the system becomes more insensitive to interference as a result of the provision of a large number of carrier frequencies. Furthermore, the security of the system against eavesdropping by third parties is increased since the third party generally does not know the carrier frequency to which a change is made after a certain period of time.
The sequence of carrier .frequencies which are used one after the other for transmission is determined by an algorithm. Such an algorithm is implemented in an identical manner in the fixed station and also in each mobile station of the mobile radio transmission.
Consequently, if a mobile part is synchronized with the associated fixed station, the mobile part and the fixed station will perform the carrier frequency change pre-determined by the sequence of the (identical) algorithm.
in synchronism with one another.
The algorithm should ensure that each carrier frequency is used in the same number of instances and for the same length in a certain period of time.
The present invention therefore has the object of providing a method and a device for generating a random number sequence for carrier frequencies of a mobile radio transmission which make it possible to realize a random number algorithm in a simple manner.
This object is achieved by means of the features of the independent claims. The dependent claims develop the central concept of the invention in a particularly advantageous manner.
The invention, then, provides a method for generating. a random number sequence, the random number sequence being converted into carrier frequencies for a mobile radio transmission. In this case, first of all a shift register with n bits is provided. This is followed by feedback modulo-2 addition of one bit of the shift register with one or more other bits of the shift regis-ter. The register content of the shift register is then shifted cyclically by one bit. The result of the modulo-2 addition is then inserted into the bit position freed by the shifting operation. The content of the shift register is cyclically converted into a~carrier frequency fx for a mobile radio transmission. Consequently, as a result of the feedback of the shift register, a random number sequence having a maximum periodicity (depending on the type of feedback) of 2n-1, where n is the number of bits of the shift register, is created in a particularly simple manner.
Different sequences can be generated by altering the feedback, that is to say by altering the shift register bits which are used for the modulo-2 addition.
For example, 2048 different sequences having a maximum length of (2n-1) can be generated given a shift register with 16 bits.
The step of converting the content of the shift register into carrier frequencies for a mobile radio.
transmission has the addition of the content of the shift register to the current carrier frequency. Afterwards, it is decided whether the result of the addition is greater than the number of carrier frequencies that are present.
If the decision is positive, the result of the addition is then decremented by the number of carrier frequencies that are present until the decision turns out negative, that is to say until the result of the addition is no longer greater than the number of carrier frequencies that are present. If the decision turns out negative, the result of the addition is used as the next carrier frequency. Subsequently, the shift register is shifted by one bit and the sequence starts afresh.
The invention furthermore provides a device for converting a random number sequence into carrier fre-quencies fx for a mobile radio transmission. This device has a shift register with n bits. An addition device fo;~.~
the modulo-2 addition of one bit of the shift register with one or more other bits of the shift register after the manner of a feedback is furthermore provided. After the addition, the register content is shifted cyclically by one bit, preferably to the right. The result of the addition device is then inserted into the bit position freed by the shifting operation. A device for converting the content of the shift register cyclically into a carrier frequency for a mobile radio transmission is furthermore provided.
The nature of the feedback, that is to say the bits used for the modulo-2 addition and also the number of these bits, can be altered in order to generate different sequences.
The device for converting the content of the shift register into carrier frequencies furthermore has means for adding the content of the shift register to the current carrier frequency. Furthermore, means for decid-ing whether the result of the addition is greater than the number of carrier frequencies that are present are provided. In this case, if the decision is positive, the result of the addition is decreased by the number of.
carrier frequencies that are present until the decision turns out negative, that is to say until the result of the addition is no longer greater than the number of carrier frequencies that are present. If the decision turns out negative, the result of the addition is used as the next carrier frequency and the shift register is then shifted cyclically by one position to the right.
The shift register preferably has 16 bits.
The shift register can be implemented in an 8-bit or 16-bit processor.
The invention furthermore relates to a mobile radio transceiver having a device of the abovementioned type.
The invention will now be explained in more detail using an exemplary embodiment and with reference to the accompanying drawings, in which:
Figure 1 shows a mobile radio transmission system having a fixed station according to the inven-tion, Figure 2 shows a time frame of a data trans mission standard of the kind that can be employed in the case of the present invention, Figure 3 shows, in detail, the internal structure of a fixed station according to the invention, and Figure 4a shows a shift register of the kind used in the present invention.
Figure 4b shows the content of the shift register for the various clock cycles of a period, and Figure 5 shows a flow diagram for the conversion of the random number sequence into carrier fre-quencies.
Referring to Figure 1, it is intended first of all to give an explanation of the general structure of a mobile radio transmission. As is generally customary, the arrangement for the radio transmission of data has a fixed station 1 and a plurality of mobile parts (mobile stations), cordless telephones 2, 3 ... The fixed station 1 is connected by a terminal line 10 to the fixed net-work. For the purpose of communication, it is possible to provide an interface device (not illustrated) between the fixed station 1 and the terminal line 10. The fixed station 1 has an antenna 6 by means of which, for example, a communication with the mobile part 2 takes place via a first radio transmission path 8 or a communi-cation with the mobile part 3 takes place via a second radio transmission path 9. The mobile parts 2, 3 ... each have an antenna 7 for receiving and/or for transmitting data. Figure 1 diagrammatically illustrates the state in which the fixed station 1 is actively communicating with the mobile part 2 and, consequently, is exchanging data.
The mobile part 3, on the other hand, is in the so-called idle locked mode, in which it Waits in standby-like fashion for a call from the fixed station 1. In this state, the mobile part 3 is not communicating with the fixed station 1, but rather it receives only periodically the data for example of a time slot from the fixed station, in order to be able to be resynchronized with the carrier frequencies fx.
The internal structure of the fixed station 1 is illustrated diagrammatically in Figure 1. The voice information data are fed to an RF module 4, which is driven by a carrier frequency sequence unit. The exact structure of a fixed station 1 according to the invention will be described later.
Referring to Figure 2, it is now intended to give an explanation of a transmission standard of the kind that can be used in the case of the present invention. As is evident from Figure 2, data are transmitted chronologically successively on a plurality of carrier frequencies fx, ten of which are illustrated, in a plurality of time slots, 24 time slots Zx in the case illustrated, using a time division multiplex method TDMA
(Time Division Multiple Access) . In the case illustrated, operation is in the duplex mode, that is to say after the first twelve time slots Zx have been transmitted from the fixed station l, a switch is made to reception, and the fixed station 1 receives, in the opposite direction, the -second twelve time slots (Z13 to Z24) from one or more mobile stations.
If the so-called DECT standard is used for the transmission, the time duration of a time frame is 10 ms, and 24 time slots Zx are provided, namely twelve time slots for transmission from the fixed station to mobile parts and a further twelve time slots Zx for transmission from the mobile parts to the fixed statiori. According to the DECT standard, ten carrier frequencies fx between 1.88 GHz and 1.90 GHz are provided.
Of course, other frame structures can also be used in the present invention, for example those having a number of time slots that is halved in comparison with the DECT standard.
However, the present invention is also used in particular for transmissions in the so-called 2.4 GHz ISM
(Industrial, Scientific, Medical) frequency band. The generally accessible ISM frequency band has a bandwidth of 83.5 MHz. In accordance with the FCC part 15, at least 75 carrier frequencies fx must be distributed over these 83.5 MHz. What is particularly advantageous is a division of the bandwidth of 83.5 MHz between 96 carrier fre-quencies, i.e. a channel spacing of 864 kHz. The above-mentioned frequency bands and standards are cited purely as an example. The only fundamental precondition for applicability of the present invention is that a so-called frequency hopping spread spectrum is used, i.e.
that a plurality of carrier frequencies are available, and that the carrier frequency selected for transmission is periodically changed. For such a change, it is advan-tageous if the data are transmitted in time slots Zx (time division multiplex method). The DECT standard is therefore suitable, for example, as well as any other modified standard based on this DECT staadard.
Referring to Figure 3, it is now intended to give a more detailed explanation of the internal structure of a fixed station 1 according to the invention. As can be seen in Figure 3. information data are fed to the RF
module 4 when transmission is to be effected from the -fixed station 1 to a mobile part 2, 3 ... by means of the antenna 6, and information data are output from the RF
module 4 when data from mobile parts are received. The RF
module 4 modulates the digital encoded information data onto a carrier frequency fx. The carrier frequency fx that is currently to be used is in this case predeter-mined by a carrier frequency sequence unit, which is designated in general by 20. Provided in the carrier frequency sequence unit 20 is a detection device 24, to which the demodulated signal from the RF module 4 is fed.
Interference in this context means that either inter-ference in the actual sense or seizure by another trans-mitter is present. Interference in the sense of the present description can therefore be detected by demodulating a received signal on a carrier frequency and detecting whether or not a signal level is present on this carrier frequency. In this case, a carrier frequency which is subjected to interference is therefore a carrier frequency onto which a signal which exceeds a specific threshold value is modulated.
Interference in the actual sense can be detected by the occurrence of CRC errors or burst losses.
The detection device 24 therefore uses the demodulated signal from the RF module 4 to determine how high the signal component modulated onto a specific carrier frequency fx is. If the signal component detected lies above a predetermined limit value or if one of the abovementioned errors has occurred, the detection device 24 passes an interference detection signal to an inhibit/enable unit 21. Depending on the interference-source detection signal from the detection device 24, the inhibit/enable unit 21 passes an inhibit/enable informa-tion item to a processor 23. This inhibit/enable informs-tion item indicates which of the carrier frequencies fx are inhibited or enabled again on account of the detec-tion of interference by the detection device 24, as will be explained later.
In other words, the detection device 24 and the inhibit/enable device 21 provide an independent procedure by means of which frequencies subjected to interference can be inhibited and enabled again. In addition to the inhibit/enable information items from the inhibit/enable unit 21, a sequence from a random number generator 22 is fed to the processor 23. On the basis of a random algorithm implicit in it, the random number generator 22 generates a randomly distributed sequence of carrier frequency values within the predetermined frequency band.
The random number generator 22 consequently carries out a procedure which is independent of the procedure of frequency inhibition for the case of interference.
Finally, the processor 23 passes to the RF module 4 a drive signal which predetermines for the RF module 4 the carrier frequency value that is to be used.
As is illustrated in Figure 3 by an arrow from the processor 23 to the random number generator 22, the processor 23 predetermines how many different values the said random number generator is to generate. This number of values to be generated corresponds- to the number of carrier frequencies to be generated, which, for example in accordance with the US specification "FCC part 15", must be at least 75.
In particular in a mobile part, the processor 23 furthermore predetermines for the random number generator 22 a start value for the algorithm thereof . This start value is communicated to the mobile station by the fixed station for the purpose of synchronization, which is achieved by virtue of the fact that the same start value and the same algorithm are used. Given the same start value and the same algorithm, the same sequences are compulsorily generated by the fixed station and the mobile part.
The fixed station 1 is the master during fre-quency allocation, i.e. at the beginning of a connection set-up, the random number generator in a mobile part is initialized with the state of the random number generator 22 of the fixed station 1. The random number generators in the mobile part 2, 3 ... and in the fixed station 1 then generate the same carrier frequency values.
synchronously in timing and autonomously of one another.
The procedure for frequency inhibition which is carried out by the detection device 24 and the inhibit/enable unit 21 uses a unidirectional protocol on the radio interface during the entire connection time between the fixed station 1 and a mobile part 2, 3 ... If the detection device 24 finds one of the possible fre-quencies fx from the fixed station 1 to be subjected to interference, then the fixed station 1 therefore coa~uni-cates to all mobile parts with which it is operating connections that this frequency which is subjected to interference, if it is generated by the sequence of the random number generator, must be replaced by a different carrier frequency that is not detected as being subjected to interference. The random number generator 22 is not influenced by the frequency inhibition. This frequency inhibition is cancelled again by the inhibit/enable unit 21 when the inhibited carrier frequency is again suitable for transmission, or when it has been inhibited for longer than a previously defined time.
Referring to Figures 4a and 4b, it is now intended to give an explanation of how the random numbers can be generated by an algorithm which can be implemented in a simple manner in a processor, and, at the same time, how the computing time required can be kept short.
As is evident in Figure 4a, the basis of the algorithm is a feedback shift register 25 having the length x, where the length x is equal to 4 in the example illustrated. The feedback structure of the register is I==f1,4~. In accordance with the example illustrated, this means that in the sense of a feedback, the first bit is combined with the fourth bit by modulo-2 addition 26 and the result of this modulo-2 addition 26 is inserted at the position of the most significant bit, this posi-tion becoming free as a result of the register content being shifted by one bit to the right.
At the beginning, the shift register 25 is loaded with the value 0001, as illustrated. For each new value, the contents of the shift register 25 are shifted by one bit to the right, the left-hand bit being recalculated each time in the manner illustrated. The aature of the feedback, that is to say the modulo-2 addition of the left-hand bit with the extreme right-hand bit of the shift register 25 in the present example, can be altered.
Consequently, different sequences of varying length can be generated by altering the nature of the feedback 27 and the number of bits that are fed back. Depending on the feedback, the sequence length, that is to say the periodicity according to which the sequence generated is periodically repeated, is a maximum of 2n-l, where n is the number of bits of the shift register 25. In the case of the arrangement illustrated (n=4, Ir~l,4~), the sequence length is thus equal to 15 (and thus a maximum for a four-bit register), that is to say after 15 gener-ated values, the generated values are repeated period-ically. The value 0 is not generated in feedback shift registers. Figure 4b illustrates the content of the shift register 25 for the corresponding clock cycles of a period for the example illustrated in Figure 4a.
Figure 4a should be understood in particular as being an example of the generation of random numbers by a feedback shift register. In practice, a shift register with 16 bits can be used, for example. Such a shift register can be easily implemented in 8- and 16-bit processors. As a result of the various possible options for the feedback 27, it is possible to generate 2048 different sequences given a 16-bit shift register. The sequence length is a maximum of 216-1=65535 given a 16-bit shift register. Consequently, if a carrier frequency corresponding to a value of the random number sequence generated is maintained for the duration of a frame of ms, for example, the time duration of the period is 65535 x 10 ms = 10.9 min. This means that a sequence of maximum leagth is repeated only every 10.9 min given a 10 16-bit register.
The use of a random number generator having the algorithm illustrated furthermore has the advantage that it is possible to generate different carrier frequency.
hopping sequences by means of feedbacks which can be defined in a simple manner.
In the case of a shift register with 16 bits, the number of possible values of the sequence of carrier frequencies is 65535, as explained. However, the number of actually used carrier frequencies may be significantly smaller and, furthermore, variable. Consequently, the carrier frequency cannot be obtained directly by a conversion of the values of the random number sequence.
Figure 5 illustrates how the actually used frequencies are obtained in an endless loop from the content of the shift register 25. As is evident in Figure 5, first of all the frequency fxn_1 is set to 0. The current content of the shift register 25 is then added (28) to this value. Subsequently, a calculation is made and it is decided whether the result of the addition calculated in step 28 is greater than the number y of useable carrier frequencies fx. If the result of this decision 29 is positive, that is to say if the result of the addition in step 28 is greater than the number y of actually useable carrier frequencies fx, then this value is decreased (30) by the value of the number y of useable carrier frequencies. This decrease in the result of the addition 28 by the number y of useable carrier fre-quencies fx is carried out until the decision in step 29 yields a negative result, that is to say until the value fxn_1 is used as the carrier frequency of the next time slot or time frame fx. Subsequently, the shift register 25 is shifted (32) further by one bit, for example to the right. The procedure is thus ended and the sequence returns to step 28.
The maximum number of used frequencies can be adapted by altering the variable y.
Consequently, the invention enables the gener ation of random numbers by means of an algorithm which can be implemented in a simple manner in a processor. At the same time, the computing time required is kept short.
List of reference symbols 1: Fixed station 2: Mobile part 3: Mobile part 4: RF module 6: Antenna fixed station 7: Antenna mobile part 8: First radio transmission path 9: Second radio transmission path 10: Terminal line 20: Carrier frequency sequence unit 21: Inhibit/enable unit 22: Random number generator 23: Processor 24: Detection device 25: Shift register 26: Adder 27: Feedback 28: Addition 29: Decision 30: Decrease 31: Conversion 32: Shifting fx: Carrier frequency Rx: Frame Zx: Time slot
Claims (9)
1. Method for generating a random number sequence which is converted into carrier frequencies fx for a mobile radio transmission (8), characterized by the following steps:
- provision of a shift register (25) with n bits, - feedback modulo-2 addition (26) of one bit of the shift register (25) with at least one other bit of the shift register (25), - cyclic shifting of the register content by one bit, - insertion of the result of the modulo-2 addition (26) into the bit position freed by the shifting-operation, and - conversion (23) of the content of the shift register (25) into a carrier frequency fx for a mobile radio transmission.
- provision of a shift register (25) with n bits, - feedback modulo-2 addition (26) of one bit of the shift register (25) with at least one other bit of the shift register (25), - cyclic shifting of the register content by one bit, - insertion of the result of the modulo-2 addition (26) into the bit position freed by the shifting-operation, and - conversion (23) of the content of the shift register (25) into a carrier frequency fx for a mobile radio transmission.
2. Method according to Claim 1, characterized in that the feedback (27) is altered in order to generate different sequences.
3. Method according to one of the preceding claims, characterized in that the step (23) of converting the content of the shift register into y carrier frequencies fx has the following steps:
a) addition (28) of the content of the shift register to a current carrier frequency fx n-1, b) decision (29) as to whether the result of the addition (28) is greater than the number y of carrier frequencies fx, c) if the decision (29) is positive, decrementing (30) of the result of the addition by the number y until the decision (29) turns out negative, d) if the decision (29) turns out negative, use (31) of the result of the addition of a) as the next carrier frequency fx n, and e) shifting (32) of the shift register (25).
a) addition (28) of the content of the shift register to a current carrier frequency fx n-1, b) decision (29) as to whether the result of the addition (28) is greater than the number y of carrier frequencies fx, c) if the decision (29) is positive, decrementing (30) of the result of the addition by the number y until the decision (29) turns out negative, d) if the decision (29) turns out negative, use (31) of the result of the addition of a) as the next carrier frequency fx n, and e) shifting (32) of the shift register (25).
4. Device for generating a random number sequence for conversion into carrier frequencies fx for a mobile radio transmission, characterized by:
- a shift register (25) with n bits, - an addition device (26) for the modulo-2 addition of one bit of the shift register (25) with at least one other bit of the shift register (25) after the meaner of a feedback (27), - the register content being shifted cyclically by one bit, - the result of the addition device (26) being inserted into the bit position freed by the shifting operation, and - a device (23) for converting the content of the shift register (25) into a carrier frequency fx for a mobile radio transmission (8) being provided.
- a shift register (25) with n bits, - an addition device (26) for the modulo-2 addition of one bit of the shift register (25) with at least one other bit of the shift register (25) after the meaner of a feedback (27), - the register content being shifted cyclically by one bit, - the result of the addition device (26) being inserted into the bit position freed by the shifting operation, and - a device (23) for converting the content of the shift register (25) into a carrier frequency fx for a mobile radio transmission (8) being provided.
5. Device according to Claim 4, characterized in that the feedback (27) can be altered in order to generate different sequences.
6. Device according to either of Claims 4 and 5, characterized in that the device (23) for converting the content of the shift register (25) into y carrier frequencies fx furthermore has:
a) means (28) for adding the content of the shift register (25) to the current carrier frequency fx n-1, b) means (29) for deciding whether the result of the addition (28) is greater than the number y of the carrier frequencies, in which case, c) if the decision (29) is positive, the result of the addition is decreased by the number y until the decision (29) turns out negative, d) if the decision (29) turns out negative, the result of the addition (28) of a) is used (30) as the next carrier frequency fx n, and then e) the shift register (25) is shifted (31).
a) means (28) for adding the content of the shift register (25) to the current carrier frequency fx n-1, b) means (29) for deciding whether the result of the addition (28) is greater than the number y of the carrier frequencies, in which case, c) if the decision (29) is positive, the result of the addition is decreased by the number y until the decision (29) turns out negative, d) if the decision (29) turns out negative, the result of the addition (28) of a) is used (30) as the next carrier frequency fx n, and then e) the shift register (25) is shifted (31).
7. Device according to one of Claims 4 to 6, characterized in that the shift register (25) has 16 bits.
8. Device according to one of Claims 4 to 7, characterized in that the shift register (25) is implemented in an 8-bit or 16-bit processor.
9. Mobile radio transceiver, characterized in that it has a device (22, 23) according to one of Claims 4 to 8.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/DE1997/001734 WO1999009668A1 (en) | 1997-08-14 | 1997-08-14 | Method and device for producing a random number sequence for carrier frequencies in a mobile radiotelephone system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2300064A1 true CA2300064A1 (en) | 1999-02-25 |
Family
ID=6918534
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002300064A Abandoned CA2300064A1 (en) | 1997-08-14 | 1997-08-14 | Method and device for generating a random number sequence for carrier frequencies of a mobile radio transmission |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP1002375A1 (en) |
| CA (1) | CA2300064A1 (en) |
| WO (1) | WO1999009668A1 (en) |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4066964A (en) * | 1967-01-06 | 1978-01-03 | Rockwell International Corporation | Communication system |
| IN159180B (en) * | 1982-01-27 | 1987-04-04 | Marconi Co Ltd | |
| IL82561A (en) * | 1986-05-27 | 1991-12-15 | Fairchild Weston Systems Inc | Secure communication system for multiple remote units |
| NL8700930A (en) * | 1987-04-17 | 1988-11-16 | Hollandse Signaalapparaten Bv | SYSTEM OF ORTHOGONALLY OPERATING CODE GENERATORS, RADIOS EQUIPPED WITH A CODE GENERATOR AND CODE GENERATORS OF SUCH A SYSTEM. |
| US5031129A (en) * | 1989-05-12 | 1991-07-09 | Alcatel Na Network Systems Corp. | Parallel pseudo-random generator for emulating a serial pseudo-random generator and method for carrying out same |
| SE9200607D0 (en) * | 1992-02-28 | 1992-02-28 | Ericsson Telefon Ab L M | COMMUNICATION METHODS AND MEAN IN A TDMA CELLULAR MOBILE RADIO SYSTEM |
| US5394433A (en) * | 1993-04-22 | 1995-02-28 | International Business Machines Corporation | Frequency hopping pattern assignment and control in multiple autonomous collocated radio networks |
-
1997
- 1997-08-14 WO PCT/DE1997/001734 patent/WO1999009668A1/en not_active Application Discontinuation
- 1997-08-14 CA CA002300064A patent/CA2300064A1/en not_active Abandoned
- 1997-08-14 EP EP97938761A patent/EP1002375A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP1002375A1 (en) | 2000-05-24 |
| WO1999009668A1 (en) | 1999-02-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5940765A (en) | Radio communications systems and methods for jittered beacon transmission | |
| US6028853A (en) | Method and arrangement for radio communication | |
| KR100203002B1 (en) | Synchronization communication environment supply method | |
| EP0477862B1 (en) | Spread spectrum communications system | |
| US6041046A (en) | Cyclic time hopping in time division multiple access communication system | |
| JP3683399B2 (en) | System and method for generating spread spectrum code position modulated waveforms | |
| JP4128747B2 (en) | Access method in channel hopping communication system | |
| EP1080547B1 (en) | Frequency-hopping radio system with hybrid direct-sequence/frequency-hopping mode during startup | |
| AU767521B2 (en) | Method for forming or detecting a signal sequence and transmitter unit and receiver unit | |
| US7522689B2 (en) | Clock recovery in communication systems | |
| US6496532B1 (en) | Frequency hopping method and radio system | |
| CA2300068A1 (en) | Method and device for generating a carrier frequency | |
| EP1738480B1 (en) | Device for use in a frequency hopping system | |
| US5995571A (en) | Synchronizing apparatus for spread spectrum communications | |
| WO2002025832A2 (en) | System and method for avoiding interference in spread spectrum systems | |
| CA2300064A1 (en) | Method and device for generating a random number sequence for carrier frequencies of a mobile radio transmission | |
| EP1262029B1 (en) | System and method for adaptive carrier occupancy in a frequency hopping spread spectrum system | |
| US7133390B1 (en) | Method and system for logging on a mobile unit at a fixed station | |
| KR100473738B1 (en) | Wireless Transceiver Synchronization Method and Apparatus in Cellular System | |
| CA2300067A1 (en) | Method and transmission system for the signalling of a carrier frequency | |
| JPH07183828A (en) | Spread spectrum transmitter and receiver | |
| JPH09247049A (en) | Fast frequency hopping transmitting method and device for the same | |
| JPH07264097A (en) | Spatial transmission method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20030814 |