WO1999066653A1

WO1999066653A1 - Method and device for converting a random number sequence into carrier frequencies for mobile radio transmission

Info

Publication number: WO1999066653A1
Application number: PCT/DE1998/001685
Authority: WO
Inventors: Jürgen KOCKMANN; Olaf Dicker
Original assignee: Siemens Aktiengesellschaft
Priority date: 1998-06-18
Filing date: 1998-06-18
Publication date: 1999-12-23
Also published as: EP1088404A1; CA2335302A1

Abstract

The current invention relates to a method and a device for converting a random number sequence into carrier frequencies fx for mobile radio transmission. A shift register (25) with a register content of n bits is provided. The register content is shifted by 1 bit, whereupon a decision is made as to whether the value of a number of k bits of the register content is greater than the overall number Y of possible carrier frequencies fx, whereby k is less than or equal to n. If the decision is positive, the value of the k bits is used to select the next carrier frequency fx. The carrier frequency is selected, for instance, from a table in which the possible carrier frequencies are allocated to certain positions. The inventive method and the inventive device can be carried out and used in a mobile radio device in an easy, reliable and economical manner.

Description

description

Method and device for converting a random number sequence m carrier frequencies for a mobile radio transmission

The present invention relates to a method and a device for converting a random number sequence m carrier frequencies for a mobile radio transmission.

The so-called Frequency Hopper Spread Spectrum (frequency hopping spread spectrum) system is known as a method for the transmission of data on several carrier frequencies. A frequency spectrum spread spectrum system is understood to mean a system in which a large number of carrier frequencies are provided for the radio transmission of data and the carrier frequency currently used is changed periodically. In a time division multiplex (TDMA) system in particular, the carrier frequency can be changed after each time slot or time frame of the time division multiplex transmission (or a multiple thereof). Such a frequency hopping spread spectrum system has advantages in that the energy of the entire radio transmission is distributed over all carrier frequencies. This is particularly important when a generally detectable frequency band, such as the 2.4 GHz ISM (Industrial, Scientific, Medical) band, is used. For the use of this frequency band the einschlagigen rules to keep interference with other subscribers as low as MOG borrowed, according to (FCC part 15) sets a limit on the maximum per carrier frequency occurring energy Festge ^¬. Furthermore, the FCC part 15 stipulates that at least 75 different carrier frequencies must be provided.

In the DECT standard, 24 time slots, 12 each for upl k and for downlmk, are defined in a 10 ms frame. However, the FCC part 15 only provides a bandwidth of less than 1 MHz for the ISM band. To meet this requirement the number of time slots was reduced to 12 time slots in a 10 ms time frame, ie 6 time slots each for uplink and for downlink.

With 6 time slots for each direction and while maintaining the DECT time frame of 10 ms, each time slot would have a length of 833 μs. The time slots in the DECT standard have a length of 417 μs. In the case of a slow frequency hopping system, an inactive DECT time slot of 417 μs between adjacent active time slots in which data is transmitted is required. With such systems, only 6 active time slots in each direction are used for data transmission. If such systems, which operate on the basis of slow frequency hopping, are also to meet the requirements of FCC part 15 in the ISM band, an inactive blind time slot of 417 μs must also be present between adjacent active time slots. This blind time slot thus has half the length of a full time slot of 833 μs, which means that if a base time frame of 10 ms is maintained, four active time slots are available in each frame for uplink and downlink, between each of which blind time slots are sent. The four active time slots each have a length of 833 μs, while the blind time slots each have a length of 417 μs. With this structure, frequency programming for frequency hopping in the next following active time slot can also be carried out at the end of the previous active time slot. During the blind time slots, the programmed initial sequence can be set in the next active time slot.

An advantage of the frequency hopping spread spectrum system is that by providing a large number of carrier frequencies, the system becomes less sensitive to interference. In addition, the system's security against eavesdropping is increased, as the third party gel does not know which carrier frequency will be changed after a certain period of time.

The sequence of carrier frequencies that are used for transmission one after the other is determined by an algorithm. Such an algorithm is implemented in an identical manner in the base station and in each mobile station of the mobile radio transmission. If a mobile part is thus synchronized with the associated base station, the handset and the base station will synchronously carry out the carrier frequency changes specified by the sequence of the (identical) algorithm.

The algorithm should ensure that each carrier frequency is used the same number of times and for the same length of time.

FCC part 15 stipulates that at least 75 different frequencies must be used within a period of 30 ms, whereby each frequency may be used for a maximum of 0.4 s. On average, all frequencies must be used equally frequently. As a rule, the base stations and the associated mobile stations each have identical random number generators, on the basis of which the algorithm for selecting or assigning the carrier frequencies works. The different carrier frequencies and associated Tragerfrequenzwerte can, for example, m be stored in a table, wherein each Tra ^¬ associated gerfrequenz a specific position. The polyvinyl sition will pay generator determined by the algorithm on the basis of chance ^¬, the particular carrier frequency is read out from the table.

The present invention has for its object to provide a method and a device which enable simple implementation of a random number sequence m carrier frequencies for a mobile radio transmission. This task is solved by the features of the independent claims. The dependent claims develop the invention in a particularly advantageous manner.

According to the invention, a method for implementing a random number sequence is provided for carrier frequencies for a mobile radio transmission. A shift register with a register content of n bits is provided. The register content is shifted by 1 bit. A decision is then made as to whether the value of a number of k bits in the register content is greater than a total number y of possible carrier frequencies, where k is less than n. If this decision is positive, the register content is shifted again by 1 bit and the decision is repeated. If the decision is negative, the value of the k bits is used to select a next carrier frequency.

Advantageously, the k bits are consecutive lower bits (least significant bits) of the shift register. Since at least 75 carrier frequencies may be used in FCC part 15, but a maximum of 96 carrier frequencies are available, it is particularly advantageous if k = 7, since values from 0 to 127 can be generated with 7 bits, so that the maximum of 96 address values of the carrier frequencies or the carrier frequency values m in the table can be generated.

Advantageously, the shift register comprises 16 bits, so that the shift register can easily be implemented in 8- and 16-bit processors.

According to the present invention, a device for converting a random number sequence m carrier frequencies is further provided for a mobile radio transmission. This device comprises a shift register with a register content of n bits. Furthermore, a device for shifting the register content by 1 bit is provided. The invention The device additionally comprises a device for deciding whether the value of a number of k bits of the register content is greater than a total number y of possible carrier frequencies, where k <n. If the decision is positive, the register content is shifted by 1 bit and the decision is repeated. If the decision is negative, the value of the k bits is used to select a next carrier frequency.

The k bits are advantageously successive lower bits of the shift register. It is also advantageous if the number k = 7, since up to 127 different values can be generated by 7 bits, which are used to select the maximum of 96 different carrier frequencies from the corresponding table.

It is also advantageous if the register content n of the shift register is 16. This allows the shift register to be easily implemented in 8-bit or 16-bit processors.

The invention will now be explained in more detail using an exemplary embodiment and with reference to the accompanying drawings. Show it:

1 shows a mobile radio transmission system with a base station according to the invention,

2 shows a time frame of a data transmission standard as can be used in the present invention,

Fig. 3 shows in detail the internal structure of a base station according to the invention, and

4a shows a shift register as used in the present invention. Fig. 4b the content of the shift register for the different clocks of a period, and

Fig. 5 em flow chart to explain the method and the device for implementing the random sequence m carrier frequencies.

1, the general structure of a mobile radio transmission will be explained first. As is generally customary, the arrangement for radio transmission of data has a base station 1 and a plurality of mobile parts (mobile stations), wireless telephones 2, 3 .... The base station 1 is connected to the fixed network by a terminal line 10. An interface device, which is not shown, can be provided for communication between the base station 1 and the terminal line 10. The base station 1 has an antenna 6, by means of which communication with the mobile part 3 takes place, for example, via a first radio transmission path 8 with the mobile part 2 or via a second radio transmission path 9. The handsets 2, 3 ... each have an antenna 7 for receiving or transmitting data. 1 schematically shows the state in which the base station 1 actively communicates with the mobile part 2 and thus exchanges data. The handset 3, on the other hand, is in the so-called idle locked mode, in which it waits stand-by for a call from the base station 1. In this state, the mobile part 3 does not communicate with the base station 1, but rather only periodically receives the data, for example of a time slot, from the base station in order to be able to re-synchronize with the carrier frequencies fx.

The internal structure of base station 1 is shown schematically in FIG. 1. The voice information data are fed to an RF module 4, which is carried out by a carrier frequency sequence unit is controlled. The exact structure of a base station 1 according to the invention will be described later.

With reference to FIG. 2, a transmission standard that can be used in the present invention will now be explained. As can be seen from FIG. 2, data in a plurality of time slots, in the illustrated case 24 time slots Zx, in a time division multiplex method TDMA (Time Division Multiple Access) are transmitted in succession on a plurality of carrier frequencies fx, ten of which are shown. In the case shown, work is carried out in alternating mode (duplex), i. that is, after the first twelve time slots Zx have been transmitted by base station 1, the system switches to reception and receives the second twelve time slots (Z13 to Z24) from one or more mobile stations in the opposite direction.

In the event that the so-called DECT standard is used for transmission, the time duration of a time frame is 10 ms, and 24 time slots Zx are provided, namely twelve time slots for the transmission from the base station to handsets and a further twelve time slots Zx for transmission from the handsets to the base station. 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 with a number of timeslots halved compared to the DECT standard.

However, the present invention also finds particular application 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. According to FCC part 15, at least 75 carrier frequencies fx must be distributed over this 83.5 MHz. A division of the bandwidth of 83.5 is particularly advantageous MHz on 96 carrier frequencies, ie a channel spacing of 864 kHz. The frequency bands and standards mentioned above are given purely as an example. The basic requirement for applicability in the present invention is that a so-called frequency hopping spread

Spectrum is used, d. H. that several carrier frequencies are available and that the carrier frequency selected for transmission is changed periodically. For such a change, it is advantageous if the data are transmitted in time slots Zx (time division multiplex method). For example, the DECT standard and any other modified standard based on this DECT standard are suitable.

The internal structure of a base station 1 according to the invention will now be explained in more detail with reference to FIG. 3. As can be seen in FIG. 3, the RF module 4 is supplied with information data if the base station 1 is to transmit to a handset 2, 3 Data can be received from handsets. The RF module 4 modulates the digitally coded information data onto a carrier frequency fx. The carrier frequency fx currently to be used is predetermined by a carrier frequency sequence unit, which is generally designated 20. A detection device 24 is provided in the carrier frequency sequence unit 20, to which the demodulated signal is supplied by the RF module 4. Interference means that there is either a disturbance in the actual sense or an assignment by another transmitter. A disturbance in the sense of the present description can thus be detected, for example, by demodulating a received signal on a carrier frequency and by determining whether a signal level is present on this carrier frequency or not. In this case, a disturbed carrier frequency is a carrier frequency onto which a signal is modulated that exceeds a certain threshold value. Faults in the true sense can be detected by the occurrence of CRC errors or burst losses.

The detection device 24 thus uses the demodulated signal from the RF module 4 to determine how high the signal portion modulated onto a specific carrier frequency fx is. If the detected signal component lies above a predetermined limit value or one of the abovementioned errors has occurred, the detection device 24 emits the fault detection signal to a blocking / releasing device 21 21 shows a blocking / release format to a processor 23. This blocking / release format indicates which of the carrier frequencies fx are blocked or released again due to the detection of a fault by the detection device 24, as will be explained later.

By means of the detection device 24 and the blocking / releasing device 21, an independent procedure is thus created, by means of which disturbed frequencies can be blocked and released again. In addition to the lock release information from the lock / release unit 21, the processor 23 is supplied with a sequence from a random generator 22. Based on the implied random algorithm, the random generator 22 generates a randomly distributed sequence of carrier frequency values within the predetermined frequency band. The random generator 22 thus executes a procedure which is independent of the procedure for frequency blocking in the event of a fault. The processor 23 finally sends a control signal to the RF module 4, which specifies the carrier frequency value to be used for the RF module 4.

As shown in FIG. 3 by an arrow from the processor 23 to the random number generator 22, the processor 22 specifies how many different values it is to generate. This number of values to be generated corresponds to the number of values to be generated generating carrier frequencies, which must be at least 75, for example, according to the US regulation FCC part 15.

In a mobile part in particular, the processor 23 also provides the random number generator 22 with a starting value for its algorithm. The mobile station receives this start value from the base station for synchronization, which is achieved by using the same start value and the same algorithm. With the same start value and the same algorithm, the same sequences are forcibly generated by the base station and the handset.

Base station 1 is the master in frequency allocation, i. H. at the start of a connection establishment, the random number generator is initialized in a mobile part with the state of the random number generator 22 of the base station 1. The random number generators in the handset 2, 3 ... and in the base station 1 then generate the same carrier frequency values synchronously and independently of one another.

The procedure for frequency blocking, which is carried out by the detection device 24 and the blocking / releasing unit 21, uses a unidirectional protocol on the air interface during the entire connection time between the base station 1 and a handset 2, 3. If the detection device 24 finds one of the possible frequencies fx as disturbed by the base station 1, the base station 1 thus informs all the mobile parts with which it operates connections that this disturbed frequency, if it is generated by the frequency of the random number generator, is to be replaced by another carrier frequency which is not detected as being disturbed. The random number generator 22 is not influenced by the frequency blocking. This frequency blocking is withdrawn by the blocking / release unit 21 when the blocked carrier frequency is again suitable for transmission or when it was blocked for longer than a previously defined time. 4a and 4b, it will now be explained how the random numbers can be generated by an algorithm that is simple to implement in a processor and at the same time the required computing time can be kept low.

As can be seen in FIG. 4a, the basis of the algorithm is a feedback shift register 25 with the length x, the length x being 4 in the example shown. The feedback structure of the register is I _r = {l, 4}. This means that, according to the example shown, the first bit is linked to the fourth bit by a modulo2 addition 26 and the result of this modulo2 addition 26 is put in the place of the most significant bit, this position being replaced by a Moving the register content one bit to the right becomes free.

At the beginning, the shift register 25 is loaded with the value 0001 as shown. For each new value of the contents of the shift register are shifted by one bit to the right 25, wherein as shown in each case the left bit is re-calculation ^¬ net. The type of feedback, ie in the present example the modulo2 addition of the left bit with the rightmost bit of the shift register 25 can be changed. By changing the type of feedback 27 and the number of feedback bits, different sequences with different lengths can thus be generated. The sequence length, that is the periodicity according to which the ER sired sequence repeated periodically depending on feedbackers ^¬ lung maximum of 2 ⁿ -L, where the number of bits n of the shift register 25 is. In the arrangement shown (n = 4, I _r {1, 4), the sequence length is therefore 15 (and thus maximum for a four-bit register), ie after 15 generated values, the generated values are repeated periodically. The value 0 is not generated with feedback shift registers. 4b shows how the content of the slide Beregisters 25 for the example shown in Fig. 4a for the corresponding clocks of a period.

4a is to be understood in particular as an example of the generation of random numbers by feedback shift register. In practice, for example, a 16-bit shift register can be used. Such a shift register can be easily implemented with m 8 and 16 bit processors. Due to the different possibilities of feedback 27, different sequences can be generated with a 16 bit shift register 2048. The sequence length for a 16-bit recording register is a maximum of 2 ¹⁶ -1 = 65535. Thus, if a carrier frequency corresponding to a value of the generated random sequence is maintained for the duration of a frame of, for example, 10 ms, the duration of the period is 65535 x 10 ms ~ 10.9 mm. This means that a maximum length sequence is repeated only every 10.9 mm for a 16 bit register.

The use of a random generator with the algorithm shown has the further advantage that different carrier frequency hop sequences can be generated by easy-to-define feedback couplings.

In the case of a shift register with 16 bits, the number of possible values of the sequence of the carrier frequencies is 65535 as explained. In the meantime, the number of actually used carrier frequencies can be considerably smaller and moreover variable. Thus the carrier frequency cannot be obtained directly by converting the values of the random sequence.

The values of the random sequence are used by means of the method explained in the flowchart of FIG. 5 for selecting or setting the next carrier frequency in each case. The various stages of the flowchart shown in FIG. 5 are randomized with appropriate devices. numbers generator 22 implemented. Initially, the shift register 25 is initialized with an initialization step 28 with a corresponding initialization device. The shift register can, for example, be set to the value "1". In a subsequent shift step 29, the content of the shift register is shifted by 1 bit in a corresponding shifting device. A decision step 30 m of a corresponding decision device is then used to decide whether the value of a number of k bits is greater than the total number y of the possible carrier frequencies fx. The total number y of carrier frequencies can be 96, for example. Furthermore, it is advantageous if the value k = 7, as explained above. These 7 bits are advantageously the 7 lower (least significant) bits at the beginning of the shift register 25. The 7 bits can represent a maximum of 127, while the total number of carrier frequencies is a maximum of 96. Thus, if the value of the 7 bits is greater than the total number of carrier frequencies, the process would return to step 29, in which the shift register 25 is again shifted by 1 bit. Then it is checked again whether the value of the k bits is greater than the total number of carrier frequencies. If the decision in step 30 is negative, ie if the value of the k bits is less than the total number of carrier frequencies, the corresponding value of the k bits in step 31 is used to select or to determine the next carrier frequency fx. Here, for example, the 96 possible different transmitter frequencies fx m ^¬ a table addresses from 1 to 96 conces- arranged. If the value of the k bits is 73, for example, then this value 73 is smaller than the total number 96 of the carrier frequencies. The value 73 is thus used in step 31 or m of a corresponding device for selecting the carrier frequency located at the address 73 in the table. Carrier frequency values can also be stored in the table, each of which is assigned to a specific carrier frequency. The present invention thus enables the conversion of a random number sequence into carrier frequencies in a simple manner, which is simple to implement in a processor. Furthermore, the method according to the invention and thus the device according to the invention are simple, reliable and, moreover, can be implemented without great expense, while at the same time keeping the computing time required low.

Claims

claims

1. A method for converting a random number sequence into carrier frequencies fx for a mobile radio transmission, with the following steps:

Providing a shift register (25) with a register content of n bits,

Shifting the register content by 1 bit,

Decide whether the value of a number of k bits of the register content is greater than a total number y of possible carrier frequencies fx, where k <n if the decision is positive, shift the register content by 1 bit and repeat the decision if the If the decision is negative, use the value of the k bits to select a next carrier frequency fx.

2nd A method according to claim 1, characterized in that the k bits successive lower bits of the shift registers are ^¬.

3. The method according to claim 1 or 2, characterized in that the total number y of possible carrier frequencies fx is at least 75.

4. The method according to claim 1, 2 or 3, characterized in that n is 16.

5. The method according to any one of the preceding claims, characterized in that k is 7.

6. Device for converting a random number sequence into carrier frequencies fx for a mobile radio transmission, with a shift register (25) with a register content of n bits, a device (29) for shifting the register content by 1 bit, a device (30) for deciding whether the value of a number of k bits of the register content is greater than a total number y of possible Carrier frequencies fx, where k <n, where, if the decision is positive, the register content is shifted by 1 bit and the decision is repeated, or, if the decision is negative, the value of the k bits for selecting a next carrier frequency fx is used.

7. The device according to claim 6, characterized in that the k bits are consecutive lower bits of the shift register.

8. Apparatus according to claim 6 or 7, characterized in that the total number y of the possible carrier frequencies fx min ^{¬ is at} least 75.

9. The device according to claim 6, 7 or 8, characterized in that the register content n of the shift register (25) is equal to 16.

10. Device according to one of claims 6 to 9, characterized in that the number k is 7.

11. Device according to one of claims 6 to 10, characterized in that the shift register (25) is integrated in an 8-bit or 16-bit pro ^¬ processor.