DE10211235A1 - Generating frequency hopping frequency sequence involves dividing available frequency band into defined number of non-overlapping sub-bands, selecting defined bands per time marker of hopping timer - Google Patents

Abstract

The method involves determining a periodic step frequency sequence by specifying a hop bandwidth and an n-ary integral sequence. It involves dividing the available frequency band into a non-overlapping sub-bands and using a first periodic sequence to select a defined band per time marker of a hopping timer. Each sub-band has a defined number of different hop frequencies. A second periodic sequence is used to select a defined band per time marker. The method involves determining a periodic frequency hopping step frequency sequence by specifying a frequency hop bandwidth and an n-ary integral sequence. It involves dividing the available frequency band into a defined number of non-overlapping sub-bands and using a first periodic sequence to select a defined band per time marker of a frequency hopping timer. Each sub-band contains a defined number of different hop frequencies and a second periodic sequence is used to select a defined band per time marker of a frequency hopping timer in order to satisfy a given relationship between frequency and bandwidth.

Description

The invention relates to a method for generating frequency hopping Frequency sequence according to the preamble of claim 1.

Frequency hopping FH is a well-known method in the field of wireless Communication to counter frequency-selective fading and interference. The transmission frequency (carrier frequency) jumps over a wide range Frequency band according to a set hop frequency sequence, which both the Sender as well as the receiver is known. For transmission channels with frequency-dependent transmission conditions and relatively high error rates can be achieved using frequency Hopping to ensure that transmission is of sufficient quality and sufficiently low error rate occurs. Combined with Error monitoring methods - such as FEC (Forward Error Correction) or ARQ (Automatic Repeat Request) - is often a reliable one using a frequency hopping system Communication achievable.

The basics of frequency hopping are, for example, from J.G. Proakis, Digital Communications, McGraw Hill, 1983, Section 8.3, pp. 580-587.

Furthermore, reference is made to the specialist book K. Dostert, Powerline Kommunikation, Francis Verlag GmbH Poing, 2000, pages 116-123.

With standardized wireless communication with frequency hopping these are Frequency hopping Frequency sequences are often defined as pseudo-random sequences. It is it is possible to use periodic frequency hopping hop frequency sequences like this determine that the frequency sequences have little correlation, which in particular is of great importance if frequency hopping is used for multiple access becomes.

A frequency hopping frequency sequence can be represented by an n-ary integer sequence X (.). An n-ary representation is generally a representation based on 1, 2, 3.. ., n characters or numbers. The clock pulse of the frequency hopping clock generator reads the integer component of the sequence with index i

X (i) ∈ [0. .n - 1]

which is then used when the current transmission frequency f (i) = f ₀ + X (i) .B _H is formed, where f _{0 represents} the predefined base frequency and B _H the predefined frequency hopping bandwidth. With a suitable selection of the number of links, the frequency hopping frequency sequence spans the entire assigned frequency band over its period, ie all frequencies of this frequency band are used, always taking into account the frequency hopping bandwidth.

For this, reference is made to A. A. Shaar and P. A. Davies, "A survey of one-coincidence sequences for frequency-hopped spread spectrum systems ", IEE Proceedings, Vol. 131, Pt.F, No. 7, December 1984, pp. 719-724.

The known periodic frequency hopping jump frequency sequences do not take into account the frequency spacing between immediately successive frequency jumps. As a result, consecutive transmissions often have high error rates, especially if there are immediately consecutive frequency hops at similar frequencies, in those cases where the coherence bandwidth of the transmission channel influenced by fading is large or where an interference signal with a large bandwidth - compared to the frequency hopping - Bandwidth B _{H of} the frequency hopping system - occurs.

Such an occurrence of errors during the successive transmission can not be satisfactorily through failure monitoring procedures be corrected if high demands regarding the tolerable There is a total transmission delay.

The invention has for its object a method for generating a optimized frequency hopping frequency sequence in wireless communication systems specify.

This task is combined with the features of the generic term solved according to the invention by the features specified in the characterizing part of claim 1.

The advantages that can be achieved with the invention are in particular that a Method for generating a frequency hopping frequency sequence is proposed at the immediately successive frequency hops in terms of their frequency advantageously have a wide distance.

Further advantages are evident from the description below.

Advantageous embodiments of the invention are in the subclaims characterized.

The invention is illustrated below with reference to that in the single drawing Embodiment explained in more detail.

• 1. Das verfügbare Gesamt-Frequenzband wird in eine Anzahl n_B nicht überlappende Teil-Frequenzbänder aufgeteilt, so daß diese n_B Teil-Frequenzbänder zusammen das zur Verfügung stehende Gesamt-Frequenzband vollständig abdecken, wobei jedes Teil-Frequenzband eine Anzahl n_I unterschiedliche Sprungfrequenzen enthält. Die Bandbreite eines Teil-Frequenzbandes
  
  B_S = n_I.B_H
  
  muß größer sein als die Bandbreite von auftretendem Fading oder von auftretenden Interferenzen. Eine ganzzahlige Folge W(.) wird benutzt, um ein bestimmtes Teil- Frequenzband bei jeder Zeitmarke n des Frequency Hopping Taktgebers auszuwählen, wobei für die ganzzahligen Komponenten W(j) der Folge W(.) mit Index j gilt:
  
  W(j) ∈ [0. .n_B - 1].
  

The details of the method according to the invention are as follows:

• 1. The available total frequency band is divided into a number n _{B of} non-overlapping sub-frequency bands, so that these n _B sub-frequency bands together completely cover the available total frequency band, each sub-frequency band having a number n _I different hopping frequencies contains. The bandwidth of a sub-frequency band
  
  B _S = n _I .B _H
  
  must be greater than the range of fading or interference that occurs. An integer sequence W (.) Is used to select a specific sub-frequency band at each time stamp n of the frequency hopping clock generator, where the integer components W (j) of the sequence W (.) With index j apply:
  
  W (j) ∈ [0. .n _B - 1].
  

When the sub-frequency band is selected, a separate integer sequence X (.) Determines the hopping frequencies within this sub-frequency band, whereby for the integer components X (i) of the sequence X (.) With i terms:

X (i) ∈ [0. .n _I - 1].

The current transmission frequency is then f

f = f ₀ + WB _S + XB _H.

• 1. Eine spezielle und bevorzugte Art der Erzeugung derartiger Frequency Hopping Frequenzfolgen mit geringer Kreuzkorrelation beginnt mit der Auswahl aus zwei separaten Gruppen von periodischen Folgen W und X
  
  W = {W₁(j), . . .W_K(j)} (erste Gruppe) und
  
  X = {X₁(i), . . .X_I(i)} (zweite Gruppe),
  
  wobei geringe Kreuzkorrelation bei den Folgen innerhalb einer jeden Gruppe auftritt. K entspricht dabei der Anzahl der nicht überlappenden Teil-Frequenzbänder und I der Anzahl der Sprungfrequenzen eines Teil-Frequenzbandes, d. h. es gibt prinzipiell K unterschiedliche Folgen W und I unterschiedliche Folgen X mit guten Korrelationseigenschaften. Somit sind bei Kombination beider ausgewählten Folgen K.I unterschiedliche Kombinationen und damit Folgen realisierbar. Die Auswahl einer Folge aus den Gruppen erfolgt durch Vorgabe von c_o und c_i, wobei c_o eine ausgewählte Zahl zwischen 1 und K sowie c_i eine ausgewählte Zahl zwischen 1 und I ist. Die ausgewählten Folgen werden dann entsprechend
  
  f = f₀ + W_co(j).B_S + X_ci(i).B_H,
  
  miteinander kombiniert, um Frequenzfolgen zu erzeugen, welche ebenfalls wie gewünscht niedrige Kreuzkorrelation haben. W_co(j) und X_ci(i) repräsentieren somit die ausgewählten, geeigneten Folgen zur Generierung der Übertragungsfrequenzen.

Since W changes at every time stamp of the frequency hopping clock generator, this proposed frequency hopping method generates, as desired, frequency sequences with successive frequency hops, the frequency spacing of which inevitably corresponds to the bandwidth B _{S of} a sub-frequency band.

• 1. A special and preferred way of generating such frequency hopping frequency sequences with low cross correlation begins with the selection from two separate groups of periodic sequences W and X.
  
  W = {W ₁ (j),. , .W _K (j)} (first group) and
  
  X = {X ₁ (i),. , .X _I (i)} (second group),
  
  with low cross correlation in the consequences within each group. K corresponds to the number of non-overlapping sub-frequency bands and I to the number of hopping frequencies of a sub-frequency band, ie there are in principle K different sequences W and I different sequences X with good correlation properties. Thus, when combining the two selected AI sequences, different combinations and thus sequences can be realized. A sequence is selected from the groups by specifying c _o and c _i , where c _{o is} a selected number between 1 and K and c _{i is} a selected number between 1 and I. The selected episodes will then be corresponding
  
  f = f ₀ + W _co (j) .B _S + X _ci (i) .B _H ,
  
  combined with each other to produce frequency sequences which also have low cross-correlation as desired. W _co (j) and X _ci (i) thus represent the selected, suitable sequences for generating the transmission frequencies.

• 1. Bei bidirektionalen Übertragungen - beispielsweise für Uplink UL und Downlink DL eines zellulären drahtlosen Frequency Hopping Kommunikations Systems - kann das erfindungsgemäße Verfahren auf ein Frequency Division Duplex (FDD) System mit Frequency Hopping ausgedehnt werden, wobei Uplink UL und Downlink DL vorteilhaft das gleiche Gesamt-Frequenzband benutzen können und dennoch in jedem Augenblick ein großer Frequenzabstand zwischen einer Uplink-Übertragung und einer Downlink-Übertragung sichergestellt ist. Ein derart großer Duplex-Abstand ist bei Funkübertragungen wünschenswert. Mit anderen Worten: Es ist zur Implementierung eines Duplex Frequency Hopping Systems vorteilhaft nicht erforderlich, unterschiedliche, nichtüberlappende Frequenzbänder vorzugeben. Dies wird erreicht, indem folgende Zuteilungen erfolgen:
  Übertragungsfrequenz bei Downlink: f^DL = f₀ + W_co(j).B_S + X_ci(i).B_H
  Übertragungsfrequenz bei Uplink: f^UL = f₀ + ((W_co(j) + n_I/2)mod n_B).B_S + X_ci(i).B_H.

In particular, the measures according to the document AA Shaar and PA Davies, "A survey of one-coincidence sequences for frequency-hopped spread spectrum systems", IEE Proceedings, Vol. 131, Pt.F, No. 7, December 1984, pp. 719-726 can be used to obtain periodic sequences W and X with low correlation. If these sequences W or X have a period p _W (≍ n _B ) or p _X (≍ n _I ) in accordance with this document, then the time stamps n of the clock of the frequency hopping system should be corresponding
j = n mod p _W and
i = n mod p _X
can be classified to select W _co (j) and X _ci (i). The resulting sequences have a period p _W .p _X (Note: a mod b is used to determine the remainder of the division for integer division, e.g. 0 mod 4 = 0, 1 mod 4 = 1, 2 mod 4 = 2, 3 mod 4 = 3 , 4 mod 4 = 0, 5 mod 4 = 1, 6 mod 4 = 2...)

• 1. In the case of bidirectional transmissions - for example for uplink UL and downlink DL of a cellular wireless frequency hopping communication system - the method according to the invention can be extended to a frequency division duplex (FDD) system with frequency hopping, with uplink UL and downlink DL advantageously having the same total -Frequency band can be used and yet a large frequency spacing between an uplink transmission and a downlink transmission is ensured at any moment. Such a large duplex distance is desirable for radio transmissions. In other words: to implement a duplex frequency hopping system, it is advantageously not necessary to specify different, non-overlapping frequency bands. This is achieved by making the following allocations:
  Downlink transmission frequency: f ^DL = f ₀ + W _co (j) .B _S + X _ci (i) .B _H
  Transmission frequency with uplink: f ^UL = f ₀ + ((W _co (j) + n _I / 2) mod n _B ) .B _S + X _ci (i) .B _H.

This modification uses the same frequencies and ensures that between the frequencies f ^DL , f ^UL used in the downlink direction and in the uplink direction there is at any moment a frequency distance represented by at least one partial frequency band.

Overall, the proposed method ensures that between successive frequency hops of a group of a frequency hopping frequency sequence there is a large frequency spacing and low correlation. With additional combination with error monitoring methods such as FEC (Forward Error Correction) and / or ARQ (Automatic Repeat Request), the proposed method ensures a reliable, low-delay data transmission (with low Total transmission delay). In addition, the proposed method can be simple and How to use a Frequency Division Duplex (FDD) scheme Realize system with frequency hopping in a common frequency band.

The proposed method is both for the "Slow (Slow) Frequency Hopping "as well as" Fast (Fast) Frequency Hopping ", in which a Change of time stamps for each TDMA frame at a TDMA System (Time Division Multiple Access), occurs with every symbol or with every chip.

• - n_B = 4, d. h. vier Teil-Frequenzbänder, Periode p_W = 4:
• - n_I = 17, d. h. 17 Übertragungsfrequenzen pro Teil-Frequenzband, Periode P_X = 17,
• - f₀ = 2404 MHz,
• - Frequenzsprung-Bandbreite B_H = 1 MHz,
• - Bandbreite eines Teil-Frequenzbandes B_S = 20 MHz,
• - Die Folge W_co ist willkürlich (als eine von vier Möglichkeiten) gewählt zu:
  3 2 1 0
• - Die Folge X_ci ist willkürlich (als eine von 17 Möglichkeiten) gewählt zu:
  0 12 7 2 14 9 4 16 11 6 1 13 8 3 15 10 5
• - Die kombinierten Folgen für f^DL (Downlink) und f^UL (Uplink) haben jeweils eine Periode p_W.p_X = 68

The single figure shows an exemplary embodiment of a bidirectional frequency hopping system operated in accordance with the method according to the invention in the 2.4 GHz frequency band. There are time stamps n of the clock generator in the range 0. .67 and the assigned transmission frequencies f (n) in the range 2400.. .2480 MHz shown. The following applies to the exemplary embodiment:

• - n _B = 4, ie four sub-frequency bands, period p _W = 4:
• - n _I = 17, ie 17 transmission frequencies per sub-frequency band, period P _X = 17,
• - f ₀ = 2404 MHz,
• - frequency hopping bandwidth B _H = 1 MHz,
• Bandwidth of a sub-frequency band B _S = 20 MHz,
• - The sequence W _co is chosen arbitrarily (as one of four possibilities) to:
  3 2 1 0
• - The sequence X _ci is chosen arbitrarily (as one of 17 possibilities) to:
  0 12 7 2 14 9 4 16 11 6 1 13 8 3 15 10 5
• - The combined sequences for f ^DL (downlink) and f ^UL (uplink) each have a period p _W .p _X = 68

• - das erste Teil-Frequenzband den Bereich von 2404 MHz bis 2420 MHz,
• - das zweite Teil-Frequenzband den Bereich von 2424 MHz bis 2440 MHz,
• - das dritte Teil-Frequenzband den Bereich von 2444 MHz bis 2460 MHz,
• - das vierte Teil-Frequenzband den Bereich von 2464 MHz bis 2480 MHz.

As can be seen in the figure, the four sub-frequency bands cover the following frequency ranges:

• - the first sub-frequency band covers the range from 2404 MHz to 2420 MHz,
• - the second sub-frequency band covers the range from 2424 MHz to 2440 MHz,
• - the third sub-frequency band covers the range from 2444 MHz to 2460 MHz,
• - The fourth sub-frequency band covers the range from 2464 MHz to 2480 MHz.

In the figure, the frequency hops taking place at downlink DL are shown with a full circle and a solid line, while the frequency hops taking place at uplink are shown by means of a circular ring and dashed lines. For the frequency hops taking place at Downlink, the relationships according to the following table apply (the beginning of a period of the sequences W _co and X _ci is marked):

example

For the time stamp n = 41, this results from the relationship given above

f ^DL = f ₀ + W _co (j) .B _S + X _ci (i) .B _H → f ^DL = 2404 + 3.20 + 4.1 = 2468 MHz.

The method according to the invention can advantageously be used in combination with an error monitoring method - such as FEC (Forward Error Correction) and / or ARQ (Automatic Repeat Request) - the signal repetitions or redundancies used in these error monitoring methods in successive hopping frequencies and thus (by the inventive Depending on the method) take place in different of the non-overlapping sub-frequency bands, so that within successive transmissions it is very likely that individual transmissions will take place undisturbed. In combination of the method according to the invention with the known methods FEC or ARQ, this results in a secure transmission of data with the desired small delay. List of reference symbols B _H Frequency hopping bandwidth
B _S bandwidth of a sub-frequency band
c _o selected number between 1 and K
c _i selected number between 1 and I.
DL downlink
f ₀ base frequency
f, f (i) current transmission frequency
f ^DL transmission frequency with downlink
f ^UL transmission frequency for uplink
FH frequency hopping
i index in sequence X
I Number of hopping frequencies in a sub-frequency band
j Index in the sequence W
K Number of separate sub-frequency bands
n Timestamp of the clock
n _B Number of separate sub-frequency bands
n _I Number of hopping frequencies in a sub-frequency band
p _W period of the sequence W
p _X period of the sequence X
UL uplink
W (.) Integer sequence
W (j) ∈ [0. , .n _B - 1] integer components of the sequence
W = {W ₁ (j),. , .W _K (j)} group of periodic sequences
W _co (j) episode
X _ci (i) sequence
X (i) ∈ [0. , .n _I - 1] integer components of the sequence
X (.) N-ary integer sequence
X = {X ₁ (i),. , .X _I (i)} group of periodic sequences

Claims (4)

1. A method for generating a frequency hopping frequency sequence, a periodic frequency hopping jump frequency sequence being defined by specifying a frequency hopping bandwidth and an n-ary integer sequence, characterized in that
that the available total frequency band is divided into a predetermined number n _B non-overlapping sub-frequency bands, each sub-frequency band having the bandwidth B _S ,
that a first n _B -ary integer periodic sequence W with index j is used to select a specific frequency band at each time stamp (s) of the frequency hopping clock generator,
that each sub-frequency band contains a predetermined number n _{I of} different hopping frequencies, the frequency hopping bandwidth being B _H ,
that a second n _I -ary integer periodic sequence X with index i is used to select a specific hopping frequency at each time stamp (s) of the frequency hopping clock generator,
so that the current transmission frequency is f:
f = f ₀ + WB _S + XB _H ,
where f _{0 is} the base frequency. 2. The method according to claim 1, characterized by the use of a Error monitoring method - such as FEC (Forward Error Correction) and / or ARQ (Automatic Repeat Request) - being the ones used in these procedures Signal repetitions or redundancies in successive hopping frequencies and thus in different of the non-overlapping sub-frequency bands. 3. The method according to claim 1 or 2, characterized in that to form a frequency hopping frequency sequence with low cross-correlation, a selection W _co (j), X _ci (i) is made from two separate groups of periodic sequences W and X: - W = {W ₁ (j),. , .W _K (j)}, - X = {X ₁ (i),. , .X _I (i)}, where low cross correlation occurs in the sequences within each group, K corresponds to the number of non-overlapping sub-frequency bands and I corresponds to the number of hopping frequencies of a sub-frequency band. 4. The method according to claim 3, characterized in that for bidirectional transmission uplink UL and downlink DL use the same total frequency band, the following applies to the transmission frequency f ^DL for downlink and for the transmission frequency for uplink f ^UL : - f ^DL = f ₀ + W _co (j) .B _S + X _ci (i) .B _H - f ^UL = f ₀ + ((W _co (j) + n _I / 2) mod n _B ) .B _S + X _ci (i) .B _H.