JPS594243A - Code generator for frequency selection - Google Patents

Abstract

PURPOSE:To increase remarkably the number of frequency selecting codes led out from one kind of M series formed with an n-stage in series connection shift register, by extracting a consecutive n-bit at each m-bit of the generated M series (where; m is a natural number being prime number with 2n-1 and smaller than 2n-1). CONSTITUTION:A frequency-divided signal is applied to an M series generating circuit 13 consisting of n-stage of shift registers of series connection, and the n- bit signal generated from the generating circuit 13 is applied to a latch circuit 14. On the other hand, a signal outputted from a basic clock generating circuit 11 is applied to the 2nd frequency dividing circuit 15 and frequency-givided into a period, e.g., m-times the period of the 1st frequency division circuit 12. This signal is applied to the latch circuit 14, from which the consective n-bit at each m-bit is extracted from the M series, and the frequency selecting code is produced. Thus, the number of channels possible for simultaneous communication is increased in the spread spectrum communication system using the frequency hopping system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency selection code generator used in spread spectrum communication using a frequency hollaging method (hereinafter referred to as 5SFH communication method).

As is well known, in the 5SFH communication system, if frequencies that are sequentially selected according to hopping are arranged in the order of their appearance and are called a "frequency sequence," this frequency sequence has the following properties. @Property 1) As a property of a single frequency sequence, all frequencies used must be uniformly and randomly selected during its cycle.

Property 2) To avoid crosstalk and interference between multiple 11j4 channels, there must be no correlation between frequency sequences used in both channels.

When property 2) is considered in a practical sense, it can be considered that the following judgment condition is not satisfied. That is, reference 1. shown in Figure 1. temple 2
For the frequency strings, [frequency difference at the corresponding hop point 111"-f:"I PI f2"-f2+21
, .
2 on the time axis by one hop at a time.'' However, f is determined depending on the operating method.

Conventionally, the frequency selection code (pseudorandom code) used in spray and spectrum communications is as follows:
An M-sequence is being considered which is obtained by a device in which n stages of shift registers are connected in series and the exclusive OR of the signals outputted from each of the shift registers is fed back to the input of the first stage shift register. A basic example in which this M sequence is used as a frequency selection code will be explained.

Figure 2 (,) shows a code of 27-1 obtained by setting n = 7 and feeding back the exclusive OR of the output signals of the 2.4th and 6.7th stages of the 7-stage series-connected shift register to the first stage. It is an M sequence with length. By sequentially extracting 7 consecutive bits from this M series, 63, 31 as shown in FIG.
, 79, . . . frequencies 1 to 127 can be selected in this order. This frequency sequence (generally expressed as (fi)) satisfies the above-mentioned property 1, as is well known from the properties of the M sequence. As a means of creating another frequency sequence that satisfies property 2) using this method, it is possible to create a different M sequence by changing the combination of the outputs of each stage that constitutes the feedback section. However, there are very few types of M-sequences that can be created using shift registers with the same number of stages; for example, in the case of seven stages, there are only nine types. Therefore, there are only nine channels that can communicate simultaneously in this frequency band.

This invention was made based on the above circumstances, and its purpose is to dramatically increase the number of frequency selection codes derived from one type of M sequence created by n-stage series-connected shift registers. The present invention aims to provide a frequency selection code generator capable of increasing the number of channels capable of simultaneous communication in the 5SFH communication system.

An embodiment of the present invention will be described below with reference to the drawings.

This invention also basically utilizes the M series formed by the aforementioned n-stage series-connected shift registers. However, when extracting n bits and gs for selecting the rotation number from the M series of In this invention, consecutive n bits shifted by m bits are taken out for each hog. However, m must be a natural number that is coprime to (2''-1) and smaller than (2''-1).

That is, Fig. 2(c) shows an example frequency (f'tl) with rn = 2 for the M sequence used to generate the fundamental frequency sequence (fl) in Fig. 2(b). In this frequency example, the frequency is 63°79.1
15. You will end up with a hog like... The first frequency f/ of the newly obtained frequency sequence is 8=fM using the elements of the frequency sequence (f+) in FIG. 2(b).

However, Ml = [(1-1)・m) Mod(z”-1)+
It is expressed as 1-(1). At this time, t=i, Tsuma, b
If the time point at which the frequency selected at the i-first time point appears again is the hop time point, then (I-1) ・m=(2”-1) ・P-・(2) (where P is a natural number) This holds true. Among the combinations of l and P that satisfy equation (2), the smallest ■ is 2n because m and (2''-1) are relatively prime. This corresponds to the end of one cycle of the frequency sequence. Therefore, the same frequency does not appear twice within one cycle of the frequency sequence, and all frequencies used are uniformly selected, and moreover, they are selected at random to the same degree as the basic frequency sequence. That is, the frequency string created according to the present invention satisfies property 1), and regarding property 2), it is necessary to perform a test by actually applying a judgment condition to the obtained frequency strings. After all, according to this embodiment, it is possible to generate as many frequency sequences as natural numbers that are smaller than 2n-1 at most and coprime to 2n-1 from one type of M sequence, and to use channels that can communicate simultaneously. The number can be increased.

FIG. 3 shows an example of a circuit configuration based on the above principle.

11 is a basic clock generation circuit, and the signal output from this circuit 11 is supplied to a first frequency dividing circuit 12 and divided into a predetermined period. This frequency-divided signal is supplied to an M-sequence generation circuit 13 consisting of n stages of shift renostars connected in series, and the n-bit signal generated in this generation circuit 13 is supplied to a latch circuit 14. On the other hand, the signal outputted from the basic clock generating circuit 11 is supplied to a second frequency dividing circuit 15, and is frequency-divided into a period that is, for example, m times that of the first frequency dividing circuit 12. This signal is supplied to the latch circuit 14, and from this latch circuit 14,
Consecutive n bits are extracted bit by bit, and a frequency selection code is generated.

Note that the clock frequency can be changed by configuring the first and second frequency dividing circuits 12t to 15 so that their frequency division ratios can be varied arbitrarily.

As detailed above, according to the present invention, the generated M
m pitches of the series) (m is coprime to 2n-1, and 2n
By extracting consecutive n bits and gs for every (natural number smaller than -1), the number of frequency selection codes derived from one type of M sequence created by n stages of series-connected shift registers can be dramatically increased. It is possible to provide a frequency selection code generator that can increase the number of channels that can be simultaneously communicated in the 5SFH communication system.

[Brief explanation of the drawing]

FIG. 1 is a diagram shown to explain the relationship between frequency and time in spread spectrum communication using the frequency hopping method, and FIG. FIG. 3, which is a diagram for explaining the principle of the generator, is a configuration diagram showing an embodiment of the frequency selection code generator according to the present invention. 11... Basic clock generation circuit, 12.15... 1st. Second frequency dividing circuit, 13...M sequence generation circuit, 14
...Latch circuit. Figure 1 Figure 2 c) 6379 +7'. (f*'c'f+' 6 f; Fig. 3

Claims (1)

[Claims] In a frequency hopping type frequency selection code generator, the system is generated by feeding back the exclusive OR of signals output from n stages of serially connected shift registers and a predetermined stage of the shift registers to the first stage shift register. M of n pit
A circuit that generates a sequence, and m from this generated M sequence.
A frequency selection code generator characterized by a structure in which consecutive n bits are extracted as a frequency selection code every time (m is a natural number that is coprime to 2n-1 and smaller than 2n-1).