CN103957181B - Modulation and demodulation method allowing width of chip to have non-stationary characteristic - Google Patents

Abstract

The invention relates to the technical field of wireless communication, in particular to a modulation and demodulation method of communication signals. According to the method, a parameter generator and a pseudorandom sequence generator in a traditional variable parameter direct sequence spread spectrum modulation method are combined into a pseudo random number generator, and an accumulator, a parameter unrolling device and a chip generator are added among the pseudo random number generator, and a mould 2 and an summator. Due to the fact that pseudo-random numbers generated by the pseudo random number generator are accumulated continuously, unrolling is performed after the accumulated parameters exceed a preset range, then the result serves as the input of the chip generator, and the chip corresponding to the input in width is generated by the chip generator. The method has the advantages that wireless communication data have very high anti-detection capacity, difficulty for obtaining signals characteristics by a detection party is greatly improved, and safety in a wireless signal transmission process is enhanced. The method is particularly suitable for modulation and demodulation of communication signals.

Description

A Modulation and Demodulation Method with Non-stationary Characteristic of Chip Width

technical field

The invention relates to the technical field of wireless communication, in particular to a method for modulating and demodulating communication signals.

Background technique

In the field of wireless communication, modulated signals usually have stationary characteristics, that is, their statistical characteristics (such as distribution, mean value, variance, etc.) do not change with time. For such a signal, we can calculate some important features of the signal through power spectrum, cyclic spectrum or some high-order cumulants. These could be the signal's carrier frequency, symbol rate, modulation scheme, and so on. After obtaining these important features, the signal can be interfered, or demodulated, deciphered, and so on.

Therefore, in some fields, it is very important to hide the characteristics of the signal. These fields include the military field as well as the civilian field. In the civilian field, this mainly involves information security and network security.

Traditional methods of concealing signal features include direct sequence spread spectrum, frequency hopping and linear frequency modulation and so on. They all design the signal to expand the power of the signal to be greater than the symbol rate, thereby reducing the signal-to-noise ratio and increasing the difficulty of extracting signal features. However, these methods still cannot change the stationary characteristics of signal features, and can still suppress noise and improve the signal-to-noise ratio by increasing the correlation accumulation length when extracting features, so as to extract the required signal features.

In order to further increase the difficulty for the detector to obtain the signal characteristics, the modulation parameters can be continuously changed according to the predetermined rules when the signal is modulated. Traditionally, the symbol rate, chip rate, frequency hopping rate, etc. can be changed according to a predetermined rule. Changing modulation parameters greatly increase the difficulty of detection. This is the traditional variable parameter modulation. Traditionally, these parameters are chosen from a predetermined set of parameters by a pseudo-random sequence. However, since the number of elements in the parameter set is always limited, and the selection is carried out according to a certain or some limited number of pseudo-random sequences, from a mathematical point of view, the mathematical expectation of the signal characteristics is always constant and unchanged of. Therefore, the characteristics of the signal generated by this conventional variable parameter modulation method can still be detected.

Therefore, the essence of the traditional modulation method is to use the characteristic that the statistical characteristics of the stationary signal remain unchanged, to accumulate signal energy through autocorrelation and cross-correlation calculations, improve the signal-to-noise ratio, and extract the characteristics of the signal, so there are always problems that are easy to be cracked.

Contents of the invention

What the present invention aims to solve is to propose a modulation and demodulation method with a non-stationary characteristic of the chip width in view of the above-mentioned problems existing in the traditional variable parameter direct-sequence spread spectrum.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a modulation and demodulation method with non-stationary characteristics in the chip width, characterized in that it includes:

After the data at the sending end is modulated, it is sent through the carrier modulator and the power amplifier. The specific method for modulating the sending data is: the sending end uses a pseudo-random number generator to generate a random number, and the random number passes through the accumulator and the parameter wrapper in turn. Input to the chip generator, the chip generator generates a chip with a corresponding width to the input random number, and the chip is input to the modulo 2 and adder, and the sending data and the chip are modulo 2 and the adder 2 and output after calculation;

The data at the receiving end is demodulated and output after being amplified by a mixer and an intermediate frequency. The specific method of the demodulated output is: the receiving end uses a pseudo-random number generator to generate a random number, and the random number passes through the accumulator and the parameter wrapper in turn. The input terminal is connected to the chip generator, and the chip generator generates a chip with a width corresponding to the input random number, and inputs the chip to the modulo 2 and adder, and receives data and chips in the modulo 2 and adder The modulo 2 sum is calculated and output to the demodulator demodulation output;

Wherein, the pseudo-random number generator and the accumulator of the receiving end have the same structure as the pseudo-random number generator and the accumulator of the transmitting end; the pseudo-random number generator and the accumulator of the receiving end are connected to a clock synchronization module, and the clock synchronization module is used for Synchronize the clock signal of the pseudo-random number generator and the accumulator of the receiving end with the clock signal of the pseudo-random number generator and the accumulator of the sending end, so that the pseudo-random number generator and the accumulator of the sending end are synchronized with the pseudo-random number generator and accumulator of the receiving end The accumulators have the same initial value.

The general technical scheme of the present invention combines the parameter generator and the pseudo-random sequence generator in the traditional variable parameter direct-sequence spread spectrum modulation method into a pseudo-random number generator, and in the pseudo-random number generator and the modulus 2 and the adder An accumulator, a parameter wrapper, and a chip generator are added in between. By continuously accumulating the pseudo-random numbers generated by the pseudo-random number generator, wrapping around after the accumulated parameters exceed the predetermined range, and then using the result as the input of the chip generator, the chip generator generates a width corresponding to this input. chips. Through the above processing of the present invention, the chip width can be regarded as an independent incremental process, which is also a Markov process. It can be shown that its probability distribution over any time interval is independent of its probability over any other time interval. It therefore has non-stationary properties. Unless the initial value of the chip time and the accumulated value each time are known, the signal cannot be demodulated correctly in the receiver. The chip time with non-stationary characteristics cannot be calculated by conventional detection means.

Specifically, the accumulator is used to accumulate the random number received each time with the original storage data of the accumulator; the parameter wrapper is used to constrain the output data of the accumulator within a preset range.

Further, the specific method used by the parameter wrapper to constrain the data output by the accumulator within a preset range is: after the data output by the accumulator exceeds the preset range, the parameter wrapper divides the data output by the accumulator by the preset After the parameter is set, the data is sent back to the accumulator as storage data; the preset parameter is a positive integer.

The beneficial effect of the present invention is that the modulated signal generated by the present invention has non-stationary statistical characteristics, and it is difficult to obtain signal characteristics when the detection party does not know the predetermined sequence and the initial state, so it has extremely high anti-detection ability, It greatly increases the difficulty for the detection party to obtain the signal characteristics, and improves the security in the process of wireless signal transmission.

Description of drawings

Fig. 1 is a schematic block diagram of the structure of a traditional direct-sequence spread spectrum modem;

Fig. 2 is a schematic block diagram showing the structure of a modulator and demodulator whose chip width has a non-stationary characteristic according to an embodiment.

detailed description

Below in conjunction with accompanying drawing and embodiment, describe technical solution of the present invention in detail:

The purpose of the present invention is to overcome the shortcomings of the traditional direct-sequence spread spectrum technology with variable parameters, and provide a new direct-sequence spread spectrum modulation method and a corresponding demodulation method with non-stationary statistical characteristics of the chip width.

As shown in Figure 1, it is a schematic block diagram of the structure of a traditional direct-sequence spread-spectrum modem. The transmitting end of a traditional direct-sequence spread-spectrum modem uses a parameter generator and a pseudo-random sequence generator to improve the random sequence in the modulo 2 and adder and send data Carry out modulo 2 sum operation and send it through the carrier modulator and power amplifier; the receiving end adopts the parameter generator and the pseudo-random sequence generator with a synchronous clock signal with the parameter generator and pseudo-random sequence generator at the transmitting end and passes through the mixer The received signal obtained after amplifying the intermediate frequency and the intermediate frequency is subjected to a modulo 2 sum operation in a modulo 2 sum adder and outputted through a demodulator.

The modulation and demodulation method of the present invention is different from the traditional ones in that the traditional parameter generator and the pseudo-random sequence generator are combined into a pseudo-random number generator, and the pseudo-random number generator and the traditional parameter generator and pseudo-random The sequence generator also generates random numbers, but the random numbers generated in the present invention are not directly used for the modulo 2 sum operation with the data, but are accumulated through the accumulator, and the range of the data is also constrained by the parameter wrapper, As a result, the generated chip width has non-stationary characteristics, and it is difficult to demodulate the signal normally when the initial value and each accumulation value are not known.

The concrete steps of the method of the present invention are:

1. Under the guarantee of the synchronization mechanism, both ends of the transceiver set the accumulator to the same initial value at the same time;

2. Pseudo-random number generators with the same structure at the sending and receiving ends;

3. The two pseudo-random number generators generate the same pseudo-random number each time under the excitation of the same clock. The distribution of this pseudo-random number can be a normal distribution, or a uniform distribution, etc.;

4. The accumulators at both ends of the transceiver also have the same structure, and the pseudo-random number input and the original value of the accumulator are accumulated once per clock beat;

5. When the output of the accumulator is outside the predetermined range, the parameter wrapper constrains the output of the accumulator to be within the predetermined range. The parameter wrapper can calculate the output of the accumulator modulo m, and m is the predetermined parameter range; it can also be other processing, as long as the output of the parameter wrapper is within the predetermined range;

6. The chip generator generates chips having a width corresponding to the output of the wrapper;

7. In the sending end, a series of chips generated by the chip generator and the data are modulo 2 and added;

8. In the sending end, the output of step 6 is sent out through the antenna after passing through the carrier modulator and power amplifier;

9. In the receiving end, the signal from the antenna is mixed with the local oscillator, and then passed through the intermediate frequency amplifier, and in the modulus 2 and adder, a series of chips generated by the chip generator and the signal from the intermediate frequency amplifier are modeled 2 and add;

10. In the receiving end, the demodulator demodulates the modulo 2 and the output of the adder, and outputs the data.

Example:

As shown in Figure 2, it is a structural block diagram of the modulation and demodulator of this example. The sending end of this example includes a pseudo-random number generator, an accumulator, a parameter wrapper, a chip generator, a modulus 2, and an adder connected in sequence , carrier modulator and power amplifier; the receiving end includes a random number generator, an accumulator, a parameter wrapper, a chip generator, a modulus 2 and an adder, an intermediate frequency amplifier and a mixer connected in sequence, and the modulus 2 and the adder are also connected with Modem connection.

This example works as follows:

In the sending end, the pseudo-random number generator generates random numbers according to predetermined rules under the impetus of the clock. The random number is output to the accumulator, and each input is accumulated in the accumulator with the original state of the accumulator. The result of the accumulator is output to the parameter wrapper. The parameter wrapper constrains the output of the accumulator to be within a certain range when the output of the accumulator is outside the certain range. The method of constraint can be, for example, modulo m calculation. The parameter wrapper outputs parameters constrained within specific ranges to the chip generator. The chip generator generates chips with a width corresponding to this parameter. The chip and the data are respectively used as the two inputs of the modulo 2 and adder for modulo 2 and calculation. Modulo 2 and the output of the adder are output through the carrier modulator and power amplifier.

At the receiving end, after the signal from the transmitting end propagates through the channel, the signal is mixed to the intermediate frequency by the mixer at the receiving end, and after being amplified by the intermediate frequency, it enters the modulo 2 and adder as an input of the modulo 2 and adder. The synchronization module at the receiving end ensures that the clock generated by the clock generator is synchronized with the clock at the sending end, and also ensures that the initial value of the accumulator is consistent with that at the sending end. Similar to the sending end, the pseudo-random number generator at the receiving end generates pseudo-random numbers driven by the clock, and the pseudo-random numbers are continuously accumulated by the accumulator. Due to the function of the synchronization module, the output of the accumulator can be consistent with the output of the accumulator at the sending end. The output of the accumulator at the receiving end is constrained within a predetermined range by the parameter wrapper, and is output to the chip generator, and a chip of a corresponding width is generated in the chip generator. The chips output by the chip generator and the signal from the intermediate frequency amplifier are used as the two inputs of the modulo 2 and adder for modulo 2 sum calculation, and the settlement result can output data through the demodulator.

In this embodiment, the clock cycle of the sending end is 1us. The pseudo-random number generates a random number every 1us. The statistical distribution of the random number is a Gaussian distribution with a mean value of 0 and a variance of 1. The random numbers generated at different times are independent of each other, that is, the autocorrelation function of the random number is a shock function. The accumulator accumulates the pseudo-random number every clock cycle, and the parameter wrapper judges whether it exceeds the predetermined range. In this example, the range is [-10,10]. When the output of the accumulator exceeds this range, the parameter wrapper divides the output of the accumulator by 10 and uses the remainder as the new state of the accumulator. Thereafter, the accumulator continues to accumulate the output of the pseudo-random number generator in this new state. The output of the parameter wrapper is sent to the chip generator, and the chip generator generates a chip pulse corresponding to the width according to the input. In this example, the corresponding relationship is to round the input and use this integer as the clock number of the chip width. For example, if the input is 4.3, it will be 4 after rounding, and the corresponding chip width is 4us. When the rounded result is 0, the chip width is set to 1us. The period of the data symbol is 127 chips, and it is calculated with the chip in the modulo 2 sum adder, that is, the multiplication calculation. It is then output to the carrier modulator and power amplifier, and then transmitted.

At the receiving end, the chip generation and modulation methods and parameters are the same as those at the sending end. The difference is that its clock signal is generated by the synchronization module. The synchronization module can be the same as the clock synchronization module of traditional direct-sequence spread spectrum. The synchronization module also ensures that the accumulator at the receiving end and the accumulator at the sending end start from the same initial value.

Claims (1)

1. a kind of chip width has the modulation and demodulation method of non-stationary property it is characterised in that including：

Send and send through carrier modulator and power amplifier after end data is modulated, described transmission data is modulated Concrete grammar is：Transmitting terminal adopts pseudorandom number generator to produce random number, and this random number passes sequentially through accumulator and parameter is returned It is input to chipping code generators after device, chipping code generators generate the chip with the random number inputting with corresponding width, and by code Piece is input to mould 2 and adder, sends data and chip carries out mould 2 in mould 2 and adder and exports after calculating；

Receive end data to be demodulated exporting after frequency mixer and intermediate frequency amplify, the concrete grammar of described demodulation output is：Connect Receiving end adopts pseudorandom number generator to produce random number, and after this random number passes sequentially through accumulator and parameter is unrolled device, input arrives Chipping code generators, chipping code generators generate the chip with the random number of input with corresponding width, and chip is input to mould 2 He Adder, receiving data and chip carry out mould 2 in mould 2 and adder and export demodulator demodulation output after calculating；

Wherein, the pseudorandom number generator of receiving terminal and accumulator have phase with the pseudorandom number generator of transmitting terminal and accumulator Same structure；The pseudorandom number generator of receiving terminal and accumulator connect clock synchronization module, and described clock synchronization module is used for By the pseudorandom number generator of the clock signal of the pseudorandom number generator of receiving terminal and accumulator and transmitting terminal and accumulator The pseudorandom number generator of clock signal synchronization, the pseudorandom number generator of transmitting terminal and accumulator and receiving terminal and cumulative utensil There is identical initial value；

Described accumulator is used for original to the random number receiving every time and accumulator data storage is added up；Parameter is unrolled device For the data constraint that exports accumulator in default scope；Described parameter unrolls device for the data exporting accumulator The concrete grammar constraining in default scope is：After the data of accumulator output exceeds preset range, the parameter device that unrolls will tire out Plus the data of device output is divided by sending data back to accumulator as data storage after parameter preset；Described parameter preset is just whole Number.