CN102082661A

CN102082661A - PCM/FM telemetering system-based data security communication method

Info

Publication number: CN102082661A
Application number: CN 201110024224
Authority: CN
Inventors: 赵泽茂; 戴绍港; 陈集炜
Original assignee: Hangzhou Dianzi University
Current assignee: Hangzhou Dianzi University
Priority date: 2011-01-21
Filing date: 2011-01-21
Publication date: 2011-06-01

Abstract

The invention relates to a pulse code modulation (PCM)/frequency modulation (FM) telemetering system-based data security communication method. The method comprises the following steps of: assigning a cipher key until an initial key generator generates an initial key; generating a key stream through a clock-controlled key stream generator, and generating a next group of data cipher keys; generating ciphertext from data to be transmitted and key stream exclusive OR, packaging into a frame, and performing Turbo encoding on the packaged data frame; and finally, performing signal sampling on the data subjected to the Turbo encoding, performing preset filtering on the sampled data, feeding the data into a channel through FM modulation, wherein a receiving end receives and synchronizes the signal, and at the receiving end, the signal is processed in an inverted sequence in turn and is successively subjected to coherent demodulation, data sampling, Turbo code decoding and decryption through the FM so as to obtain the needed data finally. The method has high linear complexity, can effectively protect the data, and improves security of the PCM/FM telemetering system.

Description

Data security communication method based on PCM/FM remote measurement system

Technical field

The invention belongs to the telemetry intelligence (TELINT) technical field, relate to a kind of data security communication method based on PCM/FM remote measurement system.

Background technology

Contain a large amount of important informations in the reentry telemetry system in the data, be included in the scouting information in the electronic warfare, the state of flight information of aircraft etc.For preventing that the third party from intercepting and capturing or utilizing these information, then require the telemetry of wireless transmission is carried out effective scrambled.The encryption of telemetry requires when guaranteeing high Cipher Strength, and the encryption and decryption computing is simple, and mistake and diffusion of information are little, also require the reasonable combination of error correcting code and encryption and decryption during realization.

PCM/FM is one of time-devision system standard remote measurement system, also is a kind of telemetry system code modulation mode that extensively adopts at present, realizes the time division multiplexing Digital Transmission of multichannel analog signals, reaches the purpose of utilizing limited channel to carry out the high accuracy remote measurement.At present, the most frequently used coding method is divided in data encryption: sequence (stream) password, block cipher and public key cryptography three classes.Stream cipher is pressed bit and is encrypted, and real-time is good, fast operation, and the error diffusion in the transmission course is little, is fit to very much telemetry and encrypts, and this also is the reason that current telemetry mainly adopts stream cipher.

In reentry telemetry system was used, the document of publishing that the research of relevant data encryption method and technology realize was actually rare, and does not see the documents and materials that the box-like clock key stream of set of applications carries out data encryption.

Summary of the invention

Purpose of the present invention is exactly at the deficiencies in the prior art, proposes a kind of data security communication method based on PCM/FM remote measurement system.

The inventive method concrete steps are:

At first produce initial key, generate key stream by the clock key stream generator then, and generate group data seed key down with seed key assignment to initial key maker;

Described clock key stream generator comprises the first shift register A, the second shift register B, the 3rd shift register C and the 4th shift register D, its length is respectively L1, L2, L3 and L4, and the second shift register B, the 3rd shift register C and the 4th shift register D form the clock key stream generator; Wherein L2, L3 and L4 are coprime in twos;

The described first shift register A is used for producing the initial value of the second shift register B, control linear feedback shift register (LFSR) is the L2 level, controlled LFSR is respectively L3 level and L4 level, and the initial condition of the tap position of controlled LFSR and control LFSR is by default;

Then data to be sent and key stream XOR are generated ciphertext, encapsulation incoming frame, the Barker code that frame head adopts telemetry standards to recommend, postamble are the seed key behind 31 codings, and packaged Frame is through the Turbo coding.

Then the data behind the Turbo coding are shone upon, the data after the mapping are carried out signal sampling, and the data after the sampling are carried out preset filtering, and channel is sent in modulation through FM at last; Receiving terminal received signal and synchronously at receiving terminal, is handled with backward successively, successively by FM coherent demodulation, data sampling, Turbo code decoding and deciphering, obtains desired data at last.

The present invention directly adopts the clock key stream generator, the cycle of the pseudo random sequence that this maker produces is that the cycle of three linear feedback shift register output sequences is long-pending, combination and cross complaint by maker like this makes cycle of formation sequence near 2 131 powers.Have good linear complexity, effectively protected data strengthens the fail safe of PCM/FM telemetry system self.

Because the present invention adopts the mode of sequential encryption, it is expressly encrypted one by one by code element or byte, so it doesn't matter between each ciphertext code element and the adjacent code element, so there is not the problem of error code diffusion in principle.Encryption key is not directly exposed in the ciphertext yet, uses seed key to guarantee Cipher Strength, and the encryption and decryption that is used to set up encryption device simultaneously is synchronous.

Description of drawings

Fig. 1 is the key stream generator model;

Fig. 2 is the Frame model;

Fig. 3 is a reentry telemetry system simplified model block diagram;

Fig. 4 is the MF transmitter block diagram;

Fig. 5 is the intermediate-frequency receiver block diagram.

Embodiment

The present invention is further described below in conjunction with drawings and Examples.

The present invention is based on PCM/FM remote measurement system data ciphering method principle as shown in Figure 1, clock key stream generator among the figure is made up of three linear feedback shift registers (LFSR), wherein controlling LFSR is 31 grades, controlled LFSR is respectively 47 grades and 53 grades, and the initial condition of the tap position of controlled LFSR and control LFSR is by default (maintaining secrecy); The key of decision clock key stream generator is the initial condition of shift register, and this initial condition is called as seed key.After the recipient receives ciphertext and seed key, start identical clock key generator, produce the decruption key identical, thereby recover expressly with encryption key.The cycle of the pseudo random sequence that the clock key stream generator produces in this scheme is that the cycle of three linear feedback shift register output sequences is long-pending, like this by the combination and the cross complaint of maker, makes cycle of formation sequence near 2 131 powers.

Length 4～the 1024Byte of telemetry frame does not wait, and can define the frame length of oneself according to actual needs.Consider the code length needs of the Turbo code that adopts in the native system, the employing frame length is 128Byte.According to telemetry standards, synchronous head length generally accounts for 5% ~ 10% of frame length and is advisable, in remote measurement, also can get below 5%, the optimal synchronisation sign indicating number that the native system synchronous head adopts bit synchronization sign indicating number and telemetry standards to recommend, account for 25, the seed key key accounts for 15 bits in frame, the shared bit of ciphertext is 984 so.Frame structure as shown in Figure 2.

When first frame is encrypted, set the initial value of 5,47,53 grades of registers, 5 grades register produces the initial value of 31 seed keys as 31 grades of registers, and the clock key stream generator was started working and produced key 984 bits this moment.Produce ciphertext with this 984 bit keys and ciphertext XOR, and ciphertext is encapsulated into frame.Get in this key stream last 5 bits as the seed key of next frame, this seed key is carried out (3,1) coding, produce 15 bits, and be encapsulated in this frame and transmit.Promptly finished the encryption and the transmission problem of first frame data this moment.When the first frame end of transmission, 5 bit seed keys and clock key stream generator produce 984 bit keys once more thus, are waiting for the encryption of next frame data.When second frame data arrived, 984 bit keys stream can be finished with expressly direct XOR and encrypt and encapsulated frame thus.Get the seed key of last 5 bits as next frame equally, this seed key is carried out (3,1) coding, produce 15 bits, frame is advanced in encapsulation.Can enter the chnnel coding stage after finishing this process.

Chnnel coding adopts Turbo code.Signal divides three the tunnel to handle, and carries out compound at last.First supported signal is the signal that only joins delay and handle.Second supported signal carries out compound after time delay, coding and puncturing process.The 3rd supported signal earlier through interleaver, to encode, delete surplus back compound.Interleaving mode uses matrix to interweave, and promptly reads every 8.Coded system adopts the RSC coding, and it is synchronous to use FIFO to carry out the time delay of data.After finishing chnnel coding, the data behind the coding being shone upon, binary data 1,0 is mapped to respectively+and 1 ,-1.Use 64 times of clock frequencies that the signal after shining upon is sampled to the code check behind the Turbo coding.

Then, the gained signal is carried out preset filtering, adopt raised cosine window.Use the clock frequency identical to carry out the FM modulation with sampling.Frequency modulation(FM) adopts the method for DDS to realize.The amplitude of the SIN function of one-period is deposited among the ROM as carrier wave, read data among the ROM at interval by certain address.Modulation signal can change the modulation of address realization to frequency by adding up as input signal.Flow chart as shown in Figure 3.

Pass through the DA transducer afterwards to digital signal imitationization, filtering is amplified the back and is sent by MF transmitter.Shown in Figure 4 and 5.Intermediate-frequency receiver receives signal and handles, and converts digital signal to, and signal is carried out the synchronous of strictness.Handle with backward successively then, successively, obtain desired data at last by FM coherent demodulation, data sampling, Turbo code decoding and deciphering.

Claims

1. based on the data security communication method of PCM/FM remote measurement system, it is characterized in that this method may further comprise the steps:

The described first shift register A is used for producing the initial value of the second shift register B, and control LFSR is the L2 level, and controlled LFSR is respectively L3 level and L4 level, and the initial condition of the tap position of controlled LFSR and control LFSR is by default;

2. at last the data behind the Turbo coding are carried out signal sampling, the data after the sampling are carried out preset filtering, channel is sent in modulation through FM; Receiving terminal received signal and synchronously at receiving terminal, is handled with backward successively, successively by FM coherent demodulation, data sampling, Turbo code decoding and deciphering, obtains desired data at last.