CN107302515B - Cell encryption method based on synchronous signal - Google Patents
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Abstract
The invention discloses a cell encryption method based on synchronous signals, which realizes cell encryption from the encryption of a main synchronous signal and an auxiliary synchronous signal; the encryption of the master synchronization signal adopts a mode of replacing a root index to obtain different master synchronization sequences; the encryption of the secondary synchronization signal includes the in-sequence interleaving and changing of the standard secondary synchronization sequence
Scrambling patterns and changes to sequences
X (i) three modes of the recursion formula of the sequence; the encryption methods can be used separately or in superposition. The invention utilizes the correlation characteristic of the synchronous signal to realize the cell encryption by the customization of the synchronous signal, fundamentally reduces the possibility of searching the cell to a great extent, and has the advantages of easy realization, difficult cracking and no influence on other services in the cell.
Description
Technical Field
The invention relates to an encryption method, in particular to a cell encryption method based on a synchronous signal, and belongs to the technical field of wireless communication.
Background
LTE (Long Term Evolution ) is a Long Term Evolution of UMTS (universal mobile telecommunications system) technical standard formulated by 3GPP organizations, which introduces key transmission technologies such as OFDM (orthogonal frequency division multiplexing) and MIMO (multiple input multiple output), significantly increases spectrum efficiency and data transmission rate, supports multiple bandwidth allocation, and supports a global mainstream 2G/3G frequency band and some newly-added frequency bands, thus spectrum allocation is more flexible, and system capacity and coverage are significantly improved. Therefore, LTE is expected to become the first truly worldwide-popular wireless communication standard, with extremely wide applicability. At present, most of communication services in a cell are based on an LTE system, but because a protocol of the LTE system is public, a planned frequency band is limited and basically fixed, on the premise of a known frequency band, a standard terminal developed according to the protocol can search for a cell of a standard base station to implement tracking and monitoring; but in some scenarios this is desirably avoided by the listening cell as much as possible. At present, the discussion of encryption and security mechanisms of an LTE system mostly focuses on key systems and security architectures of an Access Stratum (AS), a non-access stratum (NAS), and the like, and relates to various complex algorithms, the management of keys is also tedious, and no cell encryption method based on a synchronization signal exists.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a cell encryption method based on a synchronous signal.
In order to solve the technical problems, the invention adopts the technical scheme that: a cell encryption method based on synchronous signals is based on an LTE base station; the LTE base station has 504 physical cells which are divided into 3 sectors, each sector is divided into 168 groups, and the cell ID is a unique identifier formed by a group ID and a sector ID and expressed as a formula I;
wherein,
the group ID is set to be in a value range of 0-167;
the sector ID is selected from the range of 0-2;
for the transmitting side of the base station, the unique cell ID determines a group of primary and secondary synchronous signals unique to the cell; wherein the primary synchronization signal adopts a ZC sequence with strong correlation, and
associating; the secondary synchronization signal adopts M sequences with certain correlation, and
associating;
the encryption method comprises the following specific steps:
step one, encrypting a main synchronous signal: the generation mode of the main synchronization signal is expressed as a formula II;
wherein u is the generating sequenceRoot, it and
one-to-one correspondence is realized;
according to the characteristics of the ZC sequence and the generation mode of the main synchronization sequence, a customized version main synchronization sequence different from a protocol is obtained by replacing a root index u, and then an obvious correlation peak of a main synchronization signal cannot be obtained in cell search by a standard terminal; in addition, the generation process of the secondary synchronization sequence utilizes
Carry out scrambling if
The secondary synchronization sequence is decoded by mistake, so that the correct cell ID cannot be obtained finally, and the encryption effect on the cell is realized;
step two, encrypting the auxiliary synchronizing signal: the generation mode of the standard secondary synchronization sequence is expressed as a formula three:
wherein,
m0m' mod 31 equation four
Sequence of
Are obtained by the following formulas:
wherein,
0 ≦ i ≦ 30, and x (i) is defined as:
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
scrambling sequence c0(n) and c1(n) is related to the sector ID, and is obtained by the following equations, respectively:
wherein,
i is more than or equal to 0 and less than or equal to 30; where x (i) is defined as;
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
scrambling sequence
And
is formed by
The sequence is obtained by cyclic shift, as follows:
wherein,
0 ≦ i ≦ 30, and x (i) is defined herein as:
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
according to the characteristics of the M sequence and the generation method of the secondary synchronization sequence, the encryption method of the secondary synchronization signal is divided into the following three types:
i, performing intra-sequence interleaving on the standard secondary synchronization sequence:
performing intra-sequence interleaving on the standard auxiliary synchronization sequences, namely changing the arrangement sequence of 62 values in each sequence to obtain 168 auxiliary synchronization sequences different from the protocol, so that the standard terminal cannot obtain an obvious correlation peak of an auxiliary synchronization signal in cell search;
II, change
The recursion formula for x (i) sequences in the sequence: replacing a formula eight, a formula ten and a formula twelve with a formula thirteen, a formula fourteen and a formula fifteen respectively, and ensuring that the initial value of x (i) is unchanged to obtain 168 auxiliary synchronization sequences different from the protocol;
III, modification
Scrambling mode of sequence: replacing the formula nine and the formula eleven with a formula sixteen and a formula seventeen respectively to obtain the productTo 168 secondary synchronization sequences different from the protocol;
the encryption modes I, II and III are used independently or used in a pairwise matching way or used together, and the more encryption modes are selected, the better the encryption effect on the cell is.
In step one, in order to maintain low cross correlation of ZC sequences, the root index u is selected to ensure that the custom version master sync sequence is not in a period defined by the protocol, or the mapping relationship between the custom version master sync sequence and the root index u is different from each defined by the protocol, and 0 and 63 are not selected so that the master sync sequence becomes a value of all 1 or all-1 sequence.
In the encryption method II in the second step, the replacement methods of the three formulas are used independently or matched in pairs or used together.
In the encryption mode III of the step II, the substitution methods of the two formulas are used independently or together.
The encryption modes in the first step and the second step are used independently or together, and the encryption effect of the joint use is better than that of the single use.
The invention utilizes the correlation characteristic of the synchronous signal to realize the cell encryption by the customization of the synchronous signal, fundamentally reduces the possibility of searching the cell to a great extent, and has the advantages of easy realization, difficult cracking and no influence on other services in the cell.
Drawings
Fig. 1 is a mapping position diagram of primary and secondary synchronization signals of TDD and FDD.
Fig. 2 is a constellation diagram of primary and secondary synchronization signals.
Fig. 3 shows a primary synchronization sequence correlation test pattern.
Fig. 4 shows the correlation detection pattern of the standard PSS.
Fig. 5 is a comparative detection pattern replacing the PSS.
Fig. 6 is a related test pattern for a standard SSS.
FIG. 7 is a related test pattern replacing the first type custom plate SSS.
Fig. 8 is a related test pattern replacing the second type customized version SSS.
Fig. 9 is a related test pattern replacing the third type customized version SSS.
FIG. 10 is a PSS correlation test pattern replacing custom master and secondary synchronization sequences.
Fig. 11 is an SSS correlation test pattern replacing the custom version primary and secondary synchronization sequences.
Fig. 12 is a schematic view of the overall process of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
As shown in fig. 12, the present invention is based on the synchronization principle of the LTE system; an LTE base station has 504 physical cells which are divided into 3 sectors, each sector is divided into 168 groups, and a cell ID (identity) forms a unique identifier by a group ID (group ID) and a sector ID (section ID), and is expressed as a formula I;
wherein,
the group ID is set to be in a value range of 0-167;
the sector ID is selected from the range of 0-2;
timing synchronization of LTE is realized by means of primary and secondary synchronization signals, and a Primary Synchronization Signal (PSS) adopts a ZC sequence with strong correlation and
associating; secondary synchronization signal (Secondary synchronization)signal, SSS) employs M sequences with certain correlation with
And (4) associating. For a base station transmitting side, a unique cell ID determines a unique group of main and auxiliary synchronizing signals of the cell, and the main and auxiliary synchronizing signals of TDD and FDD respectively occupy fixed time-frequency resources according to protocol regulations; for the receiving side of the terminal, the main and auxiliary synchronization sequences of the base station can be determined according to the related detection algorithm, the associated sector ID and group ID are further determined to determine the cell ID, and the frame structure and the frame head are determined according to the positions of the main and auxiliary synchronization sequences appearing in the time domain, so as to complete 5ms and 10ms synchronization.
The resource mapping mode of the main and auxiliary synchronous signals is as follows:
for TDD, the primary synchronization signal is mapped to the middle 6 RBs of the 3 rd symbol (symbol 2) of the special subframe (subframe 1, 6), and the secondary synchronization signal is mapped to the middle 6 RBs of the last 1 symbol (symbol 13) of the 1 st subframe (subframe 0, 5) of 5 ms; for FDD, the primary and secondary synchronization signals are mapped to the middle 6 RBs of symbol 6 of the 1 st subframe (subframes 0, 5) of 5ms, and the secondary synchronization signals are mapped to the middle 6 RBs of symbol 5 of the 1 st subframe (subframes 0, 5) of 5 ms. Wherein, the front and back of the 72 REs contained in the 6 RBs are respectively empty with 5 REs, and 62 values of the primary and secondary synchronization signals are mapped on the middle 62 REs. The mapping positions of the primary and secondary synchronization signals of TDD and FDD are shown in fig. 1.
Taking cell ID 95 (sector ID 2, group ID 31) as an example, the constellation of the primary and secondary synchronization signals is shown in fig. 2.
The method comprises the following specific steps:
step one, an encryption method of a main synchronous signal:
the primary synchronization signal sequence consists of ZC sequences, which mainly have the following characteristics:
1) constant envelope property: the amplitude of the ZC sequence with any length is constant;
2) ideal periodic autocorrelation properties: after any ZC sequence is shifted by n bits, when n is not an integral multiple of the period of the ZC sequence, the shifted sequence is irrelevant to the original sequence;
3) good cross-correlation properties: the cross-correlation and partial correlation values are close to 0;
4) low peak-to-average ratio characteristic: the ratio of the peak value to the mean value of a signal consisting of any ZC sequence is very low;
5) the ZC sequence remains after fourier transform: any ZC sequence is still a ZC sequence after the positive and negative change of the Fourier.
ZC sequences are often used in synchronization algorithms for communication systems due to their excellent correlation properties.
The generation mode of the main synchronization signal is expressed as a formula II;
where u is the root of the generating sequence, it is compared with
One-to-one correspondence is realized; the root index of the primary synchronization sequence is shown in table 1;
TABLE 1
Adding a primary synchronization sequence generated by formula one to the head of a group of signals to form a signal Stest, and taking 29 (corresponding to the root index u)
) And 3 main synchronous sequences are adopted to respectively solve the cross correlation with the signal Stest to obtain the result shown in the figure 3.
As can be seen from fig. 3, the obvious correlation peak can be obtained only by using the primary synchronization sequence with the same protocol, and if the transmitting side of the base station uses the primary synchronization sequence with a different protocol, the standard terminal cannot obtain the obvious correlation peak of the primary synchronization signal in the cell search, there is a probability of 2/3 for error resolution
And the generation process of the secondary synchronization sequence is beneficialUse up
Carry out scrambling if
The secondary synchronization sequence is decoded by mistake correspondingly, and finally the correct cell ID cannot be obtained; even if it happens to be correct
And the frame header of the cell cannot be found due to the search error of the peak position, so that the cell cannot be synchronized with the frame header.
To facilitate the comparative analysis, the spectrometer is used to capture the transmitted signal of the standard base station TDD cell 95
After downsampling and filtering, a signal s to be processed is obtained, and 3 primary synchronization sequences specified by a protocol are adopted to perform correlation detection on the signal s respectively, and the detection result is shown on the left side of fig. 4. As can be seen from the figures, it is,
then an obvious correlation peak (left 3) is obtained, and the appearance position of the main synchronization sequence of the signal s to be processed is changed into
The time domain signal of the standard primary synchronization sequence (multiplied by the channel influence factor and added with random noise to simulate the real situation) is respectively subjected to correlation detection in the same way to obtain a correlation pattern on the right side of the graph 4, which is consistent with the state on the left side and is also in the state on the right side
A clear correlation peak was obtained (right 3).
According to the characteristics of the ZC sequence and the generation mode of the primary synchronization sequence, the primary synchronization sequence is replaced by replacing the root index, so that the encryption effect on the cell is achieved.
Replacing the root index u of the master synchronization sequence (taking the root index of table 2 as an example), obtaining 3 master synchronization sequences different from the protocol, hereinafter called customized version master synchronization sequences, and replacing the appearance position of the master synchronization sequence of the signal s to be processed with the appearance position of the master synchronization sequence
The time domain signal of the customized version main synchronization sequence (multiplied by the channel influence factor and added with random noise to simulate the real situation) adopts 3 standard main synchronization sequences to respectively carry out correlation detection on the signal s, an obvious correlation peak (the left side of figure 5) cannot be obtained, adopts 3 customized version main synchronization sequences to respectively carry out correlation detection on the signal s, and can still be used in the prior art
A clear correlation peak was obtained (fig. 5, right 3).
TABLE 2
The above shows that the encryption effect on the primary synchronization signal and the cell is realized by replacing the root index of the primary synchronization sequence.
It should be noted that, since ZC sequences have ideal periodic autocorrelation characteristics, to maintain low cross-correlation of ZC sequences, the root index u is selected to ensure that the custom-built master sync sequence is not periodic (so that no significant correlation peak is obtained in correlation detection) or so that the protocol defines the custom-built master sync sequence
The mapping relation with u is different from each other specified by the protocol (so that even if a significant correlation peak is obtained in the correlation detection, an error is obtained
) And 0, 63 are not selected such that the primary synchronization sequence becomes the value of an all-1 or all-1 sequence. According to the generation formula one of the primary synchronization sequence, the selection range of the root index group is the open interval of (0, 63)Optionally 3 values (6 permutations per group) were removed, and 25, 29, 34 and
the corresponding relation of (2) and the agreement are consistent, and the common is
And (4) selecting. It can be seen that when the root index u of the custom version master sync sequence selection is not known, it is difficult to crack.
Therefore, according to the characteristics of the ZC sequence and the generation method of the primary synchronization sequence, the root index u is replaced to obtain a customized version of the primary synchronization sequence different from the protocol, and the standard terminal cannot obtain an obvious correlation peak of the primary synchronization signal in cell search.
Step two, encrypting the auxiliary synchronizing signal:
the secondary synchronization signal adopts an M sequence. Among all the pseudo-random sequences, the M sequence is the most important and basic pseudo-random sequence, which is easy to generate, strong in regularity, and has good autocorrelation and good cross-correlation properties. Generation and reception of secondary synchronization signal
Associating, using in the generation process
Scrambling, and sub-frames 0, 5 employ different secondary synchronization signals to achieve 5ms timing.
In the M sequence groups in the same period, the difference between the cross-correlation characteristics of every two M sequence pairs is large, some M sequence pairs have good cross-correlation characteristics (small cross-correlation value) and some M sequence pairs have poor cross-correlation characteristics (large cross-correlation value), and in actual use, the M sequence groups with good cross-correlation characteristics need to be selected to achieve the purposes of convenience in detection and interference resistance.
The aforementioned signal s to be processed is still the object of analysis. 168 sets of auxiliary synchronization sequences specified by the protocol are used to perform correlation detection on the signals respectively, and the detection results are shown in fig. 6. As can be seen from the view in figure 6,
a clear correlation peak is obtained (as shown in fig. 6), and the appearance position of the secondary synchronization sequence of the signal s to be processed is changed into
The time domain signal of the standard secondary synchronization sequence (multiplied by the channel influence factor and added with random noise to simulate the real situation) is respectively subjected to correlation detection in the same way to obtain a lower correlation pattern, and the visible correlation pattern is consistent with the upper state and is also in the upper state
A clear correlation peak was obtained (as under fig. 6).
The generation mode of the standard secondary synchronization sequence is expressed as a formula three:
wherein,
m0m' mod 31 equation four
Sequence of
Are obtained by the following formulas:
wherein,
0 ≦ i ≦ 30, and x (i) is defined as:
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
scrambling sequence c0(n) and c1(n) is related to the sector ID, and is obtained by the following equations, respectively:
wherein,
i is more than or equal to 0 and less than or equal to 30; where x (i) is defined as;
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
scrambling sequence
And
is formed by
The sequence is obtained by cyclic shift, as follows:
wherein,
0 ≦ i ≦ 30, and x (i) is defined herein as:
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
according to the characteristics of the M sequence and the generation mode of the auxiliary synchronization sequence, the encryption modes of the auxiliary synchronization signal in the invention are divided into the following three modes:
i, performing intra-sequence interleaving on the standard secondary synchronization sequence:
and performing in-sequence interleaving on the standard auxiliary synchronization sequences, namely changing the arrangement sequence of 62 values in each sequence to obtain 168 auxiliary synchronization sequences different from the protocol, which are hereinafter referred to as first plate-making-specific auxiliary synchronization sequences.
Taking the interleaving table shown in table 3 as an example, the standard secondary synchronization sequence is subjected to in-sequence interleaving. Replacing the appearance position of the secondary synchronization sequence of the signal s to be processed with
The time domain signal of the first type of customized plate secondary synchronization sequence (multiplied by the channel influence factor and added with random noise to simulate the real situation) is detected by adopting 168 standard secondary synchronization sequences to respectively carry out correlation detection on the signal s, the result is shown in fig. 7, no obvious correlation peak (shown in fig. 7) can be obtained, the correlation detection is carried out on the signal s by adopting the first type of 168 customized plate secondary synchronization sequences, and the method can still be used for detecting the correlation of the signal s by adopting the first type of 168 customized plate secondary synchronization sequences
A clear correlation peak was obtained (as under fig. 7).
TABLE 3
II, change
The recursion formula for x (i) sequences in the sequence: replacing the formula eight, formula ten and formula twelve with the formula thirteen, formula fourteen and formula fifteen respectively, and ensuring the initial value of x (i) to be unchanged, namely168 secondary synchronization sequences different from the protocol are obtained, and are referred to as a second type of customized secondary synchronization sequences.
Description of the drawings:
A) the purpose of encryption can be achieved by adopting any one of the change formulas to generate an auxiliary synchronization sequence, and the auxiliary synchronization sequence can be superposed for use in order to enhance the effect and increase the decoding difficulty when in use;
B) the M-sequence cross-correlation under the above-mentioned 3 methods of generating the formula change is good, and the correlation detection contrast patterns are similar, but not listed one by one, and here, only the correlation detection contrast pattern of changing the formula eight into the formula thirteen is taken as an example.
Replacing the appearance position of the secondary synchronization sequence of the signal s to be processed with
The time domain signal of the second type of customized version of the secondary synchronization sequence (multiplied by the channel influence factor and added with random noise to simulate the real situation) is detected by respectively adopting 168 standard secondary synchronization sequences to carry out correlation detection on the signal s, so that no obvious correlation peak can be obtained (as shown in fig. 8), and the correlation detection is carried out on the signal s by respectively adopting the first type of 168 customized version of the secondary synchronization sequence, which can still be carried out on the signal s
A clear correlation peak was obtained (as under fig. 8).
III, modification
Scrambling mode of sequence: the formula nine and the formula elevenAnd respectively replacing with a formula sixteenth and a formula seventeenth to obtain 168 auxiliary synchronization sequences different from the protocol, which are hereinafter referred to as a third type of customized auxiliary synchronization sequences.
Description of the drawings:
A) the purpose of encryption can be achieved by adopting any one of the change formulas to generate an auxiliary synchronization sequence, and the auxiliary synchronization sequence can be used together for enhancing the effect and increasing the decoding difficulty when in use;
B) the M-sequence cross-correlation under the above 2 methods of generating the formula change is good, the correlation detection contrast patterns are similar, but not listed one by one, and here, only the correlation detection contrast pattern that changes the formula nine into the formula sixteen is taken as an example.
Replacing the appearance position of the secondary synchronization sequence of the signal s to be processed with
The time domain signal of the third type of customized version of the secondary synchronization sequence (multiplied by the channel influence factor and added with random noise to simulate the real situation) is detected by adopting 168 standard secondary synchronization sequences to respectively carry out correlation detection on the signal s, so that no obvious correlation peak can be obtained (as shown in fig. 9), and the correlation detection is still carried out on the signal s by adopting the third type of 168 customized version of the secondary synchronization sequences
A clear correlation peak was obtained (as under fig. 9).
The encryption modes I, II and III are used independently or used in a pairwise matching way or used together, and the more encryption modes are selected, the better the encryption effect on the cell is.
The above shows that by changing
X (i) recurrence formula, change of sequence
Scrambling mode of sequence, and carrying out intra-sequence interweaving on standard auxiliary synchronous sequence.
It should be noted that, first, the three modes can be used selectively or jointly; in addition, there are several ways to change the formula, and the interleaving table has 62! 3.147 x 10 ═ d85The selection shows that when the encryption mode used by the plate-making auxiliary synchronization sequence or the selected interleaving table is not known, the decoding is difficult.
Because the ID of the physical cell is uniquely determined by the primary and secondary synchronous signals, and the primary and secondary synchronous sequences have good correlation characteristics, the invention realizes the encryption mode of the cell from the encryption of the primary synchronous signal and the secondary synchronous signal, has good encryption effect on the cell and has great cracking difficulty. The generation mode of the main and auxiliary synchronous signals is simple, but the influence factors are various, so that the invention can realize the purpose of difficult cracking with lower cost, and the base station and the terminal adopt the customized main and auxiliary synchronous signal sequences, thereby not increasing the realization complexity of protocol stack software and not influencing other services in a cell.
The customization of the synchronization signal causes that other standard terminals cannot correctly search the cell, and even cannot perform timing synchronization, in addition, scrambling of the cell signal is related to the cell ID, and other terminals cannot correctly descramble other channels of the cell, such as PBCH, PDSCH and the like, when searching the wrong cell ID, that is, cannot track any content of the cell.
The effect of the present invention will be described in detail with reference to a specific example.
The first embodiment is as follows:
in this embodiment, the encryption method of the primary synchronization signal provided by the present invention is used in combination with the encryption methods of the three types of secondary synchronization signals to perform comprehensive synchronous encryption on a cell, and the effects are as follows:
respectively replacing the appearance positions of the main and auxiliary synchronous sequences of the signal s to be processed with
Time domain signal sum of customized version master synchronization sequence by modifying root index u
The time domain signals of the customized version of the secondary synchronization sequence (the main synchronization signal and the secondary synchronization signal are multiplied by a channel influence factor and added with random noise to simulate the real situation) which commonly use the three types of encryption modes, the signal s is respectively subjected to related detection by adopting the standard main synchronization sequence and the standard secondary synchronization sequence, and the detection results are respectively shown in fig. 10 and fig. 11; in the figure, no obvious correlation peak is obtained in the detection of the main and auxiliary synchronous signals (on the left of figure 10 and figure 11), the signal s is respectively subjected to correlation detection by adopting the customized version main and auxiliary synchronous sequences, and still the correlation detection can be carried out on the signal s
And
a clear correlation peak was obtained (right in fig. 10, bottom in fig. 11). Looking up the detection result, the cell ID searched by the standard primary and secondary synchronization sequence correlation detection is 279 (the sector ID is 0, and the group ID is 93), which is wrong, and obviously the frame header position searched at this time is also wrong; the cell ID detected by using the correlation detection of the customized version master and the secondary synchronization sequence is 95 (sector ID is 2, group ID is 31), which is correct, and the frame header position searched correspondingly is also correct.
The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above examples, and those skilled in the art may make variations, modifications, additions or substitutions within the technical scope of the present invention.
Claims (5)
1. A cell encryption method based on a synchronization signal is characterized in that: it is based on an LTE base station; the LTE base station comprises 504 physical cells which are divided into 3 sectors, each sector is divided into 168 groups, and the cell ID is a unique identifier formed by a group ID and a sector ID and expressed as a formula I;
wherein,
the group ID is set to be in a value range of 0-167;
the sector ID is selected from the range of 0-2;
for the transmitting side of the base station, the unique cell ID determines a group of primary and secondary synchronous signals unique to the cell; wherein the primary synchronization signal adopts a ZC sequence with strong correlation, and
associating; the secondary synchronization signal adopts M sequences with certain correlation, and
associating;
the encryption method comprises the following specific steps:
step one, encrypting a main synchronous signal: the generation mode of the main synchronization signal is expressed as a formula II;
where u is the root of the generating sequence, it is compared with
One-to-one correspondence is realized;
according to the characteristics of ZC sequence and the generation mode of primary synchronization sequence, the method obtains the difference from LTE protocol by replacing root index uCustomizing a version master synchronization sequence, so that an obvious correlation peak of a master synchronization signal cannot be obtained in cell search by an LTE standard terminal; in addition, the generation process of the secondary synchronization sequence utilizes
Carry out scrambling if
The secondary synchronization sequence is decoded by mistake, so that the correct cell ID cannot be obtained finally, and the encryption effect on the cell is realized;
step two, encrypting the auxiliary synchronizing signal: the generation mode of the standard secondary synchronization sequence is expressed as a formula three:
wherein,
m0m' mod 31 equation four
Sequence of
Are obtained by the following formulas:
wherein,
0 ≦ i ≦ 30, and x (i) is defined as:
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
scrambling sequence c0(n) and c1(n) is related to the sector ID, and is obtained by the following equations, respectively:
wherein,
i is more than or equal to 0 and less than or equal to 30; where x (i) is defined as;
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
scrambling sequence
And
is formed by
The sequence is obtained by cyclic shift, as follows:
wherein,
0 ≦ i ≦ 30, and x (i) is defined herein as:
the initial values of x (i) are: x (0) ═ 0, x (1) ═ 0, x (2) ═ 0, x (3) ═ 0, and x (4) ═ 1;
according to the characteristics of the M sequence and the generation method of the secondary synchronization sequence, the encryption method of the secondary synchronization signal is divided into the following three types:
i, performing intra-sequence interleaving on the standard secondary synchronization sequence:
performing intra-sequence interleaving on the standard auxiliary synchronization sequences, namely changing the arrangement sequence of 62 values in each sequence to obtain 168 auxiliary synchronization sequences different from the LTE protocol, so that an obvious correlation peak of an auxiliary synchronization signal cannot be obtained in cell search by an LTE standard terminal;
II, change
The recursion formula for x (i) sequences in the sequence: replacing a formula eight, a formula ten and a formula twelve with a formula thirteen, a formula fourteen and a formula fifteen respectively, and ensuring that the initial value of x (i) is unchanged to obtain 168 auxiliary synchronization sequences different from the protocol;
III, modification
Scrambling mode of sequence: replacing the formula nine and the formula eleven with a formula sixteen and a formula seventeen respectively to obtain 168 auxiliary synchronization sequences different from the protocol;
the encryption modes I, II and III are used independently or in pairwise collocation or are used together, and the more encryption modes are selected, the better the encryption effect on the cell is.
2. The synchronization signal based cell encryption method of claim 1, wherein: in the first step, in order to maintain low cross correlation of ZC sequences, the root index u is selected to ensure that the customized version master synchronization sequence is not in a period defined by the LTE protocol, or the mapping relationship between the customized version master synchronization sequence and the root index u is different from each defined by the LTE protocol, and the master synchronization sequence is changed to a value of all 1 or all-1 sequence by not selecting 0 and 63.
3. The synchronization signal based cell encryption method of claim 1, wherein: in the encryption method II in the second step, the replacement methods of the three formulas are used independently or matched in pairs or used together.
4. The synchronization signal based cell encryption method of claim 1, wherein: in the encryption mode III of the second step, the substitution methods of the two formulas are used independently or together.
5. The synchronization signal based cell encryption method of claim 1, wherein: the encryption modes in the first step and the second step are used independently or together, and the encryption effect of the joint use is better than that of the single use.
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