CN112994827B - OVSF code estimation method - Google Patents
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Abstract
The invention discloses an OVSF code estimation method, which screens an OVSF code sequence in an OVSF code tree by setting a power threshold value and a near-zero rate threshold value so as to estimate an OVSF code actually used by a user and solve the problem that the OVSF code sequence is difficult to estimate under a low signal-to-noise ratio.
Description
Technical Field
The invention belongs to the field of WCDMA (wideband code division multiple access), and relates to an OVSF code (Orthogonal Variable Spreading Factor Codes) estimation method.
Background
WCDMA (wideband code division multiple access) is one of the 3G standards, has a flexible, multi-service multiplexing high-speed radio air interface technology, and can support multimedia/group/IP access service transmission up to 2Mbit/s, with the same quality as fixed networks, and is widely used in many countries. The power spectrum density of the WCDMA signal is very low and is usually submerged by noise, so that the WCDMA signal has good anti-interference and anti-interception capabilities.
WCDMA supports services with different rates, and the spread bandwidth is fixed, so orthogonal codes (OVSF) with different lengths are used as address codes for various services. The OVSF code ensures orthogonality between different physical channels, and has the following characteristics:
(1) Spreading factor to an integer power of 2, i.e. SF =2 n In the uplink of the MCDMA, the SF is in the range of 4-256; for the downlink of MCDMA, the range of SF is 4-512;
(2) For OVSF code groups with a certain length, SF code words with SF length are shared;
(3) Different code words in the same layer are mutually interacted, and the correlation value is 0;
(4) OVSF codes located in different layers are also interactive as long as there is no derivation relationship between them.
Most of the existing literature is directed to general PN (pseudo random) code sequences, and the estimation of OVSF codes is less studied.
Disclosure of Invention
Aiming at the defects in the prior art, the OVSF code estimation method provided by the invention solves the problem that the OVSF code sequence in the existing WCDMA is difficult to obtain under the condition of low signal-to-noise ratio.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that: an OVSF code estimation method includes the following steps:
s1, preprocessing a received signal;
s2, setting an initial search spreading factor Sf =512, an initial search serial number i =1 and a near-zero rate threshold Tnzr of a symbol;
s3, taking a current spreading factor Sf in an OVSF code tree, carrying out despreading processing on the preprocessed signal through an OVSF code sequence with a code number i, and calculating an average power value ap (i) of all symbols after despreading processing;
s4, judging whether the Sf is more than i;
if yes, increasing the sequence number i by 1, and returning to the step S3;
if not, the step S5 is executed;
s5, setting a power value threshold Tap, finding out all serial numbers i meeting ap (i) > Tap in an OVSF code tree, and entering step S6;
s6, sequentially calculating the near-zero rate nzr of the de-spread processed symbols corresponding to the serial number i obtained in the step S5, and judging whether nzr is less than Tnzr;
if yes, entering step S7;
if not, the step S8 is carried out;
s7, determining that the code sequence with the code sequence number i is used, storing the corresponding spreading factor Sf and the code sequence number i into an OVSF code use set OVSF _ used, and entering a step S9;
s8, judging that the code sequence with the serial number i is not used, excluding the code sequence, and entering the step S9;
s9, halving the spreading factor Sf, setting a code sequence number i to be 1, and entering a step S10;
s10, judging whether the current spreading factor Sf is equal to 2 or not;
if yes, entering step S11;
if not, returning to the step S3;
s11, parent codes on the same code tree branch are removed from the OVSF code usage set OVSF _ used to obtain a final OVSF code usage set, and OVSF code estimation is achieved.
Further, the step S1 specifically includes:
s11, performing down-conversion processing on the received signal to obtain an IQ baseband signal corresponding to one frame;
s12, sequentially carrying out A/D conversion and descrambling processing on the IQ baseband signal to obtain baseband IQ data after descrambling synchronization;
s13, carrying out normalization processing on the independent I-path signal or Q-path signal in the baseband IQ data to obtain a preprocessed received signal;
the expression of the I path signal or the Q path signal is as follows:
wherein X is I-path signal or Q-path signal, X 1 ,x 2 ,...,x 38400 Is a data sample point of a WCDMA frame, V is white Gaussian noise, N is the number of users, C n (m) is m symbols of the nth user, OVSF n And (SF, j) the spreading factor used by the nth user is SF, and the OVSF code sequence with the code number of j.
Furthermore, the OVSF codes of the users are orthogonal to each other, and the product of the number M of symbols of each user and the corresponding spreading factor SF is the data amount of one frame, that is, M × SF =38400.
Further, in step S3, the average power value ap (i) of all despread symbols is:
in the formula, y k K =38400, which is a data sample point of the signal Y obtained after despreading processing;
wherein Y = [ Y = 1 ,y 2 ,...,y k ]And an OVSF code sequence with spreading factor Sf and serial number i in an OVSF (Sf, i) code tree.
Further, in step S5, the set power threshold value Tap is:
in the formula, i is a code sequence number; ap (i) average power value of all symbols after despreading; sf is the spreading factor.
The beneficial effects of the invention are as follows:
the invention provides a thought for estimating the OVSF code sequence in the WCMMA, solves the problem that the OVSF code sequence is difficult to estimate under low signal-to-noise ratio, and lays a foundation for the subsequent despreading and demodulation processing of WCDMA signals.
Drawings
Fig. 1 is a flowchart of an OVSF code estimation method provided by the present invention.
Fig. 2 is a schematic diagram of a code tree numbering scheme according to the present invention.
Fig. 3 is a graph of the average power after despreading all code sequences with a spreading factor of 512 according to the present invention.
Fig. 4 is a diagram of the correct curvature of OVSF code sequence estimation under different signal-to-noise ratios provided by the present invention.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
Example 1:
as shown in fig. 1, an OVSF code estimation method includes the following steps:
s1, preprocessing a received signal;
s2, setting an initial search spreading factor Sf =512, an initial search serial number i =1 and a near-zero rate threshold Tnzr of a symbol;
s3, acquiring a current spreading factor Sf in an OVSF code tree, carrying out despreading processing on the preprocessed signal through an OVSF code sequence with a code number i, and calculating an average power value ap (i) of all symbols after despreading processing;
s4, judging whether the Sf is more than i;
if yes, increasing the sequence number i by 1, and returning to the step S3;
if not, the step S5 is carried out;
s5, setting a power value threshold Tap, finding out all serial numbers i meeting ap (i) > Tap in an OVSF code tree, and entering step S6;
s6, sequentially calculating the near-zero rate nzr of the de-spread symbols corresponding to the serial number i obtained in the step S5, and judging whether nzr is less than Tnzr or not;
if yes, entering step S7;
if not, the step S8 is carried out;
in this step, the temporary spreading factor is Sf, and the OVSF code with code number i may be used, so that only zero rate nzr of the despreading symbol corresponding to the OVSF code is calculated and compared with a set near-zero rate threshold value Tnzr, so as to determine whether the code sequence with code number i is used;
s7, determining that the code sequence with the code sequence number i is used, storing the corresponding spreading factor Sf and the code sequence number i into an OVSF code use set OVSF _ used, and entering a step S9;
s8, judging that the code sequence with the serial number i is not used, excluding the code sequence, and entering the step S9;
s9, halving the spreading factor Sf, setting a code sequence number i to be 1, and entering a step S10;
s10, judging whether the current spreading factor Sf is equal to 2 or not;
if yes, go to step S11;
if not, returning to the step S3;
s11, parent codes on the same code tree branch are removed from the OVSF code usage set OVSF _ used to obtain a final OVSF code usage set, and OVSF code estimation is achieved.
Step S1 in this embodiment specifically includes:
s11, performing down-conversion processing on the received signal to obtain an IQ baseband signal corresponding to one frame;
s12, sequentially carrying out A/D conversion and descrambling processing on the IQ baseband signal to obtain baseband IQ data after descrambling synchronization;
s13, carrying out normalization processing on the independent I-path signal or Q-path signal in the baseband IQ data to obtain a preprocessed received signal;
the expression of the I path signal or the Q path signal is as follows:
wherein X is I-path signal or Q-path signal, X 1 ,x 2 ,...,x 38400 Is a data sample point of a WCDMA frame, V is white Gaussian noise, N is the number of users, C n (m) is m symbols of the nth user, OVSF n (SF, j) an OVSF code sequence with spreading factor SF and code number j used by the nth user;
for the OVSF code sequence with the code number j, the OVSF codes of all users are mutually orthogonal, and the product of the number of symbols M of each user and the corresponding spreading factor SF is the data volume of one frame, namely, M × SF =38400;
in step S3 of this embodiment, the average power values ap (i) of all despread symbols are:
in the formula, y k K =38400, which is a data sample point of the signal Y obtained after despreading processing;
wherein Y = [ Y = 1 ,y 2 ,...,y k ]And an OVSF code sequence with spreading factor Sf and serial number i in an OVSF (Sf, i) code tree.
For OVSF (Sf, i) and OVSF (Sf, j), the spreading factor of the OVSF code sequence actually used by the user is denoted by capital Sf, and the code sequence number is denoted by j; the spreading factor of the OVSF code sequence selected in the code tree for despreading is denoted by Sf, and the code number is denoted by i, so as to distinguish the code sequence actually used by the user.
If a certain OVSF (Sf, i) and a code sequence used by a certain user are positioned in the same branch of an OVSF code tree, the average power value of the despread symbols is larger; otherwise, due to the orthogonality of the OVSF codes, the despread symbol value is close to zero, and the average power value of the symbol is small, so that whether the code has a derivative relationship with the code used by the user can be distinguished through a power threshold Tap, but the specific spreading factor needs to be determined through a near-zero rate threshold, in step S5 of this embodiment, the set power threshold value Tap is:
in the formula, i is a code sequence number; ap (i) average power values of all the despread symbols; sf is the spreading factor. .
Example 2:
in this embodiment, there are 2 users in total, where the spreading factor used by user 1 is 256, the OVSF code with code number 162 is used as its spreading code, user 2 uses the OVSF code with spreading factor 128 and code number 2 as its spreading code, and the SNR is = -10dB, and the method of the present invention is used to estimate the OVSF code sequence of each user, and the specific steps are:
firstly, codes of each layer in the OVSF code tree are numbered according to the serial number i = 1.. Sf, as shown in fig. 2;
s1, preprocessing a received signal: before estimating the OVSF code sequence, the I-path or Q-path signals need to be normalized, that is:
X＝X/max(X)
and S2, setting an initial factor Sf =512, setting an initial search number i =1, considering that a despread symbol is close to 0 if the absolute value of the symbol is less than 0.006, defining a near-zero rate as the ratio of all symbols close to 0 to the total number of the symbols, and setting a near-zero rate threshold Tnzr =1% of the symbols.
S3, a code sequence with a spreading factor Sf and a sequence number i in the OVSF code tree is taken to de-spread the preprocessed signal to obtain Y, and the average power value ap (i) of all the de-spread symbols is calculated;
s4, judging whether the conditions that i is larger than Sf are met or not, and finding out all sequence numbers i meeting ap (i) > Tap;
when Sf =512, the despread symbol average power value is as shown in fig. 3, tap = -30.7475dB is calculated by the formula in embodiment 1, and it can be seen that the symbol average power after despreading by the OVSF code sequence with sequence numbers i =5, i =6, i =7, i =8, i =323, i =324 is greater than the threshold value because they are located on the same code tree branch as the OVSF code used by the user and have a derivative relationship.
S5, temporarily setting a spreading factor Sf, possibly using an OVSF code with a code number i, counting a near-zero rate nzr of a despread symbol, and if the code is a sub-code of OVSFn (Sf, j) used by a certain user actually, enabling values of despread partial symbols to be close to zero;
the near-zero rate of symbols after despreading by an OVSF code sequence with spreading factor Sf =512 and code number i =5,i =6,i =7,i =8,i =323,i =324 is 0.1876,0.1867,0.2133,0.1200,0.2533,0.2800.
S6, comparing the size relation between nzr and Tnzr, judging whether the OVSF codes are used, wherein the near zero rate of the symbols is larger than a threshold value Tnzr =0.01, so that the codes are judged to be not used, then performing the subsequent steps, and when Sf =2, ending the cycle to obtain the spreading factors and the code sequence numbers in the OVSF _ used set as shown in Table 1:
table 1: set of used OVSF codes
| |
16 | 32 | 64 | 128 | 32 | 64 | 128 | 256 |
| |
1 | 1 | 1 | 2 | 21 | 41 | 81 | 162 |
S7, finally, parent codes on the same code tree branch are removed from the used OVSF code set OVSF _ used, and the obtained OVSF code used by the end user 1 has the spreading factor Sf =128 and the code number 2; the OVSF code used by user 2 has a spreading factor Sf =256 and a code number of 162.
Example 3:
1-8 user signals are randomly generated, the spreading factor and the code sequence number of the OVSF code used by each user are random, the OVSF code used by each user meets the mutual orthogonal relation, the signal-to-noise ratio value range is from-24 dB to-2 dB, 100 independent experiments are carried out under each signal-to-noise ratio, the accuracy rate of the OVSF code spreading factor estimation is counted, as shown in figure 4, when the signal-to-noise ratio is higher than-15 dB, the accuracy rate of the identification of the OVSF code sequence can reach more than 90%, and the excellent performance of the method under the low signal-to-noise ratio is reflected.
Claims (5)
1. An OVSF code estimation method, comprising the steps of:
s1, preprocessing a received signal;
s2, setting an initial search spreading factor Sf =512, an initial search sequence number i =1 and a near-zero rate threshold Tnzr of a symbol;
s3, acquiring a current spreading factor Sf in an OVSF code tree, carrying out despreading processing on the preprocessed signal through an OVSF code sequence with a code number i, and calculating an average power value ap (i) of all symbols after despreading processing;
s4, judging whether the Sf is more than i;
if yes, increasing the sequence number i by 1, and returning to the step S3;
if not, the step S5 is carried out;
s5, setting a power value threshold Tap, finding out all serial numbers i meeting ap (i) > Tap in an OVSF code tree, and entering step S6;
s6, sequentially calculating the near-zero rate nzr of the de-spread symbols corresponding to the serial number i obtained in the step S5, and judging whether nzr is less than Tnzr or not;
if yes, entering step S7;
if not, the step S8 is carried out;
s7, judging that the code sequence with the code sequence number i is used, storing the corresponding spreading factor Sf and the code sequence number i into an OVSF code use set OVSF _ used, and entering the step S9;
s8, judging that the code sequence with the serial number i is not used, excluding the code sequence, and entering the step S9;
s9, reducing the spreading factor Sf by half, setting a code sequence number i to be 1, and entering a step S10;
s10, judging whether the current spreading factor Sf is equal to 2 or not;
if yes, entering step S11;
if not, returning to the step S3;
s11, parent codes on the same code tree branch are removed from the OVSF _ used set of the OVSF codes to obtain a final OVSF code used set, and OVSF code estimation is achieved.
2. The OVSF code estimation method according to claim 1, wherein the step S1 specifically comprises:
s11, performing down-conversion processing on the received signal to obtain an IQ baseband signal corresponding to one frame;
s12, sequentially carrying out A/D conversion and descrambling processing on the IQ baseband signal to obtain baseband IQ data after descrambling synchronization;
s13, carrying out normalization processing on the independent I-path signal or Q-path signal in the baseband IQ data to obtain a preprocessed received signal;
the expression of the I path signal or the Q path signal is as follows:
wherein X is I-path signal or Q-path signal, X 1 ,x 2 ,...,x 38400 Is a data sample point of a frame of WCDMA, V is white Gaussian noise, N is the number of users, C n (m) m symbols for the nth user, OVSF n And (SF, j) the spreading factor used by the nth user is SF, and the OVSF code sequence with the code number of j.
3. The method of claim 2, wherein the OVSF codes of each user are orthogonal to each other, and a product of the number of symbols M of each user and the corresponding spreading factor SF is a data amount of one frame, i.e., M x SF =38400.
4. The OVSF code estimation method of claim 2, wherein in step S3, the average power value ap (i) of all despread symbols is:
in the formula, y k K =38400, which is a data sample point of the signal Y obtained after despreading processing;
wherein Y = [ Y = 1 ,y 2 ,...,y k ]And an OVSF code sequence with spreading factor Sf and serial number i in an OVSF (Sf, i) code tree.
5. The OVSF code estimation method of claim 4, wherein in step S5, the set power threshold value Tap is:
in the formula, i is a code sequence number; ap (i) average power values of all the despread symbols; sf is the spreading factor.
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| EP1710927A2 (en) * | 2002-11-06 | 2006-10-11 | QUALCOMM Incorporated | Noise and channel estimation using low spreadindg factors |
| CN103560803A (en) * | 2013-11-18 | 2014-02-05 | 武汉大学 | Code-hopping direct spread communication method and system based on OVSF codes |
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| CN106789789B (en) * | 2016-12-29 | 2019-11-22 | 杭州电子科技大学 | The estimation of WCDMA signal scrambling code and information source information blind decoding method |
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| EP1710927A2 (en) * | 2002-11-06 | 2006-10-11 | QUALCOMM Incorporated | Noise and channel estimation using low spreadindg factors |
| CN1801682A (en) * | 2004-12-31 | 2006-07-12 | 方正通信技术有限公司 | Anti-interference method in CDMA system |
| CN103560803A (en) * | 2013-11-18 | 2014-02-05 | 武汉大学 | Code-hopping direct spread communication method and system based on OVSF codes |
| CN109951406A (en) * | 2019-01-11 | 2019-06-28 | 杭州电子科技大学 | Connection the asynchronous WCDMA number of accepting and believing number of users and scrambling code blind estimating method in fact |
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