CN115175378B - SrsRAN-based world fusion 5G terminal simulator and implementation method - Google Patents
SrsRAN-based world fusion 5G terminal simulator and implementation method Download PDFInfo
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Abstract
The invention discloses a srsRAN G terminal simulator realization method based on the integration of the heaven and earth, which utilizes cyclic prefixes of a plurality of orthogonal frequency division multiplexing symbols as auxiliary information to improve the synchronization performance on the basis of a PSS time-frequency estimation algorithm, and estimates decimal frequency offset by using a CP first and then estimates complete carrier frequency offset by using the PSS; and matching with the existing 5G NSA network architecture embedded in srsRAN open source projects to obtain the srsRAN-based heaven-earth fusion 5G terminal simulator. According to the invention, under the condition that the existing NR ground mobile communication standard is not required to be changed, an NR synchronization sequence is utilized, a time-frequency synchronization technology suitable for a satellite-ground link is designed, and a terminal simulator oriented to a 5G fusion low-orbit satellite is built, so that a ground 5G system and a low-orbit satellite communication system can be switched seamlessly.
Description
Technical Field
The invention belongs to the field of 5G fusion low-orbit satellite terminal simulators, and particularly relates to a srsRAN G fusion 5G terminal simulator based on srsRAN and an implementation method.
Background
With the explosive growth of mobile traffic, massive connection of devices and the advent of various new scenarios, a fifth generation mobile communication system has evolved. The satellite communication system and the ground communication system can form good complementary relation: satellite communication has the characteristics of wide coverage, small influence by factors such as terrain, natural disasters and the like, so that on one hand, satellite communication can be utilized to realize communication in areas which are difficult to cover by a ground network such as remote areas and the like; on the other hand, when the ground network is damaged due to the influence of natural disasters and other factors, the communication system is ensured not to be damaged; and the ground 5G system and the low-orbit satellite communication system are integrated, so that the advantages of the two communication systems can be fully exerted, and the network with seamless coverage and seamless switching worldwide is realized. However, since the two communication systems have great differences in network architecture, communication standards and the like, the two communication systems only reach the degree of interconnection and interworking at present.
Disclosure of Invention
In order to enable a ground 5G system and a low-orbit satellite communication system to be switched seamlessly, the invention provides a srsRAN-based terrestrial fusion 5G terminal simulator and an implementation method.
Based on the background, the applicability problem of the 5G air interface signal in the satellite-ground link is developed, the time-frequency synchronization technology under the large Doppler frequency shift scene is explored, the time-frequency synchronization problem under the large frequency shift environment is solved, and a terminal simulator based on srsRAN NR protocol stacks is designed.
The invention provides a method for realizing a srsRAN G terminal simulator based on the terrestrial fusion,
Based on a PSS time-frequency estimation algorithm, cyclic prefixes of a plurality of orthogonal frequency division multiplexing symbols are used as auxiliary information to improve synchronization performance, decimal frequency offset is estimated by using a CP first, and then complete carrier frequency offset is estimated by using the PSS; and matching with the existing 5G NSA network architecture embedded in srsRAN open source projects to obtain the srsRAN-based heaven-earth fusion 5G terminal simulator.
Further, the specific method for estimating the decimal frequency offset by using the CP and then estimating the complete carrier frequency offset by using the PSS comprises the following steps:
s1, receiving a baseband signal from a radio frequency buffer memory, and performing anti-aliasing filtering treatment;
S2, calculating a cross-correlation result of the received signal processed by the S1 and the K groups of local synchronous sequences to obtain K time-frequency estimation results;
S3, carrying out two-dimensional search on the K time-frequency estimation results in the S2, and updating a time-frequency estimation peak value;
s4, repeating the steps S1-S3 until the whole wireless frame is traversed, and obtaining a plurality of time-frequency estimation two-dimensional search results;
s5, carrying out one-dimensional search on the two-dimensional search results of the plurality of time-frequency estimation obtained in the S4, and searching for a time offset estimation value corresponding to the maximum peak value And integer frequency offset estimation value
S6, calculating the signal to noise ratio corresponding to the maximum peak value searched in the S5, if the signal to noise ratio is larger than a threshold value, completing time synchronization and frequency coarse synchronization, and if the signal to noise ratio is smaller than the threshold value, repeating the steps S1-S6;
s7, utilizing a plurality of OFDM cyclic prefixes to multiply and deviate decimal frequency of the received signal processed by S1 Estimating; combined with integer frequency biasAnd completing frequency synchronization.
Further, the method comprises the steps of,
In the S2, the generation mode of the local synchronous sequences is as follows
Wherein s l is a primary synchronization sequence of a multipath channel with a length L, v i is a eigenvector corresponding to the ith eigenvalue of the modulated DPSS matrix A k; the (i, j) th element of the modulated DPSS matrix A k may be represented as
Wherein the method comprises the steps of
Dividing the frequency offset searching range [ epsilon min,εmax ] into K segments to obtain K modulated DPSS matrixes A k and corresponding K groups of local synchronous sequences.
A srsRAN G terminal simulator based on the world fusion is realized according to the method.
A computer readable storage medium having stored therein at least one instruction, at least one program, code set, or instruction set loaded and executed by a processor to implement a srsRAN-based heaven-earth fusion 5G terminal simulator implementation method as described above.
The beneficial effects of the invention are as follows:
(1) The invention realizes the design of the terminal simulator in a mode of a software radio and USRP semi-physical communication simulation platform, and compared with a hardware communication simulation system, the invention has the advantages of low cost and easy optimization, and avoids the requirement of special communication hardware; compared with a software simulation communication system, the software simulation communication system is difficult to restore a complex satellite-ground link communication environment in a mathematical modeling mode, and the terminal simulator can adopt a real channel to carry out experiments;
(2) Compared with the prior art, the method realizes coarse time offset estimation and integer frequency offset estimation through the cyclic prefix of the OFDM signal used by 5G NR; and a sliding correlation algorithm based on a modulation DPSS matrix is provided, and the complexity of time-frequency synchronization in a large frequency offset environment is effectively reduced through a characteristic value decomposition and approximate calculation mode, so that the time-frequency synchronization algorithm is optimized;
(3) The time-frequency synchronization technology of the 5G fusion low-orbit satellite system can utilize an NR synchronization sequence to design a time-frequency synchronization technology suitable for a satellite-ground link under the condition that the existing NR ground mobile communication standard is not required to be changed, and a terminal simulator facing the 5G fusion low-orbit satellite is built.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention;
FIG. 2 is a top-to-bottom fusion 5G terminal simulator functional architecture in the present invention;
FIG. 3 is a flow of a downlink synchronization algorithm in the present invention;
Fig. 4 is a baseband IQ signal reception synchronization flow of srsRAN.
Detailed Description
The technical scheme of the invention is further described in detail below with reference to the accompanying drawings:
The invention provides a 5G terminal simulator based on a satellite-ground link, which specifically considers a time-frequency synchronization technology under a large Doppler frequency shift scene so as to solve the time-frequency synchronization problem under a large frequency shift environment. There are many significant differences between satellite and terrestrial communication systems, which also present many challenges for the convergence of air interface technologies. The most important problem is the large doppler shift caused by the high-speed motion of the low-orbit satellite, so that the 5G transmission method designed for the ground communication system cannot be directly applied to the low-orbit satellite communication system. In a converged communication network, in order to achieve high-speed data transmission, orthogonal frequency division multiplexing is used for downlink, so symbol timing synchronization and carrier frequency synchronization are critical to ensure performance. Through receiving the cell synchronization signal, the user equipment obtains symbol timing, frame timing, frequency offset estimation, cell ID and the like of the system. Considering that the 5G transmission method designed by the ground communication system cannot be directly applied to the low-orbit satellite communication system, but the ground mobile communication flow is explosively increased, in order to realize the global seamless coverage and seamless switching of the communication network, a more accurate time-frequency synchronization in a satellite-ground link is required to be realized by using a synchronization sequence specified by a 5G novel wireless air interface under the condition that the existing NR ground mobile communication standard is not required to be changed.
The m-sequence is a binary digital pseudo-random sequence generated by a linear feedback shift register, which is easy to generate, has good auto-correlation and cross-correlation properties, and is insensitive to frequency offset. And the NR selects m sequences as the generation sequences of the downlink main synchronization sequences, and the defined main synchronization signals are mainly used for acquiring the physical layer ID in the cell group and realizing time-frequency synchronization. Next, a brief description will be given of the PSS signal generation process of 5G NR
The 5G NR physical layer protocol specifies that PSS generation sequence d pss (k) occupies contiguous 127 subcarriers d pss (k) in the frequency domain, which can be expressed as
Wherein the method comprises the steps ofThe cell ID number of the physical layer in the group with the value range of 0-2 is expressed, and the parameter is used for distinguishing the main synchronous sequence of the adjacent cells. The sequence x (p) is generated in an iterative manner, and the generation formula is that
x(p+7)＝(x(p+4)+x(p))mod2 (2)
The initial value of the sequence x (p) is defined as
The frequency domain OFDM symbol containing the primary synchronization signal can be expressed as after resource mapping
Where k 0 denotes the sequence number of the frequency domain mapping position start subcarrier. N-point inverse fast Fourier transform is performed on the sequence d (k) to obtain a time domain synchronization signal s pss (N)
The invention adopts the following technical scheme for solving the technical problems by utilizing the PSS synchronization sequence specified by NR:
The system uses n=1536 subcarriers and for each OFDM time domain transmitted symbol, a cyclic prefix of length N g is added at its starting position to prevent ISI and to preserve orthogonality between the subcarriers. Assuming that the mth OFDM symbol transmitted is s m (N), where n=0, 1,..n+n g -1, the corresponding received signal r m (N) can be expressed as
Where ε is the normalized frequency offset for the subcarrier spacing, θ is the normalized time offset for the sampling spacing, h (L) is the impulse response of the first path of the multipath channel with length L, and z (n) is the additive Gaussian white noise at the receiving end.
The received signal removed cyclic prefix portion may be written as
rm＝D(ε)Smh+z (7)
And taking the cross-correlation property of the m sequence and different frequency offsets thereof into consideration, and performing frequency offset compensation on the received signals at frequency points within a specified frequency offset range. Based on the method, the traditional time-frequency two-dimensional optimization problem is converted into two one-dimensional search problems, the optimization problem is converted into an approximate objective function maximization problem, and an approximate expression of the time offset estimation objective function is given:
after the above-mentioned method is unfolded, the following forms can be obtained:
Wherein the method comprises the steps of
Parameter omega,Respectively defined as
It can be found that Matrix a can be split into a sphere Matrix (pro Matrix) multiplied by the modulation coefficients, so that it can be feature decomposed using a modulated DPSS Matrix to reduce the estimation algorithm complexity. Finally, the following time-frequency estimation expression is obtained:
Where v i is the ith column vector of the modulated DPSS matrix, Is the i-th local synchronization sequence.
Furthermore, when the frequency offset searching range is larger, the performance of the DPSS-assisted time-frequency synchronization algorithm (DPSS algorithm for short) is reduced, so that the larger frequency offset searching range is decomposed into a plurality of relatively smaller frequency offset searching ranges, and the maximum peak position is found in the ranges, so that the timing performance is improved under the condition of not improving the complexity. Dividing the frequency offset searching range [ epsilon min,εmax ] into K segments to obtain K modulated DPSS matrixes A k and corresponding K groups of local synchronous sequences.
Based on the PSS time-frequency estimation algorithm, cyclic prefixes of a plurality of orthogonal frequency division multiplexing symbols are used as auxiliary information to improve synchronization performance, and the CPs are used for estimating decimal frequency offset first and then the PSS is used for estimating complete carrier frequency offset, so that estimation complexity is effectively reduced. Based on the proposed downlink time-frequency synchronization algorithm suitable for the satellite-ground link, the terminal simulator oriented to the 5G fusion low-orbit satellite network can be designed by matching with the existing 5G NSA network architecture embedded in srsRAN open-source projects and is responsible for realizing terminal high-layer protocol processing and physical layer baseband signal processing.
The terminal simulator oriented to the 5G fusion low-orbit satellite network is responsible for realizing terminal high-layer protocol processing and physical layer baseband signal processing. When the terminal is just started, as the terminal does not have any cell information, firstly, blind detection is performed on the downlink synchronous signals sent by the base station. The terminal simulator firstly receives the intermediate frequency signal in the downlink, obtains the digital baseband IQ signal through the ADC, then completes the peak search of the downlink synchronous signal, completes the frame timing and obtains the physical cell identifier 2. And then performing operations such as OFDM symbol demodulation, physical resource demapping and the like to receive the physical broadcast channel, the physical downlink control channel and the physical downlink shared channel signals. After the downlink channel signal receiving and processing process is completed, the terminal simulator sends the processed signal to the higher layer protocol processing module. After the downlink time-frequency synchronization is completed, if the higher layer of the terminal has data to be transmitted, the physical layer of the terminal will receive the TB transmitted by the higher layer protocol processing module and respectively transmit the uplink control channel and the physical uplink shared channel signals. And secondly, the physical layer of the terminal performs resource mapping on the transmitted data to obtain frequency domain information and performs OFDM modulation on the frequency domain information, and meanwhile, the physical layer transmits PRACH signals through an uplink random access process according to downlink frame timing information and clock signals, and the PRACH signals are converted into intermediate frequency signals through DAC (digital-to-analog converter) and are transmitted.
As shown in fig. 3, (1) the UE starts to receive downlink air interface data, and at the same time, the sliding window starts to perform sliding interception on the received data and store the received data. srsRAN each TTI of the physical layer receives and processes one subframe length data from the USRP, and the sliding window length of the initial state is set to be 14 OFDM time domain symbol data lengths;
(2) And continuously receiving half-frame length data, and carrying out initial synchronous DPSS related calculation and related result peak search on the intercepted data.
(3) After the detection of the field data is completed, the maximum result peak position meeting the synchronization threshold can be obtained, and the system enters an initial synchronization state. At the moment, the initial position of the sliding window is adjusted to the position of the maximum energy PSS detected by initial synchronization, a CP sequence in the PSS is intercepted, and the frequency offset is calculated;
(4) And recording the synchronous frame number according to the relation between the detection threshold and the initial synchronous threshold, and if the continuous synchronous frame number reaches 3 times, entering a tracking synchronous state by the system. The length of a sliding window for tracking synchronization is shortened to 3 OFDM symbol lengths, meanwhile, the tracking synchronization algorithm is utilized for calculation so as to improve timing performance, and the window position is adjusted so that the PSS sequence is positioned at the center position of the sliding window, therefore, the position of the PSS sequence is predicted according to the dynamic time delay characteristic of a low-orbit satellite communication system;
(5) Recording the out-of-step frame number according to the relation between the synchronous detection threshold and the tracking synchronous threshold, and if the continuous out-of-step frame number is smaller than 3, searching the next half frame data according to the tracking synchronous flow; if the continuous step-out frame number is more than 3, returning to an initial synchronous state, and restarting the system to perform sliding search;
the above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.
Claims (4)
1. A method for realizing a srsRAN G terminal simulator based on the space-earth fusion is characterized in that cyclic prefixes of a plurality of orthogonal frequency division multiplexing symbols are used as auxiliary information on the basis of a PSS time-frequency estimation algorithm to improve the synchronization performance, decimal frequency offset is estimated by using a CP first, and then complete carrier frequency offset is estimated by using the PSS; matching with the existing 5G NSA network architecture embedded in srsRAN open source projects to obtain a srsRAN-based heaven-earth fusion 5G terminal simulator;
the specific method for estimating the decimal frequency offset by using the CP and then estimating the complete carrier frequency offset by using the PSS comprises the following steps:
s1, receiving a baseband signal from a radio frequency buffer memory, and performing anti-aliasing filtering treatment;
S2, calculating a cross-correlation result of the received signal processed by the S1 and the K groups of local synchronous sequences to obtain K time-frequency estimation results;
S3, carrying out two-dimensional search on the K time-frequency estimation results in the S2, and updating a time-frequency estimation peak value;
s4, repeating the steps S1-S3 until the whole wireless frame is traversed, and obtaining a plurality of time-frequency estimation two-dimensional search results;
s5, carrying out one-dimensional search on the two-dimensional search results of the plurality of time-frequency estimation obtained in the S4, and searching for a time offset estimation value corresponding to the maximum peak value And integer frequency offset estimation value
S6, calculating the signal to noise ratio corresponding to the maximum peak value searched in the S5, if the signal to noise ratio is larger than a threshold value, completing time synchronization and frequency coarse synchronization, and if the signal to noise ratio is smaller than the threshold value, repeating the steps S1-S6;
s7, utilizing a plurality of OFDM cyclic prefixes to multiply and deviate decimal frequency of the received signal processed by S1 Estimating; combined with integer frequency biasCompleting frequency synchronization;
the method also comprises the following downlink synchronization algorithm:
The UE starts to receive downlink air interface data, and simultaneously the sliding window starts to work to slide, intercept and store the received data; srsRAN each TTI of the physical layer receives and processes one subframe length data from the USRP, and the sliding window length of the initial state is set to be 14 OFDM time domain symbol data lengths;
continuously receiving half-frame length data, and carrying out initial synchronous DPSS (digital video sequence) related calculation and related result peak search on intercepted data;
After the detection of the field data is completed, the maximum result peak position meeting the synchronization threshold value can be obtained, the system enters an initial synchronization state, at the moment, the initial position of the sliding window is adjusted to the position of the maximum energy PSS detected by initial synchronization, the CP sequence in the PSS is intercepted, and the frequency offset is calculated;
according to the relation between the detection threshold and the initial synchronization threshold, recording the synchronization frame number, if the continuous synchronization frame number reaches 3 times, enabling the system to enter a tracking synchronization state, shortening the length of a sliding window for tracking synchronization to 3 OFDM symbol lengths, simultaneously utilizing a tracking synchronization algorithm to calculate so as to improve timing performance, adjusting the window position to enable the PSS sequence to be located at the center position of the sliding window, and predicting the position of the PSS sequence according to the dynamic time delay characteristic of a low-orbit satellite communication system;
recording the out-of-step frame number according to the relation between the synchronous detection threshold and the tracking synchronous threshold, and if the continuous out-of-step frame number is smaller than 3, searching the next half frame data according to the tracking synchronous flow; if the number of continuous step-out frames is greater than 3, returning to an initial synchronous state, and restarting the system to perform sliding search.
2. The method according to claim 1, wherein in S2, the K-group local synchronization sequences are generated by
Wherein S 1 is a primary synchronization sequence of a multipath channel with a length of L, V i is a eigenvector corresponding to the i-th eigenvalue of the modulated DPSS matrix a k; the (i, j) th element of the modulated DPSS matrix A k may be represented as
Wherein the method comprises the steps of
Dividing the frequency offset searching range [ epsilon min,εmax ] into K segments to obtain K modulated DPSS matrixes A k and corresponding K groups of local synchronous sequences.
3. A srsRAN G terminal simulator based on heaven and earth fusion, characterized by an implementation of the srsRAN terminal simulator based on heaven and earth fusion implementation method according to any of claims 1-2.
4. A computer readable storage medium having stored therein at least one instruction, at least one program, code set, or instruction set loaded and executed by a processor to implement a srsRAN-day fusion 5G terminal simulator implementation method according to any one of claims 1-2.
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| CN106658402A (en) * | 2016-09-30 | 2017-05-10 | 北京云格智道科技有限公司 | Mobile front-end part and mobile location information processing system comprising same |
| WO2018072521A1 (en) * | 2016-10-17 | 2018-04-26 | 深圳市中兴微电子技术有限公司 | Method and device for detecting primary sidelink synchronization signal and storage medium |
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| CN106658402A (en) * | 2016-09-30 | 2017-05-10 | 北京云格智道科技有限公司 | Mobile front-end part and mobile location information processing system comprising same |
| WO2018072521A1 (en) * | 2016-10-17 | 2018-04-26 | 深圳市中兴微电子技术有限公司 | Method and device for detecting primary sidelink synchronization signal and storage medium |
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