CN108540278A - A kind of fast decoding method of Physical Broadcast Channel system message in LTE communication system - Google Patents

Abstract

The invention relates to a fast decoding method of a physical broadcast channel system message in an LTE communication system, and belongs to the technical field of mobile communication. The method includes the following steps: (1) In order to quickly realize downlink synchronization, use the PSS code segmentation aliasing fast correlation method to find the frame start position; (2) Extract all possible antenna ports according to the number of antenna ports that may be used for sending data. CRS information, and obtain the complete channel information H by linear interpolation; (3) use the Kalman filter algorithm to smooth the phase scatter diagram of the channel information H, and get the difference between the fitting curve and the original scatter diagram absolute phase error (4) According to the absolute error of the set threshold and 4 ports A decision is made to obtain the number of antenna ports. Then perform PBCH decoding, and if the CRC check passes, the decoding is successful. The method speeds up the speed of downlink synchronization, avoids the PBCH blind detection operation caused by the unknown number of antenna ports, and can greatly speed up the decoding speed of the PBCH.

Description

A Fast Decoding Method of Physical Broadcast Channel System Messages in LTE Communication System

technical field

The invention belongs to the technical field of wireless communication, and relates to a fast decoding method of physical broadcast channel system messages.

Background technique

LTE (Long Term Evolution, Long Term Evolution) is a long-term evolution technology of the UMTS (Universal MobileTelecommunications System, Universal Mobile Communications System) technical standard formulated by 3GPP (The 3rd Generation Partnership Project, Third Generation Partnership Project). The project was formally established and launched at the 3GPP Toronto meeting in July. The Ministry of Industry and Information Technology officially issued the "LTE/4th Generation Digital Cellular Mobile Communication Service (TD-LTE)" business license to China Mobile, China Unicom and China Telecom in December 2013, and officially issued it to China Telecom and China Unicom in February 2015 "LTE/Fourth Generation Digital Cellular Mobile Communication Service (FDD-LTE)" business license. At the same time, the LTE system introduces key technologies such as OFDM (Orthogonal Frequency Division Multiplexing) and MIMO (Multi-Input&Multi-Output, multiple input multiple output), which significantly increases the spectrum efficiency and data transmission rate, compared with the previous generation Compared with LTE, mobile communication better satisfies people's demand for high-speed information transmission. Its downlink peak rate can reach 100Mbps, and its uplink can reach 50Mbps.

The LTE network is mainly composed of E-UTRAN (access network) and EPC (core network), the access network is composed of eNodeB, the core network is composed of MME (Mobility Management Entity), S-GW (Serving Gateway) and P-GW (PDNGateway )constitute. The UE (user terminal) connects to the eNodeB, and then the eNodeB connects to the EPC, providing a seamless mobile IP connection between the UE and the packet data network. The LTE communication system protocol stack is the RRC layer, PDCP layer, RLC layer, MAC layer, and physical layer from top to bottom. Among them, the physical layer realizes the function of mapping the transport channel to the physical channel. The downlink of the physical layer mainly includes PBCH (Physical Broadcast Channel), PDSCH (Physical Downlink Shared Channel), PMCH (Physical Multicast Channel), and PDCCH (Physical Downlink Control Channel) , PCFICH (Physical Control Format Indicator Channel) and PHICH (Physical HARQ Indicator Channel). Wherein the present invention relates to the process of quickly deciphering MIB messages on the physical broadcast (PBCH) channel in the physical layer.

On the eNodeB side, the PBCH transmission block is subjected to channel coding and rate matching, followed by scrambling and QPSK modulation. After layer mapping and precoding operations, RE mapping and IFFT transformation are performed, and then digital up-conversion operation is performed, and multi-antenna diversity transmission is used for signal transmission. broadcast. The MIB message transmitted by the PBCH contains 24 bits of data, the first 14 bits are information bits, and the last 10 bits are blank bits. The contents contained in the MIB information bits are: 3-bit bandwidth indication bits, used to indicate dl-Bandwidth (n6, n15, n25, n50, n100); 3-bit PHICH config indication bits, of which 1 bit indicates the PHICH duration (normal/ extend), 2 bits indicate the number of PHICH resources (1/6, 1/2, 1, 2); the last 8 bits are used to indicate the upper 8 bits of SFN (System Frame Number, system frame number), and the lower 2 bits of SFN pass PBCH blind detection get.

In the LTE system, the traditional cell search and downlink synchronization process mainly rely on the good constant modulus zero autocorrelation characteristic of the primary synchronization PSS sequence. The complete PSS sequence is generated locally to correlate with the received PSS sequence, and the position of the correlation peak is used to judge The position of the main synchronization code, so as to further obtain the frame start position. A set of PSS sequences consists of 63 ZC sequences with values, and there are 168 sets of local PSS sequences. The traditional sliding correlation algorithm has a large amount of calculation and a high time delay. In addition, the signal sending end can send the PBCH message through four antennas with port numbers 0, 1, 2, and 3, and the antenna port number information is implied in the cyclic redundancy check code (Cyclic Redundancy Check) in the physical broadcast channel MIB message Check, CRC). The traditional blind detection algorithm needs to perform a complete PBCH decoding operation on all the antenna port numbers that may be used for transmission, and then perform port number verification by judging whether the CRC check is passed. It may go through three complete decoding processes, which requires a large amount of calculation and has a great impact on the delay of the system.

Contents of the invention

The purpose of the present invention is to overcome above-mentioned weak point, provide a kind of fast decoding method of physical broadcast channel system message, this method can realize the fast correlation of primary synchronization code, effectively reduce the time that downlink synchronization process consumes; And by Kalman The filtering algorithm performs smooth filtering on the phase of the channel estimation value, and makes a difference between the filtering result and the phase of the actual received value. The resulting difference is recorded as ε, and the threshold γ is set. Compared with γ, the number of antenna ports used by the transmitting end can be obtained without blind detection.

To achieve the above object, the present invention provides the following technical solutions:

A fast decoding method of an LTE system physical broadcast channel system message, comprising the following steps:

S1: After the eNodeB sends downlink PBCH data, the UE first performs cell search and downlink synchronization. The downlink synchronization process utilizes the strong autocorrelation of the PSS code ZC sequence to take half-frame-long receiving sequence for segmentation superposition operation, and then perform sliding correlation between the superimposed sequence and the local PSS code, and the position where the correlation peak appears is the position of the PSS code . The possible SSS code positions are deduced from the PSS code positions, and all possible positions are correlated with the local SSS code group to obtain the frame start position.

S2: Extract the information of subframe 0 where the PBCH channel message is located, perform OFDM demodulation, de-subcarrier mapping, and antenna port number detection operations, and extract cell-specific reference signals ( CRS) message, the channel information is obtained according to the ratio of the received CRS and the local CRS, and the complete channel information H is obtained by linear interpolation.

S3: According to the channel information H, obtain the phase discrete point diagram of the resource particle in the time-frequency resource map of the transmitted data, and use the Kalman filter algorithm to perform smoothing and filtering to obtain a fitting curve, and take the absolute value after making a difference between the fitting curve and the discrete point diagram to obtain average error Will Compare with the threshold value γ to get the number of antenna ports.

S4: Extract the corresponding PBCH message according to the identified number of antenna ports, so as to perform deprecoding, delayer mapping, QPSK demodulation, descrambling, derate matching, and de-channel coding operations on the PBCH channel, and then perform antenna port calibration. If the CRC check passes at this time, it means that the detection of the number of antenna ports is successful, and the decoding of the PBCH channel is successful.

Further, in step S1, the specific methods of fast cell search and downlink synchronization are as follows:

First, after receiving downlink data, the UE needs to perform cell search and downlink synchronization. Take the length of the half-frame baseband data as M, and the baseband sequence as s. According to the LTE frame structure, there must be PSS (Primary Synchronization) code and SSS (Secondary Synchronization) code in any half-frame data. The half-frame data, etc. The length is divided into b sections and then superimposed directly, and the length of the last section can be different from the length of other sections. The superimposed sequence still has the strong autocorrelation characteristics of the ZC sequence, and the correlation peak can be obtained by correlating with the local PSS code sequence. Formula (1) represents the i-th segmented sequence, and formula (2) represents the superimposed segmented sequence.

The result obtained by performing sliding correlation between the superimposed sequence and the locally generated PSS code sequence is denoted as r(n), and the position r _max (n)=r(k) of the maximum value in r(n), then the PSS code may Exist at the position k of each segment, take the position k of each segment to perform correlation calculation to obtain the correlation value sequence: r ₁ (k), r ₂ (k), r ₃ (k),...,r _b (k). Note that the sequence where the maximum value is located is b _max , then the position p of the PSS code can be obtained as: Thus, field detection is completed. According to the position of the PSS code, all possible SSS code positions are inferred, and the whole frame detection is completed by correlation with the local sequence; then, the frame start position is obtained by referring to the synchronization code mapping position in the LTE time-frequency resource map.

Further, in step S2, the specific method of determining the corresponding CRS position through the number of possible antenna ports, thereby extracting the channel information H is as follows:

Extract the information of subframe 0 where the PBCH channel message is located, perform OFDM demodulation, desubcarrier mapping, and antenna port number detection operations, and the sending end uses 1/2/4 antenna ports to send data, corresponding to port 0/port 0 , 1/port 0, 1, 2, 3 three cases. According to the agreement, using different ports will map CRS on resource elements with different time-frequency resource diagrams. The received value Y(k) is extracted according to all possible CRS mapping positions, and divided by the local CRS, so as to obtain the channel state information H(k) corresponding to the possible CRS positions.

Using the linear interpolation method, the channel information H of the remaining positions is estimated, so as to obtain the complete channel information:

Where m represents the sequence number of the cell reference signal within a symbol, _If represents the interval between the frequency domains of the diamond-shaped cell reference signals, and k and l are the frequency domain and time domain indexes of REs, respectively.

Further, in step S3, the specific method for calculating the number of antenna ports by the Kalman filter algorithm is:

Extract the data of subframe 0 where the PBCH message is located to detect the number of antenna ports, traverse all possible mapping methods of the reference signal, and obtain the channel estimation value H in the three cases where the number of antenna ports is 1, 2, and 4, and use Kalman filtering The phase discrete points of H are smoothed to obtain the fitted line, and the absolute value of the difference between the phase discrete points and the fitted line is averaged to obtain the average error The value is shown in formula (4):

Wherein, X(k) represents the phase value of point k on the fitting line after Kalman filtering, Y(k) represents the phase value of point k of the received data, and H(k) represents the channel information of point k. By comparing the set threshold γ with the average error , so as to determine the number of antenna ports.

Further, in step S4, the specific method for verifying whether the number of antenna ports is successfully detected is as follows:

The corresponding PBCH message is extracted according to the determined number of antenna ports, so as to perform deprecoding, layer mapping, QPSK demodulation, descrambling, rate matching, and channel coding operations on the PBCH channel, and then check the number of antenna ports. Because the information of the number of antenna ports of the PBCH is implicit in the mask information of the cyclic redundancy check code of the PBCH, if the CRC check passes at this time, it means that the detection of the number of antenna ports is successful, and the decoding of the PBCH channel is successful. This method determines the number of antenna ports before decoding, which avoids the problem that the traditional blind detection method may need to complete decoding three times, and greatly reduces the computational complexity.

Description of drawings

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic flow diagram of wireless frame data aliasing and sliding correlation algorithm for PSS fast synchronization of LTE system;

FIG. 2 is a CRS time-frequency resource mapping diagram using different antenna ports;

Fig. 3 is the algorithm flowchart of the phase estimation value of Kalman filter optimization channel information;

FIG. 4 is a flow chart of an algorithm for detecting the number of antenna ports based on Kalman filtering.

Detailed ways

In order to enable those skilled in the art to better understand the purpose, technical solutions and beneficial effects of the present invention, a complete description will be given below in conjunction with specific embodiments and accompanying drawings.

Fig. 1 is a schematic flow diagram of wireless frame data aliasing and sliding correlation algorithm for PSS fast synchronization of LTE system;

After receiving the downlink message sent by the base station side, the LTE terminal user first performs cell search and downlink synchronization. Take the length of the half-frame baseband data as M. According to the LTE frame structure, there must be PSS (Primary Synchronization) code and SSS (Secondary Synchronization) code in any half-frame data. After dividing the half-frame data into b segments Directly superimposed, the length of the last segment during segmentation can be different from the length of other segments, if the length is different, N chips are extended to make up for it. The superimposed sequence still has the strong autocorrelation characteristics of the ZC sequence, and the correlation peak can be obtained by correlating with the local PSS code sequence. The result obtained by performing sliding correlation between the superimposed sequence and the locally generated PSS code sequence is denoted as r(n), and the position r _max (n)=r(k) of the maximum value in r(n), then the PSS code may exists at the position k of each segment, and the correlation value sequence obtained by taking the position k of each segment for correlation calculation: r ₁ (k), r ₂ (k), r ₃ (k),..., r _b ( k). Note that the sequence where the maximum value is located is b _max , then the position p of the PSS code can be obtained as: Thus, field detection is completed. According to the position of the PSS code, all possible SSS code positions are inferred, and the whole frame detection is completed by correlation with the local sequence; then, the frame start position is obtained by referring to the synchronization code mapping position in the LTE time-frequency resource map.

FIG. 2 is a CRS time-frequency resource mapping diagram using different antenna ports;

When the base station sends the PBCH signal, it can only choose to use ports 0, 1, 2, and 3 to send data, so it is necessary to determine which port is used to send the received data during detection at the receiving end. After the downlink synchronization operation is completed, the information of subframe 0 where the PBCH message is located is extracted, and OFDM demodulation, de-subcarrier mapping, and antenna port number detection operations are performed. The sending end uses 1/2/4 antenna ports to send data, corresponding to Use port 0/port 0, 1/port 0, 1, 2, 3 three cases. According to the agreement, using different ports will map CRS on different resource elements in the time-frequency resource graph. Figure 2 shows the corresponding mapping positions of the CRS in the time-frequency resource diagram when the four ports transmit data. The received value Y(k) is extracted according to all possible CRS mapping positions, and divided by the local CRS, so as to obtain channel information H(k) estimated from three possible CRS positions.

Equation (3) uses the linear interpolation method to estimate the channel information H of the remaining positions, so as to obtain the complete channel information:

Where m represents the sequence number of the cell reference signal within a symbol, _If represents the interval between the frequency domains of the diamond-shaped cell reference signals, and k and l are the frequency domain and time domain indexes of REs, respectively.

Fig. 3 is the algorithm flowchart of the phase estimation value of Kalman filter optimization channel information;

According to the complete channel information estimated by S2, the phase value of each resource element in the time-frequency resource map is smoothed by the Kalman filter algorithm. Figure 3 is the flow chart of the processing process. The specific update algorithm is as follows:

Based on the known optimal initial phase and covariance, predict and estimate the phase and covariance of the next state:

p(k|k-1)＝A·p(k-1|k-1)·A'+Q (5)

in, is the optimal result in k-1 state, It is the result predicted according to the previous state, U(k) represents the control amount of the system at time k, and A and B are system parameters. The phase measurement value of state k is Z(k), and the optimal estimated value of current state k is obtained according to the measured value and predicted value

The Kalman gain is:

Kg(k)＝p(k|k-1)·H'/(H·p(k|k-1)·H'+R) (7)

At the same time, the covariance in state k needs to be updated:

p(k|k)=(l-Kg(k)·H)·p(k|k-1) (8)

FIG. 4 is a flow chart of an algorithm for detecting the number of antenna ports based on Kalman filtering.

The phase value obtained after Kalman filtering is fitted to the point on the regression line and the discrete point of the received phase value is taken as the difference, and then the absolute value is taken, which is recorded as the average value of the absolute error

By judging the mean value of the error The size of the threshold γ is used to determine whether the current antenna port is configured with CRS, thereby determining the number of antenna ports used by the sending end. First determine the port 2 and port 3 Whether it is less than the threshold value, if so, the number of transmitting antenna ports is 4; otherwise, it is judged that the port 1 Whether it is less than the threshold value, if so, the number of sending antenna ports is 2; otherwise, the number of sending antenna ports is 1. After detecting the number of antenna ports, decode the PBCH information and perform a CRC check. If the check is passed, it means that the number of antenna ports is checked successfully, and the PBCH message is successfully decoded.

Claims (2)

1. A method for fast decoding of a physical broadcast channel system message in an LTE communication system, the method comprising the steps of:

   s1: after an eNodeB side sends data of a downlink Physical Broadcast Channel (PBCH), a UE side firstly carries out cell search and downlink synchronization; the method comprises the following steps that downlink synchronization uses strong autocorrelation of a ZC sequence of a primary synchronization code (PSS), a half-frame-length receiving sequence is taken for carrying out segmentation superposition operation, the superposed sequence and a local PSS code are subjected to sliding correlation, and the position where a correlation peak appears is the position of the PSS code; calculating possible secondary synchronization code (SSS) positions through PSS code positions, and correlating all the possible positions with a local SSS code group to obtain a frame starting position;

   s2: extracting information of a subframe 0 in which a PBCH channel message is positioned, performing OFDM demodulation, subcarrier mapping removal and antenna port number detection operations, respectively extracting CRS messages under the condition that antenna ports are 0,1,2 and 3, obtaining channel information according to the ratio of received CRS to local CRS, and obtaining complete channel information H by a linear interpolation method;

   s3: obtaining a phase discrete point diagram of each resource particle in a time-frequency resource diagram of the transmission data according to the channel information H, performing smooth filtering by using a Kalman filtering algorithm to obtain a fitting curve, taking the absolute value and the average value after the phase point of the corresponding position of the fitting curve is differed from the discrete point diagram to obtain an average errorWill be provided withComparing with a self-set threshold value gamma to obtain the number of antenna ports;

   s4: extracting corresponding PBCH information according to the judged number of the antenna ports, performing operations of de-precoding, de-layer mapping, QPSK demodulation, descrambling, de-rate matching and de-channel coding on the PBCH information, and then performing antenna port verification, wherein if CRC verification passes at this time, the detection of the number of the antenna ports is successful, and the decoding of the PBCH channel is successful.
2. 2. The method of claim 1 for fast decoding of a physical broadcast channel system message in an LTE communication system, characterized in that: extracting data of a subframe 0 in which PBCH channel information is located to detect the number of antenna ports, traversing all possible mapping modes of a reference signal to respectively obtain channel estimation values H under the three conditions that the number of the antenna ports is 1,2 and 4, smoothing phase discrete points of H by using Kalman filtering to obtain a fitting curve with high stability, and averaging absolute values of differences between the phase discrete points and the fitting curve to obtain an average error The values are shown in formula (3):

   x (k) represents a phase value of a k point on a fitting line after Kalman filtering, Y (k) represents a phase value of a k point of received data, and H (k) represents channel information of the k point;

   by comparing a set threshold gamma with the mean errorSo as to judge the number of antenna ports; and carrying out PBCH decoding operation according to the judged number of the antenna ports, wherein if CRC verification is successful, the decoding of the physical broadcast channel system message is successful.