CN116760667A - Method for multi-cell channel joint estimation in time division duplex cellular network - Google Patents
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Abstract
The invention discloses a method for jointly estimating multi-cell channels in a time division duplex cellular network, and belongs to the technical field of wireless communication. The method comprises the following steps: in the cell searching stage, firstly searching a main cell according to the conventional steps, acquiring system information and a current frame number, then applying interference deletion to PBCH/PSS/SSS signals to acquire neighbor cell system information, and reconstructing a PBCH/PSS/SSS local sequence of the cell in each frame by only updating the frame number when the system information of one neighbor cell is solved; in the channel estimation stage, the received signal of each frame PBCH/PSS/SSS is taken out, the received signal, the multi-cell multi-port local sequence and the equation set of the channel information thereof are listed, and the number of unknown variables is reduced by assuming that adjacent time-frequency resource channels are kept unchanged, so that the equation set has a unique solution. The method can simultaneously obtain the multi-cell multi-port interference-free channel information, and can obtain high recognition accuracy under different scenes when being applied to wireless gesture recognition.
Description
Technical Field
The invention relates to a method for jointly estimating multi-cell channels in a time division duplex cellular network, belonging to the technical field of wireless communication.
Background
Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD) are widely used in mobile communication networks as two important duplexing modes. TDD is widely used in high frequency bands because of its channel reciprocity, which is more suitable for the advantage of beamforming. Because the TDD adopts different time slots to distinguish uplink and downlink data, the whole network is synchronous in actual deployment and the same uplink and downlink subframe proportion is adopted to prevent uplink and downlink self-interference.
Mobile communication networks typically employ cellular networking to achieve coverage of different areas. Compared with different-frequency networking, the same-frequency networking has high spectrum utilization rate, is convenient for a terminal (UE) to carry out neighbor cell measurement, and is widely applied to fourth-generation (4G) and fifth-generation (5G) mobile communication systems. But the biggest drawback of co-channel networking is inter-cell interference (ICI). Inter-cell interference occurs when neighboring cells simultaneously transmit data in the same Resource Block (RB). Especially, when reference symbols used for channel estimation are interfered, the estimation result of Channel State Information (CSI) may be inaccurate. For conventional communication systems, inter-cell interference may reduce the signal-to-interference-and-noise ratio, resulting in an increase in bit error rate and a decrease in cell throughput. When the method is applied to a general sense integrated system, the result of channel estimation is inaccurate, and the perceptual performance is reduced.
In practical applications, the inter-cell interference can be reduced to a certain extent by some network deployment schemes and physical layer signal designs. The 4G/5G network ensures that the adjacent cell reference symbols are distributed in different frequency domain subcarriers through a Physical Cell Identification (PCI) distribution scheme. For example, in 4G physical layer standard Long Term Evolution (LTE), the subcarrier index of the single-port reference symbol is PCI modulo 6, the subcarrier indexes of the dual-port and four-port are PCI modulo 3, and the Cell Reference Symbol (CRS) can be made on different subcarriers by allocating PCIs with different modulo values to neighboring cells. Also, in the physical layer standard new air interface (NR) of 5G, the PCIs of adjacent cells are set to different modulo-4 values to ensure that different synchronization signals and frequency domain positions of demodulation reference symbols (DMRS) in a downlink broadcast channel block (SSB) are different.
Although the above method ensures that there is no interference between reference symbols, interference between reference symbols and other signals still exists. For example, in LTE, when a certain RB is used for scheduling a downlink control channel (PDCCH) or a downlink shared channel (PDSCH), subcarriers other than the CRS of the own cell are used to fill PDCCH or PDSCH data. The CRS of the primary cell may interfere with the PDCCH and PDSCH of the neighbor cell. Common interference suppression methods include beamforming and interference cancellation. Beamforming can be applied in scenarios where the direction of the interfering incoming wave is known, but relies on multi-antenna processing. When the number of interference streams becomes large, the effect of beamforming becomes poor. However, the interference cancellation can be implemented under a single antenna, but requires that the interference source sequence is known, and the implementation complexity is high when the number of interference flows is high. Considering that in a cellular network, PDCCH/PDSCH of a neighboring cell is difficult to solve in the cell, and the method for deleting interference is difficult to apply.
In addition, in the application of positioning based on cellular signals, gesture recognition and other through sense integration, accuracy can be improved through multi-cell channel joint sensing. Since the CRS of each cell is distributed over different subcarriers, it is theoretically possible to acquire the channels of the terminal to multiple cells based on the CRS. However, in general, the signal of the main cell is stronger than that of the neighboring cell, and the reference symbols of the neighboring cell are also interfered by the signal of the main cell, and the interference is larger than that of the neighboring cell to the main cell. Therefore, neighbor CSI obtained based on CRS is less accurate than the own cell CSI.
Disclosure of Invention
In order to inhibit inter-cell interference without depending on multiple antennas and obtain the CSI of multiple cells at the same time, the invention provides a method for jointly estimating multiple cell channels in a time division duplex cellular network. And then simultaneously solving the multi-cell multi-port CSI by a simultaneous equation system solving method. Under the condition that the number of equations is smaller than the number of CSI streams to be solved, the number of unknown CSI variables is reduced by assuming that the frequency domain channels of the cells are identical on adjacent time-frequency resource grids (REs), and the realization equation has unique solution.
A method for multi-cell channel joint estimation under a time division duplex cellular network comprises the following specific steps:
step 1: and searching and acquiring main cell system information in the received multi-cell mixed signal, and sequentially calculating the frame numbers of all subsequent frames according to the frame number of the current frame.
Step 2: and searching and acquiring all neighbor cell system information in the received multi-cell mixed signal.
Step 3: the local sequence of the PBCH/PSS/SSS of all the main cells and the neighbor cells at each transmitting port of each frame is reconstructed.
Step 4: taking any one signal in PBCH/PSS/SSS every frame, listing the equations of the received signal, the multi-cell multi-port local sequence and the multi-cell multi-port channel under each RE as follows:
the relation of the received signal under each RE, the transmitted signal of each port of each cell and the channel thereof is established as follows:
wherein y (k, l), w (k, l) represent the received signal and white noise of subcarrier k and OFDM symbol l, respectively; h is a p,c (k,l)，x p,c (k, l) represent the frequency domain channel and local signal sequence, respectively, of the antenna port p of cell c; c is the total number of cells; p (c) is the number of transmit ports per cell.
Keeping the channels of adjacent REs unchanged, and keeping the frequency domain channels of K subcarriers and L symbols around each subcarrier as the center the same, the above equation is approximated for each RE (K, L):
step 5: and (3) solving the equation set obtained in the step (4) by taking each RE as a center to obtain a multi-cell multi-port channel estimated value.
The invention has the advantages that:
1. according to the method for multi-cell channel joint estimation under the time division duplex cellular network, according to the LTE/NR frame format and the broadcasting channel characteristics, the broadcasting channel local sequence of all frames can be reconstructed through the decoding result of any frame broadcasting channel;
2. the method for jointly estimating the multi-cell channels in the time division duplex cellular network solves the channels from the terminal to the multi-transmitting antennas of the multiple cells in a combined mode, and the solved result is not affected by inter-cell interference;
3. the method for jointly estimating the multi-cell channels in the time division duplex cellular network can simultaneously estimate the multi-cell interference-free channels under the single receiving antenna;
4. the method for multi-cell channel joint estimation under the time division duplex cellular network only needs to meet the minimum system bandwidth requirements of LTE and NR, and can reduce power consumption and complexity.
Drawings
Fig. 1 is a flow chart of a method for multi-cell channel joint estimation in a time division duplex cellular network according to the present invention;
fig. 2 is a multi-cell frequency domain channel acquired based on LTE CRS in a conventional method in an embodiment of the invention;
fig. 3 is a diagram of a multi-cell frequency domain channel acquired based on LTE PBCH in an embodiment of the present invention;
FIG. 4 is a comparison of the results of the time domain main path channel extraction applied to wireless sensing in an embodiment of the present invention;
FIG. 5 is a diagram of the types of gestures to be recognized in an embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
The invention is further described below with reference to the accompanying drawings.
In a communication system, channel estimation is not limited to use with specific reference symbols, and any known or solvable sequence may be used for channel estimation. In cellular signals, many channels, in addition to reference symbols, are periodically transmitted in broadcast form. The downlink broadcast channel (PBCH)/Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in LTE and NR are transmitted at a fixed period in fixed slots and subcarriers. The PBCH/PSS/SSS of LTE are respectively located in different time domains, and NR puts the three together to form SSB.
Wherein, PSS/SSS local sequence is fixed; the local sequence of each frame of the PBCH is different, but the bits of the Master Information Block (MIB) carried by the PBCH are kept unchanged except for the frame number, and in the LTE/NR frame transmission mode, the frame numbers of all frames can be calculated by only acquiring the frame number of one frame. Generation of MIB to PBCH strictly follows 3GPP protocol, and when one cell system information is known, PBCH local sequence of all frames can be easily reconstructed. In a TDD system, the PBCH/PSS/SSS of the primary cell and the neighbor cell are both superimposed on the same time-frequency resource grid (RE) thanks to full network synchronization. The receiving end receives the mixed signal overlapped by the multi-cell signal on the time-frequency resource grid corresponding to the PBCH/PSS/SSS. Through cell search, not only the cell can be searched, but also a plurality of adjacent cells can be searched through an interference deletion technology, so as to obtain the total number of cells, the number of antenna ports of each cell and the system information of each cell.
From these system information, the multi-cell PSS/SSS/PBCH local sequence under all frames can be reconstructed. In case the local sequence is known, the multi-cell channel can be solved from the mixed multi-cell received signal. In LTE, PSS/SSS/PBCH can be used for multi-cell joint channel estimation. Wherein, the PSS/SSS period is shorter, but only single-port transmission is supported; the PBCH period is twice as long as PSS/SSS, but occupies more resource blocks and supports up to four port transmissions. The PSS/SSS/PBCH in the NR are combined into SSBs, but SSBs transmitted by different ports are mapped to different time domain positions, respectively, and a multi-cell multi-port channel is also available through SSBs.
Based on the above, the method for multi-cell channel joint estimation in the time division duplex cellular network according to the present invention, as shown in fig. 1, comprises the following specific steps:
step 1: searching a main cell in a 4G-LTE or 5G-NR signal according to a traditional method, synchronizing time and frequency, decoding MIB to obtain main cell system information such as frame numbers, bandwidth and the like, sequentially pushing out frame numbers of all subsequent frames according to the decoded frame numbers, and collecting multi-cell mixed signals of PBCH, PSS and SSS in a plurality of continuous system frames;
step 2: and deleting signals of the main cell from the mixed signals by adopting an interference deletion method in the PBCH/PSS/SSS of the acquired multiframe, then finding out the adjacent cell with the highest signal-to-noise ratio according to a conventional cell searching method, and judging whether the adjacent cell is successfully solved or not by taking Cyclic Redundancy Check (CRC) of the MIB decoded by the PBCH as a basis. And (5) each new neighbor cell is solved, and the MIB and the number of transmitting ports of the neighbor cell are recorded. And then deleting the neighbor cell which is solved currently to solve the next neighbor cell until no new cell is solved.
Step 3: and (2) reconstructing the master cell and all neighbor MIB information of each frame according to the frame numbers of all frames of the master cell system deduced in the step (1) and the MIB and the transmitting port numbers of each neighbor cell recorded in the step (2), replacing bits representing the frame numbers in the MIB with bits corresponding to the frame numbers of each frame, and keeping the rest bits unchanged. And reconstructing the local sequence of the PBCH/PSS/SSS of all the main cells and the neighbor cells in each transmitting port of each frame and the reference symbols inserted in the middle of the PBCH according to the 3GPP protocol.
Step 4: taking any signal in PBCH/PSS/SSS in each frame, listing equations of a received signal, a multi-cell local sequence and a multi-cell channel under each RE, wherein the received signal and the local sequence are used as known variables, and the multi-cell channel is a variable to be solved, and specifically comprises the following steps:
401. establishing an equation about a received signal, a multi-cell multi-port local sequence and a multi-cell multi-port channel under each RE;
the invention considers the general multi-cell and multi-port situation, and for any signal in PBCH/PSS/SSS, the relation among the received signal under each RE, the transmitted signal of each port of each cell and the channel thereof is as follows:
wherein y (k, l), w (k, l) represent the received signal and white noise of subcarrier k and OFDM symbol l, respectively; h is a p,c (k,l)，x p,c (k, l) represent the frequency domain channel and the local sequence of the antenna port p of cell c, respectively. C is the total number of cells (including the primary cell); p (c) is the number of transmit ports per cell. If noise is ignored, for each equation, the received signal y (k, l) and the transmitted signal local sequence x p,c (k, l) is a known variable, frequency domain channel h p,c (k, l) is an unknown variable. However, because of the number of unknown variables in each equationGreater than 1, a unique solution cannot be obtained, and therefore a system of equations with unique solutions needs to be built.
402. Establishing an equation set with a unique solution;
in general, the channel variation of adjacent REs is small, so that the equation can be solved, the channel of the adjacent REs is kept unchanged, and the frequency domain channels of K subcarriers and L symbols around each subcarrier are the same, for each RE (K, L), equation (1) can be approximated as an equation set:
thus, for any group (k, l), the unknown variable h p,c The number of (k, l) is stillBut the number of equations becomes (2K+1) (2L+1), which requires +.>A unique solution can exist for the system of equations.
To simplify the expression, the above formula is written in matrix form:
y(k,l)＝X(k,l)h(k,l)+w(k,l),
wherein,,respectively representing the aggregate vector of received signal and noise centered on RE (k, l), respectively>Set vector for multicell multiport channel, for example>The matrix is assembled for a multi-cell multi-port local sequence.
And 5, solving an equation set by adopting least square estimation (LS) or other estimation methods (LMMSE, MMSE and the like) by taking each RE as a center to obtain a multi-cell multi-port channel estimation value.
In the invention, the channel estimation value is obtained by a least square method:
examples:
taking wireless gesture recognition as an example, by receiving mobile communication signals in a space, channel state information is estimated, and the change rule of a propagation channel along with time is analyzed, so that which gesture action is made by a user is recognized. In a home scenario, the main TDD-LTE signal source is a B40 band signal of chinese mobile, with a center frequency of 2.3498GHz and a bandwidth of 20MHz. The primary cell PCI is 252 and there are two neighbors with PCIs 249 and 256 in this scenario, all in a single port configuration. Firstly, a frequency domain channel of a plurality of cells is estimated by using a CRS, and as shown in fig. 2, a plurality of burrs exist in the channel estimation result based on the CRS under the influence of inter-cell interference, and the burrs are distributed irregularly in a time-frequency domain. When the method of the present invention is adopted to perform channel estimation, the obtained result is shown in fig. 3, wherein, PBCH is adopted to perform channel estimation, k=2, and l=1 are taken, so that it can be seen that the estimated multi-cell channel has no interference, and even if the estimated multi-cell channel is a neighboring cell with weaker signal, the channel estimation result is very smooth.
To realize gesture recognition, the invention converts the frequency domain channel into the time domain through inverse Fourier transform, and the result is shown in FIG. 4. By extracting the primary path over a 20MHz bandwidth, the primary path channel of the CRS is significantly less subject to interference during the first half of the sampling time. However, in the second half of the sampling time, when the PDCCH/PDSCH of the neighboring cell occupies a large number of REs, the number of interfered CRSs increases, and the extracted main path interference also increases. And the magnitude of the disturbance is comparable to the magnitude of the fluctuation caused by the hand movement (between sampling points 100-150), which obviously affects the outcome of gesture recognition. And the main path extracted based on PBCH is smooth, the gesture effect is obvious, and obvious fluctuation of CSI can be observed even in the neighboring region of PCI 256. The PBCH-based method only uses the minimum system bandwidth of 1.4MHz of LTE, and the effect is obviously better than that of CRS based on 20MHz bandwidth.
And after the main path channel is extracted, the channel estimation based on the CRS and the channel estimation based on the PBCH are respectively further processed by adopting the same method. The influence of phase noise is removed through multi-antenna CSI division, a dynamic path is extracted through band-pass filtering, and finally, the change of hand speed and direction relative to time can be obtained through calculating Doppler frequency shift, so that corresponding gestures are identified. Several gestures shown in fig. 5 are designed, experiments are carried out in two home scenes of a living room and a bedroom, and the recognition accuracy of each gesture is counted. In each scene, 400 gestures are tested, and compared with the accuracy under the CRS-based channel estimation method. As shown in Table 1, when the channel estimation method is used for gesture recognition, the high accuracy of 93% can be achieved in both scenes, and compared, the accuracy of the channel estimation method is far higher than that of the channel estimation method based on CRS.
TABLE 1 gesture recognition accuracy under the present invention and conventional methods
Claims (4)
1. A method for multi-cell channel joint estimation in a time division duplex cellular network, characterized by:
the method comprises the following specific steps:
step 1: searching and acquiring main cell system information in the received multi-cell mixed signal, and sequentially calculating the frame numbers of all subsequent frames according to the frame number of the current frame;
step 2: searching and acquiring all neighbor cell system information in the received multi-cell mixed signal;
step 3: reconstructing the local sequences of PBCH/PSS/SSS of all the main cells and the adjacent cells at each transmitting port of each frame;
step 4: taking any signal in PBCH/PSS/SSS in each frame, listing equations of a received signal, a multi-cell multi-port local sequence and a multi-cell multi-port channel under each RE, wherein the method comprises the following steps:
the relation of the received signal under each RE, the transmitted signal of each port of each cell and the channel thereof is established as follows:
wherein y (k, l), w (k, l) represent the received signal and white noise of subcarrier k and OFDM symbol l, respectively; h is a p,c (k,l)，x p,c (k, l) represent the frequency domain channel and local signal sequence, respectively, of the antenna port p of cell c; c is the total number of cells; p (c) is the number of transmit ports per cell;
considering that the channels of adjacent REs remain unchanged and the frequency domain channels of K subcarriers and L symbols around each RE are the same, the above equation is approximated for each RE (K, L):
step 5: and (3) solving the equation set obtained in the step (4) by taking each RE as a center to obtain a multi-cell multi-port channel estimated value.
2. The method for multi-cell channel joint estimation in a time division duplex cellular network according to claim 1, wherein: the neighbor cell system information acquisition method comprises the following steps: deleting signals of a main cell from the multi-cell mixed signals obtained in the step 1, then finding a neighbor cell with the highest signal-to-noise ratio, and judging whether the neighbor cell is successfully solved or not according to the cyclic redundancy check of the MIB decoded by the PBCH; every new solution of a neighboring cell, recording MIB and the number of transmitting ports of the neighboring cell; and then deleting the neighbor cell which is solved currently to solve the next neighbor cell until no new cell is solved.
3. The method for multi-cell channel joint estimation in a time division duplex cellular network according to claim 1, wherein: in step 3, firstly, the master cell and all neighbor MIB information of each frame need to be reconstructed, and bits representing frame numbers in the MIB are replaced by bits corresponding to the frame numbers of each frame; and then reconstructing the local sequence of the PBCH/PSS/SSS of all the main cells and the adjacent cells at each transmitting port of each frame.
4. The method for multi-cell channel joint estimation in a time division duplex cellular network according to claim 1, wherein: in step 4, K and L need to satisfy:
wherein C is the total number of cells; p (c) is the number of transmit ports per cell.
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