Far field bit division multiple access method, system and device based on frequency control array and medium

Abstract

The invention discloses a far field bit division multiple access method, system and device based on a frequency control array and a medium. The method comprises the following steps: determining a base station coverage range; designing a frequency deviation sequence of the frequency control array; calculating a space-frequency domain multi-user channel matrix; pre-equalizing the frequency domain; performing spatial domain digital precoding; performing orthogonal frequency division multiplexing modulation; mixing a frequency offset component; processing by a receiver; the system, the device and the medium are used for bearing and implementing the method. The invention provides a far-field bit division multiple access scheme in a down link by combining a frequency control array and an orthogonal frequency division multiplexing (OFDM) technology, so that a base station can distinguish users at different angles and distances in an electromagnetic wave far-field area; the method has the advantages of small user mutual interference and high system spectrum efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a far-field bit division multiple access method, system, device and medium based on a frequency control array. Background Art

[0002] The phased array adjusts the initial phase of the signal sent by each array element. After the far-field superposition of the signals sent by different antennas, a high-gain beam is generated in a specific direction, thereby controlling the direction of the overall beam. In the downlink, SDMA uses precoding technology. The base station will select a set of steering vectors. Each vector corresponds to the position angle of a user. These steering vectors are designed in space so that they are mutually orthogonal, thereby ensuring that the signal of each user can be correctly separated at the receiving end. The frequency-controlled array introduces a small frequency offset between different array elements. This frequency diversity allows the signals from different array elements to form a peak after superposition at a specific distance. Therefore, the beam steering vector of the frequency-controlled array is not only related to the angle, but also to the distance. However, there is a strong mutual coupling relationship between the distance domain and the angle domain of the traditional frequency-controlled array beam. In addition, the frequency offset actively introduced by the transmitter will also cause interference to the communication signal. Therefore, the application of frequency-controlled arrays in communication systems is still limited.

[0003] In the existing technical solution (Z.Wu and L.Dai, "Multiple Access for Near-Field Communications: SDMA or LDMA?", in IEEE Journal on Selected Areas in Communications, vol.41, no.6, pp.1918-1935, June 2023, doi:10.1109 / JSAC.2023.3275616.), the near-field position division multiple access technology follows the spherical wave model in the near-field environment (within the Rayleigh distance). By adjusting the phase and amplitude of each element in the antenna array, the signal energy has a focusing effect at a specific distance and angle to form a high-gain beam. The near-field position division multiple access technology uses ultra-large-scale arrays and millimeter wave band (or even higher frequency band) electromagnetic waves for communication, which can effectively increase the Rayleigh distance and form a focused beam in the distance angle domain within hundreds of meters. Based on the beam steering vector model of near-field spherical waves, the base station calculates the optimal precoding matrix according to the user's location information to achieve parallel transmission of multi-stream data to user devices at different angles and distances.

[0004] However, existing technologies rely heavily on ultra-large-scale array antennas and high-frequency electromagnetic implementations. Ultra-large-scale array antennas typically require hundreds or even thousands of antenna elements, which leads to high hardware costs and complexity. Each antenna element requires independent phase control, which increases the overall complexity and cost of the system. High-frequency electromagnetic waves (such as millimeter waves) suffer greater losses during propagation, especially when encountering obstacles, the received signal strength is severely attenuated. This limits the coverage of the signal in the near-field environment, resulting in signal attenuation and unstable connection. Finally, the coverage range that can be achieved by existing technologies is only a few hundred meters, which is difficult to meet the communication needs of large-scale coverage.

[0005] The paper "Multiple Access for Near-Field Communications: SDMA or LDMA?" proposes a bit-division multiple access technology that uses the beam focusing characteristics of ultra-large-scale array antennas in near-field communications to precisely control the energy of the signal to focus at a specific angle and distance in the near-field area, thereby providing services to users in different locations. This method can make full use of channel resources in the additional distance domain and improve the spectrum efficiency of the system. However, since the near-field range of electromagnetic waves is very limited, it is extremely dependent on ultra-large-scale arrays and higher electromagnetic wave frequency bands to improve the near-field range of electromagnetic waves, and can only cover users within a few hundred meters, and cannot effectively distinguish users at different distances in the far-field area. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a far-field position division multiple access method, system, device and medium based on frequency control array. By combining the frequency control array with orthogonal frequency division multiplexing (OFDM) technology, a far-field position division multiple access scheme for the downlink is proposed, which enables the base station to distinguish users at different angles and distances in the far-field area of ​​electromagnetic waves. The present invention has the advantages of small user mutual interference and high system spectrum efficiency.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A far-field bit division multiple access method based on a frequency control array comprises the following steps:

[0009] S1: Establish base station coverage

[0010] Assume that the length of the cyclic prefix (CP) in OFDM is TCP , the maximum multipath delay within the base station coverage range R is τ max , then the base station coverage range R satisfies: R≤(T CP -τ max ) / c, where c is the speed of light;

[0011] S2: Design frequency deviation sequence of frequency-controlled array

[0012] Set the basic frequency offset interval δf, first construct an equally spaced frequency offset sequence [0, δf, …, (N t -1)δf], where N t is the number of transmitting antennas at the base station, and then the frequency offset sequence of the frequency control array is reordered using a random permutation function to obtain the frequency offset sequence

[0013]

[0014] S3: Calculate the multi-user channel matrix in the space-frequency domain

[0015] Using the channel state information fed back to the base station by the user end in the uplink channel, combined with the frequency control array frequency offset sequence obtained in step S2, the space-frequency domain multi-user channel matrix H = [H0, H1, ..., H K-1 ] T , where K is the number of users in the system, H k is the spatial frequency domain channel matrix of the kth user, which is calculated by the following formula:

[0016]

[0017] Where P is the number of multipaths in the channel, is the complex gain of each propagation path, R k,p ,θ k,p and φ k,p are the propagation distance, departure angle and arrival angle of each path wave respectively, a and b are the sending steering vector and receiving steering vector respectively, expressed as:

[0018]

[0019] Among them, F M is the M-dimensional discrete Fourier transform matrix, M is the number of subcarriers, is the frequency offset matrix, expressed as:

[0020]

[0021] Where Δf is the subcarrier spacing, Φ k,p The phase offset matrix generated by the propagation delay of the pth path in the kth user channel is expressed as:

[0022]

[0023] S4: Frequency domain pre-equalization

[0024] The frequency domain pre-equalization matrix is ​​calculated using the space-frequency domain multi-user channel matrix obtained in step S3. First, the ideal space-frequency domain channel matrix is ​​calculated. in Calculated by the following formula:

[0025]

[0026] Then the frequency domain pre-equalization matrix P = H H (HH H )H ideal ; Then, after symbol mapping of the bit stream sent to K users, M data symbols are taken and arranged in columns according to the user order to obtain the MK-dimensional column vector s. Finally, the vector s is pre-equalized in the frequency domain to obtain

[0027] S5: Spatial digital precoding

[0028] Calculate the spatial channel matrix in Calculated as:

[0029]

[0030] The symbol pre-equalized in step S4 is Rearrange horizontally into a matrix S with K rows and M columns, and then perform digital precoding on the matrix S to obtain the precoded transmission symbol X=WS, where W is the digital precoding matrix, and the zero forcing (ZF) precoding matrix is ​​calculated as:

[0031]

[0032] The minimum mean square error (MMSE) precoding matrix is ​​calculated as:

[0033]

[0034] Where ρ is the power normalization coefficient, is the noise power, I is the unit matrix;

[0035] S6: Orthogonal Frequency Division Multiplexing Modulation

[0036] Perform an M-dimensional inverse discrete Fourier transform on each row of the precoded transmission symbol X obtained in step S5 to obtain a baseband OFDM symbol, and add a cyclic prefix before each baseband OFDM symbol, and then add N tThe baseband OFDM symbols of each channel are upsampled and pulse-shaped to obtain the baseband signal of each transmission channel;

[0037] S7: Mixed frequency offset component

[0038] The baseband signal of each transmission channel obtained in step S6 is respectively mixed with a corresponding frequency offset component, and is sent to the RF transmission end for transmission after passing through a digital-to-analog converter;

[0039] S8: Receiver Processing

[0040] After the clocks of the receiving end and the transmitting end are synchronized, the signal generated in step S7 is received. The received signal is sent to the analog-to-digital converter for sampling after down-conversion, and then passes through a low-pass filter and down-sampled to obtain a baseband received signal. The received baseband signal is clipped to retain the baseband signal within the time [0, T], where T is an OFDM symbol length. The retained baseband signal is subjected to an M-dimensional discrete Fourier transform to restore the information symbol, and the original bit stream can be obtained after demodulation.

[0041] The present invention also provides a far-field bit division multiple access system based on a frequency control array, comprising:

[0042] The base station coverage range establishment module is used to implement the assumption that the length of the cyclic prefix (CP) in OFDM is T CP , the maximum multipath delay within the base station coverage range R is τ max , then the base station coverage range R satisfies: R≤(T CP -τ max ) / c, where c is the speed of light;

[0043] The frequency control array frequency deviation sequence design module is used to set the basic frequency deviation interval δf. First, an equally spaced frequency deviation sequence [0, δf, …, (N t -1)δf], where N t is the number of transmitting antennas at the base station, and then the frequency offset sequence of the frequency control array is reordered using a random permutation function to obtain the frequency offset sequence

[0044] The space-frequency domain multi-user channel matrix calculation module is used to use the channel state information fed back to the base station by the user end in the uplink channel, combined with the frequency offset sequence of the frequency control array, to calculate the space-frequency domain multi-user channel matrix H = [H0, H1, ..., H K-1 ] T , where K is the number of users in the system, H kis the spatial frequency domain channel matrix of the kth user, which is calculated by the following formula:

[0045]

[0046] Where P is the number of multipaths in the channel, is the complex gain of each propagation path, R k,p ,θ k,p and φ k,p are the propagation distance, departure angle and arrival angle of each path wave respectively, a and b are the sending steering vector and receiving steering vector respectively, expressed as:

[0047]

[0048] Among them, F M is the M-dimensional discrete Fourier transform matrix, M is the number of subcarriers, is the frequency offset matrix, expressed as:

[0049]

[0050] Where Δf is the subcarrier spacing, Φ k,p The phase offset matrix generated by the propagation delay of the pth path in the kth user channel is expressed as:

[0051]

[0052] The frequency domain pre-equalization module is used to calculate the frequency domain pre-equalization matrix using the space-frequency domain multi-user channel matrix. First, the ideal space-frequency domain channel matrix is ​​calculated. in Calculated by the following formula:

[0053]

[0054] Then the frequency domain pre-equalization matrix P = H H (HH H )H ideal ; Then, after symbol mapping of the bit stream sent to K users, M data symbols are taken and arranged in columns according to the user order to obtain the MK-dimensional column vector s. Finally, the vector s is pre-equalized in the frequency domain to obtain

[0055] Spatial digital precoding module, used to calculate the spatial channel matrix in Calculated as:

[0056]

[0057] The pre-equalized symbol Rearrange horizontally into a matrix S with K rows and M columns, and then perform digital precoding on the matrix S to obtain the precoded transmission symbol X=WS, where W is the digital precoding matrix, and the zero forcing (ZF) precoding matrix is ​​calculated as:

[0058]

[0059] The minimum mean square error (MMSE) precoding matrix is ​​calculated as:

[0060]

[0061] Where ρ is the power normalization coefficient, is the noise power, I is the unit matrix;

[0062] The orthogonal frequency division multiplexing modulation module is used to perform an M-dimensional inverse discrete Fourier transform on each row of the precoded transmission symbol X to obtain a baseband OFDM symbol, and add a cyclic prefix before each baseband OFDM symbol, and then add N t The baseband OFDM symbols of each channel are upsampled and pulse-shaped to obtain the baseband signal of each transmission channel;

[0063] The frequency offset component mixing module is used to mix the baseband signal in each transmission channel with the corresponding frequency offset component, and send it to the RF transmitting end for transmission after passing through the digital-to-analog converter;

[0064] The receiver processing module is used to receive the signal generated in step S7 after the clock of the receiving end is synchronized with that of the transmitting end. The received signal is sent to the analog-to-digital converter for sampling after down-conversion, and then passes through a low-pass filter and down-sampled to obtain a baseband receiving signal. The received baseband signal is clipped to retain the baseband signal within the time [0, T], where T is the length of an OFDM symbol. The retained baseband signal is subjected to an M-dimensional discrete Fourier transform to restore the information symbol, and the original bit stream can be obtained after demodulation.

[0065] The present invention also provides a far-field bit division multiple access device based on a frequency control array, comprising:

[0066] Memory: a computer program storing the above-mentioned far-field bit division multiple access method based on frequency control array, which is a computer-readable device;

[0067] Processor: used to implement the far-field bit division multiple access method based on frequency control array when executing the computer program.

[0068] The present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it can implement the far-field bit division multiple access method based on a frequency control array.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] 1. Existing airspace communication technologies for far-field multi-users can only distinguish different users by relying on the angle domain. When multiple users are located at the same angle, there is serious mutual interference between users, resulting in a decrease in the system spectrum efficiency. The present invention combines the frequency control array with orthogonal frequency division multiplexing (OFDM) technology and uses random linear frequency offset to enable the base station to distinguish users at different angles and distances in the far-field area of ​​electromagnetic waves, thereby creating the possibility of multi-stream data communication for different users at the same angle in the airspace. At the same time, frequency domain pre-equalization technology is used to avoid the introduced frequency offset from causing subcarrier interference at the user receiving end, which greatly improves the system spectrum efficiency compared to traditional space division multiple access technology.

[0071] 2. The existing bit-division multiple access technology utilizes the beam focusing effect of ultra-large-scale antenna arrays and high-frequency electromagnetic waves in the near field to distinguish users at different angles and distances. However, the existing technology not only has a high hardware implementation cost, but also its effective near-field coverage can only reach a few hundred meters at most. The present invention only needs to adopt a digital signal processing method, perform frequency domain pre-equalization at the transmitting end and mix the designed spectrum frequency shift into the digital channel, so as to effectively distinguish users at different distances within a few kilometers. Therefore, it has a low implementation cost and good compatibility with the existing system, and greatly improves the coverage of bit-division multiple access.

[0072] In summary, the present invention combines the frequency control array with orthogonal frequency division multiplexing (OFDM) technology, so that the base station can distinguish users at different angles and distances in the far field of electromagnetic waves, and has the advantages of small user mutual interference and high system spectrum efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 The flowchart of the base station transmitting end and the user receiving end system processing in the method proposed by the present invention is shown.

[0074] Figure 2 A schematic diagram showing signal clipping performed by a user receiving end in the method proposed by the present invention is shown.

[0075] Figure 3A comparison chart of the spectrum efficiency of the method proposed in the present invention and the traditional space division multiple access technology under different numbers of users is shown.

[0076] Figure 4 The graph shows a comparison of the spectrum efficiency of the method proposed in the present invention and the traditional space division multiple access technology under different multipath numbers and Ricean factors.

[0077] Figure 5 The diagram shows a comparison of the spectrum efficiency of the method proposed in the present invention with the traditional space division multiple access technology at different sector angles when having different maximum frequency deviation ratios.

[0078] Figure 6 The spectrum efficiency comparison diagram of the method proposed in the present invention with different maximum frequency deviation ratios and the traditional space division multiple access technology at different sector coverage distances is shown. DETAILED DESCRIPTION

[0079] The technical solution adopted by the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0080] In existing mobile communication systems, Space Division Multiple Access (SDMA) technology allocates independent beams to different users in the angle domain through a large-scale multi-input and multi-output array, thereby realizing multi-stream data transmission in the air domain and improving the capacity of the communication system. However, when the angle difference between users is small, it is difficult for the base station to make a fine distinction, resulting in serious inter-user interference in the user received signal, causing serious degradation of the communication system. In addition, the performance of space division multiple access depends on a rich scattering environment to ensure the independence between array elements, so the performance in the millimeter wave band is also degraded. In response to the above problems, the present invention proposes a far-field location division multiple access scheme (Far-field Location Division Multiple Access). The scheme uses the ability of the frequency-controlled array to manipulate beams in the far-field distance domain, performs beamforming in the dual dimensions of angle and distance, and designs a random linear frequency offset sequence, so that the base station can accurately distinguish users at different angles and distances. At the same time, the cyclic prefix (CP) in orthogonal frequency division multiplexing (OFDM) is used to eliminate the inter-symbol interference caused by the propagation delay, meeting the use requirements of the frequency control array in the broadband transmission system. Finally, by designing the frequency domain pre-equalization matrix, the inter-subcarrier interference that may be caused by frequency offset in the OFDM system can be effectively offset. This solution can provide communication services to users at the same angle but different distances in a time-frequency resource block, which significantly improves the system spectrum efficiency compared to the traditional SDMA system; Figure 1 As shown, the base station performs symbol mapping on the information bit stream of each user and then performs parallel-to-serial conversion. The channel information fed back by the user's uplink channel is used to design a frequency domain pre-equalization matrix, and the parallel symbols are pre-equalized in the frequency domain; the pre-equalized symbols are converted from serial to parallel and then digitally precoded in the spatial domain, and the precoded symbols are sent to the OFDM modulator. The modulated OFDM symbols are upsampled and pulse-formed to obtain a digital baseband signal. The designed frequency offset component is mixed into the digital baseband signal of each channel, and finally sent to the RF front end for transmission. After the user receiver is synchronized with the base station clock, it starts to receive the signal from time 0. After being processed by a traditional OFDM receiver, the information bit stream sent by the base station to the user can be obtained. Specifically:

[0081] A far-field bit division multiple access method based on a frequency control array comprises the following steps:

[0082] S1: Establish base station coverage

[0083] Assume that the CP length in OFDM is T CP , the maximum multipath delay within the base station coverage range R is τ max , then the base station coverage range R needs to satisfy: R≤(T CP -τ max ) / c, where c is the speed of light;

[0084] S2: Design frequency deviation sequence of frequency-controlled array

[0085] Set the basic frequency offset interval δf, first construct an equally spaced frequency offset sequence [0, δf, …, (N t -1)δf], where N t is the number of transmitting antennas at the base station, and then the frequency offset sequence of the frequency control array is reordered using a random permutation function to obtain the frequency offset sequence

[0086]

[0087] S3: Calculate the multi-user channel matrix in the space-frequency domain

[0088] Using the channel state information fed back to the base station by the user end in the uplink channel, combined with the frequency control array frequency offset sequence obtained in step S2, the space-frequency domain multi-user channel matrix H = [H0, H1, ..., H K-1 ] T , where K is the number of users in the system, H k is the spatial frequency domain channel matrix of the kth user, which is calculated by the following formula:

[0089]

[0090] Where P is the number of multipaths in the channel, is the complex gain of each propagation path, R k,p ,θ k,p and φ k,p are the propagation distance, departure angle and arrival angle of each path wave respectively, a and b are the sending steering vector and receiving steering vector respectively, expressed as:

[0091]

[0092] Among them, F M is the M-dimensional discrete Fourier transform matrix, M is the number of subcarriers, is the frequency offset matrix, expressed as:

[0093]

[0094] Where Δf is the subcarrier spacing, Φ k,p The phase offset matrix generated by the propagation delay of the pth path in the kth user channel is expressed as:

[0095]

[0096] S4: Frequency domain pre-equalization

[0097] The frequency domain pre-equalization matrix is ​​calculated using the space-frequency domain multi-user channel matrix obtained in step S3. First, the ideal space-frequency domain channel matrix is ​​calculated. in Calculated by the following formula:

[0098]

[0099] Then the frequency domain pre-equalization matrix P = H H (HH H )H ideal ; Then, after symbol mapping of the bit stream sent to K users, M data symbols are taken and arranged in columns according to the user order to obtain the MK-dimensional column vector s. Finally, the vector s is pre-equalized in the frequency domain to obtain

[0100] S5: Spatial digital precoding

[0101] Calculate the spatial channel matrix in Calculated as:

[0102]

[0103] The symbol pre-equalized in step S4 is Rearrange horizontally into a matrix S with K rows and M columns, and then perform digital precoding on the matrix S to obtain the precoded transmission symbol X=WS, where W is the digital precoding matrix, and the zero forcing (ZF) precoding matrix is ​​calculated as:

[0104]

[0105] The minimum mean square error (MMSE) precoding matrix is ​​calculated as:

[0106]

[0107] Where ρ is the power normalization coefficient, is the noise power, I is the unit matrix;

[0108] S6: Orthogonal Frequency Division Multiplexing Modulation

[0109] Perform an M-dimensional inverse discrete Fourier transform on each row of the precoded transmission symbol X obtained in step S5 to obtain a baseband OFDM symbol, and add a cyclic prefix before each baseband OFDM symbol, and then add N t The baseband OFDM symbols of each channel are upsampled and pulse-shaped to obtain the baseband signal of each transmission channel;

[0110] S7: Mixed frequency offset component

[0111] The baseband signal of each transmission channel obtained in step S6 is respectively mixed with a corresponding frequency offset component, and is sent to the RF transmission end for transmission after passing through a digital-to-analog converter;

[0112] S8: Receiver Processing

[0113] After the clock of the receiving end is synchronized with that of the transmitting end, the signal generated in step S7 is received. The received signal is sent to the analog-to-digital converter for sampling after down-conversion, and then passes through a low-pass filter and down-sampled to obtain a baseband received signal. The received baseband signal is clipped to retain the baseband signal within the time [0, T], where T is the length of an OFDM symbol, see Figure 2 The retained baseband signal is subjected to an M-dimensional discrete Fourier transform to recover the information symbols, and the original bit stream can be obtained after demodulation.

[0114] Simulation experiment

[0115] Simulation parameter settings:

[0116] The carrier frequency is set to 4 GHz, the array spacing is configured as half-wavelength spacing, the subcarrier spacing is set to 15 kHz, the number of subcarriers is 512, and the cyclic prefix length is 1 / 4 of the OFDM modulation symbol period, which is about 16.67 μs. The maximum coverage distance of the base station is 3 km, and the maximum multipath delay spread of the channel is 6.67 μs. Therefore, the user equipment is set to be evenly distributed in the angle distribution [-θ max ,θ max ] and the distance distribution [0,3km]$ is defined in the sector. The base station is equipped with an array antenna with 128 elements and the user equipment is equipped with a single antenna.

[0117] Simulation results and analysis:

[0118] See also Figure 3 , the figure shows the signal-to-noise ratio of 30dB, the maximum frequency deviation ratio ρ max =30, and users are distributed in the [-60°, 60°] sector. The performance of the method of the present invention is compared with that of traditional SDMA. When the number of users exceeds 10, the spectral efficiency of the method of the present invention begins to surpass SDMA. For SDMA using ZF precoding, the spectral efficiency begins to decline when the number of users reaches 30, and approaches zero when it reaches 80. Even with MMSE precoding, the spectral efficiency of SDMA only increases slowly as the number of users increases. However, the spectral efficiency of FLDMA systems using ZF and MMSE precoding increases rapidly with the increase in the number of users. This comparison shows the superiority of the method of the present invention in improving spectral efficiency in multi-user communication scenarios, especially when simple ZF precoding is used, the performance will not be significantly reduced.

[0119] See also Figure 4 , which shows the spectrum efficiency comparison of the method proposed in the present invention and the traditional space division multiple access technology under different multipath numbers and Ricean factors among 100 users. Figure 4 As shown in the figure, when the number of multipaths is small, the spectrum efficiency of the traditional space division multiple access technology is low. Only when the number of multipaths increases, the spectrum efficiency of the space division multiple access technology is significantly improved. The spectrum efficiency of the method proposed in the present invention is almost unaffected by the number of multipaths. In addition, the spectrum efficiency of the traditional space division multiple access technology decreases significantly with the increase of the Rice factor. This comparison shows that the spectrum efficiency of the method of the present invention does not depend on the rich scattering channel environment, so it has a good performance advantage in the millimeter wave and even higher frequency bands.

[0120] See also Figure 5, which shows the spectrum efficiency comparison of the method proposed in the present invention with different maximum frequency deviation ratios and the traditional space division multiple access technology at different sector angles when the signal-to-noise ratio is 20dB and the number of users is 100. It can be seen that the spectrum efficiency of the method proposed in the present invention is significantly better than that of the traditional space division multiple access technology under different simulation conditions. Especially when θ max = 0°, all users are arranged in a straight line, the spectrum efficiency of traditional space division multiple access approaches 0, and the method proposed in the present invention still has communication capability. This comparison shows that the method of the present invention can effectively distinguish different users at the same angle, thereby achieving the purpose of improving spectrum efficiency.

[0121] See also Figure 6 , the figure shows the signal-to-noise ratio is 20dB, the number of users is 100, see Figure 6 , the figure shows the spectrum efficiency comparison of the method proposed in the present invention with different maximum frequency deviation ratios and the traditional space division multiple access technology at different sector coverage distances when the signal-to-noise ratio is 20dB and the number of users is 100. It can be seen that the spectrum efficiency of the traditional space division multiple access technology has nothing to do with the base station coverage distance, while the method proposed in the present invention can effectively improve the system spectrum efficiency as the communication coverage distance increases.

[0122] The key points and protection points of the present invention are:

[0123] 1. The present invention proposes a randomly arranged frequency offset sequence, which overcomes the problem of strong coupling between the distance domain and the angle domain of traditional linear frequency offset, while ensuring the asymptotic orthogonality of the spatial domain steering vector when the number of antennas tends to infinity, and realizes the mutual conversion between the distance domain and the spatial domain by using discrete Fourier transform similar to phased array.

[0124] 2. The present invention designs a far-field bit division multiple access scheme for a broadband communication system using OFDM modulation. Since frequency-controlled array technology requires the use of channel propagation delay, single-carrier modulation technology cannot fully receive information symbols in a long-distance, large-bandwidth system, and will produce serious inter-symbol interference. The present invention utilizes the cyclic prefix in OFDM to achieve a broadband communication system that can fully receive information in an OFDM even if the propagation delay spans several code elements, and designs a frequency domain pre-equalization method to maintain the orthogonality of frequency domain information symbols.

[0125] The present invention also provides a far-field bit division multiple access system based on a frequency control array, comprising:

[0126] The base station coverage range establishment module is used to implement the assumption in step 1 that the length of the cyclic prefix (CP) in OFDM is T.CP , the maximum multipath delay within the base station coverage range R is τ max , then the base station coverage range R satisfies: R≤(T CP -τ max ) / c, where c is the speed of light;

[0127] The frequency control array frequency deviation sequence design module is used to implement the setting of the basic frequency deviation interval δf in step 2. First, an equally spaced frequency deviation sequence [0, δf, …, (N t -1)δf], where N t is the number of transmitting antennas at the base station, and then the frequency offset sequence of the frequency control array is reordered using a random permutation function to obtain the frequency offset sequence

[0128] The space-frequency domain multi-user channel matrix calculation module is used to implement the channel state information fed back to the base station by the user end in the uplink channel in step 3, combined with the frequency offset sequence of the frequency control array obtained in step S2, and calculate the space-frequency domain multi-user channel matrix H = [H0, H1, ..., H K-1 ] T , where K is the number of users in the system, H k is the spatial frequency domain channel matrix of the kth user, which is calculated by the following formula:

[0129]

[0130] Where P is the number of multipaths in the channel, is the complex gain of each propagation path, R k,p ,θ k,p and φ k,p are the propagation distance, departure angle and arrival angle of each path wave respectively, a and b are the sending steering vector and receiving steering vector respectively, expressed as:

[0131]

[0132] Among them, F M is the M-dimensional discrete Fourier transform matrix, M is the number of subcarriers, is the frequency offset matrix, expressed as:

[0133]

[0134] Where Δf is the subcarrier spacing, Φ k,p The phase offset matrix generated by the propagation delay of the pth path in the kth user channel is expressed as:

[0135]

[0136] The frequency domain pre-equalization module is used to implement the calculation of the frequency domain pre-equalization matrix using the space-frequency domain multi-user channel matrix obtained in step S3 in step 4. First, the ideal space-frequency domain channel matrix is ​​calculated. in Calculated by the following formula:

[0137]

[0138] Then the frequency domain pre-equalization matrix P = H H (HH H )H ideal ; Then, after symbol mapping of the bit stream sent to K users, M data symbols are taken and arranged in columns according to the user order to obtain the MK-dimensional column vector s. Finally, the vector s is pre-equalized in the frequency domain to obtain

[0139] Spatial digital precoding module, used to implement the calculation of the spatial channel matrix in step 5 in Calculated as:

[0140]

[0141] The symbol pre-equalized in step S4 is Rearrange horizontally into a matrix S with K rows and M columns, and then perform digital precoding on the matrix S to obtain the precoded transmission symbol X=WS, where W is the digital precoding matrix, and the zero forcing (ZF) precoding matrix is ​​calculated as:

[0142]

[0143] The minimum mean square error (MMSE) precoding matrix is ​​calculated as:

[0144]

[0145] Where ρ is the power normalization coefficient, is the noise power, I is the unit matrix;

[0146] The orthogonal frequency division multiplexing modulation module is used to implement the M-dimensional inverse discrete Fourier transform of each row of the precoded transmission symbol X obtained in step S5 in step 6 to obtain a baseband OFDM symbol, and add a cyclic prefix before each baseband OFDM symbol, and then add N t The baseband OFDM symbols of each channel are upsampled and pulse-shaped to obtain the baseband signal of each transmission channel;

[0147] The frequency offset component mixing module is used to implement the mixing of the baseband signal in each transmission channel obtained in step S6 in step 7 with the corresponding frequency offset component, and then send it to the RF transmitting end for transmission after passing through the digital-to-analog converter;

[0148] The receiver processing module is used to implement the reception of the signal generated in step S7 after the clocks of the receiving end and the transmitting end are synchronized in step 8. The received signal is sent to the analog-to-digital converter for sampling after down-conversion, and then passes through a low-pass filter and down-sampled to obtain a baseband received signal. The received baseband signal is clipped to retain the baseband signal within the time [0, T], where T is an OFDM symbol length. The retained baseband signal is subjected to an M-dimensional discrete Fourier transform to restore the information symbol, and the original bit stream can be obtained after demodulation.

[0149] The present invention also provides a far-field bit division multiple access device based on a frequency control array, comprising:

[0150] Memory: a computer program storing the above-mentioned far-field bit division multiple access method based on frequency control array, which is a computer-readable device;

[0151] Processor: used to implement the far-field bit division multiple access method based on frequency control array when executing the computer program.

[0152] The present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it can implement the far-field bit division multiple access method based on a frequency control array.

Claims

1. A far-field bit division multiple access method based on frequency control array, characterized in that: The following steps are involved: S1: Establish base station coverage Assume that the length of the cyclic prefix (CP) in OFDM is T CP , the maximum multipath delay within the base station coverage range R is τ max , then the base station coverage range R satisfies: R≤(T CP -τ max ) / c, where c is the speed of light; S2: Design frequency deviation sequence of frequency-controlled array Set the basic frequency offset interval δf, first construct an equally spaced frequency offset sequence [0, δf, …, (N t -1)δf], where N t is the number of transmitting antennas at the base station, and then the frequency offset sequence of the frequency control array is reordered using a random permutation function to obtain the frequency offset sequence S3: Calculate the multi-user channel matrix in the space-frequency domain Using the channel state information fed back to the base station by the user end in the uplink channel, combined with the frequency control array frequency offset sequence obtained in step S2, the space-frequency domain multi-user channel matrix H = [H0, H1, ..., H K-1 ] T , where K is the number of users in the system, H k is the spatial frequency domain channel matrix of the kth user, which is calculated by the following formula: Where P is the number of multipaths in the channel, is the complex gain of each propagation path, R k,p ,θ k,p and φ k,p are the propagation distance, departure angle and arrival angle of each path wave respectively, a and b are the sending steering vector and receiving steering vector respectively, expressed as: Among them, F M is the M-dimensional discrete Fourier transform matrix, M is the number of subcarriers, is the frequency offset matrix, expressed as: Where Δf is the subcarrier spacing, Φ k,p The phase offset matrix generated by the propagation delay of the pth path in the kth user channel is expressed as: S4: Frequency domain pre-equalization The frequency domain pre-equalization matrix is ​​calculated using the space-frequency domain multi-user channel matrix obtained in step S3. First, the ideal space-frequency domain channel matrix is ​​calculated. in Calculated by the following formula: Then the frequency domain pre-equalization matrix P = H H (HH H )H ideal ; Then, after symbol mapping of the bit stream sent to K users, M data symbols are taken and arranged in columns according to the user order to obtain the MK-dimensional column vector s. Finally, the vector s is pre-equalized in the frequency domain to obtain S5: Spatial digital precoding Calculate the spatial channel matrix in Calculated as: The symbol pre-equalized in step S4 is Rearrange horizontally into a matrix S with K rows and M columns, and then perform digital precoding on the matrix S to obtain the precoded transmission symbol X=WS, where W is the digital precoding matrix, and the zero forcing (ZF) precoding matrix is ​​calculated as: The minimum mean square error (MMSE) precoding matrix is ​​calculated as: Where ρ is the power normalization coefficient, is the noise power, I is the unit matrix; S6: Orthogonal Frequency Division Multiplexing Modulation Perform an M-dimensional inverse discrete Fourier transform on each row of the precoded transmission symbol X obtained in step S5 to obtain a baseband OFDM symbol, and add a cyclic prefix before each baseband OFDM symbol, and then add N t The baseband OFDM symbols of each channel are upsampled and pulse-shaped to obtain the baseband signal of each transmission channel; S7: Mixed frequency offset component The baseband signal of each transmission channel obtained in step S6 is respectively mixed with a corresponding frequency offset component, and is sent to the RF transmission end for transmission after passing through a digital-to-analog converter; S8: Receiver Processing After the clocks of the receiving end and the transmitting end are synchronized, the signal generated in step S7 is received. The received signal is sent to the analog-to-digital converter for sampling after down-conversion, and then passes through a low-pass filter and down-sampled to obtain a baseband received signal. The received baseband signal is clipped to retain the baseband signal within the time [0, T], where T is an OFDM symbol length. The retained baseband signal is subjected to an M-dimensional discrete Fourier transform to restore the information symbol, and the original bit stream can be obtained after demodulation.

2. A frequency-controlled array-based far-field bit division multiple access system based on the method of claim 1, characterized in that: include: The base station coverage range establishment module is used to implement the assumption that the length of the cyclic prefix (CP) in OFDM is T CP , the maximum multipath delay within the base station coverage range R is τ max , then the base station coverage range R satisfies: R≤(T CP -τ max ) / c, where c is the speed of light; The frequency control array frequency deviation sequence design module is used to set the basic frequency deviation interval δf. First, an equally spaced frequency deviation sequence [0, δf, …, (N t -1)δf], where N t is the number of transmitting antennas at the base station, and then the frequency offset sequence of the frequency control array is reordered using a random permutation function to obtain the frequency offset sequence The space-frequency domain multi-user channel matrix calculation module is used to use the channel state information fed back to the base station by the user end in the uplink channel, combined with the frequency offset sequence of the frequency control array, to calculate the space-frequency domain multi-user channel matrix H = [H0, H1, ..., H K-1 ] T , where K is the number of users in the system, H k is the spatial frequency domain channel matrix of the kth user, which is calculated by the following formula: Where P is the number of multipaths in the channel, is the complex gain of each propagation path, R k,p ,θ k,p and φ k,p are the propagation distance, departure angle and arrival angle of each path wave respectively, a and b are the sending steering vector and receiving steering vector respectively, expressed as: Among them, F M is the M-dimensional discrete Fourier transform matrix, M is the number of subcarriers, is the frequency offset matrix, expressed as: Where Δf is the subcarrier spacing, Φ k,p The phase offset matrix generated by the propagation delay of the pth path in the kth user channel is expressed as: The frequency domain pre-equalization module is used to calculate the frequency domain pre-equalization matrix using the space-frequency domain multi-user channel matrix. First, the ideal space-frequency domain channel matrix is ​​calculated. in Calculated by the following formula: Then the frequency domain pre-equalization matrix P = H H (HH H )H ideal ; Then, after symbol mapping of the bit stream sent to K users, M data symbols are taken and arranged in columns according to the user order to obtain the MK-dimensional column vector s. Finally, the vector s is pre-equalized in the frequency domain to obtain Spatial digital precoding module, used to calculate the spatial channel matrix in Calculated as: The pre-equalized symbol Rearrange horizontally into a matrix S with K rows and M columns, and then perform digital precoding on the matrix S to obtain the precoded transmission symbol X=WS, where W is the digital precoding matrix, and the zero forcing (ZF) precoding matrix is ​​calculated as: The minimum mean square error (MMSE) precoding matrix is ​​calculated as: Where ρ is the power normalization coefficient, is the noise power, I is the unit matrix; The orthogonal frequency division multiplexing modulation module is used to perform an M-dimensional inverse discrete Fourier transform on each row of the precoded transmission symbol X to obtain a baseband OFDM symbol, and add a cyclic prefix before each baseband OFDM symbol, and then add N t The baseband OFDM symbols of each channel are upsampled and pulse-shaped to obtain the baseband signal of each transmission channel; The frequency offset component mixing module is used to mix the baseband signal in each transmission channel with the corresponding frequency offset component, and send it to the RF transmitting end for transmission after passing through the digital-to-analog converter; The receiver processing module is used to receive the signal generated in step S7 after the clock of the receiving end is synchronized with that of the transmitting end. The received signal is sent to the analog-to-digital converter for sampling after down-conversion, and then passes through a low-pass filter and down-sampled to obtain a baseband receiving signal. The received baseband signal is clipped to retain the baseband signal within the time [0, T], where T is the length of an OFDM symbol. The retained baseband signal is subjected to an M-dimensional discrete Fourier transform to restore the information symbol, and the original bit stream can be obtained after demodulation.

3. A far-field bit division multiple access device based on frequency control array, characterized in that: include: Memory: a computer program storing the far-field bit division multiple access method based on frequency control array as described in claim 1, which is a computer-readable device; Processor: used to implement the far-field bit division multiple access method based on frequency control array described in claim 1 when executing the computer program.

4. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it can implement the far-field bit division multiple access method based on a frequency control array as described in claim 1.

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