Millimeter-wave massive MIMO hybrid precoding design method for URLLC

Abstract

The present invention discloses a millimeter wave massive MIMO hybrid precoding design method for URLLC, the network side equipment adopts a hybrid precoding architecture, adopts a short packet transmission signal, measures the transmission performance according to the finite block length information theory, and establishes a millimeter wave massive MIMO hybrid precoding optimization model for URLLC based on the performance measurement criteria such as maximization and rate or maximum and minimum fairness under the service requirements of multi-user communication business, total transmission power constraints and feasible phase set constraints of different resolution phase shifters; reconstructs the optimization problem so that its augmented Lagrangian problem has a decomposable structure, and solves the hybrid precoding optimization problem by double iteration; quickly solves the augmented Lagrangian problem in the inner iteration to update the original optimization variable, and adaptively updates the dual variable and penalty factor in the outer iteration. The present invention can effectively improve system performance and reduce system implementation cost and energy consumption.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a millimeter wave large-scale MIMO hybrid precoding design method for URLLC. Background Art

[0002] With the rapid development of technologies such as the Internet of Things, delay-sensitive services have begun to receive widespread attention, especially Ultra-Reliable Low-Latency Communications (URLLC). In order to reduce latency, the system often uses short packet transmission. At the same time, in order to meet the bandwidth requirements of ultra-large-scale Internet of Things, millimeter-wave massive multiple-input multiple-output (MIMO) has become a key technology for next-generation communications. By configuring large-scale array antennas at the base station end, millimeter-wave massive MIMO technology can make full use of wireless resources, and the use of precoding technology can effectively control inter-user interference and significantly improve system performance. However, the RF link in the millimeter-wave frequency band has extremely high energy consumption and hardware cost. Therefore, the traditional all-digital precoding structure is not suitable for millimeter-wave massive MIMO. In order to balance communication performance, energy consumption and system cost, hybrid precoding technology is widely used. Therefore, it is necessary to design a reasonable hybrid precoding method for URLLC to effectively suppress inter-user interference, reduce communication delay, and balance transmission performance, energy consumption and implementation complexity.

[0003] In the hybrid precoding structure, the network side equipment first uses full digital baseband precoding to perform weighted processing on the baseband signal, and then converts the weighted baseband signal to the carrier frequency band through a small number of RF links. The carrier frequency band signal to be transmitted is then further processed by a variable phase shifter network before being sent out. Generally speaking, phase shifters can be divided into high-precision continuous and low-precision discrete phase shifters according to resolution. High-precision continuous phase shifters can be described as constant modulus complex variables, while low-precision discrete phase shifters can be modeled as discretized constant modulus complex sets.

[0004] There are currently a large number of designs for hybrid precoding, among which weighted sum rate and maximum and minimum fairness are widely used performance metrics. However, most existing studies are based on the assumption of infinite block length and use Shannon capacity to measure transmission performance. However, in order to achieve low-latency communication, the actual system must use short packet transmission. According to the finite block length information theory, the error probability in short packet transmission cannot be ignored, and the achievable rate of short packet transmission is completely different from Shannon capacity and is more complicated. At the same time, URLLC services often have minimum transmission rate requirements, and most existing designs do not consider the user's service quality requirements. Therefore, traditional hybrid precoding designs cannot be applied to URLLC communication systems, and effective URLLC millimeter-wave massive MIMO hybrid precoding designs are urgently needed to meet the communication service requirements of low-latency services while effectively balancing system cost and transmission performance. However, due to the very complex achievable rate of finite block length, and the serious coupling of digital precoding and analog precoding. At the same time, communication service requirements such as service transmission delay and minimum transmission rate must also be considered. Therefore, the optimization problem of URLLC millimeter-wave massive MIMO hybrid precoding design is seriously non-convex and non-smooth, and it is very difficult to solve. Summary of the invention

[0005] The purpose of the present invention is to provide a millimeter-wave large-scale MIMO hybrid precoding design method for URLLC, which is based on the millimeter-wave hybrid precoding architecture, adopts short packet transmission to reduce latency, and comprehensively considers the requirements of multi-user URLLC transmission reliability, latency and minimum transmission rate, which can effectively improve system performance and reduce system implementation cost and energy consumption.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A millimeter wave massive MIMO hybrid precoding design method for URLLC, the method comprising the following steps:

[0008] Step 1: For a downlink single-cell multi-user URLLC millimeter-wave massive MIMO communication system with a fully connected hybrid precoding architecture for the base station, a maximum transmission power constraint is constructed for network-side equipment, a QoS (Quality of Service, QoS) requirement including reliability, delay and rate is constructed for the user terminal, and a feasible phase set constraint is constructed for the hybrid precoding phase shifter. Based on the system performance measurement criteria, a millimeter-wave massive MIMO hybrid precoding optimization problem for URLLC is established;

[0009] Step 2, calculate and check whether the hybrid precoding optimization problem established in step 1 is feasible. If it is feasible, proceed to step 3; otherwise, determine that there is no feasible solution to the hybrid precoding optimization problem established in step 1, and end the process;

[0010] Step 3, reconstructing the hybrid precoding optimization problem established in step 1 and obtaining its corresponding partial augmented Lagrangian problem;

[0011] Step 4, initialize the original optimization variables, dual variables and penalty function;

[0012] Step 5, under fixed penalty factor and dual variable, solve the partial augmented Lagrangian problem and update the original optimization variable; calculate the constraint error norm, if the error norm is less than the preset termination condition threshold or the number of iterations exceeds the preset maximum value, output the optimal hybrid precoding design and objective function value; otherwise, when the constraint error norm is less than the set threshold, use the subgradient method to update the dual variable, and when the constraint error norm is greater than or equal to the set threshold, update the penalty factor.

[0013] Furthermore, in step 1, the process of constructing QoS requirements including reliability, delay and rate for the user terminal includes:

[0014] In order to meet the delay requirements of URLLC, finite block length is used to transmit signals, and the block error rate (BLER) is set to ensure transmission reliability. Under given delay and reliability requirements, finite block length information theory is used to measure the transmission rate, and the user terminal transmission performance requirements are ultimately modeled as QoS constraints represented by different user SINRs.

[0015] Furthermore, the process of finally modeling the user terminal transmission performance requirements as QoS constraints represented by different user SINRs includes:

[0016] Given the maximum error probability of user transmission and the transmission block length, the minimum received SINR (Signal-to-Interference-Plus-Noise ratio, SINR) constraint corresponding to the minimum URLLC rate constraint is calculated according to the monotonically increasing characteristic of the finite block length achievable rate expression with respect to the user SINR within the non-negative rate range, and the minimum URLLC rate constraint is equivalently converted into the user terminal QoS constraint expressed in user SINR.

[0017] Further, in step 1, the system performance measurement criteria include a weighted sum rate criterion and a maximum-minimum fairness criterion;

[0018] When the system performance is measured by the weighted sum rate criterion, the millimeter wave massive MIMO hybrid precoding optimization problem is specifically: maximizing the multi-user URLLC weighted sum rate under power constraints, user QoS constraints and different feasible phase sets of phase shifters;

[0019] When the system performance is measured by the maximum-minimum fairness criterion, the millimeter-wave massive MIMO hybrid precoding optimization problem is specifically: maximizing the minimum user URLLC rate under power constraints, user QoS constraints and different feasible phase sets of phase shifters.

[0020] Step 2 further includes:

[0021] Solve the problem of minimizing the hybrid precoding transmission power under the constraints of user QoS constraints and the feasible phase set of phase shifters. If the solution satisfies the multi-user QoS constraints, the feasible phase set of phase shifters and the power constraints, then there is a feasible solution that satisfies the multi-user QoS constraints, the feasible phase set of phase shifters and the power constraints; otherwise, there is no feasible solution.

[0022] Step 3 further includes:

[0023] Auxiliary variables are introduced to rewrite some constraints on the original variables into constraints on the auxiliary variables, so that all constraints with variable coupling are equality constraints and their optimization variables can be divided into blocks;

[0024] The equality constraints between the auxiliary variables and the original optimization variables are transformed into the objective function through the penalty function method, so that each optimization variable corresponds to at most one constraint condition, and the optimization variables are processed in blocks.

[0025] Furthermore, in step 5, under fixed penalty factors and dual variables, the partial augmented Lagrangian problem is solved using fast coordinate descent and interior point approximation criterion.

[0026] Furthermore, the interior point approximation criterion method includes continuous convex approximation and controlled optimization MM (Majorization-Minimization, MM) method.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] First, the millimeter-wave large-scale MIMO hybrid precoding design method for URLLC of the present invention adopts short packet transmission to meet the low latency requirements of multi-user URLLC communication services; adopts a hybrid precoding architecture to effectively improve the system transmission performance, reduce energy consumption and system implementation costs; and adopts finite block length information theory to measure short packet transmission performance, which can strictly guarantee the transmission requirements of multi-user communication services such as reliability and latency.

[0029] Second, the millimeter-wave massive MIMO hybrid precoding design method for URLLC of the present invention uses finite block length information theory to convert service transmission requirements into QoS constraints represented by user SINR, and through reconstruction and transformation of the optimization problem, using penalty functions and duality methods, and adopting block coordinate descent and other methods to update the optimization variables in parallel, the computational complexity can be significantly reduced.

[0030] Third, the millimeter-wave large-scale MIMO hybrid precoding design method for URLLC of the present invention takes into account the influence of transmission block length, which can significantly improve the system spectrum efficiency and greatly improve the utilization of wireless resources.

[0031] Fourth, the millimeter-wave massive MIMO hybrid precoding design method for URLLC of the present invention is applicable to commonly used system performance measurement criteria, including but not limited to weighted sum rate and maximum and minimum fairness, and has high universality.

[0032] Fifth, the millimeter-wave massive MIMO hybrid precoding design method for URLLC of the present invention is applicable to phase shifters of different resolutions, which can further reduce the system implementation complexity and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the flow chart of a millimeter wave massive MIMO hybrid precoding design method for URLLC according to an embodiment of the present invention;

[0034] Figure 2 It is a weighted sum rate performance comparison diagram of the hybrid precoding design of the embodiment of the present invention, the finite block length pure digital precoding transmission design, and the matrix approximation hybrid precoding design when the base station is configured with different transmission signal-to-noise ratios;

[0035] Figure 3 is a weighted sum rate performance comparison diagram of a hybrid precoding design and a matrix approximation hybrid precoding design in an embodiment of the present invention using phase shifters with different resolutions under different numbers of radio frequency links;

[0036] Figure 4 It is a minimum URLLC rate performance comparison diagram of the hybrid precoding design of the embodiment of the present invention, the finite block length pure digital precoding transmission design, and the matrix approximation hybrid precoding design when the base station is configured at different transmission signal-to-noise ratios;

[0037] Figure 5 This is a comparison chart of the minimum URLLC rate performance of the hybrid precoding design of an embodiment of the present invention and the matrix approximation hybrid precoding design using phase shifters with different resolutions under different numbers of RF links. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0039] The present invention discloses a millimeter wave massive MIMO hybrid precoding design method for URLLC, the method comprising the following steps:

[0040] Step 1: For a downlink single-cell multi-user URLLC millimeter-wave massive MIMO communication system with a fully connected hybrid precoding architecture for the base station, a maximum transmission power constraint is constructed for network-side equipment, a QoS (Quality of Service, QoS) requirement including reliability, delay and rate is constructed for the user terminal, and a feasible phase set constraint is constructed for the hybrid precoding phase shifter. Based on the system performance measurement criteria, a millimeter-wave massive MIMO hybrid precoding optimization problem for URLLC is established;

[0041] Step 2, calculate and check whether the hybrid precoding optimization problem established in step 1 is feasible. If it is feasible, proceed to step 3; otherwise, determine that there is no feasible solution to the hybrid precoding optimization problem established in step 1, and end the process;

[0042] Step 3, reconstructing the hybrid precoding optimization problem established in step 1 and obtaining its corresponding partial augmented Lagrangian problem;

[0043] Step 4, initialize the original optimization variables, dual variables and penalty function;

[0044] Step 5, under fixed penalty factor and dual variable, solve the partial augmented Lagrangian problem and update the original optimization variable; calculate the constraint error norm, if the error norm is less than the preset termination condition threshold or the number of iterations exceeds the preset maximum value, output the optimal hybrid precoding design and objective function value; otherwise, when the constraint error norm is less than the set threshold, use the subgradient method to update the dual variable, and when the constraint error norm is greater than or equal to the set threshold, update the penalty factor.

[0045] Example 1

[0046] like Figure 1 As shown, the embodiment of the present invention discloses a millimeter wave massive MIMO hybrid precoding design method for URLLC. In order to clearly and in detail demonstrate the application of the method of the present invention, the millimeter wave massive MIMO hybrid precoding design for URLLC based on the weighted sum rate criterion is hereby demonstrated, including the following steps:

[0047] Step 1: Consider a downlink single-cell multi-user URLLC millimeter-wave massive MIMO communication system, equipped with The base station's transmitting antennas simultaneously serve single antenna user, using the collection The base station adopts a fully connected hybrid precoding architecture, where the number of RF links is expressed as Considering that users are randomly distributed around the base station, the user channel is expressed as , where L is the number of paths, represents the path gain, is the antenna array response, is the direction angle, in the interval The bandwidth used by the base station is B = 1MHz, and the noise power spectrum density of the user receiving end is -174dBm / Hz, so the noise power of user k is The base station learns the multi-user URLLC communication service requirements, including the transmission error probability requirements ,in , minimum transmission rate requirement , the transmission delay requirement is , the maximum transmission power of the base station is PmW.

[0048] Step 2: Use finite block length information theory to measure URLLC transmission performance, where the base station transmits a signal ,in, is the digital precoding vector of user k, and the digital precoding matrix is ​​defined as , is the zero mean and unit variance signal sent by the base station to user k, is the analog precoding matrix. If the phase shifter has arbitrary precision, the analog precoding can be modeled as:

[0049] ;

[0050] If the phase shifter is If the bits are uniformly quantized, the analog precoding can be modeled as:

[0051] .

[0052] In order to meet the delay requirements, the system uses short packet transmission (such as transmission block length ), the transmission block length is The received signal of user k is , is the background noise, user k will Treat it as background Gaussian noise and demodulate the decoded signal Therefore, the received SINR of user k is:

[0053] .

[0054] According to the finite block length information theory, the achievable rate of short packets for user k is:

[0055] ;

[0056] in, , , is the Gaussian Q function, is the inverse Gaussian Q function, that is .

[0057] Therefore, the multi-user communication service transmission requirement can be expressed as For a given , the finite block length achievable rate About User SINR Monotonically increasing, can be calculated using binary search The only positive real solution of , , , , , This allows the short packet multi-user transmission requirement to be converted into a QoS constraint expressed by the user SINR: .

[0058] Step 3: Considering the constraints of QoS, power and feasible phase sets of phase shifters with different resolutions, a model of maximizing the weighted sum rate hybrid precoding optimization problem is established:

[0059] ;

[0060] in, is the weight of user k, which is set to , are feasible phase constraints imposed by analog precoding on continuous and discrete phase shifters.

[0061] Step 4: Calculate and check whether there is a solution that satisfies the power constraint ,QoS constraints And simulate the feasible phase constraints of precoding A feasible solution and , if it exists, execute step 5; otherwise, it cannot meet the current service requirements and exits the calculation.

[0062] Step 5: Hybrid precoding optimization problem in step 3 Non-convex and coupled optimization variables, reconstruct the optimization problem. Introduce the following auxiliary variables , .definition , and Therefore, the optimization problem can be rewritten as

[0063] ;

[0064] in, , , .

[0065] Step 6: Use the penalty function method to obtain the problem The augmented Lagrangian problem:

[0066] ;

[0067] in, is the dual variable,

[0068] ;

[0069] is the channel matrix, is the penalty factor.

[0070] Step 7. Set the number of iterations ,initialization , , , .

[0071] Step 8: Fix the dual variables and penalty factor Under this condition, we solve the short packet massive MIMO hybrid precoding augmented Lagrangian optimization problem Update the original optimization variables .

[0072] Step 9: Calculate the constraint error norm .like , then update the dual variable:

[0073] ;

[0074] ;

[0075] .

[0076] Otherwise, update the penalty factor: , , .renew .

[0077] Step 10: If or , then stop the iteration and output the optimal hybrid precoding ; Otherwise, proceed to step 8.

[0078] More specifically, in this embodiment, in step 4, the method of checking whether there is a power constraint satisfied ,QoS constraints And simulate the feasible phase constraints of precoding The feasible solution method is to solve the QoS constraints And simulate the feasible phase constraints of precoding For the problem of minimizing the transmission power under , if the solution meets the QoS constraint and the power constraint, then there is a feasible solution that meets the QoS and power constraints; otherwise, there is no feasible solution. Specifically, it includes:

[0079] (1) Initialization , under the constraints of the feasible phase set Randomly generate simulated precoding , define the equivalent channel as , therefore, solve the following digital precoding optimization problem:

[0080] ;

[0081] Due to The uniform phase flipping of all elements in does not affect the objective function and constraints. Therefore, assuming Therefore, the above optimization problem can be transformed into

[0082] .

[0083] (2) The above optimization problem is a convex optimization problem. The interior point method can be used to solve the above optimization problem and obtain the optimal solution. .

[0084] (3) Check hybrid precoding Whether the power constraint is met and QoS constraints , if satisfied, then end and output hybrid precoding If not satisfied and ,but , execute step (1); if If no feasible solution is found, it is considered that there is no feasible solution under the current conditions.

[0085] More specifically, in the present embodiment, in step 8, the method for solving the URLLC-oriented millimeter-wave massive MIMO hybrid precoding augmented Lagrangian optimization problem first divides the optimization variables into blocks. , and Then, the Lagrangian optimization problem is solved by using methods such as fast coordinate descent and interior point approximation criteria, and it is iterated until the termination condition is met. The specific steps are as follows:

[0086] (1) Set the number of iterations ,initialization .

[0087] (2) Update .

[0088] (3) Update by solving the following optimization problem :

[0089] .

[0090] (4) Update .

[0091] (5) Yes , by solving the following optimization problem to update :

[0092] .

[0093] (6) Calculate the continuous relative target difference:

[0094] ;

[0095] make ,like or , the algorithm terminates and outputs ; Otherwise, execute step (2).

[0096] More specifically, in this embodiment, in step 8, the update The method specifically comprises the following steps:

[0097] (1) Rewrite the updated optimization problem as

[0098] ;

[0099] in, , , .matrix and are all semi-positive matrices, so we can use the fast coordinate descent method to solve the above optimization problem;

[0100] (2) Initialization ;

[0101] (3) ;

[0102] (4) Yes , execute steps (5)-(8) respectively;

[0103] (5) Calculation ;

[0104] (6) If the base station uses an infinite precision continuous phase shifter, calculate Otherwise, calculate ;

[0105] (7) Calculation ;

[0106] (8) Update ;

[0107] (9) Update ;

[0108] (10) If the objective function is a continuous difference or , then the output simulated precoding matrix ; Otherwise, execute step (3).

[0109] More specifically, in this embodiment, in step 8, the update The method specifically comprises the following steps:

[0110] (1) To update , we need to solve the following optimization problem:

[0111] ;

[0112] Since the finite block length rate expression and the constraints are non-convex, the above optimization problem is non-convex and difficult to solve.

[0113] (2) Initialization number of iterations , .

[0114] (3) Based on the MM criterion, using methods such as Taylor expansion, based on continuous convex approximation or MM method, in the feasible solution Constructing the MM sub-optimization problem

[0115] ;

[0116] in,

[0117] ;

[0118] ;

[0119] ;

[0120] .

[0121] (4) Solve the MM sub-optimization problem to obtain the optimal solution. , the optimal solution is:

[0122] ;

[0123] in, is arbitrary. , then the optimal solution is:

[0124] ;

[0125] Among them, if , ;otherwise, .definition ,like , then the dual variable ;otherwise, is to satisfy the equation The only positive real number solution of is equivalent to solving a quartic equation of one variable, which can be obtained in closed form.

[0126] (4) Update .

[0127] (5) If or , then terminate the algorithm and output ; Otherwise, execute step (3).

[0128] The above is the specific implementation and application of the method of the present invention in Example 1.

[0129] In order to verify the effect of the short packet massive MIMO hybrid precoding design method based on the maximization and rate criteria provided in Example 1, a simulation experiment is provided. In the simulation experiment, the results of each experimental parameter configuration are obtained by averaging the experimental results of 100 random sample samples of user channels.

[0130] Figure 2 It is a weighted sum rate performance comparison diagram of the hybrid precoding design of an embodiment of the present invention, the finite block length pure digital precoding transmission design, and the matrix approximation hybrid precoding design when the base station is configured under different transmission signal-to-noise ratios and based on the maximization weighted sum rate criterion; wherein the matrix approximation hybrid precoding design is obtained by minimizing the norm of the hybrid precoding and finite block length pure digital precoding matrices. Figure 2 The performance of different precoding schemes in Example 1 at different transmit signal-to-noise ratios (defined as the ratio of transmit power to user background noise power) is analyzed. users. It can be seen from the figure that the use of finite block length pure digital precoding can achieve optimal performance, while the use of traditional infinite block length pure digital precoding has performance losses. The hybrid precoding proposed by the present invention can always achieve the optimal hybrid precoding URLLC transmission performance, especially better than the hybrid precoding scheme based on matrix approximation, wherein the matrix approximation scheme is to solve the hybrid precoding obtained by minimizing the minimum Euclidean distance between the hybrid precoding and the finite block length pure digital precoding. It is worth noting that when the base station adopts 24 RF links, the hybrid precoding design proposed by the present invention can achieve the same performance as the finite block length pure digital precoding, which reflects the superiority of the present invention.

[0131] Figure 3 This is a comparison chart of the weighted sum rate performance of the hybrid precoding design of an embodiment of the present invention and the matrix approximation hybrid precoding design using phase shifters with different resolutions based on the maximization weighted sum rate criterion under different numbers of RF links. Figure 3 The performance of different precoding schemes in base stations equipped with different RF links is analyzed, where the transmit signal-to-noise ratio is -7dB. Figure 3 It can be seen that the best performance is achieved by using pure digital precoding with finite block length, and the hybrid precoding scheme proposed in the present invention always achieves the best hybrid precoding transmission performance. It is worth noting that the comparison scheme based on matrix approximation hybrid precoding design cannot guarantee the transmission performance because it is a heuristic algorithm and is easy to violate the user transmission requirements. Therefore, when the base station is equipped with a small number of RF links, the transmission performance is extremely poor, which fully demonstrates the superiority of the method of the present invention.

[0132] Example 2

[0133] An embodiment of the present invention discloses a millimeter-wave massive MIMO hybrid precoding design method for URLLC, which performs millimeter-wave massive MIMO hybrid precoding design for URLLC based on the maximum-minimum fairness criterion. The scenario setting and problem conversion in step 1 and step 2 in the main steps are consistent with those in embodiment 1 and will not be repeated here.

[0134] Step 3: Based on the maximum and minimum criteria, a millimeter-wave hybrid precoding optimization problem model for maximizing the minimum user URLLC rate is established under the constraints of QoS constraints, power constraints, and feasible phase sets of phase shifters with different resolutions:

[0135] .

[0136] Step 4: Calculate and check whether there is a solution that satisfies the power constraint ,QoS constraints And simulate the feasible phase constraints of precoding A feasible solution and , if it exists, execute step 5; otherwise, it cannot meet the current service requirements and exits the calculation.

[0137] Step 5: Hybrid precoding optimization problem in step 3 Non-convex, reconstruct the optimization problem. Introduce the following auxiliary variables , , , .definition , , , , , Therefore, the optimization problem can be reconstructed as the following optimization problem

[0138] ;

[0139] in, .

[0140] Step 6: Use the penalty function method to obtain the problem The augmented Lagrangian problem:

[0141] ;

[0142] in, is the dual variable, is the penalty factor,

[0143] .

[0144] Step 7. Set the number of iterations ,initialization , , , , , .

[0145] Step 8: Fix the dual variables and penalty factor Under this condition, we solve the augmented Lagrangian problem of mm-wave massive MIMO hybrid precoding for URLLC. Update the original optimization variables .

[0146] Step 9: Calculate the constraint error norm:

[0147] ;

[0148] like , then update the dual variable,

[0149] ;

[0150] ;

[0151] ;

[0152] ;

[0153] .

[0154] Otherwise, update the penalty factor: , , , , .renew .

[0155] Step 10: If or , then stop the iteration and output the optimal hybrid precoding ; Otherwise, proceed to step 8.

[0156] More specifically, in this embodiment, in step 4, the method of checking whether there is a power constraint satisfied ,QoS constraints And simulate the feasible phase constraints of precoding The feasible solution method is to solve the QoS constraints And simulate the feasible phase constraints of precoding For the problem of minimizing the transmission power under , if the solution meets the QoS constraint and the power constraint, then there is a feasible solution that meets the QoS and power constraints; otherwise, there is no feasible solution. Specifically, it includes:

[0157] (1) Initialization , under the constraints of the feasible phase set Randomly generate simulated precoding , the equivalent channel is defined as , therefore, solve the following digital precoding optimization problem:

[0158] ;

[0159] Due to The uniform phase flipping of all elements in does not affect the objective function and constraints. Therefore, assuming Therefore, the above optimization problem can be transformed into

[0160] .

[0161] (2) The above optimization problem is a convex optimization problem. The interior point method can be used to solve the above optimization problem and obtain the optimal solution. .

[0162] (3) Check hybrid precoding Whether the power constraint is met and QoS constraints , if satisfied, then end and output hybrid precoding If not satisfied and ,but , execute step (1); if If no feasible solution is found, it is considered that there is no feasible solution under the current conditions.

[0163] More specifically, in this embodiment, in step 8, the method for solving the millimeter wave massive MIMO hybrid precoding augmented Lagrangian optimization problem for URLLC is The method first divides the optimization variables into blocks, , and Then, the Lagrangian optimization problem is solved by using methods such as fast coordinate descent and interior point approximation criteria, and it is iterated until the termination condition is met. The specific steps are as follows:

[0164] (1) Set the number of iterations ,initialization .

[0165] (2) Update

[0166] ;

[0167] .

[0168] (3) Update by solving the following optimization problem :

[0169] .

[0170] Solving the above optimization problem is similar to that in Example 1 and will not be repeated here.

[0171] (4) Update .

[0172] (5) Yes , solve the following optimization problem to update and :

[0173] .

[0174] (6) Yes , solve the following optimization problem to update :

[0175] ;

[0176] like ,but:

[0177] ;

[0178] in, is arbitrary. ,but

[0179] ;

[0180] Among them, if , ;otherwise, .definition ,if , then the dual variable ;otherwise, It is the equation The only real root of , solving this equation is equivalent to solving a quartic equation of one variable, which can be solved in closed form.

[0181] (7) Calculate the continuous relative target difference

[0182] ;

[0183] make ,like or , the algorithm terminates and outputs ; Otherwise, execute step (2).

[0184] More specifically, in this embodiment, in step 8, the update and The method specifically comprises the following steps:

[0185] (1) To update and , we need to solve the following optimization problem:

[0186] .

[0187] Since the finite block length rate expression and the constraints are non-convex, the above optimization problem is non-convex and difficult to solve.

[0188] (2) Initialization number of iterations , , .

[0189] (3) Based on the MM criterion, using methods such as Taylor expansion, based on continuous convex approximation or MM method, in the feasible solution and Construct the MM sub-optimization problem:

[0190] ;

[0191] in, It is the same as that in Example 1 and will not be repeated here.

[0192] (4) Solve the MM sub-optimization problem to obtain the optimal solution:

[0193] ;

[0194] ;

[0195] in, is the dual variable. Definition , ,but ;otherwise, It is the equation The only positive real root of . Solving this equation is equivalent to solving a cubic equation of one variable, which can be solved in closed form.

[0196] (5) Update .

[0197] (4) If or , then terminate the algorithm and output and Otherwise, execute step (3).

[0198] In order to verify the effect of the millimeter wave massive MIMO hybrid precoding design method for URLLC based on the maximum and minimum fairness criterion provided in Example 2, a simulation experiment is provided. In the simulation experiment, the results of each experimental parameter configuration are obtained by averaging the experimental results of 100 random sample samples of user channels.

[0199] Figure 4 It is a comparison chart of the minimum URLLC rate performance of the hybrid precoding design of an embodiment of the present invention, the finite block length pure digital precoding transmission design, and the matrix approximation hybrid precoding design when the base station is configured under different transmission signal-to-noise ratios based on the maximum and minimum fairness criterion. Figure 4 The performance of different precoding schemes in Example 2 at different transmit signal-to-noise ratios (defined as the ratio of transmit power to user background noise power) is analyzed. users. It can be seen from the figure that the use of finite block length pure digital precoding can achieve optimal performance, while the use of traditional infinite block length pure digital precoding has performance loss. The hybrid precoding proposed in the present invention has the best hybrid precoding transmission performance, and is particularly superior to the hybrid precoding scheme based on matrix approximation, wherein the matrix approximation scheme is a hybrid precoding obtained by solving the minimum Euclidean distance between the hybrid precoding and the finite block length pure digital precoding. It is worth noting that when the base station adopts 24 RF links, the hybrid precoding design proposed in the present invention can achieve the same performance as the finite block length pure digital precoding, which reflects the superiority of the present invention.

[0200] Figure 5 This is a comparison chart of the minimum URLLC rate performance of the hybrid precoding design of an embodiment of the present invention and the matrix approximation hybrid precoding design using phase shifters with different resolutions under different numbers of RF links based on the maximum and minimum fairness criterion. Figure 5 The performance of different precoding schemes in base stations equipped with different RF links is analyzed, where the transmit signal-to-noise ratio is -7dB. Figure 5 It can be seen that the best performance is achieved by using pure digital precoding with finite block length, and the hybrid precoding scheme proposed in the present invention always achieves the best hybrid precoding transmission performance. It is worth noting that the comparison scheme based on matrix approximation hybrid precoding design cannot guarantee the transmission performance because it is a heuristic algorithm and is easy to violate the user transmission requirements. Therefore, when the base station is equipped with a small number of RF links, the transmission performance is extremely poor, which fully demonstrates the superiority of the method of the present invention.

[0201] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

[0202] The present invention proposes a millimeter-wave massive MIMO hybrid precoding design method for URLLC. The network side equipment adopts a hybrid precoding architecture to balance transmission performance, energy consumption and system implementation cost, while considering the URLLC service transmission requirements and power constraints of different users, and meets the low latency requirement with short packet transmission. The proposed transmission method has a certain universality and is suitable for performance measurement criteria such as weighted sum rate and maximum and minimum fairness. It is also suitable for phase shifters of different resolutions. It can strictly meet the transmission requirements of communication services for reliability and latency, and greatly improve the system performance transmission.

[0203] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A millimeter-wave massive MIMO hybrid precoding design method for URLLC, characterized in that: The method comprises the following steps: Step 1: For a downlink single-cell multi-user URLLC millimeter-wave massive MIMO communication system in which the base station adopts a fully connected hybrid precoding architecture, a maximum transmission power constraint is constructed for network-side equipment, QoS requirements including reliability, latency, and rate are constructed for user terminals, and a feasible phase set constraint is constructed for the hybrid precoding phase shifter. Based on the system performance metric, a millimeter-wave massive MIMO hybrid precoding optimization problem for URLLC is established; Step 2, calculate and check whether the hybrid precoding optimization problem established in step 1 is feasible. If it is feasible, proceed to step 3; otherwise, determine that there is no feasible solution to the hybrid precoding optimization problem established in step 1, and end the process; Step 3, reconstructing the hybrid precoding optimization problem established in step 1 and obtaining its corresponding partial augmented Lagrangian problem; Step 4, initialize the original optimization variables, dual variables and penalty function; Step 5: Under the condition of fixed penalty factor and dual variable, solve the partial augmented Lagrangian problem and update the original optimization variable; calculate the constraint error norm, if the error norm is less than the preset termination condition threshold or the number of iterations exceeds the preset maximum value, output the optimal hybrid precoding design and the objective function value; otherwise, when the constraint error norm is less than the set threshold, use the subgradient method to update the dual variable, and when the constraint error norm is greater than or equal to the set threshold, update the penalty factor; In step 1, the process of building QoS requirements including reliability, delay and rate for the user terminal includes: In order to meet the delay requirements of URLLC, finite block length is used to transmit signals, and the block error rate (BLER) is set to ensure transmission reliability. Under given delay and reliability requirements, finite block length information theory is used to measure the transmission rate, and the user terminal transmission performance requirements are ultimately modeled as QoS constraints represented by different user SINRs. The process of finally modeling the user terminal transmission performance requirements as QoS constraints expressed by different user SINRs includes: Given the maximum error probability of user transmission and the transmission block length, the minimum receiving SINR constraint corresponding to the minimum URLLC rate constraint is calculated based on the monotonically increasing characteristic of the finite block length achievable rate expression with respect to the user SINR within the non-negative rate range, and the minimum URLLC rate constraint is equivalently converted into the user terminal QoS constraint expressed in terms of the user SINR. In step 1, the system performance measurement criteria include a weighted sum rate criterion and a maximum-minimum fairness criterion; When the system performance is measured by the weighted sum rate criterion, the millimeter wave massive MIMO hybrid precoding optimization problem is specifically: maximizing the multi-user URLLC weighted sum rate under power constraints, user QoS constraints and different feasible phase sets of phase shifters; When the system performance is measured by the maximum-minimum fairness criterion, the millimeter-wave massive MIMO hybrid precoding optimization problem is specifically: maximizing the minimum user URLLC rate under power constraints, user QoS constraints and different feasible phase sets of phase shifters.

2. The URLLC-oriented millimeter-wave massive MIMO hybrid precoding design method according to claim 1, characterized in that: Step 2 further includes: Solve the problem of minimizing the hybrid precoding transmission power under the constraints of user QoS constraints and the feasible phase set of phase shifters. If the solution satisfies the multi-user QoS constraints, the feasible phase set of phase shifters and the power constraints, then there is a feasible solution that satisfies the multi-user QoS constraints, the feasible phase set of phase shifters and the power constraints; otherwise, there is no feasible solution.

3. The URLLC-oriented millimeter-wave massive MIMO hybrid precoding design method according to claim 1, characterized in that: Step 3 further includes: Auxiliary variables are introduced to rewrite some constraints on the original variables into constraints on the auxiliary variables, so that all constraints with variable coupling are equality constraints and their optimization variables can be divided into blocks; The equality constraints between the auxiliary variables and the original optimization variables are transformed into the objective function through the penalty function method, so that each optimization variable corresponds to at most one constraint condition, and the optimization variables are processed in blocks.

4. The URLLC-oriented millimeter-wave massive MIMO hybrid precoding design method according to claim 1, characterized in that: In step 5, under fixed penalty factors and dual variables, the fast coordinate descent and interior point approximation criterion method are used to solve the partial augmented Lagrangian problem.

5. The URLLC-oriented millimeter wave massive MIMO hybrid precoding design method according to claim 4, characterized in that: The interior point approximation criterion methods include continuous convex approximation and controlled optimization MM method.

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