Downlink transmission system and method for user center alignment in asynchronous cellular-free network

Abstract

The invention discloses a user center aligned downlink transmission system and method for an asynchronous cellular-free network. The system comprises radio frequency access points (AP) of all frequency bands, a central processing unit (CPU) and an Ethernet switching unit, the AP completes beamforming, sending and receiving of wireless radio frequency signals of all frequency bands, digital-analog and analog-digital conversion, waveform signal processing of a physical channel and active delay processing of waveforms; the CPU completes a user-centered joint beam selection and power distribution calculation task; and the Ethernet exchange unit exchanges information. The method comprises the following steps: step 1, an AP (Access Point) establishes a local analog beam codebook and carries out distance measurement on users who may serve; step 2, analog domain processing: the AP estimates channels of users who may serve, and performs beam selection with the users as the center; and step 3, digital domain processing: after the service users are selected by the APs and the service users on which paths are determined, aligning transmission is carried out on different paths on different APs of the unified users, and then digital pre-coding is carried out on the equivalent digital channels. According to the method, the beams are selected by taking the user as the center, and multi-user interference and asynchronous interference can be inhibited at the same time in combination with aligned transmission.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a downlink transmission system and method for an asynchronous non-cellular network with user center alignment. Background Art

[0002] Cell-free networks are considered to be an important implementation architecture for the next generation of wireless communication networks. Since the concept of traditional cells is eliminated, cell-free networks can provide equally good services to all users. However, the existing cell-free network design is mainly suitable for indoor scenarios. For large outdoor scenarios, cell-free networks will face the problem of asynchronous transmission. Most academics currently believe that cell-free networks are perfectly synchronized, and transmission schemes are designed based on this assumption. However, since cell-free networks use a large number of APs scattered in the service area to jointly serve users, in large outdoor scenarios, the distances from these APs to each user will be significantly different, which will cause serious asynchronous reception problems. It should be noted that unlike the traditional single base station scenario, where the distance from the base station to the user is different, the cell-free network cannot be simply achieved by delayed reception at the user end, because even for the same user, the distance from each AP to the user is different.

[0003] Therefore, in order to achieve a high-performance cellular-free network with wide coverage, it is necessary to design an asynchronous downlink transmission solution that can synchronize signals from different APs. Summary of the invention

[0004] Purpose of the invention: The present invention provides a downlink transmission system and method for an asynchronous non-cellular network with user-centered alignment, which selects beams based on users and combines aligned transmission to simultaneously suppress multi-user interference and asynchronous interference.

[0005] Technical solution: The asynchronous non-cellular network user-centered aligned downlink transmission system described in the present invention includes: radio frequency access points (AP) of each frequency band, a central processing unit (CPU) and an Ethernet switching unit; the AP completes beamforming, sending and receiving wireless radio frequency signals of each frequency band, digital-to-analog and analog-to-digital conversion, waveform signal processing of the physical channel and active delay processing of the waveform; the CPU completes user-centered joint beam selection and power allocation calculation tasks; the Ethernet switching unit exchanges information.

[0006] Furthermore, after determining the user-centric beam, the AP performs aligned transmission and digital precoding for the user.

[0007] Furthermore, the AP actively delays the transmitted symbols on the data stream, and not only aligns the multipath signal from the AP to the user, but also aligns all the multipaths of all APs serving the user, so that the multipath gains are superimposed at the same time; after completing the user-centric beam selection and aligned transmission, the AP performs digital precoding calculations, and the numbers are calculated on the equivalent channel after analog precoding and aligned transmission.

[0008] Accordingly, a method for downlink transmission in an asynchronous non-cellular network with user center alignment comprises the following steps:

[0009] Step 1: The AP establishes a local analog beam codebook and performs ranging for users that may be served;

[0010] Step 2: Analog domain processing: the AP estimates the channels of the users that may be served and performs user-centric beam selection.

[0011] Step 3: Digital domain processing: After the AP has selected the service user and determined which multipaths to serve the user, it first aligns the transmission of different multipaths on different APs of the same user, and then digitally precodes the equivalent digital channel.

[0012] Furthermore, in step 1, the AP establishes a local simulated beam codebook and performs ranging for users that may be served, specifically including the following steps:

[0013] Step 11: The AP discretizes the base station transmission angle and constructs a simulated beam codebook according to the antenna array response.

[0014] Step 12: The AP measures the distance of the users that it can possibly serve. The users within a certain distance from the first AP are considered as the user set that the AP can possibly serve. The distance obtained is divided by the speed of light to obtain the user delay set. The maximum delay of the kth user in all multipaths on all APs is

[0015] Further, in step 11, the simulated beam codebook is a discrete Fourier codebook or an angle-range two-dimensional discrete codebook.

[0016] Furthermore, in step 2, analog domain processing, the AP estimates the channels of the users that may be served, and performs user-centric beam selection, which specifically includes the following steps:

[0017] Step 21: AP estimates the beam angle to obtain the transmission angle of each multipath for each user. The AP also needs to estimate the multipath channel gain, that is,

[0018] Step 22: The AP either transmits the data back to the CPU or collaborates with the CPU to perform user-centric joint beam selection. The optimization problem to be solved is as follows:

[0019]

[0020]

[0021]

[0022] in, express The ath codeword in the ath codeword, the variables to be optimized are α lkp and respectively represent whether the lth AP serves the kth user in the pth multipath and which codeword the lth AP uses to serve the kth user in the pth multipath.

[0023] Furthermore, in step 3, digital domain processing, after the AP has selected the service user and determined on which multipaths to serve the user, first aligns the different multipaths on different APs of the same user for transmission, and then digitally precodes the equivalent digital channel, specifically including the following steps:

[0024] Step 31: In the digital domain, the AP delays the digital signal to be sent by each data stream. The delay of the data stream of the kth user on the pth multipath by the lth AP is Δ lkp , that is, the digital signal s on the data stream k [t] becomes s k Mt-Δ lkp P, obviously, when it satisfies When the channel impulse responses of all multipaths used by the user on all APs are aligned to the time

[0025] Step 32: The AP calculates the optimal digital precoding on the equivalent digital channel, aiming to completely eliminate the constraints that are not fully satisfied in the analog domain. The problem to be solved is as follows:

[0026]

[0027]

[0028] in, and The simulated precoding matrix composed of the codewords finally selected by the lth AP.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: first, the different multipaths of different users are separated in the airspace, and then the multipaths of the same user from different APs are synchronized by using an aligned transmission method to make full use of the different multipath gains of different APs, thereby realizing a high-performance cellular-free network with wide coverage. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0031] Figure 2 This is a schematic diagram of the structure of an AP transceiver with a data stream delayer to achieve aligned transmission used in the present invention.

[0032] Figure 3 It is a schematic diagram of the method flow of the present invention.

[0033] Figure 4 This is a Monte Carlo simulation result diagram of asynchronous downlink transmission based on user-centric aligned transmission without a cellular network in the present invention. DETAILED DESCRIPTION

[0034] like Figure 1 and Figure 2 As shown, an asynchronous non-cellular network user-centered aligned downlink transmission system includes: radio frequency access points (AP) of each frequency band, a central processing unit (CPU) and an Ethernet switching unit; the AP completes beamforming, sending and receiving wireless radio frequency signals of each frequency band, digital-to-analog and analog-to-digital conversion, waveform signal processing of the physical channel and active delay processing of the waveform; the CPU completes user-centered joint beam selection and power allocation calculation tasks; the Ethernet switching unit exchanges information.

[0035] The AP is connected to a CPU, either through a wired optical fiber or an efficient and reliable wireless connection. The CPU can obtain all statistical information of all APs, and the AP can report all or part of the real-time information to the CPU without error. The AP has the ability to measure the distance to the user. The accuracy of the ranging should reach the order of the quotient of the speed of light and the bandwidth in order to accurately align the transmission. The AP performs joint distance estimation to improve the accuracy of the ranging, or the AP performs ranging independently to meet the fronthaul capacity limit between APs. The AP has a certain computing power and caching capacity, and can build a local codebook and cache it. The AP can build a discrete Fourier codebook to discretize the beam angle. The AP estimates the channels of users that may be served. The AP performs beam scanning to determine which beams have the greatest gain, or the AP estimates the incident angle / arrival angle to estimate the channel.

[0036] The CPU performs centralized joint user-centric beam selection, or the AP and CPU perform distributed collaborative joint user-centric beam selection, which may depend on the deployment conditions of the network. Joint user-centric beam selection determines the number of beams and specific beam codewords that each AP allocates to a user. The selected beam should maximize the gain of a certain multipath and suppress interference to other multipaths of the user and other users. The goal of joint user-centric beam selection can be transient or long-term. The former optimizes the beam of each time slot, while the latter optimizes a series of beam selection strategies within a period of time. Typically, it can be modeled as a Markov continuous decision problem.

[0037] After the AP determines the user-centric beam, it performs aligned transmission and digital precoding for the user. The AP actively delays the sent symbols on the data stream, and not only aligns the multipath signal from the AP to the user, but also aligns all multipaths of all APs serving the user, so that the multipath gains are superimposed at the same time. After completing the user-centric beam selection and aligned transmission, the AP performs digital precoding calculations, which are calculated on the equivalent channel after analog precoding and aligned transmission.

[0038] like Figure 3 As shown, a method for downlink transmission in an asynchronous non-cellular network with user center alignment includes the following steps:

[0039] Step 1: The AP establishes a local analog beam codebook and performs ranging for users that may be served;

[0040] Step 2: Analog domain processing: the AP estimates the channels of the users that may be served and performs user-centric beam selection.

[0041] Step 3: Digital domain processing: After the AP has selected the service user and determined which multipaths to serve the user, it first aligns the transmission of different multipaths on different APs of the same user, and then digitally precodes the equivalent digital channel.

[0042] For ease of presentation, K is defined as the number of users, N is the number of antennas per AP (here we assume a linear array), L is the number of APs, and P is the maximum number of multipaths. For simplicity, we assume that the number of RF links is equal to the number of data streams N. s Specifically, Figure 1 As shown, the channel between AP and user is assumed to be a geometrically decomposed channel used in common high-frequency wireless communications.

[0043]

[0044] Among them, β lkpis the complex channel gain of the p-th multipath from the l-th AP to the k-th user, a(·) is the antenna array response

[0045]

[0046] If the number of multipaths from the lth AP to the kth user is less than P, the expression of the extra multipath channel is considered to be zero.

[0047] Asynchronous downlink transmission without cellular network is divided into three steps:

[0048] Step S1: AP establishes a local analog beam codebook and performs ranging for users that may be served.

[0049] The specific steps include the following:

[0050] Step S101: The AP discretizes the base station transmission angle and constructs a simulated beam codebook according to the antenna array response. However, the present invention is not limited to the discrete Fourier codebook. Similarly, if the near-field effect is taken into consideration, the codebook can naturally be an angle-distance two-dimensional discrete codebook.

[0051] Step S102: The AP measures the distance of the users that it may serve. Specifically, the users within a certain distance from the first AP are regarded as the user set that the AP may serve. The distance obtained is divided by the speed of light to obtain the user delay set. The maximum delay of the kth user in all multipaths on all APs is

[0052] Step S2: analog domain processing: the AP estimates the channels of users that may be served and performs user-centric beam selection.

[0053] The specific steps include the following:

[0054] Step S201: AP can estimate the beam angle to obtain the transmission angle of each multipath of each user. In addition, the AP also needs to estimate the multipath channel gain, that is,

[0055] In step S202, the AP either transmits the data back to the CPU or collaborates with the CPU to perform user-centric joint beam selection. The optimization problem to be solved is as follows:

[0056]

[0057]

[0058] in, express The ath codeword in the ath codeword, the variables to be optimized are α lkp and respectively represent whether the lth AP serves the kth user in the pth multipath and which codeword the lth AP uses to serve the kth user in the pth multipath.

[0059] Step S3, digital domain processing, after the AP has selected the service user and determined on which multipaths to serve the user, it first aligns the transmission of different multipaths on different APs of the same user, and then digitally precodes the equivalent digital channel.

[0060] The specific steps include the following:

[0061] Step S301: In the digital domain, the AP delays the digital signal to be sent data stream by data stream. The delay of the data stream of the kth user in the pth multipath by the lth AP is Δ lkp , that is, the digital signal s on the data stream k [t] becomes s k Mt-Δ lkp P, obviously, when it satisfies When the channel impulse responses of all multipaths used by the user on all APs are aligned to the time

[0062] Step S302: The AP calculates the optimal digital precoding on the equivalent digital channel, aiming to completely eliminate the constraints that are not fully satisfied in the analog domain. The problem to be solved is as follows:

[0063]

[0064] in, and The simulated precoding matrix composed of the codewords finally selected by the lth AP.

[0065] Through the above three major steps, asynchronous downlink transmission based on user-centric aligned transmission in a non-cellular network is completed, thus realizing a wide coverage and high-performance non-cellular network. The effect example can be seen Figure 4 .

Claims

1. An asynchronous non-cellular network user-centered downlink transmission system, characterized in that: include: Radio access points AP for each frequency band, central processing unit CPU and Ethernet switching unit; AP completes beamforming, sending and receiving wireless radio frequency signals for each frequency band, digital-to-analog and analog-to-digital conversion, waveform signal processing of physical channels and active delay processing of waveforms; CPU completes user-centric joint beam selection and power allocation calculation tasks; Ethernet switching unit exchanges information.

2. The asynchronous non-cellular network user-centered aligned downlink transmission system as claimed in claim 1, characterized in that: After the AP determines the user-centered beam, it aligns the transmission and performs digital precoding for the user.

3. The asynchronous non-cellular network user-centered aligned downlink transmission system as claimed in claim 2, characterized in that: The AP actively delays the transmitted symbols on the data stream, and not only aligns the multipath signal from the AP to the user, but also aligns all the multipaths of all APs serving the user, so that the multipath gains are superimposed at the same time; after completing the user-centric beam selection and aligned transmission, the AP performs digital precoding calculations, which are calculated on the equivalent channel after analog precoding and aligned transmission.

4. A transmission method based on the asynchronous non-cellular network user-centered aligned downlink transmission system as claimed in claim 1, characterized in that: The steps include: Step 1: The AP establishes a local analog beam codebook and performs ranging for users that may be served; Step 2: Analog domain processing: the AP estimates the channels of the users that may be served and performs user-centric beam selection. Step 3: Digital domain processing: After the AP has selected the service user and determined which multipaths to serve the user, it first aligns the transmission of different multipaths on different APs of the same user, and then digitally precodes the equivalent digital channel.

5. The method for downlink transmission in an asynchronous non-cellular network with user center alignment as claimed in claim 4, characterized in that: In step 1, the AP establishes a local analog beam codebook and performs ranging for users that may be served. The specific steps include: Step 11: The AP discretizes the base station transmission angle and constructs a simulated beam codebook according to the antenna array response. Step 12: The AP measures the distance of the users that it can possibly serve. The users within a certain distance from the first AP are considered as the user set that the AP can possibly serve. The distance obtained is divided by the speed of light to obtain the user delay set. The maximum delay of the kth user in all multipaths on all APs is 6. The method for downlink transmission in an asynchronous non-cellular network with user center alignment as claimed in claim 5, characterized in that: In step 11, the simulated beam codebook is a discrete Fourier codebook or an angle-range two-dimensional discrete codebook.

7. The method for downlink transmission in an asynchronous non-cellular network with user center alignment as claimed in claim 4, characterized in that: In step 2, analog domain processing, the AP estimates the channels of the users that may be served and performs user-centric beam selection, which specifically includes the following steps: Step 21: AP estimates the beam angle to obtain the transmission angle of each multipath for each user. The AP also needs to estimate the multipath channel gain, that is, Step 22: The AP either transmits the data back to the CPU or collaborates with the CPU to perform user-centric joint beam selection. The optimization problem to be solved is as follows: in, represents the ath codeword in F, and the variables to be optimized are α lkp and respectively represent whether the lth AP serves the kth user in the pth multipath and which codeword the lth AP uses to serve the kth user in the pth multipath.

8. The method for downlink transmission in an asynchronous non-cellular network with user center alignment as claimed in claim 4, characterized in that: In step 3, digital domain processing, after the AP has selected the service user and determined which multipaths to serve the user, it first aligns the different multipaths on different APs of the same user for transmission, and then digitally precodes the equivalent digital channel. Specifically, the steps include: Step 31: In the digital domain, the AP delays the digital signal to be sent data stream by data stream. The delay of the data stream of the kth user on the pth multipath by the lth AP is Δ lkp , that is, the digital signal s on the data stream k [t] becomes s k Mt-Δ lkp P, obviously, when it satisfies When the channel impulse responses of all multipaths used by the user on all APs are aligned to the time Step 32: The AP calculates the optimal digital precoding on the equivalent digital channel, aiming to completely eliminate the constraints that are not fully satisfied in the analog domain. The problem to be solved is as follows: in, and The simulated precoding matrix composed of the codewords finally selected by the lth AP.

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