A simple receiving multiple access method based on symbol and bit stream joint distribution

Abstract

The application discloses a simple receiving multiple access method based on symbol and bit stream joint distribution, first, a transmitter distributes symbol streams and bit streams of each user based on a hierarchical quadrature amplitude modulation constellation diagram; different interference management schemes are adopted for inter-user interference in different beams and inter-user interference in the same beam to inhibit the influence of inter-user interference on system performance; channel equalization processing is performed on signals received by each user receiver, each user calculates log likelihood ratios of each bit stream allocated to each user according to a bit stream distribution result, and the calculation result is sent into a channel decoder to obtain original bit data. The above method jointly optimizes symbol and bit stream distribution schemes of each user and constellation diagram design, and can realize efficient user access in a large-scale access scene while satisfying a constraint condition of signal processing complexity of the receiver.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wireless communication multiple access technology, and particularly relates to a simple receiving multiple access method based on symbol and bit stream joint allocation. BACKGROUND

[0002] With the continuous iteration of wireless communication technology and the intelligent development of various devices, the number of user equipment in the existing communication network has increased dramatically, and further exacerbates the interference level between users in the existing cellular network, reducing the quality of service of users, so it is necessary to design an efficient multiple access scheme to manage the interference between users to provide high-speed data transmission services for a large number of user equipment. In the past first to fourth generation mobile communication standards, the user service data is mainly accessed to the network through orthogonal multiple access technology, that is, the user data is orthogonally divided into different time-frequency resource blocks without interference to completely avoid the influence of user-to-user interference on user rate. With the increase in the number of base station antennas, spatial division multiple access (SDMA) technology is widely studied and applied in current wireless communication systems, which separates the service data of each user in space by specially designing the linear precoding of the base station side to avoid interference between different data streams, that is, a kind of orthogonal multiple access technology in spatial dimension. Since the user-to-user interference is eliminated in the spatial dimension by the design of the transmitting end, each user receiver only needs to perform a simple signal processing procedure to recover the original information data. However, in the actual system, due to the limitation of the number of base station antennas and the spatial distribution characteristics of users, the user channel may exhibit strong spatial correlation, so it is difficult to separate the strong user data in the spatial domain. At this time, the spatial division multiple access technology will have obvious performance loss; at the same time, the method has high requirements for the accuracy of user channel state information, and inaccurate user channel state information will cause serious residual inter-stream interference and affect the system performance.

[0003] Due to the need for orthogonal division of time-frequency resource blocks, the number of users that can be simultaneously served by an orthogonal multiple access scheme cannot be too high, thereby limiting the spectral efficiency of the actual system. In contrast, non-orthogonal multiple access technology (Non-Orthogonal Multiple Access, NOMA) allows different user data to be overlapped and sent on the same resource block to improve spectral efficiency, but at the cost of using a complex successive interference cancellation technology (Successive Interference Cancellation, SIC) for data detection at the receiving end. Unlike spatial division multiple access technology, non-orthogonal multiple access benefits from strong spatial correlation and channel gain differences between user channels. However, the high receiver complexity and error propagation problems caused by SIC, as well as the loss of degrees of freedom in the multi-antenna scenario, limit its deployment and application in actual systems. In recent years, a new method called rate-splitting multiple access (Rate-Splitting Multiple Access, RSMA) has been proposed, which splits the original data of each user into two parts, public data and private data, and transmits them through different precoding vectors, combining the advantages of SDMA and NOMA technologies to achieve performance gains in complex channel environments. However, since each user needs to decode the superimposed signals of the public data stream and the private data stream, the receiver also needs to use the high-complexity SIC technology.

[0004] In summary, although there are many related works focusing on efficient user access in future wireless communication scenarios, they all have problems such as limited performance or high receiver complexity. Therefore, how to achieve efficient large-scale multiple access in various channel scenarios under the constraint of a simple receiver is still a problem to be solved. SUMMARY

[0005] The purpose of the present application is to provide a simple receiving multiple access method based on joint allocation of symbols and bit streams, which jointly optimizes the allocation scheme of symbols and bit streams of each user and the constellation design, and can realize efficient user access in a large-scale access scenario while meeting the constraint condition of receiver signal processing complexity.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A simple receiving multiple access method based on joint allocation of symbols and bit streams, the method comprising:

[0008] Step 1: The transmitter allocates the symbol stream and the bit stream of each user based on a hierarchical quadrature amplitude modulation constellation;

[0009] Step 2, different interference management schemes are used for the inter-user interference in different beams and the inter-user interference in the same beam to suppress the influence of the inter-user interference on the system performance;

[0010] Step 3, low-complexity signal processing is performed on the signal received by each user receiver, and according to the bit stream allocation result of Step 1, each user calculates the log-likelihood ratio of each bit stream allocated to the user through channel equalization and linear polynomial approximation, and then sends the calculation result to the channel decoder to recover the original bit data.

[0011] As can be seen from the technical solutions provided by the above-mentioned application, the above-mentioned method jointly optimizes the symbol and bit stream allocation scheme of each user and the constellation design, and can realize efficient user access in a large-scale access scenario while meeting the constraint condition of the complexity of receiver signal processing. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0013] Figure 1 The flowchart of the simple receiving multiple access method based on symbol and bit stream joint allocation provided by the embodiment of the present application;

[0014] Figure 2 The structure diagram of the hierarchical quadrature amplitude modulation H-64QMA constellation described in the embodiment of the present application;

[0015] Figure 3 The signal processing flowchart of the transmitter of the example of the present application;

[0016] Figure 4 The user-beam and bit stream joint allocation diagram of the example of the present application. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments, which do not constitute a limitation on the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0018] The embodiments of the present application will be described in further detail below with reference to the drawings. The content not described in detail in the embodiments of the present application belongs to the prior art known to those skilled in the art. If the specific conditions are not specified in the embodiments of the present application, the conventional conditions or the conditions suggested by the manufacturer are adopted. If the reagents or instruments used in the embodiments of the present application are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0019] As Figure 1 shown is a simple receiving multiple access method flowchart based on symbol and bit stream joint allocation provided by the embodiments of the present application, the method comprises:

[0020] Step 1, the transmitter allocates symbol streams and bit streams of each user based on a hierarchical quadrature amplitude modulation (H-QAM) constellation diagram;

[0021] In this step, the transmitter first allocates each user to a certain beam according to the channel state information of each user. Considering that the number of users K is greater than the number of beams N when a large number of users access, the situation that multiple users are allocated to the same beam may occur. The symbol stream in each beam is selected from a hierarchical quadrature amplitude modulation (H-QAM) constellation diagram.

[0022] For example, it is assumed that the base station transmits N beams through beamforming technology, wherein each beam carries a symbol stream. After pre-coding, each symbol stream is transmitted by the base station through superposition coding, and after channel propagation, the received signal y k of the kth user can be represented as:

[0023]

[0024] wherein is the channel vector of the kth user; s n ,p n respectively represent the symbol stream carried in the nth beam and the pre-coding vector; w k represents the additive white Gaussian noise received by the user.

[0025] Based on the system model of formula (1), as Figure 2 shown is a structure diagram of a hierarchical quadrature amplitude modulation H-64QMA constellation diagram described in the embodiments of the present application. The constellation diagram has a dimension of M, and each symbol stream carries log2M bit streams, Figure 2 a H-QAM constellation diagram with a dimension of 64 is given. Each of the three bit streams carried on the I and Q branches carries three bit streams, and the Euclidean distance of each bit stream on the constellation diagram is adjustable, so as to eliminate the influence of the interference between users in the beam on the user rate.

[0026] In which, the users allocated to one beam completely occupy all the bit streams in the symbol stream, i.e. the data to be transmitted is directly mapped to the complete constellation point;

[0027] On the contrary, the users allocated to one beam are further allocated to a certain number of bit streams on the symbol stream, and each user maps the original data bit to the constellation according to the allocation result of its own bit stream together with other users in the beam.

[0028] Step 2, different interference management schemes are used for the interference between users in different beams and the interference between users in the same beam to suppress the influence of the inter-user interference on the system performance;

[0029] In this step, for each beam, the beam precoding vector is set to be a linear combination of the user channel vectors according to the service requirements of the users in the beam to improve the spectral efficiency of the system; on this basis, the transmitter realizes the mutual orthogonality between beams through specific precoding design, i.e. each user can only receive the symbol stream in the beam allocated to it, which is expressed as:

[0030]

[0031] In which represents the user set allocated to the nth beam; is the channel vector of the kth user; p n represents the precoding vector of the nth beam;

[0032] Specifically, the orthogonal projection matrix of the interference space of the nth beam is expressed as:

[0033]

[0034] In which H n and respectively represent the space linearly combined by the user channel of the nth beam and the channel of other users except the beam;

[0035] By projecting all the user channels in the nth beam to the null space of the interference space, a set of basis vectors B n of the effective space of the precoding vector of the nth beam is obtained, which is expressed as:

[0036]

[0037] β k represents the kth basis vector of the effective space of the precoding vector of the nth beam, and β k is Schmidt-orthogonalized to obtain the standard orthogonal basis, which is expressed as i.e. On this basis, the precoding vector direction of the beam is represented as a linear combination of the orthogonal basis , represented as:

[0038]

[0039] where v k represents the weight corresponding to the basis vector of the user;

[0040] When the base station perfectly knows the user channel information, the above precoding design can completely eliminate the inter-beam user interference;

[0041] At the same time, under the constraint condition of a simple receiver, the receiver does not use the serial interference cancellation technology SIC to eliminate the intra-beam user interference, but dynamically adjusts the Euclidean distance between the constellation points in each layer of each symbol stream according to the channel conditions of the users, that is, adjusts the power of each layer of user bit stream to eliminate the intra-beam user interference, so that each user can achieve almost the same rate performance as SIC with ordinary demodulation complexity;

[0042] In the actual system, the transmitter needs the current channel conditions of each user, jointly optimizes the symbol and bit stream allocation of each user and the intra-beam symbol stream constellation structure, and combines the specific precoding vector direction to achieve higher user rate.

[0043] Step 3, perform low-complexity signal processing on the signal received by each user receiver, and according to the bit stream allocation result of step 1, each user calculates the log-likelihood ratio of each bit stream allocated through channel equalization and linear polynomial approximation, and then sends the calculation result to the channel decoder to recover the original bit data.

[0044] In this step, after the orthogonal precoding processing of the transmitter, the signal received by each user receiver is represented as:

[0045]

[0046] where, is the channel vector of the kth user; and w k represent the precoding vector and the symbol stream carried by the nth beam allocated to the kth user, respectively;

[0047] Omit the subscript related to a specific user k in formula (6) to obtain a unified reception signal model for each user, represented as:

[0048] y = Hs + w (7)

[0049] Wherein, y, H, s, w respectively represent the received signal corresponding to each user, transmission channel gain, sending symbol and noise;

[0050] The signal received by each user receiver is processed by channel equalization, and the I and Q branch signal processing procedures of the constellation diagram are the same. Taking the I branch signal as an example, the processing procedure is represented as:

[0051]

[0052] Wherein represents the real part operation; the superscript i represents the I branch signal, which carries bit streams, and M is the constellation dimension; represents the component of the equalized noise on the I branch, and the power is For each bit stream on the I branch, the log-likelihood ratio is directly calculated, wherein the log-likelihood ratio of the κth bit stream is The calculation formula is:

[0053]

[0054] Wherein and respectively represent the sub-constellation point set corresponding to the bit taking 0 or 1; in the specific implementation, a polynomial linear mapping is further used to reduce the calculation complexity of each bit on this basis;

[0055] According to the above process, each user calculates the log-likelihood ratio of each bit stream allocated to each user according to the bit stream allocation result of step 1, and then sends the calculation result to the channel decoder to obtain the original bit data.

[0056] The method described in the embodiment of the application will be described in detail below with a specific example. In the example, a single base station 3-user downlink access scenario is considered, as shown in FIG. 1. Figure 3 The signal processing flow block diagram of the transmitter of the example of the application is shown in FIG. 2. The signals of each user are processed according to the flow of FIG. 2 and then transmitted, and each user only needs to recover the original bit data through a simple receiver signal processing flow. Specifically: Figure 3

[0057] Firstly, the transmitter allocates each user to multiple beams according to the channel conditions of the users. In the example, the users with strong channel spatial correlation are allocated to the same beam, and another user with strong channel orthogonality is allocated to another beam.

[0058] On this basis, the base station allocates bit streams to the users in each beam, as shown in FIG. 3. Figure 4 ​Fig. 1 shows a schematic diagram of user-beam and bit stream joint allocation according to an embodiment of the present application, where each dashed line represents a bit stream. Each symbol stream is sampled from the H-16QAM constellation to obtain a symbol, i.e. there are four bit streams in each symbol stream of each beam. For example, for the first beam with two users, each user is allocated two bit streams, and the user with smaller channel gain, i.e. the user farther from the base station, is allocated the two bit streams with higher protection level; while for the other beam with only one user, the user is allocated all the bit streams of the beam.

[0059] For a given user-symbol and bit stream joint allocation result, the constellation structure corresponding to each symbol stream and its precoding vector direction also need to be adjusted. The precoding vector of the beam serving only one user should be orthogonal to the channel vectors of the other two users, and the precoding vector of the other beam should be orthogonal to the channel vector of the single user. The actual precoding vector direction can be determined according to formula (3)-(5) with the current user allocation result. After determining the equivalent channel gains of each user according to the precoding vector, the transmitter further adjusts the Euclidean distance between each level of the H-QAM constellation corresponding to each symbol stream, so as to ensure that each user can achieve almost the same rate as SIC under the simple receiver constraint. The optimal Euclidean distance can be determined by calculating and comparing the mutual information rates that can be achieved under different Euclidean distances, and then selecting the optimal solution. Table 1 below shows the constellation parameters corresponding to the optimal operating point when the equivalent signal-to-noise ratios of the two users are (0, 6) dB:

[0060] Table 1: Constellation parameters corresponding to the optimal operating point

[0061]

[0062] where R1, R2 represent the mutual information rates of the two users respectively under the parameter configuration of this group; represent the number of bit streams allocated to each user respectively; d i ,d q represent the Euclidean distance parameter vectors corresponding to the I and Q paths of the constellation under the combination of the two users respectively.

[0063] It should be noted that the user-symbol and bit stream joint allocation result in the above embodiment is only one possible allocation scheme under this channel condition. The present application does not limit the specific allocation algorithm, but emphasizes the process of optimizing the user-symbol and bit stream joint allocation according to the specific scene and business requirements. Similarly, for different user business requirements, the distance vector of each layer bit stream on the constellation can be adjusted accordingly to maximize the user rate that can be achieved by the present application.

[0064] At the receiving end, each user first separates the received I and Q channels after channel equalization, calculates the log-likelihood ratio of the allocated bit stream according to the user-bit stream allocation result and formula (9), and then sends the calculation result to the channel decoder to recover the original bit data.

[0065] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0066] In summary, the method described in this embodiment of the invention can flexibly optimize the symbol and bitstream allocation scheme for each user and the symbol stream constellation diagram structure within each beam according to the actual channel conditions of each user, and makes special designs for the precoding vector direction. Compared with existing space division multiple access (SDMA) technologies, it can achieve higher user rates by allocating channel-correlated users to different bitstreams on the same symbol stream under the same receiver complexity; at the same time, it has a more flexible user-beam allocation method, thereby avoiding the degree of freedom loss of existing non-orthogonal multiple access technologies, and its receiver can achieve almost consistent user rates without complex SIC. Even compared with the more advanced rate division multiple access schemes, the method described in this embodiment of the invention effectively reduces the signal processing complexity of the receiver with tolerable rate loss, and has better practical prospects.

[0067] Furthermore, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware, and the corresponding program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk.

[0068] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A simple receiving multiple access method based on joint allocation of symbols and bit streams, characterized in that, The method comprises: Step 1, the transmitter allocates symbol streams and bit streams of each user based on a hierarchical quadrature amplitude modulation constellation diagram; Step 2, different interference management schemes are used to suppress the influence of inter-user interference on system performance, including inter-user interference in different beams and inter-user interference in the same beam; Step 3, low-complexity signal processing is performed on the signals received by the receiver of each user, and corresponding to the bit stream allocation result of step 1, each user calculates the log-likelihood ratio of each bit stream allocated to each user through channel equalization and linear polynomial approximation, and then sends the calculation result to a channel decoder to recover the original bit data.

2. The method of claim 1, wherein the method further comprises: In step 1, the transmitter first allocates each user to a certain beam according to the channel state information of each user, and the symbol stream in each beam is selected from a hierarchical quadrature amplitude modulation constellation diagram; Among them, the user allocated to a certain beam completely occupies all bit streams in the symbol stream, that is, the data to be sent is directly mapped to a complete constellation point; On the contrary, multiple users allocated to the same beam are further allocated to a certain number of bit streams on the symbol stream, and each user maps the original data bits to the constellation diagram together with other users in the beam according to the allocation result of the bit stream.

3. The method of claim 1, wherein the method further comprises: The process of step 2 is as follows: For each beam, the beam precoding vector is set to be a linear combination of the user channel vector to improve the spectral efficiency of the system; On this basis, the transmitter realizes the mutual orthogonality between beams through specific precoding design, that is, each user can only receive the symbol stream in the allocated beam, which is expressed as: wherein denotes a set of users allocated to the nth beam; is a channel vector for the kth user; p n denotes a precoding vector for the nth beam; Specifically, the orthogonal projection matrix of the nth beam interference space is expressed as: where H n and denote the space formed by linear combination of the nth beam user channel and other user channels except the beam as the base vectors, respectively; By projecting all user channels within the nth beam onto the null space of the interference space, a set of basis vectors B of the effective space of the nth beam precoding vector is obtained n is expressed as: β k denotes the k-th basis vector of the effective space of the n-th beam precoding vector, β k Schmidt orthogonalization yields an orthonormal basis, denoted as i.e. On this basis, the precoding vector direction of the beam is denoted as a linear combination of the orthonormal basis is denoted as where v k represents the weight corresponding to this basis vector. When the base station perfectly knows the user channel information, the above precoding design can completely eliminate the inter-user interference between beams; Meanwhile, according to the channel condition of the user, the Euclidean distance between the constellation points of each level in each symbol stream is dynamically adjusted, that is, the power of each user bit stream is adjusted to eliminate the inter-user interference in the beam.

4. The method of claim 1, wherein the method further comprises: In step 3, after the orthogonal precoding processing of the transmitter, the signal received by each user receiver is expressed as: wherein, is the channel vector for the kth user; respectively represent the precoding vector and the carried symbol stream of the nth beam to which the kth user is allocated; w k denotes the additive white Gaussian noise received by the user; By omitting the subscript related to a specific user k in formula (6), the unified receiving signal model of each user is obtained, which is expressed as: y = Hs + w (7) Where y, H, s, and w represent the receiving signal, transmission channel gain, sending symbol, and noise corresponding to each user, respectively; The channel equalization processing is performed on the signal received by the receiver of each user, and the I and Q branch signal processing procedures of the constellation diagram are the same. Taking the I branch signal as an example, the processing process is expressed as: wherein represents the real part operation; the superscript i represents the I channel signal, which carries bits, and M is the constellation dimension; represents the component of the equalized noise on the I channel, and the power of the component is For each bit stream on the I channel, the log likelihood ratio is directly calculated, wherein the log likelihood ratio of the κth bit stream is The calculation formula is: wherein with respectively represent the set of sub-constellation points corresponding to the bit taking 0 or 1. According to the above process, each user calculates the log-likelihood ratio of each bit stream allocated to each user according to the bit stream allocation result of step 1, and then sends the calculation result to a channel decoder to obtain the original bit data.

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