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

Abstract

The invention discloses a simple receiving multiple access method based on joint allocation of symbols and bit streams. The method comprises the following steps: firstly, allocating the symbol streams and the bit streams of all users by a transmitter based on a layered orthogonal 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, so that the influence of the inter-user interference on the system performance is suppressed; and performing channel equalization processing on signals received by each user receiver, calculating the log-likelihood ratio of each bit stream allocated to each user by each user according to a bit stream allocation result, and sending a calculation result to a channel decoder to obtain original bit data. According to the method, each user symbol and bit stream allocation scheme and constellation diagram design are jointly optimized, and efficient user access in a large-scale access scene can be realized under the condition of meeting the signal processing complexity constraint condition of a receiver.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communication multiple access, and in particular to a simple receiving multiple access method based on joint allocation of symbols and bit streams. Background Art

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

[0003] Due to the need for orthogonal division of time-frequency resource blocks, the number of users that can be served simultaneously by orthogonal multiple access schemes cannot be too high, which in turn limits the spectrum efficiency of the actual system. In contrast, non-orthogonal multiple access technology (NOMA) allows different user data to be transmitted on the same resource block in an overlapping manner to improve the spectrum efficiency, but at the cost of using complex successive interference cancellation technology (SIC) when performing data detection at the receiving end. Unlike space division multiple access technology, non-orthogonal multiple access benefits from the strong spatial correlation between user channels and the difference in channel gain. However, the high receiver complexity and error propagation problems caused by SIC and the loss of freedom in multi-antenna scenarios limit its deployment and application in actual systems. In addition, in recent years, a new method called Rate-Splitting Multiple Access (RSMA) has been proposed. It splits the original data of each user into public data and private data and sends them through different precoding vectors. It combines the respective 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 more complex SIC technology.

[0004] In summary, although there are many related works focusing on the problem of 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 constraints of simple receivers remains an unresolved problem. Summary of the invention

[0005] The purpose of the present invention is to provide a simple receiving multiple access method based on joint allocation of symbols and bit streams, which jointly optimizes the symbol and bit stream allocation scheme of each user and the constellation diagram design, and can achieve efficient user access in large-scale access scenarios while satisfying the constraints of receiver signal processing complexity.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A simplified 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 the hierarchical orthogonal amplitude modulation constellation diagram;

[0009] 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 interference between users on the system performance;

[0010] Step 3: Perform signal processing with low computational complexity on the signals received by each user's receiver. Corresponding to the bit stream allocation result of step 1, each user calculates the log-likelihood ratio of each allocated bit stream through channel equalization and linear polynomial approximation, and then sends the calculation result to the channel decoder to restore the original bit data.

[0011] It can be seen from the technical solution provided by the present invention that the above method jointly optimizes each user symbol and bit stream allocation scheme and constellation diagram design, which can meet the constraints of receiver signal processing complexity and achieve efficient user access in large-scale access scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0013] Figure 1 A schematic flow chart of a simplified receiving multiple access method based on joint allocation of symbols and bit streams provided in an embodiment of the present invention;

[0014] Figure 2 It is a schematic diagram of the structure of the hierarchical quadrature amplitude modulation H-64QMA constellation diagram according to an embodiment of the present invention;

[0015] Figure 3 This is a flow chart of signal processing of a transmitter according to an example of the present invention;

[0016] Figure 4 This is a schematic diagram of the joint allocation of user beams and bit streams in the example of the present invention. DETAILED DESCRIPTION

[0017] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The following will further describe the embodiments of the present invention in detail in conjunction with the accompanying drawings. The contents not described in detail in the embodiments of the present invention belong to the prior art known to professionals in the field. In the embodiments of the present invention, if specific conditions are not specified, they are carried out according to the conditions of normal conditions in the field or the manufacturer's recommendations. If the manufacturer is not specified in the reagents or instruments in the embodiments of the present invention, they are all conventional products that can be purchased commercially.

[0019] like Figure 1 FIG. 1 is a flow chart of a simplified receiving multiple access method based on joint allocation of symbols and bit streams provided by an embodiment of the present invention, wherein the method comprises:

[0020] Step 1: The transmitter allocates the symbol stream and bit stream of each user based on the Hierarchical Quadrature Amplitude Modulation (H-QAM) constellation diagram;

[0021] In this step, the transmitter first allocates each user to a 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 large-scale users access, multiple users may be allocated to the same beam. The symbol streams in each beam select constellation points from the Hierarchical QAM (H-QAM) constellation diagram.

[0022] For example, suppose that the base station sends out N beams through beamforming technology, where each beam carries a symbol stream. Each symbol stream is precoded and then sent out by the base station through superposition coding. After propagation through the channel, the received signal y of the kth user is k It can be expressed as:

[0023]

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

[0025] The system model based on formula (1) is as follows: Figure 2 FIG. 1 is a schematic diagram of the structure of the hierarchical quadrature amplitude modulation H-64QMA constellation diagram according to an embodiment of the present invention. The dimension of the constellation diagram is M, and each symbol stream carries log2M bit streams. Figure 2 An H-QAM constellation with a dimension of 64 is given. Its I and Q branches each carry 3 bit streams. The Euclidean distance of each bit stream on the constellation is adjustable to eliminate the impact of interference between users within the beam on the user rate.

[0026] Among them, the user that is individually assigned to a certain beam fully occupies all the bit streams in the symbol stream, that is, the data to be sent is directly mapped to the complete constellation points;

[0027] In contrast, multiple users assigned to the same beam are further assigned a certain number of bit streams on the symbol stream. Each user maps the original data bits to the constellation diagram together with other users in the beam based on the allocation result of its own bit stream.

[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 interference between users on the system performance;

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

[0030]

[0031] in represents the set of users assigned 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 nth beam interference space is expressed as:

[0033]

[0034] Among them, H n and They represent the space formed by linear combination of the user channel of the nth beam and other user channels outside the beam as basis vectors;

[0035] By projecting all user channels in 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 , expressed as:

[0036]

[0037] β k represents the kth basis vector of the effective space of the nth beam precoding vector, for β k Schmidt orthogonalization obtains the standard orthogonal basis, which is expressed as Right now On this basis, the precoding vector direction of the beam The orthogonal basis The linear combination of is expressed as:

[0038]

[0039] where v k Represents the weight corresponding to this basis vector;

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

[0041] At the same time, due to the constraints of a simple receiver, the receiver does not use the serial interference cancellation technology SIC to eliminate the interference between users in the beam. Instead, the Euclidean distance between the constellation points of each level in each symbol stream is dynamically adjusted according to the user's channel conditions. That is, the power of the user bit stream of each layer is adjusted to eliminate the interference between users in the beam, so that each user can achieve a rate performance that is almost the same as that of SIC with ordinary demodulation complexity;

[0042] In actual systems, the transmitter needs the current channel conditions of each user, jointly optimizes the symbol and bit stream allocation of each user and the constellation structure of the symbol stream in each beam, combined with a specific precoding vector direction to achieve a higher user rate.

[0043] Step 3: Perform signal processing with low computational complexity on the signals received by each user's receiver. Corresponding to the bit stream allocation result of step 1, each user calculates the log-likelihood ratio of each allocated bit stream through channel equalization and linear polynomial approximation, and then sends the calculation result to the channel decoder to restore the original bit data.

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

[0045]

[0046] in, is the channel vector of the kth user; They represent the precoding vector of the nth beam to which the kth user is assigned and the symbol stream it carries; w k represents the additive Gaussian white noise received by the user;

[0047] The subscripts related to the specific user k in formula (6) are omitted, and a unified receiving signal model for each user is obtained, which is represented as:

[0048] y=Hs+w (7)

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

[0050] Channel equalization is performed on the signals received by each user receiver. The processing flow of the I and Q branch signals of the constellation diagram is the same. Taking the I signal as an example, the processing process is expressed as follows:

[0051]

[0052] in Indicates the real part operation; the superscript i indicates the I-way signal, which carries bit streams, M is the dimension of the constellation diagram; It represents the component of the noise on the I path after equalization, and its power is For each bit stream on path I, the log-likelihood ratio is directly calculated, where the log-likelihood ratio of the κth bit stream is The calculation formula is:

[0053]

[0054] in and They represent the corresponding sub-constellation point sets when the bit takes 0 or 1 respectively; in the specific implementation, polynomial linear mapping is used on this basis to further reduce the computational complexity of each bit;

[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 present invention is described in detail below with a specific example. In this example, a downlink access scenario of 3 users in a single base station is considered. Figure 3 The signal processing flow chart of the transmitter according to the present invention is shown as follows. Figure 3 Each user's signal is processed and sent out through a simple receiver signal processing process. Each user can restore the original bit data through a simple receiver signal processing process. Specifically:

[0057] First, the transmitter allocates each user to multiple beams according to the user's channel status. In this example, users with strong channel spatial correlation are allocated to the same beam, while another user with strong channel orthogonality is allocated to another beam alone.

[0058] On this basis, the base station allocates bit streams to users in each beam, such as Figure 4The figure shows a schematic diagram of the joint allocation of user-beam and bit stream in the example of the present invention, in which each dotted line represents a bit stream. Each symbol stream is sampled from the H-16QAM constellation diagram to obtain a transmission symbol, that is, there are 4 bit streams on the symbol stream of each beam. For example, for the first beam to which two users are allocated, two bit streams can be allocated to each user, in which the user with a smaller channel gain, that is, the user farther from the base station, is allocated to two bit streams with a higher protection level; and since there is only one user in the other beam, the user is allocated to all the bit streams of the beam.

[0059] For a given user-symbol and bit stream joint allocation result, the constellation structure and precoding vector direction corresponding to each symbol stream need to be adjusted. The beam precoding vector that serves only one user should be orthogonal to the channel vectors of the other two users, while 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 by substituting formulas (3)-(5) into the current user allocation result. After determining the equivalent channel gain 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, thereby ensuring that each user can achieve a rate that is almost consistent with SIC under simple receiver constraints. The optimal Euclidean distance can be determined by calculating and comparing the mutual information rates that can be achieved under different Euclidean distances, thereby selecting the optimal solution. Table 1 below gives the constellation parameter settings corresponding to the optimal working point when the equivalent signal-to-noise ratio of the two users is (0,6) dB:

[0060] Table 1 Optimal operating point constellation point parameters

[0061]

[0062] Where R1 and R2 represent the mutual information rates of two users under this group of parameter configurations; Indicates the number of bit streams allocated to each of the two users; d i ,d q They respectively represent the Euclidean distance parameter vectors corresponding to the I-path and Q-path of the constellation diagram under the combination of the two users.

[0063] It should be noted that the user-symbol and bit stream joint allocation result in the above embodiment is only a possible allocation scheme for the channel condition. The present invention does not limit the specific allocation algorithm, but emphasizes the process of optimizing the joint allocation of user-symbol and bit stream according to specific scenarios and business requirements. Similarly, for different user business requirements, the distance vectors of the bit streams of each layer on the constellation diagram can be adjusted accordingly as needed to maximize the user rate achievable by the present invention.

[0064] At the receiving end, each user first separates the I and Q paths of the received signal after channel equalization, calculates the log-likelihood ratio of the bit stream assigned to it according to the user-bit stream allocation result and refers to formula (9), and further sends the calculation result to the channel decoder to restore 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 professional and technical personnel in the field.

[0066] In summary, the method described in the embodiment of the present invention can flexibly optimize the symbol and bit stream allocation scheme of each user and the symbol stream constellation structure in each beam according to the actual channel conditions of each user, and specially design the precoding vector direction. Compared with the existing space division multiple access technology, it can achieve a higher user rate by allocating users with strong channel correlation to different bit streams 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 loss of freedom of the existing non-orthogonal multiple access technology, and its receiving end can achieve almost the same user rate without complex SIC. Even compared with the current more advanced rate division multiple access scheme, the method described in the embodiment of the present invention effectively reduces the signal processing complexity of the receiver under a tolerable rate loss, and has a better practical prospect.

[0067] In addition, a person skilled in the art can understand that all or part of the steps in the above-mentioned embodiment method can be implemented by instructing related hardware through a program, and the corresponding program can be stored in a computer-readable storage medium. The above-mentioned storage medium can be a read-only memory, a disk or an optical disk, etc.

[0068] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A simplified receiving multiple access method based on joint allocation of symbols and bit streams, characterized in that: The method comprises: Step 1: The transmitter allocates the symbol stream and the bit stream of each user based on the hierarchical orthogonal amplitude modulation constellation diagram; 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 interference between users on the system performance; Step 3: Perform signal processing with low computational complexity on the signals received by each user's receiver. Corresponding to the bit stream allocation result of step 1, each user calculates the log-likelihood ratio of each allocated bit stream through channel equalization and linear polynomial approximation, and then sends the calculation result to the channel decoder to restore the original bit data.

2. The simplified receiving multiple access method based on joint allocation of symbols and bit streams according to claim 1, characterized in that: In step 1, the transmitter first allocates each user to a beam according to the channel state information of each user, and the symbol streams in each beam are all selected from the constellation points of the hierarchical orthogonal amplitude modulation constellation diagram; Among them, the user that is individually assigned to a certain beam fully occupies all the bit streams in the symbol stream, that is, the data to be sent is directly mapped to the complete constellation points; In contrast, multiple users assigned to the same beam are further assigned a certain number of bit streams on the symbol stream. Each user maps the original data bits to the constellation diagram together with other users in the beam based on the allocation result of its own bit stream.

3. The simplified receiving multiple access method based on joint allocation of symbols and bit streams according to claim 1, characterized in that: The process of step 2 is specifically as follows: For each beam, the beam precoding vector is set to a linear combination of the user channel vectors according to the service requirements of each user in the beam to improve the system spectral efficiency; On this basis, the transmitter realizes mutual orthogonality between beams through specific precoding design, that is, each user can only receive the symbol stream in the assigned beam, which is expressed as: in represents the set of users assigned to the nth beam; is the channel vector of the kth user; p n represents the precoding vector of the nth beam; Specifically, the orthogonal projection matrix of the nth beam interference space is expressed as: Among them, H n and They represent the space formed by linear combination of the user channel of the nth beam and other user channels outside the beam as basis vectors; By projecting all user channels in 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 , expressed as: β k represents the kth basis vector of the effective space of the nth beam precoding vector, for β k Schmidt orthogonalization obtains the standard orthogonal basis, which is expressed as Right now On this basis, the precoding vector direction of the beam The orthogonal basis The linear combination of is expressed as: where v k Represents the weight corresponding to this basis vector; When the base station knows the user channel information perfectly, the above precoding design can completely eliminate the inter-beam user interference; At the same time, the Euclidean distance between the constellation points of each level in each symbol stream is dynamically adjusted according to the user's channel status, that is, the power of the user bit stream of each layer is adjusted to eliminate interference between users in the beam.

4. The simplified receiving multiple access method based on joint allocation of symbols and bit streams according to claim 1, characterized in that: In step 3, after the orthogonal precoding process of the transmitter, the signal received by each user receiver is expressed as: in, is the channel vector of the kth user; They represent the precoding vector of the nth beam to which the kth user is assigned and the symbol stream it carries; w k represents the additive Gaussian white noise received by the user; The subscripts related to the specific user k in formula (6) are omitted, and a unified receiving signal model for each user is obtained, which is represented as: y=Hs+w (7) Where y, H, s, and w represent the received signal, transmission channel gain, transmitted symbol, and noise corresponding to each user, respectively; Channel equalization is performed on the signals received by each user receiver. The processing flow of the I and Q branch signals of the constellation diagram is the same. Taking the I signal as an example, the processing process is expressed as follows: in Indicates the real part operation; the superscript i indicates the I-way signal, which carries bit streams, M is the dimension of the constellation diagram; It represents the component of the noise on the I path after equalization, and its power is For each bit stream on path I, the log-likelihood ratio is directly calculated, where the log-likelihood ratio of the κth bit stream is The calculation formula is: in and Respectively represent the corresponding sub-constellation point set when the bit takes 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 the channel decoder to obtain the original bit data.

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