CN111371540B - Large-scale MIMO system pilot frequency distribution method based on user grouping - Google Patents
Large-scale MIMO system pilot frequency distribution method based on user grouping Download PDFInfo
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Abstract
The invention relates to a pilot frequency distribution method of a large-scale MIMO system based on user grouping, which is characterized by comprising the following steps: the method comprises the steps that a primary grouping strategy based on user intensity, a secondary grouping strategy based on inter-user interference and a pilot frequency distribution strategy among multiple cells are adopted, and users in the cells are divided into a central user group and an edge user group through twice screening according to the self anti-interference capacity of the users and the interference strength of the users respectively; for a pilot frequency distribution strategy among multiple cells, the pilot frequency distribution strategy among the multiple cells is provided, a pilot frequency sequence set is generated according to the number of center users and the number of edge users after grouping is completed, a group of pilot frequency sequences are multiplexed by a center user group, and the pilot frequency sequences which are mutually orthogonal are distributed by an edge user group, so that mutual interference among users distributed with the same pilot frequency sequence is reduced, pilot frequency pollution in a large-scale MIMO system is inhibited, and system performance is improved. Has the advantages of scientific and reasonable structure, high performance, high accuracy and the like.
Description
Technical Field
The invention belongs to the technical field of mobile communication, and relates to a large-scale MIMO system pilot frequency distribution method based on user grouping.
Background
In a large-scale multiple-input multiple-output (MIMO) system, a large-scale antenna array is configured on a base station side, the same time-frequency resources are utilized to provide communication services for multiple users, and each user can select to access multiple antenna units, so that the connection density of the users can be increased, and the energy efficiency and the system capacity can be improved. The same time-frequency resource is utilized to provide communication service for multiple users, each user can select to access multiple antenna units, the signal power can be obviously reduced, the spectrum efficiency of the system can be improved by multiple times, and a supporting effect is achieved for guaranteeing the low power consumption and high capacity of a fifth generation mobile communication technology (5G) system. Therefore, massive MIMO technology becomes one of the key technologies to be applied to 5G communication.
In a large-scale MIMO system, users in each cell are required to periodically transmit a pilot sequence to a base station, a base station performs channel estimation according to the received pilot sequence to obtain Channel State Information (CSI), and then performs uplink signal detection and downlink precoding according to the channel estimation. However, in a complex and variable wireless propagation environment, the coherence time of a channel is very short, the time for pilot training cannot be too long, the length and the number of pilot sequences are severely limited, the same pilot sequence has to be multiplexed by a plurality of users, and a base station cannot effectively distinguish the users using the same pilot sequence, so that errors occur in estimated CSI, and signal detection and precoding performed by using CSI are also correspondingly affected, thereby causing a pilot pollution problem. In a large-scale MIMO system, as the number of base station antennas increases, incoherent interference such as noise can be gradually eliminated, and pilot pollution becomes a bottleneck limiting the performance of the large-scale MIMO system.
In a conventional massive MIMO system, a pilot allocation method is usually adopted to randomly allocate mutually orthogonal pilot sequences to users in a cell, and the remaining cells reuse the set of pilot sequences, but the allocation method causes mutual interference between users allocated with the same pilot; some proposals propose to increase the number of the orthogonal pilot frequency sequence, distribute many sets of orthogonal pilot frequency sequences among different cells to reduce the interference among users, but this pilot frequency distribution mode will cause the pilot frequency overhead to be too big, take up the frequency band resource of the system; the method also provides a scheme for distributing partial pilot frequency multiplexing, users in a cell are divided into two groups of central users and edge users according to the distance from a base station, because the distance between the edge users in the cell is short, the mutual influence is large, the distance between the central users is relatively long, and the relative influence is small, pilot frequency sequences with mutually orthogonal pilot frequency vectors are distributed to all the edge users in all the cells, and the multiplexed pilot frequency sequences are distributed among the central users in each cell.
Disclosure of Invention
The invention aims to provide a scientific, reasonable, high-performance and high-accuracy large-scale MIMO system pilot frequency distribution method based on user grouping, which can inhibit the problem of large-scale MIMO system pilot frequency pollution, aiming at the problems of unreasonable pilot frequency distribution of the large-scale MIMO system and unreasonable user division in a cell.
The purpose of the invention is realized by the following technical scheme: a pilot frequency distribution method of a large-scale MIMO system based on user grouping is characterized in that the method comprises the following steps: a primary grouping strategy based on user intensity, a secondary grouping strategy based on interference among users and a pilot frequency distribution strategy among multiple cells:
1) a primary grouping strategy based on user intensity;
respectively acquiring large-scale fading coefficients from users in each cell to a base station in the cell within a set time interval, designing a primary grouping threshold according to the large-scale fading coefficients of the users, and for an arbitrarily selected target cell, selecting a primary grouping threshold rho1The calculation formula is as follows:
where K is the total number of users in a cell, dkIs the distance from the user k to the base station in the target cell, R is the radius of the target cell, beta0kIs a large-scale fading coefficient, beta, from a user k to a base station in a target cell0k 2For the gain from the user to the base station of the target cell, representing the user strength of the user, each cell calculates a primary grouping threshold according to the formula (1), and then the user strength of each user in the cell is compared with the primary grouping threshold rho1Make a comparison if beta0k 2≥ρ1Then the user is assigned to a central group of users, if beta0k 2＜ρ1Then the user is primarily distributed to the edge user group;
2) a secondary grouping strategy based on inter-user interference;
after the primary grouping is finished, obtaining the large-scale fading coefficient from users distributed with the same pilot frequency sequence in N adjacent cells of the target cell to the base station of the target cell again, then designing a secondary grouping threshold according to the obtained large-scale fading coefficient, and for the arbitrarily selected target cell, obtaining the secondary grouping threshold rho2The calculation formula is as follows:
wherein, δ is a secondary grouping parameter, dynamic division of cell edge users and central users can be realized by adjusting δ values, and finally, an optimal parameter is selected according to system performance, and k, β for any user in a target celljk 2The large-scale fading coefficient from the user k to the base station in the target cell, which allocates the same pilot sequence to the user k in the adjacent cell j of the cell, the users will cause interference to the users in the target cell,
representing all the inter-user interference suffered by the user, and then carrying out the inter-user interference of each user in the target cell and the secondary grouping threshold rho2Make a comparison if
The user is assigned to a central group of users, if
The user still remains in the edge user group, and when all users in the target cell are grouped, a new cell is selected as the target cell until all cells are grouped;
3) pilot frequency distribution strategy among multiple cells;
after the central user group and the edge user group in all the cells are completely distributed, counting the number of the central users and the number of the edge users which are divided in all the L cells, wherein the number of the central users is expressed as { K }m1,Km2,...,KmLDenoted as K, edge users1,Ks2,...,KsLGet the maximum central user number Km0And the number of edge users Ks0Alpha (3-7) adjacent cells are grouped into a cluster, and the maximum central user number K is obtainedm0And the maximum number of edge users Ks0Generating a pilot sequence collection
Within each cluster, a set of secondary pilots is collected for the central user group of each cell
In the method, orthogonal pilot frequency sequences are randomly selected for distribution, and pilot frequency sets are respectively selected from a pilot frequency set for alpha edge user groups
And selecting orthogonal pilot frequency sequence for distribution.
The invention discloses a large-scale MIMO system pilot frequency distribution method based on user grouping, which comprises the following steps: the method comprises the steps that a primary grouping strategy based on user intensity, a secondary grouping strategy based on inter-user interference and a pilot frequency distribution strategy among multiple cells are adopted, and users in the cells are divided into a central user group and an edge user group through twice screening according to the self anti-interference capacity of the users and the interference strength of the users respectively; for a pilot frequency distribution strategy among multiple cells, the pilot frequency distribution strategy among the multiple cells is provided, a pilot frequency sequence set is generated according to the number of center users and the number of edge users after grouping is completed, a group of pilot frequency sequences are multiplexed by a center user group, and the pilot frequency sequences which are mutually orthogonal are distributed by an edge user group, so that mutual interference among users distributed with the same pilot frequency sequence is reduced, pilot frequency pollution in a large-scale MIMO system is inhibited, and system performance is improved. Has the advantages of scientific and reasonable structure, high performance, high accuracy and the like.
Drawings
Fig. 1 is a flowchart of a pilot allocation method for a massive MIMO system based on user grouping according to the present invention.
Detailed Description
The invention is further illustrated by the following figures and detailed description.
Referring to fig. 1, the pilot allocation method for a large-scale MIMO system based on user grouping of the present invention mainly includes three parts: a primary grouping strategy based on user intensity, a secondary grouping strategy based on interference among users and a pilot frequency distribution strategy among multiple cells:
firstly, grouping once, respectively acquiring large-scale fading coefficients from users in each cell to a base station in the cell within a set time interval, then designing a primary grouping threshold according to the large-scale fading coefficients of the users, and for an arbitrarily selected target cell, performing primary grouping on a threshold rho1The calculation formula is as follows:
where K is the total number of users in a cell, dkFor the target intra-cell userk distance to the base station, R is the radius of the target cell, beta0kIs a large-scale fading coefficient, beta, from a user k to a base station in a target cell0k 2For the gain from the user to the base station of the target cell, representing the user intensity of the user, each cell calculates the primary grouping threshold value according to the formula (1), and then the user intensity of each user in the cell and the primary grouping threshold value rho are compared1Make a comparison if beta0k 2≥ρ1Then the user is assigned to a central group of users, if beta0k 2＜ρ1Then the user is primarily distributed to the edge user group;
then, carrying out secondary grouping, after primary grouping is finished, obtaining the large-scale fading coefficient from users distributed with the same pilot frequency sequence in N adjacent cells of the target cell to the base station of the target cell again, then designing a secondary grouping threshold according to the obtained large-scale fading coefficient, and for the arbitrarily selected target cell, carrying out secondary grouping on the threshold rho2The calculation formula is as follows:
wherein, δ is a secondary grouping parameter, dynamic division of cell edge users and central users can be realized by adjusting δ values, and finally, an optimal parameter is selected according to system performance, and k, β for any user in a target celljk 2The large-scale fading coefficients from the base station in the target cell to the users in the neighboring cell j of the cell, which are allocated with the same pilot frequency sequence as the user k, will cause interference to the users in the target cell,
representing all the inter-user interference suffered by the user, and then carrying out the inter-user interference of each user in the target cell and the secondary grouping threshold rho2Make a comparison if
The user is assigned to a central group of users, if so
The user still remains in the edge user group, and when all users in the target cell are grouped, a new cell is selected as the target cell until all cells are grouped;
and finally, generating and distributing a pilot frequency sequence, counting the number of the center users and the number of the edge users which are divided in all L cells after the center user groups and the edge user groups in all the cells are completely distributed, wherein the number of the center users is expressed as { K }m1,Km2,...,KmLDenoted as K, edge users1,Ks2,...,KsLGet the maximum central user number and the maximum edge user number respectively, and define them as Km0And Ks0Forming a cluster by alpha (alpha is more than or equal to 3 and less than or equal to 7) adjacent cells, and calculating the maximum central user number Km0And the maximum number of edge users Ks0Generating a pilot sequence collection
Within each cluster, a set of secondary pilots is collected for the central user group of each cell
The orthogonal pilot frequency sequence is randomly selected for distribution, and is respectively selected from pilot frequency collection sets for alpha edge user groups
And selecting orthogonal pilot frequency sequence for distribution.
The software routines involved in the present invention are organized according to automation, networking, and computer processing techniques, and are well known to those skilled in the art.
Claims (1)
1. A pilot frequency distribution method of a large-scale MIMO system based on user grouping is characterized in that the method comprises the following steps: a primary grouping strategy based on user intensity, a secondary grouping strategy based on interference among users and a pilot frequency distribution strategy among multiple cells:
1) a primary grouping strategy based on user intensity;
respectively acquiring large-scale fading coefficients from users in each cell to a base station in the cell within a set time interval, designing a primary grouping threshold according to the large-scale fading coefficients of the users, and for an arbitrarily selected target cell, selecting a primary grouping threshold rho1The calculation formula is as follows:
where K is the total number of users in a cell, dkIs the distance from the user k to the base station in the target cell, R is the radius of the target cell, beta0kIs a large-scale fading coefficient, beta, from a user k to a base station in a target cell0k 2For the gain from the user to the base station of the target cell, representing the user intensity of the user, each cell calculates the primary grouping threshold value according to the formula (1), and then the user intensity of each user in the cell and the primary grouping threshold value rho are compared1Make a comparison if beta0k 2≥ρ1Then the user is assigned to a central group of users, if beta0k 2＜ρ1Then the user is primarily distributed to the edge user group;
2) a secondary grouping strategy based on inter-user interference;
after the primary grouping is finished, obtaining the large-scale fading coefficient from users distributed with the same pilot frequency sequence in N adjacent cells of the target cell to the base station of the target cell again, then designing a secondary grouping threshold according to the obtained large-scale fading coefficient, and for the arbitrarily selected target cell, obtaining the secondary grouping threshold rho2The calculation formula is as follows:
wherein, the delta is a secondary grouping parameter, and the value of the delta can be adjusted to realize the control of cell edge users and central usersDynamic division, finally selecting optimal parameters according to system performance, and for any user k, beta in the target celljk 2The large-scale fading coefficient from the user k to the base station in the target cell, which allocates the same pilot sequence to the user k in the adjacent cell j of the cell, the users will cause interference to the users in the target cell,
representing all the inter-user interference suffered by the user, and then carrying out the inter-user interference of each user in the target cell and the secondary grouping threshold rho2Make a comparison if
The user is assigned to a central group of users, if so
The user still remains in the edge user group, and when all users in the target cell are grouped, a new cell is selected as the target cell until all cells are grouped;
3) pilot frequency distribution strategy among multiple cells;
after the central user group and the edge user group in all the cells are completely distributed, counting the number of the central users and the number of the edge users which are divided in all the L cells, wherein the number of the central users is expressed as { K }m1,Km2,...,KmLDenoted as K, edge users1,Ks2,...,KsLGet the maximum central user number Km0And the number of edge users Ks0Forming a cluster by alpha (alpha is more than or equal to 3 and less than or equal to 7) adjacent cells, and calculating the maximum central user number Km0And the maximum number of edge users Ks0Generating a pilot sequence collection
Within each cluster, a set of secondary pilots is collected for the central user group of each cell
In the method, orthogonal pilot frequency sequences are randomly selected for distribution, and pilot frequency sets are respectively selected from a pilot frequency set for alpha edge user groups
And selecting orthogonal pilot frequency sequence for distribution.
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