CN105049098A - Partial pilot frequency multiplexing method for overcoming pilot pollution in large-scale MIMO system - Google Patents

Abstract

The invention discloses a partial pilot frequency multiplexing method for overcoming pilot pollution in a large-scale MIMO system. The method includes following steps: (1) in the training stage, users determine the size of the interference according to received signals and transmit the information to a base station; (2) the base station determines a signal to interference and signal ratio threshold according to different numbers of the users in a cell and divides the users into strong interference users (edge users) and weak interference users (central users) according to the information uploaded by the users; and (3) the same set of pilot frequency is distributed to the weak interference users (central users) of different cells, and different pilot frequencies are distributed to strong interference users (edge users) of adjacent cells. According to the method, the same set of pilot frequency is multiplexed by central users of different cells so that the same pilot frequency is multiplexed by them and the utilization rate of the pilot frequency is increased; the edge users of the adjacent cells employ different pilot frequencies so that interferences are reduced; and in this way, the influence of pilot pollution is reduced, and the utilization rate of the pilot frequency is increased.

Description

The portion of pilot multiplexing method of pilot pollution is overcome in extensive mimo system

[technical field]

The invention belongs to communication technical field, relate to a kind of portion of pilot multiplexing method overcoming pilot pollution in extensive mimo system.

[background technology]

In today that available spectrum resources is day by day deficient, opening up new spatial domain resource has become one of effective means promoting system capacity and performance.Therefore, how to utilize spatial domain resource to meet the focus that growing communication requirement is all wireless communication technology field research all the time more fully.

In recent years, along with the progress of electronic device and system integration technology, use large-scale aerial array to become possibility completely in base station end, correspondingly extensive MIMO technology is also just met the tendency life.Existing research shows: when the antenna number of base station end configuration is tending towards infinite, receive channel vector corresponding to each user will be tending towards orthogonal, beam-forming technology so just can be utilized to reduce presence of intercell interference, and improve the availability of frequency spectrum and the energy efficiency of system significantly.Due to these significant advantages, extensive MIMO technology has been subject to the extensive concern of industry and academia, and is seen as one of key technology realizing the green wide-band mobile communication system of following high energy efficiency.

Although extensive MIMO technology illustrates a very fine application prospect with its significant performance advantage to everybody, but these performance advantages above-mentioned can must obtain, because the channel information of each user to base station must be known in base station when doing Wave beam forming or input under the known prerequisite of all channel informations.If base station is when doing Channel Detection, the different pilot tone of user's use of neighbor cell, so, base station will be the combined channel of these users by what detect, thus send signal together can to when downlink these users, cause pilot pollution.

[summary of the invention]

The object of the present invention is to provide a kind of portion of pilot multiplexing method overcoming pilot pollution in extensive mimo system, by distributing different pilot tones to interference user to reduce the impact of pilot pollution.

For achieving the above object, the present invention by the following technical solutions:

In extensive mimo system, overcome a portion of pilot multiplexing method for pilot pollution, comprise the following steps:

(1), the training stage: user judges the size self be disturbed according to the signal received, and these information are passed to base station;

(2), base station according to the difference of intra-cell users number, determine a Signal to Interference plus Noise Ratio thresholding, and according to the information that user uploads, user be divided into edge customer and central user;

(3), to the central user of different districts distribute same set of pilot tone, the edge customer of neighbor cell distributes different pilot tones.

The concrete steps of described step (2) are:

After the base station of this community receives the information of reporting of user, according to the quantity information determination Signal to Interference plus Noise Ratio thresholding of user; And according to Signal to Interference plus Noise Ratio, user is divided into interference user and weak jamming user; The signal interference ratio of user is expressed as:

$SIR=\frac{{r_i}^{-2\mathrm{\α}}(2\mathrm{\α}-2)}{2{\mathrm{\π\ρ}}_{BS}{(2R_C-r_i)}^{2-2\mathrm{\α}}}$

Wherein, 2R _c-r _irepresent the distance of user from nearest base station, interfered cell, r _ifor the distance of this cell base station of user distance, for central user, R _c=R is radius of society, for edge customer, ρ _bSrepresent cell density; For central user: ρ _bS=π R ², for edge customer: α is path-loss factor; The signal interference ratio of user is converted to this cell base station of user distance distance r _ifunction, by a distance threshold R _thuser is divided into central user and edge customer:

M _c＝{i:r _i≤R _th},M _e＝{i:r _i>R _th}

Wherein, i represents user's sequence number, M _cand M _erepresent the set of central user and edge customer respectively;

The average size calculating Cell Center User and edge customer is respectively:

$C_C=\frac{2\mathrm{\Δ}f}{R_{th}^2-R_0^2}{\∫}_{R_0}^{R_{th}}{r}_i\[{\log }_2(1+{\mathrm{SIR}}_C)\]{\mathrm{dr}}_i$

$C_E=\frac{2\mathrm{\Δ}f}{R^2-R_{th}^2}{\∫}_{R_{th}}^{R_0}{r}_i\[{\log }_2(1+{\mathrm{SIR}}_E)\]{\mathrm{dr}}_i$

Δ f represents the bandwidth of system, R ₀represent the minimum range of user distance base station, SIR _cand SIR _erepresent signal interference ratio when user-center user and edge customer respectively;

Pilot tone is distributed according to the area at center of housing estate and edge, and central guiding frequency and edge pilot number are respectively:

$N_E=\[\frac{R^2-R_{th}^2}{3R^2-2R_{th}^2-R_0^2}N\]$

N _C＝N-3N _E

Wherein [x] expression rounds under x; N is total number of pilots;

The total capacity c of community is finally expressed as:

$\begin{array}{c}C=\underset{k=1}{\overset{N_C}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^k{(R^2-R_{th}^2)}^{M-k}}{{(R^2-R_0^2)}^M}{\mathrm{kC}}_C+\underset{k=N_C}{\overset{M}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^k{(R^2-R_{th}^2)}^{M-k}}{{(R^2-R_0^2)}^M}{N}_C{C}_C\\ +\underset{k=1}{\overset{N_E}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^{M-k}{(R^2-R_{th}^2)}^k}{{(R^2-R_0^2)}^M}{\mathrm{kC}}_E+\underset{k=N_E}{\overset{M}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^{M-k}{(R^2-R_{th}^2)}^k}{{(R^2-R_0^2)}^M}{N}_E{C}_E\end{array}$

Wherein, M is the total number of users in community; $\left(\begin{array}{c}M\\ k\end{array}\right)$ Represent the possibility selecting k element from M element;

By obtaining best division thresholding R to community total capacity maximizing _th.

The concrete steps of described step (3) are:

By the optimum thresholding R calculated _th, user is divided into central user and edge customer, distributes same set of pilot tone to the central user of different districts, the edge customer of neighbor cell distributes different pilot tones.

The present invention is in extensive mimo system, and in neighbor cell, different user uses identical pilot tone can cause mutual interference.In order to alleviate this interference, cell base station distributes different pilot tones to the user of diverse location, makes the interference user of neighbor cell use different pilot tones to reduce interference.

Relative to prior art, the present invention has following beneficial effect:

The present invention is directed to the pilot pollution problem existed in extensive mimo system, propose a kind of pilot resource distribution method adopting portion of pilot multiplex technique, to reduce pilot pollution, improve systematic function; User is divided into central user and edge customer according to the position of user by the inventive method; For disturbing more weak central user each other, the multiplexing same set of pilot tone of central user of different districts, can allow their multiplexing same pilot tone to improve the utilance of pilot tone; For disturbing stronger edge customer each other, the edge customer of neighbor cell uses different pilot tones to reduce interference; Thus reduce the impact of pilot pollution and improve the utilance of pilot tone.Using the cell optimum thresholding obtained by computer sim-ulation to divide user can the capacity of maximized raising system.

[accompanying drawing explanation]

Fig. 1 is the Scene case figure that the inventive method is applied;

Fig. 2 gives functional realiey module frame chart;

Fig. 3 gives the network structure of community;

Fig. 4 is the graph of a relation between system divides thresholding and community total capacity obtained by Computer Simulation;

Fig. 5 gives and is 50 at pilot number, the cumulative distribution function curve of cell capacity under Different Strategies when number of users is 36.

[embodiment]

Below in conjunction with accompanying drawing, the present invention is described in further detail:

In extensive MIMO communication system, because total number of pilots is limited, all distribute different orthogonal guide frequencies, so the problem of pilot pollution exists all the time cannot to all users.In order to reduce pilot pollution, the present invention is disturbed stronger user to distribute different pilot tones each other, user's then multiplexing same pilot that interference is more weak mutually.When dividing user, need setting signal interference ratio thresholding, and be divided into central user and edge customer according to the signal interference ratio of user self, wherein the multiplexing same pilot of the central user of different districts, the edge customer of neighbor cell uses different pilot tones, as shown in Figure 1.

By this pilot frequency distribution mode, we can see, the central user of different districts is apart from each other, use identical pilot tone allow and produce strong jamming each other, and at a distance of comparatively near between the edge customer of neighbor cell, the impact of pilot pollution effectively can be reduced by distributing different pilot tones to them.

A kind of portion of pilot multiplexing method overcoming pilot pollution in extensive mimo system of the present invention, comprises the following steps:

(1), the training stage, user judges the size self be disturbed according to the signal received, and these information are passed to base station;

(2), base station according to the difference of intra-cell users number, determine a Signal to Interference plus Noise Ratio thresholding, and according to the information that user uploads, user be divided into interference user (edge customer) and weak jamming user (central user);

(3), to the weak jamming user (central user) of different districts distribute same set of pilot tone, neighbor cell interference user (edge customer) distributes different pilot tones.As shown in Figure 2.

The concrete steps of step (2) are: after the base station of this community receives the information of reporting of user, according to the quantity information determination Signal to Interference plus Noise Ratio thresholding of user.And according to the Signal to Interference plus Noise Ratio of thresholding and user, user is divided into interference user (edge customer) and weak jamming user (central user).Suppose that the number of antennas of base station is tending towards infinite many, so the signal interference ratio of user can be expressed as:

$SIR=\frac{{r_i}^{-2\mathrm{\α}}(2\mathrm{\α}-2)}{2{\mathrm{\π\ρ}}_{BS}{(2R_C/r_i)}^{2-2\mathrm{\α}}}$

Wherein, 2R _c-r _irepresent the distance of user from nearest base station, interfered cell, r _ifor the distance of this cell base station of user distance, for central user, R _c=R is radius of society, for edge customer, ρ _bSrepresent cell density, for central user: ρ _bS=π R ², for edge customer: α is path-loss factor.The signal interference ratio of user can be converted to this cell base station of user distance distance r by a series of being similar to _ifunction, therefore can pass through a distance threshold R _thuser is divided into central user and edge customer:

M _c＝{i:r _i≤R _th}，M _e＝{i:r _i>R _th}

M _cand M _erepresent the set of central user and edge customer respectively, i represents user's sequence number.

The average size that can calculate Cell Center User and edge customer is respectively:

$C_C=\frac{2\mathrm{\Δ}f}{R_{th}^2-R_0^2}{\∫}_{R_0}^{R_{th}}{r}_i\[{\log }_2(1+{\mathrm{SIR}}_C)\]{\mathrm{dr}}_i$

$C_E=\frac{2\mathrm{\Δ}f}{R^2-R_{th}^2}{\∫}_{R_{th}}^{R_0}{r}_i\[{\log }_2(1+{\mathrm{SIR}}_E)\]{\mathrm{dr}}_i$

Δ f represents the bandwidth of system, R ₀represent the minimum range of user distance base station, SIR _cand SIR _erepresent signal interference ratio when user-center user and edge customer respectively.

Suppose that total number of pilots is N, user is uniformly distributed in community, and pilot tone is also distributed according to the area at center of housing estate and edge, and so central guiding frequency and edge pilot number are respectively:

$N_E=\[\frac{R^2-R_{th}^2}{3R^2-2R_{th}^2-R_0^2}N\]$

N _C＝N-3N _E

Wherein [x] expression rounds under x.

Therefore, suppose that the total number of users in community is M, so the total capacity of community finally can be expressed as:

$\begin{array}{c}C=\underset{k=1}{\overset{N_C}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^k{(R^2-R_{th}^2)}^{M-k}}{{(R^2-R_0^2)}^M}{\mathrm{kC}}_C+\underset{k=N_C}{\overset{M}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^k{(R^2-R_{th}^2)}^{M-k}}{{(R^2-R_0^2)}^M}{N}_C{C}_C\\ +\underset{k=1}{\overset{N_E}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^{M-k}{(R^2-R_{th}^2)}^k}{{(R^2-R_0^2)}^M}{\mathrm{kC}}_E+\underset{k=N_E}{\overset{M}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^{M-k}{(R^2-R_{th}^2)}^k}{{(R^2-R_0^2)}^M}{N}_E{C}_E\end{array}$

Wherein represent the possibility selecting k element from M element.

By can obtain best division thresholding R to community total capacity maximizing _th.

User in community is divided into central user and edge customer according to optimum thresholding by step (3).Refer to shown in Fig. 3, for No. 0 community, central user uses P ₀representative pilot set, edge customer uses P ₁representative pilot set.Other community uses identical strategy, all multiplexing P of central user of all communities ₀representative pilot set, the edge customer of neighbor cell uses different pilot tones, and wherein 0,8,10,12,14,16, No. 18 communities use P ₁representative pilot set, 2,4,6,7,11, No. 15 communities use P ₂representative pilot set, other community uses P ₃representative pilot set.Because the central user of different districts is apart from each other, so distribute identical a set of pilot tone to them can't cause too large interference; And at a distance of comparatively near between the edge customer of neighbor cell, therefore distribute different pilot tones to them and effectively can reduce interference between them.

Fig. 4 gives the relation between system divides thresholding and community total capacity by Computer Simulation, provides according to the difference of number of users the capacity that different optimum thresholdings can maximize system.

Fig. 5 gives and is 50 at pilot number, and under Different Strategies when number of users is 36, the cumulative distribution function curve of cell capacity, can find out, adopts the overall performance of portion of pilot multiplex technique energy elevator system.

Claims (3)

1. overcome the portion of pilot multiplexing method of pilot pollution in extensive mimo system, it is characterized in that, comprise the following steps:

(1), the training stage: user judges the size self be disturbed according to the signal received, and these information are passed to base station;

(2), base station according to the difference of intra-cell users number, determine a Signal to Interference plus Noise Ratio thresholding, and according to the information that user uploads, user be divided into edge customer and central user;

(3), to the central user of different districts distribute same set of pilot tone, the edge customer of neighbor cell distributes different pilot tones.

2. a kind of portion of pilot multiplexing method overcoming pilot pollution in extensive mimo system as claimed in claim 1, it is characterized in that, the concrete steps of described step (2) are:

After the base station of this community receives the information of reporting of user, according to the quantity information determination Signal to Interference plus Noise Ratio thresholding of user; And according to Signal to Interference plus Noise Ratio, user is divided into interference user and weak jamming user; The signal interference ratio of user is expressed as:

$SIR=\frac{{r_i}^{-2\mathrm{\α}}(2\mathrm{\α}-2)}{2{\mathrm{\π\ρ}}_{BS}{(2R_C/r_i)}^{2-2\mathrm{\α}}}$

Wherein, 2R _c-r _irepresent the distance of user from nearest base station, interfered cell, r _ifor the distance of this cell base station of user distance, for central user, R _c=R is radius of society, for edge customer, ρ _bSrepresent cell density; For central user: ρ _bS=π R ², for edge customer: α is path-loss factor; The signal interference ratio of user is converted to this cell base station of user distance distance r _ifunction, by a distance threshold R _thuser is divided into central user and edge customer:

M _c＝{i：r _i≤R _th}，M _e＝{i：r _i>R _th}

M _cand M _erepresent the set of central user and edge customer respectively; I represents user's sequence number;

The average size calculating Cell Center User and edge customer is respectively:

$C_C=\frac{2\mathrm{\Δ}f}{R_{th}^2-R_0^2}{\∫}_{R_0}^{R_{th}}{r}_i\[{\log }_2(1+{\mathrm{SIR}}_C)\]{\mathrm{dr}}_i$

$C_E=\frac{2\mathrm{\Δ}f}{R^2-R_{th}^2}{\∫}_{R_{th}}^{R_0}{r}_i\[{\log }_2(1+{\mathrm{SIR}}_E)\]{\mathrm{dr}}_i$

Δ f represents the bandwidth of system, R ₀represent the minimum range of user distance base station, SIR _cand SIR _erepresent signal interference ratio when user-center user and edge customer respectively;

Pilot tone is distributed according to the area at center of housing estate and edge, and central guiding frequency and edge pilot number are respectively:

$N_E=\[\frac{R^2-R_{th}^2}{3R^2-2R_{th}^2-R_0^2}N\]$

N _c＝N-3N _E

Wherein [x] expression rounds under x; N is total number of pilots;

The total capacity c of community is finally expressed as:

$\begin{array}{c}C=\underset{k=1}{\overset{N_C}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^k{(R^2-R_{th}^2)}^{M-k}}{{(R^2-R_0^2)}^M}{\mathrm{kC}}_C+\underset{k=N_C}{\overset{M}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^k{(R^2-R_{th}^2)}^{M-k}}{{(R^2-R_0^2)}^M}{E}_C{C}_C\\ +\underset{k=1}{\overset{N_E}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^{M-k}{(R^2-R_{th}^2)}^k}{{(R^2-R_0^2)}^M}{\mathrm{kC}}_E+\underset{k=N_E}{\overset{M}{\Σ}}\left(\begin{array}{c}M\\ k\end{array}\right)\frac{{(R_{th}^2-R_0^2)}^{M-k}{(R^2-R_{th}^2)}^k}{{(R^2-R_0^2)}^M}{N}_E{C}_E\end{array}$

Wherein, M is the total number of users in community; $\left(\begin{array}{c}M\\ k\end{array}\right)$ Represent the possibility selecting k element from M element;

By obtaining best division thresholding R to community total capacity maximizing _th.

3. a kind of portion of pilot multiplexing method overcoming pilot pollution in extensive mimo system as claimed in claim 1, it is characterized in that, the concrete steps of described step (3) are:

By the optimum thresholding R calculated _th, user is divided into central user and edge customer, distributes same set of pilot tone to the central user of different districts, the edge customer of neighbor cell distributes different pilot tones.