CN112953864B - Honeycomb-free hybrid large-scale MIMO system channel estimation method for protecting privacy - Google Patents

Honeycomb-free hybrid large-scale MIMO system channel estimation method for protecting privacy Download PDF

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CN112953864B
CN112953864B CN202110404584.9A CN202110404584A CN112953864B CN 112953864 B CN112953864 B CN 112953864B CN 202110404584 A CN202110404584 A CN 202110404584A CN 112953864 B CN112953864 B CN 112953864B
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matrix
privacy
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time slot
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CN112953864A (en
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朱鹏程
徐军
江鹏
李佳珉
尤肖虎
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Southeast University
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202Channel estimation
    • H04L25/024Channel estimation channel estimation algorithms
    • H04L25/0242Channel estimation channel estimation algorithms using matrix methods
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202Channel estimation
    • H04L25/0204Channel estimation of multiple channels
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202Channel estimation
    • H04L25/0224Channel estimation using sounding signals
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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    • Y02D30/70Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses a method for estimating a channel of a honeycomb-free hybrid large-scale MIMO system for protecting privacy, which is suitable for the field of communication. Each AP obtains an incomplete baseband signal sampling matrix for channel estimation by establishing an uplink signal transmission model and a mixed structure sampling model; designing a privacy protection matrix completion algorithm, taking an incomplete baseband signal sampling matrix obtained by each AP as input, and outputting a complete matrix by each AP while protecting the position privacy of a user; each AP carries out channel estimation according to the output complete matrix and the known pilot frequency matrix, thereby achieving the best channel estimation performance while effectively protecting the privacy of the single-antenna user position. The method can well protect the position privacy of the user and simultaneously obtain good channel estimation performance.

Description

Honeycomb-free hybrid large-scale MIMO system channel estimation method for protecting privacy
Technical Field
The invention relates to the technical field of wireless communication, in particular to a method for estimating a channel of a non-cellular hybrid large-scale MIMO system for protecting privacy.
Background
A non-cellular hybrid large-scale Multiple Input Multiple Output (MIMO) system usually has a large number of Access Points (APs) distributed in a region, and uses the same time-frequency resources to cooperatively serve users. To reduce the high cost associated with equipping each antenna with a Radio Frequency (RF) chain containing a high resolution analog-to-digital converter, systems typically employ a hybrid analog/digital architecture, in which the antennas are typically randomly connected to a small number of RF chains in an analog combination based on switches or phase shifters.
In order to implement a large-scale MIMO system without cellular mixing, it is important to acquire Channel State Information (CSI). In order to obtain a better channel estimation result, each AP needs to send the received signal observed by each AP to a Central Processing Unit (CPU) for uniform processing, and the CPU performs channel estimation and data detection on all users. However, this is highly likely to cause the positional information of the user to leak to the CPU. Since large-scale fading in CSI highly depends on the distance between a user and an AP, and the AP location is generally fixed, theoretically, a CPU has the capability of estimating the user location after obtaining CSI between a certain user and three or more APs, and thus leakage of user location information may occur. Therefore, how to provide accurate channel estimation under the premise of protecting the privacy of the user position is a crucial problem, and no suitable solution exists in the prior art.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects of the prior art, the invention provides a privacy-protecting channel estimation method of a honeycomb-free hybrid large-scale MIMO system, which can effectively protect the position privacy of a user, aims to estimate a channel and protect the position privacy of the user,
The technical scheme is as follows: in order to achieve the technical purpose, the invention provides a method for estimating a channel of a non-cellular hybrid massive MIMO system for protecting privacy, which comprises the following steps:
s1, establishing an uplink signal transmission model and a mixed structure sampling model of a non-cellular mixed large-scale MIMO system, and obtaining an incomplete baseband signal sampling matrix for channel estimation by each AP;
s2, designing a privacy protection matrix completion algorithm, wherein the algorithm takes an incomplete baseband signal sampling matrix obtained by each AP as input, and each AP outputs a complete matrix while protecting the position privacy of a user;
and S3, each AP carries out channel estimation according to the output complete matrix and the known pilot frequency matrix, so that the privacy of the position of the single-antenna user is effectively protected and the optimal channel estimation performance is achieved.
The step S1 specifically includes:
by using
Figure BDA0003021782680000021
Representing a set of APs, utilizing
Figure BDA0003021782680000022
Representing a set of single antenna users; within the coherence intervalThe set of time slots is represented as
Figure BDA0003021782680000023
Wherein front τ is p One slot is used for uplink channel estimation and is represented as
Figure BDA0003021782680000024
The rest of tau d =τ cp One time slot is used for uplink data transmission and is represented as
Figure BDA0003021782680000025
Using s [ t ]]A vector of transmitted signals representing K single-antenna users in time slot t, wherein
Figure BDA0003021782680000026
Time s [ t ]]Represents a pilot signal used to estimate the channel when
Figure BDA0003021782680000027
Time s [ t ]]Representing data symbols containing information; by using
Figure BDA0003021782680000028
Representing channel vectors of the m-th AP to the k-th single-antenna user, wherein
Figure BDA0003021782680000029
Representing a complex field;
n on mth AP a Received signal vector of root antenna in time slot t
Figure BDA00030217826800000210
Expressed as:
Figure BDA00030217826800000211
wherein
Figure BDA00030217826800000212
Channel matrix for mth AP to all users, n m [t]Is the noise received by the mth AP at time slot t, subject to mean 0 and variance σ 2 Circularly symmetric complex gaussian distribution of (a);
defining the following matrix
Figure BDA00030217826800000213
In the formula: r m Represents N at the mth AP a Root antenna at c Received signal matrix of one time slot, N m Represents N at the mth AP a Root antenna at c A received noise matrix of one time slot, P denotes the front tau p Pilot matrix sent by user in one time slot, D represents rear tau d The matrix of data transmitted by the users in one time slot, S represents the total of tau c A signal matrix sent by a user in each time slot comprises pilot frequency and data; wherein N on the mth AP a Root antenna at c The received signal matrix for a time slot is represented as:
Figure BDA00030217826800000214
each AP adopts a switch-based hybrid structure, and each time slot is from N a Randomly selecting N from root antenna r Root antenna and N r RF-coupled and then converted to baseband signals using high precision analog-to-digital converters, so that the m-th AP receives a signal vector r in time slot t m [t]Total N a Only N in a received signal r The reception signal becomes a baseband signal; let omega m For the set of m-th AP upsampling indexes (n, t), i.e. representing r m [t]N th element of (3) m (n, t) is sampled onto a certain RF and then becomes a baseband signal, let
Figure BDA00030217826800000215
And the baseband signal sampling matrix of the mth AP meets the following mapping relation:
Figure BDA0003021782680000031
the mapping table is shown as
Figure BDA0003021782680000032
It is obvious that Y m Each column having only N r A non-zero baseband signal, therefore Y m Is an incomplete matrix.
The matrix completion algorithm for protecting privacy in step S2 specifically includes:
with incomplete total baseband signal sampling matrix
Figure BDA0003021782680000033
As input, a complete low rank matrix is output
Figure BDA0003021782680000034
The low rank matrix completion problem of (a) can be expressed as a least squares problem as shown below
Figure BDA0003021782680000035
Wherein | · | purple nuc The number of the kernel norms is expressed,
Figure BDA0003021782680000036
represents the Frobenius norm,
Figure BDA0003021782680000037
represents a set of sampling indices across all APs; the problem (5) is a convex optimization problem, and the invention designs a matrix completion algorithm for protecting privacy to solve the problem; the matrix completion algorithm for protecting privacy is an iterative algorithm, and each AP m outputs a complete estimation matrix in the nth iteration
Figure BDA0003021782680000038
And estimating the output estimation matrix of the Tth iteration
Figure BDA0003021782680000039
As a low rank matrix
Figure BDA00030217826800000310
The method comprises the following concrete steps:
s31, inputting a specific numerical value of the privacy parameter (epsilon, delta); inputting an algorithm iteration number T; the baseband signal sampling matrix Y of each AP m is input m (ii) a Y is estimated from m Upper bound L of
Figure BDA00030217826800000311
Wherein beta is k,m Represents the large-scale fading coefficients, σ, of the m-th AP to k-th user channels 2 Representing the channel noise variance;
s32. Initialization
Figure BDA00030217826800000312
Giving weight values η for T iterations (1) =1,η (n) =1/T,n≠1,
S33, initializing iteration times, and enabling n =1;
s34, each AP m calculates a signal matrix according to the following formula
Figure BDA00030217826800000313
Figure BDA00030217826800000314
Figure BDA00030217826800000315
Then sending the signal matrix after noise interference to the CPU through an optical fiber return link
Figure BDA00030217826800000316
Wherein
Figure BDA00030217826800000317
For randomly generated tau c ×τ c The hermite of (a) perturbs the noise matrix,
Figure BDA00030217826800000318
subject to mean 0 and variance μ of the upper triangle element and diagonal element, respectively 2 The cyclic symmetric complex gaussian distribution and gaussian distribution of (a), wherein μ is calculated according to the following formula:
Figure BDA0003021782680000041
s35.CPU accumulates signal matrix sent by each AP m through optical fiber return link
Figure BDA0003021782680000042
To obtain
Figure BDA0003021782680000043
First of all, calculate
Figure BDA0003021782680000044
Maximum eigenvalue of
Figure BDA0003021782680000045
And corresponding feature vectors
Figure BDA0003021782680000046
Then correcting according to
Figure BDA0003021782680000047
Figure BDA0003021782680000048
S36. The CPU sends the corrected data to all APs through the optical fiber return link
Figure BDA0003021782680000049
And feature vectors
Figure BDA00030217826800000410
S37, each AP m is calculated according to the following formula
Figure BDA00030217826800000411
Figure BDA00030217826800000412
Figure BDA00030217826800000413
S38, if n is larger than T, going to S39, otherwise, making n = n +1 and returning to the step S34 for recalculation;
s39, each AP obtains a complete matrix:
Figure BDA00030217826800000414
as H m And (5) estimating S.
In step S34, the signal matrix including the location privacy information
Figure BDA00030217826800000415
Before sending to the CPU, in the signal matrix
Figure BDA00030217826800000416
And a disturbance noise matrix is added for protection, so that the position privacy of a user is protected from being disclosed to a CPU, the variance of disturbance noise is calibrated by using a calculation formula in a formula (9), and the proposed privacy protection matrix completion algorithm strictly realizes the combined differential privacy (belonging to the element and delta).
The step S3 specifically includes:
fetch a complete matrix for each AP m
Figure BDA00030217826800000417
Front τ of p Column, is marked as
Figure BDA00030217826800000418
As
Figure BDA00030217826800000419
Is estimated by the estimation of (a) a,
each AP m calculates its channel H according to m Estimation of (2):
Figure BDA00030217826800000420
wherein
Figure BDA00030217826800000421
Representing the pseudo-inverse of P.
Has the advantages that: the method can excavate the low-rank characteristic of the receiving signal matrix under the condition of no receiving noise of the large-scale MIMO, and estimate the channel with lower training overhead by utilizing the low-rank characteristic. In addition, the method applies the differential privacy technology to the channel estimation of the wireless communication system for the first time, and achieves better channel estimation performance while well protecting the position privacy of the user.
Drawings
FIG. 1 is an algorithmic flow diagram of an embodiment of the present invention;
FIG. 2 is a schematic diagram of a hybrid massive MIMO system without cells, in accordance with an embodiment of the present invention;
fig. 3 is a comparison graph of normalized mean square error curves of channel estimates obtained by the method of the embodiment of the present invention and the method of estimating its channel by using only pilots for each AP alone, and the Frank-Wolfe iteration-based matrix completion method without privacy protection.
Detailed Description
The technical solutions of the present invention are further described below with reference to the accompanying drawings and the following embodiments, which should be understood as merely illustrative of the present invention and not limiting the scope of the present invention.
The invention considers a non-cellular hybrid large-scale MIMO system, which is configured with 1 CPU, M APs and K random antennasThe machine is distributed with single antenna users, each AP connected to the CPU through a fiber backhaul link, as shown in fig. 2. Each AP adopts a mixed structure and is provided with N a Root antenna and N r <N a An RF link. Are used separately
Figure BDA0003021782680000051
And
Figure BDA0003021782680000052
representing the AP and the set of users.
Figure BDA0003021782680000053
Represents the channel vectors of the m-th AP to the k-th user, where
Figure BDA0003021782680000054
Representing a complex field. Assuming that the channels between all users and all APs are block-faded, the channel coefficients have τ c The coherence interval of a time slot remains unchanged. The set of slots in the coherence interval is denoted as
Figure BDA0003021782680000055
Wherein front τ is p One time slot is used for uplink channel estimation and is expressed as
Figure BDA0003021782680000056
The rest of tau d =τ cp One time slot is used for uplink data transmission and is represented as
Figure BDA0003021782680000057
s[t]A vector of transmitted signals representing K users in time slot t, wherein
Figure BDA0003021782680000058
Time s [ t ]]Represents a pilot signal used to estimate the channel when
Figure BDA0003021782680000059
Time s [ t ]]Representing data symbols containing information.
A method for estimating a channel of a non-cellular hybrid massive MIMO system for protecting privacy comprises the following steps:
s1, establishing an uplink signal transmission model and a mixed structure sampling model of a non-cellular mixed large-scale MIMO system, and obtaining an incomplete baseband signal sampling matrix for channel estimation by each AP;
s2, designing a privacy-protecting matrix completion algorithm, wherein the algorithm takes an incomplete baseband signal sampling matrix obtained by each AP as input, and each AP outputs a complete matrix while protecting the privacy of the user position;
and S3, each AP carries out channel estimation according to the output complete matrix and the known pilot frequency matrix, so that the privacy of the position of the single-antenna user is effectively protected and the optimal channel estimation performance is achieved.
N on mth AP a Signal vector received by root antenna in time slot t
Figure BDA00030217826800000510
Can be expressed as
Figure BDA00030217826800000511
Wherein
Figure BDA00030217826800000512
Channel matrix for mth AP to all users, n m [t]Is the noise received by the mth AP at time slot t subject to mean 0 and variance σ 2 Circularly symmetric complex gaussian distribution. The following matrix is defined:
Figure BDA0003021782680000061
Figure BDA0003021782680000062
Figure BDA0003021782680000063
Figure BDA0003021782680000064
Figure BDA0003021782680000065
in the formula: r m Represents N at the mth AP a Root antenna at c Received signal matrix of time slots, N m Represents N at the mth AP a Root antenna at c A received noise matrix of one slot, P denotes the front τ p Pilot matrix sent by user in one time slot, D represents rear tau d The matrix of data transmitted by the users in one time slot, S represents the total of tau c The signal matrix sent by the user in each time slot comprises pilot frequency and data. N on mth AP a Root antenna at c The received signal matrix for a time slot may be represented as:
Figure BDA0003021782680000066
each AP adopts a switch-based hybrid structure, and each time slot is from N a Randomly selecting N in root antenna r Root antenna and N r The RF signals are coupled and then converted to baseband signals by a high precision analog to digital converter. Therefore, the m-th AP receives the signal vector r in the time slot t m [t]Total N a Only N in a received signal r The received signal becomes a baseband signal. Let omega m For the set of m-th AP upsampling indexes (n, t), i.e. representing r m [t]N th element of (3) m (n, t) is sampled onto a certain RF and then becomes a baseband signal. Is provided with
Figure BDA0003021782680000067
And the baseband signal sampling matrix of the mth AP meets the following mapping relation:
Figure BDA0003021782680000068
the mapping table is shown as
Figure BDA0003021782680000069
It is obvious that Y m Each column having only N r A non-zero baseband signal, thus Y m Is an incomplete matrix.
Based on
Figure BDA00030217826800000610
The invention designs a privacy-protecting channel estimation algorithm, which can improve the accuracy of channel estimation while protecting the privacy of the user position. The algorithm flow is shown in fig. 1, and specifically includes the following steps:
s1, inputting a specific numerical value of a privacy parameter (epsilon, delta); inputting an algorithm iteration number T; inputting baseband signal sampling matrix Y of each AP m m (ii) a Y is estimated from m Upper bound L of
Figure BDA00030217826800000611
Wherein beta is k,m Represents the large-scale fading coefficients of the m-th AP to k-th user channels, sigma 2 Representing the channel noise variance;
s2. Initialization
Figure BDA00030217826800000612
Giving weight values η for T iterations (1) =1,η (n) =1/T,n≠1,
S3, initializing iteration times, and enabling n =1;
s4, each AP m calculates a signal matrix according to the following formula
Figure BDA0003021782680000071
Figure BDA0003021782680000072
Figure BDA0003021782680000073
Then sending the signal matrix after noise interference to the CPU through the optical fiber return link
Figure BDA0003021782680000074
Wherein
Figure BDA0003021782680000075
For randomly generated tau c ×τ c The hermite of (a) perturbs the noise matrix,
Figure BDA0003021782680000076
respectively obeys the mean value of 0 and the variance of mu 2 The cyclic symmetric complex gaussian distribution and gaussian distribution of (a), wherein μ is calculated according to the following formula:
Figure BDA0003021782680000077
s5.CPU accumulates the signal matrix sent by each AP m through the optical fiber return link
Figure BDA0003021782680000078
To obtain
Figure BDA0003021782680000079
First of all, calculate
Figure BDA00030217826800000710
Maximum eigenvalue of
Figure BDA00030217826800000711
And corresponding feature vectors
Figure BDA00030217826800000712
Then according toCorrection of formula
Figure BDA00030217826800000713
Figure BDA00030217826800000714
S6. The CPU sends the corrected data to all APs through the optical fiber return link
Figure BDA00030217826800000715
And feature vectors
Figure BDA00030217826800000716
S7, calculating each AP m according to the following formula
Figure BDA00030217826800000717
Figure BDA00030217826800000718
Figure BDA00030217826800000719
S8, if n is larger than T, S9 is reached, otherwise, n = n +1 is made and the step S4 is returned to for recalculation;
s9, each AP obtains a complete matrix
Figure BDA00030217826800000720
As X m =H m Estimating S;
s10, taking out each AP m
Figure BDA00030217826800000721
Front τ of p Column, is marked as
Figure BDA00030217826800000722
As
Figure BDA00030217826800000723
(ii) an estimate of (d);
s11. Each AP m calculates its channel H according to the following formula m Is estimated by
Figure BDA00030217826800000724
Wherein
Figure BDA00030217826800000725
Representing the pseudo-inverse of P.
Fig. 3 is a comparison graph of normalized mean square error curves of channel estimation obtained by using the channel estimation method (Algorithm 1) for privacy protection of a non-cellular hybrid large-scale multiple-input multiple-output system according to the present embodiment when the radius of a cell is 1km, each AP has 100 APs in the cell, each AP has 2 RF links with 4 antennas, and total 5 users, and the method (PO) for estimating its channel by using only pilots alone for each AP and the matrix completion method (NPFW) based on Frank-Wolfe iteration without privacy protection. The Frank-Wolfe iteration based matrix completion method, in which privacy is not protected, is a theoretical upper bound of this particular embodiment, but it does not have the ability to protect privacy. As can be seen from fig. 3, the channel estimation obtained by the method of the present embodiment is more accurate than the method using pilot estimation alone, and the accuracy of channel estimation can be significantly improved while maintaining a certain privacy level.

Claims (2)

1. A method for estimating a channel of a non-cellular hybrid massive MIMO system for protecting privacy is characterized in that: the cellular-free hybrid large-scale MIMO system comprises 1 baseband central processing unit CPU, M randomly distributed access points AP and K randomly distributed single-antenna users; each AP adopts a mixed structure and is provided with N a Root antenna and N r <N a All APs are connected to the CPU through optical fiber backhaul links; the channels between all single-antenna users and all APs are block-faded with channel coefficients at τ c Within a coherence interval of one time slotKeeping the original shape;
the method comprises the following steps:
s1, establishing an uplink signal transmission model and a mixed structure sampling model of a non-cellular mixed large-scale MIMO system, and obtaining an incomplete baseband signal sampling matrix for channel estimation by each AP;
s2, designing a privacy protection matrix completion algorithm, wherein the algorithm takes an incomplete baseband signal sampling matrix obtained by each AP as input, and each AP outputs a complete matrix while protecting the position privacy of a user;
s3, each AP carries out channel estimation according to the output complete matrix and the known pilot frequency matrix, so that the privacy of the position of the single-antenna user is effectively protected and the optimal channel estimation performance is achieved;
the step S1 specifically includes:
by using
Figure FDA0003828852060000011
Representing a set of APs, utilizing
Figure FDA0003828852060000012
Representing a set of single antenna users; the set of slots in the coherence interval is denoted as
Figure FDA0003828852060000013
Wherein front τ is p One time slot is used for uplink channel estimation and is expressed as
Figure FDA0003828852060000014
The rest of tau d =τ cp One time slot is used for uplink data transmission and is represented as
Figure FDA0003828852060000015
Using s [ t ]]A vector of transmitted signals representing K single-antenna users in time slot t, wherein
Figure FDA0003828852060000016
Time s [ t ]]Represents a pilot signal used to estimate the channel when
Figure FDA0003828852060000017
Time s [ t ]]Representing data symbols containing information; by using
Figure FDA0003828852060000018
Represents the channel vectors of the m-th AP to the k-th single-antenna user, where
Figure FDA0003828852060000019
Representing a complex field;
n on mth AP a Received signal vector of root antenna in time slot t
Figure FDA00038288520600000110
Expressed as:
Figure FDA00038288520600000111
wherein
Figure FDA00038288520600000112
Channel matrix for mth AP to all users, n m [t]Is the noise received by the mth AP at time slot t, subject to mean 0 and variance σ 2 Circularly symmetric complex gaussian distribution of (a);
defining the following matrix
Figure FDA00038288520600000113
In the formula: r m Represents N at the mth AP a Root antenna at c Received signal matrix of one time slot, N m Represents N at the mth AP a Root antenna at c A received noise matrix of one slot, P denotes the front τ p Pilot matrix sent by user in time slot, D represents rear tau d The matrix of data transmitted by the users in one time slot, S represents the total of tau c A signal matrix sent by a user in each time slot comprises pilot frequency and data; wherein N on the mth AP a Root antenna at c The received signal matrix for a time slot is represented as:
Figure FDA0003828852060000021
each AP adopts a switch-based hybrid structure, and each time slot is from N a Randomly selecting N in root antenna r Root antenna and N r RF-coupled and then converted to baseband signals using high precision analog-to-digital converters, so that the m-th AP receives a signal vector r in time slot t m [t]Total of N a Only N in a received signal r The received signal becomes a baseband signal; let omega m For the set of m-th AP upsampling indexes (n, t), i.e. representing r m [t]N th element of (3) m (n, t) is sampled onto a certain RF and then becomes a baseband signal, let
Figure FDA0003828852060000022
And the baseband signal sampling matrix of the mth AP meets the following mapping relation:
Figure FDA0003828852060000023
the mapping table is shown as
Figure FDA0003828852060000024
Y m Each column having only N r A non-zero baseband signal, thus Y m Is an incomplete matrix;
the matrix completion algorithm for protecting privacy in step S2 specifically includes:
with incomplete total baseband signal sampling matrix
Figure FDA0003828852060000025
As input, a complete low rank matrix is output
Figure FDA0003828852060000026
The low rank matrix completion problem of (a) can be expressed as a least squares problem as shown below
Figure FDA0003828852060000027
Wherein | · | purple nuc The number of the nuclear norms is represented,
Figure FDA0003828852060000028
represents the Frobenius norm,
Figure FDA0003828852060000029
represents a set of sampling indices across all APs; problem (5) is a convex optimization problem; the matrix completion algorithm for protecting privacy is an iterative algorithm, and the mth AP of the nth iteration outputs a complete estimation matrix
Figure FDA00038288520600000210
And estimating the output estimation matrix of the Tth iteration
Figure FDA00038288520600000211
As a low rank matrix
Figure FDA00038288520600000212
The method comprises the following concrete steps:
s31, inputting a specific numerical value of the privacy parameter (epsilon, delta); inputting an algorithm iteration number T; inputting the baseband signal sampling matrix Y of the mth AP m (ii) a Y is estimated from m Upper bound L of
Figure FDA00038288520600000213
Wherein beta is k,m Represents the large-scale fading coefficients, σ, of the m-th AP to k-th user channels 2 Representing the channel noise variance;
s32. Initialization
Figure FDA0003828852060000031
Giving weight values η for T iterations (1) =1,η (n) =1/T,n≠1,
S33, initializing iteration times, and enabling n =1;
s34. The mth AP firstly calculates a signal matrix according to the following formula
Figure FDA0003828852060000032
Figure FDA0003828852060000033
Figure FDA0003828852060000034
Then sending the signal matrix after noise interference to the CPU through an optical fiber return link
Figure FDA0003828852060000035
Wherein
Figure FDA0003828852060000036
For randomly generated tau c ×τ c The hermite of (a) perturbs the noise matrix,
Figure FDA0003828852060000037
respectively obeys the mean value of 0 and the variance of mu 2 The cyclic symmetric complex gaussian distribution and gaussian distribution of (a), wherein μ is calculated according to the following formula:
Figure FDA0003828852060000038
s35.CPU accumulates the signal matrix sent by mth AP through the optical fiber return link
Figure FDA0003828852060000039
To obtain
Figure FDA00038288520600000310
First of all, calculate
Figure FDA00038288520600000311
Maximum eigenvalue of
Figure FDA00038288520600000312
And corresponding feature vectors
Figure FDA00038288520600000313
Then correcting according to
Figure FDA00038288520600000314
Figure FDA00038288520600000315
S36. The CPU sends the corrected data to all APs through the optical fiber return link
Figure FDA00038288520600000316
And feature vectors
Figure FDA00038288520600000317
S37, the mth AP is calculated according to the following formula
Figure FDA00038288520600000318
Figure FDA00038288520600000319
Figure FDA00038288520600000320
S38, if n is larger than T, going to S39, otherwise, making n = n +1 and returning to the step S34 for recalculation;
s39, each AP obtains a complete matrix:
Figure FDA00038288520600000321
as H m Estimating S;
in the step S34, the signal matrix including the location privacy information
Figure FDA00038288520600000322
Before sending to the CPU, in the signal matrix
Figure FDA00038288520600000323
And a disturbance noise matrix is added for protection, so that the position privacy of a user is protected from being disclosed to a CPU, the variance of disturbance noise is calibrated by using a calculation formula in a formula (9), and the proposed privacy protection matrix completion algorithm strictly realizes the combined differential privacy (belonging to the element and delta).
2. The method for channel estimation in a hybrid massive MIMO system without cellular according to claim 1, wherein the step S3 specifically comprises:
taking out the complete matrix from the mth AP
Figure FDA0003828852060000041
Front τ of p Column, is marked as
Figure FDA0003828852060000042
As
Figure FDA0003828852060000043
Is estimated by the estimation of (a) a,
the mth AP calculates its channel H according to the following equation m Estimation of (2):
Figure FDA0003828852060000044
wherein
Figure FDA0003828852060000045
Representing the pseudo-inverse of P.
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