CN104219189A - Wideband Massive MIMO Communication Method with Pilot Multiplexing in Angle-Delay Domain - Google Patents

Abstract

The invention proposes an angle-delay domain pilot multiplexing wideband massive MIMO communication method. The base station side performs wireless communication with multiple users simultaneously on each subcarrier. The sounding sequence of each user is generated by the same constant modulus sequence through frequency domain modulation, and different users simultaneously send uplink sounding signals on multiple subcarriers of one or more consecutive OFDM symbols, and the base station side obtains the angle-delay domain of each user based on this Two-dimensional statistical channel information, and thus determine the pilot modulation factor of each user. The pilot sequence of each user is generated by the same constant modulus sequence through frequency domain modulation. Different users send uplink pilot signals on multiple subcarriers of one or more consecutive OFDM symbols at the same time, and the base station side obtains the pilot frequency segment and data of each user accordingly. segment channel estimates. On each subcarrier, the base station implements uplink and downlink robust transmission according to the channel estimation value and the estimation error spatial correlation matrix. The invention can reduce system pilot overhead and improve system frequency spectrum and power efficiency.

Description

Wideband Massive MIMO Communication Method with Pilot Multiplexing in Angle-Delay Domain

technical field

The invention relates to a wideband massive MIMO wireless communication method using multiple antennas, in particular to a wideband massive MIMO wireless communication method for angle-delay domain pilot multiplexing.

Background technique

The massive MIMO wireless communication technology equipped with a large-scale antenna array on the base station side can deeply utilize the spatial dimension resources of the wireless channel. Compared with the traditional small-scale MIMO technology, it can further improve the effectiveness and reliability of the wireless communication system. widespread attention in the world. The actual wireless propagation channels are all broadband channels, and Orthogonal Frequency Division Multiplexing (OFDM) technology can decompose the broadband channel into multiple parallel narrowband channels. Massive MIMO combined with OFDM is one of the development trends of the next generation broadband mobile communication system. one.

The transmission quality of a wireless communication system depends on the accuracy of channel parameter estimation. In order to obtain channel parameter estimates accurately and timely, pilot-assisted channel estimation methods are often used in practice. For massive multi-user MIMO-OFDM wireless communication systems, there are a large number of channel parameters to be estimated, which will lead to a large amount of pilot overhead. At the same time, the linear minimum mean square error channel estimation requires a high-dimensional matrix inversion operation, and the implementation complexity is relatively high. The pilot overhead and the complexity of channel estimation become the bottleneck of massive MIMO-OFDM wireless communication.

The actual broadband wireless propagation channel exhibits energy concentration characteristics in the angle-delay domain, and the use of this characteristic can effectively reduce the pilot overhead of the system. Massive MIMO-OFDM channels exhibit decorrelation properties in the angle-delay domain, which can effectively reduce the implementation complexity of linear minimum mean square error channel estimation. Based on the above characteristics, the present invention provides an angle-delay domain pilot multiplexing wideband massive MIMO wireless communication method based on two-dimensional statistical channel information in the angle-delay domain.

Contents of the invention

Technical problem: The purpose of the present invention is to provide an angle-delay domain pilot multiplexing broadband massive MIMO wireless communication method based on two-dimensional statistical channel information in the angle-delay domain, and fully tap the pilot frequency in the angle-delay domain resources, save the pilot overhead of the system, and reduce the complexity of channel estimation. The basic feature of this method is that each user in the cell simultaneously sends uplink sounding signals on multiple subcarriers of one or more continuous OFDM symbols, and the base station side obtains the angle-delay domain two-dimensional statistical channel information of each user based on this. Each user simultaneously transmits uplink pilot signals on multiple subcarriers of one or more consecutive OFDM symbols, and the frequency domain pilot sequences of different users are generated from the same sequence through frequency domain modulation. The base station uses the two-dimensional statistical channel information in the angle-delay domain of each user to dynamically determine the pilot modulation mode, that is, the frequency domain pilot sequence modulation factor of each user.

Technical solution: an angle-delay domain pilot multiplexing broadband massive MIMO communication method, characterized in that the method is specifically:

a. It is suitable for time-division duplex broadband massive MIMO wireless communication system, adopts OFDM modulation mode, and the base station performs wireless communication with multiple users at the same time on each sub-carrier;

b. The communication process is composed of multiple consecutive frames, each frame signal is composed of an uplink detection signal at the frame header and multiple subframes; the signal of each subframe is composed of multiple OFDM symbols, and each subframe is sequentially composed of uplink data signals segment, uplink pilot signal segment, and downlink data signal segment, respectively transmitting the uplink transmission signal and uplink pilot signal sent by the user to the base station and the downlink transmission signal sent by the base station to the user;

c. The base station side obtains the angle-delay domain two-dimensional statistical channel information of each user in the cell through the uplink detection of each user, and the detection signals of different users do not require the use of orthogonal time-frequency resources;

Each user in the cell simultaneously sends uplink pilot signals on multiple subcarriers of one or more continuous OFDM symbols in the uplink pilot signal segment of each subframe, and different users in the same cell transmit multiple continuous OFDM symbols in the uplink pilot signal segment. The pilot sequence used on the symbol is generated by the same pilot sequence through frequency domain modulation, and the pilot modulation factors of different users are dynamically determined by the base station according to the two-dimensional statistical channel information in the angle-delay domain of each user;

e. According to the two-dimensional statistical channel information in the angle-delay domain of each user, the base station side uses the pilot signal received by the uplink pilot signal segment of the current subframe to analyze the OFDM symbols of each user in the pilot signal segment of the current subframe Estimate the channel parameters, and use the pilot modulation factor of each user to determine the channel estimation error spatial correlation matrix of each user on each OFDM symbol of the pilot signal segment of the current subframe;

f. The base station uses the time-domain correlation characteristics of the channel and the channel parameter estimation value of the pilot signal segment of the current subframe to implement the channel parameter estimation of each user on each OFDM symbol of the uplink and downlink data signal segments of the current subframe, and obtain the data signal The channel estimation error spatial correlation matrix of each user on each OFDM symbol of the segment;

g. In the uplink data transmission stage, each user sends uplink data signals on each subcarrier at the same time, and the base station side stores the received data signals, and waits for the base station side to receive the uplink pilot signal and complete the uplink data signal segment of the current subframe After the channel parameters of each user on each OFDM symbol are estimated, the uplink data signal is subjected to robust reception processing using the channel parameter estimation value and the estimation error spatial correlation matrix;

h. In the downlink data transmission phase, the base station side sends data signals to each user on each subcarrier at the same time, and the base station side uses the channel parameter estimates of each user on each OFDM symbol in the downlink data signal segment of the current subframe and the spatial correlation of the estimation error implement robust precoding on each sub-carrier, send data signals to each user at the same time, and each user performs reception processing on each sub-carrier;

i. The base station side determines the pilot modulation mode of each user in the cell according to the angle-delay domain two-dimensional statistical channel information of each user, that is, the pilot sequence modulation factor of each user in the cell, and notifies each user in the cell user.

The time division duplex broadband massive MIMO wireless communication system adopts OFDM modulation mode, and the base station side communicates with multiple users simultaneously on each subcarrier respectively.

The uplink transmission signal includes an uplink sounding signal, an uplink data signal and an uplink pilot signal, and the downlink transmission signal includes a downlink data signal. The transmission process can be divided into multiple consecutive frames, and each frame signal is composed of an uplink detection signal at the frame header and multiple subframes. The signal of each subframe is composed of a plurality of OFDM symbols, and each subframe is sequentially composed of an uplink data signal segment, an uplink pilot signal segment and a downlink data signal segment.

The acquisition of the angle-delay domain two-dimensional statistical channel information of each user is completed by an uplink channel detection process. Each user simultaneously sends uplink sounding signals on multiple subcarriers of one or more consecutive OFDM symbols at the frame header of each frame, and the sounding signals of different users do not require the use of orthogonal time-frequency resources. The frequency-domain sounding signals of different users in the same cell are generated by the same constant modulus sequence (called the basic sounding sequence of the cell) through frequency-domain modulation, and the basic sounding sequences of adjacent cells are required to have better cross-correlation characteristics, that is, cross-correlation less than the threshold required by the system. The base station of each cell obtains the least squares estimation of the channel parameters in the angle-delay domain of each user in the current frame of the cell according to the received uplink sounding signal, and then uses the iterative method to estimate the two-dimensional statistics of the angle-delay domain of each user in the current frame Channel information, that is, the channel energy coupling matrix in the angle-delay domain.

Each user in the cell simultaneously sends uplink pilot signals on multiple subcarriers of one or more continuous OFDM symbols in each subframe uplink pilot signal segment. The pilot sequences used by different users in the same cell are generated by the same pilot sequence (called the basic pilot sequence of the cell) through frequency domain modulation, and the modulation factor is determined by the base station side according to the angle-delay domain of each user in the cell Two-dimensional statistical channel information is determined dynamically. The basic pilot sequences of adjacent cells are required to have better cross-correlation characteristics, that is, the cross-correlation is smaller than the threshold value required by the system.

The base station estimates the channel parameters of each user on each OFDM symbol in the current subframe by using the pilot signal received in the uplink pilot signal segment of the current subframe. The base station side utilizes the angle-delay domain two-dimensional statistical channel information of each user to realize low-complexity linear minimum mean square error channel parameter estimation. First, the least squares estimation is performed on the channel parameters in the angle-delay domain of each user, and then according to the decorrelation characteristics of the channel in the angle-delay domain, a low-complexity element-by-element least squares estimation is implemented on the angle-delay domain channel, Finally, the space-frequency domain channel parameter estimation value of each user in the pilot signal segment of the current subframe is obtained by unitary transformation. The channel estimation error spatial correlation matrix of each user in the pilot signal segment is determined by the two-dimensional statistical channel information in the angle-delay domain of each user and the pilot modulation mode.

The base station side uses the time-domain correlation characteristics of the channel and the channel parameter estimation value of the pilot signal segment of the current subframe to implement the channel parameter estimation of each user on each OFDM symbol of the uplink and downlink data signal segments of the current subframe, and obtain the data signal The spatial correlation matrix of the channel estimation error on each OFDM symbol of the segment. The channel estimation error spatial correlation matrix of each user in the data signal segment is determined by the two-dimensional statistical channel information in the angle-delay domain of each user, the correlation characteristics of the channel in the time domain, and the pilot modulation mode.

In the uplink data sending phase, each user simultaneously sends uplink data signals on each subcarrier, and the base station side stores the received data signals. After the base station has received the uplink pilot signal and completed the channel parameter estimation of each user on each OFDM symbol in the uplink data signal segment of the current subframe, use the channel parameter estimation value and the estimation error spatial correlation array on each subcarrier to pair the uplink data The signal undergoes robust reception processing.

In the downlink data transmission phase, the base station side transmits data signals to each user on each subcarrier at the same time. The base station implements robust precoding on each subcarrier by using the channel parameter estimates of each user on each OFDM symbol in the downlink data signal segment of the current subframe and the estimated error spatial correlation matrix, and sends data signals to each user at the same time. Reception processing is performed on each subcarrier.

The base station side determines the pilot modulation mode of each user in the cell according to the angle-delay domain two-dimensional statistical channel information of each user, that is, the frequency domain pilot modulation factor of each user in the cell, and notifies the user in the cell of each user. The pilot modulation factor of each user is adaptively changed according to the two-dimensional statistical channel information in the angle-delay domain.

Beneficial effects: The angle-delay domain pilot multiplexing wideband massive MIMO wireless communication method based on angle-delay domain two-dimensional statistical channel information provided by the present invention has the following advantages:

1. Utilize the statistical characteristics of the broadband wireless propagation channel in the angle-delay domain, fully tap the pilot resources in the angle-delay domain, greatly reduce the pilot overhead of the system, and then improve the spectrum efficiency and power efficiency of the system.

2. Based on the angle-delay domain two-dimensional statistical channel information of each user, adaptive dynamic scheduling of pilot resources is performed, while reducing pilot overhead, ensuring channel estimation performance and improving system flexibility.

3. Utilizing the decorrelation characteristics of wideband massive MIMO channels in the angle-delay domain, the implementation complexity of linear minimum mean square error channel estimation can be greatly reduced. The time-domain correlation characteristic of the channel is used to estimate the channel in the data transmission stage, which further improves the accuracy of the channel estimation in the data segment.

4. The uplink data signal of each frame is sent before the uplink pilot signal, which reduces the impact of inaccurate channel estimation on uplink data transmission performance and improves the robustness of the system.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the descriptions of the embodiments or prior art. Obviously, the accompanying drawings in the following description only show the technical aspects of the present invention. For some embodiments, those of ordinary skill in the art can also obtain the drawings of other embodiments according to these drawings without creative work.

FIG. 1 is a schematic diagram of a transmission signal frame structure of a massive MIMO-OFDM system based on two-dimensional statistical channel information in an angle-delay domain.

Detailed ways

In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

1. System configuration, transmission signal frame structure and communication process

In a multi-cell cellular system, each cell base station is configured with a large-scale antenna array containing more than dozens of antenna units, and the large-scale antenna array can adopt one of various array structures such as a line array, a circular array, or a plate array. Assume that the number of antenna units equipped on the base station side is M, and each antenna unit can use an omnidirectional antenna or a sector antenna. When each antenna unit uses an omnidirectional antenna, a 120-degree sector antenna, and a 60-degree sector antenna, the The spacing between them can be configured as 1/2 wavelength, wavelength and 1 wavelength. Each antenna unit can adopt a single-polarization or multi-polarization antenna. Suppose there are K users equipped with a single antenna in the cell, with Represents a collection of users. The communication between the user and the base station adopts the time division duplex transmission mode, adopts the Orthogonal Frequency Division Multiplexing (OFDM) modulation technology with a cyclic prefix, the number of subcarriers is N _c , and the length of the cyclic prefix is N _g .

Figure 1 is a schematic diagram of the transmission signal frame structure of the angle-delay domain pilot multiplexing wideband massive MIMO wireless communication system based on two-dimensional statistical channel information in the angle-delay domain, where the uplink transmission signal sent by the user to the base station includes The uplink sounding signal, the uplink data signal and the uplink pilot signal, and the downlink transmission signal sent by the base station to the user include the downlink data signal. The system transmission process can be divided into multiple consecutive frames, and each frame signal is composed of an uplink detection signal at the frame header and multiple subframes. The signal of each subframe is composed of a plurality of OFDM symbols, and each subframe signal is sequentially composed of an uplink data signal segment, an uplink pilot signal segment and a downlink data signal segment.

Under this system configuration, the broadband massive MIMO-OFDM wireless communication process based on two-dimensional statistical channel information in the angle-delay domain includes the following six steps:

1) Acquisition of two-dimensional statistical channel information in the angle-delay domain: the acquisition of the two-dimensional statistical channel information in the angle-delay domain of each user is completed by the uplink channel detection process. Each user simultaneously sends uplink sounding signals on multiple subcarriers of one or more consecutive OFDM symbols in the frame header of each frame. The sounding signals of different users do not require the use of orthogonal time-frequency resources, and the frequency domain sounding signals of each user are composed of the same The constant modulus sequence is generated through frequency domain modulation. The base station obtains the least squares estimation of the angle-delay domain channel parameters of each user in the current frame according to the received sounding signal, and then uses an iterative method to estimate the angle-delay domain two-dimensional statistical channel information of each user in the current frame, that is, the angle - Delay domain channel energy coupling matrix.

2) Pilot resource scheduling: each user in the cell simultaneously sends pilot signals on multiple subcarriers of one or more continuous OFDM symbols in the uplink pilot signal segment of each subframe, and the pilot signals of different users do not require the use of regular For time-frequency resources, the frequency-domain pilot sequence used by each user is generated by the same constant modulus sequence through frequency-domain modulation. The base station side uses the obtained two-dimensional statistical channel information in the angle-delay domain of each user to implement pilot resource scheduling, determine the pilot modulation mode, that is, the uplink pilot sequence modulation factor of each user, and notify each user in the cell.

3) Uplink data signal transmission: At the beginning of each subframe, each user simultaneously transmits uplink data signals on each subcarrier. The base station side stores the received uplink data signal without processing it.

4) Uplink pilot signal transmission and channel parameter estimation: Each user sends its own uplink pilot signal, and the base station side uses the received pilot signal to obtain the channel parameters of each user on each OFDM symbol in the pilot signal segment of the current subframe estimate. Furthermore, the time-domain correlation characteristic of the channel is used to obtain the channel parameter estimation of each user on each OFDM symbol of the uplink data signal segment and the downlink data signal segment of the current subframe. The base station side determines the channel estimation error spatial correlation matrix of each user on each OFDM symbol in the pilot signal segment according to the two-dimensional statistical channel information of each user in the angle-delay domain and the pilot modulation factor of each user.

5) Uplink robust data receiving processing: the base station side performs receiving processing on each user's uplink data on each subcarrier respectively. The base station side uses the obtained channel parameter estimation and estimation error spatial correlation matrix of each user on each OFDM symbol in the uplink data signal segment of the current subframe, and performs robust reception processing on the stored uplink data signals on each subcarrier, and obtains Each user transmits the estimated value of the data signal uplink, and then obtains the transmitted bit data stream.

6) Downlink robust precoding data transmission: the base station side performs robust precoding transmission on each user's downlink data on each subcarrier respectively. The base station side uses the channel parameter estimation of each user on each OFDM symbol in the downlink data signal segment of the current subframe and the estimation error spatial correlation matrix to calculate the Lux required for sending data signals to each user signal on each subcarrier in the downlink data signal segment of the current subframe. stick precoding matrix, thereby generating downlink transmission signals, which are simultaneously transmitted by the base station to each user on each subcarrier, and each user performs reception processing on each subcarrier according to the received signal to obtain the downlink transmission bit data stream .

2. Acquisition of two-dimensional statistical channel information in the angle-delay domain

The acquisition of the angle-delay domain two-dimensional statistical channel information of each user on the base station side is completed by the uplink channel detection process of each user. Each user simultaneously sends uplink sounding signals on multiple subcarriers of one or more consecutive OFDM symbols at the head of each frame, and the sounding signals of different users are generated by the same constant modulus sequence through frequency domain modulation.

Let g _{t, k, n, m} denote the channel parameters on the nth subcarrier in the detection phase of frame t between user k and the mth antenna unit on the base station side. Let g _{t, k, n} = [g _{t, k, n, 1} g _{t, k, n, 2} ... g _{t, k, n, M} ] ^T , where the superscript T represents the vector transpose operation, $G_{t,k}=\left[\begin{array}{cccc}{g}_{t,k,0}& g_{t,k,1}& \·\·\·& g_{t,k,N_c-1}\end{array}\right].$ Let the statistical model of Gt,k be where U is a fixed matrix (called the spatial eigenmode matrix) depending on the antenna configuration on the base station side, _{and Mk} is a matrix composed of channel statistical parameters specific to user k (each element is a positive value), Each element of is subject to the assumption of independent and identical distribution (each element has a mean of zero and a variance of 1), is a matrix composed of the first N _g columns of an N _c- dimensional DFT matrix, and ⊙ represents an element-wise product. Call H _t,k the angle-delay two-dimensional eigenmode domain channel matrix of user k in the detection phase of frame t, referred to as the angle-delay domain channel matrix. Let Ω _k =M _k ⊙M _k , in the case where the spatial characteristic pattern matrix U is known, Ω _k is the angle-delay domain two-dimensional statistical channel information of user k to be obtained, which is called angle-delay The two-dimensional eigenmode domain channel energy coupling matrix, referred to as the angle-delay domain channel energy coupling matrix.

It is assumed that each user transmits simultaneously on Q _sd consecutive OFDM symbols at the head of each frame, where Q _sd satisfies KN _g ≤ _{Q sd} N _c . by Indicates the sounding signal sent by user k (0≤k≤K-1) in the cell on the nth subcarrier of the qth (0≤q≤Q _sd -1) OFDM symbol at the head of each frame. Denote the sounding signal of user k on the qth OFDM symbol at the head of each frame as where the superscript T represents the vector transpose operation.

The transmission signals of different users on each OFDM symbol in the uplink detection phase are generated by the same sequence x ^sd through frequency domain modulation, where x ^sd is a constant modulus sequence with a dimension of N _c ×1, satisfying diag{x} represents a diagonal matrix whose diagonal elements are x. For user k, the transmitted signal on the qth OFDM symbol in the uplink detection phase can be generated by the following formula:

in is the transmission power of the detection signal, Indicates the modulo operation of k on Q _sd , Indicates the largest integer not exceeding x, V _sd is a unitary matrix of any Q _sd × Q _sd dimension, [V] _{a, b} represent the elements located in row a and column b of matrix V, ⊙ represents the element-wise product of vectors, the derivative frequency modulation vector The expression for any x is as follows:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; =</span>{\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; 0</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>& <span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span>& \mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>\end{array}\right]}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, exp(x) represents the x-th power operation of the natural base exp, j is the imaginary number unit, and π is the pi constant.

by Indicates the sounding signal received by the mth antenna at the base station side on the nth subcarrier of the qth sounding OFDM symbol in the tth frame. set up ${\mathrm{the\; y}}_{t,q,\mathrm{no}}^{\mathrm{sd}}={\left[\begin{array}{cccc}{\mathrm{the\; y}}_{t,q,\mathrm{no},1}^{\mathrm{sd}}& {\mathrm{the\; y}}_{t,q,\mathrm{no},2}^{\mathrm{sd}}& \&Center\; Dot;\&CenterDot;\&Center\; Dot;& {\mathrm{the\; y}}_{t,q,\mathrm{no},m}^{\mathrm{sd}}\end{array}\right]}^T,$ $Y_{t,q}^{\mathrm{sd}}=\left[\begin{array}{cccc}{\mathrm{the\; y}}_{t,q,0}^{\mathrm{sd}}& {\mathrm{the\; y}}_{t,q,1}^{\mathrm{sd}}& \&CenterDot;\&CenterDot;\&CenterDot;& {\mathrm{the\; y}}_{t,q,N_c-1}^{\mathrm{sd}}\end{array}\right].$ make $Y_t^{\mathrm{sd}}=\left[\begin{array}{cccc}{Y}_{t,0}^{\mathrm{sd}}& Y_{t,1}^{\mathrm{sd}}& \&Center\; Dot;\&Center\; Dot;\&Center\; Dot;& Y_{t,Q_{\mathrm{sd}}-1}^{\mathrm{sd}}\end{array}\right],$ $x_k^{\mathrm{sd}}=\left[\begin{array}{cccc}\mathrm{diag}\left\{x_{0,k}^{\mathrm{sd}}\right\}& \mathrm{diag}\left\{x_{1,k}^{\mathrm{sd}}\right\}& \&CenterDot;\&Center\; Dot;\&Center\; Dot;& \mathrm{diag}\{x_{Q_{\mathrm{sd}}-1,k}^{\mathrm{sd}}\end{array},\}\right],$ in is the sounding signal sent by user k on the qth OFDM symbol at the head of each frame. In the uplink sounding phase of frame t, the sounding signal received by the base station side is

Where diag{x} represents a diagonal matrix whose diagonal elements are x, is an additive white Gaussian noise matrix, the mean of each element is zero, and the variance is

In the tth transmission frame, firstly by the received sounding signal Obtain the estimated value of the channel matrix in the angle-delay domain of each user, and the calculation formula is as follows:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; sd</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; sd</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; sd</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; sd</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

where the superscript H represents the vector conjugate transpose operation. Let the estimated value of the angle-delay domain channel energy coupling matrix Ω _k for user k in the tth transmission frame be Then an iterative method can be used to obtain the estimated value of the channel energy coupling matrix in the current frame in the angle-delay domain, and the calculation formula is as follows:

The superscript * indicates that each element of the matrix is conjugated, and χ is the forgetting factor, which satisfies 0<χ<1.

3. Pilot signal layout and angle-delay domain pilot multiplexing

Taking advantage of the sparseness of different user channels in the angle-delay domain, different users can simultaneously transmit pilot signals on the same time-frequency resource, thereby effectively reducing the pilot overhead of massive MIMO-OFDM wireless communication systems.

Different users in the cell simultaneously send uplink pilot signals on one or more continuous OFDM symbols of each subframe pilot signal segment. The frequency domain pilot sequence sent by each user in the cell is generated by a constant modulus sequence (called the basic pilot sequence of the cell) through frequency domain modulation, and its modulation factor is determined by the base station side according to the angle-delay of each user in the cell Domain two-dimensional statistical channel information is determined dynamically. The basic pilot sequences of adjacent cells are required to have better cross-correlation characteristics, that is, the cross-correlation is smaller than the threshold value required by the system.

It is assumed that the uplink pilot signal transmission process of each user in the cell is performed on Q _tr consecutive OFDM symbols from t _p to t _p +Q _tr -1 in each subframe. For user u, its pilot modulation factor is Δ _u , and the modulation factor is from the modulation factor set Selected in , the frequency-domain pilot sequence sent on the qth(t _p ≤q≤t _p +Q _tr -1)th OFDM symbol is:

Where x ^tr represents the basic pilot sequence of the current cell, satisfying V _tr is any unitary matrix of Q _tr ×Q _tr dimension, is the transmit power of the pilot signal, is a pilot sequence modulation vector of N _c ×1, and its i-th element is

The base station side determines the modulation factor of the pilot sequence of each user in the cell according to the angle-delay domain two-dimensional statistical channel information of each user in the cell, and notifies each user. Each user generates its own pilot sequence, and sends the uplink pilot sequence in the uplink pilot signal segment of each subframe.

4. Low-complexity two-dimensional channel parameter estimation for the pilot signal segment

The uplink channel parameter estimation of each user is performed separately at the base station side of each cell. In the uplink pilot signal segment of each subframe, all users in the cell simultaneously transmit uplink pilot signals on multiple subcarriers of one or more consecutive OFDM symbols, and the base station side obtains the channel of the current subframe pilot signal segment accordingly Parameter estimation and estimation error spatial correlation matrix.

In each subframe, each user in the cell simultaneously transmits uplink pilot signals on multiple subcarriers of Q _tr consecutive OFDM symbols from t _p to t _p +Q _tr -1. by Indicates the pilot signal received by the mth antenna on the base station side on the _nth subcarrier of the tpth OFDM symbol in the current subframe, Indicates the channel parameters on the _nth subcarrier of the tpth OFDM symbol in the current subframe between user k and the mth antenna unit on the base station side. set up ${\mathrm{the\; y}}_{t_p,\mathrm{no}}^{\mathrm{tr}}={\left[\begin{array}{cccc}{\mathrm{the\; y}}_{t_p,\mathrm{no},1}^{\mathrm{tr}}& {\mathrm{the\; y}}_{t_p,\mathrm{no},2}^{\mathrm{tr}}& \&CenterDot;\&CenterDot;\&CenterDot;& {\mathrm{the\; y}}_{t_p,\mathrm{no},m}^{\mathrm{tr}}\end{array}\right]}^T,Y_{t_p}^{\mathrm{tr}}=\left[\begin{array}{cccc}{\mathrm{the\; y}}_{t_p,0}^{\mathrm{tr}}& {\mathrm{the\; y}}_{t_p,1}^{\mathrm{tr}}& \&Center\; Dot;\&Center\; Dot;\&CenterDot;& {\mathrm{the\; y}}_{t_p,N_c-1}^{\mathrm{tr}}\end{array}\right],$ $Y^{\mathrm{tr}}=\left[\begin{array}{cccc}{Y}_{t_p}^{\text{tr}}& Y_{t_p+1}^{\mathrm{tr}}& \&CenterDot;\&Center\; Dot;\&Center\; Dot;& Y_{t_p+Q_{\mathrm{tr}}-1}^{\mathrm{tr}}\end{array}\right],g_{t_p,k,\mathrm{no}}={\left[\begin{array}{cccc}{g}_{t_p,k,\mathrm{no},1}& g_{t_p,k,\mathrm{no},2}& \&Center\; Dot;\&Center\; Dot;\&Center\; Dot;& g_{t_p,k,\mathrm{no},m}\end{array}\right]}^T,$ $G_{t_p,k}=\left[\begin{array}{cccc}{g}_{t_p,k,0}& g_{t_p,k,1}& \&CenterDot;\&CenterDot;\&CenterDot;& g_{t_p,k,N_c-1}\end{array}\right],$ $x_k^{\mathrm{tr}}=\left[\begin{array}{cccc}\mathrm{diag}\left\{x_{t_p,k}^{\mathrm{tr}}\right\}& \mathrm{diag}\left\{x_{t_p+1,k}^{\mathrm{tr}}\right\}& \&Center\; Dot;\&Center\; Dot;\&Center\; Dot;& \mathrm{diag}\{x_{t_p+Q_{\mathrm{tr}}-1,k}^{\mathrm{tr}}\end{array}\}\right].$ Then in the uplink pilot signal transmission phase of the current subframe, the pilot signal received by the base station side is

where Z ^tr is an additive white Gaussian noise matrix, the mean of each element is zero, and the variance is

The base station side utilizes the decorrelation characteristics between the channel elements in the angle-delay domain, and the base station side can realize low-complexity linear minimum mean square error large-scale MIMO-OFDM channel parameter estimation.

For user k in the current cell, first obtain the least squares estimate of its channel parameters in the angle-delay domain as follows:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; LS</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; tr</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; tr</span>}}}{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}^{\mathrm{<span\; class="notranslate">\; tr</span>}}{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; tr</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

According to the two-dimensional statistical channel information of the massive MIMO-OFDM channel in the angle-delay domain, the linear minimum mean square error estimation of the channel parameters in the angle-delay domain can be obtained. Since the massive MIMO-OFDM channel exhibits decorrelation properties in the angle-delay domain, it can be Each element of is estimated by the linear minimum mean square error, thereby reducing the implementation complexity. The estimation formula of the i-th row and j-th column element is:

in $\mathrm{\&delta;}(a-b)=\left\{\begin{array}{cc}1,& a=b\\ 0,& a\&NotEqual;b\end{array}\right.,$ Ω _k is the estimated value of the channel energy coupling matrix of user k in the current frame in the angle-delay domain, The calculation formula for any integer Δ is

in accordance with The space-frequency domain channel parameter estimation value of the uplink pilot signal segment of the current subframe can be obtained as follows:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; G</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; MMSE</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

The channel estimation error spatial correlation matrix of user k in the uplink pilot signal segment is as follows:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Udiag</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; \}</span>{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

in The calculation formula for the i-th element is:

5. Two-dimensional channel parameter estimation of data signal segment

The channel parameters of the uplink and downlink data signal segments of the current subframe can be estimated (also called channel prediction) by using the obtained estimated channel parameter values of the pilot signal segment of the current subframe and the time-domain correlation characteristics of the channel. For user k, it is assumed that the maximum channel Doppler frequency offset of user k estimated by the base station is v _k , and its uplink pilot signal segment (t _p to t _p +Q _tr -1 OFDM symbol) channel estimate is Then the estimated value of the channel parameter in the space-frequency domain located in the data signal segment of the current subframe (the _tp + _Δtth OFDM symbol) can be calculated as follows:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; G</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; tr</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; G</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

Where ρ _k (x)=J ₀ (2πv _k T _sym x), T _sym is the system OFDM symbol length, J ₀ (x) is the first kind of zero-order Bessel function whose variable is x.

The channel estimation error spatial correlation matrix of user k in the data signal segment is calculated as follows:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Udiag</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; g</span>}}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}{<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; \}</span>{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

in The formula for calculating the i-th element of is:

6. Uplink robust data reception

In each subframe, each user first transmits an uplink data signal on each subcarrier at the same time, and the base station side stores the received signal. When the base station side receives the uplink pilot signal and completes the channel parameter estimation of the uplink data signal segment, use the channel estimation value of the uplink data signal segment and the channel estimation error spatial correlation matrix to perform a Ludicrous Great reception.

The uplink robust data receiving process is described by taking the nth subcarrier of the tth OFDM symbol of the uplink data signal segment in each subframe as an example. by Indicates that the uplink data signal sent by user k in the cell on the nth subcarrier of the tth OFDM symbol in the current subframe has a mean value of zero and a variance of The transmission data signal of each user is a data signal obtained after channel coding, interleaving and modulation symbol mapping of the information bit stream for which it transmits. by Indicates the data signal received by the mth antenna on the base station side on the nth subcarrier of the tth OFDM symbol in the current frame, g _{t, k, n, m} means the current subcarrier between user k and the mth antenna unit on the base station side Channel parameters on the nth subcarrier of the tth OFDM symbol in the frame.

set up ${\mathrm{the\; y}}_{t,\mathrm{no}}^{\mathrm{ul}}={\left[\begin{array}{cccc}{\mathrm{the\; y}}_{t,\mathrm{no},1}^{\mathrm{ul}}& {\mathrm{the\; y}}_{t,\mathrm{no},2}^{\mathrm{ul}}& \&CenterDot;\&CenterDot;\&CenterDot;& {\mathrm{the\; y}}_{t,\mathrm{no},m}^{\mathrm{ul}}\end{array}\right]}^T,$ g _{t, k, n} = [g _{t, k, n, 1} g _{t, k, n, 2} ... g _{t, k, n, M} ] ^T , G _{t, n} = [g _{t, 0, n} g _{t ,1,n} ...gt _,K-1,n ], Then the uplink data signal received by the base station side on the current subcarrier is:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; ul</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; ul</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; ul</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 17</span>}<span\; class="notranslate">\; )</span>$

in is an additive white Gaussian noise vector whose elements have a mean of zero and a variance of

The base station side stores the received uplink data signal, and after the base station side receives the uplink pilot signal of each user and completes the channel parameter estimation of the uplink data signal segment, estimates the uplink data signal sent by each user.

The channel parameter estimates obtained by the base station side for each user on the current subcarrier of the current OFDM symbol are denoted as in is the estimated value of the channel parameters g _{t, k, n} at the base station side. Under the average minimum mean square error criterion, the robust estimation of each user's uplink data signal on the current subcarrier of the current OFDM symbol is calculated by the following formula:

in is the transmit signal-to-noise ratio of each user’s uplink data transmission, is the channel estimation error spatial correlation matrix of user k on the current OFDM symbol. Using the robust estimation value of the data signal sent by each user on the current subcarrier of the current OFDM symbol, through the processes of demodulation, deinterleaving and channel decoding, the estimated value of the information bit stream sent by each user on the current subcarrier of the current OFDM symbol can be obtained.

7. Downlink Robust Precoding

In the downlink data transmission phase, the base station side sends data signals to each user on each subcarrier at the same time. The downlink robust precoding transmission is implemented on each subcarrier by using the obtained channel parameter estimation values of each user in the downlink data signal segment and the channel estimation error spatial correlation matrix. The average minimum mean square error criterion may be used for the downlink robust precoding transmission, so that the average value of the mean square error of the minimum mean square error precoding transmission is the smallest within the channel estimation error range.

The following transmission process takes the nth subcarrier on the tth OFDM symbol of the downlink data signal segment as an example. by Indicates the data signal before precoding sent by the base station to K users in the cell on the current subcarrier of the current OFDM symbol, where the kth element is the data signal sent to user k, with a mean value of zero and a variance of The transmission data signal of each user is a data signal obtained after channel coding, interleaving and modulation symbol mapping of the information bit stream for which it transmits. Let B _{t, n} represent the base station precoding matrix on the current subcarrier of the current OFDM symbol, and the actual signal sent by the base station side is Due to the time division duplex transmission mode, the downlink channel can be expressed as the transposition of the uplink channel G _t,n on the same subcarrier of the same OFDM symbol. The received signal at the user end can be expressed as:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; dl</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; dl</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; dl</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 19</span>}<span\; class="notranslate">\; )</span>$

in Indicates the data signals received by K users on the current subcarrier, where the kth element is the data signal received by user k, is an additive white Gaussian noise vector whose elements have a mean of zero and a variance of

Under the average minimum mean square error criterion, the robust precoding matrix at the base station side is calculated by the following formula:

in is the estimated value of the current subcarrier uplink channel parameter G _{t, n} at the base station side, is the average transmit signal-to-noise ratio of each user's downlink transmission, γt _{, n} is the transmit power constraint parameter at the base station side, which can be calculated by the following formula:

Where tr{.} represents the matrix trace operation.

Each user can obtain the estimated value of the downlink transmission information bit stream on each sub-carrier by using the signal received on each sub-carrier and through processes such as demodulation, de-interleaving, and channel decoding.

8. Angle-delay domain pilot scheduling

Pilot scheduling is implemented on the base station side. The base station uses the obtained two-dimensional statistical channel information in the angle-delay domain of each user to determine the pilot frequency of the user in the cell according to a given criterion, such as the minimum criterion of the sum of channel estimation mean square errors. The frequency modulation mode, that is, the frequency domain modulation factor of the pilot sequence of each user, is notified to each user in the cell. by Indicates the pilot modulation mode of the current cell, where k represents the user number, and Δ _k represents the frequency-domain modulation factor of the pilot sequence used by user k.

The sum of channel estimation mean square error can be obtained according to the two-dimensional statistical channel information in the angle-delay domain of each user by the following formula:

The pilot scheduling based on the minimum criterion of the sum of channel estimation mean square errors is to search for the pilot modulation pattern that minimizes ε ^tr This pilot scheduling can be done by exhaustive search or greedy algorithm.

9. Dynamic adjustment of pilot multiplexing wideband massive MIMO transmission in angle-delay domain

During the mobile process of each user, as the angle-delay domain two-dimensional statistical channel information Ω _k changes between the base station and each user, the base station side dynamically implements the aforementioned pilot scheduling to form an updated pilot modulation pattern, and then Implement the aforementioned angle-delay domain pilot multiplexing wideband massive MIMO wireless transmission based on angle-delay domain two-dimensional statistical channel information. The change of channel statistical characteristics is related to specific application scenarios. The typical statistical time window is several times or tens of times the frame length, and the acquisition of related channel statistical information is also carried out in a relatively large time width.

In the embodiments provided in the present application, it should be understood that the disclosed methods can be implemented in other ways without exceeding the spirit and scope of the present application. The present embodiment is only an exemplary example and should not be taken as a limitation, and the specific content given should not limit the purpose of the present application. For example, several units or components may be combined or may be integrated into another system, or some features may be omitted, or not implemented.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (10)

1. the extensive MIMO communication means in angle-time delay domain pilot frequency multiplexing broadband, is characterized in that the method is specially:

A. be applicable to the extensive mimo wireless communication system in time division duplex broadband, adopt modulating in OFDM mode, radio communication is carried out with multiple user in base station on each subcarrier simultaneously;

B. communication process is made up of multiple successive frame, and each frame signal is made up of the uplink detection signal of frame head and multiple subframe; The signal of each subframe is made up of multiple OFDM symbol, each subframe is made up of upstream data. signals section, uplink pilot signal section and downlink data signal section successively, and transmission user sends to the uplink transmission signals of base station and uplink pilot signal and base station to issue the downlink transmission signal of user respectively;

C. base station side obtains the angle-time delay domain Two-dimensional Statistical channel information of each user in community by the uplink detection of each user, and the detectable signal of different user does not require to use orthogonal resource;

D. in community, each user sends uplink pilot signal on multiple subcarriers of the one or more continuous OFDM symbol of each subframe uplink pilot signal section simultaneously, the pilot frequency sequence that in same community, different user uses in the multiple continuous OFDM symbol of uplink pilot signal section is generated through frequency domain modulation by same pilot frequency sequence, and the pilot modulated factor of different user is dynamically determined according to each user perspective-time delay domain Two-dimensional Statistical channel information by base station side;

E. according to the angle-time delay domain Two-dimensional Statistical channel information of each user, the pilot signal that base station side utilizes present sub-frame uplink pilot signal section to receive is estimated the channel parameter of each user in each OFDM symbol of present sub-frame pilot signal section, and utilize the pilot modulated factor of each user, determine the channel estimation errors space correlation battle array of each user in each OFDM symbol of present sub-frame pilot signal section;

F. base station side utilizes the time domain related features of channel and the channel parameter estimation value of present sub-frame pilot signal section, implement each subscriber channel parameter Estimation in the up and each OFDM symbol of downlink data signal section of present sub-frame, and obtain the channel estimation errors space correlation battle array of each user in each OFDM symbol of data-signal section;

G. in upstream data transmission phase, each user sends upstream data. signals respectively on each subcarrier simultaneously, data-signal received by base station side stores, after base station side receives uplink pilot signal and completes each subscriber channel parameter Estimation in each OFDM symbol of present sub-frame upstream data. signals section, channel parameter estimation value and evaluated error space correlation battle array is utilized to carry out robust reception process to uplink data signals;

H. in the downlink data transmission stage, base station side sends data-signal to each user respectively on each subcarrier simultaneously, base station side utilizes each subscriber channel estimates of parameters in each OFDM symbol of present sub-frame downlink data signal section and evaluated error space correlation battle array, each subcarrier implements robust pre-coding respectively, send data-signal to each user, each user carries out reception process respectively on each subcarrier simultaneously;

I. base station side is according to the angle-time delay domain Two-dimensional Statistical channel information of each user, determines the pilot modulated pattern of each user in this community, i.e. the pilot sequence modulates factor of each user in community, and notifies each user in this community.

2. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, it is characterized in that: the extensive mimo wireless communication system in described time division duplex broadband adopts OFDM modulation mode, and base station side communicates with multiple user respectively on each subcarrier simultaneously.

3. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, it is characterized in that: described uplink transmission signals comprises uplink detection signal, upstream data. signals and uplink pilot signal, and downlink transmission signal comprises downlink data signal; Transmitting procedure can be divided into multiple continuous print frame, and each frame signal is made up of the uplink detection signal of frame head and multiple subframe; The signal of each subframe is made up of multiple OFDM symbol, and each subframe is made up of upstream data. signals section, uplink pilot signal section and downlink data signal section successively.

4. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, is characterized in that: the angle-time delay domain Two-dimensional Statistical channel information acquisition of described each user is completed by the channel detection process of up link; Each user sends uplink detection signal on multiple subcarriers of the one or more continuous OFDM symbol of each frame frame head simultaneously, and the detectable signal of different user does not require to use orthogonal resource; In same community, the frequency domain detectable signal of different user is generated through frequency domain modulation by same permanent mode sequence (being called the basic detection sequence of this community), the basic detection sequence of neighbor cell requires to have good their cross correlation, and namely cross-correlation is less than the threshold value required by system; Each cell base station obtains the least-squares estimation of angle-time delay domain channel parameter in each user's present frame in community according to the uplink detection signal received, and then utilize iterative method to estimate the angle-time delay domain Two-dimensional Statistical channel information of each user in present frame, i.e. angle-time delay domain channel energy coupling matrix.

5. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, is characterized in that: in described community, each user sends uplink pilot signal on multiple subcarriers of the one or more continuous OFDM symbol of each subframe uplink pilot signal section simultaneously; The pilot frequency sequence that in same community, different user uses is called the basic pilot frequency sequence of this community by same pilot frequency sequence, generate through frequency domain modulation, its modulation factor is dynamically determined according to the angle-time delay domain Two-dimensional Statistical channel information of each user in community by base station side; The basic pilot frequency sequence of neighbor cell requires to have good their cross correlation, and namely cross-correlation is less than the threshold value required by system.

6. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, is characterized in that: the pilot signal that described base station side utilizes present sub-frame uplink pilot signal section to receive is estimated the channel parameter of each user in each OFDM symbol of present sub-frame; Base station side utilizes the angle-time delay domain Two-dimensional Statistical channel information of each user, realizes the linear minimum mean-squared error channel parameter estimation of low complex degree; First least-squares estimation is implemented to the angle-time delay domain channel parameter of each user, and then the decorrelation characteristic of foundation angle-time delay domain channel, to angle-time delay domain channel implement low complex degree by element least-squares estimation, obtain the space-frequency domain channel parameter estimation value of each user in present sub-frame pilot signal section finally by unitary transformation; Pilot signal section each subscriber channel evaluated error space correlation battle array is determined by each user perspective-time delay domain Two-dimensional Statistical channel information and pilot modulated pattern.

7. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, it is characterized in that: described base station side utilizes the time domain related features of channel and the channel parameter estimation value of present sub-frame pilot signal section, implement each subscriber channel parameter Estimation in the up and each OFDM symbol of downlink data signal section of present sub-frame, and obtain the channel estimation errors space correlation battle array in each OFDM symbol of data-signal section; Data-signal section each subscriber channel evaluated error space correlation battle array is determined by each user perspective-time delay domain Two-dimensional Statistical channel information, channel time domain correlation properties and pilot modulated pattern.

8. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, it is characterized in that: described in upstream data transmission phase, each user sends upstream data. signals respectively on each subcarrier simultaneously, the data-signal received by base station side stores; Receive uplink pilot signal until base station and complete in each OFDM symbol of present sub-frame upstream data. signals section after each subscriber channel parameter Estimation, on each subcarrier, utilizing channel parameter estimation value and evaluated error space correlation battle array to carry out robust reception process to uplink data signals respectively.

9. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, is characterized in that: described in the downlink data transmission stage, base station side sends data-signal to each user respectively on each subcarrier simultaneously; Base station utilizes each subscriber channel estimates of parameters in each OFDM symbol of present sub-frame downlink data signal section and evaluated error space correlation battle array, each subcarrier implements robust pre-coding respectively, send data-signal to each user, each user carries out reception process respectively on each subcarrier simultaneously.

10. the extensive MIMO communication means in angle according to claim 1-time delay domain pilot frequency multiplexing broadband, it is characterized in that: described base station side is according to the angle-time delay domain Two-dimensional Statistical channel information of each user, determine the pilot modulated pattern of each user in this community, the i.e. pilot tone modulation factor of each user in community, and notify each user in this community; The pilot modulated factor of each user is according to angle-time delay domain Two-dimensional Statistical channel information adaptive change.