CN106301502B - Extensive MIMO downlink wireless communications method under radio circuit mismatch condition - Google Patents
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Abstract
The present invention proposes extensive MIMO downlink wireless communications method under a kind of radio circuit mismatch condition, is suitable for the extensive mimo wireless communication system of TDD.Base station intermittently obtains the radio circuit gain coefficient of base station side and user side.Each user sends respective pilot signal, and base station obtains the down channel estimation and the statistical property of down channel evaluated error of each user accordingly and in conjunction with radio circuit gain coefficient.Make the robust pre-coding transmission of downlink according to the statistical property of down channel estimation and down channel evaluated error in base station.The present invention can obtain down channel estimation under there are radio circuit mismatch condition, reduce the loss of downlink precoding transmission performance caused by being unsatisfactory for by uplink and downlink channel reciprocity, implement the spectrum efficiency that wireless communication system can be effectively further improved for the robust downlink precoding transmission of down channel evaluated error accordingly, while base station can also predict user's downlink rate of traversal according to radio circuit gain coefficient and statistic channel information.
Description
Technical Field
The present invention relates to a MIMO wireless communication system using multiple antennas, and more particularly, to a MIMO wireless communication system for a large scale in the presence of a mismatch of radio frequency circuits.
Background
With the popularization and application of intelligent mobile terminals and the continuous development of new mobile service requirements, the transmission rate requirements of mobile communication continue to increase exponentially. In order to meet the application requirements of future mobile communication, space wireless resources need to be deeply excavated and utilized, and the frequency spectrum utilization rate and the power utilization rate of wireless communication are greatly improved. The MIMO wireless transmission technology using multi-antenna transmission and multi-antenna reception is a basic technology for improving the spectrum and power efficiency of wireless communication, and has been one of the mainstream technologies in the research field of wireless communication in the past decade. Due to the limitation of the number of antennas (e.g. in the LTE-a standard of 3GPP, a maximum of 8 antennas can be configured at the base station side), the spectrum and power efficiency of the conventional MIMO technology is still low. A large-scale antenna array (tens of antennas or more) is configured on the base station side to deeply mine and utilize space dimension resources, which is one of the development trends of future wireless communication.
In a Time Division Duplex (TDD) massive MIMO wireless communication system, uplink signals and downlink signals share the same frequency band, so that uplink and downlink signals have the same propagation path, and uplink and downlink channels have reciprocity. However, in an actual system, each antenna rf front-end frequency unit on the base station side and the user side is respectively completed with two sets of circuits for signal transmission and reception, as shown in fig. 1. Due to factors such as hardware process errors and different working environments of radio frequency units, gain coefficients of radio frequency circuits are different, mismatch of the radio frequency circuits is generated, and reciprocity of channels is damaged. The mismatch is especially severe for large-scale MIMO systems with large-scale antenna arrays. If the uplink channel estimation is directly used for downlink precoding transmission, the system performance will be obviously lost. The invention provides a large-scale MIMO downlink wireless communication method under the condition of radio frequency circuit mismatch, which comprises the steps of obtaining gain coefficients of radio frequency circuits at a base station side and a user side, obtaining downlink channel estimation and downlink channel estimation error statistical information by using the gain coefficients of the radio frequency circuits, and implementing robust downlink pre-coding transmission and traversal reachable rate prediction aiming at downlink channel estimation errors.
Disclosure of Invention
The technical problem is as follows: the invention aims to provide a large-scale MIMO downlink wireless communication method under the condition of radio frequency circuit mismatch. The method is basically characterized in that downlink channel estimation and estimation error statistical information are obtained based on the gain coefficient estimation of the radio frequency circuit, robust downlink precoding transmission is carried out aiming at estimation errors, and the system spectrum efficiency is improved.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the technical scheme that:
a large-scale MIMO downlink wireless communication method under the condition of radio frequency circuit mismatch is suitable for a Time Division Duplex (TDD) large-scale MIMO wireless communication system, a large-scale array antenna is arranged on a base station side, the number of the antennas reaches more than dozens, and the base station carries out wireless communication with a plurality of users on the same time frequency resource; the method specifically comprises the following steps:
(1) obtaining a gain coefficient of a radio frequency circuit: setting a gain coefficient measuring unit in a radio frequency circuit at the front end of a transmitting-receiving antenna, wherein the measuring unit sends a reference signal to the radio frequency circuit and receives a signal feedback to estimate the gain coefficients of absolute radio frequency circuits at a base station side and a user side; or, obtaining bidirectional channel estimation through receiving and transmitting reference signals between a reference antenna at the base station side and other antennas, further obtaining a gain coefficient of a relative radio frequency circuit at the base station side, obtaining uplink and downlink channel parameters through receiving and transmitting reference signals between the reference antenna and a user, and further obtaining a gain coefficient of a relative radio frequency circuit at the user side;
(2) user downlink channel estimation: each user sends respective uplink pilot signals on the same time frequency resource, the base station carries out downlink channel estimation of each user according to the received pilot signals and the obtained gain coefficients of the radio frequency circuits at the base station side and the user side, and estimation error statistical information is obtained; the downlink channel estimation is obtained by calculation based on an absolute radio frequency circuit gain coefficient, or is obtained by calculation based on a relative radio frequency circuit gain coefficient combined with the uplink channel estimation;
(3) downlink robust pre-coding data transmission: in the downlink data transmission stage, the base station obtains a robust precoding matrix required by sending data to each user signal by using the acquired downlink channel estimation and the statistical information of the downlink channel estimation error, implements robust precoding, and simultaneously sends data signals to each user on the same time-frequency resource.
The base station side antenna array in the TDD large-scale MIMO wireless communication system comprises more than ten antenna units, the distance between each antenna unit is less than the wavelength of a carrier, and when each antenna adopts an omnidirectional antenna or a 120-degree sector antenna or a 60-degree sector antenna, the distance between each antenna is 1/2 wavelengths orWavelength or 1 wavelength; each antenna unit can adopt a single-polarization antenna or a multi-polarization antenna; the communication process comprises three stages of obtaining of gain coefficients of radio frequency circuits at a base station side and a user side, downlink channel estimation and downlink robust pre-coded data transmission.
The absolute radio frequency circuit gain coefficient in step (1) is calculated by the following formula:
wherein,the reference signal power is transmitted for the gain factor measurement unit,represents the reference signal sent by the gain coefficient measuring unit to the front-end radio frequency circuit module of the antenna m in the t period,for the gain factor measurement unit to receive the reference signal,and an estimated value of a gain coefficient of a radio frequency circuit at the front end of a transmitting antenna or a receiving antenna at the base station side or the user side.
The relative radio frequency circuit gain coefficient of the base station side in the step (1) is calculated by the following formula:
wherein,for the relative RF circuit gain coefficient estimation of the mth antenna on the base station side,for the channel estimation from the mth antenna to the reference antenna on the base station side,channel estimates for the reference antenna to the mth antenna.
The relative gain coefficient of the user side radio frequency circuit in the step (1) is obtained by the following formula:
wherein,for the relative rf circuit gain coefficient estimate for user k,representing the downlink channel estimate from the reference antenna to user k,representing the uplink channel estimation of user k to the reference antenna.
The downlink channel estimation based on the absolute radio frequency circuit gain coefficient in the step (2) specifically comprises: absolute radio frequency circuit gain coefficient estimation based on base station side receiving antennaTransmit antenna absolute radio frequency circuit gain coefficient estimationAbsolute RF circuit gain coefficient for user k receiving antennaAbsolute RF circuit gain factor for transmit antennaAnd pilot signal Y sent by user and received by base stationtrThe downlink channel estimation is obtained by any one of the following three ways:
the first method is as follows: the partial estimation of the wireless channel of user k is obtained by the following formula:
then, the downlink channel estimation is obtained by the following formula:
wherein,for the estimation of the radio channel for user k,covariance matrix, rho, for user k radio channeltrThe signal-to-noise ratio is trained for pilot,the orthogonal pilot sequence transmitted for user k,sending pilot frequency sequence power for a user K, wherein the K is the number of users;
the second method comprises the following steps: firstly, obtaining the uplink channel estimation of a user k by the following formula:
then, the downlink channel estimation is obtained by the following formula:
in the formula,a covariance matrix of an uplink channel for user j;
the third method comprises the following steps: obtaining user k down channel estimation directly by following formula
In the formula,a covariance matrix of a downlink channel for user j;
the covariance matrix of the downlink channel estimation error is calculated as follows:
the downlink channel estimation based on the relative radio frequency circuit gain coefficient in the step (2) specifically comprises the following steps: gain coefficient estimation based on base station side relative radio frequency circuitUser k versus RF circuit gain coefficient estimationAnd the uplink channel estimation obtains the downlink channel estimation, and the downlink channel estimation of the user k is calculated according to the following formula:
whereinFor user k, the uplink channel estimate is calculated by:
the downlink channel estimation error covariance matrix is obtained by the following formula:
whereinFor user k, the uplink channel estimation error is calculated by:
the robust precoding matrix in step (3) is calculated by the following formula:
wherein,for downlink channel estimation, pdlAnd gamma is a base station side transmission power constraint parameter for the average transmission signal-to-noise ratio of downlink transmission of each user, and is calculated by the following formula:
wherein tr represents a matrix trace-solving operation.
Has the advantages that: the large-scale MIMO downlink wireless communication method under the condition of radio frequency circuit mismatch provided by the invention has the following advantages:
1. and under the condition that the channel reciprocity is not satisfied due to the mismatch of the radio frequency circuit, acquiring the downlink channel estimation and the estimation error statistical property thereof, and ensuring the downlink precoding transmission performance.
2. And channel estimation errors are considered during downlink data transmission, so that the robustness and efficiency of system data transmission are improved.
3. The base station may predict the user downlink traversal rate based on the absolute rf circuit gain factor.
Drawings
Fig. 1 is a schematic diagram of a base station side and user side antenna front end transceiving system.
FIG. 2 is a schematic diagram of a gain measurement unit of the RF circuit.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
1. System configuration and communication procedures
Fig. 1 is a schematic diagram of a large-scale antenna array configuration on a base station side, in which an antenna array including more than tens of antenna units is configured on the base station side in consideration of a single-cell base station, and the large-scale antenna array may adopt a linear array, a circular array, a plate array or other array structures. Each antenna unit can adopt an omnidirectional antenna or a sector antenna, and when each antenna unit adopts the omnidirectional antenna, the 120-degree sector antenna and the 60-degree sector antenna, each antennaThe spacing therebetween may be configured to be 1/2 wavelengths,Wavelength and 1 wavelength. Each antenna unit may employ a single-polarized or multi-polarized antenna.
In this embodiment, only narrowband channels are considered, with only a single composite path in the narrowband channels considered, which can be considered as a single subcarrier channel in a conventional wideband OFDM system. Considering Time Division Duplex (TDD) transmission mode, and setting the number of antennas equipped at the base station side as M and the number of users as K, each user is equipped with a single antenna.
The communication process based on the massive MIMO system comprises the following three stages:
i. obtaining gain coefficients of radio frequency circuits at a base station side and a user side: the radio frequency circuit absolute gain coefficient can be obtained by adding a measuring device to a radio frequency circuit at the front end of a receiving and transmitting antenna, the model is shown in fig. 2, the measuring device estimates the radio frequency circuit gain coefficient by sending a reference signal to the radio frequency circuit and receiving a signal feedback, and when a user accesses a base station, the user sends the user-side radio frequency circuit absolute gain coefficient to the base station through a special feedback link; the base station side can select a reference antenna, a bidirectional channel estimation is obtained by transmitting and receiving a reference signal between the reference antenna and other antennas, the base station obtains a relative gain coefficient of a radio frequency circuit at the base station side according to the channel estimation between the reference antenna and other antennas, when a user accesses the base station, the base station refers to the reference signal transmitted and received between the antenna and the user to obtain an uplink and downlink channel parameter between the reference antenna and the user, and then obtains the relative gain coefficient of the radio frequency circuit at the user side.
User downlink channel estimation: each user sends an uplink pilot signal, and the base station side calculates and acquires downlink channel estimation and downlink channel estimation error statistical information by using the received pilot signal and combining the acquired gain coefficient of the radio frequency circuit.
Downlink robust precoded data transmission: the base station utilizes the downlink channel parameter estimation and the statistical information of the estimation error to obtain a robust precoding matrix required by sending data to each user signal, thereby generating a downlink sending signal, the base station sends the downlink sending signal to each user at the same time, and each user carries out receiving processing according to the received signal to obtain a downlink sending bit data stream. In addition, the base station can also predict the user traversal rate based on the gain coefficient of the absolute radio frequency circuit.
2. Obtaining gain coefficients of radio frequency circuits at a base station side and a user side:
(1) absolute gain coefficient acquisition
The gain coefficient of the radio frequency circuit can be obtained by adding a measuring device to the radio frequency circuit at the front end of the receiving and transmitting antenna, the model is shown in fig. 2, the measuring device estimates the gain coefficient of the radio frequency circuit by sending a reference signal to the radio frequency circuit and receiving a signal feedback, and when a user accesses a base station, the user sends the gain coefficient of the radio frequency circuit at the user side to the base station through a special feedback link.
The radio frequency gain coefficient measuring unit sends reference signals to the radio frequency module at the front end of the antenna in a clearance mode, and the gain coefficient of the radio frequency circuit is estimated according to received feedback signals of the radio frequency module. To be provided withRepresents a reference signal sent by the rf gain coefficient measuring unit to the rf circuit module at the front end of the antenna m in the t-th period,the measurement unit of the gain coefficient of the radio frequency circuit estimates the gain coefficient of the radio frequency circuit according to the following formula, wherein the measurement unit of the gain coefficient of the radio frequency circuit receives a feedback signal from the radio frequency circuit module at the front end of the antenna m in the t-th period:
wherein,for the purpose of the reference signal power,which represents an estimate of the gain factor of the rf circuit at the front end of the transmit antenna or receive antenna.
(2) Relative gain factor acquisition
And the base station intermittently transmits the detection signal through the internal antenna to obtain the relative gain coefficient of the radio frequency circuit at the base station side. It is necessary to select one antenna as the reference antenna or to provide a separate additional antenna as the reference antenna.
Suppose that the ith antenna on the base station side is selected as a reference antenna toDenotes a reference signal transmitted to other antennas by the reference antenna during the t-th period,indicating the reference signal received by the mth antenna in the tth period,indicating the reference signals sequentially transmitted by the other antennas to the reference antenna during the t-th period,denotes the reference signal transmitted by the mth antenna received by the reference antenna in t periods, h0→mDenotes the channel parameter from the reference antenna to the m-th antenna, where h0→m＝rbmvmtb0，rbmRepresents the gain coefficient, v, of the RF circuit in the m-th antenna receiving channelmDenotes the radio channel parameter, t, from the reference antenna to the m-th antennab0Indicating the gain factor of the rf circuit in the transmit path of the reference antenna. The reference signal received by the mth antenna can be expressed as:
wherein,is additive white Gaussian noise, has a mean value of zero and a variance ofThe reference signal received by the reference antenna from the mth antenna may be represented as:
wherein h ism→0＝rb0vmtbmFor the channel parameter from the m-th antenna to the reference antenna, rb0Denotes the gain factor, t, of the RF circuit in the receive path of the reference antennabmShows the gain coefficient of the radio frequency circuit in the m-th antenna transmission channel,is additive white Gaussian noise, has a mean value of zero and a variance of
Assuming that the reference signal powers are allThen the channel estimate between the reference antenna and the mth antenna is:
then the relative gain coefficient of the rf circuit of the mth antenna is obtained by:
when user k accesses the base station, the base station firstly sends downlink reference signals to user k through the reference antennaThen user k feeds back the received reference signal to the base station through a special link so as toRepresenting the user k feedback signal received by the reference antenna and assuming the feedback signal received by the base station is accurate, g0→kDenotes the downlink channel parameter from the reference antenna to user k, where g0→k＝rukvktb0，rukRepresenting the gain, v, of the radio frequency circuit in the reception channel of user kkRepresenting the reference antenna to user k radio channel parameters. All downlink reference signal powers areThe downlink channel estimate between the reference antenna and user k is:
wherein,is additive white Gaussian noise, has a mean value of zero and a variance of
User k then transmits uplink reference signal to base stationTo be provided withRepresenting the reference signal received by the reference antenna, gk→0Representing the uplink channel parameters of user k to the reference antenna, where gk→0＝rb0vktuk，tukIndicating the gain of the radio frequency circuit in the transmit channel of reference antenna user k. All uplink reference signal powers areThe uplink channel estimate between user k to the reference antenna is:
wherein,is additive white Gaussian noise, has a mean value of zero and a variance of
The relative gain coefficient of the radio frequency circuit at the user side is obtained by the following formula:
3. user downlink channel estimation
(1) Estimation of downlink channel based on absolute radio frequency circuit gain coefficient
Based on the obtained gain coefficient of the absolute radio frequency circuit, the acquisition of the statistical channel information of each user is completed by an uplink channel detection process. In the uplink, each user intermittently transmits a sounding signal, and the sounding signals of the users are orthogonal to each other.
To be provided withIndicating the probing signal sent by the kth user in the cell in the t-th probing period,represents the detection signal received by the mth antenna of the base station side in the tth detection period, gt,k→mThe channel parameter of the t-th detection period between the k-th user and the m-th antenna at the base station side is shown,represents the channel vector between the k-th user and the M antennas at the base station side,the m-th element of (a) is gt,k→m. Is provided with Where T denotes a matrix transpose. Is provided withWhere H represents the conjugate transpose of the matrix,for the power of the transmitted signal, I is the identity matrix and L is the length of the sounding signal. The sounding signal received by the base station may be represented as:
whereinIs an additive white Gaussian noise matrix, the mean value of each element of the matrix is zero, and the variance is
Is provided withIs a statistical model ofWhere U is a fixed matrix (called a characteristic pattern matrix, e.g., DFT matrix when the base station side antenna employs uniform linear arrays) depending on the base station side antenna configuration, and R isb＝diag{rb1,rb2,…,rbMThe matrix is a gain coefficient matrix of the radio frequency circuit of the receiving antenna at the base station side, rbmThe gain coefficient t of the radio frequency circuit of the mth antenna at the base station sideukTransmitting antenna RF circuit gain coefficient, m, for user kkA vector of channel statistics (each element being a positive value) specific to the kth user,subject to independent homographic assumptions (mean of each element is zero and variance is 1),representing the element-by-element product. BalanceSetting a characteristic mode domain channel vector of the kth user in the t detection periodIn the case where the eigenmode matrix U is known, rkThe statistical channel information of the kth user to be obtained is called a characteristic mode domain channel energy coupling vector.
In the t-th detection period, the signal is firstly receivedObtaining the estimated value of the channel vector of each user characteristic mode domain, wherein the calculation formula is as follows:
wherein denotes that each element takes a conjugate,for the estimation of the gain coefficient of the absolute RF circuit of the antenna at the side of the base station,the antenna absolute rf circuit gain coefficient estimate is sent for user k. Then useAnd sample-enhanced averaging, i.e. the obtainable eigen-mode-domain channel energy coupling vector ekThe calculation formula is as follows:
in the formula, αt'Is a weighting factor, satisfiesNsIs the window size. By ekAnd U can obtain the spatial correlation array of each user wireless channel in the t detection period:
in the formula, diag (e)k) Represents a diagonal matrix whose diagonal elements form a vector ek. Spatial correlation matrix of uplink channel:
spatial correlation matrix of downlink channel:
in the formula,for the base station side transmit antenna absolute rf circuit gain coefficient estimation,receive antenna absolute rf circuit gain coefficient estimation for user k.
And finishing the uplink channel estimation of each user in an uplink training stage. If there are K single-antenna users in a cell, the pilot signals transmitted by the users are orthogonal, i.e.WhereinIn order to transmit the power of the pilot signal,to be provided withIndicating the pilot signal received by the mth antenna of the base station side, gk→m＝rbmwkmtukRepresenting the uplink channel parameter between the kth user and the mth antenna of the base station side in the current training period, wherein wkmRepresenting the radio channel from user k to the mth antenna on the base station side,representing the uplink channel vector between the kth user and the M antennas at the base station side, gkThe m-th element of (a) is gk→m. Is provided withThe pilot signal received by the base station may be represented as:
Ytr＝GulXtr+Ztr (16)
wherein ZtrIs an additive white Gaussian noise matrix, the mean value of each element of the matrix is zero, and the variance is
The base station performs Minimum Mean Square Error (MMSE) estimation according to the received pilot signal, and can obtain downlink channel estimation through the following three ways:
(1) the partial estimation of the wireless channel of user k is obtained by the following formula:
then, the downlink channel estimation is obtained by the following formula:
(2) firstly, obtaining the uplink channel estimation of a user k by the following formula:
then, the downlink channel estimation is obtained by the following formula:
(3) obtaining user k down channel estimation directly by following formula
The downlink channel estimation obtained by the three methods is the same. The estimated mean square error can be calculated as follows:
wherein,
(2) downlink channel estimation based on relative radio frequency circuit gain coefficient
And finishing the uplink channel estimation of each user in the uplink training stage. If there are K single-antenna users in a cell, the pilot signals transmitted by the users are orthogonal, i.e.WhereinFor transmitting pilot signalsThe power of the electric motor is controlled by the power controller,to be provided withIndicating the pilot signal received by the mth antenna of the base station side, gk→m＝rbmvkmtukRepresenting the uplink channel parameter between the kth user and the mth antenna of the base station side in the current training period, wherein vkmRepresenting the radio channel from user k to the mth antenna on the base station side,representing the uplink channel vector between the kth user and the M antennas at the base station side, gkThe m-th element of (a) is gk→m. Is provided withThe pilot signal received by the base station may be represented as:
Ytr＝GulXtr+Ztr (23)
wherein ZtrIs an additive white Gaussian noise matrix, the mean value of each element of the matrix is zero, and the variance is
The statistical information of the uplink channel of each user is assumed to be known by the base station sideThe base station performs Minimum Mean Square Error (MMSE) channel estimation according to the received pilot signal to obtain the estimation value and the MMSE of the uplink channel of each user. The k-th user channel estimate is calculated as:
the estimated mean square error is calculated as:
whereinAnd transmitting the signal-to-noise ratio of each user in the uplink training stage.
By using the obtained uplink channel estimation value and the mean square error of the channel estimation of each user, the downlink channel estimation value can be obtained by the following formula:
in the formula,the mean square error of the downlink channel estimation is obtained by the following formula:
4. downlink robust precoding
With xdlRepresenting the data signals before precoding, which are sent by the base station to K users in the cell at the current moment, wherein the kth element is the sending data signal of the kth user, and the mean value and the variance are set as zero and zeroThe transmission data signal of each user is a data signal obtained by channel coding, interleaving and modulation symbol mapping of the transmission information bit stream. B represents a base station precoding matrix, and the base station side actually transmitsThe signal is Bxdl. With ydlRepresenting data signals received by K users, wherein the kth element is the data signal received by the kth user. With GdlIndicating the downlink channel. The received signal may be expressed as:
ydl＝GdlBxdl+zdl (28)
wherein z isdlIs an additive white Gaussian noise vector, the mean value of each element of the additive white Gaussian noise vector is zero, and the variance is
Under the criterion of average minimum mean square error, the robust precoding matrix of the base station side is calculated by the following formula:
wherein,for the average transmission signal-to-noise ratio of downlink transmission of each user, γ is a base station side transmission power constraint parameter, and can be calculated by the following formula:
wherein tr represents a matrix trace-solving operation.
Each scheduling user can obtain the estimated value of the downlink transmission information bit stream by utilizing the received signal through the processes of demodulation, de-interleaving, channel decoding and the like.
5. User traversal rate prediction based on absolute radio frequency circuit gain coefficient
If the gain coefficient of the absolute rf circuit is obtained, the downlink signal-to-interference-and-noise ratio of user k may be approximated by the following equation:
wherein,
wherein,
in the formula,Ψ is calculated by the following formula,
e[e1,e2,…,eK]the element in (A) is defined as… for t ═ 1,2
And initial valueWhen in useWhen the value is less than the given iteration end value, the iteration is stopped, and the functionAndare respectively defined as:
in the formula,Ψ′IΨ '(I), where Ψ' (D) is defined as a function with respect to D as:
wherein e' (D) ═ e1′(D)…e′K(D)]TCalculated from the following formula:
e′(D)＝[In-J]-1q(D) (43)
wherein J and q (D) are calculated by the formula:
the traversal rate for user k can be approximated by:
the above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (9)
1. A large-scale MIMO downlink wireless communication method under the condition of radio frequency circuit mismatch is suitable for a TDD large-scale MIMO wireless communication system, and is characterized by comprising the following steps:
(1) obtaining a gain coefficient of a radio frequency circuit: setting a gain coefficient measuring unit in a radio frequency circuit at the front end of a transmitting-receiving antenna, wherein the measuring unit sends a reference signal to the radio frequency circuit and receives a signal feedback to estimate the gain coefficients of absolute radio frequency circuits at a base station side and a user side; or, obtaining bidirectional channel estimation through receiving and transmitting reference signals between a reference antenna at the base station side and other antennas, further obtaining a gain coefficient of a relative radio frequency circuit at the base station side, obtaining uplink and downlink channel parameters through receiving and transmitting reference signals between the reference antenna and a user, and further obtaining a gain coefficient of a relative radio frequency circuit at the user side;
(2) user downlink channel estimation: each user sends respective uplink pilot signals on the same time frequency resource, the base station carries out downlink channel estimation of each user according to the received pilot signals and the obtained gain coefficients of the radio frequency circuits at the base station side and the user side, and estimation error statistical information is obtained; the downlink channel estimation is obtained by calculation based on the gain coefficient of an absolute radio frequency circuit in combination with the uplink channel estimation, or is obtained by calculation based on the gain coefficient of a relative radio frequency circuit in combination with the uplink channel estimation;
(3) downlink robust pre-coding data transmission: in the downlink data transmission stage, the base station obtains a robust precoding matrix required by sending data to each user signal by using the acquired downlink channel estimation and the statistical information of the downlink channel estimation error, implements robust precoding, and simultaneously sends data signals to each user on the same time-frequency resource.
2. The large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the base station side antenna array in the TDD large-scale MIMO wireless communication system comprises more than ten antenna units, the distance between each antenna unit is less than the wavelength of a carrier, and each antenna unit can adopt a single-polarization antenna or a multi-polarization antenna.
3. The large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the absolute radio frequency circuit gain coefficient in step (1) is calculated by the following formula:
wherein,the reference signal power is transmitted for the gain factor measurement unit,represents the reference signal sent by the gain coefficient measuring unit to the front-end radio frequency circuit module of the antenna m in the t period,for the gain factor measurement unit to receive the reference signal,and an estimated value of a gain coefficient of a radio frequency circuit at the front end of a transmitting antenna or a receiving antenna at the base station side or the user side.
4. The large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the relative radio frequency circuit gain coefficient of the base station side in the step (1) is calculated by the following formula:
wherein,for the relative RF circuit gain coefficient estimation of the mth antenna on the base station side,for the channel estimation from the reference antenna to the mth antenna, it is calculated by:
wherein,in order to transmit the power of the reference signal,for reference signals transmitted by the antenna during the t-th period,a reference signal transmitted by a reference antenna received by the mth antenna;
for the channel estimation from the mth antenna to the reference antenna on the base station side, the channel estimation is calculated by the following formula:
wherein,for the reference signal transmitted by the mth antenna to the reference antenna in the tth period,the reference signal is the reference signal sent by the mth antenna received by the reference antenna in the tth period.
5. The large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the relative gain coefficient of the user side radio frequency circuit in the step (1) is obtained by the following formula:
wherein,for the relative rf circuit gain coefficient estimate for user k,representing the downlink channel estimate from the reference antenna to user k, is calculated by:
wherein,for the purpose of the reference signal power,for the reference signal received by the user k,a downlink reference signal transmitted for a reference antenna;
representing the uplink channel estimate for user k to the reference antenna, is calculated by:
wherein,for reference to the reference signal received by the antenna,and transmitting an uplink reference signal to the base station for the user k.
6. The large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the downlink channel estimation based on the absolute radio frequency circuit gain coefficient in the step (2) specifically comprises: absolute radio frequency circuit gain coefficient estimation based on base station side receiving antennaTransmit antenna absolute radio frequency circuit gain coefficient estimationAbsolute RF circuit gain coefficient for user k receiving antennaAbsolute RF circuit gain factor for transmit antennaAnd pilot signal Y sent by user and received by base stationtrThe downlink channel estimation is obtained by any one of the following three ways:
the first method is as follows: the partial estimation of the wireless channel of user k is obtained by the following formula:
then, the downlink channel estimation is obtained by the following formula:
wherein,for the estimation of the radio channel for user k,for the covariance matrix of the radio channel for user k,the covariance matrix of the wireless channel for user j, K being the number of users, ρtrThe signal-to-noise ratio is trained for pilot,the orthogonal pilot sequence transmitted for user k,transmitting pilot sequence power for user k;
the second method comprises the following steps: firstly, obtaining the uplink channel estimation of a user k by the following formula:
then, the downlink channel estimation is obtained by the following formula:
in the formula,the covariance matrix of the uplink channel for user j,a covariance matrix of an uplink channel for a user k;
the third method comprises the following steps: obtaining user k down channel estimation directly by following formula
In the formula,for the covariance matrix of the downlink channel for user j,a covariance matrix of a downlink channel for user k;
the covariance matrix of the downlink channel estimation error is calculated as follows:
7. the large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the downlink channel estimation based on the relative radio frequency circuit gain coefficient in the step (2) specifically comprises the following steps: gain coefficient estimation based on base station side relative radio frequency circuitUser k versus RF circuit gain coefficient estimationAnd the uplink channel estimation obtains the downlink channel estimation, and the downlink channel estimation of the user k is calculated according to the following formula:
whereinFor user k, the uplink channel estimate is calculated by:
where ρ istrThe signal-to-noise ratio is trained for pilot,orthogonal pilot sequence, Y, transmitted for user ktrThe pilot signals transmitted for the users received by the base station,the pilot sequence power is transmitted for user k,a covariance matrix of an uplink channel of a user j is obtained, and K is the number of users;
the downlink channel estimation error covariance matrix is obtained by the following formula:
whereinFor user k, the uplink channel estimation error is calculated by:
8. the large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the robust precoding matrix in step (3) is calculated by the following formula:
wherein,for the purpose of the estimation of the downlink channel,for the downlink channel estimation for user k,estimating an error covariance matrix, ρ, for a downlink channeldlAnd gamma is a base station side transmission power constraint parameter for the average transmission signal-to-noise ratio of downlink transmission of each user, and is calculated by the following formula:
wherein tr represents a matrix trace-solving operation.
9. The large-scale MIMO downlink wireless communication method according to claim 1, wherein the method comprises: the method also comprises the step that the base station predicts the user traversal rate based on the absolute radio frequency circuit gain coefficient, and the user traversal rate is calculated according to the following formula:
wherein,the downlink signal-to-interference-and-noise ratio prediction for user k is calculated by the following formula:
wherein,
wherein,
in the formula,Ψ is calculated by the following formula,
e[e1,e2,…,eK]the element in (A) is defined as… for t ═ 1,2
And initial valueWhen in useLess than a given iterationAt the end value, the iteration stops, the functionAndare respectively defined as:
wherein,Ψ′IΨ '(I), where Ψ' (D) is defined as a function with respect to D as:
wherein e '(D) ═ e'1(D)…e′K(D)]TCalculated from the following formula:
e′(D)＝[In-J]-1q(D)
wherein J and q (D) are calculated by the formula:
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| CN103546264A (en) * | 2013-11-13 | 2014-01-29 | 东南大学 | Large-scale MIMO wireless communication method based on pilot frequency multiplex |
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