CN111988250B - Simulation full-connection hybrid beam forming system and transmitter - Google Patents
Simulation full-connection hybrid beam forming system and transmitter Download PDFInfo
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Abstract
A digital predistortion architecture, an analog full-link hybrid beamforming system and a transmitter, the digital predistortion architecture comprising: the time delay alignment module is used for aligning the equivalent power amplifier output signal of the power amplifier array in the digital domain with the equivalent power amplifier input signal of the power amplifier array in the digital domain in time; the multi-beam estimation module is used for synthesizing the equivalent power amplifier output signals after time alignment into equivalent multi-beam signals in a digital domain according to the beam forming conditions; the predistorter training module is used for training based on the equivalent multi-beam signal and a transmitting signal of a transmitting link to obtain a model of the Q input predistorter, wherein Q is more than or equal to 2; and the multi-input multi-output predistorter module comprises Q input predistorters, and each predistorter is used for carrying out linearization correction on Q transmitting signals transmitted by the connected transmitting link. The adjacent channel frequency spectrum leakage is obviously inhibited, and the signal linearity in the beam direction is obviously improved.
Description
Technical Field
The present disclosure belongs to the field of mobile communication technologies, and relates to a digital predistortion structure, a simulated full-connection hybrid beamforming system, and a transmitter, and in particular, to a digital predistortion structure for a simulated full-connection hybrid beamforming system, a simulated full-connection hybrid beamforming system including the digital predistortion structure, and a transmitter.
Background
Modern wireless communication systems widely employ multiple-input multiple-output (MIMO) technology to support a dramatically increasing number of users. In the coming 5G era, the number of radio frequency links of the transmitter is further increased, and correspondingly, a large-scale MIMO (MIMO) technology becomes a vital technology in the 5G transmitter, so that the network capacity and the transmission data rate are expected to be remarkably increased, and the communication reliability is improved. Massive MIMO systems are often combined with Beamforming (BF) techniques to improve spectral efficiency, and Hybrid Beamforming (HBF) architectures make a trade-off between flexibility and complexity of beamforming, which is a promising beamforming solution in massive MIMO systems.
There are two typical architectures for massive MIMO hybrid beamforming systems, namely, sub-array-based architecture (SA) and analog-connected architecture (FC). A Power Amplifier (PA) is one of the most power consuming devices in a transmitter and produces significant nonlinear distortion when operating in the high efficiency region. In order to meet the requirements of transmitter linearity and efficiency, digital Predistortion (DPD) technology has been widely used in transmitters. In a conventional digital predistortion architecture, each PA requires a dedicated predistorter and feedback loop to observe and cancel the nonlinear distortion itself generates. However, in the hybrid massive MIMO transmitter, the number of transmission chains is far less than the number of antennas and PAs, and each path of digital signal needs to drive multiple PAs, so the conventional scheme of configuring one DPD module for each PA for independent linearization is practically impossible.
Most of the existing researches are mainly directed to digital predistortion schemes for hybrid beam forming systems of subarray connection architectures, because of the structural difference between the hybrid beam forming systems of subarray connection architectures and the hybrid beam forming systems of analog full connection architectures, the existing digital predistortion schemes for hybrid beam forming systems of subarray connection architectures are not suitable for analog full connection hybrid beam forming systems, signals from different transmission links are combined before a power amplifier, and radio frequency signals containing each path of transmission signals generate complex nonlinear intermodulation distortion after passing through the power amplifier.
Disclosure of Invention
Technical problem to be solved
The present disclosure provides a digital predistortion architecture, an analog full-link hybrid beamforming system and a transmitter to at least partially solve the technical problems set forth above.
(II) technical scheme
According to one aspect of the present disclosure, a digital predistortion architecture is provided. The digital predistortion architecture comprises: the time delay alignment module is used for aligning the equivalent power amplifier output signal of the power amplifier array in the digital domain with the equivalent power amplifier input signal of the power amplifier array in the digital domain in time; the multi-beam estimation module is used for synthesizing the equivalent power amplifier output signals after time alignment into equivalent multi-beam signals in a digital domain according to the beam forming conditions; the predistorter training module is used for training based on the equivalent multi-beam signal and the transmitting signal of the transmitting link to obtain a Q input predistorter model, wherein Q is more than or equal to 2; and the multi-input multi-output predistorter module comprises Q input predistorters, and each predistorter is used for carrying out linearization correction on Q transmission signals transmitted by the connected transmission link.
According to an embodiment of the present disclosure, the inputs of the model of the Q input predistorter are: equivalent multi-beam signal r 1 、r 2 、…r Q The output is: transmission signal x of a transmission chain 1 、x 2 、…x Q The solved parameter is the coefficient vector of the model
The goal of the training is to achieve a linearized relationship of the output and the input.
According to an embodiment of the present disclosure, the predistorter training module includes: the model construction submodule is used for constructing a Q-dimensional behavior model with K-order nonlinear orders and M-order memory depth; and the model training sub-module is used for taking the beam signal as input, taking the transmitting signal of the transmitting link as output, and training on the basis of the Q-dimensional behavior model to obtain a Q-input predistorter model.
According to an embodiment of the present disclosure, the model of the Q input predistorter is:
wherein the content of the first and second substances,
is a vector of dimension L multiplied by 1, L represents the number of sample points;
a transmitting signal matrix formed by sample points of L transmitting signals of a q transmitting chain of a digital domain; the value of Q is 1,2, …, Q;
is r q (n)，…，r q A matrix of (n + L-1); r is a radical of hydrogen q (n)，…，r q (n + L-1) represents the q wave beam signal sample points of the digital domain at the sampling time n, … …, n + L-1 corresponding to the 1 st, …, L wave beam signal sample points respectively; n, … …, n + L-1 all represent sampling time;
representing a coefficient vector; m represents the memory depth; k represents the maximum value of the non-linear order.
According to the embodiment of the present disclosure, in the Q-dimensional behavior model, the expression of the qth, Q =1,2, …, Q, beam signal satisfies:
wherein r is q (n) represents the beam signal sample point of the q-th beam signal at sampling instant n; m represents the memory depth; k represents the maximum value of the nonlinear order; k is a radical of 1 、k 2 、…、k Q-1 Respectively represent|x 1 (n-m)|、 |x 2 (n-m)|、...、|x Q-1 The non-linear order of the (n-m) | term; c. C q (m，k...k Q-1 ) Representing the coefficients; x is the number of 1 (n-m)、…、 x q (n-m)、…、x Q-1 (n-m)、x Q (n-m) represents the signal value of the 1 st, the.
According to an embodiment of the present disclosure, the digital predistortion structure further includes: and the equivalent analog beam forming module is used for weighting and summing the digitally coded transmission signals of the Q transmission links to obtain equivalent power amplifier input signals of each power amplifier in the power amplifier array.
According to the embodiment of the disclosure, the equivalent power amplifier output signal of the power amplifier array in the digital domain is obtained by the following method: and filtering, down-converting and analog-to-digital converting the power amplifier output signals of the power amplifier array to obtain equivalent power amplifier output signals.
Another aspect of the present disclosure also provides an analog fully-connected hybrid beamforming system. The system comprises: q transmitting links, wherein Q is more than or equal to 2; and any of the digital predistortion architectures mentioned above. The input ends of the Q transmission links are connected with the output ends of the multi-input multi-output predistorter modules in the digital predistortion structure, and each predistorter is used for carrying out linearization correction on Q transmission signals transmitted by the connected transmission links.
According to an embodiment of the present disclosure, the analog fully-connected hybrid beamforming system further comprises sequentially connected: the antenna comprises a digital-to-analog conversion module, a mixer, a power division module, an analog beam forming module, a power amplifier array and P antennas, wherein Q is less than or equal to P, and the power amplifier array comprises P power amplifiers.
Yet another aspect of the present disclosure also provides a transmitter including a digital predistortion architecture or an analog fully connected hybrid beamforming system as described above.
(III) advantageous effects
According to the technical scheme, the digital predistortion structure, the analog full-connection hybrid beam forming system and the transmitter have the following beneficial effects:
the method comprises the steps that a plurality of beam signals transmitted by an antenna array are used as linearization targets, equivalent multi-beam signals for beam forming based on a digital domain and transmission signals of a transmission link are trained to obtain a model of a Q input predistorter, and the Q input predistorter can carry out linearization correction on Q-path transmission signals transmitted by each connected transmission link (radio frequency link), so that the problem of poor quality of received signals caused by intermodulation distortion of signals from each transmission channel and nonlinear distortion of each transmission channel in the array beam signals is solved. Based on the digital predistortion structure provided by the disclosure, adjacent channel frequency spectrum leakage of a full-connection hybrid beam forming system is remarkably inhibited, and signal linearity in a beam direction is obviously improved.
Drawings
Fig. 1 is a block diagram of (a) a hybrid beamforming system of a sub-array connection architecture and (b) a hybrid beamforming system of an analog full-connection architecture in the prior art.
Fig. 2 is a block diagram illustrating a digital predistortion architecture for an analog fully-connected hybrid beamforming system according to an embodiment of the present disclosure.
Fig. 3 is a simulated array radiation pattern of an analog fully-connected hybrid beamforming system including a digital predistortion structure according to an embodiment of the present disclosure.
Fig. 4 is a diagram illustrating simulated Adjacent Channel Power Ratio (ACPR) as a function of azimuth for an analog fully-connected hybrid beamforming system including a digital predistortion architecture, according to an embodiment of the present disclosure.
Fig. 5 is a graph of experimental comparison results comparing power spectrum analysis of signals in one exemplary beam direction for a simulated fully-connected hybrid beamforming system with and without a digital predistortion structure.
Fig. 6 is a graph of experimental comparison results comparing power spectrum analysis of signals in one exemplary beam direction for a simulated fully-connected hybrid beamforming system with and without a digital predistortion structure.
[ description of symbols ]
11-a predistortion training module; 12-a multi-beam estimation module;
13-a delay alignment module; 14-equivalent analog beamforming module;
20-multiple input multiple output predistorter module.
Detailed Description
The massive MIMO hybrid beamforming system has two typical architectures, namely a subarray connection-based architecture and an analog full-connection architecture.
Fig. 1 is a block diagram of (a) a hybrid beamforming system of a sub-array connection architecture and (b) a hybrid beamforming system of an analog full-connection architecture in the prior art.
Referring to fig. 1 (a), assuming that the size of a massive MIMO antenna array is P, the system includes N transmit chains, and in a hybrid beamforming array based on a sub-array connection architecture, each transmit chain generates P/N (P divided by N) radio frequency signals, which are respectively illustrated as a radio frequency chain 1, … …, and a radio frequency chain N, through a power division network and a phase shifter network, and then is respectively connected to a part of antennas (P/N) in the array. Each sub-array generates a beam to transmit signals of a corresponding transmission link, so that a hybrid beamforming array based on a sub-array connection architecture can be considered to be composed of a plurality of active phased arrays. Since each transmit chain is connected to only a portion of the antennas, the available antenna array gain is reduced.
Referring to fig. 1 (b), in order to fully utilize the high directional gain of the large-scale antenna array, in the hybrid beamforming array of the analog fully-connected architecture, signals in each transmit link are recombined into P radio frequency signals through a power division-phase shift-combining network, and the P radio frequency signals are respectively connected to all antennas in the array. The entire antenna array generates N beams, which respectively transmit N signals corresponding to each transmit link.
Currently, the research on the predistortion linearization scheme of the hybrid beamforming array is mainly directed to the hybrid beamforming array based on the sub-array connection architecture, and there is a fresh research on simulating the linearization of the HBF array under the full connection architecture. In a sub-array connection-based architecture, since each transmit chain is connected to only one antenna sub-array, the complete array can be seen as being formed by a series of independent sub-phased arrays. In this case, the antennas and amplifiers in each sub-array only transmit the signal stream from one transmit chain, so one single-input single-output (SISO) model can be used for modeling and linearization for each sub-array, and one predistorter is configured for each transmit chain to linearize the beam signal of each sub-array. The scheme is that a main beam synthesis module is configured in a digital domain to estimate a main beam signal of each sub-array.
However, since the analog fully-connected architecture is very different from the sub-array-connected architecture, the above scheme is not suitable for the hybrid beamforming array of the analog fully-connected architecture. In the analog fully-connected hybrid beamforming array, as can be seen from comparing (a) and (b) in fig. 1, since the transmit signals from all the transmit chains are phase-shifted and combined by the analog beamforming network located at the front end of the amplifier, the intermodulation distortion between different transmit signals is generated after the mixed signals pass through the amplifier, and then the problem of linearization of digital predistortion in the hybrid beamforming array of the analog fully-connected architecture is more troublesome.
Therefore, it is desirable to provide a technical solution that can not only eliminate the independent nonlinear distortion of each signal in the transmission link, but also eliminate the intermodulation distortion between different transmission signals. In this case, the conventional single-input single-output (SISO) DPD modeling scheme, which is applicable to sub-array architectures, is no longer applicable to HBF arrays that are capable of linearizing analog full connections.
The present disclosure provides a digital predistortion structure, an analog full-link hybrid beamforming system and a transmitter. The method comprises the steps of taking beam signals simultaneously transmitted by an antenna array as a linearization target, configuring a predistorter for linearizing the beam signals corresponding to each transmission link signal in each radio frequency link based on a multi-input multi-output predistorter module as intermodulation distortion of each transmission channel signal exists in the array beam signals, wherein each predistorter is of a multi-input (Q-input) structure, calculating and generating predistortion signals by using the transmission signals of all the radio frequency links, and training Q-dimensional predistorter models according to digitally synthesized multi-beam signals and all the transmission signals so as to compensate for severe nonlinear distortion in the beam signals.
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
A first exemplary embodiment of the present disclosure provides a digital predistortion architecture that may be used in an analog fully connected hybrid beamforming system to achieve linearization correction.
Fig. 2 is a block diagram illustrating a digital predistortion architecture for an analog fully-connected hybrid beamforming system according to an embodiment of the present disclosure. In fig. 2, the blocks of the digital domain are filled with dots.
Referring to fig. 2, a digital predistortion structure of an embodiment of the present disclosure includes: a mimo predistorter module 20, a predistorter training module 11, a multi-beam estimation module 12, and a delay alignment module 13.
The mimo predistorter module 20 includes Q number of input predistorters, each predistorter is configured to perform a linearization correction on Q number of transmit signals transmitted by a connected transmit chain.
The time delay alignment module 13 is configured to perform time alignment between an equivalent power amplifier output signal of the power amplifier array in the digital domain and an equivalent power amplifier input signal of the power amplifier array in the digital domain.
The multi-beam estimation module 12 is configured to synthesize the time-aligned equivalent power amplifier output signals into equivalent multi-beam signals in a digital domain according to a beam forming condition.
The predistorter training module 11 is configured to train based on the equivalent multi-beam signal and the transmission signal of the transmission link to obtain a model of the Q-input predistorter.
Referring to fig. 2, the equivalent power amplifier output signal of the power amplifier array in the digital domain can be obtained by: the power amplifier output signal (analog signal) of the power amplifier array is filtered, down-converted and analog-to-digital converted to obtain an equivalent power amplifier output signal. In fig. 2, a mixer is illustrated, the local oscillator frequency of which is LO, and an analog-to-digital converter (ADC).
According to an embodiment of the present disclosure, the digital predistortion structure may further include: an equivalent analog beamforming module 14. The equivalent analog beamforming module 14 is configured to perform weighted summation on the digitally encoded transmit signals of the Q transmit chains to obtain an equivalent power amplifier input signal of each power amplifier in the power amplifier array.
Referring to fig. 2, the equivalent power amplifier input signal of the power amplifier array in the digital domain can be obtained by: and weighting the transmission signal of the transmission link after digital coding by an equivalent analog beam forming module 14 to obtain an equivalent power amplifier input signal. The equivalent analog beamforming module performs weighted summation on the transmission signals of the Q transmission chains in the digital domain to form equivalent input signals of each power amplifier in the power amplifier array, for example, refer to the form in the following expression (1).
In fig. 2, the equivalent power amplifier output signal of the power amplifier array in the digital domain is represented as:
the equivalent power amplifier input signal in the digital domain of the power amplifier array is represented as:
the user represents the total number of transmit chains.
The multi-beam estimation module 12 is configured to synthesize the time-aligned equivalent power amplifier output signals into equivalent multi-beam signals in a digital domain according to a beam forming condition. The multi-beam estimation matrix is shown, for example, with reference to the subsequent expression (4), (10) or (14)
Is h as an element of pq 。
The predistorter training module 11 is configured to train based on the equivalent multi-beam signal and the transmission signal of the transmission link to obtain a model of the Q-input predistorter. The inputs to the model of the Q-input predistorter are: equivalent multi-beam signal r 1 、r 2 、…r Q Output as a transmission signal x of the transmission chain 1 、x 2 、…x Q The solved parameter is the coefficient vector of the model
The goal is to achieve a linearized relationship of output and input. Coefficient vectors of the model can be subjected to machine learning or deep learning or iteration
And (6) solving. For example, the coefficient vector of the model can be calculated by the least square method shown in equation (19)
And (6) solving.
In this embodiment, the predistorter training module 11 includes: the model construction submodule is used for constructing a Q-dimensional behavior model with K-order nonlinear orders and M-order memory depth; and the model training sub-module is used for taking the beam signal as input, taking the transmitting signal of the transmitting link as output, and training on the basis of the Q-dimensional behavior model to obtain a Q-input predistorter model. The specific training process comprises the following steps: constructing a Q-dimensional behavior model with K-order nonlinear order and M-order memory depth; and taking the beam signal as input, taking the transmitting signal of the transmitting link as output, and training based on the Q-dimensional behavior model to obtain a Q-input predistorter model. The expression form of the model of the Q-input predistorter can be shown by referring to the subsequent expression (16), and the model is trained based on the Q-dimensional behavior model to obtain the coefficient vector of the model
Coefficient vector of model
The expression of (c) can be expressed with reference to the formula (18).
The predistorter is of a Q-input single-output structure and can generate independent predistortion signals of each channel according to the transmission signals of all the channels.
In the present disclosure, a behavior model of the response of the power amplifier array in the analog fully-connected hybrid beamforming system without the digital predistortion structure is derived to illustrate the mechanism of the array nonlinearity, that is, the nonlinear behavior of the power amplifier array in the analog fully-connected hybrid beamforming system is presented without linearization processing. Then, by combining the characteristics of the hybrid beam forming system, a simplified multi-dimensional nonlinear behavior model is further provided, the model can be used in a pre-distorter training module, and the model is trained in the pre-distorter training module to obtain the coefficients of each pre-distorter model, so that modeling and linearization correction of multi-beam signals simultaneously transmitted by the simulation fully-connected hybrid beam forming system are realized.
The input signal of the p-th power amplifier in the power amplifier array can be regarded as a weighted sum of the transmission signals of the respective transmission chains, and the input signal of the p-th power amplifier in the power amplifier array is expressed by the following expression:
wherein s is p (n) represents the input signal of the p-th power amplifier in the power amplifier array at the sampling time n; n represents a sampling instant; x is the number of q (n) represents the transmitted signal from the qth transmit chain at sampling instant n; w is a pq A beamforming weight coefficient, w, representing that the transmit signal of the qth transmit chain forms the input signal of the pth power amplifier p1 ，...，w pQ Q =1, …, Q, respectively. The transmit signal and the input signal are both complex envelope signals.
The same parameters are directly defined in the following description using the previous definitions and will not be described in detail after the following description.
The non-linear behavior of the power amplifier array (power amplifier may be referred to as power amplifier in the following description) can be represented by a memory polynomial model. The output signal of the pth power amplifier in the power amplifier array can be expressed as the following expression:
wherein, y p (n) represents the output signal of the p-th power amplifier in the power amplifier array at the sampling time n; s p (n-m) represents the input signal of the p-th power amplifier in the power amplifier array at the sampling time n-m; n, m and n-m all represent sampling time; m represents the memory depth; k represents the nonlinear order; k represents the maximum value of the nonlinear order;
representing the coefficients of the p-th power amplifier.
For the convenience of analysis, in the present disclosure, referring to fig. 2, it is assumed that P power amplifiers are in the array, and the behavior model of each power amplifier has the same nonlinear order and memory depth.
Substituting formula (1) into formula (2), the output signal of the pth power amplifier in the power amplifier array can be expressed as the following expression:
the output signals of the P power amplifiers are sent to each user end distributed in space through P transmitting antennas, refer to user 1, user 2, …, and user Q illustrated in fig. 2, where Q is not greater than P. In consideration of beamforming and spatial phase superposition effects, the beam signal received by the qth user receiver may be represented in the form:
wherein r is q (n) represents the beam signal sample point of the q-th beam signal at sampling instant n; h is a total of pq Representing the channel response from the p-th transmit antenna to the q-th user receiver.
As can be seen from equation (4), significant intermodulation distortion from each transmit channel signal is generated in the far-field beam signal, which severely degrades the quality of the user's received signal, and thus, linearization compensation is urgently needed.
Equation (4) represents a nonlinear system with Q input signals. In general, a multidimensional Volterra series model based on Q-inputs can accurately describe such nonlinear systems. However, the Volterra model consumes a huge amount of calculation, and considering that the predistortion algorithm needs to be implemented in a simulated full-connected hybrid beam forming system in real time, the amount of calculation needs to be reduced, so the model needs to be simplified. The following formula (5) is a simplified form of the multidimensional Volterra model, the simplified multidimensional Volterra model is a multidimensional polynomial model having only odd-order,
although the model illustrated by the above formula (5) is simplified to some extent, the complexity of the model is still unbearable in a practical system. Therefore, the invention further provides a simplified multidimensional nonlinear behavior model by combining the characteristics of the hybrid beam forming system, and realizes modeling and linear correction of multi-beam signals simultaneously transmitted by the simulation fully-connected hybrid beam forming system.
To derive a multi-dimensional nonlinear behavior model and to illustrate the concept behind it, the present disclosure reduces the nonlinear model of the power amplifier to a memoryless fifth-order polynomial model, and for simplicity of illustration, the input signal s of the pth power amplifier, assuming that only two transmit chains are included in the transmitter comprising the massive MIMO system, is p And an output signal y p Corresponding to tableExpressions (6) and (7):
s p ＝w p1 x 1 +w p2 x 2 (6)，
in the above expressions of equations (6) and (7), the time argument is omitted for the sake of simplifying the expression, e.g., s p Is s p Abbreviation of (n).
Substituting the formula (6) into the formula (7) and obtaining the output signal of the pth power amplifier through direct mathematical operation, wherein the expression is as follows:
wherein, the shape is as follows () * Represents the conjugate of ().
In an analog beamforming network, phase shifters are used to control the beam direction so that the individual beams transmitted by the array are directed to the receiver of each user, and typically, the beamforming weight coefficients satisfy:
|w pq |＝1(q＝1，2) (9)。
at this time, the beam signal received by the qth (q =1,2) user receiver can be expressed as:
beamforming can be equivalent to a kind of spatial filtering by designing beamforming weight coefficients to achieve a certain "spatial shape" of the radiation pattern. Therefore, the intermodulation terms in equation (10) can be classified into three categories, which are referred to as (1), (2), and (3), respectively, according to the beamforming effect.
First, in order to achieve Maximum Ratio Transmission (MRT), the beamforming weight coefficients should be properly selected so that the signal-to-noise ratio at the user receiver is maximized. In this case, h pq And w pi The constraints that should be satisfied are:
h pq w pi ＝1，i＝q (11)，
this indicates that, for the received signal of user 1 (q = 1), the terms in the (1) group are superimposed in phase. Similarly, for the received signal of user 2 (q = 2), the terms in the (2) group are superimposed in phase.
Second, to eliminate multi-user interference at the target receiver, a corresponding "Zero Forcing (ZF)" design is required, having the following relationship:
h pq w pi →0，i≠q (12)。
thus, the item numbered (2) group in the beam signal of user 1 and the item numbered (1) group in the beam signal of user 2 are minimized, so that these items can be ignored in the user reception signal.
Finally, due to the high beam directivity of large antenna arrays and the influence of some power control mechanisms, the radiation power of the side lobes and other directions is much lower than that of the beam direction, so the item numbered in the group (3) in the beam signals of user 1 and user 2 can be ignored.
Based on the above analysis, the beam signal received by the q-th (q =1,2) user receiver is simplified as follows:
wherein, the first and the second end of the pipe are connected with each other,
and
representing the recombined coefficients.
Without loss of generality, the model can be generalized to a Q-dimensional behavior model with K-order nonlinear order and M-order memory depth, and then the model expression r of the Q-th (Q =1,2, …, Q) beam signal q (n) may be expressed as:
wherein r is q (n) represents a beam signal sample point of the q-th beam signal at sampling instant n; k is a radical of 1 、 k 2 、…、k Q-1 Respectively represent | x 1 (n-m)|、|x 2 (n-m)|、...、|x Q-1 The non-linear order of the (n-m) | term; c. C q (m，k...k Q-1 ) Representing the coefficients; x is a radical of a fluorine atom 1 (n-m)、…、x q (n-m)、…、x Q-1 (n-m)、x Q (n-m) represents the signal value of the 1 st, the. In the whole text, the subscript of a certain parameter indicates the serial number corresponding to the parameter.
The inverse model as shown in (14) is used to approximate the model of the predistorter by exchanging input and output signals, with the beam signal as input and the transmit signal of the transmit chain as output, as shown with reference to the following expression (15):
wherein d is q (m，k...k Q-1 ) Representing the coefficients of the qth predistorter model.
The predistorter model shown in the above equation (15) can be expressed in a matrix form, and the expression is as follows:
wherein the content of the first and second substances,
is a vector of dimension L multiplied by 1, L represents the number of sample points;
a transmitting signal matrix formed by sample points of L transmitting signals of a q transmitting chain of a digital domain; the value of Q is 1,2, …, Q;
is r q (n)，…，r q A matrix of (n + L-1); r is q (n)，…，r q (n + L-1) represents the q wave beam signal sample points of the digital domain at the sampling time n, … …, n + L-1 corresponding to the 1 st, …, L wave beam signal sample points respectively; n, … …, n + L-1 all represent sampling time;
representing a coefficient vector; m represents the memory depth; k represents the maximum value of the non-linear order. Matrix [ 2 ]]The T in the upper right corner represents the transpose of the matrix.
The coefficient vector in the model of the predistorter can be determined by a Least Squares (LS) algorithm, and the calculation expression is:
wherein H represents the conjugate transpose symbol of the matrix;
to represent
The conjugate transpose of (1); () -1 Representing the inverse of the matrix.
On the basis of the first embodiment, a second exemplary embodiment of the present disclosure provides an analog fully-connected hybrid beamforming system including the above-described digital predistortion structure.
Referring to fig. 2, the analog fully-connected hybrid beamforming system of the present embodiment includes: q transmit chains, P antennas, and a digital predistortion structure, the digital predistortion structure comprising: a mimo predistorter module 20, a predistorter training module 11, a multi-beam estimation module 12, and a delay alignment module 13.
The mimo predistorter module 20 includes Q number of input predistorters, each predistorter is configured to perform a linearization correction on Q number of transmit signals transmitted by a connected transmit chain. Each predistorter is a Q-input single-output predistorter, with the Q predistorters having Q × Q inputs and Q outputs overall.
The time delay alignment module 13 is configured to perform time alignment between an equivalent power amplifier output signal of the power amplifier array in the digital domain and an equivalent power amplifier input signal of the power amplifier array in the digital domain.
The multi-beam estimation module 12 is configured to synthesize the time-aligned equivalent power amplifier output signals into equivalent multi-beam signals in a digital domain according to a beam forming condition.
The predistorter training module 11 is configured to train based on the equivalent multi-beam signal and the transmission signal of the transmission link to obtain a model of the Q-input predistorter.
The input ends of the Q transmit chains are connected to the output end of the mimo predistorter module 20, and each predistorter is configured to perform linearization correction on Q transmit signals transmitted by the connected transmit chains. The radio frequency link 1, the radio frequency link 2, … …, and the radio frequency link Q are used to represent Q transmission links, and referring to fig. 2, an input end of each of the Q transmission links is connected to one predistorter, for example, an output end of the predistorter 1, the predistorter 2, … …, and the predistorter Q is sequentially connected to an input end of the radio frequency link 1, the radio frequency link 2, the radio frequency link … …, and the radio frequency link Q. The input signal in each transmitting link is processed by a digital-to-analog conversion module, a mixer, a power division module and a beam forming module in sequence, recombined into a P-path radio frequency signal and input into a power amplifier array. The power amplifier array includes P power amplifiers. The analog beam forming module is used for synthesizing a plurality of beam signals simultaneously transmitted by the power amplifier array according to the beam forming coefficient and the channel response. The analog beamforming module may include: phase shift module and combiner module.
Because the input signal in each transmission link is already linearized and corrected in the predistorter, the signal transmitted in the transmission link is recombined into P paths of radio frequency signals after digital-to-analog conversion, up-conversion, power division-phase shift-combining processing, and the P paths of radio frequency signals are input into the power amplifier array, and the linearized signals are sent to each user end distributed in space through P antennas, refer to user 1, user 2, … and user Q illustrated in fig. 2, where Q is not more than P, and thus, the improvement of the quality of the signal received by the user is achieved.
The third exemplary embodiment of the present disclosure also provides a transmitter including the above-mentioned digital predistortion structure or analog full-link hybrid beamforming system.
The present disclosure also performs feasibility simulation and experimental verification on the fully-connected hybrid beamforming system including predistortion structure simulation.
Fig. 3 is a simulated array radiation pattern of an analog fully-connected hybrid beamforming system including a digital predistortion structure according to an embodiment of the present disclosure.
The simulation scenario is that a 4-channel 64-unit simulation full-connected hybrid beamforming system, beamforming coefficients are designed, beam directions pointing to four users are 20 °, 64 °, 110 °, and 122 °, respectively, and a simulated array radiation pattern is as shown in fig. 3. The power amplifier model is extracted based on actually measured GaN power amplifier input and output data, and the simulation signals are 4 irrelevant 10MHz bandwidth 64QAM modulation signals. QAM is short for quadrature amplitude modulation.
Fig. 4 is a diagram illustrating simulated Adjacent Channel Power Ratio (ACPR) as a function of azimuth for an analog fully-connected hybrid beamforming system including a digital predistortion architecture, according to an embodiment of the present disclosure.
Tables 1 and 2 show that the Adjacent Channel Power Ratio (ACPR) and the Normalized Mean Square Error (NMSE) index in each beam direction before and after applying the proposed digital predistortion structure (DPD) in simulation verification are compared, and it can be seen by referring to tables 1,2 and fig. 4 that the ACPR index of the signal in each beam direction is improved by at least-12dbc, the NMSE index is improved by 8dB after applying the digital predistortion scheme of the present disclosure, and the linearity performance is significantly improved.
Table 1 simulation performance: ACPR index (unit: dBc)
Table 2 simulation performance: NMSE index (unit: dB)
The present disclosure also experimentally verifies the above-described fully connected hybrid beamforming system including predistortion structure simulation.
Fig. 5 is a graph of experimental comparison results comparing power spectrum analysis of signals in one exemplary beam direction for a simulated fully-connected hybrid beamforming system with and without a digital predistortion structure. Fig. 6 is a graph of experimental comparison results comparing power spectrum analysis of signals in one exemplary beam direction for a simulated fully-connected hybrid beamforming system with and without a digital predistortion structure.
The present disclosure was experimentally verified based on a 2-channel 4-unit simulation fully-connected hybrid beamforming system. The test signals are two uncorrelated 20MHz bandwidth 64QAM modulated signals. The beamforming coefficients are adjusted to steer the two simultaneously transmitted beams to 70 and 99. Referring to fig. 5 and 6, in the analog fully-connected hybrid beamforming system including the digital predistortion structure, ACPR indices for both 70 ° and 99 ° beam direction signals are improved by 14dBc compared to the analog fully-connected hybrid beamforming system not including the digital predistortion structure. The NMSE indicator for both 70 ° and 99 ° beam direction signals is improved by 12dB for systems containing DPD compared to systems not containing DPD. It can be seen that, based on the digital predistortion structure proposed by the present disclosure, adjacent channel frequency spectrum leakage of the fully-connected hybrid beamforming system is significantly suppressed, and signal linearity in the beam direction is significantly improved.
In summary, the disclosure provides a digital predistortion structure, an analog full-connection hybrid beam forming system, and a transmitter, where multiple beam signals transmitted by an antenna array are used as linearization targets, and an equivalent multi-beam signal for beam forming and a transmission signal of a transmission link are trained based on a digital domain to obtain a model of a Q input predistorter, and the Q input predistorter can perform linearization correction on Q-path transmission signals transmitted by each connected transmission link (radio frequency link), so as to solve a problem of poor quality of a received signal caused by intermodulation distortion from each transmission channel signal and nonlinear distortion of each transmission channel itself existing in an array beam signal. Based on the digital predistortion structure provided by the disclosure, adjacent channel frequency spectrum leakage of a full-connection hybrid beam forming system is remarkably inhibited, and signal linearity in a beam direction is obviously improved.
Those skilled in the art will appreciate that the modules in the device in an embodiment may be adaptively changed and disposed in one or more devices different from the embodiment. The modules or units or components of the embodiments may be combined into one module or unit or component, and furthermore they may be divided into a plurality of sub-modules or sub-units or sub-components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Also in the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware.
Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.
The above-mentioned embodiments, objects, technical solutions and advantages of the present disclosure are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present disclosure, and should not be construed as limiting the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Claims (10)
1. A transmitter comprising a digital predistortion architecture, characterized in that the digital predistortion architecture comprises:
the time delay alignment module is used for aligning the equivalent power amplifier output signal of the power amplifier array in the digital domain with the equivalent power amplifier input signal of the power amplifier array in the digital domain in time;
the multi-beam estimation module is used for synthesizing the equivalent power amplifier output signals after time alignment into equivalent multi-beam signals in a digital domain according to the beam forming conditions;
a predistorter training module to: constructing a Q-dimensional behavior model of a K-order nonlinear order and an M-order memory depth, and training based on the equivalent multi-beam signal and a transmitting signal of a transmitting link to obtain a Q-input predistorter model, wherein Q is more than or equal to 2, and in the training process, beam signals transmitted by the antenna array at the same time are used as a linearization target; and
and the multi-input multi-output predistorter module comprises Q input predistorters, and each predistorter is used for carrying out linearization correction on Q transmission signals transmitted by the connected transmission link.
2. The transmitter of claim 1, wherein the inputs to the model of the Q-input predistorter are: equivalent multi-beam signal r 1 、r 2 、…r Q The output is: transmission signal x of a transmission chain 1 、x 2 、…x Q The solved parameter is the coefficient vector of the model
The goal of the training is to achieve a linearized relationship of the output and the input.
3. The transmitter of claim 1, wherein the predistorter training module comprises:
the model construction submodule is used for constructing a Q-dimensional behavior model with K-order nonlinear order and M-order memory depth; and
and the model training sub-module is used for taking the beam signal as input, taking the transmitting signal of the transmitting link as output, and training on the basis of the Q-dimensional behavior model to obtain a Q-input predistorter model.
4. The transmitter of claim 1, wherein the Q-input predistorter is modeled by:
wherein the content of the first and second substances,
is a vector of dimension L multiplied by 1, L represents the number of sample points;
a transmitting signal matrix formed by sample points of L transmitting signals of a q transmitting chain of a digital domain; the value of Q is 1,2, …, Q;
is r of q (n)，…，r q A matrix of (n + L-1); r is q (n)，…，r q (n + L-1) represents the q wave beam signal sample points of the digital domain at the sampling time n, … …, n + L-1 corresponding to the 1 st, …, L wave beam signal sample points respectively; n, … …, n + L-1 all represent sampling time;
representing a coefficient vector; m represents the memory depth; k represents the maximum value of the non-linear order.
5. The transmitter of claim 3, wherein in the Q-dimensional behavior model, the expression of the Q-th, Q =1,2, …, Q, beam signal satisfies:
wherein r is q (n) represents the beam signal sample point of the q-th beam signal at sampling instant n; m represents the memory depth; k represents a non-linearityThe maximum value of the order; k is a radical of 1 、k 2 、…、k Q-1 Respectively represent | x 1 (n-m)|、|x 2 (n-m)|、...、|x Q-1 The non-linear order of the (n-m) | term; c. C q (m，k...k Q-1 ) Representing the coefficients; x is the number of 1 (n-m)、…、x q (n-m)、…、x Q-1 (n-m)、x Q (n-m) represents the signal value of the 1 st, the.
6. The transmitter of claim 1, further comprising: and the equivalent analog beam forming module is used for weighting and summing the digitally coded transmission signals of the Q transmission links to obtain equivalent power amplifier input signals of each power amplifier in the power amplifier array.
7. The transmitter of claim 1, wherein the equivalent power amplifier output signal of the power amplifier array in the digital domain is obtained by: and filtering, down-converting and analog-to-digital converting the power amplifier output signals of the power amplifier array to obtain equivalent power amplifier output signals.
8. An analog fully-connected hybrid beamforming system, comprising:
q transmitting links, wherein Q is more than or equal to 2; and
a digital predistortion structure;
wherein the digital predistortion structure comprises:
the time delay alignment module is used for aligning the time of the equivalent power amplifier output signal of the power amplifier array in the digital domain with the time of the equivalent power amplifier input signal of the power amplifier array in the digital domain;
the multi-beam estimation module is used for synthesizing the equivalent power amplifier output signals after time alignment into equivalent multi-beam signals in a digital domain according to the beam forming conditions;
a predistorter training module to: constructing a Q-dimensional behavior model of a K-order nonlinear order and an M-order memory depth, and training based on the equivalent multi-beam signal and a transmitting signal of a transmitting link to obtain a Q-input predistorter model, wherein Q is more than or equal to 2, and in the training process, beam signals transmitted by the antenna array at the same time are used as a linearization target; and
a multi-input multi-output predistorter module comprising Q of said Q-input predistorters, each predistorter for performing a linearization correction on a Q-path transmit signal transmitted by a connected transmit chain,
the input ends of the Q transmission links are connected to the output ends of the mimo predistorter modules in the digital predistortion architecture, and each predistorter is configured to perform linearization correction on Q transmission signals transmitted by the connected transmission links.
9. The analog fully-connected hybrid beamforming system of claim 8, further comprising, connected in sequence: the antenna comprises a digital-to-analog conversion module, a mixer, a power division module, an analog beam forming module, a power amplifier array and P antennas, wherein Q is less than or equal to P, and the power amplifier array comprises P power amplifiers.
10. A transmitter comprising the analog fully-connected hybrid beamforming system of claim 8 or 9.
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| CN113131976A (en) * | 2021-03-11 | 2021-07-16 | 西安电子科技大学 | Decimetric wave mixed beam forming method, system and application |
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