CN111555787A

CN111555787A - Artificial noise weight iterative correction and low bit feedback method for multi-transmitting single-receiving system

Info

Publication number: CN111555787A
Application number: CN202010333794.9A
Authority: CN
Inventors: 王文杰; 张冉; 洪玺
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2020-04-24
Filing date: 2020-04-24
Publication date: 2020-08-18
Anticipated expiration: 2040-04-24
Also published as: CN111555787B

Abstract

The invention discloses an artificial noise weight iteration correction and low bit feedback method of a multi-transmitting-single-receiving system, under a TDD communication mode, an N-antenna sender Alice obtains an erroneous channel estimation value at an access time slot

Generating an initial main beam weight w₀And the artificial noise weight q_0,i. And the receiving end Bob calculates error data Er after receiving the signal containing the artificial noise, and feeds back the result after quantizing. After receiving the data, the Alice terminal carries out comparison on the main beam weight w and the artificial noise weight q_i(i 1.., N-1) is updated and transmission and error feedback for the next slot is performed. After a certain number of iterations, the original results are not matchedThe matched weights are corrected to the actual channel response. The invention can realize the function of weight correction by using a small number of return bits in each uplink time slot under the condition of not changing the existing TDD communication mode and not using additional equipment, has the advantage of low complexity and can meet the real-time requirement of communication.

Description

Artificial noise weight iterative correction and low bit feedback method for multi-transmitting single-receiving system

Technical Field

The invention belongs to the field of wireless communication, and particularly relates to an artificial noise weight iterative correction and low bit feedback method for a multi-transmitting and single-receiving system.

Background

With the development of wireless communication technology and the popularization of intelligent terminal equipment, people pay more attention to the information security problem in the wireless communication process. The wireless communication signals are easy to intercept and steal due to natural openness and boundless, and are one of the sources of information leakage problems. Therefore, how to ensure the effectiveness and reliability of communication without the help of an upper layer protocol encryption means becomes a first problem to solve the potential safety hazard. In view of this, it is critical to research the secure transmission of information in the physical layer, and a physical layer secure transmission technology that is a powerful supplement to the conventional encryption technology has also gained wide attention.

For a traditional Multiple Input Single Output (MISO) system, a widely accepted zero-space artificial noise scheme is an effective wireless physical layer secure transmission method. The null space artificial noise scheme requires the originator to transmit useful signals carrying secret information in the main channel direction, while uniformly transmitting artificial noise signals in the null space of the main channel. Artificially introducing a gap in transmission performance between legitimate and illegitimate channels at the cost of reducing the power utilization of the transmitting end.

However, in an actual TDD system, since the result of channel estimation is developed based on channel reciprocity, the uplink end estimates the uplink channel using the received signal, and at the same time, uses the estimated value of the uplink channel as the estimation result of the downlink channel. Due to the fact that estimation is inaccurate, uplink and downlink channels are not completely reciprocal, errors between channels exist in practical systems, and the like, the difference between a channel estimation result and real channel response exists. For the main lobe signal, such an error is not critical, and the signal gain in the main lobe direction is still guaranteed. However, for the artificial noise scheme, the transmission using the zero space weight generated by the channel estimation result with error introduces noise in the direction of the legitimate user. Due to the characteristics of artificial noise nulling, the additionally introduced noise can have a significant effect on the original characteristics.

The traditional engineering scheme is based on channel calibration expansion, and aims to correct errors among multiple antenna receiving and transmitting channels to meet the condition of channel reciprocity so as to enable a channel estimation result to be close to the real response of a channel. However, the traditional offline and online calibration, wired and wireless calibration, require additional equipment and a more cumbersome processing procedure in terms of implementation, and the calibration accuracy is limited by the accuracy of the existing equipment, which is difficult to reach a high level, and even impossible to process the estimation error and slow channel change influence except the inter-channel error, and it is difficult to ensure that the artificial noise does not affect the information transmission in the legal user direction.

The above facts indicate that in practical communication engineering, a method for correcting the artificial noise weight of the MISO system, which is really simple, effective and meets practical requirements, is still lacking at present.

Disclosure of Invention

The invention aims to solve the problems in the prior art, and provides a transmitting-end distributed beam weight iteration and low-bit feedback method, which can realize transmitting weight correction in a single-parameter feedback iteration mode on the premise of not using additional equipment and communication time slots, and provides a low-bit quantization feedback scheme to enhance the safe transmission performance of artificial noise.

In order to achieve the above purpose, the method for iteration of the transmit-side distributed beam weight and low-bit feedback of the invention comprises the following steps:

step 1, an N-antenna sender Alice establishes a communication link with a single-antenna receiver Bob according to access information and obtains an initial channel estimation result by receiving an uplink pilot signal

Under the MISO line-of-sight model, the channel is considered to be slowly changed, and the channel estimation value

Is an Nx1 dimensional column vector. Generating a main beam weight w and N-1 groups of artificial noise weights q according to the existing information_i(i 1.., N-1), and artificial noise is simultaneously transmitted to protect a useful signal when the signal is transmitted.

And 2, after the single-antenna receiving end Bob contains artificial noise signals at the receiving end, calculating the error between the received signal and the known signal according to the known pilot signal, and carrying out differential quantization on the error. And feeding back the quantized result to the Alice terminal.

And 3, using the received data to obtain a current error value by the Alice of the N antenna sender, correcting the weight of the main beam according to the error value, and updating the main beam and the artificial noise beam according to the corrected result. And using the updated weight value to continuously send the signal of the next time slot, and going to the step 2.

The communication system based on the weight correction method comprises an N-antenna sender Alice and a single-antenna expected receiver Bob, which form a communication pair through access. In TDD communication mode, the N-antenna sender Alice sends a signal containing artificial noise, and the signal received at the single-antenna receiver Bob can be represented as

Where s (t) represents the carrier of a known signal for training, y_i(t) represents the standard Gaussian distribution of the artificial noise signal with mean value of zero and energy of 1, sigma_iIs ith artificial noise y_i(t) complex amplitude, h is the true response of the channel, w is the main beam transmitting the desired signal, and initially the channel estimate

Namely, it is

q_iIs the ith artificial noise weight, which is taken from the null space of the current main beam weight

It may be represented again as q_i＝U₀(: i), n (t) is environmental noise. In a line-of-sight environmentIn the following, the channel true response h is considered to remain unchanged during iterative convergence.

The step 1 is to use the channel estimation value in the access time slot

Generating an initial value w of the main beam₀And accordingly generates a null space omega₀To obtain the weight q of the artificial noise_iConsistent with conventional artificial noise generation schemes.

The step 2 is that the receiving end Bob generates the return error quantization bit according to the known signal when receiving the signal, and the specific operation steps are as follows:

step 2.1, the single-antenna receiver Bob receives a pilot signal containing artificial noise from the Alice terminal, and the received signal is

The useful signal s (t) is completely known to Bob, from which the error term e (t) in the received signal can be derived_k) X (t) -s (t). Is not difficult to obtain according to the expression of the received signal

Here Λ₀＝diag(σ₁，σ₂，..，σ_N-1) And y (t) ═ y₁(t)，y₂(t)...，y_N-1(t))。

Suppose there is a known signal s (t) under a certain time slot_k) And error term e (t)_k) And calculating the cross-correlation value Er of the known signal and the error term at the moment_k＝E{s(t_k)e(t_k)^*And applying a useful signal s (t) thereto_k) The energy of (a) is normalized.

Step 2.2, the normalized complex number Er_kRespectively carrying out Q-format quantization on the real parts and the imaginary parts, and carrying out L-bit truncation on the quantized bit sequences. L represents the effective bit length of the real part or the imaginary part, without including the sign bit, and the specific value depends on the introduced noise and the environmental signal-to-noise ratio SNR. According to the quantization length and equivalent quantization noiseAs a result of the rough calculation of the sound, when L > SNR/6, it can be considered that the introduced quantization noise is lower than the environment and has no influence on the convergence performance after the quantization noise is introduced.

The error bit sequence after the real part/imaginary part truncation is E_k[l]Bit sequence E from the previous instant_k-1[l]And the bit sequence obtained by the difference is D_k[l]. Due to the convergent nature of the algorithm, the high-order number of the differential bit will quickly become 0 during the iteration and will not change during subsequent iterations. If the significant digit of the differential bit sequence is M bits in the lower order, the M bits are intercepted and transmitted. M selection rule according to error Er of initial weight₀Determining the maximum representation d of the last M digits_maxTo be reacted with Er₀And (4) the equivalent. And for the direct sequence taking of the differential data with the expression range M after exceeding, the sequence is obtained when the differential data is transmitted back again. For the sequence of the differential data beyond the M-bit expression range, splitting is carried out according to the following rule, the feedback is carried out in sequence in a plurality of time slots, and no additional calculation and quantization are carried out in the process of multiple feedback:

when the real part or imaginary part data value of a certain returned difference sequence is larger than the maximum value d expressed by the M rear bits_maxDividing the larger Q into Q ═ n × d_max+ q, wherein q is a number that can be expressed with the last M. In the process of returning later, n times of returning M-bit full 1 sequences and sequences corresponding to 1 time of transmission q occupy n +1 times of returning, so that the processing of the receiving end on the differential numerical value is always kept in addition operation. And the other side of the real part and the imaginary part is split in the same way, and 0 is supplemented for transmission.

It is noted that, since the all-1 sequence has a special meaning in degree, when the error data just corresponds to the all-1 sequence and does not exceed the expression range, the end bit of the corresponding differential sequence is modified to 0.

And 2.3, the single-antenna receiver Bob transmits the generated real-imaginary part differential bit sequence back through the uplink time slot.

And 3, after the N-antenna sender Alice receives the differential bit sequence of the Bob end, error data Er is obtained_kAnd calculating the main beam weight and artificial noise beam weight of the next time slot according to the calculated weightsThe method comprises the following steps:

step 3.1, the sender Alice of the N antenna calculates a difference result delta according to the received difference bits under the premise that the sender Alice of the N antenna intercepts M bits after the known L bit difference is quantized_kAnd accumulating error data Er, i.e. Er_k＝Er_k-1+Δ_k。

At this time, different operations are taken according to different received differential bits: if the received bit sequence contains the all 1 sequence, turning to step 3.3, namely not updating the weight; if the received bit sequence does not contain all 1 bit, go to step 3.2, i.e. modify the weight.

Step 3.2, the receiving end obtains the error value Er at the moment according to the feedback bit_kThen, the original beam forming weight value is updated and calculated

Wherein w_kAs a weight of the current beam forming, w_k+1For the updated weight, μ is the iteration step, U_0，kThe null space of the current weights, i.e. the current artificial noise weight space, Λ₀＝diag(σ₁，σ₂，..，σ_N-1) For the energy allocation of artifacts, y (t) ═ y₁(t)，y₂(t)...，y_N-1(t)) are each artificial noise sequence. After updating the main beam weight w_k+1Thereafter, a null space U of responses is also generated_0，k+1And updating the artificial noise weights of all paths and turning to the step 3.3.

Step 3.3, according to the main beam weight w and the artificial noise weight U₀And transmitting the signal of the next time slot. And (5) carrying out communication of the next time slot, and turning to the step (2) to carry out iterative correction on the weight.

Compared with the prior art, the invention has the following advantages: the calculation complexity is low, and the real-time requirement of communication can be met in actual use; the time slot design of the main stream communication is matched, and under the traditional TDD time slot communication structure, additional time frequency code domain resources are not occupied; the design starts from the background of artificial noise, fully utilizes the airspace resources of the multi-antenna, fully plays the role of multi-beam, can cover pilot frequency time slot by the artificial noise, and enhances the safety performance. The invention can overcome the influence of channel mismatching by using the minimum resources and optimize the performance of the artificial noise beam without changing the traditional TDD communication framework.

Drawings

FIG. 1 is a schematic diagram of an artificial noise weight iterative correction process under MISO time division communication

FIG. 2 is a flow chart of the differential quantization method of the present invention

FIG. 3 is a convergence curve of SINR output by the receiving end Bob with iteration number under given conditions

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

As shown in fig. 1, the communication system adopted by the present invention includes an N-antenna sender Alice and a single-antenna intended receiver Bob, the dual-transmission time-division uplink and downlink communication is performed according to the TDD communication method, and the pilot sequences of the Bob end and the Alice end at the front end of the dual-transmission time slot are completely known.

In TDD communication mode, the N-antenna sender Alice sends a signal containing artificial noise, and the signal received at the single-antenna receiver Bob can be represented as

It may be represented again as q_i＝U₀(: i), n (t) is environmental noise.

And 3, completing the generation of the initial weight in the step 1, wherein the generation is consistent with the artificial noise weight generation method in the traditional method.

In the process of downlink communication, after receiving a signal, the single-antenna receiving end Bob generates a return error quantization bit according to a known signal. A single-antenna receiver Bob receives a pilot signal containing artificial noise from an Alice terminal, and the received signal is

Now, Bob is completely known about the useful signal s (t), and thus the error term e (t) in the received signal can be obtained_k) X (t) -s (t). The operation steps of calculating the error value and the differential quantization are as follows:

step 2.1, assume that there is a known signal s (t) in each communication_k) And error term e (t)_k) And calculating the cross-correlation value Er of the known signal and the error term at the moment_k＝E{s(t_k)e(t_k)^*And applying a useful signal s (t) thereto_k) The energy of (a) is normalized.

Step 2.2, the normalized complex number Er_kRespectively carrying out Q-format quantization on the real parts and the imaginary parts, and carrying out L-bit truncation on the quantized bit sequences. L represents the effective bit length of the real part or the imaginary part, without including the sign bit, and the specific value depends on the introduced noise and the environmental signal-to-noise ratio SNR. According to the rough calculation result of the quantization length and the equivalent quantization noise, when L is more than SNR/6, the introduced quantization noise is considered to be lower than the environment, and has no influence on the subsequent convergence performance.

The error bit sequence after the real part or the imaginary part is truncated is E_k[l]Bit sequence E from the previous instant_k-1[l]And the bit sequence obtained by the difference is D_k[l]. Due to the convergent nature of the algorithm, the high-order number of the differential bit will quickly become 0 during the iteration and will not change during subsequent iterations. If the significant digit of the differential bit sequence is M bits in the lower order, the M bits are intercepted and transmitted. M rule base of selectionError Er of initial weight₀Determining the maximum representation d of the last M digits_maxTo be reacted with Er₀And (4) the equivalent. And when the differential data is a direct sequence taking the expression range M after exceeding, returning. When the error data just correspond to the all-1 sequence and do not exceed the expression range, the tail bit of the corresponding differential sequence is modified into 0. For the sequence of the differential data beyond the M-bit expression range, splitting is carried out according to the following rule, the feedback is carried out in sequence in a plurality of time slots, and no additional calculation and quantization are carried out in the process of multiple feedback:

And 2.3, the single-antenna receiver Bob transmits the generated differential bit sequence of the real part and the imaginary part back through the uplink time slot.

In the process of uplink communication, after receiving error differential bits fed back by the Bob end, the N-antenna sender Alice sends error data Er_kAnd accumulating and calculating the main beam weight and the artificial noise beam weight of the next time slot according to the accumulated values. The specific operation steps of accumulating error data and updating weight are as follows:

Step 3.3, according to the main beam weight w and the artificial noise weight U₀And transmitting the signal of the next time slot.

It can be seen that the iterative process of the algorithm is consistent with the uplink and downlink transmission mode, no convergence condition needs to be additionally set, and the method has a tracking effect on slowly-varying channels in the continuous correction process. Channel estimation value by simulation method

And a gain error of 10 percent and a phase error of 5 degrees exist between the signal and the real response h of the channel, and the optimization performance is realized under the condition that the environmental signal-to-noise ratio is 30 dB. Wherein, the length of each frame pilot frequency is 127bit, the length of the truncation is 6bit, the length of the difference is 3bit, so the length of each feedback data is 8 bit. The original artificial noise performance can only be about 20dB of signal-to-interference-and-noise ratio at the output end.

As can be seen from fig. 3, under the above conditions, the method of the present invention is used to modify the artificial noise weight, so that the signal-to-interference-and-noise ratio output by the Bob end is within the signal-to-noise ratio of the convergence value environment after a finite number of iterations, i.e., the transmission artificial noise does not affect the communication performance of the legal receiving end, and the cost is that each time slot occupies 8 backhaul bits.

In summary, the effective role of the method in correcting the artificial noise weight value and optimizing the transmission performance can be verified from the theoretical analysis and simulation results of the technical scheme.

The foregoing is only a preferred embodiment of the invention and is not intended to be limiting in any way, as it will be appreciated by those skilled in the art that changes may be made in this invention without departing from the principles and spirit of the invention, which is defined in the appended claims.

Claims

1. An artificial noise weight iteration correction and low bit feedback method of a multi-transmitter-receiver system is characterized by comprising the following steps:

Generating a main beam weight w and N-1 groups of artificial noise weights q for an Nx1 dimensional column vector according to the existing information_i(i 1.., N-1), and when transmitting a signal, simultaneously sending artificial noise to protect a useful signal;

step 2, after the single-antenna receiving end Bob contains artificial noise signals at the receiving end, calculating errors between the received signals and the known signals according to the known pilot signals, carrying out differential quantization on the errors, and feeding back quantized results to the Alice end;

and 3, using the received data to obtain a current error value by the Alice of the N-antenna sender, correcting the weight of the main beam according to the error value, updating the main beam and the artificial noise beam according to the corrected result, and using the updated weight to continuously send a signal of the next time slot.

2. The artificial noise weight iterative correction and low bit feedback method for multi-transmission single-reception system according to claim 1, wherein: the communication system comprises an N-antenna sender Alice and a single-antenna expected receiver Bob;

Namely, it is

It may be represented again as q_i＝U₀And (i), n (t) is environmental noise, and in a line-of-sight environment, the real response h of the channel is considered to be kept unchanged in the iterative convergence process.

3. The artificial noise weight iterative correction and low bit feedback method for multi-transmission single-reception system according to claim 1, wherein: step 2 and step 3 are to correct the weight value by feeding back the error and feed back the error information by using a small number of bits.

4. The iterative artificial noise weight correction and low bit feedback method according to claim 3, wherein the method for correcting the weight by feeding back the error data comprises the following steps:

The useful signal s (t) is completely known to Bob, from which the error term e (t) in the received signal can be derived_k) X (t) -s (t), which is not difficult to obtain from the expression of the received signal

Here Λ₀＝diag(σ₁，σ₂，..，σ_N-1) And y (t) ═ y₁(t)，y₂(t)...，y_N-1(t))；

Suppose there is a known signal s (t) under a certain time slot_k) And error term e (t)_k) And calculating the cross-correlation value Er of the known signal and the error term at the moment_k＝E{s(t_k)e(t_k)^*And applying a useful signal s (t) thereto_k) Normalizing the energy, and feeding the error data back to an Alice end;

Wherein w_kAs a weight of the current beam forming, w_k+1For the updated weight, μ is the iteration step, U_0，kThe null space of the current weights, i.e. the current artificial noise weight space, Λ₀＝diag(σ₁，σ₂，..，σ_N-1) For the energy allocation of artifacts, y (t) ═ y₁(t)，y₂(t)...，y_N-1(t)) is the artificial noise sequence of each path, and the main beam weight w is updated after the updating_k+1Then, the same appliesNull space U for generating response_0，k+1。

5. The method for iterative modification of artificial noise weight and low bit feedback in a multi-transmission single-reception system according to claim 3, wherein the error information is transmitted through a small number of bits, comprising the steps of:

step 2.2, the normalized complex number Er_kRespectively carrying out Q-format quantization on the real part and the imaginary part, carrying out L-bit truncation on a bit sequence after quantization, wherein L represents the effective bit length which is obtained under the condition that the real part or the imaginary part does not comprise a sign bit, and the specific value of the effective bit length depends on introduced noise and an environment signal-to-noise ratio (SNR). according to the rough calculation result of the quantization length and equivalent quantization noise, when L is more than SNR/6, the introduced quantization noise is considered to be lower than the environment, and the convergence performance after the quantization is not influenced;

the error bit sequence after the real part/imaginary part truncation is E_k[l]Bit sequence E from the previous instant_k-1[l]And the bit sequence obtained by the difference is D_k[l]After interception, M bits are transmitted, and the selection rule of M is according to the error Er of the initial weight₀Determining the maximum representation d of the last M digits_maxTo be reacted with Er₀Equivalently, for the sequence of the differential data which is directly taken when the differential data exceeds the expression range, M is the expression range, the sequence of the differential data which exceeds the expression range of M bits is split according to the following rule, the feedback is carried out in sequence in a plurality of time slots, and no additional calculation and quantization are carried out in the process of multiple feedback:

when the real part or imaginary part data value of a certain returned difference sequence is larger than the maximum value d expressed by the M rear bits_maxDividing the larger Q into Q ═ n × d_max+ q, where q is a numerical value that can be expressed by the last M, and n times of returning M-bit full 1 sequence and a sequence corresponding to 1 time of q transmission occupy n +1 times of returning, so that the processing of the receiving end on the differential numerical value always keeps addition operation, and the other side of the real and imaginary parts is split in the same way to complement 0 transmission;

it is worth noting that because the all-1 sequence has a special meaning in the times, when the error data just corresponds to the all-1 sequence and does not exceed the expression range, the tail bit of the corresponding differential sequence is modified to be 0;

step 3.1, the sender Alice of the N antenna calculates a difference result delta according to the received difference bits under the premise that the sender Alice of the N antenna intercepts M bits after the known L bit difference is quantized_kAnd accumulating error data Er, i.e. Er_k＝Er_k-1+Δ_k；