Bit and power allocation method for OFDM shared waveform subcarriers with integrated perceptual communication

Abstract

The present invention relates to a method for allocating bits and power of OFDM shared waveform subcarriers for integrated sensing and communication, comprising the following steps: establishing a transmission signal model; establishing a radar detection model with the goal of maximizing conditional mutual information under total power constraints; establishing a communication model with the goal of maximizing data information rate under total power and BER constraints; establishing an optimization model of a robust OFDM shared waveform based on the radar detection model and the communication model, taking into account radar and communication performance; and adjusting the comprehensive performance of the optimization model of the robust OFDM shared waveform by adjusting the bits and powers of different subcarriers. The present invention fully considers the uncertainty of channel conditions and has good robustness.

Description

Technical Field

[0001] The present invention relates to the technical field of perception and communication integration, and in particular to a method for allocating bits and power of OFDM shared waveform subcarriers for perception and communication integration. Background Art

[0002] Radar and wireless communication are the two most common typical applications of modern electromagnetic technology, which are extremely valuable and far-reaching in both military and civilian fields. Radar systems and communication systems are different in design purpose and function. Radar is mainly used to detect, monitor and track targets, while communication systems achieve end-to-end information transmission by establishing communication links between the transmitter and the receiver. In the past, the development of radar technology and wireless communication technology was independent of each other. Based on their respective functional requirements, they were designed and deployed separately without affecting each other. In recent years, with the exponential growth of mobile devices and the emergence of new services, the transmission rate requirements for communication have become higher and higher, and the corresponding demand for bandwidth has also shown a significant growth trend. Low-frequency band resources can no longer meet current needs. For example, the millimeter wave band has received extensive attention and research in the new generation of mobile communications due to its bandwidth advantage. It can be seen that the communication system is gradually developing towards higher frequency bands, thus using the frequency bands occupied by radar technology. The operating frequency bands of radar systems and communication systems overlap, and the current severe shortage of spectrum resources has become an important factor restricting the rapid development of radar systems and communication systems. What is more serious is that when the radar system and the communication system coexist, they will generate strong electromagnetic interference between each other, affecting the performance and stability of both. Therefore, if it is possible to realize an integrated system with both communication and radar detection functions under the condition that the radar and communication systems share the spectrum, it can effectively solve the problems of resource shortage and electromagnetic interference.

[0003] The integration of perception and communication is one of the potential directions for the development of 6G. Its design will bring many advantages, which are mainly reflected in the following aspects: (1) It can maximize the use of spectrum resources, improve spectrum utilization, and alleviate the current situation of insufficient spectrum resources. (2) Based on the similarity of the subsystem structure in the radar system and the communication system, the integrated system can share some hardware devices such as transmitters, power amplifiers, antennas, etc. This can greatly reduce the complexity of the system, improve hardware utilization, help control costs, and effectively improve system integration and reduce the volume occupied by the system. (3) It has a promoting effect on communication performance. Radar technology mainly processes echo signals, so radar generally uses a larger transmission power than the communication system to meet the needs of echo signals. This feature can be used for communication to provide a wider range of communication capabilities. Moreover, radar, especially phased array radar, has the inherent advantage of strong directionality, so the signal has a strong anti-interference ability, and can also reduce the signal interception rate and have a certain degree of confidentiality. (4) The integrated design of perception and communication helps to build an intelligent radar network. Through the communication function, each node is integrated into an information perception network, which quickly completes the information interaction between the master and slave nodes, and combines the latest computer artificial intelligence technology to form an intelligent whole. (5) The joint design can realize the combination of radar and communication through the bottom layer, avoid the use of distance isolation and other means to achieve electromagnetic compatibility of the two systems, and suppress the performance loss caused by electromagnetic interference between each other. Figure 1 A typical application scenario of integrated perception and communication is given. It is no longer a simple communication transmission channel, but can also perceive everything, thus realizing the intelligence of all things.

[0004] From the above analysis, it can be seen that the research on perception-communication integrated network has far-reaching significance.

[0005] Among them, the optimization design of the waveform of the integrated perception and communication network is the research focus of the integrated system, which mainly studies how to design a waveform that can realize both communication data transmission and target detection. The optimization design of the waveform time domain and frequency domain resources is crucial and will directly affect the system performance. At present, there have been many domestic and foreign research works on the optimization design of the waveform of the integrated perception and communication network. The existing design methods can be divided into two types: the first is to use multiplexing technology, and the second is to use sharing technology. Multiplexing technology includes: (1) time division multiplexing, in which time is divided into different time slots and allocated to radar waveforms with detection functions or communication waveforms with data transmission functions. (2) frequency division multiplexing, frequency division multiplexing refers to the superposition of radar waveforms or communication waveforms transmitted within the same bandwidth to simultaneously complete radar and communication functions. (3) space division multiplexing, space division multiplexing is to divide the surface of the phased array into different areas, and use the existing beamforming technology to control the direction of the beam energy to complete radar detection and communication data transmission. (4) Code division multiplexing. Code division multiplexing is based on spread spectrum orthogonal technology and uses spread spectrum sequences to eliminate interference between communication signals and radar signals to achieve waveform sharing. Radar signals are usually deterministic sequences with good autocorrelation, while the transmitted communication information is random data. The implementation complexity of the signal multiplexing technology design method is low, and it is relatively independent and easy to implement in hardware. It does not require the modification of the architecture and waveform of the electromagnetic transceiver system. However, this type of design method has not truly achieved integrated fusion under the same waveform system transceiver framework. Sharing technology, that is, radar and communication equipment use a shared signal waveform together. In the fusion waveform, information can be carried by certain differences to achieve the communication transmission function while completing the radar detection function. At present, the integrated waveform design mainly uses signal sharing technology, and the designed integrated waveform can be roughly classified into the following two ideas: (1) Shared waveform design based on radar linear frequency modulation LFM. (2) Shared waveform design based on communication multi-carrier OFDM. OFDM shared waveform has far-reaching research value due to its advantages such as good resolution, anti-multipath performance and flexible parameter setting.

[0006] In recent years, there have been a lot of studies on OFDM-based shared waveform design in the integration of perception and communication. The existing technology generally selects a communication indicator to measure the communication performance and a radar indicator to measure the radar performance. In the establishment of communication and radar models, the frequency impulse response h(t) of the communication channel and the impulse response g(t) of the radar channel are used. Most of the existing technologies directly give or determine the channel conditions through channel estimation. However, in practical applications, the feedback of the channel environment is not accurate, which makes the actual performance of the designed perception and communication integrated shared waveforms gap with theoretical analysis. The research on the perception and communication integrated shared waveform that can still have good comprehensive performance and robustness under uncertain channel conditions has become a focus. In addition, a suitable bit and power allocation algorithm is needed to adjust the comprehensive performance of the shared waveform by adjusting the bits and powers of different subcarriers. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a bit and power allocation method for OFDM shared waveform subcarriers with integrated perception communication, which has good robustness considering the uncertainty of channel conditions.

[0008] The technical solution adopted by the present invention to solve the technical problem is: to provide a bit and power allocation method for OFDM shared waveform subcarriers of perception communication integration, including the following steps:

[0009] Establish a signal sending model;

[0010] Under the total power limitation, a radar detection model is established with the goal of maximizing conditional mutual information.

[0011] Under the constraints of total power and BER, a communication model is established with the goal of maximizing the data information rate;

[0012] Based on the radar detection model and the communication model, an optimization model of a robust OFDM shared waveform is established under the condition of comprehensive consideration of radar and communication performance;

[0013] The comprehensive performance of the optimization model of the robust OFDM shared waveform is adjusted by adjusting the bits and powers of different subcarriers.

[0014] The sending signal model is Among them, s(t) represents the transmitted time domain signal, f c Indicates the carrier center frequency, N s Indicates the number of subcarrier symbols, N c Indicates the number of subcarriers, a m represents the complex weight of the mth subcarrier, c m,n represents the phase encoding of the nth symbol in the mth subcarrier, Δf is the subcarrier spacing, Ts represents the entire OFDM symbol duration, and rect[·] represents the rectangular function.

[0015] The radar detection model is: y(t) represents the received echo signal, g(t) represents the response signal of the radar channel, T p =N S T S Indicates the duration of the signal; |a m | 2 =p m represents the transmission power of the mth subcarrier, G(f m ) represents the impulse response of the radar channel, N(f m ) represents the noise power spectral density of the mth subcarrier, f m represents the power of the mth subcarrier, p T Indicates the given total transmit power.

[0016] The communication model is: C t represents the data information rate, |a m | 2 =p m represents the transmission power of the mth subcarrier, H(f m ) represents the communication channel frequency response of the mth subcarrier, represents the noise power of the communication channel, BER stands for bit error rate.

[0017] The optimization model of the robust OFDM shared waveform is:

[0018] Θ g represents the radar channel impulse response G(f m ) Given a set of upper and lower limits, Θ h Represents the given upper and lower limits of the communication channel frequency response, ω 1 and ω 2 Respectively represent the weights of the radar detection model and the communication transmission model function, and ω 1 +ω 2 =1,U 1 is the optimal value of the radar detection model, U 2 is the optimal value of the communication model, T p =N S T S Indicates the duration of the signal; |a m |2 =p m represents the transmission power of the mth subcarrier, Θ g,m =G(f m ), represents the impulse response of the radar channel, N(f m ) represents the noise power spectral density of the mth subcarrier; Θ h,m =H(f m ), represents the communication channel frequency response of the mth subcarrier, represents the noise power of the communication channel, BER stands for bit error rate.

[0019] The comprehensive performance of the optimization model of the robust OFDM shared waveform is adjusted by adjusting the bits and powers of different subcarriers, specifically:

[0020] Initialize the bit b assigned to the mth subcarrier m , the allocated transmit power p of the mth subcarrier m , weighted function value U m and the ratio r m ;

[0021] Calculate the total power allocated on the m subcarriers. If the total power allocated on the m subcarriers exceeds p T , the algorithm terminates and subtracts the excess power from the last allocated subcarrier power;

[0022] If the total power allocated to the m subcarriers does not exceed p T , then assume that one more bit is allocated to the mth subcarrier, and calculate the transmission power p′ required to be allocated at this time m , weighted function value U′ m and the ratio r m '; find the ratio r of all subcarriers m ′ takes the subcarrier number m corresponding to the maximum value, and gives the subcarrier an index number index_max; let m=index_max, assign a bit to the subcarrier, and return to the previous step.

[0023] The transmission power p′ m pass Calculated, f(b m ) is the transmission power required when MPSK modulation is used, and the expression is: Among them, p e Represents the bit error rate; the weighted function value U′ m pass Calculated; the ratio r m 'pass Calculated.

[0024] Beneficial Effects

[0025] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention can be widely used in perception communication integrated network scenarios, such as unmanned driving, drones, etc. The waveform design method proposed in the present invention can have the functions of communication transmission and radar detection while comprehensively considering radar and communication performance, and can adjust the weight factor according to the actual demand for communication and radar to achieve the purpose of adjusting the comprehensive system performance. In addition, the method fully considers the uncertainty of channel conditions and has good robustness; the bit and power allocation algorithm in the present invention provides an effective bit and power allocation scheme for OFDM shared waveform subcarriers in perception communication integrated networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of typical application scenarios of perceptual communication networks;

[0027] Figure 2 is a schematic diagram of a system model in an embodiment of the present invention;

[0028] Figure 3 It is a flow chart of the bit and power allocation algorithm in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0030] The embodiment of the present invention relates to a method for allocating bits and power of OFDM shared waveform subcarriers for integrated perceptual communication. The system model of the method is as follows: Figure 2 As shown in the figure, vehicle A sends an OFDM shared waveform s(t), which is transmitted through the radar and communication channels to vehicle B. Vehicle B receives the transmitted information and completes the information transmission. The radar echo signal y(t) returns to vehicle A and is processed by the radar signal to complete the radar detection.

[0031] This embodiment includes the design of a robust OFDM-aware communication integrated shared waveform and a bit and power allocation method.

[0032] The design of the robust OFDM-aware communication integrated shared waveform includes the following steps:

[0033] Step 1: Establish a signal transmission model

[0034] The transmitted time domain signal s(t) is as follows:

[0035]

[0036] Among them, f c Indicates the carrier center frequency, N s Indicates the number of subcarrier symbols, N c Indicates the number of subcarriers, a m represents the complex weight of the mth subcarrier, c m,n represents the phase encoding of the nth symbol in the mth subcarrier, Δf is the subcarrier spacing, T s Represents the duration of the entire OFDM symbol, rect[t / T s ] represents a rectangular function, in 0≤t≤T s The value is 1 when it is, otherwise the value is 0.

[0037] Step 2: Establish a radar detection model: Radar is used to track and detect targets. The larger the conditional mutual information (MI), the higher the estimation accuracy of the target impulse response. Therefore, conditional MI is used to measure radar performance. Assuming that the radar impulse response g(t) is a Gaussian random process, the echo signal y(t) received by vehicle A is as follows:

[0038]

[0039] Where n(t) is zero-mean additive white Gaussian noise, and its power spectral density is N(f). The conditional mutual information between the radar impulse response and the received echo signal is as follows:

[0040]

[0041] Among them, T p =N S T S Indicates the duration of the signal; |a m | 2 =p m represents the transmission power of the mth subcarrier, G(f m ) represents the impulse response of the radar channel, N(f m ) represents the noise power spectral density of the mth subcarrier, f m represents the mth subcarrier frequency, p T Indicates the given total transmit power.

[0042] In order to improve radar performance, the conditional mutual information is maximized under the total power limit. The optimization problem P1 is described as follows:

[0043]

[0044] Step 3, establish a communication model: Communication is used to achieve end-to-end information transmission. The data information rate (DIR) is used to measure communication performance. Assume that the communication channel is slowly time-varying and frequency-dependent. The data information rate DIR of the Gaussian white noise channel is as follows:

[0045]

[0046] Among them, H(f m ) represents the communication channel frequency response of the mth subcarrier, represents the noise power of the communication channel, BER stands for bit error rate.

[0047] In order to improve the communication performance, DIR is maximized under the given total power limit and BER. This optimization problem can be expressed as follows:

[0048]

[0049] Step 4: Design of robust OFDM shared waveform: Considering the uncertainty of channel conditions, the communication channel frequency response H(f m ) and radar channel impulse response G(f m ) is given in a set with known upper and lower bounds.

[0050]

[0051] Among them, Θ h,m =H(f m ), Θ g,m =G(f m ), l h,m and u h,m Respectively represent Θ h The next and previous term, l g,m and u g,m Respectively represent Θ g The next and previous term.

[0052] Under the condition of comprehensive consideration of radar and communication performance, the weighted optimization function of the robust OFDM shared waveform can be expressed as:

[0053]

[0054] in, U 1 is the optimal value of formula (4), U 2 is the optimal value of formula (6).

[0055] The optimization problem of robust OFDM shared waveform is to maximize the minimum value of the weighted optimization function in a given set of channel conditions. The optimization problem can be expressed as follows:

[0056]

[0057] Since I(p,Θ g ,Θ h )With Θ g,m and θ h,m increases with the increase of , so when Θ g,m and θ h,m Take the minimum value l g,m and l h,m When I(p,Θ g ,Θ h ) reaches the minimum value. Therefore, the P4 optimization problem can be further simplified as follows:

[0058]

[0059] Among them, I(p,l g,m ,l h,m ) is to convert l g,m and l h,m Substitute I(p,Θ g ,Θ h ) and the value after:

[0060]

[0061] The bit and power allocation method of this embodiment is as follows Figure 3 As shown, the following steps are included:

[0062] (1) Initialize the bit b allocated to the mth subcarrier m , the allocated transmit power p of the mth subcarrier m , weighted function value U m and the ratio r m ;

[0063] (2) Calculate the sum of the total power allocated to m subcarriers If the sum of the total power allocated on m subcarriers The algorithm terminates, and the excess power is subtracted from the last allocated subcarrier power;

[0064] (3) Assuming that one more bit is allocated to the mth subcarrier, the required transmit power p′ m , weighted function value U′ m and the ratio r m ′. Among them, the transmission power p′ m pass Calculated, f(b m ) is the transmission power required when MPSK modulation is used, and the expression is: Among them, p eRepresents the bit error rate; the weighted function value U′ m pass Calculated; the ratio r m 'pass Calculated.

[0065] (4) Find the ratio r among all subcarriers m ′ takes the subcarrier number m corresponding to the maximum value, and gives the subcarrier an index number index_max;

[0066] (5) Let m = index_max, assign one bit to the subcarrier, and let b m =b m +1, p m =p′ m , U m =U′ m , return to step (2).

[0067] It is not difficult to find that the present invention can be widely used in perception and communication integrated network scenarios, such as unmanned driving, drones, etc. The waveform design method proposed in the present invention can have the functions of communication transmission and radar detection while comprehensively considering radar and communication performance, and can adjust the weight factor according to the actual demand for communication and radar to achieve the purpose of adjusting the comprehensive system performance. In addition, the method fully considers the uncertainty of channel conditions and has good robustness; the bit and power allocation algorithm in the present invention provides an effective bit and power allocation scheme for OFDM shared waveform subcarriers in perception and communication integrated networks.

Claims

1. A method for allocating bits and power of OFDM shared waveform subcarriers for integrated perceptual communication, characterized in that: The following steps are involved: Establish a signal transmission model; wherein the signal transmission model is Among them, s(t) represents the transmitted time domain signal, f c Indicates the carrier center frequency, N s Indicates the number of subcarrier symbols, N c Indicates the number of subcarriers, a m represents the complex weight of the mth subcarrier, c m,n represents the phase encoding of the nth symbol in the mth subcarrier, Δf is the subcarrier spacing, T s represents the duration of the entire OFDM symbol, rect[·] represents the rectangular function; Under the total power limitation, a radar detection model is established with the goal of maximizing conditional mutual information. Under the constraints of total power and BER, a communication model is established with the goal of maximizing the data information rate; Based on the radar detection model and the communication model, an optimization model of a robust OFDM shared waveform is established under the condition of comprehensively considering the radar and communication performances; wherein the optimization model of the robust OFDM shared waveform is: Θ g represents the radar channel impulse response G(f m ) Given a set of upper and lower limits, Θ h represents the given upper and lower limits of the communication channel frequency response, ω1 and ω2 represent the weights of the radar detection model and the communication transmission model function, respectively, and ω1+ω2=1, U1 is the optimal value of the radar detection model, U2 is the optimal value of the communication model, T p =N S T S Indicates the duration of the signal; |a m | 2 =p m represents the mth subcarrier f m The transmission power, Θ g,m =G(f m ), represents the impulse response of the radar channel, N(f m ) represents the mth subcarrier f m The noise power spectral density; Θ h,m =H(f m ), indicating the mth subcarrier f m The communication channel frequency response, represents the noise power of the communication channel, BER stands for error rate; By adjusting the bits and powers of different subcarriers, the comprehensive performance of the optimization model of the robust OFDM shared waveform is adjusted, specifically: Initialize the bit b assigned to the mth subcarrier m , the allocated transmit power p of the mth subcarrier m , weighted function value U m and the ratio r m ; Calculate the total power allocated on the m subcarriers. If the total power allocated on the m subcarriers exceeds p T , the algorithm terminates and subtracts the excess power from the last allocated subcarrier power; If the total power allocated to the m subcarriers does not exceed p T , then assume that one more bit is allocated to the mth subcarrier, and calculate the transmission power p′ required to be allocated at this time m , weighted function value U′ m and the ratio r m '; find the ratio r of all subcarriers m ′ takes the subcarrier number m corresponding to the maximum value, and gives the subcarrier an index number index_max; let m = index_max, assign a bit to the subcarrier, and return to the previous step; Wherein, the transmission power p′ m pass Calculated, f(b m ) is the transmission power required when MPSK modulation is used, and the expression is: Among them, p e Represents the bit error rate; the weighted function value U′ m pass Calculated; the ratio r m 'pass Calculated.

2. The method for allocating bits and power of OFDM shared waveform subcarriers for integrated perceptual communication according to claim 1, characterized in that: The radar detection model is: y(t) represents the received echo signal, g(t) represents the response signal of the radar channel, G(f m ) represents the impulse response of the radar channel, p T Indicates the given total transmit power.

3. The method for allocating bits and power of OFDM shared waveform subcarriers for integrated perceptual communication according to claim 1, characterized in that: The communication model is: C t represents the data information rate, |a m | 2 =p m represents the transmission power of the mth subcarrier, H(f m ) represents the communication channel frequency response of the mth subcarrier.

Images