A distance and speed estimation method based on offset constant envelope OFDM

Abstract

To improve the perception performance of an integrated communication and perception system using offset constant envelope OFDM (OFDM), this paper proposes a distance and velocity estimation method based on offset constant envelope OFDM. This method uses an offset constant envelope OFDM signal as the transmission signal for the integrated communication and perception system and uses a 2D-FFT algorithm based on conjugate multiplication to estimate target range and velocity. This method effectively reduces the impact of a non-flat signal spectrum and achieves superior distance and velocity estimation performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication and perception integration, and specifically relates to a distance and speed estimation method based on offset constant envelope orthogonal frequency division multiplexing (OFDM). Background Art

[0002] OFDM signals have strong amplitude fluctuations and suffer from high peak-to-average power ratio (PAPR) issues. Applying phase modulation to OFDM signals yields constant envelope orthogonal frequency division multiplexing (CE-OFDM) signals. Its 0dB PAPR prevents the impact of HPA nonlinearities on communication transmission and target perception, making CE-OFDM a suitable multi-carrier waveform for integrated communication and perception systems. Phase modulation imparts a large DC component to CE-OFDM signals, leading to uneven frequency domain power distribution and impacting spectrum sensing performance. To limit the DC component of CE-OFDM, a shifted constant envelope OFDM waveform is developed by shifting the DC component by a certain amount and performing power compensation on other subcarriers. However, the spectrum of this shifted constant envelope OFDM is not completely flat, resulting in poor range and velocity estimation performance using traditional two-dimensional fast Fourier transform (2D-FFT) sensing algorithms. Therefore, in order to improve the perception performance, the present invention proposes a distance and speed estimation method based on offset constant envelope OFDM for target perception in an offset constant envelope OFDM communication and perception integrated system. Summary of the Invention

[0003] To improve the perception performance of an integrated communication and perception system using offset constant envelope OFDM, this paper proposes a distance and velocity estimation method based on offset constant envelope OFDM. This method uses an offset constant envelope OFDM signal as the transmission signal for the integrated communication and perception system and uses a 2D-FFT algorithm based on conjugate multiplication to estimate target range and velocity. This method effectively reduces the impact of a non-flat signal spectrum and achieves superior distance and velocity estimation performance.

[0004] For ease of understanding, the offset constant envelope OFDM communication and perception integrated system is defined as follows:

[0005] Assume that the number of symbols in the transmitted data frame is U, the number of subcarriers per symbol is N, the subcarrier spacing is Δf, the symbol period is T, the speed of light is c0, the distance to the perceived target is R, and the speed is v.

[0006] The technical solution of the present invention is:

[0007] The distance and speed estimation method based on offset constant envelope OFDM includes:

[0008] Transmitter:

[0009] Step 1: Generate information bit stream. The number of subcarriers in the symbol is N, and Quadrature Amplitude Modulation (QAM) is used with a modulation order of M. Taking the uth symbol in the data frame as an example, the information bit sent is b u =[b u (1),...,b u (((N-2) / 2-1)×log2M)].

[0010] Step 2: Data modulation and conjugate symmetry. The transmitted information bit b of the uth symbol is converted to u Perform M-order QAM modulation to obtain a modulated signal with a length of (N-2) / 2-1:

[0011] X=[X[0],X[1],...,X[((N-2) / 2-1)-1]]

[0012] To ensure that the phase-modulated OFDM signal is a real signal, the M-order modulated QAM symbol X[k], k = 0, 1, ..., (N-2) / 2-1 needs to be mapped into a conjugate symmetric data format before performing IFFT transformation:

[0013]

[0014] Step 3: Subcarrier mapping and IFFT transformation. Mapped to the N subcarriers of the multicarrier symbol, and then after N-point IFFT operation, the time domain discrete real number OFDM signal is obtained.

[0015]

[0016] in are the imaginary and real parts of X[k] respectively.

[0017] Step 4: Phase modulation. For OFDM signal Perform phase modulation to obtain a discrete time domain CE-OFDM signal:

[0018]

[0019] Where A represents the amplitude of the carrier signal, and 2πh represents the phase modulation index of CE-OFDM. The variance of is (2πh) 2 , set the normalization constant factor C N The value of in Indicates the average energy of M-order QAM modulation.

[0020] Step 5: DC offset and power compensation. DC offset the CE-OFDM signal s[n] and perform power compensation on the signal to ensure the normalization of the transmitted signal power. The transmitted time domain signal of the offset constant envelope OFDM can be expressed as:

[0021]

[0022] Where κ represents the power compensation coefficient and λ represents the DC offset length. The maximum DC offset length λ max is the DC component strength of the CE-OFDM signal, that is:

[0023]

[0024] Among them, μ represents the DC offset ratio, and its value range is [0,1]. The corresponding power compensation coefficient κ is:

[0025]

[0026] Step 6: Construct the transmission data frame and add the cyclic prefix. Define that the transmission data frame contains U offset constant envelope OFDM symbols, then the nth time domain signal of the uth symbol in the subframe is expressed as s OCE [u,n],n=0,1,...,N-1,u=0,1,...,U-1. Finally, in each time domain symbol s OCE [n] adds length N CP The cyclic prefix (CP) is added to obtain the final time domain transmission symbol and sent through the base station transmitting antenna.

[0027] Receiver:

[0028] Step 7: Remove cyclic prefix and convert time domain to frequency domain. After receiving the echo signal from the target, the base station performs CP removal to obtain the time domain received signal z[u,n], and performs FFT transformation on each symbol of the received signal to obtain the frequency domain symbol Z[u,k]. When the signal bandwidth B is much smaller than the carrier frequency f cWhen , the Doppler frequency shift will produce an identical linear phase shift on each subcarrier. Considering the subcarrier spacing △f, the impact of target distance and speed on the received frequency domain symbol Z[u,k] can be quantified as follows:

[0029]

[0030] Where S[u,k] represents the transmitted data on the kth subcarrier of the uth symbol in the data frame, Z[u,k] represents the received data on the kth subcarrier of the uth symbol in the echo data frame, and W[u,k] represents the power σ 2 Gaussian white noise, A[u,k] represents the attenuation and phase shift caused by signal propagation and scattering.

[0031] Step 8: Conjugate multiplication. Perform conjugate multiplication on the echo frequency domain signal Z[u,k] and the known transmitted frequency domain signal S[u,k] to eliminate the influence of the transmitted frequency domain signal:

[0032] Z[u,k]×(S[u,k]) * =|S[u,k]| 2 ×k R [u,k]×k v [u,k]+W[u,k]×(S[u,k]) *

[0033] in:

[0034]

[0035] Step 9: 2D-FFT operation and target information estimation. Perform 2D-FFT operation on the echo frequency domain data frame, which is equivalent to the maximum likelihood estimation (MLE) algorithm for target distance and speed. Perform IFFT operation on the frequency axis of the data frame to obtain the target information from k R [u,k] to obtain the distance information of the perceived target; perform FFT operation on the time axis of the data frame to obtain the distance from k v [u,k] gets the speed information of the perceived target:

[0036]

[0037]

[0038] After 2D-FFT processing, the conditions for peak generation are:

[0039]

[0040]

[0041] Numbered according to the peak position and A distance estimate can be obtained and velocity estimates

[0042]

[0043]

[0044] When the data frame is upsampled in the frequency and time dimensions at the perception receiving end, the number of 2D-FFT operation points increases exponentially. At this time, the equivalent time interval and frequency interval of perception become smaller, the perception accuracy is improved, but the computational complexity also increases. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of an offset constant envelope OFDM transmitter.

[0046] Figure 2 Schematic diagram of an offset constant envelope OFDM sensing receiver. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0048] Example:

[0049] Below, the target distance R = 1000m, the target speed v = 30m / s, and the cyclic prefix N CP =4, signal bandwidth B = 1.92MHz, symbol period T = 0.33us, carrier frequency f c =60 GHz, using Quadrature Phase Shift Keying (QPSK) modulation. Each symbol contains N = 64 subcarriers, with a subcarrier spacing of Δf = 30 kHz. The data frame contains U = 16 symbols. u (u = 1, ..., 16) denotes the offset constant envelope OFDM symbol number, n (n = 1, ..., 64) denotes the time domain sampling point number within the symbol, and k (k = 1, ..., 64) denotes the subcarrier number.

[0050] During phase modulation, the amplitude A=1, the phase modulation index 2πh=0.6, the DC offset ratio μ=0.6, and the DC component λ max =0.8353, and the channel environment adopts an ideal transmission environment A[u,k]=1, and the specific implementation mode of the present invention is introduced as an example.

[0051] Transmitter:

[0052] Step 1: Generate an information bit stream. The number of subcarriers in a symbol is N = 64, and Quadrature Phase Shift Keying (QPSK) is used with a modulation order of M = 4. Taking the first symbol in a data frame as an example, the transmitted information bits are b1 = [b1(1), ..., b1(30 × log24)].

[0053] Step 2: Data modulation is symmetrical with conjugate modulation. The transmitted information bit b1 of the first symbol is modulated by QPSK to obtain a modulated signal with a length of 31:

[0054] X=[X[0],X[1],...,X

[30] ]

[0055] To ensure that the phase-modulated OFDM signal is a real signal, the QPSK symbol X[k], k = 0, 1, ..., 30 needs to be mapped into a conjugate symmetric data format before the IFFT transformation:

[0056]

[0057] Step 3: Subcarrier mapping and IFFT transformation. Mapped to the 64 subcarriers of the multicarrier symbol, and then after a 64-point IFFT operation, the time domain discrete real number OFDM signal is obtained.

[0058]

[0059] in are the imaginary and real parts of X[k] respectively.

[0060] Step 4: Phase modulation. For OFDM signal Perform phase modulation to obtain a discrete time domain CE-OFDM signal:

[0061]

[0062] Among them, the normalization constant factor C N The value of in Indicates the average energy of QPSK modulation.

[0063] Step 5: DC offset and power compensation. DC offset the CE-OFDM signal s[n] and perform power compensation on the signal to ensure the normalization of the transmitted signal power. The transmitted time domain signal of the offset constant envelope OFDM can be expressed as:

[0064]

[0065] Where κ represents the power compensation coefficient and λ represents the DC offset length. The maximum DC offset length λ max is the DC component strength of the CE-OFDM signal, that is:

[0066] λ=μλ max =0.6×0.8353=0.5012

[0067] The corresponding power compensation coefficient κ is:

[0068]

[0069] Step 6: Construct the transmission data frame and add the cyclic prefix. Define that the transmission data frame contains U offset constant envelope OFDM symbols, then the nth time domain signal of the uth symbol in the subframe is expressed as s OCE [u,n],n=0,1,...,63,u=0,1,...,15. Finally, in each time domain symbol s OCE [n] adds length N CP =4 cyclic prefix (CP), the final time domain transmission symbol is obtained and sent through the base station transmitting antenna.

[0070] Receiver:

[0071] Step 7: Remove the cyclic prefix and convert the time domain to the frequency domain. After receiving the echo signal from the target, the base station performs a cyclic prefix removal operation to obtain the time domain received signal z[u,n]. Each symbol of the received signal is transformed by FFT to obtain the frequency domain symbol Z[u,k]. The signal bandwidth B = 1.92MHz is much smaller than the carrier frequency f c =60GHz, considering the subcarrier spacing ∆f = 30kHz, the impact of target distance and speed on the received frequency domain symbol Z[u,k] can be quantified as follows:

[0072]

[0073] Where S[u,k] represents the transmitted data on the kth subcarrier of the uth symbol in the data frame, Z[u,k] represents the received data on the kth subcarrier of the uth symbol in the echo data frame, and W[u,k] represents the power σ 2 Gaussian white noise, A[u,k] represents the attenuation and phase shift caused by signal propagation and scattering.

[0074] Step 8: Conjugate multiplication. Perform conjugate multiplication on the echo frequency domain signal Z[u,k] and the known transmitted frequency domain signal S[u,k] to eliminate the influence of the transmitted frequency domain signal:

[0075] Z[u,k]×(S[u,k]) *=|S[u,k]| 2 ×k R [u,k]×k v [u,k]+W[u,k]×(S[u,k]) *

[0076] in:

[0077]

[0078] Step 9: 2D-FFT operation and target information estimation. Perform 2D-FFT operation on the echo frequency domain data frame, which is equivalent to the maximum likelihood estimation (MLE) algorithm for target distance and speed. Perform IFFT operation on the frequency axis of the data frame to obtain the target information from k R [u,k] to obtain the distance information of the perceived target; perform FFT operation on the time axis of the data frame to obtain the distance from k v [u,k] gets the speed information of the perceived target:

[0079]

[0080]

[0081] Among them, R=1000m, v=30m / s.

[0082] After 2D-FFT processing, the conditions for peak generation are:

[0083]

[0084]

[0085] Numbered according to the peak position and A distance estimate can be obtained and velocity estimates

[0086]

[0087]

[0088] When the data frame is upsampled in the frequency and time dimensions at the perception receiving end, the number of 2D-FFT operation points increases exponentially. At this time, the equivalent time interval and frequency interval of perception become smaller, the perception accuracy is improved, but the computational complexity also increases.

Claims

1. A distance and speed estimation method based on offset constant envelope OFDM, defining the number of offset constant envelope OFDM symbols as , the number of subcarriers per symbol is ; Symbol number express, , subcarrier numbering is express, , the time domain sampling point number is express, ; The system adopts QPSK modulation with an order of , the subcarrier spacing is , the symbol period is , the carrier frequency is , the speed of light is ; The target distance is , the speed is ; The amplitude of phase modulation is , the phase modulation index is , the DC offset ratio is ; It is characterized in that, The method comprises the following steps: Transmitter: Step 1: For the first symbols, the transmitter generates the information bits to be sent as ； Step 2: Symbols of transmitted information bits Perform QPSK modulation and obtain a length of The modulation signal : ， Before IFFT transformation, QAM symbols with 1-order modulation Mapping to conjugate symmetric data form : ； Step 3: Set the length to QAM data Mapped to multi-carrier symbols subcarriers, and then pass through After the IFFT operation, the time domain discrete real number OFDM signal is obtained : ， in They are The imaginary and real parts of Step 4: OFDM signal Perform phase modulation to obtain discrete time domain CE-OFDM signal ,in, represents the amplitude of the carrier signal, Indicates the phase modulation index of CE-OFDM; in order to make the signal phase The variance of , set the normalization constant factor The value of ,in express Average energy of QAM modulation; Step 5: CE-OFDM signal Perform DC offset and power compensation on the signal to ensure the normalization of the transmitted signal power. The obtained offset constant envelope OFDM transmission time domain signal is expressed as ,in, represents the power compensation coefficient, Indicates the DC offset length, the maximum DC offset length is the DC component strength of the CE-OFDM signal: ， in, Indicates the DC offset ratio, the value range is , the corresponding power compensation coefficient for: ； Step 6: Define the transmitted data frame offset constant envelope OFDM symbols, then the first The symbol The time domain signal is represented as ; In each time domain symbol Add the length The cyclic prefix is obtained to obtain the final time domain transmission symbol and send it through the base station transmitting antenna; Receiver: Step 7: After receiving the echo signal from the target, the base station performs a CP removal operation to obtain the time domain received signal , perform FFT transformation on each symbol of the received signal to obtain the frequency domain symbol , considering the subcarrier spacing , the target distance and speed are received in the frequency domain symbol The impact is quantified as follows: ， in, Indicates the first The symbol The data transmitted on the subcarriers is Indicates the echo data frame The symbol The received data on the subcarriers, Indicates power is Gaussian white noise, Represents the attenuation and phase shift that occurs due to signal propagation and scattering; Step 8: Echo frequency domain signal and known transmitted frequency domain signals Perform a conjugate multiplication operation to remove the effect of the transmitted frequency domain signal: ， in: ； Step 9: Echo frequency domain data frame Perform 2D-FFT operation and IFFT operation on the frequency axis of the data frame to obtain Get the distance information of the perceived target: ， Perform FFT operation on the time axis of the data frame to obtain Get the speed information of the perceived target: ， After 2D-FFT processing, the conditions for peak generation are: ， ， Numbered according to the peak position and Get a distance estimate and velocity estimates : ， 。

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