Transmitter and receiver for transmitting and receiving symbols on time-varying channels with Doppler shift and methods thereof

Abstract

A communication frame for an orthogonal time-frequency space transmission system includes a first class of blocks and a second class of blocks. The first class of blocks comprise pilot signals, protection signals and data signals, and the second class of blocks only comprise the data signals. Pilot symbols, guard signal and data symbols of the first class of blocks and data symbols of the second class of blocks are arranged along points of a grid in the delayed Doppler domain. In a communication frame, the second type of blocks are followed by the first type of blocks, and the first type of blocks are followed by the second type of blocks. In the first class of blocks, at least one pilot symbol is surrounded on at least three sides by one or more guard symbols. Points, which are not occupied by the pilot symbols or the protection symbols, in the grids of the first class of blocks in the delay Doppler domain are used for data symbols. Communication frames allow for determination of oscillator frequency offsets and channel coefficients in a receiver.

Description

Technical Field

[0001] The present invention relates to a method for receiving symbols on an orthogonal time-frequency-space (OTFS) communication channel affected by Doppler spread and a receiver implementing the method. Background Art

[0002] The sixth-generation (6G) wireless communication and subsequent technologies are expected to serve a large number of high-speed mobile users, such as vehicles, subways, highways, trains, drones, low Earth orbit (LEO) satellites, etc.

[0003] The previous fourth-generation and fifth-generation (5G) wireless communications adopt orthogonal frequency-division multiplexing (OFDM) technology, which has high spectral efficiency and high robustness to frequency-selective fading channels, and also allows the use of low-complexity equalizers. However, due to speed-related Doppler frequency shift or spread and fast-changing multipath reception, high-speed mobile communications suffer from severe time and frequency dispersion. Both time and frequency dispersion can cause signal fading at the receiver, so this fading is also called double-selective channel fading. Double-selective channel fading can seriously damage the performance of OFDM communications.

[0004] As an alternative to OFDM, OTFS modulation has been proposed as a solution to cope with double-selective fading channels, providing higher reliability than OFDM.

[0005] OTFS modulation is a 2D modulation scheme that multiplexes information QAM symbols onto carrier waveforms corresponding to local pulses in the signal representation, which is called the delay-Doppler representation. OTFS waveforms are distributed in both time and frequency, but under common delay-Doppler channel impairments, they generally remain orthogonal to each other. Theoretically, OTFS combines the reliability and robustness of spread spectrum and the high spectral efficiency and low complexity of narrowband transmission.

[0006] Figure 1A block diagram of a general OTFS transmission system is shown. The transmitter 200 includes a first transmitter-side transformation unit 202 and a second transmitter-side transformation unit 204. Serial binary data is input to a signal mapper (not shown in the figure), which outputs a two-dimensional sequence x[k, l] of information symbols, where QAM symbols are arranged along the delay period and Doppler period in the delay-Doppler domain. The information symbols include data symbols, pilot symbols, and guard symbols surrounding the pilot symbols. The two-dimensional sequence x[k, l] of information symbols is input to the first transmitter-side transformation unit 202 and undergoes an inverse finite symplectic Fourier transform (iSFFT) to generate a matrix X[n, m], which represents the two-dimensional sequence of information symbols x[k, l] in the time-frequency domain. When the transmitter transmits in the time domain, a further transformation needs to be performed in the second transmitter-side transformation unit 204 to generate a signal s[t] in the time domain, such as a Heisenberg transform. Then, the signal s[t] is transmitted via the antenna 206 over the communication channel.

[0007] In a real environment, when the transmitted signal reaches the receiver from the transmitter through the communication channel, it is subject to doubly selective fading with Doppler spread. The received signal is a superposition of the direct copy of the transmitted signal and multiple reflected copies, where each copy is delayed due to the path delay depending on the length of the signal path and frequency-shifted due to the Doppler shift depending on the differential velocity between the transmitter, reflector, and receiver. Each signal copy is weighted according to its specific path delay and differential velocity. Typical Doppler shifts are on the order of 10 Hz - 1 kHz, but larger values may occur in cases of extremely high mobility (such as high-speed trains) and / or high carrier frequencies. Since it is very likely that there are multiple reflectors and / or moving reflectors in a real environment, the received superimposed signal is spread over a frequency range rather than just frequency-shifted, so the signal distortion is also called Doppler shift. In the following description, the real communication channel is also referred to as the actual communication channel.

[0008] In Figure 1 it, the actual communication channel is represented by the unperturbed radio waves transmitted by the transmitter antenna 206 and various disordered radio waves from different directions and at different distances from each other at the receiver antenna 302. The radio waves can reach the receiver's antenna directly or after being reflected one or more times at one or more stationary and / or moving objects, which may introduce Doppler shifts and different delays to the reflected radio waves.

[0009] The receiver 300 picks up the received signal r[t] in the time domain and provides it to the first receiver-side transformation unit 304, where a Wigner transform is performed on it to transform the received signal r[t] into a matrix Y[n,m] representing the received signal r[t] in the time-frequency domain. To be able to detect signals in the delay-Doppler domain, the matrix Y[n,m] is then provided to the second receiver-side transformation unit 306, where a finite symplectic Fourier transform (SFFT) is performed on it, and the SFFT outputs a two-dimensional sequence of information symbols y[k,l] in the delay-Doppler domain. The two-dimensional sequence of information symbols y[k,l] is input to the channel estimation and equalization block 310, which performs channel estimation CE and signal detection SD and reconstructs the originally transmitted symbol, which is finally input to a demapper to output the originally transmitted binary data (the demapper is not shown in the figure).

[0010] Although the superiority of OFTS modulation is indisputable under ideal conditions, its practical limitations in cost-effective applications may pose obstacles to its widespread adaptation, especially for carrier frequency offset (CFO).

[0011] CFO is the carrier frequency mismatch between the transmitter and the receiver and is caused by the Doppler effect and radio frequency (RF) device components. The CFO caused by the Doppler effect is usually called Doppler frequency shift or Doppler spread, while the CFO caused by the local crystal oscillator (XO) is called oscillator frequency offset (OFO).

[0012] There are mainly three types of crystal oscillators, namely free-running XO, temperature-controlled XO (TCXO), and oven-controlled XO (OCXO). Free-running XO is the cheapest but has the largest frequency error, for example, between ±10 to ±20 ppm, where ppm represents one part per million. OCXO can reduce the frequency error to 0.0015 ppm, but the device cost is very high, 2000 times that of free-running XO, and it also increases the power cost. TCXO is a good balance between free-running XO and OCXO. It is much cheaper than OCXO, about one-fifth of the cost, and the frequency error can be reduced to ±1.5 ppm.

[0013] OFO is usually much larger than the Doppler frequency shift or spread. For example, when the carrier frequency is 4 GHz, a TCXO with a frequency error of ±1.5 ppm may result in an OFO of ±6 kHz, which is more significant than the Doppler frequency shift of 0.5 to 2 kHz at speeds between 125 and 500 km / h. It should be noted that the Doppler frequency shift is added to the OFO, further increasing the maximum Doppler frequency shift at the receiver.

[0014] Therefore, in the presence of OFO and using a communication channel affected by Doppler shift, it is necessary to optimize the performance of the OTFS communication system in terms of spectral efficiency and reliability. Summary of the Invention

[0015] The present invention aims to solve this problem, and for this purpose, a method for estimating and compensating large OFO (e.g., greater than 0.5 ppm) in an OTFS receiver is proposed, especially in OTFS transmissions with low pilot overhead and high spectral efficiency. The present invention also proposes a two-dimensional arrangement of pilot symbols and data symbols of a communication frame for an OTFS transmission system used in this method, having dual-rate data and dedicated pilots (DP), and also proposes a time-frequency distortion resilient OTFS (TFDR-OTFS) transmitter and a corresponding receiver for transmitting and receiving respectively a communication frame according to the present invention for high-mobility communications affected by OFO caused by local XO. The term "dual-rate" refers to the multiplexing of low-rate data and high-rate data, and also allows in-band signaling in the control and user planes. In-band signaling can be used to transmit UE-specific control information and common control information.

[0016] In the following description, an OTFS analysis system model considering OFO will be proposed, then a two-dimensional arrangement of pilot symbols and data symbols of a communication frame for an OTFS transmission system used in the method of the present invention will be proposed, and finally, the proposed TFDR-OTFS receiver having dual-rate data and DP will be discussed in detail.

[0017] Throughout this specification, bold symbols represent vectors or matrices. Superscripts T, H, and represent the transpose, complex conjugate transpose, and pseudo-inverse of a vector or matrix, respectively. diag{a} is a diagonal matrix with vector a on its diagonal, while diag{A} is a vector whose elements come from the diagonal of matrix A. is the Kronecker product.

[0018] In the OTFS system model including OFO, N and M represent the dimensions of the delay grid and the Doppler grid in which the symbols are arranged, respectively. The transmitted complex OTFS matrix x is defined as

[0019] x = [x[0, 0], x[0, 1],..., x[0, M - 1],..., x[N - 1, 0], x[N - 1, 1],..., x[N - 1, M - 1]] T

[0020] The received OTFS matrix y is defined as

[0021] y = [y[0, 0], y[0, 1],..., y[0, M - 1],..., y[N - 1, 0], y[N - 1, 1],..., y[N - 1, M - 1]] T

[0022] H t is an MN×MN time - varying channel matrix in the time domain, where the Jakes model is considered, and the maximum Doppler frequency is denoted as f D . Let φ (φ ∈ [-e ofo , e ofo )) be defined as OFO, where e ofo is the maximum frequency error of XO, in ppm. In the presence of OFO, the received OTFS signal vector y can be written as

[0023]

[0024] where is the OFO matrix, F N is the discrete Fourier transform (DFT) matrix, I M is the M×M identity matrix, and w is the additive white Gaussian noise vector. By applying the generalized complex - exponential basis - expansion modeling (GCE - BEM) to the model H t , for example, as described in German Patent Application No. 102022 106 409.3, the entire content of which is incorporated herein by reference, y is further expressed as

[0025]

[0026] where b q and c q are the q - th GCE - BEM basis function and coefficient respectively, Q represents the GCE - BEM order related to f D , F MN is the DFT matrix, and z mod is the GCE - BEM modeling error.

[0027] Next, by considering the complex - exponential basis - expansion modeling (CE - BEM), the element - wise input - output relationship between x[k, l] and y[k, l] is derived. At the transmitter side, after applying the inverse symplectic finite Fourier transform (iSFFT) and the Heisenberg transform, the time - domain symbol s[n, m] is written as

[0028]

[0029] Define h[t, l′] as the channel gain of the l′-th path (l′ = 0, 1,..., L) at the t-th (t = 0, 1,..., MN - 1) moment, where L represents the channel length. After propagation through the doubly selective fading channel, the received time-domain symbol r[n, l] is expressed as

[0030]

[0031] where it is assumed that e[n, l] is the time-domain modeling error due to CE-BEM modeling. At the receiver side, after performing SFFT and Wigner transform, the received symbol y[k, l] in the delay-Doppler domain is given by

[0032]

[0033] where z[k, l] is the modeling error in the delay-Doppler domain due to CE-BEM modeling. Compared with the ideal system without OFO, there are two problems:

[0034] - i) More symbols in the Doppler domain interfere with each other, so the inter-carrier interference is stronger, and

[0035] ii) The phase of the received signal is changed by introducing an additional exponential term Thus, if the OFO problem is not properly solved, OTFS modulation will lose its excellent performance in high-mobility communications.

[0036] In addition, due to the existence of OFO, OTFS channel estimation becomes more challenging. Referring to

[0037] Figure 2 , assume such a scenario where the carrier frequency f c is set to 4 GHz, the speed is v = 125 km / h, and the frequency error of XO is ±1.5 ppm. The maximum Doppler frequency is calculated as f D = 500 Hz, and the OFO frequency is f OFO = ±6 KHz. Figure 2 depicts an example of a possible Doppler spectrum, where f D = 500 Hz, f OFO = -6 KHz, 0, 6 KHz. It can be easily seen that OFO will shift the Doppler spectrum to the left or right, so the maximum Doppler frequency increases to f D + f OFO . Among the known OTFS channel estimators, such as those discussed in German Patent Application No. 102022 106 409.3 or German Patent Application No. 10 2021 126321.2, it is necessary to be based on the new maximum Doppler frequency (i.e., f D ​+f OFO ) Regenerate subspace or basis expansion modeling (BEM) basis functions. Since the frequency offset caused by OFO is much larger than that caused by the Doppler effect, the number of required subspace or BEM basis functions will increase significantly, resulting in high pilot overhead. Therefore, it is very important to estimate and compensate for OFO before implementing the OTFS channel estimator.

[0038] According to the first aspect of the present invention, a two-dimensional arrangement of pilot symbols and data symbols for a dual-rate communication frame in an OTFS transmission system is proposed. The DP part is carefully designed for initial OFO estimation and subsequent joint estimation of the channel and residual OFO.

[0039] The communication frame includes a first type of block and a second type of block. The first type of block includes pilot signals, guard signals, and data signals, and the second type of block includes only data signals. The pilot symbols, guard signals, and data symbols of the first type of block and the data symbols of the second type of block are arranged along the grid points in the delay-Doppler domain. The communication frame is characterized in that the corresponding first type of block is located before and after or follows the second type of block. In the first type of block, at least one pilot symbol is surrounded by one or more guard symbols on at least three sides, and the points in the grid of the first type of data block in the delay-Doppler domain that are not occupied by pilot symbols or guard symbols are used for data symbols.

[0040] Figure 3 a) in depicts an exemplary dual-rate OTFS frame with DP. Two low-rate data and DP blocks are placed in front of and behind the OTFS frame along the delay dimension respectively for OFO estimation. The low-rate data symbols are shown in a diagonal cross-hatch pattern. The DP symbols are shown in black, and the guard symbols or guard spaces are shown in a cross-hatch pattern. Note that the guard symbols are considered part of the pilot symbols, especially for determining the pilot overhead. The number of pilots required for correct channel estimation is preferably at least (2Q + 1)(2L + 1), where Q is the BEM order (Q << N) and L is the channel length. The dimension of the low data rate block is 2N(L + 1). The dimension of the pilot block nested in the low data rate block is 2P(L + 1), while P >= 2Q + 1. P is the number of pilot symbols and guard symbols along the Doppler dimension and is selected according to the maximum Doppler frequency. For example, assuming Q = 2, L = 5, N = 16, the minimum number of pilots required for correct channel estimation is 5 * 11 = 55. The size of the low data rate block is 2 * 16 * 6 = 192, and the size of its pilot block is at least 2 * 5 * 6 = 60. Therefore, since 60 > 55, no additional pilots are required in the high-rate block, and pilot-assisted channel estimation can be performed using only the pilots in the low-rate block. However, for whatever reason, additional pilots can be used in the high-rate block. The size of the high-rate data block represented by the white box is (M - 2(L + 1))N.

[0041] In Figure 3 a) of, the front end of the dedicated pilot (DP) symbol is configured with two guard symbols. Due to the cyclic convolution processing in the receiver, the guard symbol of the first type of block following the first type of block can be regarded as the trailing DP symbol of the first type of block located in front of the second type of block. Therefore, the DP symbol is surrounded by guard symbols on both sides. This effect is shown in Figure 3 b). Here, the second low-rate block behind the high-rate block is folded in front of the first low-rate block in front of the high-rate block, and the leading guard interval of the first low-rate block in front of the high-rate block actually becomes the trailing guard interval, as shown by the dashed box. It should be noted that the distance between the two low-rate blocks is added only for clarity.

[0042] Providing two low-rate blocks, one in front of the high-rate block and one behind it, allows the OFO to be determined in the receiver. At the same time, each low-rate block carrying a DP symbol can be made smaller in the delay dimension, but with appropriate guard symbols surrounding the DP symbol. Therefore, the benefit of being able to determine the OFO in the receiver is achieved without increasing the pilot overhead or only increasing a small amount of pilot overhead.

[0043] The length of the high-rate block separating the low-rate blocks in the time-delay dimension determines the range of the OFO that can be estimated. A shorter high-rate block length supports the estimation of a wider OFO range, but the estimation accuracy will decrease.

[0044] It should be noted that the DP symbol can have trailing / post trailing guard symbols instead of leading / pre leading guard symbols, as exemplarily shown in c) of Figure 3 . As mentioned above, due to the cyclic convolution processing in the receiver, the guard symbols of the first type of block on both sides of the second type of block will surround the DP symbol from both sides in the same way as discussed in b) of reference Figure 3 .

[0045] In one or more embodiments of the communication frame, the pilot and guard symbols in the first type of block at least before and after the second type of block are the same, for example, in terms of their amplitudes and arrangements in the delay-Doppler grid.

[0046] In one or more embodiments of the communication frame, the number of guard symbols located before and / or after the pilot symbol in the direction of the delay domain is twice the maximum time-delay value in units of delay bins / delay cells.

[0047] According to a second aspect of the present invention, a transmitter of an OTFS transmission system includes a signal mapper disposed upstream of a first transmitter-side transformation unit and a second transmitter-side transformation unit. The signal mapper is adapted to receive a binary data sequence and output a two-dimensional arrangement of pilot symbols, guard symbols, and data symbols of a communication frame in the delay-Doppler domain according to the first aspect of the present invention described above. The first transmitter-side transformation unit is adapted to receive, at an input, the two-dimensional communication frame in the delay-Doppler domain output from the signal mapper and output a two-dimensional arrangement of information symbols in the time-frequency domain. The two-dimensional arrangement of information symbols in the time-frequency domain includes and represents both pilot symbols and data symbols. The output of the first transmitter-side transformation unit is provided to the input of the second transmitter-side transformation unit, and the second transmitter-side transformation unit is adapted to output a continuous time-domain signal representing the communication frame for transmission over a communication channel.

[0048] In one or more embodiments, the first transmitter-side transformation unit is adapted to perform precoding and / or inverse symplectic finite Fourier transform.

[0049] In one or more embodiments, the second transmitter-side transformation unit is adapted to perform a Heisenberg transform or an inverse finite Fourier transform (IFFT).

[0050] In a practical scenario, there are limitations on the transmission power, which cover both data transmission and pilot transmission. Define P T as the total transmission power, and α (α ∈ (0, 1)) as the data power allocation ratio. It indicates that P T and (1 - α)P T are used for transmitting data symbols and pilots, respectively. Generally, if more power is used for pilot transmission, i.e., α is smaller, the initial channel estimation performance will be better. However, the power available for data transmission will be reduced, resulting in a lower data signal-to-noise ratio (SNR) and thus lower reliability. Conversely, a smaller allocated pilot power, i.e., α is larger, will lead to poor initial channel estimation and signal estimation, which is not a good starting point for subsequent channel estimation and equalization refinement and also results in low reliability. Therefore, an appropriate power allocation between data and pilots is crucial for achieving high reliability.

[0051] Thus, in one or more embodiments, the transmitter is arranged to allocate 50% to 99% (preferably 90% to 99%) of the total transmit power to data symbols and the remaining transmit power to pilot symbols.

[0052] In one or more embodiments, the transmitter is arranged to adapt the power allocated to data symbols and pilot symbols respectively according to the communication channel used, the carrier frequency used, and / or the speed difference between the transmitter and the receiver. For example, if the communication channel, the carrier frequency, and / or the speed difference between the transmitter and the receiver change, the adaptation can be dynamic for individual or groups of subsequent communication frames.

[0053] In one or more embodiments, the signal mapper is arranged to adapt the pilot overhead according to the communication channel used, the carrier frequency used, the maximum delay, and / or the speed difference between the transmitter and the receiver. For example, if the communication channel, the carrier frequency, and / or the speed difference between the transmitter and the receiver change, the adaptation can be dynamic for individual or groups of subsequent communication frames.

[0054] The static adaptation of the pilot overhead and / or the power allocation ratio in the transmitter can be based on the assumption that the communication channel used, the carrier frequency, and / or the speed difference between the transmitter and the receiver are static or vary negligibly within tolerable limits. The static adaptation can also consider worst-case scenarios, for example, when the receiver and the transmitter are in communication connection (e.g., within the radio range), the maximum expected or allowed speed difference between the transmitter and the receiver, the maximum expected delay, etc. The expected maximum speed difference can be provided by external input data - for example, the speed limit of a moving entity (such as a car or a train) within the coverage area of a fixed transmitter.

[0055] The dynamic adaptation of the pilot overhead and / or the power allocation ratio in the transmitter can be based on the actual speed difference between the transmitter and the receiver. Such information can be provided by the receiver, such as the speed vector of the receiver, or based on information available at the transmitter (such as the number of receivers within the range of the transmitter). In a fixed transmitter (such as a base station, etc.), this number can correspond to the current or average number of receivers attached to or in communication connection with the transmitter. The dynamic adaptation can also be based on information received from the receiver, such as channel state information, bit error rate, or the number of iterations of the channel estimation required to decode a previously received signal.

[0056] However, the power allocation and / or the pilot overhead can also be adjusted for special requirements. For example, to achieve fast convergence performance of the receiver, the power allocation ratio α can be selected to be less than the power allocation ratio when the data SNR and the pilot SNR are equal, and / or the BEM order of the first channel estimation unit can be set to be greater than 1 (but this will result in an increase in the pilot overhead). Simulation experiments show that a power allocation ratio of about 95% can achieve an optimal balance between the bit error rate (BER) and the convergence performance.

[0057] By performing training before the actual transmission begins, a near-optimal power allocation for the pilot signal and data signal ratio can be obtained dynamically. As further mentioned above, a favorable power allocation ratio can be obtained when the average data SNR and the average pilot SNR are equal.

[0058] According to a third aspect of the present invention, there is provided a receiver for an OTFS transmission system, including a first receiver-side transformation unit and a second receiver-side transformation unit. The receiver is configured to receive, at an input part of the first receiver-side transformation unit, a time-domain signal representing a communication frame according to claim 1, the time-domain signal being transmitted over an actual communication channel (i.e., a communication channel with Doppler spread), and the first receiver-side transformation unit outputs a two-dimensional representation of the received communication frame in the time-frequency domain. The output of the first receiver-side transformation unit is provided to the input of the second receiver-side transformation unit, and the second receiver-side transformation unit outputs a two-dimensional representation of the received communication frame including a pilot signal and a data signal in the delay-Doppler domain. The receiver includes an OFO estimator configured to perform an initial OFO estimation and compensation using symbols carried in a first type of block of the received communication frame, and further includes an iterative two-stage channel estimation and equalization block, the iterative two-stage channel estimation (CE) and equalization block (EQ) being configured to perform a joint estimation of the residual OFO and the communication channel based on all symbols carried in the received communication frame.

[0059] The first type of blocks located before and after the second type of block in the communication frame are located at L and (M - 1) respectively along the delay dimension. Then, the OFO is estimated by using the autocorrelation processing of two received first type of blocks of low-rate data - these two first type of blocks contain DPs at both ends of the OTFS frame without additional pilots.

[0060] Define g k =[y[k,L],y[k,M - 1]] T .

[0061] The proposed OFO estimation includes the following three steps:

[0062] 1) Autocorrelation matrix calculation: The correlation matrix R is calculated by the following formula

[0063]

[0064] 2) Eigenvalue decomposition: Perform eigenvalue decomposition on R to obtain a signal eigenvector u of length 2.

[0065] 3) OFO extraction: Define u1 and u2 as the first and last elements of u respectively. Due to the constant phase shift property, u1 and u2 have the following relationship: Therefore, the OFO can be easily estimated as:

[0066]

[0067] Therefore, the OFO estimation adopts a closed-form solution and does not require additional pilots. Note that the complexity of the OFO estimation process is 4N.

[0068] Therefore, according to one or more embodiments, the initial OFO estimation includes: performing autocorrelation processing on the received OTFS symbols (corresponding to low-rate data and DP) carried in the first type of blocks of the received communication frame. The initial OFO compensation includes providing the initial OFO estimation to the iterative two-stage channel estimation and equalization block to be combined with the BEM basis functions for channel estimation.

[0069] The OFO estimation value is incorporated into the GCE-BEM basis function b q to obtain a new GCE-BEM basis function:

[0070]

[0071] By considering (Q + 1) BEM basis functions, the OFO compensation method has a linear complexity of MN(Q + 1). Therefore, the system model further proposed above can be re-modeled as

[0072]

[0073] After the initial OFO estimation and compensation, due to the BEM modeling error and noise, a small amount of residual OFO remains, which will be solved in the joint estimation of the residual OFO and the communication channel.

[0074] According to one or more embodiments, the joint estimation of the residual OFO and the channel uses an iterative two-stage channel estimation architecture: performing an initial channel estimation and subsequent initial equalization and symbol estimation; and performing an iterative channel estimation and subsequent corresponding equalization and symbol estimation.

[0075] According to one or more embodiments, at least the pilot signal output from the second receiver-side transformation unit is provided to the first channel estimation unit, and the first channel estimation unit outputs a first estimation of the time-domain channel matrix i＝0 of. The time-domain channel matrix The first estimate and at least the data signal output by the second receiver-side transformation unit, or the pilot signal and the data signal output by the second receiver-side transformation unit, are provided to an equalizer unit, which outputs a set of estimates of at least the data signal. The set of estimates of at least the data signal and at least the pilot signal output by the second receiver-side transformation unit, or the pilot signal and the data signal output by the second receiver-side transformation unit, are provided to a second channel estimation unit, which outputs a time-domain channel matrix The second estimate. The output of the second channel estimation unit and at least the data signal output by the second receiver-side transformation unit, or the pilot signal and the data signal output by the second receiver-side transformation unit, are provided to an equalizer unit, which outputs a further set of estimates of at least the data signal. The channel estimation in the second channel estimation unit and the estimation of the set of estimates of at least the data signal in the equalizer unit are iteratively repeated until a termination criterion is met. In other words, the process of estimating the time-domain channel matrix i in the second channel estimation unit and the set of at least data symbols in the equalizer unit, and feeding back the corresponding latest output of the equalizer unit and at least the pilot signal output by the second receiver-side transformation unit, or the pilot signal and the data signal output by the second receiver-side transformation unit, to the second receiver-side channel estimation unit is repeated until a termination criterion is met.

[0076] The termination criterion may include the convergence of the output of the equalizer unit. For example, when the bit error rate of the decoded output of the equalizer unit for two successive iterations is lower than a predetermined threshold, such convergence may be assumed. The threshold may be, for example, a difference in bit error rate less than 10 -6 . Another conceivable termination criterion may be a predetermined number of iterations. A maximum number of iterations may also be set, after which the iteration is terminated, but the iteration is terminated prematurely when the bit error rate in two successive iterations is lower than the predetermined threshold before the maximum number of iterations is reached.

[0077] In one or more embodiments of the receiver, the first receiver-side transformation unit is adapted to perform a finite Fourier transform, an inverse Heisenberg transform, or a Wigner transform.

[0078] In one or more embodiments of the receiver, the second receiver-side transformation unit is adapted to perform a symplectic finite Fourier transform.

[0079] In one or more embodiments of the receiver, the first channel estimation unit is adapted to perform channel estimation based on basis expansion modeling of a first BEM order of a time-varying communication channel. The first BEM order refers to the order of the basis expansion used to model the communication channel. The first channel estimation is preferably pilot-assisted channel estimation, i.e., estimation is performed using the known position and / or other attributes of the pilot signal in the communication frame.

[0080] In one or more embodiments of the receiver, the equalizer performs message passing, zero-forcing, and / or minimum mean square error equalization.

[0081] In one or more embodiments of the receiver, the second channel estimation unit is adapted to perform channel estimation based on basis expansion modeling of a second BEM order of the time-varying communication channel. The second BEM order refers to the order of the basis expansion used to model the communication channel. The second channel estimation is preferably data-aided channel estimation, i.e., in addition to the pilot signals in the communication frame, the signals estimated in the equalizer unit are also used for estimation.

[0082] The first and second BEM orders of the first and second channel estimation units may be the same or different. It should be noted that when a lower pilot overhead is required, a smaller BEM order Q and a lower BEM resolution T can be used. However, a smaller BEM order generally results in slower convergence. A higher BEM order with a higher resolution can bring excellent performance and faster convergence, but may require more pilots, i.e., have a higher pilot overhead. For example, when the BEM order increases from Q = 2 to Q = 4, the resolution T can advantageously increase from 1 to 2.

[0083] Since the OFO of the transmitter is estimated in the receiver, the residual OFO is relatively small. This allows a smaller BEM order Q and a smaller resolution T to be used in the initial pilot-aided channel estimation while still achieving fast convergence.

[0084] One or more embodiments of the receiver further include a control unit, which is adapted to receive information about the direction and absolute speed of the receiver on the ground, the direction and absolute speed of the transmitter on the ground, and / or the relative speed between the receiver and the transmitter, and is also adapted to determine the BEM order Q S , and / or is adapted to receive the BEM order Q used at the transmitter for composing the communication frame S . The received or determined BEM order Q S and / or the received information is passed to the first channel estimation unit and / or the second channel estimation unit for determining the corresponding order of the BEM to be applied or used. For example, when the mobile terminal attaches to the base station, or more generally, when a communication connection is established between the transmitter and the receiver, information about the BEM order Q S used at the transmitter can be sent. Since only a few bytes are required, this does not significantly reduce the overhead, but can actually improve the spectral efficiency with a smaller overhead than the default overhead.

[0085] If the dynamic adaptation of the BEM order Q S is not used, the receiver can adopt a predefined default value.

[0086] The various elements of the above transmitter and receiver can be implemented in a hardware manner (i.e., hardware controlled and / or parameterized by software), software modules, or a combination thereof. Specifically, the first channel estimation unit and the second channel estimation unit of the receiver can rely on the same hardware or software module, and can be parameterized for corresponding pilot-assisted or data-assisted channel estimation by using corresponding input data and GCE-BEM parameters.

[0087] A wireless device according to a fourth aspect of the present invention includes a transmitter and / or a receiver for an OTFS transmission system as described above.

[0088] According to a fifth aspect of the present invention, a method for transmitting a binary data sequence through an OTFS communication channel includes mapping the binary data sequence into a two-dimensional arrangement of pilot symbols and data symbols along grid points in the delay-Doppler domain in a signal mapper. In the two-dimensional arrangement according to the present invention, the number of guard symbols around the pilot symbols in each direction of the Doppler domain is twice the number of BEM basis functions for modeling the communication channel in the receiver. The signal mapper can provide a plurality of guard symbols around the pilot symbols in each direction of the delay domain, and the number thereof is twice the time delay value represented by the delay bins. The two-dimensional arrangement forms a communication frame of the OTFS transmission system. The mapping may include receiving the binary data sequence at an input portion of the signal mapper and providing a two-dimensional arrangement of pilot symbols and data symbols at an output portion of the signal mapper.

[0089] The method further includes mapping the two-dimensional communication frame in the delay-Doppler domain into a two-dimensional arrangement of information symbols in the time-frequency domain in a first transmitter-side transformation unit. The first transformation may include receiving the two-dimensional communication frame in the delay-Doppler domain at an input portion of the first transmitter-side transformation unit and providing a two-dimensional arrangement of information symbols at an output portion of the first transmitter-side transformation unit.

[0090] The method further includes transforming the two-dimensional arrangement of information symbols into a continuous time-domain signal representing the communication frame in a second transmitter-side transformation unit. The second transformation may include receiving the two-dimensional arrangement of information symbols in the time-frequency domain at an input portion of the second transmitter-side transformation unit and providing a continuous time-domain signal representing the communication frame at an output portion of the second transmitter-side transformation unit.

[0091] The method further includes transmitting the continuous time-domain signal representing the communication frame through the communication channel. The transmission may include steps known to a conventional transmitter, such as amplification, beamforming, and pointing, etc.

[0092] In one or more embodiments of the method, the first transformation step includes performing an inverse symplectic finite Fourier transform on the two-dimensional communication frame in the delay-Doppler domain.

[0093] In one or more embodiments of the method, the second transformation step includes performing a Heisenberg transformation or an inverse finite Fourier transform (IFFT) on a two-dimensional arrangement of information symbols.

[0094] In one or more embodiments, the method further includes setting a power allocation ratio between data symbols and pilot symbols to be in a range of 0.5 to 0.99, preferably in a range of 0.9 to 0.99.

[0095] In one or more embodiments, the method further includes adapting the power allocation ratio between data symbols and pilot symbols according to the communication channel used, the carrier frequency used, and / or the speed difference between the transmitter and the receiver.

[0096] In one or more embodiments, the method further includes adapting the pilot overhead according to the communication channel used, the carrier frequency used, and / or the speed difference between the transmitter and the receiver.

[0097] According to a sixth aspect of the present invention, a method for receiving a binary data sequence through an actual OTFS communication channel includes receiving, through the communication channel, a continuous time-domain signal representing a communication frame according to a first aspect of the present invention. The method further includes transforming, in a first receiver-side transformation unit, the continuous time-domain signal representing the communication frame into a two-dimensional arrangement of information symbols in a time-frequency domain obtainable at an output portion of the first receiver-side transformation unit. In a next step of the method, the two-dimensional arrangement of information symbols including pilot signals and data signals in the time-frequency domain is transformed, in a second receiver-side transformation unit, into a two-dimensional communication frame including pilot signals and data signals in a delay-Doppler domain, the two-dimensional communication frame being obtainable at an output portion of the second receiver-side transformation unit. Next, the OFO is estimated from a first type of block of the communication frame, and the OFO is provided to a channel estimation unit to incorporate the OFO estimation into an applied CE function.

[0098] To obtain a first estimation of a time-domain channel matrix at an output portion of the first channel estimation unit, at least the pilot signals included in the two-dimensional communication frame in the delay-Doppler domain are provided to the first channel estimation unit. Then the time-domain channel matrix The first estimate and at least the data signal output from the second receiver-side transformation unit or the pilot signal and the data signal output from the second receiver-side transformation unit are provided to the equalizer unit for obtaining a set of estimates of at least the data signal at the output part of the equalizer unit. Next, the set of estimates of at least the data signal output from the equalizer unit and at least the pilot signal obtainable after the second transformation in the second receiver-side transformation unit or the pilot signal and the data signal output from the second receiver-side transformation unit are provided to the second channel estimation unit for estimating the time-domain channel matrix for further estimation. Then, the further estimation of the time-domain channel matrix obtainable at the output part of the second channel estimation unit and at least the data signal obtained after the second transformation in the second receiver-side transformation unit or the pilot signal and the data signal output from the second receiver-side transformation unit are provided to the equalizer unit to obtain a further set of estimates of at least the data signal. Iteratively repeat the estimation of the time-domain channel matrix in the second channel estimation unit and the estimation of the set of estimates of at least the data signal in the equalizer unit until a termination criterion is met. During the iterative process, use the respective latest further set of estimates of at least the data signal and the pilot signal to estimate the time-domain channel matrix and use the respective latest estimated time-domain channel matrix and at least the data signal obtained after the second transformation in the second receiver-side transformation unit or the pilot signal and the data signal output from the second receiver-side transformation unit to perform the next estimation of at least the data signal.

[0099] In one or more embodiments of the method, transforming a continuous time-domain signal representing a communication frame into a two-dimensional arrangement of information symbols in the time-frequency domain includes subjecting the continuous time-domain signal representing the communication frame to a finite Fourier transform, an inverse Heisenberg transform, or a Wigner transform.

[0100] In one or more embodiments of the method, transforming a two-dimensional arrangement of information symbols including pilot signals and data signals in the time-frequency domain into a two-dimensional communication frame including pilot signals and data signals in the delay-Doppler domain includes subjecting the two-dimensional arrangement of information symbols including pilot signals and data signals in the time-frequency domain to a symplectic finite Fourier transform.

[0101] In one or more embodiments of the method, estimating OFO from a first type of block includes separating the first type of block from the received communication frame, performing autocorrelation calculation at least on the pilot symbols contained therein, and extracting OFO information from the result of the autocorrelation calculation.

[0102] In one or more embodiments of the method, obtaining the time-domain channel matrix The first estimation includes performing channel estimation based on the basis expansion modeling of a time-varying communication channel with a first BEM order.

[0103] In one or more embodiments of the method, the estimation of the time-domain channel matrix in the second channel estimation unit includes performing channel estimation based on the basis expansion modeling of a time-varying communication channel with a second BEM order.

[0104] As further mentioned above, the first and second BEM orders Q, and / or the resolutions T of the first and second channel estimation units can be the same or different, respectively.

[0105] In one or more embodiments of the method, obtaining at least an estimated set of data signals in the equalizer unit includes subjecting at least the data signals obtained after the second transformation in the second transformation unit on the receiver side to message passing, zero-forcing, and / or minimum mean square error equalization.

[0106] In one or more embodiments, the method further includes receiving, in a control unit, information about the direction and absolute velocity of the receiver on the ground, the direction and absolute velocity of the transmitter on the ground, and / or the relative velocity between the receiver and the transmitter, and determining the BEM order Q S , and / or receiving the BEM order Q used at the transmitter for composing the communication frame S . The received information can be used to determine the corresponding BEM orders to be used in the first channel estimation unit and / or the second channel estimation unit. The correspondingly received or determined BEM orders are provided to the first channel estimation unit and / or the second channel estimation unit.

[0107] The method of transmitting and / or receiving can be represented by computer program instructions that, when executed by a microprocessor, respectively cause the computer and / or control hardware components of the transmitter or receiver of the OFTS transmission system as described above to perform the transmitting or receiving method as described above.

[0108] The computer program instructions can be stored or transmitted in a retrievable manner on a computer-readable medium or data carrier. The medium or data carrier can be physically embodied in the form of, for example, a hard disk, a solid-state disk, a flash device, etc. However, the medium or data carrier can also include a modulated electromagnetic, electrical, or optical signal that is received by the computer by means of a corresponding receiver and is transmitted to and stored in the memory of the computer.

[0109] XOs with very small OFO are usually more expensive and require more power to operate. In the transmitter and receiver that execute the corresponding method according to the present invention, the proposed communication frame allows processing larger OFO in cheaper XOs with larger OFO with lower power requirements, thus also allowing reduction of power consumption while reducing the device cost.

[0110] Benefiting from the careful design of the communication frame with the first and second types of blocks, where the first type of block provides a low data rate and DP, the proposed TFDR-OTFS receiver performs excellently in terms of bit error rate (BER), OFO estimation mean square error (MSE), and MSE of channel estimation, while having a lower pilot overhead. Its BER performance is close to the BER lower bound assuming perfect estimation and compensation of OFO and the channel.

[0111] The proposed communication frame and its DP pattern have two purposes: first, estimate OFO and low-rate data, and then estimate the OTFS channel, thus saving more resources for high-rate data. By utilizing the low-rate data and carefully designing its position, OFO can be estimated without additional dedicated pilots. By estimating and compensating OFO before channel estimation, the dedicated pilot overhead is significantly reduced. Description of the Drawings

[0112] In the following sections, exemplary embodiments of the present invention will be described in more detail with reference to the drawings. In the drawings,

[0113] Figure 1 a block diagram of a general OTFS transmission system is shown,

[0114] Figure 2 an exemplary visualization result of the Doppler spectral shift in the OTFS communication channel in the presence of OFO is shown,

[0115] Figure 3 an exemplary OTFS frame pattern at the transmitter according to the present invention is shown.

[0116] Figure 4 a block diagram of OFO estimation, channel estimation, and equalization of an exemplary receiver according to the present invention is shown,

[0117] Figure 5 a flowchart of a method for transmitting a binary data sequence through an OTFS communication channel is shown, and

[0118] Figure 6 a flowchart of a method for receiving a binary data sequence through an OTFS communication channel vulnerable to double-selective fading is shown.

[0119] In all the drawings, the same reference numerals can be used to refer to the same or similar elements. Detailed implementation manner

[0120] Figures 1 to 3 has been further described above and will not be discussed further.

[0121] Figure 4 A schematic block diagram showing initial OFO estimation and compensation and joint residual OFO and channel estimation in an exemplary receiver 300 according to the present invention is shown. After performing SFFT and Wigner transform, the received symbols in the delay-Doppler domain y[k, l] can be used for further processing.

[0122] The OFO estimation 312, channel estimations 321, 322, and equalization 324 replace the Figure 1 general channel estimation and equalization block 310 shown in Figure 1 All other elements of the receiver 300 shown in

[0123] The two-dimensional arrangement y[k, l] of the pilot signal and data signal in the delay-Doppler domain output from the second receiver-side transformation unit 306 can first be provided to the OFO estimation unit 312. The OFO estimation unit 312 includes a block separation unit 314 that separates the first type of block of the communication frame from the second type of block and provides the first type of block to the autocorrelation unit 316. The autocorrelation process may include eigenvalue decomposition (not shown in the figure), or eigenvalue decomposition is performed after the autocorrelation process. The result of the autocorrelation process is provided to the OFO extraction unit 318, which determines the OFO and provides it to the BEM basis generation unit 319. Based on the OFO estimate output from the OFO extraction unit 318 the BEM basis generation unit 319 determines the BEM order Q to be used in the channel estimation units 321 and 322, and forwards the corresponding information thereto to the first channel estimation unit 321 and the second channel estimation unit 322 accordingly.

[0124] The two-dimensional arrangement y[k, l] of the pilot signal and data signal in the delay-Doppler domain output from the low-rate block extraction unit 314 can also be provided to the pilot extraction unit 326, which is essentially a window function that uses the knowledge of the structure of the transmitted two-dimensional array to remove or suppress the data signal. The extracted pilot signal y p is provided to the first channel estimation unit 321, which performs a pilot-assisted, OFO-included first channel estimation using the GCE-BEM channel model with the first BEM order Q S The first BEM order Q Scan be small, using a low-resolution T, e.g., if a low pilot overhead is desired, albeit at the cost of slower convergence. However, the first BEM order Q S can also be quite large, using a higher-resolution T, resulting in faster convergence, but at the cost of a higher pilot overhead. The result of the channel estimation in the first channel estimation unit 321 is provided to the equalizer 324, along with the received data signal y d or the two-dimensional arrangement y[k,l] of the entire received pilot signal and data signal. The first estimate of the transmitted symbol is fed back to the second channel estimation unit 322, which outputs a data-aided channel estimation including OFO using the GCE-BEM channel model. The second channel estimation unit may use a higher BEM order Q L and a higher resolution T, although the same BEM order Q L and resolution T are also conceivable. The second channel estimation unit 322 also receives the two-dimensional arrangement y[k,l] of the received pilot signal and data signal. The result of the channel estimation in the second channel estimation unit 322 is provided to the equalizer 324, together with at least the received data signal y d or the two-dimensional arrangement y[k,l] of the entire received pilot signal and data signal, to obtain an improved estimate of the transmitted symbol compared to the previous one. This process is repeated until a termination criterion is met.

[0125] Figure 5 FIG. shows a flowchart of a method 400 for transmitting a binary data sequence over an OTFS communication channel. In step 402, the binary data sequence is mapped to a two-dimensional communication frame in the delay-Doppler domain, which includes a first type of block and a second type of block according to the first aspect of the present invention. In step 404, the two-dimensional communication frame in the delay-Doppler domain is transformed into a two-dimensional arrangement of information symbols in the time-frequency domain. In step 406, the two-dimensional arrangement of information symbols in the time-frequency domain is transformed into a continuous time-domain signal representing the communication frame, which is transmitted over the channel in step 408. Before transforming the two-dimensional arrangement of information symbols in the delay-Doppler domain into the two-dimensional arrangement of information symbols in the time-frequency domain, the power allocation ratio and / or pilot overhead between the pilot signal and the data signal may be determined or adapted in an optional step 410, and these parameters are set in an optional step 412.

[0126] Figure 6FIG. 500 is a flowchart of a method for receiving a binary data sequence over an OTFS communication channel vulnerable to double-selective fading. At step 502, a continuous time-domain signal representing a communication frame is received over the communication channel. At step 504, the continuous time-domain signal representing the communication frame is transformed into a two-dimensional arrangement of information symbols in the time-frequency domain. At step 506, the two-dimensional arrangement of information symbols in the time-frequency domain, including pilot signals and data signals, is transformed into a two-dimensional communication frame in the delay-Doppler domain, which includes a first type of block and a second type of block according to the first aspect of the present invention. At step 508, the OFO from the first type of block of the communication frame is estimated, and at step 510, the OFO is provided from the OFO estimator 312 to the channel estimation unit 320. At step 512, an initial estimate of the time-domain channel matrix is obtained in the first channel estimation unit 320, and the first channel estimation unit 321 performs channel estimation based on the basis expansion modeling of the time-varying communication channel at the first BEM order and at the first resolution. At step 514, based on the channel estimation and the communication frame in the delay-Doppler domain, an estimated set of at least the data signals is determined in the equalizer unit 324. Step 516 checks whether a termination criterion is satisfied. If satisfied (the "yes" branch of step 516), then at step 520, it is signaled that the estimated received symbols can be output to the demapper and ultimately output as the received binary sequence. If the termination criterion is not satisfied (the "no" branch of step 516), then at step 520, a further estimate of the time-domain channel matrix is obtained in the second channel estimation unit 322, and the second channel estimation unit 322 performs channel estimation based on the basis expansion modeling of the time-varying communication channel at the second BEM order and at the second resolution, using the estimated data signals in addition to the pilot signals. The result of the channel estimation is provided to the equalizer 324, and the equalizer 324 repeats step 514 using the further estimate from step 520.

[0127] Optionally, at step 522, the BEM order Q used at the transmitter may be received S , or information allowing determination of the BEM order to be used in channel estimation. At step 524, the BEM order Q to be used is determined S , and at step 526, the order Q S is provided to the channel estimation unit.

[0128] Definition and list of reference numerals (part of the specification)

[0129] f c Carrier frequency

[0130] Δf Subcarrier spacing

[0131] L Channel length

[0132] Number of M delay bins

[0133] Number of N Doppler bins

[0134] P T Total transmit power

[0135] α Data power allocation ratio

[0136] λ Pilot overhead

[0137] Q S BEM order in initial low - order channel estimation

[0138] Q L BEM order in subsequent iterative channel estimation

[0139] AWGN Additive white Gaussian noise

[0140] BEM Basis expansion model

[0141] CE - BEM Complex exponential basis expansion model

[0142] GCE - BEM Generalized complex exponential basis expansion model

[0143] DFT Discrete Fourier transform

[0144] MSE Mean square error

[0145] OTFS Orthogonal time - frequency - space

[0146] SNR Signal - to - noise ratio

[0147] BER Bit error rate

[0148] OFDM Orthogonal frequency - division multiplexing

[0149] MP Message passing

[0150] SFFT Finite symplectic Fourier transform

[0151] 200 Transmitter

[0152] 202 First transmitter - side transformation unit

[0153] 204 Second transmitter - side transformation unit

[0154] 206 Antenna

[0155] 300 Receiver

[0156] 302 Antenna

[0157] 304 First receiver - side transformation unit

[0158] 306 Second receiver - side transformation unit

[0159] 310 Channel Estimation and Equalization Block

[0160] 312 OFO Estimator

[0161] 314 Low-Rate Block Extraction

[0162] 316 Autocorrelation

[0163] 318 OFO Extraction

[0164] 319 BEM Basis Generation Containing OFO

[0165] 320 Two-Stage CE and EQ

[0166] 321 First Channel Estimation Unit

[0167] 322 Second Channel Estimation Unit

[0168] 324 Equalizer Unit

[0169] 326 Pilot Extraction Unit

[0170] 400 Transmission Method

[0171] 402 Mapping to Delay-Doppler Domain

[0172] 404 Transformation to Time-Frequency Domain

[0173] 406 Transformation into Continuous-Time Domain Signal

[0174] 408 Transmission Through Channel

[0175] 410 Adjust Power Allocation / Pilot Overhead

[0176] 412 Set Power Allocation / Pilot Overhead

[0177] 500 Reception Method

[0178] 502 Receive Continuous-Time Domain Signal

[0179] 504 Transform the Continuous-Time Domain Signal into a Two-Dimensional Arrangement of Information Symbols in the Time-Frequency Domain

[0180] 506 Transform the Two-Dimensional Arrangement of Information Symbols in the Time-Frequency Domain into a Two-Dimensional Communication Frame in the Delay-Doppler Domain

[0181] 508 Estimate OFO

[0182] 510 Provide the Estimated OFO to the BEM Basis Generation Unit and Provide the Generated BEM Basis to Channel Estimation

[0183] 512 Estimate the Time-Domain Channel Matrix in the First Channel Estimation Unit

[0184] 514 Estimated symbol

[0185] 516 Does it meet the termination criterion?

[0186] 518 Estimate the time-domain channel matrix in the second channel estimation unit

[0187] 520 Output the estimation result to the demapper

[0188] 522 Receive

[0189] 524 Determine the BEM to be used

[0190] 526 Provide the BEM to the channel estimation unit

Claims

1. A two-dimensional arrangement of pilot symbols and data symbols in a communication frame for an Orthogonal Time Frequency Space (OTFS) transmission system, wherein, The communication frame includes a first type of block (low rate) and a second type of block (high rate). The first type of block (low rate) includes a pilot signal, a guard signal, and a data signal. The second type of block (high rate) includes only a data signal. The pilot symbols, guard signals, and data symbols of the first type of block (low rate) and the data symbols of the second type of block (high rate) are arranged along grid points in the delay-Doppler domain. It is characterized in that the first type of block (low rate) is followed by the second type of block (high rate), and the second type of block (high rate) is followed by the first type of block (low rate). Among them, in the first type of block (low rate), at least one pilot symbol is surrounded by one or more guard symbols on at least three sides. Among them, the points in the grid of the first type of block (low rate) in the delay-Doppler domain that are not occupied by pilot symbols or guard symbols are used for data symbols.

2. The two-dimensional arrangement of symbols in a communication frame for an orthogonal time-frequency-space transmission system according to claim 1, wherein, At least the pilot symbols and guard symbols in the first type of block (low rate) before and after the second type of block (high rate) are the same.

3. The two-dimensional arrangement of symbols in a communication frame for an orthogonal time-frequency-space transmission system according to claim 1 or 2, wherein, The number of guard symbols located before and / or after the pilot symbol in the direction of the delay domain is twice the maximum time delay value in units of delay bins.

4. A transmitter for an orthogonal time-frequency-space transmission system, the transmitter includes a first transmitter-side transformation unit (202), a second transmitter-side transformation unit (204), and a signal mapper arranged upstream of the first transmitter-side transformation unit and the second transmitter-side transformation unit. Among them, The signal mapper is adapted to receive a binary data sequence and output a two-dimensional communication frame (x[k, l]) in the delay-Doppler domain, where pilot symbols (P), data symbols, and guard symbols (G) are arranged two-dimensionally in the two-dimensional communication frame according to any one of claims 1 to 3. Among them, the first transmitter-side transformation unit (202) is adapted to receive, at an input part, the two-dimensional communication frame in the delay-Doppler domain output from the signal mapper and output a two-dimensional arrangement of information symbols in the time-frequency domain. And Among them, the output of the first transmitter-side transformation unit (202) is provided to the input part of the second transmitter-side transformation unit (204). The second transmitter-side transformation unit is adapted to output a continuous time-domain signal representing the communication frame for transmission on a communication channel.

5. The transmitter (200) for an orthogonal time-frequency-space transmission system according to claim 4, wherein, The first transmitter-side transformation unit (202) is adapted to perform precoding and / or inverse symplectic finite Fourier transform.

6. The transmitter (200) for an orthogonal time-frequency-space transmission system according to claim 4 or 5, wherein, The second transmitter-side transformation unit (204) is adapted to perform a Heisenberg transform or an inverse finite Fourier transform (IFFT).

7. The transmitter (200) for an orthogonal time-frequency-space transmission system according to any one of claims 4 to 6, wherein, The transmitter (200) is arranged to allocate 50% to 99%, preferably 90% to 99% of the total transmission power to data symbols and allocate the remaining transmission power to pilot symbols.

8. The transmitter (200) for an orthogonal time-frequency-space transmission system according to any one of claims 4 to 7, wherein, The transmitter (200) is arranged to adapt the power allocated to data symbols and pilot symbols (P) respectively according to the communication channel used, the carrier frequency used, and / or the speed difference between the transmitter and the receiver.

9. The transmitter (200) for an orthogonal time-frequency-space transmission system according to any one of claims 4 to 8, wherein, The signal mapper is arranged to adapt the pilot overhead according to the communication channel used, the carrier frequency used, and / or the velocity difference between the transmitter and the receiver.

10. A receiver (300) for an orthogonal time-frequency-space transmission system, the receiver comprising a first receiver-side transformation unit (304) and a second receiver-side transformation unit (306), wherein, The receiver (300) is adapted to receive, at an input of the first receiver-side transformation unit (304), a time-domain signal transmitted through a communication channel and representing a communication frame according to any one of claims 1 to 3. The first receiver-side transformation unit outputs a two-dimensional representation of the received communication frame in the time-frequency domain. The output of the first receiver-side transformation unit (304) is provided to an input of the second receiver-side transformation unit (306), which outputs a two-dimensional representation of the received communication frame including pilot signals and data signals in the delay-Doppler domain. The receiver (300) includes an oscillator frequency offset (OFO) estimator (312), which is configured to perform an initial oscillator frequency offset estimation and compensation using symbols carried in a first type of block (low rate) of the received communication frame. The receiver further includes an iterative two-stage channel estimation and equalization block (320), which is configured to use all symbols of the received communication frame to determine a residual oscillator frequency offset and perform channel estimation.

11. The receiver (300) according to claim 10, wherein, The oscillator frequency offset estimator (312) is configured to perform an autocorrelation process (316) on received orthogonal time-frequency space symbols carried in a first type of block (low rate) of the received communication frame, and an initial oscillator frequency offset estimation is provided to the iterative two-stage channel estimation and equalization block (320).

12. The receiver (300) according to claim 10 or 11, wherein, The iterative two-stage channel estimation and equalization block (320) performs the following operations to jointly estimate the residual oscillator frequency offset and the channel: perform an initial channel estimation (321) and subsequent initial equalization and symbol estimation (324); and perform iterative channel estimation (322) and subsequent corresponding equalization and symbol estimation (324).

13. The receiver (300) according to claim 12, wherein, Provide at least the pilot signal output from the second receiver-side transformation unit (306) to the first channel estimation unit (321), and the first channel estimation unit outputs a first estimate of the time-domain channel matrix wherein provide the first estimate of the time-domain channel matrix and at least the data signal output from the second receiver-side transformation unit (306) or the pilot signal and the data signal output from the second receiver-side transformation unit (306) to the equalizer unit (324), and the equalizer unit outputs a set of estimates of at least the data signal, wherein provide the set of estimates of at least the data signal and at least the pilot signal output from the second receiver-side transformation unit (306) or the pilot signal and the data signal output from the second receiver-side transformation unit (306) to the second channel estimation unit (322), and the second channel estimation unit outputs a second estimate of the time-domain channel matrix wherein provide the output of the second channel estimation unit (322) and at least the data signal output from the second receiver-side transformation unit (306) or the pilot signal and the data signal output from the second receiver-side transformation unit (306) to the equalizer unit (324), and the equalizer unit outputs a further set of estimates of at least the data signal, wherein the receiver (300) is adapted to iteratively repeat the channel estimation in the second channel estimation unit (322) and the estimation of the set of estimates of at least the data signal in the equalizer unit (324) until a termination criterion is met.

14. The receiver (300) according to claim 13, wherein, The first channel estimation unit (321) is adapted to perform channel estimation based on a basis expansion model of a time-varying communication channel having a first basis expansion model (BEM) order.

15. The receiver (300) for an orthogonal time-frequency-space transmission system according to claim 13 or 14, wherein, The second channel estimation unit (322) is adapted to perform channel estimation based on a basis expansion model of a time-varying communication channel having a second basis expansion model order.

16. The receiver (300) for an orthogonal time-frequency-space transmission system according to any one of claims 10 to 15, wherein, The first receiver-side transformation unit (304) is adapted to perform a finite Fourier transform, an inverse Heisenberg transform, or a Wigner transform.

17. The receiver (300) for an orthogonal time-frequency-space transmission system according to any one of claims 10 to 14, wherein, The second receiver-side transformation unit (306) is adapted to perform decoding and / or a symplectic finite Fourier transform.

18. The receiver (300) for an orthogonal time-frequency-space transmission system according to any one of claims 10 to 16, wherein, The equalizer unit (324) performs message passing, zero-forcing, and / or minimum mean square error equalization processing.

19. Receiver (300) for an orthogonal time-frequency-space transmission system according to any one of claims 10 to 18, the receiver further comprising a control unit adapted to receive information on the direction and absolute velocity of the receiver (300) on the ground, the direction and absolute velocity of the transmitter (200) on the ground and / or the relative velocity between the receiver (300) and the transmitter (200), and the control unit further adapted to determine the basis expansion modeling order Q S， and / or adapted to receive the basis expansion modeling order Q used at the transmitter (200) for composing the communication frame S and adapted to pass the received information and / or the basis expansion modeling order Q S to the first channel estimation unit and / or the second channel estimation unit (321, 322).

20. A wireless device for an orthogonal time-frequency space transmission system, the wireless device including a transmitter (200) according to any one of claims 4 to 9 and / or a receiver (300) according to any one of claims 10 to 19.

21. A method (400) for transmitting a binary data sequence over an orthogonal time-frequency space communication channel, the method including: - Map (402) the binary data sequence in a signal mapper into a two-dimensional communication frame in the delay-Doppler domain according to any one of claims 1 to 3. - Transform (404) the two-dimensional communication frame in the delay-Doppler domain into a two-dimensional arrangement of information symbols in the time-frequency domain in a first transmitter-side transformation unit (202). - Transform (406) the two-dimensional arrangement of information symbols in the time-frequency domain into a continuous time-domain signal representing the communication frame in a second transmitter-side transformation unit (204), and - Transmit (408) the continuous time-domain signal representing the communication frame over a communication channel.

22. The method (400) according to claim 21, wherein, The first transformation step (404) includes performing an inverse symplectic finite Fourier transform on the two-dimensional communication frame in the delay-Doppler domain.

23. The method (400) according to claim 21 or 22, wherein, The second transformation step (406) includes performing a Heisenberg transform or an inverse finite Fourier transform (IFFT) on the two-dimensional arrangement of information symbols.

24. The method (400) according to any one of claims 21 to 23, further comprising setting (410) the power allocation ratio between data symbols and pilot symbols to be in the range of 0.5 to 0.99, preferably in the range of 0.9 to 0.

99.

25. The method (400) according to any one of claims 21 to 24, further comprising adapting (412) the power allocation ratio between data symbols and pilot symbols according to the communication channel used, the carrier frequency used, and / or the speed difference between the transmitter and the receiver.

26. The method (400) according to any one of claims 21 to 25, further comprising adapting (412) the pilot overhead according to the communication channel used, the carrier frequency used, and / or the speed difference between the transmitter and the receiver.

27. A method (500) for receiving a binary data sequence over an orthogonal time-frequency-space communication channel susceptible to double-selective fading, the method comprising: - Receive (502) a continuous time-domain signal representing the communication frame according to any one of claims 1 to 3 over the communication channel. - Transform (504) the continuous time-domain signal representing the communication frame into a two-dimensional arrangement of information symbols in the time-frequency domain that can be obtained at the output of the first receiver-side transformation unit (304) in a first receiver-side transformation unit (304). - Transform (506) the two-dimensional arrangement of information symbols including pilot signals and data signals in the time-frequency domain into a two-dimensional communication frame including pilot signals and data signals in the delay-Doppler domain, which can be obtained at the output of the second receiver-side transformation unit (306) in a second receiver-side transformation unit (306). - Estimate (508) the oscillator frequency offset according to a first type of block of the communication frame. - The estimated oscillator frequency offset is provided (510) to the basis expansion modeling basis generation unit (319), and the generated basis expansion modeling basis is provided to the channel estimation unit (320) for estimating the oscillator frequency offset to be incorporated into the applied channel estimation function - Provide at least a pilot signal output from the second receiver side conversion unit (306) to the first channel estimation unit (321) so as to obtain a first estimation of a time domain channel matrix at an output section of the first channel estimation unit (321). of - Provide the first estimate of the time-domain channel matrix and at least the data signal output from the second receiver-side transformation unit (306) or the pilot signal and the data signal output from the second receiver-side transformation unit (306) to the equalizer unit (324), so as to obtain (510) a set of estimates of at least the data signal at the output of the equalizer unit (324). - Estimate (512) the time-domain channel matrix in the second channel estimation unit (322) based on at least an estimated set of data signals output from the equalizer unit (324) and at least pilot signals obtained after a second transformation in the second receiver-side transformation unit (306) or pilot signals and data signals output from the second receiver-side transformation unit (306). The estimation result of - Provide the estimation result of the time-domain channel matrix that can be obtained at the output part of the second channel estimation unit (322) and at least the data signal obtained after the second transformation in the second receiver-side transformation unit (306) or the pilot signal and the data signal output from the second receiver-side transformation unit (306) to the equalizer unit (324) to obtain (510) a further estimation set of at least the data signal, and provide the estimation result of the time-domain channel matrix that can be obtained at the output part of the second channel estimation unit (322) and at least the data signal obtained after the second transformation in the second receiver-side transformation unit (306) or the pilot signal and the data signal output from the second receiver-side transformation unit (306) to the equalizer unit (324) to obtain (510) a further estimation set of at least the data signal, and - Iteratively repeat estimating (512) the time-domain channel matrix in the second channel estimation unit (322) and estimating (510) at least a set of data signals in the equalizer unit (324) until a termination criterion is met.

28. The method (500) according to claim 27, wherein, The first transformation step (504) includes performing a finite Fourier transform, an inverse Heisenberg transform, or a Wigner transform on the continuous time-domain signal representing the communication frame.

29. The method (500) according to claim 27 or 28, wherein, The second transformation step (506) includes subjecting the two-dimensional arrangement of information symbols including pilot signals and data signals in the time-frequency domain to a symplectic finite Fourier transform.

30. The method (500) according to any one of claims 27 to 29, wherein, Estimating (508) the oscillator frequency offset from a first type of block of the communication frame includes: - Separating the first type of block from the received communication frame, - Performing autocorrelation processing on at least pilot symbols included in the first type of block, and - Extracting oscillator frequency offset information from the autocorrelation processing.

31. The method (500) according to any one of claims 27 to 30, wherein, The time-domain channel matrix is obtained (508) in the first channel estimation unit (320). A first estimation of includes performing channel estimation based on basis expansion modeling of a time-varying communication channel having a first basis expansion modeling order.

32. The method (500) according to any one of claims 27 to 31, wherein, Obtaining (512) the time-domain channel matrix in the second channel estimation unit (322) The estimation includes performing channel estimation based on basis expansion modeling of a time-varying communication channel having a second basis expansion modeling order.

33. The method (500) according to any one of claims 27 to 32, wherein, Obtaining (510) at least an estimated set of data signals in the equalizer unit (324) includes subjecting at least the data signals obtained after the second transformation (506) in the second receiver-side transformation unit (306) to message passing, zero-forcing, and / or minimum mean square error equalization processing.

34. The method (500) according to any one of claims 27 to 33, further comprising: - Receive (520) in the control unit information about the direction and absolute velocity of the receiver (300) on the ground, the direction and absolute velocity of the transmitter (200) on the ground, and / or the relative velocity between the receiver (300) and the transmitter (200), and / or receive the basis expansion modeling order Q used at the transmitter (200) for composing the communication frame S , - Determining (522) a respective basis expansion modeling order to be used in the first channel estimation unit and / or the second channel estimation unit (320, 322), and - Providing (524) the respective determined basis expansion modeling order to the first channel estimation unit and / or the second channel estimation unit (320, 322).

35. A computer program product comprising computer program instructions which, when executed by a microprocessor, cause a computer and / or control hardware component of a transmitter for an orthogonal time-frequency-space transmission system according to any one of claims 4 to 9 or a receiver for an orthogonal time-frequency-space transmission system according to any one of claims 10 to 19 to respectively execute a method (400, 500) according to one or more of claims 21 to 26 or one or more of claims 27 to 34.

36. A computer-readable medium or data carrier for retrievably transmitting or storing the computer program product according to claim 35.

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