Devices and methods for PTRS insertion in n-DFT-s-OFDM for integrated sensing and communication
Patent Information
- Application Number
- PCT/EP2025/054914
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-02-24
- Publication Date
- 2026-08-27
Smart Images
Figure EP2025054914_27082026_PF_FP_ABST
Abstract
Description
[0001] DEVICES AND METHODS FOR INTEGRATED SENSING AND COMMUNICATION
[0002] TECHNICAL FIELD
[0003] The present disclosure relates to wireless technology. More specifically, the present disclosure relates to devices and methods for integrated sensing and communication, ISAC, in a wireless network, in particular a mobile network.
[0004] BACKGROUND
[0005] Integrated sensing and communication, ISAC, in future mobile networks represents a paradigm shift where communication and sensing functions are unified within a single framework, enabling networks and devices to gather and share data beyond traditional wireless communication. To achieve an acceptable performance for both sensing and communication functionalities, the waveform design is of high importance. Orthogonal frequency division multiplexing (OFDM), the waveform commonly used in LTE and 5G systems, is effective for lower frequencies and has been applied to sensing due to its range and velocity resolution capabilities. However, OFDM suffers from a high peak-to-average power ratio (PAPR), which strains RF components and amplifiers, particularly at higher frequencies where linear amplifiers are costly and inefficient. High PAPR also reduces communication and sensing range. To mitigate PAPR, discrete Fourier transform spread OFDM (DFT-s-OFDM) has been proposed, offering single-carrier characteristics more suitable for communications at higher frequencies. DFT-s-OFDM has been used in LTE and 5G uplink systems to provide extensive coverage for low-cost user equipment. However, it impacts sensing accuracy due to noise enhancement when a least squares (LS) receiver is used. A flexible waveform based on DFT-s-OFDM that outperforms OFDM in terms of PAPR and exceeds conventional DFT-s-OFDM in terms of sensing accuracy is the MB DFT-s-OFDM waveform disclosed in TIMES 6G consortium, "Intermediate report on PHY layer enhancements for THz links supporting sensing and communication functionalities," 2023. The MB-DFT-s-OFDM waveform is a variant of OFDM that incorporates spreading / de-spreading operations prior to and post OFDM IFFT modulation / FFT demodulation. Such additional operations are intended to reduce the PAPR of the transmitted waveform, thus making the transmitted waveform less susceptible to the detrimental effects imposed by PA nonlinearities.
[0006] SUMMARY
[0007] It is an object of the disclosure to provide improved devices and methods for integrated sensing and communication, ISAC, in a wireless network, in particular a mobile network, allowing for phase noise mitigation.
[0008] The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. In the following one or more of the following acronyms and abbreviations may be used:
[0009] 5G Fifth-generation mobile network. The latest generation of cellular network technology.
[0010] AWGN Additive white Gaussian noise. Noise added at the receiver.
[0011] BS Base station. A base station is a transmitter / receiver that is the main communication point for one or more user equipments.
[0012] CCDF Complementary cumulative distribution function. A statistical tool to describe the distribution of a signal's peak-to-average power ratio (PAPR).
[0013] CFR Channel frequency response. Channel response in the frequency domain.
[0014] CPE Common-phase error. A phase error that equally affects all constellation symbols.CP Cyclic prefix. Prefix added to the OFDM symbol to transform the linear convolution with the channel to a circular convolution.
[0015] DAC Digital-to-analog converter. An electronic component in the RF chain that converts digital signals into analog signals.
[0016] DFT Discrete Fourier transform. Fourier transform for a finite sequence.
[0017] DFT-s-OFDM Discrete Fourier transform-spread orthogonal frequency division multiplexing. Single-carrier waveform.
[0018] FFT / IFFT Fast Fourier transform / Inverse fast Fourier transform. Technique to efficiently implement DFT / IDFT.
[0019] FDD Frequency division duplex. A communication scheme where different frequencies are used for sending and receiving signals simultaneously.
[0020] ISAC Integrated sensing and communication. Framework where sensing and communications functionalities are combined.
[0021] LS Least squares. A mathematical method used for estimating parameters by minimizing the sum of the squares of the residuals.
[0022] LIE Long-Term Evolution. A standard for high-speed wireless communication for mobile devices and data terminals.
[0023] MB-DFT-s-OFDM Multi-block discrete Fourier transform-spread orthogonal frequency division multiplexing.
[0024] Variant of the DFT-s-OFDM waveform that is suitable for ISAC applications.
[0025] MF Matched filter. A signal processing technique used to maximize the signal-to-noise ratio. OFDM Orthogonal frequency division multiplexing. Multi-carrier waveform.
[0026] PAPR Peak-to-average power ratio. A metric that quantifies a ratio between the maximum power of a signal and its average power over time.
[0027] PSD Power spectral density. A measure of the power present in a signal per unit of frequency. PTRS Phase tracking reference signal. A reference signal used to track phase errors in wireless communication systems.
[0028] QAM Quadrature amplitude modulation. A modulation scheme that conveys data by varying the amplitude of two carrier waves.
[0029] RF Radio-frequency. Oscillation rate of an electric wave in the range between 20 kHz and 300 GHz.
[0030] RMSE Root mean square error. A measure of the differences between values predicted by a model or system and the actual values.
[0031] SNR Signal-to-noise ratio. A communication performance metric that quantifies the performance of a communication system by calculating the ratio of signal to noise powers.
[0032] UE User-equipment. Device used by a user to communicate.
[0033] According to a first aspect a wireless transmitter apparatus is provided for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless receiver apparatus in a mobile network. The wireless transmitter apparatus according to the first aspect comprises a serial-to-parallel converter configured to convert a sequence of input symbols into a plurality of parallel processed subsets of the sequence of input symbols. Moreover, the wireless transmitter apparatus according to the first aspect comprises a plurality of frequency spreading blocks, in particular FFT spreading blocks, wherein each frequency spreading block is configured to spread in frequency a respective subset of the sequence of input symbols. The wireless transmitter apparatus according to the first aspect further comprises an IFFT OFDM modulator configured to generate an OFDM signal based on the output of the plurality of frequency spreading blocks. Moreover, the wireless transmitter apparatus according to the first aspect furthercomprises a parallel-to-serial converter configured to convert the output of the IFFT OFDM modulator into a serial stream for transmission to the wireless receiver apparatus. At least one subset of the plurality of subsets of the sequence of input symbols processed by at least one frequency spreading block of the plurality of frequency spreading blocks comprises only pilot symbols, in particular phase tracking reference signal, PTRS, symbols, but no data symbols. By allocating the pilot symbols in this way, the wireless transmitter apparatus according to the first aspect allows for an improved estimation and mitigation of phase noise by the wireless receiver apparatus.
[0034] In a further possible implementation form, the wireless transmitter apparatus according to the first aspect further comprises a cyclic prefix, CP, appender configured to add a respective CP to the output of the IFFT OFDM modulator.
[0035] In a further possible implementation form, each of the plurality of frequency spreading blocks is associated with a respective frequency band, wherein the wireless transmitter apparatus is configured to select the at least one frequency spreading block of the plurality of frequency spreading blocks for processing the at least one subset of the plurality of subsets of the sequence of input symbols comprising only pilot symbols.
[0036] In a further possible implementation form, the wireless transmitter apparatus is configured to select the at least one frequency spreading block of the plurality of frequency spreading blocks for processing the at least one subset of the plurality of subsets of the sequence of input symbols comprising only pilot symbols based on feedback information provided by the wireless receiver apparatus.
[0037] In a further possible implementation form, the wireless transmitter apparatus according to the first aspect is configured to adjust a number, a respective size and / or a respective frequency band of the plurality of frequency spreading blocks based on one or more sensing and / or communication requirements.
[0038] In a further possible implementation form, the wireless transmitter apparatus is configured to provide information about the number, respective size, respective frequency band, and / or the at least one selected frequency spreading block of the plurality of frequency spreading blocks to the wireless receiver apparatus.
[0039] In a further possible implementation form, the wireless transmitter apparatus is a user equipment, UE, and the wireless receiver apparatus is a base station of the mobile network.
[0040] In a further possible implementation form, the wireless transmitter apparatus is an Integrated Sensing and Communication, ISAC, wireless transmitter apparatus.
[0041] In a further possible implementation form, the plurality of frequency spreading blocks comprise a plurality of FFT spreading blocks.
[0042] According to a second aspect a method is provided for operating a wireless transmitter apparatus for Multi-Band Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless receiver apparatus in a mobile network. The method according to the second aspect comprises the steps of:
[0043] converting with a serial-to-parallel converter a sequence of input symbols into a plurality of parallel processed subsets of the sequence of input symbols;
[0044] spreading with a plurality of frequency spreading blocks a respective subset of the plurality of subsets of the sequence of input symbols, wherein at least one subset of the plurality of subsets of the sequence of input symbols processed by at leastone frequency spreading block of the plurality of frequency spreading blocks comprises only pilot symbols, in particular phase tracking reference signal, PTRS, symbols, but no data symbols;
[0045] generating with an IFFT OFDM modulator an OFDM signal based on the output of the plurality of frequency spreading blocks; and
[0046] converting with a parallel-to-serial converter the output of the IFFT OFDM modulator into a serial stream for transmission to the wireless receiver apparatus.
[0047] The method according to the second aspect can be performed by the wireless transmitter apparatus according to the first aspect. Thus, further features of the method according to the second aspect result directly from the functionality of the wireless transmitter apparatus according to the first aspect and its different implementation forms described above and below.
[0048] According to a third aspect a wireless receiver apparatus is provided for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless transmitter apparatus in a mobile network. The wireless receiver apparatus according to the third aspect comprises a serial-to-parallel converter configured to convert a serial signal stream received from the wireless transmitter apparatus into a received MB-DFT-s-OFDM signal. Moreover, the wireless receiver apparatus according to the third aspect comprises a FFT OFDM demodulator configured to perform OFDM de-modulation of the MB-DFT-s-OFDM signal provided by the serial-to-parallel converter. The wireless receiver apparatus according to the third aspect comprises a processing unit configured to perform channel and phase noise estimation and equalization based on the de-modulated MB-DFT-s-OFDM signal. Moreover, the wireless receiver apparatus according to the third aspect comprises a plurality of frequency de-spreading blocks, wherein each frequency de-spreading block is configured to de-spread a respective portion of the equalized signal. The wireless receiver apparatus according to the third aspect further comprises a parallel-to-serial converter configured to convert the output of the plurality of frequency de-spreading blocks into a sequence of received symbols. The input to at least one of the plurality of frequency de-spreading blocks is based on only pilot symbols, in particular phase tracking reference signal, PTRS, symbols, but no data symbols. Allocating the pilot symbols in this way allows for an improved estimation and mitigation of phase noise by the wireless receiver apparatus according to the third aspect.
[0049] In a further possible implementation form, the wireless receiver apparatus further comprises a cyclic prefix, CP, extractor configured to extract a respective CP from the MB-DFT-s-OFDM signal.
[0050] In a further possible implementation form, each of the plurality of frequency de-spreading blocks is associated with a respective frequency band, wherein the frequency band of the frequency de-spreading block whose input is based on only pilot symbols is equal to the frequency band of a frequency spreading block selected by the wireless transmitter apparatus.
[0051] In a further possible implementation form, the wireless receiver apparatus according to the third aspect is configured to provide feedback information to the wireless transmitter apparatus for allowing the wireless transmitter apparatus to select one or more frequency spreading blocks.
[0052] In a further possible implementation form, the wireless receiver apparatus according to the third aspect is configured to adjust a number, a respective size and / or a respective frequency band of the plurality of frequency de-spreading blocks based on one or more sensing and / or communication requirements.
[0053] In a further possible implementation form, the wireless receiver apparatus is configured to receive information about the number, size, frequency band, and / or the selected frequency spreading block from the wireless transmitter apparatus.In a further possible implementation form, the wireless transmitter apparatus is a user equipment, UE, and the wireless receiver apparatus is a base station of the mobile network.
[0054] In a further possible implementation form, the wireless receiver apparatus is an Integrated Sensing and Communication, ISAC, wireless receiver apparatus.
[0055] In a further possible implementation form, the plurality of frequency de-spreading blocks comprise a plurality of IFFT despreading blocks.
[0056] According to a fourth aspect a method is provided for operating a wireless receiver apparatus for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless transmitter apparatus in a mobile network. The method according to the fourth aspect comprises the steps of: converting a serial signal stream received from the wireless transmitter apparatus into a MB-DFT-s-OFDM signal; performing OFDM de-modulation of the MB-DFT-s-OFDM signal;
[0057] performing channel and phase noise estimation and equalization based on the de-modulated MB-DFT-s-OFDM signal; de-spreading a plurality of portions of the equalized signal using a plurality of frequency de-spreading blocks; and converting the output of the plurality of frequency de-spreading blocks into a sequence of received symbols; wherein the input to at least one of the plurality of frequency de-spreading blocks of the plurality of frequency de-spreading blocks is based on only pilot symbols, in particular phase tracking reference signal, PTRS, symbols, but no data symbols.
[0058] The method according to the fourth aspect can be performed by the wireless receiver apparatus according to the third aspect. Thus, further features of the method according to the fourth aspect result directly from the functionality of the wireless receiver apparatus according to the third aspect and its different implementation forms described above and below.
[0059] According to a fifth aspect a computer program or a computer program product is provided, comprising a computer-readable storage medium carrying program code which causes a computer or a processor to perform the method according to the second aspect or the method according to the fourth aspect when the program code is executed by the computer or the processor.
[0060] The different aspects of the disclosure can be implemented in software and / or hardware.
[0061] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.
[0062] BRIEF DESCRIPTION OF THE DRAWINGS
[0063] In the following embodiments of the disclosure are described in more detail with reference to the attached figures and drawings, in which:
[0064] Fig. 1 shows a schematic diagram illustrating a conventional MB-DFT-s-OFDM wireless transmitter apparatus;
[0065] Fig. 2a shows a diagram comparing PAPRs for different waveforms for 16-QAM modulation;
[0066] Fig. 2b shows a diagram illustrating RMSE for a weak target estimation using different waveforms;Fig. 2c shows a diagram illustrating the effect of phase noise on a 16-QAM constellation using a MB-DFT-s-OFDM waveform;
[0067] Fig. 2d shows a diagram illustrating a phase noise PSD as a function of the frequency offset for a bandwidth of 1 GHz;
[0068] Fig. 2e shows a diagram illustrating the phase noise evolution as a function of time for a bandwidth of 1 GHz;
[0069] Fig. 3 shows a schematic diagram illustrating a wireless transmitter apparatus and a wireless receiver apparatus according to an embodiment;
[0070] Fig. 4 shows a schematic diagram illustrating in more detail the PTRS insertion approach implemented by a wireless transmitter apparatus according to an embodiment;
[0071] Fig. 5 shows a diagram illustrating the performance of a wireless receiver apparatus according to an embodiment using different received signal equalization techniques;
[0072] Fig. 6 shows a signalling diagram illustrating the exchange of information between a wireless transmitter apparatus and a wireless receiver apparatus according to an embodiment;
[0073] Fig. 7 shows a flow diagram illustrating a method according to an embodiment for operating a wireless transmitter apparatus; and
[0074] Fig. 8 shows a flow diagram illustrating a method according to an embodiment for operating a wireless receiver apparatus.
[0075] In the following identical reference signs refer to identical or at least functionally equivalent features.
[0076] DETAILED DESCRIPTION
[0077] In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.
[0078] For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.As already described above, the MB-DFT-s-OFDM waveform is a variant of OFDM that incorporates spreading / de-spreading operations prior to and post OFDM IFFT modulation / FFT demodulation. Such additional operations are intended to reduce the PAPR of the transmitted waveform, thus making the transmitted waveform less susceptible to the detrimental effects imposed by PA nonlinearities. Figure 1 shows a schematic diagram illustrating a conventional MB-DFT-s-OFDM wireless transmitter apparatus 10, which comprises, in addition to a serial-to-parallel converter 11 , a CP appender 14 and a parallel-to-serial converter 15, multiple DFT blocks 12a-n arranged upstream of a OFDM IDFT modulator 13 for generating the MB-DFT-s-OFDM waveform structure.
[0079] Figure 2a shows the CCDF of the PAPR for different numbers of DFT spreading blocks 12a-n at the transmitter 10 of figure 1. As will be appreciated from figure 2a, the more DFT blocks 12a-n are inserted, the closer the PAPR performance is to the OFDM waveform, and the less DFT blocks 12a-n are inserted, the closer the PAPR is to the single-carrier case, i.e., DFT-s-OFDM.
[0080] For the sensing feature, the range estimation performance is depicted as a function of the SNR. A plain DFT-s-OFDM, “proposed MB-DFT-s-OFDM”, and OFDM root mean-squared error (RMSE) performance results are depicted in figure 2b. As will be appreciated from figure 2b, MB-DFT-s-OFDM achieves a trade-off between OFDM and DFT-s-OFDM. Thus, a trade-off is captured between PAPR and RMSE when MB-DFT-s-OFDM is used for different DFT blocks.
[0081] The phase errors caused by the radio-frequency (RF) oscillator responsible for the up / down conversion processes are one of the main causes of phase noise. Phase noise is a major impairment that degrades the performance of multi-carrier systems. Its effect can be categorized into two types, namely a first effect of an average rotation of the constellation, and a second effect of an interference between the frequency components of the multi-carrier waveform. Figure 2c illustrates the effect of phase noise on a 16-QAM constellation, which is uniformly rotated around the origin due to the first effect, while each constellation point has its phase dispersed around due to the second effect.
[0082] The oscillator’s phase noise effect can be described by its power spectral density. Figure 2d shows the PSD of a phase noise process generated by a dielectric resonator oscillator, showing the power distribution in dBc / Hz as a function of the offset from the carrier. Figure 2e shows the phase noise evolution as a function of time, where it can be noticed that high values of phase errors can be reached. Especially for higher-order modulation, such phase errors are a major cause of performance degradation that are addressed by embodiments described in the following.
[0083] Embodiments disclosed herein allow to at least mitigate the adverse effects of phase noise in MB-DFT-s-OFDM waveforms by inserting pilot signals, in particular PTRSs, in the transmission chain in such a way that (a) non-iterative phase noise estimation is possible and (b) PAPR properties of the waveform are maintained. Thus, embodiments disclosed herein allow to estimate and mitigate the effect of phase noise in MB-DFT-s-OFDM systems using an improved PTRS allocation scheme.
[0084] The pilot, e.g. PTRS allocation scheme implemented by embodiments disclosed herein allows for non-iterative accurate phase noise estimation post-DFT spreading. Using the structure of the MB-DFT-s-OFDM, at least one DFT spreading block is reserved for pilot, e.g. PTRS allocation. The selection of a DFT spreading block for pilots, e.g. PTRSs may simplify both the implementation and the related signalling based on the feedback from the receiver apparatus to the transmitter apparatus according to an embodiment. Moreover, the pilot, e.g. PTRS allocation scheme implemented by embodiments disclosed herein allows for adaptive pilot, e.g. PTRS locations to maintain acceptable channel conditions while estimating phase noise, thus improving the accuracy of phase noise estimation and maintaining good PAPR properties of the MB-DFT-s-OFDM waveform.Figure 3 shows a schematic diagram illustrating a wireless transmitter apparatus 100 and a wireless receiver apparatus 200 according to an embodiment for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication. In an embodiment, the wireless transmitter apparatus 100 and the wireless receiver apparatus 200 may be an Integrated Sensing and Communication, ISAC, wireless apparatus 100, 200. In an embodiment, the wireless transmitter apparatus 100 may be a user equipment, UE, 100 and the wireless receiver apparatus 200 may be a base station 200 of a mobile network.
[0085] As illustrated in figure 3, the wireless transmitter apparatus 100 comprises a serial-to-parallel converter 110 configured to convert a sequence of input symbols into a plurality of parallel processed subsets of the sequence of input symbols.
[0086] Moreover, the wireless transmitter apparatus 100 comprises a plurality of frequency spreading blocks 120a-n, in particular FFT spreading blocks 120a-n, wherein each frequency spreading block 120a-n is configured to spread in frequency a respective subset of the sequence of input symbols. The wireless transmitter apparatus 100 further comprises an IFFT OFDM modulator 130 configured to generate an OFDM signal based on the output of the plurality of frequency spreading blocks 120a-n. Moreover, the wireless transmitter apparatus 100 further comprises a parallel-to-serial converter 150 configured to convert the output of the IFFT OFDM modulator 130 into a serial stream for transmission to the wireless receiver apparatus 200. As alreadv mentioned above and described in more detail below, at least one subset of the plurality of subsets of the sequence of input symbols processed by at least one frequency spreading block of the plurality of frequency spreading blocks 120a-n comprises only pilot symbols, in particular phase tracking reference signal, PTRS, symbols, but no data symbols. By allocating the pilot symbols in this way, the wireless transmitter apparatus 100 allows for an improved estimation and mitigation of phase noise by the wireless receiver apparatus 200. In the embodiment shown in figure 3, the wireless transmitter apparatus 100 further comprises a cyclic prefix, CP, appender 140 configured to add a respective CP to the output of the IFFT OFDM modulator 130.
[0087] The signal then goes through the effective wireless channel, where the effects in this case include: (a) transmitter phase noise is added to the signal due to the up-conversion process 310; (b) the effect of the wireless channel 320 is added; (c) receiver phase noise is added due to the down-conversion process 330; and (d) at the receiver 200 AWGN 340 is added.
[0088] As illustrated in figure 3, the wireless receiver apparatus 200 comprises a serial-to-parallel converter 250 configured to convert the serial signal stream received from the wireless transmitter apparatus 100 into a received MB-DFT-s-OFDM signal. Moreover, the wireless receiver apparatus 200 comprises a FFT OFDM demodulator 230 configured to perform OFDM de-modulation of the MB-DFT-s-OFDM signal provided by the serial-to-parallel converter 250. The wireless receiver apparatus 200 further comprises a processing unit 225 configured to perform channel and phase noise estimation and equalization based on the de-modulated MB-DFT-s-OFDM signal and the improved pilot allocation scheme implemented by the wireless transmitter apparatus 100. Moreover, the wireless receiver apparatus 200 comprises a plurality of frequency despreading blocks 220a-n, wherein each frequency de-spreading block is configured to de-spread a respective portion of the equalized signal. The wireless receiver apparatus 200 further comprises a parallel-to-serial converter 210 configured to convert the output of the plurality of frequency de-spreading blocks into a sequence of received symbols. As already described above, the input to at least one of the plurality of frequency de-spreading blocks 220a-n is based on only pilot symbols, in particular phase tracking reference signal, PTRS, symbols, but no data symbols. In the embodiment of figure 3, the wireless receiver apparatus 200 further comprises a cyclic prefix, CP, extractor 240 arranged downstream of the serial-to-parallel converter 250 and upstream of the FFT OFDM demodulator 230 and configured to extract a respective CP from the MB-DFT-s-OFDM signal.
[0089] According to embodiments disclosed herein only transmitter phase noise may be present. This may be the case, for instance, in uplink scenarios where only the phase noise of the transmitter apparatus 100 in the form of a UE is considered, while thephase noise generated at the receiver 200, e.g. a BS 200, can be neglected due to the assumption that the BS 200 may comprise higher-end RF components. In an embodiment, a frequency division duplexing, FDD, scheme may be implemented by the wireless transmitter and receiver apparatus 100, 200 to highlight the importance of the receiver feedback in improving the quality of phase noise estimation using PTRS.
[0090] The system model illustrated in figure 3 may be expressed mathematically in the following way:
[0091] r = WHFNBHEAF^WX + WHFwBn,
[0092] where the definitions of the symbols are defined below. The operator (. )His the Hermitian transpose of a matrix, and the operator Blkdiag(X) is an operator that constructs a block diagonal matrix with the matrix X as its block diagonal elements.
[0093] N IFFT size
[0094] M DFT size
[0095] NpPilot sequence length
[0096] v CP length
[0097] FNN X N DFT matrix
[0098] W Blkdiag(FM)
[0099] A CP addition matrix
[0100] B CP removal matrix
[0101] H Toeplitz Channel Matrix
[0102] E Diagonal phase noise matrix
[0103] x N x 1 data vector
[0104] n N + v x 1 AWGN vector
[0105] Embodiments disclosed herein focus on phase noise estimation and mitigation, while not addressing channel estimation, where it may be assumed that perfect estimates of the channel exist. Channel and phase noise estimation may be performed sequentially with a front-loaded pilot allocation scheme. Then, phase noise is tracked with the assumption that the channel coherence time is equal to or larger than the time span of several MB-DFT-s-OFDM symbols, i.e. a MB-DFT-s-OFDM frame. Further details about this approach are disclosed in Q. Zou, A. Tarighat and A. Sayed, "Compensation of phase noise in OFDM wireless systems," IEEE transactions on signal processing, pp. 5407-5424., 2007, which is fully incorporated herein by reference.
[0106] The evaluation criteria to quantify the effectiveness of the phase noise mitigation scheme implemented by the wireless transmitter apparatus 100 and the wireless receiver apparatus 200 according to an embodiment may be a communication centric performance metric, such the uncoded BER. As will be appreciated, however, other metrics may be used to quantify the effect as well.
[0107] As alreadv described above, in the phase noise estimation procedure, a processing step implemented by the processing unit 225 is added before the de-spreading operation at the wireless receiver apparatus 200, where phase noise estimation and mitigation are performed. The following approximation may be applied:
[0108] r ~ FwBHAEF^Wx + FwBn,wherein this approximation implies that the phase noise impact on the CP may be neglected (as shown in V. Syrjala and M. Valkama, "Iterative receiver signal processing for joint mitigation of transmitter and receiver phase noise in OFDM-based cognitive radio link," in 7th International Conference on Cognitive Radio Oriented Wireless Networks, 2012). If the CP length is greater than the delay spread of the channel, then Hc= BHA is a circulant matrix that can be diagonalized with FFT matrices. Then, r can be re-written in the following form:
[0109] r = HEy + n,
[0110] where H = F,VHCF”. E = F,VEF”, n = FwBn, y = Wx. Since E is a diagonal matrix with
[0111]
[0112] as its diagonal elements, E is a circulant matrix. Thus, r may be re-written as:
[0113] r = HYe + n,
[0114] where Y = circul(y), circul(.) is an operator that constructs a circulant matrix from the vector in its argument which constitutes its first column.
[0115] As alreadv described above, the pilot allocation scheme implemented by the wireless transmitter apparatus 100 makes sure that at least one DFT block of the plurality of frequency spreading blocks 120a-n at the transmitter 100 is fully allocated with pilots, e.g. PTRS. As will be shown in the following, this pilot allocation implemented by the wireless transmitter apparatus 100 allows estimating phase noise in a non-iterative fashion. Let H' be a diagonal channel matrix where its diagonal entries correspond to the channel frequency response at the location of the PTRS, and let Y' correspond to the DFT spreaded PTRSs, i.e. Y' = circul(FMx'), then, the estimated phase noise vector may be acquired by applying:
[0116] e = (H"'Y"iH'Y')-1H"'Y",r.
[0117] An important point here is that x'is fully composed of PTRSs, because otherwise, i.e. if x’ contains unknown variables at the reception, an estimation procedure of these variables is needed, which complicates the process of phase noise estimation. Figure 4 depicts a schematic diagram of the PTRS insertion approach implemented by the wireless transmitter apparatus 100 according to an embodiment.
[0118] When e is acquired, the center-most spectral components of phase noise may be selected as they are the most reliable to use. For instance, the seven centre-most components of the low-pass phase noise spectral components may be used as the basis of phase noise mitigation. The phase noise deconvolution using the estimated phase noise vector is applied by first constructing the matrix E = circul(e), where e is an N x 1 vector containing the center-most phase noise estimates, while the rest of the vector consists of zeros. Then, the phase noise mitigation is achieved by applying:
[0119] f = (HHEHHE)1RHEHr.
[0120] Finally, the de-spreading operation is applied, i.e. x = WHf.
[0121] In the following some simulation results are provided to demonstrate the effectiveness of the phase noise mitigation technique implemented by embodiments of the wireless transmitter apparatus 100 and the wireless receiver apparatus 200. The adopted MB-DFT-s-OFDM waveform is of size N = 2048 operating over a 2 GHz bandwidth. The DFT spreading / IDFT de-spreading block size M = N / S. The wireless channel 320 is assumed to have a Ricean profile with K-factor of 5 and a delay spread of 5 ns, similar to delay-spread values found in indoor-factory measurements at a centre frequency of around 300 GHz. Regarding the phase noise effect, a model is adopted that is composed of a mixture of correlated and uncorrelated noises. The phase noise parameters are f = 30 MHz and Ko= —113 dBc / Hz. The modulation order is selected to be 16-QAM.
[0122] Figure 5 shows the un-coded BER performance of the MB-DFT-s-OFDM waveform that was impacted by phase noise, where the phase noise mitigation technique (referred to as “Estimated PHN” in figure 5) implemented by the wireless transmitter apparatus 100 and the wireless receiver apparatus 200 according to an embodiment is compared with three benchmarks, namely a first benchmark referred to as "No PHN compensation”, where only single tap channel equalization is adopted; a second benchmark which is a CPE mitigation approach referred to as "Estimated CPE”, where the average phase error is estimated and compensated along with channel equalization; and a third benchmark referred to as "Perfect Low-pass PHN knowledge”, which is an approach that follows the same phase noise least-squares mitigation approach, but with perfect knowledge of the seven centre-most frequency components (i.e. low-pass phase noise behaviour) of the phase noise. As can be taken from figure 5, although the estimation approach implemented according to embodiments disclosed herein is always lower bounded by the mitigation technique since it is using the perfect knowledge of the phase noise low-pass behaviour, it clearly outperforms the CPE based approach, the “No PHN compensation” approach, and significantly reduced the BER performance especially in the high SNR regime.
[0123] Since the PTRS allocation scheme implemented by the wireless transmitter apparatus 100 according to an embodiment is contiguous, the wireless transmitter apparatus 100 according to an embodiment is capable of changing the location of the PTRSs. This may be advantageous, for instance, when the originally selected PTRS locations coincide with a deep wireless channel fade. In FDD systems where the channel CFRs are almost independent in up-link and down-link, the UE 100 may need to estimate its own CFR. Assuming that the CFR does not vary over several MB-DFT-s-OFDM symbols, the wireless transmitter apparatus 100, e.g. UE 100 according to an embodiment is configured to feedback to the wireless receiver apparatus 200 the DFT spreading block index where the CFR is reliable. Reliability can be quantified by a metric such high SNR.
[0124] Figure 6 shows a signalling diagram illustrating in more detail the sequence followed when Node B (the UE 100) feedbacks the selected index of the DFT block to carry PTRSs to Node A (the BS 200). In step 601 of figure 6 the UE 100 and the BS 200 exchange information about DFT blocks lengths and locations. The UE 100 configures itself based on information from the BS 200. In steps 602, 603 of figure 6 the UE 100 performs channel estimation and computes performance metric(s). In step 604 of figure 6 the UE 100 determines DFT block size and position. In step 605 of figure 6 the BS 200 receives the information about the size and position of the DFT allocated for pilots from the UE 100 and determines, based on this information, the pilot sequence and its length. In step 606 of figure 6 the BS 200 and the UE 100 start a communication session. In step 607 of figure 6 the previous sequence may be repeated, for instance, when the channel conditions are changing.
[0125] According to an embodiment, the wireless receiver apparatus 200 is configured to feedback the DFT block number that the receiver apparatus 200 determines as the most suitable DFT block for the purpose of performing phase noise estimation. As will be appreciated, the signalling overhead related to PTRS allocation is low since it may only convey the DFT spread block number. As will be further appreciated, more than one DFT spreading blocks 120a-n may be assigned as PTRS bearing blocks. This feature is useful when the DFT spreading block size is small. Furthermore, the configuration of the DFT spreading blocks may be adjusted, e.g., depending on the severity of phase noise and / or channel conditions.Figure 7 is a flow diagram illustrating a method 700 for operating the wireless transmitter apparatus 100 for MB DFT-s-OFDM communication with the wireless receiver apparatus 200. The method 700 comprises a step 701 of converting with the serial-to-parallel converter 110 a sequence of input symbols into a plurality of subsets of the sequence of input symbols. Moreover, the method 700 comprises a step 703 of spreading with the plurality of frequency spreading blocks 120a-n a respective subset of the plurality of subsets of the sequence of input symbols in frequency. As already described above, at least one subset of the plurality of subsets of the sequence of input symbols processed by at least one frequency spreading block of the plurality of frequency spreading blocks 120a-n comprises only pilot symbols, but no data symbols. The method 700 comprises a further step 705 of generating with the IFFT OFDM modulator 130 an OFDM signal based on the output of the plurality of frequency spreading blocks 120a-n. Moreover, the method 700 comprises a step 707 of converting with the parallel-to-serial converter 150 the output of the IFFT OFDM modulator 130 into a serial stream for transmission to the wireless receiver apparatus 200.
[0126] Figure 8 is a flow diagram illustrating a method 800 for operating the wireless receiver apparatus 200 for MB DFT-s-OFDM communication with the wireless transmitter apparatus 100. The method 800 comprises a step 801 of converting a serial signal stream received from the wireless transmitter apparatus 100 into a MB-DFT-s-OFDM signal. Moreover, the method 800 comprises a step 803 of performing OFDM de-modulation of the MB-DFT-s-OFDM signal. The method 800 comprises a further step 805 of performing channel and phase noise estimation and equalization based on the de-modulated MB-DFT-s-OFDM signal. Moreover, the method 800 comprises a step 807 of de-spreading a plurality of portions of the equalized signal using the plurality of frequency de-spreading blocks 220a-n. As already described above, the input to at least one of the plurality of frequency de-spreading blocks 220a-n is based on only pilot symbols. The method 800 comprises a further step 809 of converting the output of the plurality of frequency de-spreading blocks 220a-n into a sequence of received symbols.
[0127] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).
[0128] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described apparatus embodiment is merely exemplary. For example, the unit division is merely logical function division and may be other division in actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.
[0129] The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.
[0130] In addition, functional units in the embodiments of the disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.
Claims
CLAIMS1. A wireless transmitter apparatus (100) for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless receiver apparatus (200), wherein the wireless transmitter apparatus (100) comprises:a serial-to-parallel converter (110) configured to convert a sequence of input symbols into a plurality of subsets of the sequence of input symbols;a plurality of frequency spreading blocks (120a-n), wherein each frequency spreading block (120a-n) is configured to spread a respective subset of the sequence of input symbols;an inverse Fast Fourier transform, IFFT, OFDM modulator (130) configured to generate an OFDM signal based on the output of the plurality of frequency spreading blocks (120a-n); anda parallel-to-serial converter (150) configured to convert the output of the IFFT OFDM modulator (130) into a serial stream for transmission to the wireless receiver apparatus (200),wherein at least one subset of the plurality of subsets of the sequence of input symbols processed by at least one frequency spreading block of the plurality of frequency spreading blocks (120a-n) comprises only pilot symbols.
2. The wireless transmitter apparatus (100) of claim 1, wherein the wireless transmitter apparatus (100) further comprises a cyclic prefix, CP, appender (140) configured to add a respective CP to the output of the IFFT OFDM modulator.
3. The wireless transmitter apparatus (100) of claim 1 or 2, wherein each of the plurality of frequency spreading blocks (120a-n) is associated with a respective frequency band and wherein the wireless transmitter apparatus (100) is configured to select the at least one frequency spreading block of the plurality of frequency spreading blocks (120a-n) for processing the at least one subset of the plurality of subsets of the sequence of input symbols comprising only pilot symbols.
4. The wireless transmitter apparatus (100) of claim 3, wherein the wireless transmitter apparatus (100) is configured to select the at least one frequency spreading block of the plurality of frequency spreading blocks (120a-n) for processing the at least one subset of the plurality of subsets of the sequence of input symbols comprising only pilot symbols based on feedback information provided by the wireless receiver apparatus (200).
5. The wireless transmitter apparatus (100) of any one of the preceding claims, wherein the wireless transmitter apparatus (100) is configured to adjust a number, a size and / or a frequency band of the plurality of frequency spreading blocks (120a-n) based on one or more sensing and / or communication requirements.
6. The wireless transmitter apparatus (100) of claim 5, wherein the wireless transmitter apparatus (100) is configured to provide information about the number, size, frequency band, and / or the at least one selected frequency spreading block of the plurality of frequency spreading blocks (120a-n) to the wireless receiver apparatus (200).
7. The wireless transmiter apparatus (100) of any one of the preceding claims, wherein the wireless transmitter apparatus (100) is a user equipment, UE, (100) and the wireless receiver apparatus (200) is a base station (200) of a mobile network.
8. The wireless transmiter apparatus (100) of any one of the preceding claims, wherein the wireless transmitter apparatus (100) is an Integrated Sensing and Communication, ISAC, wireless transmiter apparatus (100).
9. The wireless transmiter apparatus (100) of any one of the preceding claims, wherein the plurality of frequency spreading blocks (120a-n) comprise a plurality of Fast Fourier transform, FFT, spreading blocks (120a-n).
10. A method (700) for operating a wireless transmitter apparatus (100) for Multi-Band Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless receiver apparatus (200), wherein the method (700) comprises:converting (701) with a serial-to-parallel converter (110) a sequence of input symbols into a plurality of subsets of the sequence of input symbols;spreading (703) with a plurality of frequency spreading blocks (120a-n) a respective subset of the plurality of subsets of the sequence of input symbols, wherein at least one subset of the plurality of subsets of the sequence of input symbols processed by at least one frequency spreading block of the plurality of frequency spreading blocks (120a-n) comprises only pilot symbols;generating (705) with an inverse Fast Fourier, IFFT, OFDM modulator (130) an OFDM signal based on the output of the plurality of frequency spreading blocks (120a-n); andconverting (707) with a parallel-to-serial converter (150) the output of the IFFT OFDM modulator (130) into a serial stream for transmission to the wireless receiver apparatus (200).
11. A wireless receiver apparatus (200) for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless transmiter apparatus (100), wherein the wireless receiver apparatus (200) comprises:a serial-to-parallel converter (250) configured to convert a serial signal stream received from the wireless transmitter apparatus (100) into a MB-DFT-s-OFDM signal;a Fast Fourier transform, FFT, OFDM demodulator (230) configured to perform OFDM de-modulation of the MB-DFT-s-OFDM signal;a processing unit (225) configured to perform channel and phase noise estimation and equalization based on the demodulated MB-DFT-s-OFDM signal;a plurality of frequency de-spreading blocks (220a-n), wherein each frequency de-spreading block (220a-n) is configured to de-spread a respective portion of the equalized signal; anda parallel-to-serial converter (210) configured to convert the output of the plurality of frequency de-spreading blocks (220a-n) into a sequence of received symbols;wherein the input to at least one of the plurality of frequency de-spreading blocks (220a-n) is based on only pilot symbols.
12. The wireless receiver apparatus (200) of claim 11 , wherein the wireless receiver apparatus (200) further comprises a cyclic prefix, CP, extractor (240) configured to extract a respective CP from the MB-DFT-s-OFDM signal.
13. The wireless receiver apparatus (200) of claim 11 or 12, wherein each of the plurality of frequency de-spreading blocks (220a-n) is associated with a respective frequency band and wherein the frequency band of the frequency de-spreading block whose input is based on only pilot symbols is equal to the frequency band of a frequency spreading block selected by the wireless transmitter apparatus (100).
14. The wireless receiver apparatus (200) of claim 13, wherein the wireless receiver apparatus (200) is configured to provide feedback information to the wireless transmitter apparatus (100) for allowing the wireless transmitter apparatus (100) to select one or more frequency spreading blocks (120a-n).
15. The wireless receiver apparatus (200) of any one of claims 11 to 14, wherein the wireless receiver apparatus (200) is configured to adjust a number, a size and / or a frequency band of the plurality of frequency de-spreading blocks (220a-n) based on one or more sensing and / or communication requirements.
16. The wireless receiver apparatus (200) of claim 15, wherein the wireless receiver apparatus (200) is configured to receive information about the number, size, frequency band, and / or the selected frequency spreading block from the wireless transmitter apparatus (100).
17. The wireless receiver apparatus (200) of any one of claims 11 to 16, wherein the wireless transmitter apparatus (100) is a user equipment, UE, (100) and the wireless receiver apparatus (200) is a base station (200) of a mobile network.
18. The wireless receiver apparatus (200) of any one of claims 11 to 17, wherein the wireless receiver apparatus (200) is an Integrated Sensing and Communication, ISAC, wireless receiver apparatus (200).
19. The wireless receiver apparatus (200) of any one of claims 11 to 18, wherein the plurality of frequency despreading blocks (220a-n) comprise a plurality of Inverse Fourier transform, IFFT, de-spreading blocks (220a-n).
20. A method (800) for operating a wireless receiver apparatus (200) for Multi-Block Discrete Fourier Transform Spread Orthogonal Frequency-Division Multiplexing, MB DFT-s-OFDM, communication with a wireless transmitter apparatus (100), wherein the method (800) comprises:converting (801) a serial signal stream received from the wireless transmitter apparatus (100) into a MB-DFT-s-OFDM signal;performing (803) OFDM de-modulation of the MB-DFT-s-OFDM signal;performing (805) channel and phase noise estimation and equalization based on the de-modulated MB-DFT-s-OFDM signal;15de-spreading (807) a plurality of portions of the equalized signal using a plurality of frequency de-spreading blocks (220a-n), wherein the input to at least one of the plurality of frequency de-spreading blocks (220a-n) is based on only pilot symbols; andconverting (809) the output of the plurality of frequency de-spreading blocks (220a-n) into a sequence of received symbols.
21. A computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method (700) of claim 10 or the method (800) of claim 20 when the program code is executed by the computer or the processor.