Iterative Sampling Frequency Offset Estimation for MB-OFDM UWB Systems With Long Transmission Packet

In orthogonal frequency division multiplexing (OFDM) systems, most of the conventional sampling frequency offset (SFO) estimation methods work under the assumption of time-invariant or slow time-variant channels. In mobile environment, the time-variant channel significantly degrades the accuracy of SFO estimation. To solve the problem, we first analyze the properties of time-variant channels. If terminal moves within some tens of the wavelength of radio frequency (RF) signal, channel path delay almost remains unchanged. For most practical OFDM systems, our analysis indicates that channel path delay can be regarded as unchanged during the interval of some tens of OFDM symbols in time-variant channels. Based on the analysis, we propose a novel SFO estimation method for pilot-aided OFDM systems. Different from the conventional methods, the proposed method estimates SFO by detecting the variation of the symbol timing error caused by SFO. The detection is finished by implementing correlation between the channel impulse responses (CIRs) estimated by different OFDM symbols. Performance of the proposed method is simulated and compared with that of two conventional post-FFT methods. Numerical results show that, the proposed SFO estimation method performs better than the conventional methods not only in time-variant channels, but also at low SNRs and large residual carrier frequency offsets (CFOs).

In this paper, a residual frequency offset (RFO) and sampling frequency offset (SFO) estimator is proposed for ultra- wideband multi-band orthogonal frequency division multiplexing (UWB MB-OFDM) systems. The proposed scheme uses a time-domain spreaded data samples which is provided in MB-OFDM system. To demonstrate the efficiency of the proposed RFO and SFO estimator, comparisons are made with other existing estimator.

A precise estimation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose a SFO estimation method which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation /compensation are mainly based on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has a good performance and stable operation through extensive simulation.

A precise estimation and compensation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system, because sampling frequency mismatch between the transmitter and the receiver dramatically degrades the system performance due to the loss of orthogonality between the subcarriers. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose two SFO estimation methods which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation / compensation are mainly specialized on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has good performance and stable operation through extensive simulation.

Enabling bistatic radar sensing within the context of integrated sensing and communication (ISAC) for future sixth-generation (6G) mobile networks demands strict synchronization accuracy, which is particularly challenging to be achieved with over-the-air (OTA) synchronization. Existing algorithms handle time and frequency offsets adequately but provide insufficiently accurate sampling frequency offset (SFO) estimates that result in the degradation of obtained radar images in the form of signal-to-noise ratio loss and migration of range and Doppler shift. This article introduces an SFO estimation algorithm named tilt inference of time offset (TITO) for orthogonal frequency-division multiplexing (OFDM)-based ISAC. Using available pilot subcarriers, TITO obtains channel impulse response (CIR) estimates and extracts information on the SFO-induced delay migration to a dominant reference path with constant range, Doppler shift, and angle between transmit and receive ISAC nodes. TITO then adaptively selects the delay estimates that are only negligibly impaired by SFO-induced intersymbol interference (ISI), ultimately employing them to estimate the SFO. Assuming a scenario without a direct line of sight (LoS) between the aforementioned transmitting and receiving ISAC nodes, a system concept with a relay reflective intelligent surface (RIS) that is used to create the aforementioned reference path is proposed. Besides a mathematical derivation of accuracy bounds, simulation and measurements at 26.2 GHz are presented to demonstrate TITO’s superiority over existing methods in terms of SFO estimation accuracy and robustness.

Symbol synchronization and sampling frequency synchronization techniques in real-time DDO-OFDM systems

We investigate the estimation error, convergence speed, and computational complexity of the three commonly used sampling frequency offset (SFO) estimation algorithms based on training sequence (TS), cyclic prefix (CP), and pilot under different signal-to-noise ratios (SNRs) and received optical powers (ROPs) by numerical simulation and offline experiment in a short-reach direct-detection optical OFDM transmission system. The results showed that the pilot-based algorithm’s estimation accuracy (< 14 ppm) is relatively low for the initial SFOs in the range of ±200 ppm, while the estimation error of both TS-based and CP-based algorithms is stable within 0.6 ppm. Moreover, pilot-based and TS-based algorithms exhibit a faster convergence speed than the CP-based one. And the computational complexity of the SFO estimation algorithms based on CP, TS, and pilot decreases sequentially.

A pilot-aided scheme is proposed for the joint estimation and tracking of channel impulse response (CIR), carrier frequency offset (CFO) and sampling frequency offset (SFO) in burst mode, multiple-input-multiple-output (MIMO), and orthogonal frequency division multiplexing(OFDM) systems. First, a received signal model that takes into account nonlinear CFO/SFO effects is formulated. Then, based on the derived signal model and the received multicarrier signal samples containing the pilot tones in the frequency domain, an objective function that includes MIMO CIR, CFO, and SFO is introduced to develop a vector recursive-least-square (RLS)-based joint channel estimation and synchronization algorithm. The analysis and simulation results show that, over the large ranges of the CFO and SFO values, the proposed estimation and tracking scheme offers fast convergence, high stability, and a near-optimum receiver performance that is remarkably close to the ideal performance in the case of perfect channel estimation and synchronization over quasi-static Rayleigh multipath fading channels.

This paper proposes an efficient phase-error suppression scheme for multiband (MB) orthogonal frequency-division multiplexing (OFDM)-based ultrawideband (UWB) communication systems. The proposed scheme consists of a clock-recovery loop and a common phase-error (CPE) tracking loop. The clock-recovery loop performs estimation of the sampling frequency offset (SFO) and its 2-D (time and frequency) compensation, while the CPE tracking loop estimates and corrects the phase errors caused by residual carrier frequency offset (CFO), residual SFO, and phase noise (PHN). The SFO and CPE estimators employ pilot-tone-based and channel-frequency-response (CFR)-weighted low-complexity approaches, each of which uses a robust error-reduction scheme without using angle calculations or divisions. Analytical results and numerical examples show the effectiveness of the proposed scheme in different multipath fading scenarios and signal-to-noise ratio (SNR) regimes.

Analog-to-digital and digital-to-analog interfaces (ADIs and DAIs) constitute the essential link between the analog physical world and digital signal processing systems. As modern communication systems demand higher bandwidths,improved linearity, and increased energy efficiency, imperfections such as linear and nonlinear distortion and sampling errors increasingly limit achievable performance. Such imperfections require compensation techniques that are both effective and computationally efficient for high-speed, high-resolution implementations. This thesis contributes low-complexity solutions for linearization,equalization, and sampling-frequency synchronization, enabling efficient signal processing in high-speed data-conversion systems. Firstly, the design of low-complexity digital linearizers for ADIs is addressed. Several novel linearizers are introduced that are inspired by neuralnetwork architectures, but avoid the high training complexity associated with neural-network-based approaches. These linearizers can outperform classical linearizers, such as Wiener and Hammerstein, while requiring lower implementation complexity. The proposed designs cover both memoryless and memory (frequency-dependent) linearizers and are applicable to nonlinear distortion occurring either before or after sampling. All designs enable closed-form parameter estimation via matrix inversion, thereby eliminating the need for unpredictable iterative nonconvex optimization. In addition,an efficient memoryless linearizer based on 1-bit quantization is introduced,enabling lookup-table-based implementations with only one multiplication per corrected sample. Secondly, equalization of digital-to-analog converters (DACs) frequency response using linear-phase finite impulse response (FIR) filters is considered. For several DAC pulse shapes operating across multiple Nyquist bands,minimax-optimal equalizers are designed, and their properties are analyzed. Based on these designs, expressions for the required filter order are derived as explicit functions of bandwidth and target equalization accuracy, using symbolic regression followed by further refinement. The resulting expressions provide accurate order estimates across different pulse shapes and operating conditions. Thirdly, a low-complexity time-domain sampling frequency offset (SFO)estimation and compensation framework based on the Farrow structure for interpolation is presented. By reusing the Farrow structure already employed for SFO compensation, the proposed approach enables a unified estimation and compensation architecture with significantly reduced overall implementation complexity. The method operates on arbitrary bandlimited signals, supports joint estimation of SFO and sampling time offset, and allows estimation using only a single component (real or imaginary) of a complex signal. A Newton-based estimator exploiting the structure of the problem is developed to reduce computational complexity, while an alternative iterative least-squares-based design provides an even lower-complexity solution. The resulting estimators are robust to other synchronization errors and are well suited for practical receiver implementations. In addition, motivated by the appearance of low-order time-index-powered sums in the Farrow-based formulation, a general cascaded-accumulator framework is developed as a supplementary contribution, enabling efficient causal computation of time-index-powered weighted sums of arbitrary order without data buffering and reducing the multiplicative complexity from order K N to only K+1 constant multiplications (where N is the number of terms and K is the power in the sum), which is applicable both to SFO estimators and to other signal processing applications beyond the SFO problem.

A successive interference cancellation (SIC)-based weighted least-squares (WLS) estimation for the carrier frequency offset (CFO) and the sampling frequency offset (SFO) is presented for wireless local area networks (WLANs) based on orthogonal frequency division multiplexing (OFDM). The proposed SIC-based WLS performs the estimation by exploiting the phase rotation in the frequency domain caused by the CFO and the SFO. SIC-based WLS estimates the CFO and the SFO successively instead of by traditional simultaneous estimation. The estimation of CFO based on the Taylor series is performed first, and then the WLS estimation of SFO based on successive cancellation of the CFO is carried out. The simulation results show that the SIC-based WLS can estimate the CFO and the SFO effectively. Compared to the WLS scheme, a performance improvement of more than 0.6 dB is achieved by SIC-based WLS, and nearly 10 percent of the complexity is reduced.

The new radio (NR) is a cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) based the fifth generation (5G) mobile communication standard of the third-generation partnership project (3GPP). This paper proposes a sidelink primary synchronization signal (SPSS) based sampling frequency offset (SFO) estimation scheme in the CP-OFDM based NR sidelink system with a severely frequency selective fading. To do this, the SPSS-based differential correlation and correlation operation between adjacent symbol are used in the post-fast Fourier transform (FFT) synchronization procedure. This paper shows via computer simulations that such a design achieves a robustness against frequency selectivity fading.

Digital radio mondiale (DRM) is a terrestrial radio broadcasting standard to replace existing analogue AM and FM broadcasting, which is based on an orthogonal frequency division multiplexing (OFDM) technique. This paper focuses on the issue of estimating a sampling frequency offset (SFO) in OFDM-based broadcasting systems under frequency selective fading channels. In order to design a robust SFO estimation scheme and to benchmark its performance, the performance of the various conventional SFO estimation schemes is discussed and some improvements on the conventional estimation algorithms are highlighted. The simulation results show that such a design enhances the robustness of the proposed scheme against frequency selective fading.

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).

UWB(Ultra-Wideband)는 낮은 전력으로 초고속 통신을 실현하는 근거리 무선 통신 기술로서 주파수 부족 현상을 넘어서서 신규 기술을 도입할 수 있는 획기적인 기술 방식이다. UWB 전송방식 중의 하나인 MB-OFDM(Multiband Orthogonal Frequency Division Multiplexing) 시스템은 다양한 무선 통신 서비스에 적용이 가능하다. 본 논문에서는 협력 전송에서 전송률이 감소하는 문제를 해결하기 위한 UWB 시스템에서 계층 변조(HM : Hierarchical Modulation)와 순환 중복 검사를 통해 중계기에서 적응적으로 변조방식을 변경하는 새로운 중계 기법을 제시한다. 이는 기존 방법에 비해 비트 에러율은 비슷하며 처리량을 33%까지 증가시키는 장점이 있다. Recently, various transmission techniques for communication and broadcasting systems have been developed to meet the dramatically increasing requirement of consumers. Because UWB (Ultra-Wideband) is a wireless communication technique that supports high data rate with low power, it can satisfy the requirement and can be applied to various wireless communication services. The multi-band orthogonal frequency division multiplexing (MB-OFDM) system, one of UWB system, is the wireless communication system that satisfies the transmission characteristic for UWB and so it can be used for various wireless communication services. In this paper, we propose a scheme that uses hierarchical modulation which is applied in digital video broadcasting system at the source and adaptive modulation based on the channel quality at the relays. The simulation results have shown that the proposed scheme has both the advantages of the increased throughput by 33% and similar BER performance to conventional scheme.