Large Doppler Frequency Shift Research Articles

Разработка математической модели интерферометрической системы определения доплеровского сдвига частоты.

This work presents the result of the received signal measuring system for processing Doppler frequency theoretical research. In the researching device means of controlling laser frequency whose amplitude is proportional to the Doppler frequency shift of the received RF signal is realized. The coherent laser beam is divided in two forming interference pattern. In this case, one of the beams passes through the delay line, which leads to a phase shift in the optical wave. The rate of this phase shift is proportional to the laser frequency, changes in which cause corresponding changes in the interference pattern. Changes in the interference pattern in center analysis makes it possible to determine the changes of the laser frequency, which depends on Doppler frequency shift of the received RF signal. In this work opposition of the requirements for the Doppler frequency shift determination interferometric system parameters (the coefficient of proportionality to conversion Doppler frequency shift of the received RF signal in laser frequency and time delay) is discovered: large dynamic measurement range and high Doppler frequency shift measurement resolution. The processing the received RF signal method is proposed. This method take into consideration these requirements. The proposed measurement algorithm implements the multiscale principle. It is pointed that the proposed processing the measurements results method can be implemented both the parallel processing in channels with different values of conversion coefficients, and sequential – with their iterative change.

Adaptive Doppler compensation method for coherent LIDAR based on optical phase-locked loop

Coherent LIDAR is a potential and effective technology to detect and identify space debris. However, for the high-speed space debris, the large Doppler frequency shift (DFS) generated by high-speed relative motion challenges the bandwidth of the photoelectric detection system and increases the difficulty of datasampling and processing. In this paper, we propose an effective method to compensate this large DFS adaptively by using an optical phase-locked loop (OPLL), and thus the relative velocity between the target and LIDAR platform can be obtained. A laboratory experiment for moving targets with our OPLL method has been conducted, and it revealed that our method worked well to compensate for 64 MHz frequency difference, thus the relative velocity is about 26 m/s based on the compensated DFS. And the beat frequency is always locked to the reference frequency, while the DFS generated by variable speed motion is compensated adaptively. The proposed compensation method could improve the performance of coherent LIDAR significantly, especially when detecting high-speed target.

Application of 5G new radio for satellite links with low peak‐to‐average power ratios

SummaryThe aim of the paper is to consider feasibility of 5G new radio (NR) over satellite links also known as nonterrestrial networks (NTNs). Large propagation delay and Doppler frequency shift are challenges like is high peak‐to‐average power ratio (PAPR) of 5G NR signal because satellite systems would like to operate at very low‐power amplifier back‐off values. This paper provides a brief summary of progress made in initial synchronization and uplink random access process both in the literature and standardization. Furthermore, the paper explains what is the relationship between low PAPR and power amplifier back‐off and the density of reference symbols by showing that 2‐dB back‐off values can be attained using sufficient reference symbol density. Finally, open issues that need clarification are listed. Interestingly, all solutions to these problems do not mean changes in the standard but proper actions from vendors and operators.

Deriving L-Band Tilting Ocean Surface Roughness From Measurements by Operational Systems

Waves much shorter than those measured by operational systems make significant contribution to the ocean surface roughness. This article describes a method to obtain the L-band tilting ocean surface roughness using wind speed and windsea dominant wave period coupled with a wind-wave spectrum model. Examples are presented with wind and dominant wave data from ocean buoys and hurricane hunters. Several related issues are discussed: high-frequency wave spectrum, integration limit, swell contribution, and measurements in extreme winds: 1) it is well known since the 1970s that with stationary sensors, extending the frequency range in measuring elevation spectrum does not yield useful short-wave information because of the low signal level and large Doppler frequency shift involved in measuring short waves. 2) Low-pass mean square slopes (LPMSSs) integrated to 5 and 11 rad/m are computed to quantify their difference as a function of wind speed and inverse wave age (IWA). The normalized difference decreases with increasing wind speed and decreasing IWA. 3) Swell contribution to the L-band LPMSS is almost negligible for wind speed greater than 5 m/s (less than 5% in 99% of observations). In low-wind conditions (wind speed less than 5 m/s), the swell contribution is difficult to assess because of inaccuracy in identifying the weak windsea system. 4) The coarse resolution in National Data Buoy Center (NDBC) wave spectra causes large data scatter in the computed LPMSS in very high winds (greater than 20 m/s). A mitigating solution is offered.

一种带有ICI自消除的多OFDM符号时变信道估计方法

高速移动环境下，由于多普勒频移增大，信道的时变性破坏了正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)系统子载波之间的正交性，从而产生子载波间干扰(Inter Carrier Interference, ICI)，导致系统性能严重下降。为了减少待估计量，通常采用基扩展模型(BEM)来近似模拟时变信道。为了提升性能，当信道的相干时间与发送码元的周期可相比拟的时候，本文采用多块(多个OFDM符号)。同时在使用导频符号对参数估计时，忽略了相邻非导频符号的ICI干扰，降低了整个时变信道下的估计准确性。因此我们通过分析子载波所产生的ICI系数变化特点，提出了一种带有ICI自消除的多OFDM符号时变信道估计方法，提高估计的准确性。但是由于基于多OFDM符号的信道估计性能在归一化多普勒频移较大时该方法成立条件不再满足，因此性能呈现明显的衰减，为了解决此问题，我们提出一种带有ICI自消除的自适应OFDM符号个数时变信道估计方法。仿真实验从误码率，归一化均方误差两方面分别验证了该方法的有效性。 In high-speed mobile environment, time-varying channel destroys the orthogonality between subcarriers of orthogonal frequency-division multiplexing (OFDM) systems, giving rise to in-ter-carrier interference (ICI), and degrading the performance of the systems. Basis expansion model (BEM) is usually used to approximate the time-varying channels to reduce the estimators. In order to improve performance, this paper adopts multi block (multiple OFDM symbols) when the coherent time of the channel variations and the symbols can be compared. However, when using pilot-symbol to parameter estimation, the ICI interference from near non-pilot-symbol is ignored, reducing its estimated accuracy of time-varying channel. And in this work the paper proposes a multiple OFDM symbols time-varying channel estimation method with ICI self-cancellation after analyzing the high correlation between subcarriers, improving the accuracy of estimation. But due to the condition of utilizing the multiple OFDM symbols channel estimation method is no longer met in large Doppler frequency shift, the performance of resulting channel estimation attenuates obviously. In order to solve this problem, we put forward a kind of adaptive OFDM symbol time-varying channel estimation method with the ICI self-cancellation. The simulation results show that the proposed method is effective from two aspects of error rate and normalized mean square error.

Improved Carrier Frequency Offset Estimation Algorithms for PUCCH Format 1 in LTE-Advanced

Physical Uplink Control Channel (PUCCH) is an important narrow-band channel in LTE-Advanced system, which carries the uplink control information, such as acknowledge/non-acknowledge (ACK/NACK) bits, downlink channel quality indicator (CQI), HARQ-ACK feedback information, and it requires much higher transmission quality than the other channels. With the aid of orthogonal CDMA, multiple users share the same time-frequency resource, the multiuser interference has been the main factor that limits the transmission quality of the control information [1]. In the high-speed mobile scenario, there exists a large Doppler frequency shift, which leads to loss of code orthogonality and also introduces inter-carrier interference (ICI) within a single SCFDMA symbol. Besides, the multiuser interference in high-speed mobile environment is severe. In this paper, the carrier frequency offset estimation algorithms are analyzed, and a double-iteration carrier frequency offset (CFO) estimation algorithm is proved to perform the best for PUCCH Format 1 in high-speed mobile scenario. The estimation process is achieved by coarse estimation and fine estimation, which enlarges the estimation range and improves the estimation accuracy.

Timing advanced estimation algorithm of low complexity based on DFT spectrum analysis for satellite system

In satellite mobile communication system, relative movement of the satellite and the terminal will cause a large Doppler offset. Timing advanced estimation with Zadoff-Chu sequence is sensitive to the frequency offset. When the frequency offset is larger than one times subcarrier spacing, the value of peak cannot be detected at the receiving end. To suppress the larger Doppler frequency shift, this paper proposes a novel timing advanced estimation scheme (TAE-MCD) for satellite communication system. In this algorithm, transmitted signal is divided into ZC sequence and its conjugate sequence. Using multiplication and DFT operation to find the estimated peak at the receiving end, and make subtraction with the obtained sequences at last. The scheme can not only inhibit the adverse effects of large Doppler frequency shift in timing estimation effectively, but also reduce the computational complexity at the receiving end and improve the work efficiency of the hardware. Simulations results show that TAE-MCD ouperform the existing timing advanced estimation methods, on the condition of no additional time and frequency resource are needed.

Cold Start Strategy of the CubeSat GPS Receiver

The cold start of the LEO satellite GPS receiver is complicated due to a large Doppler frequency shift, Doppler frequency rate of the navigation signals and a rapid change of the satell ...

An Adaptive Channel Estimation Based on Polynomial Fitting for LTE Uplink in High Doppler Spread Scenario

Channel estimation plays a crucial role in improving the overall system performance in long term evolution (LTE) systems. However, it is demonstrated that conventional channel estimation algorithms have poor performance in the presence of a large Doppler frequency shift. To mitigate the adverse effect of Doppler frequency shift on transmission signals, an adaptive anti-Doppler shift method based on polynomial fitting for LTE uplink is proposed in this paper. Furthermore, an adaptive strategy is exploited to improve estimation accuracy and reduce estimation mean square error (MSE), achieving better system performance. Simulations results validate the effectiveness of anti-Doppler algorithm.

Multilevel concatenated-coded M-DPSK modulation schemes for the shadowed mobile satellite communication channel

This paper presents a bandwidth-efficient multilevel concatenated-coded modulation scheme for reliable data transmission over the shadowed mobile satellite communication (MSAT) channel. In this scheme, bandwidth-efficient block modulation codes are used as the inner codes, and Reed-Solomon codes of various error correcting capabilities are used as the outer codes. The inner and outer codes are concatenated in multiple levels. A general method for constructing multilevel concatenated modulation codes is presented, and a multistage closest coset decoding for these codes is proposed. Specific multilevel concatenated 8-PSK modulation codes have been constructed. These codes are designed to lower the bit error rate (BER) of the error floor caused by the large Doppler frequency shift due to the motion of vehicles. Simulation results show that these codes perform very well and achieve large coding gains over the uncoded reference modulation systems.

Performance of DS/CDMA systems with differential M-ary orthogonal modulation and RS-coding for LEO satellite communications

This paper presents a coded modulation scheme based on M-ary orthogonal modulation by means of Walsh–Hadamard (WH) sequences, suitable for low-earth-orbit (LEO) direct sequence/code division multiple access (DS/CDMA) satellite communication systems. Based on the IS-95 scheme, we consider Reed–Solomon (RS)-coded M-ary orthogonal modulation with error or erasures decoding, which presents good performance enhancement with low complexity. LEO satellite links are characterized by large Doppler frequency shifts caused by the difference in velocity between the satellite and the earth mobile terminal, which make conventional non-coherent detection ineffective. In order to overcome the phase shift variations during the symbol period, which result in orthogonality loss of the WH sequences, we applied a differential encoding process to the spreading sequences or the WH chips prior to transmission. A special diversity process suitable for the environment under consideration is also applied. Simulation results show that the proposed diversity/coding/modulation scheme attains very good performance at low transmitter/receiver complexity. © 1998 John Wiley & Sons, Ltd.

Performance of DS/CDMA systems with differentialM-ary orthogonal modulation and RS-coding for LEO satellite communications

This paper presents a coded modulation scheme based on M-ary orthogonal modulation by means of Walsh–Hadamard (WH) sequences, suitable for low-earth-orbit (LEO) direct sequence/code division multiple access (DS/CDMA) satellite communication systems. Based on the IS-95 scheme, we consider Reed–Solomon (RS)-coded M-ary orthogonal modulation with error or erasures decoding, which presents good performance enhancement with low complexity. LEO satellite links are characterized by large Doppler frequency shifts caused by the difference in velocity between the satellite and the earth mobile terminal, which make conventional non-coherent detection ineffective. In order to overcome the phase shift variations during the symbol period, which result in orthogonality loss of the WH sequences, we applied a differential encoding process to the spreading sequences or the WH chips prior to transmission. A special diversity process suitable for the environment under consideration is also applied. Simulation results show that the proposed diversity/coding/modulation scheme attains very good performance at low transmitter/receiver complexity. © 1998 John Wiley & Sons, Ltd.