Effect Of Doppler Frequency Shift Research Articles

CSI-F: A Human Motion Recognition Method Based on Channel-State-Information Signal Feature Fusion.

The recognition of human activity is crucial as the Internet of Things (IoT) progresses toward future smart homes. Wi-Fi-based motion-recognition stands out due to its non-contact nature and widespread applicability. However, the channel state information (CSI) related to human movement in indoor environments changes with the direction of movement, which poses challenges for existing Wi-Fi movement-recognition methods. These challenges include limited directions of movement that can be detected, short detection distances, and inaccurate feature extraction, all of which significantly constrain the wide-scale application of Wi-Fi action-recognition. To address this issue, we propose a direction-independent CSI fusion and sharing model named CSI-F, one which combines Convolutional Neural Networks (CNN) and Gated Recurrent Units (GRU). Specifically, we have introduced a series of signal-processing techniques that utilize antenna diversity to eliminate random phase shifts, thereby removing noise influences unrelated to motion information. Later, by amplifying the Doppler frequency shift effect through cyclic actions and generating a spectrogram, we further enhance the impact of actions on CSI. To demonstrate the effectiveness of this method, we conducted experiments on datasets collected in natural environments. We confirmed that the superposition of periodic actions on CSI can improve the accuracy of the process. CSI-F can achieve higher recognition accuracy compared with other methods and a monitoring coverage of up to 6 m.

Investigation of Doppler Frequency Shift Effect on the Performance of Four-Channel Space Chaotic Laser Communication

In this article, the wavelength division multiplexing (WDM) technology is applied to the space chaotic laser communication system. We deduce the bit error rate (BER) model of multi-channel space chaotic laser communication with Doppler frequency shift. Based on the BER model, the effect of Doppler frequency shift on the performance of four-channel space chaotic laser communication systems on the synchronous orbit(GEO)-low earth orbit(LEO) and GEO-mid earth orbit(MEO) has been discussed in detail. The numerical simulation results indicate that the effect of Doppler frequency shift on GEO-LEO system is much less than GEO-MEO system. Therefore, the Doppler frequency shift effect of GEO-LEO system can be overcome by redundant design, and the Doppler frequency shift effect of GEO-MEO system must be paid more attention to the optimum design. Besides, the relationship between the performance of communication system and frequency shift under different channels are similar. The result has an important implication for reducing the complexity of the system design. These results of the article are significant for the design of the four-channel space chaotic laser communication system.

Note on electron energy can oscillate near a crystal dislocation

Recently Li et al. proposed an exactly-solvable one-dimensional quantum field theory of a dislocation for both edge as well as screw dislocations in an isotropic medium and, via the electron self-energy calculation, Li et al. claimed they can investigate directly the electron-dislocation relaxation time which is reducible to classical results obtained in [T. Ninomiya, J. Phys. Soc. Japan 25, 830 (1968)]. As the qualitative comparison is rather good thus Li et al. claimed the classical fluttering model prior to quantization has already obtained excellent agreement with experiments. However, as the present authors here point out, Ninomiya's approach and results are of doubt (violation of the principle of detailed balance; cf. V.I. Alshits and Yu. M. Sandler, Phys. Stat. Solidi (b) 64, K45 (1974) which performed the corrections: Doppler frequency shift effect included). In fact Ninomiya published a more complete paper latter on: Scr. Metal. 18, 669 (1984) which confirmed the critical remarks by Alshits and Sandier but Li et al. didn't notice or cite it. With above evidences Li et al. should seek quantitative. agreement with realistic materials so that the valid comparison with previous corrected theories considering the classical fluttering mechanism of dislocations can be confirmed. • Li et al.‘s dynamic fluttering dislocation scattering process was reexamined. • Li et al.‘s treatment of dislocation-phonon interaction was of doubt. • We illustrate Doppler frequency shift effect and violation of the principle of detailed balance.

Doppler-free coherent detection using period-one nonlinear dynamics of semiconductor lasers for OFDM-RoF links.

This study investigates coherent detection that is free from the Doppler frequency shift effect for orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) links using period-one (P1) nonlinear dynamics of semiconductor lasers. Even under a dynamically time-varying Doppler frequency shift of up to 100kHz, corresponding to a relative motion between a transmitter and a receiver with a velocity of more than 3850km/h at 28GHz, the microwave carrier of a received OFDM-RoF signal can be successfully regenerated instantaneously and uninterruptedly with its phase highly preserved through the P1 dynamics. No carrier frequency offset (CFO) due to the Doppler frequency shift effect happens if the regenerated microwave carrier is used as a microwave local oscillator for coherent detection of the received OFDM-RoF signal. As a result, a bit-error ratio of around 10-9 is achieved for coherent detection of a 28GHz OFDM-RoF signal carrying 4Gb/s 16-quadrature amplitude modulation data. Thus, no digital signal processing, either photonic or electronic, is required to compensate for such a CFO. This all-optical system is capable of operation up to at least 100GHz.

SC-FDMA LTE Performance Through High Altitude Platforms Communications Channel

It is known that HAPS is one of the promising wireless infrastructures in the years to come. HAPS exploit many advantages from cellular satellite system as well as from cellular terrestrial system. Therefore, HAPS is envisaged as a novel technology for communication. This paper aims at evaluating the performance of a pilot-based channel estimation for uplink LTE using SC-FDMA over Ricean HAPS communication channel. Pilot-based channel estimation is used to estimate an uplink channel of LTE users who transmit the data to HAPS as a base transceiver station (BTS). Analysis is performed to determine the effect of users elevation angle with respect to user position inside HAPS coverage, LTE channel bandwidth, modulation type, and the Doppler frequency shift effect. We found that user’s elevation angle contribute major effect to the pilot-based channel estimation of LTE SC-FDMA performance. System capability to overcome fading effect that users with low elevation angle would be needed to increase the performance. In particular to keep an acceptable performance, in this paper we compensate the channel bandwidth, changing modulation type, and limit the Doppler effect through vehicle speed limitation.

Modified Omega-K algorithm for processing helicopter-borne frequency modulated continuous waveform rotating synthetic aperture radar data

With appropriate geometry configuration, helicopter-borne rotating synthetic aperture radar (ROSAR) can break through the limitations of monostatic synthetic aperture radar (SAR) on forward-looking imaging. With this capability, ROSAR has extensive potential applications, such as self-navigation and self-landing. Moreover, it has many advantages if combined with the frequency modulated continuous wave (FMCW) technology. A novel geometric configuration and an imaging algorithm for helicopter-borne FMCW-ROSAR are proposed. Firstly, by performing the equivalent phase center principle, the separated transmitting and receiving antenna system is equalized to the case of system configuration with antenna for both transmitting and receiving signals. Based on this, the accurate two-dimensional spectrum is obtained and the Doppler frequency shift effect induced by the continuous motion of the platform during the long pulse duration is compensated. Next, the impacts of the velocity approximation error on the imaging algorithm are analyzed in detail, and the system parameters selection and resolution analysis are presented. The well-focused SAR image is then obtained by using the improved Omega-K algorithm incorporating the accurate compensation method for the velocity approximation error. Finally, correctness of the analysis and effectiveness of the proposed algorithm are demonstrated through simulation results.

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.

An approach to forward looking FMCW radar imaging based on two-dimensional Chirp-Z transform

Airborne forward looking radar imaging, which is an important work mode of imaging radar system, has many advantages combined with frequency modulated continuous wave (FMCW) technology. This paper studies the configuration with one central antenna element for signal transmitting and other antenna elements for signal receiving. According to its imaging geometry, the analytical expression of the received signal for forward looking imaging radar based on FMCW is given. By performing the equivalent phase center principle, the received signal is equalized to the case of system configuration with antenna both for transmitting and receiving signals. The Doppler frequency shift effect, induced by the platform’s continuous motion while radar transmits and receives signals, is analyzed in detail and the approximate compensation method is shown. Based on this, a novel method for forward looking FMCW radar imaging is developed, which adopts two-dimensional Chirp-Z transform to implement scaling operation. Also the complete derivation process of the algorithm and the expression of each compensation factor are presented. The whole algorithm only includes FFT and complex multiplication, with interpolation free, and is easy to implement in reality. Simulation results verify the correctness of the analysis and the validity of the proposed algorithm.

Preliminary results on the sensitivity of atmospheric bending angles retrieved from COSMIC radio occultations to Doppler frequency shift and satellite velocity variationsThis article is one of a series of papers published in this Special Issue on the theme GEODESY.

We describe and present preliminary results from an independent bending-angle algorithm implementation for the calculation of radiowave bending angles propagated from a Global Positioning System (GPS) to a Low Earth Orbiting (LEO) satellite. The algorithm utilizes raw atmospheric excess phases and satellite kinematics to determine Doppler frequency shifts of the GPS signals from which bending-angle profiles are derived. The intent is twofold: (a) perform a series of sensitivity studies to investigate the effect of Doppler frequency shift and satellite velocity variations on bending-angle profiles; and (b) examine and compare our results against the bending-angle profiles provided by the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) Data Analysis and Archive Centre (CDAAC). In this paper, we employ the same GPS observations as by CDAAC to analyze various occultation events in 2006, 2007, 2008, and 2009. Our principal finding is that radiowave bending angles exhibit an inversely proportional behaviour to orbital velocity variations while they change proportionally to the variations of Doppler frequency shift. Our studies also reveal that bending angles are more sensitive to orbital velocity than to Doppler frequency shift variations and show “wave-like” structures in the upper part of the atmosphere, unlike COSMIC-derived profiles. We discuss the differences between our derived bending-angle profiles and the COSMIC-derived profiles, emphasizing the advantages of our algorithm implementation.

Performance analysis of MMSE detectors for high speed VSF-OFCDM

This letter investigates the effect of Doppler frequency shift on the performance of MMSE receivers for high speed variable spreading factor (VSF) orthogonal frequency and code division multiplexing (OFCDM) systems in broadband wireless communications. In VSF-OFCDM systems, the existence of multicode interference (MCI) resulting from multiple code channels occupying the same bandwidth degrades the performance. A full MMSE receiver is analytically studied in this letter, exploiting correlation properties among transmitted data on different subcarriers to combat the MCI. Furthermore, considering the fact that the fast time-varying fading destroys the orthogonality of the time domain spreading codes and thus introduces time domain MCI, its effect on system performance is evaluated accurately. It is also shown that it is expected to use time domain spreading factor NT of 8 for a large range of Doppler frequencies, and frequency domain spreading factor as large as possible, especially in high signal to noise ratio. Moreover, in order to improve performance, the pilot channel should occupy around 20% to 25% of the total transmitted power for a large range of Doppler.

Orthogonal Discrete Frequency-Coding Waveform design for MIMO radar

Design of orthogonal code sets with ideal correlation properties is crucial for orthogonal Multiple Input Multiple Output (MIMO) radar. A modified Genetic Algorithm (GA) is proposed to numerically design orthogonal Discrete Frequency-Coding Waveforms (DFCWs) with good correlation properties for MIMO radar. Some of the designed results are presented, and their correlation properties are better than those presented in literatures. The effect of Doppler frequency shift on the performance of these signals is simply investigated. Simulation results and comparisons show that the proposed algorithm is more effective for the design of DFCWs with superior aperiodic correlation properties.

Linear antenna arrays with bidirectional phase center motion

The theoretical and experimental studies of linear antenna arrays with bidirectional phase center motion (BPCM) is presented. BPCM is achieved by exciting only part of the linear array elements and sweeping the excited part from one end to the other and back. The sidelobes of the linear arrays with BPCM experience both upper and lower Doppler frequency shift effect in turn, as compared to linear arrays with unidirectional phase center motion (UPCM). Numerical results show that linear arrays with BPCM are also capable of synthesizing low/ultralow sidelobes, but with a much lower excitation dynamic range ratio as compared to that in conventional arrays. In addition, some characteristics, such as passband bandwidth or sideband levels, are better than those of arrays with UPCM or time modulated variable aperture size arrays. An L-band 16-element printed dipole linear array with BPCM was designed. Experimental results show that a -35 dB relative sidelobe level (SLL) can be achieved.

Symbol Error Probability of Two-Dimensional Signaling in Ricean Fading With Imperfect Channel Estimation

In this paper, a general analytical framework is developed for calculating the symbol error rate of two-dimensional (2-D) signaling in Ricean fading with imperfect channel estimation. We show that in the presence of channel estimation errors, the symbol error rate of arbitrary 2-D signaling in Ricean fading can be expressed as a two-fold proper integral with finite integration limits, which is suitable for numerical evaluation. This new analysis is applicable to any channel estimation scheme where the estimated and the actual channel gains are jointly complex-Gaussian. System parameters related to specific channel estimation schemes are optimized and the effect of Doppler frequency shift in the channel line-of-sight component on the error performance is investigated using our analysis.

Polyphase Code Design for Orthogonal Netted Radar Systems

Orthogonal netted radar systems (ONRS) can fundamentally improve radar performance by using a group of specially designed orthogonal signals. A novel hybrid algorithm is proposed to numerically optimize such orthogonal polyphase code sets. The proposed algorithm integrates a statistical simulated annealing algorithm with the traditional iterative code selection method and is demonstrated to be effective for the design of polyphase signals used in ONRS. Some of the design results are presented and discussed. The effect of Doppler frequency shift on the performance of the designed signals is also investigated.