Interference Multipath Mitigation Research Articles

On the multipath interference mitigation for high-speed IM-DD transmissions with Nyquist subcarrier modulation.

The performance of high-speed intensity modulation direct detection (IM-DD) transmissions is severely degraded due to the occurrence of multipath interference (MPI), especially when a higher-order modulation format is utilized. Here, we propose and demonstrate, for the first time to the best of our knowledge, that a Nyquist subcarrier modulation (Nyquist-SCM) format inherently exhibits resistance to the MPI. We experimentally evaluate the MPI tolerance by transmitting 56 Gbit/s PAM-4 signals and Nyquist-SCM 16QAM signals over the 2 km standard single-mode fiber (SSMF) when the C-band semiconductor laser with a linewidth of 1.7 MHz is utilized. In comparison with the PAM-4 format, the Nyquist-SCM 16QAM format can lead to an enhanced MPI tolerance of 4 dB at the KP4-FEC threshold of BER = 2 × 10-4. In addition, even with the help of MPI mitigation for the PAM-4 signals based on two newly reported methods, the utilization of Nyquist-SCM 16QAM signal can still guarantee an improved MPI tolerance of 1 dB.

Feedforward Neural Network Enabled Optical Multi-Path Interference Mitigation for High-speed IM-DD Transmissions

Feedforward Neural Network Enabled Optical Multi-Path Interference Mitigation for High-speed IM-DD Transmissions

Optical Multi-Path Interference Mitigation for PAM4-IMDD Systems Using Balanced Coding

Optical Multi-Path Interference Mitigation for PAM4-IMDD Systems Using Balanced Coding

Toward Full Passive Internet of Things: Symbiotic Localization and Ambient Backscatter Communication

In this paper, we proposed a symbiotic localization and ambient backscatter communication (SLABC) architecture, which uses existing ambient backscatter communication (AmBC) hardware and received signals to help Internet of Things (IoT) localize target objects. The SLABC can be viewed as a specific realization of integrated passive/symbiotic sensing and communication, which has two mutually beneficial stages: 1) sensing stage with generalized Prony with homologous matching (GPHM) method; 2) communication stage with multi-source constant modulus algorithm (MSCMA) method. To formulate SLABC, we propose a unified TMSC signal model to characterize the complex multi-source, multi-path and multi-reflection symbiotic communication (TMSC) and facilitate the key information extraction. Utilizing the frequency domain expression of the unified signal model and the similarity between multi-path channel coefficients and tap coefficients of equalizers, our proposed GPHM and MSCMA methods are efficient to mitigate the TMSC interference and retrieve the interested information to locate targets and communicate. The proposed SLABC concept updates the symbiotic AmBC IoT with the least cost and reduces the dependence on hardware stacking. The simulation results show that: 1) information extracted by GPHM and MSCMA can help localization achieve high accuracy and reduce the complexity of multi-path interference mitigation; 2) both of the two methods have a positive influence on each other.

Polarization-based approach for multipath interference mitigation in time-of-flight imaging.

The existence of nearby obstruction causes significant errors in depth sensing for time-of-flight cameras, namely multipath interference. A polarized time-of-flight system is established for multipath interference mitigation. Based on polarization cues and the phasor representation of time-of-flight imaging, the proposed method acquires depth maps in high accuracy when specular dominant obstruction is in path. Both rough and smooth targets are applicable in our approach even though they have distinct polarization characteristics. Several experiments with different types of targets and various obstructions confirm the effectiveness of our method qualitatively and quantitatively.

Tow ship interference mitigation in shallow ocean using correlated mode decomposition technique

Passive towed arrays assume great importance in shallow ocean surveillance, owing to their capability to detect long range underwater acoustic targets. The detection and classification performance is severely impacted by the tow ship interference manifestation in the pressure sensor array towed behind the ship. In this work, a robust tow ship multipath interference mitigation algorithm intended for shallow ocean operation is developed, based on the dynamic mode decomposition (DMD) technique, which in turn exploits the coherent structure of the multimode acoustic wave propagation inherent in the shallow ocean scenario. The proposed algorithm effectively identifies the coherent normal mode interference subspace and eliminates its components from the received array data vector. Further, this approach compliments the shallow ocean normal mode acoustic field propagation and ensures simultaneous mitigation of all the multipath generated interferences, making it a superior method to reduce the azimuth spread of the interference and tow ship spectral leakage into the panoramic detection beams. This greatly enhances the detection and classification capability of sonar, especially for distant stealthy targets. The efficacy of the algorithm is validated using Monte Carlo simulations and further ratified by experimental data captured during the field trials in the Arabian Sea.

Adaptive Nonlinear Equalization Combining Sparse Bayesian Learning and Kalman Filtering for Visible Light Communications

Nonlinear post equalization (NPE) based on Volterra series (VS) is considered as an effective way to mitigate the severe light emitting diode (LED) nonlinearity and multipath effect in a visible light communication (VLC) system. However, it is restricted by kernel complexity in practical applications. In this paper, we formulate the kernel extraction of VS-based NPE to be a sparse recovery problem, and propose an efficient sparsity-aware approach, using combined sparse Bayesian learning (SBL) and Kalman filtering (KF) to extract the active VS kernels and thus to reduce the redundancy of NPE. First, from the view of probability, a Bayesian strategy is applied to select the dominant regressors from the original measurement matrices by exploiting the learning of hyperparameters, which encourages the sparseness of VS kernels with an imposed prior. Then, based on the specified regression matrix, the improved KF iteration is used in the estimation of the kernel coefficients to overcome the system instability in a dynamic noise environment. With this methodology, the active VS kernels can be effectively extracted and the corresponding kernel quantity is significantly reduced at least by 65%. Moreover, the system can still work effectively in the case of a lower size of training samples. The simulation results show that the proposed scheme is beneficial to both the nonlinearity compensation and multipath interference mitigation, and exhibits better overall performance than some existing methods, which demonstrates the potential and validity of kernel extraction in VS-based NPE.

A Wi-Fi-Based Wireless Indoor Position Sensing System with Multipath Interference Mitigation.

Wi-Fi-based indoor position sensing solutions have the advantages of easy integration in mobile phones and low cost by using existing Wi-Fi access points. The mainstream methods are commonly based on the received signal strength indicator (RSSI), which suffers from multipath interference in complicated indoor environments. Through the in-depth analysis of the multipath interference, an RSSI-assisted time difference of arrival (TDoA) method is proposed for Wi-Fi-based indoor position sensing in this work. The key idea is to compensate for the multipath interference in the received signals based on the coarse estimation using RSSI and TDoA calculation. A prototype system has been implemented to validate the proposed method. Experimental results have demonstrated the effectiveness of the proposed method, especially for handling the multipath interference with small propagation delay difference. Experimental results show that the indoor position sensing system can achieve a 90th percentile error of 0.3 m. The proposed method can also achieve moderate computational complexity and moderate real-time performance compared to other methods.

An EM-based multipath interference mitigation in GNSS receivers

In multipath (MP) environments, the received signals depend on several factors related to the global navigation satellite systems (GNSS) receiver environment and motion. Thus it is difficult to use a specific propagation model to accurately capture the dynamics of the MP signal when the GNSS receiver is moving in urban canyons. This paper formulates the problem of MP interference mitigation in the GNSS receiver as a joint state (containing the direct signal parameters) and time-varying model parameter (containing the MP signal parameters) estimation. Accordingly, we propose to exploit the EM algorithm for achieving the joint state and time-varying parameter estimation in the context of MP interference mitigation in GNSS receivers. More precisely, the proposed EM-based MP mitigation approach is decomposed into two iterative steps: (a) the posterior pdf of the direct signal parameters and the expected log-likelihood function necessary in the expectation step of the EM algorithm are approximated by using an appropriate particle filter; (b) the maximum likelihood solution for MP signal parameters is then obtained using Newton’s method in the maximization step. The convergence of the proposed approach is analyzed based on the existing convergence theorem associated with the EM algorithm. Finally, a comprehensive simulation study is conducted to compare the performance of the proposed EM-based MP mitigation approach with other state-of-the-art MP mitigation approaches in static and realistic scenarios.

Multipath interference mitigation in GNSS via WRELAX

In order to suppress the multipath interference in global navigation satellite system, two algorithms based on NLS (nonlinear least square) parameter estimation are proposed. Instead of the classic...

Linear Frequency Domain Equalization of SOQPSK-TG for Wideband Aeronautical Telemetry Channels

This work explores multipath interference mitigation for a single transmit antenna, single receive antenna system with SOQPSK-TG using a linear single-carrier frequency domain equalization (SCFDE) technique. Linear SCFDE with maximum likelihood (ML) channel estimation is shown to greatly improve system Bit Error Rates (BER). Simulation results also demonstrate that three samples per bit at the receiver are adequate to achieve the best BER performance.

PSWF-Based Direct-Sequence UWB Transmission Using Orthogonal Ternary Code Sets

An enhanced Ultra Wideband (UWB) signaling scheme that employs PSWF (Prolate Spheroidal Wave Functions)-based orthogonal chip pulses and ternary complementary code sets is proposed for Direct-Sequence (DS) UWB systems. Every information bit of each user is modulated and transmitted over a set of parallel sequences of PSWF-based orthogonal chip pulses and are further assigned to a ternary complementary code set with additional zero padding if necessary. Moreover, the ternary complementary code sets are generated to be mutually orthogonal and assigned to any pair of multiple users. Hence, the mitigation of multipath interference as well as multiple user interference (MUI) can be expected. Furthermore, the ternary code length can be greatly shortened by taking advantage of pulse and code orthogonality. Thus, the proposed transmission scheme is especially suitable for high data rate DS-UWB systems that offer very high flexibility.

A new multipath interference mitigation technique for high-speed packet transmission in WCDMA downlink

In order to increase throughput using high order data modulations in wide-band code-division multiple-access (WCDMA) downlink, it is necessary to eliminate multipath interferences. In a multipath interference canceller (MPIC) was proposed, which enables the use of high order modulations in multipath fading channels. However, only packet channels and pilot channels were considered as transmitted code channels. Code channels dedicated to other users and remaining common code channels coexist in practice, and such unknown code channels degrade the performance of MPIC significantly. In this letter, we propose a multipath interference mitigation scheme that removes all the intracell interferences by orthogonal variable spreading factor (OVSF) code characteristics. Simulation results show that the proposed scheme makes it possible to improve total throughput using high order modulations in WCDMA downlink.