Multipath Channel Environment Research Articles

Compact UWB MIMO antenna with dual band-notch characteristics

ABSTRACT This article describes a quad-port ultra-wideband multiple-input multiple-output (MIMO) antenna with dual-band notch characteristics that is very compact and highly isolated. The compactness and high isolation of this design are achieved by etching a modified Minkowski fractal structure and an inverted L-shaped stub made available by the partial ground plane. Simply by incorporating ‘C’- and ‘U’-shaped slots in the radiating patch, it is possible to obtain dual-band rejection characteristics that are very suitable for wireless local area network band and X-band downlink satellite communication of 5.0–5.9 GHz and 7.1–7.9 GHz, respectively, in this proposed structure. The entire design is housed in a very compact size of 30 mm × 30 mm. A few key parameters, such as channel capacity loss (CCL), envelope correlation coefficient (ECC), diversity gain (DG) and total active reflection coefficient (TARC), are examined to ensure that the MIMO system meets its requirements. Furthermore, a mutual coupling value of less than −22 dB and an operating frequency band of 3.1–12 GHz allow the design to be very effective in a multipath channel environment.

A Novel Combined Double Binary Turbo Coding and Color Shift Keying Technique for Flicker Mitigation in Multi Carrier Visible Light Communications

Although radio frequency (RF) systems have been developed at a level that can operate almost within theoretical limits in terms of spectral efficiency due to increasing demands, the RF spectrum allocated for wireless mobile communication has started to fill up rapidly and become insufficient. Visible light communication (VLC), one of the optical wireless communication systems, stands out as a promising technology that can be an alternative to RF technology in some application areas and can help meet the demands by playing a complementary role in some application areas. However, VLC systems face the flickering problem. In this study, it is proposed to combine the double binary Turbo coding (DBTC) technique with color shift keying (CSK) modulation, which does not have a flickering problem, as a solution to the flicker problem of VLC systems. The proposed combined DBTC-CSK method is tested on optical OFDM systems from multi-carrier wireless communication systems. Monte-Carlo simulations are performed to verify the performance of the proposed DBTC-CSK-OFDM system in terms of bit-error-rate (BER) over AWGN channel, single-path optical LOS channel and multi-path optical channel. According to the simulation results it is observed that, DBTC-CSK-OFDM system has better BER performance than that of RS–CC coded CSK-OFDM and un-coded CSK-OFDM systems, providing 5.5 dB and 14 dB SNR gain at multi-path optical channel environments, respectively.

Multi-User Joint Detection Using Bi-Directional Deep Neural Network Framework in NOMA-OFDM System.

Non-orthogonal multiple access (NOMA) has great potential to implement the fifth-generation (5G) requirements of wireless communication. For a NOMA traditional detection method, successive interference cancellation (SIC) plays a vital role at the receiver side for both uplink and downlink transmission. Due to the complex multipath channel environment and prorogation of error problems, the traditional SIC method has a limited performance. To overcome the limitation of traditional detection methods, the deep-learning method has an advantage for the highly efficient tool. In this paper, a deep neural network which has bi-directional long short-term memory (Bi-LSTM) for multiuser uplink channel estimation (CE) and signal detection of the originally transmitted signal is proposed. Unlike the traditional CE schemes, the proposed Bi-LSTM model can directly recover multiuser transmission signals suffering from channel distortion. In the offline training stage, the Bi-LTSM model is trained using simulation data based on channel statistics. Then, the trained model is used to recover the transmitted symbols in the online deployment stage. In the simulation results, the performance of the proposed model is compared with the convolutional neural network model and traditional CE schemes such as MMSE and LS. It is shown that the proposed method provides feasible improvements in performance in terms of symbol-error rate and signal-to-noise ratio, making it suitable for 5G wireless communication and beyond.

High-Reliability Underwater Acoustic Communication Using an M-ary Cyclic Spread Spectrum

Multipath propagation, frequency selective fading, low-propagation velocity, and narrow bandwidth are all characteristics of underwater acoustic channels. Doppler shifts and diffusions can occur as a result of the low transmission speed of an acoustic signal, which can be caused by the movement of ocean currents or the transceiver. Furthermore, frequency selective fading and excessive noise interference can disrupt underwater acoustic communication on a continual basis. Because of its high anti-interference ability and high confidentiality, spread spectrum technology is commonly adopted in underwater acoustic communications. Although the direct sequence spread spectrum method has a low data rate, it is advantageous in a multipath propagation channel environment or an environment with a low signal-to-noise ratio (SNR). This advantage is suitable for long-distance transmission or LPD (Low Probability of Detection) communication, and the direct sequence spread spectrum method is applied. In this paper, we propose a highly reliable M-ary cyclic spread spectrum technique by superimposing the M-ary spread spectrum, an extension of the direct sequence spread spectrum technique, and cyclic shift keying. Furthermore, by estimating the Doppler frequency using M-ary spread spectrum codes and performing synchronization correction of the ensuing symbol based on the estimation results, higher performance can be attained. Simulations and experiments showed that the M-ary cyclic spread spectrum method can reduce Doppler estimation and synchronization error accumulation while maintaining a high data rate. Furthermore, the MCSS method had a lower bit error rate than the standard spread spectrum method.

A Comparative Study of SC and MC Underwater Acoustic Communication Systems

In this study, comparative performance analyzes of single carrier (SC) and multi carrier (MC) underwater acoustic communication (UWAC) schemes are performed in underwater acoustic channel environments. Computer simulation studies are carried out to compare SC and MC UWAC communication systems in multi-path underwater acoustic channel environments based on bit error rate (BER) and mean square error (MSE) accomplishment benchmarks. From the acquired outcomes, it is perceived that the MC-UWAC communication scheme has approximately 3 dB better achievement than the SC-UWAC communication scheme.

Energy-Efficient Hybrid Routing Protocol for IoT Communication Systems in 5G and Beyond.

One of the major concerns in wireless sensor networks (WSNs) is most of the sensor nodes are powered through limited lifetime of energy-constrained batteries, which majorly affects the performance, quality, and lifetime of the network. Therefore, diverse clustering methods are proposed to improve energy efficiency of the WSNs. In the meantime, fifth-generation (5G) communications require that several Internet of Things (IoT) applications need to adopt the use of multiple-input multiple-output (MIMO) antenna systems to provide an improved capacity over multi-path channel environment. In this paper, we study a clustering technique for MIMO-based IoT communication systems to achieve energy efficiency. In particular, a novel MIMO-based energy-efficient unequal hybrid clustering (MIMO-HC) protocol is proposed for applications on the IoT in the 5G environment and beyond. Experimental analysis is conducted to assess the effectiveness of the suggested MIMO-HC protocol and compared with existing state-of-the-art research. The proposed MIMO-HC scheme achieves less energy consumption and better network lifetime compared to existing techniques. Specifically, the proposed MIMO-HC improves the network lifetime by approximately as long as the first node and the final node dies as compared with the existing protocol. Moreover, the energy that cluster heads consume on the proposed MIMO-HC is 40% less than that expended in the existing protocol.

Deep-Learning-Based Frame Format Detection for IEEE 802.11 Wireless Local Area Networks

Backward compatibility is one of the key issues for radio equipment that supports IEEE 802.11, which is a typical communication protocol for wireless local area networks (WLANs). For achieving successful packet decoding with backward compatibility, frame format detection is the core precondition. In this study, we present a novel, deep-learning-based frame format detection method for IEEE 802.11 WLANs. Considering that the detection performance of conventional methods is mainly degraded because of poor performance in symbol synchronization and/or channel estimation in environments with a low signal-to-noise ratio, we propose a novel detection method based on a deep learning network to replace conventional detection procedures. The proposed deep-learning network method achieves robust detection directly from the received (Rx) data. Through extensive computer simulations performed in multipath fading channel environments (modeled by Project IEEE 802.11 Task Group ac), we confirmed that the proposed method exhibits significantly higher frame format detection performance than that of the conventional method.

Symbol cyclic reconstruction scheme for UFMC‐based systems

This Letter proposes a symbol cyclic reconstruction scheme for universal-filtered multi-carrier (UFMC) systems. In this scheme, the overlap-add technique is employed to reduce the computational complexity of the system transmitter. At the receiver, ISI cancellation is performed to remove the interference between neighbouring overlapped symbols. Then, a cyclic reconstruction algorithm is proposed to eliminate the interference caused by the linear shift. This scheme effectively improves the transmission efficiency in multipath channel environments while ensuring the bit error rate performance. Simulation results show that the TE of the proposed scheme is much higher than that of standard UFMC and cyclic prefix -OFDM systems.

Optimal Power Allocation Algorithm for Multi-Mode OFDM-OAM Communication Systems in Multipath Channel

Vortex wave carrying orbital angular momentum (OAM), an important property of electromagnetic wave, has bridged a new way to achieve high-capacity radio-frequency communications using different OAM-modes. However, the system performance of OAM multiplexing with orthogonal-frequency-division multiplexing (OFDM) technologies has not been thoroughly investigated in multipath channel environment. In this paper, we first built up the uniform circular array (UCA)-based multi-mode OFDM-OAM communication system, where the reflected paths has been generated based on ideal specular reflector. Based on the multi-mode OFDM-OAM communication system model, we also derived the two-path OAM channel model with the direct and reflected paths. Then, we proposed a robust optimal power allocation algorithm by decomposing the whole optimization problem into inner-layer OAM-modes optimization and outer-layer OFDM subcarriers optimization in order to control the allocated power flexibly based on the channel quality differences between OAM-modes. The simulation results demonstrate that the proposed algorithm can significantly increase the channel capacity for multi-mode OFDM-OAM communications in multipath channel as compared with the traditional equal power allocation method and has a considerable low computational complexity than the binary search water-filling method when the number of OFDM subcarriers is large enough.

FPGA Implementation of Rake Receiver in Broadband Micro-power Wireless Communication System

Aiming at the problem that receiver performance is seriously degraded by multipath fading in multipath channel, a three-finger Rake receiver design scheme is proposed, based on Chirp spread spectrum technology for multipath search, delay estimation and phase estimation. Firstly, the windowed algorithm is adopted in multipath search to improve the accuracy of multipath search. Secondly, detecting the spacing between multipath peaks can realize the delay estimation of multipath signals. Finally, the multipath signals are merged to enhance the receiving effect, significantly improving the system’s block error rate performance under the multipath channel environment. Matlab simulation shows that adding a Rake receiver in the system can improve performance by about 1.2dB. A multi-switching mechanism is applied in FPGA implementation, in order to reduce the hardware power consumption. FPGA simulation results verify rationality and correctness of the design, indicating that the system meets the requirements of block error rate less than 1% in actual transmission, when the signal-to-noise ratio is -2dB.

Faster-than-Nyquist Signal Processing Based on Unequal Error Probability for High-Throughput Wireless Communications

Faster-than-Nyquist (FTN) signal processing, which transmits signals faster than the Nyquist rate, is a representative method for improving throughput efficiency sacrificed performance degradation due to inter-symbol interference. To overcome this problem, this paper proposed FTN signal processing based on the unequal error probability to improve performance. The unequal error probability method divides encoded bits into groups according to priority, and FTN interference rates are differently applied to each group. A lower FTN interference ratio is allocated to the group to which high-priority encoded bits belong and a higher FTN interference ratio is allocated to the group to which low-priority encoded bits belong, thus performance improvement can be obtained compared to the conventional FTN method, with the same interference ratio. In addition, we applied the proposed FTN signal processing, based on the unequal error probability method, to the OFDM (orthogonal frequency division multiplexing) system in multipath channel environments. In the simulations, the performance of the proposed method was better than that of the conventional FTN method by about 0.2 dB to 0.3 dB, with an interference ratio of 20%, 30%, and 40%. In addition, in multipath channels, we confirmed that by applying the proposed unequal error probability, the OFDM-FTN method improves performance to a larger extent than the conventional OFDM-FTN method.

Comparative Analysis of ML-PSO DOA Estimation with Conventional Techniques in Varied Multipath Channel Environment

In the field of array signal processing, direction of arrival (DOA) estimation is a prime area of research. DOA estimation and adaptive beamforming (ABF) are the main issues in smart antennas, which dynamically find the direction of desired and interfering users and finds the optimum weights for beamforming. There are numerous spectral and eigen structure algorithms for estimating the direction of narrow band sources. However, in a complex multipath channel environment, received signals from different directions are fully or partially correlated, which prevents the applications of high resolution techniques to estimate the direction of incoming signals. Maximum likelihood (ML) is an efficient technique for DOA estimation in a low signal to noise ratio (SNR) and coherent channel environment. In this paper, we use particle swarm optimization (PSO) for estimating ML solution by optimizing complex non linear multimodal function over a high dimensional space in linear arrays. PSO-ML estimator has been compared with conventional DOA estimation techniques in uncorrelated, partially correlated and coherent channel environment. The performance of PSO-ML estimator and conventional algorithms are analyzed in varying partially correlated channel environment. The simulation results demonstrate that PSO based estimator gives superior statistical performance.

Research and implementation of synchronization for ultra-wide bandwidth receiver within enclosed metal cabin

Aiming at solving the problem of wireless communications within the enclosed metal cabin, such as, spacecraft and aircraft cabin, the enclosed metal cabin statistical channel parameters are given based on channel measurements which prove the channel characteristics of the strong multipath channel environments. Ultra-wideband wireless communications technology is suitable to apply in such enclosed metal cabin with the strong anti-multipath ability. Due to the extremely wide bandwidth, design and implementation of synchronization with low complexity is important for the receiver. In this paper, an improved parallel synchronization scheme consists of 1-bit quantization and multipath energy accumulation is proposed. Owing to 1-bit quantization, the computation of correlation can be simplified by transferring complex operation of multiplication into the easy operation of addition in FPGA. The synchronization performance is observed through analytical expressions corroborated by simulations which show that the 1-bit quantization can reduce the complexity significantly with a little loss in signal noise ratio. By investigating the probabilities of false alarm and missed detection in simulation, the optical threshold of synchronization is also obtained. On this basis, the hardware implementation of the physical layer algorithm and the experimental verification in the enclosed metal cabin are performed. Experiments show that the design of synchronization scheme can overcome the strong multipath effect and achieve large capacity and low bit error rate transmission.

Improving ultra wideband (UWB) system by modified random combination of pulses

Ultra-Wideband (UWB) technology uses very narrow pulses of nano-seconds duration to provide very high data rates. The pulses to be used for the UWB are very important and should meet the emission mask regulatory requirements to get good performance when transmitted over the channel. To meet these requirements, a combination of higher order derivatives of Gaussian pulses can be considered to form a combined pulse instead of transmitting them separately. The main aim of this paper is to improve the performance of Ultra Wideband (UWB) multiple access modulation system with a newly Proposed combined pulse, generated using a modified random pulse combining of the first five Gaussian derivative pulses with optimal shaping factors as basic functions. In order to meet the UWB power spectrum regulations, the power spectral utilization of the newly designed pulse is calculated and the bit error rate performance of the pulse position modulation time hopping system using the newly proposed pulse is analyzed in a multi-path channel environment using RAKE receiver. The simulation results carried out in MATLAB software shows that the new proposed combined pulse has higher pulse energy matching the spectral limits of UWB and an improved bit error rate performance as compared to the previous literature results.

Design of Effective Receiver in Hospital Wireless Network Using Turbo Code

In this paper, we considered the received signal of the wideband CDMA systems using turbo code in the multipath channel environments, and analyze the performance of the system. This study is to analyze the performance for the variable system bandwidth according to the number of branches of rake receiver by passing the received signal through a rake receiver with a turbo code in Rayleigh fading channel environments. For the design of receiver in wideband CDMA systems, we presented the efficient parameters for the number of iterative decoding and the number of branches of rake receiver.

Cyclic Prefix-Based Universal Filtered Multicarrier System and Performance Analysis

Recently proposed universal filtered multicarrier (UFMC) system is not an orthogonal system in multipath channel environments and might cause significant performance loss. In this paper, the authors propose a cyclic prefix (CP) based UFMC system and first analyze the conditions for interference-free one-tap equalization in the absence of transceiver imperfections. Then the corresponding signal model and output signal-to-noise ratio expression are derived. In the presence of carrier frequency offset, timing offset, and insufficient CP length, the authors establish an analytical system model as a summation of desired signal, intersymbol interference, intercarrier interference, and noise. New channel equalization algorithms are proposed based on the derived analytical signal model. Numerical results show that the derived model matches the simulation results precisely, and the proposed equalization algorithms improve the UFMC system performance in terms of bit error rate.

Indoor Global Localisation in Anchor-based Systems using Audio Signals

This paper presents a method that allows mobile devices to be globally self-localised in indoor localisation systems by transmitting to them data from position reference anchors. The objective is to establish a reliable one-way down-link communication through signals used in the localisation process in a typically strong fading and multipath channel environment. This is accomplished by using signal processing techniques, including coding and forward error correction, to transmit data using a specific transmission control protocol. Experimental results, using audio as the signal between anchors and the mobile device, demonstrate successful data transmission in realistic scenarios like a common noisy and reverberant room. Spread spectrum noise-like masked signals 4·9 dB below background noise were sufficient to attain correct data reception at four metres distance between a loudspeaker anchor and a mobile device's microphone.

Time–Frequency Multiplex Transceiver Design with RX IQ Imbalance, CFO, and Multipath Channel Estimation and Compensation for Multicarrier Systems

The low complexity time---frequency multiplex estimator and equalizer transceiver design are proposed to combat the RF impairment problems for the zero-IF transceiver of multi-carrier systems. Moreover, the proposed preamble can estimate and compensate the receiver (Rx) in-phase and quadrature-phase (IQ) imbalance, carrier frequency offset (CFO), and channel impulse response parameters. There are two parts in the proposed system. Firstly, all parameters of impairments are estimated by the proposed time---frequency multiplex estimator design with the iterative cancellation scheme. Secondly, the iterative group pair equalizer with the estimated parameters is proposed to eliminate the RF impairments effect and detect the transmitted signal with low complexity advantage. Simulation results confirm that the proposed estimator can provide the reliable performance over the severe IQ imbalance, CFO, and multipath fading channel environments.

PN code acquisition using smart antennas and adaptive thresholding for spread spectrum communications

In this paper, we consider a pseudo-noise (PN) code acquisition for direct sequence spread spectrum communication in a Rayleigh fading multipath channel environment using smart antenna and adaptive thresholding automatic trimmed-mean constant false alarm rate (ATM-CFAR) processing. A smart antenna is an array of antenna elements that can modify the array pattern adaptively to minimize the effect of multiple access interference (MAI) from other users and multipath. PN code acquisition using a fixed threshold may lead to an excessive number of false alarms, and thus, adaptive thresholding ATM-CFAR processing is considered. In addition, since the interference (MAI and multipath) can be considered as outliers, an outlier determiner is embedded to the proposed system based on the interquartile range. This novel approach of combining smart antennas and adaptive thresholding ATM-CFAR detection with an outlier determiner proved to be very robust since it resulted in a serious enhancement of the probability of detection.

Robust Digital Retrodirective Beamforming Technique for Multipath Channel Environment

Abstract In this paper, we describe the effect of temporal and spatial focusing obtained by using the digital retrodirective beamforming (DRDB) system and analyze BER performance of DRDB in multipath channel. There is a problem with reception performance degraded due to inter symbol interference (ISI) in multipath channel. In order to reduce ISI, the existing communication system use complex equalizer. In order to reduce ISI, we propose a DRDB system which can retransmit data information toward direction as the received signal without any prior information. Also, we explain ISI mitigation by temporal and spatial focusing of the proposed system. Simulation results show that the proposed system has better BER performance than that without DRDB becauseof ISI mitigation effect in multipath channel environment.