Number Of Multipath Components Research Articles

Smart Radio Environments with Intelligent Reflecting Surfaces for 6G Sub-Terahertz-Band Communications

Technology for sixth-generation (6G) mobile communication system is now being widely studied. A sub-Terahertz band is expected to play a great role in 6G to enable extremely high data-rate transmission. This paper has two goals. (1) Introduction of 6G concept and propagation characteristics of sub-Terahertz-band radio waves. (2) Performance evaluation of intelligent reflecting surfaces (IRSs) based on beamforming in a sub-Terahertz band for smart radio environments (SREs). We briefly review research on SREs with reconfigurable intelligent surfaces (RISs), and describe requirements and key features of 6G with a sub-Terahertz band. After that, we explain propagation characteristics of sub-Terahertz band radio waves. Important feature is that the number of multipath components is small in a sub-Terahertz band in indoor office environments. This leads to an IRS control method based on beamforming because the number of radio waves out of the optimum beam is very small and power that is not used for transmission from the IRS to user equipment (UE) is little in the environments. We use beams generated by a Butler matrix or a DFT matrix. In simulations, we compare the received power at a UE with that of the upper bound value. Simulation results show that the proposed method reveals good performance in the sense that the received power is not so lower than the upper bound value.

UNJUK KERJA KODE ORTHOGONAL M-SEQUENCE DALAM SISTEM DIRECT SEQUENCE SPREAD SPECTRUM MELALUI KANAL MULTIPATH FA

Multipath and multi-user interference are the main challenges in wireless communication systems. This has become a driving force for the development of data transmission technology that is focused to overcome these problems, one of which is spread spectrum. Spread spectrum is applied to CDMA technology which has the limitations of MAI, so a spreading code is required with specifications that have a very low cross-correlation value as in the orthogonal m-sequence code. In this study, simulate the orthogonal m-sequence code with a length of 8 chips on a multipath fading channel using the Direct Sequence Spread Spectrum system with aims of assessing the performance of the orthogonal m-sequence code on a multipath fading channel, based on the effect of changes in the number of multipath components. The research method used is a Monte Carlo simulation on simulink with the output data in the form of a graph of the comparison value of BER with Eb/No. The results show that on the flat fading channel with the number of components multipath 1, the BER value of the simulation results is in accordance with the BER theory so that the simulation is valid and can be applied to frequency selective fading channels. In the frequency selective fading channel with the number of multipath components 4,6, and 8, the best performance was shown in the multipath 4 component with the smallest BER value, this was influenced by the ACF and CCF values so that the multipath 4 component had the lowest ISI and interference between users.

Long-range VNA-based channel sounder: Design and measurement validation at MmWave and sub-THz frequency bands

With the increasing demand for high bandwidth wireless communication systems, and with a congested spectrum in the sub-6 GHz frequency bands, researchers have been looking into exploration of millimeter wave (mmWave) and sub-terahertz (sub-THz) frequency bands. Channel modeling is essential for system design and performance evaluation of new wireless communication systems. Accurate channel modeling relies on reliable measured channel data, which is collected by high-fidelity channel sounders. Furthermore, it is of importance to understand to which extent channel parameters are frequency dependent in typical deployment scenario (including both indoor short-range and outdoor long-range scenarios). To achieve this purpose, this paper presents a state-of-art long-range 28 GHz and 300 GHz VNA-based channel sounder using optical cable solutions, which can support a measurement range up to 300 m and 600 m in principle, respectively. The design, development and validation of the long-range channel sounders at mmWave and sub-THz bands are reported, with a focus on their system principle, link budget, and back-to-back measurements. Furthermore, a measurement campaign in an indoor corridor is performed using the developed 300 GHz system and 28 GHz channel sounding systems. Both measured channels at the 28 GHz and 300 GHz channels are shown to be highly sparse and specular. A higher number of Multi Path Components (MPC) are observed for the 28 GHz system, while the same main MPC are observed for both systems.

DESAIN SIMULASI UNJUK KERJA BARKER CODE PADA KANAL FREQUENCY SELECTIVE FADING

The signal that arrives at the receiving end is the sum of the various transmissions passed by the signal (multipath) which is influenced by the channel so that there is signal interference. Many innovations have been made so that the received signal can have high security, one of which is spread spectrum with a dual access scheme to increase the ability of many spectrum users in a limited number without disturbing one another. This simulation was tested with the aim of spreading the spectrum with different code lengths for the same bit length of information, and observed from the change in the BER value obtained from the MATLAB 2018a simulation results to find out how the barker code performance on the frequency selective fading channel on a single user. The analysis of this research is obtained from the simulation results in the form of a graph that shows the BER value compared to Eb/No. The BER value shown by the barker code performance on the flat fading channel, which is compared based on the existing flat theory, shows the graph trend and the BER value generated from the simulation is close to the theoretical flat BER value. The performance of the barker code on the frequency selective fading channel is carried out by varying the number of multipath components 7, 5, and 3. The simulation results show that multipath 3 is the best with the smallest bit error value compared to multipath 7 and 5. Barker code performance is strongly influenced by the number of multipath components, the more the number of multipath components, the more performance of the barker code bit error, and vice versa.

Design of Orthogonal Variable Spreading Factor (OVSF) Performance Simulation Program in Multipath Fading Channels

The characteristics of wireless channel are determined by multipath propagation. The transmitted signal will be scattered so that it produces fading. Fading influenced by multipath component will cause delay spread which damages the signal. Thus, spread spectrum technology is used by using a bandwidth that is greater than the original signal. The objective of this study was to determine the effect of the number of multipath components on orthogonal variable spreading factor (OVSF) codes on multipath fading channels viewed from values and Bit Error Rate (BER) graphs versus Energy Bits per Noise (Eb/No). This study would compare the performance of OVSF code communication system on multipath channels by varying multipath components of 4, 8, 12, 16 and the length of OVSF codes used of 16, 8 and 4. The simulation results showed an increase in BER values when the number of multipath components was added. The more the number of multipath components used, the more the number of reflected signals that will interfere with the desired signal in the receiver. The length of the OVSF code influences the performance of the OVSF code on the multipath fading channel, because each code has a different processing gain value that is affected by the length of the code used

Design of Attenuation loss and Multipath propagation Model for Underwater Acoustic Communication in Tank

The wireless sensor network uses some sort of sensors to detect in general physical quantity of interest. The wireless sensor network has potential to explore difficult-to access area on the earth and the concept is extended to underwater applications in future. Past several years studies has been focused on development of reliable and robust communication systems for underwater wireless sensor network for various underwater applications. The scenario of communication is different in underwater compared to that on land as environment is completely different. Also radio waves cannot propagate for longer distance, so instead of that acoustic waves are used. The efforts are made to devise a model for acoustic frequency ranges in the environment for underwater tanks using basic equations governing various physical phenomena occurring during acoustic wave propagation. The model uses scenario of underwater tank filled with raw water diluted with sodium chloride with communicating devices placed at various distances. Attenuation model can be proposed for such communication scenario with respect to distance between transmitter and receiver for acoustic frequency ranges. The acoustic wave travelling through propagating medium suffers from multiple reflections resulting into multipath propagation. The multipath propagation model is proposed for calculation of length of multipath signals propagating in bounded shallow water. Propagation delays of each multipath signals are proposed. Empirical relationship is developed between number of multipath components and distance between transmitter and receiver. Arrival time lag jitter of various multipath signals are developed with respect to distance between transmitter and receiver and height of transmitter and receiver with respect to water bottom is also proposed.

Tensor-Based Framework With Model Order Selection and High Accuracy Factor Decomposition for Time-Delay Estimation in Dynamic Multipath Scenarios

Global Navigation Satellite Systems (GNSS) are crucial for applications that demand very accurate positioning. Tensor-based time-delay estimation methods, such as CPD-GEVD, DoA/KRF, and SECSI, combined with the GPS3 L1C signal, are capable of, significantly, mitigating the positioning degradation caused by multipath components. However, even though these schemes require an estimated model order, they assume that the number of multipath components is constant. In GNSS applications, the number of multipath components is time-varying in dynamic scenarios. Thus, in this paper, we propose a tensor-based framework with model order selection and high accuracy factor decomposition for time-delay estimation in dynamic multipath scenarios. Our proposed approach exploits the estimates of the model order for each slice by grouping the data tensor slices into sub-tensors to provide high accuracy factor decomposition. We further enhance the proposed approach by incorporating the tensor-based Multiple Denoising (MuDe).

Evaluation of OFDM Channel Sounding Techniques with Three Modulation Sequences

This paper presents an evaluation of multicarrier channel sounding techniques using different random and pseudo-random sequences to modulate the OFDM sounding signal. The Random (Rand), Pseudo-Noise (PN) and Zadoff-Chu (ZC) were tested, both in laboratory simulations and in field measurements. For the laboratory simulations Matlab routines were used to generate OFDM signals modulated with each of the three sounding signals, that were then convoluted with a synthesized transfer function of a test channel with six multipath components and added Gaussian noise and Doppler fading. The resulting signals are then correlated with a copy of the original signal to provide the multipath power delay profiles. The root mean square deviation (RMSD) and the relationship between peak power and mean power (PAPR) were used as metrics for the comparison between the test transfer function and the simulation detected multipath delay profiles, showing slight advantages of the ZC sequence. The three sequences were then used in field measurements to characterize an urban channel at 700 MHz. In the field measurements, the ZC sequence showed the lowest detection threshold, allowing for the detection of a larger number of multipath components.

Experiment and Analysis for Air-to-Ground Channel in 400 MHz Band

Background/ Objectives: Recently, air-to-ground wireless communication systems have been used in various equipment such as unmanned aerial vehicle (UAV). In this paper, we analyze the air-to-ground channel in 400 MHz band with experiment using light aircraft. Methods/ Statistical analysis: The characteristics of the air-to-ground channel are analyzed as follows. We generate and store a pilot signal in commercial vector signal generator and an aircraft equipped with the signal generator takes off. As a pilot signal, Zadoff-Chu sequence is used for its good autocorrelation characteristics. In the ground station, the received waveform is stored by using spectrum analyzer. When an airplane approaches near the ground station, airplane transmits the pilot signal and the ground station begins to store the received signals. After completing the signal storing, air-to-ground channel analysis is performed. Findings: From the experiments, we obtained several hundreds of received waveforms, and those waveforms are used for statistical air-to-ground channel analysis. According to the analysis results, most of the measurement channels are single path or line of sight channels. However, in a certain measurement, multiple paths or non-line of sight channels are observed. Those results confirm that multipath environments exist at certain air-to-ground condition. The maximum number of multipath components is 4 and the maximum delay spread is 0.4 μsec. Therefore, when designing a wireless communication system considering air-to-ground environments, the design should consider 4-path fading channels and maximum delay spread over 0.4 μsec. When designing air-to-ground wireless communication systems such as aircraft and drone systems, the experimental and analyzed channels in this paper might be useful. Improvements/ Applications: In this paper, we analyze the air-to-ground channel characteristics of a mountainous area in Korea with field experiment using light aircraft. The analyzed channel characteristics are helpful to those who want to design wireless communication systems between aircraft to ground or UAV to ground. In addition, the analyzed channel can be used for verification of compatibility for the existing communication systems to air-to-ground applications.

Low‐altitude UAV air‐ground propagation channel measurement and analysis in a suburban environment at 3.9 GHz

Unmanned aerial vehicles (UAVs) have been applied to various promising applications because of their features of high-mobility, portability, rapid deployment, and modest power consumption. Small UAVs fly at low altitudes and typically short distances from the ground controller. It is of interest and value to model the propagation channel between low-altitude UAVs and ground stations. This article presents results of channel measurements at 3.9 GHz carried out in a suburban environment with a small-size UAV flying at low altitudes, up to 40 m. The authors also present comparative results from ray-tracing simulations. Height-dependent models for path loss, root mean square (RMS) delay spread, and the number of multipath components are provided. The results illustrate that although multipath effects exist at low altitudes in this environment, the two-ray path loss model works reasonably well in describing the channel behaviour. Initial ray tracing simulations show reasonable agreement with measurements. In addition, RMS delay spread results indicate that distant scatterers have an appreciable effect on the UAV air-ground (AG) propagation channels, which can be different from some terrestrial channels. Authors' results should be of use in the modelling of low-altitude AG propagation channels and in the performance analysis of UAV-enabled AG communication systems.

Millimeter-Wave Radio Channels vs. Synthetic Beamwidth

High-gain narrow-beam antennas or beamformed antenna arrays will likely be used in millimeter- wave (mmWave) bands and 5G to mitigate the high path loss. Since many multipath components may be excluded by the narrow beam, the mmWave radio channel (consisting of the transmit antenna, the propagation channels, and the receive antenna) strongly depends on the beamwidth, orientation, and shape of the narrow beam. In this article, a procedure is proposed to measure and model the channels vs. synthetic beamwidth. Based on experimental data collected at 60 GHz in an indoor hallway/lobby scenario, the results show that the number of multipath components and the delay dispersion of the channel are significantly reduced by the narrow beams. In addition, the path loss can be decreased by more than 20 dB with an optimized beam-center orientation. The impact of the study on future 5G mmWave system design is discussed, including frequency reuse, antenna design, receiver design, equalization, and link budget.

An Iterative Receiver for OFDM With Sparsity-Based Parametric Channel Estimation

In this work we design a receiver that iteratively passes soft information between the channel estimation and data decoding stages. The receiver incorporates sparsity-based parametric channel estimation. State-of-the-art sparsity-based iterative receivers simplify the channel estimation problem by restricting the multipath delays to a grid. Our receiver does not impose such a restriction. As a result it does not suffer from the leakage effect, which destroys sparsity. Communication at near capacity rates in high SNR requires a large modulation order. Due to the close proximity of modulation symbols in such systems, the grid-based approximation is of insufficient accuracy. We show numerically that a state-of-the-art iterative receiver with grid-based sparse channel estimation exhibits a bit-error-rate floor in the high SNR regime. On the contrary, our receiver performs very close to the perfect channel state information bound for all SNR values. We also demonstrate both theoretically and numerically that parametric channel estimation works well in dense channels, i.e., when the number of multipath components is large and each individual component cannot be resolved.

Secrecy Performance of Finite-Sized In-Band Selective Relaying Systems With Unreliable Backhaul and Cooperative Eavesdroppers

This paper investigates the secrecy performance of a finite-sized in-band selective relaying system with $M$ transmitters connected via unreliable backhaul links, $N$ decode-and-forward relays, and $K$ collaborative eavesdroppers. To send the source message to the destination, a transmitter-relay pair that achieves the highest end-to-end signal-to-noise ratio is selected for transmissions, while the $K$ eavesdroppers combine all the received signals from the selected transmitter and relay using maximal ratio combining. The proposed model introduces backhaul reliability and eavesdropping probability parameters to investigate practical constraints on the transmitter-relay cooperation and eavesdropper collaboration, respectively. Closed-form expressions are derived for the secrecy outage probability, probability of non-zero achievable secrecy rate, and ergodic secrecy rate for non-identical frequency-selective fading channels with robust cyclic-prefixed single carrier transmissions. These results show that the asymptotic secrecy outage probability and probability of non-zero achievable secrecy rate are exclusively determined by the number of transmitters $M$ and their corresponding set of backhaul reliability levels. Under unreliable backhaul connections, it is found that the secrecy diversity gain is determined by $M$ , $N$ , and the number of multipath components in the frequency selective fading channels. Link-level simulations are conducted to verify the derived impacts of backhaul reliability and collaborative eavesdropping on the secrecy performance.

Impulse Radio Ultra-Wideband Communications for Localization and Tracking of Human Body and Limbs Movement for Healthcare Applications

Accurate and precise motion tracking of limbs and human subjects has technological importance in various healthcare applications. The use of impulse radio-ultra wideband technology (IR-UWB) technology due its inherent properties is of recent interest for high-accuracy localization. This paper presents experimental investigations and analysis of indoor human body localization and tracking of limb movements in 3-D based on IR-UWB technology using compact and cost-effective body-worn antennas. The body-centric wireless channel characterization has been analyzed in detail using parameters such as path loss magnitude, number of multipath components, rms delay spread, signal amplitude, and Kurtosis with the main focus to differentiate between line-of-sight (LOS) and non-LOS situations. Fidelity of the received signal is also calculated for different activities and antenna positions to study the pulse preserving nature of the UWB antenna, when it is placed on the human body. The results reported in this paper have high localization accuracy with 90% in the range from 0.5 to 2.5 cm using simple and cost-effective techniques which is comparable to the results obtained by the standard optical motion capture system.

Performance Analysis of Distributed Single Carrier Systems With Distributed Cyclic Delay Diversity

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain.

Detailed Analysis of Directional Radio Channel Measurements

Physical models describe the radio channel by characterizing the multipath propagation. Also, measurements are frequently employed in the establishment of such models, or for tuning the existing ones. This paper presents a systematic analysis of double-directional radio channel data, obtained by combining two single-input multiple-output measurements (forward and reverse), each, containing the channel frequency responses at the locations of a virtual rectangular antenna array. The measurement setup uses a vector network analyzer, which, together with the adopted data processing, represents an affordable, but very consistent, alternative to more sophisticated equipment, given that, a physical analysis of the identified channel contributions provided sensible results. The study comprised three main steps: 1) the characterization of each single-directional channel by employing a high-resolution algorithm to obtain the parameters of a chosen number of multipath components (MPCs); 2) the classification of the obtained MPCs in a twofold way, first, by grouping MPCs using clustering tools, and, second, by classifying these clusters according to their type of interaction with the propagation scenario; and 3) the extraction of typical values for the number of clusters, the number of MPCs per cluster, rules for power decay, and statistical distributions for inter and intracluster delays and azimuths.

A Comparison of Outdoor-to-Indoor Wideband Propagation at S-Band and C-Band for Ranging

Indoor positioning using mobile radio signals at different frequency bands has gained remarkable attention. Thus, evaluating the influence of the radio propagation channel at different carrier frequencies with respect to the ranging performance is of interest. This paper presents a measurement-based comparison of the outdoor-to-indoor wideband propagation channel at S-band and C-band. We evaluate channel parameters that have an impact on the ranging and, in turn, on the positioning performance. Our comparison is threefold and is based on large-scale channel parameters, ranging performance, and spatial characteristics of the channel. In the first set of comparisons, we consider received power, power delay profile (PDP), delay spread, mean delay, and a number of multipath components (MPCs). The second set of comparisons considers ranging performance: Both the correlator-based and recursive-Bayesian-filter-based ranging estimators are evaluated using the measurement data. In the third set of comparisons, spatial characteristics of the propagation channel at S-band and C-band are compared and analyzed for range estimates to provide an insight for positioning applications.

A NOVEL CHANNEL ESTIMATION TECHNIQUE FOR COMPLEXITY REDUCTION OF LEAST MINIMUM MEAN SQUARE ERROR

Channel estimation technique is to predict the freq uency response of the radio channel using pilot signal. Channel estimation technique is important p art of LTE receiver design. Such technique is used to recover the transmitted signal correctly and to know how the channel conditions are changed over frequency and time. Each channel estimator has a sp ecified complexity computed according to its mathematical model. Complexity Reduction of any channel estimator is very important to achieve high performance. This paper studied in details the perf ormance enhancement of LMMSE channel estimation technique in the downlink of LTE system . The proposed algorithm is based on Roza Zheng channel model and the matrix transpose rather than matrix inverse. This dramatically reduces the complexity of LMMSE. In adition, the complexity of the proposed algorithm is invariant with the number of multipath components in case of fast fadi ng channels. Moreover, the received signal quality has been improved as compared to the LS. The processing time of the proposed algorithm is reduced by using new criteria of auto correlation. The perf ormance of the proposed algorithm has been evaluated using the mean squared error as the perfo rmance metric. Simulation results showed that the MSE is reduced by 89.5% for LS and by 38.7% for LMMSE. Finally, the bit error rate has been enhanced using the proposed algorithm.

UHF Propagation Along a Cargo Hold on Board a Merchant Ship

The characterization of a Line of Sight (LOS) and a Non-Line of Sight (NLOS) link is performed over the military Ultra High Frequency (UHF) band (225 to 450 MHz). This is done using experimental results collected inside the cargo hold of a merchant ship. By analyzing the guiding effect associated with the cargo hold and its sub-structures, the channel characteristics of the environment can be determined. This important propagation mechanism is analyzed using the 3-D ray tracing simulator. Path loss for both topologies is studied and linear path loss models are proposed. Small-scale channel characteristics, such as the number of multipath components, decay factor of the multipath components and Root-Mean-Square (RMS) delay spread are studied and compared for the LOS and NLOS scenarios. Due to the guiding effect and multiple reflections along the cargo hold, both the LOS and NLOS scenarios are found to exhibit similar channel characteristics. A linear decay function is proposed to model the average Power Delay Profiles (PDPs). It is concluded that the linear model provides a good representation for the shape of the impulse responses for a cluttered environment with reflective substructures. This study is useful for the implementation of wireless sensor networks for status monitoring in maritime applications.

Nondata-Aided Joint Channel Estimation and Equalization for OFDM Systems in Very Rapidly Varying Mobile Channels

This paper is concerned with the challenging and timely problem of joint channel estimation and equalization for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. The resulting algorithm is based on the space alternating generalized expectation maximization—maximum a posteriori probability (SAGE-MAP) technique which is particularly well suited to multicarrier signal formats. The algorithm is implemented in the time-domain which enables one to use the Gaussian approximation of the transmitted OFDM samples. Consequently, the averaging process of the nonpilot data symbols becomes analytically possible resulting in a feasible and computationally efficient channel estimation algorithm leading to a receiver structure that yields also an equalized output from which the data symbols are detected with excellent symbol error rate (SER) performance. Based on this Gaussian approximation the exact Bayesian Cramér Rao lower bound (CRLB) as well as the convergence rate of the algorithm are derived analytically. To reduce the computational complexity of the algorithm, discrete Legendre orthogonal basis functions are employed to represent the rapidly time-varying fading channel. It is shown that, depending on the normalized Doppler frequency, only a small number of expansion coefficients is sufficient to approximate the channel very well and there is no need to know the correlation function of the input signal. The computational complexity of the algorithm is shown to be <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}O(NL)$</tex></formula> per detected data symbol and per SAGE-MAP algorithm cycle where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$N$</tex></formula> is the number of OFDM subcarriers and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> is the number of multipath components.