Ultra-wideband Channel Research Articles

Statistical Modeling of Indirect Paths for UWB Sensors in an Indoor Environment.

In this paper, we present a statistical model of an indirect path generated in an ultra-wideband (UWB) human tracking scenario. When performing moving target detection, an indirect path signal can generate ghost targets that may cause a false alarm. For this purpose, we performed radar measurements in an indoor environment and established a statistical model of an indirect path based on the measurement data. The proposed model takes the form of a modified Saleh–Valenzuela model, which is used in a UWB channel model. An application example of the proposed model for mitigating false alarms is also presented.

Window-Based Channel Impulse Response Prediction for Time-Varying Ultra-Wideband Channels.

This work proposes channel impulse response (CIR) prediction for time-varying ultra-wideband (UWB) channels by exploiting the fast movement of channel taps within delay bins. Considering the sparsity of UWB channels, we introduce a window-based CIR (WB-CIR) to approximate the high temporal resolutions of UWB channels. A recursive least square (RLS) algorithm is adopted to predict the time evolution of the WB-CIR. For predicting the future WB-CIR tap of window wk, three RLS filter coefficients are computed from the observed WB-CIRs of the left wk−1, the current wk and the right wk+1 windows. The filter coefficient with the lowest RLS error is used to predict the future WB-CIR tap. To evaluate our proposed prediction method, UWB CIRs are collected through measurement campaigns in outdoor environments considering line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. Under similar computational complexity, our proposed method provides an improvement in prediction errors of approximately 80% for LOS and 63% for NLOS scenarios compared with a conventional method.

Analysis of Ultrawideband Pulse Distortion Due to Lossy Dielectric Walls and Indoor Channel Models

Ultrawideband (UWB) communication channels cause pulse distortion and result in many multipath components arriving at the receiver in clusters. In this paper, the effects of lossy dielectric walls on UWB pulses are analyzed. The frequency-dependent parameters of commonly used building materials are used to analyze the effects of multiple reflections and transmissions, material distortion, and interpulse interference on the UWB pulse waveform. The possibility of polarization-dependent distortion is discussed. Various thicknesses of walls and angles of incidence are considered. The distortion due to each effect is quantified in terms of maximum correlation coefficients (MCCs). The overall effect of the wall is modeled as a tapped-delay-line filter based on the MCC. The results are used to specify the multicluster structure of UWB channel models for indoor communication.

ARIMA-based time variation model for beneath the chassis UWB channel

Intra-vehicular wireless sensor network (IVWSN) enables the integration of the wireless sensor network technology into the vehicle architecture through either eliminating the wires between the existing sensors and the corresponding electronic controller units (ECUs) or empowering new sensor technologies that are not currently implemented due to technical limitations. Ultra-wideband (UWB) has been determined to be the most appropriate technology for IVWSNs since it provides energy efficiency through the low duty-cycle operation and high reliability by exploiting the large bandwidth. In this paper, we propose a time variation model for UWB-based IVWSN-based on the extensive amount of data collected from the transmitter and receiver antennas at various locations and separation distances beneath the chassis of a vehicle moving at different speeds on different types of roads. We adopt the commonly used Saleh-Valenzuela (SV) model to represent the clustering phenomenon in the received power delay profiles (PDPs). The proposed novel time variation model then determines the time evolution of the PDPs by representing the changes in their cluster breakpoints, slopes, and break point amplitudes with the auto-regressive integrated moving average (ARIMA) model. ARIMA(5,1,0) has been demonstrated to fit the breakpoint, cluster slope, and breakpoint amplitude sequences collected at different vehicle speeds with different transmitter and receiver locations on asphalt and stone roads by using Box-Jenkins procedure. This model is validated with diagnostic checking. The absolute values of the model coefficients are observed to be mostly larger on asphalt road than their counterparts on the stone road while exhibiting no dependence on the vehicle speed nor the location of transmitter and receiver antennas.

Permutation-Based Noncoherent Space-Time Codes With Analog Energy Detection for IR-UWB Communications With PPM

In this paper, we consider the problem of space-time (ST) coding for the noncoherent ultra-wideband (UWB) systems with pulse position modulation (PPM). In particular, we propose the first known family of ST codes that lends itself to optimal decoding with the energy detectors. Energy detection avoids the sampling of the received signal where the sampling rates can be prohibitively high and escapes from the challenging task of estimating the dense multi-path UWB channel. In the absence of design criteria that are adapted to the problem under consideration, we derive two novel design criteria and propose the novel construction accordingly. The proposed code is based solely on permutations, and hence it does not introduce any constellation expansion on the totally-real and unipolar PPM signal set. In other words, the components of the constructed codewords are limited to either zero or one indicating the absence or presence of an UWB pulse in the corresponding PPM slot, respectively. The above characteristics result in a remarked simplicity of the ST encoder/decoder making it an appealing solution to low-cost and low-power UWB systems. For a system equipped with $n$ transmit antennas, we prove that the proposed code is capable of achieving a full transmit diversity order with $M$ -PPM constellations for $M>n+1$ while transmitting at the rate of $({1}/{n})\log _{2}\binom {M-1}{n}$ bits per channel use.

Ultra wideband channel coefficient measurements for detecting methane gas in a multipath environment

In this paper, an investigation was carried out into the effect of a non-explosive methane gas mixture on various ultra wide band channel coefficients. Using simplified apparatus consisting of a rubberised tube (6 mm diameter) connected for significant periods to either a (pressurised) source of mixed methane and nitrogen or alternatively to a nitrogen only source. The tube containing either gas feed was wrapped using two complete turns around a 160 mm diameter PVC pipe. Several flows of the mixed gas, containing 2.57% methane, were introduced and flowed through the pipe before being sealed in the tube. Removal of any methane in the tube was achieved by flushing it with the pure nitrogen source, initially and in-between samples of the mixed source. A Vector Network Analyser was connected using two identical directional antennas with the wrapped section of tubing placed between the two antennas and the wireless channel coefficients were measured over the ultra wide band frequency span of 0.3–8 GHz. Magnitude differences were taken between the baseline condition (tube flushed out with nitrogen) and alternatively containing the methane mixture. It was found that consistent and repeatable experiments produced the same trend of differences over the same frequency span. This system based on this approach could thus be used as a simple sensor to detect the accumulation of methane gas in an environment well before it becomes explosive at around a concentration of 5%.

Diversity-Multiplexing Tradeoff for Log-Normal Fading Channels

Although there has been a growing interest on the study of diversity-multiplexing tradeoff (DMT), the existing works are mostly restricted to the outcomes reported for Rayleigh, Rician, and Nakagami fading channels. In this paper, we investigate the optimal tradeoff in the presence of log-normal fading, which provides an accurate model for indoor wireless, optical wireless, and ultra-wideband channels. We consider a multiple-input multiple-output (MIMO) log-normal channel, derive the outage probability expression, and then present the asymptotical DMT expression. It is shown that the asymptotical maximum diversity gain tends to infinity with logarithm of signal-to-noise ratio (SNR). To have further insight, we normalize the DMT with that of single-input single-output case and express the relative asymptotical DMT of the MIMO log-normal channel as a function of the number of transmit and receive antennas. We further study DMT for finite SNRs and demonstrate convergence to the asymptotical case. Extensive numerical results are provided to corroborate the analytical derivation.

Performance improvement by transmit diversity technique for implant ultra‐wideband communication

In implant body area networks (BANs), an ultra-wideband (UWB) technology is a promising candidate to accomuplish high data rate. However, due to its frequency, the UWB signals suffer from large attenuation in the implant communication link. This fact suggests the difficulty on achieving reliable communication. For achieving reliable communication, it is well known that a spatial diversity technique is efficient. In this study, the authors pay attention to the fact that it is possible to further miniaturise the UWB antenna due to its very high frequency. Then, the authors aim to develop a transmit polarisation diversity antenna for implant UWB communications, and apply the developed transmit diversity system to a UWB-impulse radio (UWB-IR) scheme and a multiband-orthogonal frequency division multiplexing (MB-OFDM) scheme, respectively. For evaluating the proposed system, the authors first analyse the propagation characteristics in the implant UWB channel, using the finite difference time domain numerical analysis technique. Then, the authors evaluate and discuss the communication performances of the both modulation schemes for the transmit polarisation diversity. As a result, at a communication distance of 7 cm, the throughputs have accomplished to 300 Mbps for the MB-OFDM scheme and 30 Mbps for UWB-IR scheme, respectively.

Path loss variation of on-body UWB channel in the frequency bands of IEEE 802.15.6 standard.

The wireless body area network (WBAN) has gaining tremendous attention among researchers and academicians for its envisioned applications in healthcare service. Ultra wideband (UWB) radio technology is considered as excellent air interface for communication among body area network devices. Characterisation and modelling of channel parameters are utmost prerequisite for the development of reliable communication system. The path loss of on-body UWB channel for each frequency band defined in IEEE 802.15.6 standard is experimentally determined. The parameters of path loss model are statistically determined by analysing measurement data. Both the line-of-sight and non-line-of-sight channel conditions are considered in the measurement. Variations of parameter values with the size of human body are analysed along with the variation of parameter values with the surrounding environments. It is observed that the parameters of the path loss model vary with the frequency band as well as with the body size and surrounding environment. The derived parameter values are specific to the particular frequency bands of IEEE 802.15.6 standard, which will be useful for the development of efficient UWB WBAN system.

Frequency-Domain In-Vehicle UWB Channel Modeling

This paper aims to present a simple but robust model characterizing the frequency-dependent transfer function of an in-vehicle ultrawideband (UWB) channel. A large number of transfer functions spanning the UWB (3–11 GHz) are recorded inside the passenger compartment of a four-seated sedan. It is found that the complex transfer function can be decomposed into two terms, the first term being a real-valued long-term trend that characterizes frequency dependence with a power law and the second term forming a complex correlative discrete series that may be represented via an autoregressive (AR) model. An exhaustive simulation framework is laid out based on empirical equations characterizing trend parameters and AR process coefficients. The simulation of the transfer function is straightforward as it involves only a handful of variables; however, it is in good agreement with the actual measured data. The proposed model is further validated by comparing different channel parameters, such as coherence bandwidth, power delay profile, and root-mean-square delay spread, obtained from raw and synthetic data sets. It is also shown how the model can be compared with existing time-domain Saleh–Valenzuela-influenced models and related IEEE standards.

Measurement of ultra wideband channel coefficient through carbon dioxide in a multipath environment

This paper reports an investigation into the effect of carbon dioxide (CO2) gas on various ultra wideband channel coefficients. Measurements were conducted using apparatus consisting of a rubberized tube (6 mm diameter) connected to a source of CO2 or nitrogen (N2). For support, the rubberized tube was wrapped twice around a PVC pipe (160 mm diameter). The rubberized tube was flushed with 100% CO2 several times before being sealed in the tube at atmospheric pressure. In between measurement trials, removal of CO2 was achieved by flushing with pure nitrogen. A Vector Network Analyzer (VNA) using two identical directional antennas, with the wrapped section of tubing placed in-between, measured the channel coefficients over ultra wideband frequency spans of (0.3–8) GHz and (1–2) GHz. Significant magnitude differences between the baseline condition and that of CO2 were observed. We found the same signature of difference curves over the same frequency spans for different measurements. Difference in shape in the frequency band of (1–2) GHz is the same as that of the measured difference over 1–2 GHz in entire frequency band of 300 MHz to 8 GHz for the measured channel coefficients. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1543–1546, 2016

Experimental measurement and statistical analysis of the RMS delay spread in time-varying ultra-wideband communication channel

The statistical analysis of the RMS delay spread is achieved based on the results obtained from an outdoor time-varying ultra-wideband (UWB) channel measurement. The paper reports on the RMS delay spread values, the cumulative distribution functions (CDFs) and the probability density functions (PDFs) for the measured channel configurations with their estimated parameters. Findings show how the RMS delay spread values are fluctuating for different channel configurations within the same measurement campaign. For example, 35ns and 2.5ns have been obtained for different channels. The differences in the measured instantaneous RMS delay spread leads to obtaining different PDFs that fit the measured data where Generalized Pareto distribution is dominant. The relation between the RMS delay spread and the channel path loss has been studied. Positive correlation is seen for all measured channels with different amounts. The highest correlation value is 0.7675 while the lowest is 0.2951. The coherence bandwidth analysis is also conducted, and the values are fluctuating as the case of the RMS delay spread. The obtained values varies between 325.3MHz and 5.7MHz.

Design and implementation of UWB systems with timing synchronization in MATLAB Simulink

Ultra wide band (UWB) bandwidth is much higher than the system bandwidth requirement. Due to large bandwidth in UWB, its systems must have time resolution for system time distribution. But we need to improve data rate and efficiency of the system which uses ultra wide band channels as data rate may trade for power spectral density and performance in multipath. In order to increase data rate, here in this project the orthogonal frequency division multiplexing (OFDM) system is used. But we need to overcome the drawbacks in OFDM like peak to average power ratio (PAPR) (5), carrier frequency offset (CFO), inter symbol interference (ISI), inter carrier interference (ICI). In order to control the effect of PAPR and CFE the single carrier with frequency domain equalization (SC-FDE) can be used, as it has lower PAPR and lower sensitivity to CFO compared to OFDM but the problem is that it is less robust to timing error. As the data rate in UWB systems is high, there is heavy requirement of accuracy in timing synchronization constraints. Moreover the high dispersive nature of UWB channels is an extra challenge to acquire timing synchronization. In general, synchronization can be done based on auto correlation and cross correlation methods. Joint timing and channel estimation (JTCE) can also be done but the computational complexity while correlating will be more compared to correlation methods. But, for UWB systems the timing schemes cannot perform well as multi path UWB channels are denser and longer than wideband channels. Due to trade off's and computational complexity the implementation of large size Fast Fourier transform (FFT) and Inverse FFT (IFFT) can't be employed. In this paper, we discuss the design and implementation of UWB systems with timing synchronization by avoiding all the above discussed PAPR, CFO, ISI, ICI and timing synchronization in UWB channel problems and results are compared by transmitting signal through three different channels (dispersive, fading and addictive white Gaussian noise (AWGN) channels).

UKF-based channel estimation and LOS/NLOS classification in UWB wireless networks

The paper addresses ultra-wideband (UWB) channel estimation and line-of-sight (LOS) vs. non-line-of-sight classification based on the application of the unscented Kalman filter (UKF) and the analysis of the multipath channel response characteristics. For non-linear models, the UKF provides an efficient recursive minimum mean squared error estimation technique that is successfully applied in this work, and supported by numerical results demonstrating its effectiveness in UWB multipath channel gain and time delay estimation. The multipath channel response obtained from a limited number of channel taps is subsequently characterized in terms of relevant statistical parameters including kurtosis and mean excess delay. This characterization reveals clear differences in the statistics of these parameters under LOS and NLOS propagation conditions for various channel types in residential, office, outdoor and industrial environments. Based on the estimated parameters probability density functions under LOS/NLOS conditions, a likelihood ratio test (LRT) for hypothesis classification is performed for the different UWB channel models, and numerical results show that highly reliable LOS vs. NLOS classification is achievable, with accuracy exceeding 90% for most cases of practical interest. These results can then be further exploited in enhancing the performance of positioning applications.

A Measurement-Based Model for Outdoor Near-Ground Ultrawideband Channels

Deployment of wireless devices with transceivers in close proximity to the ground has become increasingly attractive for a wide range of applications such as distributed sensor networks and broadband tactical communications. Furthermore, the use of ultrawideband (UWB) signals is attractive for these communications due to their robustness and their suitability for precision ranging and localization. For the development and performance simulation of such systems, accurate channel models are required. The current paper thus presents details of an extensive measurement campaign for near-ground UWB propagation channels and a channel model-based thereon. The measurements were performed with a self-built channel sounder based on arbitrary waveform generation at the transmitter, high-bandwidth sampling oscilloscope at the receiver, and synchronization via electro-optical connections. Various combinations for the antenna height at transmitter and receiver, ranging from 10 cm to 2 m above ground, were measured. We find that the pathloss coefficient ( $\gamma$ ) depends significantly on the Tx–Rx antenna heights, while shadowing variance ( $\sigma^2$ ) and rms delay-spread ( ${\tau}_{rms}$ ) shows smaller dependence. The pathloss shows a slight dependence on frequency; the frequency-dependent pathloss exponent ( $\kappa$ ) increases as antennas get closer to the ground. We also found a linear dependency of the rms delay-spread on distance for various antenna height configurations measured. Statistical distributions of all parameters including $\gamma$ , ${\tau}_{rms}$ , $\sigma^2$ , and $\kappa$ are extracted from the measurements. Results are verified by comparing with a second measurement campaign.

Modeling of UWB Channel With Population Density in Indoor LOS Environments

This letter deals with the effect of multiple human bodies on an ultrawideband (UWB) channel in indoor line-of-sight (LOS) environments. To assess this, we choose four environments and consider four scenarios that have a different number of people in each environment. A distance-dependent path-loss model, a frequency-dependent path-loss model, and time dispersion parameters are considered. We found that the distance-dependent path-loss exponent increases as population density increases, while the frequency-dependent path-loss exponent decreases. The time dispersion parameters decrease as population density increases. The results suggest that the effect of the presence of people on UWB channels should be considered when assessing the performance of UWB systems.

Stationarity Regions for Ultrawideband Channels

In this letter, extracting the stationarity regions (SRs), where the channel statistics changes are insignificant, for ultrawideband (UWB) channel is achieved. SRs are found based on the correlation between consecutive power delay profiles (PDPs). The PDPs are found from channel measurement data for a frequency range of 3.1-5.3 GHz. The measured channel exhibits the sparsity behavior. Results show that the obtained SRs are between 0.27-0.32 m, where short distances show the variability of the channel. Moreover, the results are compared to standard probability density functions (PDFs). The generalized extreme value, Weibull, and exponential distributions are seen as the best fitted PDFs.

Spatial Stationarity of Ultrawideband and Millimeter Wave Radio Channels

For radio channels with broad bandwidth resource, such as those often used for ultrawideband (UWB) and millimeter wave (mmwave) systems, the Wide-Sense Stationary Uncorrelated Scattering (WSSUS) and spatial stationary assumptions are more critical than typical cellular channels with very limited bandwidth resource. This paper studies spatial stationarity and bandwidth dependency of the Multipath Component (MPC) parameters, and the concept of local region of stationarity (LRS) is used as the measure of the physical stationarity region. LRS calculation results based on channel measurements show that the size of LRS is bandwidth dependent in all measured bands, 2–4 GHz, 14–16 GHz, and 28–30 GHz. The results in this paper point out that an inappropriate choice of bandwidth in channel parameter estimation could violate spatial stationary assumptions. The paper indicates LRS sizes for different bandwidths in the three bands.

An Efficient Transmission Scheme for DCSK Cooperative Communication Over Multipath Fading Channels

Differential-chaos-shift-keying cooperative communication (DCSK-CC) has attracted a great deal of attention in the past five years, because it can overcome the negative effect of wireless multipath fading. However, the conventional DCSK-CC system suffers from a major disadvantage of low data rate due to the resource consumption in cooperation. To address the issue, this paper proposes an efficient cooperative scheme, called partial-sequence CC (PS-CC) scheme , for the DCSK-CC system. In the PS-CC framework, the source and relays only transmit a partial chaotic sequence corresponding to one bit to the destination, while consuming the same transmission energy as DCSK-CC. To validate the feasibility of the DCSK PS-CC system, this paper carries out the error performance, diversity order, and data rate analyses under different cooperative conditions over multipath fading channels. Both numerical and simulated results show that the proposed PS-CC system outperforms the DCSK-based non-cooperative system and DCSK-CC systems over the range of signal-to-noise ratio under study. Moreover, the proposed system can enhance data rate and reduce the computational overhead of the relays as compared with the DCSK-CC system. In addition, it will be demonstrated that the DCSK PS-CC system preserves its advantages in typical ultra-wideband (UWB) channels. Overall, the PS-CC appears to be a desirable cooperative scheme for those applications featured by high-data-rate, low-power, and low-complexity, such as wireless sensor networks using the transmitted reference UWB technique.

Channel measurement and time dispersion analysis for outdoor mobile ultrawideband environment

Ultrawideband (UWB) technology offers short-range high-data transmission rates. Most researchers in recent times have focused on indoor UWB channel measurements and in instances where outdoor cases were reported, they focused on static scenarios. This paper reports on mobile outdoor channel measurements typical of roadway and recreation park Infostation scenarios. It also chronicles the delay spread as well as channel stationarity analysis of the measurement data. We carried out measurements in the 3.1{5.3 GHz frequency range in various line-of-sight scenarios. The results of this research show that the delay spread values generally decrease with increasing mobile speed. Additionally, the degree of variation in the channel statistics show that systems designed with the obtained reference parameter values will perform well on average, but with low resource utilization.