Ultra-wideband Channel Model Research Articles

Performance of MB-OFDM network in a UWB channel under people shadowing and channel fading statistics

Ultra Wideband (UWB) systems transmit signals across a much wider frequency than conventional systems and are usually very difficult to detect. Due to the extremely low emission levels currently allowed by regulatory agencies, UWB systems tend to be useful for short-range and indoor applications. However, due to the short duration of the UWB pulses, it is easier to engineer extremely high data rates. Conventional Orthogonal Frequency Division Multiplexing (OFDM) technology is used subject to the minimum bandwidth requirement of the regulations. By turning to Multiband OFDM (MB-OFDM) architecture, designers gain the flexibility, power consumption, high spectral efficiency and costs needed to make UWB come to life. A packet-level UWB channel model is incorporated in MB-OFDM system and the performance of the link is determined on the basis of link throughput and delay in servicing the packets.

Channel Modeling Approach Based on the Concept of Degradation Level Discrete-Time Markov Chain: UWB System Case Study

In this work an approach to obtain an accurate high level channel model based on Discrete-Time Markov Chain, useful in some simulation context, is provided. In particular, this model is based on the concept of error trace analysis and on the degradation level of given observation windows: an observation window is fixed and the degradation level of the link, the Packet Error Rate (PER) relative to the specific window, is evaluated. This approach is useful for any wireless transmission scheme, but in our work, we apply it to the Ultra Wideband (UWB) system. Many researchers have already treated UWB channel modeling. However, to the best of our knowledge, all the proposed channel models work at the physical level investigating only some aspects of channel interaction. It has been shown through a comparative analysis, based on the occurrence of correctly and wrongly received packets, that the degradation level approach is more accurate than the classic Gilbert-Elliot model, the 3rd order Markov model and the Markov-based Trace Analysis (MTA) model.

On-Body Area UWB Channel Modeling Including Reflection from Surroundings

This study aims how to contain the environment reflection in a dynamic on-body ultra wideband (UWB) channel model. Based on a measurement approach, it is demonstrated that a complete body area channel model can be regarded as a combination of the on-body propagation characteristic and additional components from the environment. Based on such a channel model, the effect of environment reflection on the average bit error rate performance was investigated for a typical impulse radio UWB system.

Understanding the Ultrawideband Channel Characteristics Within a Computer Chassis

A measurement-based, statistical ultrawideband (UWB) channel model is presented for the unique environment within a computer chassis. The channel impulse response parameters are derived from measurement data. Because of the short-range communications, a mixture of near-field and far-field propagation is characterized by the use of a breakpoint path-loss model. Due to the near-field nature of this environment, an unusually large number of clusters and rapid cluster decay time is noted in the channel impulse response. Additionally, electromagnetic interference measured inside a computer chassis that is generated by the motherboard in a custom fully operational mode is presented, wherein it is observed that the CPU clock does not appear as a significant interference source.

Preliminary UWB channel study for wireless body area networks in medical applications

Ultra wideband (UWB) communications is a promising technology for wireless body area networks (WBAN) due to its very low power emission and robustness against multipath fading characteristics. The use of WBANs in the areas of healthcare and telemedicine is being seriously considered as a way of increasing the quality of medical services and of keeping under control the associated costs. Because the human body has a complex shape and consists of different tissues it is expected that the propagation of electromagnetic signals will have different characteristics than the ones found in other environments, e.g., offices, streets, etc. The contribution of the work described in this paper is to expand the knowledge of the UWB channel, for WBAN applications, in the frequency range of 3-11 GHz under scenarios expected to be found in the medical care field. The experimental measurements are used to develop UWB channel models which can then be applied to the design of efficient communications protocols.

Low complexity RAKE receiver for TH-based multiuser UWB system with realistic UWB indoor channel

We have considered multiuser communication scenario with ultra wideband (UWB) communication. UWB device is transmitting the data by time hopping (TH)-based system, TH-PPM, TH-PAM and DS-UWB. The UWB device is transmitting data over multipath rich channel model recommended by IEEE 802.15.3a working group. This channel model is based on Saleh-Valenzuela model. For better performance at receiver side, adaptive equaliser is required; this increases the complexity of receiver. Here we have considered the RAKE receiver for TH-based UWB system. This RAKE receiver structure is not a conventional RAKE, but it is pre-RAKE structure. In this case, we have evaluated performance of system by considering the RAKE receiver at the transmitter side. Here we have assumed the condition that channel sounding is available before transmission for quasi static UWB channel. Based on this knowledge RAKE fingers are selected for pre-RAKE. UWB channel is multipath rich channel so full RAKE adds more complexity in receiver and hence put limitation on effective data rate. Here we have considered low branch RAKE receiver. Performance of the system model is evaluated with realistic UWB channel model.

Analytical Approach to Model the Fade Depth and the Fade Margin in UWB Channels

In this paper, the variations of the ultrawideband (UWB) channel power as a function of the channel bandwidth are investigated. An analytical approach to characterize the fade depth and the fade margin due to small-scale fading in indoor environments is proposed. The approach is based on the IEEE 802.15.4a ultrawideband channel model and the assumption that the channel power can be modeled by a Gamma distribution. This analytical approach is checked by comparison with results derived through Monte Carlo simulations. The results show that the fade depth and the fade margin are closely related to the channel bandwidth. This analytical approach can be used to design and implement UWB communications systems.

UWB Channel Modeling in Roadway and Indoor Parking Environments

In this paper, the characteristics of ultrawideband (UWB) channels on outdoor roadway and indoor parking environments are investigated. A set of propagation measurements were conducted on roadways and in underground parking garages, and the resulting propagation data consist of approximately 1200 measured signals. Multipath properties are characterized using tapped-delay-line and Saleh-Valenzuela (S-V) models. Power-law-type decay patterns are observed in the ray-energy decay, as well as in the power delay profile. Results are compared with existing UWB models, including the IEEE 802.15.4a channel model.

Some interesting results on compatible BER analysis issues related to multi-band timing and frequency synchronizers applicable for MB-OFDM based UWB communications

A closed form expression of bit-error-rate (BER) has immense importance for insightful understanding on the performance of a communication system. In this paper we provide the BER analysis of a convolution coded MB-OFDM Ultra-Wideband (UWB) system that captures the log-normal fading statistics of UWB channels and also considers the estimation error variances of timing and carrier frequency offset (CFO) estimation by our already published synchronizers ATS (Sen et al., 2008 [1,2]) and MBAFS (Sen et al., 2008 [3,4]) respectively. By invoking the moment generating function (MGF) for log-normal fading statistics and using the Gauss-Hermite quadrature integration the average BER for rate Rc coded QPSK modulation with ATS and MBAFS synchronizers and channel estimation by least square (LS) method is obtained. We compare the analytical result with simulation results in highest delay spread UWB channel model CM4 and validate the consistency of our theoretical analysis.

Modeling the Ultra-Wideband Outdoor Channel: Model Specification and Validation

In this paper we establish a geometry-based stochastic ultra-wideband channel model for gas stations. We statistically describe the two-dimensional spatial location and power of clustered scatterers, and the shape of their visibility and shadowing regions. We also separately model the diffuse part of the impulse response (i.e., the part that cannot be explained by the scatterers' multipath components), and show that its amplitude fading statistics can be best described by a Weibull distribution with a delay dependent beta-parameter. A step-by-step implementation recipe demonstrates how the model can be built. Finally, we validate our model by comparing simulated and measured channel parameters such as the rms delay spread.

Efficacy of Multiband OFDM Approach in High Data Rate Ultra WideBand WPAN Physical Layer Standard using Realistic Channel Models

Multiband Orthogonal Frequency Division Multiplexing (MBOFDM) approach using UWB signals with short duration of pulses provide unique advantages in short-range high data rate wireless applications which include easy penetration through obstacles, high precision ranging and low processing power. In this paper a performance study on MB-OFDM is attempted for high data rate ultra wideband (UWB) WPAN physical layer standard according to modulation techniques such as QPSK, 16-QAM, 64-QAM etc. Different multipath components in the UWB channels are characterized by different delays and attenuation. The channel models chosen in simulation of MB-OFDM UWB communication system are different from standard UWB channels considering realistic multipath resolution and operating frequencies. In this research different amplitude fading statistics for UWB channel (IEEE 802.15.3a) are analysed. The BER performance of MB-OFDM UWB on modified UWB channel models are investigated through simulation study. It is observed that QPSK modulation for the MB-OFDM UWB system performs better than 16-QAM and 64-QAM in the CM3 (NLOS) and CM4 (NLOS) channel environment. We show that, at low data rate (55 Mbps) the MB-OFDM system performs better in the CM4 channel environment than in the CM3, CM2 and CM1 channel model due to its inherent frequency diversity. In high data rate (480 Mbps), the BER performance in CM1 channel model is found to be better than in CM2, CM3, CM4 channel model.

Blind linear equalization of PPM signals using third-order moments

A novel blind equalization strategy for pulse position modulation (PPM) based on maximizing the third-order moment of the equalizer output is presented. Compared to traditional fourth-order (e.g. kurtosis-based) methods, third-order moments give faster convergence and are less sensitive to noise. This work demonstrates that the intersymbol interference that plagues typical indoor ultra wideband (UWB) channels can be combatted using a third-moment maximizing blind equalizer which could therefore provide a cold start-up for a decision-directed scheme. Adaptation is shown to be asymptotically globally convergent with increasing time-hopped PPM frame length. Simulation experiments compare the performance to standard fourth-order schemes in practical settings, taking into account the conditions of time-hopping,multiple-access interference and a realistic UWB channel model.

UWB channel modelling for wireless body area networks in a hospital

This paper describes an experimental study of the ultra wideband (UWB) wireless body area network (WBAN) channel in a hospital environment. The measured data are used to develop statistical models for the channel, which can then be used to design efficient and safe communication networks. WBANs are expected to be used in the healthcare field to enable concepts such as telemedicine. The human body has a complex shape and consists of different tissues. It is then expected that the propagation of the electromagnetic waves near a patient's body will have unique characteristics. In a hospital environment, there are also a variety of electronic devices and specialised medical equipment, which have impact on the electromagnetic propagation. To properly design WBANs is then necessary to have a good understanding of the characteristics of the radio channel in the proximity of the human body within a hospital.

UWB Channel Modeling Improvement in Indoor Line-of-Sight (LOS) Environments

Channel measurement and modeling is an important issue when designing ultra wideband (UWB) communication systems. A Precise model of the channel response is inevitable for designing an ultra wideband telecommunication system. In this article signal propagation in indoor environment and LOS condition is evaluated and the appropriate model of this scenario is presented. Parameters such as the power delay profile, mean excess delay, delay spread, “NP10dB” are analyzed and simulated. Based on analysis results, the proposed model is presented. This model is based on Two-cluster approach but its average power delay profile is described with power function and cluster time of arrival is modeled by the modified exponential distribution. Finally UWB channel parameters of proposed model, Saleh and Valenzuela (S-V) and Two-cluster models are compared. Measurement and simulation results show that considerable improvement for mean excess delay, delay spread and “NP10dB” of proposed model comparing with S-V and Two-cluster model, this means the channel is better described, which mean the channel is described more precisely.

Average SINR Analysis of DS-BPSK UWB Systems With IPI, ICI, ISI, and MAI and Its Application

Analytical expressions for the average output signal-to-interference-plus-noise ratio (SINR) of direct-sequence (DS) binary-phase-shift-keying (BPSK) ultra-wideband (UWB) receivers are derived using the IEEE UWB channel models. The derivation takes into account the interpath interference, the interchip interference (IPI), the intersymbol interference (ISI), and the multiple-access interference (MAI). The effects of the spreading gain and the pulse duration on the average output SINR are examined. Using these results, the optimal integration interval for a transmitted reference UWB receiver is studied.

A Technique for Frequency Synchronization in Multi-Band OFDM in Realistic UWB Channel

This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the Cramer---Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1---CM4. Next, we modify the estimation algorithm by proposing a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1---CM4. Both analysis and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to verify their feasibility of implementation in practical UWB receiver design.

Frequency Offset Estimation by Multi-Band Averaging Method: A New Approach for MB-OFDM Based Ultra-Wideband Communication System

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).

Multiuser performance of M-ary orthogonal coded/balanced UWB transmitted-reference systems

A tractable and compact closed-form expression on the channel-averaged signal-to-interference-plus-noise ratio (SINR) is derived for M-ary orthogonal coded/balanced transmitted-reference (BTR) systems, taking into consideration both inter-pulse interference (IPI) and multiple-access interference (MAI) in dense multipath ultra-wideband (UWB) channels. The UWB channel here is a realistic and standard one with lognormal channel gain distribution and double independent Poisson arrival distribution of cluster and ray. Hence, the analytical framework developed here can be applied to typical UWB channel models, especially considering the channel sparseness and cluster overlapping observed in realistic UWB channels. Based on the channel-averaged SINR, the effect of inter-pulse distance (between the reference and data pulses in BTR) on the multiuser performance is fully investigated. A proper selection of user-specific inter-pulse distances in multiuser scenario is then determined to maximize the user capacity for a given UWB channel.

An Adaptive Timing Synchronization Scheme for Multi-Band Orthogonal Frequency Division Multiplexing Based Ultra-Wideband Communication Systems

This article deals with a new energy based adaptive timing synchronization scheme (ATS) which estimates the symbol timing information within two (2) OFDM symbols and updates the information with different frequency bands (adaptive in sense) in a multi-band orthogonal frequency division multiplexing (MB-OFDM) based system. The new approach provides significant improvement in system performance for high delay spread ultra-wideband (UWB) channel model (CM) environments where fast and low-complexity timing synchronization is a critical issue. This paper also addresses a crucial aspect of UWB channel which is frequency dependent delay characteristics. This effect contributes to different dispersion and timing shift of an UWB signal for different frequency bands. In this work, the wideband channel delay characteristics are studied and delay parameters are found considerably different over frequency bands 3.1---4.6 GHz. Based on this observation, the ATS which estimates and maintains the timing delays of each band separately is presented. The performance of ATS algorithm is measured by mean-squared error (MSE), synchronization probability, signal to interference ratio (SIR) reduction due to synchronization errors and bit error rate (BER) through the computer simulation for several UWB CM environments CM2---CM4. Each of these UWB CMs is simulated for 100,000 noisy channel realizations for both coded and uncoded MB-OFDM system. It is shown that ATS gives signal-to-noise ratio (SNR) improvement of 1.1 dB at BER of 1 × 10?3, 1.2 dB at BER of 2 × 10?4, and 0.7 dB at BER of 2 × 10?4 for CM4, CM3, and CM2 respectively for coded MB-OFDM system over a non-adaptive synchronization scheme [Yak et al., Proceedings of IEEE PIMRC, Berlin, Germany, vol 1, pp 471---475, September 11---14, 2005].

Ultra-Wideband Channel Modeling for Intravehicle Environment

With its fine immunity to multipath fading, ultra-wideband (UWB) is considered to be a potential technique in constructing intravehicle wireless sensor networks. In the UWB literature, extensive measuring and modeling work have been done for indoor or outdoor propagation, but very few measurements were performed in intravehicle environments. This paper reports our effort in measuring and modeling the UWB propagation channel in commercial vehicle environment. In our experiment, channel sounding is performed in time domain for two environments. In one environment, the transmitting and the receiving antennas are put beneath the chassis. In another environment, both antennas are located inside the engine compartment. It is observed that paths arrive in clusters in the latter environment but such clustering phenomenon does not exist in the former case. Different multipath models are used to describe the two different propagation channels. For the engine compartment environment, we describe the multipath propagation with the classical S-V model. And for the chassis environment, the channel impulse response is just represented as the sum of multiple paths. Observation reveals that the power delay profile (PDP) in this environment does not start with a sharp maximum but has a rising edge. A modified S-V PDP model is used to account for this rising edge. Based on the analysis of the measured data, channel model parameters are extracted for both environments.