Qammer H. Abbasi

On-Body Radio Channel Characterization and System-Level Modeling for Multiband OFDM Ultra-Wideband Body-Centric Wireless Network

Given the trend towards a user-centric concept in mobile communications, body area networks have received increasing attention within the wireless personal and body area networks community. In this paper, an experimental investigation is presented to derive suitable radio propagation models for ultra wideband (UWB) body-centric wireless communications. The performance of the body-centric UWB radio channel is investigated by considering several on-body links, including different body postures. System-level modeling of potential multiband orthogonal frequency-division multiplexed UWB system has been conducted and system performance is measured using bit error rate (BER) and signal-to-noise ratio. The conducted system analysis demonstrated that for 78% in the static case and 75% and 61% for stable and unstable transmitter locations in the pseudodynamic in-motion scenarios (respectively) of the specified on-body radio links, the BER is equal to or less than 0.1%. This demonstrates promising applications of the proposed UWB body-centric radio system. Based on these results, clear recommendations are given for best on-body locations leading to optimal system performance.

Numerical Characterization and Modeling of Subject-Specific Ultrawideband Body-Centric Radio Channels and Systems for Healthcare Applications

The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network.

Ultrawideband Band-Notched Flexible Antenna for Wearable Applications

This letter presents the design of an ultrawideband (UWB) band-notched wearable antenna and its validation using simulation and measurement results. The antenna can be used for ultrawideband applications, while rejecting the higher band assigned to wireless local area network (WLAN 5.25-GHz band). The presented return loss and radiation pattern results demonstrate that antenna properties have negligible variations when bent at different angles (a possible condition when placed on body) or placed in adverse conditions (under extreme heat and humidity). Moreover, reliable performance of antenna for on-body scenario makes the designed antenna a promising candidate for wearable applications.

Arm movements effect on ultra wideband on-body propagation channels and radio systems

This paper presents experimental investigation of ultra wideband on-body radio channel in both the anechoic chamber and indoor environments including effects of time varying movements of various body parts on the the channel characteristics. Measured data are used to extract radio propagation channel parameters and investigate the influence of body movements on derived channel models. These models are applied in conjunction with different modulation techniques commonly used for impulse radios to evaluate the system performance of on-body UWB radio systems. Bit error rate and signal-to-noise ratio studies show that careful considerations need to be taken when choosing the modulation technique for optimal ultra wideband body-centric systems.

Experimental investigation of ultra wideband diversity techniques for on-body radio communications

This paper presents an experimental investigations and analyses of ultra-wideband antenna diversity techniques and their efiect on the on-body radio propagation channels. Various diversity- combining techniques are applied to highlight; how the overall system performance may be enhanced. Diversity gain is calculated for flve difierent on-body channels and the impact of variation in the spacing between diversity branch antennas is discussed, with an emphasis on mutual coupling, correlation and power imbalance. Results demonstrate the repeatability and reliability of the analysis with error variations as low as 0.8dB. The study highlights the signiflcance of diversity techniques for non-line-of-sight propagation scenarios in body-centric wireless communications.

Terahertz Channel Characterization Inside the Human Skin for Nano-Scale Body-Centric Networks

This paper focuses on the development of a novel radio channel model inside the human skin at the terahertz range, which will enable the interaction among potential nano-machines operating in the inter cellular areas of the human skin. Thorough studies are performed on the attenuation of electromagnetic waves inside the human skin, while taking into account the frequency of operation, distance between the nano-machines and number of sweat ducts. A novel channel model is presented for communication of nano-machines inside the human skin and its validation is performed by varying the aforementioned parameters with a reasonable accuracy. The statistics of error prediction between simulated and modeled data are: mean (μ)= 0.6 dB and standard deviation (σ)= 0.4 dB, which indicates the high accuracy of the prediction model as compared with measurement data from simulation. In addition, the results of proposed channel model are compared with terhaertz time-domain spectroscopy based measurement of skin sample and the statistics of error prediction in this case are: μ = 2.10 dB and σ = 6.23 dB, which also validates the accuracy of proposed model. Results in this paper highlight the issues and related challenges while characterizing the communication in such a medium, thus paving the way towards novel research activities devoted to the design and the optimization of advanced applications in the healthcare domain.

Experimental Characterization and Statistical Analysis of the Pseudo-Dynamic Ultrawideband On-Body Radio Channel

This letter investigates the effect of body movements on the ultrawideband (UWB) on-body radio channel. A measurement campaign was performed considering four different body-links, namely: belt-to-head, belt-to-chest, belt-to-wrist, and belt-to-ankle, with the subject performing movements of different nature, in order to cover a wide range of scenarios. Transient and spectral characteristics were extracted from the measured channel data. The post-measurement analysis concluded that the normal distribution provides the best fitting for the path loss, while the root mean square delay is better modeled with a log-normal distribution. In addition to first-order statistics, this letter analyzes and discusses second-order channel parameters such as level crossing rate, average fade duration, and fade probability for the proposed on-body propagation links.

Spatial Correlation Analysis of On-Body Radio Channels Considering Statistical Significance

On-body radio channel modeling and measurement has been studied extensively. However, the spatial correlation properties of channel parameters and the reliability of on-body channel measurements remain poorly understood. In this letter, a K-weight-based spatial autocorrelation model and corresponding Z-score is used to investigate the spatial correlation of on-body radio propagation and the degree of confidence in measurement results. It is demonstrated that, due to rich multipath scattering in an indoor environment, both the spatial autocorrelation and corresponding confidence level are higher compared to those in the chamber environment. These findings have the profound implication that, for less scattered environments, the locations of transmitter (Tx) and receiver (Rx) need to be very accurate in order to achieve high repeatability in on-body channel measurements.

An Advanced UWB Channel Model for Body-Centric Wireless Networks

This paper presents a novel ultra wideband (UWB) channel model in the 3{10GHz range for body-centric wireless communications. The tests are performed in both indoor anechoic chamber environments, addressing on-body and ofi-body propagation scenarios. The body channel model is extracted by using a single spatial grid over all the body, and by distinguishing between LOS and NLOS condition. The large number and the uniform placement of the receiver locations attempt a representation of the body propagation links more comprehensive than previously published models. The statistical reliability of the model is investigated by applying jointly the Kolmogorov-Smirnov and the Akaike criteria. The analysis suggested that the Lognormal model flts the channel amplitude distributions with a percentage ‚ 64%. The on-body indoor channel amplitudes are modeled with a stochastic terms of about 4{5dB higher than previously published models. Finally, a Negative-Binomial and Inverse Gaussian distribution are used to model the expected number of paths and interarrival time, respectively. Based on the results presented in this paper, clear recommendations are given with regards to the optimum statistical distribution of an accurate UWB body-centric radio channel modeling.

System-level modelling of optimal ultra wideband body-centric wireless network

Given the trend towards a user-centric concept in mobile communications, body area networks have received increasing attention within the wireless personal area community. Ultra Wideband (UWB) radio channel propagation model with the inclusion of dynamic body environment is derived and applied to investigate the performance of potential radio systems to be used in body are networks. System-level modelling of potential UWB impulse radio is conducted and system performance is measured using bit error rate (BER) and signal-to-noise ratio parameters corresponding to modulation techniques such as pulse position modulation and bi-phase modulation. Impact of movements on system performance is investigated and degradation in system performance due to movements shows the importance of considering the dynamic channel statistics when designing optimal UWB system for body-centric wireless communications.