An Efficient Backoff Algorithm for IEEE 802.15.4 Wireless Sensor Networks

IEEE 802.15.4 is one of the most prominent MAC protocol standard designed to achieve low-power, low-cost, and low-rate wireless personal area networks. The contention access period of IEEE 802.15.4 employs carrier sense multiple access with collision avoidance (CSMA/CA) algorithm. A long random backoff time causes longer average delay, while a small one gives a high collision rate. In this paper, we propose an efficient backoff algorithm, called EBA-15.4MAC that enhances the performance of slotted CSMA/CA algorithm. EBA-15.4MAC is designed based on two new techniques; firstly, it updates the contention window size based on the probability of collision parameter. Secondly, EBA-15.4MAC resolves the problem of access collision via the deployment of a novel Temporary Backoff (TB) and Next Temporary Backoff (NTB). In this case, the nodes not choose backoff exponent randomly as mentioned in the standard but they select TB and NTB values which can be 10–50 % of the actual backoff delay selected by the node randomly. By using these two new methods, EBA-15.4MAC minimizes the level of collision since the probability of two nodes selecting the same backoff period will be low. To evaluate the performance of EBA-15.4MAC mechanism, the network simulator has been conducted. Simulation results demonstrate that the proposed scheme significantly improves the throughput, delivery ratio, power consumption and average delay.     

Terahertz Absorption of Nematic Liquid Crystals

We present the first systematic study of cyanobiphenyls (CBs) and the phenylcyclohexanes in the range between 50 cm^-1 (1.5 THz) and 500 cm^-1 (15 THz). The impact of the alkyl chain length and of variations in the core structure on the spectrum is investigated using liquid crystals from the cyanobiphenyl and phenylcyclohexane families. Our measurements are supported by calculations based on density functional theory. This enables us to shine light on the vibrational dynamics of liquid crystal molecules in the terahertz frequency range.     

Characterization and Investigation of Magnetic and Microwave Properties of Multiwalled Carbon Nanotube/SrFe10MnSn0.5Ti0.5O19 Nanocomposites

SrFe₁₀MnSn_0.5Ti_0.5O₁₉/multiwalled carbon nanotube (MWCNT) nanocomposites with different volume percentages of MWCNT content were synthesized by a sol–gel method. The results of x-ray diffraction, field-emission scanning electron microscopy, and Fourier-transform infrared spectrometry analyses demonstrated that the SrFe₁₀MnSn_0.5Ti_0.5O₁₉ nanoparticles were attached on the external surfaces of the MWCNTs. Mössbauer spectroscopy indicates that the substituted cations preferentially occupy the 12k sites. Magnetic properties were measured using a vibrating-sample magnetometer, and microwave absorption properties were investigated using a vector network analyzer. It was found that, with increasing volume percentage of MWCNT content, the saturation magnetization as well as the coercivity decrease, but the reflection loss widely increases. To investigate the effect of sample thickness on the absorption properties, different values of thickness (1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, and 2 mm) were selected. The results showed that, with increasing thickness of the absorber, the reflection loss and bandwidth broadly increase.     

Adaptive single snapshot beamforming: a new concept for therejection of nonstationary and coherent interferers

An approach to adaptive beamforming (adaptive reconstruction of a desired signal in the presence of interferers and noise) that uses just a single snapshot to calculate the antenna weights is presented. As in previous studies, a structured and grouped array of sensor elements is assumed. The concept exploits the induced special data structure, which can be described as a generalized rank-one eigenvalue problem and can be solved by means of a linear (overdetermined) system solver. Arbitrary signal statistics are allowed and no difficulties with nonstationary, and coherent interferers arise. Furthermore, the algorithm does not exhibit any transient behavior. Simulations verify its good performance in comparison with the optimum beamformer     

Millimeter wave propagation in arid land-a field study in Riyadh

A field study on wave propagation has been actively running for four years in Riyadh, Saudi Arabia. The study involves the operation and monitoring of two links at a frequency of 40 GHz, and an infrared link at 0.88-μm wavelength. A meteorological station is also operated and monitored. The effect of sand storms on propagation is studied by measuring storm parameters, namely, visibility, particle size and size distribution, and induced attenuation. The results are compared with long-term visibility data for Riyadh, and a complete statistical analysis is given. The effect of rain is studied by measuring both rain rate and rain attenuation. Long-term rain data are utilized to derive long-term rain statistics. It is shown that the measured attenuation due to sand storms is about four times larger than the calculated attenuation at 40 GHz. The measured rain attenuation at infrared is found to be smaller by a factor of 0.3 than theoretically predicted attenuation     

A translinear principle based low-power high-precision RMS-to-DC converter in CMOS technology

Analog Integrated Circuits and Signal Processing - In the present study, a low-power high-precision current-mode CMOS true root mean square (RMS)-to-DC converter is presented based on the...     

Performance Evaluation of Cost-Effective Multicast–Unicast Key Management Method

Group key management is one of the key security issues in multicast networks. The main challenge is to provide a secure group key management method which avoids high key update cost in terms of the number of transmitted keys. In order to achieve low key update cost for group key management, most of the existing methods increase their encryption/decryption cycles which requires a strong cryptographic function. In this paper, a cost-effective key management method is proposed to address the problem of high key update cost without increasing the encryption/decryption cycles. We evaluated our proposed method with existing tree-based methods by using Markov chain and Poisson Arrival Process. Results indicate the efficiency of our proposed method in reducing the key update cost significantly compared to the existing tree-based key management methods.     

Enhancing inter-PMIPv6-domain for superior handover performance across IP-based wireless domain networks

As a network-based localized mobility management protocol, Proxy Mobile IPv6 (PMIPv6) enables a Mobile Host (MH) to roam within a localized domain without MH intervention in the mobility-related signalling. However, the PMIPv6 maintains MH mobility support in a restriction domain. Therefore, whenever the MH roams away from the PMIPv6 domain, its reachability status will be broken-down causing high handover latency and inevitable traffic loss for its communication session. This article proposes a proactive mechanism to mange the MH handover and maintain its data session continually across inter-PMIPv6-domains. The proposed mechanism introduces an intermediate global mobility anchor entity, called, which is responsible to coordinate MH handover as well as redirect its traffic across inter-PMIPv6-domains. Through various simulation evaluations, via ns-2, several experiments were conducted, revealing numerous results that verify the proposed mechanism superior performance over the conventional inter-PMIPv6-domain handover schemes in terms of handover latency, achieved throughput, protocol signalling cost and end-to-end traffic delivery latency.     

On the realization of the current controlled current-mode amplifier using the current controlled conveyor

The current controlled current-mode amplifier proposed by Fabre et al. (1996, IEEE Transactions on Circuits and Systems—I, 43, 82) is reanalysed to show that it can work not only under small signal conditions, as suggested by Fabre et al., but also under large signal conditions. Simulation results which confirm the theory presented are included.