Ahmad El Assaf

Approximation algorithms for maximum link scheduling under SINR-Based interference model

An accurate localization algorithm tailored for anisotropic wireless sensors networks (WSNs) is proposed in this paper. Using the proposed algorithm, each regular or position-unaware node estimates its distances only to reliable anchors or position-aware nodes. The latter are properly chosen following a new reliable anchor selection strategy that ensures an accurate distance estimation making thereby our localization algorithm more precise. It is shown that the proposed algorithm is implementable in both 2-dimensional (2D) and 3-dimensional (3D) scenarios. A power saving mechanism aiming to enhance the WSN lifetime is also envisaged in this paper. It is proven that the proposed algorithm could easily incorporate such a mechanism. Simulations show that our algorithm, whether combined or not with the power saving mechanism, consistently outperforms the best representative localization algorithms currently available in the literature in terms of accuracy, even with the presence of nonuniform node distribution or radiation irregularities.

Efficient range-free localization algorithm for randomly distributed wireless sensor networks

In this paper, we propose a novel range-free localization algorithm able to reduce errors due to mapping the hops into distance units. Using the proposed algorithm, the mean hop size h̅s is locally derived at each regular or position-unaware node, thereby avoiding its broadcast by anchors (i.e., a few nodes aware of their exact position) as usually required in current state-of-the-art solutions and, hence, resulting in less battery power depletion. The analytical expression of h̅s is derived for different node distributions. Furthermore, it is shown that it is possible to locally compute h̅s at each regular node with or even without prior knowledge of the node distribution. Simulations results show that the proposed scheme outperforms the most representative range-free localization schemes in terms of accuracy.

Range-free localization algorithm for heterogeneous Wireless Sensor Networks

In this paper, we propose a novel range-free localization algorithm tailored for heterogeneous wireless sensor networks (WSNs), where nodes have different transmission capabilities. Two different approaches are developed to accurately derive the expected hop progress (EHP). It is shown that the obtained EHP depends solely on the information locally available at each node and, hence, can be computed in a localized manner. Furthermore, a localization correction mechanism which accounts for the heterogeneous nature of WSNs is developed. Simulations results show that the proposed algorithm, whether with or without correction, outperforms in accuracy the most representative range-free localization algorithms in the literature.

Range-Free Localization Algorithm for Anisotropic Wireless Sensor Networks

In this paper, we propose a novel range-free localization algorithm tailored for anisotropic wireless sensors networks (WSN)s. Using the proposed algorithm, each regular or positionunaware node estimates its distances only to reliable anchors or position-aware nodes. The latter are properly chosen following a new reliable anchor selection strategy that ensures an accurate distance estimation making thereby our localization algorithm more precise. Indeed, simulations suggest that it outperforms the best representative range- free localization algorithms currently available in the literature in terms of accuracy.

Hop-count based localization algorithm for wireless sensor networks

In this work, we propose a novel hop-count based localization algorithm able to reduce errors due to mapping the hops into distance units. Using the proposed algorithm, the mean hop size hs is locally derived at each regular or position-unaware node, thereby avoiding its broadcast by anchors (i.e., a few nodes aware of their exact position) as usually required in current state-of-the-art solutions and, hence, resulting in less battery power depletion. The analytical expression of hs is derived for different node distributions. Furthermore, it is shown that it is possible to locally compute h̅s at each regular node with or even without prior knowledge of the node distribution. Simulations results show that the proposed scheme outperforms the most representative hop count based localization schemes in terms of accuracy.

Efficient Node Localization in Energy-Harvesting Wireless Sensor Networks

In this paper, we propose a novel localization algorithm tailored for energy-harvesting wireless sensor networks EH-WSNs where both the power budgets available at the EH sensors and hence their transmission capabilities are random. This characteristic, if not taken into account when designing the localization algorithm, may severely hinder its accuracy. Assuming a random transmission capability at each EH sensor, we develop a new approach to derive the expected hop progress (EHP). Exploiting the latter, we propose a localization algorithm that is able to accurately locate the EH sensors owing to a new implementation requiring no additional power consumption. Furthermore, we develop a correction mechanism which complies with the heterogeneous coverage nature of EH sensors to further improve localization accuracy without incurring any additional power cost. Simulation results show that the proposed algorithm, whether applied with or without correction, outperforms in accuracy the most representative WSN localization algorithms in EH powering contexts.

Accurate Sensors Localization in Underground Mines or Tunnels

In this paper, a novel localization algorithm tailored for underground mines is proposed. Using the proposed algorithm, each regular (i.e position-unaware) node estimates its distances to the anchor (i.e., position-aware) nodes exploiting only its locally available information. Furthermore, a new hop count adjustment scheme, which complies with the labyrinthic nature of underground mines, is developed to ensure an accurate distance estimation, thereby making our localization algorithm more precise. Simulations show that our proposed algorithm, consistently outperforms in underground mines the best representative localization algorithms currently available in the literature in terms of accuracy, even with the presence of radiation irregularities.

A study of 60 GHz channel estimation techniques using pilot carriers in OFDM systems in a confined area

In recent years, there has been an increased need for digital wireless applications to use high rate data transmission. OFDM (Orthogonal Frequency Division Multiplexing) offers an interesting solution that allows for the exploitation of the 60 GHz band with optimal spectral efficiency, a robustness to frequency selective fading, and a resistance to inter-symbol interference (ISI) that is a major problem in high speed data communications. Transmitted data in an OFDM system is divided on different subcarriers, after applying PSK (phase shift keying) or QAM (Quadrature Amplitude Modulation) modulation. The bandwidth of the obtained signal is converted to the time domain by using an IFFT (Inverse Fast Fourier Transform) in order to transmit it through a wireless channel. To recover the distorted data at the receiver, the effects of the channel must be estimated and compensated by the receiving system [1, 2]. In this paper, the 60 GHz channel estimation methods for OFDM systems based on comb-type pilot arrangement are investigated, as the algorithm of channel estimation based on comb-type is divided into pilot signal estimation and channel interpolation. The pilot signal estimation based on LS (Least Squares) or LMMSE (Linear Minimum Mean Square Error) criteria is studied along with the channel interpolation based on LI (linear interpolation). The performances of various estimation algorithms are evaluated and compared by measuring the Bit Error rate (BER) and Mean Square Error (MSE) where 16-QAM modulation scheme is applied.