Amin Haj-Ali

RSSI range estimation for indoor anchor based localization for wireless sensor networks

Range estimation using RSSI (received signal strength indicator) for localization application for wireless sensor networks is a challenging task. Interference from the shared 2.4GHz channel and fading due to multipath propagation and shadowing deteriorate the process of range estimation. In this work an estimation of these noise levels that are present in the environment is being carried out by anchor nodes which are placed throughout the sensing field. These anchor nodes will compare the actual distance between them with distance computed from the measured RSSI. Four different techniques have been devised that applies a smoothing coefficient on the measured RSSI taking into consideration information about the environment from the anchor nodes. Simulation shows that even when the error introduced is equivalent to 100% of the transmission range, the error in range estimation was around 25%.

Asynchronous relay selection protocol for distributed cooperative networks

This paper proposes a novel relay selection protocol for distributed cooperative networks, that eliminates the effect of asynchronism between different received signals. The suggested protocol maintains a high diversity order, with minimum message complexity and overall time delay, and it also provides a better performance in terms of power consumption and error rates than existing selection protocols. From several relayed signals, the receiver chooses signals which verify a certain predefined SNR (Signal to Noise Ratio) and some conditions on time delays. The overall enhancement of the system performance, compared to other relay selection protocols, is shown by measurements and numerical simulations.

Secure localization for wireless sensor networks using decentralized dynamic key generation

Security frameworks for wireless sensor network localization application can no longer be ignored. Wireless sensor network are being deployed in sensitive environment that require high levels of confidentiality, integrity and authenticity. Employing already existing security algorithms dedicated for wireless networks are infeasible for sensor network environment due to limited resources. In this context, a security framework tailored for wireless sensor network localization applications is proposed. The algorithm uses symmetric key encryption where the keys are generated in a decentralized fashion. These keys are computed on the fly, never transmitted and, changes autonomously with each transmission. Furthermore, the algorithm utilizes the bitwise XOR function for all its encryption needs which presents low overhead. Simulations show the robustness of the proposed algorithm in case of malicious node attack on the localization process and on key deduction and computation.

Decentralized clustering in VANET using adaptive resonance theory

Nowadays VANETs are becoming a dominating technology in automotive industries where vehicles communicate with each other to deliver safety messages or any type of information to other vehicles. However, the increasing numbers of vehicles on the roads poses a challenge on designing an efficient communication protocol for VANETs. The scalability issue in VANETs has a deteriorating effect on latency and on the stability of the network. Clustering is one technique used for solving this issue. In this work, we propose a clustering technique that creates mini clusters that are in the same communication range of the vehicles with the help of Adaptive resonance theory (ART). These mini clusters are created based on speed where it categorizes the vehicle in one of three levels: high, medium or low speeds. ART is an unsupervised neural network model that classifies inputs based on the degree of similarities of the input. By carefully tuning ART, three clusters are always obtained corresponding to the above speed classifications. The proposed work was simulated and compared against traditional clustering methods where our work presented a 50% advantage over these techniques.

Improving the performance of Transport Control Protocol over 802.11 wireless networks

One of the main reasons for TCPs (Transport Control Protocol) degraded performance in 802.11 wireless networks is the TCPs interpretation that the packet loss is caused by network congestion. However, in wireless networks packet loss occurs mostly due to high bit error rate, packet corruption, and link failure. TCP performance in wired/wireless networks may be substantially improved if the causes of packet loss could be identified and appropriate rectifying measures could be taken dynamically during the lifetime of a TCP session. This paper proposes an end-to-end improvement approach to the current TCP protocol by extending the used RTO (Retransmission Time Out) in such a way it allows TCP an additional waiting time for wireless errors to get fixed. This approach is validated through numerical analysis and simulations, and then compared to the current implemented TCP protocol. The simulation results have demonstrated higher TCP performance in terms of traffic sent, and retransmission attempts. This is highly recommended for a wide range of applications in mixed wired and wireless scenarios.