Link stability issues are significant for the route selection process in mobile ad hoc networks (MANETs). A link can be instable due to the random characteristics of the wireless channel, and/or the mobility of nodes. This paper considers instability due to mobility, and proposes a scheme to predict the link stability in mobile scenarios of MANETs. The prediction scheme is based on link connectivity changes and can be performed on the network layer, without the need of low layer data. We assume that the link connectivity follows the continuous-time Markov chain model, and consider the case of non-stationary movements. We propose a method to estimate the transition rates of the link connectivity model. The stability of the link is evaluated based on the transition rates. The prediction scheme is derived analytically and requires no prior information about parameters of the mobility model. Simulation results show that the proposed scheme can provide correct prediction in both stationary and non-stationary scenarios.Keywords-link stability; link connectivity; mobile ad hoc network; analytical model I.

Ad hoc networks do not depend on any predefined infrastructure or centralized administration to operate. Their security characters require more complex security preventions. As the second line of defense, Intrusion detection is the necessary means of getting the high survivability. In this paper the security characters of ad hoc networks and the related contents of intrusion detection are discussed. Mobile Agent and Multi-layer Integrated Distributed Intrusion Detection Model (MAMIDIDM) and a heuristic global detection algorithm are proposed tentatively by combining the mobile agent technology with the multi-layer conception. This heuristic global detection algorithm combines the mobile agent detection engine with the multi-layer detection engines and analyzes the results obtained by the corresponding detection engines. MAMIDIDM has the better flexibility and extensibility, can execute the intrusion detection in clustering ad hoc networks effectively.

Terahertz (THz) frequency band has been widely used in indoor, outdoor and space communications due to its advantage of large available bandwidth. However, limited research has been conducted to apply THz technique in maritime communications as hostile sea conditions cause significant path loss, thus leading to unacceptable signal error rate. In this paper, we propose a novel adaptive THz maritime communication system to tackle the above-mentioned challenge. Specifically, we design a joint source-channel coding scheme by using system random linear network coding (sRLNC) and Reed-Solomon (RS) to ensure transmission reliability. To further improve the transmission efficiency, we propose a novel triple-channel communication architecture facilitated by a very high frequency (VHF) feedback channel. With this design, the source data can be transmitted via the THz main channel while the coding redundancy is dispatched in the auxiliary channel. Meanwhile, the feedback channel allows sender to use an adaptive mechanism to achieve the transmission efficiency with higher transmission rate over long communication distance. In addition, we adopt the Doppler frequency offset in maritime environment to compensate both relative movement between communication parties and adversarial maritime factors, e.g., strong wind and extreme sea states. Simulation results demonstrate that our proposed THz system has remarkable capability not only to improve the communication efficiency up to 20Gbps compared to those conventional high frequency (HF), VHF and millimeter wave communication systems but also to transmit data over a longer distance with lower BERs.

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