An Algorithm for Global Multi-Resolution Terrain Simulation Based on the Method of Hash Table

During the simulation of global multi-resolution terrain environment, we need to build a multi-resolution terrain data cache pool and use a certain indexing mechanism. Based on the scheme of global data delamination and division by terrain data pyramid model structure, this paper presented a hash indexing algorithm adapted to terrain data block cache, and discussed the keyword design method and the collision solution method. Finally, some experiments on the key questions of hash technique including collision ratio and time cost are carried out.

An Improved Backoff Scheme for the IEEE 802.15.4 MAC Protocol

To solve the impact on network performance by the mobile nodes and data transfer rate constantly changing,this paper proposes a improved backoff scheme for IEEE802.15.4, which uses Probability Judgement based on Network Load and Exponentially Weighted Moving Average (PJNL_EWMA). According to a real-time monitoring of current network status by probability judgement of network load , this method dynamically adjust backoff exponent by EWMA when the CSMA/CA begins. Compared the IEEE802.15.4 and MBS+EWMA schemes, the simulation experiments on NS2 platform show that the PJNL_EWMA scheme not only improves the throughput of the network, but also reduces the packet loss rate and the collision ratio,significantly improve the network performance.

Efficient Beacon Collision Detection/Avoidance Mechanism in WLAN-Based Mesh Networks

Every node in wireless multi-hop mesh networks periodically transmits its own beacon and then monitors the existence or activity of other nodes by checking their beacons. So, the loss of beacon message in wireless multi-hop mesh networks causes the inefficient network overhead. This paper proposed a dynamic beacon collision detection and avoidance (BCDA) mechanism that can actively adapt to beacon collision status due to node movement. Each node checks the collision status by comparing the received beacon timing information from neighboring nodes with that of its own. It is shown from the performance evaluations that the proposed BCDA mechanism provides the decrease of beacon collision ratio and the throughput enhancement.