Concerning the coverage overlapping areas and blind spots caused by random deployment of nodes in three-dimensional directional heterogeneous network, a Particle Swarm Optimization (PSO) based coverage optimization algorithm for three-dimensional directional heterogeneous network, namely PSOTDH, was proposed. Through involving the concepts of three-dimensional overlapping centroid, three-dimensional effective centroid and three-dimensional boundary centroid, three-dimensional overlapping area, and three-dimensional boundary nodes were optimized in a new three-dimensional directed perception model by using PSO. The sensing directions of the nodes were changed by PSOTDH, which made the distribution of three-dimensional overlapping centroids, three-dimensional effective centroids and three-dimensional boundary centroids more uniform, and achieved the purpose of improving coverage. Simulation results show that the proposed algorithm can improve coverage rate by about 27.82% after 25 iterations, which means the proposed algorithm can improve the coverage rate quickly and effectively.

According to the IEEE 802.15.4 slotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) algorithm, a network analysis model using analysis method of two-dimensional Markov chain was proposed. Not only the sleep mode of IEEE 802.15.4 agreement but also the condition where the backoff window reached the maximum value before the Number of Backoff (NB) were especially considered in the model. On this basis, combined with M/G/1/K queuing theory, the throughput expression was derived, and the packet arrival rate effect on the throughput was analyzed under unsaturated network. Using the simulation platform Network Simulator Version2 (NS2), the experimental results show that the theoretical analysis fits well with the simulation result, and the network throughput is described accurately. Then the effectiveness of the analytical model is validated.

Concerning the impact on network performance of the mobile nodes and the constantly changing data transmission rate, the authors proposed a new backoff scheme for IEEE802.15.4, which used Probability Judgment based on Network Load and Exponentially Weighted Moving Average (PJNL_EWMA) method. According to a realtime monitoring of current network status by probability judgment of network load, this method dynamically adjusted backoff exponent by EWMA when Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) began. Compared with the IEEE802.15.4 standard protocol and MBS (Memorized Backoff Scheme)+EWMA algorithm, the simulation experiments on NS2 platform show that the PJNL_EWMA algorithm not only improves the throughput of the network, but also reduces the packet loss rate and the collision ratio, significantly improving the network performance.