The routing scheme is one of the key factors which influence the lifetime of Wireless Sensor Network (WSN). The network can be paralyzed easily as a result of large energy consumption of key nodes by heavy communication. To solve the problem of energy consumption of key nodes in WSNs, a new ant colony routing algorithm on Dynamic Adjustment of Forward Angle based on Residual Energy (DAFARE) was proposed. Firstly, the nodes chose the next-hop node according to residual energy and distance in the range of initial forward angle; secondly, the forward angle was adjusted dynamically in the view of residual energy of nodes within the scope of forward angle; finally, early death of key nodes was avoided successfully. The simulation suggested that the effective life could be improved approximately 50% by DAFARE, compared with ant colony optimization algorithm based on Function of Multi-object Evaluation and Positive-Negative Feedback (FMEPNF). The experimental results show that, the network energy consumption of DAFARE can be balanced effectively, the lifetime is prolonged, and the coverage of WSN is guaranteed.

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.