To solve the problems of synchronization error accumulation and unbalanced energy consumption in multi-hop wireless sensor networks (WSN), this paper proposes a high-precise and energy-balanced time synchronization algorithm based on hierarchy clustering topology. First, based on the analysis of the source of multi-hop error, cluster heads between adjacent layers adopt pairwise broadcast mechanism to reduce send time and use Bayesian theory to improve synchronization precision. Then, cluster members synchronize to the cluster head by the combination of bidirectional pair-wise synchronization and reference broadcast synchronization to reduce overhead, while a replier is selected according to residual energy to balance nodes’ energy consumption. The simulation results reveal that the proposed algorithm performs better on the aspect of synchronization precision and power consumption compared with traditional algorithms.

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The error performance of APSK signals in additive white Gaussian noise channel are analyzed in this letter. A closed-form expression for symbol error rate (SER) of 16APSK signal is derived in polar coordinates, which can be approximated by the weighted sum of the SER of the inner and the outer rings. Based on this observation, the expressions of SER for 32APSK and 64APSK signals are given. It is shown that the proposed approximated SER expressions are very close to the simulation results. It is much simpler than the results based on union bound and can be extended to high-order APSK signals directly.

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Conventional methods using precoding in MIMO transmission generally need channel state information (CSI) at the transmitter. In this paper we consider a method where precoding weights are temporally varied. The method does not require the transmitter to obtain CSI. By combining the method with FEC and a block interleaver, it outperforms the existing MIMO transmission schemes without precoding. We evaluate the performance of the proposed system by computer simulations and clarify the effectiveness of the system quantitatively. Since the method does not require CSI at the transmitter, it is particularly effective where MIMO transmission is applied to broadcast-type wireless communication systems.

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In this paper, we propose an optimization model for solving the channel assignment problem in multi-cell WLANs which is based on maximizing the minimum distance between access points that operate on the same channel. The formulation of the proposed model is presented in the form of a mixed integer linear program (MILP). The main advantage of the proposed algorithm is that it guarantees non-overlapping channel assignment without measurement overhead. The proposed algorithm can be implemented in real time. Simulation results show that the proposed algorithm provides better performance compared to the pick-first greedy and the single channel assignment methods.

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This paper presents a comparison of measured and theoretically predicted results of ground-wave propagation characteristics over a land-sea mixed path at a medium frequency (MF) band. One of the techniques employed here is the theory provided by Rotheram, and the other is the empirical formula for mixed-path problems developed by Millington. The results show that the theoretically predicted and experimental results are in good agreement.

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