Energy limitation is an adverse problem in designing routing protocols for underwater sensor networks (UWSNs). To prolong the network lifetime with limited battery power, an energy balanced and efficient routing protocol, called energy balanced and lifetime extended routing protocol (EBLE), is proposed in this paper. The proposed EBLE not only balances traffic loads according to the residual energy, but also optimizes data transmissions by selecting low-cost paths. Two phases are operated in the EBLE data transmission process: (1) candidate forwarding set selection phase and (2) data transmission phase. In candidate forwarding set selection phase, nodes update candidate forwarding nodes by broadcasting the position and residual energy level information. The cost value of available nodes is calculated and stored in each sensor node. Then in data transmission phase, high residual energy and relatively low-cost paths are selected based on the cost function and residual energy level information. We also introduce detailed analysis of optimal energy consumption in UWSNs. Numerical simulation results on a variety of node distributions and data load distributions prove that EBLE outperforms other routing protocols (BTM, BEAR and direct transmission) in terms of network lifetime and energy efficiency.

Underwater wireless sensor networks (UWSNs) have attracted increasing attention in recent years because of their numerous applications in ocean monitoring, resource discovery and tactical surveillance. However, the design of reliable and efficient transmission and routing protocols is a challenge due to the low acoustic propagation speed and complex channel environment in UWSNs. In this paper, we propose a novel cross-layer routing protocol based on network coding (NCRP) for UWSNs, which utilizes network coding and cross-layer design to greedily forward data packets to sink nodes efficiently. The proposed NCRP takes full advantages of multicast transmission and decode packets jointly with encoded packets received from multiple potential nodes in the entire network. The transmission power is optimized in our design to extend the life cycle of the network. Moreover, we design a real-time routing maintenance protocol to update the route when detecting inefficient relay nodes. Substantial simulations in underwater environment by Network Simulator 3 (NS-3) show that NCRP significantly improves the network performance in terms of energy consumption, end-to-end delay and packet delivery ratio compared with other routing protocols for UWSNs.

Underwater Acoustic Sensor Networks (UASNs) have attracted increasing interest in recent years due to their extensive commercial and military applications. However, the harsh underwater channel causes many challenges for the design of reliable underwater data transport protocol. In this paper, we propose an energy efficient data transport protocol based on network coding and hybrid automatic repeat request (NCHARQ) to ensure reliability, efficiency and availability in UASNs. Moreover, an adaptive window length estimation algorithm is designed to optimize the throughput and energy consumption tradeoff. The algorithm can adaptively change the code rate and can be insensitive to the environment change. Extensive simulations and analysis show that NCHARQ significantly reduces energy consumption with short end-to-end delay.

This paper addresses the security issues for a spatial modulation system. Here, a multi-antenna transmitter equipped with a single radio frequency (RF) chain attempts to communicate secretly with a legitimate receiver, and the secret messages are modulated into the index of an active transmit antenna and a baseband symbol. Multiple RF mirrors are placed near the transmit antennas to facilitate the secure transmission. Particularly, in each transmission, one symbol duration is equally divided into multiple sub-symbol periods. During each sub-symbol period, a specific RF mirrors activation pattern are determined, and the sub-symbol is sent along with the weighted interfering signals. The weighting coefficients of the intentionally interfering signals are properly designed to defend against eavesdropping by severely degrading the wiretap channel. The proposed secure SM scheme has two main advantages. First, the dimensionality for jamming is significantly enhanced by deploying multiple RF mirrors at the transmitter. This would on one hand improve the secrecy performance, and on the other hand guarantee the proposed scheme to be immune and resilient to eavesdroppers with a large number of antennas. Second, the usage of RF mirrors and sub-symbol division approach provides massive degrees of freedom to preprocess the modulated symbol for further secrecy performance improvement. Numerical results show that the proposed secure SM scheme significantly outperforms the benchmark techniques in secrecy rate.