One of the critical concerns in wireless sensor networks (WSNs) is the continuous maintenance of sensing coverage. Many particular applications, such as battlefield intrusion detection and object tracking, require a full-coverage at any time, which is typically resolved by adding redundant sensor nodes. With abundant energy, previous studies suggested that the network lifetime can be maximized while maintaining full coverage through organizing sensor nodes into a maximum number of disjoint sets and alternately turning them on. Since the power of sensor nodes is unevenly consumed over time, and early failure of sensor nodes leads to coverage loss, WSNs require dynamic coverage maintenance. Thus, the task of permanently sustaining full coverage is particularly formulated as a hybrid of disjoint set covers and dynamic-coverage-maintenance problems, and both have been proven to be nondeterministic polynomial-complete. In this paper, a hybrid memetic framework for coverage optimization (Hy-MFCO) is presented to cope with the hybrid problem using two major components: 1) a memetic algorithm (MA)-based scheduling strategy and 2) a heuristic recursive algorithm (HRA). First, the MA-based scheduling strategy adopts a dynamic chromosome structure to create disjoint sets, and then the HRA is utilized to compensate the loss of coverage by awaking some of the hibernated nodes in local regions when a disjoint set fails to maintain full coverage. The results obtained from real-world experiments using a WSN test-bed and computer simulations indicate that the proposed Hy-MFCO is able to maximize sensing coverage while achieving energy efficiency at the same time. Moreover, the results also show that the Hy-MFCO significantly outperforms the existing methods with respect to coverage preservation and energy efficiency.

Wireless real-time surveillance systems are very valuable for monitoring ecology of wildlife, since the in-situ situation could be grasped immediately. Power source is usually constrained in the wild areas. Thus, in this paper, we developed a low power-consumption image transmission system (called energy-efficient visual eyes system) by integrating a MSP430 micro controller, FPGA circuit, a solar powered battery, a digital camera, and a GPRS (General Packet Radio Service) modem. In order to make a monitoring system suitable for circumstances of wild islands, the proposed system is designed with a packet transmitting strategy capable of enhancing pixel validity while effectively decreasing power consumption. Practically, the proposed system is deployed on a wild island in Taiwan near East China Sea, where is a habitat for migrant seabirds. The experimental results show that the system design is feasible to ecological monitoring and able to effectively maintain the completeness of images with energy efficiency.

In this paper, we derive the minimum noncoherent distance of block-coded 16QAM, and propose noncoherent block-coded 16QAM (NBC-16QAM) accordingly. Various noncoherent block coding schemes are compared via computer simulations. We find that for both NBC-16QAM and the noncoherent 16QAM scheme proposed in 2002, the curves of bit error rates do not decade exponentially. When the block length is very small, NBC-16QAM performs worse due to its small minimum noncoherent distance. However, if the block is not short, NBC-16QAM has the best error performance because the codewords with small noncoherent distances are rare.

In this paper, we derive minimum noncoherent distances of block-coded TAPSK (twisted amplitude and phase shift keying) and 16QAM (quadrature-amplitude modulation), both using linear component codes. According to the derived distances, noncoherent block-coded TAPSK (NBC-TAPSK) and noncoherent block-coded 16QAM (NBC-16QAM) are proposed. If the block length is very small, NBC-16TAPSK performs best among all noncoherent schemes and NBC-16QAM performs worse due to its small minimum noncoherent distance. However, if the block is not short, NBC-16QAM has the best error performance because the codewords with small noncoherent distances are rare.