K.-K. Chi’s scientific contributions

In Radio Frequency Powered Wireless Sensor Network(RFP-WSN), improving network energy efficiency and throughput is an important topic. A data collection scheme with high energy-efficiency and high throughput is proposed in this paper, which integrates channel allocation, energy threshold and MAC(Medium Access Control) frame block-level retransmission mechanism. In addition, the charging time of nodes, the average energy consumption and the average delay for transmitting a MAC frame, and the energy efficiency and throughput of the network are derived. The network utility function is defined, and the optimization problem(OP) of maximizing network utility is formed. By adjusting the utility coefficient and solving the OP, the optimal energy threshold and the optimal number of blocks per MAC frame can be obtained to maximize the energy efficiency and throughput. The simulation results show that the energy efficiency and throughput of the proposed scheme are higher than that of existing schemes.

With the breakthrough in the technology of wireless power transmission, wireless-powered body sensor nodes are able to harvest radio frequency (RF) energy from RF-based chargers and thus operate continuously. Rational planning of the number and positions of the chargers is an effective way to improve the charging efficiency and save deployment budget. Previous studies on RF-based charger placement mainly consider the scenario that nodes are static, or convert to the static scenario using probability statistical model. With the background of mobile body area network, this paper considers the situation that users carrying sensor nodes have specific sojourn-move behavior patterns. Based on this behavior model, charger placement optimization problem is formulated with the constraint of node's non-outage probability. Both greedy and divide-and-conquer based particle swarm optimization (D&C-PSO) approaches are proposed to solve the problem. Finally, performances of the two proposed algorithms are evaluated and compared with existing path provisioning approach through various simulations. Simulation results show that the divide-and-conquer based particle swarm optimization outperforms both greedy and path provisioning approaches in the charger placement cost while it guarantees the node's non-outage probability. © Copyright 2017, Institute of Software, the Chinese Academy of Sciences. All rights reserved.

The nodes in Wireless Sensor Networks (WSNs) are usually powered by battery. It is extremely important to let the nodes deliver data to the destination in an energy-efficient manner such that the WSNs have longer runtime. In this paper, the Energy-efficient Reliable Opportunistic Routing (EROR) is presented. The EROR uses the forwarding cost, which takes into account node's residual energy and the total energy consumption expended by the nodes over a wireless link; chooses the forwarding set consisting of forwarding nodes (FNs), the main FN, and the assistant FNs; and allows a node to change its transmission power to transmit the encoded packets, which are generated by randomly linear network coding, to the forwarding set such that the data are delivered to the destination in a multi-hop, reliable, and energy-efficient way. Simulation results indicate that the EROR outperforms the existing CodePower routing in terms of network lifetime and energy consumption.

Wireless Sensor Network (WSN) usually adopts the low-power and low-rate IEEE 802.15.4 standard in its Medium Access Control (MAC) and Physical (PHY) layers. In the WSN, the nodes are powered by battery with very limited energy and wireless links are prone to losing packet. Moreover, in some WSN applications, it is required that the collected data are delivered to the sink node within a given time. Hence, it is extremely significant to develop an energy-efficient, low-delay, and reliable data gathering scheme for WSN applications. In this paper, Reed-Solomon (RS) code is applied to improve the reliability of packet delivery. It aims to form an Optimization Problem (OP) that integrates with energy consumption, Data Gathering Ratio (DGR), data gathering delay, and coding schemes. The set that contains the Simple Reed-Solomon (S-RS) codes is presented, and it is proved that any n members of the set are linearly independent. The data gathering scheme, called the S-RS data gathering scheme, which applies the S-RS codes, intra-segment coding, and inter-segment coding, is described in detail. In addition, based on probability theory, the Overall Energy Consumption (OEC), the DGR, and the data gathering delay under the S-RS scheme are derived, which are used to build the OP that minimizes the OEC with the constraints of DGR and data gathering delay. The number of the feasible solutions of the OP is small such that it can be easily solved using enumeration method. Through solving the OP, the nodes are able to find the optimal values of the parameters for packet encoding and packet retransmissions such that energy consumption in the S-RS scheme is minimized while the constraints of DGR and data gathering ratio are met. Numeric analysis and simulation results show that the S-RS scheme achieves a higher DGR and a lower delay with lower energy consumption. Moreover, the derived OEC, DGR, and data gathering delay can be used in optimizing the parameters by using the S-RS scheme so as to maximize the DGR, minimize the data gathering delay, or optimize two or three of the OEC, DGR, and data gathering delay.

6LoWPAN protocol supports IPv6 datagram delivering over IEEE 802.15.4-based low-power wireless personal area network, and its main functions include fragmenting and reassembling IPv6 datagrams, header compression, and routing. In this paper, the number of transmissions, the delay and the throughput of multi-path routing for delivering an IPv6 datagram to the destination from the source are derived based on probability theory. Moreover, the model that optimizes the throughput of multi-path routing is developed, and based on this model the optimal fragmentation scheme is proposed. The proposed scheme is able to improve the throughput of IPv6 datagrams in 6LoWPAN.