Papers by Keyword: Opportunistic Networks

Abstract: Opportunistic networks are similar to the mobile ad hoc networks (MANETs) that does not have fixed infrastructure, and the messages can be transmitted by nodes in a "store - carry - forward" approach. The mobile nodes randomly move, which result in a constantly changed network topology and frequently interrupted link. Thus, multipath routing has been proposed to improve the stability of link, extend path lifetime and reduce packet loss rate. The paper first analyzes the traditional multipath routing protocol and its path selection theory, and then investigates quality of service (QoS) metric to improve transmission efficiency of opportunistic networks, and finally proposes a reliable node based on multipath QoS routing protocol, named as RNMR. In RNMR, the stable path contains primary path and two backup paths. The primary path consists of reliable nodes and intermediate nodes, and the two backup paths are formed by two disjoint sub-paths selected from two adjacent and reliable nodes. By comparing with the backup source routing (BSR) protocol and greed-based routing (GBR-WB) protocol, the paper proves RNMR protocol has longer path lifetime, deliver rate and relay are also improved.

Abstract: In Opportunistic networks, mobile nodes communicate with each other through store-carry-and-forward manner by use of short message transmission technologies such as Bluetooth or WiFi. Message delivery relies mainly on cooperation among nodes. The incentive mechanism which aims to stimulate cooperation and prevent self-ish behavior is important. Reputation-based mechanism is one of the most popular motivations to tackle this problem. This paper surveys the recent reputation-based incentive mechanisms in Opportunistic Networks.

Abstract: To address the problems in Opportunistic Networks that nodes employing routing algorithms based on epidemic mechanism cant sense their neighboring nodes timely and many redundant data packets permeate through the network, an efficient routing algorithm based on XOR network coding was proposed (Xor Network Coding based Epidemic Routing, XNCER). When a node gets a Hello message, it broadcasts, instead of unicasting, a SV(Summary Vector) packet, in return, to all its neighboring nodes. Therefore, the data transmission can be initiated immediately, and the XOR network coding can also be leveraged so as to enhance the efficiency of data transmission. Moreover, the packets destined to the one hop neighboring nodes obtain the priority in transmission, and are determined whether to be deleted based on the ACK mechanism running in the MAC layer in order to cut down the memory overhead and restrain redundant packets from dissemination. Theoretical analysis and extensive simulation results show that the new algorithm obtains an overall improvement in terms of network overhead, average end-to-end delay as well as delivery rate. The novel algorithm can effectively solve the problems of sensing neighboring nodes and data redundancy.

Abstract: Opportunistic Networks (ONs) are the newly emerging type of Delay Tolerant Network (DTN) systems that opportunistically exploit unpredicted contacts among nodes to share information. As with all DTN environments ONs experience frequent and large delays, and an end-to-end path may only exist for a brief and unpredictable time. In this paper, we employ optimal theory to propose a novel buffer management strategy named Optimal Buffer Scheduling Policy (OBSP) to optimize the sequence of message forwarding and message discarding. In OBSP, global optimization considering delivery ratio, transmission delay, and overhead is adopted to improve the overall performance of routing algorithms. The simulation results show that the OBSP is much better than the existing ones.

Abstract: In order to resolve the problem of data packets losing abruptly in opportunistic networks, a fault-tolerant transfer algorithm based on interweaving code is proposed. The algorithm includes two parts: one is used by nodes sending data and another is used by receiving nodes to recover lost data. When the packets are sent, interweaving idea is used to disperse the packets. When the packets are received, interpolation method is used to recover the sequence of lost packets based on the strong autocorrelation of transferred packet. Then, interpolation method is used to recover lost data.