| With the development of Internet of Things (IoT) and Ubiquitous Network, the centralized controlling access mode is unable to satisfy the requirements of "Internet of Everything". Wireless multi-hop networks (WMN) become an important bridge to establish the connection between thing and thing, between thing and human and between human and human due to the distributed controlling, flexibility and scalability. It would be widely used in various fields.Since the birth of WMN, routing, as the key technique of networking, has attracted a great deal of attention from researchers. However, due to the unique features of WMN such as instability and asymmetry in the wireless link, interference and competition among the neighbors, dynamic changes in the networks topology and the restriction in the memory, computing and bandwidth, routing design becomes a big challenge. The research on more reliable and efficient routing for practical application is still the key issue and difficulty for future research.This paper presents a systematic and comprehensive survey of the existing routings. According to the sound survey, the focuses of routing research can be categorized into two fundamental scientific issues: reliability and efficiency. What’s more, we investigate these two issues in some typical routings deeply. To achieve reliable transmission, Opportunistic routing (OR) determines the transmission path by exploiting the inherent broadcast nature in wireless channels instead of pre-defining path in traditional routings. It could be integrated well with the traditional routings such as On-demand routing, Table-driven routing and so on. Owing to the spatial diversity among the forwarding candidates, OR could cope well with the unreliable and varying link that are typical in wireless networks.As for the issue of transmission efficiency, improving the spectral efficacy and saving power are the focuses of researchers. Considering the development of multi-channel technology in existing systems(i.e.,3 orthogonal channels are supported in 802.11b/g and 12 orthogonal channels are supported in 802.11a) and the maturity and low cost in implementing the multi-interfaces, designing low power and multi-channel routings in WMN is one of the simplest and most practical ways to improve the transmission efficiency.After investigating the reliability and efficiency, we move our focus to the evolution of WMN. Considering the shortage in the IP assignment, mobility and security, it is very necessary to combine the architecture of future Internet and WMN for future study.Meanwhile, with the explosive application of IoT in various industries, the number of smart terminals would become huge. Various communication manners and the different ability in the memory and computing are brought accordingly. Hence, the future WMN would become a heterogeneous network. The feature would become more obvious in Delay tolerant Network such as social network. Moreover, it is very prospective to integrate the research of the future Information-Centric Internet and the research of Heterogeneous Delay Tolerant Network.The main work and contribution of this paper are illustrated as follows:We investigate the transmission reliability by following the principle of from simple to complex and from easy to difficult. We start with theory modeling and performance analyzing for ORs in simple scenarios based on the discrete time queue theory. The contributions are summarized as follows.1) A new mathematical distribution named generalized geometric distribution (GGD) is proposed to model the forwarding feature of OR in wireless multi-hop networks.2) A new methodology for analyzing the OR’s mean end-to-end delay is presented. With the knowledge of priority rule and delivery probability, the forwarding probability could be calculated based on GGD. Afterwards, the generating function of the queue length distribution could be derived. According to the property of the multivariate generating function, closed form expressions of MED (Mean End-to-end Delay) are obtained. These analysis results could be applied to arbitrary directly connected networks and some special non-directly connected networks.3) An approximate analysis is also developed for the general cases in the non-directly connected networks. The rationale behind the proposed approximation is that for approximating the behavior of a node, it might suffice to consider the behavior of a substitute node which has a similar communication environment like that of the analyzed node. The behavior of a node in the complexity scene can be approximated as the behaviors of substitute nodes in several simple scenes.For the more complicated scenarios, this paper addresses the general issues existing in ORs such as long back-off time, acknowledgement failure, and duplicate transmission by proposing a new scheme called dual priority cooperative opportunistic routing (DPCOR). The followings summarize the main contributions.1) An analytical model based on open queuing network with Markov chains is proposed. Since more duplicate transmissions lead to longer queue delay and ineffective back-off mechanism causes larger back-off time for transmission, modeling the time overhead in this proposed model can reveal the root reason of duplicate transmission and collision effectively. When deriving the closed expression of time overhead, the multidimensional Markov chains could be divided into several independent one-dimensional Markov chains.2) A new scheme called DPCOR was proposed. The global priority is determined according to the hop counts to the destination, which is used to guarantee the broadcast data packet has been acknowledged successfully. The local priority is determined based on the quality of the link and the adjacent relation between the candidates, which is used to decide whether to forward the received data packet and when to forward it. The dual priority enables the network to classify forwarding candidates more effectively so as to reduce the back-off time and obtain more diversity gain.For the study of transmission efficiency, small world theory is employed to study the multi-channel technology. The main contributions are as follows.1) Model the mean number of links in network. By deriving the distribution of distance between two independent nodes randomly distributed in a one-dimensional line and two-dimensional rectangular area, the closed expression including the number of nodes, transmission range and other network parameters are obtained.2) By abstracting the channel switch problem to how to build appropriate shortcuts in small world theory, the exact relationship between rewiring probability and network parameters are obtained. Specifically, the whole network is divided into low-level part and high-level part. The traditional single channel network falls in to the low-level part and the nodes working on double channels form the relatively sparse high-level network. The communication between high-level nodes is similar to building shortcuts in small world.3) By replacing the global network parameters with the information from neighbor nodes, the global problems could be converted into a local problem which is easy to be solved. Based on relationship between the optimal switching probability and network parameters such as degree of nodes, communication range and so on, a distributed channel switching algorithm is proposed. The proposed algorithm achieves power saving purpose without the network performance degradation.In the aspect of the evolution direction in WMN, the main contributions are:1) The history, key technologies and main characteristics for the Information-Centric network architecture are summarized. The necessity of importing the Information-Centric technology in to WMN is validated from three aspects:addresses assignment, mobility and security.2) The research status of Information-Centric WMN is surveyed in this part. Furthermore, the process of message distribution in non-IP network is elaborated on the basis of two typical routings.3) The network with the characteristics of un-center, delay tolerant, multi-hop, content-centric and heterogeneous are selected as the basic scenario for the future study of WMN. Three typical forwarding strategies are analyzed by applying the Susceptibles-Infectives-Recovered model. The closed expressions for the number of infectious nodes, cumulative distribution function of packet delivery delay are derived. From the numerical results and analysis, the impact of transmission range and information number on the network performance is revealed.
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