Relaying in the Internet of Things (IoT): A Survey

The deployment of relays between Internet of Things (IoT) end devices and gateways can improve link quality. In cellular-based IoT, relays have the potential to reduce base station overload. The energy expended in single-hop long-range communication can be reduced if relays listen to transmissions of end devices and forward these observations to gateways. However, incorporating relays into IoT networks faces some challenges. IoT end devices are designed primarily for uplink communication of small-sized observations toward the network; hence, opportunistically using end devices as relays needs a redesign of both the medium access control (MAC) layer protocol of such end devices and possible addition of new communication interfaces. Additionally, the wake-up time of IoT end devices needs to be synchronized with that of the relays. For cellular-based IoT, the possibility of using infrastructure relays exists, and noncellular IoT networks can leverage the presence of mobile devices for relaying, for example, in remote healthcare. However, the latter presents problems of incentivizing relay participation and managing the mobility of relays. Furthermore, although relays can increase the lifetime of IoT networks, deploying relays implies the need for additional batteries to power them. This can erode the energy efficiency gain that relays offer. Therefore, designing relay-assisted IoT networks that provide acceptable trade-offs is key, and this goes beyond adding an extra transmit RF chain to a relay-enabled IoT end device. There has been increasing research interest in IoT relaying, as demonstrated in the available literature. Works that consider these issues are surveyed in this paper to provide insight into the state of the art, provide design insights for network designers and motivate future research directions

Efficient Routing Protocol in Delay Tolerant Networks (DTNs)

Modern Internet protocols demonstrate inefficient performance in those networks where the connectivity between end nodes has intermittent property due to dynamic topology or resource constraints. Network environments where the nodes are characterized by opportunistic connectivity are referred to as Delay Tolerant Networks (DTNs). Highly usable in numerous practical applications such as low-density mobile ad hoc networks, command/response military networks and wireless sensor networks, DTNs have been one of the growing topics of interest characterized by significant amount of research efforts invested in this area over the past decade. Routing is one of the major components significantly affecting the overall performance of DTN networks in terms of resource consumption, data delivery and latency. Over the past few years a number of routing protocols have been proposed. The focus of this thesis is on description, classification and comparison of these protocols. We discuss the state-of-the-art routing schemes and methods in opportunistic networks and classify them into two main deterministic and stochastic routing categories. The classification is based on forwarding decisions in routing methods adopted with or without the knowledge about the network topology and nodes trajectories. The protocols in each class have their own advantages and shortcomings. In the stochastic routing protocols category, simple flooding-based protocols are feasible approaches in those networks where there is a little or no information about the network topology and there is no resource restriction. Epidemic routing is a flooding- based protocol relying upon the distribution of messages through the networks to deliver information to their destinations. To demonstrate the performance of the epidemic routing protocol for information delivery in networks with intermittent connectivities, we provide several simulation experiments and show that this protocol with reasonable aggregate resource consumption, ensures eventual message delivery in networks, using minimal assumptions regarding nodes trajectories, network topology and connectivity of underlying networks and only based on sufficient number of random pair-wise exchanges of messages among mobile nodes. In the following, we introduce the recently proposed network coding concept and discuss coding-based information delivery advantages in wireless networks. Network coding is a recently introduced paradigm to efficiently disseminate data in wireless networks in which data flows coming from multiple sources are combined to increase throughput, reduce delay, and enhance robustness against node failures. Finally, we present some simulation experiments to show the superiority of network coding for information delivery in wireless networks, compared to pure flooding-based mechanisms. /Kir1

Network Coding For Star and Mesh Networks

This thesis introduces new network coding techniques to improve the file sharing and video streaming performance of wireless star and mesh networks. In this thesis we propose a new XOR based scheduling algorithm for network coding in cooperative local repair. The proposed algorithm commences in three phases. In the first phase, nodes exchange packets availability vectors. These vectors are functions of the probability of correct packet reception over the channel. This is followed by a short period of distributed scheduling where the nodes execute the processing algorithm which tries to minimize the total transmission time. In the third phase, nodes transmit the encoded packets as per the decision of the scheduling algorithm. Simulation results show improvement in system throughput and processing delay for the proposed algorithm. We also study the trade-offs between file sizes, processing delays, number of users and packet availability. In the sequel we display the favorable effects of file segmentation on the performance of the proposed scheduling algorithm. Furthermore, the upper bound on the performance and the analysis of the proposed scheduling algorithm are derived. Also, in this thesis, the effects of random network coding on code division multiple access/time division duplex (CDMA/TDD) platforms for wireless mesh networks are studied and evaluated. A multi-hop mesh network with single source and multiple receiving nodes is assumed. For reliable data transfer, a Selective Repeat ARQ protocol is used. Two scenarios are evaluated for their efficiency. In scenario 1, but not in scenario 2, random network coding is applied to CDMA/TDD wireless mesh networks. The delay and delay jitter for both scenarios are computed. The study also focuses on the effects of uncontrolled parameters such as the minimum number of neighbors and the network connectivity, and of controlled parameters such as Galois Field (GF) size, packet size, number of Walsh functions employed at each node and the Processing Gain. The analysis and simulation results show that applying random network coding to CDMA/TDD systems in wireless mesh networks could provide a noticeable improvement in overall efficiency. We also propose a cross layer approach for the Random Network coded-Code Division Multiple Access/Time Division Duplex (RNC-CDMA/TDD) wireless mesh networks. The proposed algorithm selects the number of assigned Walsh functions depending on the network topology. Two strategies of Walsh function assignments are proposed. In the first, nodes determine the number of their assigned Walsh functions depending on the neighbor with the maximum number of neighbors, which we call the worst case assignment. In the second, nodes determine the number of their assigned Walsh functions depending on the need for each transmission. Simulation results show the possible achievable improvement in the system performance, delay and delay jitter due to cross layer design

Instantly Decodable Network Coding: From Centralized to Device-to-Device Communications

From its introduction to its quindecennial, network coding has built a strong reputation for enhancing packet recovery and achieving maximum information flow in both wired and wireless networks. Traditional studies focused on optimizing the throughput of the system by proposing elaborate schemes able to reach the network capacity. With the shift toward distributed computing on mobile devices, performance and complexity become both critical factors that affect the efficiency of a coding strategy. Instantly decodable network coding presents itself as a new paradigm in network coding that trades off these two aspects. This paper review instantly decodable network coding schemes by identifying, categorizing, and evaluating various algorithms proposed in the literature. The first part of the manuscript investigates the conventional centralized systems, in which all decisions are carried out by a central unit, e.g., a base-station. In particular, two successful approaches known as the strict and generalized instantly decodable network are compared in terms of reliability, performance, complexity, and packet selection methodology. The second part considers the use of instantly decodable codes in a device-to-device communication network, in which devices speed up the recovery of the missing packets by exchanging network coded packets. Although the performance improvements are directly proportional to the computational complexity increases, numerous successful schemes from both the performance and complexity viewpoints are identified