Routing for Wireless Multi-Hop Networks: Distinguishing Features

Routing within wireless mobile multi-hop networks is a challenging task. Therefore, in the past several routing protocols have been developed with various extensions and adoptions to certain specific scenarios. The consensus of the discussion about routing is that depending on all aspects of their application reaching from number of nodes, mobility, to the data traffic profile of the application developers can choose an optimal routing protocol. In the meantime some routing protocols have evolved as standard choice like AODV, DSR, OLSR, TBRPF. With the advent of sensor networks, requirements like scalability and resource consumption are added to the research domain. This resulted in additional extremely specialized routing algorithms or special extensions to existing protocols. So is there really a need and room for another routing protocol? We are convinced that a really simple, efficient, scalable protocol that allows for mobility and is suited for various performance classes of devices does not exist. We propose GRAPE as a completely new approach for routing in wireless multi-hop networks and present performance results based on simulations and measurements that demonstrate the potential of the routing approach.

A general framework for efficient geographic routing in wireless networks

We consider the problem of quality of service (QoS) routing in multi-hop wireless networks where data are transmitted from a source node to a destination node via multiple hops. The routing component of a QoS-routing algorithm essentially involves the link and path metric calculation which depends on many factors such as the physical and link layer designs of the underlying wireless network, transmission errors due to channel fading and interference, etc. The task of link metric calculation basically requires us to solve a tandem queueing problem which is the focus of this paper. We present a unified tandem queue framework which is applicable for many different physical layer designs. We present both exact and approximated decomposition approaches. Using the queueing framework, we can derive different performance measures, namely, end-to-end loss rate, end-to-end average delay, and end-to-end delay distribution. The proposed decomposition approach is validated and some interesting insights into the system performance are highlighted. We then present how to use the decomposition queueing approach to calculate the link metric and incorporate this into the route discovery process of the QoS routing algorithm. The extension of the queueing and QoS routing framework to wireless networks with class-based queueing for QoS differentiation is also presented.

We have developed a cost-effective wireless multi-hop network system for accessing core networks. Cost-effectiveness can be provided to users by offering them a wireless multi-hop network in which a wireless link enables multiple hops between access points (APs) and reduces the number of APs connected to a wired network. The key issues of wireless multi-hop networks are routing and security. We proposed a hybrid routing for wireless multi-hop networks that combines on-demand and table-driven routing, a packet check scheme between APs, and an authentication scheme. To ensure both correct routing and security, the system makes use of a wireless multi-hop (WM) layer between the IP and medium access control (MAC) layers. This paper evaluates the system based on its FTP throughput, round-trip time, and route creation time. The FTP throughput was about 3.5 Mbps even when there were four hops in an 802.11b wireless LAN. We believe that our wireless multi-hop network system is useful for providing cost-effective broadband access service.

Nodes in a multi-hop wireless network rely on each other to maintain network connectivity. A primary design objective of these networks is to eliminate or minimize the unavailability of network at some point. However, the movement of nodes creates service disruption and delay as path failure detection and re-establishment consume considerable amount of time. Existing solutions for link classification and prediction operate on discrete values resulting in performance degradation. This problem can best be modelled using fuzzy logic. This work presents a new fuzzy logic based link status classification mechanism for the use with multipath routing protocols in multi-hop wireless networks. The new Enhanced Adhoc On-demand Multipath Distance Vector (eAOMDV) uses fuzzy logic to classify the link status as active, about-to-break or broken. On the basis of fuzzy input parameters RSSI, velocity, distance and bit error rate, the fuzzy based classification mechanism predicts in advance that a particular link, on the active path between the sender and receiver, is about-to-break and helps the reactive multipath routing protocol to start the rerouting operation, thus minimizing the service disruption time, route discovery frequency, end-to-end delay and the packet loss.

Wireless ad hoc networks rely on exchanging information among the nodes to find a feasible route between source and destination. Routing protocols require periodically flooding the entire system with the updated state of the network. Routing protocols define the rules and semantics of how this information is spread throughout the network and can be classified into proactive and reactive protocols, both of which eventually sends out control packets to the network. However, with the increase of the scale of the network, the amount of packets exchanged uses resources that could be otherwise used for application messages. In this paper, we explore the use of machine learning techniques to restrict the flooding radius of control packets. We define the problem objective as a regression problem and use neural networks to model it. The model can be used in networks that share similar attributes, suggesting that transfer learning can be used to re-purpose the initial model. The results show that using machine learning reduces the amount of resources used to maintain the network state up to date, which could be subsequently used to improve the overall performance of the networked system. We anticipate machine learning to be the starting point for more sophisticated models of cross-layer routing mechanisms.

Routing in multihop wireless networks is challenging, mainly due to unreliable wireless links/channels. Geographic opportunistic routing (GOR) was proposed to cope with the unreliable transmissions by exploiting the broadcast nature of the wireless medium and the spatial diversity of the network topology. Previous studies on GOR have focused on networks with a single channel rate. The capability of supporting multiple channel rates, which is common in current wireless systems, has not carefully been studied for GOR. In this paper, we carry out a study on the impacts of multiple rates, as well as candidate selection, prioritization, and coordination, on the performance of GOR. We propose a new local metric, i.e., the opportunistic effective one-hop throughput (OEOT), to characterize the tradeoff between one-hop packet advancement and packet forwarding time. We further propose a local rate adaptation and candidate-selection algorithm to approach the optimum of this metric. The simulation results show that the multirate GOR (MGOR) incorporating the rate adaptation and candidate-selection algorithm achieves higher throughput and lower delay than the corresponding single-rate and multirate traditional geographic routing and single-rate opportunistic routing protocols.

In this paper, we design grid-based routing (GBR) protocols for wireless multi-hop networks. The objective is to effectively reduce the protocol overhead for network management with the assistance of position information. GBR divides networks into equally spaced grids. To perform a routing operation, GBR requires as few grids as possible to participate while preserving network connectivity. We design different protocols for different environments and deduce analytical results to observe the high performance of the designed protocols.

In this paper, we introduce the stable path topology control problem for link-state routing in mobile multi-hop networks. We formulate the topology control problem of selective link-state broadcast as a graph pruning problem with restricted local neighborhood information. We develop a multi-agent optimization framework where the decision policies of each agent are restricted to local policies on incident edges and independent of the policies of other agents. We show that under a condition called the positivity condition, these independent local policies preserve the stable routing paths globally. We then provide an efficient algorithm, which we call the Stable Path Topology Control algorithm, to compute this local policy that yields a pruned graph. Using simulations, we demonstrate that this algorithm, when used with the popular ETX metric, outperforms topology control mechanisms commonly used for Mobile Ad Hoc Networks.

This paper examines the question, whether iterative routing based on Dijkstra's algorithm is a suitable routing algorithm for the operation of cellular multi-hop or mesh network scenarios with gateway access to some backbone network. For that purpose, the general performance of different routing metrics is examined. Various load scenarios are generated in order to illustrate load-balancing effects and stability issues, as permanent re-routing may also lead to oscillations, where traffic is shifted back-and-forth between alternative paths. Therefore, different methods to stabilize the network are presented additionally. It turns out that the omission of the impact of a flow's own traffic on its routing metrics manages to prevent these oscillations efficiently

The definition of new radio network topologies and deployment concepts capable of providing a ubiquitous radio coverage area for beyond 3G systems is one of the main objectives of the WINNER project [1]. Within this context, routing and forwarding algorithms for infrastructure-based multi-hop networks are investigated. We first present a new mathematical model of the routing problem in infrastructure-based multi-hop wireless networks that takes into account QoS requirements considering bandwidth constraints. Since the characteristics of such new networks allow to control the path selection of each flow, we then propose a new routing algorithm based on a heuristic. Finally, to show the performance of the proposed algorithm several simulation results are presented.

Recent research has shown that interference can make a significant impact on the performance of multihop wireless networks. Researchers have studied interference-aware topology control recently [M. Burkhart et al., 2004]. In this paper, we study routing problems in a multihop wireless network using directional antennas with dynamic traffic. We present new definitions of link and path interference that are suitable for designing better routing algorithms. We then formulate and optimally solve two power constrained minimum interference single path routing problems. Routing along paths found by our interference-aware algorithms tends to have less channel collisions and higher network throughput. Our simulation results show that, compared with the minimum power path routing algorithm, our algorithms can reduce average path interference by 40% or more at the cost of a minor power increase. We also extend our work towards survivable routing by formulating and solving the power constrained minimum interference node-disjoint path routing problem.

Network coding is a technology with great potentiality in improving wireless multi-hop network throughput. And some routings combined with network coding have been proposed for wireless multi-hop network. In the routings combined with network coding, network coding condition is used to find network coding opportunities, which is very important to the performance improving of routings combined with network coding. However, the network coding conditions defined by existing routings combined with network coding unilaterally focus on the growth of network coding opportunities, which results in the increasing of cost and delay in routing discovery. Moreover, the more flows participating network coding, the higher probability of decoding failure, which degrade the network coding gain. In this paper, low complexity network coding condition (LCNC) is proposed. LCNC only detects two-flows network coding opportunity, and ensures the destination make successful decoding. In addition, the actual network coding gain is designed through analysis of link quality. Network coding opportunity will be ignored in case the actual network coding gain is negative. Based on LCNC, a low complexity network coding aware routing (LNCR) is designed aiming wireless multi-hop network. Simulation results demonstrate that LNCR obtain a balance between network coding gain and routing discovery cost, and can obtain higher network throughput when the network load is high compared with the classical network coding aware routings.

The authors introduce the idea of multiple protocols and illustrate its validity by considering the problem of routing in multihop radio networks. A continuing, simulation-based performance evaluation at Naval Research Laboratory's (NRL) Distributed Simulation and Prototyping facility shows that overall network performance improves significantly when multiple protocols are switched in response to changing environmental conditions rather than using a single routing protocol. Dynamic conditions illustrated in the simulations are implemented as changes in topological connectivity. Important new issues that arise when multiple protocols are employed are identified for further research.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multi-hop wireless networks have advantages over the single-hop ones in terms of reliability and coverage range. Moreover, the capacity of multi-hop wireless network can be substantially increased via multiple radios tuned to non-overlapping channels. However, the channel allocation, network interface cards assignment and routing selecting remain challenging due to the interference of the neighboring transmissions. These three problems have proved to be a NP-hard problem. Previous studies separating the routing selecting from the channel allocation, instead of considering the three problems as a whole, cannot get the overall optimal solution. In this work, we employ an improved Multi-Objective Genetic Algorithm to optimize the channel allocation, interface assignment and the routing selection, so as to minimize the overall network interference. The proposed algorithm includes two parts: 1) dynamic genetic mutation based on diversity measure; and 2) elite preservation based on ideal points. In order to eliminate the impact of illegal solutions, a new individual encoding method is proposed. In addition, an interference model taking into account the effects of channel separation and the traffic of neighbor links is applied to evaluate the quality of the interference of the network. Finally, a fitness function is defined to obtain the best search results. Simulation results show that our improved Multi-Objective Genetic Algorithm can reduce the interference and cost of total network compared to the standard Genetic Algorithm.