Unmanned aerial vehicles (UAVs) have enormous potential in the public and civil domains. These are particularly useful in applications, where human lives would otherwise be endangered. Multi-UAV systems can collaboratively complete missions more efficiently and economically as compared to single UAV systems. However, there are many issues to be resolved before effective use of UAVs can be made to provide stable and reliable context-specific networks. Much of the work carried out in the areas of mobile ad hoc networks (MANETs), and vehicular ad hoc networks (VANETs) does not address the unique characteristics of the UAV networks. UAV networks may vary from slow dynamic to dynamic and have intermittent links and fluid topology. While it is believed that ad hoc mesh network would be most suitable for UAV networks yet the architecture of multi-UAV networks has been an understudied area. Software defined networking (SDN) could facilitate flexible deployment and management of new services and help reduce cost, increase security and availability in networks. Routing demands of UAV networks go beyond the needs of MANETS and VANETS. Protocols are required that would adapt to high mobility, dynamic topology, intermittent links, power constraints, and changing link quality. UAVs may fail and the network may get partitioned making delay and disruption tolerance an important design consideration. Limited life of the node and dynamicity of the network lead to the requirement of seamless handovers, where researchers are looking at the work done in the areas of MANETs and VANETs, but the jury is still out. As energy supply on UAVs is limited, protocols in various layers should contribute toward greening of the network. This paper surveys the work done toward all of these outstanding issues, relating to this new class of networks, so as to spur further research in these areas.

Survey of Important Issues in UAV Communication Networks

This paper presents Glossy, a novel flooding architecture for wireless sensor networks. Glossy exploits constructive interference of IEEE 802.15.4 symbols for fast network flooding and implicit time synchronization. We derive a timing requirement to make concurrent transmissions of the same packet interfere constructively, allowing a receiver to decode the packet even in the absence of capture effects. To satisfy this requirement, our design temporally decouples flooding from other network activities. We analyze Glossy using a mixture of statistical and worst-case models, and evaluate it through experiments under controlled settings and on three wireless sensor testbeds. Our results show that Glossy floods packets within a few milliseconds and achieves an average time synchronization error below one microsecond. In most cases, a node receives the flooding packet with a probability higher than 99.99 %, while having its radio turned on for only a few milliseconds during a flood. Moreover, unlike existing flooding schemes, Glossy's performance exhibits no noticeable dependency on node density, which facilitates its application in diverse real-world settings.

https://homepages.dcc.ufmg.br/~mmvieira/cc/papers/ferrari11glossy.pdf

Efficient network flooding and time synchronization with Glossy

The chapter provides a survey of routing protocols in vehicular ad hoc networks. The routing protocols fall into two major categories of topology-based and position-based routing. The chapter discusses the advantages and disadvantages of these routing protocols, explores the motivation behind their design and trace the evolution of these routing protocols. Finally, it concludes the chapter by pointing out some open issues and possible direction of future research related to VANET routing. INTRODUCTION With the sharp increase of vehicles on roads in the recent years, driving has not stopped from being more challenging and dangerous. Roads are saturated, safety distance and reasonable speeds are hardly respected, and drivers often lack enough attention. Without a clear signal of improvement in the near future, leading car manufacturers decided to jointly work with national government agencies to develop solutions aimed at helping drivers on the roads by anticipating hazardous events or avoiding bad traffic areas. One of the outcomes has been a novel type of wireless access called Wireless Access for Vehicular Environment (WAVE) dedicated to vehicle-to-vehicle and vehicle-to-roadside communications. While the major objective has clearly been to improve the overall safety of vehicular traffic, promising traffic management solutions and on-board entertainment applications are also expected by the different bodies (C2CCC, VII, CALM) and projects (VICS (Yamada, 1996), CarTALK 2000 (Reichardt D, 2002), NOW, CarNet (Morris R, 2000), FleetNet (Franz, 2001)) involved in this field. When equipped with WAVE communication devices, cars and roadside units form a highly dynamic network called a Vehicular Ad Hoc Network (VANET), a special kind of Mobile AdHoc Networks (MANETs). While safety applications mostly need local broadcast connectivity, it is expected that some emerging scenarios (Lee, 2009) developed for intelligent transportation systems (ITS) would benefit from unicast communication over a multi-hop connectivity. Moreover, it is conceivable that applications that deliver contents and disseminate useful information can flourish with the support of multi-hop connectivity in VANETs. Although countless numbers of routing protocols (Mauve, 2001; Mehran, 2004) have been developed in MANETs, many do not apply well to VANETs. VANETs represent a particularly challenging class of MANETs. They are distributed, self-organizing communication networks formed by moving vehicles, and are thus characterized by very high node mobility and limited degrees of freedom in mobility patterns. As shown in Figure 1, there are two categories of routing protocols: topology-based and geographic routing. Topology-based routing uses the information about links that exist in the network to perform packet forwarding. Geographic routing uses neighboring location information to perform packet forwarding. Since link information changes in a regular basis, topology-based routing suffers from routing route breaks. Car 2 Car Communication Consortium, http://www.car‐to‐car.org The Vehicle Infrastructure Integration (VII) Initiative, http://www.vehicle‐infrastructure.org Continuous Air Interface for Long and Medium Interface (CALM), http://www.calm.hu Vehicle Information and Communication System Network On Wheels, www.network‐on‐wheels.de Figure 1: Taxonomy of Various Routing Protocols in VANET Despite many surveys already published on routing protocols in MANETs (Mauve, 2001; Mehran, 2004Giordano, 2003; Stojemnovic, 2004), a survey of newly developed routing protocols specific to VANETs has long been overdue. Li et al. (2007) have made an effort to introduce VANET routing protocols, yet there is still deficiency in a thorough and comprehensive treatment on this subject. A discussion of VANET topics and applications is incomplete without detailed coverage of relevant routing protocols and their impact on overall VANET architecture. In this book chapter, we seek to provide the missing building blocks by detailing the advances in VANET routing protocols. Section III describes the VANET architecture and its characteristics. Section IV presents a survey of these protocols experimented on or tailored to VANET and their advantages and disadvantages. It will explore the motivation behind their design and trace the evolution of these routing protocols. Finally, Section V will point out some open issues and possible direction of future research, and then conclude the book chapter.

Survey of Routing Protocols in Vehicular Ad Hoc Networks

Over the last decade, the paradigm of Wireless Mesh Networks (WMNs) has matured to a reasonably commonly understood one, and there has been extensive research on various areas related to WMNs such as design, deployment, protocols, performance, etc. The quantity of research being conducted in the area of wireless mesh design has dramatically increased in the past few years, due to increasing interest in this paradigm as its potential for the "last few miles", and the possibility of significant wireless services in metropolitan area networks. This recent work has focused increasingly on joint design problems, together with studies in designing specific aspects of the WMN such as routing, power control etc. in isolation. While excellent surveys and tutorials pertaining to WMNs exist in literature, the explosive growth of research in the area of specific design issues, and especially joint design, has left them behind. Our objective in this paper is to identify the fundamental WMN design problems of interference modeling, power control, topology control, link scheduling, and routing, and provide brief overviews, together with a survey of the recent research on these topics, with special stress on joint design methods. We believe this paper will fulfill an outstanding need in informing the interested student and researcher in getting familiar with this abundant recent research area, and starting research.

A Survey of Network Design Problems and Joint Design Approaches in Wireless Mesh Networks

Underwater mobile sensor networks have recently been proposed as a way to explore and observe the ocean, providing 4D (space and time) monitoring of underwater environments. We consider a specialized geographic routing problem called pressure routing that directs a packet to any sonobuoy on the surface based on depth information available from on-board pressure gauges. The main challenge of pressure routing in sparse underwater networks has been the efficient handling of 3D voids. In this respect, it was recently proven that the greedy stateless perimeter routing method, very popular in 2D networks, cannot be extended to void recovery in 3D networks. Available heuristics for 3D void recovery require expensive flooding. In this paper, we propose a Void-Aware Pressure Routing (VAPR) protocol that uses sequence number, hop count and depth information embedded in periodic beacons to set up next-hop direction and to build a directional trail to the closest sonobuoy. Using this trail, opportunistic directional forwarding can be efficiently performed even in the presence of voids. The contribution of this paper is twofold: a robust soft-state routing protocol that supports opportunistic directional forwarding; and a new framework to attain loop freedom in static and mobile underwater networks to guarantee packet delivery. Extensive simulation results show that VAPR outperforms existing solutions.

/pdf/vapr-void-aware-pressure-routing-for-underwater-sensor-xzms64rz0x.pdf

VAPR: Void-Aware Pressure Routing for Underwater Sensor Networks

We reconsider the problem of geographic routing in wireless ad hoc networks. We are interested in local, memoryless routing algorithms, i.e. each network node bases its routing decision solely on its local view of the network, nodes do not store any message state, and the message itself can only carry information about O(1) nodes. In geographic routing schemes, each network node is assumed to know the coordinates of itself and all adjacent nodes, and each message carries the coordinates of its target. Whereas many of the aspects of geographic routing have already been solved for 2D networks, little is known about higher-dimensional networks. It has been shown only recently that there is in fact no local memoryless routing algorithm for 3D networks that delivers messages deterministically. In this paper, we show that a cubic routing stretch constitutes a lower bound for any local memoryless routing algorithm, and propose and analyze several randomized geographic routing algorithms which work well for 3D network topologies. For unit ball graphs, we present a technique to locally capture the surface of holes in the network, which leads to 3D routing algorithms similar to the greedy-face-greedy approach for 2D networks.

Randomized 3D Geographic Routing

ALGO is a distributed location service to track the position of mobile nodes and to route messages between any two nodes. The lookup of nodes is achieved by searching in a hierarchy of pointers that each node maintains. We show that ALGO has constant stretch for lookup requests. In contrast to previous work, we consider a concurrent setup where nodes are truly mobile and move even while messages are being routed towards them. We prove correctness and efficiency of ALGO and determine the maximum speed at which the nodes might move, which is up to 1/15 of the routing speed. To the best of our knowledge, this is the first work that bounds the node speed, a necessity to prove the success of a lookup algorithm. We verified our theoretical results through extensive simulation and show that the average lookup stretch is around 6.

/pdf/mls-an-efficient-location-service-for-mobile-ad-hoc-networks-25avflk4ku.pdf

MLS: an efficient location service for mobile ad hoc networks

Greedy routing is a novel routing paradigm where messages are always forwarded to the neighbor that is closest to the destination. Our main result is a polynomial-time algorithm that embeds combinatorial unit disk graphs (CUDGs - a CUDG is a UDG without any geometric information) into O(log
 2
n)- dimensional space, permitting greedy routing with constant stretch. To the best of our knowledge, this is the first greedy embedding with stretch guarantees for this class of networks. Our main technical contribution involves extracting, in polynomial time, a constant number of isometric and balanced tree separators from a given CUDG. We do this by extending the celebrated Lipton-Tarjan separator theorem for planar graphs to CUDGs. Our techniques extend to other classes of graphs; for example, for general graphs, we obtain an O(log n)-stretch greedy embedding into O(log
 2
n)-dimensional space. The greedy embeddings constructed by our algorithm can also be viewed as a constant-stretch compact routing scheme in which each node is assigned an O(log
 3
n)-bit label. To the best of our knowledge, this result yields the best known stretch-space trade-off for compact routing on CUDGs. Extensive simulations on random wireless networks indicate that the average routing overhead is about 10%; only few routes have a stretch above 1.5.

/pdf/greedy-routing-with-bounded-stretch-5ejhhxfdxy.pdf

Greedy Routing with Bounded Stretch

We advocate a novel programming approach we call slotted programming that not only addresses the specific hardware capabilities of sensor nodes, but also facilitates coding through a truly modular design. The approach is based on the temporal decoupling of the different tasks of a sensor node such that at any time at most one task is active. In contrast to traditional sensor network programming, slotted programming guarantees that each of these tasks can be implemented as an independent software module, simplifying not only the coding and testing phase, but also the code reuse in a different context. In addition, we believe that the proposed approach is highly qualified for energy efficient and real time applications. To substantiate our claims, we have implemented slotos, an extension to TinyOS that supports slotted programming. Within this framework, we demonstrate the advantages of the slotted programming paradigm.

Slotted programming for sensor networks

This paper studies routing schemes and their distributed construction in limited wireless networks, such as sensor or mesh networks. We argue that the connectivity of such networks is well captured by a constant doubling metric and present a constant stretch multicast algorithm through which any network node u can send messages to an arbitrary receiver set U. In other words, we describe a distributed approximation algorithm which is only a constant factor off the NP-hard minimum Steiner tree on u cupU. As a building block for the multicasting, we construct a 1 + epsiv stretch labeled routing scheme with label size O(log ominus) and storage overhead O(1/epsiv)alpha(log ominus)(O(alpha) + log Delta), where ominus is the diameter of the network, Delta the maximum degree of any network node, and alpha a constant representing the doubling dimension of the network. In addition to unicast and multicast, we present a constant approximation for anycasting on the basis of radic(6)-approximate distance queries. We provide a distributed algorithm to construct the required labeling and routing tables.

Roland Flury

Papers

Randomized 3D Geographic Routing

MLS: an efficient location service for mobile ad hoc networks

Greedy Routing with Bounded Stretch

Slotted programming for sensor networks

Routing, Anycast, and Multicast for Mesh and Sensor Networks