Wireless multi-hop networks

B. Multi-Streaming Rate Control The issue of multi-streaming rate control is still an open problem and has received considerable attention recently. A mathematical framework of multi-user rate allocation is presented in [17], where the authors also analyzed two classes of distributed solutions, corresponding to the primal and dual decomposition of the optimization objective. In wireless networks, adaptive transmission techniques are typically used to protect the video stream against the time-varying channel [18]. When multiple streams are involved, centralized channel time allocation among multiple wireless stations has been investigated in [19]. Distributed algorithms have also been proposed, using rate-distortion optimized packet scheduling in [20] for rate allocation among streams sharing a bottleneck link. What’s more, rate allocation algorithm combined with a packet partitioning algorithm has been proposed to support video streaming from multiple sources to a receiver over the Internet [21]. The rates are chosen to adapt the available network bandwidth for each stream, and the packet partitioning is designed to minimize the start up delay. For video streaming over a wireless multihop networks, a rate control scheme has been proved to efficiently utilize the available wireless link capacity [22].

Thus, many works have been lead in order to optimize broadcast in wireless multi-hop networks but, as far as we know, none has tried to use structures already built over such networks. 3.2 Hierarchical organization Some studies have proposed to organize networks into clusters to introduce a hierarchical routing, in order to allow scalability in wireless multi-hop networks. Indeed, over large scale, flat routing proto- cols (reactive or proactive) become ineffective because of bandwidth (flooding of control messages) and processing overhead (routing table computation). Introducing a hierarchy by grouping geo- graphically close nodes into clusters and by using an "hybrid" routing scheme: classically proactive approach inside each cluster and reactive approach between clusters ([7, 15]) can solve this scala- bility problem. Such an organization also presents numerous advantages as to synchronize stations in a group or to attribute new service zones more easily. As far as we know, none of these struc- tures have been studied for other purposes. All these clustering algorithms aim to identify subsets of nodes within the network and most of them bind each of these subsets to an unique leader to identify the clusters. In this case, all nodes having the same leader belong to the same cluster. Generally, nodes locally elect their cluster-head in a distributed way by using a metric to decide. This metric can be either an identity criteria (e.g. the lowest identity [3]), a connectivity criteria (as maximum

Providing real-time multimedia applications over wireless multi-hop networks is a challenging problem because the wireless channels are highly sensitive to delay, interference and topology change. Multiple description coding (MDC), as a new emerging error-resilient technique, has been widely used recently in wireless video transmission. Its fundamental principle is to generate multiple correlated descriptions such that each description approximates the source information with a certain level of fidelity. Inevitably, MDC introduces many description streams which may influence each other and thus, reasonable system scheduling is needed to provide a satisfied video quality. The novelty of this work is to investigate the optimal distributed scheduling for multiple competing MDC streams in a resource- limited wireless multi-hop network. This is achieved by joint optimization of MDC, rate control and multipath routing. Two joint optimal algorithms, namely a distributed rate control and routing (DRCR) and a simplified DRCR algorithm, are proposed to solve this problem with constraints that arise from the multiple description streams among multiple users via multiple paths. Both algorithms are designed in a distributed manner that is amenable to on-line implementation for wireless networks. Theoretical analysis and simulation results are provided which demonstrate the effectiveness of our proposed joint schemes.

This thesis starts investigating the given research area by providing a description of key challenges that need to be addressed while designing a MAC protocol for wireless ad hoc and sensor networks. The thesis presents, then, a review on the masterpiece works achieved to address the defined challenges. We show that the standardization efforts of IEEE 802.11 still perform poorly in multi-hop environment and highly loaded networks. On the other hand, our work focus on alternative solutions to carrier sensing, mainly Time Division Multiple Access based ones. We show that TDMA wireless multi-hop networks still perform poorly because of the inflexibility of their frame size design. On the other hand, this drift between the achieved performance and the optimal ones can be justified by the dilemma of frame size dimensioning: an over-dimensioned frame size with respect to the number of users in the network infers an underutilization of the available resources; while an under-dimensioned frame size yields to a famine risk. Achieving an optimal frame size, in this context, is NP complete. For instance, [11] shows that an optimal TDMA schedule is equivalent to a k-hop coloring problem which is NP hard. We investigate then, a distributed and dynamic solution to provide a solution that tends to the optimum. In particular, we highlight the limited scientific research efforts that have addressed a dynamic frame size concept for wireless ad hoc and sensor networks. We argue that a dynamic frame size coupled with an appropriate distributed slot allocation scheme can drastically increase the overall system performance. More precisely, the thesis contributes to the research problem by developing a new frame size increase technique that achieves four main objectives:

end delay, network reliability, TSCH I. I NTRODUCTION Wireless multi-hop networks (i.e., sensor and mesh net- works) will be increasingly employed in safety-related indus- trial systems, such as factory automation, industrial surveil- lance and monitoring of nuclear plants, due to their appealing ease of deployment and scalability. In order to ensure safety, time evolution of such systems is constrained by strict dead- lines and requires a high degree of reliability in communica- tion. For wireless networks to be deployed in such systems, deterministic wireless communications have to be guaranteed.

Index Terms— multi-radio multi-channel multi-hop; wireless networks; distributed scheduling; video; QoS. I. I NTRODUCTION T HE problem of video scheduling over multi-channel multi-radio multi-hop networks is, compared to tradi- tional data communications in wireless multi-hop networks, further complicated by the heterogeneity in both the network conditions and the application contents, including i) channel- assignment: what are the set of channels that each link should be operated on? ii) rate allocation: how to allocate the appropriate rate to the given channels and links? and iii) routing: how to select the potential channels that minimize total video distortion? These three problems are interact with each other, and thus form a challenging cross-layer control problem across the MAC layer and the application layer. For ease of exposition, in the rest of the paper whenever there is no source of confusion, we will use of the term “scheduling” to refer to the combined action of channel assignment, rate allocation and routing.

Recently, many scheduling schemes have been proposed for video streaming over wireless multi-hop networks ( [11] and [12] provide a good overview). We summarize our contributions and the differences between our work and previous related works in the following. • We provide a novel distributed video scheduling scheme in the context of multi- channel multi-radio multi-hop wireless networks. The support for multi-user video streams in this network requires appropriate joint channel assignment, rate control and multi-path routing measure, ascertaining the reasonable routes for transmitting each stream and the rate of the video to be delivered over the chosen routes. Different from previous works on video scheduling in single-channel multi-hop wireless networks [9], [11], [13] in which channel assignment is not a concern, we consider the scheduling problem in the newly emerged networks and propose an efficient assignment algorithm. Moreover, unlike conventional works that consider routing for data traffic over wireless networks [6], [8], [9], we take into account the specific video characteristics in the routing and rate control scheme. Network congestion is considered in the channel assignment, rate allocation and routing metric, to meet the stringent delay requirement for video transmission. In addition, each video’s rate-distortion characteristic is also incorporated in the joint routing and rate control procedure to provide multiple streams with various video contents. To the best of our knowledge, this work is the first one to consider the video scheduling problem in the newly multi-channel networks.

Michalis Faloutsos Abstract In this paper, we propose a new integrated framework for joint routing and rate adaptation in multi- rate multi-hop wireless networks. Unlike many previous efforts, our framework considers several factors that affect end-to-end performance. Among these factors, the frame- work takes into account the effect of the relative positions of the links on a path when choosing the rates of operation and the importance of avoiding congested areas. The key element of our framework is a new comprehensive path metric that we call ETM (for expected transmission cost in multi-rate wireless networks). We analytically derive the ETM metric. We show that the ETM metric can be used to determine the best end-to-end path with a greedy routing approach. We also show that the metric can be used to dynamically select the best transmission rate for each link on the path via a dynamic programming approach. We implement the ETM-framework on an indoor wireless mesh network and compare its performance with that of

I. I NTRODUCTION In wireless networks, the communication channels are shared among the terminals. Thus, one of the major problems faced is the reduction of capacity due to interferences caused by simultaneous transmissions [1]. In this work, we call a round a collection of links that can be simultaneously activated in the network. We address the problem called Round Weight- ing Problem (RWP) [2] that consider joint routing and schedul- ing. We present a cross-layer formulation of the problem. We have to find a minimum-length schedule of selected links in a TDMA (Time Division Multiple Access) based wireless network. As we deal with multi-hop networks, these selected links represent a routing solution (paths) providing enough capacity to achieve the routers requirements of bandwidth. Scheduling methods such TDMA can guarantee achieving higher capacities by allowing time slots to be shared by simultaneous transmissions.

Michalis Faloutsos Abstract In this paper, we propose a new integrated framework for joint routing and rate adaptation in multi- rate multi-hop wireless networks. Unlike many previous efforts, our framework considers several factors that affect end-to-end performance. Among these factors, the frame- work takes into account the effect of the relative positions of the links on a path when choosing the rates of operation and the importance of avoiding congested areas. The key element of our framework is a new comprehensive path metric that we call ETM (for expected transmission cost in multi-rate wireless networks). We analytically derive the ETM metric. We show that the ETM metric can be used to determine the best end-to-end path with a greedy routing approach. We also show that the metric can be used to dynamically select the best transmission rate for each link on the path via a dynamic programming approach. We implement the ETM-framework on an indoor wireless mesh network and compare its performance with that of

[11] Xun Chen, Peng Han, Qiu-Sheng He, Shi liang Tu, and Zhang long Chen. A Multi-Channel MAC Protocol for Wireless Sensor Networks. In CIT. IEEE, 2006. [12] M.D. Jovanovic and G.L. Djordjevic. TFMAC: Multi-channel MAC Protocol for Wireless Sensor Networks. In TELSIKS. IEEE, sept. 2007. [13] Youngmin Kim, Hyojeong Shin, and Hojung Cha. Y-MAC: An Energy- Efficient Multi-channel MAC Protocol for Dense Wireless Sensor Net- works. In IPSN, pages 53–63. IEEE/ACM, 2008.

Email: {firstname.lastname}@imag.fr, {firstname.lastname}@st.com Abstract—Sustainable power management techniques in en- ergy harvesting wireless sensors currently adapt the consumption of sensors to their harvesting rate within the limits of their battery residual energy, but regardless of the traffic profile. To provide a fairer distribution of the energy according to applica- tion needs, we propose a new sustainable traffic aware duty-cycle adaptation scheme (STADA) that takes into account the traffic load in addition to previous factors. We evaluate our protocol in the specific context of multi-hop IEEE 802.15.4 beacon-enabled wireless sensor networks powered by solar energy. Simulations show that our solution outperforms traffic-unaware adaptation schemes while minimizing the variance of the quality of service provided to applications.

User cooperation has evolved as a popular coding technique in wireless relay networks (WRNs). Using the neighboring nodes as relays to establish a communication between a source and a destination achieves an increase of the diversity order. The relay nodes can be seen as a distributed multi-antenna system, which can be exploited for transmit diversity by using distributed space–time block coding (STBC). In this paper, we investigate the bit error rate (BER) of multi-hop WRNs employing distributed STBC at the relay nodes. We develop the general model of WRNs using distributed STBC, and we derive the pairwise error probability and an approximation of the BER. We examine the impact of several parameters, such as distributed STBC at the relays, the number of relays, the distances between the nodes, and the channel state information available at the receivers, on the BER performance of the multi-hop WRN. The obtained results provide guidelines about the expected error performance and the design of channel estimation for these networks. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract In this paper, we address the rate control, the medium access control (MAC) and the routing problem for cooperative multi-hop wireless networks (MHWN) in the framework of the utility function maxi- mization. Compared to its counterpart in traditional wireless network, control method in the cooperative wireless network is much more complex, which is due to the constraints arising from the cooperation among the users and the contention for the wireless channel access. At first, we construct a general mathematics model for the cooperative MHWN. And then, we develop a cross-layer solution which consists of the link capacity detection by adjusting persistence probability at the MAC layer, the flow rate control by achieving the maximal utility at the transport layer and the optimal routing at the network layer. This proposal is designed in distributed manner in order to support a simple and efficient implementation for MHWN. Finally, fairness issue for the cooperative network is presented to improve the practical performance of the proposed solution. The simulation results show the effectiveness of the proposed solution for the cooperative network.

† CNRS, University of Strasbourg, UMR 7005, France Email: {oliveira,duda}@imag.fr, theoleyre@unistra.fr Abstract—We can improve the performance of wireless mesh networks by using multiple interfaces tuned to non-overlapping channels. A Channel and Interface Assignment (CIA) decides when to switch interfaces and which channel to use. Surprisingly, the impact of CIAs on connectivity has received little attention so far. In this paper, we present a comparison and performance evaluation of the existing CIA strategies addressing the connectiv- ity issues: network topology, density of connections, and neighbor discovery. The results presented in this paper provide guidelines for network designers in planning multi-channel multi-interface network deployments.

architectures, the seamless migration of services under a multi-operator environ- ment yields not only technical but also other types of challenges. Generally, roaming occurs when a subscriber of one wireless provider uses the facilities of another service provider. Moreover, roaming can be classified in horizontal roaming when switching network operators and vertical roaming when switching wireless access technologies. The combination of horizontal and ver- tical handover in a converged wireless world yields a new form of roaming: the heterogeneous multi-operator roaming. This type of roaming occurs when a mobile user switches not only network operator but also access network, as depicted by Figure 3.17. Heterogeneous multi-operator roaming poses several challenges for network operators and service providers, some of them can be solved by tech- nical means but some others require redefining business models, new wireless regulations, standardization and most important the adaptation of applications to the new wireless world. Traditionally, terminal mobility is controlled from the core network of the cellular network however it must also be locally managed by the UWN once the user roam in. Current inter-working architectures rely on the assumption that both wireless access networks are controlled by the same operator, or in the best case scenario, both network operators have established roaming agreements. However, in the absence of such agreements the presence of NAT (Network Address Translation) and firewall rules cause problems to Internet telephony and slow down the deployment of transparent heterogeneous wireless access solutions. In this respect, we have identified two major potential preven- ters of service mobility in this scenario, these are: network access and seamless service mobility.

When cooperation decision is made, the sharing partners have to agree on several aspects such as: how much of the network should be shared, how to share costs for investment and use of the network, how to make decision for network expansion, etc. Thus, a sharing agreement must be settled between different competitors in order to manage radio resources in such multi-operator, multi-access, wireless networks. In [14], authors describe the business models for shared networks, based on fragmented wireless access and service market. Two examples are presented, the first includes Mobile Network Operators (MNOs) that offer wide area wireless access to specialized service providers, and the second includes Local Service and Access Providers (LSAPs), interactingwith service providers and mobile operators via Inter-Connection Provider (ICP). In such a fragmented market, an LSAP may also provide services via other LSAPs or MNOs networks, and MNOs can also lease capacity from LSAPS, thus a cooperative environment can be envisaged. Moreover, authors propose that network selection is performed by either the service provider or an ICP to preserve competition and reduce transaction costs. This ICP will also maintain the Service Level Agreement between radio access providers and service providers. The concept of a third trusty party is adopted also in [5] for inter-operators joint resource management. Inter-operators agreements for network selection decision and users’ transaction cost are maintained and guaranteed by a meta-operator acting as a trading agent between cooperating operators.

We analyze the performance of CSMA in multi-channel wireless networks, accounting for the random nature of traffic. Specifically, we assess the ability of CSMA to fully utilize the radio resources and in turn to stabilize the network in a dynamic setting with flow arrivals and departures. We prove that CSMA is optimal in ad-hoc mode but not in infrastructure mode, when all data flows originate from or are destined to some access points, due to the inherent bias of CSMA against downlink traffic. We propose a slight modification of CSMA, that we refer to as flow-aware CSMA, which corrects this bias and makes the algorithm optimal in all cases. The analysis is based on some time-scale separation assumption which is proved valid in the limit of large flow sizes.

6.1 Thesis Contributions This thesis has investigated radio access selection and pricing in multi-operator sharing networks. Our work is in the context of heterogeneous wireless networks, where various RATs covering the same region and managed by dierent operators are being integrated in a shared RAN. One of the main motivations behind RAN sharing is to reduce the total cost of network deployment and management and increase revenues. Another motivation is to reduce the network deployment period and accelerate the rollout of new technology, in order to handle the rapid growth of mobile broadband demand. A inter-operators sharing agreement must address radio access selection process, devoted to decide which operator to connect to. Access selection decision is a key for common radio resource management in a multi-operator networks. It serves to improve network performance and user satisfaction. Moreover, a sharing agreement includes nancial conciliation for the service cost between partners, which represents the cooperation fees between them. Furthermore, the inter-operator agreement determines how to share resource, and the adopted access mode. Indeed, determining the amount of shared resources with partners aects the operators' benets from cooperation and allows to maintain own network performance.

Received: 12 June 2014; in revised form: 25 August 2014 / Accepted: 26 August 2014 / Published: 3 September 2014 Abstract: Designing secure authentication mechanisms in wireless sensor networks in order to associate a node to a secure network is not an easy task due to the limitations of this type of networks. In this paper, we propose different multi-hop node authentication protocols for wireless sensor networks. For each protocol, we provide a formal proof to verify the security of our proposals using Scyther, which is an automatic cryptographic protocols verification tool. We also provide implementation results in terms of execution time consumption obtained by real measurements on TelosB motes. These protocols offer different security mechanisms depending on the design of the protocol itself. Moreover, we evaluate the overhead of protection of each solution by studying the effect on execution time overhead of each protocol. Finally, we propose a mechanism to detect possible attack based on our evaluation results.