Hybrid Wireless Networks Research Articles

On the Capacity of Hybrid Wireless Networks with Opportunistic Routing

This paper studies the capacity of hybrid wireless networks with opportunistic routing (OR). We first extend the opportunistic routing algorithm to exploit high-speed data transmissions in infrastructure network through base stations. We then develop linear programming models to calculate the end-to-end throughput bounds from multiple source nodes to single as well as multiple destination nodes. The developed models are applied to study several hybrid wireless network examples. Through case studies, we investigate several factors that have significant impacts on the hybrid wireless network capacity under opportunistic routing, such as node transmission range, density and distribution pattern of base stations (BTs), and number of wireless channels on wireless nodes and base stations. Our numerical results demonstrate that opportunistic routing could achieve much higher throughput on both ad hoc and hybrid networks than traditional unicast routing (UR). Moreover, opportunistic routing can efficiently utilize base stations and achieve significantly higher throughput gains in hybrid wireless networks than in pure ad hoc networks especially with multiple-channel base stations.

Throughput and Delay in Cooperative Wireless Networks With Partial Infrastructure

Hybrid wireless networks have been shown to scale only when the number of base stations m is on the same order of the number of nodes n in the network. Pure wireless ad hoc networks with multiple-input-multiple-output (MIMO) distributed communications have also been shown to scale. A natural question arises: Do hybrid wireless networks always scale no matter how many base stations are placed if MIMO distributed communications are used? In this paper, we address this question and show that hybrid wireless networks cannot always scale with the proposed resource-allocation strategy. Specifically, they can only scale either when m = Theta(1) and all resources are exclusively allocated to ad hoc mode transmissions or when m = Theta(n), and all resources are exclusively allocated to infrastructure mode transmissions; moreover, the delay is significantly large in the first case, whereas it is Theta(1) in the second case, where Theta(f(n)) means on the order of f(n) when n is large.

JANUS: A Framework for Scalable and Secure Routing in Hybrid Wireless Networks

Hybrid networks consisting of cellular and Wi-Fi networks were proposed as a high-throughput architecture for cellular services. In such networks, devices equipped with cellular and Wi-Fi network cards access Internet services through the cellular base station. The Wi-Fi interface is used to provide a better service to clients that are far away from the base station, via multihop ad hoc paths. The modified trust model of hybrid networks generates a set of new security challenges as clients rely on intermediate nodes to participate effectively in the resource reservation process and data forwarding. In this paper, we introduce JANUS, a framework for scalable, secure, and efficient routing for hybrid cellular and Wi-Fi networks. JANUS uses a scalable routing algorithm with multiple channel access, for improved network throughput. In addition, it provides protection against selfish nodes through a secure crediting protocol and protection against malicious nodes through secure route establishment and data forwarding mechanisms. We evaluate JANUS experimentally and show that its performance is 85 percent of the optimum algorithm, improving with a factor greater than 50 percent over previous work. We evaluate the security overhead of JANUS against two types of attacks: less aggressive, but sufficient for some applications, selfish attacks and purely malicious attacks.

Scalability and Performance Evaluation of Hierarchical Hybrid Wireless Networks

This paper considers the problem of scaling ad hoc wireless networks now being applied to urban mesh and sensor network scenarios. Previous results have shown that the inherent scaling problems of a multihop ldquoflatrdquo ad hoc wireless network can be improved by a ldquohybrid networkrdquo with an appropriate proportion of radio nodes with wired network connections. In this work, we generalize the system model to a hierarchical hybrid wireless network with three tiers of radio nodes: low-power end-user mobile nodes (MNs) at the lowest tier, higher power radio forwarding nodes (FNs) that support multihop routing at intermediate level, and wired access points (APs) at the highest level. Scalability properties of the proposed three-tier hierarchical hybrid wireless network are analyzed, leading to an identification of the proportion of FNs and APs as well as transmission range required for linear increase in end-user throughput. In particular, it is shown analytically that in a three-tier hierarchical network with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nA</i> APs, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nF</i> FNs, and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nM</i> MNs, the low-tier capacity increases linearly with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nF</i> , and the high-tier capacity increases linearly with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nA</i> when <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nA</i> = Omega(radic{ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nF</i> }) and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> = O( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nF</i> ). This analytical result is validated via <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ns</i> -2 simulations for an example dense network scenario, and the model is used to study scaling behavior and performance as a function of key parameters such as AP and FN node densities for different traffic patterns and bandwidth allocation at each tier of the network.

Utilizing detours for energy conservation in mobile wireless networks

Autonomous robotic systems have been gaining the attention of research community in mobile ad hoc network since the past few years. While motion cost and communications cost constitute the primary energy consumers, each of them is investigated independently. By taking into account the power consumption of both entities, the overall energy efficiency of a system can be further improved. In this paper, the energy optimization problem of radio communication and motion is examined. We consider a hybrid wireless network in two scenarios: first, a single autonomous mobile node communicating with multiple static relays through single hop, and secondly, a single mobile node communicating with a static base station via a mobile relay. The mobile node interacts with the relays within its vicinity by continuously transmitting high-bandwidth data, e.g. triggered by a multimedia application like video surveillance. The goal is to find the best paths such that the energy consumption for both mobility and communications is minimized for all mobile nodes. We introduce Radio-Energy-Aware (REA) path computation strategy by utilizing node mobility. Given the starting point, the target point and the position of the relays, our simulation results show that the proposed strategy improves the energy efficiency of mobile node compared to Motion-Energy-Aware (MEA) path constructed based only on the mobility cost.

Capacity and delay of hybrid wireless broadband access networks

An optical network is too costly to act as a broadband access network. On the other hand, a pure wireless ad hoc network with n nodes and total bandwidth of W bits per second cannot provide satisfactory broadband services since the pernode throughput diminishes as the number of users goes large. In this paper, we propose a hybrid wireless network, which is an integrated wireless and optical network, as the broadband access network. Specifically, we assume a hybrid wireless network consisting of n randomly distributed normal nodes, and m regularly placed base stations connected via an optical network. A source node transmits to its destination only with the help of normal nodes, i.e., in the ad hoc mode, if the destination can be reached within L (L /spl geq/ 1) hops from the source. Otherwise, the transmission will be carried out in the infrastructure mode, i.e., with the help of base stations. Two transmission modes share the same bandwidth of W bits/sec. We first study the throughput capacity of such a hybrid wireless network, and observe that the throughput capacity greatly depends on the maximum hop count L and the number of base stations m. We show that the throughput capacity of a hybrid wireless network can scale linearly with n only if m = Omega(n), and when we assign all the bandwidth to the infrastructure mode traffics. We then investigate the delay in hybrid wireless networks. We find that the average packet delay can be maintained as low as Theta(1) even when the per-node throughput capacity is Theta(W).

Multiagent Based Information Dissemination in Vehicular Ad Hoc Networks

Vehicular Ad hoc Networks (VANETs) are a compelling application of ad hoc networks, because of the potential to access specific context information (e.g. traffic conditions, service updates, route planning) and deliver multimedia services (Voice over IP, in-car entertainment, instant messaging, etc.). This paper proposes an agent based information dissemination model for VANETs. A two-tier agent architecture is employed comprising of the following: 1) 'lightweight', network-facing, mobile agents; 2) 'heavyweight', application-facing, norm-aware agents. The limitations of VANETs lead us to consider a hybrid wireless network architecture that includes Wireless LAN/Cellular and ad hoc networking for analyzing the proposed model. The proposed model provides flexibility, adaptability and maintainability for traffic information dissemination in VANETs as well as supports robust and agile network management. The proposed model has been simulated in various network scenarios to evaluate the effectiveness of the approach.

Trust-Assisted Handover Approach in Hybrid Wireless Networks

In Next-Generation (NG) hybrid wireless networks, Mobile-Controlled Handover (MCHO) is expected to be employed as the handover control mechanism, in contrast to Network-Controlled Handover (NCHO) used in homogeneous wireless networks. As more independent network operators get involved in providing Internet access, roaming mobile users would have to deal with complex trust relationships between heterogeneous network domains. The state-of-the-art handover approaches just take into account Quality of Service (QoS), but ignore the complexities arising from the coexistence of multiple network operators in the NG networks. The existence of a complex trust relationship between networks may lead to unnecessary handover attempts in service roaming. In this regard, this paper introduces a novel approach of dynamically retrieving network trust information, and using it in MCHO. We show how network trust information can be utilised to obtain a 35% reduction in handover delay, meanwhile retain QoS in a handover. The proposed scheme does not need bulk storage in mobile handsets, and can react to changes to network topology and trust relationships dynamically. Analytical results are provided to demonstrate how roaming mobile users make more intelligent and reliable handover if implementing the proposed handover approach in a multi-operator and multi-technology environment.

Key Exchange Protocol Supporting Mobility and Multihoming

In this work, a new key exchange protocol for IP-based mobile networks is introduced. This protocol is called KEPSOM (Key Exchange Protocol Supporting Mobility and Multihoming). The goals of designing KEPSOM are to develop key exchange protocol proposal characterized by its secrecy, simplicity, efficiency, resistivity, and its ability to support mobility and multihoming. The protocol requires only two roundtrips. The design limits the private information revealed by the initiator. An old security association (SA) can be replaced with a new one by rekeying without the need of restarting the protocol with a new session. On the other hand, the changes in IP address due to mobility or multihoming need not restart the protocol with a new SA session. The proposed protocol can also support key exchange in hybrid wireless networks, in which the mobile node can operate in both Ad Hoc and Base Station-oriented wireless network environments using different transmission modes. KEPSOM has been analyzed and proven secure. Several tests have been done to measure and evaluate the performance of the protocol. In these tests, it is found that the required time for rekeying is about 27% of the total required time for exchanging the keys. And the required time to detect and update the change in IP address, which may occur due to mobility or multihoming, is less than 10% of the total required time to establish a new SA session.

Resource Sharing via Planed Relay for

We present an improved version of adaptive distributed cross-layer routing algorithm (ADCR) for hybrid wireless network with dedicated relay stations ( ) in this paper. A mobile terminal (MT) may borrow radio resources that are available thousands mile away via secure multihop RNs, where RNs are placed at pre-engineered locations in the network. In rural places such as mountain areas, an MT may also communicate with the core network, when intermediate MTs act as relay node with mobility. To address cross-layer network layers routing issues, the cascaded ADCR establishes routing paths across MTs, RNs, and cellular base stations (BSs) and provides appropriate quality of service (QoS). We verify the routing performance benefits of over other networks by intensive simulation.

HyMN-injection-based multimedia content distribution in hybrid wireless networks

Infrastructured networks typically employ centralized approaches for group management and information provisioning. In contrast to that, in multi-hop ad hoc networks each node acts as a router as well as sender and receiver. In pure ad hoc networks, no Internet access is available. An additional challenge is to deal with mobility that causes network partitioning and re-organizations. Technically, these problems can be tackled by providing additional uplinks to a backbone network. Those can be used to access resources in the Internet as well as to inter-link multiple ad hoc network partitions, creating a hybrid wireless network. In this paper, we present HyMN, a prototypically implemented hybrid wireless network system optimized for multimedia content providing. Within the ad hoc network, adequate devices are elected to maintain uplinks to a backbone, which can provide for instance multimedia news from certain sports events like Football Championships, Olympic Games and alike. In order to efficiently manage the ad hoc communicating devices, a weighted clustering algorithm is employed.

Uplink relaying in hybrid wireless networks with out-of-cell interference reduction

The next generation broadband access networks must provide high speed bidirectional data channels and support more concurrent subscribers than ever before. While mega-bits-per-second data rates have been demonstrated for the downlink channels, progress on uplink has been slow. We propose a hybrid architecture for CDMA uplink that seamlessly integrates short-range radio and WCDMA interfaces in the same network. In our scheme, mobile stations (subscribers) can operate as Relaying Mobile Terminal (RMT) to relay uplink traffic for nearby mobile stations. Our analysis and simulations show that the deployment of RMTs significantly reduces the radio transmissions in the CDMA uplink. Moreover, the scheme results in a much lower out-of-cell interference to the neighboring network cells. The problem of finding the optimum RMT set turns out to be NP-hard. Several heuristics are evaluated in terms of RMT size and out-of-cell interference. In particular, we investigated a novel vertex cover based heuristic algorithm. Our method uses mobile pilot signals and mobile location to estimate a interference function for each node. This function is then used in selecting a maximum matching for the candidate RMT set. Simulation results are somewhat surprising: the simple greedy algorithm has very close performance to that of the optimum algorithm when only the RMT size is concerned. When out-of-cell interference is considered, the proposed algorithm outperforms both greedy and 2-approximation algorithm.

A Network Selection Algorithm Considering Power Consumption in Hybrid Wireless Networks

In this paper, we propose a novel network selection algorithm considering power consumption in hybrid wireless networks for vertical handover. CDMA, WiBro, WLAN networks are candidate networks for this selection algorithm. This algorithm is composed of the power consumption prediction algorithm and the final network selection algorithm. The power consumption prediction algorithm estimates the expected lifetime of the mobile station based on the current battery level, traffic class and power consumption for each network interface card of the mobile station. If the expected lifetime of the mobile station in a certain network is not long enough compared the handover delay, this particular network will be removed from the candidate network list, thereby preventing unnecessary handovers in the preprocessing procedure. On the other hand, the final network selection algorithm consists of AHP (Analytic Hierarchical Process) and GRA (Grey Relational Analysis). The global factors of the network selection structure are QoS, cost and lifetime. If user preference is lifetime, our selection algorithm selects the network that offers longest service duration due to low power consumption. Also, we conduct some simulations using the OPNET simulation tool. The simulation results show that the proposed algorithm provides longer lifetime in the hybrid wireless network environment.

Any Resource Sharing via HWN* Routing

In this paper we present an adaptive distributed cross-layer routing algorithm (ADCR) for hybrid wireless network with dedicated relay stations (HWN*). To support versatile multimedia communication for Mobile Terminals (MTs), the HWN* integrates a cellular network, an ad hoc network and fixed relay nodes (RNs). A MT may borrow cellular data channels that are available thousands mile away via secure multi-hop RNs, where RNs are placed at flexible locations in the network. The MT can also communicate with each other or access internet ubiquitously. We discuss cross media access and network layers routing issues. The ADCR establishes routing paths across RNs or cellular network while providing appropriate QoS (quality of service). Through simulation, we verify the routing performance benefits of HWN* over conventional cellular systems and other hybrid network frameworks. It is anticipated that the simulation results reported in this paper will serve as a guideline for research based on distributed source routing involving heterogeneous wireless technologies.

An efficient Hash Table-Based Node Identification Method for bandwidth reservation in hybrid cellular and ad-hoc networks

Hybrid cellular and wireless ad-hoc network architectures are currently considered to be promising alternative solutions to the standalone cellular or ad-hoc network architectures. In this paper, we propose an efficient Hash Table-Based Node Identification (HTNI) Method using which bandwidth for various flows can be reserved in such network environments. Bandwidth reservation depends on the type of the traffic and its priorities. We define a bandwidth reservation factor for use in such hybrid network environments. We propose a cross-layer-based architecture for bandwidth reservation to maintain Quality-of-Service (QoS). We use a priority re-allocation method for flows which starve for long time. The proposed method is useful for finding the position of nodes with low communication cost.

Mobile ad hoc relaying for upward vertical handoff in hybrid WLAN/cellular systems

One of the main issues in hybrid wireless networks is vertical handoff. Dropping probability is one of the important parameters that must be considered in planning the wireless communication systems. However, there has not been much effort in dropping rate reduction in loosely coupled hybrid wireless networks. In loosely coupled WLAN/cellular systems the system administrator of the WLAN is different from the cellular one. Therefore, in these situations, reducing the dropping probability based on classical methods such as using reserved guard channels is difficult. A handoff from a WLAN to a cellular system occurs when a multi-mode device moves out of the WLANs coverage area. This is an upward vertical handoff in a hybrid network. In this paper, we propose to employ ad hoc relaying during the upward vertical handoff in a hybrid WLAN/cellular system. Two-hop and multi-hop relaying approaches, which we propose in this paper, improve the dropping probability regardless of the number of reserved channels. Simulation results support the effectiveness of the proposed methods. Also, practical routing protocols are proposed in order to implement the suggested relaying methods.

Adaptive peer-to-peer streaming over hybrid wireless networks

In this paper, we propose a centralised Peer-to-Peer (P2P) streaming over hybrid wireless networks to mitigate the congestion at the Access Point (AP) in Wireless Local Area Networks (WLANs). In our proposed architecture, an adaptive receiver-driven mechanism is used to coordinate the streaming from multiple senders. We also propose a peer handoff scheme and an AP handoff scheme for video streaming over hybrid wireless networks. The simulation results show that (1) centralised P2P video streaming over a hybrid wireless network can achieve a much better quality compared to traditional WLAN deployment with heavy background traffic, (2) the adaptive receiver-driven mechanism can synchronise packet delivery from multiple senders, thus increasing streaming quality, (3) the peer handoff scheme enables the receiver to maintain a high aggregate throughput from multiple serving-peers and (4) the AP handoff scheme enables the receiver to roam freely through different cells, while maintaining continuous video streaming.

Load-Balancing Routing in Multichannel Hybrid Wireless Networks With Single Network Interface

A hybrid wireless network is an extension to an infrastructure network, where a mobile host may connect to an access point (AP) using multihop wireless routes via other mobile hosts. The APs are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select their operating channels dynamically through channel switching. In this environment, we propose a routing protocol that finds routes to balance load among channels while maintaining connectivity. The protocol works with nodes equipped with a single network interface, which distinguishes our work with other multichannel routing protocols that require multiple interfaces per node. The protocol discovers multiple routes to multiple APs, possibly operating on different channels. Based on traffic load information, each node selects the best route to an AP and synchronizes its channel with the AP. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The protocol assures that every node has at least one route to an AP, where all intermediate nodes are operating on the same channel. Our simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a multichannel protocol with no load balancing

Key Exchange Protocol Supporting Mobility and Multihoming

In this work, a new key exchange protocol for IP-based mobile networks is introduced. This protocol is called KEPSOM ( Key Exchange Protocol Supporting M obility and Multihoming). The goals of designing KEPSOM are to develop key exchange protocol proposal characterized by its secrecy, simplicity, efficiency, resistivity, and its ability to support mobility and multihoming. The protocol requires only two roundtrips. The design limits the private information revealed by the initiator. An old security association (SA) can be replaced with a new one by rekeying without the need of restarting the protocol with a new session. On the other hand, the changes in IP address due to mobility or multihoming need not to restart the protocol with a new SA session. The proposed protocol can also support key exchange in hybrid wireless network, in which the mobile node can operate in both Ad Hoc and Base Station-oriented wireless network environments using different transmission modes. KEPSOM has been analyzed and proven secure. Several tests have been done to measure and evaluate the performance of the protocol. In these tests, it is found that the required time for rekeying is about 27% of the total required time for exchanging the keys. And the required time to detect and update the change in IP address, which may occur due to mobility or multihoming, is less than 10% of the total required time to establish a new SA sessions.

Uplink scheduling in clustered 3G network with mobile relaying

Hybrid wireless networks are characterized by simultaneously using several radio interfaces to boost system performances. A practical and promising architecture to achieve a better uplink throughput in the traditional CDMA cell is to locally aggregate mobile-generated traffic to some cluster heads through WLAN. Such an architecture opens up questions of the desired clustering structures as well as new uplink scheduling strategies. The scheduling of the aggregated traffic at the cluster heads (called relayed mobile terminals later) is investigated in this work. The proposed uplink scheduling algorithm takes the aggregated traffic nature into account. The scheduling goal is to achieve good throughput under the traffic QoS requirements (e.g. BER, bit-error-rates) and limited power budget at the mobile station. The proposed scheduling algorithm consists of two levels: (1) we use a proportional scheduling algorithm to coordinate the transmission among relaying mobile terminals (RMTs), where the main objective is to achieve high spectrum efficiency and reasonable fairness; (2) within RMT, packets from different leave nodes, with different BER requirements are further scheduled via a link-adaptive CDMA (LA-CDMA) transmission scheme. By exploiting the QoS diversity of the queued packets, the LA-CDMA scheduler is able to generate better usage of power budget, which allows some BER-stringent packets to be transmitted at a higher data rate. The performance improvement of the LA-CDMA scheduler is demonstrated by our simulation results. The system goodput is increased by up to 17% for some traffic type. Our simulation also shows the dynamic of expected BERs, the allocation of transmission power and the modulation depth of the LA-CDMA scheduler.