Huei-jiun Ju

Ad hoc wireless networks with mobile backbones

We introduce an ad hoc wireless mobile network that employs a hierarchical networking architecture and uses high and low capacity nodes. We present a topological synthesis algorithm that selects a subset of high capacity nodes to form a backbone network (Bnet). The latter is multi-tiered and consists of interconnected backbone nodes that intercommunicate across higher power (or regular) links, and also makes use of unmanned vehicles, both airborne (UAV) and ground based (UGV). For such a mobile backbone network (MBN), we introduce a protocol, MBNP, to implement the key networking schemes. The MBNP system serves to allocate resources across the network to ensure acceptable user application QoS performance, and also a highly robust backbone-oriented networking architecture. We introduce a new class of on-demand (MBNP-OD) routing algorithms that use the backbone network for selective forwarding of route-request messages, while striving to achieve an efficient MAC layer operation. We enhance these new protocols by incorporating link stability estimates to attain a robust routing operation. To ensure service quality for admitted flows, we introduce flow admission control mechanisms. We present new power control spatial reuse based algorithms for efficient utilization of the net MAC resources through the use of time slot allocations and of CSMA/CA based (IEEE 802.11 type) protocols. We present elements of the protocol and key involved algorithms, and illustrate the advantages offered by the MBNP system.

An adaptive RTS/CTS control mechanism for IEEE 802.11 MAC protocol

We study the impact of using or disengaging the RTS/CTS dialogue in IEEE 802.11 DCF MAC protocol under the fact that carrier sensing, transmission and interference ranges are distinctively different. The resulting throughput performance features of a linear topology network configuration are demonstrated when applying constant bit rate (CBR) UDP as well as TCP type traffic flows. Based on these results, we propose a new RTS/CTS control mechanism. Under our scheme, a terminal node decides dynamically and individually whether to use a RTS/CTS dialogue for the transmission of its current data packet. We show that this new mechanism yields distinctive performance improvements.

A distributed mobile backbone formation algorithm for wireless ad hoc networks

In this paper, we present a novel fully distributed version of a mobile backbone network topology synthesis algorithm (MBN-TSA) for constructing and maintaining a dynamic backbone in mobile wireless ad hoc networks. The following features induce the key advantages offered by the algorithm: a) the MBN-TSA algorithm is designed to work with the unreliable natural of wireless environment; b) the backbone layout is dynamically formed and locally modified in response to communications link quality fluctuations, nodal failures and nodal mobility; c) a control mechanism employing the BN/spl I.bar/neighbor/spl I.bar/limit threshold as a key parameter, is introduced to control the size of the backbone network (BNet) and improve stability; d) analytical results show that the MBN-TSA has very little control overhead: time complexity in the order of O(l) and message complexity in the order of O(l) per node. In addition, we present an on-demand routing protocol that makes use of the underlying dynamically self-configured MBN network infrastructure. By carrying out extensive simulations, we demonstrate the performance advantages when compared to a non backbone oriented on-demand ad hoc routing protocol such as AODV.

A distributed stable backbone maintenance protocol for ad hoc wireless networks

We have introduced a hierarchical structure for ad hoc wireless networks that classifies nodes into backbone capable nodes (BCNs) and regular nodes (RNs). Under our TBONE protocol, a backbone network (Bnet) is formed by dynamically electing backbone nodes (BNs) among BCNs. However the current TBONE protocol requires global topological information to elect and de-elect BNs, which can induce high control message overhead and slow down the Bnet layout adaptation process. In this paper, we resolve this problem by proposing a modified MBN protocol (MBNP) for electing and de-electing BNs, which requires each candidate node to employ only local connectivity information (within two hops). While such schemes tend many times to be unstable, we prove and demonstrate that our process involving BN-BCN conversions is oscillation free. We show that the synthesized network configuration demonstrates desirable robustness and connectivity features, while demanding low control message overhead. Key performance characteristics of the modified protocol are exhibited by conducting simulation-based evaluations.

Topological performance of mobile backbone based wireless ad hoc network with unmanned vehicles

We have recently introduced a hierarchical structure for ad hoc wireless networks that classifies nodes into two categories: backbone capable nodes (BCNs) and regular nodes (RNs). BNCs are better equipped, have higher capacities, and have the ability to operate at multiple power levels and employ multiple radio modules. Under our protocol, identified as TBONE, when a BCN is elected to function as a backbone node (BN), it uses its high power link to communicate with other BNs, thus forming a backbone network (Bnet). To access the network, each RN or BCN must associate itself with a nearby BN (if any). The BN manages transmissions across its access network (Anet), whereby messages are transmitted to/from the BN and among Anet members at lower power levels. Our protocol dynamically initiates and maintains the configuration and association functions of such a mobile backbone network (MBN) under nodal mobility, topological changes and traffic flow variations. We further employ unmanned vehicles (UVs) to aid in maintaining the connectivity of the MBN as well as to upgrade the network capacity when required to sustain real-time and messaging flows that demand quality-of-service (QoS) performance assurance. In this paper, we present the performance features of this protocol, evaluating the number of nodes that are activated as BNs, characterizing the extent to which the system covers its client mobile station using its prescribed BCNs, and presenting the rate of various protocol interactions as a function of the mobility speed of nodal users. We also evaluate the impact of employed UVs on the systems connectivity and coverage features.

Backbone Topology Synthesis for Multiradio Mesh Networks

Wireless local area network (WLAN) systems are widely implemented today to provide hot-spot coverage. Operated typically in an infrastructure mode, each WLAN is managed by an access point (AP). Wireless mesh networks (WMNs) are employed for the purpose of extending the wireless coverage scope by interconnecting the underlying AP nodes. The capability and performance behavior of the WMN can further be upgraded by using multiple communications channels and by having more capable nodes use multiple radio modules. In this paper, we present a fully distributed multiradio backbone synthesis algorithm, which serves to construct a mesh backbone network of APs. We assume more capable nodes, such as APs, to be equipped with two radio modules, while less capable nodes employ a single radio module. Multihop communications among distant client stations take place in accordance with a routing algorithm that uses the mesh backbone to establish inter-WLAN routes. The presented backbone construction algorithm and the associated on-demand backbone-based routing mechanism are shown to improve the systems delay-throughput performance, as well as its asynchronous and distributed behavior in a stable fashion

Mobile backbone synthesis for ad hoc wireless networks

In this paper, we present an extended mobile backbone network topology synthesis algorithm (ETSA) for constructing and maintaining a dynamic backbone structure for mobile ad hoc wireless networks. We present and analyze the mathematical features of the proposed scheme. Using these results, we prove that: (1) The ETSA scheme converges in constant time; (2) The length of each control packet is bounded by a constant value that is independent of the number of network nodes; (3) The size of the backbone network depends only on the size of the operational area and is independent of nodal density. We compare the performance features of this scheme with those characterizing other protocols that employ clustering operations and/or use selective forwarding on demand routing methods. In addition, we present an on-demand routing protocol (MBNR) that makes use of the underlying dynamically self-configuring backbone network infrastructure and demonstrate its performance advantages when compared with an on-demand routing protocol that is based on a flat architecture, as well as with other backbone-based routing protocols.

Performance analysis and enhancement for backbone based wireless mobile ad hoc networks

In this paper, we present an extended mobile backbone network (MBN) topology synthesis algorithm (ETSA) for constructing and maintaining a dynamic backbone structure in mobile wireless ad hoc networks. For conventional backbone formation algorithms (such as Connected Dominating Set construction algorithms) to operate correctly, perfect neighborhood knowledge is required. However, in a wireless ad hoc network, both control message losses and asynchronous timers among nodes can lead to imperfect neighborhood information. Thus, two restricting rules are introduced in this paper for the election of backbone nodes that are shown to improve asynchronous, distributed and stable operation of the algorithm. The scalability and efficiency of backbone based routing in ad hoc networks depend on the overhead introduced by the formation of a connected backbone network (BNet) and the size of the backbone network. We prove that the size of the backbone network synthesized by this algorithm is independent of nodal density. We also prove that the extended topology synthesis algorithm introduced in this paper has constant O(1) time complexity and yields a constant O(1) communication overhead factor per node.

A mobile backbone network routing protocol with flow control

We have recently introduced a mobile backbone network based architecture to support applications transported across ad hoc wireless networks. Under our MBN topological synthesis algorithm, backbone capable nodes (BCN) are elected as backbone nodes (BN) to form a mobile backbone network (Bnet). Once constituted, the mobile backbone network provides a preferred infrastructure for supporting the transport of multimedia streams and other message flows across the ad hoc network, and is exploited to make the routing, access control and congestion control problems tractable. In this paper, a so-called mobile backbone network routing with flow control (MBNR-FC) is introduced. We define an on-demand routing protocol under which route discovery messages are distributed solely across the mobile backbone, leading to a highly scalable and robust mobile ad hoc network operation. We use the embedded signaling mechanism that is used for the route discovery process to regulate the admission of flows by guiding admitted flows through less congested areas. The employed flow control mechanism is also used to protect the quality-of-service performance of supported message flows. We show our new flow controlled based routing method to significantly improve network throughput, packet delay, packet delay jitter, and packet loss ratio performance.

Mesh topology construction for interconnected wireless LANs

A wireless mesh network extends wireless local area network systems, which are widely implemented today to provide hot spot coverage, by implementing a reliable meshed network that serves to interconnect the access points managing each wireless local area network. The 802.11s working group has been formed recently to recommend an extended service set (ESS) that enables wider area communications among distributed clients, each of which has access to an IEEE 802.11 wireless LAN (WLAN). Such coverage can be provided by the implementation of a mesh backbone network that serves to interconnect the WLAN access points (APs). In this paper, we present a scalable, fully distributed topology control algorithm for constructing such a mesh backbone network of access points. Multi-hop communications among distant client stations take place in accordance with a routing algorithm that uses the mesh backbone to establish inter-WLAN routes. The presented topology construction algorithm and its employment by the presented routing mechanism are shown to improve the asynchronous, distributed and stable operation of the network. We prove that the topology construction and control algorithm introduced in this paper is highly scalable and efficient. The implementation complexity of the required communications control (and its associated overhead) and its temporal convergence features are independent of the number of network nodes.