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ABSTRACT: Providing air-time guarantees across a group of clients forms a fundamental building block in sharing an access point (AP) across different virtual network providers. Though this problem has a relatively simple solution for downlink group scheduling through traffic engineering at the AP, solving this problem for uplink (UL) traffic presents a challenge for fair sharing of wireless hotspots. Among other issues, the mechanism for uplink traffic control has to scale across a large user base, and provide flexible operation irrespective of the client channel conditions and network loads. In this study, we propose the SplitAP architecture that address the problem of sharing uplink airtime across groups of users by extending the idea of network virtualization. Our architecture allows us to deploy different algorithms for enforcing UL airtime fairness across client groups. In this study, we will highlight the design features of the SplitAP architecture, and present results from evaluation on a prototype deployed with: (1) LPFC and (2) LPFC+, two algorithms for controlling UL group fairness. Performance comparisons on the ORBIT testbed show that the proposed algorithms are capable of providing group air-time fairness across wireless clients irrespective of the network volume, and traffic type. The algorithms show up to 40% improvement with a modified Jain fairness index.
Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE; 01/2011
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ABSTRACT: The 802.16e standard for broadband wireless access mandates the presence of QoS classes, but does not specify guidelines for the scheduler implementation or mechanisms to ensure air time fairness. Our study demonstrates the feasibility of controlling downlink airtime fairness for slices while running above a proprietary WiMAX basestation (BS) scheduler. We design and implement a virtualized infrastructure that allows users to obtain at least an allocated percentage of BS resources in the presence of saturation and link degradation. Using Kernel virtual machines for creating slices and Click modular router for implementing the virtual network traffic shaping engine we show that it is possible to adaptively control slice usage for downlink traffic on a WiMAX Basestation. The fairness index and coupling coefficient show an improvement of up to 42%, and 73% with preliminary indoor walking mobility experiments. Outdoor vehicular measurements show an improvement of up to 27%, and 70% with the fairness index and coupling coefficient respectively
Communications (ICC), 2010 IEEE International Conference on; 06/2010
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ABSTRACT: The Cache-and-Forward (CNF) protocol architecture was proposed to support efficient mobile content delivery services in the future Internet. In contrast to the TCP/IP protocol stack which is based upon the assumption of reliable end-to-end path through the network, the CNF architecture considers varying access link speed/quality and periods of disconnection as inherent properties of the network. Routers in a CNF network are built with large memory space for in-network caching and temporary storage to support transient disconnections due to mobility or link quality variation. Content delivery through the network follows a hop-by-hop transport method in which files move as single entities from one router to the next rather than as end-to-end packet streams. A novel storage aware routing protocol (STAR) is proposed to efficiently support mobile and wireless end-users through the use of a two-dimensional metric that takes into account both short-term and long-term path quality in making forwarding and storage decisions. A reliable link layer provides per hop file transfer reliability. This paper provides an outline of the three basic protocol components of CNF i.e., transport, routing and link layers and describes a proof-of-concept implementation of the protocol stack on the ORBIT testbed. Performance evaluation results in multi-hop wireless scenarios with lossy link conditions show 66% improvement in wireless network throughput compared to TCP and 60% lower packet loss rate when compared to UDP.
Local and Metropolitan Area Networks (LANMAN), 2010 17th IEEE Workshop on; 06/2010
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ABSTRACT: Multi-hop wireless mesh networks are designed as a cost-effective solution for last-mile broadband Internet access. Equipping mesh nodes with multiple radios further improves network capacity by using multiple radios to transmit simultaneously on orthogonal channels. In addition, multiple input multiple output (MIMO) antennas have emerged as a physical layer breakthrough for increasing throughput and suppressing interference from neighboring links. These wireless technologies are viewed as the key components in improving the performance of next-generation wireless networks. However, to obtain the full benefits of these technologies, the networking protocols should exploit their capabilities in a systematic way due to their interdependence. In this paper, we provide the first formal study on cross-layer optimization in multi-radio, multi-channel wireless mesh networks with MIMO links. We formulate a framework where data routing at the network layer, link scheduling and channel assignment at the MAC layer, and MIMO stream control at the physical layer can be jointly optimized for maximizing network throughput subject to fairness constraint among mesh nodes. We then present an algorithm in which routing is established on a longer-time scale for system stability, while scheduling, channel assignment and stream control are jointly determined for opportunistic bandwidth access and sharing in time, frequency and space dimensions based on instantaneous channel conditions and traffic dynamics.
Communications Workshops, 2009. ICC Workshops 2009. IEEE International Conference on; 07/2009
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ABSTRACT: This paper presents delay and throughput performance results for a "cache-and-forward" (CNF) network architecture for mobile content delivery services. The CNF network uses hop-by-hop transport and in-network storage to deliver large media files to mobile users. The CNF protocol is designed to deal with fluctuating wireless link quality and occasional periods of disconnection, and is therefore expected to be more robust and efficient than conventional TCP/IP based services. A detailed ns-2 simulation model is developed for CNF, including implementations of the reliable link layer and hop-by- hop routing protocol. The GT-ITM transit-stub with extensions for wireless access networks is used for the performance study, and network throughput and delay are measured as a function of offered traffic and radio link quality. The results show that the CNF network performance is competitive with TCP/IP even for the wired-only case, while providing significant capacity improvements as the wireless link quality degrades. It is observed that the network throughput gain for a given value of file transfer delay can be as much as ~3-5x depending on the radio link quality parameters.
Communications Workshops, 2009. ICC Workshops 2009. IEEE International Conference on; 07/2009
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ABSTRACT: Cache-and-Forward (CNF) is a future Internet architecture designed for content delivery to mobile users over wireless networks with varying link quality and intermittent connectivity. The CNF protocol is based on strict hop-by-hop transport of media files with in-network storage at each router or wireless access point. The protocol also incorporates content caching capabilities for efficient delivery of popular media files. In this paper, we briefly describe the CNF architecture, present a survey of prior work, and describe new CNF link and routing protocols. Throughput results comparing CNF with TCP/IP are summarized for an example wide-area Internet scenario with wireless access networks. The design of a reliable CNF link layer protocol is discussed and performance results are given for multihop wireless scenarios. The paper concludes with an outline of dynamic CNF routing algorithms which consider both short-term and long-term path quality along with available in-network storage.
Sarnoff Symposium, 2009. SARNOFF '09. IEEE; 05/2009
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ABSTRACT: In multi-hop infrastructure wireless mesh networks (WMNs), the association mechanism, by which a client station (STA) affiliates with a mesh access point (MAP), and the routing algorithm, through which MAPs form a multi-hop backhaul for relaying STAs' traffic, determine a two-tier logical topology. Apparently the STA-MAP association mechanism and the backhaul routing impact the available bandwidth that can be allocated to each STA. In this paper, we formulate a joint optimization problem of STA-MAP association, backhaul routing and bandwidth allocation. Our rigorous framework maximizes the network throughput while guaranteeing network-wide fairness among STAs, taking into account the bandwidth constraints of both access and backhaul links, as well as the wireless interference. We then develop approximation algorithms for efficiently solving the joint optimization problem. A method to decouple topology construction and bandwidth allocation is proposed to simplify the optimization problem under integral association and single- path routing, which is NP hard in the original formulation. We also use the clique approximation to alleviate the complexity for constructing the wireless interference constraints. Furthermore a scheduling algorithm is proposed, which coordinates channel access to provide bandwidth guarantee and can recover certain performance loss due to the clique approximation. Our evaluation demonstrates that constructing a good logical topology can improve throughput while enhancing fairness, and our algorithms can achieve performance close to the optimal solution to the joint association, routing and bandwidth allocation problem.
Global Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE; 01/2009
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ABSTRACT: This paper presents an experimental study on the spectrum coexistence problems between multi-radio platforms in dense-radio physical world environments. Computing and communication devices such as laptops and cellular phones with multiple radios including WiFi, Bluetooth, UWB, WiMax and Zigbee in a small conference room face significant interference problems. A realistic small office/home office (SOHO) scenario with ~10-25 multi-radio platforms is mapped onto the ORBIT radio grid testbed, and system throughput results are obtained experimentally, demonstrating significant degradation due to inter-platform interference. The CSCC (Common Spectrum Coordination Channel) protocol proposed in earlier work is used as the basis for implementing a set of distributed spectrum coexistence algorithms intended to improve system performance. Detailed results from ORBIT testbed experiments are given for the proposed CSCC-based distributed spectrum coordination algorithms. The results show significant performance gains due to CSCC coordination, typically achieving ~2x improvement in system throughput for WiFi/Bluetooth dual radio scenarios.
New Frontiers in Dynamic Spectrum Access Networks, 2008. DySPAN 2008. 3rd IEEE Symposium on; 11/2008
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ABSTRACT: This paper presents an integrated routing and MAC scheduling protocol (IRMA) for multihop wireless mesh networks. The IRMA approach is motivated by the fact that the overall performance achieved by conventional layered approaches (802.11 MAC combined with independent ad hoc routing protocols) is significantly lower than the underlying network capacity. We propose to integrate the routing and MAC into a single protocol layer and use joint optimization techniques to establish end-to-end path and TDMA schedules for flows across the network. This approach achieves non-conflicting allocation of channel resources based on global or local traffic flow specifications and the network graph. The proposed method not only establishes interference-free MAC link schedules, but also helps to find optimal routes which can route around congested areas of the network. Two specific IRMA algorithms are proposed and evaluated in this paper. The first method solves min-hop routing, then optimizes link scheduling based on routing results and real-time flow demands. The second approach attempts to optimize routing and scheduling decisions simultaneously, using available MAC bandwidth information to route around congested areas. Both centralized and distributed algorithms based on these methods are proposed and evaluated with detailed simulations. Results show significant 2-3x improvements in network throughput when compared with baseline 802.11-based mesh networks using independent routing protocols.
World of Wireless, Mobile and Multimedia Networks, 2008. WoWMoM 2008. 2008 International Symposium on a; 07/2008
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ABSTRACT: We report the design, implementation and evaluation of Merged Hybrid ARQ with staggered FEC (MHARQ) system for video multicast over wireless LANs. MHARQ combines the advantages of receiver-driven staggered FEC and hybrid ARQ schemes to compensate the large dynamic range of WLAN channels and to achieve high reliability, scalability and wireless bandwidth efficiency for video multicast. The FEC packets generated by a cross-packet FEC code are divided into multiple streams according to the pre-configured overhead and are transmitted in different multiple IP multicast groups. Certain FEC streams are delayed from the original video stream. The receivers dynamically join/leave the FEC multicast groups based on the channel conditions. For efficient utilization of WLAN bandwidth, FEC data for a multicast group would not be transmitted by the APs in wireless networks if no receiver joins this group. The time shift between the video stream and the FEC streams introduces temporal diversity and compensates for the client join delay and handoff interruption. In addition, when delayed FEC packets are not enough to recover the lost packets, the receivers can send a hybrid ARQ request to the video server. We design a channel estimation algorithm for a receiver to dynamically determine the delayed FEC multicast groups to join and/or send ARQ NACK to request for retransmission. Using the ORBIT radio grid testbed, we have investigated the performance of the proposed MHARQ system with various numbers of users per AP and different number of APs per video server. It is demonstrated via real system implementation on ORBIT that MHARQ improves wireless bandwidth efficiency and scalability for reliable video multicast, compared with existing reliable multicast schemes.
World of Wireless, Mobile and Multimedia Networks, 2008. WoWMoM 2008. 2008 International Symposium on a; 07/2008
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ABSTRACT: The decreasing cost of wireless hardware and ever increasing number of wireless testbeds has led to a shift in the protocol evaluation paradigm from simulations towards emulation. In addition, with a large number of users demanding experimental resources and lack of space and time for deploying more hardware, fair resource sharing among independent co-existing experiments is important. We study the proposed approaches to wireless virtualization with a focus on schemes conserving wireless channels rather than nodes. Our detailed comparison reveals that while experiments sharing a channel by space separation achieve better efficiency than those relying on time separation of a channel, the isolation between experiments in both cases is comparable. We propose and implement a policy manager to alleviate the isolation problem and suggest scenarios in which either of the schemes would provide a suitable virtualization solution.
Next Generation Internet Networks, 2008. NGI 2008; 05/2008
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ABSTRACT: In a wireless mesh network, a client station needs to associate with a mesh access point for network access. Conventional association mechanisms assume a high-speed backhaul and only the access link being the bottleneck. This assumption holds for most WLANs, but in wireless mesh networks traffic could be bottlenecked either by the access link or by the bandwidth-limited wireless backhaul. In this paper, we propose an association mechanism for wireless mesh networks to improve stations' end- to-end communication performance with the Internet. A station makes its association decision by jointly considering the quality of the access link between the station and the candidate mesh access point as well as the cost of the multi-hop path from the mesh access point to the gateway. In addition, we design two access link metrics, Contention Aware Expected Transmission Time (CAETT) and Load Aware Expected Transmission Time (LAETT). The main strength of CAETT is incorporating the impact of 802.11 MAC layer contention on the bandwidth sharing among the multi-rate stations. LAETT further captures the traffic load. We evaluate the performance of our system through simulations and demonstrate that the proposed joint association mechanism with the CAETT/LAETT metric can significantly improve the end-to-end performance for wireless mesh networks by up to 60%.
Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE; 05/2008
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ABSTRACT: We report the implementation experience and experimental evaluation of a staggered adaptive forward error correction (FEC) system for video multicast over wireless LANs. In the system, the parity packets generated by a cross-packet FEC code are transmitted at a time delay from the original video packets, i.e. staggercasting video stream and FEC stream in different multicast groups. The delay provides temporal diversity to improve the robustness of video multicast, especially to enable the clients to correct burst packet loss using FEC and to achieve seamless handoff. A wireless client dynamically joins the FEC multicast groups based upon its channel conditions and handoff events. We have implemented the system including the streaming server and client proxy. A novel software architecture is designed to integrate the FEC functionality in the clients without requirement for changing the existing video player software. We conduct extensive experiments to investigate the impact of FEC overhead and the delay between the video stream and FEC stream to the video quality under different interference levels and mobile handoff durations. The efficacy of staggered adaptive FEC system on improving video multicast quality is demonstrated in real system implementation.
Multimedia, 2007. ISM 2007. Ninth IEEE International Symposium on; 01/2008
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ABSTRACT: This paper investigates a three-tier hierarchical hybrid wireless network designed to provide significant improvements in system capacity and performance relative to conventional "flat" ad hoc and two-tier "hybrid" networking approaches. The analytical results illustrate that in a three-tier hierarchical network with n<sub>A</sub> access points (AP), n<sub>F</sub> dual-radio forwarding nodes (FN), and n<sub>M</sub> mobile nodes (MN), linear scaling of low-tier capacity can be achieved when the low-tier transmission range satisfies r<sub>L</sub> = O(1/radic(n<sub>F</sub>)); linear scaling of high-tier capacity can be approached in the scaling regime n<sub>A</sub> = Omega(radic(n<sub>F</sub>)) and n<sub>A</sub> = O(n<sub>F</sub>/log n<sub>F</sub>), when the high-tier transmission range satisfies r<sub>H</sub> = O(1/radic(n<sub>A</sub>)). The scaling properties of the three-tier hierarchical ad hoc network are studied using ns-2 based system simulation models. In particular, we investigate the impact of relative node densities and traffic pattern on the scalability of the network. The simulation results are consistent with the analysis, and demonstrate that system throughput can be scaled by using the right proportions of FN's and AP's, making it possible to design high-capacity, low-cost mesh networks with a moderate number of radio FN's and only a few wired AP's.
Global Telecommunications Conference, 2007. GLOBECOM '07. IEEE; 12/2007
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ABSTRACT: In wireless municipal mesh (muni mesh) networks, a client station needs to associate with a mesh access point (MAP) in order to access the network. The end-to-end performance of a station depends on the access link quality between the station and the associated MAP as well as the multi-hop path quality from the associated MAP to the Internet gateway. However conventional association mechanisms used for single-hop WLANs assume that the wireless access link is the bottleneck and do not take the backhaul conditions into account, which may result in poor performance in muni mesh networks. In this paper, we propose a new joint MAP association mechanism for muni mesh networks to achieve optimal end-to-end communication performance from the station to the gateway. A station associates to one of its nearby MAPs by jointly considering the transmission capability of the access link and the backhual path. In addition, we design a new metric, called CAETT, to measure the access link quality. Different from previously proposed link metrics, CAETT takes into account the impact of 802.11 MAC layer contention on bandwidth sharing among the stations with multi-rate capability. It yields more accurate link throughput estimation. Furthermore, in order to reduce the association time, we develop an analytical model and propose a hybrid measurement/estimation method to enable a station to quickly determine the CAETT. We evaluate the performance of our system through simulations and demonstrate that the proposed joint association mechanism with the CAETT metric can greatly improve the end-to-end performance for the stations.
Globecom Workshops, 2007 IEEE; 12/2007
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ABSTRACT: This paper presents an architecture for adaptive cognitive radio networks based on the concept of a "global control plane". The proposed control architecture uses a predetermined common coordination channel for spectrum etiquette, network establishment and adaptation to changing interference environments. The focus of this work is on design and evaluation of three key components of the control protocol - bootstrapping, discovery and naming/addressing. The bootstrapping protocol uses beacons to inform neighboring nodes about a node's PHY/MAC capabilities and current status. The network discovery protocol helps nodes to obtain a global view of reachability and end-to-end paths in the network by exchanging and propagating local link states. Further, nodes obtain their IP addresses and perform name to network address translations using a distributed naming/addressing scheme. An ns2 simulation model of the cognitive radio network with global control has been developed and used to evaluate performance in terms of network setup time, control overhead and achievable data throughput.
Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
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ABSTRACT: Video streaming over wireless networks is a challenging problem because of limited bandwidth, high bit error rates and fluctuations in channel quality. This paper investigates the problem of video multicast over an infrastructure-mode 802.11b wireless local area network. In particular, a multirate simulcasting model is considered to deal with variations in channel conditions, and both distributed and centralized algorithms are developed for receiver rate adaptation. OPNET simulations are used to validate the algorithms which aim to maximize the user satisfaction index. Simulation results show that the centralized scheme is better than the distributed scheme as it maximizes the aggregate user satisfaction index under the available bandwidth and channel conditions. It is also observed that FEC increases the user satisfaction index when the channel errors are low; however with higher channel errors EEC cannot increase the user satisfaction index. Based on these results, both open and closed loop algorithms have been developed to maximize the received video quality
Wireless Communications and Networking Conference, 2006. WCNC 2006. IEEE; 05/2006
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ABSTRACT: This paper presents an analysis of the scaling properties of a three-tier hierarchical hybrid wireless network. The network under consideration, which arises in mesh networking scenarios such as 802.11s, aims to achieve better capacity than ad hoc networks without infrastructure support, and also reduces the investment on wired infrastructure. In particular, the hierarchical hybrid network has three tiers consisting of mobile nodes, radio forwarding nodes and wired access points. For a three-level network of n<sub>1</sub>, access points, n<sub>2</sub> forwarding nodes and n<sub>3</sub> mobile nodes, we analyze throughput in terms of two tiers of packets: those transmitted by mobile nodes (low-tier) and those transmitted by forwarding nodes and access points (high-tier). It is shown that low-tier capacity increases linearly with n<sub>2</sub>, and high-tier capacity increases linearly with n<sub>1</sub> when n<sub>1</sub> grows asymptotically faster than radicn<sub>2</sub>. These results, which are consistent with earlier simulation studies, demonstrate the value of adding radio forwarding nodes to improve scaling behavior and reduce the required number of wired access points. In order to model the capacity of the proposed network, we also study the capacity and traffic distribution of random aggregate networks.
Information Sciences and Systems, 2006 40th Annual Conference on; 04/2006
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ABSTRACT: This paper describes work-in-progress on a new adaptive QoS-based application programming interface (API) for ATM networking. This ATM API, referred to as the ATM Service Manager (ASM) is motivated by the observation that current transport interfaces do not provide QoS features necessary for multimedia applications to achieve desired performance/cost objectives on multiservice ATM networks. In general, an application connected to ATM has a choice of transport protocols (e.g. TCP, UDP, alternative multimedia stream protocols), ATM service class (e.g. ABR, VBR, CBR) and QoS parameters for each media type. It is our view that application software should be shielded from the complexity of QoS-based service management by an adaptive API which is responsible for mapping the application requirements to ATM.
04/2006: pages 285-288;
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Consumer Communications and Networking Conference, 2006. CCNC 2006. 3rd IEEE; 02/2006
