Optimal Selection of Soft-combining Cells in a Multicast CDMA Network

This paper deals with one of the most important cell planning issues in a CDMA based multicast network. In a CDMA based wireless network, a terminal can significantly reduce the bit error rate via the cohesion of data streams from multiple base stations that share a common time line and are operated according to it. The cells whose base stations are operated as such are called soft-combining cells. Therefore, a terminal in a soft-combining cell can take advantage of error rate reduction, if the cell has at least one neighboring soft-combining cell. However, as soft-combining operation gives heavy burden to the network controller, the number of soft-combining cells should be limited. Our problem is to find a limited number of soft-combining cells such that each soft-combining cell has at least one neighboring soft-combining cell and that the sum of traffic demands of the selected cells is maximized.

高清视频直播业务应用研究

当前互联网视频质量普遍偏低,高清视频将是未来互联网视频的发展趋势。利用应用层组播技术承载高清视频直播业务能有效地降低网络建设成本、解决P2P及传统CDN技术承载视频直播业务中存在的问题。通过分析应用层组播原理,提出一种基于应用层组播技术的新型网络架构,分析了通过应用层组播实现互联网高清视频直播业务的技术特点、商业模式、市场推广策略和关键流程等。     

Multicast scheduling with resource fairness constraints

Integration of multicast and unicast data in future radio access networks will be necessary in order to improve the resource efficiency and provide new services. Such integration requires new and efficient resource sharing mechanisms. These mechanisms need to be optimized to provide the best possible trade-off between resource efficiency and fairness. In this article, we consider a case where streaming multicast users are multiplexed together with elastic unicast users on a common time-slotted channel. We derive a system model to study the performance of various resource allocations strategies under proportional and resource fairness constraints. Fairness is directly defined in terms of the users’ utilities rather than of the throughputs they are assigned to. We also describe an extension of the well-known unicast proportional fair scheduler to the multicast scenario. Through extensive simulations we demonstrate the performance of this scheduler for various traffic loads and multicast group sizes.

Online multicasting in WDM networks with shared light splitter bank

We study online multicasting in WDM networks with shared light splitter bank. Our objective is either to maximize the network throughput or to minimize the blocking probability. Due to the nature of dynamic requesting for network resources by online multicast requests, the network usually is unable to allocate the resources needed for each request in advance. Instead, it either accepts the request by building an economic multicast tree for the request, in terms of the utilization of the network resources if it has sufficient resources available, or rejects the request, otherwise. It is desirable that the cost of realizing each multicast request be minimized, and the network throughput will be maximized ultimately through the cost saving on each individual request. Since optical light splitting and wavelength conversion switching in optical networks is cost expensive and its fabrication is difficult, it is assumed that only a limited number of light splitters and wavelength converters are installed at a node, which will be shared by all the incoming signals at the node. In addition, it is further assumed that only a fraction of nodes in the network are installed with such optical switches. In this article we first propose a cost model for realizing an online multicast request under such network environments with limited light splitters and wavelength converters, which models the cost of utilization of network resources, particularly in modeling the light splitting and wavelength conversion ability at nodes. We then show that finding a cost-optimal multicast tree for a multicast request under the proposed cost model is NP-complete, and instead devise approximation and heuristic algorithms for it. We finally conduct experiments to evaluate the performance of the proposed algorithms. The results show that the proposed algorithms are efficient and effective in terms of network throughput.

Morphing distribution trees—On the evolution of multicast states under mobility and an adaptive routing scheme for mobile SSM sources

Source Specific Multicast (SSM) promises a wider dissemination of group distribution services than Any Source Multicast, as it relies on simpler routing strategies with reduced demands on the infrastructure. However, SSM is designed for á priori known and changeless addresses of multicast sources and thus withstands any easy extension to mobility. Up until now only few approaches arose from the Internet research community, leaving SSM source mobility as a major open problem. The purpose of this paper is twofold. At first we analyze characteristic properties of multicast shortest path trees evolving under source mobility. Analytically and by stochastic simulations we derive measures on the complexity of SSM routing under source mobility. At second we introduce a straightforward extension to multicast routing for transforming (morphing) source specific delivery trees into optimal trees rooted at a relocated source. All packet forwarding is done free of tunneling. Multicast service disruption and signaling overhead for the algorithms remain close to minimal. Further on we evaluate the proposed scheme using both, analytical estimates and stochastic simulations based on a variety of real-world Internet topology data. Detailed comparisons are drawn to bi-directional tunneling, as well as to proposals on concurrent distribution trees.     

A GRASP heuristic for the delay-constrained multicast routing problem

The increasing development of real-time multimedia network applications, many of which require multiple participants, has created the need for efficient multicast routing algorithms. Examples of such applications include video and tele-conferencing, video-on-demand, tele-medicine, distance education, etc. Several of them require multicasting with a certain Quality of Service (QoS) with respect to elements such as delay or bandwidth. This paper deals with Delay-Constrained Multicast Routing (DCMR) where the maximum end-to-end delay in a multicast session is bounded. The DCMR problem can be reduced to the Constrained Minimum Steiner Tree Problem in Graphs (CMStTG) which has been proven to be NP-complete. As a result, several heuristics have been developed to help solve it. In this paper, we developed a GRASP heuristic for the DCMR problem. Computational experiments on medium sized problems (50-100 nodes) from literature and comparison with existing algorithms have shown that the suggested GRASP heuristic is superior in quality for this set of problems.     

Power proximity based key management for secure multicast in ad hoc networks

As group-oriented services become the focal point of ad hoc network applications, securing the group communications becomes a default requirement. In this paper, we address the problem of group access in secure multicast communications for wireless ad hoc networks. We argue that energy expenditure is a scarce resource for the energy-limited ad hoc network devices and introduce a cross-layer approach for designing energy-efficient, balanced key distribution trees to perform key management. To conserve energy, we incorporate the network topology (node location), the “power proximity” between network nodes and the path loss characteristics of the medium in the key distribution tree design. We develop new algorithms for homogeneous as well as heterogeneous environments and derive their computational complexity. We present simulation studies showing the improvements achieved for three different but common environments of interest, thus illustrating the need for cross-layer design approaches for security in wireless networks. Loukas Lazos received the B.S. and M.S. degrees from the Electrical Engineering Department, National Technical University of Athens, Athens, Greece, in 2000 and 2002, respectively. He is currently working towards the Ph.D. degree in the Electrical Engineering Department, University of Washington, Seattle. His current research interests focus on cross-layer designs for energy-efficient key management protocols for wireless ad-hoc networks, as well as secure localization systems for sensor networks. Radha Poovendran received the Ph.D. degree in electrical engineering from the University of Maryland, College Park, in 1999. He has been an Assistant Professor in the Electrical Engineering Department, University of Washington, Seattle, since September 2000. His research interests are in the areas of applied cryptography for multiuser environment, wireless networking, and applications of information theory to security. Dr. Poovendran is a recipient of the Faculty Early Career Award from the National Science Foundation (2001), Young Investigator Award from the Army Research Office (2002), Young Investigator Award from the Office of Naval Research (2004), and the 2005 Presidential Early Career Award for Scientists and Engineers, for his research contributions in the areas of wired and wireless multiuser security.     

Layered-routing approach for solving multicast routing and wavelength assignment problem

We have developed a new layered-routing approach to address the problem of all-optical multicast over wavelength-routed wavelength division multiplexing (WDM) networks. We model the WDM network as a collection of wavelength layers with sparse light- splitting (LS) and wavelength conversion (WC) capabilities. We apply the degree constraint technique to solve the problem. The approach is capable of completing multicast routing and wavelength assignment (MCRWA) in one step. We propose two generic frameworks to facilitate heuristic development. Any heuristic that is derived from either Prim’s or Kruskal’s algorithm can be easily imported to solve the MCRWA problem. One example is given for each framework to demonstrate heuristic development. Extensive simulations were carried out to measure the performance of heuristics developed from the frameworks. The results show that the STRIGENT scheme is suitable for hardware design and it is advisable to deploy light splitters and wavelength converters to the same node for better performance.     

A Power-Aware Multicast Routing Protocol for Mobile Ad Hoc Networks With Mobility Prediction

A mobile ad hoc network (MANET) is a dynamically reconfigurable wireless network that does not have a fixed infrastructure. Due to the high mobility of nodes, the network topology of MANETs changes very fast, making it more difficult to find the routes that message packets use. Because mobile nodes have limited battery power, it is therefore very important to use energy in a MANET efficiently. In this paper, we propose a power-aware multicast routing protocol (PMRP) with mobility prediction for MANETs. In order to select a subset of paths that provide increased stability and reliability of routes, in routing discovery, each node receives the RREQ packet and uses the power-aware metric to get in advance the power consumption of transmitted data packets. If the node has enough remaining power to transmit data packets, it uses the global positioning system (GPS) to get the location information (i.e., position, velocity and direction) of the mobile nodes and utilizes this information to calculate the link expiration time (LET) between two connected mobile nodes. During route discovery, each destination node selects the routing path with the smallest LET and uses this smallest link expiration time as the route expiration time (RET). Each destination node collects several feasible routes and then selects the path with the longest RET value as the primary routing path. Then the source node uses these routes between the source node and each destination node to create a multicast tree. In the multicast tree, the source node will be the root node and the destination nodes will be the leaf nodes. Simulation results show that the proposed PMRP outperforms MAODV (Royer, E. M. & Perkins, C. E. (1999). In Proceedings of the ACM MOBICOM, pp. 207–218, August 1999.) and RMAODV (Baolin, S. & Layuan, L. (2005). In Proceeding of the 2005 IEEE International symposium on microwave antenna, propagation and EMC technologies for wireless communications, Vol. 2, pp. 1514–1517, August 2005.).     

QoS multicast routing by using multiple paths/trees in wireless ad hoc networks

In this paper, we investigate the issues of QoS multicast routing in wireless ad hoc networks. Due to limited bandwidth of a wireless node, a QoS multicast call could often be blocked if there does not exist a single multicast tree that has the requested bandwidth, even though there is enough bandwidth in the system to support the call. In this paper, we propose a new multicast routing scheme by using multiple paths or multiple trees to meet the bandwidth requirement of a call. Three multicast routing strategies are studied, SPT (shortest path tree) based multiple-paths (SPTM), least cost tree based multiple-paths (LCTM) and multiple least cost trees (MLCT). The final routing tree(s) can meet the user’s QoS requirements such that the delay from the source to any destination node shall not exceed the required bound and the aggregate bandwidth of the paths or trees shall meet the bandwidth requirement of the call. Extensive simulations have been conducted to evaluate the performance of our three multicast routing strategies. The simulation results show that the new scheme improves the call success ratio and makes a better use of network resources.