Multicluster, mobile, multimedia radio network

A multi-cluster, multi-hop packet radio network architecture for wireless adaptive mobile information systems is presented. The proposed network supports multimedia traffic and relies on both time division and code division access schemes. This radio network is not supported by a wired infrastructure as conventional cellular systems are. Thus, it can be instantly deployed in areas with no infrastructure at all. By using a distributed clustering algorithm, nodes are organized into clusters. The clusterheads act as local coordinators to resolve channel scheduling, perform power measurement/control, maintain time division frame synchronization, and enhance the spatial reuse of time slots and codes. Moreover, to guarantee bandwidth for real time traffic, the architecture supports virtual circuits and allocates bandwidth to circuits at call setup time. The network is scalable to large numbers of nodes, and can handle mobility. Simulation experiments evaluate the performance of the proposed scheme in static and mobile environments. 1. I n t r o d u c t i o n Current wireless systems are constrained by fixed bandwidth allocation (on a per connection basis), fixed network configuration such as cellular systems, and by a reliance on a tethered infrastructure of fixed base stations or servers that are linked by a wireline network. In some cases, such as emergency disaster relief or battlefield communications, when the wireline network is not available, this type of architecture is infeasible. In addition, current systems support only a narrow range of services representing applications that are generally nar rowband in nature. To overcome these constraints and advance the state of the art in Wireless Adaptive Mobile Informat ion Systems (WAMIS), we propose a novel architecture which enables rapid deployment and dynamic reconfiguration of a network of wireless stations. We use SS-CDMA (Spread Spectrum Code Division Multiple Access) to allow flexible spectrum sharing, and to combat interference and mult ipath fading [1,2]. In consideration of SS-CDMA and efficient spatial reuse of communicat ion bandwidth, power control and mult i-hop support become critical and essential [1]. Thus, we develop distributed algorithms for adaptive power adjustment and mult ihop routing. A key requirement in W A M I S is the support of multimedia applications which combine real-time traffic (voice, video) and bursty traffic (data, image). Real-t ime sessions require bandwidth and delay guarantee, and are generally carried on virtual circuits which are established at call setup time. Bursty traffic, on the other * This work was supported by the U.S. Department of Justice/ Federal Bureau of Investigation, ARPA/CSTO under Contract J-FBI-93-112 Computer Aided Design of High Performance Wireless Networked Systems. hand, is carried in a connectionless, (i.e. da tagram) mode. For connection oriented traffic (voice, video), admission control must be exercised before the call is accepted in the network. After call establishment, the virtual circuit (VC) connection must guarantee bandwidth and quality of service (QoS). Da t ag ram traffic is not subject to call acceptance control as virtual circuit traffic is. Thus, it may create congestion in the network. To avoid congestion, link-by-link and end-to-end flow and congestion control schemes must be introduced. For efficient and reliable da tagram transport, explicit acknowledgments are used. Note that the passive acknowledgment scheme (i.e., the transmission on the next hop acts as an A C K on the previous hop) first introduced in the A R P A packet radio network [3] will not be suitable here since C D M A is used, and therefore the forwarding node might not use the same code as the originating node. In this paper, we present a multi-cluster, mult i -hop packet radio network architecture that addresses the above challenges and implements all required features. In a mobile, multi-channel (code), and mult i -hop environment, the topology is dynamically reconfigured to handle mobility. Routing and bandwidth assignment are designed so as to meet the various types of traffic requirements. Node clustering, VC setup and channel access control are the underlying features which support this architecture, and will thus be the main focus of this paper. The rest of the paper is organized as follows: in section 2, the multi-cluster network architecture is presented. Channel access scheme and VC establishment are presented in section 3. Performance results are shown in section 4. Section 5 will discuss the extensions of the basic algorithm. Finally, conclusions are given in section 6. 9 J.C. Baltzer AG, Science Publishers 256 M. Gerla, J. T.-C. Tsai / Multicluster, mobile, multimedia radio network 2. Mult i -c luster ne twork archi tec ture and clustering a lgor i thm Several network alternatives can be considered for WAMIS. In our case, because of the requirements of efficient network resource control, multimedia traffic support and suitability to CDMA, we have selected a distributed cluster approach [4]. In fact, clustering provides a convenient framework for the development of important features such as code separation (among clusters), channel access, routing, power control, virtual circuit support and bandwidth allocation. Following the clustering approach, the entire population of nodes is grouped into clusters. A cluster is a subset of nodes which can (two-way) communicate with a clusterhead and (possibly) with each other. In Fig. 1, nodes A, B and C are clusterheads for their coverage area respectively. Each of them serves as a regional broadcast node, and as a local coordinator to enhance channel throughput. Within a cluster, we can easily enforce time-division scheduling. Across clusters, we can facilitate spatial reuse of time slots and codes. The objective of the clustering algorithm is to find a feasible interconnected set of clusters covering the entire node population. A good clustering algorithm should be stable to radio motion, i.e. it should not change the cluster configuration too drastically when a few nodes are moving and the topology is slowly changing. Otherwise, the clusterheads will not control their clusters efficiently and thus lose their role as local coordinators. To this end, two distributed clustering algorithms are considered. One is the lowest-ID algorithm [5]: the lowest-ID node in a neighborhood is elected as the clusterhead. The other is the highest-connectivity (degree) algorithm, which is a modified version of [6]. In this case, the highest degree node in a neighborhood becomes the clusterhead. The algorithms are described below: / Each node is assigned a distinct ID. Periodically, the node broadcasts the list of nodes that it can hear (including itself). Fig. 1. Example of clustering. Fig. 2. Example of cluster formation (lowest-ID). 9 A node which only hears nodes with ID higher than itself is a "clusterhead" (CH). 9 The lowest-ID node that a node hears is its clusterhead, unless the lowest-ID specifically gives up its role as a clusterhead (deferring to a yet lower ID node). 9 A node which can hear two or more clusterheads is