Multimedia support in a wireless mobile local area network.

摘要

The recent common model for wireless, mobile PCS networks is the cellular model: namely, user communicates via radio with base stations which are interconnected via a wired backbone. There is, however, a growing area of mobile, wireless applications which will depart from the cellular model, and will require peer to peer communications possibly with multihopping over several mobile stations. Typical applications correspond to the situation where a wired infrastructure is not available or is not costeffective to use. Examples include, battlefield, search and rescue, disaster (fire, flood, earthquake) recovery, ad hoc collaborative computing networks, and ad hoc multimedia communications among members of a moving team. In general, the main motivation for wireless multihopping is rapid deployment without need of any existing infrastructure. The multihop networks can be standalone, or can be connected to a wired network.; Basic wireless, mobile, multihop capabilities were demonstrated in the ARPA Packet Radio experiments of the mid 70's. However, those experiments involved only datagram traffic. The protocols did not provide efficient support of real time traffic (voice, video). In this dissertation, we advance the state of the art, in the sense that we address both mobility management and multimedia support in multihopped, wireless networks.; To achieve these goals, we develop the following techniques: (1) Clustering: A distributed, dynamically reconfigurable clustering algorithm partitions the multihop network into clusters so that controlled, accountable bandwidth sharing can be accomplished in each cluster. More specifically, within a cluster, we can easily enforce time-division scheduling. Across clusters, we can facilitate spatial reuse of time slots and codes. (2) TDMA+PRMA channel access scheme: In view of the real time traffic component which requires dedicated bandwidth, VC (Virtual Circuit) connection must guarantee bandwidth and QoS (Quality of Service). Bandwidth guarantee is performed by reserving the time slot(s) in the TDMA frame to each VC. In a highly mobile environment, the conventional VC setup scheme is not suitable because of frequent breakage of the connection. The time required to set up a new VC is comparable to the interval between path changes. In order to catch up with station movements, we propose a "soft state", i.e. fast set-up and dynamic rerouting, VC scheme. The first packet in the VC stream follows PRMA (Packet Reservation Multiple Access) scheme to capture and to reserve a slot in the TDMA frame. When the path fails, the PRMA protocol allows the VC stream to dynamically select a new path to destination. (3) QoS routing: To keep track of bandwidth available to each destination is useful to call acceptance control. (4) Embedded voice/video coding: Low priority substreams are dropped when bandwidth is scarce.; The above techniques span several subnet layers, namely: network layer, topology/connectivity management, MAC layer, and physical layer. In order to evaluate the proposed strategy, the entire protocol stack has been implemented in the Maisie simulator. A subset of the protocols was implemented on laptop PCs and tested in a four node testbed.