No abstract

We consider the following queuing system which arises as a model of a wireless link shared by multiple users+ There is a finite number N of input flows served by a server+ The system operates in discrete time t ϭ 0,1,2, + + + + Each input flow can be described as an irreducible countable Markov chain; waiting customers of each flow are placed in a queue+ The sequence of server states m~t !, t ϭ 0,1,2, + + + , is a Markov chain with finite number of states M+ When the server is in state m, it can serve µ i m customers of flow i~in one time slot!+ The scheduling discipline is a rule that in each time slot chooses the flow to serve based on the server state and the state of the queues+ Our main result is that a simple online scheduling discipline, Modified Largest Weighted Delay First, along with its generalizations, is throughput optimal; namely, it ensures that the queues are stable as long as the vector of average arrival rates is within the system maximum stability region+

Abstract-The combination of multiple radio nodes in conjunction with a suitably structured multi-hop or mesh architecture has the potential to solve some of the key limitations of present day wireless access networks that are based on single-radio nodes. This paper addresses the channel assignment problem for multi-channel multi-interface (radio) wireless mesh networks. We focus on static wireless mesh networks where multiple nonoverlapping channels are available for each wireless interface. In this network environment, our objective is to find a fixed channel assignment which maximizes the number of bidirectional links that can be activated simultaneously, subject to interference constraints. We present two mixed integer linear programming models for solving the fixed channel assignment problem with multiple radios. Detailed computational results on various grid topologies are also presented and discussed.

The combination of multiple radio nodes in conjunction with a suitably structured multi-hop or mesh architecture has the potential to solve some of the key limitations of present day wireless access networks that are based on single-radio nodes. This paper addresses the static channel assignment problem for multi-channel multi-radio static wireless mesh networks. We present four metrics based on which mesh channel assignments can be obtained. In particular, we focus on minimization of the average and maximum collision domain sizes and show that these problems are closely related to problems in combinatorial optimization such as MAX k-CUT and MIN k-PARTITION. We also present heuristic algorithms for solving the channel assignment problems using the above two metrics.

ABSTRACT:A new series of liquid crystalline polymers containing aromatic triad ester mesogen and 1,1Ј-disubstituted ferrocene as a nonmesogenic unit along with polymethylene spacer was synthesized. The polymer was synthesized by a room temperature polycondensation reaction between bis(4-chloroformyl phenyloxy alkyl ferrocene dicarboxylate) and quinol. The alkyl groups have been varied by an even number of methylene groups with a range from two to ten groups. All the polymers were found to possess liquid crystalline properties. The identification of the mesophase is more transparent with an increase in the spacer. The thermal characteristics were studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results reveal that the thermal stability of the polymers was decreased with increasing spacer length. The T g , T m , and T i of the polymers decreased with increasing methylene groups. The incorporation of the ferrocene moiety also has a considerable effect on the glass transition temperature. The char yield of the polymer decreases with an increasing methylene chain length. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3494 -3501, 2002