Showing papers by "Duan-Shin Lee published in 2006"

A Necessary and Sufficient Condition for the Construction of 2-to-1 Optical FIFO Multiplexers by a Single Crossbar Switch and Fiber Delay Lines

Abstract: In this paper, we prove a necessary and sufficient condition for the construction of 2-to-1 optical buffered first-in-first-out (FIFO) multiplexers by a single crossbar switch and fiber delay lines. We consider a feedback system consisting of an (M+2)times(M+2) crossbar switch and M fiber delay lines with delays d1,d2,...,dM. These M fiber delay lines are connected from M outputs of the crossbar switch back to M inputs of the switch, leaving two inputs (respectively, two outputs) of the switch for the two inputs (respectively, two outputs) of the 2-to-1 multiplexer. The main contribution of this paper is the formal proof that d1=1 and di les di+1 les 2d i, i=1,2,...,M-1, is a necessary and sufficient condition on the delays d1,d2,...,dM for such a feedback system to be operated as a 2-to-1 FIFO multiplexer with buffer Sigmai=1 Mdi under a simple packet routing policy. Specifically, the routing of a packet is according to a specific decomposition of the packet delay, called the C- transform in this paper. Our result shows that under such a feedback architecture a 2-to-1 FIFO multiplexer can be constructed with M=O(log B), where B is the buffer size. Therefore, our construction improves on a more complicated construction recently proposed by Sarwate and Anantharam that requires M=O(radicB) under the same feedback architecture (we note that their design is more general and works for priority queues)

A Joint Design of Distributed QoS Scheduling and Power Control for Wireless Networks

Abstract: The capacity of a power controlled wireless network can be changing due to user’s mobility, fading or shadowing effects. As a result, the quality of service (QOS) of users accepted by call admission control may not be guaranteed in a wireless network. In this paper, we propose a two-phase distributed scheduling algorithm to identify a subset of wireless users whose QOS is guaranteed. In the first phase, each link transmits with a probing power and each user determines whether it can be a member of the basic feasible set or not in a distributed manner. In the second phase, we develop a generalized call admission control algorithm that attempts to merge as many as possible the rest links into the basic feasible set. We consider a variation that attempts to enlarge the set of feasible links. For starvation prevention, we discuss conflict resolution in the power domain and in the time domain. Through simulation we evaluate the performance of the proposed scheme in terms of average execution time, average packet delay and maximum of the cycle time.

Multistage Constructions of Linear Compressors, Non-Overtaking Delay Lines, and Flexible Delay Lines

Abstract: Queueing theory is generally known as the theory to study the performance of queues. In this paper, we are interested in another aspect of queueing theory, the theory to construct queues via switched delay lines. We consider three types of discrete-time queues: linear compressors, non-overtaking delay lines and flexible delay lines. These three types of queues correspond to certain conditional nonblocking switches and (strict sense) nonblocking switches in switching theory. Analogous to their counterparts in switching theory, there exist multistage constructions for these three types of queues. Specifically, we develop a two-stage construction of a linear compressor and a three-stage construction of a non-overtaking delay line. Similarly, there is a three-stage construction of a flexible delay line. Moreover, a flexible delay line can also be constructed by a layered Cantor network.

From switching theory to "queueing" theory

Abstract: Queueing theory is generally known as the theory to study the performance of queues. In this extended abstract, we are interested in another aspect of queueing theory, the theory to construct queues. Our interest in constructing queues originates from optical packet switching. Traditionally, queues are relatively cheap to build via electronic memory. However, it is very costly to convert optical packets into electronic packets. As such, building optical queues with minimum complexity has become an important research topic.