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University: Polytechnic Institute of New York University
Name of sponsoring Professor: Shivendra S. Panwar
Department: Electrical and Computer Engineering

Research:

1. Distributed Scheduling Algorithm Design for High-Speed Switching Systems

Given the rapid increase in traffic, greater demands have been put on research in high speed switching systems. Such systems have to simultaneously meet several constraints, e.g., high throughput, low delay and low complexity. This makes it challenging to design an efficient scheduling algorithm, and has consequently drawn considerable research interest. However, previous results either cannot provide a 100% throughput guarantee without a speedup, or require a complex centralized scheduler.

In this research project, we designed a scheduling algorithm with as low as a O(1) computation complexity for an input-queued switch, which is the first scheduling algorithm that can guarantee a 100% throughput with a computation complexity that does not depend on the size of the switch. We also design a distributed 100% throughput algorithm for crosspoint buffered switches, called DISQUO, and a distributed algorithm for an input-queued hybrid optoelectronic switch, called LIOS. We prove that both DISQUO and LIOS can achieve 100% throughput for any admissible Bernoulli traffic, with a low time complexity of O(1) per port. To the best of our knowledge, they are the first distributed algorithms that can provide a 100% throughput without speedup. Simulation results also show that DISQUO can provide a good delay performance as compared to an output-queued switch.

We used Opnet Modeler software to simulate and analysis of the algorithms proposed. The results show that the router can provide good throughput, with realistic on-off bursty traffic and asynchronous packet arrivals.

2. Cooperative Communications in Wireless LANs

Relay-assisted cooperative wireless communication has been shown to have significant performance gains over the legacy direct transmission scheme. Compared with single relay based cooperation schemes, utilizing multiple relays further improves the reliability and rate of transmissions. Distributed space-time coding (DSTC), as one of the schemes to utilize multiple relays, requires tight coordination between relays and does not perform well in a distributed environment with mobility. In this paper, a cooperative medium access control (MAC) layer protocol, called STiCMAC, is designed to allow multiple relays to transmit at the same time in an IEEE 802.11 network. The transmission is based on a novel DSTC scheme called randomized distributed space-time coding (R-DSTC), which requires minimum coordination. Unlike conventional cooperation schemes that pick nodes with good links, STiCMAC picks a transmission mode that could most improve the end-to-end data rate. Any station that correctly receives from the source can act as a relay and participate in forwarding. The MAC protocol is implemented in a fully decentralized manner and is able to opportunistically recruit relays on the fly, thus making it robust to channel variations and user mobility..

In order to evaluate the performance of the proposed STiCMAC scheme, we developed a detailed simulation model using OPNET modeler. We compare STiCMAC with direct transmission, CoopMAC and DSTC MAC for both stationary and mobile environments. The comparison and evaluation was done on a typical single-cell WLAN.

Authored papers:

Pei Liu, Chun Nie, Thanasis Korakis, Elza Erkip, Shivendra Panwar, Francesco Verde and Anna Scaglione, "STiCMAC: A MAC Protocol for Robust Space-Time Coding in Cooperative Wireless LANs", IEEE Transactions on Wireless Communications, to appear

Teaching:

EL7353 - Communication Networks I: Analysis, Modeling and Performance

The course introduces the analytical techniques used in the design and performance analysis of networks. Building on their knowledge of networking technology and applied mathematics, especially probability, students learn basic queuing theory, to be applied to performance analysis of multiplexers, switches and multiple access networks. Newer techniques such as the network calculus, the study of non-Poissonian long range dependent traffic sources and applications to TCP, admission control, advanced packet switches and IEEE 802.11 networks are introduced.

OPNET is a commercial network simulation platform widely used in academia and industry for wireline/wireless network design, performance evaluation and optimization. A set of lab-based exercises will be used in EL735 to familiarize the students with the concept of discrete time event-driven simulation in general, and the OPNET simulation environment in particular.

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