Projects:

Scalable Modulation and Network Modulation

Scalable Modulation: One challenge for wireless communication is that the channel is varying and not easy to estimate accurately. In the literature, super-positioning coding (SPC) has been proposed which can superimpose different symbols (say QPSK and BPSK) and transmit them simultaneously. If the channel quality is good, all bits (3bits/symbol) can be decoded successfully; if the channel quality is poor, part of the bits (2bits/symbol) can be decoded successfully. SPC has been used in the Digital Video Broadcast-Terrestrial (DVB-T) standard. The downside of SPC is that it requires complicated hardware support which is not desirable for mobile devices. We propose a simple, software-based solution that can remap the typical  quadrature amplitude modulation (QAM) constellation to transmit bits with different channel quality requirements simultaneously. This software-based approach is not only simple, but also can out-perform the state-of-the-art SPC in some cases.

Network Modulation: In current wireless systems, when  source transmits data to the receiver through a single-hop or multi-hop wireless path, the physical layer modulates and demodlates the information bits hop-by-hop, and the transmission over each hop is treated the same as in a point-to-point communication link. Given the broadcast nature of wireless medium and the wide variation of wireless channel quality, we let a sender transmit messages to multiple receivers simultaneously, using a software mapping technology, called network modulation (similar to scalable modulation), to redefine the constellation of typical QAM schemes. Network modulation can be used to improve network performance in a wide range of scenarios, for anycast (broadcast, multicast and unicast) services, one-way or two-way traffic, and single-hop or multi-hop wireless paths, in infrastructure or ad hoc networks. The minimum requirement for applying network modulation is that there are no less than three nodes within each others' transmission ranges, so we can consider modulation, topology control, resource allocation, and routing jointly.

Primary research member(s): Zhe Yang, Yuanqian Luo, Siyuan Xiang
Main publications:
* L. Cai, S. Xiang, Y. Luo and J. Pan, "Scalable modulation for video transmission in wireless networks," IEEE Trans. on Veh. Tech., accepted, Oct. 2011. [PDF]
* Z. Yang, Y. Luo, and L. Cai, “Network Modulation: A New Dimension to Enhance Wireless Network Performance," IEEE Infocom'11, Shanghai, China, May 2011. [PDF]

Scalable Video Streaming

Design and implement a framework for Adaptive Scalable Video (H.264/SVC) Streaming over HTTP.  The framework includes three parts. 1) An extractor is designed and implemented to analyze  H.264/SVC bitstream Network Abstraction Layer (NAL) units and split the encoded bitstream into layer segments. 2) A rate adaptation algorithm is designed and implemented to adapt the video bitrate to the varying bandwidth and heterogeneous client requirements. 3) A simple video player is implemented using Open SVC decoder(GPL2) and SDL to demonstrate the practical potential of the framework. More detailed framework and implementation information can be found in https://sites.google.com/site/svchttpstreaming/

Primary research member(s): Siyuan Xiang

Hybrid Medium Access Control Protocol (HMAC)

To reserve or not for bursty video traffic over wireless networks has been a long-debated issue. Reservation can ensure the quality of service (QoS) provisioning at the cost of a lower degree of resource utilization. Contention- based MAC protocols are more flexible and efficient in sharing resources by bursty traffic to achieve a higher multiplexing gain, but the performance may degrade severely when the network is congested. More and more wireless standards adopt a hybrid approach which allos the coexistence of resource reservation and contention-based MAC protocols. However, how to cost-effectively support video using hybrid MAC needs further investigation.

Primary research member(s): Ruonan Zhang, Rukhsana Ruby

Main publications: R. Zhang, R. Ruby, J. Pan, L. Cai and X. Shen, "A Hybrid Reservation/Contention-based MAC for Video Streaming over Wireless Networks," IEEE JSAC, vol. 28, issue 3, pp. 389-398, April 2010. [PDF]

Packet Level Channel Modeling

In an indoor ultra-wideband (UWB) communication environment, the line-of-sight (LOS) between the transmitter and receiver may be frequently blocked by moving people. Blocking of LOS may significantly affect the quality of service (QoS) of on-going UWB communications. Based on the Angular Power Spectrum and the human blocking models, this project builds a packet-level UWB channel model considering the shadowing processes. The model is simple enough to be incorporated into existing network simulators and can be used to facilitate protocol design and QoS analysis for UWB based wireless personal area networks (WPANs).

Primary researcher(s): Rounan Zhang 

IPTV In-Home Distribution

This project studies the feasability of using different wireless network architectures for in-home IPTV distribution. To identify the bottleneck in the home network and estimate the network capacity, we develop an analytical framework to quantify the maximum number of IPTV connections that can be supported with guaranteed QoS in the wired and multi-hop wireless networks, respectively. We extend the fluid flow model analysis to capture both the burstiness of IPTV sources and the time-varying characteristics of multi-hop wireless channels. Extensive NS-2 simulations with H.264 HDTV sources over wired and multihop wireless paths are given, which validate the analysis. The analytical and simulation results provide important guidelines for the planning of future home networks and IPTV systems.

Primary researcher(s): Fengdan Wan, Emad Shihab

Directional-to-Directional MAC Protocol for Ad hoc Networks

In this project, we study the issues related to directional MAC protocols and use this knowledge to carefully design a MAC protocol where both, the sender and the receiver are only equipped with directional antennae. The protocol is fully distributed, does not require any synchronization, and alleviates deafness problems.We show that the DtD MAC protocol can provide significant throughput improvement in Ad-hoc networks when the number of antennae sectors is chosen approprietly. In addition, we also study the performance of this MAC protocol for high data rate technologies such as Millimeter Wave. The results are promising and prove the feasibility of the protocol for use with such technologies.

Primary researcher(s): Emad Shihab and Dr. Lin Cai

Randomized Aloha Protocol 

In this project, an ALOHA like MAC protocol is proposed to be used for sensor networks. The main goal of the protocol is to cope with the strict energy requirments of sensor nodes. Analytical models are being built to study the performance of the proposed protocol and verified through simulations. In addition, the feasability of this protocol for use with satellite systems is being studied. The proposed MAC protocol aims to improve the access capacity of satellite systems by ensuring successful trasnmission by ground stations.

Primary researcher(s): Haoling Ma and Dr. Lin Cai