My research is in the area of computer networks, with particular emphasis on wireless networks and systems. My research goal is to design, analyze, and build wireless networks, systems, platforms, and protocols that handle the required capacity, reliability, and security of next generation computer networks and connected devices. Some examples of my research projects are highlighted below. More recently, I have started new projects that apply machine learning tools to IoT use cases such as connected cars and drones.

 

Heterogeneous Wireless Networks

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Heterogeneous networks (HetNets) have recently emerged as the de-facto networking architecture to address the capacity and service demand of next generation 5G networks. The architecture comprises a hierarchy of 3GPP (Third Generation Partnership Project) LTE macro cells for ubiquitous coverage, and small cells of various sizes (e.g., micro, pico, femto) and across different radio technologies (e.g., LTE, WiFi, WiGig, 5G mmWave) to augment the capacity. To realize the gains associated with HetNets, consumer devices are also increasingly being equipped with multiple radio access technologies (RATs), and some are already capable of simultaneously utilizing various radio transceivers. My research in this area addresses the problem of client-network pairing for optimal network utilization. In particular, we developed several game theoretical models for network selection and analyzed the convergence and optimality properties of client-centric network selection (INFOCOM 2013 and INFOCOM 2015). Later, we looked at the problem when clients have the capability to split their traffic to/from the network (ICDCS 2017).

 

Wireless Networking with Smart Antennas

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Advanced multi-antenna techniques are one of the core wireless technologies that promise to significantly boost the spectral efficiency and performance of all next generation wireless technologies. Although a significant amount of research in the physical layer community has focused on theoretical capacity analysis, little is known about integrating such techniques with higher layer network protocols, and their performance in practice. My research in this area bridges the gap between the physical layer and networking communities by introducing a series of system designs on how to integrate and leverage these techniques at the MAC and higher network layers. Through rigorous implementation and experimental evaluation, my research identifies and addresses several important challenges to realize these techniques in practice and provides a deep understanding of the limitations and gains of such systems when applied in the real world. In particular, we designed and implemented the first multi-user beamforming system that significantly increases the unicast capacity of wireless networks (MOBICOM 2010). Multi-User beamforming is now a key feature of IEEE 802.11ac. Later, we introduced a new wireless system that uses multiantenna techniques to enable full duplex multi-stream operation (MOBICOM 2012).

 

Wireless Mesh Networks

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Mesh networks provide high-bandwidth wireless access over large coverage areas with substantially reduced deployment cost as compared to other broadband alternatives. Mesh networks are increasingly deployed in urban areas to offload cellular traffic or in rural areas to enable broadband Internet with low cost. As part of our research on mesh networks, we deployed a large-scale multi-tier mesh network (named as “TFA network”) in one of Houstonʼs most economically disadvantaged neighborhoods. Despite the significant benefits associated with mesh networks, issues such as unfairness, low capacity, and unreliability pose significant challenges to their operation in practice. My research in this area combines a deep understanding of deployed and operational mesh networks—learned through deployment and network measurement—with rigorous analysis to design protocols and systems that substantially improve mesh network performance and reliability. Using this approach, we designed a low-cost mesh architecture that substantially increases the capacity (INFOCOM 2008). We also identified and modeled the origins of performance unpredictability in operational mesh networks (INFOCOM 2010), and designed MAC solutions that provide guaranteed fairness (INFOCOM 2009).

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