Projects and publications
Cellular networks in developing regions rely heavily on diesel for energy to provide network coverage due to the paucity of reliable grid power which directly impacts the economic viability of the network and long-term sustainability while also leaving a massive carbon footprint. In this paper, we propose the design, implementation, deployment and evaluation of GreenLinks, an intermittency-aware green cellular network architecture that provides a virtual cell abstraction to extend cellular coverage to areas with unreliable power in a sustainable manner with minimal carbon footprint.
Mobile devices are increasingly becoming vulnerable to a variety of network-level security threats including different types of man-in-the-middle (MITM) attacks such as message interceptions and modifications, eavesdropping on calls and text messages, message spoofing and phishing attacks. In this paper, we propose the design and implementation of Secure Mobile Identities (SMI), a secure key-exchange protocol that enables a mobile user to establish a secure and trustworthy communication channel with other mobile users in the face of external adversaries.
While the cellular revolution has made voice connectivity ubiquitous in the developing world, data services are largely absent or are prohibitively expensive. Hermes is a point-to-point data connectivity solution that works by modulating data onto acoustic signals that are sent over a cellular voice call. The main challenge is that most voice codecs greatly distort signals that are not voice-like; furthermore, the backhaul can be highly heterogeneous and of low quality, thereby introducing unpredictable distortions. Hermes modulates data over the extremely narrow-band (approximately 3kHz bandwidth) acoustic carrier, while being severely constrained by the requirement that the resulting sound signals are voice-like, as far as the voice codecs are concerned. Hermes uses a robust data transcoding and modulation scheme to detect and correct errors in the face of bit flips, insertions and deletions; it also adapts the modulation parameters to the observed bit error rate on the actual voice channel. Through real-world experiments, we show that Hermes achieves approximately 1.2 kbps goodput which when compared to SMS, improves throughput by a factor of 5x and reduces the cost-per-byte by over a factor of 50x.
Rural areas lack sustainable electrification solutions. Although solar solutions hold promise, they are fundamentally constrained by high maintenance costs (due to low user densities, equipment failure, poor handling) and a complete lack of accountability. In this paper, we describe our experiences deploying more than 5,000 Solar Home Systems in Ethiopia and the sustainability problems we faced. Towards developing a decentralized and sustainable solar solution, we have designed SIMbaLink, an extremely low-cost real-time solar monitoring system that significantly reduces both the maintenance costs and the time to repair. By explicitly exposing the real-time status of a solar system to all parties concerned, SIMbaLink addresses the lack of accountability and trust concerns. SIMbaLink can be easily integrated with existing solar systems and can reduce equipment failure rates through early detection of system malfunctions.
Realizing the full potential of a multi-radio mesh network involves two main challenges: how to assign channels to radios at each node to minimize interference and how to choose high throughput routing paths in the face of lossy links, variable channel conditions and external load. ROMA is a practical, distributed channel assignment and routing protocol that achieves good multi-hop path performance between every node and one or moredesignated gateway nodes in a dual-radio network. ROMA assigns non-overlapping channels to links along each gateway path to eliminate intra-path interference. ROMA reduces inter-path interference by assigning different channels to paths destined for different gateways whenever possible. Evaluations on a 24-node dual-radio testbed show that ROMA achieves high throughput in a variety of scenarios.
WiFi-based Long Distance (WiLD) networks with links as long as 50–100 km have the potential to provide connectivity at substantially lower costs than traditional approaches. However, real-world deployments of such networks yield very poor end-to-end performance. First, the current 802.11 MAC protocol has fundamental shortcomings when used over long distances. Second, WiLD networks can exhibit high and variable loss characteristics, thereby severely limiting end-to-end throughput. This paper describes the design, implementation and evaluation of WiLDNet, a system that overcomes these two problems and provides enhanced end-to-end performance inWiLD networks. To address the protocol shortcomings, WiLDNet makes several essential changes to the 802.11 MAC protocol, but continues to exploit standard (low-cost) WiFi network cards. To better handle losses and improve link utilization, WiLDNet uses an adaptive loss-recovery mechanism using FEC and bulk acknowledgments. Based on a real-world deployment, WiLDNet provides a 2–5 fold improvement in TCP/UDP throughput (along with significantly reduced loss rates) in comparison to the best throughput achievable by conventional 802.11. WiLDNet can also be configured to adapt to a range of end-to-end performance requirements (bandwidth, delay, loss).