Mariya Zheleva

Kwiizya: local cellular network services in remote areas

Cellular networks have revolutionized the way people communicate in rural areas. At the same time, deployment of commercial-grade cellular networks in areas with low population density, such as in rural sub-Saharan Africa, is prohibitively expensive relative to the return of investment. As a result, 48\% of the rural population in Africa remains disconnected. To address this problem, we design a local cellular network architecture, Kwiizya, that provides basic voice and text messaging services in rural areas. Our system features an interface for development of text message based applications that can be leveraged for improved health care, education and support of local businesses. We deployed an instance of Kwiizya in the rural village of Macha in Zambia. Our deployment utilizes the existing long distance Wi-Fi network in the village for inter-base station communication to provide high quality services with minimal infrastructure requirements. In this paper we evaluate Kwiizya in-situ in Macha and show that the network maintains low delay and jitter (20ms and 3ms, respectively) for voice call traffic, while providing high call Mean Opinion Score of 3.46, which is the theoretical maximum supported by our system.

The increased bandwidth fallacy: performance and usage in rural Zambia

Broadband Internet access has become a critical part of socio-economic prosperity; however, only 6 in 100 inhabitants have access to broadband in developing countries. This limited access is driven predominately by subscriptions in urban areas. In rural developing communities, access is often provided through slow satellite, or other low-bandwidth long-distance wireless links, if available at all. As a result, the quality of the Internet access is often poor and at times unusable. In this paper we study the performance and usage implications of an Internet access upgrade, from a 256kbps satellite link to a 2Mbps terrestrial wireless link in rural Zambia. While usage did not immediately change, performance improved soon after the upgrade. By three months post-upgrade, however, subscribers began to use the faster connection for more bandwidth-hungry applications such as video-streaming and content upload. This change in usage resulted in dramatic deterioration of network performance, whereby the average round trip time doubled, the amount of bytes associated with failed uploads increased by 222% and that of failed downloads by 91%. Thus, while an Internet access upgrade should translate to improved performance and user experience, in rural environments with limited access speed and growing demand, it can bring unexpected consequences.

TxMiner: Identifying transmitters in real-world spectrum measurements

Knowledge about active radio transmitters is critical for multiple applications: spectrum regulators can use this information to assign spectrum, licensees can identify spectrum usage patterns and better provision their future needs, and dynamic spectrum access applications can leverage such knowledge to pick operating frequency. Despite the importance of transmitter identification the current work in this space is limited and requires prior knowledge of transmitter signatures to identify active radio transmitters. More naive approaches are limited to detecting power levels and do not identify characteristics of the active transmitter. To address these challenges we propose TxMiner; a system that identifies transmitters from raw spectrum measurements without prior knowledge of transmitter signatures. TxMiner harnesses the observation that wireless signal fading follows a Rayleigh distribution and applies a novel machine learning algorithm to mine transmitters. We evaluate TxMiner on real-world spectrum measurements between 30MHz and 6GHz. The evaluation results show that TxMiner identifies transmitters robustly. We then make use of TxMiner to map the number of active transmitters and their frequency and temporal characteristics over 30MHz-6GHz, we detect rogue transmitters and identify opportunities for dynamic spectrum access.

VillageLink: Wide-area wireless coverage

White spaces promise to revolutionize the way wireless connectivity is delivered over wide areas. However, large-scale white space networks face the problem of allocating channels to multiple contending users in the wide white space band. To tackle the issue, we first examine wireless propagation in a long-distance outdoor white space testbed and find that a complex combination of free-space loss and antenna effects impacts transmission in white spaces. Thus, a need arises for a strategy that goes beyond simple channel utilization balancing, and uses frequency probing to profile channels according to their propagation properties. We devise VillageLink, a Gibbs sampling-based method that optimizes channel allocation in a distributed manner with a minimum number of channel switching events. Through extensive simulations we demonstrate that VillageLink results in a significant capacity improvement over alternative solutions.

Smallholder Agriculture in the Information Age: Limits and Opportunities

Recent projections by the United Nations show that the food production needs to double by 2050 in order to meet the nutrition demand of the worlds growing population. A key enabler of this growth are smallholder family farms, that form the backbone of agricultural (AG) production worldwide. To meet this increasing demand, smallholder farms need to implement critical advances in task management and coordination, crop and livestock monitoring and efficient farming practices. Information and Communication Technology (ICT) will play a critical role in these advances by providing integrated and affordable cyber-physical systems (CPS) that can longitudinally measure, analyze and control AG operations. In this paper we make headway towards the design and integration of such AG-CPS. We begin by characterizing the information and communication technology demand of smallholder agriculture based on traffic analysis of farm Internet use. Our findings inform the design and integration of an end-to-end AG-CPS called FarmNET that provides (i) robust control mechanisms for multi-sensor AG data collection and fusion, (ii) wide-area, heterogeneous wireless networks for ubiquitous farm connectivity, (iii) algorithms and models for farm data analytics that produce actionable information from the collected agricultural data, and (iv) control mechanisms for autonomous, proactive farming.

AirLab: consistency, fidelity and privacy in wireless measurements

Accurate measurements of deployed wireless networks are vital for researchers to perform realistic evaluation of proposed systems. Unfortunately, the difficulty of performing detailed measurements limits the consistency in parameters and methodology of current datasets. Using different datasets, multiple research studies can arrive at conflicting conclusions about the performance of wireless systems. Correcting this situation requires consistent and comparable wireless traces collected from a variety of deployment environments. In this paper, we describe AirLab, a distributed wireless data collection infrastructure that uses uniformly instrumented measurement nodes at heterogeneous locations to collect consistent traces of both standardized and user-defined experiments. We identify four challenges in the AirLab platform, consistency, fidelity, privacy, security, and describe our approaches to address them.

Enabling a Nationwide Radio Frequency Inventory Using the Spectrum Observatory

Knowledge about active radio transmitters is critical for multiple applications: spectrum regulators can use this information to assign spectrum, licensees can identify spectrum usage patterns and provision their future needs, and dynamic spectrum access applications can efficiently pick operating frequency. To achieve these goals, we need a system that continuously senses and characterizes the radio spectrum. Current measurement systems, however, do not scale over time, frequency and space and cannot perform transmitter detection. We address these challenges with the Spectrum Observatory, an end-to-end system for spectrum measurement and characterization. This paper details the design and integration of the Spectrum Observatory, and describes and evaluates the first unsupervised method for detailed characterization of arbitrary transmitters called TxMiner. We evaluate TxMiner on real-world spectrum measurements collected by the Spectrum Observatory between 30 MHz and 6 GHz and show that it identifies transmitters robustly. Furthermore, we demonstrate the Spectrum Observatory’s capabilities to map the number of active transmitters and their frequency and temporal characteristics, to detect rogue transmitters, and identify opportunities for dynamic spectrum access.

Poster: Camera Images Offloading in Low-resource Wireless Networks

Camera snapshot images are widely used in IoT applications. However, when the applications are deployed in rural areas or poorly-performing networks, the images offloading usually exhausts the limited network resources. While we can certainly revamp the network links, we can also optimize the payload at the same time. In this paper, we propose a middlebox system design that exploits the patterns of similarity between consecutive camera snapshots to alleviate the network load. Our preliminary results show that despite of small errors introduced in the images, the amount of reduced payloads could be a valuable choice to alleviate poorly performing networks.

PhoneHome: Robust Extension of Cellular Coverage

Ubiquitous cellular coverage is often taken for granted, yet numerous people live outside, or at the fringes, of commercial cellular coverage. Further, natural disasters and human rights violations cause the displacement of millions of people annually worldwide, with many of these people relocating to shelters and camps in areas at or just beyond the margins of existing cellular infrastructure. In this work we design PhoneHome, a system prototype that extends existing cellular coverage to areas with no or damaged cellular infrastructure, or infrastructure that is otherwise poorly performing. We explore the feasibility of PhoneHome and address current limitations and future directions for independently operated, user-extensible cellular infrastructure.