In order to evaluate, improve, or expand a deployed, citywide wireless mesh network, it is necessary to assess the network’s spatial performance. In this paper, we present a general framework to accurately predict a network’s wellserved area, termed the metric region, via a small number of measurements. Assessment of deployed networks must address two key issues: non-uniform physical-layer propagation and high spatial variance in performance. Addressing nonuniformity, our framework estimates a mesh node’s metric region via a data-driven sectorization of the region. We find each sector’s boundary (radius) with a two-stage process of estimation and then measurement-driven “push-pull ” refinement of the estimated boundary. To address high spatial variation, our coverage estimation couples signal strength measurements with terrain information from publicly available digital maps to estimate propagation characteristics between a wireless node and the client’s location. To limit measurements and yield connected metric regions, we consider performance metrics (such as signal strength) to be monotonic with distance from the wireless node within each sector. We show that despite measured violations in coverage monotonicity, we obtain high accuracy with this assumption. We validate our estimation and refinement framework with measurements from 30,000 client locations obtained in each of two currently operational mesh networks, Google-WiFi and TFA. We study three illustrative metrics: coverage, modulation rate, and redundancy, and find that to achieve a given accuracy, our framework requires two to five times fewer measurements than grid sampling strategies. Finally, we use the framework to evaluate the two deployments and study the average size and location of their coverage holes as well as the impact of client association policies on load-balancing.

With the proliferation of WiFi technology, many WiFi networks are accessible from vehicles on the road making vehicular WiFi access realistic. However, several challenges exist: long latency to establish connection to a WiFi access point (AP), lossy link performance, and frequent disconnections due to mobility. We argue that people drive on familiar routes frequently, and thus the mobility and connectivity related information along their drives can be predicted with good accuracy using historical information – such as GPS tracks with timestamps, RF fingerprints, and link and network-layer addresses of visible APs. We exploit such information to develop new handoff and data transfer strategies. The handoff strategy reduces the connection establishment latency and also uses pre-scripted handoffs triggered by change in vehicle location. The data transfer strategy speeds up download performance by using prefetching on the APs yet to be encountered. Experimental performance evaluation reveals that the predictability of mobility and connectivity is high enough to be useful in such protocols. In our experiments with a vehicular client accessing road-side APs, the handoff strategy improves download performance by roughly a factor of 2 relative to the state-of-the-art. The data transfer strategy further improves this performance by another factor of 2.5.

We perform a head-to-head comparison of the performance characteristics of a 3G network operated by a nation-wide provider and a metro-scale WiFi network operated by a commercial ISP, from the perspective of vehicular network access. Our experience shows that over a wide geographic region and under vehicular mobility, these networks exhibit very different throughput and coverage characteristics. WiFi has frequent disconnections even in a commercially operated, metro-scale deployment; but when connected, indeed delivers high throughouts even in a mobile scenario. The 3G network offers lower throughputs, but provides excellent coverage and less throughput variability. The two network characteristics are often complementary. It is conceivable that these properties can be judiciously exploited for a hybrid network design where 3G data can be offloaded to WiFi for better performance and to reduce 3G network congestion. 1.

We investigate if WiFi access can be used to augment 3G capacity. To understand the feasibility of 3G augmentation, we conduct a detailed study of 3G and WiFi access from moving vehicles, in three different cities. We find that the average 3G and WiFi availability across the testbeds is 87 % and 11%, respectively. We also find that, unlike stationary environments, WiFi throughput is lower than 3G throughput in mobile environments, and WiFi loss rates are higher. We then design a system, called Wiffler, that uses two key ideas—leveraging delay tolerance and fast switching. For delay tolerant applications, Wiffler uses a simple model of the environment to predict WiFi connectivity, and delays applications to offload more data on WiFi. But Wiffler delays applications only if it results in 3G savings. For applications that are extremely sensitive to delay or loss (e.g., VoIP), Wiffler quickly switches to 3G if WiFi is unable to successfully transmit the packet within a small time window. We implement and deploy Wiffler in our vehicular testbed. Both our implementation and trace-driven experiments show that Wiffler significantly increases 3G savings. For example, for a realistic workload, Wiffler reduces 3G usage by 45 % for a delay tolerance of 60 seconds. 1.

Abstract—We investigate a transport layer protocol design that integrates 3G and WiFi networks, specifically targeting vehicular mobility. The goal is to move load from the expensive 3G network to the less expensive WiFi network without hurting the user experience. As the test platform we choose a nationwide 3G network and a commercially operated metro-scale WiFi network. We exploit the often complementary characteristics of these networks for a hybrid design at the transport layer. To this end, we modify the stock Linux SCTP implementation to support ‘striping ’ across multiple interfaces and the ability to handle frequent path failures and recovery in a seamless fashion. Instead of simply striping data over two network connections, we develop a utility and cost-based formulation that decides the right amount of load that can be put on the 3G network to maximize the user’s benefit. We develop and experiment with a transport level scheduler to do this. We call the new SCTP design as oSCTP, meaning ‘SCTP to be used for offloading. ’ We demonstrate the effectiveness of oSCTP and show that it is able to deliver superior network throughput and user experience, while significantly reducing the load on the 3G network. I.

We investigate if WiFi access can be used to augment 3G capacity in mobile environments. We first conduct a detailed study of 3G and WiFi access from moving vehicles, in three different cities. We find that the average 3G and WiFi availability across the cities is 87 % and 11%, respectively. WiFi throughput is lower than 3G throughput, and WiFi loss rates are higher. We then design a system, called Wiffler, to augments mobile 3G capacity. It uses two key ideas— leveraging delay tolerance and fast switching—to overcome the poor availability and performance of WiFi. For delay tolerant applications, Wiffler uses a simple model of the environment to predict WiFi connectivity. It uses these predictions to delays transfers to offload more data on WiFi, but only if delaying reduces 3G usage and the transfers can be completed within the application’s tolerance threshold. For applications that are extremely sensitive to delay or loss (e.g., VoIP), Wiffler quickly switches to 3G if WiFi is unable to successfully transmit the packet within a small time window. We implement and deploy Wiffler in our vehicular testbed. Our experiments show that Wiffler significantly reduces 3G usage. For a realistic workload, the reduction is 45 % for a delay tolerance of 60 seconds.

In this poster we describe initial findings regarding Internet usage characteristics, in particular TCP flows from a field study with 25 iPhone users. We present details regarding their usage characteristics, and provide a solution for migrating flows between different networks and/or network interfaces without requiring infrastructure support or changes to current applications and protocols, and with minimal impact to the user. 1.

Abstract—Deploying city-wide 802.11 access points has made possible internet access in a vehicle, nevertheless it is challenging to maintain client performance at vehicular speed especially when multiple mobile users exist. This paper considers the association control problem for vehicular networks in drivethru Internet scenarios. In particular, we aim to improve the overall throughput and fairness for all users. We design efficient algorithms to achieve the objectives through several techniques including approximation. Our simulation results confirm the performance of our algorithms. I.

We have deployed a large-scale multi-tier wireless network in one of Houston’s most economically disadvantaged neighborhoods. The network serves two objectives: empowering under-resourced communities with access to technology, education and work-at-home tools, and providing an unprecedented platform for research of wireless communication technologies. In this paper, we present the joint societal objectives of the network, its technical and economical properties, the obtained research results, and future research challenges.

We investigate a hybrid wireless access network design that integrate 3G and WiFi networks, specifically targeting vehicular mobility. The goal is to shift the load from the expensive 3G network to the less expensive WiFi network without hurting the user experience. As a test platform we choose a nationwide 3G network and a commercially operated metroscale WiFi network. We show that over a wide geographic region and under vehicular mobility, these networks exhibit different throughput and coverage characteristics, The characteristics are often complementary and can be judiciously exploited for the hybrid design. Instead of simply striping data over two network connections, we develop a utility and cost-based formulation that decides the right amount of load that can be put on the 3G network to maximize user’s benefit. We develop and experiment with a scheduler to do this. We show that the hybrid design is able to deliver much superior mobile video streaming experience for the user while reducing the load on the 3G network by three-fourth. 1.