Aditya Dhananjay

Practical, distributed channel assignment and routing in dual-radio mesh networks

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. This paper presents ROMA, a practical, distributed channel assignment and routing protocol that achieves good multi-hop path performance between every node and one or more designated 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.

Hermes: data transmission over unknown voice channels

While the cellular revolution has made voice connectivity ubiquitous in the developing world, data services are largely absent or are prohibitively expensive. In this paper, we present Hermes1, 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 5× and reduces the cost-per-byte by over a factor of 50x

Comparing web interaction models in developing regions

Internet connections in developing regions are scarce and often unreliable. While options for connecting to the Internet are gradually being realized, progress is slow. We observed people performing web search and browsing in a low bandwidth environment in Kerala, India. We found that people in this environment experienced frustration and boredom while waiting for page loads compared to typical experiences in the developed world. Following these observations, we conducted a formal study with 20 participants at the same location comparing the conventional web search and browsing process with an asynchronous queueing model. Participants using the asynchronous queueing system performed as well as the status quo in terms of the number of tasks completed, and we observed greater interaction and information viewed for the asynchronous system. Our participants also preferred the asynchronous system over conventional search. Finally, we found evidence that the asynchronous system would have greater benefits in environments where the network is even more constrained.

WiRE: a new rural connectivity paradigm

Many rural areas in developing regions remain largely disconnected from the rest of the world due to low purchasing power and the exorbitant cost of existing connectivity solutions. Wireless Rural Extensions (WiRE) is a low-power rural wireless network architecture that provides inexpensive, self-sustainable, and high-bandwidth connectivity. WiRE relies on a high-bandwidth directional wireless backbone with local distribution networks to provide focused IP coverage. WiRE also provides cellular connectivity using OpenBTS-based GSM microcells. It supports a naming and addressing framework that inter-operates with traditional telecom networks and enables a wide range of mobile services on a common IP framework. The entire name network can be built by integrating a range of off-the-shelf components and existing open source tools.Many rural areas in developing regions remain largely disconnected from the rest of the world due to low purchasing power and the exorbitant cost of existing connectivity solutions. Wireless Rural Extensions (WiRE) is a low-power rural wireless network architecture that provides inexpensive, self-sustainable, and high-bandwidth connectivity. WiRE relies on a high-bandwidth directional wireless backbone with local distribution networks to provide focused IP coverage. WiRE also provides cellular connectivity using OpenBTS-based GSM microcells. It supports a naming and addressing framework that inter-operates with traditional telecom networks and enables a wide range of mobile services on a common IP framework. The entire name network can be built by integrating a range of off-the-shelf components and existing open source tools.

Public Safety Communications above 6 GHz: Challenges and Opportunities

Advanced public safety communication (PSC) services call for fast, reliable and low-latency communication technologies, capable of supporting diverse communication modes (aerial, unmanned, vehicular, and peer-to-peer), fast channel dynamics, and ad hoc or mesh structures. For this reason, PSC has been identified as one of the key potential uses cases for the next generation of communication systems, the so-called 5G. In this scenario, the millimeter wave (mmWave) bands and other frequencies above 6 GHz are particularly interesting, since they are largely untapped and offer vastly more spectrum than current cellular allocations in the highly congested bands below 6 GHz, thus enabling orders of magnitude greater data rates and reduced latency. For example, new PSC networks in the mmWave bands could support high-definition video, virtual reality, and other broadband data to large numbers of first responders. Surveillance drones or ambulances could also be provided high-speed connectivity along with machine-type communication for remotely controlled robotic devices entering dangerous areas. However, the way towards this ambitious goal is hindered by a number of open research challenges. In this paper, after a brief introduction to PSC services and requirements, we illustrate the potential of the frequencies above 6 GHz for PSC and discuss the open problems that need to be solved in order to pave this way. Finally, we describe the main components of a test platform for mmWave systems that is functional to the study of such complex scenarios and that we plan to develop as an invaluable tool for realizing mmWave PSC networks.