Rupa Krishnan

MiNT-m: an autonomous mobile wireless experimentation platform

Limited fidelity of software-based wireless network simulations has prompted many researchers to build testbeds for developing and evaluating their wireless protocols and mobile applications. Since most testbeds are tailored to the needs of specific research projects, they cannot be easily reused for other research projects that may have different requirements on physical topology, radio channel characteristics or mobility pattern. In this paper, we describe the design, implementation and evaluation of MiNT-m, an experimentation platform devised specifically to support arbitrary experiments for mobile multi-hop wireless network protocols. In addition to inheriting the miniaturization feature from its predecessor MiNT [9], MiNT-m enables flexible testbed reconfiguration on an experiment-by-experiment basis by putting each testbed node on a centrally controlled untethered mobile robot. To support mobility and reconfiguration of testbed nodes, MiNT-m includes a scalable mobile robot navigation control subsystem, which in turn consists of a vision-based robot positioning module and a collision avoidance-based trajectory planning module. Further, MiNT-m provides a comprehensive network/experiment management subsystem that affords a user full interactive control over the testbed as well as real-time visualization of the testbed activities. Finally, because MiNT-m is designed to be a shared research infrastructure that supports 24x7 operation, it incorporates a novel automatic battery recharging capability that enables testbed robots to operate without human intervention for weeks.

Client-Centered, Energy-Efficient Wireless Communication on IEEE 802.11b Networks

In mobile devices, the wireless network interface card (WNIC) consumes a significant portion of overall system energy. One way to reduce energy consumed by a device is to transition its WNIC to a lower-power steep mode when data is not being received or transmitted. In this paper, we investigate client-centered techniques for energy efficient communication, using IEEE 802.11b, within the network layer. The basic idea is to conserve energy by keeping the WNIC in high-power mode only when necessary. We track each connection, which allows us to determine inactive intervals during which to transition the WNIC to sleep mode. Whenever necessary, we also shape the traffic from the client side to maximize sleep intervals-convincing the server to send data in bursts. This trades lower WNIC energy consumption for an increase in transmission time. Our techniques are compatible with standard TCP and do not rely on any assistance from the server or network infrastructure. Results show that during Web browsing, our client-centered technique saved 21 percent energy compared to PSM and incurred less than a 1 percent increase in transmission time compared to regular TCP. For a large file download, our scheme saved 27 percent energy on average with a transmission time increase of only 20 percent

Client-centered energy savings for concurrent HTTP connections

In mobile devices, the wireless network interface card (WNIC) consumes a significant portion of overall system energy. One way to reduce energy consumed by a WNIC is to transition it to a lower-power sleep mode when data is not being received or transmitted.This paper investigates client-centered techniques for saving energy during web browsing. The basic idea is that the client predicts when packets will arrive, keeping the WNIC in high-power mode only when necessary. This is challenging because web browsing generally results in concurrent HTTP connections. To handle this, we maintain the state of each open connection on the client and then transition the WNIC to sleep mode when no connection is receiving data. Our technique is compatible with standard TCP and does not rely on any assistance from the server, a proxy, or IEEE 802.11b power-saving mode (PSM). Our technique combines the performance of regular TCP with nearly all the energy-saving of PSM during web downloads, and we save more energy than PSM during client think times. Results show that over an entire web browsing session (downloads and think times), our scheme saves up to 21% energy compared to PSM and incurs less than a 1% increase in transmission time compared to regular TCP.

Design of a Channel Characteristics-Aware Routing Protocol

Radio channel quality of real-world wireless networks tends to exhibit both short-term and long-term temporal variations that are in general difficult to model. To maximize the utilization efficiency of radio resources, it is critical that these temporal fluctuations in radio signal quality be incorporated into wireless routing decisions. In this paper, we explore the design considerations in leveraging accurate real-time radio channel quality information when making routing decisions. Specifically, we propose a channel characteristics-aware routing protocol (CARP) that (1) uses per-packet transmission time to estimate the effective residual capacity of a wireless link, (2) employs a bandwidth probability distribution model to better approximate a wireless paths capacity profile, and (3) applies multi-path routing to exploit diversity among alternative paths and deliver more robust throughputs despite temporal fluctuations in wireless link quality. We evaluated the performance gains of incorporating each of these mechanisms on a miniaturized multi-hop wireless network testbed- MiNT-m.

Globally fair radio resource allocation for wireless mesh networks

Network flows running on a wireless mesh network (WMN) may suffer from partial failures in the form of serious throughput degradation, sometimes to the extent of starvation, because of weaknesses in the underlying MAC protocol, dissimilar physical transmission rates or different degrees of local congestion. Most existing WMN transport protocols fail to take these factors into account. This paper describes the design, implementation and evaluation of a coordinated congestion control (C3L) algorithm that guarantees fair resource allocation under adverse scenarios and thus provides end-to-end max-min fairness among competing flows. The C3L algorithm features an advanced topology discovery mechanism that detects the inhibition of wireless communication links, and a general collision domain capacity re-estimation mechanism that effectively addresses such inhibition. A comprehensive ns-2-based simulation study as well as empirical measurements taken from an IEEE 802.11a-based multi-hop wireless testbed demonstrate that the C3L algorithm greatly improves inter-flow fairness, eliminates the starvation problem, and at the same time maintains high radio resource utilization efficiency.

A networked robot system for wireless network emulation

A major barrier to advancing modern wireless networking research is the lack of an effective wireless network simulation platform that simultaneously offers high fidelity, scalability, reproducibility and ease of use. MiNT [8], [7] is an innovative wireless network emulation platform that is specifically designed to satisfy all these desirable properties. To support reconfigurable network topology and wireless node mobility, MiNT is built on a networked robot system that carries wireless networking equipments and is designed to be completely tetherless, capable of supporting 24X7 operation, and low-cost. This paper describes the design, implementation and evaluation of this networked robot system. Each robot node in MiNT is an iRobots Roomba, which is modified to house an embedded PC equipped with multiple wireless networking interfaces and to re-charge the embedded PC through Roombas built-in self-charging mechanism. For robot navigation and movement, MiNTs networked robot system supports a computer vision-based robot positioning mechanism and a collision avoidance-driven trajectory planning component. Finally, MiNT provides an interactive control interface and visualization interface to give users real-time visibility into and full control over the MiNT testbed.

An empirical comparison of throughput-maximizing wireless mesh routing protocols

Communication quality of wireless network links is heavily dependent on various external factors such as physical geometry of environmental objects and interference among radio signal sources. As a result, the radio channel quality of real-world wireless networks tends to exhibit both short-term and long-term temporal variations that are in general difficult to model analytically. There has been a large body of research on maximizing the overall throughput of wireless mesh networks through dynamic load/capacity measurement and adaptive routing. However, so far there is no comprehensive evaluation of different protocol mechanisms on a real wireless network testbed. In this paper we first identify the major design dimensions of throughput-maximizing wireless mesh network routing protocols: wireless link capacity estimation, routing path selection, and adaptation to temporal link quality fluctuation, and empirically quantify the performance comparison of various alternatives in each dimension using both software simulations and a miniaturized multi-hop wireless network testbed-MiNT-m.