Parmesh Ramanathan

NULLHOC : a MAC protocol for adaptive antenna array based wireless ad hoc networks in multipath environments

A medium access control (MAC) protocol for ad hoc networks of nodes with antenna arrays is presented. The antenna array is used for transmit and receive beamforming with the purpose of increasing spatial reuse by directing nulls at active transmitters and receivers in the neighborhood. In contrast to previous work with directional antennas, our approach is applicable to flat fading multipath channels, such as in indoor or in other rich scattering environments. The MAC protocol is designed to support the control information exchange needed to direct nulls toward other users involved in existing communication sessions. Knowledge of the channel coefficients between a transmitter or receiver and its neighbors is used to design transmit or receive beamformer weights that implement the requisite nulling. Simulations are used to demonstrate the improvements in throughput and transmit powers that are obtained in this approach relative to the conventional IEEE 802.11 MAC protocol.

60 GHz Indoor Networking through Flexible Beams: A Link-Level Profiling

60 GHz technology holds tremendous potential to upgrade wireless link throughput to Gbps level. To overcome inherent vulnerability to attenuation, 60 GHz radios communicate by forming highly-directional electronically-steerable beams. Standards like IEEE 802.11ad have tailored MAC/PHY protocols to such flexible-beam 60 GHz networks. However, lack of a reconfigurable platform has thwarted a realistic proof-of-concept evaluation. In this paper, we conduct an in-depth measurement of indoor 60 GHz networks using a first-of-its-kind software-radio platform. Our measurement focuses on the link-level behavior with three major perspectives: (i) coverage and bit-rate of a single link, and implications for 60 GHz MIMO; (ii) impact of beam-steering on network performance, particularly under human blockage and device mobility; (iii) spatial reuse between flexible beams. Our study dispels some common myths, and reveals key challenges in maintaining robust flexible-beam connection. We propose new principles that can tackle such challenges based on unique properties of 60 GHz channel and cognitive capability of 60 GHz links.

Battery power sensitive video processing in wireless networks

Mobile computers typically have limited energy for computing and communications due to short battery lifetimes. Encoding, decoding, and transmission of video information require significant computing and communication resources. Low power encoding and decoding schemes have been researched extensively. In this paper, we focus on processing encoded video for transmission under low battery power conditions. Such processing, while conserving battery power, attempts to reduce deterioration of video quality.

A cross layer scheme for adaptive antenna array based wireless ad hoc networks in multipath environments

A medium access control (MAC) protocol (NULLHOC) for ad hoc networks of nodes with antenna arrays is presented. The antenna array is used for transmit and receive beamforming with the purpose of increasing spatial reuse by directing nulls at active transmitters and receivers in the neighborhood. In contrast to previous work with directional antennas, our approach is applicable to multipath channels, such as occur indoors or in other rich scattering environments. The MAC protocol is designed to support the control information exchange needed to direct nulls toward other users involved in existing communication sessions. Knowledge of the channel coefficients between a transmitter or receiver and its neighbors is used to design transmit or receive beamformer weights that implement the requisite nulling. Simulations are used to demonstrate the improvements in throughput and transmit powers that are obtained in this approach relative to the IEEE 802.11 MAC protocol. We also analyze the effects of channel estimation errors on our protocol and propose a simple modification of the basic (NULLHOC) protocol to minimize their impact.

Collaborative sensing using sensors of uncoordinated mobility

Wireless sensor networks are useful for monitoring physical parameters and detecting objects or substances in an area. Most ongoing research consider the use of stationary sensors or controlled mobile sensors, which incur substantial equipment costs and coordination efforts. Alternatively, this paper considers using uncoordinated mobile nodes, who is not directed for any specific sensing activity. Each node independently observes a cross section of the field along its own path. The limited observation can be extended via information exchange among nodes coming across each other. For this model, the inherently noisy mobile measurements, incomplete individual observations, different sensing objectives, and collaboration policies must be addressed. The paper proposes a design framework for uncoordinated mobile sensing and one sensing approach based on profile estimation for target detection, field estimation, and edge detection. With simulations, we study its strengths and tradeoffs with stationary and controlled mobile approaches.

Distributed Boundary Estimation using Sensor Networks

We examine the problem of determining boundaries occurring in natural phenomena using sensor networks. Sensor nodes remotely collect data about various points on the boundary. From this data, we estimate the boundary along with the confidence intervals using a regression relationship among sensor locations and the distances to the boundary. The confidence intervals are guaranteed to be narrower than a specified maximum width. Our distributed boundary estimation strategy uses a hierarchical structure of clusters of sensor nodes and requires 20-50% less messages as compared to a centralized scheme. The computed intervals show desired coverage of the true boundary points. Further, motivated by the practical need to estimate the boundary with a minimum number of sensors, we develop an adaptive approach for turning sensors on and off. The number of ON sensors in this scheme is only about 15% more than what a practical Oracle needs, to evaluate the boundary and confidence intervals around it. Our algorithms are also evaluated using data from real sensors on a testbed

Spatial reuse through adaptive interference cancellation in multi-antenna wireless networks

Efficient medium access control in wireless networks has been a challenging task. While the IEEE 802.11 standard coordinates contention effectively, it severely limits the number of concurrent communications. This results in reduced throughput and efficiency. Recent research has focused on employing multiple antennas to increase throughput in a multipath environment by enabling multiple streams between a transmit-receive pair. In this paper we show that exploiting multiuser diversity to enable concurrent communications has certain advantages over multiple streaming. We propose a medium access control (MAC) protocol that uses adaptive interference cancellation with multiple antennas to increase network throughput and to provide better fairness, while requiring minimal change to the widely-deployed 802.11 MAC structure

Collaborative virtual environments for orthopedic surgery

Virtual reality simulators can be beneficial in increasing the quality of training while decreasing the time needed for training a specific skill. These simulators can provide a risk free environment which has the benefit of repetition and correction of the users error. It has been years since the introduction of these simulators into the medical applications. The application of VR in orthopedic surgery, however, is a relatively new area of interest. In this paper, collaborative virtual reality based environments with the application in orthopedic surgery, with a focus on LISS (Less Invasive Stabilization System) plating, is presented. They can be used for training medical residents in orthopedic surgery.

Combining Hard Periodic and Soft Aperiodic Real-Time Task Scheduling on Heterogeneous Compute Resources

Effectively scheduling tasks on heterogeneous resources is critical to maximizing the overall benefit of those resources in system-on-a-chip architectures. In this paper we focus on scheduling soft a periodic tasks alongside periodic tasks with hard deadline constraints on heterogeneous real-time systems. We introduce a method to improve a periodic task responsiveness without breaking periodic task deadline guarantees, by first scheduling periodic tasks offline, then dynamically scheduling a periodic tasks in the remaining resource slack time. Experimental results indicate that the quality of a periodic task scheduling depends highly on the slack distribution within and across resources after periodic task scheduling, and on the flexibility of the a periodic task scheduler to rearrange these compute slacks to accommodate incoming a periodic tasks.

Exploiting spatial multiplexing and reuse in multi-antenna wireless ad hoc networks

Efficient exploitation of multiple antenna capabilities in ad hoc networks requires carefully designed cross-layer techniques. The work presented in this paper provides a medium access control (MAC)/physical cross-layer scheme for ad hoc networks to address several of the challenges involved in cross-layer design. Multiple antenna systems can be used to increase data rate by spatial multiplexing, that is communicating multiple parallel streams, and to increase spatial reuse by interference suppression. Our proposed scheme, called HYB, exploits both spatial multiplexing and reuse so a receiver node can receive multiple simultaneous data streams from a desired transmitter while suppressing interference from other transmitters in the neighborhood. HYB partitions the available degrees of freedom in the antenna array between spatial multiplexing and reuse which allows the user to obtain different performance characteristics. The applicability of HYB spans across all wireless environments, including line-of-sight and dense multipath scenarios. Simulations demonstrate the significant performance gains and flexibility offered by HYB. The simulation results also offer key insights into the multi-antenna resource allocation problem in ad hoc networks based on traffic patterns and network/transport layer protocols, and consequently provide guidelines for network configuration/management. We show that throughput increases when the degrees of freedom allocated to spatial multiplexing increases, while fairness increases when the degrees of freedom allocated to spatial reuse increases.