Maximizing Transmission Opportunities in Wireless Multihop Networks

Being readily available in most of 802.11 radios, multirate capability appears to be useful as WiFi networks are getting more prevalent and crowded. More specifically, it would be helpful in high-density scenarios because internode distance is short enough to employ high data rates. However, communication at high data rates mandates a large number of hops for a given node pair in a multihop network and thus, can easily be depreciated as per-hop overhead at several layers of network protocol is aggregated over the increased number of hops. This paper presents a novel multihop, multirate adaptation mechanism, called multihop transmission opportunity (MTOP), that allows a frame to be forwarded a number of hops consecutively to minimize the MAC-layer overhead between hops. This seemingly collision-prone nonstop forwarding is proved to be safe via analysis and USRP/GNU Radio-based experiment in this paper. The idea of MTOP is in clear contrast to the conventional opportunistic transmission mechanism, known as TXOP, where a node transmits multiple frames back-to-back when it gets an opportunity in a single-hop WLAN. We conducted an extensive simulation study via OPNET, demonstrating the performance advantage of MTOP under a wide range of network scenarios

Soft Pneumatic Actuator Skin with Embedded Sensors

Soft Pneumatic Actuator skin (SPA-skin) is a novel concept of ultra-thin (< 1 mm) sensor embedded actuators with distributed actuation points that could cover soft bodies. This highly customizable and flexible SPA-skin is ideal for providing proprioceptive sensing by covering pre-existing structures and robots bodies. Having few limitation of the surface quality, dynamics, or shape, these mechanical attributes allow potential applications in autonomous flexible braille, active surface pattern reconfiguration, distributed actuation and sensing for tactile interface improvements. In this paper, the authors present a proof-of-concept SPA-skin. The mechanical parameters, design criteria, sensor selection, and actuator construction process are illustrated. Two control schemes, actuation mode and force sensing mode, are also demonstrated with the latest prototype

Joint Rate and Voltage Adaptation to Save Energy of Software Radios in Underutilized WLAN

This paper proposes an energy-saving bit-rate adaptation algorithm for Software-defined Radio (SDR)-based wireless systems, called Joint Rate and Voltage Fallback (JRF). It exploits the unused network time in underutilized networks by using a lower bit-rate than what an underlying rate adaptation algorithm such as Auto-rate Fallback (ARF) or Robust Rate Adaptation Algorithm (RRAA) dictates. While slow or low bitrate communication potentially consumes more energy due to its extended communication time, it saves energy in SDR due to the possibility of reducing the speed and the voltage of the microprocessor that runs the SDR software. The net result favors a lower rate communication in terms of energy performance. To analyze the tradeoff quantitatively, this paper evaluates the computational complexity of SDR communication software by using BBN 802.11b implementation in GNU Radio. Moreover, for an extensive evaluation, we conducted the simulation study based on OPNET, which shows that JRF improves energy cost by as much as 78.0% compared to No Rate and Voltage Scaling (NoRVS) and as much as 51.3% compared to Independent Rate and Voltage Scaling (IRVS)

Latency Analysis in GNU Radio/USRP-based Software Radio Platforms

Software-Defined Radio (SDR) is a promising radio technology that implements radio communication functionalities in software instead of hardware. Advantages of a SDR system are reconfigurability and flexibility whereas disadvantages are low throughput and high latency. Our research focuses on analyzing and measuring latency of a SDR system based on GNU Radio with three versions of Universal Software Radio Peripherals (USRP) devices - USRP1, USRP2 and USRP E100. This research identifies the sources of the latency and quantifies them by using both analytical and experimental methods. For the analysis, we identify all types of buffers in the SDR platforms and estimate the time that these buffers contribute. The corresponding results are compared with experimental measurement, which estimates the round-trip time between two SDR systems. This can be done by using TUN/TAP components and GNU Radio tunnel program. Alternatively, we also propose a method called hwlatency to measure the latency in hardware side. We believe this study offers the better understanding of the latency in SDR platforms and will lead to correct implementations of high-level network protocols for SDR systems

Joint Rate and Voltage Adaptation to Save Energy of Software Radios in Underutilized WLAN

This paper proposes an energy-saving bit-rate adaptation algorithm for Software-defined Radio (SDR)-based wireless systems, called Joint Rate and Voltage Fallback (JRF). It exploits the unused network time in underutilized networks by using a lower bit-rate than what an underlying rate adaptation algorithm such as Auto-rate Fallback (ARF) or Robust Rate Adaptation Algorithm (RRAA) dictates. While slow or low bitrate communication potentially consumes more energy due to its extended communication time, it saves energy in SDR due to the possibility of reducing the speed and the voltage of the microprocessor that runs the SDR software. The net result favors a lower rate communication in terms of energy performance. To analyze the tradeoff quantitatively, this paper evaluates the computational complexity of SDR communication software by using BBN 802.11b implementation in GNU Radio. Moreover, for an extensive evaluation, we conducted the simulation study based on OPNET, which shows that JRF improves energy cost by as much as 78.0% compared to No Rate and Voltage Scaling (NoRVS) and as much as 51.3% compared to Independent Rate and Voltage Scaling (IRVS)

Latency Analysis in GNU Radio/USRP-based Software Radio Platforms

Software-Defined Radio (SDR) is a promising radio technology that implements radio communication functionalities in software instead of hardware. Advantages of a SDR system are reconfigurability and flexibility whereas disadvantages are low throughput and high latency. Our research focuses on analyzing and measuring latency of a SDR system based on GNU Radio with three versions of Universal Software Radio Peripherals (USRP) devices - USRP1, USRP2 and USRP E100. This research identifies the sources of the latency and quantifies them by using both analytical and experimental methods. For the analysis, we identify all types of buffers in the SDR platforms and estimate the time that these buffers contribute. The corresponding results are compared with experimental measurement, which estimates the round-trip time between two SDR systems. This can be done by using TUN/TAP components and GNU Radio tunnel program. Alternatively, we also propose a method called hwlatency to measure the latency in hardware side. We believe this study offers the better understanding of the latency in SDR platforms and will lead to correct implementations of high-level network protocols for SDR systems

Fast and Accurate Wi-Fi Localization in Large-Scale Indoor Venues

An interest and development of indoor localization has grown along with the scope of applications. In a large and crowded indoor venue, the population density of access points (APs) is typically much higher than that in small places. This may cause a client device such as a smartphone to capture an imperfect Wifi fingerprints (FPs), which is essential piece of data for indoor localization. This is due to the limited access time allocated per channel and collisions of responses from APs. It results in an extended delay for localization and a massive unnecessary traffic in addition to a high estimation error. This paper proposes a fast and accurate indoor localization method for large-scale indoor venues using a small subset of APs, called representative APs (rAPs). According to our experimental study in a large venue with 1,734 APs, the proposed method achieves the estimation error of 1.8∼2.1m, which can be considered a very competitive performance even in small-scale places with a few hundreds of APs

Energy Efficient Wifi Tethering on a Smartphone

While numerous efforts have been made to save energy of “client” devices but it has not been addressed for access points (APs) as they are assumed to be supported by AC power. This paper proposes E-MAP, which is an energy saving algorithm for a tethering smartphone that plays a role of mobile AP (MAP) temporarily. It saves MAP\u27s energy by introducing the sleep cycle as in power save mode (PSM) in 802.11 but successfully keeps clients from transmitting while it sleeps. One important design goal of E-MAP is backward compatibility, i.e., it requires no modification on the client side and supports PSM and adaptive PSM (A-PSM) as well as normal constant awake mode (CAM) clients. Experiments show that E-MAP reduces the energy consumption of a Wifi tethering smartphone by up to 54% with a little impact on packet delay under various traffic patterns derived from real-life traces