Steven Lanzisera

Low-Power 2.4-GHz Transceiver With Passive RX Front-End and 400-mV Supply

An ultra low power 2.4-GHz transceiver targeting wireless sensor network applications is presented. The receiver front-end is fully passive, utilizing an integrated resonant matching network to achieve voltage gain and interface directly to a passive mixer. The receiver achieves a 7-dB noise figure and -7.5-dBm IIP3 while consuming 330 muW from a 400-mV supply. The binary FSK transmitter delivers 300 muW to a balanced 50-Omega load with 30% overall efficiency and 45% power amplifier (PA) efficiency. Performance of the receiver topology is analyzed and simple expressions for the gain and noise figure of both the passive mixer and matching network are derived. An analysis of passive mixer input impedance reveals the potential to reject interferers at the mixer input with characteristics similar to an extremely high-Q parallel LC filter centered at the switching frequency

SoC Issues for RF Smart Dust

Wireless sensor nodes are autonomous devices incorporating sensing, power, computation, and communication into one system. Applications for large scale networks of these nodes are presented in the context of their impact on the hardware design. The demand for low unit cost and multiyear lifetimes, combined with progress in CMOS and MEMS processing, are driving development of SoC solutions for sensor nodes at the cubic centimeter scale with a minimum number of off-chip components. Here, the feasibility of a complete, cubic millimeter scale, single-chip sensor node is explored by examining practical limits on process integration and energetic cost of short-range RF communication. Autonomous cubic millimeter nodes appear within reach, but process complexity and substantial sacrifices in performance involved with a true single-chip solution establish a tradeoff between integration and assembly.

RF Time of Flight Ranging for Wireless Sensor Network Localization

A simple system for measuring the peer to peer radio frequency time of flight between two identical sensor motes for distance measurement is presented. This scheme uses a 2.4 GHz radio, simple real time processing, and offline range extraction. Methods for reducing error from clock offset and multipath propagation are presented and implemented on prototype hardware. Measurement results are presented including measurements taken in a coal mine. Typical ranging accuracies are between 1 mRMS and 3 mRMS

An ultra-low power 900 MHz RF transceiver for wireless sensor networks

A 900 MHz, ultra-low power RF transceiver is presented for wireless sensor networks. It radiates -6 dBm in transmit mode and has a receive sensitivity of -94 dBm while consuming less than 1.3 mW in either mode from a 3 volt battery. Two of these transceivers have been demonstrated communicating over 16 meters through walls at a bit rate of 20 kbps while using only 4 off-chip components.

An Ultra-Low Power 2.4GHz RF Transceiver for Wireless Sensor Networks in 0.13/spl mu/m CMOS with 400mV Supply and an Integrated Passive RX Front-End

A 2.4GHz RF transceiver in 130nm CMOS for sensor networks is presented. The transceiver operates from 400mV to accommodate a single solar cell power supply. The RX dissipates 200 to 750muW and achieves a 6.7dB NF and a -6.2dBm IIP3 at 330muW. At 300muW output power, the PA is 44% efficient and the overall TX is 30% efficient

Mitigating Multipath Fading through Channel Hopping in Wireless Sensor Networks

Wireless communication between a pair of nodes can suffer from self interference arising from multipath propagation reflecting off obstacles in the environment. In the event of a deep fade, caused by destructive interference, no signal power is seen at the receiver, and so communication fails. Multipath fading can be overcome by shifting the location of one node, or by switching the communication carrier frequency. The effects of such actions can be characterized by the coherence length (L) and coherence bandwidth (B), respectively, given as the amount of shift necessary to transition from a deep fade to a region of average signal strength. Experimental results for a representative 2.4GHz wireless link indicate L = 5.5cm and B can vary from 5MHz at long ranges up to 15MHz for short links. For wireless sensor networks (WSNs), typically operating under the IEEE802.15.4 standard, multipath effects are therefore best handled by a channel hopping scheme in which successive communication attempts are widely spread across available carrier frequencies.

Radio Frequency Time-of-Flight Distance Measurement for Low-Cost Wireless Sensor Localization

Location-aware wireless sensor networks will enable a new class of applications, and accurate range estimation is critical for this task. Low-cost location determination capability is studied almost entirely using radio frequency received signal strength (RSS) measurements, resulting in poor accuracy. More accurate systems use wide bandwidths and/or complex time-synchronized infrastructure. Low-cost, accurate ranging has proven difficult because small timing errors result in large range errors. This paper addresses estimation of the distance between wireless nodes using a two-way ranging technique that approaches the Cramér-Rao Bound on ranging accuracy in white noise and achieves 1-3 m accuracy in real-world ranging and localization experiments. This work provides an alternative to inaccurate RSS and complex, wide-bandwidth methods. Measured results using a prototype wireless system confirm performance in the real world.

Reducing Average Power in Wireless Sensor Networks through Data Rate Adaptation

The use of variable data rate can reduce network latency and average power consumption, and automatic rate selection is critical for improving scalability and minimizing network overhead. In the IEEE 802.15.4 standard the SNR can be inferred through the radio reported link quality or received signal strength, and an extension to the standard leads to highly dynamic and accurate rate selection. Using data from an experimental study of 44 IEEE 802.15.4 nodes in an industrial mesh network, SNR is extracted to show sufficient margin exists for higher data rate communication. A variable rate signaling scheme with automatic rate selection is proposed to provide links at the standard 250kb/s as well as 500kb/s, 1000kb/s and 2000kb/s with a minimum of hardware changes. Using the experimental data to generate a model of the real world system, total network energy is compared using legacy and variable rate signaling showing over 40% savings.

@scale: insights from a large, long-lived appliance energy WSN

We present insights obtained from conducting a year-long, 455 meter deployment of wireless plug-load electric meters in a large commercial building. We develop a stratified sampling methodology for surveying the energy use of Miscellaneous Electric Loads (MELs) in commercial buildings, and apply it to our study building. Over the deployment period, we collected over nine hundred million individual readings. Among our findings, we document the need for a dynamic, scalable IPv6 routing protocol which supports point-to-point routing and multiple points of egress. Although the meters are static physically, we find that the set of links they use is dynamic; not using such a dynamic set results in paths that are twice as long. Finally, we conduct a detailed survey of the accuracy possible with inexpensive AC metering hardware. Based on a 21-point automated calibration of a population of 500 devices, we find that it is possible to produce nearly utility-grade metering data.

Theoretical and Practical Limits to Sensitivity in IEEE 802.15.4 Receivers

This paper addresses the performance limits of the IEEE 802.15.4 standard 2.4 GHz PHY for wireless personal area and sensor networks. As designers start considering the addition of power amplifiers to improve link margin, other methods that do not increase power significantly are of high value. Minimizing power consumption is the key goal of 802.15.4 systems, and improvements in sensitivity can be traded for power savings. The limits from communication theory are compared to the performance of common system topologies, and methods for improving system performance without significant cost are discussed and verified through simulation. Approximately 6.6 dB of sensitivity is shown to be commonly sacrificed, and 5.8 dB is recoverable without large increases in design complexity.