Scatter Radio Research Articles

Reconstructing Meteoroid Trajectories Using Forward Scatter Radio Observations From the BRAMS Network

AbstractIn this paper, we aim to reconstruct meteoroid trajectories using a forward scatter radio system transmitting a continuous wave (CW) with no modulation. To do so, we use the meteor echoes recorded at the receivers of the BRAMS (Belgian RAdio Meteor Stations) network. This system consists, at the time of writing, of a dedicated transmitter and 44 receiving stations located in and nearby Belgium, all synchronized using GPS clocks. Our approach processes the meteor echoes at the BRAMS receivers and uses the time delays as inputs to a nonlinear optimization solver. We compare the quality of our reconstructions with and without interferometric data to the trajectories given by the optical CAMS (Cameras for Allsky Meteor Surveillance) network in Benelux. We show that the general CW forward scatter trajectory reconstruction problem can be solved, but we highlight its strong ill‐conditioning. With interferometry, this high sensitivity to the inputs is alleviated and the reconstructed trajectories are in good agreement with optical ones, displaying an uncertainty smaller than 10% on the velocity and 2° on the inclination for most cases. To increase accuracy, the trajectory reconstruction with time delays only should be complemented by information about the signal phase. The use of at least one interferometer makes the problem much easier to solve and greatly improves the accuracy of the retrieved velocities and inclinations. Increasing the number of receiving stations also enhances the quality of the reconstructions.

Multistatic Scatter Radio Sensor Networks for Extended Coverage

Scatter radio, i.e., communication by means of reflection, has been recently proposed as a viable ultra-low power solution for wireless sensor networks (WSNs). This paper offers a detailed comparison between monostatic and multistatic scatter radio architectures. In monostatic architecture, the reader consists of both the illuminating transmitter and the receiver of signals scattered back from the sensors. The multistatic architecture includes several ultra-low cost illuminating carrier emitters and a single reader. Maximum-likelihood coherent and noncoherent bit error rate (BER), diversity order, average information, and energy outage probability comparison is performed, under dyadic Nakagami fading and filling a gap in the literature. It is found that: 1) diversity order, BER, and tag location-independent performance bounds of multistatic architecture outperform monostatic; 2) energy outage due to radio frequency (RF) harvesting for passive tags, is less frequent in multistatic than monostatic architecture; and 3) multistatic coverage is higher than monostatic. Furthermore, a proof-of-concept digital multistatic scatter radio WSN with a single receiver, four low-cost emitters, and multiple ambiently-powered low-bitrate tags, perhaps the first of its kind, is experimentally demonstrated (at 13 dBm transmission power), covering an area of 3500 m2. Research findings are applicable in the industries of WSNs, RF identification, and emerging Internet-of-Things.

Noncoherent Short Packet Detection and Decoding for Scatter Radio Sensor Networking

Scatter radio, i.e., communication by means of reflection, has been recently proposed as a promising technology for low-power wireless sensor networks (WSNs). Specifically, this paper offers noncoherent receivers in scatter radio frequency-shift keying, for either channel-coded or uncoded scatter radio reception, in order to eliminate the need for training bits of coherent schemes (for channel estimation) at the packet preamble. Noncoherent symbol-by-symbol and sequence detectors based on hybrid composite hypothesis test (HCHT) and generalized likelihood-ratio test, for the uncoded case and noncoherent decoders based on HCHT, for small block-length channel codes, are derived. Performance comparison under Rician, Rayleigh, or no fading, taking into account fixed energy budget per packet is presented. It is shown that the performance gap between coherent and noncoherent reception depends on whether channel codes are employed, the fading conditions (e.g., Rayleigh versus Rician versus no fading), as well as the utilized coding interleaving depth; the choice of one coding scheme over the other depends on the wireless fading parameters and the design choice for extra diversity versus extra power gain. Finally, experimental outdoor results at 13-dBm transmission power corroborate the practicality of the proposed noncoherent detection and decoding techniques for scatter radio WSNs.

Soil Moisture Scatter Radio Networking With Low Power

A low-cost (6 Euro per sensor), low-power (in the order of $200~\mu \text{W}$ per sensor), with high communication range (on the order of 250 m), scatter radio sensor network is presented, for soil moisture monitoring at multiple locations. The proposed network utilizes analog frequency modulation in a bistatic network architecture (i.e., the emitter and reader are not colocated), while the sensors operate simultaneously, using frequency-division multiple access. In contrast to prior art, this paper utilizes an ultralow-cost software-defined radio reader and offers custom microstrip capacitive sensing with simple calibration, as well as modulation pulses for each scatter radio sensor with 50% duty cycle; the latter is necessary for scalable network designs. The overall root mean squared error below 1% is observed, even for the range of 250 m. This is another small (but concrete) step for the adoption of scatter radio technology as a key enabling technology for scalable, large-scale, low-power, and cost environmental sensor networking.

Converting a Plant to a Battery and Wireless Sensor with Scatter Radio and Ultra-Low Cost

Electric potential (EP) signals are produced in plants through intracellular processes, in response to external stimuli (e.g., watering, mechanical stress, light, and acquisition of nutrients). However, wireless transmission of a massive amount of biologic EP signals (from one or multiple plants) is hindered by existing battery-operated wireless technology and increased associated monetary cost. In this paper, a self-powered batteryless EP wireless sensor is presented that harvests near-maximum energy from the plant itself and transmits the EP signal tens of meters away with a single switch, based on inherently low-cost and low-power bistatic scatter radio principles. The experimental results confirm the ability of the proposed wireless plant sensor to achieve a fully autonomous operation by harvesting the energy generated by the plant itself. In addition, EP signals experimentally acquired by the proposed wireless sensor from multiple plants have been processed using nonnegative matrix factorization, demonstrating a strong correlation with environmental light irradiation intensity and plant watering. The proposed low-cost batteryless plant-as-sensor-and-battery instrumentation approach is a first but solid step toward large-scale electrophysiology studies of important socioeconomic impact in ecology, plant biology, and precision agriculture.

Coherent Detection and Channel Coding for Bistatic Scatter Radio Sensor Networking

With rapid advances of scatter radio systems, the principle of reflection rather than active transmission employed by backscatter sensor networks, has emerged as a potential key enabler for low-cost, large-scale and dense ubiquitous sensor networks. Despite the presence of three different unknown channel links due to the bistatic setup (i.e., carrier emitter and receiver are dislocated), as well as multiple unknown scatter radio-related parameters, this work offers a novel coherent receiver of frequency-shift keying (FSK) modulation for the bistatic scatter radio channel. Furthermore, with the objective of range maximization, specific short block-length cyclic channel codes are utilized. The proposed approach requires minimum encoding complexity, ideal for resource-constrained, ultra-low power (e.g. microcontroller unit-based), low-bit rate scatter radio tags, adheres to simple low-complexity decoding at the receiver and achieves high-order signal diversity. Analysis is followed by experimental validation with a commodity software-defined radio (SDR) reader and a custom scatter radio tag; tag-to-reader ranges up to 150 meters are demonstrated with as little as 20 milliWatt transmission power, increasing sensing ranges by approximately 10 additional meters, compared to state-of-the-art bistatic scatter radio receivers. With the imminent emergence of backscatter sensor networks, this work serves as a small step forward towards the realization of low-cost, low-power, increased-range, wireless sensing applications.

Wireless Environmental Sensor Networking With Analog Scatter Radio and Timer Principles

Environmental variables monitoring with wireless sensor networks (WSNs) is invaluable for precision agriculture applications. However, the effectiveness of existing low-power, conventional (e.g., ZigBee-type) radios in large-scale deployments is limited by power consumption, cost, and complexity constraints, while the existing WSN solutions employing nonconventional, scatter-radio principles have been restricted to communication ranges of up to a few meters. In this paper, the development of a novel analog scatter-radio WSN is presented, that employs semipassive sensor/tags in bistatic topology (i.e., carrier emitter placed in a different location from the reader), consuming <;1 mW of power, with communication range exceeding 100 m. The experimental results indicate that the multipoint surface fitting calibration, in conjunction with the employed two-phase filtering process, both provide a mean absolute error of 1.9% environmental relative humidity for a temperature range of 10 °C-50 °C. In addition, the energy consumption per measurement of the proposed environmental monitoring approach can be lower than that of conventional radio WSNs. Finally, the proposed approach operational characteristics are presented through a real-world network deployment in a tomato greenhouse.

Increased Range Bistatic Scatter Radio

Scatter radio achieves communication by reflection and requires low-cost and low-power RF front-ends. However, its use in wireless sensor networks (WSNs) is limited, since commercial scatter radio (e.g. RFID) offers short ranges of a few tens of meters. This work redesigns scatter radio systems and maximizes range through non-classic bistatic architectures: the carrier emitter is detached from the reader. It is shown that conventional radio receivers may show a potential 3dB performance loss, since they do not exploit the correct signal model for scatter radio links. Receivers for on-off-keying (OOK) and frequency-shift keying (FSK) that overcome the frequency offset between the carrier emitter and the reader are presented. Additionally, non-coherent designs are also offered. This work emphasizes that sensor tag design should accompany receiver design. Impact of important parameters such as the antenna structural mode are presented through bit error rate (BER) results. Experimental measurements corroborate the long-range ability of bistatic radio; ranges of up to 130 meters with 20 milliwatts of carrier power are experimentally demonstrated, with commodity software radio and no directional antennas. Therefore, bistatic scatter radio may be viewed as a key enabling technology for large-scale, low-cost and low-power WSNs.

Result of Bandwidth Tests on the 185-Mile Florida-Cuba Tropospheric Scatter Radio System

Some proposed tropospheric scatter paths are several hundred miles long, and their geometry suggests the possibility that the increased relative delays of signal components traveling the higher-altitude paths could result in significant interchannel modulation interference in an FM system. Therefore, a program of experimental investigation has been undertaken by Bell Telephone Laboratories to determine the extent of the intermodulation problem. Tone amplitude stability tests have been included as part of the study. The first in a planned series of tests was conducted during March, 1960, over the 185-mile FM system between Florida City, Fla. and Guanabo, Cuba. The system was loaded with random noise of various bandwidths up to 2.5 Mc, and peak deviations up to ±8 Mc were used. Tests were made with no diversity and with dual diversity. It was found that intermodulation, resulting from multipath propagation can _limit system performance. Both deviation and base bandwidth are important and have an influence on intermodulation and tone stability. Diversity has little effect on intermodulation but improves tone stability appreciably. The paper presents numerical results of the measurements of average intermodulation and some information on cumulative probability distributions for various combinations of base bandwidth, deviation, and diversity.