Increased range bistatic scatter radio

Summarization: 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.Παρουσιάστηκε στο: IEEE Transactions on Communication

Simple, Zero-Feedback, Distributed Beamforming With Unsynchronized Carriers

This work studies zero-feedback distributed beamforming; we are motivated by scenarios where the links between destination and all distributed transmitters are weak, so that no reliable communication in the form of pilot signals or feedback messages can be assumed. Furthermore, we make the problem even more challenging by assuming no specialized software/hardware for distributed carrier synchronization; we are motivated by ultra-low complexity transceivers. It is found that zero-feedback (i.e. blind), constructive, distributed signal alignment at the destination is possible; the proposed scheme exploits lack of carrier synchronization among M distributed transmitters and provides beamforming gains. Possible applications include reachback communication in low-cost sensor networks with simple (i.e. conventional, no carrier frequency/phase adjustment capability) radio transceivers.Greece. Ministry of Developmen

Interference-limited opportunistic relaying with reactive sensing

Summarization: This work evaluates opportunistic relaying in the presence of thermal noise as well as interference, when channel sensing is conducted reactively, in slow fading environments. The studied scenario employs a single gateway that provides access towards several destinations with weak links and exploits a network of intermediate relays. In sharp contrast to prior art, no inter-relay channel state information or communication is assumed, no network coding is needed, while low-complexity receivers at each destination are employed. It is shown that information can be relayed without delay, while harvesting benefits of cooperative diversity, even at the presence of interference. The participating relays are required to offer strong paths towards source and destination, while at the same time they are as "isolated" as possible from each other. From that perspective, the notion of relay "usefulness" is redefined in both noise and interference-limited environments, under opportunistic relaying.Presented on: IEEE Wireless Communication

Anti-collision backscatter sensor networks

Summarization: Sensor collision (interference) is studied in a large network of low bit-rate sensors that communicate via backscatter, i.e. modulate the reflection of a common carrier transmitted by a central reader. Closed-form analysis is provided, quantifying sensor collision (interference) in high-density, backscatter sensor networks (BSN), as a function of number of tags and aggregate bandwidth. Analysis is applicable to a broad class of sensor subcarrier modulations, propagation environments and reader antenna directivity patterns. It is discovered that anti-collision performance in high-density backscatter sensor networks is feasible provided that appropriate modulation is used at each sensor. That is due to the round-trip nature of backscatter communication as well as the extended target range, which both impose stringent requirements on spectrum efficiency, not easily met by all modulations. Furthermore, aggregate bandwidth savings for given anti-collision performance are quantified, when simple division techniques on subcarrier (modulating) frequency and space (via moderately directive hub antenna) are combined.Presented on: IEEE Wireless Communication

Improving backscatter radio tag efficiency

Summarization: This paper studies tag properties for optimized tag-to-reader backscatter communication. The latter is exploited in RF identification (RFID) systems and utilizes binary reflection coefficient change of the tag antenna-load circuit. It is shown that amplitude maximization of complex reflection coefficient difference between the two states is not sufficient for optimized tag-to-reader backscatter communication, contrary to what is commonly believed in the field. We provide a general tag load selection methodology that applies to any tag antenna, including minimum scattering antennas as a special case. The method is based on tag antenna structural mode closed-form calculation (given three values of tag radar cross section), employs simple antenna/communication theory, and applies to both passive, as well as semipassive RFID tags.Presented on: IEEE Transactions on Microwave Theory and Technique

Room-coverage improvements in UHF RFID with commodity hardware

Summarization: This work studies the three-dimensional (3D) identification performance of UHF RFID systems with commodity hardware. Detailed three-dimensional propagation modeling is developed, with ray-tracing that allows examination of tag- as well as reader-antenna diversity. It is shown that multipath can enhance identification performance compared to free-space conditions. Furthermore, it is found that tag diversity can enhance identification performance on the order of 10%. Reader-antenna diversity becomes beneficial only when special attention is given to controlling the destructive summation of the transmitted fields and simple, general antenna-installation rules are provided. Performance can be further enhanced with the introduction of a phase shifter or appropriate transmission scheduling, and various examples are discussed. Measurements inside a room with a dense three-dimensional grid of passive RFID tags confirmed the results. Finally, a method to perform power-measurements with commodity RFID hardware that exploits the sensitivity-during-read threshold of each tag is put forth.Presented on: IEEE Antennas and Propagation Magazin

A site-specific stochastic propagation model for passive UHF RFID

Summarization: This letter proposes a computationally inexpensive, site-specific propagation model, useful in coverage evaluation of radio frequency identification (RFID) networks with passive tags. The parameters of a Rice distribution for each point in the volume of interest are computed using site-specific approximations that address overall space geometry, materials, and polarization. The probability of successful identification of passive RFID tags is calculated. Coverage statistics and performance evaluation of complex RFID networks can be quickly conducted. Experimental results at the UHF regime corroborate the accuracy of the model.Presented on: IEEE Antennas and Wireless Propagation Letter

Theoretical findings and measurements on planning a UHF RFID system inside a room

Summarization: This paper investigates the problem of im-proving the identification performance of a UHF RFID system inside a room. We assume static reader, passive tags and availability of commodity antennas. A ray-tracing propagation model is developed that includes multipath in 3D space. It is found that careful selection of reader antenna placement and tilting must be performed to control destructive interference effects. Furthermore, 3D coverage performance gains on the order of 10% are observed by implementing tags' diversity. A device that successfully manipulates destructive interference is intro-duced. All theoretical findings are verified by meas-urements. Finally, a method to perform propagation measurements with commodity RFID hardware is demonstrated.Presented on: Radioengineerin

On the design, installation, and evaluation of a radio frequency identification system for healthcare applications

Summarization: In this paper, we present the design, implementation, and testing of a radio-frequency identification (RFID) system for healthcare applications. The constantly growing passive RFID technology at ultra-high frequencies (UHF), in conjunction with current state-of-the-art information and communication technologies (ICTs), was used for the system design. The end product was installed at an oncology hospital in Cyprus, where it was thoroughly evaluated by medical staff and hospital administrators. This pilot project had three main objectives: a) automatic and error-free patient identification of in-hospital patients using RFID-enabled cards or wristbands; b) Real-time location service (RTLS) for locating and tracking medical assets and high-value equipment in the hospital ward; c) quick and hassle-free drug inventory management through the use of inexpensive smart labels and cost-effective stationary readers. Here, we present a detailed description of the three major subsystems of the pilot project, emphasizing the main features and capabilities of the system, important design and implementation issues, as well as system evaluation and testing. During the design stage of the project, special emphasis was placed on user friendliness, system capabilities, adequate coverage and tag readability, privacy and security of sensitive patient data, system reliability, and the daily practices of medical personnel and hospital administrators.Presented on: IEEE Antennas and Propagation Magazin

Conformal Array Antenna Modelling within EUCLID CEPA-1 / Modern Radar Technology

The mounting of antennas on military platforms, land-, sea- and air-based is a well-known problem due to the conflict it generates between platform and sensor interests. Most visibly this situation arises in aircraft where platform interests gain the highest priority and lead to sub-optimum antennas and antenna positions. Examples are limited field-of-view nose-mounted radar antennas and aerodynamically radomed communication antennas