The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. One of the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference that the modem's transmitter causes to its own receiver. This tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems.

/pdf/in-band-full-duplex-wireless-challenges-and-opportunities-djlyhtrciu.pdf

In-Band Full-Duplex Wireless: Challenges and Opportunities

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. Because one the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference caused by an IBFD node's own transmissions to its desired receptions, this tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems.

We present an experiment-based characterization of passive suppression and active self-interference cancellation mechanisms in full-duplex wireless communication systems. In particular, we consider passive suppression due to antenna separation at the same node, and active cancellation in analog and/or digital domain. First, we show that the average amount of cancellation increases for active cancellation techniques as the received self-interference power increases. Our characterization of the average cancellation as a function of the self-interference power allows us to show that for a constant signal-to-interference ratio at the receiver antenna (before any active cancellation is applied), the rate of a full-duplex link increases as the self-interference power increases. Second, we show that applying digital cancellation after analog cancellation can sometimes increase the self-interference, and thus digital cancellation is more effective when applied selectively based on measured suppression values. Third, we complete our study of the impact of self-interference cancellation mechanisms by characterizing the probability distribution of the self-interference channel before and after cancellation.

/pdf/experiment-driven-characterization-of-full-duplex-wireless-3u33o8w3q1.pdf

Experiment-Driven Characterization of Full-Duplex Wireless Systems

LoRa is a long-range, low-power, low-bitrate, wireless telecommunications system, promoted as an infrastructure solution for the Internet of Things: end-devices use LoRa across a single wireless hop to communicate to gateway(s), connected to the Internet and which act as transparent bridges and relay messages between these end-devices and a central network server. This paper provides an overview of LoRa and an in-depth analysis of its functional components. The physical and data link layer performance is evaluated by field tests and simulations. Based on the analysis and evaluations, some possible solutions for performance enhancements are proposed.

https://www.mdpi.com/1424-8220/16/9/1466/pdf

A Study of LoRa: Long Range & Low Power Networks for the Internet of Things

Measurements of SAW (surface acoustic wave) velocities on the entire surface of free and metallized substrates of 128 degrees rotY-LiNbO/sub 3/ are reported. The influence of mechanical loading is examined. All experimental data are given as trigonometric expansions. Improved sets of material constants for LiNbO/sub 3/ and LiTaO/sub 3/ are calculated by fitting them to the experimentally determined SAW velocities. In agreement with R. Graham (1977), a significantly larger value of e/sub 33/ was found for LiNbO/sub 3/. While all material constants of LiBnO/sub 3/ and most of LiTaO/sub 3/ have reasonable error bounds, further improvements are expected from more accurately measured unclamped permittivities. >

Improved material constants for LiNbO/sub 3/ and LiTaO/sub 3/

Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

Acoustic Wave Filter Technology–A Review

This paper surveys applications of acoustic waves in microwave devices. After a general and historical introduction to bulk acoustic waves (BAWs), surface acoustic waves (SAWs), practical wave types, and acoustoelectric transducers, a review is given of technologically important materials for microwave acoustic applications. Following this, we discuss BAW and SAW microwave devices and their technologies. Specifically reviewed are thin-film resonators and filters, transversal filters, and filters for correlative analog signal processing. Finally, an overview of the most important microwave applications is given, along with manufacturing and packaging issues.

Microwave acoustic materials, devices, and applications

A passive surface wave sensor for obtaining measurement values in which the measurement value is transmitted by radio from the remote point of measurement to an interrogation device (1) which transmits energy by radio to the sensor component (5, 15) as an interrogation pulse. The surface wave sensor of the invention is suitable for contactless measurement value collection. In this sensor a surface wave arrangement is the sensor component and there is a surface wave reference component for phase discrimination and/or propagation time measurement. As a further embodiment there is a sensor operated by chirped transmission signals with chirped reflectors in which there is a reference function in the arrangement replacing the reference component. An embodiment of the sensor with a chirp function has the property of an immanent temperature-compensated sensor (Fig. 12, 13) for measuring physical or similar quantities elsewhere.

Passive surface wave sensor which can be wirelessly interrogated

We report on the use of broadband chirp signals for spread spectrum systems in indoor applications. The presented system concepts make use of chirp transmission and pulse compression. Different modulation schemes for the chirp signals resulting in different system performance and complexity are compared in terms of bit error rate for the AWGN channel and for frequency selective indoor radio channels. We present simulations and measurement results from demonstrator systems which use surface acoustic wave (SAW) devices for the generation and matched altering of the chirp signals. The RF and IF frequency and transmission bandwidth of the presented systems are 2.4 GHz, 348.8 MHz, and 80 MHz, respectively. Due to the processing gain of 16 dB-made possible by the use of SAW devices-and the large transmission bandwidth the system is insensitive against frequency selective fading, CW interference and noise.

Clemens Ruppel

Papers

Improved material constants for LiNbO/sub 3/ and LiTaO/sub 3/

Acoustic Wave Filter Technology–A Review

Microwave acoustic materials, devices, and applications

Passive surface wave sensor which can be wirelessly interrogated

Spread spectrum communications using chirp signals