RF Channel Research Articles

Multifunctional Optical Interface for Fiber-Radio Systems in Heterogeneous Access Networks

In this paper, we investigate through simulation a proposed multi-functional optical interface incorporating an arrayed waveguide grating (AWG) that multiplexes multiple wavelength-interleaved dense-wavelength-division-multiplexed (DWDM) optical RF channels while simultaneously reducing intermodulation distortion (IMD) in fiber-radio systems incorporating optical single sideband with carrier (OSSB+C) modulation. The proposed optical interface is also able to simultaneously support multiple baseband transmission in an integrated wireless/wired heterogeneous access environment. We derive an analytical model and present a detailed analysis of the proposed interface to establish the viability of its operation and quantify performance limitations. Our results show that the proposed scheme is not dependent on the inherent characteristics of the optical carrier and a maximum IMD suppression of >9 dB can be achieved. The proposed interface was also investigated via simulation for a larger number of DWDM channels to establish the viability and subsequently quantify the overall performance of a heterogeneous millimeter-wave fiber-radio system with other wired-access infrastructure.

General implementation of the ERETIC™ method for pulsed field gradient probe heads

A capacitive coupling between a secondary radiofrequency (rf) channel and the gradient coil of a standard commercially available high resolution NMR spectrometer and probe head is described and used to introduce a low level exponentially damped rf signal near the frequency of the primary rf channel to serve as an external concentration standard, in analogy to the so-called ERETIC™ method. The stability of this inexpensive and simple to implement method, here referred to as the Pulse Into the Gradient (PIG) approach, is superb over a 14-h period and both gradient tailored water suppression and one-dimensional imaging applications are provided. Since the low level signal is introduced via the pulsed field gradient coil, the coupling is identical to that for a free induction signal and thus the method proves to be immune (within 5%) to sample ionic strength effects up to the 2 M NaCl solutions explored here.

A 16–18.8-GHz Sub-Integer-N Frequency Synthesizer for 60-GHz Transceivers

An 18-GHz range frequency synthesizer is implemented in 0.13-mum SiGe BiCMOS technology as part of a 60-GHz superheterodyne transceiver chipset. It provides for RF channels of 56.5-64 GHz in 500-MHz steps, and features a phase-rotating multi-modulus divider capable of sub-integer division. Output frequency range from the synthesizer is 16.0 to 18.8 GHz, while the enabled RF frequency range is 3.5 times this, or 55.8 to 65.8 GHz. The measured RMS phase noise of the synthesizer is 0.8deg (1 MHz to 1 GHz integration), while phase noise at 100-kHz and 10-MHz offsets are -90 and -124 dBc/Hz, respectively. Reference spurs are 69 dBc; sub-integer spurs are -65 dBc; and combined power consumption from 1.2 and 2.7 V is 144 mW.

A broadband RF 65 nm CMOS front-end for cable TV reception

A novel broadband RF front-end in 65nm CMOS technology is presented. The front-end serves to precondition the incoming RF spectrum for further processing in a cable TV receiver architecture where RF channel selection and down conversion are done in digital domain. The analog front-end consists of a broadband highly linear low-noise amplifier followed by a variable gain RF amplifier. An original broadband circuit topology for the amplifiers is adopted.The fabricated front-end exhibits a bandwidth of 50–1050MHz, a variable gain, which spans from 12 to 37dB with a 0.2dB step, an OIP3 of 28.4dBm (77.5dBmV), an OIP2 of 65dBm (114dBmV), and a noise figure of 5.8dB, dissipating 125mW at 1.2V supply, and a core silicon area of 0.4mm2.

A novel modular probe base design

AbstractCommercially available probe bases often impose limitations for their use with different setups. The goal of this work was to design and construct a universally applicable probe base to be used in radio frequency (rf) applications such as NMR imaging and spectroscopy. The concept is to support several arbitrarily combinable rf channels as well as additional devices, for example, a climate chamber for plants, an animal handling system, a perfusion device, or further specialized equipment. The concept and a prototype of such a probe base were successfully developed and are presented in this work. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 33B: 55–61, 2008

Local B1+ shimming for prostate imaging with transceiver arrays at 7T based on subject‐dependent transmit phase measurements

High-quality prostate images were obtained with transceiver arrays at 7T after performing subject-dependent local transmit B(1) (B(1) (+)) shimming to minimize B(1) (+) losses resulting from destructive interferences. B(1) (+) shimming was performed by altering the input phase of individual RF channels based on relative B(1) (+) phase maps rapidly obtained in vivo for each channel of an eight-element stripline coil. The relative transmit phases needed to maximize B(1) (+) coherence within a limited region around the prostate greatly differed from those dictated by coil geometry and were highly subject-dependent. A set of transmit phases determined by B(1) (+) shimming provided a gain in transmit efficiency of 4.2 +/- 2.7 in the prostate when compared to the standard transmit phases determined by coil geometry. This increased efficiency resulted in large reductions in required RF power for a given flip angle in the prostate which, when accounted for in modeling studies, resulted in significant reductions of local specific absorption rates. Additionally, B(1) (+) shimming decreased B(1) (+) nonuniformity within the prostate from (24 +/- 9%) to (5 +/- 4%). This study demonstrates the tremendous impact of fast local B(1) (+) phase shimming on ultrahigh magnetic field body imaging.

Device Performance and Reliability Characterization of Interface and Bulk Effect in Amorphous Indium Gallium Zinc Oxide (a-IGZO) Thin Film Transistor

Abstracta-IGZO TFT is a promising candidate device for an alternative to poly-Si TFTs or a-Si TFTs, because they provide better uniformity in terms of their important device parameters, including the threshold voltage and mobility due to their amorphous phase, and a high mobility (>10 cm2/Vs) is attainable with these devices even in the amorphous phase. Recently, a-IGZO TFTs have been extensively studied by various groups. However, there is little report on interface and bulk effect on device performances and reliability as separately. For investigating the interface and bulk effect, we fabricated two a-IGZO thin film transistors with different channel deposition conditions, RF and DC magnetron sputtering. Specific conditions of RF and DC sputtering are described as follows; magnetron power density of 1.4 W/cm2/2.0 W/cm2 in Ar/O2 gas ratio of (65/35)/(72/28), and the entire gas pressure was 5.0 mTorr and 3.4 mTorr, respectively.In order to characterize the channel quality, C-V curve was measured with various frequencies of (10KHz˜1MHz). RF sputtered channel has higher frequency dependency compared to DC sputtered channel. It means that RF sputtered channel has higher bulk traps in channel compared to DC sputtered channel.Device performance was characterized through the ID-VG measurement. Electrical parameters of RF and DC sputtered devices are VT=3.5/2.7V, on-off ratio=105/08, SS=2/0.4 V/decade, and uFE= 5/11 cm2/V-s, respectively. It is thus clear that the device performance of DC sputtered device is more superior to RF sputtered device. Therefore, it can be said that the poor device performance of RF device is ascribed to insufficient channel quality, as mentioned in C-V curve.For reliability study, we measured PBTI and ID-VG hysteresis with normalized gate stress bias and high temperature hot chuck system. Through the unchanged field effect mobility during the stress and relaxation time, and nearly recovered VT and subthreshold slope (SS) after long relaxation time, we were able to know that pre-existed trap was main factor of reliability degradation. Moreover, SS degradation during stress time is more severe in RF device than DC device. It is also proving that RF channel characteristic is worse than DC channel. In high temperature, leakage current increments of RF device were more severe than DC device. This also indicates that bulk traps of RF device in channel region are larger than that of DC device. VT shift of DC sputtered device for PBT stress and hysteresis was higher than that of RF sputtered device. As well known, PBTI is closely related to insulator bulk traps, which shows that channel deposition conditions affect insulator trap characteristics. In summary, device performance of a-IGZO deposited by DC sputtering is better than RF sputtering, which is because DC sputtering improves channel quality of a-IGZO. However, VT shift of DC sputtered device are worse than RF sputtering, which may be related with high magnetron power density.

Large-Scale Fading and Time Dispersion Parameters of UWB Channel in Underground Mines

RF channel measurements in underground mines have important applications in the field of mobile communications for improving operational efficiency and worker safety. This paper presents an experimental study of the ultra wideband (UWB) radio channel, based on extensive sounding campaigns covering the underground mine environment. Measurements were carried out in the frequency band of 2–5 GHz. Various communication links were considered including both line-of-sight (LOS) and non-LOS (NLOS) scenarios. In this paper, we are interested in more details of the variations of the RMS delay spread and mean excess delay with Tx/Rx separation, and the variation of RMS with mean excess. The distance dependency of path loss and shadowing fading statistics is also investigated. To give an idea about the behaviour of UWB channel in underground mines, a comparison of our approach with other published works is given including path loss exponent, shadow fading variance, mean excess delay, and RMS delay spread.

A New Approach to Synthesing Radio Frequency Channel Characteristics Models for TestinG of WCDMA Cellular Communication System

Channel modeling for mobile cellular communication systems is a rapidly changing area, and the models are becoming increasingly accurate and more comprehensive to allow radio channel simulators to be implemented either by software or hardware to simulate diversity systems with many users. However, the challenge is to develop models that exhaustively reproduce the propagation scenarios accounted in reality.The paper introduces a new method of synthesizing RF channels of cellular communication systems for computer simulation and for controlled laboratory testing that is based on extensive observations of real signals in the field. Channel parameters are utilized as time histories of deterministic estimates derived from the field measurements. The stored channel data then be used to reconstruct the field channel conditions for laboratory testing.An iterative gradient search is performed to refine the state estimate (measurements are compared to the modeled output). The processing is performed using a WCDMA acquire search (Primary Synchronization Code Acquisition) to estimate the CPICH power and PN position of detectable primary scrambling. Full description of this deterministic stored channel impulse response model is presented. Using this methodology, an accurate channel model is possible, because it provides actual information from the channel. This was done to show how some physical link aspects such as power control and data rate can be tested for quality performance of these systems under real field conditions due to the ability of constructing controlled laboratory testing, though this type of controlled testing is extremely difficult to accomplish in the field due to the practical constraints.

Basic and Tailored RF Shimming in a Multi-transmit Whole Body MR System

Wave propagation efiects diminish the quality of MR images at main flelds of 3T or above. Parallel RF transmission has the potential of compensating for these efiects through RF shimming. RF shimming can be performed in two difierent ways. The basic way of RF shimming is to adjust the global amplitude and phase of the currents in each transmit element, aiming at a constant B1 in the region of interest. For 3D volume imaging, 3D RF shimming is facilitated using multiple frequencies for the difierent transmit elements. On the other hand, \tailored RF shimming can be performed via multi-dimensional RF pulses designed to achieve a spatially constant excitation pattern. Using an MR system equipped with parallel RF channels, these multi-dimensional RF pulses can be accelerated via Transmit SENSE. The potential of both, basic and tailored RF shimming, can be enhanced signiflcantly, if only a constant B1 amplitude is demanded, and an arbitrary spatial distribution of the resulting B1 phase is allowed. This is the case, if only magnitude images are of interest. However, this approach introduces a non-linear problem, requiring corresponding numerical techniques. Optimal results for basic RF shimming are obtained with transmit arrays owning preferably homogeneous sensitivity distributions of the individual elements. On the other hand, for tailored shimming, the transmit elements require orthogonal sensitivity distributions, which are easier to achieve with inhomogeneous sensitivity distributions. Thus, the transmit coil array cannot be optimized for both, basic and tailored RF shimming simultaneously, and a suitable compromise has to be found. This study compares the difierent RF shimming approaches using a whole-body, 8-channel Tx/Rx system at 3T. It shows, that basic RF shimming is able to remove B1 inhomogeneities to a high degree, both in phantoms and in vivo. Tailored RF shimming is able to achieve even higher levels of B1 homogeneity, which, however, might not be necessary for the majority of clinical applications.

Six time- and frequency- selective empirical channel models for vehicular wireless LANs

Three vehicle-to-vehicle (V2V) models and three roadside-to-vehicle (RTV) models, each suitable for RF channel emulation and based on measurements at 5.9 GHz, are presented. Each model captures the joint Doppler-delay characteristics of a different environment. The packet error rate (PER) for each model, measured with an emulator and an 802.11p wireless access in vehicular environments (WAVE) prototype, is presented.

A highly integrated FPGA-based nuclear magnetic resonance spectrometer

The digital circuits required for a nuclear magnetic resonance (NMR) spectrometer, including a pulse programmer, a direct digital synthesizer, a digital receiver, and a PC interface, have been built inside a single chip of the field-programmable gate-array (FPGA). By combining the FPGA chip with peripheral analog components, a compact, laptop-sized homebuilt spectrometer has been developed, which is capable of a rf output of up to 400 MHz with amplitude-, phase-, frequency-, and pulse-modulation. The number of rf channels is extendable up to three without further increase in size.

Fuzzy Logic Control of Adaptive ARQ for Video Distribution over a Bluetooth Wireless Link

Bluetooth's default automatic repeat request (ARQ) scheme is not suited to video distribution resulting in missed display and decoded deadlines. Adaptive ARQ with active discard of expired packets from the send buffer is an alternative approach. However, even with the addition of cross-layer adaptation to picture-type packet importance, ARQ is not ideal in conditions of a deteriorating RF channel. The paper presents fuzzy logic control of ARQ, based on send buffer fullness and the head-of-line packet's deadline. The advantage of the fuzzy logic approach, which also scales its output according to picture type importance, is that the impact of delay can be directly introduced to the model, causing retransmissions to be reduced compared to all other schemes. The scheme considers both the delay constraints of the video stream and at the same time avoids send buffer overflow. Tests explore a variety of Bluetooth send buffer sizes and channel conditions. For adverse channel conditions and buffer size, the tests show an improvement of at least 4 dB in video quality compared to nonfuzzy schemes. The scheme can be applied to any codec with I-, P-, and (possibly) B-slices by inspection of packet headers without the need for encoder intervention.

Safe magnetic resonance scanning of patients with metallic middle ear implants

To determine the MR scanning risk to patients with otologic implants. We used a repeated-measures study with an additional control measure to assess two aspects of risk; (i) movement of the device in the magnetic field, and (ii) absorption of energy leading to local heating. We used an ex vivo test method that met with international standards. We measured the effects in a Philips Intera Achieva 3 Tesla (T) MR scanner using a Sense Head 8 channel RF coil. University-based magnetic resonance research facility. Heating or displacement of the stapedectomy pistons. No evidence of displacement or heating was found. Complying with the ex vivo standard testing protocols, the Schuknecht and McGee wire pistons (device product numbers 140106 and 140108, respectively) were found to be safe in a 3 T MR scanner. These conclusions can be extrapolated to the in vivo case.

Amplitude statistics for high-frequency underwater acoustic communications

Amplitude statistics is one major channel characteristic of a communication system, particularly when an energy detector is used as an incoherent receiver. The amplitude statistics is usually modeled as a Rayleigh or a Rician distribution for an rf channel. From our recent study, the amplitude statistics of high-frequency underwater acoustic communications channel is found to be a K-distribution based on M-sequence data collected during the TREX04 experiment. The TREX04 experiment was conducted in shallow water (∼70-m depth) off the coast of New Jersey. The source and receivers were located about 35 m deep. The M-sequence signal was operated at 17 kHz with a 5-kHz bandwidth. The K-distribution is one of non-Rayleigh family and may be approximated by a combination of a long-term fading and a short-term fading statistics. The long-term and short-term fading statistics are close to a lognormal distribution and a Rayleigh distribution, respectively. [Work supported by the Office of Naval Research.]

Performance Evaluation of DVB-RCT Return Path in Fading Channels with added Diversity

The radio spectrum is a finite resource and it is important that all users exploit it efficiently. Consequently, modulation schemes used for the wireless environment should utilize the RF channel bandwidth, and the transmitted power, as efficiently as possible. Across Europe, the digital video broadcasting (DVB) group has proposed a technique for a high data-rate return path known as DVB-return channel through terrestrial (DVB-RCT) specifically for consumer device convergence (full Internet connectivity through a television set). The introduction of adaptive M-ary quadrature amplitude modulation (MQAM) into the DVB-RCT standards as opposed to static modulation (as used in the DVB-terrestrial (DVB-T) standard) has enhanced the performance of bidirectional communication. In this paper, the impact of using diversity techniques in such systems is investigated. In specific, the gain, obtained from utilizing this combination of adaptive MQAM and diversity techniques in the system, is also shown.

How fast is too fast? [Super-fast Internet access

This paper discusses how super-fast Internet access can be achieved with a new technology that involves channel bonding to take access speeds over cable into the hundreds of megabits per second. A key element of this cable broadband service technology is DOCSIS 3.0, which allows several downstream and upstream radio frequency carriers to be bundled into a single logical channel to multiply capacity. It has been estimated that speeds up to 1 Gbit/s could theoretically be achieved by bonding an n number of RF channels. Apart from an obvious marketing advantage, operators can use the technology as a way of increasing network efficiency since statistical multiplexing works more effectively with wider channels.

Mobile terminal with a text-to-speech converter

A mobile terminal includes a receiver for receiving text messages over an RF channel. The mobile terminal also includes a text-to-speech (TTS) converter that converts the transmitted text messages to an audible form. In this way, the present invention takes advantage of the reduced bandwidth required for transmitting text messages to provide an audible message to subscribers that use the mobile terminals. In an exemplary embodiment, the mobile terminal operates in a GSM communication system and receives text messages that are defined under short message service (SMS) protocol. Also, the TTS converter in the mobile terminal can be used to output the text menus of the mobile terminal's interface in speech (voice) format.

Continuous arterial spin labeling with separate labeling and imaging coils: Implementation using a single RF channel and amplifier

This work describes the implementation of two-coil continuous arterial spin labeling (CASL) using a single RF channel and amplifier, avoiding the need for costly additional hardware—namely, a second 1H RF channel and amplifier dedicated to the labeling coil. This is possible in principle, as labeling and imaging RF pulses are never applied simultaneously in the CASL pulse sequence. Simple and inexpensive electronics, together with minor pulse programming modification, were used to create the waveforms (TTL and RF pulses) necessary to drive the two coils. A custom-built RF switch of single-pole double-throw (SPDT) design alternated the output of the RF amplifier between the imaging and labeling coils. Bipolar bias waveforms controlled the switch and also provided active decoupling between the two coils. These waveforms were created from the original TTL waveform, which gated the RF amplifier, using a flip-flop. The method was implemented in a small-bore MRI scanner and enabled good-quality CASL measurements of functional cerebral blood flow changes during whisker electrical stimulation. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 29B: 145–152, 2006

Compact polarisation and spatial multiplexing antenna for MIMO applications

A compact size, polarisation and spatial multiplexing slot antenna utilising the Spatial Multiplexing of Local Elements (SMILE) technique, is proposed. The antenna is used to explore diversity gain with a single RF channel in the applications of a multiple-input multiple-output (MIMO) wireless communication system.