A Digital Frequency Multiplication Technique for Energy Efficient Transmitters

A logic gate-based digital frequency multiplication technique for low-power frequency synthesis is presented. The proposed digital edge combining approach offers broadband operation with low-power and low-area advantages and is a promising candidate for low-power frequency synthesis in deep submicrometer CMOS technologies. Chip prototype of the proposed frequency multiplication-based 2.4-GHz binary frequency-shift-keying (BFSK)/amplitude shift keying (ASK) transmitter (TX) was fabricated in 0.13-mu m CMOS technology. The TX achieves maximum data rates of 3 and 20 Mb/s for BFSK and ASK modulations, respectively, consuming a 14-mA current from 1.3 V supply voltage. The corresponding energy efficiencies of the TX are 3.6 nJ/bit for BFSK and 0.91 nJ/bit for ASK modulations.

Self-healing Techniques for RF and mm-Wave Transmitters and Receivers

With continuing advances in CMOS technology, feature sizes of modern Silicon chip-sets have gone down drastically over the past decade. In addition to desktops and laptop processors, a vast majority of these chips are also being deployed in mobile communication devices like smart-phones and tablets, where multiple radio-frequency integrated circuits (RFICs) must be integrated into one device to cater to a wide variety of applications such as Wi-Fi, Bluetooth, NFC, wireless charging, etc. While a small feature size enables higher integration levels leading to billions of transistors co-existing on a single chip, it also makes these Silicon ICs more susceptible to variations. A part of these variations can be attributed to the manufacturing process itself, particularly due to the stringent dimensional tolerances associated with the lithographic steps in modern processes. Additionally, RF or millimeter-wave communication chip-sets are subject to another type of variation caused by dynamic changes in the operating environment. Another bottleneck in the development of high performance RF/mm-wave Silicon ICs is the lack of accurate analog/high-frequency models in nanometer CMOS processes. This can be primarily attributed to the fact that most cutting edge processes are geared towards digital system implementation and as such there is little model-to-hardware correlation at RF frequencies.

All these issues have significantly degraded yield of high performance mm-wave and RF CMOS systems which often require multiple trial-and-error based Silicon validations, thereby incurring additional production costs. This dissertation proposes a low overhead technique which attempts to counter the detrimental effects of these variations, thereby improving both performance and yield of chips post fabrication in a systematic way. The key idea behind this approach is to dynamically sense the performance of the system, identify when a problem has occurred, and then actuate it back to its desired performance level through an intelligent on-chip optimization algorithm. We term this technique as self-healing drawing inspiration from nature's own way of healing the body against adverse environmental effects. To effectively demonstrate the efficacy of self-healing in CMOS systems, several representative examples are designed, fabricated, and measured against a variety of operating conditions.

We demonstrate a high-power mm-wave segmented power mixer array based transmitter architecture that is capable of generating high-speed and non-constant envelope modulations at higher efficiencies compared to existing conventional designs. We then incorporate several sensors and actuators into the design and demonstrate closed-loop healing against a wide variety of non-ideal operating conditions. We also demonstrate fully-integrated self-healing in the context of another mm-wave power amplifier, where measurements were performed across several chips, showing significant improvements in performance as well as reduced variability in the presence of process variations and load impedance mismatch, as well as catastrophic transistor failure. Finally, on the receiver side, a closed-loop self-healing phase synthesis scheme is demonstrated in conjunction with a wide-band voltage controlled oscillator to generate phase shifter local oscillator (LO) signals for a phased array receiver. The system is shown to heal against non-idealities in the LO signal generation and distribution, significantly reducing phase errors across a wide range of frequencies.

Interactions Between Platform Terminal Transmitters and Turtle Excluder Devices

Satellite telemetry is a common tool for examining sea turtle movements, and many research programs have successfully tracked adults. Relatively short satellite track durations recorded for juvenile Kemp’s ridley sea turtles, Lepidochelys kempii, in the northwestern Gulf of Mexico raised questions regarding premature transmission loss. We examined interactions between juvenile sea turtles outfitted with platform terminal transmitters (PTT’s) and turtle excluder devices (TED’s) and the potential for transmission loss due to this interaction. A pilot study was conducted with eight 34-month-old, captive-reared loggerhead sea turtles, Caretta caretta; a larger trial the following year used twenty 34-month-olds. Half of the turtles in each trial were outfitted with dummy PTT’s (8×4×2 cm), and all turtles were sent through a trawl equipped with a bottom-opening Super-Shooter TED. No apparent damage was sustained by any PTT, but four of five PTT-outfitted loggerheads encountering the TED carapace-first exhibited increased escape times when the PTT wedged between the TED deflector bars (10.2 cm apart). Overall, 15 loggerheads (54%) impacted the TED carapace-first. Attachment of PTT’s to smaller sea turtles may slow or, in worst cases, inhibit escape from TED’s. Likewise, loose or poorly secured PTT’s could impede escape or be shed during such an interaction. Researchers tracking small turtles in or near regions with trawling activity should consider PTT size and shape and the combined PTT/adhesive profile to minimize potentially detrimental interactions with TED’s.

Application of Suction-cup-attached VHF Transmitters to the Study of Beluga, Delphinapterus leucas, Surfacing Behavior in Cook Inlet, Alaska

Suction-cup-attached VHF radio transmittes were deployed on belugas, Delphinapterus leucas, in Cook Inlet, Alaska, in 1994 and 1995 to characterize the whales' surfacing behavior. Data from video recordings were also used to characterize behavior of undisturbed whales and whales actively pursued for tagging. Statistics for dive intervals (time between the midpoints of contiguous surfacings) and surfacing intevals (time at the surface per surfacing) were estimated. Operations took place on the tidal delta of the Susitna and Little Susitna Rivers. During the 2-yr study, eight whales were successfully tagged, five tags remained attached for >60 min, and data from these were used in the analyses. Mean dive interval was 24.1 sec (interwhale SD=6.4 sec, n=5). The mean surfacing interval, as determined from the duration of signals received from the radio transmitters, was 1.8 sec (SD=0.3 sec, n=125) for one of the whales. Videotaped behaviors were categorized as "head-lifts" or "slow-rolls." Belugas were more likely to head-lift than to slow-roll during vessel approaches and tagging attempts when compared to undisturbed whales. In undisturbed groups, surfacing intervals determined from video records were significantly different between head-lifting (average = 1.02 sect, SD=0.38 sed, n=28) and slow-rolling whales (average = 2.45 sec, SD=0.37 sec, n=106). Undisturbed juveniles exhibited shorter slow-roll surfacing intervals (average = 2.25 sec, SD=0.32 sec, n=36) than adults (average = 2.55 sec, SD=0.36 sec, n=70). We did not observe strong reactions by the belugas to the suction-cup tags. This tagging method shows promise for obtaining surfacing data for durations of several days.

Colourless adaptively modulated optical OFDM transmitters using SOAs as intensity modulators.

The wavelength dependent transmission performance of adaptively modulated optical OFDM (AMOOFDM) signals is investigated, for the first time, over optical amplification- and chromatic dispersion compensation-free IMDD SMF systems using semiconductor optical amplifiers (SOAs) as intensity modulators. A theoretical SOA model describing both optical gain saturation and gain spectral dynamics is developed, based on which optimum SOA operating conditions are identified for various wavelengths varying in a broad range of 1510 nm- 1590 nm. Results show that, SOA intensity modulators operating at the identified optimum conditions enable the realization of colourless AMOOFDM transmitters within the aforementioned wavelength window. Such transmitters are capable of supporting >30 Gb/s signal transmission over 60 km SMFs.

Contrasting the efficiency of radiation belt losses caused by ducted and nonducted whistler-mode waves from ground-based transmitters

It has long been recognized that whistler-mode waves can be trapped in plasmaspheric whistler ducts which guide the waves. For nonguided cases these waves are said to be "nonducted", which is dominant for L < 1.6. Wave-particle interactions are affected by the wave being ducted or nonducted. In the field-aligned ducted case, first-order cyclotron resonance is dominant, whereas nonducted interactions open up a much wider range of energies through equatorial and off-equatorial resonance. There is conflicting information as to whether the most significant particle loss processes are driven by ducted or nonducted waves. In this study we use loss cone observations from the DEMETER and POES low-altitude satellites to focus on electron losses driven by powerful VLF communications transmitters. Both satellites confirm that there are well-defined enhancements in the flux of electrons in the drift loss cone due to ducted transmissions from the powerful transmitter with call sign NWC. Typically, ∼80% of DEMETER nighttime orbits to the east of NWC show electron flux enhancements in the drift loss cone, spanning a L range consistent with first-order cyclotron theory, and inconsistent with nonducted resonances. In contrast, ∼1% or less of nonducted transmissions originate from NPM-generated electron flux enhancements. While the waves originating from these two transmitters have been predicted to lead to similar levels of pitch angle scattering, we find that the enhancements from NPM are at least 50 times smaller than those from NWC. This suggests that lower-latitude, nonducted VLF waves are much less effective in driving radiation belt pitch angle scattering. Copyright 2010 by the American Geophysical Union.

A Vector Approach for the Analysis and Synthesis of Directional Modulation Transmitters

In order to formalize and extend on previous ad-hoc analysis and synthesis methods a theoretical treatment using vector representations of directional modulation (DM) systems is introduced and used to achieve DM transmitter characteristics. An orthogonal vector approach is proposed which allows the artificial orthogonal noise concept derived from information theory to be brought to bear on DM analysis and synthesis. The orthogonal vector method is validated and discussed via bit error rate (BER) simulations.

Vector representation of directional modulation transmitters

Directional Modulation (DM) is a recently proposed technique for securing wireless communication. In this paper we point out that modulation-directionality is a consequence of varying the beamforming network, either in baseband or in the RF stage, at the information rate In order to formalize and extend on previous analysis and synthesis methods a new theoretical treatment using vector representations of directional modulation (DM) systems is introduced and used to obtain the necessary and sufficient con

Orthogonal Vector Approach for Synthesis of Multi-beam Directional Modulation Transmitters

An orthogonal vector approach is proposed for the synthesis of multi-beam directional modulation (DM) transmitters. These systems have the capability of concurrently projecting independent data streams into different specified spatial directions while simultaneously distorting signal constellations in all other directions. Simulated bit error rate (BER) spatial distributions are presented for various multi-beam system configurations in order to illustrate representative examples of physical layer security performance enhancement that can be achieved.

Experiment of Digital Directional Modulation Transmitters

A digital directional modulation (DM) transmitter structure is proposed from a practical implementation point of view in this paper. This digital DM architecture is built with the help of several off-the-shelf physical layer wireless experiment platform hardware boards. When compared with previous analogue DM transmitter architectures, the digital means offers more precise and fast control on the updates of the array excitations. More importantly, it is an ideal physical arrangement to implement the most universal DM synthesis algorithm, i.e., the orthogonal vector approach. The practical issues in digital DM system calibrations are described and solved. The bit error rates (BERs) are measured via real-time data transmissions to illustrate the DM advantages, in terms of secrecy performance, over conventional non-DM beam-steering transmitters.