Design of a flexible and low-power ionospheric sounder

Thesis (M.S.) University of Alaska Fairbanks, 2014Characterizing the structure of the ionosphere has practical applications for telecommunications and scientific applications for studies of the near-earth space environment. Among several methods for measuring parameters of the ionosphere is ionospheric sounding, a radar technique that determines the electron content of the ionosphere as a function of height. Various research, military, and commercial institutions operate hundreds of ground-based ionosondes throughout the globe, and new ionosondes continue to be deployed in increasingly remote and distant locations. This thesis presents the design of an ionospheric sounder that reduces the power, size, and cost compared to existing systems. Key improvements include the use of an open-source software-defined radio platform and channel-aware dynamic sounding scheduling.Chapter 1. Introduction -- 1.1. A brief historical background -- 1.2. The ionosphere -- 1.3. Instruments for studying the ionosphere -- 1.4. Thesis organization -- Chapter 2. Radio waves and the ionosphere -- 2.1. Dispersion relation of electromagnetic waves in the ionosphere -- 2.2. Power reflected from the ionosphere -- 2.3 Noise in the HF spectrum -- 2.4. Ionograms -- Chapter 3. Radar principles -- 3.1. Target detection -- 3.2. Range and doppler elocity -- 3.3. Range-doppler ambiguity -- 3.4. Resolution and precision --3.5. Multi-pulse integration -- 3.6. Pulse compression -- 3.7. Practical limits of performance -- Chapter 4. Survey of current systems -- 4.1. Coherent transmission/reception and digital systems -- 4.2. Phase-coded pulses -- 4.3. Coherent integration of multiple pulses -- 4.4. Phased antenna arrays -- 4.5. O- and X-mode discrimination -- Chapter 5. System description -- 5.1. Design approach -- 5.2. Overview of the Ettus Research USRP -- 5.3. Using the USRP as a radar -- 5.4. Waveform Generation -- 5.5. Processing the received signal -- 5.6. Scheduling -- 5.7. Completing the system -- Chapter 6. Sounding results -- 6.1. Single frequency soundings -- 6.2. Swept frequency soundings -- Chapter 7. Conclusion -- 7.1. Evaluation of performance -- 7.2. Costs -- 7.3. Future improvements -- 7.4. Deploying a terrestrial ionosonde -- 7.5. Deploying a space-borne ionosonde -- References

Evaluation of spectrally efficient indoor optical wireless transmission techniques

Optical wireless communications (OWC) has the potential to become a remedy for the shortage of the radio frequency (RF) spectrum. Especially in indoor environments, OWC could enable wireless home networking systems which offload data traffic from existing RF systems. In OWC, data is transmitted by modulating the intensity of light sources, typically incoherent light emitting diodes (LEDs). Thus, OWC systems employ intensity modulation (IM) and direct detection (DD) of the optical carrier. Since off-the-shelf LEDs have a limited modulation capability, the transmission bandwidth of practical OWC systems is restricted. Consequently, the available bandwidth has to be used efficiently. In this thesis, spectrally efficient optical wireless transmission techniques are evaluated. Firstly, multiple transmitter-receiver techniques are investigated. These multiple-input-multiple-output (MIMO) techniques provide high spectral efficiency, and therefore high data rates. Specifically, the MIMO techniques repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) are analysed for indoor OWC. The performance of these techniques is evaluated analytically and by means of computer simulations. It is shown that inducing power imbalance between the multiple optical transmitters can substantially improve the performance of optical MIMO techniques as the power imbalance improves the differentiability of the multiple channels. In addition, it is found that link blockage and the utilisation of transmitters having different optical wavelengths enhance channel differentiability as well. These methods enable the utilisation of optical MIMO techniques under conditions which typically disallow the application of MIMO schemes due to little differences between the multiple links. Secondly, a novel optical wireless transmitter concept is developed. This concept uses discrete power level stepping to generate intensity modulated optical signals, such as orthogonal frequency division multiplexing (OFDM) waveforms. The transmitter consists of several on-off-switchable LED groups which are individually controlled to emit scaled optical intensities. As a result, the digital-to-analogue conversion of the signals to be sent is done in the optical domain. This method enables the implementation of low-complex and power-efficient optical transmitter front-ends – the major shortcoming of conventional optical OFDM transmitters. Thirdly, a novel approach for wireless data transmission within an aircraft cabin is presented. The data is transferred by 2-dimensional visual code sequences. These sequences are displayed on the in-flight entertainment (IFE) screen and are captured by the built-in camera of a user device which acts as receiver. Transmission experiments within an aircraft cabin mock-up demonstrate the functionality of the implemented system under realistic conditions, such as ambient illumination and geometric configuration. Altogether, this thesis has analysed the potential of spectrally efficient optical wireless transmission techniques. It is shown that OWC systems can greatly benefit from these techniques

Enhancing Digital Controllability in Wideband RF Transceiver Front-Ends for FTTx Applications

Enhancing the digital controllability of wideband RF transceiver front-ends helps in widening the range of operating conditions and applications in which such systems can be employed. Technology limitations and design challenges often constrain the extensive adoption of digital controllability in RF front-ends. This work focuses on three major aspects associated with the design and implementation of a digitally controllable RF transceiver front-end for enhanced digital control. Firstly, the influence of the choice of semiconductor technology for a system-on-chip integration of digital gain control circuits are investigated. The digital control of gain is achieved by utilizing step attenuators that consist of cascaded switched attenuation stages. A design methodology is presented to evaluate the influence of the chosen technology on the performance of the three conventionally used switched attenuator topologies for desired attenuation levels, and the constraints that the technology suitable for high amplification places on the attenuator performance are examined. Secondly, a novel approach to the integrated implementation of gain slope equalization is presented, and the suitability of the proposed approach for integration within the RF front-end is verified. Thirdly, a sensitivity-aware implementation of a peak power detector is presented. The increased employment of digital gain control also increases the requirements on the sensitivity of the power detector employed for adaptive power and gain control. The design, implementation, and measurement results of a state-of-the-art wideband power detector with high sensitivity and large dynamic range are presented. The design is optimized to provide a large offset cancellation range, and the influence of offset cancellation circuits on the sensitivity of the power detector is studied. Moreover, design considerations for high sensitivity performance of the power detector are investigated, and the noise contributions from individual sub-circuits are evaluated. Finally, a wideband RF transceiver front-end is realized using a commercially available SiGe BiCMOS technology to demonstrate the enhancements in the digital controllability of the system. The RF front-end has a bandwidth of 500 MHz to 2.5 GHz, an input dynamic range of 20 dB, a digital gain control range larger than 30 dB, a digital gain slope equalization range from 1.49 dB/GHz to 3.78 dB/GHz, and employs a power detector with a sensitivity of -56 dBm and dynamic range of 64 dB. The digital control in the RF front-end is implemented using an on-chip serial-parallel-interface (SPI) that is controlled by an external micro-controller. A prototype implementation of the RF front-end system is presented as part of an RFIC intended for use in optical transceiver modules for fiber-to-the-x applications

QUANTITATIVE METHODS AND DETECTION TECHNIQUES IN HYPERSPECTRAL IMAGING INVOLVING MEDICAL AND OTHER APPLICATIONS

This research using Hyperspectral imaging involves recognizing targets through spatial and spectral matching and spectral un-mixing of data ranging from remote sensing to medical imaging kernels for clinical studies based on Hyperspectral data-sets generated using the VFTHSI [Visible Fourier Transform Hyperspectral Imager], whose high resolution Si detector makes the analysis achievable. The research may be broadly classified into (I) A Physically Motivated Correlation Formalism (PMCF), which places both spatial and spectral data on an equivalent mathematical footing in the context of a specific Kernel and (II) An application in RF plasma specie detection during carbon nanotube growing process. (III) Hyperspectral analysis for assessing density and distribution of retinopathies like age related macular degeneration (ARMD) and error estimation enabling the early recognition of ARMD, which is treated as an ill-conditioned inverse imaging problem. The broad statistical scopes of this research are two fold- target recognition problems and spectral unmixing problems. All processes involve experimental and computational analysis of Hyperspectral data sets is presented, which is based on the principle of a Sagnac Interferometer, calibrated to obtain high SNR levels. PMCF computes spectral/spatial/cross moments and answers the question of how optimally the entire hypercube should be sampled and finds how many spatial-spectral pixels are required precisely for a particular target recognition. Spectral analysis of RF plasma radicals, typically Methane plasma and Argon plasma using VFTHSI has enabled better process monitoring during growth of vertically aligned multi-walled carbon nanotubes by instant registration of the chemical composition or density changes temporally, which is key since a significant correlation can be found between plasma state and structural properties. A vital focus of this thesis is towards medical Hyperspectral imaging applied to retinopathies like age related macular degeneration targets taken with a Fundus imager, which is akin to the VFTHSI. Detection of the constituent components in the diseased hyper-pigmentation area is also computed. The target or reflectance matrix is treated as a highly ill-conditioned spectral un-mixing problem, to which methodologies like inverse techniques, principal component analysis (PCA) and receiver operating curves (ROC) for precise spectral recognition of infected area. The region containing ARMD was easily distinguishable from the spectral mesh plots over the entire band-pass area. Once the location was detected the PMCF coefficients were calculated by cross correlating a target of normal oxygenated retina with the de-oxygenated one. The ROCs generated using PMCF shows 30% higher detection probability with improved accuracy than ROCs based on Spectral Angle Mapper (SAM). By spectral unmixing methods, the important endmembers/carotenoids of the MD pigment were found to be Xanthophyl and lutein, while β-carotene which showed a negative correlation in the unconstrained inverse problem is a supplement given to ARMD patients to prevent the disease and does not occur in the eye. Literature also shows degeneration of meso-zeaxanthin. Ophthalmologists may assert the presence of ARMD and commence the diagnosis process if the Xanthophyl pigment have degenerated 89.9%, while the lutein has decayed almost 80%, as found deduced computationally. This piece of current research takes it to the next level of precise investigation in the continuing process of improved clinical findings by correlating the microanatomy of the diseased fovea and shows promise of an early detection of this disease

Reduced-complexity Digital Predistortion in Flexible Radio Spectrum Access

Wireless communications is nowadays seen as one of the main foundations of technological advancements in, e.g., healthcare, education, agriculture, transportation, computing, personal communications, media, and entertainment. This requires major technological developments and advances at different levels of the wireless communication systems and networks. In particular, it is required to utilize the currently available frequency spectrum in a more and more efficient way, while also adopting new spectral bands. Moreover, it is required that cheaper and smaller electronic components are used to build future wireless communication systems to facilitate increasingly cost-effective solutions. Meanwhile, energy efficiency becomes extremely important in wide scale deployments of the networks both from a running cost point of view, and from an environmental impact point of view. This is the big picture, or the so called ‘bird’s eye view’ of the challenges that are yet to be met in this very interesting and fast developing field of science.The power amplifier (PA) is the most power-hungry component in most RF transmitters. Consequently, its energy efficiency significantly contributes to the overall energy efficiency of the transmitter, and in fact the whole wireless network. Unfortunately, energy efficiency enhancement implies operating the PA closer to its saturation region, which typically results in severe nonlinear distortion that can deteriorate the signal quality and cause interference to neighboring users, both of which negatively impact the system spectral efficiency. Moreover, in flexible spectrum access scenarios, which are essential for improving the spectral efficiency, particular in the form of non-contiguous radio spectrum access, the nonlinear distortion due to the PA becomes even more severe and can significantly impact the overall network performance. For example, in noncontiguous carrier aggregation (CA) in LTE-Advanced, it has been demonstrated that in addition to the classical in-band distortion and regrowth around the main carriers, harmful spurious emission components are generated which can easily violate the spurious emission limits even in the case of user equipment (UE) transmitters.Technological advances in the digital electronics domain have enabled us to approach this problem from a digital signal processing point of view in the form of widely-adopted and researched digital predistortion (DPD) technology. However, when the signal bandwidth gets larger, and flexible or non-contiguous spectrum access is introduced, the complexity of the DPD increases and the power consumed in the digital domain by the DPD itself becomes higher and higher, to the extent that it might be close to, or even surpass, the energy savings achieved from using a more efficient PA. The problem becomes even more challenging at the UE side which has relatively limited computational capabilities and lower transmit power. This dilemma can be resolved by developing novel reduced-complexity DPD solutions in such flexible spectrum access and/or wide bandwidth scenarios while not sacrificing the DPD performance, which is the main topic area that this thesis work contributes to.The first contribution of this thesis is the development of a spur-injection based sub-band DPD structure for spurious emission mitigation in noncontiguous transmission scenarios. A novel and effective learning algorithm is also introduced, for the proposed sub-band DPD, based on the decorrelation principle. Mathematical models of the unwanted emissions are formulated based on realistic PA models with memory, followed by developing an efficient DPD structure for mitigating these emissions with reducedcomplexity in both the DPD main processing and learning paths while providing excellent spurious emission suppression. In the special case when the spurious emissions overlap with the own RX band in frequency division duplexing (FDD) transceivers, a novel subband DPD solution is also developed that uses the main RX for DPD learning without requiring any additional observation RX, thus further reducing the DPD complexity.The second contribution is the development of a novel reduced-complexity concurrent DPD, with a single-feedback receiver path, for carrier aggregation-like scenarios. The proposed solution is based on a simple and flexible DPD structure with decorrelationbased parameter learning. Practical simulations and RF measurements demonstrate that the proposed concurrent DPD provides excellent linearization performance, in terms of in-band error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR), when compared to state-of-the-art concurrent DPD solutions, despite its reduced computational complexity in both the DPD main path processing and parameter learning.The third contribution is the development of a new and novel frequency-optimized DPD solution which can tailor its linearization capabilities to any particular regions of the spectrum. Detailed mathematical expressions of the power spectrum at the PA output as a function of the DPD coefficients are formulated. A Newton-Raphson optimization routine is then utilized to optimize the suppression of unwanted emissions at arbitrary pre-specified frequencies at the PA output. From a complexity reduction perspective, this means that for a given linearization performance at a particular frequency range, an optimized and reduced-complexity DPD can be used.Detailed quantitative complexity analysis, of all the proposed DPD solutions, is performed in this thesis. The complexity and linearization performance are also compared to state-of-the-art DPD solutions in the literature to validate and demonstrate the complexity reduction aspect without sacrificing the linearization performance. Moreover, all the DPD solutions developed in this thesis are tested in practical RF environments using real cellular power amplifiers that are commercially used in the latest wireless communication systems, both at the base station side and at the mobile terminal side. These experiments, along with the strong theoretical foundation of the developed DPD solutions prove that they can be commercially used as such to enhance the performance, energy efficiency, and cost effectiveness of next generation wireless transmitters

Interference Management Techniques for Cellular Wireless Communication Systems

The growing demand for higher capacity wireless networks can be met by increasing the frequency bandwidth, spectral efficiency, and base station density. Flexible spectrum access, multiantenna, and multicarrier techniques are key enablers in satisfying the demand. In addition, automation of tasks related to network planning, optimization, interference management, and maintenance are needed in order to ensure cost-efficiency. Effective, dynamic, and automated interference management tailored for bursty and local data traffic plays a central role in the task. Adjacent channel interference (ACI) management is an enabler for flexible spectrum use and uncoordinated network deployments. In this thesis the impact of ACI in local area time division duplex (TDD) cellular systems is demonstrated. A method is proposed where the transmitters optimize their transmitted spectral shape on-line, such that constraints on ACI induced by power amplifier non-linearity are met. The proposed method increases the fairness among spectrum sharing transceivers when ACI is a limiting factor. A novel interference-aware scheduling technique is proposed and analyzed. The technique manages co-channel interference (CCI) in a decentralized fashion, relying on beacon messages sent by data receivers. It is demonstrated that the proposed technique is an enabler for fair spectrum sharing among operators, independent adaptation of uplink/downlink switching points in TDD networks, and it provides overall more fair and spectrally efficient wireless access. Especially, the technique is able to improve the cell-edge throughput tremendously. New services are emerging that generate local traffic among the users in addition to the data traffic between the users and the network. Such device-to-device (D2D) traffic is effectively served by direct transmissions. The thesis demonstrates the possibilities for allowing such direct D2D transmissions on a shared band together with the cellular communication. It is shown that interference management is needed in order to facilitate reliable and efficient shared band operation. For this purpose, three methods are proposed that provide interference aware power control, interference aware multiuser and multiband resource allocation, and interference avoiding spatial precoding. It is shown that enabling direct transmission itself provides most of the gains in system capacity, while the interference management schemes are more important in promoting fairness and reliability.Langattomien tietoliikenneverkkojen käyttö kasvaa erittäin nopeasti mobiilien internet-palvelujen ja älykkäiden päätelaitteiden suosion myötä. Järjestelmien tiedonsiirtokapasiteettiä voidaan lisätä kasvattamalla kaistanleveyttä, spektritehokkuutta ja tukiasemaverkon tiheyttä. Kehityksen mahdollistaa mm. joustava taajuuksien käyttö ja moniantenni- ja monikantoaaltotekniikat. Lisäksi radioverkkojen suunnitteluun, optimointiin, ylläpitoon ja interferenssinhallintaan liittyvien tehtävien automatisoinnilla voidaan pienentää verkko-operaattoreiden kustannuksia. Tässä hetkellisen ja paikallisen tietoliikenteen tehokas, dynaaminen ja automatisoitu interferenssinhallinta on keskeisessä asemassa. Viereisen kanavan interferenssin hallinta mahdollistaa osaltaan joustavan spektrinkäytön ja koordinoimattoman verkkojen asennuksen. Väitöskirjassa on analysoitu viereisen kanavan interferenssin vaikutusta aikajakoiseen dupleksilähetykseen perustuvien paikallisten radioverkkojen toimintaan. Lisäksi väitöskirjassa on kehitetty menetelmä, jolla voidaan hallita interferenssiä reaaliaikaisesti. Menetelmä maksimoi lähetetyn signaalin spektritehokkuuden siten, että tehovahvistimen epälineaarisuuden aiheuttama viereisen kanavan interferenssi on rajoitettu. Väitöskirjassa on kehitetty ja analysoitu uudenlainen interferenssitietoinen lähetysten ajoitustekniikka. Tekniikka hallitsee reaaliaikaisesti ja hajautetusti saman kanavan interferenssiä vastaanottimien lähettämien majakkasignaalien avulla. Esitetyt simulaatiot osoittavat, että tämä mahdollistaa operaattoreiden välisen taajuuskaistojen jaon, ja alas- ja yloslinkkien aikajaon joustavan säädön. Tämän lisäksi on mahdollista saavuttaa korkeampi yleinen spektritehokkuus. Erityisesti tiedonsiirtonopeus solujen reunoille kasvaa esitetyn tekniikan avulla huomattavasti. Uudenlaiset tietoliikennepalvelut lisäävät laitteidenvälisen paikallisen tietoliikenteen määrää. Spektrinkäytön kannalta tämä liikenne on tehokkainta lähettää suoraan laitteesta toiseen. Väitöskirjassa on tutkittu joustavaa spektrinkäyttöä suorien laitteidenvälisten lähetysten ja soluverkon välillä. Interferenssin hallinta takaa luotettavan ja tehokkaan spektrin yhteiskäytön. Tätä varten väitöskirjassa on kehitetty kolme menetelmää, jotka perustuvat tehonsäätöön, lähetysten ajoitukseen ja moniantennilähetykseen

Circuit Design Techniques For Wideband Phased Arrays

University of Minnesota Ph.D. dissertation.June 2015. Major: Electrical Engineering. Advisor: Ramesh Harjani. 1 computer file (PDF); xii, 143 pages.This dissertation focuses on beam steering in wideband phased arrays and phase noise modeling in injection locked oscillators. Two different solutions, one in frequency and one in time, have been proposed to minimize beam squinting in phased arrays. Additionally, a differential current reuse frequency doubler for area and power savings has been proposed. Silicon measurement results are provided for the frequency domain solution (IBM 65nm RF CMOS), injection locked oscillator model verification (IBM 130nm RF-CMOS) and frequency doubler (IBM 65nm RF CMOS), while post extraction simulation results are provided for the time domain phased array solution (the chip is currently under fabrication, TSMC 65nm RF CMOS). In the frequency domain solution, a 4-point passive analog FFT based frequency tunable filter is used to channelize an incoming wideband signal into multiple narrowband signals, which are then processed through independent phase shifters. A two channel prototype has been developed at 8GHz RF frequency. Three discrete phase shifts (0 & +/- 90 degrees) are implemented through differential I-Q swapping with appropriate polarity. A minimum null-depth of 19dB while a maximum null-depth of 27dB is measured. In the time domain solution, a discrete time approach is undertaken with signals getting sampled in order of their arrival times. A two-channel prototype for a 2GHz instantaneous RF bandwidth (7GHz-9GHz) has been designed. A QVCO generates quadrature LO signals at 8GHz which are phase shifted through a 5-bit (2 extra bits from differential I-Q swapping with appropriate polarity) cartesian combiner. Baseband sampling clocks are generated from phase shifted LOs through a CMOS divide by 4 with independent resets. The design achieves an average time delay of 4.53ps with 31.5mW of power consumption (per channel, buffers excluded). An injection locked oscillator has been analyzed in s-domain using Paciorek's time domain transient equations. The simplified analysis leads to a phase noise model identical to that of a type-I PLL. The model is equally applicable to injection locked dividers and multipliers and has been extended to cover all injection locking scenarios. The model has been verified against a discrete 57MHz Colpitt's ILO, a 6.5GHz ILFD and a 24GHz ILFM with excellent matching between the model and measurements. Additionally, a differential current reuse frequency doubler, for frequency outputs between 7GHz to 14GHz, design has been developed to reduce passive area and dc power dissipation. A 3-bit capacitive tuning along with a tail current source is used to better conversion efficiency. The doubler shows FOM$_{T}$ values between 191dBc/Hz to 209dBc/Hz when driven by a 0.7GHz to 5.8GHz wide tuning VCO with a phase noise that ranges from -114dBc/Hz to -112dBc/Hz over the same bandwidth