Phase manipulation for efficient radio frequency transmission

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 109-112).Power amplifiers (PAs) for microwave communications are generally the most power-hungry element of a transmitter. High linearity is required for modern digital communications standards, and often is achieved at the expense of efficiency. Outphasing architectures, which combine multiple nonlinear but efficient switching PAs into a system with an overall linear response, represent a promising strategy for breaking the efficiency/linearity tradeoff inherent to conventional PAs. This work explores methods for efficient PA design using outphasing techniques. Two aspects of outphasing design are considered. First, a wide-band phase modulator is introduced that uses a single current-steering digital to analog converter (DAC) structure and discrete clock prerotation. This topology takes advantage of specifications particular to outphasing architectures to reduce matching requirements as compared to a two-DAC phase modulator while providing wideband capability. The phase modulator is demonstrated in 65-nm CMOS, operates over a carrier frequency range of 1.2-4.2 GHz and has a 12-bit phase resolution and sample rate of 160 MSamples/second. The second technique is a novel four-way lossless power combiner and outphasing system which provides ideally lossless power combining along with resistive loading of switching power amplifiers over a wide output range. This work presents the first-ever demonstration of this system at microwave frequencies. Particular attention is paid to the microwave-specific aspects of implementation. A 60-W GaN prototype demonstrates the outphasing and dynamic performance, which closely matches the expected performance despite the challenges of operating at microwave frequencies.by Taylor Wallis Barton.Sc.D

Channel Estimation Error, Oscillator Stability And Wireless Power Transfer In Wireless Communication With Distributed Reception Networks

This dissertation considers three related problems in distributed transmission and reception networks. Generally speaking, these types of networks have a transmit cluster with one or more transmit nodes and a receive cluster with one or more receive nodes. Nodes within a given cluster can communicate with each other using a wired or wireless local area network (LAN/WLAN). The overarching goal in this setting is typically to increase the efficiency of communication between the transmit and receive clusters through techniques such as distributed transmit beamforming, distributed reception, or other distributed versions of multi-input multi-output (MIMO) communication. More recently, the problem of wireless power transfer has also been considered in this setting. The first problem considered by this dissertation relates to distributed reception in a setting with a single transmit node and multiple receive nodes. Since exchanging lightly quantized versions of in-phase and quadrature samples results in high throughput requirements on the receive LAN/WLAN, previous work has considered an approach where nodes exchange hard decisions, along with channel magnitudes, to facilitate combining similar to an ideal receive beamformer. It has been shown that this approach leads to a small loss in SNR performance, with large reductions in required LAN/WLAN throughput. A shortcoming of this work, however, is that all of the prior work has assumed that each receive node has a perfect estimation of its channel to the transmitter. To address this shortcoming, the first part of this dissertation investigates the effect of channel estimation error on the SNR performance of distributed reception. Analytical expressions for these effects are obtained for two different modulation schemes, M-PSK and M2-QAM. The analysis shows the somewhat surprising result that channel estimation error causes the same amount of performance degradation in ideal beamforming and pseudo-beamforming systems despite the fact that the channel estimation errors manifests themselves quite differently in both systems. The second problem considered in this dissertation is related to oscillator stability and phase noise modeling. In distributed transmission systems with multiple transmitters in the transmit cluster, synchronization requirements are typically very strict, e.g., on the order of one picosecond, to maintain radio frequency phase alignment across transmitters. Therefore, being able to accurately model the behavior of the oscillators and their phase noise responses is of high importance. Previous approaches have typically relied on a two-state model, but this model is often not sufficiently rich to model low-cost oscillators. This dissertation develops a new three-state oscillator model and a method for estimating the parameters of this model from experimental data. Experimental results show that the proposed model provides up to 3 dB improvement in mean squared error (MSE) performance with respect to a two-state model. The last part of this work is dedicated to the problem of wireless power transfer in a setting with multiple nodes in the transmit cluster and multiple nodes in the receive cluster. The problem is to align the phases of the transmitters to achieve a certain power distribution across the nodes in the receive cluster. To find optimum transmit phases, we consider a iterative approach, similar to the prior work on one-bit feedback for distributed beamforming, in which each receive node sends a one-bit feedback to the transmit cluster indicating if the received power in that time slot for that node is increased. The transmitters then update their phases based on the feedback. What makes this problem particularly interesting is that, unlike the prior work on one-bit feedback for distributed beamforming, this is a multi-objective optimization problem where not every receive node can receive maximum power from the transmit array. Three different phase update decision rules, each based on the one-bit feedback signals, are analyzed. The effect of array sparsity is also investigated in this setting

Performance characterization of long-distance digital microwave radio systems

Imperial Users onl

Linearization techniques to suppress optical nonlinearity

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis is shown the implementation of the linearization techniques such as feedforward and pre-distortion feedback linearization to suppress the optical components nonlinearities caused by the fibre and semiconductor optical amplifier (SOA). The simulation verified these two linearization techniques for single tone direct modulation, two tone indirect modulation and ultra wideband input to the optical fibre. These techniques uses the amplified spontaneously emission (ASE) noise reduction in two loops of SOA by a feed-forward and predistortion linearizer and is shown more than 6dB improvement. Also it investigates linearization for the SOA amplifier to cancel out the third order harmonics or inter-modulation distortion (IMD) or four waves mixing. In this project, more than 20 dB reductions is seen in the spectral re-growth caused by the SOA. Amplifier non-linearity becomes more severe with two strong input channels leading to inter-channel distortion which can completely mask a third adjacent channel. The simulations detailed above were performed utilizing optimum settings for the variable gain, phase and delay components in the error correction loop of the feed forward and Predistortion systems and hence represent the ideal situation of a perfect feed-forward and Predistortion system. Therefore it should be consider that complexity of circuit will increase due to amplitude, phase and delay mismatches in practical design. Also it has describe the compatibility of Software Defined Radio with Hybrid Fibre Radio with simulation model of wired optical networks to be used for future research investigation, based on the star and ring topologies for different modulation schemes, and providing the performance for these configurations

Application of knowledge-based techniques to fault diagnosis of 16 QAM digital microwave radio equipment

SIGLEAvailable from British Library Document Supply Centre- DSC:D86372 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Digital data transmission over mobile radio channels

The aim of this work is to study data transmission over a microwave digital mobile radio channel at 900 MHz, where the channel is subjected to multipath fading. Besides the fading, the other impairments assumed here are additive noise, co-channel interference and adjacent channel interference. Two modulation techniques are investigated in this work, namely Quadrature-Amplitude-Modulation (QAM) and Quadrature-Phase-Shift- Keying (QPSK). The channel is characterised digitally, assuming multipath Rayleigh fading in the presence of noise. The detection process studied here are near-maximum likelihood schemes: non-linear equalisation methods are also considered in detail. The thesis is also concerned with carrier synchronisation and channel estimation under conditions of Rayleigh fading. Since the carrier syncn,honisation is a most important requirement in mobile radio, a Digital Phase Locked Loop (DPLL) technique has been designed and investigated in the form of a feedback digital synchronisation system. Two types of channel estimation technique, namely feedforward and feedback estimators, are also investigated in this work. The feedback estimator is modified by the addition of a digital control system, in order to reduce its delay, and to cope with rapidly fading signals. Successful carrier synchronisation is demonstrated by the use of space diversity. The study was completed using models of the component parts of the system, and by the use of extensive computer simulations to analyse the system under various operating conditions

MIMO techniques for higher data rate wireless communications

The demand for higher data rate, higher spectral efficiency and better quality of service in wireless communications is growing fast in the past few years. However, obtaining these requirements become challenging for wireless communication systems due to the problems of channel multi-path fading, higher power loss and power bandwidth limitations. A lot of research interest has been directed towards implementing new techniques in wireless communication systems, such as MIMO an OFDM, to overcome the above mentioned problems. Methods of achieving higher data rate and better spectral efficiency have been dealt with in the thesis. The work comprised three parts; the first part focuses on channel modelling, the second looks at fading mitigation techniques, and the third part deals with adaptive transmission schemes for different diversity techniques. In the first part, we present multiple-input multiple-output (MIMO) space-time geometrical channel model with hyperbolically distributed scatterers (GBHDS) for a macro-cell mobile environment. The model is based on one-ring scattering assumption. This MIMO model provides statistics of the time of arrival (TOA) and direction of arrival (DOA). Our analytical results are validated with measurement data and compared to different geometrical based signal bounce macro-cell (GBSSBM) channel models including Gaussian scatterer density (GSD) channel model, the geometrical based exponential (GBE) channel model. On the other hand, for the same channel model we investigate the analytical methods which capture physical wave and antenna configuration at both ends representing in a matrix form. In the second part, we investigate the proposed channel model using joint frequency and spatial diversity system. . We combine STBC with OFDM to improve the error performance in the fading channels. We consider two different fading scenarios namely frequency selective and time selective fading channels. For the first scenario we propose a new technique to suppress the frequency error offset caused by the motion of mobile (Doppler shift). On the other hand, we examine the performance of STBC-OFDM in time selective macro-cell channel environment. In the last part, we evaluate the spectral efficiency for different receiver diversity namely maximal ratio combiner (MRC), selection combiner (SC), and Hybrid (MRC/SC). We derive closed form expressions for the single user capacity, taking into account the effect of imperfect channel estimation at the receiver. The channel considered is a slowly varying spatially independent flat Rayleigh fading channel. Three adaptive transmission schemes are analysed: 1) optimal power rate and rate adaptation (opra), constant power with optimal rate adaptation (ora), and 3) channel inversion with fixed rate (cifr). Furthermore, we derive analytical results for capacity statistics including moment generating function (MGF), complementary cumulative distribution function (CDF) and probability density function (pdf)

Diversity techniques for broadband wireless communications: performance enhancement and analysis

The diversity techniques have been proven to be effective for next generation broadband wireless communications, and are the focus of this thesis. The diversity techniques can be broadly categorized into three types: Space, Time, and Frequency. In this thesis, we are mainly concerned with frequency and space diversity techniques. Orthogonal Frequency Division Multiplexing (OFDM) is a frequency diversity technique which offers several benefits such as easier digital implementation, immunity to multipath channels, low complexity channel equalization, etc. Despite these desirable features, there are few inherent problems in OFDM such as high peak-to-average power ratio (PAPR). High PAPR demands large dynamic range in the transmitted chain such as digital to analog converter (DAC) and power amplifier (PA). Unless pre-processed, the transmitted signal gets distorted due to quantization errors and inter-modulation. In the initial stage of PhD candidature, the author focused on PAPR reduction techniques. A simple modification on conventional iterative clipping and filtering (ICF) technique was proposed which has less computational complexity. The power savings achievable from clipping and filtering method was considered next. Furthermore the ICF is compared with another distortion-less PAPR reduction technique called Selective Mapping (SLM) based on power savings. Finally, impact of clipping and filtering on the channel estimation was analyzed. Space diversity seeks to exploit the multi-path characteristics of wireless channels to improve the performance. The simplest form of the space diversity is the receive diversity where two or more antennas with sufficient spacing collect independent copies of the same transmitted signal, which contributes to better signal reception. In this thesis new analytical expressions for spectral efficiency, capacity, and error rates were presented for adaptive systems with channel estimation error. Beamforming (steering signal towards desired receiver) is another useful technique in multiple-antenna systems to further improve the system performance. MRT (Maximal Ratio Transmission) or MIMO-MRC is such system where the transmitter, based on channel feedback from the receiver, uses weighting factors to steer the transmitted signal. Closed form expressions for symbol error rates were derived for MRT system with channel estimation error. The results were extended to evaluate closed form expressions of error rates for Rectangular QAM. Antenna correlation was considered in another contribution on MRC systems. Relay and Cooperative networks represent another form of spatial diversity and have recently attracted significant research attention. These networks rely on intermediate nodes called "relays" to establish communication between the source and the destination. In addition to coverage extension, the relay networks have shown to offer cooperative diversity when there is a direct link or multiple relays. The first contribution is to analyze a dual-hop amplify-forward relay networks with dissimilar fading scenarios. Next error rates of Rectangular QAM for decode-forward selection relay system are derived. Multiple antenna at relay is included to analyze the benefits of dual spatial diversity over Rayleigh and Nakagami fading channels. Antenna selection is a cost-effective way to exploit the antenna diversity. General Order Antenna Selection (GOAS), based on Ordered Statistics, is used to evaluate signal statistics for a MIMO relay network

Performance Analysis, Resource Allocation and Optimization of Cooperative Communication Systems under Generalized Fading Channels

The increasing demands for high-speed data transmission, efficient wireless access, high quality of service (QoS) and reliable network coverage with reduced power consumption impose demanding intensive research efforts on the design of novel wireless communication system architectures. A notable development in the area of communication theory is the introduction of cooperative communication systems. These technologies become promising solution for the next-generation wireless transmission systems due to their applicability in size, power, hardware and price constrained devices, such as cellular mobile devices, wireless sensors, ad-hoc networks and military communications, being able to provide, e.g., diversity gain against fading channels without the need for installing multiple antennas in a single terminal. The performance of the cooperative systems can in general be significantly increased by allocating the limited power efficiently. In this thesis, we address in detail the performance analysis, resource allocation and optimization of such cooperative communication systems under generalized fading channels. We focus first on energy-efficiency (EE) optimization and optimal power allocation (OPA) of regenerative cooperative network with spatial correlation effects under given power constraint and QoS requirement. The thesis also investigates the end-to-end performance and power allocation of a regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is realistic case in practical wireless communication scenarios. Furthermore, the study investigates the end-to-end performance, OPA and energy optimization analysis under total power constraint and performance requirement of full-duplex (FD) relaying transmission scheme over asymmetric generalized fading models with relay self-interference (SI) effects.The study first focuses on exact error analysis and EE optimization of regenerative relay systems under spatial correlation effects. It first derives novel exact and asymptotic expressions for the symbol-error-rates (SERs) of M -ary quadrature amplitude and M -ary phase-shift keying (M -QAM) and (M -PSK) modulations, respectively, assuming a dual-hop decode-and-forward relay system, spatial correlation, path-loss effects and maximum-ratio-combing (MRC) at the destination. Based on this, EEoptimization and OPA are carried out under certain QoS requirement and transmit power constraints.Furthermore, the second part of the study investigates the end-to-end performance and power allocation of MRC based regenerative multi-relay cooperative system over non-homogeneous scattering environment. Novel exact and asymptotic expressions are derived for the end-to-end average SER for M -QAM and M -PSK modulations.The offered results are employed in performance investigations and power allocation formulations under total transmit power constraints.Finally, the thesis investigates outage performance, OPA and energy optimization analysis under certain system constraints for the FD and half-duplex (HD) relaying systems. Unlike the previous studies that considered the scenario of information transmission over symmetric fading conditions, in this study we considered the scenario of information transmission over the most generalized asymmetric fading environments.The obtained results indicate that depending on the severity of multipath fading, the spatial correlation between the direct and relayed paths and the relay location, the direct transmission is more energy-efficient only for rather short transmission distances and until a certain threshold. Beyond this, the system benefits substantially from the cooperative transmission approach where the cooperation gain increases as the transmission distance increases. Furthermore, the investigations on the power allocation for the multi-relay system over the generalized small-scale fading model show that substantial performance gain can be achieved by the proposed power allocation scheme over the conventional equal power allocation (EPA) scheme when the source-relay and relay-destination paths are highly unbalanced. Extensive studies on the FD relay system also show that OPA provides significant performance gain over the EPA scheme when the relay SI level is relatively strong. In addition, it is shown that the FD relaying scheme is more energy-efficient than the reference HD relaying scheme at long transmission distances and for moderate relay SI levels.In general, the investigations in this thesis provide tools, results and useful insights for implementing space-efficient, low-cost and energy-efficient cooperative networks, specifically, towards the future green communication era where the optimization of the scarce resources is critical

High Performance Optical Transmitter Ffr Next Generation Supercomputing and Data Communication

High speed optical interconnects consuming low power at affordable prices are always a major area of research focus. For the backbone network infrastructure, the need for more bandwidth driven by streaming video and other data intensive applications such as cloud computing has been steadily pushing the link speed to the 40Gb/s and 100Gb/s domain. However, high power consumption, low link density and high cost seriously prevent traditional optical transceiver from being the next generation of optical link technology. For short reach communications, such as interconnects in supercomputers, the issues related to the existing electrical links become a major bottleneck for the next generation of High Performance Computing (HPC). Both applications are seeking for an innovative solution of optical links to tackle those current issues. In order to target the next generation of supercomputers and data communication, we propose to develop a high performance optical transmitter by utilizing CISCO Systems®\u27s proprietary CMOS photonic technology. The research seeks to achieve the following outcomes: 1. Reduction of power consumption due to optical interconnects to less than 5pJ/bit without the need for Ring Resonators or DWDM and less than 300fJ/bit for short distance data bus applications. 2. Enable the increase in performance (computing speed) from Peta-Flop to Exa-Flops without the proportional increase in cost or power consumption that would be prohibitive to next generation system architectures by means of increasing the maximum data transmission rate over a single fiber. 3. Explore advanced modulation schemes such as PAM-16 (Pulse-Amplitude-Modulation with 16 levels) to increase the spectrum efficiency while keeping the same or less power figure. This research will focus on the improvement of both the electrical IC and optical IC for the optical transmitter. An accurate circuit model of the optical device is created to speed up the performance optimization and enable co-simulation of electrical driver. Circuit architectures are chosen to minimize the power consumption without sacrificing the speed and noise immunity. As a result, a silicon photonic based optical transmitter employing 1V supply, featuring 20Gb/s data rate is fabricated. The system consists of an electrical driver in 40nm CMOS and an optical MZI modulator with an RF length of less than 0.5mm in 0.13&mu m SOI CMOS. Two modulation schemes are successfully demonstrated: On-Off Keying (OOK) and Pulse-Amplitude-Modulation-N (PAM-N N=4, 16). Both versions demonstrate signal integrity, interface density, and scalability that fit into the next generation data communication and exa-scale computing. Modulation power at 20Gb/s data rate for OOK and PAM-16 of 4pJ/bit and 0.25pJ/bit are achieved for the first time of an MZI type optical modulator, respectively