495 research outputs found

    Efficient Radiometric Signature Methods for Cognitive Radio Devices

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    This thesis presents the first comprehensive study and new methods for radiometric fingerprinting of the Cognitive Radio (CR) devices. The scope of the currently available radio identification techniques is limited to a single radio adjustment. Yet, the variable nature of the CR with multiple levels of parameters and adjustments renders the radiometric fingerprinting much more complex. We introduce a new method for radiometric fingerprinting that detects the unique variations in the hardware of the reconfigurable radio by passively monitoring the radio packets. Several individual identifiers are used for extracting the unique physical characteristics of the radio, including the frequency offset, modulated phase offset, in-phase/quadrature-phase offset from the origin, and magnitude. Our method provides stable and robust identification by developing individual identifiers (classifiers) that may each be weak (i.e., incurring a high prediction error) but their committee can provide a strong classification technique. Weighted voting method is used for combining the classifiers. Our hardware implementation and experimental evaluations over multiple radios demonstrate that our weighted voting approach can identify the radios with an average of 97.7% detection probability and an average of 2.3% probability of false alarm after testing only 5 frames. The probability of detection and probability of false alarms both rapidly improve by increasing the number of test frames

    Joint Satellite-Transmitter and Ground-Receiver Digital Pre-Distortion for Active Phased Arrays in LEO Satellite Communications

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    A novel joint satellite-transmitter and ground-receiver (JSG) digital pre-distortion (DPD) (JSG-DPD) technique is proposed to improve the linearity and power efficiency of the space-borne active phased arrays (APAs) in low Earth orbit (LEO) satellite communications. Different from the conventional DPD technique that requires a complex RF feedback loop, the DPD coefficients based on a generalized memory polynomial (GMP) model are extracted at the ground-receiver and then transmitted to the digital baseband front-end of the LEO satellite-transmitter via a satellite–ground bi-directional transmission link. The issue of the additive white Gaussian noise (AWGN) of the satellite–ground channel affecting the extraction of DPD coefficients is tackled using a superimposing training sequences (STS) method. The proposed technique has been experimentally verified using a 28 GHz phased array. The performance improvements in terms of error vector amplitude (EVM) and adjacent channel power ratio (ACPR) are 7.5% and 3.6 dB, respectively. Requiring limited space-borne resources, this technique offers a promising solution to achieve APA DPD for LEO satellite communications

    Digital Predistorion of 5G Millimeter-Wave Active Phased Arrays using Artificial Neural Networks

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    ワイヤレス通信のための先進的な信号処理技術を用いた非線形補償法の研究

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    The inherit nonlinearity in analogue front-ends of transmitters and receivers have had primary impact on the overall performance of the wireless communication systems, as it gives arise of substantial distortion when transmitting and processing signals with such circuits. Therefore, the nonlinear compensation (linearization) techniques become essential to suppress the distortion to an acceptable extent in order to ensure sufficient low bit error rate. Furthermore, the increasing demands on higher data rate and ubiquitous interoperability between various multi-coverage protocols are two of the most important features of the contemporary communication system. The former demand pushes the communication system to use wider bandwidth and the latter one brings up severe coexistence problems. Having fully considered the problems raised above, the work in this Ph.D. thesis carries out extensive researches on the nonlinear compensations utilizing advanced digital signal processing techniques. The motivation behind this is to push more processing tasks to the digital domain, as it can potentially cut down the bill of materials (BOM) costs paid for the off-chip devices and reduce practical implementation difficulties. The work here is carried out using three approaches: numerical analysis & computer simulations; experimental tests using commercial instruments; actual implementation with FPGA. The primary contributions for this thesis are summarized as the following three points: 1) An adaptive digital predistortion (DPD) with fast convergence rate and low complexity for multi-carrier GSM system is presented. Albeit a legacy system, the GSM, however, has a very strict requirement on the out-of-band emission, thus it represents a much more difficult hurdle for DPD application. It is successfully implemented in an FPGA without using any other auxiliary processor. A simplified multiplier-free NLMS algorithm, especially suitable for FPGA implementation, for fast adapting the LUT is proposed. Many design methodologies and practical implementation issues are discussed in details. Experimental results have shown that the DPD performed robustly when it is involved in the multichannel transmitter. 2) The next generation system (5G) will unquestionably use wider bandwidth to support higher throughput, which poses stringent needs for using high-speed data converters. Herein the analog-to-digital converter (ADC) tends to be the most expensive single device in the whole transmitter/receiver systems. Therefore, conventional DPD utilizing high-speed ADC becomes unaffordable, especially for small base stations (micro, pico and femto). A digital predistortion technique utilizing spectral extrapolation is proposed in this thesis, wherein with band-limited feedback signal, the requirement on ADC speed can be significantly released. Experimental results have validated the feasibility of the proposed technique for coping with band-limited feedback signal. It has been shown that adequate linearization performance can be achieved even if the acquisition bandwidth is less than the original signal bandwidth. The experimental results obtained by using LTE-Advanced signal of 320 MHz bandwidth are quite satisfactory, and to the authors’ knowledge, this is the first high-performance wideband DPD ever been reported. 3) To address the predicament that mobile operators do not have enough contiguous usable bandwidth, carrier aggregation (CA) technique is developed and imported into 4G LTE-Advanced. This pushes the utilization of concurrent dual-band transmitter/receiver, which reduces the hardware expense by using a single front-end. Compensation techniques for the respective concurrent dual-band transmitter and receiver front-ends are proposed to combat the inter-band modulation distortion, and simultaneously reduce the distortion for the both lower-side band and upper-side band signals.電気通信大学201

    A digital polar transmitter for multi-band OFDM Ultra-WideBand

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    Linear power amplifiers used to implement the Ultra-Wideband standard must be backed off from optimum power efficiency to meet the standard specifications and the power efficiency suffers. The problem of low efficiency can be mitigated by polar modulation. Digital polar architectures have been employed on numerous wireless standards like GSM, EDGE, and WLAN, where the fractional bandwidths achieved are only about 1%, and the power levels achieved are often in the vicinity of 20 dBm. Can the architecture be employed on wireless standards with low-power and high fractional bandwidth requirements and yet achieve good power efficiency? To answer these question, this thesis studies the application of a digital polar transmitter architecture with parallel amplifier stages for UWB. The concept of the digital transmitter is motivated and inspired by three factors. First, unrelenting advances in the CMOS technology in deep-submicron process and the prevalence of low-cost Digital Signal processing have resulted in the realization of higher level of integration using digitally intensive approaches. Furthermore, the architecture is an evolution of polar modulation, which is known for high power efficiency in other wireless applications. Finally, the architecture is operated as a digital-to-analog converter which circumvents the use of converters in conventional transmitters. Modeling and simulation of the system architecture is performed on the Agilent Advanced Design System Ptolemy simulation platform. First, by studying the envelope signal, we found that envelope clipping results in a reduction in the peak-to-average power ratio which in turn improves the error vector magnitude performance (figure of merit for the study). In addition, we have demonstrated that a resolution of three bits suffices for the digital polar transmitter when envelope clipping is performed. Next, this thesis covers a theoretical derivation for the estimate of the error vector magnitude based on the resolution, quantization and phase noise errors. An analysis on the process variations - which result in gain and delay mismatches - for a digital transmitter architecture with four bits ensues. The above studies allow RF designers to estimate the number of bits required and the amount of distortion that can be tolerated in the system. Next, a study on the circuit implementation was conducted. A DPA that comprises 7 parallel RF amplifiers driven by a constant RF phase-modulated signal and 7 cascode transistors (individually connected in series with the bottom amplifiers) digitally controlled by a 3-bit digitized envelope signal to reconstruct the UWB signal at the output. Through the use of NFET models from the IBM 130-nm technology, our simulation reveals that our DPA is able to achieve an EVM of - 22 dB. The DPA simulations have been performed at 3.432 GHz centre frequency with a channel bandwidth of 528 MHz, which translates to a fractional bandwidth of 15.4%. Drain efficiencies of 13.2/19.5/21.0% have been obtained while delivering -1.9/2.5/5.5 dBm of output power and consuming 5/9/17 mW of power. In addition, we performed a yield analysis on the digital polar amplifier, based on unit-weighted and binary-weighted architecture, when gain variations are introduced in all the individual stages. The dynamic element matching method is also introduced for the unit-weighted digital polar transmitter. Monte Carlo simulations reveal that when the gain of the amplifiers are allowed to vary at a mean of 1 with a standard deviation of 0.2, the binary-weighted architecture obtained a yield of 79%, while the yields of the unit-weighted architectures are in the neighbourhood of 95%. Moreover, the dynamic element matching technique demonstrates an improvement in the yield by approximately 3%. Finally, a hardware implementation for this architecture based on software-defined arbitrary waveform generators is studied. In this section, we demonstrate that the error vector magnitude results obtained with a four-stage binary-weighted digital polar transmitter under ideal combining conditions fulfill the European Computer Manufacturers Association requirements. The proposed experimental setup, believed to be the first ever attempted, confirm the feasibility of a digital polar transmitter architecture for Ultra-Wideband. In addition, we propose a number of power combining techniques suitable for the hardware implementation. Spatial power combining, in particular, shows a high potential for the digital polar transmitter architecture. The above studies demonstrate the feasibility of the digital polar architecture with good power efficiency for a wideband wireless standard with low-power and high fractional bandwidth requirements

    Tolerance to in-band crosstalk of virtual carrier-assisted direct detection multi-band OFDM system

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    The tolerance to in-band crosstalk of virtual carrier (VC)-assisted direct detection (DD) multi-band orthogonal frequency division multiplexing (MB-OFDM) system is assessed numerically through Monte-Carlo simulation and considering a single interferer. The influence of the virtual carrier-to-band power ratio (VBPR) and the virtual carrier-to-band gap (VBG) of the interferer on the in-band tolerance is also studied. We show that, for interferers with the same VBG as the selected signal, the increase of the VBPR of the interferer leads to lower optical signal-to-noise ratio (OSNR) penalties. The increase of the VBG of the interferer with central frequency different from the selected signal also leads to lower OSNR penalties. When the central frequencies of the interferer and selected bands are the same, the variation VBG of the interferer can lead to 11 dB less tolerance to in-band crosstalk of the VC-assisted DD OFDM system.info:eu-repo/semantics/acceptedVersio

    Digital predistortion of RF amplifiers using baseband injection for mobile broadband communications

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    Radio frequency (RF) power amplifiers (PAs) represent the most challenging design parts of wireless transmitters. In order to be more energy efficient, PAs should operate in nonlinear region where they produce distortion that significantly degrades the quality of signal at transmitter’s output. With the aim of reducing this distortion and improve signal quality, digital predistortion (DPD) techniques are widely used. This work focuses on improving the performances of DPDs in modern, next-generation wireless transmitters. A new adaptive DPD based on an iterative injection approach is developed and experimentally verified using a 4G signal. The signal performances at transmitter output are notably improved, while the proposed DPD does not require large digital signal processing memory resources and computational complexity. Moreover, the injection-based DPD theory is extended to be applicable in concurrent dual-band wireless transmitters. A cross-modulation problem specific to concurrent dual-band transmitters is investigated in detail and novel DPD based on simultaneous injection of intermodulation and cross-modulation distortion products is proposed. In order to mitigate distortion compensation limit phenomena and memory effects in highly nonlinear RF PAs, this DPD is further extended and complete generalised DPD system for concurrent dual-band transmitters is developed. It is clearly proved in experiments that the proposed predistorter remarkably improves the in-band and out-of-band performances of both signals. Furthermore, it does not depend on frequency separation between frequency bands and has significantly lower complexity in comparison with previously reported concurrent dual-band DPDs

    RF Transceiver system design for IoT in wide area networks

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    Abstract. Wireless communication has grown rapidly in the last two decades. New applications and advancement in technology is boosting the demand. Internet of things (IoT) is nowadays topic of discussion for everyone related to the wireless communication industry. IoT is a system of interconnected devices which can be people, animals, things or machines each with a unique identifier and the ability to transfer data over a network without any interaction with humans or computers. The aim of this thesis is system design of RF transceiver for IoT devices operating in wide area networks. Several service providers are struggling to capture the IoT market. In this thesis detailed system design of third generation partnership project (3GPP) newly specified user equipment category M1 also known as long term evolution machine (LTE-M) is presented. LTE-M can operate in both full duplex and half duplex and it uses the same signal structure as the current operational standard long term evolution (LTE). The designed transceiver is able to operate in half duplex and meet the performance requirement (95 % throughput) specified by 3GPP. Radio frequency transceivers have various architectures and each architecture has its own pros and cons associated with it. This transceiver is designed to be integrated in a wearable device. Constraints like small size and low power restrictions led to the choice of direct conversion architecture for the design. Simulations were performed in ADS to verify the theoretical results

    Design and demonstration of digital pre-distortion using software defined radio

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    Abstract. High data rates for large number of users set tight requirements for signal quality measured in terms of error vector magnitude (EVM). In radio transmitters, nonlinear distortion dominated by power amplifiers (PAs) often limits the achievable EVM. However, the linearity can be improved by linearization techniques. Digital pre-distortion (DPD) is one of these widely used linearization techniques for an effective distortion reduction over a wide bandwidth. In DPD, the nonlinearity of the transmitter is pre-compensated in the digital domain to achieve linear output. Moreover, DPD is used to enable PAs to operate in the power-efficient region with a decent linearity. As we are moving towards millimetre-wave frequencies to enable the wideband communications, the design of the DPD algorithm must be optimized in terms of performance and power consumption. Moreover, continuous development of wireless infrastructure motivates to make research on programmable and reconfigurable platforms in order to decrease the demonstration cost and time, especially for the demonstration purposes. This thesis illustrates and presents how software defined radio (SDR) platforms can be used to demonstrate DPD. Universal software defined peripheral (USRP) X300 is a commercial software defined radio (SDR) platform. The chosen model, X300, has two independent channels equipped with individual transceiver cards. SIMULINK is used to communicate with the device and the two channels of X300 are used as transmitter and receiver simultaneously in full-duplex mode. Hence, a single USRP device is acting as an operational transmitter and feedback receiver, simultaneously. The implemented USRP design consists of SIMULINK based transceiver design and lookup table based DPD in which the coefficients are calculated in MATLAB offline. An external PA, i.e. ZFL-2000+ together with a directional coupler and attenuator are connected between the TX/RX port and RX2 port to measure the nonlinearity. The nonlinearity transceiver is measured with and without the external PA. The experimental results show decent performance for linearization by using the USRP platform. However, the results differ widely due to the used USRP transceiver parameterization and PA operational point. The 16 QAM test signal with 500 kHz bandwidth is fed to the USRP transmit chain. As an example, the DPD algorithm improves the EVM from 7.6% to 2.1% and also the ACPR is reduced around 10 dB with the 16 QAM input signal where approximately + 2.2 dBm input power applied to the external PA
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