102 research outputs found

    Concurrent Dual Band Radio-over-Fiber Transmission Using 1-bit Envelope Delta-Sigma Modulation

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    With the growing demand for bandwidth and transmission speed, mobile communication network designs must stay adaptable, efficient and cost-effective. A key integration has been Radio-over-Fiber (RoF) transmission systems that provide a cheaper option and low loss for high frequency signal transfer. For the optical transmitter, delta-sigma modulation (DSM) can be a beneficial addition. The partnership simplifies the Digital-Radio-over-Fiber setup by removing the need for additional converters and prompts adjustments based on system need. Main factors in delta-sigma modulators are the amount of quantization bits and the order of the modulator. Changing quantization bits to a single bit allows the system to use less processing bandwidth and less error experienced from optical transmission. High order structures provide more noise shaping to shift noise away from the band of interest. Still, such setups are prone to linearity problems due to clock jitter from multiple feedback loops. Different adaptations of delta-sigma modulation have been designed to combat the problems, but a key standout is the implementation of an envelope delta-sigma modulation (EDSM). Envelope delta-sigma modulation’s separate processing of envelope and phase delivers time alignment and noise shaping counter the negative implications from high order DSMs. Combining envelope delta-sigma modulation with RoF transmission is an attractive option, but research has yet to delve into carrier aggregation with these setups. This thesis explores concurrent dual band 64-QAM 20 MHz LTE Radio-over-Fiber using 1-bit envelope delta-sigma modulation. It expands transmitter functionality by concurrent signal integration. Inside the EDSM is a 4th order bandpass delta-sigma modulator custom tailored one of two carrier frequencies. The two frequencies come from two different LTE bands to show interband compatibility. The carrier frequencies are 2.112 GHz from LTE band 1 and 2.64 GHz from LTE band 7. Simulation and experimental results confirm the functionality of the proposed envelope delta-sigma modulation RoF system in single and dual band for LTE standards (error vector magnitude < 8%). Experimental results confirm that EDSM is more resilient to RoF transmission than BP-DSM. However, the EVM values for BP-DSM are better for carrier aggregated transmission

    Rotation Measure Synthesis of Galactic Polarized Emission with the DRAO 26-m Telescope

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    Radio polarimetry at decimetre wavelengths is the principal source of information on the Galactic magnetic field. The diffuse polarized emission is strongly influenced by Faraday rotation in the magneto-ionic medium and rotation measure is the prime quantity of interest, implying that all Stokes parameters must be measured over wide frequency bands with many frequency channels. The DRAO 26-m Telescope has been equipped with a wideband feed, a polarization transducer to deliver both hands of circular polarization, and a receiver, all operating from 1277 to 1762 MHz. Half-power beamwidth is between 40 and 30 arcminutes. A digital FPGA spectrometer, based on commercially available components, produces all Stokes parameters in 2048 frequency channels over a 485-MHz bandwidth. Signals are digitized to 8 bits and a Fast Fourier Transform is applied to each data stream. Stokes parameters are then generated in each frequency channel. This instrument is in use at DRAO for a Northern sky polarization survey. Observations consist of scans up and down the Meridian at a drive rate of 0.9 degree per minute to give complete coverage of the sky between declinations -30 degree and 90 degree. This paper presents a complete description of the receiver and data acquisition system. Only a small fraction of the frequency band of operation is allocated for radio astronomy, and about 20 percent of the data are lost to interference. The first 8 percent of data from the survey are used for a proof-of-concept study, which has led to the first application of Rotation Measure Synthesis to the diffuse Galactic emission obtained with a single-antenna telescope. We find rotation measure values for the diffuse emission as high as approximately 100 rad per square metre, much higher than recorded in earlier work.Comment: Accepted for publication in The Astronomical Journa

    Adaptive multibeam phased array design for a Spacelab experiment

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    The parametric tradeoff analyses and design for an Adaptive Multibeam Phased Array (AMPA) for a Spacelab experiment are described. This AMPA Experiment System was designed with particular emphasis to maximize channel capacity and minimize implementation and cost impacts for future austere maritime and aeronautical users, operating with a low gain hemispherical coverage antenna element, low effective radiated power, and low antenna gain-to-system noise temperature ratio

    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

    Millimetre-Wave Fibre-Wireless Technologies for 5G Mobile Fronthaul

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    The unprecedented growth in mobile data traffic, driven primarily by bandwidth rich applications and high definition video is accelerating the development of fifth generation (5G) mobile network. As mobile access network evolves towards centralisation, mobile fronthaul (MFH) architecture becomes essential in providing high capacity, ubiquitous and yet affordable services to subscribers. In order to meet the demand for high data rates in the access, Millimetre-wave (mmWave) has been highlighted as an essential technology in the development of 5G-new radio (5G-NR). In the present MFH architecture which is typically based on common public radio interface (CPRI) protocol, baseband signals are digitised before fibre transmission, featuring high overhead data and stringent synchronisation requirements. A direct application of mmWave 5G-NR to CPRI digital MFH, where signal bandwidth is expected to be up to 1GHz will be challenging, due to the increased complexity of the digitising interface and huge overhead data that will be required for such bandwidth. Alternatively, radio over fibre (RoF) technique can be employed in the transportation of mmWave wireless signals via the MFH link, thereby avoiding the expensive digitisation interface and excessive overhead associated with its implementation. Additionally, mmWave carrier can be realised with the aid of photonic components employed in the RoF link, further reducing the system complexity. However, noise and nonlinearities inherent to analog transmission presents implementation challenges, limiting the system dynamic range. Therefore, it is important to investigate the effects of these impairments in RoF based MFH architecture. This thesis presents extensive research on the impact of noise and nonlinearities on 5G candidate waveforms, in mmWave 5G fibre wireless MFH. Besides orthogonal frequency division multiplexing (OFDM), another radio access technology (RAT) that has received significant attention is filter bank multicarrier (FBMC), particularly due to its high spectral containment and excellent performance in asynchronous transmission. Hence, FBMC waveform is adopted in this work to study the impact of noise and nonlinearities on the mmWave fibre-wireless MFH architecture. Since OFDM is widely deployed and it has been adopted for 5G-NR, the performance of OFDM and FBMC based 5G mmWave RAT in fibre wireless MFH architecture is compared for several implementations and transmission scenarios. To this extent, an end to end transmission testbed is designed and implemented using industry standard VPI Transmission Maker® to investigate five mmWave upconversion techniques. Simulation results show that the impact of noise is higher in FBMC when the signal to-noise (SNR) is low, however, FBMC exhibits better performance compared to OFDM as the SNR improved. More importantly, an evaluation of the contribution of each noise component to the overall system SNR is carried out. It is observed in the investigation that noise contribution from the optical carriers employed in the heterodyne upconversion of intermediate frequency (IF) signals to mmWave frequency dominate the system noise. An adaptive modulation technique is employed to optimise the system throughput based on the received SNR. The throughput of FBMC based system reduced significantly compared to OFDM, due to laser phase noise and chromatic dispersion (CD). Additionally, it is shown that by employing frequency domain averaging technique to enhance the channel estimation (CE), the throughput of FBMC is significantly increased and consequently, a comparable performance is obtained for both waveforms. Furthermore, several coexistence scenarios for multi service transmission are studied, considering OFDM and FBMC based RATs to evaluate the impact inter band interference (IBI), due to power amplifier (PA) nonlinearity on the system performance. The low out of band (OOB) emission in FBMC plays an important role in minimising IBI to adjacent services. Therefore, FBMC requires less guardband in coexistence with multiple services in 5G fibre-wireless MFH. Conversely, OFDM introduced significant OOB to adjacent services requiring large guardband in multi-service coexistence transmission scenario. Finally, a novel transmission scheme is proposed and investigated to simultaneously generate multiple mmWave signals using laser heterodyning mmWave upconversion technique. With appropriate IF and optical frequency plan, several mmWave signals can be realised. Simulation results demonstrate successful simultaneous realisation of 28GHz, 38GHz, and 60GHz mmWave signals

    Signal processing and display interface studies

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    Signal processing equipment specifications, operating and test procedures, and systems design and engineering are described. Five subdivisions of the overall circuitry are treated: (1) the spectrum analyzer; (2) the spectrum integrator; (3) the velocity discriminator; (4) the display interface; and (5) the formatter. They function in series: (1) first in analog form to provide frequency resolution, (2) then in digital form to achieve signal to noise improvement (video integration) and frequency discrimination, and (3) finally in analog form again for the purpose of real-time display of the significant velocity data. The formatter collects binary data from various points in the processor and provides a serial output for bi-phase recording. Block diagrams are used to illustrate the system

    Design analysis tracking and data relay satellite simulation system

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    The design and development of the equipment necessary to simulate the S-band multiple access link between user spacecraft, the Tracking and Data Relay Satellite, and a ground control terminal are discussed. The core of the S-band multiple access concept is the use of an Adaptive Ground Implemented Phased Array. The array contains thirty channels and provides the multiplexing and demultiplexing equipment required to demonstrate the ground implemented beam forming feature. The system provided will make it possible to demonstrate the performance of a desired user and ten interfering sources attempting to pass data through the multiple access system

    Linearity Requirements in LTE-Advanced Mobile Transmitter

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    LTE-Advanced (LTE-A) is an emerging wireless communication system, which builds on the foundation of Long Term Evolution (LTE), adding many unprecedented arrangements in utilization of radio resources. Most notably LTE-A allows allocating non-contiguous resources in frequency domain, which significantly enhances the flexibility of the multiple access scheme. Contiguous and non-contiguous carrier aggregation, both intra- and inter-band, are essential components of LTE-A. However, these features set very high requirements especially for mobile transmitters, which simultaneously should be cheap, small, linear and power efficient. Linearity in particular is an important aspect because non-contiguous allocation is prone to produce severe intermodulation distortion, which will degrade transmit signal quality and cause interference to users operating on adjacent frequency ranges. Because variety of wireless systems have to coexist and interoperate in the scarce spectrum supply, there are stringent requirements for unwanted spectrum emissions. There is an inherent trade-off between linearity and power efficiency. Therefore it is significantly difficult to fulfill regulatory spectrum emission requirements with current transmitter technology without sacrificing battery life when operating near the maximum output power. As a compromise LTE-A allows relaxations to maximum output power requirement according to the used submodulation, number of used resource blocks and possible coexistence situations. In practice the transmitter power amplifier (PA) input power is reduced which linearises the PA response. However, this forces the PA to operate less efficiently. This simultaneously constrains using larger constellations and/or higher coding rates because of degraded link budget. Therefore maximum power reduction (MPR) should be minimized. In this thesis LTE and LTE-A are introduced and the models and effects of transmitter nonlinearity are discussed. Linearity requirements of mobile LTE-A transmitter are evaluated using both simulations and measurements in different transmission scenarios, including LTE and LTE-A releases from 8 to 12. The results of the analysis can be used in development of intelligent radio resource management algorithms, advanced MPR specifications and digital predistortion systems

    Applications of nonuniform sampling in wideband multichannel communication systems

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    This research is an investigation into utilising randomised sampling in communication systems to ease the sampling rate requirements of digitally processing narrowband signals residing within a wide range of overseen frequencies. By harnessing the aliasing suppression capabilities of such sampling schemes, it is shown that certain processing tasks, namely spectrum sensing, can be performed at significantly low sampling rates compared to those demanded by uniform-sampling-based digital signal processing. The latter imposes sampling frequencies of at least twice the monitored bandwidth regardless of the spectral activity within. Aliasing can otherwise result in irresolvable processing problems, as the spectral support of the present signal is a priori unknown. Lower sampling rates exploit the processing module(s) resources (such as power) more efficiently and avoid the possible need for premium specialised high-cost DSP, especially if the handled bandwidth is considerably wide. A number of randomised sampling schemes are examined and appropriate spectral analysis tools are used to furnish their salient features. The adopted periodogram-type estimators are tailored to each of the schemes and their statistical characteristics are assessed for stationary, and cyclostationary signals. Their ability to alleviate the bandwidth limitation of uniform sampling is demonstrated and the smeared-aliasing defect that accompanies randomised sampling is also quantified. In employing the aforementioned analysis tools a novel wideband spectrum sensing approach is introduced. It permits the simultaneous sensing of a number of nonoverlapping spectral subbands constituting a wide range of monitored frequencies. The operational sampling rates of the sensing procedure are not limited or dictated by the overseen bandwidth antithetical to uniform-sampling-based techniques. Prescriptive guidelines are developed to ensure that the proposed technique satisfies certain detection probabilities predefined by the user. These recommendations address the trade-off between the required sampling rate and the length of the signal observation window (sensing time) in a given scenario. Various aspects of the introduced multiband spectrum sensing approach are investigated and its applicability highlighted
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