Cancellation of Power Amplifier Induced Nonlinear Self-Interference in Full-Duplex Transceivers

Recently, full-duplex (FD) communications with simultaneous transmission and reception on the same channel has been proposed. The FD receiver, however, suffers from inevitable self-interference (SI) from the much more powerful transmit signal. Analogue radio-frequency (RF) and baseband, as well as digital baseband, cancellation techniques have been proposed for suppressing the SI, but so far most of the studies have failed to take into account the inherent nonlinearities of the transmitter and receiver front-ends. To fill this gap, this article proposes a novel digital nonlinear interference cancellation technique to mitigate the power amplifier (PA) induced nonlinear SI in a FD transceiver. The technique is based on modeling the nonlinear SI channel, which is comprised of the nonlinear PA, the linear multipath SI channel, and the RF SI canceller, with a parallel Hammerstein nonlinearity. Stemming from the modeling, and appropriate parameter estimation, the known transmit data is then processed with the developed nonlinear parallel Hammerstein structure and suppressed from the receiver path at digital baseband. The results illustrate that with a given IIP3 figure for the PA, the proposed technique enables higher transmit power to be used compared to existing linear SI cancellation methods. Alternatively, for a given maximum transmit power level, a lower-quality PA (i.e., lower IIP3) can be used.Comment: To appear in proceedings of the 2013 Asilomar Conference on Signals, Systems & Computer

Design considerations for direct RF sampling receiver in GNSS environment

ABSTRACT In this paper, an advanced direct RF sampling receiver architecture is studied for the GNSS environment. The architecture is based on sampling the signal directly at RF, which in the GNSS case are in the 1.5 GHz range. The high-frequencies in the signals to be sampled pose then very high demands for the accuracy and quality of the sampling process, and thus quantization and especially the timing jitter must be considered in detail. The study shows that the quantization and jitter requirements are, however, feasible when the presampling filtering is done properly

Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit-Receive Systems

This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear TX power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation principle, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear TX PA with memory, finite passive isolation, and a nonlinear RX LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the RX LNA input, even at considerably high transmit power levels and with wide transmission bandwidths. Such novel cancellation solution can therefore substantially improve the TX-RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.Comment: accepted to IEE

Randomised sham-controlled double-blind trial evaluating remote ischaemic preconditioning in solid organ transplantation : a study protocol for the RIPTRANS trial

Introduction Remote ischaemic preconditioning (RIPC) using a non-invasive pneumatic tourniquet is a potential method for reducing ischaemia-reperfusion injury. RIPC has been extensively studied in animal models and cardiac surgery, but scarcely in solid organ transplantation. RIPC could be an inexpensive and simple method to improve function of transplanted organs. Accordingly, we aim to study whether RIPC performed in brain-dead organ donors improves function and longevity of transplanted organs. Methods and analyses RIPTRANS is a multicentre, sham-controlled, parallel group, randomised superiority trial comparing RIPC intervention versus sham-intervention in brain-dead organ donors scheduled to donate at least one kidney. Recipients of the organs (kidney, liver, pancreas, heart, lungs) from a randomised donor will be included provided that they give written informed consent. The RIPC intervention is performed by inflating a thigh tourniquet to 300 mm Hg 4 times for 5 min. The intervention is done two times: first right after the declaration of brain death and second immediately before transferring the donor to the operating theatre. The sham group receives the tourniquet, but it is not inflated. The primary endpoint is delayed graft function (DGF) in kidney allografts. Secondary endpoints include short-term functional outcomes of transplanted organs, rejections and graft survival in various time points up to 20 years. We aim to show that RIPC reduces the incidence of DGF from 25% to 15%. According to this, the sample size is set to 500 kidney transplant recipients. Ethics and dissemination This study has been approved by Helsinki University Hospital Ethics Committee and Helsinki University Hospital's Institutional Review Board. The study protocol was be presented at the European Society of Organ Transplantation congress in Copenhagen 14-15 September 2019. The study results will be submitted to an international peer-reviewed scientific journal for publication.Peer reviewe

Analysis and Mitigation of Oscillator Impairments in Modern Receiver Architectures

The ever-increasing complexity of radio devices is phenomenon fed by the ever-growing demands of users for higher data rates and more services from a single device. Today, advanced cellular phones have transceivers for reception of multiple different kinds of communications signals. Moreover, even reception of signals from a single communications system might require multiple transceivers, when the system utilizes multiple antennas or multiple frequency bands for transmission. At the same time, communications waveforms are getting more complex since more and more data should be transmitted in the same bandwidth. These highly dynamic signals set very tight demands for the quality of transceiver electronics. The above aspects are, on the other hand, in contradiction with the other strong demands of utilizing smaller, cheaper and less power consuming radio transceivers. From the point-of-view of communications receiver design, the above demands are mapped to challenges of designing very simple receivers with high-quality output, or receivers that are very flexible to process many different signals at the same time but that are still relatively simple. One solution to the design of simple receivers with high-quality output is moving the complexity of devices from the analogue side to the digital side. This means using very simple receiver architecture, possibly with low-cost components, and using digital signal processing to compensate for the impairments caused by the simple design and the low-cost electronics. On the other hand, a solution to obtain a flexible and simple receiver is moving the sampling and analogue-to-digital interface as near to the antenna as possible, and processing the reception of wide spectrum in a single receiver. Naturally, this is also moving the complexity from the analogue side to the digital side. All this is also partially motivated by the well-known Moore’s law. This thesis focuses on the both of the scenarios proposed above from the point-of-view of oscillator impairments in two modern receiver architectures, namely direct-conversion receiver architecture and direct-RF-sampling receiver architecture. Special emphasis is given to Orthogonal frequency division multiplexing (OFDM) signals since they are very vulnerable to phase-noise like effects and are very widely used nowadays. The direct-conversion receiver architecture is based on direct downconversion of signals from radio frequencies to baseband. The phase noise of the downconverting oscillator naturally causes errors to the signal in the downconversion process. In this thesis, the effects of the phase noise are analysed in OFDM communications link using downconverting oscillator with arbitrary phase-noise spectral shape. Also, existing algorithms for phase-noise mitigation in OFDM are reviewed and four new iterative digital-signal-processing based mitigation algorithms are proposed. The first algorithm is fairly simple, stemming from the idea of using linear interpolation between two common-phase-error estimates to obtain an estimate of the underlying time-varying phase characteristics. The second algorithm on the other hand is an extension to existing intercarrier-interference estimation method. Simply put, the idea is to improve the phase-noise estimates given by the existing algorithm with interpolation near the boundaries of OFDM symbols. The last two of the algorithms work in time-domain and are stand-alone algorithms. In both of them, an estimate of the received time-domain waveform is reconstructed after initial symbol detection, and the time-varying phase noise process is estimated from the received signal with the aid of the reconstructed waveform with various digital-signal-processing methods. The proposed algorithms are compared to the state-of-the-art algorithms in different scenarios with both transmitter and receiver phase noises present. In general, the proposed algorithms offer significant performance improvement over the state-of-the-art algorithms in the literature. The contributions from the point-of-view of direct-RF-sampling receiver are in the modelling of sampling-jitter phenomenon in voltage sampling based and charge sampling based direct-RF-sampling receivers. Based on the analysis of the voltage-sampling based direct-RF-sampling receiver, OFDM phase-noise mitigation algorithms are proposed to be used in sampling-jitter mitigation. Furthermore, one reference tone based sampling-jitter mitigation algorithm is proposed. The proposed techniques are also compared to the state-of-the-art techniques, and the results show that clear performance improvements can be attained with the proposed techniques. Simulations are also carried out in the challenging case where nearby interferers are also considered present in the sampled signal, as is practical because of challenging implementation of RF filtering in high-frequency sampling. The results show that the proposed algorithms still manage to provide relatively good performance when interference level is reasonable. In addition to sampling-jitter mitigation algorithms, the analysis of charge-sampling based direct-RF-sampling receiver showed interesting filtering phenomenon in the spectrum of the error caused by the sampling jitter in some of the charge-sampler implementations. The phenomenon is so powerful that it should be taken into account in receiver design

Podcast vuonna 2018 : Podcastien paikka audiomarkkinoilla eurooppalaisin silmin

Tämän opinnäytetyön tavoitteena on selvittää, mikä on podcastin nykytila vuonna 2018 eurooppalaisin silmin. Teoriaosuudessa käydään läpi, mikä podcast on, miten podcast määritellään, kuinka se eroaa muusta audiosta ja ketkä sen kuluttajia ovat. Lisäksi tutkitaan, miten podcastien suosio eroaa Yhdysvaltojen ja Euroopan välillä ja mitkä ovat Euroopan sisäiset erot. Tutkimuksen teoria-aineisto koostuu erilaisista podcast- ja audiokulutustutkimuksista Yhdysvalloissa ja Euroopassa. Opinnäytetyötä varten on haastateltu podcastien asiantuntijoina RadioMedian toimitusjohtajaa Stefan Mölleriä, Jakso.fi-podcastpalvelun Olli Sulopuistoa ja Kieku-podcastpalvelun Sampsa Fabritiusta. Haastattelut suoritettiin teemahaastatteluina syksyllä vuoden 2018 aikana. Opinnäytetyön tulosten mukaan podcasteja tehdään innokkaasti ja podcastit yleisesti nähdään enemmän mahdollisuutena kuin uhkana Euroopassa. Radioala on suhtautumisessaan vielä varovainen ja epäilevä, sillä podcastien koetaan vievän enemmän resursseja kuin tuovan tuottoja. Yleisradiolla ja suurilla mediayhtiöillä on suuri vaikutus siihen, millaiseksi podcastien muoto ja niiden markkinat muodostuvat. Vaikkeivät podcastit ole valtavirtaa, voi yksittäinen tekijä tienata niillä. Vaikkeivät podcastit syrjäyttäisivätkään radiota, on podcastien mahdollista muodostaa Youtuben kaltainen yhteisöllisen median markkina. Podcasteilla on löydettävyyden kanssa ongelma, johon tarvitaan ratkaisu pian. Opinnäytetyön johtopäätös on se, että podcastaus on Euroopassakin tasaisessa kasvussa, mutta mediakenttä on podcastien kohdalla odottavassa tilassa. Podcastien laatuerot ovat kasvaneet, mitä enemmän tekijöitä on. Podcastien parhaimmisto tulee löydettäväksi vasta, kun yleisöt löytävät podcastit yhdestä julkaisualustasta. Euroopassa ei välttämättä tapahdu samanlaista mantereen kokoista läpimurtoa podcastien kohdalla kuin Amerikassa, mutta pienempiä alueellisia ja maidensisäisiä menestyjiä on mahdollista syntyä.This Bachelor’s thesis explores podcasting and it is current state and place in the audio market in Europe. The thesis defines what a podcast is; what is the definition of a podcast; how it differs from other audio media; and who are the people consuming it. It also studies what the difference between the USA and Europe is in the magnitude and popularity of podcast consumption. The theoretical part of this thesis contains variables of podcast and radio research around USA and Europe. In addition to the written references, this Bachelor´s thesis uses interviews of the CEO of RadioMedia (Association of Finnish Broadcasters) and the President of AER (The Association of European Radios) Stefan Möller, podcast producer & co-Founder of Jaksomedia Olli Sulopuisto and CEO and Founder of Kieku Labs Oy Sampsa Fabritius. Interviews were conducted as theme interviews and individually in the end of Summer and Fall of 2018 in Helsinki. According to the results of this thesis, there are considerable amounts of podcasts made in Europe and podcasting is seen as an opportunity more than a threat. The radio industry seems to be cautious and sceptical about podcasting because the podcasts are seen more as a waste of resources than a potential revenue. Public broadcasting companies and large media corporates in Europe will be able to impact to the factor of what will be the forms and the markets of podcast. Podcasts may not be a part of the mainstream media, but singular and independent podcaster can make a profit from podcasting. Even if the radio is not dethroned by podcast any time soon there can be a sizeable social medialized market for podcasting compared to YouTube. Podcasts still have an issue of discovering which must be dealt by soon than later. The conclusions of this Bachelor´s thesis indicate that the popularity of podcasting is slowly but steadily rising but media business is still in a hold when it comes to podcasting. The more there are podcasters, the greater gap there is in the quality of podcasting. When there is just one platform for podcasters to publish their podcasts and audience to find those podcasts, it will be easier to define a quality podcast as well. Perhaps, podcasting will never be mainstream media in Europe but there can still be microsocial and domestic success stories in podcasting

Analysis and Mitigation of Oscillator Impairments in Modern Receiver Architectures

The ever-increasing complexity of radio devices is phenomenon fed by the ever-growing demands of users for higher data rates and more services from a single device. Today, advanced cellular phones have transceivers for reception of multiple different kinds of communications signals. Moreover, even reception of signals from a single communications system might require multiple transceivers, when the system utilizes multiple antennas or multiple frequency bands for transmission. At the same time, communications waveforms are getting more complex since more and more data should be transmitted in the same bandwidth. These highly dynamic signals set very tight demands for the quality of transceiver electronics. The above aspects are, on the other hand, in contradiction with the other strong demands of utilizing smaller, cheaper and less power consuming radio transceivers. From the point-of-view of communications receiver design, the above demands are mapped to challenges of designing very simple receivers with high-quality output, or receivers that are very flexible to process many different signals at the same time but that are still relatively simple. One solution to the design of simple receivers with high-quality output is moving the complexity of devices from the analogue side to the digital side. This means using very simple receiver architecture, possibly with low-cost components, and using digital signal processing to compensate for the impairments caused by the simple design and the low-cost electronics. On the other hand, a solution to obtain a flexible and simple receiver is moving the sampling and analogue-to-digital interface as near to the antenna as possible, and processing the reception of wide spectrum in a single receiver. Naturally, this is also moving the complexity from the analogue side to the digital side. All this is also partially motivated by the well-known Moore’s law. This thesis focuses on the both of the scenarios proposed above from the point-of-view of oscillator impairments in two modern receiver architectures, namely direct-conversion receiver architecture and direct-RF-sampling receiver architecture. Special emphasis is given to Orthogonal frequency division multiplexing (OFDM) signals since they are very vulnerable to phase-noise like effects and are very widely used nowadays. The direct-conversion receiver architecture is based on direct downconversion of signals from radio frequencies to baseband. The phase noise of the downconverting oscillator naturally causes errors to the signal in the downconversion process. In this thesis, the effects of the phase noise are analysed in OFDM communications link using downconverting oscillator with arbitrary phase-noise spectral shape. Also, existing algorithms for phase-noise mitigation in OFDM are reviewed and four new iterative digital-signal-processing based mitigation algorithms are proposed. The first algorithm is fairly simple, stemming from the idea of using linear interpolation between two common-phase-error estimates to obtain an estimate of the underlying time-varying phase characteristics. The second algorithm on the other hand is an extension to existing intercarrier-interference estimation method. Simply put, the idea is to improve the phase-noise estimates given by the existing algorithm with interpolation near the boundaries of OFDM symbols. The last two of the algorithms work in time-domain and are stand-alone algorithms. In both of them, an estimate of the received time-domain waveform is reconstructed after initial symbol detection, and the time-varying phase noise process is estimated from the received signal with the aid of the reconstructed waveform with various digital-signal-processing methods. The proposed algorithms are compared to the state-of-the-art algorithms in different scenarios with both transmitter and receiver phase noises present. In general, the proposed algorithms offer significant performance improvement over the state-of-the-art algorithms in the literature. The contributions from the point-of-view of direct-RF-sampling receiver are in the modelling of sampling-jitter phenomenon in voltage sampling based and charge sampling based direct-RF-sampling receivers. Based on the analysis of the voltage-sampling based direct-RF-sampling receiver, OFDM phase-noise mitigation algorithms are proposed to be used in sampling-jitter mitigation. Furthermore, one reference tone based sampling-jitter mitigation algorithm is proposed. The proposed techniques are also compared to the state-of-the-art techniques, and the results show that clear performance improvements can be attained with the proposed techniques. Simulations are also carried out in the challenging case where nearby interferers are also considered present in the sampled signal, as is practical because of challenging implementation of RF filtering in high-frequency sampling. The results show that the proposed algorithms still manage to provide relatively good performance when interference level is reasonable. In addition to sampling-jitter mitigation algorithms, the analysis of charge-sampling based direct-RF-sampling receiver showed interesting filtering phenomenon in the spectrum of the error caused by the sampling jitter in some of the charge-sampler implementations. The phenomenon is so powerful that it should be taken into account in receiver design