Passive Intermodulation Distortion in Radio Communication Systems : Signal Models and Digital Cancellation

Cellular networks and technology have evolved substantially since the late 1970s, with successive generations bringing a variety of new features. Each upcoming generation is better and more advanced in technology when compared to the previous generation. To this end, a huge amount of research in the field of wireless communications has been dedicated to the following two major aspects: the increasing demand for user data rate requirements and the exponential growth of internet-dependent devices around the world. It is undeniable that the outcome of this phenomenon is a heavy congestion of the available spectral resources. This has inspired the utilization of many innovative solutions for improving the spectral efficiency in wireless communication systems by facilitating simultaneous transmission at a high data rate without having the need for additional spectrum. Some of these technologies include in-phase/quadrature (I/Q) modulation, multiple-input-multiple-output (MIMO) systems, and orthogonal frequency-division multiplexing (OFDM). In part because of these existing solutions, the spectral efficiency of wireless communication has improved considerably. However, more advanced techniques are necessary if future data transfer requirements are to be met, for example in the sub-6 GHz band. Given this, the frequency division duplex (FDD) in Long Term Evolution-Advanced (LTE-Advanced) has suggested carrier aggregation (CA) technology as another step towards the better utilization of the spectral resources. The CA techniques enable the utilization of multiple contiguous or noncontiguous parts of the spectrum, thus allowing for flexibility in transmission bandwidth. By using CA, spectral resources can be combined from the same operating frequency band (intraband CA) or from multiple frequency bands (interband CA). In CA, multiple transmitters and receivers are integrated into a single chip to reduce costs, space, and power consumption. Additionally, the industry is moving towards low-cost radio frequency (RF)- front-end solutions containing duplex filters with limited isolation capabilities in order to cope with ever-increasing CA combinations. This results in the leakage of the own transmit (TX) signal and other so-called blocker signals. One of the challenges in the utilization of the CA is when the combined noncontiguous signal propagates through the TX chain passing through the RF front-end passive components, the cross-modulation of the transmitted signal further creates unwanted passive intermodulation (PIM) products. These PIM products in some cases may fall onto their own receiver (RX) band and may cause receiver desensitization. In this thesis, we present novel solutions for modeling and suppressing PIM distortion and passive harmonic distortion (PHM) in FDD based radio transceivers. This distortion results from nonlinear RF components and simultaneous transmission and reception, with a particular focus on modern carrier aggregation networks. PIM-induced distortion terms generally have a higher power than the weak received signal, even with state-of-the-art RF components, because of the linearity characteristics of the passive components. Consequently, it is necessary to minimize the harmful impact of such distortion, which can be achieved by taking a variety of approaches. A simple technique can be to decrease the transmit power or relax the receiver reference sensitivity requirements. This is known as maximum power reduction (MPR) and maximum sensitivity degradation (MSD), respectively, for LTE-Advanced and new radio (NR) user equipment (UEs). In addition to preventing receiver desensitization, these approaches will negatively affect coverage, so they are not very appealing. Uplink (UL) and downlink (DL) resource allocation and scheduling can also be optimized to avoid inband distortion. This approach, however, will be very complex, and could also result in reduced peak throughput and spectrum utilization. The PIM/PHM distortion power can, however, be controlled by improving RF component quality and isolation. Nevertheless, this solution has the drawback of increasing the overall cost of the device. In addition, even with the more expensive components PIM-induced distortion might not be avoided. In this thesis, we take an alternative approach by using the original transmit data as a reference to cancel such PIM in the transceiver digital front-end. For the generation of an accurate cancellation signal, we derive different advanced signal models for the observable intermodulation distortion in the receiver band that incorporate also power amplifier nonlinearities, together with the passive component nonlinearities and the frequency-selective responses of the duplex filters. Real-life RF measurements are conducted with an actual LTE-Advanced user equipment (UE) transceiver system to evaluate the performance and processing complexity of the devised digital cancellation and parameter estimation solutions. The experiments show that PIM-induced self-interference is almost 20 dB above the noise floor even while utilizing state-of-the-art RF components. However, the results show that each of the proposed signal models and the related digital cancellers in this thesis are able to cancel the PIM-induced interference up to 15 dB. The results also indicate that in many cases it is necessary to account for nonlinear distortions caused by amplifiers. This is even if the individual component carriers are combined after the amplification stage. In general, when the nonlinear distortion of the power amplifiers is taken into account the amount of cancellation is further improved by 4-5 dB, in contrast to the linear power amplifier based cancellers

Bronchial Carcinoid Presenting as Multiple Lung Abscesses

Bronchial carcinoid tumours is a rare group of pulmonary malignant neoplasm that is derived from neuroendocrine system. Bronchial carcinoid usually present with hilar masses, atelactasis, bronchiectasis, or post-obstructive pneumonia. This case describes a very unusual presentation of bronchial carcinoid tumour with multiple lung abscesses involving the whole lung. This report is of an adult lady who presented with multiple lung abscesses involving her whole of the right lung. She was found to have an endo-bronchial lesion in her right main bronchus which eventually turned out to be carcinoid tumour. She responded to resection and antibiotic therapy

Tobacco Cessation Treatment: Knowledge, Attitude and Practices of Physician in Karachi, Pakistan: A Cross Sectional Study

Introduction: Tobacco smoking is a public health problem leading to substantial morbidity and mortality with around 80% of the deaths occurring in developing countries. Physician intervention has been shown to increase cessation rates. The study aims to assess knowledge, attitudes and practices of physicians in tobacco cessation treatment in Karachi Pakistan. Methods: A descriptive cross sectional study was carried out between June to December 2013. All practicing physicians from Karachi were recruited. Survey questionnaire was distributed among randomly selected physicians after obtaining their consent. The study was approved by ethics review committee of The Aga Khan University Hospital. Results: A total of 189 physicians were approached and 163 consented to take part. Around 58.3% of the physicians reported high levels of confidence for discussing tobacco cessation, 40.5% of them developing tobacco cessation plan and only 26.4% were confident in recommending pharmacological treatment. Regarding knowledge of pharmacotherapy on a five-point scale majority (45.4%) rated themselves four or five. However, very Low rates of correct answers were noted for objective knowledge assessment (5.5%). Most physicians (78.5%) reported that they identify every patient’s tobacco use status. Most physicians (61.4%) reported always or almost always advising tobacco users to quit. Conclusion: Majority of the physicians believed in the importance of tobacco cessation treatment and understand their primary role. Most feel they have adequate knowledge regarding smoking cessation but lacked the skills required to implement tobacco cessation treatment strategies. Effective training is required to enhance physicians’ capacity to intervene in the field of tobacco cessation

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

Treatment Outcome of Multi-Drug Resistant Tuberculosis Treated As Outpatient in a Tertiary Care Center

INTRODUCTION: Community-based out-patient treatment for multidrug-resistant tuberculosis (MDR TB) is relatively new concept with reported successful outcomes. OBJECTIVE: To assess the treatment outcomes of HIV negative multidrug-resistant tuberculosis (MDR TB) patients treated as outpatient at a tertiary care center in Karachi, Pakistan. METHODS: A retrospective observational study of 53 consecutive, culture proven HIV negative MDR TB patients (resistant at least to both Isoniazid (H) and Rifampin(R) treated at Aga Khan University Hospital, Karachi between August 1999 and March 2007. Data were collected on predesigned performa regarding patient’s demography, clinical features, radiological findings, drug sensitivity, treatment and outcome. RESULTS: A total of 53 HIV negative patients (27 males), with mean age of 37±15 years (range 15-76 years), received treatment as outpatient for culture proven MDR TB. 51 patients (96.2%) had pulmonary while 3 patients (5.6%) had extra-pulmonary TB. History of exposure to tuberculosis patients was found in 36 (67.9%) patients. Treatment regimen with 2nd line drugs was decided on individual basis according to DST on sputum culture results. The mean duration of treatment was 18 months. Successful outcome was seen in 25 patients (47.2%), 25 patients (47.2%) were loss to follow up and defaulted while 3 (5.6%) patients remain smear positive at the end of treatment. Success rate was 89 .2% in those who completed the treatment. CONCLUSION: Community-based out-patient treatment strategy is both feasible and safe for the treatment of MDR-TB patients in resource limited country like Pakistan and this strategy should be integrated into the routine approach to treatment of MDR-TB patients in the country where the expertise are available. High default rate is this strategy is the main challenge which should be addressed

Anthesis and Booting: Two Critical Stages Vulnerable to Water Stress in Wheat (Triticum aestivum L.) With Respect to Yield Production

Six spring bread wheat varieties (AAS-11, BARS-09, Dharabi-11, Faisalabad-08, Chakwal-50 and Fatehjang-2016) and 4 elite lines of wheat (10FJ01, 12FJ26, 12FJ01 and 11FJS309) were analyzed with respect to water stress by providing them two types of treatments i.e., control (no stress) and strained treatment (20 days of stoppage of irrigation at booting and further 20 days of drought after anthesis) at Barani Agricultural Research Station, Fatehjang during 2017-18. Results of this study exhibited highly significant variations prevailed in all the wheat genotypes by viewing their mean performance with respect of all physiological and yield traits. AAS-11, Fatehjang-2016 and Dharabi-11 exhibited their best performance and pointed out elevated mean productivity (MP), stress tolerance index (STI), relative water content (RWC) and geometric mean productivity (GMP). Moreover, stress susceptibility index (SSI) and tolerance (TOL) was anticipated at lowest among the above-mentioned wheat varieties and lines. Based multivariate analysis (biplot) and dendrogram studies; AAS-11, Fatehjang-2016 and Dharabi-11 are most suitable wheat cultivars for drought tolerance at booting and anthesis stage. MP, STI, RWC, GMP, SSI and TOL are renowned to be favourable gauges for identification of drought tolerance wheat ideotype. Likewise, same wheat varieties also exhibited higher grain yield per plant that put them in higher ranked genotypes for making selections and recombination while improving wheat through breeding for drought resistant

Assessing two spirometric criteria of pre-bronchodilator and post-bronchodilator FEV1/FVC ratio in detecting air flow obstruction

OBJECTIVES: To assess the Pre-bronchodilator criteria and the Post-bronchodilator criteria of FEV1/FVC ratio in diagnosing Airflow obstruction. METHODS: An observational study was conducted from 1988 to 2006 at the Aga Khan University Hospital Patients referred to the pulmonary function test laboratory for spirometry with bronchodilator reversibility at the hospital during the above said period were enrolled. Forced spirometry was performed according to ATS guidelines. All patients who had pre-bronchodilator criteria of airflow obstruction were analyzed and compared with the post bronchodilator criteria. RESULTS: A total of 4222 individuals underwent spirometry out of which 4072 individuals were studied. Using the pre bronchodilator criteria, 1375 (34%) patients had airflow obstruction. Applying the post bronchodilator criteria on the same patients, 1098 (27%) had evidence of airway obstruction. Out of these 1375 patients who had airflow obstruction by using pre-bronchodilator criteria, 277 (20%) patients had no airflow obstruction by using the post bronchodilator criteria. Out of these 277 patients, 52% had significant airways reversibility as evidenced by \u3e12% increase in their FEV1 pre and post bronchodilator. CONCLUSION: Pre bronchodilator criteria for detection of airflow obstruction overestimate the diagnosis of airflow obstruction and by using post bronchodilator criteria for airway obstruction on spirometry, decreases this over diagnosis of the conditio

Modeling and Digital Suppression of Passive Nonlinear Distortion in Simultaneous Transmit—Receive Systems

In frequency division duplexing (FDD) based simultaneous transmit-receive systems, nonlinear behavior of the active and passive RF components can cause nonlinear distortion products falling at the receiver band. Such distortion may also arise over-the-air, if there are for example metallic objects in close vicinity of the antenna system. In this work, we focus on the modeling and digital cancellation of such distortion products, especially in case of passive harmonic distortion of the transmit waveform landing at the receiver band. We provide behavioral modeling of the problem, while also use the models to derive corresponding digital distortion cancellers. Practical RF measurement based numerical results are provided, focusing on a timely dual-band cellular transceiver scenario covering 5G NR bands n3 (1.8 GHz) and n78 (3.5 GHz). The RF measurement results demonstrate accurate modeling and distortion cancellation in the considered example cases.Peer reviewe