Improved Multi-GPU parallelization of a Lagrangian Transport Model

This report highlights our work on improving GPU parallelization by supporting compute nodes with multiple GPUs. However, since the default support for multi-GPUs in OpenACC is limited[6], the current implementation allows each MPI process to access only a single GPU. Thus, the only way to take full advantage of multi-GPU nodes in the current version is to launch multiple processes, which increases resource contention. We investigated the benefits of having only one process offload to all available GPU devices.Comment: Technical Repor

A low complexity SI sequence estimator for pilot-aided SLM–OFDM systems

Selected mapping (SLM) is a well-known method for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. However, as a consequence of implementing SLM, OFDM receivers often require estimation of some side information (SI) in order to achieve successful data recovery. Existing SI estimation schemes have very high computational complexities that put additional constraints on limited resources and increase system complexity. To address this problem, an alternative SLM approach that facilitates estimation of SI in the form of phase detection is presented. Simulations show that this modified SLM approach produces similar PAPR reduction performance when compared to conventional SLM. With no amplifier distortion and in the presence of non-linear power amplifier distortion, the proposed SI estimation approach achieves similar data recovery performance as both standard SLM–OFDM (with perfect SI estimation) and also when SI estimation is implemented through the use of an existing frequency-domain correlation (FDC) decision metric. In addition, the proposed method significantly reduces computational complexity compared with the FDC scheme and an ML estimation scheme

A joint OFDM PAPR reduction and data decoding scheme with no SI estimation

The need for side information (SI) estimation poses a major challenge when selected mapping (SLM) is implemented to reduce peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. Recent studies on pilot-assisted SI estimation procedures suggest that it is possible to determine the SI without the need for SI transmission. However, SI estimation adds to computational complexity and implementation challenges of practical SLM-OFDM receivers. To address these technical issues, this paper presents the use of a pilot-assisted cluster-based phase modulation and demodulation procedure called embedded coded modulation (ECM). The ECM technique uses a slightly modified SLM approach to reduce PAPR and to enable data recovery with no SI transmission and no SI estimation. In the presence of some non-linear amplifier distortion, it is shown that the ECM method achieves similar data decoding performance as conventional SLM-OFDM receiver that assumed a perfectly known SI and when the SI is estimated using a frequency-domain correlation approach. However, when the number of OFDM subcarriers is small and due to the clustering in ECM, the modified SLM produces a smaller PAPR reduction gain compared with conventional SLM

Investigation of changes in Briksdalsbreen, western Norway from 1966 - 2020

Briksdalsbreen in western Norway was studied using remote sensing. Sets of optical aerial photographs captured between 1966 to 2020 were used with LiDAR-based Digital Elevation Models (DEMs) and glacier outlines derived from satellite images to estimate the changes in length, area, surface elevation and mass balance of the glacier. The results show that Briksdalsbreen retreated a total of ~ 450 m and shrunk by 0.25 Km2 (0.04 % a-1) between 1966 and 2020; however, it advanced between 1966 to 2001 before it retreated between 2001 – 2010. The glacier fronts thickened by less than ~ 0.5 m during the period of advancement in the late 90s but the total glacier thinned by ~ 3 m in the whole period of 54 years (1966 – 2020). The estimated mass balance is -0.045 m w. e. a-1 for Briksdalsbreen between 1966 and 2020 and -0.246 m w. e. a-1 for the period of 2010 – 2020. The result of the length estimate from this study agrees with field observation and the surface elevation change found for 2010 - 2020 conforms with the results from regional remote sensing investigation. However, the lack of published mass balance data for Briksdalsbreen and high uncertainty in comparing the mass balance of glaciers limited a comparative assessment of the estimated mass balance. Nevertheless, this study confirms that Briksdalsbreen is retreating rapidly and losing mass like many other glaciers in Norway. It also identifies increased summer temperature as the driving force of the glacier retreat since early 2000, although high winter precipitation had early caused its expansion between 1966 to 2001. The study demonstrates that remote sensing is a useful tool in glacier change assessment.Master's Thesis in Earth ScienceGEOV399MAMN-GEO

A selective control information detection scheme for OFDM receivers

In wireless communications, both control information and payload (user-data) are concurrently transmitted and required to be successfully recovered. This paper focuses on block-level detection, which is applicable for detecting transmitted control information, particularly when this information is selected or chosen from a finite set of information that are known at both transmitting and receiving devices. Using an orthogonal frequency division multiplexing architecture, this paper investigates and evaluates the performance of a time-domain decision criterion in comparison with a form of Maximum Likelihood (ML) estimation method. Unlike the ML method, the proposed time-domain detection technique requires no channel estimation as it uses the correlation (in the time-domain) that exists between the received and the transmitted selective information as a means of detection. In comparison with the ML method, results show that the proposed method offers improved detection performance, particularly when the control information consists of at least 16. However, the implementation of the proposed method requires a slightly increased number of mathematical computations