Off-grid Direction of Arrival Estimation Using Sparse Bayesian Inference

Direction of arrival (DOA) estimation is a classical problem in signal processing with many practical applications. Its research has recently been advanced owing to the development of methods based on sparse signal reconstruction. While these methods have shown advantages over conventional ones, there are still difficulties in practical situations where true DOAs are not on the discretized sampling grid. To deal with such an off-grid DOA estimation problem, this paper studies an off-grid model that takes into account effects of the off-grid DOAs and has a smaller modeling error. An iterative algorithm is developed based on the off-grid model from a Bayesian perspective while joint sparsity among different snapshots is exploited by assuming a Laplace prior for signals at all snapshots. The new approach applies to both single snapshot and multi-snapshot cases. Numerical simulations show that the proposed algorithm has improved accuracy in terms of mean squared estimation error. The algorithm can maintain high estimation accuracy even under a very coarse sampling grid.Comment: To appear in the IEEE Trans. Signal Processing. This is a revised, shortened version of version

FDD Massive MIMO Channel Estimation with Arbitrary 2D-Array Geometry

This paper addresses the problem of downlink channel estimation in frequency-division duplexing (FDD) massive multiple-input multiple-output (MIMO) systems. The existing methods usually exploit hidden sparsity under a discrete Fourier transform (DFT) basis to estimate the cdownlink channel. However, there are at least two shortcomings of these DFT-based methods: 1) they are applicable to uniform linear arrays (ULAs) only, since the DFT basis requires a special structure of ULAs, and 2) they always suffer from a performance loss due to the leakage of energy over some DFT bins. To deal with the above shortcomings, we introduce an off-grid model for downlink channel sparse representation with arbitrary 2D-array antenna geometry, and propose an efficient sparse Bayesian learning (SBL) approach for the sparse channel recovery and off-grid refinement. The main idea of the proposed off-grid method is to consider the sampled grid points as adjustable parameters. Utilizing an in-exact block majorization-minimization (MM) algorithm, the grid points are refined iteratively to minimize the off-grid gap. Finally, we further extend the solution to uplink-aided channel estimation by exploiting the angular reciprocity between downlink and uplink channels, which brings enhanced recovery performance.Comment: 15 pages, 9 figures, IEEE Transactions on Signal Processing, 201

A Human Powered Micro-generator for Charging Electronic Devices

A hand-pulled generator has been designed and tested. A preliminary result has been obtained and discussed. This device was created to provide no outlet and off-grid charging. Nothing is worse than going out into the wilderness and having a phone or a necessary electronic device run out of battery. This presentation overviews the device\u27s design, build, and electrical system. Two different tests are run to prove the device is capable of charging the storage battery. The device presented can provide 14 minutes of charging time with one hour of string-pulling. It is concluded that this device can be beneficial to people with electronic devices that need off-grid charging

The I3a Framework – Enhancing Off-grid Photovoltaic Energy Service Delivery in Indonesia

This paper describes an interdisciplinary research project to investigate the sustainability of off-grid Photovoltaic Energy Service (PVES) delivery in Indonesia. The paper describes results from the preliminary fieldwork undertaken in late 2002 and early 2003, more substantive fieldwork was carried out in 2005. The general objective of this research project is to understand how PVES can contribute to improving the life of rural Indonesian communities having no access to the electricity grid. It adopts an interdisciplinary approach that combines social and engineering perspectives to address sustainability issues. The I3A (Implementation, Accessibility, Availability, Acceptability) Sustainable PVES Delivery framework was developed to assess sustainability and was used to assess three off-grid PVES case studies in Lampung, West Java and Nusa Tenggara Timur (NTT) provinces. The overall objectives of the I3A framework are to acknowledge the interests of stakeholders, maximize equity, assure PVES continuity and institutionalize PVES by utilizing and enhancing pre-existing community resources to leave host communities with the capacity to meet evolving needs. A key conclusion is that, to be sustainable and equitable, off-grid PVES projects should be implemented in an institutional framework that provides sound project management and addresses PVES accessibility (financial, institutional and technological), availability (technical quality and continuity) and acceptability (social and ecological)