Digital Signal Processing

1502 Submissions

[2] viXra:1502.0126 [pdf] submitted on 2015-02-15 21:11:02

Stereoscopic Camera Geometry –How to Shoot 3D with Two Cameras

Authors: Michael Starks
Comments: 5 Pages.

Anyone shooting 3D is immediately confronted with the problem of stereo camera geometry—how to align the cameras for best results. This looks like it should be the easiest part of the entire project but in fact it’s by far the hardest. Just aligning the cams perfectly in all 3 axes and locking them down is tough and keeping them aligned when changing interaxial, convergence or zoom is extremely hard. There is very little in the way of comprehensive reviews of this subject in the literature. Some may be surprised to learn that these problems are not new, nor are they unique to 3D video and photography. In addition to attention from stereographers for over 150 years, they have been the subject of intensive research in the fields of photogrammetry going back well over 100 years, and more recently in computer vision. Every book in these arenas has extensive discussions on multiple camera geometry and essentially the entire texts revolve around the problems of camera registration and image rectification for human viewing and/or computer image understanding. Algorithmic transforms for producing rectified images from single moving cameras, polydioptric (plenoptic or multiple image single lens cameras) or multiple cameras take up large sections of these books and thousands of papers, which blend into the literatures of robotics, machine vision, artificial intelligence, virtual reality, telepresence and every aspect of 3D imaging. Here I provide a cursory review with a few pertinent references.
Category: Digital Signal Processing

[1] viXra:1502.0079 [pdf] submitted on 2015-02-11 08:41:01

Channel Access-Aware User Association with Interference Coordination in Two-Tier Downlink Cellular Networks

Authors: Uzma Siddique, Hina Tabassum, Ekram Hossain
Comments: 14 Pages. Submitted to the IEEE Transactions of Communications

The diverse transmit powers of the base stations (BSs) in a multi-tier cellular network, on one hand, lead to uneven distribution of the traffic loads among different BSs when received signal power (RSP)-based user association is used. This causes under utilization of the resources at low-power BSs. On the other hand, strong interference from high-power BSs affects the downlink transmissions to the users associated with low-power BSs. In this context, this paper proposes a channel access-aware (CAA) user association scheme that can simultaneously enhance the spectral efficiency (SE) of downlink transmission and achieve traffic load balancing among different BSs. The CAA scheme is a network-assisted user association scheme that requires traffic load information from different BSs in addition to the channel quality indicators. We develop a tractable analytical framework to derive the SE of downlink transmission to a user who associates with a BS using the proposed CAA scheme. To mitigate the strong interference, the almost blank subframe (ABS)-based interference coordination is exploited first in macrocell-tier and then in smallcell-tier. The performance of the proposed CAA scheme is analyzed in presence of these two interference coordination methods. The derived expressions provide approximate solutions of reasonable accuracy compared to the results obtained from Monte-Carlo simulations. Numerical results comparatively analyze the gains of CAA scheme over conventional RSP-based association and biased RSP-based association with and without the interference coordination method. Also, the results reveal insights regarding the selection of the proportion of ABS in macrocell/smallcell-tiers for various network scenarios.
Category: Digital Signal Processing