Millimeter-wave (mm-wave) communications sys tems offer a promising solution to meeting the increasing data demands on wireless networks. Not only do mm-wave systems allow orders of magnitude larger bandwidths, they also create a high-dimensional spatial signal space due to the small wavelengths, which can be exploited for beamforming and multiplexing gains. However, the complexity of digitally processing the entire high-dimensional signal is prohibitive. By exploiting the inherent channel sparsity in beamspace due to highly directional propagation at mm-wave, it is possible to design near-optimal transceivers with dramatically lower complexity. In such beamspace MIMO systems, it is first necessary to determine the set of beams which define the low-dimensional communication subspace. In this paper, we address this beam selection problem and introduce a simple power-based classifier for determining the beamspace sparsity pattern that characterizes the communication subspace. We first introduce a physical model for a small cell which will serve as the setting for our analysis. We then develop a classifier for the physical model, and show its optimality for a class of ideal signals. Finally, we present illustrative numerical results and show the feasibility of the classifier in mobile settings.
typical s c a n n e r used in facsimile transmission h a s b e e n of w h a t m a y b e called t h e " l a t h e " t y p e . I n s u c h scanners t h e subject c o p y , whose g r a p h i c c o n t e n t is g e n erally to b e delivered elec trically to a d i s t a n t r e c o r d i n g p o i n t , is w r a p p e d a r o u n d a n d s o m e h o w fastened to t h e surface of a c y l i n d r i c a l d r u m .T h e c o p y -c a r r y i n g d r u m t h e n is r o t a t e d a n d , b y m e a n s of a track a n d lead-screw, a p h o t o e l e c t r i c " t o o l " is m o v e d axially a l o n g t h e r o t a t i n g c y l i n d e r so as to t r a c e a h e l i c a l p a t h over t h e w h o l e c o p y surface. Successive t u r n s of t h e helix so t r a c e d c o n s t i t u t e t h e successive s c a n n e d lines of t h e i m a g e to b e t r a n s m i t t e d . T h e m e c h a n i c a l o p e r a t i o n is a n a l o g o u s to t h a t of a s c r e w -c u t t i n g l a t h e , a n d t h e design p r o b l e m s a n d limitations a r e q u i t e similar. S u c h a design h a s c e r t a i n i n h e r e n t o p e r a t i n g l i m i t a t i o n s , in t h a t (a) after e a c h transmission (except for " r e p e a t s " ) t h e old subject c o p y m u s t b e r e m o v e d from t h e d r u m a n d n e w c o p y w r a p p e d a r o u n d a n d fastened to it, a n d (b) t h e subject m a t e r i a l m u s t b e in t h e form of t h i n flexible single sheets, so t h a t t h e p a g e s of a b o u n d b o o k or m a g a z i n e a r e diflicult to h a n d l e unless t h e b i n d i n g is d e s t r o y e d . M o r e recently t h e r e h a v e b e e n a n u m b e r of a t t e m p t s , b y t h e a u t h o r s ' l a b o r a t o r i e s as well as b y o t h e r s , to design facsimile s c a n n e r s t h a t w o u l d b e m o r e versatile for v a r i o u s a p p l i c a t i o n s , a n d w o u l d n o t h a v e t h e o p e r a t i n g l i m i t a t i o n s j u s t e n u m e r a t e d . N o t a b l e a m o n g these n e w e r designs a r e t h e s c a n n e r s devised b y C h a r l e s J. Y o u n g a n d his associates erf R a d i o C o r p o r a t i o n of A m e r i c a L a b o r a t o r i e s , I n c . , in w h i c h a b r i g h t spot of light is d e v e l o p e d u p o n t h e screen of a c a t h o d e -r a y t u b e , s w e p t in a s t r a i g h t line across t h e screen, a n d p r o j e c t e d u p o n t h e subject c o p y to p r o v i d e fast or side-to-side s c a n n i n g . Slow, or e n d -t oe n d , s c a n n i n g is o b t a i n e d b y c o n t i n u o u s l y a n d progressively m o v i n g t h e c o p y itself. T h u s t h e old d r u m a n d l e a d -s c r e w a r e e l i m i n a t e d a n d t h e e q u i p m e n t is e n a b l e d to h a n d l e c o p y t h a t is in b o u n d form or w h i c h is l o n g e r t h a n w o u l d be feasible for d r u m -m o u n t i n g . O t h e r suggestions h a v e involved t h e p r o d u c t i o n of a m o v i n g light spot b y i l l u m i n a t i n g or o b s e r v ...
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.