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ThinkMind // International Journal On Advances in Intelligent Systems, volume 2, number 4, 2009 // View article intsys_v2_n4_2009_3


Spatial Diversity Solutions for Short Range Communication in Home Care Systems using One Antenna Element

Authors:
Markku J. Rossi
Jukka Ripatti
Fikret Jakupovic
Reijo Ekman

Keywords: home care; short range radio; sensors; ZigBee; shadowing; fading; spatial diversity; avoiding gain minima; diversity adaptability

Abstract:
It is becoming increasingly important for countries like Japan, Finland and Italy to enable as wide as possible home care for their elderly citizens because of the rapidly changing age structure of the population and high hospital costs. Wireless sensors hidden in furnishings ( as a reference to a Finnish ongoing project ) can provide necessary information for the high quality planning of home care visits. The relative positions of the radios are now fixed because of their relations to the furnishings. When conductive or metallic walls, floors or objects are found in the apartment, an antenna can hit a radio fade caused by shadowing or the summing up of waves. The Link Quality Indicator of a ZigBee® receiver can vary by up to 50 units within a short distance because of the floor, compromising the radio range. This paper describes the principles of a radio construction which is able to move the antenna element inside the enclosure of the radio unit along an Xshaped path along the major mechanical plane of the radio unit. Two electrical motors dynamically optimise the location of the internal antenna element to fit the current radio propagation environment. The paper also describes the feasibility and cost factors associated with the new structure. The achieved effect is a useful countermeasure against shadowing and multipath in the 2.44 GHz band but provides only a partial solution to the problem in the 868 MHz band, due to the space limitations in a typical radio unit. A prototype of the Diversity Adaptability radio was built and the capability to remarkably enhance the received power in difficult fading conditions was verified in an anechoic chamber. The observed side effects to the directional pattern of the radio were analysed to be removable by carefully selecting the route of the coaxial cable from the radio unit to the moving antenna element.

Pages: 422 to 433

Copyright: Copyright (c) to authors, 2009. Used with permission.

Publication date: March 17, 2010

Published in: journal

ISSN: 1942-2679

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