Home // International Journal On Advances in Telecommunications, volume 4, numbers 1 and 2, 2011 // View article

CDMA-Based UHF-RFID System with Semi-Passive UHF Transponders

Authors:
Andreas Loeffler
Ingo Altmann
Fabian Schuh

Keywords: Radio frequency identification; cdma; uhf; transponder; digital signal processors.

Abstract:
RFID systems, in general, increase the efficiency of logistic systems, e.g., inventory of stocks. Unfortunately, present existing systems come fast to their limits if a certain number of RFID transponders must be inventoried in a limited period of time, as the channel access method of current RFID systems is based on Time Division Multiple Access. To shorten the inventory process, this work shows an implementation of an UHF RFID system based on semi-passive UHF transponders, using Code Division Multiple Access as anti-collision method. The work focuses on the uplink channel (tag to reader) that covers the transponders' backscattered signals. This channel access method enables simultaneous transfer of transponder data; i.e., all transponders in the field may respond at the same time within the same frequency band. The data transfer realized for the uplink channel uses a set of orthogonal spreading sequences (Gold codes) being different for every transponder. The RFID reader designed in this work despreads the backscattered signals and decodes the data of the different transponders. This work shows, in principle, the opportunity for a simultaneous data transfer on the uplink channel in RFID systems, which in turn may reduce the time needed for a complete inventory round. The entire system is build upon dedicated hardware, which is, also, a new aspect of this paper.

Pages: 127 to 142

Copyright: Copyright (c) to authors, 2011. Used with permission.

Publication date: September 15, 2011

Published in: journal

ISSN: 1942-2601