A space-time coding approach for RFID MIMO systems

Abstract

This paper discusses the space-time coding (STC) problem for RFID MIMO systems. First, a mathematical model for this kind of system is developed from the viewpoint of signal processing, which makes it easy to design the STC schemes. Then two STC schemes, namely Scheme I and Scheme II, are proposed. Simulation results illustrate that the proposed approaches can greatly improve the symbol-error rate (SER) or bit-error rate (BER) performance of RFID systems, compared to the non space-time encoded RFID system. The SER/BER performance for Scheme I and Scheme II is thoroughly compared. It is found that Scheme II with the innate real-symbol constellation yields better SER/BER performance than Scheme I. Some design guidelines for RFID-MIMO systems are pointed out.

Trade-off between maximum cardinality of collision sets and accuracy of RFID reader-to-reader collision detection

“…The power of the interfering signal that reader x receives from reader y is calculated in the same way as Equation 9:…”

“…RFID is used for many applications, such as traceability [2], item removal detection [3], anti-counterfeit [4] and positioning [5], and for the establishment of smart environments, such as smart retailers [6], smart hospitals [7], and smart universities [8]. Although the need of covering large areas has been partially satisfied by using MIMO RFID readers [9], the majority of the RFID applications, especially the largest, require a dense reader deployment, where RFID readers operate in close proximity. Consequently, UHF RFID systems are easy to suffer from the interference generated during simultaneous interrogation activities [10].…”

A differential space-time coded RFID system

“…To mitigate such fading, the use of multiple antennas at the reader or tag has been investigated by a number of researchers [3]- [6]. In [3], it was shown that pinhole diversity is available in a rich scattering environment caused by modulating backscatter with multiple tag antennas, and can yield a significant reduction in the power required to maintain a certain bit error rate (BER).…”

“…In [5], the authors showed how transmit diversity and spatial multiplexing can be applied to a multiple-antenna RFID system to dramatically increase the interrogation range and data rates. In [6], the space-time coding problem for multiple-antenna RFID systems was discussed, and coherent space-time coding schemes capable of achieving spatial diversity were proposed. It is noteworthy that [4]- [6] assume perfect knowledge of the forward and backward channels at either the transmitter side or the receiver side of the reader.…”

“…In [6], the space-time coding problem for multiple-antenna RFID systems was discussed, and coherent space-time coding schemes capable of achieving spatial diversity were proposed. It is noteworthy that [4]- [6] assume perfect knowledge of the forward and backward channels at either the transmitter side or the receiver side of the reader. However, to obtain such information in practice is still an open problem.…”