A Software-Defined Radio System for Backscatter Sensor Networks

A Software-Defined Radio System for Backscatter Sensor Networks

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2170 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 7, NO. 6, JUNE 2008 A Software-De f ned Radio System for Backscatter Sensor Networks Giovanni Vannucci, Senior Member, IEEE , Aggelos Bletsas, Member, IEEE , and Darren Leigh, Member, IEEE Abstract —Backscatter radio is proposed for sensor networks. In that way, the transmitter for each sensor is simpli f ed to a transistor connected to an antenna and therefore, the cost for each sensor’s communicator becomes negligible, while en- ergy used for wireless communication per sensor is minimized. A software-de f ned transceiver is built to transmit a carrier, receive the re F ections from various sensors and extract their transmitted messages. This work presents a thorough model of the backscatter radio link, the system architecture and a set of data extraction techniques for each sensor’s information, testing in practice a sensor communicating through backscatter at a range of approximately 15 meters indoors, with 5 milliwatt transmission power at 10 bits per second. This work highlights the idiosyncrasies of the backscatter channel and provides a new communication perspective in the fertile area of scalable sensor networks, especially when low bit-rate, ultra-low cost sensors are required. Index Terms —RFID, fading channel, bit error rate, wireless sensor networks. I. INTRODUCTION T HE technique of radio backscatter is commonly used in RFID (Radio Frequency IDenti f cation) systems. In a typical application, a RFID tag communicates to a reader (sometimes called an interrogator) its identi f cation number and in some cases additional information stored in its memory. Radio backscatter communication is an attractive solution in such systems because the tag does not need to actively transmit any radio signal; the tag simply re F ects a radio signal transmitted by the interrogator and modulates the re F ection, by controlling its own re F ection coef f cient [1]–[3]. This leads to very-low-cost implementations and also very low power requirements in the tag. Indeed, in systems where the distance between tag and interrogator is short (i.e., less than 2-5 m or so), RFID tags may derive their power from the signal received from the interrogator. Such batteryless tags are known as “passive” and the maximum distance (range) achieved by such systems is determined by the tag’s ability to extract enough voltage from the received signal. Even though passive RFID technology has matured since the f rst work on modulated backscattered signals [1], the range of typical passive RFID systems is limited, at most within a room [4], spanning a Manuscript received October 6, 2006; revised July 11, 2007; accepted September 4, 2007. The Associate Editor coordinating the review of this paper and approving it for publication was A. Stefanov. This research was supported by Mitsubishi Electric Research Laboratories (MERL), 201 Broadway Avenue, Cambridge, MA 02139 USA. Part of this work was presented at IEEE PIMRC 2007, Athens Greece. The authors are with Mitsubishi Electric Research Laboratories (MERL),
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A Software-Defined Radio System for Backscatter Sensor Networks

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