RTC Magazine

The challenge of RFID readers no longer consists of merely reading tags. Instead, now that the technology has moved past the stage of pilot programs and is being deployed for supply-chain management, these readers are taking on new strategic importance. The scope has widened to include issues such as integration into the corporate network, manageability, scalability, security, low total cost of ownership and especially avoiding obsolescence.

Adopters of radio frequency identification technology are continually challenged to accommodate new RFID tags, update their RFID systems with the latest technology and implement new protocols, including EPCglobal Generation 2, which allows more information to be stored on each tag, greater security, and better addresses noisy RFID environments with multiple interference sources (Figure 1). Since RFID readers do the bulk of the tag processing required, users are tasked with determining which readers will perform best through their ability to utilize new technologies, protocols and upgrades.

Recognizing that the reader is key to ensuring that RFID systems remain current with fast-changing technology, ThingMagic engineers made a critical commitment when designing the Mercury reader system. They decided to design an advanced software defined radio (SDR)-based reader platform for fixed, embedded and mobile readers. The result is an intelligent, network-ready reader that reads any tag.

Mercury RFID Reader Hardware System Architecture

Conventional RFID readers were unintelligent data radios, reading a single tag protocol in a single radio frequency and communicating with a PC via a serial interface. Today’s SDR-based RFID readers are agile, intelligent data readers, TCP/IP network nodes and data processors able to simultaneously read multiple tags while filtering out interference from other RFID readers and wireless devices.

The Mercury platform hardware consists of analog front-ends (AFEs), a DSP, a network processor, memory and communications ports (Figure 2).

The AFEs are essentially stateless; their hardware is designed to be protocol-neutral. They are, however, optimized by frequency band to meet the requirements of the radio regulations in the geographical region in which they operate, for example, FCC Part 15 regulations in the U.S. or ETSI EN302-208 regulations in Europe. They are connected via high-speed A/D and D/A converters to a real-time signal processing system that is currently based on a 600 MIPS Texas Instruments DSP. This DSP uses ThingMagic’s proprietary, real-time, signal processing software engine to manage all aspects of transmission and reception.

The AFEs are capable of fully general I/Q modulation and demodulation with bandwidths up to a Nyquist anti-aliasing filter limit of 5 MHz (double sideband), allowing up to 10 MHz of incoming signal spectrum to be simultaneously digitized and processed. Protocol-related software is loaded into the DSP, which then controls how the AFEs communicate with RFID tags. In turn, the DSP is controlled by a network processor, currently an Intel IXP42x running at 266 MHz. The Mercury4 was the first RFID reader to use an Intel processor, the result of close teamwork between Intel and ThingMagic. The main function of the IXP42x in this architecture is to initiate tag searches, load protocols and process the results. It also handles backend networking and high-level developer interfaces.

The DSP in both the Mercury4 and the Mercury5 is a high-performance, low-power Texas Instruments TMS320VC5502. It provides 600 MIPS of processing on parallel multiply-accumulate pipelines at a clock speed of 300 MHz. Using a high-performance DSP allows the reader to switch between protocols in real time and quickly separate signal from noise. The most common RFID tags have no battery and reflect power from the reader, resulting in weak and noisy responses that often require advanced signal processing to decode.

Coupled with the protocol-neutral AFEs, the high-speed DSP ensures that the reader’s hardware can read any tag that falls within its frequency band and regulatory setup, up to the limits of a tag subcarrier frequency of 5 MHz on either side of the transmitted carrier. This accommodates all Generation 2 waveforms.