Design and Exploration of Radio Frequency Identification Systems by Rapid Prototyping

In this thesis I describe the setup and design of a flexible rapid prototyping platform for RFID systems to provide an experimental verification environment for RFID systems, that allows their real-time exploration in distinct measurement setups. Furthermore, I use this system to test the feasibility of novel signal processing algorithms for RFID reader receivers, which promise a performance increase to state-of-the-art-receivers. Three different scenarios are considered: 1. In the first scenario, a single tag communicates with a single receive antenna reader. The performance of the optimal maximum likelihood sequence decoder is identified, and losses due to channel estimation and synchronisation are discussed. Due to the wide deviation from the nominal data rate in the uplink communication, especially synchronisation shows to be a critical issue. 2. In the second scenario, the single tag communicates with a multiple receive antenna RFID reader. This multiple receive antenna system allows for mainly two advances: in a strong line of sight environment I demonstrate that a direction of arrival estimation of the tag signal is feasible, while for an environment with strong multipath components, I propose a maximum ratio combining for diversity combining at the reader receiver. Hence, in the line of sight case I address localisation of RFID tags, while the diversity combining addresses the topic of reliability of the communication in a high fading environment. 3. Finally, in the third scenario multiple tags communicate with the reader simultaneously and generate a collision. Such collisions are modeled on the physical layer, and different receivers with either a single or multiple receive antennas are proposed to recover from a collision at the physical layer. Hence, the topic of throughput in multiple tag communications is addressed here, which is shown to increase by a factor of 1.6 compared to the throughput of a conventional system, in the case a reader can recover from collisions of up to two tags. Moreover, performance tradeoffs regarding throughput, reliability and receiver complexity are shown. For all three scenarios, models for the signal constellations at the reader receiver are developed and supported by measurement data. Implementation aspects of the receivers are discussed, and performance comparisons not only by means of simulations but also by measurements are presented.