Main objective of this contribution is to evaluate the overall performance of the Ultra Wide Band (UWB) Radio Frequency Identification (RFID) system based on chipless RFID tags, within the UWB range from 3.1 to 10.6 GHz. In this work, a ray-tracing tool "Wireless Insite" is used to consider the channel multipath components and the real environmental effects as fading, frequency dependence, transmission, reflections, diffractions and polarization dependence. Furthermore, an Electromagnetic (EM) simulation tool "CST Microwave Studio" is used to compute the Frequency Coding Response (FCR) and the Radar Cross Section (RCS) of the UWB-chipless-RFID tag. The system is based on an 8-bit FCR concept of a compact printable orientation independent chipless RFID tag. The tag consists of a circular patch loaded with N multiple slot ring resonators, where each resonator is relevant to a frequency component in the FCR. Simulation results show constructive guidelines for designing multiuser UWB RFID communications and enhancing the channel estimation process of the chipless RFID tag systems. System evaluation would consider several parameters as Bit Error Rate (BER), FCR word length, and the maximum reader-tag range. This enables the insertion of the advanced communication techniques as Interference Alignment (IA), Cognitive Radio (CR) and Massive Multiple Input Multiple Output (MIMO) for passive RFID systems.