Spectral Efficiency Increase for Passive Backscatter Communication Based on Discrete Pulse Shaping

The Internet of Things comprises the network of billions of devices. The need for wireless systems is leading to bandwidth becoming an extremely limited resource. For this reason, the spectral efficiency of radio systems is playing an increasingly important role. While active radios already use pulse shaping techniques to improve the efficiency, passive systems still make a little use of them. The reason for this is that the energy available for shaping is very low and would, therefore, massively influence the range. This paper presents a concept that enables pulse shaping especially for passive"ultra-high-frequency radio frequency identification" transponders without significantly reducing the range at the same time. For this purpose, all approaches were designed to meet the requirements for chip integration. A 41-stage discrete Gaussian pulse was used which can be generated by a field-effect transistor. The transistor is controlled by a simple voltage divider which is operated by the digital part of the transponder. The total power consumption of the concept with simultaneously acceptable space requirement is estimated with 200 nW. The results of both the simulation and the measurements show that even a small number of steps improve the spectral efficiency. In adjacent channels, less energy is radiated compared with a rectangular pulse. According to the measurements, the adjacent channel power ratio in the directly adjacent channel for the discrete Gaussian is 7.5 dBc lower than for the rectangular shape. This effect is more pronounced with an increasing distance and is already 32 dBc for the fourth adjacent channel.