Interference Mitigation

About

​Description Passive wireless sensors and RFID tags operate without battery and harvest energy from Radio Frequency (RF) signals emitted to them from a reader or interrogator.  The simplest use of these tags is for identification purposes. However, these sensors are mostly used for measuring physical parameters such as temperature and humidity as well as various forms chemical and biological parameters. In all cases, when the reader emits the interrogating signal, all sensors in the vicinity of each other respond at the same time. There are three ways to separate the responses and manage the interference. These are time domain, frequency domain, and code domain techniques.  The first two methods, time and frequency, have some limitations mainly due to the synchronization need and read rate limit for time domain systems and scarcity of spectrum for frequency domain methods.  These challenges limit the use of these methods for a large number of sensors or tags.  The third method which is using orthogonal coding is capable of addressing several sensors in vicinity of each other providing fine grained measurement capability.  The residual interference from tails of cross correlated responses from other sensors may be reduced to some extent using well known interference cancellation methods at the reader side, but can not be eliminated, rendering a challenge for using this method for high resolution or high data rate applications where a large of number of sensors need to be read.   This invention addresses the residual interference problem that limits the number of sensors or tags used in code division systems by completely eliminating the interference at the source.  The main novelty of this work is based on the fact that response of the sensor under interrogation consists of a peak in the autocorrelation signal that is several times larger than the largest peak in cross correlation response of other interfering sensors.  A simple diode or transistor will be added to the input of these sensors between antenna and the sensor itself to allow high amplitude interrogating signal to come in, but only autocorrelation peak to come out. This method blocks the low amplitude cross correlation response of interfering sensors, hence allows for a large number of sensors to work in a multiple access network with no need for centralized interference management methods at the reader.   ​ The advantage of this approach is significant. All other interference management methods reduce interference to some extent, but this approach completely eliminates interference.