RFID tags attached to retail items have been successfully deployed in retail environments for inventory tracking and control. The RFID tags communicate wirelessly with RFID readers and transmit their identifiers or other data associated with items to the RFID readers on interrogation. The identifiers are used to obtain information related to the attached articles or their locations. When the RFID readers interrogate one or more RFID tags through RF waves, the tags respond to the interrogating RF waves in a process known as backscatter.
One major factor limiting with current technologies for RFID readers is the limited bandwidth available for communication with the RFID tags. Every deployed tag requires a fixed amount of bandwidth in order to be read by the RFID reader. Thus, as the number of tags increases, the bandwidth requirement increases linearly. Furthermore, the bandwidth constraints increase the time that it takes to complete a read cycle thus limiting the ability to use RFID in real-time for environments with dense tags. Since, real time tracking is extremely useful for many applications there is a demand for real-time tracking of RFID tags.
There are many methods for increasing the available bandwidth. Current mechanisms focus on variation of CDMA and TDMA in order to increase bandwidth. For example, Ultra Wide Band (UWB) a CDMA technology has been proposed as a means of increasing bandwidth. While TDMA does not increase bandwidth, it allows for segmentation of the RFID tags into different time spots thus reducing collisions and enabling a higher density of tags. However, the bandwidth of TDMA is quite limited and hence reads can take quite a while. Additionally, these methods suffer from increased overhead when scaling to a large number of tags and only partially increase the required bandwidth. By far, the most prevalent method for increasing bandwidth is to divide the geographical area into small regions. By using a large number of RFID readers, each reader can read the tags in a small region around it. While each reader has limited bandwidth, the total system bandwidth is increased by the large number of readers, each of which reads from a different region.
However, even when a large number of readers are deployed, RFID tags mostly used in retail environments have limited computational power, thus coordination among tags to efficiently utilize bandwidth becomes increasingly difficult. Additionally, in some cases, smart tags are utilized. The existing systems allow only a small subset of tags to broadcast at a given time period, and the smart tags include microcontrollers to control the tags' broadcast for a given time period. Such smart tags are relatively expensive. Thus, limited coordination among tags and the demand for bandwidth continue to be major limiting factors for reducing the read cycles for identifying tags by an RFID reader.
Also, increasing the number of RFID readers incurs significant cost in deployment, power consumption and maintenance as well as technical issues due to reader-reader interference. The benefits of multiple readers are also limited by the number of channels which are available for RFID readers.
In view of the above, there is a need for improved readings by RFID readers to utilize bandwidth availability, and reduce the deployment and maintenance cost of RFID in retail environments.