Orthogonal Channelization of Backscattering Tags using Golay Complementary Sequences

In this paper, we show a novel technique for multi-channel transmission in networks of backscattering tags. Backscattering tags are generally passive and send data by simply switching the load connected to the antenna, thereby modulating the reflection coefficient. Unlike traditional transmitters, it may not be feasible to implement multiple access techniques in these devices. Furthermore, transmissions from multiple tags in a network may be totally uncoordinated. In this letter, we use Golay complementary sequences as the interrogating signals to create orthogonal channels based on signal propagation times. The backscattered signals from different tags can be combined so that they are orthogonal to each other if the reader-tag propagation times differ by at least one chip duration of the complementary sequence. The primary limitation of the proposed technique is that it will work only on frequency-flat channels. This technique is therefore suitable for low-to-medium data rate backscatter communication.