Intra-Band LTE Backscatter

Due to the continuity of long term evolution (LTE) downlink traffic, LTE signal has been considered as a promising excitation signal for ubiquitous backscatter communication. But this continuity also brings challenges in performing self-interference cancellation. Existing backscatter designs commonly use frequency shifting to move backscattered signal away from the entire excitation band to avoid self-interference. However, due to the continuity of LTE signal, LTE bands are occupied continuously. So, there is no enough white spectrum for frequency shifting. To solve this problem, we in this paper propose a novel LTE backscatter design, which can avoid self-interference without leveraging extra spectrum. Our idea is proposed based on a full understanding of the LTE resource grid, where we find that although a band is occupied by an excitation signal, there are still reserved resource elements in the traffic. We can leverage such resource elements as in-band white space to transmit backscatter signal. Meanwhile, we address the self-cancellation issue caused by double sideband modulation, and deal with the aligning issue. Our design is evaluated using a testbed of backscatter hardware and software defined radio (SDR). The results show that our system achieves a distance of 24 m for line-of-sight (LOS) transmit-to-tag communication. Besides, we demonstrate that our system can operate on off-the-shelf eNodeB. It can achieve reliable backscatter in multi-path scenarios, with a power consumption 6.3 times less than its least counterpart.