  The 3GPP has recently conducted a study on the Ambient Internet of Things
(AIoT), with a particular emphasis on examining backscatter communications as
one of the primary techniques under consideration. Previous investigations into
Ambient Backscatter Communications (AmBC) within the long term evolution (LTE)
downlink have shown that it is feasible to utilize the user equipment channel
estimator as a receiver for demodulating frequency shift keyed (FSK) messages
transmitted by the backscatter devices. In practical deployment scenarios, the
backscattered link often experiences a low signal-to-noise ratio, leading to
subpar bit error rate (BER) performance in the case of uncoded transmissions.
In this paper, we propose the adoption of the same convolutional coding
methodology for backscatter links that is already employed for LTE downlink
control signals. This approach facilitates the reuse of identical demodulation
functions at the modem for both control signals and backscattered AIoT
messages. To assess the performance of the proposed scheme, we conducted
experiments utilizing real LTE downlink signals generated by a mobile operator
within an office environment. When compared to uncoded FSK, convolutional
channel coding delivers a notable gain of approximately 6 dB at a BER of
$10^{-3}$. Consequently, the AmBC system demonstrates a high level of
reliability, achieving a BER of $10^{-3}$ at a Signal-to-Noise Ratio (SNR) of 5
dB.
