  In ambient backscatter communication (AmBC) systems, passive tags connect to
a reader by reflecting an ambient radio frequency (RF) signal. However, the
reader may not know the channel states and RF source parameters. The
traditional energy detector (TED) appears to be an ideal solution. However, it
performs poorly under these conditions. To address this, we propose two new
detectors: (1) A joint correlation-energy detector (JCED) based on the
first-order correlation of the received samples and (2) An improved energy
detector (IED) based on the p-th norm of the received signal vector. We compare
the performance of IED and TED under the generalized noise model using McLeish
distribution and derive a general analytical formula for the area under the
receiver operating characteristic (ROC) curves. Based on our results, both
detectors outperform TED. For example, the probability of detection with a
false alarm rate of 1\% for JCED and IED is 22.97\% and 5.41\% higher,
respectively, compared to TED for a single-antenna reader. Using the direct
interference cancellation (DIC) technique, these gains are 34.92\% and 3.7\%,
respectively. With a four-antenna array at the reader and a 5\% false alarm
rate, the JCED shows a significant BER improvement of 28.68\% without DIC and
48.21\% with DIC.
