GLRT for Packet Detection With Practical Analog AGC

We study packet detection in wireless networks in the presence of a practical analog automatic-gain-control (AGC) amplifier, which is adopted to scale the average power of received signals to an appropriate fixed level. However, when packets are not received, the input of AGC is pure noise, which has a small amplitude and may not be scaled to the desired level, due to the limited gain of AGC. In light of this feature, a generalized likelihood ratio test (GLRT) detector, which is termed AGC-GLRT, is proposed and formulated in this paper for packet detection. The effect of AGC on AGC-GLRT is analyzed, and it is proven that the performance of AGC-GLRT depends on the ratio of output power in hypotheses H₁ and H₀. A comparison is performed between AGC-GLRT and general GLRT (GEN-GLRT), which considers the output power of AGC in the two hypotheses, as well as some other common detectors. Results show that, in the presence of a practical AGC, AGC-GLRT outperforms GEN-GLRT and the other detectors. Moreover, as the maximum gain of AGC decreases, the ratio of the output power in the two hypotheses increases, and the performance of AGC-GLRT is improved. In addition, it is shown that AGC-GLRT is more sensitive to fading effects than the other detectors. Based on these analysis and comparisons, a general rule on AGC design is achieved to take full advantage of AGC-GLRT.