Methods and apparatuses for encoding and decoding a physical layer (PHY) protocol data unit (PPDU) for low power indoor (LPI) wireless communication, which includes a preamble portion and a payload portion. The preamble portion includes a first universal signal field (U-SIG), the first U-SIG comprising information regarding a payload portion of the PPDU. The preamble portion further includes a second U-SIG, which contains identical information regarding the payload portion of the PPDU. The repetition of the U-SIG may improve robustness of the preamble portion detection and also enable auto-detection of the PPDU for LPI communication.