SHR (synchronization header)

The SHR (Synchronization Header) is a component of the IEEE 802.11 standard for wireless LANs (WLANs). It is used for synchronization and signal timing purposes between the transmitting and receiving devices. The SHR is part of the Physical Layer Convergence Procedure (PLCP) protocol, which operates at the physical layer of the OSI model.

The main purpose of the SHR is to provide a known pattern of bits that helps the receiving device synchronize its timing with the transmitter. It consists of a predefined bit pattern called the PLCP preamble, followed by a Start Frame Delimiter (SFD).

The PLCP preamble is a sequence of alternating ones and zeros that serves as a distinctive pattern for the receiving device to identify the start of a transmission. It allows the receiver to detect and synchronize its clock to the transmitter's clock. The preamble also helps in estimating the channel conditions and provides a reference for subsequent signal processing.

The Start Frame Delimiter (SFD) immediately follows the PLCP preamble. It is a fixed 16-bit pattern that indicates the start of the actual data frame. The SFD is a known pattern that distinguishes the preamble from the rest of the frame. Once the receiving device detects the SFD, it knows that the actual data frame is about to begin.

By using the SHR, the receiving device can align its clock and establish synchronization with the transmitter, enabling it to accurately decode the subsequent data frame. This synchronization is crucial for maintaining reliable communication in wireless networks.

To summarize, the SHR (Synchronization Header) in the IEEE 802.11 standard provides a known pattern of bits, including the PLCP preamble and the Start Frame Delimiter (SFD). It helps the receiving device synchronize its timing with the transmitter, allowing for accurate decoding of the data frames in wireless LANs.