What is the use of PSS and SSS in LTE?
In LTE, two important signals that play a crucial role in helping your device connect to the network are the PSS (Primary Synchronization Signal) and the SSS (Secondary Synchronization Signal). These signals are part of the initial cell search process, which is vital for ensuring that your device can synchronize with the LTE network when you power it on or move to a new location.
When you connect to an LTE network, your device must first identify and synchronize with the cell tower (eNodeB) in your vicinity. The PSS and SSS signals help your device achieve this synchronization and, ultimately, allow it to communicate with the LTE network. Let me walk you through the specific roles of these signals:
PSS – Primary Synchronization Signal
The Primary Synchronization Signal (PSS) is responsible for helping your device get an initial frame synchronization with the LTE cell. The PSS is transmitted by the eNodeB every 5 ms, and it contains information that allows your device to detect the start of a frame in the LTE downlink transmission.
What does this mean for you? Essentially, the PSS helps your device figure out the timing of the transmission. Without it, your device wouldn’t be able to understand when a transmission begins, making it impossible to decode further data. Think of it as a “time marker” for the start of a data stream, without which your device would be lost.
In simpler terms, the PSS allows your device to lock onto a specific LTE cell and align its timing with the cell tower, ensuring that data packets are received in the correct sequence. The PSS uses a 3-symbol sequence in the frequency domain, and it’s repeated multiple times to ensure that it’s easily detectable by your device.
SSS – Secondary Synchronization Signal
The Secondary Synchronization Signal (SSS) works hand-in-hand with the PSS, providing additional information about the LTE cell’s identity. While the PSS helps your device lock onto the timing of the transmission, the SSS helps your device identify the cell itself. It carries critical information such as the physical cell identity and the cell’s system frame number, which are necessary for your device to establish a complete connection with the cell.
Once your device locks onto the timing provided by the PSS, it needs the SSS to fully synchronize and identify the exact LTE cell it’s dealing with. The SSS is transmitted every 10 ms and contains a 31-bit sequence that’s crucial for your device to identify and decode the cell’s unique information. The SSS also helps your device determine the proper system configuration of the cell, ensuring that your device can communicate effectively with it.
Why are PSS and SSS so important?
In LTE, synchronization is key. Without proper synchronization, your device wouldn’t be able to communicate with the network at all. The PSS and SSS signals enable this synchronization process, ensuring that the device can lock onto the right cell and correctly decode the transmitted data. They are essential for initial access and maintaining a stable connection with the network.
In previous articles, we’ve talked about how LTE technology ensures fast, high-speed connections. The PSS and SSS are foundational components of this process, enabling your device to quickly and accurately synchronize with the network, which is crucial for the overall user experience.