Physical channels and signals for the initial access procedure

We have covered the general aspects of the initial access procedure. In this section, we will be discussing the details of how the SS blocks and the PRACH are defined. The channels that define SS block are the Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS), and they are placed at the PBCH. These downlink signals are the only ones that are periodically transmitted in NR. Note that they can be turned off by the network thanks to NR’s ultra-lean design.

As we emphasized, coexistence and forward compatibility with LTE are crucial for NR. To achieve this, it is necessary to have as few blocked resources as possible. So, even though SS block transmission is periodic, having the option to turn off certain SS block locations or opportunities will help the network avoid interference with LTE or other featured services.

SS block

The SS block is composed of four consecutive OFDM symbols...