ally, a HARQ codebook can be a semi-static codebook (Type 1) or a dynamic codebook (Type 2). In this section, we listed the channel coding schemes for NR, and we showed how they are introduced in channel processing chains. We've also discussed the retransmission schemes by comparing them with LTE. Now, it is time to learn the final revolutionary aspect of the NR physical layer. In this last section of this chapter, we will cover another concept introduced in NR, which is the BWPs. This concept is new in NR and very powerful for a few interesting and important use cases. In this section, we will learn what BWPs are and how they are configured, activated, and deactivated. We will also describe the main use cases for BWPs to better understand their importance in the NR physical layer. 5G Air Interface and Physical Layer Procedures - Part 3 Defining a BWP So, let's start by defining what a BWP is. A BWP is a set of contiguous PRBs with nested bandwidths where the devices are only allowed to transmit or receive. Each BWP has its own configuration with a specific numerology to use and a set of reserved resources for which transmission is not allowed. Devices always operate using BWPs. This means that at least one initial BWP must be defined by the PBCH SO that all devices can access it. This initial BWP will also contain the CORESET and PDSCH for the RMSI. However, a BWP does not need to contain an SS block. BWP parameters A device must be configured with one uplink and one downlink BWP at least. However, it can be configured with multiple BWPs as well. It is important to know that these configured BWPs may overlap in the frequency domain. Note that in Release 15, only one of them is active, SO only one uplink and one downlink BWP can be active at the same time. Among others, the main parameters that can be configured for BWPs are the numerology, the frequency location, the number of PRBs, and the CORESET with which the control channel must be monitored. BWP operations Devices can only transmit and receive using the ac