In principle, there may be two ways for a device to operate over multiple sub-bands. One way is that the transmitter/receiver bandwidth may be changed depending on which sub-bands are sensed as free. In this setup, there is only one component carrier (CC) and the multiple sub-bands are treated as a single channel with a larger bandwidth. The other way is that the device operates almost independent processing chains for each channel. Depending on how independent the processing chains are, this option can be referred to as carrier aggregation (CA) or dual connectivity (DC).

As mentioned previously, a channel access procedure in NR unlicensed spectrum may use an LBT mechanism to acquire a channel for transmission. The LBT mechanism is designed for the unlicensed spectrum co-existence with other radio access technologies (RATs). In this mechanism, a radio device may apply a clear channel assessment (CCA) check (i.e. channel sensing) before any transmission. The transmitter involves energy detection (ED) over a time period compared to a certain threshold (e.g., an ED threshold) in order to determine if a channel is idle. In the case that the channel is determined to be occupied, the transmitter can perform a random back-off within a contention window before next CCA attempt. In order to protect the acknowledgement (ACK) transmissions, the transmitter can defer a period after each busy CCA slot prior to resuming back-off. As soon as the transmitter has grasped access to a channel, the transmitter is allowed to perform transmission up to a maximum time duration (namely, the maximum channel occupancy time (MCOT)). For quality of service (QoS) differentiation, a channel access priority based on the service type can be defined. For example, there may be four LBT priority classes defined for differentiation of contention window sizes (CWS) and MCOT between services.