ly, the signals on the input ports can coexist on the output port without interfering with each other. On the other hand, a duplexer is a device that allows bidi- rectional communication over a single channel. In radar and radio communications systems the duplexer isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer. Duplexers are designed for operation in the frequency band used by the receiver and transmitter and must be capable of handling the output power of the transmitter. They must provide sufficient isolation between transmitter and receiver to prevent receiver desensitization [30]. created by the UE by not receiving the last OFDM symbol(s) of a downlink subframe immediately preceding an uplink subframe in which the UE is active. The length of the guard period is the sum of the maximum round-trip propagation delay in the cell, transmit- to-receive and receive-to-transmit switching delay at the UE. New Radio Access Physical Layer Aspects (Part 1) 373 Cell A Classic Cell B Cell A Flexible duplexing Cell B Cell A Flexible duplexing with Cell B synchronization Interference Victim cell Figure 3.38 Examples of flexible duplexing schemes in TDD mode. The choice of duplex scheme is typically determined by the spectrum allocation. For lower frequency bands, allocations are often paired, implying FDD mode is dominant. However, in higher frequency bands, unpaired spectrum allocations are increasingly common; thus TDD mode is used. 3GPP NR supports both duplexing methods. However, unlike LTE where the TDD uplink-downlink allocation does not change over time, NR supports dynamic TDD as a key technology component. In dynamic TDD, parts of slot can be dynamically allocated to either uplink or downlink based on the scheduler decision. This enables network adaptation to traffic variation, which is particularly common in dense deployments with a relatively small number of users per base station. The device follows any scheduling decisions