ve at the receiver. This will depend upon the distances involved (i.e., cell radius) and (2) a time-allowance for the transceiver to switch from receive-to-transmit mode. The switching times can vary considerably depending on the implementation but can take a few microse- conds. As a result, TDD is not normally suitable for use over very large cell sizes as the guard time increases and the spectral efficiency decreases. is often found that traffic in both directions is not balanced. Typically, there is more data transmitted in the downlink direction of a cellular system. This means that the capacity should be ideally greater in the downlink direction. Using a TDD system, it is possible to New Radio Access Physical Layer Aspects (Part 1) 371 change the capacity in either direction simply by changing the number of time slots allo- cated to each direction. This is often dynamically configurable SO it can be adapted to meet the demand. A further aspect to be noted with TDD transmission is the latency. Since data may not be able to be routed immediately to the transmission chain as a result of the time multiplexing between transmit and receive circuitry, there will be a small delay between the data being generated and being actually transmitted. Typically, this may be a few millise- conds depending on the frame timing. Both TDD and FDD have their advantages and each can be used in different deployment scenarios. Before deciding on a particular type of duplex scheme, it is necessary to analyze the advantages and disadvantages of each duplex mode. Table 3.7 summarizes and compares the relative attributes of TDD and FDD systems. The new radio can operate in paired and unpaired spectrum using a common frame structure unlike LTE where two different frame structures were used, which was later expanded to three for support of unlicensed operation introduced in 3GPP Rel-13. The basic NR frame structure is designed such that it can support both half-duplex and full-duplex operation. In half duplex the device cannot transmit an