 the network. Let's examine the ultra-lean design concept of NR and understand the energy efficiency of NR by making a comparison of Power Amplifier (PA) usage of an empty cell in NR and LTE. Ultra-lean design NR minimizes network transmissions that are not directly related to user-data delivery. Today Ultra-lean ((<<) Reference signals No "always-on" reference signals Broadcast system information Minumum amount of "always-broadcast" system information Figure 4.9 - NR ultra-lean design In LTE, the reference signals are always on. However, in NR there are no always-on reference signals. NR schedules transmissions and measurements of reference signals. This design is also good for energy efficiency and minimizing interference. PA on time ratio - LTE versus NR The ultra-lean design concept of NR brings energy efficiency. This can be analyzed by comparing power amplifiers on time ratios of LTE and NR. The following figure shows the power amplifier usage of an empty LTE cell. Due to always-on reference signals, the power amplifier is on around 50% of the time. LTE: PA on time ration = 50% Time [ms] Figure 4.10 - LTE power amplifier usage in an empty cell 5G Air Interface and Physical Layer Procedures - Part 1 Due to the ultra-lean design of NR, reference signal transmissions and measurements are not done periodically; they are scheduled instead. SS blocks are sent periodically. System Information Block (SIB) Sync Signal NR: PA on time ration 2 5% Time [ms] Figure 4.11 - NR power amplifier usage in an empty cell In the preceding figure, you can see that the SS blocks are sent at intervals of 20 milliseconds, and there are no always-on signals in an empty NR cell. This lowers power amplifier usage by around 5%, which is one of the building blocks of energy efficiency in NR. In this section, we have made a quick introduction to NR physical layer procedures and the air interface. In the following section, we are going to analyze waveform, numerology, and frame structure. Waveform, numerology, and frame structure In this s