d the new eCPRI spec- ification supports 5G. In terms of functionality split, the RE mostly implements radio frequency functions and A/D-D/A conversion, while all the other gNB functionality is implemented in the REC. This is summarized in Table 4.1.1. 4 NG-RAN Architecture Figure 4.1.2 gNB architecture with CPRI REC and RE split. Table 4.1.1 Common Public Radio Interface (CPRI) Radio Equipment Control (REC) and Radio Equipment (RE) functions. Functions of REC (combined central unit/distributed unit) Functions of RE (remote unit) Downlink Uplink Downlink Uplink Network interfaces termination, protocol stack, Cyclic prefix (CP) radio resource management (RRM), scheduling, etc. addition (optional) Channel filtering Digital to analog (D/A) Analog to digital (A/D) conversion conversion Channel coding, Channel decoding, Up conversion Down conversion interleaving, modulation deinterleaving, demodulation Inverse Fast Fourier Fast Fourier Transform (FFT) ON/OFF control of Automatic gain control Transform (iFFT) each carrier CP addition (optional) CP removal Carrier multiplexing Carrier demultiplexing Multiple-input and multiple-output (MIMO) processing Power amplification Low noise amplification and limiting Signal aggregation from Signal distribution to signal Antenna supervision signal processing units processing units Transmit power control Transmit power control and RF filtering RF filtering of each physical channel feedback information detection Frame and slot signal Time Division Duplexing (TDD) switching generation (including in the case of TDD mode clock stabilization) CPRI protocol supports: Transfer of user-plane data (IQ samples) Transfer of control and management messages Transfer of synchronization signals Transfer of vendor-specific information. 4.1 Introduction Figure 4.1.3 CPRI protocol stack. Control & User Plane Management Plane Time Division Multiplex Electrical Optical Transmission Transmission This is illustrated in Figure 4.1.3. In terms of CPRI network topology, multiple CPRI links can be used betw