dex into a memory stored table that contains associated amplitude and phase coefficients. A separate table is used for every lagging or leading memory stage. Interpolation can be used to further increase performance between entries in the table. The advantage of the LUT approach is that it consumes less multiply-accumulate com- pute resources as compared to the polynomial methods but is more memory intensive. Both 234 Open Radio Access Network (O-RAN) Systems Architecture and Design implementation options are used in deployed systems using either FPGAs or (vector) DSP architectures. DPD coefficient calculation is implemented to support dynamic calculation of the para- meters going into the DPD actuator. DPD coefficient calculation is done through least- squares-type algorithm. Assuming (or given) that the PA model changes with parameters like temperature and aging, this piece can be implemented in a nonreal-time environment, including computation on General-Purpose CPU cores. Parameters like power envelope, aging, and temperature are monitored by sensors embedded in the RF Front End Module. Transmit power envelopes can also be calculated in the digital baseband domain, like Received Signal Strength Indicator (RSSI) measurements as explained for Receive Side Gain Control as discussed below. Performance of the resulting DPD implementation is measured as algorithmic (ACLR perfor- mance meeting or beating 3GPP and regulatory requirements) and in terms of PA DC power effi- ciency. State-of-the-art implementations near a 50% PA efficiency when meeting 3GPP -45dB ACLR targets. Receive side gain control The goal of Gain Control algorithms is to manage the ADC dynamic range, SO it operates at highest possible efficiency - avoid both saturation and underflow and thus utilize the avail- able effective number of bits precision in the data converter. Gain setting can either be manual, automatic or combination of both. Manual implies the receive chain being fully under user control. This requires user to have perfect knowledge