In ths note, let's think of how to implement each components of the RAN in terms of Software vs Firmware vs Hardware. By firmware, I mean FPGA type of implementation and by hardware I mean pure electronics (like ADC/DAC). Software is software -:).

Ideally there is only one component that should be done by hardware. That is the section [6] because antenna, ADC / DAC cannot be done by software or firmware.

So the best way for the impelementation in terms of flexibility and easiness of maintenance (e.g software upgrade, bug fix etc) to implement everything except [6] in pure software running on COTS hardware. There are some small scale system handling relatively small amount of user data which is implemented this way.

But practically there are many cases where it is hard to achieve full performance by purely software, in such a case some components would be implmented in firmware (FPGA+Firmware) or Hardware (IC or ASIC). The most common candidates for this type of implmenetation would be the ones that would be in RU. For example, [5] / [9] would be the most common target for this type of implementation.

Reference