LTE: What is RRH and BBU based LTE network architecture ? And how it work and in which cases operators will prefer ?

Question

I was searching for RRH and BBU related stuff and found a query related to that.
Reference:
http://tech.queryhome.com/145400/what-based-network-architecture-which-cases-operators-prefer

I gone through the content and understood at a very high level. Now I have related but deep queries as following:

How this architecture handle the delay that comes due to gap between RRH and BBU ? Is there any specific hardware/software or combination of both needed to mitigate the delay affect ? And one more related question, is there any one to one mapping with BBU and RRH or it can be in any combination ?

Answer 1

As far as I know, RRH/RRU and BBU is not new architecture. It might have you heard first time and working in LTE technology so you thought it is solely related to LTE network. RRH/RRU (Remote Radio Head/Remote Radio Unit) and BBU (Base band unit) are two components which are separated to each other and located at different places. In case of C-RAN (cloud RAN/centralized RAN), BBU would be running in data center environment while RRH will be located near to antennas.
RRH and BBU inter connect on optical fiber interface and both can be separated in km distance unit. RRH and BBU based network deployment will reduce CAPEX/OPEX for operator.

One more thing to remember is that when UE sends the data at 'n' the subframe, ACK-NACK should be received at 'n' + 4 subframe from eNodeB otherwise UE re-transmit the data. In other words, total delay from RRH to BBU + eNodeB processing should be less than or equal to 3. This constraint derives the distance between RRH and BBU.

Reference:
http://www.netmanias.com/en/post/blog/6276/c-ran-fronthaul-lte/fronthaul-size-calculation-of-maximum-distance-between-rrh-and-bbu