Traditional cellular networks rely on RANs, in which baseband signal processing is carried out at the location of the cellular antennas. As traffic has increased, cell sizes are decreasing, dramatically increasing the number of cell sites and their capacity. In order to improve the scalability of these large numbers of access points, equipment vendors and network operators have proposed the separation of the RRUs and the BBUs. The general trend of decreased cell size and separation of RRUs and BBUs gives rise to the small cell radio deployments.

Small cells transmit substantially less power than traditional RRUs. The coverage area of small cells have the following benefits:

1. Sufficient cell size and power level to cover the necessary indoor or pre-defined outdoor area.
2. Utilizing optical network to cover the the bulk of data connection from BBU. Since the power required for transmission over the optical link can be less than that of the wireless link, the transmission power for a given bit rate can be smaller with small cells compared to the traditional macro cells.
3. Different RAN options have different BBU function split. Regardless of the split, small cells can improve the local area capacity through increased frequency reuse due to their smaller cell size, and reduce indoor coverage gaps by minimizing signal loss.
4. When multiple small cell radios are connected to a common BBU, the BBU can coordinate the radio resource allocation and interference management across cells, improving overall throughput and end-user-experience in a given area.
5. Service providers can choose to deploy aggregates of small cells and combination of power levels of each cell to achieve overall network level power efficiency. The service providers can use this as an alternative strategy, compared to the traditional strategy of high-power macro RRUs, to potentially improve network level energy efficiency.

On the other hand, network operators do have to exercise caution when deploying small cell networks to avoid possible interference with existing macro cells. The quantity of small cell radios depends on network coverage and performance. Based on estimate^[3], the range is from 4000 to 10000 square feet per radio. Moreover, within office buildings or apartment buildings where RF reception is poor, the building owner may choose to deploy combinations of small cells, repeaters, or distributed antenna system to expand the coverage. When designing for indoor coverage, typically 0.25W to 1W coverage per antenna may be sufficient. For areas such as suburban areas with medium to low traffic, the remote macro radio provides sufficient capacity and coverage. In between buildings or in areas where data traffic is high such as stadiums and shopping plazas, the building owner may choose to deploy outdoor small cells in the range of 5W to 10W to ensure coverage.