One thing is certain: outdoor small cells are getting ever larger attention as a solution to projected operator’s capacity woes. For the uninitiated, small cells are all-outdoor compact base stations that are easy to deploy on public infrastructure assets such as light poles or utility poles. They typically feature lower power output than their larger siblings – the macro base stations. So, what are the necessary elements to enable mass small cell deployments?
In my opinion, the top three gating items are:
- Site acquisition & deployment.
- Backhaul solutions.
- Interference management.
To start, an efficient way to acquire and deploy small cell sites is critical because it’s simply not feasible to discuss leasing on a site-by-site basis as it is done for macro-cells. When it comes to small cells, a blanket agreement with a municipality and/or a utility company is needed for site selection in addition to a simple approval process. Then it comes to the issue of ‘crowding’: how many operators will go after very few poles. Remember that we’re talking about small cells with radius of 50 m used to target capacity hotspots. Therefore, there is little flexibility in locating small cells which will intensify competition for the few suitable poles in localized hotspots.
The second gating item is backhaul and specifically its cost. This is mainly a business case issue. Traditional fiber or wireline solutions would generally not be available at the exact spot where a small cell is needed. So, much of both time and money is needed which would limit the deployment potential of small cell deployment unless some other techniques, mainly wireless backhaul, are made available. There are such solutions, which are in the process of getting refined that will potentially address this problem.
The third gating item, which is purely a technical issue, is interference management. Should small cells operate on the same frequency or a different frequency from the macro-cell? How about the handoff between the two layers? What load-balancing techniques need to be implemented? All these questions and some more have to be answered. Operating small cells at the same frequency as the macrocell will cut into the capacity of the network but is positively viewed in general when it comes to features such as handover. Nevertheless, LTE has built in capability to coordinate the multiple layers especially through features like fractional frequency reuse and inter-cluster interference cancellation (ICIC). This is a definitive advantage over 3G networks where no such coordination is available leading to greater benefits of small cell deployments in LTE networks than there could be in 3G networks.
We are at the early stages of serious consideration of heterogeneous networks. Small cells have been deployed in operators’ networks on tactical basis (in GSM they are commonly referred to as micro-cells, and there are plenty of them around). When it comes to mass deployments to accommodate projected capacity requirements, the three above gating factors will prove critical to the success of heterogeneous network as a network architecture.