Small Cells, Big Impact (my version)

I was reading the now few month old announcement from AT&T around small cell strategy here and a few things came to mind. First, the story. AT&T announced back at the end of January that they were planning to roll-out 40,000 small cells by the end of 2015. They have also posted a video on the link above that shows one of the products they are trialing, which although the logo is purposefully out of focus can easily be identified as the Alcatel Lucent 9364 Metro Cell described here. The video also mentions that AT&Ts plan is to roll these out to improve coverage which is where an important distinction in my opinion has to be made.

Small cells can be used for two scenarios. Scenario 1: Not spot. Scenario 2: Hot spot.

Scenario 1 is the easier of the two and the one AT&T has opted for. Regardless of how much an operator can try some areas will always suffer from poor/no coverage. Once these areas are identified a small cell can easily be installed to provide coverage. Small cells due to their femto background are easily deployed, mostly auto-configure and require just a backhaul connection which can be of xDSL nature. Due to their small size they are also usually exempt from the usual painful planning permission process.

Scenario 2 is the more difficult one. Here there is macro coverage, but due to the high amount of traffic the macro network cannot cope. The solution? Either try to use Wi-Fi offload (with the problems described in my previous post here) or use a small cell to absorb some of the traffic. However placing a small cell among large powerful macro cells is not as easy as some people make. At best the range of the small cell is severely interference limited and at worst it acts as a noise source affecting macro network performance. In addition to this UE uplink power can interfere with the small cell when power controlled by a macro cell further away. The solution to these problems is the new industry buzz word "HetNets" (Heterogeneous Networks). But what does Heterogenous mean anyway?

heterogeneous [ˌhɛtərəʊˈdʒiːnɪəs]adj

1. composed of unrelated or differing parts or elements

2. not of the same kind or type

When it comes to mobile telecoms, HetNets is essentially an umbrela term to descibe a number of features (some standardised and some not) that allow nodes of different types (macro cells, small cells etc) to co-exist. To date most of it is theoretical or simulation based so it is too soon to draw any conclusions as to how well HetNets will perform.

Another thing to bear in mind is that HetNets require close co-operation between the small cell and the macro cells which is where the small cells from a femto background might face some problems due to their flat architecture (combined RNC/nodeB) which essentially makes interactions between small cell and macro cell inter-RNC based. Traditional macro cell vendors have recognised this opportunity, which is why most of them are introducing small cells in their product portfolio.

All is not lost though, as vendors from a femto background already have a lot of experience in interference mitigation techniques and also auto configuration which when dealing with a large number of cells is a strong requirement.

It also worth remembering that LTE is based on a flat architecture so any advantages traditional macro vendors have might be short lived.

So, it will be interesting to see which small cells are the eventual winners. Will it be the enhanced femto cells or the miniaturised macro cells?