OnQ Blog

Small Cells and The Art of Reusing the Limits of Physics

There are ways to get around Shannon's Law

Oct 24, 2012

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Do you know Shannon? No, not your friend across the street. But that other guy who has a law by his name. Nice guy, but his law is kind of tough though! I won’t bore you with the technical jargon but Shannon’s law basically defines how much data can be sent over wireless links, considering the amount of spectrum, number of antennas, amount of interference, etc.

Now, with all the advances in technology, we are almost reaching the theoretical limit of capacity, as defined by Shannon’s law. If so, how can we address this goal of being able to meet the insatiable demand for 1000x more data? Well, there are a couple of ways to do it. You could increase the amount of spectrum, or you could also increase the number of antennas, as done with MIMO (multiple input multiple output). But the most attractive way is to utilize small cells.

Small cells, which transmit lower power, can be deployed wherever needed, using the same spectrum over and over. This means data capacity is being added and Shannon’s law is being repeated without ever crossing the limit! Since small cells are cost-effective and easy to deploy, especially compared to other options, it’s no wonder that they are becoming a popular choice of operators worldwide. 

It goes without saying that we will need a lot more of these small cells, of various kinds and shapes, everywhere, resulting in a densely deployed heterogonous mix of cells. With such hyper-dense networks, comes the problem of interference—between the macro cells and small cells as well as among the small cells themselves. So, how do we solve this challenge? Technology to the rescue again!

Interference is never a good thing, and wireless networks in particular are very sensitive to it. So our guiding principle is “if you decrease interference, then you increase system performance.” Well, there really are two simple (but not easy!) ways to reduce interference—avoid it in the first place or cancel the part that can’t be avoided.

One way to avoid interference is to facilitate coordination between cells and share the resources wisely and based on the need. For example, if there is more traffic on small cells than the macro cell, then the small cells gets larger portions of the shared resources, and vice versa. The current releases of LTE Advanced and HSPA+ achieve this through an enhancement called “range expansion” that supports coordination between the macro network and small cells. Future releases of LTE and HSPA will take this further by supporting the coordination among small cells as well. Another new technique being introduced is “opportunistic small cells,” which dynamically turns the small cells “ON” or “OFF” based on the need for capacity. This not only minimizes the interference, but also saves energy. Go green!

Now, regarding cancelling interference, there are HSPA+ devices with Q-ICE (Qualcomm Interference Cancellation and Equalizer) already available in the market today. In LTE Advanced, interference cancellation is a key component in improving the performance of small cells. Many more such techniques are in development.

So, to summarize, hyper-dense networks are an essential part of the 1000x vision. Solutions currently exist to maximize the performance of these networks. And industry leaders such as Qualcomm are continuing to further enhance these solutions.  If you would like to know more, visit our webpage www.qualcomm.com/hetnets

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Prakash Sangam

Director, Technical Marketing

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