Small cells are currently the big buzz word in the wireless industry. Many of the major wireless operators in the US including AT&T, Verizon Wireless, and Sprint have committed to use small cells throughout their networks. In fact AT&T has committed to deploy 40,000 small cells by the end of 2015, which reveals that wireless operators are serious about this technology. This begs the question what are small cells and why are they needed?
Macro vs Small Cell in New York City
Small cells as its name suggests are smaller cellular base stations. By smaller this includes physical size, RF coverage area, and cost. Another term which is used in the same context as small cells is distrusted antenna systems or DAS. A DAS is made up of a number of small antennas nodes which then connect back via fiber to a cellular base station. With a small cell all the intelligence is housed within the device, while a DAS node is just a dumb transmitter and receiver and the intelligence is housed at remote location. DAS technology has been in the marketplace for a couple of years and has been successfully deployed in both outdoor and indoor environments. Small cells are brand new to the market, and they are gaining popularly as they should be cheaper and simpler to deploy than a DAS.
The need for small cells is being driven by the surge in mobile data consumption. The popularity of smartphones and tablets means that people are consuming large amounts of data on their mobile devices. People are not just using their mobiles devices to surf the web, but they are streaming videos and uploading pictures using applications such as Netflix, YouTube, and Instagram. While LTE was designed to support these mobile applications, the usage is growing quicker than improvements in wireless efficiency which is making networks congested.
To better understand the situation it is important to look at the capacity of an LTE base station which is called an eNB. LTE is similar in technology to the 802.11N Wi-Fi standard. Both use similar modulation schemes and data transmissions technologies. Many LTE networks in the US use 10MHz LTE carriers using a technology called frequency division duplex, or FDD. This means that 10MHz of spectrum is used in separate downlink and uplink channels. This allows for full duplex communication and means the total amount of spectrum that is used is 20MHz. Wi-Fi along with some forms of LTE use a technology called time division duplex or TDD. With this technology the downlink and uplink data is interleaved in the time domain using the same channel.
The standard Wi-Fi channel is 20MHz wide which uses the same amount of spectrum as a 10MHz FDD LTE carrier. While a normal Wi-Fi access point might only serve a few people, an LTE base station has to support hundreds of users in the same bandwidth. An LTE base station is really a high tech Wi-Fi router with advanced resource and user scheduling technology. If a hundred people tried streaming videos from the same Wi-Fi router the performance would be mediocre, and the same holds true with LTE. To improve performance a simple solution is to decrease the number of people using the connection. While this might seem obvious this is one way cellular operations ensure that their networks do not become overloaded and congested.
For the last twenty years the number of cell sites has been growing while the coverage area of each cell has been shrinking. The concept is relatively simple and is known as cell splitting. Instead of having one large cell site which serves an area, if two smaller cell sites are used which serve the same geographical area there will be close to double the capacity. This concept has been successfully used for a long time, but today there is so much usage in major cities that a cell site is need on every block. It is impractical due to cost and space requirements to put conventional cellular base stations on every block. This is why small cells are being utilized. They allow for a denser deployment as they can be mounted on light poles and sides of buildings instead on towers or rooftops. Instead of having one conventional cell site every four blocks, now it is possible to have a small cell on every block greatly increasing capacity.
Give that small cells are a new technology there are still many questions that still need to be answered. Will small cells be economic viable? Will small cells be reliable? The big question remains whether small cells are the solution to the explosive mobile data growth that is occurring. Regardless of the success of small cells, the increase in mobile data consumption will force wireless operators to come up with innovative ways to meet mobile data demands.