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Small Cell an Introduction

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What is a Small Cell:

Small cells are low-powered radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 meters to 1 or 2 kilometers. They are "small" compared to a mobile macrocell, which may have a range of a few tens of kilometers. With mobile operators struggling to support the growth in mobile data traffic, many are using Mobile data offloading as a more efficient use of radio spectrum. Small cells are a vital element to 3G data offloading, and many mobile network operators see small cells as vital to managing LTE Advanced spectrum more efficiently compared to using just macrocells.

Types of Small Cells

Types of Small Cell:

There are four types of small cells i.e. femtocells, picocells, microcells and metrocells – broadly increasing in size from femtocells (the smallest) to metrocells (the largest). All the small cells are based on the femtocell technology.

Advantage of Small Cell

  1. Using femtocells solves residential challenges with a device that employs power and backhaul via the user’s existing resources. It also enables capacity equivalent to a full 3G network sector at very low transmit powers, dramatically increasing battery life of existing phones, without needing to introduce WiFi enabled handsets.
  2. Small cells also make sense in many enterprise contexts, providing a simpler, low-cost alternative to traditional in-building solutions. Enterprise femtocells enable business users to take advantage of high-quality mobile services in the office, while improving coverage, accelerating data rates and significantly reducing capital costs.
  3. Due to their low cost and easy deployment, small cells are also a viable and cost-effective alternative to traditional macro networks in remote rural areas with little or no terrestrial network infrastructure . Likewise in metro hotspots, operators can deploy small cells to improve local coverage, increase capacity and offload macro network traffic.
posted Jul 31 by Samardeep Acharya

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LTE Femtocell Architecture

  1. UE interfaces with a Home eNodeB (HeNB) over air interface. The HeNB is a small eNodeB providing wireless LTE coverage in the customer’s home.
  2. The HeNB interfaces to the mobile network operator (MNO) over a broadband network by interfacing with a broadband access gateway (broadband modem). The mobile operator’s core network obtains access to the HeNB connected to a broadband access device via a security gateway. The security gateway is used to protect the core network against attacks.
  3. In Some cases security gateway resides in Home eNodeB Gateway HeNB GW which is responsible for aggregating traffic from a large number of HeNBs and interfacing with the mobile operator’s Evolved Packet Core (EPC) network.
  4. For the core network HeNB GW bahaves like a regular eNodeB.
  5. The S1-MME interface carries signalling using the LTE S1-MME interface and S1-U carries the data to the GSW.
  6. In the alternate architecture S1-U can directly connect eNB to SGW whereas signalling is passed via the HeNB-GW.
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The femtocell appears to the standard 3G phone as just another cellsite from the host mobile operator. MSC and SGSN communicate to the femtocell gateway in the same way as for other mobile calls. Therefore, all services including phone numbers, call diversion, voicemail etc. operate in exactly the same way as previous.
The connection between the femtocell and the femtocell gateway uses secure IP encryption (IPsec), which avoids interception and there is also authentication of the femtocell itself to ensure it is a valid access point.

Femtocell Architecture Overview

Inside the femtocell are the complete workings of a mobile phone basestation. Additional functions are also included such as some of the RNC (Radio Network Controller) processing, which would normally reside at the mobile switching centre. Some femtocells also include core network element so that data sessions can be managed locally without needing to flow back through the operators switching centres.

The extra capabilities of a femtocell demand it to be self-installing and self-configuring. This requires considerable extra software which scans the environment to determine the available frequencies, power level and/or scrambling codes to be used. This is a continuous process to adapt to changing radio conditions, for example if the french windows are opened in a room containing the femtocell.

Within the operators network, femtocell gateways aggregate large numbers of femtocell connections (typically 100,000 to 300,000) which are first securely connected through high capacity IP security firewalls.

Enterprise Small Cells
The same technology and architecture is also used for small to medium businesses. Typically the small cells have higher capacity and slightly higher RF power to give a larger range. Some enterprise small cell vendors have developed solutions where small cells co-operate in clusters to provide seamless service. For larger enterprises, a small cell controller may be used to provide additional local services including direct connection to the enterprise network.

Metrocells and Rural Small Cells
Public areas, both inside and out, may use specially designed metrocells which are also based on the same architecture. These can also take advantage of the same small cell/femtocell gateway, sharing its use between residential, enterprise and metrocell installations. These products must be weather proof and vandal proof, operating in sometimes harsh unsupervised environments with wide temperature fluctuations. Metrocells are installed by the network operator themselves, and a broadband IP connection (called the backhaul) is also required.

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