Femtocells For 4G Cellular Systems Computer Science Essay

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The ever-increasing growth of user demand and the limitations of 3rd generation of wireless mobile communication have prompted the need for femtocells for 4G cellular system. Femtocells are basically small, low power wireless access points, designed typically for use in home or office. Femtocells are provided by a mobile network operator (MNO) to enterprise customers or its residential end-users and makes use of a broadband connection (DSL/Cable) to connect to the service provider's network. As a result of using femtocells, wider cellular coverage can be established without having to improve the cellular carrier infrastructure (cell towers etc).Femtocell technology helps provide high speed signal with high quality that improves voice calls and data download rate while still utilizing the benefits of licensed spectrum. Advantages include an improved capacity, wider coverage and special tariffs for end-users and the need for only a single phone, contact list for enterprise users. The rising need for implementing femtocells in 4G cellular system is to enable carriers to optimize spectrum use, maximize network coverage whilst reducing the subscriber's spectrum. This paper provides an idea of femtocells being used in the current standards such as GSM, CDMA 2000, TD-SDMA and the possibility of integrating it into technologies in the 4th generation such as WIMAX and LTE Networks.

Femtocells are devices that are used to solve the problem of poor cell phone coverage within buildings. It is basically an indoor base station that can be placed in your household or small offices wherein the coverage is defined by the distance between the box to your mobile handset, and also on the number of floors and walls the signal would have to penetrate. This does not cost anything to the carrier as the power and backhaul are provided by the user itself. As a result of using Femtocell, the user gets full coverage at home. The most important benefit for the customer is definitely the full time coverage that is available. However, Femtocells can only be operated by those companies that have an appropriate licence and hence it is only through cellcos that these boxes can be supplied. Femtocells help the operators to strengthen their position in home market.


Femtocells off load Macro network

Achieves cell splitting gains

Less expensive alternative in improving the coverage

Generate opportunities for home and other value added services.



These types of routers are basically small and compact and help in creating an internet Hotspot for up to 5 users in Wi-Fi. MIFI Routers gives 3G speeds and has got the advantage of allowing the customer to carry the WI-Fi Hotspot with them.


Femtocells are 3G access points that connect via the consumer's broadband IP/DSL connection to the core network of the operator and provides a home phone solution to the wireless service providers. They offer lower or flat-rate tariffs for home made calls since they utilise power and consumer-supplied backhaul. The macro-cellular network will be offloaded that allows subscribers to be added to the network without the need of purchasing additional macro-cellular equipments. A femtocell ensures excellent cell coverage and voice quality to the consumers and provides a cost effective way of making calls at home from their preferred mobile devices


Femtocells are cellular access points that form only part of the femtocell system. The remaining items that are needed include:

Femtocell Itself


Internet link

Internet Router

Service provider core network gateway


Femtocells make use of a low-power integrated antenna that enables voice and data cellular signals to be transmitted within the home or small office. They make use of the broadband internet connection to connect to the mobile operator's network.


Femtocell Network Architecture is defined to provide maximum scalability and flexibility so as to easily incorporate the deployment of femtocells into existing structures. This deployment is achieved on an ad-hoc basis.


Femtocell must be located in the users building

Low cost, accessible backhaul

Gateway that enables traffic from femtocells that are carried via internet so that they can access the core network of the operator.

3G Femtocell Network Architecture

3GPP defines three main elements to the network architecture which are:

Home NodeB: Standard Node B and radio resource management functions

HNB Gateway: Core network entry point

Iu-h Interface: Link/Interface that connects HNB and HNB-GW


Femtocell Installation needs to be totally plug and play, and should not have any intervention from the users part and this involves a considerable amount of intelligence.


a. Femtocell Self Configuration: The initial parameters such as channel, power, neighbour list etc are to be properly selected for the operation to start.

b. Femtocell Self Optimization: The environment is monitored to check for any changes in the channel and resources.

c. Femtocell Self Healing: Resolve problems that can possibly occur after set-up.


The customer needs to plug the femtocell into the power and connect it to the Internet connection to provide the backhaul connection. This is followed by the registration of the femtocell within the network. On successful registration of the femtocell, the latest software check would be undertaken. The next step is the configuration of radio interference parameters which has 2 main elements to this:

Primary Femtocell Configuration Information: Scrambling Codes and RF Channel Information

Network Femtocell Configuration: RF Parameters,neighbour list,Physical cell id and service area code and information


1. Moblie Operator benefits

a. Minimum network costs

b. Capacity Relief for macro layer

c. Improved home coverage

d. Stickiness increase and churn reduction

2. End User benefits

a. Improved in-home coverage

b. Increased talk time

c. High data rates

d. Highest quality voice



3G CDMA Femtocell Standard makes use of SIP/IMS core network in a very simple manner but effectively to pass through most of the signalling messages to 2G/3G core network. It makes use of the SIP based protocol for call control and core network registration procedures. This means that the current 3G features and services like SMS text messaging and location are present in the same way. It helps the operator to enable wider deployment of the IMS network which is used as the core network for telephony services, both wired and wireless.


1. All existing mobile services are available which include emergency calls location services, E911 and SMS text messaging.

2. Femtocells have to be registered themselves and authenticated on the IMS HSS server which allows it to control access to the network.

3. Femtocell access points directly handle the access control of individual users.


LTE (Long Term Evolution) is the next generation 3GPP standard born out of the GSM family of cellular technology for mobile networks.LTE Networks for mobile are based on OFDMA( Orthogonal frequency-division multiple access. This follows the simple concept of more bandwidth/user with fewer users in a cell. Moreover, the user device has the benefit of a smaller cell radius and is closer to the radio which reduces signal degradation and increases throughput. LTE Femtocell deployment can be performed in 2 ways: One way is to directly interface the HeNB with the Serving Gateway (SGW) and Mobility Management Entity(MME) within the LTE Evolved Packet Core(EPC).The other way is to interface HeNB through an HeNB Gateway against the femtocell architecture standard.

The most critical step in LTE Femtocell deployments is to develop Self Organizing Network (SON) techniques, algorithms and standards. Self-configuration is the basic requirement. The base station needs to be configured by itself based on location, core network and surrounding cells. For this, operators can introduce the 3G femtocell market developments into LTE. Beyond Self-configuration, LTE small cells need to be self-optimizing which is the ability of the LTE femtocells to modify their configuration depending on the surrounding cells, loading of the cell and other environmental considerations. The final and perhaps the greatest challenge for SON is its standardization.

The best metric for these types of femtocells is their deployments. However, regardless of the type of strategy used in the initial deployment, the user base can enjoy the LTE femtocell performance boost.LTE femtocells however face the backhaul problem which can be divided into two: residential backhaul scenario and the metro backhaul scenario. Fiber to the Home (FTTH) and Fiber to the Curb(FTTC) proliferation is required for successful implementation of in building or residential LTE femtocells. The LTE outdoor femtocells make use of the fixed WiMax technology for the metro backhaul service.

LTE femtocells play a key role in the metro and enterprise areas of deployment. They provide a rich data experience indoors and take the mobile data load off the macro network.LTE femtocells lower the cost of delivery and backhaul costs. Self Optimising Networks (SONS) used in LTE femtocells for network auto-configuration and to add self healing capabilities to them. These type of femtocells serves as a key weapon for mobile operators due to the advantages of the targeted, inside-out deployment including the staged investment involved and improved quality of experience and mobile broadband performance. The use of small cells provides vast opportunities for SON specialists, software, backhaul optimization providers and silicon vendors.


Plug-n-play operation

Enterprise requirements

Coverage requirements


Device management



Dynamic interference management


WiMAX is based on IEEE 802.16 standard and gives a strong mobility platform for high-speed broadband services in mobile .However, WiMAX networks suffer from high cost of macro network deployment and poor coverage.

WiMAX Femtocell is a system that consists of customer premise equipment (CPE) also known as the WiMAX Femtocell Access Point (WFAP) and WiMAX enabled Mobile Station (MS) or Subscriber station(SS)inside buildings. It's a low power, small sized indoor base station that connects to the WiMAX core network via a broadband connection that acts as a backhaul wherein the core network services are provided by the WiMAX core network.

Required Features of WiMAX Femtocell

SPECTRUM: Operation is only possible over licensed spectrum

TRANSPORT: Transport network of subscribers' DSL/FTTH or cable-based broadband connection is to be used by WFAP

FORM FACTOR: WFAP can be integrated or stand alone with cable modems or DSL.

POWER OUTPUT: Very low power outputs are required less than 2.4 GHz.

LOCAL BREAKOUT: WFAP should have the capability of routing incoming or outgoing traffic through the ISP network to the destination.

USER CAPACITY: WFAP must have the capability to support a minimum of 5-6 subscribers.

DEPLOYMENT SUPPORT: WFAP should have the capability to adjust automatically to reduce the interference.

HANDOVER: Handovers should be allowed between adjacent WFAPs or between WFAP and WiMAX.

SECURITY: A secure channel of communication must be used.

AIR INTERFACE: WFAP should provide a minimum of 10 meters of coverage area within a residential setup.

LOCATION INFORMATION: For location based services and emergency services, WFAP must support location identification procedures with core network.

ACCOUNTING: WFAP should make sure that it is identified by the core network.

QUALITY OF SERVICE: WFAP must support marking of incoming or outgoing packets according to the appropriate DSCP code configured by a service provider.

NETWORK SYNCHRONISATION: WFAP must be able to synchronise with the external network for providing services such as soft handovers and multicast-broadcast (MCBCS) services.

MANAGEABILITY: WFAP must implement TR069 protocol that allows the operator to remotely manage them.


Lower cost for transport network

Zero cost for cell site acquisition

No CAPEX/OPEX for setting up backhaul networks.

Increased network coverage

Improved customer satisfaction

Macro cell sites are offloaded

Reduced service cost

Compelling user experience


NETWORK ARCHITECTURE: WiMAX Femtocells must be autonomous and powerful depending on the kind of architecture that is adopted by the femtocells.The network architecture must also consider infrastructure support during handover for seamless mobility.

INTERFERENCE MANAGEMENT: The accumulated interference is a serious issue with increase in the number of Femto-APs. Several interference mitigation strategies for example fractional frequency reuse (FFR) can be used to guarantee an almost certain 100 percent coverage.

SYNCHRONIZATION: Synchronization is essential for successful handover between base stations and for interference management using TDD in outdoor systems. The requirement of synchronization for WiMAX is however not as much as required in 2G or 3G technology.

SECURITY AND PERFORMANCE: Femto-APs make use of local ISP networks that are difficult to protect. A possible solution to this is to encrypt IP packets. Agreements in service level and collaboration among landline and cellular operators are essential to ensure user and system performance.

SELF-ORGANIZATION & AUTONOMOUS OPERATION: Higher level of self-organisation is required due to the flat network architecture. Even higher autonomy is essential because femtocells must be able to operate without any user intervention.Another important requirement is the possibility of having updates for firmware and software.


a. FEMTOCELL SPECTRUM ISSUES: For large amounts of data, radio spectrum is particularly scarce. Hence it requires careful attention to plan the available spectrum.

b.FEMTOCELL REGULATORY ISSUES: Femtocells require a regulatory approval to operate in a licensed/regulatory spectrum. These regulations are to be changed for different countries. In certain cases, International agreement should be required.

c. FEMTOCELL INTERFERENCE ISSUES: It is necessary to ensure that the femtocells operate within the normal spectrum shared among different cellular base stations in order to avoid degradation in the level of service. This can be achieved by using cognitive radio technology, interference tolerant systems and proper spectrum planning.

The main interference scenarios would be:

INTERFERENCE CAUSED BY FEMTOCELLS WITH BASE STATIONS ON THE SAME FREQUENCY: When femtocells operate on the same channel as the base stations, interference may be caused that reduce the overall network performance.

INTERFERENCE CAUSED BY BASE STATIONS WITH FEMTOCELLS ON THE SAME FREQUENCY: When a macro network operates on the same channel as the femtocells, interference results.

INTERFERENCE BETWEEN CLOSELY SPACED FEMTOCELLS: If femtocells are installed close to one another, background noise results that reduce the sensitivity of each of the femtocell.


This cause an increase in the overall noise level received by the base station.

Solutions to Interference Problems

ADAPTIVE PILOT POWER CONTROL: Femtocell detects surrounding cell signals and automatically adjusts its transmitter power while still maintaining its coverage area.

DYNAMIC FEMTOCELL RECEIVER GAIN MANAGEMENT: A satisfactory form of automatic gain/attenuation can be installed which enables mobile operation without any increase in the transmitted output power than which is absolutely necessary. This minimizes an otherwise increase in noise and interference.

MOBILE PHONE UPLINK POWER CAPPING: This scheme involves capping or limiting the maximum mobile power output in a femtocell environment thus ensuring that the phone would hand off to macro network before the transmitter power adds noise to the network.

EXTENDED FEMTOCELL RECEIVER DYNAMIC RANGE: The receiver needs to have a high dynamic range in order to be able to operate in the presence of very strong signals.



USER PRIVACY: It is necessary to give security for IP communications and detect any data monitoring.

DENIAL OF SERVICE AND SERVICE AVAILABILTY: The network can be overloaded with denial of service attacks which can result in service degradation or total prevention of legitimate users from accessing the cellular network

FRAUD AND SERVICE THEFT: Unauthorised users can connect to the femtocell which can result in its use in an unauthorised fashion leading to significant adverse publicity not wanted by the operator.


The main areas of security vulnerabilities are:

WIRELESS LINK INTO THE FEMTOCELL: It is possible for wireless transmissions externally to gain access to the femtocell.

THE FEMTOCELL ITSELF: Hackers can gain access into the femtocell and use it for their use.

INTERNET LINK: Backhaul link between femtocell and femtocell gateway into the core network of the service provider.


USE OF IPsec: To ensure femtocell security across the internet, IPSec/IP Security is used.

FEMTOCELL SECURE AUTHENTICATION: To ensure the connection of valid femtocells to the core network, service provider or operator requires authentication.

WIRELESS LINK SECURITY: Wireless link requires femtocell security to ensure that no unauthorised users connect or take over the femtocell. The techniques involved include making sure that the femtocell coverage area will not exceed the physical area of femtocell use.

EAP (Extensible Authentication Protocol): This type of protocol is made use of in a number of wireless networks for providing femtocell security.


Health and safety issues are of concern due to the dangers of RF radiation. However, femtocells emit less power levels and do not cause a great concern.


Femtocells are now an important part of the development strategy for mobile telecommunications operators. Femtocells not only provide users with advantages such as improved performance within the home and small offices but also provide additional services and the promise of reduced costs. Also, a change in convergence is offered where in a single phone can be used for landline as well as roaming. They provide a cost effective scheme for the operators along with improved coverage and also extra revenue by means of additional services. The use of femtocells would definitely be a mainstay in cellular telecommunications roadmap for the future. Predictions on the femtocell business are bullish, with the expectation of millions of boxes to be installed over the next few years worldwide. So, it will be interesting to look out for the service models that are expected to would emerge to make that a reality.