Femtocell
Encyclopedia
In telecommunications, a femtocell is a small cellular base station
, typically designed for use in a home or small business. It connects to the service provider’s network via broadband (such as DSL
or cable
); current designs typically support 2 to 4 active mobile phones in a residential setting, and 8 to 16 active mobile phones in enterprise settings. A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. Although much attention is focused on WCDMA
, the concept is applicable to all standards, including GSM, CDMA2000
, TD-SCDMA
, WiMAX
and LTE solutions.
For a mobile operator, the attractions of a femtocell are improvements to both coverage and capacity, especially indoors. Consumers benefit from improved coverage and potentially better voice quality and battery life. Depending on the carrier they may also be offered more attractive tariffs e.g. discounted calls from home.
Femtocells are an alternative way to deliver the benefits of fixed-mobile convergence (FMC). The distinction is that most FMC architectures require a new (dual-mode) handset which works with existing unlicensed spectrum home/enterprise wireless access point
s, while a femtocell-based deployment will work with existing handsets but requires installation of a new access point that uses licensed spectrum.
Many operators have launched femtocell service including Vodafone
, AT&T
, Sprint Nextel
, Verizon and Mobile TeleSystems
.
In 3GPP
terminology, a Home NodeB
(HNB) is a 3G femtocell. A Home eNodeB (HeNB) is an LTE
femtocell.
Typically the range of a microcell
is less than two kilometers wide, a picocell
is 200 meters or less, and a femtocell is on the order of 10 meters, although AT&T calls its product, with a range of 40 feet (12.2 m), a "microcell".
(MNO) to its residential or enterprise customers. A femtocell is typically the size of a residential gateway
or smaller, and connects to the user's broadband
line. Integrated femtocells (which include both a DSL router and femtocell) also exist. Once plugged in, the femtocell connects to the MNO's mobile network, and provides extra coverage. From a user's perspective, it is plug and play, there is no specific installation or technical knowledge required — anyone can install a femtocell at home.
In most cases the user must then declare which mobile phone numbers are allowed to connect to his/her femtocell, usually via a web interface provided by the MNO. This only needs to be done once. When these mobile phones arrive under coverage of the femtocell, they switch over from the macrocell
(outdoor) to the femtocell automatically. Most MNOs provide a way for the user to know this has happened, for example by having a different network name appear on the mobile phone. All communications will then automatically go through the femtocell. When the user leaves the femtocell coverage (whether in a call or not) area, his phone hands over seamlessly to the macro network.
Femtocells require specific hardware, so existing WiFi or DSL routers cannot be upgraded to a femtocell.
Once installed in a specific location, most femtocells have protection mechanisms so that a location change will be reported to the MNO. Whether the MNO allows femtocells to operate in a different location depends on the MNO's policy. International location change of a femtocell is not permitted because the femtocell transmits licensed frequencies which belong to different network operators in different countries.
, LTE
and WiMAX
. These all broadly conform to an architecture with three major elements:
The key interface in these architectures is that between the femtocell access points and the femtocell gateway. Standardisation enables a wider choice of femtocell products to be used with any gateway, increasing competitive pressure and driving costs down. For the common WCDMA femtocells, this is defined as the Iuh interface. In the Iuh architecture, the femtocell gateway sits between the femtocell and the core network and performs the necessary translations to ensure the femtocells appear as a radio network controller to existing MSC’s. Each femtocell talks to the femtocell gateway and femtocell gateways talk to the CNE (MSC for CS calls, SGSN for PS calls). This model was proposed by 3GPP and the Femto Forum. New protocols (HNBAP and RUA) have been derived; HNBAP is used for the control signaling between the HNB and HNB-GW while RUA is a lightweight mechanism to replace the SCCP and M3UA protocols in the RNC; its primary function is transparent transfer of RANAP messages.
In March 2010 the Femto Forum and ETSI conducted the first Plugfest to progress interoperability of the Iuh standard.
The CDMA2000 standard released in March 2010 differs slightly by adopting the SIP protocol to set up a connection between the femtocell and a femtocell convergence server (FCS). Voice calls are routed through the FCS which emulates a Mobile Switching Centre (MSC). SIP is not required or used by the mobile device itself. In the SIP architecture, the femtocell connects to a core network of the mobile operator that is based on the SIP/IMS architecture. This is achieved by having the femtocells behave toward the SIP/IMS network like a SIP/IMS client by converting the circuit-switched 3G signaling to SIP/IMS signaling, and by transporting the voice traffic over RTP as defined in the IETF standards.
Airave in 2007.
Femtocells are also under development or commercially available for GSM, TD-SCDMA
, WiMAX
and LTE
.
The H(e)NB functionality and interfaces are basically the same as for regular HSPA or LTE base stations except few additional functions. The differences mostly to support differences in access control to support closed access for residential deployment or open access for enterprise deployment, as well as handover functionality for active subscribers and cell selection procedures for idle subscribers. For LTE additional functionality was added in 3GPP Release 9 which is summarized in.
Femtocells incorporate interference mitigation techniques—detecting macrocells, adjusting power and scrambling codes accordingly. Ralph de la Vega, AT&T President, reported in June 2011 they recommended against using femtocells where signal strength was middle or strong because of interference problems they discovered after widescale deployment. This differs from previous opinions expressed by AT&T and others.
A good example is the comments made by Gordon Mansfield, Executive Director of RAN Delivery, AT&T, speaking at the Femtozone at CTIA March 2010:
The Femto Forum has some extensive reports on this subject, which have been produced together with 3GPP and 3GPP2.
To quote from the Summary Paper — Summary of Findings:
requirements.
(or 999
, 112
, etc.
) emergency service, as is the case for VoIP phone providers in some jurisdictions. This service must meet the same requirements for availability as current wired telephone systems. There are several ways to achieve this, such as alternative power sources or fall-back to existing telephone infrastructure.
or ADSL home backhaul connection, an Access Point Base Station must either share the backhaul bandwidth with other services, such as Internet browsing, gaming consoles, set-top boxes and triple-play
equipment in general, or alternatively directly replace these functions within an integrated unit. In shared-bandwidth approaches, which are the majority of designs currently being developed, the effect on Quality of Service
may be an issue.
The uptake of femtocell services will depend on the reliability and quality of both the cellular operator’s network and the third-party broadband connection, and the broadband connection's subscriber understanding the concept of bandwidth utilization by different applications a subscriber may use. When things go wrong, subscribers will turn to cellular operators for support even if the root cause of the problem lies with the broadband connection to the home or workplace. Hence, the effects of any third-party ISP broadband network issues or traffic management policies need to be very closely monitored and the ramifications quickly communicated to subscribers.
A key issue recently identified is active Traffic shaping
by many ISPs on the underlying transport protocol IPSec
. UK-based femtocell authority Epitiro have recently provided significant publicly available research and insight into many of these IP-focused QoS issues. A femtocell deployment guide from Epitiro is available for download here.
(FCC) / Ofcom
spectrum mask
requirements, femtocells must generate the radio frequency
signal with a high degree of precision. To do this over a long period of time is a major technical challenge. The solution to this problem is to use an external, accurate signal to constantly calibrate the oscillator to ensure it maintains its accuracy. This is not simple (broadband backhaul introduces issues of network jitter/wander and recovered clock accuracy), but technologies such as the IEEE 1588 time synchronisation standard may address the issue. Also, Network Time Protocol
(NTP) is being pursued by some developers as a possible solution to provide frequency stability. Conventional (macrocell) base stations often use GPS timing for synchronization and this could be used, although there are concerns on cost and the difficulty of ensuring good GPS coverage.
Standards bodies have recognized the challenge of this and the implications on device cost. For example, 3GPP has relaxed the 50ppb parts-per-billion
precision to 100ppb for indoor base stations in Release 6 and a further loosening to 250ppb for "Home NodeB" in Release 8.
Femtocell shipments are estimated to have reached almost 2 million at the end of 2010. Research firm Berg Insight estimates that the shipments will grow to 12 million units worldwide in 2014.
Within the United States, the most significant deployments up to December 2010 are by Sprint Nextel
, Verizon Wireless
and AT&T Wireless
. Sprint started in the third quarter of 2007 as a limited rollout (Denver and Indianapolis
) of a home-based femtocell built by Samsung Electronics called the Sprint Airave that works with any Sprint handset. From 17 August 2008, the Airave was rolled out on a nationwide basis. Other operators in the United States have followed suit. In January 2009 Verizon rolled out its Wireless Network Extender, based on the same design as the Sprint/Samsung system. In late March 2010, AT&T announced nationwide roll-out of its 3G MicroCell, which commenced in April. The equipment is made by Cisco Systems
and ip.access
, and was the first 3G femtocell in US, supporting both voice and data HSPA
. Both Sprint and Verizon upgraded to 3G CDMA femtocells during 2010, with capacity for more concurrent calls and much higher data rates.
In Asia, several service providers have rolled out Femtocell networks. In Japan, SoftBank Mobile launched its residential 3G femtocell service in January 2009 with devices provided by Ubiquisys. In the same year the operator launched a project to deploy femtocells to deliver outdoor services in rural environments where existing coverage is limited. In May 2010, SoftBank Mobile launched the first free femtocell offer, providing open access femtocells free of charge to its residential and business customers. In Singapore, Starhub rolled out its first nation-wide commercial 3G Femtocell services with devices provided by Huawei Technologies, though the uptake is low, while Singtel's offering is targeted at small medium enterprises. In 2009, China Unicom announced its own Femtocell network. NTT DoCoMo in Japan launched their own Femtocell service on the 10th November 2009.
In July 2009 Vodafone released the first Femtocell network in Europe, the Vodafone Access Gateway provided by Alcatel-Lucent. This was rebranded as SureSignal in January 2010, after which Vodafone also launched service in Spain, Greece, New Zealand, Italy and Ireland. Other operators in Europe have followed since then, with SFR
in France with femtocells provided by Ubiquisys and Optimus Telecomunicações, S.A.
in Portugal.
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...
, typically designed for use in a home or small business. It connects to the service provider’s network via broadband (such as DSL
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
or cable
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
); current designs typically support 2 to 4 active mobile phones in a residential setting, and 8 to 16 active mobile phones in enterprise settings. A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. Although much attention is focused on WCDMA
W-CDMA (UMTS)
W-CDMA , UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks. It is the basis of Japan's NTT DoCoMo's FOMA service and the most-commonly used member of the UMTS family and sometimes used as a synonym for UMTS...
, the concept is applicable to all standards, including GSM, CDMA2000
CDMA2000
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...
, TD-SCDMA
TD-SCDMA
Time Division Synchronous Code Division Multiple Access or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate , is an air interface found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA. Together with TD-CDMA, it is also known as UMTS-TDD or IMT 2000 Time-Division .The term...
, WiMAX
WiMAX
WiMAX is a communication technology for wirelessly delivering high-speed Internet service to large geographical areas. The 2005 WiMAX revision provided bit rates up to 40 Mbit/s with the 2011 update up to 1 Gbit/s for fixed stations...
and LTE solutions.
For a mobile operator, the attractions of a femtocell are improvements to both coverage and capacity, especially indoors. Consumers benefit from improved coverage and potentially better voice quality and battery life. Depending on the carrier they may also be offered more attractive tariffs e.g. discounted calls from home.
Femtocells are an alternative way to deliver the benefits of fixed-mobile convergence (FMC). The distinction is that most FMC architectures require a new (dual-mode) handset which works with existing unlicensed spectrum home/enterprise wireless access point
Wireless access point
In computer networking, a wireless access point is a device that allows wireless devices to connect to a wired network using Wi-Fi, Bluetooth or related standards...
s, while a femtocell-based deployment will work with existing handsets but requires installation of a new access point that uses licensed spectrum.
Many operators have launched femtocell service including Vodafone
Vodafone
Vodafone Group Plc is a global telecommunications company headquartered in London, United Kingdom. It is the world's largest mobile telecommunications company measured by revenues and the world's second-largest measured by subscribers , with around 341 million proportionate subscribers as of...
, AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
, Sprint Nextel
Sprint Nextel
Sprint Nextel Corporation is an American telecommunications company based in Overland Park, Kansas. The company owns and operates Sprint, the third largest wireless telecommunications network in the United States, with 53.4 million customers, behind Verizon Wireless and AT&T Mobility...
, Verizon and Mobile TeleSystems
Mobile TeleSystems
MTS is the largest mobile operator in Russia and CIS with over 102,4 million subscribers as of 31 December 2009.Having started in the Moscow license zone in 1994, МТS in 1997 received licenses for further areas and began expansion, later entering other countries of the CIS...
.
In 3GPP
3GPP
The 3rd Generation Partnership Project is a collaboration between groups of telecommunications associations, known as the Organizational Partners...
terminology, a Home NodeB
Home Node B
A Home Node B, or HNB, is the 3GPP's term for a 3G femtocell.A Node B is an element of a 3G macro Radio Access Network, or RAN. A femtocell performs many of the function of a Node B, but is optimized for deployment in the home.-Standard:...
(HNB) is a 3G femtocell. A Home eNodeB (HeNB) is an LTE
3GPP Long Term Evolution
3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
femtocell.
Typically the range of a microcell
Microcell
A microcell is a cell in a mobile phone network served by a low power cellular base station , covering a limited area such as a mall, a hotel, or a transportation hub. A microcell is usually larger than a picocell, though the distinction is not always clear...
is less than two kilometers wide, a picocell
Picocell
A picocell is a small cellular basestation typically covering a small area, such as in-building , or more recently in-aircraft...
is 200 meters or less, and a femtocell is on the order of 10 meters, although AT&T calls its product, with a range of 40 feet (12.2 m), a "microcell".
Operating mode
Femtocells are sold by a Mobile Network OperatorMobile network operator
A mobile network operator , also known as mobile phone operator , carrier service provider , wireless service provider, wireless carrier, or cellular company, or mobile network carrier is a telephone company that provides services for mobile phone subscribers.One essential...
(MNO) to its residential or enterprise customers. A femtocell is typically the size of a residential gateway
Residential gateway
A residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
or smaller, and connects to the user's broadband
Broadband
The term broadband refers to a telecommunications signal or device of greater bandwidth, in some sense, than another standard or usual signal or device . Different criteria for "broad" have been applied in different contexts and at different times...
line. Integrated femtocells (which include both a DSL router and femtocell) also exist. Once plugged in, the femtocell connects to the MNO's mobile network, and provides extra coverage. From a user's perspective, it is plug and play, there is no specific installation or technical knowledge required — anyone can install a femtocell at home.
In most cases the user must then declare which mobile phone numbers are allowed to connect to his/her femtocell, usually via a web interface provided by the MNO. This only needs to be done once. When these mobile phones arrive under coverage of the femtocell, they switch over from the macrocell
Macrocell
A macrocell is a cell in a mobile phone network that provides radio coverage served by a high power cellular base station . Generally, macrocells provide coverage larger than microcell. The antennas for macrocells are mounted on ground-based masts, rooftops and other existing structures, at a...
(outdoor) to the femtocell automatically. Most MNOs provide a way for the user to know this has happened, for example by having a different network name appear on the mobile phone. All communications will then automatically go through the femtocell. When the user leaves the femtocell coverage (whether in a call or not) area, his phone hands over seamlessly to the macro network.
Femtocells require specific hardware, so existing WiFi or DSL routers cannot be upgraded to a femtocell.
Once installed in a specific location, most femtocells have protection mechanisms so that a location change will be reported to the MNO. Whether the MNO allows femtocells to operate in a different location depends on the MNO's policy. International location change of a femtocell is not permitted because the femtocell transmits licensed frequencies which belong to different network operators in different countries.
Benefits for users
The main benefits for an end-user are the following:- "5 bar" coverage when there is no existing signal or poor coverage
- Higher mobile data capacity, which is important if the end-user makes use of mobile data on their mobile phone (may not be relevant to a large number of subscribers who instead use WiFiWIFIWIFI is a radio station broadcasting a brokered format. Licensed to Florence, New Jersey, USA, the station is currently operated by Florence Broadcasting Partners, LLC.This station was previously owned by Real Life Broadcasting...
where femtocell is located) - Depending on the pricing policy of the MNO, special tariffs at home can be applied for calls placed under femtocell coverage
- For enterprise users, having femtos instead of DECT phones enables them to have a single phone, so a single contact list etc.
Standardised architectures
The standards bodies have published formal specifications for femtocells for the most popular technologies, namely WCDMA, CDMA2000CDMA2000
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...
, LTE
3GPP Long Term Evolution
3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
and WiMAX
WiMAX
WiMAX is a communication technology for wirelessly delivering high-speed Internet service to large geographical areas. The 2005 WiMAX revision provided bit rates up to 40 Mbit/s with the 2011 update up to 1 Gbit/s for fixed stations...
. These all broadly conform to an architecture with three major elements:
- The femtocell access points themselves, which embody greater network functionality than found in macrocell basestations, such as the radio resource control functions. This allows much greater autonomy within the femtocell, enabling self-configuration and self-optimisation. Femtocells are connected using broadband IP, such as DSL or cable modems, to the network operator's core switching centres.
- The femtocell gateway, comprising a security gateway that terminates large numbers of encrypted IP data connections from hundreds of thousands of femtocells, and a signalling gateway which aggregates and validates the signalling traffic, authenticates each femtocell and interfaces with the mobile network core switches using standard protocols, such as Iu.
- The management and operational system which allows software updates and diagnostic checks to be administered. These typically use the same TR.069 management protocol published by the Broadband ForumBroadband ForumThe Broadband Forum is a non-profit industry consortium dedicated to developing broadband network specifications. Members include telecommunications networking and service provider companies, broadband device and equipment vendors, consultants and independent testing labs...
and also used for administration of residential modems.
The key interface in these architectures is that between the femtocell access points and the femtocell gateway. Standardisation enables a wider choice of femtocell products to be used with any gateway, increasing competitive pressure and driving costs down. For the common WCDMA femtocells, this is defined as the Iuh interface. In the Iuh architecture, the femtocell gateway sits between the femtocell and the core network and performs the necessary translations to ensure the femtocells appear as a radio network controller to existing MSC’s. Each femtocell talks to the femtocell gateway and femtocell gateways talk to the CNE (MSC for CS calls, SGSN for PS calls). This model was proposed by 3GPP and the Femto Forum. New protocols (HNBAP and RUA) have been derived; HNBAP is used for the control signaling between the HNB and HNB-GW while RUA is a lightweight mechanism to replace the SCCP and M3UA protocols in the RNC; its primary function is transparent transfer of RANAP messages.
In March 2010 the Femto Forum and ETSI conducted the first Plugfest to progress interoperability of the Iuh standard.
The CDMA2000 standard released in March 2010 differs slightly by adopting the SIP protocol to set up a connection between the femtocell and a femtocell convergence server (FCS). Voice calls are routed through the FCS which emulates a Mobile Switching Centre (MSC). SIP is not required or used by the mobile device itself. In the SIP architecture, the femtocell connects to a core network of the mobile operator that is based on the SIP/IMS architecture. This is achieved by having the femtocells behave toward the SIP/IMS network like a SIP/IMS client by converting the circuit-switched 3G signaling to SIP/IMS signaling, and by transporting the voice traffic over RTP as defined in the IETF standards.
Air interfaces
Although much of the commercial focus seems to have been on UMTS, the concept is equally applicable to all air-interfaces. Indeed, the first commercial deployment was the cdma2000CDMA2000
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...
Airave in 2007.
Femtocells are also under development or commercially available for GSM, TD-SCDMA
TD-SCDMA
Time Division Synchronous Code Division Multiple Access or UTRA/UMTS-TDD 1.28 Mcps Low Chip Rate , is an air interface found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA. Together with TD-CDMA, it is also known as UMTS-TDD or IMT 2000 Time-Division .The term...
, WiMAX
WiMAX
WiMAX is a communication technology for wirelessly delivering high-speed Internet service to large geographical areas. The 2005 WiMAX revision provided bit rates up to 40 Mbit/s with the 2011 update up to 1 Gbit/s for fixed stations...
and LTE
3GPP Long Term Evolution
3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques...
.
The H(e)NB functionality and interfaces are basically the same as for regular HSPA or LTE base stations except few additional functions. The differences mostly to support differences in access control to support closed access for residential deployment or open access for enterprise deployment, as well as handover functionality for active subscribers and cell selection procedures for idle subscribers. For LTE additional functionality was added in 3GPP Release 9 which is summarized in.
Issues
Femtocells are a complicated technology and there have been a number of issues and concerns which need to be addressed.Interference
The placement of a femtocell has a critical effect on the performance of the wider network, and this is the key issue to be addressed for successful deployment. Because femtocells can use the same frequency bands as the conventional cellular network, there has been the worry that rather than improving the situation they could potentially cause problems.Femtocells incorporate interference mitigation techniques—detecting macrocells, adjusting power and scrambling codes accordingly. Ralph de la Vega, AT&T President, reported in June 2011 they recommended against using femtocells where signal strength was middle or strong because of interference problems they discovered after widescale deployment. This differs from previous opinions expressed by AT&T and others.
A good example is the comments made by Gordon Mansfield, Executive Director of RAN Delivery, AT&T, speaking at the Femtozone at CTIA March 2010:
“We have deployed femtocells co-carrier with both the hopping channels for GSM macrocells and with UMTS macrocells. Interference isn’t a problem. We have tested femtocells extensively in real customer deployments of many thousands of femtocells, and we find that the mitigation techniques implemented successfully minimise and avoid interference. The more femtocells you deploy, the more uplink interference is reduced”
The Femto Forum has some extensive reports on this subject, which have been produced together with 3GPP and 3GPP2.
To quote from the Summary Paper — Summary of Findings:
The simulations performed in the Femto Forum WG2 and 3GPP RAN4 encompass a wide spectrum of
possible deployment scenarios including shared channel and dedicated channel deployments. In addition, the
studies looked at the impact in different morphologies, as well as in closed versus open access. The following
are broad conclusions from the studies:
- 1. When femtocells are used in areas of poor or no coverage, macro/femto interference is unlikely to be a problem.
- 2. If the femto network is sharing the channel (co-channel) with the macro network, interference can occur. However, if the interference management techniques advocated by the Femto Forum are adopted, the resulting interference can be mitigated in most cases.
- 3. A femtocell network deployed on an adjacent dedicated channel is unlikely to create interference to a macro network. Additionally, the impact of a macro network on the performance of a femtocell on an adjacent channel is limited to isolated cases. If the interference mitigation techniques advocated by the Femto Forum are used, the impact is further marginalised.
- 4. Closed access represents the worst-case scenario for creation of interference. Open access reduces the chances of User Equipment (mobile phone handsets, 3G data dongles, etc.) on the macro network interfering with a proximate femtocell.
- 5. The same conclusions were reached for both the 850 MHz (3GPP Band 17) and 2100 MHz (3GPP Band 1) deployments that were studied.
The conclusions are common to the 850 MHz and 2100 MHz bands that were simulated in the studies, and can be
extrapolated to other mobile bands. With interference mitigation techniques successfully implemented, simulations show
that femtocell deployments can enable very high capacity networks by providing between a 10 and 100 times
increase in capacity with minimal deadzone impact and acceptable noise rise.
Femtocells can also create a much better user experience by enabling substantially higher data rates than can be obtained with a macro network and net throughputs that will be ultimately limited by backhaul in most cases (over 20 Mbps in 5 MHz).
Lawful interception
Access point base stations, in common with all other public communications systems, are, in most countries, required to comply with lawful interceptionLawful interception
Lawful interception is obtaining communications network data pursuant to lawful authority for the purpose of analysis or evidence. Such data generally consist of signalling or network management information or, in fewer instances, the content of the communications...
requirements.
Equipment location
Other regulatory issues relate to the requirement in most countries for the operator of a network to be able to show exactly where each base-station is located, and for E911 requirements to provide the registered location of the equipment to the emergency services. There are issues in this regard for access point base stations sold to consumers for home installation, for example. Further, a consumer might try to carry their base station with them to a country where it is not licensed. Some manufacturers are using GPS within the equipment to lock the femtocell when it is moved to a different country; this approach is disputed , as GPS is often unable to obtain position namely indoors because of weak signal.Emergency calls
Access Point Base Stations are also required, since carrying voice calls, to provide a 9119-1-1
9-1-1 is the emergency telephone number for the North American Numbering Plan .It is one of eight N11 codes.The use of this number is for emergency circumstances only, and to use it for any other purpose can be a crime.-History:In the earliest days of telephone technology, prior to the...
(or 999
999 (emergency telephone number)
999 is an official emergency telephone number in a number of countries which allows the caller to contact emergency services for urgent assistance....
, 112
1-1-2
112 is the principal emergency telephone number that can be dialed free of charge from any telephone or any mobile phone in order to reach emergency services in the European Union , its candidates for accession, members of the EEA agreement, as well as several other countries in the world...
, etc.
Emergency telephone number
Many countries' public telephone networks have a single emergency telephone number, sometimes known as the universal emergency telephone number or occasionally the emergency services number, that allows a caller to contact local emergency services for assistance. The emergency telephone number may...
) emergency service, as is the case for VoIP phone providers in some jurisdictions. This service must meet the same requirements for availability as current wired telephone systems. There are several ways to achieve this, such as alternative power sources or fall-back to existing telephone infrastructure.
Quality of service
When using an ethernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
or ADSL home backhaul connection, an Access Point Base Station must either share the backhaul bandwidth with other services, such as Internet browsing, gaming consoles, set-top boxes and triple-play
Triple play (telecommunications)
In telecommunications, triple play service is a marketing term for the provisioning of two bandwidth-intensive services, high-speed Internet access and television, and a less bandwidth-demanding service, telephone, over a single broadband connection. Triple play focuses on a combined business...
equipment in general, or alternatively directly replace these functions within an integrated unit. In shared-bandwidth approaches, which are the majority of designs currently being developed, the effect on Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
may be an issue.
The uptake of femtocell services will depend on the reliability and quality of both the cellular operator’s network and the third-party broadband connection, and the broadband connection's subscriber understanding the concept of bandwidth utilization by different applications a subscriber may use. When things go wrong, subscribers will turn to cellular operators for support even if the root cause of the problem lies with the broadband connection to the home or workplace. Hence, the effects of any third-party ISP broadband network issues or traffic management policies need to be very closely monitored and the ramifications quickly communicated to subscribers.
A key issue recently identified is active Traffic shaping
Traffic shaping
Traffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...
by many ISPs on the underlying transport protocol IPSec
IPsec
Internet Protocol Security is a protocol suite for securing Internet Protocol communications by authenticating and encrypting each IP packet of a communication session...
. UK-based femtocell authority Epitiro have recently provided significant publicly available research and insight into many of these IP-focused QoS issues. A femtocell deployment guide from Epitiro is available for download here.
Spectrum accuracy
To meet Federal Communications CommissionFederal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) / Ofcom
Ofcom
Ofcom is the government-approved regulatory authority for the broadcasting and telecommunications industries in the United Kingdom. Ofcom was initially established by the Office of Communications Act 2002. It received its full authority from the Communications Act 2003...
spectrum mask
Spectral mask
In telecommunications, a spectral mask, also known as a channel mask or transmission mask, is a mathematically-defined set of lines applied to the levels of radio transmissions. The spectral mask is generally intended to reduce adjacent-channel interference by limiting excessive radiation at...
requirements, femtocells must generate the radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
signal with a high degree of precision. To do this over a long period of time is a major technical challenge. The solution to this problem is to use an external, accurate signal to constantly calibrate the oscillator to ensure it maintains its accuracy. This is not simple (broadband backhaul introduces issues of network jitter/wander and recovered clock accuracy), but technologies such as the IEEE 1588 time synchronisation standard may address the issue. Also, Network Time Protocol
Network Time Protocol
The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L...
(NTP) is being pursued by some developers as a possible solution to provide frequency stability. Conventional (macrocell) base stations often use GPS timing for synchronization and this could be used, although there are concerns on cost and the difficulty of ensuring good GPS coverage.
Standards bodies have recognized the challenge of this and the implications on device cost. For example, 3GPP has relaxed the 50ppb parts-per-billion
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...
precision to 100ppb for indoor base stations in Release 6 and a further loosening to 250ppb for "Home NodeB" in Release 8.
Controversy on consumer proposition
The impact of a femtocell is most often to improve cellular coverage, without the cellular carrier needing to improve their infrastructure (cell towers, etc.). This is net gain for the cellular carrier. However, the user must provide and pay for an internet connection to route the femtocell traffic, and then (usually) pay an additional one-off or monthly fee to the cellular carrier. Some have objected to the idea that consumers are being asked to pay to help relieve network shortcomings. On the other hand, residential femtocells normally provide a 'personal cell' which provides benefits only to the owner's family and friends.Deployment
According to market Research firm Informa and the Femto Forum, as of December 2010 18 operators have launched commercial femtocell services, with a total of 30 committed to deployment.Femtocell shipments are estimated to have reached almost 2 million at the end of 2010. Research firm Berg Insight estimates that the shipments will grow to 12 million units worldwide in 2014.
Within the United States, the most significant deployments up to December 2010 are by Sprint Nextel
Sprint Nextel
Sprint Nextel Corporation is an American telecommunications company based in Overland Park, Kansas. The company owns and operates Sprint, the third largest wireless telecommunications network in the United States, with 53.4 million customers, behind Verizon Wireless and AT&T Mobility...
, Verizon Wireless
Verizon Wireless
Cellco Partnership, doing business as Verizon Wireless, is one of the largest mobile network operators in the United States. The network has 107.7 million subscribers as of 2011, making it the largest wireless service provider in America....
and AT&T Wireless
AT&T Wireless
AT&T Wireless Services, Inc., founded in 1987 as McCaw Cellular Communications, Inc., and now legally known as New Cingular Wireless Services, Inc., formerly part of AT&T Corp., is a wireless telephone carrier in the United States, based in Redmond, Washington, and later traded on the New York...
. Sprint started in the third quarter of 2007 as a limited rollout (Denver and Indianapolis
Indianapolis
Indianapolis is the capital of the U.S. state of Indiana, and the county seat of Marion County, Indiana. As of the 2010 United States Census, the city's population is 839,489. It is by far Indiana's largest city and, as of the 2010 U.S...
) of a home-based femtocell built by Samsung Electronics called the Sprint Airave that works with any Sprint handset. From 17 August 2008, the Airave was rolled out on a nationwide basis. Other operators in the United States have followed suit. In January 2009 Verizon rolled out its Wireless Network Extender, based on the same design as the Sprint/Samsung system. In late March 2010, AT&T announced nationwide roll-out of its 3G MicroCell, which commenced in April. The equipment is made by Cisco Systems
Cisco Systems
Cisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...
and ip.access
Ip.access
ip.access Limited is a multinational corporation that designs, manufactures, and markets picocell and femtocell technologies and infrastructure equipment for GSM, GPRS, EDGE, and 3G...
, and was the first 3G femtocell in US, supporting both voice and data HSPA
High Speed Packet Access
High Speed Packet Access is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access and High Speed Uplink Packet Access , that extends and improves the performance of existing WCDMA protocols...
. Both Sprint and Verizon upgraded to 3G CDMA femtocells during 2010, with capacity for more concurrent calls and much higher data rates.
In Asia, several service providers have rolled out Femtocell networks. In Japan, SoftBank Mobile launched its residential 3G femtocell service in January 2009 with devices provided by Ubiquisys. In the same year the operator launched a project to deploy femtocells to deliver outdoor services in rural environments where existing coverage is limited. In May 2010, SoftBank Mobile launched the first free femtocell offer, providing open access femtocells free of charge to its residential and business customers. In Singapore, Starhub rolled out its first nation-wide commercial 3G Femtocell services with devices provided by Huawei Technologies, though the uptake is low, while Singtel's offering is targeted at small medium enterprises. In 2009, China Unicom announced its own Femtocell network. NTT DoCoMo in Japan launched their own Femtocell service on the 10th November 2009.
In July 2009 Vodafone released the first Femtocell network in Europe, the Vodafone Access Gateway provided by Alcatel-Lucent. This was rebranded as SureSignal in January 2010, after which Vodafone also launched service in Spain, Greece, New Zealand, Italy and Ireland. Other operators in Europe have followed since then, with SFR
SFR
SFR is a French mobile phone company. It has over 20 million customers, and provides over 4.6 million households with high-speed internet access...
in France with femtocells provided by Ubiquisys and Optimus Telecomunicações, S.A.
Optimus Telecomunicações, S.A.
Optimus Telecomunicações, S.A. is a Portuguese GSM/UMTS mobile operator. The company was incorporated at the end of 1997 after winning the bid for Portugal's third GSM license...
in Portugal.
See also
- 5G5G5G is a name used in some research papers and projects to denote the next major phase of mobile telecommunications standards beyond the 4G/IMT-Advanced standards effective since 2011...
- Cellular repeaterCellular repeaterA cellular repeater, cell phone repeater, or wireless cellular signal booster, a type of bi-directional amplifier as commonly named in the wireless telecommunications industry, is a device used for boosting the cell phone reception to the local area by the usage of a reception antenna, a signal...
- MicrocellMicrocellA microcell is a cell in a mobile phone network served by a low power cellular base station , covering a limited area such as a mall, a hotel, or a transportation hub. A microcell is usually larger than a picocell, though the distinction is not always clear...
- PicocellPicocellA picocell is a small cellular basestation typically covering a small area, such as in-building , or more recently in-aircraft...
- Small CellsSmall CellsSmall Cells are low-powered radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 meter to 200 meters, compared to a mobile Macrocell which might have a range of a few kilometres. With mobile operators struggling to support the growth in mobile data traffic,...
- Wireless access pointWireless access pointIn computer networking, a wireless access point is a device that allows wireless devices to connect to a wired network using Wi-Fi, Bluetooth or related standards...
External links
- Femto Forum web pages
- University of Texas: Overview of the technical and business arguments for femtocells
- ThinkFemtocell: Technical detail, business case and analysis
- Home Cells Signal Mobile Change, BBC News OnlineBBC News OnlineBBC News Online is the website of BBC News, the division of the BBC responsible for newsgathering and production. The website is the most popular news website in the United Kingdom and forms a major part of BBC Online ....
- Reuters: Video news and femtocell demonstration
- World’s First Commercially Available 3G Femto Cell
- Femtocells tutorial Multiple page tutorial addressing a number of aspects of femtocell technology.
- BeFEMTO webpage (Broadband Evolved FEMTO Networks) Future use of femtocells
- Femtocells on Wilson Street Resource dealing with the social impact , and business case for femto cell technology