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{{Confusing|date=March 2008}}
In [[telecommunications]], a '''femtocell'''—originally known as an '''Access Point Base Station'''—is a small cellular [[base station]], typically designed for use in residential or small business environments. It connects to the service provider’s network via broadband (such as DSL or cable); current designs typically support 2 to 5 mobile phones in a residential setting. A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. The femtocell incorporates the functionality of a typical [[base station]] but extends it to allow a simpler, self contained deployment; for example, a [[UMTS]] femtocell containing a [[Node B]], [[Radio Network Controller|RNC]] and [[GPRS Support Node|GSN]] with Ethernet for backhaul. Although much attention is focussed on UMTS, the concept is applicable to all standards, including [[GSM]], [[CDMA2000]], [[TD-SCDMA]] and [[WiMAX]] solutions.

For a mobile operator, the attractions of a femtocell are improvements to both coverage and capacity, especially indoors. There may also be opportunity for new services and reduced cost. The cellular operator also benefits from the improved capacity and coverage but also can reduce both [[capital expenditure]] and [[operating expense]].

Femtocells are an alternative way to deliver the benefits of [[Fixed mobile convergence#Fixed Mobile Convergence|Fixed Mobile Convergence]]. The distinction is that most FMC architectures require a new (dual-mode) handset which works with existing home/enterprise Wi-Fi access points, while a femtocell-based deployment will work with existing handsets but requires installation of a new access point.

==History==
In 2002, a group of engineers at [[Motorola]] in [[Swindon]], [[England]], started a [[skunkworks]] team, called the "AFG", to develop new technologies. Some of their major achievements included the world's smallest full-power UMTS base station, one of the first demonstrations of television to mobile, and the invention and development of the access point base station (ie. Femtocell). The original design was intended to provide a direct equivalent to a WiFi access point, but for mobile cellular (UMTS, CDMA-2000 or WiMAX). The unit contained all the core network elements and did not require a cellular core network, requiring only a data connection to the Internet or WiFi core network<ref>Motorola Swindon Labs BTS500D Concept Document</ref>.

By mid-2004 a number of companies were independently investigating femtocells (although mostly using other terms such as "residential base station" or "3G access point").<ref>[http://disruptivewireless.blogspot.com/2007/12/femtocell-who-coined-term-and-when.html Disruptive Wireless]</ref>

Also in 2004, two femtocell-focussed companies were registered<ref>Companies House File Numbers 05213514 and 05247998, respectively</ref> at [[Companies House]] in the United Kingdom: 3Way Networks (now part of [[Airvana]], Inc.) and [[Ubiquisys]]. By 2005, the idea had become more widely recognised with demonstrations and conference discussion. By this stage more companies were involved, including more established suppliers [[Samsung]], [[Airwalk (Radio Equipment Vendor)|Airwalk]], [[ip. Access]] and [[RadioFrame Networks]].

By early 2007, the idea had become mainstream, with a number of major companies publicly demonstrating systems at the cellular industry [[3GSM]] conference in February, and operators announcing trials. In July, the [[Femto Forum]] trade organisation was founded to promote femtocell deployment worldwide, {{Fact|date=April 2008}} comprising mobile operators, telecoms hardware and software vendors, content providers and start-ups. Its main work is conducted via four working groups, tackling regulatory issues, network and interoperability, radio and physical layer, and marketing and promotion.

In 3Q 2007, [[Sprint Nextel]] started a limited rollout in [[Denver]], [[Indianapolis]] and [[Tennessee]] of a home-based UbiCell femtocell built by [[Samsung]] called the "Sprint Airave", which worked with any Sprint handset.<ref>[http://www2.sprint.com/mr/news_dtl.do?id=18000 Airave]</ref> Airave was rolled out nationwide on 17 August 2008.<ref>[http://blog.treonauts.com/2008/07/sprint-airave-n.html Sprint AIRAVE Nationwide Launch August 17]</ref>

As well as system manufacturers, [[Semiconductor industry|semiconductor companies]] have announced chip-level products to address this application. [[Analog Devices]] has developed a chipset for the [[RF-IF]] and [[baseband]], while [[picoChip]] claims significant commercial traction on their baseband Digital Signal Processor{{fact|date=July 2008}}.

==Issues==

Although claims are made that Femtocells could be a panacea for straightforward system deployment, there are a number of complications that need to be overcome.

===Interference===
The placement of a femtocell has a critical effect on the performance of the wider network, and this is one of the key issues to be addressed for successful deployment.

Without unique spectrum for the femtocell 'underlay network', or very careful spectrum planning in the wider network, there is a concern that femtocells could suffer from severe interference problems. For example, in a femtocell handover between a macrocell network to a home femtocell access point, there are limitations in the standards which must be taken into account. For example, there is a limitation in the number of adjacent cell sites - typically 16 - for which the mobile unit can scan for, measure and then pass to the RAN handover algorithm (for 2G and 3G standards, for example). Further, if a single frequency CDMA system is being operated, where the macro and femtocell network utilise the same frequency band (a typical situation for many operators who licensed only one 3G frequency band), then the power control algorithms of the macro cell and femtocell can create interference ,<ref>[http://arxiv.org/abs/cs/0702132v7 "Uplink Capacity and Interference Avoidance for Two-Tier Femtocell Networks", Vikram Chandrasekhar and Jeffrey G. Andrews]</ref> where for example a mobile unit increases its transmit power to the femtocell as part of the 'near-far' power control inherent in CDMA systems, whilst it is within the coverage area of a macro unit. The resultant high power transmitter in the macro field acts as an interferer since the frequency is shared. Finally, there is the issue of coverage area, where in high-rise accommodation, femtocell users on different floors can create interference to other users. There are several partial solutions to this problem, but primarily the only way to prevent interference is to use a different frequency for the femtocell coverage, particularly for CDMA deployments. The partial solutions include utilising the mode-2 fixed power option available in the 3G configuration parameters, which would prevent the mobile unit power from increasing and causing interference, though there is an obvious performance trade-off if this approach is used.

Many vendors are reported to have developed sophisticated algorithms to address the problem, and modelling by carriers indicates this is viable.{{Fact|date=April 2008}} As such, the trials now in place are designed to test these techniques and to determine to what degree interference is a problem and under what circumstances. In his paper for 'PIMRC 07',<ref>Performance of Macro- and co-channel femtocells in a hierarchical cell structure", Holger Claussen, Bell Laboratories Alcatel-Lucent, The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2007 (PIMRC'07)</ref> Claussen describes the UMTS femtocell/macrocell interference problem and concludes that to manage the interference that "Essential requirements such as autoconfiguration and public access" are needed. In this case 'public access' means that all deployed femtocells using the same frequency (ie. of the same operator) would need to allow anyone to access the femtocell; there are obvious backhaul issues with this if the user is paying for the DSL or Cable backhaul connection. It is suggested in the paper that this could be offset by low cost calls. In another paper,<ref>"Effects of user-deployed, co-channel femtocells on the call drop probability in a residential scenario", Lester T. W. Ho, Holger Claussen, Bell Laboratories Alcatel-Lucent, The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2007 (PIMRC'07)</ref> Ho and Claussen identify the pre-requisite for auto-configuration of the femtocell power level in order to reduce interference - though in Claussen's first paper the algorithm requires knowledge of the macrocell transmit power, which would require the operator to configure the femtocells centrally, and line-of-sight distance to the femtocell, which requires knowledge of where the femtocell is installed. In his second paper, Ho highlights the issue of increased network traffic due to handover messages between the macrocell and femtocell.

The 3GPP meeting reported that:
"To the extent investigated so far co-channel deployment is feasible for open access.
For closed access, analysis conducted so far indicates that co-channel deployment is feasible if adaptive interference mitigation techniques are used. Further work is required to summarise the trade-off between HNB performance and the impact on the macro layer and to determine whether an acceptable tradeoff can be identified".<ref>3GPP TR 25.820 V1.0.0 (2007-11)</ref>

A number of companies <ref>http://www.picochip.com/downloads/PC8209ProductBrief.pdf</ref> are using the approach of using the femtocell as a mobile phone (UE) in order to measure, synchronise and build a neighbour list of nearby base stations. From this information, power levels, spreading codes and other parameters can be determined and resolved in order to avoid interfering with existing infrastructure.

===Spectrum===
Crucially, access point base-stations operate in licensed spectrum. As licensed spectrum allocation is made to operators on a fee basis, deployment of equipment must meet the strict requirements of the licenses. To make best use of spectrum, operators use frequency and cellular planning tools to optimise the best coverage for a given amount of spectrum. The introduction of access point base stations using licensed spectrum that are sold directly to the customer has implications for frequency and cellular planning, since an unexpectedly located access point base station could interfere with other closely-located base stations.

===Access control===
There is also the related issue of what happens when a neighbor's mobile appliance attaches to the network using another neighbor's femtocell, or how that can be prevented from occurring.

===Lawful interception===
Access point base stations, in common with all other public communications systems, are, in most countries, required to comply with [[lawful interception]] requirements.

===Equipment location===
Other regulatory issues<ref>[http://www.fcc.gov/pshs/911/voip/challenges.html FCC requirements for 911 provision by VoIP providers]</ref> 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 (see [[Ubicell]]) are using [[GPS]] within the equipment to lock the femtocell when it is moved to a different country;<ref>[http://www.engadget.com/2007/03/28/hands-on-with-the-samsung-ubicell/ Hands on with the Samsung Ubicell]</ref> this approach is disputed, as [[GPS]] is often unable to obtain position namely indoors because of weak signal.

===Network integration===
From an operational or deployment perspective, one of the key areas that needs to be considered is that of network integration. A conventional cellular network is designed to support a relatively small number (thousands, tens-of-thousands) of base stations, whereas a femtocell deployment of millions of consumer access points requires a different architecture to support this scaling. The issue of increase in network traffic as a result of co-channel macrocell / femtocell deployment is discussed in the paper by Ho and Claussen.<ref>"Effects of user-deployed, co-channel femtocells on the call drop probability in a residential scenario", Lester T. W. Ho, Holger Claussen, Bell Laboratories Alcatel-Lucent, The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2007 (PIMRC'07)</ref>

===Emergency calls===
Access Point Base Stations are also required, since carrying voice calls, to provide a 911 (or 999, or 112) emergency service, as is the case for [[VoIP]] phone providers.<ref>[http://www.fcc.gov/pshs/911/voip/challenges.html FCC requirements for 911 provision by VoIP providers]</ref> 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 utilising an [[Ethernet]] 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 [[QoS]] may be an issue.

===Spectrum accuracy===
To meet [[FCC]]/[[RA]] spectrum mask requirements, Access Point Base Stations must generate the [[RF]] signal with a high degree of precision, typically around 50 parts-per-billion (ppb) or better. To do this over a long period of time is a major technical challenge, since meeting this accuracy over a period longer than perhaps 12 months requires an ovenised crystal oscillator ([[OCXO]]). These oscillators are generally large and expensive, and still require calibration in the 12-to-24 month time frame. Use of lower-cost temperature-compensated oscillators (TCXO) provides accuracy over only a 6-to-18 month time frame. Both depend on a number of factors.

The solutions to this problem of maintaining accuracy are either to make the units disposable/replaceable after an 18-month period and thus keep the cost of the system low, or 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, potentially providing 100-nanosecond accuracy (standard deviation),<ref>[http://ieee1588.nist.gov/distributech_2003_paper.pdf IEEE-1588 Standard for a precision clock synchronization protocol]</ref> depending on the location of the master clock. 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 to calibrate the oscillator.<ref>[http://www.engadget.com/2007/03/28/hands-on-with-the-samsung-ubicell/ Hands on with the Samsung Ubicell]</ref> However, for a domestic femtocell, 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 precision to 100ppb for indoor base stations in Release 6 and has proposed a further loosening to 250ppb for "Home NodeB" in Release 8.

===Handover===
In order to ensure that the user gets the best data rate out of the system, the mobile appliance must somehow know to connect to the femtocell when within range, even if there is still sufficient signal from, for example, an external macrocell base station. Forcing the mobile appliance to do this, whilst preventing your neighbor's mobile appliance from doing the same, is quite a challenge. In addition, handoff from the femtocell to the wider area macrocell and back again is potentially quite complex.

== 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 is the [[cdma2000]] Airave.<ref>[http://www2.sprint.com/mr/news_dtl.do?id=18000 Sprint Customers in Select Areas of Denver and Indianapolis Get AIRAVE for Enhanced In-Home Coverage<!-- Bot generated title -->]</ref> Femtocells are also under development for [[GSM]], [[TD-SCDMA]], [[WiMAX]] and [[LTE]]. The LTE study groups have identified femtocells ("Home eNode B") as a priority area.

==Architectures==
===Home Node B ([[Home Node B|HNB]])===
In May, 2008, the 3GPP completed a feasibility study of femtocell network architectures. Architectures including '''Cellular Base Station''', '''Collapsed Stack''' and '''UMA/GAN''' were evaluated. As a result, the 3GPP is pursuing a new [[Home Node B]] (or HNB) reference architecture which builds on elements from both the Collapsed Stack and UMA/GAN approaches.

As the 3GPP completes the formal standard towards at the end of 2008, vendors and operators will migrate to support this new architecture for [[3G]] femtocells.

Note the 3GPP refers to 3G femtocells as Home Node Bs (HNBs).


===Cellular Base Station ([[Picocell]])===

One approach for a femtocell is to use the traditional base station architecture. In this case, the femtocell is a base station, connecting to the core network using a standard interface; for example, a [[WCDMA]] Node B connecting to a [[RNC]] via a backhaul connection (the [[Iub]]). The slight difference to a typical base station deployment is that the backhaul would be carried over broadband ("Iub over IP") which may have quality & security concerns. A more significant drawback of this architecture is that standards based base station controllers are designed to support only a limited number of high-capacity base stations, not large numbers of simple ones. This architecture was previously referred to in the literature as a [[picocell]] deployment and is one in which a base station controller is introduced to provide the necessary support to the numerous small pico-head base stations.

===Collapsed Stack===
More common architectures collapse some of the network functionality into the base station ("collapsed stack" or "Base Station Router"), not just the base station itself (Node B or BTS) but also the controller (eg RNC) and enable local radio resource control. This would then connect back to the mobile operator core at a higher point eg Iu interface for WCDMA for central authentication and management. This addresses the scalability concerns above, as the resource is located locally. The original Access Point Base Station followed this architecture but also incorporated the core MSC/GSN functions of authentication, control and switching.

===Collapsed Stack with UMA Backhaul===
A variant of the above is to use [[Generic Access Network|GAN/EGAN Unlicensed Mobile Access]] (UMA) standards. In this case, the UMA/GAN client is integrated into the femtocell. UMA/GAN protocol provides the connection to the mobile core, tunneling the Iu protocol. This approach uses UMA/GAN's existing security, transport and device management capabilities.

UMA/GAN is an attractive option for operators to leverage their investment in the UMA Network Controller to support applications beyond femtocells, including [[dual-mode handsets]]/[[WiFi]] or fixed line VoIP with terminal adapters.

The approach for UMA-based femtocells differs from a dual-mode handset approach where the UMA client is integrated in the device. In the former system the terminal is not affected and the air-interface is still standard - the UMA client is incorporated in the femtocell.

===SIP or IMS===

The final, and most sophisticated structure is to move to a full IP-based architecture. This approach was utilised in the original Access Point Base Station. In this case, even more functionality is included within the femtocell, and the integration to the core is done using an IP-based technology, e.g. [[Session Initiation Protocol|SIP]], [[IMS]] or [[H.323]].

== Deployment ==

Currently, the most significant deployment is that of Sprint. This started in 3Q/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.<ref>[http://www2.sprint.com/mr/news_dtl.do?id=18000 Airave]</ref> As of 17 August 2008, Airave has been rolled out on a nationwide basis.

A number of operators have announced intention to have field trials in 2008, including O2,<ref>[http://www.o2.com/media/press_releases/press_release_14135.asp O2]</ref> Softbank,<ref>[http://www.softbank.co.jp/en/news/release/2007/070629_0002.html Softbank]</ref> TeliaSonera,<ref>[http://www.unstrung.com/document.asp?doc_id=143665&f_src=unstrung_gnews TeliaSonera]</ref> and Vodafone.<ref>[http://www.eetimes.eu/206800077 Vodafone]</ref>

Most analysts agree that 2008 will primarily be field trials and soft launch, while commercial launch will be in 2009 <ref>[http://www.businesswire.com/portal/site/google/?ndmViewId=news_view&newsId=20080505005848&newsLang=en 100,000 Femtocells Will Ship in 2008, But 2010 Will Be the Year of Real Volume, says ABI Research]</ref> <ref>[http://www.networkworld.com/newsletters/converg/2008/041408converge2.html Network World: interview with Motorola VP GM Alan Lefkof]</ref>.

==References==
{{reflist}}

==See also==
*[[Wireless access point]]

==Further reading==
* A survey on femtocells: [http://aps.arxiv.org/abs/0803.0952]
* [http://www.airvana.com/products/products_559.htm Airvana femto FAQ]
* [http://www.thinkfemtocell.com/ ThinkFemtocell: Technical detail, business case and analysis]
* [http://news.bbc.co.uk/1/hi/technology/6916125.stm BBC News: Home Cells Signal Mobile Change]
* [http://uk.reuters.com/news/video?videoId=59291&videoChannel=6 Reuters video news about femtocell]
* Dead Link: [http://biz.yahoo.com/prnews/070626/aqtu006.html?.v=21 Netgear and Ubiquisys team to develop femtocell home gateway]
* [http://www.softbank.co.jp/en/news/release/2007/070629_0002.html Japan Softbank (formerly Vodafone Japan) conducts six month field trial with all leading vendors]
* [http://www.mobileeurope.co.uk/news_wire/112796/Yet_another_IP%252F_IMS_femto_cell_release.html Tatara Systems and picoChip partnership to collaborate on femtocell market]
* [http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9027536 Google invests in femtocell vendor]
* [http://www.eetasia.com/ART_8800481182_499488_NT_ae264150.HTM Sequans, PMC-Sierra team on Mobile WiMAX femtocell solution]
* [http://www.theregister.co.uk/2006/11/22/o2_picocell_trial/ O2 trial could see a picocell in every home]
* [http://www.mobileeurope.co.uk/news_wire/112839/Ubiquisys_and_Kineto_successfully_test_UMA_for_femtocells_.html Ubiquisys and Kineto successfully test UMA for femtocells]
* [http://www.picochip.com/press/press_releases/press079 picoChip works with Semtech to enhance femtocell reference designs]
* [http://www.unstrung.com/document.asp?doc_id=128344 "Ubiquisys and Motorola responded to the RFP together, according to one industry source."]
*[http://www1.alcatel-lucent.com/products/productsummary.jsp?productNumber=tcm:228-1303921635 Alcatel-Lucent 9365 Base Station Router Femto]

==External links==
{{External links}}
===Equipment===
* [http://www.3waynetworks.com/mobile_prod01.htm 3Way Networks Femtocell] (Now Airvana)
* [http://www.airvananet.com/files/Femto_Overview_Whitepaper_FINAL_12-July-07.pdf Airvana Femtocell]
* [http://www.bbwexchange.com/pubs/2007/03/26/page1393-513355.asp Airwalk Femtocell]
* [http://www.tmcnet.com/usubmit/2007/07/07/2767084.htm Alcatel-Lucent Femtocell]
* [http://www.ericsson.com/ericsson/press/releases/20070209-1103860.shtml Ericsson Femtocell]
* [http://www.haysystems.com/mobile-networks/hsl-femtocell/ HSL 2.75G Femtocell]
* [http://www.mydigitallife.info/2007/07/25/huawei-demonstrated-new-femtocell-prototype-in-japan/ Huawei Femtocell]
* [http://www.ipaccess.com/products/oyster3G.htm ip.access Oyster Femtocell]
* [http://www.kineto.com/products/downloads/wp_UMA_Femto_3GPP_2007.pdf Kineto Femtocell core network solution]
* [http://www.motorola.com/femtocell Motorola Femtocell]
* [http://computerworld.co.nz/news.nsf/tech/16F747624A78774DCC25730F007C4D4C Nokia Siemens Networks' Femtocell]
* [http://www.radioframenetworks.com/americas/products/sseries/sseries.htm RadioFrame Networks Femtocell]
* [http://www.samsung.com/global/business/telecommunication/productInfo.do?ctgry_group=11&ctgry_type=20&b2b_prd_id=201 Samsung Ubicell Femtocell]
* [http://www.ubiquisys.com/ubiquisys2/zonegate.php Ubiquisys Femtocell]
* [http://www.infinetwireless.com InfiNet Wireless Femtocell]
*[http://www.airwalkcom.com/html/news_release.php?press_id=14&]

===Software stacks===
* [http://www.ccpu.com/products/trillium/femtocell.html Trillium Femtocell Software]
* [http://www.tatarasystems.com/contentmgr/showdetails.php/id/688]

===Chips and reference designs===
* [http://www.percello.com Percello: Femtocells silicon vendor]
* [http://www.bitwavesemiconductor.com/news-events/press-releases/pr-launch-20080211.html Bitwave Semiconductor, Programmable 700-3800MHz Radio Transceiver for Femtocells, Handsets & Datacards]
* [http://www.ceva-dsp.com/products/system/ceva-xs1200.php CEVA-XS1200 baseband device: CEVA DSP]
* [http://www.picochip.com/products_and_technology/femtocells_products_PC8208_PC8209_WCDMA Picochip's WCDMA Femtocell Reference design.]
* [http://www.picochip.com/products_and_technology/femtocells_products_PC6530_PC6532_WiMAX Picochip's WiMAX Femtocell Reference design.]
* [http://www.picochip.com/products_and_technology/femtocells_products_CDMA2000_with_GWT Picochip's CDMA2000 Femtocell Reference design.]
* [http://www.pmc-sierra.com/products/details/pm8800/ PMC-Sierra PM8800 WiZIRD 2x2 MIMO WiMAX RF chip]
* [http://www.sequans.com/site/sqn1130.html Sequans SQN1130 WiMAX 802.16e chip]
* [http://www.st.com/stonline/products/literature/bd/11278.pdf ST Microelectronics GreenSIDE STW51000 multi-standard baseband device: DSP + ARM9]
* [http://www.technoconcepts.com/Products/RFD.aspx Terocelo Lycon(TM) RF chipset]
* [http://www.mindspeed.com/web/product/category.html?id=763&trail=562,1039 Mindspeed Comcerto100 Series Broadband Gateway Processors]

===Industry body===
* [http://www.femtoforum.org Femto Forum]
* [http://www.UMAToday.com UMA Today]

===Independent research===
* [http://www.soundpartners.com/femtocellpage.aspx Sound Partners Research]

===Market===
====Equipment to chipset mapping====
* Airvana ([http://www.eetimes.com/showArticle.jhtml?articleID=199203187 acquired 3-way Networks], which was using [http://edageek.com/2007/02/02/3way-picocell-analog-devices-tigersharc/ Analog Devices BlackFin]) (3GPP2 CDMA 1X unit)
* Airwalk ([http://www.airwalkcom.com/html/content.php?content_id=38 3GPP2 CDMA 1X unit])
* Alcatel-Lucent (3GPP UMTS unit) picoChip chipset
* Ericsson (3GPP UMTS WiFi unit)
* GWT (3GPP2 1x + EvDO unit)
* Huawei
* ip.access: [http://voipservices.tmcnet.com/news/2006/09/26/102414.htm Picochip chipset] (3GPP GSM UMTS unit)
* RadioFrame Networks: [http://edageek.com/2007/06/22/radioframe-wireless-ceva/ Structured ASIC using CEVA-X1620(TM) DSP core] (3GPP GSM unit)
* Sagem (3GPP UMTS unit) picoChip chipset
* Samsung ZTE: [http://www.electronicsweekly.com/Articles/2007/09/18/42202/samsung+an+investor+reveals+picochip.htm] (3GPP2 CDMA 1X unit)
* Ubiquisys: [http://www.ubiquisys.com/ubiquisys3/pressreleasesarc.php?id=18 Picochip chipset] (3GPP UMTS unit)

====Cellular equipment vendor to femtocell vendor partnerships====
* [http://www.unstrung.com/document.asp?doc_id=143834 Cisco <-> ip.access]
* [http://biz.yahoo.com/ap/070917/nokia_siemens_networks_airvana.html?.v=1 Nokia Siemens Networks <-> Airvana], [http://www.nokiasiemensnetworks.com/global/Press/Press+releases/news-archive/Nokia_Siemens_Networks_and_Ubiquisys_Cooperate_on_3G_Femto_Home_Access_Solution.htm Nokia Siemens Networks <-> Ubiquisys]
* [http://www.unstrung.com/document.asp?doc_id=128344 Motorola <-> Ubiquisys]
* [http://www.lightreading.com/document.asp?doc_id=118232 Thomson <-> ip.access]

====Reported market estimates====
* [http://www.eetimes.com/news/semi/showArticle.jhtml?articleID=206903201 "Forward Concepts forecasts $4.9 billion femtocell equipment revenue in 2012"]
* [http://www.dri.co.jp/auto/report/abi/abifemt07.htm "36 Million Femtocell Shipments Expected in 2012"]
* [http://www.picochip.com/downloads/WiMAX_Paris%20Feb_07_Femto.pdf "We forecast 17 million residential Femtocells in Western Europe in 2011”]
* [http://www.picochip.com/downloads/WiMAX_Paris%20Feb_07_Femto.pdf “By 2011 there are forecast to be 102 million femtocell users"]
* [http://mobcomment.blogspot.com/feeds/posts/default "3G femtocell deployment to 20% of households by 2012 would only save about USD20 per customer per year, because significant numbers of macrocells would still be needed"]
* [http://www.unstrung.com/document.asp?doc_id=128344 "estimates that there will be 50,000 femtocell units shipped this year and 1 million units next year"]
* [http://news.independent.co.uk/business/news/article2739785.ece "market will be worth $2bn by 2011 "]

====Target product and service costs====
* [http://www.kinetowireless.com/products/downloads/kineto_wp_UMA_Femto_2007.pdf "Under €150 in volume"]
* [http://www.picochip.com/downloads/WiMAX_Paris%20Feb_07_Femto.pdf "Very aggressive price targets (<<$200)"]
* [http://www2.sprint.com/mr/news_dtl.do?id=18000 Airave unit and service plan costs: $49.95 plus a flat monthly rate for unlimited local and nationwide calling]

[[Category:Communication]]

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2008年10月2日 (木) 03:32時点における版

フェムトセル (femtocell) は半径数十m程度のきわめて小さな範囲の携帯電話の通話エリア（セル）、およびその基地局のこと。

本項目では特に断らない限り、日本におけるフェムトセルについてのみ記述する。

概要と経緯

現在の携帯電話基地局の多くは、半径数百m～十数kmの通話エリアを持っており、その大きさから「マクロセル」と呼ばれている。マクロセル同士の境界領域やビルの奥、地下では電波強度が微弱となり通信しづらい場所が生まれる。このような状況に対して携帯電話ヘビーユーザやこれらの人々を顧客とするサービス業から改善要望が寄せられていた。

これに答えるために、たとえばNTTドコモでは「ナノセル」や「ピコセル」と呼ばれる、従来に比べれば小さな通話エリアの小型基地局を設置することで対応してきたが、それでもまだ接続できない小さな場所が残ることになり、「フェムトセル」と呼ばれるさらに狭い範囲の通話エリアで弱い電波出力の小型携帯電話基地局の設置を開始した。

2007年11月現在、このような小さな携帯基地局にはいくつかの利点があるため、個人レベルや小企業レベルでの簡易な設置と運用が携帯電話事業者から求められ、監督官庁である総務省も規制している省令の改正を予定と11月10日に公表している。2008年秋には新しいフェムトセルが登場する予定である。

詳細

現在

NTTドコモでは設置希望者の要望に基づいて、新しくフェムトセルと呼ばれる出力20mW程度で半径数十m程度のきわめて小さな範囲の通話エリアを持つ小型の携帯電話基地局の設置を2007年秋頃より開始した[1]。同時接続数も4ユーザー程度となっている。この基地局は外見が、無線機能付きブロードバンドルーターのようにも見えるくらいに小さい。

関連省令改正の予定

現在は省令によって、携帯電話の無線基地局の設置にはそれぞれ1局ごとに総務省の免許取得が必要とされ、携帯電話事業者によって申請されなければならない。また、基地局は携帯電話事業者の持ち物であり、設置工事もこの携帯電話事業者から工事資格を持った担当者が派遣されて行なうことになっている。今後この省令が改正される予定と公表されている。予定通り、関連省令が改正され規制が緩和されれば、希望する個人や会社が家電販売店などで小型の基地局を購入して設置できるようになる[2]。報道によれば総務省の予定では、無線基地局は10万円程度で2008年の秋頃をめどに販売される[3]。

将来の実施案

回線
現在のマクロセル基地局の大半はAsynchronous Transfer Mode (ATM) 専用線で接続されているが、フェムトセルの基地局では現実的にFTTHやADSLによるブロードバンド回線によって接続することが考えられている。すでに設置が開始されているNTTドコモでのフェムトセル基地局はIP専用線を使って接続している。これは現在の法律が専用線の使用を規定しているため。
盗聴・漏話
インターネットによる公衆回線を使う場合は、IPsecによる暗号化・トンネリング技術を利用して盗聴などのリスクを避ける予定である。
停電
現在の携帯電話基地局は、停電時にも一定の時間サービスが維持できるようにバッテリーや非常用発電機が備えられているが、新しいフェムトセルの基地局ではこれらの制約も解除される予定である。
機器の販売と設置
携帯電話事業者は新しいフェムトセルの基地局を、ブロードバンドルーターやADSLモデム、無線アクセスポイントとの一体製品として、携帯電話販売代理店や家電量販店より、1台数万円程度で販売されることを考えている[2]。また11月10日の報道では総務省の予定ではNTTドコモからは10万円程度での販売としている。
緊急通話
緊急通話については不明。停電時のバックアップ電源の設置義務がなければ、考慮されても限定的となる。
排他利用
携帯電話事業者は狭い電波覆域という特性から、場所を限定したコンテンツのサービス・ビジネスを考えている。レストランのクーポン券配布や会社での業務連絡である。会社の業務連絡などの場合には、利用者を限定することも考えている。

新フェムトセルのメリット

既にNTTドコモによって開始されている従来型のマクロセル基地局に対して、新しいフェムトセル基地局が実施された場合のメリットを示す。

  • 通話圏外の解消・減少
  • データ通信時の通信速度の向上
  • 通話料金の割引（総務省の見込み）
  • 携帯電話事業者の投資負担の軽減[2]

計画中の携帯電話事業者

  • NTTドコモ - 計画中
NTTドコモとソフトバンクモバイルは既に商品化のための機器を開発中[2]。
ソフトバンクモバイルは2007年6月29日に総務省より2007年6月～12月の期間の無線実験局の免許を取得した[4]。ベンダー8社が参加した実証実験を2007年の6月から行い、英アイピー・アクセス、英ユビキシス、米モトローラの小型基地局での利用実験をメディアに公開した。
  • KDDI（au） - 検討中
KDDIでは、フェムトセルの研究はしているが、様々な問題から採用には消極的な姿勢を見せている[5]

その他

2007年の第3四半期にスプリント・ネクステル（Sprint Nextel）社がデンバーとインディアナポリスで、限定的ながら、スプリントの携帯電話と使用するサムスン製の「Sprint Airave」という製品の出荷を開始したとされている。

関連項目

出典

  • 日経NETWORK 2007年11月号
  1. ^ NTTドコモ「フェムトセル用超小型基地局装置を開発」
  2. ^ a b c d 日本経済新聞 2007年11月4日 朝刊
  3. ^ NHK TVニュース11月10日15時
  4. ^ ソフトバンクモバイル「フェムトセルを使った通信システムのの無線実験局免許の取得について」
  5. ^ 問題点を知っているからフェムトセルには消極的――KDDI - ITmedia +D モバイル

外部リンク

Template:Confusing In telecommunications, a femtocell—originally known as an Access Point Base Station—is a small cellular base station, typically designed for use in residential or small business environments. It connects to the service provider’s network via broadband (such as DSL or cable); current designs typically support 2 to 5 mobile phones in a residential setting. A femtocell allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. The femtocell incorporates the functionality of a typical base station but extends it to allow a simpler, self contained deployment; for example, a UMTS femtocell containing a Node B, RNC and GSN with Ethernet for backhaul. Although much attention is focussed on UMTS, the concept is applicable to all standards, including GSM, CDMA2000, TD-SCDMA and WiMAX solutions.

For a mobile operator, the attractions of a femtocell are improvements to both coverage and capacity, especially indoors. There may also be opportunity for new services and reduced cost. The cellular operator also benefits from the improved capacity and coverage but also can reduce both capital expenditure and operating expense.

Femtocells are an alternative way to deliver the benefits of Fixed Mobile Convergence. The distinction is that most FMC architectures require a new (dual-mode) handset which works with existing home/enterprise Wi-Fi access points, while a femtocell-based deployment will work with existing handsets but requires installation of a new access point.

History

In 2002, a group of engineers at Motorola in Swindon, England, started a skunkworks team, called the "AFG", to develop new technologies. Some of their major achievements included the world's smallest full-power UMTS base station, one of the first demonstrations of television to mobile, and the invention and development of the access point base station (ie. Femtocell). The original design was intended to provide a direct equivalent to a WiFi access point, but for mobile cellular (UMTS, CDMA-2000 or WiMAX). The unit contained all the core network elements and did not require a cellular core network, requiring only a data connection to the Internet or WiFi core network[1].

By mid-2004 a number of companies were independently investigating femtocells (although mostly using other terms such as "residential base station" or "3G access point").[2]

Also in 2004, two femtocell-focussed companies were registered[3] at Companies House in the United Kingdom: 3Way Networks (now part of Airvana, Inc.) and Ubiquisys. By 2005, the idea had become more widely recognised with demonstrations and conference discussion. By this stage more companies were involved, including more established suppliers Samsung, Airwalk, ip. Access and RadioFrame Networks.

By early 2007, the idea had become mainstream, with a number of major companies publicly demonstrating systems at the cellular industry 3GSM conference in February, and operators announcing trials. In July, the Femto Forum trade organisation was founded to promote femtocell deployment worldwide, [要出典] comprising mobile operators, telecoms hardware and software vendors, content providers and start-ups. Its main work is conducted via four working groups, tackling regulatory issues, network and interoperability, radio and physical layer, and marketing and promotion.

In 3Q 2007, Sprint Nextel started a limited rollout in Denver, Indianapolis and Tennessee of a home-based UbiCell femtocell built by Samsung called the "Sprint Airave", which worked with any Sprint handset.[4] Airave was rolled out nationwide on 17 August 2008.[5]

As well as system manufacturers, semiconductor companies have announced chip-level products to address this application. Analog Devices has developed a chipset for the RF-IF and baseband, while picoChip claims significant commercial traction on their baseband Digital Signal Processor[要出典].

Issues

Although claims are made that Femtocells could be a panacea for straightforward system deployment, there are a number of complications that need to be overcome.

Interference

The placement of a femtocell has a critical effect on the performance of the wider network, and this is one of the key issues to be addressed for successful deployment.

Without unique spectrum for the femtocell 'underlay network', or very careful spectrum planning in the wider network, there is a concern that femtocells could suffer from severe interference problems. For example, in a femtocell handover between a macrocell network to a home femtocell access point, there are limitations in the standards which must be taken into account. For example, there is a limitation in the number of adjacent cell sites - typically 16 - for which the mobile unit can scan for, measure and then pass to the RAN handover algorithm (for 2G and 3G standards, for example). Further, if a single frequency CDMA system is being operated, where the macro and femtocell network utilise the same frequency band (a typical situation for many operators who licensed only one 3G frequency band), then the power control algorithms of the macro cell and femtocell can create interference ,[6] where for example a mobile unit increases its transmit power to the femtocell as part of the 'near-far' power control inherent in CDMA systems, whilst it is within the coverage area of a macro unit. The resultant high power transmitter in the macro field acts as an interferer since the frequency is shared. Finally, there is the issue of coverage area, where in high-rise accommodation, femtocell users on different floors can create interference to other users. There are several partial solutions to this problem, but primarily the only way to prevent interference is to use a different frequency for the femtocell coverage, particularly for CDMA deployments. The partial solutions include utilising the mode-2 fixed power option available in the 3G configuration parameters, which would prevent the mobile unit power from increasing and causing interference, though there is an obvious performance trade-off if this approach is used.

Many vendors are reported to have developed sophisticated algorithms to address the problem, and modelling by carriers indicates this is viable.[要出典] As such, the trials now in place are designed to test these techniques and to determine to what degree interference is a problem and under what circumstances. In his paper for 'PIMRC 07',[7] Claussen describes the UMTS femtocell/macrocell interference problem and concludes that to manage the interference that "Essential requirements such as autoconfiguration and public access" are needed. In this case 'public access' means that all deployed femtocells using the same frequency (ie. of the same operator) would need to allow anyone to access the femtocell; there are obvious backhaul issues with this if the user is paying for the DSL or Cable backhaul connection. It is suggested in the paper that this could be offset by low cost calls. In another paper,[8] Ho and Claussen identify the pre-requisite for auto-configuration of the femtocell power level in order to reduce interference - though in Claussen's first paper the algorithm requires knowledge of the macrocell transmit power, which would require the operator to configure the femtocells centrally, and line-of-sight distance to the femtocell, which requires knowledge of where the femtocell is installed. In his second paper, Ho highlights the issue of increased network traffic due to handover messages between the macrocell and femtocell.

The 3GPP meeting reported that: "To the extent investigated so far co-channel deployment is feasible for open access. For closed access, analysis conducted so far indicates that co-channel deployment is feasible if adaptive interference mitigation techniques are used. Further work is required to summarise the trade-off between HNB performance and the impact on the macro layer and to determine whether an acceptable tradeoff can be identified".[9]

A number of companies [10] are using the approach of using the femtocell as a mobile phone (UE) in order to measure, synchronise and build a neighbour list of nearby base stations. From this information, power levels, spreading codes and other parameters can be determined and resolved in order to avoid interfering with existing infrastructure.

Spectrum

Crucially, access point base-stations operate in licensed spectrum. As licensed spectrum allocation is made to operators on a fee basis, deployment of equipment must meet the strict requirements of the licenses. To make best use of spectrum, operators use frequency and cellular planning tools to optimise the best coverage for a given amount of spectrum. The introduction of access point base stations using licensed spectrum that are sold directly to the customer has implications for frequency and cellular planning, since an unexpectedly located access point base station could interfere with other closely-located base stations.

Access control

There is also the related issue of what happens when a neighbor's mobile appliance attaches to the network using another neighbor's femtocell, or how that can be prevented from occurring.

Lawful interception

Access point base stations, in common with all other public communications systems, are, in most countries, required to comply with lawful interception requirements.

Equipment location

Other regulatory issues[11] 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 (see Ubicell) are using GPS within the equipment to lock the femtocell when it is moved to a different country;[12] this approach is disputed, as GPS is often unable to obtain position namely indoors because of weak signal.

Network integration

From an operational or deployment perspective, one of the key areas that needs to be considered is that of network integration. A conventional cellular network is designed to support a relatively small number (thousands, tens-of-thousands) of base stations, whereas a femtocell deployment of millions of consumer access points requires a different architecture to support this scaling. The issue of increase in network traffic as a result of co-channel macrocell / femtocell deployment is discussed in the paper by Ho and Claussen.[13]

Emergency calls

Access Point Base Stations are also required, since carrying voice calls, to provide a 911 (or 999, or 112) emergency service, as is the case for VoIP phone providers.[14] 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 utilising an Ethernet 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 QoS may be an issue.

Spectrum accuracy

To meet FCC/RA spectrum mask requirements, Access Point Base Stations must generate the RF signal with a high degree of precision, typically around 50 parts-per-billion (ppb) or better. To do this over a long period of time is a major technical challenge, since meeting this accuracy over a period longer than perhaps 12 months requires an ovenised crystal oscillator (OCXO). These oscillators are generally large and expensive, and still require calibration in the 12-to-24 month time frame. Use of lower-cost temperature-compensated oscillators (TCXO) provides accuracy over only a 6-to-18 month time frame. Both depend on a number of factors.

The solutions to this problem of maintaining accuracy are either to make the units disposable/replaceable after an 18-month period and thus keep the cost of the system low, or 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, potentially providing 100-nanosecond accuracy (standard deviation),[15] depending on the location of the master clock. 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 to calibrate the oscillator.[16] However, for a domestic femtocell, 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 precision to 100ppb for indoor base stations in Release 6 and has proposed a further loosening to 250ppb for "Home NodeB" in Release 8.

Handover

In order to ensure that the user gets the best data rate out of the system, the mobile appliance must somehow know to connect to the femtocell when within range, even if there is still sufficient signal from, for example, an external macrocell base station. Forcing the mobile appliance to do this, whilst preventing your neighbor's mobile appliance from doing the same, is quite a challenge. In addition, handoff from the femtocell to the wider area macrocell and back again is potentially quite complex.

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 is the cdma2000 Airave.[17] Femtocells are also under development for GSM, TD-SCDMA, WiMAX and LTE. The LTE study groups have identified femtocells ("Home eNode B") as a priority area.

Architectures

Home Node B (HNB)

In May, 2008, the 3GPP completed a feasibility study of femtocell network architectures. Architectures including Cellular Base Station, Collapsed Stack and UMA/GAN were evaluated. As a result, the 3GPP is pursuing a new Home Node B (or HNB) reference architecture which builds on elements from both the Collapsed Stack and UMA/GAN approaches.

As the 3GPP completes the formal standard towards at the end of 2008, vendors and operators will migrate to support this new architecture for 3G femtocells.

Note the 3GPP refers to 3G femtocells as Home Node Bs (HNBs).


Cellular Base Station (Picocell)

One approach for a femtocell is to use the traditional base station architecture. In this case, the femtocell is a base station, connecting to the core network using a standard interface; for example, a WCDMA Node B connecting to a RNC via a backhaul connection (the Iub). The slight difference to a typical base station deployment is that the backhaul would be carried over broadband ("Iub over IP") which may have quality & security concerns. A more significant drawback of this architecture is that standards based base station controllers are designed to support only a limited number of high-capacity base stations, not large numbers of simple ones. This architecture was previously referred to in the literature as a picocell deployment and is one in which a base station controller is introduced to provide the necessary support to the numerous small pico-head base stations.

Collapsed Stack

More common architectures collapse some of the network functionality into the base station ("collapsed stack" or "Base Station Router"), not just the base station itself (Node B or BTS) but also the controller (eg RNC) and enable local radio resource control. This would then connect back to the mobile operator core at a higher point eg Iu interface for WCDMA for central authentication and management. This addresses the scalability concerns above, as the resource is located locally. The original Access Point Base Station followed this architecture but also incorporated the core MSC/GSN functions of authentication, control and switching.

Collapsed Stack with UMA Backhaul

A variant of the above is to use GAN/EGAN Unlicensed Mobile Access (UMA) standards. In this case, the UMA/GAN client is integrated into the femtocell. UMA/GAN protocol provides the connection to the mobile core, tunneling the Iu protocol. This approach uses UMA/GAN's existing security, transport and device management capabilities.

UMA/GAN is an attractive option for operators to leverage their investment in the UMA Network Controller to support applications beyond femtocells, including dual-mode handsets/WiFi or fixed line VoIP with terminal adapters.

The approach for UMA-based femtocells differs from a dual-mode handset approach where the UMA client is integrated in the device. In the former system the terminal is not affected and the air-interface is still standard - the UMA client is incorporated in the femtocell.

SIP or IMS

The final, and most sophisticated structure is to move to a full IP-based architecture. This approach was utilised in the original Access Point Base Station. In this case, even more functionality is included within the femtocell, and the integration to the core is done using an IP-based technology, e.g. SIP, IMS or H.323.

Deployment

Currently, the most significant deployment is that of Sprint. This started in 3Q/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.[18] As of 17 August 2008, Airave has been rolled out on a nationwide basis.

A number of operators have announced intention to have field trials in 2008, including O2,[19] Softbank,[20] TeliaSonera,[21] and Vodafone.[22]

Most analysts agree that 2008 will primarily be field trials and soft launch, while commercial launch will be in 2009 [23] [24].

References

  1. ^ Motorola Swindon Labs BTS500D Concept Document
  2. ^ Disruptive Wireless
  3. ^ Companies House File Numbers 05213514 and 05247998, respectively
  4. ^ Airave
  5. ^ Sprint AIRAVE Nationwide Launch August 17
  6. ^ "Uplink Capacity and Interference Avoidance for Two-Tier Femtocell Networks", Vikram Chandrasekhar and Jeffrey G. Andrews
  7. ^ Performance of Macro- and co-channel femtocells in a hierarchical cell structure", Holger Claussen, Bell Laboratories Alcatel-Lucent, The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2007 (PIMRC'07)
  8. ^ "Effects of user-deployed, co-channel femtocells on the call drop probability in a residential scenario", Lester T. W. Ho, Holger Claussen, Bell Laboratories Alcatel-Lucent, The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2007 (PIMRC'07)
  9. ^ 3GPP TR 25.820 V1.0.0 (2007-11)
  10. ^ http://www.picochip.com/downloads/PC8209ProductBrief.pdf
  11. ^ FCC requirements for 911 provision by VoIP providers
  12. ^ Hands on with the Samsung Ubicell
  13. ^ "Effects of user-deployed, co-channel femtocells on the call drop probability in a residential scenario", Lester T. W. Ho, Holger Claussen, Bell Laboratories Alcatel-Lucent, The 18th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2007 (PIMRC'07)
  14. ^ FCC requirements for 911 provision by VoIP providers
  15. ^ IEEE-1588 Standard for a precision clock synchronization protocol
  16. ^ Hands on with the Samsung Ubicell
  17. ^ Sprint Customers in Select Areas of Denver and Indianapolis Get AIRAVE for Enhanced In-Home Coverage
  18. ^ Airave
  19. ^ O2
  20. ^ Softbank
  21. ^ TeliaSonera
  22. ^ Vodafone
  23. ^ 100,000 Femtocells Will Ship in 2008, But 2010 Will Be the Year of Real Volume, says ABI Research
  24. ^ Network World: interview with Motorola VP GM Alan Lefkof

See also

Further reading

Equipment

Software stacks

Chips and reference designs

Industry body

Independent research

Market

Equipment to chipset mapping

Cellular equipment vendor to femtocell vendor partnerships

Reported market estimates

Target product and service costs

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