Issues Femtocell

1 issues

1.1 interference
1.2 lawful interception
1.3 equipment location
1.4 emergency calls
1.5 quality of service
1.6 spectrum accuracy
1.7 security

issues
interference

the placement of femtocell has critical effect on performance of wider network, , key issue addressed successful deployment. because femtocells can use same frequency bands conventional cellular network, there has been worry rather improving situation potentially cause problems.

femtocells incorporate interference mitigation techniques—detecting macrocells, adjusting power , scrambling codes accordingly. ralph de la vega, at&t president, reported in june 2011 recommended against using femtocells signal strength middle or strong because of interference problems discovered after widescale deployment. differs previous opinions expressed at&t , others.

a example comments made gordon mansfield, executive director of ran delivery, at&t, speaking @ femtozone @ ctia march 2010:

have deployed femtocells co-carrier both hopping channels gsm macrocells , umts macrocells. interference isn’t problem. have tested femtocells extensively in real customer deployments of many thousands of femtocells, , find mitigation techniques implemented minimise , avoid interference. more femtocells deploy, more uplink interference reduced.

the femto forum has extensive reports on subject, have been produced 3gpp , 3gpp2.

to quote summary paper — summary of findings:

the simulations performed in femto forum wg2 , 3gpp ran4 encompass wide spectrum of possible deployment scenarios including shared channel , dedicated channel deployments. in addition, studies looked @ impact in different morphologies, in closed versus open access. following broad conclusions studies:

1. when femtocells used in areas of poor or no coverage, macro/femto interference unlikely problem.
2. if femto network sharing channel (co-channel) macro network, interference can occur. however, if interference management techniques advocated femto forum adopted, resulting interference can mitigated in cases.
3. femtocell network deployed on adjacent dedicated channel unlikely create interference macro network. additionally, impact of macro network on performance of femtocell on adjacent channel limited isolated cases. if interference mitigation techniques advocated femto forum used, impact further marginalised.
4. closed access represents worst-case scenario creation of interference. open access reduces chances of user equipment (mobile phone handsets, 3g data dongles, etc.) on macro network interfering proximate femtocell.
5. same conclusions reached both 850 mhz (3gpp band 17) , 2100 mhz (3gpp band 1) deployments studied.

the conclusions common 850 mhz , 2100 mhz bands simulated in studies, , can extrapolated other mobile bands. interference mitigation techniques implemented, simulations show femtocell deployments can enable high capacity networks providing between 10 , 100 times increase in capacity minimal deadzone impact , acceptable noise rise.

femtocells can create better user experience enabling substantially higher data rates can obtained macro network , net throughputs limited backhaul in cases (over 20 mbps in 5 mhz).

lawful interception

access point base stations, in common other public communications systems, are, in countries, required comply lawful interception requirements.

equipment location

other regulatory issues relate requirement in countries operator of network able show each base-station located, , e911 requirements provide registered location of equipment emergency services. there issues in regard access point base stations sold consumers home installation, example. further, consumer might try carry base station him country not licensed. manufacturers using gps within equipment lock femtocell when moved different country; approach disputed, gps unable obtain position indoors because of weak signal.

emergency calls

access point base stations required, since carrying voice calls, provide 911 (or 999, 112, etc.) emergency service, case voip phone providers in jurisdictions. service must meet same requirements availability current wired telephone systems. phones must work if ac mains grid blacked out. there several ways achieve this, such alternative power sources or fall-back existing telephone infrastructure.

quality of service

when using ethernet or adsl home backhaul connection, access point base station must either share backhaul bandwidth other services, such internet browsing, gaming consoles, set-top boxes , triple-play equipment in general, or alternatively directly replace these functions within integrated unit. in shared-bandwidth approaches, majority of designs being developed, effect on quality of service may issue.

the uptake of femtocell services depend on reliability , quality of both cellular operator’s network , third-party broadband connection, , broadband connection’s subscriber understanding concept of bandwidth utilization different applications subscriber may use. when things go wrong, subscribers turn cellular operators support if root cause of problem lies broadband connection home or workplace. hence, effects of third-party isp broadband network issues or traffic management policies need closely monitored , ramifications communicated subscribers.

a key issue identified active traffic shaping many isps on underlying transport protocol ipsec.

spectrum accuracy

to meet federal communications commission (fcc) / ofcom spectrum mask requirements, femtocells must generate radio frequency signal high degree of precision. on long period of time major technical challenge. solution problem use external, accurate signal calibrate oscillator ensure maintains accuracy. not simple (broadband backhaul introduces issues of network jitter/wander , recovered clock accuracy), technologies such ieee 1588 time synchronisation standard may address issue. also, network time protocol (ntp) being pursued developers possible solution provide frequency stability. conventional (macrocell) base stations use gps timing synchronization , used, although there concerns on cost , difficulty of ensuring gps coverage.

standards bodies have recognized challenge of , implications on device cost. example, 3gpp has relaxed 50ppb parts per billion precision 100ppb indoor base stations in release 6 , further loosening 250ppb home node b in release 8.

security

at 2013 black hat hacker conference in las vegas, nv, pair of security researchers detailed ability use verizon femtocell secretly intercept voice calls, data, , sms text messages of handset connects device.

during demonstration of exploit, showed how begin recording audio cell phone before call began. recording included both sides of conversation. demonstrated how trick apple’s imessage – encrypts texts sent on network using ssl, rendering them unreadable snoopers, sms, allowing femtocell intercept messages.

they demonstrated possible clone cell phone runs on cdma network remotely collecting device id number through femtocell, in spite of added security measures prevent against cloning of cdma phones.