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GSM, Global System for Mobile
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  The   GSM   logo   is   used    to   identifycompatible   handsets   and equipment GSM From   Wikipedia , the   free   encyclopedia GSM  ( Global   System   for   Mobile   Communications , srcinally   Groupe   Spécial     Mobile ), is   a   standard    set   developed  by   the   European   Telecommunications   Standards   Institute ( ETSI ) to   describe   technologies   for    second    generation  ( or    2G ) digital   cellular    networks . Developed    as   a   replacement   for    firstgeneration   analog   cellular    networks , the   GSM   standard srcinally   described    a   digital , circuit   switched    network optimized    for    full   duplex   voice   telephony . The   standard    wasexpanded    over    time   to   include   first   circuit   switched    datatransport , then    packet   data   transport   via   GPRS . Packet   datatransmission   speeds   were   later    increased    via   EDGE . The   GSMstandard    is   succeeded     by   the   third    generation  ( or    3G ) UMTS   standard    developed     by   the   3GPP . GSM   networks   will   evolve   further    as   they    begin   to   incorporate   fourth   generation  ( or    4G ) LTEAdvanced    standards . GSM is   a   trademark    owned     by   the   GSM   Association . The   GSM   Association   estimates   that   technologies   defined    in   the   GSM   standard    serve   80 % of    theworld  ' s    population , encompassing   more   than   5    billion    people   across   more   than   212   countries   and territories , making   GSM   the   most   ubiquitous   of    the   many   standards   for    cellular    networks . Contents 1   History2   Technical   details2 . 1   GSM   carrier    frequencies2 . 2   Voice   codecs2 . 3    Network    structure2 . 4   Subscriber    Identity   Module  ( SIM ) 2 . 5   Phone   locking2 . 6   GSM   service   security3   Standards   information4   GSM   open - source   software4 . 1   Issues   with    patents   and    open   source5   See   also6   References7   Further    reading8   External   links GSM  - Wikipedia , the   free   encyclopedia http ://  en . wikipedia . org  /  wiki  /  GSM1   of    10 10  /  29  /  2011   3 : 34   AM  History Early   European   analogue   cellular    networks   employed    an   uncoordinated    mix   of    technologies   and  protocols   that   varied    from   country   to   country ,  preventing   interoperability   of    subscriber    equipmentand    increasing   complexity   for    equipment   manufacturers   who   had    to   contend    with   varyingstandards   from   a   fragmented    market . The   work    to   develop   a   European   standard    for    digital   cellular voice   telephony    began   in   1982   when   the   European   Conference   of    Postal   and    TelecommunicationsAdministrations  ( CEPT ) created    the   Groupe   Spécial   Mobile   committee   and     provided    a    permanentgroup   of    technical   support    personnel ,  based    in   Paris . In   1987 , 15   representatives   from   13European   countries   signed    a   memorandum   of    understanding   to   develop   and    deploy   a   commoncellular    telephone   system   across   Europe . The   foresight   of    deciding   to   develop   a   continentalstandard     paid    off  , eventually   resulting   in   a   unified  , open , standard  -  based    network    larger    than   thatin   the   United    States . [ 1 ][ 2 ][ 3 ][ 4 ] France   and    Germany   signed    a    joint   development   agreement   in   1984   and    were    joined     by   Italy   and the   UK    in   1986 . In   1986   the   European   Commission    proposed    to   reserve   the   900   MHz   spectrum band    for    GSM . By   1987 ,  basic    parameters   of    the   GSM   standard    had     been   agreed    upon   and    15representatives   from   13   European   nations   signed    a   memorandum   of    understanding   in   Copenhagen , committing   to   deploy   GSM . In   1989 , the   Groupe   Spécial   Mobile   committee   was   transferred    fromCEPT   to   the   European   Telecommunications   Standards   Institute  ( ETSI ). [ 3 ] Phase   I   of    the   GSM   specifications   were    published    in   1990 . The   historic   world  ' s   first   GSM   call   wasmade    by   the   Finnish    prime   minister    Harri   Holkeri   to   Kaarina   Suonio  ( mayor    in   city   of    Tampere ) inJuly   1   1991 . The   first   network    was    built    by   Telenokia   and    Siemens   and    operated     by   Radiolinja . [ 5 ] 1992 , the   first   short   messaging   service  ( SMS   or    text   message ) message   was   sent   and    Vodafone   UK and    Telecom   Finland    signed    the   first   international   roaming   agreement . Work    had     begun   in   1991   toexpand    the   GSM   standard    to   the   1800   MHz   frequency    band    and    the   first   1800   MHz   network  became   operational   in   the   UK    in   1993 . Also   in   1993 , Telecom   Australia    became   the   first   network operator    to   deploy   a   GSM   network    outside   of    Europe   and    the   first    practical   hand  - held    GSMmobile    phone    became   available . In   1995 , fax , data   and    SMS   messaging   services    becamecommercially   operational , the   first   1900   MHz   GSM   network    in   the   world     became   operational   inthe   United    States   and    GSM   subscribers   worldwide   exceeded    10   million . In   this   same   year  , theGSM   Association   was   formed  . Pre -  paid    GSM   SIM   cards   were   launched    in   1996   and    worldwideGSM   subscribers    passed    100   million   in   1998 . [ 3 ] In   2000 , the   first   commercial   GPRS   services   were   launched    and    the   first   GPRS   compatiblehandsets    became   available   for    sale . In   2001   the   first   UMTS  ( W - CDMA ) network    was   launched    and worldwide   GSM   subscribers   exceeded    500   million . In   2002   the   first   multimedia   messaging   services ( MMS ) were   introduced    and    the   first   GSM   network    in   the   800   MHz   frequency    band     becameoperational . EDGE   services   first    became   operational   in   a   network    in   2003   and    the   number    of worldwide   GSM   subscribers   exceeded    1    billion   in   2004 . [ 3 ] By   2005 , GSM   networks   accounted    for    more   than   75 % of    the   worldwide   cellular    network    market , GSM  - Wikipedia , the   free   encyclopedia http ://  en . wikipedia . org  /  wiki  /  GSM2   of    10 10  /  29  /  2011   3 : 34   AM  GSM   cell   site   antennas   in   theDeutsches   Museum , Munich , Germany serving   1 . 5    billion   subscribers . In   2005 , the   first   HSDPA   capable   network    also    became   operational . The   first   HSUPA   network    was   launched    in   2007   and    worldwide   GSM   subscribers   exceeded    two billion   in   2008 . [ 3 ] The   GSM   Association   estimates   that   technologies   defined    in   the   GSM   standard    serve   80 % of    theglobal   mobile   market , encompassing   more   than   5    billion    people   across   more   than   212   countriesand    territories , making   GSM   the   most   ubiquitous   of    the   many   standards   for    cellular    networks . [ 6 ] Technical   details GSM   is   a   cellular    network  , which   means   that   cell    phonesconnect   to   it    by   searching   for    cells   in   the   immediate   vicinity . There   are   five   different   cell   sizes   in   a   GSM   network  — macro , micro ,  pico , femto   and    umbrella   cells . The   coverage   area   of each   cell   varies   according   to   the   implementation   environment . Macro   cells   can    be   regarded    as   cells   where   the    base   stationantenna   is   installed    on   a   mast   or    a    building   above   average   roof top   level . Micro   cells   are   cells   whose   antenna   height   is   under average   roof    top   level ; they   are   typically   used    in   urban   areas . Picocells   are   small   cells   whose   coverage   diameter    is   a   fewdozen   metres ; they   are   mainly   used    indoors . Femtocells   arecells   designed    for    use   in   residential   or    small    businessenvironments   and    connect   to   the   service    provider  ’ s   network    viaa    broadband    internet   connection . Umbrella   cells   are   used    tocover    shadowed    regions   of    smaller    cells   and    fill   in   gaps   incoverage    between   those   cells . Cell   horizontal   radius   varies   depending   on   antenna   height , antenna   gain   and     propagation   conditions   from   a   couple   of hundred    metres   to   several   tens   of    kilometres . The   longest   distance   the   GSM   specification   supportsin    practical   use   is   35   kilometres  ( 22   mi ). There   are   also   several   implementations   of    the   concept   of an   extended    cell , [ 7 ]   where   the   cell   radius   could     be   double   or    even   more , depending   on   the   antennasystem , the   type   of    terrain   and    the   timing   advance . Indoor    coverage   is   also   supported     by   GSM   and    may    be   achieved     by   using   an   indoor     picocell    basestation , or    an   indoor    repeater    with   distributed    indoor    antennas   fed    through    power    splitters , todeliver    the   radio   signals   from   an   antenna   outdoors   to   the   separate   indoor    distributed    antennasystem . These   are   typically   deployed    when   a   lot   of    call   capacity   is   needed    indoors ; for    example , inshopping   centers   or    airports . However  , this   is   not   a    prerequisite , since   indoor    coverage   is   also provided     by   in -  building    penetration   of    the   radio   signals   from   any   nearby   cell . The   modulation   used    in   GSM   is   Gaussian   minimum - shift   keying  ( GMSK  ), a   kind    of continuous -  phase   frequency   shift   keying . In   GMSK  , the   signal   to    be   modulated    onto   the   carrier    is GSM  - Wikipedia , the   free   encyclopedia http ://  en . wikipedia . org  /  wiki  /  GSM3   of    10 10  /  29  /  2011   3 : 34   AM  first   smoothed    with   a   Gaussian   low -  pass   filter     prior    to    being   fed    to   a   frequency   modulator  , whichgreatly   reduces   the   interference   to   neighboring   channels  ( adjacent - channel   interference ). GSM   carrier   frequencies  Main   article : GSM     frequency   bands GSM   networks   operate   in   a   number    of    different   carrier    frequency   ranges  ( separated    into   GSMfrequency   ranges   for    2G   and    UMTS   frequency    bands   for    3G ), with   most   2G   GSM   networksoperating   in   the   900   MHz   or    1800   MHz    bands . Where   these    bands   were   already   allocated  , the850   MHz   and    1900   MHz    bands   were   used    instead   ( for    example   in   Canada   and    the   United    States ). In   rare   cases   the   400   and    450   MHz   frequency    bands   are   assigned    in   some   countries    because   theywere    previously   used    for    first - generation   systems . Most   3G   networks   in   Europe   operate   in   the   2100   MHz   frequency    band  . Regardless   of    the   frequency   selected     by   an   operator  , it   is   divided    into   timeslots   for    individual phones   to   use . This   allows   eight   full - rate   or    sixteen   half  - rate   speech   channels    per    radio   frequency . These   eight   radio   timeslots  ( or    eight    burst    periods ) are   grouped    into   a   TDMA   frame . Half    ratechannels   use   alternate   frames   in   the   same   timeslot . The   channel   data   rate   for    all   8   channels   is270 . 833   kbit  /  s , and    the   frame   duration   is   4 . 615   ms . The   transmission    power    in   the   handset   is   limited    to   a   maximum   of    2   watts   in   GSM850  /  900   and    1watt   in   GSM1800  /  1900 . Voice   codecs GSM   has   used    a   variety   of    voice   codecs   to   squeeze   3 . 1   kHz   audio   into    between   5 . 6   and    13   kbit  /  s . Originally , two   codecs , named    after    the   types   of    data   channel   they   were   allocated  , were   used  , called    Half    Rate  ( 6 . 5   kbit  /  s ) and    Full   Rate  ( 13   kbit  /  s ). These   used    a   system    based    upon   linear  predictive   coding  ( LPC ). In   addition   to    being   efficient   with    bitrates , these   codecs   also   made   iteasier    to   identify   more   important    parts   of    the   audio , allowing   the   air    interface   layer    to    prioritizeand     better     protect   these    parts   of    the   signal . GSM   was   further    enhanced    in   1997 [ 8 ]   with   the   Enhanced    Full   Rate  ( EFR  ) codec , a   12 . 2   kbit  /  scodec   that   uses   a   full   rate   channel . Finally , with   the   development   of    UMTS , EFR    was   refactored into   a   variable - rate   codec   called    AMR  -  Narrowband  , which   is   high   quality   and    robust   againstinterference   when   used    on   full   rate   channels , and    less   robust    but   still   relatively   high   quality   whenused    in   good    radio   conditions   on   half  - rate   channels . Network   structure GSM  - Wikipedia , the   free   encyclopedia http ://  en . wikipedia . org  /  wiki  /  GSM4   of    10 10  /  29  /  2011   3 : 34   AM
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