The purpose of this procedure is to teach or to help the GSM RF Engineers to effectively optimize the TCH Drop Rate. There different reason of TCH Drop Rate. In this procedure it tries to explain ...
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GSM Optimization Guide book Han Bin Jie / CMPAK 1. Call Drop Analysis........................... Analysis.................................................. .............................................. .............................................. .................................................3 ..........................3 .................................................................. ............................................. .............................................3 ......................3 1.1 Problem Description............................................ 1.2 Call Drop Caused by Coverage................................. Coverage........................................................ ........................................................ ................................. ...3 1.2.1 Reason Analysis.......................... Analysis................................................. .............................................. ........................................................3 .................................3 1.2.2 Solutions.................................... Solutions........................................................... .............................................. .............................................. ...................................4 ............4 1.3 Call Drop Caused by Handover..................................................... Handover............................................................................ .......................................4 ................4 1.3.1 Reason Analysis.......................... Analysis................................................. .............................................. ........................................................4 .................................4 1.3.2 Observation methods............................................................ methods................................................................................................. ..................................... 1.3.3 Solutions.................................... Solutions........................................................... .............................................. .............................................. ................................... ............ 1.4 Call drops !aused by "ault o" hard#are e$uipment or system parameter.............................% parameter.............................% 1.4.1 &arameter "ault........................................ "ault............................................................... .............................................. ............................................% .....................% 1.4.2 Hard#are "ault........................................................... "ault................................................................................. .................................... ..........................% ............% 1.4.3 'rong ()S longitude and latitude........................................ latitude............................................................................* ....................................* 1.4.4 +mpa!t "rom system !apa!ity e,pansion- upgrade and pat!h.................................... pat!h.................................... * 1. Call drop !aused by inter"eren!e....................... inter"eren!e.............................................. ...................................................................* ............................................* 1..1 Reason Analysis.......................... Analysis................................................. .............................................. ........................................................* .................................* 1..2 ethod to "igure out inter"eren!e type by OC/R...................................................* OC/R...................................................* 1..3 Solutions.................................... Solutions........................................................... .............................................. .............................................. ...................................0 ............0 1.% Call drop !aused by antenna and "eeder................................................ "eeder............................................................................... ............................... 1.%.1 Reason Analysis.......................... Analysis................................................. .............................................. ........................................................ ................................. 1.%.2 Analysis and solutions "or antenna and "eeder problem..........................................1 problem..........................................1 1.* Call drop !aused by b y transmission "ault.......................................... "ault................................................................. .....................................1 ..............1 1.0 Call drop !aused by utiliation o" repeater................................................. repeater.........................................................................11 ........................11 2 Assignment "ailure rate...................................... rate............................................................. .............................................. ............................................ ..................... .........11 2.1 &roblem Des!ription............................... Des!ription...................................................... .............................................. .......................................... ................... ...........11 2.2 Common "ault analysis....................................................... analysis.............................................................................. ..................................... .........................12 ...........12 2.3 Solutions....................................... Solutions.............................................................. .............................................. ............................................. ......................................... ...................13 13 3 SDCCH)CH !ongestion............................... !ongestion...................................................... .............................................. .............................................. ..................................14 ...........14 3.1 &roblem des!ription............................... des!ription...................................................... ............................................. ......................................................14 ................................14 3.2 Only SDCCH is !ongested................................ !ongested...................................................... ................................................................. ........................................... 1 3.2.1 Common problem analysis........................................................ analysis......................................................................................1 ..............................1 3.2.2 easures "or solving SDCCH !ongestion and sharing signaling load...................1% 3.3 )CH !ongestion................................ !ongestion....................................................... .............................................. ......................................................... .................................. ..1* 3.3.1 Common problem analysis........................................................ analysis......................................................................................1* ..............................1* 3.3.2 easures "or solving )CH !ongestion and sharing tra""i! load..............................1 load..............................1 4 Analysis o" handover "ailure rate....................................... rate.............................................................. ............................................................2 .....................................2 4.1 &roblem des!ription............................... des!ription...................................................... ............................................. ......................................................2 ................................2 4.2 Common "ailure analysis and solution............................................ solution........................................................................... ............................... ....21 Handover reason proportion analysis........................................................ analysis......................................................................................... ................................. ...24 .1 &roportion o" handover triggered by bad do#nlin5 $uality is high...................................24 .1.1 &roblem des!ription................................... des!ription.......................................................... ............................................. .................................... .................24 ...24
.1.2 Common "ault analysis......................................................... analysis............................................................................................2 ...................................2 .1.3 Solutions.................................... Solutions........................................................... .............................................. .............................................. .................................2 ..........2 .2 &roportion o" handover triggered by bad uplin5 $uality is high ........................................2% .2.1 &roblem des!ription................................... des!ription.......................................................... ............................................. .................................... .................2% ...2% .2.2 Common 6ault Analysis............................ Analysis................................................... .............................................. ........................................ .................2% 2% .2.3 )roubleshooting............... )roubleshooting..................................... ............................................. ..................................................................2* ...........................................2* .3 (ig proportion o" handover due to do#nlin5 level............................................................ 2* .4 (ig proportion o" handover due to uplin5 level........................................ level........................................................ ................ .........2* . big proportion o" handover due to distan!e.......................... distan!e................................................. .............................................20 ......................20 % RACH a!!ess validity.............................................. validity..................................................................... .............................................. ..............................................2 .......................2 %.1 des!ription.................................. des!ription......................................................... .............................................. .............................................. ..........................................2 ...................2 %.2 Common "ault...................................... "ault............................................................. ............................................. ................................................... ............................. .....2 %.3 Common "ault analysis....................................................... analysis.............................................................................. ..................................... .........................2 ...........2 %.4 )roubleshooting.............. )roubleshooting..................................... .............................................. .............................................. ................................................. .......................... .....3 * 7o tra""i! or handover in the !ell........................................... !ell.................................................................. ........................................................31 .................................31 *.1 des!ription................................ des!ription....................................................... .............................................. .............................................. .............................................31 ......................31 *.2 Common "ault analysis and troubleshooting......................................... troubleshooting......................................................................31 .............................31 0. !all su!!ess"ul rate..................................................... rate............................................................................ ...................................................................31 ............................................31 0.1 &A8+78 &A8+78 )+9O:)................................ )+9O:)....................................................... ............................................. ....................................................32 ..............................32 0.2 Communi!ation lin5 establishment "ail.................................................... "ail..............................................................................33 ..........................33 . reason and troubleshooting o" !overage lessening o" the sites.....................................................33 sites.....................................................33 .1 reason on sites sites side and troubleshooting................... troubleshooting.......................................... .................................................... ............................. ....34 .2 Others.................................... Others........................................................... .............................................. .............................................. ................................................3 .........................3 1 analysis and troubleshooting o" hot issues.............................................................. issues................................................................................... .....................3 3 1.1 terminating S has signaling but #hen it;s terminated- it tells that user is not in the serving area............................... area...................................................... .............................................. ............................................. .............................................. ........................ ....3 1.2 S has signaling but is impli!itly po#er/o"" po#er/o"" #hen being paged....................................3% paged....................................3% 1.3 S signaling unstable in idle state.......................................... state................................................................. ....................................... ................ ..3* 1.4 Signaling "lu!tuate during S ma5ing !alls............................................. !alls............................................................. ................ .......3* 1. 9!ho in S !ommuni!ation......................................... !ommuni!ation................................................................ ............................................ ..................... ........3* 1.% Other.................................. Other......................................................... ............................................. ............................................. .............................................. ............................30 .....30 11 typi!al !ase analysis and optimiation measures........................................... measures.........................................................................30 ..............................30 11.1 Case one................................... one.......................................................... .............................................. ..................................................................30 ...........................................30 11.2 !ase t#o......................................................... t#o................................................................................ .............................................. ............................................3 .....................3 11.3 !ase three....................................................... three.............................................................................. .............................................. ............................................4 .....................4 11.4 !ase "our.......................................... "our................................................................ ............................................. ...........................................................4 ....................................4 11. Case "ive................................... "ive.......................................................... .............................................. .............................................. ...........................................41 ....................41 11.% !ase si,................................................ si,...................................................................... ............................................. .................................................... ............................. ...41 11.* Case seven.................................. seven......................................................... .............................................. .............................................. .........................................42 ..................42 11.0 Case eight................................... eight.......................................................... .............................................. .............................................. .........................................42 ..................42
1. Call Drop Anal!i!
1.1 Problem Description SC
(SC
()S
S
1 9AS:R997) R9S:>)
2
9AS:R997) R9&OR)
... CO779C)+O7 6A+>:R9
3
C>9AR R9?
<1= Dedi!ate !hannel <)CH or SDCCH= is established <2= +" Abis spy is a!tivated <3= SACCH blo!5 not de!oded- Radio >in5 )imeout e,piry
6igure 1 Radio lin5 "ault signaling "lo#
1.2 Call Drop Caused by Coverage
1.".1 #ea!on Anal!i! Anal!i! （ 1 ） Call drop o!!urs in the "ollo#ing situations@ the server !ell;s !overage is too large due to various reasons
（2）Obvious holes #ithout being !overed e,ist in the boundary bet#een t#o !ells. （ 3 ） )oo small !overage may be be!ause hard#are e$uipment o" a !ertain !ell has problemssu!h as antenna is blo!5ed or (CCH )RB has problems
（ 4 ） Shado# e""e!t !aused by some tall buildings may bring "ast "ading o" S signal- then !all drops #hen handover !an;t be !arried out in time.
（ ） +" neighbor !ell isn;t de"ined !ompletely- S #ill be in !onne!ted status in the server !ell and !all drop o!!urs #hen S moves out o" the server !ell;s !overage.
1."." Solution! 1．6ind out #ea5 !overed areas )hrough tra""i! statisti! analysis- "irst #e shall ma5e sure #hether !ell;s !all drop rate is high 9 ACC9SS +7 to shrin5 the !overage. O" !ourse #e shall avoid blind area "rom appearing during the adustment. 4．9liminate hard#are "ault +" !all drop rate rises abruptly but other indi!ators o" the site are all normal- then #e shall !he!5 #hether its neighbor !ells #or5 #ell
1.3 Call Drop Caused by Handover
1.$.1 #ea!on Anal!i! Anal!i! 1．:nreasonable parameters 'hen ()S is !arrying out res!ue R,lev handover <#hen mobile phone;s R,lev is lo#er than +RB>9:>H- +RB>9D>H=+RB>9D>H=- some handover re$uest may "ail due to too #ea5 signal strength o" the in!oming handover !ell- and !all usually drops even i" the handover is su!!ess"ul due to too #ea5 signal strength. 2．)313 overtime )313 is overtime@ )313 starts to re!ord #hen (SC sends message HA7DO9R COA7D to S- )313 reset #hen (SC re!eives message HA7DO9R CO&>9)9 "rom target !ell "or in!oming handover or message HA7DO9R 6A+>:R9 "rom the original !ell. (SC #ill send message HA7DO9R COA7D to ()S- i" )313 re!eives none o" the upper t#o reply messages- (SC regards that radio lin5 "ails in the original !ell and then release !hannel o" the original !ell. Signaling "lo# is sho#n in 6igure 4.
6igure 4 !all drop due to )313 overtime
1.$." Ob!er%ation met&od!
+" high !all drop rate is !aused by handover problem- #e !an "ind out the main reason "or handover through analying OC/R tra""i! report. Handover may be !aused by do#nlin5 RB >99>- uplin5do#nlin5 RB ?:A>- uplin5do#nlin5 inter"eren!e- po#er budget <&(8)=- !all dire!tional retry- tra""i!- et!.
1.$.$ Solution!
Carry out D) in a large e,tent- be!ause handover is ta5en pla!e among !ells and ()S- !all drops in one !ell may be be!ause o" unreasonable handover setting #ith its neighbor !ells. &ay high emphasis on !ells have topologi!al relation #ith the original !ell and have high !ongestion rateand !he!5 #hether blind !ell e,ists around the original !ell. +" !all drop is !aused by these t#o reasons- #e shall modi"y relevant "re$uen!y and add ne# sites- or e,pand the !overage o" the original site. +" !all drop is due to unreasonable handover setting- #e !an modi"y handover parameter a!!ording to the "ield test. As to !all drops !aused by unbalan!ed tra""i! tra""i! and target ()S has no !hannel to hand over on busy hour- #e !an adust the tra""i! to solve it.
1.4 Call drops caused by fault of hardware euipment
or system parameter
1.'.1 Parameter (ault
'e !an !he!5 #hether parameters are reasonable through parameter !he!5ing tool- li5e #hether "re$uen!y planning is reasonable- #hether A+O o" )RB in the !ell !on"li!ts #ith ea!h other >;s )313 is higher than (SC;s (SSA&)0- then !all drops #hen S is !arrying out handover=. 'hen parameter +RB>9D>H and RB>9+7C9>> are unmat!hed in de"inition- it is easily to ma5e !all drop be!ause #hen S rea!hes +RB>9D>H or +RB>9:>H but there is no neighbor !ell rea!h the RB>9+7C9>>. (esides- unreasonable HOA8+7 also !auses !all drop during the handover. 'e !an observe #hether the de"initions o" )311 and )31* are so stri!t that system has no su""i!ient time to send assignment !ompleted message to (SC- and !all drops be!ause timer has already reset.
1.'." Hard)are (ault
'e !an !he!5 alarm related to hard#are in OC/R i" !all drop is !aused by hard#are "ault. +" there is no hard#are alarm in OC/R- it may be !aused by "ault o" a !ertain )RB or diversity part- then at the same time assignment "ailure rate and uplin5do#nlin5 $uality handover proportion #ill be very high. 'e !an "ind out the "ault by A(+S monitoring so"t#are or by !arrying out C?) to suspi!ious )RB a"ter turning o"" other )RB in the !ell. 'e shall repla!e the "aulted hard#are in time on!e dis!over it i" there is no e$uipment available "or repla!ing- #e shall turn turn o"" "aulted "aulted e$uipm e$uipment ent to avoid avoid !all !all drops drops that that may impa!t impa!t net#or net#or5 5 opera operatio tion n $ualit $uality. y. 8enerally- #hen "rame pro!essing unit is "aulted- assignment "ailure rate and uplin5do#nlin5 $uality handover proportion #ill be high #hen re!eiving part is "aulted- assignment "ailure rate and uplin5 $uality handover proportion #ill be high #hen transmitting part is "aulted- "aultedassignment "ailure rate and do#nlin5 $uality handover proportion #ill be high.
1.'.$ *ron+ B,S lon+itude and latitude
+n the "ield D)- #e "ind that sometimes "e# ()S;s longitude and latitude are not the same #ith those in the planning or even have huge di""eren!es #ith them. +t is mainly be!ause di""i!ulties appeared in site sele!tion ma5e it impossible to lo!ate ()S a!!ording to design demand. (ut the ne# lo!ation o" the site #asn;t updated in planning database- and #e still planned its neighbor !ells and "re$uen!ies a!!ording to the original plan- then lots o" neighbor !ells are missed or set #rong and this "inally !auses high !all drop rate.
1.'.' -mpat (rom !!tem apait epan!ion0 up+rade and
pat&
A"ter system has been adusted on a large s!ale- li5e !utting over ne#ly/added sites "or laun!h()S !apa!ity e,pansion- "re$uen!y re/planning- upgrade and pat!h- #e shall !arry out an overall !he!5ing !he!5ing and adustment adustment to its related related system parameters. parameters. 'e shall pay spe!ial spe!ial attention attention to neighbor !ell relations- "re$uen!y inter"eren!e inter"eren!e as #ell as hopping parameterparameter- !ell parameter- et!.
1.! Call drop caused by interference
1..1 #ea!on Anal!i! Anal!i!
(e!ause the "re$uen!y o" SDCCH that ()S assigns to S may not be the same #ith that o" )CH#e need to analye analye them separate separately. ly. +nter"eren!e +nter"eren!e in!ludes in!ludes !o/!hann !o/!hannel el inter"ere inter"eren!en!e- ada!ent ada!ent !hannel inter"eren!e and intermodulation inter"eren!e. 9rror rate #ill be deteriorated and mobile phone !an;t demodulate (S+C o" neighbor !ell a!!urately or !an;t re!eive S measure report !orre!tly #hen mobile phone re!eives strong !o/!hannel or ada!ent !hannel inter"eren!e signal. +ntermodulation inter"eren!e is produ!ed by transmitter o" analog ()S in digital and analog !o/ sited ()S the dire!t impa!t o" this 5ind o" inter"eren!e is ()S resour!e #aste be!ause time slot !an;t be assigned.
1.." Met&od to (i+ure out inter(erene inter(erene tpe b OMC2# 1 ） 'e !an observe OC/R !ounter related to inter"eren!e. +n some systems- #hen !hannel is idle- system #ill observe the inter"eren!e to the !hannel and report it in a !ertain period. 'hen !hannels #or5ing in inter"eren!e are too many- then #e !an udge that the s ystem has inter"eren!e. 2 ） 'e !an udge #hether uplin5 inter"eren!e e,ists through observing the absolute value o" the average level in RACH re$uest that !an be de!oded by system. 3 ） 'e !an udge through observing handover reason statisti! o" OC/R. +n normal situation&(8) handover shall be mu!h more than other handover
1..$ Solution! 1．9liminate uplin5 inter"eren!e )his is the main inter"eren!e at present. :plin5 inter"eren!e o"ten o!!urs on a period #ith the ma,imum tra""i!. +t mainly !omes "rom !o/!hannel inter"eren!e or e,terior inter"eren!e. Co/ !hannel inter"eren!e is related to the tra""i! o" intra/"re$uen!y !ell the higher tra""i!- the larger inter"eren inter"eren!e. !e. 9,terior 9,terior inter"ere inter"eren!e n!e is intermodul intermodulation ation inter"ere inter"eren!e. n!e. :plin5 :plin5 inter"ere inter"eren!e n!e !an be solved by analying related reports in D)- modi"ying !o/!hannel "re$uen!y in intra/"re$uen!y !ellin!re in!reasi asing ng distan distan!e !e bet#e bet#een en t#o intra/ intra/"re "re$ue $uen!y n!y !ells !ells
C9>>D)BDO'7>+7F= both o" them use AD te!hnology and stop transmitting #hen voi!e signal isn;t transmitted
1." Call drop caused by antenna and feeder
1.3.1 #ea!on Anal!i! Anal!i! 1．Call drops due to di""erent do#nup tilt angles o" t#o pairs o" antennas +n ()S installation- ea!h dire!tional !ell has t#o pairs o" antennas- then (CCH and SDCCH o" the !ell may be transmitted separately by di""erent antennas. Di""erent Di""erent do#nup tilt angles o" t#o pairs o" antennas #ill !ause di""erent !overage o" the t#o pairs o" antennas- #hi!h means !all drops may o!!ur #hen subs!riber !an re!eive (CCH but !an;t o!!upy SDCCH sent by another antenna #hile setting a !all. 2．Call drops due to antenna;s aimuth aimuth angle +n ()S installation- ea!h dire!tional !ell has t#o pairs o" antennas. +" the aimuth angles o" the t#o pairs o" antennas are di""erentdi""erent- then !all drops o!!ur #hen subs!riber !an re!eive SDCCH and be assigned to )CH sent by another pair o" antenna. 3．Call drops due to antenna "eeder )he transmitting po#er and re!eiving sensitivity #ill be de!reased due to damaged and "olded "eeder- or be!ause "eeder is a""e!ted by #ater or loose !onta!t. Conse$uently- !all drop o!!urs severely. 'e !an as!ertain the reason through testing S'R. 4 ． Call drops due to too short distan!e bet#een antennas "or diversity or unparallel R, and ),
antennas A !ertain horiontal distan!e bet#een t#o pairs o" antennas should be insured to realie diversity re!eiving other#ise re!eiving sensitivity #ill be de!reased and !all drops #ill o!!ur. 'hen #e use diversity re!eiving antenna- generally an ideal e""e!t #ill be obtained and gain is 3d( i" distan!e bet#een R, and ), antennas is about 3 to meters. (ut diversity re!eiving #ill be hard to realie i" the distan!e bet#een R, and ), antennas is shorter than 1 meter. (esides- i" R, and ), antennas are unparallel- or even transmitting antenna dire!ts re!eiving antenna- or there is a very tall iron pole not "ar a#ay "rom R, and ), antennas- signals #ill be obstru!ted and re"le!ted easily and inter"eren!e #ill be produ!ed. ．Call drops due to too strong ba!5#ard signal strength "rom dire!tional antenna +" ba!5#ard signal "rom a !ell;s dire!tional antenna antenna is too strong- !all drops #hen S o!!upies the signal but !an;t "ind its neighbor !ell.
1.3." Anal!i! and !olution! (or antenna and (eeder problem 1．Che!5 antenna;s aimuth aimuth angle and do#nup tilt angle +" !all drops due to in!orre!t antenna;s aimuth angle and do#nup tilt angle- #e shall "irst observe the ()S. 'e !an "ind out "ault reason by !arrying out C?)- D) #hile !ombining #ith statisti!s "rom OC in "aulted !ells- and de!rease !all drop rate through adusting antenna aimuth angle and do#nup tilt angle. +" it is be!ause o" too strong ba!5#ard signal strength "rom dire!tional antenna- #e shall repla!e the antenna in time. 2．9liminate "eeder problem +" !all drops are due to de!reased ()S transmitting po#er and re!eiving sensitivity !aused by damage damaged d "eeder "eeder or loose loose !onta! !onta!tt- #e !an as!er as!ertai tain n "ault "ault reason reason and "aulte "aulted d pla!e pla!e throug through h measuring "eeder by "eeder test instrument- so as to repla!e "aulted "eeders and !onne!tors in time. 7oti!es in "eeder system@ system@ Avoid Avoid "eeders "rom being !onne!ted reversely be!ause they are #rong labeled avoid "eeders "rom getting a""e!ted by #ater- pay attention to dust prevention and "irmness o" "eeder;s !ombination parts be "amiliar #ith "eeder;s #or5ing environment and physi!al nature- !he!5 #hether "eeder is aging a!!ording to pra!ti!al installation and !abling rather than doing analysis simply relying on S'R tested by instrument avoid other things "rom getting inside !onne!tors so that situations su!h as "eeder;s short !ir!uit or dust entry #on;t happen. 3．:se reasonable antenna type (e!ause presently sites distribute more densely and net#or5 stru!ture 5eeps on !hanging- #e suggest using some small/sied antennas #ith lo# gain and high "or#ard and ba!5#ard isolation in ()S in urban areas or areas #ith densely/distributed sites. 'e don;t need to #orry about any bad impa!t that small antenna may impose to signal !overage at all !ontrarily- radio spa!e #ill be purer and easier to be !ontrolled than be"ore be!ause o" antenna;s lo#er gain and higher "or#ard
and ba!5#a ba!5#ard rd isolat isolation ion.. A!!or A!!ordin ding g to the pra!ti pra!ti!al !al e""e e""e!t !t o" using using small small antenn antennaa- net#or net#or5 5 per"orman!e has has been improved obviously. obviously. 4．9liminate inter"eren!e "rom antenna ba!5#ard signal Antennas are usually installed on poles- to#ers or rails on top "loor in urban area- there"ore they may be too high and it;s not easy to !ontrol signal !overage- even ba!5#ard signal may be inter"eren!e to the net#or5. 'e suggest installing antennas on a "loor;s #alls- and then antenna;s ba!5#ard signal #ill be obstru!ted by buildings.
1.# Call drop caused by transmission fault 6aults 6aults in Abis inter"a!e inter"a!e in!lude in!lude that (SC doesn;t doesn;t re!eive re!eive measure measure report "rom ()S "ailed signaling during handover and some internal reasons impa!t o" error rate on Abis inter"a!e. )here isn;t many "aults o!!urs on A inter"a!e- most o" them are handover "ailure
1.$ Call drop caused by utili%ation of repeater Some business and trade !enters li5e shopping mall as #ell as some small ()S in !ounties use repeater to ampli"y signals dire!tly "or redu!ing investment and e,panding !overage. Signals are transmitted by "iber or in mi!ro#ave. Due to topography- environment and engineering e$uality reasons- demanded indi!ators !an;t be satis"ied and then !all drop o!!urs. 'hen #e use repeater- distan!e !ontrol parameter setting <)A setting= re$uires spe!ial attention. Other#ise distan!e reason #ill !ause handover "ailure- !onse$uently !all drop or !all !learing. 'e usually transmit signals in mi!ro#av mi!ro#avee #hen using outdoor outdoor repeater repeater.. )here"or )here"oree repeater repeater ampli"ies inter"eren!e as #ell #hile ampli"ying re$uired ()S uplin5 and do#nlin5 signals. )hen signal $uality gets #orse and "inally !all drops a!!ompanied #ith obvious assignment "ailure rate raise. 'e shall survey repeater;s real surrounding !ells a!!ording to its neighbor !ell de"inition #hile installing it- and pay spe!ial to #hether it #ill !ause mutual inter"eren!e inter"eren!e to its surrounding !ells i" so- !all drop due to handover "ailure <)313 overtime= and inter"eren!e #ill o!!ur. A"ter repeater
has been installed- #e shall observe #hether assignment "ailure rate- !all drop rate and handover proportion due to $uality reason are deteriorated suddenly i" so- #e !an as!ertain there is inter"eren!e. +" the situation mentioned above o!!urs- #e shall re/plan "re$uen!y- modi"y neighbor !ell listadust handover parameter and po#er !ontrol parameter. Any#ay- no matter #hat 5ind o" reason !auses !all drop- #e shall analye it through all 5inds o" test methods and test reports "rom OC- and !arry out C?) and D) periodi!ally.
" A!!i+nment (ailure rate
2.1 Problem Description Signaling "lo# assigned by )CH is sho#n in "igure*/. SC SS+87 R9?:9S) SS+87 6A+>:R9 <1= SS+87 6A+>:R9 <2=
<1= )he (SC !an;t allo!ate the resour!e re$uested by the 7SS <2= )he ()S !an;t a!tivate the !hannel re$uested by the (SC <3= )he mobile !an;t get hoo5ed on the proposed !hannel
6igure Signaling "lo# assigned by )CH )he "ollo#ing reasons !ause assignment "ailure@ ()S do#nlin5 "ault prevents assignment message "rom sending !orre!tly S !an;t re!eive the assignment message S !an;t identi"y the assignment message S !an;t o!!upy the assigned !hanne !hannel l ()S !an;t !an;t re!ei re!eive ve or !an;t !an;t identi identi"y "y SA( SA( "rom "rom S S ()S uplin5 uplin5 "ault "ault preven prevents ts assignment assignment !ompletion !ompletion message message "rom sending to (SC. 'hen S !an;t !an;t o!!upy o!!upy the !hannel assigned by net#or5- it #ill send ba!5 assignment "ailure message. Other situations #ill ma5e )31* overtime.
2.2 Common fault analysis 1．6aulted transmitter or re!eiver 8enerally assignment "ailure rate #ill be very high #hen )RB is "aulted in!oming handover "ailure rate #ill also be very high be!ause (SC assigns !hannel "or S during in!oming handover. +" a !ell;s assignment "ailure rate is over 1E- then it is most probably due to )RB "ault i" the rate is over E- usually #e suspe!t it is due to )RB "ault or inter"eren!e i" the rate is 3EGE- then it may be !aused by !ongestion or inter"eren!e i" the rate is lo#er than 3E- !ommonly it is be!ause o" radio environment in"luen!e. 2．Co/!hannel inter"eren!e or ada!ent !hannel inter"eren!e 'e shall analye it a!!ording to inter"eren!e value. High error rate !aused by inter"eren!e prevents prevents S "rom establishing the se!ond layer lin5 #ith ()S and then !auses "ailed assignment. 3．6eeder problem +" "eeder is bro5en or get !orroded- then S'R #ill be so high that it may impa!t re!eiving and transmitting per"orman!e. per"orman!e. 4．ain diversity antenna is blo!5ed or !an;t o""er symmetri! !overage 'hen antenna that only transmits )CH )RB is blo!5ed or its !overed area is di""erent "rom another antenna that transmits (CCH )RB or SDCCH )RB- then S may not o!!upy the )CH. ．:nreasonable parameters （HS7- A+O- )31* setting ） 'hen net#or5 uses hopping te!hnology- i" HS7 or A+O are set unreasonably- then !o/!hannel inter"eren!e or ada!ent !hannel inter"eren!e in one !ell or among !ells on the same A >ist #ill be severe and then assignment "ailure rate #ill be very high. 8enerally8enerally- #hen this situation happens- all indi!ators #ill not be good. Che!5 #hether )31* is set so stri!t that net#or5 n et#or5 has already released the !hannel be!ause )31* is overtime be"ore it gets assignment !ompletion message. %．)ransmission )ransmission "ault on A inter"a!e or Abis inter"a!e +" transmitting error rate is too high on A inter"a!e or Abis inter"a!e- then signaling e,!hange bet#een S and net#or5 net#or5 !an;t be be a!!omplished normallynormally- and then assignment "ailure "ailure happens. *．+mpa!t "rom repeater &lease re"er to !all drop analysis.
2.3 &olutions 1．'e shall shall !he!5 !ell;s in!oming handover e,e!ution "ailure rate "or better lo!ating the problem As!ertain #hether handover "ailure rate <
Che!5 #hether transmission problem e,ists through testing error rate by instruments i" yes- solve the problem.
$ SDCCH/,CH on+e!tion
3.1 Problem description )here are t#o 5inds o" !ongestions@ one is that net#or5 has no signaling !hannel to use in immediate assignment another is that net#or5 has no )CH to use in voi!e !hannel assignment. +n this se!tion #e mainly analye !ongestion problems as #ell as propose solutions and balan!e method to signaling load and tra""i! load. +n immediate immediate assignmentassignment- SDCCH assignment assignment "ailure "ailure !ounter !ounter a!!umulate a!!umulatess on!e (SC sends sends +9D+A)9 ASS+8797) R9I9C) a!!ording to !ommand that !hannel !an;t be a!tivated. 'hen there is no available SDCCH or ground resour!e on Abis inter"a!e- )3122 is in!luded in +9D+A)9 ASS+8797) R9I9C) message sent by (SC to S. )3122 de"ines the minimum interval "or S to set up the ne,t !all. Signaling "lo# is sho#n in 6igure %. .SC
(SC
()S
.S RACHCHA779>
CHA779>
CHA779>
R9?:+R9D
AC)+A)+O7
CHA779 > AC)+A)+O7 AC)+A)+O7 7ACF
（1 ）
+..9D+A)9 ASS+879.97) R9I9C)
+..9D+A)9 ASS+879.97) R9I9C)
.S 启动
（1）(SC 无法 无法给 给 MS 的请 的请求分 求分配无 配无线资 线资源 源
)3122
6igure % SDCCH !ongestion signaling "lo# 'hen assigning )CH- assignment "ailure o!!urs :R9 to SC
3.2 'nly &DCCH is congested
$.".1 Common problem anal!i!
1．>AC boundary problem +" a !ell lo!ates on the boundary o" >AC- then "re$uent >AC updating program triggers )CH !ongestion be!ause the !ell;s boundary may !ross a high tra""i! area. 'hen this situation happens- #e !an !he!5 that the !ell hands over "re$uently into #hi!h !ells #ith di""erent >AC and (SC by observing its hando"" status- and then optimie >AC AC=. +" #e use this method- #e shall also ta5e into a!!ount parameters related to C1C2 algorithm- !ell resele!tion hysteresis parameter and handover margin parameter- et!. 2．+mproper parameter !on"iguration )oo less signaling !hannels are !on"igured relevant parameters o" C1- C2 algorithm are set improperly )311- )3122 and )3212 are set improperly. improperly. 3．Hard#are "ault 6aulted or unstable hard#are su!h as )RB #ill trigger that (SC !an;t a!tivate the !hannel;s ground resour!e in immediate assignment. 4． 7eighbor !ell "ault "ault 7eighbor !ell;s !ell;s "ault #ill !ause server !ell !ongestion !ongestion be!ause it absorbs absorbs some e,tra tra""i!. tra""i!. ．+llegal subs!ribers; "re$uent registration Che!5 Che!5 #hethe #hetherr !onges !ongestio tion n is trigge triggere red d by "re$ue "re$uent nt regis registra tratio tion n o" some some roam/r roam/rest estri! ri!ted ted subs!ribers. +" a roam/restri!ted subs!riber enters a restri!ted area and 5eeps the mobile phone turning on- then the subs!riber #ill try to register on the lo!al net#or5 !easelessly but al#ays "ails due to authenti!ation "ailure. )his #ill aggravate the signaling load and e$ual the subs!riber o!!upies the !apa!ity o" a lo!al signaling !hannel.
$."." Mea!ure! (or !ol%in+ SDCCH on+e!tion and !&arin+
!i+nalin+ load 1．+n!rease the value o" !ell resele!tion hysteresis +" SDCCH !ongestion is due to >AC boundary problem and the !ongestion is not severe- #e !an in!rease the value o" !ell resele!tion hysteresis- so as to de!rease "re$uent S lo!ation update as mu!h as possible. 2．Re!on"igure !hannel type +" the method mentioned above doesn;t have mu!h e""e!t- #e !an re!on"igure )DA a!!ording a!!ording to )CH tra""i! status- li5e to !hange )CH time slot as SDCCH0 #hile re"erring to the times that )CH used as signaling !hannel. 3．De!rease )311 Adust Adust )311 )311 to redu!e redu!e system system resour resour!e !e #aste #aste.. 8ener 8enerall ally y- immedi immediate ate assign assignme ment nt !an !an be a!!omplished #ithin 3 se!onds. )hen #e set )311 as 3 se!onds to avoid (SC "rom assigning resour!e be!ause o" resending !hannel re$uest and to release resour!es that have been #asted "or other re$uests. 4．Adust ABretrans （ma,imum retransmission times） On the premise that the radio environment is "avorable- #e try to de!rease ABretrans to redu!e system resour!e #aste as mu!h as possible. 8enerally #e shall try to in!rease its value i" !ell;s load is normal. ．Adust )31* and )313 'e !an redu!e redu!e )CH #aste #aste by adust adusting ing )31* )31* and )313. )313. On the premise premise that the radio environment is "avorable"avorable- it only ta5es system about about 2 se!onds to assign )CH)CH- so #e !an set the lo#est )31* as 2s. 8enerally #e set both )31* and )313 as s. %．Adust )3122 'e !an prevent subs!ribers "rom "re$uently sending !hannel re$uest message #hi!h #ill in!rease net#or5 RACH and CCCH load by in!reasing )3122 #hen system has no resour!e > R9S9>9C) O66S9)
!ells as mu!h as possible. 0．+n!rease )3212 properly )3212 is used "or limiting the time o" periodi!al lo!ation update. 'e !an alleviate SDCCH load "rom periodi!al lo!ation update by in!reasing )3212. (ut #e shall be a#are that its value has to be shorter than SC !onnotative turning o"" time limit #hile modi"ying it. Connotative turning o"" time limit shall be set a little bit longer than Jperiodi!al lo!ation updateK other#ise- S #ill be regarded to be turned o"" by the net#or5 i" it doesn;t have any !onta!t #ith the net#or5 during a period o" time. ．9liminate hard#are "ault Che!5 #hether !ell and its neighbor !ells are #or5ing normally. Che!5 #hether )CH is available to as!ertain unstable e$uipment. +" neighbor !ell isn;t #or5ing normally- the !ell #ill ta5e the e,tra tra""i!.
3.3 (CH congestion
$.$.1 Common problem anal!i! 1．)ra""i! )ra""i! density is higher than ()S designed !apa!ity +" )CH 5eeps !ongested during a period o" time- it means subs!riber group has !hanged that ma5es the ()S tra""i! density higher than the original designed !apa!ity. As "or this situation- the easiest solution is to e,pand !apa!ity. 2．Handover problem :nreasonable !all model !aused by too "re$uent handovers among !ells #ill de!rease system !apa!ity !apa!ity.. &ing &ong handover handover !aused !aused by boundary boundary problemproblem- !overage !overage problem- inter"ere inter"eren!en!ehard#are "ault or parameter problem #ill trigger )CH !ongestion. 'hen system has inter"eren!e or hard#are problem- S re!eiving level #ill be high but signal $uality is bad. +" this happensS may be handed over out due to bad signal $uality and handed over in due to po#er budget reason- and then &ing &ong handover o!!urs. Some similar situations happen su!h as S !an also be handed over out due to )A reason and handed over in due to po#er budget reason. 3．)ransmission )ransmission problem +" transmission brea5s o"" "or an instant or high error rate o!!urs on Abis inter"a!e- be!ause the "ault hasn;t been transmitted to (SC and ground !ir!uit resour!e is unavailable #hen (SC is a!tivating !hannel- it is !ounted as !ongestion. +t is espe!ially obvious a"ter $ueuing "un!tion has
been a!tivated. )his problem #ill also trigger severe in!oming handover "ailure. (e!ause SC doesn;t 5no# the ()S has transm transmiss ission ion proble problem m and still still sends sends in!omi in!oming ng handov handover er re$ue re$uest st to the (SC(SC- then then !onse$uently in!oming handover re$uest "ails. (SC #ill also !ount this event as !ongestion. )his problem #ill last till S that try to handover in deletes the !ell on handover !ell list reported to the system. 4．+solated island problem 'hen a !ell;s !overage is isolated in an area- mostly the !ell !an;t "ind pre/de"ined neighbor !ellsand then S #ill al#ays stay in the !ell #here !all set up and !an;t be handed over no matter ho# signal !hanges till !all drops. 'e !an ta5e t#o measures to avoid this@ the "irst measure is to adust antenna o" the isolated !ell and eliminate isolated island phenomenon. 'e have to do tests many times to eliminate isolated island #ithout in"luen!ing !overed area- but tall tall buildi building; ng;ss isolat isolated ed island island phenom phenomeno enon n still still !an;t !an;t be elimin eliminate ated d !omple !ompletely tely be!aus be!ausee o" !omple,ity o" #ave propagation. So the se!ond measure is to de"ine ne# neighbor !ells "or isolated !ell. )he prin!iple "or de"ining parameters is that isolated !ell has the priority in lo!ation update and priority to be handed over in normal !ells. ． 7eighbor !ell problem problem &lease re"er to SDCCH !ongestion analysis. %． 7eighbor !ell de"inition de"inition problem 7eighbor !ells are not de"ined !ompletely !ompletely prevents !alls "rom "rom timely handover out and and then !auses !all drop. *．+mproper parameter setting )31* and )313 are set too long- $ueuing parameter is unreasonable handover threshold and handover margin are set unreasonably the de"inition o" !ell;s minimum a!!essing level and ()S po#er are unreasonable. unreasonable. 0．)CH is used as signaling !hannel +dle )CH is used as signaling !hannel due to la!5 o" SDCCH. )hen there is no resour!e available #hen SC is assigning !hannels. ．Coverage problem )hese problems e,ist in urban areas@ )oo )oo large !overage !aused by too high antenna height or unreasonable antenna do#nup tilt angle (S )B&'R AB is set too high due to RB>9 ACC9SS +7 is set too lo# the ()S overlaps its neighbor !ells be!ause its !overage is per"e!t in some dire!tions
a!tivated #hile assigning !hannel that #ill trigger !ongestion.
$.$. $.$." " Mea! Mea!ur ure! e! (or (or !ol% !ol%in in+ + ,CH ,CH on+ on+e! e!ti tion on and and !&ar !&arin in+ +
tra((i load 1．()S !apa!ity e,pansion +" !hanne !hannell !onges !ongestio tion n is !ause !aused d by limite limited d !apa! !apa!ity ity-- then then #e shall shall !al!u !al!ulat latee !ell; !ell;ss tra"" tra""i! i! re$uir re$uireme ement nt a!!or a!!ordin ding g to !ell; !ell;ss !onges !ongestio tion n rate rate and pra!ti pra!ti!al !al loaded loaded tra"" tra""i!i!- and in!re in!rease ase !orresponding radio resour!e in the planning. 2．&revent &ing &ong handover 'ithin the )313 time limit- )CH o" both server !ell and target !ell #ill be o!!upied at the same time during the handover- so too many handovers #ill #aste resour!e. )hen possibly #e shall redu!e handover times espe!ially #hen resour!e is tight. +" the ratio o" handover times to total !all times is too high- #e !an avoid unne!essary &ing &ong handover by in!reasing !ell;s handover po#er margin. &ossibly algorithm "or &ing &ong handover !ontrol shall also be a!tivated in proper situation. 6or instan!e- i" the outgoing handover is be!ause o" $uality reason- then in!oming handover due to po#er budget shall be re"used in a period o" time. 'e 'e shall pay spe!ial attention to it in dual dual band handover. handover. 3．A!tivate $ueuing "un!tion ?ueuing "un!tion has obvious e""e!t "or solving !ongestion !aused by temporary tra""i! summit. 4．Adust )313 and )31* De!rease time limits o" )31* and )313 to redu!e system resour!e #aste as mu!h as possible. ．Control SDCCH !ongestion 'hen 'hen SDCCH SDCCH is not enoughenough- (SC #ill #ill use )CH to transm transmit it signal signaling ing.. )here )here"or "oree i" )CH )CH !ongestion is !aused by la!5 o" SDCCH- #e shall !ontrol SDCCH !ongestion by the method mentioned above. %．9liminate neighbor !ell "aults Che!5 #hether there are "aults e,ist in neighbor !ells- "ind out unde"ined !ells through D) and neighbor !ell parameter !he!5ing. *．Shrin5 ()S !overage +" !ongestion is !aused by too large ()S !overage- then #e !an in!rease RB>9 ACC9SS +7 and de!rease (S )B&'R AB a!!ording to pra!ti!al situation.
．C2 algorithm optimiation +" a !ell is severely !ongested but its surrounding !ells are relatively idle- #e !an optimie the !ell;s tra""i! load through adusting parameter &) and CRO > (AR ?:A>+)L as 1=this is e$ual to shrin5 the a!!ess range o" the !ell;s RACH into an area that only the !ell !an !overso that part tra""i! #ill be shared. ean#hile- #e shall in!rease its neighbor !ell;s C2 and handover margin to avoid shared tra""i! "rom being handed over in again. 1．Adust antenna;s installation installation height as #ell as do#n tilt angle and up tilt angle &ossibly !ontrol ()S !overage by adusting antenna;s installation height as #ell as do#n tilt angle and up tilt angle- so as to optimie tra""i! load. (ut #e shall prevent blind area "rom appearing. 11．9liminate e$uipment "ault Repair "aulted e$uipment i" it is the reason "or in!omplete !hannel utiliation.
' Anal!i! o( &ando%er (ailure rate
4.1 Problem description 6rom vie# o" signaling- handover "ailure !ould be divided into t#o aspe!ts@ handover sele!tion "ailure and handover e,e!ution "ailure. >et;s ma5e deep analysis. Signaling pro!edure is illustrated in 6igure .
6igure handover "ailure pro!edure Handover sele!tion "ailure （ HA7DO9R S9>9C)+O7 6A+>:R9 6A+>:R9 ） is the di""eren!e bet#een amount o" HO COA7D "rom (SC to ()S and amount o" HO +7D+CA)+O7 re!eived by (SC. )he reasons o" handover "ailure sometimes are !hannel resour!e absen!e o" target !ell- or system system parameter parameterss or hard#are hard#are issues issues 2 !onne!tio !onne!tion n bet#een bet#een (SC and ()S=. ()S=. Handover e,e!ution "ailure （ HA7DO9R 9B9C:)+O7 6A+>:R9 ） is the di""eren!e bet#een amount o" HO COA7D "rom (SC to ()S and amount o" HO CO&>9)9 re!eived by (SC. )his re"le!ts the $uality o" radio inter"a!e in the air. 'hen handover su!!eeds- S #ill send HO CO&>9)9 message to target !ell. A"ter target !ell re!eives the message- one handover/in su!!ess #ill be !ounted i" this handover is +7)RA SC handover- a"ter originating (SC re!eives C>9AR COA7D message 9AR R9?:9S) to target (SC- the message in!ludes !lear reason #hi!h is handover "ailure. And then- one handover/in "ailure #ill be !ounted.
4.2 Common failure analysis and solution 1．Hard#are "ailure 'hen 'hen handov handover er e,e!ut e,e!ution ion "ailur "ailuree rate rate is very very highhigh- hard#a hard#are re "ailur "ailuree is most most possibl possiblee
allo!ation "ailure=. Here- #e have to lo!ate "ailure hard#are by tra""i! analysis- and dispose #ell in time. 2． 7eighbor !ell relationship relationship issue +n dedi!ated mode- S send measurement report to system by SACCH- and distinguish di""erent !ell RB po#er level #ith (CCH and (S+C. +" t#o !ells have same (S+C and (CCH- in normal situation- the distan!e bet#een the t#o !ells should be "ar enough- so nothing should be bet#een them. (ut due to isolated !ell environment- S o"ten send invera!ious report to system- this invera invera!io !ious us neighb neighbor or !ell !ell report report #ill #ill misgui misguide de handov handover er !ontro !ontroll progr program am send send handov handover er inun!tion- it #ill !ause !onne!tions in !ell attempt sending handover re$uest to !ell #ith lo# RB po#er level- named ping/pong handover- and result in higher handover/out handover/out "ailure rate "rom isolated !ell to target !ell. On the other hand- higher handover/in "ailure rate #ill appear at target !ell #hi!h has the same (S+C and (CCH #ith isolated !ell. Due to !ompa!t "re$uen!y reuse in urban- it sometimes results in isolated e""e!tiveness. )he prin!iple ho# to udge isolated point is- that observes #hether advantaged radio propagation environment e,ists bet#een isolated point C and Cell A- "or e,ample@ higher antenna height and small do#n tilt "or Cell C- open land- high#ay and river bet#een Cell A and Cell C- et!.
6igure 1 isolated e""e!tiveness e""e!tiveness +n the area o" !ity boundary- #hen more +7)RA/SC handover "ailure happens- and e,!ludes other possible "ailures- here !he!5 #hether "re$uen!y !hange on boundary neighbor !ell- #hi!h results in isolated e""e!tiveness. 6or a pair o" neighbor !ells- i" higher handover e,e!ution "ailure due to isolated e""e!tivenessAbis inter"a!e test !ould be done to "ind isolated !ell by !he!5ing time ahead <)A=. )hen bigger do#n tilt !ould abate isolated e""e!tiveness- or !hange (S+C to eliminate same (CCH(S+C. Che!5 #hether neighbor !ell table mat!hes ()S parameters- i" not- modi"i!ation should be done in OC/R. 3． 7eighbor !ell !hannel !hannel resour!e absen!e absen!e or transmission transmission "ailure +" handover sele!tion "ailure rate （ HO S9>9C)+O7 6A+>:R9 RA)9 ） is very high- it is possible that the load o" target !ell is very heavy- and #ithout available )CH. Here (SC re!eives HO +7D+CA)+O7 message- but handover !ould not be e,e!uted. 6or higher handover sele!tion "ailure rate bet#een a pair o" neighbor !ells- !he!5 #hether it is the load problem o" target !ell. 'hen 'hen tran transm smis issi sion on "ail "ailur uree happ happen enss in neig neighb hbor or !ell !ell
intra SC handover or inter SC handover- the problem #ill be more serious. (e!ause SC does not 5no# transmission "ailure bet#een (SC and ()S- i" handover re$uest happens- it #ill !ause !hannel allo!ation re$uest is sent to target (SC- and results in handover "ailure. )his problem #ill !ontinue until originating (SC does not re!eive S measurement measurement report about target target !ell. +" neighbor !ell !hannel resour!e absen!e results in handover "ailure- #e !ould re"er to solution o" )CHSDCCH !ongestion. +n addition- !on"iguring handover re$uest priority higher than allo!ation re$uest priority is also an e""e!tive solution "or handover sele!tion "ailure problem. 4．)errible radio environment +" handover e,e!ution "ailure rate （HA7DO9R 9B9C:)+O7 6A+>:R9R RA)9 ）is high- it is possible radio environment problem o" target !ell or originating !ell. )errible )errible radio environment #ill !ause that S !ould not re!eive handover !ommand "rom originating !ell- or !apture !hannel allo!ated by target !ell. 7ormally- the reason o" terrible radio environment is overlap !overage absen!e bet#een !ells. 'e 'e !ould !he!5 !overage predi!tion- espe!ially some spe!ial pla!es
)o !on"irm !ell inter"eren!e- proportion o" handover due to uplin5 do#nlin5 $uality !ould be estimated. +" !on"irming !ell inter"eren!e- !hange !ell "re$uen!y in time or eliminate inter"eren!e sour!e. *．Antenna issue Due to obstru!tion be"ore antenna or t#o antennae !overage asymmetry o" the same !ell- "or solution- please see allo!ation "ailure analysis. 0．Repeater issue "or analysis and solution- please see !all drop analysis. ．&arameters issue Due to in!onse$uent or mismat!h parameters- e.g. !on"iguring )313 #ith a small number results in S !ould not !apture !hannel i" target !ell. +" parameter des!ription o" neighbor !ell about >AC and C+ o" target !ell- it #ill result in higher handover sele!tion "ailure rate. 1．+n!omplete >AC list o" SC +" the de"inition o" R9O)9>AC table o" SC "aultiness or error- and there is SC boundary !ell de"inition on (SS side- it #ill result in handover sele!tion "ailure. 'hen handover re$uest rea!hes SC- SC "inds >AC does not belong to itsel"- SC #ill sear!h in remote >AC table. +" remote >AC table has no in"ormation about >AC- it #ill result in handover "ailure. 'hen e,e!uting +7)9R SC !ontinuous handover- i" there is no de"inition o" >AC o" target SC in originating SC- it #ill result in handover "ailure. 11．Higher signaling lin5 load impa!t Due to !ongestion !aused by heavy load on inter"a!e A- there is no available resour!e #hen sending handover re$uest and handover !ommand bet#een intra SC or inter SC. +n this situation- trun5 lin5 !apa!ity should be e,panded.
Hando%er rea!on proportion anal!i!
!.1 Proportion of handover triggered by bad downlin)
uality is high
.1.1 Problem de!ription
+t is one o" the res!ue handovers and it;s di""erent "rom normal po#er handover. Res!ue handover is !arried out not be!ause a server !ell #ith stronger signal has been dis!overed- but be!ause the present server !ell;s signal $uality is too bad to support normal !all. Handover triggered by bad do#nlin5 $uality is !arried out be!ause server !ell;s signal $uality is too bad RB?:A> D> H.
.1." Common (ault anal!i! 1．:nreasonable handover parameter +" > RB?:A> D> H is set too lo#- then it;s very easy "or voi!e $uality error rate to rea!h $uality handover threshold. +" handover algorithm udging period is too short- then $uality handover #ill ta5e pla!e even ust a "e# samplings are lost. 2．Hard#are problem +t may be do#nlin5 hard#are problem i" handover "ailure rate is high- su!h as ()S transmitter po#er ampli"ierampli"ier- transmitting antenna antenna or "eeder has has problem. 3．8S inter"eren!e Che!5 #hether !o/!hannel inter"eren!e or ada!ent !hannel inter"eren!e e,ists. +" there is severe inter"eren!e inside system- $uality handover #ill also be triggered during the !all be!ause o" bad voi!e $uality even i" subs!riber subs!riber !an o!!upy o!!upy the assigned !hannel. !hannel. (ut $uality handover handover usually !auses &ing &ong handover@ i" $uality handover is triggered by inter"eren!e- then !ommonly the original !ell;s signal strength is high but $uality is bad there"ore S #ill be handed over ba!5
into the original !ell again be!ause o" po#er budget even i" it #as handed over out due to $uality reason.
.1.$ Solution! 1．&arameter !he!5ing Che!5 #hether !ell handover parameter is set properly. properly. 2．9liminate hard#are problem +" there is do#nlin5 hard#are problem- "or instan!e- too small transmitting po#er o" some )RB- it #ill ma5e re!eiving signal;s strength and $uality o" S that uses the )RB is bad. +" this situation happe happensns- high high do#nli do#nlin5 n5 level level handov handover er #ill #ill a!!om a!!ompan pany y high high do#nli do#nlin5 n5 $ualit $uality y handov handover er.. )here"ore- #e !an !he!5 tra""i! !hange as #ell as the ratio o" in!oming handover to outgoing handover. Do#nlin5 hard#are problem #ill also ma5e do#nlin5 $uality handover- assignment "ailure- radio lin5 "ailure in!rease and mu!h higher than those o" other !ells. Some do#nlin5 hard#are problems #ill be sho#n in S'R alarm in OC/R. Solutions are@ tra!5 Abis inter"a!e- !he!5 #hether uplin5 and do#nlin5 are balan!ed- !he!5 do#nlin5 level status- measure S'R o" ()S- as #ell as !he!5 !ables in transmitter. 3．9liminate 8S system internal inter"eren!e 1 ） )ra!5 Abis inter"a!e. Abis analysis so"t#are !an "ind out do#nlin5 )RB #ith high level and bad $uality 2= Observe OC/R tra""i! report. +" the !ell;s tra""i! is high- then uplin5 $uality handover #ill also be very high 3 ） Analye !ell;s planning "igure. )ry to "ind out inter"ering !ell
!.2 Proportion of handover triggered by bad uplin)
uality is high
.".1 Problem de!ription
+t is one o" the emergen!e emergen!e handovers- !arried out i" server !ell;s uplin5 signal is too bad. )he target "or outgoing handover is a !ell #ith strongest (CCH signal among #ell/per"ormed neighbor !ells. Handover trigger threshold is > RB?:A> :> H- #hi!h is net#or5 uplin5 $uality handover threshold.
."." Common 4ault Anal!i! 1．)oo )oo stri!t parameter setting )his ma5es S easily rea!h the threshold o" handover !aused by $uality and handover be!ome "re$uent. 2．6a!ility "ault +" uplin5 handover times is great- it may probably !aused by the hard#are o" radio uplin5 transmission "a!ilities <)RB- antenna- diversity and "eeder=. 3．Coverage problem Che!5 #hether it relates to handover !aused by uplin5 and do#nlin5 po#er level. +" it;s the !ase，it may be result "rom inade$uate !overage. 4．:plin5 inter"eren!e See #hether uude!oded RACH level is too great in OC/R tra""i! statisti!s report- i" so- the "ault may !aused by uplin5 inter"eren!e. )a5e )a5e D) to see #hether there are inter"eren!e in the !ell. ．8S inter"eren!e 'hen there is inter"eren!e is 8S s ystem- handover !aused by voi!e $uality #ill be !onsiderably large.
.".$ ,rouble!&ootin+ 1．&arameter !he!5ing Che!5 the parameters o" !ell handover. 2．Che!5 the hard#are +" there are problems !on!erning uplin5 hard#are- loss o" !ell or some )RB #ill be great. At the same time- #e shall !he!5 the "ailure rate o" handover in. (e!ause i" uplin5 (9R is high- even i"
the do#nlin5 is normal- handover !an be hard to !arry out. +" there are problems !on!erning the uplin5- handover due to uplin5 po#er level- assignment "ailure and R> "ailure #ill be more than normal !ell. 3．9liminate e,ternal inter"eren!e )a5e the "ollo#ing measures to ma5e sure #hether it;s !aused by (CCH uplin5 inter"eren!e@ !he!5 related RACH demodulation level analye and !he!5 8S uplin5 "re$uen!y band using spe!trum analyer in ()S tra!5 Aibs !he!5 uplin5 M do#nlin5 balan!e and uplin5 distributed level !he!5 ()S transmission !able et!. 4．9liminate 8S interior inter"eren!e &lease re"er to the !ause o" handover due to do#nlin5 $uality.
!.3 *ig proportion of handover due to downlin) level 1．des!ription )his handover is an emergen!y one due to the signaling o" serving !ell is lo#er than normal !all re$uirements. )he target is the ada!ent !ell #ith strong (CCH signaling. note ： i" handover parameter setting is unreasonable- the !ell #hi!h handover is implemented out to is hard to "ind. Other#ise &(8) handover #ill be pro!essed. )hus this 5ind o" handover "ailure rate is great. Alarm threshold is > RB>9 D> H- that is- net#or5 do#nlin5 level threshold. 2．Common 6ault Analysis )his is not usually seen and it;s !aused mainly by the "ollo#ing reasons： 1） parameter setting is improper ； 2）do#nlin5 hard#are problem 3．)roubleshooting +t;s the same #ith handover due to do#nlin5 $uality !aused by problems o" parameter and hard#are.
!.4 *ig proportion of handover due to uplin) level 1．des!ription )his handover is an emergen!y type #hi!h is invo5ed #hen signaling level o" the serving !ell is lo#er than normal !all. )he target is the ada!ent !ell #ith the strongest (CCH signaling. 7ote@ i" handover parameter setting is reasonable- the !ell #hi!h handover is implemented out to is hard to "ind. Other#ise &(8) handover #ill be pro!essed. )hus this 5ind o" handover "ailure rate is great. Alarm threshold is > RB>9 :> H ，that is- net#or5 do#nlin5 level threshold. 2．&henomenon analysis 1）inade$uate !overage is a!!ompanied by mu!h handover due to uplin5 $uality 2）!ell handover parameter setting is improper ；
3）hard#are problem i" uplin5 M do#nlin5 is imbalan!e ； 4 ） &ing/pong handover bet#een t#o !ells. 6or e,ample- handover in to the ada!ent !ell #ith lo#er level due to $uality and ba!5 to the previous !ell due to &(D8 or level 3．troubleshooting parameter. !he!5 the handover parameters o" related !ell in!luding po#er handover （ 1 ） parameter. toleran!e- po#er level handover threshold- and minimum a!!ess level
（2）hard#are. !he!5 the hard#are using the "ollo#ing methods@ ma5e Abis tra!5- !he!5 !ell lin5 budget and spe!ial attention attention shall be given to balan!e balan!e o" uplin5 M do#nlin5. do#nlin5.
（3）!overage or ada!ent !ells. Che!5 the de"inition o" ada!ent !ells o" related sites is !onsistent #ith !overage predi!tions. Che!5 #hether there are are a great proportion o" handover bet#een bet#een ada!ent !ells due to $uality. $uality. +" there are ping/pong handover o" ada!ent !ells- inter"eren!e shall be 5ept in !ontrol. &lease re"er to $uality handoverM inter"eren!e !hapter +" isolated island or !overage problem is not "ound via )A gotten by Abis tra!5- D) is needed to solve the problem.
!.! big proportion of handover due to distance 1．&roblem des!ription )his handover is an emergent one due to large distan!e bet#een site and S. )he threshold is S RA789 AB- #hi!h is the ma,imum distan!e bet#een sites and S. 7oti!e@ the priority o" handover due to to distan!e is lo#er than handover due due to $uality and level- as a result- #hen handover due to distan!e is triggered- level and $uality shall all belo# the threshold. 'e !an redu!e isolated island e""e!tively by setting the distan!e threshold. 7oti!e：great proportion handover due to distan!e indi!ated that the !overage s!ope o" this !ell is greater than S RA789 AB （ it may be !aused by too high antenna- broad terrain and high building et!.） 2．Common "ault analysis 1 ） parameter S RA789 AB is too small < noti!e@ this unit o" this parameter is )A
