Politecnico di Milano Facoltà di Ingegneria dell Informazione. MRN -3 Mobility. Mobile Radio Networks Prof. Antonio Capone

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1 Politenio di Milano Faoltà di Ingegneia dell Infomazione MRN -3 Mobility Mobile Radio Netwos Pof. Antonio Capone

2 Mobility management o In mobile adio netwos, uses an feely move in te aea of te system anging te ell to wi tey ae assoiated o Tis obviously poses outing poblems (bot fo voie alls and data sessions) o All te poedues tat te system adopts fo allowing uses mobility wit seamless onnetivity ae denoted as mobility management A. Capone: Mobile Radio Netwos 2

3 Mobility management o Uses wile oaming te in sevie aea an: n Call n Be alled n Have an ative all/session o It is neessay to use some meanisms fo taing use position in te netwo and adapt outing aodingly A. Capone: Mobile Radio Netwos 3

4 Mobility management o In te ase of voie sevie, mobility management poedues diffes aoding to te use state, IDLE (no all in pogess) o ACTIVE (all in pogess) n ACTIVE: tee is an ative onnetion tat must be eouted at ea ell ange to guaanty ontinuous onnetivity (Handove) n IDLE: use must be loalized in ode to be eaed in ase of an inoming all (Loation Update, Cell Seletion, Cell Reseletion) A. Capone: Mobile Radio Netwos 4

5 Mobility management: Cell seletion o Use teminal autonomously selets te base station based on te level of te signal eeived by base station s o Base stations peiodially tansmits boadast message on a ommon ontol annel, wi inludes system infomation and its identity (ell ID) o Use teminal sans fequenies fo eeiving boadast messages of base stations in te neigboood o Teminal selet te base station fom wi it eeives te stongest signal o Teminal ontinues to san fequenies and weneve a base station wit a stonge signal is eeived te new ell is eseleted o In te ell seletion and eseletion poess also ote system infomation ae usually onsideed (lie te netwo identifiation) A. Capone: Mobile Radio Netwos 5

6 Handove A. Capone: Mobile Radio Netwos 6

7 Mobility management: Handove o Tis is te poedue tat allows a teminal wit an ative session to ange its base station witout loosing onnetivity o Handove is always stated by te netwo, based on measuements (signal stengt, quality, et.) pefomed bot on use and netwo sides o In ode to guaanty onnetivity and avoid infomation losses, andove poedues need to be fast and effiient o Fo te MRN tenologies we ll see ow andove is andled wit signaling and eouting poedues A. Capone: Mobile Radio Netwos 7

8 Mobility management: Handove Wen to stat a Handove? o Te seletion of andove ativation tesolds is a itial element o If is too small we may loose te onnetion beause time is not enoug o If is too big we may ave too many andove poedues even wen not neessay A. Capone: Mobile Radio Netwos 8 Dt t Handove TH Reeive TH

9 Mobility management: Handove o Tee ae diffeent possible appoaes 1 stongest signal o andove is initiated in A Due to signal flutuations onnetion an be swited ba-and-fot seveal times (ping-pong effet) A. Capone: Mobile Radio Netwos 9

10 Mobility management: Handove 2 stongest signal wit tesold o If signal of pevious BS is below a tesold (e.g. T2) and te powe of te new BS is stonge; andove is initiated in B A. Capone: Mobile Radio Netwos 10

11 Mobility management: Handove 3 stonge signal wit ysteesis o If te powe of te new BS is stonge wit a diffeene ³ ; andove is initiated in C A. Capone: Mobile Radio Netwos 11

12 Mobility management: Handove types o Had Handove (GSM-2G) In ea time only one onnetion is ative o Soft Handove (UMTS-3G) Use is ontempoay onneted to moe tan one base station A. Capone: Mobile Radio Netwos 12

13 Handove pefomane o Wen a andove is neessay a annel is eleased in te pevious ell and anote one must be available in te new ell o Let us define te andove failue pobability (P f ) as te pobability tat a andove equest is ejeted sine tee ae no annel available, and bloing pobability (P b ) as te pobability tat a new all is ejeted o If te system does not mae distintion between andove equests and all equestswe ave P f P b o Atually, it is usually moe toleable to blo new alls ate tan dopping aleady ative ones o We an ty to pivilege andoves A. Capone: Mobile Radio Netwos 13

14 Guad annels o Guad Cannels n Some annels ae eseved fo andove equests n P f beomes lowe but system apaity fo new alls is edued (P b is ineased) n Dimensioning guad annels may be itial and equies taffi and mobility estimations (ow many guad annels do we need?) A. Capone: Mobile Radio Netwos 14

15 Handove pefomane Witout guad annels New alls l i Completed alls Handove equests l Assumptions: Taffi flows of new alls and andoves ae Poisson poesses and ae independent m available annels µ We an simply use Elang-B wit B(A,m) A l i l µ A. Capone: Mobile Radio Netwos 15

16 Handove pefomane Wit guad annels New alls l i Completed alls Handove equests l µ Assumptions: Taffi flows of new alls and andoves ae Poisson poesses and ae independent m g available annels g eseved fo andoves Let us define: i li µ l µ A. Capone: Mobile Radio Netwos 16

17 Handove pefomane l l i l l i l l i l l g µ 2µ µ ( 1 ) µ ( ) g µ π 1 λ λ i π 0 ( ρ ρ i )π 0 µ π 2 1 ( 2 ρ ρ i ) 2 π 0... # % $ % &% π 1 (! ρ ρ i) π 0 1 π 1 (! ρ ρ i ) ρ π 0 < g A. Capone: Mobile Radio Netwos 17

18 Handove pefomane A. Capone: Mobile Radio Netwos 18 ( ) ( ) ( ) ( ) ( ) ( ) ( ) å å ( ) å å å å å å g i i g i g f g i i g i g b g i i g P P !! )! (!!!!! 1 p p p

19 Handove pefomane o Te model taes as input te paametes: l, l i, µ o Unfotunately, tese paametes ae dependent ea ote and basially detemined by taffi intensity and use mobility o Paamete t 1/µ epesents te aveage of te annel olding time X o Let us define te paamete t 1/ as te aveage time spent by a use in a ell X A. Capone: Mobile Radio Netwos 19

20 Handove pefomane o Let us define te paamete t1/µ as te aveage value of te all duation X o We ave: X min{ X, X } o Assuming X and X ae exponential andom values we an obseve tat : t 1 µ 1 µ A. Capone: Mobile Radio Netwos 20

21 Handove pefomane o Te pobability tat a all equies a andove is given by : P P X > X [ ] dx ηe ηx µe µy dy o Let us define n as te aveage numbe of andoves pe all: ν τ η τ µ 0 x η e (µη)y dx η µ η 0 A. Capone: Mobile Radio Netwos 21

22 Handove pefomane o We an now ompute l as a funtion of l i : 1/6 of taffi moving out of te ell o Solving by l : [( 1- P ) l ( P ) l ] l P 1- b i f l P ( 1- P ) [ 1- P ( 1- P )] i b f l A. Capone: Mobile Radio Netwos 22

23 Handove pefomane o Unfotunately te equation depends on te pobabilities P b and P f wi ae te values we want to ompute wit te Maov ain l ( 1- P ) [ 1- P ( 1- P )] i o We an adopt an iteative appoa to solve te poblem: P 1. We assign initial values to P b and P f and we ompute l 2. We solve te ain and ompae te esults wit te two values 3. If te diffeene us geate tat a tesold we set te values of P b and P f aoding to step 2 and tan go ba to step 1; otewise STOP. b f l A. Capone: Mobile Radio Netwos 23

24 Handove pefomane o In most ases oweve, it is easonable to assume tat P b and P f ae small o And teefoe: P ( 1- P ) l b l f [ ( )] i ( ) i i i 1- P 1- P 1- P o Obviously te assumption must be veified solving te ain P l µ nl A. Capone: Mobile Radio Netwos 24

25 Handove pefomane o Te andove failue pobability P f is not oweve a paamete dietly elated to sevie quality o We need to alulate te pobability tat a all is dopped due to andove failue: d P P P f f P 1- P P å i 0 P f P i P f P 2 ( 1- P ) n P f ( 1- P ) f ( 1- P ) A. Capone: Mobile Radio Netwos 25 i f... P P 1- P f 1

26 Handove pefomane o We still need to alulate paamete as a funtion of te teminal speed and ell size o Let us onside fist a simple ase wit squae ells: l a o # of andoves g # of oizontal lines # of vetial lines ossed A. Capone: Mobile Radio Netwos 26

27 Handove pefomane A. Capone: Mobile Radio Netwos 27 o We get: ( ) l V V l l d l l p g p a a p a a a p g p p 4 4 os sin 2 sin os 2 2 / 0 2 / 0 ú û ù ê ë é - ò wee V is te speed

28 Handove pefomane o In geneal we ave: L V p S Wee L is te peimete and S te aea o Poof: Let us onside an infinitesimal segment of te peimete dl and te pobability tat a teminal osses it in te time intenal dt. o Let f V (v) be te pobability density of te speed and a te inidene angle on segment dl o Teminal will oss te segment only if it is in te infinitesimal aea: dl a vdt osa A. Capone: Mobile Radio Netwos 28

29 Handove pefomane o Te pobability is ten given by te aea divided by te total aea: v osa dtdl p S o Aveaging on v and on a, we get: 1 2πS π /2 π /2 dv vf V ( v)osα dl dt dα 0 2πS 2 vf v V V 0 πs dldt VL o Integating along te peimete: p dt ps o And teefoe te ell L ossing fequeny: V p S 1 ( ) dl dt dv A. Capone: Mobile Radio Netwos 29

30 Mobility management: Handove LETTURA CONSIGLIATA: Tends in andove design Pollini, G.P. IEEE Communiations Magazine, Volume: 34 Issue: 3, Ma 1996 Page(s): A. Capone: Mobile Radio Netwos 30

31 Loation update A. Capone: Mobile Radio Netwos 31

32 Mobility Management: Loation Update o Loation Aea: topologial entity ieaially on top of te ell (goup of ells) o An IDLE teminal is loalized based on te Loation Aea (and not based on ell) o Te last Loation Aea visited is stoed into netwo data bases Data Base LA 1 LA 2 A. Capone: Mobile Radio Netwos 32

33 Mobility Management: Loation Update o If a IDLE teminal moves fom a LA to anote, it initiates a Loation Update poedue o Te infomation on te LA uently visited by a teminal is used by te netwo to oute inoming alls Data Base LA 1 LA 2 A. Capone: Mobile Radio Netwos 33

34 Paging o Wen a new all is oming, te data base is seaed to now te LA uently isited o Ten a paging poedue is stated o Evey base stations in te LA stat tansmitting a paging message wit te ID of te teminal on a boadast ontol annel o Wen te teminal eplies on te aess annel te exat ell is identified and te all is outed eply paging paging Data Base A. Capone: Mobile Radio Netwos 34

35 Paging vs. Loation Update o QUESION: n Wat is te most onvenient size (numbe of ells) of te Loation Aeas? o small o big n Wat does suggest to mae tem big and wat small? Data Base LA 1 LA 2 A. Capone: Mobile Radio Netwos 35

36 Paging vs. Loation Update o Te dimensioning of te loation aeas is a tadeoff between two opposite needs: n Ineasing te loation aea size (numbe of ells) we inease te signaling taffi due to paging n Deeasing te size we inease te signaling taffi due to loation updates o Tus tee is an optimal size tat depends on a numbe of paametes inluding te teminal mobility and te aival fequeny of alls A. Capone: Mobile Radio Netwos 36

37 Loation Aea dimensioning o A simple metod fo te dimensioning is based on te alulation of te signaling ost pe use o Let us onside squaed ells of edge l, and squaed loation aeas wit ells o Let us denote wit n C p te signaling ost pe use pe ell due to an inoming all [bytes/paging/ell] n C u te signaling ost due to a loation update [bytes/update] n l inoming all aival fequeny pe use [alls/ou/use] n u loation update fequeny pe use [update/ou/use] A. Capone: Mobile Radio Netwos 37

38 Loation Aea dimensioning o Te signaling ost pe use an be expessed as: ( ) Cu 2 C, l, u lcp u o Let us denote wit n m te aveage numbe of uses getting out of te loation aea in te time unit n te density of uses pe unit aea n v te speed of te use (VE[v]) A. Capone: Mobile Radio Netwos 38

39 Loation Aea dimensioning o Similaly to wat we did fo te alulation of te paamete fo te andove we an alulate: o And teefoe m m ( l 4l p V 4V lp u 1 u 2 ) A. Capone: Mobile Radio Netwos 39

40 Loation Aea dimensioning o Nomalizing C u to 1 and defining (,l) C(,l)/C u we an give te nomalized ost as: o wee, l) 2 lg u / ( 1 g C p / C u u 1 4V lp A. Capone: Mobile Radio Netwos 40

41 Loation Aea dimensioning o Let us define: D(, l, u ) (2 1 (, l, u -1) ( -1) gl - u ( -1) 1 ) - ( 1-1, l, u 1 ) o Te optimal value of, opt, an be omputed looing fo te maximum value of fo wi D is negative: # % opt (λ,u 1 ) $ &% 1 se Δ(2, λ,u 1 ) > 0 max Δ(, λ,u 1 ) 0 [ ] otewise A. Capone: Mobile Radio Netwos 41

42 Loation Aea dimensioning o Example: o We get: l 300 m V 8 m/ γ C p / C u 0.1 λ 0.6 [alls//use] opt u 4V lp [update//use] D(2, l, u D(3, l, u D(4, l, u D(5, l, u D(6, l, u D(7, l, u D(8, l, u ) ) ) ) ) ) ) 0.29 A. Capone: Mobile Radio Netwos