Slide môn Mạng Giảng viên Đỗ Trọng Tuấn

8/10/2019 Slide mn Mng Ging vin Trng Tun

1/20

1

1. Mt s khi nim

Tnh ton dung lng

trong mng GSM


2/20

2

Khi nim lu lng

Lu lng - traffic:

L thng tin (ngi s dng/bo hiu) mang trncc knh truyn dn

Lu lng gi bn (Busy hour traffic):

Thi gian chim knh trong gi bnA = C*t/T = C*t/3600

[Erlangs = (Calls/busy hour)*(mean call holding time) ]

Trong : A: lu lng [Erl]C: s cuc gi trong gi bn

t: thi gian trung bnh ca mt cuc gi (s)

T: thi gian kho st = 1h = 3600 s


3/20

3

Gi bn B.H - Busy Hour

B.H l gi c lu lng trao i qua cc knh ln nht trong ngy v

c xc nh theo s liu thng k.(Busy hour is that continuous 60 minutes time span of the day during

which the highest usage occurs).

Note:

may not occur at the same time every day

weekly variation

week day /weekend variation

seasonal variation


4/20

4

V d

Cho bit ti lu lng ca MS l bao nhiu khi thu bao di ng

tin hnh 2 cuc gi trong gi bn vi thi gian trung bnhl 90 s.

Ti lu lng Lu lng gi bn (Busy hour traffic):

A = C*t/T = C*t/3600 = 2*90/3600 = 50 mErl

ngha: thi gian chim knh ti gi bn ca MS l 180 s

tng ng vi ti lu lng 50 mErl

Thi gian trung bnh 1 cuc gi ca MS trong gi bn khong50 s90 s


5/20

5

Traffic Density / Intensity

Mt lu lng - Traffic Density is defined as the number

of simultaneous calls at a given moment.

Cng lu lng - Traffic Intensity represents the

average traffic density (occupancy) during any one hour

period.

Chim knh- occupancy is any use of of a traffic resource

regardless of whether or not a connection (call) is completed.


6/20


7/207

Quan h gia cc loi lu lng

Thit lp cuc gi

(knh bo hiu)

Knh

lu lng

Ao

Ab

Ac= Ao Ac

Ab

Ao= Ac+ Ab


8/208

Cp dch v GoS (Grade of Service)

Khi nim:GoS l thng s nh gi xc sut lu lngnghn (Ab) i vi mt s knh xc nh:

GoS = Ab/ Ao

Quan h gia lu lng v cp dch v GoS:Ab= GoS * Ao

Ac= (1 - GoS) * Ao

Gi tr GoS in hnh ca mng PLMN = 2%

-> lu lng nghn = 2% ; lu lng thc hin = 98%


9/209

Quan h gia lu lng v GoS

Thit lp cuc gi

(knh bo hiu)

Knh

lu lng

Ao

Ab

Ac= Ao Ac

Ab

A

c= f(Ao) = ?

Ac= (1-GoS)Ao = (1-GoS)*(1-GoS)*Ao

GoS GoS


10/2010

Loss and Delay Systems

H thng tn tht- A Loss System is one in which a callattempt is rejected when there is no idle resource to serve

the call. (GSM system)

Blocked callscuc gi b nghn

Resource = signalling channels + traffic channels

H thng tr- A Delay System is one in which call

attempts are held in a waiting queue until resource are

available to serve the calls.

Delayed calls


11/2011

M hnh Erlang B

L m hnh h thng thng tin theo kiu tn tht.

M hnh Erlang B c s dng tnh ton dung lng cho mng

thng tin di ng GSM.

Bng Erlang B: tra cu thng s theo m hnh Erlang B

* Th hin mi quan h gia 3 i lng:- S knh c s dng N

- Cp dch v GoS

- Lu lng yu cu Ao

* Khi bit 2 thng s => tra cu thng s th 3

[*] V d:

Hy xc nh lu lng thc hin ca 6 knh c GoS = 2%


12/2012

Bng Erlang B

Ao = 2,2759 Erl

Ac = (1-GoS)Ao = (1 - 0,02)*2,2759 = 2,2304 (Erl)


13/2013

Hiu sut s dng knh

Khi nim: L t s gia lu lng p ng v s knh

c s dng:

= Ac*100/ N (%)

Vi v d trn: N = 6, GoS = 2% ; Ac = 2,2304 Erl

= Ac/ N = 2,2304*100/6 = 37%

= ? Khi GoS = 10%

= Ac/ N = 3,3826*100/6 = 56%

Nhn xt: Hiu sut s dng knh thp -> xc sut nghn

nh -> GoS nh -> cht lng tt.


14/2014

2. Tnh ton vng ph sng


15/2015

Bi ton

Cn quy hoch vng ph sng cho th trn C, s dng cng ngh

GSM900, dng 3 cp tn s cho mi cell vi cu hnh cp pht knh

bo hiu chun. Yu cu GoS = 2% vi mc lu lng d on c

th hin nh hnh v. Gi thit mi thu bao tin hnh 2 cuc gi

trong gi bn vi thi gian trung bnh ca mt cuc gi l 90 s.[*] Hy xc nh:

- Lu lng gi bn d kin trn 1 km2

- Dung lng ca 1 cell.

- Bn knh cc i ca cell (din tch cell hnh lc gic S = 2,6 R2)

- S cell cn thit ph sng cho c th trn C.

- Lp li cc php tnh trn khi cp pht 4 tn s cho mi cell.


16/2016

Mc lu lng d on th trn C


17/2017

Li gii

1. T hnh v ta c MS tch cc trong B.H l: 40 MS/km2

- Ti lu lng ca 1 MS l A = 2*90/3600 = 0,05 (Erl) Lu lng d kin trn 1 km2 trong gi bn l:

40 MS/km2* 0,05 Erl/MS = 2 Erl/km2

2. Mi cell c cp pht 3 cp tn s, s dng cu hnhknh bo hiu chun ti C0 , nh sau:

TS1TS0 TS3TS2 TS5TS4 TS7TS6

BCCH/CCCH SDCCH/8 TCH



RFC1

RFC2

RFC3

Sngmang

C0


18/2018

Bng Erlang B

Ao = 14,896 Erl


19/2019

- S knh lu lng ti mi cell l: 3*8 2 = 22 (TCH)

- Khi GoS = 2%, lu lng yu cu ca 1 cell l: 14,896 Erl

- Khi ti lu lng ca 1 MS l 33 mErl, s thu bao c th c

phc v trong 1 cell l: 14,896/0,033 451 MS

3. Din tch 1 cell l:

S = lu lng c cell / lu lng trn 1 km2

= 14,896 (Erl) / 2 (Erl/km2) = 7,448 (km2)

=> Bn knh cc i ca cell : R = (7,448/2,6)0,5 = 1,69 (km)

4. S cell ph sng c th trn C:

Ncell = Din tch th trn/Din tch 1 cell=35/7,448 5 (cell)


20/20

B mnK thut Thng tin

H ni, 9 - 2007

Email: [email protected]

Ging vin Trng Tun

Trng i Hc Bch Khoa H NiKhoa in t -Vin thng

Mn hc:Thng tin di ng

( Mobile Communications )

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