Basic Comcept of GSM
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Basic Concept of GSM Cellular Communications
Miftadi Sudjai, Ir., MSc., [email protected]
PT. StreamComBandung
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A Little Piece of History
AMPS, TACS, NMT, etc
GSMGPRS & EDGE
IMT-2000/
UMTS
1G 2G 2.5G 3G
Analog speech
Digial speech, low speed data
Digial speech,
low speed data,
medium speed
up to 384 kbs
4 QoS Class :
Conversational, streaming, interactive, & background
1983 1991 1998 200x
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Cellular Communication System• It provide wireless
connection from users to PSTN or between its users.
• Use “cells” in order to increase the total capacity, given a limited spectrum, by re-using the frequency over different areas.
• Use a Handover mechanism to enable an uninterrupted call connection when users move from one cell to another.
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What makes Cellular Radio work?• Allows frequency reuse
• Requires handover from one cell to the next • Attenuation of the propagating radio waves like
d-n, n > 2• High Quality services comparable to PSTN.• Other important considerations
– Multipath/fading
– Other-user interference– Spectral efficiency
– Quality of service
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Power Received at Mobile from Two Base Stations
• Power received at mobile
from station l:
• If stations A and B are using the
same channel,the signal power from B is cochannel interference:
Normalized Distance from Base A
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Rec
eive
d P
ow
er d
Bm
-130
-120
-110
-100
-90
-80
-70
-60
base A base B
from base C
received powerfrom base A
received powerfrom base B
received powerfrom base C
0 1 10 0
0 0
1
log / dBm
where distance from MS to BS
reference distance (power )
rate of change constant
l l l
l
P d K K d d
d
d K
K
1 10SIR , log / 1 dBA A A B A Ad D P d P D d K D d
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Radio Propagation has major impact …
0 50 100 150 200 250 30030
20
10
0
10
20
30
Time slot (0.67 ms)
Sign
al lev
el (d
B)
Received signal amplitude Controlled transmit power Controlled SIR (target = 10 dB)
TX power
Target SIR
RSL
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Handover Mechanism
BS1 BS2
A B
RS
L
Level at B
Level which HO occured
time
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Hexagonal Cell Geometry• Define coordinate axes,
U & V, at 60o angles• For given frequency
reuse plan, go i steps
in U directionand j
steps in V direction
• Number of cells in
reuse pattern is 2 2N i ij j
U
V
(2,1)
(1,3) (u,v)
1 3/
i = 2
j = 1
N = 7 reuse pattern
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Frequency Re-use Plan• Consider closest ring
of interfering BSs:
• No. of cells in reuse plan:
• It shows that
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Dco
R
min 1 10 10
1 10
SIR log / 1 10log 7 -1 dB
= log / 1 7.78 dB
co
co
K D R
K D R
2 2N i ij j
/ 3coD R N
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Interference and Capacity
MS
D
D-R
R
D-R
D-R/2
D+R
D+R/2
1st tier of co-ch cell, N=7
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Interference and Capacity• Co-ch reuse ratio, Q = (D/R)0.5 = (3N)0.5
• B spectrum is divided into k ch per Sel, then each cluster has k.N channel. If N cluster is repeated M times to cover the whole area/coverage, so the total capacity is: C = M.k.N
612i=2, j=2, etc
4.587i=1, j=2
33i=1, j=1
QCluster size (N)
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Interference • SIR of a MS:
where m = number of interfering cells in 1st tier
• Propagation law (path loss exponent):
n = 2 ..5
• If the interfering BS are equidistant:
∑=
=m
iiI
S
I
S
1
n
oor d
dPP
−
=
m
N
m
RD
D
R
I
S nn
m
i
ni
n )3()/(
)(1
===∑
=
−
−
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The GSM
Spectrum variant with 200 kHz ch Bandwidth:• GSM900 at 900 MHz
– 124 carriers @ 2x25 MHz band• GSM1800 at 1800 MHz (DCS1800)
– 375 carriers @ 2x75 MHz band• GSM1900 at 1900 MHz (PCS1900)
– 300 carriers @ 2x60 MHz band
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GSM Architecture
Base TransceiverStation (BTS)
Base TransceiverStation (BTS)
Base StationController (BSC)
Abis interface
Base Station (BS)
Base TransceiverStation (BTS)
Base TransceiverStation (BTS)
Base StationController (BSC)
Mobile Stations(MS)
Um interface
A interface
Base Station (BS)
Abis interface
CCITTSignalling
System No. 7(SS7)
interface
MobileSwitching
Centre(MSC)
GMSC
PSTN
VLRHLR
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Elements of the Network
• Subscriber: user who pays subscription charges for using mobile communication services.
• Mobile Station: is a subscriber unit intended for use while on the move at unspecified locations. It could be a hand-held or a portable terminal.
• Base Station: a fixed radio station used for communication with MS. It is located at the centre of a cell and consist of Transmitters and Receivers.
• Mobile Switching Centre : it coordinates the routing of calls, do the billing, etc.
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Mobile Station• MS consist of :
– Mobile Equipment (ME)– Subscriber Identification Module (SIM)
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SIM Card
• Subscriber Identity Module (SIM) is a smart card which stores information about the subscription and feature of services.
• Stored information including:• Authentication Key “Ki”• Encryption• IMSI and TMSI
• SIM card is protected by a Personal Identity Number (PIN) of the user
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Base Transceiver Station (BTS)• BSS consist of two part :
Base Transceiver Station (BTS)
Base Station Controller (BSC)
• BTS is a radio-end which determine a cell coverage and provide link with MS.
• BTS include Transmitters and Receivers, antenna and signal processing unit as well as interface.
• BTS communicate with MS via Um (air) interface
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Base Station Controller
• BSC control RRM for BTSs.
• BSC handle radio-channel setup, frequency hopping, and handover within BSC
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Mobile Switching Center (MSC)
• As a central switch for routing the traffic• Control BSC via A-interface• As a interconnection between GSM network with
other Networks via Internetworking Function (IWF)
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Home Location Register (HLR)
• HLR contain database of users, including all the subscription records
• HLR records the update location of every user for mobility management purposes
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Visitor Location Register (VLR)• VLR is a temporary
database of user • VLR is used to
handle a roamer connection.
• VLR could be accessed by MSC for every call set up.
• Every MSC is connected to a VLR, but a VLR could be connected to several MSC
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3G UMTS W-CDMA
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UMTS W-CDMA Services• High bit rates theoretically up to 2 Mbps in 3GPP Release
’99, and beyond 10 Mbps in 3GPP Release 5. Practical bit rates are up to 384 kbps initially, and beyond 2 Mbps with Release 5;
• Low delays with packet round trip times below 200 ms;• Seamless mobility also for packet data applications;• Quality of Service differentiation for high efficiency of
service delivery;• Simultaneous voice and data capability;• Interworking with existing GSM/GPRS networks.
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Class of Services
• 4 QoS Classes : 1. Conversational Service 2. Streaming
3. Interactive 4. Background • The main distinguishing factor is flow delay
sensitive of the traffic. • Conversational class is very delay sensitive,
while background class is the most delay insensitive.
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Characteristics of the Services
• Conversational :– e.g. Telephony/speech, VoIP, Video conferencing– Communication is real time between peers– Human perception of audio and video conversation
determine max. tolerable delay– Low delay
• Streaming :– Real time data flow to human/live destination– Delay is limited– Preserve time relation between info. Entities of the
stream
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Characteristics of the Services
• Interactive :– e.g. web browsing, data retrieval, server access,
LBS.– Request response pattern – Preserve payload content– More tolerant to delay
• Background :– e.g. Background delivery of e-mail, SMS, download,
data base, etc.– The destination not expecting data within certain
time– Preserve payload content, and not sensitive to delay
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UMTS W-CDMA Application
Multimedia Communication
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Multiplayer Games
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UMTS Basic Parameter
• Frequency Bands (FDD : 2x60 MHz):– 1920 to 1980 MHz (Uplink)– 2110 to 2170 MHz (Downlink)
• Frequency Bands (TDD: 20 + 15 MHz):– 1900 – 1920 MHz and 2010 – 2025 MHz
• RF Carrier Spacing:– 4.4 - 5 MHz
• RF Channel Raster:– 200 KHz
• Power Control Rate:– 1500 Cycles per Second
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UMTS W-CDMA Architecture
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Thank You