Transcript (BTS).

The Higher Institute of Industry
Postgraduate Program
Mobile Networks
GSM-GPRS-UMTS
Chapter 2
Course Instructor
Dr. Majdi Ali Ashibani
Email: [email protected]
Next Generation Networks (NGN)






Introduction
PSTN
Mobile IP
GPRS/UMTS
4G mobile networks
VOIP


VOIP QoS issues
Multimedia Control Protocols



course agenda
H323
H324
Session Initiation Protocol (SIP)

Soft Switching
Convergent Networks

Service Delivery Platforms (SDP)





IP Multimedia Subsystem (IMS)
OSA/Parlay
Next Generation Billing Systems
Ad Hoc Networks


Ad hoc routing issues
Ad hoc network security
(GSM) Global System for Mobile
Communication
services
1. Asynchronous and synchronous data, 300-9600
bps.
2. Alternate speech and data, 300-9600 bps.
3. Asynchronous PAD (packet-switched, packet
assembler/disassembler) access, 300-9600 bps.
4. Synchronous dedicated packet data access,
2400-9600 bps.
Network Architecture
PSTN/ISDN
MS
BSS
ME/SIM
MT
Um
NSS
BTS
(G)MSC
BSC
A
A-bis
X.25
X.25
B
F
D
VLR
C
OSS
•MS: Mobile Station.
OMC
•BSS: Base Station Subsystem.
SM
•NSS: Network Switching Subsystem.
EIR
AuC
HLR
Network Architecture
Used to get and make calls and it is
PSTN/ISDN
composed of two entities:
•Mobile
Equipment (ME).NSS
BSS
•Subscriber Identity Module (SIM).
ME/SIM
BTS
(G)MSC
MT
Um
BSC
•Mobile Terminal (MT).
A
A-bis
B
VLR
ME: Represents the cell phone itself without the SIM-card.
MT: Generally a PDA, PC, …
Each cell phone has a unique
International Mobile
X.25
X.25
F
D
C
Equipment
Identity (IMEI)
number.
Can communicate
with
ME
via
a
serial
(DTE-DCE)
OSS
interface; e.g. serial cable,
PCMCIA,
Bluetooth,…
EIR
AuC
HLR
OMC
SIM: Is a smart card used for storing and handling
Use ATinformation.
commands. SM
subscriber
MS
Often
User is
it authenticated
is owned by the
viaoperator
a Personal Identity Number (PIN).
Contains
International
Mobile
Subscriber
Identity
(IMSI). for all
If PIN entered
incorrectly,
N times,
then phone
is locked
but emergency calls, until you enter a PIN Unblocking Key (PUK).
Contains both fixed and changeable subscriber information
Network Architecture
MS
BSS
ME/SIM
MT
Um
BTS
Which is responsible for the radio path
PSTN/ISDN
control and every call that is made in
the system is connected through it. This
NSS
part of the network is divided in two
(G)MSC
entities:BSC
A
A-bis
B
VLR(BTS).
•Base Transceiver Station
•Base Station Controller (BSC).
X.25
X.25
F
D
C
BSC takes
BTS
is responsible
care of air
for
interface
maintaining
signaling,
radio
ciphering
connections
and
OSS
speech
with
thecontrol,
MS and i.e.,
its main
it is responsible
task is to
administrate
forAuCmaintaining the
EIR
HLR
OMC
air interface.
frequency,
control
It is usually
BTS and
located
function-exchange.
at the center of Up
theto
cell.
40
SM
A basecan
BTSs
station
be controlled
has between
by one
oneBSC.
and sixteen
transceivers, each representing a separate Radio
Frequency (RF) channel.
Network Architecture
is the element in the network that
takes care of call control functions.
for call control,
MSMSC is responsible
BSS
BSS
control functions, charging,
ME/SIM
BTS
MT
statistics and
Um interface signaling
BSC
A
A-bis
towards BSS and interfacing
with the
external network, i.e., it is
responsible for routing calls to
and
X.25
from mobile users. The capacity of X.25
OSS
one MSC is several tens of
EIR
thousands of subscriber and OMC
it can
control some tens of BSCs. One
SM or
several MSCs can act as a Gateway
MSC (GMSC). It is an interface that
makes it possible to route calls
between the fixed network and an
individual mobile station.
PSTN/ISDN
NSS
(G)MSC
B
F
D
AuC
VLR
C
HLR
Network Architecture
NSS
Home Location Register (HLR): Is a
database where all the subscriber
information is stored permanently. This
information is the International Mobile
Subscriber Identity (IMSI) number, the
authentication key, etc. HLR has to
provide the (G)MSC with the
necessary subscriber data when the
call is coming from another network,
such as the PSTN or another GSM
network.
(G)MSC
B
F
EIR
D
AuC
VLR
C
HLR
Network Architecture
NSS
Authentication Center (AuC): Which is
related to the HLR. AuC is also a
database containing subscriber identityrelated security information. It provides
HLR with the information that is needed
for a successful authentication of the
mobile station. Authentication code is
stored in this database and the same
code is also stored in the SIM.
(G)MSC
B
F
EIR
D
AuC
VLR
C
HLR
Network Architecture
NSS
Visitor Location Register (VLR): Like HLR, a
database that contains information about the
subscribers. The difference is that VLR stores
the subscriber information as long as the
mobile subscriber visits the MSC area of that
specific VLR while the information the HLR
stores is permanent. VLR provides a copy of
the subscriber’s information that is needed to
receive/make calls so that the IMSI number
does not have to be sent over the radio
interface all the time. Instead, VLR stores
another unique subscriber number,
Temporary Mobile Subscriber Identity (TMSI).
Another task of this component is to provide
host (G)MSC with the necessary subscriber
data when the call is coming from a mobile
station. In all GSM systems VLR is part of
MSC, that is they are physically combined, but
we have separate them to make it easier to
understand.
(G)MSC
B
F
EIR
D
AuC
VLR
C
HLR
Network Architecture
NSS
Equipment Identity Register (EIR):
Contains three different lists of
International Mobile Equipment Identities
(IMEI).
•The white list contains the IMEIs of all
the cell phones that can be used in the
GSM network.
•IMEIs of the phones, which are stolen or
are malfunctioning and cannot be used in
the network, are stored in the black list.
•The third list is the gray list where the
IMEIs of the mobile equipment that have
to be traced by the network for
evaluation are stored.
This part of the network is optional.
(G)MSC
B
F
EIR
D
AuC
VLR
C
HLR
Network Architecture
Operation Sub-System(OSS)
Operation and Maintenance Center (OMC): Its main
function is to handle error messages coming from the
network and control the traffic load of the BSC and the BTS
Service Management (SM): Subscription management for
registering new subscriptions, modifying and removing
subscriptions, as well as billing information
GSM Interfaces
Interface
Description
Um
Radio link between MS and BTS
Abis
Between BTS and BSC, PCM 2Mbit/s
A
Between BSC and MSC, PCM 2Mbit/s
B
Between MSC and VLR (use MAP/TCAP protocols)
C
Between MSC and HLR (MAP/TCAP)
D
Between HLR and VLR (MAP/TCAP)
E
Between two MSCs (MAP/TCAP +ISUP/TUP)
F
Between MSC and EIR (MAP/TCAP)
G
Between VLRs (MAP/TCAP)
The Radio Interface
The Radio Interface (Um) is split into several channels
•The signaling channels carry management and control information
•Traffic channels to carry user data.
Frequency bands used
Variant
Uplink (MHz)
Downlink
(MHz)
Total
Bandwidth
Duplexfrequency
Channels
GSM-900
890-915
935-960
Twice 25 MHz
45 MHz
Twice 124
DCS-1800
1,710-1,785
1,805-1,880
Twice 75 MHz
95 MHz
Twice 373
PCS-1900
1,850-1,910
1,930-1,990
Twice 60 MHz
80 MHz
Twice 300
The Radio Interface
Original Frequency bands (GSM900)
Channel Bandwidth
Number of duplex channels
Users per channel
200 kHz
124
8
Speech coding bit rate
13 kbps
Data coding bit rate
12 kbps
F1 F2 F1' F2'
Frequency
Frame size
4.6 ms
To reduce the MS’s power consumption and minimize interference on the air interface,
during pauses in speech the MS does not transmit – this is called: Discontinuous
Transmission (DTX)
It is typically only transmitting in one time slot (i.e., 1/8 of the time)
1
2
3
4
5
6
7
8
The Radio Interface
Frequency Reuse



They are grouped in units of seven
cells. Each color indicates a group
of frequencies.
Adjacent cells are assigned different
frequencies to avoid interference or
crosstalk.
Because of the limited bandwidth
resources, the same frequency have
to be reused in other nearby cells.
7 cell re-use pattern
f7
f
6
f5
f1
f4
f2
f6
f2
f6
f3
f7
f7
f5
f2
f1
f4
f2
f3
Example: Incomming Call
PSTN
BTS
1
VLR
BTS
BSC
MSC
BTS
BSC
BTS
GMSC
BTS
Incoming call is passed from the fixed network to the gateway GMSC.
HLR
Example: Incomming Call
PSTN
BTS
1
VLR
BTS
BSC
MSC
BTS
BSC
BTS
GMSC
2
BTS
Based on the IMSI numbers of the called party, HLR is determined.
HLR
Example: Incomming Call
PSTN
BTS
1
VLR
BTS
BSC
MSC
BTS
3
BSC
BTS
GMSC
HLR
2
BTS
HLR checks for the existence of the called number, then the relevant VLR is requested
to provide a mobile station roaming number (MSRN).
Example: Incomming Call
PSTN
BTS
1
VLR
BTS
BSC
MSC
4
BTS
3
BSC
BTS
GMSC
2
BTS
Replay transmitted back to the GMSC
HLR
Example: Incomming Call
PSTN
BTS
1
VLR
BTS
BSC
4
MSC
BTS
3
BSC
BTS
5 GMSC
2
BTS
Connection is switched through the responsible MSC
HLR
Example: Incomming Call
PSTN
BTS
BTS
1
BSC
6
VLR
MSC
4
BTS
3
BSC
BTS
5 GMSC
HLR
2
BTS
VLR is quarried for the location, range, and reach-ability status of the mobile
subscriber.
Example: Incomming Call
PSTN
BTS
BTS
1
BSC
6
VLR
MSC
4
7
BTS
3
BSC
BTS
5 GMSC
2
BTS
If the MS is marked reachable, than a radio call is enabled.
HLR
Example: Incomming Call
8
PSTN
BTS
1
8
BTS
8
8
8
8
VLR
MSC
4
8
BSC
8
6
7
BTS
8
BTS
3
BSC
8
5 GMSC
2
8
BTS
Radio call is executed in all radio zones assigned to the VLR
HLR
Example: Incomming Call
8
PSTN
9
BTS
1
8
BTS
8
8
8
8
VLR
MSC
4
8
BSC
8
6
7
BTS
8
BTS
3
BSC
8
5 GMSC
2
8
BTS
Replay from the MS in its current radio cell.
HLR
Example: Incomming Call
8
PSTN
9
BTS
8
BTS
8
8
6
VLR
MSC
4
8
BSC
8
8
8
1
10
7
BTS
8
BTS
3
BSC
8
5 GMSC
HLR
2
8
BTS
2
When mobile subscriber telephone responds to the page, then complete all necessary
security procedures.
Example: Incomming Call
8
PSTN
9
BTS
8
BTS
8
8
8
8
6
VLR
MSC
4
8
BSC
8
1
11
10
7
BTS
8
BTS
3
BSC
8
5 GMSC
HLR
2
8
BTS
2
If this is successful. The VLR indicates to the MSC that call can be completed.
Example: Incomming Call
8
PSTN
9
BTS
8
BTS
8
8
6
VLR
MSC
4
8
BSC
8
8
8
8
3
BSC
8
5 GMSC
2
8
BTS
Call can be completed.
7
12
BTS
BTS
1
11
10
2
HLR
Mobility Management (MM)
GSM network keeps track of which mobile telephones are powered on and
active in the network.
The network keeps track of the last known location of the MS in the VLR
and HLR.
Radio sites connected to tha MSC are divided into “location areas” (LAs),
thus when a call comes for an MS, the network looks for the MS in the last
known location area.
Each BTS is assigned (by the operator) a 40 bit ID – called a Location Area
Identity (LAI), with three parts
Mobile country code.
Mobile network code.
Location area code.
GSM Shortcomings
GSM is based on circuit switched radio
so…
transmission
 A complete traffic channel must be
allocated for the entire call period
 Data rates are slow (designed for voice)
 Connection setup takes too long
 Costs are high( time oriented charging)
 Connection requires a modem

Solution
G S
PM
R
Introduction
GPRS (General Packet Radio Services) is a non-voice, packet switched technology
with high-performance, good quality services, reliable, transmits large amounts of data
in an efficient manner, increased voice capacity, with the internet accessible features
attached to it.
GPRS is based on the GSM means that GPRS uses the GSM air Interface for its
service transmission
GPRS was designed around a number of guiding principles:
* Always on
* High bit rates
* Simultaneous voice call and data transfer.
* Billing based on volume.
GSM to GPRS
Element
Software
Hardware
MS
Upgrade required
Upgrade required
BTS
Upgrade required
No Change
BSC
Upgrade required
PCU Interface
MSC/VLR
Upgrade required
No Change
HLR
Upgrade required
No Change
SGSN
New
New
GGSN
New
New
Network Architecture
Gn
Gi
IP
SGSN
GGSN
PSDN
Gc
Gr
Gs
Gb
HLR
ME/SIM
Um
BTS
(G)MSC
BSC
MT
X.25
BSS Base Station System
BTS Base Transceiver Station
X.25
F
D
B
OSS
BSC Base Station Controller
OMC
EIR
NSS Network Sub-System
MSC Mobile-service Switching Controller
C
A
A-bis
SM
VLR Visitor Location Register
HLR Home Location Register
AuC Authentication Server
SGSN Serving GPRS Support Node
GMSC Gateway MSC
GGSN Gateway GPRS Support Node
AuC
VLR
PSTN/ISDN
Network Architecture



Requires addition of a new class of nodes called
GSNs (GPRS Support Nodes)
 SGSN: Serving GPRS Support Node,
 GGSN: Gateway GPRS Support Node
BSC requires a PCU (Packet Control Unit) and
various other elements of the GSM require software
upgrades
All GSNs are connected via an IP-based backbone.
Protocol data units (PDUs) are encapsulated and
tunneled between GSNs
Serving GPRS Support Node – SGSN







Packet routing & transfer
Mobility management
Session management
Logical link management towards the MS
Ciphering, authentication
Charging data
Connection - HLR, MSC, BSC and SMSMSC
Gateway GPRS Support Node – GGSN





Serves as the interface to external IP networks
which see the GGSN as an IP router serving all IP
addresses of the MSs
GGSN stores current SGSN address and profile of
the user in its location register
It tunnels protocol data packets to and from the
SGSN currently serving the MS
It also performs authentication and charging
GGSN can also include firewall and packet-filtering
mechanisms
BSC and others

BSC must get a Packet Control Unit to




set up, supervise and disconnect packet-switched
calls
also support cell change, radio resource
configuration and channel assignment
MSC/VLR, HLR must be enhanced for
interworking with GPRS
MS must be equipped with the GPRS
protocol stack
HLR - Home Location Register





Shared database, with GSM
Is enhanced with GPRS subscriber data and routing
information
For all users registered with the network, HLR keeps user
profile, current SGSN and Packet Data Protocol (PDP)
address(es) information
SGSN exchanges information with HLR e.g., informs HLR of
the current location of the MS
When MS registers with a new SGSN, the HLR sends the user
profile to the new SGSN
MS modes
IP
Network
MS
Three Modes of Operation



Class A
 possibility to have simultaneously a circuit switched
connection and a packet switched connection
Class B
 possibility to be attached for both Circuit and Packet
Switching but can not use both services at the same time.
Class C
 allow to be attached to only one service at a time. (pure GSM
or pure GPRS)
Applications:
Choosing a mode of operation
relative benefit
relative cost
Class B
Class C
Class A
Interfaces
Interfaces
Gn - backbone interface (SGSN-GGSN)
Gp - between GSNs (GPRS Support Nodes) in different PLMNs (Public Land
Mobile Networks)
Gi - connection to external networks (support IP).
Gb - between SGSN and BSC (Base Station Controller)
Gd - between SGSN and SMS-C (SMS Centre), it is to exchange messages of
the short message service (SMS) via GPRS, it interconnects the SMS gateway
MSC (SMS-GMSC) with the SGSN.
Gf – between SGSN and EIR (Equipment Identification Register) Across the Gf
interface, the SGSN may query the IMEI (equipment Identifier) of a mobile station
trying to register with the network.
Gs - between SGSN and MSC (Mobile Switching Centre)
Gr - between SGSN and HLR (Home Location Register) The HLR stores the user
profile, the current SGSN address, and the PDP address(es) for each GPRS user
in the PLMN. The Gr interface is used to exchange this information between HLR
and SGSN.
Gc – between GGSN and HLR, The signaling path Gc interface may be used by
the GGSN to query a user’s location and profile in order to update its location
register.
Protocols
The GPRS data communication architecture adheres to the
principle of protocol layering and has two protocol planes,
signaling plane and transmission plane.
The signaling plane consists of protocols that control and
support the transmission of user information.
The transmission plane covers the protocols for user
information transmission and associated control procedures
like flow control or error handling. Between SGSN and GGSN
GPRS Transmission Plane
* The GPRS tunnel protocol (GTP) tunnels the PDUs through the GPRS backbone
network.
* The GTP header contains mobile’s identity and PDP context identifier
* Below GTP, the Transmission Control Protocol/User Datagram Protocol (TCP/UDP)
and IP are used as GPRS backbone network-layer protocols. Any IP based network
protocols can be used below IP
* Between the SGSN and MS, SNDCP maps network-level protocol characteristics
onto the underlying logical link control and provides functionality like multiplexing of
network-layer messages onto a single virtual logical link connection.
* Segmentation and compression functionality are covered by SNDCP.
* The BSS GPRS protocol (BSSGP) has been derived from the BSSAP used in
GSM, and conveys routing and QoS-related information between the BSS and
SGSN.
Between MS and BSS the physical layer is split up PLL and RFL.
* The RFL performs the modulation and demodulation of the physical waveforms.
*The PLL provides services for information transfer over a physical channel between
the MS and the network. These functions include data unit framing, data coding, and
the detection and correction of physical medium transmission
The data link layer has been separated into two distinct sublayers. The Radio Link
RLC and MAC sublayer arbitrates access to the shared medium between a
multitude of MSs and the network. The RLC/MAC layer encompasses the efficient
multiplexing of data and signaling information, and performs contention resolution,
and error handling.
The Logical Link Control (LLC) layer operates above the MAC layer, and
provides a logical link between the MS and SGSN. To allow introduction of
alternative radio solutions without major changes to NSS
GPRS Signaling Plane
The same protocols are used as for data transmission up to the SNDCP protocol.
Only at the network layer, a GPRS-specific mobility management protocol (GMM)
is required within MS and SGSN to support the mobility functionality.
Mobility management
There are three activities related to mobility management, that is
attach, detach, and location update. Attach means entering/joining
the system. Detach means leaving the system. Location update
includes routing area (RA) update and cell update.
Before an MS is able to send data to a corresponding host, it has
to attach to the GPRS system. During the attachment procedure,
the GPRS shall do the following things:
1- Inform the network for the MS's request to be active
2- Network check the MS's identity and initiate ciphering
mode for data communication
3- If SGSN does not already have the MS’s subscription
info, download the information from HLR to SGSN
4- Update MSC/VLR
5- Signal between the MS and SGSN
Moving
MS
MS
1
HLR
SGSNn
SGSNo
GGSN
•When MS changes RA, the GPRS needs to update routing area
•The MS sends a routing update request containing the cell identity and the
identity of the previous routing area (RA) to the SGSNn
Moving
MS
MS
1
HLR
SGSNn
2
SGSNo
GGSN
If the RA is served by the same SGSN, the location information is updated and an
acknowledge is sent back to the MS. There is no need to inform the GGSN,
because the SGSN and tunneling information are not changed. However if the
previous RA is served by another SGSN, the GGSN must be informed. The
GGSN address and tunneling information can be requested from the previous
SGSNo
Moving
MS
MS
1
HLR
SGSNn
2
SGSNo
3
GGSN
The SGSNo is requested to transmit the undelivered data packets to the new
SGSN. Afterwards, the information context of the MS is deleted from the memory
of the SGSNo. As soon as the address and tunneling information is received from
the SGSNo
Moving
MS
MS
1
HLR
SGSNn
2
SGSNo
3
4
GGSN
The new SGSN address and tunneling information is delivered to GGSN.
Moving
MS
MS
1
HLR
2
SGSNn
SGSNo
3
4
5
GGSN
Update PDP context.
Moving
MS
MS
1
HLR
2
SGSNn
SGSNo
3
4
5
GGSN
Update PDP context.
Update HLR { Location + Subscriber data }
6
Benefits of GPRS:
(1) use of Packet Switching

Packet-switched



High bit rates
(up to 170kbs)
Short access times
Channels are allocated only
if needed



Circuit-switched



Friendly bill (based on
volume)
Multiple users share one line
Robust application support


Small or medium volumes
Low bit rates
(max 14.4kbs)
Long access times
Channel allocated for entire
duration


Unfriendly bill (based on
duration)
Limited application support

Large volumes
(2) Other Benefits of GPRS


greatly improves and simplifies wireless
access to packet data network
support for different levels of QoS




service precedence (high, normal, low)
reliability – (probability of loss, duplication, missequencing, corruption of packets)
delay
throughput
Limitations of GPRS





Speeds Much Lower in Reality
Packet switching can lead to delays affecting the
Quality of Service
Operators may decide to charge based on time
rather than volume
Currently, mobile stations using GPRS cannot
receive direct GPRS calls
Limited cell capacity for all users
Tree Of Mobile Telecommunications
Broadband
Fourth generation
2010
G
Services MBS/WBMCS
L
PAN (10 bps – 10 Mbps)
2005
O
High Bit Rate Multimedia services
B
3rd generation
FPLMTS/I MT-2000/ UMTS
A
Speech and data
2000
L
PACS
PHS/ PHP
International
GPRS / EDGE
PDC
2nd generation
Digital speech
TACS/ ETACS
IS54/ 136
IS95
1990
JTAC/ NTACS
RTMS
RADIOCOM-2000
C-450
NTT
NMT450/ 900
AMPS
1st generation
Branches and leaves of the telecommunication systems
family tree are not shown in chronological order.
Analog
1995
CT2/ CT2+
2nd suppl.
GSM/ DCS1800
DECT
speech
Local / international
1980
3G Evolution Path from GSM to UMTS
HSCSD
GSM
EDGE
GPRS
WCDMA
Radio – Channel Access Schemes
• Frequency-division multiple access (FDMA);
• Time-division multiple access TDMA;
• Code-division multiple access CDMA;
UMTS
“UMTS will be a mobile communications system that can
offer significant user benefits including high-quality wireless
multimedia services to a convergent network of fixed, cellular
and satellite components.
Modifications:
New methods & protocols on radio link  increased access
bandwidth
Coexistence of two domains in the core network
Packets Switched (PS)
Circuit Switched (CS)
New Services
IP Service Infrastructure: IP Based Multimedia Subsystems
(IMS) (R5)
3G UMTS

The Dream (intention)

2G and 2.5G systems are incompatible around the
world.


Worldwide devices need to have multiple technologies inside
of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted
around the world

One device should be able to work anywhere !
“Access to Information from Anyplace, Anytime”
3G UMTS

Types of Cells and Base station to use them

Macro Cell



Micro Cell



These should cover a medium area
384 Kbps max speed 120 Km/h
Pico Cell



These cover a large area and will give slow access
144 Kbps – max speed of 500 Km/h
Less than 100 metres
2 Mbps – max speed of 10 Km/h
Difficult to predict

Actual distances and bandwidth depend on local
conditions
3G UMTS

Types of Cells and Base station to use them

Cells will operate in a hierarchy overlaying each other
Global
Satellite
Suburban
Urban
In-Building
Micro-Cell
Macro-Cell
Pico-Cell
Universal Frequency Re-use in
CDMA based systems
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f1
f1
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UMTS Architecture
Channel Access Technologies
Channel Access Technologies
Hybrid FDMA/TDMA
Channel Access Technologies
CDMA
Principles of CDMA
Spread Spectrum
Spread-spectrum transmission is a technique in which the user’s original signal
is transformed into another form that occupies a larger bandwidth than the
original signal would normally need.
The original data sequence is binary multiplied with a spreading code that
typically has a much larger bandwidth than the original signal.
The bits in the spreading code are called chips to differentiate them from the
bits in the data sequence, which are called symbols.
Each user has its own spreading code. The identical code is used in both
transformations on each end of the radio channel, spreading the original signal
to produce a wideband signal, and dispreading the wideband signal back to the
original narrowband signal.
Principles of CDMA
Spread Spectrum
Considered alone, the spreading procedure might seem like a waste of time in
term of information transmission.
However, the purpose of spreading becomes clear if we consider the following
basic principles of code multiplexing:
1. All subscribers use the same frequency for the uplink and downlink.
2. Each user has its own, unique spreading code per data channel.
3. Using the spreading code, the information is encoded (“spread”) for
each data channel prior to transmission.
4. The spread data channels are added together and transmitted.
5. The receiver recognize the spreading code used for each data channel,
and can thus compute (“dispread”) each individual data channel based
on the received summation signal.
Principles of CDMA
Spread Spectrum
At transmitter side the spreading process is accomplished in the following two
steps:
•Multiplying each symbol data signal dx(t) by a unique spreading code
signal cx(t). This will produce a spread signal Sx(t).
•Find the summation of all the output Sx(t) signals.
The dispreading procedure at receiver side also divided into two stages:
•Multiplication of the received signal by the spreading code used.
•Averaging over a symbol period.
For dispreading to be successful, it is necessary to know the spreading code
used and the receiver must be precisely synchronized to the chip clock and the
symbol clock.
Principles of CDMA
Spread Spectrum
How the original symbols can be reconstructed simply just by multiplying again
by the same code ?
Multiplication table
XOR table
A
B
X
A
B
X
0
0
0
+1
+1
+1
0
1
1
+1
-1
-1
1
0
1
-1
+1
-1
1
1
0
-1
-1
+1
Note:
If we chose that; logical “0” corresponds to bipolar (+1) and logical “1”
corresponds to bipolar “-1”.
Then, a multiplication of the bipolar signals (+1/-1) corresponds to an
XOR operation for the logical signals (0/1).
UMTS Terrestrial
Radio Access
Network
UTRA modes
Frequency Division duplexing (FDD)
•Allows full-duplex operation by using two
separate frequency channels for downlink
(DL) and uplink (UL) directions.
•Each frequency channel in FDD mode has
a bandwidth of 5Mhz and divided into a 10
ms frames. It can provide a 3.84 Mcps.
•The maximum number of users that can
share the same channel is 512.
•The maximum symbol rate that one user
can reach is 960 ksybols/second.
•The obvious disadvantage of this mode is
that resources are wasted since each radio
channel between Node-B and UE consist of
frequency pair (UL,DL).
frequency
Down Link
Duplex spacing
Up Link
time
UTRA modes
Time Division duplexing (TDD)
•Both DL and UL use the same frequency channel but never simultaneously (halfduplex).
U
DL
U
DL
L
Downloading file
L
Downloading file
URL requests
time
TDD mode is suitable for
data communication,
typical example Internet
suffering.
•The frame length is 10 ms, with each frame divided into 15 time slot.
•Each time slot can be accessed by up to 16 user depending on SF which can be
1,2,4,8, or 16. So the data rate in TDD mode ranges from 240 ksymbols/second to
3.84 Msymbols/second.
•In principle, the network can allocate all the time slots freely for UL or DL.
However, at least one time slot must be allocated for DL and one for UL per frame,
as the communication between UE and the network always need a return channel.
WCDMA Communication protocol stack
Radio Resource Control
RRC
RLC
RLC
RLC
Radio Link Control
Service Access Point
SAP
Logical channels
(what is transmitted)
Medium Access Control
MAC
Transport channels
(How it is transmitted)
Physical Layer
Physical channels
(How it is transmitted)
Network Structure
UMTS Network Structure
USER
RAN
CN
UE
UTRAN
GPRS CN
UE
GERAN
GSM CN
The UMTS consists of two parts the radio access network RAN and the core network CN
For the CN the option are the GSM based CS network and the GPRS based PS network
For RAN the option are GSM EDGE RAN(GERAN) and Universal Terrestrial RAN
(UTRAN)
The GERAN is based on EDGE technology which reuses the frequency allocation of GSM
and provides higher bandwidths by using more advanced modulation and coding schemes
The UTRAN is based on WCDMA technology
An operator may migrate to 3G first upgrading the CN components to the UMTS
specification and using GERAN of the radio access
UMTS Releases
Release 99
v3.0.0
v3.1.0
v3.2.0
v3.3.0
v3.4.0
etc
.
v4.0.0
v4.1.0
v4.2.0
etc
.
v5.0.0
v5.1.0
etc
.
12/99
Release 4
03/01
Release 5
06/02
Release 6
12/03 or 03/04
v6.0.0
Corrections
New Functions
etc
.
Release 99
In Release 99 the core network is logically divided into two domains: circuit-switched (CS)
and packetswitched (PS). The CS-domain handles circuit-switched connections, and
the PS-domain handles the packet transfer.
UMTS Terrestrial Radio Access Network
The UTRAN is the new radio access network designed especially for UMTS.
Its boundaries are the Iu interface to the core network and the Uu interface (radio
interface) to user equipment (UE).
UMTS Terrestrial Radio Access Network
* The UTRAN consists of radio network controllers (RNCs) and Node Bs (base
stations). Together, these entities form a radio network subsystem (RNS).
* The internal interfaces of the UTRAN include the Iub and Iur.
Radio Network Controller (RNC)
* The RNC controls one or more Node Bs. It may be connected via the Iu interface to an
MSC (IuCS) or to an SGSN (IuPS). The interface between RNCs (Iur) is a logical interface
* RNC is comparable to a BSC in GSM networks.
Functions that are performed by the RNC include the following:
Iub transport resources management.
Control of Node B logical operation and maintenance (O&M) resources.
Modifications to active sets; that is, soft handover.
Allocation of DL channelization codes.
DL power control.
Node B
Node B is the UMTS equivalent of a base station transceiver. It may support
one or more cells.
Functions that are performed by a Node B include the following:
Node B logical O&M implementation;
Transmitting of system information messages according to scheduling parameters given
by the RNC.
Error detection on transport channels
Frequency and time synchronization and RF processing.
GSM Radio Access Network
The GSM radio access network is also known as the base station subsystem (BSS). It
consists of one BSC and one or more BTS.
The BSC controls the functionality of a BTS over the A-bis interface.
The A-bis interface is not a multivendor interface, but it contains solutions that are
proprietary to each manufacturer.
Interfaces
There are three kinds of interfaces in the UMTS/GSM network.
1- Truly open, (e.g. the A interface). This mean that an operator can buy the MSC and the
BSS equipment from different manufacturers and connect them together over the interface.
2- Specified at some level, but the interface is still proprietary. The equipment for such
interfaces must come from the same manufacturer,
3- No specification at all.
A Interface
•This interface is an open multivendor interface.
•This interface is specified in the 08-series GSM specifications.
•The A interface is a pure GSM interface and not part of the UMTS concept, it can connect
a BSS subsystem to a 3G-MSC.
Gb Interface
•The Gb interface is a non-UMTS interface.
•The Gb interface connects the packet-switched core network to the GSM network. It is
used when the GSM mobile station uses GPRS services.
•GPRS-capable GSM phones of the future will be able to use at least some of the UMTS
packet-based services, especially once enhanced GPRS (EGPRS) is launched.
Iu Interface
•It is the most important and central interface for the 3GPP concept.
•This interface is an open multivendor interface.
•This interface connects the core network and the UMTS Radio Access Network (URAN).
•The Iu can have two different physical instances, Iu-CS and Iu-PS.
General protocol model for UTRAN
The protocol model in the Iu interface is divided into two horizontal layers
1- The radio network layer
2- The transport network layer.
A protocol stack diagram has two planes, control and user. The control plane transfers
signaling information, and the user plane transfers application data.
General protocol model for UTRAN
In the vertical direction, the Iu protocol model is divided into three planes, the control plane,
the user plane, and the transport network control plane. Both radio network layer planes,
control and user, are conveyed via the transport network layer using the transport network
user plane.
General protocol model for UTRAN
The signaling protocol for the Access Link Control Application Protocol (ALCAP) may be
the same type as the signaling protocol for the Application Protocol, or it may be different.
Once the signaling bearers are in place, the Application Protocol in the radio network layer
may ask for data bearers to be set up. This request is relayed to the ALCAP in the transport
network layer. The ALCAP is responsible for the data bearer setup, and it has all the required
information about the user plane technology.
General protocol model for UTRAN
In the Iu-PS interface, no ALCAP is needed. Because the signaling bearer in the transport
network control plane is only needed for the ALCAP, the entire transport network control
plane is unnecessary in this case.
Iu interface/CS domain
•Use the asynchronous transfer mode (ATM) transport technology.
•In the case of the CS domain control plane, there are SS7-based protocols on top of the ATM
layers. In the CS domain user plane, only an ATM adaptation layer 2 (AAL2) task is needed
to handle the transport of audio and video streams.
Iu interface/PS domain
•Two alternative protocol stacks to use. The first one is the same as in CS domain, and the
second one is more IP-oriented. This version can be used once the data transmission is based
on the IP technology. The user plane in this domain is different from the one in the CS
domain. The data packet forwarding is handled by the GPRS Tunnelling Protocol for user
plane (GTP-U).
Iub Interface
•This interface is situated between the RNC and the Node B in the UTRAN.
•In GSM terms this corresponds to the A-bis interface between the BTS and the BSC.
•Is hardly an open interface.
•The protocol stack in this interface is based on the same principles as in the Iu interface;
Iur Interface
•The applicable specification states that this interface should be open,
•All RNCs connected via the Iur must belong to the same PLMN.
•The protocol stack structure is based on the same principles as the Iu and Iub.
•The Iur interface exists to support macrodiversity.
Serving and drift RNCs.
•Several base stations can have an active connection with the same mobile station at the
same time . It is possible that these base stations are controlled by different RNCs. Without
an Iur interface, this situation would have to be controlled via the Iu interface , which would
be a very clumsy method indeed.
• There is always only one RNC in control of a UE connection (SRNC)
• Any other RNC involved in the connection is a slave RNC (DRNC)