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PERSONAL COMMUNICATION
SYSTEMS: 3G (IMT2000)
Ian F. Akyildiz
Broadband & Wireless Networking Laboratory
School of Electrical and Computer Engineering
Georgia Institute of Technology
Tel: 404-894-5141; Fax: 404-894-7883
Email: [email protected]
Web: http://www.ece.gatech.edu/research/labs/bwn
IMT-2000
 Higher data rates to support multimedia applications, high
spectral efficiency, standardize as many interfaces as
possible, and provide compatibility to services within the
IMT-2000.
 Requirements include:
– Improved voice quality (wireline quality)
– Data rates up to 384 kbps everywhere and 2 Mbps
indoor
– Support for packet and circuit switched data services
– Seamless incorporation of existing 2G and satellite
systems
– Seamless international roaming
– Support for several simultaneous multimedia
connections
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Comparison of 2G and 3G Systems
2G
3G
Digital
Technology
Modulation, Speech,
Channel Coding
Increased Use
also Software Radios
Environments
Vehicular, Pedestrian,
FWA
Vehicular, Pedestrian,
Office, FWA, Satellite
Frequency
Bands
800MHz, 900MHz,
1.5GHz, 1.8GHz
2 GHz
Services
Low/Medium Rates;
Primarily Voice, Data
Higher Data Rates;
Circuit/Packet Switched
and Multimedia Services
Roaming
Restricted
Global Roaming
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3G Wireless Systems
Sixteen proposals are accepted to IMT-2000 systems family. Ten for terrestrial 3G
networks, and six for MSSs (Mobile Satellite services)
 IMT DS (Direct Sequence)
(UTRAN FDD and W-CDMA)
 IMT MC (Multi-carrier)
– 3G version of IS-95 (called cdmaOne) 
cdma2000
 IMT TC (Time Code)
– (UTRAN TDD)
 IMT SC (Single Carrier)
– Essentially a manifestation of GSM Phase2+
( EDGE)
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Proposals for 3G Standards
The most important IMT-2000 Systems  IMT-DS and IMT-MC
 W-CDMA (IMT-DS & TC):
–
–
–
–
Developed by the 3G Partnership Project (3GPP)
UTRA TDD and UTRA-FDD
Backers  Ericsson, Nokia, NTT DoCoMo.
Korea TTA II is similar to W-CDMA
 cdma2000 (IMT-MC):
– Compatible with IS-95
– Further developed by the 3G Partnership Project
Number 2 (3GPP2)
– Backers  Qualcomm, Lucent, and Motorola.
– Korea TTA I is similar to cdma2000
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3G ARCHITECTURE
Hierarchical
Cell Structure
Global Roaming
Radio Spectrum
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Key Features & Objectives of 3G
 Global System (all existing systems & terminal
types)
 Worldwide market place & Off-the-shelf
compatible equipment
 Worldwide common frequency band &
roaming
 Audio, video and data services including
packet Data & multimedia Services
 High service quality
 Flexible radio bearers
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Key Features & Objectives of 3G
 Bandwidth-On-Demand Capabilities (low
rate paging messages
high rate video or
file transfer)
 Asymmetrical channels
 Improved security
 Distributed & coherent network management
 Compatibility of services within IMT 2000
 Scalable
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Objectives of 3G
 High-quality speech using low bit rates
 Advanced addressing mechanisms
 Virtual home environment for service
 Seamless indoor, outdoor and far door
 Dual mode/band of operation of GSM/UMTS
in one network
 Roaming between GSM and UMTS networks
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UMTS
 UMTS (Universal Mobile Telecommunications
System) is the European version of a 3rd
Generation (3G) mobile communication system.
– It is proposed by 3GPP (3rd generation partnership
project).
– It includes two parts: UTRAN (Universal Terrestrial Radio
Access Network) and the Core network inherited from
GSM (Global System for Mobile Communications).
 UMTS is a wideband, circuit- and packet-based
transmission systems of text, digitized voice,
video, and multimedia with data rates up to 2
Mbps (possibly higher).
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UMTS Services and Their
Relationship to the Internets
Service
Category
Session Type
Protocols
Internet
Elements
Location-based
info- and
entertainment
WWW
HTTP, WML,
ISP, portal,
cHTML, xHTML servers
Intranet access
(mobile VPN),
mobile office,
mobile commerce
All typestransparent
tunnel
IP, higher
layers
transparent
ISP, firewall
server,
corporate portal
Internet access
All typestransparent
tunnel
IP, higher layers
transparent
ISP, portal
Multimedia
messaging
SMS, e-mail,
downloading
SMTP, SMS, IP
ISP, email, SMSserver
Audio, video,
download
File transfer,
streaming
ISP, portal,
database server
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Voice, real-time
MP3, MPEG-4,
FTP, IP-based
SIP
Interactive/dialo SIP
Media gateway
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Data rate and Spectrum
 Maximum data rate and maximum speed for different
hierarchical layer
– Macrolayer: 144 kbps with max. speed of 500km/h.
– Microlayer: 384 kbps with max speed of 120km/h
– Picolayer: 2Mbps with 10km/h
 Bit Error Rate (BER)
– Real-time applications: 10-3 to 10-7 with maximum constant
delay: 20ms to 300 ms
– No real-time applications: 10-5 to 10-8 with maximum delay
>= 150ms.
 Spectrum: 1900 MHz-2025 MHz, and 2110 -2200 MHz
– FDD (macro- and micro- cells: uplink is from 1920 MHz to
1980 MHz, downlink is from 2110 MHz to 2170 MHz
– TDD (pico- cells: not divided by use of different frequency
carriers (not suitable for large prop delays).
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Network Architecture
CN
UTRAN
VLR
PSTN
Node B
UMTS
Subscriber
Identity
module
Radio
Network
controller
GMSC
ISDN
Node B
HLR
User
equipment
Mobile
equipment
MSC
Node B
Radio
Network
controller
SGSN
GGSN
Internet
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Radio Network Controller (RNC)
 One RNC controls one or more Node Bs.
 It may be connected via Iu interface to an
MSC (IuCS), or to an SGSN via Iu (IuPS).
 The interface between RNCs (Iur) is logical
interface, and a direct physical connection
does not necessarily exist.
 An RNC is comparable to a base station
controller (BSC) in GSM networks.
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RNC Functions

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Iub (Node B and RNC) transport resources management
Control of Node B logical O&M resources
System information management and scheduling
Traffic management of common channels
Soft handover
Power control for uplink and downlink
Admission control
Traffic management of shared channels
Macro diversity combining/splitting of data streams transferred
over several Node Bs.
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Node B
 Node B is the UMTS equivalent of a base station
transceiver. It may support one or more cells, although in
general only one cell one Node B.
 It is a logical terminal and the base station is often used
for physical entity.
 Functions
– Mapping of Node B logical resources onto hardware resources
– Uplink power control
– Reporting of uplink interference measurements and downlink
power information
– Contains the air interface physical layer, it has to perform many
functions such as RF processing, modulations, coding, and so on.
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WCDMA Air Interface
 In UMTS, the UTRAN is used to keep the mobility management
(MM) and connection management (CM) layers independent of
the air interface radio technology
 This idea is realized as the concepts of access stratum (AS) and
nonaccess stratum (NAS)
– AS: functional entity that includes radio access protocols
between the user equipment (UE) and the UTRAN (terminate
here).
– NAS: includes core network (CN) protocols between the UE
and the CN itself.
 The NAS protocols can be kept the same, thus, the GSM’s MM and
CM resources are used almost unchanged in 3G NAS.
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UMTS Architecture
UE
UTRAN
Core network
protocols
CN
Non-access Stratum
Core network
protocols
Access Stratum
Radio
Protocols
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lu
Protocols Protocols
Uu-interface
lu
Protocols
Iu-interface
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Layered Architecture
 There are three protocol layers in the AS
– Physical layer (L1)
– Data link layer (L2)
 Medium access control (MAC)
 Radio link control (RLC)
 Broadcast/multicast control (BMC)
 Packet data convergence protocol (PDCP)
– Network layer (L3)
 Radio resource control (RRC)
 There is one layer (L3) in the NAS
– Mobility management
– Call management
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RLC Services
These functions are provided to upper layers:
 Segmentation and reassembly of higher-layer
PDUs (Protocol Data Unit) into/from smaller
RLC payload units
 Padding
 Transfer of user data
 Error corrections
 In-sequence delivery of higher-layer PDUs
 Ciphering
 Sequence number check
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RLC Functions
These functions (for itself) are supported by the RLC:
 Segmentation and reassembly of higher-layer PDUs
(Protocol Data Unit) into/from smaller RLC payload
units
 Padding
 Transfer of user data
 Error corrections
 In-sequence delivery of higher-layer PDUs
 Flow control
 Ciphering
 Sequence number check
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RRC Services
 General control: this is an information broadcast service. The
information transferred in unacknowledged, and it is broadcast
to all mobiles within a certain area.
 Notification: This includes paging and notification broadcast
services.
– The paging services broadcasts paging information in a
certain geographical area, but it is addressed to a specific UE
or UEs.
– The notification broadcast service is defined to provide
information broadcast to all UEs in a cell or cells.
 Dedicated control: This service includes the establishment and
release of a connection and transfer of messages using this
connection.
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RRC Functions
These functions (for itself) are supported by the RRC:

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Initial cell selection and cell reselection
Broadcast of information
Reception of paging and notification messages
Establishment, maintenance, and release of RRC connections
Establishment, reconfiguration, and release of radio bearers
Assignment, reconfiguration, and release of radio resources for
the RRC connection
Handover
Measurement control
Power control
Security mode control
QoS control
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Transport Channels in UTRAN
 Common Transport Channel Types
– Random Access Channel (RACH)
– ODMA (Opportunity Driven Multiple Access) Random Access
Channel (ORACH)
– Common Packet Channel (CPCH)
– Forward Access Channel (FACH)
– Downlink Shared Channel (DSCH)
– Uplink Shared Channel (USCH)
– Broadcast Channel (BCH)
– Paging Channel (PCH)
 Dedicated Transport Channel Types
– Dedicated Channel (DCH)
– Fast Uplink Signaling Channel (FAUSCH)
– ODMA Dedicated Channel (ODCH)
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Logical Channels in UTRAN
Control Channel (CCH)
Broadcast Control Channel (BCCH)
Paging Control Channel (PCCH)
Dedicated Control Channel (DCCH)
Common Control Channel (CCCH)
Shared Channel Control Channel (SHCCH)
ODMA Dedicated Control Channel (ODCCH)
ODMA Common Control Channel (OCCCH)
Traffic Channel (TCH)
Dedicated Traffic Channel (DTCH)
ODMA Dedicated Traffic Channel (ODTCH)
Common Traffic Channel (CTCH)
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Quality of Services Classes
 The UMTS allows the UEs to negotiate the QoS parameters for
a radio bearer (RB).
 Negotiation
– The procedure is always initiated by the application in
the UE.
– It sends a request defining the resources it needs
– The network checks whether it can provide the requested
resources.
– It can either grant the requested resources, offer a small
amount of resources, or reject the request.
– The UE can either accept or reject the modified offer.
– It is also possible to renegotiate these parameters if the
application requirements change or resource status
change.
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QoS Classes (2)
 There are four types of QoS classes
– Conversational real-time class such as voice
traffic
– Interactive class (best-effort) such as web
browsing
– Streaming real-time class such as streaming
video
– Background class (best-effort) such as emails.
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Conversational Real-Time Services
 Bidirectional and more or less symmetric
 Technically the most challenging class
– Very short delay is acceptable
– Traditional retransmission protocols (ARQ) cannot be
easily used. Instead, forward-error-correction (FEC)
must be used.
– Small delay requirements means also that buffers
cannot be used in receiving end to smooth the
variations in delay (jitter).
 Some errors are acceptable because people cannot sense
small errors in voice or video information.
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Interactive Services
 A user requests data from a remote server, and the response
contains the requested data.
– Web browsing, e-shopping, and database inquires.
 Difference between conversational and interactive services
– The data traffic in the conversational class is symmetric,
whereas in the interactive class, the traffic is highly
asymmetric.
– Timing requirements are not quite so strict with interactive
services (up to 4 seconds) as they are for conversational
services (a few hundred of ms).
– Interactive services do not tolerate any more transmission
errors than conversational services.
 With the relaxation of delay requirements, the goal of less errors
is easier to achieve with interactive services.
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Streaming Services
 Typically includes video and audio applications.
 Differences from interactive services:
– The data transferring is almost totally one-way and
continuous: highly asymmetric.
– There are some strict delay variation requirements for the
data, which are presented to the user, whereas delay
variation is not really a problem with interactive services.
– The requirements for maximum delay could be as long as 10
seconds.
– The only data traffic in the opposite direction ( usually in the
uplink) consists of a few control signals like starting and
stopping.
– The incoming data packets are buffered to smooth delay
variation.
 This class is provided through packet-switched networks.
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Background Services
 These services do not have precise delay requirements at all (fax
and SMS).
 However, it may use timers to make sure that the data transfer
has not stalled altogether.
 The data should be error free, but it is especially easy to achieve
in this case. Because there are no time constraints.
 Retransmission protocol will be used, but it must also be
efficient.
 Delay variation is not considered with background services. The
data are presented to the user only after the whole file has been
received correctly.
 The bandwidth requirement is not large in either direction.
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RRC Connection Procedures
 The UTRAN separates the concepts of a radio connection from a
radio bearer (RB).
– A radio connection is created first, and then the network can
create one or more RBs independently of the radio connection.
– An RB can also exist without a dedicated radio connection. In
this case, the RB uses the common channels.
 An RRC connection implies that a radio connection exists, but this
connection can use either dedicated or common resources.
– An RRC connection is a logical concept, and radio connection is a
physical concept.
– The physical entity implements and enables the logical concepts.
– A dedicated connection allocates the resource exclusively to one
user, so common channels should be used whenever possible.
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RRC Establishment/Release
 RRC connection establishment
– It is always initiated by the UE, even with a mobileterminated call (e.g.,paging).
– The UE initiates this procedure, but the UTRAN controls it. It
may decide that no radio resources can be allocated for the
UE, and respond with an RRC connection reject message.
 Signaling connection establishment
– The RRC connection establishment procedure is used by the
higher layer; that is, by the NAS.
– All higher-layer signaling messages, including the initial
messages are relayed through the radio interface.
 RRC connection release
– The normal procedure is finished through a dedicated channel
(DCH). The PDU here are sent in unacknowledged mode.
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Radio Bearer Procedures
 Radio connection and an RB are two separate
concepts in UMTS.
– Radio connection is a static concept. It is established
once, and survives until it is released. There is only one
radio connection per terminal.
– The RB defines what kind of properties this radio
connection has. There may be several RBs on one radio
connection, each having different capabilities for data
transfer. The capabilities are based on the QoS
parameters.
– The RBs are dynamic and can be reconfigured.
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Radio Bearer Procedures (2)
– It is possible to have an RB without a
dedicated radio connection
Circuit-switched bearers or bearers using rt services
need dedicated radio channels to meet their strict
delay requirements.
Packet-switched bearers or bearers using nrt services,
often do not need a permanent association to a
dedicated radio resource.
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Radio Bearer establishment
Radio Bearer release
 An RB establishment is always initiated by the UTRAN. This
because each RB uses some radio resources, and only the
network knows what kind of resources it can grant to a UE.
 At the RRC level, the signaling is simple: the UTRAN sends a
radio bearer setup message, and the UE responds with a radio
bearer setup complete.
 Interlayer signaling can be quite different depending on the
requested QoS parameter and whether there is already a
suitable physical channel in place.
 When an RB is released, the physical channel can be modified or
released together depending on whether it can be “reused” after
the RB release.
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Control of Requested QoS
 The UTRAN air interface is very flexible, which allows
for the dynamic allocation of system resources.
 In the connected mode, the UE may be required to
perform traffic volume measurements in its MAC
layer. If the UE suspects that the present
configuration is not the optimal one, it sends a
measurement report to the network.
 The network can trigger a channel-reconfiguration
procedure.
– Increased data
– Decreased data
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