Transcript Forward Traffic Channels

Chapter 10:
Existing Wireless Systems:
3G, IS-95 and IMT-2000
Associate Prof. Yuh-Shyan Chen
Dept. of Computer Science and
Information Engineering
National Chung-Cheng University
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IS-95
IS-95 uses the existing 12.5-MHz cellular bands to
derive 10 different CDMA bands (1.25 MHz per band)
The frequency reuse is 1
The channel rate is 1.228 Mbps
RAKE receivers are used to combine the output of
several received signals
Sixty-four-bit orthogonal Walsh codes (W0 to W64) are
used to provide 64 channels in each frequency band
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Logical Channels in IS-95
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Cont.
Four different rates are used
The downlink or forward link has a power control
subchannel that allows the mobile to adjust its
transmitted power by +/- 1 dB every 1.25 ms
The pilot channel W0 is always required
There can be one sync channel and seven paging
channels;
• The remaining fifty-six (56 = 64 - 1 - 7) channels are
called traffic channels
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The Pilot Channel
The pilot channel is used by the base station as
a reference for all MSs
It does not carry any information and is used for
strength comparisons and to lock onto other
channels on the same RF carrier
The signals (pilot, sync, paging, and traffic) are
spread using high frequency spread signal I and
Q using modulo 2 addition
This spread signal is then modulated over a high
frequency carrier and sent to the receiver, where the
entire process is inverted to get back the original
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Pilot and Sync Channels in IS-95
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Sync channel
The sync channel is an encoded, interleaved,
and modulated spread-spectrum signal that is
used with the pilot channel to acquire initial time
synchronization
It is assigned the W32
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Paging channel
The paging channels is used transmit control
information to the MS
When the MS is to receive a call, it will receive a
page from the BS on an assigned paging channel
There is no power control for the paging channel on a
per-frame basis
The paging channel provides the MSs system
information and instructions
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Paging Channel Generation in IS-95
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Access Channel
The access channel is used by the MS to transmit
control information to the BS
The access rate is fixed at 4800 bps
All MSs accessing a system share the same
frequency
When any MS places a call, it uses the access
channel to inform the BS
This channel is also used to respond to a page
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Access Channel Generation in IS-95
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Forward Traffic Channels
Forward traffic channel are grouped into rate
sets
Rate set 1 has four elements
• 9600, 4800, 2400, and 1200 bps
Rate set 2 has four elements
• 14400, 7200, 3600, and 1800 bps
Walsh codes that can be assigned to forward traffic
channels are available at a cell or sector
• W2 through W31
• W33 through W63
 Only 55 Walsh codes are available for forward traffic
channels
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The speed is encoded using a variable rate encoder
to generate forward traffic data depending on voice
activity
The power control subchannel is continuously
transmitted on the forward traffic channel (Fig. 10.28
and Fig. 10.29)
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Rate Set 1 Forward Traffic Channel
Generation in IS-95
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Rate Set 2 Forward Traffic Channel
Generation in IS-95
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The Forward and Reverse Channel
Frame Structure is given
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Reverse Traffic Channel
For rate set 1, the reverse traffic channel uses 9600,
4800, 2400 and 1200 data rate for transmission
The duty cycle for transmission varies proportionally,
with the data rate being 100% at 9600 bps to 12.5 %
at 1200 bps
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Rate Set 1 Reverse Traffic Generation
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Rate Set 2 Reverse Traffic Generation
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International Mobile
Telecommunications (IMT-2000)
The key futures
High degree of commonality of design worldwide
Compatibility of service within IMT-2000 and with
fixed networks
High quality
Small terminal for worldwide use, including pico,
micro, macro, and global satellite cells
Worldwide roaming capability
Capability for multimedia applications and a wide
range of services and terminals
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International Spectrum Allocation
In 1992, the World Administration Radio
Conference (WARC) specified the spectrum for
the 3G mobile radio system
Europe and Japan followed the FDD specification
The lower-band parts of the spectrum are currently
used for DECT and PHS (Personal Handyphone
System)
The FCC in the United States has allocated a
significant part of the spectrum in the lower band to
2G PCS systems
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Cont.
Most of the North American countries are following
the FCC frequency allocation
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Spectrum Allocation
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Service Provided by Third-Generation
Cellular Systems
High bearer rate capabilities
2 Mbps for fixed environment
384 kbps for indoor/outdoor and pedestrian
environment
144 kbps for vehicular environment
Standardization work
Europe (ETSI: European Telecommunication
Standardization Institute) => UMTS (W-CDMA)
Japan (ARIB: Association of Radio Industries and
Business) => W-CDMA
USA (TIA: Telecommunication Industry Assoication)
=> cdma2000
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Schedules service
Service started in Oct. 2001 (Japan’s W-CDMA)
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Approved Radio Interfaces
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Harmonized 3G Systems
A harmonized 3G Systems based on the
Operators Harmonization Group (OHG)
supports
High-Speed data service, including Internet and
Intranet applications
Voice and nonvoice applications
Global roaming
Evolution from the embedded base of 2G systems
ANSI-41 (American National Standards Institute – 41)
and GSM – MAP core networks
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Cont.
Regional spectrum needs
Minimization of mobile equipment and infrastructure
cost
Minimization of the impact of intellectual property
rights (IPRs)
The free flow of IPRs
Customer requirements on time
 A diagram representing the terrestrial
component of the harmonization efforts for IMT2000 is given in Fig. 10.36
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Modular IMT-2000 Harmonization
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Universal Mobile Telecommunication
System (UMTS)
Network reference architecture
It is partly based on 3G specification, while some 2G
elements have been kept
UMTS Release’99 architecture inherits a lots from
the global system for mobile (GSM) model on the
core network (CN) side
The MSC basically has very similar functions both in
GSM and UMTS
Instead of circuit-switched services for packet data, a
new packet node, packet data access node (PDAN),
or 3G serving general packet radio service (GPRS)
support node (SGSN) is introduced
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UMTS Network Architecture
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Cont.
This new element is capable of supporting data rates
up to 2 Mbit/s
CN elements are connected to the radio network via
the Iu interface, which is very similar to the Ainterface used in GSM
The main changes in the new architecture are in the
radio access network (RAN), which is also called
UMTS terrestrial RAN (UTRAN)
There is a totally new interface called Iur, which
connects two neighboring radio network controllers
(RNC)
• This interface is used for combining macrodiversity,
which is a new WCDMA-based function implemented in
the RNC
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Cont.
BSs (NBs) are connected to the RNC via the Iub
interface
Throughout the standardization process, extra effort
has been made so that most of the 2G core elements
can smoothly support both generations, and any
potential changes are kept to a minimum
In 2G, the RAN is separated from the CN by an open
interface, called A in circuit-switched (CS) and Gb in
packet-switched (PS) networks.
• The former uses time division multiplex (TDM) transport,
while packet data are carried over frame reply
In 3G, the corresponding interfaces are called IuCs
and IuPs
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Cont.
The circuit-switched interface will utilize ATM
The packet switched interface will be based on IP.
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UTRAN Architecture
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General Protocol Model for UTRAN
Interface
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Logical Channels in UTRAN
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