Transcript Wireless Personal Communications Systems

Wireless Personal Communications
Systems – CSE5807
Lecture: 05
Stephen Giles and Satha K. Sathananthan
School of Computer Science and Software Engineering
Monash University
Australia
These slides contain figures from Stallings, and are based on a set developed by Tom Fronckowiak .
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CDMA System
• Multiple access: Direct sequence spread spectrum (DS-SS).
• Uplink/Downlink: Frequency Division Duplexing.
• Advantages:
– Frequency diversity:
• Frequency-dependent transmission impairments have less effect on
signal.
– Multipath resistance:
• Chipping codes used for CDMA exhibit low cross correlation and low
autocorrelation.
– Privacy:
• Privacy is inherent since spread spectrum is obtained by use of noiselike signals.
– Graceful degradation:
• System only gradually degrades as more users access the system
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CDMA System
• Drawbacks:
– Self-jamming:
• Arriving transmissions from multiple users not aligned on chip
boundaries unless users are perfectly synchronized.
– Near-far problem:
• Signals closer to the receiver are received with less attenuation than
signals farther away.
– Soft handoff:
• Requires that the mobile acquires the new cell before it relinquishes
the old.
• This is more complex than hard handoff used in FDMA and TDMA
schemes.
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CDMA System
• Design Consideration:
– RAKE receiver:
• When multiple versions of a signal arrive more than one chip
interval apart, RAKE receiver attempts to recover signals from
multiple paths and combine them.
• This method achieves better performance than simply
recovering dominant signal and treating remaining signals as
noise
– Soft Handoff:
• Mobile station temporarily connected to more than one base
station simultaneously.
– Power control:
• Multi-user interference is the major problem.
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Principle of RAKE Receiver
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CDMA IS-95: Forward Link
• Consists of up to 64 logical CDMA channels each occupying
1228 kHz bandwidth.
• Four types of channels:
– Pilot (channel 0):
• Allows the mobile unit to acquire timing information, provides phase
reference and provides means for signal strength comparison.
– Synchronization (channel 32):
• Used by mobile station to obtain identification information about
cellular system.
– Paging (channels 1 to 7):
• Contain messages for one or more mobile stations.
– Traffic (channels 8 to 31 and 33 to 63):
• Supports 55 traffic channels.
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ITU’s View of Third-Generation Capabilities
• High voice quality.
• High data rate services:
* 144 kbps: Users in high-speed motor vehicles over large areas.
* 384 kbps: Users standing or moving slowly over small areas.
* 2.048 Mbps: Users in indoors.
• Symmetrical / asymmetrical data transmission rates.
• Support for both packet and circuit switched data services.
• An adaptive interface to the Internet to reflect efficiently the
common asymmetry between inbound and outbound traffic.
• More efficient use of the available spectrum in general.
• Support for a wide variety of mobile equipment.
• Flexibility to allow the introduction of new services and
technologies.
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3G Proposals
• Wideband CDMA (W-CDMA):
– 3G Partnership Project (3GPP) to include GSM technologies.
– Based on UMTS Terrestrial Radio Access (UTRA) FDD/TDD
proposals.
• DS-CDMA
• Asynchronous operation.
• Chip rate: 3.844 Mcps
– (DS-CDMA
• CDMA 2000:
– 3G Partnership Project 2 (3GPP2) to include non-GSM technologies.
– Backward compatible with CDMA IS-95.
• Uplink: DS-CDMA and Downlink: MC-CDMA/DS-CDMA
• Synchronous operation (timing from GPS).
• Chip rate: N x 1.2288 Mcps where N=1,3,6,9,12
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3G Proposals
Radio Transmission
Technologies (RTT)
FDD Mode:
DS
FDD Mode:
MC
TDD
Mode:
Interface between RTT and core networks
Core Network family
of 3G systems
Core Network 3G
interface
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Evolved
GSM Map
Evolved nonGSM Map
Network-tonetwork
interface
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Evolution towards 3G
GSM => HSCSD => GPRS => EDGE => GERAN/UTRAN => UMTS
2G
2.5G
9.6kbps
115kbps 171kbps
3G
3G
384kbps
>2Mbps
HSCSD: High Speed Circuit Switched Data
GPRS: General Packet Radio Service
EDGE: Enhanced Data rate for Global Evolution
GERAN: GSM/EDGE Radio Access Network
UMTS: Universal Mobile Telecommunications System
UTRAN: UMTS Terrestrial Radio Access Network
IS-95A => IS-95B => cdma2000 1x/3x => cdma2000 1xEV
2G
2.5G
cdmaOne
14.4kbps
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115kbps
3G
2Mbps
3G
>2.4Mbps
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Mobile Data Networks
Independent
Overlay
Shared
Ex:
CDPD
Licensed
bands
Unlicensed
bands
Ex: ARDIS
Ex: Metricom
Overlay on
traffic
channels
Overlay on
signaling
channels
Ex: GPRS
Ex: SMS
CDPD: Cellular Digital Packet Data
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GPRS
• Overlay on top of the GSM physical layer and network entities.
– Provides connection to external packet data networks through GSM
infrastructure.
– New logical GPRS channels are defined.
– Common pool of channels.
• Dynamically allocated => Capacity on demand
– Three types of mobile terminals => Class A, B and C
– Various network services:
• Point-to-multipoint-multicast (PTM-M) and Point-to-multipointgroup (PTM-G)
– Based on IP or X.25
• Bearer service for GSM’s SMS
• Access for MS at no charge.
• QoS based services.
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GPRS Architecture
BTS
BSC
SGSN
GGSN
IP based
Backbone
network
GR
HLR
BTS
BSC
MSC
SGSN: Serving GPRS Support Node
GGSN: Gateway GPRS Support Node
GR: GPRS Register
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Short Messaging Services (SMS)
• Transmission of alphanumeric characters (up to 160).
• Developed as part of GSM Phase 2 specifications.
• Instant delivery service / store and forward service.
• Cell broadcast service / Point-to-point service.
• SMS center (SMSC):
– Sorts and routes messages.
– Use SS-7 signaling.
• Messages are transmitted on control channels.
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Mobile Application Protocols
• How internet based applications are being adapted to cellular
system.
– Major problems:
• Lack of bandwidth, processing power, memory, display sizes and
interfaces.
• More latency, less connection stability, and less predictive
availability.
– Examples:
• Wireless Application Protocol (WAP).
• i-Mode
• WAP:
– Integrating cellular telephony and the internet by providing web content
and advanced services.
• Attempts to optimize the web and existing tools for wireless.
• i-Mode:
– Eliminate the gateway and provide direct access to the internet to the
extent possible.
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Wireless Application Protocol (WAP)
WAE user
agent
WAP
Gateway
Web
Server
Application (WAE)
Session (WSP)
Transaction (WTP)
Security (WTLS)
Transport (WDP)
Bearer (GSM, GPRS and etc.)
WAE: Wireless Application Environment
WTLS: Wireless Transport Layer Security
WSP: Wireless Session Protocol
WDP: Wireless Datagram Protocol
WTP: Wireless Transport Protocol
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Required Reading
• W. Stallings, “Wireless Communications and Networks”
Prentice-Hall, 2000.
>> Chapter 10
Reference
• K. Pahlavan and K. Krishnamurthy “Principles of
Wireless Networks”, Prentice-Hall, 2002.
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