1. 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 .

2. 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 noise-like signals.
Graceful degradation:
System only gradually degrades as more users access the system

3. 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.

4. 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.

5. Principle of RAKE Receiver

6. 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.

7. 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.
* 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.

8. 3G Proposals Wideband CDMA (W-CDMA): CDMA 2000:
3G Partnership Project (3GPP) to include GSM technologies.
Based on UMTS Terrestrial Radio Access (UTRA) FDD/TDD proposals.
DS-CDMA
Asynchronous operation.
Chip rate: 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 Mcps where N=1,3,6,9,12

9. 3G Proposals Radio Transmission Technologies (RTT)
Core Network family of 3G systems
Core Network 3G interface
Radio Transmission Technologies (RTT)
FDD Mode: DS
FDD Mode: MC
TDD Mode:
Interface between RTT and core networks
Evolved GSM Map
Evolved non-GSM Map
Network-to-network interface

10. Evolution towards 3G cdmaOne
GSM => HSCSD => GPRS => EDGE => GERAN/UTRAN => UMTS
2G G 3G 3G
9.6kbps kbps 171kbps kbps >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 G G 3G
cdmaOne
14.4kbps kbps 2Mbps >2.4Mbps

11. Mobile Data Networks Independent Overlay Shared
Ex: CDPD
Overlay on traffic channels
Ex: GPRS
Overlay on signaling channels
Ex: SMS
Licensed bands
Ex: ARDIS
Unlicensed bands
Ex: Metricom
CDPD: Cellular Digital Packet Data

12. 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-multipoint-group (PTM-G)
Based on IP or X.25
Bearer service for GSM’s SMS
Access for MS at no charge.
QoS based services.

13. GPRS Architecture SGSN: Serving GPRS Support Node
IP based
Backbone
network
MSC
GGSN
SGSN
HLR
BTS
BSC GR
SGSN: Serving GPRS Support Node
GGSN: Gateway GPRS Support Node
GR: GPRS Register

14. 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.

15. 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.

16. 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
WSP: Wireless Session Protocol
WTP: Wireless Transport Protocol
WTLS: Wireless Transport Layer Security
WDP: Wireless Datagram Protocol

17. Required Reading Reference
W. Stallings, “Wireless Communications and Networks” Prentice-Hall, 2000.
>> Chapter 10
Reference
K. Pahlavan and K. Krishnamurthy “Principles of Wireless Networks”, Prentice-Hall, 2002.