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 .
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
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.
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.
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.
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.
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
FDD Mode: DS FDD Mode: MC TDD Mode: Interface between RTT and core networks Evolved GSM Map Evolved non-GSM Map Core Network family of 3G systems Core Network 3G interface Radio Transmission Technologies (RTT) Network-to-network interface 3G Proposals
GSM => HSCSD => GPRS => EDGE => GERAN/UTRAN => UMTS IS-95A => IS-95B => cdma2000 1x/3x => cdma2000 1xEV 2G 2.5G 3G 3G 2G 2.5G 3G 3G 9.6kbps 115kbps 171kbps 384kbps >2Mbps cdmaOne 14.4kbps 115kbps 2Mbps >2.4Mbps Evolution towards 3G 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
Mobile Data Networks Independent Overlay Shared Ex: CDPD Overlay on traffic channels Ex: GPRS Overlay on signaling channels Ex: SMS Unlicensed bands Ex: Metricom Licensed bands Ex: ARDIS CDPD: Cellular Digital Packet Data
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.
IP based Backbone network SGSN GGSN HLR BTS BTS BSC BSC MSC GPRS Architecture GR SGSN: Serving GPRS Support Node GGSN: Gateway GPRS Support Node GR: GPRS Register
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.
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.
WAE user agent WAP Gateway Web Server Application (WAE) Session (WSP) Transaction (WTP) Security (WTLS) Transport (WDP) Bearer (GSM, GPRS and etc.) Wireless Application Protocol (WAP) WTLS: Wireless Transport Layer Security WDP: Wireless Datagram Protocol WAE: Wireless Application Environment WSP: Wireless Session Protocol WTP: Wireless Transport Protocol
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.