Mobile Computing - Unit II

UNIT - II Introduction:  The analog mobile systems were originally targeted for a relatively select group of users who mostly had the mobiles telephones installed in their vehicles.  Reduced RF transmission power and longer battery life.  International and wide-area roaming capability.  compatibility with ISDN, leading to wider range of services.

GSM:THE EUROPEAN TDMA DIGITAL CELLULAR STANDARD  Fully digital system utilizing the 900 MHz frequency band.  TDMA over radio carriers (200 kHz carrier spacing).  8 full-rate or half-rate TDMA channels per carrier.  user/terminal authentication for fraud control.  encryption of speech and data transmissions over the radio path

 Full international roaming capability.  low speed data services (up to 9.6kb/s).  compatibility with ISDN for supplementary services.  Support of short message service(SMS).  The common ISDN – like supplementary service supported by GSM include :  call offering services – call forwarding.  Call restriction services – call barring.  Call waiting service.  Call hold service.

 Multi party service – tele conferencing.  Calling line presentation restriction services.  Advice of charge service.  Closed user group service.  The GSM standard has been undergoing continuous extensions and enhancements to support more services and capabilities like high speed circuit-switched data (HSCSD),general packet radio service (GPRS), and CAMEL (customized applications for mobile network – enhanced logic).

IS –136:The North American TDMA Digital cellular Standard (D-AMPS)  Background on North American Digital cellular.  Service Aspects for D – AMPS (IS–136).  Protocol Model and Typical call Flow Sequence.

Background on north american TDMA digital cellular:  ten told increase in capacity over the analog (AMPS) system.  ease of transition and compatibility with the analog system.  short time to service and low cost dual – mode operation.  enhanced security, privacy, and quality.  new and enhanced services/features.

SERVICE ASPECTS FOR D – AMPS (IS – 136)  Short message service (SMS) – point to point.  emergency (E.911) service.  lawfully authorized electronic surveillance (LAES).  on – the – air activation(OTA).  sleep mode terminal operation.  rolling mask message encryption.

DECT(DIGITAL ENHANCED DORDLESS TELECOMMUNICATIONS)  The European Digital Enhanced Cordless Telecommunications standard was developed by ETSI to serve a range of applications that included :  residential systems  small business systems (single site, single cell)  large business systems(multisite, multicell)  public cordless access systems  wireless data (LAN) access systems  evolutionary systems (fixed wireless access, cordless access to cellular

Protocol model and typical call flow sequences  GSM specifications provide complete definitions of the bis interface (between BTS and BSC) and the A interface (between the BSC and the MSC), till recently these interfaces were not defined for D – AMPS.  Further the, Mobile Application Protocol (MAP) used in D - AMPS was developed by the TIA as part of IS – 41standard to facilitate cellular system interoperability and roaming.

 The PSTN user dials the phone number of the called mobile.  The serving CO routes the call to the Home MSC of the called mobile.  MSC – H sends an IS – 41 Location Request to the HLR using called bile’s MIN.  The VLR sends TLDN to the HLR.  MSC – S pages the mobiles (over the paging area).  Called mobile responds to the page.

THE NORTH AMERICAN CDMA DIGITAL CELLULAR STANDARD  Introduction : One of the targets set by the CTIA for the digital cellular systems for North America was a tenfold increase in traffic capacity over the analog AMPS system. Commercial CDMA systems are now being implemented in North America and also operational in many other countries.

Service Aspects  Short message service (SMS)  Slotted paging  Over – the – air activation(OTA)  Enhanced mobile station identities  Temporary mobile station identities  Asynchronous data and group 3 fax  Synchronous data  packet data  supplementary services

Forward Link Structure in IS – 95  The CDMA common air interface (CAI) specifies a forward physical channel (known as forward waveform) design that uses a combination of frequency division, and orthogonal signal multiple – access techniques.  These 1.23 MHz channels can be increased from the initial single CDMA channel to multiple such channels as demand for digital service increases.

Low power wireless communications systems and north American PCS  CT2(Cordless Telephony 2)Systems  DECT (Digital Enhanced Cordless Telecommunications  PHS(Personal Handy Phone Systems)

CT2(Cordless Telephony 2)Systems  CT2 is a second – generation cordless telecommunication system – a digital cordless standard designed to be used for wireless PABX and key systems, cordless residential telephones, and public cordless access (telepoint) services.  A number of systems for business and public cordless applications based on the CT2 standard are in operation in countries around the world.

 The main application environments for CT2 include residential cordless setups, public telepoint systems, and wireless PBX and systems.  In principle, a CT2 handset purchased for use in one environment (e.g., home or work) can also be used in other environments (e.g) telepoint.  Radio Aspects: The spectrum allocation for CT2 is a 4 MHz slot from 864 to 868 MHz.This is divided into 40 channels, each with 100MHz. The CAI specifies the modulation as two – levels frequency shift keying (FSK) shaped with a Gaussian filter.

Layer 1 Signaling Signaling layer 1 provides the mechanism for initiation of a two – way digital link over radio path and the selection of a suitable radio channel for information transfer. Layer 2 Signaling Layer 2 packets sent over the radio interface consist of up to six code words. The first code word is a 64 bit address code word (ACW), and subsequent code words contain data form of 64 – bit data code words(DCWs).

PHS(PERSONAL HANDYPHONE SYSTEM)  The Japanese PHS (Personal Handyphone System) standard for cordless telecommunications was completed at the end of 1993 by the research and development center for Radio Systems (RCR). Features for PHS:  Error detection using CRC (PHS does not provide error correction)  Dedicated control channels  Handoff (as an option) at walking speeds  Transmission diversity on the forward link(base to handset)  Group 3 fax at 2.4 – 4.8 kb/s  Full duplex modem transmission at 2.4 – 9.6kb/s and recently at 32kb/s  Terminals with standby times up to 800 hours

PHS Radio Aspects  CCH (common control channels)  TCH (traffic channels)  BCCH (broadcast control channel)  CCCH (common control channel)  PCH (paging control channel)  SCCH (signaling control channel)  UPCH (user packet channel)  ACCH (associated control channel)

PHS Network and protocol aspects  Providing subscribed services to a PHS user regardless of IPS location.  Charging to the same PS based on the distance between the called and calling parties based on current PS location.  Maintaining location information for all the PS in the system.  Routing and delivery of incoming calls to the current location of the PS.  Authentication of the PS as required by the PHS service provider