IT 284 Seminar Unit 9
Dec 14, 2015
One-Way Paging Systems• The traditional way to handle paging is to have a network
of powerful transmitters, all of which transmit all of the pages on all of the transmitters
• Frequencies are reused by using the same frequencies for every transmitter
• In a voice system, this would result in low capacity, but as messages are typically very short, the transmission times are also short
• TDMA systems are used for many paging systems• Each pager has a unique address called a capcode
Spectrum
• Wireless uses a portion of the total spectrum• Bands are regulated for different uses
– AM Radio: 520-1710kHz; FM Radio: 87.5 – 108mHz– Paging: 30-50mHz, 150-170mHz, 450-570mHz, 900mHz– Cellular: 800mHz (analog, TDMA, CDMA-Verizon)– PCS Cellular: 1900mHz (GSM, CDMA-Sprint)
Basic Paging Networks
• Because all pages are sent from all transmitters, there is no need to know the location of any pager
• Satellites are often used to transmit pages great distances to local systems, which are relayed using terrestrial transmitters
• LEO satellites are used for this
Wide-Area Paging System
PSTN
Base stationTelephone
PagingTerminal
PagingTerminal
PagingTerminal
Base station
Base station
pager
Satellite
Paging Control Center
Terrestrial Link
Terrestrial Link
Satellite Link
City 1
City 2
City N
Paging Terminal Overview
CallersCallers
PSTNPSTN
PagersPagers
Operators Entering Alphanumeric MessagesOperators Entering Alphanumeric Messages
Wide-Area ApplicationsWide-Area Applications
TNPPTNPP
Paging Paging TerminalTerminal
Simulcast (Multicast)
• Simulcast versus Single transmission– Better in building penetration
• paging networks simulcast from multiple towers at up to 3500 watts (high power)
• Cellular type networks transmit from a single tower at 60 watts ERP (low power)
Simulcast
Transmitter A
Transmitter BTransmitter B
LinkLink
Overlap AreaOverlap Area
15 m. sec15 m. sec
10 m. sec10 m. sec
??
FLEX (One-way paging)
• 1600, 3200, 6400 bps• Four-minute FLEX
protocol cycle• Short capcodes: 7 digits• Long capcodes: 9 digits
ReFLEX (Two-way paging)• 1920 Frames per Hour, 128 Frames per 4 Minute Cycle• 128 frames per 4 minutes = 1920 frames of 1.76 usable time (seconds) per hour
• Forward - 6400 bps, 3200 bps, 1600 bps• • Reverse - 9600 bps, 6400 bps, 1600 bps, 800 bps• • • Reverse Channel• Number of packets vary with data speed, about 120 bits per frame• 800 bps = 11 packets per frame • 1600 bps = 23 packets per frame• 6400 bps = 96 packets per frame• 9600 bps = 116 packets per frame
•
Each pager is assigned to a base frame in a set of 128 frames – these frames repeat every four minutes. 15 of these repetitions occur during an hour.
The pager awakes depending on the collapse value assigned to it – each set of pagers have a base frame in which they are synchronized.
Page collapse value defines how often the pager awakens. Collapse of 0 = pager scans every frame Collapse of 1 scans every other frameCollapse of 2 scans every 4th frameCollapse of 3 scans every 8th frameCollapse of 4 scans every 16th frameCollapse of 5 scans every 32nd frameCollapse of 6 scans one out of every 64th frameCollapse of 7 scans every 128th frame
ReFLEX ReFLEX (Two-way paging continued)(Two-way paging continued)
ReFLEX (Two-way paging)
• Narrowband PCS• Nationwide frequencies• Forward: 896-902 MHz• Reverse: 929 - 931, 940 -
941 MHz
Current Trends• Cellular / PCS
– Cell phones– PDA’s– PC cards
• Location-based Services– Network– Handset
• SIM Cards– Personal data– Stored minutes (prepay)– Stored value (m-cash)
• Messaging Technologies– Email– SMS– IM
• Telematics– Private vehicles (Onstar)– Commercial
• Telemetry
9.6 to 14.4 Kb/sec 115 Kb/sec 384 Kb/sec 384+ Kb/sec(GPRS) (EDGE) (UMTS)
9.6 to 43.2 Kb/sec
9.6 Kb/sec 60-70 Kb/sec ???
19.2 Kb/sec
4.8 to 19.2 Kb/sec
9.6 Kb/sec 64 Kb/sec
2G 2.5G 3G
14.4 – 64 Kb/sec 144 Kb/sec 384 Kb/seccdmaOne (95A-95B) (cdma2000 1XRTT) (cdma2000
EVDV)
GSM
TDMA
CDMA
iDEN
CDPD
Mobitex &
DataTAC
ReFLEX
2000 2001 2002 2003 2004 2005
Cellular Standards & Evolution
Devices• Faster processors• More memory• Screens
– Bigger– More color depth– Bitmap addressable
• New user interfaces– Keyboards (built-in / attachable)– Joysticks
• Device convergence– Hybrid phone/PDA
• Cameras / MP3 players• Virtual machines/browsers
Existing Mobile Terminals and Devices
Handset
PersonalInformation
Manager
Personal Communicator
Handheld PC
LaptopPC
Low EndLow End High EndHigh End
Voice andSMS
Data Voice andData
Data Data
How do Applications run on Devices?
Three Paths
Processor
Device OS
Application
Processor
Device OS
VM (App)
VM Application
Processor
Device OS
Browser (App)
ML Application
Native OSNative OS PalmPalm SymbianSymbian Windows Windows
CECE LinuxLinux
Virtual MachineVirtual Machine Sun J2MESun J2ME Qualcomm Qualcomm
BREWBREW AppForgeAppForge Syclo AgentrySyclo Agentry
Markup LanguageMarkup Language
Location-based Services• 911 locator
– Government mandate– Find someone within 50m
• Advertising– Impulse buying, walking
past a store– Discounts
• Telematics– Mapping and Directions
• Weather forecasts– Truly local
• Find things:– Restaurants– Movie theaters– ATMs– Gas Stations
• Significant PrivacyIssues
SMS – Short Message Service
• Integral part of GSM standard– Added to other standards as well
• Uses control channel of phone– Send/Receive short text messages– Sender pays (if from mobile phone)
• Phone has "email" address– SMTP Interface– [email protected]
TechnologyTechnology Message Message LengthLength
2- way?2- way?
GSMGSM 160 bytes160 bytes YesYes
TDMA/PDCTDMA/PDC 160 bytes160 bytes No*No*
CDMACDMA 256 bytes256 bytes YesYes
iDENiDEN 140 bytes140 bytes YesYes
SMS Around the World• Hugely successful in Europe and Far East• 1 Billion phone-to-phone messages / day
worldwide– 1.3 Billion messages / day if alerts from Internet
phone are included• Avg 30-40 msgs / month / person
– Especially by young people• Cheaper than in the US• Interchange agreements between carriers
SMS Advantages SMS Disadvantages
• Adopted by young people• Simple• Fast• Inexpensive• 2-way (some networks)• “Poor person's” email
• Bare bones– No support for fonts,
alignment• UI - hard to type
– Letter “s” requires 4 presses– Wait for next letter
• No guarantee of delivery• Not suitable for interactive
conversations• Interoperability in the US
– Recently addressed