Wireless Networks Lecture 8 Evolution of Wireless Networks Dr. Ghalib A. Shah
Review of previous lecture #7 • 1G wireless cellular networks • NMT • AMPS • TACS • 2G cellular systems • GSM • IS-136 • PDC • IS-95 • Summary of today’s lecture
Last Lecture Review • CSMA • Versions of CSMA • CSMA/CA • Example • Spread Spectrum • Frequency Hoping • Direct Sequence
Evolution of Wireless Systems • The worldwide success of cellular telephone has lead to the development of newer wireless systems and standards for other types of communications besides mobile voice. • For example • Cellular networks to facilitate high speed data traffic • Replace fiber optics and copper lines between fixed points several kms apart. • Replacement of wires within homes, offices etc (evolution of Bluetooth)
First-Generation Cellular Networks • Analog systems • Standards • NMT (Nordic Mobile Telephone) • used in Nordic countries, Switzerland, Netherlands, Eastern Europe and Russia. • AMPS (Advanced Mobile Phone System) • used in the United States, • TACS (Total Access Communications System) • Used in the United Kingdom, • C-450 • in West Germany, Portugal and South Africa, • Radiocom 2000 in France • RTMI in Italy. • In Japan there were multiple systems. Three standards, TZ-801, TZ-802, and TZ-803
NMT • First fully-automatic cellular phone system • Started in 1970, in service 1981 • Two standards NMT-450 and NMT-900 • Corresponds to frequency and the later has higher bands. • Cell size range from 2 km to 30 km. • Use smaller size in urban areas for better quality and larger in less-populated areas. • Handsets 1 watt and Car phone uses 6-15 watt • Automatic switching (dialing) and handover.
NMT Contd. • No spec. for voice traffic encryption • Buy a scanner, tune to the desired channel and intercept. • NMT also supported a simple data transfer mode called DMS (Data and Messaging Service) or NMT-Text • Using DMS, also text messaging was possible between two NMT handsets before SMS service started in GSM • but this feature was never commercially available except in Russian and Polish NMT networks. • NMT Suspended • In FinlandTeliaSonera's NMT on December 31, 2002. • Norway's last NMT network on December 31, 2004. • Sweden's TeliaSonera NMT on December 31, 2007.
AMPS • 1G cellular phone used in US, which uses FDMA • Operates in 800 MHz band • Total of 832 channels; • 416 in 824–849 MHz for transmissions from mobile to the base • 416 in 869–894 MHz for transmissions from base to the mobile. • Each channel is 30 KHz wide • Require large bandwidth for large base population. • No protection against eavesdropper • ESN (Electronic Serial Number) was cloned in 1990s to make free calls from different cells. • Replaced with D-AMPS, GSM and CDMA for better security and capacity
TACS • A variant of AMPS developed by Motorola. • It has been used in some European countries (including the UK & Ireland), as well as Japan and Hong Kong. • ETACS was an extended version of TACS with more channels. • The last ETACS service operated by Vodafone was discontinued on 31 May2001
Second-Generation Cellular Networks • Digital system i.e. voice is digitized • Unlike 1G that relies on FDMA/FDD, 2G use digital modulation formats and TDMA/FDD, CDMA/FDD multiple access techniques • Can be divided into two standards; TDMA and CDMA • The main 2G standards are • GSM (TDMA-based), originally from Europe but used worldwide • IS-136akaD-AMPS, TDMA-based, used in the Americas • IS-95akacdmaOne, CDMA-based, used in the Americas and parts of Asia • PDC (TDMA-based), used exclusively in Japan
2G Contd. • Using digital signals between the handsets and the towers increases system capacity in two key ways: • Digital voice data can be compressed and multiplexed much more effectively than analog voice encodings through the use of various CODECs, allowing more calls to be packed into the same amount of radio bandwidth. • The digital systems were designed to emit less radio power from the handsets. This meant that cells could be smaller, so more cells could be placed in the same amount of space. This was also made possible by cell towers and related equipment getting less expensive.
2G Advantages • The lower powered radio signals require less battery power, so phones last much longer between charges, and batteries can be smaller. • The digital voice encoding allowed digital error checkingwhich could increase sound quality by reducing dynamic and lowering the noise floor. • Going all-digital allowed for the introduction of digital data services, such as SMS and email. • Better security, harder to be scanned
GSM • 2.27 billion subscribers across more than 212 countries, 81% of the global mobile market • Its ubiquity provides international roaming very common • 8-slots TDMA with 200 KHz radio channel, with frame duration of 4.615 ms • The channel data rate is 270.833 kbit/s • Operates in four different bands • Mostly 900 MHz or 1800 MHz • US and Canada use 850 MHz and 1900 MHz • 25 MHz bandwidth of each subdivided into 124 channels • E.g. in 900 MHz, uplink 890-915 MHz, downlink 935-960 MHz
Others Systems • IS-136 or D-AMPS • 3-Slot TDMA, used in North and South America, Australia • Channel bandwidth is 30 KHz. • Frequency bands (824-849MHz and 869-894 MHz) • Pacific Digital Cellular (PDC) • Japanese standard similar to IS-136 • 25 KHz channel • 11.2 kbps at 3-slot and 5.6 kbps at 6-slot • Operates in 800 MHz downlink 810-888 MHz, uplink 893-958 MHz) • In 1.5 GHz (downlink 1477-1501 MHz, uplink 1429-1453 MHz)
Other Systems Contd.. • IS-95 or cdmaOne • Supports up to 64 users that are orthogonally coded • Channel bandwidth is 1.25 MHz • Widely deployed in N. America, Korea, Japan, China, S. America, Australia • Channel data rate is 1.2288 Mchips/s (Mega Chips)
Summary of today’s lecture • 1G analog systems • NMT • AMPS • TACS • C-450 • 2G digital cellular systems • GSM • IS-136 • IS-95 • Next Lecture • 3G and 4G