2. 1G
(<1Kbps)
1 Kbps
10 Kbps
100 Kbps
2 Mbps
1 Mbps
Data Rates
1980 1990 2000 2010
2G
(9.6Kbps)
2.5G
(10-150Kbps)
3G
(144Kbps to 2Mbps)
Years
Overview
3. Cellular networks: From 1G to 3G
• 1G: First generation wireless cellular: Early 1980s
– Analog transmission, primarily speech: AMPS (Advanced Mobile
Phone Systems) and others
• 2G: Second generation wireless cellular: Late 1980s
– Digital transmission
– Primarily speech and low bit-rate data (9.6 Kbps)
– High-tier: GSM, IS-95 (CDMA), etc
– Low-tier (PCS): Low-cost, low-power, low-mobility e.g. PACS
• 2.5G: 2G evolved to medium rate (< 100kbps) data
• 3G: future Broadband multimedia
– 144 kbps - 384 kbps for high-mobility, high coverage
– 2 Mbps for low-mobility and low coverage
• Beyond 3G: research in 4G
4. Multiple Access Techniques: How to allocate users
Time
Frequency
Session1
Session2
Session3
Session4
Frequency Division
Multiple Access (FDMA)
1G Cellular (AMPS)
Time
Frequency
Time Division
Multiple Access (TDMA)
2G TDMA
3G TDMA
Session2
Session3
Session1
Session4
Time
Frequency
Code Division
Multiple Access (CDMA)
All sessions
based on a
code
2G CDMA (IS-95)
3G CDMA
6. Frequency Reuse
The concept of frequency reuse is based on assigning to
each cell a group of radio channels used within a small
geographic area
Cells are assigned a group of channels that is completely
different from neighbouring cells
The coverage area of cells is called the footprint and is
limited by a boundary so that the same group of channels can
be used in cells that are far enough apart
7. Frequency Reuse
• Cells with the
same number have
the same set of
frequencies
Frequency Reuse
8. Frequency Reuse using 7
frequencies allocations
f4
f3
f2
f1
f6
f7
f5 f4
f3
f2
f1
f6
f7
f5
f4
f3
f2
f1
f6
f7
f5
f4
f3
f2
f1
f6
f7
f5
f4
f3
f2
f1
f6
f7
f5
Each cell is generally 4 to 8 miles in diameter with a lower limit
around 2 miles.
9.
10. Problem with Smaller Clustersize
Interfering cells are closer by when clustersize is smaller.
11.
12.
13. 0G Wireless
• Mobile radio telephones were used for military
communications in early 20th century
• Car-based telephones first introduced in mid 1940s
– Single large transmitter on top of a tall building
– Single channel used for sending and receiving
– To talk, user pushed a button, enabled transmission and disabled
reception
– Became known as “push-to-talk” in 1950s
– CB-radio, taxis, police cars use this technology
• IMTS (Improved Mobile Telephone System) introduced in
1960s
– Used two channels (one for sending, one for receiving)
– No need for push-to-talk
– Used 23 channels from 150 MHz to 450 MHz
14. First-Generation Cellular
• Advanced Mobile Phone Service (AMPS) invented at Bell Labs
and first installed in 1982
• Used in England (called TACS) and Japan (called MCS-L1)
• Key ideas:
– Exclusively analog
– Geographical area divided into cells (typically 10-25km)
– Cells are small: Frequency reuse exploited in nearby (not adjacent) cells
– As compared to IMTS, could use 5 to 10 times more users in same area by
using frequency re-use (divide area into cells)
– Smaller cells also required less powerful, cheaper,smaller devices
15.
16. Second Generation Cellular
• Based on digital transmission
• Different approaches in US and Europe
• US: divergence
– Only one player (AMPS) in 1G
– Became several players in 2G due to competition
– Survivors
• IS-54 and IS-135: backward compatible with AMPS frequency
allocation (dual mode - analog and digital)
• IS-95: uses spread spectrum
• Europe: Convergence
– 5 incompatible 1G systems (no clear winner)
– European PTT development of GSM (uses new
frequency and completely digital communication)
17.
18. Differences Between First and
Second Generation Systems
• Digital traffic channels – first-generation systems
are almost purely analog; second-generation
systems are digital
• Encryption – all second generation systems
provide encryption to prevent eavesdropping
• Error detection and correction – second-generation
digital traffic allows for detection and correction,
giving clear voice reception
• Channel access – second-generation systems allow
channels to be dynamically shared by a number of
users
19. Integrating Data Over Cellular
• Direct access to digital channel
• Voice and data using one handset
• PCS 1900 (GSM-1900)
– 9.6 kbps circuit switched data
– 14.4 kbps under definition
– Packet mode specified
– Short message service
• IS-95-based CDMA
– 13 kbps circuit switched data
– Packet mode specified
– Short message service
20. GSM (Global System for Mobile Communications)
• Completely designed from scratch (no backward
compatability)
• Uses 124 channels per cell, each channel can
support 8 users through TDM (992 users max)
• Some channels used for control signals, etc
• Several flavors based on frequency:
– GSM (900 MHz)
– GSM 1800 (called DCS 1800)
– GSM 1900 (called DCS 1900) - used in North America
• GSM 1900 phone only works in North America.
• In Europe, you can transfer your SIM (Subscriber
Identity Module) card to a phone of the correct
frequency. This is called SIM-roaming.
21.
22.
23.
24. 2G CDMA Cellular
IS-95 is the best known example of 2G with
CDMA
Advantages of CDMA for Cellular
• 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
25. Drawbacks of CDMA Cellular
• 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
27. Alternatives to 3G Cellular
• Major technical undertaking with many
organizational and marketing overtones.
• Questions about the need for the additional
investment for 3G (happy with 2.5G)
• Wireless LAN in public places such as shopping
malls and airports offer options
• Other high-speed wireless-data solutions compete
with 3G
– Mobitex low data rates (nominally 8 Kbps), it uses a narrowband
(2.5KHz) as compared to 30 KHz (GSM) and 5 MHz (3G).
– Ricochet: 40 -128 kbps data rates. Bankruptcy
– Flash-OFDM: 1.5 Mbps (upto 3 Mbps)
28. 4G Systems
• Wireless networks with cellular data rates of 20
Mbits/second and beyond.
• AT&T has began a two-phase upgrade of its wireless
network on the way to 4G Access.
• Nortel developing developing features for Internet
protocol-based 4G networks
• Alcatel, Ericsson, Nokia and Siemens found a new
Wireless World Research Forum (WWRF) for research on
wireless communications beyond 3G.
• Many new technologies and techniques (multiplexing,
intelligent antennas, digital signal processing)
• Industry response is mixed (some very critical)
29. What is WiMax?
• Worldwide Interoperability for
Microwave Access
• Last mile wireless broadband access
• Alternative to cable and DSL
• Deliver data, voice, video
• Support hundreds to thousands of
homes/business
30. • Defined by IEEE as 802.16
• Typical target environment:
• Targets fixed, portable, and mobile stations
• Environments with and without line of sight
• Cell radius of 3-10 kilometers
• Capacities of up to 40 Mbps per channel
• Mobile network deployments of up to 15
Mbps, 3 km radius
31. Builds on and
Extends WiFi Technology
• Advantages of WiFi are:
• Easy to deploy, unlicensed spectrum, low
cost
• Supports (limited) mobility
• But WiMax needs to address the
following:
32. WiFi limitations
• Susceptible to interference
• 802.11 targets short-range indoor
operation (mostly)
• Security is a concern
• Limited level of mobility
• WiMax is intended to complement WiFi
• WiMax Forum: promotes WiMax and
looks after interoperability
