Transcript Cellular technologies 2G, 3G, 4G

COMP1706: MOBILE AND NETWORK TECHNOLOGIES
Cellular technologies
2G, 3G, 4G
Dr. George Loukas
University of Greenwich
1981
1nd Gen Vs. 2nd Gen
1991

Voice channels using FM

Digital traffic channels

Digital traffic supported only by
using a modem

Voice is digitised
(Although, still, user traffic is converted to
analogue signal to transmit to base
station)

No encryption

Encryption: Easy to encrypt digitized
traffic, leading to better security.

Channel access: One channel
allocated to one user.

Error detection and correction: Again,
easier with digitized traffic, leading to
clear voice reception

Shared channel access. Multiple users
sharing one channel, leading to
greater capacity.
Shared channel access
FDMA
TDMA
CDMA
Frequency Division
Multiple Access
Time Division Multiple
Access
Code Division Multiple
Access
Each phone call is
allocated a frequency
band for the entire
duration
Each transmitter is
allocated a different
time slot
Multiple message
signals sent
simultaneously over the
same spectrum, but
with different code
FDMA
FDMA
Frequency Division
Multiple Access
Each phone call is
allocated a frequency
band for the entire
duration
1G uses FDMA
Shared channel access: TDMA
TDMA
Time Division Multiple
Access
Each transmitter is
allocated a different
time slot.
Shared channel access: CDMA
CDMA
Code Division Multiple
Access
Multiple message
signals sent
simultaneously over the
same sprectrum, but
with different code
Originally by Suresh Goyal & Rich Howard
Originally by Suresh Goyal & Rich Howard
Originally by Suresh Goyal & Rich Howard
Code Division Multiple Access (CDMA)
Each cell is allocated a frequency bandwidth, split into:
Half for reverse (mobile to base station)
Half for forward (base station to mobile)
Transmission uses the spread spectrum principle
Spread Spectrum
Frequency hopping (FHSS)
Signal broadcast over seemingly random series
of frequencies
Receiver hops between frequencies in sync with
transmitter
Jamming on one frequency affects only a few
bits
CDMA
uses DSSS
Direct Sequence (DSSS)
Each bit represented by multiple
bits using a “spreading code”
Spreading code spreads signal across wider
frequency band
In proportion to number of bits used
10 bit spreading code spreads signal across 10
times bandwidth of 1 bit code
One method:
Combine input with spreading code using XOR
Input bit 1 inverts spreading code bit
Input zero bit doesn’t alter spreading code bit
Countering multipath fading
To counter multipath fading:
We take into account only the
dominant signal and ignore the
rest as noise
or
Use a rake receiver, which takes
into account all signals based
on appropriate weights and
time delays for each signal.
CDMA advantages

frequency diversity
The transmission is spread out over
different frequencies. So, selective
fading has little effect on signal.

privacy
Inherent in spread-spectrum.
Receiver needs to know the code


multipath resistance
graceful degradation
Versions of a signal that arrive
delayed do not interfere much
with the dominant signal
In FDMA and TDMA there is a hard
limit to number of users.
In CDMA, number of users depends
on noise level (error rate). The more
the users, the more the error, but no
hard limit.
CDMA disadvantages

near-far problem
Signals closer to the receiver are
received with less attenuation
than signals farther away
So, remote transmissions might be
more difficult to recover

self-jamming
Some cross correlation between
users
Hard Vs. Soft handover
Hard handover
(Break, then make)

Existing radio link must be dropped for
a small period of time and then taken
over by another base station

A call in progress redirected from
current base station and transmit–
receive frequency pair to another base
station and frequency pair.

An ongoing call can not exchange
data or voice for this duration

Handover takes place in a few ms (at
best in 60 ms) - hardly discernible by
the user

Handover to other cell is required when
low signal strength and high error rate
Soft handover
(Make, then break)

A mobile device can be
simultaneously connected to
several base stations

Soft handover does not require
breaking of the radio link for cellto-cell transfer of a call
Two main 2G technologies
Also known as IS-95
Uses CDMA
Greater capacity
Very large cells
Speed originally 14.4 Kbps
Even low signal is enough for good
quality
Dropped calls less likely (Soft
handover)
Monopoly of a single company bars
new entrants in market
Uses FDMA, TDMA
More interference
and cells limited to 120 km
Speed originally 9.6 Kbps
Many more subscribers.
Covers the whole world, so
roaming not an issue
Introduced SMS messages
Introduced SIM cards. (for
authentication and
data/contact storage)
Short Message Service
Introduced as part of the GSM
standard
First SMS was sent in the UK over the
Vodafone GSM network (1992).
Now, 200,000 SMS are sent every
second
Limited to ~160 characters
Larger SMS messages can be sent, but
need to be split and recombined
when received
Includes control information (e.g.
destination number, timestamp,
data coding scheme …)
Best-effort delivery
Short Message Service
Centre (SMSC): store-andforward
2.5G
1999
GSM/GPRS
 Introduces packet-switching as opposed to circuitswitching



Voice/data broken into packets routed through the network
Can charge by data rather than time
Best-effort service (the more the users, the worse the
quality of service)
Much higher data rate than 2G
Even higher in next upgrade, EDGE (“2.75G”).

Auction of 20-year 3G licences in the UK (27 April 2000)
Biggest auction at the time. Raised £22 billion
Thirteen bidders.
The winners:
Licence A TIW UMTS (UK) Limited
Licence B Vodafone Limited
Licence C BT (3G) Limited
Licence D One2One
Licence E Orange 3G Limited
£4,384,700,000
£5,964,000,000
£4,030,100,000
£4,003,600,000
£4,095,000,000
http://www.ofcom.org.uk/static/archive/spectrumauctions/auction/auction_index.htm
3rd Generation
2002
High-speed wireless communications to support multimedia, data,
and video in addition to voice
Based on CDMA
voice quality comparable to PSTN
 Up to 2 Mbps. Originally 144 / 384 kbps
available to users (vehicles / pedestrians)
 symmetrical and asymmetrical data rates
 packet-switched and circuit-switched services
 adaptive interface to Internet
 support for variety of mobile equipment
 allowed introduction of new services and technologies

The most popular 3G technology is UMTS (also known as WCDMA)
Add-on technologies (UMTS + *)
HSPA
Extends UMTS
originally 14 Mbps downlink, 5.76 Mbps uplink
Hybrid automatic repeat-request
Error-free packets through combination of error
corrections bits and efficient retransmissions where necessary.
HSPA+ (Evolved HSPA)
337 Mbps downlink, 34 Mbps uplink
UMTS – QoS classes
Traffic class
Conversational
class
Streaming
class
Interactive
class
Background
Fundamental
characteristics
Preserve time
relation between
information
entities of the
stream
Preserve time
relation
between
information
entities of the
stream
Request
response
pattern
Destination is
not expecting
the data within
a certain time
Streaming
multimedia
Web browsing,
network games
Preserve data
integrity
Conversational
pattern (stringent
and low delay)
Example of the Voice,
application
videotelephony,
video games
Preserve data
integrity
Background
download of
emails
CDMA Design Considerations – Multirate

provision of multiple fixed-data-rate channels to user
- different data rates provided on different logical channels
- flexibly supports multiple simultaneous applications
- efficiently uses available capacity by only providing the
capacity required for each service

uses TDMA within single CDMA channel

uses multiple CDMA codes
Typical capacity demands addressed by 3G
Average monthly
capacity
requirement
Device
Applications
Feature phone
Primarily phone calls.
Stripped-down web
browser
< 100MB
Early smart phone
Phone calls, emails and
light web browsing
~ 150MB
3G smart phone
Web browsing, GPS, net
radio, youtube videos
~ 500MB
Tablet computer
Web browsing, GPS, net
radio, cloud computing,
movies
> 1GB
4th Generation
2009
rapid increase in data traffic on wireless
networks
•
•
•
•
more terminals accessible to the Internet
permanent connections to e-mail
multimedia services
support for real time services
Completely IP-based. Unlike 3G and previous
generations, it used IP even for voice data.
4G technologies
Two main candidates
Similar performance
and both based on use of orthogonal
frequency division multiple access (OFDMA)
OFDMA
• Reduces crosstalk
• Efficiently
overcomes
frequency-selective
(narrowband)
fading caused by
multipath
Number of customers of 4G LTE (2014)
http://media.tefficient.com/2014/12/4G-LTE-population-coverage-Sep-2014.png
Coverage of 4G LTE (Sep. 2014)
http://media.tefficient.com/2014/12/4G-LTE-population-coverage-Sep-2014.png
Mobile Network Generations
1G
2G
2.5G
3G
4G
Design began
1970
1980
1985
1990
2000
Implemented
1984
1991
1999
2002
2009
Provides
Analogue
voice
Digital voice
Higher
capacity
packetised
data
Higher
capacity,
broadband
Completely IP
based
Data Rate
1.9 kbps
14.4 kbps
384 kbps
2 Mbps
200 Mbps
Multiplexing
FDMA
TDMA,
FDMA,
CDMA
TDMA, FDMA,
CDMA
CDMA
OFDMA
Core network
PSTN
PSTN
PSTN, packet
network
Packet network
IP backbone
1-G
2-G
3-G
4-G
5G – Tactile Internet
2020?
In development. To be rolled out by 2020.
Several research projects at the moment.
No consensus yet on technology
Indicative requirements:
http://networks.nokia.com/news-events/insight-newsletter/articles/5g-is-moving-beyond-the-hype