WIRELESS NETWORKS _ BABU M_ unit 3 ,4 & 5 PPT EC 6802 WIRELESS NETWORKS PPT POWER POINT PRESENTAION ON WIRELESS NETWORKS BABU M ASST PROFESSOR/ ELECTRONICS AND COMMUNICATION ENGINEERING, RMK COLLEGE OF ENGINEERING AND TECHNOLOGY CHENNAI, THIRUVALLUR DISTRICT

1. EC6802
WIRELESS NETWORKS
1
By
BABU M
Asst Professor
RMKCET

2. UNIT III
MOBILE TRANSPORT LAYER
2

3. Contents
 Traditional TCP
 Congestion control
 Slow start
 fast retransmit/fast recovery
 Implications on mobility
 Classical TCP improvements
 Indirect TCP
 Snooping TCP
 Mobile TCP
 Time out freezing
 Selective retransmission
3

4. Transport Layer
E.g. HTTP (used by web services)
typically uses TCP
 Reliable transport between
client and server required
TCP
 Steam oriented, not
transaction oriented
 Network friendly: time-out
 congestion
 slow down transmission
Well known – TCP guesses quite
often wrong in wireless and mobile
networks
 Packet loss due to
transmission errors
 Packet loss due to change of
network
Result
 Severe performance
Client Server
Connection
setup
Data
transmission
Connection
release
TCP SYN
TCP SYN/ACK
TCP ACK
HTTP request
HTTP response
GPRS: 500ms!
>15 s
no data

5. Congestion Control
 Transport protocols typically designed for
Fixed end-systems
Fixed, wired networks
 TCP congestion control
packet loss in fixed networks typically due
to (temporary) overload situations
router have to discard packets as soon as
the buffers are full
TCP recognizes congestion only indirect
via missing acknowledgements,
retransmissions unwise, they would only
5

6. Slow-start Algorithm
sender calculates a congestion window for
a receiver and start with a congestion
window size equal to one segment
exponential increase of the congestion
window up to the congestion threshold,
then linear increase
missing acknowledgement causes the
reduction of the congestion threshold to
6

7. Fast Retransmit/Fast Recovery
 TCP sends an acknowledgement only after receiving
a packet
 if a sender receives several acknowledgements for
the same packet, this is due to a gap in received
packets at the receiver
 however, the receiver got all packets up to the gap
and is actually receiving packets
 therefore, packet loss is not due to congestion,
continue with current congestion window (do not use
slow-start)
7

8. Implications on mobility
 TCP assumes congestion if packets are dropped
 typically wrong in wireless networks, here we often
have packet loss due to transmission errors
 furthermore, mobility itself can cause packet loss, if
e.g. a mobile node roams from one access point
(e.g. foreign agent in Mobile IP) to another while
there are still packets in transit to the wrong access
point and forwarding is not possible
 The performance of an unchanged TCP degrades severely
 however, TCP cannot be changed fundamentally
due to the large base of installation in the fixed
network, TCP for mobility has to remain compatible
 the basic TCP mechanisms keep the whole Internet
together
8

9. Indirect TCP
 Indirect TCP or I-TCP segments the connection
 no changes to the TCP protocol for hosts connected to the
wired Internet, millions of computers use (variants of) this
protocol
 optimized TCP protocol for mobile hosts
 splitting of the TCP connection at, e.g., the foreign agent
into 2 TCP connections, no real end-to-end connection
any longer
 hosts in the fixed part of the net do not notice the
characteristics of the wireless part
mobile host
access point
(foreign agent) „wired“ Internet
„wireless“ TCP standard TCP
9

10. I-TCP Socket and State Migration
mobile host
access point2
Internet
access point1
socket migration
and state transfer
10

11. Indirect TCP
 Advantages
 no changes in the fixed network necessary, no changes
for the hosts (TCP protocol) necessary, all current
optimizations to TCP still work
 transmission errors on the wireless link do not propagate
into the fixed network
 simple to control, mobile TCP is used only for one hop
between, e.g., a foreign agent and mobile host
 therefore, a very fast retransmission of packets is possible,
the short delay on the mobile hop is known
 Disadvantages
 loss of end-to-end semantics, an acknowledgement to a
sender does now not any longer mean that a receiver
really got a packet, foreign agents might crash
 higher latency possible due to buffering of data within the
foreign agent and forwarding to a new foreign agent
11

12. Snooping TCP
 Transparent extension of TCP within the foreign agent
 buffering of packets sent to the mobile host
 lost packets on the wireless link (both directions!) will be
retransmitted immediately by the mobile host or foreign
agent, respectively (so called “local” retransmission)
 the foreign agent therefore “snoops” the packet flow and
recognizes acknowledgements in both directions, it also
filters ACKs
 changes of TCP only within the foreign agent
„wired“ Internet
buffering of data
end-to-end TCP connection
local retransmission correspondent
hostforeign
agent
mobile
host
snooping of ACKs
12

13. Snooping TCP
 Data transfer to the mobile host
 FA buffers data until it receives ACK of the MH, FA detects packet
loss via duplicated ACKs or time-out
 fast retransmission possible, transparent for the fixed network
 Data transfer from the mobile host
 FA detects packet loss on the wireless link via sequence numbers,
FA answers directly with a NACK to the MH
 MH can now retransmit data with only a very short delay
 Integration of the MAC layer
 MAC layer often has similar mechanisms to those of TCP
 thus, the MAC layer can already detect duplicated packets due
to retransmissions and discard them
 Problems
 snooping TCP does not isolate the wireless link as good as I-TCP
 snooping might be useless depending on encryption schemes
13

14. Mobile TCP
 Special handling of lengthy and/or frequent disconnections
 M-TCP splits as I-TCP does
 unmodified TCP fixed network to supervisory host (SH)
 optimized TCP SH to MH
 Supervisory host
 no caching, no retransmission
 monitors all packets, if disconnection detected
 set sender window size to 0
 sender automatically goes into persistent mode
 old or new SH reopen the window
 Advantages
 maintains semantics, supports disconnection, no buffer
forwarding
 Disadvantages
 loss on wireless link propagated into fixed network
 adapted TCP on wireless link
14

15. Fast retransmit/fast recovery
 Change of foreign agent often results in packet loss
 TCP reacts with slow-start although there is no congestion
 Forced fast retransmit
 as soon as the mobile host has registered with a new
foreign agent, the MH sends duplicated
acknowledgements on purpose
 this forces the fast retransmit mode at the communication
partners
 additionally, the TCP on the MH is forced to continue
sending with the actual window size and not to go into
slow-start after registration
 Advantage
 simple changes result in significant higher performance
 Disadvantage
 further mix of IP and TCP, no transparent approach
15

16. Transmission/time-out freezing
 Mobile hosts can be disconnected for a longer time
 no packet exchange possible, e.g., in a tunnel, disconnection
due to overloaded cells or mux. with higher priority traffic
 TCP disconnects after time-out completely
 TCP freezing
 MAC layer is often able to detect interruption in advance
 MAC can inform TCP layer of upcoming loss of connection
 TCP stops sending, but does now not assume a congested link
 MAC layer signals again if reconnected
 Advantage
 scheme is independent of data
 Disadvantage
 TCP on mobile host has to be changed, mechanism depends on
MAC layer
16

17. Selective retransmission
 TCP acknowledgements are often cumulative
 ACK n acknowledges correct and in-sequence receipt of
packets up to n
 if single packets are missing quite often a whole packet
sequence beginning at the gap has to be retransmitted
(go-back-n), thus wasting bandwidth
 Selective retransmission as one solution
 RFC2018 allows for acknowledgements of single packets,
not only acknowledgements of in-sequence packet
streams without gaps
 sender can now retransmit only the missing packets
 Advantage
 much higher efficiency
 Disadvantage
 more complex software in a receiver, more buffer needed
at the receiver
17

18. Transaction oriented TCP
 TCP phases
 connection setup, data transmission, connection release
 using 3-way-handshake needs 3 packets for setup and release,
respectively
 thus, even short messages need a minimum of 7 packets!
 Transaction oriented TCP
 RFC1644, T-TCP, describes a TCP version to avoid this overhead
 connection setup, data transfer and connection release can be
combined
 thus, only 2 or 3 packets are needed
 Advantage
 efficiency
 Disadvantage
 requires changed TCP
 mobility not longer transparent
18

19. Comparison Of Different
ApproachesApproach Mechanism Advantages Disadvantages
Indirect TCP splits TCP connection
into two connections
isolation of wireless
link, simple
loss of TCP semantics,
higher latency at
handover
Snooping TCP “snoops” data and
acknowledgements, local
retransmission
transparent for end-to-
end connection, MAC
integration possible
problematic with
encryption, bad isolation
of wireless link
M-TCP splits TCP connection,
chokes sender via
window size
Maintains end-to-end
semantics, handles
long term and frequent
disconnections
Bad isolation of wireless
link, processing
overhead due to
bandwidth management
Fast retransmit/
fast recovery
avoids slow-start after
roaming
simple and efficient mixed layers, not
transparent
Transmission/
time-out freezing
freezes TCP state at
disconnect, resumes
after reconnection
independent of content
or encryption, works for
longer interrupts
changes in TCP
required, MAC
dependant
Selective
retransmission
retransmit only lost data very efficient slightly more complex
receiver software, more
buffer needed
Transaction
oriented TCP
combine connection
setup/release and data
transmission
Efficient for certain
applications
changes in TCP
required, not transparent

20. TCP Improvements I
 Initial research work
 Indirect TCP, Snoop TCP, M-TCP, T/TCP,
SACK, Transmission/time-out freezing, …
 TCP over 2.5/3G wireless networks
 Fine tuning today’s TCP
 Learn to live with
 Data rates: 64 kbit/s up, 115-384 kbit/s down; asymmetry: 3-6, but also up to 1000
(broadcast systems), periodic allocation/release of channels
 High latency, high jitter, packet loss
 Suggestions
 Large (initial) sending windows, large maximum transfer unit, selective
acknowledgement, explicit congestion notification, time stamp, no header
compression
 Already in use
 i-mode running over FOMA
 WAP 2.0 (“TCP with wireless profile”)
pRTT
MSS
BW
*
*93.0

• max. TCP BandWidth
• Max. Segment Size
• Round Trip Time
• loss probability
20

21. TCP Improvements II
 Performance enhancing proxies (PEP, RFC 3135)
 Transport layer
 Local retransmissions and acknowledgements
 Additionally on the application layer
 Content filtering, compression, picture downscaling
 E.g., Internet/WAP gateways
 Web service gateways?
 Big problem: breaks end-to-end semantics
 Disables use of IP security
 Choose between PEP and security!
 More open issues
 RFC 3150 (slow links)
 Recommends header compression, no timestamp
 RFC 3155 (links with errors)
 States that explicit congestion notification cannot be used
 In contrast to 2.5G/3G recommendations!
Mobile system
PEP
Comm. partner
wireless
Internet
21

22. UNIT-V
4G NETWORKS

23.  SYLABUS
Introduction To 4G Networks
4G Vision
4G Features And Challenges
Benefits
Applications Of 4G
4G Technologies
Multicarrier Modulation
Smart Antenna Techniques
OFDM - MIMO Systems
Adaptive Modulation And Coding With Time Slot
Scheduler
Cognitive Radio

24. Evolution of 4G

25.  Future technology – Mobile and Wireless communications.
 It is a heterogeneous network
 Expectation of 4G:
 Top quality audio /video over finish to finish net protocol
Introduction to 4G Networks

26. Technology moving towards
4G
26
Mobility
Data Rates
High speed
Medium
speed
Low speed
1995 2000 2005 2010+
~14.4 kbps 144 kbps 384 kbps <50 Mbps <100 Mbps
1G
(Analog)
2G
(Digital)
3G
(IMT2000)
3G LTE
4G
2.4 GHz
WLAN
5 GHz
WLAN
High Speed
WLAN
Mobile
WiMAX
(WiBRO)
Bluetooth
WPAN
CDMA/GSM/TDMA
CDMA/GSM/TDMA

27. 27Mobility
Data Rates
High speed
Walking/
Local area
Standing/
Indoor
0.1 1 10 100
Medium
speed
4th Generation
(2007-2010)
3th Generation
(IMT-2000)
(2001)2G2G
2.5G

28. Generation Timeline

29.  3G - concentrate in standards & hardware implementation.
 4G
-encompass all networks
- interoperable with 2G,3G and other service.
- provides seamless integration of various technologies.
- IP based heterogeneous network.(IPv6 Core)
- OFDM used instead of CDMA
Why 3G to 4G?

30. Wireless World Research Forum defines 4G as:
-A network that operates on Internet technology, combines it with
other applications and technologies such as Wi-Fi, and runs at
speeds ranging from 100 Mbps (in cell-phone networks-Outdoor)
to 1 Gbps(in local Wi-Fi networks-Indoor).
4G Fourth generation Mobile
Communications

31. 4G -Objective
 4G is being developed to accommodate the Quality
of Service (QOS) and rate requirements set by forth
coming applications like
1. MMS (Multimedia Messaging Service).
2. Wireless Broadband Service.
3. Video Chat.
4. Mobile TV.
5. Digital Video Broadcasting.
6. High Network Capacity.
7. Data Rate of 100 Mbps for mobile and 1 Gbps while
stationary .
8. Smooth handoff across heterogeneous network..
9. Seamless Connectivity and Global Roaming across
multiple networks.

32.  Providing new service with high quality voice,high
definition video with high data rate
 4G is defined as MAGIC
 MAGIC – Mobile multimedia, Anytime anywhere, Global
mobility support, Integrated wireless solution and Customized
Personal services
4G Vision

33.  4G is IP based - Various network using IP as a Common Protocol
 "Seamless" and "wireless," when put together, represent a
technology of wireless Internet that hands you off to another
network without interruption so you may continue your activities
online without even noticing that you connected into another
network. Another name for it is "seamless roaming."
Seamless Connection

34. 4G Systems
High data rate
Broad BW
Smoother
handoff

35. Features of 4G
 Autonomous Networks
 Software Independence
 Fully coated service(Entirely packet – switched
network).
 Scalability
 Interoperability and simple roaming
 Support for multimedia services like
teleconferencing and wireless internet
 Wider band width and higher bitrates
 Global mobility and service portability
 High internet speed
 Tight network security

37.  a) Convergence of cellular mobile networks and WLANs
Benefits for Operators:
 Higher bandwidths.
 Lower cost of networks and equipment.
 The use of license-exempt spectrum.
 Higher capacity and QoS enhancement.
Benefits for Users:
 Access to broadband multimedia
services with lower cost and where
mostly needed.
 Inter-network roaming.
 b) Convergence of mobile communications and broadcasting
From broadcaster point of view
From the cellular mobile operator point of view:
 c) Convergence benefits
Benefits of 4G

38.  Various categories of Challenges
Based on Mobile Station
Based on System
Based on Service
 Mobile Station Challenges
Multimedia User terminals
Discovery of Wireless System
Selection of Wireless System
Incompatible roaming Frequencies
 System Challenges
Terminal Mobility
QOS support and Network Infrastructure
Privacy and Security issues
Fault Tolerance and Survivability
 Service Challenges
Service and Charge
Personal Mobility
Meeting Consumer Expectation
Challenges of 4G

39. The applications of 4G are called “KILLER APPLICATIONs” as it is going to bring
to revolution in the internet world.
Virtual Presence – User service at all times
Virtual Navigation -User can access a database of the streets and
buildings
Tele-Geoprocessing Applications – GIS + GPS
(Geographical Information System) + (Global Positioning System)
Tele-Medicine and Education –Support remote health Monitoring of
patients and Education in online
Gaming – High Speed Multi user gaming
Cloud Computing – Safe and Secure
Crisis Management – restore crisis issues in a few hours
Applications of 4G

40.  NTT DoCoMo (JAPAN)
 DIGIWEB (IRELAND)
 SPRINT (CHICAGO)
 VERIZON WIRELESS
 VODAFONE GROUP
 AMERICAN WIRELESS PROVIDER CLEARWIRE ETC..
Telecom Companies Developing 4G

41. Multi carrier Modulation (MCM)
Smart Antenna techniques
OFDM-MIMO Systems
Adaptive modulation and Coding
with Time slot Scheduler
Cognitive Radio
UWB(Ultra Wide Band)
Software defined radio
KEY 4G TECHNOLOGIES

42.  It is a derivative of FDM
 MCM derivative:
Digital Audio and Video Broadcasting (DAB/DVB)
Digital Subscriber Loop Modems (DSL)
 Principle
A transmitted bit stream is divided into many different sub
streams, which are sent in parallel over many sub channels.
Sub channels are typically orthogonal
MCM efficiently implemented digitally using the FFT(OFDM)
Multicarrier Modulation(MCM)

43. MCM transmitter

44. MCM Receiver

45.  Consider a MC system with a total passband bandwidth of 1 MHz.
Suppose the channel delay-spread is Tm = 20µs. How many
subchannels are needed to obtain approximately flat fading in each
subchannel?
The channel coherence bandwidth is
Bc = 1/Tm = 1/0.00002 = 50 KHz
To ensure flat fading on each subchannel, we take
BN = B/N = 0.1 x Bc
Hence,
N = B/(0.1 x Bc) = 1000000/5000 = 200 subcarriers.
An example

46. MC Modulated Signal
 2 types of MCM for 4G
MC-CDMA – QPSK
modulation
OFDM with TDMA – QAM
modulation

47. Fading Mitigation Techniques in MCM

48.  The data rate on each of the subcarriers is much lower than the
total data rate
 Subchannels experience flat fading.
 Small ISI in each subchannel
 Avoidance of single frequency interference
MCM
Advantages
MCM Drawbacks
 Increase PAPR.
 To overcome ISI, a cyclic extension (Guard
bit) is to be added

49.  DAB/DVB (Europe)
 WLAN –IEEE 802.11a,g,n,ac,ad etc…
 Fixed wireless broadband services
 Mobile wireless broadband communications
 UWB Communication

50.  A smart antenna is a multi-element antenna where the signals received
at each antenna element are intelligently combined to improve the
performance of the wireless system.
 Technologies Combined to design smart antenna systems
 Antenna design
 Signal processing
 Hardware implementation
Smart Antenna Techniques

51. • Smart Antenna
Beam radio signals directly at a users to follow the
users as they move.
•Allow the same radio frequency to be used for
other users without worry of interference.
•Seamless handoff between towers/access points.
•One transmit antenna, two receive antennas.
–Allows connection to two access points at once.
51

52. 52
Smart Antenna
Technology
Beam
Tracking
Space Division
Multiple Access
(SDMA)
Smart Antenna
Same time
and frequency
Past
Now
Past
Now

53.  Reduction in Co channel Interfernce
 Range improvement
 Increase in Capacity
 Reduction in transmitted power
 Reduction in Handoff
Benefits

54.  MIMO supports multiple independent channel in the same BW,
Provided multipath environment.
Single-Input, Single Output (SISO)
Single-Input, Multiple Output (SIMO)
Multiple –Input, Single Output (MISO)
Multiple -Input, Multiple Output(MIMO)
Smart Antenna Technique- MIMO

56. Transmission

57. Smart antenna Strategy
Level of Intelligence
Switched Lobe – Switching function between separate
directive antennas
Dynamically phased array (PA)–DOA algorithm is
included
Adaptive array - DOA is used to determine
interference sources

59. Orthogonal Frequency Division Modulation (OFDM)
Basic idea:
Using a large number of parallel narrow-band subcarriers instead of a
single wide-band carrier to transport information.
 Advantages:
-Very easy and efficient in dealing with multi-path.
-Robust again narrow-band interference
59

60.  Enhancement in data rate and spectral efficiency.
 Both schemes are indeed parallel transmission
technologies (Space & Frequency Domain).
 MIMO -OFDM helps to achieve
Diversity
High gain
 Implementation is based on
FFT/IFFT algorithm
MIMO Encoding
MIMO -OFDM

61. MIMO-OFDM
••••
•
1
S
OFDM
MOD
OFDM
MOD
tM
Coding
1
rM
OFDM
DEMOD
••••
•
Decoding

S
OFDM
DEMOD
T
1
1
1 cc 
T1
tt MM cc 
T: Number of OFDM symbols
N: Number of subcarriers
Mt: Number of Tx
Mr: Number of Rx

62.  Time Slot Scheduler:
 To share the spectrum efficiency between the users by satisfying QoS
requirements
Adaptive Modulation and Coding
with Time Slot Scheduler
 FCC defined
A radio that is “aware of its
surroundings and adapts
intelligently”

63.  Cognitive Radio Means “Smart” and “Alert”
Cognitive Radio* is Built on SDR*
D
Cognitive
Radio
Adaptive Radio
Intelligent
radio
Functions
 Spectrum Sensing
 Spectrum Management
 Spectrum Mobility
 Spectrum Sharing

64. Cognitive Architecture

65.  Optimal Diversity
 Spectral Efficiency
 Improved QoS
 Benefits to the Service provider
 Benefits to the Regulator
 Emergency Radio System
 Covert Military radio
 Multi technology Phone
 Mobile video services
 Open Air events
 Extending mobile networks
Benefits

66. Software defined ratio(SDR)
 A software defined radio is one that can be configured to any
radio or frequency standard through the use of software.
 The phone should automatically switch from operating on a
CDMA frequency to a TDMA frequency whenever it is required.
 Roaming can be an issue with different standards, but with a
software defined radio, users can just download the interface
upon entering new territory, or the software could just
download automatically.

67. G4
 Earth's population stands at around 6.6 billion.
 The Internet has a population of just 1.3 billion.
 IPv6 uses 128 bits for IPv6 addresses which allows for 340 billion billion
billion billion (3.4x1038) unique addresses.
67
22%

68. 4G Phones
T3’s 3D GOGGLE
PHONE
NOKIA’s WRISTBAND
PHONE
SAMSUNG

69. FUTURE OF 4G:5G
 The idea of WWWW, World Wide Wireless Web, is started
from 4G technologies. The following evolution will based on 4G
and completed its idea to form a Real wireless world.
 Thus, 5G should make an important difference and add more
services and benefit to the world over 4G. 5G should be a
more intelligent technology that interconnects the entire world
without limits.