1. Wireless Communication Systems
Background of Wireless Communication
Wireless Communication Technology
Wireless Networking and Mobile IP
Wireless Local Area Networks
Wireless Personal Area Networks
Wireless Metropolitan Area Networks
Wireless Wide Area Networks
Wireless Communication Systems

2. Overview Wireless LANs Paging Systems Cellular systems
Communication Systems
Wireless Communications
Current Wireless Systems
Wireless LANs
Paging Systems
Cellular systems
Satellite Systems
Bluetooth
Design challenges
4G Systems
Cognitive Radios

3. Communication Systems
Provide electronic exchange of multimedia Data, Voice, Video, Music, , Web pages, etc.
Communication Systems of today are used for Radio, TV broadcasting, Data and Public Switched Telephone Network (voice, fax, modem)
Cellular Phones
Computer networks (LANs, WANs, and the Internet)
Satellite systems (pagers, voice/data, movie broadcasts)
Bluetooth (Cable replacement)

4. Block diagram of a Communication Systems

5. Wireless Communications
Multimedia wireless Communications at any Time and Anywhere
Brief history
Ancient Systems: Smoke Signals, Carrier Pigeons
Radio invented in the 1880s by Marconi
Many sophisticated military radio systems were developed during and after WW2
Cellular has enjoyed exponential growth since 1988, with more than 2 billion users worldwide today
Ignited the recent wireless revolution,
Ubiquitous

6. Current Wireless Systems
Cellular systems
Wireless LANs
Satellite Systems
Paging Systems
Bluetooth
Ultra Wide Band Systems
Zigbee

7. Wireless Systems: Range Comparison
Satellite
Links SW
Radio MW FM
Mobile
Telephony
WLANs
Blueooth
1,000 Km
100 Km
10 Km
1 Km
100 m
10 m
1 m
Q1. Suggest any system whose range of communication is more than that of satellite links?
A: Command centers on Earth have traditionally helped space crews to resolve their problems. But a signal from Earth would take 40 minute to reach Mars, when decisions may have to be taken in seconds. Speed of light is the maximum that one can achieve for communication.
Q2. Describe any system whose range of communication is shorter than Infrared communication links? A:
Q3. Describe why communication range increase and decreases on logarithm scale?
A: ,

8. Cellular Systems: Reuse channels to maximize capacity
Geographic region divided into cells
Frequencies/timeslots/codes reused at spatially-separated
locations.
Co-channel interference between same color cells.
Base stations/MTSOs coordinate handoff and control functions
Shrinking cell size increases capacity, as well as networking burden
BASE
STATION
MTSO

9. Type of Cells Global Satellite Suburban Urban In-Building Picocell
Macrocell
Microcell
Urban
In-Building
Picocell
Global
Suburban
Basic Terminal
PDA Terminal
Audio/Visual Terminal

10. Type of Cells
Cell radii can be vary from 10’s of meters in buildings to 100’s of meters in the cities, up to several km’s in the countryside.
Macrocells, provide overall area coverage
Microcells, focus on slow moving subscribers moving between buildings.
Picocells, focus on the halls of a theater, or exhibition centre.

11. Cellular Phone Networks
Taxila BS BS
Internet
Lahore
MTSO
MTSO
PSTN BS

12. The Wireless Revolution
Cellular is the fastest growing sector of communication
industry (exponential growth since 1982, with over 2 billion users worldwide today)
Three generations of wireless
First Generation (1G): Analog 25 or 30 KHz FM, voice only, mostly vehicular communication
Second Generation (2G): Narrowband TDMA and CDMA, voice and low bit-rate data, portable units.
2.5G increased data transmission capabilities
Third Generation (3G): Wideband TDMA and CDMA, voice and high bit-rate data, portable units

13. Wireless Local Area Networks (WLANs)
1011
0101
Access
Point
WLANs connect “local” computers (100m range)
Breaks data into packets
Channel access is shared (random access)
Backbone Internet provides best-effort service
Poor performance in some apps (e.g. video)

14. Wireless LAN Standards
802.11b (Current Generation)
Standard for 2.4GHz ISM band (80 MHz)
Frequency hopped spread spectrum
Mbps, 500 ft range
802.11a (Emerging Generation)
Standard for 5GHz NII band (300 MHz)
OFDM with time division
20-70 Mbps, variable range
Similar to HiperLAN in Europe
802.11g (New Standard)
Standard in 2.4 GHz and 5 GHz bands
OFDM
Speeds up to 54 Mbps
Since 2008,
all WLAN
Cards have
all 3
standards

15. Satellite Systems Cover very large areas Different orbit heights
GEOs (39000 Km)
LEOs (2000 Km)
Optimized for one-way transmission
Radio (XM, DAB) and movie (SatTV) broadcasting
Most two-way systems struggling or bankrupt
Expensive alternative to terrestrial system
A few ambitious systems on the horizon

16. Paging Systems Broad coverage for short messaging
Message broadcast from all base stations
Simple terminals
Optimized for 1-way transmission
Answer-back hard
Overtaken by cellular

17. Bluetooth Cable replacement RF technology (low cost)
Short range (10m, extendable to 100m)
2.4 GHz band (crowded)
1 Data (700 Kbps) and 3 voice channels
Widely supported by telecommunications, PC, and consumer electronics companies
Few applications beyond cable replacement

18. Wireless Comm. Design Challenges
Hardware Design
Precise components
Small, lightweight, low power
Cheap
High frequency operations
System Design
Converting and transferring information
High data rates
Robust to noise and interference
Supports many users
Network Design
Connectivity and high speed
Energy and delay constrains

19. 4G Wireless Communication Systems
Evolution to 4G wireless communication systems
4G: New paradigm shift from technology centric to user centric
4G: Integrated All-IP Architecture
Efficient spectrum sharing concept in 4G wireless networks

20. Evolution towards to 4G
B. Walke, IEEE 802 System: Protocol, Multihop mesh/relaying, Performance and Spectrum Coexistence, John Wiley and Sons, January 2007

21. The growth of number of mobile subscribers
M.A. Uusitalo, “ The Wireless World Research Forum - Global Vision of Wireless World,” IWCT2005, Oulu, Finland, June 2005.

22. Why mobile subscribers are increasing ?
Movement from the Personal Computing Age (one computing device per person) to Ubiquitous Computing Age (several platforms at user’s disposal whenever and wherever needed)
The convergence of media
Numerous demands of multimedia applications arose from huge number of personal wireless devices, which are small, cheap, more convenient and more powerful.

23. Road map of wireless communication systems
L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,” Microwave Review, June 2007

24. Key Concept of 4G Global wireless communication system
All-IP based seamless connectivity
4G is foreseen as an integrator of all existing and future wireless and wired networks, both terrestrial and satellite.
4G is not a new system design from scratch but 4G is a concept of integration and convergence

25. 4G systems will deliver All digital all-IP communication
End-to-end QoS guarantees
Efficient spectrum sharing and dynamic spectrum allocation
Diversified radio access (e.g. cellular, WLAN, ad hoc networks)
Adaptive multimode user terminals (cognitive approach)
Seamless and transparent user roaming with fully support of various handovers.

26. 4G systems will deliver Support for huge multimedia traffic
Integration of navigation and communication system in order to offer a variety of location/situation/context aware service
Increased level of security
Increased personalization
Quickly deployable user services (anytime, anywhere, and from any device) in cost effective manner

27. All-IP based 4G network
RAN - Radio Access Network: The portion of a mobile phone network that relates to the transmission or radio communications between the terminal device and the network base station.
L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,” Microwave Review, June 2007

28. Research Challenge in Future Wireless Communication Systems
Crucial issues needed to be investigated are
User terminals issue
Mobile Services issue
Access network issue
Communication issue
Spectrum efficiency and channel capacity
Provisioning of ubiquitous coverage
Cost-effective solution for high data rates
Increased bandwidth usability
Efficient spectrum allocation by using cognitive approach

29. The Spectrum and Its Management
Most governments consider the electromagnetic spectrum to be a public resource.
It is usually allocated by a governmental organization (FCC, CRTC, ETSI, ARIB, etc.) that defines the spectrum management policy.
Most of the spectrum is currently licensed to users to further the public good, e.g., radio, television, etc.
Examples of licensing
TV channels, radio,
Cellular service,
Unlicensed “free for all”, subject to some constraints (e.g., 900 Mhz cordless phones, 2.4 Ghz wireless WiFi).
Common belief: we are running out of usable radio frequencies. Is that true?

30. Current Spectrum Management Policy
Fixed allocation
Rigid requirements on how to use
Little sharing

31. Spectrum Usage in Space, Time, & Frequency
Actual measurements by the FCC have shown that many licensed spectrum bands are unused most of the time. In NYC, spectrum occupancy is only 13% between 30 MHZ – 3.0 GHz.

32. Spectrum Usage Good quality spectrum is under-utilized.
Hence the problem is more a spectrum management policy issue than a physical scarcity.
The problem is begging for a solution based on dynamic spectrum management or access. There are many possibilities.
Cognitive Radio is a synonym of dynamic spectrum access.

33. Dynamic Spectrum Sharing
There are 3 ways to share the spectrum dynamically
Dynamic Exclusive Access: extension to the current licensing policy. Flexible licensing. An improvement but not “fast” enough.
Open Sharing Model: horizontal sharing, a generalization of the unlicensed band policy. All users/nodes have equal regulatory status. Based on the huge success of WiFi and other technologies working in the ISM band.
Hierarchical Access Model: vertical sharing. All users do not have equal regulatory status (i.e., primary users and secondary users). Secondary users can opportunistically access the spectrum as long as it does not affect the primary users’ performance. Allows for prioritized spectrum sharing provided no harmful interference caused to primary users.

34. Harmful Interference Ultimately depends on the application.
What is harmful interference?
Ultimately depends on the application.
There are generally two broad approaches to avoid harmful interference:
Interference avoidance (spectrum overlay)
Interference control (spectrum underlay)
Of course they can be combined (overlay) (underlay)

35. Spectrum Overlay: Interference Avoidance
Spectrum overlay approach impose restrictions on when and where the secondary users may transmit. Secondary users have to identify and exploit the spectrum holes defined in space, time, and frequency.
Compatible with the existing spectrum allocation –legacy systems can continue to operate without being affected by the secondary users.
Regulatory policies define basic etiquettes for secondary users to ensure compatibility with legacy systems.
In principle, interference avoidance involves only two steps:
Look for holes in spectrum/time.
Transmit only in those bands at those times.
Sounds a lot easier than it is.
Detection of spectral holes is difficult due to the large range of potential modulation/coding schemes: careful measurements based on actual primary signal statistics and signatures is needed.
Hidden terminal problem: we have to protect the primary receivers (but where are they?).
Fast detection time needed.

36. How to Use frequency gaps?
Suppose that after some sophisticated signal processing, we determine that spectrum occupancy is:
How do we use these (non-contiguous) holes?
OFDM based approach solves the problem naturally.
OFDM has the advantages that
It is low complexity (FFT and IFFT based)
Can be naturally adjusted to fit almost any configuration of spectral holes.
Is growing in popularity (802.11a, , )

37. Spectrum Underlay: Interference Control
Interference avoidance is worst-case design
In practice, this may be too “soft” and overly limit throughput of secondary users.
Spectrum underlay approach constraints the transmission power of secondary users so that they operate below the interference temperature limit of primary users (i.e., the receivers).
Interference temperature introduces new opportunities at a cost:
Additional difficulties
Secondary user needs to measure/know temp. at primary receivers.
Secondary measurements
Feedback from primary
Treats interference as noise.

38. Spectrum Opportunity
Channel is available at A (tx) if no primary rx nearby.
Channel is available at B (rx) if no primary tx nearby.
Channel is an opportunity if available at both A and B.

39. A Definition of Cognitive Radio (CR)
A cognitive radio is an unlicensed communication system
that is aware of its environment
learns from its environment
adapts to the statistical variations of its environment
and uses these to
achieve reliable communication and spectral efficiency by employing spectral holes or opportunities and does not generate harmful interference to the incumbents.
 Cognitive Radios will be complex devices.

40. Some Examples Two examples of star networks with cognitive features:
IEEE h (WiMAX) provides extensions to support unlicensed co-existence
IEEE is an explicit cognitive WRAN that will exploit vacant TV broadcast bands
TV Transmitter
WRAN
Base Station
: CPE
: WRAN Base Station
Typical ~33km
Max. 100km

41. A little more about IEEE 802.22
IEEE has the following interesting characteristics:
Has a complex architecture to detect primary users.
Follows the spectrum overlay approach (avoids interfering with primary users altogether)
Is OFDM based

42. Spectrum sharing of cognitive radios
Horizontal Spectrum Sharing: Sharing of spectrum between users of equal regulatory spectrum access rights
Vertical Spectrum Sharing: Sharing of spectrum between users of different regulatory spectrum access rights
Overlay Spectrum Sharing:
L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,” Microwave Review, June 2007

43. Emerging paradigm of cognitive network
L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,” Microwave Review, June 2007

44. IEEE 802.21 framework of Multimedia Independent Handover- Network
Network controlled handover
L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,” Microwave Review, June 2007

45. IEEE 802.21 framework of Multimedia Independent Handover - User
L.M. Gavrilovska and V. M. Atanasovski, “Interoperability in future wireless communications system: A roadmap to 4G,” Microwave Review, June 2007

46. 4G Summary The 4G paradigm is already on the road.
4G wireless system provide high speed, high capacity, low cost per bits.
4G is IP-based services for broadband multimedia.
Concept of 4G is all about an integrated, global network based on open system approach.
4G wireless systems utilize spectrum efficiently via cognitive approach, and optimize the choice of radio access technology.
Cognitive radio and networking will become the key in reconfigurable wireless system.

47. Network Simulation Platforms
NS-3
OMNeT++ 4.0

48. Q&A ?

49. Assignment #3 Answer the questions given on Slide No. 7
Send your assignments in Word Document Format to or
Last date of submission of assignment is 14th April