1. Wireless Networks
In this paper we present a communication platform dedicated to support a vehicular communication model developed by the authors for the exchange of safety-related data between traffic participants.
Wireless networks

2. Wireless Networks Background Overview of Cellular Networks
Lecture Outline
Wireless Networks Background
Overview of Cellular Networks
Overview of Satellite Networks
Overview of Wireless Local Area Networks
Other Wireless Networks
In this paper we present a communication platform dedicated to support a vehicular communication model developed by the authors for the exchange of safety-related data between traffic participants.
Based on the book: “Wireless communication and networks”
by © William Stallings, 2002 Prentice Hall

3. Communication Frequency Spectrum
Electromagnetic spectrum and applications (Tanenbaum 2003)

4. Wireless Networks Background
Aspects of Wireless Networks
mobility and convenient deployment
scarce frequency spectrum
wireless implications such as transmission problems (e.g. interference, path loss, fading), security, battery, installation, health
Wireless networks
Cellular: GSM, PCS, IMT 2000
Satellite: IRIDIUM, Globalstar
WLAN: IEEE , HiperLAN
Ad-Hoc, PAN, HAN
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

5. Wireless Cellular Networks
Extensive evolution and fast deployment
First-Generation Mobile Phones: analog voice (e.g. AMPS, NMT)
Second-Generation Mobile Phones: digital voice and some data (e.g. GSM, IS-95)
Third-Generation Mobile Phones: digital voice and data (e.g. 3G)
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

6. Principles of cellular networks [1]
Mobile Terminals and Base Stations
Communication area divided in hexagonal cells
Cell dimensions from hundreds of meters till tens of kilometers (e.g. GSM: 100m to 35 Km)
Each cell served by a base station formed by a transceiver and a control unit
Each cell allocated a frequency band for communication
Communication from MS to BS -> reverse link
Communication from BS to MS -> forward link
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

7. Principles of cellular networks [2]
Frequency reuse: use the same frequency spectrum in different set of cells
Cells that reuse the same frequency must be distant enough for avoiding interference
Transmission power control
Migration of a mobile station from one cell to another with continuance of communication -> handoff
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

8. Methods for increase capacity in cellular networks
Adding new channels
Frequency borrowing: congested cells use frequencies taken from adjacent cells
Cell splitting:
due to initial network design
high-used cells are divided in smaller cells and frequencies are reallocated
Cell sectoring:
cells divided in sectors (e.g. 3, 6 sectors)
each sector has allocated its own set of channels
base stations use directional antennas for covering sectors
Microcells and picocells: very small cells
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

9. Cellular systems - general architecture
General cellular system:
Mobile Station (MS)
Base Station (BS)
Mobile telecommunication switching office (MTSO)
Communication between mobile station and base station use:
Control channels: exchange control data for calls management
Traffic channels: data or voice connections between users
Dominant switching mode: circuit-switch MS BS

10. Cellular systems operation example [1]
(a) Mobile station initialization
(b) Mobile-originated call
(c) Paging
(d) Call accepted
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

11. Cellular systems operation example [2]
(e) Ongoing call
(f) Handoff
Other operations:
call blocking
call termination
call drop
calls to/from fixed and remote mobile subscriber
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

12. Aspects of Cellular Networks [1]
Radiowave propagation:
signal strength
fading
diverse propagation patterns
Handoff: assigning a MS to a BS other than the current one when MS move from one cell toward other cell
Different handoff parameters: cell blocking probability, call dropping, call completion, handoff success, handoff blocking, ...
Handoff strategies:
relative signal strength
relative signal strength with threshold
relative signal strength with hysteresis
relative signal strength with hysteresis and threshold
prediction techniques
injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

13. Aspects of Cellular Networks [2]
Power control requirements:
reduce interference
increase battery life
overcome transmission conditions
equalize received power (SS)
other...
Open-loop power control (a)
depends on mobile station
Closed-loop power control (b)
depends on base station
(b) Closed-loop power control
(a) Open-loop power control

14. Aspects of Cellular Networks [3] - Access Methods
Frequency Division Multiple Access ->FDMA
two (frequency) channels assigned per user, one for forward and one for reverse
used in first generation cellular (e.g. AMPS)
Time Division Multiple Access ->TDMA
each physical channel divided in logical subchannels
two logical channels assigned for user, for forward and reverse links
transmission in repetitive sequence of frames divided in time slots
each time slot position forms a logical channel that is assigned to the user
used in second generation cellular (e.g. GSM)
Code Division Multiple Access -> CDMA
direct-sequence spread spectrum transmission -> use a chipping code for data
two logical channels per user
used in second and third generation cellular

15. Second Generation Cellular Networks - Example

16. GSM Cellular Network - 9000 injuries each day in E.U. in 1999
- interest in developing ITS service for traffic safety and convenience
- vehicular communication can offer extensive support to ITS safety services
- nevertheless., as the literature shows due to the specific requirements of the data exchange between traffic participants, vehicular communication differ from a regular one and therefore new methodologies are needed

17. First, Second, Third Generation Cellular Networks
More in 2G than 1G:
2G have digital traffic channels, 1G pure analog
encryption
error detection and correction
dynamic channel access -> users share dynamically channels
3G capabilities:
voice quality comparable with switched telephone network
up to 384 kbps data rate outdoor
support for up to Mbps indoor
symmetrical/asymmetrical data transmission rates
support for circuit switched and packet switched data services
support for wide variety of equipment
efficient spectrum usage
Internet interface
flexibility

18. Satellite Communication
Communication between earth stations and satellites
Uplink-> earth station to satellite
Downlink-> satellite to earth station
Satellite categorization:
Coverage area: global, regional, national
Service type: fixed service satellite (FSS), broadcast service satellite (BSS), mobile service satellite (MSS)
General usage: commercial, military, amateur, experimental

19. Satellite Networks Configurations
Point-to-point link
Broadcast link

20. Satellite Communication and Wireless Terrestrial Communication
Advantages of satellite communication:
extensive area of coverage
relative slowly variant conditions for communication between satellites
transmission cost independent of distance
support for broadcast, multicast and point-to-point communication
high bandwidth and high data rates
high quality of transmission
Drawbacks of satellite communication :
expensive installation
transmission delay
needed terminals power
needed number of satellites for global coverage

21. Satellite and Orbits GEO - geostationary orbit satellites
LEO - low earth orbit satellites
MEO - medium earth orbit satellites

22. GEO and LEO GEO characteristics: LEO characteristics:
no problems with the frequency change due to satellite movement
simplified tracking of satellite
very large area coverage (e.g. 3 satellite for almost whole Earth)
weak signal and extensive delay (e.g. 0.5 s) due to long distance
polar region poorly served
LEO characteristics:
small coverage area-> big number of satellites
satellite visibility cca. 20 minutes
frequency changes due to satellite movement
significant atmospheric drag
small latency
high data rates, up to few Mbps for Big LEOs

23. Frequency Bands for Satellite Communication

24. Issues in Satellite Communication
Problems:
Distance between earth station antenna and satellite antenna
Downlink: terrestrial distance between earth antenna and the “aim point” of the satellite
Atmospheric attenuation: oxygen, water, higher frequencies
Capacity Allocation Strategies:
frequency division multiple access (FDMA)
time division multiple access (TDMA)
code division multiple access (CDMA)

25. Satellite Communication Examples
IRIDIUM LEO Satellite System
TDMA Satellite Transmission

26. Wireless Local Area Networks (WLAN)
General considerations:
limited utilization till last decade but extensive development lately
usually in spaces where wired networks were difficult or not appropriate to deploy
may increase reliability
cost effective
different standards
different transmission medium used
Some WLAN implications:
transmission problems: connection, multipath propagation, path loss and radio signal interference
network security
system interoperability
installation issues and health risks

27. WLAN Applications [1] LAN Extension: Cross-Building Interconnect:
wireless extensions to fixed LANs
stations in large open areas
single or multiple cells
Cross-Building Interconnect:
connect nearby building
usually point-to-point communication
connected devices: usually routers and bridges

28. WLAN Applications [2] Nomadic Access:
connect mobile terminals with a LAN hub
Ad-hoc Networking:
spontaneous established temporary networks

29. WLAN Requirements [1]
Throughput: efficient use of the transmission medium
Number of nodes: large number of nodes may be needed
Connection to backbone LAN: usually a connection with a wired networks is needed
Service area: typical 100 to 300 m
Battery life time: efficient management of mobile station battery
Transmission robustness and security: WLAN may be interference prone and may be eavesdropped

30. WLAN Requirements [2]
Collocated network operations: more than one WLAN in the same area
License free operation: user oriented approach
Handoff and roaming: moving between cells and even networks may be needed
Dynamic configuration: addition, deletion and reallocation of end systems without affecting the network functionality

31. WLAN Technologies [1]
Categorized according with the used transmission technology:
Infrared (IR) LAN :
IR does not penetrate walls
limited to a single room
Spread Spectrum LAN:
use spread spectrum
usually operate in ISM band
Narrowband microwave LAN:
operate at microwave frequency (e.g. above 1 GHz)
can use ISM or licentiate frequency spectrum
do not use spread spectrum

32. WLAN Technologies [2]

33. Infrared (IR) WLAN Directed Beam IR (a) point-to-point links
range depend on power and wave focus
(a)
Omnidirectional IR (b)
single base station in LOS of all stations
the base station acts as a repeater
(b)
Diffused (c)
all transmitter focus at a point on ceiling
IR radiation is retransmitted (reradiate)
reradiated IR waves are received by all stations in the area
(c)

34. Infrared (IR) WLAN vs. Microwave WLAN
Strengths
virtual unlimited spectrum
unregulated spectrum
simple equipment needed -> inexpensive
reflected by light-colored objects
does not penetrate walls: more secure against eavesdropping and does not introduce interference
Drawbacks:
sunlight, indoor lighting and other ambient radiation perceived as noise
high-power transmitter required -> may introduce health problem (i.e. eye safety) and power consumption problems
limited range

35. Spread Spectrum and Narrowband WLAN
Spread Spectrum WLAN
usually multi-cell with different frequencies
hub or peer-to-peer topology in a cell
hub topology: the hub may provide access control and repeater operations and is usually connected to a backbone network
peer-to-peer topology: use ad-hoc connectivity without any hub
usually unlicensed spectrum
interference prone
Narrowband WLAN
usually use narrow microwave band for transmission
unlicensed as well as licensed frequency spectrum
does not use spread spectrum
licensed -> interference-free

36. Other Wireless Networks - Cordless Systems
Characteristics
Residential: single base station with support for voice and data
Office: single base station for small offices, multiple base stations deployed using a cellular configuration for larger offices
Telepoint: a base station set up in a public place (e.g. an airport)
Small range for hand set -> low power
Inexpensive base station and hand set -> simple technical approaches
Limited frequency flexibility -> must work in different places
Cordless Systems Example: DECT
Band: GHz; Bandwidth: 20 MHz; Number of channels 120
Access Method : TDMA/FDMA
Data rate: Mbps; Speech rate: 32 kbps
Mean power: 10 mW
Maximum cell radius: 30 to 100 m
Provide handoff

37. Other Wireless Networks - Wireless Local Loops (WLL)
Narrowband WLL - replacement for telephony services
Broadband WLL - high-speed voice and data services
Usually use milimetric waves (e.g. above 10 GHz)
Advantages: cost, installation time, selective installation
Propagation problems: free space loss, rainfall attenuation, atmospheric and gaseous absorption, mutipath losses, vegetation effects
Multichannel Multipoint Distribution Service: MMDS (ex GHz)
Local Multipoint Distribution Service: LMDS, standardized as IEEE
(ex GHz)

38. Other Wireless Networks - Personal Area Networks (PAN) and Home Area Networks (HAN)
Network serving a single person or a small group
Usually accommodate diverse mobile devices
Provide support for virtual docking station, peripheral sharing
Examples: Bluetooth, Infrared Data Association (IrDA), HomeRF
HAN
Broadband smart house with intelligent appliances
HANs over phone lines, powerline and wireless HANs: diverse combination possible
Examples: HomeRF, Home Audio Video interoperability HAVi
Control Networks: low-speed powerline networks
specify protocols that are used via the power line
examples: LonWorks, X10, CEBus

39. Lecture Summary
Overview of wireless networks and frequency spectrum for wireless communication
Cellular networks, cellular principles, channel access, different generations of cellular networks
Satellite communication, GEO, LEO, MEO
WLAN, infrared, spread spectrum, microwave
Other wireless networks: WLL, HAN, PAN, ad-hoc