1. Wireless Networking Technologies
Chapter 16
Wireless Networking Technologies
© Bobby Hoggard, Department of Computer Science, East Carolina University
These slides may not be used or duplicated without permission

2. Wireless Network Classification
Wireless networks come in a wide variety of sizes and types – part of which comes from government regulations on ranges of the electromagnetic spectrum available for communication
Communication in some parts of the spectrum requires a license, while other parts of the spectrum is unlicensed (in the US, a required license would come from the FCC)
Wireless
Networks
Personal Area Networks (PAN)
Local Area Networks (LAN)
Metropolitan Area Networks (MAN)
Wide Area Networks (WAN)

3. Personal Area Networks (PANs)
Intended for short distance communication with devices owned & operated by a single user
Bluetooth
Intended as a wireless replacement for cables (i.e. headphones, mouse, etc.)
Devices are masters or slaves, where the master grants permissions to the slave device
Ultra Wideband (UWB)
Originally designed for commercial radar systems
Spreads data across several frequencies; requires less power to reach the same distance
Consumes very low power
Signal can go through obstacles, such as walls
ZigBee
Used in low data rate applications requiring a long battery life
Home automation, wireless sensors, smoke/intruder alarms, medical data collection
Typically for short distances, but can transmit longer distances through a mesh network
Infrared (IrDA)
Often used in remote controls, and as a cable replacement (i.e. wireless mouse)
RFID
Radio Frequency Identification / Used for inventory control, sensors, passports, etc.
Small tags contain identification information that a receiver can pull/extract from the tag
Passive tags draw power from the receiver's signal / active tags contain batteries
Limited distance, but active tags extend further

4. Wireless Bands Used by PANs and LANs
Uses areas of the electromagnetic spectrum reserved by governments for Industrial, Scientific and Medical use
These are unlicensed frequencies
26 MHz
bandwidth
83.6 MHz
bandwidth
125 MHz
bandwidth
902
928
2.4
2.484
5.725
1200
MHz
MHz
GHz
GHz
GHz
KHz

5. Wireless LAN Technologies
Popular standards for wireless LAN technologies:
Standard
Frequency Band
Data Rate
Notes
802.11
2.4 GHz
2 Mbps
Equipment no longer manufactured / too slow
Unregulated frequency means interference from microwaves, cordless phones, etc.
802.11a
5 GHz
54 Mbps
Higher frequency = shorter range
Regulated frequency prevents interference from other devices
802.11b
11 Mbps
Not compatable with a equipment
802.11g
Attempt to combine the better range of b with the faster speed of a
Supported by practically all network equipment in use today
Backward compatable with b so it works with b equipment – however, if any b equipment is used, the entire network slows to 11 Mbps
802.11n
300 Mbps
Uses several wireless signals and antennas (MIMO technology)
Increased signal intensity = better range
Backward compatable with b and g equipment
Use of multiple signals may interfere with nearby b/g networks

6. Wireless LAN Technologies
Current popular standard:
Standard
Frequency Band
Data Rate
Notes
802.11ac
2.4 GHz and 5 GHz
Up to Mbps
Supports simultaneous connections on both the 2.4 and 5 GHz bands
Vendors advertise AC1300 / AC1750 / AC1900 etc. to indicate the maximum possible speed of the equipment
40 MHz bandwidth for 2.4 GHz stations / 80 MHz for 5.0 GHz stations with support for 160 MHz channels
Supports up to 8 MIMO streams (several wireless signals and antennas)
Supports beamforming (target signal in direction of station for better/stronger signal)
Uses 256-QAM (8 bits per signal change), with some vendors using 1024-QAM (10 bits per signal change)
Next Step:
802.11ax with support for up to 10,000 Mbps and range of over 500 ft

7. Spread Spectrum Technologies
Uses multiple frequencies to send data
Increased data rate (send multiple bits in parallel)
Increased immunity to noise (send multiple copies of the data)
These techniques help wireless LANs function in noisy enviroments
Major spread spectrum technologies used in wireless LANS include:
Name
Expansion
Description
DSSS
Direct Sequence Spread Spectrum
Similar to CDMA where a "chip sequence" is used to divide the data into blocks to send over multiple frequencies. Receiver uses the same sequence to decode the data
FHSS
Frequency Hopping Spread Spectrum
Data is spread over a pseudorandom sequence of frequencies, which is known in advance by both sender and receiver
OFDM
Orthogonal Frequency Division Multiplexing
FDM where the band is divided into multiple carriers such a way as to minimize interference from the other channels

8. Wireless LAN Architecture
Ad-hoc – wireless hosts communicate among themselves without a base station
Also called peer-to-peer networks
Used for technologies such as Wi-Fi Direct
Infrastructure – wireless hosts communicate only with a base station, which relays packets
Access points are deployed throughout buildings, and devices (hosts) communicate with the access point to gain access to a network

9. Wireless LAN Architecture
hub or switch
Basic Service Set (BSS)
The set of devices serviced by an access point
range of access point
access point

10. Wireless LAN Architecture
Internet
hub or switch
router
modem

11. Wireless LAN Architecture
Dead zones exist when access points are too far apart
Hosts in this area have no wireless connectivity
Overlap occurs when access points are too close together
Hosts in this area can reach multiple access points
dead zone
overlap

12. successful transmission
Wireless Frame Format
Overlap is handled by requiring the host to associate with only one access point
frame format requires the address of an access point
2 bytes
2 bytes
6 bytes
6 bytes
6 bytes
2 bytes
0 – 2312 bytes
4 bytes
control
duration AP
address
source
address
destination
address
sequencecontrol
payload
CRC
frame
type
connection ID or
time in ms
the channel
is allocated for
successful transmission
access
point's
MAC
address
sender's
MAC
address
receiver's
MAC
address
cyclic
redundency
check
used to help
reassemble
multiple packets in
the correct order

13. Access Point Coordination
Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another
This is often attempted by measuring signal strength
connected
strength=10
strength=2

14. Access Point Coordination
Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another
This is often attempted by measuring signal strength
strength=5
strength=4
connected

15. Access Point Coordination
Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another
This is often attempted by measuring signal strength
hand off
strength=4
strength=5
connected

16. Access Point Coordination
Complex access points coordinate with each other to ensure a smooth handoff as a device moves from one BSS (basic service set) into another
This is often attempted by measuring signal strength
Simpler, lower cost, access points leave it to the hosts to handle changing from one access point to another
An argument for this is that signal strength isn't a good measure point

17. Multi-Access Coordination
Although defines two approaches for channel access, only DCF is actually used
Point Coordinated Function (PCF) requires the access point to ensure that station transmissions do not interfere with each other
For example, by assigning each station a different frequency to use
Distributed Coordinated Function (DCF) requires each station in a BSS to run a random access protocol networks use CSMA/CA
Before sending a packet of data, CSMA/CA requires:
sending station to transmit a Ready To Send message
receiving station to transmit a Clear To Send message

18. Multi-Access Coordination
The standard also defines how long stations must wait
Short Inter-Frame Space of 10 μs Amount of time receiver waits before sending response
Distributed Inter-Frame Space of 50 μs (SIFS + 2*slot time) Amount of time channel must be free before a station attempts a transmission
Slot Time of 20 μs Twice the time it takes for a pulse to travel the theoretical distance between two stations
DIFS
Ready To Send
SIFS
Clear To Send
SIFS
Data
SIFS
Acknowledgement

19. Wireless MAN Technology
WiMAX (World-wide Interoperability for Microwave Access) is a specific MAN technology with potential for commercial success
Uses licensed spectrum
Standard
Description
Fixed WiMAX
Does not provide for handoff among access points
Designed for fixed/stationary connections between user and service provider (such as a provider to an office building or residence)
Mobile
WiMAX
Technology offers handoffs as users move between access points
Designed for moving connections
(such as laptops or cell phones)

20. Wireless MAN Technology
Potential Uses
Speed
Requires
Use
High Data Rates
Line-of-Sight
Backhaul from access points to a service provider
Private connections among sites in a company
Connections between small and large ISPs
Lower Data Rates
Non Line-of-Sight
Last-mile Internet access (instead of DSL, cable, satellite, cellular)
High speed connection for mobile users (instead of cellular)
Backup for a site's normal Internet connection

21. WiMAX Deployment Non Line-Of-Sight Backhaul Line-of-Sight Access
wired
connection
Wi-Fi
Non
Line-of-Sight
Access

22. Wireless WAN Technology
WAN technologies consist of:
Cellular
Satellite

23. Cellular Communications
Originally designed for voice services to mobile customers, and so was designed to interconnect to the public telephone network
Now, cellular services provide data connectivity and Internet access and so the technologies have evolved over time to adapt to this

24. Cellular Architecture
Towers provide cellular service to an area, called a cell
Mobile Switching Center tracks a mobile user and manages handoff as user moves from cell to cell
public switched telephone network + Internet connection
mobile switching center
mobile switching center
wired connections
cell

25. Cellular Coverage
In theory, perfect coverage occurs if each cell forms a hexagon, because they can be arranged into a honeycomb pattern
In reality, cell towers use omnidirectional antennas and transmit in a circular pattern.
In addition, interference and obstructions distort signal patterns and create overlap and dead zones.

26. Micro Cells
In rural areas, density of cell phones is low and cell size is large
One tower may be enough to cover a large geographic area
In cities, many cell phones are concentrated in a given area
A region may be broken into several cells, in order to handle more cell phones
Cells can even be broken so small that a few floors of a building could be a cell
Micro cells are used to create these extremely small cell sizes, and use much less power so as to avoid interference
They can also be used to provide cellular service to a customer in a rural area where cellular service is not available

27. public switched telephone network + Internet connection
Micro Cells
Micro cells connect to a wired Internet connection and are configured to recognize a specific set of cell phones
public switched telephone network + Internet connection
switching center
micro
cell

28. Frequency Reuse A I B A A F B J C A C H K G C B E C L D B D G E D F
To avoid interference, adjacent pairs of cells should not use the same frequency
A cluster approach is used so that
Clusters are cells arranged in a pattern that can be replicated
Each cell in the pattern is assigned a different frequency
Cluster Size 12
Cluster Size 7 A
Cluster Size 4
Cluster Size 3 I B A A F B J C A C H K G C B E C L D B D G E D F

29. Frequency Reuse A G D B C F E A G D B C F E A G D B C F E A G D B C F

30. Cellular Generations Generation Description 1G
First generation used analog signals to carry voice telephone calls 2G
Second generation used digital signals to carry voice calls 3G
Focused on addition of higher-speed data services of up to 2 Mbps
Example supported applications include web browsing and photo sharing
Allows a single phone to roam across North America, Japan, and Europe 4G
Focused on support for real-time multimedia
Example supported applications include television programs and high-speed video
Includes multiple connection technologies, such as Wi-Fi and Satellite

31. Standards
At creation of 2G, many groups attempted to choose an approach and create a standard
Standard
Description
GSM
Uses TDMA technology and was intended to be a world-wide standard
Created in Europe
iDEN
Uses TDMA technology
Created for use in the United States by Motorola
IS-95A
Uses CDMA technology
Adopted by most US and Asian carriers

32. Standards
3G systems were designed using voice standards, with data as an added feature
4G systems were designed to use the Internet Protocol and packet switching
Voice transmission is just another application
Standard
Description
HSPA+
HTC Evo 4G
LTE
WiMAX
Although marketed as 4G technologies, these do not technically meet the standards defined for 4G
LTE Advanced
WiMAX Advanced
Meets the specifications for 4G and thus is referred to as "True 4G"