Wireless MAN Technology and WiMAX (cont`d)

CECS 474 Computer Network Interoperability
Wireless Networking
Tracy Bradley Maples, Ph.D.
Computer Engineering & Computer Science
Cal ifornia State University, Long Beach
Notes for Douglas E. Comer, Computer Networks and Internets (5th Edition)
Wireless Network Taxonomy
• Wireless communication includes a wide range of network types and sizes.
• Government regulations that make specific ranges of the electromagnetic
spectrum available for communication
• A license is required to operate transmission equipment in some parts of the
spectrum and other parts of the spectrum are unlicensed
Personal Area Networks (PANs)
• A PAN technology provides communication over a short distance.
• It is intended for use with devices that are owned and operated by a single user.
• IEEE has assigned the number 802.15 to PAN standards.
The IEEE 802.15.1a Standard evolved after vendors created Bluetooth technology as
a short-distance wireless connection technology.
The characteristics of the Bluetooth technology are:
• Wireless replacement for cables (e.g., headphones or mouse)
• Uses 2.4 GHz frequency band
• Short distance (up to 5 meters, with variations up to 10 or 50 meters)
• Device is either master or slave
• Master grants permission to slave
• Data rate is up to 721 Kbps
Wireless LAN Standards (WiFi)
Standards from the first years of WiFi:
Wireless LAN Standards (WiFi) (cont’d)
More recent WiFi standards:
802.11n – Standardized in 2009.
-- Extends 802.11b and .11g
-- Uses the 2.4 GHz and 5 GHz
frequency bands
-- Expected total multi-station
throughput of 600 Mbps
-- Uses MIMO (Multiple Input
Multiple Output) by having
multiple antennae at both sender
and receiver
-- Up to 4 more MIMO spatial
802.11ac – Preliminary versions now showing up in new WiFi Routers.
-- WLANs on the 5 GHz frequency bands
-- Final standard approval expected in early 2014
-- Expected total multi-station throughput of 1 Gbps; single link throughput 500 Mbps
-- Extends 802.11n capabilities with: wider RF band & up to 8 MIMO spatial streams
Wireless Local Area Network (WLAN) Architecture
Note: The set of computers within range of a given access point is known
as a Basic Service Set (BSS).
RTS: Request to Send
(frame sent to request
communication and
reserve channel)
Contention and Contention-Free Access
CTS: Clear to Send
(frame sent confirming
reserved channel)
ACK: Acknowledgement
DIFS: Distributed
Interframe Space (enough
time for the station to
sense the medium to see
that it is idle)
SIFS: Short Interframe
Space (enough time for
the transmitting station to
switch back to receive
Note: More on this will be discussed in the Wireless
Supplement notes.
Wireless MAN Technology and WiMAX
Standardized by IEEE under the category IEEE 802.16.
Two main versions of WiMAX are being developed that differ in their overall
Fixed WiMAX
• refers to systems built using IEEE 802.16-2004 (informally called 802.16d)
• does not provide for handoff among access points
• provides connections between a service provider and a fixed location
Mobile WiMAX
• Standard 802.16e-2005 (informally called 802.16e)
• handoffs among Aps
• used for mobile hosts
Wireless MAN Technology and WiMAX (cont’d)
WiMAX offers broadband communication that can be used in a variety of ways:
Wireless MAN Technology and WiMAX (cont’d)
The key features of WiMAX can be summarized as follows:
• Uses licensed spectrum (i.e., offered by carriers)
• Each cell can cover a radius of 3 to 10 Km
• Uses scalable orthogonal FDM
• Guarantees quality of services (for voice or video)
• Can transport 70 Mbps in each direction at short distances
• Provides 10 Mbps over a long distance (10 Km)
Cellular Communication Systems
• When moving between two cells belonging to the same MSC the switching
center handles the change.
• When a user passes from one geographic region to another, MSCs are involved
in the handoff.
Cellular Communication Systems (cont’d)
(a) Perfect cellular coverage occurs if each cell is a hexagon:
• because the cells can be arranged in a honeycomb
• in practice, cellular coverage is imperfect
(b) Most cell towers use omnidirectional antennas:
• transmit in a circular pattern
• obstructions and electrical interference can attenuate a signal or cause an
irregular pattern
o in some cases, cells overlap and in others, gaps exist with no coverage
Generations of Cellular Technologies
Telecommunications industry divides cellular technologies into four generations: 1G,
2G, 3G, and 4G (with intermediate versions labeled 2.5G and 3.5G)
Simplified Descriptions:
• Began in the late 1970s, and extended through the 1980s
• Originally called cellular mobile radio telephones
• used analog signals to carry voice
2G and 2.5G
• Began in the early 1990s and continues to be used
• One standard: GSM (General System for Communications)
• The main distinction between 1G and 2G arises because 2G uses digital
signals to carry voice
• The label 2.5G is used for systems that extend a 2G system to include some
3G features
Generations of Cellular Technologies (cont’d)
3G and 3.5G
• Began in the 2000s
• Focuses on the addition of higher-speed data services
• A 3G system offers download rates of 400 Kbps to 2 Mbps, and is intended to
support applications such as web browsing and photo sharing
• Includes EDGE (Enhanced Data Rates for GSM Evolution) (amongst other
• 3G allows a single telephone to roam across the world
4G and 4G LTE (Long Term Evolution)
• Began around 2008
• Incompatible with 2G and 3G networks and must be implemented separatedly.
• Based on GSM/EDGE
• Focuses on support for real-time multimedia
o such as a television program or high-speed video
• They include multiple connection technologies
o such as Wi-Fi and satellite
o at any time, the phone automatically chooses the best connection technology

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