Wireless & Mobile Networks - 8. WiMAX and Wi-Fi

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WiMAX

Agenda

o What is WiMAX

o WiMAX Services and Applications

o WiMAX Network Architecture

o IEEE 802.16 Standards

1Wireless and Mobile Networks © Imad J. Eid

WiMAX is a broadband wireless data communications technology.

A standards-based technology enabling the delivery of last mile wireless

broadband access as an alternative to cable and DSL.

The standard for WiMAX has been developed by the working group IEEE 802.16.

IEEE 802 set up the IEEE 802.16 in 1999 to develop standards that:

o Use wireless links with microwave or millimeter wave radios

o Use licensed spectrum (typically)

o Are metropolitan in scale

o Provide public network service to fee-paying customers (typically)

o Use point-to-multipoint architecture with stationary rooftop or tower-mounted

antennas

o Provide efficient transport of heterogeneous traffic supporting quality of service

(QoS)

o Are capable of broadband transmissions (>2 Mbps)

Wireless and Mobile Networks 2

Worldwide Interoperability for Microwave Access ( )

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IEEE 802.16 is a standard for Wireless Metropolitan Area Networks (WMANs)

o Metropolitan: A large network that spans a metropolitan (city) area.

The WiMAX Forum, has been formed in 2001 to promote the 802.16

standards, to develop interoperability specifications, and to certify the

WiMAX products.

WiMAX is capable of providing high speed data communications (>70 Mbps)

over a wide area.

WIMAX can provide broadband wireless access up to 50 km for fixed stations

and 5-15 km for mobile stations.


Worldwide Interoperability for Microwave Access (WiMAX)

WiMAX can provide two forms of wireless service:

o Non-line-of-sight: where a small antenna on your computer connects to the tower in the low frequency range of 2-11 GHz.

o Line-of-sight: where a fixed antenna points straight at the WiMAX tower from a rooftop or pole. The LOS connection is stronger and more stable, so it is able to send a lot of data with fewer errors. Uses higher frequencies, with ranges reaching 66 GHz.

In addition to the fixed point-to-point and point-to-multipoint, WiMAX supports four mobility-related usage scenarios:

o Nomadic: The user is allowed to take a fixed subscriber station and reconnect from a different point of attachment.

o Portable: Nomadic access is provided to a portable device, such as a PC card, with expectation of a best-effort handover.

o Simple mobility: The subscriber may move at speeds up to 60 km/h with brief interruptions (less than 1 sec) during handover.

o Full mobility: Up to 120 km/h mobility and seamless handover (less than 50 mslatency and < 1% packet loss) is supported.


WiMAX Services and Applications

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Support of multiple services (voice, video, and Internet data) with QoS.

Suitable for the following potential applications:

o Connecting Wi-Fi hotspots with each other and to other parts of the Internet.

o Providing a wireless alternative to cable and DSL for last mile (last km)

broadband access.

o Providing high-speed mobile data and telecommunications services (4G).

o Providing a diverse source of Internet connectivity as part of a business

continuity plan. That is, if a business has a fixed and a wireless internet

connection they are unlikely to be affected by the same service outage.


WiMAX Services and Applications

Two major components:o Subscriber Stations (SSs)

• Typically serves a building (business or residence)o Base Station (BS)

• Connected to public networks and serves Subscriber Stations• Provide SS with first-mile(or last mile) access to public networks


WiMAX Network Architecture

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The Major IEEE 802.16 Standards/Amendments:


IEEE 802.16 Standards

Standard/Amendment Description

802.16

Now withdrawn. This is the basic 802.16 standard that was released in

2001. It provided for basic high data links at frequencies between 10 and

66 GHz.

802.16a Now withdrawn. This amendment addressed certain spectrum issues and

enabled the standard to be used at frequencies between 2 and 11 GHz.

802.16d

(802.16-2004)

It was a major revision of the 802.16 standard and upon its release, all

previous documents were withdrawn. The standard / amendment provided a

number of fixes and improvements to 802.16a including the use of 256

carrier OFDM. The standard only addressed fixed operation.

802.16e

(802.16-2005)

This standard, also known as 802.16-2005 in view of its release date,

provided for nomadic and mobile use. With lower data rates of 15 Mbps

against to 70 Mbps of 802.16d, it enabled full nomadic and mobile use

including handover. Introduced SOFDMA (scalable orthogonal frequency-

division multiple access)

802.16m (2011)

Advanced Air Interface with data rates of 100 Mbit/s mobile and 1 Gbit/s

fixed. Also known as Mobile WiMAX Release 2 or WirelessMAN-Advanced.

Aiming at fulfilling the IMT-Advanced requirements on 4G systems.

OFDM, also called multicarrier modulation,

uses multiple carrier signals (subcarriers) at

different frequencies, sending some of the

bits on each subcarrier.

This is similar to FDM. However, in the case

of OFDM, all of the sub-channels are

dedicated to a single data source.

The OFDM scheme uses advanced digital

signal processing techniques to distribute the

data over multiple subcarriers at precise

frequencies.

The precise relationship among the

subcarriers is referred to as orthogonality.


Orthogonal Frequency Division Multiplexing (OFDM)

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Orthogonality: The peak of the power spectral density of each subcarrier

occurs at a point at which the power of other subcarriers is zero

OFDM overcomes the problem of inter-symbol-interference (lSI) in a

multipath environment (so it may not be necessary to use Equalizers).

lSI has a greater impact at higher bit rates, because the distance between

bits, or symbols, is smaller.

With OFDM, the data rate is reduced by a factor of N (number of

subcarriers), which increases the symbol time by a factor of N.


OFDM

Duplexing: supports both FDD and TDD

Medium Access

o The 802.16 MAC uses a scheduling algorithm for which the subscriber station

need to compete once (for initial entry into the network). After that it is

allocated an access slot by the base station. The time slot can enlarge and

contract, but remains assigned to the subscriber station which means that other

subscribers cannot use it.

o The scheduling algorithm also allows the base station to control QoS

parameters by balancing the time-slot assignments among the application

needs of the subscriber stations.

o 802.16d utilizes OFDM to serve multiple users in a time division fashion in a

sort of a round-robin technique, but done extremely quickly so that users have

the perception that they are always transmitting/receiving.

o 802.16e utilizes OFDMA and can serve multiple users simultaneously by

allocating sets of tones (sub-channels) to each user.


802.16 (WiMAX) MAC

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Support for mobility (soft and hard handover between base stations). This

is seen as one of the most important aspects of 802.16e-2005, and is the

very basis of Mobile WiMAX (802.16m).

Scalable Bandwidth from 1.25 to 20 MHz

Scalable Orthogonal Frequency Division Multiple Access (SOFDMA)

Hybrid Automatic-Repeat Request (HARQ) for retransmission

MIMO Antenna

Adaptive modulation and coding


Mobile WiMAX Specifications

Competes with the 3GPP 3G and 4G technologies (HSPA, HSPA+, LTE,

LTE-Advanced) and Wi-Fi.

WiMAX can be complementary to Wi-Fi and cellular networks, by using it

for providing the backhauling.

Limited mobile phones can use directly WiMAX to access the internet.


WiMAX Competing Technologies

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Wireless Local Area Network (WLAN)

Agenda

o Wireless Local Area Network (WLAN)

• Wireless LAN Applications

• Wireless LAN Configurations

o Wi-Fi and the IEEE 802.11 WLAN Standard

• Wi-Fi and the IEEE 802.11

• IEEE 802.11 Architecture

• IEEE 802.11 Medium Access Control

• IEEE 802.11 Physical Layer

• IEEE 802.11 Standards

• WiMAX vs. Wi-Fi


A wireless LAN is a Local Area Network that makes use of a wireless

transmission medium.

Wireless LAN Applications:

o LAN Extension: A wireless LAN saves the cost of the installation of LAN cabling

and eases the task of relocation and other modifications to network structure.

o Cross-Building Interconnect: To connect LANs in nearby buildings, be they wired

or wireless LANs (point-to-point links)

o Nomadic (and Mobile) Access: To provide a wireless link between a LAN hub

and a mobile data terminal equipped with an antenna, such as a laptop

computer or notepad computer.

o Ad Hoc Networking: A peer-to-peer network (no centralized server) set up

temporarily to meet some immediate need.


WLAN

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Example: Single cell WLAN configuration

CM (Access Point), UM (Wi-Fi repeater, also called Customer Premises Equipment - CPE)


WLAN

Example: Multiple cell WLAN configuration


WLAN

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Infrastructure WLAN: Forms a stationary infrastructure consisting of one or more

cells with a control module (Access Point – AP) for each cell.

Infrastructure-less (Ad-Hoc) WLAN: A peer collection of stations within range of

each other may be configured into a temporary network.

Other Configurations:

o Combination of Infrastructure and Ad-Hoc.

o Mesh: Every client in the network also acts as an access or relay point, creating a “self-

healing” and (in theory) infinitely extensible network.


WLAN Configurations

Infrastructure WLAN Ad-Hoc WLAN Mesh WLAN

In 1990, the IEEE 802 committee formed a new working group, IEEE 802.11,

specifically devoted to wireless LANs, with a charter to develop a MAC

protocol and physical medium specification.

The initial interest was in developing a WLAN operating in the ISM (industrial,

scientific, and medical) band.

Since that time, the demand for WLANs, at different frequencies and data

rates, has exploded.

Keeping pace with this demand, the IEEE 802.11 working group has issued a

list of standards.

The Wi-Fi (Wireless Fidelity) Alliance, has been formed in 1999 to promote

the 802.11 standards, to develop interoperability specifications, and to

certify the Wi-Fi products.


Wi-Fi and the IEEE 802.11 WLAN Standard

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Basic Service Set (BSS): The smallest building block of a wireless LAN

which consists of some number of stations executing the same MAC

protocol and competing for access to the same shared wireless medium. A

BSS may be isolated or it may be connected to a backbone Distribution

System (DS) through an Access Point (AP).

o The BSS generally corresponds to a radio cell.

o The AP functions as a bridge and a relay point

o The DS can be a switch, a wired network, or a wireless network.

o When all the stations in the BSS are mobile stations, with no connection to other

BSSs, the BSS is called an Independent BSS (IBSS).

o An IBSS is typically an ad-hoc network.

o In an IBSS, the stations all communicate directly, and no AP is involved.


IEEE 802.11 Architecture

Extended Service Set (ESS): Consists

of two or more basic service sets

interconnected by a distribution

system (DS)

To integrate the IEEE 802.11

architecture with a traditional wired

LAN, a Portal is used (may be

implemented in a switch or router)

STA = Station



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The standard defines three transition types based on mobility:

o No transition

• Station is stationary or moves only within a BSS

o BSS transition

• Station moving from one BSS to another BSS in same ESS

o ESS transition

• Station moving from BSS in one ESS to BSS within another ESS

The Service Set IDentifier (SSID):

o The name of a wireless local area network (WLAN).

o All wireless devices on a WLAN must employ the

same SSID in order to communicate with each other.

o The SSID can be up to 32 characters (octets) long.



Duplexing:

o Wi-Fi networks are Half Duplex.

Medium Access:

o Uses CSMA/CA with ACK and RTS/CTS

o This technique is referred to as Distributed Coordination Function DCF.


IEEE 802.11 Medium Access

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May use an optional medium access mechanism called point coordination

function (PCF) that is implemented in the access points (in addition to the

mandatory DCF) that provides delivery of time-bounded data using

station-polling mechanisms. This mechanism is capable of transporting

video effectively as compared to the DCF.

PCF uses a Point Inter Frame Space PIFS which is smaller than the DIFS to

grant priority to some kinds of traffic.


IEEE 802.11 Medium Access

Three physical media as defined in the original 802.11 standard:

o Direct sequence spread spectrum (DSSS):

• Operating in the 2.4-GHz ISM band,

• Data rates of 1 Mbps and 2 Mbps.

o Frequency-hopping spread spectrum (FHSS):

• Operating in the 2.4-GHz ISM band,

• Data rates of 1 Mbps and 2 Mbps.

o Infrared:

• Operating at a wavelength between

850 and 950nm

• Data rates of 1 Mbps and 2 Mbps


IEEE 802.11 Physical Layer

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Mainly: 2.4 GHz and 5 GHz

The 2.4 GHz band is from 2.40 to 2.4835 GHz

o The total Bandwidth = 83.5 MHz

o Divided into 13 overlapping channels (channel 14 used only in Japan).

o Channel Bandwidth = 22 MHz

o Only 3 non-overlapping channels (typically, channels 1, 6, and 11 are used)


IEEE 802.11 Frequency Bands


IEEE 802.11 WLAN Standards

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IEEE 802.11a

o Introduced in 1999

o Operates in the 5-GHz band

o Channel Bandwidth: 20 MHz

o Uses orthogonal frequency division multiplexing (OFDM)

o Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAM

o Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps

IEEE 802.11b


o Operates in the 2.4 GHz band


o Uses Direct Sequence Spread Spectrum (DSSS)

o Modulation: Complementary code keying (CCK)

o Provides data rates of 5.5 and 11 Mbps



802.11g


o Operates in the 2.4 GHz band


o Uses DSSS & OFDM

o Modulation: CCK, BPSK, QPSK, 16-QAM or 64-QAM

o Provides data rates of 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, and 54 Mbps

802.11n


o Operates in the 2.4 and 5 GHz bands

o Channel Bandwidth: 20 and 40 MHz

o Uses OFDM

o Modulation: BPSK, QPSK, 16-QAM or 64-QAM

o Uses MIMO antennas (up to 4 spatial streams).

o Provides data rates up to 600 Mbps



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802.11ac

o Introduced in 2012 (commercial use in 2013)

o Operates in the 5 GHz band

o Channel Bandwidth: 20, 40, 80, 160 MHz

o Uses OFDM

o Modulation: BPSK, QPSK, 16-QAM, 64-QAM or 256-QAM

o Uses MIMO antennas (up to 8 spatial streams).

o Provides data rates up to 6.93 Gbps

802.11ad

o Expected in 2014

o Operates in the 60 GHz band

o Provides data rates up to 7 Gbps



Wi-Fi is based on the standard IEEE 802.11, WiMAX is based on IEEE 802.16

Wi-Fi is a WLAN, WiMAX is a WMAN

Wi-Fi coverage is limited (outdoor & LOS <200m), WiMAX up to 50 Km

WiMAX can be a complementary to Wi-Fi (using WiMAX for backhauling)

Most of the mobile and portable devices are equipped with Wi-Fi adaptors, but

are not equipped with WiMAX adaptors.

Applications

Licensed/Unlicensed

QoS Support

….


Wi-Fi vs. WiMAX

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Cellular Network Planning


Cellular Network Optimization

Why Optimization?

o To Achieve:

• Best Performance of the Network.

(e.g.: best speech quality, minimum drop calls,

maximum data throughput, minimum delay … etc.)

• Best Quality of Service (QoS) & Maximum Customer Experience.

• Maximum Utilization of the Frequency Spectrum.

• Optimum Capacity: Maximum utilization of the hardware and software

resources.

• Maximum Coverage of the Radio Network.

o Trade-Off:

Coverage Capacity Quality Cost

Wireless & Mobile Networks - 8. WiMAX and Wi-Fi

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