Mobile Computing and Wireless

Communication (3170710)

Unit - 3
(WLL and WiMAX)

Prepared by:
Viral H. Panchal
Assistant Professor
SNPIT & RC, Umrakh.
 WIRELESS LOCAL LOOP (WLL)
• Traditionally, the provision of voice and data
communications to the end user, over the local loop, or
subscriber loop, has been provided by wired systems.
• For residential subscribers, twisted pair has been and
continues to be the standard means of connection. For
business and government subscribers, twisted pair,
coaxial cable, and optical fiber are in use.
• As subscribers have demanded greater capacity,
particularly to support Internet use, traditional twisted
pair technology has become inadequate.
• Telecommunications providers have developed a number
of technologies to meet the need, including ISDN
(integrated services digital network), and a family of
digital subscriber loop technologies, known as xDSL.
• In addition, cable operators have introduced two-way
highspeed service using cable modem technology. Thus,
wired technologies are responding to the need for
reliable, high-speed access by residential, business, and
government subscribers.
• However, increasing interest is being shown in competing
wireless technologies for subscriber access. These
approaches are generally referred to as wireless local
loop (WLL), or fixed wireless access.
• WLL alternatives are narrowband, which offer a
replacement for existing telephony services, and
broadband, which provide high-speed two-way voice and
data service.
Figure 1: WLL Configuration
• Figure 1 illustrates a simple WLL configuration.
• A WLL provider services one or more cells. Each cell
includes a base station antenna, mounted on top of a tall
building or tower.
• Individual subscribers have a fixed antenna mounted on a
building or pole that has an unobstructed line of sight to
the base station antenna.
• From the base station, there is a link, which may either
be wired or wireless, to a switching center.
• The switching center is typically a telephone company
local office, which provides connections to the local and
long-distance telephone networks.
• An Internet service provider (ISP) may be collocated at
the switch or connected to the switch by a high-speed
link.
 Advantages of WLL over Wired Approach
• The WLL has a number of advantages over a wired
approach to subscriber loop support:
• Cost: Wireless systems are less expensive than wired
systems.
- Although the electronics of the wireless
transmitter/receiver may be more expensive than
those used for wired communications, with WLL the
cost of installing kilometers of cable, either
underground or on poles, is avoided, as well as the
cost of maintaining the wired infrastructure.
• Installation time: WLL systems typically can be installed
rapidly.
- The key stumbling blocks are obtaining permission to
use a given frequency band and finding a suitable
elevated site for the base station antennas.
- Once these hurdles are cleared, a WLL system can be
installed in a small fraction of the time required for a
new wired system.
• Selective installation: Radio units are installed only for
those subscribers who want the service at a given time.
- With a wired system, typically cable is laid out in
anticipation of serving every subscriber in a local area.
• WLL needs to be evaluated with respect to two
alternatives:
1. Wired scheme using existing installed cable: A large
fraction of the earth’s inhabitants do not have a
telephone line.
- For high-speed applications, many subscribers with
telephone lines do not have a line of sufficient quality
or are too far from the central office to effectively use
xDSL.
- Many of these same subscribers also do not have
cable TV or their cable provider does not offer two-
way data services.
- Finally, because WLL has become cost-competitive
with wired schemes, new installations face a genuine
choice between the wired and wireless approaches.
2. Mobile cellular technology: Current cellular systems
are too expensive and do not provide sufficient
facilities to act as a realistic alternative to WLL.
- Even when 3G systems become available, they are
likely to be more expensive and less functional than
broadband WLL alternatives.
- A major advantage of WLL over mobile cellular is that,
because the subscriber unit is fixed, the subscriber can
use a directional antenna pointed at the base station
antenna, providing improved signal quality in both
directions.
 Propagation Considerations for WLL
• Most high-speed WLL schemes use millimeter wave
frequencies (10 GHz to about 300 GHz).
• The reasons for using frequencies in this range for WLL
include the following:
1. There are wide unused frequency bands available
above 25 GHz.
2. At these high frequencies, wide channel bandwidths
can be used, providing high data rates.
3. Small size transceivers and adaptive antenna arrays
can be used.
• However, millimeter wave systems have some
undesirable propagation characteristics:
1. Free space loss increases with the square of the
frequency; thus losses are much higher in this range
than in the ranges used for traditional microwave
systems.
2. Generally, below 10 GHz, we can ignore attenuation
due to rainfall and atmospheric or gaseous
absorption. Above 10 GHz, these attenuation effects
are large.
3. Multipath losses can be quite high.
• Because of these negative propagation characteristics,
WLL systems can only serve cells of a limited radius,
usually just a few kilometers.
• Also, obstructions, including foliage, must be avoided
along or near the line of sight.
• Finally, rainfall and humidity effects limit the range and
availability of WLL systems.
 Wireless Broadband (WiMAX)
• Wireless broadband is a high-speed Internet and data
service delivered through a wireless local area network
(WLAN) or wireless wide area network (WWAN).
• Wireless broadband may be either fixed or mobile.
• A fixed wireless service provides wireless Internet for
devices in relatively permanent locations such as homes
and offices.
• Fixed wireless broadband technologies include LMDS
(Local Multipoint Distribution Service) and MMDS
(Multichannel Multipoint Distribution Service) systems.
• A Mobile broadband service provides connectivity to
users who may be in temporary locations such as coffee
shops.
• Mobile broadband works through a variety of devices
including portable modems and mobile phones, and a
variety of technologies including WiMAX, GPRS, and LTE
(Long Term Evaluation).
• WiMAX stands for Worldwide Interoperability for
Microwave Access.
• WiMAX supports both fixed and mobile wireless
broadband and is often predicted to become the
standard for wireless broadband.
• WiMAX refers to broadband wireless networks that are
based on the IEEE 802.16 standard, which ensures
compatibility and interoperability between broadband
wireless access equipment.
• WiMAX can provide broadband wireless access (BWA) up
to 30 miles (50 kms) for fixed stations and 3 – 10 miles (5
– 15 kms) for mobile stations.
• In contrast, the Wi-Fi/802.11 wireless local area network
standard is limited to only 30 – 100 meters.
WiMAX Protocol Layers

Figure 1: WiMAX Protocol Layers

• Figure 1 depicts the multiple layers of WiMAX.
• The WiMAX system has four key layers:
- Physical Layer,
- MAC Security Layer (MAC Privacy),
- MAC Layer and
- MAC Convergence Layer
• Physical Layer:
- It is responsible for converting bits of information into
radio bursts.
- It performs the conversion of data to a physical
transmission medium (such as copper, radio, or
optical) and coordinates the transmission and
reception of these physical signals.
- The physical layer receives data for transmission from
an upper layer and converts it into physical format
suitable for transmission through a network (such as
frames and bursts).
- An upper layer provides the physical layer with the
necessary data and control (e.g. maximum packet size)
to allow conversion to a format suitable for
transmission on a specific network type and
transmission line.
• MAC security layer (MAC privacy):
- It is responsible for identifying the users
(authentication) and keeping the information private
(encrypting).
• MAC layer:
- It is responsible for requesting access and
coordinating the flow of information.
- The MAC layer is composed of one or more logical
communication channels that are used to coordinate
the access of communication devices to a shared
communications medium or channel (microwave
radio).
- MAC channels typically communicate the availability
and access priority schedules for devices that may
want to gain access to a communication system.
• MAC convergence layer:
- It is used to adapt the WiMAX system to other
systems such as ATM, Ethernet or IP data systems.
- The MAC convergence layer is a functional process
within a communication device or system that adapts
one or more transmission mediums (such as radio
packet or circuit data transmission) to one or more
alternative transmission formats (such as ATM or IP
data transmission).
 Benefits of WiMAX
• Speed
• Faster than broadband service
• Wireless
• Not having to lay cables reduces cost
• Easier to extend to suburban and rural areas
• Broad Coverage
• Much wider coverage than Wi-Fi hotspots
 Benefits to Customers
• Range of technology and service level choices from both
fixed and wireless broadband operators
• DSL-like services at DSL prices but with portability
• Rapidly declining fixed broadband prices
• No more DSL “installation” fees from incumbent
 Advantages of WiMAX over 3G
• Using an assortment of proprietary and standards-based
technologies, such as OFDM and W-CDMA, WiMAX has a
clear advantage over 3G.
• The advantages include
• Higher Throughput
• Low Cost
• Lower Latency
 Wi-Fi vs. WiMAX
Wi-Fi WiMAX
Wi-Fi stands for Wireless Fidelity WiMAX stands for Worldwide
Interoperability for Microwave
Access
Wi-Fi has been defined under IEEE WiMAX is standardized under IEEE
802.11x standards where x is various 802.16y family of wireless
Wi-Fi versions. networking where y refers to various
WiMAX versions.
Wi-Fi has several versions of it such WiMAX has a number of different
as 802.11b, 802.11g, 802.11n. versions too: 802.16a, 802.16d and
802.16e.
Wi-Fi has been defined under the WiMAX protocols might work in the
ISM bands (The industrial, scientific, ISM bands or they might use a
and medical radio bands) where user licensed frequency version for which
has to pay no extra charging for the user probably would be charged.
utilizing those bands.
Wi-Fi range is up to 100 meters WiMAX range is up to 50 kms
Wi-Fi based networking can transfer WiMAX networks exchange data at
data at speed up to 54 Mbps speed of 70 Mbps or more
Wi-Fi networks have a channel WiMAX networks have a flexible
bandwidth of 20 MHz option which ranges from 1.25 MHz
to 20 MHz
Wi-Fi is mostly an end user WiMAX is mostly deployed by service
technology where users can providers.
purchase Wi-Fi devices and configure
them by themselves.
Applications: Wi-Fi is needed to Applications: WiMAX serves a larger
serve for household and corporate inter-operable network. WiMAX can
needs of interconnectivity. Wi-Fi be used to provide internet services
technology connects printers to to a larger area where it can serve
computers, gaming console to households, mobile phones, and
routers, etc. even Wi-Fi spots.