IT-3303-3
Broadband Networks
Punjab University College of Information Technology,
University of the Punjab.
Wireless Local Loop (WLL)
Objectives
Wireless Local Loop (WLL)
Advantages of WLL
WLL Architecture
WLL Technologies
WLL-OAM management Functions
Upstream Transmission
Downstream Transmission
Propagation Consideration for WLL
Effect of Rain
Wireless Local Loop (WLL)
Local loop/ Subscriber line/ Last mile
Wireless Local Loop (WLL) is a new
communications access method that uses radio
waves for transmission of information between
customers and service provider sites, rather
than traditional fixed methods such as copper
or fiber optic delivery.
WLL is a system that connects subscribers to
the local telephone station wirelessly.
WLL can be used to provide voice, fax, and data
connections.
WLL
Wireless
local
loop
provides
two-way
communication services to stationary or nearstationary users within a small service area.
This technology is intended to replace the
wireline local loop.
WLL
Wireless local loop (WLL)
Narrowband offers a replacement for
existing telephony services
Broadband provides high-speed two-way
voice and data service
Other names
Radio In The Loop (RITL)
Fixed-Radio Access (FRA).
Services delivered over WLL
Wireless Local Loop, offers a range of services
up to a maximum of 6Mbs
IP Line - always-on Internet access.
Leased line to connect 2 sites for example for
LAN Interconnect and Video Conferencing.
Frame Relay - for data networks between
multiple sites.
ISDN (PRI) - 30 digital channels which can be
used for voice, Internet or voice conferencing.
Advantages of WLL
Wireless
local
loop
offers
following
advantages over wireline local loop:
Cost: Wireless systems are less expensive
than wired systems with the cost of
installing cables, either underground or on
poles, and avoided the cost of maintaining
the wired infrastructure.
Ease of Installation and deployment
WLL systems can be installed and deployed
easily.
Advantages of WLL
Installation time: WLL systems can be
installed in a small fraction of the time required
for a new wired system. WLL eliminates the
wires, poles, and ducts essential for a wireline
network; in other words the WLL approach
significantly speeds the installation process.
WLL
Applications:
WLL
systems
find
applications in competitive telecommunications
markets, in developing telecommunications
markets, and in rural and remote markets that
would
not
be
economically
served
by
conventional wireline access technologies.
How wireless local loop works
Wireless local loop phones in homes, offices connect
with a wireless system in a manner similar to that of
CDMA cell phones. The difference is that WLL phones
usually stay in a relatively fixed location.
WLL phones often connect to AC current rather than
using batteries.
The telephone company will install a small antenna
on the customers building, the size and shape of
which will not require planning permission to be
obtained.
Direct line of sight is required between the customer
antenna and the nearest base station antenna.
WLL Architecture
WANU
UWLL
Transceiver
WASU
AWLL
Trunk
PSTN
Switch
function
WLL
Controller
AM
HLR
Air
Interface
TWLL
WLL Architecture
The architecture consists of three major
components:
Wireless Access Network Unit (WANU)
Wireless Access Subscriber Unit (WASU)
Switching Function (SF)
WLL Architecture
Wireless Access Network Unit (WANU)
Interface between underlying telephone
network and wireless link
consists of
Base Station Transceivers (BTS)
Radio Ports (RP)
Radio Port Controller Unit (RPCU)
Access Manager (AM)
Home Location Register (HLR)
Wireless Access Subscriber Unit (WASU)
located at the subscriber
translates wireless link into a traditional
telephone connection
WLL Architecture
SU
Terminal
RP
RPCU
Intermediate
Network
Remote
Network
IWF
Host
Generalized network architecture for wireless-to-wireline data interworking
Wireless Local Loop Technologies
Systems WLL is based on:
Satellite-Based Systems
Cellular-Based Systems
WLL OAM Management Functions
WLL-OAM
describe
the
WLL
Operation,
Administration and Maintenance functions.
Written in 35,000 lines of C++ code, WLL-OAM
provides the OAM services necessary to control and
monitor the equipment in a DECT WLL system.
The network elements managed by WLL-OAM are:
WANU, including the base station controller (BSC)
and radio base station (RBS)
WASU, called radio network termination (RNT)
Customer premise equipment (CPE; e.g., a
telephone set) connected to the RNT.
Transmission Mechanism on Air Interface
WLL standard specifies two modes of operation,
one targeted to support a continuous
transmission stream (mode A), such as audio or
video, and one targeted to support a burst
transmission stream (mode B), such as IP-base
traffic.
Bursty Data Transmission - Upstream and
Downstream
In upstream and downstream direction, data
(burst data) transmission uses a DAMA-TDMA
(demand assignment multiple access time
division multiple access) technique.
Voice and Video Transmission Downstream and Upstream
For voice and video transmission FAMA-FDMA
(fixed assignment multiple accessfrequency
division multiple access) scheme is used.
This is equivalent to a FDD (frequency division
duplex).
FDD simply means that a different frequency
band is used for transmission in each direction.
FDD implies that all subscribers can transmit
and receive simultaneously, each on their own
assigned frequencies.
Voice and Video Transmission Downstream and Upstream
There are also some other methods that can be
used:
Time Division Duplexing (TDD): A TDMA
frame is used, with part of the time allocated for
upstream
transmission
and
part
for
downstream transmission.
FDD with adaptive modulation: This is the
same FDD, but with a dynamic capability to
change the modulation and error correction
schemes.
Propagation Considerations for
WLL
For most high speed WLL schemes,
frequencies in what is referred to as the
millimeter wave region are used.
Frequencies above 10 GHz up to about
300 GHz, are considered to be in the
millimeter wave region.
Atmospheric Absorption
Radio waves at frequencies above 10 GHz are
subject to molecular absorption
Peak of water vapor absorption at 22 GHz
Peak of oxygen absorption near 60 GHz
Favorable windows for communication:
From 28 GHz to 42 GHz
From 75 GHz to 95 GHz
Effect of Rain
Attenuation due to rain
Presence of raindrops can severely degrade the
reliability and performance of communication links
The effect of rain depends on drop shape, drop size, rain
rate, and frequency
Estimated attenuation due to rain:
A aR
A = attenuation (dB/km)
R = rain rate (mm/hr)
a and b depend on drop sizes and frequency
Comparison
WLL
Mobile Wireless
Wireline Local Loop
Narrow
beam Omni
directional Expensive wires
directed antennas
antennas
High Channel reuse
Less Channel reuse
Reuse Limited by wiring
Simple design
Expensive to design, Expensive to build and
build, power control
maintain
Low in-premises
High
mobility Low in-premises mobility,
mobility, easy access allowed, easy access wiring of distant areas
cumbersome
Weather
effects,
reliable
conditions Weather
not
very effects,
reliable
conditions Very reliable
Not
very
Reference Material
Wireless and Mobile Network Architecture
by YiBing Lin
Wireless Communications and Networks
by William Stallings
