16 Basics of Wimax
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Gemini Communication Ltd.Gemini Communication Ltd.
Innovation & LeadershipInnovation & Leadership
Basics of RF TechnologyRef. 1040001100
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WIMAX BASICS
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Introduction
Broadband Wireless concept
Evolution of WiMAX
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What is AccessSystem designed to transfer signals from their point
of generation (the user), to the first node of the
(transport) network is known as Access System
Operator / ISP
Network
Access System
useruser
Access System
user
AccessSyste
m
user
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Broad band Wireless Access Point to Multi
point Features
Base station serving many customers
Distribute costs over large number of users
Typically data rates in excess of 256 kbps per Customer
Line of Sight Technology
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Prevailing Wireless Access Technologies
Local Multipoint Distribution Services (LMDS)
Multi-channel Multipoint Distribution Services (MMDS)
W-CDMA
TD-CDMA
Wi-Fi
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What is WiMAX
Worldwide Interoperability for Microwave Access (WiMAX)is the common name associated to the IEEE 802.16a/d/e
standards that originally covered the Wireless Local Looptechnologies with radio spectrum from 10 to 66 GHz.
The technology on which we are working is IEEE 802.16-2004/d
Why WiMAX
Standard based (IEEE 802.16 Series of Standards)
Lower CostEnsures compatibility and interoperabilityBetter Performance & Coverage
IEEE 802 16 Broadband Access System
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Traffic is generated as Service Flows (SF)
Service Flow is a flow of packets to which specific QoS level is guaranteed
Service Flows and their associated QoS parameters are defined before the operation
of the network, but can also be modified, added or deleted during operation.
Packets are identified as belonging to a specific Service Flow based on Connection
Identifier CID
CID is used by Subscriber Stations (SS) to request uplink bandwidth grants from
Base Station (BS)
WAN
(Internet /Intranet)
userLAN
user
user
user
userLAN
user
BaseStation
(BS)
SubscriberStation
(SS)
IEEE 802.16 Broadband Access SystemConcept
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Why Broadband Wireless Access ?
Copper Wire (DSL)
Optical Fiber Cable
Wireless Access System.Satellite Communication System
Ways of providing Broadband Access?
Lower Capital Expenditure
Lower Operational Expenditure Faster Deployment Time Scalable & Easy Relocation
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Evolution of Standards
IEEE 802.16 (2001) Air Interface for Fixed Broadband Wireless Access System MAC
and PHY Specifications for 10 66 GHZ (LoS)
One PHY: Single Carrier
Connection-oriented, TDM/TDMA MAC, QoS, Privacy IEEE 802.16a (January 2003) Amendment to 802.16, MAC Modifications and Additional PHY
Specifications for 2 11 GHz (NLoS)
Three PHYs: OFDM, OFDMA, Single Carrier Additional MAC functions: OFDM and OFDMA PHY support,
Mesh topology support, ARQ
IEEE 802.16d (July 2004)
Combines both IEEE 802.16 and 802.16a Some modifications to the MAC and PHY
IEEE 802.16e (November 2005) Amendment to 802.16-2004
MAC Modifications for limited mobility
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WiMAX Technology
Description
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Modulation
Modulation is the process by which a carrier wave isable to carry the message or digital signal (series ofones and zeroes).
There are three basic methods to this:-
Amplitude,
Frequency
Phase shift keying
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Binary Phase Shift Keying (BPSK)
BPSK is the simplest form of PSK.
It uses two phases which are separated by 180and socan also be termed 2-PSK.
It does not particularly matter exactly where theconstellation points are positioned
It is, only able to modulate at 1bit/symbol and so isunsuitable for high data-rate applications.
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Quadrature Phase-shift Keying (QPSK)
Sometimes known as quaternary or quadriphase PSK or 4-PSK, QPSK uses four points on the constellation diagram,equispaced around a circle.
With four phases, QPSK can encode two bits per symbol-twice the rate of BPSK.
This is used either to double the data rate compared to a
BPSK system while maintaining the bandwidth of the signalor to maintain the data-rate of BPSK but halve thebandwidth needed.
BPSK is used on both carriers and they can be
independently demodulated.
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16-QAM,64-QAM
The number before QAM (for example 16QAM) refers directly tothe number of decision points in the constellation. Meaning,256QAM has 192 more decision points than 64QAM. The
number before QAM is also always a power of two. (EG.
2^6=64QAM) The more Decision points, the more throughput per channel.
The more Decision points, the more susceptible the channel is to
noise (as the decision boundaries get smaller to accommodate
more decision points, it becomes harder to distinguish whichboundary the point was intended to lie in).
More Decision points=More Bandwidth=Higher susceptibility to
noise or poor signal (the same applies inversely as well).
Deliver the same number of customers incrementally faster
speeds.-or-
Deliver a larger number of customers the same speeds as
before.
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Adaptive Modulation
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Line Of Sight & Near Line of Sight
For LoS First Fresnel Zone should be clear of any
obstructions (at least 60% area)
This requires both BS and SS to be placed outdoor
In case of any obstruction in the transmission path then
30% clearance of FFZ may be taken and is known as Near
LOS
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Non-Line Of Sight (NLOS)
Signal reaches the receiver through reflections, scattering,and diffractions.
These signals have different delay spreads, attenuation,
polarizations, and stability relative to the direct path.NLOS technology also make CPE installation easy & less
expenses
The technology also reduces the need for pre installationsite surveys.
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FDM & OFDM
FDM OFDM
+=
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Orthogonal Frequency Division Multiplexing
OFDM: a form of MultiCarrier Modulation & Multiplexing technique.
Different symbols are transmitted over different SUBCARRIERS. Spectra overlap, but signals are orthogonal.
The basic idea is that each bit occupies a frequency-time
window which ensures little or no distortion of the waveform
Signals are orthogonal if they are mutually independent of each other.
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OFDM technology
28 Guard carriers on left 27 on right 8 pilots 1 DC and 192data sub carrier
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OFDM operation OFDM is a multicarrier block transmission system
Conversion of a high-data rate stream into several low-rate streams
Parallel streams are modulated onto orthogonal carriers Data symbols modulated on these carriers can be recovered without mutual
interference
Overlap of the modulated carriers in the frequency domain - different from FDM
Block of N symbols are grouped and sent parallely
No interference among the data symbols sent in a block
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Link Budget Calculations
Receiver
Antenna
Antenna
Cable
Transmitter
Cable
Power output
Cable Loss
Gain
Path Loss
Gain
Cable Loss
Sensitivity
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Q & A
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Thank YouContact : [email protected]