Introduction to WiMAX - ku.ac.th · 4 7 Agenda Introduction to Broadband Wireless Overview of WiMAX and Application WiMAX: PHY layer Broadband Wireless Channel OFDM Technology OFDMA

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Introduction to WiMAXDr. Piraporn Limpaphayom

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WiMAX : Broadband Wireless

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Agenda

� Introduction to Broadband Wireless

� Overview of WiMAX and Application

� WiMAX: PHY layer

� Broadband Wireless Channel

� OFDM Technology

� OFDMA

� Duplexing Scheme

� Multiple-Antenna Techniques

� WiMAX: MAC layer

� WiMAX Equipment

� Trial results

� Future of WiMAX

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� Technology

�Digital Subscriber Line (DSL) – broadband over telephone wires

�Cable Modem – broadband over coax cable TV

� Applications

� Fast Web surfing, Quick file download

�Real time Video/Audio streaming

� Interactive gaming

�VoIP

Today’s Broadband Access

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Advanced Broadband Access

� Technology

�Very High Data Rate Digital Subscriber Loop (VDSL)

� Fiber-to-the-Home (FTTH)

� Applications

�Broadcast High-Definition TV (HDTV)

�Video on demand (VoD)

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Wireless Broadband Access

� Broadband wireless is about bringing the broadband experience to a wireless context, which offers users certain unique benefits and convenience technologies.

� Two types of broadband wireless services

� Fixed wireless broadband

� Alternative to DSL or cable modem

� Fixed WiMAX

�Mobile wireless broadband

� Add portability, nomadicity and mobility

� Mobile WiMAX

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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What is WiMAX?

� WiMAX stands for

Worldwide Interoperability for Microwave Access

� Support both fixed and mobile wireless broadband

� Advance Features of WiMAX� OFDM-based physical layer

� High data rate

� Adaptive modulation and coding

� Multiple-antenna techniques

� Quality of Service support

� Support both TDD and FDD

� IP-based architecture

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WiMAX Applications

INTERNET

BACKBONE

Telco Core

Network or

Private (Fiber) Network

Non Line of Sight

Point to Multi-pointPoint to Point BACKHAUL

OUTDOORCPE

INDOORCPE

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WiMAX Applications

Point to Point BACKHAUL

INTERNET

BACKBONE

Telco Core

Network or


Non Line of Sight

Point to Multi-point

FRACTIONAL

E1/T1 for SMALL BUSINESS

E1/T1+ LEVEL

SERVICE ENTERPRISE

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WiMAX Applications

INTERNET

BACKBONE

Telco Core

Network or


Non Line of Sight

Point to Multi-point

Laptop Connected

Through 802.16

Line of Sight BACKHAUL

802.16 PC Card

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WiMAX Standard (IEEE 802.16)

� IEEE 802.16 group was formed in 1998

� IEEE 802.16 (Dec’01)

� Single carrier PHY layer and TDM MAC layer

� IEEE 802.16a (Jan’03)

� Include NLOS application

� OFDM PHY layer and OFDMA MAC layer

� IEEE 802.16d (June’04)

� “Fixed WiMAX”

� Combine previous versions

� IEEE 802.16e (Dec’05)

� “Mobile WiMAX”

� Add mobility support

� Scalable OFDM PHY layer and Scalable OFDMA MAC layer

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Basic Data on IEEE 802.16 Standards

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Basic Data on IEEE 802.16 Standards

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IEEE vs. WiMAX Forum

� IEEE 802.16 is a collection of standards with a very broad scope.

� IEEE developed the spec but left to the industry the task of converting them into an interoperable standard that can be certified.

� WiMAX Forum was formed in 2003 to define a limited number of system profiles and certification profiles.

� Industry-led, non-profit corporation

� Objective: Global interoperability of equipment and systems

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Roles of IEEE and WiMAX Forum

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WiMAX Spectrum by Region

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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Broadband Wireless Channel: Fading

� Fading is caused by the reception of multiple versions of the same signal.

� The multiple received versions are caused by reflections that are referred to as multipath.

� The elapsed time between the 1st arrival and the last arrival is called “delay spread”.

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Broadband Wireless Channel: NLOS

� NLOS = Non line of sight

� Problem occurred by NLOS condition� Multipath Fading � Severe Inter Symbol Interference (ISI)

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WiMAX Technology : PHY Layer

� WiMAX solves or mitigates the problems resulting from NLOS conditions by using:

� Advanced Radio Technique

� OFDM technology

� OFDMA scheme

� Sub-Channelization

� Adaptive modulation and coding

� Error correction techniques

� Advanced Antenna System

� Transmit and Receive diversity

� Beamforming

� Spatial Multiplexing

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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OFDM Technology

� OFDM stands for Orthogonal Frequency Division Multiplexing.

� OFDM is a special case of multicarrier modulation technique where carriers are orthogonal to each other.

� OFDM is used in high data rate communication: DSL, wireless LANs (802.11a/g/n), and WiMAX.

� Concept

� Divide high-rate transmit bit stream into L lower-rate streams such that the new symbol time is much greater than delay spread of the channel.

� Modulate each lower-rate stream with orthogonal subcarriers.

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OFDM Concept

� Basic multicarrier transmitter: A high-rate stream of Rbps is broken into L parallel streams, each with rate R/L and then multiplied by a carrier frequency.

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Time-domain signal

Frequency-domain signal

OFDM Concept

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OFDM Concept

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OFDM Advantage

� Mitigate Frequency-selective fading

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Implementation of OFDM

� IFFT/FFT can be used to generate OFDM signal with low complexity.

� Cyclic Prefix is used to mitigate delay spread.

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Cyclic Prefix

� The cyclic prefix is a copy of the last portion of the data symbol appended to the front of the symbol during the guard interval.

� If delay spread is less than cyclic prefix, no ISI.

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PAR Problem

� What is it ?

� The OFDM Symbol has a very large Peak to Average Ratio (PAR).

� Power Amplifiers cannot handle wide linear range.

� Reduce the efficiency of the RF power amplifier.

� One of the major drawbacks of OFDM.

� How can it be corrected ?

� Clipping – truncate the amplitude of signals that exceeding clipping level

� Selective Mapping – multiply data signal by a set of codes, do IFFT and select the one with least PAR

� Partial IFFT – divide signal in clusters, do IFFT on each and then combine them

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Agenda






� OFDM Technology

� OFDMA



� WiMAX Equipment

� Trial results

� Future of WiMAX

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OFDMA

� Previous OFDM systems, such as DSL, 802.11a/g and earlier 802.16 WiMAX uses single-user OFDM � all subcarriers are used by one user at a time

� WiMAX (802.16e-2005) uses OFDMA (orthogonal frequency division multiple access) � users share subcarriers and time slots

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OFDMA

� High performance of OFDMA comes from

� Multiuser Diversity – gains available by selecting a user or subset of users having good conditions

� Adaptive Modulation and Coding – transmit as high a data rate as possible when the channel is good, and transmit at a lower rate when the channel is poor

BPSK : SNR = 6 dB

QPSK : SNR = 9 dB

16QAM : SNR = 16dB

64QAM : SNR = 22dB

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Subcarriers

� WiMAX has 3 classes of subcarriers

� Data subcarriers for carrying data symbols

� Pilot subcarriers for carrying pilot symbols (used for channel estimation and tracking)

� Null subcarriers used for guard subcarriers and DC subcarriers

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Subchannel and Subcarrier Permutations

� In WiMAX, users are allocated blocks of subcarriers, called “subchannel”.

� The number and exact distribution of the subcarriers that constitute a subchannel depend on the “subcarrier permutation mode”.

� The subcarrier permutation mode has 2 types� Distributed subcarrier mode = subcarriers that constitute a subchannel are distributed throughout frequency band

- Provide better frequency diversity

- DL-FUSC, DL-PUSC, UL-PUSC

� Adjacent subcarrier mode = subcarriers that constitute a subchannel are adjacent

- More desirable for beamforming and allows the system to use multiuser diversity

- AMC

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Downlink Full Usage of Subcarriers

� All the data subcarriers are used to create the various subchannels.

� Each subchannel is made up of 48 data subcarriers, which are distributed evenly throughout the entire frequency band.

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Downlink Partial Usage of Subcarriers

� DL PUSC is similar to FUSC except that all the subcarriers are first divided into six groups.

� Permutation of subcarriers to create subchannels is performed independently within each group,

� In essence, logically separating each group from the others.

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Downlink Partial Usage of Subcarriers

� In PUSC, it is possible to allocate all or only a subset of the six groups to a given transmitter.

� By allocating disjoint subsets of the six available groups to neighboring transmitters, �thus enabling a tighter frequency reuse at the cost of data rate.

� For example, in a BS with three sectors, it is possible to allocate two distinct groups to each sector, thus reusing the same RF frequency in all of them.

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Uplink Partial Usage of Subcarriers

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Band Adaptive Modulation and Coding

� All subcarriers constituting a subchannel are adjacent to each other.

� Lost frequency diversity but exploit of multiuser diversity is easier.

� A subchannel at any given time is allocated to the user with the highest SNR in that subchannel.

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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Duplexing Scheme

� WiMAX supports both frequency division duplexing (FDD) and time division duplexing (TDD).

� Advantages of TDD

� Flexible sharing of bandwidth between UL and DL

� Need less spectrum

� Has a reciprocal channel that can be exploited

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A Sample of TDD Frame Structure

� Preamble is used for time and frequency synchronization.

� Frame Control Header gives frame configuration info: MAP message length, modulation & coding scheme.

� MAP messages provide information on subchannel allocation for each user.

� Ranging message is used by MS to perform time/frequency/power adjustment & bandwidth request.

� CQICH (Channel-Quality Indicator Channel) is used by MS to feedback CSI to BS.� ACK is used by MS to provide HARQ acknowledgement.

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Multiple-Antenna Techniques

� Multiple antennas can be used to provide

� Spatial Diversity

� Receive Diversity

� Transmit Diversity

� Beamforming

� Spatial Multiplexing

� When multiple antennas are used at both the transmitter and the receiver, these approaches are collectively referred to multiple-input multiple-output (MIMO) communication.

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Multiple-Antenna Techniques

� MIMO can be used to

� Increase system reliability (decrease bit/packet error rate)

� Increase achievable data rate and therefore system capacity

� Increase the coverage area

� Decrease the required transmit power

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Receive Diversity

� Receive diversity places no requirements on the transmitter but requires a receiver that processes Nr received streams and combines them in some fashions.

� Two of widely used combining algorithms

a) Selection Combining b) Maximal Ratio Combining

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Transmit Diversity

� Widely implemented only in early 2000s

� Because signals sent from different transmit antennas interfere with one another, processing is required at both the transmitter and the receiver in order to achieve diversity while removing the spatial interference.

� Attractive for DL due to power constraint at MS

� Two types of transmit diversity

� Open-loop transmit diversity

- Do not require knowledge of channel at the transmitter

� Closed-loop transmit diversity

- Require channel knowledge at the transmitter

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Open-Loop Transmit Diversity

� Most popular scheme is ‘space/time coding’

� Alamouti code (Orthogonal space/time block code)

� 2x1 STBC transmitter

� The decoder can combines receive samples to eliminate all spatial interference and enhance system coverage.

� It is also known in WiMAX as MIMO Matrix A.

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Closed-Loop Transmit Diversity

� Transmitter uses the knowledge of the channel, channel state information (CSI), to effectively use its Nt available channels.

� For example, Transmit Selection Diversity method uses only subset N* best channels at a given time.

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Beamforming

� Use available antenna elements to adjust the strength of the transmitted and received signal based on their direction by choosing appropriate weights for each element.

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Spatial Multiplexing

� With Spatial Multiplexing, also known as MIMO Matrix B, each of the base station transmit antennas sends a different downlink data stream.

� This technique uses multipath to distinguish between the different data streams and theoretically has the potential to double the DL capacity under favorable channel conditions.

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PHY-Layer Data Rate at Various Channel Bandwidths

Assuming

a) 3:1 DL-to-UL bandwidth ratio

b) Frame size 5 ms, 12.5% OFDM guard interval

c) PUSC subcarrier permutation scheme

d) No MIMO

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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Functions of MAC layers in WiMAX

� Segment or concatenate the service data units (SDUs) received from higher layers into the MAC PDU (protocol data units), the basic building block of MAC-layer payload

� Select the appropriate burst profile and power level to be used for the transmission of MAC PDUs

� Retransmission of MAC PDUs that were received erroneously by the receiver when automated repeat request (ARQ) is used

� Provide QoS control and priority handling of MAC PDUs belonging to different data and signaling bearers

� Schedule MAC PDUs over the PHY resources

� Provide security and key management

� Provide support to the higher layers for mobility management

� Provide power-saving mode and idle-mode operation

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MAC layer of WiMAX

Perform all operations that are dependent on the nature of the higher-layer protocol, such as header compression and address mapping.

Performs all the packet operations that are independent of the higher layers, such as fragmentation and concatenation of SDUs into MAC PDUs, transmission of MAC PDUs, QoS control, and ARQ.

Responsible for encryption, authorization, and proper exchange of encryption keys between the BS and the MS.

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Quality of Service (QoS)

CBR = Constant Bit Rate

CIR = Committed Information Rate

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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WiMAX Equipment

� Base Station

BCU – Base Control Unit

BBU – Base Band Unit, RRU – Remote Radio Unit

MSS – Main Subsystem, RSS – Remote Subsystem

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WiMAX Equipment

� Terminal

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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Trial Result

� Coverage Test

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Trial Result

� Coverage Test

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Agenda





� OFDM Technology

� OFDMA




� WiMAX Equipment

� Trial results

� Future of WiMAX

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Forecast of WiMAX users by region 2007-2012

Source: WiMAX Forum® WiMAX™ Technology Forecast (2007-2012)

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Source: WiMAX Forum® WiMAX™ Technology Forecast (2007-2012)

WiMAX user penetration by region 2007 & 2012

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Q&A

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THANK YOU

Documents

Introduction to WiMAX - ku.ac.th · 4 7 Agenda Introduction to Broadband Wireless Overview of WiMAX and Application WiMAX: PHY layer Broadband Wireless Channel OFDM Technology OFDMA