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By: Eng. Mohammed Hassan AbdulMontakem

‫منتدى اكلهندسة اكلكهربائية والكلكترونية‬ DVD4ARAB


Contents            

Broadband Wireless Accesses General Over View Of WiMAX Wimax Versus Wi-Fi 802.16 Frequency bands 802.16 Family of Standards 802.16 Applications and scenarios Components of WiMAX systems 802.16e and data mobility to the current standard System profiles for 2-11 GHZ WiMAX Applications WiMAX Forum WiMAX PHY 2


Wireless Communication

3


LOS Propagation

4


NLOS Propagation

CPE: Customer Premises Equipment 5


LOS & NLOS Operation

6


Coverage Performance Trends

7


Broadband Wireless Accesses (BWA)

ď °

BWA is a point to multipoint system, which is made up of base station and subscriber equipment 8


BWA 

The increased demand on multimedia services led to the need for BWA (Broadband Wireless Access) This led to the appearance of WiMAX technology

Advantages of BWA:

  

Fast connection (several Mbps/user) Relatively cheap (no cable infrastructure) Not limited by location (wireless links)

BWA  Data services 

Wireless Broadband Internet 9


WiMAX Worldwide Interoperability for Microwave Access  IEEE 802.16 standard (dated back to 2003)  Describes PHY and MAC layers  IEEE 802.16-2004  Fixed and Nomadic applications in 2-11 GHz frequency band  Several amendments have followed (IEEE 802.16e/g) 

10


WiMAX Applications 

Private Networks     

Public Networks  

Cellular backhaul Wireless service provider backhaul Education networks (university campus) Public safety (police, fire) Offshore communications (oil rigs) Wireless service provider access network Rural connectivity

Triple Play

11


Triple Play Appearance of VoIP made it possible for Voice over WiMAX  Voice services  Appearance of IPTV made it possible for TV over WiMAX  Video services  Integrated network: Data, Voice and Video  + Mobility  WiMAX becomes a strong candidate for future mobile networks 

12


Why do we need broadband wireless access? 

Fill the gap between high data rate wireless LAN and very tight Bandwidth mobile cellular networks. Wireless alternative to cable and DSL for last-mile broadband access  

Developing countries Rural areas

Provide high-speed mobile data and telecommunications services

13


General Overview Of WiMAX 

WiMAX (Worldwide Interoperability for Microwave Access) is the trade name for a group of wireless technologies that emerged from the IEEE 802.16 Wireless MAN (Wireless Metropolitan Area Network) family of standards. A key facet of the IEEE standards process is that it is limited to the Physical and MAC (Medium Access Control) layers and that it does nothing to ensure interoperability, RF constraints, or minimum performance levels The WiMAX Forum was created in 2001 to fulfill a much needed requirement and to help ensure compatibility and interoperability across multiple vendors. .

14


General Overview Of WiMAX (Cont.) ď °

Filling the gap between Wireless LANs and wide area networks, WiMAX-compliant systems will provide a costeffective fixed wireless alternative to conventional wire-line DSL and cable in areas where those technologies are readily available ,and in areas beyond the reach of DSL and cable.

ď °

The ongoing evolution of IEEE 802.16 will expand the standard to address mobile applications thus enabling broadband access directly to WiMAX-enabled portable devices.

15


General Over View Of WiMAX (Cont.) 

WiMAX technology advantages : 

The high speed of broadband service

Wireless rather than wired access, so it would be a lot less expensive than cable or DSL and much easier to extend to suburban and rural areas

Broad coverage like the cellular mobile network.

16


General Overview Of WiMAX (Cont.) 

To meet the requirements of different types of access, two versions of WiMAX have been defined. 

The first is based on IEEE 802.16-2004 and is optimized for fixed and nomadic access. The initial WiMAX Forum CERTIFIED products will be based on this version of WiMAX. The second version is designed to support portability and mobility, and will be based on the IEEE 802.16e amendment to the standard

17


Mobile WiMAX Salient Features

18


WiMAX Potential Applications     

Connecting Wi-Fi hotspots with each other and to other parts of the Internet. Providing a wireless alternative to cable and DSL for last mile broadband access. Providing high-speed data and telecommunications services. Providing a diverse source of Internet connectivity as part of a business continuity plan. Providing nomadic connectivity.

19


WiMAX applications in 2005 Fixed Services IEEE 802.16-2004 WiFi

Mobile PC/PAD Business services

WiMAX Base Station

Nomadic PC Residential Fixed DSL Access

NB or BTS

WiFi-Hotspot Feeding

2G/3G Feeding

Airport

Campus

Hot Zones20


WiMAX applications starting from 2006-2007 Nomadic, Solutions for Laptops WiFi

Mobile PC/PAD Business, SME, SOHO Access

WiMAX Base Station

IEEE 802.16-2004 & IEEE 802.16e

Nomadic PC Residential Fixed WDSL BB Access

NB or BTS

WiFi-Hotspot Feeding

2G/3G Feeding

Airport

Campus

Hot Zones21


WiMAX applications in 2007-2008 Fully Mobile, Integrated Solutions in Laptops and PDA IEEE 802.16e WiFi

Mobile PC/PDA Business, SME, SOHO Access

WiMAX Base Station

Portable PC Residential Fixed WDSL BB Access

NB or BTS

WiFi-Hotspot Feeding

2G/3G Feeding

Airport

Campus

Hot Zones22


WiMAX & Other Broadband Wireless Technologies There are wireless technologies other than WiMAX, each has its Pros and Cons where the tradeoff is between MOBILITY and SPEED.

23


WiMAX Positioning: Wireless Technology Comparison WiMAX Network Simplicity

Large Coverage

WiFi Broad Band

Full Mobility

Security

QoS

3G /HSDPA 24


WiMAX Speed

General packet Radio Services Enhanced Data Rates for GSM Evolution Evolution Data optimized (Only)

25


IEEE Standards

26


WiMax (802.16x)Standards Genealogy

27


802.16 Standards Evolution

28


802.16 General Characteristics 

Wireless MAN operation in 2-11 GHz spectrum Non-line-of-sight (NLOS) operation designed to address multi-path Eliminates need for directional LOS propagation

Greater range and higher data rates Multiple options for:

 

  

Duplexing modes:  

Flexible channel bandwidths from 1.75 to 20MHz Flexible frame lengths: frame sizes ranging from 2.5 to 20ms Flexible channel coding & FEC

Time Division Duplex (TDD) and Frequency Division Duplex (FDD)

Support for multiple antenna technology   

Adaptive and smart antennas (AAS) TX diversity Beamforming and spatial multiplexing (MIMO)

29


802.16 General Characteristics (Cont)       

Point-to-multipoint topology, with mesh extensions Protocol independent supporting ATM and packet-based protocols True Quality of Service (QoS) supports multiple services simultaneously, with different QoS priorities Scalable system capacity allows more efficient use of available spectrum than other wireless technologies Supports both licensed and licensed-exempt frequencies Supports a variety of services such as IP, voice over IP and streaming video Bandwidth on demand (frame by frame)

30


802.16 Family of Standards 

IEEE 802.16a  It was approved in January 2003  It covers frequency band between 2 GHz and 11GHz,  Its lower frequencies make non-line of sight a possibility  Total data rate can be up to 100 Mb/s in each 20MHz channel.  It has up to 30 miles (48.28 Km) of range with a typical cell radius of 4-6 miles.  It provides an ideal wireless backhaul technology to connect 802.11 wireless LANs and commercial hotspots with the Internet.  It will be mostly used for small businesses, residential users and for backhaul or hotspot  The most common 802.16 configurations consist of base station mounted on building or tower that communicates on a point to multi-point basis with subscriber station located in businesses and homes. 31


802.16 Family of Standards (Cont.) 

802.16b 

802.16c  

Aims at the needs of license-exempt applications around 5-6 GHz Approved in December 2002 by the IEEE Standards Board. The aim was to develop 10-66 GHz system profiles to aid interoperability specifications for Line-of-sight broadband wireless access. Its peak (shared) data rate 70Mbits/s, with range up to 50km.

802.16d  

It was approve by the IEEE-SA Standards Board on 24 June 2004 The aim is to implement system profiles for 802.16("Air Interface for Fixed Broadband Wireless Access Systems") as modified by Standards IEEE 802.16a and 802.16c. It will be published as IEEE Standard 802.16-2004, replacing IEEE Standards 802.16-2001, 802.16c-2002, and 802.16a-2003.

32


802.16 Family of Standards (Cont.) 

802.16-2004  

It was approved on 23rd of September 2004 by the IEEE –SA Standards Board, Its aim is to provide a list of errors with their corrections to the IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems.

802.16/Confermance04   

It was approved on 25th of March 2004 It is developed by the IEEE 802.16's Task Group C under IEEE PAR P802.16/Conformance04. Its draft is to perform a new research for IEEE 802.16 - Part 4: Protocol Implementation Conformance Statement (PICS) for Frequencies below 11 GHz.

33


802.16 Family of Standards (Cont.) 

IEEE 802.16e (Mobile Wireless MAN)  In December, 2005 the IEEE ratified the 802.16e amendment to the 802.16 standard.  It covers "Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation.  The IEEE802.16e introduces nomadic capabilities which allow users to connect to a Wireless Internet Service Provider (WISP) when they travel outside their home or business, or go to another city that also has a WISP  It is targeted at mobile users, who will be able to keep their connection while moving or driving .

34


802.16e and data mobility to the current standard (Cont.) 

Some of the salient features supported by Mobile WiMAX are: 

High Data Rates: The inclusion of MIMO antenna techniques along with flexible sub-channelization schemes, Advanced Coding and Modulation all enable the Mobile WiMAX technology to support peak DL data rates up to 63 Mbps per sector and peak UL data rates up to 28 Mbps per sector in a 10 MHz channel.

Quality of Service (QoS): The fundamental premise of the IEEE 802.16 MAC architecture is QoS.

Scalability: Mobile WiMAX technology is designed to be able to scale to work in different channelizations from 1.25 to 20 MHz to comply with varied worldwide requirements as efforts proceed to achieve spectrum harmonization in the longer term.

35


802.16e and data mobility to the current standard (Cont.) ď °

Some of the salient features supported by Mobile WiMAX are: (Cont.) ď Ž

Security: Mobile WiMAX supports best in class security features by

adopting the best technologies available today. Support exists for mutual device/user authentication, flexible key management protocol, strong traffic encryption, control and management plane message protection and security protocol optimizations for fast handovers. ď Ž

Mobility: Mobile WiMAX supports optimized handover schemes with latencies less than 50 milliseconds to ensure real-time applications such as VoIP perform without service degradation.

36


WiMAX 

Fixed WiMAX   

Specified in IEEE Std 802.16 -2004. Wide range of frequencies from 2.5,2.4,3.5,5.8 GHz. Radio interface based on orthogonal frequency division multiplexing (OFDM). Enables data rates theoretically up to 37.5Mbit/s with 10MHz channel bandwidth, reality closer to 2Mbit/s over 5−10 km radius.

Mobile WiMAX  

 

Specified in IEEE Std 802.16e. operates in the 3.5,5.8 GHz range using channel bandwidth ranging from 1.25 to 10 MHz. Radio interface based on scalable OFDMA. Data rates theoretically up to 12-15Mbit/s at 10 MHz.

37


WiMAX Technology 

 

WiMAX, a single technology can deliver fixed, portable & mobile services with scalable bandwidths & higher data rates WiMAX is a well-supported, cost-effective, standardsbased, flexible, broadband technology that is ready to deliver significant benefits for:  

Operators in a wide range of markets (enterprise, consumer, emerging, public service) Over a wide range of geographies and demographics (urban, suburban, rural)

Advantages of WiMAX      

Large coverage Higher capacity Scalable Faster to implement Performs well in high delay spread environments Supports multiple antenna technologies 38


WiMAX Coverage Range

39


OFDM vs CDMA 

OFDMA+   

Slow and fast fading immunity Maximum Data Rate Frequency selective fading immunity

CDMA+  

Seamless soft-handoff capability Easy network planning and re-configuration

40


WiMAX Worldwide Penetration

41


WiMax Standards 802.16

802.16-2004

802.16e-2005

Date Completed

December 2001

June 2004

December 2005

Spectrum

10-66 GHz

< 11 GHz

< 6 GHz

Operation

LOS

LOS & Non-LOS

Non-LOS

Bit Rate

32-134 Mbps in 28 MHZ channel BW

Up to 75 Mbps in 20 MHz channel BW

Up to 15 Mbps in 5MHz channel BW

Cell Radius

Over 10Km

7-10 km

2-5Km

Mobility

Fixed

Fixed

Mobile (up to 125Km/h)

Channel BW

20,25 and 28 MHZ

Scalable 1.5 to 20MHz

Scalable 1.25 to 20 MHz

Modulation

Single carrier modulation

OFDM 256/OFDMA 2K

Scalable OFDMA (1282K) 42


WiMAX Vs Wi-Fi 

WiMAX is targeted for longer range Metropolitan Area (indoor & outdoor) Different from Wi-Fi, which is primarily targeted for Local Area Network (indoor) applications.

The mail distinction between WiFi and WiMAX is speed and coverage distances: 

WiFi has a typical bandwidth of 2MBps whereas WiMAX can have a bandwidth of up to 75MBps.

The coverage distances also differ to a great extent. A WiFi hotspot typically covers a few hundred feet radius (fraction of a kilometer) whereas a WiMAX can practically cover up to a distance of 10 kilometers.

43


802.16 Frequency bands (Cont.)

44


802.16 Frequency bands (Cont.) 

Licensed Bands  The licensed spectrum is found at 2.3GHz, 2.5GHz and 3.5GHz, with the latter two frequency bands currently receiving the most attention. Advantages of Licensed Bands  The greatest advantage of having licensed spectrum is that the licensee has exclusive use of the spectrum.  It is protected from outside interference while competitors can only enter the market if they also own or lease spectrum. Disadvantages Licensed Bands  Licensed spectrum comes at a potentially high price

45


802.16 Frequency bands (Cont.) 

Unlicensed Bands 

In most markets, the unlicensed spectrum that could be used for WiMAX is 2.4GHz and 5.8GHz.

Advantages of Unlicensed Bands 

Since the spectrum is unlicensed, the barrier to entry is low, thus making it easier for a potential operator to begin offering services using the spectrum.

46


802.16 Frequency bands (Cont.) 

Disadvantages of Unlicensed Bands  Interference : unlicensed spectrum can be used by several different RF systems  Increased Competition : Operators who use unlicensed spectrum have to assume that another operator could easily enter the market using the very same spectrum.  Limited Power :government regulators typically limit the amount of power than can be transmitted. especially at 5.8GHz where the higher power could offset the propagation loss associated with spectrum in higher frequencies.  Availability :While the 2.4GHz spectrum is universally available, the 5.8GHz spectrum is not currently available in a number of countries.

47


Example of WiMAX System Components

48


Base station unit        

A WiMAX base station consists of indoor electronics and a WiMAX tower, base station can cover up to 10 km or 6 miles radius. Each base station provides wireless coverage over an area called a cell. Any wireless node within the coverage area would be able to access the Internet

49


Subscriber Units There  

are two versions:

Indoor SU. Outdoor SU.

Indoor

units are comparable in size to a cable modem or DSL modem. Outdoor units are roughly the size of a laptop PC, and their installation is comparable to a residential satellite dish.  There is an increasing focus on portable units including handsets and PC peripherals.

Outdoor subscriber unit

Indoor subscriber unit 50


Outdoor CPE

51


Practical System Components

52


Practical WiMAX Systems

53


802.16 Reference Model

54


IEEE 802.16 Protocol Stack

(IEEE 802.16 is a collection of standards, not one single interoperable standard) 55


Physical Layer It

is 802.16e uses scalable orthogonal frequency-division multiple access (SOFDMA). Also bring Multiple Antenna Support through Multiple-input multiple-output communications (MIMO). This brings potential benefits in coverage:   

power consumption frequency re-use. Bandwidth efficiency.

56


Design Options for WiMAX Networks 

The various IEEE 802.16 standards offer a variety of fundamentally different design options: 

Multiple physical-layer choices:

Single-carrier-based physical layer.  

OFDM-based physical layer . OFDMA based physical layer.

Multiple choices for :   

MAC architecture. Duplexing (TDD,FDD). Frequency band of operation.  10-66GHZ  2-11GHZ

(FOR LOS Operation). (FOR NLOS Operation).

So, it suit a variety of applications and deployment scenarios and offer a plethora of design choices for system developers.

57


Design Options for WiMAX Networks (Cont.) 

WiMAX equipment are certified for interoperability against a particular certification profile.

Design options   

  

3.5GHz systems. Operating over a 3.5MHz channel. Use the fixed system profile based on the IEEE 802.16-2004 OFDM physical layer . Point-to-multipoint MAC. One uses frequency division duplexing (FDD). The other uses time division duplexing (TDD).

58


WiMAX Physical Layer


OFDM Spectral Overlap

Conventional Frequency Division Multiplex (FDM) Multi-carrier Modulation Technique

Saving of the bandwidth

Orthogonal Frequency Division Multiplex (OFDM) Multi-carrier Modulation Technique

60


OFDM: Orthogonal Frequency Division Multiplexing   

Is a digital multi-carrier modulation scheme. Uses a large number of closely spaced orthogonal sub-carriers where it manages the inter symbol interference. OFDM signals are generated and detected using the Fast Fourier transform algorithm.

 Orthogonality  

Principle:

In OFDM the sub-carrier pulse used for transmission is chosen to be rectangular. According to the theorems of the Fourier Transform, the rectangular pulse shape will lead to sinc(x) type of spectrum of the sub-carrier as shown:

Pulse Fourier transform 61


Thus, for N sub-carriers we’ll have the following spectrum

 

The spectrums of the sub-carriers are not separated but overlap. The information transmitted over the subcarriers can still be separated as the nulls in each sub-carrier’s spectrum land at the center of all other sub-carriers. 62


802.16 PHY Layer Characteristics 

Physical layers (SC, OFDM, OFDMA)  OFDMA is the focus today  Non-line of sight operation Multiple options for:  Channel bandwidths  Duplexing modes (TDD, FDD)  Channel coding  Cyclic prefixes Link adaptation  Adaptive modulation and coding per subscriber  Trade off capacity and robustness in real time

63


WiMAX Physical Layer Main Block Diagram Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 64


Randomizer Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 65


Randomizer â&#x2014;?

Types of Randomizers: -

Multiplicative (self-synchronizing) scramblers Additive Synchronous Randomizer (modulo -2 addition)

66


Benefits of Randomization ● ● ●

Avoid long sequences of bits of the same sense (i.e. increase entropy) It facilitates the work of a timing recovery It eliminates the dependence of a signal's power spectrum upon the actual transmitted data (selective scrambling to avoid PAPR)

67


Benefits of Randomization â&#x2014;?

Introduce the ability to distinguish signals by properly initializing the seed of the randomizer at the beginning of each burst (key generation ) -

Unique to a BS Unique to a connection (BS-SS) Uncorrelated from frame to frame

68


Convolutional Coder Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 69


½ Rate Convolutional Coder

● ●

IEEE 802.16-2004 specifications: Constraint length = 7 Generator polynomials codes = (171)oct =(1 1 1 1 0 0 1) for o/p X (133)oct =(1 0 1 1 0 1 1) for o/p Y Treated as Finite State Machine (FSM) Illustrated using state or Trellis diagrams

70


Trellis Structure

71


Puncturer Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 72


Puncturer â&#x2014;?

Puncturing is a very useful technique to generate additional rates from a single Convolutional code

â&#x2014;?

The basic idea behind Puncturing is not to transmit some of the bits output by the Convolutional encoder

73


Puncturer ●

Code rates :

Puncturing rules: -

1  Transmitted Bit 0  Removed Bit

74


Interleaver Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 75


Interleaving   

Block Interleaving Applied to each FEC block Two step permutation • 1st step permutation – Mapping adjacent coded bits onto nonadjacent subcarriers • 2nd step permutation – Mapping adjacent coded bits alternatively onto less or more significant constellation bits

76


Interleaving (2) Error isolated

De-interleaving Interleaving

Error Transmission

77


Interleaver Types ●

Block Interleaver

Convolutional Interleaver

Helical Interleaver

The IEEE 802.16d standard uses the block Interleaver

78


Digital Modulator Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 79


Modulation Techniques ●

BPSK

QPSK

16-QAM

64-QAM 80


Adaptive Modulation and Coding in WiMAX 

WiMAX supports a variety of modulation and coding schemes and allows for the scheme to change on a burst-by-burst basis per link, depending on channel conditions. The base station scheduler can take into account the channel quality of each user’s uplink and downlink and assign a modulation and coding scheme that maximizes the throughput for the available signal-to-noise ratio.

81


BPSK MODEM ●

Constellation Diagram

Mapping Table

Input

-1

0

I-Out

1

Output

0

-1

1

1 82


QPSK MODEM ●

Mapping Table Input (b1b0)

Output

00

-1-j

01

-1+j

10

1-j

11

1+j 83


QPSK MODEM â&#x2014;?

Constellation Diagram Q-out 01

.

j

-1 00

.

. 11 1

-j

I-out

. 10 84


Modulation Schemes 

Quadrature amplitude modulation (QAM) a combination of PSK and ASK (two degrees of freedom).  

16-QAM (4 bits/symbol-Gray coded). 64-QAM (6 bits/symbol-Gray coded).

85


Threshold based on decision regions for 16-QAM

86


IFFT/FFT Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 87


IFFT/FFT Growth ejw0t

+

g(t)

ejw1t g(t)

ejwN-1t g(t)

High speed data

Serial To Parallel

IFFT

Parallel To Serial 88


Preamble Insertion Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 89


Preamble CP

64

64

64

64

CP + 256   

Preamble is used for channel estimation One preamble is used in simulation The preamble is constructed from a predefined pattern in the standard

90


Cyclic Prefix Preamble Insertion

Data

Randomizer

Shortened Reed Solomon Encoder

Convolutional Encoder

Puncturer

Interleaver

Digital Modulator

IFFT

Add Cyclic Prefix AWGN

Multi-path Channel Remove Cyclic Prefix

De-Randomizer

Data

Shortened Reed Solomon Decoder

Viterbi Decoder

De-Puncturer

De-Interleaver

Digital De-Modulator

FFT

Channel Estimator (LS/MMSE) 91


Cyclic Prefix (1) Cyclic prefix â&#x20AC;˘Extension before the time domain symbol â&#x20AC;˘Collect multi-path and maintain orthogonality

92


Cyclic Prefix (2)

93


Cyclic Prefix

94


Cyclic Prefix

CP

CP

CP

CP

CP

Preamble

OFDM symb.

OFDM symb.

OFDM symb.

OFDM symb.

CP + 256

95


WiMAX system

96


Wimax presentation