part 3 - wimax air interface

8/11/2019 Part 3 - WiMAX Air Interface

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WiMAX Air Interface

2007 Rohde & Schwarz

1

WiMAX Air Interface

Heinz MELLEIN, R&S

Technology Management Systems & Projects

[email protected]


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List of content

WiMAX TDD Reference Signal Maps

OFDMA key parameters

Permutation zones

Map information

PHY

MAC

MIMO


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c+9

c+8

c+7

c+6

c+5

c+4

c+2

c+1

c

k+8k+7k+6k+5k+4k+3k+2k+1k

OFDM(A) signal description

Number

of subchannels

Number of OFDM

symbols

Dataregion

Burst

symbol

offset

sub channeloffset

DL PUSC SLOT:

Minimum possible data unit:

2 symbols x 1 subchannel

= 48 symbols

= 96 Bits (QPSK)

= 192 Bits (16QAM)= 288 Bits (64QAM)

symbol

index

subchannel index

Reminder: 1 subchannel = 24 not necessarily adjacent frequency carriers


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OFDMA frequency domain sub channelisation

f

ffc

Sub

channel


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MRCT default Frame structure: normal MAP


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OFDM key parameters BW = Nominal channel bandwidth

Nused= No of used sub-carriers

NFFT= Smallest power of 2 greater than Nused

Sampling frequency Fs

Sub-carrier spacing = Fs/NFFT (frequency bin)

Useful symbol time Tb= 1/

CP time Tg= G

@

Tb

OFDMA symbol time Ts= Tb+ Tg= (1+G) @Tb

Sampling time Tb/NFFT


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Multiple permutation zones

1 TDD frame


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OFDMA sub carrier allocation modes for PHY layer

scalability

AdjacentAdjacentsubsubcarriercarrierpermutationpermutation

ForForfixedfixed((ororlowlowmobilitymobility))channelschannels

DistributedDistributedsubsubcarriercarrierpermutationpermutation

For mobile (For mobile (multipathmultipath))channelschannels

DistributedDistributedsubsubcarriercarrierpermutationspermutations FUSC (FUSC (FullyFullyUsedUsedSubSubchannelisationchannelisation) (DL) (DLonlyonly))

AllAllsubsubchannelschannelsavailableavailable

SubSubcarrierscarriersdistributeddistributedtotosubsubchannelschannelsbybypermutationpermutationmechanismmechanism

MinimiseMinimisethetheprobabiliyprobabiliyofofsubsubcarriercarrierclashesclashes

MaximiseMaximisefrequencyfrequencydiversitydiversitytotominimiseminimisefadingfadingimpactimpact

PUSC (PUSC (PartiallyPartiallyUsedUsedSubSubchannelisationchannelisation))


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Partially Used Subchannelisation (PUSC) Distributed permutation type

First divide available subcarriers into subchannels

Allocate pilots within each subchannel

Each subchannel contains ist own set of pilots

Pilot permutation is designed to

minimise the risk of physical subcarrier hits between adjacent cells/sectors

maximise frequency diversity to minimise degradation due to fading

DL PUSC

Cluster structure (14 adjacent subcarriers per cluster incl. 2 pilots) Subchannels are assigned to 3 segments(e.g. representing 3 sectors of the same cell)

UL PUSC

Tile structure (3 symbols x 4 subcarriers incl. 4 pilots)


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Downlink PUSC symbol structure

6 (3)30 (15)60 (30)120 (60)No of clusters Ncluster(subchannels)

723607201440No of data subcarriers Ndata

Scalable OFDMA (Rel. 16e)Rel. 2004

642565121024DC subcarrier index

1260120240No of pilot subcarriers Npilot

844208401680No of used subcarriers Nused (excl. DC)

22/2146/4592/91184/183Guard subcarriers (Left/Right)

128 FFT(1.25 MHz)

512 FFT(5 MHz)

1024 FFT(10 MHz)

2048 FFT(20 MHz)

DL PUSC slot = 1 subchannel x 2 OFDMA symbols

Cluster structure: 14 adjacent subcarriers incl. 2 pilots

k k+1

Pilot

Data

Symbol

index

Subcarrier

index


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Uplink PUSC symbol structure

Scalable OFDMA (Rel. 16e)Rel. 2004

642565121024DC subcarrier index

24102210420No of tiles Ntiles

4173570No of subchannels Nsubchannels

964088401680No of used subcarriers Nused (excl. DC)


128 FFT(1.25 MHz)

512 FFT(5 MHz)

1024 FFT(10 MHz)

2048 FFT(20 MHz)

Tile structure:

(3 OFDM symbols) x (4 subcarriers)

No of tiles per subchannel: 6

Pilot

Data

1 slot = 1 subchannel x 3 OFDMA symbolsSymbol

index

Subcarrier

index


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Subchannel group allocation

N/A526 .. 295

2420 .. 254N/A316 .. 193

1210 .. 152

N/A16 .. 91

001280 .. 501024N/A552 .. 595

10 .. 14440 .. 514

N/A332 .. 393

5 .. 9220 .. 312

N/A112 .. 191

0 .. 405120 .. 1102048

Subchannel

range

Subchannel

groupFFT size

Subchannel

range

Subchannel

groupFFT size

Profile 1A


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WiMAX PHY signal processing chain

Randomisation

(energy dispersal) FEC

Interleaving

Symbol mapping

Space Time Coding

Beam Forming

MIMO encoding

Data from

MAC

Subchannelisation

Pilot Insertion IFFT CP

RF

frontend

SubchannelisationPilot Insertion

IFFT CPRF

frontend

SISOOuter

Coding

Inter

leaving

Inner

Coding

CP = Cyclic Prefix


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Mobile WiMAX FEC channel coding schemes

HARQ Incremental Redundancy

OPTIONAL

CTC:

Convolutional Turbo CodeHARQ chase combining

OPTIONAL

CRC:

Cyclic Redundancy Check (Block code)

OPTIONALLDPC:

Low Density Parity Check Code

OPTIONALBTC:

Block Turbo Code

Coding rates: , 2/3, , 5/6

MANDATORY

RS-CC / CC:

Concatenated Reed-Solomon convolutional code

Mobile WiMAX Application


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ARQ and HARQ


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Example: DL Frame Prefix Processing

24 Bits of Data containing DL Frame Prefix Information Elements

Duplicate to 48 Bits (minimum FEC block length)

CC 1:2 coding results in 96 Bits

Repetition Factor 4 results in 384 Bits

QPSK Modulation creates 192 Modulation OFDM Symbols

Map onto FCH that spreads over 4 DL PUSC slots

(1 slot = 2 OFDM Symbols x 1 subchannel a 24 physical channels)

2 OFDM symbols x 4 x 24 subcarriers = 192 OFDM Symbols


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OFDMA DLFP Format and FCH mapping

Segment 0

Segment 1

OFDM symbol index

Segment 2

FCH

FCH

FCH

SubchannelIndex

(1

subchannel=

24

subcarriers

)

DL subframe

FEC Input Block (48 Bits)

Convolutional Coder

Bit Interleaver

96 Bit block

4 X Repeater

96 Bit block

QPSK Modulator

384 Bit Sequence

24 Bit DLFP 24 Bit DLFP

Slot 0

Slot 1

Slot 2

Slot 3

48 Symbols

per slot

DL_Frame_Prefix_Format (IEEE 802.16e-2005)

Used subchannel bitmapBit#0 enables subchannel group #0

Bit#5 enables subchannel group #5

RESERVED

Repetition Coding Indication for DL-MAP{ 0, 2, 4, 6 }

Coding Indication for DL-MAP{ CC, BTC, CTC, ZTCC, LDPC }

DL-MAP length(max. 255)

RESERVED

6

Bits

8Bits

3Bits

2

1

4


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OFDMA FCH: DL frame prefix (FP) (excerpt)

Indicates length of DL map message in terms

of slots

8 bitsDL MAP length

000b = CC encoding used on DL-MAP

001b = BTC encoding

010b = CTC encoding

011b = ZT CC encoding

100b = CC encoding with interleaver

101b = LDPC encoding

3 bitsCoding indication

Flag indicating change of ranging regions1 bitRanging change indication

Bit #0: subchannel group 0






6 bitsUsed subchannel bitmap

RemarksSize/RangeParameter

CC = Convolutional Code

BTC = Block Turbo Coding

CTC = Convolutional Turbo Coding

ZT = Zero Tailing

LDPC = Low Density Parity Check


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DL-MAP management message

DL_MAP MAC Management

Management

Message Type

OFDMA PHY SYNC field

Frame duration codeFrame Number ( mod 224)

DCD count

Base Station Identifier

Number of OFDMA symbols inthe dowlink subframe

DL-MAP_IE #1

describes burst #1

DL-MAP_IE #n

DL_MAP_IE

DIUCDownlink Interval Usage Code

CID(MAC) Connection Identifier

OFDMA Symbol Offset

Subchannel Offset

Boosting

Number of OFDMA symbols

Number of subchannels

Repetition Coding Indication

SymbolOffset

Subchannelindex

0

Subchannel

Offset

Number

of symbols

Numbero

f

subchanne

ls

OFDMA symbol index


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OFDMA DL-MAP Format and mapping

SubchannelIndex

(1

subchannel=

24

subcarrier

s)

DL subframe

Min FEC block size

Padding

FEC (rate r)(as indicated in FCH)

j Bit block

Bit Interleaver

j / r Bit block

Repeater (R)(as indicated in FCH)

j / r Bit block

2N-QAM Modulator

R x j / r Bit sequence

i Bits DL_MAP message

Slot 4

Slot 5

...Slot n

R x j / r / N symbols:

48 symbols per slot

Number of required DL-MAP slots:

n = R x j / r / N / 48

DL_MAP MAC Management

Management

Message Type

OFDMA PHY SYNC fieldFrame duration code

Frame Number ( mod 224)

DCD count

Base Station Identifier

Number of OFDMA symbols in

the dowlink subframe

DL-MAP_IE #1

describes burst #1

DL-MAP_IE #n


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UL-MAP management message

Reserved Bits; Set to 0

UL_MAP MAC Management

Management

Message Type

UCD count

UL allocation start time

[physical slots 4/Fs]

Number of OFDMA symbols in

the uplink subframe

UL-MAP_IE #1describes burst #1

UL-MAP_IE #n

UL_MAP_IE: Ranging zone

UIUC = 12Uplink Interval Usage Code


OFDMA Symbol Offset

Subchannel Offset

Number of OFDMA symbols

Number of subchannels

Ranging method

(initial, periodic)

UL_MAP_IE: Burst allocation

UIUC = 1..10Uplink Interval Usage Code


Duration

(number of slots!)

Repetition coding

(0,2,4,6)


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MRCT default Frame structure: normal MAP

Data


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Downlink Preamble structure

36143284568No of pilot subcarriers per set

(size of modulating PN series)


128 FFT512 FFT1024 FFT2048 FFT

3 sets of preamble carriers are defined, i.e. 1 set per segment.

PreambleCarrierSet(n) = n + 3k ; n = {0,1,2}; k = {0 .. 567} Note: DC carrier not used (n=0)

0xADBC1B844

Map 1B -1 and 0B +1

1234

PN series (e.g. FFT-128)Segment 0 .. 2IDcell 0.. 31Index 0 .. 113

0 3 6 9 1695 1698 1701

38 PN series per segment.


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Cell searchSpectral power detection

C

Signal Bandwidth

(Carrier spacing: FFT size)

C

Position estimate of pilots(3 optionsB Segment number, FCH position)

C

Preamble set search(38 possible PN series)

CPN series correlation process

(Knowledge: BPSK)

C

IDCellDefines subcarrier permutation for first PUSC zone:

Used as DL_PermBase

Segment 1

Preamble set 1

PN index 36

IDCell 4

Segment 2

Preamble set 2

PN index 76

IDCell 12

Segment 0

Preamble set 0

PN 9

IDCell 9


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WIMAX Protocol Architecture

PHY

MAC-CSConvergence Sublayer*:ATM and packet

MAC-CPSCommon Part Sublayer

MAC-SSSecurity Sublayer

MAC SAP

PHY SAP

CS SAP

Higher layers:

ATMIEEE 802.3 (Ethernet)

ISO/IEC 8802-3 (CSMA/CD)

*Vendor specific MAC-CS applicable to

support vendor specific higher layers

SAP = Service Access Point

Classification of higher layer data (e.g. for QoS purposes)

Payload header suppression (PHS) 16 Bit CID assignment (output of classification procedure)

Layer for IP connection

Defines multiple access: PtP, multicast, broadcast

Duplexing: FDD, TDD Framing, fragementation, packing, etc.

Issue/Analyse MAC management messages

Hyphering


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WiMAX MAC features

MAC provides intelligence to PHY

Designed for point-to-multipoint communication

Supporting continuous and bursty traffic

Connection oriented: 16 Bit CID (connection identifier)

Independant handling of downlink and uplink CIDs

Dynamic bandwidth allocation

48 Bit MAC address = Equipment identifier


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WiMAX PMP connection overview

MandatoryMandatorymanagementmanagementconnectionsconnectionsat SSat SSinitialisationinitialisation

3 different3 differentlevelslevelsofofQoSQoSforfor managementmanagementtraffictrafficPMP = Point to Multipoint


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MAC connection types

Basic CID: 0x0001 m

Primary Management CID: m+1 2m

BSBase

Station

SS

(MS)Subscriber

(Mobile)

Station

unique

MAC

address48 bit

unique

MAC

address48 bit

according to

IEEE 802-2001

according to

IEEE 802-2001

Transport CID: 2m+1 0xFEFE

Initial ranging CID: 0x0000

AAS initial Ranging CID: 0xFEFF

Multicast Polling CID: 0xFF00 0xFFFC

Broadcast CID: 0xFFFF

Padding CID: 0xFFFE

Fragmentable Broadcast CID: 0xFFFD

Secondary Management CID: 2m+1 0xFEFE


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INITIAL SS REGISTERING

BROADCAST: FP, UCD, DCD, DL-MAP, UL-MAP

RNG-REQRNG-RSP

REG-REQPKM-REQ

REG-RESP

PKM-RSP

BASIC MANAGEMENT

PRIMARY MANAGEMENT

Description of downlink and uplink

Ranging to determine power and burst profile changes

Registration and Privacy management

Own CID

for eachconnection!

REG = Registry

PKM = Private Key Management aquivalent to SIM cards


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SERVICE FLOW HANDLING

CREATE SERVICE FLOW: DSA-REQ : DSA-RSP : DSA-ACK

CHANGE SERVICE FLOW: DSC-REQ : DSC-RSP : DSC-ACK

DELETE SERVICE FLOW: DSD-REQ : DSD-RSP

BASIC MANAGEMENTRNG-RSP RNG-REQ

BROADCAST: FP, UCD, DCD, DL-MAP, UL-MAP

DSA = Dedicated Service Access


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Default Service flow setup

BS DDD DCD (Downlink Channel Descriptor, CID 0xFFFF) DDDDE SS

BS DDD UCD (Uplink Channel Descriptor, CID 0xFFFF) DDDDDDE SS

BS FDDDDDDD RNG-REQ (Ranging Request, CID 0x0000) DDDDDDD SSBS DDDDDDDD RNG-RSP (Ranging Response, CID 0x0000) DDDDDDDE SS

BS FDDDDDDDDD SBC-REQ (SS Basic Capability Request) DDDDDD SS

BS DDDDDDDDDD SBC-RSP (SS Basic Capability Response) DDDDDE SS

BS FDDDDDDDDDD REG-REQ (Registration Request) DDDDDDDDDDD SS

BS DDDDDDDDDDD REG-RSP (Registration Response) DDDDDDDDDDE SSBS DDDDD DSA-REQ (Dynamic Service Addition Request) DDDDDE SS

BS FDDDD DSA-RSP (Dynamic Service Addition Response) DDDDDD SS

BS D DSA-ACK (Dynamic Service Addition Acknowledgement) DE SS

BS DDD REP-REQ (Channel Measurement Report Request) DDDDDE SS

BS FDDDD REP-RSP (Channel Measurement Report Response) DDDD SS


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MAC Formats: Generic MAC Header(GMH)

Generic

MAC header

PAYLOAD

(optional)

CRC

(optional)

HT EC Type (6)

LEN LSB (8)

CID LSB (8)

CID MSB (8)

HCS (8)

CI Rsv LEN MSB

EK

S

(2)

CI CRC Indicator

CID Connection Identifier (16 Bits)

EC Encryption Control

EKS Encryption Key Sequence

HCS Header Check Sequence

(for header protection)HT Header Type

LEN Length (bytes) of PDU

Type subheader, payload indicator

ESF Extended subheader field (16e)

Rsv ReservedCRC Cyclic Redundancy Check

(for payload protection)

ESF

16e

16e: Additional subheader types introduced (extended subheaders) incl. appropriate indicator bit ESF

MAC PDU (Protocol Data Unit) of length LEN bytes

Rsv


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MIMO and friends

SISO

SIMO1xMM

ISO

Nx1

Single/MultipleOutput

Transm

itter

1

N Single/MultipleOutput

Recei

ver

1

M

MIMONxM


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WiMAX types of MIMO

STBC Space Time Block Coding Referred to as Matrix A in IEEE 802.16e-2005

Same data is space-time coded and transmitted through different antennas

Impoving downlink SNR and increasing coverage areas

Invented by Mr. Alamouti

SM Spatial Multiplexing Referred to as Matrix B in IEEE 802.16e-2005 Delivers parallel data streams on different antennas

Increases downlink throughput

Uplink collaborative MIMO link Two MS transmit collaboratively on the same uplink subchannel

Increasing uplink throughput without need for mulitple power PA in MS devices


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MISO: STBC according to Alamouti(increase performance, i.e. coverage)

TX

Ant 1

TX

Ant 2

Time

RX

Ant

h1

h2

n

r2*

r1

HH

de2

de1

Estimates

Space

Time

Space

-d2

*

d1

*

d1

d2

de

Space-Time-Block

LO

( ) ' 21 nIhhnHdHHrHd HHHe rr

r

r

r

++=+==

( )( )

2221

*

211

*

22

1121*

221*

11

'

'

ndhhrhrhd

ndhhrhrhd

e

e

++=+=

+

+=

+

=


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True MIMO: Spatial Multiplex(increase throughput or coverage)


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WiMAX MIMO DL PUSC profile

Open-Loop 2 transmit MIMO at BS

Matrix A or Matrix B mode

Vertical* STBC transmit matrix A (Alamouti)

Vertical* spacial multiplexing of transmit of matrix B

Multiple receive antennas at MS

Maximum ratio combining techniques

2 receive antennas mandatory

4 receive antennas as applicable (e.g. in notebooks)

Increasing SNR and thus coverage area, primarily

*Vertical Encoding: Single FEC encoded stream over multiple antennas

Matrix

A or B

Pilot


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WiMAX MIMO UL PUSC profile

Open-loop collaborative MIMO

2 MS transmit on the same subchannel

Horizontal** spatial multiplexing transmit on

matrix B BS to perform Maximum Likelihood detection

Increasing the uplink capacity (throughput)

Conventional single PA at MS

OFDM symbol

Subcarriers

Pilot

Data

MS #1 MS #2

Uplink PUSC tile structure

**Horizontal Encoding:

Multiple separately FEC encoded streams over multiple antennas

Matrix

B

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