IEEE802.16OFDMAPHY

8/3/2019 IEEE802.16OFDMAPHY

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I E E E 802.16 OF D M A PH Y

Wen-bin Lin

[email protected]
mailto:[email protected]:[email protected]:[email protected]


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Proprietary of NTHU Communication SOC Lab, Copyright @ 2006

Contents

W iM A X I ntroduct ion OFDMA Symbol Description, Parameters, and Frame Structure

OFDMA Subcarrier Allocation

OFDMA Ranging

Channel Coding and Control

Reference

Back up


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802.16 History

The initial 802.16 standard in 2002, operates in the 10-to-66-GHzfrequency band and requires LOS towers.

The 802.16a extension, ratified in March 2003, allows use of 2 to 11GHz frequency. It boasts a 50 km range and 74.7Mbit/sec. datatransfer rates and doesn't require LOS transmission.

Additional 802.16 standards are in the works:

802.16bQuality of service

802.16cInteroperability, with protocols and test-suite structures

802.16dFixing things not covered by 802.16c, which is the standardfor developing access points

802.16eSupport for mobile as well as fixed broadband (802.16-2005)


4/64Proprietary of NTHU Communication SOC Lab, Copyright @ 2006

802.16 Application



802.16 PHY

SC

OFDM-256

(S)OFDMA

FFT: 128, 512, 1k, 2k



802.16 Duplexing

Frequency division duplexing (FDD)

Licensed band

FFD SSs may be H-FDD

Time division duplexing (TDD)

Licensed and license-exempt band



OFDM Transceiver



Contents

IEEE 802.16 Introduction

OF D M A Symbol D escript ion, Paramet ers, and F rame St ruct ure OFDMA Subcarrier Allocation

OFDMA Ranging


Reference

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OFDMA Symbol Description (1/2)

Based on OFDM modulation

Designed for NLOS operation < 11 GHz

Frequency domain description

Subcarrier Type: Data, Pilot, null (guard and DC)

Number: 128, 512, 1024, 2048 (at least one)

Subchannel

A set of subcarriers forms a subchannel

The subcarriers may and may not be adjacent



OFDMA Symbol Description (2/2)

Time domain description

Created by IFFT operation of freq. domain symbol

Cyclic prefix

Extension before the time domain symbol Collect multi-path and maintain orthogonality

Causes SNR loss

CP

Ts

Tg Tb



Basic Parameters

Useful symbol time1/f = 89.6usTb

Frequency spacingFs/NFFT = 11.16kHzf

Sampling frequencyFloor( n*BW/8000 )*8000Fs

FFT size128, 512, 1024, 2048Nfft

Guard time ratio1/4, 1/8, 1/16, 1/32G

Sampling factor8/7, 28/25n

# of used subcarriersNused

bandwidth1.25, 5, 10,20BW

DESCRIPTIONVALUEITEM


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Basic Terms Definition

Slot

The minimum possible data allocation unit

Requires time and subchannel allocation mode information

Data region Two-dimensional allocation of a group of subchannels, in a group of

OFDMA symbols

Segment

A subdivision of the available subchannels

Permutation zone

A number of OFDMA symbols which use the same permutation formula

A subframe may contain more than one zone


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Slot Data region

Subchannel offset

Symbol

offset

No. of OFDMA symbols

No. ofsubchannels

Segment Permutation zone


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OFDMA Data Mapping DL, PUSC


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OFDMA Data Mapping UL

Two steps mapping:

1. Draw the data regionhorizontally (gray sha-dowed zone)

2. Mapping the slotvertically (slot index)


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Subchannel Permutations

Partial usage of sub-channels(PUSC)

Partial employment of cellplanning, 1/3 for the right handexample

FCH stands for frame control

header c.f. Full usage of sub-channels

(FUSC)


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Subchannel Permutations

AMC permutation

Enables efficient resource allocation with optimal transmit power andmodulation/coding scheme for each SS in a cell


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OFDMA Frame Structure (TDD)

DL subfram UL subfram


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FCH and DL_MAP

Frame control header

Contains the DL_Frame Prefix, and specifies the length of the DL-MAPmessage

Transmitted using QPSK rate 1/2 with four repetitions using themandatory coding scheme

sent on four subchannels with successive logical subchannel numbers

DL_MAP Transmitted with QPSK modulation at FEC rate 1/2.

Repetition 0, 2, 4, or 6

The length and FEC is described in the DL_MAP prefix


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Multiple Zones In a Frame

Zone transition is indicated in the DL-Map by the STC_DL_Zone

The maximum number of downlink zones is 8 in one downlink subframe

the maximum number of bursts to decode in one downlink subframe is

64 If the BS allocates more bursts or zones, then the SS is required to

decode the first bursts/zones until the limit is reached

PUSC zone first


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Contents


OFDMA Symbol Description, Parameters, and Frame Structure

OFD M A Subcarrier A llocat ion OFDMA Ranging Channel Coding and Control

Reference

Back up


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Preamble

The first symbol of the downlink transmission is the preamble

Three types of preamble carrier-sets

Defined by allocation of different subcarriers

Modulated using a boosted BPSK with a PN code DC subcarrier is always set to be zero

10128

42512

861024

1722048

Guard-band leftand right

FFT Size


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Preamble

Frequency domain description

Non-zero pilot tones every 3 subcarriers (DC subcarrier is notmodulated)

(NFFT guardband*2)/3 bit predefined sequenced is modulated n = 0 for segment 0

n = 1 for segment 1

n = 2 for segment 2

Time domain description 1, the first OFDMA symbol

Implicitly repeats itself 3 times within the basic OFDMA symbol time

n = 0 example

3*

0...567

n preambleCarrierSet n k

k

= +

=


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Downlink FUSC (1/4)

71

12

71

12


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Downlink FUSC (2/4)

There are two variable and constant pilot set

Mapping all pilot first, where the remaining subcarriers are used todefine data subcarriers

Allocate data subcarriers (48 subcarrier/subchannel ) Partition the remaining subcarrier into groups of contiguous form

Each subchannel consists of one subcarrier from each of theses groups

The exact allocation is according to a permutation formula:

( , ) { [ mod ] }modsubcahnnel k s k subchannels subchannels

subcarrier k s N n p n N PermBase N = + +


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Downlink FUSC (3/4)

constant pilot setvariable pilot set

Nsubcarriers

fpilot allocation

GP0 GP1 GP47

S0 S1 SNsch

remaining subcarriers

divide into groups

extract one fromeach group


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Downlink FUSC (4/4)

SubchannelIndex

Subcarrier index belongs to the corresponding subchannel

For PermBase = 2


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Downlink PUSC (1/4)


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Downlink PUSC (2/4)

1. Dividing the subcarriers into Ncluster physical clusters containing 14adjacent subcarriers

2. Renumbering the physical clusters into logical clusters

3. Dividing the clusters into six major groups (2048 example)

G0: 0-23, G2: 40-63, G4: 80:103

G1: 24-39, G3: 64-79, G5: 104-119 4. Allocate the pilot subcarrier first, the remaining subcarriers are used as

data subcarriers

(( 13* _ ) mod ) L P cluster C RS C DL PermBase N = +

time

Increasing index

datapilot

SC


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Downlink PUSC (3/4)

Nsubcarriers 2 OFDMA symbols

PC0 Physical clusters(14 subcarriers)PC1 PCNcluster

LC0 LC1 LCNcluster

Divide clusters intomajor groups

Renumbering sequence

LC0~23 LC24~39 LC64~79 LC80~103 LC104~119LC24~39 LC40~63

G0

Logical clusters(14 subcarriers)

S0 S1 SNsch

Same process asFUSC permutation

G23 G0G23 G0 G23 G0G23 G0 G23 G0G23

D li k PUSC (4/4)


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Downlink PUSC (4/4)

Allocation Example

FFT size: 2048

Major group: G0

PermBase: 2

su

bchannelin

dex

subcarrier index

UL b i ll ti (1/3)


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UL subcarrier allocation (1/3)

UL b i ll ti (2/3)


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Tile based allocation

The subchannel is constructed from six uplink tiles, each tile hasfour subcarriers

The allocated frequency band shall be divided into 420 tiles Divide the 420 tiles into six groups, containing 70 adjacent tiles

each

Tile

(s,n

) = 70n

+(Pt

[(s+n)mod

70]+ UL_IDcell)mod

70

time

Increasing index

pilot data

UL b i ll ti (3/3)


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Nsubcarriers

T0

S0 S1 SNsbc

divide subcarriersinto tiles

divide into groups

extract one from

each group

T1 TNtiles

G0 G1 G5

3 OFDMA symbols

Tile inde


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Tile indexSu

bchannelindex

Increasing index

time

A subchannel

Mini Subchannelization


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Mini-Subchannelization

An uplink subchannel is composed of six tiles, while minisubchannelization will be created by:

Concatenating multiples of 2, 3, or 6 subchannels

Allocating traffic for more than one SS on this concatenation

There are 4 possible mini-subchannelization

AAS Support (1/2)


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AAS Support (1/2)

Indicated by IEs in the DL and UL broadcast maps

AAS zone

A contiguous block of OFDMA symbols

Defined permutation Defined preamble structure

May contain an optional Diversity-Map scan zone (D-Msz)

AAS frame structure

Consists of subchannels

PUSC, FUSC, oFUSC permutation

Two highest numbered subchannels of DL frame may contain D-Msz

AMC permutation

The first and last numbered subchannels of AAS DL zone may contain D-Msz

A 2 bin by 3 symbol tile structure is used

AAS Support (2/2)


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AAS Support (2/2)

Optional Diversity Map scan(1/2)


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Optional Diversity-Map scan(1/2)

AAS-DLFP (Down Link Frame Prefix)

A robust transmission of the required BS parameters

Enable SS initial ranging

SS paging and access allocation

QPSK-1/2, 2 repetitions

Start with an AAS DL preamble

Specified the permutation of AAS UL Zone

Transmitted in a D-Msz may not carry the same information Supports the ability to transmit a compressed DL-MAP IE

Not randomized



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AAS preambles

Training information in both UL and DL AAS zone

Preceding all data allocation and AAS DLFP in AAS zone

Made exclusive for UL(1-D) and DL(2-D) Length is specified in the AAS_DL_IE

Either time or frequency shifted

AAS DL preamble

Formed by concatenating the original preamble sequence

Used for the burst is a subset of basic preamble

Occupies 9 subcarriers in AMC allocation

AAS UL preamble

Similar with AAS DL preamble

Contents


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Contents




OF D M A Ranging Channel Coding and Control

Reference

Back up

OFDMA Ranging


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OFDMA Ranging

The MAC layer shall define a single ranging channel Ranging channel

One or more groups of 6 adjacent subchannels

PUSC

Tile structure

8 adjacent subchannels for optional (AMC mode)

The indices of the subchannels that compose the ranging channelare specified in the UL-MAP message

1. Initial ranging

2. Periodic / BW request ranging

In the process of user code detection, the BS gets the channelimpulse response of the code, thus acquiring for the BS vastinformation about the user channel and condition

Initial / Handover Ranging


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Initial / Handover Ranging

The initial ranging code For initial network entry and association

Initial-ranging transmission shall be performed during two or fourconsecutive symbols

Initial Ranging Structure


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Initial Ranging Structure

The BS can allocate two consecutive initial ranging slot, the SStransmits two consecutive ranging code within 4 symbol time

Periodic / BW Request Ranging (1/2)


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Periodic-ranging transmissions Sent periodically for system periodic ranging

Bandwidth requests transmissions

For requesting uplink allocations from the BS Sent only by SS that have already synchronized to the system

Two ways to perform the ranging:

Modulate one ranging code on the ranging subchannel for a period of

one OFDMA symbol



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Modulating three consecutive ranging codes (starting code shall alwaysbe a multiple of 3) on the ranging subchannel for a period of threeOFDMA symbols

Ranging Codes (1/2)


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Ranging Codes (1/2)

Pseudo noise code produced by a PRBS Polynomial: 1+x1+x4+x7+x15

Initial seed: [L] 0 0 1 0 1 0 1 1 s0 s1 s2 s3 s4 s5 s6 [M]

s6~s0: UL_PermBase

BPSK transmission

Code length: 144 bits

Ranging Codes (2/2)


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g g ( )

Selection There are 256 available ranging code

Each BS use a subgroup of these code

The group of codes will be between S and (S+N+M+L+O) mod 256(cyclic manner)

0 1 2 14 15 25 26 39 40

N M L

57

S

Contents


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OFDMA Ranging Channel Coding and Cont rol Reference

Channel coding


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g

Repetition

R = 1, 2, 4, or 6

Group-wise of the encoded and interleaved block

Lower code rates of 1/4, 1/8, and 1/12 by repetition of 2, 4, and 6 of aR=1/2 encoded block

Randomization


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Randomizer

Generator polynomial = 1 + x14 + x15

The randomizer sequence is applied to information bits

Initial value for HARQ: [M]011011100010101[L]

MSBLSB

Encoding


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g

Mandatory: convolutional encoding (Tail biting) Optional: ZTCC, BTC, CTC

Concatenation

Performed in order to make larger blocks of coding where it is possible. Not exceeding the largest supported block size for the applied

modulation and coding

For CTC, the concatenation, interleaver, and HARQ support are

defined separately

Convolutional Coding


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Forward Error Correction convolutional code with w/wo puncture

Tile biting encoding

Block turbo code

Convolutional turbo code

Low density parity check code

Rate = K = 7G1 = (171)oct

G2 = (133)oct

Interleaving


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Interleaver All encoded data bits shall be interleaved by a block interleaver with a

block size

Two-step permutation

1. ensures that adjacent coded bits are mapped onto nonadjacentsubcarriers.

2. insures that adjacent coded bits are mapped alternately onto less or moresignificant bits of the constellation

Input order

output order

Modulation (1/3)


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Subcarrier randomization In all permutations except uplink PUSC and downlink TUSC1, the pilot

signal are boosted 2.5 dB over common data tones

The pilot signal are generated by a PRBS with the polynomial x11 + x9 +

1

Modulation (2/3)


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Data modulation

QPSK, 16-QAM, 64-QAM(optional)

Re-modulated with the random sequence used to generate pilot signal( 2*(1/2 - wk) )

Power is normalized to unit

UL ACK Channel


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Provides feedback for Downlink ARQ One ACK channel occupies half subchannel

3 pieces of 4x3 uplink tile in the case of PUSC

3 pieces of ex3 uplink tile in the case of optional PUSC

1 for NACK, while 0 for ACK (ACK encoding)

Channel Quality Measurements


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Implementation of the RSSI and CINR statistics and their reports ismandatory

RSSI Measurements

Not necessarily require receiver demodulation lock

Offer reasonably reliable channel strength assessments

CINR Measurements

require receiver demodulation lock

Provide information on the actual operating conditions, including interference,noise levels, and signal strength

As channel behavior is time-variant, both mean and stand deviationare defined

RSSI and CINR Measurements


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Unit of mean and standard deviation

Quantized: 1dB

RSSI: dBm (-40 ~ -123)

CINR: dB (-10 ~ 53)

Relative (absolute) accuracy

RSSI: dB

CINR: dB The estimation methods are both left to individual implementation,

while the standard give the possible methods:

2( 4)

1( 2)

Contents


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IEEE 802.16 Introduction OFDMA Symbol Description, Parameters, and Frame Structure


OFDMA Ranging Channel Coding and Control

Reference

Reference


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IEEE Standards 802.16-2004

802.16-2004/Corrigendum D3

802.16-2004/Corrigendum D5

802.16e-2005

Intel Technology vol.08

Standardization and Specifications of Standardization and

Specifications of WiBro PHY Fixed, nomadic, portable and mobile applications for 802.16-2004

and 802.16e WiMAX networks

Summary


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IEEE 802.16 Introduction Comparison with 802.16d(2004)

Duplexing


Basic term definition

Frame and FCH introduction


FUSC, PUSC AAS support

OFDMA Ranging

Initial ranging, periodic ranging

Ranging code


Randomization, channel coding, modulation


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Thank you

IEEE802.16OFDMAPHY

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