1 Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN Advisor: Dr. Kai-Wei Ke Speaker: Chao-Sung yah Date:12/3/2007

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Scalable OFDMA Physical Layer iScalable OFDMA Physical Layer in IEEE 802.16n IEEE 802.16WirelessMANWirelessMAN

Advisor: Dr. Kai-Wei KeAdvisor: Dr. Kai-Wei KeSpeaker: Chao-Sung yahSpeaker: Chao-Sung yah

Date:12/3/2007Date:12/3/2007

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OutlineOutline

• IntroductionIntroduction• Multicarrier design requirement and Multicarrier design requirement and tradeoffstradeoffs• Basic of OFDMA frame structureBasic of OFDMA frame structure• ConclusionConclusion• ReferenceReference• Q&AQ&A

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Introduction(1/3)Introduction(1/3)

• Line of Sight(LOS)Line of Sight(LOS)• Operation in the 10Operation in the 10 ～～ 66GHz66GHz 、傳輸距離、傳輸距離

為為 55 公里左右，當頻寬在公里左右，當頻寬在 28MHz28MHz 時，速度時，速度最高可達約最高可達約 134Mbps 134Mbps

• Non Line of Sight (NLOS)Non Line of Sight (NLOS)• 22 ～～ 11GHz11GHz 頻段、傳輸距離約頻段、傳輸距離約 1010 公里，通公里，通

道頻寬為道頻寬為 20MHz20MHz 時最高速度約時最高速度約 75Mbps 75Mbps

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• Support variable bandwidth sizes betweSupport variable bandwidth sizes between 1.25 and 20 MHz for NLOS operationsen 1.25 and 20 MHz for NLOS operations

• Makes the need for a scalable design of Makes the need for a scalable design of OFDM signaling inevitableOFDM signaling inevitable

• OFDM andOFDM and OFDMAOFDMA ,if no scalability enh ,if no scalability enhancements ,then no guarantee fixed subancements ,then no guarantee fixed subcarrier spacingcarrier spacing

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• Other featuresOther features1.1. AMC subchannelsAMC subchannels2.2. Hybrid Automatic Repeat Request((H-ARQ)Hybrid Automatic Repeat Request((H-ARQ)3.3. high-efficiency Uplink (UL) subchannel structurhigh-efficiency Uplink (UL) subchannel structur

eses4.4. Multiple-Input-Multiple-Output (MIMO) diversitMultiple-Input-Multiple-Output (MIMO) diversit

yy5.5. enhanced Advanced Antenna Systems (AAS)enhanced Advanced Antenna Systems (AAS)6.6. coverage enhancing safety channelscoverage enhancing safety channels

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Multicarrier designMulticarrier designrequirement and tradeoffsrequirement and tradeoffs• Two main elements of the Wide-Sense Two main elements of the Wide-Sense

Stationary Uncorrelated Scattering (WStationary Uncorrelated Scattering (WSSUS) model are briefly discussed hereSSUS) model are briefly discussed here

1.1. Doppler spread and coherence time of Doppler spread and coherence time of channelchannel

2.2. Multipath delay spread and coherence Multipath delay spread and coherence bandwidth.bandwidth.

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OutlineOutline


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Doppler spread and coherence Doppler spread and coherence time of channeltime of channel

• A maximum speed of 125 km/hr is used A maximum speed of 125 km/hr is used here The maximum Doppler shift here The maximum Doppler shift corresponding to the operation at 3.5 corresponding to the operation at 3.5 GHz is given by EquationGHz is given by Equation

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Doppler spreadDoppler spread

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• The coherence time of the channel, a The coherence time of the channel, a measure of time variation in the channel, measure of time variation in the channel, corresponding to the Doppler shift corresponding to the Doppler shift specified above, is calculated in Equationspecified above, is calculated in Equation

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• This means an update rate of ~1 KHz This means an update rate of ~1 KHz is required for channel estimation is required for channel estimation and equalization.and equalization.

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Multipath delay spread and coherMultipath delay spread and coherence bandwidth.ence bandwidth.The International Telecommunications Union The International Telecommunications Union

(ITU-R) Vehicular Channel Model shows del(ITU-R) Vehicular Channel Model shows delay spread values of up to 20 μs for mobile eay spread values of up to 20 μs for mobile environments.nvironments.

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Multipath delay spread and coherMultipath delay spread and coherence bandwidth.ence bandwidth.• This means that for delay spread values This means that for delay spread values

of up to 20 μs,multipath fading can be cof up to 20 μs,multipath fading can be considered as flat fading over a 10 KHz suonsidered as flat fading over a 10 KHz subcarrier width.bcarrier width.

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Formula Formula EX:5MHzEX:5MHz

• Fs = floor(8/7 *BW/0.008)x0.008Fs = floor(8/7 *BW/0.008)x0.008• over-sampling factor used is 8/7over-sampling factor used is 8/7• Sampling frequency Fs = 8/7 * 5 =~5.714MHzSampling frequency Fs = 8/7 * 5 =~5.714MHz• Sample time = 1/Fs =~175nsSample time = 1/Fs =~175ns• Subcarrier frequency spacing Subcarrier frequency spacing delta F = Fs/Nfft = 5.714M/512 = 11.16KHzdelta F = Fs/Nfft = 5.714M/512 = 11.16KHz• Tb = 1/deltaF = 1/11.16K = 89.6μsTb = 1/deltaF = 1/11.16K = 89.6μs• Tg = Tb/8 =11.2μs,Ts=Tb+Tg =100.8μsTg = Tb/8 =11.2μs,Ts=Tb+Tg =100.8μs

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WirelessMAN OFDMA supports a wide range of frame sizes to flexibly address the need forvarious applications and usage model requirements

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Drivers of scalability Drivers of scalability

• Subcarrier spacing is independent of bandwidth.Subcarrier spacing is independent of bandwidth.• The number of used subcarriers (and FFT size) shThe number of used subcarriers (and FFT size) sh

ould scale with bandwidth.ould scale with bandwidth.• The smallest unit of bandwidth allocation, specifThe smallest unit of bandwidth allocation, specif

ied based on the concept of subchannels.ied based on the concept of subchannels.• The number of subchannels scales with FFT The number of subchannels scales with FFT • Tools are provided to trade mobility for capacity.Tools are provided to trade mobility for capacity.

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OutlineOutline


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three types of OFDMA subcarriersthree types of OFDMA subcarriers

• There are three types of OFDMA subcarrieThere are three types of OFDMA subcarriers:rs:

1.1. Data subcarriers for data transmission.Data subcarriers for data transmission.2.2. Pilot subcarriers for various estimation aPilot subcarriers for various estimation a

nd synchronization purposes.nd synchronization purposes.3.3. Null subcarriers for no transmission at alNull subcarriers for no transmission at al

l, used for guard bands and DC carriers.l, used for guard bands and DC carriers.

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three types of OFDMA subcarriersthree types of OFDMA subcarriers

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Basic of OFDMA frame Basic of OFDMA frame structurestructure

• Subchannel :Active subcarriers are dividSubchannel :Active subcarriers are divided into subsets of subcarriersed into subsets of subcarriers

• In FUSC, there is one set of common piloIn FUSC, there is one set of common pilot subcarriers, but in PUSC, each subchant subcarriers, but in PUSC, each subchannel contains its own set of pilot subcarrinel contains its own set of pilot subcarriersers

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OFDMA slotOFDMA slot

• For downlink FUSC and downlink optional FUSC using For downlink FUSC and downlink optional FUSC using the distributed subcarrier permutation, one slot is one the distributed subcarrier permutation, one slot is one subchannel by one OFDMA symbol.subchannel by one OFDMA symbol.

• For downlink PUSC using the distributed subcarrier peFor downlink PUSC using the distributed subcarrier permutation , one slot is one subchannel by two OFDMA rmutation , one slot is one subchannel by two OFDMA symbols.symbols.

• For uplink PUSC using either of the distributedFor uplink PUSC using either of the distributed• subcarrier permutations ,one slot is one subchannel bsubcarrier permutations ,one slot is one subchannel b

y three OFDMA symbolsy three OFDMA symbols• For uplink and downlink using the adjacent subcarrier For uplink and downlink using the adjacent subcarrier

permutation, one slot is one subchannel by one, two,tpermutation, one slot is one subchannel by one, two,three, or six OFDMA symbols.hree, or six OFDMA symbols.

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OFDMA slotOFDMA slot

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OFDMA frame structureOFDMA frame structure

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SS ubcarrier allocation modesubcarrier allocation modes

• There are two main types of subcarrier permThere are two main types of subcarrier permutations:utations:

1.1. distributed : subcarrier permutations perfordistributed : subcarrier permutations perform very well in mobile applicationsm very well in mobile applications

2.2. adjacent :subcarrier permutations can be pradjacent :subcarrier permutations can be properly used for fixed, portable, or low mobilioperly used for fixed, portable, or low mobility environmentsty environments

This mechanism is designed to minimize the proThis mechanism is designed to minimize the probability of hits between adjacent sectors/cellbability of hits between adjacent sectors/cells by reusing subcarrierss by reusing subcarriers

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DL Distributed Subcarrier PermDL Distributed Subcarrier Permutations: (FUSC)utations: (FUSC)

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DL and UL Distributed SubcarrieDL and UL Distributed Subcarrier Permutation:(PUSC)r Permutation:(PUSC)

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exampleexample

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exampleexample

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Optional DL Distributed SubcarrierOptional DL Distributed SubcarrierPermutation:(OFUSC)Permutation:(OFUSC)

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Optional DL Distributed SubcarrierOptional DL Distributed SubcarrierPermutation:(OFUSC)Permutation:(OFUSC)

• Compared to FUSC mode, the number of Compared to FUSC mode, the number of used subcarriers in this method is consiused subcarriers in this method is considerably larger (1681 vs. 1729). As a result,derably larger (1681 vs. 1729). As a result, compliance with spectral mask require compliance with spectral mask requirements, without a change in the over-saments, without a change in the over-sampling factor, may be a challenge for thimpling factor, may be a challenge for this mode.s mode.

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Optional UL Distributed SubcarrierOptional UL Distributed SubcarrierPermutation: (OPUSC)Permutation: (OPUSC)

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Optional UL Distributed SubcarrierOptional UL Distributed SubcarrierPermutation: (OPUSC)Permutation: (OPUSC)

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Optional DL and UL Adjacent SubcarrierOptional DL and UL Adjacent SubcarrierPermutation: Advanced Modulation and CodingPermutation: Advanced Modulation and Coding(AMC)(AMC)

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Sector 1

Sector 2

Sector 3

Sector 1

Sector 2

Sector 3

Sector 3

Sector 1

Sector 2

FUSCPUSC

PUSCPUSC

PUSCPUSC

PUSC

PUSC

PUSC

PUSC

FUSC

FUSC

FUSC

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ConclusionConclusion

• The IEEE 802.16 WirelessMAN OFDMA suThe IEEE 802.16 WirelessMAN OFDMA supports a comprehensive set of system ppports a comprehensive set of system parameters and advanced optional featurarameters and advanced optional features for mobile, portable, and fixed usage es for mobile, portable, and fixed usage models. Scalability enables the technolomodels. Scalability enables the technology to operate optimally in different usaggy to operate optimally in different usage scenarios.e scenarios.

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ReferenceReference

• Scalable OFDMA Physical Layer in 802.16 WirelessMAN, IntelScalable OFDMA Physical Layer in 802.16 WirelessMAN, Intel Technology JournalTechnology Journal

• J. Yun and M. Kavehrad,”PHY/MAC Cross-Layer issues in Mobile WiMAX.J. Yun and M. Kavehrad,”PHY/MAC Cross-Layer issues in Mobile WiMAX.” January 2006 Bechtel elecommunications Technical Journal” January 2006 Bechtel elecommunications Technical Journal

• An Introduction to WiMAX. An Introduction to WiMAX. 暨南大學通訊所暨南大學通訊所 . . 魏學文魏學文 www.cm.nctu.edu.twww.cm.nctu.edu.t

w/~IEEEITComSoc/slide/2007_summer/20070806B.pdfw/~IEEEITComSoc/slide/2007_summer/20070806B.pdf • IEEE Std 802.16-2004, “IEEE Standard for Local and Metropolitan Area IEEE Std 802.16-2004, “IEEE Standard for Local and Metropolitan Area

Networks – Part 16: Air Interface for Fixed Broadband Wireless Access SyNetworks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” October 2004. subscribers.stems,” October 2004. subscribers.

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Q&AQ&A

Documents

1 Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN Advisor: Dr. Kai-Wei Ke Speaker: Chao-Sung yah Date:12/3/2007