NTU Confidential

Progress Report of 802.16aProgress Report of 802.16a--- OFDM mode --- OFDM mode

Advisor : Tzi-Dar ChiuehStudent : Sang-Jung Yang Date : October 6th, 2003

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OutlineOutline

• Reviewing IEEE 802.16a• Designing Issues of 802.16a• SUI Channel Model

– Description and Simulation• Preambles in 802.16a

– Frame Synchronization– CFO Estimation – Simulation Result

• Conclusion• Reference

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Application of 802.16aApplication of 802.16a

• 802.11 drives demand for 802.16a

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Scope of 802.16Scope of 802.16

• IEEE 802.16– Two main parts of the standard

• 802.16 : The original standard. For frequencies between 11-60 GHz. The PHY is single carrier solution. The MAC is TDMA.

• 802.16a : For licensed and unlicensed bands below 11 GHz. Defined 3 non-interoperable PHYs. The MAC is TDMA or FDMA.

– In development• 802.16e : Extending 802.16a for vehicular mobility.

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Nomenclatures of 802.16/802.16aNomenclatures of 802.16/802.16a

High-Speed Unlicensed Metropolitan Area Network

802.16

WirelessMAN-SC

WirelessMAN-SCa

WirelessMAN-OFDM

WirelessMAN-OFDMA

WirelessHUMAN

10-66GHz

2-11GHzLicensed bands

2-11GHzLicensed-

exempt bands802.16a

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Features of 802.16a OFDM Features of 802.16a OFDM PHYPHY

• Uses 256 points FFT, and 200 points are used for data.• Variable cyclic prefix length (8, 16, 32 or 64 samples).• 8 pilot symbols are inserted per OFDM symbol, at locations

-84, -60, -36, -12, 12, 36, 60, 84.• Reed-Solomon code and Convolution code are mandatory.• Adaptive modulation(QPSK,16QAM,64QAM) and coding

rate.• Frame structure can be either Time Division Duplex (TDD) or

Frequency Division Duplex (FDD).

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OFDM Frame Structure(TDD)OFDM Frame Structure(TDD)

PS : DCD,UCD,MAPs are some controlling info for MAC Layer

[2]

• Download and upload are transmitted in the same frequency band, but at different time.

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OFDM Frame Structure(FDD)OFDM Frame Structure(FDD)

[2]

• Download andupload are transmitted in different frequency band, but at the same time.

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Designing Issues in 802.16aDesigning Issues in 802.16a

• Packet based transmission :– A fast and reliable time and frequency synchronization is require

d, usually need to be done within the preamble period• Is it possible to perform these jobs in Time domain ?

• Various Channelization, Modulation and Coding Rate :– Since spec of 802.16a defined various choices of Channelization,

modulation and coding rate, the transceiver design should be adaptive and robust in each operation mode

• Carrier Frequency Offset tolerance : – Max CFO = ±4ppm Max Carrier Frequency=8 ppm * 11GHz = 88k

Hz– 88kHz > min Sucarrier Spacing (~7kHz) still need integer frequ

ency offset compensation

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OFDM Channelization OFDM Channelization Parameters Parameters

[2]

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SUI Channel Model SUI Channel Model ---Description ---Description (1/4)(1/4)

• The original SUI Channel Model defined many other parameters, such as : Antenna Correlation, K-factor under omni/30o ant……These parameters are not taken into simulation yet.

• Since the Doppler frequency defined in SUI-1~6 are very small (MAX 2.5Hz), the simulation is assumed to be under “quasi-static channel”

Model Tap1 Tap2 Tap3 K factor

SUI-1Delay (us) 0 0.4 0.9

3.3Power (dB)

0 -15 -20

SUI-2Delay (us) 0 0.4 1.1

1.6Power (dB)

0 -12 -15

SUI-3Delay (us) 0 0.4 0.9

0.5Power (dB)

0 -5 -10

SUI-4Delay (us) 0 1.5 4

0.2Power (dB)

0 -4 -8

SUI-5Delay (us) 0 4 10

0.1Power (dB)

0 -5 -10

SUI-6Delay (us) 0 14 20

0.1Power (dB)

0 -10 -14

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SUI Channel Model SUI Channel Model ---Simulation ---Simulation (2/4)(2/4)

P.S. Sampling Time (Ts) is set to 0.5us, i.e. Tb = 128us, and Tg is set to 32 us.

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SUI Channel Model SUI Channel Model ---Simulation ---Simulation (3/4)(3/4)

Long Preamble and Pilots are transmitted

with BPSK

Data Symbols can use either

QPSK,16QAM or 64QAM. Short

Preamble are QPSK, too

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SUI Channel Model SUI Channel Model ---Simulation (4/4) ---Simulation (4/4)

# of Total transmitted bits = 115200 = 192 * 600

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What does preamble do ? What does preamble do ? • Example : 802.11a

• For packet based transmission, fast and reliable time/frequency synchronization is required, and a well-designed preamble should be responsible for this.

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Efficient Preamble design Efficient Preamble design for OFDM Systemfor OFDM System[4][4]

• Good Correlation properties• Low PAPR,• Suitable for parameter estimation,• Suitable for frequency offset estimation

over a wide range,• Low computational complexity and low

overhead.

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Preamble Structure in 802.16a Preamble Structure in 802.16a OFDMOFDM

PAPR=3.0103dBPAPR=3.0103dB

PAPR=2.6715dBPAPR=2.6715dB

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Autocorrelation propertyAutocorrelation property

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Symbol Boundary DetectionSymbol Boundary Detectionand Carrier Frequency Offset Estimationand Carrier Frequency Offset Estimation

• Coarse Symbol Boundary Detection : – By Delayed Correlation :

• Fine Symbol Boundary Detection :– By Time domain Correlator Bank

• Using the PN-property of Long Preamble

• Fractional part CFO Estimation :– By the phase of Delayed Correlation near the right timing point :

• Integer part CFO Estimation : – Under Construction……

128,)(1

0

*

LrrdP Lmd

L

m md

))((ˆoptdPphase

)*(2

ˆ

)2(2

ˆˆ

sFrame TLTf

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Simulation ResultsSimulation Results

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Encountered Problem……Encountered Problem……

• While CFO is larger than 1~2 Subcarrier spacing, the PN-property is destroyed and no peak can be found around the estimated coarse symbol boundary.

Possible Solutions :1. Use PLL to track CFO…2. Solve in Frequency Domain…3. Find other algorithm…

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ConclusionConclusion

• Scope of IEEE 802.16/802.16a have been reviewed.• Some features of 802.16a OFDM PHY have been

introduced.• Simulation over SUI Channel Model is presented.• Preamble structure in 802.16a and its usage over Symbol

Boundary Detection are introduced.

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ReferencesReferences

• [1] IEEE 802.16 standard.• [2] IEEE 802.16a draft version 7.• [3] “IEEE 802.16a-the future of high-speed wireless”, Aditya Agrawal, Fujitsu Microelectronics and Shawn Ta

ylor, Wi-LAN • [4] “Preamble Design for 802.16 SISO and MIMO OFDM Systems”, Apurva. N. Mody, Georgia Institute of Te

chnology, November 11th 2001.• [5]Robust frequency and timing synchronization for OFDM

Schmidl, T.M.; Cox, D.C.; Communications, IEEE Transactions on , Volume: 45 Issue: 12 , Dec. 1997 Page(s): 1613 -1621

• [6]Burst frame synchronization for OFDM transmission in multipath fading links Baoguo Yang; Letaief, K.B.; Cheng, R.S.; Zhigang Cao; Vehicular Technology Conference, 1999. VTC 1999 - Fall. IEEE VTS 50th , Volume: 1 , 19-22 Sept. 1999 Page(s): 300 -304 vol.1

• [7]Time and frequency synchronization for OFDM using PN-sequence preambles Tufvesson, F.; Edfors, O.; Faulkner, M.; Vehicular Technology Conference, 1999. VTC 1999 - Fall. IEEE VTS 50th , Volume: 4 , 19-22 Sept. 1999 Page(s): 2203 -2207 vol.4