Progress Report of OFDM-based Agile Baseband Transceiver for Spectrum Pooling Wireless Systems

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NTU Confidential

Progress Report of OFDM-based

Agile Baseband Transceiver for

Spectrum Pooling Wireless Systems

Advisor : Tzi-Dar Chiueh Student : Jui-Ping Lien Date : Nov 29th , 2004

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Outline

• Overview of Spectrum Pooling System – Feature

– Specification

• Transmit Power Spectrum

– Two approaches of reducing signal sidelobe • Simulation Result

– SISO perfect channel estimation in AWGN • Conclusion

• Future Work • Reference

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Overview of Spectrum Pooling System

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Flexible Spectrum

• Coexist with LU in the same frequency band without interfering LU.

• Use idle bands which LU does not use. • Band Allocation: totally 15 combinations

sub-band No. #1 #2 #3 #4

RU LU

LU LU LU

LULU RU RU RU

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Adaptive Transmission

• Pros

– Enhance the capacity • Cons

– Increase the complexity

– Assume transmitter knows CSI (channel state information)

• Adaptive transmission using water-filling technique s [3]

– Power allocation

– Bit loading (adaptive modulation)

• SBLA ( Simple Blockwise Loading Algorithm ) [1] B f f u f P _Alloc _          ) ( 1 ) ( 

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MIMO Scheme

• 2x2 MIMO: enhance higher data rate

– VBLAST

– SVD-based (Singular Value Decomposition)

Pros: support adaptive modulation Cons: Assume transmitter knows CSI Channel matrix Transmit signal Received signal H UDV H  Dx Vx UDV U HVx U y _ H _ H H _                    1 0 1 0 0 0 1 0 x x d d y y         1 1 1 0 0 0 x d y x d y [2] [3] Vx

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System specifications

FFT size 256

Bandwidth 100MHz (use 80MHz _actually)

Sampling rate 80MHz (4 times faster than _802.11a) Sub-carrier spacing 312.5KHz (=80 MHz/256) FFT period 3.2us (=1/312.5 KHz) Guard interval duration 0.8us OFDM symbol

duration 4.0us (=3.2+0.8 us)

Sub-carrier in

use variable

Modulation type BPSK, QPSK, 16QAM, _64QAM Operating

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Transmit Power Spectrum Analysis

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Transmitter Block Diagram

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Transmit Spectrum Mask

• 802.11a spec has transmit spectrum mask

• Two approaches to reduce sidelobes of transmitted wavefo rm

– Time domain windowing – Frequency domain filtering

RU #1234 RU #13

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Time domain windowing

• Raised cosine windowing

• Larger roll-off factor improves the spectrum, at the cost of decreased delay spread

tolerance.                       _ _             _  ) 2 / 2 / ( / ) ( 5 . 0 2 sin ) 2 / 2 / ( 1 ) 2 / 2 / ( / 5 . 0 2 sin ) ( 2 2 TR TR TR TR TR TR TR TR T T T t T T T T t T T t T T t T T t t w  

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Frequency domain filtering (1/2)

• Filter Requirement

– Interpolator filer

– Band-limited filter: reduce out-of-band spectrum – Reconfigurable filter

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Frequency domain filtering (2/2)

] [ 1 n c j n e n c 4 1[ ]  n j e n c 4 1[ ]   Ite

m Elliptic Filter (IIR) CoefficientFilter Case

1 N=6 Wp=19/80 Ws = 23/80 Rp=0.1 dB Rs=40 dB RU#23 2 RU#1, RU#2, RU#12 3 RU#3, RU#4, RU#34 4 N=7 Wp=29/80 Ws = 33/80 Rp=0.1dB Rs=40 dB RU#13, RU#123 5 complex conjugate of item4 RU#24. RU#234 6 N=7 Wp=39/80 Ws = 43/80 Rp=0.1, Rs=40 RU#14, RU#124, RU#134, RU#1234 ] [ 1 n c n j e n c 4 1[ ]  n j e n c 4 1[ ]  

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Simulation Transmit Spectrum

-- 1 sub-band (1/3)

β=0, 1/160, 1/40

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Simulation Transmit Spectrum

-- 2 sub-bands (2/3)

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Simulation Transmit Spectrum

-- 3 or 4 sub-bands (3/3)

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Simulation of Perfect Channel Estimation

in AWGN

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Receiver Architecture

Inner receiver

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SISO Perfect Channel Estimation

in AWGN Channel

• Simulation Environment

• More available sub-band → higher data rate

→ higher BER @ same SNR per OFDM symbol

RU#1

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Simulation Result (1/2)

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Simulation Result (2/2)

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Conclusion

• Features of SP system has been introduced. • Since transmit power spectrum should

achieve the mask requirement, we use both techniques

– time domain raised cosine windowing (overlap 1 pt )

– frequency domain filtering

• SISO perfect channel estimation in AWGN has been simulated.

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Future Work

• Extend SISO to MIMO scheme

• Build up timing recovery block of receiver • Support adaptive modulation

• System modification according to final specification

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Reference

• [1] Rainer Gr¨unheid, Edgar Bolinth, and Hermann Rohling,

“A Blockwise Loading Algorithm for the Adaptive Modulation

Technique in OFDM Systems,” in IEEE VTC-2001, Atlantic City,

USA, October 2001. • [2]

http://www.tgnsync.org/techdocs/tgnsync-proposal-technical-sp ecification.pdf

• [3] Juha Heikala, John Terry, “OFDM Wireless LANs: A Theoret