Progress%20Report%20of%20OFDM-based%20Agile%20Baseband%20Transceiver%20for%20Spectrum%20Pooling%20Wireless%20Systems

1
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

2
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

3
Overview of Spectrum Pooling System
4
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
LU/RU licensed/rental user
5
Adaptive Transmission

• Pros
• Enhance the capacity
• Cons
• Increase the complexity
• Assume transmitter knows CSI (channel state
  information)
• Adaptive transmission using water-filling
  techniques 3
• Power allocation
• Bit loading (adaptive modulation)
• SBLA ( Simple Blockwise Loading Algorithm ) 1

6
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

2 3
7
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 (3.20.8 us)
Sub-carrier in use variable
Modulation type BPSK, QPSK, 16QAM, 64QAM
Operating frequency Upper UNII bands
8
Transmit Power Spectrum Analysis
9
Transmitter Block Diagram
CSI
10
Transmit Spectrum Mask

• 802.11a spec has transmit spectrum mask
• Two approaches to reduce sidelobes of transmitted
  waveform
• Time domain windowing
• Frequency domain filtering

RU 1234
RU 13
11
Time domain windowing

• Raised cosine windowing
• Larger roll-off factor improves the spectrum, at
  the cost of decreased delay spread tolerance.

12
Frequency domain filtering (1/2)

• Filter Requirement
• Interpolator filer
• Band-limited filter reduce out-of-band spectrum
• Reconfigurable filter
• Complex filter for asymmetric spectrum case

13
Frequency domain filtering (2/2)
Item Elliptic Filter (IIR) Elliptic Filter (IIR) Filter Coefficient Case
1 N6 Wp19/80 Ws 23/80 Rp0.1 dB Rs40 dB RU23
2 N6 Wp19/80 Ws 23/80 Rp0.1 dB Rs40 dB RU1, RU2, RU12
3 N6 Wp19/80 Ws 23/80 Rp0.1 dB Rs40 dB RU3, RU4, RU34
4 N7 Wp29/80 Ws 33/80 Rp0.1dB Rs40 dB RU13, RU123
5 N7 Wp29/80 Ws 33/80 Rp0.1dB Rs40 dB complex conjugate of item4 RU24. RU234
6 N7 Wp39/80 Ws 43/80 Rp0.1, Rs40 RU14, RU124, RU134, RU1234
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Simulation Transmit Spectrum -- 1 sub-band
(1/3)
ß0, 1/160, 1/40
ß0, 1/160, 1/40
15
Simulation Transmit Spectrum -- 2 sub-bands
(2/3)
16
Simulation Transmit Spectrum -- 3 or 4
sub-bands (3/3)
17
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 _at_ same SNR per OFDM symbol

RU1
RU1234
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Simulation Result (1/2)
16 QAM of 15 cases
4 modulation types of RU1234
21
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.

23
Future Work

• Extend SISO to MIMO scheme
• Build up timing recovery block of receiver
• Support adaptive modulation
• System modification according to final
  specification

24
Reference

• 1 Rainer Grunheid, 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-propos
  al-technical-specification.pdf
• 3 Juha Heikala, John Terry, OFDM Wireless
  LANs A Theoretical and Practical Guide 2002