1. NTU Confidential Packet Format Report of OFDM-based Agile Baseband Transceiver for Future Spectrum Pooling Wireless Systems Advisor : Tzi-Dar Chiueh Student : Jui-Ping Lien Date : Sept 13th, 2004

2. NTU Confidential 2 Outline Motivation Spectrum pooling OFDM-based agile baseband transceiver –Specifications –Band allocation Packet Format Design –Short/Long preamble –Pilot/ data sub-carrier allocation Conclusion and Future Work Reference

3. NTU Confidential 3 Motivation The demand for more bandwidth is increasing but spectrum is scarce. Large chunks of frequency bands are used rarely, which is inefficient. [1]

4. NTU Confidential 4 Spectrum Pooling Basic idea: merging spectral ranges from different spectrum owners into a common pool. The licensed system do not need to be changed. [1]

5. NTU Confidential Introduction of OFDM-based Agile Baseband Transceiver

6. NTU Confidential 6 Overview Point-to-point (initially one way with return channel), fixed to slowly mobile terminals OFDM structure: frequency as basis data return channel

7. NTU Confidential 7 Band allocation sub-band No. #1#2#3#4 RULU RU LU RU Divided into 4 sub-bands Totally 15 combinations The available bandwidth is variable. LU/RU: licensed/rental user

8. NTU Confidential 8 Features Capable of sensing spectral occupancy. –sub-carrier scanning Capable of using the spectrum flexibly. –Select sub-carrier adaptively to avoid sub-carriers occupied by active 802.11a systems –Reconfigurable number of FFT points, range of points –Adaptive and dynamic power allocation and/or variable modulation/coding among sub-carriers – to achieve QoS as often as possible.

9. NTU Confidential 9 System specifications FFT size256 Bandwidth100MHz (use 80MHz actually) Sampling rate80MHz (4 times faster than 802.11a) Subcarrier spacing312.5KHz (=80 MHz/256) FFT period3.2us (=1/312.5 KHz) Guard interval duration0.8us OFDM symbol duration4.0us (=3.2+0.8 us) Sub-carrier in usevariable Modulation typeBPSK, QPSK, 16QAM, 64QAM Code rate1/2, 2/3, 3/4 Operating frequencyUpper UNII bands

10. NTU Confidential Packet Format Report

11. NTU Confidential 11 Packet Format It is basically the same as 802.11a.

12. NTU Confidential 12 Short Preamble (1/3) Requirement –Not interfere to LU: can only use part or all the available sub-bands. –Coarse symbol boundary/CFO : good auto-correlation property –Low PAPR (peak to average power ratio) One possible approach –Modify 802.11a short preamble LURU

13. NTU Confidential 13 Short Preamble (2/3) Use the lowest available sub-band Generation method 802.11a padding zero shift padding zeros in freq. domain  interpolation in time domain X(f-Δf)  x[n] e j2pi* Δf*nTs

14. NTU Confidential 14 Short Preamble (3/3) Length = 64 pt PAPR is about 2.24 dB (2.08 dB in 802.11a) Auto-correlation property –Time resolution is the same as 802.11a 802.11a result

15. NTU Confidential 15 Long Preamble (1/2) Requirement –Fine symbol boundary/CFO: good auto-correlation property –Channel estimation: use all the available sub-bands. –Low PAPR One possible approach –Use M-sequence, r=8 primitive polynomial p(x)= =x 8 +x 6 +x 5 +x 4 +1 LURU [3]

16. NTU Confidential 16 Long Preamble (2/2) Length = 256 point PAPR range from 4.55-6.8 dB (3.16dB in 802.11a system) Good auto-correlation property RU at sub-band #1 RU at sub-band #1-2 RU at sub-band #1-3 RU at sub-band #1-4

17. NTU Confidential 17 Rate & Data sub-carriers The number of data sub-carriers is variable, so the system can offer more different kinds of rate (6M-256.5Mbps). available band No. available band number data sub-carrier number #1 or #2 or #3 or #4148 #13 or #24 or #14296 (=48*2) #12 or #342108 (=48*2+12) #232108 (=48*2+11+1) #134 or #1243156 (=48*3+12) #123 or #2343168 (=48*3+12+11+1) #12344228 (=48*4+12*3) ModulationCoding rate BPSK1/2 BPSK3/4 QPSK1/2 QPSK3/4 16-QAM1/2 16-QAM3/4 64-QAM2/3 64-QAM3/4

18. NTU Confidential 18 SIGNAL field SIGNAL field: use the lowest available sub-band to transmit. Separate RATE1-4: for variable modulation/coding among sub-bands

19. NTU Confidential 19 Pilot allocation & Data Interleaver Pilot spacing: 16 pt (while 14 pt in 802.11a) Data interleaving Service field (SERVICE), tail bit field (TAIL), Pad bits (PAD), DATA scrambler and descrambler, convolutional encoder are remained the same as 802.11a system. N CBPS : coded bit in one OFDM symbol N BPSC : the number of coded bit per sub-carrier

20. NTU Confidential 20 Conclusion OFDM-based agile baseband transceiver for future spectrum pooling wireless systems has been introduced. Packet format has been proposed.

21. NTU Confidential 21 Future Work Sub-carrier scanning design Survey about variable modulation/coding rate issue Survey about reconfigurable FFT Construct transmitter & receiver

22. NTU Confidential 22 Reference [1] Spectrum pooling: an innovative strategy for the enhancement of spectrum efficiency Weiss, T.A.; Jondral, F.K.; Communications Magazine, IEEE, Volume: 42, Issue: 3, Mar 2004 Pages:S8 – 14 [2] IEEE Std 802.11a-1999 [3] http://www.mathworks.com/access/helpdesk/help/toolbox/commblks/ref/pnseq uencegenerator.html http://www.mathworks.com/access/helpdesk/help/toolbox/commblks/ref/pnseq uencegenerator.html