1. NTU Confidential Progress Report of 802.16a --- OFDM mode Advisor : Tzi-Dar Chiueh Student : Sang-Jung Yang Date : October 6 th, 2003

2. NTU Confidential 2 Outline 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

3. NTU Confidential 3 Application of 802.16a 802.11 drives demand for 802.16a

4. NTU Confidential 4 Scope 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.

5. NTU Confidential 5 Nomenclatures of 802.16/802.16a High-Speed Unlicensed Metropolitan Area Network 802.16 WirelessMAN-SC WirelessMAN-SCa WirelessMAN-OFDM WirelessMAN-OFDMA WirelessHUMAN 10-66GHz 2-11GHz Licensed bands 2-11GHz Licensed- exempt bands 802.16a

6. NTU Confidential 6 Features of 802.16a OFDM PHY 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).

7. NTU Confidential 7 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.

8. NTU Confidential 8 OFDM Frame Structure(FDD) OFDM Frame Structure(FDD) [2] Download and upload are transmitted in different frequency band, but at the same time.

9. NTU Confidential 9 Designing Issues in 802.16a Packet based transmission : –A fast and reliable time and frequency synchronization is required, 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 = 88kHz –88kHz > min Sucarrier Spacing (~7kHz)  still need integer frequency offset compensation

10. NTU Confidential 10 OFDM Channelization Parameters [2]

11. NTU Confidential 11 SUI Channel Model ---Description (1/4) The original SUI Channel Model defined many other parameters, such as : Antenna Correlation, K-factor under omni/30 o 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” ModelTap1Tap2Tap3K factor SUI-1 Delay (us)00.40.9 3.3 Power (dB)0-15-20 SUI-2 Delay (us)00.41.1 1.6 Power (dB)0-12-15 SUI-3 Delay (us)00.40.9 0.5 Power (dB)0-5-10 SUI-4 Delay (us)01.54 0.2 Power (dB)0-4-8 SUI-5 Delay (us)0410 0.1 Power (dB)0-5-10 SUI-6 Delay (us)01420 0.1 Power (dB)0-10-14

12. NTU Confidential 12 SUI Channel Model ---Simulation (2/4) P.S. Sampling Time (Ts) is set to 0.5us, i.e. Tb = 128us, and Tg is set to 32 us.

13. NTU Confidential 13 SUI Channel Model ---Simulation (3/4) Long Preamble and Pilots are transmitted with BPSK Data Symbols can use either QPSK,16QAM or 64QAM. Short Preamble are QPSK, too

14. NTU Confidential 14 SUI Channel Model ---Simulation (4/4) # of Total transmitted bits = 115200 = 192 * 600

15. NTU Confidential 15 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.

16. NTU Confidential 16 Efficient Preamble design for OFDM System [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.

17. NTU Confidential 17 Preamble Structure in 802.16a OFDM PAPR=3.0103dB PAPR=2.6715dB

18. NTU Confidential 18 Autocorrelation property

19. NTU Confidential 19 Symbol Boundary Detection and 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……

20. NTU Confidential 20 Simulation Results

21. NTU Confidential 21 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…

22. NTU Confidential 22 Conclusion 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.

23. NTU Confidential 23 References [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 Taylor, Wi-LAN [4] “Preamble Design for 802.16 SISO and MIMO OFDM Systems”, Apurva. N. Mody, Georgia Institute of Technology, November 11 th 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