Progress Report of 802.16a --- OFDM mode. Advisor : Tzi-Dar Chiueh Student : Sang-Jung Yang Date : October 6 th , 2003. Outline. Reviewing IEEE 802.16a Designing Issues of 802.16a SUI Channel Model Description and Simulation Preambles in 802.16a Frame Synchronization CFO Estimation
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Progress Report of 802.16a--- OFDM mode Advisor : Tzi-Dar Chiueh Student : Sang-Jung Yang Date : October 6th, 2003
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
Application of 802.16a • 802.11 drives demand for 802.16a
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.
2-11GHz Licensed bands 802.16a High-Speed Unlicensed Metropolitan Area Network Nomenclatures of 802.16/802.16a 10-66GHz WirelessMAN-SC WirelessMAN-SCa 802.16 WirelessMAN-OFDM WirelessMAN-OFDMA 2-11GHz Licensed-exempt bands WirelessHUMAN
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).
OFDM Frame Structure(TDD) • Download and upload are • transmitted in the same frequency band, but at different time.  PS : DCD,UCD,MAPs are some controlling info for MAC Layer
OFDM Frame Structure(FDD) • Download and • upload are • transmitted in • different frequency • band, but at the • same time. 
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
SUI Channel Model ---Description (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”
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.
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
SUI Channel Model ---Simulation (4/4) • # of Total transmitted bits = 115200 = 192 * 600
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.
Efficient Preamble design for OFDM System • Good Correlation properties • Low PAPR, • Suitable for parameter estimation, • Suitable for frequency offset estimation over a wide range, • Low computational complexity and low overhead.
Preamble Structure in 802.16a OFDM PAPR=3.0103dB PAPR=2.6715dB
Symbol Boundary Detectionand 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 partCFOEstimation : • By the phase of Delayed Correlation near the right timing point : • Integer partCFOEstimation : • Under Construction……
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. • PossibleSolutions : • Use PLL to track CFO… • Solve in Frequency Domain… • Find other algorithm…
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.
References •  IEEE 802.16 standard. •  IEEE 802.16a draft version 7. •  “IEEE 802.16a-the future of high-speed wireless”, Aditya Agrawal, Fujitsu Microelectronics and Shawn Taylor, Wi-LAN •  “Preamble Design for 802.16 SISO and MIMO OFDM Systems”, Apurva. N. Mody, Georgia Institute of Technology, November 11th 2001. • 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 • 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 • 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