1 Scalable OFDMA Physical Layer in IEEE WirelessMAN Advisor: Dr. Kai-Wei Ke Speaker: Chao-Sung yah Date:12/3/2007

2 Outline Introduction Introduction Multicarrier design requirement and Multicarrier design requirement and tradeoffs tradeoffs Basic of OFDMA frame structure Basic of OFDMA frame structure Conclusion Conclusion Reference Reference Q&A Q&A

3 Introduction(1/3) Line of Sight(LOS) Line of Sight(LOS) Operation in the 10 ～ 66GHz 、傳輸距離為 5 公里左右，當頻寬在 28MHz 時，速度最高 可達約 134Mbps Operation in the 10 ～ 66GHz 、傳輸距離為 5 公里左右，當頻寬在 28MHz 時，速度最高 可達約 134Mbps Non Line of Sight (NLOS) Non Line of Sight (NLOS) 2 ～ 11GHz 頻段、傳輸距離約 10 公里，通道 頻寬為 20MHz 時最高速度約 75Mbps 2 ～ 11GHz 頻段、傳輸距離約 10 公里，通道 頻寬為 20MHz 時最高速度約 75Mbps

4 Introduction(2/3) Support variable bandwidth sizes between 1.25 and 20 MHz for NLOS operations Support variable bandwidth sizes between 1.25 and 20 MHz for NLOS operations Makes the need for a scalable design of OFDM signaling inevitable Makes the need for a scalable design of OFDM signaling inevitable OFDM and OFDMA,if no scalability enhancements,then no guarantee fixed subcarrier spacing OFDM and OFDMA,if no scalability enhancements,then no guarantee fixed subcarrier spacing

5 Introduction(3/3) Other features Other features 1. AMC subchannels 2. Hybrid Automatic Repeat Request((H-ARQ) 3. high-efficiency Uplink (UL) subchannel structures 4. Multiple-Input-Multiple-Output (MIMO) diversity 5. enhanced Advanced Antenna Systems (AAS) 6. coverage enhancing safety channels

6 Multicarrier design requirement and tradeoffs Two main elements of the Wide-Sense Stationary Uncorrelated Scattering (WSSUS) model are briefly discussed here Two main elements of the Wide-Sense Stationary Uncorrelated Scattering (WSSUS) model are briefly discussed here 1. Doppler spread and coherence time of channel 2. Multipath delay spread and coherence bandwidth.

7 Outline Introduction Introduction Multicarrier design requirement and Multicarrier design requirement and tradeoffs tradeoffs Basic of OFDMA frame structure Basic of OFDMA frame structure Conclusion Conclusion Reference Reference Q&A Q&A

8 Doppler spread and coherence time of channel A maximum speed of 125 km/hr is used here The maximum Doppler shift corresponding to the operation at 3.5 GHz is given by Equation A maximum speed of 125 km/hr is used here The maximum Doppler shift corresponding to the operation at 3.5 GHz is given by Equation

9 Doppler spread

10 Doppler spread and coherence time of channel The coherence time of the channel, a measure of time variation in the channel, corresponding to the Doppler shift specified above, is calculated in Equation The coherence time of the channel, a measure of time variation in the channel, corresponding to the Doppler shift specified above, is calculated in Equation

11 Doppler spread and coherence time of channel This means an update rate of ~1 KHz is required for channel estimation and equalization. This means an update rate of ~1 KHz is required for channel estimation and equalization.

12 Multipath delay spread and coherence bandwidth. The International Telecommunications Union (ITU-R) Vehicular Channel Model shows delay spread values of up to 20 μs for mobile environments.

13 Multipath delay spread and coherence bandwidth. This means that for delay spread values of up to 20 μs,multipath fading can be considered as flat fading over a 10 KHz subcarrier width. This means that for delay spread values of up to 20 μs,multipath fading can be considered as flat fading over a 10 KHz subcarrier width.

14

15 Formula EX:5MHz Fs = floor(8/7 *BW/0.008)x0.008 Fs = floor(8/7 *BW/0.008)x0.008 over-sampling factor used is 8/7 over-sampling factor used is 8/7 Sampling frequency Fs = 8/7 * 5 =~5.714MHz Sampling frequency Fs = 8/7 * 5 =~5.714MHz Sample time = 1/Fs =~175ns Sample time = 1/Fs =~175ns Subcarrier frequency spacing Subcarrier frequency spacing delta F = Fs/Nfft = 5.714M/512 = 11.16KHz Tb = 1/deltaF = 1/11.16K = 89.6μs Tb = 1/deltaF = 1/11.16K = 89.6μs Tg = Tb/8 =11.2μs,Ts=Tb+Tg =100.8μs Tg = Tb/8 =11.2μs,Ts=Tb+Tg =100.8μs

16 WirelessMAN OFDMA supports a wide range of frame sizes to flexibly address the need for various applications and usage model requirements

17 Drivers of scalability Subcarrier spacing is independent of bandwidth. Subcarrier spacing is independent of bandwidth. The number of used subcarriers (and FFT size) should scale with bandwidth. The number of used subcarriers (and FFT size) should scale with bandwidth. The smallest unit of bandwidth allocation, specified based on the concept of subchannels. The smallest unit of bandwidth allocation, specified based on the concept of subchannels. The number of subchannels scales with FFT The number of subchannels scales with FFT Tools are provided to trade mobility for capacity. Tools are provided to trade mobility for capacity.

18 Outline Introduction Introduction Multicarrier design requirement and Multicarrier design requirement and tradeoffs tradeoffs Basic of OFDMA frame structure Basic of OFDMA frame structure Conclusion Conclusion Reference Reference Q&A Q&A

19 three types of OFDMA subcarriers There are three types of OFDMA subcarriers: There are three types of OFDMA subcarriers: 1. Data subcarriers for data transmission. 2. Pilot subcarriers for various estimation and synchronization purposes. 3. Null subcarriers for no transmission at all, used for guard bands and DC carriers.

20 three types of OFDMA subcarriers

21 Basic of OFDMA frame structure Subchannel :Active subcarriers are divided into subsets of subcarriers Subchannel :Active subcarriers are divided into subsets of subcarriers In FUSC, there is one set of common pilot subcarriers, but in PUSC, each subchannel contains its own set of pilot subcarriers In FUSC, there is one set of common pilot subcarriers, but in PUSC, each subchannel contains its own set of pilot subcarriers

22 OFDMA slot For downlink FUSC and downlink optional FUSC using the distributed subcarrier permutation, one slot is one subchannel by one OFDMA symbol. For downlink FUSC and downlink optional FUSC using the distributed subcarrier permutation, one slot is one subchannel by one OFDMA symbol. For downlink PUSC using the distributed subcarrier permutation, one slot is one subchannel by two OFDMA symbols. For downlink PUSC using the distributed subcarrier permutation, one slot is one subchannel by two OFDMA symbols. For uplink PUSC using either of the distributed For uplink PUSC using either of the distributed subcarrier permutations,one slot is one subchannel by three OFDMA symbols subcarrier permutations,one slot is one subchannel by three OFDMA symbols For uplink and downlink using the adjacent subcarrier permutation, one slot is one subchannel by one, two,three, or six OFDMA symbols. For uplink and downlink using the adjacent subcarrier permutation, one slot is one subchannel by one, two,three, or six OFDMA symbols.

23 OFDMA slot

24 OFDMA frame structure

25 Subcarrier allocation modes There are two main types of subcarrier permutations: There are two main types of subcarrier permutations: 1. distributed : subcarrier permutations perform very well in mobile applications 2. adjacent :subcarrier permutations can be properly used for fixed, portable, or low mobility environments This mechanism is designed to minimize the probability of hits between adjacent sectors/cells by reusing subcarriers

26 DL Distributed Subcarrier Permutations: (FUSC)

27

28 DL and UL Distributed Subcarrier Permutation:(PUSC)

29 DL and UL Distributed Subcarrier Permutation:(PUSC)

30 example

31 DL and UL Distributed Subcarrier Permutation:(PUSC)

32 example

33 Optional DL Distributed Subcarrier Permutation:(OFUSC)

34 Optional DL Distributed Subcarrier Permutation:(OFUSC) Compared to FUSC mode, the number of used subcarriers in this method is considerably larger (1681 vs. 1729). As a result, compliance with spectral mask requirements, without a change in the over-sampling factor, may be a challenge for this mode. Compared to FUSC mode, the number of used subcarriers in this method is considerably larger (1681 vs. 1729). As a result, compliance with spectral mask requirements, without a change in the over-sampling factor, may be a challenge for this mode.

35 Optional UL Distributed Subcarrier Permutation: (OPUSC)

36 Optional UL Distributed Subcarrier Permutation: (OPUSC)

37 Optional DL and UL Adjacent Subcarrier Permutation: Advanced Modulation and Coding (AMC)

38 Sector 1 Sector 2 Sector 3 Sector 1 Sector 2 Sector 3 Sector 1 Sector 2 FUSC PUSC FUSC

39 Conclusion The IEEE WirelessMAN OFDMA supports a comprehensive set of system parameters and advanced optional features for mobile, portable, and fixed usage models. Scalability enables the technology to operate optimally in different usage scenarios. The IEEE WirelessMAN OFDMA supports a comprehensive set of system parameters and advanced optional features for mobile, portable, and fixed usage models. Scalability enables the technology to operate optimally in different usage scenarios.

40 Reference Scalable OFDMA Physical Layer in WirelessMAN, Intel Technology Journal Scalable OFDMA Physical Layer in WirelessMAN, Intel Technology Journal J. Yun and M. Kavehrad, ” PHY/MAC Cross-Layer issues in Mobile WiMAX. ” January 2006 Bechtel elecommunications Technical Journal J. Yun and M. Kavehrad, ” PHY/MAC Cross-Layer issues in Mobile WiMAX. ” January 2006 Bechtel elecommunications Technical Journal An Introduction to WiMAX. 暨南大學通訊所. 魏學文 An Introduction to WiMAX. 暨南大學通訊所. 魏學文 IEEE Std , “ IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems, ” October subscribers. IEEE Std , “ IEEE Standard for Local and Metropolitan Area Networks – Part 16: Air Interface for Fixed Broadband Wireless Access Systems, ” October subscribers.

41 Q&A