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Behind Mobile WiMAX
Chenxi Zhu, Ph.D.
Fujitsu Labs of AmericaCollege Park, MD
Email: [email protected]
What is mobile WiMAX?
Mobile broadband wireless accessDefined by IEEE and WiMAX Forum.
IEEE 802.16e_2005: wireless MAN-OFDMAPHY and MAC layer.
WiMAX Forum: System profiles, testing, networking protocols, applications, certification, etc.Marketing and promotion.
Mobile WiMAX network
TDD or FDD spectrum 802.16e air interface:
• OFDMA-based PHY,• QoS-oriented MAC
Mobile IP-basedNetworking layer
Cellulardeployment
Core Network
Radio Access Network
OFDM PHY layer
Frequency domain signaling.ICI-free: orthogonal between subcarriers.ISI-free: guard interval between symbols.Robust against multiple paths.
No equalization required at receiver.
Time domain Frequency domain
OFDMA: OFDM for multiple access
User 1
User 2
User 3
User 4
Base station assigns the subcarriers to users in DL and UL.Radio resources (subcarriers, transmission powers) are allocated based on user channel quality and BW requirement (QoS).
Scalable PHY layer TDD or FDD, variable frame length (2—20 ms). Different FFT sizes (128, 512, 1024, 2048) for variable BW (1.25MHz--20MHz).Variable CP length (1/32,1/16,1/8,1/4) for different cell size.Same inter-subcarrier spacing (97.2KHz).Multi-modes supported with a single SoC.Adaptive modulation and coding.
QPSK, 16QAM, 64QAM.CC, CTC, BTC, LDPC (1/2, 2/3, ¾, 5/6).
Beamforming and MIMO.Common or dedicated pilots.HARQ (Chase, IR).
Different subchannelization for different mobility.
Diversity permutation(PUSC, FUSC)
Contiguous permutation(AMC)
TDD Frame structure
Preamble: power boosted for BS identification and synchronization.Control channel (FCH, DL-MAP, UL-MAP): assign
subchannels to users, power level, modulation/coding.DL/UL Burst: data packets BS MS.
Multiple antennas (MIMO)
Close loop transmitter beamforming.Space time code (Alamouti scheme).Spatial multiplexing.Up link: virtual MIMO.
IFFT
IFFT
IFFT
IFFT
FFT
FFT
FFT
FFT
MIM
O e
ncod
er
MIM
O d
ecod
er
MIM
O S
C m
appi
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MIM
O S
C de
-map
ping
WiMAX QoS classes
Maximum Rate, Traffic PriorityData Transfer, Web browsing
BE(Best Effort Service)
Minimum Rate, Maximum Rate, Traffic Priority
FTPNRT-VR(Non-Real-Time Variable Rate)
Minimum Rate, Maximum Rate, Maximum Delay, Jitter Tolerance, Traffic Priority
VoIP with Activity Detection
ERT-VR(Extended Real-Time Variable Rate service)
Minimum Rate, Maximum Rate, Maximum Delay, Traffic Priority
Streaming Audio or Video
RT-VR(Real-Time Variable Rate service)
Maximum Rate, Maximum DelayJitter Tolerance
VoIPUGS (CBR)(Unsolicited Grant Service)
QoS SpecificationsApplicationsQoS Category
OFDMA PHY layerQoS oriented MAC layerMIP-based networking layer
defined by WiMAX Forum NWG
Future of WiMAX
Current development of 802.16
802.16j: multi-hop relayEnhance coverage and capacity of 802.16e with relay stations.
802.16m: targeting IMT-AdvancedSupport BW ≥ 20MHz. Backward compactable with 802.16e. 100 Mbps at high mobility.1 Gbps for fixed user.
Industry synergySystem vendors
Samsung, Motorola, Alcatel-Lucent, Nortel,Nokia-Siemens, Huawei, ZTE, …
Chip manufacturesIntel, Fujitsu, Runcom, Beecem, …
Device manufacturesNokia, Samsung, Motorola, Sony-Ericsson,…
Service providersSprint, AT&T, Nextwave, SK-Telecom, KDDI, French-telecom, Telecom-Italia, DirectTV, ….
Content providerDisney
Who may deploy WiMAX?Fixed point-to-point (LOS): 802.16d-OFDM
Wireless backhaulFixed point-to-multipoint (NLOS): 802.16d/e-OFDM/OFDMA
DSL/cable replacementCCTV
Nomadic data application (Laptop, Handhold): OFDM/OFDMABetter coverage than WiFi Hotspot
Mobile data, data/voice (OFDMA)4G?
Intelligent transportation system (OFDMA)Transportation infrastructureVehicle to curb
Scalable OFDMA PHY layer
4 FFT sizes (128, 512, 1024, 2048) for variableBandwidth.
AdaptiveModulationand codingfor differentchannel quality
802.16e Subcarrier allocation
Pilot sub-carrier for channel estimation.Data sub-carrier for data transmission.No transmission in Null sub-carriers (DC, guard-band).