Post on 04-Jun-2018
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Outline
Part I: What is OFDM?
Part II: Introducing multiple access: OFDMA, SC-FDMA
Part III: Wireless standards based on OFDMA
Part IV: Radio planning of OFDMA
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Wireless standards
Mobile WiMAX
3GPP Evolved UTRA
Basic OFDMA parameters
Resource mappings andscheduling
Multi-antenna support
Comparison
Other standards which useOFDM / OFDMA:
3GPP2 Ultra Mobile Broadband(UMB)
WLAN, 802.11a, .11g, .11n
Terrestrial Digital Broadcast:DVB-T, DVB-H
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Mobile WiMAX R1IEEE 802.16e
Based on the air-interface of IEEE 802.16e-2005
Amendment to Fixed WiMAX IEEE 802.16-2004
Adopted by ITU-R as member of the IMT-2000 family at RA-07as OFDMA TDD WMAN
WiMAX Release 1 ready since 2006
Scalable OFDMA. Bandwidth support: 5, 7, 8.75 and 10 MHz
Multi-antenna support (MIMO)
Expected peak data rates:
72 Mb/s combined (TDD UL+DL); BW = 10 MHz, MIMO 2x2
First working products in 2008
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Basic parameters for Mobile WiMAX
Supported system
bandwidths [MHz]
1.25 5 10 20 7 8.75
Sub-carrier frequencyspacing, f[kHz]
10.94 7.81 9.77
Useful symbol time, TU[s]
91.4 128.0 102.4
Cyclic prefix/Guard time,TCP[s]
11.4 16.0 12.8
Guard time overhead,TCP/(TCP+TU) [%]
11.1
Sampling frequency, fs[MHz]
1.4 5.6 11.2 22.4 8.0 10.0
FFT size, NFFT 128 512 1024 2048 1024 1024
Occ. Sub-carriers (PUSC) 360/272 720/560
Resource mapping Distributed or contiguous
Duplex methods TDD only
Modulation schemes QPSK, 16-QAM, 64-QAM - adaptive
Coding schemes
1/2, 2/3, 3/4, 5/6 rate convolutional code1/2, 2/3, 3/4, 5/6 rate convolutional turbo code
x2, x4, x6 repetition code
Multi-antenna support Yes
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Resource mapping for Mobile WiMAX
Diversity permutations (Distributed mappings):
DL-FUSC Fully Used Sub-Carrier
DL-PUSC, UL-PUSC Partially Used Sub-Carrier
DL-TUSC Tile Usage of Subcarriers
Contiguous permutation (Localized mapping):
Band AMC Adaptive Modulation and Coding
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Mobile WiMAX DL PUSC
Downlink Partially Used Sub-Carriers
Clusters of 14 contiguous SCs and two symbol intervals
Re-arranged to 6 groups
Permutation within each group to form sub-channels with 28 subcarriers (24 data + 8pilot)
Obtains diversity gain over the whole bandwidth
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Mobile WiMAX DL PUSC - explored
PPP
P
Frequency
Physical mapping
Logical mapping
Cluster: 14 SC x 2 symbols
30 clusters/420 SCs
Major group: 10 clusters/120 data SCs
Logical sub-channel/24 data SCs from a group
Sub-carr ier mapp ing
Cluster renum bering
DL-PUSC, NFFT
= 512
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Mobile WiMAX UL PUSC
Uplink Partially Used Sub-Carrier
Tiles of 4 contiguous SCs and 3 symbol intervals
Re-arranged to 6 groups
Permutation within each group to form sub-channels with 28 subcarriers(24 data + 8 pilot)
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3GPP Evolved UTRA LTE
Long Term Evolution (LTE). 4G technology from 3GPP.Standard more or less finalized in 2007
Scalable OFDMA. Bandwidth support from 1.4 20 MHz
SC-FDMA on the uplink
Multi-antenna support (MIMO)
Expected data rate above 100 Mb/s DL, 50 Mb/s UL; BW= 20 MHz, 2x2 MIMO
Pilot tests in 2007/8, first products in 2009/10
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Basic parameters for E-UTRA
Supported systembandwidths [MHz]
1.4 1.6
(TDDonly)
3 3.2
(TDDonly)
5 10 15 20
Sub-carrier frequencyspacing, f[kHz]
15 (7.5)
Useful symbol time, TU[s] 66.67 (133.33)
Cyclic prefix/Guard time,TCP[s]
Normal CP: 5.21/4.69Extended CP: 16.67
Guard time overhead,TCP/(TCP+TU) [%]
Normal CP: 6.67Extended CP: 20.0
Sampling frequency, fs[MHz]
7.68 15.36 23.04 30.72
FFT-size, NFFT 512 1024 1536 2048
Occ. subcarriers 72 84 180 192 300 600 900 1200
Resource mapping Distributed or contiguous
Duplex methods FDD and TDD
Modulation schemes QPSK, 16-QAM, 64-QAM, adaptive
Coding schemes 1/3 rate tail-biting convolutional code1/3 rate Turbo code
Multi-antenna support Yes
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Resource mapping for E-UTRA
Time-frequency resources are organised in Resource blocksspanning 12 SC x 7 symbol intervals (180 kHz x 0.5 ms)
Diversity permutation is by mapping virtual resource blocks tophysical resource blocks
Uplink is always localized mapping using SC-FDMA
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E-UTRA frame structures
DL
symbN OFDM symbols
0l 1DL
symb Nl
RB
sc
N
subcarriers
Resource
block
Resource element:
One time-frequency symbol
Frequency
Time
Symb#0 Symb#1 Symb#2 Symb#3 Symb#4 Symb#5 Symb#6CP0 CP1 CP2 CP3 CP4 CP5 CP6
Slot: 0.5 ms
#0 #1 #2 #3 #19#18
One radio frame, Tf = 307200Ts = 10 ms
One slot, Tslot = 15360Ts = 0.5 ms
One subframe
Frame structure type 1 (FDD)
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Multi-antenna support
Beamforming
Multiple antennas are used to transmit or receive weighted signals to improvecoverage and capacity
Space-Time Coding (STC)
Transmit diversity such as Alamouti coding to provide spatial diversity and reducefading margin
Spatial Multiplexing (SM) - MIMO
Higher peak rates and increased throughput. Multiple streams are transmitted overmultiple antennas. The receiver must also have multiple antennas to separate thedifferent streams.
E-UTRA
Baseline configuration: 2x2 (DL)1x2 (UL)
Mobile WiMAX
Minimum requirements, Wave II: 2x2 (DL), 1x2 (UL)
Reference signal (pilot) positionsidentify the different Tx antennas
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E-UTRA vs. Mobile WiMAX
Sub-carrier distance and usefulsymbol time
E-UTRA more robust to Doppler
Cyclic prefix/guard interval
Mobile WiMAX more robust to multipathdelays
Extended CP of E-UTRA an option for longdelays
Bandwidth support Basically same
Complexity
Similar
No clear winner when it comes toperformance on the physical layer
Migration and co-existence
E-UTRA is taylored to ease co-existencewith and migration from WCDMA/HSPA
Df= 15 kHz
Df= 10.94 kHz
TCP 5 ms T
U= 66.67 ms
TCP
= 11.4 ms TU
= 91.4 ms
E-UTRA
Mobile WiMAX
Frequency Time
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Mobile WiMAX R2 IEEE 802.16m
Completed Q4/07 ?
System profile R2 in 2008 ?
Bandwidth support: 5, 10, 20, 40 MHz
Peak data rates (requirements)
DL: > 350 Mb/s, 4x4 MIMO
UL: > 200 Mb/s, 2x4 MIMO
Average throughput per sector, BW = 20 MHz
DL: > 40 Mb/s
UL: > 12 Mb/s
Mobility support up to 350 km/h
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Ultra Mobile Broadband (UMB)
Next generation mobile broadband access from 3GPP2
Evolution from cdma2000 EV-DO Rev. C
Published September 2007
Bandwidths: 1.25 2.5 5 10 20 MHz
Number of subcarriers: 128, 256, 512, 1024, 2048 (FFT size) Subcarrier spacing: 9.6 kHz
Useful symbol duraton: 104.17 ms
Cyclic prefix duration: 6.51, 13.02, 19.53, or 26.04 ms
Windowing guard interval: 3.26 ms
Modulation: QPSK, 8-PSK, 16-QAM, 64-QAM, hierarchicalmodulation
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Wi-Fi, IEEE 802.11
WLAN standards 802.11a, g and n uses OFDM
Multiple access is not OFDMA but CSMA (TDMA variant)
Channel bandwidth: 22 MHz
Number of subcarriers: 52
Subcarrier spacing: 312.5 kHz
Useful symbol length: 3.2 ms
Guard interval (cyclic prefix): 0.8 ms
Modulation: BPSK, QPSK, 16-QAM, 64-QAM
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Summary - standards
Major future mobile broadband standards employ OFDMA
Mobile WiMAX, E-UTRA, UMB
Bandwidths are scalable
Flexible multi-user access
Multiple antennas (MIMO) supported
OFDM transmission is employed in several wirelessstandards
Fixed and nomadic wireless broadband: Wi-Fi, Fixed WiMAX
Digitial terrestrial broadcast: DVB-T, DVB-H