OFDM(A) Competence Development – part III

OFDM(A) Competence Development – part IIIPer Hjalmar Lehne, Frode Bøhagen, Telenor R&I

R&I seminar, 23 January 2008, Fornebu, Norway

[email protected]

[email protected]

23 Jan 2008

OFDM Competence Development

2

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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3

Wireless standards

• Mobile WiMAX

• 3GPP Evolved UTRA

• Basic OFDMA parameters

• Resource mappings and scheduling

• Multi-antenna support

• Comparison

• Other standards which use OFDM / OFDMA:

– 3GPP2 Ultra Mobile Broadband (UMB)

– WLAN, 802.11a, .11g, .11n

– Terrestrial Digital Broadcast: DVB-T, DVB-H

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Mobile WiMAX R1– IEEE 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-07 as “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 WiMAXSupported system bandwidths [MHz]

1.25 5 10 20 7 8.75

Sub-carrier frequency spacing, 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 + 8 pilot)

• 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-carrier mapping

Cluster renumbering

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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Mobile WiMAX frame structure

• Mobile WiMAX currently supports Time Division Duplex (TDD)

– 802.16e also supports Frequency Division Duplex (FDD), Full- and half-duplex operation

• All permutation schemes can be supported in each frame

• DL PUSC is mandatory in first ”zone”

Pream

ble

PU

SC

(FC

H, M

AP

)

FU

SC

PU

SC

AM

C

TU

SC

PU

SC

AM

C

DL ULFrame length: 48 OFDMA symbols/5 ms

(Guard

interval)

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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 system bandwidths [MHz]

1.4 1.6

(TDD only)

3 3.2

(TDD only)

5 10 15 20

Sub-carrier frequency spacing, 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 code”1/3 rate Turbo code

Multi-antenna support Yes

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Resource mapping for E-UTRA

• Time-frequency resources are organised in ”Resource blocks” spanning 12 SC x 7 symbol intervals (180 kHz x 0.5 ms)

• Diversity permutation is by mapping ”virtual resource blocks” to ”physical resource blocks”

• Uplink is always localized mapping using SC-FDMA

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E-UTRA frame structures

DLsymbN OFDM symbols

One downlink slot slotT

0l 1DLsymb Nl

RB

sc

DL

RBN

N

su

bcarr

iers

RB

scNsu

bcarr

iers

RBsc

DLsymb NN

Resource block

resource elements

Resource element ),( lk

Resourceblock

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 improve

coverage and capacity

• Space-Time Coding (STC)– Transmit diversity such as Alamouti coding to provide spatial diversity and reduce

fading margin

• Spatial Multiplexing (SM) - MIMO– Higher peak rates and increased throughput. Multiple streams are transmitted over

multiple antennas. The receiver must also have multiple antennas to separate the different streams.

• E-UTRA – ”Baseline” configuration: 2x2 (DL)

1x2 (UL)

• Mobile WiMAX– Minimum requirements, Wave II: 2x2 (DL), 1x2 (UL)

• Reference signal (pilot) positions identify the different Tx antennas

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E-UTRA vs. Mobile WiMAX

• Sub-carrier distance and useful symbol time

– E-UTRA more robust to Doppler

• Cyclic prefix/guard interval– Mobile WiMAX more robust to multipath

delays

– Extended CP of E-UTRA an option for long delays

• Bandwidth support– Basically same

• Complexity– Similar

• No clear winner when it comes to performance on the physical layer

• Migration and co-existence– E-UTRA is taylored to ease co-existence

with and migration from WCDMA/HSPA

f = 15 kHz

f = 10.94 kHz

TCP 5 s TU = 66.67 s

TCP = 11.4 s TU = 91.4 s

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 s

• Cyclic prefix duration: 6.51, 13.02, 19.53, or 26.04 s

– Windowing guard interval: 3.26 s

• Modulation: QPSK, 8-PSK, 16-QAM, 64-QAM, hierarchical modulation

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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 s

• Guard interval (cyclic prefix): 0.8 s

• Modulation: BPSK, QPSK, 16-QAM, 64-QAM

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Digital Terrestrial Broadcast, DVB-T/-H

• Broadcast technologies using OFDM– No multiple access!

• Channel bandwidths: 5, 6, 7, 8 MHz

• Number of subcarriers (incl pilots): – 2K mode: 1705 (2048),

– 4K mode: 3409 (4096) - only DVB-H

– 8K mode: 6817 (8192)

• Subcarrier spacing (8 MHz channel): – 4.464 kHz, 2.232 kHz, 1.116 kHz

• Useful symbol length: – 224 s, 448 s, 896 s

• Guard interval (Cyclic prefix): – 1/32, 1/16, 1/8, 1/4 of useful symbol length:

• Modulation: QPSK, 16-QAM, 64-QAM, hierarchical modulation

1/32 1/16 1/8 1/4

2K 7 s 14 s 28 s 56 s

4K 14 s 28 s 56 s 112 s

8K 28 s 56 s 112 s 224 s

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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 wireless standards

– Fixed and nomadic wireless broadband: Wi-Fi, Fixed WiMAX

– Digitial terrestrial broadcast: DVB-T, DVB-H

Documents

OFDM(A) Competence Development – part III