4G requirement

• Mobility

• High bandwidth

• Long distance

• Low power consumption

• High speed when move

• Asymmetry Traffic

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Today’s Networks

Term DuplexWCDMA FDD

CDMA 2000 FDDTD/CDMA TDD

UMC-136(EDGE) FDDDECT TDD

ADSL/VDSL FDDWiMax FDD/TDD

Half-duplex CSMA TDD

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Frequency Division DuplexU1 U2 U3 U4 D1 D2 D3 D4

Up stream Down stream

Wu Wd

Frequency Offset Wo

Guard Band

• Continuous uplink and downlink transmissions

• Higher immunity to system interference

• Feedback required for CSIT acquisition

• Inflexible traffic allocation

• Restrictive band allocation

• Guard band

• Higher hardware cost4

Time Division Duplex

• Channel reciprocity

• Dynamic traffic allocation/Traffic Asymmetry

• Higher frequency diversity

• Unpaired band allocation

• Lower hardware cost

C1 C2 C3 C4

Wu+Wd

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TDD Challenges

• Cross-slot interference

• Inter-operator interference

• Guard time between downlink and uplink transitions

• Duplexing delay in MAC and ARQ

• Outdated CSIT

TS0 TS1 TS2 TS3 TS4 TS5 TS6

Up stream Down streamTTG RTG

TS0 TS1

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Solution for cross-slot interference

• Synchronization

• Sectorization

• Time slot grouping

7

Cross Slot Interference

BS-BBS-A

MSB1

MS-A

MS-B

BS-BBS-B

BS-A

MSB1

MS-A

MS-B

BS-B

3

4

3

3

2

1

2

4

1

4

1

2

1

3

1

4

1

2

1

8

Hybrid FDD

U1 U2 U3 U4

D1 D2 D3 D4

Up streamFrequency

Down streamFrequency

C1 C2 C3 C4Time Frame

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Conclusions

• TDD easier to asymmetry traffic

• TDD has higher bit-rate

• TDD use unpaired spectrum

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Reference Documents• The evolution path of 4G networks: FDD or TDD?

IEEE Communications Magazine, December 2006, Page 42 - 50

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