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Access Schemes Used In LTE

By: Zunaira TahirPerformance and Optimisation trainee engineer at Ericsson

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The purpose of this topic is to give a brief overview of how OFDMA and SC FDMA works in LTE

Objective:

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OFDM Block Diagram:

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POP UP:

How FFT works?

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DFT Computation Using FFT:

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DFT Computation Using FFT:

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DFT Computation Using FFT:

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POP UP:

How IFFT works in OFDM?

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Serial to Parallel

IFFT

1234

1

2

3

4

1 2 43

10

224

Synthesis:

_

Decomposition:

1 2 3 4

+ + + +

2

_

2 2 4 6 2 2 4 6

2, 2 4, 6

2 4 2 6

FFT is discrete in time domain so the output will be sum of discrete time signals modulated with different

frequency

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4 6

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POP UP:

How FFT will workin OFDM?

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Serial to Parallel

FFT

1234

1

2

3

4

1 2 43

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Decomposition: 1 2 3 4 1, 3 2, 4

_

1 3 2 4

+ + + +

1 1 3 7

_

Synthesis:FFT will be discrete in

frequency domain but continuous in time domain so can not help to

achieve modulation

1 3 2 4

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OFDM Block Diagram:

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Cyclic Prefix Concept:

Before CP Insertion After CP Insertion

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SC FDMA Block Diagram:

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POP UP:

How DFT and IFFT works in SC-FDMA?

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Serial to Parallel

DFT

1234

1

2

3

4

1 2 43

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Decomposition: 1 2 3 4 1, 3 2, 4

_

1 3 2 4

+ + + +

1 1 3 7

_

Synthesis:FFT will be discrete in

frequency domain but continuous in time domain so can not help to

achieve modulation

1 3 2 4

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DFT IFFT

12340

0

0

1 1 73

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224

Synthesis:

_

Decomposition:

1 0 0 0

+ + + +

1137 0 1137 0

_

1137 0 1137 0

1137 0 1137 0

1137, 0 1137, 0

1137 1137 0 0

1 1 73

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Comparison Between OFDM and SCFDMA :

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THANK YOU