2004/12/231 Techniques for and DSP Software Implementation of IEEE 802.16a TDD OFDMA Downlink...

2004/12/23 1

Techniques for and DSP Software Implementation of IEEE 802.16a TDD OFDMA Downlink Pilot-Symbol-Aided Channel Estimation

Student: Chen, Ching

Advisor: Prof. D. W. Lin

Time: 2005/6/1

2004/12/23 2

Outline

Review of frequency and time domain interpolation approaches Frequency: Linear and 2nd-order interpolation Time: 2-D interpolation

Simulation results DSP code acceleration Conclusion & future work Reference

2004/12/23 3

LS Estimator LS estimation objective

Channel matrix considering pilot carriers only:

The Transform can reformulated :

LS estimator

2||ˆ|| XHY LS

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Interpolation in Frequency domain Linear Interpolation The need for interpolation Mathematical expression:

Example

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Interpolation in Frequency domain Second-Order Interpolation Mathematical expression:

Example

2004/12/23 6

Interpolation in Time domain 2-D InterpolationWe have pilots

to do interpolation.

568324)8142(4)( tsFixLocPilosPilotsCoincidenttsVarLocPilo NNN

2004/12/23 7

Interpolation in Time domain 2-D Interpolation Using previous symbol information

with 2 kinds of formulas :

(1) Formula 1:

(2) Formular 2:

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2

1)(

~

2

1)(

~

2

1)(

~

2

1

)(~

2

1)(

~

2

1)(

~

2

1)(

~

2

1)(

~

7362

514012

4

fhfhfhfh

fhfhfhfhfh

pppp

ppppformulaDsets

)(~

4

3)(

~

4

7)(

~

2

1)(

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2

3

)(~

4

1)(

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4

5)(

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~

7362

51022

4

fhfhfhfh

fhfhfhfh

pppp

pppformulaDsets

2004/12/23 8

Channel Model

ATTC (Advanced Television Technology Center) and the Grande Alliance DTV Laboratory’s ensemble E model:

6-tap multi-path channel:

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Simulation on Static Channel Comparison between 1st and 2nd formulas by using linear interpolation

MSE SER

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Simulation on Static Channel Comparison between 1st and 2nd formulas by using 2nd-order interpolation

MSE SER

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Simulation on Static Channel Comparison between linear and 2nd-order interpolation by using 1st formula.

MSE SER

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Simulation on Static Channel Comparison between linear and 2nd-order interpolation by using 2nd formula.

MSE SER

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Simulation on Rayleigh Fading Channel fdT=0.01, V=27km/h Comparison between linear and 2nd-order interpolation by using 2nd formula.

MSE SER

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Simulation on Rayleigh Fading Channel fdT=0.02, V=54km/h Comparison between linear and 2nd-order interpolation by using 2nd formula.

MSE SER

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Summation

1st formula works better than 2nd one when suffering static channel condition.

Linear interpolation performs almost the same with 2nd-order one on static channel but better on rayleigh fading channel .

Besides, it is of low complexity.

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DSP Acceleration

Data type modification. Using intrinsic functions. Coding style optimization.

2004/12/23 17

Different Data Types Simulation ResultsFloating-point v.s. Fixed-point 32 bits

Function

Name

Floating-point

Code size

(Bytes)

Floating-point

ExecutetionCycles

Fixed-point

32bits

Code size

(Bytes)

Fixed-point

32bits

Executetion Cycles

Improve-ment

Complex_Multiplier 284 899,603 484 88,513 90.16%

Complex_Divier 404 1,900,051 440 688,850 63.75%

Linear_Interpolation 548 579,794 632 441,423 23.87%

64QAM 580 92,169 456 104,458 -13.33%

De-64QAM 2472 1,305,239 1088 225,016 82.76%

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Different Data Types Simulation ResultsFixed-point 32 bits v.s. Fixed-point 16 bits

Function

Name

Fixed-point

32bits

Code size

(Bytes)

Fixed-point

32bitsExecutetion Cycles

Fixed-point

16bits

Code size

(Bytes)

Fixed-point

16bits

Executetion Cycles

Improve-ment


Complex_Divier 440 688,850 280 283,122 58.89%


64QAM 456 104,458 440 104,458 0%

De-64QAM 1088 225,016 1076 224,055 0.4%

2004/12/23 19

Different Coding Style Simulation Results

Function

Name

Fixed-point

16bits

Code size

(Bytes)

Before

Fixed-point


Before

Fixed-point

16bits

Code size

(Bytes)

After

Fixed-point

16bits

Executetion Cycles

After

Improve-ment


Complex_Divier 280 283,122 348 201,427 28.86%


64QAM 440 104,458 404 104,458 0%

De-64QAM 1076 224,055 1052 218,894 2.3%

2004/12/23 20

Using Intrinsic Functions

For TI C6000 DSP Special functions which have best optimized assembly code on

the TI DSP architecture

(1)_amemd8_const: Allows aligned loads of 8 bytes to memory.

2004/12/23 21

Using Intrinsic Functions

(2)_dotp2 & _dotpn2: Works for complex multiplier.

(3)_add2: 32 bits adder .

2004/12/23 22

Simulation Results by Using Intrinsic Functions

Function

Name

Fixed-point

16bits

Code size

(Bytes)

Before

Fixed-point


Before

Fixed-point

16bits

Code size

(Bytes)

After

Fixed-point

16bits

Executetion Cycles

After

Improve-ment


Complex_Divier 348 201,427 428 193,764 3.8%

Linear_Interpolation 308 132,442 308 132,442 0%

64QAM 404 104,458 404 104,458 0%

De-64QAM 1052 218,894 1052 218,894 0%

2004/12/23 23

Different Coding Style Simulation Results(Interpolation, De-QAM)

Function

Name

Fixed-point

16bits

Code size

(Bytes)

Before

Fixed-point


Before

Fixed-point

16bits

Code size

(Bytes)

After

Fixed-point

16bits

Executetion Cycles

After

Improve-ment

Complex_Multiplier 268 3426 272 3421 0%

Complex_Divier 428 193,764 428 162,960 15.89%


64QAM 404 104,458 396 101,308 3.02%

De-64QAM 1052 218,894 1068 148,169 32.31%

2004/12/23 24

Performance Comparison between Floating-point and Fixed-point version

MSE SER

2004/12/23 25

Future Work

More optimization of DSP code.

2004/12/23 26

Reference Chen, Ying Ying , “Study and Techniques of IEE

E 802.16a TDD OFDMA Downlink Channel Estimation,” June 2004

Texas Instrument, TMS320C6000 Optimizing Compiler User Guild, literature no. SPRU187K, Oct. 2002.

Texas Instrument, TMS320C6000 Programmer’s guide, literature no. SPRU198F, Feb. 2001.

2004/12/231 Techniques for and DSP Software Implementation of IEEE 802.16a TDD OFDMA Downlink...

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