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802.16 work including

Performance of DSP-based TX-RX emulator

Contribution to WP2 and WP3

Daniele Borio, Laura Camoriano, Letizia Lo Presti

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Summary

WP2.1IEEE802.16a : a possible choice for the communication standard

WP2.2a simplified channel model

WP2.3the transmitter scheme

WP3.3Beamforming algorithms for ground antenna

The DSP

emulator

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OFDM IEEE802.16a

Matlab simulation in a simplified scenario

The DSP experiment

Objective: Contribute to the standard choice

Analysis of the degradations due to an implementation on a real digital device

Test of the algorithm efficiency in a real time varying scenario

give indications about performances of a 802.16a based TX-RX system

WP2.1

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Why DSP analysis?

To validate the receiver in a real-HW environment

- Real time (low rate)

- DAC and ADC effects

- DSP arithmetic

Expected results

- Feasibility study of a DSP implementation

- Analysis of the degradation of the performances due to HW limitations

WP2.1

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OFDM suitability formobile applications

Delay spread

Fast fading

WP2.1

Handled by synchronization mechanisms

Handled by channel estimation mechanisms

Handled by OFDM large cyclic prefix

Handled by beamforming techniques

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Other motivations

OFDM is suitable for mobile communications even if multipaths are absent

The WirelessMan group is working to an amendment of 802.16a standard for mobile communication

standard 802.16e (OFDM based)

Beamformig & ODFM for efficiently recover the LOS ray

Doppler shift adaptively compensated using correlation properties of cyclic prefix

WP2.1

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Channel model

The channel model wasn’t completely available at the beginning of the study

Studies carried on a simplified scenario

Next steps:

WP2.2

Beamformer & ODFM performances considering a more complex channel model (MATLAB environment)

E.g. the POLITO channel model

Once the more suitable channel model will be defined -> integration in the DSP emulator

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Considered scenario

Two paths

Doppler

OFDM RX +

AWGN

Beam formerSymbol synchronization

WP2.2

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The Transmitter scheme

IDFT: Search for simplified algorithms (No multiplications)

Adoption of a traditional IFFT

WP2.3

exploit the QAM constellation

symmetry

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Beamforming algorithms for ground antennas

Advantages

Negative aspects

WP3.3

Real time adaptation of the array factor-> suitability for mobile communication with a time varying channel

-> LOS ray recovery, multipaths and interfering cancellation

-> Noise reduction by spatial filtering

Cost: a smart antenna results expensive in comparison with mechanical steerable antenna

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First two steps of the study

Analysis of the state of the art of the beamforming techniques for OFDM

Selection and design of the beamformer

Analysis of the beamformer based on Matlab and C, and tuning of the algorithm parameters.

Porting of the algorithm from Matlab to DSP

Analysis of the beam former based on Matlab and C,

and tuning of the algorithm parameters.

Porting of the algorithm from Matlab to DSP

WP3.3

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State of the art & selection

N.A. (preamble necessary: weights in each subcarrier)

1. Medium complexity

2. Continuous mode

1. Low complexity

2. Continuous mode

1. High complexity

2. Burst mode

1. Medium complexity

2. Burst mode

1. Low complexity

2. Burst mode

N.A. N.A. N.A.

Post-FFT Pre-FFT

Post-FFTSubcarrier clustering

LMSon pilot carriers

LMSon preamble

BlindSemiblind

WP3.3

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Third step of the study

Analysis of the state of the art of the beamforming techniques for OFDM

Selection and design of the beam former

Analysis of the beamformer based on Matlab and C, and tuning of the algorithm parameters.

Porting of the algorithm from Matlab to DSP

Analysis of the state of the art of the beam forming

techniques for OFM

Selection and design of the beamformer

Porting of the algorithm from Matlab to DSP

WP3.3

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Simulation results

BER evaluation as a function of Eb/No.Constellation in presence of AWGN only, Eb/N0 = 10 dB

Constellation in presence of AWGN,

multi-path and Doppler shift, Eb/N0 = 10 dB

Constellation recovered by the beamformer (AWGN multi-path, Doppler shift, Eb/N0 = 10 dB)

Performances evaluation: BER curve

WP3.3

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Other aspects

OFDM Synchronization

Doppler estimation and correction

Correction of phase distortions due to a bad clock signal recovery

WP3.3

Estimation of the Doppler shift using cyclic prefix correlation property

Correction in the frequency domain using pilot tones information

Frame synchronization based on a ML estimator

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Fourth step of the study

Analysis of the state of the art of the beam forming techniques for OFDM

Selection and design of the beam former

Analysis of the beam former based on Matlab and C, and tuning of the algorithm parameters.

Porting of the algorithm from Matlab to DSP

Analysis of the state of the art of the beamforming

techniques for OFM

Selection and design of the beamformer

Analysis of the beamformer based on Matlab and C,

and tuning of the algorithm parameters

WP3.3

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DSP implementation

Lab-demo

RX

DSPDAC

DSPADC

TX

Audio cable

WP3.3

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Problems due to the audio channel

Multiplexing

Synchronization

WP3.3

How transmit several spatially diversified replicas of the same signal on a SIGLE STEREO CHANNEL

How recover the different replicas

-> exploit correlation between replicas

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Problems due to the audio channel

Channel frequency selective

Channel “angle” selective 

WP3.3

“Sample and Hold” audio

channel

Distortion dependent on

the arrival angle

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Lab Demo WP3.3

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Lab Demo WP3.3

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Beamforming

Comparison

DSP

Matlab

WP3.3

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Conclusions

The DSP implementation works

MP mitigated

Open problem: performances with a more realistic channel model

Synchronization OK Open problem: performances with a more realistic channel

model

Analysis with a planar array (to be done)

Doppler >

f