work including Performance of DSP-based TX-RX emulator Contribution to WP2 and WP3 Daniele Borio, Laura Camoriano, Letizia Lo Presti

2 Summary WP2.1 IEEE802.16a : a possible choice for the communication standard WP2.2 a simplified channel model WP2.3 the transmitter scheme WP3.3 Beamforming algorithms for ground antenna The DSP emulator

3 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 a based TX-RX system WP2.1

4 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

5 OFDM suitability for mobile 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

6 Other motivations OFDM is suitable for mobile communications even if multipaths are absent The WirelessMan group is working to an amendment of a standard for mobile communication standard e (OFDM based) Beamformig & ODFM for efficiently recover the LOS ray Doppler shift adaptively compensated using correlation properties of cyclic prefix WP2.1

7 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

8 Considered scenario Two paths Doppler OFDM RX + AWGN Beam former Symbol synchronization WP2.2

9 The Transmitter scheme IDFT: Search for simplified algorithms (No multiplications) Adoption of a traditional IFFT WP2.3 exploit the QAM constellation symmetry

10 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

11 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

12 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. Post-FFTPre-FFT Post-FFT Subcarrier clustering LMS on pilot carriers LMS on preamble Blind Semiblind WP3.3

13 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

14 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

15 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

16 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

17 DSP implementation Lab-demo RX DSP DAC DSP ADC TX Audio cable WP3.3

18 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

19 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

20 Lab Demo WP3.3

21 Lab Demo WP3.3

22 Beamforming Comparison DSP Matlab WP3.3

23 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 >

24 Document Properties Document title work including performance of DSP- based TX-RX emulator Document numberCAP-0243-WP21-EUC-CON-P00 Author (s)Daniele Borio, Laura Camoriano, Letizia Lopresti Date24/11/2004 Participant (s) (short name)EUC Workpackage (s)WP 2.1, 2.2, 2.3, 3.3 Total number of slides (including title and this slide) 24 Security level (PUB, RES, CON)CON Description/AbstractEuroconcepts’ contribution for the standard choice: DSP analysis of norm IEEE802.16a