Wireless multimedia systems: equalization techniques, nonlinearities on OFDM signals and echo suppression

Transcription

1 DEIS - Doctorate in Electronics, Computer Science and Telecommunications XXII Cycle final presentation Bologna, 13th January 2010 Wireless multimedia systems: equalization techniques, nonlinearities on OFDM signals and echo suppression Flavio Zabini flavio.zabini2@unibo.it Wireless Communication Laboratory (WiLAB) Tutor: Chiar.mo Prof. Ing. Oreste Andrisano Co-Tutor: Prof. Ing Andrea Conti Consiglio Nazionale delle Ricerche IEIIT

2 Items Partial equalization techniques in the down-link of MC-CDMA systems (in collaboration with: School of Electronics and Computer Science University of Southampton, UK) Reduction of out of band radiation in OFDM systems with nonlinearities (developed at: DoCoMo Eurolabs, Munich, Germany) Echo canceller for DVB-T repeaters ( DVB 2006 project: Metasystem S.p.A.) x

3 Outline Scenario description Coupling channel effects Low-complexity repeater and echo-canceller architecture Coupling channel estimation based on Pulse Sounding Echo-canceller performance: MRR, ES, ESNP Results from theory and measurements Conclusions

4 Scenario description Single Frequency Network (SFN) constituted by: a DVB-T/H broadcasting station an on-channel relay station or repeater (OCR) many stationary and mobile users

5 Coupling channel effects Coupling effects between the transmitting and the receiving antennas (positive feedback) Limited amplifier gains instability risk performance degradation at the final user reduced areas covered by the service Possible countermeasures exploitation of the environment exploitation of the antenna directional characteristics insertion of a digital echo-canceller unit (negative feedback)

6 Basic scheme of the OCR Coupling channel Receiving filter DVB signal Transmitting filter AWGN Amplifier Freq. fs=1/ts Equivalent low-pass representation of signals and processing blocks.

7 Coupling channel estimation Start-up mode pm = p[mr] HT D/A d[nr+k] p(t) G HC(f) A/D HR + pr[nr+k] n[nr+k] Ti : time sample Tp=RTs, with R integer : time interval between two consecutive pulses (of amplitude A) N : Lenght of the estimation pulse train G : Power Amplifier

8 Coupling channel estimation Transmitted pulse train: Equivalent channel transfer function: where Received pulse train at the instant ntp+kts:

9 Coupling channel estimation Averaging the normalized received pulses: where:

10 Cancelling filter structure D stages P taps Transfer function:

11 Search and cancelling window Condition for a perfect echo cancellation: for Set the filter taps to mimic the behaviour of the equivalent channel

12 Echo-canceller performance Heq (f) PS ( f ) (*) W(f) We define the Rejection Ratio (RR) as where is the PSD of the DVB signal to repeat at the output of the D/A. The Mean Rejection Ratio (MRR) is defined as

13 Mean Rejection Ratio After some computations, we obtain: MRR = autocorrelation function of h(t)

14 Echo Suppresion The value of MRR in the absence of the canceller is: The Echo Suppression can be defined as: It quantifies the reduction of the echo power due to the echo canceller

15 Echo Suppresion at Nominal Position Let be s0(t) the signal returning in the repeater in the absence of the canceller and s1(t) the returning signal in the presence of the canceller, and being t* the instant in which the power of the echo pulse response is maximum The Echo Suppression at Nominal Position is defined as: It is an over-estimation of the actual Echo Suppression

16 Theoretical Results

17 FPGA design and implementation FPGA Stratix II Altera EP2S180F1020C3 Analog I/O: Two-channel, 12-bit, 125-million samples per second (MSPS) analog-to digital (A/D) Two-channel, 14-bit, 165-MSPS digital-to-analog (D/A) Digital I/O Connector for the Texas Instruments (TI) Evaluation Module (TI-EVM) Two 40-pin connectors for Analog Devices' A/D converter evaluation boards Mictor connector for Agilent and Tektronix logic analyzers RS-232 serial port 10/100 Ethernet physical layer/media access control (PHY/MAC) and RJ-45 jack Memory 32-Mbyte SDR SDRAM 16-Mbyte flash 1-Mbyte SRAM 16-Mbyte compact flash

18 Test-bed DVB-T Modulator Anritsu Repeater with Echo Canceller

19 Measured impulse response of the channel between the modulator and the demodulator.

20 Echo suppression when the echo level is 10dB lower than the input DVB-T signal.

21 Echo suppression when the echo level is 0.2dB lower than the input DVB-T signal

22 Comparison between ESNP theoretical values and measurements

23 Conclusions A low-complexity digital echo-canceller based Pulse Sounding has been presented The problem of cancelling window position and dimension has been discussed Analytical expressions for MRR, ES and ESNP has been obtained The performance of the canceller in the term of echo suppression have been analytically quantified The measurement done with the test-bed on-board have shown a perfect agreement with the theoretical results

24 Pubblications (1) Journal papers A. Conti, B. M. Masini, F. Zabini and O. Andrisano, On the down-link performance of multi-carrier CDMA systems with partial equalization, Wireless Communications, IEEE Transactions on, Vol.6, n 1, Jan 2007, pp F. Zabini, B.M. Masini, A. Conti, and L. Hanzo, Partial Equalization for MC-CDMA Systems in NonIdeally Estimated Correlated Fading, submitted to IEEE Transactions on Vehicular Technology M. Mazzotti, F. Zabini, D. Dardari, and O. Andrisano, Echo Cancellers based on Pseudo-Noise Training Sequences and on Pulse method: Performance and Stability to be submitted to IEEE Transactions Journals International conferences F. Zabini, A. Conti, B. M. Masini and O. Andrisano, Impact of Partial Equalization on the Downlink Performance of Multi-Carrier CDMA Systems, Vehicular Technology Conference, VTC 2005-Spring IEEE 61, Stockholm, Sweden, May 2005 F. Zabini, B. M. Masini, A. Conti, ON THE PERFORMANCE OF MC-CDMA SYSTEMS WITH PARTIAL EQUALIZATION IN THE PRESENCE OF CHANNEL ESTIMATION ERRORS, 6th International Workshop on Multi-Carrier Spread Spectrum MC-SS, MC-CDMA, OFDM, and related topics, Herrsching, Germany, May 2007 F. Zabini, B. M. Masini, A. Conti, Slow and Fast Adaptation of Partial Equalization for MC-CDMA Systems, Wireless Communication Systems, ISWCS th International Symposium on, Trondheim, Norway, Oct 2007

25 Pubblications (2) F. Zabini, B. M. Masini, A. Conti, On the Performance of MC-CDMA Systems with Partial Combining and Multiple Antennas in Fading Channels, Vehicular Technology Conference, VTC Spring IEEE, Marina Bay, Singapore, May 2008 M. Mazzotti, F. Zabini, D. Dardari, O. Andrisano, Performance of an Echo Canceller based on Pseudo-Noise Training Sequences, BTS 2008 Alexandria, Usa, Oct 2008 B. M. Masini, F. Zabini, On the Effect of Combined Equalization for MC-CDMA Systems in Correlated Fading Channels, Wireless Communications and Networking Conference, WCNC IEEE, Budapest, Hungary, Apr 2009 F. Zabini, G. Chiurco, M. Mazzotti, R. Soloperto, FPGA design and performance evaluation of a pulse-based echo canceller for DVB-T/H, GTTI 2009, Parma, Italia, Jun 2009 L. Toni, A. Conti, F. Zabini and O. Andrisano, Effective Spectral Efficiency for Adaptive QAM with Diversity and Pilot Assisted Channel Estimation, ISWCS 2009The Sixth International Symposium on Wireless Communication Systems 2009 (ISWCS 09), Siena, Italia, Sept 2009