Investigation of high data rate digital. modulations in optical-microwave links. Yannis Le Guennec. Márk Csörnyei

Transcription

1 Investigation of high data rate digital modulations in optical-microwave links Márk Csörnyei Yannis Le Guennec, IMEP Institut de Microélectronique d'electromagnétisme et de Photonique ENSERG

2 Outline Introduction Nonlinearities in the optical link Nonlinearities in the wireless section Conclusions References

3 Introduction Next generation LAN and Mobile networks Large number of low-cost and small BS-s Impairment: Multipath fading Solution: Optically fed picocell mobile networks Combination of Subcarrier Multiplexed Optical transmission and OFDM

4 Optically fed mobile network Diode Pump Picocell MMW Source Microchip laser RIN Suppression Information signals Mach- Zehnder Base station Optically fed fiber radio system. The mode-locked laser transmitter architecture eliminates the need for a millimeter-wave local oscillator in the basestation. Relative Intensity Noise module has to suppress the low frequency RIN peak of the microchip laser, which could be very disturbing at the optical heterodyning.

5 Nonlinearities in the optical link Mach-Zehnder Interferometric External modulator MZI is the most important source of nonlinear behaviour in the optical section of the information network t P + π v V f IN M P O 1 cos = 2 π P o is the output power of the modulator, P IN is the input power, v M is the voltage at the modulator electrodes, V is the voltage required to produce a phase shift of 180 degree between the two interferometric modulator arms

6 Nonlinearities in the optical link II Optical transfer function, Pout/Pin M odulation voltage, V m Optical transfer function P OUT /P IN versus v M for a Mach-Zehnder Interferometric external modulator. Biasing point at v M =0.35V. There are three modulation amplitudes around the biasing point, one in the linear range of the optical transfer function and the others in the nonlinear regime of the device.

7 Characterisation of nonlinear effects 1.E E-01 1.E-02 BER a) b) c) 1.E-03 1.E-04 Signal to Noise ratio (db) BER plots versus signal-to-noise ratio. a) ideal characteristics for 16QAM combined with OFDM modulation, input amplitude 100mV (Fig.1.), b) modulation amplitude at the RF input of the Mach-Zehnder Intererometric modulator is 200mV (Fig.1.), c) the modulation device is driven far in the nonlinear regime with an amplitude of 350mV (Fig.1.).

8 Nonlinearities in the wireless section Nonlinear saturation of a HPA Pout;dBm Nonlinear saturation of MGa Pin;dBm 2.7 V 3.0 V 3.3 V Parameter is the drain-source voltage

9 Nonlinearities in the wireless section II. Adjacent Channel Power Ratio versus amplifier back-off 60 ACPR vs. Backoff 50 ACPR (db) Backoff (db)

10 Nonlinearities in the wireless section III. OFDM transmission spectrum without back-off ACPR 26dB Frequency,MHz dbm

11 Nonlinearities in the wireless section IV. OFDM transmission spectrum at 4dB back-off ACPR 35dB Frequency,MHz dbm

12 Eye diagram measurement with Communication Signal Analyzer HP70004A Display ClkIn DataIn TrigIn Tektronix Communications Signal Analyzer TrigIn DataIn HP70841B Generator Range 0.1-3Gbit/s ClkOut DataOut TrigOut Laser Photo receiver Current Supply Voltage supply

13 Eye diagram of a 3Gbit/sec NRZ optical transmission.

14 Vector signal measurements Agilent Agilent 89605B 89605B 250kHz-6GHz 250kHz-6GHz ESG ESG Vector Vector Signal Signal Generator Generator PC PC Digital Modulation Out Software: Software: Agilant Agilant Vector Vector Signal Signal Analyzer Analyzer IEEE 1394 Ports SMA Coax Agilent Agilent E80401A E80401A VXI VXI Mainframe Mainframe Vector Vector Signal Signal Analyzer Analyzer Hardw. Hardw. Agilent Agilent 89605B 89605B Input Input Module Module SMA Coax Laser Photo Laser Photo receiver receiver Current Current Supply Voltage supply Supply Voltage supply

15 Constellation diagram and spectrum of a QPSK signal in the otpical link. The carrier frequency: 1GHz, data rate: 1Msymbol/sec, filter alpha factor 0.35

16 Constellation diagram and spectrum of a QPSK signal in the otpical link. Filter alpha factor: 1.

17 Conclusions Combined SCM OFDM transmission setup is optimal for WLAN applications Sensitivity to the nonlinearities were studied in both the optical and the wireless section Optimal solutions were given concerning the required output power, efficiency, and quality

18 References HER,2001] Peter.R.Herczfeld, Overview of Microwave Photonics Activity under MARC, Optical/Wireless Workshop Dig., Budapest, Hungary, 12 March [JEM,2000] W.D.Jemison, P.R.Herczfeld, W.Rosen, A.Vieira, A.Rosen, A.Paolella, A.Joshi, Hybrid Fiberoptic-Millimeter Wave Links, IEEE Microwave Magazine Vol. 1, Number 2, June 2000 [COX,1990] Charlses H. Cox, Gary E.Betts, Leonard M.Johnson, An analytic and experimental comparison of direct and external modulation in analog fiber-optic links, IEEE Trans. on Microwave Theory and Techniques Vol.38, No 5, May [ACK,1993] E.Ackerman, S.Wanuga, D.Kasemset, A.Daryoush, N.Samant, Balanced receiver external modulation fiber-optic link architecture with reduced noise figure, IEEE MTT-S Int.Microwave Symp.Dig., Atlanta, GA, June 1993, pp [FRI,1998] M. Friesex, On the degradation of OFDM-signals due to peak-clipping in optimally predistorted power amplifiers, Global Telecommunications Conference, GLOBECOM The Bridge to Global Integration. IEEE, vol.2, pp [DIX,1999] B.J.Dixon, R.D.Pollard, S.Iexekiel, "A discussion of the effects of amplifier back-off on OFDM", pp 14-19, High Frequency Postgraduate Student Colloquium, 1999 [FRI,1999] Friese, M.; Havezov, P., "Power back-off strategies for very high bit rate digital subscriber line transmission systems " Global Telecommunications Conference, GLOBECOM '99, pp , vol.2, 1999