1 / 16

Quadrature Amplitude Modulation (QAM) format

Quadrature Amplitude Modulation (QAM) format. Features of QAM format:. Two carriers with the same frequency are amplitude-modulated independently. The phase of the two carriers is 90 deg. shifted each other.

naomi
Download Presentation

Quadrature Amplitude Modulation (QAM) format

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Quadrature Amplitude Modulation (QAM) format Features of QAM format: • Two carriers with the same frequency are amplitude-modulated independently. • The phase of the two carriers is 90 deg. shifted each other. • 2NQAM processes N bits in a single channel, so it has N times spectral efficiency compared with OOK. Quadrature-phase (Q) Quadrature-phase (Q) 0000 0100 1100 1000 0001 0101 1101 1001 1 0 In-phase (I) In-phase (I) 0011 0111 1111 1011 0010 0110 1110 1010 With OOK Constellation map for 16 (=24) QAM

  2. Various modulation formats for microwaves and their spectral efficiencies [1] Large Small Fixed amplitude Amplitude change (-1.6 dB) Quadrature modulation type ASK type MSK type FSK type PSK type Shannon limit 1024 256 64 16 ・16 QAM • Multi-level FSK • Quadrature • modulation • Associated • quadrature • modulation M-QAM C/W (bit/s/Hz) 4 ・64 QAM • Duobinary • FSK Correlation PSK Coded Satellite communication ・256 QAM Adoption of coding technique Mobile communication Coded modulation Fixed wireless communication Eb/N0 (dB) C: Channel capacity(bit/s), W: Bandwidth (Hz) Eb/N0: Energy to noise power density ratio per bit Eb/N0 at BER = 10-4 is shown assuming synchronous detection Increase in power efficiency Increase in spectral efficiency Modulation schemes and their application fields Spectral efficiency of various modulation schemes [1] Y. Saito, “Modulation and demodulation in digital wireless communication,” IEICE (in Japanese)

  3. Integrated global network 100 Gb/s~1 Tb/s per wavelength Regional IP backbone network 10 Gb/s~40 Gb/s per wavelength User access network 10 Mb/s~1 Gb/s Advantages of QAM optical transmission Microwave transmission Drawbacks of QAM wireless or metallic cable transmission: Obstacle Transmitted point Fading noise caused by obstacles Narrow bandwidth transmission Free space Received point Metallic cable Optical fiber transmission Advantages of QAM optical transmission: No fading noise in optical fibers Broad bandwidth transmission

  4. Configuration for QAM coherent transmission IF signal fIF=fs- fL Optical fiber fs Coherent light source Demodulator PD QAM modulator fL Local oscillator (LO) Optical phase- locked loop (OPLL) circuit Key components of QAM coherent transmission: - Coherent light source: C2H2 frequency-stabilized laser - QAM modulator: Single sideband (SSB) modulator - OPLL circuit: Tunable tracking laser as an LO - Demodulator: Digital demodulator using a software (DSP)

  5. 1.5 GHz Reflection [dB] Wavelength [nm] A C2H2 frequency-stabilized fiber laser[1] Feedback Circuit Low Pass Filter 1.48 mm LD VPZT PZT EDF WDM Electrical Amp Cavity Length ~ 4 m (FSR= 49.0 MHz) PM- FBG[2] DBM Circulator MLP Electrical Amp 80/20 Coupler Phase Sensitive Detection Circuit PD Coupler 13C2H2 Cell LN Frequency Modulator 1.54 mm Optical Output (No Frequency Modulation) Laser Frequency Stabilization Unit Single-frequency Fiber Ring Laser • Frequency stability: 2x10-11 • Line width: 4 kHz [1] K. Kasai et al., IEICE ELEX., vol. 3, 487 (2006). [2] A. Suzuki et al., IEICE ELEX., vol. 3, 469 (2006).

  6. QAM modulator[1] Electrical magnitude of optical signal I data RFA: F1(t)+DCA time MZA MZC Optical input Optical output MZB Electrical magnitude of optical signal p/2 DCC Q data RFB: F2(t)+DCB time MZ: Mach-Zehnder interferometer Configuration of QAM modulator I data Q data DCC [1] S. Shimotsu et al., IEEE Photon. Technol. Lett., vol. 13, 364 (2001).

  7. -40 Phase error: 0.3 deg. -60 -80 SSB phase noise [dBc/Hz] -100 -120 -140 10 Hz 1 MHz Frequency offset SSB phase noise spectrum OPLL circuit with a tunable fiber laser as an LO[1] Resolution: 10 Hz RF spectrum analyzer 500 Hz Less than 10 Hz IF signal: fIF=fs-fL Loop filter1 (Fast operation: 1 MHz) DBM fs PD fsyn Loop filter2 (Slow operation: 10 kHz) Synthesizer to PZT fL LO IF signal spectrum to LN phase modulator Tunable fiber laser - Linewidth: 4 kHz - Bandwidth of frequency response：1.5 GHz [1] K. Kasai et al., IEICE ELEX., vol. 4, 77 (2007).

  8. LPF LPF Configuration of digital demodulator (Software Processing) DSP I(t) QAM Signal S(t) = I(t)cos(wIFt+f0) -Q(t)sin(wIFt+f0) 2cos(wIFt+f) Clock signal Save to file Decode A/D 0, 1, 0, 0, • • • p/2 -2sin(wIFt+f) Q(t) Bit Error Rate Measurement Accumulation of QAM Data Signal Digital Demodulation Circuit Our system operates in an off-line condition by using softwares.

  9. I QAM data signal Pilot Intensity 2.5 GHz Q Optical Frequency Polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) coherent optical transmission system[1] Arbitrary Waveform Generator Delay Line QAM( ) I ⊥ QAM Modulator Arbitrary Waveform Generator Q QAM(//) Optical Filter (~ 5nm) QAM Modulator Att PBS C2H2 Frequency-Stabilized Fiber Laser OFS PC DSF 75 km DSF 75 km Pilot EDFA (MUX) (fOFS =2.5 GHz) 2 GHz FBG IF Signal fIF=fsyn+fOFS=4 GHz Digital Signal Processor A/D PD Att PBS ( or ) (DEMUX) DBM PD EDFA: Erbium-doped Fiber Amplifier PC: Polarization Controller OFS: Optical Frequency Shifter PBS: Polarization Beam Splitter DSF: Dispersion-shifted Fiber FBG: Fiber Bragg Grating PD: Photo-detector DBM: Double Balanced Mixer (fsyn= 1.5 GHz) Feedback Circuit Synthesizer LO [1] M. Nakazawa, et al., OFC2007, PDP26 (2007).

  10. (//) (//) (//) Electrical spectrum of IF signal ( ) (//) ( ) Demodulation bandwidth Demodulation bandwidth 2 GHz 2 GHz (a) Orthogonal polarization (b) Parallel polarization

  11. Experimental result for polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) transmission over 150 km Constellation diagram Eye pattern (I) Eye pattern (Q) (a) Back-to-back (Received power: -29 dBm) (b) 150 km transmission for orthogonal data (Received power: -26 dBm) (c) 150 km transmission for parallel data (Received power: -26 dBm)

  12. Transfer function Impulse response Bandwidth narrowing f f Data signal spectrum Improvement of spectral efficiency by using a Nyquist filter[1] Nyquist filter: Bandwidth reduction of data signal without intersymbol interference [1] H. Nyquist, AIEEE Trans, 47 (1928).

  13. ( ) ( ) (//) Electrical spectrum of IF data signal ( ) (//) ( ) Demodulation bandwidth Demodulation bandwidth 2 GHz 1.5 GHz (a) Without Nyquist filter (b) With Nyquist filter Roll off factor: 0.35

  14. Experimental result for polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) transmission over 150 km[1] Q Q Q Constellation diagram Eye pattern (I) Eye pattern (Q) (a) Back-to-back (Received power: -29 dBm) (b) 150 km transmission for orthogonal data (Received power: -26 dBm) (c) 150 km transmission for parallel data (Received power: -26 dBm) [1] K. Kasai et al., OECC2007, PDP, PD1-1 (2007).

  15. Orthogonal polarization (Back-to-back) Orthogonal polarization (150 km transmission) Parallel polarization (Back-to-back) Parallel polarization (150 km transmission) Bit error rate (BER) characteristics 3 dB

  16. Conclusion • Two emerging optical transmission technologies were described. • (1) Ultrahigh-speed OTDM transmission • 160 Gbit/s-1,000 km transmission was successfully achieved by combing DPSK and time-domain OFT. • OFT has crucial potential especially for high bit rate, thus it is expected to play an important role for OTDM transmission at 320 Gbit/s and even faster. • (2) Coherent QAM transmission • We have successfully transmitted a polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) coherent optical signal over 150 km within an optical bandwidth of 1.5 GHz using a Nyquist filter. • Thus, a spectral efficiency of 8 bit/s/Hz has been achieved in a single-channel.

More Related