Quadrature Amplitude Modulation (QAM) format Features of QAM format: Two carriers with the same frequency are amplitude-m odulated independently. The phase of the two carriers is 90 deg. shifted eac h other. 2 N QAM processes N bits in a single channel, so it has N times spectral efficiency compared with OOK. Constellation map for 16 (=2 4 ) QAM 0000 0100 1000 1100 0101 1101 1001 0001 1111 0011 0111 1011 0110 0010 1110 1010 r θ 同同同(I) 同同同同(Q) In-phase (I) Quadrature-phase (Q) 0 1 With OOK In-phase (I) Quadrature-phase (Q)
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Quadrature Amplitude Modulation (QAM) format Features of QAM format: Two carriers with the same frequency are amplitude-modulated independently. The phase.
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Quadrature Amplitude Modulation (QAM) formatQuadrature 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.
2N QAM processes N bits in a single channel, so it has N times spectral efficiency compared with OOK.
Constellation map for 16 (=24) QAM
0000 0100 10001100
0101 1101 10010001
11110011 0111 1011
01100010 1110 1010
rθ 同位相(I)
直交位相(Q)
In-phase (I)
Quadrature-phase (Q)
0 1
With OOK
In-phase (I)
Quadrature-phase (Q)
Modulation schemes and their application fields
Eb/N0 (dB)
C/W
(b
it/s
/Hz)
M-QAM
4
1664
2561024
(-1.6 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
[1] Y. Saito, “Modulation and demodulation in digital wireless communication,” IEICE (in Japanese)
Various modulation formats for microwaves and their spectral efficiencies [1]
Various modulation formats for microwaves and their spectral efficiencies [1]
Shannon limit
Increase in power efficiencyIncrease in spectral efficiency
Experimental result for polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) transmission over 150 km
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 transmissionfor orthogonal data
(Received power: -26 dBm)
(c) 150 km transmission for parallel data(Received power: -26 dBm)
Improvement of spectral efficiency by using a Nyquist filter[1]
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).Data signal spectrum
Bandwidth narrowing
f f
Impulse response
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
-4 -2 0 2 4
Am
plitu
de
Symbol period
0
0.2
0.4
0.6
0.8
1
1.2
-1.5 -1 -0.5 0 0.5 1 1.5
H(f
)
Normalized frequency
Transfer function
-100
-80
-60
-40
-20
0
1 2 3 4 5 6
Po
wer
[dB
]
Frequency [GHz]
LO (//)Pilot(⊥)QAM data signal (//)
4 GHz
2.5GHz
Inte
nsit
y
1.5GHz
Optical Frequency
-100
-80
-60
-40
-20
0
1 2 3 4 5 6
Po
wer
[dB
]
Frequency [GHz]
Demodulation bandwidth2 GHz 1.5 GHz
(a) Without Nyquist filter (b) With Nyquist filter Roll off factor: 0.35
(//)
( )
( ) LO (//)Pilot(⊥)QAM data signal (//)
4 GHz
2.5GHz
Inte
nsit
y
1.5GHz
Optical Frequency
( )
(//)
Demodulation bandwidth
( )
Electrical spectrum of IF data signal Electrical spectrum of IF data signal
Constellation diagram
Eye pattern (I)
Eye pattern (Q)
(a) Back-to-back(Received power: -29 dBm)
(b) 150 km transmissionfor orthogonal data
(Received power: -26 dBm)
(c) 150 km transmission for parallel data(Received power: -26 dBm)
Q Q Q
Experimental result for polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) transmission over 150 km[1]
Experimental result for polarization-multiplexed 1 Gsymbol/s, 64 QAM (12 Gbit/s) transmission over 150 km[1]
[1] K. Kasai et al., OECC2007, PDP, PD1-1 (2007).
Orthogonal polarization (Back-to-back)Orthogonal polarization (150 km transmission)Parallel polarization (Back-to-back)Parallel polarization (150 km transmission)
10-5
10-4
10-3
-38 -36 -34 -32 -30 -28 -26
Bit
Err
or
Ra
te
Received Power [dBm]
3 dB
Bit error rate (BER) characteristicsBit error rate (BER) characteristics
ConclusionConclusion
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.