March 2004
10GBASE-T: A new proposal for improving PAM performance with OFDM
Yuji Kasai, Eiichi Takahashi, Tetsuya Higuchi(National Institute of Advanced Industrial Science and Technology )
Masahiro Murakawa(Evolvable Systems Research Institute)
Shinji Nishimura(Hitachi, Ltd.)
2
Supporters
• The Tokyo Electric Power Company, Inc.
• POWEREDCOM, Inc.
3
• OFDM signal transmission method applied to 10GBASE-T
• PAM-based frequency division multiplexing – 10-Gbps data transmission– 6.1-dB noise margin
• 100-m signal transmission with CAT-7 cable
Objectives
4
1. Current 10GBASE-T proposals
+3 -3 -1-4 Noise Margin (dB)with 6 dB coding gain
0.5-2us
20
-
500
1000
4D-PAM8
192633 RequiredSNR (dB)
< 100 ns
2
625
1250
PAM-5
< 100 ns< 100 nsLatency
3-LaunchVoltage (Vp-p)
417312.5Bandwidth(MHz)
833625Symbol Rate(Mbps)
PAM-10PAM-20
5
1. Issues with current proposals
6005004003002001000Freq. [MHz]
700 800
20
40
60
0
SNR [dB]
PAM20
PAM10
PAM5 Class-E 55m
Class-F 100m10
30
50
70
4D-PAM
6-dB coding gain included
6
2. OFDM Technique for 10GBASE-T
● Orthogonal Frequency Division Multiplexing (OFDM)– Special form of multi-carrier modulation– High spectral efficiency – Less sensitive to inter-symbol interference
● 7 PAM signals transmitted over 7 frequency-nonselective channels
● Required frequency bandwidth: 547 MHz + pilot signal● Symbol rate: 156.25 MHz (=10GHz/(4chx16bit))● Low latency: < 100 ns
7
OFDMSignal
f1-I
f1-Q
f2-I
f2-Q
f3-I
f3-Q
Data Signals
f1 f2 f3156.25MHz 312.5MHz 468.75MHz
546.88MHz0 Freq.
Spectrum
2. OFDM Technique
Σ
OFDM technique distributes the data over a number of carriers that are spaced apart at precise frequencies. This spacing provides the "orthogonality" which prevents the demodulators from seeing frequencies other than their own.
8
2. Signaling in OFDM
01+12+23+3
4
Data bits
3468.75 MHz (I,Q)0
51020
PAM Level
625 MHzpilot signal
312.5 MHz (I,Q)156.25 MHz (I,Q)Base signal
Carrier Frequency
Total 16 bitsI: In-phase, Q: Quadrature-phase
156.25 MHz
I Q
312.5 MHz
I Q
468.75 MHz
I Q
Frequency: Base signal
9
2. SNR Margins
6005004003002001000Freq. [MHz]
700 800
20
40
60
0
SNR [dB]
(PAM20)
(PAM10)
(PAM3)
Class-E 55m
Class-F 100m10
30
50
70
(PAM5)
8dB
6dB
7dB
7dB
6-dB coding gain included
10
DSP
2. Block Diagram
RJ45Hybrid
LineDriver
RxAmp.
AnalogFiltering
AnalogFiltering
DAC
ADC
OFDMDecoder
OFDMEncoder
Scrambler
De-scrambler
MACIF
ClockGeneratorClock
Detector
625MHz
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2. OFDM Modulation on DSP
● DSP processing on TX– 7 PAM signals (pi) are converted into 12 OFDM signals (xi,xpi,xni).– One symbol consists of 8 OFDM signals (xi).
tp7time
Symbol period (6.4 ns)x
−−−−−−−−−−
−−−−−
−−−−−
−−−−−
−−−−−−−−−
−−−−
=
ppppppp
xnxnxxxxxxxxxpxp
7
6
5
4
3
2
1
2
1
8
7
6
5
4
3
2
1
8
7
04.001.002.004.003.004.005.015.020.023.017.029.009.031.015.052.040.047.061.028.069.067.031.062.059.034.086.095.072.030.063.063.037.090.0130.072.063.063.090.037.0130.072.063.063.090.037.0172.030.063.063.037.090.0167.031.062.059.034.086.095.015.052.040.047.061.028.069.015.020.023.017.029.009.031.004.001.002.004.003.004.005.0
tp8 t1 t2 t3 t4 t5 t6 t7 t8 tn1 tn2
x1
x2
x3
x4 x5
x6
x7
x8
● RX can be handled in reverse fashion of TX. ● Major overhead of OFDM is only 20-ns matrix computation.
Low Latency
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2. Advantages of OFDM Method● OFDM achieves high spectral efficiency
– Required bandwidth is 547 MHz + pilot signal
● Slow symbol rate: 156.25 MHz– Inter-symbol interference is small
● Large noise margin: 6.1dB (with 6-dB coding gain)
● Latency: < 100 ns
● Add-on available: PAM-20,10,5, and 4D-PAM8
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3. Experimental Setup (1)
Hybrid
Cat-7 cable(100 m)
DataGenerator
EqualizerADCLogic
Analyzer
RX
TX
DAC
PLL: Waveform measured point
Hybrid
1-symbol and 1-channel data transmission
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Data GeneratorLogic Analyzer
CAT-7 Cable (100 m)
Testbed Board
3. Experimental Setup (2)
15
3. Experimental Results (Waveform)
TX side RX side
156.25 MHz
I Q
312.5 MHzI Q
468.75 MHz
I Q
Frequency: Base signal
Clock jitter: < 20 ps (RMS)
156.25 MHz
I Q
312.5 MHzI Q
468.75 MHzI Q
Frequency: Base signal
16
3. Experimental Results (DSP)
156.25 MHz
I Q
312.5 MHz
I Q
468.75 MHz
Frequency: Base signal
PAM Level
PAM Level PAM Level
PAM Level PAM Level
I QPAM Level PAM Level
6.4 ns
6.4 ns 6.4 ns 6.4 ns 6.4 ns
6.4 ns 6.4 ns
Inter-symbol interference is canceledSNR is measured
SNR: 32.1 dB
SNR: 31.9 dB SNR: 26.5 dB
SNR: 28.8 dB SNR: 24.4 dB
SNR: 21.1 dB SNR: 18.9 dB
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3. BER Estimation (1)
16SNR [dB]
20 24 28 32 3612 40
PAM20PAM10PAM8PAM5PAM3
without coding
468.75 MHz-Q 312.5MHz-Q
156.25MHz-Q
156.25MHz-I
Base signal
468.75 MHz-I 312.5MHz-I
1E-2
BER
1E-4
1E-6
1E-8
1E-10
1E-12
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3. BER Estimation (2)
1.2E-11< 1E-122.4E-10< 1E-128.5E-42.1E-113.0E-3BERwithout coding
18.8921.0824.3828.8126.4631.8532.09SNR (dB)
1
3
468.75 I-phase
3
10
156.25 Q-phase
12234AssignedNumber of bit
3551020PAM Level
468.75 Q-phase
312.5Q-phase
312.5 I-phase
156.25 I-phase
BaseSignal
CarrierFrequency(MHz)
Averaged BER without coding: 9.1E-4
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3. BER Estimation (3)
9.1x10-4
6dBCoding Gain
SNR [2dB/div]
1E-2BER
1E-4
1E-6
1E-8
1E-10
1E-14
1E-0
1E-12
BER < 10E-12with 6dB coding gain
WithCoding Gain
WithoutCoding Gain
20
Conclusion
• OFDM method applied to 10GBASE-T– Required bandwidth: 547 MHz + pilot signal– Noise margin: 6.1 dB (with coding gain)– Low latency: < 100 ns
• Experimental result– 100-m data transmission with BER of < 1E-12