Chapter 4 Experimental Demonstration of System for Wire
4.4 Experimental results for OFDM signal with bit-loading
4.4.2 Transmission results of bit-loading OFDM signal
is optical power of un-modulated subcarrier over power of signals modulated optical carrier. And inset (a), (b), (c) of figure 5-5 are OPR = 1 dB, OPR = 3 dB, OPR = 5 dB before frequency quadrupling system, respectively. Inset (d), (e) and (f) illustrate OPR = 1 dB, OPR = 3 dB, OPR = 5 dB after frequency quadrupling system and interleaver.
4.4.2 Transmission results of bit-loading OFDM signal
1549.8 1550.0 1550.2 1550.4 -70
1549.5 1549.8 1550.1 1550.4 1550.7 -60
Figure 4-22 Electrical spectrums of bit-loading OFDM signals.
Figure 4-22 illustrates the electrical spectrums for bit-loaidng signals and indicates where the spectrums belong to. Inset (a) of Fig. 4-22 is the electrical spectrum of transmitter terminal OFDM signals and 12-GHz subcarrier. Inset (b) of Fig. 4-22 is the optical spectrum of I/Q up-conversion. Inset (c) of Fig.
4-22 receiver is the optical spectrum of frequency quadrupling. Inset (d) of Fig.
4-22 is the electrical spectrum of bit-loading OFDM signals. We down-convert the signals to center frequency 5-GHz and the bandwidth is 7-GHz.
-10 -9 -8 -7 -6 -5 -4
Received Power (dBm)
Bit-loading_BTB
Received Power (dBm)
Bit-loading_BTB
(Data rate = 32.0313 Gbps) Bit-loading_25km
FEC limit
Figure 4-23 SNR and BER vs. Received power for 16-QAM OFDM signal.
Figure 4-23 shows the SNR and BER curves of the 32Gbps bit-loading OFDM signals using optimal OPR after transmission over 25-km SMF. After transmission 25-km, the sensitivity penalties is about 0.3dB. Although it still worsens the performance a little, it does better than using electrical mixer with noise figure (NF) 8-dB.
0 10 20 30 40 50 60 70 80 90 16
17 18 19 20 21 22 23 24 25 26
SNR (dB)
Subcarier Number
BTB@-5dBm
(Data rate = 32.0 Gbps)
16-QAM 32-QAM 64-QAM
Figure 4-24 Constellations of the bit-loading OFDM signal.
Figure 4-24 shows bit-loading OFDM signals constellation diagrams and SNR vs. subcarrier number after the system in back-to-back and 25km SMF transmission. They are captured at PD received power equal to -6dBm.
Figure 4-25 shows data rate and BER vs. received power after the system in back-to-back and 25km SMF transmission. We fixed BER of each point below then 10−3. They have different data throughput of received power.
Figure 4-25 (a) Fixed BER of each received power below then 10−3.
-9 -8 -7 -6 -5
28 29 30 31 32
Data Rate (Gbps)
Received Power (dBm)
BTB 25km
Figure 4-25 (b) Data rate vs. received power of BER below then 10−3. Fiber Transmission = BTB Fiber Transmission = 25km
Received Power (dBm)
Data rate
(Gbit/sec) BER Received Power (dBm)
Data rate
(Gbit/sec) BER
-5 32.0 2.79E-04 -5 32.0 1.16E-04
-6 31.1 7.84E-04 -6 32.0 1.04E-04
-7 30.3 7.40E-04 -7 30.3 4.79E-04
-8 28.9 5.15E-04 -8 29.4 8.39E-04
-9 28.1 6.37E-04 -9 28.3 4.18E-04
-9 -8 -7 -6 -5 4.0
3.8 3.6 3.4 3.2 3.0
-Log(BER)
Received Power (dBm)
BTB 25km
FEC limit
Figure 4-25 (c) BER vs. received power of BER below then 10−3.
Chapter 5
Experimental Demonstration of System for Wireless
5.1 Experimental steup
32.65-Gb/s OFDM signal
φ φ
φ
φ
bias 0 V =
bias 0 V =
Figure 5-1 Experimental setup for all optical up-conversion with wireless transmission.
Figure 5-3 depicts the experimental setup for all optical I/Q up conversion system via a I/Q modulator. We use a continue wave tunable laser (CW-TL) to generate light source about 1550nm. The light source is then passed through a polarization controller to achieve max optical power when the I/Q modulator is biased at full point. The signals (signal-I and signal-Q) are generated by a Tektronix ○R AWG7102 arbitrary waveform generator (AWG) using a
Matlab○R program. The sample rate and digital-to-analog converter (DAC) resolution of the AWG are 10 Gb/s and 8 bits, respectively. And we generation four different OFDM signals, 20.625Gb/s 8-QAM OFDM signals, 27.5Gb/s 16-QAM OFDM signals and 34.375Gb/s 32-QAM OFDM signals, all of them have the same parameter, the IFFT length is 128, a 78.125MSyn/s m-QAM symbol is encoded at 88 channels (i.e. channels 2-45 and 85-128) with the remaining 40 channels set to zero. Therefore, an optical m-QAM OFDM signals that has 88 subcarriers and occupies a total bandwidth of 7GHz can be generated. And then we use two the same type low noise amplifier to amplify signal-I and signal-Q to reach the best modulation index (MI) condition.
Following, we use tunable phase shift to control 900 phase delay between signal-I and signal-Q. In order to realize optical direct-detection OFDM signal, a new optical subcarrier is generated at the lower sideband of the original carrier by 12GHz. In there, we use a 900 phase delay coupler to divide the sinusoidal wave into two parts. And combine the OFDM signals and clock signal. Then we bias both MZ-a and MZ-b at null point and set the phase modulator to delay 900. After the first MZM, the generated OFDM signals is up-converted by using frequency quadrupling technique. After 50/100 optical inter-leaver to filter out the sideband we don’t want, the OFDM signals at 60GHZ is generated at (a) of Figure 5-1. A 25-km single mode fiber (SMF) is used to evaluate the transmission penalty of the system. After square-law photo diode (PD) detection, an electrical OFDM signals at 60GHz is generated and down-converted to 5GHz at (b) of Figure 5-1. The down-converted OFDM signals is captures by a Tektronix○R DPO 71254 with a 50GHz sample rate and a 3-dB bandwidth of 12.5GHz. An off-line DSP program is employed to demodulate the OFDM signal. The demodulation process includes
synchronization, Fast Fourier Transform (FFT), one-tap equalization, I/Q imbalance compensation and QAM symbols decoding. The bit error rate (BER) performance is calculated from the measured signal-to-noise ratio (SNR).
5.2 Experimental results for OFDM signal without bit-loading algorithms 5.2.1 Transmission results of 8-QAM
Figure 5-2 illustrates the electrical spectrums for 8-QAM signals and indicates where the spectrums belong to. Inset (a) of Fig. 5-2 is the electrical spectrum of 8-QAM OFDM signals. We down-convert the signals to center frequency 5-GHz and the bandwidth is 7-GHz.
Figure 5-2 Electrical spectrums of 8-QAM OFDM signals with wireless transmission.
Figure 5-3 shows the SNR and BER curves of the 20.625Gbps 8-QAM OFDM signals using optimal OPR after transmission over 25-km SMF. After transmission 25-km, the sensitivity penalties is about 0.3dB. Although it still worsens the performance a little, it does better than using electrical mixer with
AWG Interleaver
0 1 2 3 4 5 6 7 8 9 10
-80 -70 -60 -50 -40
Level (dBm)
Frequency (GHz) 8QAM_BTB
-10 -9 -8 -7 -6 -5 -4 16.5
17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0
SNR (dB)
Received Power (dBm)
8QAM_BTB 8QAM_25km
-10 -9 -8 -7 -6 -5 -4
6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5
-Log(BER)
Received Power (dBm)
8QAM_BTB 8QAM_25km
FEC limit
Figure 5-3 SNR and BER vs. Received power for 8-QAM OFDM signal with wireless transmission.
Figure 5-4 shows 8-QAM constellation diagrams and SNR vs. subcarrier number after the system in back-to-back and 25km SMF transmission. They are captured at PD received power equal to -6dBm.
Figure 5-4 (a) Constellations of the 8-QAM OFDM signal with wireless transmission.
0 10 20 30 40 50 60 70 80 90 16
17 18 19 20 21 22 23 24 25
SNR (dB)
Subcarrier Number
BTB 25km
Figure 5-4 (b) SNR vs. Subcarrier Number of the 8-QAM OFDM signal with wireless transmission.
0 10 20 30 40 50 60 70 80 90
Figure 5-4 (c) BER vs. Subcarrier Number of the 8-QAM OFDM signal with wireless transmission.
5.2.2 Transmission results of 16-QAM
Figure 5-5 Electrical spectrums of 16-QAM OFDM signals with wireless transmission.
Figure 5-5 illustrates the electrical spectrums for 16-QAM signals and indicates where the spectrums belong to. Inset (a) of Fig. 5-5 is the electrical
12GHz
55 GHz Remote Antenna Unit
0 1 2 3 4 5 6 7 8 9 10
spectrum of 16-QAM OFDM signals. We down-convert the signals to center frequency 5-GHz and the bandwidth is 7-GHz.
-10 -9 -8 -7 -6 -5 -4
17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0
SNR (dB)
Received Power (dBm)
16QAM_BTB 16QAM_25km
-10 -9 -8 -7 -6 -5 -4
4.0 3.5 3.0 2.5
-Log(BER)
Received Power (dBm)
16QAM_BTB 16QAM_25km
FEC limit
Figure 5-6 SNR and BER vs. Received power for 8-QAM OFDM signal with wireless transmission.
Figure 5-6 shows the SNR and BER curves of the 27.5Gbps 16-QAM OFDM signals using optimal OPR after transmission over 25-km SMF. After transmission 25-km, the sensitivity doesn’t have penalties. Although it still
worsens the performance a little, it does better than using electrical mixer with noise figure (NF) 8-dB.
Figure 5-7 (a) Constellation for 8-QAM OFDM signal with wireless transmission.
0 10 20 30 40 50 60 70 80 90 17
18 19 20 21 22 23 24
SNR (dB)
Subcarrier Number
BTB 25km
Figure 5-7 (b) SNR vs. Subcarrier Number for 8-QAM OFDM signal with wireless transmission.
0 10 20 30 40 50 60 70 80 90 15
12 9 6 3
-Log(BER)
Subcarrier Number
BTB 25km
FEC Limit
Figure 5-7 (c) BER vs. Subcarrier Number for 8-QAM OFDM signal with wireless transmission.
Figure 5-7 shows 16-QAM constellation diagrams and SNR vs. subcarrier number after the system in back-to-back and 25km SMF transmission. They are captured at PD received power equal to -6dBm.
5.3 Experimental results for OFDM signal with bit-loading algorithms 5.3.1 Transmission results of bit-loading algorithm
Figure 5-8 illustrates the electrical spectrums for bit-loading OFDM signals and indicates where the spectrums belong to. Inset (a) of Fig. 5-8 is the electrical spectrum of receiver 32-QAM OFDM signals. We down-convert the signals to center frequency 5-GHz and the bandwidth is 7-GHz.
Figure 5-8 Electrical spectrums of Bit-loading OFDM signals with wireless transmission.
Figure 5-9 shows the SNR and BER curves of the bit-loading OFDM signals using optimal OPR after transmission over 25-km SMF. After transmission 25-km, the sensitivity penalties is about 1dB. Although it still worsens the performance a little, it does better than using electrical mixer with noise figure (NF) 8-dB.
-10 -9 -8 -7 -6 -5 -4
Received Power (dBm)
Bit-loading_BTB Bit-loading_25km
Figure 5-9 (a) SNR vs. Received power for Bit-loading OFDM signal with wireless transmission.
12GHz
55 GHz Remote Antenna Unit
0 1 2 3 4 5 6 7 8 9 10
-10 -9 -8 -7 -6 -5 -4 3.8
3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0
-Log(BER)
Received Power (dBm)
Bit-loading_BTB Bit-loading_25km
FEC limit
Figure 5-9 (b) BER vs. Received power for Bit-loading OFDM signal with wireless transmission.
Figure 5-10 (a) BTB Constellation for Bit-loading OFDM signal with wireless transmission.
0 10 20 30 40 50 60 70 80 90 16
17 18 19 20 21 22 23 24 25
SNR (dB)
Subcarrier Number
BTB@-5dBm
(Data Rate = 32.0 Gbps)
16-QAM 32-QAM 64-QAM
Figure 5-10 (b) BTB SNR vs. Subcarrier Number for Bit-loading OFDM signal with wireless transmission.
Figure 5-11 (a) Constellation for 25km of Bit-loading OFDM signal with wireless transmission.
0 10 20 30 40 50 60 70 80 90
Figure 5-11 (b) SNR vs. Subcarrier Number for 25km of Bit-loading OFDM signal fiber with wireless transmission.
Figure 5-10 shows 32-QAM constellation diagrams and Fig. 5-11 shows SNR vs. subcarrier number after the system in back-to-back and 25km SMF transmission. They are captured at PD received power equal to -8dBm.
-9 -8 -7 -6 -5
Data Rate (Gbps)
Received Power (dBm)
BTB
Received Power (dBm)
BTB 25km
FEC limit
Figure 5-12 (a) Data rate vs. received power of BER below then 10−3.
Figure 5-12 (b) Fixed BER of each received power below then 10−3.
Figure 5-12 shows data rate and BER vs. received power after the system in back-to-back and 25km SMF transmission. We fixed BER of each point below then 10−3. They have different data throughput of received power.
Fiber Transmission = BTB Fiber Transmission = 25km
Received Power (dBm)
Data rate
(Gbit/sec) BER Received Power (dBm)
Data rate
(Gbit/sec) BER
-5 32.0 5.37E-04 -5 32.0 2.76E-04
-6 31.1 4.12E-04 -6 31.1 3.67E-04
-7 30.3 3.55E-04 -7 30.3 2.20E-04
-8 28.9 5.12E-04 -8 30.3 6.86E-04
-9 28.1 0.00111 -9 28.9 1.00E-03
Chapter 6
Conclusion
Bit-loading algorithms that have high system throughput while guaranteeing a mean BER below a given target value for multicarrier systems are presented. Results showed that the bit-loading algorithm could be used to optimize the signal and increase performance of system to achieve higher data rate, even the channel response have non-flat channel response, especially for 60 GHz RoF system with up to 10 dB deviation within the 7 GHz spectrum.
This algorithm provides a solution that can satisfy the demand of 60GHz application within 7GHz license-free band.
Bit-loading algorithm significantly improves performance and data throughput of ultra-wideband mm-wave RoF systems, it has a great potential to allocate appropriate modulation format for each subcarriers. As the results, we used bit-loading algorithm to optimize OFDM signals at different received power and record 32Gbps 25km fiber transmission on 3m wireless distance was achieved. We demonstrate the dynamic OFDM modulation in 60GHz RoF system.
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