Chapter 3 The theoretical calculations of proposed system
3.3 Theoretical calculations and simulation results
The theoretical calculations of proposed system, the driving RF signal V t( ) consisting of an electrical sinusoidal signal and a dc biased voltage can be written as
1 1 2 2
( ) bias cos( ) cos( )
V t =V +V ωt +V ω t (Eq. 3-21)
where Vbias is the dc biased voltage, V1, V2 and ω1, ω2 are the amplitude and the angular frequency of the electrical driving signals, respectively. The optical carrier phase difference induced by ( )V t is given by
0 1 1 2 2
biased voltage, and 1 1 2
= is the phase modulation index.
mm-wave signal using DSBCS modulation can be written as
0 1 1 2 2
The optical sidebands with the Bessel function higher than J m3( ) can be ignored. Consequently, the electrical field can be written as
1 1 2 2 shown in Fig. 3-3. Therefore, the optical sidebands with the Bessel function
2 2 3 1
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Figure 3-3 The different order of Bessel functions vs. m.
To expand equation cos cos t sin cos t
Add time component cos(ωct)
The output electrical filed can be rewritten as
{ }
Figure 3-4 Illustration of the optical spectrum at the output of the MZM.
( 6 )
Chapter 4
Experimental Demonstration of System for Wire
4.1 Preface
In chapter 3, we show the principle of bit-loading algorithm and we also provide the theoretical and numerical results for the concept of system.
Therefore, the results can be tried to apply to the radio-over-fiber system. In this chapter, we will build the experimental setup for the system based on DSBCS modulation.
4.2 Experimental setup
32.65-Gb/s OFDM signal
π/2
π
Frequency Quadrupling
Photonic Up-conversion
φ φ
φ
φ
bias 0 V =
bias 0 V = Scope
Wireless Application
Figure 4-1 Experimental setup for all optical up-conversion.
Figure 4-1 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 Fig 4-1. 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 Fig 4-2. 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).
4.3 Experimental results for OFDM signal without bit-loading algorithms
The equalizer in OFDM transceiver is used to combat both frequency response of various millimeter-wave components at 60GHz and fiber dispersion. Since the proposed OFDM transmitter can generate high-purity two-tone light-wave, the generated OFDM signals do not suffer from periodic fading issue due to fiber dispersion. Only in-band distortion of the OFDM-encoded subcarrier induced by fiber dispersion is considered. Since the symbol rate of each subcarrier is only 78.125MSym/s, the fiber chromatic penalty can be ignored.
4.3.1 Optimal condition for 8-QAM OFDM signal
The relative intensity between optical un-modulated and data-modulated subcarriers strongly influences the performance of the optical OFDM signals.
intensity between optical un-modulated and data-modulated subcarriers can be easily tuned by adjusting the individual amplitude of the driving sinusoidal and OFDM signals to optimize the performance of the direct-detection OFDM signals, respectively.
1 2 3 4 5
21.0 21.1 21.2 21.3 21.4 21.5
SNR (dB)
OPR (dB)
8QAM
1 2 3 4 5
6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2
-Log(BER)
OPR (dB)
8QAM
Figure 4-2 SNR and BER vs. OPR for 8-QAM OFDM signal.
Figure 4-2 illustrates the SNR and BER of the 8-QAM OFDM signals versus different optical power ratios (OPR) of the um-modulated subcarrier to
the OFDM-encoded subcarrier as optical power of 60-GHz OFDM signals are normalized before detection. The optimal OPR is 2 dB.
1549.5 1549.8 1550.1 1550.4 1550.7 -60
1549.5 1549.8 1550.1 1550.4 1550.7 -60
1549.5 1549.8 1550.1 1550.4 1550.7 -60 1549.8 1550.0 1550.2 1550.4
-70
1549.8 1550.0 1550.2 1550.4 -70
1549.8 1550.0 1550.2 1550.4 -70
Figure 4-3 Optical spectrums for 8-QAM OFDM signal.
Figure 4-3 shows the optical spectrums of different OPR. We define OPR is optical power of un-modulated subcarrier over power of signals modulated optical carrier. And inset (a-1), (a-2), (a-3) of Fig. 4-3 are OPR = 1 dB, OPR =
2 dB, OPR = 5 dB before frequency quadrupling system, respectively. Inset (b-1), (b-2) and (b-3) illustrate OPR = 1 dB, OPR = 2 dB, OPR = 5 dB after frequency quadrupling system and interleaver.
4.3.2 Optimal condition for 16-QAM OFDM signal
2 3 4 5 6 7
20.4 20.6 20.8 21.0 21.2 21.4 21.6
SNR (dB)
OPR (dB)
16QAM_OPR
2 3 4 5 6 7
4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7
-Log(BER)
OPR (dB)
16QAM_OPR
Figure 4-4 SNR and BER vs. OPR for 16-QAM OFDM signal.
Figure 4-4 illustrates the SNR and BER of the 16-QAM OFDM signals
versus different optical power ratios (OPR) of the um-modulated subcarrier to the OFDM-encoded subcarrier as optical power of 60-GHz OFDM signals are normalized before detection. The optimal OPR is 4 dB.
1549.8 1550.0 1550.2 1550.4 1550.6 -70
1549.8 1550.0 1550.2 1550.4 1550.6 -70
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60 1549.8 1550.0 1550.2 1550.4 1550.6
-70
Figure 4-5 Optical spectrums for 16-QAM OFDM signal.
Figure 4-5 shows the optical spectrums of different OPR. And inset (a-1), (a-2), (a-3) of Fig. 4-5 are OPR = 2dB, OPR = 4 dB, OPR = 6.2 dB before
frequency quadrupling system, respectively. Inset (d), (e) and (f) illustrate OPR
= 2 dB, OPR = 4 dB, OPR = 6.2 dB after frequency quadrupling system and interleaver.
4.3.3 Optimal condition for 32-QAM OFDM signal
1 2 3 4 5 6 7 8
20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7
SNR (dB)
OPR (dB)
32QAM_OPR
1 2 3 4 5 6 7 8
2.55 2.50 2.45 2.40 2.35
-Log(BER)
OPR (dB)
32QAM_OPR
Figure 4-6 SNR and BER vs. OPR for 32-QAM OFDM signal.
Figure 4-6 illustrates the SNR and BER of the 32-QAM OFDM signals
versus different optical power ratios (OPR) of the um-modulated subcarrier to the OFDM-encoded subcarrier as optical power of 60-GHz OFDM signals are normalized before detection. The optimal OPR is 4.5 dB.
1549.8 1550.0 1550.2 1550.4
-70
1549.8 1550.0 1550.2 1550.4
-70
1549.8 1550.0 1550.2 1550.4
-70
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60
32QAM_OPR = 1.3dB
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60
32QAM_OPR = 4.5dB
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60
32QAM_OPR = 7.3dB
Figure 4-7 Optical spectrums for 32-QAM OFDM signal.
Figure 5-11 shows the optical spectrums of different OPR. And inset (a-1), (a-2), (a-3) of Fig. 4-7 are OPR = 1.3 dB, OPR = 4.5 dB, OPR = 7.3 dB before
frequency quadrupling system, respectively. Inset (b-1), (b-2) and (b-3) illustrate OPR = 1.3 dB, OPR = 4.5 dB, OPR = 7.3 dB after frequency quadrupling system and interleaver.
4.3.4 Transmission results of 8-QAM
1549.5 1549.8 1550.1 1550.4 1550.7 -60
1549.8 1550.0 1550.2 1550.4 -70
Figure 4-8 Electrical spectrums of 8-QAM OFDM signals.
Figure 4-8 illustrates the electrical spectrums for 8-QAM signals and indicates where the spectrums belong to. Inset (a) of Fig. 4-8 is the electrical spectrum of transmitter terminal OFDM signals and 12-GHz subcarrier. Inset (b) of Fig. 4-8 is the optical spectrum of I/Q up-conversion. Inset (c) of Fig. 4-8 receiver is the optical spectrum of frequency quadrupling. Inset (d) of Fig. 4-8 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 4-9 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 zero dB. Although it still worsens the performance a little, it does better than using electrical mixer with
noise figure (NF) 8-dB.
-11 -10 -9 -8 -7 -6 -5 -4 -3
17 18 19 20 21 22
SNR (dB)
Received Power (dBm)
8QAM_BTB 8QAM_25km
(Data rate = 21 Gbps)
-11 -10 -9 -8 -7 -6 -5 -4 -3
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
(Data rate = 21Gbps )
Figure 4-9 SNR and BER vs. Received power for 8-QAM OFDM signal.
Figure 4-10 shows 8-QAM constellation diagrams and Fig. 4-11 shows SNR (and BER) vs. subcarrier number after the system in back-to-back and 25km SMF transmission. They are captured at PD received power equal to -6dBm. The equalizer in OFDM transceiver is used to combat both frequency
dispersion. Since the OFDM transmitter can generate high-purity two-tone lightwave, the generated OFDM signals do not suffer from periodic fading issue due to fiber dispersion. Only in-band distortion of the OFDM-encoded subcarrier induced by fiber dispersion is considered. Since the symbol rate of each subcarrier is only 78.125 MSym/sec, the fiber chromatic penalty can be ignored.
Figure 4-10 Constellations of the 8-QAM OFDM signal.
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 4-11 (a) SNR vs. Subcarrier Number of the 8-QAM OFDM signal.
0 10 20 30 40 50 60 70 80 90
Figure 4-11 (b) BER vs. Subcarrier Number of the 8-QAM OFDM signal.
4.3.5 Transmission results of 16-QAM
1549.8 1550.0 1550.2 1550.4 1550.6 -70
1549.5 1550.0 1550.5 1551.0 -70
Figure 4-12 Electrical spectrums of 16-QAM OFDM signals.
Figure 4-12 illustrates the electrical spectrums for 16-QAM signals and indicates where the spectrums belong to. Inset (a) of Fig. 4-12 is the electrical spectrum of transmitter terminal OFDM signals and 12-GHz subcarrier. Inset (b) of Fig. 4-11 is the optical spectrum of I/Q up-conversion. Inset (c) of Fig.
4-11 receiver is the optical spectrum of frequency quadrupling. Inset (d) of Fig.
4-11 is the electrical 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
Received Power (dBm)
16QAM_BTB
Received Power (dBm)
16QAM_BTB 16QAM_25km
(Data rate = 27.5Gbps)
Figure 4-13 SNR and BER vs. Received power for 16-QAM OFDM signal.
Figure 4-13 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 penalties is zero dB. Although it still worsens the performance a little, it does better than using electrical mixer with noise figure (NF) 8-dB.
Figure 4-14 Constellations of the 16-QAM OFDM signal.
0 10 20 30 40 50 60 70 80 90 17
18 19 20 21 22 23 24 25
SNR (dB)
Subcarrier Number
BTB 25km
Figure 4-15 (a) SNR vs. Subcarrier Number of the 16-QAM OFDM signal.
0 10 20 30 40 50 60 70 80 90 15
12 9 6 3
-Log(BER)
Subcarrier Number
BTB 25km
FEC Limit
Figure 4-15 (b) BER vs. Subcarrier Number of the 16-QAM OFDM signal.
Figure 4-14 shows 16-QAM constellation diagrams and Fig 4.15 shows SNR (and BER) vs. subcarrier number after the system in back-to-back and 25km SMF transmission. They are captured at PD received power equal to -6dBm.
4.3.6 Transmission results of 32-QAM
Figure 4-16 illustrates the electrical spectrums for 32-QAM signals and indicates where the spectrums belong to. Inset (a) of Fig. 4-16 is the electrical spectrum of transmitter terminal OFDM signals and 12-GHz subcarrier. Inset (b) of Fig. 4-16 is the optical spectrum of I/Q up-conversion. Inset (c) of Fig.
4-16 receiver is the optical spectrum of frequency quadrupling. Inset (d) of Fig.
4-16 is the electrical spectrum of 32-QAM OFDM signals. We down-convert the signals to center frequency 5-GHz and the bandwidth is 7-GHz.
1549.8 1550.0 1550.2 1550.4
1549.6 1549.8 1550.0 1550.2 1550.4 1550.6 -60 32QAM_OPR = 4.5dB
0 1 2 3 4 5 6 7 8 9 10
Figure 4-16 Electrical spectrums of 32-QAM OFDM signals.
Figure 4-17 shows the SNR and BER curves of the 34.375Gbps 32-QAM OFDM signals using optimal OPR after transmission over 25-km SMF. After transmission 25-km, the sensitivity penalties is about 0.2dB. 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)
32QAM_BTB 32QAM_25km
Figure 4-17(a) SNR vs. Received power for 32-QAM OFDM signal.
-10 -9 -8 -7 -6 -5 -4 2.6
2.4 2.2 2.0 1.8
-Log(BER)
Received Power (dBm)
32QAM_BTB 32QAM_25km
Figure 4-17(b) BER vs. Received power for 32-QAM OFDM signal.
Figure 4-18 shows 32-QAM constellation diagrams and Fig. 4-19 SNR (and BER) 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 4-18 Constellations of the 32-QAM OFDM signal.
0 10 20 30 40 50 60 70 80 90
Figure 4-19 SNR and BER vs. Subcarrier Number of the 16-QAM OFDM signal.
4.4 Experimental results for OFDM signal with bit-loading algorithms 4.4.1 Optimal condition for bit-loading OFDM signal
The relative intensity between optical un-modulated and data-modulated subcarriers strongly influences the performance of the optical OFDM signals.
One of the advantages of the proposed OFDM transmitter is that relative intensity between optical un-modulated and data-modulated subcarriers can be easily tuned by adjusting the individual amplitude of the driving sinusoidal and OFDM signals to optimize the performance of the direct-detection OFDM signals, respectively.
1 2 3 4 5
20.00 20.02 20.04 20.06 20.08 20.10 20.12 20.14 20.16 20.18
SNR (dB)
OPR (dB)
Bit-loading_OPR
1 2 3 4 5
3.40 3.35 3.30 3.25 3.20 3.15
-Log(BER)
OPR (dB)
Bit-loading_OPR
Figure 4-20 SNR and BER vs. OPR for bit-loading OFDM signal.
Figure 4-20 illustrates the SNR and BER of the bit-loading OFDM signals versus different optical power ratios (OPR) of the um-modulated subcarrier to the OFDM-encoded subcarrier as optical power of 60-GHz OFDM signals are normalized before detection. The optimal OPR is 3 dB.
1549.8 1550.0 1550.2 1550.4 -70
1549.8 1550.0 1550.2 1550.4 -70
1549.8 1550.0 1550.2 1550.4 -70
1549.5 1549.8 1550.1 1550.4 1550.7 -60
1549.5 1549.8 1550.1 1550.4 1550.7 -60
1549.5 1549.8 1550.1 1550.4 1550.7 -60
Figure 4-21 Optical spectrums for bit-loading OFDM signal.
Figure 4-21 shows the optical spectrums of different OPR. We define OPR 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.
spectrum of 16-QAM OFDM signals. We down-convert the signals to center frequency 5-GHz and the bandwidth is 7-GHz.