**6.1. Description of RoFSO system**

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the fall in the received signal power. In order to realize stable communication even under strong atmospheric turbulence more improvement in is needed is required in the tracking system performance. Moreover, it is important to clarify the link design technique about the

**Figure 20.** 10 Gbps transmission test eye pattern. (a) Before transmission (b) After 1 km transmission

(a) (b)

The next-generation optical wireless communication system offered seamless connection of free space and fiber system. The transceiver incorporates a FPM for high-speed beam tracking and control function, therefore, having the capability to mitigate the effects of atmospheric turbulence on the transmitted optical beam. The FSO system performance was verified and error free transmission over an extended period of time was demonstrated. The system performance expressed in terms of BER performance was also evaluated and showed to be consistently above acceptable levels. Stable performance after increasing the

**Bit Error Rate Throughput**

**12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 Time**

**0**

**20**

**40**

**60**

**Throughput [Mbps]**

**80**

**100**

application distance of atmospheric turbulence and a FSO system.

**5.6. Conclusions of the NG-FSO system** 

system bandwidth using WDM technology was also attained.

**Figure 21.** Throughput and BER characteristics in DWDM transmission

**1.0E-10**

**Error Free**

**1.0E-08**

**1.0E-06**

**1.0E-04**

**Bit Error Rate**

**1.0E-02**

**1.0E+00**

Examination of a RoFSO system which expands RoF technology to a free-space using alloptical connection technology is shown. RoF technologies [Al-Raweshidy 2002][Hai 2006] can realize a cost effective universal platforms for future ubiquitous wireless services. Furthermore, RoF networks can be extended to virtual radio free-space network with layer 1 routing realized [Komaki 2003][Tsukamoto 2005]. By using RoF, architecture for radio access zones easily employs micro or pico cellular systems. However, the optical fiber as an infrastructure is needed for a RoF network. We aim at quick and effective provide of heterogeneous wireless services for not only urban area but rural area, that has a little or no infrastructure for broadband services by the system with which developed next-generation FSO and a RoF system were united.

**Figure 22.** Outline of RoFSO system setup

We developed the RoFSO antenna which is improved the optical antenna, and installed in the same experimental field [Kazaura 2009][ Kim 2009][Tsukamoto 2008]. Moreover, RF interface which represents the RoF system, and optical interface which performs multi/demultiplex and amplification of the optical signal carrying the various services developed for an experiment as indoor equipment. A new optical antenna of 80 mm of the main aperture aimed at better tracking accuracy by feeding back the influence of the atmospheric fluctuation which signal light receives itself by diverting and using a part of signal light for fine tracking. RF interface unit consists of a RoF module which performs the electro/optical conversion of RF signal corresponding to the planned service (3G cellular, WLAN 11g/a, DBV-T), and its control circuit. Each light signal transmitted is matched with the ITU grid wavelength of a 100 GHz space. The optical interface unit consists of a DWDM multi/demultiplex device, EDFA (booster/post) and optical circulator for separation of transmit/receive signal. A figure showing the whole system just described is depicted in Figure 22. In this experiment, signal generators and analyzers for evaluating the transmission quality of various services are connected to RF interface unit.

#### **6.2. Consideration of optical antenna specification**

The average expansion and fluctuation of light intensity of the laser beam at 1.550 μm wavelength with the atmospheric turbulence are calculated by using the above expressions (Section 3). The relation between the beam radius at the transmitter and the average beam expansion at receiver point is shown in Figure 23.

**Figure 23.** Rx beam radius versus Tx beam radius

**Figure 24.** Scintillation index depend on Tx beam radius

**Figure 25.** Probability of fading level

According to these results, the radius of received beam is varied slightly and the expansion rate of the radius of received beam is constant when the radius of transmit beam is more than 20 mm. Moreover, the larger the transmission beam diameter is, the smaller the amount of the decrease of center strength of the received beam, and the free space transmission loss is less than 5 dB for a transmit beam diameter of 40 mm or more. We calculated the fluctuation of the received light intensity (scintillation index) by varying the transmitted beam radius. The result is shown in figure 24. The change is small in weak fluctuation case and there is no big received optical power changes for propagation distance of 1~2 km with laser beam transmit and receive aperture diameter of 10~100 mm therefore an optical antenna having this range of aperture beam transmission is possible. Figure 25 shows the cumulative probability distribution when the transmit beam radius is set at 40 mm and pointing error is 5 μradian. We found that the fluctuation of receiving optical intensity is ± 3 dB at 10 % and ± 8 dB at 0.001%. In other words, it is necessary to consider fading margins that are 9.6 dB for the uplink and 9.2 dB for the downlink if inoperable ratio is 10-7.

In addition, the previous NG-FSO system, the beam for fine tracking systems was a beacon light which was different from the signal light. In that case, the propagation path of the beacon light signal and signal beam is not exactly consistent therefore the atmospheric fluctuation behavior is also not similar. Especially, in the case of the data rate is high, such tendency is significantly. Therefore, it was not possible to get enough fine tracking characteristics. That is why in the new system for fine tracking the signal light is used for detection of angle of arrival by utilizing beam splitter.

Based on these calculations, if a diffraction-limited Gaussian beam is transmitted, it is desirable for the pointing error to be less than 5 μradian considering fading. The pointing error of the FPM used for the fine tracking of the RoFSO system is approximately 20 μradian and the angular magnification of the optical antenna is 40. The tracking accuracy of the entire system can be calculated by the division of those two values and it is 0.5 μradian. Thus, it is possible to expect the improvement of the atmosphere fluctuation.

#### **6.3. Results of optical design**

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multiplex device, EDFA (booster/post) and optical circulator for separation of transmit/receive signal. A figure showing the whole system just described is depicted in Figure 22. In this experiment, signal generators and analyzers for evaluating the

The average expansion and fluctuation of light intensity of the laser beam at 1.550 μm wavelength with the atmospheric turbulence are calculated by using the above expressions (Section 3). The relation between the beam radius at the transmitter and the average beam

> **0 0.01 0.02 0.03 0.04 0.05 0.06 Tx beam radius (m)**

> **0 0.01 0.02 0.03 0.04 0.05 0.06 Tx beam radius (m)**

**1.00E-09 1.00E-07 1.00E-05 1.00E-03 1.00E-01 Probability**

**Uplink W0 Downlink W0**

**Uplink s(0,L) Downlink s(0,L)**

> **Uplink Downlink**

transmission quality of various services are connected to RF interface unit.

**6.2. Consideration of optical antenna specification** 

expansion at receiver point is shown in Figure 23.

**Figure 23.** Rx beam radius versus Tx beam radius

**Scintilation index**

**Rx beam radiu (m)**

**0 0.02 0.04 0.06 0.08 0.1 0.12**

**Figure 24.** Scintillation index depend on Tx beam radius

**Fading level (dB)**

**0 0.05 0.1 0.15 0.2 0.25**

**Figure 25.** Probability of fading level

A constitution of the prototype of the optical antenna module [Takahashi 2008] which had a QD feedback type built-in fine tracking system by a micro-miniaturized fine pointing mirror with the part of SMF coupling components is shown in figure 26, the photograph of SMF coupling part and tracking system is shown in figure 27 and the photograph of entire prototype optical system is shown in figure 28. Based on this design, results of the calculation of coupling efficiency and spot diagram when an ideal lens is deployed in the radiation side are shown in figure 29. The on-axis SMF coupling loss is -1.02 dB with less the -5 dB loss for up to full size field angle 25 μradian. Optical performance for on-axis and offaxis of the designed optical system is summarized in table 1. It is observed that it is possible to obtain almost twice image formation efficiency of the diffraction limit of the design requirement for field angle ±0.5 degrees.

**Figure 27.** Photograph of SMF coupling part and tracking system

Transmitting lens for beacon SMF coupling part

**Figure 28.** Photograph of entire optical antenna of prototype RoFSO system

To evaluate real performance in the trial product; the coupling efficiency that measured in experiment system deploy a coupling lens after an object lens and a collimator, and to be received light to SMF is approximately - 5dB.

**Figure 29.** RoFSO antenna optical performance (a) Coupling efficiency (b) Spot diagram


**Table 1.** Optical performance of the RoFSO optical antenna in design condition

#### **6.4. Evaluation of prototype RoFSO system**

#### *6.4.1. Experimental evaluation setup*

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**Forward / Backward**

**Figure 26.** Optical layout of the antenna of RoFSO system

**Collimator & Fine pointing mirror**

**Transmitting lens for beacon light** 

**Figure 27.** Photograph of SMF coupling part and tracking system

Objective lens

**Figure 28.** Photograph of entire optical antenna of prototype RoFSO system

Transmitting lens for beacon SMF coupling part

received light to SMF is approximately - 5dB.

To evaluate real performance in the trial product; the coupling efficiency that measured in experiment system deploy a coupling lens after an object lens and a collimator, and to be

**Rough tracking sensor with beacon light**

> **Fine tracking sensor by QD**

**Direct coupling between space and SMF**

**Dichroic BS**

**signals**

**SMF DWDM RoF** 

We installed the developed RoFSO system at a same place of NG-FSO system in Waseda University and performed experiments [Kazaura 2009] [Kim 2009] [Tsukamoto 2008] [Takahashi 2008]. Photographs showing the devices setup on the rooftop as well as the various measurement devices setup in the laboratory is depicted in Figure 30(a) and 30(b) respectively. Three FSO antennas are placed on the rooftop of one building as shown in Figure 30(a), which include the DWDM RoFSO antenna under investigation and two other conventional antennas used for measuring and quantifying the deployment environment characteristics for example atmospheric turbulence induced scintillation.

#### *6.4.2. Basic performance*

As a result, the system's stability and tracking properties satisfied the design requirements (tracking response is more than 2 kHz, turbulence suppression characteristics of this feedback system are more than suppression ability 20 dB in frequency less than 100 Hz with Cn2 < 1.7×10-14), and we confirmed that the system can transmit WDM with sufficient performance regarding not only error-free transmission of digital signals but also RF signal transmission. Figure 31 shows the intensity fluctuation characteristics of received beam

when the fine tracking of antenna is set OFF or ON, and the average of turbulence Cn2 is 2×10-14. If the fine tracking is set OFF, the fluctuation of receiving optical intensity largely and frequently decays because it is not possible to control arrival angle, also because location of beam spot of SMF consistently fluctuates. In addition, the mean of receiving optical intensity is low because it is not possible to control location of light focus accurately. On the other hand, the fine tracking of antenna is set to ON, the entire fluctuation decreases and the mean of receiving optical intensity is improved. Figure 32 shows the receiving optical spectrum when four of wireless service signals are transmitted with 1 km distance and WDM transmission using this RoFSO. It can be found that each service signal is clearly separated and is transmitted without mutual interaction.

**Figure 30.** RoFSO system experimental device (a) rooftop setup and (b) devices setup in the laboratory

**Figure 31.** Optical intensity fluctuation characteristics of received beam with tracking OFF (upper) and tracking ON (lower)

**Figure 32.** Optical spectrum of four wireless service signals using WDM RoFSO system

#### *6.4.3. W-CDMA (Cellarer phone)*

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tracking ON (lower)

Received optical power (dBm)



when the fine tracking of antenna is set OFF or ON, and the average of turbulence Cn2 is 2×10-14. If the fine tracking is set OFF, the fluctuation of receiving optical intensity largely and frequently decays because it is not possible to control arrival angle, also because location of beam spot of SMF consistently fluctuates. In addition, the mean of receiving optical intensity is low because it is not possible to control location of light focus accurately. On the other hand, the fine tracking of antenna is set to ON, the entire fluctuation decreases and the mean of receiving optical intensity is improved. Figure 32 shows the receiving optical spectrum when four of wireless service signals are transmitted with 1 km distance and WDM transmission using this RoFSO. It can be found that each service signal is clearly

**Figure 30.** RoFSO system experimental device (a) rooftop setup and (b) devices setup in the laboratory

(a) (b)

<sup>0</sup> 0.5 <sup>1</sup> 1.5 <sup>2</sup> 2.5 <sup>3</sup> -60

**Figure 31.** Optical intensity fluctuation characteristics of received beam with tracking OFF (upper) and

<sup>0</sup> 0.5 <sup>1</sup> 1.5 <sup>2</sup> 2.5 <sup>3</sup> -60

Time (s)

Tracking ON

Tracking OFF

separated and is transmitted without mutual interaction.

In W-CDMA system, the downlink signal transmitted by the base station is designed to fulfill the specifications set in 3GPP standard [3FPP 2002]. The spectral properties of the signal are measured by he adjacent channel leakage ratio (ACLR) which is considered to be a more stringent quality metric parameter, and is defined as the ratio of the amount of leakage power in an adjacent channel to the total transmitted power in the main channel. The 3GPP specifies one main channel and two adjacent channels. The standard requires the ACLR to be better than 45 dB at 5 MHz offset and 50 dB at 10 MHz offset. In our experimental setup, we use a signal generator to generate a test signal (W-CDMA Test Model 1) with a signal power of -20 dBm which is transmitted over the RoFSO link and at the receiver side a digital mobile radio transmission tester is used to measure and record the quality of the W-CDMA signal. Figure 33(a) shows a received W-CDMA signal ACLR spectrum after transmission over the 1 km RoFSO link. It is observed that the signals' spectral properties shown on Figure 33(a) satisfy the 3GPP specified values of ACLR at the 5 MHz and 10 MHz offsets.

The variation of the measured received optical power and the W-CDMA signal ACLR characteristics is shown in Figure 33(b). Two cases are considered i.e. first case is back-toback (B-to-B) measurement using the RoF modules, signal generator and analyzer and an optical attenuator for incrementing the attenuation to represent channel losses and in the offsets. The B-to-B actual transmission over the RoFSO system measurements shows almost similar characteristics and the minimum optical received power to satisfy the prescribed 3GPP value at 5 MHz at 10 MHz offsets is about -15 dBm. Using a post EDFA the required received optical power can be even as low as -25 dBm and -20 dBm and still satisfy the 3GPP specification for W-CDMA signal transmission at 5 MHz and 10 MHz offsets respectively.

**Figure 33.** (a) Received W-CDMA signal ACLR spectrum and (b) variations of ACLR and optical received power

#### *6.4.4. Wireless LAN*

In another example the RoFSO system is evaluated by transmitting a WLAN IEEE802.11 based signal. In this experiment, an IEEE802.11g compliant waveform is generated by a vector signal generator at -24 dBm which is applied to the RoF module in the RF interface unit. After transmission through the RoFSO link a spectrum analyzer is utilized to measure and analyze the quality of the received WLAN signal. A pass/fail judgment of the spectrum mask as defined in the IEEE specification 802.11a/b/g is used. As a test signal, IEEE802.11g waveform at 2.4 GHz with 54 Mbps 64QAM is used. Figure 34(a) depicts a WLAN signal with spectrum mask in this case. A constellation graph of the WLAN signal modulation analysis is shown in Figure 34(b).

**Figure 34.** WLAN (a) spectrum mask and (b) modulation analysis constellation

The recorded RMS of Error Vector Magnitude (EVM) value is within the acceptable tolerance for WLAN signal transition. The result of continuous measurement of the spectral mask test collected over two days is shown in Figure 35. The mask pattern Pass/Fall judgment is measured per second and recorded. This result is accumulated for every 1 minute, and the passed number is plotted in the figure. Moreover, in order to evaluate the variation with respect to the condition of the propagation path, the metrological data such as visibility and rain rate data which is simultaneously collected is plotted.

**Figure 35.** Mask test pass counts per 1 min. vs. weather condition

The measurement data depicted in the figure represent a fine weather condition before noon on the first day which later turned cloudy. On the second day it rained. The drop in visibility because of rain is significant around 8:00am on the second day. Because of the rain there is an increase in attenuation in the propagation path, so the received optical signal power falls therefore increasing the rate of the spectrum mask test failure. It can be observed in the figure that on the first day, there is an increase of spectrum mask failure rate around noon, this is due to the effect of atmospheric turbulence.

#### *6.4.5. ISDB-T (Digital TV)*

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received power

*6.4.4. Wireless LAN* 

analysis is shown in Figure 34(b).

**Figure 33.** (a) Received W-CDMA signal ACLR spectrum and (b) variations of ACLR and optical

(a) (b)

**Figure 34.** WLAN (a) spectrum mask and (b) modulation analysis constellation

(a) (b)

In another example the RoFSO system is evaluated by transmitting a WLAN IEEE802.11 based signal. In this experiment, an IEEE802.11g compliant waveform is generated by a vector signal generator at -24 dBm which is applied to the RoF module in the RF interface unit. After transmission through the RoFSO link a spectrum analyzer is utilized to measure and analyze the quality of the received WLAN signal. A pass/fail judgment of the spectrum mask as defined in the IEEE specification 802.11a/b/g is used. As a test signal, IEEE802.11g waveform at 2.4 GHz with 54 Mbps 64QAM is used. Figure 34(a) depicts a WLAN signal with spectrum mask in this case. A constellation graph of the WLAN signal modulation

ACLR [dB]


B-B 5MHz B-B 10MHz RoFSO 5MHz RoFSO 10MHz RoFSO with EDFA 5MHz RoFSO with EDFA 10MHz

> Digital terrestrial television broadcasting, referred to as Integrated Service Digital Broadcasting – Terrestrial (ISDB-T) in Japan, is designed to provide reliable high-quality video, sound and data broadcasting not only for fixed receivers but also for mobile receivers. The system is designed to provide flexibility, expandability and interoperability for multimedia broadcast. The ISDB-T system uses the UHF band at frequencies between 470 MHz and 770 MHz, giving a total bandwidth of 300 MHz. The bandwidth is divided into 50 channels named from 13 to 62. Each channel is further divided into 13 OFDM segments which includes a single segment, (A-Layer or 1seg), for mobile receivers (LDTV,

audio and data) and the remainder can be allocated as one 12-segment for high definition television (HDTV) programs [DiBEG]. In this setup, channel 32 is used for ISDB-T signal transmission. A vector signal generator (Anritsu MG3700A) is used to output simple BER data and video waveforms for ISDB-T transmission evaluation. In this example, two signals are set simultaneously with the following waveform patterns (a) ISDBT\_16QAM\_1\_2 (A-Layer: 1seg, 16QAM and B-Layer: 12seg, 64QAM) and (b) ISDBT\_2layer\_Movie, both at -20 dBm with a 6 MHz frequency offset. The combined signal at -17 dBm is fed into the RoF module. The optical modulation index (OMI) for each channel (at -20 dBm input) is 10%. The signal is subsequently transmitted over the RoFSO link. At the receiving site a digital broadcasting signal analyzer (Anritsu MS8901A) is used to measure the quality of the received ISDB-T signal. A received signal spectrum showing the two transmitted ISDB-T signals is depicted in Figure 36(a). A modulation error ratio (MER) quality metric parameter used to evaluate the modulation signal quality of the digital terrestrial television broadcasting signal directly and quantitatively is measured and analyzed. An example of modulation analysis constellation for the digital terrestrial broadcasting signal made of A-Layer 16QAM and B-Layer 64QAM is shown in Figure 36(b) and 36 (c) respectively which were captured when the recorded average received optical power was -5.92 dBm and -5.88 dBm respectively (i.e. the monitor output measured power adjusted for the respective RF signal). The constellation is very useful for analyzing the condition of the received signal by monitoring the modulation symbol movement. In Figure 36(b) and 36(c) the received signals exhibit little signal distortion (in terms of amplitude or frequency fluctuations) and the signal deterioration is minimal thus confirming the suitability of the RoFSO system for ISDB-T signal transmission conforming to the specified standard [ARIB]. In this example the measurement was made in the evening after 20:00 hrs considered to be weak atmospheric turbulence conditions. The ISDB-T signal transmission using the RoFSO system is also evaluated using a BER quality metric parameter. Figure 37 shows the BER measurement and the mean received optical power characteristics for one-segment (1seg) and 12-segment transmission collected over a 24 hour period on 11 December 2008. Increased bit errors are observed at around midday because of increase in the atmospheric turbulence which affects the received optical power. The variation of the measured mean received optical power can be correlated with the BER in this case. For 1seg transmission (A-Layer) the BER characteristics shows satisfactory performance with most values being below the error correction limit (2×10-4) demonstrating the suitability of the RoFSO system for ISDB-T 1seg transmission. Unfortunately, occasionally the automatic gain control (AGC) is inadequate in the case for 12-segment HDTV (B-Layer) transmission. As an example the ISDB-T transmitted video captured screen shots for 1seg and 12-segment are shown in Figure 38(a) and 38(b) respectively. The 1seg video quality was consistently clear and continuous without any stoppages. However, the 12-segment video is clear and continuous only in the absence of atmospheric turbulence or other effects which contribute to the deterioration of the transmitted RoFSO signal quality.

signal quality.

audio and data) and the remainder can be allocated as one 12-segment for high definition television (HDTV) programs [DiBEG]. In this setup, channel 32 is used for ISDB-T signal transmission. A vector signal generator (Anritsu MG3700A) is used to output simple BER data and video waveforms for ISDB-T transmission evaluation. In this example, two signals are set simultaneously with the following waveform patterns (a) ISDBT\_16QAM\_1\_2 (A-Layer: 1seg, 16QAM and B-Layer: 12seg, 64QAM) and (b) ISDBT\_2layer\_Movie, both at -20 dBm with a 6 MHz frequency offset. The combined signal at -17 dBm is fed into the RoF module. The optical modulation index (OMI) for each channel (at -20 dBm input) is 10%. The signal is subsequently transmitted over the RoFSO link. At the receiving site a digital broadcasting signal analyzer (Anritsu MS8901A) is used to measure the quality of the received ISDB-T signal. A received signal spectrum showing the two transmitted ISDB-T signals is depicted in Figure 36(a). A modulation error ratio (MER) quality metric parameter used to evaluate the modulation signal quality of the digital terrestrial television broadcasting signal directly and quantitatively is measured and analyzed. An example of modulation analysis constellation for the digital terrestrial broadcasting signal made of A-Layer 16QAM and B-Layer 64QAM is shown in Figure 36(b) and 36 (c) respectively which were captured when the recorded average received optical power was -5.92 dBm and -5.88 dBm respectively (i.e. the monitor output measured power adjusted for the respective RF signal). The constellation is very useful for analyzing the condition of the received signal by monitoring the modulation symbol movement. In Figure 36(b) and 36(c) the received signals exhibit little signal distortion (in terms of amplitude or frequency fluctuations) and the signal deterioration is minimal thus confirming the suitability of the RoFSO system for ISDB-T signal transmission conforming to the specified standard [ARIB]. In this example the measurement was made in the evening after 20:00 hrs considered to be weak atmospheric turbulence conditions. The ISDB-T signal transmission using the RoFSO system is also evaluated using a BER quality metric parameter. Figure 37 shows the BER measurement and the mean received optical power characteristics for one-segment (1seg) and 12-segment transmission collected over a 24 hour period on 11 December 2008. Increased bit errors are observed at around midday because of increase in the atmospheric turbulence which affects the received optical power. The variation of the measured mean received optical power can be correlated with the BER in this case. For 1seg transmission (A-Layer) the BER characteristics shows satisfactory performance with most values being below the error correction limit (2×10-4) demonstrating the suitability of the RoFSO system for ISDB-T 1seg transmission. Unfortunately, occasionally the automatic gain control (AGC) is inadequate in the case for 12-segment HDTV (B-Layer) transmission. As an example the ISDB-T transmitted video captured screen shots for 1seg and 12-segment are shown in Figure 38(a) and 38(b) respectively. The 1seg video quality was consistently clear and continuous without any stoppages. However, the 12-segment video is clear and continuous only in the absence of atmospheric turbulence or other effects which contribute to the deterioration of the transmitted RoFSO

**Figure 36.** ISDB-T signal transmission experiment (a) received ISDB-T signal spectrum and modulation analysis constellations for (b) A-Layer 1 Seg (16QAM) and (c) B-Layer (64QAM)

**Figure 37.** Digital terrestrial television broadcasting BER and received optical power characteristics

#### **6.5. Conclusions of the RoFSO system**

Simultaneous transmission of different kinds of wireless services using a newly developed RoFSO system has been presented. As the result, we have been presented that an all-optical connection FSO system could treat not only digital signal transmission but RF signal on a par with an optical fiber. And it is shown that the new generation optical wireless optical communication technology has a possibility of uniting radio environment and cable environment also with a service level, and the thing expectable as a solution of a heterogeneous network is shown.

### **7. Conclusions**

We have described the concept and technology for the next-generation optical wireless communication systems. We explained the optics design method and the design results of the optical antennas considering laser propagation phenomena such as the scintillation and arrival beam angle fluctuation which occurs by atmospheric turbulence. We also mentioned the fine tracking mechanism using the FPM for the optical antennas. The FSO system incorporating high speed and highly precise tracking mechanism in which the influence of angle of arrival change is compensated succeed in maintaining free-space to SMF stably. A free-space optical communication system using specially designed compact antenna for easy, cost effective means of constructing a robust and reliable high-speed link for next generation optical wireless communication system was developed and investigated. The actual proof experiment using the developed NG-FSO system shows that this system enabled offer of a link equivalent to the fiber independent of the bit rate or a transmission protocol. Furthermore, we tried to unite this system with a RoF system and also enabled offer of various wireless services further. RoFSO system which expands RoF technology to a free-space using all-optical connection technology also shows the possibility of RF signal transmission through the field experiment. As these results, a next-generation optical wireless communication system using all-optical connection technology shows a possibility of becoming an effective solution of extension of a next-generation optical fiber system and heterogeneous wireless service.

## **Author details**

228 Optical Communication

**Figure 38.** ISDB-T captured video screen shots (a) A-Layer 1seg and (b) B-Layer 12-segment

(a) (b)

Simultaneous transmission of different kinds of wireless services using a newly developed RoFSO system has been presented. As the result, we have been presented that an all-optical connection FSO system could treat not only digital signal transmission but RF signal on a par with an optical fiber. And it is shown that the new generation optical wireless optical communication technology has a possibility of uniting radio environment and cable environment also with a service level, and the thing expectable as a solution of a

We have described the concept and technology for the next-generation optical wireless communication systems. We explained the optics design method and the design results of the optical antennas considering laser propagation phenomena such as the scintillation and arrival beam angle fluctuation which occurs by atmospheric turbulence. We also mentioned the fine tracking mechanism using the FPM for the optical antennas. The FSO system incorporating high speed and highly precise tracking mechanism in which the influence of angle of arrival change is compensated succeed in maintaining free-space to SMF stably. A free-space optical communication system using specially designed compact antenna for easy, cost effective means of constructing a robust and reliable high-speed link for next generation optical wireless communication system was developed and investigated. The actual proof experiment using the developed NG-FSO system shows that this system enabled offer of a link equivalent to the fiber independent of the bit rate or a transmission protocol. Furthermore, we tried to unite this system with a RoF system and also enabled offer of various wireless services further. RoFSO system which expands RoF technology to a free-space using all-optical connection technology also shows the possibility of RF signal transmission through the field experiment. As these results, a next-generation optical wireless communication system using all-optical connection technology shows a possibility

**6.5. Conclusions of the RoFSO system** 

heterogeneous network is shown.

**7. Conclusions** 

Koichi Takahashi *Future Creation Laboratory, Olympus Corporation, Japan* 
