1、Rec. ITU-R F.1332-1 1RECOMMENDATION ITU-R F.1332-1*RADIO-FREQUENCY SIGNAL TRANSPORT THROUGH OPTICAL FIBRES(Question ITU-R 204/9)(1997-1999)Rec. ITU-R F.1332-1The ITU Radiocommunication Assembly,consideringa) that optical fibres are widely used in subscriber networks or in-building wiring;b) that rad
2、io-frequency signal transport through optical fibres may be applied to access links to radio base stationsin many wireless applications;c) that by using a HFR (see Annex 1, 2 for acronyms) system the following advantages are expected: intensive deployment of modulators and demodulators and other fun
3、ctional equipment in an optical line terminationin front of an optical feeder system contributes to simplification of equipment in remote antenna units as well as tomaintenance and operation cost reduction; efficient use of spectral bandwidth available on the radio link;d) that the reduction of equi
4、pment at the radio base station is realized by the above technique;e) that the above technique has advantages in maintenance and operation aspects,recommends1 that Fig. 1 should be referred to for the basic configuration of a HFR system in which radio-frequency signalsare transported directly throug
5、h optical fibres;2 that Table 1 should be referred to for possible applications to the fixed service using a HFR system;3 that when using high-frequency bands above about 10 GHz, the centre frequency of a modulator may beselected to be in intermediate-frequency bands;4 that Fig. 2 should be referred
6、 to for the reference configuration of a HFR system between service nodes andcustomer premises networks. This is in agreement with the reference configuration for optical access networks in ITU-TRecommendation G.983. To support system interoperability the HFR access link is defined between the refer
7、ence pointsV and T or between service node interface and user network interface, and comprises the following functional blocks: optical line termination, optical distribution network and remote antenna unit (Part 1) in the optical distributionsegment; and remote antenna unit (Part 2), drop medium ra
8、dio and network termination antenna unit in the drop segment.To enable transverse system compatibility (mid-span meet) additional reference points (interfaces) within the HFRaccess link are recommended: optical reference points: O1between optical line termination and optical distribution network, Or
9、between opticaldistribution network and remote antenna unit (according to ITU-T Recommendation G.982); radio reference points: R1between remote antenna unit and drop medium radio, R2between drop medium radio andnetwork termination antenna unit;5 that for the design of HFR systems the technical infor
10、mation contained in the Annex 1 should be referred to foradditional guidance in the application of this Recommendation._*This Recommendation should be brought to the attention of Radiocommunication Study Group 8 (Working Party 8A) andTelecommunication Standardization Study Group 15 (Working Party 4/
11、15).2 Rec. ITU-R F.1332-11332-01RAUFibre splitterCorenetworksIncludingopticaltransceiverOpticalfeeder systemOLT ODNFibreRadioIntranetworking E/O O/ERFamplifierRFtransmissionOptical line termination Remote antenna unitFibresplitterCPNCPNCPNNTAUe.g. four 90 antenna sectors per RAUFIGURE 1Basic configu
12、ration of HFR systemFIGURE 1332-01 = 16 CMTABLE 1Possible applications for the fixed service using HFR systemsService area Indoor OutdoorApplication RLAN FWA Transportable serviceUsers terminal LAN module Cellular system terminal forfixed use, point-to-point/point-to-multipointfixed terminalTranspor
13、table video/data/voice terminalPossible RF(1)UHF/SHF/EHF UHF/SHF/EHF SHF/EHFAccess schemein the radio linkTDMA/CDMA/FDMA TDMA/CDMA/FDMA TDMA/CDMA/FDMA(1)UHF (decimetric waves): 300-3 000 MHzSHF (centimetric waves): 3-30 GHzEHF (millimetric waves): above 30 GHzRec. ITU-R F.1332-1 31332-02TR2R1OrO1VFI
14、GURE 2Reference configuration of HFR access linkDrop medium:radioService nodeUNIRAUNTAUCPN ODN OLTSNIRadio drop segment Optical distribution segmentFIGURE 1332-02 = 6 CMANNEX 11 IntroductionFor future broadband (interactive) services optical fibres will be extensively introduced in subscriber networ
15、ks realizingthe concept of what is called FTTC, FTTO or FTTH. On the other hand, customers may wish to use various servicesprovided by different core networks also in wireless applications due to increasing demand and competition, lack ofavailable bandwidth or fast and cost effective deployment. The
16、se applications include FWA, transportable data/videovoice terminals or transportable personal computers used for RLAN modules. In order to satisfy these demands, it willbe effective to introduce HFR systems in which radio-frequency signals are transmitted directly through optical fibres.This Annex
17、discusses the basic concept and technical basis of HFR systems.2 AcronymsAGC Automatic gain controlCDMA Code division multiple accessC/N Carrier-to-noise-ratioCPN Customer premises networkE/O Electric-to-optic conversionFDMA Frequency division multiple accessFM Frequency modulationFTTC Fibre to the
18、curbFTTH Fibre to the homeFTTO Fibre to the office4 Rec. ITU-R F.1332-1FWA Fixed wireless accessHFR Hybrid fibre radioIF Intermediate-frequencyIM Inter-modulationLAN Local area networkLD Laser diodeNTAU Network termination antenna unitODN Optical distribution networkO/E Optic-to-electric conversionO
19、LT Optical line terminationRAU Remote antenna unitRF Radio-frequencyRLAN Radio local area networkSCM Subcarrier multiplexSEFA Signal extraction and frequency arrangementSLC Signal level compressionSNI Service node interfaceTDD Time division duplexTDMA Time division multiple accessUNI User network in
20、terface3 Basic configuration of HFR systemsAs shown in Figs. 1 and 2 a HFR system is composed of OLT, ODN, RAU, NTAU and fibre/radio links connectingthese stations. It can form an infrastructure for access networks providing wireless services to customer premisesnetwork which may include many differ
21、ent terminals.In conventional digital radio equipment, a modulator/demodulator and a power amplifier are generally installed at thesame station. However, in HFR systems OLT and RAU comprise many intranetworking functions which are commonlyused for more than one RAU (see Fig. 1) depending on the spli
22、tting factor of the ODN. Examples for theseintranetworking functions are: modulation/demodulation, multiplexing/demultiplexing, control functions and errorcorrection functions the latter of which are mainly necessary because of the worse transmission performance (comparedto optical fibre transmissio
23、n) of the radio link. The system presented in Fig. 1 requires a multiple access technique tocope with upstream traffic demands from many customer terminals. OLT also has a function to control the accesstechnique efficiently utilizing the frequency spectrum. In such cases, the relation between OLT an
24、d RAU corresponds tothat of point-to-multipoint radio systems for subscriber networks. If radio-frequency signals are already opticallytransported over the ODN all these functions are located at OLT and the RAUs connected to one OLT are kept small andsimple (see lower part of Fig. 1).However, there
25、is a technical upper limit for the radio frequency to be transmitted through optical fibres due to theoperating speed of the E/O (and O/E). When a cost-effective E/O (and O/E) is required to implement HFR systems, anIF transmission could be suitable since the cost effective E/O (and O/E) operates wi
26、thin the IF bands. After beingtransmitted over the optical fibre link, the IF carriers are converted into radio frequencies at the remote antenna unit(see Fig. 3).Rec. ITU-R F.1332-1 51332-03Intranetworking E/O O/ERFamplifierIFtransmissionOptical line termination Remote antenna unitFibresplitterFIGU
27、RE 3IF transmission in HFR systemFrequencyconverterFIGURE 1332-03 = 6 CMAnother reason to use IF is that filtering of single radio transmission channels (several 10 MHz bandwidth) is muchmore easier and less expensive in the IF range allowing for channel selection at single RAUs. In this case only r
28、elevantdata will be sent out of a specific RAU even if the optical feeder includes a passive optical distribution network.Otherwise the limited bandwidth of the shared transmission medium “air” would be wasted. If filtering of IF/RFchannels is not possible, single RAUs also could be addressed by opt
29、ical routing functions in the optical feeder systemtogether with optical filter functions inside the RAU or by a point-to-point fibre feeder to further keep the RAU lesscomplex. Optical routing or point-to-point fibre connection also may be necessary due to high traffic rates as one RAUhas to serve
30、more than 10 000 subscribers with an increasing number of BB-services in the far future.4 Application of HFR systemsFigure 4 illustrates two specific applications of HFR systems. In Fig. 4a) a RAU works as a central module for a RLANoperating at each office room, while the OLT controls the assignmen
31、t of radio channels used by all the RAUs. Asillustrated in this Figure, HFR systems have the following merits: Since a modulator/demodulator is separated from a power amplifier in this system, equipment in a RAU becomessmaller. Thus, efforts for site selection of RAUs can be reduced. OLT equipments
32、including network interfaces and service units which provide voice service, digital packet serviceand so on are concentrated in one room. For that reason, maintenance work and replacement of any equipment isefficiently done in a short time.Figure 4b) gives an example of outdoor applications. A RAU p
33、rovides wireless access link to individual homes within aservice coverage. The function of the OLT is almost the same as for indoor systems and the above merits can also beexpected in this application. In conventional systems, since radio equipment is usually installed on a high pole, somedanger is
34、unavoidable in maintenance works. However, in HFR systems, such works can be much reduced.This outdoor application is considered to be a last-100 m (or in some cases last-10 m) wireless extension of FTTH. Ifmillimetre-wave bands above 30 GHz can be exploited for this usage, the HFR system will be ab
35、le to have a capacity ashigh as 150 to 600 Mbit/s per carrier. Each zone radius of a RAU is assumed to be the order of 300 m to enhance thefrequency utilization efficiency as well as to reduce the transmitter power.When utilizing millimetre-wave, attenuation due to rainfall has to be taken into acco
36、unt. AGC at the base station (RAU)works as an effective countermeasure in particular for the up-link direction (NTAU to RAU), since noise in the opticalfibre section can be well suppressed by the input RF signal with constant level.6 Rec. ITU-R F.1332-11332-04-RAU5RAU6RAU1RAU2RAU3RAU1RAU2RAU4RAU3RAU
37、4FIGURE 4Examples of applications using HFR systemsa) Indoor applicationFibreFibreb) Outdoor applicationO/E AmplifierNetworkinterfaceIntranetworking E/OFibreBuildingOLTOLTFIGURE 1332-04 = 23 CMRec. ITU-R F.1332-1 75 Implementation examplesHFR systems generally use an SCM technique. At the E/O side,
38、several outputs from the modulators with differentfrequencies are multiplexed in the combiner. Then the combined signal composed of the several subcarriers directlymodulates the LD. Thus, the subcarriers can simultaneously transmit through the optical fibre. The LD produce amodulated optical signal
39、whose intensity is proportional to the input electrical current. The maximum frequency islimited by the LD characteristics.In the opposite direction, a photodiode in the O/E converts the received optical power into electrical power with a linearresponse. Each desired radio channel is separated after
40、 the photodetection.Direct modulation of the laser diode with the combined radio-frequency signal allows only for limited fibre feederlengths due to optical loss and chromatic dispersion. The former factor can be sufficiently compensated by using anoptical amplifier. The problem caused by the latter
41、 factor can be eliminated by means of the heterodyne principle where2 optical carriers separated by the radio frequency are transported via fibre (see Fig. 5). In this case one optical carrier isused as local oscillator for heterodyning in the RAU and the other carrier bears the information stream.
42、By means of thismethod up to 100 km feeder lengths can be achieved, depending on data rates and transmission performance. Also, theradio-frequency is not limited by the LD modulation bandwidth in this case. However, the usefulness of this heterodynemillimeter-wave source technique depends on the opt
43、ical filter characteristics.1332-05ModulatorLDIntensitymodulatorOpticalfilterStandardmonomode fibremm-wavereceivermm-waveradio signalDriver DataFrequencyfradiofradio 1/2FIGURE 5Heterodyne mm-wave source (double frequency source, double sideband modulation)Optical mm-wave source * This is an example
44、of an optical mm-wave sourceimplementation. Alternative designs exist, e.g. laserinjection locking techniques.FIGURE 1332-05 = 12 CM8 Rec. ITU-R F.1332-1For outdoor microcell applications, the received signal power is subject to a slow or shadow fading and decreasesaccording to the well-known invers
45、e fourth-power law between a RAU and a wireless terminal. When a mobile terminalloses line-of-sight condition, the received signal drops sharply due to the diffraction loss.Since two or more signals with quite different levels are commonly received at the RAU receiver, it is difficult to select asui
46、table gain for all the signals. Therefore, for the uplink (from RAU to OLT) a HFR system needs a wide dynamicrange. This is called a near/far problem. The dynamic range is limited by the noise and non-linear performance of thewhole link. It is important to improve the non-linearity of the optic devi
47、ces as well as radio equipment.The non-linearity of the E/O mainly determines the upper limit of E/O input level. In Fig. 6 the input level of A producesthe maximum permissible IM3 level of E. On the other hand, the lowest limit of E/O input level is decided by therequired C/N D corresponding to the
48、 level of B. In this case, the dynamic range of the E/O converter is defined by(A - B) dB.1332-06DBAEIM3D:E:FIGURE 6Dynamic range of fibre optic linkE/O input power (dB)Dynamic rangeReceivedC/Nrequired C/N (threshold level)maximum permissible IM3 levelFIGURE 1332-06 = 14 CMRec. ITU-R F.1332-1 9An im
49、provement technique using an FM modulator has been proposed for increasing a dynamic range. Figure 7illustrates overview of this method. When using the conventional method, the low-level carrier is likely to be affected byIM3 interference due to the non-linearity. On the other hand, the input signal level to the E/O converter is kept constantby using an FM modulator. Although the bandwidth of the FM signal varies depending on the highest frequency andpeak voltage of the modulation signal, the peak injection current of the LD is almost fixed.1332-07f1f2f3f4FIGURE
