250Km Transmission of Frequency Multiplexed 64QAM Signals for Digital CATV Backbone Application Shinji TSUJI Yuji HAMASAKI
Total Page：16
File Type：pdf, Size：1020Kb
THE COMPLETE TECHNICAL PAPER PROCEEDINGS FROM: 250km Transmission of Frequency Multiplexed 64QAM Signals For Digital CATV Backbone Application Shinji TSUJI Yuji HAMASAKI 64QAM is recognized as a standard for the invest in digital headend such as CS-IRDs, digital television transmission method on cable real-time encoders, scramblers, 64QAM plants. This is more robust than the traditional modulators and management systems. VSB-AM analog method in white noise and Especially in the case of the contents nonlinear distortion environment that is typical provider, satellite operator and cable operator in the CATV environment. As it is a digital which are all independent. We propose that method, it can be regenerated as necessary. several operators share one digital headend Therefore, it will be a better format for long and transmit digital signals to each operator’s distance transmission using optical fiber. In this analog headend using optical fiber and paper, we propose an economical CATV EDFAs for long distance. This is clearly cost- backbone solution using a 64QAM transmission efficient. system. The system has one digital headend and several analog headends connected by optical There are two methods of trunk fiber cable. The digital headend facility is transmission. One is the PCM/ATM method shared by other headends. We conducted that uses time division multiplexing in the experiments to verify the concept of the digital trunk line; at each local headend signals are 64QAM backbone. The experimental system has 250km fiber with 5 cascaded erbium doped CATV Op tical F in iber CATV optical fiber amplifiers (EDFA) and 11 Plant channels of 64QAM signal or 60CW signals CATV CATV were transmitted as test signals. Such UPGRADE INDIVIDUALY parameters as input/output of EDFAs and CATV Individual each CATV modulation depth of laser diode were Investment Doubled intentionally changed to find the optimized Digital Headend value. We conclude that it is feasible to transmit CATV Opti cal F 30 channels of 64QAM signals through 250km iber of optical fiber with EDFAs without CATV regeneration. DIGITAL TRUNK SYSTEM CATV mp. ical A QAM DIGITAL TRUNK SYSTEM Opt Fig.1 Image of digital services Network Architecture QAM Digital Trunk system PCM/ATM system Optical Optical Coupler Digital Rx DEMUX We propose here the QAM digital trunk Rx Tx system. An image of this system is shown in QAM BPF modulator Figure 1. There are some cable operators or cable plants made up of the HFC system with Analog HE facility Analog HE facility radial optical fibers. If the operator plans to serve digital services individually, he must Fig.2a Example of local headend facility 64QAM Satellite IRD MUX SCR OPT. Tx MOD USUAL capacity cash servers and fast Internet backbone can be connected. MPEG2 64QAM BACKUP MUX SCR OPT. Tx ENCODER MOD Figure 3 illustrates the system image. The ANALOG HEADEND left ring shows that digital signals from the DATA digital headend are transmitted in the trunk IP line via local headends (CATV1, CATV2,…, OPT. Rx USUAL CATV6) clockwise and counterclockwise. At PROGRAM CONDITIONAL SECURITY MANAGEMENT ACCESS local headend, digital signals are combined 64QAM BACKUP OPT. Rx DEMOD with analog signals, and both signals are transmitted in the CATV plant. Each local Fig.2b Example of digital headend facility headend is identified by its configuration and has the function shown on the right. The D OPTICAL DROP STATION simplest configuration is called “Optical drop CATV1 Drop optical signal CATV2 Conversion to electric signal Opt. Rx station”. It consists of an optical coupler, REPEATER STATION optical receiver and BPF. Digital signals from CATV3 Opt. Rx Conversion to electric Re-conversion to optical the digital headend are filtered to eliminate DIGITAL Ability to send to digital Opt. Tx HEADEND headend out-of-band noise and mixed with analog CATV4 REGENERATOR STATION signals here. The next configuration called Long distance transmission QAM demodulation & “Repeater station” consists of an optical QAM modulation Eliminating noise & distortion CATV5 receiver and optical transmitter. Optical signal CATV6 Connection to other lines Frequency reallocation is once converted to an electric signal and A D again converted to an optical signal. Therefore, if the transmission line is designed Fig.3 Function of local headends in a loop scheme, it is possible to transmit a de-multiplexed and converted to QAM format signal to the digital headend from here. The at every RF channel. An example of the local third configuration is called “Regenerator headend facility is shown in Figure 2a. The station”. All QAM signals are demodulated to other is a method that transmits QAM signals bit stream and modulated to QAM again. The in RF from the digital headend. In this purpose of regeneration is to remove noise method, each local headend consists of simple and distortion integrated as long distance equipment including an optical receiver and transmission. It is possible to add and delete a band pass filter (BPF). The latter is a QAM signal. It is also possible to change frequency digital trunk system, which is lower cost at allocation. each local headend than the former. Here we show application examples using At the digital headend, received and/or this system. An example in Figure 4 transmits served digital contents are transmitted. Figure the contents of local UHF broadcasting to 2b illustrates the configuration of the digital other CATV plants. An operator in a local headend. It consists of satellite and terrestrial UHF area receives the signal and encodes it to receivers, MPEG2 real-time encoders, MPEG2 format, then modulates it to QAM multiplexers, conditional access equipment, signal in R1 channel and transmits it to the QAM modulators, management system, digital headend. At the digital headend, the mixers and optical transmission equipment. received signal in R1 channel is demodulated For higher reliability, the optical transmission and multiplexed with other contents, and line should be doubled. As the need arises, QAM modulated to D1 channel. Then fast data transmission equipment, ultra subscribers in every CATV plant can enjoy UHF broadcasting by tuning to D1 channel at CATV - Add usually 550-750MHz.In this case, digital D1 D2 D3 R1 Local Broadcasting signals are transmitted as simul-frequency Optical Tuner Rx from the digital headend. At the local headend Optical QAM Tx Encoder MUX of the 450MHz plant, signals for 450MHz MOD Digital HE R1 plants are filtered and transmitted to the plant. Other Other Figure 6 is an example of a backup system in Optical signals signals Optical case signals via satellites are hindered by rain Rx QAM QAM Tx CATV - Drop DEMOD MOD attenuation. There are two digital headends, R1 D1 BPF separated enough distance to reduce the QAM HFC Trunk QAM Decoder TV probability of co-hindrance. The main digital MOD MOD D1 headend selects better signals from the D1 D2 D3 satellite receivers or the signals that are Fig.4 Application – Transmission of local received at the sub digital headend and broadcasting to every plants transmitted through the trunk line. Then disturbed time will be shorter. A D1 D2 D3 CATV 70 450 D1 D2 D3 d1 d2 d3 450MHz 450 750 System Performance Local HE HFC QAM Optical Digital HE Trunk Rx BPF In this system, QAM signals are D1 D2 D3 transmitted from the digital headend to IRD UP1 MOD CATV ENC subscriber terminals via the optical trunk line, UP2 750MHz local headend, and CATV plant. On the other Local HE HFC hand, analog signals are transmitted from the QAM Optical Trunk Rx BPF local headend to subscriber terminals. We d1 d2 d3 assume here that C/N of analog signal (4MHz A d1 d2 d3 70 750 bandwidth) is 43dB. As C/N of 64QAM Fig.5 Application – Transmission to combination annex C needs more than 31dB per 4MHz, we bandwidth of 450MHz and 750MHz distribute the system performance under the condition of 30dB C/N (averaged per Nyquist Local HE CW bandwidth) including margin. When QAM O/E CCW A/B BPF averaged power is NTSC signal –10dB, O/E QAM C/N in CATV plant is 31.8dB. To Ordinary Digital HE main Digital HE sub 1 2 3 S1 S2 S3 D1 D2 D3 S S S obtain 30dB as total C/N, C/N in the trunk Sat. IRD Rainfall MOD UP Opt.DEMOD IRD MOD UP s1 s2 s3 D1 D2 D3 line should be more than 34.7dB. (Based on V A ENC MOD UP s1 s2 s3 4MHz carrier level, total C/N is 34.9dB, trunk D1 D2 D3 line C/N is 39.6dB. Here expression of C/N S1 S2 S3 D1 D2 D3 s1 s2 s3 means averaged value per Nyquist bandwidth S1 S2 S3 D1 D2 D3 without notice.) Fig.6 Application – Backup system for 250KM TRANSMISSION EXPERIMENT eliminating interruption from satellite as high quality as in the broadcasting area. An Outline of Experiment example in Figure 5 is a combined system of 450MHz plants and 750MHz plants. In 450MHz plants, digital signals are usually We conducted a transmission experiment located in higher range such as 300- to investigate the feasibility of a QAM digital 450MHz.In 750MHz plants, they are trunk system and system design. Another QAM 11ch 1558nm located 222~288 MHz and 60 CWs are MOD +7dBm Optical EDFA spec. Tx between 91.25MHz and 445.25MHz. We 60ch Category Post amp. Mullet SG (For comparison) Wavelength 1560}5nm measured 64QAM characteristics at the center Out power +16.5dBm channel located at 252~258MHz. This EDFA channel modulator is connected to BER #1 ATT #2 ATT #3 ATT 50km 50km measuring equipment and other modulators Total 261.3km self-generate PRBS signals individually.