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Fig. 3Repeater spacings and hardware complexity withdifferent types of codes. The choice of the 5B6Bcode gives a good compromise between hardwarecomplexity and dispersion limiting17 MHz) and regenerated. The signal isthen recoded to a binary serial bitstream and passed to the line coder Inthe case of loss of input signal an alarmis given to the alarm unit. Violations ofthe HDB3 coding law result in an errorpulse which is available at a test pointThe line coder carries out the code conversionto adapt the data bit stream for alaser or LED transmitter. The chosencode is of type 5B6B, i.e. five binary symbolsare recoded as six binary symbols.This gives a symbol rate on the fibrecable of 6 345 = 41 MBaud Since thenumber of incoming binary states.2 5 = 32, is less than the number of outgoingbinary states. 2 6 = 64, the codehas built-in redundancy This redundancyis used to create a code spectrumwith a constant d.c voltage componentand a spectral energy distribution that issuited for optical transmission. The redundancyis also used for error supervisionof the signal and to get alow-capacityasynchronous data channelThe choice of code is by necessity acompromise. Other codes, i.e. 3B4Bwhich is used in ZAM 34-1. give a greaterdispersion penalty in LED systems.Higher order codes would require toocomplex equipment, fig.3.The bit rate conversion that is neededfor the coding is carried out with the aidof a crystal-controlled phase lockedloop, PLL. The loop bandwidth has beenchosen so that the jitter on the incomingsignal is reduced, resulting in a decreasedalignment jitter requirement inthe receivers of the repeater.Line code errors can be injected in theline coder at an optional rate in order totest the fault location system and alarmunit. The coding ensures that none ofthese bit errors remain after the decodingof the line signal.The laser transmitter receives the coded41 MBaud NRZ (Non Return to Zero) bitstream and the clock signal from the linecoder and converts them to a 41 MBaudRZ (Return to Zero) bit stream This isdone in order to reduce the problems ofinter-symbol interference in the receiver.The RZ signal modulates a laserwhich provides an optical signal on thefibre cable The operating point of thelaser is mean value regulated by meansof optical feedback with a photo diode atthe rear mirror of the laser. This stabilizesthe laser operation and compensatesfor temperature variations andageing effects.The laser is cooled by a thermoelectricelement to a constant temperature inorder to obtain maximum reliability. Aspecial laser unit has been developedwhich meets the system requirements.fig. 4.The laser temperature can be checkedby measuring a voltage in a test point onthe front of the unit.The operating life of the laser systemdepends mainly on the life of the laser,and the system is therefore equippedwith a circuit which supervises the conditionof the laser. An alarm is givenwhen the laser has degraded. The alarmis given well in advance, before the systemperformance is affected.Fig. 4The laser transmitter with the laser unit.The laser is cooled to a constant temperature inorder to obtain the highest possible reliability.The laser is stabilized by means of mean valueregulation of the operating pointAn alternative to the laser transmitterhas been developed, namely an LEDtransmitter which is intended for shorttransmission distances. It is fully compatiblewith the laser transmitter as regardsits connection. The LED transmittergives the system even higher reliabilitythan the laser transmitter. Likethe latter, the LED transmitter convertsthe incoming 41 MBaud NRZ flow to anoutgoing optical 41 MBaud RZ flow. TheLED is mounted on a cooling flange inorder to reduce its operating temperature.The receiver detects the incoming opticalsianal and converts it tn a 41 MRaurl
181Fig. 6Oscilloscope picture of the signal at the detectionpoint in the form of an eye diagram tor a lasersystem. Cable length: 10kmFig. 5aAPD receiver.The phase-locked loop is built up around avoltage controlled crystal oscillator, which ensureslow output jitterNRZ electrical bit stream. An avalanchephoto diode, APD, is used as the photodetector in order to obtain the best possiblereceiver sensitivity and dynamicrange. After the conversion in the APDthe signal is amplified in an input stage.This is followed by an amplifier with automaticgain control, AGC. The APD ismounted direct on the hybrid-type inputcircuit, fig.5. This minimizes the inputcapacitance, which would otherwise reducethe sensitivity of the input stageThe use of hybrid technology also minimizesthe effects of any electromagneticdisturbances. The sensitivity and dynamicrange are further improved byregulation of the APD reverse voltage.When an LED transmitter is used, a dispersionequalizer is automatically connectedin after the AGC amplifier Theamplified signal is filtered in a low-passfilter so that the highest possible signalto-noiseratio is obtained at the detectionpoint. Fig. 6 shows the signal at thedetection point in the form of an eyediagram for a laser system with 10 km offibre cable.The timing recovery from the signal flowtakes place in a PLL containing a voltagecontrolled crystal oscillator, whichprovides the necessary compensationfor temperature variations and ageingeffects. The relatively high Q value of theoscillator and its insensitivity to disturbancesensure low output jitter. The signalis regenerated with the aid of therecovered timing. The binary regenerated41 MBaud signal and the clock signalare fed to the decoder. These signalsare also accessible for an optional errordetector, ED The voltage across theAPD can be measured at a test point onthe front of the unit. For reasons of safetythe voltage is divided down to a hundredthof the actual valueThe binary input bit stream to the decoderis series/parallel converted andcode converted in a 5B6B decoder. Thedata signal and timing signal are thenfed to the previously described interfaceunit.The redundant words that are not usedin the normal encoding process causeerror pulses These pulses are fed to aresynchronization circuit and also to analarm unit. The resynchronization logicensures that the system is resynchronizedif the error rate of the incoming bitstream is too high. The logic is fittedwith error burst blocking in order to preventresynchronization for high errorrates of very short duration. The informationtransmitted over the data channelis also accessible in the decoderThe timing conversion required for thecode conversion is carried out with theaid of a crystal-controlled PLL. The loopbandwidth has been chosen so that theline signal jitter is reduced The jitter outtowards the multiplex equipment isthereby minimized. The serial datastream from the line decoder is HDB3coded in the send side of the interfaceunit.Fig. 5bA part of the APD receiver with the lid removedfrom the unit containing the hybrid circuit withthe avalanche photo diode. The APD is mounteddirect on a hybrid circuit in order to ensure thebest possible receiver sensitivity. A wide dynamicrange is obtained through regulation of the APDvoltaae combined with an AGC amplifier
Page 1: ERICSSONREVIEW41982REMOTE AXE 10 SU
Page 4 and 5: ;2Remote AXE 10 Subscriber Switchin
Page 6 and 7: Fig. 3The container is brought out
Page 8 and 9: An Optical Fibre Line Systemfor 34
Page 12 and 13: 182The primary alarms are those rec
Page 14 and 15: 184Technical dataDigital interface
Page 16 and 17: Fig. 2, leftThe transmultiplexer as
Page 18 and 19: 188Fig. 9Synchronization of the tra
Page 20 and 21: Fig. 13The M5/BYB bay equipped with
Page 22 and 23: Fig. 17ZAJ 5x24/2x60, transmultiple
Page 24 and 25: ERITEX10 for Teletex and WordProces
Page 26 and 27: Fig. 5The central processing unit i
Page 28 and 29: 198Fig. 8The floppy disc unit with
Page 30: 200- finding space for a document o
Page 33 and 34: Local Area Radio System-LARSHans Li
Page 35 and 36: Fig. 5One of the thick film hybrids
Page 37 and 38: 207Technical data for LARSSelective
Page 39 and 40: 209BERTH EKLUNDHDAVID RAPPDepartmen
Page 41 and 42: 211over, the type of traffic handle
Page 43 and 44: 213Models of CPA comparison between
Page 45 and 46: ETable 2The table shows the differe
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