CA1090425A - Digital radio relay systems - Google Patents
Digital radio relay systemsInfo
- Publication number
- CA1090425A CA1090425A CA271,085A CA271085A CA1090425A CA 1090425 A CA1090425 A CA 1090425A CA 271085 A CA271085 A CA 271085A CA 1090425 A CA1090425 A CA 1090425A
- Authority
- CA
- Canada
- Prior art keywords
- channel
- normal
- standby
- digital
- channels
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/22—Arrangements for detecting or preventing errors in the information received using redundant apparatus to increase reliability
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Detection And Prevention Of Errors In Transmission (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
ABSTRACT
In a digital relay system, a standby channel is arranged to replace any one Or five operational channels and the standby channel contains a variable delay which is automatically controlled prior to change-over to ensure that there is no slip or break in the data of the switched channel. Preferably the data is transmitted in a 'double-rate' binary code in which binary 'O' is transmitted as '01' or '10' and binary '1' is transmitted alternately as '00' or '11'.
In a digital relay system, a standby channel is arranged to replace any one Or five operational channels and the standby channel contains a variable delay which is automatically controlled prior to change-over to ensure that there is no slip or break in the data of the switched channel. Preferably the data is transmitted in a 'double-rate' binary code in which binary 'O' is transmitted as '01' or '10' and binary '1' is transmitted alternately as '00' or '11'.
Description
'` lOg~Z~
~his invention relates to digital relay system~ and to apparatus for such system~. Such digital relay systems may operate over radio links or over land lines.
With digital relay system~ having a number of channels it is often desirable to replace one of thé
channels with another ch~nnel while said one channel is operating, and in such circumstances the problem arises that some of the data being transmitted may be 10 lost, or some of the data may be transm~tted twice, when the cha~geover to the other ch~nnel takes place.
hn object of this invention i~ to provide a digital relay system which overcomes the above-mentioned problem.
According to the present invention there i8 provided a digital signal transmission system comprising transmitting apparatus at a first station and receiving apparatus at a second station for providing a plurality of normal transmission channelQ and a standby channel 20 between 3aid first and second stations, means for apply-in~ digital information signals to the transmitting apparatus for transmission over the normal channels, switching means for selecting digital information sig-nals in respect of any o~e Or the normal channels for 25 transmission oYer said standby channel, means providing a predetermined delay in each normal transmig~ion channel, means providing a variable delay in ~aid stand-by channel, comparator mean~ for comparing digital information siEnals received over said standby channel ~0 and said selected normal channel and for adjusting said variable delay means until ~aid received signals are substantially in synchronism, and switching means re-spon~i~e to an output signal from the comparator indicating that said received signals are in synchronism ~5 to effect the replacement of the selected normal transmission channel by the standby channel.
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Preerably, a variable delay arrangement is connected in the standby channel and is arranged to ad~ust the phase of the data signal~ pa~sing along the standby channel.
The control means may include means for com- ;~
paring the phase of the data signals passing along the standby channel with the phase of the data signals passing along the selected channel and providing an error ~ignal which is used to adjust the phase of the 10 data signals passing alo~g the standby channel.
~he normal channel which is to be replaced ~-by the standby channel may be selected manually or may be selected automatically.
~he in~ention will now be described, by way 15 of example, with reference to the accompanying drawings in which:-Figure 1 i~ a bloc~ schematic diagram of a digi tal r~dio relay s~stem in accordance with the invention;
and ~igure 2 i8 a block s¢hematic diagram of a ?
s~itching arrangement sho~n in block ~orm in ~igure 1.
Referring in the first instance to Figure l~the ~igita1 ~dl~ relay system co~prises five normal cha~nels 1 to 5 and a standb~ channel 6 which extend between 25 respective input terminal~ I and correspondIng output terminals 0 and have their input terminals I connected to associated fixed contacts of a rotar~ ~witc~ 7.
~he input terminals I of the five normal channels 1 to 5 are arranged to have applied thereto 'double rate'' 30 binary signal~ o~ the ~ind described in co-pending Canadian Patent ~pplication ~o. 211355. Such 'double rate' binary signals carry the data of a normal binary signal at twice the digit rate of the normal binary signal, each digit of the normal binar~ signal ha~ing ~5 one particular binary value being represented in the - . .
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'double rate' binary signal by a pair of digits having the values '01' ~or '10') and the digits Or the n~rmal binary signal having the other binary value being represented by pairs of digits having the values '00' 5 and '11' alternately.
~ he input terminals I of the five normal channels 1 to 5 are connected to the inputs of five associated signal processing arrangements 8 each of which is arranged to derive from the 'double rate' 10 binary signal applied to the input terminals I of the associated normal channel, a normal binary sisnal and a clock signal comprising a train of clock pulses.
Each signal processi~g arrangement 8 i~ also arranged to convert the normal binar~ signal and the clock signal -~
15 into a *orm suitable for modulating an associated radio channel 9 Or a radio link 10. A movable contact 11 of the rotary switch 7 is connected to the input of a standby signal processing arrangement 12 also arranged to derive from a 'double rate' binary signal a normal 20 binary signal and a clock signal, and to convert theæe signals into form suitable for modulating a standby radio chaunel 13 of the radio link 10.
~ he output signals from each of the radio channels 9 are arranged to be fed tO respective digital 25 processing circuits 14, each arranged to derive from an output signal a normal binary signal and a clock signal.
Similarly, the output signal from the standby radio chan~el 13 i8 fed to a standby digital processing circuit 15 arranged to derive from the output ~ignal a 30 normal binary signal and a clock sisnalD The normal ~
binary signal~ and the clock signal~ from the proce~ing ~;
circuits 14 are fed to respective input leads 16 to 20 of a switching arrangement 21, the corresponding output leads 22 to 26 of which are fed to respective circuit 35 arran~ements 27 for converting the ~ormal binary signals ,, . . - - , - . . , ~.
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to 'dollble rate r binary signals. The normal binary signals and the clock signals from the standby process-ing circuit 15 are also fed to an input lead 28 of the switching arrangement 21 a correspondiDg output lead 29 5 of which i~ fed to a standby circuit arransement 30 for converting normal binary signals to 'double rate' binary signals.
~ he po~ition of the movable contact 11 of the rotary switch 7 is monitored and controlled by a monitor 10 and control arrangement 31 which i8 connected o~er an auxiliar~ channel 32 of the radio link 10 to a further monitor and control arrangement ~3 arranged to monitor and control the operation of the switching arrangement 21.
Referring now also to Figure 2, the switching :-arrangement 21 comprises five change-over switching contacts 34 to 38 each having one fixed contact conn-ected to one of the input leads 16 to 20 and its movable contact connected to one of the output leads 22 to 26.
20 The other fixed contacts of the change-over contacts 34 to 38 are connected in common to the output of a variabb .:~
delay arrangement 39 to which an input is fed from ` input lead 28. ~he output of the variable delay arrange-ment 39 forms one input of an error detector 40`which 25 receives another input by way of the movable contact 41 of a rotary switch 42 having fi~e fixed contacts each connected to one of the input leads 16 to 20. ~he output of the error detector 40 i8 fed to the input of .
a control logic circuit 43 ha~ing five output leadc 44 30 to 48 each of which controls the operation of one of the change-over ¢onta~ts 34 to 38. ~ further output lead 49 controls the operation of the variable delay arrange-ment 39. ~ ~: ~he apparatus desc~ibed above operates in the 35 following manner to effect replacement of the equipment which forms a selected one of the normal channel~ 1 to : -~'; , ' , . ' ' . ' . . ' .. :' ' ~, ' . ~
lfl~90 ~ Z~i 5, say for example normal chAnnel 1, by the equipment which forms the standby channel 6. When the normal channel 1 which is to be replaced is selected the moni-tor and control arrangement 33 passes a signal to the 5 control circuit 43 and also passes a signal o~er the auxiliary channel 32 of the radio link to the monitor and control arrangement 31. The monitor and control arrangement 31 monitors the position of the movable contact 11 and moves it so that it connects the input 10 termQnal I of normal ch~nnel 1 to the standby signalling proces~ing arrangement 12, while the monitor and control arrangement 33 monitors the position of the movable contact 41 and moves it so that it connects the input lead 16 to the input of the error detector 40. At 15 this time the po~itions of all the movable contacts of the change-over switching contacts 34 to 38 are as shown in Figure 2.
~ he error detector 40 therefore receives the signals passing along normal channel 1 by way Or signal 20 processing arrangement 8, radio channel 9, digital pro-cessing circuit 14t input lead 16, movable contact 41 and input lead 5~j and Plso receives the signals which are applied to the input terminal I of normal channel ~:
1 but which pass along standby channel 6 by way of 25 movable contact 11, standby signalling processing arrangement 12, standby radio link 13, standby digital processing circuit 15, input lead 28 and the variable delay arrangement 39 and input lead 51. The error detector 4~ compares the phase of the signals received 30 over these two routes-and provides an error signal which is fed to the control circuit 43 by wa~ of lead 52.
q'he control circuit 43 provide~ an output signal on output lead 49 which ad~usts the delay provided b~ --variable delay arrangement 39 until the phase Or the 35 data supplied to the error detector 4~:~by way of ,~.. ....
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~0 ~ 0~ 5 input lead 51 is bit synchronous with the phase of the data ~upplied to the error detector 40 by way of input lead 50.
The normal channel 1 and standby channel 6 5 are then synchronous and the signal fed to the control circuit 43 by way of lead 52 produces an output sig~al on lead 48 which operates change-over contacts 34. ~he signals applied to input terminal I of normal channel 1 then pass by way of standby signal proce~sing arrange-10 ment 12, 9tandby radio channel 13, standby digitAlprocessing circuit 15 to the associated output circuit arrangement 27. ~hus the equipment forming standby channel 6 is caused to replace the equipment forming normal ch~nnel 1 without causing any significant ~lip 15 or break in the data which is being transmitted by the replaced channel, ~n associated circuit arrangment 53 may be connected between each of the output leads 22 to 26 and 29 and the associated circuit arrangements 27 and 30 to reduce any ~jitter' being transmitted to 20 the output terminal 0.
~he apparatus may also be used to perform - the reverse procedure, that i~ to say to ef$e¢t re-placement of the equipment which forms the standby channel 6 by the equipment which forms the selectea 25 normal channel 1. As before the error detector 40 receives signals passing along normal channel 1 by way of sig~al proces~ing arrangement 8, radio channel 9, digital processing circuit 14, input lead 16, mov~
abl~ contact 41 and input lead 50, and also receives the 30 signals which are applied to the input terminal I of normal channel 1 but which pass along standby channel 6 by way of movable contact 11, standby signalling processing arrangeme~t 12, standby radio link 13, : standby digital processing circuit 15, input lead 28~.
35 and the variable delay arrangement 39 and input lead 51.
~he error detector 40 compares the phase of the signals -~
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-recei~ed over these two route~ and provides an error signal which i~ fed to the control circuit 43 by way of lead 52. The control circuit 43 provides an output signal on output lead 49 which adjusts the delay pro-5 vided by variable delay arrangement 39 until the phaseof the data supplied to the error detector 40 by way of input lead 51 i8 bit synchronous with the phase of the data supplied to the error detector 40 by way of input lead 50.
The normal chan~el 1 and stPndby channel 6 are then synchronous and the signal fed to the control circuit 43 by way of lead 52 produces an output signal on lead 48 which operates changeover contacts 34 to restore them to their originPl position. The signal~
15 applied to input terminal I of normal channel 1 then pass by way of its signal processing arrangement 8~
radio channel 9, digital processi~g circuit 14, circuit arrangement 53 to the output circuit arrangement 27.
Thus the equipment forming the standby channel 6 i8 20 replaced by the eguipment forming the normal channel 1 withou~ causing any significant slip or brea~ in the data which i~ being transmitted the circuit arrangement 5~ acting to reduce any '~itter~ being transmitted.
~pically, the 'double rate' binary ~ignals 25 and the normal binary signals and cloc~ pulses are transmitted at 139.264 megabits per second and the total spread of the delay through digital sections is arranged to be not more thAn l 3 digits or 21 nanos~econds. In order that the variable delay in standby channel 6 is 30 always positive, channels 1 to 5 may be delayed by a fixed delay o~ 3 digits or 21 nanoseco~ds. Thus the delay produced by the variable delay arrangement 39 need be no more than from 0 to 6 digits or 0 to 42 nanoseconds in order to cater~for the maximum spread` of 35 delay~ between channels.
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.
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1~911~
_9_ The channel which is to be replaced by the standby ch~nnel 6 may be selected manually or may be selected automatically. The channels may include radio links as described above or may comprise land 5 lines which may be conventional conductors or ma~ com-prise optic ribres.
The most difficult combination of circumstances i~ which to test for synchronism is in the high error '~
rate ~greater than 1 in 104), and quiescent data in the 10 traffic i.e. all l's or ~0~8 in the traffic except ~or the frame alignment signal which is assumed to be'of the form 1111101000000 occurring approximately every 3000 bits. In this case if the two data ~treams entering the error detector 40 are not properly aligned then 15 no more than 4 errors (plus noise) can be guaranteed in approximately 3000 digits. Thus the problem is to ~, recognise the 1 in 103 error rate due to non-alignment in the presence of a ~oise error rate greater than 1 in 104. In order to overcome this difficulty use is ~ ~
20 made of the fact that the four errors due to non-align- ~, ment of the two data streams occur within a spread of 8 digits.
' ~he strategy for determi,ning alignment between the two data streams entering the error detector is '~
25 thus as follows:
1. If 4 in any 8 digits are in error, i.e. not ~'g~
equivalent, the two data streams are not aligned ~ ~
or are not the same data. - ' '
~his invention relates to digital relay system~ and to apparatus for such system~. Such digital relay systems may operate over radio links or over land lines.
With digital relay system~ having a number of channels it is often desirable to replace one of thé
channels with another ch~nnel while said one channel is operating, and in such circumstances the problem arises that some of the data being transmitted may be 10 lost, or some of the data may be transm~tted twice, when the cha~geover to the other ch~nnel takes place.
hn object of this invention i~ to provide a digital relay system which overcomes the above-mentioned problem.
According to the present invention there i8 provided a digital signal transmission system comprising transmitting apparatus at a first station and receiving apparatus at a second station for providing a plurality of normal transmission channelQ and a standby channel 20 between 3aid first and second stations, means for apply-in~ digital information signals to the transmitting apparatus for transmission over the normal channels, switching means for selecting digital information sig-nals in respect of any o~e Or the normal channels for 25 transmission oYer said standby channel, means providing a predetermined delay in each normal transmig~ion channel, means providing a variable delay in ~aid stand-by channel, comparator mean~ for comparing digital information siEnals received over said standby channel ~0 and said selected normal channel and for adjusting said variable delay means until ~aid received signals are substantially in synchronism, and switching means re-spon~i~e to an output signal from the comparator indicating that said received signals are in synchronism ~5 to effect the replacement of the selected normal transmission channel by the standby channel.
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. . . . , . ; .
.. : - ~ - ;, , - , , ~- ... ..
.
. : , .
l~V~
Preerably, a variable delay arrangement is connected in the standby channel and is arranged to ad~ust the phase of the data signal~ pa~sing along the standby channel.
The control means may include means for com- ;~
paring the phase of the data signals passing along the standby channel with the phase of the data signals passing along the selected channel and providing an error ~ignal which is used to adjust the phase of the 10 data signals passing alo~g the standby channel.
~he normal channel which is to be replaced ~-by the standby channel may be selected manually or may be selected automatically.
~he in~ention will now be described, by way 15 of example, with reference to the accompanying drawings in which:-Figure 1 i~ a bloc~ schematic diagram of a digi tal r~dio relay s~stem in accordance with the invention;
and ~igure 2 i8 a block s¢hematic diagram of a ?
s~itching arrangement sho~n in block ~orm in ~igure 1.
Referring in the first instance to Figure l~the ~igita1 ~dl~ relay system co~prises five normal cha~nels 1 to 5 and a standb~ channel 6 which extend between 25 respective input terminal~ I and correspondIng output terminals 0 and have their input terminals I connected to associated fixed contacts of a rotar~ ~witc~ 7.
~he input terminals I of the five normal channels 1 to 5 are arranged to have applied thereto 'double rate'' 30 binary signal~ o~ the ~ind described in co-pending Canadian Patent ~pplication ~o. 211355. Such 'double rate' binary signals carry the data of a normal binary signal at twice the digit rate of the normal binary signal, each digit of the normal binar~ signal ha~ing ~5 one particular binary value being represented in the - . .
lV9f~ZS
~.
~_ .
'double rate' binary signal by a pair of digits having the values '01' ~or '10') and the digits Or the n~rmal binary signal having the other binary value being represented by pairs of digits having the values '00' 5 and '11' alternately.
~ he input terminals I of the five normal channels 1 to 5 are connected to the inputs of five associated signal processing arrangements 8 each of which is arranged to derive from the 'double rate' 10 binary signal applied to the input terminals I of the associated normal channel, a normal binary sisnal and a clock signal comprising a train of clock pulses.
Each signal processi~g arrangement 8 i~ also arranged to convert the normal binar~ signal and the clock signal -~
15 into a *orm suitable for modulating an associated radio channel 9 Or a radio link 10. A movable contact 11 of the rotary switch 7 is connected to the input of a standby signal processing arrangement 12 also arranged to derive from a 'double rate' binary signal a normal 20 binary signal and a clock signal, and to convert theæe signals into form suitable for modulating a standby radio chaunel 13 of the radio link 10.
~ he output signals from each of the radio channels 9 are arranged to be fed tO respective digital 25 processing circuits 14, each arranged to derive from an output signal a normal binary signal and a clock signal.
Similarly, the output signal from the standby radio chan~el 13 i8 fed to a standby digital processing circuit 15 arranged to derive from the output ~ignal a 30 normal binary signal and a clock sisnalD The normal ~
binary signal~ and the clock signal~ from the proce~ing ~;
circuits 14 are fed to respective input leads 16 to 20 of a switching arrangement 21, the corresponding output leads 22 to 26 of which are fed to respective circuit 35 arran~ements 27 for converting the ~ormal binary signals ,, . . - - , - . . , ~.
, ~ .
z~
to 'dollble rate r binary signals. The normal binary signals and the clock signals from the standby process-ing circuit 15 are also fed to an input lead 28 of the switching arrangement 21 a correspondiDg output lead 29 5 of which i~ fed to a standby circuit arransement 30 for converting normal binary signals to 'double rate' binary signals.
~ he po~ition of the movable contact 11 of the rotary switch 7 is monitored and controlled by a monitor 10 and control arrangement 31 which i8 connected o~er an auxiliar~ channel 32 of the radio link 10 to a further monitor and control arrangement ~3 arranged to monitor and control the operation of the switching arrangement 21.
Referring now also to Figure 2, the switching :-arrangement 21 comprises five change-over switching contacts 34 to 38 each having one fixed contact conn-ected to one of the input leads 16 to 20 and its movable contact connected to one of the output leads 22 to 26.
20 The other fixed contacts of the change-over contacts 34 to 38 are connected in common to the output of a variabb .:~
delay arrangement 39 to which an input is fed from ` input lead 28. ~he output of the variable delay arrange-ment 39 forms one input of an error detector 40`which 25 receives another input by way of the movable contact 41 of a rotary switch 42 having fi~e fixed contacts each connected to one of the input leads 16 to 20. ~he output of the error detector 40 i8 fed to the input of .
a control logic circuit 43 ha~ing five output leadc 44 30 to 48 each of which controls the operation of one of the change-over ¢onta~ts 34 to 38. ~ further output lead 49 controls the operation of the variable delay arrange-ment 39. ~ ~: ~he apparatus desc~ibed above operates in the 35 following manner to effect replacement of the equipment which forms a selected one of the normal channel~ 1 to : -~'; , ' , . ' ' . ' . . ' .. :' ' ~, ' . ~
lfl~90 ~ Z~i 5, say for example normal chAnnel 1, by the equipment which forms the standby channel 6. When the normal channel 1 which is to be replaced is selected the moni-tor and control arrangement 33 passes a signal to the 5 control circuit 43 and also passes a signal o~er the auxiliary channel 32 of the radio link to the monitor and control arrangement 31. The monitor and control arrangement 31 monitors the position of the movable contact 11 and moves it so that it connects the input 10 termQnal I of normal ch~nnel 1 to the standby signalling proces~ing arrangement 12, while the monitor and control arrangement 33 monitors the position of the movable contact 41 and moves it so that it connects the input lead 16 to the input of the error detector 40. At 15 this time the po~itions of all the movable contacts of the change-over switching contacts 34 to 38 are as shown in Figure 2.
~ he error detector 40 therefore receives the signals passing along normal channel 1 by way Or signal 20 processing arrangement 8, radio channel 9, digital pro-cessing circuit 14t input lead 16, movable contact 41 and input lead 5~j and Plso receives the signals which are applied to the input terminal I of normal channel ~:
1 but which pass along standby channel 6 by way of 25 movable contact 11, standby signalling processing arrangement 12, standby radio link 13, standby digital processing circuit 15, input lead 28 and the variable delay arrangement 39 and input lead 51. The error detector 4~ compares the phase of the signals received 30 over these two routes-and provides an error signal which is fed to the control circuit 43 by wa~ of lead 52.
q'he control circuit 43 provide~ an output signal on output lead 49 which ad~usts the delay provided b~ --variable delay arrangement 39 until the phase Or the 35 data supplied to the error detector 4~:~by way of ,~.. ....
, . . . .
- . - .
.
'~ , . ' .
~0 ~ 0~ 5 input lead 51 is bit synchronous with the phase of the data ~upplied to the error detector 40 by way of input lead 50.
The normal channel 1 and standby channel 6 5 are then synchronous and the signal fed to the control circuit 43 by way of lead 52 produces an output sig~al on lead 48 which operates change-over contacts 34. ~he signals applied to input terminal I of normal channel 1 then pass by way of standby signal proce~sing arrange-10 ment 12, 9tandby radio channel 13, standby digitAlprocessing circuit 15 to the associated output circuit arrangement 27. ~hus the equipment forming standby channel 6 is caused to replace the equipment forming normal ch~nnel 1 without causing any significant ~lip 15 or break in the data which is being transmitted by the replaced channel, ~n associated circuit arrangment 53 may be connected between each of the output leads 22 to 26 and 29 and the associated circuit arrangements 27 and 30 to reduce any ~jitter' being transmitted to 20 the output terminal 0.
~he apparatus may also be used to perform - the reverse procedure, that i~ to say to ef$e¢t re-placement of the equipment which forms the standby channel 6 by the equipment which forms the selectea 25 normal channel 1. As before the error detector 40 receives signals passing along normal channel 1 by way of sig~al proces~ing arrangement 8, radio channel 9, digital processing circuit 14, input lead 16, mov~
abl~ contact 41 and input lead 50, and also receives the 30 signals which are applied to the input terminal I of normal channel 1 but which pass along standby channel 6 by way of movable contact 11, standby signalling processing arrangeme~t 12, standby radio link 13, : standby digital processing circuit 15, input lead 28~.
35 and the variable delay arrangement 39 and input lead 51.
~he error detector 40 compares the phase of the signals -~
. - .
. , . . , ....................... -. . . . . ;
~: ; : ' ' ' . ~,- ,, . .:
10~
-recei~ed over these two route~ and provides an error signal which i~ fed to the control circuit 43 by way of lead 52. The control circuit 43 provides an output signal on output lead 49 which adjusts the delay pro-5 vided by variable delay arrangement 39 until the phaseof the data supplied to the error detector 40 by way of input lead 51 i8 bit synchronous with the phase of the data supplied to the error detector 40 by way of input lead 50.
The normal chan~el 1 and stPndby channel 6 are then synchronous and the signal fed to the control circuit 43 by way of lead 52 produces an output signal on lead 48 which operates changeover contacts 34 to restore them to their originPl position. The signal~
15 applied to input terminal I of normal channel 1 then pass by way of its signal processing arrangement 8~
radio channel 9, digital processi~g circuit 14, circuit arrangement 53 to the output circuit arrangement 27.
Thus the equipment forming the standby channel 6 i8 20 replaced by the eguipment forming the normal channel 1 withou~ causing any significant slip or brea~ in the data which i~ being transmitted the circuit arrangement 5~ acting to reduce any '~itter~ being transmitted.
~pically, the 'double rate' binary ~ignals 25 and the normal binary signals and cloc~ pulses are transmitted at 139.264 megabits per second and the total spread of the delay through digital sections is arranged to be not more thAn l 3 digits or 21 nanos~econds. In order that the variable delay in standby channel 6 is 30 always positive, channels 1 to 5 may be delayed by a fixed delay o~ 3 digits or 21 nanoseco~ds. Thus the delay produced by the variable delay arrangement 39 need be no more than from 0 to 6 digits or 0 to 42 nanoseconds in order to cater~for the maximum spread` of 35 delay~ between channels.
- . ' . . . .. . .
..
, - ~ . .
.
,' '. : ~ ' . , ' ~ ," ' ' ' ' ~ ' , . : , ,' :
1~911~
_9_ The channel which is to be replaced by the standby ch~nnel 6 may be selected manually or may be selected automatically. The channels may include radio links as described above or may comprise land 5 lines which may be conventional conductors or ma~ com-prise optic ribres.
The most difficult combination of circumstances i~ which to test for synchronism is in the high error '~
rate ~greater than 1 in 104), and quiescent data in the 10 traffic i.e. all l's or ~0~8 in the traffic except ~or the frame alignment signal which is assumed to be'of the form 1111101000000 occurring approximately every 3000 bits. In this case if the two data ~treams entering the error detector 40 are not properly aligned then 15 no more than 4 errors (plus noise) can be guaranteed in approximately 3000 digits. Thus the problem is to ~, recognise the 1 in 103 error rate due to non-alignment in the presence of a ~oise error rate greater than 1 in 104. In order to overcome this difficulty use is ~ ~
20 made of the fact that the four errors due to non-align- ~, ment of the two data streams occur within a spread of 8 digits.
' ~he strategy for determi,ning alignment between the two data streams entering the error detector is '~
25 thus as follows:
1. If 4 in any 8 digits are in error, i.e. not ~'g~
equivalent, the two data streams are not aligned ~ ~
or are not the same data. - ' '
2. If les~ than 4 in any 8 digits are in error for ~0 a period greater than the time between two frame alignment signals, then the two data streams are regarded as being ide~tical and in alignment.
~sing the above criteria the following situations ma~ -be considered.-35 1- If the two data stream~ are not aligned and the ~` .
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gl[)~;~5 traffic approximate~ to random data, then oYer a sample of 12 digit~ non-alignment will be de-tected to a probability of approximately 99%.
2. If the two data strea~ are correctly aligned but noise is producing a Poisson error rate of 1 in 102 the probability of more than 3 errors occurring in a sample of 8 is approximatel~ l in 10~. Thus over the time between the frame alignment signals probability of a spurious detection of non-align-ment i~ of the order o~ l in 1 ~ .
. If the two data streams are not aligned and all traffic is quiescent, except the frame alignment signal~, the probability of the frame alignment signal being masked in a line error rate of 1 in 102 i8 approximately l in 25. 2 ~hus in a noise error rate of l in 10 non-alignment can be detected in about 12 data bits or approximately lO0 nanosecond~. If the band width of the control loop of the variable delay is about 500 EHz 20 the time to change the delay by 1 bit i8 approximately 2 microseconds. ~u~ all 6 delay positions can be sampled in about 10 micro~econd~. If data i8 all 'zero~' o~ 'one~" except for frame alignment 5ignal8 the time increases to about 100 microseconds with a 25 failure rate (depending on the 1 in 102 line error rate) of l in 25. In lower noise conditions (l ~n 104 or better) the failure rate of correct alignment -1B tO lower than l in lO~ or better.
`. -: - .
.. -, ~ . - . - . . -' ' . : " ~ . - '
~sing the above criteria the following situations ma~ -be considered.-35 1- If the two data stream~ are not aligned and the ~` .
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gl[)~;~5 traffic approximate~ to random data, then oYer a sample of 12 digit~ non-alignment will be de-tected to a probability of approximately 99%.
2. If the two data strea~ are correctly aligned but noise is producing a Poisson error rate of 1 in 102 the probability of more than 3 errors occurring in a sample of 8 is approximatel~ l in 10~. Thus over the time between the frame alignment signals probability of a spurious detection of non-align-ment i~ of the order o~ l in 1 ~ .
. If the two data streams are not aligned and all traffic is quiescent, except the frame alignment signal~, the probability of the frame alignment signal being masked in a line error rate of 1 in 102 i8 approximately l in 25. 2 ~hus in a noise error rate of l in 10 non-alignment can be detected in about 12 data bits or approximately lO0 nanosecond~. If the band width of the control loop of the variable delay is about 500 EHz 20 the time to change the delay by 1 bit i8 approximately 2 microseconds. ~u~ all 6 delay positions can be sampled in about 10 micro~econd~. If data i8 all 'zero~' o~ 'one~" except for frame alignment 5ignal8 the time increases to about 100 microseconds with a 25 failure rate (depending on the 1 in 102 line error rate) of l in 25. In lower noise conditions (l ~n 104 or better) the failure rate of correct alignment -1B tO lower than l in lO~ or better.
`. -: - .
.. -, ~ . - . - . . -' ' . : " ~ . - '
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A digital signal transmission system comprising transmitting apparatus at a first station and receiving apparatus at a second station for providing a plurality of normal transmission channels and a standby channel between said first and second stations, means for applying digital information signals to the transmitting apparatus for transmission over the normal channels, switching means for selecting digital informa-tion signals in respect of any one of the normal channels for transmission over said standby channel, means providing a predetermined delay in each normal transmission channel, means providing a variable delay in said standby channel, comparator means for comparing digital information signals received over said standby channel and said selected normal channel and for adjusting said variable delay means until said received signals are substantially in synchronism, and switching means reponsive to an output signal from the comparator indicating that said received signals are in synchronism to effect the replacement of the selected normal transmission channel by the standby channel.
2. A digital relay system as claimed in claim 1, wherein the normal channel which. is to be replaced by the standby channel is selected manually.
3. A digital relay system as claimed in claim 1, wherein the channels include radio links.
4. A digital relay system as claimed in claim 1, wherein the channels comprise land lines.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4730/76 | 1976-02-06 | ||
| GB473076A GB1520153A (en) | 1976-02-06 | 1976-02-06 | Digital relay systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090425A true CA1090425A (en) | 1980-11-25 |
Family
ID=9782714
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA271,085A Expired CA1090425A (en) | 1976-02-06 | 1977-02-04 | Digital radio relay systems |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS52103910A (en) |
| CA (1) | CA1090425A (en) |
| CH (1) | CH615546A5 (en) |
| DE (1) | DE2703625A1 (en) |
| GB (1) | GB1520153A (en) |
| IT (1) | IT1073255B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5443408A (en) * | 1977-09-13 | 1979-04-06 | Nippon Telegr & Teleph Corp <Ntt> | Error control system |
| JPS55143850A (en) * | 1979-04-26 | 1980-11-10 | Nec Corp | Pcm line switching system |
| FR2462065A1 (en) * | 1979-07-24 | 1981-02-06 | Thomson Csf | Switching of numeric signal equipment - using memory and coincidence detector techniques with two circuits transmitting same data under different conditions |
| DE2939253A1 (en) * | 1979-09-27 | 1981-04-30 | Siemens AG, 1000 Berlin und 8000 München | Multiple redundant data transmission system - uses test signal to control change-over of transmission lines if line failure occurs |
| JPS5758419A (en) * | 1980-09-25 | 1982-04-08 | Fujitsu Ltd | Uninterruptible transmission line switching system |
| JPS58177042A (en) * | 1982-04-09 | 1983-10-17 | Nec Corp | Transmission failure reduction system |
| JP3561787B2 (en) * | 1994-06-30 | 2004-09-02 | 和通 藤原 | Method and apparatus for imparting acoustic vibration sensation |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2106835C3 (en) * | 1971-02-13 | 1982-07-15 | Philips Patentverwaltung Gmbh, 2000 Hamburg | Modem coupler |
-
1976
- 1976-02-06 GB GB473076A patent/GB1520153A/en not_active Expired
-
1977
- 1977-01-28 DE DE19772703625 patent/DE2703625A1/en not_active Withdrawn
- 1977-02-04 IT IT6726477A patent/IT1073255B/en active
- 1977-02-04 CA CA271,085A patent/CA1090425A/en not_active Expired
- 1977-02-04 CH CH139977A patent/CH615546A5/en not_active IP Right Cessation
- 1977-02-04 JP JP1153877A patent/JPS52103910A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| IT1073255B (en) | 1985-04-13 |
| CH615546A5 (en) | 1980-01-31 |
| DE2703625A1 (en) | 1977-08-11 |
| GB1520153A (en) | 1978-08-02 |
| JPS52103910A (en) | 1977-08-31 |
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| MKEX | Expiry |