WO1999029078A2 - Improvements in, or relating to, data scramblers - Google Patents

Improvements in, or relating to, data scramblers Download PDF

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Publication number
WO1999029078A2
WO1999029078A2 PCT/SE1998/002193 SE9802193W WO9929078A2 WO 1999029078 A2 WO1999029078 A2 WO 1999029078A2 SE 9802193 W SE9802193 W SE 9802193W WO 9929078 A2 WO9929078 A2 WO 9929078A2
Authority
WO
WIPO (PCT)
Prior art keywords
data
synchronisation
frame
transmission system
carrier transmission
Prior art date
Application number
PCT/SE1998/002193
Other languages
French (fr)
Other versions
WO1999029078A3 (en
Inventor
Tomas NORDSTRÖM
Gunnar Bahlenberg
Daniel Bengtsson
Siwert HÅKANSSON
Anders Isaksson
Mikael Isaksson
Magnus Johansson
Lis-Marie Ljunggren
Hans Lundberg
Sven-Rune Olofsson
Lennart Olsson
Tomas Stefansson
Hans Öhman
Göran ÖKVIST
Original Assignee
Telia Ab (Publ)
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Telia Ab (Publ) filed Critical Telia Ab (Publ)
Publication of WO1999029078A2 publication Critical patent/WO1999029078A2/en
Publication of WO1999029078A3 publication Critical patent/WO1999029078A3/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03828—Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties
    • H04L25/03866—Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties using scrambling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only

Definitions

  • the present invention relates to data scramblers and descramblers, suitable for use with a multi-carrier transmission system, multi-carrier transmission systems incorporating data scramblers and de-scramblers, and methods for scrambling and descrambling data in multi-carrier transmission systems.
  • Known data scramblers employ an algorithm to combine user data with a random data string, thereby producing an uncorrelated data stream for transmission.
  • the present invention simplifies known data scramblers by making use of the synchronisation frames, normally used for measuring channel characteristics, as a source of pseudo-random data which can be combined with incoming user data.
  • the present invention has particular application to multi-carrier transmission systems, including copper based transmission systems such as ADSL, VDSL and HDSL which employ DMT, and/or radio based transmission systems employing OFDM.
  • Many of these transmission systems send known data, usually referred to as synchronisation frames, to measure channel characteristics such as signal to noise ratio.
  • the known data contained in a synchronisation frame is selected to have a suitable statistical distribution, e.g. pseudo-random.
  • the known synchronisation frame data comprises two bits per sub-carrier. In other words, a predetermined 4-QAM signal is transmitted on each sub-carrier.
  • user data bits are combined with the known synchronisation frame data bits, typically the two most significant bits, using an exclusive-OR function. This results in a statistically and computationally efficient scrambling of the user data.
  • a data scrambler for use in a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, characterised in that combiner means are provided to combine user data with frame synchronisation data.
  • Said combiner means may have a XOR function.
  • Said frame synchronisation data is pseudo random.
  • Said combiner means may be adapted to combine said user data with the two most significant bits of a synchronisation frame.
  • a data descrambler for use in a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, and transmitted data is scrambled using a data scrambler as claimed in any of claims 1 to 4, characterised in that combiner means are provided to combine received data with frame synchronisation data.
  • Said combiner means may have a XOR function.
  • Said frame synchronisation data may be pseudo random.
  • Said combiner means may be adapted to combine said received data with the two most significant bits of a synchronisation frame.
  • a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, characterised in that said transmission system incorporates a data scrambler as set forth in any preceding paragraph, connected to said transmitter.
  • Said receiver may be connected to a data descrambler as set forth in any preceding paragraph.
  • Said multi-carrier transmission system may employ DMT.
  • Said multi-carrier transmission system may employ OFDM.
  • Means may be provided for transmitting frame synchronisation data from said data scrambler to said data descrambler.
  • a method of scrambling user data prior to transmission characterised by combining user data with frame synchronisation data.
  • User data maybe combined with frame synchronisation data by mean of an XOR function.
  • Said frame synchronisation data may be pseudo random.
  • Said user data may be combined with the two most significant bits of a synchronisation frame.
  • a fifth aspect of the present invention there is provided, In a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, a method of descrambling received data which has been scrambled by a scrambling method as set forth in preceding, characterised by combining received data with frame synchronisation data.
  • Received data may be combined with frame synchronisation data using an XOR function.
  • Said frame synchronisation data may be pseudo random.
  • Said received data may be combined with the two most significant bits of a synchronisation frame.
  • Said multi-carrier transmission system may employ DMT.
  • Said multi-carrier transmission system may employ OFDM.
  • Figure 1 illustrates data scramblers and descramblers, according to the present invention, in a multi-carrier transmission system
  • A/D Analogue to Digital
  • ADSL Asynchronous Digital Subscriber Line
  • D/A Digital to Analogue
  • DMT Digital Multi Tone
  • HDSL High bit rate Digital Subscriber Line
  • OFDM Orthogonal Frequency Division Multiplex
  • VDSL Very high bit rate Digital Subscriber Line
  • Figure 1 shows a transmitter and receiver, in a multi-carrier transmission system, linked by a communications channel.
  • the communications channel may be a copper pair (VDSL etc.), or a radio channel (OFDM).
  • Incoming user data, intended for transmission over the communications channel is passed via a sync frame switch, to a XOR gate.
  • the sync frame switch permits one of the inputs to the XOR gate to be switched between user data and a string of "0"s.
  • the second input to the XOR gate receives the known synchronisation frame data.
  • the output from the XOR gate is the synchronisation data, i.e. the "known data” appears at the output of the XOR gate.
  • the incoming user data will almost certainly be far from random, i.e. it will be highly correlated.
  • the incoming user data is combined with the "known data" in the XOR gate.
  • the "known data” is pseudo random, i.e. uncorrelated.
  • the output from the XOR gate will, therefore, also be uncorrelated, i.e. will itself be pseudo-random. This data has the necessary properties to permit good transmission over the transmission channel.
  • the scrambled data is then passed to the receiver where it is first processed by an Inverse Fast Fourier Transform unit, IFFT, converted from parallel form to serial form, passed to a digital to analogue converter, D/A, prior to QAM modulation and transmission over the channel.
  • IFFT Inverse Fast Fourier Transform unit
  • D/A digital to analogue converter
  • the signal received from the transmission channel is demodulated and demultiplexed in the receiver by, inter alia, an A/D converter, a serial to parallel converter, and a fast Fourier transform unit FFT.
  • the received data is, of course, scrambled.
  • the received scrambled data is passed to the XOR gate, where it is combined with the "known data", i.e. the same data that was mixed into the signal in the transmitter.
  • the output from the XOR gate will contain the user data, or a string of "0"s depending on the setting of the sync frame switch in the transmitter.
  • the sync frame switch in the receiver is used for synchronisation purposes, i.e.
  • the output from the XOR gate will be a string of "0"s. Details of transmitter and receiver synchronisation in multi-carrier systems will be well known to those skilled in the art.
  • synchronisation frame data is stored in both the transmitter and receiver, so the receiver always has prior knowledge of the "known data" used by the transmitter.
  • the present invention scrambles user data by mixing that data with known data normally used in a synchronisation frame, typically the two most significant bits of the synchronisation frame data, using an exclusive-OR function. This results in both statistically and computationally efficient scrambling.
  • Descrambling is achieved by the reverse process, i.e. combining the received scrambled data with the same known data used for scrambling in an exclusive-OR function.
  • the present invention results in a much improved statistical distribution of modulated sub-carriers, in a multi-carrier transmission system, compared to the case where no scrambling is used for correlated, or null data situations.
  • the scrambling technique of the present invention does not increase system complexity.
  • the scrambler of the present invention can be used in all transmission systems that measure channel characteristics by sending known data from transmitter to receiver and use OFDM, DMT, or related multiplexing techniques to spread out the transmitted data over a number of sub-carriers, i.e. multi-carrier transmission techniques.

Abstract

The present invention simplifies known data scramblers by making use of the synchronisation frames, normally used for measuring channel characteristics, as a source of pseudo-random data which can be combined with incoming user data. The present invention has particular application to multi-carrier transmission systems which employ DMT, or OFDM. Many of these transmission systems send known data, usually referred to as synchronisation frames, to measure channel characteristics such as signal to noise ratio. The known data contained in a synchronisation frame is selected to have a suitable statistical distribution, e.g. pseudo-random. In the data scrambler of the present invention, user data bits are combined with the known synchronisation frame data using an exclusive-OR function. This results in a statistically and computationally efficient scrambling of the user data.

Description

Improvements in. or Relating to. Data Scramblers
The present invention relates to data scramblers and descramblers, suitable for use with a multi-carrier transmission system, multi-carrier transmission systems incorporating data scramblers and de-scramblers, and methods for scrambling and descrambling data in multi-carrier transmission systems.
Most telecommunications transmission systems are designed to give optimum performance when uncorrelated data is transmitted over them. Unfortunately, user data is not usually uncorrelated and may, for example, include relatively long strings of binary "0"s, or "1"s. If such data is transmitted over a transmission system intended for uncorrelated data, it can result in saturation, i.e. too large a dynamic range, synchronisation drift, etc.. This problem has long been recognised by telecommunications engineers and the conventional solution is to scramble the incoming user data so that it behaves as though it was uncorrelated data.
Known data scramblers employ an algorithm to combine user data with a random data string, thereby producing an uncorrelated data stream for transmission.
The present invention simplifies known data scramblers by making use of the synchronisation frames, normally used for measuring channel characteristics, as a source of pseudo-random data which can be combined with incoming user data.
The present invention has particular application to multi-carrier transmission systems, including copper based transmission systems such as ADSL, VDSL and HDSL which employ DMT, and/or radio based transmission systems employing OFDM. Many of these transmission systems send known data, usually referred to as synchronisation frames, to measure channel characteristics such as signal to noise ratio. The known data contained in a synchronisation frame is selected to have a suitable statistical distribution, e.g. pseudo-random. In a typical DMT system, used at the present time, the known synchronisation frame data comprises two bits per sub-carrier. In other words, a predetermined 4-QAM signal is transmitted on each sub-carrier.
In the present invention, user data bits are combined with the known synchronisation frame data bits, typically the two most significant bits, using an exclusive-OR function. This results in a statistically and computationally efficient scrambling of the user data.
According to a first aspect of the present invention, there is provided a data scrambler, for use in a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, characterised in that combiner means are provided to combine user data with frame synchronisation data.
Said combiner means may have a XOR function.
Said frame synchronisation data is pseudo random.
Said combiner means may be adapted to combine said user data with the two most significant bits of a synchronisation frame.
According to a second aspect of the present invention, there is provide a data descrambler, for use in a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, and transmitted data is scrambled using a data scrambler as claimed in any of claims 1 to 4, characterised in that combiner means are provided to combine received data with frame synchronisation data.
Said combiner means may have a XOR function.
Said frame synchronisation data may be pseudo random. Said combiner means may be adapted to combine said received data with the two most significant bits of a synchronisation frame.
According to a third aspect of the present invention, there is provided a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, characterised in that said transmission system incorporates a data scrambler as set forth in any preceding paragraph, connected to said transmitter.
Said receiver may be connected to a data descrambler as set forth in any preceding paragraph.
Said multi-carrier transmission system may employ DMT.
Said multi-carrier transmission system may employ OFDM.
Means may be provided for transmitting frame synchronisation data from said data scrambler to said data descrambler.
According to a fourth aspect of the present invention, there is provided, In a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, a method of scrambling user data prior to transmission, characterised by combining user data with frame synchronisation data.
User data maybe combined with frame synchronisation data by mean of an XOR function.
Said frame synchronisation data may be pseudo random.
Said user data may be combined with the two most significant bits of a synchronisation frame. According to a fifth aspect of the present invention, there is provided, In a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, a method of descrambling received data which has been scrambled by a scrambling method as set forth in preceding, characterised by combining received data with frame synchronisation data.
Received data may be combined with frame synchronisation data using an XOR function.
Said frame synchronisation data may be pseudo random.
Said received data may be combined with the two most significant bits of a synchronisation frame.
Said multi-carrier transmission system may employ DMT.
Said multi-carrier transmission system may employ OFDM.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which:
Figure 1 illustrates data scramblers and descramblers, according to the present invention, in a multi-carrier transmission system
In order to facilitate an understanding of the present invention a glossary of terms used in the description of the present invention is provided below:
A/D: Analogue to Digital
ADSL: Asynchronous Digital Subscriber Line
D/A: Digital to Analogue DMT: Digital Multi Tone
FFT: Fast Fourier Transform
HDSL: High bit rate Digital Subscriber Line
IFFT: Inverse Fast Fourier Transform
OFDM: Orthogonal Frequency Division Multiplex
QAM: Quadrature Amplitude Modulation
VDSL: Very high bit rate Digital Subscriber Line
XOR: Exclusive OR
Figure 1 shows a transmitter and receiver, in a multi-carrier transmission system, linked by a communications channel. The communications channel may be a copper pair (VDSL etc.), or a radio channel (OFDM). Incoming user data, intended for transmission over the communications channel, is passed via a sync frame switch, to a XOR gate. The sync frame switch permits one of the inputs to the XOR gate to be switched between user data and a string of "0"s. The second input to the XOR gate receives the known synchronisation frame data. When the string of "0"s is passed to the XOR gate, the output from the XOR gate is the synchronisation data, i.e. the "known data" appears at the output of the XOR gate.
The incoming user data will almost certainly be far from random, i.e. it will be highly correlated. The incoming user data is combined with the "known data" in the XOR gate. The "known data" is pseudo random, i.e. uncorrelated. The output from the XOR gate will, therefore, also be uncorrelated, i.e. will itself be pseudo-random. This data has the necessary properties to permit good transmission over the transmission channel.
The scrambled data is then passed to the receiver where it is first processed by an Inverse Fast Fourier Transform unit, IFFT, converted from parallel form to serial form, passed to a digital to analogue converter, D/A, prior to QAM modulation and transmission over the channel. Details of the multiplexing techniques and modulation techniques used in multi-carrier transmission systems will be familiar to those skilled in the art and are not described in detail in this patent specification.
The signal received from the transmission channel is demodulated and demultiplexed in the receiver by, inter alia, an A/D converter, a serial to parallel converter, and a fast Fourier transform unit FFT. The received data is, of course, scrambled. The received scrambled data is passed to the XOR gate, where it is combined with the "known data", i.e. the same data that was mixed into the signal in the transmitter. The output from the XOR gate will contain the user data, or a string of "0"s depending on the setting of the sync frame switch in the transmitter. The sync frame switch in the receiver is used for synchronisation purposes, i.e. when the receiver is properly synchronised with the transmitter, and a sync frame is transmitted, rather than user data, the output from the XOR gate will be a string of "0"s. Details of transmitter and receiver synchronisation in multi-carrier systems will be well known to those skilled in the art.
It should, however, be noted that synchronisation frame data is stored in both the transmitter and receiver, so the receiver always has prior knowledge of the "known data" used by the transmitter.
In summary, the present invention scrambles user data by mixing that data with known data normally used in a synchronisation frame, typically the two most significant bits of the synchronisation frame data, using an exclusive-OR function. This results in both statistically and computationally efficient scrambling.
Descrambling is achieved by the reverse process, i.e. combining the received scrambled data with the same known data used for scrambling in an exclusive-OR function.
The present invention results in a much improved statistical distribution of modulated sub-carriers, in a multi-carrier transmission system, compared to the case where no scrambling is used for correlated, or null data situations.
As synchronisation data must be present in a multi-carrier receiver and transmitter for use in the synchronisation process, the scrambling technique of the present invention does not increase system complexity.
Transmission of the known data is very simple because it only needs to be combined with a string of "0"s.
The scrambler of the present invention can be used in all transmission systems that measure channel characteristics by sending known data from transmitter to receiver and use OFDM, DMT, or related multiplexing techniques to spread out the transmitted data over a number of sub-carriers, i.e. multi-carrier transmission techniques.

Claims

1. A data scrambler, for use in a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, characterised in that combiner means are provided to combine user data with frame synchronisation data.
2. A data scrambler, as claimed in claim 1, characterised in that said combiner means has a XOR function.
3. A data scrambler, as claimed in either claim 1 , or claim 2, characterised in that said frame synchronisation data is pseudo random.
4. A data scrambler, as claimed in any previous claim, characterised in that said combiner means is adapted to combine said user data with the two most significant bits of a synchronisation frame.
5. A data descrambler, for use in a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, and transmitted data is scrambled using a data scrambler as claimed in any of claims 1 to 4, characterised in that combiner means are provided to combine received data with frame synchronisation data.
6. A data descrambler, as claimed in claim 5, characterised in that said combiner means has a XOR function.
7. A data descrambler, as claimed in either claim 5, or claim 6, characterised in that said frame synchronisation data is pseudo random.
8. A data descrambler, as claimed in any of claims 5 to 7, characterised in that said combiner means is adapted to combine said received data with the two most significant bits of a synchronisation frame.
9. A multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, characterised in that said transmission system incorporates a data scrambler as claimed in any of claims 1 to 4, connected to said transmitter.
10. A multi-carrier transmission system, as claimed in claim 9, characterised in that said receiver is connected to a data descrambler as claimed in any of claims 5 to 8.
11. A multi-carrier transmission system, as claimed in claim 10, characterised in that said multi-carrier transmission system employs DMT.
12. A multi-carrier transmission system, as claimed in claim 10, characterised in that said multi-carrier transmission system employs OFDM.
13. A multi-carrier transmission system, as claimed in any of claims 10 to 12, characterised in that means are provided for transmitting frame synchronisation data from said data scrambler to said data descrambler.
14. In a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, a method of scrambling user data prior to transmission, characterised by combining user data with frame synchronisation data.
15. A method, as claimed in claim 14, characterised by combining user data with frame synchronisation data by mean of an XOR function.
16. A method, as claimed in either claim 14, or claim 15, characterised by said frame synchronisation data being pseudo random.
17. A method, as claimed in any of claims 14 to 16, characterised by combining said user data with the two most significant bits of a synchronisation frame.
18. In a multi-carrier transmission system in which synchronisation frame data is periodically transmitted from a transmitter to a receiver to measure transmission channel characteristics, a method of descrambling received data which has been scrambled by the method claimed in any of claims 14 to 17, characterised by combining received data with frame synchronisation data.
19. A method, as claimed in claim 18, characterised by combining received data with frame synchronisation data using an XOR function.
20. A method, as claimed in either claim 18, or claim 19, characterised by said frame synchronisation data being pseudo random.
21. A method, as claimed in any of claims 18 to 20, characterised by combining said received data with the two most significant bits of a synchronisation frame.
22. A method, as claimed in any of claims 14 to 21 , characterised by said multi- carrier transmission system employing DMT.
23. A method, as claimed in any of claims 14 to 21 , characterised by said multi- carrier transmission system employing OFDM.
PCT/SE1998/002193 1997-12-03 1998-12-01 Improvements in, or relating to, data scramblers WO1999029078A2 (en)

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SE9704497A SE9704497L (en) 1997-12-03 1997-12-03 Improvements to, or with respect to, data scramblers
SE9704497-8 1997-12-03

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US7539172B2 (en) 1999-06-23 2009-05-26 At&T Mobility Ii Llc System and method for data scrambling to reduce the crest factor in an OFDM waveform
US8705338B2 (en) 1999-06-23 2014-04-22 At&T Mobility Ii Llc System and method for data scrambling to reduce the crest factor in an OFDM waveform
US8498196B2 (en) 1999-06-23 2013-07-30 At&T Mobility Ii Llc System and method for data scrambling to reduce the crest factor in an OFDM waveform
US8014272B2 (en) 1999-06-23 2011-09-06 At&T Mobility Ii Llc System and method for data scrambling to reduce the crest factor in an OFDM waveform
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US9088314B2 (en) 1999-06-23 2015-07-21 At&T Mobility Ii Llc System and method for data scrambling to reduce the crest factor in an OFDM waveform
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