Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
  • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
  • H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
  • H04L27/3411—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set

Definitions

• the invention relates to a method and a circuit arrangement for improved data transmission according to the preamble of patent claim 1 and of patent claim 9.
• Transmission methods are known in telecommunications and are also used in practice which use orthogonal basic functions to represent the signal to be transmitted. Such transmission methods are described, for example, in the book R.E. Blahut, Digital Transmission of Information, Addison-Wesley, Reading, 1990, Chapters 2 and 3.
• a message signal can therefore be regarded as a point in K-dimensional space and is characterized by the value tuple (m 0 , m., . , ... (m ⁇ ).
• the entirety of all permissible signals is called the signal constellation.
• Two-dimensional signal constellations are popular, such as the so-called 16-QAM signal constellation shown in Fig. 1. This 16-QAM signal constellation is described, for example, in the above-mentioned book, page 63. All of those considered here
• the invention is therefore based on the object of providing a method and a circuit arrangement for improved data transmission with efficient use of multi-stage modulation methods, which enable optimal use of the signal energy of signal constellations and thereby frequently used signal constellations, such as 16-QAM, in a simple and can be optimally used to transmit lower data rates.
• the achievement of the object of the method according to the invention is characterized in the characterizing part of patent claim 1.
• the method described here and the circuit arrangement described enable the optimal use of the signal energy of signal constellations. This can be advantageous for technical applications in two ways.
• frequently used signal constellations such as 16-QAM
• the 16-QAM signal constellation can be used to transmit an average of 3 bits per signal point instead of the usual 4 bits per signal point.
• the process has another property that can be used advantageously. This is the recoding which is particularly easy to carry out if the input data stream is an equally distributed sequence, in particular a bit sequence. The recoding can then be carried out using a lossless decompression method such as the Huffman method.
• the inverse transcoding operation on the receiver side is accordingly carried out using the associated compression method.
• An equally distributed sequence or bit sequence is obtained, for example, by encryption. This means that the annoying guarantee or generation of such a sequence can be achieved by adding an added value, namely encryption. Since encryption will play an increasingly important role in future transmission systems and is already included in many systems today, the new method is particularly practical.
• an intermediate register is used as a buffer, which serves to adapt the time-varying bit rate occurring due to the transmission through the channel to the bit rate of the source data. In a circuit implementation, this intermediate register has a certain fixed length. In practice, this results in the problem of a so-called buffer overflow.
• the channel data rate is chosen to be larger than the source data rate, it being advantageous to choose the channel data rate to be slightly larger than the source data rate.
• the channel data rate is greater than the source data rate, the channel may be ready to transmit information that has not yet been provided by the source become. This effect is used here, for example by transferring synchronization data instead of the source data.
• Another solution is to transfer other header or user data instead of the synchronization data. The higher the channel data rate, the shorter the intermediate register can be selected.
• Fig. 3 + 6 is a schematic diagram of a circuit arrangement which is used for improved data transmission with the help of efficient use of multi-stage modulation methods
• Fig. 4 is a table 1, which gives the probabilities pl, p2, p3, p4 for the signal points of Fig. 2 and
• Fig. 5 is a table 2, which represents the mapping of the binary data to the signal points and vice versa.
• known transmission methods use orthogonal basic functions to represent the signal to be transmitted.
• a message signal s (t) is represented here as the sum of orthogonal basic functions.
• a message signal can be viewed as a point in K-dimensional space.
• the entirety of all permissible signal points is referred to as the signal constellation, the so-called 16-QAM signal constellation shown in FIG. 1, which represents one of the two-dimensional signal constellations, being particularly popular.
• a signal constellation has a total of M signal points, each of which Mj has the signal energy E., and if the probability of such a signal point occurring is pj, the optimum values according to the power or information rate for this power are achieved by setting the probabilities according to formula given below.
• the value L indicates how many different energy levels occur in total.
• the hexagonal signal constellation in FIG. 2 is given here as an example.
• the minimum distance between the signal points is chosen to be one.
• L 4 energy levels.
• a lossless data compression algorithm such as the Huffan method.
• This data compression algorithm ensures that the corresponding signal points occur with the probability specified above.
• the Huffman method is described, for example, in DA Huffman, "A Method for the Construction of Minimum Redundancy Codes", Proc. IRE, Vol. 40, Sept. 1952, pages 1098-1101.
• the probabilities for the occurrence of the individual signal points are then obtained from the table 1 shown in FIG. 4.
• Use of a data compression method leads to an assignment, as can be found, for example, in Table 2.
• An average signal energy of 1.8125 is obtained.
• the conventional 16-QAM signal constellation has an average signal energy of 2.5.
• this simple method gives an improvement of 10 lg (2.5 / 1.8125) dB, that is about 1.4 dB.
• With more complex assignments one can approach the optimal value as desired.
• the bit sequence 01110100001111100111011110001 generated with a coin would then be transmitted with the signal points Z 32 Z x Z 2S Z 23 Z 2S Z 21 Z 24 Z 25 .
• j 1..6
• the signal points with energy 1 Z 3J are the signal points with energy 3
• Z 4 -j are the points with energy 4.
• a data source 1 supplies a data stream 2.
• a recoder 3 then ensures that a modulator 4 selects the corresponding signal points with the correct probability.
• the corresponding inverse operation follows a downstream demodulator 6 with the aid of a recoder 7, whereupon the data stream 2 finally arrives at a data sink 8.
• the respective data stream 2 is represented on the connecting or transmission lines or channels between components 1, 3 to 8 by arrowheads on the respective lines or channels.
• an intermediate register (not shown) is inserted as a buffer, which serves to adapt the temporally fluctuating bit rate occurring due to the transmission through the channel to the bit rate of the source data.
• the intermediate register or the buffer has a certain length in the form of a circuit in each implementation, which in practice can result in a problem which consists in the possibility of an overflow. This problem can be solved by making the channel data rate somewhat larger than the source data rate.
• the buffer length or intermediate register length can thus be specified with relatively little effort, so that a buffer overflow or intermediate register overflow occurs only with a negligible (known) probability. If the channel data rate is selected to be slightly larger than the source data rate, it can happen in the practical implementation of a circuit arrangement that the channel is ready to transmit information which is not yet provided by the source.
• This effect can be used to advantage by transmitting synchronization data instead of the source data.
• other header or user data can also be transmitted instead of the synchronization data.
• Another variant to deal with this buffer overflow or underflow is to provide in the recoder 3 two or possibly even more recoding tables, one table leading to a channel data rate that is greater than the source data rate and the other table to a channel data rate that is smaller than the source data rate is.
• the recoder 3 can then be controlled depending on the state of the buffer. This means that if the buffer runs the risk of overflowing, the channel data rate is selected which is greater than the source data rate. In the opposite case, when there is almost no more data in the buffer, the channel data rate is chosen which is lower than the source data rate.
• FIG. 6 which is derived from FIG. 3, shows the most general case, which includes the above possibility.
• the possibility of controlling the recoder 3 as a function of the buffer 9 is indicated in FIG. 6 by the dashed line from the buffer with the control unit or computing unit 9 to the recoder 3.
• An optional second data source 1 ' is also shown in FIG. 6 (for the special case that the rate of this Data source is zero, this source disappears). As described above, the second data source 1 'enables the transmission of additional data.
• the dashed lines from the recoder 3 to the second data source 1 ' show how, for example, test data for error correction can be integrated into the method. The source data rate and the rate of the generated test marks together may not exceed the average channel data rate.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Priority Applications (4)

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Publications (2)

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ID=7847693

Family Applications (1)

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Cited By (2)

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• 1997
  • 1997-11-06 DE DE19748880A patent/DE19748880C1/de not_active Expired - Fee Related
• 1998
  • 1998-07-31 JP JP2000519983A patent/JP4121701B2/ja not_active Expired - Fee Related
  • 1998-07-31 US US09/530,934 patent/US6925129B1/en not_active Expired - Fee Related
  • 1998-07-31 ES ES98945128T patent/ES2289793T3/es not_active Expired - Lifetime
  • 1998-07-31 EP EP98945128A patent/EP0958685B1/de not_active Expired - Lifetime
  • 1998-07-31 DE DE59814079T patent/DE59814079D1/de not_active Expired - Lifetime
  • 1998-07-31 WO PCT/EP1998/004789 patent/WO1999025103A2/de not_active Ceased
  • 1998-07-31 AT AT98945128T patent/ATE371325T1/de not_active IP Right Cessation

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