WO1999053662A1 - Systeme, dispositif et procede visant a ameliorer une propriete definie de signaux du domaine des transformees - Google Patents

Systeme, dispositif et procede visant a ameliorer une propriete definie de signaux du domaine des transformees Download PDF

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Publication number
WO1999053662A1
WO1999053662A1 PCT/US1999/007840 US9907840W WO9953662A1 WO 1999053662 A1 WO1999053662 A1 WO 1999053662A1 US 9907840 W US9907840 W US 9907840W WO 9953662 A1 WO9953662 A1 WO 9953662A1
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symbols
perturbation
domain
vector
time
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PCT/US1999/007840
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English (en)
Inventor
Frank Robert Kschischang
Aradhana Narula
Jian Yang
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Motorola Inc.
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Priority to AU34870/99A priority Critical patent/AU740189B2/en
Priority to KR1020007011221A priority patent/KR20010042558A/ko
Priority to BR9909525-4A priority patent/BR9909525A/pt
Priority to EP99916577A priority patent/EP1068706A4/fr
Priority to CA002328145A priority patent/CA2328145A1/fr
Priority to JP2000544104A priority patent/JP2002511707A/ja
Publication of WO1999053662A1 publication Critical patent/WO1999053662A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/02—Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation
    • H04L27/04—Modulator circuits; Transmitter circuits
    • 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
    • H04L27/2614—Peak power aspects
    • 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
    • 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

  • This invention relates to a system, device and method for improving a defined property of transform-domain signals, and more particularly to a system and method for reducing the peak-to-average energy ratio (PAR) of time- domain signals.
  • PAR peak-to-average energy ratio
  • a large PAR requires implementation of a high-precision digital-to-analog converter (DAC), or else requires the system to be tolerant of signal distortion (clipping) introduced when input signals exceed the DAC range.
  • DAC digital-to-analog converter
  • clipping signal distortion
  • the second class of PAR reduction techniques is based on determining sequences which have good PAR properties. See for example, S. Shepherd, J. Orriss, and S. Barton, "Asymptotic limits in peak envelope power reduction by redundant coding in orthogonal frequency-division multiplex modulation," IEEE Trans, on Commun., vol. 46, pp. 5-10, Jan. 1998. These methods generally involve removing "bad" time-domain sequences from the set of possible transmitted symbols and thus result in a data rate loss. Furthermore, these methods require mapping the data to the "good” symbols. This map is generally accomplished via a lookup table. The size of the required lookup table becomes impractical in a DMT system with many tones and large constellation sizes.
  • PAR reduction is achieved via a redundant signal representation, in which a given data block can be represented by any of a number of possible transmitted signals from some equivalence class, with the "most desirable" class representative — in this case, a representative with small time-domain peak value— chosen for transmission.
  • the receiver is designed to operate "modulo equivalence classes" producing the data block associated with an equivalence class whenever it detects an element of that class. In this way, the receiver requires no knowledge of the precise algorithm used to select a class representative at the transmitter.
  • One way to operate "modulo equivalence classes" in the DMT case is to have the receiver simply ignore the contents of various frequency bins. See A. Gatherer and M.
  • FIG. 1A is a schematic block diagram of a DMT transmitter configured according to this invention.
  • FIG. 1 B is a schematic block diagram of an alternative DMT transmitter configuration according to this invention.
  • FIG. 2 is an expanded signal point constellation in accordance with this invention.
  • FIG. 3 is an alternative expanded signal point constellation in accordance with this invention
  • FIG. 4 is a block diagram of the perturbation selector of FIG. 1 A;
  • FIG. 5 is an illustration of the perturbation vectors of the modulo M k perturbation device of FIG. 4;
  • FIG. 6 is a flow diagram illustrating a perturbation vector search used by the modulo M k perturbation device of FIG. 4
  • FIG. 7 is a flow diagram illustrating an alternative perturbation vector search used by the modulo M k perturbation device of FIG. 4;
  • FIG. 8 depicts a set of perturbation vectors according to this invention.
  • FIG. 9 depicts a three dimensional table used in the perturbation vector search illustrated in the flow diagram of FIG. 10;
  • FIG. 10 is a flow diagram illustrating another alternative perturbation vector search used by the modulo M k perturbation device of FIG. 4;
  • FIG. 11 is a schematic block diagram of the receiver depicted in FIGS. 1A and 1 B;
  • FIG. 12 is a schematic block diagram of an alternative perturbation selector according to this invention
  • FIG. 13 is a schematic block diagram of another alternative perturbation selector according to this invention.
  • FIG. 14 is a flow diagram of a perturbation vector search performed by the alternative perturbation selectors of FIGS. 15-18;
  • FIG. 15 is a flow diagram illustrating the operation of another alternative perturbation selector according to this invention.
  • FIG. 16 is a flow diagram illustrating the operation of yet another alternative perturbation selector according to this invention.
  • FIG. 17 is flow diagram illustrating the operation of another alternative perturbation selector according to this invention.
  • FIG. 18 is flow diagram illustrating the operation of another alternative perturbation selector according to this invention.
  • the present invention is generally directed to a system and method for improving a defined property of a signal after block transformation, hereinafter referred to as a transform-domain signal.
  • a transform-domain signal In order to provide a more readily understandable description of the invention we describe herein an actual application of the invention to reduce the peak-to-average energy (PAR) of the time-domain signal (more generally referred to herein as the transform-domain signal) in discrete multitone modulation schemes.
  • PAR peak-to-average energy
  • the invention is generally applicable to other modulation schemes, such as orthogonal frequency division multiplexing (OFDM), orthogonal quadrature amplitude modulation (OQAM), and discrete wavelength multitone (DWMT).
  • OFDM orthogonal frequency division multiplexing
  • OFQAM orthogonal quadrature amplitude modulation
  • DWMT discrete wavelength multitone
  • the invention may be used to improve other defined properties in the transform- domain signal in addition to PAR.
  • a DMT transmitter 10 that includes a signal mapper 12 which receives input data and outputs a sequence of blocks of frequency-domain symbols X, (X 0 -X N - ⁇ )- Each symbol in a block corresponds to a different frequency bin and for each frequency bin signal mapper 12 selects a symbol from a constellation of points.
  • Signal mapper 12 chooses the constellation for each frequency bin based on the channel quality for the frequency bin.
  • the channel quality is typically determined by probing the channel during a training sequence.
  • the size of the constellation, and hence the number of input data bits that can be represented by the symbol chosen from the constellation is dependent upon the quality of the channel in the frequency range of the bin.
  • a channel having better quality can use a denser constellation with more points and therefore more bits can be transmitted with each symbol.
  • the number of input data symbols represented by a block of symbols is dependent upon the quality of the channel.
  • the output of the signal mapper 12 is X 0 -X 31 .
  • ADSL digital subscriber line
  • There are symbols transmitted in the lower fifteen complex frequency bins (XrX 15 ) and the upper fifteen complex frequency bins (X 17 -X 31 ) are selected as the complex conjugate images of the lower fifteen bins so that the resulting frequency-domain signal possesses the Hermitian symmetry needed to make the time-domain signal real-valued.
  • Inverse Discrete Fourier Transform (IDFT) device 14 receives each block or vector of frequency-domain symbols X, X 0 -X N- ⁇ . and transforms them into blocks or vectors of time-domain symbols x, x 0 -x N-1 , which are provided to perturbation selector 16. IDFT device 14 and perturbation selector 16 together form perturbation transform device 17. In other applications different types of invertible transform devices may be used and the outputs of the IDFT and the other invertible transform devices may generally be referred to as the transform- domain symbols.
  • Perturbation selector 16 perturbs the time-domain symbols, as described in detail below, in order to reduce the PAR (or, more generally, improve a defined property) of the transmitted symbols and outputs blocks or vectors of perturbed or modified time-domain symbols y, y 0 -y N . ⁇ - Perturbed or modified time-domain symbols y are provided to parallel to serial converter 18 and these symbols are transmitted in serial form over the channel to receiver 19.
  • perturbation selector 16 perturbs the time-domain symbols, or more generally the transform-domain symbols
  • transmitter 10' has a perturbation selector 16' which perturbs the symbols prior to IDFT device 14, i.e. in this example, the frequency-domain symbols would be modified instead of the time-domain symbols.
  • Perturbation selector 16' and IDFT 14 together form perturbation transform device 17'.
  • the prior art techniques for reducing PAR do so by either placing values in "unused" frequency bins and/or complex frequency bins which transmit data. In some cases the channel quality may be so poor in some frequency bins that several complex frequency bins in addition to the DC and Nyquist bins are not used to transmit data.
  • Perturbation selector 16 uses the complex data carrying frequency bins to reduce PAR without affecting the data rate using a technique referred to herein as modulo M k perturbation and additionally uses the unused frequency bins (DC, Nyquist and N/4) in novel ways to further reduce PAR.
  • modulo M k perturbation uses the unused frequency bins (DC, Nyquist and N/4) in novel ways to further reduce PAR.
  • DC, Nyquist and N/4 the unused frequency bins
  • Modulo M k Perturbation With this approach, the signal constellations are expanded relative to the minimum necessary constellation size to support the given data rate in each complex frequency bin and the expanded constellation is partitioned into equivalence classes.
  • the receiver 19, FIGS. 1A and 1 B, is designed to detect equivalence classes (not individual constellation points or symbols). This provides the transmitter some flexibility in choosing the transmitted symbols. This extra degree of freedom can be used to optimize some objective function of the resulting signal— in particular, the time-domain peak amplitude.
  • the objective function is optimized without a reduction in the transmitted bit rate, but the transmit power must be increased to accommodate the additional points in the expanded signal constellations.
  • significant PAR reduction can be achieved with almost no increase in the average signal power, so the net performance penalty is negligible.
  • Expanded constellation 20 includes a base constellation 22 (the constellation in the innermost dashed box) containing points A, B, C and D, from which the symbols are chosen by signal mapper 12, FIG.1. Expanded constellation 20 also includes expansion areas 24, 26, 28 and 30 each containing four points labeled A-D. All of the constellation points having the same label, i.e.
  • A are elements of the same equivalence class and a receiver receiving any one of the points in the equivalence class decodes the point into the same data.
  • a receiver receiving any one of the points in the equivalence class decodes the point into the same data.
  • the time-domain peak value can be reduced.
  • Every block of symbols X contains N symbols, (X 0 -X N- ⁇ ). each of which is modulated on a separate carrier frequency.
  • the transmitted time-domain signal vector is given by the inverse Fourier Transform as follows:
  • F the Fourier Transform matrix
  • H denotes Hermitian transpose.
  • these complex symbols X k are chosen from an L 2 k -QAM constellation, corresponding to transmitting 2log 2 L k bits on complex frequency k.
  • Each L 2 k - QAM constellation may altematively described as the Cartesian product of two independent L k -PAM constellations, one for each real and imaginary component of symbol X k .
  • a value m k is defined as the largest of the PAM signal magnitudes in the kth channel and d k is the distance between the PAM symbols.
  • a value M k is equal to 2m k +d k . The value M k is used to define the equivalence class points in the expanded constellation.
  • the base constellation may be expanded to include for each base constellation point all points that are congruent to each of the base constellation points modulo-M k in either of the two real and imaginary dimensions. All points congruent modulo-M k are considered to be in the same equivalence class. See, for example, that one of the points "A" in expansion area 24 outside of the base constellation 22 is +Mk from point "A" in base constellation 22. Also, another point “A” in expansion area 26 is +jMk from point "A” in base constellation 22.
  • the receiver implements a modulo-M k operation in the real and imaginary components of the kth complex frequency so that any translation of the received symbol by a multiple of M k in dimension k is transparent to the receiver. It should be noted that other expanded constellations are possible and will be apparent to those skilled in the art.
  • each equivalence class could contain an infinite number of points which are multiples of M k away from the point in the base constellation; however, as described below, it is practical to choose the points that are close (e.g., 1M k ) to the points in the base constellation to achieve PAR reduction while minimizing the transmitter power requirements.
  • the base constellation 22 of FIG. 2 may be expanded to constellation 40, FIG. 3.
  • This expanded constellation includes base constellation 42 and expansion areas 44, 46, 48, 50, 52 and 54.
  • the receiver would then be required to operate modulo ⁇ .
  • a wide variety of similar possible perturbation sets involving other sublattices of the integer lattice in one, two, or more dimensions, are possible.
  • signal constellations based on other lattices for example, the hexagonal lattice in two dimensions, still other perturbations sets are appropriate, as will be apparent to persons skilled in the art.
  • the perturbation selector 16 is shown in more detail to include modulo M k perturbation device 60, which perturbs the block of time-domain symbols x to form a plurality of blocks of modified symbols z it (z, 0 - Z. N ..,).
  • modulo M k perturbation device 60 which perturbs the block of time-domain symbols x to form a plurality of blocks of modified symbols z it (z, 0 - Z. N ..,).
  • There is an unused frequency bin perturbation device 62 which further modifies the blocks of symbols Z; by adding energy to the unused (DC and Nyquist) frequency bins, forming blocks of symbols z '.
  • selection device 64 which selects the block of modified symbols z' that has the minimum peak, in the case of PAR reduction, or generally, selects the block of symbols which most improves the defined property.
  • Modulo M k perturbation device 60 modifies the block of time-domain symbols x by adding to it all valid perturbation vectors V;, (v i 0 -v i N ..,), forming modified blocks or vectors, z,, of time-domain symbols. As discussed below, the modified blocks or vectors of symbols, z are further modified by unused frequency bin perturbation device to form vectors, z , from which the vector with the minimum peak is chosen and its symbols are transmitted as output symbols y, y 0 -y N-1 . Perturbation selector 16 operates in the time-domain to perturb the symbols, however, it can be readily modified to operate in the frequency- domain for use in transmitter 10' depicted in FIG. 1B.
  • any perturbation vector V (V 0 -V N . 1 ), such that each V k is an integer multiple of M k in the kth dimension, may be added to the block of symbols X, (X Q -X N . T ), as a valid perturbation vector as is done in perturbation selector 16', FIG. 1 B.
  • the perturbation vector is added in the time-domain; therefore, all valid perturbation vectors V, must be transformed from the frequency to the time-domain and added to the blocks of time-domain symbols x. Since the requirement for a valid perturbation vector is that each V k be an integer multiple of M k in the kth dimension, there are therefore an infinite number of valid perturbation vectors.
  • Signal mapper 12 maps input data to a block of (not necessarily optimum) N symbols or class representatives which are chosen from the base constellations, and then modulo M k perturbation device 60 operates in the transform-domain by searching for the best valid perturbation, where a perturbation is valid if it transforms a given block of symbols to another block of symbols, which are symbol by symbol in the same equivalence class.
  • N-2 frequency bins which can be perturbed.
  • Each frequency bin can be perturbed by one of four non-zero perturbations, namely, +M k , -M k , +jM k and
  • the block of time-domain symbols x,(x 0 -x N ..,), is added to each of the valid perturbation vectors V j , (v 0 through v 2 , N . 2) ), to produce vectors z,, (z 0 through z 2(N . 2) ) .
  • the frequency-domain perturbation vector V 0 is the all zero perturbation vector.
  • the frequency-domain perturbation vectors must be transformed into a time-domain perturbation vector v, before being added to the time-domain symbols x.
  • the Inverse Discrete Fourier transform, v impart of these 2(N-2) vectors (and the all zero vector) V may, for example, be stored in memory and used to perturb the time-domain symbols x as illustrated in flow diagram 70, FIG. 6.
  • step 72 the next block of time-domain symbols x is obtained from IDFT device 14, FIG. 1, and in step 74 x is added to vector v ( to form z,.
  • step 76 z t is provided to unused frequency bin perturbation device 62, FIG. 4.
  • step 78 i becomes i+1 and in step 80 it is determined if i is greater than 2(N-2)+1 , i.e., have all 2(N-2)+1 vectors (including the all zero vector) been added to the present block of symbols x. If not, then the flow proceeds to step 74 where x is added to the next perturbation vector v,. If i is greater than 2(N-2)+1 , then in step 82 i is set to zero and flow returns to step 72 where the next block of symbols is obtained. It must be noted that the each block of time-domain symbols z, is provided to the unused frequency bin perturbation device 62, FIG. 4.
  • PAR reduction performance is expected to increase as the search space is enlarged. For example, where up to two non-zero components are allowed in the perturbation vector V,. This requires searching over an additional (N-2) * (N- 3) possible vectors. Although searching over this larger space provides a greater time-domain peak reduction, performance improvement may not be significant enough to warrant the tremendous increase in complexity. For larger values of N, (e.g. 256), it may be useful to allow perturbations of +/- 2M k or larger multiples of M k as well.
  • each of the vectors z from modulo M k perturbation device 60 is modified by unused frequency bin perturbation device 62 and the modified vectors Z j ' are provided to modified
  • ⁇ symbol selection device 64 where the modified vector z with the smallest peak is chosen and transmitted as symbols y 0 -y N .
  • DC and Nyquist Bins This technique can be used when the DC and Nyquist bins are unused.
  • Shifting the even symbols of z ; by one value and shifting the odd symbols of z- t by another value is equivalent to changing the values of both the DC and Nyquist frequency components of corresponding frequency-domain vector Z r
  • the even symbols are defined as any component z, of the vector z for which i is even and the odd symbols are defined as any component z, of the vector z for which i is odd.
  • the time-domain peak of z, is reduced by adding to the odd symbols of z,:
  • Odd perturbation - (TM* ⁇ ('J + TM. «(*,)) (4)
  • Symbols z 3 , z 7 , z etc. of vector z, are shifted by
  • Z j ' is equal to Z, modified by Z 0 ⁇
  • max and min are the maximum and minimum values of the time-domain vector Zj.
  • Zj' should be equal to Z j modified by Z N/2 as described below:
  • the search method described above with regard to FIG. 6 involves 5 searching all 2(N-2)+1 perturbation vectors v, in the modulo M k perturbation device 60 to determine which most reduces PAR or most improves the defined property of the transform-domain signal. Described below, there are two alternative search methods which reduce the complexity of the search for the perturbation vector which most reduces PAR or most improves the defined
  • the next block or vector x of time-domain symbols is obtained, step 92.
  • the peak value for the symbols x 0 -x N . 1 ( peak(x), in time-domain symbol vector x is determined and the
  • 35 peak time sample location, I is also determined, step 94. Then, a limited set of all nonzero 2(N-2) perturbation vectors V j is established. That set of vectors, V j ', includes each of the N-2 perturbation vectors corresponding to +M k , +jM k .
  • N-2 perturbation vectors are simply negatives of these N-2 perturbation vectors Vj'.
  • the vector Vj' is compared to x and it is determined if the sign of the vector v,' at location I is equal to the sign of the peak(x), step 100. If it is, then at step 102 that vector is subtracted from x, thereby forming z> which is provided to unused frequency bin perturbation device 62, FIG. 4. In step 104, j becomes j+1 and in step 106 i becomes i+1.
  • step 108 it is determined if i is greater than N-2. If it is, this indicates all N-2 nonzero vectors (and the all zero vector) have been considered and flow proceeds to step 110 where i and j are set to zero and then the next block or vector x of time-domain symbols is obtained.
  • step 112 it is determined if the sign of the vector Vj at location I is the opposite sign of the sign of the peak(x). If it is, then that vector is added to x in step 114, thereby forming z, which is provided to unused frequency bin perturbation device 62, FIG. 4. In step 104 j becomes j+1 and in step 106 i becomes i+1. And, as described above, in step 108 it is determined if i is greater than N-2.
  • step 110 If it is, this indicates all N-2 nonzero vectors (and the all zero vector) have been considered and flow proceeds to step 110 where i is reset to zero and then the next block or vector x of time-domain symbols is obtained. If in step 112 it is determined that the sign of vector v, at location I is not the opposite sign as the sign of the peak (x), then the system moves to step 106 where i becomes i + 1 and flow proceeds as described above.
  • FIGS. 8-10 Another alternative search method is depicted in FIGS. 8-10. This method successively reduces the search space by eliminating perturbation vectors which do not sufficiently reduce the peak at each time sample.
  • the set includes 2(N-2)+1 time-domain perturbation vectors if we allow one real or imaginary component of one frequency bin to be perturbed by +/-M k and include the all zero perturbation vector.
  • the vectors each include N components corresponding to the number of time symbols. Each component in the vectors may be represented as v,,, where i indicates the
  • the third dimension is a set of vectors one corresponding to each time index j and each of the N/2+1 I's, where the ith component of the corresponding 2(N-2)+1 point vector is a one if v, j in set 120 is greater than vals(l). Otherwise, the value of the ith component of the 2(N-2)+1 point vector is a zero.
  • This three dimensional table is used in the perturbation vector search algorithm, described below.
  • a threshold, T which is the maximum allowable peak after the modulo M k perturbation. Since the unused frequency bin perturbation device further reduces the peak, this is not necessarily the maximum allowable peak of the system.
  • the threshold, T is system dependent and is chosen to be some value to which it is desired to reduce the peak.
  • Another value, A which is the maximum perturbation, is set equal to 2M/ N . With a +/-M k perturbation in one real or imaginary component of one frequency bin, this is the largest perturbation in a time-domain sample generated. Then, a vector goodT is defined. This vector initially has each of its 2(N-2)+1 components set to one, [1 ,1 ,..., 1].
  • the components correspond to the 2(N-2)+1 perturbation vectors of the set of vectors 120, FIG. 8, and a one indicates that the corresponding vector is a "good" vector and should be considered for reducing PAR, while a zero indicates that the vector is not a good candidate and should not be considered.
  • the flow diagram 140 describes how the vector goodT is established for each block of time-domain symbols x (x 0 -x N . ⁇ ) obtained, step 142.
  • the time index, j is set to zero.
  • the time index, j is incremented to the next time sample and in step 150 it is determined if j>N-1. If it is, this indicates that all of the symbols in block x have been considered.
  • step 152 from the vector goodT the "good" vectors, or some subset thereof, are used to produce the blocks of modified symbols Z j which are provided to
  • step 142 the next block of symbols x is obtained. If it is determined that j is not greater than N-1 in step 150, flow loops back to step 146.
  • step 154 it is determined if
  • the index j indicates time, e.g., 0, 1...N-1 , and pertindexl , calculated as described below, indicates which of the set of N/2+1 vectors corresponding to time index j the vector is to be chosen.
  • a value for pertindexl is calculated by first determining a value for maxp as follows:
  • pertindexl is calculated as follows:
  • inverse cosine may be determined by using a stored lookup table and "ceil" corresponds to rounding up to the nearest integer. Pertindexl could also alternatively be determined from maxp directly using a stored lookup table. After goodT has been set in step 156, the time index j is incremented in step 148 and flow proceeds as described above.
  • step 154 If in step 154 it is determined that
  • the index j indicates time, e.g., 0, 1...N-1 , and pertindex2, calculated as described below, indicates which of the set of N/2+1 vectors corresponding to time index j the vector is to be chosen.
  • a value for pertindex2 is calculated by first determining a value for minp as follows:
  • pertindex2 is calculated as follows:
  • inverse cosine may be determined by using a stored lookup table and "ceil" corresponds to rounding up to the nearest integer.
  • Pertindex2 could also alternatively be determined from minp directly by using a stored lookup table.
  • step 158 If in step 158 it is determined that
  • the vector goodT is evaluated.
  • a one in any component of that vector indicates that the corresponding vector in the set of vectors 120, FIG. 8, is a good candidate for a perturbation vector.
  • the first involves choosing any one of the good vectors, adding it to the present block of symbols x to form a block of modified symbols and providing the block of modified symbols to the unused frequency bin perturbation device.
  • Another option involves adding each of the good vectors to the present block of symbols x to form blocks of modified symbols and providing the blocks of modified symbols to the unused frequency bin perturbation device.
  • Yet another option involves adding some specified number of the good vectors to the present block of symbols x to form blocks of modified symbols and providing the blocks of modified symbols to the unused frequency bin perturbation device.
  • the first option reduces complexity but also reduces performance to a certain degree.
  • performance loss should be minimal, but complexity reduction is not as significant as option 1.
  • option 3 the balance between performance and complexity reduction falls between options 1 and 2.
  • table 130 must be modified if all the M k 's are not equal. Two options for modifying table 130 are described below.
  • each base constellation is expanded modulo-M.
  • table 130 is generated assuming that the kth base constellation is expanded modulo-M k and that different values of M k are possible for different frequency bins k. This implies that the time sample values of the valid perturbation vectors can take on more than N/2+1 values.
  • maxval and minval denote the maximum and minimum values that the components of the valid perturbation vectors take on. Equivalent ⁇ , maxval will be equal to
  • the table size may be larger.
  • Pertindexl floor( (maxp - minval)/granularity) where floor corresponds to rounding down to the nearest integer
  • Pertindex2 ceil((minp-minval)/granularity) where ceil corresponds to rounding up to the nearest integer.
  • Receiver 19 In FIG. 11 there is shown a schematic block diagram of receiver 19 depicted in FIGS. 1A and 1 B.
  • the modified symbols y after going through the channel, are received as symbols w at receiver 19.
  • Receiver 19 includes a serial to parallel converter 170 which receives the time-domain symbols w in serial form and converts them to blocks of received time-domain symbols w, w 0 - w N .,.
  • the blocks of received time-domain symbols w, w 0 -w N .., are provided to Discrete Fourier Transform device 172 which converts the time domain symbols
  • the blocks of received frequency-domain symbols W, W 0 -W N _. are provided to Frequency domain equalizer device 174 which takes into account the effect of the channel on the transmitted modified frequency domain symbols Y, Y 0 -Y N - ⁇ . and scales the received symbols W, W 0 -W N ..,, to produce symbols Y', Y' 0 -YV ⁇ which are estimates of the transmitted symbols Y.Yo-Y ⁇ .
  • the estimates of the transmitted symbols are provided to inverse signal mapper 176 which converts the estimates of the transmitted modified frequency domain symbols Y', Y' 0 -Y' N - I, into output bits 178 corresponding to the input bits provided to transmitters 10 and 10' of FIGS. 1 A and 1 B, respectively.
  • Inverse signal mapper 176 is designed to detect equivalence classes (not individual constellation points or symbols) or it is said to operate modulo equivalence classes.
  • the symbols Y', Y' 0 -YV ⁇ . correspond to estimates of the frequency-domain points selected from e.g., expanded constellation 20, FIG. 2, however, they may not be equal to those constellation points due to noise on the channel.
  • inverse signal mapper 176 must account for this channel noise when inverse mapping the symbols to output bits 178.
  • the inverse signal mapper may first map each of the symbols Y' 0 -Y' N - I to the nearest point in the expanded constellation and then map this expanded constellation point to the equivalent point in the base constellation.
  • Other possible implementations of the inverse signal mapper will be clear to those skilled in the art.
  • alternative Perturbation Selectors In alternative perturbation selector 16a, Fig 12, the modulo-M k perturbation is applied to the input symbols b times. The number of times that the modulo-M k perturbation should be applied will be dependent on block size N and desired system complexity. Each iteration (i.e. each time the modulo-M k perturbation is applied), the peak of the time domain symbol is reduced. The reduction will decrease to zero after several iterations.
  • Perturbation selector 16b is very similar to perturbation Selector 16a. The only difference is that before being passed to the first stage modulo- M k perturbation device 180, the input symbol x is provided to unused frequency bin perturbation device 190 which chooses the unused frequency bin perturbations to minimize the peak value of x. Oftentimes, applying the unused frequency bin perturbation device prior to the modulo-M k perturbations will allow the peak value to be reduced more quickly in the first few stages. However, it may also lead to a slightly higher peak value after several stages. In other words, after a sufficient number of stages perturbation Selector 16a may produce a symbol with lower peak value than perturbation Selector 16b.
  • FIGS. 15-18 A number of alternative perturbation selectors are shown in FIGS. 15-18. These alternative perturbation selectors apply several iterations of perturbations derived from a reduced complexity perturbation vector search which is illustrated in flow diagram 200, FIG 14.
  • the operation of flow diagram 200, steps 202-220, is essentially the same as that of flow diagram 140, FIG. 10, and is therefore not described again.
  • the reduced complexity perturbation search achieves its threshold T, the threshold T is reduced. If the threshold is not achieved, the threshold is raised. If the number of iterations allocated, numloops, have not been completed, the reduced complexity perturbation search is applied to the modified symbols and another perturbation is determined.
  • the thresholds T and the number of iterations, numloops are system dependent. Note that the amount that T is raised or lowered does not have to be the same at each iteration.
  • step 232 the next blocks of time-domain symbols x and an initial threshold T are obtained and in step 234 an index k is initialized to zero.
  • step 236 using the symbol x and threshold T the reduced complexity perturbation search (flow diagram 200, FIG. 14) which determines a set of "good" perturbation vectors, described by goodT, is performed.
  • the first good vector is chosen first, i.e.
  • step 242 the threshold T is lowered and in step 244 the index k is incremented. It is then determined in step 246 if k ⁇ numloops. If it is then the reduced complexity perturbation search is performed again with the
  • step 268 it is determined that goodT is not non-zero, the threshold T is raised in step 280, but the index k is not incremented. Instead, flow proceeds to step 266 where the reduced complexity perturbation search is performed without incrementing the index k. In this implementation the time- domain symbol's peak value is always reduced numloops times. This may lead to a lower peak value.
  • two additional alternative perturbation selectors are illustrated in flow diagram 290, FIG. 17, steps 292-312 and flow diagram 320, FIG. 18, steps 322-342.
  • these perturbation selectors is similar to the operation of the selectors of FIGS. 15 and 16, respectively.
  • the only difference is that the input time-domain symbols x, prior to being used in the reduced complexity perturbation search (step 298, FIG. 17 and step 328, FIG. 18) for the first time, are modified by performing an unused frequency bin perturbation (step 294, FIG. 17 and step 324, FIG. 18) which uses the unused frequency bin perturbations to reduce the peak value of x. Then a reduced complexity perturbation search is performed on the modified symbol.
  • this invention may be embodied in software and/or firmware, which may be stored on a computer useable medium, such as a computer disk or memory chip.
  • the invention may also take the form of a computer data signal embodied in a carrier wave, such as when the invention is embodied in software/firmware, which is electrically transmitted, for example, over the Internet.

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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)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)

Abstract

Selon cette invention, dans un émetteur (10) de transmission de données en blocs sur un canal vers un récepteur (19), un dispositif permettant d'améliorer une propriété définie des symboles du domaine des transformées comprend: un analyseur (mappeur) (12) de signaux qui fait correspondre les données d'entrée à des blocs de symboles dans un premier domaine, chacun des symboles étant choisi dans une constellation de base contenue dans une constellation expansée possédant des symboles d'expansion, et au moins certains de ces symboles possédant un ou plusieurs symboles d'expansion correspondants; un dispositif à perturbations/transformées (14 et 16), sensible aux blocs de symboles, qui produit pour chaque bloc de symboles du premier domaine un bloc de symboles du domaine des transformées qui permet d'améliorer une propriété définie des symboles du domaine des transformées.
PCT/US1999/007840 1998-04-10 1999-04-09 Systeme, dispositif et procede visant a ameliorer une propriete definie de signaux du domaine des transformees WO1999053662A1 (fr)

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AU34870/99A AU740189B2 (en) 1998-04-10 1999-04-09 System, device and method for improving a defined property of transform-domain signals
KR1020007011221A KR20010042558A (ko) 1998-04-10 1999-04-09 변환-영역 신호의 규정된 특성을 개선하기 위한 시스템,장치 및 방법
BR9909525-4A BR9909525A (pt) 1998-04-10 1999-04-09 Dispositivo para melhorar uma propriedade definida de sinais de transformação-domìnio
EP99916577A EP1068706A4 (fr) 1998-04-10 1999-04-09 Systeme, dispositif et procede visant a ameliorer une propriete definie de signaux du domaine des transformees
CA002328145A CA2328145A1 (fr) 1998-04-10 1999-04-09 Systeme, dispositif et procede visant a ameliorer une propriete definie de signaux du domaine des transformees
JP2000544104A JP2002511707A (ja) 1998-04-10 1999-04-09 変換領域信号の定義特性を改善するシステム，装置および方法

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WO2003019791A2 (fr) * 2001-08-23 2003-03-06 Nortel Networks Limited Systeme et procede permettant de reduire la puissance de crete dans une modulation multiporteuse
WO2004054193A2 (fr) * 2002-12-09 2004-06-24 Nortel Networks Limited Procede et appareil de reduction du rapport puissance de crete sur puissance moyenne par embrouillage sans information secondaire
EP1435714A2 (fr) * 2002-12-27 2004-07-07 Lg Electronics Inc. Procédé de récupération de séquences à rapport minimum de pouvoir de crête à pouvoir moyenne dans un système de communication MDFO
WO2009006121A2 (fr) * 2007-06-29 2009-01-08 Qualcomm Incorporated Étalement de domaine fréquentiel amélioré

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Cited By (15)

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Publication number Priority date Publication date Assignee Title
WO2002093822A1 (fr) * 2001-05-17 2002-11-21 Telefonaktiebolaget Lm Ericsson Procedes et agencements concernant un systeme de communication
US7778341B2 (en) 2001-08-23 2010-08-17 Nortel Networks Limited System and method performing quadrature amplitude modulation by combining co-sets and strongly coded co-set identifiers
WO2003019791A2 (fr) * 2001-08-23 2003-03-06 Nortel Networks Limited Systeme et procede permettant de reduire la puissance de crete dans une modulation multiporteuse
WO2003019791A3 (fr) * 2001-08-23 2003-07-10 Nortel Networks Ltd Systeme et procede permettant de reduire la puissance de crete dans une modulation multiporteuse
US8526547B2 (en) 2001-08-23 2013-09-03 Apple Inc. System and method performing Quadrature Amplitude Modulation by combining co-sets and strongly coded co-set identifiers
US7151804B2 (en) 2001-08-23 2006-12-19 Nortel Networks Limited System and method for reducing the peak power in multi-carrier modulation
US7318185B2 (en) 2001-08-23 2008-01-08 Nortel Networks Limited Method and apparatus for scrambling based peak-to-average power ratio reduction without side information
US8290078B2 (en) 2001-08-23 2012-10-16 Apple Inc. System and method performing quadrature amplitude modulation by combining co-sets and strongly coded co-set identifiers
KR100896352B1 (ko) 2001-08-23 2009-05-08 노오텔 네트웍스 리미티드 멀티 캐리어 변조에서 최대 전력을 감소시키는 시스템 및방법
WO2004054193A2 (fr) * 2002-12-09 2004-06-24 Nortel Networks Limited Procede et appareil de reduction du rapport puissance de crete sur puissance moyenne par embrouillage sans information secondaire
WO2004054193A3 (fr) * 2002-12-09 2004-07-29 Nortel Networks Ltd Procede et appareil de reduction du rapport puissance de crete sur puissance moyenne par embrouillage sans information secondaire
EP1435714A3 (fr) * 2002-12-27 2006-11-15 Lg Electronics Inc. Procédé de récupération de séquences à rapport minimum de pouvoir de crête à pouvoir moyenne dans un système de communication MDFO
EP1435714A2 (fr) * 2002-12-27 2004-07-07 Lg Electronics Inc. Procédé de récupération de séquences à rapport minimum de pouvoir de crête à pouvoir moyenne dans un système de communication MDFO
WO2009006121A3 (fr) * 2007-06-29 2009-06-04 Qualcomm Inc Étalement de domaine fréquentiel amélioré
WO2009006121A2 (fr) * 2007-06-29 2009-01-08 Qualcomm Incorporated Étalement de domaine fréquentiel amélioré

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AU3487099A (en) 1999-11-01
AU740189B2 (en) 2001-11-01
CN1300493A (zh) 2001-06-20
EP1068706A1 (fr) 2001-01-17
JP2002511707A (ja) 2002-04-16
BR9909525A (pt) 2000-12-12
CA2328145A1 (fr) 1999-10-21
EP1068706A4 (fr) 2001-09-12

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