WO2009135886A1 - Procédé et appareil pour modulation multitonalité filtrée utilisant une convolution circulaire - Google Patents

Procédé et appareil pour modulation multitonalité filtrée utilisant une convolution circulaire Download PDF

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Publication number
WO2009135886A1
WO2009135886A1 PCT/EP2009/055501 EP2009055501W WO2009135886A1 WO 2009135886 A1 WO2009135886 A1 WO 2009135886A1 EP 2009055501 W EP2009055501 W EP 2009055501W WO 2009135886 A1 WO2009135886 A1 WO 2009135886A1
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WIPO (PCT)
Prior art keywords
data
sub
transmission
coefficients
channel
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PCT/EP2009/055501
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English (en)
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Andrea Tonello
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Universita' Degli Studi Di Udine
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Publication of WO2009135886A1 publication Critical patent/WO2009135886A1/fr

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    • 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
    • H04L25/03834—Arrangements for spectral shaping; Arrangements for providing signals with specified spectral properties using pulse shaping
    • 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
    • H04L27/2627—Modulators
    • H04L27/264—Pulse-shaped multi-carrier, i.e. not using rectangular window
    • 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
    • H04L27/2649—Demodulators
    • H04L27/26534—Pulse-shaped multi-carrier, i.e. not using rectangular window

Definitions

  • the present invention concerns a modulation/demodulation method and apparatus for the multichannel transmission of signals on radio channels, cable and broad band electric lines.
  • the invention concerns a digital modulation technique that is applied in particular, although not exclusively, to radio communications or broad band cable characterized by effects of frequency distortion and of variance time.
  • Numerical modulation and demodulation techniques are known for communication systems.
  • broad band communication systems use multi-carrier transmission techniques which consist in sending the information signal in a certain number of narrow band channels.
  • Multi-carrier techniques are used to overcome the phenomenon of distortion introduced by the broad band channels, both radio and cable, which do not have a constant frequency response.
  • Dividing the broad band signal into a plurality of narrow band signals allows each of said signals to see the relative sub-channel as non-distorting. This translates into a greater simplicity of the reception algorithms and better performance, in particular in terms of better quality of the signal received and reconstructed.
  • OFDM orthogonal frequency division multiplexing
  • IEEE 802.11 standards to terrestrial digital and to ADSL. This technique has also been proposed for future generation cell radio systems.
  • FMT Frtered Multitone
  • Purpose of the present invention is to achieve a modulation/demodulation method and the relative apparatus for multichannel broad band transmission which allows to increase the OFDM performance, at the same time reducing computational complexity required by FMT.
  • a method for multichannel transmission according to the present invention is usable for digital modulation/demodulation of signals transmitted on radio channels, cable, or broad band electric lines.
  • the transmission of the information signal through the communication channel takes place by modulating sequences of data blocks, representing the signal, by one or more transmitters to one or more demodulators.
  • the communication channel comprises a plurality of sub-channels, each of which is associated both with a predeterminate sub-sequence of data blocks of said sequence of data blocks, and also with a predeterminate modulation sub-carrier of each subsequence. Each subsequence of data blocks is modulated in the associated sub-channel at a predeterminate transmission speed.
  • the transmitter comprises a stand of transmission or synthesis filters, each transmission filter being associated with a predeterminate sub-channel.
  • the receiver comprises a stand of reception or analysis filters, each reception filter being associated with a predeterminate sub-channel.
  • each transmission filter a cyclic convolution is effected of each data block of the sequence of data blocks associated with the relative sub-channel, with predeterminate reference transmission wave forms.
  • each reception filter in each reception filter a cyclic convolution is effected of each data block of the sequence of data blocks received and associated with the relative sub-channel, with predeterminate reference reception wave forms.
  • both the reference transmission signals and the reference reception signals comprise prototype impulses of the FIR (Finite Impulse Response) type.
  • one advantage of the modulation/demodulation method for multichannel transmissions according to the present invention allows to improve the performance, compared with known modulations, in time variant and frequency selective communication channels
  • the channels are typical in wireless mobile communications, cable communications and in-line conveyed-wave transmission or powerline.
  • a further advantage of the method according to the invention is that it is possible to receive signals with very limited time latencies. This renders the modulation/demodulation process particularly suitable for the transmission of data streams comprising multimedia contents or for applications in which a high quality service is required, such as for example for telephone services.
  • the method according to the invention allows to maintain the orthogonality of the sub-channels even when the means of communication is selective in frequency. This allows to prevent the unwanted introduction of inter- symbol interferences or inter-channel interferences and hence to prevent the introduction of a complex sub-channel equalization.
  • the method according to the present invention is associated with the transmission of signals for multiple users, in time variant and frequency selective channels in the presence of temporal misalignments, frequency misalignments, such as for example those deriving from maladjustments in the frequency generators and carrier generators, and phase misalignments.
  • each communication sub-channel is associated with different transmission speeds.
  • each demodulation device for example a palmtop and/or mobile device, with fewer processing resources - A -
  • the method according to the present invention is associated with the transmission of signals from multiple antennas for transmission in time variant and frequency selective channels.
  • - fig. 1 is a block diagram of a modulation/demodulation in the state of the art
  • - fig. 2 is a block diagram of a modulation/demodulation according to the present invention
  • - fig. 3 is a block diagram of a transmission according to the present invention.
  • - fig. 4 is a block diagram of a reception according to the present invention.
  • - fig. 5 is an example of an impulsive and in frequency response of the prototype impulse achieved with the technique of the present invention
  • FIG. 6 is a block diagram of a variant reception according to the present invention.
  • - fig. 7 is a block diagram of a second transmission variant
  • - fig. 8 is a block diagram of a third transmission variant. DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF
  • a modulation/demodulation method for multichannel transmission is applicable for radio or cable communications characterized by effects of frequency distortion and variance time.
  • Fig. 1 shows a conventional communication pattern FMT (Filtered Multitone) according to the state of the art.
  • a transmitter 112 also called synthesis stage, generates a signal given by the expression:
  • Zt O Z e Z
  • Z is the domain of the integers and a (IT 0 ) is a sequence of data represented by complex symbols (for example belonging to a QAM constellation
  • T is the sampling period used in the digital synthesis of the system, assuming that T constitutes the unit of time.
  • M is the number of sub-channels 113
  • g(nT) is the prototype impulse.
  • the signal in the expression (1) is converted from digital to analogical (with a digital-analogical convertor (DAC)), transmitted on the channel 14, after having been converted into Radio Frequency (if the transmission is on radio channel).
  • the signal received is made to pass through a stand of exponential multipliers 134 which convert it into base band and subsequently through a stand of analysis filters 116 with a prototype filter h(nT) .
  • the output sampled, by a relative sampler 130B, at frequency HT 0 and corresponding to the sub-channel 113 index k is given by the following expression:
  • g * h(nT) is an ideal limited band Nyquist impulse with a narrower bandwidth than the spacing between the sub-carriers, and if the channel 14 has a flat frequency response, the modulation/demodulation system is orthogonal, that is, there is no inter-channel interference (ICI) or inter-symbol interference (ISI) to the output sampled by the stand of analysis filters 116.
  • ICI inter-channel interference
  • ISI inter-symbol interference
  • a frequency selective channel 14 introduces temporal dispersions so that normally a sub- channel equalization is required, which can be effected by means of sub-channel equalizers of a known type.
  • the embodiment of the conventional FMT system as described heretofore is complex inasmuch as it requires the use of exponential modulators, filtering operations on a plurality of sub-channels, and equalization operations. Furthermore, it is not suitable for transmissions that require low latencies, unlike those that provide data block transmission, for example OFDM.
  • the modulation/demodulation method for multichannel transmission according to the present invention is hereafter also called CB-FMT or Cyclic Block FMT Modulation.
  • the method according to the invention (fig. 2) provides the transmission of a block of L data symbols, one block per sub-channel 13, and K sub-channels 13 (fig. 2).
  • the linear convolutions of the expression (1) are replaced by cyclic convolutions, to obtain an output signal from the transmitter 12, or synthesis stage according to the following expression: x(iT) ® g (iT)]e j2 ⁇ f ik> ⁇ T (4) 0,...,M 2 - l
  • (iT- /T 0 ) ⁇ ((J - lN)mo ⁇ M 2 )T so that g((iT - IT 0 ) M J indicates the response of the impulse rotated in circular manner on a duration support M 2 samples, from left to right, of the quantity IT 0 .
  • the circular convolution with period M 2 is indicated by the operator ® (M 2 ) 5 an d is substantially a convolution of discrete time information signals and periodic discrete time reference signals, wherein the temporal displacements (delays/advances) of the signals are achieved in a cyclic or circular manner.
  • the information signals are divided into blocks of L data symbols.
  • the operator (a mod b) indicates the remainder operation in the division between the integers a and b.
  • the data blocks can be transmitted continuously operating block after block, as described by transformation (4).
  • the stand of analysis filters 16 at exit from the exponential demodulators 32 with carriers 15, exactly like the stand of synthesis filters 19, works with circular convolutions, that is, the output of the &-th filter at instant IT 0 is obtained as follows: z m ( . ⁇ 0 ) L _, (5) i 0 where h((lT Q — ⁇ T) M ⁇ ) indicates the analysis impulse turned over and translated in a circular manner.
  • Each of the K subchanels 13 in fig. 2 transports a block of L data symbols in a time interval of LT 0 seconds. Therefore the speed of transmission R is given by the following equation
  • each complex data symbol transports a number of bits n b — ⁇ og 2 (C) where C is the size of the constellation, for example n b — 4 with a 16 level QAM (Quadrature Amplitude Modulation).
  • the CB-FMT modulation pattern is efficiently achieved by discrete Fourier transforms (DFT), and even more efficiently by fast Fourier transforms (FFT).
  • DFT discrete Fourier transforms
  • FFT fast Fourier transforms
  • a transmitter 12 by means of the series-parallel convertors 34, generates blocks of LK data starting from the input stream of data. Then, by means of a DFT unit 38 associated with each sub- channel 13, it effects a DFT of L points, followed by a cyclic extension by a cyclic extension unit 42 with Q coefficients which are weighed, that is, multiplied, by the Q coefficients 44 different from zero of the DFT of the prototype synthesis impulse.
  • an inverse transform IDFT is effected of M 2 points, followed by a parallel-series conversion by means of a P/S converter 36, which generates the signal x( ⁇ T) of the expression (4).
  • FIG. 4 One embodiment in the frequency domain of a demodulation according to the present invention is illustrated in fig. 4 with a diagram of a receiver 18.
  • the symbol /-th of the block transmitted on the &-th sub-channel is obtained by the following transformation: if the stand of CB-FMT filters has a perfect reconstruction, where H(f t ) is the frequency response of the analysis filter.
  • the first condition translates into the absence of inter-channel interference because the sub-channels 13 in fig. 2 are separated by QfM 2 T .
  • the second condition translates into the absence of inter-symbol interference in every sub-channel 13.
  • the prototype impulse FIR, lasting M 2 T is orthogonal to its cyclic translations by multiples of T 0 only if the periodic repetition of period 1/T 0 of the DFT of its M 2 coefficients is constant. This condition is generated by the Nyquist criterion for discrete periodic time signals.
  • Q 7,11,19.
  • a cyclic prefix is added (fig. 4) by the cyclic prefix extension unit 46, with a duration ⁇ T greater than the dispersion introduced by the channel. That is, a prefix is prefixed, consisting of ⁇ identical coefficients to the last ⁇ coefficients of the original block.
  • the insertion of the cyclic prefix allows to effect an equalization in the frequency domain of a CB-FMT signal with an equalizer of the single coefficient type, or also single tap.
  • ⁇ C H Ut the DFT of the channel impulse response
  • the single-tap equalization is carried out to produce a decision metric of the data transmitted.
  • the metric for the index symbol /in the block transmitted on the sub-channel k is obtained as follows:
  • MMSE minimum mean square error
  • the data transmitted are detected by means of a maximum probability detector, that is, a decision is taken on the data transmitted using the criterion of the minimum Euclid distance between (19) and the possible data transmitted: a (IT 0 ) - (2 i )
  • A is the set of data symbols
  • Cl ( ⁇ T Q ) is the estimated datum
  • argmin is the function that restores the corresponding argument to the minimum.
  • the propagation of the channel can have a flat frequency response so that Gc H ⁇
  • the detector is simplified since the coefficient of the equalizer remains constant for every sub-channel.
  • the CB-FMT modulation/demodulation method according to the present invention is robust for transmissions on a frequency selective channel 14 (dispersive time).
  • the CB-FMT modulation/demodulation method is also suitable for the transmission of a signal in a time variant channel 14 which is known as detrimental for the performance of modulation systems, such as for example for OFDM modulation.
  • a time variant channel 14 which is known as detrimental for the performance of modulation systems, such as for example for OFDM modulation.
  • the K sub-channels 13 in fig. 2 are well confined in frequency, therefore the temporal variations of the channel 14, produced for example by the Doppler effect or rapid dissolvence of the wireless channels, do not introduce any inter-channel interference.
  • Any possible inter-block interference such as for example interference between the L symbols of a data block, can be eliminated as described hereafter.
  • the sub-channels 13 were spaced by a quantity of Qj 'M 2 T Hertz. If an impulse withg, ⁇ Q components in frequency is used, it is possible to increase the separation between the subchannels 13. Equivalently, it is possible to space the sub-carriers more, so that the sub-channels 13 have a greater frequency separation. This can be done by inserting zeroes between the sub-channels 13 in the embodiment in the frequency domain described before.
  • the expression (26) is the convolution between the block A (f m )G(f m ) and i ' J m+k Q ) which has a lesser extension than the separation between the sub-channels 13 in accordance with the above hypotheses.
  • the demodulation of the signal received through a time variant and frequency selective channel 14 occurs by effecting a conversion of the serial stream of data received into a parallel stream by means of a series/parallel convertor 234 and removal of the cyclic prefix, if any, by means of a second unit to remove the cyclic prefix 248.
  • a DFT of M 2 points is performed by means of a second DFT unit of M 2 points 238.
  • the outputs of the DFT relating to each of K sub-channels 13 are grouped together and each output is subjected to zero padding by an extension unit with zeroes 49 to obtain a block of M 2 coefficients.
  • the CB-FMT modulation/demodulation method described provides a stand of filters in reception which allows the perfect reconstruction of the signal.
  • the formation of the impulse is divided in half between the stand of filters of the transmitter, or synthesis stage, and the stand of filters of the receiver, or analysis stage, by means of a root Nyquist impulse.
  • the perfect reconstruction is also obtained by using a Nyquist impulse on the transmitter.
  • the signals are reconstructed perfectly if an inverse transform IDFT of M 2 points is performed (sampled with a factor N by means of a sampler) in every sub-channel on the coefficients equalized by means of zero forcing as shown in the following transformation:
  • the CB-FMT modulation/demodulation method also allows to make a transmission at multiple transmission speed. That is, it is possible to transmit a different quantity of information on each sub-channel 13 in fig. 2.
  • the CB-FMT modulation/demodulation method also allows to be linked to a channel code for the correction and/or detection of errors.
  • One possibility is to use codes of the bit-interleaved type, as shown in fig. 7.
  • a bit interleaver 52 At exit from a channel encoder 50 there is a bit interleaver 52, to diffuse the encoded bits both temporally and through the sub-channels 13. In this way it is possible to protect the transmission effectively from errors introduced by the channel 14. In particular this allows to exploit the selectivity of the channel 14 both in time and frequency in the form of gains in code and diversity after the decoding operation to the receiver.
  • Another possible embodiment is to diffuse the bits/symbols data both in time and in frequency using expansion codes, such as for example Walsh codes (fig.
  • the CB-FMT modulation/demodulation method also allows to transmit data for multi-users both in up-link and in down-link, such as for example in the connection of a wireless system between a portable device and a base, and vice versa.
  • the multi-user transmission can be made either using a transmission pattern with time division multiple access (TDMA) or by assigning each subchannel 13 to a single user.
  • TDMA time division multiple access
  • the second embodiment entails the sharing of the K sub-channels 13 among the users, thus achieving a kind of frequency division multiple access (FDMA), or the transmission of data symbols in a predeterminate block of L symbols that belong to different users.
  • FDMA frequency division multiple access
  • the modulation/demodulation method according to the present invention is suitable for transmission on time variant and frequency selective channels 14, the method is suitable for user multipling in channels 14 with asynchronous multiple accesses which have temporal misalignments, frequency misalignments, phase misalignments and noise.
  • the CB-FMT modulation/demodulation method can also be applied for radio transmissions with multiple transmission antennas 60 (fig. 8). This can be obtained in two ways. Firstly, a signal modulated according to the CB-FMT modulation is transmitted by each antenna 60. After reception on the receiver antenna a connected demodulation algorithm is provided to decode the signals of the transmission antennas. Secondly, it is possible to divide the sub-channels 13 and/or the blocks of data symbols by means of a division device 62 and transfer them to different antennas 60. In this way we achieve a form of space-temporal code. It is also possible to obtain orthogonality between signals transmitted by different antennas 60 by exploiting the orthogonality of the CB-FMT channels. The method according to the present invention therefore allows to achieve a frequency division multiplexing also between devices that are not synchronized, guaranteeing in any case the orthogonality of the signals.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Power Engineering (AREA)
  • Transceivers (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

La présente invention concerne un procédé de modulation/démodulation destiné à la transmission à large bande multivoie d'un signal, représenté par une pluralité de séquences de blocs de données, à travers un canal (14) depuis un ou plusieurs modulateurs (12) vers un ou plusieurs démodulateurs (18). Le canal (14) comprend K sous-canaux (13), chacun étant associé à une sous-séquence de données prédéfinie de la séquence de données ainsi qu'à une sous-porteuse prédéterminée (15) apte à moduler la sous-séquence de données transmise et à démoduler la sous-séquence de données reçue, chaque sous-séquence de données étant assujettie à une filtration de modulation au niveau de la transmission et à une filtration de démodulation au niveau de la réception. La filtration de modulation comprend une convolution cyclique de chaque sous-séquence de données, de la séquence de données, avec des signaux de transmission de référence prédéfinis. Le principal mode de réalisation de la présente invention concerne une modulation multitonalité filtrée (FMT).
PCT/EP2009/055501 2008-05-08 2009-05-06 Procédé et appareil pour modulation multitonalité filtrée utilisant une convolution circulaire WO2009135886A1 (fr)

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ITUD2008A000099 2008-05-08
IT000099A ITUD20080099A1 (it) 2008-05-08 2008-05-08 Procedimento ed apparato di modulazione/demodulazione per trasmissione multicanale

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Cited By (1)

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US9209923B2 (en) 2013-11-06 2015-12-08 Electronics And Telecommunications Research Institute Method and apparatus for transmitting of OFDM signal

Citations (2)

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US9209923B2 (en) 2013-11-06 2015-12-08 Electronics And Telecommunications Research Institute Method and apparatus for transmitting of OFDM signal

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