WO2008102356A1

WO2008102356A1 - Filtered multi-tone modulation system and method for transmission of information data

Info

Publication number: WO2008102356A1
Application number: PCT/IL2008/000226
Authority: WO
Inventors: Roman Vitenberg
Original assignee: Data Jce Ltd.
Priority date: 2007-02-22
Filing date: 2008-02-21
Publication date: 2008-08-28

Abstract

A multicarrier transceiver system for transmission of an information data signal over a communication line is provided. The transceiver system comprises a transmitter and a receiver. The transmitter includes a forward error-correcting system, a synthesis filter bank, and an overlapping unit. The overlapping unit includes a parallel adder, a modulo-calculator, a comparator, a switch, and a shift register. The overlapping unit is configured for (i) starting the overlapping from storing in the shift register zero values; (ii) cyclically calculating by the modulo-calculator for each modulated subchannel non-overlapped wavelet a maximal magnitude of a wavelet amplitude; (iii) comparing by the comparator the maximal magnitude of the wavelet amplitude with a predetermined value, and if the maximal magnitude does not exceed the predetermined value, adding data representing the modulated subchannel non-overlapped wavelet to the shift register, otherwise discarding the wavelet by the switch; (iv) shifting in the shift register for every cycle the data stored in the shift register on a predetermined number P of points; (v) providing every cycle the data from first P points of the shift register to the communication line for transmitting therethrough; (vi) filling the last P points of the shift register with zeros; and (vii) repeating steps (ii) to (vi) L times for providing and transmitting the entire overlapped wavelet sequence over the communication line.

Description

Filtered Multi-Tone Modulation system and method for transmission of information data

FIELD OF THE INVENTION

The present invention relates to a method and system for multicarrier transmission of information data using a Wavelet based Filtered Multi-Tone (WFMT) modulation, and, more particularly, to a method and system for reducing peak-to-average power ratio (PAPR) values.

BACKGROUND OF THE INVENTION

One of the major drawbacks of multicarrier transmission systems is a large envelope fluctuation of the transmitted signal that is usually quantified by a large value of the Peak-to-Average Power Ratio (PAPR). The PAPR (measured in dB) is defined as:

PAPR dMB = I O IO"* ^Ppeak average J

where P_peak is the peak power and P averag_e is the average power of the signal. The large values of PAPR can distort the transmitted signal if the transmitter contains nonlinear components, for example, power amplifiers. Since most practical transmission systems are peak-power limited systems, designing the multicarrier system to operate in a linear region often implies operating at power levels well below the maximum power available. This in turn reduces the range of multicarrier transmission. A number of approaches have been proposed to deal with the PAPR problem. These techniques include amplitude clipping [11], clipping and filtering [16], coding [11- 16], tone reservation (TR) [11], tone injection (TI) [13], active constellation extension (ACE) [14], and multiple signal representation techniques such as partial transmit sequence (PTS) [11,12], selected mapping (SLM) [11,13], and interleaving [H]. These techniques achieve PAPR reduction at the expense of transmit signal power increase, bit error rate (BER) increase, data rate loss, computational complexity increase, and so on.

Theoretically, the PAPR in a multicarrier system depends on the number of subchannels, and therefore can be decreased for a lower number of sub-channels [8]. However, OFDM multicarrier systems having a low number of sub-channels can generate a high level of side-lobes that decrease a spectral efficiency of the communication line.

Recently, the concept of multicarrier transmission has been generalized with the introduction of filter-bank based multicarrier systems [1, 3]. hi filter-bank based systems, the data symbols are transmitted over different sub-channels after suitable pulse shaping. For the same bandwidth, a number of carriers in filter-bank systems is significantly less than the number of carriers in OFDM systems. Therefore, filter-bank multicarrier systems have a lower PAPR than OFDM systems.

A wavelet based Filtered Multi-Tone Modulation (WFMT) multicarrier system is disclosed in [4], a description of which is herein incorporated by reference. Referring to Fig. 1, a schematic block diagram of a WFMT multicarrier transceiver system 1 for transmission of an information data signal over a communication line (channel) 2 is illustrated. The transceiver system 1 comprises a transmitter 3 and a receiver 4. The transmitter 3 includes a synthesis filter bank 31 and an overlapping unit 32 coupled to the synthesis filter bank 31. The transmitter also includes a digital-to-analog (D/ A) converter 33 coupled to the overlapping unit 32 and, when required, a line driver (amplifier) 34 arranged after the D/A converter 33 and coupled to the communication line 2.

The synthesis filter bank 31 is configured for obtaining information data and generating a set of "non-overlapped" wavelets and modulating the wavelets by the information data. The synthesis filter bank 31 includes one or more modulators 311 and an N-points IFFT unit 312 coupled to the modulator 311. The modulator 311 is configured for each subchannel obtaining input stream of the information data, providing amplitudes of K frequency components of a corresponding subchannel prototype wavelet (i.e., wavelet coefficients) and modulating the wavelet coefficients by the input information data by multiplying the information data of the corresponding data component by the amplitudes of the frequency components. The EFFT unit 312 for each subchannel generates over a time interval T a sequence of L subchannel modulated non-overlapped wavelets by applying an N-point Inverse Fast Fourier Transform (IFFT) to the signal representing modulated wavelet coefficients that is provided by the modulators 311.

The overlapping unit 32 is configured for (i) obtaining a sequence of the non- overlapped wavelets, (ii) generating a multi-carrier signal comprising overlapped wavelets carrying the information data and (iii) providing this FMT multi-carrier signal to the communication line 2. The overlapping unit 32 includes a parallel adder 321 coupled to the output terminals of the IFFT unit 312 and a shift register 322 coupled to the adder 321.

In operation, L modulated non-overlapped wavelets generated by the IFFT unit

312 over the time interval T are fed to the parallel adder 321 that adds the wavelets with the data provided from the shift register 322, and then loads a result of the summing back to the shift register 322. The data stored in the shift register 322 are shifted on N_IFFJ/L samples after every EFFT transform cycle. These shifted samples are provided to the communication line over the time interval T/L for transmitting. Thus, an output signal provided by the shift register 322 represents a sum of the L overlapped wavelets. An exemplary time diagram for signals generated by the shift register 322 for the case of L =6 is illustrated in Fig. 2.

The receiver 4 includes an analog-to-digital (A/D) converter 41 coupled to the communication line 2, a separating unit 42 coupled to the A/D converter 41 and an analyzing filter bank 43 coupled to the separating unit 42. The separating unit 42 includes a separating shift register 421, and a parallel register 422 including N latch circuits (not shown) configured for storing the output of the separating shift register 421. The separating shift register 421 includes a serial input port 4211 and N parallel output ports 4212 and configured for obtaining the multicarrier signal comprising overlapped wavelet sequences Q(t) from the communication line 2 by the input port 4211 (via the A/D converter 41) and shifting the obtained data on the predetermined number of points.

The separating shift register 421 shifts samples of input signal Q(t) on N/L samples (i.e. FFT points) every T/L time interval in the manner opposite to that of the shift register - A -

322 of the transmitter 3. After the shifting, the parallel register 422 stores the data obtained from the output ports 4212 of the separating shift register 421. The data stored in the parallel register 422 are fed to the analyzing filter bank 43 for a further treatment.

The analyzing filter bank 43 includes an TV-points FFT unit 431, at least one equalizer 432 and at least one demodulator 433. The N-points FFT unit 431 obtains the data from the parallel register and calculates K spectral frequency components (phases and amplitudes) of each subchannel wavelet. The equalizer 432 obtains the K spectral frequency components of each subchannel wavelet and eliminates distortions which these components received in the communication line 2, independently for each component. The demodulator 433 obtains the K spectral frequency components for each subchannel wavelet and generates the information data signal.

The peak-to-average power ratio problem in such a prior art WFMT system was investigated in [8]. It was shown that a WFMT system has lower PAPR than OFDM systems.

SUMMARY OF THE INVENTION

The present invention describes a novel wavelet based Filtered Multi-Tone Modulation (WFMT) transmission method and system having reduced values of peak-to- average power ratio (PAPR) when compared to the PAPR values of the WFMT system described above in the background section. According to one aspect, the present invention provides a method for transmission of information data by modulated wavelets over a communication line through a plurality of subchannels.

At the transmission end, the method includes the following steps all carried out by a transmitter: obtaining the information data; encoding the information data with an error correction code, thereby forming an encoded information data; for each subchannel, generating over a time interval T a sequence of L subchannel non-overlapped wavelets modulated by the encoded information data; and overlapping over the time interval T the sequence of L modulated subchannel non-overlapped wavelets for generating a multi- carrier signal comprising overlapped wavelets carrying the encoded information data. According to one embodiment of the present invention, the overlapping of the modulated subchannel non-overlapped wavelets comprises the steps of: (i) starting the overlapping from storing in a shift register zero values; (ii) cyclically calculating for each modulated subchannel non-overlapped wavelet a maximal magnitude of a wavelet amplitude; (iii) comparing the maximal magnitude of the wavelet amplitude with a predetermined value, and if the maximal magnitude does not exceed the predetermined value, adding data representing the modulated subchannel non-overlapped wavelet to the shift register, otherwise discarding the wavelet; (iv) shifting for every cycle the data stored in the shift register on a predetermined number P of points; (v) providing every cycle the data from first P points of the shift register to the communication line for transmitting therethrough; and (vi) filling the last P points of the shift register with zeros; (vii) repeating steps (ii) to (vi) L times for providing and transmitting the entire overlapped wavelet sequence over the communication line.

According to one embodiment of the present invention, the step of generating over a time interval T a sequence of L subchannel non-overlapped wavelets modulated by the encoded information data comprises: providing predetermined wavelet coefficients representing amplitudes of frequency components of a prototype wavelet; for each subchannel, generating a signal representing modulated wavelet coefficients by multiplying the encoded information data by the amplitudes of frequency components; and applying an N-point Inverse Fast Fourier Transform (IFFT) to the signal representing modulated wavelet coefficients. According to one embodiment of the present invention, the step of encoding of the information data with an error correction code includes Reed-Solomon encoding and interleaving the information data.

At the receiving end, the method includes the following steps all carried out by a receiver: receiving a distorted multicarrier signal including a signal representing a sequence of L overlapped subchannel modulated wavelets generated by the method of any one of the preceding claims together with a noise signal provided by the communication line during the transmission; separating the overlapped wavelets to provide a sequence of non-overlapped wavelets carrying the encoded information data distorted by the noise signal; analyzing the sequence of the non-overlapped wavelets and generating spectral frequency amplitudes of wavelet components of the non-overlapped wavelets; demodulating the spectral frequency amplitudes of the wavelet components, thereby to generate the encoded information data; and decoding the encoded information data with the error correction code thereby to provide the information data.

According to one embodiment of the present invention, at the receiving end, the method further includes equalizing the spectral frequency amplitudes of the wavelet components before the demodulating step for eliminating phase-amplitude distortions of the distorted multicarrier signal, thereby providing corrected spectral frequency components.

According to one embodiment of the present invention, the decoding of the encoded information data with the error correction code includes de-interleaving and Reed-Solomon decoding the encoded information data.

According to one aspect, the present invention provides a transceiver system for transmission of information data by modulated wavelets over a communication line through a plurality of subchannels. The transceiver system comprises a transmitter and a receiver. The transmitter for use with a multicarrier transceiver system comprises: an encoding unit and interleaving unit configured for encoding the information data with an error correction code thereby forming an encoded information data; a synthesis filter bank configured for obtaining the encoded information data for each subchannel and generating over a time interval T a sequence of L subchannel non-overlapped wavelets modulated by the encoded information data; and an overlapping unit coupled to the synthesis filter bank.

According to one embodiment of the present invention, the overlapping unit includes: a parallel adder coupled to N output terminals of said synthesis filter bank; a modulo-calculator coupled to the parallel adder, a comparator arranged downstream of the modulo-calculator, a switch coupled to the parallel adder and to the comparator, and a shift register coupled to the switch.

According to one embodiment of the present invention, the synthesis filter bank comprises: at least one modulator having at least one multiplier configured for multiplying the encoded information data by amplitudes of frequency components of a prototype wavelet, thereby modulating said wavelet coefficients by the encoded information data; and an iV-points IFFT unit coupled to the modulator, the TV-points IFFT unit being configured for obtaining the signal representing the modulated wavelet coefficients, and for each sub-channel generating over a time interval T the sequence of L modulated non- overlapped wavelets modulated by the encoded information data. The encoding unit can be a Reed-Solomon encoder.

The receiver for use with a multicarrier transceiver system comprises: a separating unit configured for (i) receiving a distorted multicarrier signal including a signal representing a sequence of L overlapped subchannel modulated wavelets generated by the transmitter together with a noise signal provided by said communication line during the transmission, and (ii) separating the overlapped wavelets to provide a sequence of non- overlapped wavelets carrying the encoded information data distorted by the noise signal; an analyzing filter bank downstream of the separating unit configured for (a) obtaining the sequence of the non-overlapped wavelets, (b) analyzing the sequence, (c) generating spectral frequency amplitudes of wavelet components of the non-overlapped wavelets; and (d) demodulating said spectral frequency amplitudes of the wavelet components, thereby to generate the encoded information data; and decoding and de-interleaving units arranged downstream of the analyzing filter bank, and configured for decoding in tandem said encoded information data with the error correction code thereby to provide said information data. The decoding unit can be a Reed-Solomon decoder.

According to one embodiment of the present invention, the analyzing filter bank includes: an iV-points FFT unit configured for obtaining the sequence of the non- overlapped wavelets from the separating unit and generating spectral frequency amplitudes of the wavelet components of said non-overlapped wavelets; and a demodulator coupled to said N-points FFT unit and configured for obtaining said spectral frequency amplitudes of the wavelets and generating a signal representing said encoded information data; and at least one equalizer coupled to iV-points FFT unit and to the demodulator, and configured for correcting amplitudes of spectral frequency components of the wavelets by a obtaining said spectral frequency amplitudes of the wavelets and eliminating phase-amplitude distortions of said distorted multicarrier signal received in the communication line.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows hereinafter may be better understood. Additional details and advantages of the invention will be set forth in the detailed description, and in part will be appreciated from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

Fig. 1 illustrates a schematic block diagram of a prior art WFMT system for transmission of a data signal over a communication line; Fig. 2 is an exemplary time diagram of overlapping signals generated by the shift register of the WFMT system shown in Fig. 1 ;

Fig. 3 illustrates a schematic block diagram of an WFMT system for transmission of a data signal over a communication line, according to one embodiment of the present invention; and Figs. 4A and 4B illustrate exemplary output signals of the transmitter without

PAPR reduction scheme and with the PAPR reduction scheme of the present invention, correspondingly.

DETAILED DESCRIPTION OF THE INVENTION

The principles and operation of the process and system according to the present invention may be better understood with reference to the drawings and the accompanying description. It is understood that these drawings are given for illustrative purposes only and are not meant to be limiting. It should be noted that the blocks in the drawings illustrating various embodiments of the system of the present invention are intended as functional entities only, such that the functional relationships between the entities are shown, rather than any physical connections and/or physical relationships.

Some portions of the detailed descriptions, which follow hereinbelow, are presented in terms of algorithms and symbolic representations of operations on data represented as physical quantities within registers and memories of a computer system. An algorithm is here conceived to be a sequence of steps requiring physical manipulations of physical quantities and leading to a desired result. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. In the present description, these signals will be referred to as values, elements, symbols, terms, numbers, or the like. Unless specifically stated otherwise, throughout the description, utilizing terms such as "processing" or "computing" or "calculating" or "determining" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data.

Referring to Fig. 3, a schematic block diagram of a multicarrier transceiver system 30 for transmission of an information data signal over a communication line (channel) 2 is illustrated, in accordance with an embodiment of the present invention. Where it is convenient for the description, like reference numerals are used for designation of identical elements of the prior art system shown in Fig. 1 and in the system of the present invention. The transceiver system 30 comprises a transmitter 35 and a receiver 36. The transmitter 35 includes a Reed-Solomon encoding unit 351, an interleaving unit 352 arranged downstream of the Reed-Solomon encoding unit 351, a synthesis filter bank 353 arranged downstream of the interleaving unit 352, and an overlapping unit 354 coupled to

, the synthesis filter bank 353. The transmitter 35 also includes a digital-to-analog (D/A) converter 33 coupled to the overlapping unit 354 and, when required, a line driver (amplifier) 34 arranged downstream of the D/A converter 33 and coupled to the communication line 2. Examples of the communication line include, but are not limited to, a pair of copper wires, wireless communication line, etc. When desired, the transmitter 35 can include a randomization unit (not shown) arranged before the encoding unit 351. The Reed-Solomon encoding unit 351 and interleaving unit 352 is a known error- correcting tandem encoding system of forward error correction (FEC) by transmission of an error correction code together with information data. FEC is accomplished by adding redundancy to the transmitted information signal using a predetermined algorithm. The redundant data allows the receiver to detect and correct errors, if such erros are presented in the transmitted signal. The randomization unit, Reed-Solomon encoding unit 351 and interleaving unit 352 can be standard units prepared in accordance with current ITU-T J.83 standard. The synthesis filter bank 353, line driver 34 and the D/ A converter 33 of the transmitter 35 can, for example, be identical to the synthesis filter bank 31 of the prior art system shown in Fig. 1.

According to one embodiment, the synthesis filter bank 353 can include at least one modulator 311 having at least one multiplier (not shown) configured for multiplying the encoded information data by amplitudes of frequency components of a prototype wavelet, thereby modulating the wavelet coefficients by the encoded information data.

Moreover, the synthesis filter bank 353 can include the iV-points IFFT unit 312 coupled to the modulator 311. The iV-points IFFT unit 312 can be configured for obtaining the signal representing the modulated wavelet coefficients, and for each sub-channel generating over a time interval T the sequence of L modulated non-overlapped wavelets modulated by the encoded information data.

According to one embodiment of the present invention, the prototype wavelet is represented as a sum of K cosine functions, to wit:

W(t)= ∑a_H cos(2mt/T)_t

where n is a natural number counting the frequency components; K is a number of the all frequency components; and a_n is an amplitude of n-th frequency component.

According to one embodiment of the present invention, the overlapping unit 354 includes a parallel adder 321 a modulo-calculator 323 coupled to the parallel adder 321, a comparator 324 arranged downstream of the modulo-calculator 323, a switch 325 coupled to the parallel adder 321 and to the comparator 324, and a shift register 322 coupled to the switch 325. The parallel adder 321 is coupled to the output terminals of the IFFT unit 312 of the synthesis filter bank 353. The overlapping unit 354 is configured for (i) starting the overlapping from storing in a shift register 322 zero values; (ii) cyclically calculating by the modulo-calculator 323 for each modulated subchannel non-overlapped wavelet a maximal magnitude of a wavelet amplitude; (iii) comparing by the comparator 324 the maximal magnitude of the wavelet amplitude with a predetermined value, and if the maximal magnitude does not exceed the predetermined value, adding data representing the modulated subchannel non-overlapped wavelet to the shift register, otherwise discarding - l i ¬

the wavelet by the switch 325; (iv) shifting in the shift register 322 for every cycle the data stored in the shift register on a predetermined number P of points; (v) providing every cycle the data from first P points of the shift register 322 to the communication line 2 for transmitting therethrough; (vi) filling the last P points of the shift register 322 with zeros; and (vii) repeating steps (ii) to (vi) L times for providing and transmitting the entire overlapped wavelet sequence over the communication line 2.

In operation, before the transmission, the shift register 322 can store signals of 0 values in each of its internal memory cells. At the first IFFT cycle, the adder 321 adds the output of the IFFT unit (i.e., wavelet Wi) to the contents of the shift register 322, and the result is fed to the modulo-calculator 323 that calculates a maximal magnitude of the amplitude wavelet. The maximal amplitude is compared by the comparator 324 with a predetermined reference level. If the maximal magnitude does not exceed the predetermined value, the data provided by the adder 321 are transferred through the switch 325 and are written into the shift register 322. Thus, after the first IFFT transform cycle the shift register 322 can store the wavelet W]. Otherwise, if this maximal amplitude exceeds the predetermined reference level, the comparator 324 generates a signal to close the switch 325, thereby the data in the shift register 322 are not updated. The predetermined reference level is an empirical parameter that is determined by the possibility to correct signal errors in the case when the overlapped wavelets having the amplitudes higher than this predetermined value are discarded.

Thereafter, the data stored in shift register 322 are shifted on N_/p_fj/L points (e.g., 21 points for the case when N_IFFT=126 and L=6). Then, the first N_IFF1/L points (samples) of the signal Q{t) are provided to the communication line from a serial output (not shown) of shift register 322 via the D/ A converter 33 and the line driver 34, while the last N_/Ffj/L memory cells of shift register 322 are filled with zeros.

Further, the second EFFT transform provides ΛW samples of the wavelet W2 to the adder 321. As can be understood, at this moment, the N_JFFJ/L memory cells of the shift register 322 stores zeros while other (N_JFFT - N_JFFJ/L) memory cells store a remaining portion of the shifted Wi (that was not transmitted yet). The data stored in the shift register 322 is provided to the adder 321 for summing with the samples of the wavelet W ₂ provided from the IFFT unit 312. The result is again fed to the modulo-calculator 323 that calculates a maximal magnitude of the signal's amplitude, and then to the comparator 324. If the maximal magnitude does not exceed the predetermined value, the data provided by the adder 321 are transferred through the switch 325 and are written into the shift register 322.

Then, the data in the shift register 322 are shifted on N_IFΠ/L points, and the first shifted samples are provided to the communication line 2 for transmission, while the last Ni_FFi/L cells of the memory of the shift register are filled with zeros. After this step, the shift register stores zeros in the last N_IFF/L memory cells of the shift register 322 along with a combination of the remaining portions of the shifted wavelets Wi and W₂ in other (NiFFT - NIFΠ/L) memory cells. Otherwise, if this maximal amplitude of the signal calculated by the adder 321 exceeds the predetermined reference level, the comparator 324 generates a signal, which closes the switch 325 to forbid a change of the shift register content. Then, the data in the shift register 322 are shifted on N_IFΠ/L points, and the first shifted samples are provided to the communication line 2 for transmission, while the last N_JFFI/L cells of the memory of the shift register are filled with zeros. After this step, the shift register stores zeros hi the last N_IFF/L memory cells of the shift register 322 along with the remaining portions of the shifted wavelet Wj in other (N_IFFT — N_IFΠ/L) memory cells. As a result, an amplitude of the overlapped wavelets Q(t) does not exceed the predetermined reference level. It should be understood that in this case, the transmitter 35 generates an erroneous signal that has a length equal to the length of one wavelet. However, since the signal is encoded with an error correction code, the error can further be corrected by the receiver 36.

The process continues L IFFT transform cycles for providing and transmitting the entire overlapped wavelet sequence Q(t) over the communication line 2. It should be appreciated that although the transmission for one subchannel has been described here, the overlapping process described above may be extended to any number of subchannels of the Synthesis Filter-Bank, due to the linearity of the IFFT transform.

The receiver 36 includes an analog-to-digital (A/D) converter 41 coupled to the communication line 2, a separating unit 42 coupled to the A/D converter 41, an analyzing filter bank 43 coupled to the separating unit 42, a decoding unit 45 and de-interleaving unit 46 arranged downstream of the analyzing filter bank 43. When required, the receiver 4 can include an amplifier 44 arranged before the A/D converter 41. The separating unit 42 is configured for receiving a distorted multicarrier signal including a signal representing a sequence of L overlapped subchannel modulated wavelets generated by the transmitter 35 together with a noise signal provided by the communication line 2 during the transmission, and separating the overlapped wavelets to provide a sequence of non-overlapped wavelets carrying the encoded information data distorted by the noise signal. The analyzing filter bank 43 is configured for obtaining the sequence of the non-overlapped wavelets, analyzing this sequence, generating spectral frequency amplitudes of wavelet components of the non-overlapped wavelets, and demodulating the spectral frequency amplitudes of the wavelet components, thereby to generate the encoded information data. The separating unit 42 and the analyzing filter bank 43 of the receiver 36 can, for example, be identical to the corresponding units of the prior art system shown in Fig. 1.

The decoding unit 45 and interleaving unit 46 are configured for decoding in tandem the encoded information data with the error correction code, thereby to provide the information data. The decoding unit 45 can be a Reed-Solomon decoder.

The essence of the present invention can be better understood from the following non-limiting example of output signals generated by the transmitter of the present invention. This example is intended to illustrate the present invention and to teach a person of the art how to make and use the invention. This example is not intended to limit the scope of the invention or its protection in any way.

Example

The described above PAPR reduction technique was tested for a Simulink model of the WFMT system. This model has been realized for an exemplary Cable TV Broadcast System. This exemplary system comprised a physical interface, a randomization unit, an

Reed-Solomon encoder (forward error correction (FEC) block) and an interleaver, all prepared in accordance with current ITU-T J.83 standard.

The physical interface included input and output FIFO memory blocks, each of them being able to store up to 512 bytes of data. The randomization block comprised a scrambler with the polynomial for Pseudo Random Binary Sequence (PRBS) Generator: Y = \ + X^H + X¹⁵ The period of the PRBS sequence was 1503 bytes. The forward error correction block performed a systematic shortened Reed-Solomon encoding on each randomized

MPEG 2 transport packet. Up to 8 erroneous bytes per transport packet were corrected by using RS (204,188) code. The coding process added 16 parity bytes to the MPEG 2 transport packet.

The interleaver provided the convolution of interleaving over error-protected packets with a depth of I = 12. The interleaver frame was composed of overlapping error- protected packets, and was delimited by MPEG 2 sync bytes (preserving the periodicity of 204 bytes). The data frame structure was based on MPEG 2 transport layer that is defined in

ISO/TEC 13818-1. Coded information data were converted to a multicarrier wavelet signal having a 6-MHz bandwidth. This signal passed through RF UP-Converter to a cable network. The integrated WFMT Transmitter performed all DSP operations that were necessary for transforming an information data to intermediate frequency (TF) signal spectrum of 41 - 47MHz, and then to high frequency RF signal of 300 - 500MHz.

At the receiver end, a down converter transferred the received high frequency RF signals to IF frequency band 41-47 MHz. An integral WFMT receiver processed the IF signal and decoded the received information data. After de-interleaving and FEC decoding, the corrected data were converted in MPEG 2 Transport stream. In accordance with the Simulink Model of the integral WFMT Transmitter, error- protected and interleaved information data were transferred to the input of a demultiplexer, which distributed these data between five QAM-modulators. Each of the QAM-modulators served to a corresponding sub-channel of the multicarrier WFMT signal. Data from output of each QAM-modulator generated a set of 21 frequency components of sub-channel wavelets. All frequency components of all sub-channel wavelets were relayed to 256-point IFFT core. Only N=21x5=105 inputs of the IFFT core were used for synthesis of a WFMT signal. Other inputs of the IFFT core were assigned a zero value (i.e., "0"). As a result, the IFFT core output signal comprised real and imaginary components. This output signal was fed to an overlapping unit prepared in accordance with the present invention (as shown in Fig. 3), and to a prior art overlapping unit (as shown in Fig. 1). After the overlapping units, the real and imaginary components of the signal passed through low-pass filters. These filters were necessary for proper generation of passband WFMT signals. After low pass filtering, real and imaginary WFMT baseband packets were multiplied by cosine and sine waves of the IF carrier frequency. Digital IF passband WFMT signals were relayed to an input of 14-bit Digital-to- Analogous converter that provided analogous IF passband signals of 41-47 MHz at the output of the WFMT Transmitter.

Exemplary output signals of the transmitter without PAPR reduction scheme and with a PAPR reduction scheme of the present invention are shown in Fig. 4 A and Fig. 4B, correspondingly. As can be seen, the technique proposed by the present invention provides significant reduction of the Peak-to- Average Ratio in the WFMT system.

It should be understood that although the proposed invention has been described above in connection with transmission data over cable wires, the concept of the invention can be also extended to the transmitting of data over wireless channels, radio channels, coaxial lines, fiber optical lines, power lines, etc. Moreover, the concept of the invention may be utilized not only in communication, but also in different applications with digital signal processing, e.g., radiolocation, acoustics, signal recording, etc.

Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. hi the method claims that follow, alphabetic characters used to designate claim steps are provided for convenience only and do not imply any particular order of performing the steps.

It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments and examples set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims and their equivalents. REFERENCES

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Claims

CLAIMS:

1. A method for transmission of information data by modulated wavelets over a communication line through a plurality of subchannels, the method characterized by the following steps all carried out by a transmitter: (a) obtaining the information data;

(b) encoding the information data with an error correction code, thereby forming an encoded information data;

(c) for each subchannel, generating over a time interval T a sequence of L subchannel non-overlapped wavelets modulated by said encoded information data; (d) overlapping over the time interval T the sequence of L modulated subchannel non-overlapped wavelets for generating a multi-carrier signal comprising overlapped wavelets carrying the encoded information data, said overlapping comprising the steps of:

(i) starting the overlapping from storing in a shift register zero values;

(ii) cyclically calculating for each modulated subchannel non- overlapped wavelet a maximal magnitude of a wavelet amplitude;

(iii) comparing said maximal magnitude of the wavelet amplitude with a predetermined value, and if the maximal magnitude does not exceed said predetermined value, adding data representing the modulated subchannel non-overlapped wavelet to the shift register, otherwise discarding the wavelet;

(iv) shifting for every cycle the data stored in the shift register on a predetermined number P of points; (v) providing every cycle the data from first P points of the shift register to said communication line for transmitting therethrough; and (vi) filling the last P points of the shift register with zeros; (vii) repeating steps (ii) to (vi) L times for providing and transmitting the entire overlapped wavelet sequence over the communication line.

2. The method of claim 1, wherein the step of generating over a time interval T a sequence of L subchannel non-overlapped wavelets modulated by said encoded information data comprises: providing predetermined wavelet coefficients representing amplitudes of frequency components of a prototype wavelet; for each subchannel, generating a signal representing modulated wavelet coefficients by multiplying the encoded information data by said amplitudes of frequency components; and applying an N-point Inverse Fast Fourier Transform (EFFT) to said signal representing modulated wavelet coefficients.

3. The method of claim 2, wherein the prototype wavelet is represented as a sum of K cosine functions, to wit:

where n is a natural number counting the frequency components; AT is a number of the all frequency components; and a_n is an amplitude of n-th frequency component.

4. The method of any one of the preceding claims, wherein said encoding of the information data with an error correction code includes Reed-Solomon encoding and interleaving the information data.

5. A method for transmission of information data by modulated wavelets over a communication line through a plurality of subchannels, the method characterized by the following steps all carried out by a receiver:

(A) receiving a distorted multicarrier signal including a signal representing a sequence of L overlapped subchannel modulated wavelets generated by the method of any one of the preceding claims together with a noise signal provided by said communication line during the transmission;

(B) separating said overlapped wavelets to provide a sequence of non-overlapped wavelets carrying the encoded information data distorted by the noise signal; (C) analyzing said sequence of the non-overlapped wavelets and generating spectral frequency amplitudes of wavelet components of the non-overlapped wavelets;

(D) demodulating said spectral frequency amplitudes of the wavelet components, thereby to generate the encoded information data;

(E) decoding said encoded information data with the error correction code thereby to provide said information data.

6. The method of claim 5, further comprising equalizing said spectral frequency amplitudes of the wavelet components before the demodulating step for eliminating phase- amplitude distortions of said distorted multicarrier signal, thereby providing corrected spectral frequency components.

7. The method of claim 5, wherein said decoding of the encoded information data with the error correction code includes de-interleaving and Reed-Solomon decoding the encoded information data.

8. A transmitter (35) for use with a multicarrier transceiver system (30) for transmission of information data by modulated wavelets over a communication line (2) through a plurality of subchannels, the transmitter comprising:

(a) an encoding unit (351) and interleaving unit (352) configured for encoding the information data with an error correction code thereby forming an encoded information data;

(b) a synthesis filter bank (353) configured for obtaining said encoded information data for each subchannel and generating over a time interval T a sequence of L subchannel non-overlapped wavelets modulated by said encoded information data; (c) an overlapping unit (304) coupled to said synthesis filter bank (353), including: a parallel adder (321) coupled to N output terminals of said synthesis filter bank (353); a modulo-calculator (323) coupled to the parallel adder (321), a comparator (324) arranged downstream of the modulo-calculator (323), a switch (325) coupled to the parallel adder (321) and to the comparator (324), and a shift register (322) coupled to the switch (325); said overlapping unit (32) being configured for

(i) starting the overlapping from storing in a shift register (322) zero values; (ii) cyclically calculating by the modulo-calculator (323) for each modulated subchannel non-overlapped wavelet a maximal magnitude of a wavelet amplitude; (iii) comparing by the comparator (324) said maximal magnitude of the wavelet amplitude with a predetermined value, and if the maximal magnitude does not exceed said predetermined value, adding data representing the modulated subchannel non-overlapped wavelet to the shift register, otherwise discarding the wavelet by the switch (325); (iv) shifting in the shift register (322) for every cycle the data stored in the shift register on a predetermined number P of points;

(v) providing every cycle the data from first P points of the shift register (322) to said communication line (2) for transmitting therethrough; (vi) filling the last P points of the shift register (322) with zeros; and (vii) repeating steps (ii) to (vi) L times for providing and transmitting the entire overlapped wavelet sequence over the communication line.

9. The transmitter of claim 8, wherein said synthesis filter bank (353) comprises: at least one modulator (311) having at least one multiplier configured for multiplying the encoded information data by amplitudes of frequency components of a prototype wavelet, thereby modulating said wavelet coefficients by the encoded information data; and an N-points IFFT unit (312) coupled to the modulator (311), said N-points IFFT unit (312) being configured for obtaining said signal representing said modulated wavelet coefficients, and for each sub-channel generating over a time interval T the sequence of L modulated non-overlapped wavelets modulated by the encoded information data.

10. The transmitter of claim 8 or 9, wherein said encoding unit (351) is a Reed-Solomon encoder.

11. A receiver (36) for use with a multicarrier transceiver system (30) for transmission of information data by modulated wavelets over a communication line (2) through a plurality of subchannels, the receiver comprising:

(A) a separating unit (42) configured for (i) receiving a distorted multicarrier signal including a signal representing a sequence of L overlapped subchannel modulated wavelets generated by the transmitter of any one of claims 8 to 10 together with a noise signal provided by said communication line during the transmission, and (ii) separating said overlapped wavelets to provide a sequence of non-overlapped wavelets carrying the encoded information data distorted by the noise signal;

(B) an analyzing filter bank (43) downstream of the separating unit (42) configured for obtaining said sequence of the non-overlapped wavelets, analyzing the sequence, generating spectral frequency amplitudes of wavelet components of the non-overlapped wavelets; and demodulating said spectral frequency amplitudes of the wavelet components, thereby to generate the encoded information data;

(C) a decoding unit (45) and de-interleaving unit (46) arranged downstream of the analyzing filter bank (43), and configured for decoding in tandem said encoded information data with the error correction code thereby to provide said information data.

12. The receiver of claim 11, wherein said decoding unit (45) is a Reed-Solomon decoder.

13. The receiver of any one of claims 11 or 12, wherein said analyzing filter bank (43) includes: an N-points FFT unit (431) configured for obtaining said sequence of the non- overlapped wavelets from the separating unit (42) and generating spectral frequency amplitudes of the wavelet components of said non-overlapped wavelets; and a demodulator (433) coupled to said iV-points FFT unit (431) and configured for obtaining said spectral frequency amplitudes of the wavelets and generating a signal representing said encoded information data; and at least one equalizer (432) coupled to TV-points FFT unit (431) and to the demodulator (433), and configured for correcting amplitudes of spectral frequency components of the wavelets by a obtaining said spectral frequency amplitudes of the wavelets and eliminating phase-amplitude distortions of said distorted multicarrier signal received in the communication line.