MXPA00009992A - Coarse frequency synchronisation in multicarrier systems - Google Patents

Abstract

A method for generating a signal having a frame structure, each frame of the frame structure comprising at least one useful symbol (12), a guard interval (14) associated to the at least one useful symbol (12) and a reference symbol (16), comprises the step of performing an amplitude modulation of a bit sequence such that the envelope of the amplitude modulated bit sequence defines a reference pattern of the reference symbol (16). A method for frame synchronization of a signal having such a frame structure comprises the steps of receiving the signal, down-converting the received signal, performing (164) an amplitude-demodulation of the down-converted signal in order to generate an envelope, correlating (166) the envelope with a predetermined reference pattern in order to detect a signal reference pattern of the reference symbol (16) in the signal, and performing the frame synchronization based on the detection of the signal reference pattern.

Description

STRUCTURE OF PICTURES AND SYNCHRONIZATION OF PICTURES FOR MULTIPLE CARRIER SYSTEMS FIELD OF THE INVENTION The present invention relates to methods and apparatus for generating a signal having a frame structure in which each frame of the frame structure is formed by useful symbols, an associated protection interval for each useful symbol and a reference symbol. In addition, the present invention relates to methods and apparatus for synchronizing signal frames having the above structure. The present invention is particularly useful in a MCM transmission system (MCM = Multi-carrier modulation) using a simultaneous orthogonal frequency division (OFDM) transmission for digital transmission. BACKGROUND OF THE INVENTION In an MCM transmission system (OFDM), the binary information is represented in the form of a complex spectrum, that is, a different number of complex subcarrier symbols in the frequency domain. In the modulator, a bit stream is represented by a sequence of spectra. Using a Fourier Inverse Transformation (IFFT), a MCM time domain signal is produced from this sequence of spectra.

In the case of a transmission of this MCM signal described through the multi-channel memory channel, inter-symbol interference (ISI) occurs due to the dispersion of the multiple tracks. To avoid ISI, a fixed-length protection interval is added between adjacent MCM symbols over time. The protection interval is chosen as a cyclic prefix. This means that the last part of an MCM symbol of the time domain is placed in front of the symbol to obtain a periodic extension. If the fixed length of the chosen protection interval is greater than the maximum delay of the multiple channels, an ISI will not occur. In the receiver, the information that is in the frequency and time domain (MCM) has to be retrieved from the time domain signal of the MCM. This takes place in two steps. Firstly, optimally locating the FFT window, thus eliminating the protection interval against each symbol of the time domain of the MCM. Second, performing a Fourier Transformation of the sequence of useful time samples obtained in this way. As a result, a sequence of the symbols of the spectrum is recovered in this way. Each of the symbols contains a different number of information that carries symbols of the subcarrier. Out of these the information bits are retrieved using the inverse modulator process. When performing the method described above, the following problem occurs in the receiver. The exact position of the protection interval and therefore the position of the original useful parts of the MCM symbols of the time domain is usually unknown. The extraction of the protection interval and the transformation of the subsequent FFT of the useful part resulting from the time signal is not possible without additional information. To provide this additional information, a known sequence (single carrier) is inserted in the form of a reference symbol (time domain) into the time signal. Knowing the positions of the reference symbols in the received signal, the exact positions of the protection intervals and therefore the interesting information carried by the time samples are known. The periodic insertion of the reference symbol results in a frame structure of the MCM signal. This frame structure of an MCM signal is shown in Figure 1. A frame of the signal of the MCM signal is formed by a variety of symbols of MCM 10. Each symbol of MCM 10 is formed by a useful symbol 12 and a protection interval 14 associated with it. As shown in Figure 1, each frame includes a reference symbol 16.

A synchronization in functions within the receiver, ie frame, frequency, phase, synchronization of the protection interval, is necessary for the subsequent demodulation of the MCM. As a consequence, the first most important task 5 of baseband processing in the receiver is to find and synchronize the reference symbol. DESCRIPTION OF THE PREVIOUS TECHNIQUE Most of the prior art methods for frame synchronization have been developed for 0 a single carrier transmission on the AWGN (AWGN = Additive White Gaussian Noise) channel (Gaussian Noise).

White Additive). These prior art methods based on the correlation, without major changes, are not applicable for transmission over multiple channel fading channels with large frequency compensations or MCM transmission systems using, for example, a simultaneous transmission of the division of the orthogonal frequency. For the transmission systems of the MCM, synchronization methods of particular frames have been developed. Warner, W.D., Leung C: OFDM / FM Frame Synchronization for Mobile Radio Data Communication (Synchronization of Frames for Data Communication by Z Mobile Radio), IEEE Trans. On vehicle technology, vol.

VT-42, August 1993, pp. 302 to 313, instructs on the insertion of reference symbols in the form of tones in parallel with the data within the symbol of the MCM. The reference symbols occupy several carriers of the MCM signal. In the receiver, the synchronization carriers are extracted in the frequency domain, after an FFT transformation (FFT = fast Fourier Transform) using a correlation detector. In the presence of large frequency offsets, this algorithm becomes very complex because several correlators must be implemented in parallel. An additional technique of the above embodiment is to insert a periodic reference symbol into the modulated MCM signal. This reference symbol is a CAZAC sequence (CAZAC = Constant Amplitude Zero Autocorrelation) (Zero Autocorrelation of Constant Amplitude). These techniques are taught by: Classen, F., Meyr, H.: Synchronization algorithms for an OFDM system for mobile communication (Synchronization algorithms for an OFDM system for Mobile communication), in Codierung für Codierung für Quelle, Kanal und Übertragung : ITG-Fachbericht 130, pp. 105-114, Munich, October 1994, ITG, VDE-Verlag, Berlin Offenbach; Lambrette, U., Horstmannshoff, J., Meyr, H .: Techniques for Frame Synchronization on Unknown Frequency Selective Channels (Techniques for the Synchronization of Frames on Selective Frequencies of Unknown Frequency), technology conference Proc. Vehic 1997; Schmidl, T.M., Cox, D.C .: Low-Overhead, Low-Complexity [Burst] Synchronization for OFDM Transmission (Low Overload Synchronization and Low Complexity [Synchronism] for OFDM Transmission), Proc. IEEE of the international conference on communication, 1996. In these systems, the processor of the receiver seeks a periodic repetition. For these algorithms, the synchronization of the approximate frequency has to be achieved before or at least simultaneously with frame synchronization. Van de Beek, J, Sandell, M., Isaksson, M, Borjesson, P .: Low-Complex Frame Synchronization in OFDM Systems (Synchronization of Low Complexity Frames in OFDM Systems), ICUPC Procedure, 1995, avoids the insertion of additional reference symbols or pilot carriers and instead uses the periodicity in the MCM signal that is inherent in the protection interval and the associated cyclic extension. This method is only suitable for varied and slow fading channels and small frequency compensations. US-A-5, 191, 576 relates to a method for the dissemination of digital data designed to be received primarily by mobile receivers moving in an urban environment. In this method, the title of each frame of a transmission signal having a frame structure has a first empty synchronization symbol and a second unmodulated oscillating signal forming a two-stage analog synchronization system. The recovery of the synchronization signal is achieved in an analog form, without the prior extraction of a clock signal at the primary level. EP 0631406 A refers to data signals, COFDM signals, for example, and to methods and apparatus for propagating these signals. The COFDM signals comprise a sequence of symbols, where each symbol has a useful portion and a protection interval. Two symbols of a COFDM signal are provided as synchronization symbols. One of the two symbols is a zero symbol, while the other is a synchronization symbol that is formed by an unmodulated multiplexer of the carrier frequencies that have a constant envelope. In addition to the two symbols as synchronization symbols, it is indicated in EP 0631406 A to modulate the pilot frequency of the data signal with a reference signal carrying information about synchronization. This reference signal modulated in the pilot frequency of the data signal can be used by a MABRL demodulator.

WO 98/00946 A refers to a system for synchronization of time and frequency regulation of the OFDM signals. Two OFDM preparation symbols are used to obtain a complete synchronization in less than two data frames. The OFDM preparation symbols are placed within the OFDM signal, preferably at least one each frame. The first OFDM preparation symbol is produced by modulating the OFDM subcarriers with even numbers, while the OFDM subcarriers with odd numbers are suppressed. Thus, in accordance with WO 98/00946 A, the first OFDM preparation symbol is produced by modulating the carriers with even numbers of this symbol with a first predetermined PN sequence. Moose: "A technique for orthogonal frequency division multi-plexing frequency offset correction (A technique for the correction of the frequency compensation in the simultaneous transmission of the division of the orthogonal frequency)" OPERATIONS ON COMMUNICATIONS OF THE IEEE, Volume 42, Number 10, October 1994, pages 2908 to 2914, instructs on the methods to correct the frequency compensations in the digital communications of the OFDM. The methods involve the repetition of a data symbol and the comparison of the phases of each of the carriers between the successive symbols. The change of phases of each of the carriers between the repeated symbols is due to the compensation of the frequency since the values of the modulation phase do not change in the repeated symbols. Keller; Hanzo: "Orthogonal frecuency division multiplex sinchronization techniques for wireless local area networks" ("Synchronous transmission synchronization techniques of orthogonal frequency division for wireless local area networks"), IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL RADIO COMMUNICATIONS, INTERNAL AND MOBILE, October 15, 1996, pages 963 to 967, instructs on frequency acquisition, frequency tracking, symbol synchronization and frame synchronization techniques. With respect to frame synchronization, it is indicated that a reference symbol consisting of repetitive copies of a pseudorandom sample synchronization pattern should be used. Frame synchronization is achieved by autocorrelation techniques using the periodic synchronization segments in such a way that for the proposed synchronization algorithms a prior knowledge of the synchronization sequences is not required. The methods for synchronizing frames available to date require either a synchronization of the previously achieved frequency or become very complex when the signal in the receiver is corrupted by a large frequency offset. If there is frequency compensation in the receiver, as can easily be the case when a receiver is turned on and the frequency synchronization circuit is still not blocked, problems will arise. When performing a simple correlation there will be only noise at the output of the correlator, that is, a maximum value can not be found if the compensation of the frequency exceeds a certain link. The size of the • Frequency compensation depends on the length (time) of the correlation to be carried out, that is, the longer it takes, the lower the allowable frequency compensation. In general, the compensation of frequency increases the complexity of the implementation. Frequency compensations occur after the ignition or later due to the frequency deviation of the oscillators used for the conversion-reduction to the baseband. The typical precisions for the The frequency of a free-running local oscillator (LO) is ± 50 ppm of the carrier frequency. With a carrier frequency in the S-band (eg 2.34 GHz) there will be a deviation from the maximum LO frequency of more than 100 kHz (117.25 kHz). A deviation of this magnitude achieves a greater demand for the above methods.

In the case of a damaged multipath transmission channel, a correlation method produces several maximum points of correlation in addition to the different maximum point for an AWGN channel. The best position of the title of possible frame, that is, the reference symbol, must be selected to match this maximum value number. In multi-channel channels, frame synchronization methods with correlations can not be used without making major changes. Also, it is not possible to use the demodulated data of the MCM system, because the l ^ k demodulation is based on the knowledge of the position of the protection interval and the useful part of the MCM symbol. SUMMARY OF THE INVENTION An objective of the present invention is to offer a The method and apparatus for generating a signal having a frame structure that allows a synchronization of frames after the signals have been transmitted even in the case of compensation of the carrier frequency or in the case of a transmission through a channel multi-way fading. Another object of the present invention is to provide a method and an apparatus for the synchronization of frames of a signal having a frame structure even in the case of compensation of the carrier frequency.

In accordance with a first aspect, the present invention provides a method for generating a signal having a frame structure, each frame of the frame structure includes at least one useful symbol, a protection interval associated with at least one symbol useful and a reference symbol, the method includes the steps of performing an amplitude modulation of a bit sequence, the envelope of the amplitude-modulated bit sequence defining a reference pattern of the reference symbol and the insertion of the sequence of bits modulated by amplitude within the signal mentioned as the aforementioned reference symbol. In accordance with a second aspect, the present invention provides a method for generating a modulated signal of multiple carriers having a frame structure, each frame of the frame structure includes at least one useful symbol, a protection interval associated with at least one useful symbol and a reference symbol, where the method includes the steps of: Offering a bit stream; Map the bits of the bitstream to the carriers in order to offer a sequence of spectra; Perform a Fourier inverse transformation in order to offer modulated symbols of multiple carriers; Associate a protection interval to each symbol modulated by multiple carriers; Generate the reference symbol by amplitude modulation of a bit sequence, where the envelope of the amplitude-modulated bit sequence defines the reference pattern of the reference symbol; Associate the reference symbol with a predetermined number of symbols modulated by multiple carriers and associated protection intervals in order to define the table; and Inserting the aforementioned amplitude-modulated bit sequence within the aforementioned signal as the aforementioned reference symbol. In accordance with a third aspect, the present invention provides a method for synchronizing frames of a signal having a frame structure, each frame of the frame structure includes at least one useful symbol, a protection interval associated with the At least one useful symbol and a reference symbol, where the method includes the steps of: Receiving the signal; Convert-reduce the received signal; Perform a demodulation by amplitude of the reduced converted signal in order to generate an envelope; Correlating the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal; And Perform the synchronization of frames based on the detection of the reference pattern of the signal. In accordance with a fourth aspect, the present invention provides a method for the synchronization of frames of a signal modulated by multiple carriers having a frame structure, each frame of the structure of Jfc frames includes at least one useful symbol, a protection interval associated with the at least one useful symbol and a reference symbol, where the method includes the steps of: Receiving the signal modulated by multiple carriers; 15 Convert-reduce the signal modulated by received multiple carriers; Performing an amplitude demodulation of the reduced converted multiple carrier signal in order to generate a shell; 20 Correlating the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal modulated by multiple carriers; Perform the synchronization of frames based on the detection of the reference pattern of the signal; Extract the reference symbol and at least one protection interval of the received multipoint modulated signal received converted-reduced based on the synchronization of frames; Performing a Fourier transform in order to offer a sequence of spectra from the at least one useful symbol; Eliminate the mapping of the sequence of spectra in order to offer a bit stream. In accordance with a fifth aspect, the present invention provides an apparatus for generating a signal having a frame structure, wherein each frame of the frame structure includes at least one useful symbol, a range of protection associated with at least one useful symbol and a reference symbol, where the apparatus includes an amplitude modulator for performing amplitude modulation of a bit sequence, the envelope of the amplitude modulated bit sequence defines the reference pattern of the reference symbol; and means for inserting the amplitude-modulated bit sequence into said signal as the aforementioned reference symbol.

In accordance with a sixth aspect, the present invention provides an apparatus for generating a signal modulated by multiple carriers having a frame structure, wherein each frame of the frame structure includes at least one useful symbol, a range of protection associated with the at least one useful symbol and a reference symbol, and the apparatus includes: Offering a bit stream; Means for mapping the bits of the bit stream to the carriers in order to offer a sequence of spectra; Means for performing a Fourier inverse transformation with the aspect of offering modulated symbols of multiple carriers; Means for associating a protection interval with each symbol modulated by multiple carriers; Means for generating the reference symbol by means of an amplitude modulator by amplitude modulation of a bit sequence, wherein the envelope of the amplitude modulated bit sequence defines the reference pattern of the reference symbol; Means for associating the reference symbol with a predetermined number of symbols modulated by multiple carriers and associated protection intervals in order to define the frame; and Means for inserting the aforementioned amplitude-modulated bit sequence into said signal as the aforementioned reference symbol. In accordance with a seventh aspect, the present invention provides an apparatus for synchronizing frames of a signal having a frame structure, wherein each frame of the frame structure includes at least one useful symbol, a range of protection associated with the at least one useful symbol and a reference symbol, and the apparatus includes: A receiver for receiving the signal modulated by multiple carriers; A converter-reducer to convert-reduce the signal modulated by multiple carriers received; An amplitude demodulator for performing an amplitude demodulation of the reduced converted multiple carrier signal in order to generate a wrapper; A correlator to correlate the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal modulated by multiple carriers; Means for performing the synchronization of frames based on the detection of the reference pattern of the signal; Means for extracting the reference symbol and the at least one protection range of the received multipoint modulated signal received on the basis of frame synchronization in order to generate the at least one useful symbol; Means for performing a Fourier transform in order to offer a sequence of spectra from the at least one useful symbol; Means to eliminate the mapping of the sequence of spectra in order to offer a bit stream. The present invention offers a new structure of the reference symbol together with a method for determining the position of the reference symbol and therefore the start of a frame in a signal with a frame structure as shown for example in Figure 1 The invention relates to a method for finding frame titles independently of other synchronization information and therefore for positioning the FFT windows correctly. This includes the extraction of a protection interval. The method is based on the detection of a known reference symbol of the frame title in the reception signal, for example, in the complex digital baseband. Synchronization of the new frame will be done as the first synchronization task.

The synchronization for the reference symbol, that is, the title of the frame is the first step to start radio reception. The reference symbol is structured to achieve this. The information contained in the reference symbol must therefore be independent of other synchronization parameters, for example, frequency compensation. For this reason, according to the present invention, the shape of the selected reference symbol is an amplitude-modulated sequence (AM sequence) in the complex baseband. In this way, the information contained in the reference symbol is only that provided in the amplitude and not that of the phase. Observe that the information of the phase will be corrupted by a possible compensation of the frequency. In the preferred embodiments of the present invention, the AM information is constructed from a sequence of bits with special characteristics. The sequence of information is selected in a way that is easy and secure to find in the time domain. A bit sequence with good autocorrelation properties is chosen. Good autocorrelation properties means a maximum value of different correlation in a correlation signal that would be as white as possible.

A pseudo-random bit sequence (PRBS) with good autocorrelation properties meets the above requirements. Using the envelope of the signal to transport the bit information offers additional flexibility. First, you have to decide which envelope values should correspond to the binary values of zero and one. The parameters are the average amplitude and the percentage of modulation. Care should be taken in selecting the average amplitude of the reference symbol (performance) in a manner identical to the average amplitude of the rest of the frame. This is due to the normalization of the amplitude (AGC; AGC = Automatic Gain Control), performed on the receiver. It is also possible to select the mean amplitude of the reference symbol greater than the amplitude of the average signal, but then care should be taken that the time constant of the AGC (1 / sensitivity) is selected high enough to ensure that the strong (boosted) signal of the reference symbol has no influence on the AGC control signal and therefore attenuates the signal after the reference symbol. Another degree of freedom can be characterized as the degree of modulation d. This parameter is responsible for the information density of the modulation signal mod (t) formed by the binary sequence bin (t) in the following way: mod (t) = bin (t / d). This degree of modulation can be chosen as a free parameter set by an integer or real relation with the sampling percentage. It is appropriate to choose the degree of modulation d as an integer value due to the discrete values of the binary sequence: d = 1: mod (m) = bin (m) d = 2: mod (m) = bin (m / 2) for par m = bin_int (m / 2) for non md = 3: mod (m) = bin (m / 3) for m = 0, +3, ± 6, ± 9, bin_int (m / 3) other The values of the signal bin_int (m / d) are calculated from the binary bin m) by ideal interpolation (between discrete integer values m ) with the factor of d. This is similar to an expansion of the ideal sampling percentage (with interpolation without (x) / x), but the sampling percentage remains, only fewer bits of the binary sequence bin (m) correspond to the resulting interpolated sequence mod (m) . This parameter m indicates the discrete time. By increasing m the modulation signal mod (t) expands in time relative to the basic binary sequence, this results in a compression of the bandwidth of the resulting AM spectrum with respect to the basic binary sequence. An expansion of time by a factor of 2 results in a compression of the bandwidth by the same factor 2. In addition to the compression of the bandwidth, an advantage over a greater degree of modulation d is a reduced complexity of the search method in the receiver "due to the fact that only each sample dth has a corresponding binary value." Choosing the factor d = 1 is not preferred because this would result in a pseudonym due to the lack of attention of the sampling theorem. in a preferred embodiment of the present invention d is chosen as 2. The choice of the length and repetition percentage of the reference symbol is, on the other hand, dominated by the properties of the channel, for example, the coherence time of the On the other hand, the choice depends on the requirements of the receiver with respect to the average time to the initial synchronization and the average time for the new synchronization after the loss of synchronization due to a fading of the channel. In the receiver, the first step after the conversion-reduction of the received signal is to perform an amplitude demodulation of the converted-reduced signal in order to generate an envelope, that is, in order to i 'finish the amplitude of the signal. This envelope correlates with a duplicate reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal. In the case of an AWGN channel, the result of this correlation will be a white noise signal with a mean value of zero and a clearly visible maximum value (positive). In the case of a multi-way channel, several maximum points will occur in the correlation signal calculated by this correlation. In the previous case, the location of the reference symbol is determined based on the maximum value of the signal, while in the latter case a weighing procedure is performed in order to find the maximum value corresponding to the location of the reference symbol . Therefore, the present invention shows how to find a reference symbol by a detection method that is simple. In addition, the present invention can be used for one carrier systems or several carriers. The present invention is particularly useful in multi-carrier modulation systems using a simultaneous transmission of orthogonal frequency division, for example in the field of digital transmission. The synchronization methods according to the present invention are independent of other synchronization steps. Since the information necessary for synchronization is contained in the preamble envelope, that is, the reference symbol, the reference symbol is independent of the possible frequency compensations. Therefore, a derivation of the correct reduced sampling time and the correct positioning of the FFT window can be achieved, the reference symbol of the present invention can be detected even when the frequency synchronization circuit is not blocked or even in the case of a compensation on the carrier frequency. The frame synchronization method in accordance with the present invention is preferably performed before others and without knowledge of other synchronization efforts. BRIEF DESCRPTION OF THE ILLUSTRATIONS Below, the preferred embodiments of the present invention will be explained in detail based on the appended illustrations, wherein: Figure 1 shows a schematic view of a signal having a frame structure; Figure 2 shows a block diagram of an MCM system to which the present invention can be applied; Figure 3 shows a schematic block diagram of a frame and frequency synchronization system in an MCM receiver; Figure 4 shows a schematic diagram of an apparatus for the synchronization of frames; and Figure 5 shows a typical channel impulse response of a single frequency network in the S-band. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the present invention is mainly explained by referring to an MCM system, it is obvious that the present invention can be used in connection with different signal transmissions based on different types of modulation. Figure 2 shows an overview of the MCM system on the basis of which the present invention will be described in detail. At 100 an MCM transmitter is shown which substantially corresponds to an MCM transmitter of the prior art, with the exception of the kind of reference symbol that is added to each frame of an MCM signal. A description of this MCM transmitter can be found, for example, in William Y. Zou, Yiyan Wu, "COFDM: AN OVERVIEW" ("COFDM: A PANORAMA"), transmission operations of the IEEE, Vol. 41 No. 1, March 1995. A data source 102 provides a serial bit stream 104 to the MCM transmitter. The incoming serial bit stream 104 is applied to a bit-carrying cartographer 106 which produces a sequence of spectra 108 from the incoming serial bit stream 104. A fast inverse Fourier transform (FFT) 110 is performed in the sequence of the spectra 108 in order to produce a time domain signal of MCM 112. The MCM time domain signal forms the useful MCM symbol of the MCM time signal. To avoid intersymbol interference (ISI) caused by multipath distortion, a unit 114 is provided to insert a fixed length protection interval between adjacent MCM symbols in time. In accordance with a preferred embodiment of the present invention, the last part of the useful MCM symbol is used as the protection interval by placing the mime in front of the useful symbol. The resulting MCM symbol is shown at 115 in Figure 2 and corresponds to the MCM symbol 10 shown in Figure 1. In order to obtain the final frame structure shown in Figure 1, a unit 116 is provided to add a symbol reference for each predetermined number of MCM symbols. In accordance with the present invention, the reference symbol is a sequence of bits modulated by amplitude. In this way, an amplitude modulation of a bit frequency is performed in such a way that the envelope of the amplitude-modulated bit sequence defines a reference pattern of the reference symbol. This reference pattern defined by the envelope of the amplitude-modulated bit sequence must be detected upon receiving the MCM signal in an MCM receiver. In a preferred embodiment of the present invention, a pseudo-random bit sequence having good autocorrelation properties is used as the bit sequence for amplitude modulation. The choice of the length and the repetition percentage of the reference symbol depends on the properties of the channel through which the MCM signal is transmitted, for example, the coherence time of the channel. In addition, the repetition percentage and the length of the reference symbol, in other words, the number of useful symbols in each frame, depends on the requirements of the receiver with respect to the average time for the initial synchronization and the average time for the new synchronization. after the loss of synchronization caused by a fading of the channel. The resulting MCM signal having the structure shown at 118 in Figure 2 is applied to the front end of the transmitter 120. So to speak, on the front end of the transmitter 120, a digital / analog conversion and an upconversion of the MCM signal is carried out. Therefore, the MCM signal is transmitted through a channel 122. Subsequently, the mode of operation of an MCM receiver 130 is briefly described with reference to Figure 2. The MCM signal is received at the front end of the receiver 132. At the front end of the receiver 132, the MCM signal is converted-reduced and subsequently, an analog-digital conversion of the converted-reduced signal is carried out. The converted-reduced MCM signal is supplied to a frame synchronization unit 134. The frame synchronization unit 134 determines the location of the reference symbol in the MCM symbol. Based on determination of the frame synchronization unit 134, an extraction unit of the reference symbol 136 extracts the information from the frame, ie, the reference symbol, from the MCM symbol that comes from the front end of the receiver 132. After the extraction of the reference symbol, the MCM signal is applied to a protection interval elimination unit 138. The operation mode of the frame synchronization unit 134 representing the present invention will be described in detail with reference to Figures 3 and 4 later. The result of the processing of the signal made up to now in the MCM receiver are the useful MCM symbols. The output of the useful MCM symbols of the protection interval elimination unit 138 are supplied to a Fourier fast transformation unit 140 in order to provide a sequence of spectra from the useful symbols. Subsequently, the sequence of spectra is supplied to a cartographer of bits of the carrier 142 where the serial bit stream is recovered. This serial bitstream is supplied to a data collector 144. Subsequently, the mode of operation of the frame synchronization unit will be described in detail with reference to Figures 3 and 4. Figure 3 represents an additional high level diagram. of an apparatus for synchronizing frames of an MCM signal. At the front end of receiver 150, the incoming MCM signal is converted-reduced. In Figure 3, an analog / digital converter 152 is shown separated from the front end of the receiver 150. The output signal of the analog / digital converter 152 is applied to a frame synchronization unit 154. This frame synchronization unit 154 performs the synchronization of frames in accordance with the present invention which will be described in detail with reference to Figure 4 below. Depending on the frame synchronization of the frame synchronization unit 154, an MCM demodulator 156 demodulates the MCM signal in order to provide a demodulated serial bit stream. As shown in Figure 3, the reference symbol described in accordance with the present invention can also be used for an approximate frequency synchronization of the MCM signal. Primarily, the frame synchronization unit 154 also serves as an approximate frequency synchronization unit for determining an approximate frequency offset of the carrier frequency caused, for example, by a difference in the frequencies between the local oscillator of the transmitter and the transmitter. local receiver oscillator. The compensation of the determined frequency is used in order to perform a correction of the approximate frequency at a point 158. In Figure 4, a detailed scheme of the frame synchronization according to the present application is shown. An MCM signal transmitted through the channel 122 is received at the RF front end of the receiver 132. The converted-reduced MCM signal is sampled at the front end of the receiver 132 and is supplied, in the preferred embodiment, to a fast operation automatic gain control (time constant <; duration of the MCM symbol) in order to eliminate the rapid fluctuations of the channel (channel coherence time duration of the MCM symbol) the fast AGC 162 is used in addition to the normally slow AGC in the signal path in the case of the transmission over a multi-channel channel with a long channel impulse response and selective frequency fading. The fast AGC adjusts the average amplitude range of the signal to the known average amplitude of the reference symbol. The symbol processed in this way is supplied to an amplitude determining unit 164. The amplitude determining unit 164 can ^ * fc use the simple method of alfamax + betam? n_ in order to Calculate the amplitude of the signal. This method is described for example in Palachels A .: DSP-mP Routine Computes Magnitude (Magnitude of DSP-mP Routine Calculations), EDN, October 26, 1989; and Adams, W. T., and Bradley, J.: Magnitude Approximations for Microprocessor Implementation (Magnitude Approximations) for Microprocessor Operation), and IEEE Micro, Vol. 3, No. 5, October 1983. The output signal of the amplitude determination unit 164 is applied to a correlator 166. In the correlator 166, a cross-correlation between the output of the amplitude signal from the amplitude determination unit 164 and the known ideal amplitude information. The information of the known ideal amplitude is stored in the correlator. For both, the amplitude and information of the known ideal amplitude, its amplitudes are symmetrically relative to zero with their average amplitude. In the case of ideal AWGN, the result will be a white noise signal with a mean value of zero and a positive maximum value clearly visible. In this case of ideal AWGN, the position of the single maximum point is devalued in a maximum position unit 172. Based on this evaluation, the reference symbol and protection intervals are extracted from the MCM signal in a combined reference symbol / protection extraction 136/138 unit. Although these units are shown as a combined unit 136/138 in Figure 4, it is clear that separate units can be provided. The MCM signal is transmitted from the front end RF 150 to the unit of the reference symbol / protection extraction 136/138 through a slow-pass filter 174. In the case of the time propagation found in a channel of multiple pathways, several maximum points occur corresponding to the number of groups in the impulse response of the channel, in the output signal of the correlator. A schematic view of three of these groups located in a time window of a maximum point of approximately 60 microseconds is shown in Figure 5. Of the various maximum points caused by the propagation of time found in a multi-channel channel, the best it must be selected as the position of the box title, that is, the reference symbol. Therefore, a threshold unit 168 and a weighing unit 170 are supplied between the correlator 166 and the maximum position unit 172. The threshold unit 168 is supplied to eliminate the maximum value possessed by an amplitude below a threshold. predetermined. The weighing unit 164 is supplied in order to perform a weighing procedure at the remaining maximum values in such a way that the maximum value corresponding to the reference symbol can be determined. Next, a weighing procedure as an example carried out in the weighing unit 170 is explained. The first important maximum value is considered as the best. The output signal of the correlator is observed from the first maximum value detected upwards for the maximum length of the impulse response of the channel and an amplitude weighing function is applied to the signal. Because the impulse response length of the real channel is unknown, the following fact can be remembered. During the design of the system, the length of the impulse response of the channel has to be investigated. In an MCM system, the protection interval will be equivalent to or greater than the impulse response of the maximum expected channel. For this reason, the part (interval with samples II, II corresponding to the maximum expected channel impulse response, that is, the length of the protection interval) of the output signal of the correlation starting with the first maximum value, I 0 (n) = r (k0 + n), 0 n lj, - 1 (Equation 1) Since k0 is the position of the first maximum value, it will be examined to find the best starting position of the frame. The part of the previous signal is weighed with the function, W (n) = 10 Weight dB n 10 i "(Equation 2) The position (nmax) of the maximum value in the interval of the resulting signal I o, weighted (n) = [r (k0 + n) W (n)] = [r (k0 + n) = 10 Weight dB n 10 1 -1 I n lj. - 1 (Equation 3) will be chosen as the best starting position of the table. r (k) designates the output signal of the correlator (166) at time k. The signal is present with a clock frequency that is determined by multiplication: additional sampling factor * frequency of the subcarrier symbol. The parameter k designates the discrete time in the sample clocks. This signal is displayed in the window with information from the unit of the threshold 168. A range having the length of the values lt is extracted from the signal r (k). The first value written within the range is the start value of the correlation at time k0, at which the output value r (k0) exceeds the threshold value of the unit of threshold 168 for the first time. The interval with the signal displayed on the screen is designated by the term I (K0). The parameter n designates the relative time, that is, the position of a value within the interval. Using the described weighing operation, the first correlation maximum values are most likely chosen as the initial position of the correct frame. A resulting maximum value will subsequently be chosen only as the initial position of the table, if the maximum point value is significantly greater than the first. This operation is applicable specifically for the MCM because here it is better to detect the starting positions of the box in some samples too before some samples too many later. Placing the start of the frame in some samples too soon results in the positioning of the FFT window in a small bit within the protection range, this contains information of the same MCM symbol and therefore produces very few effects. If the starting position of the frame is detected in some samples too later, then the FFT window includes some samples of the next protection interval. This results in more visible degradation, because the next protection interval contains information from the next MCM symbol (an ISI occurs). It is important to know that the first maximum correlation value visible after the receiver is turned on does not necessarily correspond to the first CIR group (Channel Impulse Response). It is possible that this corresponds to a later group, see Figure 5. For this reason, during start-up, you should wait for the start of a second frame before starting the demodulation. It is obvious that methods to determine the amplitude different from the described method of alfamax + betam? N- can be used. For simplicity it is possible to reduce the calculation of the amplitude to a detection with respect to whether the current amplitude is above or below the average amplitude. The output signal then consists of a -1 / + 1 sequence that will be correlated with a known bit sequence, also in the values -1 / + 1. This correlation can be easily performed using a simple integrated circuit (IC). In addition, additional sampling of the signal received at the RF front end can be performed. For example, the received signal can be expressed with an additional double sampling. This sampled signal is passed to a fast-acting AGC to eliminate the fast-channel fluctuations before calculating the amplitude of the signal. The information on the amplitude will be fully quantized. The values greater than the average amplitude, the average amplitude being one, will be expressed as +1, the values smaller than the average amplitude will be expressed as -1. This -1 / + 1 signal passes to the correlator that performs a cross-correlation between the quantized signal and the stored ideal amplitude values of the reference symbol: amp_sto (k) = 2 * bin (k / 4), if k = 2 ( additional sampling factor) * 2 (interpolation factor) * 1, 2, 3 ... 92 (92 for 184 reference symbol and interpolation factor) * 92 amp_sto (k) = 0, other, k < = 2 (additional sampling factor) * 2 (interpolation factor) * 92 (first part of amp_sto = [0 0 0 -1 0 0 0 0 1 0 0 0 1 0 0 0 -1 0] With this algorithm a maximum correlation value of 92 can be achieved. Again, the maximum value in the correlator output signal corresponds to different initial frame positions due to different multipath groups. In this signal with different maximum values, the best starting position of the frame must be selected.

This is done with the following steps: the correlator output is provided for a threshold detection.

If the first time of the signal exceeds the threshold (a threshold of 50 has proved to be applicable) the search algorithm of the best position is initialized. The correlator output signal in the interval after the value that exceeds the threshold will be weighed with the weighing function, see above. The position of the maximum value resulting in the heavy signal will be chosen as the best position at the start of the frame. With the knowledge of the best initial position of the frame, the extraction of the protection interval and the following demodulation of the MCM will be carried out. Some more efforts can be carried out to increase the precision of frame synchronization. These methods will be explained below. Further processing of the initial decision of the table is made in order to a) increase the reliability of the frame synchronization; b) ensure that no starting position of the table is overlooked; and c) improve the starting position of the frame in the case that there are different positions of the CIR group. Using information from other positions at the beginning of the table. It is known that a reference symbol is inserted inside the signal on the front of each frame. If the position of the start of the currently detected frame has changed significantly with respect to the last start of the detected frame, the demodulation of the two frames in total and completely independent of each other is possible. It is also possible to damp the frame of the last signal and make the required change of the position of the beginning of the frame gradually with the MCM symbols of the frame. This results in the interpolation positioning of the simple MCM symbols including the extraction of the simultaneous asynchronous protection interval for the different MCM symbols. This interpolation positioning of the FFT window is also possible if a position of the start of the frame is missing, that is, if the start of the frame has not been detected. If a position is missing at the beginning of the frame, the extraction of the protection interval can be done in the same way as in the previous frame without a higher performance degradation. This is due to the positions of the CRI group that vary very little normally, but only if the signing of the signal is too good. Stopping the demodulation and waiting for the next start position of the detected frame can also be but is not convenient due to the greater interruption. Below is an example of a reference symbol of 184 sample (symbols of the subcarrier) supplied by the apparatus of the invention to generate a signal with a frame structure. The implicit binary sequence of length 92 is: bin = [0 1 1 0 1 1 0 1 0 1 1 0 1 0 1 0 0 0 1 1 1 0 0 0 0 0 0 0 0 1 1 0 1 1 1 1 1 0 0 0 1 1 1 0 0 0 0 0 0 0 1 1 1 0 1 1 1 0 0 1 1 0 1 1 1 0 1 1 0 1 0 1 0 1 1 0 1 1 0 1 1 0 1 0 0 0 0 1 0 1 1 0] the binary modulated sequence is: i_q = [0.5 1.5 1.5 0.5 1.5 1.5 0.5 1.5 0.5 1.5 1.5 0.5 1.5 0.5 1.5 0.5 0.5 0.5 1.5 1.5 1.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.5 1.5 0.5 1.5 1.5 1.5 1.5 1.5 0.5 0.5 0.5 1.5 1.5 1.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.5 1.5 1.5 0.5 1.5 1.5 1.5 0.5 0.5 1.5 1.5 0.5 1.5 1.5 1.5 0.5 1.5 1.5 0.5 1.5 0.5 1.5 0.5 1.5 1.5 0.5 1.5 1.5 0.5 1.5 0.5 1.5 0.5 0.5 0.5 0.5 1.5 0.5 1.5 1.5 0.5 ] This binary sequence modulated i_q is interpolated in order to produce the interpolated sequence i_q_int = 0.5000 1.0635 1.5000 1.7195 1.5000 0.8706 0.5000 0.8571 1.5000 1.7917 1.5000 0.8108 0.5000 1.0392 1.5000 1.0392 0.5000 0.8108 1.5000 1.7984 1.5000 0.8018 0.5000 1.0460 1.5000 0.9997 0.5000 0.9063 1.5000 1.1424 0.5000 0.3831 0.5000 0.4293 0.5000 0.9997 1.5000 1 5769 1.5000 1.5769 1.5000 1.0065 0.5000 0.3899 0 5000 0 .5325 0 .5000 0 .4931 0 .5000 0.5000 0.3899 0 5000 0 .5325 0 .5000 0 .4931 0 .5000 0.4999 0.5000 0 4931 0 .5000 0 .5325 0 .5000 0 .3967 0.5000 0.9603 1 5000 1, .7522 1, .5000 0, .8571 0. .5000 0. 8965 1.5000 1 6422 1, .5000 1, .4669 1, .5000 1, .4737 1.5000 1.6096 1 5000 0 .9929 0 .5000 0 .4226 0,, 5000 0.4226 0.5000 0 9997 1, .5000 1, .5769 1 .5000 1, .5769 1.5000 1.0065 0 5000 0, .3899 0. .5000 0 .5325 0, .5000 0.4931 0.5000 0 4931 0. .5000 0, .5325 0, .5000 0. .3899 0. 5000 1.0065 1 5000 1, .5701 1, .5000 1, .6096 1. .5000 0.8965 0.5000 0 8965 1, .5000 1, .6096 1, .5000 1. .5633 1.5000 1.0392 0 5000 0, .2867 0, .5000 0, .9929 1, .5000 1.7454 1.5000 0 8571 0. .5000 0, .9033 1, .5000 1. .6028 1.5000 1.6028 1 5000 0. .9033 0. .5000 0. .8503 1. .5000 1. 7917 1.5000 0 8108 0. .5000 1. .0460 1. .5000 0. .9929 0.5000 0.9929 1 5000 1. .0460 0. .5000 0. .8108 1. .5000 1.7917 1.5000 0 8571 0. .5000 0. .8571 1. .5000 1. .7849 1.5000 0.8571 0 5000 0. .8571 1. .5000 1. .7917 1. .5000 0.8176 0.5000 1 0065 1., 5000 1. .1424 0. .5000 0., 3436 0. 5000 0.5788 0 5000 0., 3436 0. .5000 1. .1424 1., 5000 1. 0065 0.8312 1 5000 1., 7263 1. .5000 1. .0635 0., 5000 0. 0637] amp_int = I_q_int + j * I _q_int amp_int is the reference symbol inserted periodically into the signal after insertion of the protection interval. As is clear from the above specification, the present invention offers methods and apparatus for generating a signal having a frame structure and methods and apparatus for synchronizing frames when these signals are received, which are superior when compared with systems of the art. previous. The frame synchronization algorithm in accordance with the present invention offers all the properties shown in Table 1 as opposed to the known frame synchronization procedures. Table 1 shows a comparison between the system according to the present invention using an AM sequence as a reference symbol and prior art systems (single carrier and MCM Eureka 147). Table 1 From what can be seen in Table 1, different tasks and synchronization parameters can be derived using the synchronization of frames with an AM sequence in accordance with the present invention. The frame synchronization procedure of the MCM Eureka 147 corresponds to the procedure described in EU-A-5, 191, 576.

Claims (46)

1. CLAIMS 1. A method for generating a signal having a frame structure, each frame of the said frame structure includes at least one useful symbol, a protection interval associated with the at least one useful symbol and a reference symbol , wherein said method includes the step of performing an amplitude modulation of a sequence of bits, wherein the envelope of the amplitude-modulated bit sequence defines the reference pattern of said reference symbol; and Insert the amplitude-modulated bit sequence into the aforementioned signal as the aforementioned reference symbol.
2. 2. The method according to claim 1, wherein said signal is a multiplexed orthogonal frequency division signal.
3. 3. The method according to claim 1, wherein said amplitude modulation is performed in such a way that an average amplitude of said reference symbol corresponds substantially to an average amplitude of the remaining signal.
4. 4. A method for generating a modulated signal from multiple carriers having a frame structure, each frame of the frame structure includes at least one useful symbol, a protection interval associated with the at least one useful symbol and a symbol of reference, where the method includes the steps of: Offering a bit stream; Map the bits of the bitstream to the carriers in order to offer a sequence of spectra; Perform a Fourier inverse transformation with the aspect of offering modulated symbols of multiple carriers; Associate a protection interval to each symbol modulated by multiple carriers; Generate the reference symbol by amplitude modulation of a bit sequence, where the envelope of the amplitude-modulated bit sequence defines the reference pattern of the reference symbol; Associate the reference symbol with a predetermined number of symbols modulated by multiple carriers and associated protection intervals in order to define the table; and Inserting the aforementioned amplitude-modulated bit sequence within the aforementioned signal as the aforementioned reference symbol.
5. The method according to claim 4, wherein the aforementioned multiple carrier modulated signal is a simultaneous transmission signal of the orthogonal frequency division.
6. 6. The method according to claim 4, wherein said amplitude modulation is performed in such a way that a mean amplitude of said reference symbol corresponds substantially to an average amplitude of the remaining modulated multicarrier signal.
7. The method according to claim 1, wherein said bit sequence is a pseudorandom bit sequence having good autocorrelation characteristics.
8. The method according to claim 1, wherein a number of symbols useful in each frame is defined depending on the properties of the channel of a channel through which the signal or the signal modulated by multiple carriers is transmitted.
9. 9. A method for synchronizing frames of a signal having a frame structure, each frame of the frame structure includes at least one useful symbol, a protection interval associated with the at least one useful symbol and a symbol of reference, where the method includes the steps of: Receiving the signal; Convert-reduce the received signal; Perform a demodulation by amplitude of the reduced converted signal in order to generate an envelope; Correlating the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal; and Perform the synchronization of frames based on the detection of the reference pattern of the signal.
10. The method according to claim 9, further comprising the step of performing a fast automatic gain control of the aforementioned received converted-reduced signal before proceeding to perform said amplitude demodulation.
11. 11. The method according to claim 9, wherein the step of performing said amplitude demodulation includes the step of calculating an amplitude of the mentioned signal using the alphamax + betamin_ method.
12. The method according to claim 9, further including the steps of sampling the respective amplitudes of the aforementioned received converted-reduced signal and comparing said sampled amplitudes with a predetermined threshold in order to generate a sequence of bits to perform the amplitude demodulation mentioned.
13. 13. The method according to claim 12, wherein the step of sampling the respective amplitudes of the received converted-reduced signal mentioned further includes the step of performing an additional sampling of the aforementioned received low-converted signal.
14. The method according to claim 9, further including the step of applying a result of frame synchronization for a frame in the signal mentioned for at least one subsequent frame in the signal mentioned.
15. 15. A method for synchronizing frames of a signal modulated by multiple carriers having a frame structure, each frame of the frame structure includes at least one useful symbol, a range of protection associated with the at least one symbol useful and a reference symbol, where the method includes the steps of: Receiving the signal modulated by multiple carriers; Convert-reduce the signal modulated by multiple carriers received; Performing an amplitude demodulation of the reduced converted multiple carrier signal in order to generate a shell; Correlating the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal modulated by multiple carriers, - Performing the synchronization of frames based on the detection of the reference pattern of the signal; Extract the reference symbol and the at least one protection interval of the multipoint modulated signal received from the converted-reduced carrier based on frame synchronization; Performing a Fourier transform in order to offer a sequence of spectra from the at least one useful symbol; Eliminate the mapping of the sequence of spectra in order to offer a bit stream.
16. 16. The method according to claim 15, further comprising the step of performing a fast automatic gain control of the aforementioned received converted-reduced multiple carrier modulated signal before proceeding to perform said amplitude demodulation.
17. The method according to claim 15, wherein the step of performing said amplitude demodulation includes the step of computing an amplitude of the multipoint modulated carrier signal mentioned using the alphamax + betamin_ method.
18. The method according to claim 15, further including the steps of sampling the respective amplitudes of the aforementioned received converted-reduced multiple carrier signal and comparing said sampled amplitudes with a predetermined threshold in order to generate a sequence of bits to perform the aforementioned amplitude demodulation.
19. The method according to claim 18, wherein the step of sampling the respective amplitudes of the aforementioned received converted-reduced multiple carrier signal includes further the step of performing an additional sampling of the aforementioned received low-converted signal.
20. The method according to claim 15, further including the step of applying a result of the frame synchronization for a frame in the signal mentioned for at least one subsequent frame in the aforementioned multi-carrier modulated signal.
21. The method according to claim 9 further including the step of detecting a location of the reference pattern of the aforementioned signal based on the occurrence of a maximum value of a correlation signal by correlating the mentioned envelope with the pattern of predetermined reference mentioned.
22. The method according to claim 21, further comprising the steps of: weighing a plurality of maximum values of the mentioned correlation signal in such a way that a maximum value occurring for the first time is weighed more firmly than any maximum value that occurs later; And detect the mentioned site of the pattern reference of the mentioned signal based on the largest of the maximum heavy values.
23. 23. The method according to claim 22 further comprising the step of: removing the step of performing said frame synchronization for a predetermined period of time after having connected a receiver performing said method for frame synchronization.
24. 24. An apparatus for generating a signal having a frame structure each frame of said frame structure includes at least one useful symbol, a protection interval associated with the at least one useful symbol and a reference symbol mentioned, wherein said apparatus includes: an amplitude modulator for performing an amplitude modulation of a sequence of bits, wherein the envelope of the sequence of amplitude-modulated bits defines the reference pattern of the reference symbol mentioned; and means for inserting the amplitude-modulated bit sequence into said signal as the aforementioned reference symbol (16).
25. 25. The apparatus according to claim 24, wherein said signal is a multiplexed signal of the orthogonal frequency division.
26. 26. The apparatus according to claim 24, wherein a mean amplitude of said reference symbol substantially corresponds to a mean amplitude of the remaining signal.
27. 27. An apparatus for generating a modulated signal from multiple carriers having a frame structure, wherein each frame of the frame structure includes at least one useful symbol, a range of protection associated with the at least one useful symbol and a reference symbol, and the apparatus includes: Offer a bit stream; Means for mapping the bits of the bit stream to the carriers in order to offer a sequence of spectra; Means for performing an inverse transformation of Fourier with the appearance of offering modulated symbols of multiple carriers; Means for associating a protection interval with each symbol modulated by multiple carriers; Means for generating the reference symbol by means of an amplitude modulator by amplitude modulation of a bit sequence, wherein the envelope of the amplitude modulated bit sequence defines the reference pattern of the reference symbol; Means for associating the reference symbol with a predetermined number of symbols modulated by multiple carriers and associated protection intervals in order to define the frame; and Means for inserting the aforementioned amplitude-modulated bit sequence into said signal as the aforementioned reference symbol.
28. 28. The apparatus according to claim 27, wherein said multipoint modulated signal is a signal of simultaneous transmission of the orthogonal frequency division.
29. 29. The apparatus according to claim 26, wherein said means for generating said reference symbol performs amplitude modulation such that an average amplitude of said reference symbol substantially corresponds to a mean amplitude of the modulated signal of multiple carriers remaining.
30. 30. The apparatus according to claim 24, wherein said means for generating said reference symbol generates a pseudorandom bit sequence having good autocorrelation characteristics as the aforementioned bit sequence.
31. 31. The apparatus according to claim 24 including means for determining a number of useful symbols in each frame depending on the channel properties of a channel through which the signal or modulated signal of multiple carriers is transmitted.
32. 32. An apparatus for an apparatus for synchronizing frames of a signal having a frame structure, wherein each frame of the frame structure includes at least one useful symbol, a range of protection associated with the at least one symbol useful and a reference symbol, and the apparatus includes: A receiver for receiving the signal modulated by multiple carriers; A converter-reducer for converting-reducing the received modulated signal by multiple carriers; An amplitude demodulator for performing an amplitude demodulation of the reduced converted multiple carrier signal in order to generate a wrapper; A correlator to correlate the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal modulated by multiple carriers; and Means for performing the synchronization of frames based on the detection of the reference pattern of the signal.
33. 33. The apparatus according to claim 32, further including means for performing a fast automatic gain control of the aforementioned received converted-reduced signal before said amplitude demodulator.
34. 34. The apparatus according to claim 32, wherein said amplitude demodulator includes means for calculating an amplitude of said signal using the alphamax + betamin- method.
35. 35. The apparatus according to claim 32, further including means for sampling the respective amplitudes of the aforementioned received low-converted signal, wherein said amplitude demodulator includes means for comparing said sampled amplitudes with predetermined threshold in order to generate a sequence of bits.
36. 36. The apparatus according to claim 35, wherein said means for sampling includes means for additional sampling of the aforementioned received converted-reduced signal.
37. 37. The apparatus according to claim 32, further including means for applying a result of frame synchronization for a frame in the signal mentioned for at least one subsequent frame in the aforementioned signal.
38. 38. An apparatus for an apparatus for synchronizing frames of a signal having a frame structure, wherein each frame of the frame structure includes at least one useful symbol, a protection interval associated with the at least one useful symbol and a reference symbol, and the apparatus includes: A receiver to receive the signal modulated by carriers multiple; A converter-reducer for converting-reducing the received modulated signal by multiple carriers; An amplitude demodulator for performing an amplitude demodulation of the reduced converted multiple carrier signal in order to generate a wrapper; A correlator to correlate the envelope with a predetermined reference pattern in order to detect the reference pattern of the signal of the reference symbol in the signal modulated by multiple carriers; Means for performing the synchronization of frames based on the detection of the reference pattern of the signal; Means for extracting the reference symbol and the at least one protection range of the received multipoint modulated signal received on the basis of frame synchronization in order to generate the at least one useful symbol; Means for performing a Fourier transform in order to offer a sequence of spectra from the at least one useful symbol; and Means to eliminate the mapping of the sequence of spectra in order to offer a bit stream.
39. 39. The apparatus according to claim 38, further including means for performing a fast automatic gain control of the received converted-reduced multiple carrier modulated signal mentioned before said amplitude demodulator.
40. 40. The apparatus according to claim 38, wherein said amplitude demodulator includes means for calculating an amplitude of the modulated multicarrier signal mentioned using the alphamax + betamin method.
41. 41. The apparatus according to claim 38, further including means for sampling the respective amplitudes of the aforementioned received converted-reduced multiple carrier modulated signal, wherein said amplitude demodulator includes means for comparing said sampled amplitudes with predetermined threshold. in order to generate a sequence of bits.
42. 42. The apparatus according to claim 41, wherein said means for sampling includes means for additional sampling of the aforementioned received converted-reduced multiple carrier signal.
43. 43. The apparatus according to claim 38, further including means for applying a result of the frame synchronization for a frame in the aforementioned multi-carrier modulated signal for at least one subsequent frame in the aforementioned multi-carrier modulated signal. .
44. 44. The apparatus according to claim 32 further including means for detecting the location of the reference pattern of said signal based on an occurrence of a maximum value of an output of the correlation signal of said correlator.
45. 45. The apparatus according to claim 44, further including means for weighing a plurality of maximum values of the mentioned correlation signal in such a way that the maximum value that occurs first is weighed more firmly than any maximum value that occurs later; and means for detecting the aforementioned location of the reference pattern of the aforementioned signal based on the greater of the aforementioned heavy maximum values.
46. 46. The apparatus according to claim 45, further including means for deactivating said means for performing said frame synchronization for a predetermined period of time after having connected a receiver including said apparatus for frame synchronization.