WO2014122086A1

WO2014122086A1 - Method for the synchronous transmission of messages

Info

Publication number: WO2014122086A1
Application number: PCT/EP2014/052008
Authority: WO
Inventors: Jaroslaw Kussyk
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-02-07
Filing date: 2014-02-03
Publication date: 2014-08-14
Also published as: CN105052103A; EP2954651A1; DE102013201999A1

Abstract

The invention relates to a method for the synchronous transmission of messages (D1, D2). The messages (D1, D2) are composed of a sequence (C1, C2) of information bits and are transmitted in the form of sub-symbols (SU1, SU2) by means of a synchronous multi-carrier transmission method. Said sub-symbols (SU1, SU2) are composed of individually modulated carrier signals (TA1, TA2), wherein the carrier signals (TA1, TA2) are associated with different sub-channels (B) of a transmission channel (UE). The first carrier signals (TA1, TA2) that are used for forming a first sub-symbol (SU1) are arranged in a frequency time range for the transmission such that a protection interval (Tg) is created within a signal transmission period (T). The protection interval (Tg) is then used for transmitting at least one second sub-symbol (SU2), wherein the at least second sub-symbol (SU2) is formed from second carrier signals (TA2) that differ from the first carrier signals (TA1) of the first sub-symbol (SU1). Said first carrier symbols (TA1) of the first sub-symbol (SU1) may optionally be partially overlapped in the time and/or frequency range by at least the second carrier signals (TA2) of the at least second sub-symbol. The method ideally and simply combines an increase in interference immunity for a transmission of messages (D1, D2) with good spectral efficiency that is provided by a synchronous transmission of messages (D1, D2) via a plurality of sub-channels (B) of a transmission channel (UE). DRAWING: No translation required.

Description

Besehreibung

Method for the synchronous transmission of messages

Technical area

The invention relates to a method for the synchronous transmission of messages. The messages are composed of a sequence of information bits and are transmitted by means of a so-called synchronous multicarrier transmission method in the form of sub-symbols. These sub-symbols are composed of individually modulated carrier signals, wherein the carrier signals are assigned to different subchannels of a transmission channel.

State of the art

Communication system or communication network is in telecommunications usually a device or an infrastructure for transmitting information, which may be present, for example, in the form of composed of a sequence of information units or information bits messages. In this case, a communication system establishes a communication link between a plurality of terminals or between one or more transmitters and one or more receivers. If a same clock is used by transmitters and receivers, or if the transmitter and receiver, each comprising a sufficiently accurate clock source, synchronize or process at the beginning or during the transmission, the transmitter and receiver process the information units and / or signals to be transmitted or received synchronously or quasi-synchronous with each other (ie with an allowable deviation in synchronicity), this is referred to as synchronous transmission. This means that the transmission of a message or of the individual units or information bits of a message between the transmitter and receiver is synchronized in time or quasi-synchronized by means of a clock signal - ie, there is a permissible deviation. synchronization in the transmission of a message or of the individual information units of the message between transmitter and receiver.

In the transmission of messages, it is often important for economic reasons to replace existing communication systems such as e.g. Optimum use of telecommunications networks, telephone networks, radio networks or electricity grids. One possibility for achieving a higher transmission rate in a communication system, in particular for frequency-selective fading, is, for example, a use of a so-called multi-carrier transmission method or a so-called multi-carrier modulation. In this case, a transmission channel is divided into several narrow-band subcannals, which are then assigned so-called carrier signals. If a message in the form of a sequence of information bits is to be transmitted, the bit stream to be transmitted is split among the several different carrier signals and simultaneously transmitted via the narrowband subcannels. For synchronous transmission of the message so-called subsymbols are used as information carrier, which are composed of individually modulated carrier signals. These modulated carrier signals are assigned to the different subchannels of the transmission channel. The modulated carrier signals are thereby formed in the sub-channels by modulating or keying the respective carrier signal through a respective element (e.g., bit, etc.) of the information sequence or message.

However, the narrowband nature of the subchannels in a multicarrier transmission method can create several interrelated problems or disruptions in the transmission of messages. These problems must be considered in a communication system design. Such interferences may be, for example, so-called inter-channel interferences or inter-channel interferences (ICI), in which interference between the carriers may occur in the transmission of a message. Furthermore, so-called intersymbol interference (ISI) can occur, in particular in a transmission channel with increased temporal dispersion. So-called intersymbol interferences, which are also referred to as symbol crosstalk, are interference between temporally successive transmitted or to be received subsymbols and can be caused for example by limiting the bandwidth of the transmission channel in frequency-selective fading or by multipath signal propagation.

In addition, in a multicarrier transmission method, a peak-to-average ratio (PAR) can be greatly increased in a sum signal over all subchannels. The so-called peak-to-average ratio (PAR), which is also referred to as crest factor or crest factor, is a measure of the ratio between peak value and effective value of a signal to be transmitted.

Particularly in the case of uncoordinated signal transmission over a plurality of subchannels in a multicarrier transmission method, the interchannel interference or ICI problem is solved by suitably placing the subchannels with a sufficient protective distance to adjacent subchannels - such as in the so-called frequency division or carrier frequency method or frequency division Multiplexing (FDM). In the frequency division multiplex method, several elements or bits of a message can be transmitted to several carrier signals at the same time. For this purpose, a bandwidth available overall for the transmission (eg frequency band, transmission channel) is subdivided into different, individual narrowband frequency bands - ie subchannels - which are separated from one another by a small, unused guard band. As a result, a sufficiently good attenuation of a signal and / or a disturbance at frequencies outside the frequency band used can be achieved, for example by filtering. A more and more frequently used special implementation of frequency division multiplexing is the so-called orthogonal frequency division multiplexing or Orthogonal Frequency Division Multiplexing (OFDM). In orthogonal frequency division multiplexing, multiple orthogonal carriers will be used for the transmission of digital data or messages. Each carrier is first separately modulated and may carry information of one or more bits. From a sum of all modulated carriers or carrier signals, a signal curve of the so-called sub-symbol is then formed within a temporal window, whereby a large number of bits can be transmitted in parallel in the orthogonal frequency-division multiplexing method. Due to the orthogonality of the carrier, a so-called crosstalk is further reduced between signals to be transmitted, which are modulated onto adjacent carriers. That is, orthogonal frequency division multiplexing achieves better use of the frequency spectrum and hence efficient synchronous transmission of messages, but the problem of intersymbol interference and a large increase in the peak-to-average ratio still persists.

For example, to improve intersymbol interference, sophisticated equalization algorithms can be used, e.g. based on an estimate of a channel condition. This is for transmission channels with strong interference or with increased temporal dispersion such as. in the case of so-called power line communication (PLC) or distribution line carriers (DLC) - ie in the data transmission via power grids, certain radio channels or point-to-multipoint transmissions only with increased effort possible.

Another possibility for reducing or preventing intersymbol interferences is, for example, to introduce a guard interval between consecutive sub-symbols in the transmission in a frequency channel, as used for example in a transmission based on an orthogonal frequency-division multiplexing method. In about- However, transmission channels with an increased temporal dispersion such as in PLC, DLC, etc., a relatively large guard interval - in comparison with a duration of a sub-symbol to be transmitted - must be selected. This reduces the efficiency of channel usage in the time domain.

Furthermore, the large increase in the so-called peak-to-average ratio (PAR) of the sum signal of all subchannels represents a major challenge, in particular in the case of FDM and OFDM. This increase makes it possible to use a dynamic range or a performance of a transmission amplifier only with low efficiency , That it must be increased to increase the efficiency of the dynamic range of such an amplifier, for example, to be able to transmit levels in the individual subchannels on a same level as e.g. For signals with low PAR and thus the receiving side to achieve a similar signal-to-noise ratio. Increasing the dynamic range of the amplifier, however, involves additional hardware costs.

For example, to obtain a low peak-to-average ratio for FDM or OFDM, Han, Seung Hee; Lee, Jae Hong. An Overview of Peak-to-Average Power Ratio Reduction Techniques for Multicarrier Transmission. IEEE Wireless Communications, Vol. 12, Iss. 2, pp. 56-65, April 2005. Various methods such as the introduction of a special coding in the subchannels, a limitation of signal peaks with subsequent filtering and receiving side bit error correction, etc. known. However, these methods mentioned in the above-mentioned document have the disadvantage that the peak-to-average ratio can only be reduced by means of additional expenditure for eg coding, filtering, etc. or by additional transmission of accompanying information for individual transmitted subsymbols. Furthermore, losses in the channel utilization efficiency and / or a reduction of the interference immunity, especially in OFDM, are accepted. In addition, in particular, a limitation of signal peaks, for example, by a non-linear operation in turn Promote or enhance subchannel crosstalk or interchannel inference.

Presentation of the invention

The invention is therefore based on the object of specifying a method for the synchronous transmission of messages by means of a synchronous multicarrier transmission method, in which messages are transmitted with a good spectral efficiency and with a lower peak-to-average ratio, and which has a high robustness to intersymbol - Interference and inter-channel interference.

This object is achieved by a method of the type mentioned above with the features according to the independent claim. Advantageous embodiments of the present invention are described in the dependent claims.

According to the invention, the object is achieved by a method of the type mentioned in which first carrier signals, which are used for forming a first sub-symbol, are arranged in a frequency-time domain such that a guard interval is formed within a signal transmission period , This guard interval is then used for a transmission of at least one second subsymbol. This second sub-symbol is formed from second carrier signals, which differ from the first carrier signals of the first sub-symbol. The main aspect of the solution proposed according to the invention is that the method according to the invention combines a good spectral efficiency of the synchronous transmission of messages over a plurality of subchannels with the advantages of a so-called frequency hopping spread spectrum or Frequency Hopping Spread Spectrum (FHSS). The advantages of the FHSS are in particular a low peak-to-average ratio (PAR) and a high robustness against interferences such as intersymbol interference and interchannel interference. Inferences. Frequency Hopping Spread Spectrum (FHSS) is a method of spread spectrum technology in which a carrier frequency used for transmission of a message is spun / discretized several times within a transmission period a so-called frequency hopping sequence for the subchannels used is changed.

By the method proposed according to the invention, a reduction of the peak-to-average ratio, in particular over conventional synchronous and asynchronous multicarrier transmission methods such as FDM or OFDM, etc., is achieved with a sufficiently large guard interval. Furthermore, an increase in the interference immunity of the transmission is achieved above all by a better utilization of an existing dynamic range or by an increase in the transmission level. This can be used advantageously to distribute the power evenly over the signal transmission period for the transmission of the entire subsymbols, wherein a subsymbol is formed in a certain signal transmission period. This makes the transmission more robust, particularly to non-Gaussian combined narrowband and pulse noise in the transmission channel. Due to the uniform distribution of the power, the peak-to-average ratio within the individual sub-symbols which are shifted in time with respect to one another is advantageously also reduced, the method according to the invention having an improved or higher transmission rate than a conventional method with frequency-hopping spread (eg FHSS, etc.). The inventive method thus enables a robust transmission of messages based on a synchronous multi-carrier transmission method (eg OFDM, etc.) in systems with simultaneous and possibly (quasi) synchronous forwarding of messages or data packets such as Powerline Communications (PLC), Distribution Line Carriers ( DLC), etc., which have an increased temporal signal dispersion. It is advantageous if the first carrier signals of the first sub-symbol in the time and / or in the frequency domain of at least the second carrier signals of the at least second sub-symbol are partially overlapped. The carrier signals used to form the respective subsymbols can be chosen such that a time-frequency representation of the respective carrier signals does not overlap or only to a reasonable extent with time-frequency representations of further carrier signals. A reasonable degree of overlap of carrier signals results from compliance with the intended temporal and spectral guard interval between adjacent modulated carrier signals in order to avoid intersymbol interference and / or interchannel interference.

This means that spectral bandwidths of modulated carrier signals can overlap if the time intervals have been chosen to be sufficiently large. At the same time, it is thereby also possible for temporal courses of modulated carrier signals to have at least partial overlaps, if the spectral distances have been chosen to be sufficiently large. Thus, a temporal and / or spectral interleaving of adjacent sub-symbols within a signal transmission period is possible by a partial overlap in the time and / or frequency range of carrier signals, wherein the guard interval is maintained. The overlap may not extend from overlapping between sub-symbols to interleaving a sub-symbol having a plurality of preceding and / or subsequent sub-symbols. This can advantageously the

Guard interval can be used for a transmission of sub-symbols. It distributes the power of a message to be transmitted evenly within the signal transmission period, reduces the peak-to-average ratio, and improves the interference immunity of the transmission by making better use of the available dynamic range or by increasing the transmission level. Appropriately, only a portion of all possible carrier signals is used to form sub-symbols within a sub-symbol duration. In this way, a smaller number of modulated carrier signals is summed and thus very easily further reduces the peak-to-average ratio of a sum signal in the transmission channel.

It is favorable if harmonic signals from a discrete Fourier transformation with a window function, so-called wavelets or orthogonal signals, are used as carrier signals. Carrier signals are usually periodically changing technical quantities (eg AC voltage, radio wave, etc.) with characteristic parameters (eg frequency, amplitude, phase, etc.) and usually provide a reference signal for demodulating a previously for the purpose of transmitting a message element (eg bit, etc.) modulated carrier signal. In the field of telecommunications, for example, for the transmission of messages or message elements harmonic signals (eg sinusoidal signals, etc.) are used from a discrete Fourier transform with a so-called window function, this example the signal is folded in the frequency domain with the frequency spectrum of the window function. So-called window function can e.g. have different shapes in the time domain, such as e.g. Rectangle windows, Gaussian windows, etc. and are distinguished in the frequency domain by a concentrated around a center frequency spectrum with a fixed bandwidth with respect to its maximum. By a window function, a signal is usually displayed at the beginning of the window and hidden again at the end of the window, whereby a so-called frequency-leakage effect is prevented when using the discrete Fourier transformation.

Alternatively, so-called wavelets may be used as carrier signals, which designate the underlying functions of a continuous or discrete wavelet transformation. The wavelet transformation represents a family of linear time-frequency transformations and can eg be regarded as an improvement of the short-time Fourier transform. In this case, a signal is divided into temporally narrow and only very few oscillations comprehensive signal elements, which are referred to as wavelets. Wavelets are used in particular for analyzing very unsteady signals (eg signals in time-invariant transmission channels, speech signals, image signals, etc.) or filtering noisy signals.

Furthermore, carrier signals may be (weakly) orthogonal signals or signals having reasonable cross-correlation properties. For (weak) orthogonal signals, the scalar product is (nearly) zero - i. the signals are (nearly) normal to each other. Orthogonal signals are e.g. used in transmissions of messages according to the OFDM method as carrier signals. For signals with reasonable cross-correlation properties, cross correlation - i. for describing a correlation between two signals at different time shifts - set to obtain carrier signals suitable for transmission.

In a preferred development of the method according to the invention, the discretely modulated subsymbols are formed by means of an inverse time-frequency transformation such as an inverse discrete Fourier transform with a window function, inverse wavelet transformation, etc.). These are then assembled into a time-discrete signal after a parallel-to-serial conversion. The parallel-to-serial wall can be done with adjacent sub-symbols - with at least one preceding sub-symbol and / or with at least one subsequent sub-symbol. An assembly to the time-discrete signal can then also be carried out, for example, at least partially overlapping. Thereafter, the discrete-time signal is converted into an analog signal to be transmitted for coupling into the transmission channel. This analog signal is then possibly amplified, adapted as a transmission signal in the transmission channel coupled and so easily transferred to a receiver.

It is furthermore advantageous if a sequence of modulated carrier signals to be transmitted is formed according to at least one frequency hopping sequence. In this simple manner, a number of the modulated carrier signals is further reduced or a thinning of subsymbols takes place. On the one hand, this reduces inter-channel interference and, on the other hand, further reduces the peak-to-average ratio of the sum signal or the (analog) signal to be transmitted. As frequency hopping or frequency spreading is usually understood in telecommunications a method in which a narrow-band signal is converted into a signal with a larger bandwidth than necessary for the information transfer. The transmission energy, which was previously concentrated in a small frequency range, is thereby divided over a larger frequency range. Of the frequency hopping sequence while a sequence of frequency change in the frequency hopping is specified.

It is also advantageous if an insert in a transmission system with simultaneous forwarding of data packets is provided. In such transmission systems, the same data packets are transmitted by means of modulated transmission signals from different transmitters quasi-synchronously to one or more receivers via a transmission channel. The transmission channel in such a transmission system can e.g. be highly dispersive in time, which in particular when using an OFDM-based transmission must be paid to a greater temporal protection interval. In this way, the same messages can be transmitted by several transmitters quasi-synchronously to one or more receivers and thus a transmission system can be used optimally and efficiently.

In a further development of the invention, an analog received signal is sampled at the receiving end and then, in particular under the condition that on one side of the receiver a Synchronization with a time frame for the individual transmitted subsymbols is present, these transmitted sub- bols decomposed by means of a time-frequency transformation into their received carrier signals. Thereafter, a demodulation and after a so-called Deinterleaving a decoding is performed. The so-called deinterleaving is the opposite of interleaving, in which to be transmitted data or sub-symbol are nested. During deinterleaving, this interleaving or overlapping of the subsymbols is reversed on the receiver side. Ideally, a noise suppression technology based on a non-linear estimation is used to receive the signals. In this simple manner, interference signals in the received signal can be suppressed on the receiver side. Only useful components of the received signal are evaluated or further processed, which are distinguished from estimated interference components in a time-frequency distribution of the received signal.

Brief description of the drawing

The invention will now be described by way of example with reference to the accompanying drawings.

They show schematically:

FIG. 1 shows an exemplary constellation of sub-symbols in FIG

Frequency-time range in a conventional OFDM method Figure 2a shows an exemplary constellation of subsymbols in

Frequency-time range according to the inventive method

FIG. 2b shows an exemplary constellation of two exemplary modulated carrier signals in the time domain according to the method according to the invention FIG. 3 shows an exemplary constellation of sub-symbols with partial overlap in the frequency-time domain according to the method according to the invention

FIG. 4 shows an exemplary constellation of sub-symbols with a reduced number of carrier signals in the frequency-time domain according to the method according to the invention

FIG. 5 shows an exemplary transmission system for simultaneous

Message transmission according to the method of the invention

Embodiment of the invention

FIG. 1 schematically shows an exemplary constellation of sub-symbols SU in a frequency-time domain in a conventional synchronous multicarrier transmission method such as so-called orthogonal frequency division multiplexing or OFDM, in which a constant use of the frequencies fj is present. In this case, a time domain t is plotted on a horizontal coordinate axis and a frequency domain f is plotted on a vertical coordinate axis. A transmission channel UE, which is used for a transmission of messages in the form of a sequence of information elements or bits, in this case has a bandwidth which is limited by an upper limit frequency f _BÜ and a lower limit frequency f _BL . This bandwidth or this transmission channel UE is subdivided into different, narrow-band subchannels, with a subchannel B being shown by way of example in FIG.

This subchannel B is assigned, for example, a carrier signal TA with a carrier frequency fj, onto which a respective information element is modulated. By this Aufmodulation then, for example, a modulated carrier signal TA is formed. In this case, the subsymbols SU to be transmitted are made, for example, from individual modulated carrier signals TA. whose formation is started, for example, at a time ti and terminated at a time ti + Ts, where the variable Ts represents a sub-symbol duration. A beginning of the formation of a next subsymbol SU is then shifted by a duration of a guard interval Tg - ie the formation of the next subsymbol begins only after a signal transmission period T, which is composed of the subsymbol duration Ts and the guard interval Tg, in particular to prevent interchannel interference , A signal course in the time domain of a subsymbol SU is composed, for example, in OFDM from a sum of all modulated carrier signal TA. In this case, the sum signal as a disadvantage then has a relatively high peak-to-average ratio and, in particular, in the case of channels with increased temporal dispersion, additional intersymbol interference.

Such disadvantages or disturbances are solved by the method according to the invention shown schematically in FIG. 2a by means of an exemplary constellation of subsymbols SU1, SU2 in the frequency-time domain f, t. FIG. 2b shows, in an exemplary and schematic manner, an associated constellation of two exemplary modulated carrier signals TAI, TA2 in the time domain t.

FIG. 2a again shows a coordinate system in which a time domain t is plotted on a horizontal axis and a frequency domain f is plotted on a vertical axis. For the transmission of a message Dl, D2 a transmission channel UE is used, which has a bandwidth which is formed by an upper limit frequency f _BÜ and a lower limit frequency f _BL . In this case, the transmission channel UE is subdivided into subchannels, wherein in turn a subchannel B with a carrier frequency fj is shown in FIG. 2a by way of example. This sub-channel B is used, for example, for the transmission of the modulated first carrier signal TAI, while an example, an example modulated second carrier signal TA2 is transmitted in a sub-channel with a carrier frequency fj + 1. A sequence of carrier signals TAI, TA2 to be transmitted can be be formed, for example, according to at least one so-called frequency hopping sequence.

The first modulated carrier signal TAI is formed, for example, by modulation of a first carrier signal TAI by a first element Cl of an information sequence of the message Dl, D2 to be transmitted. The second modulated carrier signal TA2 is generated, for example, by modulation of a second carrier signal TA2 by a second element C2 of the information sequence of the message Dl, D2 to be transmitted. In each case to be transmitted sub-symbols SUl, SU2 are composed of the individual modulated carrier signals TAI, TA2. As carrier signals TAI, TA2, e.g. harmonic signals from a discrete Fourier transform with a rectangular or other window function, so-called wavelets or other mutually orthogonal signals or signals can be used with reasonable cross-correlation properties.

A formation of an exemplary first subsymbol SU1 is started at a time ti and the first carrier signals TAI used for this purpose are arranged in the frequency-time domain such that within a signal transmission period T an intended temporal guard interval Tg to the next subsymbol SU3, from which the same carrier frequencies fj, fj + 2, etc. or carrier signals TAI are used, is complied with. For a transmission of the second subsymbol SU2, of which the carrier signals TA2 and the carrier frequencies fj + 1, fj + 3, etc. are used, then the guard interval Tg is used.

That is, by the method according to the invention, the first subsymbol SU2 is transmitted in a subsymbol duration Ts which, for example, lasts from a time ti to a time ti + Ts. The transmission of, for example, the adjacent second subsymbol SU2 whose second carrier signals TA2 or carrier frequencies fj + 1 differ from the first carrier signals TAI or carrier frequencies fj of the first subsymbol SU1, are transmitted in the guard interval Tg. As a result, for example, in the signal transmission period T, an equal number of sub-symbols SU1, SU2 are transmitted, as in the conventional OFDM method in FIG. 1, but an equal resistance to intersymbol interferences is retained and, at the same time, the peak-to-average Ratio of the respective sum signal of the respective subsymbol SU1, SU2 reduced as will be explained below with reference to Figure 2b. FIG. 2b shows, by way of example, the constellation of the two modulated carrier signals TAI, TA2 shown by way of example in FIG. 2a in the time domain or a temporal course of the corresponding signals S1, S2 belonging to the subsymbols SU1, SU2 in the time domain. In this case, in a top coordinate system in which a time range t is shown on the horizontal axis and an amplitude A of the first signal S1 is shown on the vertical axis, a time profile of the first subsymbol SU1 is shown, which is formed by the first modulated carrier signals TAI becomes. At a time ti, the timing of the first modulated carrier signal TAI is started and ended at a time ti + Ts. The transmission of the first modulated carrier signal TAI is repeated with a period of the duration of the signal transmission period T. The amplitude A of the first modulated carrier signal TAI has, for example, a fluctuation between the values + A and -A.

In a coordinate system shown in the middle in FIG. 2b, which again has a horizontal time axis and on the vertical axis an amplitude A of a second signal S2, a time profile of the second subsymbol SU2, which is formed by the second modulated carrier signals TA2, is shown , A timing of the second modulated carrier signal TA2 is e.g. at a time ti + Ts, thus after completion of the transmission of the first carrier signal

TAI, started and, for example, at a time ti + Ts + Tg - ie at the end of the signal transmission period T - terminated. That is, for the transmission of the second modulated carrier signal TA2 For example, the guard interval Tg is used without there being - in the example shown in FIGS. 2a and 2b - a temporal overlap of the modulated carrier signals TAI, TA2. For example, the amplitude A of the second modulated carrier signal TA2 also has a fluctuation between the values + A and -A.

In a lowermost coordinate system in FIG. 2b, a time profile of a sum signal s (t) is then shown by way of example, wherein the horizontal axis again shows the time domain t and the vertical axis shows an amplitude A of the sum signal s (t). For example, it can be seen from this coordinate system that a value of the amplitude A has the same variation between + A and -A as the signals Sl, S2 of the first and second modulated carrier signals TAI, TA2, respectively, thus representing the e.g. a peak-to-average ratio of the sum signal s (t) is kept low and a capacity of the transmission channel can be optimally and efficiently utilized. Furthermore, it can be seen from the example shown in FIG. 2b (from the lowest coordinate system) that the first modulated carrier signal TAI and the second modulated carrier signal TA2 repeat periodically in the time domain, the second modulated carrier signal TA2 being inserted into the duration of the guard interval Tg is. In the illustrated example, the modulated carrier signals TAI, TA2 and the corresponding subsymbol SU1, SU2 do not overlap.

However, it is possible that an acceptable or slight or partial overlap occurs in the frequency-time domain between the carrier signals TA21, TA22, TA23, TA24, TA25. A related constellation of sub-symbols SU21 is shown schematically and by way of example in FIG. FIG. 3 again shows a coordinate system in the frequency-time domain, with a horizontal time axis t and a vertical frequency axis f. The transmission channel UE with upper and lower limit frequency f _BÜ and f _B L as well as the carrier frequencies fj used for the subchannels B are again entered as examples on the frequency axis f. In the exemplary subchannel B, a first modulated carrier signal TA21 of a subsymbol SU21 is formed, for example, by means of a first carrier signal TA21 having a carrier frequency fj by modulating an information element C1. The formation of the subsymbol SU21 is started at a time ti and ends at a time ti + Ts, where the variable Ts again represents the subsymbol duration Ts. Taking into account a corresponding spectral distance df, however, the transmission of a second modulated carrier signal TA22 can already be started at a time ti + dt, the duration dt being smaller than the subsymbol duration Ts. The time ti + Ts of the first modulated carrier signal TA21 may be, for example, ti + 2dt - as shown in Fig. 3. That is to say, at the end of the transmission of the first modulated carrier signal TA21, for example, one half of the second carrier symbol TA22 has already been transmitted, although attention must be paid to a corresponding distance df in the spectral / frequency range. The carrier frequency fj + 2 of the second modulated carrier signal TA22 is to be selected, for example, such that there is no or only an acceptable overlap in the spectral / frequency range. This is ensured, for example, when the spectral distances df between the respective carrier signals TA21, TA22 are selected to be sufficiently large.

Furthermore, for example, a transmission of a third modulated carrier signal TA23 can be started at a time ti + Ts = ti + 2dt. This third modulated carrier signal TA23 also has a sufficient temporal and spectral distance dt, df to the other modulated carrier signals TA21, TA22, in which, for example, a carrier frequency fj + 4 is used, and for example the guard interval Tg is selected to be correspondingly large. Furthermore, further modulated carrier signals TA24, TA25 of sub-symbols adjacent to the first modulated carrier signal TA21, for example, may be transmitted at least partially in the guard interval until a time ti + Ts + Tg corresponding to the signal transmission period T2 again a subsymbol SU21 of the first Carrier TA21 is transmitted. In this way, as shown by way of example in FIG. 3, temporal and / or spectral interleaving of adjacent subsymbols SU31 with different carrier signals TA21, TA22, TA23, TA24, TA25 is possible within the signal transmission period T2 while maintaining the guard interval Tg. In this case, the overlapping can not extend from an overlap such as, for example, in FIG. 2a between sub-symbols SU1, SU2 to interleaving of a sub-symbol SU21 with two preceding and / or two subsequent sub-symbols, as shown in FIG. Thus, a power of a signal to be transmitted can be distributed more uniformly within a signal transmission period T2. Furthermore, it very simply reduces the peak-to-average ratio and improves the interference immunity of the transmission by making better use of the available dynamic range or by increasing the transmission level.

Furthermore, there is the possibility that only a part of all possible carrier signals TA31, TA32 are used for the formation of subsymbols SU31, SU32 within the subsymbol time Ts in order to further reduce, for example, the peak-to-average of a respectively resulting sum signal, since such a small number of modulated carrier signals TA31, TA32 are summed up. Such an example is shown schematically in FIG. FIG. 4 again shows a coordinate system in the frequency-time domain, with a horizontal time axis t and a vertical frequency axis f. On the frequency axis f is again exemplified the transmission channel UE with upper and lower limit frequency f _BÜ and f _B L and the subchannels

B used carrier frequencies fj registered. The adjacent carrier frequencies fj used for the carrier signals TA31, TA32 are separated from one another by a spectral distance df. For example, a first carrier signal TA31 is used to form a first sub-symbol SU21. For a second sub-symbol SU22, for example, a second carrier signal TA32 is used. The first carrier signal TA31 is a first carrier frequency fj and the second carrier signal TA32 a second carrier frequency associated fj + 1, which have a spectral distance df to each other. As shown by way of example in FIG. 4, the carrier frequencies fj, fj + 1 and thus the first and second carrier signals TA31, TA32 are further apart in the frequency range than in the preceding examples, which are shown in FIG. 2a or FIG possible carrier signal TAx is used.

The formation of the exemplary first subsymbol SU31 is performed as described e.g. in FIG. 2a at a time t.sub.i and the first carrier signals TA31 used for this purpose are arranged in the frequency-time range in such a way that within a signal transmission period T an intended temporal guard interval Tg arises for the next subsymbol to be transmitted, from which e.g. the same carrier frequency fj, etc. or carrier signals TA31 are used. For a transmission of the second subsymbol SU32, from which the carrier signals TA32 and the carrier frequencies fj + 1 are used, the guard interval Tg is then used again. A sequence of carrier signals TA31, TA32 to be transmitted can also be formed, for example, according to at least one so-called frequency sequence.

In the example illustrated in FIG. 4, too, nesting or overlapping of a subsymbol SU31 with up to two preceding and / or two subsequent subsymbles SU32 is possible, in addition to a reduced peak-to-average ratio of the respective summation signals to achieve a more even distribution of power within the signal transmission period T.

FIG. 5 schematically shows an exemplary transmission system for simultaneous, synchronous message transmission or signal transmission according to the method according to the invention. On a sender side, for example, two identical messages Dl, D2 are simultaneously / quasi-synchronously transmitted by two different transmission devices into a unit BSM1 or BSM2 for processing these messages D1, D2. fed. The messages D1, D2 are generally the same, but are transmitted by different transmitters or transmission branches, for example in the context of a simultaneous forwarding procedure. A simultaneous forwarding procedure means, for example, the following: a first transmission device sends an initial message with a number of remaining possible forwarding or re-transmissions. Copies of the initial message are then received as messages D1 or D2 from at least two further transmission devices and the number of retransmissions both in the initial message and in the copies is decremented accordingly. Then, as shown by way of example in FIG. 5, the copies of the initial message modified in this way are forwarded as messages D 1, D 2 simultaneously. This retransmission process can be continued by the previous transmission facilities or other arbitrary transmission facilities until the number of possible retransmissions of the initial message is zero.

All these retransmissions occur (quasi) synchronously within the framework of a given time frame, and the messages D 1, D 2 which have been retransmitted are thus identical and were formed from the initial message according to defined rules. Quasi-synchronous means that, for example, the channel delays in a reception of the (intial) message before retransmission and a frequency drift of the clock sources in the transmission directions are not taken into account. However, the effects of these deviations in the synchronicity can be limited or controlled by a suitable selection of the guard intervals between the sub-symbols SU1, SU2 and the clock sources and can thus be kept correspondingly low - ie. not equal to zero, but reasonably low, whereby the transmission is just not synchronous, but quasi-synchronous.

In FIG. 5, by way of example, there are two transmission devices which, for example, consist of several units, such as the unit BSM1, BSM2 for processing messages, a transformation unit TRI, TR2 and a coupling unit KE1, KE2 consist. However, it is also possible for the procedure or the application of the method according to the invention to use further transmission facilities for (quasi) synchronous forwarding of the same messages D1, D2 or else only one transmission facility can be used - in FIG. 5, for example, the upper branch on the sender side - to use for forwarding a (first) message Dl.

In the units BSM1 and BSM2 for processing messages D1, D2, in each case a so-called bit or symbol modulation mapping is carried out, as well as a so-called interleaving and a channel coding. This means that from the messages Dl, D2 to be transmitted, corresponding sequences of information elements C1, C2 (eg information bits, information symbols) to be transmitted are respectively generated in the units BSM1, BSM2 for processing messages D1, D2, which if necessary are interleaved by interleaving and can be channel coded as protection of transmission errors. In the

Units BSM1, BSM2 for processing messages D1, D2, the sequences of information elements to be transmitted C1, C2 are prepared for a proposed modulation of the carrier signals TA41, TA42 using the method according to the invention - i. precoded and possibly with additional information e.g. provided for a receiver-side demodulation and / or decoding.

The sequences of information elements C1, C2 are then forwarded to a transformation units TR1, TR2. In these transformation units TRI, TR2, for example, sub-symbols SU1, SU2 are first respectively formed using the method according to the invention-as illustrated for example in FIGS. 2a, 3, 4 -using the carrier signals TA41, TA42. In this case, for example, while maintaining a guard interval Tg and optionally a corresponding spectral distance df using the carrier signals TA41, TA42, these carrier signals TA41, TA42 da- are the same but are used in different transmission devices. In each case, information elements are modulated onto the carrier signals TA41, TA42 and thus sub-symbols SU1, SU2, which are modulated in a discrete manner, are generated. In this case, the discretely modulated subsymbols SU1, SU2 are formed, for example, by means of an inverse time-frequency transformation such as, for example, an inverse discrete Fourier transformation, an inverse wavelet transformation, etc. Then, so-called signal syntheses are performed in the transformation unit TRI, TR2 after a parallel-to-serial conversion. In this case, adjacent sub-symbols SU1, SU2-for example, with at least one preceding subsymbol SU1, SU2 and / or with at least one subsequent subsymbol SU1, SU2-are combined to form a discrete-time signal. Assembling to discrete-time signal can for example also be partially overlapping. Thereafter, the respective discrete-time signals are still converted into analog signals sl (t), s2 (t), which are then coupled via a respective coupling unit KE1, KE2 - possibly amplified and adapted - as transmission signals tsl, ts2 in the transmission channel UE and in this way be transmitted to a receiver side.

On the receiver side, an analog received signal rs is then received by a decoupling unit KA and forwarded to an optionally provided first interference suppression ST1. The analog received signal rs is subjected to a serial-parallel conversion SPW and then a transformation unit ZFT is a time-frequency transformation and a frequency channel separation by means of several different reference carrier signals rTA. In this case, assuming that there is a synchronization with a time frame for the individual subsymbols SU1, SU2 on the receiver side, the transmitted subsymbols SU1, SU2 are decomposed into their individual components or received carrier signals mTA with the aid of the time-frequency transformation. These received signals mTA can then be supplied to an optionally provided second interference suppression ST2 in the frequency-time domain. If the second interference suppression ST2 is present, it supplies a reception signal mTA 'reduced by one interference signal component as well as additionally an estimated interference component gSF to the next units of the transmission system. If the second interference suppression ST2 is missing, the received carrier signal mTA is forwarded directly to a demodulation and bit / symbol decision unit DM. The demodulation and bit / symbol decision unit DM then provides at its output individual elements rC of the received information / bit sequence which have been formed, for example, based on a hard and / or soft decision. These elements rC of the received information / bit sequence are then subjected to deinterleaving and channel decoding in a decoding unit DK, which then delivers a received message rD at the output.

By means of the transmission system shown in Figure 5, e.g. the same data packets or identical messages D1, D2 by means of modulated transmission signals tsl, ts2 of different transmitters quasi-synchronously to one or more receivers via a e.g. strongly dispersive transmission channel UE are transmitted. By using the method according to the invention on the transmitter side of the system, in particular in the respective transformation unit TRI, TR2, a high level of immunity to interference is achieved at a lowest possible peak-to-average ratio, in particular against inter-channel and intersymbol interferences.

Claims

claims

1. A method for the synchronous transmission of messages (Dl, D2), which are composed of a sequence (Cl, C2) of information bits, and which by means of a synchronous

Multi-carrier transmission method in the form of subsymbols (SU1, SU2) are transmitted, wherein the subsymbols (SU1, SU2) from individually modulated carrier signals (TAI, TA2) are assigned to which different subchannels (B) of a transmission channel (UE) are assigned, characterized in that the first carrier signals (TAI) used to form a first sub-symbol (SU1) are arranged in a frequency-time domain such that a guard interval (Tg) is formed within a signal transmission period (T), and this Protection interval (Tg) is used for a transmission of at least a second sub-symbol (SU2), which is formed from second carrier signals (TA2), which differ from the first carrier signals (TAI) of the first sub-symbol (SU1).

2. The method according to claim 1, characterized in that the first carrier signals (TA21) of the first sub-symbol (SU21) in the time and / or in the frequency range of at least the second carrier signals (TA22, TA23, TA24,

TA25) of the at least second sub-symbol are partially overlapped.

3. The method according to any one of claims 1 to 2, characterized

characterized in that to form subsymbols

(SU31, SU32) within a sub-symbol duration (Ts) only a part of all possible carrier signals (TA31, TA32) is used.

4. The method according to any one of claims 1 to 3, characterized

characterized in that as carrier signals (TAI, TA2) harmonic signals from a discrete Fourier Transformation with a window function, so-called Wavets or orthogonal signals are used.

Method according to one of claims 1 to 4, characterized in that the discretely modulated subsymbols (SU1, SU2) are formed by means of an inverse time-frequency transformation (TRI, TR2) and after a parallel-to-serial conversion (TRI, TR2) are combined to a discrete-time signal, and then that for a coupling (KE) in the transmission channel (UE), the time-discrete signal is converted into an analog signal to be transmitted (sl, s2).

Method according to one of Claims 1 to 5, characterized in that a sequence of modulated carrier signals (TAI, TA2) to be transmitted is formed in accordance with at least one frequency hopping sequence.

Method according to one of claims 1 to 6, characterized in that an insert is provided in a transmission system with simultaneous forwarding of data packets.

Method according to one of claims 1 to 7, characterized in that on the receiving side an analog received signal (rs) is sampled, that then the transmitted subsymbols by means of a time-frequency transformation (ZFT) into their received carrier signals (mTA) are decomposed, and that then a demodulation (DM) and after a so-called Deinterleaving a decoding (DK) is performed.

Method according to one of Claims 1 to 8, characterized in that a noise suppression technology (ST1, ST2) based on a nonlinear estimation is used for receiving the signals (rs, mTA).