DE10128353B4 - Digital message transmission method and system for carrying out the method - Google Patents

Abstract

Digital message transmission method in which the frequency spectrum of a transmission signal to be transmitted in a continuous series of transmission frames is expanded by means of spreading sequences consisting of N chips per transmission frame, and on the receiving side this widening of the frequency spectrum by forming the cross-correlation between the spreading sequences contained in the received signal and the identical copies of the ones generated in the receiving signal Sender spreading sequences used is reversed again, the transmitted information being detected on the receiving end from the correlation peak of the cross-correlation function formed and the synchronization being carried out independently of the data transmission on a separate synchronization channel, i.e. not using the spreading sequences, characterized in that for the transmission of further information the spread sequence c (t) impressed on the transmission signal on the transmission side in phase by verse Chiebungen is modulated by multiples of the chip duration Tc and that the cross-correlation function is used at the receiving end to detect this transmitted further information in such a way that the position of the correlation peak of this cross-correlation function is used to draw conclusions about the transmitted phase of the spreading sequence by using a synchronous to the transmission signal using the separate synchronization channel made segmentation of the received signal into time sections of the transmission frames and thus a generation of signal sections is carried out, each containing exactly one phase, and the segmented received signal is subjected to a correlation in which the identical signal section generated from the respective signal section and the reception side Transmitter used spreading sequence c (t) determines the cross-correlation function with its correlation peak position indicating the respective shift of spreading sequence c (t) in the transmission signal approx.

Description

The invention relates to a digital message transmission method in which the frequency spectrum of a transmission string to be transmitted in a continuous transmission signal spread by each consisting of N chips spreading sequences per transmission frame and the receiving side this expansion of the frequency spectrum by forming the cross-correlation between the spreading signals contained in the received signal and the receiving end produced, identical copies of the spreading sequences used in the transmitter is reversed again, the transmitted information detected on the receiving side from the correlation peak of the cross-correlation function formed and the synchronization is carried out independently of the data transmission on a separate synchronization channel, ie not using the spreading sequences.

The invention also relates to a system for carrying out the digital message transmission method.

Out EP 05 26 040 A2 a digital message transmission method is known in which the frequency spectrum of a transmission signal expanded by means of N chip spreading sequences and the receiving side, the expansion of the frequency spectrum by forming the autocorrelation between the received signal and a model signal is reversed, including the received signal with a model signal, which in his Time dependence with the spreading sequence used in the transmitter coincides, is correlated. In this message transmission method, the transmitted information is detected on the receiving side from the correlation peak of the autocorrelation formed and the synchronization is independent of the data transfer, not using the spreading sequence, but not on its own synchronization channel, but, as usual in GPS, by the navigation receiver even.

EP 05 08 621 B1 describes a method for processing L1 and L2 signals received from a GPS satellite. Each of the signals has a carrier signal to which a known pseudorandom P-code and an unknown code are modulated. The L1 and L2 signal is demodulated with a locally generated copy of the known P-code contained therein. Subsequently, a signal is derived from one of the demodulated signals associated with the unknown modulated code. The derived signal is combined with the other of the L1 and L2 signals, determining the relative phase of the other of the L1 and L2 signals from the combined signal. The relative phase is useful for estimating the location of the receiving position.

Out EP 0 777 129 A1 A GPS receiver is known which calculates its position by generating replicas of time signals transmitted by satellites. The propagation delay of signals from four satellites in known positions is measured. It is z. For example, an RDS receiver that receives FM signals to correct the local frequency reference is used.

At present, there are essentially three different areas of use for digital communication methods in which spreading sequences are used.

Spreading sequences are used in spread-spectrum transmission systems. Here, the spreading sequence serves to widen the frequency spectrum of the transmission signal. These transmission systems are often used in the military field. The spreading of the frequency spectrum by the spreading sequence causes the transmission signal to be hidden in the general noise level and the transmission signal to become insensitive to intended jamming.

In the receiver, the widening of the frequency spectrum is reversed by forming the autocorrelation of the spreading sequence. For this purpose, the received signal is correlated with an identical copy of the spreading sequence used in the transmitter. The transmitted information is in the polarity of the correlation peak of the cross-correlation function thus formed. By appropriate selection of the spreading sequence ensures that the cross-correlation peak is pronounced.

Spreading sequences are also used in "Code Division Multiple Access" (CDMA) systems. With multiple access ("multiple access") several users access a common transmission channel. In principle, time division multiple access (TDMA), frequency division multiple access (FDMA) or user-specific code (code division multiple access CDMA) respectively. In CDMA systems, each user receives a specific one Code that is realized as a spreading sequence. The spreading sequence thus serves in CDMA systems not only for widening the frequency spectrum, but also for user separation.

The user separation takes place in the receiver by correlation of the received signal with an identical copy of the user-specific spreading sequence which was used in the transmitter whose transmitted information is to be recovered in the receiver. The transmitted information is also here in the polarity of the cross-correlation peak, which is pronounced with a suitable selection of the spreading sequences used. The formation of the correlation in the receiver also suppresses the signals that originate from other users.

Spreading sequences are also used for synchronization or navigation. Since, with a suitable choice, the cross-correlation functions of spreading sequences have pronounced correlation peaks, they are very well suited for synchronization tasks. Spreading sequences are used in a variety of digital message transmission methods for synchronization, for example, for frame, symbol and bit synchronization. In addition, spreading sequences are also used in navigation, for example in the "Global Positioning System" (GPS) or in the planned European navigation system GALILEO. In navigation, the problem of positioning is attributed to the synchronization problem.

In all three applications described, the receiver performs a correlation of the received signal with an identical copy of the spreading sequence used in the transmitter. In the first two applications, "Spread Spectrum" and CDMA transmission system, the polarity of the cross-correlation peak formed in the receiver is used for information transmission. When using spreading sequences for synchronization, on the other hand, one uses the position of the cross-correlation peak.

In spread-spectrum and CDMA transmission systems, the spreading sequences used can in principle also be used for synchronization. Frequently, however, the synchronization takes place independently of the data transmission on a separate "synchronization channel". In this case, the spreading sequences are not used for synchronization, but are used exclusively for data transmission, expansion of the spectrum and / or user separation. Thus, only the polarity of the cross-correlation peak is evaluated in the receiver. The additional information that is in the position of the cross-correlation peak is not used.

In conclusion, the following can be said: All digital message transmission methods in which spreading sequences are used which are not used for synchronization are not efficient. Not only the polarity of the cross-correlation peak but also the additional information located in the position of the cross-correlation peak is used for data transmission, the efficiency of these digital communication methods can be significantly improved.

In particular, the above considerations apply to data transmission in navigation systems, such as GPS or GALILEO, and for applications in which combined navigation and communication receivers are used. In these cases, there is already a highly accurate synchronization by the navigation receiver and the data transfer does not require its own synchronization, but can rely on the synchronization by the navigation receiver.

Increasing the efficiency of digital news broadcasting is a fundamental issue in the research and development of communications engineering. In this case, an increase in efficiency can be measured by the following four characteristics of a digital message transmission method, namely by the transmission power, the bandwidth, the data rate and by the performance. The performance of a digital messaging technique is often referred to in the art as "performance" and quantified by the bit error rate.

Comparing digital messaging methods based on equal "performance", the better approach is characterized by saving on transmit power and / or saving bandwidth and / or increasing the transferable data rate. On the other hand, when compared based on equal transmit power, bandwidth and data rate, the digital messaging technique that has the better "performance" wins.

The invention is based on the object, digital message transmission methods in which spreading sequences are used to increase in their efficiency, the spreading sequences used are not used for synchronization, since the synchronization takes place independently of the data transmission on a separate "synchronization channel", and this efficiency increase can be expressed in the parameters by the profits achieved in comparison to other digital message transmission methods. In addition, the invention is also intended to provide a system for carrying out the increased efficiency of its digital message transmission method.

According to the invention, which relates to a digital message transmission method of the type mentioned above, this object is achieved in that for transmission of further information, the spreading signal c (t) impressed on the transmission signal at the transmitting end in the phase modulated by shifts by multiples of the chip duration T _c and that the receiving side for detection of this transmitted further information, the cross-correlation function is used in such a way that is deduced from the position of the correlation peak of this cross-correlation function on the transmitted phase of the spreading sequence by a synchronous to the transmission signal using the separate synchronization channel segmentation of the received signal in Time intervals of the transmission frames and thus a generation of signal sections is carried out, each containing exactly one phase, and the segmented received signal is subjected to a correlation, b ei from the respective signal section and the receiver side generated, identical copy of the spreading sequence c (t) used in the transmitter, the cross-correlation function is determined with their respective shift of the spreading sequence c (t) in the transmission signal indicating correlation peak position.

The advantage of the novel phase modulation of the spreading sequences mentioned in the following spreading sequence phase modulation (SFPM) is that the information lying in the position of the cross-correlation peak is utilized. If the SFPM is used in a digital communication system, an increase in efficiency will be achieved. The use according to the invention of the SFPM makes it possible for the first time not only to use the polarity in a digital message transmission system, but also the position of the cross-correlation peak formed in the receiver for transmitting digital messages.

There are two advantageous embodiments of the SFPM in a digital message transmission system with spreading sequence use, which are based on the same basic principle, namely the SFPM, but differ in the practical implementation of this basic principle.

The first possibility is that the displacement of the spreading sequence c (t) is linear, the phase p and thus the shifted spreading sequence c _p (t) being generated by simple translation of the unshifted spreading sequence by p · T _c , on the time axis. Advantageously, a transmission frame of duration T _r = 2 * N * T _c or T _r = 2 * T _{s is} provided in the time domain, within which the linear displacement of the spreading sequence can be carried out, where T _{c is} the chip duration, T _s the spreading sequence duration and N is the number of chips in the spreading sequence.

The second possibility is that the displacement of the spreading sequence c (t) is cyclic, wherein in the time domain, a transmission frame of T _r = N · T _c or T _r = T _{s is} provided, within which chip, the on the time axis after have been moved to the right over the time period T _s also, be attached to the left back to the beginning of the shifted spreading sequence, and wherein T _{c s} is the spreading sequence length and N is the chip duration, T is the number of chips in the spreading sequence.

Advantageous and expedient developments of the digital message transmission method according to the invention are specified in claims 6 to 22, which relate directly or indirectly to claim 1.

The stated object, to provide appropriate systems for carrying out the increased in its efficiency digital message transmission method, is achieved by the measures indicated in claims 21 and 22. In the claims 23 to 25 advantageous developments or expedient variants of these systems are given.

Claims 26 to 28 include possibilities for a useful use of the digital communication method according to any one of claims 1 to 20 or the systems according to any one of claims 21 to 25.

The digital communication method according to the invention and advantageous embodiments thereof are explained below with reference to drawings. Show it:

1 in two time diagrams arranged one above the other, the generation of different phases of a spreading sequence c (t) by means of linear displacement, where c ₀ (t) (= phase 0) and c ₅ (t) (= phase 5) of a spreading sequence c (t) of length N = 8 are shown,

2 likewise in two time diagrams arranged one above the other, the generation of different phases of a spreading sequence c (t) by means of cyclic shifting, where c ₀ (t) (= phase 0) and c ₅ (t) (= phase 5) of a spreading sequence c (t) of length N = 8 are shown,

3 1 shows a block diagram of the principle structure of a transmitter for the SFPM implementation in a first system realization version (linear phase shift) for carrying out the efficiency-enhanced digital message transmission method according to the invention, wherein in the example shown spreading sequences of length N = 2 ⁿ are used,

4 in a block diagram the possible basic structure of a receiver for the first system realization version (linear phase shift), where as in the transmitter 3 exemplary spreading sequences of length N = 2 ^{n are} considered,

5 an example of the synchronous segmentation of the baseband receive signal y (t) in two time diagrams arranged one below the other, wherein the baseband receive signal y (t) is shown here for the noise-free case,

6 an example for determining the correlation function R _rc (τ) between the signal section r (t) and the spreading sequence c (t) with linear displacement for the range 0 ≦ τ ≦ T _s -T _c = (N-1 ) · T _c , where the signal section r (t) is shown here for the noise-free case,

7 in a block diagram the basic structure of a transmitter for SFPM implementation in a second system realization version (cyclic phase shift) for performing the increased in its efficiency digital message transmission method according to the invention, in the example shown spreading sequences of length N = 2 ⁿ are used,

8th in a block diagram the possible basic structure of a receiver for the second system realization version (cyclic phase shift), where as in the transmitter of 7 exemplary spreading sequences of length N = 2 ^{n are} considered, and

9 an example for determining the correlation function R _rc (τ) in cyclic correlation between the signal section r (t) and the spreading sequence c (t) for the range 0 ≤ τ ≤ T _s -T _c = (N-1 ) · T _c , where the signal section r (t) is shown here for the noise-free case.

A digital data transmission with a symbol duration of T _{s is} considered below. The spreading sequences consist of N chips, each having a chip duration T _c . Usually, T _s and T _c in digital communication systems according to T _s = N * T _c (1) selected. This convention is used to describe the SFPM. It should be noted that the equation (1) is not a prerequisite for the spreading sequence phase modulation (SFPM) and is only used for description. The SFPM can also be applied if equation (1) is not satisfied.

Spreading sequences with good correlation properties, such as m-sequences, gold or Kasami sequences, usually have a length N = 2n-1, n ε {2, 3, 4, ...}. These spreading sequences can be extended by one chip to give spreading sequences with a length N = 2 ⁿ , which is a power of two. The thus-extended spreading sequences are referred to as "extended spreading sequences" and can be produced as described, for example, in Fiebig, U.-C .; Schnell, M .: "Correlation Properties of Extended m-Sequences", Electronics Letters, Vol. 29 (1993), No. 20, pp. 1753-1755, and in Fiebig, U.-C .: "Auto and Cross Correlation Properties for Extended m-Sequences and Related Sequences ", Conf. Proc. of the 3rd IEEE Int. Symposium on Spread Spectrum Techniques and Applications (ISSTA '94), Oulu, Finland, July 1994, pp. 406-410.

In addition, there are spreading sequences whose length N is a power of two due to the design. An example of this is the orthogonal Hadamard codes, which, however, have poor correlation properties and therefore are scrambled by a second spreading sequence for most applications. The SFPM has a particularly high efficiency when spreading sequences with a length N = 2 ⁿ are used.

The following description is made using spreading sequences of length N = 2 ⁿ . It should be noted that the SFPM can be done not only with spreading sequences of length N = 2 ⁿ , but with all possible spreading sequences. However, the use of spreading sequences of length N = 2 ⁿ is particularly efficient in the SFPM, as will be shown. In the following, the spreading sequence used in the transmitter is denoted by c (t).

The different phases of a spreading sequence c (t) are obtained from shifts in the spreading sequence by multiples of the chip duration T _c . Thus, there are N possible phases for each spreading sequence. The original, unshifted spreading sequence is referred to as phase 0 of the spreading sequence. Accordingly, the spreading sequence shifted by 1 * T _{c is referred} to as phase 1 of the spreading sequence. The spreading sequence shifted by 2 × T _c is referred to as phase 2 of the spreading sequence, etc. In general, the spreading sequence c _p (t) shifted by p × T _{c is} referred to as the phase p of the spreading sequence c (t), p = 0 , 1, 2, ..., N - 1.

There are two possibilities (versions) to realize shifts in the spreading sequence, namely the "linear shift" and the "cyclic shift". In the case of the linear displacement, the phase p and thus c _p (t) are generated to the right by a simple translation of the unshifted spreading sequence c (t) by p × T _c chips on the time axis.

In 1 the linear displacement is illustrated and shows, by way of example, the phases 0 and 5 of a spreading sequence c (t) of length N = 8. In order to be able to generate all possible phases of a spreading sequence by means of linear displacement, a transmission frame of T _r = 2 * N is obtained in the time domain · T _c or T _r = 2 · T _s provided. Mathematically, a linear displacement of p × T _c chips can be achieved c _p (t) = c (t - pT _c) (2) describe. The linear displacement is used in the first SFPM implementation version.

beschreiben. Die zweite SFPM-Realisierungsversion beruht auf der zyklischen Verschiebung.Using the same example is in 2 illustrates the cyclic shift. It can be seen that only one transmission frame of T _r = N · T _c or T _r = T _{s is to be} provided in the cyclic shift in the time domain. This is achieved in that in the cyclical shift chips that have been shifted on the time axis to the right over the time range T _s addition, are left again appended to the beginning of the shifted spreading sequence. Mathematically, a cyclic shift can be performed by p × T _c chips

describe. The second SFPM realization version is based on the cyclic shift.

The basic principle of the SFPM is that the different phases of the spreading sequence used are used for the transmission of information. With a spreading sequence of length N, N different information symbols can thus be transmitted. The transmitter selects according to the information symbol to be transmitted from a spreading sequence phase, which is in turn detected in the receiver. From the detected spread sequence phase, the receiver can return to the transmitted information symbol.

If the information to be transmitted is present in the form of bits, for example, M bits are combined into M-ary symbols, where M = ⌊ldN⌋ (4) to choose. Where ⌊x⌋ is the largest integer less than or equal to x. The generation of the M-ary symbols and thus the SFPM is particularly efficient when spreading sequences of length N = 2 ⁿ are used. In this case, the number of M bits per symbol is maximized and the following applies: M = ⌊ldN⌋ = n. (5)

Each M-valued symbol is then assigned a spreading sequence phase. This assignment can be made for example by a simple mapping rule ("mapping"). Table 1 shows such a mapping rule for N = 8 and thus M = n = 3, the bits being represented by "+" and "-". Conveniently, the mapping rule is chosen such that the symbols mapped to adjacent spreading sequence phases differ only in one bit. If the receiver does not detect the correct spreading sequence phase but an adjacent one, then this symbol error results in only a single bit error. This special assignment is very similar to the "gray mapping" and is referred to in the following as "extended gray mapping".

The difference to the "gray mapping" is that also the first and the last symbol differ in only one bit. This property is particularly important for the second SFPM implementation version, as it uses the cyclic shift. For the first version of SFPM, however, it does not matter if the "Gray" or the "Gray Mapping" is used. In the following Table 1, the expanded "Gray Mapping" is shown using an example N = 8 and M = n = 3 for a mapping rule for mapping between M-valued symbol and spreading sequence phase based on the extended "Gray Mapping". M-valued symbols Spreading sequence phase p + + + 0 - + + 1 - + - 2 + + - 3 + - - 4 - - - 5 - - + 6 + - + 7 Table 1

The first SFPM realization version relies on the linear shift to generate the different phases of the spreading sequence in the transmitter. A possible basic structure of a transmitter for the first SFPM realization version is in 3 represented, for example, a spreading sequence of length N = 2 ^{n was used} as a basis.

In each case n bits of the bit stream d (k) to be transmitted are combined to form M-valued symbols, where nT _b denotes the sampling rate. Note that M = n due to the choice for the spreading sequence length N. A "symbol mapper" SM, which is part of a spreading sequence phase generator SP, implements the mapping rule for the association between the M-valued symbol and the spreading sequence phase p. The linear displacement for generating the various spreading sequence phases can be found, for example, in US Pat 3 shown manner can be achieved with a simple delay element VG, the delays τ realized by multiples of the chip duration T _c τ = p * T _c. (6)

The delay element VG is also part of the spreading sequence phase generator SP. The factor p and thus the selected spreading sequence phase is provided to the delay element VG by the "symbol mapper" SM.

With each beginning of a transmission frame, which has a duration T _r = 2 * T _s due to the linear displacement, a spreading sequence generator SG, which likewise forms part of the Spreading sequence phase generator SP is the unshifted spreading sequence c (t). This is positioned by the delay element VG corresponding to the selected spreading sequence phase p in the transmission frame in order to realize the desired output signal c _p (t) of the spreading sequence phase generator SP. The baseband transmit signal s (t) arises from the continued stringing of transmission frames. During the duration T _{r of} a transmission frame s (t) = _cp (t), (7) if the phase p of the spreading sequence c (t) has been selected for this transmission frame.

In 4 is a possible basic structure of a receiver for the first SFPM implementation version shown, wherein as already in the basis of the 3 described description of the transmitter are considered example spreading sequences of length N = 2 ⁿ . The baseband transmission signal s (t) is influenced by the transmission channel h (t) and due to the additive, white gaussian noise (AWGN) n (t) and reaches the receiver as the reception signal y (t) y (t) = s (t) * h (t) + n (t) (8) applies. The operator "*" specifies the convolution operation. The SFPM can be used with any transmission channels h (t).

For the sake of clarity and clarity, a pure AWGN channel with h (t) = δ (t) is used for the further description, where δ (t) denotes the Dirac function. In this case, the expression for the baseband received signal y (t) y (t) = s (t) + n (t), (9) which is identical to the baseband transmission signal s (t) except for the additive noise term n (t). First, a segmentation of the received signal y (t) is carried out by means of a segmentation element SEG in time segments of length T _r = 2 * T _{s of} a transmission frame, thus producing the signal section r (t).

This segmentation takes place in the in 5 shown in synchronism with the transmission signal, wherein the means of a synchronization SYN synchronization to the transmission signal and thus the compensation for the signal delay time t ₀ without using the received signal y (t) takes place, but using a separate synchronization channel. The synchronization ensures that the signal section r (t) always contains exactly one phase p of the spreading sequence c (t) and, because of equation (7) and equation (9), r (t) = _cp (t) + n (t). (10)

In a correlator KO, an identical copy of the spreading sequence c (t) used in the transmitter is generated from the signal section r (t) and the spread sequence generator SGE arranged in a receiver-side spreading sequence generator SGE 6 As shown, the correlation function R _rc (τ) for the range 0 ≤ τ ≤ T _s -T _c = (N-1) · T _c determines:

For the in 6 illustrated linear displacements c (t - l · T _c) = c _l (t), l = 0, ..., N - 1, the spreading sequence c (t), the correlation function R _rc (τ) to the discrete sites τ = l · T _c , l = 0, ..., N - 1. For the detection of the correlation peak, a determination of the correlation function R _rc (τ) at these discrete locations is completely sufficient. Of course, it is also possible to use a correlator KO which determines the entire correlation function R _rc (τ) for the range 0 ≦ τ ≦ T _s -T _c = (N-1) * T _c .

umformen. Während der zweite Term in der Gleichung (12) eine additive Rauschstörung darstellt, repräsentiert der erste Term die Kreuzkorrelationsfunktion der Spreizungsfolge c(t), die aufgrund der linearen Verschiebung zur Erzeugung der Phase p der Spreizungsfolge c(t) ihr Maximum für τ = p·T_c aufweist. Diese Korrelationsspitze wird durch einen in 4 eingetragenen Korrelationsspitzendetektor (”Peak”-Detektor) PD bestimmt. Aus der Position τ = p·T_c der Korrelationsspitze kann auf die ubertragene Phase p der Spreizungsfolge c(t) zurückgeschlossen werden. Über einen ”Symbol-Demapper” SD wird aus der Spreizungsfolgenphase p das entsprechende M-wertige Symbol und daraus der ursprüngliche Bitstrom d(k) zurückgewonnen, wobei mit nT_b die Abtastrate bezeichnet ist. Detektion und Zurückgewinnen des ursprünglichen Bit-stroms d(k) sind bei rauschfreier Übertragung stets fehlerfrei möglich.Using equation (2) and equation (10), equation (11) can be added

reshape. While the second term in equation (12) represents an additive noise penalty, the first term represents the cross-correlation function of the spreading sequence c (t) which, due to the linear shift to produce the phase p of the spreading sequence c (t), is its maximum for τ = p · T _c has. This correlation peak is indicated by a in 4 registered correlation peak detector ("peak" detector) PD. From the position τ = p · T _{c of} the correlation peak it is possible to deduce the transferred phase p of the spreading sequence c (t). Via a "symbol demapper" SD, the corresponding M-valued symbol is retrieved from the spread sequence phase p and the original bit stream d (k) is retrieved therefrom, where nT _b denotes the sampling rate. Detection and recovery of the original bit stream d (k) are always error-free possible with noise-free transmission.

Subsequently, the gains in the transmittable data rate which the first SFPM realization version achieves over a DS-CDMA transmission method with BPSK (Binary Phase Shift Keying) modulation are determined. In the case of DS ("Direct Sequence") CDMA with BPSK modulation, each user can transmit exactly 1 bit during a symbol duration T _s = N * T _c , and the transferable data rate R _BPSK results in:

In contrast, in the first SFPM implementation version, each user can transmit M bits in total during a transmission frame T _r = 2 × T _s . Conveniently, a spreading sequence of length N = ^{2n is} used to maximize the number of transmissible bits according to equation (5) to M = n. This results in a transferable data rate R _SFPM of:

Table 2 below shows the gains for the first SFPM implementation version in the transmittable data rate for different spreading sequence lengths from N = 8 to N = 1024. Spreading sequence length N Number of M bits per symbol: M = n Profit: R _SFPM / R _BPSK 8th 3 1.5 16 4 2 32 5 2.5 64 6 3 128 7 3.5 256 8th 4 512 9 4.5 1024 10 5 Table 2

Since SFPM, in contrast to BPSK bipolar modulation, is a quasi-orthogonal modulation method, a performance loss of SFPM compared to BPSK modulation of about 3 dB is to be expected. This performance loss is to be offset against the profit in the transferable data rate.

To conclude the description of the first version of SFPM realization, it should be noted that the transmission frame can also be reduced to a duration T _r = 2 * T _s -T _c , whereby the gains indicated in Table 2 can still be slightly increased.

The second SFPM realization version relies on the cyclic shift to generate the different phases of the spreading sequence in the transmitter. A possible basic structure of a transmitter for the second SFPM realization version is in 7 represented as in the first SFPM implementation version again exemplified a spreading sequence of length N = 2 ^{n was used} as a basis.

In each case n bits of the bit stream d (k) to be transmitted are combined to form M-valued symbols, where nT _b denotes the sampling rate. Note that M = n due to the choice for the spreading sequence length N. A "symbol mapper" SYM, which is part of a spreading sequence phase generator SGN, implements the mapping rule for the association between the M-valued symbol and the spreading sequence phase p. The cyclic shift for generating the various spreading sequence phases can be found, for example, in US Pat 7 illustrated manner directly in the generation of the spreading sequence c (t) can be realized. In this case, the spreading sequence c (t) is realized in an advantageous manner by means of feedback shift registers.

Depending on the selection of the start assignment for the shift registers, any phase of the spreading sequence can be realized. A block "spread-order generator with cyclical shift" SZV, which is also part of the spread sequence phase generator SGN, receives the selected spread sequence phase p from the "symbol mapper" SYM and selects the start assignment for the shift registers used to generate the cyclically shifted spread sequence c _p (t) is needed.

With each start of a transmission frame, which has only a duration T _r = T _s due to the cyclical shift, the block "Spreading sequence generator with cyclic shift" SZV directly generates the cyclically shifted spreading sequence c _p (t) and thus the desired output signal c _p (t ) of the spreading sequence phase generator SGN. The baseband transmit signal s (t) arises from the continued stringing of transmission frames. During the duration T _{r of} a transmission frame s (t) = _cp (t), (15) if the phase p of the spreading sequence c (t) has been selected for this transmission frame.

In 8th a possible basic structure of a receiver for the second version of SFPM implementation is shown, wherein, as already described in the description of the transmitter example spreading sequences of length N = 2 ⁿ . A comparison with 4 shows that the receivers for the first and second version of SFPM realization differ only in the performance of the correlation, see block "correlator" KO in 4 or Block "Cyclic Correlator" ZKO in 8th , This difference is due to the fact that the first SFPM implementation version uses the linear shift and the second SFPM realization version the cyclic shift. In the further description of the receiver for the second SFPM implementation version, therefore, only the implementation of the cyclic correlation will be discussed.

The synchronous segmentation of the received signal y (t) into time segments of length T _r = T _{s of} a transmission frame carried out in a segmentation element SGL with the aid of a synchronization device SYH using a separate synchronization channel ensures that the resulting signal section r (t) is always accurate includes a phase p of the spreading sequence c (t) and according to the equation (10) also for the second SFPM realization version r (t) = _cp (t) + n (t) (16) applies. In the cyclic correlator ZKO, from the signal section r (t) and the identical copy of the spreading sequence c (t) used in the transmitter in a spreading sequence generator SPG of the receiver, in the in 9 As shown, the correlation function R _rc (τ) for the range 0 ≤ τ ≤ T _s -T _c = (N-1) · T _c determines:

For the in 9 cyclic shifts c ₁ (t), l = 0,..., N-1, the spreading sequence c (t) can be the correlation function R _rc (τ) at the discrete locations τ = 1 · T _c , l = 0, ..., N - 1. For the detection of the correlation peak, a determination of the correlation function R _rc (τ) at these discrete locations is completely sufficient. Of course, it is also possible to use a cyclic correlator ZKO which determines the entire correlation function R _rc (τ) for the range 0 ≦ τ ≦ T _s -T _c = (N-1) * T _c .

umformen. Während die zweite Zeile der Gleichung (18) eine additive Rauschstörung darstellt, repräsentiert die erste Zeile die zyklische bzw. periodisch fortgesetzte Kreuzkorrelationsfunktion der Spreizungsfolge c(t). Aufgrund der zyklischen Verschiebung zur Erzeugung der Phase p der Spreizungsfolge c(t) tritt das Maximum für τ = p·T_c auf. Diese Korrelationsspitze wird durch den in 8 eingetragenen Korrelationsspitzendetektor (”Peak”-Detektor) KD bestimmt.Considering the equation (16), the equation (17) can be added

reshape. While the second row of equation (18) represents an additive noise disorder, the first row represents the cyclic or periodically continued cross-correlation function of the spreading sequence c (t). Due to the cyclic shift for generating the phase p of the spreading sequence c (t), the maximum occurs for τ = p · T _c . This correlation peak is determined by the in 8th registered correlation peak detector ("peak" detector) KD.

As with the first SFPM realization version, the correlation peak can be deduced from the position τ = p · T _{c of} the spread phase c of the spreading sequence c (t) and thus finally converted to the original bit stream d (using a "symbol demapper" SDM). k), where nT _{b is} the sampling rate. Detection and recovery of the original bitstream d (k) are always error-free possible with noise-free transmission.

In the following, the gains in the transmissible data rate which the second SFPM realization version achieves over a DS-CDMA transmission method with BPSK modulation are determined. For the transmittable data rate R _BPSK in DS-CDMA with BPSK modulation again the equation (13) applies. In the second version of SFPM implementation, each user can transmit a total of M bits during a transmission frame T _r = T _s .

Advantageously, a spreading sequence of length N = 2 ^{n is} used to maximize the number of transferable bits according to equation (5) to M = n. This results in a transferable data rate R _SFPM of

In the following Table 3, the gains in the transferable data rate for different spreading sequence lengths of N = 8 to N = 1024 are given for the second SFPM implementation version. It can be seen that the profits in the case of the second SFPM realization version are twice as high as in the first SFPM implementation version. Spreading sequence length N Number of M bits per symbol: M = n Profit: R _SFPM / R _BPSK 8th 3 3 16 4 4 32 5 5 64 6 6 128 7 7 256 8th 8th 512 9 9 1024 10 10 Table 3

In order to achieve a good performance in digital message transmission methods in which spreading sequences are used, spreading sequences with well-suited auto and / or cross-correlation properties are of particular interest. This also applies to the SFPM. In particular, when selecting the spreading sequences c (t) for the SFPM, it is advantageous if all N phases p, p = 0,..., N-1, of the spreading sequences c (t) are different.

This applies in particular to the second SFPM implementation version, since in this case it is only possible to ensure that all possible information symbols can be unambiguously detected in the receiver. Commonly used spreading sequences, such as m-sequences, gold or Kasami sequences, have this property.

The generation of the linear and cyclic shift can also be done in other ways than previously described. For example, both the generation of the linear shift and the generation of the cyclical shift can be carried out using a so-called look-up table. A "look-up table" is a large addressable memory. In this memory 0, the N-phase spreading sequence c _p (t) = p, ..., N - 1, stored in digital form. With an appropriate arrangement in the look-up table, for example, the phase p which is provided by the "symbol mapper" SM or SYM can be used as the address for reading out the spreading sequence phases c _p (t).

The correlation in the receiver can also be done in other ways than previously described. For example, the correlation may be performed using a look-up table. In this memory, the N spreading sequence phases c _p (t), p = 0,..., N-1, of the identical copy of the spreading sequence c (t) used in the transmitter are stored in digital form. The signal section r (t) of the received signal y (t) is correlated with all possible N spreading sequence phases. The phase p, which provides the largest correlation coefficient, is considered to be sent and passed to the "symbol demapper" SD or SDM. Note that the correlation formation can be parallelized by means of a look-up table.

The SFPM method according to the invention can be used not only for spreading sequences with a rectangular pulse shape but also for spreading sequences of any desired pulse shape. The pulse shape of the spreading sequences in no way restricts the applicability of the SFPM.

In addition, the SFPM transmission method according to the invention can be used not only for real-valued spreading sequences but also for complex-valued spreading sequences. In particular, the SFPM is applicable if the complex spreading sequences are represented by two real spreading sequences in each case. In this case, the one real spreading sequence in the in-phase component and the other real spreading sequence in the quadrature component is used.

The SFPM method according to the invention can be used both as an independent modulation method and combined with another modulation method. Any modulation scheme that is suitable for digital communications transmission systems that use spreading sequences is also suitable for combining with the SFPM. For example, the SFPM can be combined with BPSK (Binary Phase Shift Keying) modulation or QPSK (Quarternary Phase Shift Keying) modulation. While in the SFPM the transmitted information is in the position of the cross-correlation peak, the modulation method combined with SFPM uses the polarity of the cross-correlation peak for information transmission.

As an example, consider a combination between SFPM and BPSK modulation. The bitstream d (k) to be transmitted is split appropriately to SFPM and BPSK modulation. After the SFPM, the BPSK modulation can be realized, for example, by simply tapping the selected spreading sequence phases c _p (t). Whether the original or the keyed spread sequence phase is transmitted is decided via the respective bit assigned to the BPSK modulator for transmission. In total, n + 1 bits per symbol can thus be transmitted, namely the n bits of the SFPM and the one bit of the BPSK modulation.

For detection in the receiver, the n bits of the SFPM are recovered from the position and the one bit of BPSK modulation is recovered from the polarity of the cross correlation peak. The combination of SFPM with another modulation method leads to a further increase in efficiency, since more bits can be transmitted per symbol than when using the SFPM alone. Increasing the data rate by combining SFPM with another modulation method is achievable with the same transmission power, bandwidth and performance.

The transmission method according to the invention can be used in many fields.

For example, use in navigation systems is possible. In navigation systems, such as GPS or GALILEO, due to the navigation signal is already a highly accurate synchronization. Furthermore, in navigation systems in addition to the actual navigation signal and digital data signals are used for information exchange. Since the synchronization for the data transmission can be obtained via the navigation signal, the SFPM offers itself as a digital modulation method for the data transmission. The SFPM thus enables a very efficient digital data transmission method for navigation systems.

For example, it is also possible to use it in CDMA systems. The use of SFPM in CDMA transmission systems is possible if the synchronization can not be obtained from the actual data signal, but via a separate synchronization channel. Under this condition, the SFPM enables the realization of very efficient CDMA transmission systems. For the application of SFPM, for example, DS ("Direct Sequence") - CDMA systems or MC ("multi-carrier") - CDMA systems in question. While DS-CDMA systems are proposed for the third generation of mobile radio, MC-CDMA systems are being discussed for use with new generations of mobile radio systems.

Finally, use of the transmission method according to the invention in combined navigation and communication systems is also possible. By combining the navigation and communication system, the synchronization in the communication system can be obtained via the navigation signal. Thus, the SFPM can be used as a digital modulation method in the communication system, thus enabling a very efficient method of data transmission in the communication system. The combination of navigation and communication systems is currently being discussed intensively, for example for use in control systems.

LIST OF REFERENCE NUMBERS

• EF

  Device for combining n bits

  EZ

  Device for combining n bits

  KD

  Correlation peak detector ("peak" detector)

  KO

  correlator

  PD

  Correlation peak detector ("peak" detector)

  SD

  Symbol demapper

  SDM

  Symbol demapper

  SEG

  segmentation link

  SG

  Spreading sequence generator

  SGE

  Spreading sequence generator

  SGL

  segmentation link

  SGN

  Spreading sequence phase generator

  SM

  Symbol mapper

  SP

  Spreading sequence phase generator

  SPG

  Spreading sequence generator

  SYM

  Symbol mapper

  SYN

  synchronizer

  SZV

  Spread sequence generator with cyclic shift

  SYH

  synchronizer

  VG

  delay

  ZKO

  Cyclic correlator

Claims (28)

Digital message transmission method in which the frequency spectrum of a transmitted in a continuous sequence of transmission frame transmission signal expanded by each consisting of N chips spreading sequences per transmission frame and the receiving side this expansion of the frequency spectrum by forming the cross-correlation between the spreading signals contained in the received signal and receiving side generated identical copies of the Transmitter sequences used is reversed again, the transmitted information detected on the receiving side from the correlation peak of the cross-correlation function formed and the synchronization is carried out independently of the data transmission on a separate synchronization channel, ie not using the spreading sequences, characterized in that for the transmission of further information the spreading sequence c (t) impressed on the transmission signal at the transmitting end in phase is modulated by shifts multiples of the chip duration T _c and that the receiving side for detecting this transmitted further information, the cross-correlation function is used in such a way that is deduced from the position of the correlation peak of this cross-correlation function on the transmitted phase of the spreading sequence by a synchronous to the transmission signal Use of the separate synchronization channel made segmentation of the received signal in time segments of the transmission frame and thus a generation of signal sections is carried out, each containing exactly one phase, and the segmented received signal is subjected to a correlation in which from the respective signal section and the receiver side generated, identical copy of those used in the transmitter Spreading sequence c (t) the cross-correlation function is determined with their respective displacement of the spreading sequence c (t) in the transmission signal indicating correlation peak position. Digital message transmission method according to Claim 1, characterized in that the displacement of the spreading sequence c (t) is linear, the phase p and thus the shifted spreading sequence c _p (t) being generated by simple translation of the unshifted spreading sequence by p · T _c on the time axis becomes. Digital message transmission method according to claim 2, characterized in that in the time domain, a transmission frame of duration T _r = 2 · N · T _c or T _r = 2 · T _{s is} provided, within which the linear displacement of the spreading sequence can be made, where T _{c is} the chip duration, T _{s is} the spreading sequence time and N is the number of chips in the spreading sequence. Digital message transmission method according to claim 1, characterized in that the displacement of the spreading sequence c (t) is cyclic, wherein in the time domain, a transmission frame of T _r = N · T _c or T _r = T _{s is} provided, within which chip on the time axis have been shifted to the right over the time range T _s , left again appended to the beginning of the shifted spreading sequence and where T _{c is} the chip duration, T _{s is} the spreading sequence time and N is the number of chips in the spreading sequence. Digital message transmission method according to one of the preceding claims, characterized in that a spreading sequence phase is selected on the transmitting side according to the information symbol to be transmitted, wherein in a spreading sequence with a length of N chips N different information symbols are transferable, that the selected spreading sequence is detected on the receiver side and that from detected spreading sequence phase is the receiver side back to the transmitted information symbol. Digital message transmission method according to claim 5, characterized in that in the event that the information to be transmitted is in the form of bits, in each case M bits are combined to form M-valued symbols, wherein M = ⌊ldN⌋ is to be selected and in this case ⌊x⌋ indicates the largest integer that is less than or equal to x. Digital message transmission method according to claim 6, characterized in that spreading sequences of length N = 2 ⁿ are used so that the number of M bits per symbol is maximized and M = ⌊ldN⌋ = n, and that each M-ary symbol then has a spreading sequence phase is assigned. Digital message transmission method according to claim 7, characterized in that the assignment of the spreading sequence phases to the M-ary symbols is performed by a mapping rule in the manner of "mapping". Digital message transmission method according to claim 8, characterized in that the mapping rule is chosen so that the symbols that are mapped to adjacent spreading sequence phases differ only in one bit. Digital message transmission method according to one of the preceding claims, characterized in that the pulse shape of the spreading sequences used is rectangular. Digital message transmission method according to one of claims 1 to 9, characterized in that the pulse shape of the spreading sequences used is arbitrary. Digital message transmission method according to one of the preceding claims, characterized in that the spreading sequences used are real-valued. Digital communication method according to any one of claims 1 to 11, characterized in that the spreading sequences used are complex. Digital message transmission method according to claim 13, characterized in that the complex-valued spreading sequences are represented by two real spreading sequences, wherein the one real spreading sequence in the in-phase component and the other real spreading sequence in the external component is used. Digital message transmission method according to one of the preceding claims, characterized in that the phase modulation of the spreading sequences is used as an independent modulation method. Digital messaging method according to one of claims 1 to 14, characterized in that the phase modulation of the spreading sequences is combined with another modulation method, each modulation method suitable for digital communication systems in which spreading sequences are used, also for combination with the phase modulation of Spreading sequences is suitable. Digital message transmission method according to claim 16, characterized by a combination with BPSK (Binary Phase Shift Keying) modulation or QPSK (Quartenary Phase Shift Keying) modulation, wherein the modulation method combined with the phase modulation of the spreading sequences, the polarity uses the correlation peak of the cross-correlation function for information transmission and detection. Digital message transmission method according to one of the preceding claims, characterized by the use of spreading sequences with suitable auto and / or cross-correlation properties. Digital message transmission method according to claim 18, characterized by the selection of spreading sequences c (t) in which all N phases p, p = 0,..., N-1, are different. Digital message transmission method according to claim 18 and 19, characterized by the selection of m-sequences, gold or Kasami sequences as spreading sequences used. System for implementing the digital message transmission method according to claims 2 and 3, characterized in that in a transmitter means (EZ) for combining n bits of a bitstream d (k) to be transmitted to M-ary symbols is provided to the device connected to summarize n bits is a symbol mapper (SM), which belongs to a spreading sequence phase generator (SP) and the mapping rule for mapping between M-valued symbol and spreading sequence phase p realizes that in the spreading sequence phase generator, a spreading sequence generator (SG) is provided whose generated Spreading sequences are supplied to a delay element (VG) whose delay is controlled by the spreading sequence phase p-containing signal of the symbol mapper and the delays formed by multiples of the chip duration T _c , that with each start of a transmission frame, due to the linear displacement of a duration T _r = 2 · T _s or T _r = 2 * T _s -T _c , the spreading sequence generator generates an unshifted spreading sequence c (t) which is positioned by the delay element corresponding to the selected spreading sequence phase p in the transmission frame to produce the output signal c _p (t) of the delay element and thus of the delay In order to realize spread sequence phase generator, wherein the base band end signal s (t) to be transmitted by the transmitter results from the continued stringing of transmission frames, a segmentation element (SEG) is provided in a receiver which transmits the baseband receive signal in time segments of length T _r = 2 * T _{s of} a transmission frame segmented and signal sections r (t) generates that for synchronous control of the segmentation with the transmission signal to the segmentation a synchronization device (SYN) is connected, which operates via a separate synchronization channel and ensures that the signal section r (t) always exactly one phase p the spreading sequence c (t) comprises that the segmented received signal is fed to a correlator (KO) which generates from the respective signal section r (t) and the identical copy of the spreading sequence c (s) generated in a spread sequence generator (SGE) of the receiver. t) the correlation function R _rc (τ) for the range 0 ≦ τ ≦ T _s -T _c = (N-1) * T _c determines that a correlation peak detector (PD) for detecting the correlation peak is connected to the correlator so that from the position τ = p · T _{c of} the correlation peak on the transmitted phase p of the spreading sequence c (t) can be deduced, and in that a symbol demapper (SD) is connected to the correlation peak detector, on the basis of the spreading sequence phase p the corresponding M -valued symbol and from this the original bitstream d (k) is recovered. System for implementing the digital message transmission method according to claim 4, characterized in that in a transmitter means (EF) is provided for combining n bits of a bitstream d (k) to be transmitted to M-ary symbols, where M = n by choice for the spreading sequence length N, a symbol mapper (SYM), which belongs to a spreading sequence phase generator (SGN) and realizes the mapping rule for assignment between M-valued symbol and spreading sequence phase p, that in the spreading sequence phase generator is connected to the means for combining n bits a spreading sequence generator (SZV) with cyclic shift for generating the different spreading sequence phases is provided that the spreading sequence generator p is provided by the symbol mapper the spreading sequence phase, wherein the spreading sequence generator selects that starting assignment, for generating the cyclic shifted spreading sequence c _p (t) is needed that with each start of a transmission frame, which has a duration T _r = T _s due to the cyclic shift, the spreading sequence generator with cyclic shift directly the cyclically shifted spreading sequence c _p (t) and thus the output signal c _p (t) is generated, whereby the base band transmission signal s (t) to be transmitted by the transmitter arises from the continued sequence of transmission frames, that a segmentation element (SGL) is provided in a receiver which transmits the baseband reception signal in time segments of length T _r = 2 · T segmented _s of a transmission frame and signal segments r (t) that for synchronous control of the segmentation with the transmission signal to the segmentation member comprises a synchronization device (SYH) is connected, operated via a separate synchronization channel and ensuring that the signal portion s (t) is always exactly a phase p of the spreading sequence c (t) means that the segmented received signal is fed to a cyclic correlator (ZKO) consisting of the respective signal section r (t) and the identical copy of the spreading sequence c (t) used in a spreading sequence generator (SPG) of the receiver. the correlation function R _rc (τ) for the range 0 ≦ τ ≦ T _s -T _c = (N-1) * T _c determines that a correlation peak detector (KD) is connected to the correlator, so that from the position τ = p T _{c of} the correlation peak on the transmitted phase p of the spreading sequence c (t) can be deduced, and in that a symbol demapper (SDM) is connected to the correlation peak detector, from the spreading sequence phase p the corresponding M-ary symbol and from there original bitstream d (k) is recovered. System according to Claim 22, characterized in that feedback registers which are fed back as a spread sequence generator (SZV) with cyclical displacement are provided. System according to one of claims 21 to 23, characterized in that for generating the linear or cyclic shift a so-called "look-up table" is provided, which is a large addressable memory in which the N spreading sequence phases c _p (t), p = 0, ..., N-1, are stored in digital form and in which, for example, the phase p which is provided by the symbol mapper (SM, SYM) can be used as an address for reading out the spreading sequence phases with a corresponding arrangement , System according to one of Claims 21 to 24, characterized in that a "look-up table" is provided for correlation in the receiver, which is a large addressable memory in which the N spreading sequence phases of the identical copy of the spreading sequence c (t ) are stored in digital form, wherein the signal section r (t) of the received signal y (t) is correlated with all possible N spreading sequence phases and the phase p, which provides the largest correlation coefficient, considered sent and the symbol demapper (SD; SDM ). Use of the digital communication method according to one of claims 1 to 20 or the system according to any one of claims 21 to 25 in a navigation system, such. B. GPS. Use of the digital communication method according to any one of claims 1 to 20 or the system according to any one of claims 21 to 25 in a CDMA transmission system, such as e.g. DS (Direct Sequence) CDMA or MC (Multi-Carrier) CDMA. Use of the digital communication method according to any one of claims 1 to 20 or the system according to any one of claims 21 to 25 in combined navigation and communication systems, such as e.g. B. in control systems.

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