HK1107460B - Method for generating preamble structures and signaling structures in a mimo-ofdm transmission system - Google Patents

Description

Method for generating preamble and signaling structure in MIMO-OFDM transmission system

The invention relates to a method for generating a preamble and a signaling structure for a multi-antenna OFDM transmission system, which method can be used in particular in future high-rate WLANs (Wireless local area networks), but also in mobile radio systems with multi-antenna technology.

The transmission of a known or at least partly known preamble signal generally has the following purpose: enabling the receiver to achieve fast synchronization and channel estimation so that subsequent data can be analyzed as error-free as possible (i.e. ideally only degraded also by input noise and/or interference). Regarding synchronization, clock, frequency and symbol synchronization may be distinguished from each other. Clock synchronization involves synchronization of the D/a and a/D converter clocks in the transmitter and receiver, while frequency synchronization involves synchronization of the mixer frequency. In OFDM transmission systems with guard intervals, as is considered in the present invention, symbol synchronization is additionally required, the task of which is to position the evaluation window for the data symbols (transmitted in a frequency division multiplexed manner) in such a way that no intersymbol interference (channel impulse response shorter than the duration of the guard interval) or as little intersymbol interference as possible (channel impulse response longer than the duration of the guard interval) occurs.

Conventional wireless OFDM transmission systems, as used for example in so-called WLANs (wireless local area networks), generally use only one antenna in the transmitter and/or receiver.

In contrast, MIMO-OFDM transmission systems (MIMO, multiple input multiple output) are a novel extension that can achieve significant increases in spectral efficiency through spatial "multiplexing" based on channel characteristics.

In this case, the preamble signal must not only support estimation of a single channel in the receiver, but must also be able to determine channel characteristics based on the preamble signal in the receiver for each spatially "multiplexed" data stream.

Finally, the task of the signaling is to inform the receiver of the physical transmission parameters used in the transmitter, such as modulation and coding.

The object on which the invention is based is to provide a method for generating a preamble structure and a signaling structure for packet-oriented data transmission based on MIMO-OFDM transmission technology, which enables good estimation accuracy of synchronization and channel parameters in a receiver with relatively little processing effort while being simultaneously compatible with already existing OFDM transmission systems (in particular IEEE802.11 a, 802.11 g).

According to the invention, this object is achieved by the measures of claim 1 and alternatively by the measures of claim 8.

In particular by using synchronization sequences in the synchronization segments of the respective antennas according to the following formula: s_m(n)＝DFT^-1{S_m(k) Therein ofN1.. N, all addressed receivers are able to analyze not only the signaling field but also the useful data field even when there is no detailed a priori information about the channel in the transmitter. If the relation s is used for the synchronization sequence of the respective antenna_m(n)＝DFT^-1{S_m(k) Therein ofN1.. N, the addressed receiver can then in turn analyze not only the signaling field but also the useful data field, wherein, however, detailed a priori information about the channel is present in the transmitter. The addressed receiver may in this case be a MIMO receiver with multiple receive antennas or a receiver with only one receive antenna, whereby also a high degree of backward compatibility with already existing transmission systems can be achieved.

Alternatively, according to claim 8, the channel estimation sequences c for the respective antennas_m(n) may be formed from OFDM symbols c_m，x(n) are successively arranged according to the following formula:

c_m(n)＝g_m，1(n)c_m，1(n)g_m，2(n)c_m，2(n)…g_m，D(n)c_m，D(n)

wherein c is_m，x(n)＝DFT^-1{C_m，x(k) And C_m，x(k)＝p_k，m，xC (k), N1.. multidot.n, so that not only signaling fields but also useful data fields can be analyzed in the same manner for all addressed receivers and backward compatibility with conventional transmission systems can be achieved.

Naturally, these two alternatives can also be combined with each other in terms of the construction of the synchronization sequence and the channel estimation sequence, thereby improving the reliability of the overall system.

In a synchronization sequence s_m(n) may be preceded by a guard interval typical of OFDM or a symbol-reversed guard interval, wherein the synchronization sequence is repeated periodically at least once.

Furthermore, to implement a particular transmit diversity approach, the correlation of the phase values may be according to the equationAs small as possible, all stations of the transmission system are thereby able to analyze the complete transmitted data packet, i.e. the signaling field and the useful data field, in order to obtain general information about the network and about the reserved time region.

Preferably, the so-called transmit diversity method is based on a special implementationTo thereby enable a so-called "cyclic delay diversity" approach (CDD). This method is advantageous from an implementation point of view, since, unlike the general approach, only one inverse fourier transform is required per OFDM symbol in the transmitter.

In order to apply the proposed method to a WLAN according to the IEEE802.11 standard, a WLAN according to the IEEE802.11 standard is used

And based on

C(k)_-26:26＝{1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，0，

1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, -1, -1, 1, 1, -1, 1, -1, 1, 1, 1, 1} thereby enabling straightforward implementation in such already existing systems.

As far as the channel estimation sequence is concerned, the channel estimation sequence for each antenna can also be formed by OFDM symbols c_m，x(n) according to

Is formed of successive permutations of where j is an OFDM symbol c_m，x(n) the number of repetitions.

In terms of the guard interval used, the guard interval may be made up of a simple OFDM typical guard interval sequence

g_m，x(n)＝c_m，x(n+N-N_G) n＝1，...，N_G

Or by a guard interval sequence typical of a double OFDM

g_m，x(n)＝c_m，x(n+N-2N_G) n＝1，...，2N_GForm wherein N is_GIs the number of samples of the guard interval.

Furthermore, a signaling section can be arranged in the time domain between the useful data structure and the channel estimation section of the preamble structure, wherein the signaling section contains a signaling sequence for the individual antennas, which is composed of OFDM symbols a_m，x(n) and typical guard interval sequence g for OFDM_m，x(n)＝a_m，x(n+N-N_G) n＝1，...，N_GFormed by successively arranging according to the following formula:

a_m(n)＝g_m，1(n)a_m，1(n)g_m，2(n)a_m，2(n)…g_m，V(n)a_m，V(n) wherein

a_m，x(n)＝DFT^-1{A_m，x(k) Andn＝1，...，N。

alternatively, there is a channel estimation sequence c_mThe channel estimation segment of (n) may be divided to have a partial channel estimation sequence c_m ¹(n) and c_m ²(n) a first partial channel estimation segment and a second partial channel estimation segment, and the signaling segment may be divided to have a partial signaling sequence a_m ¹(n) and a_m ²(n) the first partial signaling segment and the second partial signaling segment, and the first partial channel estimation segment, the first partial signaling segment, the second partial channel estimation segment, and the second partial signaling segment are recombined in chronological order, wherein the first and second partial channel estimation sequences are based on

Or according to

Formed using a guard interval typical of simple or double OFDM, and wherein the first part of the signalling sequence is according toAnd a second partial signaling sequence rootAccording toWherein a is_m，x(n)＝DFT^-1{A_m，x(k) Andand a guard interval sequence g typical of OFDM_m，x(n)＝a_m，x(n+N-N_G) n＝1，...，N_GTo form the composite material. In this case, backward compatibility can again be achieved, since stations in conventional transmission systems are now also able to analyse the signalling fields, whereby the number of subsequent channel estimation sequences is known a priori.

Preferably, the matrix P_kColumn vector P of_k，x(x＝1，...，D_k) Are ordered such that the power values1, D, taking into account the relationship for x > D_kSay p_k，m，xAs small as possible in the case of 0. Here, for each subcarrier k, a spatial predistortion matrix P_kColumn vector P of_k，x(x＝1，...，D_k) In a first step, the data are sorted according to size in such a way that the data satisfyFor z > x, and according to the rule in the second stepRandom permutation is performed.

Further advantageous embodiments of the invention are indicated in the further dependent claims.

The invention is further described below with reference to examples.

Fig. 1 shows a simplified illustration of data transmission in the time domain according to the IEEE802.11 standard;

fig. 2 shows a simplified diagram of a preamble structure according to the IEEE802.11 standard;

fig. 3 shows a simplified illustration of a signaling structure according to IEEE802.11 in the time domain;

FIG. 4 shows a simplified table for explaining the meaning of the individual bits according to FIG. 3;

fig. 5 shows the preamble and signaling structure of the present invention according to the first embodiment; and

fig. 6 shows the preamble and signaling structure of the present invention according to a second embodiment.

The invention is described below with the aid of a WLAN transmission system (wireless local area network) according to the IEEE802.11 standard as an OFDM transmission system, although alternative OFDM transmission systems are also conceivable in principle. According to the IEEE802.11 standard, which is explicitly referred to herein, OFDM symbols are used in OFDM transmission systems (orthogonal frequency division multiplexing). This multiplexing method is particularly suitable for terrestrial transmission of strongly interfered digital radio broadcast signals, since it is not echo-sensitive.

Therefore, a rough overview of data packets on the physical layer phy (physical layer) and in the transmission medium Access control mac (medium Access control) is first prepared according to fig. 1, as is known from IEEE 802.11. For a detailed description, reference is made to this standard.

According to fig. 1, MAC denotes a transmission Medium Access Control (Medium Access Control) and PHY denotes a Physical Layer (Physical Layer). The physical layer is further subdivided into a convergence process PLCP (physical layer convergence process) and the so-called PMD (physical medium dependence). The MAC Protocol Data Unit (MAC Protocol Data Unit) is denoted by MPDU, and the PSDU is a corresponding PLCP Service Data Unit (PLCP Service Data Unit). In order to achieve substantially power matching or "automatic gain control" AGC, synchronization and channel estimation, the data sequence has training symbols in the form of a so-called PLCP preamble, which is referred to below as preamble structure PS and is shown simplified in fig. 2.

In WLAN, the preamble structure PS consists of 12 OFDM symbols, which 12 OFDM symbols are followed by a signaling field or signaling structure with a signaling segment SI (1 OFDM symbol). The signaling section SI according to the WLAN standard is shown simplified in fig. 3, wherein fig. 3 also shows a part of a so-called "header". A real useful data field DA is arranged downstream of the signaling field or signaling segment SI, in which a variable number of OFDM symbols is stored and which contains the above-mentioned PLCP service data unit PSDU.

Request "is issued on the MAC side, in order to transmit data, whereby the physical layer PHY is put in a transmitting state. The physical layer convergence procedure PLCP then sends a number of commands to the layer PMD depending on the transmission medium, thereby causing the transmission of the preamble structure PS and the signalling segments SI. The actual scrambling and encoding of the data is performed as soon as the transmission of the preamble structure PS starts. The scrambled and encoded numbers are then exchanged between the transmission medium access control MAC and the physical layer convergence procedure PLCP by means of a plurality of data exchange commands "PHY _ data.req" and "PHY _ data.conf". When the physical layer PHY has a reception status, data transmission or transmission of data packets is ended, wherein each command "PHY _ txend.request" is acknowledged by the physical layer by means of the command "PHY _ txend.confirm".

Thus, a data packet is basically composed of three parts on the physical layer PHY. First is the preamble structure PS for parameter estimation, i.e. power matching AGC (automatic gain control), frequency and OFDM symbol synchronization, and channel estimation. This preamble structure PS is followed by a signaling structure or signaling section SI with which the signaling (code rate, modulation) of the used operating mode of the physical layer and the determination of the length of the data packet are carried out. Finally, the actual useful data, which are composed of a variable number of OFDM symbols, are located in the following data field DA. Its data rate is already indicated in the signalling field SI.

Fig. 2 shows a detailed illustration of the preamble signal structure PS according to fig. 1, wherein the same reference numerals denote the same or corresponding signal sequences, and a repetitive description is omitted below.

According to fig. 2, the preamble structure PS is composed of four OFDM symbols, wherein two OFDM symbols are set for power matching AGC and coarse synchronization and two OFDM symbols are set for channel estimation and fine synchronization.

In this case, G denotes a guard interval with a guard interval sequence, wherein GG is a double guard interval, i.e. a guard interval of twice the duration. The sample values s (n) represent a synchronization sequence, i.e. a sequence of signals used to support synchronization in the receiver. The synchronization sequence is composed of

0, 0, 0, -1-j, 0, 0, 0, -1-j, 0, 0, 0, 1+ j, 0, 0, 0, 1+ j, 0, 0, 0 + j. Similarly, c (n) denotes a channel estimation sequence, i.e. a signal sequence for supporting channel estimation in a receiver, which in turn is formed by

C(k)_-26:26＝{1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，0，

1, -1, -1, 1, 1, -1, 1, -1, 1, -1, -1, -1, 1, 1, -1, 1, -1, 1, 1} is obtained by inverse fourier transformation.

In this case, s (k) represents the basic synchronization signal in the frequency domain and c (k) represents the basic channel estimation signal in the frequency domain, as determined explicitly in the IEEE802.11 standard for WLANs.

Fig. 3 shows a simplified diagram for explaining the signaling structure according to fig. 1, wherein the same reference numerals again describe the same data fields or signal sequences, and a repeated description is omitted below.

The sample sequence of the corresponding signalling OFDM symbol is in turn derived from an inverse fourier transform of the bit sequence shown in figure 3. The bit sequence thus contains a data field RATE with 4 bits R1 to R4 for determining the data RATE, a data field with reserved bits R, a data field with bits R5 to R16 for determining the data length(length), check bits P, and a field RATE for data RATE and a field for data length having 6 bits for directly after receiving tail bitsA signaling tail SIGNAL TAIL (signal tail) for decoding.

The meaning of the individual bits R1 to R23 is shown in the table according to fig. 4. Here, the data packet is transmitted using the operation mode (PHY mode) of the physical layer specified in the RATE field.

Such an OFDM transmission system should now be applied to a MIMO-OFDM transmission system having multiple antennas in respective transmitters and receivers, according to the present invention, in which the following three cases can be distinguished in terms of the definition of a suitable preamble and signaling structure.

According to the first case, all stations, i.e. MIMO (multiple input multiple output) stations and SISO (single input single output) stations, must be able to analyze the complete transmitted data packet, i.e. the signaling field and the data field, in order to obtain general information about the network and about the reserved time region. This relates in particular to the frames "Beacon", RTS (request to send), CTS (clear to send), CTS-self and CF-end (contention free).

In the second case, all stations must be able to analyze at least the signalling field SI.

In the third case, only the addressed receiver must be able to analyze the signaling field and the data field.

The considerations for implementing a MIMO-OFDM transmission system so far are only for case 2. In this second case, although it may be based on the sum of "RATE" and "The "field accurately predicts the end of the data packet. However, collisions are avoided even in the absence of knowledge of these parameters by the carrier access method with collision avoidance (CSMA/CA, carrier sense multiple access with collision avoidance) that is always used in the transmission system. Even when the parity check provides erroneous results, in which the presence of a valid signaling field is indicated, although this signaling field does not actually exist and thus begins to analyze data portions that do not exist in a known form, the PLCP receiving method described in IEEE802.11 avoids all negative data transmissions between the respective devices that are valid for positive data transmissionThe surface effect.

It is therefore assumed in the subsequent consideration of cases 1 to 3 that the MIMO signal processing applied in the transmitter for each subcarrier k can be described by linear operations, so that there is a signal in the receiver after OFDM or OFDM processingHerein, R is_kDenotes a received vector, H_kRepresenting the channel matrix, P_kRepresents a MIMO "pre-processing" matrix and I_kRepresenting a data vector. All noise contributions or other interference quantities are ignored here. The subscripts next to the square brackets indicate the matrix dimension, where the square brackets are inserted only to achieve a clear separation between the matrix index and the matrix dimension index.

Before describing the various cases and the associated preamble and signaling structures in the following, the abbreviations used are first defined:

g: guard interval

GG: guard interval of twice duration (double guard interval)

DFT: discrete Fourier transform

DFT^-1: inverse discrete Fourier transform

OFDM: orthogonal frequency division multiplexing

M_T: number of transmitting antennas

n: time index (sample value)

x: yet another time index (OFDM symbol index)

m: antenna index

d: indexing of spatial data streams

k: subcarrier index (frequency index; precondition: transmission system based on OFDM)

V': number of OFDM symbols required for transmitting partial signaling information

V: number of OFDM symbols required for transmitting total signaling information

L: number of OFDM symbols with which useful data is transmitted

N: number of samples per OFDM symbol (dependent on D/A or A/D converter rate)

D_k: number of spatial data streams transmitted on the k-th subcarrier

D: the maximum number of spatial data streams on all sub-carriers,

_k，m: pseudo-random (of the primary synchronization signal), but known to the receiver, frequency-dependent (index k) and antenna (index m) dependent phase rotation

_k，m，d: pseudo-random (of the primary synchronization signal), but known to the receiver, phase rotation dependent on frequency (index k), antenna (index m) and space (index d)

Dimension M_T×D_kIs used for spatial pre-distortion (Vorverzerrung) of the useful data on the k-th subcarrier

P_k，d: matrix [ P ]_k]_MT×DkOf the d-th column vector

P_k，m，d: matrix [ P ]_k]M row and d column elements of

s_m(n): a synchronization sequence transmitted via antenna m (═ a signal sequence used to support synchronization in the receiver).

S (k): basic synchronization signal in frequency domain

S_m(k) The method comprises the following steps Synchronization signal in frequency domain transmitted via antenna m

c_m，x(n): the xth channel estimation sequence transmitted via antenna m (═ signal sequence used to support channel estimation in the receiver)

C (k): fundamental channel estimation signal in frequency domain

C_m，x(k) The method comprises the following steps The x-th channel estimation signal in the frequency domain transmitted through antenna m

a_m，x(n): the xth signal sequence transmitted via antenna m (data sequence with signaling information about the transmission mode used)

A_m，x(k) The method comprises the following steps The x-th signalling sequence in the frequency domain transmitted via antenna m

I_x ^sig(k) The method comprises the following steps Signaling information transmitted on the kth subcarrier of the xth OFDM signaling symbol (containing information such as coding and modulation for each individual spatial data stream, length of data packet.

d_m，x(n): the x-th data sequence transmitted via antenna m

I_d，x(k) The method comprises the following steps Information transmitted on the d-th spatial data stream of the k-th subcarrier of the x-th OFDM useful data symbol.

D_m，x(k) The method comprises the following steps X-th data signal in frequency domain transmitted via antenna m

Description of the drawings: what is referred to herein as a "sequence" is the sample values of an OFDM symbol, i.e., N1

Case 1:

it applies in principle that those data packets which contain important information about the reserved resources or network elements must not only be analyzable by all stations of different types, i.e. MIMO or SISO stations, but also within the maximum communication reach, so that the application of spatial multiplexing here is of little consequence. Instead, the data stream is transmitted only at the smallest possible data rate. If for example there is a MIMO transmitter, i.e. the transmitter has multiple antennas, the detection security in the receiver can be improved by applying transmit diversity methods. The restriction applies here that the method used must be transparent to all stations for compatibility reasons.

Transmit diversity methods meeting this characteristic, for example, by

A form of the preprocessed vector. More precisely, each subcarrier k is subjected to a pseudo-random phase rotation on each antenna m_k，m. Without limiting the generality, it is possible to arrange_k，10 so that the SISO single antenna case is invariably included as a special case. It can generally be required that the correlation of the phase values is as small as possible without first specifying the phase sequence in detail. This corresponds to the relationship:

a special realization form of this proposed pre-processing is to haveSo-called CDD method (cyclic delay diversity). This CDD method is advantageous from an implementation point of view because, unlike the general method, only one inverse fourier transform is required per OFDM symbol in the transmitter.

According to this first case, MIMO stations equipped with multiple antennas are therefore used, which transmit data packets that are understood by all stations, i.e. MIMO and SISO stations. In this case, a pseudo-random phase rotation form of transmit diversity method is applied on each subcarrier and each antenna, wherein in particular the CDD method is used. In this case, the phase vector Pk used is the same for all OFDM symbols including the preamble symbols s (k) and c (k). Furthermore, the same "PLCP transmission procedure" as that in fig. 1, for example, according to IEEE802.11, is used. This approach also still makes sense when no SISO device is active, i.e., there is no compatibility requirement.

It is further noted that the described method is truly transparent for SISO devices only if only time-wise filtering, i.e. averaging of the two c (n) sequences and no frequency-wise filtering, is performed in combination with the channel estimation in the receiver.

Fig. 5 shows a simplified illustration of a data packet with the preamble and signaling structure of the invention according to the first embodiment.

According to fig. 5, for each antenna 1, 2_TAssociated data packets in the frequency domain are shown, wherein the data packets of the individual antennas correspond essentially to the data packets according to fig. 1 to 4, as long as the MIMO-OFDM transmission system is to be implemented according to a WLAN.

The preamble structure for the respective antennas shown in fig. 5 is thus shown in the time domain and discretely.

Case 3:

the freedom in the design of the preamble structure PS and the used signaling structure SI is maximal when according to case 3 only the addressed MIMO receiver has to be able to actually analyze the transmitted data packet. The number D of channel estimation sequence pairs c (n) used for channel estimation corresponds in this case to the maximum number of data streams that should be transmitted per subcarrier k, i.e. D max { D ═ D {_k}. Matrix of data usage on each subcarrier

Is transmitted. In terms of preprocessing, according to the invention, the following processing is considered to be particularly efficient:

two different variants can be used for the synchronization sequence s (n):

according to variant a), the synchronization sequences for the individual antennas satisfy a relationship

s_m(n)＝DFT^-1{S_m(k) Therein ofN1.. N, so that signals that are as uncorrelated as possible are transmitted via the respective antennas. This variant a can be applied in particular when there is no detailed a priori information about the respective channel in the transmitter.

According to variant b), the synchronization sequences for the individual antennas satisfy the equation

s_m(n)＝DFT^-1{S_m(k) Therein ofN1.. N, wherein this variant b) applies in particular when there is detailed a priori information about the respective channel in the transmitter.

For adapting the method to e.g. a WLAN transmission system, use is made of basic synchronization signals

As specified in the standard IEEE 802.11.

According to fig. 5, these synchronization sequences s can be used_m(n) preceded by a guard interval G typical for OFDM, respectively, in which the synchronization sequence s_m(n) is repeated periodically at least once. Alternatively, a guard interval with pre-symbol inversion is also possible.

However, alternatively or additionally, the channel estimation sequence c (n) may also be used to implement a SISO-compatible MIMO transmission system.

Thus, for each antenna 1 to M_TMay correspond to an OFDM symbol c_m，x(n) successive arrangement c_m(n)＝g_m，1(n)c_m，1(n)g_m，2(n)c_m，2(n)…g_m，D(n)c_m，D(n) is present in the corresponding channel estimation segment KA according to the preamble structure PS of fig. 5 and satisfies the following equation

c_m，x(n)＝DFT^-1{C_m，x(k) And C_m，x(k)＝p_k，m，x·C(k)，n＝1，...，N。

It is assumed in this case that the receiver can derive the number D of channel estimation sequence pairs for channel estimation directly from the received signal (e.g. by determining the autocorrelation function (AKF) over a time window of the same length from 64 sample values at an interval 4), so that signaling of this parameter is not necessarily necessary.

In order to be adapted to the WLAN transmission system described at the outset, the basic channel estimation signals specified in IEEE802.11 can be used in turn

C(k)-_26:26＝{1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，0，

1，-1，-1，1，1，-1，1，-1，1，-1，-1，-1，-1，-1，1，1，-1，-1，1，-1，1，-1，1，1，1，1}。

If D is_kIf < D. > then in region D_kNo P present in < x ≦ D_k，m，xAnd P is_k，m，xShould be set to zero accordingly.

Channel estimation sequence c_m(n) may also be repeated at least once again periodically. E.g. channel estimation sequences c for each antenna_m(n) by OFDM symbols c_m，x(n) according to

Is formed of successive permutations of where j is an OFDM symbol c_m，x(n) the number of repetitions.

Although the guard interval GG is represented by a double OFDM typical guard interval sequence g for the channel estimation sequence according to fig. 5_m，x(n)＝c_m，x(n+N-2N_G) n＝1，...，2N_GIs formed of N_GIs the number of sampled values of the guard interval, which may also be represented by a simple guard interval sequence g typical of OFDM_m，x(n)＝c_m，x(n+N-N_G) n＝1，...，N_GAnd (4) forming.

Here, a description about power normalization is attached.

In general, the transmission power is constant over all OFDM useful symbols (i.e. those containing useful information), i.e.

1.. L for all x

Where E { } represents a desired value.

The transmit power of the channel estimation sequence is:

x＝1，...，D

in this case the following argument is made:

in general these two terms differ, since the above term also includes the sum of all spatial data streams. This difference is in turn usually compensated by a weight w of the basic channel estimation signal c (k) which is known to the receiver, i.e.E.g. messaging²＝w·E{|I_d，x(k)|²}。

In this case, the following problems may occur:

if it is notFor all x 1.. D, the power of the channel estimation sequence fluctuates according to the above terms. The disadvantage here is that the available power is not optimally used for channel estimation. This problem can be solved by performing [ P ]_k]Such that the relation p is taken into account_k，m，x0 (for x > D)_k) In the case of (1), D, the power values for all xIs minimized.

Example (c):

for all subcarriers k, first according to size pair [ P ]_k]Or column vectors thereof, such that for z > x, the ordering appliesThen according to the ruleThese column vectors are randomly permuted.

Alternatively or additionally, the signaling sequence of the signaling segment SI may also be determined for each antenna in order to implement a suitable MIMO transmission system.

According to fig. 5, the signalling segment SI contains information about the physical processing of the data sequence, i.e. for example the number of data streams per subcarrier k and their coding and modulation, the length of the data packets, etc. The size of this information varies according to the type of physical processing, so that in general it is possible to start with an OFDM symbol (described by the parameter V in fig. 5) for which more than one is required for its transmission.

To avoid repeated measurements (erbestimmung) or "Overhead", the length of the signaling field SI should be adaptively matched to the size of the information, which may be indicated, for example, in the first OFDM symbol.

In order to be able to extract the information correctly again in the receiver, the information must be encoded in a predefined manner, wherein the type of encoding should be as robust as possible, i.e. not prone to errors, due to the sensitivity of the information. This implies that the transmission should be performed in diversity mode rather than in multiplexing mode as much as possible. In order for the channel estimation to prove its validity, the same information is transmitted on all parallel spatial data streams. Due to the fact thatThus, from the OFDM symbol a_m，x(n) and typical guard interval sequence g for OFDM_m，x(n)＝a_m，x(n+N-N_G) n＝1，...，N_GAccording to a_m(n)＝g_m，1(n)a_m，1(n)g_m，2(n)a_m，2(n)…g_m，v(n)a_m，v(n) (wherein a)_m，x(n)＝DFT^-1{A_m，x(k) Andn-1, N) are arranged in succession to obtain a signaling sequence a_m(n)。

Then equation

d_m，x(n)＝DFT^-1{D_m，x(k) Therein ofIs suitable for data sequences in the data field DA, where in this case I_d，x(k)Represents data symbols or information on the d-th spatial data stream of the k-th subcarrier of the x-th OFDM useful data symbol, i.e. on spatial, temporal and spectral resource elementsIs transported on the substrate.

Although the signaling structure SI is arranged in the time domain according to fig. 5 between the useful data structure DA and the channel estimation segment KA of the preamble structure PS, the signaling structure may alternatively be constructed.

Case 2:

the preamble and signaling structure according to the second embodiment shown in fig. 6 is proposed for case 2, where the SISO station must also be able to analyze the signaling field or signaling structure SI. In this case, the same reference numerals denote the same or corresponding data sequences, and thus, a repetitive description will be omitted hereinafter.

According to fig. 6, an alternative preamble or signaling structure is proposed, in which there is a channel estimation sequence c_m(n) the channel estimation segment KA is divided to have a partial channel estimation sequence c_m ¹(n) and c_m ²(n) a first partial channel estimation segment KA1 and a second partial channel estimation segment KAD, and the signalling segment SI is divided to have a partial signalling sequence a_m ¹(n) and a_m ²(n) the first partial signaling segment SI1 and the second partial signaling segment SIV, and the first partial channel estimation segment KA1, the first partial signaling segment SI1, the second partial channel estimation segment KAD, and the second partial signaling segment SIV are recombined in chronological order. In the signalling segment, the first part of the signalling sequence is according to

And the second partial signaling sequence is based on

Wherein

a_m，x(n)＝DFT^-1{A_m，x(k) Andand isAnd typical guard interval sequence according to OFDM

g_m，x(n)＝a_m，x(n+N-N_G) n＝1，...，N_GTo form the composite material.

The channel estimation sequence used corresponds to the channel estimation sequence described above, wherein for example a first partial channel estimation segment KA1 is determined for x ═ 1 and a second partial channel estimation segment KAD is determined for x ═ 2 to D. Unlike the embodiment according to fig. 5, in this second embodiment a part of the signalling is shifted forward and corresponds for example to the signalling field of an already existing SISO transmission system. In this way, downward or backward compatibility with the SISO transmission system (802.11a system) is again obtained.

The complete signaling may also be selectively moved forward. In this case, the parameter D may be explicitly transmitted together as part of the signaling information, so that the number of subsequent channel estimation sequences is known a priori.

The invention has been described above with the aid of an OFDM transmission system according to the IEEE802.11 standard. The invention is not limited thereto and equally encompasses alternative MIMO-OFDM transmission systems.

Claims (19)

1. For use in a vehicle having a plurality of antennas (1,. multidot., M)_T) In a MIMO-OFDM transmission system, wherein for each antenna (1,... multidot.m), a method of generating a preamble structure and a signaling structure for a data packet_T) Each comprising a synchronization Segment (SY) with a synchronization sequence and a channel estimation segment (KA) with a channel estimation sequence, and the signalling structure for each antenna comprising at least one signalling Segment (SI) with a signalling sequence, respectively,

synchronization sequences s for the individual antennas_m(n) according to the relationship

s_m(n)＝DFT^-1{S_m(k) Therein ofn＝1，...，N

Or according to a relationship

s_m(n)＝DFT^-1{S_m(k) Therein ofn＝1，...，N

Where s (k) is the basic synchronization signal in the frequency domain, M1_TIs an antenna index, M_TIs the number of transmit antennas, N is the sample index, k is the subcarrier index, N is the number of sample values per OFDM symbol, D is the index of the spatial data stream, D_kIs the number of spatial data streams, p, transmitted on subcarrier k_k，m，dIs a matrix P used for spatial pre-distortion of useful data on the k-th subcarrier_kThe mth row and the d-th column of elements,is pseudo-random and depends on the frequency and phase rotation of the antenna andis a pseudo-random frequency, antenna and space dependent phase rotation.

2. Method according to claim 1, characterized in that in said synchronization sequence s_m(n) is preceded by a guard interval (G) typical of OFDM.

3. Method according to claim 1, characterized in that in said synchronization sequence s_m(n) a sign-reversed guard interval is set before.

4. Method according to one of claims 1 to 3, characterized in that the synchronization sequence s_m(n) is repeated periodically at least once.

5. A method according to one of claims 1 to 3, characterized in that the correlation of the phase values is as small as possible according to the following relation:

wherein E is the expected value.

6. A method according to claims 1 to 3, characterized in that the pseudo-random frequency-and antenna-dependent phase rotation satisfies the equation:

7. method according to one of claims 1 to 3, characterized in that the expression of said basic synchronization signal according to IEEE802.11 satisfies the equation:

8. for use in a vehicle having a plurality of antennas (1,. multidot., M)_T) In a MIMO-OFDM transmission system, wherein for each antenna (1,... multidot.m), a method of generating a preamble structure and a signaling structure for a data packet_T) Each comprising a synchronization Segment (SY) with a synchronization sequence and a channel estimation segment (KA) with a channel estimation sequence, and the signalling structure for each antenna comprising at least one signalling Segment (SI) with a signalling sequence, respectively,

channel estimation sequences c for individual antennas_m(n) by OFDM symbols c_m，x(n) are arranged in succession according to the following formula:

c_m(n)＝g_m，1(n)c_m，1(n)g_m，2(n)c_m，2(n)…g_m，D(n)c_m，D(n)，

wherein c is_m，x(n)＝DFT^-1{C_m，x(k) Andn1, N, where c (k) is the basic channel estimation signal in the frequency domain, M1_TIs an antenna index, M_TIs the number of transmit antennas, x 1, D is the index of the spatial data stream, n is the sample index, D is all subcarriersMaximum number of spatial data streams, g_m，x(N) is a guard interval sequence of a guard interval (G), k is a subcarrier index, N is the number of sample values per OFDM symbol, and p_k，m，xIs a matrix P used for spatial pre-distortion of useful data on the k-th subcarrier_kRow m and column x.

9. The method of claim 8, wherein the channel estimation sequence c_m(n) is repeated periodically at least once.

10. A method as claimed in claim 8, characterized in that the channel estimation sequences c for the individual antennas_m(n) by OFDM symbols c_m，x(n) according to

Are arranged consecutively, where j is an OFDM symbol c_m，x(n) the number of repetitions.

11. Method according to one of claims 8 to 10, characterized in that the guard interval (G) or the double guard interval (GG) is formed by a simple OFDM typical guard interval sequence

g_m，x(n)＝c_m，x(n+N-N_G) n＝1，...，N_G

Or by a guard interval sequence typical of a double OFDM

g_m，x(n)＝c_m，x(n+N-2N_G) n＝1，...，2N_G

Form wherein N is_GIs the number of samples of the guard interval.

12. Method according to one of claims 8 to 10, characterized in that the expression of said basic channel estimation signal according to IEEE802.11 satisfies the equation:

C(k)_-26：26＝{1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，1，1，-1，-1，1，1，-1，1，-1，1，1，1，1，0，1，-1，-1，1，1，-1，1，-1，1，-1，-1，-1，-1，-1，1，1，-1，-1，1，-1，1，-1，1，1，1，1}

13. method according to one of claims 8 to 10, characterized in that the signaling Segment (SI) is arranged in the time domain between a useful data structure (DA) and a channel estimation segment (KA), wherein the signaling Segment (SI) contains a signaling sequence a for each antenna_m(n) the signaling sequence consists of OFDM symbols a_m，x(n) and typical guard interval sequence g for OFDM_m，x(n)＝a_m，x(n+N-N_G) n＝1，...，N_GFormed by successively arranging according to the following formula:

a_m(n)＝g_m，1(n)a_m，1(n)g_m，2(n)a_m，2(n)…g_m，V(n)a_m，V(n)

wherein a is_m，x(n)＝DFT^-1{A_m，x(k) Andn1, N, wherein a_m，x(n) is the x-th signaling signal in the frequency domain transmitted through the m-th antenna, and I_x ^sig(k) Is the signaling information transmitted on the kth subcarrier of the xth OFDM signaling symbol.

14. Method according to one of claims 8 to 10, characterized in that there is a channel estimation sequence c_mThe channel estimation segment (KA) of (n) is divided to have a partial channel estimation sequence c_m ¹(n) and c_m ²(n) a first partial channel estimation segment (KA1) and a second partial channel estimation segment (KAD), and the signalling Segment (SI) is divided with a partial signalling sequence a_m ¹(n) and a_m ²(n) a first partial signaling segment (SI1) and a second partial signaling Segment (SIV), and the first partial channel estimation segment (KA1), the first partial signaling segment (SI1), the second partial channel estimation segment (KAD), and the second partial signaling Segment (SIV) are recombined in chronological order, wherein the first and second partial channel estimation sequences are in accordance with

Or according to

Formed using a simple or double guard interval typical of OFDM and wherein said first partial signalling sequence is in accordance with

And the second partial signaling sequence is according to

Wherein

a_m，x(n)＝DFT^-1{A_m，x(k) Andn＝1，...，N，

and typical guard interval sequence according to OFDM

g_m，x(n)＝a_m，x(n+N-N_G) n＝1，...，N_G

Where j is an OFDM symbol c_m，x(n) number of repetitions, A_m，x(k) Is the x-th signalling signal in the frequency domain transmitted via the m-th antenna, and I_x ^sig(k) At the x-th OFDM signalling symbolSignalling information transmitted on the kth sub-carrier, and wherein V' represents the number of OFDM symbols required to transmit partial signalling information, and V represents the number of OFDM symbols required to transmit total signalling information.

15. Method according to one of claims 8 to 10, characterized in that a synchronization sequence s according to one of claims 1 to 7 is present_mThe synchronization Segment (SY) of (n) is pre-positioned to form a common preamble and signalling structure (PS).

16. Method according to one of claims 8 to 10, characterized in that the column vectors P of the matrix Pk_k，x，x＝1，...，D_kAre ordered such that the power values

x＝1，...，D

The variance of (c) is as small as possible taking into account the following relationship:

p_k，m，x0 for x > D_k。

17. Method according to one of claims 8 to 10, characterized in that for each subcarrier k, a spatial predistortion matrix P_k1, D_kColumn vector P of_k，xIn a first step, the values are sorted according to size such that

For z > x

And randomly permuted in a second step.

18. A method as claimed in claim 17, characterized in that the permutation of the column vectors is according to a ruleTo be executed.

19. Method according to one of claims 1 to 3 and 8 to 10, characterized in that the OFDM transmission system is designed according to the IEEE802.11 standard.